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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
|
2013-04-17
|
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
|
2013-04-28
|
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
|
2013-05-08
|
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
|
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
|
Scaling of spin Hall angle in 3d, 4d and 5d metals from Y3Fe5O12/metal spin pumping
|
Pure spin currents generated by spin pumping in ferromagnet/nonmagnet (FM/NM)
bilayers produce inverse spin Hall effect (ISHE) voltages in the NM, from which
spin pumping and transport characteristics of the NM can be extracted. Due to
its exceptionally low damping, Y3Fe5O12 (YIG) is an important and widely used
FM for microwave devices and ferromagnetic resonance (FMR) spin pumping. Here
we report systematic investigation of spin pumping from 20-nm thick YIG thin
films to a series of 3d, 4d and 5d normal metals (Cu, Ag, Ta, W, Pt and Au)
with various spin-orbit coupling strengths. From enhanced Gilbert damping
obtained from the frequency dependence of FMR linewidths and ISHE signals, the
spin Hall angles and YIG/NM interfacial spin mixing conductances are
quantitatively determined for these metals. The spin Hall angles largely vary
as the fourth power of the atomic number, corroborating the dominant role of
spin-orbit coupling across a broad range in the inverse spin Hall effect.
|
1307.2648v2
|
2013-07-10
|
Absence of damping of low energy excitations in a quasi-2D dipolar Bose gas
|
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.
|
1307.2910v2
|
2013-07-31
|
Intrabeam Scattering Studies at CesrTA
|
Intrabeam scattering (IBS) limits the emittance and single-bunch current that
can be achieved in electron or positron storage ring colliders, damping rings,
and light sources. Much theoretical work on IBS exists, and while the theories
have been validated in hadron and ion machines, the presence of strong damping
makes IBS in lepton machines a different phenomenon. We present the results of
measurements at CesrTA of IBS dominated beams, and compare the data with
theory. The beams we study have parameters typical of those specified for the
next generation of wiggler dominated storage rings: low emittance, small bunch
length, and few GeV energy. Our measurements are in good agreement with IBS
theory, provided a tail-cut procedure is applied.
|
1308.0035v2
|
2013-08-01
|
Inverse Spin Hall Effect in nanometer-thick YIG/Pt system
|
High quality nanometer-thick (20 nm, 7 nm and 4 nm) epitaxial YIG films have
been grown on GGG substrates using pulsed laser deposition. The Gilbert damping
coefficient for the 20 nm thick films is 2.3 x 10-4 which is the lowest value
reported for sub-micrometric thick films. We demonstrate Inverse spin Hall
effect (ISHE) detection of propagating spin waves using Pt. The amplitude and
the lineshape of the ISHE voltage correlate well to the increase of the Gilbert
damping when decreasing thickness of YIG. Spin Hall effect based
loss-compensation experiments have been conducted but no change in the
magnetization dynamics could be detected.
|
1308.0192v1
|
2013-08-05
|
Radiative damping and emission signatures of strong superluminal waves in pulsar winds
|
We analyse the damping by radiation reaction and by Compton drag of strong,
superluminal electromagnetic waves in the context of pulsar winds. The
associated radiation signature is found by estimating the efficiency and the
characteristic radiation frequencies. Applying these estimates to the gamma-ray
binary containing PSR B1259-63, we show that the GeV flare observed by
Fermi-LAT can be understood as inverse Compton emission by particles scattering
photons from the companion star, if the pulsar wind termination shock acquires
a precursor of superluminal waves roughly 30 days after periastron. This
constrains the mass-loading factor of the wind $\mu=L/\dot{N}mc^2$ (where $L$
is the luminosity and $\dot{N}$ the rate of loss of electrons and positrons) to
be roughly $6\times 10^4$.
|
1308.0950v2
|
2013-08-09
|
Scale breaking and fluid dynamics in a dilute two-dimensional Fermi gas
|
We study two observables related to the anomalous breaking of scale
invariance in a dilute two dimensional Fermi gas, the frequency shift and
damping rate of the monopole mode in a harmonic confinement potential. For this
purpose we compute the speed of sound and the bulk viscosity of the two
dimensional gas in the high temperature limit. We show that the anomaly in the
speed of sound scales as $(2P-\rho c_s^2)/P\sim z/[\log(T/E_B)]^2$, and that
the bulk viscosity $\zeta$ scales as $\zeta/\eta \sim z^2/[\log(T/E_B)]^6$.
Here, $P$ is the pressure, $c_s^2$ is the speed of sound, $\eta$ is the shear
viscosity, $z$ is the fugacity, and $E_B$ is the two-body binding energy. We
show that our results are consistent with the experimental results of Vogt et
al. [Phys. Rev. Lett. 108, 070404 (2012)]. Vogt et al. reported a frequency
shift $\delta\omega/\omega$ of the order of a few percent, and a damping rate
smaller than the background rate $\Gamma/\omega_0\sim 5%$.
|
1308.2004v1
|
2013-08-14
|
Reentrant classicality of a damped system
|
For a free particle, the coupling to its environment can be the relevant
mechanism to induce quantum behavior as the temperature is lowered. We study
general linear environments with a spectral density proportional to {\omega}^s
at low frequencies and consider in particular the specific heat of the free
damped particle. For super-Ohmic baths with s>=2, a reentrant classical
behavior is found. As the temperature is lowered, the specific heat decreases
from the classical value of k_B/2, thereby indicating the appearence of quantum
effects. However, the classical value of the specific heat is restored as the
temperature approaches zero. This surprising behavior is due to the suppressed
density of bath degrees of freedom at low frequencies. For s<2, the specific
heat at zero temperature increases linearly with s from -k_B/2 to k_B/2. An
Ohmic bath, s=1, is thus very special in the sense that it represents the only
case where the specific heat vanishes at zero temperature.
|
1308.3049v1
|
2013-08-20
|
Group classification and exact solutions of variable-coefficient generalized Burgers equations with linear damping
|
Admissible point transformations between Burgers equations with linear
damping and time-dependent coefficients are described and used in order to
exhaustively classify Lie symmetries of these equations. Optimal systems of
one- and two-dimensional subalgebras of the Lie invariance algebras obtained
are constructed. The corresponding Lie reductions to ODEs and to algebraic
equations are carried out. Exact solutions to particular equations are found.
Some generalized Burgers equations are linearized to the heat equation by
composing equivalence transformations with the Hopf-Cole transformation.
|
1308.4265v2
|
2013-08-31
|
Recent developments in the determination of the amplitude and phase of quantum oscillations for the linear chain of coupled orbits
|
De Haas-van Alphen oscillations are studied for Fermi surfaces (FS)
illustrating the model proposed by Pippard in the early sixties, namely the
linear chain of orbits coupled by magnetic breakdown. This FS topology is
relevant for many multiband quasi-two dimensional (q-2D) organic metals such as
$\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ and
$\theta$-(BEDT-TTF)$_4$CoBr$_4$(C$_6$H$_4$Cl$_2$) which are considered in
detail. Whereas the Lifshits-Kosevich model only involves a first order
development of field- and temperature-dependent damping factors, second order
terms may have significant contribution on the Fourier components amplitude for
such q-2D systems at high magnetic field and low temperature. The strength of
these second order terms depends on the relative value of the involved damping
factors, which are in turns strongly dependent on parameters such as the
magnetic breakdown field, effective masses and, most of all, effective
Land\'{e} factors. In addition, the influence of field-dependent Onsager phase
factors on the oscillation spectra is considered.
|
1309.0102v1
|
2013-09-04
|
Surface Waves in the paritally ionized solar plasma slab
|
The properties of surface waves in the partially ionized, incompressible
magnetized plasma slab are investigated in the present work. The waves are
affected by the non ideal MHD effects which causes the finite drift of the
magnetic field in the medium. When the finite drift of the magnetic field is
ignored, the characteristics of the wave propagation in the partially ionized
plasma fluid is similar to the ideal MHD except now the propagation properties
depend on the fractional ionization of the medium. In the presence of Hall
diffusion, the propagation of the sausage and kink surface waves depends on the
level of fractional ionization of the medium. When both the Hall and Pedersen
diffusion are present in the medium, the waves undergoes damping. For typical
solar parameters, waves may damp over few minutes.
|
1309.0881v1
|
2013-09-04
|
Origin and reduction of wakefields in photonic crystal accelerator cavities
|
Photonic crystal (PhC) defect cavities that support an accelerating mode tend
to trap unwanted higher-order modes (HOMs) corresponding to zero-group-velocity
PhC lattice modes at the top of the bandgap. The effect is explained quite
generally from photonic band and perturbation theoretical arguments. Transverse
wakefields resulting from this effect are observed in a hybrid dielectric PhC
accelerating cavity based on a triangular lattice of sapphire rods. These
wakefields are, on average, an order of magnitude higher than those in the
waveguide-damped Compact Linear Collider (CLIC) copper cavities. The avoidance
of translational symmetry (and, thus, the bandgap concept) can dramatically
improve HOM damping in PhC-based structures.
