Initial-susceptibility method

For thin films with a perpendicular anisotropy (easy axis normal to the film plane), Huang et al. (199S) determined magnetostriction (As) and anisotropy (Iff) values, by using the so-called initial-susceptibility method. An ac magnetic field was applied in the film direction, and the induced magnetisation component in the field direction was measured. These authors deduced K and As from the x 1 vs. o plots, using ... 

Initial susceptibility measurements were carried out from room temperature to 873 K for the compositions, using a field of 0.5 Oe by a double coil method. From the plots of x/Xi vs T, the Curie temperatures (Tc) of the compounds were determined. 

The molar diamagnetic susceptibility of thiazole and some derivatives was initially determined by the classical Curie-Cheneveau method (5,315,316) and later confirmed by a method (317) based on the difference of NMR proton chemical shift of a sample of tetramethylsilane immersed in the liquid to be investigated, according to the shape (cylindrical or spherical) of the sample tube (Table 1-47) (318),... 

The treatments used to recover nickel from its sulfide and lateritic ores differ considerably because of the differing physical characteristics of the two ore types. The sulfide ores, in which the nickel, iron, and copper occur in a physical mixture as distinct minerals, are amenable to initial concentration by mechanical methods, eg, flotation (qv) and magnetic separation (see SEPARATION,MAGNETIC). The lateritic ores are not susceptible to these physical processes of beneficiation, and chemical means must be used to extract the nickel. The nickel concentration processes that have been developed are not as effective for the lateritic ores as for the sulfide ores (see also Metallurgy, extractive Minerals recovery and processing). 

Evidence of localized corrosion can be obtained from polarization methods such as potentiodynamic polarization, EIS, and electrochemical noise measurements, which are particularly well suited to providing data on localized corrosion. When evidence of localized attack is obtained, the engineer needs to perform a careful analysis of the conditions that may lead to such attack. Correlation with process conditions can provide additional data about the susceptibility of the equipment to locaHzed attack and can potentially help prevent failures due to pitting or crevice corrosion. Since pitting may have a delayed initiation phase, careful consideration of the cause of the localized attack is critical. Laboratory testing and involvement of an... 

The strains needed to initiate cracks in both the annealed and the sensitised materials were obtained using tapered slow-strain-rate specimens and the data are given in Fig. 8.36. As can be seen, there is little temperature dependence of the strain needed to initiate cracks in sensitised material whereas the annealed material was most susceptible to cracking at about 250°C. These results indicate the complicated response of Type 316 stainless steel to applied potential and demonstrate that, even though environmentally-assisted cracking may be generated by severe test methods, in this case the slow-strain-rate test, the results obtained must be used with care. For instance, the cracking of the annealed material at low potentials... 

Quite apart from such specific physical methods for the detection of radicals, it should be emphasised that more general indications that radical intermediates are involved in a particular reaction are provided by its high susceptibility to the addition of radical initiators (cf. p. 314) or inhibitors (cf. p. 300), and (compared with polar reactions) its relative insusceptibility to change of solvent. 

Cationic polymerization was considered for many years to be the less appropriate polymerization method for the synthesis of polymers with controlled molecular weights and narrow molecular weight distributions. This behavior was attributed to the inherent instability of the carbocations, which are susceptible to chain transfer, isomerization, and termination reactions [48— 52], The most frequent procedure is the elimination of the cation s /1-proton, which is acidic due to the vicinal positive charge. However, during the last twenty years novel initiation systems have been developed to promote the living cationic polymerization of a wide variety of monomers. 

There are a number of Physical Methods available but of all the Physical Methods, tracer analysis using C14, H3 or S35- labelled initiators or other substances has received considerable attention. However, this method is incapable of giving results specific to the actual functional group and is highly susceptible to interference by absorbed radioactive impurities. It is moreover hazardous, expensive and needs sophisticated apparatus. 

Given the unreliability of the stab-initiated tests, a second round of testing was performed using a hot nichrome wire to initiate the detonators in place of the NOL-130 stab mix and firing pin. This test was successful and all nine detonators functioned, showing that DBX-1 is more susceptible to this method of initiation. Figure 8 shows the electrical ignition setup. 

These methods do not, of course, provide certainty with regard to the probability that a particular level of exposure to a chemical will cause harm, but neither do the current animal test methods. What they do provide is information on more limited questions, questions about the capacity of the chemical to initiate changes which have the potential to cause harm to the organism. This information is, I suggest, more relevant to chemicals regulation than that provided by animal experiments, because it is of more general applicability. It is less likely to give the false reassurance of non-hazardousness that is provided by an animal test where the animal tested happens not to be susceptible to the chemical, while the species we are concerned about is. 

In redox methods, radicals are generated and removed either by chemical or electrochemical oxidation or reduction. Initial and final radicals are often differentiated by their ability to be oxidized or reduced, as determined by substituents. In oxidative methods, radicals are removed by conversion to cations. Such oxidations are naturally suited for the additions of electrophilic radicals to alkenes (to give adduct radicals that are more susceptible to oxidation than initial radicals). Reductive methods are suited for the reverse addition of alkyl radicals to electron poor alkenes to give adducts that are more easily reduced to anions (or organometallics). 

The oxidative method is often conducted on enol (or enolate) derivatives and a simplified mechanism is shown in Scheme 71. Initial chemical or electrochemical oxidation gives an electrophilic radical (68 that may be free or metal-complexed) that is relatively resistant to further oxidation. Addition to an alkene now gives an adduct radical (69) that is more susceptible to oxidation. Products are often derived from the resulting intermediate cation (70) by inter- or intra-molecular nucleophilic capture or by loss of a proton to form an alkene. The concentration and oxidizing potential of the reagent help to determine the selectivity in such reactions. 

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