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It's not just football!
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 14/05/2008, 11:19 AM
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Dogger Slipraid
 
Joined on 17/10/2007
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Re: Last one to reply wins
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14/05/2008, 12:25 PM
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Beaker
Joined on 04/02/2006
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Re: Last one to reply wins
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The oxyhemoglobin dissociation curve is an important tool for understanding how our blood carries and releases oxygen. Specifically, the oxyhemoglobin dissociation curve relates oxygen saturation (SO2) and partial pressure of oxygen in the blood (PO2), and is determined by what is called "hemoglobin's affinity for oxygen," that is, how readily hemoglobin acquires and releases oxygen molecules from its surrounding tissue.
Background
Hemoglobin (Hb), an intracellular protein, is the primary vehicle for transporting oxygen in the blood. Oxygen is also carried (dissolved) in plasma, but to a much lesser degree. Hemoglobin is contained in erythrocytes, more commonly referred to as red blood cells.
Under certain conditions, oxygen bound to the hemoglobin is released into the body tissue, and under others, it is absorbed from the tissue into the blood. Each hemoglobin molecule has a limited capacity for holding oxygen molecules. How much of that capacity that is filled by oxygen bound to the hemoglobin at any time is called the oxygen saturation. Expressed as a percentage, the oxygen saturation is the ratio of the amount of oxygen bound to the hemoglobin, to the oxygen carrying capacity of the hemoglobin. The oxygen carrying capacity is determined by the amount of hemoglobin present in the blood.
The amount of oxygen bound to the hemoglobin at any time is related, in large part, to the partial pressure of oxygen to which the hemoglobin is exposed. In the lungs, at the alveolar-capillary interface, the partial pressure of oxygen is typically high, and therefore the oxygen binds readily to hemoglobin that is present. As the blood circulates to other body tissue in which the partial pressure of oxygen is less, the hemoglobin releases the oxygen into the tissue because the hemoglobin cannot maintain its full bound capacity of oxygen in the presence of lower oxygen partial pressures.
Understanding the Dissociation Curve
In its basic form, the oxyhemoglobin dissociation curve describes the relation between the partial pressure of oxygen (x axis) and the oxygen saturation (y axis). Hemoglobin's affinity for oxygen increases as successive molecules of oxygen bind. More molecules bind as the oxygen partial pressure increases until the maximum amount that can be bound is reached. As this limit is approached, very little additional binding occurs and the curve levels out as the hemoglobin becomes saturated with oxygen. Hence the curve has a sigmoidal or S-shape. At pressures above about 60 mmHg, the standard dissociation curve is relatively flat, which means that the oxygen content of the blood does not change significantly even with large increases in the oxygen partial pressure. To get more oxygen to the tissue would require blood transfusions to increase the hemoglobin count (and hence the oxygen carrying capacity), or supplemental oxygen that would increase the oxygen dissolved in plasma.
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Standard Oxyhemoglobin Dissociation Curve showing the P50, and the SaO2 at PaO2 = 80 mmHg. |
Although binding of oxygen to hemoglobin continues to some extent for pressures below about 60 mmHg, as oxygen partial pressures decrease in this steep area of the curve, the oxygen is unloaded to peripheral tissue readily as the hemoglobin's affinity diminishes.
The partial pressure of oxygen in the blood at which the hemoglobin is 50% saturated, typically about 26.6 mmHg for a healthy person, is known as the P50. The P50 is a conventional measure of hemoglobin affinity for oxygen. In the presence of disease or other conditions that change the hemoglobin's oxygen affinity and, consequently, shift the curve to the right or left, the P50 changes accordingly. An increased P50 indicates a rightward shift of the standard curve, which means that a larger partial pressure is necessary to maintain a 50% oxygen saturation. This indicates a decreased affinity. Conversely, a lower P50 indicates a leftward shift and a higher affinity.
Factors that Affect the Standard Dissociation Curve
The effectiveness of hemoglobin-oxygen binding can be affected by several factors. The factors can be viewed as having the effect of shifting or reshaping the oxyhemoglobin curve ("the standard curve") of a typical, healthy person. The standard curve is shifted to the right by an increase in temperature, 2,3-DPG, or PCO2, or a decrease in pH. The curve is shifted to the left by the opposite of these conditions. A rightward shift, by definition, causes a decrease in the affinity of hemoglobin for oxygen. This makes it harder for the hemoglobin to bind to oxygen (requiring a higher partial pressure to achieve the same oxygen saturation), but it makes it easier for the hemoglobin to release bound oxygen. Conversely, a leftward shift increases the affinity, making the oxygen easier for the hemoglobin to pick up but harder to release.
