1.
Laboratory
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A laboratory is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratories used for scientific research take many forms because of the requirements of specialists in the various fields of science. A physics laboratory might contain a particle accelerator or vacuum chamber, a chemist or biologist might use a wet laboratory, while a psychologists laboratory might be a room with one-way mirrors and hidden cameras in which to observe behavior. In some laboratories, such as commonly used by computer scientists. Scientists in other fields will use other types of laboratories. Engineers use laboratories as well to design, build, and test technological devices, scientific laboratories can be found as research and learning spaces in schools and universities, industry, government, or military facilities, and even aboard ships and spacecraft. Early instances of laboratories recorded in English involved alchemy and the preparation of medicines, larger or more sophisticated equipment is generally called a scientific instrument. Both laboratory equipment and scientific instruments are increasingly being designed and shared using open hardware principles, open source labs use open source scientific hardware. The title of laboratory is used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories. In many labs, though, hazards are present, in laboratories where dangerous conditions might exist, safety precautions are important. Rules exist to minimize the risk, and safety equipment is used to protect the lab user from injury or to assist in responding to an emergency. This standard is referred to as the Laboratory Standard. Under this standard, a laboratory is required to produce a Chemical Hygiene Plan which addresses the specific hazards found in its location, the CHP must be reviewed annually. Many schools and businesses employ safety, health, and environmental specialists, such as a Chemical Hygiene Officer to develop, manage, and evaluate their CHP. Additionally, third party review is used to provide an objective outside view which provides a fresh look at areas. An important element of such audits is the review of regulatory compliance, training is critical to the ongoing safe operation of the laboratory facility. Educators, staff and management must be engaged in working to reduce the likelihood of accidents, injuries, efforts are made to ensure laboratory safety videos are both relevant and engaging. The dictionary definition of laboratory at Wiktionary Media related to Laboratory at Wikimedia Commons Nobel Laureates Interactive 360° Laboratories
2.
Membrane bioreactor
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When used with domestic wastewater, MBR processes can produce effluent of high quality enough to be discharged to coastal, surface or brackish waterways or to be reclaimed for urban irrigation. Other advantages of MBRs over conventional processes include small footprint, easy retrofit, recent technical innovation and significant membrane cost reduction have enabled MBRs to become an established process option to treat wastewaters. As a result, the MBR process has now become an option for the treatment and reuse of industrial and municipal wastewaters, as evidenced by their constantly rising numbers. The current MBR market has been estimated to value around US$216 million in 2006, Membrane bioreactors can be used to reduce the footprint of an activated sludge sewage treatment system by removing some of the liquid component of the mixed liquor. This leaves a waste product that is then treated using the activated sludge process. The MBR process was introduced by the late 1960s, as soon as commercial scale ultrafiltration and microfiltration membranes were available, the original process was introduced by Dorr-Oliver Inc. and combined the use of an activated sludge bioreactor with a crossflow membrane filtration loop. The flat sheet membranes used in process were polymeric and featured pore sizes ranging from 0.003 to 0.01 μm. As a result, the focus was on the attainment of high fluxes, because of the poor economics of the first generation MBRs, they only found applications in niche areas with special needs, such as isolated trailer parks or ski resorts. The breakthrough for the MBR came in 1989 with Yamamoto and co-workers idea of submerging the membranes in the bioreactor, until then, MBRs were designed with the separation device located external to the reactor and relied on high transmembrane pressure to maintain filtration. With the membrane directly immersed in the bioreactor, submerged MBR systems are preferred to sidestream configuration. The submerged configuration relies on coarse bubble aeration to produce mixing, the energy demand of the submerged system can be up to 2 orders of magnitude lower than that of the sidestream systems and submerged systems operate at a lower flux, demanding more membrane area. In submerged configurations, aeration is considered as one of the parameters in process performance both hydraulic and biological. Aeration maintains solids in suspension, scours the membrane surface and provides oxygen to the biomass, leading to a better biodegradability, the other key steps in the recent MBR development were the acceptance of modest fluxes, and the idea to use two-phase bubbly flow to control fouling. The lower operating cost obtained with the submerged configuration along with the decrease in the membrane cost encouraged an exponential increase in MBR plant installations from the mid 90s. Since then, further improvements in the MBR design and operation have been introduced and incorporated into larger plants. While early MBRs were operated at solid retention times as high as 100 days with MLSS up to 30 g/L, thanks to these new operating conditions, the oxygen transfer and the pumping cost in the MBR have tended to decrease and overall maintenance has been simplified. Typical hydraulic retention times range between 3 and 10 hours, in terms of membrane configurations, mainly hollow fiber and flat sheet membranes are applied for MBR applications. Despite the more favourable energy usage of submerged membranes, there continued to be a market for the side stream configuration, for ease of maintenance the side stream configuration can be installed on a lower level in a plant building
3.
