scispace - formally typeset
Search or ask a question
Topic

Radiative transfer

About: Radiative transfer is a research topic. Over the lifetime, 43287 publications have been published within this topic receiving 1176539 citations.


Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, the spectral inversion technique has been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region.
Abstract: This review paper outlines background information and covers recent advances made via the analysis of spectra and images of prominence plasma and the increased sophistication of non-LTE (ie when there is a departure from Local Thermodynamic Equilibrium) radiative transfer models. We first describe the spectral inversion techniques that have been used to infer the plasma parameters important for the general properties of the prominence plasma in both its cool core and the hotter prominence-corona transition region. We also review studies devoted to the observation of bulk motions of the prominence plasma and to the determination of prominence mass. However, a simple inversion of spectroscopic data usually fails when the lines become optically thick at certain wavelengths. Therefore, complex non-LTE models become necessary. We thus present the basics of non-LTE radiative transfer theory and the associated multi-level radiative transfer problems. The main results of one- and two-dimensional models of the prominences and their fine-structures are presented. We then discuss the energy balance in various prominence models. Finally, we outline the outstanding observational and theoretical questions, and the directions for future progress in our understanding of solar prominences.

241 citations

Journal ArticleDOI
TL;DR: In this article, it is shown that an indetermination in the separation of the respective effects of vacuum fluctuations and radiation reaction can be removed by imposing to the corresponding rates of variation to be Hermitian (this is necessary if we want them to have a physical meaning).
Abstract: It is generally considered that there exists in quantum radiation theory an indetermination in the separation of the respective effects of vacuum fluctuations and radiation reaction. We show in this paper that such an indetermination can be removed by imposing to the corresponding rates of variation to be Hermitian (this is necessary if we want them to have a physical meaning). Such a procedure is generalized to the case of a small system S interacting with a large reservoir % and allows the separation of two types of physical processes, those where % fluctuates and polarizes S (effects of reservoir fluctuations), those where it is S which polarizes % (effects of self reaction). We apply this procedure to an atomic electron interacting with the radiation field and we then identify the contribution of vacuum fluctuations and self reaction to radiative corrections and spontaneous emis- sion of radiation. The analysis of the results obtained in this way allows us to specify the physical pictures which must be associated with the various radiative processes.

241 citations

Journal ArticleDOI
TL;DR: In this paper, an analysis of radiative scattering for an arbitrary configuration of neighbouring spheres is presented based on the previously developed superposition solution, in which the scattered field is expressed as a superposition of vector spherical harmonic expansions written about each sphere in the ensemble.
Abstract: An analysis of radiative scattering for an arbitrary configuration of neighbouring spheres is presented. The analysis builds upon the previously developed superposition solution, in which the scattered field is expressed as a superposition of vector spherical harmonic expansions written about each sphere in the ensemble. The addition theorems for vector spherical harmonics, which transform harmonics from one coordinate system into another, are rederived, and simple recurrence relations for the addition coefficients are developed. The relations allow for a very efficient implementation of the 'order of scattering' solution technique for determining the scattered field coefficients for each sphere. Prediction of the radiative absorption and scattering characteristics of small particles is important to researchers in a number of fields, e.g. atmospheric modelling, analysis of radiative transfer from flames, and development of nonintrusive laser-based optical diagnostic methods. Computation of the radiative characteristics of spherical particles from Lorenz-Mie theory is practically a trivial matter due to the existence of efficient computer codes (Bohren & Huffman 1983). However, it is not unusual to encounter situations in which the individual particles, while spherical in shape, are so close together that the 'isolated sphere' assumption inherent in Lorenz-Mie theory is questionable. A common example is soot formed in combustion processes. Electron micrographs of the individual soot particles reveal them to be agglomerates of a large number of primary, spherical particles (Dobbins

241 citations

Journal ArticleDOI
TL;DR: This model describes quite well the energy dependence of the dipolar resonance, the full width at half maximum, and the total extinction cross section for all four metallic systems, even when 100
Abstract: Localized surface plasmons (LSPs) of metallic nanoparticles decay either radiatively or via an electron-hole pair cascade. In this work, the authors have experimentally and theoretically explored the branching ratio of the radiative and nonradiative LSP decay channels for nanodisks of Ag, Au, Pt, and Pd, with diameters D ranging from 38 to 530 nm and height h=20 nm, supported on a fused silica substrate. The branching ratio for the two plasmon decay channels was obtained by measuring the absorption and scattering cross sections as a function of photon energy. The former was obtained from measured extinction and scattering coefficients, using an integrating sphere detector combined with particle density measurements obtained from scanning electron microscopy images of the nanoparticles. Partly angle-resolved measurements of the scattered light allowed the authors to clearly identify contributions from dipolar and higher plasmonic modes to the extinction, scattering, and absorption cross sections. Based on these experiments they find that absorption dominates the total scattering cross section in all the examined cases for small metallic nanodisks (D 100 nm absorption still dominates for Pt and Pd nanodisks, while scattering dominates for Au and Ag. A theoretical approach, where the metal disks are approximated as oblate spheroids, is used to account for the trends in the measured cross sections. The field problem is solved in the electrostatic limit. The spheroid is treated as an induced dipole for which the dipolar polarizability is calculated based on spheroid geometry and the (bulk) dielectric response function of the metal the spheroid consists of and the dielectric medium surrounding it. One might expect this model to be inappropriate for disks with D>100 nm since effects due to the retardation of the incoming field across the metallic nanodisk and contributions from higher plasmonic modes are neglected. However, this model describes quite well the energy dependence of the dipolar resonance, the full width at half maximum, and the total extinction cross section for all four metallic systems, even when 100

241 citations

Book ChapterDOI
Jos Stam1
12 Jun 1995
TL;DR: This work implemented both a multi-grid finite differences scheme and a finite-element blob method to approximate the effects of multiple scattering in the limit of an optically thick medium.
Abstract: Multiple scattering in participating media is generally a complex phenomenon. In the limit of an optically thick medium, i.e., when the mean free path of each photon is much smaller than the medium size, the effects of multiple scattering can be approximated by a diffusion process. We introduce this approximation from the radiative transfer literature to the computer graphics community and propose several numerical methods for its solution. We implemented both a multi-grid finite differences scheme and a finite-element blob method.

241 citations


Network Information
Related Topics (5)
Scattering
152.3K papers, 3M citations
85% related
Magnetic field
167.5K papers, 2.3M citations
84% related
Turbulence
112.1K papers, 2.7M citations
82% related
Dark matter
41.5K papers, 1.5M citations
82% related
Electron
111.1K papers, 2.1M citations
81% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,706
20223,291
20211,335
20201,335
20191,429
20181,409