We list several of the factors here and indicate how the curve is affected:
- Variation of the hydrogen ion concentration. This changes the blood's pH. A decrease in pH shifts the standard curve to the right, while an increase shifts it to the left. This is known as the Bohr effect.
- Effects of carbon dioxide. Carbon dioxide affects the curve in two ways: first, it influences intracellular pH (the Bohr effect), and second, CO2 accumulation causes carbamino compounds to be generated through chemical interactions. Low levels of carbamino compounds have the effect of shifting the curve to the right, while higher levels cause a leftward shift.
- Effects of 2,3-DPG. 2,3-diphosphoglycerate, or 2,3-DPG, is an organophosphate, which are created in erythrocytes during glycolysis. The production of 2,3-DPG is likely an important adaptive mechanism, because the production increases for several conditions in the presence of diminished peripheral tissue O2 availability, such as hypoxemia, chronic lung disease, anemia, and congestive heart failure, among others. High levels of 2,3-DPG shift the curve to the right, while low levels of 2,3-DPG cause a leftward shift, seen in states such as septic shock and hypophosphatemia.
- Temperature. Temperature does not have so dramatic effect as the previous factors, but hyperthermia causes a rightward shift, while hypothermia causes a leftward shift.
- Carbon Monoxide. Hemoglobin binds with carbon monoxide 240 times more readily than with oxygen, and therefore the presence of carbon monoxide can interfere with the hemoglobin's acquisition of oxygen. In addition to lowering the potential for hemoglobin to bind to oxygen, carbon monoxide also has the effect of shifting the curve to the left. With an increased level of carbon monoxide, a person can suffer from severe hypoxemia while maintaining a normal PO2.
- Effects of Methemoglobinemia (a form of abnormal hemoglobin). Methemoglobinemia causes a leftward shift in the curve.
- Fetal Hemoglobin. Fetal hemoglobin (HbF) is structurally different from normal hemoglobin (Hb). The fetal dissociation curve is shifted to the left relative to the curve for the normal adult. Typically, fetal arterial oxygen pressures are low, and hence the leftward shift enhances the placental uptake of oxygen.
Some Clinical Uses of the Dissociation Curve
The oxyhemoglobin dissociation curve, and the role of hemoglobin, are important clinically in understanding the relationship of arterial, oxygen saturation to the partial pressure of oxygen in arterial blood, particularly as it relates to disease. For example, it is useful to observe in healthy patients that the slope of the curve increases significantly from the mid-sixties (PaO2) downward, which indicates to the health professional that decreases in PaO2 in this region will have dramatic effects on arterial oxygen saturation.
Also, it is useful to have a good grasp on the influence of factors that can affect the curve or the affinity of hemoglobin to oxygen. For example, it is useful to remember the powerful effects of carbon monoxide in trying to explain hypoxemia in the presence of a normal PaO2 and SaO2.
Understanding the elements of the dissociation curve, such as the basis of oxygen saturation, can also help explain clinical problems. For example, the differential diagnosis of a patient that presents with shortness of breath in the presence of adequate ventilation and SaO2 should include hemoglobin deficiency, because routine SaO2 calculations are based on normal hemoglobin values.
The Implemented Model (Shaojie Wang)
The implementation in the accompanying Java program is based on the classic oxyhemoglobin dissociation curve equation developed by Kelman [3] and from data obtained by Severinghaus [4]. The operator enters either an oxygen tension (PO2) or an oxygen saturation (SO2), then presses CALCULATE to determine the unknown variable.
Kelman's equation allows the dissociation curve to be adjusted by pH, PCO2, and T (temperature), but not by 2,3-DPG or other factors known to affect the curve.
Details. Kelman first gives an equation for the standard dissociation curve (pH=7.4, PCO2=40 mmHg, and Temp=37C), that relates the oxygen saturation (SO2) and the oxygen tension, PO2 (x):
SO2 = 100 (a1 x + a2 x^2 + a3 x^3 + x^4) / (a4 + a5 x + a6 x^2 + a7 x^3 + x^4).
