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2003-03-21
|
Global well-posedness and multi-tone solutions of a class of nonlinear nonlocal cochlear models in hearing
|
We study a class of nonlinear nonlocal cochlear models of the transmission
line type, describing the motion of basilar membrane (BM) in the cochlea. They
are damped dispersive partial differential equations (PDEs) driven by time
dependent boundary forcing due to the input sounds. The global well-posedness
in time follows from energy estimates. Uniform bounds of solutions hold in case
of bounded nonlinear damping. When the input sounds are multi-frequency tones,
and the nonlinearity in the PDEs is cubic, we construct smooth quasi-periodic
solutions (multi-tone solutions) in the weakly nonlinear regime, where new
frequencies are generated due to nonlinear interaction. When the input is two
tones at frequencies $f_1$, $f_2$ ($f_1 < f_2$), and high enough intensities,
numerical results illustrate the formation of combination tones at $2 f_1 -f_2$
and $2f_2 -f_1$, in agreement with hearing experiments. We visualize the
frequency content of solutions through the FFT power spectral density of
displacement at selected spatial locations on BM.
|
0303048v1
|
2004-05-11
|
Analytical approach to soliton ratchets in asymmetric potentials
|
We use soliton perturbation theory and collective coordinate ansatz to
investigate the mechanism of soliton ratchets in a driven and damped asymmetric
double sine-Gordon equation. We show that, at the second order of the
perturbation scheme, the soliton internal vibrations can couple {\it
effectively}, in presence of damping, to the motion of the center of mass,
giving rise to transport. An analytical expression for the mean velocity of the
soliton is derived. The results of our analysis confirm the internal mode
mechanism of soliton ratchets proposed in [Phys. Rev. E {\bf 65} 025602(R)
(2002)].
|
0405023v1
|
2005-02-16
|
Controlling soliton explosions
|
We investigate the dynamics of solitons in generalized Klein-Gordon equations
in the presence of nonlinear damping and spatiotemporal perturbations. We will
present different mechanisms for soliton explosions. We show (both analytically
and numerically) that some space-dependent perturbations or nonlinear damping
can make the soliton internal mode unstable leading to soliton explosion. We
will show that, in some cases, while some conditions are satisfied, the soliton
explodes becoming a permanent, extremely complex, spatiotemporal dynamics. We
believe these mechanisms can explain some of the phenomena that recently have
been reported to occur in excitable media. We present a method for controlling
soliton explosions.
|
0502033v1
|
2005-07-22
|
Global existence in infinite lattices of nonlinear oscillators: The Discrete Klein-Gordon equation
|
Pointing out the difference between the Discrete Nonlinear Schr\"odinger
equation with the classical power law nonlinearity-for which solutions exist
globally, independently of the sign and the degree of the nonlinearity, the
size of the initial data and the dimension of the lattice-we prove either
global existence or nonexistence in time, for the Discrete Klein-Gordon
equation with the same type of nonlinearity (but of ``blow-up'' sign), under
suitable conditions on the initial data, and some times on the dimension of the
lattice. The results, consider both the conservative and the linearly damped
lattice. Similarities and differences with the continuous counterparts, are
remarked. We also make a short comment, on the existence of excitation
thresholds, for forced solutions of damped and parametrically driven,
Klein-Gordon lattices.
|
0507044v5
|
1992-12-14
|
Poisson and Porter-Thomas Fluctuations in off-Yrast Rotational Transitions
|
Fluctuations associated with stretched E2 transitions from high spin levels
in nuclei around $^{168}$Yb are investigated by a cranked shell model extended
to include residual two-body interactions. It is found that the gamma-ray
energies behave like random variables and the energy spectra show the Poisson
fluctuation, in the cranked mean field model without the residual interaction.
With two-body residual interaction included, discrete transition pattern with
unmixed rotational bands is still valid up to around 600 keV above yrast, in
good agreement with experiments. At higher excitation energy, a gradual onset
of rotational damping emerges. At 1.8 MeV above yrast, complete damping is
observed with GOE type fluctuations for both energy levels and transition
strengths(Porter-Thomas fluctuations).
|
9212006v1
|
1993-11-25
|
Microscopic analysis of two-body correlations in light nuclei
|
Within a nonperturbative dynamical two-body approach - based on coupled
equations of motion for the one-body density matrix and the two-body
correlation function - we study the distribution of occupation numbers in a
correlated system close to the groundstate, the relaxation of single-particle
excitations and the damping of collective modes. For this purpose the nonlinear
equations of motion are solved numerically within a finite oscillator basis for
the first time adopting short-range repulsive and long-range attractive
two-body forces. We find in all cases that the formation of long- and
short-range correlations and their mixing is related to the long- and
short-range part of the nucleon-nucleon interaction which dominate the
resummation of loop or ladder diagrams, respectively. However, the proper
description of relaxation or damping phenomena is found to require both types
of diagrams as well as the mixed terms simultaneously.
|
9311031v1
|
1997-03-26
|
A self-consistent treatment of damped motion for stable and unstable collective modes
|
We address the dynamics of damped collective modes in terms of first and
second moments. The modes are introduced in a self-consistent fashion with the
help of a suitable application of linear response theory. Quantum effects in
the fluctuations are governed by diffusion coefficients D_{\mu\nu}. The latter
are obtained through a fluctuation dissipation theorem generalized to allow for
a treatment of unstable modes. Numerical evaluations of the D_{\mu\nu} are
presented. We discuss briefly how this picture may be used to describe global
motion within a locally harmonic approximation. Relations to other methods are
discussed, like "dissipative tunneling", RPA at finite temperature and
generalizations of the "Static Path Approximation".
|
9703056v1
|
1997-04-24
|
A Simple Mode on a Highly Excited Background: Collective Strength and Damping in the Continuum
|
Simple states, such as isobaric analog states or giant resonances, embedded
into continuum are typical for mesoscopic many-body quantum systems. Due to the
coupling to compound states in the same energy range, a simple mode acquires a
damping width ("internal" dynamics). When studied experimentally with the aid
of various reactions, such states reveal enhanced cross sections in specific
channels at corresponding resonance energies ("external" dynamics which include
direct decay of a simple mode and decays of intrinsic compound states through
their own channels). We consider the interplay between internal and external
dynamics using a general formalism of the effective nonhermitian hamiltonian
and looking at the situation both from "inside" (strength functions and
spreading widths) and from "outside" (S-matrix, cross sections and delay
times). The restoration of isospin purity and disappearance of the collective
strength of giant resonances at high excitation energy are discussed as
important particular manifestations of this complex interplay.
|
9704055v1
|
1998-10-12
|
Response function beyond mean field of neutron-rich nuclei
|
The damping of single-particle and collective motion in exotic isotopes is a
new topic and its study may shed light on basic problems of nuclear dynamics.
For instance, it is known that nuclear structure calculations are not able, as
a rule, to account completely for the empirical single-particle damping. In
this contribution, we present calculations of the single-particle self-energy
in the case of the neutron-rich light nucleus $^{28}$O, by taking proper care
of the continuum, and we show that there are important differences with the
case of nuclei along the valley of stability.
|
9810033v1
|
1999-04-14
|
Scaling Analysis of Fluctuating Strength Function
|
We propose a new method to analyze fluctuations in the strength function
phenomena in highly excited nuclei. Extending the method of multifractal
analysis to the cases where the strength fluctuations do not obey power scaling
laws, we introduce a new measure of fluctuation, called the local scaling
dimension, which characterizes scaling behavior of the strength fluctuation as
a function of energy bin width subdividing the strength function. We discuss
properties of the new measure by applying it to a model system which simulates
the doorway damping mechanism of giant resonances. It is found that the local
scaling dimension characterizes well fluctuations and their energy scales of
fine structures in the strength function associated with the damped collective
motions.
|
9904037v1
|
1999-07-07
|
Pair creation: back-reactions and damping
|
We solve the quantum Vlasov equation for fermions and bosons, incorporating
spontaneous pair creation in the presence of back-reactions and collisions.
Pair creation is initiated by an external impulse field and the source term is
non-Markovian. A simultaneous solution of Maxwell's equation in the presence of
feedback yields an internal current and electric field that exhibit plasma
oscillations with a period tau_pl. Allowing for collisions, these oscillations
are damped on a time-scale, tau_r, determined by the collision frequency.
Plasma oscillations cannot affect the early stages of the formation of a
quark-gluon plasma unless tau_r >> tau_pl and tau_pl approx. 1/Lambda_QCD
approx 1 fm/c.
|
9907027v1
|
2000-10-23
|
Barrier penetration and rotational damping of thermally excited superdeformed nuclei
|
We construct a microscopic model of thermally excited superdeformed states
that describes both the barrier penetration mechanism, leading to the decay-out
transitions to normal deformed states, and the rotational damping causing
fragmentation of rotational E2 transitions. We describe the barrier penetration
by means of a tunneling path in the two-dimensional deformation energy surface,
which is calculated with the cranked Nilsson-Strutinsky model. The individual
excited superdeformed states and associated E2 transition strengths are
calculated by the shell model diagonalization of the many-particle many-hole
excitations interacting with the delta-type residual two-body force. The effect
of the decay-out on the excited superdeformed states are discussed in detail
for $^{152}$Dy, $^{143}$Eu and $^{192}$Hg.
|
0010074v1
|
1996-02-22
|
Stability of Travelling Waves for a Damped Hyperbolic Equation
|
We consider a nonlinear damped hyperbolic equation in $\real^n$, $1 \le n \le
4$, depending on a positive parameter $\epsilon$. If we set $\epsilon=0$, this
equation reduces to the well-known Kolmogorov-Petrovski-Piskunov equation. We
remark that, after a change of variables, this hyperbolic equation has the same
family of one-dimensional travelling waves as the KPP equation. Using various
energy functionals, we show that, if $\epsilon >0$, these fronts are locally
stable under perturbations in appropriate weighted Sobolev spaces. Moreover,
the decay rate in time of the perturbed solutions towards the front of minimal
speed $c=2$ is shown to be polynomial. In the one-dimensional case, if
$\epsilon < 1/4$, we can apply a Maximum Principle for hyperbolic equations and
prove a global stability result. We also prove that the decay rate of the
perturbated solutions towards the fronts is polynomial, for all $c > 2$.
