Absorption (EM radiation)
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The process by which the energy of a photon is taken up by matter, typically the electrons of an atom. The electromagnetic energy is transformed to another form of energy, e.g. to heat.
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Absorption Spectroscopy
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Spectroscopic techniques that measure the absorption of radiation as a function of frequency or wavelength, due to its interaction with a sample.
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Accelerometer
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A device for measuring acceleration and gravity induced reaction forces.
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Acoustic Microscopy
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A microscopy technique that employs very high or ultra high frequency ultrasound. Acoustic microscopes operate non-destructively and penetrate most solid materials to make visible images of internal features, including defects such as cracks, delaminations and voids.
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Acoustic Tweezers
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A technology for controlling the movement of objects by sound waves. In a standing acoustic field, objects will experience an acoustic radiation force that moves the objects to special regions of the acoustic field.Depending on the properties of the objects, they can be moved to either acoustic pressure nodes or pressure antinodes.
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The divided solid is made easier to detect by concentrating it at pressure nodes or antinodes.
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Acoustics
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The the use of structures or other systems to affect the generation, propagation and reception of mechanical waves and vibrations.
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Activated Alumina
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A manufactured form of alumina (aluminium oxide) having a nanoporous structure.
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Adhesive
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A compound that adheres or bonds two items together. Adhesives may come from either natural or synthetic sources. Some modern adhesives are extremely strong, and are becoming increasingly important in modern construction and industry.
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Aeration
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The process by which air is circulated through, mixed with or dissolved in a liquid or substance.
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Aerophonics
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The geration of sound using a column of air vibrating in a tube, typically in the case of a musical wind instrument.
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Angle of Repose
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(or critical angle of repose) The minimum angle made by the inclined plane with the horizontal surface such that the body lying on the inclined plane is just at the verge of sliding down along the inclined plane. When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The internal angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area and shapes of the particles, and the coefficient of friction of the material.
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Archimedes' Principle (Buoyancy)
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The upward force on an object produced by the surrounding liquid or gas in which it is fully or partially immersed, due to the pressure difference of the fluid between the top and bottom of the object. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body. This force enables the object to float or at least to seem lighter.
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Balance
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An instrument or method of comparing the weight (and hence, usually the mass) of two objects.
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Betavoltaics
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Generators of electrical current, in effect a form of battery, which use energy from a radioactive source emitting beta particles (electrons). A common source used is the hydrogen isotope, tritium. Unlike most nuclear power sources betavoltaics use a non-thermal conversion process. Betavoltaics are particularly well-suited to low-power electrical applications where long life of the energy source is needed.
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Bioluminescence
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The production and emission of light by a living organism as the result of a chemical reaction
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Brazil Nut Effect
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A phenomenon in which the largest particles end up on the surface when a granular material containing a mixture of objects of different sizes is shaken. Also known as the muesli effect.
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Brush
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A device with bristles, wire or other filaments, used for cleaning, grooming hair, applying liquids such as paint, sealing gaps between moving surfaces, deburring and other kinds of surface finishing, and for many other purposes.
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Capacitance
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The property of a device or material medium to store an electric charge as a result of an electric potential. The most common form of charge storage device is a two-plate capacitor.
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Centrifuge
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A piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to evenly distribute substances (usually present in a solution for small scale applications) of greater and lesser density.
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Chemiluminescence
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The emission of light (luminescence) with limited emission of heat as the result of a chemical reaction.
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Chromatography
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A family of laboratory techniques for the separation of mixtures. It involves passing a mixture dissolved in a 'mobile phase' through a stationary phase, which separates the analyte to be measured from other molecules in the mixture and allows it to be isolated. Chromatography may be preparative or analytical.
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Coffee Ring Effect
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A pattern left by a puddle of particle-laden liquid after it evaporates. Named after the characteristic ring-like deposit along the perimeter of a spill of coffee. The pattern is due to capillary flow induced by the differential evaporation rates across the drop: liquid evaporating from the edge is replenished by liquid from the interior. The resulting edgeward flow can carry nearly all the dispersed material to the edge.
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Where the quantity of the material would otherwise be insufficient to be easily detected.
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Coherent Light
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Two light waves are said to be coherent if they have a constant relative phase, which also implies that they have the same frequency.
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Colloid Vibration Current
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An electroacoustic phenomenon that arises when ultrasound propagates through a fluid that contains ions and either solid particles or emulsion droplets.
