Quantum effects in the transient dynamics of a many mode Jaynes-Cummings model

Abstract

Phenomenology and mechanisms of energy exchange, due to induced atomic processes of absorption and emission, are investigated in the evolution of a two-mode Jaynes-Cummings model. One field mode is initially in a highly coherent populated state and the other one is initially empty. The field mode exchanges energy with the atom by two mechanisms, related to very different atomic dynamics, which operate in complementary phases of the system evolution. One mechanism determines the energy exchanges which involve only the populated mode and the atom. The other is responsible for mode-mode photon exchanges and becomes relevant when the first mechanism is quenched. Thus there is no competition between the atomic emission in the empty mode and processes involving the atom and the highly populated mode. Quantum features related to entanglement of atom and field states are discussed. Cooperative effects between the two field modes and their incompatibility with the predictions of neo-classical theory are evidenced.     

Description of mass-exchange processes in porous media at low values of the Peclet number

The small perturbation method is used to construct equations for two approximations with respect to the Peclet number for the problem of mass exchange in a porous medium with mass sources.     

The effect of the resonant mode structure on flux tunneling in SQUIDs

The problem of macroscopic quantum tunneling in SQUIDs is discussed, taking into account the resonant mode structure of typical devices. These are evaluated for the particular case of a SQUID formed from a conical point intersecting a hemispherical cavity, and it is shown that the conventional representation of a SQUID as a Josephson junction in parallel with an inductor and a capacitor is a good first approximation in most cases, provided the inductance and capacitance used are those of the whole device rather than of the weak link alone. The discussion is extended to another case of practical importance, where such a cavity is connected to an outer hole by a flange, and it is found that if the capacitance of the flange is large, the tunneling behavior is largely independent of the presence of the outer hole, apart from the effects of any dc bias.     

The problem of the free convection near a horizontal cylinder with constant thermal flux at the surface

Using Shvets's method we solve the problem of the stationary free convection of a viscous fluid near a horizontal cylinder with constant thermal flux at the surface. From the solution we find the thickness of the laminar boundary layer at the cylinder and the temperature and velocity distributions in it.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 4, pp. 727–730, April, 1970.     

The influence of a spatially non-homogeneous trap distribution on the transient currents in insulating layers at high fields

In this paper the influence of a spatially non-homogeneous trap distribution on the transient currents in insulating layers for high fields, weak injection and fast trapping is discussed. Two approximate solutions to the transport equations are obtained by including a non-homogeneous trap distribution in the previous formulation of Arnett (P. C. Arnett), J. Appl. Phys., 46 (1975) 5236); the discharge of the layer is also considered. The spatial behaviour of the trap density is assumed to be exponential and this is applied to the solutions obtained. Formulae relating the trap distribution parameters to electrically measurable quantities are proposed.     

On the problem of the phase relations in the B-BN system at high pressures and temperatures

Phase relations and chemical interaction in the B-BN system have been studied in situ using X-ray diffraction with synchrotron radiation at pressures to 5.3 GPa and temperatures to 2700 K. The results obtained have been used for the thermodynamic analysis of this system and for the construction of its phase diagram at 5 GPa. The values of thermodynamic functions of the phases competing in the B-BN system at high pressures and temperatures have been calculated in the framework of phenomenological models, unknown parameters of which have been found from the experimental data. It has been shown that only one thermodynamically stable boron subnitride (rhombohedral B₁₃N₂) exists in the system. It melts incongruently and forms an eutectic equilibrium with boron.     

The effects of shear and near tip deformations on energy release rate and mode mixity of edge-cracked orthotropic layers

In this paper semi-analytical expressions are derived for the energy release rate and the stress intensity factors of edge-cracked homogeneous and orthotropic layers subject to arbitrary generalized end forces. The expressions are accurate for long and short cracks. Following the work of Li et al. [Li S, Wang J, Thouless MD. The effects of shear on delamination in layered materials. J Mech Phys Solids 2004;52(1):193-214] for isotropic bi-material layers, the derivation extends the method proposed by Suo [Suo ZG. Delamination specimens for orthotropic materials. J Appl Mech 1990;57(3):627-34] for axial forces and bending moments in order to include the contribution of the shear forces. The shear contribution to the fracture parameters depends on the shear deformations along the layer and the elastic near tip deformation of the material. Li et al. [Li S, Wang J, Thouless MD. The effects of shear on delamination in layered materials. J Mech Phys Solids 2004;52(1):193-214] derived semi-analytical expressions for the fracture parameters that depend on the crack tip stress resultants, the elastic constants and five numerically-determined constants globally describing the effect of shear. In this paper analogous constants are derived for orthotropic layers and defined by semi-analytical expressions that highlight their physical significance and allow separation of the different contributions. The derivation is based on the assumption that the near tip deformation can be described by means of relative rotations between the cross sections of the different sub-layers at the crack tip (root rotations). The root rotations depend linearly on the crack tip stress resultants through compliance coefficients that are derived numerically in the paper for a wide range of orthotropic materials. Applications to different mixed mode delamination and peeling problems, for which accurate two-dimensional finite element solutions can be found in the literature, highlight the accuracy of the proposed expressions.     