|
1309.0914v2
|
2013-09-14
|
Damping of the quadrupole mode in a two-dimensional Fermi gas
|
In a recent experiment [E. Vogt et al., Phys. Rev. Lett. 108, 070404 (2012)],
quadrupole and breathing modes of a two-dimensional Fermi gas were studied. We
model these collective modes by solving the Boltzmann equation via the method
of phase-space moments up to fourth order, including in-medium effects on the
scattering cross section. In our analysis, we use a realistic Gaussian
potential deformed by the presence of gravity and magnetic field gradients. We
conclude that the origin of the experimentally observed damping of the
quadrupole mode, especially in the weakly interacting (or even non-interacting)
case, cannot be explained by these mechanisms.
|
1309.3651v2
|
2013-09-24
|
Spin-driven tidal pumping: Tidally driven changes in planetary spin coupled with secular interactions between planets
|
In a multiplanet system, tides acting on the inner planet can significantly
affect the orbital evolution of the entire system. While tides usually damp
eccentricities, a novel mechanism identified by Correia et al. (2012) tends to
raise eccentricities as a result of the tides' effect on the inner planet's
rotation. Our analytical description of this spin-driven tidal (SDT) effect
shows that, while the inner planet's eccentricity undergoes pumping, the
process is more completely described by an exchange of strength between the two
eigenmodes of the dynamical system. Our analysis allows derivation of criteria
for two-planet coplanar systems where the SDT effect can reverse tidal damping,
and may preclude the effect's being significant for realistic systems. For the
specific case quantified by Correia et al., the effect is strong because of the
large adopted tidal time lag, which may not be appropriate for the assumed
Saturn-like inner planet. On the other hand, the effective Q for any given
planet in exotic circumstances is very uncertain, so the SDT effect could play
a role in planetary evolution.
|
1309.6279v1
|
2013-10-01
|
The extrema of an action principle for dissipative mechanical systems
|
A least action principle for damping motion has been previously proposed with
a Hamiltonian and a Lagrangian containing the energy dissipated by friction.
Due to the space-time nonlocality of the Lagrangian, mathematical uncertainties
persist about the appropriate variational calculus and the nature (maxima,
minima and inflection) of the stationary action. The aim of this work is to
make numerical simulation of damped motion and to compare the actions of
different paths in order to get evidence of the existence and the nature of
stationary action. The model is a small particle subject to conservative and
friction forces. Two conservative forces and three friction forces are
considered. The comparison of the actions of the perturbed paths with that of
the Newtonian path reveals the existence of extrema of action which are minima
for zero or very weak friction and shift to maxima when the motion is
overdamped. In the intermediate case, the action of the Newtonian path is
neither least nor most, meaning that the extreme feature of the Newtonian path
is lost. In this situation, however, no reliable evidence of stationary action
can be found from the simulation result.
|
1310.0455v1
|
2013-10-02
|
Effectiveness of Depolarizing noise in causing sudden death of entanglement
|
Continuing on the recent observation that sudden death of entanglement can
occur even when a single qubit of a two qubit state is exposed to noisy
environment, we examine the local effects of several noises on bipartite
qubit-qutrit and qutrit-qutrit systems. In order to rule out any initial
interactions with environment, we consider maximally entangled pure states of
qubit-qutrit and qutrit-qutrit systems for our analysis. We show that
depolarizing and generalized amplitude damping noise can cause sudden death of
entanglement in these states even when they act only on one part of the system.
We also show that sudden death of entanglement occurs much faster under the
action of depolarizing noise when compared to that due to generalized amplitude
damping. This result strengthens the observation that depolarizing noise is
more effective than other noise models in causing sudden death of entanglement.
|
1310.0715v1
|
2013-10-11
|
New foundations and unification of basic plasma physics by means of classical mechanics
|
The derivation of Debye shielding and Landau damping from the $N$-body
description of plasmas requires many pages of heavy kinetic calculations in
classical textbooks and is done in distinct, unrelated chapters. Using Newton's
second law for the $N$-body system, we perform this derivation in a few steps
with elementary calculations using standard tools of calculus, and no
probabilistic setting. Unexpectedly, Debye shielding is encountered on the way
to Landau damping. The theory is extended to accommodate a correct description
of trapping or chaos due to Langmuir waves, and to avoid the small amplitude
assumption for the electrostatic potential. Using the shielded potential,
collisional transport is computed for the first time by a convergent expression
including the correct calculation of deflections for all impact parameters.
Shielding and collisional transport are found to be two related aspects of the
repulsive deflections of electrons.
|
1310.3096v1
|
2013-10-18
|
Analytical considerations for linear and nonlinear optimization of the TME cells. Application to the CLIC pre-damping rings
|
The theoretical minimum emittance cells are the optimal configurations for
achieving the absolute minimum emittance, if specific optics constraints are
satisfied at the middle of the cell's dipole. Linear lattice design options
based on an analytical approach for the theoretical minimum emittance cells are
presented in this paper. In particular the parametrization of the quadrupole
strengths and optics functions with respect to the emittance and drift lengths
is derived. A multi-parametric space can be then created with all the cell
parameters, from which one can chose any of them to be optimized. An
application of this approach are finally presented for the linear and
non-linear optimization of the CLIC Pre-damping rings.
|
1310.5024v1
|
2013-10-20
|
Electromagnetic waves in an axion-active relativistic plasma non-minimally coupled to gravity
|
We consider cosmological applications of a new self-consistent system of
equations, accounting for a nonminimal coupling of the gravitational,
electromagnetic and pseudoscalar (axion) fields in a relativistic plasma. We
focus on dispersion relations for electromagnetic perturbations in an initially
isotropic ultrarelativistic plasma coupled to the gravitational and axion
fields in the framework of isotropic homogeneous cosmological model of the de
Sitter type. We classify the longitudinal and transversal electromagnetic modes
in an axionically active plasma and distinguish between waves (damping,
instable or running), and nonharmonic perturbations (damping or instable). We
show that for the special choice of the guiding model parameters the
transversal electromagnetic waves in the axionically active plasma,
nonminimally coupled to gravity, can propagate with the phase velocity less
than speed of light in vacuum, thus displaying a possibility for a new type of
resonant particle-wave interactions.
|
1310.5333v2
|
2013-10-25
|
Effect of resonance on the existence of periodic solutions for strongly damped wave equation
|
We are interested in the differential equation $\ddot u(t) = -A u(t) - c A
\dot u(t) + \lambda u(t) + F(t,u(t))$, where $c > 0$ is a damping factor, $A$
is a sectorial operator and $F$ is a continuous map. We consider the situation
where the equation is at resonance at infinity, which means that $\lambda$ is
an eigenvalue of $A$ and $F$ is a bounded map. We introduce new geometrical
conditions for the nonlinearity $F$ and use topological degree methods to find
$T$-periodic solutions for this equation as fixed points of Poincar\'e
operator.
|
1310.6794v4
|
2013-10-25
|
Voltage noise, switching rates, and multiple phase-slips in moderately damped Josephson junctions
|
We study the voltage noise properties including the switching rates and
statistics of phase-slips in moderately damped Josephson junctions using a
novel efficient numerical approach combining the matrix continued-fraction
method with the full counting statistics. By analyzing the noise results
obtained for the RCSJ model we identify different dominating components, namely
the thermal noise close to equilibrium (small current-bias regime), the shot
noise of (multiple) phase-slips in the intermediate range of biases and the
switching noise for yet higher bias currents. We extract thus far inaccessible
characteristic rates of phase-slips in the shot noise regime as well as the
escape and retrapping rates in the switching regime as functions of various
junction's parameters. The method can be extended and applied to other
experimentally relevant Josephson junction circuits.
|
1310.6871v1
|
2013-11-06
|
Analytical estimation of ATF beam halo distribution
|
In order to study the background status in the ATF2 beam line and the
interaction point (IP), this paper developed an analytical method to give the
estimation of ATF beam halo distribution based on K. Hirata and K. Yokoya's
theory. The equilibrium particle distribution of beam tail in ATF damping ring,
when each electron is being affected by, in addition to the synchrotron
radiation damping effects, several stochastic processes, such as beam-gas
scattring, beam-gas bremsstrahlung and intra-beam scattering, was presented.
This method is common and can be applied on other electron rings.
|
1311.1267v3
|
2013-11-13
|
Quantum turbulence in superfluids with wall-clamped normal component
|
In Fermi superfluids, like superfluid 3He, the viscous normal component can
be considered to be stationary with respect to the container. The normal
component interacts with the superfluid component via mutual friction which
damps the motion of quantized vortex lines and eventually couples the
superfluid component to the container. With decreasing temperature and mutual
friction the internal dynamics of the superfluid component becomes more
important compared to the damping and coupling effects from the normal
component. This causes profound changes in superfluid dynamics: the
temperature-dependent transition from laminar to turbulent vortex motion and
the decoupling from the reference frame of the container at even lower
temperatures.
|
1311.3112v1
|
2013-11-19
|
Protecting qutrit-qutrit entanglement by weak measurement and reversal
|
Entangled states in high dimensional systems are of great interest due to the
extended possibilities they provide in quantum information processing.
Recently, Sun et al. [Phys. Rev. A 82, 052323 (2010)] and Kim et al. [Nat.
