Secondary initiation

Ions are also used to initiate secondary ion mass spectrometry (SIMS) [ ], as described in section BI.25.3. In SIMS, the ions sputtered from the surface are measured with a mass spectrometer. SIMS provides an accurate measure of the surface composition with extremely good sensitivity. SIMS can be collected in the static mode in which the surface is only minimally disrupted, or in the dynamic mode in which material is removed so that the composition can be detemiined as a fiinction of depth below the surface. SIMS has also been used along with a shadow and blocking cone analysis as a probe of surface structure [70]. 

Ihe rule-based approach to protein structure prediction is obviously very reliant on th quality of the initial secondary structure prediction, which may not be particularly accurate The method tends to work best if it is known to which structural class the protein belongs this can sometimes be deduced from experimental techniques such as circular dichroism... 

That this is not always the case should be expected. In fact, if it was not for heterogeneous localization of some flow phenomena, it would be very diflicult to initiate secondary explosives, or to effect shock-induced chemical reactions in solids. Heterogeneous shear deformation in metals has also been invoked as an explanation for a reduction in shear strength in shock compression as compared to quasi-isentropic loading. We present here a brief discussion of some aspects of heterogeneous deformation in shock-loaded solids. 

FIGURE 5.8 Methyl migration in 1,2,2-trimethylpropyl cation. Structure (a) is the initial secondary carbocation structure (b) is the transition state for methyl migration, and structure (c) is the final tertiary carbocation. 

In instances where the expl is to be detonated without a primer and whose output will not reliably initiate secondary HE charges, the initiator takes the form of a stab detonator (Refs 8,12 13), a diagram of which is shown in Fig 4... 

Soto C, Castano EM, Kumar RA, Beavis RC, Frangione B. Fibrillogenesis of synthetic amyloid-beta peptides is dependent on their initial secondary structure. Neurosci Lett 1995 200 105-108. 

Lead azide (PbN6) is a colorless to white crystalline explosive. It is widely used in detonators because of its high capacity for initiating secondary explosives to detonation. However, since lead azide is not particularly susceptible to initiation by impact, it is not used alone in initiator components. It is used in combination with lead styphnate and aluminum for military detonators, and is used often in a mixture with tetrazene. It is compatible with most explosives and priming mixture ingredients. Contact with copper must be avoided because it leads to formation of extremely sensitive copper azide. 

Initiation by Primers (and Boosters) is the standard method of initiating secondary explosives. Thus hot wires (or other means) are used to initiate the primer charge (Lead Azide, Mercuric Fulminate etc) explosive whose detonation then initiates the main charge of PETN,... 

It seems that the cavities enclose a vapor of the solute because of the high vapor pressure of these compounds. The primary reaction pathway for these compounds appears to be the thermal dissociation in the cavities. The activation energy required to cleave the bond is provided by the high temperature and pressure in the cavitation bubbles. This leads to the generation of radicals such as hydroxyl radical, peroxide radical, and hydrogen radical. These radicals then diffuse to the bulk liquid phase, where they initiate secondary oxidation reactions. The solute molecule then breaks down as a result of free-radical attack. The oxidation of target molecules by free radicals in the bulk liquid phase under normal operating pressures and temperatures can be presented by a second-order rate equation ... 

Wang, H. and Morrison, G.C. (2006) Ozone initiated secondary emission rates of aldehydes from indoor surfaces in four... 

Older primary prevention trials had often been undertaken in cohorts at low absolute risk of CHD events. The initial secondary prevention studies had typically involved patients with elevated cholesterol levels. In addition, these older trials had tested diet and previous lipid-lowering agents, which only lowered cholesterol by an average of approximately 10% (5). As a consequence, these trials were typically underpowered and had not shown a clear reduction in all-cause mortality. There had been good evidence that lipid-modifying therapy could prevent fatal and nonfatal CHD events (5). However, there were some concerns that noncardiovascular events particularly related to cancers and violence or trauma could be increased. In summary, there was considerable uncertainty about the overall effects of treatment. 

