publicationDate
stringlengths 1
2.79k
| title
stringlengths 1
36.5k
⌀ | abstract
stringlengths 1
37.3k
⌀ | id
stringlengths 9
47
|
|---|---|---|---|
2014-01-20
|
Analysis of mean cluster size in directed compact percolation near a damp wall
|
We investigate the behaviour of the mean size of directed compact percolation
clusters near a damp wall in the low-density region, where sites in the bulk
are wet (occupied) with probability $p$ while sites on the wall are wet with
probability $p_w$. Methods used to find the exact solution for the dry case
($p_w=0$) and the wet case ($p_w=1$) turn out to be inadequate for the damp
case. Instead we use a series expansion for the $p_w=2p$ case to obtain a
second order inhomogeneous differential equation satisfied by the mean size,
which exhibits a critical exponent $\gamma=2$, in common with the wet wall
result. For the more general case of $p_w=rp$, with $r$ rational, we use a
modular arithmetic method of finding ODEs and obtain a fourth order homogeneous
ODE satisfied by the series. The ODE is expressed exactly in terms of $r$. We
find that in the damp region $0<r<2$ the critical exponent $\gamma^{\rm
damp}=1$, in common with the dry wall result.
|
1401.4793v1
|
2014-02-13
|
On the Convergence of Approximate Message Passing with Arbitrary Matrices
|
Approximate message passing (AMP) methods and their variants have attracted
considerable recent attention for the problem of estimating a random vector
$\mathbf{x}$ observed through a linear transform $\mathbf{A}$. In the case of
large i.i.d. zero-mean Gaussian $\mathbf{A}$, the methods exhibit fast
convergence with precise analytic characterizations on the algorithm behavior.
However, the convergence of AMP under general transforms $\mathbf{A}$ is not
fully understood. In this paper, we provide sufficient conditions for the
convergence of a damped version of the generalized AMP (GAMP) algorithm in the
case of quadratic cost functions (i.e., Gaussian likelihood and prior). It is
shown that, with sufficient damping, the algorithm is guaranteed to converge,
although the amount of damping grows with peak-to-average ratio of the squared
singular values of the transforms $\mathbf{A}$. This result explains the good
performance of AMP on i.i.d. Gaussian transforms $\mathbf{A}$, but also their
difficulties with ill-conditioned or non-zero-mean transforms $\mathbf{A}$. A
related sufficient condition is then derived for the local stability of the
damped GAMP method under general cost functions, assuming certain strict
convexity conditions.
|
1402.3210v3
|
2014-03-28
|
Strichartz estimates and smooth attractors for a sub-quintic wave equation with fractional damping in bounded domains
|
The work is devoted to Dirichlet problem for sub-quintic semi-linear wave
equation with damping damping term of the form $(-\Delta)^\alpha\partial_t u$,
$\alpha\in(0,\frac{1}{2})$, in bounded smooth domains of $\Bbb R^3$. It appears
that to prove well-posedness and develop smooth attractor theory for the
problem we need additional regularity of the solutions, which does not follow
from the energy estimate. Considering the original problem as perturbation of
the linear one the task is reduced to derivation of Strichartz type estimate
for the linear wave equation with fractional damping, which is the main feature
of the work. Existence of smooth exponential attractor for the natural
dynamical system associated with the problem is also established.
|
1403.7476v1
|
2014-05-12
|
Global Existence and Nonlinear Diffusion of Classical Solutions to Non-Isentropic Euler Equations with Damping in Bounded Domain
|
We considered classical solutions to the initial boundary value problem for
non-isentropic compressible Euler equations with damping in multi-dimensions.
We obtained global a priori estimates and global existence results of classical
solutions to both non-isentropic Euler equations with damping and their
nonlinear diffusion equations under small data assumption. We proved the
pressure and velocity decay exponentially to constants, while the entropy and
density can not approach constants. Finally, we proved the pressure and
velocity of the non-isentropic Euler equations with damping converge
exponentially to those of their nonlinear diffusion equations when the time
goes to infinity.
|
1405.2842v3
|
2014-05-16
|
Damping of Confined Modes in a Ferromagnetic Thin Insulating Film: Angular Momentum Transfer Across a Nanoscale Field-defined Interface
|
We observe a dependence of the damping of a confined mode of precessing
ferromagnetic magnetization on the size of the mode. The micron-scale mode is
created within an extended, unpatterned YIG film by means of the intense local
dipolar field of a micromagnetic tip. We find that damping of the confined mode
scales like the surface-to-volume ratio of the mode, indicating an interfacial
damping effect (similar to spin pumping) due to the transfer of angular
momentum from the confined mode to the spin sink of ferromagnetic material in
the surrounding film. Though unexpected for insulating systems, the measured
intralayer spin-mixing conductance $g_{\uparrow \downarrow} = 5.3 \times
10^{19} {\rm m}^{-2}$ demonstrates efficient intralayer angular momentum
transfer.
|
1405.4203v2
|
2014-06-03
|
Persistently damped transport on a network of circles
|
In this paper we address the exponential stability of a system of transport
equations with intermittent damping on a network of $N \geq 2$ circles
intersecting at a single point $O$. The $N$ equations are coupled through a
linear mixing of their values at $O$, described by a matrix $M$. The activity
of the intermittent damping is determined by persistently exciting signals, all
belonging to a fixed class. The main result is that, under suitable hypotheses
on $M$ and on the rationality of the ratios between the lengths of the circles,
such a system is exponentially stable, uniformly with respect to the
persistently exciting signals. The proof relies on an explicit formula for the
solutions of this system, which allows one to track down the effects of the
intermittent damping.
|
1406.0731v4
|
2014-06-06
|
Damping of quasiparticles in a Bose-Einstein condensate coupled to an optical cavity
|
We present a general theory for calculating the damping rate of elementary
density wave excitations in a Bose-Einstein condensate strongly coupled to a
single radiation field mode of an optical cavity. Thereby we give a detailed
derivation of the huge resonant enhancement in the Beliaev damping of a density
wave mode, predicted recently by K\'onya et al., Phys.~Rev.~A 89, 051601(R)
(2014). The given density-wave mode constitutes the polariton-like soft mode of
the self-organization phase transition. The resonant enhancement takes place,
both in the normal and ordered phases, outside the critical region. We show
that the large damping rate is accompanied by a significant frequency shift of
this polariton mode. Going beyond the Born-Markov approximation and determining
the poles of the retarded Green's function of the polariton, we reveal a strong
coupling between the polariton and a collective mode in the phonon bath formed
by the other density wave modes.
|
1406.1669v1
|
2014-08-18
|
Kirchhoff equations with strong damping
|
We consider Kirchhoff equations with strong damping, namely with a friction
term which depends on a power of the "elastic" operator. We address local and
global existence of solutions in two different regimes depending on the
exponent in the friction term.
When the exponent is greater than 1/2, the dissipation prevails, and we
obtain global existence in the energy space assuming only degenerate
hyperbolicity and continuity of the nonlinear term. When the exponent is less
than 1/2, we assume strict hyperbolicity and we consider a phase space
depending on the continuity modulus of the nonlinear term and on the exponent
in the damping. In this phase space we prove local existence, and global
existence if initial data are small enough.
The regularity we assume both on initial data and on the nonlinear term is
weaker than in the classical results for Kirchhoff equations with standard
damping.
Proofs exploit some recent sharp results for the linearized equation and
suitably defined interpolation spaces.
|
1408.3908v1
|
2014-08-28
|
A convergent method for linear half-space kinetic equations
|
We give a unified proof for the well-posedness of a class of linear
half-space equations with general incoming data and construct a Galerkin method
to numerically resolve this type of equations in a systematic way. Our main
strategy in both analysis and numerics includes three steps: adding damping
terms to the original half-space equation, using an inf-sup argument and
even-odd decomposition to establish the well-posedness of the damped equation,
and then recovering solutions to the original half-space equation. The proposed
numerical methods for the damped equation is shown to be quasi-optimal and the
numerical error of approximations to the original equation is controlled by
that of the damped equation. This efficient solution to the half-space problem
is useful for kinetic-fluid coupling simulations.
|
1408.6630v4
|
2014-09-02
|
Damping effects in hole-doped graphene: the relaxation-time approximation
|
The dynamical conductivity of interacting multiband electronic systems
derived in Ref.[1] is shown to be consistent with the general form of the Ward
identity. Using the semiphenomenological form of this conductivity formula, we
have demonstrated that the relaxation-time approximation can be used to
describe the damping effects in weakly interacting multiband systems only if
local charge conservation in the system and gauge invariance of the response
theory are properly treated. Such a gauge-invariant response theory is
illustrated on the common tight-binding model for conduction electrons in
hole-doped graphene. The model predicts two distinctly resolved maxima in the
energy-loss-function spectra. The first one corresponds to the intraband
plasmons (usually called the Dirac plasmons). On the other hand, the second
maximum ($\pi$ plasmon structure) is simply a consequence of the van Hove
singularity in the single-electron density of states. The dc resistivity and
the real part of the dynamical conductivity are found to be well described by
the relaxation-time approximation, but only in the parametric space in which
the damping is dominated by the direct scattering processes. The ballistic
transport and the damping of Dirac plasmons are thus the questions that require
abandoning the relaxation-time approximation.
|
1409.0621v1
|
2014-10-13
|
Relaxation damping in oscillating contacts
|
If a contact of two purely elastic bodies with no sliding (infinite
coefficient of friction) is subjected to superimposed oscillations in the
normal and tangential directions, then a specific damping appears, that is not
dependent on friction or dissipation in the material. We call this effect
"relaxation damping". The rate of energy dissipation due to relaxation damping
is calculated in a closed analytic form for arbitrary axially-symmetric
contacts. In the case of equal frequency of normal and tangential oscillations,
the dissipated energy per cycle is proportional to the square of the amplitude
of tangential oscillation and to the absolute value of the amplitude of normal
oscillation, and is dependent on the phase shift between both oscillations. In
the case of low frequency tangential motion with superimposed high frequency
normal oscillations, the system acts as a tunable linear damper. Generalization
of the results for macroscopically planar, randomly rough surfaces is
discussed.
|
1410.3238v1
|
2014-11-13
|
Maximal correlation between flavor entanglement and oscillation damping due to localization effects
|
Localization effects and quantum decoherence driven by the mass-eigenstate
wave packet propagation are shown to support a statistical correlation between
quantum entanglement and damped oscillations in the scenario of three-flavor
quantum mixing for neutrinos. Once the mass-eigenstates that support flavor
oscillations are identified as three-{\em qubit} modes, a decoherence scale can
be extracted from correlation quantifiers, namely the entanglement of formation
and the logarithmic negativity. Such a decoherence scale is compared with the
coherence length of damped oscillations. Damping signatures exhibited by flavor
transition probabilities as an effective averaging of the oscillating terms are
then explained as owing to loss of entanglement between mass modes involved in
the relativistic propagation.
|
1411.3634v1
|
2015-01-20
|
Damping of long wavelength collective modes in spinor Bose-Fermi mixtures
|
Using an effective field theory we describe the low energy bosonic
excitations in a three dimensional ultra-cold mixture of spin-1 bosons and
spin-1/2 fermions. We establish an interesting fermionic excitation induced
generic damping of the usual undamped long wavelength bosonic collective
Goldstone modes. Two states with bosons forming either a ferromagnetic or polar
superfluid are studied. The linear dispersion of the bosonic Bogoliubov
excitations is preserved with a renormalized sound velocity. For the polar
superfluid we find both gapless modes (density and spin) are damped, whereas in
the ferromagnetic superfluid we find the density (spin) mode is (not) damped.
