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2013-03-19
|
Stabilization of the Gear-Grimshaw system on a periodic domain
|
This paper is devoted to the study of a nonlinear coupled system of two
Korteweg-de Vries equations in a periodic domain under the effect of an
internal damping term. The system was introduced Gear and Grimshaw to model the
interactions of two-dimensional, long, internal gravity waves propagation in a
stratified fluid. Designing a time-varying feedback law and using a Lyapunov
approach we establish the exponential stability of the solutions in Sobolev
spaces of any positive integral order.
|
1303.4759v2
|
2013-03-26
|
Current-driven domain wall motion with spin Hall effect: Reduction of threshold current density
|
We theoretically study the current-driven domain wall motion in the presence
of both the spin Hall effect and an extrinsic pinning potential. The spin Hall
effect mainly affects the damping ratio of the domain wall precession in the
pinning potential. When the pinning potential is not too strong, this results
in a significant reduction of a threshold current density for the depinning of
a domain wall with certain polarity. We also propose one way to distinguish the
spin Hall effect induced spin-transfer torque from the one induced by the
Rashba spin-orbit coupling experimentally.
|
1303.6458v1
|
2013-03-27
|
Spontaneous nucleation and dynamics of kink defects in zigzag arrays of trapped ions
|
The spontaneous nucleation and dynamics of topological kink defects have been
studied in trapped arrays of 41-43 Yb ions. The number of kinks formed as a
function of quench rate across the linear-zigzag transition is measured in the
under-damped regime of the inhomogeneous Kibble-Zurek theory. The experimental
results agree well with molecular dynamics simulations, which show how losses
mask the intrinsic nucleation rate. Simulations indicate that doubling the ion
number and optimization of laser cooling can help reduce the effect of losses.
A range of kink dynamics is observed including configural change, motion and
lifetime, and behavioral sensitivity to ion number.
|
1303.6723v1
|
2013-04-11
|
Transport of dipolar Bose-Einstein condensates in a one-dimensional optical lattice
|
We show that magnetic dipolar interactions can stabilize superfluidity in
atomic gases but the dipole alignment direction required to achieve this
varies, depending on whether the flow is oscillatory or continuous. If a
condensate is made to oscillate through a lattice, damping of the oscillations
can be reduced by aligning the dipoles perpendicular to the direction of
motion. However, if a lattice is driven continuously through the condensate,
superfluid behavior is best preserved when the dipoles are aligned parallel to
the direction of motion. We explain these results in terms of the formation of
topological excitations and tunnel barrier heights between lattice sites.
|
1304.3250v1
|
2013-04-12
|
Mechanical signaling via nonlinear wavefront propagation in a mechanically-excitable medium
|
Models that invoke nonlinear wavefront propagation in a chemically excitable
medium are rife in the biological literature. Indeed, the idea that wavefront
propagation can serve as a signaling mechanism has often been invoked to
explain synchronization of developmental processes. In this paper we suggest a
new kind of signaling based not on diffusion of a chemical species but on the
propagation of mechanical stress. We construct a theoretical approach to
describe mechanical signaling as a nonlinear wavefront propagation problem and
study its dependence on key variables such as the effective elasticity and
damping of the medium.
|
1304.3657v1
|
2013-04-15
|
Phase-sticking in one-dimensional Josephson Junction Chains
|
We studied current-voltage characteristics of long one dimensional Josephson
junction chains with Josephson energy much larger than charging energy, $E_J
\gg E_C$. In this regime, typical IV curves of the samples consist of a
supercurrent branch at low bias voltages followed by a voltage-independent
chain current branch, $I_{Chain}$ at high bias. Our experiments showed that
$I_{Chain}$ is not only voltage-independent but it is also practically
temperature-independent up to $T_C$. We have successfully model the transport
properties in these chains using a capacitively shunted junction model with
nonlinear damping.
|
1304.4046v1
|
2013-04-18
|
Nonlinear dynamical systems and bistability in linearly forced isotropic turbulence
|
In this letter, we present an extensive study of the linearly forced
isotropic turbulence. By using analytical method, we identify two parametric
choices, of which they seem to be new as far as our knowledge goes. We prove
that the underlying nonlinear dynamical system for linearly forced isotropic
turbulence is the general case of a cubic Lienard equation with linear damping.
We also discuss a Fokker-Planck approach to this new dynamical system,which is
bistable and exhibits two asymmetric and asymptotically stable stationary
probability densities.
|
1304.5019v1
|
2013-05-17
|
Nonuniversal power-law spectra in turbulent systems
|
Turbulence is generally associated with universal power-law spectra in scale
ranges without significant drive or damping. Although many examples of
turbulent systems do not exhibit such an inertial range, power-law spectra may
still be observed. As a simple model for such situations, a modified version of
the Kuramoto-Sivashinsky equation is studied. By means of semi-analytical and
numerical studies, one finds power laws with nonuniversal exponents in the
spectral range for which the ratio of nonlinear and linear time scales is
(roughly) scale-independent.
|
1305.4111v2
|
2013-05-25
|
Phonon excitation and instabilities in biased graphene nanoconstrictions
|
We calculate the phonons in a graphene nanoconstriction(GNC) in the presence
of a high current density. The Joule-heating, current-induced forces, and
coupling to electrode phonons is evaluated using first principles
nonequilibrium DFT-NEGF calculations. Close to a resonance in the electronic
structure we observe a strongly nonlinear heating with bias and breakdown of
the harmonic approximation. This behavior results from negatively damped
phonons driven by the current. The effect may limit the stability and capacity
of graphene nanoconstrictions to carry high currents.
|
1305.5907v1
|
2013-05-28
|
Optical bistability in strong-coupling cavity QED with a few atoms
|
We present exact numerical solutions of the damped-driven Jaynes--Cummings
model adapted to describe absorptive optical bistability in the limit of a few
atoms strongly coupled to a high-finesse resonator. We show that the
simplifying semiclassical result for many physical quantities of interest is
well reproduced by the quantum model including even with only a few atoms in
the strongly coupled system. Nontrivial atom-field quantum cross-correlations
show up in the strong-driving limit.
|
1305.6460v1
|
2013-06-16
|
Mapping Between Nonlinear Schödinger Equations with Real and Complex Potentials
|
A mapping between stationary solutions of nonlinear Sch\"odinger equations
with real and complex potentials is constructed and a set of exact solutions
with real energies are obtained for a large class of complex potentials. As
specific examples we consider the case of the damped dynamics of a quantum
harmonic oscillator and the case of dissipative periodic soliton solutions of
the nonlinear Schr\"odinger equation with complex potential.
|
1306.3643v1
|
2013-06-16
|
Non-determinism in the limit of nonsmooth dynamics
|
Discontinuous time derivatives are used to model threshold-dependent
switching in such diverse applications as dry friction, electronic control, and
biological growth. In a continuous flow, a discon- tinuous derivative can
generate multiple outcomes from a single initial state. Here we show that well
defined solution sets exist for flows that become multi-valued due to grazing a
discontinuity. Loss of determinism is used to quantify dynamics in the limit of
infinite sensitivity to initial conditions, then applied to the dynamics of a
superconducting resonator and a negatively damped oscillator.
