Exciton-polaritons by two-photon absorption in semiconductors

The creation of excitonic polariton states by two-photon absorption is theoretically investigated. A semi-classical approach is adopted to compute the two-photon transition probability to polariton states through an intermediate exciton state. The numerical results in CuCl show two peaks corresponding to the longitudinal exciton and transverse polariton states, respectively. These results are in good agreement with the experiment.     

Exciton-polaritons in microcavities: present and future

An overview is given of the current research trends in the physics of exciton-polaritons in microcavities. Potential applications of the Bose–Einstein condensation and superfluidity of exciton-polaritons are discussed. The perspectives for the realization of polariton lasers, polariton spin transistors and polarization modulators are presented. PACS 78.67.-n; 71.36.+c; 42.55.Sa; 42.25.Kb     

Exciton-polaritons in lattices: A non-linear photonic simulator

Microcavity polaritons are mixed light–matter quasiparticles with extraordinary nonlinear properties, which can be easily accessed in photoluminescence experiments. Thanks to the possibility of designing the potential landscape of polaritons, this system provides a versatile photonic platform to emulate 1D and 2D Hamiltonians. Polaritons allow transposing to the photonic world some of the properties of electrons in solid-state systems, and to engineer Hamiltonians for photons with novel transport properties. Here we review some experimental implementations of polariton Hamiltonians using lattice geometries.     

Employment of the scattering amplitude in solving the diffraction problems for waves in a halfspace

The problem on the diffraction of an acoustic wave by a finite-size scatterer (inclusion) located in a halfspace is considered. The method of solving this problem is based on the use of the scattering amplitude of the inclusion. A formula analogous to the Green formula is presented. It allows one to determine the scattering amplitude of the inclusion for an arbitrary incident wave (determined by the directional pattern of the source of primary waves) from the scattering amplitude corresponding to plane incident waves. The algorithm is presented for solving the problem on the operation of an acoustically opaque radiator in a halfspace whose boundary is characterized by an arbitrary reflection coefficient. As an example, the problem is solved on the generation of low-frequency oscillations by a sphere with an acoustically soft boundary near an acoustically hard or soft boundary of the halfspace.     

Diffraction of sound by an elastic cylinder near the surface of an elastic halfspace

Diffraction of an acoustic wave by an elastic cylinder near the surface of an elastic halfspace is considered. The solution relies on a Helmholtz-type integral equation and uses the Green function of an elastic halfspace. The latter function is represented in the form of an integral over the Sommerfeld contour on the plane of a complex variable that has the meaning of the angle of the wave incidence on the halfspace boundary. An integral equation for the sound pressure distribution over the cylinder surface is derived. This equation is reduced to an infinite system of equations for the Fourier-series expansion coefficients of this distribution. The results obtained are valid for the diffraction of a cylindrical wave and a plane wave. They also describe the diffraction of a spherical wave when the transmitter and receiver are far from the cylinder and lie in one plane that is orthogonal to the cylinder axis.     

Green's functions and Brewster condition for a halfspace bounded by an anisotropic impedance plane

Dyadic Green's functions are obtained for a halfspace bounded by an anisotropic impedance plane. Using the Fresnel reflection coefficients, these functions are derived in planewave spectral forms. The Brewster condition is also obtained.     

Diffraction of sound by an elastic or impedance sphere located near an impedance or elastic boundary of a halfspace

An exact solution is obtained to the problem of sound diffraction by an elastic or impedance sphere located near an impedance or elastic boundary of a halfspace. The problem is solved using the Helmholtz integral equation in which the field of a point source in the halfspace with an elastic boundary is used as the Green function. The diffracted field is represented as a series expansion in spherical harmonics. The expansion coefficients are determined from a set of independent algebraic systems of equations. The matrix coefficients of these systems are determined as integrals of the products of the associated Legendre polynomials on the complex plane with respect to the real and complex angles of the sound incidence on the halfspace boundary. To decrease the number of such integrals, expansions using the Klebsh-Gordon coefficients are applied. As a result, algorithms for calculating the scattered field in the halfspace are obtained.     

Excitation of seismoacoustic waves by a harmonic force source acting at the boundary of a liquid layer and an elastic halfspace

A problem on the excitation of seismoacoustic waves in a system of a homogeneous isotropic elastic halfspace covered with a liquid layer is solved in the case of action of a source of point harmonic force on the surface of an elastic medium. Integral expressions are obtained for the radiation powers averaged over a wave period for longitudinal and transverse waves in a solid. Mode excitation is analyzed in detail. Expressions describing parts of the mode powers radiated into a liquid layer and an elastic medium are obtained. Numerical analysis of radiation powers is conducted for spherical longitudinal and transverse waves as well as for the radiation powers of seismoacoustic modes in a solid halfspace and a liquid layer. It is determined that in the conditions characteristic of bottom rocks in the case, where the basin depth is several times and more larger than the sound’s wavelength, about 2/3 of the total power is radiated into a liquid.     

