Asymptotic behavior of neutron small-angle multiple scattering spectra

The asymptotic behavior of the spectra for large values of the scattering vector for the case of elastic multiple small-angle neutron scattering (SANS) is investigated theoretically and experimentally. An expansion of the spectrum in terms of the reciprocal of the magnitude of the momentum transfer is obtained taking account of the influence of the instrumental line. It is shown that, to within some factor, the leading term of the expansion is identical to the differential single-scattering cross section averaged over a statistical ensemble of particles; several subsequent terms in the expansion are calculated and the range of applicability of the resulting expressions is determined. The asymptotic behavior of the multiple SANS spectrum is measured, using a two-crystal neutron spectrometer, for samples of an HTSC ceramic, the alloy Fe-Ni, and Al powder. The agreement between the experimental results and the theoretical predictions is analyzed. Zh. éksp. Teor. Fiz. 114, 2194–2203 (December 1998)     

Covariant spinor derivative associated with arbitrary linear connectedness

A covariant spinor derivative is constructed in arbitrary reference frames and also in coordinates, with specified arbitrary linear connectedness. Kazan State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 78–83, November, 1998.     

Specific properties and spatial symmetry group of nonassociative spinor field

On the basis of nonassociative spinor field theory, the specific properties of a nonassociative spinor field are investigated. A new quantum number is introduced: the associator, which is a measure of the nonassociativeness of the field. To calculate the associator and spin in nonassociative algebra, open and closed products are introduced. It is shown that the spin consists of two components: the first half (calculated by the open-product rule) is similar to ordinary spin, while the second half (calculated by the closed-product rule) is attributed to the associator, i.e., is related to shear in the auxiliary isotopic space. The associator basis is expanded to a complete octonion basis, and the Poincaré group of four-dimensional space is expanded to a Poincaré group of eight-dimensional space. It is shown that, from these generators, in the particle rest system, the nonzero independent eigenvalues are: one, the sign of the particle energy, one of the spin components, one of the associator spatial components, and c₇. Tbilisi Medical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 101–109, October, 1998.     

Towards an universal classification of scale invariant processes

We consider fields which take random values over several decades. Starting from physical examples, we postulate that scale is not an absolute quantity. We then establish the equivalence between two existing approaches based on scale symmetry arguments as general as possible. This yields a classification of log-infinitely divisible laws, possibly universal. The physical significance of the parameters entering in the classification is discussed. Received: 7 November 1997 / Received in final form: 26 March 1998 / Accepted: 30 March 1998     

An Empirical Potential of Interatomic Interaction

A potential of interatomic interaction for simulating complex structural states of solids (grain boundaries and heterogeneous equilibrium states) is put forward. In simulating heterogeneous states of systems, the potential must simultaneously provide for stability conditions for several phases in equilibrium and correct values of a number of macroscopic parameters such as lattice constants, elastic moduli, internal energy, heat capacity, and stability parameters. The existing empirical potentials of interatomic interaction fail to provide agreement of the calculated and experimentally obtained parameters determining the structure of the system and structural transformations due to changes in the external parameters. The potential under discussion is a polynomial representing a solution to the problem of interpolation of functions and their derivatives to the nth order prescribed on a finite system of points (Hermit interpolation problem). The relation for a general solution to the foregoing problem is so complicated that it is virtually inapplicable. A new polynomial is constructed on the basis of the Lagrangian interpolation polynomial. The interpolation of the known interatomic potentials with allowance for the fourth-order derivatives by the polynomial is achieved with high accuracy where three to four interpolation nodes are specified. Local changes can easily be introduced to the polynomial. In doing so, the values of the potential and its derivatives in other regions of space are retained. This allows mechanical stability for stable and metastable phases to be ensured.     

Thin-layer chromatography of radioactively labelled cholesterol and precursors from biological material

Summary The investigation methods of the action of xenobiotics on sterol biosynthesis from ¹⁴C-acetate in rat hepatocyte cultures can be developed, with regard to extraction using Extrelut and the separation of the sterol pattern by thin-layer chromatography, in such a way that they are suitable for wider application, e.g., screening. Good visualisation and recognition of changes in the sterol pattern are possible using autoradiography of the thin-layer chromatogram.

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Dünnschicht-Chromatographie von radioaktiv markiertem Cholesterin und Vorstufen aus biologischem Material. Eine einfache und empfindliche Methode zur Untersuchung einer Beeinflussung des Sterolbiosynthesewegs

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Dedicated to Dr. E. Roesch on occasion of his 65th birthday     

A hybrid finite-element–volume-of-fluid method for simulating free surface flows and interfaces

A numerical technique is developed for the simulation of free surface flows and interfaces. This technique combines the strength on the finite element method (FEM) in calculating the field variables for a deforming boundary and the versatility of the volume-of-fluid (VOF) technique in advection of the fluid interfaces. The advantage of the VOF technique is that it allows the simulation of interfaces with large deformations, including surface merging and breaking. However, its disadantage is that is solving the flow equations, it cannot resolve interfaces smaller than the cell size, since information on the subgrid scale is lost. Therefore the accuracy of the interface reconstruction and the treatment of the boundary conditions (i.e. viscous stresses and surface tension forces) become grid-size-dependent. On the other hand, the FEM with deforming interface mesh allows accurate implementation of the boundary conditions, but it cannot handle large surface deformations occurring in breaking and merging of liquid regions. Combining the two methods into a hybrid FEM-VOF method eliminates the major shortcomings of both. The outcome is a technique which can handle large surface deformations with accurate treatment of the boundary conditions. For illustration, two computational examples are presented, namely the instability and break-up of a capillary jet and the coalescence collision of two liquid drops.