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Comb
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A toothed device used in hair care for straightening and cleaning hair or other fibres. More generally a device having a comb-like form.
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Compton Scattering
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The decrease in energy (increase in wavelength) of an X-ray or gamma ray photon, when it interacts with matter.
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Conduction (electrical)
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The movement of electrically charged particles through a transmission medium (electrical conductor). The movement of charge constitutes an electric current. The charge transport may result as a response to an electric field, or as a result of a concentration gradient in carrier density, that is, by diffusion .
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Coulter Counter
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An apparatus for counting and sizing particles and cells. It is used, for example, for bacteria or prokaryotic cells and air quality particle size distributions. The counter detects change in electrical conductance of a small aperture as fluid containing cells is drawn through. Cells, being non-conducting particles, alter the effective cross-section of the conductive channel.
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In the case of a divided solid suspended in a fluid.
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Creaming
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The migration of the dispersed phase of an emulsion, under the influence of buoyancy. The particles float upwards or sink, depending on how large they are and how much less dense or more dense they may be than the continuous phase, and also how viscous or how thixotropic the continuous phase might be. For as long as the particles remain separated, the process is called creaming.
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Cryptophanes
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A class of organic supramolecular compounds studied and synthesised primarily for molecular encapsulation and recognition. One possible application of cryptophanes is encapsulation and storage of hydrogen gas for potential use in fuel cell vehicles. Cryptophanes can also serve as containers in which organic chemists can carry out reactions that would otherwise be difficult to run under normal conditions.
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Cyclotron Radiation
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Electromagnetic radiation emitted by moving charged particles deflected by a magnetic field. Cyclotron radiation is emitted by all charged particles travelling through magnetic fields, not just those in cyclotrons.
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Depth of Field
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In optics, particularly as it relates to film and photography, depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image.
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Dielectric Permittivity
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The measure of how much resistance is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. Permittivity is determined by the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material. Thus, permittivity relates to a material's ability to transmit (or 'permit') an electric field.
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The presence of a material will affect the amount of electric flux produced in response to an electric charge.
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Diffraction
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Various phenomena which occur when a wave encounters an obstacle. It is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Very similar effects are observed when there is an alteration in the properties of the medium in which the wave is travelling, for example a variation in refractive index for light waves or in acoustic impedance for sound waves and these can also be referred to as diffraction effects.
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Dorn Effect
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(aka Sedimentation Potential). Potential difference resulting from motion of particles through water, typically due to gravity or centrifugation. The motion disrupts equilibrium symmetry of particle's double layer, viscous flow around the particles drags ions of the diffuse layer from them causing slight displacement between surface charge & electric charge of the diffuse layer, giving the particle a dipole moment, generating electric field.
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Drag
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A drag (sometimes called fluid resistance) is the force that resists the movement of a solid object through a fluid (a liquid or gas). The most familiar form of drag is made up of friction forces, which act parallel to the object's surface, plus pressure forces, which act in a direction perpendicular to the object's surface.
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Echo
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A reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room. A true echo is a single reflection of the sound source. The time delay is the extra distance divided by the speed of sound.
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Eddy Currents
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An electrical phenomenon caused when a conductor is exposed to a changing magnetic field due to relative motion of the field source and conductor; or due to variations of the field with time. This can cause eddys of circulating current within the conductor which create electromagnets with magnetic fields that opposes the change of the magnetic field.
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Electret
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An Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet.
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Electric Arc
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An electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air
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Electric Field
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The space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field (that can also be equated to electric flux density). This electric field exerts a force on other electrically charged objects.
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Electric Sonic Amplitude
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Occurs in colloids, emulsions and other heterogeneous fluids under the influence of an oscillating electric field. This field moves particles relative to the liquid, which generates ultrasound.
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Electrical Impedance Tomography
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A medical imaging technique in which an image of the conductivity or permittivity of part of the body is inferred from surface electrical measurements. Typically, conducting electrodes are attached to the skin of the subject and small alternating currents are applied to some or all of the electrodes. The resulting electrical potentials are measured, and the process may be repeated for numerous different configurations of applied current.
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Electrical Resistance
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The degree to which an object opposes an electric current flowing through it (usually measured in Ohms). A function of both its physical geometry and the resistivity of the material the object is made from.
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Electrical Resistivity Tomography
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Electrical resistivity tomography (ERT) or electrical resistivity imaging (ERI) is a geophysical technique for imaging sub-surface structures from electrical measurements made at the surface, or by electrodes in one or more boreholes. It is closely related to the medical imaging technique electrical impedance tomography (EIT), and mathematically is the same inverse problem. In contrast to medical EIT however ERT is essentially a direct current method.