|
1306.3648v1
|
2013-06-17
|
Uniformly exponentially stable approximations for a class of damped systems with unbounded feedbacks
|
In this paper we study time semi-discrete approximations of a class of
exponentially stable infinite dimensional systems with unbounded feedbacks. It
has recently been proved that for time semi-discrete systems, due to high
frequency spurious components, the exponential decay property may be lost as
the time step tends to zero. We prove that adding a suitable numerical
viscosity term in the numerical scheme, one obtains approximations that are
uniformly exponentially stable with respect to the discretization parameter
|
1306.3798v1
|
2013-06-19
|
Purifying entanglement of noisy two-qubit states via entanglement swapping
|
Two qubits in pure entangled states going through separate paths and
interacting with their own individual environments will gradually lose their
entanglement. Here we show that the entanglement change of a two-qubit state
due to amplitude damping noises can be recovered by entanglement swapping. Some
initial states can be asymptotically purified into maximally entangled states
by iteratively using our protocol.
|
1306.4451v4
|
2013-06-19
|
A quasi-linear spin-torque nano-oscillator via enhanced negative feedback of power fluctuations
|
We report an approach to improving the performance of spin torque
nano-oscillators (STNOs) that utilizes power-dependent negative feedback to
achieve a significantly enhanced dynamic damping. In combination with a
sufficiently slow variation of frequency with power this can result in a
quasi-linear STNO, with very weak non-linear coupling of power and phase
fluctuations over a range of bias current and field. An implementation of this
approach that utilizes a non-uniform spin-torque demonstrates that highly
coherent room temperature STNOs can be achieved while retaining a significant
tunability.
|
1306.4668v1
|
2013-06-29
|
Tkachenko polarons in vortex lattices
|
We analyze the properties of impurities immersed in a vortex lattice formed
by ultracold bosons in the mean field quantum Hall regime. In addition to the
effects of a periodic lattice potential, the impurity is dressed by collective
modes with parabolic dispersion (Tkachenko modes). We derive the effective
polaron model, which contains a marginal impurity-phonon interaction. The
polaron spectral function exhibits a Lorentzian broadening for arbitrarily
small wave vectors even at zero temperature, in contrast with the result for
optical or acoustic phonons. The anomalous damping of Tkachenko polarons could
be detected experimentally using momentum-resolved spectroscopy.
|
1307.0144v2
|
2013-07-01
|
Wigner distribution, nonclassicality and decoherence of generalized and reciprocal binomial states
|
There are quantum states of light that can be expressed as finite
superpositions of Fock states (FSFS). We demonstrate the nonclassicality of an
arbitrary FSFS by means of its phase space distributions such as the Wigner
function and the $Q$-function. The decoherence of the FSFS is studied by
considering the time evolution of its Wigner function in amplitude decay and
phase damping channels. As examples, we determine the nonclassicality and
decoherence of generalized and reciprocal binomial states.
|
1307.0452v1
|
2013-07-25
|
Vector boson excitations near deconfined quantum critical points
|
We show that the N\'eel states of two-dimensional antiferromagnets have low
energy vector boson excitations in the vicinity of deconfined quantum critical
points. We compute the universal damping of these excitations arising from
spin-wave emission. Detection of such a vector boson will demonstrate the
existence of emergent topological gauge excitations in a quantum spin system.
|
1307.6860v1
|
2013-07-29
|
Theoretical Study of Spin-Torque Oscillator with Perpendicularly Magnetized Free Layer
|
The magnetization dynamics of spin torque oscillator (STO) consisting of a
perpendicularly magnetized free layer and an in-plane magnetized pinned layer
was studied by solving the Landau-Lifshitz-Gilbert equation. We derived the
analytical formula of the relation between the current and the oscillation
frequency of the STO by analyzing the energy balance between the work done by
the spin torque and the energy dissipation due to the damping. We also found
that the field-like torque breaks the energy balance, and change the
oscillation frequency.
|
1307.7427v1
|
2013-08-06
|
Radiation Reaction Effects in Cascade Scattering of Intense, Tightly Focused Laser Pulses by Relativistic Electrons
|
Non-linear cascade scattering of intense, tightly focused laser pulses by
relativistic electrons is studied numerically in the classical approximation
including the radiation damping for the quantum parameter hwx-ray/E<1 and an
arbitrary radiation parameter Kai. The electron energy loss, along with its
side scattering by the ponderomotive force, makes the scattering in the
vicinity of high laser field nearly impossible at high electron energies. The
use of a second, co-propagating laser pulse as a booster is shown to solve this
problem.
|
1308.1608v1
|
2013-08-07
|
A general method to remove the stiffness of PDEs
|
A new method to remove the stiffness of partial differential equations is
presented. Two terms are added to the right-hand-side of the PDE : the first is
a damping term and is treated implicitly, the second is of the opposite sign
and is treated explicitly. A criterion for absolute stability is found and the
scheme is shown to be convergent. The method is applied with success to the
mean curvature flow equation, the Kuramoto-Sivashinsky equation, and to the
Rayleigh-Taylor instability in a Hele-Shaw cell, including the effect of
surface tension.
|
1308.1621v1
|
2013-08-14
|
Microscopic description of nuclear vibrations: Relativistic QRPA and its extensions with quasiparticle-vibration coupling
|
The recent extensions of the covariant energy density functional theory with
the quasiparticle-vibration coupling (QVC) are reviewed. Formulation of the
Quasiparticle Random Phase Approximation (QRPA) in the relativistic framework
is discussed. Self-consistent extensions of the relativistic QRPA imply the QVC
which is implemented in two-body propagators in the nuclear medium. This
provides fragmentation of the QRPA states describing the damping of the
vibrational motion.
|
1308.3164v1
|
2013-08-27
|
Actively coupled optical waveguides
|
We consider light propagation through a pair of nonlinear optical waveguides
with absorption, placed in a medium with power gain. The active medium boosts
the in-phase component of the overlapping evanescent fields of the guides,
while the nonlinearity of the guides couples it to the damped out-of-phase
component creating a feedback loop. As a result, the structure exhibits stable
stationary and oscillatory regimes in a wide range of gain-loss ratios. We show
that the pair of actively-coupled ($\mathcal{AC}$) waveguides can act as a
stationary or integrate-and-fire comparator sensitive to tiny differences in
their input powers.
|
1308.5862v1
|
2013-08-27
|
Collective modes in the anisotropic unitary Fermi gas and the inclusion of a backflow term
|
We study the collective modes of the confined unitary Fermi gas under
anisotropic harmonic confinement as a function of the number of atoms. We use
the equations of extended superfluid hydrodynamics, which take into account a
dispersive von Weizsacker-like term in the equaton of state. We also discuss
the inclusion of a backflow term in the extended superfluid Lagrangian and the
effects of this anomalous term on sound waves and Beliaev damping of phonons.
|
1308.5922v1
|
2013-09-05
|
Quantum speed limit of a photon under non-Markovian dynamics
|
Quantum speed limit (QSL) under noise has drawn considerable attention in
real quantum computational processes and quantum communication. Though
non-Markovian noise is proven to be able to accelerate quantum evolution for a
damped Jaynes-Cummings model, in this work we show that non-Markovianity may
even slow down the quantum evolution of an experimentally controllable photon
system. As an important application, QSL time of a photon can be well
controlled by regulating the relevant environment parameter properly, which is
close to reach the currently available photonic experimental technology.
