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1998-09-29
|
Numerical test of the damping time of layer-by-layer growth on stochastic models
|
We perform Monte Carlo simulations on stochastic models such as the
Wolf-Villain (WV) model and the Family model in a modified version to measure
mean separation $\ell$ between islands in submonolayer regime and damping time
$\tilde t$ of layer-by-layer growth oscillations on one dimension. The
stochastic models are modified, allowing diffusion within interval $r$ upon
deposited. It is found numerically that the mean separation and the damping
time depend on the diffusion interval $r$, leading to that the damping time is
related to the mean separation as ${\tilde t} \sim \ell^{4/3}$ for the WV model
and ${\tilde t} \sim \ell^2$ for the Family model. The numerical results are in
excellent agreement with recent theoretical predictions.
|
9809382v1
|
2000-01-10
|
Enhanced vortex damping by eddy currents in superconductor-semiconduc tor hybrids
|
An enhancement of vortex-motion damping in thin Pb/In superconducting films
is obtained through coupling to an adjacent two-dimensional electron gas formed
in a modulation-doped GaAs/AlGaAs heterostructure. This effect is observed by
monitoring the power dissipation at the superconductor in the vortex state
while increasing the density of the electron gas using a gate voltage.
Quantitative agreement is found with calculations based on a viscous model of
vortex damping which considers generation of eddy currents in the electron gas
by moving flux lines. In the regime of filamentary and channel vortex flow,
eddy-current damping leads to striking dissipation breakdown due to stopping of
entire vortex channels.
|
0001123v1
|
2000-10-11
|
The experimental observation of Beliaev damping in a Bose condensed gas
|
We report the first experimental observation of Beliaev damping of a
collective excitation in a Bose-condensed gas. Beliaev damping is not predicted
by the Gross-Pitaevskii equation and so this is one of the few experiments that
tests BEC theory beyond the mean field approximation. Measurements of the
amplitude of a high frequency scissors mode, show that the Beliaev process
transfers energy to a lower lying mode and then back and forth between these
modes. These characteristics are quite distinct from those of Landau damping,
which leads to a monotonic decrease in amplitude. To enhance the Beliaev
process we adjusted the geometry of the magnetic trapping potential to give a
frequency ratio of 2 to 1 between two of the scissors modes of the condensate.
The ratios of the trap oscillation frequencies $\omega_y / \omega_x$ and
$\omega_z / \omega_x$ were changed independently, so that we could investigate
the resonant coupling over a range of conditions.
|
0010157v1
|
2001-06-18
|
AC induced damping of a fluxon in long Josephson junction
|
We present a theoretical and experimental study of Josephson vortex (fluxon)
moving in the presence of spatially homogeneous dc and ac bias currents. By
mapping this problem to the problem of calculating the current-voltage
characteristic of a small Josephson junction, we derive the dependence of the
average fluxon velocity on the dc bias current. In particular we find that the
low frequency ac bias current results in an additional nonlinear damping of
fluxon motion. Such ac induced damping crucially depends on the intrinsic
damping parameter and increases drastically as this parameter is reduced. We
find a good agreement of the analysis with both the direct numerical
simulations and the experimentally measured current-voltage characteristics of
a long annular Josephson junction with one trapped fluxon.
|
0106337v1
|
2002-03-20
|
Microscopic nonequilibrium dynamics of an inhomogeneous Bose gas beyond the Born approximation
|
Using the prescription of the nonequilibrium statistical operator method, we
derive a non-Markovian generalization to the kinetic theory described by Walser
{\sl et al.} [Phys. Rev. A {\bf 59}, 3878 (1999)]. Quasi-particle damping and
effects arising from the finite duration of a collision are introduced to
include terms beyond the Born approximation. Such a self-consistent theory is
shown to conserve energy to second order in the interaction strength, even in
the Markov limit. This kinetic theory is applied to a simple model of a Bose
gas confined in a spherical trap to study the full real-time evolution towards
equilibrium. A modified form for the damping function, is seen to strongly
improve the energy conservation. Based on a linear response calculation, we
predict the damping rates and frequencies of the collective excitations. We
demonstrate the emergence of differing time scales for damping and
equilibration.
|
0203415v1
|
2003-05-12
|
Landau damping in trapped Bose-condensed gases
|
We study Landau damping in dilute Bose-Einstein condensed gases in both
spherical and prolate ellipsoidal harmonic traps. We solve the Bogoliubov
equations for the mode spectrum in both of these cases, and calculate the
damping by summing over transitions between excited quasiparticle states. The
results for the spherical case are compared to those obtained in the
Hartree-Fock approximation, where the excitations take on a single-particle
character, and excellent agreement between the two approaches is found. We have
also taken the semiclassical limit of the Hartree-Fock approximation and obtain
a novel expression for the Landau damping rate involving the time dependent
self-diffusion function of the thermal cloud. As a final approach, we study the
decay of a condensate mode by making use of dynamical simulations in which both
the condensate and thermal cloud are evolved explicitly as a function of time.
A detailed comparison of all these methods over a wide range of sample sizes
and trap geometries is presented.
|
0305251v1
|
2003-05-27
|
Damped finite-time-singularity driven by noise
|
We consider the combined influence of linear damping and noise on a dynamical
finite-time-singularity model for a single degree of freedom. We find that the
noise effectively resolves the finite-time-singularity and replaces it by a
first-passage-time or absorbing state distribution with a peak at the
singularity and a long time tail. The damping introduces a characteristic
cross-over time. In the early time regime the probability distribution and
first-passage-time distribution show a power law behavior with scaling exponent
depending on the ratio of the non linear coupling strength to the noise
strength. In the late time regime the behavior is controlled by the damping.
The study might be of relevance in the context of hydrodynamics on a nanometer
scale, in material physics, and in biophysics.
|
0305630v1
|
2003-06-05
|
On Surface Plasmon Damping in Metallic Nanoparticles
|
Two possible mechanisms of surface plasmon (SP) oscillations damping in
metallic nanoparticles (MNPs), not connected with electron-phonon interaction
are investigated theoretically: a) the radiation damping of SP, b) resonant
coupling of SP oscillations with electronic transitions in matrix. It is shown
that the radiation damping rate is proportional to the number of electrons in
MNP and therefore this channel of energy outflow from MNP becomes essential for
relatively large particles. The investigation of second mechanism shows that
the rate of SP oscillations energy leakage from MNP dos not depend on particle
size and is fully determined by the optical characteristics of the matrix. It
is demonstrated that for very small MNPs of 3-5 nm size, where the strong 3D
size quantization effect suppresses the electron-phonon interaction, the
resonance coupling in certain cases provides an effective energy outflow.
|
0306123v1
|
2003-09-11
|
Frequency and damping of hydrodynamic modes in a trapped Bose-condensed gas
|
Recently it was shown that the Landau-Khalatnikov two-fluid hydrodynamics
describes the collision-dominated region of a trapped Bose condensate
interacting with a thermal cloud. We use these equations to discuss the low
frequency hydrodynamic collective modes in a trapped Bose gas at finite
temperatures. We derive a variational expressions based on these equations for
both the frequency and damping of collective modes. A new feature is our use of
frequency-dependent transport coefficients, which produce a natural cutoff by
eliminating the collisionless low-density tail of the thermal cloud. Above the
superfluid transition, our expression for the damping in trapped inhomogeneous
gases is analogous to the result first obtained by Landau and Lifshitz for
uniform classical fluids. We also use the moment method to discuss the
crossover from the collisionless to the hydrodynamic region. Recent data for
the monopole-quadrupole mode in the hydrodynamic region of a trapped gas of
metastable $^4$He is discussed. We also present calculations for the damping of
the analogous $m=0$ monopole-quadrupole condensate mode in the superfluid
phase.
|
0309269v1
|
2003-11-13
|
Damping of Bogoliubov Excitations in Optical Lattices
|
Extending recent work to finite temperatures, we calculate the Landau damping
of a Bogoliubov excitation in an optical lattice, due to coupling to a thermal
cloud of such excitations. For simplicity, we consider a 1D Bose-Hubbard model
and restrict ourselves to the first energy band. For energy conservation to be
satisfied, the excitations in the collision processes must exhibit ``anomalous
dispersion'', analogous to phonons in superfluid $^4\rm{He}$. This leads to the
disappearance of all damping processes when $U n^{\rm c 0}\ge 6t$, where $U$ is
the on-site interaction, $t$ is the hopping matrix element and $n^{\rm c 0}(T)$
is the number of condensate atoms at a lattice site. This phenomenon also
occurs in 2D and 3D optical lattices. The disappearance of Beliaev damping
above a threshold wavevector is noted.
|
0311321v1
|
2004-09-22
|
Symmetry breaking in driven and strongly damped pendulum
|
We examine the conditions for appearance of symmetry breaking bifurcation in
damped and periodically driven pendulum in the case of strong damping. We show
that symmetry breaking, unlike other nonlinear phenomena, can exist at high
dissipation. We prove that symmetry breaking phases exist between phases of
symmetric normal and symmetric inverted oscillations. We find that symmetry
broken solutions occupy a sufficiently smaller region of pendulum's parameter
space in comparison to the statements made in earlier considerations [McDonald
and Plischke, Phys. Rev. B 27 (1983) 201]. Our research on symmetry breaking in
a strongly damped pendulum is relevant to an understanding of phenomena of
dynamic symmetry breaking and rectification in a pure ac driven semiconductor
superlattices.
|
0409572v1
|
2004-10-19
|
Strongly inhibited transport of a 1D Bose gas in a lattice
|
We report the observation of strongly damped dipole oscillations of a quantum
degenerate 1D atomic Bose gas in a combined harmonic and optical lattice
potential. Damping is significant for very shallow axial lattices (0.25 photon
recoil energies), and increases dramatically with increasing lattice depth,
such that the gas becomes nearly immobile for times an order of magnitude
longer than the single-particle tunneling time. Surprisingly, we see no
broadening of the atomic quasimomentum distribution after damped motion. Recent
theoretical work suggests that quantum fluctuations can strongly damp dipole
oscillations of 1D atomic Bose gas, providing a possible explanation for our
observations.
|
0410491v3
|
2005-08-10
|
Collective oscillations of a quasi one dimensional Bose condensate under damping
|
Influence of the damping on collective oscillations of a one-dimensional
trapped Bose gas in the mean field regime has been studied. Using the
phenomenological damping approach developed by L.P. Pitaevskii, modified
variational equations for the parameters of the condensate wave function is
derived. Analytical expressions for the condensate parameters in equilibrium
state have been obtained. Bistability in nonlinear oscillations of the
condensate under periodic variations of the trap potential is predicted. The
predictions of the modified variational approach are confirmed by full
numerical simulations of the 1D GP equation with the damping.
