13,140 research outputs found
Peristaltic Pumping of Blood Through Small Vessels of Varying Cross-section
The paper is devoted to a study of the peristaltic motion of blood in the
micro-circulatory system. The vessel is considered to be of varying
cross-section. The progressive peristaltic waves are taken to be of sinusoidal
nature. Blood is considered to be a Herschel-Bulkley fluid. Of particular
concern here is to investigate the effects of amplitude ratio, mean pressure
gradient, yield stress and the power law index on the velocity distribution,
streamline pattern and wall shear stress. On the basis of the derived
analytical expression, extensive numerical calculations have been made. The
study reveals that velocity of blood and wall shear stress are appreciably
affected due to the non-uniform geometry of blood vessels. They are also highly
sensitive to the magnitude of the amplitude ratio and the value of the fluid
index.Comment: Accepted for publication in ASME journal of Applied Mechanics. arXiv
admin note: text overlap with arXiv:1108.1285v
Rational Orbits around Charged Black Holes
We show that all eccentric timelike orbits in Reissner-Nordstr\"{o}m
spacetime can be classified using a taxonomy that draws upon an isomorphism
between periodic orbits and the set of rational numbers. By virtue of the fact
that the rationals are dense, the taxonomy can be used to approximate aperiodic
orbits with periodic orbits. This may help reduce computational overhead for
calculations in gravitational wave astronomy. Our dynamical systems approach
enables us to study orbits for both charged and uncharged particles in spite of
the fact that charged particle orbits around a charged black hole do not admit
a simple one-dimensional effective potential description. Finally, we show that
comparing periodic orbits in the RN and Schwarzschild geometries enables us to
distinguish charged and uncharged spacetimes by looking only at the orbital
dynamics.Comment: 16 pages, 21 figure
Comprehensive Spectral Analysis of Cyg X-1 using RXTE Data
We analyse a large number () pointed RXTE observations of Cyg X-1 and
model the spectrum of each one. A subset of the observations for which there is
simultaneous reliable measure of the hardness ratio by the All Sky Monitor,
shows that the sample covers nearly all the spectral shapes of Cyg X-1. The
relative strength, width of the Iron line and the reflection parameter are in
general correlated with the high energy photon spectral index . This is
broadly consistent with a geometry where for the hard state (low ) there is a hot inner Comptonizing region surrounded by a truncated cold
disk. The inner edge of the disk moves inwards as the source becomes softer
till finally in the soft state (high ) the disk fills the inner
region and active regions above the disk produce the Comptonized component.
However, the reflection parameter shows non-monotonic behaviour near the
transition region (), suggestive of a more complex geometry or
physical state of the reflector. Additionally, the inner disk temperature,
during the hard state, is on the average higher than in the soft one, albeit
with large scatter. These inconsistencies could be due to limitations in the
data and the empirical model used to fit them. The flux of each spectral
component is well correlated with which shows that unlike some other
black hole systems, Cyg X-1 does not show any hysteresis behaviour. In the soft
state, the flux of the Comptonized component is always similar to the disk one,
which confirms that the ultra-soft state (seen in other brighter black hole
systems) is not exhibited by Cyg X-1. The rapid variation of the Compton
Amplification factor with , naturally explains the absence of spectra
with , despite a large number having .Comment: 12 pages, 8 figures, accepted for publication in Research in
Astronomy and Astrophysics (RAA
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