Exchange interactions of excitons localized at opposite interfaces in type-II GaAs/AlAs superlattices: Optically detected magnetic resonance and level anticrossing

Two types of excitons, localized at opposite interfaces and characterized by different magnitudes of the exchange interactions at the same radiation energies, are simultaneously in type-II GaAs/AlAs superlattices. It is shown that the additional long-wavelength luminescence line in superlattices grown with growth interruptions after the GaAs layers is due to the recombination of an exciton localized at an inverted interface in regions where the quantum-well width is increased by one monolayer. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 10, 701–706 (25 November 1996)     

Monte Carlo simulations in the vicinity of the critical point: Vapour-liquid coexistence curve

A generalized Gibbs-ensemble methodology with a fluctuating particle is used to determine the coexistence vapor-liquid densities for a square-well fluid. It is shown that the presence of the fluctuating particle in sub-states of the Markov chain of states supresses considerably density fluctuations which makes it possible to carry out simulations efficiently even for temperatures very close to the critical temperature.     

SrZrO3-based proton conducting materials with La additions

The behaviour of La-containing strontium zirconate based ceramics is revised. La additions contribute to improve the sinterability of these materials, but transport properties are also affected. Sr_1−xLa_xZrO_3+δ show some unusual changes in transport properties when samples are exposed to H₂-containing atmospheres and then reoxidized. Nevertheless, the transport properties of (Sr,La)(Zr,Y)O_3−δ, are still mainly dependent on Y additions, at least for cases when the fraction of Y exceeds the fraction of La. In addition, lanthanum causes significant changes in lattice parameters. A combination of conductivity measurements in different atmospheres, ion blocking experiments, and emf measurements has been used to demonstrate that electron hole conductivity increases with temperature, and the protonic contribution drops. The transport properties at temperatures lower than about 800 °C might be affected by structural changes. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Sandwich plates-free vibrations and damping analysis

A new analytical approach to the optimization analysis of stacking sequences of sandwich plate faces is presented. FRP faces are assumed to be constructed of 0₂°, 90₂°, and ±45° plies. A new set of design variables was succesfully used for the optimization analysis of natural flexural vibrations and modal loss factor of sandwich plates with FRP faces. In addition, the influence of the core thickness on optimization solutions was studied. Three variants of plate theories were considered, namely those of Love-Kirchhoff and first- and higher-order transverse shear deformation. To verify the results of the models proposed, the values of the natural vibrations were compared with the results obtained using the NISA II FEM package.Submitted to the 10th International Conference on Mechanics of Composite Materials, April 20–23, 1998, Riga, Latvia.Institute of Mechanics and Machine Design, Cracow University of Technology, 31–155, Cracow, Poland. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 2, pp. 276–286, March–April, 1998.     

Resonant response of a thermalized ensemble of nonlinear oscillators

The analysis is carried out of the response of the center of gravity (dipole moment) of the distribution of noninteracting thermalized nonlinear oscillators to a sinusoidal driving force. Heat bath coupling is modeled by damping and noise. The driving is weak, but the frequency is resonant, so that there is a nonlinear resonance in the phase space. The response has a linear part that can be obtained from the perturbation analysis and a small nonlinear correction that is specific for the resonant structure.     

Contributions to the synthesis of some ferrocene-containing antibiotics

This Review discusses the synthesis and characterization by our Group of new antibiotics belonging to the class of penicillins, cephalosporins and rifamycins with ferrocenyl and 1, 1′-ferrocenilene residues in the molecule. As reactants for 6-aminopenicillanic acid (6-APA) and 7-aminocephalosporanic acid (7-ACA) the following were used: 1, 1-bis(chlorocarbonyl)ferrocene, ferrocenyl sulfochloride, 1, 1′-ferrocenylenedisulfochloride and thioglycolic acids S-modified with ferrocene. In the synthesis of rifamycins, the hydrazides of the thioglycolic acids, S-modified with ferrocene, were employed as nucleophilic agents. The synthesized intermediates were characterized by elemental analysis, TLC, IR, UV and ¹H NMR spectra. The characterization of new antibiotics was made by TLC, IR and UV spectral analysis. Biological activity was tested on Gram-negative and Gram-positive bacteria. Good activity is reported towards Gram-positive bacteria in the case of derivatives containing residues of thioglycolic acid S-modified with ferrocene, the antibacterial activity being similar to that of amoxicillin, carbenicillin and cephalothin. All compounds are inactive towards Gram-negative bacteria.     

A covariant quasipotential operator for a composite system of two scaler particles

A quasipotential operator for a system of two scalar particles, and also an integral equation and a normalization condition for the wave function of the connected state, are obtained by the method of two-time Green's functions in an explicitly covariant form. The cases are considered of scalar and electromagnetic interactions of particles of the system.Frantsiska Skoriny Gomel' State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 112–118, June, 1993.     

Spherical harmonic representation of the gravitational coupling between a truncated sector of a hollow cylinder and an arbitrary gravitational source: Relevance to the STEP experiment

The gravitational interaction between grooves machined in a hollow cylindrical mass of uniform density, and an external point mass, is derived in terms of the Associated Legendre functions, and the parametric form of the coupling coefficients is presented. The cross-sections of the grooves, which are regularly spaced in azimuth, are in the form of truncated sectors of the cylinder's end-faces. This theory is applied to the test-masses for the Satellite Test of the Equivalence Principle (STEP) experiment, for which four grooves have been assumed, and an expression for the axialforce is derived which is more than 10⁴ times faster to compute than a Monte-Carlo integration of similar accuracy. Following this analysis it is suggested that the STEP test-masses should carry at least 6 grooves. This theory has wider application to gravitational problems involving general sectored cylindrical bodies.     

Thermoluminescence of KMgF3(RE) crystals

Optical properties of pure and RE doped KMgF₃ crystals were studied. Thermoluminescence curves are independent of the introduced impurity for all dopant besides europium. Emission, radiation damage and TL are found to be significantly dependent on the types of Eu-dopant added to the melt: europium fluoride or oxide. An intensive high temperature TL peak at 390°C in KMgF₃(Eu₂O₃) may be used as a dosimetric one not only for ionizing but also for UV radiation.