464 research outputs found
Sequence-Dependent Effects on the Properties of Semiflexible Biopolymers
Using path integral technique, we show exactly that for a semiflexible
biopolymer in constant extension ensemble, no matter how long the polymer and
how large the external force, the effects of short range correlations in the
sequence-dependent spontaneous curvatures and torsions can be incorporated into
a model with well-defined mean spontaneous curvature and torsion as well as a
renormalized persistence length. Moreover, for a long biopolymer with large
mean persistence length, the sequence-dependent persistence lengths can be
replaced by their mean. However, for a short biopolymer or for a biopolymer
with small persistence lengths, inhomogeneity in persistence lengths tends to
make physical observables very sensitive to details and therefore less
predictable
Giant frequency-selective near-field energy transfer in active--passive structures
We apply a fluctuation electrodynamics framework in combination with
semianalytical (dipolar) approximations to study amplified spontaneous energy
transfer (ASET) between active and passive bodies. We consider near-field
energy transfer between semi-infinite planar media and spherical structures
(dimers and lattices) subject to gain, and show that the combination of loss
compensation and near-field enhancement (achieved by the proximity, enhanced
interactions, and tuning of subwavelength resonances) in these structures can
result in orders of magnitude ASET enhancements below the lasing threshold. We
examine various possible geometric configurations, including realistic
materials, and describe optimal conditions for enhancing ASET, showing that the
latter depends sensitively on both geometry and gain, enabling efficient and
tunable gain-assisted energy extraction from structured surfaces
Disordered, stretched, and semiflexible biopolymers in two dimensions
We study the effects of intrinsic sequence-dependent curvature for a two
dimensional semiflexible biopolymer with short-range correlation in intrinsic
curvatures. We show exactly that when not subjected to any external force, such
a system is equivalent to a system with a well-defined intrinsic curvature and
a proper renormalized persistence length. We find the exact expression for the
distribution function of the equivalent system. However, we show that such an
equivalent system does not always exist for the polymer subjected to an
external force. We find that under an external force, the effect of
sequence-disorder depends upon the averaging order, the degree of disorder, and
the experimental conditions, such as the boundary conditions. Furthermore, a
short to moderate length biopolymer may be much softer or has a smaller
apparent persistent length than what would be expected from the "equivalent
system". Moreover, under a strong stretching force and for a long biopolymer,
the sequence-disorder is immaterial for elasticity. Finally, the effect of
sequence-disorder may depend upon the quantity considered
Transport in bacteriophage P22-infected Salmonella typhimurium
There was rapid efflux of L-leucine, L-phenylalanine, and α-methyl-D-glucoside after infection of Salmonella typhimurium with the clear plaque mutant C1 of phage P22. The efflux was similar to that observed with cyanide or arsenate treatment except that there was partial recovery in the case of phage infection and almost complete recovery under the condition of lysogeny. There was no efflux after infection with the temperature-sensitive mutant ts16C1 at nonpermissive temperature. Superinfection of superinfection exclusion negative lysogen (sie A - sie B-) with C1 led to efflux, whereas the efflux was much less on superinfection of sie A+ Sie B+ lysogen. These results indicate that an effective injection process is enough to cause depression in the cellular transport processes
On the Hamiltonian structure of Ermakov systems
A canonical Hamiltonian formalism is derived for a class of Ermakov systems
specified by several different frequency functions. This class of systems
comprises all known cases of Hamiltonian Ermakov systems and can always be
reduced to quadratures. The Hamiltonian structure is explored to find exact
solutions for the Calogero system and for a noncentral potential with dynamic
symmetry. Some generalizations of these systems possessing exact solutions are
also identified and solved
Energy saving in fixed wireless broadband networks
International audienceIn this paper, we present a mathematical formulation for saving energy in fixed broadband wireless networks by selectively turning off idle communication devices in low-demand scenarios. This problem relies on a fixed-charge capacitated network design (FCCND), which is very hard to optimize. We then propose heuristic algorithms to produce feasible solutions in a short time.Dans cet article, nous proposons une modélisation en programme linéaire en nombres entiers pour le problème de minimiser la consommation d'énergie dans les réseaux de collecte à faisceaux hertziens en éteignant une partie des équipements lorsque le trafic est bas. Ce problème repose sur un problème de dimensionnement de réseaux dont les arcs ont une capacité fixe, qui est très difficile à résoudre. Nous proposons un algorithme heuristique fournissant rapidement des solutions réalisables
Thresholded Covering Algorithms for Robust and Max-Min Optimization
The general problem of robust optimization is this: one of several possible
scenarios will appear tomorrow, but things are more expensive tomorrow than
they are today. What should you anticipatorily buy today, so that the
worst-case cost (summed over both days) is minimized? Feige et al. and
Khandekar et al. considered the k-robust model where the possible outcomes
tomorrow are given by all demand-subsets of size k, and gave algorithms for the
set cover problem, and the Steiner tree and facility location problems in this
model, respectively.
In this paper, we give the following simple and intuitive template for
k-robust problems: "having built some anticipatory solution, if there exists a
single demand whose augmentation cost is larger than some threshold, augment
the anticipatory solution to cover this demand as well, and repeat". In this
paper we show that this template gives us improved approximation algorithms for
k-robust Steiner tree and set cover, and the first approximation algorithms for
k-robust Steiner forest, minimum-cut and multicut. All our approximation ratios
(except for multicut) are almost best possible.
As a by-product of our techniques, we also get algorithms for max-min
problems of the form: "given a covering problem instance, which k of the
elements are costliest to cover?".Comment: 24 page
Green's function for the Relativistic Coulomb System via Sum Over Perturbation Series
We evaluate the Green's function of the D-dimensional relativistic Coulomb
system via sum over perturbation series which is obtained by expanding the
exponential containing the potential term in the path integral
into a power series. The energy spectra and wave functions are extracted from
the resulting amplitude.Comment: 13 pages, ReVTeX, no figure
Complex Effective Path: A Semi-Classical Probe of Quantum Effects
We discuss the notion of an effective, average, quantum mechanical path which
is a solution of the dynamical equations obtained by extremizing the quantum
effective action. Since the effective action can, in general, be complex, the
effective path will also, in general, be complex. The imaginary part of the
effective action is known to be related to the probability of particle creation
by an external source and hence we expect the imaginary part of the effective
path also to contain information about particle creation. We try to identify
such features using simple examples including that of effective path through
the black hole horizon leading to thermal radiation. Implications of this
approach are discussed.Comment: 20 pages; no figures; to appear in Phys.Rev.
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