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Electro-Optic Effects
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A change in the optical properties of a material in response to an electric field that varies slowly compared with the frequency of light. The term encompasses a number of distinct phenomena, which can be subdivided into a) change of the absorption (electroabsorption, Franz-Keldysh effect, Quantum-confined Stark effect, electro-chromatic effect) and b) change of the refractive index(Pockels effect, Kerr Effect, electro-gyration)
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Electrocaloric Effect
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A phenomenon in which a material shows a reversible temperature change under an applied electric field. Often considered the physical inverse of the pyroelectric effect. The effect comes from the voltage raising or lowering the entropy of the system. Analogous to the magnetocaloric effect.
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Indirectly by measuring temperature change.
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Electroluminescence
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An optical phenomenon and electrical phenomenon in which a material emits light in response to an electric current passed through it, or to a strong electric field.
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Electromagnet
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A type of magnet whose magnetic field is produced by the flow of electric current. The magnetic field disappears when the current ceases. Electromagnets are very widely used as components of other electrical devices, such as motors, generators, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment, as well as being employed as industrial lifting electromagnets for picking up and moving heavy iron objects like scrap iron.
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Electromagnetic Induction
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The generation of electromotive force (EMF) in a current-carrying conductor exposed to a changing magnetic field
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Electromechanical Film
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A thin membrane whose thickness is related to an electric voltage. It can be used as a pressure sensor, microphone, or a speaker. It can also convert electrical energy to vibration, functioning as an actuator.
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Electron Beam
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(also called Cathode Rays or e-beam) are streams of electrons observed in vacuum tubes, i.e. evacuated glass tubes that are equipped with at least two metal electrodes to which a voltage is applied, a cathode or negative electrode and an anode or positive electrode.
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Electron Impact Desorption
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Desorption arising from electron-impact induced adsorbate surface bond breaking. Molecules on surfaces may also be chemically converted to other species by electron impact
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Electron Paramagnetic Resonance
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(EPR) or electron spin resonance (ESR) spectroscopy is a technique for studying chemical species that have one or more unpaired electrons, such as organic and inorganic free radicals or inorganic complexes possessing a transition metal ion. The basic physical concepts of EPR are analogous to those of nuclear magnetic resonance (NMR), but it is electron spins that are excited instead of spins of atomic nuclei
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Electropermanent Magnet
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A type of magnet which consists of both an electromagnet and a dual material permanent magnet, in which the magnetic field produced by the electromagnet is used to change the magnetisation of the permanent magnet. Allows creating controllable permanent magnets where the magnetic effect can be maintained without requiring a continuous supply of electrical energy.
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Electrophoresis
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The motion of dispersed particles relative to a fluid under the influence of an electric field.
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Electrostatic Induction
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A redistribution of electrical charge in an object, caused by the influence of nearby charges. Electrostatic generators, such as the Wimshurst machine, the Van de Graaff generator and the electrophorus, use this principle. Electrostatic induction should not be confused with electromagnetic induction; both are often referred to as 'induction'.
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Electrostatics
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The phenomena arising from stationary or slowly moving electric charges
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Enzyme
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Proteins that catalyze (i.e., increase the rates of) chemical reactions. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates sufficient for life. Enzymes differ from most other catalysts in that they are highly specific for their substrates
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Feedback
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A circular causal process whereby some proportion of a system's output is returned (fed back) to the input. This is often used to control the dynamic behavior of the system.
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Fermentation
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In an industrial context, fermentation refers to the breakdown of organic substances and re-assembly into other substances. Somewhat paradoxically, fermenter culture in industrial capacity often refers to highly oxygenated and aerobic growth conditions, whereas fermentation in the biochemical context is a strictly anaerobic process.
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Through detection of the by-products of fermentation.
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Ferrofluid
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A liquid which becomes strongly magnetised in the presence of a magnetic field. Ferrofluids are colloidal mixtures composed of nanoscale ferromagnetic, or ferrimagnetic, particles suspended in a carrier fluid, usually an organic solvent or water. The ferromagnetic nano-particles are coated with a surfactant to prevent their agglomeration (due to van der Waals and magnetic forces).
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Ferromagnetic Powder
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Ferromagnetic material in a powdered or finely divided form. Ferromagnetic materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets. Ferromagnetic materials lose their ferromagnetic properties above a characteristic temperature (the Curie Point).
