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2022-06-25
|
Decay estimate in a viscoelastic plate equation with past history, nonlinear damping, and logarithmic nonlinearity
|
In this article, we consider a viscoelastic plate equation with past history,
nonlinear damping, and logarithmic nonlinearity. We prove explicit and general
decay rate results of the solution to the viscoelastic plate equation with past
history. Convex properties, logarithmic inequalities, and generalised Young's
inequality are mainly used to prove the decay estimate.
|
2206.12561v1
|
2022-06-30
|
Effect of a viscous fluid shell on the propagation of gravitational waves
|
In this paper we show that there are circumstances in which the damping of
gravitational waves (GWs) propagating through a viscous fluid can be highly
significant; in particular, this applies to Core Collapse Supernovae (CCSNe).
In previous work, we used linearized perturbations on a fixed background within
the Bondi-Sachs formalism, to determine the effect of a dust shell on GW
propagation. Here, we start with the (previously found) velocity field of the
matter, and use it to determine the shear tensor of the fluid flow. Then, for a
viscous fluid, the energy dissipated is calculated, leading to an equation for
GW damping. It is found that the damping effect agrees with previous results
when the wavelength $\lambda$ is much smaller than the radius $r_i$ of the
matter shell; but if $\lambda\gg r_i$, then the damping effect is greatly
increased.
Next, the paper discusses an astrophysical application, CCSNe. There are
several different physical processes that generate GWs, and many models have
been presented in the literature. The damping effect thus needs to be evaluated
with each of the parameters $\lambda,r_i$ and the coefficient of shear
viscosity $\eta$, having a range of values. It is found that in most cases
there will be significant damping, and in some cases that it is almost
complete.
We also consider the effect of viscous damping on primordial gravitational
waves (pGWs) generated during inflation in the early Universe. Two cases are
investigated where the wavelength is either much shorter than the shell radii
or much longer; we find that there are conditions that will produce significant
damping, to the extent that the waves would not be detectable.
|
2206.15103v2
|
2022-09-07
|
Blow up and lifespan estimates for systems of semi-linear wave equations with dampings and potentials
|
In this paper, we consider the semi-linear wave systems with
power-nonlinearities and space-dependent dampings and potentials. We obtain the
blow-up regions for three types wave systems as well as the lifespan estimates.
|
2209.02920v1
|
2022-12-04
|
Inverse problem of recovering the time-dependent damping and nonlinear terms for wave equations
|
In this paper, we consider the inverse boundary problems of recovering the
time-dependent nonlinearity and damping term for a semilinear wave equation on
a Riemannian manifold. The Carleman estimate and the construction of Gaussian
beams together with the higher order linearization are respectively used to
derive the uniqueness results of recovering the coefficients.
|
2212.01815v2
|
2022-12-14
|
Gevrey regularity for the Euler-Bernoulli beam equation with localized structural damping
|
We study a Euler-Bernoulli beam equation with localized discontinuous
structural damping. As our main result, we prove that the associated
$C_0$-semigroup $(S(t))_{t\geq0}$ is of Gevrey class $\delta>24$ for $t>0$,
hence immediately differentiable. Moreover, we show that $(S(t))_{t\geq0}$ is
exponentially stable.
|
2212.07110v1
|
2022-12-28
|
On extended lifespan for 1d damped wave equation
|
In this manuscript, a sharp lifespan estimate of solutions to semilinear
classical damped wave equation is investigated in one dimensional case, when
the sum of initial position and speed is $0$ pointwisely. Especially, an
extension of lifespan is shown in this case. Moreover, existence of some global
solutions are obtained by a direct computation.
|
2212.13845v1
|
2023-02-06
|
Uniform stabilization of an acoustic system
|
We study the problem of stabilization for the acoustic system with a
spatially distributed damping. With imposing hypothesis on the structural
properties of the damping term, we identify exponential decay of solutions with
growing time.
|
2302.02726v1
|
2023-04-23
|
Decay rates for a variable-coefficient wave equation with nonlinear time-dependent damping
|
In this paper, a class of variable-coefficient wave equations equipped with
time-dependent damping and the nonlinear source is considered. We show that the
total energy of the system decays to zero with an explicit and precise decay
rate estimate under different assumptions on the feedback with the help of the
method of weighted energy integral.