|
9602004v1
|
1998-09-18
|
Stability of Propagating Fronts in Damped Hyperbolic Equations
|
We consider the damped hyperbolic equation in one space dimension $\epsilon
u_{tt} + u_t = u_{xx} + F(u)$, where $\epsilon$ is a positive, not necessarily
small parameter. We assume that $F(0)=F(1)=0$ and that $F$ is concave on the
interval $[0,1]$. Under these assumptions, our equation has a continuous family
of monotone propagating fronts (or travelling waves) indexed by the speed
parameter $c \ge c_*$. Using energy estimates, we first show that the
travelling waves are locally stable with respect to perturbations in a weighted
Sobolev space. Then, under additional assumptions on the non-linearity, we
obtain global stability results using a suitable version of the hyperbolic
Maximum Principle. Finally, in the critical case $c = c_*$, we use self-similar
variables to compute the exact asymptotic behavior of the perturbations as $t
\to +\infty$. In particular, setting $\epsilon = 0$, we recover several
stability results for the travelling waves of the corresponding parabolic
equation.
|
9809007v1
|
1999-05-28
|
Existence threshold for the ac-driven damped nonlinear Schrödinger solitons
|
It has been known for some time that solitons of the externally driven,
damped nonlinear Schr\"odinger equation can only exist if the driver's
strength, $h$, exceeds approximately $(2/ \pi) \gamma$, where $\gamma$ is the
dissipation coefficient. Although this perturbative result was expected to be
correct only to the leading order in $\gamma$, recent studies have demonstrated
that the formula $h_{thr}= (2 /\pi) \gamma$ gives a remarkably accurate
description of the soliton's existence threshold prompting suggestions that it
is, in fact, exact. In this note we evaluate the next order in the expansion of
$h_{thr}(\gamma)$ showing that the actual reason for this phenomenon is simply
that the next-order coefficient is anomalously small: $h_{thr}=(2/ \pi) \gamma
+ 0.002 \gamma^3$. Our approach is based on a singular perturbation expansion
of the soliton near the turning point; it allows to evaluate $h_{thr}(\gamma)$
to all orders in $\gamma$ and can be easily reformulated for other perturbed
soliton equations.
|
9906001v1
|
1996-10-01
|
Exact time evolution and master equations for the damped harmonic oscillator
|
Using the exact path integral solution for the damped harmonic oscillator it
is shown that in general there does not exist an exact dissipative Liouville
operator describing the dynamics of the oscillator for arbitrary initial bath
preparations. Exact non-stationary Liouville operators can be found only for
particular preparations. Three physically meaningful examples are examined. An
exact new master equation is derived for thermal initial conditions. Second,
the Liouville operator governing the time-evolution of equilibrium correlations
is obtained. Third, factorizing initial conditions are studied. Additionally,
one can show that there are approximate Liouville operators independent of the
initial preparation describing the long time dynamics under appropriate
conditions. The general form of these approximate master equations is derived
and the coefficients are determined for special cases of the bath spectral
density including the Ohmic, Drude and weak coupling cases. The connection with
earlier work is discussed.
|
9610001v1
|
1999-01-09
|
Cluster ionization via two-plasmon excitation
|
We calculate the two-photon ionization of clusters for photon energies near
the surface plasmon resonance. The results are expressed in terms of the
ionization rate of a double plasmon excitation, which is calculated
perturbatively. For the conditions of the experiment by Schlipper et al., we
find an ionization rate of the order of 0.05-0.10 fs^(-1). This rate is used to
determine the ionization probability in an external field in terms of the
number of photons absorbed and the duration of the field. The probability also
depends on the damping rate of the surface plasmon. Agreement with experiment
can only be achieved if the plasmon damping is considerably smaller than its
observed width in the room-temperature single-photon absorption spectrum.
|
9901008v1
|
2000-08-01
|
Rectangular Waveguide HOM Couplers for a TESLA Superstructure
|
Some modifications of a Rectangular Waveguide HOM couplers for TESLA
superstructure have been investigated. These RWG HOM couplers are to be
installed between the cavities of the superstructure and also at the both ends
of it. We investigated a RWG HOM coupler attached to the beam pipe through the
slots orientated along beam pipe axis (longitudinal slots), perpendicular to it
(azimutal slots) and at some angle to this axis. For dipole modes of both
polarizations damping two RWG in every design were used. This paper presents
the results obtained for scaled-up setup at 3 GHz at room temperature. The
advantages of HOM coupler with longitudinal slots for damping dipole modes and
compact HOM coupler with slots at some angle to the axis are shown. Arrangement
of HOM coupler in cryostat and heating due to HOM and FM losses are presented.
Calculations and design of the feeding RWG coupler for superstructure are also
presented.
|
0008001v1
|
2000-08-17
|
Superconducting Superstructure for the TESLA Collider: New Results
|
A new cavity-chain layout has been proposed for the main linac of the TESLA
linear collider. This superstructure-layout is based upon four 7-cell
superconducting standing-wave cavities, coupled by short beam pipes. The main
advantages of the superstructure are an increase in the active accelerating
length in TESLA and a saving in rf components, especially power couplers, as
compared to the present 9-cell cavities. The proposed scheme allows to handle
the field-flatness tuning and the HOM damping at sub-unit level, in contrast to
standard multi-cell cavities. The superstructure-layout is extensively studied
at DESY since 1999. Computations have been performed for the rf properties of
the cavity-chain, the bunch-to-bunch energy spread and multibunch dynamics. A
copper model of the superstructure has been built in order to compare with the
simulations and for testing the field-profile tuning and the HOM damping
scheme. A "proof of principle" niobium prototype of the superstructure is now
under construction and will be tested with beam at the TESLA Test Facility in
2001. In this paper we present latest results of these investigations.
|
0008104v1
|
2000-08-20
|
An Investigation of Optimised Frequency Distributions for Damping Wakefields in X-Band Linacs for the NLC
|
In the NLC (Next Linear Collider) small misalignments in each of the
individual accelerator structures (or the accelerator cells) will give rise to
wakefields which kick the beam from its electrical axis. This wakefield can
cause BBU (Beam Break Up) or at the very least it will dilute the emittance of
the beam. Several Gaussian detuned structures have been designed and tested [1]
at SLAC and in this paper we explore new distributions with possibly better
damping properties. The progress of the beam through approximately 5,000
structures is monitored in phase space and results on this are presented.
[1] J.W. Wang et al, TUA03, LINAC2000
|
0008202v2
|
2001-04-14
|
Parameters for a 30 GeV Undulator Test Facility in the FFTB/LCLS
|
The parameters for a 30 GeV test beam are outlined for use with an undulator
in the FFTB tunnel where the LCLS will eventually be housed. It is proposed to
use the SLAC linac and damping rings in their present mode of operation for PEP
II injection, where 30 GeV beams are also delivered at 10 Hz to the FFTB. High
peak currents are obtained with the addition of a second bunch compressor in
the linac. In order to minimize the synchrotron radiation induced emittance
growth in the bunch compressor it is necessary to locate the new bunch
compressor at the low-energy end of the linac, just after the damping rings.
The bunch compressor is a duplicate of the LCLS chicane-style bunch compressor.
This test beam would provide an exciting possibility to test LCLS undulator
sections and provide a unique high-brightness source of incoherent X-rays and
begin developing the LCLS experimental station. The facility will also act as a
much needed accelerator test bed for the production, diagnostics and tuning of
very short bunches in preparation for the LCLS after the photo injector is
commissioned.
|
0104045v1
|
2001-10-05
|
Characterization of a Low Frequency Power Spectral Density f^(-gamma) in a Threshold Model
|
his study investigates the modifications of the thermal spectrum, at low
frequency, induced by an external damping on a system in heat contact with
internal fluctuating impurities. Those impurities can move among locations and
their oscillations are associated with a loss function depending on the model.
The fluctuation properties of the system are provided by a potential function
shaped by wells, in such a way that jumps between the stationary positions are
allowed. The power spectral density associated with this dissipation mechanism
shows a f^(-gamma)tail. The interest of this problem is that many systems are
characterized by a typical f^(-\gamma) spectral tail at low frequency. The
model presented in this article is based on a threshold type behaviour and its
generality allows applications in several fields. The effects of an external
force, introduced to produce damping, are studied by using both analytical
techniques and numerical simulations. The results obtained with the present
model show that no reduction of the power spectral density is appreciable below
the main peak of the spectral density.
|
0110019v1
|
2002-05-13
|
Damping of electromagnetic waves in low-collision electron-ion plasmas
|
Using previously developed method of two-dimensional Laplace transform we
obtain the characteristic equations k(\omega) for electromagnetic waves in
low-collision fully ionized plasma of a plane geometry. We apply here a new,
different from the one used in our previous paper, iteration procedure of
taking into account the Coulomb collisions. The waves are collisionally damping
in the same extent as electromagnetic waves. Despite the different from
previous paper form of the dispersion (poles) equation, the obtained decrements
for fast and slow wave modes coincide with results obtained in our earlier
paper, if one neglects the terms of higher orders in v^2/c^2, (v and c are
electron and light velocities). We point out how one can determine mutually
dependent boundary conditions allowing to eliminate simultaneously both the
backward and kinematical waves for transversal as well as for longitudinal
oscillations.
|
0205035v2
|
2002-06-01
|
Intrabeam scattering analysis of measurements at KEK's ATF damping ring
|
We derive a simple relation for estimating the relative emittance growth in x
and y due to intrabeam scattering (IBS) in electron storage rings. We show that
IBS calculations for the ATF damping ring, when using the formalism of
Bjorken-Mtingwa, a modified formalism of Piwinski (where eta squared divided by
beta has been replaced by the dispersion invariant), or a simple high-energy
approximate formula all give results that agree well. Comparing theory,
including the effect of potential well bunch lengthening, with a complete set
of ATF steady-state beam size vs. current measurements we find reasonably good
agreement for energy spread and horizontal emittance. The measured vertical
emittance, however, is larger than theory in both offset (zero current
emittance) and slope (emittance change with current). The slope error indicates
measurement error and/or additional current-dependent physics at the ATF; the
offset error, that the assumed Coulomb log is correct to within a factor of
1.75.
|
0206003v1
|
2002-08-24
|
Wakefield Band Partitioning In Linac Structures
|
In the NLC project multiple bunches of electrons and positrons will be
accelerated initially to a centre of mass of 500 GeV and later to 1 TeV or
more. In the process of accelerating 192 bunches within a pulse train,
wakefields are excited which kick the trailing bunches off axis and can cause
luminosity dilution and BBU (Beam Break Up). Several structures to damp the
wakefield have been designed and tested at SLAC and KEK and these have been
found to successfully damp the wakefield [1]. However, these 2pi/3 structures
suffered from electrical breakdown and this has prompted us to explore lower
group velocity structures operating at higher fundamental mode phase advances.
