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Density Gradient
Density gradient is a spatial variation in density over a region. The term is used in the natural sciences to describe varying density of matter, but can apply to any quantity whose density can be measured. Aerodynamics In the study of supersonic flight, Schlieren photography observes the density gradient of air as it interacts with aircraft. Also in the field of Computational Fluid Dynamics, Density gradient is used to observe the acoustic waves, shock waves or expansion waves in the flow field. Water A steep density gradient in a body of water can have the effect of trapping energy and preventing convection, such a gradient is employed in solar ponds. In the case of salt water, sharp gradients can lead to stratification of different concentrations of salinity. This is called a Halocline. Biology In the life sciences, a special technique called density gradient separation is used for isolating and purifying cells, viruses and subcellular particles. Variations of this inc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Density
Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be used: \rho = \frac, where ''ρ'' is the density, ''m'' is the mass, and ''V'' is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, although this is scientifically inaccurate this quantity is more specifically called specific weight. For a pure substance, the density is equal to its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. Osmium is the densest known element at standard conditions for temperature and pressure. To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity "relative den ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halocline
A halocline (or salinity chemocline), from the Greek words ''hals'' (salt) and ''klinein'' (to slope), refers to a layer within a body of water ( water column) where there is a sharp change in salinity (salt concentration) with depth. Haloclines are typically found in oceans or large estuaries and it is a type of chemical stratification that is most commonly found in places where freshwater from rivers or melting ice, mixes with salty ocean water. Description In the midlatitudes, an excess of evaporation over precipitation leads to surface waters being saltier than deep waters. In such regions, the vertical stratification is due to surface waters being warmer than deep waters and the halocline is destabilizing. Such regions may be prone to salt fingering, a process which results in the preferential mixing of salinity. In these regions, the halocline is important in allowing for the formation of sea ice, and limiting the escape of carbon dioxide to the atmosphere. In ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Density Current
Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek language, Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be used: \rho = \frac, where ''ρ'' is the density, ''m'' is the mass, and ''V'' is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, although this is scientifically inaccurate this quantity is more specifically called specific weight. For a pure substance, the density is equal to its mass concentration (chemistry), mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. Osmium is the densest known element at standard conditions for temperature and pressure. To simplify comparisons of density across different systems of units, it is sometimes replaced by t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Seismic Wave
A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large man-made explosion that produces low-frequency acoustic energy. Seismic waves are studied by seismologists, who record the waves using seismometers, hydrophones (in water), or accelerometers. Seismic waves are distinguished from seismic noise (ambient vibration), which is persistent low-amplitude vibration arising from a variety of natural and anthropogenic sources. The propagation velocity of a seismic wave depends on density and elasticity of the medium as well as the type of wave. Velocity tends to increase with depth through Earth's crust and mantle, but drops sharply going from the mantle to Earth's outer core. Earthquakes create distinct types of waves with different velocities. When recorded by a seismic observatory, their ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fast Breeder Nuclear Reactor
A breeder reactor is a nuclear reactor that generates more fissile material than it consumes. These reactors can be fueled with more-commonly available isotopes of uranium and thorium, such as uranium-238 and thorium-232, as opposed to the rare uranium-235 which is used in conventional reactors. These materials are called fertile materials since they can be bred into fuel by these breeder reactors. Breeder reactors achieve this because their neutron economy is high enough to create more fissile fuel than they use. These extra neutrons are absorbed by the fertile material that is loaded into the reactor along with fissile fuel. This irradiated fertile material in turn transmutes into fissile material which can undergo fission reactions. Breeders were at first found attractive because they made more complete use of uranium fuel than light-water reactors, but interest declined after the 1960s as more uranium reserves were foundHelmreich, J. E. ''Gathering Rare Ores: The Diplomac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth Core
