2,395 research outputs found
Codex Enables Secure Offline Micropayments
This paper introduces a new micropayment scheme, suitable for all kinds of transactions, and does not require online transactions for either the payer or payee. The designed method uses an encrypted data structure called Codex which self replicates to represent the current values of both the payer and the payee. The model, while providing fraud detection also guarantees payment & loss recovery
People, SHGs and Social Objectives: A Formal Framework
A Self Help Group [SHG] is a small homogeneous gathering of persons who join on a voluntary basis in order to undertake some common activity through mutual trust and mutual help. SHG system is conceptualized primarily to address the problem of rural unemployment, and empowering people to make them economically self-dependent. But, there is a possibility of it being turned into a commercial unit negating the very thesis it espouses. We proposed a value based design of information system for SHGs to make them socially responsive by inculcating the social objectives such as collaboration, dependability, transparency and inclusiveness. The study includes formalization of structural and dynamic aspects of SHGs, and deals with the implementability of dynamic behavior that makes the system socially responsive by implementing the four objectives. We plan implementation of the concept in UML framework. The information system will be useful to the Funding Agency/Governing Body in identifying which of the members, SHGs, Banks, Third Party Merchants and NGOs are socially responsive i.e. collaborative, dependable, transparent and inclusive
GRB000301C with peculiar afterglow emission
The CCD magnitudes in Johnson V and Cousins R and I photometric passbands are
determined for GRB 000301C afterglow starting ~ 1.5 day after the gamma-ray
burst. In fact we provide the earliest optical observations for this burst.
Light curves of the afterglow emissions in U, B, V, R, I, J and K' passbands
are obtained by combining the present measurements with the published data.
Flux decay shows a very uncommon variation relative to other well observed
GRBs. Overall, there is a steepening of the optical and near-infrared flux
decay caused by a geometric and sideways expanding jet. This is superimposed by
a short term variability especially during early time (Delta t < 8 days). The
cause of variability is not well understood, though it has occurred
simultaneously with similar amplitude in all the filters. We derive the early
and late time flux decay constants using jet model. The late time flux decay is
the steepest amongst the GRB OTs observed so far with alpha ~ 3. Steepening in
the flux decay seems to have started simultaneously around Delta t ~ 7.6 day in
all passbands. The value of spectral index in the optical-near IR region is ~
-1.0. Redshift determination with z=2.0335 indicates cosmological origin of the
GRB having a luminosity distance of 16.6 Gpc. Thus it becomes the second
farthest amongst the GRBs with known distances. An indirect estimate of the
fluence > 20 keV indicates, if isotropic,> =10^53 ergs of release of energy.
The enormous amount of released energy will be reduced, if the radiation is
beamed which is the case for this event. Using a jet break time of 7.6 days, we
infer a jet opening angle of ~ 0.15 radian. This means the energy released is
reduced by a factor of ~ 90 relative to the isotropic value.Comment: LaTeX file, 11 pages including 4 figures, uses psfig.sty, Bull.
Astron. Society of India(accepted, Sept, 2000 issue
CCD photometric and mass function study of 9 young Large Magellanic Cloud star clusters
We present CCD photometric and mass function study of 9 young Large
Magellanic Cloud star clusters namely NGC 1767, NGC 1994, NGC 2002, NGC 2003,
NGC 2006, SL 538, NGC 2011, NGC 2098 and NGC 2136. The BVRI data reaching down
to V ~ 21 mag, are collected from 3.5-meter NTT/EFOSC2 in sub-arcsec seeing
conditions. For NGC 1767, NGC 1994, NGC 2002, NGC 2003, NGC 2011 and NGC 2136,
broad band photometric CCD data are presented for the first time. Seven of the
9 clusters have ages between 16 to 25 Myr while remaining two clusters have
ages Myr (NGC 2098) and Myr (NGC 2136). For 7 younger
clusters, the age estimates based on a recent model and the integrated spectra
are found to be systematically lower ( 10 Myr) from the present estimate.
In the mass range of , the MF slopes for 8 out of nine
clusters were found to be similar with the value of ranging from
to . For NGC 1767 it is flatter with . Mass segregation effects are observed for NGC 2002, NGC 2006,
NGC 2136 and NGC 2098. This is consistent with the findings of Kontizas et al.
for NGC 2098. Presence of mass segregation in these clusters could be an
imprint of star formation process as their ages are significantly smaller than
their dynamical evolution time. Mean MF slope of
derived for a sample of 25 young ( Myr) dynamically unevolved LMC
stellar systems provide support for the universality of IMF in the intermediate
mass range .Comment: To appear in MNRA
Continued Radio Monitoring of the Gamma Ray Burst 991208
We present radio observations of the afterglow of the bright gamma-ray burst
GRB 991208 at frequencies of 1.4, 4.9 and 8.5 GHz, taken between two weeks and
300 days after the burst. The well-sampled radio light curve at 8.5 GHz shows
that the peak flux density peaked about 10 days after the burst and decayed
thereafter as a power-law t^-1.07. This decay rate is more shallow than the
optical afterglow with t^-2.2, which was measured during the first week. These
late-time data are combined with extensive optical, millimeter and centimeter
measurements and fitted to the standard relativistic blast wave model. In
agreement with previous findings, we find that an isotropic explosion in a
constant density or wind-blown medium cannot explain these broadband data
without modifying the assumption of a single power-law slope for the electron
energy distribution. A jet-like expansion provides a reasonable fit to the
data. In this case, the flatter radio light curve compared to the optical may
be due to emission from an underlying host galaxy, or due to the blastwave
making a transition to non-relativistic expansion. The model that best
represents the data is a free-form model in which it is assumed that the
broadband emission originates from a synchrotron spectrum, while the
time-evolution of the break frequencies and peak flux density are solved for
explicitly. Although the decay indices for most of the synchrotron parameters
are similar to the jet model, the evolution of the cooling break is unusually
rapid, and therefore requires some non-standard evolution in the shock.