The wakefield partitioning amongst the bands has been found to change markedly
with increased phase advance. Here we report on general trends in the kick
factor and associated wakefield band partitioning in dipole bands as a function
of phase advance of the synchronous mode in linacs. These results are
applicable to both TW (travelling wave) and SW (standing wave) structures [1]
R.M. Jones et al, PAC99, also SLAC-PUB-8103
|
0208086v1
|
2003-01-30
|
Calculation of the Coherent Synchrotron Radiation Impedance from a Wiggler
|
Most studies of Coherent Synchrotron Radiation (CSR) have only considered the
radiation from independent dipole magnets. However, in the damping rings of
future linear colliders, a large fraction of the radiation power will be
emitted in damping wigglers. In this paper, the longitudinal wakefield and
impedance due to CSR in a wiggler are derived in the limit of a large wiggler
parameter $K$. After an appropriate scaling, the results can be expressed in
terms of universal functions, which are independent of $K$. Analytical
asymptotic results are obtained for the wakefield in the limit of large and
small distances, and for the impedance in the limit of small and high
frequencies.
|
0301073v1
|
2003-10-02
|
Damping factors for the gap-tooth scheme
|
An important class of problems exhibits macroscopically smooth behaviour in
space and time, while only a microscopic evolution law is known. For such
time-dependent multi-scale problems, the gap-tooth scheme has recently been
proposed. The scheme approximates the evolution of an unavailable (in closed
form) macroscopic equation in a macroscopic domain; it only uses appropriately
initialized simulations of the available microscopic model in a number of small
boxes. For some model problems, including numerical homogenization, the scheme
is essentially equivalent to a finite difference scheme, provided we repeatedly
impose appropriate algebraic constraints on the solution for each box. Here, we
demonstrate that it is possible to obtain a convergent scheme without
constraining the microscopic code, by introducing buffers that "shield" over
relatively short times the dynamics inside each box from boundary effects. We
explore and quantify the behavior of these schemes systematically through the
numerical computation of damping factors of the corresponding coarse
time-stepper, for which no closed formula is available.
|
0310014v1
|
2004-07-31
|
Propagation of optical excitations by dipolar interactions in metal nanoparticle chains
|
Dispersion relations for dipolar modes propagating along a chain of metal
nanoparticles are calculated by solving the full Maxwell equations, including
radiation damping. The nanoparticles are treated as point dipoles, which means
the results are valid only for a/d <= 1/3, where a is the particle radius and d
the spacing. The discrete modes for a finite chain are first calculated, then
these are mapped onto the dispersion relations appropriate for the infinite
chain. Computed results are given for a chain of 50-nm diameter Ag spheres
spaced by 75 nm. We find large deviations from previous quasistatic results:
Transverse modes interact strongly with the light line. Longitudinal modes
develop a bandwidth more than twice as large, resulting in a group velocity
that is more than doubled. All modes for which k_mode <= w/c show strongly
enhanced decay due to radiation damping.
|
0408003v2
|
2004-08-22
|
Tacoma Bridge Failure-- a Physical Model
|
The cause of the collapse of the Tacoma Narrows Bridge has been a topic of
much debate and confusion since the day it fell. Many mischaracterizations of
the observed phenomena have limited the widespread understanding of the
problem. Nevertheless, there has always been an abundance of evidence in favour
of a negative damping model. Negative damping, or positive feedback, is
responsible for many large amplitude oscillations observed in many
applications. In this paper, we will explain some well-known examples of
positive feedback. We will then present a feedback model, derived from
fundamental physics, capable of explaining a number of features observed in the
instabilities of many bridge decks. This model is supported by computational,
experimental and historical data.
|
0408101v1
|
2004-08-30
|
Short waves and cyclotron losses in the relativistic gyrokinetic theory
|
Radiation damping of the motion of charged particles in relativistic,
optically thin plasmas is described within the framework of the covariant
gyrokinetic theory. It involves description of the collisionless
single-particle dynamics as well as the Vlasov and Maxwell equations both
written in the covariant formulation. The damping causes corrections to the
phase-space trajectory of the particle, as well as to the form of the kinetic
equation itself, due to the failure of conditions of the Liouville theorem.
Both effects result independent of the gyrophase, which is retained as an
ignorable variable. In addition, the applicability range of the covariant
gyrokinetic theory is extended to describe short-wavelength perturbations with
the background of zero parallel electric field. The presented theory is
suitable for description of magnetized, relativistic, collisionless plasmas in
the context of astrophysical or laboratory problems. Non-uniquenes of the
gyrokinetic representation and consequences thereof are discussed.
|
0408128v1
|
2004-11-05
|
Wave-kinetic description of nonlinear photons
|
The nonlinear interaction, due to quantum electrodynamical (QED) effects,
between photons is investigated using a wave-kinetic description. Starting from
a coherent wave description, we use the Wigner transform technique to obtain a
set of wave-kinetic equations, the so called Wigner-Moyal equations. These
equations are coupled to a background radiation fluid, whose dynamics is
determined by an acoustic wave equation. In the slowly varying acoustic limit,
we analyse the resulting system of kinetic equations, and show that they
describe instabilities, as well as Landau-like damping. The instabilities may
lead to break-up and focusing of ultra-high intensity multi-beam systems, which
in conjunction with the damping may result in stationary strong field
structures. The results could be of relevance for the next generation of
laser-plasma systems.
|
0411058v1
|
2004-12-17
|
Optimal Determination of the Equilibrium Displacement of a Damped Harmonic Oscillator in the Presence of Thermal Noise
|
Using a matched filter technique, we derive the minimum variance, unbiased
estimator for the equilibrium displacement of a damped harmonic oscillator in
thermal equilibrium when interactions with the thermal bath are the leading
source of noise. We compare the variance in this optimal estimator with the
variance in other, commonly used estimators in the presence of pure thermal
noise and pure white noise. We also compare the variance in these estimators
for a mixture of white and thermal noise. This result has implications for
experimental design and the collection and analysis of data.
|
0412102v1
|
2006-01-13
|
Atomic collider into dual-isotope magneto-optical trap
|
When two of three pairs of the Gaussian laser beams of a traditional MOT are
misaligned in the racetrack configuration the effective coordinate-dependent
vortex force do arise. Then an atom is accelerated by this vortex force until
its velocity not balanced by the damping force. This situation may produce a
stable ring of revolving atoms of a certain radius. Due to the different
frequency and laser beams intensity dependences of the vortex, damping and
trapping forces it is possible to equalize the radii of two orbiting groups of
atoms in two-species or dual-isotope magneto-optical trap and so to arrange a
continuing collider of cooled atoms with the prescribed relative velocity. A
collider setup for atoms of two different types rotating with different angular
velocities along the same ring-like trajectory into MOT of the conventional
six-beam geometry is proposed and designed on example of two rubidium isotopes
Rb85 and Rb87.
|
0601097v1
|
2006-12-07
|
On some peculiarities of electric field pulse propagation in electron Maxwellian plasma and its back response
|
In the spirit of continued study of general plasma wave properties we
investigated the boundary problem with the simplest form of electric field
pulse at the edge x=0 of half-infinite uniform plasma slab with Maxwellian
electron distribution function. In the case of longitudinal electric field
pulse its traveling velocity is essentially other than in the case of harmonic
waves; there is also no back response. In the case of transverse field pulse
there takes place the bimodal propagation rate of the non-damping fast pulse
signal and non-damping weak slow sign reversed pulse signals; some very weak
response (echo) arises with a time delay in the near coordinate zone of
formation of the asymptotical regime.
|
0612064v4
|
1996-10-29
|
Bosonic Quantum Codes for Amplitude Damping
|
Traditional quantum error correction involves the redundant encoding of k
quantum bits using n quantum bits to allow the detection and correction of any
t bit error. The smallest general t=1 code requires n=5 for k=1. However, the
dominant error process in a physical system is often well known, thus inviting
the question: given a specific error model, can more efficient codes be
devised? We demonstrate new codes which correct just amplitude damping errors
which allow, for example, a t=1, k=1 code using effectively n=4.6. Our scheme
is based on using bosonic states of photons in a finite number of optical
modes. We present necessary and sufficient conditions for the codes, and
describe construction algorithms, physical implementation, and performance
bounds.
|
9610043v1
|
1997-01-16
|
Cooperative loss and decoherence in quantum computation and commuication
|
Cooperative effects in the loss (the amplitude damping) and decoherence (the
phase damping) of the qubits (two-state quantum systems) due to the inevitable
coupling to the same environment are investigated. It is found that the qubits
undergo the dissipation coherently in this case. In particular, for a special
kind of input states (called the coherence-preserving states), whose form
depends on the type of the coupling, loss and decoherence in quantum memory are
much reduced. Based on this phenomenon, a scheme by encoding the general input
states of the qubits into the corresponding coherence-preserving states is
proposed for reducing the cooperative loss and decoherence in quantum
computation or communication.
|
9701020v1
|
1997-03-22
|
Preserving coherence in quantum computation by pairing quantum bits
|
A scheme is proposed for protecting quantum states from both independent
decoherence and cooperative decoherence. The scheme operates by pairing each
qubit (two-state quantum system) with an ancilla qubit and by encoding the
states of the qubits into the corresponding coherence-preserving states of the
qubit-pairs. In this scheme, the amplitude damping (loss of energy) is
prevented as well as the phase damping (dephasing) by a strategy called the
free-Hamiltonian-elimination We further extend the scheme to include quantum
gate operations and show that loss and decoherence during the gate operations
can also be prevented.
|
9703040v2
|
1997-06-10
|
Perturbative expansions for the fidelities and spatially correlated dissipation of quantum bits
|
We construct generally applicable short-time perturbative expansions for some
fidelities, such as the input-output fidelity, the entanglement fidelity, and
the average fidelity. Successive terms of these expansions yield characteristic
times for the damping of the fidelities involving successive powers of the
Hamiltonian. The second-order results, which represent the damping rates of the
fidelities, are extensively discussed. As an interesting application of these
expansions, we use them to study the spatially-correlated dissipation of
quantum bits. Spatial correlations in the dissipation are described by a
correlation function. Explicit conditions are derived for independent
decoherence and for collective decoherence.
|
9706020v2
|
1998-05-27
|
Measurement Process In a Two-Barrier System
|
The description of a measuring process, such as that which occurs when a
quantum point contact (QPC) detector is influenced by a nearby external
electron which can take up two possible positions, provides a interesting
application of the method of quantum damping. We find a number of new effects,
due to the complete treatment of phases afforded by the formalism, although our
results are generally similiar to those of other treatments, particularly to
those of Buks et al.
