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Constraints polarity

The amplitude of a radiated seismic wave contains far more information about the earthquake mechanism than does its polarity alone, so amplitude data can be valuable in studies of non-DC earthquakes. Moreover, because seismic-wave amplitudes are linear functions of the moment-tensor components, determining moment tensors from observed amplitudes is a linear inverse problem, which can be solved by standard methods such as least squares. Conventional least-squares methods, however, cannot invert polarity observations such as first motions, which typically are the most abundant data available. Linear programming methods, which can treat linear inequalities, are well suited to inverting observations that include both amplitudes and polarities (Julian 1986). In this approach, bounds are placed on observed amplitudes, so that they can be expressed as linear inequality constraints. Polarities are already in... [Pg.1575]

Finally, we should mention that the asymmetry of molecular shape, polyphilic effects and conformational constraints are the dominant factors in the stabilization of polar ordering in achiral mesogens. The examples presented above are, therefore, highly significant. They show that many liquid crystalline structures are intrinsically polar and may be effectively stabilized by suitable design of the mesogenic molecules. [Pg.232]

Preparative chromatographic resolution procedures have overall freed chemists from the constraint of dependency on crystallization. They are most often performed with covalent diastereomer mixtures but ionic salts can also be separated. Recently, it was found that the lipophilicity of TRISPHAT anion 8 profoundly modifies the chromatographic properties of the cations associated with it and the resulting ion pairs are usually poorly retained on polar chromatographic phases (Si02, AI2O3) [131]. Using enantiopure TRISPHAT anion. [Pg.35]

Gas phase reactivity toward allyltrimethylsilane was used to compare the reactivity of several cyclic A-acyliminium ions and related iminium ions.203 Compounds with endocyclic acyl groups were found to be more reactive than compounds with exocyclic acyl substituents. Five-membered ring compounds are somewhat more reactive than six-membered ones. The higher reactivity of the endocyclic acyl derivatives is believed to be due to geometric constraints that maximize the polar effect of the carbonyl group. [Pg.145]

A real breakthrough of analytical SFE for in-polymer analysis is still uncertain. The expectations and needs of industrial researchers and routine laboratories have not been fulfilled. SFE presents some severe drawbacks (optimisation, quantification, coupling, and constraints as to polarity of the extractable analytes), which cannot easily be overcome by instrumental breakthroughs but... [Pg.95]

Packed column SFC and CE are both able to make inroads into the application area served by HPLC, but from opposite extremes of polarity and with little overlap. CE is likely to be more efficient and faster, but mostly applicable to very polar molecules and ions. SFC qualifies as a more reproducible, trace technique, with greater selectivity and multiple detection options. HPLC and CE have been compared [365], Owing to their orthogonality, CZE and SFC are worth developing, not in competition or as an alternative to HPLC, but as an additional method in order to augment the information obtained from the analysis. With the broad scope of possible eluents and stationary phases, HPLC has fewer constraints than SFC and CZE. The parameters influencing selectivity may be used as a guide to optimisation (Table 4.44). [Pg.245]

Protein molecules contain both polar and apolar groups. For proteins dissolved in water, these apolar groups tend to be buried in the interior of the globular structure, as a result of expulsion by the surrounding water. However, other interactions, as well as geometrical constraints, interfere with the hydrophobic effect, so that a minor fraction of the water-accessible surface of the protein molecule may be apolar. Protein molecules that do not spontaneously aggregate in water do not have pronounced apolar patches at their surfaces. [Pg.109]

In contrast, polar and resonance effects must be separated in order to analyze the data for a-substituted arylolefins [ArC(R)=CHR with R H]. Their bromination involves open carbocation intermediates only. Resonance effects cannot be fully developed at the transition states, since the aromatic ring is not in the same plane as that of the developing carbocation, because of steric constraints. Accordingly, application of (33) gives pT < pn. Attenuation of resonance arises mainly from stereochemical factors, at least in the monosubstituted 1,1-diphenylethylene [20] and a-methylstilbene [21] series the pr/pn ratios can be related to the dihedral angle between the substituted phenyl ring and the plane of the ethylenic bond. [Pg.254]

To attain a transverse field profile that is confined within the defect, the profile must exponentially increase for p < pdef, and exponentially decrease for p > pdef. This requirement determines which index-interfaces (lowhigh or highlow) should be positioned at zeros of the field and which at the extrema of the field. The constraints on the index profile are similar to the Cartesian case and differ for the TE and TM polarizations. For the TE polarization, the interfaces for decreasing (increasing) field should be at the zeros (extrema) of If, if nip ) > n(p 1) at the interface and at the extrema (zeros) of Hz if nip ) < nip 1) at the interface. For the TM polarization, the interfaces for decreasing (increasing) field should be at the extrema (zeros) of E, if n(p ) > n(p+) at the interface and at the zeros (extrema) of E, if n(p ) < nip 1) at the interface. The interfaces of the defect must be located at zeros of II, for TE and of E, for TM. [Pg.321]


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