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2016-12-28
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Quantum coherence of two-qubit over quantum channels with memory
|
Using the axiomatic definition of the coherence measure, such as the $l_{1}$
norm and the relative entropy, we study the phenomena of two-qubit system
quantum coherence through quantum channels where successive uses of the
channels are memory. Different types of noisy channels with memory, such as
amplitude damping, phase-damping, and depolarizing channels effect on quantum
coherence have been discussed in detail. The results show that, quantum
channels with memory can efficiently protect coherence from noisy channels.
Particularly, as channels with perfect memory, quantum coherence is unaffected
by the phase damping as well as depolarizing channels. Besides, we also
investigate the cohering and decohering power of quantum channels with memory.
|
1612.08791v1
|
2017-01-04
|
Hamiltonian of mean force and a damped harmonic oscillator in an anisotropic medium
|
The quantum dynamics of a damped harmonic oscillator is investigated in the
presence of an anisotropic heat bath. The medium is modeled by a continuum of
three dimensional harmonic oscillators and anisotropic coupling is treated by
introducing tensor coupling functions. Starting from a classical Lagrangian,
the total system is quantized in the framework of the canonical quantization.
Following Fano technique, Hamiltonian of the system is diagonalized in terms of
creation and annihilation operators that are linear combinations of the basic
dynamical variables. Using the diagonalized Hamiltonian, the mean force
internal energy, free energy and entropy of the damped oscillator are
calculated.
|
1701.00964v2
|
2017-01-30
|
Quantization of energy and weakly turbulent profiles of the solutions to some damped second order evolution equations
|
We consider a second order equation with a linear "elastic" part and a
nonlinear damping term depending on a power of the norm of the velocity. We
investigate the asymptotic behavior of solutions, after rescaling them suitably
in order to take into account the decay rate and bound their energy away from
zero.We find a rather unexpected dichotomy phenomenon. Solutions with finitely
many Fouriercomponents are asymptotic to solutions of the linearized
equationwithout damping, and exhibit some sort of equipartition of theenergy
among the components. Solutions with infinitely manyFourier components tend to
zero weakly but not strongly. We showalso that the limit of the energy of
solutions depends only on thenumber of their Fourier components.The proof of
our results is inspired by the analysis of asimplified model which we devise
through an averaging procedure,and whose solutions exhibit the same asymptotic
properties as thesolutions to the original equation.
|
1701.08604v1
|
2017-02-15
|
Topological Properties of a Coupled Spin-Photon System Induced by Damping
|
We experimentally examine the topological nature of a strongly coupled
spin-photon system induced by damping. The presence of both spin and photonic
losses results in a non-Hermitian system with a variety of exotic phenomena
dictated by the topological structure of the eigenvalue spectra and the
presence of an exceptional point (EP), where the coupled spin-photon
eigenvectors coalesce. By controlling both the spin resonance frequency and the
spin-photon coupling strength we observe a resonance crossing for
cooperativities above one, suggesting that the boundary between weak and strong
coupling should be based on the EP location rather than the cooperativity.
Furthermore we observe dynamic mode switching when encircling the EP and
identify the potential to engineer the topological structure of coupled
spin-photon systems with additional modes. Our work therefore further
highlights the role of damping within the strong coupling regime, and
demonstrates the potential and great flexibility of spin-photon systems for
studies of non-Hermitian physics.
|
1702.04797v2
|
2017-02-22
|
Modified quantum-speed-limit bounds for open quantum dynamics in quantum channels
|
The minimal evolution time between two distinguishable states is of
fundamental interest in quantum physics. Very recently Mirkin et al. argue that
some most common quantum-speed-limit (QSL) bounds which depend on the actual
evolution time do not cleave to the essence of the QSL theory as they grow
indefinitely but the final state is reached at a finite time in a damped
Jaynes-Cummings (JC) model. In this paper, we thoroughly study this puzzling
phenomenon. We find the inconsistent estimates will happen if and only if the
limit of resolution of a calculation program is achieved, through which we
propose that the nature of the inconsistency is not a violation to the essence
of the QSL theory but an illusion caused by the finite precision in numerical
simulations. We also present a generic method to overcome the inconsistent
estimates and confirm its effectiveness in both amplitude-damping and
phase-damping channels. Additionally, we show special cases which may restrict
the QSL bound defined by "quantumness".
|
1702.06748v3
|
2017-03-07
|
Lower Bound and optimality for a nonlinearly damped Timoshenko system with thermoelasticity
|
In this paper, we consider a vibrating nonlinear Timoshenko system with
thermoelasticity with second sound. We first investigate the strong stability
of this system, then we devote our efforts to obtain the strong lower energy
estimates using Alabau--Boussouira's energy comparison principle introduced in
\cite{2} (see also \cite{alabau}). One of the main advantages of these results
is that they allows us to prove the optimality of the asymptotic results (as
$t\rightarrow \infty$) obtained in \cite{ali}. We also extend to our model the
nice results achieved in \cite{alabau} for the case of nonlinearly damped
Timoshenko system with thermoelasticity. The optimality of our results is also
investigated through some explicit examples of the nonlinear damping term. The
proof of our results relies on the approach in \cite{AB1, AB2}.
|
1703.02599v4
|
2017-03-08
|
A Parameterized Energy Correction Method for Electromagnetic Showers in BGO-ECAL of DAMPE
|
DAMPE is a space-based mission designed as a high energy particle detector
measuring cosmic-rays and $\gamma-$rays which was successfully launched on
Dec.17, 2015. The BGO electromagnetic calorimeter is one of the key
sub-detectors of DAMPE for energy measurement of electromagnetic showers
produced by $e^{\pm}/{\gamma}$. Due to energy loss in dead material and energy
leakage outside the calorimeter, the deposited energy in BGO underestimates the
primary energy of incident $e^{\pm}/{\gamma}$. In this paper, based on detailed
MC simulations, a parameterized energy correction method using the lateral and
longitudinal information of electromagnetic showers has been studied and
verified with data of electron beam test at CERN. The measurements of energy
linearity and resolution are significantly improved by applying this correction
method for electromagnetic showers.
|
1703.02821v2
|
2017-03-08
|
A GAMP Based Low Complexity Sparse Bayesian Learning Algorithm
|
In this paper, we present an algorithm for the sparse signal recovery problem
that incorporates damped Gaussian generalized approximate message passing
(GGAMP) into Expectation-Maximization (EM)-based sparse Bayesian learning
(SBL). In particular, GGAMP is used to implement the E-step in SBL in place of
matrix inversion, leveraging the fact that GGAMP is guaranteed to converge with
appropriate damping. The resulting GGAMP-SBL algorithm is much more robust to
arbitrary measurement matrix $\boldsymbol{A}$ than the standard damped GAMP
algorithm while being much lower complexity than the standard SBL algorithm. We
then extend the approach from the single measurement vector (SMV) case to the
temporally correlated multiple measurement vector (MMV) case, leading to the
GGAMP-TSBL algorithm. We verify the robustness and computational advantages of
the proposed algorithms through numerical experiments.
|
1703.03044v2
|
2017-04-07
|
Underdamped stochastic harmonic oscillator
|
We investigate stationary states of the linear damped stochastic oscillator
driven by L\'evy noises. In the long time limit kinetic and potential energies
of the oscillator do not fulfill the equipartition theorem and their
distributions follow the power-law asymptotics. At the same time, partition of
the mechanical energy is controlled by the damping coefficient. We show that in
the limit of vanishing damping a stochastic analogue of the equipartition
theorem can be proposed, namely the statistical properties of potential and
kinetic energies attain distributions characterized by the same width. Finally,
we demonstrate that the ratio of instantaneous kinetic and potential energies
which signifies departure from the mechanical energy equipartition, follows
universal power-law asymptotics.
|
1704.02119v2
|
2017-04-13
|
Quantum behaviour of open pumped and damped Bose-Hubbard trimers
|
We propose and analyse analogs of optical cavities for atoms using three-well
inline Bose-Hubbard models with pumping and losses. With one well pumped and
one damped, we find that both the mean-field dynamics and the quantum
statistics show a qualitative dependence on the choice of damped well. The
systems we analyse remain far from equilibrium, although most do enter a
steady-state regime. We find quadrature squeezing, bipartite and tripartite
inseparability and entanglement, and states exhibiting the EPR paradox,
depending on the parameter regimes. We also discover situations where the
mean-field solutions of our models are noticeably different from the quantum
solutions for the mean fields. Due to recent experimental advances, it should
be possible to demonstrate the effects we predict and investigate in this
article.
|
1704.04021v1
|
2017-05-27
|
Power System Supplementary Damping Controllers in the Presence of Saturation
|
This paper presents the analysis and a method to design supplementary damping
controllers (SDCs) for synchronous generators considering the effects of
saturation limits. Usually such saturations of control signals are imposed in
order to enforce practical limitations such as component ratings. However, to
guarantee the stability in the presence of saturation limits, the state
trajectories must remain inside the domain of attraction (DA). In this paper,
the domain of attraction of a single-machine infinite-bus (SMIB) power system
with saturation nonlinearity is estimated and compared with the exact
description of the null controllable region. Then, state-feedback controllers
are designed to enlarge the DA. Our analysis shows that nonlinear effects of
saturation should be considered to guarantee stability and satisfactory
performance. Simulation results on a detailed nonlinear model of a synchronous
generator indicate that the DA enlarges with the proposed controller. The
results also indicate that Critical Clearing Time (CCT) and damping of the
system with saturation can be improved by the proposed method.
|
1705.09849v1
|
2017-05-26
|
Absence of Landau damping in driven three-component Bose-Einstein condensate in optical lattices
|
We explore the quantum many-body physics of a three-component Bose-Einstein
condensate (BEC) in an optical lattices driven by laser fields in $V$ and
$\Lambda$ configurations. We obtain exact analytical expressions for the energy
spectrum and amplitudes of elementary excitations, and discover symmetries
among them. We demonstrate that the applied laser fields induce a gap in the
otherwise gapless Bogoliubov spectrum. We find that Landau damping of the
collective modes above the energy of the gap is carried by laser-induced roton
modes and is considerably suppressed compared to the phonon-mediated damping
endemic to undriven scalar BECs.
|
1705.10199v2
|
2017-05-31
|
Low-energy modes of spin-imbalanced Fermi gases in BCS phase
|
The low-energy modes of a spin-imbalanced superfluid Fermi gas in the
Bardeen-Cooper-Schrieffer (BCS) side are studied. The gas is assumed to be
sufficiently dilute so that the pairing of atoms can be considered effective
only in s-wave between fermions of different internal state. The order
parameter at equilibrium is determined by the mean-field approximation, while
the properties of the collective modes are calculated within a Gaussian
approximation for the fluctuations of the order parameter. In particular we
investigate the effects of asymmetry between the populations of the two
different components and of temperature on the frequency and damping of
collective modes. It is found that the temperature does not much affect the
frequency and the damping of the modes, whereas an increase of the imbalance
shifts the frequency toward lower values and enhances the damping sensitively.
Besides the Bogoliubov-Anderson phonons, we observe modes at zero frequency for
finite values of the wave-number. These modes indicate that an instability
develops driving the system toward two separate phases, normal and superfluid.
|
1705.11162v1
|
2017-06-01
|
Global Stabilization of the Navier-Stokes-Voight and the damped nonlinear wave equations by finite number of feedback controllers
|
In this paper we introduce a finite-parameters feedback control algorithm for
stabilizing solutions of the Navier-Stokes-Voigt equations, the strongly damped
nonlinear wave equations and the nonlinear wave equation with nonlinear damping
term, the Benjamin-Bona-Mahony-Burgers equation and the KdV-Burgers equation.