|
0508262v1
|
2005-08-11
|
Influence of layer defects on the damping in ferroelectric thin films
|
A Green's function technique for a modified Ising model in a transverse field
is applied, which allows to calculate the damping of the elementary excitations
and the phase transition temperature of ferroelectric thin films with
structural defects. Based on an analytical expression for the damping function,
we analyze its dependence on temperature, film thickness and interaction
strength numerically. The results demonstrate that defect layers in
ferroelectric thin films, layers with impurities or vacancies as well as layers
with dislocations are able to induce a strong increase of the damping due to
different exchange interactions within the defect layers. The results are in
good agreement with experimental data for thin ferroelectric films with
different thickness.
|
0508287v1
|
2007-02-23
|
Parametric Resonance of Optically Trapped Aerosols
|
The Brownian dynamics of an optically trapped water droplet are investigated
across the transition from over to under-damped oscillations. The spectrum of
position fluctuations evolves from a Lorentzian shape typical of over-damped
systems (beads in liquid solvents), to a damped harmonic oscillator spectrum
showing a resonance peak. In this later under-damped regime, we excite
parametric resonance by periodically modulating the trapping power at twice the
resonant frequency. The power spectra of position fluctuations are in excellent
agreement with the obtained analytical solutions of a parametrically modulated
Langevin equation.
|
0702557v1
|
2007-03-22
|
Spin-Torque Ferromagnetic Resonance Measurements of Damping in Nanomagnets
|
We measure the magnetic damping parameter a in thin film CoFeB and permalloy
(Py) nanomagnets at room temperature using ferromagnetic resonance driven by
microwave frequency spin-transfer torque. We obtain $\alpha_{CoFeB} = 0.014 \pm
0.003$ and $\alpha_{Py}=0.010 \pm 0.002$, values comparable to measurements for
extended thin films, but significantly less than the effective damping
determined previously for similar nanomagnets by fits to time-domain studies of
large-angle magnetic excitations and magnetic reversal. The greater damping
found for the large amplitude nanomagnet dynamics is attributed to the
nonlinear excitation of non-uniform magnetic modes.
|
0703577v1
|
2007-02-28
|
Numerical Model For Vibration Damping Resulting From the First Order Phase Transformations
|
A numerical model is constructed for modelling macroscale damping effects
induced by the first order martensite phase transformations in a shape memory
alloy rod. The model is constructed on the basis of the modified
Landau-Ginzburg theory that couples nonlinear mechanical and thermal fields.
The free energy function for the model is constructed as a double well function
at low temperature, such that the external energy can be absorbed during the
phase transformation and converted into thermal form. The Chebyshev spectral
methods are employed together with backward differentiation for the numerical
analysis of the problem. Computational experiments performed for different
vibration energies demonstrate the importance of taking into account damping
effects induced by phase transformations.
|
0702172v1
|
2005-04-22
|
Constraint damping in the Z4 formulation and harmonic gauge
|
We show that by adding suitable lower-order terms to the Z4 formulation of
the Einstein equations, all constraint violations except constant modes are
damped. This makes the Z4 formulation a particularly simple example of a
lambda-system as suggested by Brodbeck et al. We also show that the Einstein
equations in harmonic coordinates can be obtained from the Z4 formulation by a
change of variables that leaves the implied constraint evolution system
unchanged. Therefore the same method can be used to damp all constraints in the
Einstein equations in harmonic gauge.
|
0504114v2
|
2005-07-05
|
Universality of Highly Damped Quasinormal Modes for Single Horizon Black Holes
|
It has been suggested that the highly damped quasinormal modes of black holes
provide information about the microscopic quantum gravitational states
underlying black hole entropy. This interpretation requires the form of the
highly damped quasinormal mode frequency to be universally of the form:
$\hbar\omega_R = \ln(l)kT_{BH}$, where $l$ is an integer, and $T_{BH}$ is the
black hole temperature. We summarize the results of an analysis of the highly
damped quasinormal modes for a large class of single horizon, asymptotically
flat black holes.
|
0507019v1
|
2005-09-07
|
Massive vector field perturbations in the Schwarzschild background: stability and quasinormal spectrum
|
We consider the perturbations of the massive vector field around
Schwarzschild black hole, (generally, with non-vanishing $\Lambda$ - term). The
monopole massive vector perturbation equations can be reduced to a single
wave-like equation. We have proved the stability against these perturbations
and investigated the quasinormal spectrum. The quasinormal behaviour for
Schwarzschild black hole is quite unexpected: the fundamental mode and all
higher overtones shows totally different dependence on the mass of the field
$m$: as $m$ is increasing, the damping rate of the fundamental mode is
decreasing, what results in appearing of the infinitely long living modes,
while, on contrary, damping rate of all higher overtones are increasing, and
their real oscillation frequencies gradually go to tiny values. Thereby, for
all higher overtones, almost non-oscillatory, damping modes can exist. In the
limit of asymptotically high damping, $Re \omega$ goes to $ln3/(8 \pi M)$,
while imaginary part shows equidistant behaviour with spacing $Im \omega_{n+1}-
Im \omega_{n}=i/4M$. In addition, we have found quasinormal spectrum of massive
vector field for Schwarzschild-anti-de Sitter black hole.
|
0509026v3
|
2006-11-27
|
The Mystery of the Asymptotic Quasinormal Modes of Gauss-Bonnet Black Holes
|
We analyze the quasinormal modes of $D$-dimensional Schwarzschild black holes
with the Gauss-Bonnet correction in the large damping limit and show that
standard analytic techniques cannot be applied in a straightforward manner to
the case of infinite damping. However, by using a combination of analytic and
numeric techniques we are able to calculate the quasinormal mode frequencies in
a range where the damping is large but finite. We show that for this damping
region the famous $\ln(3)$ appears in the real part of the quasinormal mode
frequency. In our calculations, the Gauss-Bonnet coupling, $\alpha$, is taken
to be much smaller than the parameter $\mu$, which is related to the black hole
mass.
|
0611139v1
|
1995-09-22
|
Damping rate of neutrinos in the singlet Majoron model
|
The damping rate and free path of neutrinos in the singlet Majoron model have
been calculated including both finite temperature and symmetry breaking
effects. The behaviour of right- and left-handed fermions are found inherently
different. While the damping rates of the left-handed leptons are essentially
model independent, e.g. directly applicable to the Standard Model, for the
right-handed particles the rates are crucially sensitive to parameters of the
scalar sector. In general, the damping rates are fairly large. The possibility
of the right-handed neutrinos to penetrate deep into the broken phase in the
electroweak phase transition still remains, however, for some parts of
parameter space.
|
9509359v1
|
1996-09-25
|
The hot baryon violation rate is $O(α_W^5 T^4)$
|
The rate per unit volume for anomalous electroweak baryon number violation at
high temperatures, in the symmetric phase, has been estimated in the literature
to be $O(\alpha_W^4 T^4)$ based on simple scaling arguments. We argue that
damping effects in the plasma suppress the rate by an extra power of $\alpha_W$
to give $O(\alpha_W^5 T^4)$. We show how to understand this effect in a variety
of ways ranging from an effective description of the long-distance modes
responsible for baryon number violation, to a microscopic picture of the
short-distance modes responsible for damping. In particular, we resolve an old
controversy as to whether damping effects are relevant. Finally, we argue that
similar damping effects should occur in numerical simulations of the rate in
classical thermal field theory on a spatial lattice, and we point out a
potential problem with simulations in the literature that have not found such
an effect.
|
9609481v1
|
2001-03-29
|
Phase transition dynamics in the hot Abelian Higgs model
|
We present a detailed numerical study of the equilibrium and non-equilibrium
dynamics of the phase transition in the finite-temperature Abelian Higgs model.
Our simulations use classical equations of motion both with and without
hard-thermal-loop corrections, which take into account the leading quantum
effects. From the equilibrium real-time correlators, we determine the Landau
damping rate, the plasmon frequency and the plasmon damping rate. We also find
that, close to the phase transition, the static magnetic field correlator shows
power-law magnetic screening at long distances. The information about the
damping rates allows us to derive a quantitative prediction for the number
density of topological defects formed in a phase transition. We test this
prediction in a non-equilibrium simulation and show that the relevant time
scale for defect formation is given by the Landau damping rate.
|
0103311v1
|
1996-04-12
|
Onset of Rotational Damping in Superdeformed Nuclei
|
We discuss damping of the collective rotational motion in $A\sim 150$
superdeformed nuclei by means of a shell model combining the cranked Nilsson
mean-filed and the surface-delta two-body residual force. It is shown that,
because of the shell structure associated with the superdeformed mean-field,
onset energy of the rotational damping becomes $E_x \sim 2-3 $ MeV above yrast
line, which is much higher than in normal deformed nuclei. The mechanism of the
shell structure effect is investigated through detailed analysis of level
densities in superdeformed nuclei. It is predicted the onset of damping varies
in different supedeformed nuclei along with variation in the single-particle
structure at the Fermi surface.
|
9604015v1
|
2001-09-12
|
The damping width of giant dipole resonances of cold and hot nuclei: a macroscopic model
|
A phenomenological macroscopic model of the Giant Dipole Resonance (GDR)
damping width of cold- and hot-nuclei with ground-state spherical and
near-spherical shapes is developed. The model is based on a generalized Fermi
Liquid model which takes into account the nuclear surface dynamics. The
temperature dependence of the GDR damping width is accounted for in terms of
surface- and volume-components. Parameter-free expressions for the damping
width and the effective deformation are obtained. The model is validated with
GDR measurements of the following nuclides, $^{39,40}$K, $^{42}$Ca, $^{45}$Sc,
$^{59,63}$Cu, $^{109-120}$Sn,$^{147}$Eu, $^{194}$Hg, and $^{208}$Pb, and is
compared with the predictions of other models.
|
0109034v1
|
2006-01-31
|
Small damping approach in Fermi-liquid theory
|
The validity of small damping approximation (SDA) for the quasi-classical
description of the averaged properties of nuclei at high temperatures is
studied within the framework of collisional kinetic theory. The isoscalar
collective quadrupole vibrations in hot nuclei are considered. We show that the
extension of the SDA, by accounting for the damping of the distribution
function $\delta f$ in the collision integral reduces the rate of variation
with temperature of the Fermi surface distortion effects. The damping of the
$\delta f$ in the collision integral increases significantly the collisional
width of the giant quadrupole resonance (GQR) for small enough values of the
relaxation time. The temperature dependence of the eigenenergy of the GQR
becomes much more weaker than in the corresponding SDA case.
|
0601094v1
|
2001-11-05
|
Damping of transversal plasma-electron oscillations and waves in low-collision electron-ion plasmas
|
Previously developed method for finding asymptotic solutions of Vlasov
equations using two-dimensional (in coordinate x and time t) Laplace transform
is here applied to consider transversal oscillations and waves in low-collision
quasi-neutral (n_i \simeq n_e) Maxwellian electron-ion plasmas. We obtain two
branches of electron waves: the ubiquitous one of high-frequency and
high-velocity oscillations and the unusual low-velocity one. Taking into
account Coulomb collisions in the limit m_e << m_i, \bar{v_i} << \bar{v_e}, and
T_e m_e << T_i m_i results in expressions for transversal plasma-electron
oscillation/wave decrements with a damping of the low-velocity electron branch
\sim n_i^{1/3}/\bar{v}_e^{4/3}, where n_i is the ion density and \bar{v}_e is
the mean electron velocity. It ought to rehabilitate Vlasov principal value
prescription for relevant integrals, but to supplement it with representation
of an asymptotical solution as a sum of exponents (not a single one).