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Ferromagnetism
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The mechanism by which certain materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets. Responsible for commonly observed magnetism phenomena, e.g. 'fridge magnets. A material is 'ferromagnetic' only if all its magnetic ions add a positive contribution to the net magnetisation. If some of them subtract from the net magnetisation (i.e. are partially anti-aligned), then the material is 'ferrimagnetic'.
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Filter (physical)
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A device (usually a membrane or layer) that is designed to block certain objects or substances while letting others through. Filters are often used to remove harmful substances from air or water, for example to remove air pollution, to make water drinkable, to prepare coffee. In domestic food and drink preparation where bulk solids are removed from liquids, this is often called a strainer.
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Flow Separation
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For a solid object travelling through a fluid (or alternatively a stationary object exposed to a moving fluid) flow separation occurs when the boundary layer travels far enough against an adverse pressure gradient that the speed of the boundary layer falls almost to zero.The fluid flow becomes detached from the surface of the object, and instead takes the forms of eddies and vortices.
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Fluorescence
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Fluorescence is a luminescence that is mostly found as an optical phenomenon in cold bodies, in which the molecular absorption of a photon triggers the emission of a photon with a longer (less energetic) wavelength. The energy difference between the absorbed and emitted photons ends up as molecular rotations, vibrations or heat. Sometimes the absorbed photon is in the ultraviolet range, and the emitted light is in the visible range.
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By doping or otherwise attaching a flourescent component to the substance or object to be detected and then exposing it to appropriate radiation (e.g. UV light)
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Ford Viscosity Cup
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A simple gravity device that permits the timed flow of a known volume of liquid passing through an orifice located at the bottom of the cup.
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The presence of a divided solid suspended in a liquid may affect the flow of the liquid.
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Fractal Forms
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A fractal is generally 'a rough or fragmented geometric shape that can be split into parts, each of which is (at least approximately) a reduced-size copy of the whole,' a property called self-similarity. A mathematical fractal is based on an equation that undergoes iteration, a form of feedback based on recursion.
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Fractionation
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A separation process in which a certain quantity of a mixture (solid, liquid, solute, suspension or isotope) is divided up in a number of smaller quantities (fractions) in which the composition changes according to a gradient. Fractions are collected based on differences in a specific property of the individual components.
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For example, particle size or density could be used as the separating property.
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Fractoluminescence
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The emission of light from the fracture (rather than rubbing) of a crystal. Depending upon the atomic and molecular composition of the crystal, when the crystal fractures a charge separation can occur making one side of the fractured crystal +ve charged and the other side -ve charged. As in triboluminescence, if the charge separation results in a large enough electric potential, a discharge across the gap and through the bath gas between the interfaces can occur.
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Fractolumenescence may occur as a divided solid is formed from the fracturing of a crystal.
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Free Surface Effect
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One of several mechanisms where a craft can become unstable and roll-over (capsize). It refers to the tendency of liquids — and of aggregates of small solid objects, like seeds, gravel, or crushed ore which can act as liquids — to move in response to changes in the attitude of a craft's cargo holds, decks, or liquid tanks in reaction to operator-induced motions (or sea states caused by waves & wind acting upon the craft).
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Friction
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The force resisting the relative motion of two surfaces in contact or a surface in contact with a fluid (e.g. air on an aircraft or water in a pipe).
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For example, the presence of particles will affect friction.
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Froth Floatation
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A process for selectively separating hydrophobic materials from hydrophilic. Finely ground raw material is mixed with water to form a slurry. The desired mineral is rendered hydrophobic by the addition of a surfactant or collector chemical. The slurry is there areated (e.g by air or nitrogen). The hydrophobic particles attach to the air bubbles, which rise to the surface, forming a froth which can be removed for further refining.
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Funnel
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A funnel is a pipe with a wide, often conical mouth and a narrow stem. It is used to channel liquid or fine-grained substances into containers with a small opening. Without a funnel, much spillage would occur.
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Gettering
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A process for removal of impurities by reacting them with or attracting them to a suitable agent or part of the system (a 'getter'), with the result that their harmful effect is eliminated. Gettering originated in vaccuum tubes, where Ti was used to getter trace remnant gasses. Gettering is important today for the removal of unwanted trace elements (typically metals) from Silicon integrated circuits.
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Gravitation
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A natural phenomenon by which objects with mass attract one another. In everyday life, gravitation is most commonly thought of as the agency which lends weight to objects with mass.