Phys. 8, 117 (2012)] pointed out that weak measurement and quantum weak
measurement reversal can actively combat decoherence. We generalize their
studies from qubits to qutrits under amplitude damping decoherence. We find
that the qutrit-qutrit entanglement can be partially retrieved for certain
initial states when only weak measurement reversals are performed. However, we
can completely defeat amplitude damping decoherence for any initial states by
the combination of prior weak measurements and post optimal weak measurement
reversals. The experimental feasibility of our schemes is also discussed.
|
1311.4692v2
|
2013-11-25
|
Spin-wave excitation and propagation in microstructured waveguides of yttrium iron garnet (YIG)/Pt bilayers
|
We present an experimental study of spin-wave excitation and propagation in
microstructured waveguides patterned from a 100 nm thick yttrium iron garnet
(YIG)/platinum (Pt) bilayer. The life time of the spin waves is found to be
more than an order of magnitude higher than in comparably sized metallic
structures despite the fact that the Pt capping enhances the Gilbert damping.
Utilizing microfocus Brillouin light scattering spectroscopy, we reveal the
spin-wave mode structure for different excitation frequencies. An exponential
spin-wave amplitude decay length of 31 {\mu}m is observed which is a
significant step towards low damping, insulator based micro-magnonics.
|
1311.6305v1
|
2013-11-27
|
Encapsulated formulation of the Selective Frequency Damping method
|
We present an alternative "encapsulated" formulation of the Selective
Frequency Damping method for finding unstable equilibria of dynamical systems,
which is particularly useful when analysing the stability of fluid flows. The
formulation makes use of splitting methods, which means that it can be wrapped
around an existing time-stepping code as a "black box". The method is first
applied to a scalar problem in order to analyse its stability and highlight the
roles of the control coefficient $\chi$ and the filter width $\Delta$ in the
convergence (or not) towards the steady-state. Then the steady-state of the
incompressible flow past a two-dimensional cylinder at $Re=100$, obtained with
a code which implements the spectral/hp element method, is presented.
|
1311.7000v1
|
2013-12-02
|
The spatial distribution of dark-matter-annihilation originated gamma-ray line signal
|
The GeV$-$TeV $\gamma-$ray line signal is the smoking gun signature of the
dark matter annihilation or decay. The detection of such a signal is one of the
main targets of some space-based telescopes, including Fermi-LAT and the
upcoming CALET, DAMPE and Gamma-400. An important feature of the
dark-matter-annihilation originated $\gamma-$ray line photons is their
concentration at the center of the Galaxy. So far no reliable $\gamma-$ray line
has been detected by Fermi-LAT and the upper limits on the cross section of
annihilation into $\gamma-$rays have been reported. We use these upper limits
to estimate the "maximal" number of $\gamma-$ray line photons detectable for
Fermi-LAT, DAMPE and Gamma-400 and then investigate the spatial distribution of
these photons. We show that usually the center of the distribution region will
be offset from the Galactic centre (Sgr A$^{\star}$) due to the limited
statistics. Such a result is almost independent of the dark matter distribution
models and renders the reconstruction of the dark matter distribution with the
$\gamma-$ray line signal very challenging for the foreseeable space-based
detectors.
|
1312.0357v2
|
2013-12-03
|
Inflationary Steps in the Planck Data
|
We extend and improve the modeling and analysis of large-amplitude, sharp
inflationary steps for second order corrections required by the precision of
the Planck CMB power spectrum and for arbitrary Dirac-Born-Infeld sound speed.
With two parameters, the amplitude and frequency of the resulting oscillations,
step models improve the fit by $\Delta \chi^2 = -11.4$. Evidence for
oscillations damping before the Planck beam scale is weak: damping only
improves the fit to $\Delta \chi^2 = -14.0$ for one extra parameter, if step
and cosmological parameters are jointly fit, in contrast to analyses which fix
the latter. Likewise, further including the sound speed as a parameter only
marginally improves the fit to $\Delta \chi^2 = -15.2$ but has interesting
implications for the lowest multipole temperature and polarization anisotropy.
Since chance features in the noise can mimic these oscillatory features, we
discuss tests from polarization power spectra, lensing reconstruction and
squeezed and equilateral bispectra that should soon verify or falsify their
primordial origin.
|
1312.0946v1
|
2013-12-16
|
Exploiting Intrinsic Triangular Geometry in Relativistic He3+Au Collisions to Disentangle Medium Properties
|
Recent results in d+Au and p+Pb collisions at RHIC and the LHC provide
evidence for collective expansion and flow of the created medium. We propose a
control set of experiments to directly compare particle emission patterns from
p+Au, d+Au, and He3+Au or t+Au collisions at the same sqrt(sNN). Using Monte
Carlo Glauber we find that a He3 or triton projectile, with a realistic
wavefunction description, induces a significant intrinsic triangular shape to
the initial medium and that, even with viscous damping, this survives into a
significant third order flow moment v3. By comparing systems with one, two, and
three initial hot spots, one can disentangle the effects from the initial
spatial distribution of the deposited energy and viscous damping. These are key
tools to answering the question of how small a droplet of matter is necessary
to form a quark-gluon plasma described by nearly inviscid hydrodynamics.
|
1312.4565v2
|
2013-12-17
|
Reversal time of the magnetization of magnetic nanoparticles at very low damping
|
The magnetization reversal time of ferromagnetic nanoparticles is
investigated in the very low damping regime. The energy-controlled diffusion
equation rooted in a generalization of the Kramers escape rate theory for point
Brownian particles in a potential to the magnetic relaxation of a macrospin,
yields the reversal time in closed integral form. The latter is calculated for
a nanomagnet with uniaxial anisotropy with a uniform field applied at an angle
to the easy axis and for a nanomagnet with biaxial anisotropy with the field
along the easy axis. The results completely agree with those yielded by
independent numerical and asymptotic methods.
|
1312.4904v3
|
2013-12-18
|
Quantum speed limit for arbitrary initial states
|
We investigate the generic bound on the minimal evolution time of the open
dynamical quantum system. This quantum speed limit time is applicable to both
mixed and pure initial states. We then apply this result to the damped
Jaynes-Cummings model and the Ohimc-like dephasing model starting from a
general time-evolution state. The bound of this time-dependent state at any
point in time can be found. For the damped Jaynes-Cummings model, the
corresponding bound first decreases and then increases in the Markovian
dynamics. While in the non-Markovian regime, the speed limit time shows an
interesting periodic oscillatory behavior. For the case of Ohimc-like dephasing
model, this bound would be gradually trapped to a fixed value. In addition, the
roles of the relativistic effects on the speed limit time for the observer in
non-inertial frames are discussed.
|
1312.5071v1
|
2013-12-26
|
Equilibrium of a Brownian particle in an inhomogeneous medium: An alternative approach
|
We look at the equilibrium of a Brownian particle in an inhomogeneous space
following the alternative approach proposed in ref.[1]. We consider a
coordinate dependent damping that makes the stochastic dynamics the one with
multiplicative noise. Here we show that the mapping to an additive noise gives
the equilibrium distribution of the generalized Langevin dynamics of a particle
with mass. The procedure does not need inclusion of any ad hoc current
cancelling term in the Langevin dynamics. The result shows a modified
Maxwell-Boltzmann distribution with a damping dependent amplitude.
|
1312.7075v3
|
2014-01-22
|
On Stability of Hyperbolic Thermoelastic Reissner-Mindlin-Timoshenko Plates
|
In the present article, we consider a thermoelastic plate of
Reissner-Mindlin-Timoshenko type with the hyperbolic heat conduction arising
from Cattaneo's law. In the absense of any additional mechanical dissipations,
the system is often not even strongly stable unless restricted to the
rotationally symmetric case, etc. We present a well-posedness result for the
linear problem under general mixed boundary conditions for the elastic and
thermal parts. For the case of a clamped, thermally isolated plate, we show an
exponential energy decay rate under a full damping for all elastic variables.