These are effects depending on the phase shift in the detector, effects which
depend on the direction of the measuring current, and in addition to damping or
dissipative effects, an energy shift of the measured system. In particular, the
phase shift effect leads to the conclusion that there can be effects of
"observation" even when the two barriers in question pass the same current.
The nature of the current through the barriers and its statistics is
discussed, giving a description of correlations in the current due to
"measurement" and of the origin of "telegraphic" signals.
|
9805081v2
|
1998-10-06
|
Cumulant expansion for studying damped quantum solitons
|
The quantum statistics of damped optical solitons is studied using
cumulant-expansion techniques. The effect of absorption is described in terms
of ordinary Markovian relaxation theory, by coupling the optical field to a
continuum of reservoir modes. After introduction of local bosonic field
operators and spatial discretization pseudo-Fokker-Planck equations for
multidimensional s-parameterized phase-space functions are derived. These
partial differential equations are equivalent to an infinite set of ordinary
differential equations for the cumulants of the phase-space functions.
Introducing an appropriate truncation condition, the resulting finite set of
cumulant evolution equations can be solved numerically. Solutions are presented
in Gaussian approximation and the quantum noise is calculated, with special
emphasis on squeezing and the recently measured spectral photon-number
correlations [Spaelter et al., Phys. Rev. Lett. 81, 786 (1998)].
|
9810018v3
|
1999-02-10
|
Quantum noise in the position measurement of a cavity mirror undergoing Brownian motion
|
We perform a quantum theoretical calculation of the noise power spectrum for
a phase measurement of the light output from a coherently driven optical cavity
with a freely moving rear mirror. We examine how the noise resulting from the
quantum back action appears among the various contributions from other noise
sources. We do not assume an ideal (homodyne) phase measurement, but rather
consider phase modulation detection, which we show has a different shot noise
level. We also take into account the effects of thermal damping of the mirror,
losses within the cavity, and classical laser noise. We relate our theoretical
results to experimental parameters, so as to make direct comparisons with
current experiments simple. We also show that in this situation, the standard
Brownian motion master equation is inadequate for describing the thermal
damping of the mirror, as it produces a spurious term in the steady-state phase
fluctuation spectrum. The corrected Brownian motion master equation [L. Diosi,
Europhys. Lett. {\bf 22}, 1 (1993)] rectifies this inadequacy.
|
9902040v1
|
1999-10-05
|
Uncertainty, entropy and decoherence of the damped harmonic oscillator in the Lindblad theory of open quantum systems
|
In the framework of the Lindblad theory for open quantum systems, expressions
for the density operator, von Neumann entropy and effective temperature of the
damped harmonic oscillator are obtained. The entropy for a state characterized
by a Wigner distribution function which is Gaussian in form is found to depend
only on the variance of the distribution function. We give a series of
inequalities, relating uncertainty to von Neumann entropy and linear entropy.
We analyze the conditions for purity of states and show that for a special
choice of the diffusion coefficients, the correlated coherent states (squeezed
coherent states) are the only states which remain pure all the time during the
evolution of the considered system. These states are also the most stable under
evolution in the presence of the environment and play an important role in the
description of environment induced decoherence.
|
9910019v1
|
2000-06-07
|
Phenomenological approach to introduce damping effects on radiation field states
|
In this work we propose an approach to deal with radiation field states which
incorporates damping effects at zero temperature. By using some well known
results on dissipation of a cavity field state, obtained by standard ab-initio
methods, it was possible to infer through a phenomenological way the explicit
form for the evolution of the state vector for the whole system: the
cavity-field plus reservoir. This proposal turns out to be of extreme
convenience to account for the influence of the reservoir over the cavity
field.
To illustrate the universal applicability of our approach we consider the
attenuation effects on cavity-field states engineering. A proposal to maximize
the fidelity of the process is presented.
|
0006035v2
|
2001-09-28
|
Decoherence in trapped ions due to polarization of the residual background gas
|
We investigate the mechanism of damping and heating of trapped ions
associated with the polarization of the residual background gas induced by the
oscillating ions themselves. Reasoning by analogy with the physics of surface
electrons in liquid helium, we demonstrate that the decay of Rabi oscillations
observed in experiments on 9Be+ can be attributed to the polarization phenomena
investigated here. The measured sensitivity of the damping of Rabi oscillations
with respect to the vibrational quantum number of a trapped ion is also
predicted in our polarization model.
|
0109156v1
|
2002-06-18
|
Five Lectures On Dissipative Master Equations
|
1 First Lecture: Basics
1.1 Physical Derivation of the Master Equation
1.2 Some Simple Implications
1.3 Steady State
1.4 Action to the Left
2 Second Lecture: Eigenvalues and Eigenvectors of L
2.1 A Simple Case First
2.2 The General Case
3 Third Lecture: Completeness of the Damping Bases
3.1 Phase Space Functions
3.2 Completeness of the Eigenvectors of L
3.3 Positivity Conservation
3.4 Lindblad Form of Liouville Operators
4 Fourth Lecture: Quantum-Optical Applications
4.1 Periodically Driven Damped Oscillator
4.2 Conditional and Unconditional Evolution
4.3 Physical Signicance of Statistical Operators
5 Fifth Lecture: Statistics of Detected Atoms
5.1 Correlation Functions
5.2 Waiting Time Statistics
5.3 Counting Statistics
|
0206116v1
|
2002-10-02
|
Radiation damping and decoherence in quantum electrodynamics
|
The processes of radiation damping and decoherence in Quantum Electrodynamics
are studied from an open system's point of view. Employing functional
techniques of field theory, the degrees of freedom of the radiation field are
eliminated to obtain the influence phase functional which describes the reduced
dynamics of the matter variables. The general theory is applied to the dynamics
of a single electron in the radiation field. From a study of the wave packet
dynamics a quantitative measure for the degree of decoherence, the decoherence
function, is deduced. The latter is shown to describe the emergence of
decoherence through the emission of bremsstrahlung caused by the relative
motion of interfering wave packets. It is argued that this mechanism is the
most fundamental process in Quantum Electrodynamics leading to the destruction
of coherence, since it dominates for short times and because it is at work even
in the electromagnetic field vacuum at zero temperature. It turns out that
decoherence trough bremsstrahlung is very small for single electrons but
extremely large for superpositions of many-particle states.
|
0210013v1
|
2003-01-08
|
Dissipation, Emergent Quantization and Quantum Fluctuations
|
We review some aspects of the quantization of the damped harmonic oscillator.
We derive the exact action for a damped mechanical system in the frame of the
path integral formulation of the quantum Brownian motion problem developed by
Schwinger and by Feynman and Vernon. The doubling of the phase-space degrees of
freedom for dissipative systems and thermal field theories is discussed and the
doubled variables are related to quantum noise effects. The 't Hooft proposal,
according to which the loss of information due to dissipation in a classical
deterministic system manifests itself in the quantum features of the system, is
analyzed and the quantum spectrum of the harmonic oscillator is shown to be
originated from the dissipative character of the original classical
deterministic system.
|
0301031v1
|
2004-02-12
|
Non-Markovian Quantum Trajectories Versus Master Equations: Finite Temperature Heat Bath
|
The interrelationship between the non-Markovian stochastic Schr\"odinger
equations and the corresponding non-Markovian master equations is investigated
in the finite temperature regimes. We show that the general finite temperature
non-Markovian trajectories can be used to derive the corresponding
non-Markovian master equations. A simple, yet important solvable example is the
well-known damped harmonic oscillator model in which a harmonic oscillator is
coupled to a finite temperature reservoir in the rotating wave approximation.
The exact convolutionless master equation for the damped harmonic oscillator is
obtained by averaging the quantum trajectories relying upon no assumption of
coupling strength or time scale. The master equation derived in this way
automatically preserves the positivity, Hermiticity and unity.
|
0402086v2
|
2005-04-27
|
Decoherence models and their effects on quantum maps and algorithms
|
In this work we study several models of decoherence and how different quantum
maps and algorithms react when perturbed by them. Following closely Ref. [1],
generalizations of the three paradigmatic one single qubit quantum channels
(these are the depolarizing channel, the phase damping channel and the
amplitude damping channel) for the case of an arbitrarily-sized
finite-dimensional Hilbert space are presented, as well as other types of noise
in phase space. More specifically, Grover's search algorithm's response to
decoherence is analyzed; together with those of a family of quantum versions of
chaotic and regular classical maps (the baker's map and the cat maps). A
relationship between how sensitive to decoherence a quantum map is and the
degree of complexity in the dynamics of its associated classical counterpart is
observed; resulting in a clear tendency to react the more decoherently the more
complex the associated classical dynamics is.
|
0504211v1
|
2005-09-22
|
Semiclassical quantization of non-Hamiltonian dynamical systems without memory
|
We propose a new method of quantization of a wide class of dynamical systems
that originates directly from the equations of motion. The method is based on
the correspondence between the classical and the quantum Poisson brackets,
postulated by Dirac. This correspondence applied to open (non-Hamiltonian)
systems allows one to point out the way of transition from the quantum
description based on the Lindblad equation to the dynamical description of
their classical analogs by the equations of motion and vice versa. As the
examples of using of the method we describe the procedure of the quantization
of three widely considered dynamical systems: 1) the harmonic oscillator with
friction, 2) the oscillator with a nonlinear damping that simulates the process
of the emergence of the limit cycle, and 3) the system of two periodic rotators
with a weak interaction that synchronizes their oscillations. We discuss a
possible application of the method for a description of quantum fluctuations in
Josephson junctions with a strong damping and for the quantization of open
magnetic systems with a dissipation and a pumping.
|
0509159v1
|
2005-11-15
|
Classical Phase Space Density for the Relativistic Hydrogen Atom
|
Quantum mechanics is considered to arise from an underlying classical
structure (``hidden variable theory'', ``sub-quantum mechanics''), where
quantum fluctuations follow from a physical noise mechanism. The stability of
the hydrogen ground state can then arise from a balance between Lorentz damping
and energy absorption from the noise. Since the damping is weak, the ground
state phase space density should predominantly be a function of the conserved
quantities, energy and angular momentum.
