Physical and chemical alteration

Sensitivity to heat, which can cause physical and chemical alterations during paint drying and hardening. 

In most mammals, spermatozoa become motile while in the proximal cauda epididymis. The epididymis is also a reservoir for sperm. In addition, maturation of the spermatic plasma membrane in the epididymis involves physical and chemical alterations in the membrane lipids. Seminal and prostatic fluids are added to the semen during its passage through the male reproductive tract. 

The OSI was primarily developed for oil or fat samples. It is possible to use the method on lipids extracted from foodstuffs however, such lipids may not have the same oxidative stability as the food since the physical structures are different. Additionally, muscle foods oxidize rapidly at elevated temperature due to physical and chemical alterations during cooking thus, this method probably will not be useful with raw meats. 

High Absorbency Rayons. Over the past years, disposable products have become commonplace, especially in the United States and Europe. Cellulosic fibers, particularly rayons, have served the needs of the disposables industry because of their absorbent qualities. The most useful fibers for disposable/ absorbent applications are the rayons with crenulations, crimp, and hollow regions, all of which add to the absorbency of the fiber. These characteristics are achieved in varying degrees by physical and chemical alterations in the spinning process. Crenulations, or random irregularities in the shape of the cross-section, typical for most rayon fibers, are caused by the rapid formation of skin before the dehydration is complete. As the fiber interior loses solvent, it collapses in certain areas and produces the crenulated shape. Furthermore, fabricators have learned how to... 

Corrosion may be defined as the physical and chemical alteration of a material due to its interaction with the environment of interest. It must be emphasized that corrosion resistance is not a material property but a system property and real environments have a high variability in both chemical and physical boundary conditions. 

It is misleading to say that a catalyst is totally unchanged by the reaction it catalyzes. Gradual physical and chemical alterations may take place during catalysis or with usage. Industrial catalysts are slowly deactivated by phenomena that accompany the main catalytic process. Catalyst aging, or deactivation, is indicated by the decrease in catalyst activity with time. It introduces additional complexity to the determination of rate parameters and has to be considered in macrokinetic analysis, that is, in catalytic reactor design. 

Phage DNA preparations represent extremely homogenous material. Techniques for defined physical and chemical alterations have been developed over the last two decades. Transfection offers a way to study the biological consequences of such alterations. 

The disadvantage of this procedure is that the minerals maybe physically or chemically altered during burning. Eor example, the refractive index of clay minerals is changed the color, birefringence, and pleochroism of micas is altered carbonates are destroyed and the iron sulfides are oxidized to iron oxides. 

Surface modification of a contact lens can be grouped into physical and chemical types of treatment. Physical treatments include plasma treatments with water vapor (siUcone lens) and oxygen (176) and plasma polymerization for which the material surface is exposed to the plasma in the presence of a reactive monomer (177). Surfaces are also altered with exposure to uv radiation (178) or bombardment with oxides of nitrogen (179). Ion implantation (qv) of RGP plastics (180) can greatiy increase the surface hardness and hence the scratch resistance without seriously affecting the transmission of light. 

Although surface treatments, both physical and chemical, have demonstrated the abiUty to alter specific properties of contact lens surfaces, most treatments fail as a result of alteration of bulk lens properties, instabifity of surface treatment, or poor ocular compatibifity. Research is expected to continue in the characterization and modification of contact lens surfaces. 

By changing the device architecture e.g. by building multi- instead of single layer structures the physical and chemical processes in the LED can be greatly altered. For that reason the fundamental properties of the LED, such as threshold voltage, efficiency, emission color, brightness, and lifetime can be optimized in multilayer structures [43J. 

In addition to effects on biochemical reactions, the inhibitors may influence the permeability of the various cellular membranes and through physical and chemical effects may alter the structure of other subcellular structures such as proteins, nucleic acid, and spindle fibers. Unfortunately, few definite examples can be listed. The action of colchicine and podophyllin in interfering with cell division is well known. The effect of various lactones (coumarin, parasorbic acid, and protoanemonin) on mitotic activity was discussed above. Disturbances to cytoplasmic and vacuolar structure, and the morphology of mitochondria imposed by protoanemonin, were also mentioned. Interference with protein configuration and loss of biological activity was attributed to incorporation of azetidine-2-carboxylic acid into mung bean protein in place of proline. 

In addition, naturally growing plants resist plant pathogen and Insect attack because resistance develops over time via natural selection (35). Also, most natural and crop plants have, as a part of their basic physical and chemical makeup, a wide array of mechanisms that help them resist pest attack. These Include chemical toxicants, repellents, altered plant nutrients, hairiness, thorns, and diverse combinations of these (35). 

Melo, M., Fazooli, L. C., Teixeira, A., Amorim, H. V., Chemical physical and organoleptic alterations on storage of coffee beans, Cienc. Cult. (Sao Paulo), 32, 468, 1980. (CA93 44277v)... 

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