Activated alpha-alkyl-alpha-arylacetic acid enantiomers for stereoselective thin-layer chromatographic and high-performance liquid chromatographic determination of chiral amines

The separation of racemic benoxaprofen into the two benoxaprofen enantiomers by preparative high-performance liquid chromatography and the application of the activated enantiomers as derivatization reagents for the simultaneous stereoselective determination of chiral amines in biological material is described. Activated (+)- and (-)-benoxaprofen are both shown to be very sensitive and stable chiral fluorescence markers, applicable to thin-layer chromatography as well as to high-performance liquid chromatography.     

The coherent potential approximation is a realizable effective medium scheme

The effective electrical conductivity of an aggregate, composed of grains of various conductivities, is frequently estimated by the coherent potential approximation, which embodies a local effective medium concept. It is proved rigorously that this approximation is exact for a wide class of hierarchical model composites made of spherical grains: the starting material 0 in the hierarchy is chosen arbitrarily, otherwise, materialj=1, 2, ... consists of equisized spheres, sayj-spheres, of arbitrary conductivities embedded in materialj — 1. The spatial distribution of thej-spheres must satisfy a mild homogeneity condition and their radiusr _j must, asymptotically, increase faster than exponentially withj. Furthermore, the minimum spacing, 2s _j , between thej-spheres is such that the ratios _j /r _j diverges. On the basis of these and some further ancillary conditions it is established that the coherent potential approximation becomes asymptotically exact for the effective conductivity of materialj. The results extend to other effective parameters of the composites, including the thermal conductivity, dielectric constant and magnetic permeability. In addition, the model composites and the proof of realizability may be generalized to allow non-spherical grains.     

Accuracy, latency, and listener-search behavior in localization in the horizontal and vertical planes

Thirty-six listeners localized continuous filtered noise bursts centered on 2.3 or 8.3 kHz under normal listening conditions or while wearing earmuffs. The noise bursts were from any one of 20 loudspeakers, 18 degrees apart, visible to the listeners, and arranged in the horizontal and vertical planes. Listeners were free to move, while remaining seated, throughout all trials. The noise bursts were terminated by the listeners. Measures of accuracy and latency showed that earmuff listening had a significant effect whereas, overall, signal frequency had no significant effect. There was, however, an apparent downward shift of the 2.3-kHz signals presented above the midline in the vertical plane. Analysis of video records of listeners' behavior revealed a strong tendency for initial orientation by head or eye movement to correlate with final response, even when both were inaccurate. The paradigm adopted in this latter aspect of the study illustrates an "ecological" approach to the study of auditory phenomena.     

Low Pass metallic mesh interference filters for operation in the 165 GHz to 880 GHz region

Low Pass metallic mesh interference filters have been designed and constructed for operation in the region 340 m (880 GHz) to 1.8 mm (165 GHz). These filters have been shown to have excellent edge characteristics and good rejection regions. The results show that the mesh filter can be effectively used in both millimetre and submillimetre regions.Part of this work was performed while this author was at Heriot-Watt University, Edinburgh, U.K.     

The isotopes259106,260106, and261106

In irradiations of²⁰⁷Pb and²⁰⁸Pb, respectively, with⁵⁴Cr theα-decay of the isotopes²⁵⁹106,²⁶⁰106, and²⁶¹106 could be observed for the first time. For²⁶⁰106 a spontaneous fission branch of (50 _?20 ⁺³⁰ )% was observed. The isotopes were identified by genetic relationships of α-decay after separation in-flight with the velocity filter SHIP and implantation into a position-sensitive silicon surface-barrier detector. The measured partial fission halflife of the doubly even isotope²⁶⁰106 of (7.2 _?2.7 ^+4.8 )ms exceeds the predicted values by at least a factor of 40. This result could be explained by the high shell corrections of the ground state mass, derived from the measured α-decay energies. The experimental results show evidence for an island of purely shell stabilized nuclei in the region of deformed isotopes beyond the actinides.     

On the microcanonical ensemble for a spin system interacting with one-mode electromagnetic field

A system described by the Dicke Hamiltonian is considered. It is known that for the canonical density operator describing such a system, the internal energyU is strictly negative. On the other hand, the microcanonical density operator can be defined for an arbitrary value ofU. The thermodynamic limit for the microcanonical density operator is investigated. In the caseU<0 the obtained results are completely equivalent to those of the canonical density operator. However, in the caseU>0 it turns out that the photon density is non-zero, and that the entropy and the mean spin are independent ofU. Moreover, forU>0 the coupling constant of the Hamiltonian does not appear in any thermodynamic formula after the thermodynamic limit is performed.     

Electrostatic and electromagnetic surface shape resonances

The homogeneous integral equations that give the electromagnetic field in the vicinity of a protuberance or a depression on the otherwise planar interface with vacuum of a semi-infinite dielectric medium or a thin dielectric film on a semi-infinite substrate have been obtained. The Rayleigh hypothesis, the vectorial equivalent of the Kirchhoff integral, and the extinction theorem have been used for this purpose. The assumption that the perturbation of the vacuum dielectric interface has cylindrical symmetry about the normal to the nominal surface allows a significant simplification of these integral equations to be carried out. We have used Gaussian quadrature schemes to convert the resulting integral equations into matrix equations, and have obtained the frequencies of the shape resonances by equating to zero the determinants of the matrices obtained. Calculations have been carried out for Gaussian (x ₃=Aexp(–x ² /R ²)) and exponential (x ₃=Aexp(–x /R)) surface profiles, and convergent results obtained for values ofA/R of the order of unity.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Effect of hydrostatic pressure on the static susceptibility of the spin-glass systems Ag:Mn,Au:Mn,Cu:Mn and Au:Fe

Previous studies of the magnetic susceptibility of a Ag-3 at.% Mn spin-glass under high pressure are extended to include the systems Au-3at.% Mn, Cu-3at.% Mn and Au-3at.% Fe. In all four alloys the spin-glass freezing temperatureT ₀ increases with pressure, yielding the volume dependences lnT ₀/ lnV=–3.6±0.4, –4.1±0.6, –2.1±0.4 and –1.64±0.25, respectively. These results give information about the nature of the interaction mechanisms responsible for the spin-glass freezing phenomena. The pressure dependence of the Curie temperature of ferromagnetic Au-20at.% Fe was also studied.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday