An YBCO film as a Josephson medium near T c : Frequency and field dependences and scaling relationships

The diamagnetic response of a laser-deposited YBCO film was studied in weak exciting magnetic fields H _ac =H ₀sinωt (H ₀=2–500 mOe, ω/2π=1–30 kHz). An analysis of the experimentally measured diamagnetic response showed evidence of a ring character of the electric field flowing in the sample at small H ₀ values. The plots of T _m (the temperature of maximum dissipative losses χ″₁) versus H ₀ measured at various frequencies showed the existence of a certain critical field strength H*(ω) at which the (1?T _m /T _c ) versus H ₀ ^2/3 plots exhibit a break. A logarithmic dependence of T _m on the frequency ω of the exciting field H _ac is reliably valid only in the region of (ω/2π)>5 kHz. Verification of the scaling relationship showed that this relationship is valid (to within the experimental accuracy) for the frequencies ω above 5 kHz and the field amplitudes H ₀>H*(ω). However, the exponent n in the scaling relationship under consideration is not correlated with the exponent n in the power relationship describing the current-voltage characteristic.     

Search for inert oxide matrices for carrying out solid-phase ion-exchange reactions by the internal reaction scheme

Having a goal of studying the possibility of and develop methods for controlling internal solidphase reactions inside a solid matrix that is diffusionally saturated with several components simultaneously from different source phases, we experimentally checked whether it is possible to synthesize, for use as these matrices, ZrO₂-Nb₂O₅ solid solutions having distorted fluorite structure and NiO-CuO-Cu₂O solid solutions having rock salt structure (these solid solutions had been studied by computational techniques using the ion lattice mechanic approximation), with a controlled ratio of anionic and cationic conductivities.     

Synthesis of 3-fluoroimidazo[1,2-a]pyrimidines and 5-fluoroimidazo[2,1-b][1,3]thiazoles via heterocyclization of (N-heteroarylimino)trifluoropyruvates

Synthesis of 3-fluoroimidazo[1,2-a]pyrimidines and 5-fluoroimidazo[2,1-b][1,3]thiazoles was accomplished via triethyl phosphite-induced heterocyclization of the corresponding N-(heteroarylimino)trifluoropyruvates. This method provides a convenient approach to synthesize ring-fluorinated fused imidazoles of biological relevance.     

Stability in critical cases of a holonomic mechanical system with two degrees of freedom subject to impacts

Stability conditions for a holonomic impulsive mechanical system with two degrees of freedom in the critical case of one pair of complex-conjugate multipliers are established. An analog of the first Lyapunov exponent is calculated __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 6, pp. 105–117, June 2008.     

Effect of electric current on starting characteristics and activation parameters of short dislocations in Si crystals

It is shown that the passage of an electric current through crystalline silicon may lead to the so-called galvanoplasticization, as well as the galvanostrengthening, effect. It is found that the effect is sensitive to the temperature regime of deforming and to the preliminary high-temperature treatment of the samples. The motion delay time for short dislocations and starting stresses are significantly affected by the current. The relation of these effects to the change in the electric state of the Cottrell atmosphere as a result of the passage of the current through the crystal is considered.     

On first integrals of a class of third-order differential equations

We suggest a new algorithm for constructing first integrals of a class of third-order differential equations. The algorithm is based on the use of necessary and sufficient conditions for the existence of such integrals.     

Influence of the texture and acid-base properties of the alumina-containing support on the formation of Co(Ni)-Mo catalysts for deep hydrodesulfurization of the diesel fraction

The influence of the texture of γ-Al₂O₃ on the formation of Co(Ni)-Mo catalysts for hydrodesulfurization of the diesel fraction is studied. As shown by low-temperature N₂ adsorption, X-ray diffraction, IR spectroscopy of adsorbed molecules, and high resolution electron microscopy (HREM), use of a support with a larger specific surface and a lower total concentration of terminal OH groups makes it possible to prepare more active catalysts. The electron density radial distribution method shows that the finely dispersed cobaltcontaining catalyst in its initial state contains CoMoO₄, Al₂(MoO₄)₃, and CoAl₂O₄, the last two phases being present in trace amounts. After the reaction, this catalyst contains cobalt-doped molybdenum sulfide. According to HREM data, the active phase of the cobalt-containing catalyst consists of layered sulfide association species Co_1.3Mo₂S_3.3, which differ in composition from the bulk phase CoMo₂S₄. It is assumed that, out of the 1.3 cobalt atoms in Co_1.3Mo₂S_3.3 0.3 Co occurs at the edges of the association species and 1.0 Co is intercalated into their interlayer space, and 0.7 S at the boundary between the association species and the Al₂O₃ phase is replaced by the corresponding amount of oxygen.