Showing papers on "Radiative transfer published in 1968"
TL;DR: In this paper, it has been shown that the non-radiative mode excited by light can also radiate under certain conditions if they are excited by electrons (grazing incidence of electrons on a rough surface or at normal incidence on a grating).
Abstract: There are two modes of surface plasma waves: 1) Non-radiative modes with phase velocities Cü/k smaller than the velocity of light c. They cannot decay into photons in general. 2) Radiative modes with (o/k > c which couple directly with photons 1. The following paper is concerned with the excitation of these modes by light and their decay into photons. It has been shown that the radiative mode on thin silverand potassium-films can be excited by light and that the mode reradiates light almost into all directions with an intensity maximum at the plasma frequency cOp 2. It had been further observed that the non-radiative modes radiate under certain conditions if they are excited by electrons (grazing incidence of electrons on . a rough surface3 or at normal incidence on a grating 4) . The mechanism of this emission is in these cases always the same: The \"wave vector\" of the roughness of the surface or its irregularity changes the plasmon wave vector k so that a) in the case of the radiative mode light emission is found in directions in addition to that of reflexion and transmission, b) in the case of the non-radiative mode its wave vector is reduced so that the condition /c0, the wave vector of the inhomogeneous wave is (co/c) • Vsq' sin 0O (fq = 2.16 for quartz) and thus can excite a non radiative mode on the boundary of the prism for j/fq sin 0O > 1 or 90° > @o > 43°. If one vaporises a silver film directly on the quartz surface the inhomogeneous light wave penetrates into the silver film and excites a nonradiative mode on the boundary silver/air. The excitation will be highest for those frequencies which fulfill the dispersion relation of these surface plasmons.
2,790 citations
TL;DR: In this article, a unified theory of optical and thermal outer-sphere electron transfer processes is outlined, in which the equations are obtained as special cases of general expressions for radiative and radiationless transition probabilities.
744 citations
510 citations
346 citations
TL;DR: In this article, it was shown that the first two terms of an expansion in the photon energy depend on the unpolarized, non-radiative cross-section only.
Abstract: The Low theorem is applied to the radiative cross section for unpolarized particles. It is shown that the first two terms of an expansion in the photon energy depend on the unpolarized, nonradiative cross section only.
294 citations
TL;DR: In this paper, the authors calculated radiative decay probabilities for electric and magnetic dipole transitions from several electronic states of Pr3+ in LaF3 using the Judd-Ofelt theory and experimental intensity parameters to determine the quantum efficiencies of the 1D2 and 3P0 states.
Abstract: Spontaneous emission probabilities for electric‐ and magnetic‐dipole transitions from several electronic states of Pr3+ in LaF3 are calculated using the Judd–Ofelt theory and experimental intensity parameters. The calculated radiative decay probabilities are combined with observed fluorescence lifetimes to determine the quantum efficiencies of the 1D2 and 3P0 states. Although the lifetimes were measured at low temperatures and small Pr concentrations where competing nonradiative decay by multiphonon emission and ion‐pair relaxation should be negligible, the predicted quantum efficiencies are less than unity. The radiative lifetimes obtained via the Einstein relations and measured integrated absorption and relative fluorescence intensities agree, however, with the observed lifetimes. The discrepancies appear to arise from approximations and possible limitations inherent in the approach used to calculate the radiative transition probabilities. Matrix elements of U(λ) for states of 4f2 in intermediate coupling are included in an appendix.
234 citations
TL;DR: In this article, an accurate correction for this effect is described, having the advantages of general applicability and allowing the use of high photon detection rates, and it is shown that the error introduced by using this correction is negligible under all practical experimental conditions.
Abstract: In determinations of radiative lifetimes in which time intervals are measured up to the first detected photon, an error is introduced when subsequent photons are neglected. An accurate correction for this effect is described, having the advantages of general applicability and allowing the use of high photon detection rates. It is also shown that the error introduced by the use of this correction is negligible under all practical experimental conditions.
151 citations
TL;DR: In this article, the long-wave optical modes of vibration in an ionic crystal sphere have been determined, including retardation of the Coulomb forces, and the absorption and extinction cross sections for spheres of various sizes are calculated as a function of the frequency of the incident light.
