Limits for the central production of Theta+ and Xi(--)pentaquarks in 920-GeV pA collisions

We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).     

Record values in sequences of sample ranges

The classical representation of record values in sequences of independent random variables with the standard exponential distribution E(1) as sums of exponentially distributed random summands plays an important role in the mathematical theory of records. A generalization of this representation is proposed. A new similar result that makes it possible to express the record values of sample ranges as sums of independent exponentially distributed random variables is obtained.     

On the Origin of the Lowest Excited Singlet State in Retinyl Acetate

Abstract

Employing the techniques of a circular dichroism (CD) and a fluorescence polarization (FP), the long-wavelength forbidden ¹A^?- _g → ¹A^? _g transition in the absorption spectrum of retinyl acetate at 293K has been found. The FP degree of retinyl acetate in cyclohexanol decreases from 0.28 at 330 nm (the area of a strongly allowed ¹B?_u → ¹A^? _g transition) to 0.21 at 360 nm (the area of forbidden ¹A^?- _g → ¹A^? _g transition).     

Intramolecular interactions in antiviral derivatives of 4,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-2-aminophenol

We have used Fourier transform IR (FTIR) spectroscopy to study intramolecular interactions in solutions of 4,6-di-tert-butyl-2-aminophenol in n-hexane. When the hydroxyl group in the molecule is ortho to the amino group, an O―H⋅⋅⋅N intramolecular hydrogen bond is formed in the 4-6-di-tert-butyl-2-aminophenol derivatives, where the strength of the hydrogen bond depends on the type of substituent at the para position of the phenyl ring. If there are electron-donor groups on the phenyl ring, then a stronger O―H⋅⋅⋅N bond is formed in the 4,6-di-tert-butyl-2-aminophenol derivatives than in molecules containing electron-acceptor Cl and Br atoms. Formation of the above-indicated intramolecular hydrogen bond affects the course of radiation-induced reactions occurring in n-hexane with participation of these compounds and also affects their antiviral activity. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 434–439, May–June, 2009.     

Enhancement of Raman scattering of light by ultramarine microcrystals in presence of silver nanoparticles

Approximately 10²‐fold enhancement of Raman scattering by ultramarine microcrystals is reported by means of interaction with silver nanoparticles in films and powders. Theoretical modeling predicts the maximal 10¹⁰‐fold enhancement in close vicinity of a silver spherical nanoparticle (0.24 nm) with rapid decay of enhancement factor to 1 in the range of approximately 50 nm. Experimental enhancement factor is treated as overall effect within the small portion of every microcrystal in the close vicinity of silver nanoparticle(s). The results are considered as an important extension of traditional surface enhanced molecular Raman spectroscopy towards bigger inorganic probes. Copyright © 2012 John Wiley & Sons, Ltd.     

Infrared spectra and structure of molecular complexes of aromatic acids

FTIR spectra of pharmacologically active molecules of benzoic acid and its derivatives have been measured in CCl₄ solutions and in microcrystals. Features of the formation of intra-and intermolecular hydrogen bonds have been analyzed. Spectral attributes have been revealed that characterize the participation of a carboxyl group in different types of intermolecular interactions with the formation of cyclic, linear, and criss-cross dimers. Mechanisms of the intermolecular interactions are shown to be defined by the character of the substituents attached to the benzene ring in the para- and meta-positions relative to the carboxylic group.     

Estimation of the Polarity of Stationary Phases for Gas Chromatography Based on Spectral Parameters

Journal of Applied Spectroscopy - The applicability of stationary liquid phases for gas–liquid chromatography was evaluated. The scale for quantitative one-parameter estimation of their...     

Investigation of laser energy conversion into plasma x-rays in the system Iskra-4

We present results of experimental and computational investigation of laser plasma emission in the soft x-ray spectrum. Plasma has been produced by irradiating a gold target with subnanosecond pulses at the first and second harmonics of an iodine laser. It has been shown that approximately half of the absorbed laser energy is converted into soft plasma x-rays.Presented at bilateral international seminar of High Temperature Laser Plasma and High Gain Iodine Lasers held on 4 July 1991 in the Inst. of Physics, Czechosl. Acad. Sci., in Prague (organized by Division of Optics of the Inst. of Physics, Czechosl. Acad. Sci., and Physical Section — Plasma Division of the Union of Czech Mathematicians and Physicists).