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2003-10-28
|
Chemical Abundances in the Damped Lya Systems
|
I introduce and review the data and analysis techniques used to measure
abundances in the damped Lya systems, quasar absorption-line systems associated
with galaxies in the early Universe. The observations and issues associated
with their abundance analysis are very similar to those of the Milky Way's
interstellar medium. We measure gas-phase abundances and are therefore subject
to the effects of differential depletion. I review the impact of dust depletion
and then present a summary of current results on the age-metallicity relation
derived from damped Lya systems and new results impacting theories of
nucleosynthesis in the early Universe.
|
0310814v1
|
2004-08-10
|
Cosmic Ray Scattering and Streaming in Compressible Magnetohydrodynamic Turbulence
|
Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call
for revisions in the picture of cosmic ray transport. In this paper we use
recently obtained scaling laws for MHD modes to obtain the scattering frequency
for cosmic rays. Using quasilinear theory we calculate gyroresonance with MHD
modes (Alfv\'{e}nic, 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 obtain the
scattering rate and show that fast modes provide 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 determine how the efficiency
of the scattering depends on the characteristics of ionized media, e.g. plasma
$\beta$. We calculate the range of energies for which the streaming instability
is suppressed by the ambient MHD turbulence.
|
0408172v1
|
2004-12-14
|
Radiative Effects on Particle Acceleration in Electromagnetic Dominated Outflows
|
Plasma outflows from gamma-ray bursts (GRB), pulsar winds, relativistic jets,
and ultra-intense laser targets radiate high energy photons. However, radiation
damping is ignored in conventional PIC simulations. In this letter, we study
the radiation damping effect on particle acceleration via Poynting fluxes in
two-and-half-dimensional particle-in-cell (PIC) plasma simulation of
electron-positron plasmas. Radiation damping force is self-consistently
calculated for each particle and reduces the net acceleration force. The
emitted radiation is peaked within a few degrees from the direction of Poynting
flux and strongly linear-polarized.
|
0412310v3
|
2005-09-16
|
Damped Lyman alpha Systems
|
Observations of damped Lyman alpha systems offer a unique window on the
neutral-gas reservoirs that gave rise to galaxies at high redshifts. This
review focuses on critical properties such as the H I and metal content of the
gas and on independent evidence for star formation. Together, these provide an
emerging picture of gravitationally bound objects in which accretion of gas
from the IGM replenishes gas consumed by star formation. Other properties such
as dust content, molecular content, ionized-gas content, gas kinematics, and
galaxy identifications are also reviewed. These properties point to a
multiphase ISM in which radiative and hydrodynamic feedback processes are
present. Numerical simulations and other types of models used to describe
damped Lyman alpha systems within the context of galaxy formation are also
discussed.
|
0509481v2
|
2005-11-11
|
Oscillation mode lifetimes in ksi Hydrae: Will strong mode damping limit asteroseismology of red giant stars?
|
We introduce a new method to measure frequency separations and mode lifetimes
of stochastically excited and damped oscillations, so-called solar-like
oscillations. Our method shows that velocity data of the red giant star ksi Hya
(Frandsen et al. 2002) support a large frequency separation between modes of
roughly 7 microHz. We also conclude that the data are consistent with a mode
lifetime of 2 days, which is so short relative to its pulsation period that
none of the observed frequencies are unambiguous. Hence, we argue that the
maximum asteroseismic output that can be obtained from these data is an average
large frequency separation, the oscillation amplitude and the average mode
lifetime. However, the significant discrepancy between the theoretical
calculations of the mode lifetime (Houdek & Gough 2002) and our result based on
the observations of ksi Hya, implies that red giant stars can help us better
understand the damping and driving mechanisms of solar-like p-modes by
convection.
|
0511344v1
|
1996-12-14
|
Nonlinear Landau damping in collisionless plasma and inviscid fluid
|
The evolution of an initial perturbation in Vlasov plasma is studied in the
intrinsically nonlinear long-time limit dominated by the effects of particle
trapping. After the possible transient linear exponential Landau damping, the
evolution enters into a universal regime with an algebraically damped electric
field, $E\propto1/t$. The trick used for the Vlasov equation is also applied to
the two-dimensional (2D) Euler equation. It is shown that the stream function
perturbation to a stable shear flow decays as $t^{-5/2}$ in the long-time
limit. These results imply a strong non-ergodicity of the fluid element motion,
which invalidates Gibbs-ensemble-based statistical theories of Vlasov and 2D
fluid turbulence.
|
9612021v1
|
1998-03-05
|
On how a joint interaction of two innocent partners (smooth advection & linear damping) produces a strong intermittency
|
Forced advection of passive scalar by a smooth $d$-dimensional incompressible
velocity in the presence of a linear damping is studied. Acting separately
advection and dumping do not lead to an essential intermittency of the steady
scalar statistics, while being mixed together produce a very strong
non-Gaussianity in the convective range: $q$-th (positive) moment of the
absolute value of scalar difference, $<|\theta (t;{\bf r})-\theta (t;0)|^{q}> $
is proportional to $r^{\xi_{q}}$, $\xi _{q}=\sqrt{d^{2}/4+\alpha dq/[
(d-1)D]}-d/2$, where $\alpha /D$ measures the rate of the damping in the units
of the stretching rate. Probability density function (PDF) of the scalar
difference is also found.
|
9803007v1
|
1999-02-05
|
Nonlinear Dynamics of A Damped Magnetic Oscillator
|
We consider a damped magnetic oscillator, consisting of a permanent magnet in
a periodically oscillating magnetic field. A detailed investigation of the
dynamics of this dissipative magnetic system is made by varying the field
amplitude $A$. As $A$ is increased, the damped magnetic oscillator, albeit
simple looking, exhibits rich dynamical behaviors such as symmetry-breaking
pitchfork bifurcations, period-doubling transitions to chaos,
symmetry-restoring attractor-merging crises, and saddle-node bifurcations
giving rise to new periodic attractors. Besides these familiar behaviors, a
cascade of ``resurrections'' (i.e., an infinite sequence of alternating
restabilizations and destabilizations) of the stationary points also occurs. It
is found that the stationary points restabilize (destabilize) through
alternating subcritical (supercritical) period-doubling and pitchfork
bifurcations. We also discuss the critical behaviors in the period-doubling
cascades.
|
9902005v1
|
1996-09-03
|
Mode damping in a commensurate monolayer solid
|
The normal modes of a commensurate monolayer solid may be damped by mixing
with elastic waves of the substrate. This was shown by B. Hall et al., Phys.
Rev. B 32, 4932 (1985), for perpendicular adsorbate vibrations in the presence
of an isotropic elastic medium. That work is generalized with an elastic
continuum theory of the response of modes of either parallel or perpendicular
polarization for a spherical adsorbate on a hexagonal substrate. The results
are applied to the discussion of computer simulations and inelastic atomic
scattering experiments for adsorbates on graphite. The extreme anisotropy of
the elastic behavior of the graphite leads to quite different wave vector
dependence of the damping for modes polarized perpendicular and parallel to the
substrate. A phenomenological extension of the elasticity theory of the
graphite to include bond-bending energies improves the description of substrate
modes with strong anomalous dispersion and enables a semi-quantitative account
of observed avoided crossings of the adlayer perpendicular vibration mode and
the substrate Rayleigh mode.
|
9609032v1
|
1997-12-08
|
Collective oscillations in superconductors revisited
|
In the recent paper Ohashi and Takada (OT) made statements that in the clean
limit considered by us (AV) in 1975, weakly damped collective oscillations in
superconductors do not exist due to the Landau damping and their spectrum
differs from that obtained in AV. In this Comment we would like to note that
these statements arise as a result of a misunderstanding of the term "clean"
case. OT considered the limit of frequencies larger, than elastic scattering
rate, meanwhile AV obtained weakly damped mode in the case when temperature is
larger than scattering rate, the frequencies being smaller (!) than elastic
scattering rate. All these problems were discussed in our review article in
1979 which was, presumably, unknown to OT.
|
9712086v1
|
1999-01-11
|
Vortex motion in superconducting YBCO inferred from the damping of the oscillations of a levitating magnetic microsphere
|
The damping of the oscillations of a small permanent magnet (spherical shape,
radius 0.1 mm) levitating between two parallel YBCO surfaces is measured as a
function of oscillation amplitude and temperature. The losses in the samples
(epitaxial thin films, bulk granular and bulk melt-textured) are analyzed in
terms of oscillating shielding currents flowing through trapped flux lines
whose motion gives rise to electric fields. We find dissipation to originate
from different mechanisms of flux dynamics. At small amplitudes there is a
linear regime described by a surface resistance varying from 10^-9 Ohm for bulk
samples down to 10^-13 Ohm for the thin films at low temperatures. With
increasing amplitude various nonlinear regimes are observed, firstly collective
pinning with diverging energy barriers, secondly in bulk samples above 85 K
hysteretic damping, and finally in thin films exponentially large losses which
can be described by pinning energies vanishing linearly at large currents.
|
9901085v1
|
1999-10-07
|
On the relative positions of the $2Δ$ peaks in Raman and tunneling spectra of d-wave superconductors
|
We study $B_{1g}$ Raman intensity $R(\Omega)$ and the density of states
$N(\omega)$ in isotropic 2D d-wave superconductors. For an ideal gas,
$R(\Omega)$ and $N(\omega)$ have sharp peaks at $\Omega =2\Delta$ and $\omega
=\Delta$, respectively, where $\Delta$ is the maximum value of the gap.
We study how the peak positions are affected by the fermionic damping due to
impurity scattering.
