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2012-02-14
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The kinetic temperature in a damped Lyman-alpha absorption system in Q2206-199 - an example of the warm neutral medium
|
By comparing the widths of absorption lines from OI, SiII and FeII in the
redshift z=2.076 single-component damped Lyman alpha absorption system in the
spectrum of Q2206-199 we establish that these absorption lines arise in Warm
Neutral Medium gas at ~12000 +/- 3000K. This is consistent with thermal
equilibrium model estimates of ~ 8000K for the Warm Neutral Medium in galaxies,
but not with the presence of a significant cold component. It is also
consistent with, but not required by, the absence of CII* fine structure
absorption in this system. Some possible implications concerning abundance
estimates in narrow-line WNM absorbers are discussed.
|
1202.3012v1
|
2012-02-23
|
Eigenmodes of the damped wave equation and small hyperbolic subsets
|
We study stationary solutions of the damped wave equation on a compact and
smooth Riemannian manifold without boundary. In the high frequency limit, we
prove that a sequence of $\beta$-damped stationary solutions cannot be
completely concentrated in small neighborhoods of a small fixed hyperbolic
subset made of $\beta$-damped trajectories of the geodesic flow. The article
also includes an appendix (by S. Nonnenmacher and the author) where we
establish the existence of an inverse logarithmic strip without eigenvalues
below the real axis, under a pressure condition on the set of undamped
trajectories.
|
1202.5123v3
|
2012-02-25
|
Fractional Order Phase Shaper Design with Routh's Criterion for Iso-damped Control System
|
Phase curve of an open loop system is flat in nature if the derivative of
phase with respect to frequency is zero. With a flat phase curve, the
corresponding closed-loop system exhibits an iso-damped property i.e. maintains
constant overshoot with the change of gain and with other parametric
variations. In recent past application, fractional order (FO) phase shapers
have been proposed by contemporary researchers to achieve enhanced parametric
robustness. In this paper, a simple Routh tabulation based methodology is
proposed to design an appropriate FO phase shaper to achieve phase flattening
in a control loop, comprising a system, controlled by a classical PID
controller. The method is demonstrated using MATLAB simulation of a second
order DC motor plant and also a first order with time delay system.
|
1202.5667v1
|
2012-03-04
|
Dissipation effects in random transverse-field Ising chains
|
We study the effects of Ohmic, super-Ohmic, and sub-Ohmic dissipation on the
zero-temperature quantum phase transition in the random transverse-field Ising
chain by means of an (asymptotically exact) analytical strong-disorder
renormalization-group approach. We find that Ohmic damping destabilizes the
infinite-randomness critical point and the associated quantum Griffiths
singularities of the dissipationless system. The quantum dynamics of large
magnetic clusters freezes completely which destroys the sharp phase transition
by smearing. The effects of sub-Ohmic dissipation are similar and also lead to
a smeared transition. In contrast, super-Ohmic damping is an irrelevant
perturbation; the critical behavior is thus identical to that of the
dissipationless system. We discuss the resulting phase diagrams, the behavior
of various observables, and the implications to higher dimensions and
experiments.
|
1203.0698v2
|
2012-03-22
|
Large Amplitude Longitudinal Oscillations in a Solar Filament
|
We have developed the first self-consistent model for the observed
large-amplitude oscillations along filament axes that explains the restoring
force and damping mechanism. We have investigated the oscillations of multiple
threads formed in long, dipped flux tubes through the thermal nonequilibrium
process, and found that the oscillation properties predicted by our simulations
agree with the observed behavior. We then constructed a model for the
large-amplitude longitudinal oscillations that demonstrates that the restoring
force is the projected gravity in the tube where the threads oscillate.
Although the period is independent of the tube length and the constantly
growing mass, the motions are strongly damped by the steady accretion of mass
onto the threads by thermal nonequilibrium. The observations and our model
suggest that a nearby impulsive event drives the existing prominence threads
along their supporting tubes, away from the heating deposition site, without
destroying them. The subsequent oscillations occur because the displaced
threads reside in magnetic concavities with large radii of curvature. Our model
yields a powerful seismological method for constraining the coronal magnetic
field and radius of curvature of dips. Furthermore, these results indicate that
the magnetic structure is most consistent with the sheared-arcade model for
filament channels.
|
1203.5027v1
|
2012-03-26
|
Analysis of the Energy Decay of a Degenerated Thermoelasticity System
|
In this paper, we study a system of thermoelasticity with a degenerated
second order operator in the Heat equation. We analyze the evolution of the
energy density of a family of solutions. We consider two cases: when the set of
points where the ellipticity of the Heat operator fails is included in a
hypersurface and when it is an open set. In the first case and under special
assumptions, we prove that the evolution of the energy density is the one of a
damped wave equation: propagation along the rays of geometric optic and damping
according to a microlocal process. In the second case, we show that the energy
density propagates along rays which are distortions of the rays of geometric
optic.
|
1203.5606v1
|
2012-03-26
|
Infinite Energy Solutions for Damped Navier-Stokes Equations in R2
|
We study the so-called damped Navier-Stokes equations in the whole 2D space.
The global well-posedness, dissipativity and further regularity of weak
solutions of this problem in the uniformly-local spaces are verified based on
the further development of the weighted energy theory for the Navier-Stokes
type problems. Note that any divergent free vector field $u_0\in
L^\infty(\mathbb R^2)$ is allowed and no assumptions on the spatial decay of
solutions as $|x|\to\infty$ are posed. In addition, applying the developed
theory to the case of the classical Navier-Stokes problem in R2, we show that
the properly defined weak solution can grow at most polynomially (as a quintic
polynomial) as time goes to infinity.
|
1203.5733v2
|
2012-03-28
|
Quantum-correlating power of local quantum channels
|
Quantum correlation can be created by local operations from a classically
correlated state. We define quantum-correlating power (QCP) of a local quantum
channel as the maximum amount of quantum correlation that can be created by the
channel. The quantum correlation that we discuss in this article is defined on
the left part of the bipartite state. We prove that for any local channel, the
optimal input state, which corresponds to the maximum quantum correlation in
the output state, must be a classical-classical state. Further, the
single-qubit channels with maximum QCP can be found in the class of rank-1
channels which take their optimal input states to rank-2 quantum-classical
states. The analytic expression for QCP of single-qubit amplitude damping
channel is obtained. Super-activation property of QCP, i.e., two zero-QCP
channels can consist a positive-QCP channel, is discussed for single-qubit
phase damping channels.
|
1203.6149v1
|
2012-04-12
|
On the sizes of z>2 Damped Lyman-alpha Absorbing Galaxies
|
Recently, the number of detected galaxy counterparts of z > 2 Damped
Lyman-alpha Absorbers in QSO spectra has increased substantially so that we
today have a sample of 10 detections. M{\o}ller et al. in 2004 made the
prediction, based on a hint of a luminosity-metallicity relation for DLAs, that
HI size should increase with increasing metallicity. In this paper we
investigate the distribution of impact parameter and metallicity that would
result from the correlation between galaxy size and metallicity. We compare our
observations with simulated data sets given the relation of size and
metallicity. The observed sample presented here supports the metallicity-size
prediction: The present sample of DLA galaxies is consistent with the model
distribution. Our data also show a strong relation between impact parameter and
column density of HI. We furthermore compare the observations with several
numerical simulations and demonstrate that the observations support a scenario
where the relation between size and metallicity is driven by feedback
mechanisms controlling the star-formation efficiency and outflow of enriched
gas.
|
1204.2833v1
|
2012-04-16
|
Quasi-normal modes, area spectra and multi-horizon spacetimes
|
We suggest an interpretation for the highly damped QNM frequencies of the
spherically symmetric multi-horizon spacetimes (Reissner-Nordstrom,
Schwarzschild-deSitter, Reissner-Nordstrom-deSitter) following Maggiore's
proposal about the link between the asymptotic QNM frequencies and the black
hole thermodynamics. We show that the behavior of the asymptotic frequencies is
easy to understand if one assumes that all of the horizons have the same
equispaced area spectra. The QNM analysis is then consistent with the choice of
the area spectra to be the one originally proposed for the black hole's horizon
by Bekenstein: A=8\pi n (in Planck units). The interpretation of the highly
damped QNM frequencies in the multi-horizon case is based on the similar
grounds as in the single horizon (Schwarzschild) case, but it has some new
features that are discussed in the paper.
|
1204.3566v2
|
2012-05-03
|
Explicit local time-stepping methods for time-dependent wave propagation
|
Semi-discrete Galerkin formulations of transient wave equations, either with
conforming or discontinuous Galerkin finite element discretizations, typically
lead to large systems of ordinary differential equations. When explicit time
integration is used, the time-step is constrained by the smallest elements in
the mesh for numerical stability, possibly a high price to pay. To overcome
that overly restrictive stability constraint on the time-step, yet without
resorting to implicit methods, explicit local time-stepping schemes (LTS) are
presented here for transient wave equations either with or without damping. In
the undamped case, leap-frog based LTS methods lead to high-order explicit LTS
schemes, which conserve the energy. In the damped case, when energy is no
longer conserved, Adams-Bashforth based LTS methods also lead to explicit LTS
schemes of arbitrarily high accuracy. When combined with a finite element
discretization in space with an essentially diagonal mass matrix, the resulting
time-marching schemes are fully explicit and thus inherently parallel.
Numerical experiments with continuous and discontinuous Galerkin finite element
discretizations validate the theory and illustrate the usefulness of these
local time-stepping methods.
|
1205.0654v2
|
2012-05-15
|
Molecular vibrations-induced quantum beats in two-dimensional electronic spectroscopy
|
Quantum beats in nonlinear spectroscopy of molecular aggregates are often
attributed to electronic phenomena of excitonic systems, while nuclear degrees
of freedom are commonly included into models as overdamped oscillations of bath
constituents responsible for dephasing. However, molecular systems are coupled
to various high-frequency molecular vibrations, which can cause the spectral
beats hardly distinguishable from those created by purely electronic
coherences. Models containing damped, undamped and overdamped vibrational modes
coupled to an electronic molecular transition are discussed in this paper in
context of linear absorption and two-dimensional electronic spectroscopy.
Analysis of different types of bath models demonstrates how do vibrations map
onto two-dimensional spectra and how the damping strength of the coherent
vibrational modes can be resolved from spectroscopic signals.
|
1205.3383v2
|
2012-05-16
|
Deuterium at high-redshift: Primordial abundance in the zabs = 2.621 damped Ly-alpha system towards CTQ247
|
The detection of neutral deuterium in the low-metallicity damped
Lyman-{\alpha} system at zabs = 2.621 towards the quasar CTQ247 is reported.