Radionuclides in deposition in the Ignalina NPP region in 2005

Results of radionuclide activity concentration measurements in deposition and ground-level air conducted at the station of the Institute of Physics situated 3.5 km from the Ignalina Nuclear Power Plant (Ignalina NPP) in 2005 are analyzed. Atmospheric depositional fluxes of ⁷Be, ⁶⁰Co and ¹³⁷Cs are estimated. Radionuclide particle deposition rates are calculated. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model of the global dispersion and deposition is used to explain variations in the ¹³⁷Cs activity concentration in the ground-level air in the Ignalina NPP region in 2005. An increase in the ¹³⁷Cs activity concentration of up to 17.4 μBq m⁻³ on 30 October-5 November is studied. Modelling results show that the Chernobyl NPP Unit 4 Sarcophagus and the radiocaesium resuspension from the Chernobyl NPP accident polluted regions are sources of ¹³⁷Cs to the environment of the Ignalina NPP. Results on solubility in water of aerosols — carriers of ¹³⁷Cs — are discussed.     

Scale-free phenomenon in industries in China

In this paper, we investigate the data of industries in China and find that the frequency distributions of fixed assets and fixed-assets’ investment of industries obey power laws. We show that these power-law modes can be explained by the rules of the Simon Model, rather than the existing investment theories such as the classical investment theory or acceleration principle. Moreover, the mechanism of the investment distribution may be similar to the forest-fire model of self-organizing criticality. By introducing the complex system methods, this research changes the traditional opinion of the investment and gains some meaningful understanding in the dynamics of industries and the economic cycle.     

High spin states in106in

High spin states have been investigated by the reaction⁹⁰Zr(¹⁹F, 3nγ), using an Anticompton spectrometer device, for the nucleus¹⁰⁶In, for which no in-beamγ-spectroscopic information was available up to now. A level scheme has been constructed up to anI =(13,14) state.     

Universal scaling in BCS superconductivity in three dimensions in non-s waves

The solutions of a renormalized BCS equation are studied in three space dimensions in s, p and d waves for finite-range separable potentials in the weak to medium coupling region. In the weak-coupling limit, the present BCS model yields a small coherence length and a large critical temperature, , appropriate for some high- materials. The BCS gap, , and specific heat as a function of zero-temperature condensation energy are found to exhibit potential-independent universal scalings. The entropy, specific heat, spin susceptibility and penetration depth as a function of temperature exhibit universal scaling below in p and d waves. Received: 18 July 1997 / Revised: 8 September 1997 / Accepted: 29 September 1997     

Supergravity in theory in 11 dimensions

We present the action and transformation laws of supergravity in 11 dimensions which is expected to be closely related to the O(8) theory in 4 dimensions after dimensional reduction.     

Uncertainty in prediction and in inference

The concepts of uncertainty in prediction and inference are introduced and illustrated using the diffraction of light as an example. The close relationship between the concepts of uncertainty in inference and resolving power is noted. A general quantitative measure of uncertainty in inference can be obtained by means of the so-called statistical distance between probability distributions. When applied to quantum mechanics, this distance leads to a measure of the distinguishability of quantum states, which essentially is the absolute value of the matrix element between the states. The importance of this result to the quantum mechanical uncertainty principle is noted. The second part of the paper provides a derivation of the statistical distance on the basis of the so-called method of support.     

Thermal convection in Rivlin-Ericksen elastico-viscous fluid in porous medium in hydromagnetics

The thermal instability of a layer of Rivlin-Ericksen elastico-viscous fluid in porous medium acted on by a uniform magnetic field is considered. For stationary convection, Rivlin-Ericksen elastico-viscous fluid behaves like a Newtonian fluid. The magnetic field is found to have stabilizing effect whereas medium permeability has destabilizing effect. The magnetic field introduces oscillatory modes in the system, A sufficient condition for the non-existence of overstability is also obtained.     

Fano-type features in magnetoabsorption in semiconductors

It is shown that bulk semiconductors exhibit strongly asymmetric Fano-type resonance profiles in magnetoabsorption processes involving the formation of hot electron-hole pairs (EHPs) and accompanied by the scattering of the EHPs by defects. This result is valid for transitions to electronic states with large Landau quantum numbers, when the Coulomb interaction plays a small role. The physical reason for such a sharp change in the magnetoabsorption coefficient as compared with the expected result for the ordinary density of states in a quantizing magnetic field is that the electronic excitations are quasi-one-dimensional. The form of the resonance absorption is in good qualitative agreement with the experimental data. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 619–622 (25 April 1996)