We show that while the damping generally shifts the peak positions to larger
frequencies, the peak in $R(\Omega)$ still occurs at almost twice the peak
position in $N(\omega)$ and therefore cannot account for the experimentally
observed downturn shift of the peak frequency in $R(\Omega)$ in underdoped
cuprates compared to twice that in $N(\omega)$. We also discuss how the
fermionic damping affects the dynamical spin susceptibility.
|
9910090v1
|
1999-11-22
|
Two-fluid hydrodynamics of a Bose gas including damping from normal fluid transport coefficients
|
We extend our recent work on the two-fluid hydrodynamics of the condensate
and non-condensate in a trapped Bose gas by including the dissipation
associated with viscosity and thermal conduction. For purposes of illustration,
we consider the hydrodynamic modes in the case of a uniform Bose gas. A finite
thermal conductivity and shear viscosity give rise to a damping of the first
and second sound modes in addition to that found previously due to the lack of
diffusive equilibrium between the condensate and non-condensate. The
relaxational mode associated with this equilibration process is strongly
coupled to thermal fluctuations and reduces to the usual thermal diffusion mode
above the Bose-Einstein transition. In contrast to the standard Landau
two-fluid hydrodynamics, we predict a damped mode centered at zero frequency,
in addition to the usual second sound doublet.
|
9911336v1
|
2000-03-31
|
Kinetic Theory of Collective Excitations and Damping in Bose-Einstein Condensed Gases
|
We calculate the frequencies and damping rates of the low-lying collective
modes of a Bose-Einstein condensed gas at nonzero temperature. We use a complex
nonlinear Schr\"odinger equation to determine the dynamics of the condensate
atoms, and couple it to a Boltzmann equation for the noncondensate atoms. In
this manner we take into account both collisions between
noncondensate-noncondensate and condensate-noncondensate atoms. We solve the
linear response of these equations, using a time-dependent gaussian trial
function for the condensate wave function and a truncated power expansion for
the deviation function of the thermal cloud. As a result, our calculation turns
out to be characterized by two dimensionless parameters proportional to the
noncondensate-noncondensate and condensate-noncondensate mean collision times.
We find in general quite good agreement with experiment, both for the
frequencies and damping of the collective modes.
|
0003517v1
|
2000-09-01
|
The broad Brillouin doublets and central peak of KTaO_3
|
The incipient ferroelectric KTaO3 presents low-T Brillouin spectra
anomalies,e.g. a broad central peak (CP), and some additional Brillouin
doublets (BD), whose origin is interpreted in terms of phonon-density
fluctuation processes. A parameterisation from new extensive high-resolution
neutron-scattering measurements is used to show that hydrodynamic second sound
from high damping (compared to BD frequency) TA phonons may exist in the
crystal. Furthermore, low damping thermal phonons may scatter light through
two-phonon difference processes and appear on the Brillouin spectra either as a
sharp or a broader BD, depending on the phonon damping and group velocity . The
comparison between computed anisotropies and experimental measurements favours
the second process.
|
0009012v1
|
2001-01-15
|
Temperature Dependence of Damping and Frequency Shifts of the Scissors Mode of a trapped Bose-Einstein Condensate
|
We have studied the properties of the scissors mode of a trapped
Bose-Einstein condensate of $^{87}$Rb atoms at finite temperature. We measured
a significant shift in the frequency of the mode below the hydrodynamic limit
and a strong dependence of the damping rate as the temperature increased. We
compared our damping rate results to recent theoretical calculations for other
observed collective modes finding a fair agreement. From the frequency
measurements we deduce the moment of inertia of the gas and show that it is
quenched below the transition point, because of the superfluid nature of the
condensed gas.
|
0101213v2
|
2001-03-16
|
Gap Anisotropy and de Haas-van Alphen Effect in Type-II Superconductors
|
We present a theoretical study on the de Haas-van Alphen (dHvA) oscillation
in the vortex state of type-II superconductors, with a special focus on the
connection between the gap anisotropy and the oscillation damping. Numerical
calculations for three different gap structures clearly indicate that the
average gap along extremal orbits is relevant for the magnitude of the extra
damping, thereby providing a support for experimental efforts to probe gap
anisotropy through the dHvA signal. We also derive an analytic formula for the
extra damping which gives a good fit to the numerical results.
|
0103336v3
|
2001-04-10
|
Quantum phase transitions and collective modes in d-wave superconductors
|
Fluctuations near second-order quantum phase transitions in d-wave
superconductors can cause strong damping of fermionic excitations, as observed
in photoemission experiments. The damping of the gapless nodal quasiparticles
can arise naturally in the quantum-critical region of a transition with an
additional spin-singlet, zero momentum order parameter; we argue that the
transition to a d_x^2-y^2 + i d_xy pairing state is the most likely possibility
in this category. On the other hand, the gapped antinodal quasiparticles can be
strongly damped by the coupling to antiferromagnetic spin fluctuations arising
from the proximity to a Neel-ordered state. We review some aspects of the
low-energy field theories for both transitions and the corresponding
quantum-critical behavior. In addition, we discuss the spectral properties of
the collective modes associated with the proximity to a superconductor with
d_x^2-y^2 + i d_xy symmetry, and implications for experiments.
|
0104176v1
|
2002-04-11
|
Nonequilibrium relaxation in neutral BCS superconductors: Ginzburg-Landau approach with Landau damping in real time
|
We present a field-theoretical method to obtain consistently the equations of
motion for small amplitude fluctuations of the order parameter directly in real
time for a homogeneous, neutral BCS superconductor. This method allows to study
the nonequilibrium relaxation of the order parameter as an initial value
problem. We obtain the Ward identities and the effective actions for small
phase the amplitude fluctuations to one-loop order. Focusing on the
long-wavelength, low-frequency limit near the critical point, we obtain the
time-dependent Ginzburg-Landau effective action to one-loop order, which is
nonlocal as a consequence of Landau damping. The nonequilibrium relaxation of
the phase and amplitude fluctuations is studied directly in real time. The
long-wavelength phase fluctuation (Bogoliubov-Anderson-Goldstone mode) is
overdamped by Landau damping and the relaxation time scale diverges at the
critical point, revealing critical slowing down.
|
0204239v2
|
2002-05-21
|
Linear spin waves in a trapped Bose gas
|
An ultra-cold Bose gas of two-level atoms can be thought of as a spin-1/2
Bose gas. It supports spin-wave collective modes due to the exchange mean
field. Such collective spin oscillations have been observed in recent
experiments at JILA with ${}^{87}$Rb atoms confined in a harmonic trap. We
present a theory of the spin-wave collective modes based on the moment method
for trapped gases. In the collisionless and hydrodynamic limits, we derive
analytic expressions for the frequencies and damping rates of modes with dipole
and quadrupole symmetry. We find that the frequency for a given mode is given
by a temperature independent function of the peak density $n$, and falls off as
$1/n$. We also find that, to a very good approximation, excitations in the
radial and axial directions are decoupled. We compare our model to the
numerical integration of a one dimensional version of the kinetic equation and
find very good qualitative agreement. The damping rates, however, show the
largest deviation for intermediate densities, where one expects Landau damping
-- which is unaccounted for in our moment approach -- to play a significant
role.
|
0205450v1
|
2002-08-02
|
Landau damping of transverse quadrupole oscillations of an elongated Bose-Einstein condensate
|
We study the interaction between low-lying transverse collective oscillations
and thermal excitations of an elongated Bose-Einstein condensate by means of
perturbation theory. We consider a cylindrically trapped condensate and
calculate the transverse elementary excitations at zero temperature by solving
the linearized Gross-Pitaevskii equations in two dimensions. We use them to
calculate the matrix elements between thermal excited states coupled with the
quasi-2D collective modes. The Landau damping of transverse collective modes is
investigated as a function of temperature. At low temperatures, the damping
rate due to the Landau decay mechanism is in agreement with the experimental
data for the decay of the transverse quadrupole mode, but it is too small to
explain the slow experimental decay of the transverse breathing mode. The
reason for this discrepancy is discussed.
|
0208047v1
|
2002-08-28
|
Transverse modes of a cigar-shaped Bose-Einstein condensate
|
We discuss the collective modes in a harmonically trapped, highly-elongated
Bose condensed gas. The transverse breathing mode exhibits a number of
interesting features, such as the insensitivity of the condensate mode
frequency to the interaction strength, and the closeness of the frequency to
that of the non-condensed thermal cloud in the collisionless limit. Using
finite temperature simulations, we show that these features are responsible for
the very small damping rate observed experimentally. Our results for the
temperature dependence of the damping rate and frequency shift are in excellent
agreement with experiment. We also demonstrate that the unusually small damping
rate does not arise for the $m=2$ mode or for more isotropic trap potentials,
suggesting further possible experimental tests of our theory.
|
0208567v1
|
2002-10-31
|
Stationary quantum statistics of a non-Markovian atom laser
|
We present a steady state analysis of a quantum-mechanical model of an atom
laser. A single-mode atomic trap coupled to a continuum of external modes is
driven by a saturable pumping mechanism. In the dilute flux regime, where
atom-atom interactions are negligible in the output, we have been able to solve
this model without making the Born-Markov approximation. The more exact
treatment has a different effective damping rate and occupation of the lasing
mode, as well as a shifted frequency and linewidth of the output. We examine
gravitational damping numerically, finding linewidths and frequency shifts for
a range of pumping rates. We treat mean field damping analytically, finding a
memory function for the Thomas-Fermi regime. The occupation and linewidth are
found to have a nonlinear scaling behavior which has implications for the
stability of atom lasers.
|
0210688v1
|
2003-03-23
|
Damping of micromechanical structures by paramagnetic relaxation
|
We find that the damping of micromechanical cantilevers is sensitive to the
relaxation dynamics of paramagnetic ions contained within the levers. We
measure cantilevers containing paramagnetic Mn ions as a function of
temperature, magnetic field, and the vibrational mode of the lever and find
that the levers damping is strongly enhanced by the interplay between the
motion of the lever, the ions magnetic anisotropy, and the ratio of the ions
longitudinal relaxation rate to the resonance frequency of the cantilever. This
enhancement can improve the levers ability to probe the relaxation behavior of
paramagnetic or superparamagetic systems; it may also represent a previously
unrecognized source of intrinsic dissipation in micromechanical structures.
|
0303489v1
|
2003-06-03
|
Local Relaxation and Collective Stochastic Dynamics
|
Damping and thermal fluctuations have been introduced to collective normal
modes of a magnetic system in recent modeling of dynamic thermal magnetization
processes. The connection between this collective stochastic dynamics and
physical local relaxation processes is investigated here. A system of two
coupled magnetic grains embedded in two separate oscillating thermal baths is
analyzed with no \QTR{it}{a priori} assumptions except that of a Markovian
process. It is shown explicitly that by eliminating the oscillating thermal
bath variables, collective stochastic dynamics occurs in the normal modes of
the magnetic system. The grain interactions cause local relaxation to be felt
by the collective system and the dynamic damping to reflect the system
symmetry. This form of stochastic dynamics is in contrast to a common
phenomenological approach where a thermal field is added independently to the
dynamic equations of each discretized cell or interacting grain. The dependence
of this collective stochastic dynamics on the coupling strength of the magnetic
grains and the relative local damping is discussed.
