Chromatography (from Greek χρώμα:chroma, colour and γραφειν:"grafein" to write) is the collective term for a family of laboratory techniques for the separation of mixtures. It involves passing a mixture dissolved in a "mobile phase" through a stationary phase, which separates the analyte to be measured from other molecules in the mixture and allows it to be isolated.
Contents
[hide]
* 1 History
* 2 Chromatography terms
* 3 Chromatography theory
o 3.1 Retention
o 3.2 Plate theory
* 4 Capillary-action chromatography
o 4.1 Paper Chromatography
o 4.2 Thin layer chromatography
* 5 Column chromatography
o 5.1 Fast performance liquid chromatography
o 5.2 High performance liquid chromatography
o 5.3 Ion exchange chromatography
o 5.4 Size exclusion chromatography
o 5.5 Affinity chromatography
* 6 Gas-liquid chromatography
* 7 Countercurrent chromatography
* 8 See also
* 9 References
* 10 External links
[edit] History
It was the Russian botanist Mikhail Semyonovich Tswett who invented the first chromatography technique in 1900 during his research on chlorophyll. He used a liquid-adsorption column containing calcium carbonate to separate plant pigments. The method was described on December 30, 1901 at the 11th Congress of Naturalists and Doctors (XI съезд естествоиспытателей и врачей) in St. Petersburg. The first printed description was in 1903, in the Proceedings of the Warsaw Society of Naturalists, section of biology. He first used the term chromatography in print in 1906 in his two papers about chlorophyll in the German botanical journal, Berichte der Deutschen Botanischen Gesellschaft. In 1907 he demonstrated his chromatograph for the German Botanical Society. Interestingly, Mikhail's surname "Tsvet" means "color" in Russian, so there is the possibility that his naming the procedure chromatography (literally "color writing") was a way that he could make sure that he, a commoner in Tsarist Russia, could be immortalized.
In 1952 Archer John Porter Martin and Richard Laurence Millington Synge were awarded the Chemistry Nobel Prize for their invention of partition chromatography[1]. Since then, the technology has advanced rapidly. Researchers found that the principles underlying Tsvet's chromatography could be applied in many different ways, giving rise to the different varieties of chromatography described below. Simultaneously, advances continually improved the technical performance of chromatography, allowing the separation of increasingly similar molecules.
[edit] Chromatography terms
* The analyte is the substance which is to be purified or isolated during chromatography
* Analytical chromatography is used to determine the identity and concentration of molecules in a mixture
* A chromatogram is the visual output of the chromatograph. Different peaks or patterns on the chromatogram correspond to different components of the separated mixture
Chromatogram with unresolved peaksChromatogram with two resolved peaks
Plotted on the x-axis is the retention time and plotted on the y-axis a signal (for example obtained by UV spectroscopy) corresponding to the amount of analyte exiting the system.
* A chromatograph takes a chemical mixture carried by liquid or gas and separates it into its component parts as a result of differential distributions of the solutes as they flow around or over the stationary phase
* The mobile phase is the analyte and solvent mixture which travels through the stationary phase
* Preparative chromatography is used to nondestructively purify sufficient quantities of a substance for further use, rather than analysis.
* The retention time is the characteristic time it takes for a particular molecule to pass through the system under set conditions.
* The stationary phase is the substance which is fixed in place for the chromatography procedure and is the phase to which solvents and the analyte travels through or binds to. Examples include the silica layer in thin layer chromatography.
[edit] Chromatography theory
Chromatography is a separation method that exploits the differences in partitioning behavior between a mobile phase and a stationary phase to separate the components in a mixture. Components of a mixture may be interacting with the stationary phase based on charge, relative solubility or adsorption. There are two theories of chromatography, the plate and rate theories.
[edit] Retention
The retention is a measure of the speed at which a substance moves in a chromatographic system. In continuous development systems like HPLC or GC, where the compounds are eluted with the eluent, the retention is usually measured as the retention time Rt or tR, the time between injection and detection. In interrupted development systems like TLC the retention is measured as the retention factor Rf, the run length of the compound divided by the run length of the eluent front:
R_f = \frac{distance\ moved\ by\ compound} {distance\ moved\ by\ solvent}
The retention of a compound often differs considerably between experiments and laboratories due to variations of the eluent, the stationary phase, temperature, and the setup. It is therefore important to compare the retention of the test compound to that of one or more standard compounds under absolutely identical conditions.
During the chromatographic process the analyte experiences zone broadening as a result of diffusion. Two analytes with different retention times yet with large broadening do not resolve and this is why in any chromatographic system broadening needs to be minimized. This is done by selecting the proper stationary and mobile phase, the eluent velocity, the track length and temperature. The Van Deemter's equation gives an ideal eluent velocity taking into account several physical parameters.
[edit] Plate theory
The plate theory of chromatography was developed by Archer John Porter Martin and Richard Laurence Millington Synge. The plate theory describes the chromatography system, the mobile and stationary phases, as being in equilibrium. The partition coefficient K is based on this equilibrium, and is defined by the following equation:
K = \frac{Concentration\ of\ solute\ in\ stationary\ phase} {Concentration\ of\ solute\ in\ mobile\ phase}
K is assumed to be independent of concentration, and can change if experimental conditions are changed, for example temperature is increased or decreased. As K increases, it takes longer for solutes to separate. For a column of fixed length and flow, the retention time (tR) and retention volume (Vr) can be measured and used to calculate K.
[edit] Capillary-action chromatography
Thin layer chromatography is used to separate components of chlorophyll
Thin layer chromatography is used to separate components of chlorophyll
[edit] Paper Chromatography
For more details on this topic, see Paper chromatography.
This is an older technique which involves placing a small dot of sample solution onto a strip of chromatography paper. The paper is placed into a jar containing a shallow layer of solvent and sealed. As the solvent rises through the paper it meets the sample mixture which starts to travel up the paper with the solvent. Different compounds in the sample mixture travel different distances according to how strongly they interact with the paper. This allows the calculation of an Rf value and can be compared to standard compounds to aid in the identification of an unknown substance.
[edit] Thin layer chromatography
For more details on this topic, see Thin layer chromatography.
Thin layer chromatography (TLC) is a widely-employed laboratory technique and is similar to paper chromatography. However, instead of using a stationary phase of paper, it involves a stationary phase of a thin layer of adsorbent like silica gel, alumina, or cellulose on a flat, inert substrate. Compared to paper, it has the advantage of faster runs, better separations, and the choice between different adsorbents. Different compounds in the sample mixture travel different distances according to how strongly they interact with the adsorbent. This allows the calculation of an Rf value and can be compared to standard compounds to aid in the identification of an unknown substance.
[edit] Column chromatography
For more details on this topic, see Column chromatography.
A diagram of a standard column chromatography and a flash column chromatography setup
A diagram of a standard column chromatography and a flash column chromatography setup
Column chromatography encompasses a number of techniques based around utilizing a vertical glass column filled with some form of solid support, with the sample to be separated placed on top of this support. The rest of the column is filled with a solvent which, under the influence of gravity, moves the sample through the column. Similarly to other forms of chromatography, differences in rates of movement through the solid medium are translated to different exit times from the bottom of the column for the various elements of the original sample.
In 1978, W. C. Still introduced a modified version of column chromatography called flash column chromatography (flash).[2] The technique is very similar to the traditional column chromatography, except for that the solvent is driven through the column by applying positive pressure. This allowed most separations to be performed in less than 20 minutes, with improved separations compared to the old method. Modern flash chromatography systems are sold as pre-packed plastic cartridges, and the solvent is pumped through the cartridge. Systems may also be linked with detectors and fraction collectors providing automation. The introduction of gradient pumps resulted in quicker separations and less solvent usage.
[edit] Fast performance liquid chromatography
For more details on this topic, see Fast performance liquid chromatography.
Fast performance liquid chromatography (FPLC) is a term applied to several chromatography techniques which are used to purify proteins. Many of these techniques are identical to those carried out under high performance liquid chromatography.
[edit] High performance liquid chromatography
For more details on this topic, see High performance liquid chromatography.
High performance liquid chromatography (HPLC) is a form of column chromatography used frequently in biochemistry and analytical chemistry. The analyte is forced through a column (stationary phase) by a liquid (mobile phase) at high pressure, which decreases the time the separated components remain on the stationary phase and thus the time they have to diffuse within the column. Specific techniques which come under this broad heading are listed below. It should also be noted that the following techniques can also be considered fast protein liquid chromatography if no pressure is used to drive the mobile phase through the stationary phase. See also Aqueous Normal Phase Chromatography.
[edit] Ion exchange chromatography
For more details on this topic, see Ion exchange chromatography.
Ion exchange chromatography is a column chromatography that uses a charged stationary phase. It is used to separate charged compounds including amino acids, peptides, and proteins. The stationary phase is usually an ion exchange resin that carries charged functional groups which interact with oppositely charged groups of the compound to be retained. Ion exchange chromatography is commonly used to purify proteins using FPLC.
[edit] Size exclusion chromatography
For more details on this topic, see Size exclusion chromatography.
Size exclusion chromatography (SEC) is also known as gel permeation chromatography or gel filtration chromatography and separates particles on the basis of size. Smaller molecules enter a porous media and take longer to exit the column, whereas larger particles leave the column earlier. It is generally a low resolution chromatography and thus it is often reserved for the final, "polishing" step of a purification. It is also useful for determining the tertiary structure and quaternary structure of purified proteins, especially since it can be carried out under native solution conditions.
[edit] Affinity chromatography
For more details on this topic, see Affinity chromatography.
Affinity chromatography is based on selective non-covalent interaction between an analyte and specific molecules. It is very specific, but not very robust. It is often used in biochemistry in the purification of proteins bound to tags. These fusion proteins are labelled with compounds such as His-tags, biotin or antigens, which bind to the stationary phase specifically. After purification, some of these tags are usually removed and the pure protein is obtained.
[edit] Gas-liquid chromatography
For more details on this topic, see Gas-liquid chromatography.
Gas chromatography (GC) is based on a partition equilibrium of analyte between a solid stationary phase and a mobile gas. The stationary phase is adhered to the inside of a small-diameter glass tube (a capillary column) or a solid matrix inside a larger metal tube (a packed column). It is widely used in analytical chemistry; though the high temperatures used in GC make it unsuitable for high molecular weight biopolymers, frequently encountered in biochemistry, it is well suited for use in the petrochemical, environmental monitoring, and industrial chemical fields. It is also used extensively in chemistry research.
[edit] Countercurrent chromatography
For more details on this topic, see Countercurrent chromatography.
Countercurrent chromatography (CCC) is a type of liquid-liquid chromatography, where both the stationary and liquid phases are liquids. It involves mixing a solution of liquids, allowing them to settle into layers and then separating the layers.
[edit] See also
* Paper chromatography of amino acids on Wikibooks
* Aqueous Normal Phase Chromatography
* MCSGP = Multicolumn Countercurrent Solvent Gradient Purification Process
[edit] References
1. ^ Nobelprize.org: The Nobel Prize in Chemistry 1952
2. ^ Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43(14), 2923-2925. (DOI:10.1021/jo00408a041)
Important Information
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Re: Important Information
An electromagnet is a type of magnet in which the magnetic field is produced by a flow of electric current. The magnetic field disappears when the current ceases.
Contents
[hide]
* 1 History
* 2 Introduction
* 3 Electromagnets and permanent magnets
* 4 Devices that use electromagnets
* 5 Force on ferromagnetic materials
* 6 Patents
* 7 See also
[edit] History
British electrician, William Sturgeon invented the electromagnet in 1825. The first electromagnet was a horseshoe-shaped piece of iron that was wrapped with a loosely wound coil of several turns. When a current was passed through the coil; the electromagnet became magnetized and when the current was stopped the coil was de-magnetized. Sturgeon displayed its power by lifting nine pounds with a seven-ounce piece of iron wrapped with wires through which the current of a single cell battery was sent.
Sturgeon could regulate his electromagnet; this was the beginning of using electrical energy for making useful and controllable machines and laid the foundations for large-scale electronic communications.
[edit] Introduction
The simplest type of electromagnet is a coiled piece of wire. A coil forming the shape of a straight tube (similar to a corkscrew) is called a solenoid; a solenoid that is bent so that the ends meet is a toroid. Much stronger magnetic fields can be produced if a "core" of paramagnetic or ferromagnetic material (commonly soft iron) is placed inside the coil. The core concentrates the magnetic field that can then be much stronger than that of the coil itself.
Current (I) flowing through a wire produces a magnetic field (B) around the wire. The field is oriented according to the right-hand rule.
Current (I) flowing through a wire produces a magnetic field (B) around the wire. The field is oriented according to the right-hand rule.
Magnetic fields caused by coils of wire follow a form of the right-hand rule. If the fingers of the right hand are curled in the direction of current flow through the coil, the thumb points in the direction of the field inside the coil. The side of the magnet that the field lines emerge from is defined to be the north pole.
[edit] Electromagnets and permanent magnets
The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be rapidly manipulated over a wide range by controlling the amount of electric current. However, a continuous supply of electrical energy is required to maintain the field.
As a current is passed through the electromagnet, small magnetic regions within the material, called magnetic domains, align with the applied field, causing the magnetic field strength to increase. As current is increased, all of the domains eventually become aligned, a condition called saturation. Once the core becomes saturated, a further increase in current will only cause a relatively minor increase in the magnetic field. In some materials, some of the domains may realign themselves. In this case, part of the original magnetic field will persist even after power is removed, causing the core to behave as a permanent magnet. This phenomenon called remanent magnetism, and is due to the hysteresis of the material. Applying a decreasing AC current to the coil, removing the core and hitting it, or heating it above its Curie point will reorient the domains, causing the residual field to weaken or disappear.
