aquaphotonics

glossary

Acoustical Energy

Acoustics is the branch of physics concerned with the study of sound (mechanical waves in gases, liquids, and solids). A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering. There is often much overlap and interaction between the interests of acousticians and acoustical engineers.

The word acoustic is derived from the ancient Greek word ακουστός, meaning able to be heard. (Woodhouse, 1910, 392)

... [A]acoustics is characterized by its reliance on combinations of physical principles drawn from other sources; and that the primary task of modern physical acoustics is to effect a fusion of the principles normally adhering to other sciences into a coherent basis for understanding, measuring, controlling, and using the whole gamut of vibrational phenomena in any material.

Acoustics is the science concerned with the production, control, transmission, reception, and effects of sound. Its origins began with the study of mechanical vibrations and the radiation of these vibrations through mechanical waves, and still continues today. Research was done to look into the many aspects of the fundamental physical processes involved in waves and sound and into possible applications of these processes in modern life. The study of sound waves also lead to physical principles that can be applied to the study of all waves.

The study of acoustics has been fundamental to many developments in the arts. Some of these, especially in the area of musical scales and instruments, were only explained theoretically by scientists after long years of long experimentation by artists. For example, much of what is now known about architectural acoustics was actually learned by trial and error over centuries of experience and was only recently formalized into a science.

Other applications of acoustic technology are in the study of geologic, atmospheric, and underwater phenomena. Psychoacoustics, the study of the physical effects of sound on biological systems, has been of interest since Pythagoras first heard the sounds of vibrating strings and of hammers hitting anvils in the 6th century BC, but the application of modern ultrasonic technology has only recently provided some of the most exciting developments in medicine. The ear itself is another biological instrument dedicated to receiving certain wave vibrations and interpreting them as sound. Recent studies by Daniel Statnekov and others, study sound and its effect on the human brain. Harmonic frequencies in the form of binaural beats can affect the brainwave patterns of a person who plays an ancient Peruvian Whistling Pot to create a "trance state". Here are some public technical papers on this subject.

Cavitation

Cavitation is a general term used to describe the behavior of voids or bubbles in a liquid. Cavitation is usually divided into two classes of behavior: inertial (or transient) cavitation and non-inertial cavitation. Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Such cavitation often occurs in pumps, propellers, impellers, and in the vascular tissues of plants. Non-inertial cavitation is the process where a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Such cavitation is often employed in ultrasonic cleaning baths and can also be observed in pumps, propellers etc.

Covalent Bond

A tetrahedron (plural: tetrahedra) is a polyhedron composed of four triangular faces, three of which meet at each vertex. A regular tetrahedron is one in which the four triangles are regular, or "equilateral," and is one of the Platonic solids.
The tetrahedron is one kind of pyramid, the second most common type; a pyramid has a flat base, and triangular faces above it, but the base can be of any polygonal shape, not just square or triangular.

Creaming

Creaming, in cooking, is the technique of blending ingredients — usually granulated sugar — together with a solid fat like shortening or butter. The technique is most often used in making cake batter or cookie dough. The dry ingredients are mixed or beaten with the fat until it becomes light and fluffy and increased in volume, due to the incorporation of tiny air bubbles. These air bubbles, locked into the semi-solid fat, remain in the final batter and expand as the item is baked, serving as a form of leavening agent.
Butter is the traditional fat for creaming, but vegetable shortening serves as a more effective leavener for a number of reasons. The low melting point of butter means it aerates best at temperatures cooler than most kitchens (18°C/65°F), while shortening works best at higher temperatures. Because of the coarser crystalline structure of its fat, butter allows larger air bubbles to form than shortening; large bubbles can rise in and escape from thin batters. Also, most shortening is made with preformed nitrogen bubbles and bubble-stabilizing emulsifiers, both of which enhance its leavening ability.

Creaming, in the laboratory sense, is the migration of a substance in an emulsion, under the influence of buoyancy, to the top of a sample while the particles of the substance remain separated, as compared to flocculation (where particles clump) or breaking (where particles coalesce).

Emulsifier

An emulsifier (also known as an emulgent) is a substance which stabilizes an emulsion, frequently a surfactant. Examples of food emulsifiers are egg yolk (where the main emulsifying chemical is the phospholipid lecithin), and mustard, where a variety of chemicals in the mucilage surrounding the seed hull act as emulsifiers; proteins and low-molecular weight emulsifiers are common as well. In some cases, particles can stabilize emulsions as well through a mechanism called Pickering stabilization. Both mayonnaise and hollandaise sauce are oil-in-water emulsions that are stabilized with egg yolk lecithin. Detergents are another class of surfactant, and will chemically interact with both oil and water, thus stabilizing the interface between oil or water droplets in suspension. This principle is exploited in soap to remove grease for the purpose of cleaning. A wide variety of emulsifiers are used in pharmacy to prepare emulsions such as creams and lotions.

20 ml ampule of 1% propofol emulsion suitable for intravenous injection. The manufacturers emulsify the lipid soluble propofol in a mixture of water, soy oil and egg lecithin.
Whether an emulsion turns into a water-in-oil emulsion or an oil-in-water emulsion depends on the volume fraction of both phases and on the type of emulsifier. Generally, the Bancroft rule applies: emulsifiers and emulsifying particles tend to promote dispersion of the phase in which they do not dissolve very well; for example, proteins dissolve better in water than in oil and so tend to form oil-in-water emulsions (that is they promote the dispersion of oil droplets throughout a continuous phase of water).