|
2304.11522v1
|
2023-05-22
|
Fast energy decay for wave equation with a monotone potential and an effective damping
|
We consider the total energy decay of the Cauchy problem for wave equations
with a potential and an effective damping. We treat it in the whole
one-dimensional Euclidean space. Fast energy decay is established with the help
of potential. The proofs of main results rely on a multiplier method and
modified techniques adopted in [8].
|
2305.12666v1
|
2023-08-03
|
Blow-up for semilinear wave equations with damping and potential in high dimensional Schwarzschild spacetime
|
In this work, we study the blow up results to power-type semilinear wave
equation in the high dimensional Schwarzschild spacetime, with damping and
potential terms. We can obtain the upper bound estimates of lifespan without
the assumption that the support of the initial date should be far away from the
black hole.
|
2308.01691v1
|
2023-08-22
|
Lifespan estimates for 1d damped wave equation with zero moment initial data
|
In this manuscript, a sharp lifespan estimate of solutions to semilinear
classical damped wave equation is investigated in one dimensional case when the
Fourier 0th moment of sum of initial position and speed is $0$. Especially, it
is shown that the behavior of lifespan changes with $p=3/2$ with respect to the
size of the initial data.
|
2308.11113v1
|
2023-09-01
|
Damped Euler system with attractive Riesz interaction forces
|
We consider the barotropic Euler equations with pairwise attractive Riesz
interactions and linear velocity damping in the periodic domain. We establish
the global-in-time well-posedness theory for the system near an equilibrium
state. We also analyze the large-time behavior of solutions showing the
exponential rate of convergence toward the equilibrium state as time goes to
infinity.
|
2309.00210v1
|
2023-10-02
|
The damped wave equation and associated polymer
|
Considering the damped wave equation with a Gaussian noise $F$ where $F$ is
white in time and has a covariance function depending on spatial variables, we
will see that this equation has a mild solution which is stationary in time
$t$. We define a weakly self-avoiding polymer with intrinsic length $J$
associated to this SPDE. Our main result is that the polymer has an effective
radius of approximately $J^{5/3}$.
|
2310.01631v1
|
2023-10-17
|
Indirect boundary stabilization for weakly coupled degenerate wave equations under fractional damping
|
In this paper, we consider the well-posedness and stability of a
one-dimensional system of degenerate wave equations coupled via zero order
terms with one boundary fractional damping acting on one end only. We prove
optimal polynomial energy decay rate of order $1/t^{(3-\tau)}$. The method is
based on the frequency domain approach combined with multiplier technique.
|
2310.11174v1
|
2024-03-11
|
Uniform estimates for solutions of nonlinear focusing damped wave equations
|
For a damped wave (or Klein-Gordon) equation on a bounded domain, with a
focusing power-like nonlinearity satisfying some growth conditions, we prove
that a global solution is bounded in the energy space, uniformly in time. Our
result applies in particular to the case of a cubic equation on a bounded
domain of dimension 3.
|
2403.06541v1
|
1995-10-27
|
Radiation Damping and Quantum Excitation for Longitudinal Charged Particle Dynamics in the Thermal Wave Model
|
On the basis of the recently proposed {\it Thermal Wave Model (TWM) for
particle beams}, we give a description of the longitudinal charge particle
dynamics in circular accelerating machines by taking into account both
radiation damping and quantum excitation (stochastic effect), in presence of a
RF potential well. The longitudinal dynamics is governed by a 1-D
Schr\"{o}dinger-like equation for a complex wave function whose squared modulus
gives the longitudinal bunch density profile. In this framework, the
appropriate {\it r.m.s. emittance} scaling law, due to the damping effect, is
naturally recovered, and the asymptotic equilibrium condition for the bunch
length, due to the competition between quantum excitation (QE) and radiation
damping (RD), is found. This result opens the possibility to apply the TWM,
already tested for protons, to electrons, for which QE and RD are very
important.