We argue quite generally that this holds for any mixture of bosons and fermions
that are coupled through at least a density-density interaction. We discuss the
implications of our many-body interaction results for experiments on Bose-Fermi
mixtures.
|
1501.05015v2
|
2015-01-27
|
Non-linear fluctuation effects in dynamics of freely suspended film
|
Long-scale dynamic fluctuation phenomena in freely suspended films is
analyzed. We consider isotropic films that, say, can be pulled from bulk
smectic A liquid crystals. The key feature of such objects is possibility of
bending deformations of the film. The bending (also known as flexular) mode
turns out to be anomalously weakly attenuated. In the harmonic approximation
there is no viscous-like damping of the bending mode, proportional to q^2 (q is
the wave vector of the mode), since it is forbidden by the rotational symmetry.
Therefore the bending mode is strongly affected by non-linear dynamic
fluctuation effects. We calculate the dominant fluctuation contributions to the
damping of the bending mode due to its coupling to the in-plane viscous mode,
that restores the viscous-like q^2 damping of the bending mode. Our
calculations are performed in the framework of the perturbation theory where
the coupling of the modes is assumed to be small, then the bending mode damping
is relatively weak. We discuss our results in the context of existing
experiments and numeric simulations of the freely suspended films and propose
possible experimental observations of our predictions.
|
1501.06703v1
|
2015-01-30
|
Intrinsic Damping of Collective Spin Modes in a Two-Dimensional Fermi Liquid with Spin-Orbit Coupling
|
A Fermi liquid with spin-orbit coupling (SOC) is expected to support a new
kind of collective modes: oscillations of magnetization in the absence of the
magnetic field. We show that these modes are damped by the electron-electron
interaction even in the limit of an infinitely long wavelength (q = 0). The
linewidth of the collective mode is on the order of {\Delta}^2=E_F , where
{\Delta} is a characteristic spin-orbit energy splitting and E_F is the Fermi
energy. Such damping is in a stark contrast to known damping mechanisms of both
charge and spin collective modes in the absence of SOC, all of which disappear
at q = 0, and arises because none of the components of total spin is conserved
in the presence of SOC.
|
1502.00027v1
|
2015-02-01
|
Nonlocal Damping of Helimagnets in One-Dimensional Interacting Electron Systems
|
We investigate the magnetization relaxation of a one-dimensional helimagnetic
system coupled to interacting itinerant electrons. The relaxation is assumed to
result from the emission of plasmons, the elementary excitations of the
one-dimensional interacting electron system, caused by slow changes of the
magnetization profile. This dissipation mechanism leads to a highly nonlocal
form of magnetization damping that is strongly dependent on the
electron-electron interaction. Forward scattering processes lead to a spatially
constant damping kernel, while backscattering processes produce a spatially
oscillating contribution. Due to the nonlocal damping, the thermal fluctuations
become spatially correlated over the entire system. We estimate the
characteristic magnetization relaxation times for magnetic quantum wires and
nuclear helimagnets.
|
1502.00268v2
|
2015-07-21
|
Onboard Calibration Circuit for the Front-end Electronics of DAMPE BGO Calorimeter
|
An onboard calibration circuit has been designed for the front-end
electronics (FEE) of DAMPE BGO Calorimeter. It is mainly composed of a 12 bit
DAC, an operation amplifier and an analog switch. Test results showed that a
dynamic range of 0 ~ 30 pC with a precision of 5 fC was achieved, which meets
the requirements of the front-end electronics. Furthermore, it is used to test
the trigger function of the FEEs. The calibration circuit has been implemented
and verified by all the environmental tests for both Qualification Model and
Flight Model of DAMPE. The DAMPE satellite will be launched at the end of 2015
and the calibration circuit will perform onboard calibration in space.
|
1507.05862v1
|
2015-07-30
|
Reservoir interactions during Bose-Einstein condensation: modified critical scaling in the Kibble-Zurek mechanism of defect formation
|
As a test of the Kibble-Zurek mechanism (KZM) of defect formation, we
simulate the Bose-Einstein condensation transition in a toroidally confined
Bose gas using the stochastic projected Gross-Pitaevskii equation (SPGPE), with
and without the energy-damping reservoir interaction. Energy-damping alters the
scaling of the winding number distribution with the quench time - a departure
from the universal KZM theory that relies on equilibrium critical exponents.
Numerical values are obtained for the correlation-length critical exponent
$\nu$ and the dynamical critical exponent $z$ for each variant of reservoir
interaction theory. The energy-damping reservoir interactions cause significant
modification of the dynamical critical exponent of the phase transition, whilst
preserving the essential KZM critical scaling behavior. Comparison of numerical
and analytical two-point correlation functions further illustrates the effect
of energy damping on the correlation length during freeze out.
|
1507.08357v1
|
2015-08-23
|
Melnikov chaos in a modified Rayleigh-Duffing oscillator with $ φ^6$ potential
|
The chaotic behavior of the modified Rayleigh-Duffing oscillator with $
\phi^6$ potential and external excitation which modeles ship rolling motions
are investigated both analytically and numerically. Melnikov method is applied
and the conditions for the existence of homoclinic and heteroclinic chaos are
obtained. The effects of nonlinear damping on roll motion of ships are analyzed
in detail. As it is known, nonlinear roll damping is a very important parameter
in estimating ship reponses. The predictions are tested numerical simulations
based on the basin of attraction. We conclude that certains quadratic damping
effects are contrary to cubic damping effect.
|
1508.05664v1
|
2015-09-23
|
Quantum Error-Correcting Codes for Qudit Amplitude Damping
|
Traditional quantum error-correcting codes are designed for the depolarizing
channel modeled by generalized Pauli errors occurring with equal probability.
Amplitude damping channels model, in general, the decay process of a multilevel
atom or energy dissipation of a bosonic system at zero temperature. We discuss
quantum error-correcting codes adapted to amplitude damping channels for higher
dimensional systems (qudits). For multi-level atoms, we consider a natural kind
of decay process, and for bosonic systems,we consider the qudit amplitude
damping channel obtained by truncating the Fock basis of the bosonic modes to a
certain maximum occupation number. We construct families of
single-error-correcting quantum codes that can be used for both cases. Our
codes have larger code dimensions than the previously known
single-error-correcting codes of the same lengths. Additionally, we present
families of multi-error correcting codes for these two channels, as well as
generalizations of our construction technique to error-correcting codes for the
qutrit $V$ and $\Lambda$ channels.
|
1509.06829v1
|
2015-10-09
|
Determining form and data assimilation algorithm for weakly damped and driven Korteweg-de Vries equaton- Fourier modes case
|
We show that the global attractor of a weakly damped and driven Korteweg-de
Vries equation (KdV) is embedded in the long-time dynamics of an ordinary
differential equation called a determining form. In particular, there is a
one-to-one identification of the trajectories in the global attractor of the
damped and driven KdV and the steady state solutions of the determining form.
Moreover, we analyze a data assimilation algorithm (down-scaling) for the
weakly damped and driven KdV. We show that given a certain number of low
Fourier modes of a reference solution of the KdV equation, the algorithm
recovers the full reference solution at an exponential rate in time.
|
1510.02730v1
|
2015-10-27
|
Remarks on 1-D Euler Equations with Time-Decayed Damping
|
We study the 1-d isentropic Euler equations with time-decayed damping
\begin{equation} \left\{ \begin{aligned} &\partial_t \rho+\partial_x(\rho u)=0,
\\ &\partial_t(\rho u)+ \partial_x(\rho
u^2)+\partial_xp(\rho)=-\frac{\mu}{1+t}\rho u,\\
&\rho|_{t=0}=1+\varepsilon\rho_0(x),u|_{t=0}=\varepsilon u_0(x). \end{aligned}
\right. \nonumber \end{equation}
This work is inspired by a recent work of F. Hou, I. Witt and H.C. Yin
\cite{Hou01}. In \cite{Hou01}, they proved a global existence and blow-up
result of 3-d irrotational Euler flow with time-dependent damping. In the 1-d
case, we will prove a different result when the damping decays of order $-1$
with respect to the time $t$. More precisely, when $\mu>2$, we prove the global
existence of the 1-d Euler system. While when $0\leq\mu\leq2 $, we will prove
the blow up of $C^1$ solutions.
|
1510.08115v1
|
2016-01-04
|
Generalized Bloch's theorem for viscous metamaterials: Dispersion and effective properties based on frequencies and wavenumbers that are simultaneously complex
|
It is common for dispersion curves of damped periodic materials to be based
on real frequencies versus complex wavenumbers or, conversely, real wavenumbers
versus complex frequencies. The former condition corresponds to harmonic wave
motion where a driving frequency is prescribed and where attenuation due to
dissipation takes place only in space alongside spatial attenuation due to
Bragg scattering. The latter condition, on the other hand, relates to free wave
motion admitting attenuation due to energy loss only in time while spatial
attenuation due to Bragg scattering also takes place. Here, we develop an
algorithm for 1D systems that provides dispersion curves for damped free wave
motion based on frequencies and wavenumbers that are permitted to be
simultaneously complex. This represents a generalized application of Bloch's
theorem and produces a dispersion band structure that fully describes all
attenuation mechanisms, in space and in time. The algorithm is applied to a
viscously damped mass-in-mass metamaterial exhibiting local resonance. A
frequency-dependent effective mass for this damped infinite chain is also
obtained.
|
1601.00683v1
|
2016-02-05
|
Protecting entanglement from correlated amplitude damping channel using weak measurement and quantum measurement reversal
|
Based on the quantum technique of weak measurement, we propose a scheme to
protect the entanglement from correlated amplitude damping decoherence. In
contrast to the results of memoryless amplitude damping channel, we show that
the memory effects play a significant role in the suppression of entanglement
sudden death and protection of entanglement under severe decoherence. Moreover,
we find that the initial entanglement could be drastically amplified by the
combination of weak measurement and quantum measurement reversal even under the
correlated amplitude damping channel. The underlying mechanism can be
attributed to the probabilistic nature of weak measurements.
|
1602.01998v1
|
2016-03-10
|
Stability Analysis of Networked Systems Containing Damped and Undamped Nodes
|
This paper answers the question if a qualitatively heterogeneous passive
networked system containing damped and undamped nodes shows consensus in the
output of the nodes in the long run. While a standard Lyapunov analysis shows
that the damped nodes will always converge to a steady-state value, the
convergence of the undamped nodes is much more delicate and depends on the
parameter values of the network as well as on the topology of the graph. A
complete stability analysis is presented based on an eigenvector analysis
involving the mass values and the topology of both the original graph and the
reduced graph obtained by a Kron reduction that eliminates the damped nodes.
|
1603.03477v1
|
2016-04-29
|
Nonlinear Landau damping of wave envelopes in a quantum plasma
|
The nonlinear theory of Landau damping of electrostatic wave envelopes (WEs)
is revisited in a quantum electron-positron (EP) pair plasma. Starting from a
Wigner-Moyal equation coupled to the Poisson equation and applying the multiple
scale technique, we derive a nonlinear Schr{\"o}dinger (NLS) equation which
governs the evolution of electrostatic WEs. It is shown that the coefficients
of the NLS equation, including the nonlocal nonlinear term, which appears due
to the resonant particles having group velocity of the WEs, are significantly
modified by the particle dispersion. The effects of the quantum parameter $H$
(the ratio of the plasmon energy to the thermal energy densities), associated
with the particle dispersion, are examined on the Landau damping rate of
carrier waves, as well as on the modulational instability of WEs. It is found
that the Landau damping rate and the decay rate of the solitary wave amplitude
are greatly reduced compared to their classical values $(H=0)$.
|
1604.08751v4
|
2016-05-02
|
Three types of nonlinear resonances
|
We analyse different types of nonlinear resonances in a weakly damped Duffing
oscillator using bifurcation theory techniques. In addition to (i) odd
subharmonic resonances found on the primary branch of symmetric periodic
solutions with the forcing frequency and (ii) even subharmonic resonances due
to symmetry-broken periodic solutions that bifurcate off the primary branch and
also oscillate at the forcing frequency, we uncover (iii) novel resonance type
due to isolas of periodic solutions that are not connected to the primary
branch. These occur between odd and even resonances, oscillate at a fraction of
the forcing frequency, and give rise to a complicated resonance `curve' with
disconnected elements and high degree of multistability. We use bifurcation
continuation to compute resonance tongues in the plane of the forcing frequency
vs. the forcing amplitude for different but fixed values of the damping rate.
