Instability intrinsic

This brings us to the subject of standards. In this connection a standard is simply a sample with a known hydrogen content that is used for convenience to calibrate the overall counting efficiency of a particular setup, i.e., to determine the factor AfICalibration standards must be stable under irradiation. While plastic foils of known composition can be used if precautions are taken (Rudolph et al., 1986), their intrinsic instability makes them unsuitable. The standard used by most groups is hydrogen-implanted silicon, which has the advantages that it is easily prepared, the implanted dose can be measured to 5%, and the amount of implanted hydrogen is stable at room temperature and under MeV 15N irradiation, as discussed later. 

Tanaka et al. reported a series of oxadiazole metal chelate materials (97 99) (Scheme 3.31). However, these complexes suffer stability issues due to the intrinsic instability of the excited state of the molecules. Therefore the lifetimes of OLEDs fabricated using these compounds are fairly short [153,154]. 

The intrinsic instability of organocopper] 11) compounds is most probably associated with the redox properties of copper. Decomposition of organocopper] 11) compounds can occur by two different routes (i) formation of an organocopper]I) compound and an organic radical R" that can undergo further reactions, which formally represents a one-electron reduction process, and (ii) direct formation of R-R and Cu]0), which is formally a two-electron reduction process (reductive elimination cf Eqns. 1 and 2 in Scheme 1.3). 

The intrinsic instability of the state-of-the-art electrolyte systems seems to arise mainly from the interaction between the cyclic carbonate and the Lewis acids, HF, PF5, or PO F... 

Too often the Jahn-Teller principle is presented in a reversed fashion—i.e., the distortion of a coordination polyhedron eliminates orbital degeneracy. This formulation renders the principle ineffective, because the distortion is at first sight attributed to external forces, whereas in fact it is the result of the intrinsic instability of the symmetric condition. 

These observations support the theory that, in an early stage of tumor formation, a mutation occurs in a repair system needed to maintain the integrity of the genome (Loeb, 1991, Loeb, 1998). Loss of the fimction of the repair system leads to a mutator phenotype a missing or ineffective DNA repair favors further accumulation of mutations and leads to an intrinsic instability of the genome. 

In this overview we focus our attention on some problems of optical chaos. In many optical effects and devices intrinsic instabilities occur and for over thirty years they have been extensively investigated. The literature on optical chaos is widespread and a few excellent reviews and collections of papers should be recalled [9-13]. 

Compounds with a narrow HOMO-LUMO gap (Figure 5.5d) are kinetically reactive and subject to dimerization (e.g., cyclopentadiene) or reaction with Lewis acids or bases. Polyenes are the dominant organic examples of this group. The difficulty in isolation of cyclobutadiene lies not with any intrinsic instability of the molecule but with the self-reactivity which arises from an extremely narrow HOMO-LUMO gap. A second class of compounds also falls in this category, coordinatively unsaturated transition metal complexes. In transition metals, the atomic n d orbital set may be partially occupied and/or nearly degenerate with the partially occupied n + 1 spn set. Such a configuration permits exceptional reactivity, even toward C—H and C—C bonds. These systems are treated separately in Chapter 13. 

The intrinsic instability of235 makes its existence difficult to prove intramolecular closure to 4-hydroxy-1-deoxyartemisinin 236 or simple aqueous hydrolysis leads to its destruction. If 235 (and related structures) were the bottleneck through which the artemisinin class exerted its antimalarial effect, then replacement of 0-13 by CH2 might give an isolable intermediate epoxide of greater stability, but also with lesser activity. 

For Fig. 4, the rate constant for the mutual inhibition (fo) was chosen as the bifurcation parameter however, all other parameters and the initial reactant concentrations serve as bifurcation parameters as well. Mirror-symmetry breaking in simulation is caused by the intrinsic instability of the autocat-alytic model. When placed into the proper parameter domain, this instability can be revealed by the inevitable machine round-off as well as by slightly... 

Intramolecular rearrangement of germylenes, stannylenes and plumbylenes into a doubly bonded isomer can be another cause of their intrinsic instability. For example, in the matrix IR study of l-germacyclopent-3-en-l,l-ylidene, direct experimental evidence was obtained for a photochemical germylene-germene isomerization105,357. 

Enamines have been recognized in organic chemistry as useful synthetic reagents since the early reports from Stork s laboratory1. At almost the same time similar chemical moieties were being implicated in biochemical systems. Because of their intrinsic instability in water, the biochemical enamines exist primarily as intermediates, although, some well-known coenzymes that participate in oxidation-reduction reactions also incorporate enamine structures in one of their oxidation states. The electronic structure of enamines involves two extreme resonance contributions as shown in equation 1. 

This is to be noted that the corresponding homogeneous equation would indicate intrinsic instabilities, if there are any. However, this being a simple Laplacian operator, there are no intrinsic instability identified for it so far and the noted instability is driven by interaction of velocity and... 

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