"Non-damping" kinematical waves in low-collision plasma transform in the
damping ones at reasonably chosen iteration process.
|
0111014v3
|
2002-03-13
|
Enhanced radiative ion cooling
|
Enhanced radiative cooling of ion beams in storage rings and Robinson's
damping criterion are discussed.
|
0203036v1
|
2003-05-24
|
Impact of the Wiggler Coherent Synchrotron Radiation Impedance on the Beam Instability
|
Coherent Synchrotron Radiation (CSR) can play an important role by not only
increasing the energy spread and emittance of a beam, but also leading to a
potential instability. Previous studies of the CSR induced longitudinal
instability were carried out for the CSR impedance due to dipole magnets.
However, many storage rings include long wigglers where a large fraction of the
synchrotron radiation is emitted. This includes high-luminosity factories such
as DAPHNE, PEP-II, KEK-B, and CESR-C as well as the damping rings of future
linear colliders. In this paper, the instability due to the CSR impedance from
a wiggler is studied assuming a large wiggler parameter $K$. The primary
consideration is a low frequency microwave-like instability, which arises near
the pipe cut-off frequency. Detailed results are presented on the growth rate
and threshold for the damping rings of several linear collider designs.
Finally, the optimization of the relative fraction of damping due to the
wiggler systems is discussed for the damping rings.
|
0305107v1
|
2004-09-13
|
Landau damping in thin films irradiated by a strong laser field
|
The rate of linear collisionless damping (Landau damping) in a classical
electron gas confined to a heated ionized thin film is calculated. The general
expression for the imaginary part of the dielectric tensor in terms of the
parameters of the single-particle self-consistent electron potential is
obtained. For the case of a deep rectangular well, it is explicitly calculated
as a function of the electron temperature in the two limiting cases of specular
and diffuse reflection of the electrons from the boundary of the
self-consistent potential. For realistic experimental parameters, the
contribution of Landau damping to the heating of the electron subsystem is
estimated. It is shown that for films with a thickness below about 100 nm and
for moderate laser intensities it may be comparable with or even dominate over
electron-ion collisions and inner ionization.
|
0409062v1
|
1996-06-24
|
Quantum damping of position due to energy measurements
|
Quantum theory for measurements of energy is introduced and its consequences
for the average position of monitored dynamical systems are analyzed. It turns
out that energy measurements lead to a localization of the expectation values
of other observables. This is manifested, in the case of position, as a damping
of the motion without classical analogue. Quantum damping of position for an
atom bouncing on a reflecting surface in presence of a homogeneous
gravitational field is dealt in detail and the connection with an experiment
already performed in the classical regime is studied. We show that quantum
damping is testable provided that the same measurement strength obtained in the
experimental verification of the quantum Zeno effect in atomic spectroscopy [W.
M. Itano et al., Phys. Rev. A {\bf 41}, 2295 (1990)] is made available.
|
9606024v1
|
2006-12-17
|
Influence of a classical homogeneous gravitational field on dissipative dynamics of the Jaynes-Cummings model with phase damping
|
In this paper, we study the dissipative dynamics of the Jaynes-Cummings model
with phase damping in the presence of a classical homogeneous gravitational
field. The model consists of a moving two-level atom simultaneously exposed to
the gravitational field and a single-mode traveling radiation field in the
presence of the phase damping. We present a quantum treatment of the internal
and external dynamics of the atom based on an alternative su(2) dynamical
algebraic structure. By making use of the super-operator technique, we obtain
the solution of the master equation for the density operator of the quantum
system, under the Markovian approximation. Assuming that initially the
radiation field is prepared in a Glauber coherent state and the two-level atom
is in the excited state, we investigate the influence of gravity on the
temporal evolution of collapses and revivals of the atomic population
inversion, atomic dipole squeezing, atomic momentum diffusion, photon counting
statistics and quadrature squeezing of the radiation field in the presence of
phase damping.
|
0612143v2
|
2007-04-25
|
Theory of weakly damped free-surface flows: a new formulation based on potential flow solutions
|
Several theories for weakly damped free-surface flows have been formulated.
In this paper we use the linear approximation to the Navier-Stokes equations to
derive a new set of equations for potential flow which include dissipation due
to viscosity. A viscous correction is added not only to the irrotational
pressure (Bernoulli's equation), but also to the kinematic boundary condition.
The nonlinear Schr\"odinger (NLS) equation that one can derive from the new set
of equations to describe the modulations of weakly nonlinear, weakly damped
deep-water gravity waves turns out to be the classical damped version of the
NLS equation that has been used by many authors without rigorous justification.
|
0704.3352v1
|
2007-05-25
|
The Secular Evolution of a Close Ring-Satellite System: The Excitation of Spiral Bending Waves at a Nearby Gap Edge
|
The secular perturbations exerted by an inclined satellite orbiting in a gap
in a broad planetary ring tends to excite the inclinations of the nearby ring
particles, and the ring's self-gravity can allow that disturbance to propagate
away in the form of a spiral bending wave. The amplitude of this spiral bending
wave is determined, as well as the wavelength, which shrinks as the waves
propagate outwards due to the effects of the central planet's oblateness. The
excitation of these bending waves also damps the satellite's inclination I.
This secular I damping is also compared to the inclination excitation that is
due to the satellite's many other vertical resonances in the ring, and the
condition for inclination damping is determined. The secular I damping is
likely responsible for confining the orbits of Saturn's two known gap-embedded
moons, Pan and Daphnis, to the ring plane.
|
0705.3797v1
|
2007-06-15
|
Anticorrelation between temperature and fluctuations in moderately damped Josephson junctions
|
We study the influence of dissipation on the switching current statistics of
moderately damped Josephson junctions. Different types of both low- and high-
$T_c$ junctions with controlled damping are studied. The damping parameter of
the junctions is tuned in a wide range by changing temperature, magnetic field,
gate voltage, introducing a ferromagnetic layer or in-situ capacitive shunting.
A paradoxical collapse of switching current fluctuations occurs with increasing
$T$ in all studied junctions. The phenomenon critically depends on dissipation
in the junction and is explained by interplay of two counteracting consequences
of thermal fluctuations, which on the one hand assist in premature switching
into the resistive state and on the other hand help in retrapping back to the
superconducting state. This is one of the rare examples of anticorrelation
between temperature and fluctuation amplitude of a physically measurable
quantity.
|
0706.2248v1
|
2007-08-06
|
Collisionless damping of electron waves in non-Maxwellian plasma
|
In this paper we have criticized the so-called Landau damping theory. We have
analyzed solutions of the standard dispersion equations for longitudinal
(electric) and transversal (electromagnetic and electron) waves in
half-infinite slab of the uniform collisionless plasmas with non-Maxwellian and
Maxwellian-like electron energy distribution functions. One considered the most
typical cases of both the delta-function type distribution function (the plasma
stream with monochromatic electrons) and distribution functions, different from
Maxwellian ones as with a surplus as well as with a shortage in the Maxwellian
distribution function tail. It is shown that there are present for the
considered cases both collisionless damping and also non-damping electron waves
even in the case of non-Maxwellian distribution function.
|
0708.0748v5
|
2007-08-14
|
Preliminary Results on Vibration Damping Properties of Nanoscale-Reinforced Composite Materials
|
The focus in this paper is an analysis of existing state of the arts directed
toward the development of the next generation of vibration damping systems. The
research work concentrates on an investigation related to
nanoparticles/fibres/tubes-reinforced materials and coatings dynamic
characterization and modeling of the fundamental phenomena that control
relationships between structure and damping/mechanical properties of the
materials. We simulated composite materials using finite element and mesh free
methods, using a hollow shell representation of the individual nanotube/fiber.
Results of the research work will provide a platform for the development of
nanoparticle-reinforced damping materials that are light-weight, vibration and
shock resistant. The outcome of the research work is expected to have
wide-ranging technical benefits with direct relevance to industry in areas of
transportation (aerospace, automotive, rail), electronics and civil
infrastructure development.
|
0708.1821v1
|
2007-08-18
|
Non-Riemannian geometrical asymmetrical damping stresses on the Lagrange instability of shear flows
|
It is shown that the physical interpretation of Elie Cartan three-dimensional
space torsion as couple asymmetric stress, has the effect of damping,
previously Riemannian unstable Couette planar shear flow, leading to stability
of the flow in the Lagrangean sense. Actually, since the flow speed is
inversely proportional to torsion, it has the effect of causing a damping in
the planar flow atenuating the instability effect. In this sense we may say
that Cartan torsion induces shear viscous asymmetric stresses in the fluid,
which are able to damp the instability of the flow. The stability of the flow
is computed from the sectional curvature in non-Riemannian three-dimensional
manifold. Marginal stability is asssumed by making the sectional non-Riemannian
curvature zero, which allows us to determine the speeds of flows able to induce
this stability. The ideas discussed here show that torsion plays the
geometrical role of magnetic field in hydromagnetic instability of Couette
flows recently investigated by Bonnano and Urpin (PRE, (2007,in press) can be
extended and applied to plastic flows with microstructure defects. Recently
Riemannian asymmetric stresses in magnetohydrodynamics (MHD) have been
considered by Billig (2004).
|
0708.2467v1
|
2007-12-07
|
State transition of a non-Ohmic damping system in a corrugated plane
|
Anomalous transport of a particle subjected to non-Ohmic damping of the power
$\delta$ in a tilted periodic potential is investigated via Monte Carlo
simulation of generalized Langevin equation. It is found that the system
exhibits two relative motion modes: the locking state and the running state.