In this way, we demonstrate that identified here isolated resonances explain
the intriguing structure of "patchy tongues" observed for week damping and link
it to a seemingly unrelated phenomenon of "bifurcation superstructure"
described for moderate damping.
|
1605.00858v2
|
2016-07-21
|
The Noisy Oscillator : Random Mass and Random Damping
|
The problem of a linear damped noisy oscillator is treated in the presence of
two multiplicative sources of noise which imply a random mass and random
damping. The additive noise and the noise in the damping are responsible for an
influx of energy to the oscillator and its dissipation to the surrounding
environment. A random mass implies that the surrounding molecules not only
collide with the oscillator but may also adhere to it, thereby changing its
mass. We present general formulas for the first two moments and address the
question of mean and energetic stabilities. The phenomenon of stochastic
resonance, i.e. the expansion due to the noise of a system response to an
external periodic signal, is considered for separate and joint action of two
sources of noise and their characteristics.
|
1607.06289v2
|
2016-08-09
|
Optomechanical damping of a nanomembrane inside an optical ring cavity
|
We experimentally and theoretically investigate mechanical nanooscillators
coupled to the light in an optical ring resonator made of dielectric mirrors.
We identify an optomechanical damping mechanism that is fundamentally different
to the well known cooling in standing wave cavities. While, in a standing wave
cavity the mechanical oscillation shifts the resonance frequency of the cavity
in a ring resonator the frequency does not change. Instead the position of the
nodes is shifted with the mechanical excursion. We derive the damping rates and
test the results experimentally with a silicon-nitride nanomembrane. It turns
out that scattering from small imperfections of the dielectric mirror coatings
has to be taken into account to explain the value of the measured damping rate.
We extend our theoretical model and regard a second reflector in the cavity
that captures the effects of mirror back scattering. This model can be used to
also describe the situation of two membranes that both interact with the cavity
fields. This may be interesting for future work on synchronization of distant
oscillators that are coupled by intracavity light fields.
|
1608.02799v1
|
2016-08-11
|
Decay of geodesic acoustic modes due to the combined action of phase mixing and Landau damping
|
Geodesic acoustic modes (GAMs) are oscillations of the electric field whose
importance in tokamak plasmas is due to their role in the regulation of
turbulence. The linear collisionless damping of GAMs is investigated here by
means of analytical theory and numerical simulations with the global
gyrokinetic particle-in-cell code ORB5. The combined effect of the phase mixing
and Landau damping is found to quickly redistribute the GAM energy in
phase-space, due to the synergy of the finite orbit width of the passing ions
and the cascade in wave number given by the phase mixing. When plasma
parameters characteristic of realistic tokamak profiles are considered, the GAM
decay time is found to be an order of magnitude lower than the decay due to the
Landau damping alone, and in some cases of the same order of magnitude of the
characteristic GAM drive time due to the nonlinear interaction with an ITG
mode. In particular, the radial mode structure evolution in time is
investigated here and reproduced quantitatively by means of a dedicated initial
value code and diagnostics.
|
1608.03447v1
|
2016-09-06
|
JRSP of three-particle state via three tripartite GHZ class in quantum noisy channels
|
We present a scheme for joint remote state preparation (JRSP) of
three-particle state via three tripartite Greenberger-Horne-Zeilinger (GHZ)
entangled states as the quantum channel linking the parties. We use eight-qubit
mutually orthogonal basis vector as measurement point of departure. The
likelihood of success for this scheme has been found to be $1/8$. However, by
putting some special cases into consideration, the chances can be ameliorated
to $1/4$ and $1$. The effects of amplitude-damping noise, phase-damping noise
and depolarizing noise on this scheme have been scrutinized and the analytical
derivations of fidelities for the quantum noisy channels have been presented.
We found that for $0.55\leq\eta\leq1$, the states conveyed through depolarizing
channel lose more information than phase-damping channel while the information
loss through amplitude damping channel is most minimal.
|
1609.01538v3
|
2016-09-22
|
Damping of nonlinear standing kink oscillations: a numerical study
|
We aim to study the standing fundamental kink mode of coronal loops in the
nonlinear regime, investigating the changes in energy evolution in the
cross-section and oscillation amplitude of the loop which are related to
nonlinear effects, in particular to the development of the Kelvin-Helmholtz
instability (KHI). We run idea, high-resolution three-dimensional (3D)
magnetohydrodynamics (MHD) simulations, studying the influence of the initial
velocity amplitude and the inhomogeneous layer thickness. We model the coronal
loop as a straight, homogeneous magnetic flux tube with an outer inhomogeneous
layer, embedded in a straight, homogeneous magnetic field. We find that, for
low amplitudes which do not allow for the KHI to develop during the simulated
time, the damping time agrees with the theory of resonant absorption. However,
for higher amplitudes, the presence of KHI around the oscillating loop can
alter the loop's evolution, resulting in a significantly faster damping than
predicted by the linear theory in some cases. This questions the accuracy of
seismological methods applied to observed damping profiles, based on linear
theory.
|
1609.06883v1
|
2016-09-28
|
Nonlinear damping and dephasing in nanomechanical systems
|
We present a microscopic theory of nonlinear damping and dephasing of
low-frequency eigenmodes in nano- and micro-mechanical systems. The mechanism
of the both effects is scattering of thermally excited vibrational modes off
the considered eigenmode. The scattering is accompanied by energy transfer of
$2\hbar\omega_0$ for nonlinear damping and is quasieleastic for dephasing. We
develop a formalism that allows studying both spatially uniform systems and
systems with a strong nonuniformity, which is smooth on the typical wavelength
of thermal modes but not their mean free path. The formalism accounts for the
decay of thermal modes, which plays a major role in the nonlinear damping and
dephasing. We identify the nonlinear analogs of the Landau-Rumer,
thermoelastic, and Akhiezer mechanisms and find the dependence of the
relaxation parameters on the temperature and the geometry of a system.
|
1609.08714v1
|
2016-09-24
|
Parametric Landau damping of space charge modes
|
Landau damping is the mechanism of plasma and beam stabilization; it arises
through energy transfer from collective modes to the incoherent motion of
resonant particles. Normally this resonance requires the resonant particle's
frequency to match the collective mode frequency. We have identified an
important new damping mechanism, {\it parametric Landau damping}, which is
driven by the modulation of the mode-particle interaction. This reveals new
possibilities for stability control through manipulation of both particle and
mode-particle coupling spectra. We demonstrate the existence of parametric
Landau damping in a simulation of transverse coherent modes of bunched
accelerator beams with space charge.
|
1609.09393v3
|
2016-12-13
|
Continuous-variable entanglement generated with a hybrid PT-symmetric system
|
We study a proposal of generating macroscopic continuous-variable
entanglement with two coupled waveguides respectively carrying optical damping
and optical gain. Moreover, a squeezing element is added into one or both
waveguides. We show that quantum noise effect existing in the process is
essential to the degree of the generated entanglement. It will totally
eliminate the entanglement in the setup of adding the squeezing element into
the waveguide filled with optical damping material, but will not completely
damp the entanglement to zero in the other configurations of having the
squeezing element in the gain medium or in both gain and damping medium. The
degree of the generated continuous-variable entanglement is irrelevant to the
intensities of the input light in coherent states. Moreover, the relations
between the entanglement and system parameters are illustrated in terms of the
dynamical evolutions of the created continuous-variable entanglement.
|
1612.03996v2
|
2017-01-08
|
Decentralized Robust Control for Damping Inter-area Oscillations in Power Systems
|
As power systems become more and more interconnected, the inter-area
oscillations has become a serious factor limiting large power transfer among
different areas. Underdamped (Undamped) inter-area oscillations may cause
system breakup and even lead to large-scale blackout. Traditional damping
controllers include Power System Stabilizer (PSS) and Flexible AC Transmission
System (FACTS) controller, which adds additional damping to the inter-area
oscillation modes by affecting the real power in an indirect manner. However,
the effectiveness of these controllers is restricted to the neighborhood of a
prescribed set of operating conditions. In this paper, decentralized robust
controllers are developed to improve the damping ratios of the inter-area
oscillation modes by directly affecting the real power through the turbine
governing system. The proposed control strategy requires only local signals and
is robust to the variations in operation condition and system topology. The
effectiveness of the proposed robust controllers is illustrated by detailed
case studies on two different test systems.
|
1701.02036v1
|
2017-01-18
|
Ion beam test results of the Plastic Scintillator Detector of DAMPE
|
The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). DAMPE can detect electrons, photons and ions in a
wide energy range (5 GeV to 10 TeV) and ions up to iron (100GeV to 100 TeV).
Plastic Scintillator Detector (PSD) is one of the four payloads in DAMPE,
providing e/{\gamma} separation and charge identification up to Iron. An ion
beam test was carried out for the Qualification Model of PSD in CERN with
40GeV/u Argon primary beams. The Birk's saturation and charge resolution of PSD
were investigated.
|
1701.04947v2
|
2017-01-18
|
DAMPE space mission: first data
|
The DAMPE (DArk Matter Particle Explorer) satellite was launched on December
17, 2015 and started its data taking operation a few days later.
DAMPE has a large geometric factor ($\sim~0.3\ m^2\ sr$) and provides good
tracking, calorimetric and charge measurements for electrons, gammas rays and
nuclei. This will allow precise measurement of cosmic ray spectra from tens of
$GeV$ up to about $100\ TeV$. In particular, the energy region between $1-100\
TeV$ will be explored with higher precision compared to previous experiments.