|
0306047v1
|
2003-10-09
|
Direct measurement of molecular stiffness and damping in confined water layers
|
We present {\em direct} and {\em linear} measurements of the normal stiffness
and damping of a confined, few molecule thick water layer. The measurements
were obtained by use of a small amplitude (0.36 $\textrm{\AA}$), off-resonance
Atomic Force Microscopy (AFM) technique. We measured stiffness and damping
oscillations revealing up to 7 layers separated by 2.56 $\pm$ 0.20
$\textrm{\AA}$. Relaxation times could also be calculated and were found to
indicate a significant slow-down of the dynamics of the system as the confining
separation was reduced. We found that the dynamics of the system is determined
not only by the interfacial pressure, but more significantly by solvation
effects which depend on the exact separation of tip and surface. Thus `
solidification\rq seems to not be merely a result of pressure and confinement,
but depends strongly on how commensurate the confining cavity is with the
molecule size. We were able to model the results by starting from the simple
assumption that the relaxation time depends linearly on the film stiffness.
|
0310219v1
|
2004-03-08
|
Mean-field magnetization relaxation in conducting ferromagnets
|
Collective ferromagnetic motion in a conducting medium is damped by the
transfer of the magnetic moment and energy to the itinerant carriers. We
present a calculation of the corresponding magnetization relaxation as a
linear-response problem for the carrier dynamics in the effective exchange
field of the ferromagnet. In electron systems with little intrinsic spin-orbit
interaction, a uniform magnetization motion can be formally eliminated by going
into the rotating frame of reference for the spin dynamics. The ferromagnetic
damping in this case grows linearly with the spin-flip rate when the latter is
smaller than the exchange field and is inversely proportional to the spin-flip
rate in the opposite limit. These two regimes are analogous to the
"spin-pumping" and the "breathing Fermi-surface" damping mechanisms,
respectively. In diluted ferromagnetic semiconductors, the hole-mediated
magnetization can be efficiently relaxed to the itinerant-carrier degrees of
freedom due to the strong spin-orbit interaction in the valence bands.
|
0403224v2
|
2004-04-05
|
Low-temperature specific heat of real crystals: Possibility of leading contribution of optical and short-wavelength acoustical vibrations
|
We point out that the repeatedly reported glass-like properties of
crystalline materials are not necessarily associated with localized (or
quasilocalized) excitations. In real crystals, optical and short-wavelength
acoustical vibrations remain damped due to defects down to zero temperature. If
such a damping is frequency-independent, e.g. due to planar defects or charged
defects, these optical and short-wavelength acoustical vibrations yield a
linear-in-$T$ contribution to the low-temperature specific heat of the crystal
lattices. At low enough temperatures such a contribution will prevail over that
of the long-wavelength acoustical vibrations (Debye contribution). The
crossover between the linear and the Debye regime takes place at $T^* \propto
\sqrt N$, where $N$ is the concentration of the defects responsible for the
damping. Estimates show that this crossover could be observable.
|
0404063v4
|
2004-04-20
|
Decoherence processes during active manipulation of excitonic qubits in semiconductor quantum dots
|
Using photoluminescence spectroscopy, we have investigated the nature of Rabi
oscillation damping during active manipulation of excitonic qubits in
self-assembled quantum dots. Rabi oscillations were recorded by varying the
pulse amplitude for fixed pulse durations between 4 ps and 10 ps. Up to 5
periods are visible, making it possible to quantify the excitation dependent
damping. We find that this damping is more pronounced for shorter pulse widths
and show that its origin is the non-resonant excitation of carriers in the
wetting layer, most likely involving bound-to-continuum and continuum-to-bound
transitions.
|
0404465v1
|
2004-05-02
|
Spin Dynamics and Multiple Reflections in Ferromagnetic Film in Contact with Normal Metal Layers
|
Spin dynamics of a metallic ferromagnetic film imbedded between normal metal
layers is studied using the spin-pumping theory of Tserkovnyak et al. [Phys.
Rev. Lett. 88, 117601 (2002)]. The scattering matrix for this structure is
obtained using a spin-dependent potential with quantum well in the
ferromagnetic region. Owing to multiple reflections in the well, the excess
Gilbert damping and the gyromagnetic ratio exhibit quantum oscillations as a
function of the thickness of the ferromagnetic film. The wavelength of the
oscillations is given by the depth of the quantum well. For iron film imbedded
between gold layers, the amplitude of the oscillations of the Gilbert damping
is in an order of magnitude agreement with the damping observed by Urban et al.
[Phys. Rev. Lett. 87, 217204 (2001)]. The results are compared with the linear
response theory of Mills [Phys. Rev. B 68, 0144419 (2003)].
|
0405020v1
|
2004-06-18
|
Spin pumping and magnetization dynamics in ferromagnet-Luttinger liquid junctions
|
We study spin transport between a ferromagnet with time-dependent
magnetization and a conducting carbon nanotube or quantum wire, modeled as a
Luttinger liquid. The precession of the magnetization vector of the ferromagnet
due for instance to an outside applied magnetic field causes spin pumping into
an adjacent conductor. Conversely, the spin injection causes increased
magnetization damping in the ferromagnet. We find that, if the conductor
adjacent to the ferromagnet is a Luttinger liquid, spin pumping/damping is
suppressed by interactions, and the suppression has clear Luttinger liquid
power law temperature dependence. We apply our result to a few particular
setups. First we study the effective Landau-Lifshitz-Gilbert (LLG) coupled
equations for the magnetization vectors of the two ferromagnets in a FM-LL-FM
junction. Also, we compute the Gilbert damping for a FM-LL and a FM-LL-metal
junction.
|
0406437v1
|
2004-07-29
|
From subdiffusion to superdiffusion of particles on solid surfaces
|
We present a numerical and partially analytical study of classical particles
obeying a Langevin equation that describes diffusion on a surface modeled by a
two dimensional potential. The potential may be either periodic or random.
Depending on the potential and the damping, we observe superdiffusion,
large-step diffusion, diffusion, and subdiffusion. Superdiffusive behavior is
associated with low damping and is in most cases transient, albeit often long.
Subdiffusive behavior is associated with highly damped particles in random
potentials. In some cases subdiffusive behavior persists over our entire
simulation and may be characterized as metastable. In any case, we stress that
this rich variety of behaviors emerges naturally from an ordinary Langevin
equation for a system described by ordinary canonical Maxwell-Boltzmann
statistics.
|
0407781v1
|
2004-08-18
|
Theory of Magnetic Polaron
|
The concept of magnetic polaron is analysed and developed to elucidate the
nature of itinerant charge carrier states in magnetic semiconductors and
similar complex magnetic materials. By contrasting the scattering and bound
states of carriers within the $s-d$ exchange model, the nature of bound states
at finite temperatures is clarified. The free magnetic polaron at certain
conditions is realized as a bound state of the carrier (electron or hole) with
the spin wave. Quite generally, a self-consistent theory of a magnetic polaron
is formulated within a nonperturbative many-body approach, the Irreducible
Green Functions (IGF) method which is used to describe the quasiparticle
many-body dynamics at finite temperatures. Within the above many-body approach
we elaborate a self-consistent picture of dynamic behavior of two interacting
subsystems, the localized spins and the itinerant charge carriers. In
particular, we show that the relevant generalized mean fields emerges naturally
within our formalism. At the same time, the correct separation of elastic
scattering corrections permits one to consider the damping effects (inelastic
scattering corrections) in the unified and coherent fashion. The damping of
magnetic polaron state, which is quite different from the damping of the
scattering states, finds a natural interpretation within the present
self-consistent scheme.
|
0408404v2
|
2004-09-27
|
Dephasing and delay time fluctuations in the chaotic scattering of a quantum particle weakly coupled to a complicated background
|
Effect of a complicated many-body environment is analyzed on the chaotic
motion of a quantum particle in a mesoscopic ballistic structure. The dephasing
and absorption phenomena are treated on the same footing in the framework of a
schematic microscopic model. The single-particle doorway resonance states
excited in the structure via an external channel are damped not only because of
the escape onto such channels but also due to ulterior population of the
long-lived background states. The transmission through the structure is
presented as an incoherent sum of the flow formed by the interfering damped
doorway resonances and the retarded flow of the particles reemitted by the
environment. The resulting internal damping as well as the dephasing rate are
uniquely expressed in terms of the spreading width which controls the coupling
to the background. The formation of the long-lived fine-structure resonances
strongly enhances delay time fluctuations thus broadening the delay time
distribution.
|
0409690v1
|
2004-10-30
|
Dynamics of Domain Wall in a Biaxial Ferromagnet With Spin-torque
|
The dynamics of the domain wall (DW) in a biaxial ferromagnet interacting
with a spin-polarized current are described by sine-gordon (SG) equation
coupled with Gilbert damping term in this paper. Within our frame-work of this
model, we obtain a threshold of the current in the motion of a single DW with
the perturbation theory on kink soliton solution to the corresponding
ferromagnetic system, and the threshold is shown to be dependent on the Gilbert
damping term. Also, the motion properties of the DW are discussed for the zero-
and nonzero-damping cases, which shows that our theory to describe the dynamics
of the DW are self-consistent.
|
0411005v3
|
2005-01-18
|
Damping effects and the metal-insulator transition in the two-dimensional electron gas
|
The damping of single-particle degrees of freedom in strongly correlated
two-dimensional Fermi systems is analyzed. Suppression of the scattering
amplitude due to the damping effects is shown to play a key role in preserving
the validity of the Landau-Migdal quasiparticle picture in a region of a phase
transition, associated with the divergence of the quasiparticle effective mass.
The results of the analysis are applied to elucidate the behavior of the
conductivity $\sigma(T)$ of the two-dimensional dilute electron gas in the
density region where it undergoes a metal-insulator transition.
|
0501427v2
|
2005-04-17
|
Dynamics of thermoelastic thin plates: A comparison of four theories
|
Four distinct theories describing the flexural motion of thermoelastic thin
plates are compared. The theories are due to Chadwick, Lagnese and Lions,
Simmonds, and Norris. Chadwick's theory requires a 3D spatial equation for the
temperature but is considered the most accurate as the others are derivable
from it by different approximations. Attention is given to the damping of
flexural waves. Analytical and quantitative comparisons indicate that the
Lagnese and Lions model with a 2D temperature equation captures the essential
features of the thermoelastic damping, but contains systematic inaccuracies.
