Thermal Radiation Field Research Articles

Friction force with non-instantaneous interaction between moving harmonic oscillators

The friction force acting between two weakly interacting, harmonic oscillators which move slowly with respect to each other, is considered. In a previous paper the case of instantaneous interaction was treated (J.S. H∅ye and I. Brevik, Physica A 181 (1992) 413) and the expression for the force was obtained by use of a variety of methods in statistical mechanics. The present paper deals with the case of non-instantaneous interaction. It turns out that in order to obtain a complete description one has to take into account the medium (e.g., a thermal vacuum field or crystal lattice) through which the interaction propagates. We consider successively the cases where one, respectively two, oscillators are present in interaction with the medium. Our discussion has a bearing on the self-interaction problem in classical electrodynamics. As a check of the general formalism, the self-interaction on a dielectric spherical particle moving in a thermal radiation field is evaluated by considering the momentum transfer from absorbed radiation.

A STUDY ON DISSIPATION MECHANISM IN TWO-PHOTON LASER

In this work, we have respectively investigated two-photon processes of a cascade three-level atom interacting with thermal and vacuum radiation fields by means of non-relativestic QED. We verified the important role of atomic thermal loss and two-photon transtion loss in the disspation processes. We proved the condition under which the thermal fluctuation can be neglected, and discussed, the character of laser cavity in which the two-photon laser can be produced.

Opening Remarks

The following papers formed a Joint Discussion sponsored by Commissions 40, 44, 47 and 48 of the International Astronomical Union. The topic was Cosmic Backgrounds. The plural “backgrounds” is important. Speakers considered electromagnetic radiation fields ranging from radio wavelengths to X-rays. Because other sessions at this General Assembly treated higher energy backgrounds, in particular the X-ray region, emphasis in this Joint Discussion was on radio and infrared backgrounds. In addition to the wide range of wavelengths covered, the session also dealt with a wide range of models for various backgrounds. For instance, at some wavelengths (e.g., λ ~ 1 cm) the background is truly a background, generated at very high redshifts—in this case a thermal radiation field at ~ 3 K. At other wavelengths (e.g., in the X-ray region) the “background” may consist in whole or in part of the summed emission from many unresolved or subliminal sources.

Thermal effect in the resonance fluorescence of a two-level system

The damped two-level system, driven by a strong incident classical field near resonance frequency is subjected to the effect of thermal fluctuations. To simulate the thermal bath we introduce a large system of harmonic oscillators that represents the normal modes of the thermal radiation field. From the Heisenberg equations of motion we calculate the power spectrum of the scattered field and the intensity correlation function. The results show that the presence of the bath dramatically modifies the light scattered by the two-level system when compared with the case without a thermal bath.

Quasi-stationary field of thermal radiation in the theory of contact radiothermometry

Quasi-stationary field of thermal radiation in the theory of contact radiothermometry

Lasers without inversion: A closed lifetime broadened system.

We show a model laser system which operates by an electromagnetically induced interference. Provided that an inversion condition for the thermal radiation field is satisfied, the system lases without atomic population inversion in steady state. The system is pumped by incoherent radiation on the transition on which lasing occurs.

Investigation of gamma and neutron fields around spent reactor fuel by 115In activation

Activation methods based on (γ,γ′) and (n,γ) processes have been developed for investigating hard γ and thermal neutron radiation fields in the vicinity of spent fuel assemblies stored in water. Based on experiments and practical considerations 115In was suggested as a target material both for γ and neutron activations. Fission product and actinide content of irradiated fuel can be assayed by these methods. The use of (γ,n) conversion in Be or D provides an additional tool for analyzing hard γ components. The methods may find application in non-destructive fuel assay. Results suggest the suitability of the methods for reactor operational and nuclear material safeguard purposes.