The various subdetectors allow an efficient identification of the electron
signal over the large (mainly proton-induced) background. As a result, the
all-electron spectrum will be measured with excellent resolution from few $GeV$
up to few $TeV$, thus giving the opportunity to identify possible contribution
of nearby sources. A report on the mission goals and status is presented,
together with the on-orbit detector performance and the first data coming from
space.
|
1701.05046v1
|
2017-01-25
|
Control Allocation for Wide Area Coordinated Damping
|
In this work, a modal-based sparse control allocation (CA) is proposed for
coordinated and fault-tolerant wide-area damping controllers (WADCs). In our
proposed method, the supervisory CA only communicates with necessary actuators
to achieve the required damping performance and in case of actuator failures
(e.g., due to loss of communication or scheduling), capabilities of the
remaining actuators are fully used before the nominal performance is degraded.
This method offers the advantages of modular design where WADC is initially
designed to achieve satisfactory damping without the detailed knowledge of
actuators. In the next step, CA is designed to manage actuator failures and
limitations without the need to redesign the nominal WADC. The proposed
approach is applied to a modified $286$-bus Western Electricity Coordinating
Council (WECC) system to verify the feasibility on a complex power system.
Simulation results indicate the effectiveness of the proposed method in
coordinating multiple actuators and building resiliency.
|
1701.07456v1
|
2017-03-22
|
Direct Measurement of Kramers Turnover with a Levitated Nanoparticle
|
Understanding the thermally activated escape from a metastable state is at
the heart of important phenomena such as the folding dynamics of proteins, the
kinetics of chemical reactions or the stability of mechanical systems. In 1940
Kramers calculated escape rates both in the high damping and the low damping
regime and suggested that the rate must have a maximum for intermediate
damping. This phenomenon, today known as the Kramers turnover, has triggered
important theoretical and numerical studies. However, to date there is no
direct and quantitative experimental verification of this turnover. Using a
nanoparticle trapped in a bi-stable optical potential we experimentally measure
the nanoparticle's transition rates for variable damping and directly resolve
the Kramers turnover. Our measurements are in agreement with an analytical
model that is free of adjustable parameters.
|
1703.07699v2
|
2017-04-03
|
Suppression of plasma echoes and Landau damping in Sobolev spaces by weak collisions in a Vlasov-Fokker-Planck equation
|
In this paper, we study Landau damping in the weakly collisional limit of a
Vlasov-Fokker-Planck equation with nonlinear collisions in the phase-space
$(x,v) \in \mathbb T_x^n \times \mathbb R^n_v$. The goal is four-fold: (A) to
understand how collisions suppress plasma echoes and enable Landau damping in
agreement with linearized theory in Sobolev spaces, (B) to understand how phase
mixing accelerates collisional relaxation, (C) to understand better how the
plasma returns to global equilibrium during Landau damping, and (D) to rule out
that collision-driven nonlinear instabilities dominate. We give an estimate for
the scaling law between Knudsen number and the maximal size of the perturbation
necessary for linear theory to be accurate in Sobolev regularity. We conjecture
this scaling to be sharp (up to logarithmic corrections) due to potential
nonlinear echoes in the collisionless model.
|
1704.00425v2
|
2017-04-14
|
Impulse-Based Hybrid Motion Control
|
The impulse-based discrete feedback control has been proposed in previous
work for the second-order motion systems with damping uncertainties. The
sate-dependent discrete impulse action takes place at zero crossing of one of
both states, either relative position or velocity. In this paper, the proposed
control method is extended to a general hybrid motion control form. We are
using the paradigm of hybrid system modeling while explicitly specifying the
state trajectories each time the continuous system state hits the guards that
triggers impulsive control actions. The conditions for a stable convergence to
zero equilibrium are derived in relation to the control parameters, while
requiring only the upper bound of damping uncertainties to be known. Numerical
examples are shown for an underdamped closed-loop dynamics with oscillating
transients, an upper bounded time-varying positive system damping, and system
with an additional Coulomb friction damping.
|
1704.04372v5
|
2017-04-19
|
Reliable channel-adapted error correction: Bacon-Shor code recovery from amplitude damping
|
We construct two simple error correction schemes adapted to amplitude damping
noise for Bacon-Shor codes and investigate their prospects for fault-tolerant
implementation. Both consist solely of Clifford gates and require far fewer
qubits, relative to the standard method, to achieve correction to a desired
order in the damping rate. The first, employing one-bit teleportation and
single-qubit measurements, needs only one fourth as many physical qubits, while
the second, using just stabilizer measurements and Pauli corrections, needs
only half. We show that existing fault-tolerance methods can be employed for
the latter, while the former can be made to avoid potential catastrophic errors
and can easily cope with damping faults in ancilla qubits.
|
1704.05857v1
|
2017-04-30
|
Comparison of dynamic mechanical properties of non-superheated and superheated A357 alloys
|
The influence of superheat treatment on the microstructure and dynamic
mechanical properties of A357 alloys has been investigated. The study of
microstructure was performed by the optical microscope. Dynamic mechanical
properties (storage modulus, loss modulus, and damping capacity) were measured
by the dynamic mechanical analyzer (DMA). Microstructure showed coarser and
angular eutectic Si particles with larger {\alpha}-Al dendrites in the
non-superheated A357 alloy. In contrast, finer and rounded eutectic Si
particles together with smaller and preferred oriented {\alpha}-Al dendrites
have been observed in the superheated A357 alloy. Dynamic mechanical properties
showed an increasing trend of loss modulus and damping capacity meanwhile a
decreasing trend of storage modulus at elevated temperatures for superheated
and non-superheated A357 alloys. The high damping capacity of superheated A357
has been ascribed to the grain boundary damping at elevated temperatures.
|
1705.00350v1
|
2017-05-19
|
Improving two - qubit state teleportation affected by amplitude damping noise based on choosing appropriate quantum channel
|
We consider two qubit teleportation via quantum channel affected by amplitude
damping noise. Addressing the same problem, X. Hu, Y. Gu, Q. Gong and G. Guo
[Phys. Rev. A 81, 054302, (2010)] recently showed that in presence of noise,
subjecting more qubits in quantum channel to amplitude damping can increase the
fidelity of teleportation protocol. However, in this paper, by making some
adjustments on quantum channel, we obtain teleportation fidelity which is even
higher than one in the case of X. Hu et al. Moreover, our strategy is simpler
than quantum distillation and compared to using weak measurement, it is
deterministic. Furthermore, explicit analysis of fidelity is provided, we show
that in general, choosing appropriate quantum channel enhances the ability of
teleportation better and negates the fact that more amplitude damping noise
more quality.
|
1705.07064v2
|
2017-05-27
|
Charge reconstruction study of the DAMPE Silicon-Tungsten Tracker with ion beams
|
The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). DAMPE can detect electrons, photons in a wide energy
range (5 GeV to 10 TeV) and ions up to iron (100GeV to 100 TeV).
Silicon-Tungsten Tracker (STK) is one of the four subdetectors in DAMPE,
providing photon-electron conversion, track reconstruction and charge
identification for ions. Ion beam test was carried out in CERN with 60GeV/u
Lead primary beams. Charge reconstruction and charge resolution of STK
detectors were investigated.
|
1705.09791v1
|
2017-06-09
|
Effect of oxygen plasma on nanomechanical silicon nitride resonators
|
Precise control of tensile stress and intrinsic damping is crucial for the
optimal design of nanomechanical systems for sensor applications and quantum
optomechanics in particular. In this letter we study the in uence of oxygen
plasma on the tensile stress and intrinsic damping of nanomechanical silicon
nitride resonators. Oxygen plasma treatments are common steps in micro and
nanofabrication. We show that oxygen plasma of only a few minutes oxidizes the
silicon nitride surface, creating several nanometer thick silicon dioxide
layers with a compressive stress of 1.30(16)GPa. Such oxide layers can cause a
reduction of the e ective tensile stress of a 50 nm thick stoichiometric
silicon nitride membrane by almost 50%. Additionally, intrinsic damping
linearly increases with the silicon dioxide lm thickness. An oxide layer of
1.5nm grown in just 10s in a 50W oxygen plasma almost doubled the intrinsic
damping. The oxide surface layer can be e ciently removed in bu ered HF.
|
1706.02957v1
|
2017-06-11
|
Absorbing boundary layers for spin wave micromagnetics
|
Micromagnetic simulations are used to investigate the effects of different
absorbing boundary layers (ABLs) on spin waves (SWs) reflected from the edges
of a magnetic nano-structure. We define the conditions that a suitable ABL must
fulfill and compare the performance of abrupt, linear, polynomial and tan
hyperbolic damping profiles in the ABL. We first consider normal incidence in a
permalloy stripe and propose a transmission line model to quantify reflections
and calculate the loss introduced into the stripe due to the ABL. We find that
a parabolic damping profile absorbs the SW energy efficiently and has a low
reflection coefficient, thus performing much better than the commonly used
abrupt damping profile. We then investigated SWs that are obliquely incident at
26.6, 45 and 63.4 degrees on the edge of a yttrium-iron-garnet film. The
parabolic damping profile again performs efficiently by showing a high SW
energy transfer to the ABL and a low reflected SW amplitude.
|
1706.03325v1
|
2017-07-03
|
Quantum behaviour of pumped and damped triangular Bose Hubbard systems
|
We propose and analyse analogs of optical cavities for atoms using three-well
Bose-Hubbard models with pumping and losses. We consider triangular
configurations. With one well pumped and one damped, we find that both the
mean-field dynamics and the quantum statistics show a quantitative dependence
on the choice of damped well. The systems we analyse remain far from
equilibrium, preserving good coherence between the wells in the steady-state.
We find quadrature squeezing and mode entanglement for some parameter regimes
and demonstrate that the trimer with pumping and damping at the same well is
the stronger option for producing non-classical states. Due to recent
experimental advances, it should be possible to demonstrate the effects we
investigate and predict.
|
1707.01000v1
|
2017-07-06
|
Damping optimization of parameter dependent mechanical systems by rational interpolation
|
We consider an optimization problem related to semi-active damping of
vibrating systems. The main problem is to determine the best damping matrix
able to minimize influence of the input on the output of the system. We use a
minimization criteria based on the $\mathcal{H}_2$ system norm.
The objective function is non-convex and the associated optimization problem
typically requires a large number of objective function evaluations. We propose
an optimization approach that calculates `interpolatory' reduced order models,
allowing for significant acceleration of the optimization process.
In our approach, we use parametric model reduction (PMOR) based on the
Iterative Rational Krylov Algorithm, which ensures good approximations relative
to the $\mathcal{H}_2$ system norm, aligning well with the underlying damping
design objectives. For the parameter sampling that occurs within each PMOR
cycle, we consider approaches with predetermined sampling and approaches using
adaptive sampling, and each of these approaches may be combined with three
possible strategies for internal reduction. In order to preserve important
system properties, we maintain second-order structure, which through the use of
modal coordinates, allows for very efficient implementation.
