publicationDate
stringlengths 1
2.79k
| title
stringlengths 1
36.5k
⌀ | abstract
stringlengths 1
37.3k
⌀ | id
stringlengths 9
47
|
|---|---|---|---|
2015-01-30
|
A large-scale magnetic shield with 10^6 damping at mHz frequencies
|
We present a magnetically shielded environment with a damping factor larger
than one million at the mHz frequency regime and an extremely low field and
gradient over an extended volume. This extraordinary shielding performance
represents an improvement of the state of the art in damping the difficult
regime of very low-frequency distortions by more than an order of magnitude.
This technology enables a new generation of high precision measurements in
fundamental physics and metrology, including searches for new physics far
beyond the reach of accelerator-based experiments. We discuss the technical
realization of the shield with its improvements in design.
|
1501.07861v4
|
2015-02-01
|
A Study on the Impact of Wind Generation on the Stability of Electromechanical Oscillations
|
Wind is becoming an increasingly significant source of energy in modern power
generation. Amongst existing technologies, Variable Speed Wind Turbines (VSWT)
equipped with Double Fed Induction Generators (DFIG) is widely deployed.
Consequently, power systems are now experiencing newer power flow patterns and
operating conditions. This paper investigates the impact of a DFIG based Wind
Farm (WF) on the stability of electromechanical oscillations. This is achieved
by performing modal analysis to evaluate the stability of a two-area power
network when subjected to different wind penetration levels and different
geographical installed locations. The approach via eigenvalues analysis
involves the design of voltage and Supplementary Damping Controllers (SDCs)
that contribute to network damping. The effect of Power System Stabilizer (PSS)
is also examined for several network conditions. Simulations demonstrate a
damping improvement up to 933% when the control systems are activated and the
system operates with 25% wind integration.
|
1502.00215v1
|
2015-02-16
|
Biomimetic Staggered Composites with Highly Enhanced Energy Dissipation: Design, Modeling, and Test
|
We investigate the damping enhancement in a class of biomimetic staggered
composites via a combination of design, modeling, and experiment. In total,
three kinds of staggered composites are designed by mimicking the structure of
bone and nacre. These composite designs are realized by 3D printing a rigid
plastic and a viscous elastomer simultaneously. Greatly-enhanced energy
dissipation in the designed composites is observed from both the experimental
results and theoretical prediction. The designed polymer composites have loss
modulus up to ~500 MPa, higher than most of the existing polymers. In addition,
their specific loss modulus (up to 0.43 $Km^2/s^2$) is among the highest of
damping materials. The damping enhancement is attributed to the large shear
deformation of the viscous soft matrix and the large strengthening effect from
the rigid inclusion phase.
|
1502.04568v1
|
2015-02-24
|
High Quality Yttrium Iron Garnet Grown by Room Temperature Pulsed Laser Deposition and Subsequent Annealing
|
We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG)
by annealing in oxygen atmosphere. Our findings show that well below the
melting temperature the material transforms into a fully epitaxial layer with
exceptional quality, both structural and magnetic.\\ In ferromagnetic resonance
(FMR) ultra low damping and extremely narrow linewidth can be observed. For a
56 nm thick layer a damping constant of
$\alpha$=(6.63$\pm$1.50)$\cdot$10$^{-5}$ is found and the linewidth at 9.6 GHz
is as small as 1.30$\pm$0.05 Oe which are the lowest values for PLD grown thin
films reported so far. Even for a 20 nm thick layer a damping constant of
$\alpha$=(7.51$\pm$1.40)$\cdot$10$^{-5}$ is found which is the lowest value for
ultrathin films published so far. The FMR linewidth in this case is
3.49$\pm$0.10 Oe at 9.6 GHz. Our results not only present a method of
depositing thin film YIG of unprecedented quality but also open up new options
for the fabrication of thin film complex oxides or even other crystalline
materials.
|
1502.06724v2
|
2015-03-02
|
DAMPE silicon tracker on-board data compression algorithm
|
The Dark Matter Particle Explorer (DAMPE) is an upcoming scientific satellite
mission for high energy gamma-ray, electron and cosmic rays detection. The
silicon tracker (STK) is a sub detector of the DAMPE payload with an excellent
position resolution (readout pitch of 242um), which measures the incident
direction of particles, as well as charge. The STK consists 12 layers of
Silicon Micro-strip Detector (SMD), equivalent to a total silicon area of
6.5m$^2$. The total readout channels of the STK are 73728, which leads to a
huge amount of raw data to be dealt. In this paper, we focus on the on-board
data compression algorithm and procedure in the STK, which was initially
verified by cosmic-ray measurements.
