Topic
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 investigated the radiative lifetime of electron-hole excitations in colloidal CdSe nanocrystal quantum dots over nearly three orders of magnitude in temperature (300 K to 380 mK).
Abstract: We investigate the strongly temperature-dependent radiative lifetime of electron–hole excitations in colloidal CdSe nanocrystal quantum dots over nearly three orders of magnitude in temperature (300 K to 380 mK). These studies reveal an intrinsic, radiative upper limit of ∼1 μs for the storage of excitons below 2 K. At higher temperatures, exciton lifetimes are consistent with thermal activation from the dark-exciton ground state, but with two different activation thresholds.
344 citations
TL;DR: In this article, the authors estimate that the indirect aerosol effect at the top of the atmosphere is approximately −1.3 W m−2 in the global annual mean, which is significant compared to the long-wave forcing due to increases in anthropogenic trace gases since the beginning of the industrial era, estimated at +2 to +2.5 Wm−2 (ref.
Abstract: ANTHROPOGENIC sulphate aerosols are believed to affect the radiation budget of the Earth in two ways. Through the direct effect they scatter solar radiation back to space, producing a radiative forcing whose global annual mean has been estimated to lie in the range −0.3 to −0.9 W m−2 (refs 1–3). This is significant compared to the longwave forcing due to increases in anthropogenic trace gases since the beginning of the industrial era, estimated at +2 to +2.5 W m−2 (ref. 4). Aerosols also have an indirect effect, altering the distribution and concentration of cloud condensation nuclei (CCN) and hence the number density and size distribution of cloud droplets, thus affecting the solar radiative characteristics of clouds5,6. This is harder to quantify than the direct effect, because it depends on complex and poorly understood interactions between aerosols, CCN and cloud properties. Here we use sulphate aerosol data derived from a three-dimensional chemical transport model7 to estimate the indirect radiative forcing by low-level water clouds using a general circulation model. We estimate that the indirect aerosol effect at the top of the atmosphere is approximately −1.3 W m−2 in the global annual mean. Although this value is subject to a high level of uncertainty, even if the effect is only half as large it would still exceed many estimates of the direct effect, demonstrating its potential importance in climate change.
344 citations
TL;DR: In this paper, the authors used custom-fabricated scanning probes with embedded thermocouples, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres.
Abstract: Radiative transfer of energy at the nanometre length scale is of great importance to a variety of technologies including heat-assisted magnetic recording, near-field thermophotovoltaics and lithography. Although experimental advances have enabled elucidation of near-field radiative heat transfer in gaps as small as 20-30 nanometres (refs 4-6), quantitative analysis in the extreme near field (less than 10 nanometres) has been greatly limited by experimental challenges. Moreover, the results of pioneering measurements differed from theoretical predictions by orders of magnitude. Here we use custom-fabricated scanning probes with embedded thermocouples, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica-silica, silicon nitride-silicon nitride and gold-gold surfaces to reveal marked, gap-size-dependent enhancements of radiative heat transfer. Furthermore, our state-of-the-art calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results, providing unambiguous evidence that confirms the validity of this theory for modelling radiative heat transfer in gaps as small as a few nanometres. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale radiative heat transfer.
344 citations
TL;DR: In this article, the authors investigate the possibility that long tidal tails formed during compact object mergers may produce optical transients powered by the decay of freshly synthesized r-process material.
Abstract: We investigate the possibility that long tidal tails formed during compact object mergers may produce optical transients powered by the decay of freshly synthesized r-process material. Precise modeling of the merger dynamics allows for a realistic determination of the thermodynamic conditions in the ejected debris. We combine hydrodynamic and full nuclear network calculations to determine the resultant r-process abundances and the heating of the material by their decays. The subsequent homologous structure is mapped into a radiative transfer code to synthesize emergent model light curves and determine how their properties (variability and color evolution) depend on the mass ratio and orientation of the merging binary. The radiation emanating from the ejected debris, though less spectacular than a typical supernova, should be observable in transient surveys and we estimate the associated detection rates. We find that it is unlikely that photometry alone will be able to distinguish between different binary mass ratios and the nature of the compact objects, emphasizing the need for spectroscopic follow-up of these events. The case for (or against) compact object mergers as the progenitors of short gamma-ray bursts can be tested if such electromagnetic transients are detected (or not) in coincidence with some bursts, although they may be obscured by on-axis afterglows.
344 citations
TL;DR: In this article, a simulation of the nuclear and Coulomb collisions in GRB jets was performed to reproduce the spectra of observed GRBs that typically peak near 1 MeV and extend to much higher energies with a photon index > 2.5.
Abstract: Nuclear and Coulomb collisions in GRB jets create a hot electron-positron plasma. This collisional heating starts when the jet is still opaque and extends to the transparent region. The e+- plasma radiates its energy. As a result, a large fraction of the jet energy is converted to escaping radiation with a well-defined spectrum. The process is simulated in detail using the known rates of collisions and accurate calculations of radiative transfer in the expanding jet. The result reproduces the spectra of observed GRBs that typically peak near 1 MeV and extend to much higher energies with a photon index \beta ~ -2.5. This suggests that collisional heating may be the main mechanism for GRB emission.
343 citations