This algorithm capitalizes on the fact that such infinite-dimensional
dissipative dynamical systems posses finite-dimensional long-time behavior
which is represented by, for instance, the finitely many determining parameters
of their long-time dynamics, such as determining Fourier modes, determining
volume elements, determining nodes , etc..The algorithm utilizes these finite
parameters in the form of feedback control to stabilize the relevant solutions.
For the sake of clarity, and in order to fix ideas, we focus in this work on
the case of low Fourier modes feedback controller, however, our results and
tools are equally valid for using other feedback controllers employing other
spatial coarse mesh interpolants.
|
1706.00162v1
|
2017-06-08
|
Realistic clocks for a Universe without time
|
There are a number of problematic features within the current treatment of
time in physical theories, including the "timelessness" of the Universe as
encapsulated by the Wheeler-DeWitt equation. This paper considers one
particular investigation into resolving this issue; a conditional probability
interpretation that was first proposed by Page and Wooters. Those authors
addressed the apparent timelessness by subdividing a faux Universe into two
entangled parts, "the clock" and "the remainder of the Universe", and then
synchronizing the effective dynamics of the two subsystems by way of
conditional probabilities. The current treatment focuses on the possibility of
using a (somewhat) realistic clock system; namely, a coherent-state description
of a damped harmonic oscillator. This clock proves to be consistent with the
conditional probability interpretation; in particular, a standard evolution
operator is identified with the position of the clock playing the role of time
for the rest of the Universe. Restrictions on the damping factor are determined
and, perhaps contrary to expectations, the optimal choice of clock is not
necessarily one of minimal damping.
|
1706.02531v1
|
2017-06-26
|
High $β$ Effects on Cosmic Ray Streaming in Galaxy Clusters
|
Diffuse, extended radio emission in galaxy clusters, commonly referred to as
radio halos, indicate the presence of high energy cosmic ray (CR) electrons and
cluster-wide magnetic fields. We can predict from theory the expected surface
brightness of a radio halo, given magnetic field and CR density profiles.
Previous studies have shown that the nature of CR transport can radically
effect the expected radio halo emission from clusters (Wiener et al. 2013).
Reasonable levels of magnetohydrodynamic (MHD) wave damping can lead to
significant CR streaming speeds. But a careful treatment of MHD waves in a high
$\beta$ plasma, as expected in cluster environments, reveals damping rates may
be enhanced by a factor of $\beta^{1/2}$. This leads to faster CR streaming and
lower surface brightnesses than without this effect. In this work we re-examine
the simplified, 1D Coma cluster simulations (with radial magnetic fields) of
Wiener et al. (2013) and discuss observable consequences of this high $\beta$
damping. Future work is required to study this effect in more realistic
simulations.
|
1706.08525v2
|
2017-07-02
|
Metastability of Kolmogorov flows and inviscid damping of shear flows
|
First, we consider Kolmogorov flow (a shear flow with a sinusoidal velocity
profile) for 2D Navier-Stokes equation on a torus. Such flows, also called bar
states, have been numerically observed as one type of metastable states in the
study of 2D turbulence. For both rectangular and square tori, we prove that the
non-shear part of perturbations near Kolmogorov flow decays in a time scale
much shorter than the viscous time scale. The results are obtained for both the
linearized NS equations with any initial vorticity in L^2, and the nonlinear NS
equation with initial L^2 norm of vorticity of the size of viscosity. In the
proof, we use the Hamiltonian structure of the linearized Euler equation and
RAGE theorem to control the low frequency part of the perturbation. Second, we
consider two classes of shear flows for which a sharp stability criterion is
known. We show the inviscid damping in a time average sense for non-shear
perturbations with initial vorticity in L^2. For the unstable case, the
inviscid damping is proved on the center space. Our proof again uses the
Hamiltonian structure of the linearized Euler equation and an instability index
theory recently developed by Lin and Zeng for Hamiltonian PDEs.
|
1707.00278v1
|
2017-09-06
|
Linear gyrokinetic investigation of the geodesic acoustic modes in realistic tokamak configurations
|
Geodesic acoustic modes (GAMs) are studied by means of the gyrokinetic global
particle-in-cell code ORB5. Linear electromagnetic simulations in the low
electron beta limit have been performed, in order to separate acoustic and
Alfv\'enic time scales and obtain more accurate measurements. The dependence of
the frequency and damping rate on several parameters such as the safety factor,
the GAM radial wavenumber and the plasma elongation is studied. All simulations
have been performed with kinetic electrons with realistic electron/ion mass
ratio. Interpolating formulae for the GAM frequency and damping rate, based on
the results of the gyrokinetic simulations, have been derived. Using these
expressions, the influence of the temperature gradient on the damping rate is
also investigated. Finally, the results are applied to the study of a real
discharge of the ASDEX Upgrade tokamak.
|
1709.01818v1
|
2017-09-17
|
Further insights into the damping-induced self-recovery phenomenon
|
In a series of papers, D. E. Chang, et al., proved and experimentally
demonstrated a phenomenon they termed "damping-induced self-recovery". However,
these papers left a few questions concerning the observed phenomenon unanswered
- in particular, the effect of the intervening lubricant-fluid and its
viscosity on the recovery, the abrupt change in behaviour with the introduction
of damping, a description of the energy dynamics, and the curious occurrence of
overshoots and oscillations and its dependence on the control law. In this
paper we attempt to answer these questions through theory. In particular, we
derive an expression for the infinite-dimensional fluid-stool-wheel system,
that approximates its dynamics to that of the better understood
finite-dimensional case.
|
1709.05596v5
|
2017-09-19
|
An Improved Primal-Dual Interior Point Solver for Model Predictive Control
|
We propose a primal-dual interior-point (PDIP) method for solving quadratic
programming problems with linear inequality constraints that typically arise
form MPC applications. We show that the solver converges (locally)
quadratically to a suboptimal solution of the MPC problem. PDIP solvers rely on
two phases: the damped and the pure Newton phases. Compared to state-of-the-art
PDIP methods, our solver replaces the initial damped Newton phase (usually used
to compute a medium-accuracy solution) with a dual solver based on Nesterov's
fast gradient scheme (DFG) that converges with a sublinear convergence rate of
order O(1/k^2) to a medium-accuracy solution. The switching strategy to the
pure Newton phase, compared to the state of the art, is computed in the dual
space to exploit the dual information provided by the DFG in the first phase.
Removing the damped Newton phase has the additional advantage that our solver
saves the computational effort required by backtracking line search. The
effectiveness of the proposed solver is demonstrated on a 2-dimensional
discrete-time unstable system and on an aerospace application.
|
1709.06362v1
|
2017-09-22
|
Nonlinear stage of Benjamin-Feir instability in forced/damped deep water waves
|
We study a three-wave truncation of a recently proposed damped/forced
high-order nonlinear Schr\"odinger equation for deep-water gravity waves under
the effect of wind and viscosity. The evolution of the norm (wave-action) and
spectral mean of the full model are well captured by the reduced dynamics.
Three regimes are found for the wind-viscosity balance: we classify them
according to the attractor in the phase-plane of the truncated system and to
the shift of the spectral mean. A downshift can coexist with both net forcing
and damping, i.e., attraction to period-1 or period-2 solutions. Upshift is
associated with stronger winds, i.e., to a net forcing where the attractor is
always a period-1 solution. The applicability of our classification to
experiments in long wave-tanks is verified.
|
1709.07850v2
|
2017-09-27
|
On long-time asymptotics for viscous hydrodynamic models of collective behavior with damping and nonlocal interactions
|
Hydrodynamic systems arising in swarming modelling include nonlocal forces in
the form of attractive-repulsive potentials as well as pressure terms modelling
strong local repulsion. We focus on the case where there is a balance between
nonlocal attraction and local pressure in presence of confinement in the whole
space. Under suitable assumptions on the potentials and the pressure functions,
we show the global existence of weak solutions for the hydrodynamic model with
viscosity and linear damping. By introducing linear damping in the system, we
ensure the existence and uniqueness of stationary solutions with compactly
supported density, fixed mass and center of mass. The associated velocity field
is zero in the support of the density. Moreover, we show that global weak
solutions converge for large times to the set of these stationary solutions in
a suitable sense. In particular cases, we can identify the limiting density
uniquely as the global minimizer of the free energy with the right mass and
center of mass.
|
1709.09290v2
|
2017-09-28
|
Landau Damping with Electron Lenses in Space-Charge Dominated Beams
|
Progress on the Intensity Frontier of high energy physics critically depends
on record high intensity charged particles accelerators. Beams in such machines
become operationally limited by coherent beam instabilities, particularly
enhanced in the regime of strong space charge (SC). Usual methods to control
the instabilities, such as octupole magnets, beam feedback dampers and
employment of chromatic effects, become less effective and insufficient. In [1]
it was proposed to employ electron lenses for introduction of sufficient spread
in particle oscillation frequencies needed for beam stabilization and in [2] it
was shown that electron lenses are uniquely effective for Landau damping of
transverse beam instabilities in high energy particle accelerators and their
employment does not compromise incoherent (single particle) stability, dynamic
aperture and the beam lifetime. Here we consider an important issue of
effectiveness of the Landau damping with electron lenses in space-charge
dominated beams and demonstrate that the desired stability can be assured with
proper choice of the electron beam parameters and current distributions.
|
1709.10020v1
|
2017-10-13
|
Hydrodynamic-to-ballistic crossover in Dirac fluid
|
We develop an exactly solvable classical kinetic model of transport in Dirac
materials accounting for strong electron-electron (e-e) and electron-hole (e-h)
collisions. We use this model to track the evolution of graphene conductivity
and properties of its collective excitations across the
hydrodynamic-to-ballistic crossover. We find the relaxation rate of electric
current by e-e collisions that is possible due to the lack of Galilean
invariance, and introduce a universal numerical measure of this non-invariance
in arbitrary dimension. We find the two branches of collective excitations in
the Dirac fluid: plasmons and electron-hole sound. The sound waves have small
viscous damping at the neutrality point both in the hydrodynamic and ballistic
regimes, but acquire large damping due to e-h friction even at slight doping.