|
1503.00415v1
|
2015-03-08
|
MHD Seismology of a loop-like filament tube by observed kink waves
|
We report and analyze the observational evidence of global kink oscillations
in a solar filament as observed in H alpha by National Solar Observatory
(NSO)/Global Oscillation Network Group (GONG) instrument. An M1.1-class flare
in active region 11692 on 2013 March 15 induced a global kink mode in the
filament lying in the south-west of AR11692.We find periods of about 61 - 67
minutes and damping times of 92 - 117 minutes at three vertical slice positions
chosen in and around the filament apex. We find that the waves are damped. From
the observed global kink mode period and damping time scale using the theory of
resonant absorption we perform prominence seismology. We estimate a lower
cut-off value for the inhomogeneity length-scale to be around 0.34 - 0.44 times
the radius of the filament cross-section.
|
1503.02281v1
|
2015-03-13
|
Comparison of spin-orbit torques and spin pumping across NiFe/Pt and NiFe/Cu/Pt interfaces
|
We experimentally investigate spin-orbit torques and spin pumping in NiFe/Pt
bilayers with direct and interrupted interfaces. The damping-like and
field-like torques are simultaneously measured with spin-torque ferromagnetic
resonance tuned by a dc bias current, whereas spin pumping is measured
electrically through the inverse spin Hall effect using a microwave cavity.
Insertion of an atomically thin Cu dusting layer at the interface reduces the
damping-like torque, field-like torque, and spin pumping by nearly the same
factor of ~1.4. This finding confirms that the observed spin-orbit torques
predominantly arise from diffusive transport of spin current generated by the
spin Hall effect. We also find that spin-current scattering at the NiFe/Pt
interface contributes to additional enhancement in magnetization damping that
is distinct from spin pumping.
|
1503.04104v3
|
2015-03-24
|
Global weak solutions to compressible quantum Navier-Stokes equations with damping
|
The global-in-time existence of weak solutions to the barotropic compressible
quantum Navier-Stokes equations with damping is proved for large data in three
dimensional space. The model consists of the compressible Navier-Stokes
equations with degenerate viscosity, and a nonlinear third-order differential
operator, with the quantum Bohm potential, and the damping terms. The global
weak solutions to such system is shown by using the Faedo-Galerkin method and
the compactness argument. This system is also a very important approximated
system to the compressible Navier-Stokes equations. It will help us to prove
the existence of global weak solutions to the compressible Navier-Stokes
equations with degenerate viscosity in three dimensional space.
|
1503.06894v4
|
2015-03-30
|
Suppression of Spin Pumping Between Ni$_{80}$Fe$_{20}$ and Cu by a Graphene Interlayer
|
We compare ferromagnetic resonance measurements of Permalloy
Ni$_{80}$Fe$_{20}$ (Py) films sputtered onto Cu(111) films with and without a
graphene (Gr) interlayer grown by chemical vapor deposition before Py
deposition. A two-angle sputtering method ensured that neither Gr nor Py was
degraded by the sample preparation process. We find the expected damping
enhancement from spin pumping for the Py/Cu case and no detectable enhancement
for the Py/Gr/Cu case. Since damping is sensitive to effects other than spin
pumping, we used magnetometry to verify that differences in Py magnetostatic
properties are not responsible for the difference in damping. We attribute the
suppression of spin pumping in Py/Gr/Cu to the large contact resistance of the
Gr/Cu interface.
|
1503.08777v1
|
2015-04-02
|
Protecting the $\sqrt{SWAP}$ operation from general and residual errors by continuous dynamical decoupling
|
We study the occurrence of errors in a continuously decoupled two-qubit state
during a $\sqrt{SWAP}$ quantum operation under decoherence. We consider a
realization of this quantum gate based on the Heisenberg exchange interaction,
which alone suffices for achieving universal quantum computation. Furthermore,
we introduce a continuous-dynamical-decoupling scheme that commutes with the
Heisenberg Hamiltonian to protect it from the amplitude damping and dephasing
errors caused by the system-environment interaction. We consider two
error-protection settings. One protects the qubits from both amplitude damping
and dephasing errors. The other features the amplitude damping as a residual
error and protects the qubits from dephasing errors only. In both settings, we
investigate the interaction of qubits with common and independent environments
separately. We study how errors affect the entanglement and fidelity for
different environmental spectral densities.