(abridged)Comment: ApJ, in pres
A Late-Time Flattening of Afterglow Light Curves
We present a sample of radio afterglow light curves with measured decay
slopes which show evidence for a flattening at late times compared to optical
and X-ray decay indices. The simplest origin for this behavior is that the
change in slope is due to a jet-like outflow making a transition to
sub-relativistic expansion. This can explain the late-time radio light curves
for many but not all of the bursts in the sample. We investigate several
possible modifications to the standard fireball model which can flatten
late-time light curves. Changes to the shock microphysics which govern particle
acceleration, or energy injection to the shock (either radially or azimuthally)
can reproduce the observed behavior. Distinguishing between these different
possibilities will require simultaneous optical/radio monitoring of afterglows
at late times.Comment: ApJ, submitte
Modeling a high mass turn down in the stellar initial mass function
Statistical sampling from the stellar initial mass function (IMF) for all
star-forming regions in the Galaxy would lead to the prediction of ~1000 Msun
stars unless there is a rapid turn-down in the IMF beyond several hundred solar
masses. Such a turndown is not necessary for dense clusters because the number
of stars sampled is always too small. Here we explore several mechanisms for an
upper mass cutoff, including an exponential decline of the star formation
probability after a turbulent crossing time. The results are in good agreement
with the observed IMF over the entire stellar mass range, and they give a
gradual turn down compared to the Salpeter function above ~100 Msun for normal
thermal Jeans mass, M_J. The upper mass turn down should scale with M_J in
different environments. A problem with the models is that they cannot give both
the observed power-law IMF out to the high-mass sampling limit in dense
clusters, as well as the observed lack of supermassive stars in whole galaxy
disks. Either there is a sharper upper-mass cutoff in the IMF, perhaps from
self-limitation, or the IMF is different for dense clusters than for the
majority of star formation that occurs at lower density. Dense clusters seem to
have an overabundance of massive stars relative to the average IMF in a galaxy.Comment: 19 pages, 2 figures, Astrophysical Journal, Vol 539, August 10, 200
Complete Genome Sequence of Pelosinus fermentans JBW45, a Member of a Remarkably Competitive Group of Negativicutes in the Firmicutes Phylum.
The genome of Pelosinus fermentans JBW45, isolated from a chromium-contaminated site in Hanford, Washington, USA, has been completed with PacBio sequencing. Nine copies of the rRNA gene operon and multiple transposase genes with identical sequences resulted in breaks in the original draft genome and may suggest genomic instability of JBW45
SS 433: Results of a Recent Multi-wavelength Campaign
We conducted a multi-wavelength campaign in September-October, 2002, to
observe SS 433. We used 45 meter sized 30 dishes of Giant Meter Radio Telescope
(GMRT) for radio observation, 1.2 meter Physical Research Laboratory Infra-red
telescope at Mt Abu for IR, 1 meter Telescope at the State Observatory,
Nainital for Optical photometry, 2.3 meter optical telescope at the Vainu Bappu
observatory for spectrum and Rossi X-ray Timing Explorer (RXTE) Target of
Opportunity (TOO) observation for X-ray observations. We find sharp variations
in intensity in time-scales of a few minutes in X-rays, IR and radio
wavelengths. Differential photometry at the IR observation clearly indicated
significant intrinsic variations in short time scales of minutes throughout the
campaign. Combining results of these wavelengths, we find a signature of delay
of about two days between IR and Radio. The X-ray spectrum yielded double Fe
line profiles which corresponded to red and blue components of the relativistic
jet. We also present the broadband spectrum averaged over the campaign
duration.Comment: 17 pages 10 figures MNRAS (submitted
Noise Propagation in Two-Step Series MAPK Cascade
Series MAPK enzymatic cascades, ubiquitously found in signaling networks, act as signal amplifiers and play a key role in processing information during signal transduction in cells. In activated cascades, cell-to-cell variability or noise is bound to occur and thereby strongly affects the cellular response. Commonly used linearization method (LM) applied to Langevin type stochastic model of the MAPK cascade fails to accurately predict intrinsic noise propagation in the cascade. We prove this by using extensive stochastic simulations for various ranges of biochemical parameters. This failure is due to the fact that the LM ignores the nonlinear effects on the noise. However, LM provides a good estimate of the extrinsic noise propagation. We show that the correct estimate of intrinsic noise propagation in signaling networks that contain at least one enzymatic step can be obtained only through stochastic simulations. Noise propagation in the cascade depends on the underlying biochemical parameters which are often unavailable. Based on a combination of global sensitivity analysis (GSA) and stochastic simulations, we developed a systematic methodology to characterize noise propagation in the cascade. GSA predicts that noise propagation in MAPK cascade is sensitive to the total number of upstream enzyme molecules and the total number of molecules of the two substrates involved in the cascade. We argue that the general systematic approach proposed and demonstrated on MAPK cascade must accompany noise propagation studies in biological networks
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