Under the surrounding of sub-Ohmic damping ($0<\delta<1$), the particle should
transfer into a running state from a locking state only when local minima of
the potential vanish; hence the particle occurs a synchronization oscillation
in its mean displacement and mean square displacement (MSD). In particular, the
two motion modes are allowed to coexist in the case of super-Ohmic damping
($1<\delta<2$) for moderate driving forces, namely, where exists double centers
in the velocity distribution. This induces the particle having faster
diffusion, i.e., its MSD reads $<\Delta x^2(t)> = 2D^{(\delta)}_{eff}
t^{\delta_{eff}}$. Our result shows that the effective power index
$\delta_{\textmd{eff}}$ can be enhanced and is a nonmonotonic function of the
temperature and the driving force. The mixture effect of the two motion modes
also leads to a breakdown of hysteresis loop of the mobility.
|
0712.1070v1
|
2007-12-25
|
The damped Pinney equation and its applications to dissipative quantum mechanics
|
The work considers the damped Pinney equation, defined as the model arising
when a linear in velocity damping term is included in the Pinney equation. In
the general case the resulting equation does not admit Lie point symmetries or
is reducible to a simpler form by any obvious coordinate transformation. In
this context the method of Kuzmak-Luke is applied to derive a perturbation
solution, for weak damping and slow time-dependence of the frequency function.
The perturbative and numerical solutions are shown to be in good agreement. The
results are applied to examine the time-evolution of Gaussian shaped
wave-functions in the Kostin formulation of dissipative quantum mechanics.
|
0712.4083v3
|
2008-01-01
|
Non-linear equations for electron waves in Maxwellian low-collision ion-electron plasmas
|
The before described general principles and methodology of calculating
electron wave propagation in homogeneous isotropic half-infinity slab of
Maxwellian plasma with indefinite but in principal value sense taken integrals
in characteristic equations, and the use of 2D Laplace transform method are
applied to an evaluation of collision damping decrements of plane electron
longitudinal and transverse waves. Damping decrement tends to infinity when the
wave frequency tends to electron Langmuir frequency from above values. We
considered recurrent relations for amplitudes of the overtones which form in
their sum the all solution of the plasma wave non-linear equations including
collision damping and quadratic (non-linear) terms. Collisionless damping at
frequencies more the Langmuir one is possible only in non-Maxwellian plasmas.
|
0801.0286v2
|
2008-02-22
|
Radiative Damping and Functional Differential Equations
|
We propose a general technique to solve the classical many-body problem with
radiative damping. We modify the short-distance structure of Maxwell
electrodynamics. This allows us to avoid runaway solutions as if we had a
covariant model of extended particles. The resulting equations of motion are
functional differential equations (FDEs) rather than ordinary differential
equations. Using recently developed numerical techniques for stiff FDEs, we
solve these equations for the one-body central force problem with radiative
damping with a view to benchmark our new approach. Our results indicate that
locally the magnitude of radiation damping may be well approximated by the
standard third-order expression but the global properties of our solutions are
dramatically different. We comment on the two body problem and applications to
quantum field theory and quantum mechanics.
|
0802.3390v2
|
2008-04-24
|
Analytic approximate seismology of transversely oscillating coronal loops
|
We present an analytic approximate seismic inversion scheme for damped
transverse coronal loop oscillations based on the thin tube and thin boundary
approximation for computing the period and the damping time. Asymptotic
expressions for the period and damping rate are used to illustrate the process
of seismological inversion in a simple and easy to follow manner. The inversion
procedure is formulated in terms of two simple functions, which are given by
simple closed expressions. The analytic seismic inversion shows that an
infinite amount of 1-dimensional equilibrium models can reproduce the observed
periods and damping times. It predicts a specific range of allowable values for
the Alfven travel time and lower bounds for the density contrast and the
inhomogeneity length scale. When the results of the present analytic seismic
inversion are compared with those of a previous numerical inversion, excellent
agreement is found up to the point that the analytic seismic inversion emerges
as a tool for validating results of numerical inversions. Actually it helped us
to identify and correct inaccuracies in a previous numerical investigation.
|
0804.3877v1
|
2008-10-21
|
On Wigner functions and a damped star product in dissipative phase-space quantum mechanics
|
Dito and Turrubiates recently introduced an interesting model of the
dissipative quantum mechanics of a damped harmonic oscillator in phase space.
Its key ingredient is a non-Hermitian deformation of the Moyal star product
with the damping constant as deformation parameter. We compare the
Dito-Turrubiates scheme with phase-space quantum mechanics (or deformation
quantization) based on other star products, and extend it to incorporate Wigner
functions. The deformed (or damped) star product is related to a complex
Hamiltonian, and so necessitates a modified equation of motion involving
complex conjugation. We find that with this change the Wigner function
satisfies the classical equation of motion. This seems appropriate since
non-dissipative systems with quadratic Hamiltonians share this property.
|
0810.3893v1
|
2009-01-08
|
Grand-mother clocks and quiet lasers
|
Galileo noted in the 16th century that the period of oscillation of a
pendulum is almost independent of the amplitude. However, such a pendulum is
damped by air friction. The latter may be viewed as resulting from air
molecules getting in contact with the pendulum. It follows that air friction,
not only damps the oscillation, but also introduces randomness. In the
so-called ``grand-mother'' clock, discovered by Huygens in the 18th century,
damping is compensated for, on the average, by an escapement mechanism driven
by a falling weight. The purpose of this paper is to show that such a clock is,
in its idealized form, a quiet oscillator. By ``quiet'' we mean that in spite
of the randomness introduced by damping, the dissipated power (viewed as the
oscillator output) does not fluctuate slowly. Comparison is made with quiet
laser oscillators discovered theoretically in 1984. Because the input power
does not fluctuate in both the mechanical oscillator and the quiet laser
oscillator, the output power does not fluctuate at small Fourier frequencies,
irrespectively of the detailed mechanisms involved.
|
0901.0983v1
|
2009-01-15
|
Interaction of fast charged projectiles with two-dimensional electron gas: Interaction and disorder effects
|
The results of a theoretical investigation on the stopping power of ions
moving in a disordered two-dimensional degenerate electron gas are presented.
The stopping power for an ion is calculated employing linear response theory
using the dielectric function approach. The disorder, which leads to a damping
of plasmons and quasiparticles in the electron gas, is taken into account
through a relaxation time approximation in the linear response function. The
stopping power for an ion is calculated in both the low- and high-velocity
limits. In order to highlight the effects of damping we present a comparison of
our analytical and numerical results, in the case of point-like ions, obtained
for a non-zero damping with those for a vanishing damping. It is shown that the
equipartition sum rule first formulated by Lindhard and Winther for
three-dimensional degenerate electron gas does not necessarily hold in
two-dimensions. We have generalized this rule introducing an effective
dielectric function. In addition some new results for two-dimensional
interacting electron gas have been obtained. In this case the
exchange-correlation interactions of electrons are considered via
local-field-corrected dielectric function.
|
0901.2249v1
|
2009-02-01
|
Non-Markovian Analysis of the Phase Damped Jaynes-Cummings Model in the Presence of a Classical Homogeneous Gravitational Field
|
In this paper, the non-Markovian dissipative dynamics of the phase damped
Jaynes-Cummings model in the presence of a classical homogeneous gravitational
field will be analyzed. The model consists of a moving two-level atom
simultaneously exposed to the gravitational field and a single-mode traveling
radiation field in the presence of a non-Markovian phase damping mechanism.
First, the non-Markovian master equation for the reduced density operator of
the system in terms of a Hamiltonian describing the atom-field interaction in
the presence of a homogeneous gravitational field will be presented. Then, the
super-operator technique will be generalized and an exact solution of the
non-Markovian master equation will be obtained. Assuming that initially the
radiation field is prepared in a Glauber coherent state and the two-level atom
is in the excited state, the non-Markovian effects on the temporal evolution of
collapses and revivals of the atomic population inversion and photon counting
statistics of the radiation field in the presence of both the phase damping and
a homogeneous gravitational field will be investigated.
|
0902.0114v1
|
2009-05-04
|
Models of Damped Oscillators in Quantum Mechanics
|
We consider several models of the damped oscillators in nonrelativistic
quantum mechanics in a framework of a general approach to the dynamics of the
time-dependent Schroedinger equation with variable quadratic Hamiltonians. The
Green functions are explicitly found in terms of elementary functions and the
corresponding gauge transformations are discussed. The factorization technique
is applied to the case of a shifted harmonic oscillator. The time-evolution of
the expectation values of the energy related operators is determined for two
models of the quantum damped oscillators under consideration. The classical
equations of motion for the damped oscillations are derived for the
corresponding expectation values of the position operator.
|
0905.0507v6
|
2009-05-28
|
Resonant Nonlinear Damping of Quantized Spin Waves in Ferromagnetic Nanowires
|
We use spin torque ferromagnetic resonance to measure the spectral properties
of dipole-exchange spin waves in permalloy nanowires. Our measurements reveal
that geometric confinement has a profound effect on the damping of spin waves
in the nanowire geometry. The damping parameter of the lowest-energy quantized
spin wave mode depends on applied magnetic field in a resonant way and exhibits
a maximum at a field that increases with decreasing nanowire width. This
enhancement of damping originates from a nonlinear resonant three-magnon
confluence process allowed at a particular bias field value determined by
quantization of the spin wave spectrum in the nanowire geometry.
|
0905.4699v2
|
2009-06-01
|
Effect of Decoherence in Ekert-Protocol
|
We have examined the effect of the decoherence in the Ekert91 quantum
cryptographic protocol. In order to explore this issue we have introduced two
major decoherences, the depolarizing channel and the generalized amplitude
damping, between the singlet source and one of the legitimate users. It is
shown that the depolarizing channel disentangles the quantum channel more
easily than the generalized amplitude damping. This fact indicates that the
Ekert protocol is more robust to the generalized amplitude damping. We also
have computed the Bell inequality to check the robustness or weakness of the
Ekert91 protocol. Computation of the Bell inequality also confirms the
robustness of the Ekert91 protocol to the generalized amplitude damping
compared to the depolarizing channel.
|
0906.0233v1
|
2009-08-05
|
Surface plasmon lifetime in metal nanoshells
|
The lifetime of localized surface plasmon plays an important role in many
aspects of plasmonics and its applications. In small metal nanostructures, the
dominant mechanism restricting plasmon lifetime is size-dependent Landau
damping. We performed quantum-mechanical calculations of Landau damping for the
bright surface plasmon mode in a metal nanoshell. In contrast to the
conventional model based on the electron surface scattering, we found that the
damping rate decreases as the nanoshell thickness is reduced. The origin of
this behavior is traced to the spatial distribution of plasmon local field
inside the metal shell. We also found that, due to interference of electron
scattering amplitudes from nanoshell's two metal surfaces, the damping rate
exhibits pronounced quantum beats with changing shell thickness.
|
0908.0647v3
|
2009-08-12
|
Coarse Grained Simulations of a Small Peptide: Effects of Finite Damping and Hydrodynamic Interactions
|
In the coarse grained Brownian Dynamics simulation method the many solvent
molecules are replaced by random thermal kicks and an effective friction acting
on the particles of interest. For Brownian Dynamics the friction has to be so
strong that the particles' velocities are damped much faster than the duration
of an integration timestep. Here we show that this conceptual limit can be
dropped with an analytic integration of the equations of damped motion. In the
resulting Langevin integration scheme our recently proposed approximate form of
the hydrodynamic interactions between the particles can be incorparated
conveniently, leading to a fast multi-particle propagation scheme, which
captures more of the short-time and short-range solvent effects than standard
BD. Comparing the dynamics of a bead-spring model of a short peptide, we
recommend to run simulations of small biological molecules with the Langevin
type finite damping and to include the hydrodynamic interactions.
|
0908.1685v1
|
2009-09-01
|
Quantum Stackelberg duopoly in the presence of correlated noise
|
We study the influence of entanglement and correlated noise using correlated
amplitude damping, depolarizing and phase damping channels on the quantum
Stackelberg duopoly. Our investigations show that under the action of amplitude
damping channel a critical point exists for unentangled initial state as well,
at which firms get equal payoffs. The game becomes a follower advantage game
when the channel is highly decohered. Two critical points corresponding to two
values of the entanglement angle are found in the presence of correlated noise.