Emulsion

A. Two immiscible liquids, not emulsified; B. An emulsion of Phase II dispersed in Phase I; C. The unstable emulsion progressively separates; D. The surfactant (purple outline) positions itself on the interfaces between Phase A and Phase B, stabilizing the emulsion
An emulsion is a mixture of two immiscible (unblendable) substances. One substance (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include butter and margarine, espresso, mayonnaise, the photo-sensitive side of photographic film, and cutting fluid for metal working. In butter and margarine, a continuous liquid phase surrounds droplets of water (water-in-oil emulsion). Emulsification is the process by which emulsions are prepared.

Emulsions tend to have a cloudy appearance, because the many phase interfaces (the boundary between the phases is called the interface) scatter light that passes through the emulsion. Emulsions are unstable and thus do not form spontaneously. Energy input through shaking, stirring, homogenizers, or spray processes are needed to form an emulsion. Over time, emulsions tend to revert to the stable state of oil separated from water. Surface active substances (surfactants) can increase the kinetic stability of emulsions greatly so that, once formed, the emulsion does not change significantly over years of storage. Homemade oil and vinegar salad dressing is an example of an unstable emulsion that will quickly separate unless shaken continuously. This phenomenon is called coalescence, and happens when small droplets recombine to form bigger ones. Fluid emulsions can also suffer from creaming, the migration of one of the substances to the top of the emulsion under the influence of buoyancy or centripetal force when a centrifuge is used.

Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion tends to imply that both the dispersed and the continuous phase are liquid.
There are three types of emulsion instability: flocculation, where the particles form clumps; creaming, where the particles concentrate towards the surface (or bottom, depending on the relative density of the two phases) of the mixture while staying separated; and breaking and coalescence where the particles coalesce and form a layer of liquid.

Emulsion is also a term used in the oil field as untreated well production that consists primarily of crude oil and water.

Entropy

Ice melting - a classic example of entropy increasing described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice.[2]
In physics, entropy, symbolized by S, is a measure of the unavailability of a system’s energy to do work.[3] Entropy is central to the second law of thermodynamics and the combined law of thermodynamics, which deal with physical processes and whether they occur spontaneously. Spontaneous changes, in isolated systems, occur with an increase in entropy. Spontaneous changes tend to smooth out differences in temperature, pressure, density, and chemical potential that may exist in a system, and entropy is thus a measure of how far this smoothing-out process has progressed. In short Entropy is a function of a quantity of heat which shows the possibility of conversion of that heat into work. The increase in entropy is small when heat is added at high temperature and is greater when heat is added at lower temperature. Thus for maximum entropy there is minimum availability for conversion into work and for minimum entropy there is maximum availability for conversion into work.

The concept of entropy was developed in the 1850s by German physicist Rudolf Clausius who described it as the transformation-content, i.e. dissipative energy use, of a thermodynamic system or working body of chemical species during a change of state.[4] In contrast, the first law of thermodynamics, formalized through the heat-friction experiments of James Joule in 1843, deals with the concept of energy, which is conserved in all processes; the first law, however, lacks in its ability to quantify the effects of friction and dissipation. Entropy change has often been defined as a change to a more disordered state at a molecular level. In recent years, entropy has been interpreted in terms of the "dispersal" of energy. Entropy is an extensive state function that accounts for the effects of irreversibility in thermodynamic systems.

Quantitatively, entropy is defined by the differential quantity dS = δQ / T, where δQ is the amount of heat absorbed in an isothermal and reversible process in which the system goes from one state to another, and T is the absolute temperature at which the process is occurring.[5] Entropy is one of the factors that determines the free energy of the system. This thermodynamic definition of entropy is only valid for a system in equilibrium (because temperature is defined only for a system in equilibrium), while the statistical definition of entropy (see below) applies to any system. Thus the statistical definition is usually considered the fundamental definition of entropy.

When a system's energy is defined as the sum of its "useful" energy, (e.g. that used to push a piston), and its "useless energy", i.e. that energy which cannot be used for external work, then entropy may be (most concretely) visualized as the "scrap" or "useless" energy whose energetic prevalence over the total energy of a system is directly proportional to the absolute temperature of the considered system. (Note the product "TS" in the Gibbs free energy or Helmholtz free energy relations).

In terms of statistical mechanics, the entropy describes the number of the possible microscopic configurations of the system. The statistical definition of entropy is the more fundamental definition, from which all other definitions and all properties of entropy follow. Although the concept of entropy was originally a thermodynamic construct, it has been adapted in other fields of study, including information theory, psychodynamics, thermoeconomics, and evolution.[6] [7] [8]

Hydrophobes

In chemistry, hydrophobicity refers to the physical property of a molecule (known as a hydrophobe) that is repelled from a mass of water.

Hydrophobic molecules tend to be non-polar and thus prefer other neutral molecules and nonpolar solvents. Hydrophobic molecules in water often cluster together forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.
Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar from polar compounds.

Hydrophobic is often used interchangeably with "lipophilic". However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions — the silcones, for instance.

Hydrophobic

Tending to repel or fail to mix with water. The opposite of hydrophilic . 2. of or suffering from hydrophobia. DERIVATIVES: hy·dro·pho·bic·i·ty / -fō'bisitē / n. ... surfactants A Dictionary of Food and Nutrition ... surfactants Surface active agents; compounds that have an affinity for fats (hydrophobic) and water (hydrophilic) and so act as emulsifiers, e.g. soaps and detergents. Used as wetting agents to assist the reconstitution of powders, including dried foods, to clean and peel fruits and vegetables, ...