These are attributable to the approximation for the first moment of the
temperature used in deriving the Lagnese and Lions equation. Simmonds' model
with an explicit formula for temperature in terms of plate deflection is the
simplest of all but is accurate only at low frequency, where the damping is
linearly proportional to the frequency. It is shown that the Norris model,
which is almost as simple as Simmond's, is as accurate as the more precise but
involved theory of Chadwick.
|
0504412v1
|
2005-04-29
|
Probing temperature and damping rates in Bose-Einstein condensates using ultraslow light experiments
|
We propose a method to probe Landau and Beliaev processes in dilute trapped
atomic condensates with a multiple state structure using ultraslow light
experimental configurations. Under certain conditions, damping rates from these
collisional processes are directly proportional to the dephasing rates, making
it possible to determine damping rates through measurement of the dephasing. In
the ultraslow light systems we consider, Landau decay rates are enhanced at low
momenta, which allows one to distinguish between Landau-dominated and
Beliaev-dominated regimes at the same temperature. Furthermore, the enhancement
of Landau rates potentially provides a way to measure low temperatures ($T \ll
T_c$) in dilute condensates more accurately than current methods permit.
|
0504784v2
|
2005-05-23
|
Anharmonic vs. relaxational sound damping in glasses: I. Brillouin scattering from densified silica
|
This series discusses the origin of sound damping and dispersion in glasses.
In particular, we address the relative importance of anharmonicity versus
thermally activated relaxation. In this first article, Brillouin-scattering
measurements of permanently densified silica glass are presented. It is found
that in this case the results are compatible with a model in which damping and
dispersion are only produced by the anharmonic coupling of the sound waves with
thermally excited modes. The thermal relaxation time and the unrelaxed velocity
are estimated.
|
0505558v3
|
2005-05-23
|
Anharmonic vs. relaxational sound damping in glasses: II. Vitreous silica
|
The temperature dependence of the frequency dispersion in the sound velocity
and damping of vitreous silica is reanalyzed. Thermally activated relaxation
accounts for the sound attenuation observed above 10 K at sonic and ultrasonic
frequencies. Its extrapolation to the hypersonic regime reveals that the
anharmonic coupling to the thermal bath becomes important in
Brillouin-scattering measurements. At 35 GHz and room temperature, the damping
due to this anharmonicity is found to be nearly twice that produced by
thermally activated relaxation. The analysis also reveals a sizeable velocity
increase with temperature which is not related with sound dispersion. This
suggests that silica experiences a gradual structural change that already
starts well below room temperature.
|
0505560v2
|
2005-06-06
|
Heat Bath Approach to Landau Damping and Pomeranchuk Quantum Critical Points
|
We study the problem of the damping of collective modes close to a
Pomeranchuk quantum critical point in a Fermi liquid. In analogy with problems
in dissipative open quantum systems, we derive the Landau damping of a Fermi
liquid by integrating out a macroscopic number of degrees of freedom from a
generating functional. Being a reformulation of the linearized Boltzmann
equation this approach reproduces well-known results from the theory of Fermi
liquids. We also study the Bethe-Salpeter equations within the Landau theory
and discuss the implications of these results on quantum phase transitions of
the Pomeranchuk type and its dynamical exponent, z. We apply our results to the
electronic nematic instability and find z=3 in the collisionless limit.
|
0506146v3
|
2005-07-01
|
Measurement of Dissipation of a Three-Level rf SQUID Qubit
|
The dissipation-induced relaxation (T_1) time of a macroscopic quantum system
- a \{lambda}-type three-level rf SQUID flux qubit weakly coupled to control
and readout circuitry (CRC) - is investigated via time-domain measurement. The
measured interwell relaxation time of the qubit's first excited state,
T_1=3.45+/-0.06 \{mu}s, corresponds to an effective damping resistance of the
flux qubit R=1.6+/-0.1 M\{omega} which is much lower than the intrinsic
quasiparticle resistance of the Josephson tunnel junction. An analysis of the
system shows that although the CRC is very weakly coupled to the qubit it is
the primary source of damping. This type of damping can be significantly
reduced by the use of more sophisticated circuit design to allow coherent
manipulation of qubit states.
|
0507008v1
|
2005-09-19
|
Interaction effects on magnetooscillations in a two-dimensional electron gas
|
Motivated by recent experiments, we study the interaction corrections to the
damping of magnetooscillations in a two-dimensional electron gas (2DEG). We
identify leading contributions to the interaction-induced damping which are
induced by corrections to the effective mass and quantum scattering time. The
damping factor is calculated for Coulomb and short-range interaction in the
whole range of temperatures, from the ballistic to the diffusive regime. It is
shown that the dominant effect is that of the renormalization of the effective
electron mass due to the interplay of the interaction and impurity scattering.
The results are relevant to the analysis of experiments on magnetooscillations
(in particular, for extracting the value of the effective mass) and are
expected to be useful for understanding the physics of a high-mobility 2DEG
near the apparent metal-insulator transition.
|
0509463v2
|
2005-10-31
|
Time-Resolved Spin Torque Switching and Enhanced Damping in Py/Cu/Py Spin-Valve Nanopillars
|
We report time-resolved measurements of current-induced reversal of a free
magnetic layer in Py/Cu/Py elliptical nanopillars at temperatures T = 4.2 K to
160 K. Comparison of the data to Landau-Lifshitz-Gilbert macrospin simulations
of the free layer switching yields numerical values for the spin torque and the
Gilbert damping parameters as functions of T. The damping is strongly
T-dependent, which we attribute to the antiferromagnetic pinning behavior of a
thin permalloy oxide layer around the perimeter of the free layer. This
adventitious antiferromagnetic pinning layer can have a major impact on spin
torque phenomena.
|
0510798v2
|
2005-12-20
|
Damping of zero sound in Luttinger liquids
|
We calculate the damping gamma_q of collective density oscillations (zero
sound) in a one-dimensional Fermi gas with dimensionless forward scattering
interaction F and quadratic energy dispersion k^2 / 2 m at zero temperature.
For wave-vectors | q| /k_F small compared with F we find to leading order
gamma_q = v_F^{-1} m^{-2} Y (F) | q |^3, where v_F is the Fermi velocity, k_F
is the Fermi wave-vector, and Y (F) is proportional to F^3 for small F. We also
show that zero-sound damping leads to a finite maximum proportional to |k - k_F
|^{-2 + 2 eta} of the charge peak in the single-particle spectral function,
where eta is the anomalous dimension. Our prediction agrees with photoemission
data for the blue bronze K_{0.3}MoO_3.
|
0512494v4
|
2006-04-11
|
Damping and dispersion of oscillating modes of a multicomponent ionic mixture in a magnetic field
|
The collective-mode spectrum of a multicomponent magnetized ionic mixture for
small wave number k is studied with the use of magnetohydrodynamics and formal
kinetic theory. Apart from the usual thermal and diffusive modes, the spectrum
contains a set of four oscillating modes. By evaluating the k^2 contributions
to the eigenfrequencies, the damping and the dispersion of these oscillating
modes are determined. The long-range nature of the Coulomb interactions is
shown to imply that Burnett terms with higher-order gradients in the linear
phenomenological laws have to be taken into account in order to obtain a full
description of all damping and dispersion effects.
|
0604272v1
|
2006-07-06
|
Low energy theory of a single vortex and electronic quasiparticles in a d-wave superconductor
|
We highlight the properties of a simple model (contained in our recent work)
of the quantum dynamics of a single point vortex interacting with the nodal
fermionic quasiparticles of a d-wave superconductor. We describe the
renormalization of the vortex motion by the quasiparticles: at T=0, the
quasiparticles renormalize the vortex mass and introduce only a weak sub-Ohmic
damping. Ohmic (or `Bardeen-Stephen' damping) appears at T>0, with the damping
co-efficient vanishing ~ T^2 with a universal prefactor. Conversely, quantum
fluctuations of the vortex renormalize the quasiparticle spectrum. A point
vortex oscillating in a harmonic pinning potential has no zero-bias peak in the
electronic local density of states (LDOS), but has small satellite features at
an energy determined by the pinning potential. These are proposed as the origin
of sub-gap LDOS peaks observed in scanning tunneling microscopic studies of the
LDOS near a vortex.
|
0607137v2
|
2006-09-18
|
General Form of Magnetization Damping: Magnetization dynamics of a spin system evolving nonadiabatically and out of equilibrium
|
Using an effective Hamiltonian including the Zeeman and internal
interactions, we describe the quantum theory of magnetization dynamics when the
spin system evolves non-adiabatically and out of equilibrium. The
Lewis-Riesenfeld dynamical invariant method is employed along with the
Liouville-von Neumann equation for the density matrix. We derive a dynamical
equation for magnetization defined with respect to the density operator with a
general form of magnetization damping that involves the non-equilibrium
contribution in addition to the Landau-Lifshitz-Gilbert equation. Two special
cases of the radiation-spin interaction and the spin-spin exchange interaction
are considered. For the radiation-spin interaction, the damping term is shown
to be of the Gilbert type, while in the spin-spin exchange interaction case the
results depend on a coupled chain of correlation functions.
|
0609431v2
|
2005-08-23
|
Investigations of Process Damping Forces in Metal Cutting
|
Using finite element software developed for metal cutting by Third Wave
Systems we investigate the forces involved in chatter, a self-sustained
oscillation of the cutting tool. The phenomena is decomposed into a vibrating
tool cutting a flat surface work piece, and motionless tool cutting a work
piece with a wavy surface. While cutting the wavy surface, the shearplane was
seen to oscillate in advance of the oscillation of the depth of cut, as were
the cutting, thrust, and shear plane forces. The vibrating tool was used to
investigate process damping through the interaction of the relief face of the
tool and the workpiece. Crushing forces are isolated and compared to the
contact length between the tool and workpiece. We found that the wavelength
dependence of the forces depended on the relative size of the wavelength to the
length of the relief face of the tool. The results indicate that the damping
force from crushing will be proportional to the cutting speed for short tools,
and inversely proportional for long tools.