|
1504.00592v1
|
2015-04-07
|
Damped Oscillating Dark Energy: Ideal Fluid and Scalar-Tensor description
|
In this paper, we study damped oscillating form of dark energy for explaining
dynamics of universe. First of all, we consider universe is filled with an
ideal fluid which has damped oscillating dark energy in terms of this case we
calculate several physical quantities such as Hubble parameter, acceleration
parameter, energy density, pressure and others for dark energy, dark
energy-matter coupling and non-coupling cases. Secondly, we consider as
universe is filled with scalar field instead of an ideal fluid we obtain these
physical quantities in terms of scalar potential and kinetic term for the same
cases in scalar-tensor formalism. Finally, we show that ideal fluid description
and scalar-tensor description of dark energy give mathematically equivalent
results for this EoS parameter, even if they haven't same physical meaning.
|
1504.01509v2
|
2015-04-09
|
Periodic-coefficient damping estimates, and stability of large-amplitude roll waves in inclined thin film flow
|
A technical obstruction preventing the conclusion of nonlinear stability of
large-Froude number roll waves of the St. Venant equations for inclined thin
film flow is the "slope condition" of Johnson-Noble-Zumbrun, used to obtain
pointwise symmetrizability of the linearized equations and thereby
high-frequency resolvent bounds and a crucial H s nonlinear damping estimate.
Numerically, this condition is seen to hold for Froude numbers 2 \textless{} F
3.5, but to fail for 3.5 F. As hydraulic engineering applications typically
involve Froude number 3 F 5, this issue is indeed relevant to practical
considerations. Here, we show that the pointwise slope condition can be
replaced by an averaged version which holds always, thereby completing the
nonlinear theory in the large-F case. The analysis has potentially larger
interest as an extension to the periodic case of a type of weighted
"Kawashima-type" damping estimate introduced in the asymptotically-constant
coefficient case for the study of stability of large-amplitude viscous shock
waves.
|
1504.02292v1
|
2015-04-17
|
Temperature-dependent Plasmons and Their Damping Rates for Graphene with a Finite Energy Bandgap
|
We obtained numerical and closed-form analytic expressions for
finite-temperature plasmon dispersion relations for intrinsic graphene in the
presence of a finite energy gap in the energy spectrum. The calculations were
carried out using the random-phase approximation. The analytic results have
been derived in the high temperature regime and long-wavelength limit. We have
found that the plasmon damping rate decreases in the presence of a band gap.
Our method of calculation could also be applied to silicene and other buckled
honeycomb lattice structures. The finite-temperature plasmon dispersion
relations are presented when a single graphene layer is Coulomb coupled to a
semi infinite conductor. Both cases of gapless and gapped monolayer graphene
have been investigated when a thick substrate is in their proximity. Both the
plasmon excitation frequency and damping rate are linear functions of the
in-plane wave vector in the long wavelength limit when a monolayer interacts
with a conducting substrate which is not the case for free-standing pristine or
gapped graphene.
|
1504.04552v1
|
2015-05-08
|
Existence and general stabilization of the Timoshenko system with a thermo-viscoelastic damping and a delay term in the internal feedback
|
In this paper, we consider a Timoshenko system with a thermo-viscoelastic
damping and a delay term in the internal feedback together with initial datum
and boundary conditions of Dirichlet type, where g is a positive non-increasing
relaxation function and {\mu}1, {\mu}2 are positive constants. Under an
hypothesis between the weight of the delay term in the feedback and the the
weight of the friction damping term, using the Faedo-Galerkin approximations
together with some energy estimates, we prove the global existence of the
solutions. Then, by introducing appropriate Lyapunov functionals, under the
imposed constrain on the weights of the two feedbacks and the coefficients, we
establish the general energy decay result from which the exponential and
polynomial types of decay are only special cases.
|
1505.01899v1
|
2015-05-09
|
Existence, general decay and blow-up of solutions for a viscoelastic Kirchhoff equation with Balakrishnan-Taylor damping and dynamic boundary conditions
|
Our aim in this article is to study a nonlinear viscoelastic Kirchhoff
equation with strong damping, Balakrishnan-Taylor damping, nonlinear source and
dynamical boundary condition. Firstly, we prove the local existence of
solutions by using the Faedo-Galerkin approximation method combined with a
contraction mapping theorem. We then prove that if the initial data enter into
the stable set, the solution globally exists, and if the initial data enter
into the unstable set, the solution blows up in a finite time. Moreover, we
obtain a general decay result of the energy, from which the usual exponential
and polynomial decay rates are only special cases.