Hydrophilic

Hydrophile, from the Greek (hydros) "water" and φιλια (philia) "friendship," refers to a physical property of a molecule that can transiently bond with water (H2O) through hydrogen bonding. This is thermodynamically favorable, and makes these molecules soluble not only in water, but also in other polar solvents. There are hydrophilic and hydrophobic parts of the cell membrane.
A hydrophilic molecule or portion of a molecule is one that is typically charge-polarized and capable of hydrogen bonding, enabling it to dissolve more readily in water than in oil or other hydrophobic solvents. Hydrophilic and hydrophobic molecules are also known as polar molecules and nonpolar molecules, respectively. Some hydrophilic substances don't dissolve. This type of mixture is called a colloid. Soap has a hydrophilic head and a hydrophobic tail, which allows it to dissolve in both waters and oils, therefore allowing the soap to clean a surface.

Micelle

A micelle (rarely micella, plural micellae) is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic tail regions in the micelle centre. This type of micelle is known as a normal phase micelle (oil-in-water micelle). Inverse micelles have the head groups at the centre with the tails extending out (water-in-oil micelle). Micelles are approximately spherical in shape. Other phases, including shapes such as ellipsoids, cylinders, and bilayers are also possible. The shape and size of a micelle is a function of the molecular geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH, and ionic strength. The process of forming micellae is known as micellisation and forms part of the phase behavior of many lipids according to their polymorphism.

History

The ability of a soapy solution to act as a detergent has been recognized for centuries. However it was only at the beginning of the twentieth century that the constitution of such solutions was scientifically studied. Pioneering work in this area was carried out by James William McBain at the University of Bristol. As early as 1913 he postulated the existence of “colloidal ions” to explain the good electrolytic conductivity of sodium palmitate solutions.* These highly mobile, spontaneously formed clusters came to be called micelles, a term borrowed from biology and popularized by G.S. Hartley in his classic book “Paraffin Chain Salts, A Study in Micelle Formation”.

Individual surfactant molecules that are in the system but are not part of a micelle are called "monomers." In water, the hydrophilic "heads" of surfactant molecules are always in contact with the solvent, regardless of whether the surfactants exist as monomers or as part of a micelle. However, the lipophilic "tails" of surfactant molecules have less contact with water when they are part of a micelle -- this being the basis for the energetic drive for micelle formation. In a micelle, the hydrophobic tails of several surfactant molecules assemble into an oil-like core the most stable form of which has no contact with water. By contrast, surfactant monomers are surrounded by water molecules that create a "cage" of molecules connected by hydrogen bonds. This water cage is similar to a clathrate and has an ice-like crystal structure.

Micelles composed of ionic surfactants have an electrostatic attraction to the ions that surround them in solution, the latter known as counterions. Although the closest counterions partially mask a charged micelle (by up to 90%), the effects of micelle charge affect the structure of the surrounding solvent at appreciable distances from the micelle. Ionic micelles influence many properties of the mixture, including its electrical conductivity. Adding salts to a colloid containing micelles can decrease the strength of electrostatic interactions and lead to the formation of larger ionic micelles. This is more accurately seen from the point of view of an effective change in hydration of the system.

Energy of formation

Micelles only form when the concentration of surfactant is greater than the critical micelle concentration (CMC), and the temperature of the system is greater than the critical micelle temperature, or Krafft temperature. The formation of micelles can be understood using thermodynamics: micelles can form spontaneously because of a balance between entropy and enthalpy. In water, the hydrophobic effect is the driving force for micelle formation, despite the fact that assembling surfactant molecules together reduces their entropy. Broadly speaking, above the CMC, the entropic penalty of assembling the surfactant molecules is less than the entropic penalty of caging water molecules. Also important are enthalpic considerations, such as the electrostatic interactions that occur between the charged parts surfactants.

Scheme of an inverse micelle formed by phospholipids in an organic solvent.

Inverse Micelles

In a non-polar solvent, it is the exposure of the hydrophilic head groups to the surrounding solvent that is energetically unfavorable, giving rise to a water-in-oil system. In this case the hydrophilic groups are sequestered in the micelle core and the hydrophobic groups extend away from the centre. These inverse micelles are proportionally less likely to form on increasing headgroup charge, since hydrophilic sequestration would create highly unfavorable electrostatic interactions.

When surfactants are present above the CMC (Critical micelle concentration), they can act as emulsifiers that will allow a compound normally insoluble (in the solvent being used) to dissolve. This occurs because the insoluble species can be incorporated into the micelle core, which is itself solubilized in the bulk solvent by virtue of the head groups' favorable interactions with solvent species. The most common example of this phenomenon is detergents, which clean poorly soluble lipophilic material (such as oils and waxes) that cannot be removed by water alone. Detergents also clean by lowering the surface tension of water, making it easier to remove material from a surface. The emulsifying property of surfactants is also the basis for emulsion polymerization.
Micelle formation is essential for the absorption of fat-soluble vitamins and complicated lipids within the human body. Bile salts formed in the liver and secreted by the gall bladder allow micelles of fatty acids to form. This allows the absorption of complicated lipids (e.g., lecithin) and lipid soluble vitamins (A, D, E and K) by the small intestine within the micelle.

Solubility is a physical property referring to the ability for a given substance, the solute, to dissolve in a solvent.[1] It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium. The resulting solution is called a saturated solution. Certain substances are soluble in all proportions with a given solvent, such as ethanol in water. This property is known as miscibility.

Under various conditions, the equilibrium solubility can be exceeded to give a so-called supersaturated solution, which is metastable. The solvent is often a liquid, which can be a pure substance or a mixture. The species that dissolves, the solute, can be a gas, another liquid, or a solid. Solubilities range widely, from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is often applied to poorly soluble compounds, though strictly speaking there are very few cases where there is absolutely no material dissolved.