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Halbach Array
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A special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side. Has many applications ranging from the humble refrigerator magnet through industrial applications such as the brushless AC motor and magnetic coupling, to high-tech applications such as wiggler magnets used in particle accelerators and free electron lasers.
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By attracting particles to the Halbach Array.
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Hall Effect
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The potential difference (Hall voltage) on the opposite sides of an electrical conductor through which there is an electric current, created by a magnetic field applied perpendicularly to the current.
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In the case of magnetic particles.
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Hinge
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A mechanical mechanism that allows mutal rotation of two joined objects around a joined common axis.
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For example a hinged flap will move in response to a passing solid particle.
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Holes
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A hole is a confined lack of structure in some part of an object.
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Hot Chocolate Effect
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The pitch heard from tapping a cup of hot liquid rises after addition of a soluble powder. May be observed by stirring chocolate powder into a mug of hot milk, tapping bottom of mug with a spoon while milk is in motion. Pitch of the taps will increase progressively. Subsequent stirring decreases the pitch. Due to the effect of bubble density on the speed of sound in the liquid. The note heard is the frequency of standing wave with fixed wavelength of liquid column height.
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Image Processing
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Processing of images using mathematical operations by using any form of signal processing for which the input is an image, a series of images, or a video, such as a photograph or video frame The output of image processing may be either an image or a set of characteristics or parameters related to the image.
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Incandescence
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The emission of light (visible electromagnetic radiation) from a hot body due to its temperature.
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Through detection of the radiation emitted by an incandescent divided solid.
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Infrared Radiation
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Infrared (IR) radiation is electromagnetic radiation whose wavelength is longer than that of visible light (400-700 nm), but shorter than that of terahertz radiation (3-300 µm) and microwaves (~30,000 µm). Infrared radiation spans roughly three orders of magnitude (750 nm and 1000 µm).
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Iridescence
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(also known as goniochromism) The property of certain surfaces which appear to change colour as the angle of view changes. Iridescence is commonly seen in items such as soap bubbles, butterfly wings, and sea shells. Caused by multiple reflections from multi-layered, semi-transparent surfaces in which phase shift and interference of the reflections modulates the incident light
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Joule Heating
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The process by which the passage of an electric current through a conductor releases heat. Heat generated is a function of current, resistance and time. Also known as the Joule-Lenz effect, Ohmic heating or resitive heating.
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Lamella
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A gill-shaped structure: fine sheets of material held adjacent to one another, often with fluid in-between. 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.
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Laser
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A device that emits light (electromagnetic radiation) through a process called stimulated emission.
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Laser Doppler Velocimetry
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Using the Doppler shift in a laser beam to measure the velocity in transparent or semi-transparent fluid flows, or the linear or vibratory motion of opaque, reflecting, surfaces. Particles (either naturally occurring or induced) entrained in the fluid pass through interferance fringes generated by two monochromatic laser beams. The reflected light fluctuates in intensity, the frequency of which is equivalent to the Doppler shift between the incident and scattered light, and is thus proportional to the particle velocity.
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In the case of a divided solid suspended in a moving fluid.
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Lens
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An optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam.
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Light
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Light is electromagnetic radiation of a wavelength that is visible to the human eye (in a range from about 380 or 400 nanometres to about 760 or 780 nm)
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Luminescence
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The generation of light that usually occurs at low temperatures, and is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light generated by high temperatures.
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Magnetic Field
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A vector field which surrounds magnets and electric currents, and is detected by the force it exerts on moving electric charges and on magnetic materials. When placed in a magnetic field, magnetic dipoles tend to align their axes parallel to the magnetic field. Magnetic fields also have their own energy with an energy density proportional to the square of the field intensity.
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Magnetism
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One of the phenomena by which materials exert attractive or repulsive forces on other materials. Some well-known materials that exhibit easily detectable magnetic properties (called magnets) are nickel, iron, cobalt, and their alloys; however, all materials are influenced to greater or lesser degree by the presence of a magnetic field.
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Magnetometer
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An instrument used to measure the strength and/or direction of the magnetic field.
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In the case of a magnetised divided solid or by the disturbance to an ambient magnetic field by a ferromagnetic divided solid.
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Mechanoluminescence
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Light emission resulting from any mechanical action on a solid. It can be produced through ultrasound, or through other means.