|
0508102v1
|
1999-09-27
|
R-Modes in Superfluid Neutron Stars
|
The analogs of r-modes in superfluid neutron stars are studied here. These
modes, which are governed primarily by the Coriolis force, are identical to
their ordinary-fluid counterparts at the lowest order in the small
angular-velocity expansion used here. The equations that determine the next
order terms are derived and solved numerically for fairly realistic superfluid
neutron-star models. The damping of these modes by superfluid ``mutual
friction'' (which vanishes at the lowest order in this expansion) is found to
have a characteristic time-scale of about 10^4 s for the m=2 r-mode in a
``typical'' superfluid neutron-star model. This time-scale is far too long to
allow mutual friction to suppress the recently discovered gravitational
radiation driven instability in the r-modes. However, the strength of the
mutual friction damping depends very sensitively on the details of the
neutron-star core superfluid. A small fraction of the presently acceptable
range of superfluid models have characteristic mutual friction damping times
that are short enough (i.e. shorter than about 5 s) to suppress the
gravitational radiation driven instability completely.
|
9909084v1
|
2001-02-08
|
Cyclotron damping and Faraday rotation of gravitational waves
|
We study the propagation of gravitational waves in a collisionless plasma
with an external magnetic field parallel to the direction of propagation. Due
to resonant interaction with the plasma particles the gravitational wave
experiences cyclotron damping or growth, the latter case being possible if the
distribution function for any of the particle species deviates from
thermodynamical equilibrium. Furthermore, we examine how the damping and
dispersion depends on temperature and on the ratio between the cyclotron- and
gravitational wave frequency. The presence of the magnetic field leads to
different dispersion relations for different polarizations, which in turn imply
Faraday rotation of gravitational waves.
|
0102031v2
|
2000-08-18
|
Fabrication Process of Rounded Damped Detuned Structure
|
Following the successful design and fabrication of Damped Detuned Structures
(DDS), the JLC/NLC linear collider project advanced to Rounded Damped Detuned
Structures (RDDS) with curved cross section of the cavity shape for increased
shunt impedance. Various advanced techniques for fabricating RDDS1 disks
comparing to those for DDS were established to satisfy the dimension accuracy
of +-1 micron over the entire surface made by ultra-precision turning. These
disks were assembled with almost the same stacking and bonding jigs and
processes as those of DDS3 assembly. In consequence, the assembly showed little
disk-to-disk misalignment within 1 micron before and after the process. Though,
it had 200 micron smooth bowing, which was subsequently corrected as DDS3, and
flares at both ends.
|
0008034v1
|
2000-08-18
|
Meeting Tight Frequency Requirement of Rounded Damped Detuned Structure
|
Following successful design and fabrication of damped detuned structures, the
R&D for the accelerating structures of the NLC/JLC linear collider project
proceeded to studies of Rounded Damped Detuned Structure with curved cross
section of the cavity shape for increased shunt impedance. The important
features of the structure are the accurately tuned accelerating mode frequency
and the distribution of the first dipole modes smooth and close to the design
distribution. These requirements were met based on the high-accuracy diamond
turning with its capability to realize the periphery tolerance of two microns.
The lowest dipole mode frequencies scattered by 0.6 MHz RMS. The error in the
accelerating mode frequency averaged over a structure was 0.1 MHz by applying a
feed-forward method.
|
0008035v1
|
1992-03-16
|
Comment on ``Damping of energetic gluons and quarks in high-temperature QCD''
|
Burgess and Marini have recently pointed out that the leading contribution to
the damping rate of energetic gluons and quarks in the QCD plasma, given by
$\gamma=c g^2\ln(1/g)T$, can be obtained by simple arguments obviating the need
of a fully resummed perturbation theory as developed by Braaten and Pisarski.
Their calculation confirmed previous results of Braaten and Pisarski, but
contradicted those proposed by Lebedev and Smilga. While agreeing with the
general considerations made by Burgess and Marini, I correct their actual
calculation of the damping rates, which is based on a wrong expression for the
static limit of the resummed gluon propagator. The effect of this, however,
turns out to be cancelled fortuitously by another mistake, so as to leave all
of their conclusions unchanged. I also verify the gauge independence of the
results, which in the corrected calculation arises in a less obvious manner.
|
9203211v1
|
1995-02-16
|
The Infrared Sensitivity of Screening and Damping in a Quark-Gluon Plasma
|
All the next-to-leading order contributions to the quasi-particle dispersion
laws of a quark-gluon plasma which due to infrared singularities are sensitive
to the magnetic-mass scale are calculated using Braaten-Pisarski resummation.
These relative-order-$g\ln(g)$ corrections are shown here to generally
contribute to the dynamical screening of gluonic fields with frequencies below
the plasma frequency as well as to the damping of propagating gluonic and
fermionic quasi-particles. In the limit of vanishing wave-vector the infrared
singularities disappear, but in a way that raises the possibility for formally
higher orders of the Braaten-Pisarski scheme to equally contribute at
next-to-leading order when the wave-vector is of the order of or less than the
magnetic-mass scale. This is argued to be a problem in particular for the
fermionic damping rate.
|
9502324v1
|
1997-10-30
|
Damping rate for transverse gluons with finite soft momentum in hot QCD
|
We calculate the damping rate for transverse gluons with {\nineti finite}
soft momentum to leading order in perturbative hot QCD. The internal momenta of
the one-loop contributing diagrams are soft. This means we have to use
effective vertices and propagators which incorporate the so-called hard thermal
loops. We expand the damping rate in powers of the incoming momentum and argue
that the series ought to converge within a finite radius of convergence. We
contrast such a behavior with the one obtained from a previous calculation that
produced a logarithmic behavior, a calculation based on letting the gluon
momentum come from the hard limit down towards the interior of the soft region.
This difference in behavior may point to interesting physics around some
`critical' region.
|
9710549v2
|
1998-07-21
|
An infrared singularity in the damping rate for longitudinal gluons in hot QCD
|
We calculate $\gamma_l(0)$, the damping rate for longitudinal on-shell gluons
with zero momentum in hot QCD using the hard-thermal-loop (htl) scheme. We find
it to be divergent in the infrared, which means that in this scheme
$\gamma_l(0)$ is different from $\gamma_t(0)$, the corresponding damping rate
for transverse gluons which is known to be finite. This result suggests that
the htl scheme is infrared sensitive and thus may need to be improved upon in
this sector. We discuss this issue after we present our calculation.
|
9807439v2
|
1998-09-25
|
Damping rates in the MSSM and electroweak baryogenesis
|
We present an analysis of the thermalization rate of Higgsinos and winos
based on the imaginary part of the two-point Green function in the {\it
unbroken} phase of the MSSM. We use improved propagators including resummation
of hard thermal loops and the thermalization rate is computed at the one-loop
level in the high temperature approximation. We find that the damping is
typically dominated by scattering with gauge bosons, resulting in a damping
rate of about $\gamma_{\Ht}\simeq 0.025T$, $\gamma_{\Wt}\simeq 0.065T$. The
contribution from scattering with scalars is relatively small. Implications for
baryogenesis are also discussed.
|
9809529v1
|
2006-10-27
|
The soft fermion dispersion relation at next-to-leading order in hot QED
|
We study next-to-leading order contributions to the soft static fermion
dispersion relation in hot QED. We derive an expression for the complete
next-to-leading order contribution to the retarded fermion self-energy. The
real and imaginary parts of this expression give the next-to-leading order
contributions to the mass and damping rate of the fermionic quasi-particle.
Many of the terms that are expected to contribute according to the traditional
power counting argument are actually subleading. We explain why the power
counting method over estimates the contribution from these terms. For the
electron damping rate in QED we obtain: $\gamma_{QED} = \frac{e^2
T}{4\pi}(2.70)$. We check our method by calculating the next-to-leading order
contribution to the damping rate for the case of QCD with two flavours and
three coulours. Our result agrees with the result obtained previously in the
literature. The numerical evaluation of the nlo contribution to the mass is
left to a future publication.
|
0610372v1
|
2007-03-26
|
Preheating and Affleck-Dine leptogenesis after thermal inflation
|
Previously, we proposed a model of low energy Affleck-Dine leptogenesis in
the context of thermal inflation. The lepton asymmetry is generated at the end
of thermal inflation, which occurs at a relatively low energy scale with the
Hubble parameter somewhere in the range $1 \keV \lesssim H \lesssim 1 \MeV$.
Thus Hubble damping will be ineffective in bringing the Affleck-Dine field into
the lepton conserving region near the origin, leaving the possibility that the
lepton number could be washed out. Previously, we suggested that preheating
could damp the amplitude of the Affleck-Dine field allowing conservation of the
lepton number. In this paper, we demonstrate numerically that preheating does
efficiently damp the amplitude of the Affleck-Dine field and that the lepton
number is conserved as the result. In addition to demonstrating a crucial
aspect of our model, it also opens the more general possibility of low energy
Affleck-Dine baryogenesis.
|
0703275v1
|
2002-08-31
|
Neutrino damping rate at finite temperature and density
|
A first principle derivation is given of the neutrino damping rate in
real-time thermal field theory. Starting from the discontinuity of the neutrino
self energy at the two loop level, the damping rate can be expressed as
integrals over space phase of amplitudes squared, weighted with statistical
factors that account for the possibility of particle absorption or emission
from the medium. Specific results for a background composed of neutrinos,
leptons, protons and neutrons are given. Additionally, for the real part of the
dispersion relation we discuss the relation between the results obtained from
the thermal field theory, and those obtained by the thermal average of the
forward scattering amplitude.
|
0209006v1
|
2004-10-20
|
Ergodicity for the weakly damped stochastic non-linear Schrödinger equations
|
We study a damped stochastic non-linear Schr\"{o}dinger (NLS) equation driven
by an additive noise. It is white in time and smooth in space. Using a coupling
method, we establish convergence of the Markovian transition semi-group toward
a unique invariant probability measure. This kind of method was originally
developped to prove exponential mixing for strongly dissipative equations such
as the Navier-Stokes equations. We consider here a weakly dissipative equation,
the damped nonlinear Schr\"{o}dinger equation in the one dimensional cubic
case. We prove that the mixing property holds and that the rate of convergence
to equilibrium is at least polynomial of any power.