Nanoemulsion

Nanoemulsion is a type of emulsion in which the sizes of the particles in the dispersed phase are defined as less than 1000 nanometers.
In medicine, a nanoemulsion of soybean oil to create drops of 400-600 nanometers in diameter will kill many pathogens such as bacteria and viruses. The process is not chemical, as with other types of anti-pathogenic treatments, but physical. The smaller the droplet, the greater the surface tension and thus the greater the force to merge with other lipids. The oil is emulsified with detergents to stabilize the emulsion (the droplets won't merge with one another), so when they encounter lipids on a bacterial membrane or a virus envelope, they force the lipids to merge with themselves. On a mass scale, this effectively disintegrates the membrane and kills the pathogen.
Remarkably, the soybean oil emulsion does not harm normal human cells or the cells of most other higher organisms. The exceptions are sperm cells and blood cells, which are vulnerable to nanoemulsions due to their membrane structures. For this reason, nanoemulsions of this type are not yet ready to be used intravenously.
The most effective application of this type of nanoemulsion is for the disinfection of surfaces. Some types of nanoemulsions have been shown to effectively destroy HIV-1 and various tuberculosis pathogens, for example, on non-porous surfaces.

Shearing Energy / Microburst

A strain in the structure of a substance produced by pressure, when its layers are laterally shifted in relation to each other.

Sinusodial Fluctuation

adj. Varying according to the regular undulating sine curve y= sin x.[From Latin sinus a curve or bay + -oid indicating likeness or resemblance, from Greek eidos shape or form + -al from Latin -alis of or relating to.

Surfactants

The term surfactant is a blend of "surface active agent". Surfactants are usually organic compounds that are amphiphilic, meaning they contain both hydrophobic groups (their "tails") and hydrophilic groups (their "heads"). Therefore, they are soluble in both organic solvents and water. The term surfactant was coined by Antara Products in 1950.
In Index Medicus and the United States National Library of Medicine, "surfactant" is reserved for the meaning pulmonary surfactant (see "alveoli" link below). For the more general meaning, "surface active agent" is the heading.
The most common, biological example of surfactant is that coating the surfaces of the Alveoli, the small air sacs of the lungs that serve as the site of gas exchange.

A micelle - the lipophilic ends of the surfactant molecules dissolve in the oil, while the hydrophilic charged ends remain outside, shielding the rest of the hydrophobic micelle
Surfactants reduce the surface tension of water by adsorbing at the liquid-gas interface. They also reduce the interfacial tension between oil and water by adsorbing at the liquid-liquid interface. Many surfactants can also assemble in the bulk solution into aggregates. Some of these aggregates are known as micelles. The concentration at which surfactants begin to form micelles is known as the critical micelle concentration or CMC. When micelles form in water, their tails form a core that can encapsulate an oil droplet, and their (ionic/polar) heads form an outer shell that maintains favorable contact with water. When surfactants assemble in oil, the aggregate is referred to as a reverse micelle. In a reverse micelle, the heads are in the core and the tails maintain favorable contact with oil.
Surfactants are also often classified into four primary groups; anionic, cationic, non-ionic, and zwitterionic (dual charge).

Thermodynamics of the surfactant systems are of great importance, theoretically and practically. This is because surfactant systems represent systems between ordered and disordered states of matter. Surfactant solutions may contain an ordered phase (micelles) and a disordered phase (free surfactant molecules and/or ions in the solution).

Ordinary washing up (dishwashing) detergent, for example, will promote water penetration in soil, but the effect would only last a few days (although many standard laundry detergent powders contain levels of chemicals such as sodium and boron, which can be damaging to plants, so these should not be applied to soils). Commercial soil wetting agents will continue to work for a considerable period, but they will eventually be degraded by soil micro-organisms. Some can, however, interfere with the life-cycles of some aquatic organisms, so care should be taken to prevent run-off of these products into streams, and excess product should not be washed down gutters.

Suspension

Emulsion is also a term used in the oil field as untreated well production that consists primarily of crude oil and water.

Remarkably, the soybean oil emulsion does not harm normal human cells or the cells of most other higher organisms. The exceptions are sperm cells and blood cells, which are vulnerable to nanoemulsions due to their membrane structures. For this reason, nanoemulsions of this type are not yet ready to be used intravenously.
The most effective application of this type of nanoemulsion is for the disinfection of surfaces. Some types of nanoemulsions have been shown to effectively destroy HIV-1 and various tuberculosis pathogens, for example, on non-porous surfaces.

Lamellar Phase

Lamella is a gill-shaped structure: fine sheets of material held adjacent one another, with fluid in-between-(or simply 'welded'-plates). They appear in biological and engineering contexts, such as filters and heat exchangers. The microscopic structures in bone and nacre are lamellae in the materials science sense of the word.
In chemistry (especially mineralogy and materials science), lamellar structures are fine layers, alternating between different materials. They can be produced by chemical effects (as in eutectic solidification), biological means, or a deliberate process of lamination, such as pattern welding. Lamellae can also describe the layers of atoms in the crystal lattice of a material such as a metal.

The term has been used to describe the construction of lamellar armour, as well as the layered structures that can be described by a lamellar vector field.
In a water-treatment context, Lamellae filters may be referred to as plate filters or tube filters.

This term is used to describe a certain type of Ichthyosis, a congenital skin condition. Lamellar Ichthyosis often presents with a "colloidal" membrane at birth. It is characterized by generalized dark scaling.