In applications where a variable magnetic field is not required, permanent magnets are generally superior. Additionally, permanent magnets can be manufactured to produce stronger fields than electromagnets of similar size.
[edit] Devices that use electromagnets
Electromagnets are used in many situations where a rapidly or easily variable magnetic field is desired. Many of these applications involve deflection of charged particle beams; the cathode ray tube and mass spectrometer fall into this category.
Other devices cause electromagnetic fields to interact with fields from permanent magnets or induced fields from ferromagnetic materials to produce forces. Electromagnetic actuators take advantage of the fact that, if a ferromagnetic core is displaced toward one end of a solenoid, a force will occur which tends to center the core within the solenoid. Also, a nearby plate of steel will be strongly attracted to the core within the solenoid. Typical uses include relays, electromagnetic door locks, and solenoid valves. Doorbells and similar devices are commonly made by causing the moving core to strike a bell.
A quadrupole ("four-pole") electromagnet, used to focus particle beams in a particle accelerator. There are four steel pole tips: two opposing magnetic north poles and two opposing magnetic south poles. The steel is magnetized by a large electric current that flows through coils (not shown) wound around each core.
A quadrupole ("four-pole") electromagnet, used to focus particle beams in a particle accelerator. There are four steel pole tips: two opposing magnetic north poles and two opposing magnetic south poles. The steel is magnetized by a large electric current that flows through coils (not shown) wound around each core.
Electromagnets are the essential components of many circuit-breakers, they are used in cars in electromagnet brakes and clutches. In some trams, electromagnetic brakes grip directly on to the rails. Very high powered electromagnets are even used to lift heavy scraps of iron and steel, and to magnetically separate metals at junkyards and recycling centers. Magnetic levitation trains use powerful electromagnets to hover without touching the track. Some trains use attractive forces, while others use repulsive forces.
Electromagnets are used in a rotary electric motor to produce a rotating magnetic field that turns the rotor, or in a linear motor to produce a traveling magnetic field that propels the armature. Although silver is the best conductor of electricity, copper is the most often used conductor due to its low cost, and aluminum is sometimes used to save weight and cost.
Electric guitars also use electro-magnetic pickups, which sense the motions of the strings. The pickup converts mechanical energy into a small electrical signal which is then amplified.
[edit] Force on ferromagnetic materials
Computing the force on ferromagnetic materials is, in general, quite complex. This is due to fringing field lines and complex geometries. It can be simulated using finite element analysis. However, it is possible to estimate the maximum force under specific conditions. If the magnetic field is confined within a high permeability material, such as certain steel alloys, the maximum force is given by:
F = \frac{B^2 A}{2 \mu_o}
Where:
* F is the force in newtons
* B is the magnetic field in teslas
* A is the area of the pole faces in square meters
* μo is the permeability of free space
See energy in a magnetic field for more details on the derivation.
In the case of free space (air), \mu_o = 4 \pi \cdot 10^{-7}\,\mbox{H}\cdot \mbox{m}^{-1}, the force per unit area (pressure) is:
P \approx 398 \, \mathrm{kPa} or 57.7 \, \mbox{lbf}\cdot\mbox{in}^{-2} @ B = 1 tesla
P \approx 1592 \, \mathrm{kPa} or 230.8 \, \mbox{lbf}\cdot\mbox{in}^{-2} @ B = 2 teslas
In a closed magnetic circuit:
B = \frac{\mu N I}{L}
Where:
* N is the number of turns of wire around the electromagnet
* I is the current in amperes
* L is the length of the magnetic circuit
Substituting above,
F = \frac{\mu N^2 I^2 A}{2 L^2}
In order to build a strong electromagnet, a short magnetic circuit with large area is preferred. Most ferromagnetic materials saturate around 1 to 2 teslas. This occurs at a field intensity of:
H\approx 787\ \mbox{ampere.turns/meter or}\ 20\ \mbox{ampere.turns/inch}.
For this reason, there is no point in building an electromagnet with a higher field intensity. Industrial lifting electromagnets are designed with both pole faces at one side (the bottom). This confines the field lines to maximize the magnetic field. It's like a cylinder within a cylinder. Many loudspeaker magnets use a similar geometry, although the field lines are radial from the inner cylinder rather than perpendicular to the face.
Contents
[hide]
* 1 History
* 2 Introduction
* 3 Electromagnets and permanent magnets
* 4 Devices that use electromagnets
* 5 Force on ferromagnetic materials
* 6 Patents
* 7 See also
[edit] History
British electrician, William Sturgeon invented the electromagnet in 1825. The first electromagnet was a horseshoe-shaped piece of iron that was wrapped with a loosely wound coil of several turns. When a current was passed through the coil; the electromagnet became magnetized and when the current was stopped the coil was de-magnetized. Sturgeon displayed its power by lifting nine pounds with a seven-ounce piece of iron wrapped with wires through which the current of a single cell battery was sent.
Sturgeon could regulate his electromagnet; this was the beginning of using electrical energy for making useful and controllable machines and laid the foundations for large-scale electronic communications.
[edit] Introduction
The simplest type of electromagnet is a coiled piece of wire. A coil forming the shape of a straight tube (similar to a corkscrew) is called a solenoid; a solenoid that is bent so that the ends meet is a toroid. Much stronger magnetic fields can be produced if a "core" of paramagnetic or ferromagnetic material (commonly soft iron) is placed inside the coil. The core concentrates the magnetic field that can then be much stronger than that of the coil itself.
Current (I) flowing through a wire produces a magnetic field (B) around the wire. The field is oriented according to the right-hand rule.
Current (I) flowing through a wire produces a magnetic field (B) around the wire. The field is oriented according to the right-hand rule.
Magnetic fields caused by coils of wire follow a form of the right-hand rule. If the fingers of the right hand are curled in the direction of current flow through the coil, the thumb points in the direction of the field inside the coil. The side of the magnet that the field lines emerge from is defined to be the north pole.
[edit] Electromagnets and permanent magnets
The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be rapidly manipulated over a wide range by controlling the amount of electric current. However, a continuous supply of electrical energy is required to maintain the field.
As a current is passed through the electromagnet, small magnetic regions within the material, called magnetic domains, align with the applied field, causing the magnetic field strength to increase. As current is increased, all of the domains eventually become aligned, a condition called saturation. Once the core becomes saturated, a further increase in current will only cause a relatively minor increase in the magnetic field. In some materials, some of the domains may realign themselves. In this case, part of the original magnetic field will persist even after power is removed, causing the core to behave as a permanent magnet. This phenomenon called remanent magnetism, and is due to the hysteresis of the material. Applying a decreasing AC current to the coil, removing the core and hitting it, or heating it above its Curie point will reorient the domains, causing the residual field to weaken or disappear.
In applications where a variable magnetic field is not required, permanent magnets are generally superior. Additionally, permanent magnets can be manufactured to produce stronger fields than electromagnets of similar size.
[edit] Devices that use electromagnets
Electromagnets are used in many situations where a rapidly or easily variable magnetic field is desired. Many of these applications involve deflection of charged particle beams; the cathode ray tube and mass spectrometer fall into this category.
Other devices cause electromagnetic fields to interact with fields from permanent magnets or induced fields from ferromagnetic materials to produce forces. Electromagnetic actuators take advantage of the fact that, if a ferromagnetic core is displaced toward one end of a solenoid, a force will occur which tends to center the core within the solenoid. Also, a nearby plate of steel will be strongly attracted to the core within the solenoid. Typical uses include relays, electromagnetic door locks, and solenoid valves. Doorbells and similar devices are commonly made by causing the moving core to strike a bell.
A quadrupole ("four-pole") electromagnet, used to focus particle beams in a particle accelerator. There are four steel pole tips: two opposing magnetic north poles and two opposing magnetic south poles. The steel is magnetized by a large electric current that flows through coils (not shown) wound around each core.
A quadrupole ("four-pole") electromagnet, used to focus particle beams in a particle accelerator. There are four steel pole tips: two opposing magnetic north poles and two opposing magnetic south poles. The steel is magnetized by a large electric current that flows through coils (not shown) wound around each core.
Electromagnets are the essential components of many circuit-breakers, they are used in cars in electromagnet brakes and clutches. In some trams, electromagnetic brakes grip directly on to the rails. Very high powered electromagnets are even used to lift heavy scraps of iron and steel, and to magnetically separate metals at junkyards and recycling centers. Magnetic levitation trains use powerful electromagnets to hover without touching the track. Some trains use attractive forces, while others use repulsive forces.
Electromagnets are used in a rotary electric motor to produce a rotating magnetic field that turns the rotor, or in a linear motor to produce a traveling magnetic field that propels the armature. Although silver is the best conductor of electricity, copper is the most often used conductor due to its low cost, and aluminum is sometimes used to save weight and cost.
Electric guitars also use electro-magnetic pickups, which sense the motions of the strings. The pickup converts mechanical energy into a small electrical signal which is then amplified.
[edit] Force on ferromagnetic materials
Computing the force on ferromagnetic materials is, in general, quite complex. This is due to fringing field lines and complex geometries. It can be simulated using finite element analysis. However, it is possible to estimate the maximum force under specific conditions. If the magnetic field is confined within a high permeability material, such as certain steel alloys, the maximum force is given by:
F = \frac{B^2 A}{2 \mu_o}
Where:
* F is the force in newtons
* B is the magnetic field in teslas
* A is the area of the pole faces in square meters
* μo is the permeability of free space
See energy in a magnetic field for more details on the derivation.
In the case of free space (air), \mu_o = 4 \pi \cdot 10^{-7}\,\mbox{H}\cdot \mbox{m}^{-1}, the force per unit area (pressure) is:
P \approx 398 \, \mathrm{kPa} or 57.7 \, \mbox{lbf}\cdot\mbox{in}^{-2} @ B = 1 tesla
P \approx 1592 \, \mathrm{kPa} or 230.8 \, \mbox{lbf}\cdot\mbox{in}^{-2} @ B = 2 teslas
In a closed magnetic circuit:
B = \frac{\mu N I}{L}
Where:
* N is the number of turns of wire around the electromagnet
* I is the current in amperes
* L is the length of the magnetic circuit
Substituting above,
F = \frac{\mu N^2 I^2 A}{2 L^2}
In order to build a strong electromagnet, a short magnetic circuit with large area is preferred. Most ferromagnetic materials saturate around 1 to 2 teslas. This occurs at a field intensity of:
H\approx 787\ \mbox{ampere.turns/meter or}\ 20\ \mbox{ampere.turns/inch}.
For this reason, there is no point in building an electromagnet with a higher field intensity. Industrial lifting electromagnets are designed with both pole faces at one side (the bottom). This confines the field lines to maximize the magnetic field. It's like a cylinder within a cylinder. Many loudspeaker magnets use a similar geometry, although the field lines are radial from the inner cylinder rather than perpendicular to the face.
Re: Important Information
In physics, force is an influence that may cause a body to accelerate. It may be experienced as a lift, a push, or a pull, and has a magnitude and a direction. The actual acceleration of the body is determined by the vector sum of all forces acting on it (known as net force or resultant force). In an extended body, it may also cause rotation or deformation of the body. Rotational effects and deformation are determined respectively by the torques and stresses that the forces create.
Force is a vector quantity defined as the rate of change of the momentum of the body that would be induced by that force acting alone. Since momentum is a vector, the force has a direction associated with it.
Contents
[hide]
* 1 History
* 2 Examples
* 3 Quantitative definition
o 3.1 Force in special relativity
* 4 Force and potential
* 5 Types of force
* 6 Units of measurement
o 6.1 Conversions
* 7 See also
* 8 References
[edit] History
* Force was first described by Archimedes.
* Galileo Galilei used rolling balls to disprove the Aristotelian theory of motion (1602 - 1607)
* Isaac Newton is credited for giving the first mathematical definition of force. However, he understood that the definition is not physically correct.
* Charles Coulomb is credited for experimental discovery of the inverse square law of interaction between electric charges using torsion balance (1784).
* Henry Cavendish's in 1798 measured the force of gravity between two masses (in torsion balance experiment)
* With the development of quantum field theory and general relativity in 20th century it was realised that “force” is redundant concept arising from conservation of momentum (4-momentum in GR and momentum of virtual particles in QFT). Thus currently known fundamental forces are not called forces but “fundamental interactions”.
Aristotle and others believed that it was the natural state of objects on Earth to be motionless, and that they tended toward that state (eventually settling down to inertness), if left alone. This was a common experience of humans with ordinary conditions in which friction was involved, so Newton's idea that force naturally produces a constant increase in velocity was not an obvious one. Frictional forces, acting in opposition to other kinds of forces, historically tended to hide the correct mathematical relationship between simple unopposed force and motion.
The correct behavior of objects accelerated by constant force was first discovered by Galileo in working with gravity (dropping stones and rolling cannonballs on an incline), although it was not until Newton that gravity was seen as a force. Newton generalized the behavior of constant acceleration, or constant momentum gain, to forces other than gravity. He asserted in his second law of motion that this behavior of constant momentum increase was characteristic of all forces-- including the “forces” of ordinary experience, such as tension or the stress produced by pushing on an object with a finger. In fact, he defined force as mass times acceleration, or more accurately, as a rate of change of momentum. Though, he understood that his definition is incorrect because it is a circular definition. The definition of term “force” needs a definition of the term Inertial frame of reference which is defined using the term “force”. Therefore the definition of the term “force” can be only intuitive. This problem was solved in 20th century in quantum field theory and general relativity which use this term only secondarily and it is not necessary to define it in these theories at all.