|
1309.1391v1
|
2013-09-07
|
Optomechanical effect on the Dicke quantum phase transition and quasi-particle damping in a Bose-Einstein Condensate: A new tool to measure weak force
|
We make a semi-classical steady state analysis of the influence of mirror
motion on the quantum phase transition for an optomechanical Dicke model in the
thermodynamic limit. An additional external mechanical pump is shown to modify
the critical value of atom-photon coupling needed to observe the quantum phase
transition. We further show how to choose the mechanical pump frequency and
cavity-laser detuning to produce extremely cold condensates. The present system
can be used as a quantum device to measure weak forces.
|
1309.1838v1
|
2013-09-14
|
Dynamics of the polarization of a pinned domain wall in a magnetic nanowire
|
We consider the dynamics of polarization of a single domain wall in a
magnetic nanowire, which is strongly pinned by impurities. In this case the
equation of motion for the polarization parameter does not include any other
dynamical variables and is nonlinear due to magnetic anisotropy. We calculated
numerically the magnetization dynamics for different choices of parameters
under short current pulses inducing polarization switching. Our results show
that the switching is most effective for very rapid current pulses. Damping
also enhances the switching probability.
|
1309.3687v1
|
2013-09-28
|
High-efficiency GHz frequency doubling without power threshold in thin-film Ni81Fe19
|
We demonstrate efficient second-harmonic generation at moderate input power
for thin film Ni81Fe19 undergoing ferromagnetic resonance (FMR). Powers of the
generated second-harmonic are shown to be quadratic in input power, with an
upconversion ratio three orders of magnitude higher than that demonstrated in
ferrite. The second harmonic signal generated exhibits a significantly lower
linewidth than that predicted by low-power Gilbert damping, and is excited
without threshold. Results are in good agreement with an analytic, approximate
expansion of the Landau-Lifshitz-Gilbert (LLG) equation.
|
1309.7483v1
|
2013-09-29
|
Magnetic shield of PMT used in DAMPE electromagnetic calorimeter
|
The magnetic characteristics of photomultiplier tube R5610A-01 are studied in
this paper. The experimental data shows that the gain of R5610A-01 loses about
53% when the magnetic field is 3G along its +X axis. A cylinder of one-layer
permalloy strip is able to reduce the effect of 3G magnetic field on the PMT's
gain to less than 1%.
|
1309.7638v4
|
2013-09-30
|
Dynamical regimes of dissipative quantum systems
|
We reveal several distinct regimes of the relaxation dynamics of a small
quantum system coupled to an environment within the plane of the dissipation
strength and the reservoir temperature. This is achieved by discriminating
between coherent dynamics with damped oscillatory behavior on all time scales,
partially coherent behavior being nonmonotonic at intermediate times but
monotonic at large ones, and purely monotonic incoherent decay. Surprisingly,
elevated temperature can render the system `more coherent' by inducing a
transition from the partially coherent to the coherent regime. This provides a
refined view on the relaxation dynamics of open quantum systems.
|
1309.7860v2
|
2013-10-01
|
Graphene nanoribbon based spaser
|
A novel type of spaser with the net amplification of surface plasmons (SPs)
in doped graphene nanoribbon is proposed. The plasmons in THz region can be
generated in a dopped graphene nanoribbon due to nonradiative excitation by
emitters like two level quantum dots located along a graphene nanoribbon. The
minimal population inversion per unit area, needed for the net amplification of
SPs in a doped graphene nanoribbon is obtained. The dependence of the minimal
population inversion on the surface plasmon wavevector, graphene nanoribbon
width, doping and damping parameters necessary for the amplification of surface
plasmons in the armchair graphene nanoribbon is studied.
|
1310.0136v1
|
2013-10-02
|
Stochastic Schrödinger Equations for Markovian and non-Markovian cases
|
Firstly, the Markovian stochastic Schr\"odinger equations are presented,
together with their connections with the theory of measurements in continuous
time. Moreover, the stochastic evolution equations are translated into a
simulation algorithm, which is illustrated by two concrete examples - the
damped harmonic oscillator and a two-level atom with homodyne photodetection.
Then, we consider how to introduce memory effects in the stochastic
Schr\"odinger equation via coloured noise. Specifically, the approach by using
the Ornstein-Uhlenbeck process is illustrated and a simulation for the
non-Markovian process proposed. Finally, an analytical approximation technique
is tested with the help of the stochastic simulation in a model of a
dissipative qubit.
|
1310.0644v1
|
2013-10-15
|
A new tool to study real dynamics: The Convergence Plane
|
In this paper, the author presents a new tool, called The Convergence Plane,
that allows to study the real dynamics of iterative methods whose iterations
depends on one parameter in an easy and compact way. This tool can be used,
inter alia, to find the elements of a family that have good convergence
properties and discard the bad ones or to see how the basins of attraction
changes along the elements of the family. To show the applicability of the tool
an example of the dynamics of the Damped Newton's method applied to a cubic
polynomial is presented.
|
1310.3986v1
|
2013-10-27
|
Quantum simulation of decoherence in optical waveguide lattices
|
We suggest that propagation of nonclassical light in lattices of optical
waveguides can provide a laboratory tool to simulate quantum decoherence
phenomena with high non-Markovian features. As examples, we study decoherence
of optical Schr\"{o}dinger cats in a lattice that mimics a dissipative quantum
harmonic oscillator coupled to a quantum bath, showing fractional decoherence
in the strong coupling regime, and Bloch oscillations of optical
Schr\"{o}dinger cats, where damped revivals of the coherence can be observed.
|
1310.7239v1
|
2013-11-05
|
Efficient time integration methods based on operator splitting and application to the Westervelt equation
|
Efficient time integration methods based on operator splitting are introduced
for the Westervelt equation, a nonlinear damped wave equation that arises in
nonlinear acoustics as mathematical model for the propagation of sound waves in
high intensity ultrasound applications. For the first-order Lie-Trotter
splitting method a global error estimate is deduced, confirming that the
splitting method remains stable and that the nonstiff convergence order is
retained in situations where the problem data are sufficiently regular.
Fundamental ingredients in the stability and error analysis are regularity
results for the Westervelt equation and related linear evolution equations of
hyperbolic and parabolic type. Numerical examples illustrate and complement the
theoretical investigations.
|
1311.1224v1
|
2013-11-06
|
A new optical field state as an output of diffusion channel when the input being number state
|
We theoretically propose a new optical field state which is named
Laguerre-polynomial-weighted chaotic field. We show that such state can be
implemented, i.e., when a number state enters into a diffusion channel, the
output state is just this kind of states. We solve the master equation
describing the diffusion process by using the summation method within ordered
product of operators and the entangled state representaion. The solution
manifestly shows how a pure state evolves into a mixed state. The physical
difference between the diffusion and the amplitude damping is pointed out.
|
1311.1275v1
|
2013-11-14
|
Chromo-Natural Model in Anisotropic Background
|
In this work we study the chromo-natural inflation model in the anisotropic
setup. Initiating inflation from Bianchi type-I cosmology, we analyze the
system thoroughly during the slow-roll inflation, from both analytical and
numerical points of view. We show that the isotropic FRW inflation is an
attractor of the system. In other words, anisotropies are damped within few
$e$--folds and the chromo-natural model respects the cosmic no-hair conjecture.
