An electroreflectance study of gallium antimonide in the 3.0–4.2 eV region

Results of an electroreflectance investigation of gallium antimonide in the 3.0–4.2 eV region are presented. The observed recurrence in this region of the spin-orbit splitting of the zone-center valence band states suggests a revised assignment for the observed recurrence in this region of the spin-orbit splitting of the zone-center valence band states suggests a revised assignment for the observed structure in terms of transitions to the second conduction band states.     

Surface waves in cholesterics in a magnetic field

Propagating waves on the free surface of a cholesteric liquid crystal in a vertical magnetic field are considered for the case when the anisotropy of the magnetic susceptibility is negative. Surface fluctuations distort the helical structure and the dispersion relation and penetration depth are shown to depend on three possible restoring forces: the surface tension, the twist elastic forces associated with the helix, and the magnetic field.     

The use of emission spatial profiles for the establishment of an internal reference point in ICP-AES

ICP torches are essentially unique devices. They are by necessity hand-made items. Therefore each has small variations in shape which cause individual differences in plasma configuration. As a consequence, utilization of an external reference point such as the “top of the load coil” is not adequate. It is well documented that ICP sources are complex and that different excitation mechanisms come into play in different parts of the source. This is demonstrated by the fact that generally atomic transitions have their peak intensities lower in the plasma, whereas ionic transitions peak higher in the plasma. The height-intensity relationship of both atomic and ionic species has been investigated. The use of the intersection of normalized atomic and ionic emission intensity profiles as a function of observation height has been evaluated as a possible internal reference point. This point is shown to be reproducible and easy to measure.     

Embeddings of bipartite graphs

If G is a bipartite graph with bipartition A, B then let G_m,n(A, B) be obtained from G by replacing each vertex a of A by an independent set a₁, …, a_m, each vertex b of B by an independent set b₁,…, b_n, and each edge ab of G by the complete bipartite graph with edges a_ib_j (1 ≤ i ≤ m and 1 ≤ j ≤ n). Whenever G has certain types of spanning forests, then cellular embeddings of G in surfaces S may be lifted to embeddings of G_m,n(A, B) having faces of the same sizes as those of G in S. These results are proved by the technique of “excess-current graphs.” They include new genus embeddings for a large class of bipartite graphs.     

Kinetics of substitution at ternary titanium(IV)–cyclopentadienyl,pyronato or pyridinato–halide or alkoxide complexes

Rate laws and kinetic parameters are reported for substitution at titanium(IV) complexes Ti(LL)₂X₂, where LLH=cyclopentadiene, the 4-pyrone ethylmaltol, several 4-pyridinones, and related ligands, and X=halide or alkoxide, in acetonitrile solution at 298.2 K. Reactivities are discussed in terms of the nature of the leaving group, the entering group and the non-leaving ligand LL^?. Activation volumes of ?15 and ?12 cm³ mol^?1 have been determined for thiocyanate attack at Ti(cp)₂Cl₂ and Ti(etmalt)₂Cl₂ respectively. Substitution mechanisms are discussed in the light of the kinetic parameters obtained.     

The acidity of fluorinated bicycloalkanes. 1. 1 -Undecafluoro- and 1 ,4 -decafluorobicycloheptanes

CNDO/2 Calculations have been performed on the title compounds and on the anions derived from them. The results indicate that in the anion there is significant transannular transfer of charge to the 4-position. The amount of such transfer is effectively independent of the 4-substituent. It is concluded that the effect of the substituent upon the stability of the acid must be an important factor.     

Das Vorkommen von Aconits?ure im Zuckerrohrsaft und Colonialzucker

Ohne Zusammenfassung     

The synthesis of XTT: A new tetrazolium reagent that is bioreducible to a water-soluble formazan

A new tetrazolium salt, XTT, has been synthesized. XTT is reduced by a considerable variety of cell lines to a water-soluble formazan. XTT appears to merit further investigation as a reagent for broader application to cell culture assay systems.