|
9510004v1
|
1994-02-04
|
Constraints on Models of Galaxy Formation from the Evolution of Damped Ly$α$ Absorption Systems
|
There is accumulating observational evidence suggesting that damped
Ly$\alpha$ absorption systems systems are the progenitors of present-day spiral
galaxies. We use the observed properties of these systems to place constraints
on the history of star formation in galactic disks, and on cosmological
theories of structure formation in the universe. We show that the observed
increase in $\Omega_{HI}$ contributed by damped Ly$\alpha$ systems at high
redshift implies that star formation must have been considerably less efficient
in the past. We also show that the data can constrain cosmological models in
which structure forms at late epochs. A mixed dark matter (MDM) model with
$\Omega_{\nu}=0.3$ is unable to reproduce the mass densities of cold gas seen
at high redshift, even in the absence of any star formation. We show that at
redshifts greater than 3, this model predicts that the total baryonic mass
contained in dark matter halos with circular velocities $V_c > 35$ km s$^{-1}$
is less than the observed mass of HI in damped systems. At these redshifts, the
photo-ionizing background would prevent gas from dissipating and collapsing to
form high column density systems in halos smaller than 35 km s$^{-1}$. MDM
models are thus ruled out by the observations.
|
9402015v1
|
1999-02-11
|
The HI Column Density Distribution Function at z=0: the Connection to Damped Ly alpha Statistics
|
We present a measurement of the HI column density distribution function,
f(N), at the present epoch for column densities log N > 20 cm^-2. These high
column densities compare to those measured in damped Ly alpha lines seen in
absorption against background quasars. Although observationally rare, it
appears that the bulk of the neutral gas in the Universe is associated with
these damped Ly alpha systems. In order to obtain a good anchor point at z=0 we
determine f(N) in the local Universe by using 21cm synthesis observations of a
complete sample of spiral galaxies. We show that f(N) for damped Ly alpha
systems has changed significantly from high z to the present and that change is
greatest for the highest column densities. The measurements indicate that low
surface brightness galaxies make a minor contribution to the cross section for
HI, especially for log N > 21^-2.
|
9902171v1
|
2000-10-27
|
Planetary Torques as the Viscosity of Protoplanetary Disks
|
We revisit the idea that density-wave wakes of planets drive accretion in
protostellar disks. The effects of many small planets can be represented as a
viscosity if the wakes damp locally, but the viscosity is proportional to the
damping length. Damping occurs mainly by shocks even for earth-mass planets.
The excitation of the wake follows from standard linear theory including the
torque cutoff. We use this as input to an approximate but quantitative
nonlinear theory based on Burger's equation for the subsequent propagation and
shock. Shock damping is indeed local but weakly so. If all metals in a
minimum-mass solar nebula are invested in planets of a few earth masses each,
dimensionless viscosities [alpha] of order dex(-4) to dex(-3) result. We
compare this with observational constraints. Such small planets would have
escaped detection in radial-velocity surveys and could be ubiquitous. If so,
then the similarity of the observed lifetime of T Tauri disks to the
theoretical timescale for assembling a rocky planet may be fate rather than
coincidence.
|
0010576v1
|
2000-12-27
|
Constraining Dark Matter candidates from structure formation
|
We show that collisional damping of adiabatic primordial fluctuations yields
constraints on the possible range of mass and interaction rates of Dark Matter
particles. Our analysis relies on a general classification of Dark Matter
candidates, that we establish independently of any specific particle theory or
model. From a relation between the collisional damping scale and the Dark
Matter interaction rate, we find that Dark Matter candidates must have
cross-sections at decoupling smaller than $ 10^{-33} \frac{m_{dm}}{1 MeV} cm^2$
with photons and $10^{-37} \frac{m_{dm}}{1 MeV} cm^2$ with neutrinos, to
explain the observed primordial structures of $10^9$ Solar mass. These damping
constraints are particularly relevant for Warm Dark Matter candidates. They
also leave open less known regions of parameter space corresponding to
particles having rather high interaction rates with other species than
neutrinos and photons.