Using a high signal-to-noise and high spectral resolution (R = 60000) spectrum
from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we
precisely measure the deuterium-to-oxygen ratio log N(DI)/N(OI) = 0.74+/-0.04,
as well as the overall oxygen abundance, log N(OI)/N(HI)=-5.29+/-0.10 (or
equivalently [O/H]=-1.99+/-0.10 with respect to the solar value). Assuming
uniform metallicity throughout the system, our measurement translates to (D/H)
= (2.8+0.8 -0.6)x10^-5. This ratio is consistent within errors (<0.4sigma) with
the primordial ratio, (D/H)p = (2.59+/-0.15)x10^-5, predicted by standard
Big-Bang Nucleosynthesis using the WMAP7 value of the cosmological density of
baryons (100 Omega_b h^2 = 2.249+/-0.056). The DI absorption lines are observed
to be broader than the OI absorption lines. From a consistent fit of the
profiles we derive the turbulent broadening to be 5.2 km/s and the temperature
of the gas to be T = 8800+/-1500 K, corresponding to a warm neutral medium.
|
1205.3777v1
|
2012-05-23
|
Global existence for a damped wave equation and convergence towards a solution of the Navier-Stokes problem
|
In two and three space dimensions, and under suitable assumptions on the
initial data, we show global existence for a damped wave equation which
approaches, in some sense, the Navier-Stokes problem. The proofs are based on a
refined energy method. In this paper, we improve the results in two papers by
Y. Brenier, R. Natalini and M. Puel and by M. Paicu and G. Raugel. We relax the
regularity of the initial data of the former, even though we still use energy
methods as a principal tool. Regarding the second paper, the improvement
consists in the simplicity of the proofs since we do not use any Strichartz
estimate and in requiring less regularity for the convergence to the
Navier-Stokes problem. Indeed, the convergence result we obtain is near-optimal
regularity.
|
1205.5166v2
|
2012-05-24
|
Modelling the Propagation of a Weak Fast-Mode MHD Shock Wave near a 2D Magnetic Null Point Using Nonlinear Geometrical Acoustics
|
We present the results of analytical modelling of fast-mode
magnetohydrodynamic wave propagation near a 2D magnetic null point. We consider
both a linear wave and a weak shock and analyse their behaviour in cold and
warm plasmas. We apply the nonlinear geometrical acoustics method based on the
Wentzel-Kramers-Brillouin approximation. We calculate the wave amplitude, using
the ray approximation and the laws of solitary shock wave damping. We find that
a complex caustic is formed around the null point. Plasma heating is
distributed in space and occurs at a caustic as well as near the null point due
to substantial nonlinear damping of the shock wave. The shock wave passes
through the null point even in a cold plasma. The complex shape of the wave
front can be explained by the caustic pattern.
|
1205.5327v1
|
2012-05-31
|
Quasinormal modes for the scattering on a naked Reissner-Nordstrom singularity
|
What should be the quasinormal modes associated with a spacetime that
contains a naked singularity instead of a black hole? In the present work we
address this problem by studying the scattering of scalar fields on a curved
background described by a Reissner-Nordstr\"om spacetime with $|q| > m$. We
show that there is a qualitative difference between cases with $1 < q^2/m^2
\lesssim 9/8$ and cases with $q^2/m^2 \gtrsim 9/8$. We discuss the necessary
conditions for the well-posedness of the problem, and present results for the
low damped modes in the low $l$ and large $l$ limit. We also consider the
asymptotically highly damped quasinormal modes. We present strong evidence that
such modes are absent in the case of a naked Reissner-Nordstr\"om singularity,
corroborating recent conjectures relating them to classical and quantum
properties of horizons.
|
1206.0037v3
|
2012-06-06
|
Perturbation theory for very long-range potentials
|
Systems with very long-range interactions (that decay at large distances like
$U(r)\sim r^{-l}$ with $l\le d$ where $d$ is the space dimensionality) are
difficult to study by conventional statistical mechanics perturbation methods.
Examples of these systems are gravitational and charged (non-electroneutral).
In this work we propose two alternative methodologies to avoid these
difficulties and capture some of the properties of the original potential. The
first one consists in expressing the original potential in terms of a finite
sum of hard-core Yukawa potentials. In the second one, the potential is
rewritten as a damped potential, using a damping function with a parameter that
controls the range of the interaction. These new potentials, which mimic the
original one, can now be treated by conventional statistical mechanics methods.
|
1206.2211v2
|
2012-06-10
|
Comments on "Plasma oscillations and nonextensive statistics"
|
The paper, authored by J. A. S. Lima et al, was published in Phys. Rev. E in
2000 has discussed the dispersion relation and Landau damping of Langmuir wave
in the context of the nonextensive statistics proposed by Tsallis. It has been
cited by many authors because the dispersion relation in Tsallis formalism
present a good fit to the experimental data when q<1, while the classical
result based on Maxwellian distribution only provides a crude description.
However, the results obtained in this paper are problematic. In this comments
on the paper we shall derive the correct analytic formulas both for the
dispersion relation and Landau damping in Tsallis formalism. We hope that this
comments will be useful in providing the correct results.
|
1206.2345v1
|
2012-06-25
|
Ideal MHD Ballooning modes, shear flow and the stable continuum
|
There is a well established theory of Ballooning modes in a toroidal plasma.
The cornerstone of this is a local eigenvalue lambda on each magnetic surface -
which also depends on the ballooning phase angle k. In stationary plasmas
lambda(k) is required only near its maximum, but in rotating plasmas its
average over k is required. Unfortunately in many case lambda(k) does not exist
for some range of k, because the spectrum there contains only a stable
continuum. This limits the application of the theory, and raises the important
question of whether this "stable interval" gives rise to significant damping.
This question is re-examined using a new, simplified, model - which leads to
the conclusion that there is no appreciable damping at small shear flow. In
particular, therefore, a small shear flow should not affect Ballooning mode
stability boundaries.
|
1206.5855v2
|
2012-06-26
|
A Numerical Perspective on Hartree-Fock-Bogoliubov Theory
|
The method of choice for describing attractive quantum systems is
Hartree-Fock-Bogoliubov (HFB) theory. This is a nonlinear model which allows
for the description of pairing effects, the main explanation for the
superconductivity of certain materials at very low temperature. This paper is
the first study of Hartree-Fock-Bogoliubov theory from the point of view of
numerical analysis. We start by discussing its proper discretization and then
analyze the convergence of the simple fixed point (Roothaan) algorithm.
Following works by Canc\`es, Le Bris and Levitt for electrons in atoms and
molecules, we show that this algorithm either converges to a solution of the
equation, or oscillates between two states, none of them being a solution to
the HFB equations. We also adapt the Optimal Damping Algorithm of Canc\`es and
Le Bris to the HFB setting and we analyze it. The last part of the paper is
devoted to numerical experiments. We consider a purely gravitational system and
numerically discover that pairing always occurs. We then examine a simplified
model for nucleons, with an effective interaction similar to what is often used
in nuclear physics. In both cases we discuss the importance of using a damping
algorithm.
|
1206.6081v1
|
2012-06-27
|
Dynamics of zonal flow-like structures in the edge of the TJ-II stellarator
|
The dynamics of fluctuating electric field structures in the edge of the
TJ-II stellarator, that display zonal flow-like traits, is studied. These
structures have been shown to be global and affect particle transport
dynamically [J.A. Alonso et al., Nucl. Fus. 52 063010 (2012)]. In this article
we discuss possible drive (Reynolds stress) and damping (Neoclassical
viscosity, geodesic transfer) mechanisms for the associated ExB velocity. We
show that: (a) while the observed turbulence-driven forces can provide the
necessary perpendicular acceleration, a causal relation could not be firmly
established, possibly because of the locality of the Reynolds stress
measurements, (b) the calculated neoclassical viscosity and damping times are
comparable to the observed zonal flow relaxation times, and (c) although an
accompanying density modulation is observed to be associated to the zonal flow,
it is not consistent with the excitation of pressure side-bands, like those
present in geodesic acoustic oscillations, caused by the compression of the ExB
flow field.
|
1206.6191v1
|
2012-07-13
|
Decay of capillary wave turbulence
|
We report on the observation of freely decaying capillary wave turbulence on
the surface of a fluid. The capillary wave turbulence spectrum decay is found
to be self-similar in time with the same power law exponent than the one found
in the stationary regime, in agreement with weak turbulence predictions. The
amplitude of all Fourier modes are found to decrease exponentially with time at
the same damping rate. The longest wavelengths involved in the system are shown
to be damped by viscous surface boundary layer. These long waves play the role
of an energy source during the decay that sustains nonlinear interactions to
keep capillary waves in a wave turbulent state.
|
1207.3228v1
|
2012-07-17
|
Holographic Superfluids and the Dynamics of Symmetry Breaking
|
We explore the far from equilibrium response of a holographic superfluid
using the AdS/CFT correspondence. We establish the dynamical phase diagram
corresponding to quantum quenches of the order parameter source field. We find
three distinct regimes of behaviour that are related to the spectrum of black
hole quasi-normal modes. These correspond to damped oscillations of the order
parameter, and over-damped approaches to the superfluid and normal states. The
presence of three regimes, which includes an emergent dynamical temperature
scale, is argued to occur more generally in time-reversal invariant systems
that display continuous symmetry breaking.
|
1207.4194v2
|
2012-07-18
|
Attractiveness of periodic orbits in parametrically forced systemswith time-increasing friction
|
We consider dissipative one-dimensional systems subject to a periodic force
and study numerically how a time-varying friction affects the dynamics. As a
model system, particularly suited for numerical analysis, we investigate the
driven cubic oscillator in the presence of friction. We find that, if the
damping coefficient increases in time up to a final constant value, then the
basins of attraction of the leading resonances are larger than they would have
been if the coefficient had been fixed at that value since the beginning. From
a quantitative point of view, the scenario depends both on the final value and
the growth rate of the damping coefficient. The relevance of the results for
the spin-orbit model are discussed in some detail.
|
1207.4319v1
|
2012-07-19
|
Acoustic damping and dispersion in vitreous germanium oxide
|
New Brillouin scattering measurements of velocity and attenuation of sound in
the hypersonic regime are presented. The data are analyzed together with the
literature results at sonic and ultrasonic frequencies. As usual, thermally
activated relaxation of structural entities describes the attenuation at sonic
and ultrasonic frequencies. As already shown in vitreous silica, we conclude
that the damping by network viscosity, resulting from relaxation of thermal
phonons, must be taken into account to describe the attenuation at hypersonic
frequencies. In addition, the bare velocity obtained by subtracting to the
experimental data the effect of the two above mechanisms is constant for
temperatures below 250 K, but increases almost linearly above, up to the glass
transition temperature. This might indicate the presence of a progressive local
polyamorphic transition, as already suggested for vitreous silica.
|
1207.4582v1
|
2012-07-26
|
Generic Mechanism of Optimal Energy Transfer Efficiency: A Scaling Theory of the Mean First Passage Time in Exciton Systems
|
An asymptotic scaling theory is presented using the conceptual basis of
trapping-free subspace (i.e., orthogonal subspace) to establish the generic
mechanism of optimal efficiency of excitation energy transfer (EET) in
light-harvesting systems. Analogous to Kramers' turnover in classical rate
theory, the enhanced efficiency in the weak damping limit and the suppressed
efficiency in the strong damping limit define two asymptotic scaling regimes,
which are interpolated to predict the functional form of optimal efficiency of
the trapping-free subspace. In the presence of static disorder, the scaling law
of transfer time with respect to dephasing rate changes from linear to square
root, suggesting a weaker dependence on the environment. Though formulated in
the context of EET, the analysis and conclusions apply in general to open
quantum processes, including electron transfer, fluorescence emission, and heat
conduction.
|
1207.6197v1
|
2012-07-27
|
Dissipative and Non-dissipative Single-Qubit Channels: Dynamics and Geometry
|
Single-qubit channels are studied under two broad classes: amplitude damping
channels and generalized depolarizing channels. A canonical derivation of the
Kraus representation of the former, via the Choi isomorphism is presented for
the general case of a system's interaction with a squeezed thermal bath. This
isomorphism is also used to characterize the difference in the geometry and
rank of these channel classes. Under the isomorphism, the degree of decoherence
is quantified according to the mixedness or separability of the Choi matrix.