[edit] Examples
* A heavy object on a table is pulled (attracted) downward toward the floor by the force of gravity (i.e., its weight). At the same time, the table resists the downward force with equal upward force (called the normal force), resulting in zero net force, and no acceleration. (If the object is a person, he actually feels the normal force acting on him from below.)
* A heavy object on a table is gently pushed in a sideways direction by a finger. However, it fails to accelerate sideways, because the force of the finger on the object is now opposed by a new force of static friction, generated between the object and the table surface. This newly generated force exactly balances the force exerted on the object by the finger, and again no acceleration occurs. The static friction increases or decreases automatically. If the force of the finger is increased (up to a point), the opposing sideways force of static friction increases exactly to the point of perfect opposition.
* A heavy object on a table is pushed by a finger hard enough that static friction cannot generate sufficient force to match the force exerted by the finger, and the object starts sliding across the surface. If the finger is moved with a constant velocity, it needs to apply a force that exactly cancels the force of kinetic friction from the surface of the table and then the object moves with the same constant velocity. Here it seems to the naive observer that application of a force produces a velocity (rather than an acceleration). However, the velocity is constant only because the force of the finger and the kinetic friction cancel each other. Without friction, the object would continually accelerate in response to a constant force.
* A heavy object reaches the edge of the table and falls. Now the object, subjected to the constant force of its weight, but freed of the normal force and friction forces from the table, gains in velocity in direct proportion to the time of fall, and thus (before it reaches velocities where air resistance forces becomes significant compared to gravity forces) its rate of gain in momentum and velocity is constant. These facts were first discovered by Galileo.
[edit] Quantitative definition
Force is defined as the rate of change of momentum with time:
\vec{F} = {\mathrm{d}\vec{p} \over \mathrm{d}t}.
The quantity \vec{p} = m \vec{v} (where m\, is the mass and \vec{v} is the velocity) is called the momentum. This is the only definition of force known in physics (first proposed by Newton himself). If the mass m is constant in time, then Newton's second law can be derived from this definition:
\vec{F} = \frac{\mathrm{d}\vec{p}}{\mathrm{d}t}= \frac{\mathrm{d}(m\vec{v})}{\mathrm{d}t} = m\frac{\mathrm{d}(\vec{v})}{\mathrm{d}t} = m\vec{a}
where \vec{a} = {\mathrm{d} \vec{v}} /{\mathrm{d}t} is the acceleration.
This is the form Newton's second law is usually taught in introductory physics courses in order to avoid calculus notation.
All known forces of nature are defined via the above Newtonian definition of force. For example, weight (force of gravity) is defined as mass times acceleration of free fall: w = mg; spring balance force is defined as the force equilibrating certain gravitational force (say, the weight of 1 kg mass near Earth surface results in reaction force of spring equivalent to 9.8 N), etc. Calibration of spring balances (of various kinds) using either gravitational force or motion with known acceleration is important starting procedure in measuring many other forces (such as friction forces, reaction forces, electric forces, magnetic force, etc) in various physics labs.
It is not always the case that m is independent of t. For example, the mass of a rocket decreases as its propellant is ejected. Under such circumstances, the above equation (\vec{F} = m\vec{a}) is incorrect, and the original form of Newton's second law must be used.
Because momentum is a vector, then force, being its time derivative, is also a vector - it has magnitude and direction, and four-force is a four-vector in relativity. Vectors (and thus forces) are added together by their components. When two forces act on an object, the resulting force, the resultant, is the vector sum of the original forces. This is called the principle of superposition. The magnitude of the resultant varies from the difference of the magnitudes of the two forces to their sum, depending on the angle between their lines of action. As with all vector addition this results in a parallelogram rule: the addition of two vectors represented by sides of a parallelogram, gives an equivalent resultant vector which is equal in magnitude and direction to the transversal of the parallelogram. If the two forces are equal in magnitude but opposite in direction, then the resultant is zero. This condition is called static equilibrium, with the result that the object remains at its constant velocity (which could be zero).
As well as being added, forces can also be broken down (or 'resolved'). For example, a horizontal force pointing northeast can be split into two forces, one pointing north, and one pointing east. Summing these component forces using vector addition yields the original force. Force vectors can also be three-dimensional, with the third (vertical) component at right-angles to the two horizontal components.
In most explanations of mechanics, force is usually defined only implicitly, in terms of the equations that work with it. Some physicists, philosophers and mathematicians, such as Ernst Mach, Clifford Truesdell and Walter Noll, have found this problematic and sought a more explicit definition of force.
[edit] Force in special relativity
In the special theory of relativity mass and energy are equivalent (as can be seen by calculating the work required to accelerate a body). When an object's velocity increases so does its energy and hence its mass equivalent (inertia). It thus requires a greater force to accelerate it the same amount than it did at a lower velocity. The definition \vec{F} = \mathrm{d}\vec{p}/\mathrm{d}t remains valid, but the momentum is given by:
\vec{p} = \frac{m\vec{v}}{\sqrt{1 - v^2/c^2}}
where
v is the velocity and
c is the speed of light.
The relativistic expression relating force and acceleration for a particle with non-zero rest mass m\, moving in the x\, direction is:
F_x = \gamma^3 m a_x \,
F_y = \gamma m a_y \,
F_z = \gamma m a_z \,
where the Lorentz factor
\gamma = \frac{1}{\sqrt{1 - v^2/c^2}}
Here a constant force does not produce a constant acceleration, but an ever decreasing acceleration as the object approaches the speed of light. Note that γ is undefined for an object with a non zero rest mass at the speed of light, and the theory yields no prediction at that speed.
One can however restore the form of
F^\mu = mA^\mu \,
for use in relativity through the use of four-vectors. This relation is correct in relativity when Fμ is the four-force, m is the invariant mass, and Aμ is the four-acceleration.
[edit] Force and potential
Instead of a force, the mathematically equivalent concept of a potential energy field can be used for convenience. For instance, the gravitational force acting upon a body can be seen as the action of the gravitational field that is present at the body's location. Restating mathematically the definition of energy (via definition of work), a potential field U(\vec{r}) is defined as that field whose gradient is equal and opposite to the force produced at every point:
\vec{F}=-\vec{\nabla} U
Forces can be classified as conservative or nonconservative. Conservative forces are equivalent to the gradient of a potential, and include gravity, electromagnetic force, and spring force. Nonconservative forces include friction and drag. However, for any sufficiently detailed description, all forces are conservative.
[edit] Types of force
Many forces exist: the Coulomb force (between electrical charges), gravitational force (between masses), magnetic force, frictional forces, centrifugal forces (in rotating reference frames), spring force, tension, chemical bonding and contact forces to name a few.
Only four fundamental forces of nature are known:
* The strong force
* The electromagnetic force,
* The weak force
* The gravitational force.
All other forces can be reduced to these fundamental interactions.
The modern quantum mechanical view of the first three fundamental forces (all except gravity) is that particles of matter (fermions) do not directly interact with each other but rather by exchange of virtual particles (bosons) (as, for example, virtual photons in case of interaction of electric charges).
In general relativity, gravitation is not strictly viewed as a force. Rather, objects moving free in gravitational fields (say, a basket ball) simply undergo inertial motion along a straight line in the curved space-time (straight line in curved space-time is defined as the shortest space-time path between two points, and it is called geodesic). This straight line in space-time is a curved line in space, and we call it the "ballistic trajectory" of the object (an example would be a parabola for a basketball moving in a uniform gravitational field). The time derivative of the changing momentum of the body is what we label as "gravitational force" (=weight).
Light (which has no mass but has energy and momentum contained in its electromagnetic field) also propagates in gravitational fields along a straight space-time path (geodesic).
[edit] Units of measurement
The SI unit used to measure force is the newton (symbol N), which is equivalent to kg·m·s−2. The earlier CGS unit is the dyne. The relationship F=m·a can be used with either of these. In Imperial engineering units, if F is measured in "pounds force" or "lbf", and a in feet per second squared, then m must be measured in slugs. Similarly, if mass is measured in pounds mass, and a in feet per second squared, the force must be measured in poundals. The units of slugs and poundals are specifically designed to avoid a constant of proportionality in this equation.
A more general form F=k·m·a is needed if consistent units are not used. Here, the constant k is a conversion factor dependent upon the units being used.
When the standard 'g' (an acceleration of 9.80665 m/s²) is used to define pounds force, the mass in pounds is numerically equal to the weight in pounds force. However, even at sea level on Earth, the actual acceleration of free fall is quite variable, over 0.53% more at the poles than at the equator. Thus, a mass of 1.0000 lb at sea level at the equator exerts a force due to gravity of 0.9973 lbf, whereas a mass of 1.000 lb at sea level at the poles exerts a force due to gravity of 1.0026 lbf. The normal average sea level acceleration on Earth (World Gravity Formula 1980) is 9.79764 m/s², so on average at sea level on Earth, 1.0000 lb will exerts a force of 0.9991 lbf.
The equivalence 1 lb = 0.453 592 37 kg is always true, by definition, anywhere in the universe. If you use the standard 'g' which is official for defining kilograms force to define pounds force as well, then the same relationship will hold between pounds-force and kilograms-force (an old non-SI unit is still used). If a different value is used to define pounds force, then the relationship to kilograms force will be slightly different—but in any case, that relationship is also a constant anywhere in the universe. What is not constant throughout the universe is the amount of force in terms of pounds-force (or any other force units) which 1 lb will exert due to gravity.
By analogy with the slug, there is a rarely used unit of mass called the "metric slug". This is the mass that accelerates at one metre per second squared when pushed by a force of one kgf. An item with a mass of 10 kg has a mass of 1.01972661 metric slugs (= 10 kg divided by 9.80665 kg per metric slug). This unit is also known by various other names such as the hyl, TME (from a German acronym), and mug (from metric slug).
Another unit of force called the poundal (pdl) is defined as the force that accelerates 1 lbm at 1 foot per second squared. Given that 1 lbf = 32.174 lb times one foot per second squared, we have 1 lbf = 32.174 pdl. The kilogram-force is a unit of force that was used in various fields of science and technology. In 1901, the CGPM improved the definition of the kilogram-force, adopting a standard acceleration of gravity for the purpose, and making the kilogram-force equal to the force exerted by a mass of 1 kg when accelerated by 9.80665 m/s². The kilogram-force is not a part of the modern SI system, but is still used in applications such as:
* Thrust of jet and rocket engines
* Spoke tension of bicycles
* Draw weight of bows
* Torque wrenches in units such as "meter kilograms" or "kilogram centimetres" (the kilograms are rarely identified as units of force)
* Engine torque output (kgf·m expressed in various word orders, spellings, and symbols)
* Pressure gauges in "kg/cm²" or "kgf/cm²"
In colloquial, non-scientific usage, the "kilograms" used for "weight" are almost always the proper SI units for this purpose. They are units of mass, not units of force.
The symbol "kgm" for kilograms is also sometimes encountered. This might occasionally be an attempt to distinguish kilograms as units of mass from the "kgf" symbol for the units of force. It might also be used as a symbol for those obsolete torque units (kilogram-force metres) mentioned above, used without properly separating the units for kilogram and metre with either a space or a centered dot.
[edit] Conversions
Below are several conversion factors between various measurements of force:
* 1 dyne = 10-5 newtons
* 1 kgf (kilopond kp) = 9.80665 newtons
* 1 metric slug = 9.80665 kg
* 1 lbf = 32.174 poundals
* 1 slug = 32.174 lb
* 1 kgf = 2.2046 lbf
Force is a vector quantity defined as the rate of change of the momentum of the body that would be induced by that force acting alone. Since momentum is a vector, the force has a direction associated with it.
Contents
[hide]
* 1 History
* 2 Examples
* 3 Quantitative definition
o 3.1 Force in special relativity
* 4 Force and potential
* 5 Types of force
* 6 Units of measurement
o 6.1 Conversions
* 7 See also
* 8 References
[edit] History
* Force was first described by Archimedes.
* Galileo Galilei used rolling balls to disprove the Aristotelian theory of motion (1602 - 1607)
* Isaac Newton is credited for giving the first mathematical definition of force. However, he understood that the definition is not physically correct.
* Charles Coulomb is credited for experimental discovery of the inverse square law of interaction between electric charges using torsion balance (1784).
* Henry Cavendish's in 1798 measured the force of gravity between two masses (in torsion balance experiment)
* With the development of quantum field theory and general relativity in 20th century it was realised that “force” is redundant concept arising from conservation of momentum (4-momentum in GR and momentum of virtual particles in QFT). Thus currently known fundamental forces are not called forces but “fundamental interactions”.
Aristotle and others believed that it was the natural state of objects on Earth to be motionless, and that they tended toward that state (eventually settling down to inertness), if left alone. This was a common experience of humans with ordinary conditions in which friction was involved, so Newton's idea that force naturally produces a constant increase in velocity was not an obvious one. Frictional forces, acting in opposition to other kinds of forces, historically tended to hide the correct mathematical relationship between simple unopposed force and motion.
The correct behavior of objects accelerated by constant force was first discovered by Galileo in working with gravity (dropping stones and rolling cannonballs on an incline), although it was not until Newton that gravity was seen as a force. Newton generalized the behavior of constant acceleration, or constant momentum gain, to forces other than gravity. He asserted in his second law of motion that this behavior of constant momentum increase was characteristic of all forces-- including the “forces” of ordinary experience, such as tension or the stress produced by pushing on an object with a finger. In fact, he defined force as mass times acceleration, or more accurately, as a rate of change of momentum. Though, he understood that his definition is incorrect because it is a circular definition. The definition of term “force” needs a definition of the term Inertial frame of reference which is defined using the term “force”. Therefore the definition of the term “force” can be only intuitive. This problem was solved in 20th century in quantum field theory and general relativity which use this term only secondarily and it is not necessary to define it in these theories at all.