This form is purely empirical and is not meant to imply any physiological significance. The seven coefficients (a1-a7) were determined by a least-squares fitting of the equation to Severinghaus' 38 paired values of oxygen tension (x) and saturation (SO2). The coefficients are:
a1 = -8.5322289 * 10^3
a2 = 2.1214010 * 10^3
a3 = -6.7073989 * 10^1
a4 = 9.3596087 * 10^5
a5 = -3.1346258 * 10^4
a6 = 2.3961674 * 10^3
a7 = -6.7104406 * 10^1
Kelman's strategy in predicting oxygen saturation is to take the actual oxygen tension, PO2, measured at actual conditions of pH, PCO2, and T, convert it to an oxygen tension that would be obtained at a pH of 7.40, a PCO2 of 40 mmHg, and a temperature of 37 C, then use his standard dissociation curve equation to predict oxygen saturation. The equation Kelman developed to convert the actual oxygen tension to this 'virtual' oxygen tension is
[PO2 virtual] = [PO2 actual] * 10^(0.024(37 - T) + 0.40(pH - 7.40) + 0.06(log10(40) - log10(PCO2)).
We found that the curve fit Severinghaus' data [4] well for oxygen tensions below about 100 mmHg, but above that, the accuracy greatly diminishes. However, patients on supplemental oxygen may have oxygen tensions greater than 100 mmHg. Therefore, we corrected the curve for oxygen tensions above 100 by fitting data from Severinghaus [4] up to 700 mmHg using the Lagrangian interpolation method, an approach widely used for obtaining an exact fit to a given data set.
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14/05/2008, 12:28 PM
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Dogger Slipraid
Joined on 17/10/2007
Posts 1,117
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Re: Last one to reply wins
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My thoughts exactly but i actually had it down as a3 =6.7093989*10 1, just a minor detail i know but Kelman would turn in his grave.
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14/05/2008, 12:32 PM
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Dogger Slipraid
Joined on 17/10/2007
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Re: Last one to reply wins
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[edit] Overview
Nanotechnology is a highly multidisciplinary field, drawing from fields such as applied physics, materials science, interface and colloid science, device physics, supramolecular chemistry (which refers to the area of chemistry that focuses on the noncovalent bonding interactions of molecules), self-replicating machines and robotics, chemical engineering, mechanical engineering, biological engineering, and electrical engineering. Grouping of the sciences under the umbrella of "nanotechnology" has been questioned on the basis that there is little actual boundary-crossing between the sciences that operate on the nano-scale. Instrumentation is the only area of technology common to all disciplines; on the contrary, for example pharmaceutical and semiconductor industries do not "talk with each other". Corporations that call their products "nanotechnology" typically market them only to a certain industrial cluster.[1]
Two main approaches are used in nanotechnology. In the "bottom-up" approach, materials and devices are built from molecular components which assemble themselves chemically by principles of molecular recognition. In the "top-down" approach, nano-objects are constructed from larger entities without atomic-level control. The impetus for nanotechnology comes from a renewed interest in Interface and Colloid 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 and molecular beam epitaxy, these instruments allow the deliberate manipulation of nanostructures, and lead to the observation of novel phenomena.
Examples of nanotechnology are the manufacture of polymers based on molecular structure, and the design of computer chip layouts based on surface science. Despite the promise of nanotechnologies such as quantum dots and nanotubes, real commercial applications have mainly used the advantages of colloidal nanoparticles in bulk form, such as suntan lotion, cosmetics, protective coatings, drug delivery,[2] and stain resistant clothing.
[edit] Origins
Buckminsterfullerene C 60, also known as the buckyball, is the simplest of the carbon structures known as fullerenes. Members of the fullerene family are a major subject of research falling under the nanotechnology umbrella.
The first use of the concepts in 'nano-technology' (but predating use of that name) was in "There's Plenty of Room at the Bottom," a talk given by physicist Richard Feynman at an American Physical Society meeting at Caltech on December 29, 1959. Feynman described a process by which the ability to manipulate individual atoms and molecules might be developed, using one set of precise tools to build and operate another proportionally smaller set, so on down to the needed scale. In the course of this, he noted, scaling issues would arise from the changing magnitude of various physical phenomena: gravity would become less important, surface tension and Van der Waals attraction would become more important, etc. This basic idea appears plausible, and exponential assembly enhances it with parallelism to produce a useful quantity of end products. The term "nanotechnology" was defined by Tokyo Science University Professor Norio Taniguchi in a 1974 paper[3] as follows: "'Nano-technology' mainly consists of the processing of, separation, consolidation, and deformation of materials by one atom or by one molecule." In the 1980s the basic idea of this definition was explored in much more depth by Dr. K. Eric Drexler, who promoted the technological significance of nano-scale phenomena and devices through speeches and the books Engines of Creation: The Coming Era of Nanotechnology (1986) and Nanosystems: Molecular Machinery, Manufacturing, and Computation,[4] and so the term acquired its current sense. Engines of Creation: The Coming Era of Nanotechnology is considered the first book on the topic of nanotechnology. Nanotechnology and nanoscience got started in the early 1980s with two major developments; the birth of cluster science and the invention of the scanning tunneling microscope (STM). This development led to the discovery of fullerenes in 1986 and carbon nanotubes a few years later. In another development, the synthesis and properties of semiconductor nanocrystals was studied; This led to a fast increasing number of metal oxide nanoparticles of quantum dots. The atomic force microscope was invented six years after the STM was invented. In 2000, the United States National Nanotechnology Initiative was founded to coordinate Federal nanotechnology research and development.
