Extrinsic degradation

Disproportionation of intermetallics is indicated by the changes in the shape of the isotherms and associated loss in the hydrogen capacity [20]. This phenomenon may be attributed to short-range diffusion of the atoms, the thermodynamic stability of one of the elemental species from an elemental hydride, and dissociation of the non-hydride former second atom as a metal. Note that it is not necessary for all the binary intermetallic hydride to completely dissociate into elemental hydrides. Many variants of AB5 alloys have been used for hydrogen storage over the years and these hydrides were tested for intrinsic and extrinsic degradation, mainly LaNis and FeTi-type hydrides these hydrides exhibit a propensity for disproportionation. A hydride that would hydride/dehydride really well during the first few cycles may not... 

Extrinsic degradation is attributed to chemical reactions of the active materials with its environment. The most common cause of degradation is the contact with oxygen and water in the presence of light, which leads to a rapid decrease of performance of the diodes, resulting from a modification of the structure of the active material, which is furthermore accelerated by electrical stress. The degradation onset corresponds to a formation of dark spots [33], which are nonemis-sive areas of the device surface. Most of the devices should therefore be protected by an encapsulation to prevent the contact with ambient air. A properly protected encapsulated diode will not develop chemical reactions that affect its lifetime. An alternative approach is the use of metal oxide layers combined with high work function and air-stable metals such as A1 or Au to replace the usual transport layers (PEDOTPSS or LiF) to fabricate diodes that can be used without encapsulation [34]. 

A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

Cobalamine can only be resorbed in the small intestine when the gastric mucosa secretes what is known as intrinsic factor—a glycoprotein that binds cobalamine (the extrinsic factor) and thereby protects it from degradation. In the blood, the vitamin is bound to a special protein known as trans-cobalamin. The liver is able to store vitamin Bi2 in amounts suf cient to last for several months. Vitamin B12 deficiency is usually due to an absence of intrinsic factor and the resulting resorption disturbance. This leads to a disturbance in blood formation known as pernicious anemia. 

Research has previously shown that bacteria are not uniformly distributed in soil, reflecting soil structure and available nutrients (Richaume et al., 1993). The distribution of microorganisms throughout the soil can also be considered from the applied ecological perspective of patch dynamics, where patch formation is a reflection of intrinsic and extrinsic forces (Rao et al., 1986). The same authors also showed spatial variability in the degradation of pesticides applied to a soil system. 

Fig. 15.3 The major pathways of apoptosis. The extrinsic pathway uses extracellular death ligands (Fas ligand, tumor necrosis factor (TNF)) to activate death receptors which pass the apoptotic signal to initiator caspases (e. g. capsase 8) and to the executioner caspases (e. g. caspase 3 caspase 7). In the execution phase of apoptosis, various cellular substrates are degraded leading to cellular collapse. The intrinsic pathway uses the mitochondria as a central component for activation of apoptosis. In this pathway, a multitude of intracellular signals including various stresses, DNA damage and inappropriate cell signaling lead to activation of the pro-apoptotic protein Bax which induces release of cytochrome c from mitochindria, formation of the apoptosome and activation of the initiator caspase 9. Finally, the executioner caspases are activated and cells are destructed by proteolysis. Apoptosis via this pathway can be controlled by various antiapoptotic proteins including the Bcl-2 protein and inhibitors of apoptosis.

Miyao M, Fujimura Y, Murata N. Partial degradation of the extrinsic 23 kDa protein of the Photosystem II complex of spinach. Biochim Biophys Acta 1988 936 465-474. 

A gradual decrease in efficiency and catastrophic failure represent two polar cases of instability commonly observed in OLEDs. Such classification is not particularly useful from a mechanistic point of view because it does not reflect the multitude of processes responsible for the instabilities of OLED devices. It also does not reflect the distinction between intrinsic and extrinsic causes of instability. Here we define the intrinsic degradation processes as inherent and qualitatively unavoidable for a certain type of OLED device. By... 

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