Whereas the latter channels form a 3-simplex, the former channels do not form a
convex set as seen from an ab initio perspective. Further, where the rank of
generalized depolarizing channels can be any positive integer upto 4, that of
amplitude damping ones is either 2 or 4. Various channel performance parameters
are used to bring out the different influences of temperature and squeezing in
dissipative channels. In particular, a noise range is identified where the
distinguishability of states improves inspite of increasing decoherence due to
environmental squeezing.
|
1207.6519v1
|
2012-07-27
|
Phonon Effects on Population Inversion in Quantum Dots: Resonant, Detuned and Frequency-swept Excitations
|
The effect of acoustic phonons on different light-induced excitations of a
semiconductor quantum dot is investigated. Resonant excitation of the quantum
dot leads to Rabi oscillations, which are damped due to the phonon interaction.
When the excitation frequency is detuned, an occupation can only occur due to
phonon absorption or emission processes. For frequency-swept excitations a
population inversion is achieved through adiabatic rapid passage, but the
inversion is also damped by phonons. For all three scenarios the influence of
the phonons depends non-monotonically on the pulse area.
|
1207.6660v2
|
2012-08-08
|
Mechanism of collisionless sound damping in dilute Bose gas with condensate
|
We develop a microscopic theory of sound damping due to Landau mechanism in
dilute gas with Bose condensate. It is based on the coupled evolution equations
of the parameters describing the system. These equations have been derived in
earlier works within a microscopic approach which employs the
Peletminskii-Yatsenko reduced description method for quantum many-particle
systems and Bogoliubov model for a weakly nonideal Bose gas with a separated
condensate. The dispersion equations for sound oscillations were obtained by
linearization of the mentioned evolution equations in the collisionless
approximation. They were analyzed both analytically and numerically. The
expressions for sound speed and decrement rate were obtained in high and low
temperature limiting cases. We have shown that at low temperature the
dependence of the obtained quantities on temperature significantly differs from
those obtained by other authors in the semi-phenomenological approaches.
Possible effects connected with non-analytic temperature dependence of
dispersion characteristics of the system were also indicated.
|
1208.1653v2
|
2012-08-17
|
Detection of domain wall eigenfrequency in infinity-shaped magnetic nanostructures
|
The dynamics of a magnetic infinity-shaped nanostructure has been
experimentally studied by two different techniques such as the sinusoidal
resonance excitation and the damped short pulse excitation to measure the
eigenfrequency of domain walls. Direct observation of the magnetic domain wall
nucleation has been measured in the frequency domain. Electrical measurements
of the domain wall dynamics in the frequency domain reveal the existence of
multi-eigenmodes for large excitation amplitudes. The time-resolved
measurements show that the frequency of the damped gyration is similar to that
of the frequency domain and coexistence of spin wave excitations.
|
1208.3527v1
|
2012-08-21
|
Stress field and spin axis relaxation for inelastic triaxial ellipsoids
|
A compact formula for the stress tensor inside a self-gravitating, triaxial
ellipsoid in an arbitrary rotation state is given. It contains no singularity
in the incompressible medium limit. The stress tensor and the quality factor
model are used to derive a solution for the energy dissipation resulting in the
damping (short axis mode) or excitation (long axis) of wobbling. In the limit
of an ellipsoid of revolution, we compare our solution with earlier ones and
show that, with appropriate corrections, the differences in damping times
estimates are much smaller than it has been claimed.
This version implements corrections of misprints found in the MNRAS published
text.
|
1208.4283v2
|
2012-08-21
|
Brownian transport in corrugated channels with inertia
|
The transport of suspended Brownian particles dc-driven along corrugated
narrow channels is numerically investigated in the regime of finite damping. We
show that inertial corrections cannot be neglected as long as the width of the
channel bottlenecks is smaller than an appropriate particle diffusion length,
which depends on the the channel corrugation and the drive intensity. Being
such a diffusion length inversely proportional to the damping constant,
transport through sufficiently narrow obstructions turns out to be always
sensitive to the viscosity of the suspension fluid. The inertia corrections to
the transport quantifiers, mobility and diffusivity, markedly differ for
smoothly and sharply corrugated channels.
|
1208.4401v2
|
2012-08-22
|
On unorthodox solutions of the Bloch equations
|
A systematic, rigorous, and complete investigation of the Bloch equations in
time-harmonic driving classical field is performed. Our treatment is unique in
that it takes full advantage of the partial fraction decomposition over real
number field, which makes it possible to find and classify all analytic
solutions. Torrey's analytic solution in the form of exponentially damped
harmonic oscillations [Phys. Rev. {\bf 76}, 1059 (1949)] is found to dominate
the parameter space, which justifies its use at numerous occasions in magnetic
resonance and in quantum optics of atoms, molecules, and quantum dots. The
unorthodox solutions of the Bloch equations, which do not have the form of
exponentially damped harmonic oscillations, are confined to rather small
detunings $\delta^2\lesssim (\gamma-\gamma_t)^2/27$ and small field strengths
$\Omega^2\lesssim 8 (\gamma-\gamma_t)^2/27$, where $\gamma$ and $\gamma_t$
describe decay rates of the excited state (the total population relaxation
rate) and of the coherence, respectively. The unorthodox solutions being
readily accessible experimentally are characterized by rather featureless time
dependence.
|
1208.5736v1
|
2012-08-29
|
Optically mediated nonlinear quantum optomechanics
|
We consider theoretically the optomechanical interaction of several
mechanical modes with a single quantized cavity field mode for linear and
quadratic coupling. We focus specifically on situations where the optical
dissipation is the dominant source of damping, in which case the optical field
can be adiabatically eliminated, resulting in effective multimode interactions
between the mechanical modes. In the case of linear coupling, the coherent
contribution to the interaction can be exploited e.g. in quantum state swapping
protocols, while the incoherent part leads to significant modifications of cold
damping or amplification from the single-mode situation. Quadratic coupling can
result in a wealth of possible effective interactions including the analogs of
second-harmonic generation and four-wave mixing in nonlinear optics, with
specific forms depending sensitively on the sign of the coupling. The
cavity-mediated mechanical interaction of two modes is investigated in two
limiting cases, the resolved sideband and the Doppler regime. As an
illustrative application of the formal analysis we discuss in some detail a
two-mode system where a Bose-Einstein condensate is optomechanically linearly
coupled to the moving end mirror of a Fabry-P\'erot cavity.
|
1208.5821v1
|
2012-08-31
|
Spectrums of Black Hole in de Sitter Spacetime with Highly Damped Quasinormal Modes: High Overtone Case
|
Motivated by recent physical interpretation on quasinormal modes presented by
Maggiore, the adiabatic quantity method given by Kunstatter is used to
calculate the spectrums of a non-extremal Schwarzschild de Sitter black hole in
this paper, as well as electrically charged case. According to highly damped
Konoplya and Zhidenko's numerical observational results for high overtone
modes\cite{Konoplya}, we found that the asymptotic non-flat spacetime structure
leads two interesting facts as followings: (i) near inner event horizon, the
area and entropy spectrums, which are given by $A_{en} = 8 n_1 \pi \hbar$,
$S_{en} = 2\pi n_1\hbar$, are equally spaced accurately. (ii) However, near
outer cosmological horizon the spectrums, which are in the form of $A_{cn} = 16
n_2 \pi \hbar - \sqrt{\frac{48\pi}{\Lambda}A_{cn} - 3 A_{cn}^2}$, $S_{cn} = 4
\pi n_2 \hbar - \sqrt{\frac{3\pi}{\Lambda}A_{cn} - 3/16 A_{cn}^2}$, are not
markedly equidistant. Finally, we also discuss the electrically charged case
and find the black holes in de Sitter spacetime have similar quantization
behavior no matter with or without charge.
|
1208.6485v1
|
2012-09-10
|
Rapid ramps across the BEC-BCS crossover: a novel route to measuring the superfluid gap
|
We investigate the response of superfluid Fermi gases to rapid changes of the
three-dimensional s-wave scattering length a by solving the time-dependent
Bogoliubov-de Gennes equations. In general the magnitude of the order parameter
|\Delta| performs oscillations, which are sometimes called the "Higgs" mode,
with the angular frequency 2 \Delta_{gap}/ \hbar, where \Delta_{gap} is the gap
in the spectrum of fermionic excitations. Firstly, we excite the oscillations
with a linear ramp of 1/a and study the evolution of |\Delta|. Secondly, we
continously drive the system with a sinusoidal modulation of 1/a. In the first
case, the oscillations in |\Delta| damp according to a power law. In the second
case, the continued driving causes revivals in the oscillations. In both cases,
the excitation of the oscillations causes a reduction in the time-averaged
value of |\Delta|. We propose two experimental protocols, based around the two
approaches, to measure the frequency and damping of the oscillations, and hence
\Delta_{gap}.
|
1209.2025v1
|
2012-09-12
|
Loss of Landau Damping for Bunch Oscillations
|
Conditions for the existence, uniqueness and stability of self-consistent
bunch steady states are considered. For the existence and uniqueness problems,
simple algebraic criteria are derived for both the action and Hamiltonian
domain distributions. For the stability problem, van Kampen theory is used. The
onset of a discrete van Kampen mode means the emergence of a coherent mode
without any Landau damping; thus, even a tiny couple-bunch or multi-turn wake
is sufficient to drive the instability. The method presented here assumes an
arbitrary impedance, RF shape, and beam distribution function. Available areas
on the intensity-emittance plane are shown for resistive wall wake and single
harmonic, bunch shortening and bunch lengthening RF configurations. Thresholds
calculated for the Tevatron parameters and impedance model are in agreement
with the observations. These thresholds are found to be extremely sensitive to
the small-argument behaviour of the bunch distribution function. Accordingly, a
method to increase the LLD threshold is suggested. This article summarizes and
extends recent author's publications.