The radiative deceleration of ultrarelativistic jets in active galactic nuclei

A detailed study of the dynamical interaction between a highly relativistic jet and the thermal radiation field from an AGN accretion disk is reported, and the Comptonized spectrum arising from this interaction is self-consistently determined. A simple model that captures the essential radiative and geometrical features of realistic disk configurations is presented, and the disk radiation field is calculated. The results confirm Phinney's (1987) suggestion that the thermal radiation field produced by accretion in an AGN could be very effective in decelerating ultrarelativistic jets that are accreted by electromagnetic or hydromagnetic forces closer to the central black hole. Terminal Lorentz factors are consistent with the values inferred in superluminal radio sources are readily produced in this model for plausible disk and jet parameters without additional acceleration in the interaction zone. A new interpretation of the hard X-ray component detected in BL Lac spectra is proposed.

Thermal radiation field of low-temperature sources

The asymmetric thermal radiation field of heat sources existing in industry and in the building of apartments has been determined in this work. A description was realised by vector radiant and mean radiant temperatures ( VRT, TMR) obtaining their statistic reciprocal relationships at summer and winter terms.

Geometric view factors for thermal radiation hazard assessment

Estimating the thermal radiation field surrounding a large fire involves characterization of the flame geometry and computation of radiant intensity at a given location. The latter requires computation of geometric view factors. In this article, closed form expressions that are common in the design of impoundment systems. These include tilted cylindrical and rectangular geometries. The computed geometric view factors compare very well with limited experimental data for circular geometries. The closed form expressions allow rapid computation of view factors that are necessary in estimating the fire hazards associated with large hydrocarbon pool fires.

Effect of thermal fluctuations in the resonance fluorescence of a two-level system.

In this work we study the effect of thermal fluctuations in the resonance fluorescence of a two-level system. The damped two-level system is driven by a strong incident classical field near resonance frequency. To simulate the thermal bath we introduce a large system of harmonic oscillators that represent the normal modes of the thermal radiation field. To obtain the time development of the fluorescent light intensity we solve the Heisenberg equations of motion transformed in a system of coupled integral equations by an iterative method. The results show that the presence of the bath modifies dramatically the time development of the fluorescence light intensity when compared with the case T=0 K.

Comment on axion emission rates in stars.

It is pointed out that the emission of axions from stellar plasmas and their reabsorption is stimulated by the thermal radiation field in processes with final-state photons. An expression for the bremsstrahlung emissivity of a stellar plasma is given for the nonrelativistic, degenerate regime. Some other aspects of a recent calculation by Pantziris and Kang of stellar axion emissivities are discussed.

Steepening of waves in radiative magnetohydrodynamics

Singular surface theory is used to determine the modes of wave propagation and development of discontinuities at planar and cylindrical wave fronts. It is investigated as to how the effects of thermal radiation and magnetic field strength influence the steepening and flattening of wave fronts. Although the effect of magnetic field, whether axial or azimuthal, is to increase the shock formation distance, it, unlike the effect of thermal radiation, cannot offset the tendency of a compression wave-head, carrying a jump discontinuity (no matter how weak initially), to grow into a shock wave after a finite running length. In an optically thick gas with negligible radiation pressure and energy, an increase in the radiative flux reduces the shock formation distance; this is in contrast to the corresponding result for an optically thin gas where an increase in the radiative flux causes shock formation distance to increase. However, numerical calculations show that in a temperature range 9 × 10 4 < T < 2 × 10 5, the combined effect of radiation pressure, energy and flux is to delay the formation of a shock wave. It is found that the decaying of expansion waves is enhanced (slowed down) due to the presence of thermal radiation (magnetic field).

A Method For Calculating The Configuration Factor Between A Flame And A Receiving Target For A Wide Range Of Flame Geometries Relevant To Large Scale Fires

To predict the thermal radiation field surrounding a fire, it is necessary to know the configuration factor between the flame and the receiving target. This requirement has previously imposed restrictions on the range of geometries that could be selected to represent the shape of flames. A method has therefore been developed which will enable the configuration factor to be calculated for any flame shape and has been applied to a particular geometrical configuration that can be used to represent a wide range of flame shapes associated with large fires. The method also allows the alignment of a target that is subjected to the maximum incident thermal radiation to be identified. This is of particular interest when studying radiant heat transfer.