[edit] Examples
* A heavy object on a table is pulled (attracted) downward toward the floor by the force of gravity (i.e., its weight). At the same time, the table resists the downward force with equal upward force (called the normal force), resulting in zero net force, and no acceleration. (If the object is a person, he actually feels the normal force acting on him from below.)
* A heavy object on a table is gently pushed in a sideways direction by a finger. However, it fails to accelerate sideways, because the force of the finger on the object is now opposed by a new force of static friction, generated between the object and the table surface. This newly generated force exactly balances the force exerted on the object by the finger, and again no acceleration occurs. The static friction increases or decreases automatically. If the force of the finger is increased (up to a point), the opposing sideways force of static friction increases exactly to the point of perfect opposition.
* A heavy object on a table is pushed by a finger hard enough that static friction cannot generate sufficient force to match the force exerted by the finger, and the object starts sliding across the surface. If the finger is moved with a constant velocity, it needs to apply a force that exactly cancels the force of kinetic friction from the surface of the table and then the object moves with the same constant velocity. Here it seems to the naive observer that application of a force produces a velocity (rather than an acceleration). However, the velocity is constant only because the force of the finger and the kinetic friction cancel each other. Without friction, the object would continually accelerate in response to a constant force.
* A heavy object reaches the edge of the table and falls. Now the object, subjected to the constant force of its weight, but freed of the normal force and friction forces from the table, gains in velocity in direct proportion to the time of fall, and thus (before it reaches velocities where air resistance forces becomes significant compared to gravity forces) its rate of gain in momentum and velocity is constant. These facts were first discovered by Galileo.
[edit] Quantitative definition
Force is defined as the rate of change of momentum with time:
\vec{F} = {\mathrm{d}\vec{p} \over \mathrm{d}t}.
The quantity \vec{p} = m \vec{v} (where m\, is the mass and \vec{v} is the velocity) is called the momentum. This is the only definition of force known in physics (first proposed by Newton himself). If the mass m is constant in time, then Newton's second law can be derived from this definition:
\vec{F} = \frac{\mathrm{d}\vec{p}}{\mathrm{d}t}= \frac{\mathrm{d}(m\vec{v})}{\mathrm{d}t} = m\frac{\mathrm{d}(\vec{v})}{\mathrm{d}t} = m\vec{a}
where \vec{a} = {\mathrm{d} \vec{v}} /{\mathrm{d}t} is the acceleration.
This is the form Newton's second law is usually taught in introductory physics courses in order to avoid calculus notation.
All known forces of nature are defined via the above Newtonian definition of force. For example, weight (force of gravity) is defined as mass times acceleration of free fall: w = mg; spring balance force is defined as the force equilibrating certain gravitational force (say, the weight of 1 kg mass near Earth surface results in reaction force of spring equivalent to 9.8 N), etc. Calibration of spring balances (of various kinds) using either gravitational force or motion with known acceleration is important starting procedure in measuring many other forces (such as friction forces, reaction forces, electric forces, magnetic force, etc) in various physics labs.
It is not always the case that m is independent of t. For example, the mass of a rocket decreases as its propellant is ejected. Under such circumstances, the above equation (\vec{F} = m\vec{a}) is incorrect, and the original form of Newton's second law must be used.
Because momentum is a vector, then force, being its time derivative, is also a vector - it has magnitude and direction, and four-force is a four-vector in relativity. Vectors (and thus forces) are added together by their components. When two forces act on an object, the resulting force, the resultant, is the vector sum of the original forces. This is called the principle of superposition. The magnitude of the resultant varies from the difference of the magnitudes of the two forces to their sum, depending on the angle between their lines of action. As with all vector addition this results in a parallelogram rule: the addition of two vectors represented by sides of a parallelogram, gives an equivalent resultant vector which is equal in magnitude and direction to the transversal of the parallelogram. If the two forces are equal in magnitude but opposite in direction, then the resultant is zero. This condition is called static equilibrium, with the result that the object remains at its constant velocity (which could be zero).
As well as being added, forces can also be broken down (or 'resolved'). For example, a horizontal force pointing northeast can be split into two forces, one pointing north, and one pointing east. Summing these component forces using vector addition yields the original force. Force vectors can also be three-dimensional, with the third (vertical) component at right-angles to the two horizontal components.
In most explanations of mechanics, force is usually defined only implicitly, in terms of the equations that work with it. Some physicists, philosophers and mathematicians, such as Ernst Mach, Clifford Truesdell and Walter Noll, have found this problematic and sought a more explicit definition of force.
[edit] Force in special relativity
In the special theory of relativity mass and energy are equivalent (as can be seen by calculating the work required to accelerate a body). When an object's velocity increases so does its energy and hence its mass equivalent (inertia). It thus requires a greater force to accelerate it the same amount than it did at a lower velocity. The definition \vec{F} = \mathrm{d}\vec{p}/\mathrm{d}t remains valid, but the momentum is given by:
\vec{p} = \frac{m\vec{v}}{\sqrt{1 - v^2/c^2}}
where
v is the velocity and
c is the speed of light.
The relativistic expression relating force and acceleration for a particle with non-zero rest mass m\, moving in the x\, direction is:
F_x = \gamma^3 m a_x \,
F_y = \gamma m a_y \,
F_z = \gamma m a_z \,
where the Lorentz factor
\gamma = \frac{1}{\sqrt{1 - v^2/c^2}}
Here a constant force does not produce a constant acceleration, but an ever decreasing acceleration as the object approaches the speed of light. Note that γ is undefined for an object with a non zero rest mass at the speed of light, and the theory yields no prediction at that speed.
One can however restore the form of
F^\mu = mA^\mu \,
for use in relativity through the use of four-vectors. This relation is correct in relativity when Fμ is the four-force, m is the invariant mass, and Aμ is the four-acceleration.
[edit] Force and potential
Instead of a force, the mathematically equivalent concept of a potential energy field can be used for convenience. For instance, the gravitational force acting upon a body can be seen as the action of the gravitational field that is present at the body's location. Restating mathematically the definition of energy (via definition of work), a potential field U(\vec{r}) is defined as that field whose gradient is equal and opposite to the force produced at every point:
\vec{F}=-\vec{\nabla} U
Forces can be classified as conservative or nonconservative. Conservative forces are equivalent to the gradient of a potential, and include gravity, electromagnetic force, and spring force. Nonconservative forces include friction and drag. However, for any sufficiently detailed description, all forces are conservative.
[edit] Types of force
Many forces exist: the Coulomb force (between electrical charges), gravitational force (between masses), magnetic force, frictional forces, centrifugal forces (in rotating reference frames), spring force, tension, chemical bonding and contact forces to name a few.
Only four fundamental forces of nature are known:
* The strong force
* The electromagnetic force,
* The weak force
* The gravitational force.
All other forces can be reduced to these fundamental interactions.
The modern quantum mechanical view of the first three fundamental forces (all except gravity) is that particles of matter (fermions) do not directly interact with each other but rather by exchange of virtual particles (bosons) (as, for example, virtual photons in case of interaction of electric charges).
In general relativity, gravitation is not strictly viewed as a force. Rather, objects moving free in gravitational fields (say, a basket ball) simply undergo inertial motion along a straight line in the curved space-time (straight line in curved space-time is defined as the shortest space-time path between two points, and it is called geodesic). This straight line in space-time is a curved line in space, and we call it the "ballistic trajectory" of the object (an example would be a parabola for a basketball moving in a uniform gravitational field). The time derivative of the changing momentum of the body is what we label as "gravitational force" (=weight).
Light (which has no mass but has energy and momentum contained in its electromagnetic field) also propagates in gravitational fields along a straight space-time path (geodesic).
[edit] Units of measurement
The SI unit used to measure force is the newton (symbol N), which is equivalent to kg·m·s−2. The earlier CGS unit is the dyne. The relationship F=m·a can be used with either of these. In Imperial engineering units, if F is measured in "pounds force" or "lbf", and a in feet per second squared, then m must be measured in slugs. Similarly, if mass is measured in pounds mass, and a in feet per second squared, the force must be measured in poundals. The units of slugs and poundals are specifically designed to avoid a constant of proportionality in this equation.
A more general form F=k·m·a is needed if consistent units are not used. Here, the constant k is a conversion factor dependent upon the units being used.
When the standard 'g' (an acceleration of 9.80665 m/s²) is used to define pounds force, the mass in pounds is numerically equal to the weight in pounds force. However, even at sea level on Earth, the actual acceleration of free fall is quite variable, over 0.53% more at the poles than at the equator. Thus, a mass of 1.0000 lb at sea level at the equator exerts a force due to gravity of 0.9973 lbf, whereas a mass of 1.000 lb at sea level at the poles exerts a force due to gravity of 1.0026 lbf. The normal average sea level acceleration on Earth (World Gravity Formula 1980) is 9.79764 m/s², so on average at sea level on Earth, 1.0000 lb will exerts a force of 0.9991 lbf.
The equivalence 1 lb = 0.453 592 37 kg is always true, by definition, anywhere in the universe. If you use the standard 'g' which is official for defining kilograms force to define pounds force as well, then the same relationship will hold between pounds-force and kilograms-force (an old non-SI unit is still used). If a different value is used to define pounds force, then the relationship to kilograms force will be slightly different—but in any case, that relationship is also a constant anywhere in the universe. What is not constant throughout the universe is the amount of force in terms of pounds-force (or any other force units) which 1 lb will exert due to gravity.
By analogy with the slug, there is a rarely used unit of mass called the "metric slug". This is the mass that accelerates at one metre per second squared when pushed by a force of one kgf. An item with a mass of 10 kg has a mass of 1.01972661 metric slugs (= 10 kg divided by 9.80665 kg per metric slug). This unit is also known by various other names such as the hyl, TME (from a German acronym), and mug (from metric slug).
Another unit of force called the poundal (pdl) is defined as the force that accelerates 1 lbm at 1 foot per second squared. Given that 1 lbf = 32.174 lb times one foot per second squared, we have 1 lbf = 32.174 pdl. The kilogram-force is a unit of force that was used in various fields of science and technology. In 1901, the CGPM improved the definition of the kilogram-force, adopting a standard acceleration of gravity for the purpose, and making the kilogram-force equal to the force exerted by a mass of 1 kg when accelerated by 9.80665 m/s². The kilogram-force is not a part of the modern SI system, but is still used in applications such as:
* Thrust of jet and rocket engines
* Spoke tension of bicycles
* Draw weight of bows
* Torque wrenches in units such as "meter kilograms" or "kilogram centimetres" (the kilograms are rarely identified as units of force)
* Engine torque output (kgf·m expressed in various word orders, spellings, and symbols)
* Pressure gauges in "kg/cm²" or "kgf/cm²"
In colloquial, non-scientific usage, the "kilograms" used for "weight" are almost always the proper SI units for this purpose. They are units of mass, not units of force.
The symbol "kgm" for kilograms is also sometimes encountered. This might occasionally be an attempt to distinguish kilograms as units of mass from the "kgf" symbol for the units of force. It might also be used as a symbol for those obsolete torque units (kilogram-force metres) mentioned above, used without properly separating the units for kilogram and metre with either a space or a centered dot.
[edit] Conversions
Below are several conversion factors between various measurements of force:
* 1 dyne = 10-5 newtons
* 1 kgf (kilopond kp) = 9.80665 newtons
* 1 metric slug = 9.80665 kg
* 1 lbf = 32.174 poundals
* 1 slug = 32.174 lb
* 1 kgf = 2.2046 lbf
Re: Important Information
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Re: Important Information
With the invention of bubble chambers and spark chambers in the 1950s, experimental particle physics discovered a large and ever-growing number of particles called hadrons. It seemed that such a large number of particles could not all be fundamental. First, the particles were classified by charge and isospin; then, in 1953, according to strangeness by Murray Gell-Mann and Kazuhiko Nishijima. To gain greater insight, the hadrons were sorted into groups having similar properties and masses using the eightfold way, invented in 1961 by Gell-Mann and Yuval Ne'eman. Gell-Mann and George Zweig went on to propose in 1963 that the structure of the groups could be explained by the existence of three flavours of smaller particles inside the hadrons: the quarks.
At this stage, one particle, the Δ++ remained mysterious; in the quark model, it is composed of three up quarks with parallel spins. However, since quarks are fermions, this combination is forbidden by the Pauli exclusion principle. In 1965, Moo-Young Han with Yoichiro Nambu and Oscar W. Greenberg independently resolved the problem by proposing that quarks possess an additional SU(3) gauge degree of freedom, later called colour charge. Han and Nambu noted that quarks would interact via an octet of vector gauge bosons: the gluons.
Since free quark searches consistently failed to turn up any evidence for the new particles, it was then believed that quarks were merely convenient mathematical constructs, not real particles. Richard Feynman argued that high energy experiments showed quarks to be real: he called them partons (since they were parts of hadrons). James Bjorken proposed that certain relations should then hold in deep inelastic scattering of electrons and protons, which were spectacularly verified in experiments at SLAC in 1969.
Although the study of the strong interaction remained daunting, the discovery of asymptotic freedom by David Gross, David Politzer and Frank Wilczek allowed people to make precise predictions of the results of many high energy experiments using the techniques of perturbation theory. Evidence of gluons was discovered in three jet events at PETRA in 1979. These experiments became more and more precise, culminating in the verification of perturbative QCD at the level of a few percent at the LEP in CERN.