|
1209.2715v1
|
2012-09-17
|
Generalized fluctuation-dissipation relation and statistics for the equilibrium of a system with conformation dependent damping
|
Liouville's theorem, based on the Hamiltonian flow (micro-canonical ensemble)
for a many particle system, indicates that the (stationary) equilibrium
probability distribution is a function of the Hamiltonian. A canonical ensemble
corresponds to a micro-canonical one at thermodynamic limit. On the contrary,
the dynamics of a single Brownian particle (BP) being explicitly
non-Hamiltonian with a force and damping term in it and at the other extreme to
thermodynamic limit admits the Maxwell-distribution (MD) for its velocity and
Boltmann-distribution (BD) for positions (when in a potential). This is due to
the fluctuation-dissipation relation (FDR), as was first introduced by
Einstein, which forces the Maxwell distribution to the Brownian particles. For
a structureless BP, that, this theory works is an experimentally verified fact
over a century now. Considering a structured Brownian particle we will show
that the BD and MD fails to ensure equilibrium. We will derive a generalized
FDR on the basis of the demand of zero current on inhomogeneous space. Our FDR
and resulting generalized equilibrium distributions recover the standard ones
at appropriate limits.
|
1209.3654v3
|
2012-09-20
|
High Resolution BPM Upgrade for the ATF Damping Ring at KEK
|
A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility
(ATF) damping ring has been accomplished, carried out by a KEK/FNAL/SLAC
collaboration under the umbrella of the global ILC R&D effort. The upgrade
consists of a high resolution, high reproducibility read-out system, based on
analog and processing, and also implements a new automatic gain error
correction schema. The technical concept and realization as well as results of
beam studies are presented.
|
1209.4569v1
|
2012-09-23
|
Ion Landau Damping on Drift Tearing Modes
|
Kinetic treatments of drift-tearing modes that match an inner resonant layer
solution to an external MHD region solution, characterised by
$\Delta^{\prime}$, fail to properly match the ideal MHD boundary condition on
the parallel electric field, $E_{\parallel}.$ In this paper we demonstrate how
consideration of ion sound and ion Landau damping effects achieves this and
place the theory on a firm footing. As a consequence, these effects contribute
quite significantly to the critical value of $\Delta^{\prime}$ for instability
of drift-tearing modes and play a key role in determining the minimum value for
this threshold.
|
1209.5054v3
|
2012-09-26
|
Damping of giant dipole resonance in highly excited nuclei
|
The giant dipole resonance's (GDR) width and shape at finite temperature and
angular momentum are described within the phonon damping model (PDM), which
predicts an overall increase in the GDR's total width at low and moderate
temperature T, and its saturation at high T. At T< 1 MeV the GDR width remains
nearly constant because of thermal pairing. The PDM description is compared
with the experimental systematics obtained from heavy-ion fusion, inelastic
scattering of light particles on heavy targets, and alpha induced fusion
reactions, as well as with predictions by other theoretical approaches. The
results obtained within the PDM and GDR's experimental data are also employed
to predict the viscosity of hot medium and heavy nuclei.
|
1209.5820v2
|
2012-09-26
|
Inverse Energy Cascade in Forced 2D Quantum Turbulence
|
We demonstrate an inverse energy cascade in a minimal model of forced 2D
quantum vortex turbulence. We simulate the Gross-Pitaevskii equation for a
moving superfluid subject to forcing by a stationary grid of obstacle
potentials, and damping by a stationary thermal cloud. The forcing injects
large amounts of vortex energy into the system at the scale of a few healing
lengths. A regime of forcing and damping is identified where vortex energy is
efficiently transported to large length scales via an inverse energy cascade
associated with the growth of clusters of same-circulation vortices, a
Kolmogorov scaling law in the kinetic energy spectrum over a substantial
inertial range, and spectral condensation of kinetic energy at the scale of the
system size. Our results provide clear evidence that the inverse energy cascade
phenomenon, previously observed in a diverse range of classical systems, can
also occur in quantum fluids.
|
1209.5824v2
|
2012-09-27
|
Comparison of non-Markovianity criteria in a qubit system under random external fields
|
We give the map representing the evolution of a qubit under the action of
non-dissipative random external fields. From this map we construct the
corresponding master equation that in turn allows us to phenomenologically
introduce population damping of the qubit system. We then compare, in this
system, the time-regions when non-Markovianity is present on the basis of
different criteria both for the non-dissipative and dissipative case. We show
that the adopted criteria agree both in the non-dissipative case and in the
presence of population damping.
|
1209.6331v2
|
2012-10-01
|
Gravitational Coleman-Weinberg Potential and It's Finite Temperature Counterpart
|
Coleman-Weinberg (CW) phenomena for the case of gravitons minimally coupled
to massless scalar field is studied. The one loop effect completely vanishes if
there is no self interaction term present in the matter sector. The one loop
effective potential is shown to develop an instability in the form of acquiring
an imaginary part, which can be traced to the tachyonic pole in the graviton
propagator. The finite temperature counterpart of this CW potential is computed
to study the behaviour of the potential in the high and low temperature regimes
with respect to the typical energy scale of the theory. Finite temperature
contribution to the imaginary part of gravitational CW potential exhibits a
damped oscillatory behaviour; all thermal effects are damped out as the
temperature vanishes, consistent with the zero-temperature result. Possibility
of symmetry restoration at high temperature is also depicted.
|
1210.0497v4
|
2012-10-09
|
Analytic approximate seismology of propagating MHD waves in the solar corona
|
Observations show that propagating magnetohydrodynamic (MHD) waves are
ubiquitous in the solar atmosphere. The technique of MHD seismology uses the
wave observations combined with MHD wave theory to indirectly infer physical
parameters of the solar atmospheric plasma and magnetic field. Here we present
an analytical seismological inversion scheme for propagating MHD waves. This
scheme uses in a consistent manner the observational information on wavelengths
and damping lengths, along with observed values of periods or phase velocities,
and is based on approximate asymptotic expressions for the theoretical values
of wavelengths and damping lengths. The applicability of the inversion scheme
is discussed and an example is given.
|
1210.2689v1
|
2012-10-12
|
Threshold current for switching of a perpendicular magnetic layer induced by spin Hall effect
|
We theoretically investigate the switching of a perpendicular magnetic layer
by in-plane charge current due to the spin Hall effect. We find that, in the
high damping regime, the threshold switching current is independent of the
damping constant, and is almost linearly proportional to both effective
perpendicular magnetic anisotropy field and external in-plane field applied
along the current direction. We obtain an analytic expression of the threshold
current, in excellent agreement with numerical results. This expression can be
used to determine the physical quantities associated with spin Hall effect, and
to design relevant magnetic devices based on the switching of perpendicular
magnetic layers.
|
1210.3442v2
|
2012-10-12
|
Reversal of magnetization of a single-domain magnetic particle by the ac field of time-dependent frequency
|
We report numerical and analytical studies of the reversal of the magnetic
moment of a single-domain magnetic particle by a circularly polarized ac field
of time-dependent frequency. For the time-linear frequency sweep, the phase
diagrams are computed that illustrate the dependence of the reversal on the
frequency sweep rate v, the amplitude of the ac field h, the magnetic
anisotropy field d, and the damping parameter alpha. It is shown that the most
efficient magnetization reversal requires a non-linear time dependence of the
frequency, omega(t), for which an exact analytical formula is derived with
account of damping. The necessary condition of the reversal is h > alpha d.
Implementation of a small-scale magnetization reversal is proposed in which a
nanomagnet is electromagnetically coupled to two weak superconducting links
controlled by the voltage. Dynamics of such a system is analyzed with account
of the back effect of the magnet on the superconducting links.
|
1210.3530v1
|
2012-10-15
|
Symmetries of the quantum damped harmonic oscillator
|
For the non-conservative Caldirola-Kanai system, describing a quantum damped
harmonic oscillator, a couple of constant-of-motion operators generating the
Heisenberg-Weyl algebra can be found. The inclusion of the standard time
evolution generator (which is not a symmetry) as a symmetry in this algebra, in
a unitary manner, requires a non-trivial extension of this basic algebra and
hence of the physical system itself. Surprisingly, this extension leads
directly to the so-called Bateman dual system, which now includes a new
particle acting as an energy reservoir. In addition, the Caldirola-Kanai
dissipative system can be retrieved by imposing constraints. The algebra of
symmetries of the dual system is presented, as well as a quantization that
implies, in particular, a first-order Schr\"odinger equation. As opposed to
other approaches, where it is claimed that the spectrum of the Bateman
Hamiltonian is complex and discrete, we obtain that it is real and continuous,
with infinite degeneracy in all regimes.
|
1210.4058v1
|
2012-10-18
|
SDO/AIA Observations of Large-Amplitude Longitudinal Oscillations in a Solar Filament
|
We present the first \emph{Solar Dynamics Observatory}/Atmospheric Imaging
Assembly observations of the large-amplitude longitudinal (LAL) oscillations in
the south and north parts (SP and NP) of a solar filament on 2012 April 7. Both
oscillations are triggered by flare activities close to the filament. The
period varies with filamentary threads, ranging from 44 to 67 min. The
oscillations of different threads are out of phase, and their velocity
amplitudes vary from 30 to 60 km s$^{-1}$, with a maximum displacement of about
25 Mm. The oscillations of the SP repeat for about 4 cycles without any
significant damping and then a nearby C2.4 flare causes the transition from the
LAL oscillations of the filament to its later eruption. The filament eruption
is also associated with a coronal mass ejection and a B6.8 flare. However, the
oscillations of the NP damp with time and die out at last. Our observations
show that the activated part of the SP repeatedly shows a helical motion. This
indicates that the magnetic structure of the filament is possibly modified
during this process. We suggest that the restoring force is the coupling of the
magnetic tension and gravity.
|
1210.5110v1
|
2012-10-31
|
The Kerr medium as an {\sf SU(2)} system
|
The Kerr medium in the presence of damping and associated with SU(1,1)
symmetry, is solved using the techniques of Thermo field Dynamics (TFD).These
TFD techniques, well studied earlier (Chaturvedi and Srinivasan, 1991), help us
to exactly solve the Kerr medium as a spin damped system associated with SU(2)
symmetry. Using TFD, the association with SU(2) is exploited to express the
dynamics of the system as a Schrodinger-like equation, whose solution is
obtained using the appropriate disentanglement theorem. These considerations
are extended to a system with multi-mode coupled nonlinear oscillators."
|
1210.8240v1
|
2012-12-06
|
A simple and effective Verlet-type algorithm for simulating Langevin dynamics
|
We present a revision to the well known Stormer-Verlet algorithm for
simulating second order differential equations. The revision addresses the
inclusion of linear friction with associated stochastic noise, and we
analytically demonstrate that the new algorithm correctly reproduces diffusive
behavior of a particle in a flat potential. For a harmonic oscillator, our
algorithm provides the exact Boltzmann distribution for any value of damping,
frequency, and time step for both underdamped and over damped behavior within
the usual the stability limit of the Verlet algorithm. Given the structure and
simplicity of the method we conclude this approach can trivially be adapted for
contemporary applications, including molecular dynamics with extensions such as
molecular constraints.