Solar and thermal radiation in the Venus atmosphere

Attention is given to the solar and thermal radiation fields of Venus. Direct measurements and the results of numerical models based on direct measurements are presented. Radiation outside the atmosphere is considered with emphasis placed on global energy budget parameters, spectral and angular dependences, spatial distribution, and temporal variations of solar and thermal radiation. Radiation fluxes inside the atmosphere below 90 km are also considered with attention given to the solar flux at the surface, solar and thermal radiation fluxes from 100 km to the surface, and radiative heating and cooling below 100 km.

Some soluble models for periodic decay and revival

The authors present three analytically tractable models for a two-level atom interacting with a coherent or thermal radiation field and study the behaviour of the atomic excitation energy for various initial conditions.

Improvement of the Two-Temperature Radiative Transport Model

The frequency dependence of a thermal radiation field complicates the computation of radiative energy transport in optically thin media because the spectrum may be uncoupled from local thermodynamic conditions. A model for combining the effect of the frequency dependence into a radiation temperature chosen to represent the temperature of both local and nonlocal emitting regions is described. The derived equations are much easier to solve than the frequencydependent equations and can be applied to a broad class of problems. The equations are used to investigate the response of a gas in an inertial confinement fusion (ICF) reaction chamber to target explosions. The response is compared for ambient densities of 1.77 x 10/sup 18/ and 1.77 x 10/sup 17/ atom/cm/sup 3/. The error in using the brightness temperature instead of a color temperature to evaluate the opacities is illustrated. An analytic analysis shows the cooling wave observed from energy releases > 10/sup 18/ erg will not occur in an ICF cavity. This is confirmed by the numerical calculations.

Structure of thermal radiation field in an optically thick limit

The transport of radiation in the optically thick limit is investigated when the temperature profile within the medium is specified and continuous, and when the medium under consideration is not in radiative equilibrium. Results show that the equation governing the transport of incident radiation becomes mathematically singular as the optical thickness becomes large. It is shown that this singularity is an attribute of a small parameter epsilon, which is inversely proportional to the square of the optical thickness, multiplying the highest derivative of the differential equation. It is found that in the optically thick limit, away from the wall the radiation field is near equilibrium, such that up to 0(epsilon) the rates of absorption and emission of radiation are equal. In the near-wall region, however, the absorption and emission rates are different by 0(epsilon to the 1/2). Thus, the magnitude of the divergence of radiative heat flux changes by 0(epsilon to the 1/2) as the wall is approached from the far region, and there exists a radiation boundary layer for the incident radiation in the limit of optical thickness becoming very large.

Quantum revivals of a two-level system driven by chaotic radiation

Abstract The time-evolution of a two-level system interacting with a single-mode chaotic (or thermal) radiation field is investigated using the fully quantized Jaynes-Cummings model and results are compared with a semiclassical model. Decay and a quiescent period are found in both but interfering revivals which depend critically on the mean quantum number are found only in the quantized model.

Basic research needs and opportunities at the Solid-Solid interface: Diffusion

An attempt is made to identify the basic research needs and opportunities which exist with respect to S—S interfaces and diffusion in materials and devices relevant to solar energy. Firstly, the generic problems characteristic of solar energy materials are considered. Secondly, the specific problems involving S—S interfaces and diffusion which are peculiar to solar energy materials are described and discussed. Thirdly, the research needs and opportunities associated with these phenomena are identified. General areas of research considered to be “crucial”, “important” or “useful” include the following: (1) the development of microstructure; (2) the microstructural stability; (3) the dependence of diffusion and nucleation of new structures on external influences (especially thermal cycling, electric fields and radiation fields); (4) the acquisition of standard reference data (S—S interface diffusion and electrical data); (5) the relationship between microstructure (and its time dependence) and electrical, optical and mechanical properties of composite materials. Finally, priorities are assigned to a number of research areas falling within the above categories.