On the contrary, plasmons acquire strong frictional damping at the neutrality
point and become well-defined in doped samples.
|
1710.05054v3
|
2017-10-13
|
The second hyperpolarizability of systems described by the space-fractional Schrodinger equation
|
The static second hyperpolarizability is derived from the space-fractional
Schr\"{o}dinger equation in the particle-centric view. The Thomas-Reiche-Kuhn
sum rule matrix elements and the three-level ansatz determines the maximum
second hyperpolarizability for a space-fractional quantum system. The total
oscillator strength is shown to decrease as the space-fractional parameter
$\alpha$ decreases, which reduces the optical response of a quantum system in
the presence of an external field. This damped response is caused by the
wavefunction dependent position and momentum commutation relation. Although the
maximum response is damped, we show that the one-dimensional quantum harmonic
oscillator is no longer a linear system for $\alpha \neq 1$, where the second
hyperpolarizability becomes negative before ultimately damping to zero at the
lower fractional limit of $\alpha \rightarrow 1/2$.
|
1710.05099v2
|
2017-11-08
|
Bulk viscous corrections to screening and damping in the deconfined phase at high temperature
|
Non-equilibrium corrections in a hot QCD medium modify the "hard thermal
loops" (HTL) which determine the resummed propagators for gluons with soft
momenta as well as the Debye screening and Landau damping mass scales. We focus
on bulk viscous corrections to a thermal fixed point. The screening and damping
mass scales are sensitive to the bulk pressure and perhaps to (pseudo-)
critical dynamical scaling of the bulk viscosity in the vicinity of a
second-order critical point. This would affect the properties of quarkonium
bound states in the deconfined phase.
|
1711.03072v1
|
2017-11-29
|
A model explaining neutrino masses and the DAMPE cosmic ray electron excess
|
We propose a flavored $U(1)_{e\mu}$ neutrino mass and dark matter~(DM) model
to explain the recent DArk Matter Particle Explorer (DAMPE) data, which feature
an excess on the cosmic ray electron plus positron flux around 1.4 TeV. Only
the first two lepton generations of the Standard Model are charged under the
new $U(1)_{e\mu}$ gauge symmetry. A vector-like fermion $\psi$, which is our DM
candidate, annihilates into $e^{\pm}$ and $\mu^{\pm}$ via the new gauge boson
$Z'$ exchange and accounts for the DAMPE excess. We have found that the data
favors a $\psi$ mass around 1.5~TeV and a $Z'$ mass around 2.6~TeV, which can
potentially be probed by the next generation lepton colliders and DM direct
detection experiments.
|
1711.10995v2
|
2017-11-29
|
Electrophilic dark matter with dark photon: from DAMPE to direct detection
|
The electron-positron excess reported by the DAMPE collaboration recently may
be explained by an electrophilic dark matter (DM). A standard model singlet
fermion may play the role of such a DM when it is stablized by some symmetries,
such as a dark $U(1)_X^{}$ gauge symmetry, and dominantly annihilates into the
electron-positron pairs through the exchange of a scalar mediator. The model,
with appropriate Yukawa couplings, can well interpret the DAMPE excess. Naively
one expects that in this type of models the DM-nucleon cross section should be
small since there is no tree-level DM-quark interactions. We however find that
at one-loop level, a testable DM-nucleon cross section can be induced for
providing ways to test the electrophilic model. We also find that a $U(1)$
kinetic mixing can generate a sizable DM-nucleon cross section although the
$U(1)_X^{}$ dark photon only has a negligible contribution to the DM
annihilation. Depending on the signs of the mixing parameter, the dark photon
can enhance/reduce the one-loop induced DM-nucleon cross section.
|
1711.11000v2
|
2017-11-30
|
Leptophilic dark matter in gauged $U(1)_{L_e-L_μ}$ model in light of DAMPE cosmic ray $e^+ + e^-$ excess
|
Motivated by the very recent cosmic-ray electron+positron excess observed by
DAMPE collaboration, we investigate a Dirac fermion dark matter (DM) in the
gauged $L_e - L_\mu$ model. DM interacts with the electron and muon via the
$U(1)_{e-\mu}$ gauge boson $Z^{'}$. The model can explain the DAMPE data well.
Although a non-zero DM-nucleon cross section is only generated at one loop
level and there is a partial cancellation between $Z^{'}ee$ and $Z^{'}\mu\mu$
couplings, we find that a large portion of $Z^{'}$ mass is ruled out from
direct DM detection limit leaving the allowed $Z^{'}$ mass to be close to two
times of the DM mass. Implications for $pp \to Z^{'} \to 2\ell$ and $pp \to
2\ell + Z^{'}$ , and muon $g-2$ anomaly are also studied.
|
1711.11563v3
|
2017-12-03
|
Explaining the DAMPE $e^+ e^-$ excess using the Higgs triplet model with a vector dark matter
|
We explain the $e^+ e^-$ excess observed by the DAMPE Collaboration using a
dark matter model based upon the Higgs triplet model and an additional hidden
$SU(2)_X$ gauge symmetry. Two of the $SU(2)_X$ gauge bosons are stable due to a
residual discrete symmetry and serve as the dark matter candidate. We search
the parameter space for regions that can explain the observed relic abundance,
and compute the flux of $e^+ e^-$ coming from a nearby dark matter subhalo.
With the inclusion of background cosmic rays, we show that the model can render
a good fit to the entire energy spectrum covering the AMS-02, Fermi-LAT and
DAMPE data.
|
1712.00793v2
|
2017-12-06
|
Explain DAMPE Results by Dark Matter With Hierarchical Lepton-Specific Yukawa Interactions
|
We propose to interpret the DAMPE electron excess at 1.5 TeV through scalar
or Dirac fermion dark matter (DM) annihilation with doubly charged scalar
mediators that have lepton-specific Yukawa couplings. Hierarchy of such
lepton-specific Yukawa couplings is generated through the Froggatt-Nielsen
mechanism, so that the dark matter annihilation products can be dominantly
electrons. Stringent constraints from LEP2 on intermediate vector boson
production can be evaded in our scenarios. In the case of scalar DM, we discuss
one scenario with DM annihilating directly to leptons and the other scenario
with DM annihilating to scalar mediators followed by their decays. We also
discuss the Breit-Wigner resonant enhancement and the Sommerfeld enhancement in
case that the s-wave annihilation process is small or helicity suppressed. With
both types of enhancement, constraints on the parameters can be relaxed and new
ways for model building will be open in explaining the DAMPE results.
|
1712.02381v3
|
2017-12-08
|
Kinetic damping in the spectra of the spherical impedance probe
|
The impedance probe is a measurement device to measure plasma parameter like
electron density. It consists of one electrode connected to a network analyzer
via a coaxial cable and is immersed into a plasma. A bias potential superposed
with an alternating potential is applied to the electrode and the response of
the plasma is measured. Its dynamical interaction with the plasma in
electrostatic, kinetic description can be modeled in an abstract notation based
on functional analytic methods. These methods provide the opportunity to derive
a general solution, which is given as the response function of the probe-plasma
system. It is defined by the matrix elements of the resolvent of an appropriate
dynamical operator. Based on the general solution a residual damping for
vanishing pressure can be predicted and can only be explained by kinetic
effects. Within this manuscript an explicit response function of the spherical
impedance probe is derived. Therefore, the resolvent is determined by its
algebraic representation based on an expansion in orthogonal basis functions.
This allows to compute an approximated response function and its corresponding
spectra. These spectra show additional damping due to kinetic effects and are
in good agreement with former kinetically determined spectra.
|
1712.03126v1
|
2017-12-14
|
DAMPE squib? Significance of the 1.4 TeV DAMPE excess
|
We present a Bayesian and frequentist analysis of the DAMPE charged cosmic
ray spectrum. The spectrum, by eye, contained a spectral break at about 1 TeV
and a monochromatic excess at about 1.4 TeV. The break was supported by a Bayes
factor of about $10^{10}$ and we argue that the statistical significance was
resounding. We investigated whether we should attribute the excess to dark
matter annihilation into electrons in a nearby subhalo. We found a local
significance of about $3.6\sigma$ and a global significance of about
$2.3\sigma$, including a two-dimensional look-elsewhere effect by simulating
1000 pseudo-experiments. The Bayes factor was sensitive to our choices of
priors, but favoured the excess by about 2 for our choices. Thus, whilst
intriguing, the evidence for a signal is not currently compelling.
|
1712.05089v1
|
2017-12-15
|
Radiative Seesaw Model and DAMPE Excess from Leptophilic Gauge Symmetry
|
In the light of the $e^{+}+e^{-}$ excess observed by DAMPE experiment, we
propose an anomaly-free radiative seesaw model with an alternative leptophilic
$U(1)_X$ gauge symmetry. In the model, only right-handed leptons are charged
under $U(1)_X$ symmetry. The tiny Dirac neutrino masses are generated at
one-loop level and charged leptons acquire masses though the type-I seesaw-like
mechanism with heavy intermediate fermions. In order to cancel the anomaly,
irrational $U(1)_{X}$ charge numbers are assigned to some new particles. After
the spontaneous breaking of $U(1)_{X}$ symmetry, the dark $Z_{2}$ symmetry
could appear as a residual symmetry such that the stability of inert particles
with irrational charge numbers are guaranteed, naturally leading to stable DM
candidates. We show that the Dirac fermion DM contained in the model can
explain the DAMPE excess. Meanwhile, experimental constraints from DM relic
density, direct detection, LEP and anomalous magnetic moments are satisfied.
|
1712.05722v2
|
2017-12-19
|
Damping of Josephson oscillations in strongly correlated one-dimensional atomic gases
|
We study Josephson oscillations of two strongly correlated one-dimensional
bosonic clouds separated by a localized barrier. Using a quantum-Langevin
approach and the exact Tonks-Girardeau solution in the impenetrable-boson
limit, we determine the dynamical evolution of the particle-number imbalance,
displaying an effective damping of the Josephson oscillations which depends on
barrier height, interaction strength and temperature. We show that the damping
originates from the quantum and thermal fluctuations intrinsically present in
the strongly correlated gas. Thanks to the density-phase duality of the model,
the same results apply to particle-current oscillations in a one-dimensional
ring where a weak barrier couples different angular momentum states.
|
1712.06949v2
|
2017-12-21
|
The gluon condensation effects in the DAMPE cosmic ray spectrum of electrons and positrons
|
Gluons dominate the proton behavior at high energy collisions, they can be
condensed at ultra high energy. The collisions of the accelerated high energy
protons with interplanetary matter in cosmic rays will produce a huge number of
secondary particles at the gluon condensate energy region, which break the
primary power-law of cosmic rays. The above predictions seem to be consistent
with the recent DAMPE data concerning the electron plus positron spectra. We
find that the smoothly broken power-law at $\sim 0.9 TeV$ and $3\sim 4 TeV$ in
the DAMPE data can be understood as the gluon condensation effects in proton.
|
1712.07868v2
|
2017-12-22
|
Low-momentum dynamic structure factor of a strongly interacting Fermi gas at finite temperature: The Goldstone phonon and its Landau damping
|
We develop a microscopic theory of dynamic structure factor to describe the
Bogoliubov-Anderson-Goldstone phonon mode and its damping rate in a strongly
interacting Fermi gas at finite temperature. It is based on a density
functional approach - the so-called superfluid local density approximation. The
accuracy of the theory is quantitatively examined by comparing the theoretical
predictions with the recent experimental measurements for the local dynamic
structure factor of a nearly homogeneous unitary Fermi gas at low transferred
momentum {[}S. Hoinka \textit{et al.}, Nat. Phys. \textbf{13}, 943 (2017){]},
without any free parameters. We calculate the dynamic structure factor as
functions of temperature and transferred momentum, and determine the
temperature evolution of the phonon damping rate, by considering the dominant
decay process of the phonon mode via scatterings off fermionic quasiparticles.