|
1212.1244v4
|
2012-12-10
|
Shear viscosity and the r-mode instability window in superfluid neutron stars
|
We analyze how recent computations of the shear viscosity $\eta$ in the core
of superfluid neutron stars affect the r-mode instability window. We first
analyze the contribution of superfluid phonons to the viscosity, both in their
hydrodynamical and ballistic regime. We also consider the recent computation of
$\eta$ arising from the collisions of electrons with electrons and protons by
Shternin and Yakovlev, and discuss how the interactions among superfluid
phonons and electrons might contribute to the shear viscosity. For assessing
the r-mode instability window we compare the shear viscosity due to phonons in
the hydrodynamical regime with respect to the shear viscosity due to electron
collisions. Only at high temperatures the superfluid phonon contribution to
$\eta$ starts to dominate the process of r-mode damping. While our results for
the instability window are preliminary, as other dissipative processes should
be taken into account as well, they differ from previous evaluations of the
r-mode damping due to the shear viscosity in superfluid neutron stars.
|
1212.2075v2
|
2012-12-12
|
The operator sum-difference representation for quantum maps: application to the two-qubit amplitude damping channel
|
On account of the Abel-Galois no-go theorem for the algebraic solution to
quintic and higher order polynomials, the eigenvalue problem and the associated
characteristic equation for a general noise dynamics in dimension $d$ via the
Choi-Jamiolkowski approach cannot be solved in general via radicals. We provide
a way around this impasse by decomposing the Choi matrix into simpler, not
necessarily positive, Hermitian operators that are diagonalizable via radicals,
which yield a set of `positive' and `negative' Kraus operators. The price to
pay is that the sufficient number of Kraus operators is $d^4$ instead of $d^2$,
sufficient in the Kraus representation. We consider various applications of the
formalism: the Kraus repesentation of the 2-qubit amplitude damping channel,
the noise resulting from a 2-qubit system interacting dissipatively with a
vacuum bath; defining the maximally dephasing and purely dephasing components
of the channel in the new representation, and studying their entanglement
breaking and broadcast properties.
|
1212.2780v1
|
2012-12-13
|
Efficiency improvement of the frequency-domain BEM for rapid transient elastodynamic analysis
|
The frequency-domain fast boundary element method (BEM) combined with the
exponential window technique leads to an efficient yet simple method for
elastodynamic analysis. In this paper, the efficiency of this method is further
enhanced by three strategies. Firstly, we propose to use exponential window
with large damping parameter to improve the conditioning of the BEM matrices.
Secondly, the frequency domain windowing technique is introduced to alleviate
the severe Gibbs oscillations in time-domain responses caused by large damping
parameters. Thirdly, a solution extrapolation scheme is applied to obtain
better initial guesses for solving the sequential linear systems in the
frequency domain. Numerical results of three typical examples with the problem
size up to 0.7 million unknowns clearly show that the first and third
strategies can significantly reduce the computational time. The second strategy
can effectively eliminate the Gibbs oscillations and result in accurate
time-domain responses.
|
1212.3032v2
|
2012-12-16
|
Decay of the solution to the bipolar Euler-Poisson system with damping in $\mathbb{R}^3$
|
We construct the global solution to the Cauchy's problem of the bipolar
Euler-Poisson equations with damping in $\mathbb{R}^3$ when $H^3$ norm of the
initial data is small. If further, the $\dot{H}^{-s}$ norm ($0\leq s<3/2)$ or
$\dot{B}_{2,\infty}^{-s}$ norm ($0<s\leq3/2$) of the initial data is bounded,
we give the optimal decay rates of the solution. As a byproduct, the decay
results of the $L^p-L^2$ ($1\leq p\leq2$) type hold without the smallness of
the $L^p$ norm of the initial data. In particular, we deduce that
$\|\nabla^k(\rho_1-\rho_2)\|_{L^2} \sim(1+t)^{-5/4-\frac{k}{2}}$ and
$\|\nabla^k(\rho_i-\bar{\rho},u_i,\nabla\phi)\|_{L^2}
\sim(1+t)^{-3/4-\frac{k}{2}}$. We improve the decay results in Li and Yang
\cite{Li3}(\emph{J.Differential Equations} 252(2012), 768-791), where they
showed the decay rates as $\|\nabla^k(\rho_i-\bar{\rho})\|_{L^2}
\sim(1+t)^{-3/4-\frac{k}{2}}$ and $\|\nabla^k(u_i,\nabla\phi)\|_{L^2}
\sim(1+t)^{-1/4-\frac{k}{2}}$, when the $H^3\cap L^1$ norm of the initial data
is small. Our analysis is motivated by the technique developed recently in Guo
and Wang \cite{Guo}(\emph{Comm. Partial Differential Equations} 37(2012),
2165-2208) with some modifications.
|
1212.3754v2
|
2012-12-24
|
Effects of kappa distribution function on Landau damping in electrostatic Vlasov simulation
|
Effects of non-thermal high-energy electrons on Langmuir wave-particle
interaction are investigated by an initial value approach. A Vlasov-Poisson
simulation is employed which is based on the splitting scheme by Cheng and
Knorr [Cheng, C.Z. and G. Knorr, 1976: J. Comput. Phys. 22, 330-351.]. The
kappa distribution function is taken as an example of non-thermal electrons.
The modification is manifested as an increase in the Landau damping rate and a
decrease in the real frequency for a long wavelength limit. A part of the
analyses by the modified plasma dispersion function [Summers, D. and
R.M.Thorne, 1991: Phys. Fluids, B 3, 1835-1847.] is reproduced for $\kappa =
2,3$ and 6. The dispersion relation from the initial value simulation and the
plasma dispersion function compare favorably.
|
1212.5872v1
|
2012-12-26
|
Anomalous dynamic back-action in interferometers
|
We analyze the dynamic optomechanical back-action in signal-recycled
Michelson and Michelson-Sagnac interferometers that are operated off dark port.
We show that in this case --- and in contrast to the well-studied canonical
form of dynamic back-action on dark port --- optical damping in a
Michelson-Sagnac interferometer acquires a non-zero value on cavity resonance,
and additional stability/instability regions on either side of the resonance,
revealing new regimes of cooling/heating of micromechanical oscillators. In a
free-mass Michelson interferometer for a certain region of parameters we
predict a stable single-carrier optical spring (positive spring and positive
damping), which can be utilized for the reduction of quantum noise in
future-generation gravitational-wave detectors.
|
1212.6242v2
|
2013-01-01
|
A scattering approach to some aspects of the Schwarzschild Black Hole
|
In this paper, we consider a massless field, with spin j, in interaction with
a Schwarzschild black hole in four dimensions, focusing mainly our study on the
s-wave scattering. First, using a Fourier analysis, we show that one can have a
simple and natural description of the Physics near the event horizon without
using any conformal field approaches. Then, within the same "scattering
picture", we derive analytically the imaginary part of the highly damped
quasinormal complex frequencies and, as a natural consequence of our analysis,
we show that thermal effects and in particular Hawking radiation, can be
understood through the scattering of an ingoing s-wave by the non null barrier
of the Regge-Wheeler potential associated with the Schwarzschild black hole.
Finally, with the help of the well-known expression of the highly damped
quasinormal complex frequencies, we propose a heuristic extension of the
"tripled Pauli statistics" suggested by Motl, some years ago.
|
1301.0108v1
|
2013-01-02
|
Memory models of adaptive behaviour
|
Adaptive response to a varying environment is a common feature of biological
organisms. Reproducing such features in electronic systems and circuits is of
great importance for a variety of applications. Here, we consider memory models
inspired by an intriguing ability of slime molds to both memorize the period of
temperature and humidity variations, and anticipate the next variations to
come, when appropriately trained. Effective circuit models of such behavior are
designed using i) a set of LC-contours with memristive damping, and ii) a
single memcapacitive system-based adaptive contour with memristive damping. We
consider these two approaches in detail by comparing their results and
predictions. Finally, possible biological experiments that would discriminate
between the models are discussed. In this work, we also introduce an effective
description of certain memory circuit elements.
|
1301.0209v2
|
2013-01-03
|
Collective modes of a two-dimensional spin-1/2 Fermi gas in a harmonic trap
|
We derive analytical expressions for the frequency and damping of the lowest
collective modes of a two-dimensional Fermi gas using kinetic theory. For
strong coupling, we furthermore show that pairing correlations overcompensate
the effects of Pauli blocking on the collision rate for a large range of
temperatures, resulting in a rate which is larger than that of a classical gas.
Our results agree well with experimental data, and they recover the observed
cross-over from collisionless to hydrodynamic behaviour with increasing
coupling for the quadruple mode. Finally, we show that a trap anisotropy within
the experimental bounds results in a damping of the breathing mode which is
comparable to what is observed, even for a scale invariant system.
|
1301.0358v2
|
2013-01-09
|
Synthesis of new neutron-rich heavy nuclei: An experimentalist's view
|
I attempt to experimentally evaluate the prospects of synthesizing new
neutron- rich superheavy nuclei. I consider three possible synthetic paths to
neutron- rich superheavy nuclei: (a) the use of neutron-rich radioactive beams.
(b) the use of damped collisions and (c) the use of multi-nucleon transfer
reactions. I consider the prospects of synthesizing new n-rich isotopes of
Rf-Bh using light n-rich radioactive beams and targeted beams from ReA3, FRIB
and SPIRAL2. For the damped collision path, I present the results of a study of
a surrogate reaction, 160Gd + 186W. These data indicate the formation of Au
(trans-target) fragments and the depletion of yields of target-like fragments
by fission and fragment emission. The data are compared to predictions of
Zagrebaev and Greiner. For the multi-nucleon transfer reactions, the results of
a study of the 136Xe + 208Pb reaction are discussed. I consider the possibility
of multi-nucleon transfer reactions with radioactive beams.
|
1301.1759v1
|
2013-01-13
|
Entanglement dynamics of non-inertial observers in a correlated environment
|
Effect of decoherence and correlated noise on the entanglement of X-type
state of the Dirac fields in the non-inertial frame is investigated. A two
qubit X-state is considered to be shared between the partners where Alice is in
inertial frame and Rob in an accelerated frame. The concurrence is used to
quantify the entanglement of the X-state system influenced by time correlated
amplitude damping, depolarizing and bit flip channels. It is seen that
amplitude damping and bit flip channels heavily influence the entanglement of
the system as compared to the depolarizing channel. It is found possible to
avoid entanglement sudden death (ESD) for all the channels under consideration
for {\mu}>0.75 for any type of initial state. No ESD behaviour is seen for
depolarizing channel in the presence of correlated noise for entire range of
decoherence parameter p and Rob's acceleration r. It is also seen that the
effect of environment is much stronger than that of acceleration of the
accelerated partner. Furthermore, it is investigated that correlated noise
compensates the loss of entanglement caused by the Unruh effect.
|
1301.2759v1
|
2013-01-13
|
Decoherence and multipartite entanglement of non-inertial observers
|
Decoherence effect on multipartite entanglement in non-inertial frames is
investigated. GHZ state is considered to be shared between the partners with
one partner in inertial frame whereas the other two in accelerated frames.
One-tangle and {\pi}-tangles are used to quantify the entanglement of the
multipartite system influenced by phase damping and phase flip channels. It is
seen that for phase damping channel, entanglement sudden death (ESD) occurs for
p>0.5 in the infinite acceleration limit. On the other hand, in case of phase
flip channel, ESD behaviour happens around 50% decoherence. It is also seen
that entanglement sudden birth (ESB) does occur in case of phase flip channel.