Restricting the problem to the rotationally symmetric case, we further prove
that a single frictional damping merely for the bending compoment is sufficient
for exponential stability. To this end, we construct a Lyapunov functional
incorporating the Bogovski\u{i} operator for irrotational vector fields which
we discuss in the appendix.
|
1401.5669v1
|
2014-01-24
|
Wavenumber-dependent Gilbert damping in metallic ferromagnets
|
New terms to the dynamical equation of magnetization motion, associated with
spin transport, have been reported over the past several years. Each newly
identified term is thought to possess both a real and an imaginary effective
field leading to fieldlike and dampinglike torques on magnetization. Here we
show that three metallic ferromagnets possess an imaginary effective-field term
which mirrors the well-known real effective-field term associated with exchange
in spin waves. Using perpendicular standing spin wave resonance between 2-26
GHz, we evaluate the magnitude of the finite-wavenumber ($k$) dependent Gilbert
damping $\alpha$ in three typical device ferromagnets, Ni$_{79}$Fe$_{21}$, Co,
and Co$_{40}$Fe$_{40}$B$_{20}$, and demonstrate for the first time the presence
of a $k^2$ term as $\Delta\alpha=\Delta\alpha_0+A_{k}\cdot k^2$ in all three
metals. We interpret the new term as the continuum analog of spin pumping,
predicted recently, and show that its magnitude, $A_{k}$=0.07-0.1 nm$^2$, is
consistent with transverse spin relaxation lengths as measured by conventional
(interlayer) spin pumping.
|
1401.6467v2
|
2014-01-27
|
Edge states in 2D lattices with hopping anisotropy and Chebyshev polynomials
|
Analytic technique based on Chebyshev polynomials is developed for studying
two-dimensional lattice ribbons with hopping anisotropy. In particular, the
tight-binding models on square and triangle lattice ribbons are investigated
with anisotropic nearest neighbouring hoppings. For special values of hopping
parameters the square lattice becomes topologically equivalent to a honeycomb
one either with zigzag or armchair edges. In those cases as well as for
triangle lattices we perform the exact analytic diagonalization of
tight-binding Hamiltonians in terms of Chebyshev polynomials. Deep inside the
edge state subband the wave functions exhibit exponential spatial damping which
turns into power-law damping at edge-bulk transition point. It is shown that
strong hopping anisotropy crashes down edge states, and the corresponding
critical conditions are found.
|
1401.6770v2
|
2014-01-27
|
Dynamical pattern formations in two dimensional fluid and Landau pole bifurcation
|
A phenomenological theory is proposed to analyze the asymptotic dynamics of
perturbed inviscid Kolmogorov shear flows in two dimensions. The phase diagram
provided by the theory is in qualitative agreement with numerical observations,
which include three phases depending on the aspect ratio of the domain and the
size of the perturbation: a steady shear flow, a stationary dipole, and four
traveling vortices. The theory is based on a precise study of the inviscid
damping of the linearized equation and on an analysis of nonlinear effects. In
particular, we show that the dominant Landau pole controlling the inviscid
damping undergoes a bifurcation, which has important consequences on the
asymptotic fate of the perturbation.
|
1401.6865v1
|
2014-02-05
|
On Linear Landau Damping for Relativistic Plasmas via Gevrey Regularity
|
We examine the phenomenon of Landau Damping in relativistic plasmas via a
study of the relativistic Vlasov-Poisson system (both on the torus and on
$\mathbb{R}^3$) linearized around a sufficiently nice, spatially uniform
kinetic equilibrium. We find that exponential decay of spatial Fourier modes is
impossible under modest symmetry assumptions. However, by assuming the
equilibrium and initial data are sufficiently regular functions of velocity for
a given wavevector (in particular that they exhibit a kind of Gevrey
regularity), we show that it is possible for the mode associated to this
wavevector to decay sub-exponentially if its magnitude exceeds a certain
critical size. We also give a heuristic argument why one should not expect such
rapid decay for modes with wavevectors below this threshold.
|
1402.0992v2
|
2014-02-06
|
Time dependent elastic response to a local shear transformation in amorphous solids
|
The elastic response of a two-dimensional amorphous solid to induced local
shear transformations, which mimic the elementary plastic events occurring in
deformed glasses, is investigated via Molecular Dynamics simulations. We show
that for different spatial realizations of the transformation, despite relative
fluctuations of order one, the long time equilibrium response averages out to
the prediction of the Eshelby inclusion problem for a continuum elastic medium.
We characterize the effects of the underlying dynamics on the propagation of
the elastic signal. A crossover from a propagative transmission in the case of
weakly-damped dynamics to a diffusive transmission for strong damping is
evidenced. In the latter case, the full time dependent elastic response is in
agreement with the theoretical prediction, obtained by solving the diffusion
equation for the displacement field in an elastic medium.
|
1402.1474v1
|
2014-02-07
|
A temperature dependent formation time approach for Υsuppression at LHC
|
We present here a model to describe the bottomonium suppression in Pb$+$Pb
collisions at Large Hadron Collider (LHC), at $\sqrt{s_{NN}}=2.76$ TeV by using
the quasi-particle model (QPM) equation of state (EOS) for the Quark-Gluon
Plasma (QGP) expanding under Bjorken's hydrodynamical expansion. The current
model includes the modification of the formation time based on the temperature
of QGP, color screening during bottomonium production, gluon induced
dissociation and collisional damping. The cold nuclear matter (CNM) effects and
decay of higher resonances of bottomonium have also been included in the
present work. The final suppression of the bottomonium states, at mid rapidity
is calculated as a function of centrality. The results compare closely with the
recent data at Large hadron Collider (LHC) in the mid rapidity region for
various centrality bins. {\nd \it Keywords } : Color screening, Gluonic
dissociation, Collisional damping, Survival probability, CNM effects\\ {\nd \it
PACS numbers } : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa
|
1402.1560v5
|
2014-02-12
|
A numerical comparison between degenerate parabolic and quasilinear hyperbolic models of cell movements under chemotaxis
|
We consider two models which were both designed to describe the movement of
eukaryotic cells responding to chemical signals. Besides a common standard
parabolic equation for the diffusion of a chemoattractant, like chemokines or
growth factors, the two models differ for the equations describing the movement
of cells. The first model is based on a quasilinear hyperbolic system with
damping, the other one on a degenerate parabolic equation. The two models have
the same stationary solutions, which may contain some regions with vacuum. We
first explain in details how to discretize the quasilinear hyperbolic system
through an upwinding technique, which uses an adapted reconstruction, which is
able to deal with the transitions to vacuum. Then we concentrate on the
analysis of asymptotic preserving properties of the scheme towards a
discretization of the parabolic equation, obtained in the large time and large
damping limit, in order to present a numerical comparison between the
asymptotic behavior of these two models. Finally we perform an accurate
numerical comparison of the two models in the time asymptotic regime, which
shows that the respective solutions have a quite different behavior for large
times.
|
1402.2831v2
|
2014-02-13
|
Surface Activity and Oscillation Amplitudes of Red Giants in Eclipsing Binaries
|
Among 19 red-giant stars belonging to eclipsing binary systems that have been
identified in Kepler data, 15 display solar-like oscillations. We study whether
the absence of mode detection in the remaining 4 is an observational bias or
possibly evidence of mode damping that originates from tidal interactions. A
careful analysis of the corresponding Kepler light curves shows that modes with
amplitudes that are usually observed in red giants would have been detected if
they were present. We observe that mode depletion is strongly associated with
short-period systems, in which stellar radii account for 16-24 % of the
semi-major axis, and where red-giant surface activity is detected. We suggest
that when the rotational and orbital periods synchronize in close binaries, the
red-giant component is spun up, so that a dynamo mechanism starts and generates
a magnetic field, leading to observable stellar activity. Pressure modes would
then be damped as acoustic waves dissipate in these fields.
|
1402.3027v1
|
2014-02-18
|
Cherenkov friction on a neutral particle moving parallel to a dielectric
|
Based on a fully relativistic framework and the assumption of local
equilibrium, we describe a simple mechanism of quantum friction for a particle
moving parallel to a dielectric. The Cherenkov effect explains how the bare
ground state becomes globally unstable and how fluctuations of the
electromagnetic field and the particle's dipole are converted into pairs of
excitations. Modelling the particle as a silver nano-sphere, we investigate the
spectrum of the force and its velocity dependence. We find that the damping of
the plasmon resonance in the silver particle has a relatively strong impact
near the Cherenkov threshold velocity. We also present an expansion of the
friction force near the threshold velocity for both damped and undamped
particles.
|
1402.4518v1
|
2014-02-20
|
Feed-forward control for quantum state protection against decoherence
|
We propose a novel scheme of feed-forward control and its reversal for
protecting quantum state against decoherence. Before the noise channel our
pre-weak measurement and feed-forward are just to change the protected state
into the state almost immune to the noise channel, and after the channel our
reversed operations and post-weak measurements are just to restore the
protected state. Unlike most previous state protection schemes, ours only
concerns the noise channel and does not care about the protected state. We show
that our scheme can effectively protect unknown states, nonorthogonal states
and entangled states against amplitude damping noise. Our scheme has dramatic
merits of protecting quantum states against heavy amplitude damping noise, and
can perfectly protect some specific nonorthogonal states in an almost
deterministic way, which might be found some applications in current quantum
communication technology. And it is most important that our scheme is
experimentally available with current technology.
|
1402.4921v2
|
2014-02-25
|
Elastic Anomalies Associated with the Antiferroelectric Phase Transitions of PbHfO3 Single Crystals
|
The temperature dependence of the elastic properties of antiferroelectric
PbHfO3 was investigated by Brillouin scattering. The two structural phase
transitions of antiferroelectric-antiferroelectric-paraelectric phases were
clearly identified by discontinuous changes in the acoustic mode frequencies
and the hypersonic damping. The substantial softening of the mode frequency
along with the remarkable increase in the acoustic damping observed in the
paraelectric phase indicated the formation of precursor noncentrosymmetric
(polar) clusters and their coupling to the acoustic waves. This was
corroborated by the observation of quasi-elastic central peaks, the intensity
of which grew upon cooling toward the Curie point. The obtained relaxation time
exhibited a slowing-down behavior, suggesting that the dynamics of precursor
clusters becomes more sluggish on approaching the phase transition temperature.