Abstract: The long-wave optical modes of vibration in an ionic crystal sphere have been determined, including retardation of the Coulomb forces. These modes, which correspond to coupled excitations of phonons and photons, are also known as polaritons. Their frequencies are complex, the imaginary parts arising from both anharmonic and radiative damping; hence they are virtual modes. It is found that the mode frequencies depend on the radius of the sphere only if retardation is included. The absorption and extinction cross sections for spheres of various sizes are calculated as a function of the frequency of the incident light, and it is shown how the structure in the cross sections is related to the properties of the virtual modes. The theory is used to explain the position and width of an optical absorption peak measured in a polyethylene film containing UO2 particles.
128 citations
Book•
01 Jan 1968
Abstract: Radiation and Reentry is an integrated review of a series of publications dealing with radiative transfer theory, applied spectroscopy, radiation gas dynamics, and ablation phenomena.
This book contains seven chapters and begins with a presentation of opacity calculations under conditions for which detailed considerations of spectral line structures and widths are not required. The discussion then shifts to the basic methods involved in the formulation of radiative transfer problems; origin and definition of the Planck and Rosseland mean free paths; the conservation equations for reacting, multicomponent gas mixtures with proper allowance for radiative energy flux; and similarity parameters in radiation gas dynamics. These topics are followed by a summary of data relevant to the optically thick, optically thin, and isothermal cases for air in local thermodynamic equilibrium. A chapter describes the radiative properties of spherical particles and their particle size distributions. Another chapter considers the estimation of radiant-energy transmission through atmosphere. The concluding chapters explore the radiation transfer effects on the flow about a re-entry body and the specific problems of the effect of radiant-energy transfer on acoustic waves, shock wave structure, and shock and boundary layers. These chapters also examine the theoretical and experimental studies on the ablation of re-entry vehicles. This book is of great value to educated nonspecialists who are interested in the application of radiation field to high-speed atmospheric entry.
114 citations
TL;DR: In this paper, a method based on the equation of radiative transfer has been developed for predicting the two-dimensional wind wave spectrum in the North Atlantic Ocean, taking account of wave generation by both resonance and instability mechanisms.
Abstract: A method based on the equation of radiative transfer has been developed for predicting the two-dimensional wind wave spectrum in the North Atlantic Ocean. The model takes account of wave generation by both resonance and instability mechanisms. A simple representation for wave breaking is also included, as are the effects of nonlinear wave interactions. This combination of energy transfer mechanisms is used to compute wave spectra that are in reasonable accord with observations. The results question the concept of a ‘fully developed’ spectrum. The work also points up a lack of understanding of the particulars of various energy transfer mechanisms, as well as the shortcomings of the basic predictive input data.
108 citations
TL;DR: In this article, the information content of radiation measurements used in inferring profiles is defined as a reduction in uncertainty in the estimation of a profile after the measurements are introduced, and the information is shown to depend directly on the kernel of the equation of radiative transfer.
Abstract: The information content of radiation measurements used in inferring profiles is defined as a reduction in uncertainty in the estimation of a profile after the measurements are introduced. The information is shown to depend directly on the kernel of the equation of radiative transfer, the covariance matrix of experimental error, and the covariance matrix of the a priori statistical information. Calculations based on the minimum rms inversion method are applied to the indirect probing of the vertical temperature distribution by microwave measurements of oxygen thermal emission. Choice of optimum location of measurements is discussed and comparison of the proposed method with that of Twomey is given.
TL;DR: In this article, the potential of using the 5-mm resonance lines of O2 to remotely probe the mesospheric temperature profile is analyzed in detail, and specific experiments are proposed.
Abstract: The potential of using the 5-mm resonance lines of O2 to remotely probe the mesospheric temperature profile is analyzed in detail, and specific experiments are proposed. An absorption matrix, which includes the complete Zeeman effect, is used in a tensor equation of radiative transfer to compute the microwave spectrum near the resonance lines as it would be seen from space. The conclusion is that such techniques do afford a means of remotely determining the mesospheric temperature profile to heights of approximately 80 km, and that this is possible with available 5-mm hardware. The two specific experiments that are described in detail would sound the mesosphere in the 60-km and 73-km regions. Radiometric sensitivities of 1.5–5°K are possible for these experiments, with a horizontal resolution of 100–300 km along the direction of motion.