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Metastability
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A general scientific concept which describes states of delicate equilibrium. A system is in a metastable state when it is in equilibrium (not changing with time) but is susceptible to fall into lower-energy states with only slight interaction. It is analogous to being at the bottom of a small valley when there is a deeper valley close by
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The 'tipping' of a metastable system into a lower energy state in response to a small stimulus could be used to make a senstive detector.
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Microwave Radiation
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Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz.
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Moment of Inertia
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(or mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass). The inertia of a rotating body with respect to its rotation. The moment of inertia plays much the same role in rotational dynamics as mass does in linear dynamics,
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Nanopore
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A small pore in an electrically insulating membrane, that can be used as a single-molecule detector. A nanopore is a Coulter counter for much smaller particles. It can be a biological protein channel in a lipid bilayer or a pore in a solid-state membrane. The detection principle is based on monitoring the ionic current of an electrolyte solution passing through the nanopore as a voltage is applied across the membrane.
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Nanoporous Material
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Materials consisting of a regular organic or inorganic framework supporting a regular, porous structure. Pores are by definition roughly in the nanometre range.
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Nap
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The raised (fuzzy) surface on certain kinds of cloth (such as velvet) or other materials.
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Newton's Rings
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An interference pattern caused by the reflection of light between two surfaces - a spherical surface and an adjacent flat surface. When viewed with monochromatic light it appears as a series of concentric, alternating light and dark rings centered at the point of contact between the two surfaces. When viewed with white light, it forms a concentric ring pattern of rainbow colors because the different wavelengths of light interfere at different thicknesses of the air layer between the surfaces.
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Nucleation
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The extremely localised budding of a distinct thermodynamic phase. Some examples of phases that may form via nucleation in liquids are gaseous bubbles, crystals or glassy regions. Creation of liquid droplets in saturated vapor is also characterized by nucleation. Most nucleation processes are physical, rather than chemical, but a few exceptions do exist (e.g. electrochemical nucleation).
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Ohmmeter
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An electrical instrument that measures electrical resistance.
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Indirectly by its electrical resistance
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Oxidation
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A chemical reaction that involves the loss of electrons or an increase in the oxidation state by a molecule, atom or ion.
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Particle Image Velocimetry
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An optical method of flow visualisation used to obtain instantaneous velocity measurements and related properties in fluids. The fluid is seeded with tracer particles which, for sufficiently small particles, are assumed to faithfully follow the flow dynamics. The fluid with entrained particles is illuminated so that particles are visible. The motion of the seeding particles is used to calculate speed and direction (the velocity field) of the flow being studied.
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Phosphorescence
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A specific type of photoluminescence related to fluorescence. Unlike fluorescence, a phosphorescent material does not immediately re-emit the radiation it absorbs.
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Photoacoustic Doppler Effect
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A specific kind of Doppler effect, which occurs when an intensity modulated light wave induces a photoacoustic wave on moving particles with a specific frequency. The observed frequency shift is a good indicator of the velocity of the illuminated moving particles. A potential biomedical application is measuring blood flow.
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Photodissociation
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A chemical reaction in which a chemical compound is broken down by photons. Any photon with sufficient energy can affect the chemical bonds of a chemical compound. Since a photon's energy is inversely proportional to its wavelength, electromagnetic waves with the energy of visible light or higher, such as ultraviolet light, x-rays and gamma rays are usually involved in such reactions.
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By detecting the products of photodissociation.
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Photoelectric Effect
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The emission of electrons from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light.
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Photography
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The process, activity and art of creating still pictures by recording radiation on a radiation-sensitive medium, such as a photographic film, or electronic image sensors.
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Photoluminescence
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A process in which a substance absorbs photons (electromagnetic radiation) and then re-radiates photons. Quantum mechanically, this can be described as an excitation to a higher energy state and then a return to a lower energy state accompanied by the emission of a photon. One of many forms of luminescence (light emission) and is distinguished by photoexcitation (excitation by photons).
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Piezoelectric Effect
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Generation of electrical charge in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical strain. The piezoelectric effect is a reversible process in that materials also exhibit the reverse piezoelectric effect (the internal generation of a mechanical force resulting from an applied electrical field).
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Piezoluminescence
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Luminescence produced by the action of pressure on certain solids
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Piezoresistive Effect
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The changing electrical resistivity of a semiconductor due to applied mechanical stress.
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Polarisation
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A property of waves that describes the orientation of their oscillations. For transverse waves such as many electromagnetic waves, it describes the orientation of the oscillations in the plane perpendicular to the wave's direction of travel. The oscillations may be oriented in a single direction (linear polarisation), or the oscillation direction may rotate as the wave travels (circular or elliptical polarisation).