|
1402.6175v1
|
2014-03-05
|
Short-period pulsar oscillations following a glitch
|
Following a glitch, the crust and magnetized plasma in the outer core of a
neutron star are believed to rapidly establish a state of co-rotation within a
few seconds by process analogous to classical Ekman pumping. However, in ideal
magnetohydrodynamics, a final state of co-rotation is inconsistent with
conservation of energy of the system. We demonstrate that, after the Ekman-like
spin up is completed, magneto-inertial waves continue to propagate throughout
the star, exciting torsional oscillations in the crust and plasma. The crust
oscillation is irregular and quasi-periodic, with a dominant frequency of the
order of seconds. Crust oscillations commence after an Alfv\'en crossing time,
approximately half a minute at the magnetic pole, and are subsequently damped
by the electron viscosity over approximately an hour. In rapidly rotating
stars, the magneto-inertial spectrum in the core approaches a continuum, and
crust oscillations are damped by resonant absorption analogous to
quasi-periodic oscillations in magnetars. The oscillations predicted are
unlikely to be observed in timing data from existing radio telescopes, but may
be visible to next generation telescope arrays.
|
1403.1046v2
|
2014-03-06
|
On the damped oscillations of an elastic quasi-circular membrane in a two-dimensional incompressible fluid
|
We propose a procedure - partly analytical and partly numerical - to find the
frequency and the damping rate of the small-amplitude oscillations of a
massless elastic capsule immersed in a two-dimensional viscous incompressible
fluid. The unsteady Stokes equations for the stream function are decomposed
onto normal modes for the angular and temporal variables, leading to a
fourth-order linear ordinary differential equation in the radial variable. The
forcing terms are dictated by the properties of the membrane, and result into
jump conditions at the interface between the internal and external media. The
equation can be solved numerically, and an excellent agreement is found with a
fully-computational approach we developed in parallel. Comparisons are also
shown with the results available in the scientific literature for drops, and a
model based on the concept of embarked fluid is presented, which allows for a
good representation of the results and a consistent interpretation of the
underlying physics.
|
1403.1423v1
|
2014-03-07
|
The silicon matrix for the prototype for the Dark Matter Particle Explorer
|
A new generation detector for the high energy cosmic ray - the DAMPE(DArk
Matter Particle Explorer) is a satellite based project. Its main object is the
measurement of energy spectrum of cosmic ray nuclei from 100GeV to 100TeV, the
high energy electrons and gamma ray from 5GeV to 10TeV. A silicon matrix
detector described in this paper, is employed for the sea level cosmic ray
energy and position detection while the prototype testing of the DAMPE. This
matrix is composed by the 180 silicon PIN detectors, which covers an area of
32*20 cm2. The primary testing results are shown including MIPs energy spectrum
and the position sensitive map.
|
1403.1679v2
|
2014-04-01
|
Anomalies in the specific heat of a free damped particle: The role of the cutoff in the spectral density of the coupling
|
The properties of a dissipative system depend on the spectral density of the
coupling to the environment. Mostly, the dependence on the low-frequency
behavior is in the focus of interest. However, in order to avoid divergencies,
it is also necessary to suppress the spectral density of the coupling at high
frequencies. Interestingly, the very existence of this cutoff may lead to a
mass renormalization which can have drastic consequences for the thermodynamic
properties of the dissipative system. Here, we explore the role which the
cutoff in the spectral density of the coupling plays for a free damped particle
and we compare the effect of an algebraic cutoff with that of a sharp cutoff.
|
1404.0254v1
|
2014-04-09
|
Directly imaging damped Ly-alpha galaxies at z>2. II: Imaging and spectroscopic observations of 32 quasar fields
|
Damped Ly-alpha absorbers (DLAs) are a well-studied class of absorption line
systems, and yet the properties of their host galaxies remain largely unknown.
To investigate the origin of these systems, we have conducted an imaging survey
of 32 quasar fields with intervening DLAs between z~1.9-3.8, leveraging a
technique that allows us to image galaxies at any small angular separation from
the background quasars. In this paper, we present the properties of the
targeted DLA sample, new imaging observations of the quasar fields, and the
analysis of new and archival spectra of the background quasars.
|
1404.2599v2
|
2014-04-13
|
Homotopy invariants methods in the global dynamics of strongly damped wave equation
|
We are interested in the following differential equation $\ddot u(t) = -A
u(t) - c A \dot u(t) + \lambda u(t) + F(u(t))$ where $c > 0$ is a damping
factor, $A$ is a sectorial operator and $F$ is a continuous map. We consider
the situation where the equation is at resonance at infinity, which means that
$\lambda$ is an eigenvalue of $A$ and $F$ is a bounded map. We provide
geometrical conditions for the nonlinearity $F$ and determine the Conley index
of the set $K_\infty$, that is the union of the bounded orbits of this
equation.
|
1404.3429v3
|
2014-04-14
|
Low-distance Surface Codes under Realistic Quantum Noise
|
We study the performance of distance-three surface code layouts under
realistic multi-parameter noise models. We first calculate their thresholds
under depolarizing noise. We then compare a Pauli-twirl approximation of
amplitude and phase damping to amplitude and phase damping. We find the
approximate channel results in a pessimistic estimate of the logical error
rate, indicating the realistic threshold may be higher than previously
estimated. From Monte-Carlo simulations, we identify experimental parameters
for which these layouts admit reliable computation. Due to its low resource
cost and superior performance, we conclude that the 17-qubit layout should be
targeted in early experimental implementations of the surface code. We find
that architectures with gate times in the 5-40 ns range and T1 times of at
least 1-2 us range will exhibit improved logical error rates with a 17-qubit
surface code encoding.
|
1404.3747v3
|
2014-04-21
|
Phase conversion dissipation in multicomponent compact stars
|
We propose a mechanism for the damping of density oscillations in
multicomponent compact stars. The mechanism is the periodic conversion between
different phases, i.e., the movement of the interface between them, induced by
pressure oscillations in the star. The damping grows nonlinearly with the
amplitude of the oscillation. We study in detail the case of r-modes in a
hybrid star with a sharp interface, and we find that this mechanism is powerful
enough to saturate the r-mode at very low saturation amplitude, of order
$10^{-10}$, and is therefore likely to be the dominant r-mode saturation
mechanism in hybrid stars with a sharp interface.
|
1404.5279v4
|
2014-04-29
|
Quasi-normal modes of superfluid neutron stars
|
We study non-radial oscillations of neutron stars with superfluid baryons, in
a general relativistic framework, including finite temperature effects. Using a
perturbative approach, we derive the equations describing stellar oscillations,
which we solve by numerical integration, employing different models of nucleon
superfluidity, and determining frequencies and gravitational damping times of
the quasi-normal modes. As expected by previous results, we find two classes of
modes, associated to superfluid and non-superfluid degrees of freedom,
respectively. We study the temperature dependence of the modes, finding that at
specific values of the temperature, the frequencies of the two classes of
quasi-normal modes show avoided crossings, and their damping times become
comparable. We also show that, when the temperature is not close to the avoided
crossings, the frequencies of the modes can be accurately computed by
neglecting the coupling between normal and superfluid degrees of freedom. Our
results have potential implications on the gravitational wave emission from
neutron stars.
|
1404.7512v1
|
2014-05-27
|
Nonequilibrium dynamical mean-field theory for bosonic lattice models
|
We develop the nonequilibrium extension of bosonic dynamical mean field
theory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity
solver. In contrast to Gutzwiller mean-field theory and strong coupling
perturbative approaches, nonequilibrium BDMFT captures not only dynamical
transitions, but also damping and thermalization effects at finite temperature.
We apply the formalism to quenches in the Bose-Hubbard model, starting both
from the normal and Bose-condensed phases. Depending on the parameter regime,
one observes qualitatively different dynamical properties, such as rapid
thermalization, trapping in metastable superfluid or normal states, as well as
long-lived or strongly damped amplitude oscillations. We summarize our results
in non-equilibrium "phase diagrams" which map out the different dynamical
regimes.
|
1405.6941v2
|
2014-05-28
|
Electronic control of the spin-wave damping in a magnetic insulator
|
It is demonstrated that the decay time of spin-wave modes existing in a
magnetic insulator can be reduced or enhanced by injecting an in-plane dc
current, $I_\text{dc}$, in an adjacent normal metal with strong spin-orbit
interaction. The demonstration rests upon the measurement of the ferromagnetic
resonance linewidth as a function of $I_\text{dc}$ in a 5~$\mu$m diameter
YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope
(MRFM). Complete compensation of the damping of the fundamental mode is
obtained for a current density of $\sim 3 \cdot 10^{11}\text{A.m}^{-2}$, in
agreement with theoretical predictions. At this critical threshold the MRFM
detects a small change of static magnetization, a behavior consistent with the
onset of an auto-oscillation regime.
|
1405.7415v1
|
2014-06-16
|
Study on FPGA SEU Mitigation for Readout Electronics of DAMPE BGO Calorimeter
|
The BGO calorimeter, which provides a wide measurement range of the primary
cosmic ray spectrum, is a key sub-detector of Dark Matter Particle Explorer
(DAMPE). The readout electronics of calorimeter consists of 16 pieces of Actel
ProASIC Plus FLASH-based FPGA, of which the design-level flip-flops and
embedded block RAMs are single event upset (SEU) sensitive in the harsh space
environment. Therefore to comply with radiation hardness assurance (RHA), SEU
mitigation methods, including partial triple modular redundancy (TMR), CRC
checksum, and multi-domain reset are analyzed and tested by the heavy-ion beam
test. Composed of multi-level redundancy, a FPGA design with the
characteristics of SEU tolerance and low resource consumption is implemented
for the readout electronics.