Furthermore, we demonstrate that in the slow-roll limit, the anisotropies in
both chromo-natural and gauge-flation models share the same dynamics.
|
1311.3361v2
|
2013-11-27
|
Polynomial Stability of Semigroups Generated by Operator Matrices
|
In this paper we study the stability properties of strongly continuous
semigroups generated by block operator matrices. We consider triangular and
full operator matrices whose diagonal operator blocks generate polynomially
stable semigroups. As our main results, we present conditions under which also
the semigroup generated by the operator matrix is polynomially stable. The
theoretic results are applied to deriving conditions for the polynomial
stability of a system consisting of a two-dimensional and a one-dimensional
damped wave equations.
|
1311.6960v1
|
2013-12-02
|
Critical Field of Spin Torque Oscillator with Perpendicularly Magnetized Free Layer
|
The oscillation properties of a spin torque oscillator consisting of a
perpendicularly magnetized free layer and an in-plane magnetized pinned layer
are studied based on an analysis of the energy balance between spin torque and
damping. The critical value of an external magnetic field applied normal to the
film plane is found, below which the controllable range of the oscillation
frequency by the current is suppressed. The value of the critical field depends
on the magnetic anisotropy, the saturation magnetization, and the spin torque
parameter.
|
1312.0300v1
|
2013-12-09
|
Spin-orbit torque opposing the Oersted torque in ultrathin Co/Pt bilayers
|
Current-induced torques in ultrathin Co/Pt bilayers were investigated using
an electrically driven FMR technique. The angle dependence of the resonances,
detected by a rectification effect as a voltage, were analysed to determine the
symmetries and relative magnitudes of the spin-orbit torques. Both anti-damping
(Slonczewski) and field-like torques were observed. As the ferromagnet
thickness was reduced from 3 to 1 nm, the sign of the field-like torque
reversed. This observation is consistent with the emergence of a Rashba spin
orbit torque in ultra-thin bilayers.
|
1312.2409v1
|
2013-12-10
|
Shifted Laplacian based multigrid preconditioners for solving indefinite Helmholtz equations
|
Shifted Laplacian multigrid preconditioner has become a tool du jour for
solving highly indefinite Helmholtz equations. The idea is to add a complex
damping to the original Helmholtz operator and then apply a multigrid
processing to the resulting operator using it to precondition Krylov methods,
usually Bi-CGSTAB. Not only such preconditioning accelerates Krylov iterations,
but it does so more efficiently than the multigrid applied to original
Helmholtz equations. In this paper, we compare properties of the Helmholtz
operator with and without the shift and propose a new combination of the two.
Also applied here is a relaxation of normal equations that replaces diverging
linear schemes on some intermediate scales. Finally, an acceleration by the ray
correction is considered.
|
1312.2880v1
|
2013-12-12
|
Fidelity of Fock-state-encoded qubits subjected to continuous variable Gaussian processes
|
When a harmonic oscillator is under the influence of a Gaussian process such
as linear damping, parametric gain, and linear coupling to a thermal
environment, its coherent states are transformed into states with Gaussian
Wigner function. Qubit states can be encoded in the |0> and |1> Fock states of
a quantum harmonic oscillator, and it is relevant to know the fidelity of the
output qubit state after a Gaussian process on the oscillator. In this paper we
present a general expression for the average qubit fidelity in terms of the
first and second moments of the output from input coherent states subjected to
Gaussian processes.
|
1312.3655v1
|
2013-12-16
|
Supersonic flutter analysis of flat composite panels by unified formulation
|
In this paper, the linear flutter characteristics of laminated composite flat
panels immersed in a supersonic flow is investigated using field consistent
elements within the framework of unified formulation. The influence of the
aerodynamic damping on the supersonic flutter characteristics of flat composite
panels is also investigated. The aerodynamic force is evaluated using
two-dimensional static aerodynamic approximation for high supersonic flow.
Numerical results are presented for laminated composites that bring out the
influence of the flow angle, the boundary conditions, the plate thickness and
the plate aspect ratio on the flutter characteristics.
|
1312.4233v1
|
2013-12-24
|
Fractional Entropy Decaying and the Third Law of Thermodynamics
|
The quantum thermodynamic property of the fractional damping system is
investigated extensively. A fractional power-law decaying entropy function is
revealed which presents another evidence for the validity of the third law of
thermodynamics in the quantum dissipative region. Several non-trivial
characters are excavated such as that the entropy varies from a non-linear
diverging function to a semi-linear decaying function of the fractional
exponent as the temperature tends to absolute zero.
|
1401.1425v1
|
2014-01-09
|
Universal quasinormal modes of large D black holes
|
We show that in the limit where the number of spacetime dimensions D grows to
infinity a very large class of black holes (including non-extremal, static,
asymptotically flat ones, with any number of gauge-field charges, possibly
coupled to dilatons) possess a universal set of quasinormal modes whose complex
frequencies depend only on the horizon radius and no other black hole
parameters. The damping ratio of these modes vanishes like $D^{-2/3}$, so they
are almost normal modes, or 'quasi-particle' excitations of the black hole. The
structure responsible for the existence of these modes at large D is also
present very generally in other black holes.
|
1401.1957v1
|
2014-01-10
|
Quasi PT-symmetry in passive photonic lattices
|
The concept of quasi-PT symmetry in optical wave guiding system is elaborated
by comparing the evolution dynamics of a PT-symmetric directional coupler and a
passive directional coupler. In particular we show that in the low loss regime,
apart for an overall exponentially damping factor that can be compensated via a
dynamical renormalization of the power flow in the system along the propagation
direction, the dynamics of the passive coupler fully reproduce the one of the
PT-symmetric system.
|
1401.2299v3
|
2014-01-15
|
Dirac Quasinormal modes of MSW black holes
|
In this paper we study the Dirac quasinormal modes of an uncharged 2 + 1
black hole proposed by Mandal et. al and referred to as MSW black hole in this
work. The quasi- normal mode is studied using WKB approximation method. The
study shows that the imaginary part of quasinormal frequencies increases
indicating that the oscillations are damping and hence the black hole is stable
against Dirac perturbations.
|
1401.3496v1
|
2014-02-04
|
Mode competition and anomalous cooling in a multimode phonon laser
|
We study mode competition in a multimode "phonon laser" comprised of an
optical cavity employing a highly reflective membrane as the output coupler.
Mechanical gain is provided by the intracavity radiation pressure, to which
many mechanical modes are coupled. We calculate the gain, and find that strong
oscillation in one mode suppresses the gain in other modes. For sufficiently
strong oscillation, the gain of the other modes actually switches sign and
becomes damping, a process we call "anomalous cooling." We demonstrate that
mode competition leads to single-mode operation and find excellent agreement
with our theory, including anomalous cooling.
|
1402.0714v1
|
2014-02-11
|
Radiation reaction at the level of the action
|
The aim of this paper is to highlight a recently proposed method for the
treatment of classical radiative effects, in particular radiation reaction, via
effective field theory methods. We emphasize important features of the method,
and in particular the doubling of fields. We apply the method to two simple
systems: for the mass-rope system in 1+1 dimensions we derive an effective
action for the mass which describes a damped harmonic oscillator, while for the
electromagnetic charge-field system, i.e. the system of an accelerating
electric charge in 3+1 d, we derive the leading Abraham-Lorentz-Dirac force.
|
1402.2610v2
|
2014-02-14
|
Thermodynamically self-consistent non-stochastic micromagnetic model for the ferromagnetic state
|
In this work, a self-consistent thermodynamic approach to micromagnetism is
presented. The magnetic degrees of freedom are modeled using the
Landau-Lifshitz-Baryakhtar theory, that separates the different contributions
to the magnetic damping, and thereby allows them to be coupled to the electron
and phonon systems in a self-consistent way. We show that this model can
quantitatively reproduce ultrafast magnetization dynamics in Nickel.
|
1402.3487v3
|
2014-02-25
|
Dynamics of closed ecosystems described by operators
|
We adopt the so--called \emph{occupation number representation}, originally
used in quantum mechanics and recently adopted in the description of several
classical systems, in the analysis of the dynamics of some models of closed
ecosystems. In particular, we discuss two linear models, for which the solution
can be found analytically, and a nonlinear system, for which we produce
numerical results. We also discuss how a damping effect could be {\em
effectively} implemented in the model.
|
1402.6214v1
|
2014-03-03
|
Logarithmic stabilization of the Euler-Bernoulli transmission plate equation with locally distributed Kelvin-Voigt damping
|
In this paper we will study the asymptotic behaviour of the energy decay of a
transmission plate equation with locally distributed Kelvin-Voigt feedback.
