532 research outputs found
Resonant Activation Phenomenon for Non-Markovian Potential-Fluctuation Processes
We consider a generalization of the model by Doering and Gadoua to
non-Markovian potential-switching generated by arbitrary renewal processes. For
the Markovian switching process, we extend the original results by Doering and
Gadoua by giving a complete description of the absorption process. For all
non-Markovian processes having the first moment of the waiting time
distributions, we get qualitatively the same results as in the Markovian case.
However, for distributions without the first moment, the mean first passage
time curves do not exhibit the resonant activation minimum. We thus come to the
conjecture that the generic mechanism of the resonant activation fails for
fluctuating processes widely deviating from Markovian.Comment: RevTeX 4, 5 pages, 4 figures; considerably shortened version accepted
as a brief report to Phys. Rev.
Phase retrapping in aφJosephson junction: onset of the butterfly effect
We investigate experimentally the retrapping of the phase in a
φ
Josephson junction upon return of the junction to the zero-voltage state. Since the Josephson energy profile
U
0
(
ψ
)
in
φ
JJ is a
2
π
periodic double-well potential with minima at
ψ
=
±
φ
mod
2
π
, the question is at which of the two minima
−
φ
or
+
φ
the phase will be trapped upon return from a finite voltage state during quasistatic decrease of the bias current (tilt of the potential). By measuring the relative population of two peaks in escape histograms, we determine the probability of phase trapping in the
±
φ
wells for different temperatures. Our experimental results agree qualitatively with theoretical predictions. In particular, we observe an onset of the butterfly effect with an oscillating probability of trapping. Unexpectedly, this probability saturates at a value different from 50% at low temperatures
Evaluation of a Reflection Method on an Open-Ended Coaxial Line and its Use in Dielectric Measurements
This paper describes a method for determining the dielectric constant of a biological tissue. A suitable way to make a dielectric measurement that is nondestructive and noninvasive for the biological substance and broadband at the frequency range of the network analyzer is to use a reflection method on an open ended coaxial line. A coaxial probe in the frequency range of the network analyzer from 17 MHz to 2 GHz is under investigation and also a calibration technique and the behavior of discrete elements in an equivalent circuit of an open ended coaxial line. Information about the magnitude and phase of the reflection coefficient on the interface between a biological tissue sample and a measurement probe is modeled with the aid of an electromagnetic field simulator. The numerical modeling is compared with real measurements, and a comparison is presented.
The influence of charge detection on counting statistics
We consider the counting statistics of electron transport through a double
quantum dot with special emphasis on the dephasing induced by a nearby charge
detector. The double dot is embedded in a dissipative enviroment, and the
presence of electrons on the double dot is detected with a nearby quantum point
contact. Charge transport through the double dot is governed by a non-Markovian
generalized master equation. We describe how the cumulants of the current can
be obtained for such problems, and investigate the difference between the
dephasing mechanisms induced by the quantum point contact and the coupling to
the external heat bath. Finally, we consider various open questions of
relevance to future research.Comment: 15 pages, 2 figures, Contribution to 5-th International Conference on
Unsolved Problems on Noise, Lyon, France, June 2-6, 200
On the 3D steady flow of a second grade fluid past an obstacle
We study steady flow of a second grade fluid past an obstacle in three space
dimensions. We prove existence of solution in weighted Lebesgue spaces with
anisotropic weights and thus existence of the wake region behind the obstacle.
We use properties of the fundamental Oseen tensor together with results
achieved in \cite{Koch} and properties of solutions to steady transport
equation to get up to arbitrarily small \ep the same decay as the Oseen
fundamental solution
Absolute rate coefficients for photorecombination and electron-impact ionization of magnesium-like iron ions from measurements at a heavy-ion storage ring
Rate coefficients for photorecombination (PR) and cross sections for
electron-impact ionization (EII) of Fe forming Fe and
Fe, respectively, have been measured by employing the electron-ion
merged-beams technique at a heavy-ion storage ring. Rate coefficients for PR
and EII of Fe ions in a plasma are derived from the experimental
measurements. Simple parametrizations of the experimentally derived plasma rate
coefficients are provided for use in the modeling of photoionized and
collisionally ionized plasmas. In the temperature ranges where Fe is
expected to form in such plasmas the latest theoretical rate coefficients of
Altun et al. [Astron. Astrophys. 474, 1051 (2007)] for PR and of Dere [Astron.
Astrophys. 466, 771 (2007)] for EII agree with the experimental results to
within the experimental uncertainties. Common features in the PR and EII
resonance structures are identified and discussed.Comment: 12 pages, 6 figures, 3 tables, submitted for publication to Physical
Review
Background Geometry in Gauge Gravitation Theory
Dirac fermion fields are responsible for spontaneous symmetry breaking in
gauge gravitation theory because the spin structure associated with a tetrad
field is not preserved under general covariant transformations. Two solutions
of this problem can be suggested. (i) There exists the universal spin structure
such that any spin structure associated with a tetrad field
is a subbundle of the bundle . In this model, gravitational fields
correspond to different tetrad (or metric) fields. (ii) A background tetrad
field and the associated spin structure are fixed, while
gravitational fields are identified with additional tensor fields q^\la{}_\m
describing deviations \wt h^\la_a=q^\la{}_\m h^\m_a of . One can think of
\wt h as being effective tetrad fields. We show that there exist gauge
transformations which keep the background tetrad field and act on the
effective fields by the general covariant transformation law. We come to
Logunov's Relativistic Theory of Gravity generalized to dynamic connections and
fermion fields.Comment: 12 pages, LaTeX, no figure
Absolute rate coefficients for photorecombination of berylliumlike and boronlike silicon ions
We report measured rate coefficients for electron-ion recombination for Si10+
forming Si9+ and for Si9+ forming Si8+, respectively. The measurements were
performed using the electron-ion merged-beams technique at a heavy-ion storage
ring. Electron-ion collision energies ranged from 0 to 50 eV for Si9+ and from
0 to 2000 eV for Si10+, thus, extending previous measurements for Si10+ [Orban
et al. 2010, Astrophys. J. 721, 1603] to much higher energies. Experimentally
derived rate coefficients for the recombination of Si9+ and Si10+ ions in a
plasma are presented along with simple parameterizations. These rate
coefficients are useful for the modeling of the charge balance of silicon in
photoionized plasmas (Si9+ and Si10+) and in collisionally ionized plasmas
(Si10+ only). In the corresponding temperature ranges, the experimentally
derived rate coefficients agree with the latest corresponding theoretical
results within the experimental uncertainties.Comment: 17 pages, 7 figures, 3 tables, 66 references, submitted to the J.
Phys. B special issue on atomic and molecular data for astrophysicist
Group theoretical construction of mutually unbiased bases in Hilbert spaces of prime dimensions
Mutually unbiased bases in Hilbert spaces of finite dimensions are closely
related to the quantal notion of complementarity. An alternative proof of
existence of a maximal collection of N+1 mutually unbiased bases in Hilbert
spaces of prime dimension N is given by exploiting the finite Heisenberg group
(also called the Pauli group) and the action of SL(2,Z_N) on finite phase space
Z_N x Z_N implemented by unitary operators in the Hilbert space. Crucial for
the proof is that, for prime N, Z_N is also a finite field.Comment: 13 pages; accepted in J. Phys. A: Math. Theo
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