|
1406.3928v1
|
2014-06-18
|
Damping of glacial-interglacial cycles from anthropogenic forcing
|
Climate variability over the past million years shows a strong
glacial-interglacial cycle of ~100,000 years as a combined result of
Milankovitch orbital forcing and climatic resonance. It has been suggested that
anthropogenic contributions to radiative forcing may extend the length of the
present interglacial, but the effects of anthropogenic forcing on the
periodicity of glacial-interglacial cycles has received little attention. Here
I demonstrate that moderate anthropogenic forcing can act to damp this 100,000
year cycle and reduce climate variability from orbital forcing. Future changes
in solar insolation alone will continue to drive a 100,000 year climate cycle
over the next million years, but the presence of anthropogenic warming can
force the climate into an ice-free state that only weakly responds to orbital
forcing. Sufficiently strong anthropogenic forcing that eliminates the
glacial-interglacial cycle may serve as an indication of an epoch transition
from the Pleistocene to the Anthropocene.
|
1406.4728v1
|
2014-06-27
|
Magnetoplasmons of the tilted-anisotropic Dirac cone material $α-$(BEDT-TTF)$_2$I$_3$
|
We study the collective modes of a low-energy continuum model of the
quasi-two-dimensional electron liquid in a layer of the organic compound
$\alpha-$(BEDT-TTF)$_2$I$_3$ in a perpendicular magnetic field. As testified by
zero magnetic field transport experiments and \textit{ab initio} theory, this
material hosts both massless and massive low-energy carriers, the former being
described by tilted and anisotropic Dirac cones. The polarizability of these
cones is anisotropic, and two sets of magnetoplasmon modes occur between any
two cyclotron resonances. We show that the tilt of the cones causes a unique
intervalley damping effect: the upper hybrid mode of one cone is damped by the
particle-hole continuum of the other cone in generic directions. We analyse how
the presence of massive carriers affects the response of the system, and
demonstrate how doping can tune $\alpha-$(BEDT-TTF)$_2$I$_3$ between regimes of
isotropic and anisotropic screening.
|
1406.7081v2
|
2014-06-30
|
Collective Coordinates Theory for Discrete Soliton Ratchets in the sine-Gordon Model
|
A collective coordinate theory is develop for soliton ratchets in the damped
discrete sine-Gordon model driven by a biharmonic force. An ansatz with two
collective coordinates, namely the center and the width of the soliton, is
assumed as an approximated solution of the discrete non-linear equation. The
evolution of these two collective coordinates, obtained by means of the
Generalized Travelling Wave Method, explains the mechanism underlying the
soliton ratchet and captures qualitatively all the main features of this
phenomenon. The theory accounts for the existence of a non-zero depinning
threshold, the non-sinusoidal behaviour of the average velocity as a function
of the difference phase between the harmonics of the driver, the non-monotonic
dependence of the average velocity on the damping and the existence of
non-transporting regimes beyond the depinning threshold. In particular it
provides a good description of the intriguing and complex pattern of subspaces
corresponding to different dynamical regimes in parameter space.
|
1406.7656v1
|
2014-07-04
|
Temperature Dependent Ferromagnetic Resonance via the Landau-Lifshitz-Bloch Equation: Application to FePt
|
Using the Landau-Lifshitz-Bloch (LLB) equation for ferromagnetic materials,
we derive analytic expressions for temperature dependent absorption spectra as
probed by ferromagnetic resonance (FMR). By analysing the resulting
expressions, we can predict the variation of the resonance frequency and
damping with temperature and coupling to the thermal bath. We base our
calculations on the technologically relevant L1$_0$ FePt, parameterised from
atomistic spin dynamics simulations, with the Hamiltonian mapped from ab-initio
parameters. By constructing a multi-macrospin model based on the LLB equation
and exploiting GPU acceleration we extend the study to investigate the effects
on the damping and resonance frequency in ${\mu}$m sized structures.
|
1407.1174v1
|
2014-07-07
|
Composition variation and underdamped mechanics near membrane proteins and coats
|
We study the effect of membrane proteins on the shape, composition and
thermodynamic stability of the surrounding membrane. When the coupling between
membrane composition and curvature is strong enough the nearby composition and
shape both undergo a transition from over-damped to under-damped spatial
variation, well before the membrane becomes unstable in the bulk. This
transition is associated with a change in the sign of the thermodynamic energy
and hence has the unusual features that it can favour the early stages of coat
assembly necessary for vesiculation (budding), while suppressing the activity
of mechanosensitive membrane channels and transporters. Our results also
suggest an approach to obtain physical parameters that are otherwise difficult
to measure.
|
1407.1672v2
|
2014-07-11
|
Evidence for Wave Heating of the Quiet Sun Corona
|
We have measured the energy and dissipation of Alfvenic waves in the quiet
Sun. A magnetic field was used to infer the location and orientation of the
magnetic field lines along which the waves are expected to travel. The waves
were measured using spectral lines to infer the wave amplitude. The waves cause
a non-thermal broadening of the spectral lines, which can be expressed as a
non-thermal velocity v_nt. By combining the spectroscopic measurements with
this magnetic field model we were able to trace the variation of v_nt along the
magnetic field. At the footpoints of the quiet Sun loops we find that waves
inject an energy flux in the range of 1.2-5.2 x 10^5 erg cm^-2 s^-1. At the
minimum of this range, this amounts to more than 80% of the energy needed to
heat the quiet Sun. We also find that these waves are dissipated over a region
centered on the top of the loops. The position along the loop where the damping
begins is strongly correlated with the length of the loop, implying that the
damping mechanism depends on the global loop properties rather than on local
collisional dissipation.
|
1407.3250v1
|
2014-07-16
|
Nonresonant high frequency excitation of mechanical vibrations in graphene based nanoresonator
|
We theoretically analyse the dynamics of a suspended graphene membrane which
is in tunnel contact with grounded metallic electrodes and subjected to
ac-electrostatic potential induced by a gate electrode. It is shown that for
such system the retardation effects in the electronic subsystem generate an
effective pumping for the relatively slow mechanical vibrations if the driving
frequency exceeds the inverse charge relax- ation time. Under this condition
there is a critical value of the driving voltage ampli- tude above which the
pumping overcomes the intrinsic damping of the mechanical resonator leading to
a mechanical instability. This nonresonant instability is saturated by
nonlinear damping and the system exhibits self-sustained oscillations of
relatively large amplitude.
|
1407.4278v2
|
2014-07-21
|
Non-Markovian dynamics of open quantum systems without rotating wave approximation
|
We study the non-Markovian dynamics of a damped oscillator coupled with a
reservoir. We present exact formulas for the oscillator's evolution directly
from the BCH formula by series expansion with neither Markovian nor rotating
wave approximation (RWA). Based on these, we show the existence of the
non-Markovian feature of the system's evolution for the damped oscillator. By
numerical simulation we find that the non-Markovian feature exists within a
wide range of the coupling strength, even when the coupling strength is very
small. To this problem, prior art results have assumed RWA and the existence of
non-Markovian feature was found when the system-reservoir coupling is strong
enough. However, as we show, given such a strong coupling, the original
Hamiltonian without RWA is actually not physical. Therefore, our exact study
here has thoroughly concluded the issue of non-Markovian feature.
|
1407.5359v2
|
2014-07-23
|
Global Existence of Smooth Solutions and Convergence to Barenblatt Solutions for the Physical Vacuum Free Boundary Problem of Compressible Euler Equations with Damping
|
For the physical vacuum free boundary problem with the sound speed being
$C^{{1}/{2}}$-H$\ddot{\rm o}$lder continuous near vacuum boundaries of the
one-dimensional compressible Euler equations with damping, the global existence
of the smooth solution is proved, which is shown to converge to the Barenblatt
self-similar solution for the the porous media equation with the same total
mass when the initial data is a small perturbation of the Barenblatt solution.