Precisly, we shall prove that the energy decay at least logarithmically over
the time. The originality of this method comes from the fact that using a
Carleman estimate for a transmission second order system which will be derived
from the plate equation to establish a resolvent estimate which provide, by the
famous Burq's result [Bur98], the kind of decay mentionned above.
|
1403.0356v1
|
2014-03-12
|
Graphene Plasmonics for Terahertz to Mid-Infrared Applications
|
In recent years, we have seen a rapid progress in the field of graphene
plasmonics, motivated by graphene's unique electrical and optical properties,
tunabilty, long-lived collective excitation and their extreme light
confinement. Here, we review the basic properties of graphene plasmons; their
energy dispersion, localization and propagation, plasmon-phonon hybridization,
lifetimes and damping pathways. The application space of graphene plasmonics
lies in the technologically significant, but relatively unexploited terahertz
to mid-infrared regime. We discuss emerging and potential applications, such as
modulators, notch filters, polarizers, mid-infrared photodetectors,
mid-infrared vibrational spectroscopy, among many others.
|
1403.2799v1
|
2014-03-12
|
Logarithmic stability in determining two coefficients in a dissipative wave equation. Extensions to clamped Euler-Bernoulli beam and heat equations
|
We are concerned with the inverse problem of determining both the potential
and the damping coefficient in a dissipative wave equation from boundary
measurements. We establish stability estimates of logarithmic type when the
measurements are given by the operator who maps the initial condition to
Neumann boundary trace of the solution of the corresponding initial-boundary
value problem. We build a method combining an observability inequality together
with a spectral decomposition. We also apply this method to a clamped
Euler-Bernoulli beam equation. Finally, we indicate how the present approach
can be adapted to a heat equation.
|
1403.3018v2
|
2014-03-13
|
Challenges in description of heavy-ion collisions with microscopic time-dependent approaches
|
Important efforts have been dedicated in the past few years to describe
near-barrier heavy-ion collisions with microscopic quantum theories like the
time-dependent Hartree-Fock approach and some of its extensions. However, this
field is still facing important challenges such as the description of cluster
dynamics, the prediction of fragment characteristics in damped collisions, and
sub-barrier fusion by quantum tunnelling. These challenges are discussed and
possible approaches to solve them are presented.
|
1403.3246v1
|
2014-03-14
|
Optomechanical atom-cavity interaction in the sub-recoil regime
|
We study the optomechanical interaction of a Bose-Einstein condensate with a
single longitudinal mode of an ultra-high finesse standing wave optical
resonator. As a unique feature the resonator combines three extreme regimes,
previously not realized together, i.e., strong cooperative coupling, cavity
dominated scattering with a Purcell factor far above unity, and sub-recoil
resolution provided by a cavity damping rate smaller than four times the single
photon recoil frequency. We present experimental observations in good agreement
with a two-mode model predicting highly non-linear dynamics with signatures as
bistability, hysteresis, persistent oscillations, and superradiant
back-scattering instabilities.
|
1403.3545v1
|
2014-03-21
|
Steady Fock states via atomic reservoir
|
In this letter we present a strategy that combines the action of cavity
damping mechanisms with that of an engineered atomic reservoir to drive an
initial thermal distribution to a Fock equilibrium state. The same technique
can be used to slice probability distributions in the Fock space, thus allowing
the preparation of a variety of nonclassical equilibrium states.
|
1403.5482v1
|
2014-03-23
|
Smoluchowski-Kramers approximation and large deviations for infinite dimensional gradient systems
|
In this paper, we explicitly calculate the quasi-potentials for the damped
semilinear stochastic wave equation when the system is of gradient type. We
show that in this case the infimum of the quasi-potential with respect to all
possible velocities does not depend on the density of the mass and does
coincide with the quasi-potential of the corresponding stochastic heat equation
that one obtains from the zero mass limit. This shows in particular that the
Smoluchowski-Kramers approximation can be used to approximate long time
behavior in the zero noise limit, such as exit time and exit place from a basin
of attraction.
|
1403.5743v1
|
2014-03-23
|
Smoluchowski-Kramers approximation and large deviations for infinite dimensional non-gradient systems with applications to the exit problem
|
In this paper, we study the quasi-potential for a general class of damped
semilinear stochastic wave equations. We show that, as the density of the mass
converges to zero, the infimum of the quasi-potential with respect to all
possible velocities converges to the quasi-potential of the corresponding
stochastic heat equation, that one obtains from the zero mass limit. This shows
in particular that the Smoluchowski-Kramers approximation is not only valid for
small time, but, in the zero noise limit regime, can be used to approximate
long-time behaviors such as exit time and exit place from a basin of
attraction.
|
1403.5745v1
|
2014-03-24
|
L^p-tauberian theorems and L^p-rates for energy decay
|
We prove $L^p$-analogues of the classical tauberian theorem of Ingham and
Karamata, and its variations giving rates of decay. These results are applied
to derive $L^p$-decay of operator families arising in the study of the decay of
energy for damped wave equations and local energy for wave equations in
exterior domains. By constructing some examples of critical behaviour we show
that the $L^p$-rates of decay obtained in this way are best possible under our
assumptions.
|
1403.6084v2
|
2014-03-30
|
Gauge Field Turbulence as a Cause of Inflation in Chern-Simons Modified Gravity
|
In this paper, we study the dynamics of the Chern-Simons Inflation Model
proposed by Alexander, Marciano and Spergel. According to this model, inflation
begins when a fermion current interacts with a turbulent gauge field in a space
larger than some critical size. This mechanism appears to work by driving
energy from the initial random spectrum into a narrow band of frequencies,
similar to the inverse energy cascade seen in MHD turbulence. In this work we
focus on the dynamics of the interaction using phase diagrams and a thorough
analysis of the evolution equations. We show that in this model inflation is
caused by an over-damped harmonic oscillator driving waves in the gauge field
at their resonance frequency.
|
1403.7702v1
|
2014-04-08
|
Exactly solvable model of stochastic heat engine: Optimization of power, its fluctuations and efficiency
|
We investigate a stochastic heat engine based on an over-damped particle
diffusing on the positive real axis in an externally driven time-periodic
log-harmonic potential. The periodic driving is composed of two isothermal and
two adiabatic branches. Within our specific setting we verify the recent
universal results regarding efficiency at maximum power and discuss properties
of the optimal protocol. Namely, we show that for certain fixed parameters the
optimal protocol maximizes not only the output power but also the efficiency.
