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Radiative transfer

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


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TL;DR: In this article, the authors calculate the optically thick photodissociation rate numerically, including the effects of density, temperature and velocity gradients in the gas, as well as line overlap and shielding of H2 by H 2 over a large number of sightlines.
Abstract: The ability of primordial gas to cool in protogalactic haloes exposed to ultraviolet (UV) radiation is critically dependent on the self-shielding of H2. We perform radiative transfer calculations of LW line photons, post-processing outputs from three-dimensional adaptive mesh refinement simulations of haloes with Tvir≳ 104 K at z ∼ 10. We calculate the optically thick photodissociation rate numerically, including the effects of density, temperature and velocity gradients in the gas, as well as line overlap and shielding of H2 by H i, over a large number of sightlines. In low-density regions (n ≲ 104 cm−3) the dissociation rates exceed those obtained using most previous approximations by more than an order of magnitude; the correction is smaller at higher densities. We trace the origin of the deviations primarily to inaccuracies of (i) the most common fitting formula for the suppression of the dissociation rate, from Draine and Bertoldi and (ii) estimates for the effective shielding column density from local properties of the gas. The combined effects of gas temperature and velocity gradients are comparatively less important, typically altering the spherically averaged rate only by a factor of ≲2. We present a simple modification to the Draine & Bertoldi fitting formula for the optically thick rate which improves agreement with our numerical results to within ∼15 per cent, and can be adopted in future simulations. We find that estimates for the effective shielding column can be improved by using the local Sobolev length. Our correction to the H2 self-shielding reduces the critical LW flux to suppress H2 cooling in Tvir≳ 104 K haloes by an order of magnitude; this increases the number of such haloes in which supermassive (M ∼ 105 M⊙) black holes may have formed.

219 citations

Journal ArticleDOI
TL;DR: In this paper, a Monte Carlo code to solve the transfer of Lyα photons is developed that can predict the Lyα image and two-dimensional Lyα spectra of a hydrogen cloud with any given geometry, Lyα emissivity, neutral hydrogen density distribution, and bulk velocity field.
Abstract: A Monte Carlo code to solve the transfer of Lyα photons is developed that can predict the Lyα image and two-dimensional Lyα spectra of a hydrogen cloud with any given geometry, Lyα emissivity, neutral hydrogen density distribution, and bulk velocity field. We apply the code to several simple cases of a uniform cloud to show how the Lyα image and emitted line spectrum are affected by the column density, internal velocity gradients, and emissivity distribution. We then apply the code to two models for damped Lyα absorption systems: a spherical, static, isothermal cloud and a flattened, axially symmetric, rotating cloud. If the emission is due to fluorescence of the external background radiation, the Lyα image should have a core corresponding to the region where hydrogen is self-shielded. The emission-line profile has the characteristic double peak with a deep central trough. We show how rotation of the cloud causes the two peaks to shift in wavelength as the slit is perpendicular to the rotation axis and how the relative amplitude of the two peaks is changed. In reality, damped Lyα systems are likely to have a clumpy gas distribution with turbulent velocity fields, which should smooth the line emission profile but should still leave the rotation signature of the wavelength shift across the system.

219 citations

Journal ArticleDOI
TL;DR: In this article, the problem of deriving accurate land surface temperatures (LSTs) using infrared satellite measurements is considered and the radiative transfer equation over the land is solved by linearization of the Planck function in temperature and wavenumber in the same manner as is done for obtaining the so-called splitwindow algorithm for sea surface temperature estimation.
Abstract: The problem of deriving accurate land surface temperatures (LSTs) using infrared satellite measurements is considered. The radiative transfer equation over the land is solved by linearization of the Planck function in temperature and wavenumber in the same manner as is done for obtaining the so-called split-window algorithm for sea surface temperature estimation. The effects of the atmosphere and of surface emissivity are both considered in the derivation. By making further assumptions, an approximate split-window algorithm which shows explicitly how atmospheric absorption by water vapor and surface emissivity both affect the accuracy of LSTs is derived. A new algorithm has been formulated for use with National Oceanic and Atmospheric Administration advanced very high resolution radiometer data and is compared with previously published algorithms. It has a global form with coefficients that depend upon local conditions. Dual angle algorithms are also derived. These may be used to estimate LST using data from the along-track scanning radiometer on board the first European remote-sensing satellite.

219 citations

Journal ArticleDOI
TL;DR: This corrects the article DOI: 10.1038/srep24105 to indicate that the author of the paper is a doctor of medicine rather than a scientist, as previously reported.
Abstract: Scientific Reports 6: Article number: 24105; published online: 07 April 2016; updated: 05 April 2018. This article contains an error in Figure 2, where the same image was inadvertently shown in both panel (a) and (b). The correct Figure 2 appears below:

218 citations

Journal ArticleDOI
TL;DR: In this paper, a model for calculating radiative transfer in a stratified dielectric was developed, which is used to show that the reflectivity of a stratification is primarily determined by gradients in the real part of the refractive index over distances on the order of 1/10 wavelength in the medium.
Abstract: A model is developed for calculating radiative transfer in a stratified dielectric. This model is used to show that the reflectivity of a stratified dielectric is primarily determined by gradients in the real part of the refractive index over distances on the order of 1/10 wavelength in the medium. The effective temperature of the medium is determined by the thermodynamic temperature profile over distances of the order ?T where Im (n) dx = ?/4?

218 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,706
20223,291
20211,335
20201,335
20191,429
20181,409