2,954 research outputs found
A study of the old galactic star cluster Berkeley 32
We present new CCD photometry of the distant old open star cluster Berkeley 32 in Johnson V and Cousins I passbands. A total of about 3200 stars have been observed in a field of 13X13 arcmin**2. The colour-magnitude diagram in V, (V-I) has been generated down to V = 22 mag. A broad but well defined main sequence is clearly visible. Some blue stragglers, a well developed subgiant branch and a Red Clump are also seen. By fitting isochrones to this CMD as well as to other CMDs available in the literature, and using the Red Clump location, the reddening, distance and age of the star cluster have been determined. The cluster has a distance of 3.3 kpc, its radius is about 2.4 pc; the reddening E(B-V) is 0.08 mag and the age is 6.3 Gyr. By comparison with theoretical isochrones, a metallicity of [Fe/H]= -0.2 dex has been estimated. We find a much flatter mass function than what has been found for young clusters. If the mass function is a power law dN/dm = const.*m**alpha, then we get alpha = -0.5+-0.3 in the mass range 0.6-1.1 solar masses. This may be seen as a signature of the highly evolved dynamical state of the cluster
Need of Improved Non-Destructive Technique for the Surface Condition Monitoring of High Speed Steel (HSS) Work Rolls
Over the last few years, the use of work rolls for hot rolling of flat steel has changed from clear chill rolls to indefinite chill, then came high chrome steel and now High Speed tool Steel (HSS). The hardness of HSS roll reaches 80/85 ShC, hence it becomes very much crack-sensitive and the developed crack is usually oriented parallel to the roll axis and propagates in a non-radial direction. In the next phase, a fatigue “cat’s tongue” like fracture band propagates progressively in a circumferential direction running more or less parallel to the barrel surface. The direction of propagation is opposite to that of the direction of roll rotation. Crack propagation develops within the working surface of the roll, gradually increasing in depth and width followed by a large surface spall of the overlying barrel surface. Hence it is highly recommended to eliminate all kinds of surface cracks, whenever these rolls are reground, otherwise these `cats – tongue’ band type spalls may lead to abnormal failure. This paper presents the necessity of development of improved non-destructive technique for the crack detection of HSS rolls and also highlights the recent attempts at Tata Steel in collaboration with CSIR-National Metallurgical Laboratory, Jamshedpur to develop surface wave based ultrasonic technique to detect fine cracks on the barrel surface of HSS rolls to optimise the grinding procedure for having crack free roll surface
Broad Band Optical Polarimetric Study of IC 1805
We present the BVR broad band polarimetric observations of 51 stars belonging
to the young open cluster IC 1805. Along with the photometric data from the
literature we have modeled and subtracted the foreground dust contribution from
the maximum polarization (P_{max}) and colour excess (E_{B-V}). The mean value
of the P_max for intracluster medium and the foreground are found to be 5.008
+/-0.005 % and 4.865 +/-0.022 % respectively. Moreover, the mean value of the
wavelength of maximum polarization (lambda_{max}) for intracluster medium is
0.541 +/- 0.003 micro m, which is quite similar as the general interstellar
medium (ISM). The resulting intracluster dust component is found to have
negligible polarization efficiency as compared to interstellar dust. Some of
the observed stars in IC 1805 have shown the indication of intrinsic
polarization in their measurements.Comment: 8 pages, 7 figures, Accepted for publication in MNRA
2D and 3D convective Brinkman-Forchheimer equations perturbed by a subdifferential and applications to control problems
The following convective Brinkman-Forchheimer (CBF) equations (or damped
Navier-Stokes equations) with potential
\begin{equation*}
\frac{\partial \boldsymbol{y}}{\partial t}-\mu
\Delta\boldsymbol{y}+(\boldsymbol{y}\cdot\nabla)\boldsymbol{y}+\alpha\boldsymbol{y}+\beta|\boldsymbol{y}|^{r-1}\boldsymbol{y}+\nabla
p+\Psi(\boldsymbol{y})\ni\boldsymbol{g},\ \nabla\cdot\boldsymbol{y}=0,
\end{equation*}
in a -dimensional torus is considered in this work, where ,
and . For with and
with ( for ), we establish the
existence of \textsf{\emph{a unique global strong solution}} for the above
multi-valued problem with the help of the \textsf{\emph{abstract theory of
-accretive operators}}. %for nonlinear differential equations of accretive
type in Banach spaces.
Moreover, we demonstrate that the same results hold \textsf{\emph{local in
time}} for the case with and with . We
explored the -accretivity of the nonlinear as well as multi-valued
operators, Yosida approximations and their properties, and several higher order
energy estimates in the proofs. For , we {quantize (modify)} the
Navier-Stokes nonlinearity to
establish the existence and uniqueness results, while for
( for ), we handle the Navier-Stokes nonlinearity by the
nonlinear damping term . Finally, we
discuss the applications of the above developed theory in feedback control
problems like flow invariance, time optimal control and stabilization
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
Integrated parameters of star clusters: A comparison of theory and observations
(Abridged) This paper presents integrated magnitude and colours for synthetic
clusters. The integrated parameters have been obtained for the whole cluster
population as well as for the main-sequence (MS) population of star clusters.
We have also estimated observed integrated magnitudes and colours of MS
population of galactic open clusters, LMC and SMC star clusters. It is found
that the colour evolution of MS population of star clusters is not affected by
the stochastic fluctuations, however these fluctuations significantly affect
the colour evolution of the whole cluster population. The fluctuations are
maximum in colour in the age range 6.7 log (age) 7.5. Evolution
of integrated colours of MS population of the clusters in the Milky Way, LMC
and SMC, obtained in the present study are well explained by the present
synthetic cluster model. The observed integrated colours of MS
population of LMC star clusters having age 500 Myr seem to be
distributed around 0.004 model, whereas colours are found to be
more bluer than those predicted by the 0.004 model. vs
two-colour diagram for the MS population of the Milky Way star clusters shows a
fair agreement between the observations and present model, however the diagrams
for LMC and SMC clusters indicate that observed colours are relatively
bluer. Possible reasons for this anomaly have been discussed.Comment: 35 pages, 20 figs, accepted for publication in MNRA
A Novel Technique to Enhance the Lifetime of Wireless Sensor Networks through Software Realization
In the most of the real world scenarios, wireless sensor networks are used. Some of the major tasks of these types of networks is to sense some information and sending it to monitoring system or tracking some activity etc. In such applications, the sensor nodes are deployed in large area and in considerably large numbers [1]-[3]. Each of these node will be having constrained resources whether it might be energy, memory or processing capability. Energy is the major resource constraint in these types of networks. Hence enough care to be taken in all aspects such that energy can be used very efficiently. Different Activities which will be taking place in a sensor node are sensing, radio operations and receiving and computing. Among all these operations, radio consumes maximum power. Hence there is a need of reducing the power consumption in such radio operations. In the proposed work a software module is developed which will reduce the number of transmissions done to the base station. The work compares the consecutively sensed data and if these data are same then the old data then the old data will be retained. In other case the newly sensed data will be sent to the sink node. This technique reduces the number of data transmissions in a significant way. With the reduced number of transmissions, the energy saved in each node will be more, which will increase the lifetime of the entire network
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