Reverse osmosis
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Reverse osmosis is a water purification technology that uses a semipermeable membrane to remove ions, molecules, and larger particles from drinking water. In reverse osmosis, a pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential differences of the solvent. Reverse osmosis can remove many types of dissolved and suspended species from water, including bacteria, the result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be selective, this membrane should not allow large molecules or ions through the pores, in the normal osmosis process, the solvent naturally moves from an area of low solute concentration, through a membrane, to an area of high solute concentration. Applying an external pressure to reverse the flow of pure solvent. The process is similar to other membrane technology applications, however, key differences are found between reverse osmosis and filtration. Reverse osmosis also involves diffusion, making the process dependent on pressure, flow rate, reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other effluent materials from the water molecules. The process of osmosis through semipermeable membranes was first observed in 1748 by Jean-Antoine Nollet, for the following 200 years, osmosis was only a phenomenon observed in the laboratory. In 1950, the University of California at Los Angeles first investigated desalination of seawater using semipermeable membranes, cadottes patent on this process was the subject of litigation and has since expired. Almost all commercial reverse osmosis membrane is now made by this method, by the end of 2001, about 15,200 desalination plants were in operation or in the planning stages, worldwide. In 1977 Cape Coral, Florida became the first municipality in the United States to use the RO process on a scale with an initial operating capacity of 3 million gallons per day. By 1985, due to the growth in population of Cape Coral. In most cases, the membrane is designed to only water to pass through this dense layer. This process is best known for its use in desalination, but since the early 1970s, it has also used to purify fresh water for medical, industrial. Around the world, household drinking water systems, including a reverse osmosis step, are commonly used for improving water for drinking and cooking. CTA membrane is a paper by-product membrane bonded to a layer and are made to allow contact with chlorine in the water. These require an amount of chlorine in the water source to prevent bacteria from forming on it. The typical rejection rate for CTA membranes is 85–95%, the cellulose triacetate membrane is prone to rotting unless protected by chlorinated water, while the thin film composite membrane is prone to breaking down under the influence of chlorine
4.
Biofouling
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Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or animals on wetted surfaces. Such accumulation is referred to as epibiosis when the host surface is another organism, antifouling is the ability of specifically designed materials and coatings to remove or prevent biofouling by any number of organisms on wetted surfaces. Specifically, the buildup of biofouling on marine vessels poses a significant problem, in some instances, the hull structure and propulsion systems can be damaged. The accumulation of biofoulers on hulls can increase both the volume of a vessel and the hydrodynamic friction, leading to increased drag of up to 60%. The drag increase has been seen to decrease speeds by up to 10%, with fuel typically comprising up to half of marine transport costs, antifouling methods are estimated to save the shipping industry around $60 billion per year. Increased fuel use due to biofouling contributes to environmental effects and is predicted to increase emissions of carbon dioxide. A variety of antifouling methods have historically been implemented to combat biofouling, recently, scientists have begun researching antifouling methods inspired by living organisms. This type of imitation is known as biomimicry. The variety among biofouling organisms is highly diverse, and extends far beyond attachment of barnacles, according to some estimates, over 1700 species comprising over 4000 organisms are responsible for biofouling. Biofouling is divided into microfouling — biofilm formation and bacterial adhesion —, due to the distinct chemistry and biology that determine what prevents them from settling, organisms are also classified as hard- or soft-fouling types. Calcareous fouling organisms include barnacles, encrusting bryozoans, mollusks, polychaete and other tube worms, examples of non-calcareous fouling organisms are seaweed, hydroids, algae and biofilm slime. Together, these form a fouling community. Marine fouling is typically described as following four stages of ecosystem development, the chemistry of biofilm formation describes the initial steps prior to colonization. Within the first minute the van der Waals interaction causes the surface to be covered with a conditioning film of organic polymers. In the next 24 hours, this allows the process of bacterial adhesion to occur. By the end of the first week, the nutrients and ease of attachment into the biofilm allow secondary colonizers of spores of macroalgae. Within 2 to 3 weeks, the tertiary colonizers- the macrofoulers- have attached and these include tunicates, mollusks and sessile Cnidarians. Governments and industry more than US$5.7 billion annually to prevent
5.