|
0410443v2
|
2006-07-30
|
Non-autonomous dynamics of wave equations with nonlinear damping and critical nonlinearity
|
The authors consider non-autonomous dynamical behavior of wave-type
evolutionary equations with nonlinear damping and critical nonlinearity. These
type of waves equations are formulated as non-autonomous dynamical systems
(namely, cocycles). A sufficient and necessary condition for the existence of
pullback attractors is established for norm-to-weak continuous non-autonomous
dynamical systems, in terms of pullback asymptotic compactness or pullback
$\kappa-$contraction criteria. A technical method for verifying pullback
asymptotic compactness, via contractive functions, is devised. These results
are then applied to the wave-type evolutionary equations with nonlinear damping
and critical nonlinearity, to obtain the existence of pullback attractors. The
required pullback asymptotic compactness for the existence of pullback
attractors is fulfilled by some new a priori estimates for concrete wave type
equations arising from applications. Moreover, the pullback
$\kappa-$contraction criterion for the existence of pullback attractors is of
independent interest.
|
0607774v3
|
2000-09-28
|
Quantization of Damped Harmonic Oscillator, Thermal Field Theories and q-Groups
|
We study the canonical quantization of the damped harmonic oscillator by
resorting to the realization of the q-deformation of the Weyl-Heisenberg
algebra (q-WH) in terms of finite difference operators. We relate the damped
oscillator hamiltonian to the q-WH algebra and to the squeezing generator of
coherent states theory. We also show that the q-WH algebra is the natural
candidate to study thermal field theory. The well known splitting, in the
infinite volume limit, of the space of physical states into unitarily
inequivalent representations of the canonical commutation relations is briefly
commented upon in relation with the von Neumann theorem in quantum mechanics
and with q-WH algebra.
|
0009036v1
|
2001-11-14
|
Soliton-radiation coupling in the parametrically driven, damped nonlinear Schrödinger equation
|
We use the Riemann-Hilbert problem to study the interaction of the soliton
with radiation in the parametrically driven, damped nonlinear Schr\"odinger
equation. The analysis is reduced to the study of a finite-dimensional
dynamical system for the amplitude and phase of the soliton and the complex
amplitude of the long-wavelength radiation. In contrast to previously utilised
Inverse Scattering-based perturbation techniques, our approach is valid for
arbitrarily large driving strengths and damping coefficients. We show that,
contrary to suggestions made in literature, the complexity observed in the
soliton's dynamics cannot be accounted for just by its coupling to the
long-wavelength radiation.
|
0111034v1
|
2005-10-24
|
Stability of a nonlinear oscillator with random damping
|
A noisy damping parameter in the equation of motion of a nonlinear oscillator
renders the fixed point of the system unstable when the amplitude of the noise
is sufficiently large. However, the stability diagram of the system can not be
predicted from the analysis of the moments of the linearized equation. In the
case of a white noise, an exact formula for the Lyapunov exponent of the system
is derived. We then calculate the critical damping for which the {\em
nonlinear} system becomes unstable. We also characterize the intermittent
structure of the bifurcated state above threshold and address the effect of
temporal correlations of the noise by considering an Ornstein-Uhlenbeck noise.
|
0510063v1
|
2006-10-20
|
Vibration of Generalized Double Well Oscillators
|
We have applied the Melnikov criterion to examine a global homoclinic
bifurcation and transition to chaos in a case of a double well dynamical system
with a nonlinear fractional damping term and external excitation. The usual
double well Duffing potential having a negative square term and positive
quartic term has been generalized to a double well potential with a negative
square term and a positive one with an arbitrary real exponent $q > 2$. We have
also used a fractional damping term with an arbitrary power $p$ applied to
velocity which enables one to cover a wide range of realistic damping factors:
from dry friction $p \to 0$ to turbulent resistance phenomena $p=2$.
Using perturbation methods we have found a critical forcing amplitude $\mu_c$
above which the system may behave chaotically. Our results show that the
vibrating system is less stable in transition to chaos for smaller $p$
satisfying an exponential scaling low. The critical amplitude $\mu_c$ as an
exponential function of $p$.
The analytical results have been illustrated by numerical simulations using
standard nonlinear tools such as
Poincare maps and the maximal Lyapunov exponent. As usual for chosen system
parameters we have identified a chaotic motion above the critical Melnikov
amplitude $\mu_c$.
|
0610052v1
|
1998-06-18
|
Relativity Damps OPEP in Nuclear Matter
|
Using a relativistic Dirac-Brueckner analysis the OPEP contribution to the
ground state energy of nuclear matter is studied. In the study the pion is
derivative-coupled. We find that the role of the tensor force in the saturation
mechanism is substantially reduced compared to its dominant role in a usual
nonrelativistic treatment. We show that the damping of derivative-coupled OPEP
is actually due to the decrease of $M^*/M$ with increasing density. We point
out that if derivative-coupled OPEP is the preferred form of nuclear effective
lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking
the notion of $M^*$ it cannot replicate the damping. We suggest an examination
of the feasibility of using pseudoscalar coupled $\pi$N interaction before
reaching a final conclusion about nonrelativistic treatment of nuclear matter.
|
9806054v1
|
1999-07-05
|
Damping of IVGDR - Fermi-liquid or Fermi-gas ?
|
Collisional relaxation rates of collective modes in nuclei are calculated
using the Levinson equation for the reduced density matrix with a memory
dependent collision term. Linearizing the collision integral two contribution
have to be distinguished, the one from the quasiparticle energy and the one
from occupation factors. The first one yields the known Landau formula of zero
sound damping and the second one leads to the Fermi gas model of Ref.1 with the
additional factor 3 in front of the frequencies. Adding both contribution we
obtain a final relaxation rate for the Fermi liquid model. Calculations of the
temperature dependence of the damping rates and of the shape evolution of IVGDR
are in good agreement with the experiment and show only minor differences
between both models.
|
9907012v1
|
2001-01-08
|
Collisional Damping of Giant Monopole and Quadrupole Resonances
|
Collisional damping widths of giant monopole and quadrupole excitations for
$^{120}$Sn and $^{208}$Pb at zero and finite temperatures are calculated within
Thomas-Fermi approximation by employing the microscopic in-medium
cross-sections of Li and Machleidt and the phenomenological Skyrme and Gogny
forces, and are compared with each other. The results for the collisional
widths of giant monopole and quadrupole vibrations at zero temperature as a
function of the mass number show that the collisional damping of giant monopole
vibrations accounts for about 30-40% of the observed widths at zero
temperature, while for giant quadrupole vibrations it accounts for only 20-30%
of the observed widths of zero temperature.
|
0101016v1
|
1996-12-08
|
Towards a Simple Model of Compressible Alfvenic Turbulence
|
A simple model collisionless, dissipative, compressible MHD (Alfvenic)
turbulence in a magnetized system is investigated. In contrast to more familiar
paradigms of turbulence, dissipation arises from Landau damping, enters via
nonlinearity, and is distributed over all scales. The theory predicts that two
different regimes or phases of turbulence are possible, depending on the ratio
of steepening to damping coefficient (m_1/m_2). For strong damping
(|m_1/m_2|<1), a regime of smooth, hydrodynamic turbulence is predicted. For
|m_1/m_2|>1, steady state turbulence does not exist in the hydrodynamic limit.
Rather, spikey, small scale structure is predicted.
|
9612005v2
|
1998-10-01
|
Mode-coupling and nonlinear Landau damping effects in auroral Farley-Buneman turbulence
|
The fundamental problem of Farley-Buneman turbulence in the auroral
$E$-region has been discussed and debated extensively in the past two decades.
In the present paper we intend to clarify the different steps that the auroral
$E$-region plasma has to undergo before reaching a steady state. The
mode-coupling calculation, for Farley-Buneman turbulence, is developed in order
to place it in perspective and to estimate its magnitude relative to the
anomalous effects which arise through the nonlinear wave-particle interaction.
This nonlinear effect, known as nonlinear ``Landau damping'' is due to the
coupling of waves which produces other waves which in turn lose energy to the
bulk of the particles by Landau damping. This leads to a decay of the wave
energy and consequently a heating of the plasma. An equation governing the
evolution of the field spectrum is derived and a physical interpration for each
of its terms is provided.
|
9810062v1
|
2000-08-20
|
Fabrication and Tolerance Issues and their Influence on Multi-Bunch Bbu and Emittance Dilution in the Construction of X-Band RDDS Linacs for the NLC
|
The main linacs of the Next Linear Collider (NLC) will contain several
thousand X-band RDDS (Rounded Damped Detuned Structures). The transverse
wakefield in the structures is reduced by detuning the modal frequencies such
that they destructively interfere and by four damping manifolds per structure
which provide weak damping. Errors in the fabrication of the individual cells
and in the alignment of the cells will reduce the cancellation of the modes.
Here, we calculate the tolerances on random errors in the synchronous
frequencies of the cells and the cell-to-cell alignment.
|
0008198v1
|
2003-09-17
|
A New Damping Mechanism in Non-linear Bubble Dynamics
|
Non-linear equations of radial motion of a gas bubble in a compressible
viscous liquid have been modified considering effects of viscosity and
compressibility more complete than all previous works. A new set of equations
has been derived including new terms resulted from consideration of the
viscosity and compressibility not only at the bubble interface, but also in the
bulk of liquid. The new equations are two non-linear coupled equations, which
can not be merged into one equation unlike all previously derived equations.
Numerical calculations have been performed considering effects of heat and mass
transfer at the bubble interface. The results indicate that the new terms
exhibit an important damping role at the collapse, so that their consideration
dramatically weakens the bubble rebounds after the collapse. Dependence of this
new damping mechanism to amplitude and frequency of the deriving pressure has
been investigated.
|
0309080v1
|
2003-11-26
|
Eigenvector Expansion and Petermann Factor for Ohmically Damped Oscillators
|
Correlation functions $C(t) \sim <\phi(t)\phi(0)>$ in ohmically damped
systems such as coupled harmonic oscillators or optical resonators can be
expressed as a single sum over modes $j$ (which are not power-orthogonal), with
each term multiplied by the Petermann factor (PF) $C_j$, leading to "excess
noise" when $|C_j| > 1$. It is shown that $|C_j| > 1$ is common rather than
exceptional, that $|C_j|$ can be large even for weak damping, and that the PF
appears in other processes as well: for example, a time-independent
perturbation $\sim\ep$ leads to a frequency shift $\sim \ep C_j$. The
coalescence of $J$ ($>1$) eigenvectors gives rise to a critical point, which
exhibits "giant excess noise" ($C_j \to \infty$). At critical points, the
divergent parts of $J$ contributions to $C(t)$ cancel, while time-independent
perturbations lead to non-analytic shifts $\sim \ep^{1/J}$.
|
0311127v2
|
2004-04-02
|
DAFNE injection system upgrade
|
High luminosity in DAFNE needs very high electron and positron currents
stored. A full energy (510 MeV) injection system composed by a full energy
electron and positron linac and an accumulator-damping ring is presently used.
