Showing papers on "Thermal radiation published in 1985"

Photon and dilepton emission from the quark-gluon plasma: Some general considerations.

Abstract: The emission rates for photons and di-leptons from a quark-gluon plasma is related to the thermal expectation value of an electromagnetic current-current correlation function. This correlation function possesses an invariant tensor decomposition with structure functions entirely analogous to W/sub 1/ and W/sub 2/ of deep inelastic scattering of leptons from hadronic targets. The thermal scaling properties of the appropriate structure functions for thermal emission are derived. The thermal structure functions may be computed in a weak coupling expansion at high plasma temperature. The rates for thermal emission are estimated, and for di-leptons, the thermal emissions rate is argued to dominate over the Drell-Yan process for di-lepton masses 600 MeV < M < 1 to 2 GeV using conservative estimates of the plasma temperature. We argue that higher temperatures are entirely possible within the context of the inside-outside cascade model of matter formation, perhaps temperatures as high as 500 to 800 MeV. If these high temperatures are achieved, the maximum di-lepton masses arising from thermal emission are argued to be 5 GeV. Signals for thermal emission are presented as the relative magnitude of invariant thermal structure functions, thermal scaling relations, and transverse momenta of thermal di-lepton pairs increasing with and proportionalmore » to the di-lepton pair mass. The transverse mass spectra is given for a high temperature plasma. The dependence of the spectra of thermal emission upon the existence of a first phase transition is studied. We argue that if there is a first order phase transition, as beam energy or nuclear baryon number is raised through the threshold for production of a plasma, the rate for photon or di-lepton emission might dramatically increase.« less

Radiative processes in astrophysics.