|
1505.02220v3
|
2015-06-03
|
Migration of two massive planets into (and out of) first order mean motion resonances
|
We consider the dynamical evolution of two planets orbiting in the vicinity
of a first order mean motion reso- nance while simultaneously undergoing
eccentricity damping and convergent migration. Following Goldreich &
Schlichting (2014), we include a coupling between the dissipative semimajor
axis evolution and the damping of the eccentricities. In agreement with past
studies, we find that this coupling can lead to overstability of the resonance
and that for a certain range of parameters capture into resonance is only
temporary. Using a more general model, we show that whether overstable motion
can occur depends in a characteristic way on the mass ratio between the two
planets as well as their relative eccentricity damping timescales. Moreover, we
show that even when escape from resonance does occur, the timescale for escape
is long enough such at any given time a pair of planets is more likely to be
found in a resonance rather than migrating between them. Thus, we argue that
overstability of resonances cannot singlehandedly reconcile convergent
migration with the observed lack of Kepler planet pairs found near resonances.
However, it is possible that overstable motion in combination with other
effects such as large scale orbital instability could produce the observed
period ratio distribution.
|
1506.01382v1
|
2015-06-12
|
Linear inviscid damping for monotone shear flows in a finite periodic channel, boundary effects, blow-up and critical Sobolev regularity
|
In a previous article, \cite{Zill3}, we have established linear inviscid
damping for a large class of monotone shear flows in a finite periodic channel
and have further shown that boundary effects asymptotically lead to the
formation of singularities of derivatives of the solution. As the main results
of this article, we provide a detailed description of the singularity formation
and establish stability in all sub-critical fractional Sobolev spaces and
blow-up in all super-critical spaces. Furthermore, we discuss the implications
of the blow-up to the problem of nonlinear inviscid damping in a finite
periodic channel, where high regularity would be essential to control nonlinear
effects.
|
1506.04010v1
|
2015-06-12
|
Nonlinear damped partial differential equations and their uniform discretizations
|
We establish sharp energy decay rates for a large class of nonlinearly
first-order damped systems, and we design discretization schemes that inherit
of the same energy decay rates, uniformly with respect to the space and/or time
discretization parameters, by adding appropriate numerical viscosity terms. Our
main arguments use the optimal-weight convexity method and uniform
observability inequalities with respect to the discretization parameters. We
establish our results, first in the continuous setting, then for space
semi-discrete models, and then for time semi-discrete models. The full
discretization is inferred from the previous results. Our results cover, for
instance, the Schr\"odinger equation with nonlinear damping, the nonlinear wave
equation, the nonlinear plate equation, as well as certain classes of equations
with nonlocal terms.
|
1506.04163v2
|
2015-06-17
|
Landau Damping of Electrostatic Waves in Arbitrarily Degenerate Quantum Plasmas
|
We carry out a systematic study of the dispersion relation for linear
electrostatic waves in an arbitrarily degenerate quantum electron plasma. We
solve for the complex frequency spectrum for arbitrary values of wavenumber $k$
and level of degeneracy $\mu$. Our finding is that for large $k$ and high $\mu$
the real part of the frequency $\omega_{r}$ grows linearly with $k$ and scales
with $\mu$ only because of the scaling of the Fermi energy. In this regime the
relative Landau damping rate $\gamma/\omega_{r}$ becomes independent of $k$ and
varies inversly with $\mu$. Thus, damping is weak but finite at moderate levels
of degeneracy for short wavelengths.
|
1506.05494v2
|
2015-06-25
|
Simultaneous Interconnection and Damping Assignment Passivity-based Control of Mechanical Systems Using Generalized Forces
|
To extend the realm of application of the well known controller design
technique of interconnection and damping assignment passivity-based control
(IDA-PBC) of mechanical systems two modifications to the standard method are
presented in this article. First, similarly to [1], it is proposed to avoid the
splitting of the control action into energy-shaping and damping injection
terms, but instead to carry them out simultaneously. Second, motivated by [2],
we propose to consider the inclusion of generalised forces, going beyond the
gyroscopic ones used in standard IDA-PBC. It is shown that several new
controllers for mechanical systems designed invoking other (less systematic
procedures) that do not satisfy the conditions of standard IDA-PBC, actually
belong to this new class of SIDA-PBC.