The other side of asymptotic freedom is confinement. Since the force between colour charges does not decrease with distance, it is believed that quarks and gluons can never be liberated from hadrons. This aspect of the theory is verified within lattice QCD computations, but is not mathematically proven. One of the Millennium Prizes announced by the Clay Mathematics Institute requires a claimant to produce such a proof. Other aspects of non-perturbative QCD are the exploration of phases of quark matter, including the quark-gluon plasma.
Every field theory of particle physics is based on certain symmetries of nature whose existence is deduced from observations. These can be
* local symmetries, that is the symmetry acts independently at each point in space-time. Each such symmetry is the basis of a gauge theory and requires the introduction of its own gauge bosons.
* global symmetries, which are symmetries whose operations must be simultaneously applied to all points of space-time.
QCD is a gauge theory of the SU(3) gauge group obtained by taking the colour charge to define a local symmetry.
Since the strong interaction does not discriminate between different flavors of quark, QCD has approximate flavor symmetry, which is broken by the differing masses of the quarks.
There are additional global symmetries whose definitions require the notion of chirality, discrimination between left and right-handed. If the spin of a particle has a positive projection on its direction of motion then it is called left-handed; otherwise, it is right-handed. Chirality and handedness are not the same, but become approximately equivalent at high energies.
* Chiral symmetries involve independent transformations of these two types of particle.
* Vector symmetries (also called diagonal symmetries) mean the same transformation is applied on the two chiralities.
* Axial symmetries are those in which one transformation is applied on left-handed particles and the inverse on the right-handed particles.
At this stage, one particle, the Δ++ remained mysterious; in the quark model, it is composed of three up quarks with parallel spins. However, since quarks are fermions, this combination is forbidden by the Pauli exclusion principle. In 1965, Moo-Young Han with Yoichiro Nambu and Oscar W. Greenberg independently resolved the problem by proposing that quarks possess an additional SU(3) gauge degree of freedom, later called colour charge. Han and Nambu noted that quarks would interact via an octet of vector gauge bosons: the gluons.
Since free quark searches consistently failed to turn up any evidence for the new particles, it was then believed that quarks were merely convenient mathematical constructs, not real particles. Richard Feynman argued that high energy experiments showed quarks to be real: he called them partons (since they were parts of hadrons). James Bjorken proposed that certain relations should then hold in deep inelastic scattering of electrons and protons, which were spectacularly verified in experiments at SLAC in 1969.
Although the study of the strong interaction remained daunting, the discovery of asymptotic freedom by David Gross, David Politzer and Frank Wilczek allowed people to make precise predictions of the results of many high energy experiments using the techniques of perturbation theory. Evidence of gluons was discovered in three jet events at PETRA in 1979. These experiments became more and more precise, culminating in the verification of perturbative QCD at the level of a few percent at the LEP in CERN.
The other side of asymptotic freedom is confinement. Since the force between colour charges does not decrease with distance, it is believed that quarks and gluons can never be liberated from hadrons. This aspect of the theory is verified within lattice QCD computations, but is not mathematically proven. One of the Millennium Prizes announced by the Clay Mathematics Institute requires a claimant to produce such a proof. Other aspects of non-perturbative QCD are the exploration of phases of quark matter, including the quark-gluon plasma.
Every field theory of particle physics is based on certain symmetries of nature whose existence is deduced from observations. These can be
* local symmetries, that is the symmetry acts independently at each point in space-time. Each such symmetry is the basis of a gauge theory and requires the introduction of its own gauge bosons.
* global symmetries, which are symmetries whose operations must be simultaneously applied to all points of space-time.
QCD is a gauge theory of the SU(3) gauge group obtained by taking the colour charge to define a local symmetry.
Since the strong interaction does not discriminate between different flavors of quark, QCD has approximate flavor symmetry, which is broken by the differing masses of the quarks.
There are additional global symmetries whose definitions require the notion of chirality, discrimination between left and right-handed. If the spin of a particle has a positive projection on its direction of motion then it is called left-handed; otherwise, it is right-handed. Chirality and handedness are not the same, but become approximately equivalent at high energies.
* Chiral symmetries involve independent transformations of these two types of particle.
* Vector symmetries (also called diagonal symmetries) mean the same transformation is applied on the two chiralities.
* Axial symmetries are those in which one transformation is applied on left-handed particles and the inverse on the right-handed particles.
Re: Important Information
U aare olmost as clevor as i ams.
Re: Important Information
Nanotechnology is a field of applied science and technology covering a broad range of topics. The main unifying theme is the control of matter on a scale smaller than one micrometre, as well as the fabrication of devices on this same length scale. It is a highly multidisciplinary field, drawing from fields such as colloidal science, device physics, and supramolecular chemistry. Much speculation exists as to what new science and technology might result from these lines of research. Some view nanotechnology as a marketing term that describes pre-existing lines of research applied to the sub-micron size scale.
Despite the apparent simplicity of this definition, nanotechnology actually encompasses diverse lines of inquiry. Nanotechnology cuts across many disciplines, including colloidal science, chemistry, applied physics, biology. It could variously be seen as an extension of existing sciences into the nanoscale, or as a recasting of existing sciences using a newer, more modern term. Two main approaches are used in nanotechnology: one is a "bottom-up" approach where materials and devices are built from molecular components which assemble themselves chemically using principles of molecular recognition; the other being a "top-down" approach where nano-objects are constructed from larger entities without atomic-level control.
The impetus for nanotechnology has stemmed from a renewed interest in colloidal science, coupled with a new generation of analytical tools such as the atomic force microscope (AFM) and the scanning tunneling microscope (STM). Combined with refined processes such as electron beam lithography, these instruments allow the deliberate manipulation of nanostructures, and in turn led to the observation of novel phenomena. Nanotechnology is also an umbrella description of emerging technological developments associated with sub-microscopic dimensions. Despite the great promise of numerous nanotechnologies such as quantum dots and nanotubes, real applications that have moved out of the lab and into the marketplace have mainly utilized the advantages of colloidal nanoparticles in bulk form, such as suntan lotion, cosmetics, protective coatings, and stain resistant clothing.
Contents
[hide]
* 1 Fundamental concepts
o 1.1 Usage of the term
o 1.2 Larger to smaller: a materials perspective
o 1.3 Simple to complex: a molecular perspective
o 1.4 Molecular Nanotechnology: a long-term view
* 2 Current research
o 2.1 Nanomaterials
o 2.2 Bottom-up approaches
o 2.3 Top-down approaches
o 2.4 Functional approaches
o 2.5 Speculative
o 2.6 Tools and techniques
* 3 Societal implications
* 4 See also
* 5 Further reading
* 6 External links
o 6.1 Publishers and Prospectus
o 6.2 Nanotechnology materials and projects
o 6.3 Higher Education Nanotechnology Centers
o 6.4 Nanotechnology & Ethics
o 6.5 Other
[edit] Fundamental concepts
[edit] Usage of the term
For information about the origins of nanotechnology, see History of nanotechnology.
Wikibooks
Wikibooks has more about this subject:
The Opensource Handbook of Nanoscience and Nanotechnology
Nanotechnology is an umbrella term that is used to describe a variety of techniques to fabricate materials and devices on the nanoscale. The genesis for nanotechnology has its roots in the colloidal science of the late 19th century. These early innovations have been combined with more recent developments in device manufacture. The term has served in some regards as a means to generate new lines of funding from government agencies. One nanometer (nm) is one billionth, or 10-9 of a meter. For comparison, typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range .12-.15 nm, and a DNA double-helix has a diameter around 2 nm. On the other hand, the smallest cellular lifeforms, the bacteria of the genus Mycoplasma, are around 200 nm in length.
Nanotechnological techniques include those used for fabrication of nanowires, those used in semiconductor fabrication such as deep ultraviolet lithography, electron beam lithography, focused ion beam machining, nanoimprint lithography, atomic layer deposition, and molecular vapor deposition, and further including molecular self-assembly techniques such as those employing di-block copolymers. However, all of these techniques preceded the nanotech era, and are extensions in the development of scientific advancements rather than techniques which were devised with the sole purpose of creating nanotechnology or which were results of nanotechnology research.
General fields involved with proper characterization of these systems include physics, chemistry, and biology, as well as mechanical and electrical engineering. However, due to the inter- and multidisciplinary nature of nanotechnology, subdisciplines such as physical chemistry, materials science, or biomedical engineering are considered significant or essential components of nanotechnology. The design, synthesis, characterization, and application of materials are dominant concerns of nanotechnologists. The manufacture of polymers based on molecular structure, or the design of computer chip layouts based on surface science are examples of nanotechnology in modern use. Colloidal suspensions also play an essential role in nanotechnology.
Technologies currently branded with the term 'nano' are little related to and fall far short of the most ambitious and transformative technological goals of the sort in molecular manufacturing proposals, but the term still connotes such ideas. Thus there may be a danger that a "nano bubble" will form (or is forming already) from the use of the term by scientists and entrepreneurs to garner funding, regardless of (and perhaps despite a lack of) interest in the transformative possibilities of more ambitious and far-sighted work. The above prediction has come to pass, as by 2006 over $400 million has been invested in Nanotechnology, mostly by venture capital, with very meager results. From this perspective, Nanotechnology may be viewed as a collection of wishful predictions, aimed at generating unwarranted excitement among venture capitalists.
The National Science Foundation (a major source of funding for nanotechnology in the United States) funded researcher David Berube to study the field of nanotechnology. His findings are published in the monograph “Nano-Hype: The Truth Behind the Nanotechnology Buzz". This published study (with a foreword by Mihail Roco, head of the NNI) concludes that much of what is sold as “nanotechnology” is in fact a recasting of straightforward materials science, which is leading to a “nanotech industry built solely on selling nanotubes, nanowires, and the like” which will “end up with a few suppliers selling low margin products in huge volumes."
[edit] Larger to smaller: a materials perspective
A unique aspect of nanotechnology is the vastly increased ratio of surface area to volume present in many nanoscale materials which opens new possibilities in surface-based science, such as catalysis. A number of physical phenomena become noticeably pronounced as the size of the system decreases. These include statistical mechanical effects, as well as quantum mechanical effects, for example the “quantum size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, it becomes dominant when the nanometer size range is reached. Additionally, a number of physical properties change when compared to macroscopic systems. One example is the increase in surface area to volume of materials. This catalytic activity also opens potential risks in their interaction with biomaterials.
Nanotechnology can be thought of as extensions of traditional disciplines towards the explicit consideration of these properties. Additionally, traditional disciplines can be re-interpreted as specific applications of nanotechnology. This dynamic reciprocation of ideas and concepts contributes to the modern understanding of the field. Broadly speaking, nanotechnology is the synthesis and application of ideas from science and engineering towards the understanding and production of novel materials and devices. These products generally make copious use of physical properties associated with small scales.
Materials reduced to the nanoscale can suddenly show very different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent (copper); inert materials become catalysts (platinum); stable materials turn combustible (aluminum); solids turn into liquids at room temperature (gold); insulators become conductors (silicon). Materials such as gold, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales. Much of the fascination with nanotechnology stems from these unique quantum and surface phenomena that matter exhibits at the nanoscale.
Nanosize powder particles (a few nanometres in diameter, also called nanoparticles) are potentially important in ceramics, powder metallurgy, the achievement of uniform nanoporosity and similar applications. The strong tendency of small particles to form clumps ("agglomerates") is a serious technological problem that impedes such applications. However, a few dispersants such as ammonium citrate (aqueous) and imidazoline or oleyl alcohol (nonaqueous) are promising additives for deagglomeration. (Dispersants are discussed in "Organic Additives And Ceramic Processing," by Daniel J. Shanefield, Kluwer Academic Publ., Boston.)
Another concern is that the volume of an object decreases as the third power of its linear dimensions, but the surface area only decreases as its second power. This somewhat subtle and unavoidable principle has huge ramifications. For example the power of a drill (or any other machine) is proportional to the volume, while the friction of the drill's bearings and gears is proportional to their surface area. For a normal-sized drill, the power of the device is enough to handily overcome any friction. However, scaling its length down by a factor of 1000, for example, decreases its power by 10003 (a factor of a billion) while reducing the friction by only 10002 (a factor of "only" a million). Proportionally it has 1000 times less power per unit friction than the original drill. If the original friction-to-power ratio was, say, 1%, that implies the smaller drill will have 10 times as much friction as power. The drill is useless.
This is why, while super-miniature electronic integrated circuits can be made to function, the same technology cannot be used to make functional mechanical devices in miniature: the friction overtakes the available power at such small scales. So while you may see microphotographs of delicately etched silicon gears, such devices are curiosities with limited real world applications, for example in moving mirrors and shutters. Surface tension increases in the same way, causing very small objects tend to stick together. This could possibly make any kind of "micro factory" impractical: even if robotic arms and hands could be scaled down, anything they pick up will tend to be impossible to put down. The above being said, molecular evolution has resulted in working cilia, flagella, muscle fibers, and rotary motors in aqueous environments, all on the nanoscale, so we are faced with existence proofs which technological design has not been able to duplicate and for which no design approach has been articulated.
All these scaling issues have to be kept in mind while evaluating any kind of nanotechnology.
[edit] Simple to complex: a molecular perspective
Modern synthetic chemistry has reached the point where it is possible to prepare small molecules to almost any structure. These methods are used today to produce a wide variety of useful chemicals such as pharmaceuticals or commercial polymers. The ability of this is to extend the control to the next, seeking methods to assemble these single molecules into supramolecular assemblies consisting of many molecules arranged in a well defined manner.