Abstract: Chapter 1 Fundamentals of Radiative Transfer 1.1 The Electromagnetic Spectrum Elementary Properties of Radiation 1.2 Radiative Flux Macroscopic Description of the Propagation of Radiation Flux from an Isotropic Source-The Inverse Square Law 1.3 The Specific Intensity and Its Moments Definition of Specific Intensity or Brightness Net Flux and Momentum Flux Radiative Energy Density Radiation Pressure in an Enclosure Containing an Isotropic Radiation Field Constancy of Specific Intensity Along Rays in Free Space Proof of the Inverse Square Law for a Uniformly Bright Sphere 1.4 Radiative Transfer Emission Absorption The Radiative Transfer Equation Optical Depth and Source Function Mean Free Path Radiation Force 1.5 Thermal Radiation Blackbody Radiation Kirchhoff's Law for Thermal Emission Thermodynamics of Blackbody Radiation The Planck Spectrum Properties of the Planck Law Characteristic Temperatures Related to Planck Spectrum 1.6 The Einstein Coefficients Definition of Coefficients Relations between Einstein Coefficients Absorption and Emission Coefficients in Terms of Einstein Coefficients 1.7 Scattering Effects Random Walks Pure Scattering Combined Scattering and Absorption 1.8 Radiative Diffusion The Rosseland Approximation The Eddington Approximation Two-Stream Approximation Problems References Chapter 2 Basic Theory of Radiation Fields 2.1 Review of Maxwell's Equations 2.2 Plane Electromagnetic Waves 2.3 The Radiation Spectrum 2.4 Polarization and Stokes Parameters 62 Monochromatic Waves Quasi-monochromatic Waves 2.5 Electromagnetic Potentials 2.6 Applicability of Transfer Theory and the Geometrical Optics Limit Problems References Chapter 3 Radiation from Moving Charges 3.1 Retarded Potentials of Single Moving Charges: The Lienard-Wiechart Potentials 3.2 The Velocity and Radiation Fields 3.3 Radiation from Nonrelativistic Systems of Particles Larmor's Formula The Dipole Approximation The General Multipole Expansion 3.4 Thomson Scattering (Electron Scattering) 3.5 Radiation Reaction 3.6 Radiation from Harmonically Bound Particles Undriven Harmonically Bound Particles Driven Harmonically Bound Particles Problems Reference Chapter 4 Relativistic Covariance and Kinematics 4.1 Review of Lorentz Transformations 4.2 Four-Vectors 4.3 Tensor Analysis 4.4 Covariance of Electromagnetic Phenomena 4.5 A Physical Understanding of Field Transformations 129 4.6 Fields of a Uniformly Moving Charge 4.7 Relativistic Mechanics and the Lorentz Four-Force 4.8 Emission from Relativistic Particles Total Emission Angular Distribution of Emitted and Received Power 4.9 Invariant Phase Volumes and Specific Intensity Problems References Chapter 5 Bremsstrahlung 5.1 Emission from Single-Speed Electrons 5.2 Thermal Bremsstrahlung Emission 5.3 Thermal Bremsstrahlung (Free-Free) Absorption 5.4 Relativistic Bremsstrahlung Problems References Chapter 6 Synchrotron Radiation 6.1 Total Emitted Power 6.2 Spectrum of Synchrotron Radiation: A Qualitative Discussion 6.3 Spectral Index for Power-Law Electron Distribution 6.4 Spectrum and Polarization of Synchrotron Radiation: A Detailed Discussion 6.5 Polarization of Synchrotron Radiation 6.6 Transition from Cyclotron to Synchrotron Emission 6.7 Distinction between Received and Emitted Power 6.8 Synchrotron Self-Absorption 6.9 The Impossibility of a Synchrotron Maser in Vacuum Problems References Chapter 7 Compton Scattering 7.1 Cross Section and Energy Transfer for the Fundamental Process Scattering from Electrons at Rest Scattering from Electrons in Motion: Energy Transfer 7.2 Inverse Compton Power for Single Scattering 7.3 Inverse Compton Spectra for Single Scattering 7.4 Energy Transfer for Repeated Scatterings in a Finite, Thermal Medium: The Compton Y Parameter 7.5 Inverse Compton Spectra and Power for Repeated Scatterings by Relativistic Electrons of Small Optical Depth 7.6 Repeated Scatterings by Nonrelativistic Electrons: The Kompaneets Equation 7.7 Spectral Regimes for Repeated Scattering by Nonrelativistic Electrons Modified Blackbody Spectra y"1 Wien Spectra y"1 Unsaturated Comptonization with Soft Photon Input Problems References Chapter 8 Plasma Effects 8.1 Dispersion in Cold, Isotropic Plasma The Plasma Frequency Group and Phase Velocity and the Index of Refraction 8.2 Propagation Along a Magnetic Field Faraday Rotation 8.3 Plasma Effects in High-Energy Emission Processes Cherenkov Radiation Razin Effect Problems References Chapter 9 Atomic Structure 9.1 A Review of the Schrodinger Equation 9.2 One Electron in a Central Field Wave Functions Spin 9.3 Many-Electron Systems Statistics: The Pauli Principle Hartree-Fock Approximation: Configurations The Electrostatic Interaction LS Coupling and Terms 9.4 Perturbations, Level Splittings, and Term Diagrams Equivalent and Nonequivalent Electrons and Their Spectroscopic Terms Parity Spin-Orbit Coupling Zeeman Effect Role of the Nucleus Hyperfine Structure 9.5 Thermal Distribution of Energy Levels and Ionization Thermal Equilibrium: Boltzmann Population of Levels The Saha Equation Problems References Chapter 10 Radiative Transitions 10.1 Semi-Classical Theory of Radiative Transitions The Electromagnetic Hamiltonian The Transition Probability 10.2 The Dipole Approximation 10.3 Einstein Coefficients and Oscillator Strengths 10.4 Selection Rules 10.5 Transition Rates Bound-Bound Transitions for Hydrogen Bound-Free Transitions (Continuous Absorption) for Hydrogen Radiative Recombination - Milne Relations The Role of Coupling Schemes in the Determination of f Values 10.6 Line Broadening Mechanisms Doppler Broadening Natural Broadening Collisional Broadening Combined Doppler and Lorentz Profiles Problems References Chapter 11 Molecular Structure 11.1 The Born-Oppenheimer Approximation: An Order of Magnitude Estimate of Energy Levels 11.2 Electronic Binding of Nuclei The H2+ Ion The H2 Molecule 11.3 Pure Rotation Spectra Energy Levels Selection Rules and Emission Frequencies 11.4 Rotation-Vibration Spectra Energy Levels and the Morse Potential Selection Rules and Emission Frequencies 11.5 Electronic-Rotational-Vibrational Spectra Energy Levels Selection Rules and Emission Frequencies Problems References Solutions Index