|
1506.07679v1
|
2015-07-20
|
Bifurcation of the quasinormal spectrum and Zero Damped Modes for rotating dilatonic black holes
|
It has been recently found that for the near extremal Kerr black holes
appearing of Zero Damped Modes (accompanied by qusinormal mode branching)
signifies about inapplicability of the regime of small perturbations and the
onset of turbulence. Here we show that this phenomena is not limited by Kerr or
Kerr-Newman solutions only, but also takes place for rotating dilatonic black
holes for which we have found Zero Damped Modes both numerically and
analytically. We have also shown that, contrary to recent claims, there is no
instability of a charged massive scalar field in the background of the rotating
dilatonic black hole under physically adequate boundary conditions. Analytic
expression for dominant quasinormal frequencies is deduced in the regime of
large coupling qQ, where q and Q are the field and black hole charges
respectively.
|
1507.05649v1
|
2015-07-24
|
Effect of Landau damping on alternative ion-acoustic solitary waves in a magnetized plasma consisting of warm adiabatic ions and non-thermal electrons
|
Bandyopadhyay and Das [Phys. Plasmas, 9, 465-473, 2002] have derived a
nonlinear macroscopic evolution equation for ion acoustic wave in a magnetized
plasma consisting of warm adiabatic ions and non-thermal electrons including
the effect of Landau damping. In that paper they have also derived the
corresponding nonlinear evolution equation when coefficient of the nonlinear
term of the above mentioned macroscopic evolution equation vanishes, the
nonlinear behaviour of the ion acoustic wave is described by a modified
macroscopic evolution equation. But they have not considered the case when the
coefficient is very near to zero. This is the case we consider in this paper
and we derive the corresponding evolution equation including the effect of
Landau damping. Finally, a solitary wave solution of this macroscopic evolution
is obtained, whose amplitude is found to decay slowly with time.
|
1507.06733v1
|
2015-08-05
|
Quantum discord protection from amplitude damping decoherence
|
Entanglement is known to be an essential resource for many quantum
information processes. However, it is now known that some quantum features may
be acheived with quantum discord, a generalized measure of quantum correlation.
In this paper, we study how quantum discord, or more specifically, the measures
of entropic discord and geometric discord are affected by the influence of
amplitude damping decoherence. We also show that a protocol deploying weak
measurement and quantum measurement reversal can effectively protect quantum
discord from amplitude damping decoherence, enabling to distribute quantum
correlation between two remote parties in a noisy environment.
|
1508.00972v1
|
2015-09-03
|
Stability analysis of degenerately-damped oscillations
|
Presented here is a study of well-posedness and asymptotic stability of a
"degenerately damped" PDE modeling a vibrating elastic string. The coefficient
of the damping may vanish at small amplitudes thus weakening the effect of the
dissipation. It is shown that the resulting dynamical system has strictly
monotonically decreasing energy and uniformly decaying lower-order norms,
however, is not uniformly stable on the associated finite-energy space. These
theoretical findings were motivated by numerical simulations of this model
using a finite element scheme and successive approximations. A description of
the numerical approach and sample plots of energy decay are supplied. In
addition, for certain initial data the solution can be determined in closed
form up to a dissipative nonlinear ordinary differential equation. Such
solutions can be used to assess the accuracy of the numerical examples.
|
1509.00917v1
|
2015-09-27
|
On the well-posedness and asymptotic behavior of the generalized KdV-Burgers equation
|
In this paper we are concerned with the well-posedness and the exponential
stabilization of the generalized Korteweg-de Vries Burgers equation, posed on
the whole real line, under the effect of a damping term. Both problems are
investigated when the exponent p in the nonlinear term ranges over the interval
$[1,5)$. We first prove the global well-posedness in $H^s(R)$, for $0 \leq s
\leq 3$ and $1 \leq p < 2$, and in $H^3(R)$, when $p \geq 2$. For $2 \leq p <
5$, we prove the existence of global solutions in the $L^2$-setting. Then, by
using multiplier techniques combined with interpolation theory, the exponential
stabilization is obtained for a indefinite damping term and $1 \leq p < 2$.
Under the effect of a localized damping term the result is obtained when $2
\leq p < 5$. Combining multiplier techniques and compactness arguments it is
shown that the problem of exponential decay is reduced to prove the unique
continuation property of weak solutions
|
1509.08148v1
|
2015-10-11
|
Error estimates of finite element method for semi-linear stochastic strongly damped wave equation
|
In this paper, we consider a semi-linear stochastic strongly damped wave
equation driven by additive Gaussian noise. Following a semigroup framework, we
establish existence, uniqueness and space-time regularity of a mild solution to
such equation. Unlike the usual stochastic wave equation without damping, the
underlying problem with space-time white noise (Q = I) allows for a mild
solution with a positive order of regularity in multiple spatial dimensions.
