1,500 research outputs found
Search for TeV -rays from H1426+428 during 2004-07 with the TACTIC telescope
The BL Lac object H1426+428 () is an established source of TeV
-rays and detections of these photons from this object also have
important implications for estimating the Extragalactic Background Light (EBL)
in addition to the understanding of the particle acceleration and -ray
production mechanisms in the AGN jets. We have observed this source for about
244h in 2004, 2006 and 2007 with the TACTIC -ray telescope located at
Mt. Abu, India. Detailed analysis of these data do not indicate the presence of
any statistically significant TeV -ray signal from the source
direction. Accordingly, we have placed an upper limit of
on the integrated
-ray flux at 3 significance level.Comment: 11 pages, 5 figures accepted for publication in Journal of Physics G:
Nuclear and Particle Physic
Very High Energy gamma-ray observations of Mrk 501 using TACTIC imaging gamma-ray telescope during 2005-06
In this paper we report on the Markarian 501 results obtained during our TeV
-ray observations from March 11 to May 12, 2005 and February 28 to May
7, 2006 for 112.5 hours with the TACTIC -ray telescope. During 2005
observations for 45.7 hours, the source was found to be in a low state and we
have placed an upper limit of 4.62 10 photons cm
s at 3 level on the integrated TeV -ray flux above 1 TeV
from the source direction. However, during the 2006 observations for 66.8h,
detailed data analysis revealed the presence of a TeV -ray signal from
the source with a statistical significance of 7.5 above
1 TeV. The time averaged differential energy spectrum of the
source in the energy range 1-11 TeV is found to match well with the power law
function of the form () with and .Comment: 16 pages and 8 Figures Accepted for publication in the Journal of
Physics
Artificial Neural Network-based error compensation procedure for low-cost encoders
An Artificial Neural Network-based error compensation method is proposed for
improving the accuracy of resolver-based 16-bit encoders by compensating for
their respective systematic error profiles. The error compensation procedure,
for a particular encoder, involves obtaining its error profile by calibrating
it on a precision rotary table, training the neural network by using a part of
this data and then determining the corrected encoder angle by subtracting the
ANN-predicted error from the measured value of the encoder angle. Since it is
not guaranteed that all the resolvers will have exactly similar error profiles
because of the inherent differences in their construction on a micro scale, the
ANN has been trained on one error profile at a time and the corresponding
weight file is then used only for compensating the systematic error of this
particular encoder. The systematic nature of the error profile for each of the
encoders has also been validated by repeated calibration of the encoders over a
period of time and it was found that the error profiles of a particular encoder
recorded at different epochs show near reproducible behavior. The ANN-based
error compensation procedure has been implemented for 4 encoders by training
the ANN with their respective error profiles and the results indicate that the
accuracy of encoders can be improved by nearly an order of magnitude from
quoted values of ~6 arc-min to ~0.65 arc-min when their corresponding
ANN-generated weight files are used for determining the corrected encoder
angle.Comment: 16 pages, 4 figures. Accepted for Publication in Measurement Science
and Technology (MST
On Compound Poisson Processes Arising in Change-Point Type Statistical Models as Limiting Likelihood Ratios
Different change-point type models encountered in statistical inference for
stochastic processes give rise to different limiting likelihood ratio
processes. In a previous paper of one of the authors it was established that
one of these likelihood ratios, which is an exponential functional of a
two-sided Poisson process driven by some parameter, can be approximated (for
sufficiently small values of the parameter) by another one, which is an
exponential functional of a two-sided Brownian motion. In this paper we
consider yet another likelihood ratio, which is the exponent of a two-sided
compound Poisson process driven by some parameter. We establish, that similarly
to the Poisson type one, the compound Poisson type likelihood ratio can be
approximated by the Brownian type one for sufficiently small values of the
parameter. We equally discuss the asymptotics for large values of the parameter
and illustrate the results by numerical simulations
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