These predictions can be confronted with future Bragg scattering experiments on
a unitary Fermi gas near the superfluid transition.
|
1712.08318v1
|
2017-12-22
|
A brief summary of nonlinear echoes and Landau damping
|
In this expository note we review some recent results on Landau damping in
the nonlinear Vlasov equations, focusing specifically on the recent
construction of nonlinear echo solutions by the author [arXiv:1605.06841] and
the associated background. These solutions show that a straightforward
extension of Mouhot and Villani's theorem on Landau damping to Sobolev spaces
on $\mathbb T^n_x \times \mathbb R^n_v $ is impossible and hence emphasize the
subtle dependence on regularity of phase mixing problems. This expository note
is specifically aimed at mathematicians who study the analysis of PDEs, but not
necessarily those who work specifically on kinetic theory. However, for the
sake of brevity, this review is certainly not comprehensive.
|
1712.08498v1
|
2017-12-28
|
Coherence evolution in two-qubit system going through amplitude damping channel
|
In this paper, we analyze the evolution of quantum coherence in a two-qubit
system going through the amplitude damping channel. After they have gone
through this channel many times, we analyze the systems with respect to the
coherence of their output states. When only one subsystem goes through the
channel, frozen coherence occurs if and only if this subsystem is incoherent
and an auxiliary condition is satisfied for the other subsystem. When two
subsystems go through this quantum channel, quantum coherence can be frozen if
and only if the two subsystems are both incoherent. We also investigate the
evolution of coherence for maximally incoherent-coherent states and derive an
equation for the output states after one or two subsystems have gone through
the amplitude damping channel.
|
1712.09769v1
|
2018-01-09
|
Balanced Truncation Model Reduction of a Nonlinear Cable-Mass PDE System with Interior Damping
|
We consider model order reduction of a nonlinear cable-mass system modeled by
a 1D wave equation with interior damping and dynamic boundary conditions. The
system is driven by a time dependent forcing input to a linear mass-spring
system at one boundary. The goal of the model reduction is to produce a low
order model that produces an accurate approximation to the displacement and
velocity of the mass in the nonlinear mass-spring system at the opposite
boundary. We first prove that the linearized and nonlinear unforced systems are
well-posed and exponentially stable under certain conditions on the damping
parameters, and then consider a balanced truncation method to generate the
reduced order model (ROM) of the nonlinear input-output system. Little is known
about model reduction of nonlinear input-output systems, and so we present
detailed numerical experiments concerning the performance of the nonlinear ROM.
We find that the ROM is accurate for many different combinations of model
parameters.
|
1801.02792v1
|
2018-01-18
|
Analytic solutions to various dissipation models of the simple and driven quantum harmonic oscillator
|
We obtain analytic solutions to various models of dissipation of the quantum
harmonic oscillator, employing a simple method in the Wigner function Fourier
transform description of the system; and study as an exemplification, the
driven open quantum harmonic oscillator. The environmental models we use are
based on optical master equations for the zero and finite temperature bath and
whose open dynamics are described by a Lindblad master equation, and also we
use the Caldeira-Leggett model for the high temperature limit, in the the under
damped an the over damped case. Under the Wigner Fourier transform or chord
function as it has been called, it becomes particularly simple to solve the
dynamics of the open oscillator in the sense that the dynamics of the system
are reduced to the application of an evolution matrix related to the damped
motion of the oscillator.
|
1801.05943v1
|
2018-02-12
|
Chance-constrained optimal location of damping control actuators under wind power variability
|
This paper proposes a new probabilistic energy-based method to determine the
optimal installation location of electronically-interfaced resources (EIRs)
considering dynamic reinforcement under wind variability in systems with high
penetration of wind power. The oscillation energy and total action are used to
compare the dynamic performance for different EIR locations. A linear
approximation of the total action critically reduces the computational time
from hours to minutes. Simulating an IEEE-39 bus system with 30% of power
generation sourced from wind, a chance-constrained optimization is carried out
to decide the location of an energy storage system (ESS) adding damping to the
system oscillations. The results show that the proposed method, selecting the
bus location that guarantees the best dynamic performance with highest
probability, is superior to both traditional dominant mode analysis and
arbitrary benchmarks for damping ratios.
|
1802.04354v1
|
2018-02-21
|
On the vibron-polaron damping in quasi 1D macromolecular chains
|
The properties of the intramolecular vibrational excitation (vibron) in a
quasi 1D macromolecular structure are studied. It is supposed that due to the
vibron interaction with optical phonon modes, a vibron might form partially
dressed small polaron states. The properties of these states are investigated
in dependence on the basic system parameters and temperature of a thermal bath.
We also investigate the process of damping of the polaron amplitude as a
function of temperature and vibron-phonon coupling strength. Two different
regimes of the polaron damping are found and discussed.
|
1802.07424v1
|
2018-02-27
|
Impact of damping on superconducting gap oscillations induced by intense Terahertz pulses
|
We investigate the interplay between gap oscillations and damping in the
dynamics of superconductors taken out of equilibrium by strong optical pulses
with sub-gap Terahertz frequencies. A semi-phenomenological formalism is
developed to include the damping within the electronic subsystem that arises
from effects beyond BCS, such as interactions between Bogoliubov quasiparticles
and decay of the Higgs mode. Such processes are conveniently expressed as
$T_{1}$ and $T_{2}$ times in the standard pseudospin language for
superconductors. Comparing with data on NbN that we report here, we argue that
the superconducting dynamics in the picosecond time scale, after the pump is
turned off, is governed by the $T_{2}$ process.
|
1802.09711v2
|
2018-02-28
|
Analysis of imperfections in the coherent optical excitation of single atoms to Rydberg states
|
We study experimentally various physical limitations and technical
imperfections that lead to damping and finite contrast of optically-driven Rabi
oscillations between ground and Rydberg states of a single atom. Finite
contrast is due to preparation and detection errors and we show how to model
and measure them accurately. Part of these errors originates from the finite
lifetime of Rydberg states and we observe its $n^3$-scaling with the principal
quantum number $n$. To explain the damping of Rabi oscillations, we use simple
numerical models, taking into account independently measured experimental
imperfections, and show that the observed damping actually results from the
accumulation of several small effects, each at the level of a few percents. We
discuss prospects for improving the coherence of ground-Rydberg Rabi
oscillations in view of applications in quantum simulation and quantum
information processing with arrays of single Rydberg atoms.
|
1802.10424v1
|
2018-03-07
|
Connecting dissipation and noncommutativity: A Bateman system case study
|
Quantum effects on a pair of Bateman oscillators embedded in an ambient
noncommutative space (Moyal plane) is analyzed using both path integral and
canonical quantization schemes within the framework of Hilbert-Schmidt operator
formulation. We adopt a method which is distinct from the one which employs 't
Hooft's scheme of quantization, carried out earlier in the literature where the
ambient space was taken to be commutative. Our quantization shows that we end
up finally again with a Bateman system except that the damping factor undergoes
renormalization. The corresponding expression shows that the renormalized
damping factor can be non-zero even if "bare" one is zero to begin with.
Conversely, the noncommuatative parameter $\theta$, taken to be a free one now,
can be fine-tuned to get a vanishing renormalized damping factor. This
indicates a duality between dissipative commutative theory and non-dissipative
noncommutative theory.
|
1803.03334v1
|
2018-03-18
|
A machine learning method to separate cosmic ray electrons from protons from 10 to 100 GeV using DAMPE data
|
DArk Matter Particle Explorer (DAMPE) is a general purpose high energy cosmic
ray and gamma ray observatory, aiming to detect high energy electrons and
gammas in the energy range 5 GeV to 10 TeV and hundreds of TeV for nuclei. This
paper provides a method using machine learning to identify electrons and
separate them from gammas,protons,helium and heavy nuclei with the DAMPE data
from 2016 January 1 to 2017 June 30, in energy range from 10 to 100 GeV.
|
1803.06628v2
|
2018-03-20
|
Estimating Participation Factors and Mode Shapes for Electromechanical Oscillations in Ambient Conditions
|
In this paper, a new technique is applied to conduct mode identification
using ambient measurement data. The proposed hybrid measurement- and
model-based method can accurately estimate the system state matrix in ambient
conditions, the eigenvalues and eigenvectors of which readily provide all the
modal knowledge including frequencies, damping ratios, mode shapes, and more
importantly, participation factors. Numerical simulations show that the
proposed technique is able to provide accurate estimation of modal knowledge
for all modes. In addition, the discrepancy between the participation factor
and the mode shape is shown through a numerical example, demonstrating that
using the mode shape may not effectively pinpoint the best location for damping
control. Therefore, the proposed technique capable of estimating participation
factors may greatly facilitate designing damping controls.
|
1803.07264v1
|
2018-03-21
|
Globally Stable Output Feedback Synchronization of Teleoperation with Time-Varying Delays
|
This paper presents a globally stable teleoperation control strategy for
systems with time-varying delays that eliminates the need for velocity
measurements through novel augmented Immersion and Invariance velocity
observers. The new observers simplify a recent constructive Immersion and
Invariance velocity observer to achieve globally convergent velocity estimation
with only $n+2$ states, where $n$ is the number of degrees of freedom of the
master and slave robots. They introduce dynamic scaling factors to accelerate
the speed of convergence of the velocity estimates and, thus, to limit the
energy generated by the velocity estimation errors and to guarantee sufficient
estimate-based damping injection to dissipate the energy generated by the
time-varying delays. The paper shows that Proportional plus damping control
with the simplified and augmented Immersion and Invariance-based velocity
observers can synchronize the free master and slave motions in the presence of
time-varying delays without using velocity measurements. Numerical results
illustrate the estimation performance of the new observers and the stability of
a simulated two degrees-of-freedom nonlinear teleoperation system with
time-varying delays under the proposed output feedback Proportional plus
damping control.
|
1803.08159v1
|
2018-03-29
|
Stochastic conformal multi-symplectic method for damped stochastic nonlinear Schrodinger equation
|
In this paper, we propose a stochastic conformal multi-symplectic method for
a class of damped stochastic Hamiltonian partial differential equations in
order to inherit the intrinsic properties, and apply the numerical method to
solve a kind of damped stochastic nonlinear Schrodinger equation with
multiplicative noise. It is shown that the stochastic conformal
multi-symplectic method preserves the discrete stochastic conformal
multi-symplectic conservation law, the discrete charge exponential dissipation
law almost surely, and we also deduce the recurrence relation of the discrete
global energy. Numerical experiments are preformed to verify the good
performance of the proposed stochastic conformal multi-symplectic method,
compared with a Crank-Nicolson type method. Finally, we present the mean square
convergence result of the proposed numerical method in temporal direction
numerically.
|
1803.10885v1
|
2018-04-01
|
Bounded Connectivity-Preserving Coordination of Networked Euler-Lagrange Systems
|
This paper derives sufficient conditions for bounded distributed
connectivity-preserving coordination of Euler-Lagrange systems with only
position measurements and with system uncertainties, respectively. The paper
proposes two strategies that suitably scale conventional gradient-based
controls to account for the actuation bounds and to reserve sufficient
actuation for damping injection. For output feedback control of networked
systems with only position measurements, the paper incorporates a first-order
filter to estimate velocities and to inject damping for stability. For networks
of uncertain systems, the paper augments conventional linear filter-based
adaptive compensation with damping injection to maintain the local connectivity
of the network. Analyses based on monotonically decreasing Lyapunov-like
functions and Barbalat's lemma lead to sufficient conditions for bounded local
connectivity-preserving coordination of Euler-Lagrange networks under the two
strategies. The sufficient conditions clarify the interrelationships among the
bounded actuations, initial system velocities and initial inter-system
distances. Simulation results validate these conditions.
|
1804.00333v1
|
2018-04-17
|
Modelling linewidths of Kepler red giants in NGC 6819
|
We present a comparison between theoretical, frequency-dependent, damping
rates and linewidths of radial-mode oscillations in red-giant stars located in
the open cluster NGC 6819. The calculations adopt a time-dependent non-local
convection model, with the turbulent pressure profile being calibrated to
results of 3D hydrodynamical simulations of stellar atmospheres. The linewidths
are obtained from extensive peakbagging of Kepler lightcurves. These
observational results are of unprecedented quality owing to the long continuous
observations by Kepler. The uniqueness of the Kepler mission also means that,
for asteroseismic properties, this is the best data that will be available for
a long time to come. We therefore take great care in modelling nine RGB stars
in NGC 6819 using information from 3D simulations to obtain realistic
temperature stratifications and calibrated turbulent pressure profiles. Our
modelled damping rates reproduce well the Kepler observations, including the
characteristic depression in the linewidths around the frequency of maximum
oscillation power. Furthermore, we thoroughly test the sensitivity of the
calculated damping rates to changes in the parameters of the nonlocal
convection model.
|
1804.06255v1
|
2018-04-24
|
$\text{Co}_{25}\text{Fe}_{75}$ Thin Films with Ultralow Total Damping
|
We measure the dynamic properties of $\text{Co}_{25}\text{Fe}_{75}$ thin
films grown by dc magnetron sputtering. Using ferromagnetic resonance
spectroscopy, we demonstrate an ultralow total damping parameter in the
out-of-plane configuration of < 0.0013, whereas for the in-plane configuration
we find a minimum total damping of < 0.0020. In both cases, we observe low
inhomogeneous linewidth broadening in macroscopic films. We observe a minimum
full-width half-maximum linewidth of 1 mT at 10 GHz resonance frequency for a
12 nm thick film. We characterize the morphology and structure of these films
as a function of seed layer combinations and find large variation of the
qualitative behavior of the in-plane linewidth vs. resonance frequency.
