Triterpenes from the leaves ofBetula ermanii

Summary From the unsaponifiable fraction of an ethereal extract of the leaves ofBetula ermanii a new triterpene of the dammarane series — 20,24-epoxydammarane-3,6,25-trol (II) — and its 6-O-acetyl derivative (I) have been isolated.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center of the Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 587–590, September–October, 1978.     

Oxidation of hydrogen chloride with hydrogen peroxide in aqueous solution

Evolution of chlorine into the gas phase upon mixing of aqueous solutions of hydrogen chloride and hydrogen peroxide was studied. The threshold hydrogen chloride concentration corresponding to the onset of the chlorine evolution was determined.     

Quasi-acoustic scheme for the Euler equations of gas dynamics

We suggest an original scheme and an algorithm for the numerical solution of the Euler equations of gas dynamics. The construction of the scheme is based on the mass, momentum, and energy conservation laws. The flux computation is carried out by summation of elementary fluxes formed by small-amplitude running waves that satisfy the linearized equations of gas dynamics. The scheme contains no artificial regularizers, has second-order accuracy on smooth solutions, and is quasimonotone in a neighborhood of the discontinuities. Examples of one- and two-dimensional computations are given.     

Analysis of lead and sulfur in environmental samples by double pulse laser induced breakdown spectroscopy

In the present work, a model of double pulse laser-induced breakdown spectroscopy (LIBS) spectrometer has been developed and results from two different applications of double pulse LIBS for solving the problems of environmental interest are presented. In one case, laser induced breakdown spectroscopy has been applied to the determination of heavy and toxic metals (lead) in soil samples. In the second case, laser induced breakdown spectroscopy was used in preliminary experiments for the detection of sulfur content in coal, and on the basis of spectral features, ways to improve the sensitivity of laser induced breakdown spectroscopy detection of sulfur are proposed. The detection limit for lead in soil was estimated to be approximately 20 ppm that is lower than the regulatory standards for the presence of lead in soil.     

Photoelectric properties of the GeSi/Si heterostructures with self-assembled nanoclusters grown by sublimation molecular beam epitaxy in a GeH4 medium

The photosensitivity (PS) spectra of the GeSi/Si(001) heterostructures with self-assembled nanoclusters grown by sublimation molecular beam epitaxy in a GeH₄ medium have been studied by photo-emf spectroscopy at the semiconductor/electrolyte junction (PSE) and by photo-emf and photocurrent spectroscopy of Schottky barriers including the temperature dependence of the PS spectra in the temperature range of 10–300 K. The bands related to the phonon assisted and phonon-less interband of spatially indirect optical transitions in the GeSi nanoclusters have been observed in the PS spectra even at 300 K. The scatter effect of the GeSi nanoclusters in size and/or in composition on the PS spectrum’s edge shape has been theoretically considered. The emission theory of the photoexcited carriers from the quantum wells of the GeSi/Si nanoclusters built-in to a Schottky barrier (p-tn junction, semiconductor/electrolyte junction) has been developed.     

Investigation of ferroelectric properties of strontium barium niobate crystals by second harmonic generation technique

The ferroelectric properties of Sr _x Ba_{1 − x} Nb₂O₆ (SBN-x) crystals have been investigated using noncollinear (diffuse) second harmonic generation of IR radiation converted by a disordered domain structure. The switching characteristics have been determined from the dependences of the second harmonic intensity I _2ω(t) and I _2ω(E) for the SBN-0.75 crystals. These characteristics are in good agreement with the results of measurements by traditional methods and exhibit a number of specific features (long polarization relaxation times, irreproducibility of the shape of hysteresis loops, low-frequency dependence of the quantity E _c ) associated with the relaxor nature of SBN solid solutions. The kinetics of the diffuse second harmonic generation can be described in the framework of the phenomenological approach to polarization relaxation processes in relaxor ferroelectrics. The intensity of the diffuse second harmonic in switching is determined by the parameters (duration, amplitude) of the switching field pulse.     

On Uniqueness in the General Inverse Transmisson Problem

In this paper we demonstrate uniqueness of a transparent obstacle, of coefficients of rather general boundary transmission condition, and of a potential coefficient inside obstacle from partial Dirichlet-to Neumann map or from complete scattering data at fixed frequency. The proposed transmission problem includes in particular the isotropic elliptic equation with discontinuous conductivity coefficient. Uniqueness results are shown to be optimal. Hence the considered form can be viewed as a canonical form of isotropic elliptic transmission problems. Proofs use singular solutions of elliptic equations and complex geometrical optics. Determining an obstacle and boundary conditions (i.e. reflecting and transmitting properties of its boundary and interior) is of interest for acoustical and electromagnetic inverse scattering, for modeling fluid/structure interaction, and for defects detection.     

Intershell beta- and gamma-decay transition rates in the multiparticle shell model

In the framework of the two-group configuration model we obtain formulas for the reduced transition rates for beta and gamma transitions in even-even, odd-odd, even-odd, and odd-even nuclei. We explored dependencies of the transition rates on the occupancies of the involved subshells, as well as on the spin values of the initial and final states. The obtained formulas are useful for the qualitative spectroscopic analysis of experimental data, particulary in the regions of magicity, including the regions of the “remote” nuclei.     

13C NMR spectra of 20-ketosteroids with 16α,17α three-membered ring

Conclusions ¹³C chemical shifts have been determined for 20-ketosteroids with a 16, 17 three-membered ring (X=S, NH, NAc, O, CH₂), and a linear relationship has been found between the -effects of X and the calculated changes in electron density on the C atoms C¹⁶ and C¹⁷; the - and -effects depend on the electronegativity of X. The C¹⁶ and C¹⁷ centers in the epoxysteroid (X=0) are more electrophilic than in the other analogs that were studied; this is consistent with the observed higher reactivity of the epoxide ring in reactions of cleavage by nucleophilic reagents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2189–2194, October, 1987.