2,723 research outputs found
GRB Afterglows from Anisotropic Jets
Some progenitor models of gamma-ray bursts (GRBs) (e.g., collapsars) may
produce anisotropic jets in which the energy per unit solid angle is a
power-law function of the angle (). We calculate light
curves and spectra for GRB afterglows when such jets expand either in the
interstellar medium or in the wind medium. In particular, we take into account
two kinds of wind: one () possibly from a typical red
supergiant star and another () possibly from a Wolf-Rayet
star. We find that in each type of medium, one break appears in the late-time
afterglow light curve for small but becomes weaker and smoother as
increases. When , the break seems to disappear but the afterglow decays
rapidly. Thus, one expects that the emission from expanding, highly anisotropic
jets provides a plausible explanation for some rapidly fading afteglows whose
light curves have no break. We also present good fits to the optical afterglow
light curve of GRB 991208. Finally, we argue that this burst might arise from a
highly anisotropic jet expanding in the wind () from a red
supergiant to interpret the observed radio-to-optical-band afterglow data
(spectrum and light curve).Comment: 12 pages + 10 figures, accepted by Ap
On the use of Kolmogorov-Landau approach in deriving various correlation functions in 2-D incompressible turbulence
We look at various correlation functions, which include those that involve
both the velocity and the vorticity fields, in 2-D isotropic homogeneous
decaying turbulence.We adopt the more intuitive approach due to Kolmogorov (and
subsequently, Landau in his text on fluid dynamics) and show that how the 2-D
turbulence results, obtainable using other methods, may be established in a
simpler way.Also, some experimentally verifiable correlation functions in the
dissipation range have been derived for the same system.The paper also
showcases the inability of the Kolmogorov-Landau approach to get the
``one-eighth law'' in the enstrophy cascade region.As discussed in the paper,
this may raise the spectre of logarithmic corrections once again in 2-D
turbulence.Comment: A typos-corrected version of the earlier submissio
The Near Infrared and Multiwavelength Afterglow of GRB 000301c
We present near-infrared observations of the counterpart of GRB 000301c. The
K' filter (2.1 micron) light curve shows a well-sampled break in the decay
slope at t=3.5 days post-burst. The early time slope is very shallow (~ -0.1),
while the late time slope is steep (-2.2). Comparison with the optical (R band)
light curve shows marginally significant differences, especially in the early
time decay slope (which is steeper in the optical) and the break time (which
occurs later in the optical). This is contrary to the general expectation that
light curve breaks should either be achromatic (e.g., for breaks due to
collimation effects) or should occur later at longer wavelengths (for most
other breaks). The observed color variations might be intrinsic to the
afterglow, or might indicate systematic errors of > 0.08 magnitude in all
fluxes. Even if the break is achromatic, we argue that its sharpness poses
difficulties for explanations that depend on collimated ejecta. The R light
curve shows further signs of fairly rapid variability (a bump, steep drop, and
plateau) that are not apparent in the K' light curve. In addition, by combining
the IR-optical-UV data with millimeter and radio fluxes, we are able to
constrain the locations of the self-absorption break and cooling break and to
infer the location of the spectral peak at t=3 days: f_nu = 3.4 mJy at nu=1e12
Hz. Using the multiwavelength spectral energy distribution, we are able to
constrain the blast wave energy, which was E > 3e53 erg if the explosion was
isotropic. This implies a maximum gamma ray production efficiency of ~ 0.15 for
GRB 000301C.Comment: Accepted to The Astrophysical Journal. 24 pages, 4 figures, 3 tables;
uses AASTeX 5 macros. This version includes a new figure (R-K' color vs.
time), a better sampled R band light curve, and more extensive discussion of
the optical data and error analysi
On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions
Based on the CCD observations of remote young open clusters NGC 2383, NGC
2384, NGC 4103, NGC 4755, NGC 7510 and Hogg 15, we constructed their observed
luminosity functions (LFs). The observed LFs are corrected for field star
contamination determined with the help of galactic star count model. In the
case of Hogg 15 and NGC 2383 we also considered the additional contamination
from neighbouring clusters NGC 4609 and NGC 2384 respectively. These
corrections provided the realistic pattern of cluster LF in the vicinity of the
MS turn on point and at fainter magnitudes, revealed the so called H-feature
arising due to transition of the Pre-MS phase to MS, which is dependent on the
cluster age. The theoretical LFs were constructed representing a cluster
population model with continuous star formation for a short time scale and a
power law Initial Mass Function (IMF) and these were fitted to the observed LF.