Further, we analyze a spatio-temporal discretization of the problem, performed
by a standard finite element method in space and a well-known linear implicit
Euler scheme in time. The analysis of the approximation error forces us to
significantly enrich existing error estimates of semidiscrete and fully
discrete finite element methods for the corresponding linear deterministic
equation. The main results show optimal convergence rates in the sense that the
orders of convergence in space and in time coincide with the orders of the
spatial and temporal regularity of the mild solution, respectively. Numerical
examples are finally included to confirm our theoretical findings.
|
1510.03028v1
|
2015-11-10
|
A study of energy correction for the electron beam data in the BGO ECAL of the DAMPE
|
The DArk Matter Particle Explorer (DAMPE) is an orbital experiment aiming at
searching for dark matter indirectly by measuring the spectra of photons,
electrons and positrons originating from deep space. The BGO electromagnetic
calorimeter is one of the key sub-detectors of the DAMPE, which is designed for
high energy measurement with a large dynamic range from 5 GeV to 10 TeV. In
this paper, some methods for energy correction are discussed and tried, in
order to reconstruct the primary energy of the incident electrons. Different
methods are chosen for the appropriate energy ranges. The results of Geant4
simulation and beam test data (at CERN) are presented.
|
1511.02998v1
|
2015-11-10
|
Quantum Fisher and Skew information for Unruh accelerated Dirac qubit
|
We develop a Bloch vector representation of Unruh channel for a Dirac field
mode. This is used to provide a unified, analytical treatment of quantum Fisher
and Skew information for a qubit subjected to the Unruh channel, both in its
pure form as well as in the presence of experimentally relevant external noise
channels. The time evolution of Fisher and Skew information is studied along
with the impact of external environment parameters such as temperature and
squeezing. The external noises are modelled by both purely dephasing phase
damping as well as the squeezed generalized amplitude damping channels. An
interesting interplay between the external reservoir temperature and squeezing
on the Fisher and Skew information is observed, in particular, for the action
of the squeezed generalized amplitude damping channel. It is seen that for some
regimes, squeezing can enhance the quantum information against the
deteriorating influence of the ambient environment. Similar features are also
observed for the analogous study of Skew information, highlighting the similar
origin of the Fisher and Skew information.
|
1511.03029v1
|
2015-11-23
|
Detection of high frequency oscillations and damping from multi-slit spectroscopic observations of the corona
|
During the total solar eclipse of 11 July 2010, multi-slit spectroscopic
observations of the solar corona were performed from Easter Island, Chile. To
search for high-frequency waves, observations were taken at a high cadence in
the green line at 5303 A due to [Fe xiv] and the red line at 6374 A due to [Fe
x]. The data are analyzed to study the periodic variations in the intensity,
Doppler velocity and line width using wavelet analysis. The data with high
spectral and temporal resolution enabled us to study the rapid dynamical
changes within coronal structures. We find that at certain locations each
parameter shows significant oscillation with periods ranging from 6 - 25 s. For
the first time, we could detect damping of high-frequency oscillations with
periods of the order of 10 s. If the observed damped oscillations are due to
magnetohydrodynamic (MHD) waves then they can contribute significantly in the
heating of the corona. From a statistical study we try to characterize the
nature of the observed oscillations while looking at the distribution of power
in different line parameters.
|
1511.07160v1
|
2015-11-26
|
Uniform exponential stability of Galerkin approximations for damped wave systems
|
We consider the numerical approximation of linear damped wave systems by
Galerkin approximations in space and appropriate time-stepping schemes. Based
on a dissipation estimate for a modified energy, we prove exponential decay of
the physical energy on the continuous level provided that the damping is
effective everywhere in the domain. The methods of proof allow us to analyze
also a class of Galerkin approximations based on a mixed variational
formulation of the problem. Uniform exponential stability can be guaranteed for
these approximations under a general compatibility condition on the
discretization spaces. As a particular example, we discuss the discretization
by mixed finite element methods for which we obtain convergence and uniform
error estimates under minimal regularity assumptions. We also prove
unconditional and uniform exponential stability for the time discretization by
certain one-step methods. The validity of the theoretical results as well as
the necessity of some of the conditions required for our analysis are
demonstrated in numerical tests.
