17,627 research outputs found
Temporal Decomposition Studies of GRB Lightcurves
Gamma-ray bursts (GRB) are extremely energetic events and produce highly
diverse light curves. Light curves are believed to be resulting from internal
shocks reflecting the activities of the GRB central engine. Hence their
temporal studies can potentially lead to the understanding of the GRB central
engine and its evolution. The light curve variability time scale is an
interesting parameter which most models attribute to a physical origin e.g.,
central engine activity, clumpy circumburst medium, or relativistic turbulence.
We develop a statistical method to estimate the GRB minimum variability time
scale (MVT) for long and short GRBs detected by GBM. We find that the MVT of
short bursts is distinctly shorter than that for long GRBs supprting the
possibility of a more compact central engine of the former. We find that MVT
estimated by this method is consistent with the shortest rise time of the
fitted pulses. Hence we use the fitted pulse rise times to study the evolution
of burst variability time scale. Variability time is in turn related to the
minimum bulk Lorentz factor. Using this we relate the GRB spectral evolution to
the evolution of the variability time scale. %Gamma-ray burst (GRB) light
curves are believed to result from internal shocks reflecting the activities of
the GRB central engine. %Hence their temporal deconvolution studies can
potentially lead to the understanding of the evolution of the minimum
variability %time scales which in turn is related to the minimum bulk Lorentz
factor. We relate the GRB spectral evolution to the evolution of the %minimum
variability time scale.Comment: 5 pages 6 figures. Presented at GRB2012 at Marbella, Spai
A Study on Proteolytic Enzyme Activity in the Erythrocytes of Diabetic Patients
The present study demonstrates the possibility of increased proteolytic activities in diabetic individuals. Proteolytic activity was measured by the amount of amino group released by the erythrocyte lysate of the diabetic individual using phenylhydrazine treated hemoglobin as substrate. The proteolytic activity in erythrocyte lysates against oxidatively damaged hemoglobin was significantly increased in diabetic individuals compared to controls (p<0.001).The result of this study indicates that in diabetic individuals, proteolytic enzymes degrade many oxidatively altered proteins preventing the accumulation of altered and damaged proteins in the cell
Secondary periodicities of microbursts of TeV gamma rays from the Crab pulsar
Observations were made during the past several years on the Crab pulsar using the Ooty atmospheric Cerenkov array with the aim of detecting possible emission of ultra high energy gamma rays by the pulsar. During the course of these observations, it was found that the Crab pulsar emits TeV gamma rays in bursts of short duration. The microbursts of TeV gamma rays from the Crab pulsar, which were seen in the data of at least three years, also reveal interesting secondary periodicities. It was noticed at first that some bursts could be connected with the others that occurred during the same night or during the next two nights with integral number of cycles of periods 43 + or - 1 minute. Ten possible periods in the vicinity of 43 minutes were determined for all the combinations of bursts for each year. The best values of periods thus obtained were different from year to year. But when, instead of the real time, the number of Crab cycles elapsed between the bursts was used as the unit of time, two values of burst periods - 77460 and 77770 Crab cycles - were found to be significant in the data of at least two years. A Monte Carlo simulation using 1500 trial periods chosen randomly within + or - 5 minutes of the original burst period did not reveal any value of the period as significant
Scaling of the risk landscape drives optimal life history strategies and the evolution of grazing
Consumers face numerous risks that can be minimized by incorporating
different life-history strategies. How much and when a consumer adds to its
energetic reserves or invests in reproduction are key behavioral and
physiological adaptations that structure much of how organisms interact. Here
we develop a theoretical framework that explicitly accounts for stochastic
fluctuations of an individual consumer's energetic reserves while foraging and
reproducing on a landscape with resources that range from uniformly distributed
to highly clustered. First, we show that optimal life-history strategies vary
in response to changes in the mean productivity of the resource landscape,
where depleted environments promote reproduction at lower energetic states,
greater investment in each reproduction event, and smaller litter sizes. We
then show that if resource variance scales with body size due to landscape
clustering, consumers that forage for clustered foods are susceptible to strong
Allee effects, increasing extinction risk. Finally, we show that the proposed
relationship between consumer body size, resource clustering, and Allee
effect-induced population instability offers key ecological insights into the
evolution of large-bodied grazing herbivores from small-bodied browsing
ancestors.Comment: 9 pages, 5 figures, 3 Supplementary Appendices, 2 Supplementary
Figure
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