The methodology proposed here provides a significant acceleration of the
optimization process; the gain in efficiency is illustrated in numerical
experiments.
|
1707.01789v1
|
2017-07-08
|
Nonlinear dynamics of damped DNA systems with long-range interactions
|
We investigate the nonlinear dynamics of a damped Peyrard-Bishop DNA model
taking into account long-range interactions with distance dependence |l|^-s on
the elastic coupling constant between different DNA base pairs. Considering
both Stokes and long-range hydrodynamical damping forces, we use the discrete
difference operator technique and show in the short wavelength modes that the
lattice equation can be governed by the complex Ginzburg-Landau equation. We
found analytically that the technique leads to the correct expression for the
breather soliton parameters. We found that the viscosity makes the amplitude of
the breather to damp out. We compare the approximate analytic results with
numerical simulations for the value s = 3 (dipole-dipole interactions).
|
1707.02425v1
|
2017-08-05
|
Dynamic Sensitivity Study of MEMS Capacitive Acceleration Transducer Based on Analytical Squeeze Film Damping and Mechanical Thermoelasticity Approaches
|
The dynamic behavior of a capacitive micro-electro-mechanical (MEMS)
accelerometer is evaluated by using a theoretical approach which makes use of a
squeeze film damping (SFD) model and ideal gas approach. The study investigates
the performance of the device as a function of the temperature, from 228 K to
398 K, and pressure, from 20 to 1000 Pa, observing the damping gas trapped
inside de mechanical transducer. Thermoelastic properties of the silicon bulk
are considered for the entire range of temperature. The damping gases
considered are Air, Helium and Argon. The global behavior of the system is
evaluated considering the electro-mechanical sensitivity (SEM) as the main
figure of merit in frequency domain. The results show the behavior of the main
mechanism losses of SFD, as well as the dynamic sensitivity of the MEMS
transducer system, and are in good agreement with experimental dynamic results
behavior.
|
1708.01812v1
|
2017-09-01
|
Scaling of the Rashba spin-orbit torque in magnetic domain walls
|
Spin-orbit torque in magnetic domain walls was investigated by solving the
Pauli-Schr\"{o}dinger equation for the itinerant electrons. The Rashba
interaction considered is derived from the violation of inversion symmetry at
interfaces between ferromagnets and heavy metals. In equilibrium, the Rashba
spin-orbit interaction gives rise to a torque corresponding to the
Dzyaloshinskii-Moriya interaction. When there is a current flowing, the
spin-orbit torque experienced by the itinerant electrons in short domain walls
has both field-like and damping-like components. However, when the domain wall
width is increased, the damping-like component, which is the counterpart of the
non-adiabatic spin transfer torque, decreases rapidly at the domain wall
center. In contrast to the non-adiabatic spin transfer torque, the damping-like
spin-orbit torque does not approach to zero far away from the domain wall
center, even in the adiabatic limit. The scattering of spin-up and spin-down
wave functions, which is caused by the Rashba spin-orbit interaction and the
spatial variation of magnetization profile in the domain wall, gives rise to
the finite damping-like spin-orbit torque.
|
1709.00187v3
|
2017-09-12
|
Temperature effects on MIPs in the BGO calorimeters of DAMPE
|
In this paper, we presented a study of temperature effects on BGO
calorimeters using proton MIP's collected in the first year operation of DAMPE.
By directly comparing MIP calibration constants used by DAMPE data production
pipe line, we found an experimental relation between temperature and signal
amplitudes of each BGO bar: a general deviation of -1.162%/$^{\circ}$C,and
-0.47%/$^{\circ}$C to -1.60%/$^{\circ}$C statistically for each detector
element. During 2016, DAMPE's temperature changed by about 7 degrees due to
solar elevation angle and the corresponding energy scale bias is about 8%. By
frequent MIP calibration operation, this kind of bias is eliminated to an
acceptable value.
|
1709.03735v2
|
2017-09-28
|
Universal and approximate relations for the gravitational-wave damping timescale of $f$-modes in neutron stars
|
Existing estimates of the gravitational-wave damping timescale of the
dominant quadrupole oscillation mode in the case of rapidly rotating stars are
based on using a Newtonian estimate for the energy of the mode, in combination
with the lowest-order post-Newtonian quadrupole formula for estimating the
gravitational-wave luminosity. We investigate a number of other choices for
estimating the gravitational-wave damping timescale in the nonrotating limit
and construct a highly accurate, empirically corrected formula that has a
maximum relative error of only 3% with respect to the perturbative result in
full general relativity. The expressions involved are sufficiently general to
be extended to the case of rapidly rotating stars. We also present a new
higher-order empirical relation for the gravitational-wave damping timescale of
quadrupole oscillations that is accurate in the whole range of expected values
for the compactness of neutron stars, without the need for involving the moment
of inertia.
|
1709.10067v2
|
2017-10-09
|
Time-dependent propagation speed vs strong damping for degenerate linear hyperbolic equations
|
We consider a degenerate abstract wave equation with a time-dependent
propagation speed. We investigate the influence of a strong dissipation, namely
a friction term that depends on a power of the elastic operator.
We discover a threshold effect. If the propagation speed is regular enough,
then the damping prevails, and therefore the initial value problem is
well-posed in Sobolev spaces. Solutions also exhibit a regularizing effect
analogous to parabolic problems. As expected, the stronger is the damping, the
lower is the required regularity.
On the contrary, if the propagation speed is not regular enough, there are
examples where the damping is ineffective, and the dissipative equation behaves
as the non-dissipative one.
|
1710.03602v1
|
2017-10-17
|
Entropic uncertainty relation under quantum channels with memory
|
Recently, Xu et al. [Phys. Rev. A 86, 012113(2012)] explored the behavior of
the entropic uncertainty relation under the influence of local unital and
nonunital noisy channels for a class of Bell-diagonal states. We here reform
their results and investigate the entropic uncertainty relation under the
influence of unital and nonunital noisy channels with memory. Different types
of noisy channels with memory, such as amplitude damping channel(nonunitary),
phase-damping and depolarizing channels(unitary) have been taken into account.
Some analytical or numerical results are presented. The effect of channels with
memory on dynamics of the entropic uncertainties (or their lower bounds) has
been discussed in detail. Compare with previous results, our results show that,
the entropic uncertainties (or their lower bounds) subjecting to amplitude
damping channel with memory will be reduced at first and then be lifted with
the memory coefficient of channel $\mu$ increasing, however they will be only
reduced under phase-damping and depolarizing channels with memory. Especially,
in the limit of $\mu\rightarrow1$, the entropic uncertainties (or their lower
bounds) could be well protected and immune to decoherence of channle. Moreover,
the mechanism behind these phenomena are also explored by using the purity of
state.
|
1710.06344v1
|
2017-10-31
|
Improving mechanical sensor performance through larger damping
|
Mechanical resonances are used in a wide variety of devices; from smart phone
accelerometers to computer clocks and from wireless communication filters to
atomic force microscope sensors. Frequency stability, a critical performance
metric, is generally assumed to be tantamount to resonance quality factor (the
inverse of the linewidth and of the damping). Here we show that frequency
stability of resonant nanomechanical sensors can generally be made independent
of quality factor. At high bandwidths, we show that quality factor reduction is
completely mitigated by increases in signal to noise ratio. At low bandwidths,
strikingly, increased damping leads to better stability and sensor resolution,
with improvement proportional to damping. We confirm the findings by
demonstrating temperature resolution of 50 \mu K at 200 Hz bandwidth. These
results open the door for high performance ultrasensitive resonant sensors in
gaseous or liquid environments, single cell nanocalorimetry, nanoscale gas
chromatography, and atmospheric pressure nanoscale mass spectrometry.
|
1710.11280v1
|
2017-11-30
|
The electron-flavored Z'-portal dark matter and the DAMPE cosmic ray excess
|
The DAMPE experiment has recently reported strong indications for the
existence of an excess of high-energy electrons and positrons. If interpreted
in terms of the annihilation of dark matter, the DAMPE result restricts the
dark matter mass and possible annihilation channels to a few case. In this
paper we explain the DAMPE result with the electron-flavored $Z^\prime$-portal
fermionic dark matter. We show that the Dirac dark matter scenario is promising
to explain the excess via the process $\bar \chi \chi \to\mathbf{Z}'\to \bar e
e$. The reduced annihilation cross section is limited in a range of
$10^{-26}\sim 10^{-24}~{\rm cm^3 s^{-1}}$ to interpret the excess.
|
1711.11182v2
|
2017-12-04
|
DAMPE Electron-Positron Excess in Leptophilic $Z'$ model
|
Recently the DArk Matter Particle Explorer (DAMPE) has reported an excess in
the electron-positron flux of the cosmic rays which is interpreted as a dark
matter particle with the mass about $1.5$ TeV. We come up with a leptophilic
$Z'$ scenario including a Dirac fermion dark matter candidate which beside
explaining the observed DAMPE excess, is able to pass various
experimental/observational constraints including the relic density value from
the WMAP/Planck, the invisible Higgs decay bound at the LHC, the LEP bounds in
electron-positron scattering, the muon anomalous magnetic moment constraint,
Fermi-LAT data, and finally the direct detection experiment limits from the
XENON1t/LUX. By computing the electron-positron flux produced from a dark
matter with the mass about $1.5$ TeV we show that the model predicts the peak
observed by the DAMPE.
|
1712.01239v4
|
2017-12-06
|
Confronting the DAMPE Excess with the Scotogenic Type-II Seesaw Model
|
The DArk Matter Particle Explorer (DAMPE) has observed a tentative peak at
$E\sim1.4~\TeV$ in the cosmic-ray electron spectrum. In this paper, we
interpret this excess in the scotogenic type-II seesaw model. This model
extends the canonical type-II seesaw model with dark matter (DM) candidates and
a loop-induced vacuum expectation value of the triplet scalars, $v_\Delta$,
resulting in small neutrino masses naturally even for TeV scale triplet
scalars. Assuming a nearby DM subhalo, the DAMPE excess can be explained by DM
annihilating into a pair of triplet scalars which subsequently decay to charged
lepton final states. Spectrum fitting of the DAMPE excess indicates it
potentially favors the inverted neutrino mass hierarchy. We also discuss how to
evade associated neutrino flux in our model.
|
1712.02021v3
|
2018-02-28
|
Beliaev Damping in Spin-$\frac{1}{2}$ Interacting Bosons with Spin-Orbit Coupling
|
Beliaev damping provides one of the most important mechanisms for dissipation
of quasiparticles through beyond-mean-field effects at zero temperature. Here
we present the first analytical result of Beliaev damping in low-energy
excitations of spin-$\frac{1}{2}$ interacting bosons with equal Rashba and
Dresslhaus spin-orbit couplings. We identify novel features of Beliaev decay
rate due to spin-orbit coupling, in particular, it shows explicit dependence on
the spin-density interaction and diverges at the interaction-modified phase
boundary between the zero-momentum and plane-wave phases. This represents a
manifestation of the effect of spin-orbit coupling in the beyond-mean-field
regime, which by breaking Galilean invariance couples excitations in the
density- and spin-channels. By describing the Beliaev damping in terms of the
observable dynamic structure factors, our results allow direct experimental
access within current facilities.
|
1802.10295v1
|
2018-03-03
|
Universal stabilization of single-qubit states using a tunable coupler
|
We theoretically analyze a scheme for fast stabilization of arbitrary qubit
states with high fidelities, extending a protocol recently demonstrated
experimentally [Lu et al., Phys. Rev. Lett. 119, 150502 (2017)]. That
experiment utilized red and blue sideband transitions in a system composed of a
fluxonium qubit, a low-Q LC-oscillator, and a coupler enabling us to tune the
interaction between them. Under parametric modulations of the coupling
strength, the qubit can be steered into any desired pure or mixed single-qubit
state. For realistic circuit parameters, we predict that stabilization can be
achieved within 100 ns. By varying the ratio between the oscillator's damping
rate and the effective qubit-oscillator coupling strength, we can switch
between under-damped, critically-damped, and over-damped stabilization and find
optimal working points. We further analyze the effect of thermal fluctuations
and show that the stabilization scheme remains robust for realistic
temperatures.
|
1803.01079v3
|
2018-04-15
|
Reevaluation of radiation reaction and consequences for light-matter interactions at the nanoscale
|
In the context of electromagnetism and nonlinear optical interactions damping
is generally introduced as a phenomenological, viscous term that dissipates
energy, proportional to the temporal derivative of the polarization. Here, we
follow the radiation reaction method presented in [G. W. Ford and R. F.
