10,298 research outputs found
Stoppage of Light Made Flexible by an Additional Control Field
We show how the application of a coupling field connecting the two lower
metastable states of a Lambda system facilitates stoppage of light in a coheren
tly driven Doppler broadened atomic medium via electromagnetic induced
transparencyComment: 11 pages, 3 figures, typed in Latex, Accepted in JM
Quest for consistent modelling of statistical decay of the compound nucleus
A statistical model description of heavy ion induced fusion-fission reactions
is presented where shell effects, collective enhancement of level density,
tilting away effect of compound nuclear spin and dissipation are included. It
is shown that the inclusion of all these effects provides a consistent picture
of fission where fission hindrance is required to explain the experimental
values of both pre-scission neutron multiplicities and evaporation residue
cross-sections in contrast to some of the earlier works where a fission
hindrance is required for pre-scission neutrons but a fission enhancement for
evaporation residue cross-sections.Comment: 14 pages, 2 figure
Alleviating the inconsistencies in modelling decay of fissile compound nuclei
This work attempts to overcome the existing inconsistencies in modelling
decay of fissile nucleus by inclusion of important physical effects in the
model and through a systematic analysis of a large set of data over a wide
range of CN mass (ACN). The model includes shell effect in the level density
(LD) parameter, shell correction in the fission barrier, effect of the
orientation degree of freedom of the CN spin (Kor), collective enhancement of
level density (CELD) and dissipation in fission. Input parameters are not tuned
to reproduce observables from specific reaction(s) and the reduced dissipation
coefficient is treated as the only adjustable parameter. Calculated evaporation
residue (ER) cross sections, fission cross sections and particle, i.e. neutron,
proton and alpha-particle, multiplicities are compared with data covering ACN =
156-248. The model produces reasonable fits to ER and fission excitation
functions for all the reactions considered in this work. Pre-scission neutron
multiplicities are underestimated by the calculation beyond ACN~200. An
increasingly higher value of pre-saddle dissipation strength is required to
reproduce the data with increasing ACN. Proton and alpha-particle
multiplicities, measured in coincidence with both ERs and fission fragments,
are in qualitative agreement with model predictions. The present work mitigates
the existing inconsistencies in modelling statistical decay of the fissile CN
to a large extent.Comment: 15 pages, 9 figure
Limits on the AGN activities in X-ray underluminous galaxy groups
We have observed four X-ray underluminous groups of galaxies using the Giant
Meterwave RadioTelescope. The groups NGC 524, 720, 3607, and 4697 are
underluminous in relation to the extrapolation of the Lx - T relation from rich
clusters and do not show any evidence of current AGN activities that can
account for such a departure. The GMRT observations carried out at low
frequencies (235 and 610 MHz) were aimed at detecting low surface brightness,
steep-spectrum sources indicative of past AGN activities in these groups. No
such radio emissions were detected in any of these four groups. The
corresponding upper limits on the total energy in relativistic particles is
about 3 X 10 erg. This value is more than a factor of 100 less than that
required to account for the decreased X-ray luminosities (or, enhanced
entropies) of these four groups in the AGN-heating scenario. Alternatively, the
AGN activity must have ceased about 4 Gyr ago, allowing the relativistic
particles to diffuse out to such a large extent (about 250 kpc) that their
radio emission could have been undetected by the current observations. If the
latter scenario is correct, the ICM was pre-heated before the assembly of
galaxy clusters.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter
Single polymer gating of channels under a solvent gradient
We study the effect of a gradient of solvent quality on the coil-globule
transition for a polymer in a narrow pore. A simple self-attracting
self-avoiding walk model of a polymer in solution shows that the variation in
the strength of interaction across the pore leads the system to go from one
regime (good solvent) to the other (poor solvent) across the channel. This may
be thought analogous to thermophoresis, where the polymer goes from the hot
region to the cold region under the temperature gradient. The behavior of short
chains is studied using exact enumeration whilst the behavior of long chains is
studied using transfer matrix techniques. The distribution of the monomer
density across the layer suggests that a gate-like effect can be created, with
potential applications as a sensor.Comment: 5 Pages, 7 Figures, Accepted in Phys. Rev. E (2013
Causality in Propagation of a Pulse in a Nonlinear Dispersive Medium
We investigate the causal propagation of the pulse through dispersive media
by very precise numerical solution of the coupled Maxwell-Bloch equations
without any approximations about the strength of the input field. We study full
nonlinear behavior of the pulse propagation through solid state media like ruby
and alexandrite. We have demonstrated that the information carried by the
discontinuity, {\it i.e}, front of the pulse, moves inside the media with
velocity even though the peak of the pulse can travel either with
sub-luminal or with super-luminal velocity. We extend the argument of
Levi-Civita to prove that the discontinuity would travel with velocity even
in a nonlinear medium.Comment: 4 pages, 4 figures, 2 table
Sectoral Price Changes and Output Growth: Supply and Demand in General Equilibrium
Price changes and output growth, both at the aggregate and the sectoral level, appear to be negatively correlated. At a basic level, this suggests that sectoral âsupplyâ shocks are more prevalent than sectoral âdemandâ shocks. However, it is not clear what these sectoral price-output correlations mean once one thinks in terms of general equilibrium. To help us understand the implication of these price-output correlations, this paper examines a multi-sector dynamic general equilibrium model that includes sectoral technology shocks and sectoral demand shocks, as well as aggregate money growth shocks. We show that while a model driven solely by sectoral technology shocks can generate âplausibleâ price-output correlations, âdemandâ shocks, particularly sectoral demand shocks, are needed for the model to generate the sectoral price-output correlations observed in the data. We also show that technology shocks do not always look like âsupplyâ shocks. Positive technology shocks to sectors producing goods that are used for investment frequently result in increases in output and prices in other sectors while positive technology shocks to sectors producing goods that are used primarily as intermediate inputs look like supply shocks in other sectors.
Assessment of the dynamics of microparasite infections in genetically homogeneous and heterogeneous populations using a stochastic epidemic model
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