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Porosimetry
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An analytical technique used to determine various quantifiable aspects of a material's porous nature, such as pore diameter, total pore volume, surface area, and bulk and absolute densities. Involves the intrusion of a non-wetting liquid (often mercury) at high pressure into a material through the use of a porosimeter. The pore size can be determined based on the external pressure needed to force the liquid into a pore against the opposing force of the liquid's surface tension.
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The presence of a divided solid may affect the porosity of a material by blocking pores.
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Porosity
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The quality of being porous - i.e. having voids or spaces within a solid substance within or through which fluids can be present.
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Pycnometer
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(also called pyknometer or specific gravity bottle) A flask, usually made of glass, with a close-fitting ground glass stopper with a capillary tube through it, so that air bubbles may escape from the apparatus. This enables the density of a fluid to be measured accurately, by reference to an appropriate working fluid such as water or mercury, using an analytical balance.
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Indirectly by measurement of the density of a liquid in which the divided solid is dispersed.
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Radar
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An object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain.
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Radiation
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A process in which energetic particles or waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing.
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Radioactive Tracing
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(or radioactive label) A chemical compound in which one or more atoms have been replaced by a radioisotope. By virtue of its radioactivity it can be used to explore the mechanism of chemical reactions by tracing the path that the radioisotope follows from reactants to products.
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Radioluminescence
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Luminescence produced in a material by the bombardment of ionizing radiation such as beta particles. Examples include the tritium-excited luminous paints used on watch dials and gun sights.
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Rayleigh Scattering
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The elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light.
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Redox Reactions
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Redox (shorthand for oxidation-reduction) reactions describe all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the human body through a series of complex electron transfer processes.
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Reduction
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A chemical reaction that involves the gain of electrons or a decrease in the oxidation state by a molecule, atom or ion.
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Reflection
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The change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves.
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Refraction
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The change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another at any angle other than 90° or 0°. Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth.
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Reverse Brazil Nut Effect
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Under certain conditions the reverse of the Brazil Nut Effect (granular separation) can occur i.e. following vibration or agitation large beads fall to the bottom of a container, and small beads rising to the top of the container.
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Rheometer
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A laboratory device used to measure the way in which a liquid, suspension or slurry flows in response to applied forces. It is used for those fluids which cannot be defined by a single value of viscosity and therefore require more parameters to be set and measured than is the case for a viscometer. It measures the rheology of the fluid.
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In the case of a divided solid dispersed in a fluid.
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Roller
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A cylindrical device that rotates around its principle axis, typically to perform useful work, such as the compression of sheet metal between a pair of rollers.
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Rotational Viscometer
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Rotational viscometers use the idea that the torque required to turn an object in a fluid is a function of the viscosity of that fluid. They measure the torque required to rotate a disk or bob in a fluid at a known speed.
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In the case of a divided solid dispersed in a fluid.
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Saltation (geology)
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A specific type of particle transport by fluids such as wind, or the denser fluid water. It occurs when loose material is removed from a bed and carried by the fluid, before being transported back to the surface. Examples include pebble transport by rivers, sand drift over desert surfaces, soil blowing over fields, or even snow drift over smooth surfaces such as those in the Arctic or Canadian Prairies.
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Scattering
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A general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass (includes deviation of reflected radiation from the angle predicted by the law of reflection).
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Scintillation
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A flash of light produced in a transparent material by an ionization event.
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Screw
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A helical inclined plane. A screw can convert a rotational force (torque) to a linear force and vice versa.
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Sedimentation
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The motion of molecules in solutions or particles in suspensions in response to an external force such as gravity, centrifugal acceleration or electromagnetism. 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.
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Settling
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The process by which particulates settle to the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force. For gravity settling, this means that the particles will tend to fall to the bottom of the vessel, forming a slurry at the vessel base.
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Shadow
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An area where direct light (or other radiation) from a source cannot reach due to obstruction by an object. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light (or radiation).
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Shadowgraph
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An optical method that reveals non-uniformities in transparent media like air, water, or glass. In principle, we cannot directly see a difference in temperature, a different gas, or a shock wave in the transparent air. However, these disturbances refract light rays, so they can cast shadows. The plume of hot air rising from a fire, for example, can be seen by way of its shadow cast upon a nearby surface by the uniform sunlight.
