14 research outputs found
Chaotic dynamics of off-equatorial orbits around pseudo-Newtonian compact objects with dipolar halos
In this paper, we implement a generalised pseudo-Newtonian potential and
prescribe a numerical fitting formalism to study the off-equatorial orbits
inclined at a certain angle with the equatorial plane around both Schwarzschild
and Kerr-like compact object primaries surrounded by a dipolar halo of matter.
The chaotic dynamics of the orbits are detailed for both non-relativistic and
special-relativistic test particles. The dependence of the degree of chaos on
the rotation parameter and the inclination angle is established
individually using widely used indicators, such as the Poincar\'e Map and the
Lyapunov Characteristic Number. We find that although the chaoticity of the
orbits has a positive correlation with , the growth in the chaotic behaviour
is not systematic. There exists a threshold value of the inclination angle
, after which the degree of chaos shows a sharp increase. On the
other hand, the chaoticity of the inclined orbits anti-correlates with
throughout its entire range. However, the negative correlation is systematic at
lower values of the inclination angle. At higher values of , the degree of
chaos is maximum for the maximally counter-rotating compact objects, the Kerr
parameter of which is below a threshold value . Above this
threshold value, the correlation becomes weak. Furthermore, we establish a
qualitative correlation between the threshold values and the overall
chaoticity. The studies performed with different orbital parameters and several
initial conditions reveal the intricate nature of the system.Comment: 27 pages, 13 figure
Implications of the Universal Temperature Profile for Galaxy Clusters
We study the X-ray cluster gas density distribution in hydrostatic
equilibrium using the universal temperature profile obtained from recent
simulations involving only gravitational processes. If this temperature profile
is an indicator of the influence of gravitational processes alone on the
intracluster medium, then the comparison of various X-ray parameters expected
from this profile and the observed data would point towards any additional
physics that may be required. We compare the entropy at 0.1 R_{200} and
R_{500}, the scaled entropy profile, the gas fraction at 0.3 R_{200} and the
gas fraction profile with recent observations and discuss the implications of
this temperature profile in light of these data. We find that the entropy
imparted to the gas from gravitational processes alone is larger than
previously thought. The entropy at R_{500} for rich clusters is consistent with
data, whereas the entropy at 0.1R_{200} is still less than the observed values.
We also find that the gas fraction in the inner region of clusters, expected
from gravitational processes alone, is smaller than previously thought but
larger than the observed data. It does show a trend with the emission-weighted
temperature () as shown by data. We therefore find that the role of any
additional non-gravitational process influencing the physical state of ICM
would have to be revised in light of these findings.Comment: 11 pages including 11 figures, accepted for publication in MNRAS,
uses mn.sty (included
Model dependence of the multi-transonic behavior, stability properties and corresponding acoustic geometry for accretion onto a spinning black hole
Multi-transonic accretion for a spinning black hole has been compared among
different disc geometries within post Newtonian pseudo potential framework. The
variation of stationary shock characteristics with black hole spin has been
studied in details for all the disc models and compared for adiabatic as well
as for isothermal scenario. The variations of surface gravity with spin for all
these cases have also been investigated.Comment: 18 pages. 19 figure
Gender-Based Comparative Study of Type 2 Diabetes Risk Factors in Kolkata, India: A Machine Learning Approach
Type 2 diabetes mellitus represents a prevalent and widespread global health
concern, necessitating a comprehensive assessment of its risk factors. This
study aimed towards learning whether there is any differential impact of age,
Lifestyle, BMI and Waist to height ratio on the risk of Type 2 diabetes
mellitus in males and females in Kolkata, West Bengal, India based on a sample
observed from the out-patient consultation department of Belle Vue Clinic in
Kolkata. Various machine learning models like Logistic Regression, Random
Forest, and Support Vector Classifier, were used to predict the risk of
diabetes, and performance was compared based on different predictors. Our