The internal structure of Earth are the layers of the Earth, excluding its atmosphere and hydrosphere. The structure consists of an outer silicate solid crust, a highly viscous asthenosphere, and solid mantle, a liquid outer core whose flow generates the Earth's magnetic field, and a solid inner core. Scientific understanding of the internal structure of Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through Earth, measurements of the gravitational and magnetic fields of Earth, and experiments with crystalline solids at pressures and temperatures characteristic of Earth's deep interior. Global properties Note: In chondrite model (1), the light element in the core is assumed to be Si. Chondrite model (2) is a model of chemical composition of the mantle corresponding to the model of core shown in chondrit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pheresis
Apheresis ( ἀφαίρεσις (''aphairesis'', "a taking away")) is a medical technology in which the blood of a person is passed through an apparatus that separates one particular constituent and returns the remainder to the circulation. It is thus an extracorporeal therapy. One of the uses of apheresis is for collecting hematopoietic stem cells. Method Depending on the substance that is being removed, different processes are employed in apheresis. If separation by density is required, centrifugation is the most common method. Other methods involve absorption onto beads coated with an absorbent material and filtration. The centrifugation method can be divided into two basic categories: Continuous flow centrifugation Continuous flow centrifugation (CFC) historically required two venipunctures , as "continuous" means the blood is collected, spun, and returned simultaneously. Newer systems can operate with a single venipuncture by collecting blood in a vessel and al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sucrose Gradient Centrifugation
In biochemistry and cell biology, differential centrifugation (also known as differential velocity centrifugation) is a common procedure used to separate organelles and other sub-cellular particles based on their Svedberg, sedimentation rate. Although often applied in biological analysis, differential centrifugation is a general technique also suitable for crude purification of non-living suspended particles (e.g. nanoparticles, colloidal particles, viruses). In a typical case where differential centrifugation is used to analyze cell-biological phenomena (e.g. organelle distribution), a Tissue (biology), tissue sample is first Lysis, lysed to break the cell membranes and release the organelles and cytosol. The lysate is then subjected to repeated centrifugations, where particles that sediment sufficiently quickly at a given centrifugal force for a given time form a compact "pellet" at the bottom of the centrifugation tube. After each centrifugation, the ''supernatant'' (non-pell ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isopycnic Centrifugation
An isopycnic surface is a surface of constant density inside a fluid. Isopycnic surfaces contrast with isobaric or isothermal surfaces, which describe surfaces of constant pressure and constant temperature respectively. Isopycnic surfaces are sometimes referred to as "iso-density" surfaces, although this is strictly incorrect. Isopycnic typically describes surfaces, not processes. Unless there is a flux of mass into or out of a control volume, a process which occurs at a constant density also occurs at a constant volume and is called an isochoric process and not an isopycnic process. The term "isopycnic" is commonly encountered in the fluid dynamics of compressible fluids, such as in meteorology and geophysical fluid dynamics, astrophysics, or the fluid dynamics of explosions or high Mach number flows.It may also be applied to other situations where a continuous medium has smoothly varying density, such as in the case of an inhomogeneous colloidal suspension. In general isopycni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Salinity
Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to per mille, ‰). Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a state function, thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water. A contour line of constant salinity is called an ''isohaline'', or sometimes ''isohale''. Definitions Salinity in rivers, lakes, and the ocean is conceptually simple, but technically challenging to define and measure precisely. Conceptually the salinity is the quantity of dissolved salt content of the water. Salts are compounds like sodium chloride, magnesium sulfate, potassium nitrate, and sod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Sciences
Natural science or empirical science is one of the branches of science concerned with the description, understanding and prediction of natural phenomena, based on empirical evidence from observation and experimentation. Mechanisms such as peer review and reproducibility of findings are used to try to ensure the validity of scientific advances. Natural science can be divided into two main branches: life science and physical science. Life science is alternatively known as biology. Physical science is subdivided into branches: physics, astronomy, Earth science and chemistry. These branches of natural science may be further divided into more specialized branches (also known as fields). As empirical sciences, natural sciences use tools from the formal sciences, such as mathematics and logic, converting information about nature into measurements that can be explained as clear statements of the " laws of nature". Modern natural science succeeded more classical approaches to natura ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