Furthermore, it is seen that effect of environment on multipartite entanglement
is much stronger than that of the acceleration of non-inertial frames.
|
1301.2765v2
|
2013-01-18
|
Current induced torques and interfacial spin-orbit coupling: Semiclassical Modeling
|
In bilayer nanowires consisting of a ferromagnetic layer and a non-magnetic
layer with strong spin-orbit coupling, currents create torques on the
magnetization beyond those found in simple ferromagnetic nanowires. The
resulting magnetic dynamics appear to require torques that can be separated
into two terms, damping-like and field-like. The damping-like torque is
typically derived from models describing the bulk spin Hall effect and the spin
transfer torque, and the field-like torque is typically derived from a Rashba
model describing interfacial spin-orbit coupling. We derive a model based on
the Boltzmann equation that unifies these approaches. We also consider an
approximation to the Boltzmann equation, the drift-diffusion model, that
qualitatively reproduces the behavior, but quantitatively fails to reproduce
the results. We show that the Boltzmann equation with physically reasonable
parameters can match the torques for any particular sample, but in some cases,
it fails to describe the experimentally observed thickness dependences.
|
1301.4513v1
|
2013-01-23
|
Characterization of magnetostatic surface spin waves in magnetic thin films: evaluation for microelectronic applications
|
The authors have investigated the possibility of utilizing spin waves for
inter- and intra-chip communications, and as logic elements using both
simulations and experimental techniques. Through simulations it has been shown
that the decay lengths of magnetostatic spin waves are affected most by the
damping parameter, and least by the exchange stiffness constant. The damping
and dispersion properties of spin waves limit the attenuation length to several
tens of microns. Thus, we have ruled out the possibility of inter-chip
communications via spin waves. Experimental techniques for the extraction of
the dispersion relationship have also been demonstrated, along with
experimental demonstrations of spin wave interference for amplitude modulation.
The effectiveness of spin wave modulation through interference, along with the
capability of determining the spin wave dispersion relationships electrically
during manufacturing and testing phase of chip production may pave the way for
using spin waves in analog computing wherein the circuitry required for
performing similar functionality becomes prohibitive.
|
1301.5395v1
|
2013-01-25
|
Driven skyrmions and dynamical transitions in chiral magnets
|
We study the dynamics of skyrmions in chiral magnets in the presence of a
spin polarized current. The motion of skyrmions in the ferromagnetic background
excites spin waves and contributes to additional damping. At a large current,
the spin wave spectrum becomes gapless and skyrmions are created dynamically
from the ferromagnetic state. At an even higher current, these skyrmions are
strongly deformed due to the damping and become unstable at a threshold
current, leading to a chiral liquid. We show how skyrmions can be created by
increasing the current in the magnetic spiral state. We then construct a
dynamic phase diagram for a chiral magnet with a current. The instability
transitions between different states can be observed as experimentally clear
signatures in the transport measurements, such as jumps and hysteresis.
|
1301.5963v2
|
2013-02-13
|
Entanglement of Tripartite States with Decoherence in Noninertial frames
|
The one-tangle and {\pi}-tangle are used to quantify the entanglement of a
tripartite GHZ state in noninertial frames when the system interacts with a
noisy environment in the form of phase damping, phase flip and bit flip
channel. It is shown that the two-tangles behave as a closed system. The
one-tangle and {\pi}-tangle have different behaviors in the three channel. In
the case of phase damping channel, depending on the kind of coupling, the
sudden death of both one-tangle and {\pi}-tangle may or may not happen. Whereas
in the case of phase flip channel the sudden death cannot be avoided. The
effect of decoherence may be ignored in the limit of infinite acceleration when
the system interacts with a bit flip channel. Furthermore, a sudden rebirth of
the one-tangle and {\pi}-tangle occur in the case of phase flip channel that
may be delayed when collective coupling is switched on.
|
1302.3005v1
|
2013-02-17
|
Global existence and exponential growth for a viscoelastic wave equation with dynamic boundary conditions
|
The goal of this work is to study a model of the wave equation with dynamic
boundary conditions and a viscoelastic term. First, applying the Faedo-Galerkin
method combined with the fixed point theorem, we show the existence and
uniqueness of a local in time solution. Second, we show that under some
restrictions on the initial data, the solution continues to exist globally in
time. On the other hand, if the interior source dominates the boundary damping,
then the solution is unbounded and grows as an exponential function. In
addition, in the absence of the strong damping, then the solution ceases to
exist and blows up in finite time.
|
1302.4036v1
|
2013-02-22
|
Mixing of blackbodies: Increasing our view of inflation to 17 e-folds with spectral distortions from Silk damping
|
Silk damping in the early Universe, before and during recombination, erases
anisotropies in the cosmic microwave background (CMB) on small scales. This
power, which disappears from anisotropies, appears in the monopole as y-type,
i-type and \mu-type distortions. The observation of the CMB spectral
distortions will thus make available to us the information about the primordial
power spectrum on scales corresponding to the comoving wavenumbers $8< k < 10^4
Mpc^{-1}$ increasing our total view of inflation, when combined with CMB
anisotropies, to span 17 e-folds. These distortions can be understood simply as
mixing of blackbodies of different temperatures and the subsequent
comptonization of the resulting distortions.
|
1302.5633v1
|
2013-02-26
|
Tenfold reduction of Brownian noise in optical interferometry
|
Thermally induced fluctuations impose a fundamental limit on precision
measurement. In optical interferometry, the current bounds of stability and
sensitivity are dictated by the excess mechanical damping of the
high-reflectivity coatings that comprise the cavity end mirrors. Over the
preceding decade, the mechanical loss of these amorphous multilayer reflectors
has at best been reduced by a factor of two. Here we demonstrate a new paradigm
in optical coating technology based on direct-bonded monocrystalline
multilayers, which exhibit both intrinsically low mechanical loss and high
optical quality. Employing these "crystalline coatings" as end mirrors in a
Fabry-P\'erot cavity, we obtain a finesse of 150,000. More importantly, at room
temperature, we observe a thermally-limited noise floor consistent with a
tenfold reduction in mechanical damping when compared with the best dielectric
multilayers. These results pave the way for the next generation of
ultra-sensitive interferometers, as well as for new levels of laser stability.
|
1302.6489v1
|
2013-03-01
|
Quantum error correction and detection: quantitative analysis of a coherent-state amplitude damping code
|
We re-examine a non-Gaussian quantum error correction code designed to
protect optical coherent-state qubits against errors due to an amplitude
damping channel. We improve on a previous result [Phys. Rev. A 81, 062344
(2010)] by providing a tighter upper bound on the performance attained when
considering realistic assumptions which constrain the operation of the gates
employed in the scheme. The quantitative characterization is performed through
measures of fidelity and concurrence, the latter obtained by employing the code
as an entanglement distillation protocol. We find that, when running the code
in fully-deterministic error correction mode, direct transmission can only be
beaten for certain combinations of channel and input state parameters, whereas
in error detection mode, the usage of higher repetition encodings remains
beneficial throughout.
|
1303.0273v2
|
2013-03-04
|
Transverse oscillations in solar spicules induced by propagating Alfvenic pulses
|
The excitation of Alfvenic waves in the solar spicules due to the localized
Alfvenic pulse is investigated. A set of incompressible MHD equations in two
dimensional $x-z$ plane with steady flows and sheared magnetic fields is
solved. Stratification due to gravity and transition region between
chromosphere and corona are taken into account. An initially localized Alfvenic
pulse launched below the transition region can penetrate from transition region
into the corona. We show that the period of transversal oscillations is in
agreement with those observed in spicules. Moreover, it is found that the
excited Alfvenic waves spread during propagation along the spicule length, and
suffer efficient damping of the oscillations amplitude. The damping time of
transverse oscillations elongated with decrease in k_b values.
|
1303.0833v1
|
2013-03-04
|
Tidal damping of the mutual inclination in hierachical systems
|
Hierarchical two-planet systems, in which the inner body's semi-major axis is
between 0.1 and 0.5 AU, usually present high eccentricity values, at least for
one of the orbits. As a result of the formation process, one may expect that
planetary systems with high eccentricities also have high mutual inclinations.
However, here we show that tidal effects combined with gravitational
interactions damp the initial mutual inclination to modest values in timescales
that are shorter than the age of the system. This effect is not a direct
consequence of tides on the orbits, but it results from a secular forcing of
the inner planet's flattening. We then conclude that these hierarchical
planetary systems are unlikely to present very high mutual inclinations, at
least as long as the orbits remain outside the Lidov-Kozai libration areas. The
present study can also be extended to systems of binary stars and to
planet-satellite systems.
|
1303.0864v2
|
2013-03-05
|
Anomalous velocity distributions in active Brownian suspensions
|
Large scale simulations and analytical theory have been combined to obtain
the non-equilibrium velocity distribution, $f(v)$, of randomly accelerated
particles in suspension. The simulations are based on an event-driven
algorithm, generalised to include friction. They reveal strongly anomalous but
largely universal distributions which are independent of volume fraction and
collision processes, which suggests a one-particle model should capture all the
essential features. We have formulated this one-particle model and solved it
analytically in the limit of strong damping, where we find that $f(v)$ decays
as $1/v$ for multiple decades, eventually crossing over to a Gaussian decay for
the largest velocities. Many particle simulations and numerical solution of the
one-particle model agree for all values of the damping.
|
1303.0996v3
|
2013-03-07
|
Quantum critical metals in $d=3+1$
|
We study the problem of disorder-free metals near a continuous Ising nematic
quantum critical point in $d=3+1$ dimensions. We begin with perturbation theory
in the `Yukawa' coupling between the electrons and undamped bosons (nematic
order parameter fluctuations) and show that the perturbation expansion breaks
down below energy scales where the bosons get substantially Landau damped.
Above this scale however, we find a regime in which low-energy fermions obtain
an imaginary self-energy that varies linearly with frequency, realizing the
`marginal Fermi liquid' phenomenology\cite{Varma}. We discuss a large N theory
in which the marginal Fermi liquid behavior is enhanced while the role of
Landau damping is suppressed, and show that quasiparticles obtain a decay rate
parametrically larger than their energy.
|
1303.1587v2
|
2013-03-08
|
Ultra High Energy Electrons Powered by Pulsar Rotation
|
A new mechanism of particle acceleration to ultra high energies, driven by
the rotational slow down of a pulsar (Crab pulsar, for example), is explored.