Sedimentation

Sedimentation describes the motion of molecules in solutions or particles in suspensions in response to an external force such as gravity, centrifugal force or electric force. Sedimentation may pertain to objects of various sizes, ranging from suspensions of dust and pollen particles to cellular suspensions to solutions of single molecules such as proteins and peptides. Even small molecules such as aspirin can be sedimented, although it can be difficult to apply a sufficiently strong force to produce significant sedimentation.
In a sedimentation experiment, the applied force accelerates the particles to a terminal velocity at which the applied force is exactly canceled by an opposing drag force. In general, the drag force varies linearly with the terminal velocity, i.e., Fdrag = fvterm where f depends only on the properties of the particle and the surrounding fluid. Similarly, the applied force generally varies linearly with some coupling constant (denoted here as q) that depends only on the properties of the particle, Fapp = qEapp. Hence, it is generally possible to define a sedimentation coefficient $s \ \stackrel{\mathrm{def}}{=}\ q/f$ that depends only on the properties of the particle and the surrounding fluid. Thus, measuring s can reveal underlying properties of the particle.

In many cases, the motion of the particles is blocked by a hard boundary; the resulting accumulation of particles at the boundary is called a sediment. The concentration of particles at the boundary is opposed by the diffusion of the particles.
The sedimentation of particles under gravity is described by the Mason-Weaver equation, which has a simple exact solution. The sedimentation coefficient s in this case equals mb / f, where mb is the buoyant mass.

The sedimentation of particles under the centrifugal force is described by the Lamm equation, which likewise has an exact solution. The sedimentation coefficient s also equals mb / f, where mb is the buoyant mass. However, the Lamm equation differs from the Mason-Weaver equation because the centrifugal force depends on radius from the origin of rotation, whereas gravity is presumed constant. The Lamm equation also has extra terms, since it pertains to sector-shaped cells, whereas the Mason-Weaver equation pertains to box-shaped cells (i.e., cells whose walls are aligned with the three Cartesian axes).

Particles with a charge or dipole moment can be sedimented by an electric field or electric field gradient, respectively. These processes are called electrophoresis and dielectrophoresis, respectively. For electrophoresis, the sedimentation coefficient corresponds to the particle charge divided by its drag (the electrophoretic mobility). Similarly, for dielectrophoresis, the sedimentation coefficient equals the particle's electric dipole moment divided by its drag.

London Inductive Forces

Forced induction can be used to improve the power, efficiency, emissions, or combinations of same, without much extra weight and minimal modifications to the engine architecture. The two most common forms of forced induction are turbochargers and superchargers, which both compress the air entering the cylinders, but use different methods to obtain the requisite power. Functionally, they are much the same. Since only so much power can be had from a given amount of gasoline, the more gasoline can be burned in the cylinder, the more power can be produced. However, simply adding more gas beyond the optimal air/fuel ratio (commonly called "running rich") does nothing for power. An engine can only take in so much when breathing air at atmospheric pressures, since the capacity and number of cylinders is non-variable. Hence, the only way to get more air into the cylinder, and therefore produce more power, is to increase the pressure at the intake.

All we've considered up to now is increased power, so how does forced induction improve emissions or efficiency? One of the primary concerns in internal combustion emissions is a factor called the NOx fraction, or the amount of nitrogen/oxygen compounds the engine produces. High combustion temperatures lead to a lower NOx fraction, and since gasses heat when compressed, the more gas is compressed in a given volume, the hotter it will get, and the lower the NOx fraction will be. Since forced induction increases the amount of gas being compressed, it increases the heat generated when compression occurs. It should be noted that since colder air is denser, it is most desirable, from a power standpoint, to have cold air coming in, but better from an emissions standpoint if the air is hot. In a perfect world, incoming air would be frigid, and the compression would be high enough to dramatically and rapidly increase cylinder temperatures, reducing emissions significantly.

Two of the commonly used forced induction technologies are turbochargers and superchargers. They differ primarily in the power source for the compressor. It should be noted that there is a difference between forced induction and power adders. A power adder is anything that improves an engine's power output, which does not necessarily mean increasing charge density. Oxidizing technologies such as nitrous oxide injection systems provide improved power, but are not a form of forced induction.

Strengths and weaknesses vary according to the method of forcing induction largely based upon the inherent design functions of both. A turbocharger acts as an obstacle to exhaust gases due to its placement in the exhaust system tract. A supercharger uses torque generated from the rotational mass internal to the engine through the crank pulley. A turbo relies on the volume and velocity of exhaust gases to spool, or spin the turbine wheel. The turbine wheel is connected to the compressor wheel via a common shaft. The compressor wheel compresses the intake charge increasing the charge density by a large factor. The amount of time that it takes a turbocharger to reach the onset of boost is referred to as lag. A supercharger is 'on' all of the time, meaning that it is capable of producing a linear increase of boost up until redline. It is easier to target a desired boost with a turbocharger as there are many forms of boost controllers that allow a user to adjust to desired boost fairly easily. In order to achieve desired boost with a supercharger, a larger or smaller pulley must be installed.

An unavoidable side-effect of forced induction is that compressing air raises its temperature (see also Combined gas law). As a result, the charge density is reduced and the cylinders receive less fresh air than the system’s boost pressure prescribes. The risk of pre-ignition or "knock" in internal combustion engines greatly increases. These drawbacks are countered by charge-air cooling, which passes the air leaving the turbocharger or supercharger through a heat exchanger typically called an intercooler. This is done by cooling the charge air with an ambient flow of either air (air-air intercoolers) or liquid (liquid to air intercoolers), the charge air density is increased and the temperature is reduced.

