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The results of numerical modeling of the process of multi-pulse femtosecond laser photoexcitation and heating of monocrystalline silicon are presented. It is shown that starting from a certain level of irradiance at pulse repetition rates of 10–1000 Hz, the structural changes in the surface that occur between pulses influence the spatiotemporal distribution of the electron plasma in the near-surface layer of the semiconductor at the time of irradiation with a subsequent pulse and thus accumulate, forming a stable surface microstructure in the irradiated region. A mechanism is proposed for the formation of a two-dimensional periodic microrelief on a silicon surface, which is based on a change in the type of a surface excited by electromagnetic waves with an increasing number of irradiating femtosecond pulses.

Abstract: The effect of alien-valence substitution on exchange interactions in ferromagnetic cadmium chromium selenide spinel is studied both experimentally and theoretically. The Curie temperature is calculated within the molecular field approximation. From comparing the calculated results with experimental dependences of the Curie temperature on impurity concentration and variation in NMR chromium spectra with temperature, a conclusion is drawn in favor of the model of magnetic clusters. The model suggests that, during the alien-valence substitution for nonmagnetic cations, the valence is compensated by a change in the valence state of chromium ions. The excess charge carriers hop between equivalent ions surrounding the impurity. By analogy with the double-exchange model, a detailed description of this hopping and its influence on the exchange interaction of magnetic ions is given.

Abstract: The effect of geomorphic conditions on the morphological, chemical, and physical properties; the biochemical activity; and the distribution of soil microorganisms in the plow horizon of ameliorated swampy podzolic soils has been studied along the catena on a gentle slope of the northeastern aspect of a moraine hill. The indices of soil fertility gradually improve from the top of the hill to the adjacent hollow. In this direction, the soil acidity becomes weaker under the impact of liming, the soil texture becomes somewhat heavier, and the contents of humus and the major nutrients increase in parallel with the increase in the number of soil microorganisms and their enzymatic activity.

Abstract: The spin system of the Heisenberg model (s=1/2) on a square lattice with antiferromagnetic (AFM) exchange between nearest neighbors (in which there is no long-range magnetic order at any T≠0) is treated as a spatially homogeneous isotropic spin liquid. The double-time temperature Green’s function method is used in the framework of a second-step decoupling scheme. It is shown that, as T → 0, the spin liquid goes over (without any change in symmetry) to a singlet state with energy (per bond) ɛ0=−0.352 and the correlation length diverges as ξ ∝ T −1 exp(T 0/T). The spatial spin correlators oscillate in sign with distance, as in the AFM state. The theory allows one to calculate the main characteristics of the system in all temperature ranges.

Electrophoresis in 7% polyacrylamide gel was used to analyze nonspecific esterases from different organs and tissues of Russian sturgeon. The basic enzymatic activity was observed in four zymogram zones. In sixteen cases the patterns of isozyme distribution in these zones allowed to consider them as allele systems (14 polymorphic and 2 monomorphic) corresponding to the four structural genes. The observed genotype frequencies of the nine of these systems (EST-1*of brain and intestine; EST-2*of serum and intestine; EST-3*of spleen and kidney; and EST-4*of spleen, brain, and heart) were largely concordant with Hardy–Weinberg proportions for codominant disomic inheritance. Genetic control of other polymorphic systems is unknown, but, high enzymatic activity of these esterases, sufficient for qualitative electrophretic detection, permits utilization of these polymorphisms for phenotypic monitoring of Russian sturgeon populations.

An acoustic transceiver for the monitoring of dynamic processes in the ocean by acoustic tomography methods is described, and the results of its tests are presented. At an acoustic pressure of 2–6 kPa/m produced by the transceiver in the emission mode at frequencies of ∼250 Hz and an rms error in determining time intervals no larger than 2 ms, the flow velocity component can be measured to an accuracy of 10 cm/s by using the countersounding scheme.

As a result of the performed study, the basic data were obtained on the level of lactate dehydrogenate (LDH) and malate dehydrogenase (MDH) activity in two species of sturgeons caught in various regions of the Volga basin under conditions of spreading in the population of a pathology, one of its manifestations being stratification of muscle tissue. In the sterlet, a statistically significant increase of muscle LDH was revealed in fish with a pronounced stratification, while in the Russian sturgeon a tendency for such increase was noticed. In the group of sick fish a marked increase of dispersion of individual values of the enzyme activities in tissues was observed, which appears to indicate a disbalance of biochemical processes in the organism. The data obtained indicate that the stratification is not accompanied by a damage of myofibril sheaths and of liver cells. No obvious interspecies differences in the levels of LDH and MDH were observed between the sterlet and Russian sturgeon.

An acoustohydrophysical complex for tomographic ocean surveillance is described. The complex has been developed within the framework of the US–Russia project JESAEX (The Japan / East Sea Acoustics Experiment). Technical characteristics of self-contained and mobile receiving and transmitting systems of the complex allow one to use them as building blocks in constructing tomographic systems of various configurations and complexities. Experimental tests of methods and facilities in September–October 1999 in the Japanese sea have shown that the range of reliable reception of composite phase–shift keyed signals, such as M—sequences, is 700 km at an acoustic pressure produced by a sound source of up to 7 000 Pa/m.

A quasi-two-dimensional ferromagnet (S = 1) with easy axis type anisotropy and interplanar exchange J and intraplanar exchange K is examined within the framework of the spin-wave approximation. An expression for the Curie temperature that is dependent on both the anisotropy parameter D (D/J » 1) and on the exchange parameter ratio ?=K/J is obtained from the self-consistent equations. The important role of the single-ion anisotropy in the formation of the long-range magnetic order in two-dimensional systems is shown.

Conclusions:

A function Hn(a1, a2, a3) is found, computing the number of normalized irreducible polynomials of degree n over a finite field Fq, with the first three coefficients a1, a2, and a3 fixed for n = 4. The function is expressed via some sums of characters admitting “good” estimates. In particular, the following theorem is proved: If q = 3m + 1, a ? k*, and N (a) = H4(0, 0, a), then $$N(a) = \frac{1}{4}(q - 2\operatorname{Re} [(\lambda (a) - \eta ( - 1)\bar \lambda (a/2))J(\lambda ,\lambda )] - \eta ( - 1)),$$ where ? is a quadratic character of the field k = Fq, ? is a nontrivial cubic character, and J(?, ?) is the known Jacobi sum.

Abstract: A generalized t-J-I-model is proposed for Sr2RuO4 that takes the strong intra-atomic correlations of the d electrons and the features of the electronic structure of Sr2RuO4 into account. It is shown that, in the limit of strong correlations, there are no singlet s-type solutions for the superconducting state, but triplet solutions exist because of ferromagnetic spin correlations. For typical values of the model parameters, T c ∼1 K, consistent with the value of T c for Sr2RuO4.

Conclusions 1.Ammonia water retards heat liberation of concrete and the more intensely, the higher the concentration.2.Retardation of heat liberation of concrete propared with ammonia water is considerably more effective compared to the addition of SNV.3.Regardless of the ammonia concentration in the mixing water, on reaching the same rise of temperature in an adiabatic regime the compressive strength, axial tensile strength, and modulus of elasticity of the concrete have practically the same values and only the time of reaching the specified rise of temperature varies.