The Rapidly Fading Optical Afterglow of GRB 980519

GRB 980519 had the most rapidly fading of the well-documented GRB afterglows, consistent with t^{-2.05 +/- 0.04} in BVRI as well as in X-rays during the two days in which observations were made. We report VRI observations from the MDM 1.3m and WIYN 3.5m telescopes, and we synthesize an optical spectrum from all of the available photometry. The optical spectrum alone is well fitted by a power law of the form nu^{-1.20 +/- 0.25}, with some of the uncertainty due to the significant Galactic reddening in this direction. The optical and X-ray spectra together are adequately fitted by a single power law nu^{-1.05 +/- 0.10}. This combination of steep temporal decay and flat broad-band spectrum places a severe strain on the simplest afterglow models involving spherical blast waves in a homogeneous medium. Instead, the rapid observed temporal decay is more consistent with models of expansion into a medium of density n(r) proportional to r^{-2}, or with predictions of the evolution of a jet after it slows down and spreads laterally. The jet model would relax the energy requirements on some of the more extreme GRBs, of which GRB 980519 is likely to be an example because of its large gamma-ray fluence and faint host galaxy.Comment: 13 pages, submitted to ApJ Letter

The crude protein production of grassland and the utilization by milking cows.

An attempt was made with experimental data of various origins to quantify the intake of N from pasture grass by milking cows during the grazing period. It was also demonstrated how much of this N was removed by secretion in the milk as well as the conc. of N in the faeces and in the urine remaining on the pasture after grazing. From a fertilizer application to the pasture of 450 kg N/ha yr an equal conc. was taken up by the herbage. Of this herbage N about 75-80% remained on the pasture after grazing. The conc. remaining on the grassland increased sharply with increasing N rates and this went parallel with an increasing intensity in the N circulation in the system soil-plant-animal-soil and a rising NO3 content in the surface layer of ground water. (Abstract retrieved from CAB Abstracts by CABI’s permission

The Bayesian Origins of Growth Rates in Stochastic Environments

Stochastic multiplicative dynamics characterize many complex natural phenomena such as selection and mutation in evolving populations, and the generation and distribution of wealth within social systems. Population heterogeneity in stochastic growth rates has been shown to be the critical driver of diversity dynamics and of the emergence of wealth inequality over long time scales. However, we still lack a general statistical framework that systematically explains the origins of these heterogeneities from the adaptation of agents to their environment. In this paper, we derive population growth parameters resulting from the interaction between agents and their knowable environment, conditional on subjective signals each agent receives. We show that average growth rates converge, under specific conditions, to their maximal value as the mutual information between the agent's signal and the environment, and that sequential Bayesian learning is the optimal strategy for reaching this maximum. It follows that when all agents access the same environment using the same inference model, the learning process dynamically attenuates growth rate disparities, reversing the long-term effects of heterogeneity on inequality. Our approach lays the foundation for a unified general quantitative modeling of social and biological phenomena such as the dynamical effects of cooperation, and the effects of education on life history choices.Comment: 12 pages, 4 figure

Capacitive effects and memristive switching in three terminal multilayered MoS<inf>2</inf>devices

We report on the electrical properties of gated two-terminal multilayered molybdenum disulfide (MoS2) memristor devices having a planar architecture. The approach based on highly dispersed MoS2 flakes drop cast onto a bottom gated Si/SiO2 (100nm) wafer containing metal Pd contact electrodes yields devices that exhibit a number of complex properties including memristive and capacitive effects as well as multiple non-zero-crossing current-voltage hysteresis effects. The devices also show a reaction to a varying gate bias. An increasingly positive gate led to the devices displaying a linear ohmic I-V response while an increasingly negative gate bias drove the system to behave more memristive with a widening hysteresis loop

Novel conducting polymer current limiting devices for low cost surge protection applications

We report on the development of novel intrinsic conducting polymer two terminal surge protection devices. These resettable current limiting devices consist of polyaniline nanofibres doped with methane sulphonic acid electrochemically deposited between two 55 μm spaced gold electrodes. At normal applied voltages, the low resistance devices act as passive circuit elements, not affecting the current flow. However during a current surge the devices switch from ohmic to non-ohmic behaviour, limiting current through the device. After the current surge has passed, the devices reset back to their original state. Our studies show that a partial de-doping/re-doping process caused by the rapid diffusion of moisture out of or into the polymer film during joule heating/cooling is the underlying mechanism responsible