Within the range of these limits of entanglement angle, the game is follower
advantage game. In case of depolarizing channel, the payoffs of the two firms
are strongly influenced by the memory parameter. The presence of quantum memory
ensures the existence of Nash equilibrium for the entire range of decoherence
and entanglement parameters for both the channels. A local maximum in the
payoffs is observed which vanishes as the channel correlation increases.
Moreover, under the influence of depolarizing channel, the game is always a
leader advantage game. Furthermore, it is seen that phase damping channel does
not effect the outcome of the game.
|
0909.0063v2
|
2009-09-04
|
Second sound dipole mode in a partially Bose-Einstein condensed gas
|
We study the second sound dipole mode in a partially Bose-Einstein condensed
gas. This mode is excited by spatially separating and releasing the
center-of-mass of the Bose-Einstein condensate (BEC) with respect to the
thermal cloud, after which the equilibration is observed. The oscillation
frequency and the damping rate of this mode is studied for different harmonic
confinements and temperatures. The measured damping rates close to the
collisionless regime are found to be in good agreement with Landau damping. For
increasing hydrodynamicity of the cloud we observe an increase of the damping.
|
0909.0886v1
|
2009-12-30
|
Finite dimensional attractor for a composite system of wave/plate equations with localised damping
|
The long-term behaviour of solutions to a model for acoustic-structure
interactions is addressed; the system is comprised of coupled semilinear wave
(3D) and plate equations with nonlinear damping and critical sources. The
questions of interest are: existence of a global attractor for the dynamics
generated by this composite system, as well as dimensionality and regularity of
the attractor. A distinct and challenging feature of the problem is the
geometrically restricted dissipation on the wave component of the system. It is
shown that the existence of a global attractor of finite fractal dimension --
established in a previous work by Bucci, Chueshov and Lasiecka (Comm. Pure
Appl. Anal., 2007) only in the presence of full interior acoustic damping --
holds even in the case of localised dissipation. This nontrivial generalization
is inspired by and consistent with the recent advances in the study of wave
equations with nonlinear localised damping.
|
0912.5464v2
|
2010-02-12
|
Features of ion acoustic waves in collisional plasmas
|
The effects of friction on the ion acoustic (IA) wave in fully and partially
ionized plasmas are studied. In a quasi-neutral electron-ion plasma the
friction between the two species cancels out exactly and the wave propagates
without any damping. If the Poisson equation is used instead of the
quasi-neutrality, however, the IA wave is damped and the damping is dispersive.
In a partially ionized plasma, the collisions with the neutrals modify the IA
wave beyond recognition. For a low density of neutrals the mode is damped. Upon
increasing the neutral density, the mode becomes first evanescent and then
reappears for a still larger number of neutrals. A similar behavior is obtained
by varying the mode wave-length. The explanation for this behavior is given. In
an inhomogeneous plasma placed in an external magnetic field, and for
magnetized electrons and un-magnetized ions, the IA mode propagates in any
direction and in this case the collisions make it growing on the account of the
energy stored in the density gradient. The growth rate is angle dependent. A
comparison with the collision-less kinetic density gradient driven IA
instability is also given.
|
1002.2502v1
|
2010-02-18
|
Damping mechanisms for oscillations in solar prominences
|
Small amplitude oscillations are a commonly observed feature in
prominences/filaments. These oscillations appear to be of local nature, are
associated to the fine structure of prominence plasmas, and simultaneous flows
and counterflows are also present. The existing observational evidence reveals
that small amplitude oscillations, after excited, are damped in short spatial
and temporal scales by some as yet not well determined physical mechanism(s).
Commonly, these oscillations have been interpreted in terms of linear
magnetohydrodynamic (MHD) waves, and this paper reviews the theoretical damping
mechanisms that have been recently put forward in order to explain the observed
attenuation scales. These mechanisms include thermal effects, through
non-adiabatic processes, mass flows, resonant damping in non-uniform media, and
partial ionization effects. The relevance of each mechanism is assessed by
comparing the spatial and time scales produced by each of them with those
obtained from observations. Also, the application of the latest theoretical
results to perform prominence seismology is discussed, aiming to determine
physical parameters in prominence plasmas that are difficult to measure by
direct means.
|
1002.3489v2
|
2010-03-07
|
Theory of plasmon decay in dense plasmas and warm dense matter
|
The decay of the Langmuir waves in dense plasmas is not accurately predicted
by the prevalent Landau damping theory. A dielectric function theory is
introduced, predicting much higher damping than the Landau damping theory. This
strong damping is in better agreement with the experimentally observed data in
metals. It is shown that the strong plasmon decay leads to the existence of a
parameter regime where the backward Raman scattering is unstable while the
forward Raman scattering is stable. This regime may be used to create intense
x-ray pulses, by means of the the backward Raman compression. The optimal pulse
duration and intensity is estimated.
|
1003.1523v2
|
2010-03-16
|
Justification of the symmetric damping model of the dynamical Casimir effect in a cavity with a semiconductor mirror
|
A "microscopic" justification of the "symmetric damping" model of a quantum
oscillator with time-dependent frequency and time-dependent damping is given.
This model is used to predict results of experiments on simulating the
dynamical Casimir effect in a cavity with a photo-excited semiconductor mirror.
It is shown that the most general bilinear time-dependent coupling of a
selected oscillator (field mode) to a bath of harmonic oscillators results in
two equal friction coefficients for the both quadratures, provided all the
coupling coefficients are proportional to a single arbitrary function of time
whose duration is much shorter than the periods of all oscillators. The choice
of coupling in the rotating wave approximation form leads to the "mimimum
noise" model of the quantum damped oscillator, introduced earlier in a pure
phenomenological way.
|
1003.3061v2
|
2010-04-12
|
Dissipative Transport of a Bose-Einstein Condensate
|
We investigate the effects of impurities, either correlated disorder or a
single Gaussian defect, on the collective dipole motion of a Bose-Einstein
condensate of $^7$Li in an optical trap. We find that this motion is damped at
a rate dependent on the impurity strength, condensate center-of-mass velocity,
and interatomic interactions. Damping in the Thomas-Fermi regime depends
universally on the disordered potential strength scaled to the condensate
chemical potential and the condensate velocity scaled to the peak speed of
sound. The damping rate is comparatively small in the weakly interacting
regime, and the damping in this case is accompanied by strong condensate
fragmentation. \textit{In situ} and time-of-flight images of the atomic cloud
provide evidence that this fragmentation is driven by dark soliton formation.
|
1004.1891v2
|
2010-05-23
|
Constraining phases of quark matter with studies of r-mode damping in neutron stars
|
The r-mode instability in rotating compact stars is used to constrain the
phase of matter at high density. The color-flavor-locked phase with kaon
condensation (CFL-K0) and without (CFL) is considered in the temperature range
10^8K < T <10^{11} K. While the bulk viscosity in either phase is only
effective at damping the r-mode at temperatures T > 10^{11} K, the shear
viscosity in the CFL-K0 phase is the only effective damping agent all the way
down to temperatures T > 10^8 K characteristic of cooling neutron stars.
However, it cannot keep the star from becoming unstable to gravitational wave
emission for rotation frequencies f ~ 56-11 Hz at T ~ 10^8-10^9 K. Stars
composed almost entirely of CFL or CFL-K0 matter are ruled out by observation
of rapidly rotating neutron stars, indicating that dissipation at the
quark-hadron interface or nuclear crust interface must play a key role in
damping the instability.
|
1005.4161v1
|
2010-07-07
|
Observational evidence of resonantly damped propagating kink waves in the solar corona
|
In this Letter we establish clear evidence for the resonant absorption
damping mechanism by analyzing observational data from the novel Coronal
Multi-Channel Polarimeter (CoMP). This instrument has established that in the
solar corona there are ubiquitous propagating low amplitude ($\approx$1 km
s$^{-1}$) Alfv\'{e}nic waves with a wide range of frequencies. Realistically
interpreting these waves as the kink mode from magnetohydrodynamic (MHD) wave
theory, they should exhibit a frequency dependent damping length due to
resonant absorption, governed by the TGV relation showing that transversal
plasma inhomogeneity in coronal magnetic flux tubes causes them to act as
natural low-pass filters. It is found that observed frequency dependence on
damping length (up to about 8 mHz) can be explained by the kink wave
interpretation and furthermore, the spatially averaged equilibrium parameter
describing the length scale of transverse plasma density inhomogeneity over a
system of coronal loops is consistent with the range of values estimated from
TRACE observations of standing kink modes.
|
1007.1080v1
|
2010-07-12
|
Variable damping and coherence in a high-density magnon gas
|
We report on the fast relaxation behavior of a high-density magnon gas
created by a parametric amplification process. The magnon gas is probed using
the technique of spin-wave packet recovery by parallel parametric pumping.
Experimental results show a damping behavior which is in disagreement with both
the standard model of exponential decay and with earlier observations of
non-linear damping. In particular, the inherent magnon damping is found to
depend upon the presence of the parametric pumping field. A phenomenological
model which accounts for the dephasing of the earlier injected magnons is in
good agreement with the experimental data.
|
1007.1895v3
|
2010-07-21
|
A low-power circuit for piezoelectric vibration control by synchronized switching on voltage sources
|
In the paper, a vibration damping system powered by harvested energy with
implementation of the so-called SSDV (synchronized switch damping on voltage
source) technique is designed and investigated. In the semi-passive approach,
the piezoelectric element is intermittently switched from open-circuit to
specific impedance synchronously with the structural vibration. Due to this
switching procedure, a phase difference appears between the strain induced by
vibration and the resulting voltage, thus creating energy dissipation. By
supplying the energy collected from the piezoelectric materials to the
switching circuit, a new low-power device using the SSDV technique is proposed.
