Second-harmonic generation in the interior of an isotropic medium with quadratic nonlinearity by a focused inhomogeneously polarized pump beam

This paper presents a theoretical study of second-harmonic generation (SHG) by a focused pump beam in the interior of an isotropic medium, experimentally observed earlier. It shows that the spatial dispersion of the quadratic optical response of the substance can be responsible for this nonlinear process even when a macroscopic inversion center is present in the medium. It is established that this effect, which is impossible in the plane-wave approximation, also does not occur when a Gaussian pump beam with uniform distribution of the polarization state of the wave field over the cross section is used, but that the presence in the pump beam of higher transverse modes with polarization different from the fundamental mode can cause an SHG signal to appear. The conditions for a wave to appear at the doubled frequency are found, analytical dependences for its electric field and total power on the propagation coordinate, the degree of focusing, and the other parameters of the problem are obtained, and the requirements on the optimum experimental geometry are formulated. The dependence of the signal-beam power on the wavevector detuning is studied, and it is shown that interference effects can cause the wave at the second harmonic to disappear when a normal dispersion law is obeyed in the region between the fundamental and doubled frequencies. Zh. éksp. Teor. Fiz. 113, 1261–1276 (April 1998)     

S-d Exchange Interaction and the Invar Anomaly of Thermal Expansion of Weak Band Magnets (on the Example of Fe1–x Co x Si Solid Solutions)

In the present paper, the temperature dependence of the linear thermal expansion coefficient (LTEC) of weak band magnets is studied both theoretically and experimentally on the example of Fe_1–x Co _x Si solid solutions. The contributions of electron and magnetic components are also analyzed. It is demonstrated that the experimental data obtained cannot be explained within the framework of the well-known single-particle models. A theoretical approach describing contributions of electrons and fluctuations to the LTEC of weak band magnets is developed based on the spd-model which, in addition to the interatomic exchange interaction of d-electrons, considers the spd-interaction resulting in a noticeable shift of the chemical electron potential along the energy axis. It is demonstrated that the exchange interaction of magnetic moments of s,p- and d-electrons plays the important role in the formation of the Invar LTEC anomaly in Fe_1–x Co _x Si solid solutions.     

nido‐Undecaboranes and ‐borates of the Type B11H13L and B11H12L‐

The Lewis base SMe₂ in 7‐B₁₁H₁₃(SMe₂) ( 1a ) can be replaced by the amines L = NH₂(CH₂tBu), NH₂Cy, NH₂Ph, NH₂(4‐C₆H₄Me), py, chinoline or the phosphanes L = PPh₃, PMePh₂, yielding 7‐B₁₁H₁₃L ( 1b ‐ i ). The borane 1a can be deprotonated by certain amines, alkanides, or hydrides to give the anion 7‐B₁₁H₁₂(SMe₂)^‐ ( 2a ). Replacing the base SMe₂ in the anion 2a by weak bases gives B₁₁H₁₂L^‐ (L = PPh₃, MeCN; 2h , j ). Upon reaction of 1a with the amine NH₂(CH₂tBu) in the ratio 1:2, a deprotonation and the substitution of SMe₂ by the amine are observed, 7‐B₁₁H₁₂[NH₂(CH₂tBu)]^‐ ( 2b ) being formed. At 170 °C, the 7‐isomers 1b , f are isomerized into a mixture of the corresponding 1‐ and 2‐isomers ( 1b′ , f′ and 1b″ , f″ , respectively).     

Bifurcations in a system of two identical diffusion-coupled relaxational brusselators

We propose a two-parameter bifurcation analysis of the dynamics of a system of two identical asymmetrically coupled Brusselators. The stability boundaries of the inhomogeneous steady states and periodic attractors are calculated as the functions of the constraint force and one of the free parameters. The coexistence of different attractors giving rise to multirhythmicity of the dynamics is studied as well as the bifurcation transitions between them. It is shown that the relaxation ability of an oscillator plays an important role in the simplification of the phase diagram, since it removes the overlapping of the existence region for different solutions. We assume that the results primarily characterize the properties of the diffusion coupling and, therefore, they can be applied in the study of other oscillator systems.P. N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 5, pp. 373–401, May, 1995.     

TheR-symmetry violation inN=2 supersymmetric models and the properties of lightest SUSY particle

The present paper discusses the spontaneousR-symmetry violation in theN=2 SUSYSU(4)×U(1) model [1] with soft SUSY breaking terms preserving finiteness. In particular, the mechanism producing a light photino (as a probable candidate for LSP) of a mass of up to some GeV is suggested. InR-odd versions of this model the mechanism of enhancement of the photino decay is discussed.     

Coexistence of color superconductivity and chiral symmetry breaking within the NJL model

The phase diagram for quark matter is investigated within a simple Nambu-Jona-Lasinio model without vector correlations. It is found that the phase structure in the temperature-density plane depends sensitively on the parametrization of the model. We present two schemes of parametrization of the model where, within the first one, a first-order phase transition from a phase with broken chiral symmetry to a color superconducting phase for temperatures below the triple point at T _t = 55 MeV occurs, whereas for the second one a second-order phase transition for temperatures below T _t = 7 MeV is found. In the latter case, there is also a coexistence phase of broken chiral symmetry with color superconductivity, which is a new finding within this class of models. Possible consequences for the phenomenology of the QCD phase transition at high baryon densities are discussed. Received: 3 January 2003 / Accepted: 21 February 2003 / Published online: 24 April 2003     

Flow and coupled heat transfer in the cavity between the rotor and stator

The turbulent flow and coupled heat transfer in the cavity between the rotor and stator is numerically simulated. Reynolds-averaged Navier-Stokes equations closed with equations of the k-ɛ turbulence model are used to calculate the viscous compressible gas flow characteristics and heat transfer; the unsteady heat conduction equation is used to calculate the temperature field in the metal. The influence of the mass flow rate of the coolant on the flow structure and efficiency of cooling of the rotor and stator walls is studied. The calculated results are compared with experimental data.     

Controlling the level of the sonic boom generated by a flying vehicle by means of cryogenic forcing. 3. Physical justification of the cryogenic action

The influence of the basic factors of cryogenic forcing on formation of the middle zone on the sonic boom and aerodynamic characteristics of the flying vehicle is studied by experimental and numerical methods. Experimental data obtained with alcohol or liquid nitrogen as an injected liquid are used for comparisons; as a result, the total effect of temperature and coolant evaporation can be determined. The influence of temperature is studied by means of numerical simulations of the cryogenic action of distributed injection of air. A comparison of numerical and experimental data reveals the effect of the coolant evaporation process on perturbed flow formation. It is demonstrated that evaporation of the coolant outgoing onto the vehicle surface should be intensified to increase the efficiency of cryogenic forcing (to decrease the coolant flow rate).