findings indicate a significant age-related increase in risk of diabetes for
both males and females. Although exercising and BMI was found to have
significant impact on the risk of Type 2 diabetes in males, in females both
turned out to be statistically insignificant. For both males and females,
predictive models based on WhtR demonstrated superior performance in risk
assessment compared to those based on BMI. This study sheds light on the
gender-specific differences in the risk factors for Type 2 diabetes, offering
valuable insights that can be used towards more targeted healthcare
interventions and public health strategies.Comment: 10 pages, 7 tables,3 figures, submitted to a conferenc
Solving relativistic hydrodynamic equation in presence of magnetic field for phase transition in a neutron star
Hadronic to quark matter phase transition may occur inside neutron stars (NS)
having central densities of the order of 3-10 times normal nuclear matter
saturation density (). The transition is expected to be a two-step
process; transition from hadronic to 2-flavour matter and two-flavour to
equilibrated charge neutral three-flavour matter. In this paper we
concentrate on the first step process and solve the relativistic hydrodynamic
equations for the conversion front in presence of high magnetic field. Lorentz
force due to magnetic field is included in the energy momentum tensor by
averaging over the polar angles. We find that for an initial dipole
configuration of the magnetic field with a sufficiently high value at the
surface, velocity of the front increases considerably.Comment: 16 pages, 4 figures, same as published version of JPG, J. Phys. G:
Nucl. Part. Phys. 39 (2012) 09520
Magnetic fields and Sunyaev-Zel'dovich effect in galaxy clusters
In this work we study the contribution of magnetic fields to the Sunyaev
Zeldovich (SZ) effect in the intracluster medium. In particular we calculate
the SZ angular power spectrum and the central temperature decrement. The effect
of magnetic fields is included in the hydrostatic equilibrium equation by
splitting the Lorentz force into two terms one being the force due to magnetic
pressure which acts outwards and the other being magnetic tension which acts
inwards. A perturbative approach is adopted to solve for the gas density
profile for weak magnetic fields (< 4 micro G}). This leads to an enhancement
of the gas density in the central regions for nearly radial magnetic field
configurations. Previous works had considered the force due to magnetic
pressure alone which is the case only for a special set of field
configurations. However, we see that there exists possible sets of
configurations of ICM magnetic fields where the force due to magnetic tension
will dominate. Subsequently, this effect is extrapolated for typical field
strengths (~ 10 micro G) and scaling arguments are used to estimate the angular
power due to secondary anisotropies at cluster scales. In particular we find
that it is possible to explain the excess power reported by CMB experiments
like CBI, BIMA, ACBAR at l > 2000 with sigma_8 ~ 0.8 (WMAP 5 year data) for
typical cluster magnetic fields. In addition we also see that the magnetic
field effect on the SZ temperature decrement is more pronounced for low mass
clusters ( ~ 2 keV). Future SZ detections of low mass clusters at few arc
second resolution will be able to probe this effect more precisely. Thus, it
will be instructive to explore the implications of this model in greater detail
in future works.Comment: 20 pages, 8 figure
Heating of the intracluster medium by quasar outflows
We study the possibility of quasar outflows in clusters and groups of
galaxies heating the intracluster gas in order to explain the recent
observation of excess entropy in this gas. We use the extended Press-Schechter
formalism to estimate the number of quasars that become members of a group of
cluster of a given mass and formation epoch. We also estimate the fraction of
mechanical energy in the outflows that is imparted to the surrounding medium as
a function of the density and temperature of this gas. We finally calculate the
total amount of non-gravitational heating from such outflows as a function of
the cluster potential and formation epoch. We show that outflows from broad
absorption line (BAL) and radio loud quasars can provide the required amount of
heating of the intracluster gas. We find that in this scenario most of the
heating takes place at , and that this ``preheating'' epoch
is at lower redshift for lower mass clusters.Comment: Latex (mn.sty), 8 figures, accepted for publication in the MNRA