[edit] Fundamental concepts
One nanometer (nm) is one billionth, or 10-9 of a meter. To put that scale in context, the comparative size of a nanometer to a meter is the same as that of a marble to the size of the earth.[5] Or another way of putting it: a nanometer is the amount a man's beard grows in the time it takes him to raise the razor to his face.[5]
Typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range 0.12-0.15 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.
[edit] Larger to smaller: a materials perspective
Main article: Nanomaterials
A number of physical phenomena become 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 (mechanical, electrical, optical, etc.) properties change when compared to macroscopic systems. One example is the increase in surface area to volume ratio altering mechanical, thermal and catalytic properties of materials. Novel mechanical properties of nanosystems are of interest in the nanomechanics research. The catalytic activity of nanomaterials also opens potential risks in their interaction with biomaterials.
Materials reduced to the nanoscale can show 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). A material 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 quantum and surface phenomena that matter exhibits at the nanoscale.
[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. This ability raises the question of extending this kind of control to the next-larger level, 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 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. Most useful structures require complex and thermodynamically unlikely arrangements of atoms. Nevertheless, there are many examples of self-assembly based on molecular recognition in biology, most notably Watson-Crick basepairing and enzyme-substrate interactions. The challenge for nanotechnology is whether these principles can be used to engineer novel constructs in addition to natural ones.
[edit] Molecular nanotechnology: a long-term view
Molecular nanotechnology, sometimes called molecular manufacturing, is a term given to the concept of engineered nanosystems (nanoscale machines) operating on the molecular scale. It is especially associated with the concept of a molecular assembler, a machine that can produce a desired structure or device atom-by-atom using the principles of mechanosynthesis. 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.
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 molecular machines were possible: by the countless examples found in biology, it is known that sophisticated, stochastically optimised biological machines can be produced.
It is hoped that developments in nanotechnology will make possible their construction by some other means, perhaps using biomimetic principles. However, Drexler and other researchers![Devil [6]](/cs/emoticons/emotion-14.gif) have proposed that advanced nanotechnology, although perhaps initially implemented by biomimetic means, ultimately could be based on mechanical engineering principles, namely, a manufacturing technology based on the mechanical functionality of these components (such as gears, bearings, motors, and structural members) that would enable programmable, positional assembly to atomic specification (PNAS-1981). The physics and engineering performance of exemplar designs were analyzed in Drexler's book Nanosystems.
But Drexler's analysis is very qualitative and does not address very pressing issues, such as the "fat fingers" and "Sticky fingers" problems. In general it is very difficult to assemble devices on the atomic scale, as all one has to position atoms are other atoms of comparable size and stickyness. Another view, put forth by Carlo Montemagno,[7] is that future nanosystems will be hybrids of silicon technology and biological molecular machines. Yet another view, put forward by the late Richard Smalley, is that mechanosynthesis is impossible due to the difficulties in mechanically manipulating individual molecules.
This led to an exchange of letters in the ACS publication Chemical & Engineering News in 2003.![Music [8]](/cs/emoticons/emotion-29.gif) 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.
An experiment indicating 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.
[edit] Current research
Graphical representation of a rotaxane, useful as a molecular switch.
This device transfers energy from nano-thin layers of quantum wells to nanocrystals above them, causing the nanocrystals to emit visible light. [9]
[edit] Nanomaterials
This includes subfields which develop or study materials having unique properties arising from their nanoscale dimensions.[10]
[edit] Bottom-up approaches
These seek to arrange smaller components into more complex assemblies.
[edit] Top-down approaches
These seek to create smaller devices by using larger ones to direct their assembly.