Scattering matrix approach to thermal wave propagation in layered structures

Abstract: In this paper we describe a new technique, based on Fourier optics, to explain the propagation, as well as loss, of three‐dimensional thermal waves in isotropic, homogeneous materials. Using this, the dependence of temperature distribution at any arbitrary infinite parallel plane on the aperture distribution is derived. In addition, the temperature distribution at the aperture plane, due to a given perpendicular source is formulated, by applying the boundary conditions in the spatial frequency domain. A scattering matrix theory is developed to analyze the propagation of thermal waves in multilayered structures. This directly relates the heat source characteristics to the temperature distribution at any level. The contrast mechanism in the subsurface mode of operation is explained, and the dependence of the response of a typical system on depth is explored. In addition, the theoretical amplitude and phase images of a cylindrical void are presented; the results are in good agreement with the published exper...

Spectrum of the cosmic background radiation at millimeter wavelengths.

Abstract: The spectrum of the cosmic background radiation in five frequency bands extending from 2.3 to 11.0 cm with a balloon-borne liquid-helium-cooled photometer. The photometer compares the flux from the sky to the flux from an internal blackbody at 3.2 K. All five measurements are consistent with temperatures in the range 2.78 + or = 0.11 K, which is in good agreement with tempratures measured at lower frequencies. No significant deviation from a thermal spectrum was found.

Two-dimensional model of laser-sustained plasmas in axisymmetric flowfields

Abstract: A two-dimensional numerical model of laser-sustain ed plasmas in flowing argon has been developed. Real-gas properties and a complete radiation loss mechanism have been included, but radial velocities in the flowfield are neglected. Calculated plasma size, peak temperatures, global absorption characteristics, and thermal efficiencies are in good agreement with experiment. Radiation loss is found to be the dominant process at high laser powers, although thermal conversion efficiencies in excess of 40% (at 20 kW) can be realized by operating at high flow velocities. Nomenclature c = speed of light Cp = specific heat, J/kg - K D - focus spot diameter, mm e = electronic charge / = optical / number h = Planck constant / = laser intensity, W/m2 K = thermal conductivity, W/m-K kB = Boltzmann constant ne = electron number density, m~ 3 me - electron mass r = radius, m t =time, s T = temperature, K u,v = axial and radial velocity components, respectively, m/s z = axial position, m Zeff = radiation loss correction factor a = absorption coefficient, 1/m e = emission coefficient, W/m3 p = density, kg/m3 vc = continuum cutoff frequency, s~*

A model for time dependence in shock‐induced thermal radiation of light

Abstract: High‐speed optical pyrometry has seen increasing application in the measurement of shock temperatures in initially transparent solids and liquids; however, the information contained in the time‐dependent intensity of the emitted light has frequently been overlooked. A model has been developed for this time dependence in the observed intensity of light emitted from materials undergoing high‐pressure shock loading. Most experimental observations of this time dependence can be explained on the basis of geometric effects only, without having to invoke intrinsic time dependences of the source intensity (due to changes in temperature, emissivity or shock‐wave structure). By taking advantage of this fact, observed time dependences can be used to determine the absorption coefficient of shocked materials and their effective emissivities, thereby providing more precise temperature measurements. The model is invoked under various limiting conditions to explain time dependences previously observed in NaCl, CaO, Mg2Si...

