Gamma-Ray Burst Spectra and Light Curves as Signatures of a Relativistically Expanding Plasma

Several patterns have been discovered in how some spectral characteristics change during the decaying phase of long (> few s.) GRB pulses. We compare these observed signatures with those expected from a relativistically expanding shell. Within the internal shock model and assuming a short cooling time, we show that the angular dependence in arrival time can explain the general characteristics of long GRB pulses. This includes the pulse shape, with a fast rise and a slower decay, ~ (1+t/tau)^2, and the spectral evolution, which can be described by the hardness-intensity correlation (HIC), with the intensity being proportional to the square of the hardness. A variation of the relevant time scales involved (the angular spreading and the dynamic) can explain the broad, observed dispersion of the HIC index. Reasonable estimates of physical parameters lead to situations where the HIC relation deviates from a pure power law; features that are indeed present in the observations. Depending on the relative values of the rise and decay times of the intrinsic light curve, the spectral/temporal behavior, as seen by an observer, will produce hard-to-soft or tracking pulses. The observed spectrum is a superposition of many intrinsic spectra arriving from different parts of the shell with varying spectral shifts. Therefore, it will be broader than the emitted spectrum and its spectral parameters could have complex relations with the intrinsic ones. Furthermore, we show that the softening of the low-energy power-law index, that has been observed in some pulses, can be explained by geometric effects and does not need to be an intrinsic behavior.Comment: To appear in ApJ, better resolution figures at http://www.astro.su.se/~felix/research.htm

Perturbative Description of the Fermionic Projector: Normalization, Causality and Furry's Theorem

The causal perturbation expansion of the fermionic projector is performed with a contour integral method. Different normalization conditions are analyzed. It is shown that the corresponding light-cone expansions are causal in the sense that they only involve bounded line integrals. For the resulting loop diagrams we prove a generalized Furry theorem.Comment: 34 pages, LaTeX, 2 ancillary files, minor improvements (published version

Indian Bt cotton varieties do not affect the performance of cotton aphids.

Cotton varieties expressing Cry proteins derived from the soil bacterium Bacillus thuringiensis (Bt) are grown worldwide for the management of pest Lepidoptera. To prevent non-target pest outbreaks and to retain the biological control function provided by predators and parasitoids, the potential risk that Bt crops may pose to non-target arthropods is addressed prior to their commercialization. Aphids play an important role in agricultural systems since they serve as prey or host to a number of predators and parasitoids and their honeydew is an important energy source for several arthropods. To explore possible indirect effects of Bt crops we here examined the impact of Bt cotton on aphids and their honeydew. In climate chambers we assessed the performance of cotton aphids, Aphis gossypii Glover (Hemiptera: Aphididae) when grown on three Indian Bt (Cry1Ac) cotton varieties (MECH 12, MECH 162, MECH 184) and their non-transformed near isolines. Furthermore, we examined whether aphids pick up the Bt protein and analyzed the sugar composition of aphid honeydew to evaluate its suitability for honeydew-feeders. Plant transformation did not have any influence on aphid performance. However, some variation was observed among the three cotton varieties which might partly be explained by the variation in trichome density. None of the aphid samples contained Bt protein. As a consequence, natural enemies that feed on aphids are not exposed to the Cry protein. A significant difference in the sugar composition of aphid honeydew was detected among cotton varieties as well as between transformed and non-transformed plants. However, it is questionable if this variation is of ecological relevance, especially as honeydew is not the only sugar source parasitoids feed on in cotton fields. Our study allows the conclusion that Bt cotton poses a negligible risk for aphid antagonists and that aphids should remain under natural control in Bt cotton fields

Board Composition, Firm Size, Audit Type and Voluntary Disclosure of Forward Looking Information in the Banking Sector: Evidence from Nigeria

Using a multivariate regression analysis, this study explored the effect of firm size on the disclosure level of accounting information in the Nigerian Banking sector while controlling for Board Composition, audit quality and profitability. Significant finding of the study is that size of firms significantly affects level of voluntary information disclosed in the annual reports and accounts of banks in Nigeria. Moreover, audit quality, Board Composition and profitability also affect the level of voluntary information disclosed by the banking sector in Nigeria. The implication of the findings is that Banks with high assets based disclosed more discretionary information than banks with small assets base. Also banks that have Big 4 Auditor tend to disclose more discretionary information than do those without the Big 4 Auditors. Even though, banks are most highly regulated in Nigeria and play significant roles in the development of Nigeria’s econoour, regulatory agencies in Nigeria appear not to have been taking cognizance of these special attributes in the regulation of banks accounting reporting practices. Keywords: Firm Size, Disclosure Level, Voluntary Disclosure, Nigeria Banking Sector

Comment on the paper "Calorimetric Dark Matter Detection with Galactic Center Gas Clouds"

The paper "Calorimetric Dark Matter Detection with Galactic Center Gas Clouds" (Bhoonah et al. 2018) aims to derive limits on dark matter interactions by demanding that heat transfer due to DM interactions is less than that by astrophysical cooling, using clouds in the hot, high-velocity nuclear outflow wind of the Milky Way ($T_{wind} \sim 10^{6-7}$ K, $V_{wind} \sim$ 330 km/s). We argue that clouds in such an extreme environment cannot be assumed to be stable over the long timescales associated with their radiative cooling rates. Furthermore, Bhoonah et al. (2018) uses incorrect parameters for their clouds.Comment: 2 pages, 1 figure. Version appearing in Phys. Rev. Let