Finally, we use wavevector-dependent Brillouin light scattering spectroscopy to
characterize the spin-wave dispersion at wave vectors up to 23 $\mu
\text{m}^{-1}$.
|
1804.08786v1
|
2018-04-03
|
Generalisation of Gilbert damping and magnetic inertia parameter as a series of higher-order relativistic terms
|
The phenomenological Landau-Lifshitz-Gilbert (LLG) equation of motion remains
as the cornerstone of contemporary magnetisation dynamics studies, wherein the
Gilbert damping parameter has been attributed to first-order relativistic
effects. To include magnetic inertial effects the LLG equation has previously
been extended with a supplemental inertia term and the arising inertial
dynamics has been related to second-order relativistic effects. Here we start
from the relativistic Dirac equation and, performing a Foldy-Wouthuysen
transformation, derive a generalised Pauli spin Hamiltonian that contains
relativistic correction terms to any higher order. Using the Heisenberg
equation of spin motion we derive general relativistic expressions for the
tensorial Gilbert damping and magnetic inertia parameters, and show that these
tensors can be expressed as series of higher-order relativistic correction
terms. We further show that, in the case of a harmonic external driving field,
these series can be summed and we provide closed analytical expressions for the
Gilbert and inertial parameters that are functions of the frequency of the
driving field.
|
1804.09242v1
|
2018-05-15
|
Simple Nonlinear Models with Rigorous Extreme Events and Heavy Tails
|
Extreme events and the heavy tail distributions driven by them are ubiquitous
in various scientific, engineering and financial research. They are typically
associated with stochastic instability caused by hidden unresolved processes.
Previous studies have shown that such instability can be modeled by a
stochastic damping in conditional Gaussian models. However, these results are
mostly obtained through numerical experiments, while a rigorous understanding
of the underlying mechanism is sorely lacking. This paper contributes to this
issue by establishing a theoretical framework, in which the tail density of
conditional Gaussian models can be rigorously determined. In rough words, we
show that if the stochastic damping takes negative values, the tail is
polynomial; if the stochastic damping is nonnegative but takes value zero, the
tail is between exponential and Gaussian. The proof is established by
constructing a novel, product-type Lyapunov function, where a Feynman-Kac
formula is applied. The same framework also leads to a non-asymptotic large
deviation bound for long-time averaging processes.
|
1805.05615v3
|
2018-05-29
|
Gilbert damping in non-collinear magnetic system
|
The modification of the magnetization dissipation or Gilbert damping caused
by an inhomogeneous magnetic structure and expressed in terms of a wave vector
dependent tensor $\underline{\alpha}(\vec{q})$ is investigated by means of
linear response theory. A corresponding expression for
$\underline{\alpha}(\vec{q})$ in terms of the electronic Green function has
been developed giving in particular the leading contributions to the Gilbert
damping linear and quadratic in $q$. Numerical results for realistic systems
are presented that have been obtained by implementing the scheme within the
framework of the fully relativistic KKR (Korringa-Kohn-Rostoker) band structure
method. Using the multilayered system (Cu/Fe$_{1-x}$Co$_x$/Pt)$_n$ as an
example for systems without inversion symmetry we demonstrate the occurrence of
non-vanishing linear contributions. For the alloy system bcc Fe$_{1-x}$Co$_x$
having inversion symmetry, on the other hand, only the quadratic contribution
is non-zero. As it is shown, this quadratic contribution does not vanish even
if the spin-orbit coupling is suppressed, i.e.\ it is a direct consequence of
the non-collinear spin configuration.
|
1805.11468v1
|
2018-06-18
|
Theoretical interpretations of DAMPE first results: a critical review
|
The DAMPE experiment recently published its first results on the lepton ($e^+
+ e^-$) cosmic-ray (CRs) flux. These results are of importance since they
account for the first direct detection of the lepton break around the energy of
1 TeV and confirm the discoveries of ground-based Cherenkov detectors.
Meanwhile they reveal a new high-energy feature in the spectrum which triggered
a lot of excitement on the theory side, when interpreted as the typical
signature of leptophilic dark-matter annihilation. In this proceeding I mainly
focus on the theoretical understanding of the lepton break. Then I quickly
review the status of the more speculative line-like DAMPE excess, whose
astrophysical (pulsar) or exotic (dark matter) explanation is strongly
constrained by multi-messenger astronomy.
|
1806.06534v1
|
2018-06-22
|
Optimal Design of Virtual Inertia and Damping Coefficients for Virtual Synchronous Machines
|
Increased penetration of inverter-connected renewable energy sources (RES) in
the power system has resulted in a decrease in available rotational inertia
which serves as an immediate response to frequency deviation due to
disturbances. The concept of virtual inertia has been proposed to combat this
decrease by enabling the inverters to produce active power in response to a
frequency deviation like a synchronous generator. In this paper, we present an
algorithm to optimally design the inertia and damping coefficient required for
an inverter-based virtual synchronous machine (VSM) to participate efficiently
in the inertia response portion of primary frequency control. We design the
objective function to explicitly trade-off between competing objectives such as
the damping rate the the frequency nadir. Specifically, we formulate the design
problem as a constrained and regularized H2 norm minimization problem, and
develop an efficient gradient algorithm for this non-convex problem. This
proposed algorithm is applied to a test case to demonstrate its performance
against existing methods.
|
1806.08488v1
|
2018-07-17
|
Bipartite and Tripartite Entanglement for Three Damped Driven Qubits
|
We investigate bipartite and tripartite entanglement in an open quantum
system, specifically three qubits, all of which are damped, and one of which is
driven. We adapt a systematic approach in calculating the entanglement of
various bipartite splits usinga generalized concurrence as an indicator of
entanglement. Our calculations are based on a direct detection scheme that is a
particular unravelling of the density matrix. This system has a collective
dipole-dipole energy shift that couples the atoms and the dissipation is via
partially collective spontaneous emission described by the Lehmberg-Agarwal
master equation.Our results are unravelling dependent, but apply to
applications of entanglement based on direct detection. We also calculate the
three-way tangle or residual entanglement for this system. We present
calculations for a variety of driving and damping rates, and examine what decay
rate is adequate for the system to be reduced to two qubits with a readout
port. We also consider a specific model of three atoms located at particular
positions in free space.
|
1807.06178v1
|
2018-07-17
|
Boundary-to-Displacement Asymptotic Gains for Wave Systems With Kelvin-Voigt Damping
|
We provide estimates for the asymptotic gains of the displacement of a
vibrating string with endpoint forcing, modeled by the wave equation with
Kelvin-Voigt and viscous damping and a boundary disturbance. Two asymptotic
gains are studied: the gain in the L2 spatial norm and the gain in the spatial
sup norm. It is shown that the asymptotic gain property holds in the L2 norm of
the displacement without any assumption for the damping coefficients. The
derivation of the upper bounds for the asymptotic gains is performed by either
employing an eigenfunction expansion methodology or by means of a small-gain
argument, whereas a novel frequency analysis methodology is employed for the
derivation of the lower bounds for the asymptotic gains. The graphical
illustration of the upper and lower bounds for the gains shows that that the
asymptotic gain in the L2 norm is estimated much more accurately than the
asymptotic gain in the sup norm.
|
1807.06549v1
|
2018-07-24
|
Stabilization of an unstable wave equation using an infinite dimensional dynamic controller
|
This paper deals with the stabilization of an anti-stable string equation
with Dirichlet actuation where the instability appears because of the
uncontrolled boundary condition. Then, infinitely many unstable poles are
generated and an infinite dimensional control law is therefore proposed to
exponentially stabilize the system. The idea behind the choice of the
controller is to extend the domain of the PDE so that the anti-damping term is
compensated by a damping at the other boundary condition. Additionally, notice
that the system can then be exponentially stabilized with a chosen decay-rate
and is robust to uncertainties on the wave speed and the anti-damped
coefficient of the wave equation, with the only use of a point-wise boundary
measurement. The efficiency of this new control strategy is then compared to
the backstepping approach.
|
1807.08999v2
|
2018-07-24
|
Interplay between intermittency and dissipation in collisionless plasma turbulence
|
We study the damping of collisionless Alfv\'enic turbulence by two
mechanisms: stochastic heating (whose efficiency depends on the local
turbulence amplitude $\delta z_\lambda$) and linear Landau damping (whose
efficiency is independent of $\delta z_\lambda$), describing in detail how they
affect and are affected by intermittency. The overall efficiency of linear
Landau damping is not affected by intermittency in critically balanced
turbulence, while stochastic heating is much more efficient in the presence of
intermittent turbulence. Moreover, stochastic heating leads to a drop in the
scale-dependent kurtosis over a narrow range of scales around the ion
gyroscale.
|
1807.09301v2
|
2018-07-31
|
Input-to-State Stability of a Clamped-Free Damped String in the Presence of Distributed and Boundary Disturbances
|
This note establishes the Exponential Input-to-State Stability (EISS)
property for a clamped-free damped string with respect to distributed and
boundary disturbances. While efficient methods for establishing ISS properties
for distributed parameter systems with respect to distributed disturbances have
been developed during the last decades, establishing ISS properties with
respect to boundary disturbances remains challenging. One of the well-known
methods for well-posedness analysis of systems with boundary inputs is the use
of a lifting operator for transferring the boundary disturbance to a
distributed one. However, the resulting distributed disturbance involves time
derivatives of the boundary perturbation. Thus, the subsequent ISS estimate
depends on its amplitude, and may not be expressed in the strict form of ISS
properties. To solve this problem, we show for a clamped-free damped string
equation that the projection of the original system trajectories in an adequate
Riesz basis can be used to establish the desired EISS property.
