Self-organized periodic photonic structure in a nonchiral liquid crystal

A hybrid-aligned cell of the smectic A liquid material 8CB gives two stable director configurations, one of which is periodic and gives strong diffraction of light. This photonic lattice director profile arises from "frustration" caused by conflicting constraints imposed by the boundary conditions and the constant amplitude smectic density wave. A model is proposed which accords well with the experiment results, predicting correctly the dependence of the periodicity on the cell thickness and reproducing optical polarization microscopy results.     

First observation of a negative elastic constant in intermediate valent TmSe

The sound velocities v_L, v_T1 and v_T2 have been measured at 15 MHz on Tm³⁺_0.87Se and Tm^2.8+_0.99Se between 300 K and 4.2 K and the elastic constants c_ij have been derived. In intermediate valent Tm^2.8+_0.99Se c₁₂ turned out to be negative. This sign is interpreted as being typical for intermediate valent compounds. Also for the first time experimental evidence is given for crystal field effects in Tm³⁺_0.87Se. Strong elastic nonlinearities are observed in intermediate valent Tm^2.8+_0.99Se with uniaxial pressure.     

Tunnelling with a negative cosmological constant

The point of this paper is to see what light new results in hyperbolic geometry may throw on gravitational entropy and whether gravitational entropy is relevant for the quantum origin of the universe. We introduce some new gravitational instantons which mediate the birth from nothing of closed universes containing wormholes and suggest that they may contribute to the density matrix of the universe. We also discuss the connection between their gravitational action and the topological and volumetric entropies introduced in hyperbolic geometry. These coincide for hyperbolic 4-manifolds, and increase with increasing topological complexity of the 4-manifold. We raise the question of whether the action also increases with the topological complexity of the initial 3-geometry, measured either by its 3-volume or its Matveev complexity. We point out, in distinction to the non-supergravity case, that universes with domains of negative cosmological constant separated by supergravity domain walls cannot be born from nothing. Finally we point out that our wormholes provide examples of the type of Perpetual Motion machines envisaged by Frolov and Novikov.     

Spontaneous parametric transition from periodic motion to chaos in a dynamical system with two degrees of freedom

A study is made of a spontaneous parametric transition to chaos by the disruption of periodic motion in a generating structure with two degrees of freedom. A comparison of the properties of the system examined in this study and the properties of objects with an infinite-dimensional phase space shows the universality of the spontaneous parametric scenario for a loss of stability of periodic motion that leads to randomization of the oscillatory process. Tomsk University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 2, pp. 91–95, February, 1999.     

The width of the magnetic transition in CoO from elastic constant studies

The elastic constant C₁₁ of single crystal CoO has been measured in the vicinity of the Néel temperature and the effect of annealing on the transition width has been studied. A value of 2.62×10¹¹ Nm^-2 at 295 K was obtained for C₁₁.     

Coexisting orders in the quarter-filled Hubbard chain with elastic deformations

The electronic properties of the quarter-filled extended Peierls-Holstein-Hubbard model that includes lattice distortions and molecular deformations are investigated theoretically using the bosonization approach. We predict the existence of a wide variety of charge-elastic phases depending of the values of the Peierls and Holstein couplings. We also study perturbatively the effects of the Peierls deformation in the nearest-neighbor repulsion V, that may be present in real materials where Coulomb interactions depend strongly on the distance. Our results indicate that the phase diagram may change substantially with V when this term is taken into account.     

The Planck era with a negative cosmological constant and cosmic strings

In the present Letter, we consider the DeBroglie-Bohm interpretation of quantum Friedmann-Robertson-Walker (FRW) models in the presence of a negative cosmological constant and cosmic strings. We compute Bohm's trajectories and quantum potentials for a quantity related to the scale factor.     

Measurement of the interlayer elastic constant in a liquid crystal close to the smectic A—nematic transition

Brillouin scattering has been used to obtain first order elastic constants in 8CB. In contrast to earlier measurements the interlayer constant is found to be finite as T approaches the smectic A—nematic transition. These results confirm recent theoretical predictions.     

Scattering by a random field of elastic deformations in neutron-bombarded GaAs

The contribution to electron scattering due to a random field of elastic deformations produced by defects in GaAs caused by neutron irradiation is calculated. Under the assumption of smallness of the radius of correlation of the random field and the parameter values used earlier to interpret the optical absorption spectrum, the influence of this scattering mechanism on the mobility is estimated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 51–53, June, 1987.     