A candidate for this phase space density is constructed for ground state of
the relativistic hydrogen problem of a spinless particle. The first excited
states and their spherical harmonics are also considered in this framework. The
analytic expression of the ground state energy can be reproduced, provided
averages of certain products are replaced by products of averages. This
analysis puts forward that quantum mechanics may arise from an underlying
classical level as a slow variable theory, where each new quantum operator
relates to a new, well separated time interval.
|
0511144v1
|
2006-03-13
|
Decoherence induced by a phase-damping reservoir
|
A phase damping reservoir composed by $N$-bosons coupled to a system of
interest through a cross-Kerr interaction is proposed and its effects on
quantum superpo sitions are investigated. By means of analytical calculations
we show that: i-) the reservoir induces a Gaussian decay of quantum coherences,
and ii-) the inher ent incommensurate character of the spectral distribution
yields irreversibility . A state-independent decoherence time and a master
equation are both derived an alytically. These results, which have been
extended for the thermodynamic limit, show that nondissipative decoherence can
be suitably contemplated within the EI D approach. Finally, it is shown that
the same mechanism yielding decoherence ar e also responsible for inducing
dynamical disentanglement.
|
0603109v2
|
2007-01-21
|
Casimir-Polder forces on excited atoms in the strong atom-field coupling regime
|
Based on macroscopic quantum electrodynamics in linear media, we develop a
general theory of the resonant Casimir-Polder force on an excited two-level
atom in the presence of arbitrary linear bodies, with special emphasis on the
strong-coupling regime where reabsorption of an emitted photon can give rise to
(vacuum) Rabi oscillations. We first derive a simple time-independent
expression for the force by using a dressed-state approximation. For initially
single-quantum excited atom-field systems we then study the dynamics of the
force by starting from the Lorentz force and evaluating its average as a
function of time. For strong atom-field coupling, we find that the force may
undergo damped Rabi oscillations. The damping is due to the decay of both the
atomic excitation and the field excitation, and both amplitude and mean value
of the oscillations depend on the chosen initial state.
|
0701151v2
|
2007-02-07
|
Protecting an optical qubit against photon loss
|
We consider quantum error-correction codes for multimode bosonic systems,
such as optical fields, that are affected by amplitude damping. Such a process
is a generalization of an erasure channel. We demonstrate that the most
accessible method of transforming optical systems with the help of passive
linear networks has limited usefulness in preparing and manipulating such
codes. These limitations stem directly from the recoverability condition for
one-photon loss. We introduce a three-photon code protecting against the first
order of amplitude damping, i.e. a single photon loss, and discuss its
preparation using linear optics with single-photon sources and conditional
detection. Quantum state and process tomography in the code subspace can be
implemented using passive linear optics and photon counting. An experimental
proof-of-principle demonstration of elements of the proposed quantum error
correction scheme for a one-photon erasure lies well within present
technological capabilites.
|
0702075v1
|
1995-02-03
|
Shock waves in the dissipative Toda lattice
|
We consider the propagation of a shock wave (SW) in the damped Toda lattice.
The SW is a moving boundary between two semi-infinite lattice domains with
different densities. A steadily moving SW may exist if the damping in the
lattice is represented by an ``inner'' friction, which is a discrete analog of
the second viscosity in hydrodynamics. The problem can be considered
analytically in the continuum approximation, and the analysis produces an
explicit relation between the SW's velocity and the densities of the two
phases. Numerical simulations of the lattice equations of motion demonstrate
that a stable SW establishes if the initial velocity is directed towards the
less dense phase; in the opposite case, the wave gradually spreads out. The
numerically found equilibrium velocity of the SW turns out to be in a very good
agreement with the analytical formula even in a strongly discrete case. If the
initial velocity is essentially different from the one determined by the
densities (but has the correct sign), the velocity does not significantly
alter, but instead the SW adjusts itself to the given velocity by sending
another SW in the opposite direction.
|
9502001v1
|
2007-04-04
|
An integral field spectroscopic survey for high redshift damped Lyman-alpha galaxies
|
We search for galaxy counterparts to damped Lyman-alpha absorbers (DLAs) at
z>2 towards nine quasars, which have 14 DLAs and 8 sub-DLAs in their spectra.
We use integral field spectroscopy to search for Ly-alpha emission line objects
at the redshifts of the absorption systems. Besides recovering two previously
confirmed objects, we find six statistically significant candidate Ly-alpha
emission line objects. The candidates are identified as having wavelengths
close to the DLA line where the background quasar emission is absorbed. In
comparison with the six currently known Ly-alpha emitting DLA galaxies the
candidates have similar line fluxes and line widths, while velocity offsets
between the emission lines and systemic DLA redshifts are larger. The impact
parameters are larger than 10 kpc, and lower column density systems are found
at larger impact parameters. Assuming that a single gas cloud extends from the
QSO line of sight to the location of the candidate emission line, we find that
the average candidate DLA galaxy is surrounded by neutral gas with an
exponential scale length of ~5 kpc.
|
0704.0654v1
|
2007-04-06
|
9.7 micrometer Silicate Absorption in a Damped Lyman-alpha Absorber at z=0.52
|
We report a detection of the 9.7 micrometer silicate absorption feature in a
damped Lyman-alpha (DLA) system at z_{abs} = 0.524 toward AO0235+164, using the
Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The feature
shows a broad shallow profile over about 8-12 micrometers in the absorber rest
frame and appears to be > 15 sigma significant in equivalent width. The feature
is fit reasonably well by the silicate absorption profiles for laboratory
amorphous olivine or diffuse Galactic interstellar clouds. To our knowledge,
this is the first indication of 9.7 micrometer silicate absorption in a DLA. We
discuss potential implications of this finding for the nature of the dust in
quasar absorbers. Although the feature is relatively shallow (tau_{9.7} =
0.08-0.09), it is about 2 times deeper than expected from extrapolation of the
tau_{9.7} vs. E(B-V) relation known for diffuse Galactic interstellar clouds.
Further studies of the 9.7 micrometer silicate feature in quasar absorbers will
open a new window on the dust in distant galaxies.
|
0704.0826v2
|
2007-04-17
|
Boolean network model predicts cell cycle sequence of fission yeast
|
A Boolean network model of the cell-cycle regulatory network of fission yeast
(Schizosaccharomyces Pombe) is constructed solely on the basis of the known
biochemical interaction topology. Simulating the model in the computer,
faithfully reproduces the known sequence of regulatory activity patterns along
the cell cycle of the living cell. Contrary to existing differential equation
models, no parameters enter the model except the structure of the regulatory
circuitry. The dynamical properties of the model indicate that the biological
dynamical sequence is robustly implemented in the regulatory network, with the
biological stationary state G1 corresponding to the dominant attractor in state
space, and with the biological regulatory sequence being a strongly attractive
trajectory. Comparing the fission yeast cell-cycle model to a similar model of
the corresponding network in S. cerevisiae, a remarkable difference in
circuitry, as well as dynamics is observed. While the latter operates in a
strongly damped mode, driven by external excitation, the S. pombe network
represents an auto-excited system with external damping.
|
0704.2200v1
|
2007-05-08
|
Optical dilution and feedback cooling of a gram-scale oscillator to 6.9 mK
|
We report on use of a radiation pressure induced restoring force, the optical
spring effect, to optically dilute the mechanical damping of a 1 gram suspended
mirror, which is then cooled by active feedback (cold damping). Optical
dilution relaxes the limit on cooling imposed by mechanical losses, allowing
the oscillator mode to reach a minimum temperature of 6.9 mK, a factor of
~40000 below the environmental temperature. A further advantage of the optical
spring effect is that it can increase the number of oscillations before
decoherence by several orders of magnitude. In the present experiment we infer
an increase in the dynamical lifetime of the state by a factor of ~200.
|
0705.1018v2
|
2007-05-14
|
Electron-muon heat conduction in neutron star cores via the exchange of transverse plasmons
|
We calculate the thermal conductivity of electrons and muons kappa_{e-mu}
produced owing to electromagnetic interactions of charged particles in neutron
star cores and show that these interactions are dominated by the exchange of
transverse plasmons (via the Landau damping of these plasmons in
nonsuperconducting matter and via a specific plasma screening in the presence
of proton superconductivity). For normal protons, the Landau damping strongly
reduces kappa_{e-mu} and makes it temperature independent. Proton
superconductivity suppresses the reduction and restores the Fermi-liquid
behavior kappa_{e-mu} ~ 1/T. Comparing with the thermal conductivity of
neutrons kappa_n, we obtain kappa_{e-mu}> kappa_n for T>2 GK in normal matter
and for any T in superconducting matter with proton critical temperatures
T_c>3e9 K. The results are described by simple analytic formulae.
|
0705.1963v1
|
2007-05-24
|
Measurement of Newtonian fluid slip using a torsional ultrasonic oscillator
|
The composite torsional ultrasonic oscillator, a versatile experimental
system, can be used to investigate slip of Newtonian fluid at a smooth surface.
A rigorous analysis of slip-dependent damping for the oscillator is presented.
Initially, the phenomenon of finite surface slip and the slip length are
considered for a half-space of Newtonian fluid in contact with a smooth,
oscillating solid surface. Definitions are revisited and clarified in light of
inconsistencies in the literature. We point out that, in general oscillating
flows, Navier's slip length b is a complex number. An intuitive velocity
discontinuity parameter of unrestricted phase is used to describe the effect of
slip on measurement of viscous shear damping. The analysis is applied to the
composite oscillator and preliminary experimental work for a 40 kHz oscillator
is presented. The Non-Slip Boundary Condition (NSBC) has been verified for a
hydrophobic surface in water to within ~60 nm of |b|=0 nm. Experiments were
carried out at shear rate amplitudes between 230 and 6800 /s, corresponding to
linear displacement amplitudes between 3.2 and 96 nm.
|
0705.3498v3
|
2007-06-05
|
Waves and instabilities in dissipative rotating superfluid neutron stars
|
We discuss wave propagation in rotating superfluid neutron star cores, taking
into account the vortex mediated mutual friction force. For models where the
two fluids co-rotate in the unperturbed state, our analysis clarifies the role
of chemical coupling and entrainment for sound and inertial waves. We also
investigate the mutual friction damping, providing results that demonstrate the
well-known fact that sound waves propagating along a vortex array are undamped.