|
1807.11696v2
|
2018-07-31
|
Spin absorption at ferromagnetic-metal/platinum-oxide interface
|
We investigate the absorption of a spin current at a
ferromagnetic-metal/Pt-oxide interface by measuring current-induced
ferromagnetic resonance. The spin absorption was characterized by the magnetic
damping of the heterostructure. We show that the magnetic damping of a
Ni$_{81}$Fe$_{19}$ film is clearly enhanced by attaching Pt-oxide on the
Ni$_{81}$Fe$_{19}$ film. The damping enhancement is disappeared by inserting an
ultrathin Cu layer between the Ni$_{81}$Fe$_{19}$ and Pt-oxide layers. These
results demonstrate an essential role of the direct contact between the
Ni$_{81}$Fe$_{19}$ and Pt-oxide to induce sizable interface spin-orbit
coupling. Furthermore, the spin-absorption parameter of the
Ni$_{81}$Fe$_{19}$/Pt-oxide interface is comparable to that of intensively
studied heterostructures with strong spin-orbit coupling, such as an oxide
interface, topological insulators, metallic junctions with Rashba spin-orbit
coupling. This result illustrates strong spin-orbit coupling at the
ferromagnetic-metal/Pt-oxide interface, providing an important piece of
information for quantitative understanding the spin absorption and spin-charge
conversion at the ferromagnetic-metal/metallic-oxide interface.
|
1807.11806v1
|
2018-08-16
|
Stability analysis of dissipative systems subject to nonlinear damping via Lyapunov techniques
|
In this article, we provide a general strategy based on Lyapunov functionals
to analyse global asymptotic stability of linear infinite-dimensional systems
subject to nonlinear dampings under the assumption that the origin of the
system is globally asymp-totically stable with a linear damping. To do so, we
first characterize, in terms of Lyapunov functionals, several types of
asymptotic stability for linear infinite-dimensional systems, namely the
exponential and the polynomial stability. Then, we derive a Lyapunov functional
for the nonlinear system, which is the sum of a Lyapunov functional coming from
the linear system and another term with compensates the nonlinearity. Our
results are then applied to the linearized Korteweg-de Vries equation and some
wave equations.
|
1808.05370v1
|
2018-08-30
|
The influence of the coefficients of a system of coupled wave equations with fractional damping on its stabilization
|
In this work, we consider a system of two wave equations coupled by
velocities in one-dimensional space, with one boundary fractional damping.
First, we show that the system is strongly asymptotically stable if and only if
the coupling parameter b of the two equations is outside a discrete set of
exceptional real values. Next, we show that our system is not uniformly stable.
Hence, we look for a polynomial decay rate for smooth initial data. Using
frequency domain approach combining with multiplier method, we prove that the
energy decay rate is greatly influenced by the nature of the coupling parameter
b, the arithmetic property of the ratio of the wave propagation speeds a, the
order of the fractional damping. Indeed, under the equal speed propagation
condition, we establish an optimal polynomial energy decay rate. Furthermore,
when the wave propagate with different speeds, under some arithmetic conditions
on the ratio of the wave propagation speeds, we prove that the energy of our
system decays polynomially to zero.
|
1808.10285v4
|
2018-09-05
|
On the forced Euler and Navier-Stokes equations: Linear damping and modified scattering
|
We study the asymptotic behavior of the forced linear Euler and nonlinear
Navier-Stokes equations close to Couette flow in a periodic channel. As our
main result we show that for smooth time-periodic forcing linear inviscid
damping persists, i.e. the velocity field (weakly) asymptotically converges.
However, stability and scattering to the transport problem fail in $H^{s},
s>-1$. We further show that this behavior is consistent with the nonlinear
Euler equations and that a similar result also holds for the nonlinear
Navier-Stokes equations. Hence, these results provide an indication that
nonlinear inviscid damping may still hold in Sobolev regularity in the above
sense despite the Gevrey regularity instability results of [Deng-Masmoudi
2018].
|
1809.01729v1
|
2018-09-12
|
Theory of bifurcation amplifiers utilizing the nonlinear dynamical response of an optically damped mechanical oscillator
|
We consider a standard optomechanical system where a mechanical oscillator is
coupled to a cavity mode through the radiation pressure interaction. The
oscillator is coherently driven at its resonance frequency, whereas the cavity
mode is driven below its resonance, providing optical damping of the mechanical
oscillations. We study the nonlinear coherent response of the mechanical
oscillator in this setup. For large mechanical amplitudes, we find that the
system can display dynamical multistability if the optomechanical cooperativity
exceeds a critical value. This analysis relates standard optomechanical damping
to the dynamical attractors known from the theory of optomechanical
self-sustained oscillations. We also investigate the effect of thermal and
quantum noise and estimate the noise-induced switching rate between the stable
states of the system. We then consider applications of this system and
primarily focus on how it can be used as bifurcation amplifiers for the
detection of small mechanical or optical signals. Finally, we show that in a
related but more complicated setup featuring resonant optomechanical
interactions, the same effects can be realized with a relaxed requirement on
the size of the mechanical oscillations.
|
1809.04592v2
|
2018-09-13
|
Second order asymptotical regularization methods for inverse problems in partial differential equations
|
We develop Second Order Asymptotical Regularization (SOAR) methods for
solving inverse source problems in elliptic partial differential equations with
both Dirichlet and Neumann boundary data. We show the convergence results of
SOAR with the fixed damping parameter, as well as with a dynamic damping
parameter, which is a continuous analog of Nesterov's acceleration method.
Moreover, by using Morozov's discrepancy principle together with a newly
developed total energy discrepancy principle, we prove that the approximate
solution of SOAR weakly converges to an exact source function as the
measurement noise goes to zero. A damped symplectic scheme, combined with the
finite element method, is developed for the numerical implementation of SOAR,
which yields a novel iterative regularization scheme for solving inverse source
problems. Several numerical examples are given to show the accuracy and the
acceleration effect of SOAR. A comparison with the state-of-the-art methods is
also provided.
|
1809.04971v2
|
2018-09-24
|
Oscillation Damping Control of Pendulum-like Manipulation Platform using Moving Masses
|
This paper presents an approach to damp out the oscillatory motion of the
pendulum-like hanging platform on which a robotic manipulator is mounted. To
this end, moving masses were installed on top of the platform. In this paper,
asymptotic stability of the platform (which implies oscillation damping) is
achieved by designing reference acceleration of the moving masses properly. A
main feature of this work is that we can achieve asymptotic stability of not
only the platform, but also the moving masses, which may be challenging due to
the under-actuation nature. The proposed scheme is validated by the simulation
studies.
|
1809.08819v1
|
2018-09-25
|
Theory of damping in magnetization dynamics, dispelling a myth and pointing a way forward
|
There is a widely-held belief amongst theoreticians that the Gilbert damping
parameter {\alpha} in magnetization dynamics is infinite for a pure metal at
T=0. The basic error leading to this belief is pointed out explicitly and the
various methods of calculation used are viewed in a unified way based on the
Lorentzian lineshape of ferromagnetic resonance spectra. A general torque
formula for {\alpha} is proposed as a good starting-point for treating
inhomogeneous materials such as alloys, compounds and layered structures. Local
spin density functional theory provides a simple physical picture, in terms of
a non-uniform precessional cone angle in ferromagnetic resonance, of how such
inhomogeneity contributes to the damping. In a complementary many-body theory
this contribution is given by a vertex correction to the torque-torque response
function.
|
1809.09429v1
|
2018-07-16
|
A unified N-SECE strategy for highly coupled piezoelectric energy scavengers
|
This paper proposes a novel vibration energy harvesting strategy based on an
extension of the Synchronous Electric Charge Extraction (SECE) approach,
enabling both the maximization of the harvested power and a consequent
bandwidth enlargement in the case of highly coupled/lightly damped
piezoelectric energy harvesters. The proposed strategy relies on the tuning of
the frequency of the energy extraction events, which is either N times greater
than the vibration frequency (Multiple SECE case, N > 1) or 1/N times smaller
(Regenerative SECE, N < 1). We first prove analytically than increasing or
decreasing N both lead to a damping reduction. While N has no impact on the
system's resonance frequency in the Regenerative case (N < 1), we show that
this resonant frequency becomes a function of N in the Multiple SECE case (N >
1). Experimental results on a highly coupled/lowly damped piezoelectric
harvester (k^2= 0.44, Q_m = 20) demonstrates the potential of this strategy,
leading to 257% harvested power improvement compared to SECE (N = 1). and the
possibility to tune the resonant frequency on a range as large as 35% of the
short-circuit resonant frequency of the harvester.
|
1809.09685v1
|
2018-10-15
|
Localized spin waves in isolated $kπ$ skyrmions
|
The localized magnon modes of isolated $k\pi$ skyrmions on a field-polarized
background are analyzed based on the Landau-Lifshitz-Gilbert equation within
the terms of an atomistic classical spin model, with system parameters based on
the Pd/Fe biatomic layer on Ir(111). For increasing skyrmion order $k$ a higher
number of excitation modes are found, including modes with nodes in the radial
eigenfunctions. It is shown that at low fields $2\pi$ and $3\pi$ skyrmions are
destroyed via a burst instability connected to a breathing mode, while $1\pi$
skyrmions undergo an elliptic instability. At high fields all $k\pi$ skyrmions
collapse due to the instability of a breathing mode. The effective damping
parameters of the spin waves are calculated in the low Gilbert damping limit,
and they are found to diverge in the case of the lowest-lying modes at the
burst and collapse instabilities, but not at the elliptic instability. It is
shown that the breathing modes of $k\pi$ skyrmions may become overdamped at
higher Gilbert damping values.
|
1810.06471v1
|
2018-10-24
|
Nearly isotropic spin-pumping related Gilbert damping in Pt/Ni$_{81}$Fe$_{19}$/Pt
|
A recent theory by Chen and Zhang [Phys. Rev. Lett. 114, 126602 (2015)]
predicts strongly anisotropic damping due to interfacial spin-orbit coupling in
ultrathin magnetic films. Interfacial Gilbert-type relaxation, due to the spin
pumping effect, is predicted to be significantly larger for magnetization
oriented parallel to compared with perpendicular to the film plane. Here, we
have measured the anisotropy in the Pt/Ni$_{81}$Fe$_{19}$/Pt system via
variable-frequency, swept-field ferromagnetic resonance (FMR). We find a very
small anisotropy of enhanced Gilbert damping with sign opposite to the
prediction from the Rashba effect at the FM/Pt interface. The results are
contrary to the predicted anisotropy and suggest that a mechanism separate from
Rashba spin-orbit coupling causes the rapid onset of spin-current absorption in
Pt.
|
1810.10595v4
|
2018-10-24
|
Justification of the Lugiato-Lefever model from a damped driven $φ^4$ equation
|
The Lugiato-Lefever equation is a damped and driven version of the well-known
nonlinear Schr\"odinger equation. It is a mathematical model describing complex
phenomena in dissipative and nonlinear optical cavities. Within the last two
decades, the equation has gained a wide attention as it becomes the basic model
describing optical frequency combs. Recent works derive the Lugiato-Lefever
equation from a class of damped driven $\phi^4$ equations closed to resonance.