Investigation of the fatigue strength of steel DI-22 at normal and high temperature

Strength of Materials -     

Measurement and simulation of lineal energy distribution at the CERN high energy facility with a tissue equivalent proportional counter

The response of a tissue equivalent proportional counter (TEPC) in a mixed radiation field with a neutron energy distribution similar to the radiation field at commercial flight altitudes has been studied. The measurements have been done at the CERN-EU High-Energy Reference Field (CERF) facility where a well-characterised radiation field is available for intercomparison. The TEPC instrument used by the ARC Seibersdorf Research is filled with pure propane gas at low pressure and can be used to determine the lineal energy distribution of the energy deposition in a mass of gas equivalent to a 2 mum diameter volume of unit density tissue, of similar size to the nuclei of biological cells. The linearity of the detector response was checked both in term of dose and dose rate. The effect of dead-time has been corrected. The influence of the detector exposure location and orientation in the radiation field on the dose distribution was also studied as a function of the total dose. The microdosimetric distribution of the absorbed dose as a function of the lineal energy has been obtained and compared with the same distribution simulated with the FLUKA Monte Carlo transport code. The dose equivalent was calculated by folding this distribution with the quality factor as a function of linear energy transfer. The comparison between the measured and simulated distributions show that they are in good agreement. As a result of this study the detector is well characterised, thanks also to the numerical simulations the instrument response is well understood, and it's currently being used onboard the aircrafts to evaluate the dose to aircraft crew caused by cosmic radiation.     

Creep of medium and high strength aluminum alloys at normal temperature in moist atmospheres

Direct data have been obtained for the creep of high- and medium-strength aluminum alloys in the stress range of O.6–1.2 of the nominal yield strength _0.2 in laboratory air and in aqueous NaCl solution at room temperature. On this basis using known theories approximating functions have been determined for the creep curves. Stress _0.2 serves as a natural boundary for the macroelastic and macroplastic regions in the first of which creep is only transient, and in the second there are transient, quasisteady-state, and accelerated stages. Extrapolated estimates of creep strain in the macroelastic region from data measured in the macroplastic region are not physically competent. However, a tendency towards an increase in ductility with an increase in time to failure at stresses greater than _o.2 makes it possible to estimate by extrapolation the time for onset of the accelerated creep stage with low test stresses from measured values at greater stresses in the macroplastic region. Fractographic and strain indices revealed the harmful effect of moist atmospheres on the deformation and failure resistance of alloys with prolonged loading.Translated from Problemy Prochnosti, No. 1, pp. 50–58, January, 1990.     

Experimental measurements and modeling of transient heat transfer in forced flow of He II at high velocities

An experiment has been built to study heat transfer in forced flow of He II at flow velocities up to 22 m/s. The main part of this experiment is a 10 mm ID, 0.86 m long straight test section instrumented with a heater, thermometers and pressure transducers. The high flow velocities allow clear observation of the effects of the forced convection, counterflow heat transfer and the Joule–Thomson effect. A numerical model based on the He II energy conservation equation and including pressure effects has been developed to compare with the experimental results. The model works well for low flow velocities where the heat flux is primarily driven by the temperature gradient and for high flow velocities where the heat flux is primarily driven by the pressure gradients. In the intermediate velocity region, discrepancies between the model and experiment may result from an inappropriate representation of the heat flux by counterflow when the temperature and pressure gradients have an effect of similar magnitude on the heat flux.     

The avalanche ionization rate in argon and krypton measured at the shockwave Mach numbers close to the flow instability development threshold

The ionization rates of argon and krypton were measured in a relaxation zone behind the shockwave front for the Mach numbers corresponding to stable flow regimes close to the threshold for development of the flow instability of types I and II. The experimental rates of the avalanche ionization exceed theoretical predictions. It is suggested that the discrepancy is related to the existence of an additional channel for the energy transfer between particles.     

The pinning enhancement upon the magnetic flux trapping in the clusters of a normal phase with fractal boundaries

The phenomenon of magnetic flux trapping in a hard superconductor with the normal phase clusters acting as the pinning centers is considered. The critical current distribution for the clusters of an arbitrary fractal dimension is determined. The fractal character favors the magnetic flux trapping, thus increasing the critical current.     

Effects of electric field and poling on the mode I energy release rate in cracked piezoelectric ceramics at cryogenic temperatures

We discuss the mode I energy release rate of a rectangular piezoelectric material with a crack under electromechanical loading at cryogenic temperatures. A crack was created normal or parallel to the poling direction, and electric fields were applied parallel or normal to the poling. A plane strain finite element analysis was carried out, and the effects of electric field and localized polarization switching on the energy release rate were discussed for the piezoelectric ceramics at cryogenic temperatures.     

The role of heat flux in the nonsteady thermal problem of molybdenum sphere cooling in an electrostatic levitation experiment

Abstract—The method for determining time dependences of the entropy-production density, force, and heat flux are presented. This method is based on processing the experimental thermogram at electrostatic levitation during spontaneous cooling of a solid molybdenum sphere. The results of numerical simulation of cooling a spherical sample from melting temperature T _m ≈ 2880 K showed that the isothermal approximation for the temperature field in the sphere is valid, which made it possible to pass to the entropy density and calculate its production density. It is shown that heat flux in the time-dependent thermal problem under consideration determines the time dependence of the entropy production (it tends to the minimum zero value while approaching ambient temperature) and, therefore, is responsible for the validity of the extremum principle.