These approaches utilize the concepts of molecular self-assembly and/or supramolecular chemistry to automatically arrange themselves into some useful conformation through a bottom-up approach. The concept of molecular recognition is especially important: molecules can be designed so that a specific conformation or arrangement is favored due to non-covalent intermolecular forces. The Watson-Crick basepairing rules are a direct result of this, as is the specificity of an enzyme being targeted to a single substrate, or the specific folding of the protein itself. Thus, two or more components can be designed to be complementary and mutually attractive so that they make a more complex and useful whole.
Such bottom-up approaches should, broadly speaking, be able to produce devices in parallel and much cheaper than top-down methods, but could potentially be overwhelmed as the size and complexity of the desired assembly increases. However, the bottom-up approach is viewed by many thoughtful scientists as being mostly wishful thinking. Most useful structures require complex and thermodynamically unlikely arrangements of atoms. The basic laws of probability and entropy make it very unlikely that atoms will "self-assemble" in useful configurations, or can be easily and economically nudged to do so. About the only example of this is crystal-growing, for which Nanotechnology cannot take any credit, it having been around for millenia.
[edit] Molecular Nanotechnology: a long-term view
Advanced nanotechnology, sometimes called molecular manufacturing, is a term given to the concept of engineered nanosystems (nanoscale machines) operating on the molecular scale. By the countless examples found in biology it is currently known that billions of years of evolutionary feedback can produce sophisticated, stochastically optimized biological machines, and it is hoped that developments in nanotechnology will make possible their construction by some shorter means, perhaps using biomimetic principles. However, K Eric Drexler and other researchers have proposed that advanced nanotechnology, although perhaps initially implemented by biomimetic means, ultimately could be based on mechanical engineering principles (see also mechanosynthesis)
When the term "nanotechnology" was independently coined and popularized by Eric Drexler, who at the time was unaware of an earlier usage by Norio Taniguchi, it referred to a future manufacturing technology based on molecular machine systems. The premise was that molecular-scale biological analogies of traditional machine components demonstrated that molecular machines were possible, and that a manufacturing technology based on the mechanical functionality of these components (such as gears, bearings, motors, and structural members) would enable programmable, positional assembly to atomic specification (see the original reference PNAS-1981). The physics and engineering performance of exemplar designs were analyzed in the textbook Nanosystems.
Another view, put forth by Carlo Montemagno, is that future nanosystems will be hybrids of silicon technology and biological molecular machines, and his group's research is directed toward this end.
The seminal experiment proving that positional molecular assembly is possible was performed by Ho and Lee at Cornell University in 1999. They used a scanning tunneling microscope to move an individual carbon monoxide molecule (CO) to an individual iron atom (Fe) sitting on a flat silver crystal, and chemically bound the CO to the Fe by applying a voltage.
Though biology clearly demonstrates that molecular machine systems are possible, non-biological molecular machines are today only in their infancy. Leaders in research on non-biological molecular machines are Dr. Alex Zettl and his colleagues at Lawrence Berkeley Laboratories and UC Berkeley. They have constructed at least three distinct molecular devices whose motion is controlled from the desktop with changing voltage: a nanotube nanomotor, a molecular actuator, and a nanoelectromechanical relaxation oscillator.
Manufacturing in the context of productive nanosystems is not related to, and should be clearly distinguished from, the conventional technologies used to manufacture nanomaterials such as carbon nanotubes and nanoparticles.
There exists the potential to design and fabricate artificial structures analogous to natural cells and even organisms. Note that these are just blue-sky "potentials", and fall closer to the disciplines of Applied Biology and gene-splicing than to Nanotechnology.
[edit] Current research
Space-filling model of the nanocar on a surface, using fullerenes as wheels.
Space-filling model of the nanocar on a surface, using fullerenes as wheels.
Graphical representation of a rotaxane, useful as a molecular switch.
Graphical representation of a rotaxane, useful as a molecular switch.
A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, http://www.mems.sandia.gov.
A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, http://www.mems.sandia.gov.
As nanotechnology is a very broad term, there are many disparate but sometimes overlapping subfields that could fall under its umbrella. The following avenues of research could be considered subfields of nanotechnology. Note that these categories are fairly nebulous and a single subfield may overlap many of them, especially as the field of nanotechnology continues to mature.
See also List of nanotechnology applications.
[edit] Nanomaterials
This includes subfields which develop or study materials having unique properties arising from their nanoscale dimensions.
* Colloid science has given rise to many materials which may be useful in nanotechnology, such as carbon nanotubes and other fullerenes, and various nanoparticles and nanorods.
* Nanoscale materials can also be used for bulk applications; most present commercial applications of nanotechnology are of this flavor.
* Headway has been made in using these materials for medical applications; see Nanomedicine.
[edit] Bottom-up approaches
These seek to arrange smaller components into more complex assemblies.
* DNA Nanotechnology utilizes the specificity of Watson-Crick basepairing to construct well-defined structures out of DNA and other nucleic acids.
* More generally, molecular self-assembly seeks to use concepts of supramolecular chemistry, and molecular recognition in particular, to cause single-molecule components to automatically arrange themselves into some useful conformation.
[edit] Top-down approaches
These seek to create smaller devices by using larger ones to direct their assembly.
* Many technologies descended from conventional solid-state silicon methods for fabricating microprocessors are now capable of creating features smaller than 100 nm, falling under the definition of nanotechnology. Giant magnetoresistance-based hard drives already on the market fit this description, [1] as do atomic layer deposition (ALD) techniques.
* Solid-state techniques can also be used to create devices known as nanoelectromechanical systems or NEMS, which are related to microelectromechanical systems or MEMS.
* Atomic force microscope tips can be used as a nanoscale "write head" to deposit a chemical on a surface in a desired pattern in a process called dip pen nanolithography. This fits into the larger subfield of nanolithography.
[edit] Functional approaches
These seek to develop components of a desired functionality without regard to how they might be assembled.
* Molecular electronics seeks to develop molecules with useful electronic properties. These could then be used as single-molecule components in a nanoelectronic device. For an example see rotaxane.
* Synthetic chemical methods can also be used to create synthetic molecular motors, such as in a so-called nanocar.
[edit] Speculative
These subfields seek to anticipate what inventions nanotechnology might yield, or attempt to propose an agenda along which inquiry might progress. These often take a big-picture view of nanotechnology, with more emphasis on its societal implications than the details of how such inventions could actually be created.
* Molecular nanotechnology is a proposed approach which involves manipulating single molecules in finely controlled, deterministic ways. This is more theoretical (some would say merely hypothetical) than the other subfields and is beyond current capabilities.
* Nanorobotics centers on self-sufficient machines of some functionality operating at the nanoscale.
* Programmable matter based on artificial atoms seeks to design materials whose properties can be easily and reversibly externally controlled.
[edit] Tools and techniques
Typical AFM setup. A microfabricated cantilever with a sharp tip is deflected by features on a sample surface, much like in a phonograph but on a much smaller scale. A laser beam reflects off the backside of the cantilever into a set of photodetectors, allowing the deflection to be measured and assembled into an image of the surface.
Typical AFM setup. A microfabricated cantilever with a sharp tip is deflected by features on a sample surface, much like in a phonograph but on a much smaller scale. A laser beam reflects off the backside of the cantilever into a set of photodetectors, allowing the deflection to be measured and assembled into an image of the surface.
Nanoscience and nanotechnology only became possible in the 1910's with the development of the first tools to measure and make nanostructures. But the actual development started with the discovery of electrons and neutrons which showed scientists that matter can really exist on a much smaller scale than what we normally think of as small, and/or what they thought was possible at the time. It was at this time when curiosity for nanostructures had originated.
The atomic force microscope (AFM) and the Scanning Tunneling Microscope (STM) are two early versions of scanning probes that launched nanotechnology. There are other types of scanning probe microscopy, all flowing from the ideas of the scanning confocal microscope developed by Marvin Minsky in 1961 and the scanning acoustic microscope (SAM) developed by Calvin Quate and coworkers in the 1970's, that make it possible to see structures at the nanoscale. The tip of a scanning probe can also be used to manipulate nanostructures (a process called positional assembly). However, this is a very slow process. This led to the development of various techniques of nanolithography such as dip pen nanolithography, electron beam lithography or nanoimprint lithography. Lithography is a top-down fabrication technique where a bulk material is reduced in size to nanoscale pattern.
The top-down approach anticipates nanodevices that must be built piece by piece in stages, much as manufactured items are currently made. Scanning probe microscopy is an important technique both for characterization and synthesis of nanomaterials. Atomic force microscopes and scanning tunneling microscopes can be used to look at surfaces and to move atoms around. By designing different tips for these microscopes, they can be used for carving out structures on surfaces and to help guide self-assembling structures. Atoms can be moved around on a surface with scanning probe microscopy techniques, but it is cumbersome, expensive and very time-consuming. For these reasons, it is not feasible to construct nanoscaled devices atom by atom. Assembling a billion transistor microchip at the rate of about one transistor an hour is inefficient.
One hope is that these techniques may eventually be used to make primitive nanomachines, which in turn can be used to make more sophisticated nanomachines. But the whole nanomachine concept is wild speculation, as we are unable to even conceptually design human scale machines that can independently make other machines. If we can't make them on a convenient scale, what are the chances they can be made on a nano scale? Also nanomachines have the very substantial hurdles of friction and surface-tension.
In contrast, bottom-up techniques build or grow larger structures atom by atom or molecule by molecule. These techniques include chemical synthesis, self-assembly and positional assembly. Another variation of the bottom-up approach is molecular beam epitaxy or MBE. Researchers at Bell Telephone Laboratories like John R. Arthur. Alfred Y. Cho, and Art C. Gossard developed and implemented MBE as a research tool in the late 1960s and 1970s. Samples made by MBE were key to to the discovery of the fractional quantum Hall effect for which the 1998 Nobel Prize in Physics was awarded. MBE allows scientists to lay down atomically-precise layers of atoms and, in the process, build up complex structures. Important for research on semiconductors, MBE is also widely used to make samples and devices for the newly emerging field of spintronics.
Newer techniques such as Dual Polarisation Interferometry are enabling scientists to measure quantitatively the molecular interactions that take place at the nano-scale.
[edit] Societal implications
Main article: Implications of nanotechnology
Potential risks of nanotechnology can broadly be grouped into three areas:
* the risk to health and environment from nanoparticles and nanomaterials;
* the risk posed by molecular manufacturing (or advanced nanotechnology);
* societal risks.
Nanoethics concerns the ethical and social issues associated with developments in nanotechnology, a science which encompass several fields of science and engineering, including biology, chemistry, computing, and materials science. Nanotechnology refers to the manipulation of very small-scale matter – a nanometer is one billionth of a meter, and nanotechnology is generally used to mean work on matter at 100 nanometers and smaller.
Social risks related to nanotechnology development include the possibility of military applications of nanotechnology (such as implants and other means for soldier enhancement) as well as enhanced surveillance capabilities through nano-sensors. However those applications still belong to science-fiction and will not be possible in the next decades. Significant environmental, health, and safety issues might arise with development in nanotechnology since some negative effects of nanoparticles in our environment might be overlooked. However nature itself creates all kinds of nanoobjects, so probable dangers are not due to the nanoscale alone, but due to the fact that toxic materials become more harmful when ingested or inhaled as nanoparticles (see nanotoxicology).
[edit] See also
* List of nanotechnology topics
* Femtotechnology
* Mesotechnology
* Nanoengineering
* NanoSafe
* Nanotechnology in fiction
* Nanotitanate
* Nanotoxicology
* Picotechnology
* Top-down and bottom-up design
[edit] Further reading
* Geoffrey Hunt and Michael Mehta (2006), Nanotechnology: Risk, Ethics and Law. London: Earthscan Books.
* Hari Singh Nalwa (2004), Encyclopedia of Nanoscience and Nanotechnology (10-Volume Set), American Scientific Publishers. ISBN 1-58883-001-2
* Michael Rieth and Wolfram Schommers (2006), Handbook of Theoretical and Computational Nanotechnology (10-Volume Set), American Scientific Publishers. ISBN 1-58883-042-X
* David M. Berube 2006. Nano-hype: The Truth Behind the Nanotechnology Buzz. Prometheus Books. ISBN 1-59102-351-3
* Jones, Richard A. L. (2004). Soft Machines. Oxford University Press, Oxford, United Kingdom. ISBN 0198528558.
* Akhlesh Lakhtakia (ed) (2004). The Handbook of Nanotechnology. Nanometer Structures: Theory, Modeling, and Simulation. SPIE Press, Bellingham, WA, USA. ISBN 0-8194-5186-X.
* Daniel J. Shanefield (1996). Organic Additives And Ceramic Processing. Kluwer Academic Publishers. ISBN 0-7923-9765-7.
* Fei Wang & Akhlesh Lakhtakia (eds) (2006). Selected Papers on Nanotechnology -- Theory & Modeling (Milestone Volume 182). SPIE Press, Bellingham, WA, USA. ISBN 0-8194-6354-X.
* Roger Smith, Nanotechnology: A Brief Technology Analysis, CTOnet.org, 2004. [2]
* Arius Tolstoshev, Nanotechnology: Assessing the Environmental Risks for Australia, Earth Policy Centre, September 2006
Despite the apparent simplicity of this definition, nanotechnology actually encompasses diverse lines of inquiry. Nanotechnology cuts across many disciplines, including colloidal science, chemistry, applied physics, biology. It could variously be seen as an extension of existing sciences into the nanoscale, or as a recasting of existing sciences using a newer, more modern term. Two main approaches are used in nanotechnology: one is a "bottom-up" approach where materials and devices are built from molecular components which assemble themselves chemically using principles of molecular recognition; the other being a "top-down" approach where nano-objects are constructed from larger entities without atomic-level control.