Membrane technology
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Membrane technology covers all engineering approaches for the transport of substances between two fractions with the help of permeable membranes. In general, mechanical separation processes for separating gaseous or liquid streams use membrane technology, Membrane separation processes operate without heating and therefore use less energy than conventional thermal separation processes such as distillation, sublimation or crystallization. The separation process is physical and both fractions can be used. Cold separation using membrane technology is used in the food technology, biotechnology. Furthermore, using membranes enables separations to take place that would be impossible using thermal separation methods, depending on the type of membrane, the selective separation of certain individual substances or substance mixtures is possible. In waste water treatment, membrane technology is becoming increasingly important, with the help of ultra/microfiltration it is possible to remove particles, colloids and macromolecules, so that waste-water can be disinfected in this way. This is needed if waste-water is discharged into sensitive waters especially those designated for contact water-sports, about half of the market is in medical applications such as use in artificial kidneys to remove toxic substances by hemodialysis and as artificial lung for bubble-free supply of oxygen in the blood. The importance of technology is growing in the field of environmental protection. Even in modern energy recovery techniques membranes are used, for example in fuel cells. Two basic models can be distinguished for mass transfer through the membrane, the solution-diffusion model, in real membranes, these two transport mechanisms certainly occur side by side, especially during ultra-filtration. In the solution-diffusion model, transport occurs only by diffusion, the component that needs to be transported must first be dissolved in the membrane. This principle is important for dense membranes without natural pores such as those used for reverse osmosis. During the filtration process a boundary layer forms on the membrane and this concentration gradient is created by molecules which cannot pass through the membrane. The effect is referred as concentration polarization and, occurring during the filtration, concentration polarization is, in principle, reversible by cleaning the membrane which results in the initial flux being almost totally restored. Using a tangential flow to the membrane can also minimize concentration polarization, transport through pores – in the simplest case – is done convectively. This requires the size of the pores to be smaller than the diameter of the two separate components, membranes which function according to this principle are used mainly in micro- and ultrafiltration. They are used to separate macromolecules from solutions, colloids from a dispersion or remove bacteria, during this process the retained particles or molecules form a pulpy mass on the membrane, and this blockage of the membrane hampers the filtration. This blockage can be reduced by the use of the cross-flow method, the tangential flow on the front creates a shear stress that cracks the filter cake and reduces the fouling. g
6.
Fouling
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Fouling is the accumulation of unwanted material on solid surfaces to the detriment of function. The fouling materials can consist of living organisms or a non-living substance. Other terms used in the literature to describe fouling include, deposit formation, encrustation, crudding, deposition, scaling, scale formation, slagging, and sludge formation. This article is devoted to the fouling of industrial heat exchangers. In the cooling technology and other fields, a distinction is made between macro fouling and micro fouling. Of the two, micro fouling is the one which is more difficult to prevent and therefore more important. Macro fouling is caused by coarse matter of biological or inorganic origin. Such matter enters into the water circuit through the cooling water pumps from sources like the open sea. In closed circuits, like cooling towers, the ingress of macro fouling into the tower basin is possible through open canals or by the wind. Sometimes, parts of the tower internals detach themselves and are carried into the cooling water circuit. Such substances can foul the surfaces of heat exchangers and may cause deterioration of the relevant heat transfer coefficient and they may also create flow blockages, redistribute the flow inside the components, or cause fretting damage. Examples Manmade refuse, Detached internal parts of components, Tools and other foreign objects accidentally left after maintenance, Algae, Mussels, Leaves and these are most often water solutions, but non-aqueous precipitation fouling is also known. Precipitation fouling is a common problem in boilers and heat exchangers operating with hard water. Through changes in temperature, or solvent evaporation or degasification, the concentration of salts may exceed the saturation, in general, the dependence of the salt solubility on temperature or presence of evaporation will often be the driving force for precipitation fouling. The important distinction is between salts with normal or retrograde dependence of solubility on temperature, the salts with the normal solubility increase their solubility with increasing temperature and thus will foul the cooling surfaces. The salts with inverse or retrograde solubility will foul the heating surfaces, an example of the temperature dependence of solubility is shown in the figure. Calcium sulfate is a common precipitation foulant of heating surfaces due to its retrograde solubility, precipitation fouling can also occur in the absence of heating or vaporization. For example, calcium sulfate decreases it solubility with decreasing pressure and this can lead to precipitation fouling of reservoirs and wells in oil fields, decreasing their productivity with time
7.