|
1511.08341v1
|
2015-12-01
|
Epitaxial patterning of nanometer-thick Y3Fe5O12 films with low magnetic damping
|
Magnetic insulators such as yttrium iron garnet, Y3Fe5O12, with extremely low
magnetic damping have opened the door for low power spin-orbitronics due to
their low energy dissipation and efficient spin current generation and
transmission. We demonstrate reliable and efficient epitaxial growth and
nanopatterning of Y3Fe5O12 thin-film based nanostructures on insulating
Gd3Ga5O12 substrates. In particular, our fabrication process is compatible with
conventional sputtering and liftoff, and does not require aggressive ion
milling which may be detrimental to the oxide thin films. Structural and
magnetic properties indicate good qualities, in particular low magnetic damping
of both films and patterned structures. The dynamic magnetic properties of the
nanostructures are systematically investigated as a function of the lateral
dimension. By comparing to ferromagnetic nanowire structures, a distinct edge
mode in addition to the main mode is identified by both experiments and
simulations, which also exhbits cross-over with the main mode upon varying the
width of the wires. The non-linear evolution of dynamic modes over
nanostructural dimensions highlights the important role of size confinement to
their material properties in magnetic devices where Y3Fe5O12 nanostructures
serve as the key functional component.
|
1512.00286v1
|
2015-12-03
|
Probing Bogoliubov quasiparticles in superfluid $^3$He with a 'vibrating-wire like' MEMS device
|
We have measured the interaction between superfluid $^3$He-B and a
micro-machined goalpost-shaped device at temperatures below $0.2\,T_c$. The
measured damping follows well the theory developed for vibrating wires, in
which the Andreev reflection of quasiparticles in the flow field around the
moving structure leads to a nonlinear frictional force. At low velocities the
damping force is proportional to velocity while it tends to saturate for larger
excitations. Above a velocity of 2.6$\,$mms$^{-1}$ the damping abruptly
increases, which is interpreted in terms of Cooper-pair breaking.
Interestingly, this critical velocity is significantly lower than reported with
other mechanical probes immersed in superfluid $^3$He. Furthermore, we report
on a nonlinear resonance shape for large motion amplitudes that we interpret as
an inertial effect due to quasiparticle friction, but other mechanisms could
possibly be invoked as well.
|
1512.01033v1
|
2016-01-03
|
Event-triggered Communication in Wide-area Damping Control: A Limited Output Feedback Based Approach
|
A conceptual design methodology is proposed for event-triggered based power
system wide area damping controller. The event-triggering mechanism is adopted
to reduce the communication burden between origin of the remote signal and the
wide area damping controller (WADC) location. The remote signal is transmitted
to the WADC only when an event-triggering condition based on a predefined
system output, is satisfied. The triggering condition is derived from a
stability criterion, and is monitored continuously by a separate
event-monitoring unit located at the origin of the remote signal. The stability
of the resulting closed loop system is guaranteed via the input-to-state
stability (ISS) technique. The proposed event triggered WADC (ET-WADC) is
implemented on two typical test power systems - two area four machine and IEEE
39 bus 10 machine. The validation of proposed mechanism is carried out through
non-linear simulation studies on MATLAB/Simulink platform. The numerical
results show the efficacy of the controller in managing the communication
channel usage without compromising the stated system stability objectives.
|
1601.00255v1
|
2016-01-05
|
Lie transformation method on quantum state evolution of a general time-dependent driven and damped parametric oscillator
|
A variety of dynamics in nature and society can be approximately treated as a
driven and damped parametric oscillator. An intensive investigation of this
time-dependent model from an algebraic point of view provides a consistent
method to resolve the classical dynamics and the quantum evolution in order to
understand the time-dependent phenomena that occur not only in the macroscopic
classical scale for the synchronized behaviors but also in the microscopic
quantum scale for a coherent state evolution. By using a Floquet
U-transformation on a general time-dependent quadratic Hamiltonian, we exactly
solve the dynamic behaviors of a driven and damped parametric oscillator to
obtain the optimal solutions by means of invariant parameters of $K$s to
combine with Lewis-Riesenfeld invariant method. This approach can discriminate
the external dynamics from the internal evolution of a wave packet by producing
independent parametric equations that dramatically facilitate the parametric
control on the quantum state evolution in a dissipative system. In order to
show the advantages of this method, several time-dependent models proposed in
the quantum control field are analyzed in details.
|
1601.00727v3
|
2016-02-19
|
Distinctive response of many-body localized systems to strong electric field
|
We study systems which are close to or within the many-body localized (MBL)
regime and are driven by strong electric field. In the ergodic regime, the
disorder extends applicability of the equilibrium linear--response theory to
stronger drivings, whereas the response of the MBL systems is very distinctive,
revealing currents with damped oscillations. The oscillation frequency is
independent of driving and the damping is not due to heating but rather due to
dephasing. The details of damping depend on the system's history reflecting
nonergodicity of the MBL phase, while the frequency of the oscillations remains
a robust hallmark of localization. We show that the distinctive characteristic
of the driven MBL phase is also a logarithmic increase of the energy and the
polarization with time.