In this paper, we provide a justification of the envelope approximation. From
the analysis point of view, the result is novel and non-trivial as the drive
yields a perturbation term that is not square integrable. The main approach
proposed in this work is to decompose the solutions into a combination of the
background and the integrable component. This paper is the first part of a
two-manuscript series.
|
1810.10630v1
|
2018-10-31
|
Anisotropic and controllable Gilbert-Bloch dissipation in spin valves
|
Spin valves form a key building block in a wide range of spintronic concepts
and devices from magnetoresistive read heads to spin-transfer-torque
oscillators. We elucidate the dependence of the magnetic damping in the free
layer on the angle its equilibrium magnetization makes with that in the fixed
layer. The spin pumping-mediated damping is anisotropic and tensorial, with
Gilbert- and Bloch-like terms. Our investigation reveals a mechanism for tuning
the free layer damping in-situ from negligible to a large value via the
orientation of fixed layer magnetization, especially when the magnets are
electrically insulating. Furthermore, we expect the Bloch contribution that
emerges from the longitudinal spin accumulation in the non-magnetic spacer to
play an important role in a wide range of other phenomena in spin valves.
|
1811.00020v2
|
2018-11-06
|
Decay properties and asymptotic profiles for elastic waves with Kelvin-Voigt damping in 2D
|
In this paper we consider elastic waves with Kelvin-Voigt damping in 2D. For
the linear problem, applying pointwise estimates of the partial Fourier
transform of solutions in the Fourier space and asymptotic expansions of
eigenvalues and their eigenprojections, we obtain sharp energy decay estimates
with additional $L^m$ regularity and $L^p-L^q$ estimates on the conjugate line.
Furthermore, we derive asymptotic profiles of solutions under different
assumptions of initial data. For the semilinear problem, we use the derived
$L^2-L^2$ estimates with additional $L^m$ regularity to prove global (in time)
existence of small data solutions to the weakly coupled system. Finally, to
deal with elastic waves with Kelvin-Voigt damping in 3D, we apply the Helmholtz
decomposition.
|
1811.02223v3
|
2018-12-06
|
Damping and Anti-Damping Phenomena in Metallic Antiferromagnets: An ab-initio Study
|
We report on a first principles study of anti-ferromagnetic resonance (AFMR)
phenomena in metallic systems [MnX (X=Ir,Pt,Pd,Rh) and FeRh] under an external
electric field. We demonstrate that the AFMR linewidth can be separated into a
relativistic component originating from the angular momentum transfer between
the collinear AFM subsystem and the crystal through the spin orbit coupling
(SOC), and an exchange component that originates from the spin exchange between
the two sublattices. The calculations reveal that the latter component becomes
significant in the low temperature regime. Furthermore, we present results for
the current-induced intersublattice torque which can be separated into the
Field-Like (FL) and Damping-Like (DL) components, affecting the intersublattice
exchange coupling and AFMR linewidth, respectively.
|
1812.02844v2
|
2018-12-12
|
Extreme wave events for a nonlinear Schrödinger equation with linear damping and Gaussian driving
|
We perform a numerical study of the initial-boundary value problem, with
vanishing boundary conditions, of a driven nonlinear Schr\"odinger equation
(NLS) with linear damping and a Gaussian driver. We identify Peregrine-like
rogue waveforms, excited by two different types of vanishing initial data
decaying at an algebraic or exponential rate. The observed extreme events
emerge on top of a decaying support. Depending on the spatial/temporal scales
of the driver, the transient dynamics -- prior to the eventual decay of the
solutions -- may resemble the one in the semiclassical limit of the integrable
NLS, or may, e.g., lead to large-amplitude breather-like patterns. The effects
of the damping strength and driving amplitude, in suppressing or enhancing
respectively the relevant features, as well as of the phase of the driver in
the construction of a diverse array of spatiotemporal patterns, are numerically
analyzed.
|
1812.05439v3
|
2018-12-13
|
Stability of elastic transmission systems with a local Kelvin-Voigt damping
|
In this paper, we consider the longitudinal and transversal vibrations of the
transmission Euler-Bernoulli beam with Kelvin-Voigt damping distributed locally
on any subinterval of the region occupied by the beam and only in one side of
the transmission point. We prove that the semigroup associated with the
equation for the transversal motion of the beam is exponentially stable,
although the semigroup associated with the equation for the longitudinal motion
of the beam is polynomially stable. Due to the locally distributed and
unbounded nature of the damping, we use a frequency domain method and combine a
contradiction argument with the multiplier technique to carry out a special
analysis for the resolvent.
|
1812.05923v1
|
2018-12-13
|
Energy decay estimates of elastic transmission wave/beam systems with a local Kelvin-Voigt damping
|
We consider a beam and a wave equations coupled on an elastic beam through
transmission conditions. The damping which is locally distributed acts through
one of the two equations only; its effect is transmitted to the other equation
through the coupling. First we consider the case where the dissipation acts
through the beam equation. Using a recent result of Borichev and Tomilov on
polynomial decay characterization of bounded semigroups we provide a precise
decay estimates showing that the energy of this coupled system decays
polynomially as the time variable goes to infinity. Second, we discuss the case
where the damping acts through the wave equation. Proceeding as in the first
case, we prove that this system is also polynomially stable and we provide
precise polynomial decay estimates for its energy. Finally, we show the lack of
uniform exponential decay of solutions for both models.
|
1812.05924v1
|
2018-12-20
|
Sound attenuation in stable glasses
|
Understanding the difference between universal low-temperature properties of
amorphous and crystalline solids requires an explanation of the stronger
damping of long-wavelength phonons in amorphous solids. A longstanding sound
attenuation scenario, resulting from a combination of experiments, theories,
and simulations, leads to a quartic scaling of sound attenuation with the
wavevector, which is commonly attributed to Rayleigh scattering of the sound.
Modern computer simulations offer conflicting conclusions regarding the
validity of this picture. We simulate glasses with an unprecedentedly broad
range of stabilities to perform the first microscopic analysis of sound damping
in model glass formers across a range of experimentally relevant preparation
protocols. We present a convincing evidence that quartic scaling is recovered
for small wavevectors irrespective of the glass's stability. With increasing
stability, the wavevector where the quartic scaling begins increases by
approximately a factor of three and the sound attenuation decreases by over an
order of magnitude. Our results uncover an intimate connection between glass
stability and sound damping.
|
1812.08736v2
|
2018-12-27
|
Nonexistence of global solutions for a weakly coupled system of semilinear damped wave equations of derivative type in the scattering case
|
In this paper we consider the blow-up for solutions to a weakly coupled
system of semilinear damped wave equations of derivative type in the scattering
case. After introducing suitable functionals proposed by Lai-Takamura for the
corresponding single semilinear equation, we employ Kato's lemma to derive the
blow-up result in the subcritical case. On the other hand, in the critical case
an iteration procedure based on the slicing method is employed. Let us point
out that we find as critical curve in the p-q plane for the pair of exponents
(p, q) in the nonlinear terms the same one as for the weakly coupled system of
semilinear not-damped wave equations with the same kind of nonlinearities.
|
1812.10653v1
|
2019-01-05
|
Simulations of wobble damping in viscoelastic rotators
|
Using a damped mass-spring model, we simulate wobble of spinning homogeneous
viscoelastic ellipsoids undergoing non-principal axis rotation. Energy damping
rates are measured for oblate and prolate bodies with different spin rates,
spin states, viscoelastic relaxation timescales, axis ratios, and strengths.
Analytical models using a quality factor by Breiter et al. (2012) and for the
Maxwell rheology by Frouard & Efroimsky (2018) match our numerical measurements
of the energy dissipation rate after we modify their predictions for the
numerically simulated Kelvin-Voigt rheology. Simulations of nearly spherical
but wobbling bodies with hard and soft cores show that the energy dissipation
rate is more sensitive to the material properties in the core than near the
surface. The sensitivity to viscoelastic model implies that inferred statistics
of tumbling lifetimes in asteroids might be interpreted in terms of differences
in their material properties.
|
1901.01439v3
|
2019-01-16
|
Laboratory investigations of the bending rheology of floating saline ice, and physical mechanisms of wave damping, in the HSVA ice tank
|
An experiment on the propagation of flexural-gravity waves was performed in
the HSVA ice tank. Physical characteristics of the water-ice system were
measured in different locations in the tank during the tests, with a number of
sensors deployed in the water, on the ice and in the air. Water velocity was
measured with an acoustic doppler velocimeter (ADV) and an acoustic doppler
current profiler (ADCP); wave amplitudes were measured with ultrasonic sensors
and the optical system Qualisys; in-plane deformations of the ice and the
temperature of the ice and water were measured by fiber optic sensors, and
acoustic emissions were recorded with compressional crystal sensors. All
together 61 tests were performed, with ice thicknesses of 3 cm and 5 cm. The
experimental setup and selected results of the tests are discussed in this
paper. We show that cyclic motion of the ice along the tank, imitating ice
drift, causes an increase in wave damping. We also show that the formation of
non-through cracks in the ice, caused by the action of waves, increases wave
damping.
|
1901.05333v1
|
2019-01-24
|
Generalized framework for testing gravity with gravitational-wave propagation. III. Future prospect
|
The properties of gravitational-wave (GW) propagation are modified in
alternative theories of gravity and are crucial observables to test gravity at
cosmological distance. The propagation speed has already been measured from
GW170817 so precisely and pinned down to the speed of light, while other
properties of GW propagation have not constrained tightly yet. In this paper,
we investigate the measurement precisions of the amplitude damping rate
(equivalently, the time variation of the gravitational coupling for GWs) and
graviton mass in the generalized framework of GW propagation with the future
detectors such as Voyager, Cosmic Explorer, and Einstein Telescope. As a
result, we show that the future GW observation can reach 1% error for the
amplitude damping. We also study the time variation of the gravitational
couplings in Horndeski theory by performing Monte Carlo-based numerical
simulations. From the simulation results, we find that the current accelerating
Universe prefers the models with less damping of GWs and that the equivalence
principle can be tested at the level of 1% by the future GW observation.
|
1901.08249v2
|
2019-01-31
|
Perturbed Markov Chains and Information Networks
|
The paper is devoted to studies of perturbed Markov chains commonly used for
description of information networks. In such models, the matrix of transition
probabilities for the corresponding Markov chain is usually regularised by
adding a special damping matrix multiplied by a small damping (perturbation)
parameter $\varepsilon$. We give effective upper bounds for the rate of
approximation for stationary distributions of unperturbed Markov chains by
stationary distributions of perturbed Markov chains with regularised matrices
of transition probabilities, asymptotic expansions for approximating stationary
distributions with respect to damping parameter, as well as explicit upper
bounds for the rate of convergence in ergodic theorems for $n$-step transition
probabilities in triangular array mode, where perturbation parameter
$\varepsilon \to 0$ and $n \to \infty$, simultaneously. The results of
numerical experiments are also presented
|
1901.11483v3
|
2019-02-12
|
Ultra-low damping in lift-off structured yttrium iron garnet thin films
|
We show that using maskless photolithography and the lift-off technique,
patterned yttrium iron garnet thin films possessing ultra-low Gilbert damping
can be accomplished. The films of 70 nm thickness were grown on (001)-oriented
gadolinium gallium garnet by means of pulsed laser deposition, and they exhibit
high crystalline quality, low surface roughness, and the effective
magnetization of 127 emu/cm3. The Gilbert damping parameter is as low as
5x10-4. The obtained structures have well-defined sharp edges which along with
good structural and magnetic film properties pave a path in the fabrication of
high-quality magnonic circuits and oxide-based spintronic devices.
|
1902.04605v1
|
2019-02-14
|
Dynamic Interconnection and Damping Injection for Input-to-State Stable Bilateral Teleoperation
|
In bilateral teleoperation, the human who operates the master and the
environment which interacts with the slave are part of the force feedback loop.