The pointwise convergence with a rate of density, the convergence rate of
velocity in supereme norm and the precise expanding rate of the physical vacuum
boundaries are also given. The proof is based on a construction of higher-order
weighted functionals with both space and time weights capturing the behavior of
solutions both near vacuum states and in large time, an introduction of a new
ansatz, higher-order nonlinear energy estimates and elliptic estimates.
|
1407.6111v2
|
2014-07-24
|
Decay of dark and bright plasmonic modes in a metallic nanoparticle dimer
|
We develop a general quantum theory of the coupled plasmonic modes resulting
from the near-field interaction between localized surface plasmons in a
heterogeneous metallic nanoparticle dimer. In particular, we provide analytical
expressions for the frequencies and decay rates of the bright and dark
plasmonic modes. We show that, for sufficiently small nanoparticles, the main
decay channel for the dark plasmonic mode, which is weakly coupled to light
and, hence, immune to radiation damping, is of nonradiative origin and
corresponds to Landau damping, i.e., decay into electron-hole pairs.
|
1407.6569v2
|
2014-07-29
|
Reproducing the Kinematics of Damped Lyman-alpha Systems
|
We examine the kinematic structure of Damped Lyman-alpha Systems (DLAs) in a
series of cosmological hydrodynamic simulations using the AREPO code. We are
able to match the distribution of velocity widths of associated low ionisation
metal absorbers substantially better than earlier work. Our simulations produce
a population of DLAs dominated by halos with virial velocities around 70 km/s,
consistent with a picture of relatively small, faint objects. In addition, we
reproduce the observed correlation between velocity width and metallicity and
the equivalent width distribution of SiII. Some discrepancies of moderate
statistical significance remain; too many of our spectra show absorption
concentrated at the edge of the profile and there are slight differences in the
exact shape of the velocity width distribution. We show that the improvement
over previous work is mostly due to our strong feedback from star formation and
our detailed modelling of the metal ionisation state.
|
1407.7858v2
|
2014-07-31
|
Plasmons in finite spherical ionic systems
|
The challenging question on possible plasmon type excitations in finite ionic
systems is discussed. The related theoretical model is formulated and developed
in order to describe surface and volume plasmons of ion liquid in finite
electrolyte systems. The irradiation of ionic surface plasmon fluctuations is
studied in terms of the Lorentz friction of oscillating charges. The
attenuation of surface plasmons in the ionic sphere is calculated and minimized
with respect to the sphere size. Various regimes of approximation for
description of size effect for damping of ionic plasmons are determined and a
cross-over in damping size-dependence is demonstrated. The most convenient
dimension of finite electrolyte system for energy and information transfer by
usage of ionic dipole plasmons is determined. The overall shift of size effect
to micrometer scale for ions in comparison to nanometer scale for electrons in
metals is found and by several orders red shift of plasmonic resonances in ion
systems is predicted in a wide range of variation depending of ion system
parameters. This convenient opportunity of tuning of resonances differs ionic
plasmons from plasmons in metals where electron concentration was firmly fixed.
|
1407.8369v2
|
2014-08-04
|
Collective Dynamics of Interacting Particles in Unsteady Flows
|
We use the Fokker-Planck equation and its moment equations to study the
collective behavior of interacting particles in unsteady one-dimensional flows.
Particles interact according to a long-range attractive and a short-range
repulsive potential field known as Morse potential. We assume Stokesian drag
force between particles and their carrier fluid, and find analytic
single-peaked traveling solutions for the spatial density of particles in the
catastrophic phase. In steady flow conditions the streaming velocity of
particles is identical to their carrier fluid, but we show that particle
streaming is asynchronous with an unsteady carrier fluid. Using linear
perturbation analysis, the stability of traveling solutions is investigated in
unsteady conditions. It is shown that the resulting dispersion relation is an
integral equation of the Fredholm type, and yields two general families of
stable modes: singular modes whose eigenvalues form a continuous spectrum, and
a finite number of discrete global modes. Depending on the value of drag
coefficient, stable modes can be over-damped, critically damped, or decaying
oscillatory waves. The results of linear perturbation analysis are confirmed
through the numerical solution of the fully nonlinear Fokker-Planck equation.
|
1408.0558v1
|
2014-08-13
|
Correlated decay of triplet excitations in the Shastry-Sutherland compound SrCu$_2$(BO$_3$)$_2$
|
The temperature dependence of the gapped triplet excitations (triplons) in
the 2D Shastry-Sutherland quantum magnet SrCu$_2$(BO$_3$)$_2$ is studied by
means of inelastic neutron scattering. The excitation amplitude rapidly
decreases as a function of temperature while the integrated spectral weight can
be explained by an isolated dimer model up to 10~K. Analyzing this anomalous
spectral line-shape in terms of damped harmonic oscillators shows that the
observed damping is due to a two-component process: one component remains sharp
and resolution limited while the second broadens. We explain the underlying
mechanism through a simple yet quantitatively accurate model of correlated
decay of triplons: an excited triplon is long-lived if no thermally populated
triplons are near-by but decays quickly if there are. The phenomenon is a
direct consequence of frustration induced triplon localization in the
Shastry--Sutherland lattice.
|
1408.3135v1
|
2014-08-20
|
Enhanced dissipation and inviscid damping in the inviscid limit of the Navier-Stokes equations near the 2D Couette flow
|
In this work we study the long time, inviscid limit of the 2D Navier-Stokes
equations near the periodic Couette flow, and in particular, we confirm at the
nonlinear level the qualitative behavior predicted by Kelvin's 1887 linear
analysis. At high Reynolds number Re, we prove that the solution behaves
qualitatively like 2D Euler for times t \lesssim Re^(1/3), and in particular
exhibits inviscid damping (e.g. the vorticity weakly approaches a shear flow).
For times t \gtrsim Re^(1/3), which is sooner than the natural dissipative time
scale O(Re), the viscosity becomes dominant and the streamwise dependence of
the vorticity is rapidly eliminated by an enhanced dissipation effect.
Afterward, the remaining shear flow decays on very long time scales t \gtrsim
Re back to the Couette flow. When properly defined, the dissipative
length-scale in this setting is L_D \sim Re^(-1/3), larger than the scale L_D
\sim Re^(-1/2) predicted in classical Batchelor-Kraichnan 2D turbulence theory.
The class of initial data we study is the sum of a sufficiently smooth function
and a small (with respect to Re^(-1)) $L^2$ function.
|
1408.4754v1
|
2014-09-01
|
Dynamical symmetries and crossovers in a three-spin system with collective dissipation
|
We consider the non-equilibrium dynamics of a simple system consisting of
interacting spin-$1/2$ particles subjected to a collective damping. The model
is close to situations that can be engineered in hybrid electro/opto-mechanical
settings. Making use of large-deviation theory, we find a Gallavotti-Cohen
symmetry in the dynamics of the system as well as evidence for the coexistence
of two dynamical phases with different activity levels. We show that additional
damping processes smoothen out this behavior. Our analytical results are backed
up by Monte Carlo simulations that reveal the nature of the trajectories
contributing to the different dynamical phases.
|
1409.0422v2
|
2014-09-02
|
Controlled bidirectional remote state preparation in noisy environment: A generalized view
|
It is shown that a realistic, controlled bidirectional remote state
preparation is possible using a large class of entangled quantum states having
a particular structure. Existing protocols of probabilistic, deterministic and
joint remote state preparation are generalized to obtain the corresponding
protocols of controlled bidirectional remote state preparation (CBRSP). A
general way of incorporating the effects of two well known noise processes, the
amplitude-damping and phase-damping noise, on the probabilistic CBRSP process
is studied in detail by considering that noise only affects the travel qubits
of the quantum channel used for the probabilistic CBRSP process. Also indicated
is how to account for the effect of these noise channels on deterministic and
joint remote state CBRSP protocols.
|
1409.0833v1
|
2014-09-07
|
The Effects of Long Pulse Durations and Radiation Damping in Selective Inversion Recovery Experiments
|
Long pulse durations necessary in selective inversion recovery (SIR)
experiments along with radiation damping (RD) introduce difficulties in
quantitative nuclear magnetic resonance measurements, such as those that allow
for the determination of a sample's characteristics, including the rates that
govern magnetization transfer. Because of these influences, the assumption of
perfect inversion is invalid. In this work, we present data that demonstrates
that long pulse durations as well as RD cause difficulties in SIR experiments
performed on simple one-spin systems, indicating that they will be problematic
for multiple-spin systems as well. These results emphasize the importance of
understanding the evolution of magnetization for all time points throughout an
experiment used in quantitative NMR measurements. Furthermore, experimental
parameters must be chosen carefully and understood completely.
|
1409.2136v2
|
2014-09-08
|
Self-similar solutions of the one-dimensional Landau-Lifshitz-Gilbert equation
|
We consider the one-dimensional Landau-Lifshitz-Gilbert (LLG) equation, a
model describing the dynamics for the spin in ferromagnetic materials. Our main
aim is the analytical study of the bi-parametric family of self-similar
solutions of this model. In the presence of damping, our construction provides
a family of global solutions of the LLG equation which are associated to a
discontinuous initial data of infinite (total) energy, and which are smooth and
have finite energy for all positive times. Special emphasis will be given to
the behaviour of this family of solutions with respect to the Gilbert damping
parameter.
