Spectroscopic characterization of mineral crystals produced by the bacterium Azospirillum brasilense

The results of spectroscopic structural and trace elemental analyses of mineral crystals produced by the soil nitrogen-fixing bacterium Azospirillum brasilense cultivated in a synthetic medium are presented and discussed. The mineral formed is shown to have a structure close to struvite (MgNH₄PO₄ × 6H₂O; ASTM file No. 15-762) with some differences which may be attributed to the presence of isomorphic admixtures of other cations (struvite is known to have a variety of forms). AAS/AES and ion chromatography analyses for a number of biologically important microelements and their role in the formation of the crystal structure, as well as some questions related to biomineralization are also discussed.     

Transformed steroids. 113. Cyclobuteno [16α,17α]pregnanes in cycloaddition and oxidation reactions

Conclusions The strained double bond in cyclobuteno[16,17]pregnanes is reactive toward certain dienes and oxidizing agents; here its reactivity toward dienes is increased by high pressure.See [1] for Communication 112.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1902–1904, August, 1980.     

Photoproduction of π<Superscript>0</Superscript>π<Superscript>+</Superscript> pairs on proton and deuteron

The reaction of π⁰π⁺ photoproduction on free and quasi-free protons with γ-ray energies from 0.5 to 1.5 GeV has been studied. Its cross section was measured in the range θ _π ⁰ ≥ 20°. The distributions of π⁰π⁺, π⁰n, and π⁺n invariant masses were analyzed. The experiment was performed using the Compton back-scattered γ-ray beam at the GRAAL facility (Grenoble, France), applying liquid deuterium and hydrogen targets and a large-aperture (almost 4π) detector. Particular attention was paid to analysis of systematic errors related to the neutron detection efficiency.     

First crossing time,overshoot and Appell–Hessenberg type functions

We consider a general insurance risk model with extended flexibility under which claims arrive according to a point process with independent increments, their amounts may have any joint distribution and the premium income is accumulated following any non-decreasing, possibly discontinuous, real valued function. Point processes with independent increments are in general non-stationary, allowing for an arbitrary (possibly discontinuous) claim arrival cumulative intensity function which is appealing for insurance applications. Under these general assumptions, we derive a closed form expression for the joint distribution of the time to ruin and the deficit at ruin, which is remarkable, since as we show, it involves a new interesting class of what we call Appell–Hessenberg type functions. The latter are shown to coincide with the classical Appell polynomials in the Poisson case and to yield a new class of the so called Appell–Hessenberg factorial polynomials in the case of negative binomial claim arrivals. Corollaries of our main result generalize previous ruin formulas e.g. those obtained for the case of stationary Poisson claim arrivals.     

Propagation of surface magnetostatic waves in a one-dimensional magnon crystal of a variable thickness

The propagation of surface magnetostatic waves in a ferromagnetic film of variable thickness having a planar periodic structure in the form of a grating of etched parallel strips (one-dimensional magnon crystal) has been investigated. The dispersion characteristics of surface magnetostatic waves have been calculated using the Wentzel-Kramers-Brillouin method. The intrinsic error of the method has been estimated, and the magnon spectrum of the surface magnetostatic wave has been studied. An analysis of the dispersion characteristics and the transmission capacity of these structures has demonstrated that they can be used for designing narrow-band and comb filters.     

The statistical integrals of bound and quasi-bound states of gas phase complexes formed by symmetrical nonpoint monomers

Equations for calculations of the statistical integrals of bound and quasi-bound weak binary complex states in the gas phase are extended to nonpoint monomers. The equations for states of both types are derived using a unified approach different from those reported earlier. The equations can be used for estimating the thermodynamic functions, equilibrium constants, and concentrations of weakly bound complexes in the ideal gas state and for verifying the results of numerical simulation of association processes in the gas phase.     

Response of a Bloch oscillator to a THz-field

In this paper we report on the observation of response of a Bloch oscillator at room temperature to a THz-field of a frequency larger than the Bloch frequency. The oscillator consisted of a semiconductor superlattice structure, with an applied dc voltage giving rise to a dc electron drift current. Submitting the oscillator to a field at a frequency of 3.3 THz caused a sizeable reduction of the current; the THz-field was generated by use of intense THz-radiation pulses focused on an antenna coupled to the superlattice. We attribute the THz-field induced reduction of the current to a frequency modulation of the Bloch oscillations of electrons at the frequency of the THz-field, leading to reduction of the electron drift velocity and, consequently, of the current.     

Reactions of N,N-dimethoxyamine with acid chlorides and isocyanates

N,N-Dimethoxyamines are smoothly acylated by pnitrobenzoyl chloride and phosgene and carbamoylated by isocyanates. However, N-methoxy-N-benzyloxyamine is not alkylated by benzyl bromide and unsaturated activated compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2384–2385, October, 1989.     

Electrophilically catalyzed splitting of dimethoxyamine to methoxynitrenium ion and its reactions

The electrophilically catalyzed splitting of the N-0 bond of dimethoxyamine results in the formation of methoxynitrenium ion, which in reaction with nucleophiles exhibits properties of an ambidentate cation — it methylates rigid nucleophiles and epiminates olefins. The stereospecificity of the addition of the nitrenium ion to cis-2-butene indicates its existence in a singlet electronic ground state.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1384–1389, June, 1990.