5,963 research outputs found
Long-term Spectral Variability of the Ultra-luminous X-ray source Holmberg IX X--1
We investigate the long-term spectral variability in the ultra-luminous X-ray
source Holmberg IX X--1. By analyzing the data from eight {\it Suzaku} and 13
{\it XMM-Newton} observations conducted between 2001 and 2015, we perform a
detailed spectral modeling for all spectra with simple models and complex
physical models. We find that the spectra can be well explained by a disc plus
thermal Comptonization model. Applying this model, we unveil correlations
between the X-ray luminosity () and the spectral parameters. Among
the correlations, a particular one is the statistically significant positive
correlation between and the photon index (), while at the
high luminosities of , the source becomes
marginally hard and that results a change in the slope of the correlation. Similar variability behavior is observed in the optical depth
of the source around as the
source becomes more optically thick. We consider the scenario that a corona
covers the inner part of the disc, and the correlations can be explained as to
be driven by the variability of seed photons from the disc input into the
corona. On the basis of the disc-corona model, we discuss the physical
processes that are possibly indicated by the variability of the spectral
parameters. Our analysis reveals the complex variability behavior of Holmberg
IX X--1 and the variability mechanism is likely related to the geometry of the
X-ray emitting regions.Comment: Accepted for publication in ApJ, 12 Pages, 3 Tables, 3 Figure
Fractal Measures and Nonlinear Dynamics of Overcontact Binaries
Overcontact binary stars are systems of two stars where the component stars
are in contact with each other. This implies that they share a common envelope
of gas. In this work we seek signatures of nonlinearity and chaos in these
stars by using time series analysis techniques. We use three main techniques,
namely the correlation dimension,f (\alpha) spectrum and the bicoherence. The
former two are calculated from the reconstructed dynamics, while the latter is
calculated from the Fourier transforms of the time series of intensity
variations(light curves) of these stars. Our dataset consists of data from 463
overcontact binary stars in the Kepler field of view [1]. Our analysis
indicates nonlinearity and signatures of chaos in almost all the light curves.
We also explore whether the underlying nonlinear properties of the stars are
related to their physical properties like fill-out-factor, a measure of the
extend of contact between the components of an overcontact binary system . We
observe that significant correlations exist between the fill out factor and the
nonlinear quantifiers. This correlation is more pronounced in specific
subcategories constructed based on the mass ratios and effective temperatures
of the binaries. The correlations observed can be indicative of variations in
the nonlinear properties of the star as it ages. We believe that this study
relating nonlinear and astrophysical properties of binary stars is the first of
its kind and is an important starting point for such studies in other
astrophysical objects displaying nonlinear dynamical behaviour.Comment: 17 pages, 12 figures, submitted to Communications in Nonlinear
Science and Numerical Simulatio
General Relativistic Spectra from Accretion Disks around Rapidly Rotating Neutron Stars
We compute spectra from accretion disks around rapidly rotating neutron
stars. The full effect of general relativity is considered for the structure
calculation of the stars. We take into account the Doppler shift, gravitational
redshift and light-bending effects in order to compute the observed spectra. To
facilitate direct comparison with observations, a simple empirical function is
presented which describes the numerically computed spectra well. This function
can in principle be used to distinguish between the Newtonian spectra and the
relativistic spectra. We also discuss the possibility of constraining neutron
star's equation of state using our spectral models.Comment: 2 pages, to appear in the proceedings of 'The Physics of Cataclysmic
Variables and Related Objects', Goettingen, August 5-10, 200
Development of Waste Management Culture
Development of any culture is a time consuming exercise. However, the civilized world has been developing different kinds of cultures depending upon the necessity of the time prevailing. The development of waste management/minization culture is the need of the day and the techniques opted are obviously of pollution prevention/control. Pollution generated by anthropogenic wastes has grown to horrifying levels. Though the subject is vast and general, the scope of the paper has been confined to the industrial sector only. Zones of improvements are varied and numerous like energy, raw materials, process conditions, waste genera-tion etc. Inculcation of waste minimization culture amon-gst workers and managers has been discussed. Since devel-opment of a relatively new culture is a prolonged process, it has to be introduced in the grass root level from the very beginning. However, it is never too late to introduce such waste management/minization techniques in to the present industries
Hitting forbidden minors: Approximation and Kernelization
We study a general class of problems called F-deletion problems. In an
F-deletion problem, we are asked whether a subset of at most vertices can
be deleted from a graph such that the resulting graph does not contain as a
minor any graph from the family F of forbidden minors.
We obtain a number of algorithmic results on the F-deletion problem when F
contains a planar graph. We give (1) a linear vertex kernel on graphs excluding
-claw , the star with leves, as an induced subgraph, where
is a fixed integer. (2) an approximation algorithm achieving an approximation
ratio of , where is the size of an optimal solution on
general undirected graphs. Finally, we obtain polynomial kernels for the case
when F contains graph as a minor for a fixed integer . The graph
consists of two vertices connected by parallel edges. Even
though this may appear to be a very restricted class of problems it already
encompasses well-studied problems such as {\sc Vertex Cover}, {\sc Feedback
Vertex Set} and Diamond Hitting Set. The generic kernelization algorithm is
based on a non-trivial application of protrusion techniques, previously used
only for problems on topological graph classes
Development of ductile claddings for dispersion-strengthened nickel-base alloys Final report
Development of ductile oxidation-resistant cladding alloys for thoria dispersion, strengthened nickel and nickel-chromiu
Role of terms of trade in Indian agricultural growth: a national and state level analysis
Using time series data, this paper analyses the relative contributions of terms of trade and non-price variables in explaining agricultural growth in recent decades in India. Agricultural growth is largely explained by expansion of irrigation, (which in the model is also a proxy for HYVs and other capital investments), and, until the 1970s, by increases in the net cultivated area. Agricultural output is inelastic, and is becoming increasingly more so over time. The terms of trade was not an important factor in explaining past growth. Even during the late 1960s and early 1970s when the terms of trade improved by 18 percent for agriculture, they only accounted for 15 percent of the growth in output. Increases in agricultural output are also found to worsen the terms of trade for agriculture, despite government attempts to control prices. The results highlight the importance of further investments in agricultural research, extension, irrigation and other supply-enhancing inputs if the ongoing policy reforms in India are to translate into more rapid and sustained agricultural growth.Agricultural productivity India., Terms of trade India., Investment of public funds India.,
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