Compared with the original self-powered SSDI (synchronized switch damping on
inductor), such a device can significantly improve its performance of vibration
control. Its effectiveness in the single-mode resonant damping of a composite
beam is validated by the experimental results.
|
1007.3596v1
|
2010-10-24
|
Long-time dynamics in plate models with strong nonlinear damping
|
We study long-time dynamics of a class of abstract second order in time
evolution equations in a Hilbert space with the damping term depending both on
displacement and velocity. This damping represents the nonlinear strong
dissipation phenomenon perturbed with relatively compact terms. Our main result
states the existence of a compact finite dimensional attractor. We study
properties of this attractor. We also establish the existence of a fractal
exponential attractor and give the conditions that guarantee the existence of a
finite number of determining functionals. In the case when the set of
equilibria is finite and hyperbolic we show that every trajectory is attracted
by some equilibrium with exponential rate. Our arguments involve a recently
developed method based on the "compensated" compactness and quasi-stability
estimates. As an application we consider the nonlinear Kirchhoff, Karman and
Berger plate models with different types of boundary conditions and strong
damping terms. Our results can be also applied to the nonlinear wave equations.
|
1010.4991v1
|
2010-11-05
|
Effects of Turbulence, Eccentricity Damping, and Migration Rate on the Capture of Planets into Mean Motion Resonance
|
Pairs of migrating extrasolar planets often lock into mean motion resonance
as they drift inward. This paper studies the convergent migration of giant
planets (driven by a circumstellar disk) and determines the probability that
they are captured into mean motion resonance. The probability that such planets
enter resonance depends on the type of resonance, the migration rate, the
eccentricity damping rate, and the amplitude of the turbulent fluctuations.
This problem is studied both through direct integrations of the full 3-body
problem, and via semi-analytic model equations. In general, the probability of
resonance decreases with increasing migration rate, and with increasing levels
of turbulence, but increases with eccentricity damping. Previous work has shown
that the distributions of orbital elements (eccentricity and semimajor axis)
for observed extrasolar planets can be reproduced by migration models with
multiple planets. However, these results depend on resonance locking, and this
study shows that entry into -- and maintenance of -- mean motion resonance
depends sensitively on migration rate, eccentricity damping, and turbulence.
|
1011.1486v1
|
2010-11-21
|
Quasi-normal frequencies: Semi-analytic results for highly damped modes
|
Black hole highly-damped quasi-normal frequencies (QNFs) are very often of
the form (offset)} + i n (gap). We have investigated the genericity of this
phenomenon for the Schwarzschild--deSitter (SdS) black hole by considering a
model potential that is piecewise Eckart (piecewise Poeschl-Teller), and
developing an analytic ``quantization condition'' for the highly-damped
quasi-normal frequencies. We find that the (offset) + i n(gap) behaviour is
common but not universal, with the controlling feature being whether or not the
ratio of the surface gravities is a rational number. We furthermore observed
that the relation between rational ratios of surface gravities and periodicity
of QNFs is very generic, and also occurs within different analytic approaches
applied to various types of black hole spacetimes. These observations are of
direct relevance to any physical situation where highly-damped quasi-normal
modes are important.
|
1011.4634v1
|
2011-03-08
|
Application of Explicit Symplectic Algorithms to Integration of Damping Oscillators
|
In this paper an approach is outlined. With this approach some explicit
algorithms can be applied to solve the initial value problem of $n-$dimensional
damped oscillators. This approach is based upon following structure: for any
non-conservative classical mechanical system and arbitrary initial conditions,
there exists a conservative system; both systems share one and only one common
phase curve; and, the value of the Hamiltonian of the conservative system is,
up to an additive constant, equal to the total energy of the non-conservative
system on the aforementioned phase curve, the constant depending on the initial
conditions. A key way applying explicit symplectic algorithms to damping
oscillators is that by the Newton-Laplace principle the nonconservative force
can be reasonably assumed to be equal to a function of a component of
generalized coordinates $q_i$ along a phase curve, such that the damping force
can be represented as a function analogous to an elastic restoring force
numerically in advance. Two numerical examples are given to demonstrate the
good characteristics of the algorithms.
|
1103.1455v1
|
2011-03-09
|
Nonlinear damping in mechanical resonators based on graphene and carbon nanotubes
|
Carbon nanotubes and graphene allow fabricating outstanding nanomechanical
resonators. They hold promise for various scientific and technological
applications, including sensing of mass, force, and charge, as well as the
study of quantum phenomena at the mesoscopic scale. Here, we have discovered
that the dynamics of nanotube and graphene resonators is in fact highly exotic.
We propose an unprecedented scenario where mechanical dissipation is entirely
determined by nonlinear damping. As a striking consequence, the quality factor
Q strongly depends on the amplitude of the motion. This scenario is radically
different from that of other resonators, whose dissipation is dominated by a
linear damping term. We believe that the difference stems from the reduced
dimensionality of carbon nanotubes and graphene. Besides, we exploit the
nonlinear nature of the damping to improve the figure of merit of
nanotube/graphene resonators.
|
1103.1788v1
|
2011-05-03
|
Entanglement in a Bipartite Gaussian State
|
To examine the loss of entanglement in a two-particle Gaussian system, we
couple it to an environment and use the Non-Rotating Wave master equation to
study the system's dynamics. We also present a derivation of this equation. We
consider two different types of evolution. Under free evolution we find that
entanglement is lost quickly between the particles. When a harmonic potential
is added between the particles, two very different behaviours can be observed,
namely in the over and under-damped cases respectively, where the strength of
the damping is determined by how large the coupling to the bath is with respect
to the frequency of the potential. In the over-damped case, we find that the
entanglement vanishes at even shorter times than it does in the free evolution.
In the (very) under-damped case, we observe that the entanglement does not
vanish. Instead it oscillates towards a stable value.
|
1105.0564v1
|
2011-06-15
|
Plasma damping effects on the radiative energy loss of relativistic particles
|
The energy loss of a relativistic charge undergoing multiple scatterings
while traversing an infinite, polarizable and absorptive plasma is
investigated. Polarization and damping mechanisms in the medium are
phenomenologically modelled by a complex index of refraction. Apart from the
known Ter-Mikaelian effect related to the dielectric polarization of matter, we
find an additional, substantial reduction of the energy loss due to damping of
radiation. The observed effect is more prominent for larger damping and/or
larger energy of the charge. A conceivable analog of this phenomenon in QCD
could influence the study of jet quenching phenomena in ultra-relativistic
heavy-ion collisions at RHIC and LHC.
|
1106.2856v3
|
2011-09-12
|
Reduction of compressibility and parallel transfer by Landau damping in turbulent magnetized plasmas
|
Three-dimensional numerical simulations of decaying turbulence in a
magnetized plasma are performed using a so-called FLR-Landau fluid model which
incorporates linear Landau damping and finite Larmor radius (FLR) corrections.
It is shown that compared to simulations of compressible Hall-MHD, linear
Landau damping is responsible for significant damping of magnetosonic waves,
which is consistent with the linear kinetic theory. Compressibility of the
fluid and parallel energy cascade along the ambient magnetic field are also
significantly inhibited when the beta parameter is not too small. In contrast
with Hall-MHD, the FLR-Landau fluid model can therefore correctly describe
turbulence in collisionless plasmas such as the solar wind, providing an
interpretation for its nearly incompressible behavior.
|
1109.2636v1
|
2011-09-24
|
Existence of weak solutions for the generalized Navier-Stokes equations with damping
|
In this work we consider the generalized Navier-Stoke equations with the
presence of a damping term in the momentum equation. % The problem studied here
derives from the set of equations which govern the isothermal flow of
incompressible, homogeneous and non-Newtonian fluids. % For the generalized
Navier-Stokes problem with damping, we prove the existence of weak solutions by
using regularization techniques, the theory of monotone operators and
compactness arguments together with the local decomposition of the pressure and
the Lipschitz-truncation method. The existence result proved here holds for any
$q>\frac{2N}{N+2}$ and any $\sigma>1$, where $q$ is the exponent of the
diffusion term and $\sigma$ is the exponent which characterizes the damping
term.
|
1109.5217v1
|
2011-11-14
|
New Electrodynamics of Pulsars
|
We have recently proposed that Force-Free Electrodynamics (FFE) does not
apply to pulsars -- pulsars should be described by the high-conductivity limit
of Strong-Field Electrodynamics (SFE), which predicts an order-unity damping of
the Poynting flux, while FFE postulates zero damping. The strong damping result
has not been accepted by several pulsar experts, who claim that FFE basically
works and the Poynting flux damping can be arbitrarily small.
Here we consider a thought experiment -- cylindrical periodic pulsar. We show
that FFE is incapable of describing this object, while SFE predictions are
physically plausible. The intrinsic breakdown of FFE should mean that the FFE
description of the singular current layer (the only region of magnetosphere
where FFE and the high-conductivity SFE differ) is incorrect. Then the
high-conductivity SFE should be the right theory for real pulsars too, and the
pure-FFE description of pulsars should be discarded.
|
1111.3377v1
|
2011-12-20
|
Dynamics of DNA breathing in the Peyrard-Bishop model with damping and external force
|
The impact of damping effect and external forces to the DNA breathing is
investigated within the Peyrard-Bishop model. In in the continuum limit, the
dynamics of the breathing of DNA is described by the forced-damped nonlinear
Schrodinger equation and studied by means of variational method. The analytical
solutions are obtained for special cases. It is shown that the breather
propagation is decelerated in the presence of damping factor without the
external force, while the envelope velocity and the amplitude increase
significantly with the presence of external force. It is particularly found
that the higher harmonic terms are enhanced when the periodic force is applied.
It is finally argued that the external force accelerates the DNA breathing.
|
1112.4715v1
|
2012-01-31
|
Parametric amplification and self-oscillation in a nanotube mechanical resonator
|
A hallmark of mechanical resonators made from a single nanotube is that the
resonance frequency can be widely tuned. Here, we take advantage of this
property to realize parametric amplification and self-oscillation. The gain of
the parametric amplification can be as high as 18.2 dB and tends to saturate at
high parametric pumping due to nonlinear damping. These measurements allow us
to determine the coefficient of the linear damping force. The corresponding
damping rate is lower than the one obtained from the lineshape of the resonance
(without pumping), supporting the recently reported scenario that describes
damping in nanotube resonators by a nonlinear force. The possibility to combine
nanotube resonant mechanics and parametric amplification holds promise for
future ultra-low force sensing experiments.
|
1201.6557v1
|
2012-02-22
|
Radiation Damping in the Photoionization of Fe^{14+}
|
A theoretical investigation of photoabsorption and photoionization of
Fe^{14+} extending beyond an earlier frame transformation R-matrix
implementation is performed using a fully-correlated, Breit-Pauli R-matrix
formulation including both fine-structure splitting of strongly-bound
resonances and radiation damping. The radiation damping of $2p\rightarrow nd$
resonances gives rise to a resonant photoionization cross section that is
significantly lower than the total photoabsorption cross section. Furthermore,
the radiation-damped photoionization cross section is found to be in good
agreement with recent experimental results once a global shift in energy of
$\approx -3.5$ eV is applied. These findings have important implications.
