Radiative Transfer Along Rays in Curved Spacetimes

Radiative transfer in curved spacetimes has become increasingly important to understanding high-energy astrophysical phenomena and testing general relativity in the strong field limit. The equations of radiative transfer are physically equivalent to the Boltzmann equation, where the latter has the virtue of being covariant. We show that by a judicious choice of the basis of the phase space, it is generally possible to make the momentum derivatives in the Boltzmann equation vanish along an arbitrary (including nongeodesic) path, thus reducing the problem of radiative transfer along a ray to a path integral in coordinate space.Comment: To be published in MNRAS Letter

Performance of a Haynes 188 metallic standoff thermal protection system at Mach 7

A flight weight, metallic thermal protection system (TPS) model applicable to reentry and hypersonic vehicles was subjected to multiple cycles of both radiant and aerothermal heating to evaluate its aerothermal performance and structural integrity. The TPS was designed for a maximum operating temperature of 1255 K and featured a shingled, corrugation stiffened corrugated skin heat shield of Haynes 188, a cobalt base alloy. The model was subjected to 3 radiant preheat/aerothermal tests for a total of 67 seconds and to 15 radiant heating tests for a total of 85.9 minutes at 1255 K. The TPS limited the primary structure to temperatures below 430 K in all tests. No catastrophic failures occurred in the heat shields, supports, or insulation system. The TPS continued to function even after exposure to a differential temperature 4 times the design value produced thermal buckles in the outer skin. The shingled thermal expansion joint effectively allowed for thermal expansion of the heat shield without allowing any appreciable hot gas flow into the model cavity, even though the overlap gap between shields increased after several thermal cycles

Imaging Optically-Thin Hot Spots Near the Black Hole Horizon of Sgr A* at Radio and Near-Infrared Wavelengths

Sub milli-arcsecond astrometry and imaging of the black hole Sgr A* at the Galactic centre may become possible in the near future at infrared and sub-millimetre wavelengths. Motivated by observations of short-term infrared and X-ray variability of Sgr A*, in a previous paper we computed the expected images and light curves, including polarization, associated with an compact emission region orbiting the central black hole. We extend this work, using a more realistic hot-spot model and including the effects of opacity in the underlying accretion flow. We find that at infrared wavelengths the qualitative features identified by our earlier work are present, namely it is possible to extract the black hole mass and spin from spot images and light curves of the observed flux and polarization. At radio wavelengths, disk opacity produces significant departures from the infrared behaviour, but there are still generic signatures of the black hole properties. Detailed comparison of these results with future data can be used to test general relativity and to improve existing models for the accretion flow in the immediate vicinity of the black hole.Comment: 13 pages, 26 figures, submitted to MNRA

News and the Overloaded Consumer: Factors Influencing Information Overload Among News Consumers

News producers continue to increase their volume of production and delivery platforms in an effort to reach and maintain news consumers. However, consumers may not necessarily find more news desirable. Previous studies have suggested that information surplus can lead to negative outcomes for consumers, but research of outcomes related to news production and consumption has been scant. This study explores novel areas of news surplus and overload, empirically examining factors associated with the degree of perceived overload across a broad spectrum of news delivery platforms. The findings reveal that the majority of today's news consumers feel overloaded with the amount of news they are confronted with. Gender, news interest, and the use of specific news platforms and outlets predict the degree of that overload. News access through platforms and outlets such as computers, e-readers, and Facebook is positively associated with overload, whereas other platforms such as television and the iPhone are negatively associated with overload. Implications for media psychology and news consumption are discussed.Journalis