Non-ideal artificial phase discontinuity in long Josephson 0-kappa-junctions

We investigate the creation of an arbitrary $\kappa$-discontinuity of the Josephson phase in a long Nb-AlO_x-Nb Josephson junction (LJJ) using a pair of tiny current injectors, and study the formation of fractional vortices formed at this discontinuity. The current I_inj, flowing from one injector to the other, creates a phase discontinuity kappa ~ I_inj. The calibration of injectors is discussed in detail. The small but finite size of injectors leads to some deviations of the properties of such a 0-kappa-LJJ from the properties of a LJJ with an ideal kappa-discontinuity. These experimentally observed deviations in the dependence of the critical current on I_inj$ and magnetic field can be well reproduced by numerical simulation assuming a finite injector size. The physical origin of these deviations is discussed.Comment: Submitted to Phys. Rev. B (12 figures). v 2: refs updated, long eqs fixed v 3: major changes, fractional vortex dynamics exclude

Nitrate poisoning in cattle. 3. The relationship between nitrate intake with hay or fresh roughage and the speed of intake on the formation of methemoglobin.

For part 2 see NAR/B 48, 238. 3. In 40 feeding experiments during about 5 years dry or lactating Friesian cows weighing 415 to 670 kg and 3 to 8 years old were given diets of hay, grass pellets, turnips or freshly mown grass in 2 meals daily. During experiments blood from the jugular vein was sampled every 15 min. Cows were induced to increase nitrate intake by being given at least 4 meals of roughage rich in nitrate before blood was sampled. There was a positive relation between nitrate intake and methaemoglobin per cent of total Hb but there were differences within and between different roughages in formation of methaemoglobin. With similar nitrate intake and speed of intake, more Hb was converted into methaemoglobin with hay than with freshly mown grass. That was related to the speed at which the nitrate taken with the roughage was released in the rumen as a substrate for the rumen flora. When hay was soaked in distilled water 80% of the nitrate in the cells diffused into the water within 20 min. With turnip and grass chopped to about 1 cm, 30% of the nitrate diffused into the water within 20 min. (Abstract retrieved from CAB Abstracts by CABI’s permission

The Dwarf Novae of Shortest Period

We present observations of the dwarf novae GW Lib, V844 Her, and DI UMa. Radial velocities of H-alph yield orbital periods of 0.05332 +- 0.00002 d (= 76.78 m) for GW Lib and and 0.054643 +- 0.000007 d (= 78.69 m) for V844 Her. Recently, the orbital period of DI UMa was found to be only 0.054564 +- 0.000002 d (= 78.57 m) by Fried et al. (1999), so these are the three shortest orbital periods among dwarf novae with normal-abundance secondaries. GW Lib has attracted attention as a cataclysmic binary showing apparent ZZ Ceti-type pulsations of the white dwarf primary. Its spectrum shows sharp Balmer emission flanked by strong, broad Balmer absorption, indicating a dominant contribution by white-dwarf light. Analysis of the Balmer absorption profiles is complicated by the unknown residual accretion luminosity and lack of coverage of the high Balmer lines. Our best-fit model atmospheres are marginally hotter than the ZZ Ceti instability strip, in rough agreement with recent ultraviolet results from HST. The spectrum and outburst behavior of GW Lib make it a near twin of WZ Sge, and we estimate it to have a quiescent V absolute magnitude 12. Comparison with archival data reveals proper motion of 65 +- 12 mas/yr. The mean spectrum of V844 Her is typical of SU UMa dwarf novae. We detected superhumps in the 1997 May superoutburst with superhump period = 0.05597 +- 0.00005 d. The spectrum of DI UMa appears normal for a dwarf nova near minimum light. These three dwarf novae have nearly identical short periods but completely dissimilar outburst characteristics. We discuss possible implications.Comment: Accepted for publication in Publications of the Astronomical Society of the Pacific; 16 pages, 6 figure