TL;DR: The validity of the Kubelka—Munk theory of radiative transfer is confirmed after two separable effects, “hyperchromatically” and “curvature of response”, were evaluated experimentally on silica gel layers and correspond closely to that predicted.
TL;DR: In this paper, the radiative properties of this solution are investigated by Bondi's method and the news function is found and the asymptotic behaviour of the Riemann tensor is analysed.
Abstract: An exact solution of Einstein’s vacuum equations representing uniformly accelerated particles was given by Bonnor & Swaminarayan. The radiative properties of this solution are here investigated by Bondi’s method. After the introduction of the metric due to Bondi, the news function is found and the asymptotic behaviour of the Riemann tensor is analysed. The non-vanishing news function and the radiative character of the Riemann tensor at light infinity indicate that the solution is of radiative type; in particular, the solution is radiative in the case of freely gravitating masses. By comparing the solution of Bonnor & Swaminarayan with Born’s solution in electrodynamics the results of Bondi’s method are modified for the system which is not permanently isolated. The angular distribution of the radiated energy and the total rate of radiation of energy and momentum are found in the case of freely moving particles with sufficiently small masses. Gravitational radiation of the particles in question is very similar to electromagnetic radiation of an analogous system of charges. At the moment when the masses or the charges are at rest, the resulting expressions are corroborated on the basis of the approximation method of Bonnor & Rotenberg and of the standard multipole expansion method. The radiation has octupole character. In addition to outgoing radiation, incoming radiation with similar properties is present. This incoming radiation can exist in spite of the radiation condition; an additional condition which excludes the incoming radiation is suggested.
TL;DR: In this paper, the transition rate equations for the populations of cesium states in a homogenous, optically thin plasma have been solved for the excited-state populations, the effective ground-state ionization and recombination coefficients, and the effective electron kinetic energy and radiative loss coefficients.
Abstract: The transition rate equations for the populations of cesium states in a homogenous, optically thin plasma have been solved for the excited-state populations, the effective ground-state ionization and recombination coefficients, and the effective electron kinetic-energy and radiative loss coefficients. A table of values is presented for the nonequilibrium steady-state plasma which is analogous to the Saha equation for the equilibrium plasma. Free electron densities from 1012 to 1015 cm-3 are considered, and a Maxwellian electron velocity distribution at temperatures from 1500 to 3000°K is assumed. These conditions are typical of those in thermionic and magnetohydrodynamic energy converters and other cesium discharges. The rate coefficients used for collision-induced and radiative atomic transitions are described. Molecular processes, diffusion, wall losses, etc., are discussed but not included explicitly in the model. The absorption of resonance radiation is simulated by reduction of the spontaneous emission coefficients. Other radiative absorption processes are neglected. The populations are seen to depart significantly from the Boltzmann distribution in steady state, and it is seen that many excited states participate in the ionization and recombination processes. The implications of these results for spectroscopic diagnostics, volume ion production, and energy loss in a cesium-discharge plasma are discussed.
TL;DR: In this article, the absorption coefficient α of olivine crystals was measured in the range of wavelength from 0.3 μ-10 μ at various temperatures up to 1300 °K and it was discovered that α in the pass-band (about 1.8 μ-3.0 μ) increases by a factor of about 100 in going from 300 °K to 1000 °K.
TL;DR: In this paper, the authors measured the ratio (R) of positron-proton and electronproton elastic-scattering cross sections, with the square of the four-momentum transfer (q^2) equal to 0.123.
Abstract: Measurements of the ratio (R) of positron-proton and electron-proton elastic-scattering cross sections have been made, with the square of the four-momentum transfer (q^2) equal to 0.20, 0.69, 0.73, 1.54, 2.44, 3.27, 3.79, and 5.00 (GeV/c)^2. The measurements, after radiative corrections, are consistent with R=1, with standard errors ranging from ±0.016 to ±0.123. The results give limits for the size of the two-photon effects.
TL;DR: In this article, the Monte Carlo method is applied to investigate thermal radiation to the exterior base region of a finite cylindrical dispersion of absorbing, emitting, and anisotropic scattering particles.