As a result we are able to determine for each cluster a set of parameters,
describing cluster population (the age, duration of star formation, IMF slope
and percentage of field star contamination). It was found that in spite of the
non-monotonic behaviour of observed LFs, cluster IMFs can be described as the
power law functions with slopes similar to Salpeter's value. The present MS
turn on cluster ages are several times lower than those derived from the
fitting of theoretical isochrones to the turn off region of the upper Main
Sequences.Comment: 17 pages, 5 figures, To appear in MNRA
A Novel Survey Analysis on Energy-Aware Routing Protocols for Manet Applications
MANET system applications in today situation consumes larger amounts of energy this energy becomes an important parameter and scarce resource in MANETS This energy consumption has to be reduced and harvested in the communication devices for efficient usage of energy and power Different energy aware and harvesting strategies have been devised using various protocols to achieve the reduction and minimised usage of the available energy and power resources This paper surveys and illustrates the differences of various Energy aware Routing Protocol used in MANETS based on the matrices used These protocols provide some awareness in optimizing the Energy and Power Resources and limit the consumption when nodes are idle This intern increases the life time of the node and improves the performance widely investigating the energy efficiency protocols for adhoc infrastructure less MANET environmen
Centre for Non-destructive Evaluation at CSIR-National Metallurgical Laboratory, Jamshedpur for materials characterisation and damage evaluation: an Overview
Non-Destructive Evaluation (NDE) centre established in 2003, with a partial funding from Department of Science & Technology (DST), Govt. of India at CSIR- National Metallurgical Laboratory, Jamshedpur has developed different NDE based methodologies for characterisation of microstructure and assessment of different kinds of damage (creep, fatigue, corrosion etc) for diverse components from aerospace, defence, power and steel sector.
Besides, need based development of NDE sensors and techniques for specialised applications are also the integral part of Centre activities. This paper will highlight some of the above activities particularly the research activities on fatigue and corrosion damage evaluation in structural materials by advanced NDE
REAL-TIME VIDEO WATERMARKING FOR COPYRIGHT PROTECTION BASED ON HUMAN PERCEPTION
There is a need for real-time copyright logo insertion in emerging applications, such as Internet protocol television (IPTV). This situation arises in IP-TV and digital TV broadcasting when video residing in a server has to be broadcast by different stations and under different broadcasting rights. Embedded systems that are involved in broadcasting need to have embedded copyright protection. Existing works are targeted towards invisible watermarking, not useful for logo insertion. MPEG-4 is the mainstream exchangeable video format in the Internet today because it has higher and flexible compression rate, lower bit rate, and higher efficiency while superior visual quality.The main steps for MPEG-4 are color space conversion and sampling, DCT and its inverse (IDCT), quantization, zigzag scanning, motion estimation, and entropy coding. In this work a watermarking algorithm that performs the broadcaster\u27s logo insertion as watermark in the DCT domain is been presented. The robustness of DCT watermarking arises from the fact that if an attack tries to remove watermarking at mid frequencies, it will risk degrading the fidelity of the image\video because some perceptive details are at mid frequencies. The suggested methods has implemented in matlab
Non-destructive Testing and Evaluation at CSIR-National Metallurgical Laboratory, Jamshedpur for Iron and Steel Industry: an Overview
In the area of iron and steel, the NDE centre at CSIR- National Metallurgical Laboratory has not only developed different NDE based methodologies for characterisation of microstructure and assessment of different kinds of damage (creep, fatigue, corrosion etc) in various grades of steel; but also developing methodologies for blast furnace lining thickness measurement and assessment of High Speed Steel (HSS) rolls. This paper will highlight some of the above activities particularly related to steel and allied industries
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