|
0012504v2
|
2001-07-26
|
The Contribution of HI-Rich Galaxies to the Damped Absorber Population at z=0
|
We present a study of HI-rich galaxies in the local universe selected from
blind emission-line surveys. These galaxies represent the emission-line
counterparts of local damped Lyman-alpha systems. We find that the HI
cross-section of galaxies is drawn from a large range of galaxy masses below
M_star, 66% of the area comes from galaxies in the range 8.5 < Log M_star <
9.7. Both because of the low mass galaxy contribution, and because of the range
of galaxy types and luminosities at any given HI mass, the galaxies
contributing to the HI cross-section are not exclusively L_star spirals, as is
often expected. The optical and near infrared counterparts of these galaxies
cover a range of types (from spirals to irregulars), luminosities (from L_star
to <0.01 L_star), and surface brightnesses. The range of optical and near
infrared properties as well as the kinematics for this population are
consistent with the properties for the low-z damped Lyman-alpha absorbers. We
also show that the number of HI-rich galaxies in the local universe does not
preclude evolution of the low-z damped absorber population, but it is
consistent with no evolution.
|
0107495v1
|
2003-11-17
|
Cosmic Ray Scattering by Compressible Magnetohydrodynamic Turbulence
|
Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call
for substantial revisions in the picture of cosmic ray transport. In this paper
we use recently obtained scaling laws for MHD modes to calculate the scattering
frequency for cosmic rays in the ISM. We consider gyroresonance with MHD modes
(Alfvenic, slow and fast) and transit-time damping (TTD) by fast modes. We
provide calculations of cosmic ray scattering for various phases of
interstellar medium with realistic interstellar turbulence driving that is
consistent with the velocity dispersions observed in diffuse gas. We account
for the turbulence cutoff arising from both collisional and collisionless
damping. We obtain analytical expressions for diffusion coefficients that enter
Fokker-Planck equation describing cosmic ray evolution. We calculate the
scattering rate and parallel spatial diffusion coefficients of cosmic rays for
both Alfvenic and fast modes. We conclude that fast modes provides the dominant
contribution to cosmic ray scattering for the typical interstellar conditions
in spite of the fact that fast modes are subjected to damping. We show that the
efficiency of the scattering depends on the plasma beta since it determines the
damping of the fast modes. We also show that the streaming instability is
modified in the presence of turbulence.
|
0311369v1
|
2003-11-17
|
Wave damping by MHD turbulence and its effect upon cosmic ray propagation in the ISM
|
Cosmic rays scatter off magnetic irregularities (Alfven waves) with which
they are resonant, that is waves of wavelength comparable to their gyroradii.
These waves may be generated either by the cosmic rays themselves, if they
stream faster than the Alfven speed, or by sources of MHD turbulence. Waves
excited by streaming cosmic rays are ideally shaped for scattering, whereas the
scattering efficiency of MHD turbulence is severely diminished by its
anisotropy. We show that MHD turbulence has an indirect effect on cosmic ray
propagation by acting as a damping mechanism for cosmic ray generated waves.
The hot (``coronal'') phase of the interstellar medium is the best candidate
location for cosmic ray confinement by scattering from self-generated waves. We
relate the streaming velocity of cosmic rays to the rate of turbulent
dissipation in this medium, for the case in which turbulent damping is the
dominant damping mechanism. We conclude that cosmic rays with up to 10^2 GeV
could not stream much faster than the Alfven speed, but that 10^6 GeV cosmic
rays would stream unimpeded by self-generated waves unless the coronal gas were
remarkably turbulence-free.
|
0311400v1
|
2004-10-25
|
Constraints on Dark Matter interactions from structure formation: Damping lengths
|
(Shortened) Weakly Interacting Massive Particles are often said to be the
best Dark Matter candidates. Studies have shown however that rather large Dark
Matter-photon or Dark Matter-baryon interactions could be allowed by cosmology.
Here we address the question of the role of the Dark Matter interactions in
more detail to determine at which extent Dark Matter has to be necessarily
weakly interacting. To this purpose, we compute the collisional damping (and
free-streaming) lengths of generic interacting Dark Matter candidates and
compare them to the scale of the smallest primordial structures known to exist
in the Universe. We obtain necessary conditions that any candidate must
satisfy. We point out the existence of new Dark Matter scenarios and exhibit
new damping regimes. For example, an interacting candidate may bear a similar
damping than that of collisionless Warm Dark Matter particles. The main
difference is due to the Dark Matter coupling to interacting (or even
freely-propagating) species. Our approach yields a general classification of
Dark Matter candidates which extends the definitions of the usual Cold, Warm
and Hot Dark Matter scenarios when interactions, weak or strong, are
considered.