Radiation transfer in an isotropically scattering homogeneous solid sphere

Abstract: Radiative heat transfer in an absorbing, emitting, isotropically scattering sphere with a diffusively reflecting and emitting boundary is solved by the Galerkin method. By using the expressions given in this work, the radiation heat flux, the angular distribution of radiation intensity and the divergence of the radiation heat flux anywhere in the sphere can be determined with a high degree of accuracy for all values of the single scattering albedo, from small to moderately large optical radii. Results are presented for representative cases to illustrate the accuracy and the convergence of the method.

Quiescent prominence threads models

Abstract: We have calculated prominence thread models for different values of the center temperature and pressure. We have simultaneously solved the radiative transfer, statistical equilibrium and ionization equilibrium equations assuming a three-level atom plus continuum. We have also computed the energy balance equation including the hydrogen radiative losses from our calculations, plus other radiative losses and heat conduction. Some models have been calculated assuming possible variations in thermal conductivity and heating terms. We computed the lines and continua emitted by a number of threads, in order to compare with the observations and evaluate how the different values of the parameters affect the profiles and absolute intensities of Lα, Lβ, Hα, and Ly continuum.

Optical system for the simultaneous reception of thermal and laser radiation

Abstract: An optical receiving system for heat radiation is to be used at a low modification for simultaneous, low-loss reception of laser radiation, whilst still consist of conventional joint assemblies. The Erfindng sees this after the scanner and the geometrical. step separation of thermal and laser radiation a geometric outcoupling the laser radiation from the common receive channel before, wherein the out-coupled laser radiation is directed from the heat radiation separated through a simple optical assembly, preferably to a common sensor. To use the common receiving channel (1) and therefore the optical receiving system for transmitting the laser radiation, the transmitting radiation (50) through a polarizer (52, 53) in the separated laser receiving channel (55) are coupled (Figs. 18,19). In this manner, the optical transmitting system is saved, whereby good conditions for the optical transmission radiation are given without prejudice to the common receiving channel. The invention is applicable to the combination of a thermal imaging device with a Laserentfemungsmesser.

Radiative entropy production

Abstract: THE radiative tensor obtained from the specular moments of the transfer equation is considered. The radiative entropy production is expressed in terms of this tensor. Contents The theory of gas radiation dates back to studies Rayleigh made over a century ago on the illumination and polarization of the sunlit sky. Since then, the theory has rapidly grown because of the efforts of astrophysicis ts and later of applied scientists and engineers. However, the entropy production associated with radiation apparently remains untreated and is the motivation of this study. As is well known, the entropy production results from dissipative processes (involving mass, species, momentum, and/or heat transfer and electromagnetic or nuclear transport). Less known is the fact that the dissipation may have a diffusive or hysteretic origin, the diffusion being directional and the hysteresis being cyclic. However, except for a few cases (such as strain hardening and the magnetic saturation), the majority of dissipative processes (including the dissipation of radiation) are of diffusive nature. A recent study by Arpaci 1 shows, in terms of the radiative stress obtained from the specular (kinetic) moments of the transfer equation, the diffusive nature of radiation for any optical thickness. Accordingly, the expression to be developed for entropy production is in terms of this stress and includes also the dissipation resulting from the conduction of heat and viscous friction. First, some remarks on the radiative stress are needed. These will be made in terms of spectrally averaged radiation because of its simplicity. A monochromatic approach, which may be needed for a quantitative study, is not essential here because of the conceptual nature of the intended study. As pointed out by Felske and Tien,2 there are a variety of practical situations in which scattering is not important. For these situations, consider the spectrally averaged transfer equation,

Combustion augmentation of extremely low calorific gases. Application of the effective energy conversion method from gas enthalpy to thermal radiation.

Abstract: 多孔性固体を使用し.ガス顕熱のふく射エネルギヘの効果的変換を行い,さらに多孔性固体下流側で燃焼用空気を排ガスにて予熱することにより断熱材を使用しない小形の燃焼器を可能にした.都市ガスを使用して希薄混合気の燃焼実験を行った結果,空気過剰率m=9.9(相当発熱量114Kcal/Nm3)というきわめて低い発熱量のガスの燃焼が可能になり,工業的にも非常に有用であることがわかった.