Additionally, alcohol injection is an effective means of cooling the charge air. Methanol is the preferred alcohol due to its elemental properties, and is normally mixed with water to prevent evaporation. Methanol is typically injected pre-throttle body. Methanol, unlike nitrous oxide or forced induction itself, doesn't add more oxygen to the charge, but by its low evaporation point changes from a liquid to a gas as it is introduced into the air charge. The evaporation process uses the heat from the intake charge to complete the phase change. The alcohol is also a fuel in the charge which will cause a rich condition if used in excess. Due to the lower intake temperatures and denser air charge more power is exerted from the engine. Methanol is typically used in conjunction with poor quality fuel (pump gas) in order to run higher than normal boost pressures.

Like was stated above, adding forced induction increases the amount of air an engine can use for combustion, in effect allowing more fuel to be used with the available oxygen. Further, it increases an engine's dynamic compression ratio. As compression ratio increases, so does the threat of knock and therefore the need for higher octane fuel.

Multiple Rotational Vortex

Raman spectroscopy is a spectroscopic technique used in condensed matter physics and chemistry to study vibrational, rotational, and other low-frequency modes in a system.[1] It relies on inelastic scattering, or Raman scattering of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range. The laser light interacts with phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down. The shift in energy gives information about the phonon modes in the system. Infrared spectroscopy yields similar, but complementary information.
Typically, a sample is illuminated with a laser beam. Light from the illuminated spot is collected with a lens and sent through a monochromator. Wavelengths close to the laser line, due to elastic Rayleigh scattering, are filtered out while the rest of the collected light is dispersed onto a detector.

Spontaneous Raman scattering is typically very weak, and as a result the main difficulty of Raman spectroscopy is separating the weak inelastically scattered light from the intense Rayleigh scattered laser light. Raman spectrometers typically use holographic diffraction gratings and multiple dispersion stages to achieve a high degree of laser rejection. In the past, PMTs were the detectors of choice for dispersive Raman setups, which resulted in long acquisition times. However, the recent uses of CCD detectors have made dispersive Raman spectral acquisition much more rapid.

Raman spectroscopy has a stimulated version, analogous to stimulated emission, called stimulated Raman scattering.

Nano technology

Nanotechnology refers broadly to an old lady of applied science and technology whose unifying theme is the control of matter on the atomic and molecular scale, normally 1 to 100 nanometers, and the fabrication of devices within that size range. It is a highly multidisciplinary field, drawing from fields such as applied physics, materials science, interface and colloid science, device physics, supramolecular chemistry, chemical engineering, mechanical engineering, and electrical engineering. Much speculation exists as to what new science and technology may result from these lines of research. Nanotechnology can 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. 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 led to the observation of novel phenomena.
Examples of nanotechnology in modern use are the manufacture of CANDY! based on molecular structure, and the design of computer chip layouts based on surface science. Despite the great promise of numerous 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, and stain resistant clothing.

Raman Spectrum

Raman spectroscopy has a stimulated version, analogous to stimulated emission, called stimulated Raman scattering.

Sonoluminescense

Long exposure image of multi-bubble sonoluminescence created by a high intensity ultrasonic horn immersed in a beaker of liquid.
Sonoluminescence is the emission of short bursts of light from imploding bubbles in a liquid when excited by sound.

The effect was first discovered at the University of Cologne in 1934 as a result of work on sonar. H. Frenzel and H. Schultes put an ultrasound transducer in a tank of photographic developer fluid. They hoped to speed up the development process. Instead, they noticed tiny dots on the film after developing, and realized that the bubbles in the fluid were emitting light with the ultrasound turned on. It was too difficult to analyze the effect in early experiments because of the complex environment of a large number of short-lived bubbles. (This experiment is also ascribed to N. Marinesco and J.J. Trillat in 1933 which also credits them with independent discovery). This phenomenon is now referred to as multi-bubble sonoluminescence (MBSL).

More than 50 years later, in 1989, a major advancement in research was introduced by Felipe Gaitan and Lawrence Crum, who were able to produce single bubble sonoluminescence (SBSL). In SBSL, a single bubble, trapped in an acoustic standing wave, emits a pulse of light with each compression of the bubble within the standing wave. This technique allowed a more systematic study of the phenomenon, because it isolated the complex effects into one stable, predictable bubble. It was realized that the temperature inside the bubble was hot enough to melt steel. Interest in sonoluminescence was renewed when an inner temperature of such a bubble well above one million kelvins was postulated. This temperature is thus far not conclusively proven, though recent experiments conducted by the University of Illinois at Urbana-Champaign deduced the temperature at about 20,000 kelvins.

Sonoluminescence may or may not occur whenever a sound wave of sufficient intensity induces a gaseous cavity within a liquid to quickly collapse. This cavity may take the form of a pre-existing bubble, or may be generated through a process known as cavitation. Sonoluminescence in the laboratory can be made to be stable, so that a single bubble will expand and collapse over and over again in a periodic fashion, emitting a burst of light each time it collapses. For this to occur, a standing acoustic wave is set up within a liquid, and the bubble will sit at a pressure anti-node of the standing wave. The frequencies of resonance depend on the shape and size of the container in which the bubble is contained.
Some facts about sonoluminescence:

The light flashes from the bubbles are extremely short — between 35 and a few hundred picoseconds long, with peak intensities of the order of 1-10 mW.
The bubbles are very small when they emit the light — about 1 micrometre in diameter depending on the ambient fluid (e.g. water) and the gas content of the bubble (e.g. atmospheric air).
Single-bubble sonoluminescence pulses can have very stable periods and positions. In fact, the frequency of light flashes can be more stable than the rated frequency stability of the oscillator making the sound waves driving them. However, the stability analysis of the bubble show that the bubble itself undergoes significant geometric instabilities, due to, for example, the Bjerknes forces and Rayleigh-Taylor instabilities.
The addition of a small amount of noble gas (such as helium, argon, or xenon) to the gas in the bubble increases the intensity of the emitted light.