The electron and positron beams, alternatively accelerated by the linac, are
injected and stacked in the accumulator with high efficiency thanks to its
large acceptance and short damping time. The damped beams are extracted and
transferred to the main ring through a long transfer line that has been built
inside already existing buildings. The refill time of the collider is limited
by the transfer line set-up change between the two different beams modes. In
this paper a transfer line modification is proposed in order to reduce the
switch time. A possible injection scheme for the main rings is also described.
|
0404010v1
|
2004-05-05
|
Langmuir wave self-focusing versus decay instability
|
Electron trapping in a finite amplitude Langmuir wave (LW) leads to a
frequency shift, \Delta\omega_{TP} < 0, and reduced Landau damping. These may
lead to modulational instability. Its growth rate and damping threshold, due to
escape of trapped electrons at rate \nu, are calculated for the first time in
the short wavelength regime. If the background plasma is in thermal
equilibrium, it is shown that this trapped particle modulational instability
(TPMI) is not possible when k \lambda_D > 0.46, while for 0.33 < k \lambda_D <
0.46, TPMI requires that the fluctuation wavevector have a component
perpendicular to k, the LW wavevector, with \lambda_D the electron Debye
length. Its nonlinear evolution leads to self-focusing. Comparison is made with
a re-evaluated LW ion acoustic decay instability (LDI): compared to classical
estimates, the new LDI threshold is lowered by primary LW \Delta\omega_{TP}
since frequency matching leads to wavenumber and hence damping reduction of the
daughter LW. For parameters estimates relevant to a recent stimulated Raman
scatter experiment (Kline et al., submitted to PRL), the LDI and TPMI
thresholds cross in the range 0.28 < k \lambda_D < 0.34, consistent with the
observed LDI regime change. However, if \nu exceeds a critical value, estimated
to be order 1% of the electron plasma frequency, then TPMI is not possible at
any wavenumber.
|
0405015v1
|
2005-06-16
|
Mesoscale Quantization and Self-Organized Stability
|
In the world of technology, one of the most important forms of friction is
that of rolling friction. Yet it is one of the least studied of all the known
forms of energy dissipation. In the present experiments we investigate the
oscillatory free-decay of a rigid cube, whose side-length is less than the
diameter of the rigid cylinder on which it rests. The resulting free-decay is
one of harmonic motion with damping. The non-dissipative character of the
oscillation yields to a linear differential equation; however, the damping is
found to involve more than a deterministic nonlinearity. Dominated by rolling
friction, the damping is sensitive to the material properties of the contact
surfaces. For `clean' surfaces of glass on glass, the decay shows features of
mesoscale quantization and self-organized stability.
|
0506143v1
|
2006-10-31
|
Ultimate parameters of the photon collider at the ILC
|
At linear colliders, the e+e- luminosity is limited by beam-collision
effects, which determine the required emittances of beams in damping rings
(DRs). While in gamma-gamma collisions at the photon collider, these effects
are absent, and so smaller emittances are desirable. In present damping rings
designs, nominal DR parameters correspond to those required for e+e-
collisions. In this note, I would like to stress once again that as soon as we
plan the photon-collider mode of ILC operation, the damping-ring emittances are
dictated by the photon-collider requirements--namely, they should be as small
as possible. This can be achieved by adding more wigglers to the DRs; the
incremental cost is easily justified by a considerable potential improvement of
the gamma-gamma luminosity. No expert analysis exists as of yet, but it seems
realistic to obtain a factor five increase of the gamma-gamma luminosity
compared to the ``nominal'' DR design.
|
0610285v1
|
2006-04-27
|
On the weak solutions of the McKendrick equation: Existence of demography cycles
|
We develop the qualitative theory of the solutions of the McKendrick partial
differential equation of population dynamics. We calculate explicitly the weak
solutions of the McKendrick equation and of the Lotka renewal integral equation
with time and age dependent birth rate. Mortality modulus is considered age
dependent. We show the existence of demography cycles. For a population with
only one reproductive age class, independently of the stability of the weak
solutions and after a transient time, the temporal evolution of the number of
individuals of a population is always modulated by a time periodic function.
The periodicity of the cycles is equal to the age of the reproductive age
class, and a population retains the memory from the initial data through the
amplitude of oscillations. For a population with a continuous distribution of
reproductive age classes, the amplitude of oscillation is damped. The
periodicity of the damped cycles is associated with the age of the first
reproductive age class. Damping increases as the dispersion of the fertility
function around the age class with maximal fertility increases. In general, the
period of the demography cycles is associated with the time that a species
takes to reach the reproductive maturity.
|
0604035v2
|
1999-03-05
|
Exact Diagonalization of Two Quantum Models for the Damped Harmonic Oscillator
|
The damped harmonic oscillator is a workhorse for the study of dissipation in
quantum mechanics. However, despite its simplicity, this system has given rise
to some approximations whose validity and relation to more refined descriptions
deserve a thorough investigation. In this work, we apply a method that allows
us to diagonalize exactly the dissipative Hamiltonians that are frequently
adopted in the literature. Using this method we derive the conditions of
validity of the rotating-wave approximation (RWA) and show how this approximate
description relates to more general ones. We also show that the existence of
dissipative coherent states is intimately related to the RWA. Finally, through
the evaluation of the dynamics of the damped oscillator, we notice an important
property of the dissipative model that has not been properly accounted for in
previous works; namely, the necessity of new constraints to the application of
the factorizable initial conditions.
|
9903022v2
|
1999-04-06
|
Nonclassical correlations in damped quantum solitons
|
Using cumulant expansion in Gaussian approximation, the internal quantum
statistics of damped soliton-like pulses in Kerr media are studied numerically,
considering both narrow and finite bandwidth spectral pulse components. It is
shown that the sub-Poissonian statistics can be enhanced, under certain
circumstances, by absorption, which damps out some destructive interferences.
Further, it is shown that both the photon-number correlation and the
correlation of the photon-number variance between different pulse components
can be highly nonclassical even for an absorbing fiber. Optimum frequency
windows are determined in order to realize strong nonclassical behavior, which
offers novel possibilities of using solitons in optical fibers as a source of
nonclassically correlated light beams.
|
9904017v2
|
1999-04-19
|
Quantum theory of fluctuations in a cold damped accelerometer
|
We present a quantum network approach to real high sensitivity measurements.
Thermal and quantum fluctuations due to active as well as passive elements are
taken into account. The method is applied to the analysis of the capacitive
accelerometer using the cold damping technique, developed for fundamental
physics in space by ONERA and the ultimate limits of this instrument are
discussed. It is confirmed in this quantum analysis that the cold damping
technique allows one to control efficiently the test mass motion without
degrading the noise level.
|
9904073v2
|
2000-07-04
|
Stochastic limit approximation for rapidly decaying systems
|
The stochastic limit approximation method for ``rapid'' decay is presented,
where the damping rate \gamma is comparable to the system frequency \Omega,
i.e., \gamma \sim \Omega, whereas the usual stochastic limit approximation is
applied only to the weak damping situation \gamma << \Omega. The key formulas
for rapid decay are very similar to those for weak damping, but the dynamics is
quite different. From a microscopic Hamiltonian, the spin-boson model, a Bloch
equation containing two independent time scales is derived. This is a useful
method to extract the minimal dissipative dynamics at high temperature kT >>
\hbar\Omega and the master equations obtained are of the Lindblad form even for
the Caldeira-Leggett model. The validity of the method is confirmed by
comparing the master equation derived through this method with the exact one.
|
0007007v2
|
2000-08-01
|
Full mechanical characterization of a cold damped mirror
|
We describe an experiment in which we have used a cold damping feedback
mechanism to reduce the thermal noise of a mirror around its mechanical
resonance frequency. The monitoring of the brownian motion of the mirror allows
to apply an additional viscous force without any thermal fluctuations
associated. This scheme has been experimentally implemented with the radiation
pressure of an intensity-modulated laser beam. Large noise reductions, up to 30
dB, have been obtained. We have also checked the mechanical response of the
cold damped mirror, and monitored its transient evolution between the cooled
regime and the room temperature equilibrium. A simple theoretical model allows
to fully explain the experimental results. A possible application to the active
cooling of the violin modes in a gravitational-wave interferometer is
discussed.
|
0008004v1
|
2003-11-05
|
Exact decoherence to pointer states in free open quantum systems is universal
|
In this paper it is shown that exact decoherence to minimal uncertainty
Gaussian pointer states is generic for free quantum particles coupled to a heat
bath. More specifically, the paper is concerned with damped free particles
linearly coupled under product initial conditions to a heat bath at arbitrary
temperature, with arbitrary coupling strength and spectral densities covering
the Ohmic, subohmic, and supraohmic regime. Then it is true that there exists a
time t_c such that for times t>t_c the state can always be exactly represented
as a mixture (convex combination) of particular minimal uncertainty Gaussian
states, regardless of and independent from the initial state. This exact
`localisation' is hence not a feature specific to high temperatures and weak
damping limit, but is rather a generic property of damped free particles.
|
0311022v3
|
2004-07-30
|
Kraus representation of damped harmonic oscillator and its application
|
By definition, the Kraus representation of a harmonic oscillator suffering
from the environment effect, modeled as the amplitude damping or the phase
damping, is directly given by a simple operator algebra solution. As examples
and applications, we first give a Kraus representation of a single qubit whose
computational basis states are defined as bosonic vacuum and single particle
number states. We further discuss the environment effect on qubits whose
computational basis states are defined as the bosonic odd and even coherent
states. The environment effects on entangled qubits defined by two different
kinds of computational basis are compared with the use of fidelity.
|
0407263v2
|
2005-01-31
|
The non dissipative damping of the Rabi oscillations as a "which-path" information
|
Rabi oscillations may be viewed as an interference phenomenon due to a
coherent superposition of different quantum paths, like in the Young's two-slit
experiment. The inclusion of the atomic external variables causes a non
dissipative damping of the Rabi oscillations. More generally, the atomic
translational dynamics induces damping in the correlation functions which
describe non classical behaviors of the field and internal atomic variables,
leading to the separability of these two subsystems. We discuss on the
possibility of interpreting this intrinsic decoherence as a "which-way"
information effect and we apply to this case a quantitative analysis of the
complementarity relation as introduced by Englert [Phys. Rev. Lett.
