Nonrenormalizable superpotential in four-dimensional string models

A construction of an effective nonrenormalizable superpotential has been discussed within the approach of a four-dimensional heterotic superstring with free fermions on the world sheet. On the basis of N=2 superconformal theory, useful selection rules that take into account all global symmetries have been obtained within the formalism of covariant vertices and the ghost-picture-changing operation. The results have been applied to the model featuring the effective observable gauge group U(5)×U(3)_H, which includes the non-Abelian horizontal group and which describes (3+1) generation. The full superpotential of the model up to sixth order inclusive has been obtained, and its coupling constants have been calculated. The quark-lepton mass spectrum of the model has been discussed with allowance for contributions from nonrenormalizable terms.     

Qualitative analysis of a three-dimensional population evolution model with possible nonequilibrium size preservation

A three-dimensional mathematical model of nonhomogeneous population dynamics with selection and birth-and-death processes is considered. Bifurcations of operating modes are determined and conditions for extinction, degeneration, and stabilization are established. Translated from Nelineinaya Dinamika i Upravlenie, pp. 71–89, 1999.     

Excitation and decay of low-lying nuclear states in a dense plasma produced by a subpicosecond laser pulse

The excitation of low-lying nuclear levels in a hot, dense plasma, produced by a subpicosecond pulse with intensity exceeding 10¹⁶ W/cm², is investigated theoretically and experimentally. The basic channels of electronic (inelastic scattering and inverse internal electron convergence) and photon (photoexcitation) excitations of such states as well as the influence of the broadening of a nuclear level on the excitation efficiency and the presence of hot electronic component are examined. The experimental data from measurements of the decay kinetics of the low-lying nuclear level 6.238 keV of the stable isotope ¹⁸¹Ta, which were obtained on two experimental laser systems, are presented.     

Solubility of gases in uniaxially strained crystals

The solubility of gases in uniformly strained bcc crystals is calculated. As a result of straining, interstices occupied by interstitial atoms become nonequivalent and the temperature dependence of the solubility changes. The effect of deformation depends substantially on the sign of energy of interaction v _AC between dissolved atoms and host-crystal atoms. For elastic uniaxial tension, the solubility decreases linearly with strain at v _AC >0; at v _AC <0, it increases with strain. The amount of this effect is 1–10%. The effect of complexes consisting of two nearest dissolved atoms is studied. Conditions at which the role of the complexes is substantial are found. The complexes increase the solubility and change its dependence on the gas pressure.     

Database for rapid protein classification based on small-angle X-ray scattering data

A method was developed for rapid protein classification based on comparison of the experimental small-angle X-ray scattering data with scattering curves calculated for proteins with known structures. For this purpose, a database was compiled from about 1500 theoretical scattering curves for proteins with known structures. The potential of this method was illustrated by its application to analysis of the experimental scattering data from sperm whale myoglobin.     

Chaotic tunneling in a laser field

We study the driven tunneling of a one-dimensional charged particle confined to a rectangular double well. The numerical simulation of the Schrödinger equation based on the Cranck-Nicholson finite-difference scheme shows that the modulation of the amplitude of the external field may result in parametric resonance. The latter is accompanied by the breakdown of the quasi-periodic motion characteristic of the usual driven tunneling and the emergence of irregular dynamics. We describe the above breakdown with the occupation probability for the ground state of the unperturbed system and create the visualization of the irregular dynamics with the help of Shaw-Takens’ reconstruction of the state space. Both approaches agree concerning the values of the resonant frequency for the parametric excitation. Our results indicate that the shape of the laser pulse could be essential for generating chaotic tunneling.     

Structural Parameters of Cellulose Produced by Acetobacter Xylinum and Their Variation in the Course of Drying of Gel Films

The cellulose-producing power of the VKM V-800 Acetobacter xylinum strain under conditions of static culture was studied. The culture medium was optimized with the aim to increase the cellulose yield and obtain highly crystalline cellulose I with molecular weight of about 5 × 10⁵.     

Influence of neutron irradiation on the martensitic transformations and shape-memory effect in a TiNi alloy

The paper reports measurements of the strains and electrical resistance of a TiNi shape-memory alloy under irradiation in the low-temperature helium circuit of a nuclear reactor. Irradiation of the alloy in martensitic state at 170 K revealed that the transition temperatures from cubic to rhombohedral and from rhombohedral to monoclinic phase decrease exponentially with increasing dose. No change in the shape-memory effects and transformation plasticity was observed up to a dose of 6.7×10²² n/m². Keeping the sample at 340 K without irradiation restores (increases) partially the transition temperatures. The relations observed can be assigned to a change in the degree of long-range order in the lattice caused by neutron irradiation. Fiz. Tverd. Tela (St. Petersburg) 40, 1705–1709 (September 1998)     

<Emphasis Type="Italic">ππ</Emphasis> scattering in a nonlocal chiral quark model

We consider a nonlocal version of the Nambu and Jona-Lasinio model with the SU(2) × SU(2) chiral symmetry broken by the current-quark-mass term. The nonlocality is contained in the quark-antiquark bilinears of the four-quark vertices as a form factor of the Gaussian type. The model has three parameters which can be fixed in favor of the values of the pion mass mπ, the pion decay constant fπ, and the current quark mass m _c . It is shown that, in the model, the main low-energy theorems which are known for pions are fulfilled. The s-, p-, and d-wave scattering lengths in all isotopic channels and the s-wave slope parameters are calculated, and the results are in satisfactory agreement with phenomenological data. The text was submitted by the authors in English.     

Limit Cycles Arising in a Chain of Inhibitorily Coupled Identical Relaxation Oscillators Near the Self-Oscillation Threshold

We consider the dynamic regimes arising in a linear chain of four identical stiff FitzHugh- Nagumo oscillators existing in the vicinity of the bifurcation of limit cycle emergence. It is shown that in a broad range of coupling forces, slow-variable exchange between the oscillators gives rise to multiple limit cycles with different periods and different phase relations. In addition to the expected antiphase solutions, three families of stable limit cycles that differ in the number of bursts of the fast variable in the neighboring elements and in the number of bursts per period are detected. The boundaries of attractor stability are calculated and the parameter regions of their coexistence are found.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 3, pp. 238–248, March 2005.