Thermoluminescence and radiation-induced volume changes in CaF2 (Mn,RE) materials

The thermoluminescence properties of various CaF₂ materials (natural fluorite, CaF₂-glass ceramics and enamels) doped with RE oxides and Mn are investigated in details. Volumetric measurements show that γ-irradiation leads to a change in the volume density of powder samples of these materials. Depending on the character of the sample, positive (increased volume) or negative dilatation (decreased volume) can be observed during irradiation with doses within the range 1 C/kg–9 C/kg. As time elapses, the radiation-induced alteration of the sample volume is relaxed and after 2–3 months reaches again the initial volume density of the sample. The unexpected result of radiation-induced volume changes are discussed in details accounting for supplementary X-ray, electron microscopy and EPR studies.     

New synthetic technology for efficient construction of alpha-hydroxy-beta-amino amides via the Passerini reaction

[reaction: see text] The Passerini reaction of N-protected amino aldehydes, isonitriles, and TFA using pyridine-type bases proceeds under mild conditions and directly affords alpha-hydroxy-beta-amino amide derivatives in moderate to high yields. These adducts are readily hydrolyzed to alpha-hydroxy-beta-amino carboxylic acids. Application of these key intermediates to concise syntheses of P(1)-alpha-ketoamide protease inhibitors is illustrated.     

New exact relations for improving the exchange and correlation potentials

For the purpose of improving present approximations to the exchange and correlation potentials, newly derived properties of the exact exchange and correlation potentials are summarized. Present approximations are not expected to generally satisfy these properties. The summarized properties include relations at the Fermi level, low-density requirements, and a new density functional formula for computing ionization energies. © 1995 John Wiley & Sons, Inc.     

Automerizations in benzenoid hydrocarbons. New mechanistic insights from the thermal rearrangement of benz[a]anthracene-5-13C.

Scrambling of the carbon atoms in benz[a]anthracene between positions 5 and 6 has been shown to occur at high temperatures; a mechanism involving thermal generation of a carbene is proposed.     

13C?13C spin coupling constants in tetrahydronaphthylene,hexahydrobenzanthracene and benzo[a]pyrene derivatives

The ¹³C? ¹³C spin coupling constants have been determined in substituted [1-¹³C]tetrahydronaphthylenes, [5-¹³C]hexahydrobenzanthracenes and [5-¹³C]benzanthracene. In addition, the ¹³C? ¹³C spin coupling constants for 7-hydroxy[7-¹³C]benzopyrene, trans-7,8-dihydro[7-¹³C]benzopyrene-7,8-diol and trans-7,8-dihydro[10-¹³C]benzopyrene-7,8-diol are reported, together with the one-bond carbon-carbon coupling constants between C-4 and C-5 in selected 4,5-disubstituted benzopyrenes. Values for the directly bonded coupling constants and long-range coupling constants are similar to those reported previously for other aromatic and aliphatic systems. Substituent effects on carbon-carbon coupling are compared for similarly substituted cyclic and acyclic systems.     

Use of precision colorimetry for elemental microanalysis

Spectrophotometric techniques are useful for microdeterminations of many elements in organic compounds and some inorganic compounds. It is possible to determine most metals and some non-metals (Al, Co, F, Fe, Mo, P, Pd, Pt, Si, Sn, Ti...) by applying spectrophotometric techniques described in the literature (most often for trace analysis) and using commercial reagents.     

Luminescence of AgCl excited by u.v. laser light

The spectral distribution and decay of the blue-green luminescence of AgCl has been measured at very low temperatures, using u.v. laser excitation. A structure was observed in the emission band at 77°K. The decay consists of three processes: a) a very fast process which follows the laser pulse (10^–8 sec), b) a fast exponential process which is also observed with low intensity u.v. excitation,(10^–4–10^–5 sec) and, finally, c) a slow exponential process (seconds).     

Numerical experiments on quadratically convergent algorithms for function minimization

The nine quadratically convergent algorithms for function minimization appearing in Ref. 2 are tested through several numerical examples. A quadratic function and four nonquadratic functions are investigated. For the quadratic function, the results show that, if high-precision arithmetic together with high accuracy in the one-dimensional search is employed, all the algorithms behave identically: they all produce the same sequence of points and they all lead to the minimal point in the same number of iterations (this number is equal at most to the number of variables). For the nonquadratic functions, the results show that some of the algorithms behave identically and, therefore, any one of them can be considered to be representative of the entire class. The effect of different restarting conditions on the convergence characteristics of the algorithms is studied. Proper restarting conditions for faster convergence are given.This research, supported by the Office of Scientific Research, Office of Aerospace Research, United States Air Force, Grant No. AF-AFOSR-828-67, is a condensation of the investigation described in Ref. 1.