|
0410591v1
|
2005-10-10
|
Collisional dissipation of Alfvén waves in a partially ionised solar chromosphere
|
Certain regions of the solar atmosphere are at sufficiently low temperatures
to be only partially ionised. The lower chromosphere contains neutral atoms,
the existence of which greatly increases the efficiency of the damping of waves
due to collisional friction momentum transfer. More specifically the Cowling
conductivity can be up to 12 orders of magnitude smaller than the Spitzer
value, so that the main damping mechanism in this region is due to the
collisions between neutrals and positive ions. Using values for the gas density
and temperature as functions of height taken from the VAL C model of the quiet
Sun, an estimate is made for the dependance of the Cowling conductivity on
height and strength of magnetic field. Using both analytic and numerical
approaches the passage of Alfven waves over a wide spectrum through this
partially ionised region is investigated. Estimates of the efficiency of this
region in the damping of Alfven waves are made and compared for both
approaches. We find that Alfven waves with frequencies above 0.6Hz are
completely damped and frequencies below 0.01 Hz unaffected.
|
0510265v1
|
2006-04-10
|
The Nearby Damped Lyman-alpha Absorber SBS 1543+593: A Large HI Envelope in a Gas-Rich Galaxy Group
|
We present a Very Large Array (VLA) HI 21cm map and optical observations of
the region around one of the nearest damped Lyman-alpha absorbers beyond the
local group, SBS 1543+593. Two previously uncataloged galaxies have been
discovered and a redshift has been determined for a third. All three of these
galaxies are at the redshift of SBS 1543+593 and are ~185 kpc from the damped
Lyman-alpha absorber. We discuss the HI and optical properties of SBS 1543+593
and its newly identified neighbors. Both SBS 1543+593 and Dwarf 1 have baryonic
components that are dominated by neutral gas -- unusual for damped Lyman-alpha
absorbers for which only ~5% of the HI cross-section originates in such
strongly gas-dominated systems. What remains unknown is whether low mass
gas-rich groups are common surrounding gas-rich galaxies in the local universe
and whether the low star-formation rate in these systems is indicative of a
young system or a stable, slowly evolving system. We discuss these evolutionary
scenarios and future prospects for answering these questions.
|
0604220v1
|
2006-08-02
|
SINS of Viscosity Damped Turbulence
|
The problems with explaining the Small Ionized and Neutral Structures (SINS)
appealing to turbulence stem from inefficiency of the Kolmogorov cascade in
creating large fluctuations at sufficiently small scales. However, other types
of cascades are possible. When magnetic turbulence in a fluid with viscosity
that is much larger than resistivity gets to a viscous damping scale, the
turbulence does not vanish. Instead, it gets into a different new regime.
Viscosity-damped turbulence produces fluctuations on the small scales. Magnetic
fields sheared by turbulent motions by eddies not damped by turbulence create
small scale filaments that are confined by the external plasma pressure. This
creates small scale density fluctuations. In addition, extended current sheets
create even stronger density gradients that accompany field reversals in the
plane perpendicular to mean magnetic field. Those can be responsible for the
SINS formation. This scenario is applicable to partially ionized gas. More
studies of reconnection in the viscosity dominated regime are necessary to
understand better the extend to which the magnetic reversals can compress the
gas.
|
0608046v3
|
1998-01-13
|
Comparative Study of the Adiabatic Evolution of a Nonlinear Damped Oscillator and an Hamiltonian Generalized Nonlinear Oscillator
|
In this paper we study to what extent the canonical equivalence and the
identity of the geometric phases of dissipative and conservative linear
oscillators, established in a preceeding paper, can be generalized to nonlinear
ones. Considering first the 1-D quartic generalized oscillator we determine, by
means of a perturbative time dependent technic of reduction to normal forms,
the canonical transformations which lead to the adiabatic invariant of the
system and to the first order non linear correction to its Hannay angle. Then,
applying the same transformations to the 1-D quartic damped oscillator we show
that this oscillator is canonically equivalent to the linear generalized
harmonic oscillator for finite values of the damping parameter (which implies
no correction to the linear Hannay angle) whereas, in an appropriate weak
damping limit, it becomes equivalent to the quartic generalized oscillator
(which implies a non linear correction to this angle) .