The rotation, through the time dependent centrifugal force, can very
efficiently excite unstable Langmuir waves in the e-p plasma of the star
magnetosphere via a parametric process. These waves, then, Landau damp on
electrons accelerating them in the process. The net transfer of energy is
optimal when the wave growth and the Landau damping times are comparable and
are both very short compared to the star rotation time. We show, by detailed
calculations, that these are precisely the conditions for the parameters of the
Crab pulsar. This highly efficient route for energy transfer allows the
electrons in the primary beam to be catapulted to multiple TeV ($\sim 100$ TeV)
and even PeV energy domain. It is expected that the proposed mechanism may,
partially, unravel the puzzle of the origin of ultra high energy cosmic ray
electrons.
|
1303.2093v1
|
2013-04-01
|
Fidelity of remote state preparation can be enhanced by local operation
|
Remote state preparation (RSP) is a quantum information protocol which allows
preparing a quantum state at a distant location with the help of a preshared
nonclassical resource state and a classical channel. The efficiency of
successfully doing this task can be represented by the RSP-fidelity of the
resource state. In this paper, we study the influence on the RSP-fidelity by
applying certain local operations on the resource state. We prove that
RSP-fidelity does not increase for any unital local operation. However, for
nonunital local operation, such as local amplitude damping channel, we find
that some resource states can be enhanced to increase the RSP-fidelity. We give
the optimal parameter of symmetric local amplitude damping channel for
enhancing Bell-diagonal resource states. In addition, we show RSP-fidelity can
suddenly change or even vanish at instant under local decoherence.
|
1304.0283v1
|
2013-04-06
|
Coronal loop physical parameters from the analysis of multiple observed transverse oscillations
|
The analysis of quickly damped transverse oscillations of solar coronal loops
using magneto-hydrodynamic seismology allow us to infer physical parameters
that are difficult to measure otherwise. Under the assumption that such damped
oscillations are due to the resonant conversion of global modes into Alfven
oscillations of the tube surface, we carry out a global seismological analysis
of a large set of coronal loops. A Bayesian hierarchical method is used to
obtain distributions for coronal loop physical parameters by means of a global
analysis of a large number of observations. The resulting distributions
summarise global information and constitute data-favoured information that can
be used for the inversion of individual events. The results strongly suggest
that internal Alfven travel times along the loop are larger than 100 s and
smaller than 540 s with 95% probability. Likewise, the density contrast between
the loop interior and the surrounding is larger than 2.3 and below 6.9 with 95%
probability.
|
1304.1921v1
|
2013-04-15
|
Vibrational Resonance in the Morse Oscillator
|
We investigate the occurrence of vibrational resonance in both classical and
quantum mechanical Morse oscillators driven by a biharmonic force. The
biharmonic force consists of two forces of widely different frequencies \omega
and \Omega with \Omega>>\omega. In the damped and biharmonically driven
classical Morse oscillator applying a theoretical approach we obtain an
analytical expression for the response amplitude at the low-frequency \omega.
We identify the conditions on the parameters for the occurrence of the
resonance. The system shows only one resonance and moreover at resonance the
response amplitude is 1/(d\omega) where d is the coefficient of linear damping.
When the amplitude of the high-frequency force is varied after resonance the
response amplitude does not decay to zero but approaches a nonzero limiting
value. We have observed that vibrational resonance occurs when the sinusoidal
force is replaced by a square-wave force. We also report the occurrence of
resonance and anti-resonance of transition probability of quantum mechanical
Morse oscillator in the presence of the biharmonic external field.
|
1304.3988v1
|
2013-04-15
|
Energy dissipation in DC-field driven electron lattice coupled to fermion baths
|
Electron transport in electric-field-driven tight-binding lattice coupled to
fermion baths is comprehensively studied. We reformulate the problem by using
the scattering state method within the Coulomb gauge. Calculations show that
the formulation justifies direct access to the steady-state bypassing the
time-transient calculations, which then makes the steady-state methods
developed for quantum dot theories applicable to lattice models. We show that
the effective temperature of the hot-electron induced by a DC electric field
behaves as $T_{\rm eff}=C\gamma(\Omega/\Gamma)$ with a numerical constant $C$,
tight-binding parameter $\gamma$, the Bloch oscillation frequency $\Omega$ and
the damping parameter $\Gamma$. In the small damping limit $\Gamma/\Omega\to
0$, the steady-state has a singular property with the electron becoming
extremely hot in an analogy to the short-circuit effect. This leads to the
conclusion that the dissipation mechanism cannot be considered as an implicit
process, as treated in equilibrium theories. Finally, using the energy flux
relation, we derive a steady-state current for interacting models where only
on-site Green's functions are necessary.
|
1304.4269v1
|
2013-04-17
|
An oscillating motion of a red blood cell and a neutrally buoyant particle in Poiseuille flow in a narrow channel
|
Two motions of oscillation and vacillating breathing (swing) of a red blood
cell have been observed in bounded Poiseuille flows (Phys. Rev. E 85, 16307
(2012)). To understand such motions, we have studied the oscillating motion of
a neutrally buoyant rigid particle of the same shape in Poiseuille flow in a
narrow channel and obtained that the crucial point is to have the particle
interacting with Poiseuille flow with its mass center moving up and down in the
channel central region. Since the mass center of the cell migrates toward the
channel central region, its oscillating motion of the inclination angle is
similar to the aforementioned motion as long as the cell keeps the shape of
long body. But as the up-and-down oscillation of the cell mass center damps
out, the oscillating motion of the inclination angle also damps out and the
cell inclination angle approaches to a fixed angle.
|
1304.4971v1
|
2013-04-24
|
Finite amplitude inhomogeneous waves in Mooney-Rivlin viscoelastic solids
|
New exact solutions are exhibited within the framework of finite
viscoelasticity. More precisely, the solutions correspond to finite-amplitude,
transverse, linearly-polarized, inhomogeneous motions superposed upon a finite
homogeneous static deformation. The viscoelastic body is composed of a
Mooney-Rivlin viscoelastic solid, whose constitutive equation consists in the
sum of an elastic part (Mooney-Rivlin hyperelastic model) and a viscous part
(Newtonian viscous fluid model). The analysis shows that the results are
similar to those obtained for the purely elastic case; inter alia, the normals
to the planes of constant phase and to the planes of constant amplitude must be
orthogonal and conjugate with respect to the B-ellipsoid, where B is the left
Cauchy-Green strain tensor associated with the initial large static
deformation. However, when the constitutive equation is specialized either to
the case of a neo-Hookean viscoelastic solid or to the case of a Newtonian
viscous fluid, a greater variety of solutions arises, with no counterpart in
the purely elastic case. These solutions include travelling inhomogeneous
finite-amplitude damped waves and standing damped waves.
|
1304.6748v1
|
2013-04-28
|
On the role of transition region on the Alfven wave phase mixing in solar spicules
|
Alfvenic waves are thought to play an important role in coronal heating and
solar wind acceleration. Here we investigate the dissipation of standing Alfven
waves due to phase mixing at the presence of steady flow and sheared magnetic
field in the stratified atmosphere of solar spicules. The transition region
between chromosphere and corona has also been considered. The initial flow is
assumed to be directed along spicule axis, and the equilibrium magnetic field
is taken 2-dimensional and divergence-free. It is determined that in contrast
to propagating Alfven waves, standing Alfven waves dissipate in time rather
than in space. Density gradients and sheared magnetic fields can enhance
damping due to phase mixing. Damping times deduced from our numerical
calculations are in good agreement with spicule lifetimes. Since spicules are
short living and transient structures, such a fast dissipation mechanism is
needed to transport their energy to the corona.
|
1304.7764v1
|
2013-05-03
|
Viscosity, wave damping and shock wave formation in cold hadronic matter
|
We study linear and nonlinear wave propagation in a dense and cold hadron gas
and also in a cold quark gluon plasma, taking viscosity into account and using
the Navier-Stokes equation. The equation of state of the hadronic phase is
derived from the nonlinear Walecka model in the mean field approximation. The
quark gluon plasma phase is described by the MIT equation of state. We show
that in a hadron gas viscosity strongly damps wave propagation and also hinders
shock wave formation. This marked difference between the two phases may have
phenomenological consequences and lead to new QGP signatures.
|
1305.0798v2
|
2013-05-07
|
Periodically Driven Holographic Superconductor
|
As a first step towards our holographic investigation of the
far-from-equilibrium physics of periodically driven systems at strong coupling,
we explore the real time dynamics of holographic superconductor driven by a
monochromatically alternating electric field with various frequencies. As a
result, our holographic superconductor is driven to the final oscillating
state, where the condensate is suppressed and the oscillation frequency is
controlled by twice of the driving frequency. In particular, in the large
frequency limit, the three distinct channels towards the final steady state are
found, namely under damped to superconducting phase, over damped to
superconducting and normal phase, which can be captured essentially by the low
lying spectrum of quasi-normal modes in the time averaged approximation,
reminiscent of the effective field theory perspective.
|
1305.1600v2
|
2013-05-07
|
Micromagnetic modelling of anisotropic damping in ferromagnet
|
We report a numerical implementation of the Landau-Lifshitz-Baryakhtar
theory, which dictates that the micromagnetic relaxation term obeys the
symmetry of the magnetic crystal, i. e. replacing the single intrinsic damping
constant with a tensor of corresponding symmetry. The effect of anisotropic
relaxation is studied in thin saturated ferromagnetic disk and ellipse with and
without uniaxial magneto-crystalline anisotropy. We investigate the angular
dependency of the linewidth of magnonic resonances with respect to the given
structure of the relaxation tensor. The simulations suggest that the anisotropy
of the magnonic linewidth is determined by only two factors: the projection of
the relaxation tensor onto the plane of precession and the ellipticity of the
later.
|
1305.1641v2
|
2013-05-08
|
Existence, uniqueness and analyticity of space-periodic solutions to the regularised long-wave equation
|
We consider space-periodic evolutionary and travelling-wave solutions to the
regularised long-wave equation (RLWE) with damping and forcing. We establish
existence, uniqueness and smoothness of the evolutionary solutions for smooth
initial conditions, and global in time spatial analyticity of such solutions
for analytical initial conditions. The width of the analyticity strip decays at
most polynomially. We prove existence of travelling-wave solutions and
uniqueness of travelling waves of a sufficiently small norm. The importance of
damping is demonstrated by showing that the problem of finding travelling-wave
solutions to the undamped RLWE is not well-posed. Finally, we demonstrate the
asymptotic convergence of the power series expansion of travelling waves for a
weak forcing.
|
1305.1813v1
|
2013-05-08
|
The Persistence of Uphill Anomalous Transport in Inhomogeneous Media
|
For systems out of equilibrium and subjected to a static bias force it can
often be expected that particle transport will usually follow the direction of
this bias. However, counter-examples exist where particles exhibit uphill
motion (known as absolute negative mobility - ANM), particularly in the case of
coupled particles. Examples in single particle deterministic systems are less
common. Recently, in one such example, uphill motion was shown to occur for an
inertial driven and damped particle in a spatially symmetric periodic
potential. The source of this anomalous transport was a combination of two
periodic driving signals which together are asymmetric under time reversal. In
this paper we investigate the phenomena of ANM for a deterministic particle
evolving in a periodic and symmetric potential subjected to an external
unbiased periodic driving and nonuniform space- dependent damping. It will be
shown that this system exhibits a complicated response behaviour as certain
control parameters are varied, most notably being, enhanced parameter regimes
exhibiting ANM as the static bias force is increased. Moreover, the solutions
exhibiting ANM are shown to be, at least over intermediate time periods,
superdiffusive, in contrast to the solutions that follow the bias where the
diffusion is normal.
|
1305.1841v2
|
2013-05-11
|
Dividing Line between Quantum and Classical Trajectories: Bohmian Time Constant
|
This work proposes an answer to a challenge posed by Bell on the lack of
clarity in regards to the line between the quantum and classical regimes in a
measurement problem. To this end, a generalized logarithmic nonlinear
Schr\"odinger equation is proposed to describe the time evolution of a quantum
dissipative system under continuous measurement. Within the Bohmian mechanics
framework, a solution to this equation reveals a novel result: it displays a
time constant which should represent the dividing line between the quantum and
classical trajectories. It is shown that continuous measurements and damping
not only disturb the particle but compel the system to converge in time to a
Newtonian regime. While the width of the wave packet may reach a stationary
regime, its quantum trajectories converge exponentially in time to classical
trajectories. In particular, it is shown that damping tends to suppress further
quantum effects on a time scale shorter than the relaxation time of the system.