O'Connell, Phys. Lett. A, 157, 217 (1991)], which applies to non-relativistic
electrons of finite size, to introduce an explicit reaction force in the
Newtonian equation of motion, and derive a hydrodynamic equation that offers
new insight on the influence of damping in generic plasmas, metal-based and/or
dielectric structures. In these settings, we find new damping-dependent linear
and nonlinear source terms that suggest the damping coefficient is proportional
to the local charge density, and nonlocal contributions that stem from the
spatial derivative of the magnetic field and discuss the conditions that could
modify both linear and nonlinear electromagnetic responses.
|
1804.05369v1
|
2018-04-30
|
Wave-like blow-up for semilinear wave equations with scattering damping and negative mass term
|
In this paper we establish blow-up results and lifespan estimates for
semilinear wave equations with scattering damping and negative mass term for
subcritical power, which is the same as that of the corresponding problem
without mass term, and also the same as that of the corresponding problem
without both damping and mass term. For this purpose, we have to use the
comparison argument twice, due to the damping and mass term, in additional to a
key multiplier. Finally, we get the desired results by an iteration argument.
|
1804.11073v3
|
2018-05-22
|
Uniqueness of the Cauchy datum for the tempered-in-time response and conductivity operator of a plasma
|
We study the linear Vlasov equation with a given electric field $E \in
\mathcal{S}$, where $\mathcal{S}$ is the space of Schwartz functions. The
associated damped partial differential equation has a unique tempered solution,
which fixes the needed Cauchy datum. This tempered solution then converges to
the causal solution of the linear Vlasov equation when the damping parameter
goes to zero. This result allows us to define the plasma conductivity operator
$\sigma$, which gives the current density $j = \sigma (E)$ induced by the
electric field $E$. We prove that $\sigma$ is continuous from $\mathcal{S}$ to
its dual $\mathcal{S}^\prime$. We can treat rigorously the case of uniform
non-magnetized non-relativistic plasma (linear Landau damping) and the case of
uniform magnetized relativistic plasma (cyclotron damping). In both cases, we
demonstrate that the main part of the conductivity operator is a
pseudo-differential operator and we give its expression rigorously. This
matches the formal results widely used in the theoretical physics community.
|
1805.08733v3
|
2018-05-26
|
Stabilization for the wave equation with singular Kelvin-Voigt damping
|
We consider the wave equation with Kelvin-Voigt damping in a bounded domain.
The exponential stability result proposed by Liu and Rao or T\'ebou for that
system assumes that the damping is localized in a neighborhood of the whole or
a part of the boundary under some consideration. In this paper we propose to
deal with this geometrical condition by considering a singular Kelvin-Voigt
damping which is localized faraway from the boundary. In this particular case
it was proved by Liu and Liu the lack of the uniform decay of the energy.
However, we show that the energy of the wave equation decreases logarithmically
to zero as time goes to infinity. Our method is based on the frequency domain
method. The main feature of our contribution is to write the resolvent problem
as a transmission system to which we apply a specific Carleman estimate.
|
1805.10430v1
|
2018-06-01
|
Fluctuation-damping of isolated, oscillating Bose-Einstein condensates
|
Experiments on the nonequilibrium dynamics of an isolated Bose-Einstein
condensate (BEC) in a magnetic double-well trap exhibit a puzzling divergence:
While some show dissipation-free Josephson oscillations, others find strong
damping. Such damping in isolated BECs cannot be understood on the level of the
coherent Gross-Pitaevskii dynamics. Using the Keldysh functional-integral
formalism, we describe the time-dependent system dynamics by means of a
multi-mode BEC coupled to fluctuations (single-particle excitations) beyond the
Gross-Pitaevskii saddle point. We find that the Josephson oscillations excite
an excess of fluctuations when the effective Josephson frequency,
$\tilde{\omega}_J$, is in resonance with the effective fluctuation energy,
$\tilde{\varepsilon}_m$, where both, $\tilde{\omega}_J$ and
$\tilde{\varepsilon}_m$, are strongly renormalized with respect to their
noninteracting values. Evaluating and using the model parameters for the
respective experiments describes quantitatively the presence or absence of
damping.
|
1806.00376v2
|
2018-06-05
|
Decoherence assisted spin squeezing generation in superposition of tripartite GHZ and W states
|
In the present paper, we study spin squeezing under decoherence in the
superposition of tripartite maximally entangled GHZ and W states. Here we use
amplitude damping, phase damping and depolarisation channel. We have
investigated the dynamics of spin squeezing with the interplay of superposition
and decoherence parameters with different directions of the mean spin vector.
We have found the mixture of GHZ and W states is robust against spin squeezing
generation for amplitude damping and phase damping channels for certain
directions of the mean spin vector. However, the depolarisation channel
performs well for spin squeezing generation and generates permanent spin
squeezing in the superposition of GHZ and W states.
|
1806.01730v1
|
2018-07-31
|
Dark Matter Particle Explorer observations of high-energy cosmic ray electrons plus positrons and their physical implications
|
The DArk Matter Particle Explorer (DAMPE) is a satellite-borne, high-energy
particle and $\gamma$-ray detector, which is dedicated to indirectly detecting
particle dark matter and studying high-energy astrophysics. The first results
about precise measurement of the cosmic ray electron plus positron spectrum
between 25 GeV and 4.6 TeV were published recently. The DAMPE spectrum reveals
an interesting spectral softening around $0.9$ TeV and a tentative peak around
$1.4$ TeV. These results have inspired extensive discussion. The detector of
DAMPE, the data analysis, and the first results are introduced. In particular,
the physical interpretations of the DAMPE data are reviewed.
|
1807.11638v1
|
2018-08-08
|
A Hybrid Dynamic-regenerative Damping Scheme for Energy Regeneration in Variable Impedance Actuators
|
Increasing research efforts have been made to improve the energy efficiency
of variable impedance actuators (VIAs) through reduction of energy consumption.
However, the harvesting of dissipated energy in such systems remains
underexplored. This study proposes a novel variable damping module design
enabling energy regeneration in VIAs by exploiting the regenerative braking
effect of DC motors. The proposed damping module uses four switches to combine
regenerative and dynamic braking, in a hybrid approach that enables energy
regeneration without reduction in the range of damping achievable. Numerical
simulations and a physical experiment are presented in which the proposed
module shows an optimal trade-off between task performance and energy
efficiency.
|
1808.03143v1
|
2018-08-15
|
$L^1$ estimates for oscillating integrals and their applications to semi-linear models with $σ$-evolution like structural damping
|
The present paper is a continuation of our recent paper \cite{DaoReissig}. We
will consider the following Cauchy problems for semi-linear structurally damped
$\sigma$-evolution models: \begin{equation*} u_{tt}+ (-\Delta)^\sigma u+ \mu
(-\Delta)^\delta u_t = f(u,u_t),\, u(0,x)= u_0(x),\, u_t(0,x)=u_1(x)
\end{equation*} with $\sigma \ge 1$, $\mu>0$ and $\delta \in
(\frac{\sigma}{2},\sigma]$. Our aim is to study two main models including
$\sigma$-evolution models with structural damping $\delta \in
(\frac{\sigma}{2},\sigma)$ and those with visco-elastic damping
$\delta=\sigma$. Here the function $f(u,u_t)$ stands for power nonlinearities
$|u|^{p}$ and $|u_t|^{p}$ with a given number $p>1$. We are interested in
investigating the global (in time) existence of small data solutions to the
above semi-linear models from suitable spaces basing on $L^q$ space by assuming
additional $L^{m}$ regularity on the initial data, with $q\in (1,\infty)$ and
$m\in [1,q)$.
|
1808.05484v2
|
2018-09-26
|
Permutation-invariant constant-excitation quantum codes for amplitude damping
|
The increasing interest in using quantum error correcting codes in practical
devices has heightened the need for designing quantum error correcting codes
that can correct against specialized errors, such as that of amplitude damping
errors which model photon loss. Although considerable research has been devoted
to quantum error correcting codes for amplitude damping, not so much attention
has been paid to having these codes simultaneously lie within the decoherence
free subspace of their underlying physical system. One common physical system
comprises of quantum harmonic oscillators, and constant-excitation quantum
codes can be naturally stabilized within them. The purpose of this paper is to
give constant-excitation quantum codes that not only correct amplitude damping
errors, but are also immune against permutations of their underlying modes. To
construct such quantum codes, we use the nullspace of a specially constructed
matrix based on integer partitions.
|
1809.09801v4
|
2018-09-30
|
Critical behavior of the damping rate of GHz acoustic phonons in SrTiO3 at the antiferrodistortive phase transition measured by time- and frequency-resolved Brillouin scattering
|
We determine the temperature dependent damping rate of longitudinal acoustic
phonons in SrTiO3 using frequency domain Brillouin scattering and time domain
Brillouin scattering. We investigate samples with (La,Sr)MnO3 and SrRuO3
capping layers, which result in compressive or tensile strain at the layer -
substrate interface, respectively. The different strain states lead to dif-
ferent domain structures in SrTiO3 that extend into the bulk of the SrTiO3
substrates and strongly affect the phonon propagation. Our experiments show
that the damping rate of acoustic phonons in the interfacial STO layer depends
strongly on the sample temperature and strain induced do- main structure. We
also show that the damping rate as function of temperature exhibits a critical
behavior close to the cubic-to-tetragonal phase transition of SrTiO3.
|
1810.00381v1
|
2018-12-04
|
Atmospheric oscillations provide simultaneous measurement of neutron star mass and radius
|
Neutron stars with near-Eddington observable luminosities were shown to
harbor levitating atmospheres, suspended above their surface. We report a new
method to simultaneously measure the mass and radius of a neutron star based on
oscillations of such atmospheres. In this paper, we present an analytic
derivation of a family of relativistic, oscillatory, spherically symmetric
eigenmodes of the optically and geometrically thin levitating atmospheres,
including the damping effects induced by the radiation drag. We discover
characteristic maxima in the frequencies of the damped oscillations and show
that using the frequency maxima, one can estimate mass and radius of the
neutron star, given the observed frequency and the corresponding luminosity of
the star during the X-ray burst. Thus, our model provides a new way to probe
the stellar parameters. We also show that the ratio of any two undamped
eigenfrequencies depends only on the adiabatic index of the atmosphere, while
for the damped eigenfrequencies, this ratio varies with the luminosity. The
damping coefficient is independent of the mode number of the oscillations.