|
9801017v1
|
1995-03-20
|
Quasiparticle damping in two-dimensional superconductors with unconventional pairing.
|
We calculate the damping of excitations due to four-fermionic interaction in
the case of two-dimensional superconductor with nodes in the spectrum. At zero
temperature and low frequencies it reveals gapless $\omega^3$ behavior at the
nodal points. With the frequency increasing the crossover to the normal-state
regimes appears. At high frequencies the damping strongly depends on details of
a normal-state spectrum parametrization. Two important particular cases such as
the models of almost free and tight-binding electrons are studied explicitly
and the characteristic scales are expressed through the model-free parameters
of the spectrum at the nodal points. The possibility of crossover in
temperature dependence of damping in the superconducting phase is discussed.
|
9503112v1
|
1997-10-14
|
Damping of Hydrodynamic Modes in a Trapped Bose Gas above the Bose-Einstein Transition Temperature
|
We calculate the damping of low-lying collective modes of a trapped Bose gas
in the hydrodynamic regime, and show that this comes solely from the shear
viscosity, since the contributions from bulk viscosity and thermal conduction
vanish. The hydrodynamic expression for the damping diverges due to the failure
of hydrodynamics in the outer parts of the cloud, and we take this into account
by a physically motivated cutoff procedure. Our analysis of available
experimental data indicates that higher densities than have yet been achieved
are necessary for investigating hydrodynamic modes above the Bose-Einstein
transition temperature.
|
9710130v2
|
1997-12-24
|
Thermal dephasing and the echo effect in a confined Bose-Einstein condensate
|
It is shown that thermal fluctuations of the normal component induce
dephasing -- reversible damping of the low energy collective modes of a
confined Bose-Einstein condensate. The dephasing rate is calculated for the
isotropic oscillator trap, where Landau damping is expected to be suppressed.
This rate is characterized by a steep temperature dependence, and it is weakly
amplitude dependent.
In the limit of large numbers of bosons forming the condensate, the rate
approaches zero. However, for the numbers employed by the JILA group, the
calculated value of the rate is close to the experimental one. We suggest that
a reversible nature of the damping caused by the thermal dephasing in the
isotropic trap can be tested by the echo effect. A reversible nature of Landau
damping is also discussed, and a possibility of observing the echo effect in an
anisotropic trap is considered as well. The parameters of the echo are
calculated in the weak echo limit for the isotropic trap. Results of the
numerical simulations of the echo are also presented.
|
9712287v1
|
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
|
2003-02-17
|
Magnetization dynamics with a spin-transfer torque
|
The magnetization reversal and dynamics of a spin valve pillar, whose lateral
size is 64$\times$64 nm$^2$, are studied by using micromagnetic simulation in
the presence of spin transfer torque. Spin torques display both characteristics
of magnetic damping (or anti-damping) and of an effective magnetic field. For a
steady-state current, both M-I and M-H hysteresis loops show unique features,
including multiple jumps, unusual plateaus and precessional states. These
states originate from the competition between the energy dissipation due to
Gilbert damping and the energy accumulation due to the spin torque supplied by
the spin current. The magnetic energy oscillates as a function of time even for
a steady-state current. For a pulsed current, the minimum width and amplitude
of the spin torque for achieving current-driven magnetization reversal are
quantitatively determined. The spin torque also shows very interesting thermal
activation that is fundamentally different from an ordinary damping effect.
|
0302337v1
|
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
|
2005-07-05
|
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
|
2008-12-17
|
Origin of intrinsic Gilbert damping
|
The damping of magnetization, represented by the rate at which it relaxes to
equilibrium, is successfully modeled as a phenomenological extension in the
Landau-Lifschitz-Gilbert equation. This is the damping torque term known as
Gilbert damping and its direction is given by the vector product of the
magnetization and its time derivative. Here we derive the Gilbert term from
first principles by a non-relativistic expansion of the Dirac equation. We find
that the Gilbert term arises when one calculates the time evolution of the spin
observable in the presence of the full spin-orbital coupling terms, while
recognizing the relationship between the curl of the electric field and the
time varying magnetic induction.
|
0812.3184v2
|
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
|
2011-03-09
|
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
|
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