We show that the same is not true for inertial waves, which are damped by the
mutual friction regardless of the propagation direction. We then include the
vortex tension, which arises due to local vortex curvature. Focussing on purely
transverse inertial waves, we derive the small correction that the tension
induces in the wave frequency. Finally, we allow for a relative linear flow in
the background (along the rotation axis). In this case we show how the mutual
friction coupling may induce a dynamical instability in the inertial waves. We
discuss the critical flow required for the instability to be present, its
physical interpretation and the possible relevance it may have for neutron star
physics.
|
0706.0672v1
|
2007-06-28
|
Coherent Magnetization Precession in GaMnAs induced by Ultrafast Optical Excitation
|
We use femtosecond optical pulses to induce, control and monitor
magnetization precession in ferromagnetic Ga0.965Mn0.035As. At temperatures
below ~40 K we observe coherent oscillations of the local Mn spins, triggered
by an ultrafast photoinduced reorientation of the in-plane easy axis. The
amplitude saturation of the oscillations above a certain pump intensity
indicates that the easy axis remains unchanged above ~TC/2. We find that the
observed magnetization precession damping (Gilbert damping) is strongly
dependent on pump laser intensity, but largely independent on ambient
temperature. We provide a physical interpretation of the observed light-induced
collective Mn-spin relaxation and precession.
|
0706.4270v2
|
2007-07-20
|
Dissipation-Scale Turbulence in the Solar Wind
|
We present a cascade model for turbulence in weakly collisional plasmas that
follows the nonlinear cascade of energy from the large scales of driving in the
MHD regime to the small scales of the kinetic Alfven wave regime where the
turbulence is dissipated by kinetic processes. Steady-state solutions of the
model for the slow solar wind yield three conclusions: (1) beyond the observed
break in the magnetic energy spectrum, one expects an exponential cut-off; (2)
the widely held interpretation that this dissipation range obeys power-law
behavior is an artifact of instrumental sensitivity limitations; and, (3) over
the range of parameters relevant to the solar wind, the observed variation of
dissipation range spectral indices from -2 to -4 is naturally explained by the
varying effectiveness of Landau damping, from an undamped prediction of -7/3 to
a strongly damped index around -4.
|
0707.3149v1
|
2007-08-03
|
Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles
|
The shape of ferromagnetic resonance spectra of highly dispersed, chemically
disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution
of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline
anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the
LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional
to the particle magnetic moments determined from the Langevin analysis of the
magnetization isotherms. These novel features are explained by the scattering
of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the
spin-orbit coupling, while the sd-exchange can be ruled out. The large
saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the
dominance of an overdamped 1 meV e/h-pair which seems to originate from the
discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.
|
0708.0463v1
|
2007-08-09
|
An algorithm for detecting oscillatory behavior in discretized data: the damped-oscillator oscillator detector
|
We present a simple algorithm for detecting oscillatory behavior in discrete
data. The data is used as an input driving force acting on a set of simulated
damped oscillators. By monitoring the energy of the simulated oscillators, we
can detect oscillatory behavior in data. In application to in vivo deep brain
basal ganglia recordings, we found sharp peaks in the spectrum at 20 and 70 Hz.
The algorithm is also compared to the conventional fast Fourier transform and
circular statistics techniques using computer generated model data, and is
found to be comparable to or better than fast Fourier transform in test cases.
Circular statistics performed poorly in our tests.
|
0708.1341v1
|
2007-08-22
|
The dynamics of vortex generation in superfluid 3He-B
|
A profound change occurs in the stability of quantized vortices in externally
applied flow of superfluid 3He-B at temperatures ~ 0.6 Tc, owing to the rapidly
decreasing damping in vortex motion with decreasing temperature. At low damping
an evolving vortex may become unstable and generate a new independent vortex
loop. This single-vortex instability is the generic precursor to turbulence. We
investigate the instability with non-invasive NMR measurements on a rotating
cylindrical sample in the intermediate temperature regime (0.3 - 0.6) Tc. From
comparisons with numerical calculations we interpret that the instability
occurs at the container wall, when the vortex end moves along the wall in
applied flow.
|
0708.3003v2
|
2007-09-05
|
Phonon bottleneck in the low-excitation limit
|
The phonon-bottleneck problem in the relaxation of two-level systems (spins)
via direct phonon processes is considered numerically in the weak-excitation
limit where the Schroedinger equation for the spin-phonon system simplifies.
The solution for the relaxing spin excitation p(t), emitted phonons n_k(t),
etc. is obtained in terms of the exact many-body eigenstates. In the absence of
phonon damping Gamma_{ph} and inhomogeneous broadening, p(t) approaches the
bottleneck plateau p_\infty > 0 with strongly damped oscillations, the
frequency being related to the spin-phonon splitting Delta at the avoided
crossing. For any Gamma_{ph} > 0 one has p(t) -> 0 but in the case of strong
bottleneck the spin relaxation rate is much smaller than Gamma_{ph} and p(t) is
nonexponential. Inhomogeneous broadening exceeding Delta partially alleviates
the bottleneck and removes oscillations of p(t). The line width of emitted
phonons, as well as Delta, increase with the strength of the bottleneck, i.e.,
with the concentration of spins.
|
0709.0556v1
|
2007-09-13
|
Distribution of PageRank Mass Among Principle Components of the Web
|
We study the PageRank mass of principal components in a bow-tie Web Graph, as
a function of the damping factor c. Using a singular perturbation approach, we
show that the PageRank share of IN and SCC components remains high even for
very large values of the damping factor, in spite of the fact that it drops to
zero when c goes to one. However, a detailed study of the OUT component reveals
the presence ``dead-ends'' (small groups of pages linking only to each other)
that receive an unfairly high ranking when c is close to one. We argue that
this problem can be mitigated by choosing c as small as 1/2.
|
0709.2016v1
|
2007-10-02
|
Oscillating Starless Cores: The Nonlinear Regime
|
In a previous paper, we modeled the oscillations of a thermally-supported
(Bonnor-Ebert) sphere as non-radial, linear perturbations following a standard
analysis developed for stellar pulsations. The predicted column density
variations and molecular spectral line profiles are similar to those observed
in the Bok globule B68 suggesting that the motions in some starless cores may
be oscillating perturbations on a thermally supported equilibrium structure.
However, the linear analysis is unable to address several questions, among them
the stability, and lifetime of the perturbations. In this paper we simulate the
oscillations using a three-dimensional numerical hydrodynamic code. We find
that the oscillations are damped predominantly by non-linear mode-coupling, and
the damping time scale is typically many oscillation periods, corresponding to
a few million years, and persisting over the inferred lifetime of gobules.
|
0710.0625v1
|
2007-10-08
|
Jet quenching parameter \hat q in the stochastic QCD vacuum with Landau damping
|
We argue that the radiative energy loss of a parton traversing the
quark-gluon plasma is determined by Landau damping of soft modes in the plasma.
Using this idea, we calculate the jet quenching parameter of a gluon. The
calculation is done in SU(3) quenched QCD within the stochastic vacuum model.
At the LHC-relevant temperatures, the result depends on the gluon condensate,
the vacuum correlation length, and the gluon Debye mass. Numerically, when the
temperature varies from T=T_c to T=900 MeV, the jet quenching parameter rises
from \hat q=0 to approximately 1.8 GeV^2/fm. We compare our results with the
predictions of perturbative QCD and other calculations.
|
0710.1540v2
|
2007-11-07
|
Tuning the effective coupling of an AFM lever to a thermal bath
|
Fabrication of Nano-Electro-Mechanical-Systems (NEMS) of high quality is
nowadays extremely efficient. These NEMS will be used as sensors and actuators
in integrated systems. Their use however raises questions about their interface
(actuation, detection, read out) with external detection and control systems.
Their operation implies many fundamental questions related to single particle
effects such as Coulomb blockade, light matter interactions such as radiation
pressure, thermal effects, Casimir forces and the coupling of nanosystems to
external world (thermal fluctuations, back action effect). Here we specifically
present how the damping of an oscillating cantilever can be tuned in two
radically different ways: i) through an electro-mechanical coupling in the
presence of a strong Johnson noise, ii) through an external feedback control of
thermal fluctuations which is the cold damping closely related to Maxwell's
demon. This shows how the interplay between MEMS or NEMS external control and
their coupling to a thermal bath can lead to a wealth of effects that are
nowadays extensively studied in different areas.
|
0711.1024v1
|
2007-12-11
|
Neutrino oscillations in a stochastic model for space-time foam
|
We study decoherence models for flavour oscillations in four-dimensional
stochastically fluctuating space times and discuss briefly the sensitivity of
current neutrino experiments to such models. We pay emphasis on demonstrating
the model dependence of the associated decoherence-induced damping coefficients
in front of the oscillatory terms in the respective transition probabilities
between flavours. Within the context of specific models of foam, involving
point-like D-branes and leading to decoherence-induced damping which is
inversely proportional to the neutrino energies, we also argue that future
limits on the relevant decoherence parameters coming from TeV astrophysical
neutrinos, to be observed in ICE-CUBE, are not far from theoretically expected
values with Planck mass suppression. Ultra high energy neutrinos from Gamma Ray
Bursts at cosmological distances can also exhibit in principle sensitivity to
such effects.
|
0712.1779v1
|
2008-01-21
|
Collective cyclotron motion of the relativistic plasma in graphene
|
We present a theory of the finite temperature thermo-electric response
functions of graphene, in the hydrodynamic regime induced by electron-electron
collisions. In moderate magnetic fields, the Dirac particles undergo a
collective cyclotron motion with a temperature-dependent relativistic cyclotron
frequency proportional to the net charge density of the Dirac plasma. In
contrast to the undamped cyclotron pole in Galilean-invariant systems (Kohn's
theorem), here there is a finite damping induced by collisions between the
counter-propagating particles and holes. This cyclotron motion shows up as a
damped pole in the frequency dependent conductivities, and should be readily
detectable in microwave measurements at room temperature. We also discuss the
large Nernst effect to be expected in graphene.