Natural terrain infrared radiance statistics: daily variation.

Abstract: The statistical distribution of the radiance in a thermal image of natural terrain is analyzed. The radiance of each spatial element is related through the heat balance equation to the thermal properties of this element and to the heat input from an external source. As the heat exchange factors of each spatial element over a large area are distributed, the radiance will be distributed as well. Due to nonlinear coupling of the temperature to the thermal properties and heat source, the radiance distribution varies in a complex manner while the heat source changes, the most noticeable result being the asymmetry of the distribution density of the radiance and the change in the sign of that asymmetry with changing heat source.

Solar energy converter

Abstract: The invention relates to a solar energy converter for simultaneously converting radiant energy into electrical and into thermal energy from an absorber which is combined with photovolteic solar cells. The invention consists in the fact that the solar cells, which transmit thermal radiation, are mounted on a carrier plate which is separated from the absorber in such a way that there is no thermal conduction, or only extremely slight thermal conduction, between the solar cells and the absorber.

Thermal radiation of turbulent flows in the case of large fluctuations of the absorption coefficient and the Planck function

Abstract: An expression is obtained for the mean brightness of a flat layer with a random temperature distribution that is valid for arbitrary amplitudes of the absorption coefficient and Planck's function fluctuations. The limits of applicability are set for the approximation of optically thin fluctuations.

Heat transfer model for the pyroelectric anemometer

Abstract: A resistor‐capacitor analog heat transfer model is used to calculate the thermal pyroelectric anemometer (PA) response. This is compared to the data of Frederick et al. [J. Appl. Phys. 57, 4936 (1985)] in the accompanying paper. Steady‐state gas flow conditions are assumed, and the calculations apply in the regime where the transit time of the gas over the device is much less than the time period of the heat input from the ac‐driven heater. Since the pyroelectric substrate is thin, the analysis is simplified to one dimension and excludes edge effects, heat losses due to the support, and thermal radiation. Further, no temperature difference is assumed at the interface between the gas and substrate, i.e., no temperature jump. The calculated dynamic response is in excellent agreement with measurements. However, the calculated level of response is 240 μV at a gas flow of 10 m/min, much lower than the 570 μV measured by Frederick et al.

Thermodynamics infrared imaging sensor

Abstract: An infrared imaging system is presented wherein a visual image of a scene being viewed is obtained from the thermal energy radiated from said scene. The thermal energy radiated is focused onto a plurality of means for absorbing energy from the infrared radiation, specifically a two-dimensional array of gas cells with the front end being a rigid infrared transparent window, the sides being rigid, and the rear ends being flexible membranes. Infrared radiation absorbed by the cells causes changes in the thermodynamic pressure within each cell and consequent expansion of the flexible membrane on the rear end of each cylindrical cell. The deflection of these flexible membranes is monitored and measured by either a laser interferometer system or a solid state pressure sensing system. Measurement of this deflection represents the amount of infrared radiation received at each of the plurality of gas cells. The resultant intensity of the laser interference beam is monitored with a laser interferometer and a TV vidicon camera. This resultant intensity reflects the magnitude of deflection from the cells. The TV vidicon signal which monitors the resultant intensity is processed and transmitted for two-dimensional video presentation of the viewed scene.

Temperature measuring arrangement for a cast metal furnace

Abstract: A temperature measuring device for a metal caster comprises a radiation pyrometer including an IR diode for measuring the head radiation of the metal melt in the crucible of the metal caster. For this purpose, a graphite body dips into the metal melt. The graphite body is seated coaxially around one end of a hollow tube to whose other end is coupled a glass fiber cable which is connected with the IR evaluation diode. The graphite body which dips into the metal melt and simultaneously serves in a known manner as a closing plug for the crucible, now emits thermal radiation into the interior of the tube, such radiation substantially corresponding to the composition of the thermal radiation of a blackbody having the temperature of the metal melt. This thermal radiation is coupled into the glass fiber cable at the other end of the tube and fed to the IR diode for evaluation. This solution permits a relatively inertia-free and very precise measurement, since the measured thermal radiation no longer depends on the type of metal melt employed and, on the other hand, the IR diode employed for the measurement has a certain distance from the caster and is thus free of radiation influences on the part of the caster which could falsify the measuring result.