The impetus for nanotechnology has stemmed from a renewed interest in colloidal science, coupled with a new generation of analytical tools such as the atomic force microscope (AFM) and the scanning tunneling microscope (STM). Combined with refined processes such as electron beam lithography, these instruments allow the deliberate manipulation of nanostructures, and in turn led to the observation of novel phenomena. Nanotechnology is also an umbrella description of emerging technological developments associated with sub-microscopic dimensions. Despite the great promise of numerous nanotechnologies such as quantum dots and nanotubes, real applications that have moved out of the lab and into the marketplace have mainly utilized the advantages of colloidal nanoparticles in bulk form, such as suntan lotion, cosmetics, protective coatings, and stain resistant clothing.
Contents
[hide]
* 1 Fundamental concepts
o 1.1 Usage of the term
o 1.2 Larger to smaller: a materials perspective
o 1.3 Simple to complex: a molecular perspective
o 1.4 Molecular Nanotechnology: a long-term view
* 2 Current research
o 2.1 Nanomaterials
o 2.2 Bottom-up approaches
o 2.3 Top-down approaches
o 2.4 Functional approaches
o 2.5 Speculative
o 2.6 Tools and techniques
* 3 Societal implications
* 4 See also
* 5 Further reading
* 6 External links
o 6.1 Publishers and Prospectus
o 6.2 Nanotechnology materials and projects
o 6.3 Higher Education Nanotechnology Centers
o 6.4 Nanotechnology & Ethics
o 6.5 Other
[edit] Fundamental concepts
[edit] Usage of the term
For information about the origins of nanotechnology, see History of nanotechnology.
Wikibooks
Wikibooks has more about this subject:
The Opensource Handbook of Nanoscience and Nanotechnology
Nanotechnology is an umbrella term that is used to describe a variety of techniques to fabricate materials and devices on the nanoscale. The genesis for nanotechnology has its roots in the colloidal science of the late 19th century. These early innovations have been combined with more recent developments in device manufacture. The term has served in some regards as a means to generate new lines of funding from government agencies. One nanometer (nm) is one billionth, or 10-9 of a meter. For comparison, typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range .12-.15 nm, and a DNA double-helix has a diameter around 2 nm. On the other hand, the smallest cellular lifeforms, the bacteria of the genus Mycoplasma, are around 200 nm in length.
Nanotechnological techniques include those used for fabrication of nanowires, those used in semiconductor fabrication such as deep ultraviolet lithography, electron beam lithography, focused ion beam machining, nanoimprint lithography, atomic layer deposition, and molecular vapor deposition, and further including molecular self-assembly techniques such as those employing di-block copolymers. However, all of these techniques preceded the nanotech era, and are extensions in the development of scientific advancements rather than techniques which were devised with the sole purpose of creating nanotechnology or which were results of nanotechnology research.
General fields involved with proper characterization of these systems include physics, chemistry, and biology, as well as mechanical and electrical engineering. However, due to the inter- and multidisciplinary nature of nanotechnology, subdisciplines such as physical chemistry, materials science, or biomedical engineering are considered significant or essential components of nanotechnology. The design, synthesis, characterization, and application of materials are dominant concerns of nanotechnologists. The manufacture of polymers based on molecular structure, or the design of computer chip layouts based on surface science are examples of nanotechnology in modern use. Colloidal suspensions also play an essential role in nanotechnology.
Technologies currently branded with the term 'nano' are little related to and fall far short of the most ambitious and transformative technological goals of the sort in molecular manufacturing proposals, but the term still connotes such ideas. Thus there may be a danger that a "nano bubble" will form (or is forming already) from the use of the term by scientists and entrepreneurs to garner funding, regardless of (and perhaps despite a lack of) interest in the transformative possibilities of more ambitious and far-sighted work. The above prediction has come to pass, as by 2006 over $400 million has been invested in Nanotechnology, mostly by venture capital, with very meager results. From this perspective, Nanotechnology may be viewed as a collection of wishful predictions, aimed at generating unwarranted excitement among venture capitalists.
The National Science Foundation (a major source of funding for nanotechnology in the United States) funded researcher David Berube to study the field of nanotechnology. His findings are published in the monograph “Nano-Hype: The Truth Behind the Nanotechnology Buzz". This published study (with a foreword by Mihail Roco, head of the NNI) concludes that much of what is sold as “nanotechnology” is in fact a recasting of straightforward materials science, which is leading to a “nanotech industry built solely on selling nanotubes, nanowires, and the like” which will “end up with a few suppliers selling low margin products in huge volumes."
[edit] Larger to smaller: a materials perspective
A unique aspect of nanotechnology is the vastly increased ratio of surface area to volume present in many nanoscale materials which opens new possibilities in surface-based science, such as catalysis. A number of physical phenomena become noticeably pronounced as the size of the system decreases. These include statistical mechanical effects, as well as quantum mechanical effects, for example the “quantum size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, it becomes dominant when the nanometer size range is reached. Additionally, a number of physical properties change when compared to macroscopic systems. One example is the increase in surface area to volume of materials. This catalytic activity also opens potential risks in their interaction with biomaterials.
Nanotechnology can be thought of as extensions of traditional disciplines towards the explicit consideration of these properties. Additionally, traditional disciplines can be re-interpreted as specific applications of nanotechnology. This dynamic reciprocation of ideas and concepts contributes to the modern understanding of the field. Broadly speaking, nanotechnology is the synthesis and application of ideas from science and engineering towards the understanding and production of novel materials and devices. These products generally make copious use of physical properties associated with small scales.
Materials reduced to the nanoscale can suddenly show very different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent (copper); inert materials become catalysts (platinum); stable materials turn combustible (aluminum); solids turn into liquids at room temperature (gold); insulators become conductors (silicon). Materials such as gold, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales. Much of the fascination with nanotechnology stems from these unique quantum and surface phenomena that matter exhibits at the nanoscale.
Nanosize powder particles (a few nanometres in diameter, also called nanoparticles) are potentially important in ceramics, powder metallurgy, the achievement of uniform nanoporosity and similar applications. The strong tendency of small particles to form clumps ("agglomerates") is a serious technological problem that impedes such applications. However, a few dispersants such as ammonium citrate (aqueous) and imidazoline or oleyl alcohol (nonaqueous) are promising additives for deagglomeration. (Dispersants are discussed in "Organic Additives And Ceramic Processing," by Daniel J. Shanefield, Kluwer Academic Publ., Boston.)
Another concern is that the volume of an object decreases as the third power of its linear dimensions, but the surface area only decreases as its second power. This somewhat subtle and unavoidable principle has huge ramifications. For example the power of a drill (or any other machine) is proportional to the volume, while the friction of the drill's bearings and gears is proportional to their surface area. For a normal-sized drill, the power of the device is enough to handily overcome any friction. However, scaling its length down by a factor of 1000, for example, decreases its power by 10003 (a factor of a billion) while reducing the friction by only 10002 (a factor of "only" a million). Proportionally it has 1000 times less power per unit friction than the original drill. If the original friction-to-power ratio was, say, 1%, that implies the smaller drill will have 10 times as much friction as power. The drill is useless.
This is why, while super-miniature electronic integrated circuits can be made to function, the same technology cannot be used to make functional mechanical devices in miniature: the friction overtakes the available power at such small scales. So while you may see microphotographs of delicately etched silicon gears, such devices are curiosities with limited real world applications, for example in moving mirrors and shutters. Surface tension increases in the same way, causing very small objects tend to stick together. This could possibly make any kind of "micro factory" impractical: even if robotic arms and hands could be scaled down, anything they pick up will tend to be impossible to put down. The above being said, molecular evolution has resulted in working cilia, flagella, muscle fibers, and rotary motors in aqueous environments, all on the nanoscale, so we are faced with existence proofs which technological design has not been able to duplicate and for which no design approach has been articulated.
All these scaling issues have to be kept in mind while evaluating any kind of nanotechnology.
[edit] Simple to complex: a molecular perspective
Modern synthetic chemistry has reached the point where it is possible to prepare small molecules to almost any structure. These methods are used today to produce a wide variety of useful chemicals such as pharmaceuticals or commercial polymers. The ability of this is to extend the control to the next, seeking methods to assemble these single molecules into supramolecular assemblies consisting of many molecules arranged in a well defined manner.
These approaches utilize the concepts of molecular self-assembly and/or supramolecular chemistry to automatically arrange themselves into some useful conformation through a bottom-up approach. The concept of molecular recognition is especially important: molecules can be designed so that a specific conformation or arrangement is favored due to non-covalent intermolecular forces. The Watson-Crick basepairing rules are a direct result of this, as is the specificity of an enzyme being targeted to a single substrate, or the specific folding of the protein itself. Thus, two or more components can be designed to be complementary and mutually attractive so that they make a more complex and useful whole.
Such bottom-up approaches should, broadly speaking, be able to produce devices in parallel and much cheaper than top-down methods, but could potentially be overwhelmed as the size and complexity of the desired assembly increases. However, the bottom-up approach is viewed by many thoughtful scientists as being mostly wishful thinking. Most useful structures require complex and thermodynamically unlikely arrangements of atoms. The basic laws of probability and entropy make it very unlikely that atoms will "self-assemble" in useful configurations, or can be easily and economically nudged to do so. About the only example of this is crystal-growing, for which Nanotechnology cannot take any credit, it having been around for millenia.
[edit] Molecular Nanotechnology: a long-term view
Advanced nanotechnology, sometimes called molecular manufacturing, is a term given to the concept of engineered nanosystems (nanoscale machines) operating on the molecular scale. By the countless examples found in biology it is currently known that billions of years of evolutionary feedback can produce sophisticated, stochastically optimized biological machines, and it is hoped that developments in nanotechnology will make possible their construction by some shorter means, perhaps using biomimetic principles. However, K Eric Drexler and other researchers have proposed that advanced nanotechnology, although perhaps initially implemented by biomimetic means, ultimately could be based on mechanical engineering principles (see also mechanosynthesis)
When the term "nanotechnology" was independently coined and popularized by Eric Drexler, who at the time was unaware of an earlier usage by Norio Taniguchi, it referred to a future manufacturing technology based on molecular machine systems. The premise was that molecular-scale biological analogies of traditional machine components demonstrated that molecular machines were possible, and that a manufacturing technology based on the mechanical functionality of these components (such as gears, bearings, motors, and structural members) would enable programmable, positional assembly to atomic specification (see the original reference PNAS-1981). The physics and engineering performance of exemplar designs were analyzed in the textbook Nanosystems.
Another view, put forth by Carlo Montemagno, is that future nanosystems will be hybrids of silicon technology and biological molecular machines, and his group's research is directed toward this end.
The seminal experiment proving that positional molecular assembly is possible was performed by Ho and Lee at Cornell University in 1999. They used a scanning tunneling microscope to move an individual carbon monoxide molecule (CO) to an individual iron atom (Fe) sitting on a flat silver crystal, and chemically bound the CO to the Fe by applying a voltage.
Though biology clearly demonstrates that molecular machine systems are possible, non-biological molecular machines are today only in their infancy. Leaders in research on non-biological molecular machines are Dr. Alex Zettl and his colleagues at Lawrence Berkeley Laboratories and UC Berkeley. They have constructed at least three distinct molecular devices whose motion is controlled from the desktop with changing voltage: a nanotube nanomotor, a molecular actuator, and a nanoelectromechanical relaxation oscillator.
Manufacturing in the context of productive nanosystems is not related to, and should be clearly distinguished from, the conventional technologies used to manufacture nanomaterials such as carbon nanotubes and nanoparticles.
There exists the potential to design and fabricate artificial structures analogous to natural cells and even organisms. Note that these are just blue-sky "potentials", and fall closer to the disciplines of Applied Biology and gene-splicing than to Nanotechnology.
[edit] Current research
Space-filling model of the nanocar on a surface, using fullerenes as wheels.
Space-filling model of the nanocar on a surface, using fullerenes as wheels.
Graphical representation of a rotaxane, useful as a molecular switch.
Graphical representation of a rotaxane, useful as a molecular switch.
A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, http://www.mems.sandia.gov.
A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, http://www.mems.sandia.gov.
As nanotechnology is a very broad term, there are many disparate but sometimes overlapping subfields that could fall under its umbrella. The following avenues of research could be considered subfields of nanotechnology. Note that these categories are fairly nebulous and a single subfield may overlap many of them, especially as the field of nanotechnology continues to mature.
See also List of nanotechnology applications.
[edit] Nanomaterials
This includes subfields which develop or study materials having unique properties arising from their nanoscale dimensions.
* Colloid science has given rise to many materials which may be useful in nanotechnology, such as carbon nanotubes and other fullerenes, and various nanoparticles and nanorods.
* Nanoscale materials can also be used for bulk applications; most present commercial applications of nanotechnology are of this flavor.
* Headway has been made in using these materials for medical applications; see Nanomedicine.
[edit] Bottom-up approaches
These seek to arrange smaller components into more complex assemblies.
* DNA Nanotechnology utilizes the specificity of Watson-Crick basepairing to construct well-defined structures out of DNA and other nucleic acids.
* More generally, molecular self-assembly seeks to use concepts of supramolecular chemistry, and molecular recognition in particular, to cause single-molecule components to automatically arrange themselves into some useful conformation.