Moreover, we calculate the variance of the output work and discuss the
possibility to minimize fluctuations of the output power.
|
1404.2030v1
|
2014-04-10
|
Dual pumped microresonator frequency combs
|
A study is made of the nonlinear dynamics of dual pumped microresonator Kerr
frequency combs described by a driven and damped nonlinear Schr\"odinger
equation, with an additional degree of freedom in the form of the modulation
frequency. A truncated four wave model is derived for the pump modes and the
dominant sideband pair which is found to be able to describe much of the
essential dynamical behaviour of the full equation. The stability of stationary
states within the four wave model is investigated and numerical simulations are
made to demonstrate that a large range of solutions, including cavity solitons,
are possible beyond previously considered low intensity patterns.
|
1404.2792v1
|
2014-04-11
|
Optimal control of a qubit in an optical cavity
|
We study quantum information processing by means of optimal control theory.
To this end, we analyze the damped Jaynes-Cummings model, and derive optimal
control protocols that minimize the heating or energy dispersion rates, and
controls that drive the system at the quantum speed limit. Special emphasis is
put on analyzing the subtleties of optimal control theory for our system. In
particular, it is shown how two fundamentally different approaches to the
quantum speed limit can be reconciled by carefully formulating the problem.
|
1404.3137v2
|
2014-04-13
|
Invariant sets and connecting orbits for nonlinear evolution equations at resonance
|
We study the problem of existence of orbits connecting stationary points for
the nonlinear heat and strongly damped wave equations being at resonance at
infinity. The main difficulty lies in the fact that the problems may have no
solutions for general nonlinearity. To address this question we introduce
geometrical assumptions for the nonlinear term and use them to prove index
formulas expressing the Conley index of associated semiflows. We also prove
that the geometrical assumptions are generalizations of the well known
Landesman- Lazer and strong resonance conditions. Obtained index formulas are
used to derive criteria determining the existence of orbits connecting
stationary points.
|
1404.3428v2
|
2014-04-15
|
Finite time cooling in dispersively and dissipatively coupled optomechanics
|
The cooling performance of an optomechanical system comprising both
dispersive and dissipative coupling is studied. We present a scheme to cool a
mechanical resonator to its ground state in finite time by employing a chirped
pulse. When the cavity damping strength increases, the phonon occupation of the
resonator will decrease. Moreover, the cooling behaviors of this dispersively
and dissipatively coupled system with different incident pulses, different
system coupling strengths are explored. Our scheme is feasible to cool the
resonator in a wide parameter region.
|
1404.3851v2
|
2014-04-22
|
Strong Uniform Attractors for Non-Autonomous Dissipative PDEs with non translation-compact external forces
|
We give a comprehensive study of strong uniform attractors of non-autonomous
dissipative systems for the case where the external forces are not translation
compact. We introduce several new classes of external forces which are not
translation compact, but nevertheless allow to verify the attraction in a
strong topology of the phase space and discuss in a more detailed way the class
of so-called normal external forces introduced before. We also develop a
unified approach to verify the asymptotic compactness for such systems based on
the energy method and apply it to a number of equations of mathematical physics
including the Navier-Stokes equations, damped wave equations and
reaction-diffusing equations in unbounded domains.
|
1404.5563v1
|
2014-04-26
|
Self-interaction model of classical point particle in one-dimension
|
We consider a hamiltonian system on the real line, consisting of real scalar
field $\phi(x,t)$ and point particle with trajectory $y(t)$. The dynamics of
this system is defined by the system of two equations: wave equation for the
field, <<radiated>> by the point particle, and Newton's equation for the
particle in its own field. We find the solution where the particle is strongly
damped, but the kinetic and interaction energies of the field increase linearly
in time, in despite of the full energy conservation.
|
1404.6636v1
|
2014-05-03
|
Lie Symmetry Classification and Numerical Analysis of KdV Equation with Power-law Nonlinearity
|
In this paper, a complete Lie symmetry analysis of the damped wave equation
with time-dependent coefficients is investigated. Then the invariant solutions
and the exact solutions generated from the symmetries are presented. Moreover,
a Lie algebraic classifications and the optimal system are discussed. Finally,
using Chebyshev pseudo-spectral method (CPSM), a numerical analysis to solve
the invariant solutions corresponded the Lie symmetries of main equation is
presented. This method applies the Chebyshev-Gauss-Lobatto points as
collocation points.
|
1405.0592v3
|
2014-05-08
|
Electromagnetic back-reaction from currents on a straight string
|
Charge carriers moving at the speed of light along a straight,
superconducting cosmic string carry with them a logarithmically divergent slab
of electromagnetic field energy. Thus no finite local input can induce a
current that travels unimpeded to infinity. Rather, electromagnetic
back-reaction must damp this current asymptotically to nothing. We compute this
back-reaction and find that the electromagnetic fields and currents decline
exactly as rapidly as necessary to prevent a divergence. We briefly discuss the
corresponding gravitational situation.
|
1405.2097v2
|
2014-06-03
|
Improving Cooling performance of the mechanical resonator with the two-level-system defects
|
We study cooling performance of a realistic mechanical resonator containing
defects. The normal cooling method through an optomechanical system does not
work efficiently due to those defects. We show by employing periodical
$\sigma_z$ pulses, we can eliminate the interaction between defects and their
surrounded heat baths up to the first order of time. Compared with the cooling
performance of no $\sigma_z$ pulses case, much better cooling results are
obtained. Moreover, this pulse sequence has an ability to improve the cooling
performance of the resonator with different defects energy gaps and different
defects damping rates.
|
1406.0555v1
|
2014-06-10
|
Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance
|
We show by vector network analyzer ferromagnetic resonance measurements that
low Gilbert damping {\alpha} down to 0.006 can be achieved in perpendicularly
magnetized MgO/CoFeB/MgO thin films with ultra-thin insertions of Ta in the
CoFeB layer. While increasing the number of Ta insertions allows thicker CoFeB
layers to remain perpendicular, the effective areal magnetic anisotropy does
not improve with more insertions, and also comes with an increase in {\alpha}.
|
1406.2491v2
|
2014-06-10
|
Topological self-dual vacua of deformed gauge theories
|
We propose a deformation principle of gauge theories in three dimensions that
can describe topologically stable self-dual gauge fields, i.e., vacua
configurations that in spite of their masses do not deform the background
geometry and are locally undetected by charged particles. We interpret these
systems as describing boundary degrees of freedom of a self-dual Yang-Mills
field in $2+2$ dimensions with mixed boundary conditions. Some of these fields
correspond to Abrikosov-like vortices with an exponential damping in the
direction penetrating into the bulk. We also propose generalizations of these
ideas to higher dimensions and arbitrary p-form gauge connections.
|
1406.2727v1
|
2014-06-18
|
Photonic crystal optics in cold atomic gases
|
We describe propagation of light in a gas with periodic density modulation,
demonstrating photonic-crystal-like refraction with negative refraction angles.