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In the case of a divided solid dispersed in a fluid.
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Shaking
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Moving something rapidly from side to side.
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Solar Energy
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Collection or use of energy from the Sun.
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Solenoid
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A coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create controlled magnetic fields and can be used as electromagnets.
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Sonar
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a technique that uses sound propagation (usually underwater) to navigate, communicate with or detect other vessels. There are two kinds of sonar: active and passive. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of 'targets' in the water.
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Sorption
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The action of both absorption and adsorption taking place simultaneously, i.e. the effect of gases or liquids being incorporated into a material of a different state and adhering to the surface of another molecule. Absorption is the incorporation of a substance in one state into another of a different state (e.g., liquids absorbed by solid or gas absorbed by liquid). Adsorption is the physical adherence or bonding of ions and molecules onto the surface of another molecule.
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Sound
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A mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard.
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Sponge
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A tool or cleaning aid consisting of porous material.
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Stirring
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Agitation of a fluid using repetitive action - typically rotary, usually with the intent of mixing or preventing continuous contact of the fluid with a particular part of some object.
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As a result of greater resistance to the stirring motion.
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Supercritical Fluid
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Any substance at a temperature and pressure above its critical point. It can diffuse through solids like a gas, and dissolve materials like a liquid. Additionally, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties to be 'tuned'.
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Surface of Constant Width
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A convex form whose width, measured by the distance between two opposite parallel planes touching its boundary, is the same regardless of the direction of those two parallel planes. The three-dimensional analogue of a curve of constant width, a two-dimensional shape with a constant distance between pairs of parallel tangent lines. A sphere is obviously a surface of constant width, but there are others, such as Meissner Bodies.
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Thermal Radiation
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Electromagnetic radiation emitted from the surface of an object due to the object's temperature.
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Thermionic Emission
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Emission of electrons or ions caused by thermal vibrational energy . Also known as the Edison Effect.
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Thermochromic Paint
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A paint based on colour-changing pigments. It involves the use of liquid crystals or leuco dye technology. After absorbing a certain amount of light or heat, the crystallic or molecular structure of the pigment reversibly changes in such a way that it absorbs and emits light at a different wavelength than at lower temperatures.
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Thermochromism
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The ability of substance to change color due to a change in temperature. Thermochromism is one of several types of chromism. The two basic approaches are based on liquid crystals and leuco dyes.
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Thermocouple
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A junction between two different metals that produces a voltage related to a temperature difference. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert heat into electricity.
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In the case of a hot divided solid.
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Thermography
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Thermal imaging cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 9000-14,000 nanometers or 9-14 µm) and produce images of that radiation, called thermograms.
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Thermoluminescence
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A form of luminescence that is exhibited by certain crystalline materials, such as some minerals, when previously absorbed energy from electromagnetic radiation or other ionizing radiation is re-emitted as light upon heating of the material. This phenomenon is distinct from that of black body radiation.
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Tomography
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Imaging by sections or sectioning, through the use of any kind of penetrating wave. The method is used in radiology, archaeology, biology, geophysics, oceanography, materials science, astrophysics and other sciences.
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Triboelectric Effect
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A type of contact electrification in which certain materials become electrically charged after they come into contact with another different material and are then separated (such as through rubbing). The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.
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Triboluminescence
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An optical phenomenon in which light is generated via the breaking of asymmetrical bonds in a crystal when that material is scratched, crushed, or rubbed. This is a variant of luminescence.
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Tyndall Effect
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Light scattering by colloidal particles or particles in suspension
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Valve
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A device that regulates the flow of a fluid (gases, liquids, fluidised solids, or slurries) by opening, closing, or partially obstructing various passageways.
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Vibration
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Mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.
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By detecting reflected/returned vibrations, for example: sonar.
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Vibrational Viscometer
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An instrument that operates by measuring the damping of an oscillating electromechanical resonator immersed in a fluid whose viscosity is to be determined. The resonator generally oscillates in torsion or transversely (as a cantilever beam or tuning fork). The higher the viscosity, the larger the damping imposed on the resonator.
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In the case of a divided solid dispersed in the fluid.
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Viscometer
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(also called viscosimeter) An instrument used to measure the viscosity of a fluid. For liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used. Viscometers only measure under one flow condition.
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In the case of a divided solid dispersed in the fluid.
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X-Ray
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A form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3 × 1016 Hz to 3 × 1019 Hz) and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma rays. In many languages, X-radiation is called Röntgen radiation.
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