We would like to emphasize that our analysis also includes the study of
self-similar solutions of the Schr\"odinger map and the heat flow for harmonic
maps into the 2-sphere as special cases. In particular, the results presented
here recover some of the previously known results in the setting of the
1d-Schr\"odinger map equation.
|
1409.2340v1
|
2014-09-19
|
Angular dependence of spin-orbit spin transfer torques
|
In ferromagnet/heavy metal bilayers, an in-plane current gives rise to
spin-orbit spin transfer torque which is usually decomposed into field-like and
damping-like torques. For two-dimensional free-electron and tight-binding
models with Rashba spin-orbit coupling, the field-like torque acquires
nontrivial dependence on the magnetization direction when the Rashba spin-orbit
coupling becomes comparable to the exchange interaction. This nontrivial
angular dependence of the field-like torque is related to the Fermi surface
distortion, determined by the ratio of the Rashba spin-orbit coupling to the
exchange interaction. On the other hand, the damping-like torque acquires
nontrivial angular dependence when the Rashba spin-orbit coupling is comparable
to or stronger than the exchange interaction. It is related to the combined
effects of the Fermi surface distortion and the Fermi sea contribution. The
angular dependence is consistent with experimental observations and can be
important to understand magnetization dynamics induced by spin-orbit spin
transfer torques
|
1409.5600v1
|
2014-10-01
|
Non-linear collisionless damping of Weibel turbulence in relativistic blast waves
|
The Weibel/filamentation instability is known to play a key role in the
physics of weakly magnetized collisionless shock waves. From the point of view
of high energy astrophysics, this instability also plays a crucial role because
its development in the shock precursor populates the downstream with a
small-scale magneto-static turbulence which shapes the acceleration and
radiative processes of suprathermal particles. The present work discusses the
physics of the dissipation of this Weibel-generated turbulence downstream of
relativistic collisionless shock waves. It calculates explicitly the
first-order non-linear terms associated to the diffusive nature of the particle
trajectories. These corrections are found to systematically increase the
damping rate, assuming that the scattering length remains larger than the
coherence length of the magnetic fluctuations. The relevance of such
corrections is discussed in a broader astrophysical perspective, in particular
regarding the physics of the external relativistic shock wave of a gamma-ray
burst.
|
1410.0146v1
|
2014-10-10
|
The Fate of Scattered Planets
|
As gas giant planets evolve, they may scatter other planets far from their
original orbits to produce hot Jupiters or rogue planets that are not
gravitationally bound to any star. Here, we consider planets cast out to large
orbital distances on eccentric, bound orbits through a gaseous disk. With
simple numerical models, we show that super-Earths can interact with the gas
through dynamical friction to settle in the remote outer regions of a planetary
system. Outcomes depend on planet mass, the initial scattered orbit, and the
evolution of the time-dependent disk. Efficient orbital damping by dynamical
friction requires planets at least as massive as the Earth. More massive,
longer-lived disks damp eccentricities more efficiently than less massive,
short-lived ones. Transition disks with an expanding inner cavity can
circularize orbits at larger distances than disks that experience a global
(homologous) decay in surface density. Thus, orbits of remote planets may
reveal the evolutionary history of their primordial gas disks. A remote planet
with an orbital distance ~100 AU from the Sun is plausible and might explain
correlations in the orbital parameters of several distant trans-Neptunian
objects.
|
1410.2816v1
|
2014-10-13
|
Unified Theory of Inertial Granular Flows and Non-Brownian Suspensions
|
Rheological properties of dense flows of hard particles are singular as one
approaches the jamming threshold where flow ceases, both for aerial granular
flows dominated by inertia, and for over-damped suspensions. Concomitantly, the
lengthscale characterizing velocity correlations appears to diverge at jamming.
Here we introduce a theoretical framework that proposes a tentative, but
potentially complete scaling description of stationary flows. Our analysis,
which focuses on frictionless particles, applies {\it both} to suspensions and
inertial flows of hard particles. We compare our predictions with the empirical
literature, as well as with novel numerical data. Overall we find a very good
agreement between theory and observations, except for frictional inertial flows
whose scaling properties clearly differ from frictionless systems. For
over-damped flows, more observations are needed to decide if friction is a
relevant perturbation or not. Our analysis makes several new predictions on
microscopic dynamical quantities that should be accessible experimentally.
|
1410.3535v3
|
2014-10-22
|
Landau damping in the Kuramoto model
|
We consider the Kuramoto model of globally coupled phase oscillators in its
continuum limit, with individual frequencies drawn from a distribution with
density of class $C^n$ ($n\geq 4$). A criterion for linear stability of the
uniform stationary state is established which, for basic examples of frequency
distributions, is equivalent to the standard condition on the coupling strength
in the literature. We prove that, under this criterion, the Kuramoto order
parameter, when evolved under the full nonlinear dynamics, asymptotically
vanishes (with polynomial rate $n$) for every trajectory issued from
sufficiently small $C^n$ perturbation. The proof uses techniques from the
Analysis of PDEs and closely follows recent proofs of the nonlinear Landau
damping in the Vlasov equation and Vlasov-HMF model.
|
1410.6006v1
|
2014-10-30
|
Global Solutions to the Gas-Vacuum Interface Problem of Isentropic Compressible Inviscid Flows with Damping in Spherically Symmetric Motions and Physical Vacuum
|
For the physical vacuum free boundary problem with the sound speed being
$C^{{1}/{2}}$-H$\ddot{\rm o}$lder continuous near vacuum boundaries of the
three-dimensional compressible Euler equations with damping, the global
existence of spherically symmetric smooth solutions is proved, which are shown
to converge to Barenblatt self-similar solutions of the porous media equation
with the same total masses when initial data are small perturbations of
Barenblatt solutions. The pointwise convergence with a rate of density, the
convergence rate of velocity in supreme norm and the precise expanding rate of
physical vacuum boundaries are also given by constructing nonlinear functionals
with space-time weights featuring the behavior of solutions in large time and
near the vacuum boundary and the center of symmetry, the nonlinear energy
estimates and elliptic estimates.
|
1410.8471v1
|
2014-11-03
|
Monami as an oscillatory hydrodynamic instability in a submerged sea grass bed
|
The onset of monami ~-- the synchronous waving of sea grass beds driven by a
steady flow -- is modeled as a linear instability of the flow. Unlike previous
works, our model considers the drag exerted by the grass in establishing the
steady flow profile, and in damping out perturbations to it. We find two
distinct modes of instability, which we label Mode 1 and Mode 2. Mode 1 is
closely related to Kelvin-Helmholtz instability modified by vegetation drag,
whereas Mode 2 is unrelated to Kelvin-Helmholtz and arises from an interaction
between the flow in the vegetated and unvegetated layers. The vegetation
damping, according to our model, leads to a finite threshold flow for both
these modes. Experimental observations for the onset and frequency of waving
compare well with model predictions for the instability onset criteria and the
imaginary part of the complex growth rate respectively, but experiments lie in
a parameter regime where the two modes can not be distinguished. % The
inclusion of vegetation drag differentiates our mechanism from the previous
linear stability analyses of monami.
|
1411.0365v2
|
2014-11-12
|
Dependence of the Efficiency of Spin Hall Torque on the Transparency of Pt-Ferromagnetic Layer Interfaces
|
We report that spin current transport across Pt-ferromagnet (FM) interfaces
is strongly dependent on the type and the thickness of the FM layer and on
post-deposition processing protocols. By employing both harmonic voltage
measurements and spin-torque ferromagnetic resonance measurements, we find that
the efficiency of the Pt spin Hall effect in exerting a damping-like spin
torque on the FM ranges from < 0.05 to > 0.10 under different interfacial
conditions. We also show that the temperature dependence of the spin torque
efficiencies for both the damping-like torque and field-like torque is
dependent upon the details of the Pt-FM interface. The "internal" spin Hall
angle of the Pt thin films used in this study, after taking the interfacial
spin transmission factor into account, is estimated to be ~ 0.20. This suggests
that a careful engineering of Pt-FM interfaces can improve the spin-Hall-torque
efficiency of Pt-based spintronic devices.
|
1411.3379v1
|
2014-11-13
|
Transverse dynamical magnetic susceptibilities from regular static density functional theory: Evaluation of damping and g-shifts of spin-excitations
|
The dynamical transverse magnetic Kohn-Sham susceptibility calculated within
time-dependent density functional theory shows a fairly linear behavior for a
finite energy window. This observation is used to propose a scheme where the
computation of this quantity is greatly simplified. Regular simulations based
on static density functional theory can be used to extract the dynamical
behavior of the magnetic response function. Besides the ability to calculate
elegantly damping of magnetic excitations, we derive along the way useful
equations giving the main characteristics of these excitations: effective
$g$-factors and the resonance frequencies that can be accessed experimentally
using inelastic scanning tunneling spectroscopy or spin-polarized electron
energy loss spectroscopy.
|
1411.3630v1
|
2014-11-17
|
Decoherence Effects on the Non-locality of Symmetric States
|
The observation of the non-local properties of multipartite entangled states
is of great importance for quantum information protocols. Such properties,
however, are fragile and may not be observed in the presence of decoherence
exhibited by practical physical systems. In this work, we investigate the
robustness of the non-locality of symmetric states experiencing phase and
amplitude damping, using suitable Bell inequalities based on an extended
version of Hardy's paradox. We derive thresholds for observing non-locality in
terms of experimental noise parameters, and demonstrate the importance of the
choice of the measurement bases for optimizing the robustness. For $W$ states,
in the phase damping case, we show that this choice can lead to a trade-off
between obtaining a high violation of the non-local test and optimal robustness
thresholds; we also show that in this setting the non-locality of $W$ states is
particularly robust for a large number of qubits. Furthermore, we apply our
techniques to the discrimination of symmetric states belonging to different
entanglement classes, thus illustrating their usefulness for a wide range of
practical quantum information applications.
|
1411.4489v1
|
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