Step initiation (secondary nucleation) on 100 faces virtually stops at the rate minimum, while a smaller decrease occurs in step propagation rate v. The observed minimum in v is inconsistent with the barrier to stem deposition being determined by surface energy and suggests that, as in secondary nucleation, the barrier is entropic. 

G proteins are another family of membrane proteins believed to modulate mechanochemical transduction pathways. Mechanical stimulation changes the conformation of G protein that leads to growth-factorlike changes that initiate secondary messenger cascades leading to cell growth. It has been reported that cyclic strain of smooth muscle cells significantly decreased steady-state levels of G protein and adenylate cyclase activity. Muscular stimulation also appears to be coupled with G protein activation in small arteries. 

While Brish et al. directly irradiated the explosive sample with the laser beam, Menichelli and Yang coated a glass window with a 1000 A thick aluminum film. Irradiation of this film generated shockwaves by vaporization of the metal, similar to the functionality of EBWs. [15c, 15d], The generated shockwave is able to directly initiate secondary explosives. In the work of Menichelli and Yang, a Q-switched ruby laser was successfully used (E = 0.8 to 4.0 J r = 25 ns) to initiate PETN, RDX and tetryl. 

While Region II can be compared with the hot-wire initiation of primary explosives or pyrotechnic compositions, the laser power densities in region IV also make it possible to directly shock initiate secondary explosives by laser irradiation. The laser power densities of Region IV are achieved by solid-state lasers with laser powers of at least 100 W. In contrast, laser diodes ( 1-10 W) only provide power densities which fall into the regions II and III. However, more powerful laser diodes have been gradually developed and therefore, laser diode initiators (LDI) have be-... 

The photochemical electron transfer step and the initial secondary reactions that stabilize the photochemical products all take place within the reaction center complex. For subsequent turnovers of the reaction center to take place. 

A second factor that may determine the rate of biomass accumulation is species composition. Secondary forests on sites with histories of intensive land use, and that are far from sources of tree seeds, may be depauperate in some of the fast growing pioneer species that are responsible for rapid biomass accumulation during initial secondary forest growth (Uhl et al. 1988). 

To resolve the paradox, it has been postulated that a growing chain is able to initiate secondary chains in its neighborhood by virtue of the energy of 1.6 eV... 

When Lewis acids such as SnCU and TiCU are used to promote additions of allylic trialkyltin reagents to aldehydes several reaction outcomes are possible, depending on stoichiometry and the mode of addition. If the Lewis acid is added to the aldehyde followed by the allylic stannane, the typical product (syn for crotylstannanes) derived from an acyclic transition state is formed. If, however, the stannane and Lewis acid are premixed and left to equilibrate, metathesis can occur forming the allylic halome-tal compound which reacts with the subsequently added aldehyde to give products (anti for crotyl) consistent with a cyclic transition state (Eq. 22). The initially formed allylic halostannane gives rise to the linear adduct, but if aldehyde addition is delayed, this initial secondary allylic metal halide can equilibrate to the primary isomer which then reacts with the aldehyde to afford the branched product. 

Tertiary alkyllithiums are prepared in hydrocarbons from the appropriate alkyl chlorides with Li dispersions. Once the reaction is initiated, secondary reactions between the reagent and its precursor halide may cause low yields. Slow rates of addition of the alkyl chloride minimize these secondary reactions . Polycyclic and bridgehead reagents are less susceptable to such bimolecular reactions with their precursor chlorides. 

In principle X-rays, as well as electron and gamma rays, can be used the main effect of gamma and X-rays is Compton scattering, i.e. ionisation of atoms giving rise to "primary electrons" these electrons, like those generated in an accelerator, lead to a number of other "secondary electrons" and ions. This cascade of secondary electrons (about 4000 to 6000 ionisations per initial secondary electron) loses energy in ionising the foodstuff molecules, with consequent production of free radicals and, thereby, of "radiolytic products" (Chapter 1). 

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