3,004 research outputs found
Very hard states in neutron star low-mass X-ray binaries
We report on unusually very hard spectral states in three confirmed
neutron-star low-mass X-ray binaries (1RXS J180408.9-342058, EXO 1745-248, and
IGR J18245-2452) at a luminosity between ~ 10^{36-37} erg s^{-1}. When fitting
the Swift X-ray spectra (0.5 - 10 keV) in those states with an absorbed
power-law model, we found photon indices of \Gamma ~ 1, significantly lower
than the \Gamma = 1.5 - 2.0 typically seen when such systems are in their so
called hard state. For individual sources very hard spectra were already
previously identified but here we show for the first time that likely our
sources were in a distinct spectral state (i.e., different from the hard state)
when they exhibited such very hard spectra. It is unclear how such very hard
spectra can be formed; if the emission mechanism is similar to that operating
in their hard states (i.e., up-scattering of soft photons due to hot electrons)
then the electrons should have higher temperatures or a higher optical depth in
the very hard state compared to those observed in the hard state. By using our
obtained \Gamma as a tracer for the spectral evolution with luminosity, we have
compared our results with those obtained by Wijnands et al. (2015). We confirm
their general results in that also our sample of sources follow the same track
as the other neutron star systems, although we do not find that the accreting
millisecond pulsars are systematically harder than the non-pulsating systems.Comment: Accepted for publication in MNRA
Influence of sodium pyruvate on Neurospora fructose diphosphatase
Influence of sodium pyruvate on fructose diphosphatas
A Generative-Discriminative Basis Learning Framework to Predict Clinical Severity from Resting State Functional MRI Data
We propose a matrix factorization technique that decomposes the resting state
fMRI (rs-fMRI) correlation matrices for a patient population into a sparse set
of representative subnetworks, as modeled by rank one outer products. The
subnetworks are combined using patient specific non-negative coefficients;
these coefficients are also used to model, and subsequently predict the
clinical severity of a given patient via a linear regression. Our
generative-discriminative framework is able to exploit the structure of rs-fMRI
correlation matrices to capture group level effects, while simultaneously
accounting for patient variability. We employ ten fold cross validation to
demonstrate the predictive power of our model on a cohort of fifty eight
patients diagnosed with Autism Spectrum Disorder. Our method outperforms
classical semi-supervised frameworks, which perform dimensionality reduction on
the correlation features followed by non-linear regression to predict the
clinical scores
De Sitter Holography with a Finite Number of States
We investigate the possibility that, in a combined theory of quantum
mechanics and gravity, de Sitter space is described by finitely many states.
The notion of observer complementarity, which states that each observer has
complete but complementary information, implies that, for a single observer,
the complete Hilbert space describes one side of the horizon. Observer
complementarity is implemented by identifying antipodal states with outgoing
states. The de Sitter group acts on S-matrix elements. Despite the fact that
the de Sitter group has no nontrivial finite-dimensional unitary
representations, we show that it is possible to construct an S-matrix that is
finite-dimensional, unitary, and de Sitter-invariant. We present a class of
examples that realize this idea holographically in terms of spinor fields on
the boundary sphere. The finite dimensionality is due to Fermi statistics and
an `exclusion principle' that truncates the orthonormal basis in which the
spinor fields can be expanded.Comment: 23 pages, 1 eps figure, LaTe
Generalised Separable Solution of Double Phase Flow through Homogeneous Porous Medium in Vertical Downward Direction Due to Difference in Viscosity
In this paper the instability (fingering) phenomenon in a double phase immiscible (oil and water) flow through the homogeneous porous medium with mean capillary pressure in the vertical downward direction is discussed. The mathematical formulation of this problem yields a nonlinear partial differential equation and the generalised separable solution is given in the exponential form. The numerical solution and graphical presentation is given using MAT LAB coding
Effective temperature for black holes
The physical interpretation of black hole's quasinormal modes is fundamental
for realizing unitary quantum gravity theory as black holes are considered
theoretical laboratories for testing models of such an ultimate theory and
their quasinormal modes are natural candidates for an interpretation in terms
of quantum levels. The spectrum of black hole's quasinormal modes can be
re-analysed by introducing a black hole's effective temperature which takes
into account the fact that, as shown by Parikh and Wilczek, the radiation
spectrum cannot be strictly thermal. This issue changes in a fundamental way
the physical understanding of such a spectrum and enables a re-examination of
various results in the literature which realizes important modifies on quantum
physics of black holes. In particular, the formula of the horizon's area
quantization and the number of quanta of area result modified becoming
functions of the quantum "overtone" number n. Consequently, the famous formula
of Bekenstein-Hawking entropy, its sub-leading corrections and the number of
microstates are also modified. Black hole's entropy results a function of the
quantum overtone number too. We emphasize that this is the first time that
black hole's entropy is directly connected with a quantum number. Previous
results in the literature are re-obtained in the limit n \to \infty.Comment: 10 pages,accepted for publication in Journal of High Energy Physics.
Comments are welcom
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