Thermal radiation

About: Thermal radiation is a research topic. Over the lifetime, 12290 publications have been published within this topic receiving 197186 citations. The topic is also known as: heat radiation.

High-efficiency photospheric emission of long-duration gamma-ray burst jets: the effect of the viewing angle

Abstract: We present the results of a numerical investigation of the spectra and light curves of the emission from the photospheres of long-duration gamma-ray burst jets. We confirm that the photospheric emission has high efficiency and show that the efficiency increases slightly with the off-axis angle. We show that the peak frequency of the observed spectrum is proportional to the square root of the photosphere's luminosity, in agreement with the Amati relation. However, a quantitative comparison reveals that the thermal peak frequency is too small for the corresponding total luminosity. As a consequence, the radiation must be out of thermal equilibrium with the baryons in order to reproduce the observations. Finally, we show that the spectrum integrated over the emitting surface is virtually indistinguishable from a Planck law, and therefore an additional mechanism has to be identified to explain the non-thermal behavior of the observed spectra at both high and low frequencies.

Absolute measurements of the thermal conductivity of liquids at pressures up to 500 MPa

Abstract: An apparatus for the accurate measurement of the thermal conductivity of liquids is described. The instrument, which is of the transient hot-wire type, operates over the pressure range 0.1 to 700 MPa and the temperature range 20–200°C. The precision of the thermal conductivity measurements is estimated to be one of ±0.2% over the entire range. — Experimental data are reported for the thermal conductivity of n-heptane in the temperature range 35–75°C and the pressure range 50–500 MPa. The accuracy of the present results is estimated to be one of ±0.5%, which is slightly worse than their precision because the lack of suitable data for the optical properties of the liquid at high pressures only allows an approximate correction to be applied for the systematic effects of radiative heat transfer. Along an isochore the thermal conductivity of n-heptane is found to increase with temperature although along an isobar the temperature derivative is negative. The density dependence of the thermal conductivity is almost independent of temperature.