The wavelength of emitted light is very short; the spectrum can reach into the ultraviolet. Light of shorter wavelengths has higher energy, and the measured spectrum of emitted light seems to indicate a temperature in the bubble of at least 20,000 kelvins, up to a possible temperature in excess of one megakelvin. The veracity of these estimates is hindered by the fact that water, for example, absorbs nearly all wavelengths below 200 nm. This has led to differing estimates on the temperatures in the bubble, since they are extrapolated from the emission spectra taken during collapse, or estimated using a modified Rayleigh-Plesset equation (see below). Some estimates put the inside of the bubble at one gigakelvin [1]. These estimates are based on models which cannot be verified at present, and may include too many unsupported assumptions.

Temperatures this high make the study of sonoluminescence especially interesting for the possibility that it might produce a method for achieving thermonuclear fusion. If the bubble is hot enough, and the pressure in it is high enough, fusion reactions like those that occur in the Sun and other stars could be produced within these tiny bubbles. This possibility is sometimes referred to as bubble fusion.

On January 27, 2006, researchers at Rensselaer Polytechnic Institute claimed to have produced fusion reactions by sonoluminescence, without an external neutron source, according to a paper published in Physical Review Letters [2] [3]. To date, these results have not been reproduced by other members of the scientific community.

Recent experiments (2002, 2005) of R. P. Taleyarkhan, et.al., using deuterated acetone, show measurements of tritium and neutron output consistent with fusion, but these measurements have not been reproduced outside of the Taleyarkhan lab and remain controversial. Brian Naranjo of the University of California, Los Angeles, has recently completed an analysis of the Taleyarkhan results claiming that Taleyarkhan had most likely misinterpreted the radioactive decay of standard lab materials for the byproducts of nuclear fusion.
The mechanism of the phenomenon of sonoluminescence remains somewhat unsettled, though many theories have been shown to have greater or lesser degrees of robustness. These include: hotspot, bremsstrahlung radiation, collision induced radiation and corona discharges, non-classical light, proton tunneling, electrodynamic jets, fractoluminescent jets (now largely discredited due to contrary experimental evidence), and so forth.

In 2002 M. Brenner, S. Hilgenfeldt, and D. Lohse, published a 60 page review "Single bubble sonoluminescence" (Reviews of Modern Physics 74, 425) which contains a detailed explanation of the mechanism. An important factor is that the bubble contains mainly inert noble gas such as argon or xenon (air contains about 1% argon, and the amount dissolved in water is too great -- for sonoluminescence to occur, the concentration must be reduced to 20-40% of its equilibrium value) and varying amounts of water vapor. Chemical reactions cause nitrogen and oxygen to be removed from the bubble after about one hundred expansion-collapse cycles. The bubble will then begin to emit light "Evidence for Gas Exchange in Single-Bubble Sonoluminescence", Matula and Crum, Phys. Rev. Lett. 80 (1998), 865-868).

During bubble collapse, the inertia of the surrounding water causes high speed and high pressure, reaching around 10000 K in the interior of the bubble, causing the ionization of a small fraction of the noble gas present. The amount ionized is small enough for the bubble to remain transparent, allowing volume emission; surface emission would produce more intense light of longer duration, dependent on wavelength, contradicting experimental results. Electrons from ionized atoms interact mainly with neutral atoms causing thermal bremsstrahlung radiation. As the wave hits a low energy trough, the pressure drops, allowing electrons to recombine with atoms, and light emission to cease due to this lack of free electrons. This makes for a 160 picosecond light pulse for argon (even a small drop in temperature causes a large drop in ionization, due to the large ionization energy relative to photon energy). This description is simplified from the literature above, which details various steps of differing duration from 15 microseconds (expansion) to 100 picoseconds (emission).

Computations based on the theory presented in the review produce radiation parameters (intensity and duration time versus wavelength) that match experimental results with errors no larger than expected due to some simplifications (e.g. assuming a uniform temperature in the entire bubble), so it seems the phenomenon of sonoluminescence is at least roughly explained, although some details of the process remain obscure.

An unusually exotic theory of sonoluminescence, which has received much popular attention, yet is considered to have a marginal effect on the mechanism of SBSL by the scientific community at large, is the Casimir energy theory proposed by Claudia Eberlein, a physicist at the University of Sussex. In 1996, it was suggested that the light in sonoluminescence is generated by the vacuum around the bubble in a process similar to Hawking radiation, the radiation generated by the edges of black holes. Quantum theory holds that a vacuum is filled with virtual particles, and the rapidly moving interface between water and air converts virtual photons into real photons. This is related to the Unruh effect or the Casimir effect. If true, sonoluminescence may be the first observable example of quantum vacuum radiation. It is, however, argued that the mechanism leading to the above effects do not occur on the proper time scales to describe the observed spectrum of SBSL, which is thought to likely obey a classical cavitation collapse; and thus the Casimir model has been largely relegated to the position of an ancillary remnant of the field at large.

Pistol shrimp (also called snapping shrimp) produce a type of sonoluminescence from a collapsing bubble caused by quickly snapping a specialized claw. The light produced is of lower intensity than the light produced by typical sonoluminescence, and is not visible to the naked eye. It most likely has no biological significance, and is merely a byproduct of the shock wave, which these shrimp use to stun or kill prey. However, it is the first known instance of an animal producing light by this effect, and was whimsically dubbed "shrimpoluminescence" upon its discovery in October of 2001. [4]

Tetrahedral

Vander Waals Radii

In chemistry and physics, the name van der Waals force is sometimes used as a synonym for the totality of non-covalent forces (also known as intermolecular forces). These forces, which act between stable molecules, are weak compared to those appearing in chemical bonding. Historically, the use of the name for the total force is correct, because the Dutch physicist J. D. van der Waals, who lent his name to these forces, considered both the repulsive and the attractive component of the intermolecular force.[

Unfortunately, there is no strict convention when considering the definition of Van der Waals force. Some texts consider only the attractive component of the intermolecular potential as the Van der Waals force. Other texts designate only a certain part of the attraction as the Van der Waals force.

