119,990 research outputs found
Transient Resetting: A Novel Mechanism for Synchrony and Its Biological Examples
The study of synchronization in biological systems is essential for the
understanding of the rhythmic phenomena of living organisms at both molecular
and cellular levels. In this paper, by using simple dynamical systems theory,
we present a novel mechanism, named transient resetting, for the
synchronization of uncoupled biological oscillators with stimuli. This
mechanism not only can unify and extend many existing results on (deterministic
and stochastic) stimulus-induced synchrony, but also may actually play an
important role in biological rhythms. We argue that transient resetting is a
possible mechanism for the synchronization in many biological organisms, which
might also be further used in medical therapy of rhythmic disorders. Examples
on the synchronization of neural and circadian oscillators are presented to
verify our hypothesis.Comment: 17 pages, 7 figure
Shot noise in resonant tunneling structures
We propose a quantum mechanical approach to noise in resonant tunneling
structures, that can be applied in the whole range of transport regimes, from
completely coherent to completely incoherent. In both limiting cases, well
known results which have appeared in the literature are recovered. Shot noise
reduction due to both Pauli exclusion and Coulomb repulsion, and their combined
effect, are studied as a function of the rate of incoherent processes in the
well (which are taken into account by means of a phenomenological relaxation
time), and of temperature. Our approach allows the study of noise in a variety
of operating conditions (i.e., equilibrium, sub-peak voltages, second resonance
voltages), and as a function of temperature, explaining experimental results
and predicting interesting new results.Comment: RevTeX file, 26 pages, 3 Postscript figures, uses epsf.sty. submitted
to Phys. Rev.
Double expansion in asymptotically free theories
I propose an approximation scheme for asymptotically free field theories
combining both weak coupling and strong coupling series. The weak coupling
expansion is used to integrate the high frequency modes and the resulting low
energy effective theory is solved using the strong coupling expansion. In some
models there exists an intermediate scale at which both expansions make sense.
The method is tested on few low dimensional models for which an exact solution
is known.Comment: 15 pages, written in LaTeX, figures generated using FEYNMANN are
commented and can be obtained upon request
Negative magnetoresistance in the nearest-neighbour hopping conduction in granular gold film
The low temperature (0.5-55 K) conduction of semicontinuous gold film vacuum
deposited at T \approx 50 K is studied. The film is near the percolation
threshold (thickness 3.25 nm). Its resistance is extremely sensitive to the
applied voltage U. At low enough U the film behaves as an insulator
(two-dimensional granular metal). In this state the dependences R(T) \propto
\exp (1/T) (for T \leq 20 K) and R(U) \propto \exp (1/U)) (for T \leq 1 K and U
> 0.1 V) are observed. Magnetoresistance (MR) is negative and can be described
by \Delta R(H)/R(0) \propto -H^2/T. This negative MR which manifests itself for
nearest-neighbour hopping is rather uncommon and, up to now, has not been
clarified. The possible mechanisms of such case of negative MR are discussed.Comment: 9 pages, LATEX, 6 figures. To be published in Physica B. Fig.4 is JPG
file, in case of troubles with it, appeal for help and advice to:
[email protected]
Improved Perturbation Method and its Application to the IIB Matrix Model
We present a new scheme for extracting approximate values in ``the improved
perturbation method'', which is a sort of resummation technique capable of
evaluating a series outside the radius of convergence. We employ the
distribution profile of the series that is weighted by nth-order derivatives
with respect to the artificially introduced parameters. By those weightings the
distribution becomes more sensitive to the ``plateau'' structure in which the
consistency condition of the method is satisfied. The scheme works effectively
even in such cases that the system involves many parameters. We also propose
that this scheme has to be applied to each observables separately and be
analyzed comprehensively.
We apply this scheme to the analysis of the IIB matrix model by the improved
perturbation method obtained up to eighth order of perturbation in the former
works. We consider here the possibility of spontaneous breakdown of Lorentz
symmetry, and evaluate the free energy and the anisotropy of space-time extent.
In the present analysis, we find an SO(10)-symmetric vacuum besides the SO(4)-
and SO(7)-symmetric vacua that have been observed. It is also found that there
are two distinct SO(4)-symmetric vacua that have almost the same value of free
energy but the extent of space-time is different. From the approximate values
of free energy, we conclude that the SO(4)-symmetric vacua are most preferred
among those three types of vacua.Comment: 52 pages, published versio
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