241,136 research outputs found
Conductivity rules in the Fermi and charge-spin separated liquid
Ioffe-Larkin rule applies for the pure charge-spin separation regardless of
its dimensionality. Here, an extension to this rule as a result of the
coexistence of spinon, holon and electron as a single entity in the
2-dimensional (2D) system is derived, which is also in accordance with the
original rule.Comment: To be published in Physica
Studies of dissipative standing shock waves around black holes
We investigate the dynamical structure of advective accretion flow around
stationary as well as rotating black holes. For a suitable choice of input
parameters, such as, accretion rate () and angular momentum
(), global accretion solution may include a shock wave. The post shock
flow is located at few tens of Schwarzchild radius and it is generally very hot
and dense. This successfully mimics the so called Compton cloud which is
believed to be responsible for emitting hard radiations. Due to the radiative
loss, a significant energy from the accreting matter is removed and the shock
moves forward towards the black hole in order to maintain the pressure balance
across it. We identify the effective area of the parameter space () which allows accretion flows to have some energy dissipation at
the shock . As the dissipation is increased, the parameter
space is reduced and finally disappears when the dissipation is reached its
critical value. The dissipation has a profound effect on the dynamics of
post-shock flow. By moving forward, an unstable shock whose oscillation causes
Quasi-Periodic Oscillations (QPOs) in the emitted radiation, will produce
oscillations of high frequency. Such an evolution of QPOs has been observed in
several black hole candidates during their outbursts.Comment: 13 pages, 5 figures, accepted by MNRA
Collective force generated by multiple biofilaments can exceed the sum of forces due to individual ones
Collective dynamics and force generation by cytoskeletal filaments are
crucial in many cellular processes. Investigating growth dynamics of a bundle
of N independent cytoskeletal filaments pushing against a wall, we show that
chemical switching (ATP/GTP hydrolysis) leads to a collective phenomenon that
is currently unknown. Obtaining force-velocity relations for different models
that capture chemical switching, we show, analytically and numerically, that
the collective stall force of N filaments is greater than N times the stall
force of a single filament. Employing an exactly solvable toy model, we
analytically prove the above result for N=2. We, further, numerically show the
existence of this collective phenomenon, for N>=2, in realistic models (with
random and sequential hydrolysis) that simulate actin and microtubule bundle
growth. We make quantitative predictions for the excess forces, and argue that
this collective effect is related to the non-equilibrium nature of chemical
switching.Comment: New J. Phys., 201
Giant number fluctuations in microbial ecologies
Statistical fluctuations in population sizes of microbes may be quite large
depending on the nature of their underlying stochastic dynamics. For example,
the variance of the population size of a microbe undergoing a pure birth
process with unlimited resources is proportional to the square of its mean. We
refer to such large fluctuations, with the variance growing as square of the
mean, as Giant Number Fluctuations (GNF). Luria and Delbruck showed that
spontaneous mutation processes in microbial populations exhibit GNF. We explore
whether GNF can arise in other microbial ecologies. We study certain simple
ecological models evolving via stochastic processes: (i) bi-directional
mutation, (ii) lysis-lysogeny of bacteria by bacteriophage, and (iii)
horizontal gene transfer (HGT). For the case of bi-directional mutation
process, we show analytically exactly that the GNF relationship holds at large
times. For the ecological model of bacteria undergoing lysis or lysogeny under
viral infection, we show that if the viral population can be experimentally
manipulated to stay quasi-stationary, the process of lysogeny maps essentially
to one-way mutation process and hence the GNF property of the lysogens follows.
Finally, we show that even the process of HGT may map to the mutation process
at large times, and thereby exhibits GNF.Comment: 18 pages, 5 figure
Randall-Sundrum with Kalb-Ramond field: return of the hierarchy problem?
We show that when the antisymmetric Kalb-Ramond field is included in the
Randall-Sundrum scenario, although the hierarchy problem can be solved, it
requires an extreme fine tuning of the Kalb-Ramond field (about 1 part in
). We interpret this as the return of the problem in disguise.
Further, we show that the Kalb-Ramond field induces a small negative
cosmological constant on the visible brane.Comment: 8 pages, latex, 4 figures. Contributed talk at `Recent Developments
in Gravity' (NEB XII), Nafplion, Greece, 29 June 200
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