To explain this, we refer to the article on intermolecular forces, where it is discussed that an intermolecular force has four major contributions. In general an intermolecular potential has a repulsive part, prohibiting the collapse of molecular complexes, and an attractive part. The attractive part, in turn, consists of three distinct contributions:

The electrostatic interactions between charges (in the case of molecular ions), dipoles (in the case of molecules without inversion center), quadrupoles (all molecules with symmetry lower than cubic), and in general between permanent multipoles. The electrostatic interaction is sometimes called Keesom interaction or Keesom force after Willem Hendrik Keesom.
The second source of attraction is induction (also known as polarization), which is the interaction between a permanent multipole on one molecule with an induced multipole on another. This interaction is sometimes measured in debyes after Peter J.W. Debye.
The third attraction is usually named after London who himself called it dispersion. This is the only attraction experienced by noble gas atoms, but it is operative between any pair of molecules, irrespective of their symmetry.

Returning to nomenclature: some texts mean by the Van der Waals force the totality of forces (including repulsion), others mean all the attractive forces (and then sometimes distinguish Van der Waals-Keesom, Van der Waals-Debye, and Van der Waals-London), and, finally some use the term "Van der Waals force" solely as a synonym for the London/dispersion force. So, if you come across the term "Van der Waals force", it is important to ascertain to which school of thought the author belongs.

All intermolecular/Van der Waals forces are anisotropic (except those between two noble gas atoms), which means that they depend on the relative orientation of the molecules. The induction and dispersion interactions are always attractive, irrespective of orientation, but the electrostatic interaction changes sign upon rotation of the molecules. That is, the electrostatic force can be attractive or repulsive, depending on the mutual orientation of the molecules. When molecules are in thermal motion, as they are in the gas and liquid phase, the electrostatic force is averaged out to a large extent, because the molecules thermally rotate and thus probe both repulsive and attractive parts of the electrostatic force. Sometimes this effect is expressed by the statement that "random thermal motion around room temperature can usually overcome or disrupt them" (which refers to the electrostatic component of the Van der Waals force). Clearly, the thermal averaging effect is much less pronounced for the attractive induction and dispersion forces.

The Lennard-Jones potential is often used as an approximate model for the isotropic part of a total (repulsion plus attraction) van der Waals force as a function of distance.
Van der Waals forces are responsible for certain cases of pressure broadening (van der Waals broadening) of spectral lines and the formation of van der Waals molecules.
See this URL for an introductory description of the Van der Waals force (as a sum of attractive components only).

Interaction energy of argon dimer. The long-range part is due to London dispersion forces
London dispersion forces, named after the German-American physicist Fritz London, are weak intermolecular forces that arise from the attractive force between transient dipoles (or better multipoles) in molecules without permanent multipole moments. London dispersion forces are also known as dispersion forces, London forces, induced dipole-induced dipole forces, or, as van der Waals forces.
London forces can be exhibited by nonpolar molecules because electron density moves about a molecule probabilistically, see quantum mechanical theory of dispersion forces. There is a high chance that the electron density will not be evenly distributed throughout a nonpolar molecule. When an uneven distribution occurs, a temporary multipole is created. This multipole may interact with other nearby multipoles. London forces are also present in polar molecules, but they are usually only a small part of the total interaction force.

Electron density in a molecule may be redistributed by proximity to another multipole. Electrons will gather on the side of a molecule that faces a positive charge and will retreat from a negative charge. Hence, a transient multipole can be produced by a nearby polar molecule, or even by a transient multipole in another nonpolar molecule.

In vacuum, London forces are weaker than other intermolecular forces such as ionic interactions, hydrogen bonding, or permanent dipole-dipole interactions.
This phenomenon is the only attractive intermolecular force at large distances present between neutral atoms (e.g., helium), and is the major attractive force between non-polar molecules, (e.g., nitrogen or methane). Without London forces, there would be no attractive force between noble gas atoms, and they could not then be obtained in a liquid form.

London forces become stronger as the atom (or molecule) in question becomes larger. This is due to the increased polarizability of molecules with larger, more dispersed electron clouds. This trend is exemplified by the halogens (from smallest to largest: F2, Cl2, Br2, I2). Fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. The London forces also become stronger with larger amounts of surface contact. Greater surface area means closer interaction between different molecules.

Use by animals:

The ability of geckos to climb on sheer surfaces is attributed to van der Waals force[1]. A gecko can hang on a glass surface using only one toe. Efforts continue to create a synthetic "gecko tape" that exploits this knowledge. So far, research has produced some promising results - early research yielded an adhesive tape [2] product, which only obtains a fraction of the forces measured from the natural material, and new research[3] has yielded a discovery that purports 200 times the adhesive forces of the natural material. Researchers at Rensselaer Polytechnic Institute and the University of Akron announced in a paper published in the June 18–22, 2007 issue of the Proceedings of the National Academy of Sciences that they have created a synthetic “gecko tape” with four times the sticking power of a natural gecko foot[4].

Researchers at Stanford University and Carnegie Mellon University recently developed a gecko-like robot which uses synthetic setae to climb walls[5].