Firstly, the presently available synchrotron experimental data are applicable
only to photoionization processes and not to photoabsorption; the latter is
required in opacity calculations. Secondly, our computed cross section, for
which the L-shell ionization threshold is aligned with the NIST value, shows a
series of $2p \rightarrow nd$ Rydberg resonances that are uniformly 3-4 eV
higher in energy than the corresponding experimental profiles, indicating that
the L-shell threshold energy values currently recommended by NIST are likely in
error.
|
1202.4800v1
|
2012-02-29
|
Present status of development of damping ring extraction kicker system for CLIC
|
The CLIC damping rings will produce ultra-low emittance beam, with high bunch
charge, necessary for the luminosity performance of the collider. To limit the
beam emittance blow-up due to oscillations, the pulse power modulators for the
damping ring kickers must provide extremely flat, high-voltage pulses:
specifications call for a 160 ns duration and a flattop of 12.5 kV, 250 A, with
a combined ripple and droop of not more than \pm0.02 %. The stripline design is
also extremely challenging: the field for the damping ring kicker system must
be homogenous to within \pm0.01 % over a 1 mm radius, and low beam coupling
impedance is required. The solid-state modulator, the inductive adder, is a
very promising approach to meeting the demanding specifications for the field
pulse ripple and droop. This paper describes the initial design of the
inductive adder and the striplines of the kicker system.
|
1202.6527v1
|
2012-04-03
|
Inhomogeneity of the phase space of the damped harmonic oscillator under Levy noise
|
The damped harmonic oscillator under symmetric L\'{e}vy white noise shows
inhomogeneous phase space, which is in contrast to the homogeneous one of the
same oscillator under the Gaussian white noise, as shown in a recent paper [I.
M. Sokolov, W. Ebeling, and B. Dybiec, Phys. Rev. E \textbf{83}, 041118
(2011)]. The inhomogeneity of the phase space shows certain correlation between
the coordinate and the velocity of the damped oscillator under symmetric
L\'{e}vy white noise. In the present work we further explore the physical
origin of these distinguished features and find that it is due to the
combination of the damped effect and heavy tail of the noise. We demonstrate
directly this in the reduced coordinate $\tilde{x}$ versus velocity $\tilde{v}$
plots and identify the physics of the anti-association of the coordinate and
velocity.
|
1204.0593v2
|
2012-06-20
|
Metadamping: An emergent phenomenon in dissipative metamaterials
|
We theoretically demonstrate the concept of metadamping in dissipative
metamaterials. We consider an infinite mass-spring chain with repeated local
resonators and a statically equivalent periodic chain whose wave propagation
characteristics are based on Bragg scattering. For each system we introduce
identical viscous damping (dashpot) elements and compare the damping ratio
associated with all Bloch modes. We find that the locally resonant metamaterial
exhibits higher dissipation overall which indicates a damping emergence
phenomena due to the presence of local resonance. We conclude our investigation
by quantifying the degree of emergent damping as a function of the long-wave
speed of sound in the medium or the static stiffness.
|
1206.4577v2
|
2012-07-12
|
Spin Damping in an RF Atomic Magnetometer
|
Under negative feedback, the quality factor Q of a radio-frequency
magnetometer can be decreased by more than two orders of magnitude, so that any
initial perturbation of the polarized spin system can be rapidly damped,
preparing the magnetometer for detection of the desired signal. We find that
noise is also suppressed under such spin-damping, with a characteristic
spectral response corresponding to the type of noise; therefore magnetic,
photon-shot, and spin-projection noise can be measured distinctly. While the
suppression of resonant photon-shot noise implies the closed-loop production of
polarization-squeezed light, the suppression of resonant spin-projection noise
does not imply spin-squeezing, rather simply the broadening of the noise
spectrum with Q. Furthermore, the application of spin-damping during
phase-sensitive detection suppresses both signal and noise in such a way as to
increase the sensitivity bandwidth. We demonstrate a three-fold increase in the
magnetometer's bandwidth while maintaining 0.3 fT/\surdHz sensitivity.
|
1207.2842v1
|
2012-07-12
|
Damping of phase fluctuations in superfluid Bose gases
|
Using Popov's hydrodynamic approach we derive an effective Euclidean action
for the long-wavelength phase fluctuations of superfluid Bose gases in D
dimensions. We then use this action to calculate the damping of phase
fluctuations at zero temperature as a function of D. For D >1 and wavevectors |
k | << 2 mc (where m is the mass of the bosons and c is the sound velocity) we
find that the damping in units of the phonon energy E_k = c | k | is to leading
order gamma_k / E_k = A_D (k_0^D / 2 pi rho) (| k | / k_0)^{2 D -2}, where rho
is the boson density and k_0 =2 mc is the inverse healing length. For D -> 1
the numerical coefficient A_D vanishes and the damping is proportional to an
additional power of |k | /k_0; a self-consistent calculation yields in this
case gamma_k / E_k = 1.32 (k_0 / 2 pi rho)^{1/2} |k | / k_0. In one dimension,
we also calculate the entire spectral function of phase fluctuations.
|
1207.3002v3
|
2012-08-27
|
The properties of non-thermal X-ray filaments in young supernova remnants
|
Context. Young supernova remnants (SNRs) exhibit narrow filaments of
non-thermal X-ray emission whose widths can be limited either by electron
energy losses or damping of the magnetic field. Aims. We want to investigate
whether or not different models of these filaments can be observationally
tested. Methods. Using observational parameters of four historical remnants, we
calculate the filament profiles and compare the spectra of the filaments with
those of the total non-thermal emission. For that purpose, we solve an
one-dimensional stationary transport equation for the isotropic differential
number density of the electrons. Results. We find that the difference between
the spectra of filament and total non-thermal emission above 1 keV is more
pronounced in the damping model than in the energy-loss model. Conclusions. A
considerable damping of the magnetic field can result in an observable
difference between the spectra of filament and total non-thermal emission, thus
potentially permitting an observational discrimination between the energy-loss
model and the damping model of the X-ray filaments.
|
1208.5322v1
|
2012-09-10
|
Mid-infrared plasmons in scaled graphene nanostructures
|
Plasmonics takes advantage of the collective response of electrons to
electromagnetic waves, enabling dramatic scaling of optical devices beyond the
diffraction limit. Here, we demonstrate the mid-infrared (4 to 15 microns)
plasmons in deeply scaled graphene nanostructures down to 50 nm, more than 100
times smaller than the on-resonance light wavelength in free space. We reveal,
for the first time, the crucial damping channels of graphene plasmons via its
intrinsic optical phonons and scattering from the edges. A plasmon lifetime of
20 femto-seconds and smaller is observed, when damping through the emission of
an optical phonon is allowed. Furthermore, the surface polar phonons in SiO2
substrate underneath the graphene nanostructures lead to a significantly
modified plasmon dispersion and damping, in contrast to a non-polar
diamond-like-carbon (DLC) substrate. Much reduced damping is realized when the
plasmon resonance frequencies are close to the polar phonon frequencies. Our
study paves the way for applications of graphene in plasmonic waveguides,
modulators and detectors in an unprecedentedly broad wavelength range from
sub-terahertz to mid-infrared.
|
1209.1984v1
|
2012-11-05
|
No asymptotically highly damped quasi-normal modes without horizons?
|
We explore the question of what happens with the asymptotically highly damped
quasi-normal modes ($\ell$ fixed, $|\omega_{I}|\to\infty$) when the underlying
spacetime has no event horizons. We consider the characteristic oscillations of
a scalar field in a large class of asymptotically flat spherically symmetric
static spacetimes without (absolute) horizons, such that the class accommodates
the cases that are known to be of some sort of physical interest. The question
of the asymptotic quasi-normal modes in such spacetimes is relevant to
elucidate the connection between the behavior of the asymptotic quasi-normal
modes and the quantum properties of event horizons, as put forward in some
recent important conjectures. We prove for a large class of asymptotically flat
spacetimes without horizons that the scalar field asymptotically highly damped
modes do not exist. This provides in our view additional evidence that there is
indeed a close link between the asymptotically highly damped modes and the
existence of spacetime horizons (and their properties).
|
1211.1046v2
|
2012-11-21
|
Chaotic saddles in nonlinear modulational interactions in a plasma
|
A nonlinear model of modulational processes in the subsonic regime involving
a linearly unstable wave and two linearly damped waves with different damping
rates in a plasma is studied numerically. We compute the maximum Lyapunov
exponent as a function of the damping rates in a two-parameter space, and
identify shrimp-shaped self-similar structures in the parameter space. By
varying the damping rate of the low-frequency wave, we construct bifurcation
diagrams and focus on a saddle-node bifurcation and an interior crisis
associated with a periodic window. We detect chaotic saddles and their stable
and unstable manifolds, and demonstrate how the connection between two chaotic
saddles via coupling unstable periodic orbits can result in a crisis-induced
intermittency. The relevance of this work for the understanding of modulational
processes observed in plasmas and fluids is discussed.
|
1211.5070v1
|
2012-12-18
|
Thermal activation at moderate-to-high and high damping: finite barrier effects and force spectroscopy
|
We study the thermal escape problem in the moderate-to-high and high damping
regime of a system with a parabolic barrier. We present a formula that matches
our numerical results accounting for finite barrier effects, and compare it
with previous works. We also show results for the full damping range. We
quantitatively study some aspects on the relation between mean first passage
time and the definition of a escape rate. To finish we apply our results and
considerations in the framework of force spectroscopy problems. We study the
differences on the predictions using the different theories and discuss the
role of $\gamma \dot{F}$ as the relevant parameter at high damping.
|
1212.4290v2
|
2013-01-18
|
Interfacial roughening in non-ideal fluids: Dynamic scaling in the weak- and strong-damping regime
|
Interfacial roughening denotes the nonequilibrium process by which an
initially flat interface reaches its equilibrium state, characterized by the
presence of thermally excited capillary waves. Roughening of fluid interfaces
has been first analyzed by Flekkoy and Rothman [Phys. Rev. Lett. 75, 260
(1995)], where the dynamic scaling exponents in the weakly damped case in two
dimensions were found to agree with the Kardar-Parisi-Zhang universality class.