Signatures of these atmospheres' dynamics will be reflected in the source's
X-ray light curves.
|
1812.01299v2
|
2018-12-04
|
Spin transport in a magnetic insulator with zero effective damping
|
Applications based on spin currents strongly profit from the control and
reduction of their effective damping and their transport properties. We here
experimentally observe magnon mediated transport of spin (angular) momentum
through a 13.4 nm thin yttrium iron garnet film with full control of the
magnetic damping via spin-orbit torque. Above a critical spin-orbit torque, the
fully compensated damping manifests itself as an increase of magnon
conductivity by almost two orders of magnitude. We compare our results to
theoretical expectations based on recently predicted current induced magnon
condensates and discuss other possible origins of the observed critical
behaviour.
|
1812.01334v3
|
2019-01-10
|
Data-Driven Online Optimization for Enhancing Power System Oscillation Damping
|
This paper reports an initial work on power system oscillation damping
improvement using a data-driven online optimization method. An online
oscillation damping optimization mod-el is proposed and formulated in a form
solvable by the data-driven method. Key issues in the online optimization
procedures, including the damping sensitivity identification method, its
compatibility with the dispatch plans, as well as other practical issues in
real large-scale system are discussed. Simulation results based on the 2-area
4-machine system, and the NETS-NYPS 68-bus system verify the feasibility and
efficiency of the proposed method. The results also show the capability of the
proposed method to bridge the gap between online data analysis and complex
optimization for power system dynamics.
|
1901.03167v2
|
2019-01-13
|
Nonexistence of global solutions for a weakly coupled system of semilinear damped wave equations in the scattering case with mixed nonlinear terms
|
In this paper we consider the blow-up of solutions to a weakly coupled system
of semilinear damped wave equations in the scattering case with nonlinearities
of mixed type, namely, in one equation a power nonlinearity and in the other a
semilinear term of derivative type. The proof of the blow-up results is based
on an iteration argument. As expected, due to the assumptions on the
coefficients of the damping terms, we find as critical curve in the p-q plane
for the pair of exponents (p,q) in the nonlinear terms the same one found by
Hidano-Yokoyama and, recently, by Ikeda-Sobajima-Wakasa for the weakly coupled
system of semilinear wave equations with the same kind of nonlinearities. In
the critical and not-damped case we provide a different approach from the test
function method applied by Ikeda-Sobajima-Wakasa to prove the blow-up of the
solution on the critical curve, improving in some cases the upper bound
estimate for the lifespan. More precisely, we combine an iteration argument
with the so-called slicing method to show the blow-up dynamic of a weighted
version of the functionals used in the subcritical case.
|
1901.04038v1
|
2019-01-15
|
Continuum damping effects in nuclear collisions associated with twisted boundary conditions
|
The time-dependent Skyrme Hartree-Fock calculations have been performed to
study $^{24}$Mg +$^{24}$Mg collisions. The twisted boundary conditions, which
can avoid finite box-size effects of the employed 3D coordinate space, have
been implemented. The prolate deformed $^{24}$Mg has been set to different
orientations to study vibrations and rotations of the compound nucleus
$^{48}$Cr. Our time evolution results show continuum damping effects associated
with the twist-averaged boundary condition play a persistent role after the
fusion stage. In particular, a rotational damping in continuum is presented in
calculations of both twist-averaged and absorbing boundary conditions, in which
damping widths can be clearly extracted. It is unusual that the rotating
compound nucleus in continuum evolves towards spherical but still has a
considerable angular momentum.
|
1901.04736v2
|
2019-03-03
|
Spin wave damping in periodic and quasiperiodic magnonic structures
|
We investigated the lifetime of spin wave eigenmodes in periodic and
quasiperiodic sequences of Py and Co wires. Those materials differ
significantly in damping coefficients, therefore, the spatial distribution of
the mode amplitude within the structure is important for the lifetime of
collective spin wave excitations. Modes of the lower frequencies prefer to
concentrate in Py wires, because of the lower FMR frequency for this material.
This inhomogeneous distribution of amplitude of modes (with lower amplitude in
material of higher damping and with higher amplitude in material of lower
damping) is preferable for extending the lifetime of the collective excitations
beyond the volume average of lifetimes for solid materials. We established the
relation between the profile of the mode and its lifetime for periodic and
quasiperiodic structures. We performed also the comparative studies in order to
find the differences resulting from complexity of the structure and enhancement
of localization in quasiperiodic system on the lifetime of spin waves.
|
1903.00856v1
|
2019-03-07
|
Investigating optically-excited THz standing spin waves using noncollinear magnetic bilayers
|
We investigate optically excited THz standing spin waves in noncollinear
magnetic bilayers. Using femtosecond laser-pulse excitation, a spin current is
generated in the first ferromagnetic (FM) layer, and flows through a conductive
spacer layer to be injected into the second (transverse) FM layer, where it
exerts a spin-transfer torque on the magnetization and excites higher-order
standing spin waves. We show that the noncollinear magnetic bilayer is a
convenient tool that allows easy excitation of THz spin waves, and can be used
to investigate the dispersion and thereby the spin wave stiffness parameter in
the thin-film regime. This is experimentally demonstrated using wedge-shaped Co
and CoB (absorption) layers. Furthermore, the damping of these THz spin waves
is investigated, showing a strong increase of the damping with decreasing
absorption layer thickness, much stronger than expected from interface spin
pumping effects. Additionally, a previously unseen sudden decrease in the
damping for the thinnest films is observed. A model for the additional damping
contribution incorporating both these observations is proposed.
|
1903.02802v1
|
2019-03-14
|
An analog simulation experiment to study free oscillations of a damped simple pendulum
|
The characteristics of drive-free oscillations of a damped simple pendulum
under sinusoidal potential force field differ from those of the damped harmonic
oscillations. The frequency of oscillation of a large amplitude simple pendulum
decreases with increasing amplitude. Many prototype mechanical simple pendulum
have been fabricated with precision and studied earlier in view of introducing
them in undergraduate physics laboratories. However, fabrication and
maintenance of such mechanical pendulum require special skill. In this work, we
set up an analog electronic simulation experiment to serve the purpose of
studying the force-free oscillations of a damped simple pendulum. We present
the details of the setup and some typical results of our experiment. The
experiment is simple enough to implement in undergraduate physics laboratories.
|
1903.06162v1
|
2019-03-15
|
Frictional Damping in Biomimetic Scale Beam Oscillations
|
Stiff scales adorn the exterior surfaces of fishes, snakes, and many
reptiles. They provide protection from external piercing attacks and control
over global deformation behavior to aid locomotion, slithering, and swimming
across a wide range of environmental condition. In this letter, we investigate
the dynamic behavior of biomimetic scale substrates for further understanding
the origins of the nonlinearity that involve various aspect of scales
interaction, sliding kinematics, interfacial friction, and their combination.
Particularly, we study the vibrational characteristics through an analytical
model and numerical investigations for the case of a simply supported scale
covered beam. Our results reveal for the first time that biomimetic scale beams
exhibit viscous damping behavior even when only Coulomb friction is postulated
for free vibrations. We anticipate and quantify the anisotropy in the damping
behavior with respect to curvature. We also find that unlike static pure
bending where friction increases bending stiffness, a corresponding increase in
natural frequency for the dynamic case does not arise for simply supported
beam. Since both scale geometry, distribution and interfacial properties can be
easily tailored, our study indicates a biomimetic strategy to design
exceptional synthetic materials with tailorable damping behavior.
|
1903.06819v1
|
2019-04-08
|
Damping control in viscoelastic beam dynamics
|
Viscoelasticity plays a key role in many practical applications and in
different reasearch fields, such as in seals, sliding-rolling contacts and
crack propagation. In all these contexts, a proper knowledge of the
viscoelastic modulus is very important. However, the experimental
characterization of the frequency dependent modulus, carried out through
different standard procedures, still presents some complexities, then possible
alternative approaches are desirable. For example, the experimental
investigation of viscoelastic beam dynamics would be challenging, especially
for the intrinsic simplicity of this kind of test. This is why, a deep
understanding of damping mechanisms in viscoelastic beams results to be a quite
important task to better predict their dynamics. With the aim to enlighten
damping properties in such structures, an analytical study of the transversal
vibrations of a viscoelastic beam is presented in this paper. Some
dimensionless parameters are defined, depending on the material properties and
the beam geometry, which enable to shrewdly design the beam dynamics. In this
way, by properly tuning such disclosed parameters, for example the
dimensionless beam length or a chosen material, it is possible to enhance or
suppress some resonant peaks, one at a time or more simultaneously. This is a
remarkable possibility to efficiently control damping in these structures, and
the results presented in this paper may help in elucidating experimental
procedures for the characterization of viscoelastic materials.
|
1904.03875v1
|
2019-04-28
|
On the Kolmogorov dissipation law in a damped Navier-Stokes equation
|
We consider here the Navier-Stokes equations in $\mathbb{R}^{3}$ with a
stationary, divergence-free external force and with an additional damping term
that depends on two parameters. We first study the well-posedness of weak
solutions for these equations and then, for a particular set of the damping
parameters, we will obtain an upper and lower control for the energy
dissipation rate $\varepsilon$ according to the Kolmogorov K41 theory. However,
although the behavior of weak solutions corresponds to the K41 theory, we will
show that in some specific cases the damping term introduced in the
Navier-Stokes equations could annihilate the turbulence even though the Grashof
number (which are equivalent to the Reynolds number) are large.
|
1904.12382v1
|
2019-04-23
|
Entanglement sudden death and birth effects in two qubits maximally entangled mixed states under quantum channels
|
In the present article, the robustness of entanglement in two qubits
maximally entangled mixed states (MEME) have been studied under quantum
decoherence channels. Here we consider bit flip, phase flip, bit-phase-flip,
amplitude damping, phase damping and depolarization channels. To quantify the
entanglement, the concurrence has been used as an entanglement measure. During
this study interesting results have been found for sudden death and birth of
entanglement under bit flip and bit-phase-flip channels. While amplitude
damping channel produces entanglement sudden death and does not allow re-birth
of entanglement. On the other hand, two qubits MEMS exhibit the robust
character against the phase flip, phase damping and depolarization channels.