Heat mirrors for greenhouses.

Abstract: Transparent heat-mirror films, which transmit solar radiation but reflect IR thermal radiation, have potentially important greenhouse applications. Oxide-type heat mirrors, capped with an antireflection coating, are studied. SiO2 and ZnO are considered as representative AR and heat-mirror materials, respectively. The results of calculations of transmittance and insulating U values of the glazing construction polyethylene/air gap/SiO2/ZnO/polyethylene are presented. The resulting structure is shown to give a visible light transmission spectrum which closely matches the plant sensitivity curve for plant growth and has higher thermal insulation compared to uncoated polyethylene. The cost effectiveness of the heat-mirror coatings for greenhouses is briefly considered.

On radiative heating due to polar stratospheric clouds

Abstract: Recent satellite observations of polar stratospheric clouds (PSCs) and the theoretical explanation of their formation brought up questions on the radiative effects of those thin clouds. Optical parameters are calculated for selected stages of the cloud development and for wavelengths between I and 40 μn. Radiative transfer calculations yield absolute values of heating rates of about 0.03 K/day for the thickest polar stratospheric clouds observed by the SAM II satellite. The top portion of the cloud is characterized by cooling of the order of 0.01 K/day while thr lower and denser part of the cloud may experience either cooling or warming depending on the thermal structure and on the vertical distribution of clouds in the troposphere. Due to the correlation between cold stratosphere and warm troposphere, the radiative effect appears more sensitive to the distribution of cloud than to the strength of the surface temperature inversion. Unlike most tropospheric cases and under favorable conditions, the growth of cloud particles may reach equilibrium not only by depletion of ambient moisture but also by thermal equilibrium. The hypothetical fully developed cloud would lead to absolute values of the heating rates of the order of 1 K/day. The maximum warming is found in the wings of the I5 μm CO 2 band and extends up to 24 μm, while some cooling occurs at the upper end of the thermal spectrum. A simple parameterization of optical properties of PSCs is presented for inclusion into broad band radiation models. DOI: 10.1111/j.1600-0889.1985.tb00069.x

The Diffusion-Synthetic Acceleration of Transport Iterations, with Application to a Radiation Hydrodynamics Problem

Abstract: Publisher Summary Radiation hydrodynamics treats the interactions of thermal radiation with matter. Thermal radiation is taken to mean electromagnetic radiation of atomic origin, obtained from the processes of scattering, absorption, and thermal emission. The radiation field is described by an equation of transfer, which is a Boltzmann transport equation for photons. From a computational viewpoint, time-dependent radiative transfer problems in emitting media are difficult to solve. In general, their solution involves an equation with seven independent variables for the radiation field, along with the additional equations describing the mass, momentum, and energy balance of the underlying medium. This chapter describes new numerical methods for solving such problems. It also discusses three aspects of the solution method: the time dependence, the intimate coupling between the radiation field and the medium, and the iteration acceleration of the equation of transfer. The time dependence is treated implicitly, that is, the equation of transfer is written in terms of the dependent variables evaluated at the advanced time.

Laser modulation photothermal radiometer—a new method for measuring weak absorption in bulk materials and coatings

Abstract: A new method was developed for measuring weak absorption in bulk materials and coatings It is based on recording a change in the integrated thermal radiation flux from the surfaces of samples heated by periodic laser radiation pulses The possibility is discussed of making absolute measurements by simulation of surface heat sources in the materials investigated, and also by comparing them with standard samples The sensitivity of the method is estimated and the results of absorption measurements on a number of materials are presented Consideration is given to limitations imposed on the operating range of laser pulse repetition frequencies by the thickness of the layer of the substance emitting the thermal flux and by the increase in the transverse dimensions of the illuminated area arising on account of thermal diffusion