Molecule
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A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge, however, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions. In the kinetic theory of gases, the molecule is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules as they are in fact monoatomic molecules. A molecule may be homonuclear, that is, it consists of atoms of one element, as with oxygen, or it may be heteronuclear. Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are not considered single molecules. Molecules as components of matter are common in organic substances and they also make up most of the oceans and atmosphere. Also, no typical molecule can be defined for ionic crystals and covalent crystals, the theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding, which means that solid metals are also not made of molecules. In glasses, atoms may also be together by chemical bonds with no presence of any definable molecule. The science of molecules is called molecular chemistry or molecular physics, in practice, however, this distinction is vague. In molecular sciences, a molecule consists of a system composed of two or more atoms. Polyatomic ions may sometimes be thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i. e, according to Merriam-Webster and the Online Etymology Dictionary, the word molecule derives from the Latin moles or small unit of mass. Molecule – extremely minute particle, from French molécule, from New Latin molecula, diminutive of Latin moles mass, a vague meaning at first, the vogue for the word can be traced to the philosophy of Descartes. The definition of the molecule has evolved as knowledge of the structure of molecules has increased, earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties. Molecules are held together by covalent bonding or ionic bonding. Several types of non-metal elements exist only as molecules in the environment, for example, hydrogen only exists as hydrogen molecule. A molecule of a compound is made out of two or more elements, a covalent bond is a chemical bond that involves the sharing of electron pairs between atoms
8.
Chemical plant
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A chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. The general objective of a plant is to create new material wealth via the chemical or biological transformation. Chemical plants use specialized equipment, units, and technology in the manufacturing process, some would consider an oil refinery or a pharmaceutical or polymer manufacturer to be effectively a chemical plant. Petrochemical plants are located adjacent to an oil refinery to minimize transportation costs for the feedstocks produced by the refinery. Speciality chemical and fine chemical plants are much smaller and not as sensitive to location. Tools have been developed for converting a base project cost from one location to another. Chemical plants use chemical processes, which are detailed industrial-scale methods, the same chemical process can be used at more than one chemical plant, with possibly differently scaled capacities at each plant. Also, a plant at a site may be constructed to utilize more than one chemical process. A chemical plant commonly has usually large vessels or sections called units or lines that are interconnected by piping or other material-moving equipment which can carry streams of material, such material streams can include fluids or sometimes solids or mixtures such as slurries. An overall chemical process is made up of steps called unit operations which occur in the individual units. A raw material going into a process or plant as input to be converted into a product is commonly called a feedstock. In addition to feedstocks for the plant as a whole, a stream of material to be processed in a particular unit can similarly be considered feed for that unit. Output streams from the plant as a whole are final products, however, final products from one plant may be intermediate chemicals used as feedstock in another plant for further processing. For example, some products from an oil refinery may used as feedstock in petrochemical plants, either the feedstock, the product, or both may be individual compounds or mixtures. It is often not worthwhile separating the components in these mixtures completely, specific levels of purity depend on product requirements, chemical processes may be run in continuous or batch operation. In batch operation, production occurs in time-sequential steps in discrete batches, a batch of feedstock is fed into a process or unit, then the chemical process takes place, then the product and any other outputs are removed. Such batch production may be repeated again and again with new batches of feedstock. Batch operation is used in smaller scale plants such as pharmaceutical or specialty chemicals production
9.