Ground state of a periodic elastic atomic chain in an arbitrary periodic potential

The ground state of a periodic elastic atomic chain in a periodic potential has been investigated. The tensile strain and potential energy of the chain have been found as functions of the disproportion parameter. Exact solutions differ from those found in the continuous approximation by the P symmetry and smaller regions of commensurate phases.     

On the Peierls transition in a periodic potential

The properties of a one-dimensional conductor in the presence of an external periodic potential V_Q have been investigated. The low temperature gap is enhanced, the temperature dependence of the gap Δ(T) is smeared at T_PF, the Peierls transition temperature in the absence of V_Q, and hence there is no longer a real phase transition. We also relate the phase pinning frequency ω_ø to the size of V_Q.     

Velocity and diffusion constant of a periodic one-dimensional hopping model

The velocity and the diffusion constant are obtained for a periodic onedimensional hopping model of arbitrary periodN. These two quantities are expressed as explicit functions of all the hopping rates. The velocity and the diffusion constant of random systems are calculated by taking the limit N→Β. One finds by varying the distribution of hopping rates that the diffusion constant and the velocity are singular at different points. Lastly, several possible applications are proposed.     

Propagation of acoustic waves in a fluid-filled pipe with periodic elastic Helmholtz resonators

Helmholtz resonators are widely used to reduce noise in a fluid-filled pipe system. It is a challenge to obtain lowfrequency and broadband attenuation with a small sized cavity. In this paper, the propagation of acoustic waves in a fluid-filled pipe system with periodic elastic Helmholtz resonators is studied theoretically. The resonance frequency and sound transmission loss of one unit are analyzed to validate the correctness of simplified acoustic impedance. The band structure of infinite periodic cells and sound transmission loss of finite periodic cells are calculated by the transfer matrix method and finite element software. The effects of several parameters on band gap and sound transmission loss are probed.Further, the negative bulk modulus of periodic cells with elastic Helmholtz resonators is analyzed. Numerical results show that the acoustic propagation properties in the periodic pipe, such as low frequency, broadband sound transmission, can be improved.     

Degenerate resonant interaction of light with two-photon transition in a periodic medium

The formation of soliton-like structures in a periodic medium containing impurity atoms with resonant two-photon transition degenerate over the magnetic moment projection is studied. For small field amplitudes, the evolution equations are derived and the solutions are obtained, which describe nonlinear polarization effects.     

Decay of a negative molecular ion in a constant electric field

The problem of the shift and broadening of the electron energy levels in the field of two 3D short-range potentials (e.g., the model of a negative molecular ion) by a constant electric field F is considered. The interaction of an electron with attraction centers is taken into account in the effective range approximation. We analyze the cases when both centers maintain weakly bound s states and when the electron state in the field of one of the centers is a p state. Exact numerical results for the shift and the width of the energy levels of a quasi-molecule as functions of field F, distance R between atomic centers, and the orientation of the quasi-molecule axis relative to vector F are presented, as well as the results of analytic treatment for a number of limiting cases. The exact values of complex energies of the quasi-molecule are compared with analytic results for a weak field in the case of identical s centers [26], as well as nonequivalent s centers and s-p centers; the applicability boundaries of the weak field approximation are established. It is shown that for large values of R, the position and width of the levels in a strong field are correctly described in perturbation theory in the exchange interaction. We analyze the field-induced quasi-intersection of molecular energy levels of the system with nonequivalent atomic centers and peculiarities in the energy level widths associated with this intersection. The results make it possible to qualitatively interpret the results of numerical calculations of the probability of homo- and heteronuclear molecules being ionized by a low-frequency laser field.     

Quantum glass transition in a periodic long-range Josephson array

We show that the ground state of a periodic long-range Josephson array frustrated by a magnetic field is a glass for sufficiently large Josephson energies despite the absence of quenched disorder. Like superconductors, this glass state has non-zero phase stiffness and Meissner response; for lower Josephson energies the glass “melts” and the ground state loses its phase stiffness and becomes insulating. We find the critical scaling behavior near this quantum phase transition: the excitation gap vanishes as (J−J _c )², and the frequency-dependent magnetic susceptibility behaves as . Zh. éksp. Teor. Fiz. 116, 1450–1461 (October 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Non-singular space-times with a negative cosmological constant: V. Boson stars

We prove existence of large families of solutions of Einstein-complex scalar field equations with a negative cosmological constant, with a stationary or static metric and a time-periodic complex scalar field.