Degradation definitions

Lactic acid is an example. It is conveniently added to the polyol and upon reaction with the isocyanate, it is inserted into the backbone. Upon exposure to fluids in the body, the polymer is cut at the insertion site. The reduction in tensile properties is dramatic. Although the fragments are suspect, the result is by definition degradable. A number of researchers at W.R. Grace prepared biodegradable hydrophilic polyurethanes by a similar technique but the product was never available commercially. 

Among the compounds administered by intravenous injection, the most active were 302,212 and 302,537. The Intravenous doses of these two compounds required to Induce a definite degradation in normal function in the volunteers were larger than the Intramuscular dose of... 

Decrystallization. The crystallinity of cellulose is an inherent property that is an important determinant of its mechanical properties, affinity for water, and accessibility to chemical reagents. Because cellulose comprises almost 50% of the wood, its crystallinity is a determinant of the behavior of the wood as well. Any disruption or change in the crystallinity of the cellulose will cause significant changes in properties and, thus by our definition, degradation. 

In applying the definition of rehabihty, the concept of adequate performance must be estabhshed clearly. Products usually do not fail suddenly, but degrade over time. Gasket leaks on equipment, for example, may start as a slow weep and increase in volume over time. The point at which this undesirable occurrence is called a failure must be clear before rehabihty can be measured objectively. Changing the failure definition for a product changes its rehabihty level, although the product itself has not changed. 

Litde is known about metaboHc inactivation of ( -endorphin and the dynorphins. NEP, and to a lesser extent APN, are only weaMy active against P-endorphin (183). Enzymes are known which degrade P-endorphin in vitro under nonphysiological conditions (202) or which inactivate P-endorphin by N-acetjlation (203). Alack of specific degradative enzymes for these peptides may account for their relatively long half-life in vivo though this has not been definitively estabUshed. 

International agreement is close as of 1996 on what an acceptable environmentally degradable polymer should do ia the environment succiacdy put, it must not harm the environment. There has been much progress ia the early 1990s on this issue standard protocols are available to determine degradation ia the environment of disposal, and definitions are understood and accepted ia a broad sense, if not ia detail. Fate and effects issues for these new polymers are being addressed, and these will be resolved and appropriate tests developed. 

Asbestos and other fibers in a wide variety of bundle sizes or even individual fibrils are in commercial usage. The handling of asbestos and other fibers causes degradation of the larger fiber bundles to fibers having diameters less than two micrometers that remain airborne for extended periods of time. These airborne fibers are prone to inhalation and lung entrapment. The exact definition of harmfiil fibers and the mechanism by which they affect the body is not accurately known. 

When a flocculated feed is added to a filter tank, there is a definite time lag before this material reaches the surface of the filter medium. Since this lag time is not known at the time of testing, a lag time of 8 to 10 minutes should be allowed before starting the first leaf test on a flocculated shiny. Two, or perhaps three, tests can be run before the elapsed time exceeds the probable retention time in the full-scale filter tank. With knowledge of the elapsed time after flocculation and data relating to the rate of degradation, the rates obtained on the leaf test runs can be adjusted to some constant lag time consistent with the anticipated full-sc e design. 

Practitioners of SELF explicitly include the dependencies either in the event trees or in the fault trees. Examples of the LESF method that have been examined, treat major dependencies by the definition of degraded states and reevaluate the systems and event trees for the assumed degraded state as well as for the probability of being in that state. Mathematically this is very effective but the dependency coupling is not as pictorial as the SELF method. 

Free energy of solution, containing chain molecules of a definite length (before the beginning of degradation), can be written as follows ... 

Corrosion is generally taken to be the waste of a metal by the action of corrosive agents. However, a wider definition is the degradation of a material through contact with its environment. Thus, corrosion can include non-metallic materials such as concrete and plastics and mechanisms such as cracking in addition to wastage (i.e. loss of material). This chapter is primarily concerned with metallic corrosion, through a variety of mechanisms. 

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