\textbf{77}, 2154 (1996)].
|
0501181v1
|
2006-01-12
|
Driven harmonic oscillator as a quantum simulator for open systems
|
We show theoretically how a driven harmonic oscillator can be used as a
quantum simulator for non-Markovian damped harmonic oscillator. In the general
framework, the results demonstrate the possibility to use a closed system as a
simulator for open quantum systems. The quantum simulator is based on sets of
controlled drives of the closed harmonic oscillator with appropriately tailored
electric field pulses. The non-Markovian dynamics of the damped harmonic
oscillator is obtained by using the information about the spectral density of
the open system when averaging over the drives of the closed oscillator. We
consider single trapped ions as a specific physical implementation of the
simulator, and we show how the simulator approach reveals new physical insight
into the open system dynamics, e.g. the characteristic quantum mechanical
non-Markovian oscillatory behavior of the energy of the damped oscillator,
usually obtained by the non-Lindblad-type master equation, can have a simple
semiclassical interpretation.
|
0601081v2
|
2007-05-05
|
Damped Corrections to Inflationary Spectra from a Fluctuating Cutoff
|
We reconsider trans-Planckian corrections to inflationary spectra by taking
into account a physical effect which has been overlooked and which could have
important consequences. We assume that the short length scale characterizing
the new physics is endowed with a finite width, the origin of which could be
found in quantum gravity. As a result, the leading corrections responsible for
superimposed osillations in the CMB temperature anisotropies are generically
damped by the blurring of the UV scale. To determine the observational
ramifications of this damping, we compare it to that which effectively occurs
when computing the angular power spectrum of temperature anisotropies. The
former gives an overall change of the oscillation amplitudes whereas the latter
depends on the angular scale. Therefore, in principle they could be
distinguished. In any case, the observation of superimposed oscillations would
place tight constraint on the variance of the UV cutoff.
|
0705.0747v1
|
2007-05-10
|
Effective temperature and Gilbert damping of a current-driven localized spin
|
Starting from a model that consists of a semiclassical spin coupled to two
leads we present a microscopic derivation of the Langevin equation for the
direction of the spin. For slowly-changing direction it takes on the form of
the stochastic Landau-Lifschitz-Gilbert equation. We give expressions for the
Gilbert damping parameter and the strength of the fluctuations, including their
bias-voltage dependence. At nonzero bias-voltage the fluctuations and damping
are not related by the fluctuation-dissipation theorem. We find, however, that
in the low-frequency limit it is possible to introduce a voltage-dependent
effective temperature that characterizes the fluctuations in the direction of
the spin, and its transport-steady-state probability distribution function.
|
0705.1432v3
|
2007-05-10
|
Magnetization oscillations induced by a spin-polarized current in a point-contact geometry: mode hopping and non-linear damping effects
|
In this paper we study magnetization excitations induced in a thin extended
film by a spin-polarized dc-current injected through a point contact in the
current-perpendicular-to-plane (CPP) geometry. Using full-scale micromagnetic
simulations, we demonstrate that in addition to the oscillations of the
propagating wave type, there exist also two localized oscillation modes. The
first localized mode has a relatively homogeneous magnetization structure of
its kernel and corresponds to the so called 'bullet' predicted analytically by
Slavin and Tiberkevich (Phys. Rev. Lett., 95 (2005) 237201). Magnetization
pattern of the second localized mode kernel is highly inhomogeneous, leading to
a much smaller power of magnetoresistance oscillations caused by this mode. We
have also studied the influence of a non-linear damping for this system and
have found the following main qualitative effects: (i) the appearance of
frequency jumps within the existence region of the propagating wave mode and
(ii) the narrowing of the current region where the 'bullet' mode exists, until
this mode completely disappears for a sufficiently strong non-linear damping.
|
0705.1515v1
|
2007-05-27
|
Amplitude Damping for single-qubit System with single-qubit mixed-state Environment
|
We study a generalized amplitude damping channel when environment is
initially in the single-qubit mixed state. Representing the affine
transformation of the generalized amplitude damping by a three-dimensional
volume, we plot explicitly the volume occupied by the channels simulatable by a
single-qubit mixed-state environment. As expected, this volume is embedded in
the total volume by the channels which is simulated by two-qubit enviroment.
The volume ratio is approximately 0.08 which is much smaller than 3/8, the
volume ratio for generalized depolarizing channels.
|
0705.3952v3
|
2007-06-08
|
Kinetic-Ion Simulations Addressing Whether Ion Trapping Inflates Stimulated Brillouin Backscattering Reflectivities
|
An investigation of the possible inflation of stimulated Brillouin
backscattering (SBS) due to ion kinetic effects is presented using
electromagnetic particle simulations and integrations of three-wave
coupled-mode equations with linear and nonlinear models of the nonlinear ion
physics. Electrostatic simulations of linear ion Landau damping in an ion
acoustic wave, nonlinear reduction of damping due to ion trapping, and
nonlinear frequency shifts due to ion trapping establish a baseline for
modeling the electromagnetic SBS simulations. Systematic scans of the laser
intensity have been undertaken with both one-dimensional particle simulations
and coupled-mode-equations integrations, and two values of the electron-to-ion
temperature ratio (to vary the linear ion Landau damping) are considered. Three
of the four intensity scans have evidence of SBS inflation as determined by
observing more reflectivity in the particle simulations than in the
corresponding three-wave mode-coupling integrations with a linear ion-wave
model, and the particle simulations show evidence of ion trapping.
|
0706.1236v1
|
2007-06-29
|
Driving-dependent damping of Rabi oscillations in two-level semiconductor systems
|
We propose a mechanism to explain the nature of the damping of Rabi
oscillations with increasing driving-pulse area in localized semiconductor
systems, and have suggested a general approach which describes a coherently
driven two-level system interacting with a dephasing reservoir. Present
calculations show that the non-Markovian character of the reservoir leads to
the dependence of the dephasing rate on the driving-field intensity, as
observed experimentally. Moreover, we have shown that the damping of Rabi
oscillations might occur as a result of different dephasing mechanisms for both
stationary and non-stationary effects due to coupling to the environment.
Present calculated results are found in quite good agreement with available
experimental measurements.
|
0706.4372v1
|
2007-08-06
|
Collisionsless amplifying of longitudinal electron waves in two-stream plasma
|
To better understanding the principal features of collisionless
damping/growing plasma waves we have implemented a demonstrative calculation
for the simplest cases of electron waves in two-stream plasmas with the
delta-function type electron velocity distribution function of each of the
streams with velocities v(1) and v(2). The traditional dispersion equation is
reduced to an algebraic 4th order equation, for which numerical solutions are
presented for a variant of equal stream densities. In the case of uniform
half-infinite slab one finds two dominant type solutions: non-damping forward
waves and forward complex conjugated exponentially both damping and growing
waves. Beside it in this case there is no necessity of calculation any
logarithmically divergent indefinite integrals. The possibility of wave
amplifying might be useful in practical applications.
|
0708.0767v1
|
2007-08-09
|
The Highly Damped Quasinormal Modes of Extremal Reissner-Nordström and Reissner-Nordström-de Sitter Black Holes
|
We analyze in detail the highly damped quasinormal modes of $D$-dimensional
extremal Reissner-Nordstr$\ddot{\rm{o}}$m and
Reissner-Nordstr$\ddot{\rm{o}}$m-de Sitter black holes. We only consider the
extremal case where the event horizon and the Cauchy inner horizon coincide. We
show that, even though the topology of the Stokes/anti-Stokes lines in the
extremal case is different than the non-extremal case, the highly damped
quasinormal mode frequencies of extremal black holes match exactly with the
extremal limit of the non-extremal black hole quasinormal mode frequencies.
|
0708.1333v2
|
2007-08-28
|
Resonantly damped surface and body MHD waves in a solar coronal slab with oblique propagation
|
The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a
zero-$\beta$ configuration and for parallel propagation of waves does not allow
the existence of surface waves. When oblique propagation of perturbations is
considered both surface and body waves are able to propagate. When the
perpendicular wave number is larger than a certain value, the body kink mode
becomes a surface wave. In addition, a sausage surface mode is found below the
internal cut-off frequency. When non-uniformity in the equilibrium is included,
surface and body modes are damped due to resonant absorption. In this paper,
first, a normal-mode analysis is performed and the period, the damping rate,
and the spatial structure of eigenfunctions are obtained. Then, the
time-dependent problem is solved, and the conditions under which one or the
other type of mode is excited are investigated.
|
0708.3783v1
|
2007-09-11
|
Teleportation of qubit states through dissipative channels: Conditions for surpassing the no-cloning limit
|
We investigate quantum teleportation through dissipative channels and
calculate teleportation fidelity as a function of damping rates. It is found
that the average fidelity of teleportation and the range of states to be
teleported depend on the type and rate of the damping in the channel. Using the
fully entangled fraction, we derive two bounds on the damping rates of the
channels: one is to beat the classical limit and the second is to guarantee the
non-existence of any other copy with better fidelity. Effect of the initially
distributed maximally entangled state on the process is presented; and the
concurrence and the fully entangled fraction of the shared states are
discussed. We intend to show that prior information on the dissipative channel
and the range of qubit states to be teleported is helpful for the evaluation of
the success of teleportation, where success is defined as surpassing the
fidelity limit imposed by the fidelity of 1-to-2 optimal cloning machine for
the specific range of qubits.
|
0709.1662v1
|
2007-10-03
|
Global stability of travelling fronts for a damped wave equation with bistable nonlinearity
|
We consider the damped wave equation \alpha u_tt + u_t = u_xx - V'(u) on the
whole real line, where V is a bistable potential. This equation has travelling
front solutions of the form u(x,t) = h(x-st) which describe a moving interface
between two different steady states of the system, one of which being the
global minimum of V. We show that, if the initial data are sufficiently close
to the profile of a front for large |x|, the solution of the damped wave
equation converges uniformly on R to a travelling front as t goes to plus
infinity. The proof of this global stability result is inspired by a recent
work of E. Risler and relies on the fact that our system has a Lyapunov
function in any Galilean frame.
|
0710.0794v1
|
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