The elegant behavior of all the quantum channels have been investigated with
varying parameter of quantum state MEMS in different cases.
|
1904.12630v2
|
2019-05-23
|
Strauss exponent for semilinear wave equations with scattering space dependent damping
|
It is believed or conjectured that the semilinear wave equations with
scattering space dependent damping admit the Strauss critical exponent, see
Ikehata-Todorova-Yordanov \cite{ITY}(the bottom in page 2) and
Nishihara-Sobajima-Wakasugi \cite{N2}(conjecture iii in page 4). In this work,
we are devoted to showing the conjecture is true at least when the decay rate
of the space dependent variable coefficients before the damping is larger than
2. Also, if the nonlinear term depends only on the derivative of the solution,
we may prove the upper bound of the lifespan is the same as that of the
solution of the corresponding problem without damping. This shows in another
way the \lq\lq hyperbolicity" of the equation.
|
1905.09445v2
|
2019-05-24
|
Multicomponent Dark Matter in the Light of CALET and DAMPE
|
In the light of the latest measurements on the total $e^+ + e^-$ flux by
CALET and DAMPE experiments, we revisit the multicomponent leptonically
decaying dark matter (DM) explanations to the cosmic-ray electron/positron
excesses observed previously. Especially, we use the single and
double-component DM models to explore the compatibility of the AMS-02 positron
fraction with the new CALET or DAMPE data. It turns out that neither single nor
double-component DM models are able to fit the AMS-02 positron fraction and
DAMPE total $e^+ + e^-$ flux data simultaneously. On the other hand, for the
combined AMS-02 and CALET dataset, both the single and double-component DM
models can provide reasonable fits. If we further take into the diffuse
$\gamma$-ray constraints from Fermi-LAT, only the double-component DM models
are allowed.
|
1905.10136v3
|
2019-05-30
|
Quantum dynamical speedup in correlated noisy channels
|
The maximal evolution speed of a quantum system can be represented by quantum
speed limit time (QSLT).We investigate QSLT of a two-qubit system passing
through a correlated channel (amplitude damping, phase damping, and
depolarizing).By adjusting the correlation parameter of channel and the initial
entanglement,a method to accelerate the evolution speed of the system for some
specific channels is proposed.It is shown that, in amplitude damping channel
and depolarizing channel,QSLT may be shortened in some cases by increasing
correlation parameter of the channel and initial entanglement, which are in
sharp contrast to phase damping channel.In particular, under depolarizing
channels, the transition from no-speedup evolution to speedup evolution for the
system can be realized by changing correlation strength of the channel.
|
1905.12911v3
|
2019-07-01
|
Probing superfluid $^4\mathrm{He}$ with high-frequency nanomechanical resonators down to $\mathrm{mK}$ temperatures
|
Superfluids, such as superfluid $^3\mathrm{He}$ and $^4\mathrm{He}$, exhibit
a broad range of quantum phenomena and excitations which are unique to these
systems. Nanoscale mechanical resonators are sensitive and versatile force
detectors with the ability to operate over many orders of magnitude in damping.
Using nanomechanical-doubly clamped beams of extremely high quality factors
($Q>10^6$), we probe superfluid $^4\mathrm{He}$ from the superfluid transition
temperature down to $\mathrm{mK}$ temperatures at frequencies up to $11.6 \,
\mathrm{MHz}$. Our studies show that nanobeam damping is dominated by
hydrodynamic viscosity of the normal component of $^4\mathrm{He}$ above
$1\,\mathrm{K}$. In the temperature range $0.3-0.8\,\mathrm{K}$, the ballistic
quasiparticles (phonons and rotons) determine the beams' behavior. At lower
temperatures, damping saturates and is determined either by magnetomotive
losses or acoustic emission into helium. It is remarkable that all these
distinct regimes can be extracted with just a single device, despite damping
changing over six orders of magnitude.
|
1907.00970v1
|
2019-07-10
|
Determination of the damping co-efficient of electrons in optically transparent glasses at the true resonance frequency in the ultraviolet from an analysis of the Lorentz-Maxwell model of dispersion
|
The Lorentz-Maxwell model of dispersion of light has been analyzed in this
paper to determine the true resonance frequency in the ultraviolet for the
electrons in optically transparent glasses and the damping coefficient at this
frequency. For this we needed the refractive indices of glass in the optical
frequency range. We argue that the true resonance condition in the absorption
region prevails when the frequency at which the absorption coefficient is
maximum is the same as the frequency at which the average energy per cycle of
the electrons is also a maximum. We have simultaneously solved the two
equations obtained from the two maxima conditions numerically to arrive at a
unique solution for the true resonance frequency and the damping coefficient at
this frequency. Assuming the damping coefficient to be constant over a small
frequency range in the absorption region, we have determined the frequencies at
which the extinction coefficient and the reflectance are maxima. These
frequencies match very well with the published data for silica glasses
available from the literature.
|
1907.04499v1
|
2019-07-15
|
Asymptotic profiles of solutions for regularity-loss type generalized thermoelastic plate equations and their applications
|
In this paper, we consider generalized thermoelastic plate equations with
Fourier's law of heat conduction. By introducing a threshold for decay
properties of regularity-loss, we investigate decay estimates of solutions
with/without regularity-loss in a framework of weighted $L^1$ spaces.
Furthermore, asymptotic profiles of solutions are obtained by using
representations of solutions in the Fourier space, which are derived by
employing WKB analysis. Next, we study generalized thermoelastic plate
equations with additional structural damping, and analysis the influence of
structural damping on decay properties and asymptotic profiles of solutions. We
find that the regularity-loss structure is destroyed by structural damping.
Finally, we give some applications of our results on thermoelastic plate
equations and damped Moore-Gibson-Thompson equation.
|
1907.06344v1
|
2019-07-21
|
Critical Thresholds in One Dimensional Damped Euler-Poisson Systems
|
This paper is concerned with the critical threshold phenomenon for one
dimensional damped, pressureless Euler-Poisson equations with electric force
induced by a constant background, originally studied in [S. Engelberg and H.
Liu and E. Tadmor, Indiana Univ. Math. J., 50:109--157, 2001]. A simple
transformation is used to linearize the characteristic system of equations,
which allows us to study the geometrical structure of critical threshold curves
for three damping cases: overdamped, underdamped and borderline damped through
phase plane analysis. We also derive the explicit form of these critical
curves. These sharp results state that if the initial data is within the
threshold region, the solution will remain smooth for all time, otherwise it
will have a finite time breakdown. Finally, we apply these general results to
identify critical thresholds for a non-local system subjected to initial data
on the whole line.
|
1907.09039v1
|
2019-07-23
|
Ignatyuk damping factor: A semiclassical formula
|
Data on nuclear level densities extracted from transmission data or gamma
energy spectrum store the basic statistical information about nuclei at various
temperatures. Generally this extracted data goes through model fitting using
computer codes like CASCADE. However, recently established semiclassical
methods involving no adjustable parameters to determine the level density
parameter for magic and semi-magic nuclei give a good agreement with the
experimental values. One of the popular ways to paramaterize the level density
parameter which includes the shell effects and its damping was given by
Ignatyuk. This damping factor is usually fitted from the experimental data on
nuclear level density and it comes around 0.05 $MeV^{-1}$. In this work we
calculate the Ignatyuk damping factor for various nuclei using semiclassical
methods.
|
1907.09770v1
|
2019-08-13
|
Dynamics of Riemann waves with sharp measure-controlled damping
|
This paper is concerned with locally damped semilinear wave equations defined
on compact Riemannian manifolds with boundary. We present a construction of
measure-controlled damping regions which are sharp in the sense that their
summed interior and boundary measures are arbitrarily small. The construction
of this class of open sets is purely geometric and allows us to prove a new
observability inequality in terms of potential energy rather than the usual one
with kinetic energy. A unique continuation property is also proved. Then, in
three-dimension spaces, we establish the existence of finite dimensional smooth
global attractors for a class of wave equations with nonlinear damping and
forces with critical Sobolev growth. In addition, by means of an obstacle
control condition, we show that our class of measure-controlled regions
satisfies the well-known geometric control condition (GCC). Therefore, many of
known results for the stabilization of wave equations hold true in the present
context.
|
1908.04814v1
|
2019-08-15
|
Sharp polynomial decay rates for the damped wave equation with Hölder-like damping
|
We study decay rates for the energy of solutions of the damped wave equation
on the torus. We consider dampings invariant in one direction and bounded above
and below by multiples of $x^{\beta}$ near the boundary of the support and show
decay at rate $1/t^{\frac{\beta+2}{\beta+3}}$. In the case where $W$ vanishes
exactly like $x^{\beta}$ this result is optimal by work of the second author.
The proof uses a version of the Morawetz multiplier method.
|
1908.05631v3
|
2019-08-26
|
Revisiting the Coulomb-Damped Harmonic Oscillator
|
The force of dry friction is studied extensively in introductory physics but
its effect on oscillations is hardly ever mentioned. Instead, to provide a
mathematically tractable introduction to damping, virtually all authors adopt a
viscous resistive force. While exposure to linear damping is of paramount
importance to the student of physics, the omission of Coulomb damping might
have a negative impact on the way the students conceive of the subject. In the
paper, we propose to approximate the action of Coulomb friction on a harmonic
oscillator by a sinusoidal resistive force whose amplitude is the model's only
free parameter. We seek the value of this parameter that yields the best fit
and obtain a closed-form analytic solution, which is shown to nicely fit the
numerical one.
|
1908.10363v1
|
2019-09-21
|
Resonant absorption of kink oscillations in coronal flux tubes with continuous magnetic twist
|
There are observational evidences for the existence of twisted magnetic field
in the solar corona. Here, we have investigated resonant damping of the
magnetohydrodynamic (MHD) kink waves in magnetic flux tubes. A realistic model
of the tube with continuous magnetic twist and radially inhomogeneous density
profile has been considered. We have obtained the dispersion relation of the
kink wave using the solution to the linear MHD equations outside the density
inhomogeneity and the appropriate connection formula to the solutions across
the thin transitional boundary layer. The dependence of the oscillation
frequency and damping rate of the waves on the twist parameter and longitudinal
wavenumber has been investigated. For the flux tube parameters considered in
this paper, we obtain rapid damping of the kink waves comparable to the
observations. In order to justify this rapid damping, depending on the sign of
the azimuthal kink mode number, $m=+1$ or $m=-1$, the background magnetic field
must have left handed or right handed twisted profile, respectively. For the
model considered here, the resonant absorption occurs only when the twist
parameter is in a range specified by the density contrast.
|
1909.09787v1
|
2019-10-22
|
Controlled nonlinear magnetic damping in spin-Hall nano-devices
|
Large-amplitude magnetization dynamics is substantially more complex compared
to the low-amplitude linear regime, due to the inevitable emergence of
nonlinearities. One of the fundamental nonlinear phenomena is the nonlinear
damping enhancement, which imposes strict limitations on the operation and
efficiency of magnetic nanodevices. In particular, nonlinear damping prevents
excitation of coherent magnetization auto-oscillations driven by the injection
of spin current into spatially extended magnetic regions. Here, we propose and
experimentally demonstrate that nonlinear damping can be controlled by the
ellipticity of magnetization precession. By balancing different contributions
to anisotropy, we minimize the ellipticity and achieve coherent magnetization
oscillations driven by spatially extended spin current injection into a
microscopic magnetic disk. Our results provide a novel route for the
implementation of efficient active spintronic and magnonic devices driven by
spin current.
|
1910.09801v1
|
2019-10-24
|
The lifespan of solutions of semilinear wave equations with the scale-invariant damping in two space dimensions
|
In this paper, we study the initial value problem for semilinear wave
equations with the time-dependent and scale-invariant damping in two
dimensions. Similarly to the one dimensional case by Kato, Takamura and Wakasa
in 2019, we obtain the lifespan estimates of the solution for a special
constant in the damping term, which are classified by total integral of the sum
of the initial position and speed. The key fact is that, only in two space
dimensions, such a special constant in the damping term is a threshold between
"wave-like" domain and "heat-like" domain. As a result, we obtain a new type of
estimate especially for the critical exponent.
|
1910.11692v2
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.