|
0801.2970v3
|
2008-01-25
|
Sound waves and solitons in hot and dense nuclear matter
|
Assuming that nuclear matter can be treated as a perfect fluid, we study the
propagation of perturbations in the baryon density. The equation of state is
derived from a relativistic mean field model, which is a variant of the
non-linear Walecka model. The expansion of the Euler and continuity equations
of relativistic hydrodynamics around equilibrium configurations leads to
differential equations for the density fluctuations. We solve them numerically
for linear and spherical perturbations and follow the time evolution of the
initial pulses. For linear perturbations we find single soliton solutions and
solutions with one or more solitons followed by radiation. Depending on the
equation of state a strong damping may occur. Spherical perturbations are
strongly damped and almost do not propagate. We study these equations also for
matter at finite temperature. Finally we consider the limiting case of shock
wave formation.
|
0801.3938v1
|
2008-01-28
|
Qualitative Analysis of Forced Response of Blisks With Friction Ring Dampers
|
A damping strategy for blisks (integrally bladed disks) of turbomachinery
involving a friction ring is investigated. These rings, located in grooves
underside the wheel of the blisks, are held in contact by centrifugal loads and
the energy is dissipated when relative motions between the ring and the disk
occur. A representative lumped parameter model of the system is introduced and
the steady-state nonlinear response is derived using a multi-harmonic balance
method combined with an AFT procedure where the friction force is calculated in
the time domain. Numerical simulations are presented for several damper
characteristics and several excitation configurations. From these results, the
performance of this damping strategy is discussed and some design guidelines
are given.
|
0801.4350v1
|
2008-01-29
|
Long Term Evolution of Magnetic Turbulence in Relativistic Collisionless Shocks
|
We study the long term evolution of magnetic fields generated by an initially
unmagnetized collisionless relativistic $e^+e^-$ shock. Our 2D particle-in-cell
numerical simulations show that downstream of such a Weibel-mediated shock,
particle distributions are approximately isotropic, relativistic Maxwellians,
and the magnetic turbulence is highly intermittent spatially, nonpropagating,
and decaying. Using linear kinetic theory, we find a simple analytic form for
these damping rates. Our theory predicts that overall magnetic energy decays
like $(\omega_p t)^{-q}$ with $q \sim 1$, which compares favorably with
simulations, but predicts overly rapid damping of short wavelength modes.
Magnetic trapping of particles within the magnetic structures may be the origin
of this discrepancy. We conclude that initially unmagnetized relativistic
shocks in electron-positron plasmas are unable to form persistent downstream
magnetic fields. These results put interesting constraints on synchrotron
models for the prompt and afterglow emission from GRBs.
|
0801.4583v1
|
2008-02-14
|
Light-induced magnetization precession in GaMnAs
|
We report dynamics of the transient polar Kerr rotation (KR) and of the
transient reflectivity induced by femtosecond laser pulses in ferromagnetic
(Ga,Mn)As with no external magnetic field applied. It is shown that the
measured KR signal consist of several different contributions, among which only
the oscillatory signal is directly connected with the ferromagnetic order in
(Ga,Mn)As. The origin of the light-induced magnetization precession is
discussed and the magnetization precession damping (Gilbert damping) is found
to be strongly influenced by annealing of the sample.
|
0802.2043v2
|
2008-02-20
|
Mechanical mode dependence of bolometric back-action in an AFM microlever
|
Two back action (BA) processes generated by an optical cavity based detection
device can deeply transform the dynamical behavior of an AFM microlever: the
photothermal force or the radiation pressure. Whereas noise damping or
amplifying depends on optical cavity response for radiation pressure BA, we
present experimental results carried out under vacuum and at room temperature
on the photothermal BA process which appears to be more complex. We show for
the first time that it can simultaneously act on two vibration modes in
opposite direction: noise on one mode is amplified whereas it is damped on
another mode. Basic modeling of photothermal BA shows that dynamical effect on
mechanical mode is laser spot position dependent with respect to mode shape.
This analysis accounts for opposite behaviors of different modes as observed.
|
0802.2763v2
|
2008-02-21
|
Propagation of cosmic rays in the foam-like Universe
|
The model of a classical spacetime foam is considered, which consists of
static wormholes embedded in Minkowski spacetime. We examine the propagation of
particles in such a medium and demonstrate that a single thin ray undergoes a
specific damping in the density of particles depending on the traversed path
and the distribution of wormholes. The missing particles are scattered around
the ray. Wormholes was shown to form DM halos around point-like sources.
Therefore, the correlation predicted between the damping and the amount of DM
can be used to verify the topological nature of Dark Matter.
|
0802.3109v2
|
2008-02-21
|
Damping by slow relaxing rare earth impurities in Ni80Fe20
|
Doping NiFe by heavy rare earth atoms alters the magnetic relaxation
properties of this material drastically. We show that this effect can be well
explained by the slow relaxing impurity mechanism. This process is a
consequence of the anisotropy of the on site exchange interaction between the
4f magnetic moments and the conduction band. As expected from this model the
magnitude of the damping effect scales with the anisotropy of the exchange
interaction and increases by an order of magnitude at low temperatures. In
addition our measurements allow us to determine the relaxation time of the 4f
electrons as a function of temperature.
|
0802.3206v3
|
2008-03-11
|
Domain wall motion of magnetic nanowires under a static field
|
The propagation of a head-to-head magnetic domain-wall (DW) or a tail-to-tail
DW in a magnetic nanowire under a static field along the wire axis is studied.
Relationship between the DW velocity and DW structure is obtained from the
energy consideration. The role of the energy dissipation in the field-driven DW
motion is clarified. Namely, a field can only drive a domain-wall propagating
along the field direction through the mediation of a damping. Without the
damping, DW cannot propagate along the wire. Contrary to the common wisdom, DW
velocity is, in general, proportional to the energy dissipation rate, and one
needs to find a way to enhance the energy dissipation in order to increase the
propagation speed. The theory provides also a nature explanation of the
wire-width dependence of the DW velocity and velocity oscillation beyond Walker
breakdown field.
|
0803.1531v1
|
2008-03-11
|
Equation of state for strongly interacting matter: collective effects, Landau damping and predictions for LHC
|
The equation of state (EOS) is of utmost importance for the description of
the hydrodynamic phase of strongly interacting matter in relativistic heavy-ion
collisions. Lattice QCD can provide useful information on the EOS, mainly for
small net baryon densities. The QCD quasiparticle model provides a means to map
lattice QCD results into regions relevant for a variety of experiments. We
report here on effects of collectives modes and damping on the EOS. Some
predictions for forthcoming heavy-ion collisions at LHC/ALICE are presented and
perspectives for deriving an EOS for FAIR/CBM are discussed.
|
0803.1571v1
|
2008-04-04
|
Spin-charge coupling in a band ferromagnet: magnon-energy reduction, anomalous softening, and damping
|
The effects of correlation-induced coupling between spin and charge
fluctuations on spin-wave excitations in a band ferromagnet are investigated by
including self-energy and vertex corrections within a systematic
inverse-degeneracy expansion scheme which explicitly preserves the Goldstone
mode. Arising from the scattering of a magnon into intermediate spin-excitation
states (including both magnon and Stoner excitations) accompanied with charge
fluctuations in the majority spin band, this spin-charge coupling results not
only in a substantial reduction of magnon energies but also in anomalous
softening and significant magnon damping for zone-boundary modes lying within
the Stoner gap. Our results are in good qualitative agreement with recent
spin-wave excitation measurements in colossal magneto-resistive manganites and
ferromagnetic ultrathin films of transition metals.
|
0804.0680v1
|
2008-05-01
|
Chaotic Spin Dynamics of a Long Nanomagnet Driven by a Current
|
We study the spin dynamics of a long nanomagnet driven by an electrical
current. In the case of only DC current, the spin dynamics has a sophisticated
bifurcation diagram of attractors. One type of attractors is a weak chaos. On
the other hand, in the case of only AC current, the spin dynamics has a rather
simple bifurcation diagram of attractors. That is, for small Gilbert damping,
when the AC current is below a critical value, the attractor is a limit cycle;
above the critical value, the attractor is chaotic (turbulent). For normal
Gilbert damping, the attractor is always a limit cycle in the physically
interesting range of the AC current. We also developed a Melnikov integral
theory for a theoretical prediction on the occurrence of chaos. Our Melnikov
prediction seems performing quite well in the DC case. In the AC case, our
Melnikov prediction seems predicting transient chaos. The sustained chaotic
attractor seems to have extra support from parametric resonance leading to a
turbulent state.
|
0805.0147v1
|
2008-05-07
|
Noise Analysis and Noise-based Optimization for Resonant MEMS Structures
|
This paper presents a detailed noise analysis and a noise-based optimization
procedure for resonant MEMS structures. A design for high sensitivity of MEMS
structures needs to take into account the noise shaping induced by damping
phenomena at micro scale. The existing literature presents detailed models for
the damping at microscale, but usually neglects them in the noise analysis
process, assuming instead a white spectrum approximation for the
mechano-thermal noise. The present work extends the implications of the complex
gas-solid interaction into the field of noise analysis for mechanical sensors,
and provides a semi-automatic procedure for behavioral macromodel extraction
and sensor optimization with respect to signal-to-noise ratio.
|
0805.0927v1
|
2008-05-07
|
Scaling crossovers in activated escape of nonequilibrium systems: a resonantly driven oscillator
|
The rate of metastable decay in nonequilibrium systems is expected to display
scaling behavior: i.e., the logarithm of the decay rate should scale as a power
of the distance to a bifurcation point where the metastable state disappears.