We address the role of poorly defined boundaries and damping, and derive an
optical analog of the quantum adiabatic theorem. For Cs atoms in an optical
lattice, we show that relying on semi-adiabatic propagation one can excite and
spatially split positively and negatively refracting modes at experimentally
available gas densities.
|
1406.4655v1
|
2014-06-20
|
Enhancement of quantum correlations between two particles under decoherence in finite temperature environment
|
Enhancing the quantum correlations in realistic quantum systems interacting
with the environment of finite temperature is an important subject in quantum
information processing. In this paper, we use weak measurement and measurement
reversal to enhance the quantum correlations in a quantum system consisting of
two particles. The transitions of the quantum correlations measured by the
local quantum uncertainty of qubit-qubit and qutrit-qutrit quantum systems
under generalized amplitude damping channels are investigated. We show that,
after the weak measurement and measurement reversal, the joint system shows
more robustness against decoherence.
|
1406.5267v2
|
2014-06-26
|
The plucked string: an example of non-normal dynamics
|
Motion of a single Fourier mode of the plucked string is an example of
transient, free decay of coupled, damped oscillators. It shares the rarely
discussed features of the generic case, e.g., possessing a complete set of
non-orthogonal eigenvectors and no normal modes, but it can be analyzed and
solved analytically by hand in an approximation that is appropriate to musical
instruments' plucked strings.
|
1406.6939v2
|
2014-07-01
|
Newton methods for k-order Markov Constrained Motion Problems
|
This is a documentation of a framework for robot motion optimization that
aims to draw on classical constrained optimization methods. With one exception
the underlying algorithms are classical ones: Gauss-Newton (with adaptive step
size and damping), Augmented Lagrangian, log-barrier, etc. The exception is a
novel any-time version of the Augmented Lagrangian. The contribution of this
framework is to frame motion optimization problems in a way that makes the
application of these methods efficient, especially by defining a very general
class of robot motion problems while at the same time introducing abstractions
that directly reflect the API of the source code.
|
1407.0414v1
|
2014-07-02
|
On the physics of fizzing: How bubble bursting controls droplets ejection
|
Bubbles at a free surface surface usually burst in ejecting myriads of
droplets. Focusing on the bubble bursting jet, prelude for these aerosols, we
propose a simple scaling for the jet velocity and we unravel experimentally the
intricate roles of bubble shape, capillary waves, gravity and liquid
properties. We demonstrate that droplets ejection unexpectedly changes with
liquid properties. In particular, using damping action of viscosity,
self-similar collapse can be sheltered from capillary ripples and continue
closer to the singular limit, therefore producing faster and smaller
droplets.These results pave the road to the control of the bursting bubble
aerosols.
|
1407.0560v2
|
2014-07-04
|
Metal-Dielectric-Graphene Sandwich for Surface Enhanced Raman Spectroscopy
|
Raman intensity of Rhodamine B (RhB) is enhanced by inserting a thin high
\k{appa} dielectric layer which reduces the surface plasmon damping at the
gold-graphene interface. The results indicate that the Raman intensity
increases sharply by plasmonic resonance enhancement while maintaining
efficient fluorescence quenching with optimized dielectric layer thickness.
|
1407.1129v1
|
2014-07-16
|
Internal Decoherence of a Gaussian Wave Packet in a Harmonic Potential
|
We have studied the quantum dissipative problem of a Gaussian wave packet
under the influence of a harmonic potential. A phenomenological approach to
dissipation is adopted in the light of the well-known model in which the
environment is composed of a bath of non-interacting harmonic oscillators. As
one of the effects of the coupling to the bath is the evolution of an initially
pure wave packet into a statistical mixture, we estimate the characteristic
time elapsed for this to occur for different regimes of temperature, damping,
and also different initial states.
|
1407.4204v1
|
2014-07-18
|
Conditional Ramsey Spectroscopy with Synchronized Atoms
|
We investigate Ramsey spectroscopy performed on a synchronized ensemble of
two-level atoms. The synchronization is induced by the collective coupling of
the atoms to a heavily damped mode of an optical cavity. We show that, in
principle, with this synchronized system it is possible to observe Ramsey
fringes indefinitely, even in the presence of spontaneous emission and other
sources of individual-atom dephasing. This could have important consequences
for atomic clocks and a wide range of precision metrology applications.
|
1407.5132v1
|
2014-08-02
|
Damped Electromagnetic fluctuations in the early universe?
|
This short note considers the effects of quantum theory on the linear
evolution of the magnetic fields during and after inflation. The analysis
appears to show that the magnetic fields decay exponentially in the
high-temperature radiation era due to a combination of ohmic dissipation and
vacuum polarisation.
|
1408.0367v2
|
2014-08-05
|
Scalar and Electromagnetic Quasinormal modes of Extended black hole in F(R) gravity
|
In this paper we study the scalar and electromagnetic perturbations of an
extended black hole in F(R) gravity. The quasinormal modes in two cases are
evaluated and studied their behavior by plotting graphs in each case. To study
the quasinormal mode, we use the third order WKB method. The present study
shows that the absolute value of imaginary part of complex quasinormal modes
increases in both cases, thus the black hole is stable against these
perturbations. As the mass of the scalar field increases the imaginary part of
the frequency decreases. Thus damping slows down with increasing mass of the
scalar field.
|
1408.0935v1
|
2014-08-10
|
Generalized Gradient Flow Equation and Its Application to Super Yang-Mills Theory
|
We generalize the gradient flow equation for field theories with nonlinearly
realized symmetry. Applying the formalism to super Yang-Mills theory, we
construct a supersymmetric extension of the gradient flow equation. It can be
shown that the super gauge symmetry is preserved in the gradient flow.
Furthermore, choosing an appropriate modification term to damp the gauge
degrees of freedom, we obtain a gradient flow equation which is closed within
the Wess-Zumino gauge.
|
1408.2185v3
|
2014-08-11
|
Formation of Large-Amplitude Low-Frequency Waves in Capillary Turbulence on Superfluid He-II
|
The results of experimental and theoretical studies of the parametric decay
instability of capillary waves on the surface of superfluid helium He-II are
reported. It is demonstrated that in a system of turbulent capillary waves
low-frequency waves are generated along with the direct Kolmogorov-Zakharov
cascade of capillary turbulence. The effects of low-frequency damping and the
discreteness of the wave spectrum are discussed.
|
1408.2560v1
|
2014-08-13
|
Dynamic stabilization of an optomechanical oscillator
|
Quantum optomechanics offers the potential to investigate quantum effects in
macroscopic quantum systems in extremely well controlled experiments. In this
paper we discuss one such situation, the dynamic stabilization of a mechanical
system such as an inverted pendulum. The specific example that we study is a
"membrane in the middle" mechanical oscillator coupled to a cavity field via a
quadratic optomechanical interaction, with cavity damping the dominant source
of dissipation. We show that the mechanical oscillator can be dynamically
stabilized by a temporal modulation of the radiation pressure force. We
investigate the system both in the classical and quantum regimes highlighting
similarities and differences.
|
1408.3091v2
|
2014-09-15
|
Adaptive discontinuous Galerkin methods for non-linear diffusion-convection-reaction equations
|
In this work, we apply the adaptive discontinuous Galerkin (DGAFEM) method to
the convection dominated non-linear, quasi-stationary
diffusion-convection-reaction equations. We propose an efficient preconditioner
using a matrix reordering scheme to solve the sparse linear systems iteratively
arising from the discretized non-linear equations. Numerical examples
demonstrate effectiveness of the DGAFEM to damp the spurious oscillations and
resolve well the sharp layers occurring in convection dominated non-linear
equations.