[edit] Top-down approaches
These seek to create smaller devices by using larger ones to direct their assembly.
* Many technologies descended from conventional solid-state silicon methods for fabricating microprocessors are now capable of creating features smaller than 100 nm, falling under the definition of nanotechnology. Giant magnetoresistance-based hard drives already on the market fit this description, [1] as do atomic layer deposition (ALD) techniques.
* Solid-state techniques can also be used to create devices known as nanoelectromechanical systems or NEMS, which are related to microelectromechanical systems or MEMS.
* Atomic force microscope tips can be used as a nanoscale "write head" to deposit a chemical on a surface in a desired pattern in a process called dip pen nanolithography. This fits into the larger subfield of nanolithography.
[edit] Functional approaches
These seek to develop components of a desired functionality without regard to how they might be assembled.
* Molecular electronics seeks to develop molecules with useful electronic properties. These could then be used as single-molecule components in a nanoelectronic device. For an example see rotaxane.
* Synthetic chemical methods can also be used to create synthetic molecular motors, such as in a so-called nanocar.
[edit] Speculative
These subfields seek to anticipate what inventions nanotechnology might yield, or attempt to propose an agenda along which inquiry might progress. These often take a big-picture view of nanotechnology, with more emphasis on its societal implications than the details of how such inventions could actually be created.
* Molecular nanotechnology is a proposed approach which involves manipulating single molecules in finely controlled, deterministic ways. This is more theoretical (some would say merely hypothetical) than the other subfields and is beyond current capabilities.
* Nanorobotics centers on self-sufficient machines of some functionality operating at the nanoscale.
* Programmable matter based on artificial atoms seeks to design materials whose properties can be easily and reversibly externally controlled.
[edit] Tools and techniques
Typical AFM setup. A microfabricated cantilever with a sharp tip is deflected by features on a sample surface, much like in a phonograph but on a much smaller scale. A laser beam reflects off the backside of the cantilever into a set of photodetectors, allowing the deflection to be measured and assembled into an image of the surface.
Typical AFM setup. A microfabricated cantilever with a sharp tip is deflected by features on a sample surface, much like in a phonograph but on a much smaller scale. A laser beam reflects off the backside of the cantilever into a set of photodetectors, allowing the deflection to be measured and assembled into an image of the surface.
Nanoscience and nanotechnology only became possible in the 1910's with the development of the first tools to measure and make nanostructures. But the actual development started with the discovery of electrons and neutrons which showed scientists that matter can really exist on a much smaller scale than what we normally think of as small, and/or what they thought was possible at the time. It was at this time when curiosity for nanostructures had originated.
The atomic force microscope (AFM) and the Scanning Tunneling Microscope (STM) are two early versions of scanning probes that launched nanotechnology. There are other types of scanning probe microscopy, all flowing from the ideas of the scanning confocal microscope developed by Marvin Minsky in 1961 and the scanning acoustic microscope (SAM) developed by Calvin Quate and coworkers in the 1970's, that make it possible to see structures at the nanoscale. The tip of a scanning probe can also be used to manipulate nanostructures (a process called positional assembly). However, this is a very slow process. This led to the development of various techniques of nanolithography such as dip pen nanolithography, electron beam lithography or nanoimprint lithography. Lithography is a top-down fabrication technique where a bulk material is reduced in size to nanoscale pattern.
The top-down approach anticipates nanodevices that must be built piece by piece in stages, much as manufactured items are currently made. Scanning probe microscopy is an important technique both for characterization and synthesis of nanomaterials. Atomic force microscopes and scanning tunneling microscopes can be used to look at surfaces and to move atoms around. By designing different tips for these microscopes, they can be used for carving out structures on surfaces and to help guide self-assembling structures. Atoms can be moved around on a surface with scanning probe microscopy techniques, but it is cumbersome, expensive and very time-consuming. For these reasons, it is not feasible to construct nanoscaled devices atom by atom. Assembling a billion transistor microchip at the rate of about one transistor an hour is inefficient.
One hope is that these techniques may eventually be used to make primitive nanomachines, which in turn can be used to make more sophisticated nanomachines. But the whole nanomachine concept is wild speculation, as we are unable to even conceptually design human scale machines that can independently make other machines. If we can't make them on a convenient scale, what are the chances they can be made on a nano scale? Also nanomachines have the very substantial hurdles of friction and surface-tension.
In contrast, bottom-up techniques build or grow larger structures atom by atom or molecule by molecule. These techniques include chemical synthesis, self-assembly and positional assembly. Another variation of the bottom-up approach is molecular beam epitaxy or MBE. Researchers at Bell Telephone Laboratories like John R. Arthur. Alfred Y. Cho, and Art C. Gossard developed and implemented MBE as a research tool in the late 1960s and 1970s. Samples made by MBE were key to to the discovery of the fractional quantum Hall effect for which the 1998 Nobel Prize in Physics was awarded. MBE allows scientists to lay down atomically-precise layers of atoms and, in the process, build up complex structures. Important for research on semiconductors, MBE is also widely used to make samples and devices for the newly emerging field of spintronics.
Newer techniques such as Dual Polarisation Interferometry are enabling scientists to measure quantitatively the molecular interactions that take place at the nano-scale.
[edit] Societal implications
Main article: Implications of nanotechnology
Potential risks of nanotechnology can broadly be grouped into three areas:
* the risk to health and environment from nanoparticles and nanomaterials;
* the risk posed by molecular manufacturing (or advanced nanotechnology);
* societal risks.
Nanoethics concerns the ethical and social issues associated with developments in nanotechnology, a science which encompass several fields of science and engineering, including biology, chemistry, computing, and materials science. Nanotechnology refers to the manipulation of very small-scale matter – a nanometer is one billionth of a meter, and nanotechnology is generally used to mean work on matter at 100 nanometers and smaller.
Social risks related to nanotechnology development include the possibility of military applications of nanotechnology (such as implants and other means for soldier enhancement) as well as enhanced surveillance capabilities through nano-sensors. However those applications still belong to science-fiction and will not be possible in the next decades. Significant environmental, health, and safety issues might arise with development in nanotechnology since some negative effects of nanoparticles in our environment might be overlooked. However nature itself creates all kinds of nanoobjects, so probable dangers are not due to the nanoscale alone, but due to the fact that toxic materials become more harmful when ingested or inhaled as nanoparticles (see nanotoxicology).
[edit] See also
* List of nanotechnology topics
* Femtotechnology
* Mesotechnology
* Nanoengineering
* NanoSafe
* Nanotechnology in fiction
* Nanotitanate
* Nanotoxicology
* Picotechnology
* Top-down and bottom-up design
[edit] Further reading
* Geoffrey Hunt and Michael Mehta (2006), Nanotechnology: Risk, Ethics and Law. London: Earthscan Books.
* Hari Singh Nalwa (2004), Encyclopedia of Nanoscience and Nanotechnology (10-Volume Set), American Scientific Publishers. ISBN 1-58883-001-2
* Michael Rieth and Wolfram Schommers (2006), Handbook of Theoretical and Computational Nanotechnology (10-Volume Set), American Scientific Publishers. ISBN 1-58883-042-X
* David M. Berube 2006. Nano-hype: The Truth Behind the Nanotechnology Buzz. Prometheus Books. ISBN 1-59102-351-3
* Jones, Richard A. L. (2004). Soft Machines. Oxford University Press, Oxford, United Kingdom. ISBN 0198528558.
* Akhlesh Lakhtakia (ed) (2004). The Handbook of Nanotechnology. Nanometer Structures: Theory, Modeling, and Simulation. SPIE Press, Bellingham, WA, USA. ISBN 0-8194-5186-X.
* Daniel J. Shanefield (1996). Organic Additives And Ceramic Processing. Kluwer Academic Publishers. ISBN 0-7923-9765-7.
* Fei Wang & Akhlesh Lakhtakia (eds) (2006). Selected Papers on Nanotechnology -- Theory & Modeling (Milestone Volume 182). SPIE Press, Bellingham, WA, USA. ISBN 0-8194-6354-X.
* Roger Smith, Nanotechnology: A Brief Technology Analysis, CTOnet.org, 2004. [2]
* Arius Tolstoshev, Nanotechnology: Assessing the Environmental Risks for Australia, Earth Policy Centre, September 2006
Re: Important Information
I hop that helpd.
Re: Important Information
Discrete mathematics, also called finite mathematics, is the study of mathematical structures that are fundamentally discrete, in the sense of not supporting or requiring the notion of continuity. Most, if not all, of the objects studied in finite mathematics are countable sets, such as integers, finite graphs, and formal languages.
Discrete mathematics has become popular in recent decades because of its applications to computer science. Concepts and notations from discrete mathematics are useful to study or describe objects or problems in computer algorithms and programming languages. In some mathematics curricula, finite mathematics courses cover discrete mathematical concepts for business, while discrete mathematics courses emphasize concepts for computer science majors.
For contrast, see continuum, topology, and mathematical analysis.
Discrete mathematics includes the following topics:
* Logic - a study of reasoning
* Set theory - a study of collections of elements
* Number theory
* Combinatorics - a study of counting
* Graph theory
* Algorithmics - a study of methods of calculation
* Information theory
* Computability and complexity theories - dealing with theoretical and practical limitations of algorithms
* Elementary probability theory and Markov chains
* Linear algebra - a study of related linear equations
* Functions
* Partially Ordered Sets
* Proofs
* Counting and Relations
* Collections
[edit] References and further reading
Wikibooks
Wikibooks has more on the topic of
Discrete mathematics
* Donald E. Knuth, The Art of Computer Programming
* Kenneth H. Rosen, Handbook of Discrete and Combinatorial Mathematics CRC Press. ISBN 0-8493-0149-1.
* Kenneth H. Rosen, Discrete Mathematics and Its Applications 5th ed. McGraw Hill. ISBN 0-07-293033-0. Companion Web site: http://www.mhhe.com/math/advmath/rosen/
* Richard Johnsonbaugh, Discrete Mathematics 6th ed. Macmillan. ISBN 0-13-045803-1. Companion Web site: http://wps.prenhall.com/esm_johnsonbau_discrtmath_6/
* Norman L. Biggs, Discrete Mathematics 2nd ed. Oxford University Press. ISBN 0-19-850717-8. Companion Web site: http://www.oup.co.uk/isbn/0-19-850717-8 includes questions together with solutions..
* Neville Dean, Essence of Discrete Mathematics Prentice Hall. ISBN 0-13-345943-8. Not as in depth as above texts, but a gentle intro.
* Klette, R., and A. Rosenfeld (2004). Digital Geometry. Morgan Kaufmann. ISBN 1-55860-861-3. Also on (digital) topology, graph theory, combinatorics, axiomatic systems.
* Mathematics Archives, Discrete Mathematics links to syllabi, tutorials, programs, etc. http://archives.math.utk.edu/topics/discreteMath.html
* Ronald Graham, Donald E. Knuth, Oren Patashnik, Concrete Mathematics
[edit] See also
* List of basic discrete mathematics topics
* Important publications in discrete mathematics
Discrete mathematics has become popular in recent decades because of its applications to computer science. Concepts and notations from discrete mathematics are useful to study or describe objects or problems in computer algorithms and programming languages. In some mathematics curricula, finite mathematics courses cover discrete mathematical concepts for business, while discrete mathematics courses emphasize concepts for computer science majors.
For contrast, see continuum, topology, and mathematical analysis.
Discrete mathematics includes the following topics:
* Logic - a study of reasoning
* Set theory - a study of collections of elements
* Number theory
* Combinatorics - a study of counting
* Graph theory
* Algorithmics - a study of methods of calculation
* Information theory
* Computability and complexity theories - dealing with theoretical and practical limitations of algorithms
* Elementary probability theory and Markov chains
* Linear algebra - a study of related linear equations
* Functions
* Partially Ordered Sets
* Proofs
* Counting and Relations
* Collections
[edit] References and further reading
Wikibooks
Wikibooks has more on the topic of
Discrete mathematics
* Donald E. Knuth, The Art of Computer Programming
* Kenneth H. Rosen, Handbook of Discrete and Combinatorial Mathematics CRC Press. ISBN 0-8493-0149-1.
* Kenneth H. Rosen, Discrete Mathematics and Its Applications 5th ed. McGraw Hill. ISBN 0-07-293033-0. Companion Web site: http://www.mhhe.com/math/advmath/rosen/
* Richard Johnsonbaugh, Discrete Mathematics 6th ed. Macmillan. ISBN 0-13-045803-1. Companion Web site: http://wps.prenhall.com/esm_johnsonbau_discrtmath_6/
* Norman L. Biggs, Discrete Mathematics 2nd ed. Oxford University Press. ISBN 0-19-850717-8. Companion Web site: http://www.oup.co.uk/isbn/0-19-850717-8 includes questions together with solutions..
* Neville Dean, Essence of Discrete Mathematics Prentice Hall. ISBN 0-13-345943-8. Not as in depth as above texts, but a gentle intro.
* Klette, R., and A. Rosenfeld (2004). Digital Geometry. Morgan Kaufmann. ISBN 1-55860-861-3. Also on (digital) topology, graph theory, combinatorics, axiomatic systems.
* Mathematics Archives, Discrete Mathematics links to syllabi, tutorials, programs, etc. http://archives.math.utk.edu/topics/discreteMath.html
* Ronald Graham, Donald E. Knuth, Oren Patashnik, Concrete Mathematics
[edit] See also
* List of basic discrete mathematics topics
* Important publications in discrete mathematics
Re: Important Information
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Re: Important Information
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Re: Important Information
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Re: Important Information
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Re: Important Information
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