Recently such behavior was observed and some of the earlier predicted exponents
were found in experiments on several types of systems described by a model of a
modulated oscillator. Here we establish the range where different scaling
behavior is displayed and show how the crossover between different types of
scaling occurs. The analysis is done for a nonlinear oscillator with two
coexisting stable states of forced vibrations. Our numerical calculations,
based on the the instanton method allow the mapping of the entire parameter
range of bi-stability. We find the regions where the scaling exponents are 1 or
3/2, depending on the damping. The exponent 3/2 is found to extend much further
from the bifurcation then were it would be expected to hold as a result of an
over-damped soft mode. We also uncover a new scaling behavior with exponent of
$\approx$ 1.3 which extends, numerically, beyond the close vicinity of the
bifurcation point.
|
0805.0972v2
|
2008-05-07
|
Quantum Noise, Effective Temperature, and Damping in a Superconducting Single-Electron Transistor
|
We have directly measured the quantum noise of a superconducting
single-electron transistor (S-SET) embedded in a microwave resonator consisting
of a superconducting LC tank circuit. Using an effective bath description, we
find that the S-SET provides damping of the resonator modes proportional to its
differential conductance and has an effective temperature that depends strongly
on the S-SET bias conditions. In the vicinity of a double Cooper pair
resonance, when both resonances are red detuned the S-SET effective temperature
can be well below both the ambient temperature and the energy scale of the bias
voltage. When blue detuned, the S-SET shows negative differential conductivity,
|
0805.1037v1
|
2008-05-08
|
Adaptive Affinity Propagation Clustering
|
Affinity propagation clustering (AP) has two limitations: it is hard to know
what value of parameter 'preference' can yield an optimal clustering solution,
and oscillations cannot be eliminated automatically if occur. The adaptive AP
method is proposed to overcome these limitations, including adaptive scanning
of preferences to search space of the number of clusters for finding the
optimal clustering solution, adaptive adjustment of damping factors to
eliminate oscillations, and adaptive escaping from oscillations when the
damping adjustment technique fails. Experimental results on simulated and real
data sets show that the adaptive AP is effective and can outperform AP in
quality of clustering results.
|
0805.1096v1
|
2008-06-06
|
On the stability of shocks with particle pressure
|
We perform a linear stability analysis for corrugations of a Newtonian shock,
with particle pressure included, for an arbitrary diffusion coefficient. We
study first the dispersion relation for homogeneous media, showing that,
besides the conventional pressure waves and entropy/vorticity disturbances, two
new perturbation modes exist, dominated by the particles' pressure and damped
by diffusion. We show that, due to particle diffusion into the upstream region,
the fluid will be perturbed also upstream: we treat these perturbation in the
short wavelength (WKBJ) regime. We then show how to construct a corrugational
mode for the shock itself, one, that is, where the shock executes free
oscillations (possibly damped or growing) and sheds perturbations away from
itself: this global mode requires the new modes. Then, using the perturbed
Rankine-Hugoniot conditions, we show that this leads to the determination of
the corrugational eigenfrequency. We solve numerically the equations for the
eigenfrequency in the WKBJ regime for the models of Amato and Blasi (2005),
showing that they are stable. We then discuss the differences between our
treatment and previous work.
|
0806.1113v1
|
2008-06-17
|
Damping of Fast Magnetohydrodynamic Oscillations in Quiescent Filament Threads
|
High-resolution observations provide evidence about the existence of
small-amplitude transverse oscillations in solar filament fine structures.
These oscillations are believed to represent fast magnetohydrodynamic (MHD)
waves and the disturbances are seen to be damped in short timescales of the
order of 1 to 4 periods. In this Letter we propose that, due to the highly
inhomogeneous nature of the filament plasma at the fine structure spatial
scale, the phenomenon of resonant absorption is likely to operate in the
temporal attenuation of fast MHD oscillations. By considering transverse
inhomogeneity in a straight flux tube model we find that, for density
inhomogeneities typical of filament threads, the decay times are of a few
oscillatory periods only.
|
0806.2728v1
|
2008-06-27
|
Global attractor and asymptotic smoothing effects for the weakly damped cubic Schrödinger equation in $L^2(\T)$
|
We prove that the weakly damped cubic Schr\"odinger flow in $L^2(\T)$
provides a dynamical system that possesses a global attractor. The proof relies
on a sharp study of the behavior of the associated flow-map with respect to the
weak $ L^2(\T) $-convergence inspired by a previous work of the author.
Combining the compactness in $ L^2(\T) $ of the attractor with the approach
developed by Goubet, we show that the attractor is actually a compact set of $
H^2(\T) $. This asymptotic smoothing effect is optimal in view of the
regularity of the steady states.
|
0806.4578v3
|
2008-06-30
|
Thermal depinning of fluxons in discrete Josephson rings
|
We study the thermal depinning of single fluxons in rings made of Josephson
junctions. Due to thermal fluctuations a fluxon can be excited from its energy
minima and move through the array, causing a voltage across each junction. We
find that for the initial depinning, the fluxon behaves as a single particle
and follows a Kramers-type escape law. However, under some conditions this
single particle description breaks down. At low values of the discreteness
parameter and low values of the damping, the depinning rate is larger than the
single particle result would suggest. In addition, for some values of the
parameters the fluxon can undergo low-voltage diffusion before switching to the
high-voltage whirling mode. This type of diffusion is similar to phase
diffusion in a single junction, but occurs without frequency-dependent damping.
We study the switching to the whirling state as well.
|
0806.4828v1
|
2008-07-03
|
Dependence of the decoherence of polarization states in phase-damping channels on the frequency spectrum envelope of photons
|
We consider the decoherence of photons suffering in phase-damping channels.
By exploring the evolutions of single-photon polarization states and two-photon
polarization-entangled states, we find that different frequency spectrum
envelopes of photons induce different decoherence processes. A white frequency
spectrum can lead the decoherence to an ideal Markovian process. Some color
frequency spectrums can induce asymptotical decoherence, while, some other
color frequency spectrums can make coherence vanish periodically with variable
revival amplitudes. These behaviors result from the non-Markovian effects on
the decoherence process, which may give rise to a revival of coherence after
complete decoherence.
|
0807.0536v3
|
2008-07-17
|
Planetary Migration in Resonance, the question of the Eccentricities : Les Houches contribution
|
The formation of resonant planets pairs in exoplanetary systems involves
planetary migration inside the protoplanetary disc : an inwards migrating outer
planet captures in Mean Motion Resonance an inner planet. During the migration
of the resonant pair of planets, the eccentricities are expected to rise
excessively, if no damping mechanism is applied on the inner planet. We express
the required damping action to match the observations, and we show that the
inner disk can play this role. This result applies for instance to the system
GJ 876 : we reproduce the observed orbital elements through a fully
hydrodynamical simulation of the evolution of the resonant planets.
|
0807.2828v2
|
2008-07-18
|
Heavily Damped Motion of One-Dimensional Bose Gases in an Optical Lattice
|
We study the dynamics of strongly correlated one-dimensional Bose gases in a
combined harmonic and optical lattice potential subjected to sudden
displacement of the confining potential. Using the time-evolving block
decimation method, we perform a first-principles quantum many-body simulation
of the experiment of Fertig {\it et al.} [Phys. Rev. Lett. {\bf 94}, 120403
(2005)] across different values of the lattice depth ranging from the
superfluid to the Mott insulator regimes. We find good quantitative agreement
with this experiment: the damping of the dipole oscillations is significant
even for shallow lattices, and the motion becomes overdamped with increasing
lattice depth as observed. We show that the transition to overdamping is
attributed to the decay of superfluid flow accelerated by quantum fluctuations,
which occurs well before the emergence of Mott insulator domains.
|
0807.2898v2
|
2008-07-21
|
Mutual friction in a cold color flavor locked superfluid and r-mode instabilities in compact stars
|
Dissipative processes acting in rotating neutron stars are essential in
preventing the growth of the r-mode instability. We estimate the damping time
of r-modes of an hypothetical compact quark star made up by color flavor locked
quark matter at a temperature $T \lesssim 0.01$ MeV. The dissipation that we
consider is due to the the mutual friction force between the normal and the
superfluid component arising from the elastic scattering of phonons with
quantized vortices. This process is the dominant one for temperatures $T
\lesssim 0.01$ MeV where the mean free path of phonons due to their
self-interactions is larger than the radius of the star and they can be
described as an ideal bosonic gas. We find that r-modes oscillations are
efficiently damped by this mechanism for pulsars rotating at frequencies of the
order of 1 Hz at most. Our analysis rules out the possibility that cold pulsars
rotating at higher frequencies are entirely made up by color flavor locked
quark matter.
|
0807.3264v2
|
2008-07-23
|
Dynamical Backaction of Microwave Fields on a Nanomechanical Oscillator
|
We measure the response and thermal motion of a high-Q nanomechanical
oscillator coupled to a superconducting microwave cavity in the
resolved-sideband regime where the oscillator's resonance frequency exceeds the
cavity's linewidth. The coupling between the microwave field and mechanical
motion is strong enough for radiation pressure to overwhelm the intrinsic
mechanical damping. This radiation-pressure damping cools the fundamental
mechanical mode by a factor of 5 below the thermal equilibrium temperature in a
dilution refrigerator to a phonon occupancy of 140 quanta.
|
0807.3585v3
|
2008-07-28
|
Shear Viscosity of the outer crust of Neutron stars: Ion Contribution
|
The shear viscosity of the crust might have a damping effect on the amplitude
of r-modes of rotating neutron stars. This damping has implications for the
emission of gravitational waves. We calculate the contribution to the shear
viscosity coming from the ions using both semi-analytical methods, that
consider binary collisions, and Molecular Dynamics simulations. We compare
these results with the contribution coming from electrons. We study how the
shear viscosity depends on density for conditions of interest in neutron star
envelopes and outer crusts. In the low density limit, we find good agreement
between results of our molecular dynamics simulations and classical
semi-analytic calculations.
|
0807.4353v2
|
2008-07-28
|
Unusual decoherence in qubit measurements with a Bose-Einstein condensate
|
We consider an electrostatic qubit located near a Bose-Einstein condensate
(BEC) of noninteracting bosons in a double-well potential, which is used for
qubit measurements. Tracing out the BEC variables we obtain a simple analytical
expression for the qubit's density-matrix. The qubit's evolution exhibits a
slow ($\propto1/\sqrt{t}$) damping of the qubit's coherence term, which however
turns to be a Gaussian one in the case of static qubit. This stays in contrast
to the exponential damping produced by most classical detectors. The
decoherence is, in general, incomplete and strongly depends on the initial
state of the qubit.
|
0807.4440v2
|
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