Abstract: In this work the Monte Carlo method is applied to investigate thermal radiation to the exterior base region of a finite cylindrical dispersion of absorbing, emitting, and anisotropically scattering particles. The analysis assumes a scattering function characteristic of aluminum oxide dispersions. Searchlight effect, chamber emitted radiation scattered by the particles to the surroundings, is introduced by permitting the radiation to originate from a black circular surface at the base of the cloud, as well as from within the cloud. The results obtained show that anisotropic scattering and searchlight effect play important roles in heat transfer in this geometry.
TL;DR: In this article, a modified differential approximation is used to obtain approximate expressions for the radiative flux and temperature distribution in a gray medium enclosed between concentric spheres and concentric cylinders which are held at different temperatures.
Abstract: A modified differential approximation is used to obtain approximate expressions for the radiative flux and temperature distribution in a gray medium enclosed between concentric spheres and concentric cylinders which are held at different temperatures. Quite accurate results are obtained under all conditions since the modified differential approximation correctly accounts for the anisotropy of the enclosure surface radiation. Calculated curves of flux and emissive power (temperature) illustrate the superiority of the modified differential approximation compared with the unmodified differential approximation and with a method of regional averaging.
TL;DR: In this paper, an analytical procedure is developed to investigate the interaction or coupling of radiation with the conduction and convection mechanism in a nonisothermal, nongray gas flowing in the entrance region of a tube with isothermal, black walls.
TL;DR: In this article, the quantitative use of Franck-Condon factors in radiative, excitation and ionization transitions of molecules is discussed and a FranckCondon factor array is presented for ionizing transitions of O2, CO, NO and H2.
Abstract: The quantitative use of Franck-Condon factors in radiative, excitation and ionization transitions of molecules is discussed. Franck-Condon factor arrays are presented for ionizing transitions of O2, CO, NO and H2 and for the NO+ (A 1Σ-X 1Σ) band system.
TL;DR: In this paper, the spectral radiant heat flux distribution in an absorbing and emitting gas of prescribed temperature distribution contained in a long cylinder whose internal surface is black is derived in terms of integral functions peculiar to the cylindrical geometry.
Abstract: Equations are presented for the spectral radiant heat flux distribution in an absorbing and emitting gas of prescribed temperature distribution contained in a long cylinder whose internal surface is black. The temperature of the gas is taken to vary in the radial direction only, while the absorption coefficient of the gas is taken to vary with temperature as well as frequency of radiation. Equations are also presented for the radiant heat flux distribution in a gray gas in which the absorption coefficient is a function of temperature only. The equations, which are derived from the general equation of radiative transfer, are presented in terms of integral functions peculiar to the cylindrical geometry. Radiant heat flux distributions are calculated for several absorption coefficient and temperature distributions with the gray-gas model. The effects of absorption coefficient and temperature profiles on the heat flux distribution in a cylindrical medium are compared with equivalent effects in a plane parallel medium. The effects of absorption coefficient and temperature profiles on the heat flux distribution in the annular region between two concentric cylinders are also examined for cases in which the inner cylinder is a core of very opaque gas.
TL;DR: In this article, the ground state of 6 He was obtained by using both muon capture and radiative pion capture reactions in 6 Li yielding the ground states of 6 Li and 6 He.
TL;DR: In this article, the authors compared the accuracy of the GFDL radiation model with other numerical models, including Rodgers and Walshaw's scheme, and found that it has accuracy comparable to other numerical model despite various assumptions adopted.
Abstract: The scheme of computing the temperature change due to long wave radiation, developed by Manabe and Strickler and incorporated into the general circulation models developed at the Geophysical Fluid Dynamics Laboratory of ESSA, is compared with a group of other numerical schemes for computing radiative temperature change (e.g., the scheme of Rodgers and Walshaw). It is concluded that the GFDL radiation model has the accuracy comparable with other numerical models despite various assumptions adopted.
TL;DR: In this paper, the second-order radiative corrections to general semileptonic weak decays are considered, provided that the strong interactions are restricted to renormalizable theories of elementary fermion fields coupled to neutral massive vector bosons through a conserved vector current.
Abstract: The problem of second-order radiative corrections to general semileptonic weak decays is considered. Previous results on ultraviolet divergences in the calculations for zero-momentum-transfer $\ensuremath{\beta}$ decays can be proven for the general process, provided that the models of the strong interactions are restricted to renormalizable theories of elementary fermion fields coupled to neutral massive vector bosons through a conserved vector current. A possible method for calculating finite radiative corrections to actual processes is also discussed.