If the initial wave packet width is taken to be equal to 2.8 10^{-15} m (the
approximate size of an electron), the Bohmian time constant is found to have an
upper limit, i. e., ${\tau_{B\max}} = {10^{- 26}}s$.
|
1305.2517v2
|
2013-05-11
|
Giant dipole resonance in $^{88}$Mo from phonon damping model's strength functions averaged over temperature and angular momentum distributions
|
The line shapes of giant dipole resonance (GDR) in the decay of the compound
nucleus $^{88}$Mo, which is formed after the fusion-evaporation reaction
$^{48}$Ti + $^{40}$Ca at various excitation energies $E^{*}$ from 58 to 308
MeV, are generated by averaging the GDR strength functions predicted within the
phonon damping model (PDM) using the empirical probabilities for temperature
and angular momentum. The average strength functions are compared with the PDM
strength functions calculated at the mean temperature and mean angular
momentum, which are obtained by averaging the values of temperature and angular
momentum using the same temperature and angular-momentum probability
distributions, respectively. It is seen that these two ways of generating the
GDR linear line shape yield very similar results. It is also shown that the GDR
width approaches a saturation at angular momentum $J\geq$ 50$\hbar$ at $T=$ 4
MeV and at $J\geq$ 70$\hbar$ at any $T$.
|
1305.2518v1
|
2013-05-20
|
Quench Dynamics in Bose condensates in the Presence of a Bath: Theory and Experiment
|
In this paper we study the transient dynamics of a Bose superfluid subsequent
to an interaction quench. Essential for equilibration is a source of
dissipation which we include following the approach of Caldeira and Leggett.
Here we solve the equations of motion exactly by integrating out an
environmental bath. We thereby derive precisely the time dependent density
correlation functions with the appropriate analytic and asymptotic properties.
The resulting structure factor exhibits the expected damping and thereby
differs from that of strict Bogoliubov theory. These damped sound modes, which
reflect the physics beyond mean field approaches, are characterized and the
structure factors are found to compare favorably with experiment.
|
1305.4594v2
|
2013-05-21
|
Restoration of Quantum State in Dephasing Channel
|
In this paper, we propose an explicit scheme to fully recover a
multiple-qubit state subject to a phase damping noise. We establish the
theoretical framework and the operational procedure to restore an unknown
initial quantum state for an N-qubit model interacting with either individual
baths or a common bath. We give an explicit construction of the random unitary
(RU) Kraus decomposition for an N-qubit model interacting with a common bath.
We also demonstrate how to use only one unitary reversal operation to restore
an arbitrary state with phase damping noise. In principle, the initial state
can always be recovered with a success probability of 1. Interestingly, we
found that non-RU decomposition can also be used to restore some particular
entangled states. This may open a new path to restore a quantum state beyond
the standard RU scheme.
|
1305.4627v2
|
2013-05-28
|
Generalized Plasma Dispersion Function: One-Solve-All Treatment, Visualizations, and Application to Landau Damping
|
A unified, fast, and effective approach is developed for numerical
calculation of the well-known plasma dispersion function with extensions from
Maxwellian distribution to almost arbitrary distribution functions, such as the
$\delta$, flat top, triangular, $\kappa$ or Lorentzian, slowing down, and
incomplete Maxwellian distributions. The singularity and analytic continuation
problems are also solved generally. Given that the usual conclusion
$\gamma\propto\partial f_0/\partial v$ is only a rough approximation when
discussing the distribution function effects on Landau damping, this approach
provides a useful tool for rigorous calculations of the linear wave and
instability properties of plasma for general distribution functions. The
results are also verified via a linear initial value simulation approach.
Intuitive visualizations of the generalized plasma dispersion function are also
provided.
|
1305.6476v2
|
2013-06-20
|
Linear flutter analysis of functionally graded panels using cell based smoothed finite element method and discrete shear gap technique
|
In this paper, a cell-based smoothed finite element method with discrete
shear gap technique for triangular ele- ments is employed to study the linear
flutter characteristics of functionally graded material (FGM) flat panels. The
influence of thermal environment, the presence of a centrally located circular
cutout and the aerodynamic damping on the supersonic flutter characteristics of
flat FGM panels is also investigated. The structural for- mulation is based on
the first-order shear deformation theory and the material properties are
assumed to be temperature dependent and graded only in the thickness direction
according to power law distribution in terms of the volume fraction of its
constituent materials. The aerodynamic force is evaluated by considering the
first order high mach number approximation to linear potential flow theory. The
formulation includes transverse shear deformation and in-plane and rotary
inertia effects. The influence of the plate thickness, aspect ratio, boundary
conditions, material gradient index, temperature dependent material properties,
damping, cutout size, skewness of the plate and boundary conditions on the
critical aerodynamic pressure is numerically studied.
|
1306.4978v1
|
2013-06-29
|
Resolving the effects of frequency dependent damping and quantum phase diffusion in YBa$_2$Cu$_3$O$_{7-x}$ Josephson junctions
|
We report on the study of the phase dynamics of high critical temperature
superconductor Josephson junctions. We realized YBa$_2$Cu$_3$O$_{7-x}$ (YBCO)
grain boundary (GB) biepitaxial junctions in the submicron scale, using low
loss substrates, and analyzed their dissipation by comparing the transport
measurements with Monte Carlo simulations. The behavior of the junctions can be
fitted using a model based on two quality factors, which results in a frequency
dependent damping. Moreover, our devices can be designed to have Josephson
energy of the order of the Coulomb energy. In this unusual energy range, phase
delocalization strongly influences the device's dynamics, promoting the
transition to a quantum phase diffusion regime. We study the signatures of such
a transition by combining the outcomes of Monte Carlo simulations with the
analysis of the device's parameters, the critical current and the temperature
behavior of the low voltage resistance $R_0$.
|
1307.0106v1
|
2013-07-03
|
A new mechanism for saturating unstable r-modes in neutron stars
|
We consider a new mechanism for damping the oscillations of a mature neutron
star. The new dissipation channel arises if superfluid vortices are forced to
cut through superconducting fluxtubes. This mechanism is interesting because
the oscillation modes need to exceed a critical amplitude in order for it to
operate. Once it acts the effect is very strong (and nonlinear) leading to
efficient damping. The upshot of this is that modes are unlikely to ever evolve
far beyond the critical amplitude. We consider the effect of this new
dissipation channel on the r-modes, that may be driven unstable by the emission
of gravitational waves. Our estimates show that the fluxtube cutting leads to a
saturation threshold for the instability that can be smaller than that of other
proposed mechanisms. This suggests that the idea may be of direct astrophysical
relevance.
|
1307.0985v1
|
2013-07-03
|
Exotic matter influence on the polar quasi-normal modes of neutron stars with equations of state satisfying the $2 M_{\odot}$ constraint
|
In this paper we analyze the quasi-normal mode spectrum of realistic neutron
stars by studying the polar modes. In particular we study the spatial wI mode,
the f mode, and the fundamental p mode. The study has been done for 15
different equations of state containing exotic matter and satisfying the $2
M_{\odot}$ constraint. Since f and p modes couple to matter perturbations, the
influence of the presence of hyperons and quarks in the core of the neutron
stars is more significant than for the axial component. We present
phenomenological relations for the frequency and damping time with the
compactness of the neutron star. We also consider new phenomenological
relations between the frequency and damping time of the w mode and the f mode.
These new relations are independent of the equation of state, and could be used
to estimate the central pressure, mass or radius, and eventually constrain the
equation of state of neutron stars. To obtain these results we have developed a
new method based on the Exterior Complex Scaling technique with variable angle.
|
1307.1063v1
|
2013-07-10
|
Absence of damping of low energy excitations in a quasi-2D dipolar Bose gas
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We develop a theory of damping of low energy, collective excitations in a
quasi-2D, homogenous, dipolar Bose gas at zero temperature, via processes
whereby an excitation decays into two excitations with lower energy. We find
that owing to the nature of the low energy spectrum of a quasi-2D dipolar gas,
such processes cannot occur unless the momentum of the incoming quasi-particle
exceeds a critical value k_{crit}. We find that as the dipolar interaction
strength is increased, this critical value shifts to larger momenta. Our
predictions can be directly verified in current experiments on dipolar Bose
condensates using Bragg spectroscopy, and provide valuable insight into the
quantum many-body physics of dipolar gases.
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1307.2910v2
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2013-07-14
|
Asteroseismic effects in close binary stars
|
Turbulent processes in the convective envelopes of the sun and stars have
been shown to be a source of internal acoustic excitations. In single stars,
acoustic waves having frequencies below a certain cutoff frequency propagate
nearly adiabatically and are effectively trapped below the photosphere where
they are internally reflected. This reflection essentially occurs where the
local wavelength becomes comparable to the pressure scale height. In close
binary stars, the sound speed is a constant on equipotentials, while the
pressure scale height, which depends on the local effective gravity, varies on
equipotentials and may be much greater near the inner Lagrangian point (L_1).
As a result, waves reaching the vicinity of L_1 may propagate unimpeded into
low density regions, where they tend to dissipate quickly due to non-linear and
radiative effects. We study the three dimensional propagation and enhanced
damping of such waves inside a set of close binary stellar models using a WKB
approximation of the acoustic field. We find that these waves can have much
higher damping rates in close binaries, compared to their non-binary
counterparts. We also find that the relative distribution of acoustic energy
density at the visible surface of close binaries develops a ring-like feature
at specific acoustic frequencies and binary separations.
|
1307.3709v1
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2013-07-31
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Dynamics of ions in the selectivity filter of the KcsA channel: Towards a coupled Brownian particle description
|
The statistical and dynamical properties of ions in the selectivity filter of
the KcsA ion channel are considered on the basis of molecular dynamics (MD)
simulations of the KcsA protein embedded in a lipid membrane surrounded by an
ionic solution. A new approach to the derivation of a Brownian dynamics (BD)
model of ion permeation through the filter is discussed, based on unbiased MD
simulations. It is shown that depending on additional assumptions, ion's
dynamics can be described either by under-damped Langevin equation with
constant damping and white noise or by Langevin equation with a fractional
memory kernel. A comparison of the potential of the mean force derived from
unbiased MD simulations with the potential produced by the umbrella sampling
method demonstrates significant differences in these potentials. The origin of
these differences is an open question that requires further clarifications.
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1307.8298v1
|
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