Crystal monochromator with a large curvature of the sagittal bending

A new crystal monochromator is designed and tested. The crystal monochromator allows for the use of a large curvature of the sagittal bending and makes it possible to focus synchrotron radiation at a short wavelength and a limited distance from the synchrotron radiation source to the sample.     

Molecular Mechanics Study of the Steric Structure of the Dipeptides Vilon and Thymogen

Molecular dynamics trajectories of two dipeptides, vilon (Lys-Glu) and thymogen (Glu-Trp), were traced up to 700 ps. Both structures comprise intramolecular salt bridges which make them less conformationally flexibile. Vilon is comparatively more flexible due to the aliphatic side chain of Lys, whereas thymogen is quite a rigid structure, which is defined by the mutual arrangement of salt bridges and aromatic rings in the side chain of Trp. A probable mechanism of ligand-receptor binding of dipeptides with excitable membrane was proposed. The binding can be effected via the nitrogen and oxygen atoms forming the salt bridges.     

Ground magnetic state of an assembly of single-domain particles confined in a spherical layer

The ground magnetic state of systems of finite number N of single-domain particles confined in a spherical monolayer is investigated by numeric simulations. Two model situations are considered. In the first, the particle positions are imposed and fixed, in the second, the particles are able to move freely within the layer; in the latter case the excluded volume effect is taken into account. It is found that in all the range studied (N?200) the ground state of the system retains a considerable extent of magnetic vorticity (toroid moment). Moreover, the magnetic and toroid moments are correlated: they are approximately perpendicular to one another.     

Investigations of sulfide minerals with layered structure by Mössbauer spectroscopy methods

Samples obtained as a result of the tochilinite synthesis process were investigated by ⁵⁷Fe Mössbauer spectroscopy. Tochilinite, magnetite and troilite were obtained in investigated samples. The dependences of phase relative content on different content of Mg atoms in the initial mixture were received. It was found that Mg atoms stabilized tochilinite structure. It was shown that magnesium atom entering into tochilinite structure led to Fe atom redistribution in brucite-like layer. It was confirmed that in tochilinite structure equal number of sulfide and brucite-like layers conjugated.     

Luminescence of metals excited by fast nondestructive loading

The paper reports a study of the luminescence excited on the back side of metal targets irradiated with laser pulses of energy substantially below the plasma-flare formation threshold, and calculation of the temporal and spatial distributions of temperature, thermal stresses, and rate of thermal-stress variation in a sample. The evolution of the luminescence pulse is compared with that of the laser pulse, sample temperature, thermal stresses, and rate of thermal-stress variation. It has been established that the luminescence is excited as soon as the stresses at the sample surface become approximately equal to the yield point of the sample material, its intensity grows as long as the rate of stress rise increases, after which the process decays. The temporal and spatial distributions of temperature, thermal stresses, and rate of thermal-stress variation have also been calculated for the experiments, in which anomalous electron emission from the back side of laser-pulse irradiated metal targets was detected, and which were described in the literature but not appropriately explained. The dynamics of experimental and calculated relations have been compared. A correlation closely similar to that found for mechanoluminescence has been established. Fiz. Tverd. Tela (St. Petersburg) 40, 957–965 (June 1998)     

Mössbauer study of 119Sn hyperfine interactions in the KTi1−x SnxOPO4 system

The first Mössbauer study of hyperfine interactions of ¹¹⁹Sn nuclei in the complex ferroelectric oxides KTi_1?x Sn_xOPO₄ is reported. A one-to-one correspondence between the hyperfine interaction parameters and tin atom arrangement in cis and trans positions of the structure has been established. The electric-field gradient at ¹¹⁹Sn nuclei is shown to be dominated by the contribution of valence electrons in the hybridized p and d orbitals. A linear correlation between the quadrupole displacement of the spectrum components and the average Sn-O distances has been revealed. The Mössbauer line shift data were used to estimate the number of valence s electrons of Sn⁴⁺ ions occupying the cis and trans positions throughout the x range covered.     

Difference spline scheme for modeling of convective flows using full Navier — Stokes equations

A difference scheme is constructed, in which enhanced stability is achieved by simultaneous solutions of the equations of motion, energy, and continuity. Spline approximations of spatial derivatives (with the original equations written in divergence form) substantially improve the accuracy of the scheme compared with the standard difference scheme using symmetric differences. The efficiency of the scheme is demonstrated for some problems of convective flow of compressible gas with lateral and bottom heating.Translated from Matematicheskoe Modelirovanie i Reshenie Obratnykh Zadach. Matematicheskoi Fiziki, pp. 38–45, 1993.     

Facile coupling of 2‐(1‐ethylthioethenyl)pyrroles with amines: A route to 2‐(1‐aminoethenyl)pyrroles and 1‐amino‐3‐iminopyrrolizines

2‐(2‐Cyano‐1‐ethylthioethenyl)pyrroles are readily coupled (50–55°) with primary and secondary amines at the position 1 of the ethenyl moiety to eliminate ethanethiol and afford 2‐(1‐amino‐2‐cyanoethenyl)pyrroles and/or their cyclic isomers ‐ functionalized 1‐amino‐3‐iminopyrrolizines in good to high yields.     

Physicochemical Model of Hypersonic Rarefied Gas Flow past Bodies

The effect of the internal molecular degrees of freedom on the flow field and heat transfer in hypersonic rarefied gas flow past a cylinder or sphere is investigated using the direct statistical simulation (Monte-Carlo) method. The variable-diameter rough spherical molecule model (VRS-model) is generalized to include the case of energy exchange between the translational and vibrational degrees of freedom. The interaction between diatomic molecules with allowance for vibrational degrees of freedom is simulated as the interaction of classical or quantum-mechanical harmonic and anharmonic oscillators in the external force approximation. A model of the dissociation of a diatomic gas is proposed.