[edit] Functional approaches
These seek to develop components of a desired functionality without regard to how they might be assembled.
[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 than the other subfields and is beyond current capabilities.
- Nanorobotics centers on self-sufficient machines of some functionality operating at the nanoscale. There are hopes for applying nanorobots in medicine[15][16][17], but it may not be easy to do such a thing because of several drawbacks of such devices.[18] Nevertheless, progress on innovative materials and methodologies has been demonstrated with some patents granted about new nanomanufacturing devices for future commercial applications, which also progressively helps in the development towards nanorobots with the use of embedded nanobioelectronics concept.[19][20]
- Programmable matter based on artificial atoms seeks to design materials whose properties can be easily and reversibly externally controlled.
- Due to the popularity and media exposure of the term nanotechnology, the words picotechnology and femtotechnology have been coined in analogy to it, although these are only used rarely and informally.
[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.
The first observations and size measurements of nano-particles were made during the first decade of the 20th century. They are mostly associated with the name of Zsigmondy who made detailed studies of gold sols and other nanomaterials with sizes down to 10 nm and less. He published a book in 1914.[21] He used ultramicroscope that employs a dark field method for seeing particles with sizes much less than light wavelength.
There are traditional techniques developed during 20th century in Interface and Colloid Science for characterizing nanomaterials. These are widely used for first generation passive nanomaterials specified in the next section.
These methods include several different techniques for characterizing particle size distribution. This characterization is imperative because many materials that are expected to be nano-sized are actually aggregated in solutions. Some of methods are based on light scattering. Other apply ultrasound, such as ultrasound attenuation spectroscopy for testing concentrated nano-dispersions and microemulsions.[22]
There is also a group of traditional techniques for characterizing surface charge or zeta potential of nano-particles in solutions. These information is required for proper system stabilzation, preventing its aggregation or flocculation. These methods include microelectrophoresis, electrophoretic light scattering and electroacoustics. The last one, for instance colloid vibration current method is suitable for characterizing concentrated systems.
Next group of 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 and which were results of nanotechnology research.
There are several important modern developments. 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 1970s, that made 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). Feature-oriented scanning-positioning methodology suggested by Rostislav Lapshin appears to be a promising way to implement these nanomanipulations in automatic mode. However, this is still a slow process because of low scanning velocity of the microscope. Various techniques of nanolithography such as dip pen nanolithography, electron beam lithography or nanoimprint lithography were also developed. 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 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. By using, for example, feature-oriented scanning-positioning approach, atoms can be moved around on a surface with scanning probe microscopy techniques. At present, it is expensive and time-consuming for mass production but very suitable for laboratory experimentation.
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 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.
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14/05/2008, 12:33 PM
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Dogger Slipraid
Joined on 17/10/2007
Posts 1,117
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Re: Last one to reply wins
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Find the above is more intresting
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14/05/2008, 4:50 PM
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Ginger Pele
Joined on 21/07/2006
NORWICH
Posts 1,922
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Re: Last one to reply wins
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yes very interesting, ive spent hours reading it
FOZZY is a legend :D
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14/05/2008, 4:54 PM
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buddha
Joined on 28/07/2007
Posts 1,592
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Re: Last one to reply wins
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ive spent hours trying to understand it....
for the last time, your arse looks huge in those jeans,. now, lets go!!!!!!!
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14/05/2008, 5:14 PM
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Ginger Pele
Joined on 21/07/2006
NORWICH
Posts 1,922
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Re: Last one to reply wins
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lol better than a two hour RS exam though (even though it was easy lol)
FOZZY is a legend :D
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14/05/2008, 5:37 PM
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buddha
Joined on 28/07/2007
Posts 1,592
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Re: Last one to reply wins
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yh, i went off at bit of a tangent on one question....: how has family life changed
a) well, what with divorces and bastard kids etc, not that having a bastard kid is bad, william the conquerer was a bastard, he called himself william the bastard. he still did good things.
did i do good? lol
for the last time, your arse looks huge in those jeans,. now, lets go!!!!!!!
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14/05/2008, 6:26 PM
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Ginger Pele
Joined on 21/07/2006
NORWICH
Posts 1,922
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Re: Last one to reply wins
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i think i did that on that question (not about william) but went on about whats changed not why :D
FOZZY is a legend :D
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15/05/2008, 3:50 PM
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Dogger Slipraid
Joined on 17/10/2007
Posts 1,117
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Re: Last one to reply wins
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