Yet, both have time-varying and unpredictable dynamics and are challenging to
model. A conventional strategy for sidestepping the demand for their models in
the stability analysis is to assume passive user and environment, and to
control the master-communications-slave system to be passive as well. This
paper circumvents the need to model the user and environment in a novel way: it
regards their forces as external excitations for a semi-autonomous force
feedback loop, which it outfits with a dynamic interconnection and damping
injection controller that renders bilateral teleoperation with time-varying
delays exponentially input-to-state stable. The controller uses the position
and velocity measurements of the local robot and the delayed position
transmitted from the other robot to robustly synchronize the master and slave
under the user and environment perturbations. Lyapunov-Krasovskii stability
analysis shows that the proposed strategy (i) can confine the position error
between the master and slave to an invariant set, and (ii) can drive it
exponentially to a globally attractive set. Thus, the dynamic interconnection
and damping injection approach has practical relevance for telemanipulation
tasks with given precision requirements.
|
1902.05500v1
|
2019-02-15
|
Evidence for Electron Landau Damping in Space Plasma Turbulence
|
How turbulent energy is dissipated in weakly collisional space and
astrophysical plasmas is a major open question. Here, we present the
application of a field-particle correlation technique to directly measure the
transfer of energy between the turbulent electromagnetic field and electrons in
the Earth's magnetosheath, the region of solar wind downstream of the Earth's
bow shock. The measurement of the secular energy transfer from the parallel
electric field as a function of electron velocity shows a signature consistent
with Landau damping. This signature is coherent over time, close to the
predicted resonant velocity, similar to that seen in kinetic Alfv\'en
turbulence simulations, and disappears under phase randomisation. This suggests
that electron Landau damping could play a significant role in turbulent plasma
heating, and that the technique is a valuable tool for determining the particle
energisation processes operating in space and astrophysical plasmas.
|
1902.05785v1
|
2019-02-20
|
CoFeB/MgO/CoFeB structures with orthogonal easy axes: perpendicular anisotropy and damping
|
We report on the Gilbert damping parameter $\alpha$, the effective
magnetization $4\pi M_{eff}$, and the asymmetry of the $g$-factor in
bottom-CoFeB(0.93~nm)/MgO(0.90--1.25~nm)/CoFeB(1.31~nm)-top as-deposited
systems.
Magnetization of CoFeB layers exhibits a specific noncollinear configuration
with orthogonal easy axes and with $4\pi M_{eff}$ values of $+2.2$ kG and
$-2.3$ kG for the bottom and top layers, respectively. We show that $4\pi
M_{eff}$ depends on the asymmetry $g_\perp - g_\parallel$ of the $g$-factor
measured in the perpendicular and the in-plane directions revealing a highly
nonlinear relationship. In contrast, the Gilbert damping is practically the
same for both layers. Annealing of the films results in collinear easy axes
perpendicular to the plane for both layers. However, the linewidth is strongly
increased due to enhanced inhomogeneous broadening.
|
1902.07563v1
|
2019-02-22
|
Thermal induced monochromatic microwave generation in magnon-polariton
|
We propose thermal induced generation of monochromatic microwave radiation in
magnon-polariton. Mechanism of thermal to microwave energy transformation is
based on intrinsic energy loss compensation of coupled magnon and microwave
cavity oscillators by thermal induced "negative damping". A singularity at an
exceptional point is achieved when at the critical value of "negative damping"
the damping of the system is fully compensated. At the exceptional point, the
input energy is equally distributed between the magnon and photon subsystems of
the magnon-polariton. The efficiency of transformation of thermal energy into
useful microwave radiation is estimated to be as large as 17 percent due to
magnon-photon coupling mediated direct conversation of spin current into
microwave photons.
|
1902.08383v1
|
2019-03-04
|
Nonlinear inviscid damping for zero mean perturbation of the 2D Euler Couette flow
|
In this note we revisit the proof of Bedrossian and Masmoudi
[arXiv:1306.5028] about the inviscid damping of planar shear flows in the 2D
Euler equations under the assumption of zero mean perturbation. We prove that a
small perturbation to the 2D Euler Couette flow in $\mathbb{T}\times
\mathbb{R}$ strongly converge to zero, under the additional assumption that the
average in $x$ is always zero. In general the mean is not a conserved quantity
for the nonlinear dynamics, for this reason this is a particular case.
Nevertheless our assumption allow the presence of echoes in the problem, which
we control by an approximation of the weight built in [arXiv:1306.5028]. The
aim of this note is to present the mathematical techniques used in
[arXiv:1306.5028] and can be useful as a first approach to the nonlinear
inviscid damping.
|
1903.01543v1
|
2019-03-10
|
Orbital stabilization of nonlinear systems via Mexican sombrero energy shaping and pumping-and-damping injection
|
In this paper we show that a slight modification to the widely popular
interconnection and damping assignment passivity-based control
method---originally proposed for stabilization of equilibria of nonlinear
systems---allows us to provide a solution to the more challenging orbital
stabilization problem. Two different, though related, ways how this procedure
can be applied are proposed. First, the assignment of an energy function that
has a minimum in a closed curve, i.e., with the shape of a Mexican sombrero.
Second, the use of a damping matrix that changes "sign" according to the
position of the state trajectory relative to the desired orbit, that is,
pumping or dissipating energy. The proposed methodologies are illustrated with
the example of the induction motor and prove that it yields the industry
standard field oriented control.
|
1903.04070v3
|
2019-03-11
|
Impact of thermal effects on the evolution of eccentricity and inclination of low-mass planets
|
Using linear perturbation theory, we evaluate the time-dependent force
exerted on an eccentric and inclined low-mass planet embedded in a gaseous
protoplanetary disc with finite thermal diffusivity $\chi$. We assume the
eccentricity and inclination to be small compared to the size of the thermal
lobes $\lambda\sim(\chi/\Omega)^{1/2}$, itself generally much smaller than the
scalelength of pressure $H$. When the planet is non-luminous, we find that its
eccentricity and inclination are vigorously damped by the disc, over a
timescale shorter by a factor $H/\lambda$ than the damping timescale in
adiabatic discs. On the contrary, when the luminosity-to-mass ratio of the
planet exceeds a threshold that depends on the disc's properties, its
eccentricity and inclination undergo an exponential growth. In the limit of a
large luminosity, the growth rate of the eccentricity is 2.5~times larger than
that of the inclination, in agreement with previous numerical work. Depending
on their luminosity, planetary embryos therefore exhibit much more diverse
behaviours than the mild damping of eccentricity and inclination considered
hitherto.
|
1903.04470v2
|
2019-03-14
|
The Strichartz estimates for the damped wave equation and the behavior of solutions for the energy critical nonlinear equation
|
For the linear damped wave equation (DW), the $L^p$-$L^q$ type estimates have
been well studied. Recently, Watanabe showed the Strichartz estimates for DW
when $d=2,3$. In the present paper, we give Strichartz estimates for DW in
higher dimensions. Moreover, by applying the estimates, we give the local
well-posedness of the energy critical nonlinear damped wave equation (NLDW)
$\partial_t^2 u - \Delta u +\partial_t u = |u|^{\frac{4}{d-2}}u$, $(t,x) \in
[0,T) \times \mathbb{R}^d$, where $3 \leq d \leq 5$. Especially, we show the
small data global existence for NLDW. In addition, we investigate the behavior
of the solutions to NLDW. Namely, we give a decay result for solutions with
finite Strichartz norm and a blow-up result for solutions with negative Nehari
functional.
|
1903.05887v1
|
2019-04-17
|
Decays for Kelvin-Voigt damped wave equations I : the black box perturbative method
|
We show in this article how perturbative approaches~from our work with Hitrik
(see also the work by Anantharaman-Macia) and the {\em black box} strategy
from~ our work with Zworski allow to obtain decay rates for Kelvin-Voigt damped
wave equations from quite standard resolvent estimates : Carleman estimates or
geometric control estimates for Helmoltz equationCarleman or other resolvent
estimates for the Helmoltz equation. Though in this context of Kelvin Voigt
damping, such approach is unlikely to allow for the optimal results when
additional geometric assumptions are considered (see \cite{BuCh, Bu19}), it
turns out that using this method, we can obtain the usual logarithmic decay
which is optimal in general cases. We also present some applications of this
approach giving decay rates in some particular geometries (tori).
|
1904.08318v2
|
2019-04-17
|
Non-Hermitian skin effect and chiral damping in open quantum systems
|
One of the unique features of non-Hermitian Hamiltonians is the non-Hermitian
skin effect, namely that the eigenstates are exponentially localized at the
boundary of the system. For open quantum systems, a short-time evolution can
often be well described by the effective non-Hermitian Hamiltonians, while
long-time dynamics calls for the Lindblad master equations, in which the
Liouvillian superoperators generate time evolution. In this Letter, we find
that Liouvillian superoperators can exhibit the non-Hermitian skin effect, and
uncover its unexpected physical consequences. It is shown that the
non-Hermitian skin effect dramatically shapes the long-time dynamics, such that
the damping in a class of open quantum systems is algebraic under periodic
boundary condition but exponential under open boundary condition. Moreover, the
non-Hermitian skin effect and non-Bloch bands cause a chiral damping with a
sharp wavefront. These phenomena are beyond the effective non-Hermitian
Hamiltonians; instead, they belong to the non-Hermitian physics of full-fledged
open quantum dynamics.
|
1904.08432v2
|
2019-04-19
|
Plasmon-Emitter Interactions at the Nanoscale
|
Plasmon-emitter interactions are of paramount importance in modern
nanoplasmonics and are generally maximal at short emitter-surface separations.
However, when the separation falls below 10-20 nm, the classical theory
progressively deteriorates due to its neglect of quantum mechanical effects
such as nonlocality, electronic spill-out, and Landau damping. Here, we show
how this neglect can be remedied by presenting a unified theoretical treatment
of mesoscopic electrodynamics grounded on the framework of Feibelman
$d$-parameters. Crucially, our technique naturally incorporates nonclassical
resonance shifts and surface-enabled Landau damping - a nonlocal damping effect
- which have a dramatic impact on the amplitude and spectral distribution of
plasmon-emitter interactions. We consider a broad array of plasmon-emitter
interactions ranging from dipolar and multipolar spontaneous emission
enhancement, to plasmon-assisted energy transfer and enhancement of two-photon
transitions. The formalism presented here gives a complete account of both
plasmons and plasmon-emitter interactions at the nanoscale, constituting a
simple yet rigorous and general platform to incorporate nonclassical effects in
plasmon-empowered nanophotonic phenomena.
|
1904.09279v1
|
2019-05-08
|
Discrete Energy behavior of a damped Timoshenko system
|
In this article, we consider a one-dimensional Timoshenko system subject to
different types of dissipation (linear and nonlinear dampings). Based on a
combination between the finite element and the finite difference methods, we
design a discretization scheme for the different Timoshenko systems under
consideration. We first come up with a numerical scheme to the free-undamped
Timoshenko system. Then, we adapt this numerical scheme to the corresponding
linear and nonlinear damped systems. Interestingly, this scheme reaches to
reproduce the most important properties of the discrete energy. Namely, we show
for the discrete energy the positivity, the energy conservation property and
the different decay rate profiles. We numerically reproduce the known
analytical results established on the decay rate of the energy associated with
each type of dissipation.
|
1905.03050v1
|
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