We extend this work by taking into account also the strong-damping regime and
perform extensive fluctuating hydrodynamics simulations in two dimensions using
the Lattice Boltzmann method. We show that the dynamic scaling behavior is
different in the weakly and strongly damped case.
|
1301.4468v2
|
2013-02-02
|
Achieving the Quantum Ground State of a Mechanical Oscillator using a Bose-Einstein Condensate with Back-Action and Cold Damping feedback schemes
|
We present a detailed study to show the possibility of approaching the
quantum ground-state of a hybrid optomechanical quantum device formed by a
Bose-Einstein condensate (BEC) confined inside a high-finesse optical cavity
with an oscillatory end mirror. Cooling is achieved using two experimentally
realizable schemes: back-action cooling and cold damping quantum feedback
cooling. In both the schemes, we found that increasing the two body atom-atom
interaction brings the mechanical oscillator to its quantum ground state. It
has been observed that back-action cooling is more effective in the good cavity
limit while the cold damping cooling scheme is more relevant in the bad cavity
limit. It is also shown that in the cold damping scheme, the device is more
efficient in the presence of BEC than in the absence of BEC.
|
1302.0339v1
|
2013-02-27
|
Resonantly damped oscillations of elliptically shaped stratified emerging coronal loops
|
The effects of both elliptical shape and stage of emergence of the coronal
loop on the resonant absorption of standing kink oscillations are studied. To
do so, a typical coronal loop is modeled as a zero-beta longitudinally
stratified cylindrical magnetic flux tube. We developed the connection formulae
for the resonant absorption of standing transversal oscillations of a coronal
loop with an elliptical shape, at various stages of its emergence. Using the
connection formulae, the dispersion relation is derived and solved numerically
to obtain the frequencies and damping rates of the fundamental and
first-overtone kink modes. Our numerical results show that both the elliptical
shape and stage of emergence of the loop alter the frequencies and damping
rates of the tube as well as the ratio of frequencies of the fundamental and
its first-overtone modes. However, the ratio of the oscillation frequency to
the damping rate is not affected by the tube shape and stage of its emergence
and also is independent of the density stratification parameter.
|
1302.6884v1
|
2013-02-28
|
Damping of Quantum Vibrations Revealed in Deep Sub-barrier Fusion
|
We demonstrate that when two colliding nuclei approach each other, their
quantum vibrations are damped near the touching point. We show that this
damping is responsible for the fusion hindrance phenomena measured in the deep
sub-barrier fusion reactions. To show those, we for the first time apply the
random-phase-approximation (RPA) method to the two-body $^{16}$O + $^{16}$O and
$^{40}$Ca + $^{40}$Ca systems. We calculate the octupole transition strengths
for the two nuclei adiabatically approaching each other. The calculated
transition strength drastically decreases near the touching point, strongly
suggesting the vanishing of the quantum couplings between the relative motion
and the vibrational intrinsic degrees of freedom of each nucleus. Based on this
picture, we also calculate the fusion cross section for the $^{40}$Ca +
$^{40}$Ca system using the coupled-channel method with the damping factor
simulating the vanishing of the couplings. The calculated results reproduce
well the experimental data, indicating that the smooth transition from the
sudden to adiabatic processes indeed occurs in the deep sub-barrier fusion
reactions.
|
1302.7115v2
|
2013-03-14
|
Microwave-assisted switching of a nanomagnet: analytical determination of the optimal microwave field
|
We analytically determine the optimal microwave field that allows for the
magnetization reversal of a nanomagnet modeled as a macrospin. This is done by
minimizing the total injected energy. The results are in good agreement with
the fields obtained numerically using the optimal control theory. For typical
values of the damping parameter, a weak microwave field is sufficient to induce
switching through a resonant process. The optimal field is orthogonal to the
magnetization direction at any time and modulated both in amplitude and
frequency. The dependence of the pulse shape on the applied field and damping
parameter is interpreted. The total injected energy is found to be
proportionnal to the energy barrier between the initial state and the saddle
point and to the damping parameter. This result may be used as a means for
probing the damping parameter in real nanoparticles.
|
1303.3501v4
|
2013-04-05
|
Nonlocal Gravity: Damping of Linearized Gravitational Waves
|
In nonlocal general relativity, linearized gravitational waves are damped as
they propagate from the source to the receiver in the Minkowski vacuum.
Nonlocal gravity is a generalization of Einstein's theory of gravitation in
which nonlocality is due to the gravitational memory of past events. That
nonlocal gravity is dissipative is demonstrated in this paper within certain
approximation schemes. The gravitational memory drag leads to the decay of the
amplitude of gravitational waves given by the exponential damping factor exp
(-t/\tau), where $\tau$ depends on the kernel of nonlocal gravity. The damping
time $\tau$ is estimated for gravitational waves of current observational
interest and is found to be of the order of, or longer than, the age of the
universe.
|
1304.1769v1
|
2013-07-29
|
Damping of Primordial Gravitational Waves from Generalized Sources
|
It has been shown that a cosmological background with an anisotropic stress
tensor, appropriate for a free streaming thermal neutrino background, can damp
primordial gravitational waves after they enter the horizon, and can thus
affect the CMB B-mode polarization signature due to such tensor modes. Here we
generalize this result, and examine the sensitivity of this effect to non-zero
neutrino masses, extra neutrino species, and also a possible relativistic
background of axions from axion strings. In particular, additional neutrinos
with cosmologically interesting neutrino masses at the O(1) eV level will
noticeably reduce damping compared to massless neutrinos for gravitational wave
modes with $k\tau_0 \approx 100-200$, where $\tau_0 \approx 2/H_0$ and $H_0$ is
the present Hubble parameter, while an axion background would produce a
phase-dependent damping distinct from that produced by neutrinos.
|
1307.7571v1
|
2013-08-08
|
Small global solutions to the damped two-dimensional Boussinesq equations
|
The two-dimensional (2D) incompressible Euler equations have been thoroughly
investigated and the resolution of the global (in time) existence and
uniqueness issue is currently in a satisfactory status. In contrast, the global
regularity problem concerning the 2D inviscid Boussinesq equations remains
widely open. In an attempt to understand this problem, we examine the damped 2D
Boussinesq equations and study how damping affects the regularity of solutions.
Since the damping effect is insufficient in overcoming the difficulty due to
the "vortex stretching", we seek unique global small solutions and the efforts
have been mainly devoted to minimizing the smallness assumption. By positioning
the solutions in a suitable functional setting (more precisely the homogeneous
Besov space $\mathring{B}^1_{\infty,1}$), we are able to obtain a unique global
solution under a minimal smallness assumption.
|
1308.1723v1
|
2013-08-21
|
Approximate quantum error correction for generalized amplitude damping errors
|
We present analytic estimates of the performances of various approximate
quantum error correction schemes for the generalized amplitude damping (GAD)
qubit channel. Specifically, we consider both stabilizer and nonadditive
quantum codes. The performance of such error-correcting schemes is quantified
by means of the entanglement fidelity as a function of the damping probability
and the non-zero environmental temperature. The recovery scheme employed
throughout our work applies, in principle, to arbitrary quantum codes and is
the analogue of the perfect Knill-Laflamme recovery scheme adapted to the
approximate quantum error correction framework for the GAD error model. We also
analytically recover and/or clarify some previously known numerical results in
the limiting case of vanishing temperature of the environment, the well-known
traditional amplitude damping channel. In addition, our study suggests that
degenerate stabilizer codes and self-complementary nonadditive codes are
especially suitable for the error correction of the GAD noise model. Finally,
comparing the properly normalized entanglement fidelities of the best
performant stabilizer and nonadditive codes characterized by the same length,
we show that nonadditive codes outperform stabilizer codes not only in terms of
encoded dimension but also in terms of entanglement fidelity.
|
1308.4582v2
|
2013-11-01
|
Kinetic theory of acoustic-like modes in nonextensive pair plasmas
|
The low-frequency acoustic-like modes in a pair plasma (electron-positron or
pair-ion) is studied by employing a kinetic theory model based on the Vlasov
and Poisson's equation with emphasizing the Tsallis's nonextensive statistics.
The possibility of the acoustic-like modes and their properties in both fully
symmetric and temperature-asymmetric cases are examined by studying the
dispersion relation, Landau damping and instability of modes. The resultant
dispersion relation in this study is compatible with the acoustic branch of the
experimental data [W. Oohara, D. Date, and R. Hatakeyama, Phys. Rev. Lett. 95,
175003 (2005)], in which the electrostatic waves have been examined in a pure
pair-ion plasma. Particularly, our study reveals that the occurrence of growing
or damped acoustic-like modes depends strongly on the nonextensivity of the
system as a measure for describing the long-range Coulombic interactions and
correlations in the plasma. The mechanism that leads to the unstable modes lies
in the heart of the nonextensive formalism yet, the mechanism of damping is the
same developed by Landau. Furthermore, the solutions of acoustic-like waves in
an equilibrium Maxwellian pair plasma are recovered in the extensive limit
($q\rightarrow1$), where the acoustic modes have only the Landau damping and no
growth.
|
1311.0193v1
|
2013-11-29
|
Exploring viscous damping in undergraduate Physics laboratory using electromagnetically coupled oscillators
|
We design a low-cost, electromagnetically coupled, simple harmonic oscillator
and demonstrate free, damped and forced oscillations in an under-graduate (UG)
Physics laboratory. It consists of a spring-magnet system that can oscillate
inside a cylinder around which copper coils are wound. Such demonstrations can
compliment the traditional way in which a Waves & Oscillations course is taught
and offers a richer pedagogical experience for students. We also show that with
minimal modifications, it can be used to probe the magnitude of viscous damping
forces in liquids by analyzing the oscillations of an immersed magnet. Finally,
we propose some student activities to explore non-linear damping effects and
their characterization using this apparatus.
|
1311.7489v1
|
2013-12-18
|
Radiative damping and synchronization in a graphene-based terahertz emitter
|
We investigate the collective electron dynamics in a recently proposed
graphene-based terahertz emitter under the influence of the radiative damping
effect, which is included self-consistently in a molecular dynamics approach.
We show that under appropriate conditions synchronization of the dynamics of
single electrons takes place, leading to a rise of the oscillating component of
the charge current. The synchronization time depends dramatically on the
applied dc electric field and electron scattering rate, and is roughly
inversely proportional to the radiative damping rate that is determined by the
carrier concentration and the geometrical parameters of the device. The
emission spectra in the synchronized state, determined by the oscillating
current component, are analyzed. The effective generation of higher harmonics
for large values of the radiative damping strength is demonstrated.
|
1312.5193v1
|
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