Synthetic membrane
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An artificial membrane, or synthetic membrane, is a synthetically created membrane which is usually intended for separation purposes in laboratory or in industry. Synthetic membranes have been used for small and large-scale industrial processes since the middle of twentieth century. A wide variety of membranes is known. They can be produced from materials such as polymers and liquids. The most of commercially utilized synthetic membranes in separation industry are made of polymeric structures and they can be classified based on their surface chemistry, bulk structure, morphology, and production method. The chemical and physical properties of synthetic membranes and separated particles as well as a choice of driving force define a particular membrane separation process, the most commonly used driving forces of a membrane process in industry are pressure and concentration gradients. The respective membrane process is known as filtration. Synthetic membranes utilized in a process can be of different geometry. They can also be categorized based on their application and separation regime, synthetic membrane can be fabricated from a large number of different materials. It can be made from organic or inorganic materials including solids such as metal or ceramic, homogeneous films, heterogeneous solids, ceramic membranes are produced from inorganic materials such as aluminium oxides, silicon carbide, and zirconium oxide. Ceramic membranes are very resistant to the action of aggressive media and they are very stable chemically, thermally, and mechanically, and biologically inert. Even though ceramic membranes have a weight and substantial production costs. Ceramic membranes are made as monolithic shapes of tubular capillaries. Liquid membranes refer to synthetic membranes made of non-rigid materials, several types of liquid membranes can be encountered in industry, emulsion liquid membranes, immobilized liquid membranes, molten salts, and hollow-fiber contained liquid membranes. Liquid membranes have been studied but thus far have limited commercial applications. Maintaining adequate long-term stability is the problem, due to the tendency of membrane liquids to evaporate or dissolve in the phases in contact with them, polymeric membranes lead the membrane separation industry market because they are very competitive in performance and economics. Many polymers are available, but the choice of membrane polymer is not a trivial task, a polymer has to have appropriate characteristics for the intended application. The polymer sometimes has to offer a low binding affinity for separated molecules and it has to be compatible with chosen membrane fabrication technology
10.
Cross-flow filtration
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In chemical engineering, biochemical engineering and protein purification, crossflow filtration is a type of filtration. Cross-flow filtration gets its name because the majority of the feed flow travels tangentially across the surface of the filter, rather than into the filter. The principal advantage of this is that the cake is substantially washed away during the filtration process. It can be a process, unlike batch-wise dead-end filtration. Industrial examples of this include the extraction of soluble antibiotics from fermentation liquors, in crossflow filtration, the feed is passed across the filter membrane at positive pressure relative to the permeate side. With crossflow filtration the tangential motion of the bulk of the fluid across the membrane causes trapped particles on the surface to be rubbed off. This means that a filter can operate continuously at relatively high solids loads without blinding. Filtration membranes can be polymeric or ceramic, depending upon the application, the principles of cross-flow filtration are used in reverse osmosis, nanofiltration, ultrafiltration and microfiltration. When purifying water, it can be very cost effective in comparison to the traditional evaporation methods, in protein purification, the term Tangential Flow Filtration is used to describe cross-flow filtration with membranes. The process can be used at different stages during purification, depending on the type of membrane selected, in the photograph of an industrial filtration unit, it is possible to see that the recycle pipework is considerably larger than either the feed pipework or the permeate pipework. These pipe sizes are directly related to the proportion of liquid flows through the unit, a dedicated pump is used to recycle the feed several times around the unit before the solids-rich retentate is transferred to the next part of the process. Backwashing is not applicable to spirally wound membranes and is not a practice in most applications. Clean-in-place systems are used to remove fouling from membranes after extensive use. The CIP process may use detergents, reactive agents such as sodium hypochlorite and acids and alkalis such as citric acid, sodium hypochlorite must be removed from the feed in some membrane plants. Oxidation will degrade the membranes to a point where they no longer perform at rated rejection levels and have to be replaced. Bleach can be added to a NaOH sodium hydroxide CIP during an initial system start-up before spirally-wound membranes are loaded into the plant to help disinfect the system. Bleach is also used to CIP perforated stainless steel membranes, as their tolerance for sodium hypochlorite is much higher than a spirally-wound membrane, caustics and acids are most often used as primary CIP chemicals. Caustic removes organic fouling and acid removes minerals, enzyme solutions are also used in some systems for helping remove organic fouling material from the membrane plant
11.