|
1409.4313v1
|
2014-09-17
|
Delayed-response quantum back-action in nanoelectromechanical systems
|
We present a semiclassical theory for the delayed response of a quantum dot
(QD) to oscillations of a coupled nanomechanical resonator (NR). We prove that
the back-action of the QD changes both the resonant frequency and the quality
factor of the NR. An increase or decrease in the quality factor of the NR
corresponds to either an enhancement or damping of the oscillations, which can
also be interpreted as Sisyphus amplification or cooling of the NR by the QD.
|
1409.4930v2
|
2014-09-19
|
Spreading in Integrable and Non--integrable Many--body Systems
|
We consider a finite, closed and selfbound many--body system in which a
collective degree of freedom is excited. The redistribution of energy and
momentum into a finite number of the non-collective degrees of freedom is
referred to as spreading as opposed to damping in open systems. Spreading
closely relates to thermalization, but while thermalization requires
non-integrability, spreading can also present in integrable systems. We
identify subtle features which determine the onset of spreading in an
integrable model and compare the result with a non--integrable case.
|
1409.5764v2
|
2014-09-20
|
Estimating the output entropy of a tensor product of two quantum channels
|
In this paper we find, for a class of bipartite quantum states, a nontrivial
lower bound on the entropy gain resulting from the action of a tensor product
of identity channel with an arbitrary channel. By means of that we then
estimate (from below) the output entropy of the tensor product of dephasing
channel with an arbitrary channel. Finally, we provide a characterization of
all phase-damping channels resulting as particular cases of dephasing channels.
|
1409.5881v2
|
2014-09-24
|
Dissipationless Multiferroic Magnonics
|
We propose that the magnetoelectric effect in multiferroic insulators with
coplanar antiferromagnetic spiral order, such as BiFeO$_{3}$, enables
electrically controlled dissipationless magnonics. Applying an oscillating
electric field in these materials with frequency as low as household frequency
can activate Goldstone modes that manifests fast planar rotations of spins,
whose motion is not obstructed by crystalline anisotropy. Combining with spin
ejection mechanisms, such a fast planar rotation can deliver electricity at
room temperature over a distance of the magnetic domain, which is free from the
energy loss due to Gilbert damping.
|
1409.6900v2
|
2014-09-30
|
Mixed finite elements for global tide models
|
We study mixed finite element methods for the linearized rotating shallow
water equations with linear drag and forcing terms. By means of a strong energy
estimate for an equivalent second-order formulation for the linearized
momentum, we prove long-time stability of the system without energy
accumulation -- the geotryptic state. A priori error estimates for the
linearized momentum and free surface elevation are given in $L^2$ as well as
for the time derivative and divergence of the linearized momentum. Numerical
results confirm the theoretical results regarding both energy damping and
convergence rates.
|
1410.0045v1
|
2014-10-21
|
Coherent beam-beam experiments and implications for head-on compensation
|
In polarized proton operation in the Relativistic Heavy Ion Collider (RHIC)
coherent beam-beam modes are routinely observed with beam transfer function
measurements. These modes can become unstable under external excitation or in
the presence of impedance. This becomes even more relevant in the presence of
head-on compensation, which reduces the beam-beam tune spread and hence Landau
damping. We report on experiments and simulations carried out to understand the
impact of coherent modes on operation with electron lenses.
|
1410.5623v1
|
2014-10-22
|
Optimization-based smoothing algorithm for triangle meshes over arbitrarily shaped domains
|
This paper describes a node relocation algorithm based on nonlinear
optimization which delivers excellent results for both unstructured and
structured plane triangle meshes over convex as well as non-convex domains with
high curvature. The local optimization scheme is a damped Newton's method in
which the gradient and Hessian of the objective function are evaluated exactly.
The algorithm has been developed in order to continuously rezone the mesh in
arbitrary Lagrangian-Eulerian (ALE) methods for large deformation penetration
problems, but it is also suitable for initial mesh improvement. Numerical
examples highlight the capabilities of the algorithm.
|
1410.5977v1
|
2014-10-23
|
Fully damped Mott oscillations in sub-barrier elastic scattering of identical heavy ions and the nuclear interaction
|
We investigate the possible disappearance of Mott oscillations in the
scattering of bosonic nuclei at sub-barrier energies. This effect is universal
and happens at a critical value of the Sommerfeld parameter. It is also found
that the inclusion of the short-range nuclear interaction has a profound
influence on this phenomenon. Thus we suggest that the study of this lack of
Mott oscillation, which we call, "transverse isotropy" is a potentially useful
mean to study the nuclear interaction.
|
1410.6376v1
|
2014-11-03
|
Decay rates of magnetic modes below the threshold of a turbulent dynamo
|
We measure the decay rates of magnetic field modes in a turbulent flow of
liquid sodium below the dynamo threshold.We observe that turbulent fluctuations
induce energy transfers between modes with different symmetries (dipolar and
quadrupolar). Using symmetry properties, we show how to measure the decay rate
of each mode without being restricted to the one with the smallest damping
rate.We observe that the respective values of the decay rates of these modes
depend on the shape of the propellers driving the flow. Dynamical regimes,
including field reversals, are observed onlywhen the modes are both nearly
marginal. This is in linewith a recently proposed model.
|
1411.0517v1
|
2014-11-22
|
On the symmetry of the Laplacian spectra of signed graphs
|
We study the symmetry properties of the spectra of normalized Laplacians on
signed graphs. We find a new machinery that generates symmetric spectra for
signed graphs, which includes bipartiteness of unsigned graphs as a special
case. Moreover, we prove a fundamental connection between the symmetry of the
spectrum and the existence of damped two-periodic solutions for the
discrete-time heat equation on the graph.
|
1411.6113v1
|
2014-11-22
|
Random Attractor for Stochastic Wave Equation with Arbitrary Exponent and Additive Noise on $\mathbb{R}^n$
|
Asymptotic random dynamics of weak solutions for a damped stochastic wave
equation with the nonlinearity of arbitrarily large exponent and the additive
noise on $\mathbb{R}^n$ is investigated. The existence of a pullback random
attractor is proved in a parameter region with a breakthrough in proving the
pullback asymptotic compactness of the cocycle with the quasi-trajectories
defined on the integrable function space of arbitrary exponent and on the
unbounded domain of arbitrary dimension.
|
1411.6139v1
|
2014-11-23
|
Dephasing of Kuramoto oscillators in kinetic regime towards a fixed asymptotically free state
|
We study the kinetic Kuramoto model for coupled oscillators. We prove that
for any regular asymptotically free state, if the interaction is small enough,
it exists a solution which is asymptotically close to it. For this class of
solution the order parameter vanishes to zero, showing a behavior similar to
the phenomenon of Landau damping in plasma physics. We obtain an exponential
decay of the order parameter in the case on analytical regularity of the
asymptotic state, and a polynomial decay in the case of Sobolev regularity.
|
1411.6304v1
|
2014-11-28
|
An Euler-Bernoulli beam with nonlinear damping and a nonlinear spring at the tip
|
We study the asymptotic behaviour for a system consisting of a clamped
flexible beam that carries a tip payload, which is attached to a nonlinear
damper and a nonlinear spring at its end. Characterizing the omega-limit sets
of the trajectories, we give a necessary condition under which the system is
asymptotically stable. In the case when this condition is not satisfied, we
show that the beam deflection approaches a non-decaying time-periodic solution.
|
1411.7946v2
|
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