Biological membrane
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A biological membrane or biomembrane is an enclosing or separating membrane that acts as a selectively permeable barrier within living things. Bulk lipid in membrane provides a matrix for proteins to rotate. The cellular membranes should not be confused with isolating tissues formed by layers of cells, such as mucous membranes, the lipid bilayer consists of two layers- an outer leaflet and an inner leaflet. The components of bilayers are distributed unequally between the two surfaces to create asymmetry between the outer and inner surfaces and this asymmetric organization is important for cell functions such as cell signaling. The asymmetry of the biological membrane reflects the different functions of the two leaflets of the membrane, as seen in the fluid membrane model of the phospholipid bilayer, the outer leaflet and inner leaflet of the membrane are asymmetrical in their composition. Certain proteins and lipids rest only on one surface of the membrane, in eucaryotic cells, new phospholipids are manufactured by enzymes bound to the part of the endoplasmic reticulum membrane that faces the cytosol. These enzymes, which use free fatty acids as substrates, deposit all newly made phospholipids into the half of the bilayer. To enable the membrane as a whole to grow evenly, half of the new phospholipid molecules then have to be transferred to the opposite monolayer and this transfer is catalyzed by enzymes called flippases. In the plasma membrane, flippases transfer specific phospholipids selectively, so different types become concentrated in each monolayer. Using selective flippases is not the way to produce asymmetry in lipid bilayers. In particular, a different mechanism operates for glycolipids—the lipids that show the most striking, the biological membrane is made up of lipids with hydrophobic tails and hydrophilic heads. The hydrophobic tails are hydrocarbon tails whose length and saturation is important in characterizing the cell, lipid rafts occur when lipid species and proteins aggregate in domains in the membrane. These help organize membrane components into localized areas that are involved in specific processes, red blood cells, or erythrocytes, have a unique lipid composition. The bilayer of red cells is composed of cholesterol and phospholipids in equal proportions by weight. Erythrocyte membrane plays a role in blood clotting. In the bilayer of red cells is phosphatidylserine. This is usually in the side of the membrane. However, it is flipped to the membrane to be used during blood clotting
12.
Homogeneity and heterogeneity
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Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity in a substance or organism. A material or image that is homogeneous is uniform in composition or character, the alternate spellings homogenous and heterogenous are commonly, but incorrectly, used. Heterogenous meanwhile is a term primarily confined to pathology which refers to the property of an object in the body having its origin outside the body, the concepts are the same to every level of complexity, from atoms to populations of animals or people, and galaxies. Hence, an element may be homogeneous on a larger scale and this is known as an effective medium approach, or effective medium approximations. Various disciplines understand heterogeneity, or being heterogeneous, in different ways, heterogeneous solids, liquids, and gases may be made homogeneous by melting, stirring, or by allowing time to pass for diffusion to distribute the molecules evenly. For example, adding dye to water will create a solution at first. Entropy allows for heterogeneous substances to become homogeneous over time, a heterogeneous mixture is a mixture of two or more compounds. Examples are, mixtures of sand and water or sand and iron filings, a rock, water and oil, a salad, trail mix. A mixture can be determined to be homogeneous when everything is settled and equal, various models have been proposed to model the concentrations in different phases. The phenomena to be considered are mass rates and reaction, homogeneous reactions are chemical reactions in which the reactants and products are in the same phase, while heterogeneous reactions have reactants in two or more phases. Reactions that take place on the surface of a catalyst of a different phase are also heterogeneous, a reaction between two gases or two miscible liquids is homogeneous. A reaction between a gas and a liquid, a gas and a solid or a liquid and a solid is heterogeneous, earth is a heterogeneous substance in many aspects. E. g. rocks are inherently heterogeneous, usually occurring at the micro-scale and mini-scale, in algebra, homogeneous polynomials have the same number of factors of a given kind. This can cause problems in attempts to summarize the meaning of the studies, in medicine and genetics, a genetic or allelic heterogeneous condition is one where the same disease or condition can be caused, or contributed to, by several factors. In the case of genetics, varying different genes or alleles, in cancer research, cancer cell heterogeneity is thought to be one of the underlying reasons that make treatment of cancer difficult. In physics, heterogeneous is understood to mean having physical properties that vary within the medium, in sociology, heterogeneous may refer to a society or group that includes individuals of differing ethnicities, cultural backgrounds, sexes, or ages. Academic Press Dictionary of Science and Technology
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