|
1602.06055v1
|
2016-02-24
|
Pressure of a gas of underdamped active dumbbells
|
The pressure exerted on a wall by a gas at equilibrium does not depend on the
shape of the confining potential defining the wall. In contrast, it has been
shown recently [A.P. Solon et al., Nat. Phys. 11, 673 (2015)] that a gas of
overdamped active particles exerts on a wall a force that depends on the
confining potential, resulting in a net force on an asymmetric wall between two
chambers at equal densities. Here, considering a model of underdamped
self-propelled dumbbells in two dimensions, we study how the behavior of the
pressure depends on the damping coefficient of the dumbbells, thus exploring
inertial effects. We find in particular that the force exerted on a moving wall
between two chambers at equal density continuously vanishes at low damping
coefficient, and exhibits a complex dependence on the damping coefficient at
low density, when collisions are scarce. We further show that this behavior of
the pressure can to a significant extent be understood in terms of the
trajectories of individual particles close to and in contact with the wall.
|
1602.07420v1
|
2016-03-07
|
Optimal Load and Stiffness for Displacement-Constrained Vibration Energy Harvesters
|
The power electronic interface to a vibration energy harvester not only
provides ac-dc conversion, but can also set the electrical damping to maximize
output power under displacement-constrained operation. This is commonly
exploited for linear two-port harvesters by synchronous switching to realize a
Coulomb-damped resonant generator, but has not been fully explored when the
harvester is asynchronously switched to emulate a resistive load. In order to
understand the potential of such an approach, the optimal values of load
resistance and other control parameters need to be known. In this paper we
determine analytically the optimal load and stiffness of a harmonically driven
two-port harvester with displacement constraints. For weak-coupling devices, we
do not find any benefit of load and stiffness adjustment beyond maintaining a
saturated power level. For strong coupling we find that the power can be
optimized to agree with the velocity damped generator beyond the first critical
force for displacement-constrained operation. This can be sustained up to a
second critical force, determined by a resonator figure-of-merit, at which the
power ultimately levels out.
|
1603.01909v1
|
2016-03-22
|
Generation and protection of steady-state quantum correlations due to quantum channels with memory
|
We have proposed a scheme of the generation and preservation of two-qubit
steady state quantum correlations through quantum channels where successive
uses of the channels are correlated. Different types of noisy channels with
memory, such as amplitude damping, phase-damping, and depolarizing channels
have been taken into account. Some analytical or numerical results are
presented. The effect of channels with memory on dynamics of quantum
correlations has been discussed in detail. The results show that, steady state
entanglement between two independent qubits without entanglement subject to
amplitude damping channel with memory can be generated. Besides, we compare the
dynamics of entanglement with that of quantum discord when a two-qubit system
is prepared in an entangled state. We show that entanglement dynamics suddenly
disappears, while quantum discord displays only in the asymptotic limit.
Two-qubit quantum correlations can be preserved at a long time in the limit of
$\mu\rightarrow1$.
|
1603.06676v2
|
2016-03-31
|
Recovery of time-dependent damping coefficients and potentials appearing in wave equations from partial data
|
We consider the inverse problem of determining a time-dependent damping
coefficient $a$ and a time-dependent potential $q$, appearing in the wave
equation $\partial_t^2u-\Delta_x u+a(t,x)\partial_tu+q(t,x)u=0$ in
$Q=(0,T)\times\Omega$, with $T>0$ and $\Omega$ a $ \mathcal C^2$ bounded domain
of $\mathbb R^n$, $n\geq2$, from partial observations of the solutions on
$\partial Q$. More precisely, we look for observations on $\partial Q$ that
allow to determine uniquely a large class of time-dependent damping
coefficients $a$ and time-dependent potentials $q$ without involving an
important set of data. We prove global unique determination of $a\in
W^{1,p}(Q)$, with $p>n+1$, and $q\in L^\infty(Q)$ from partial observations on
$\partial Q$.
|
1603.09600v2
|
2016-04-22
|
Feedback-induced Bistability of an Optically Levitated Nanoparticle: A Fokker-Planck Treatment
|
Optically levitated nanoparticles have recently emerged as versatile
platforms for investigating macroscopic quantum mechanics and enabling
ultrasensitive metrology. In this article we theoretically consider two damping
regimes of an optically levitated nanoparticle cooled by cavityless parametric
feedback. Our treatment is based on a generalized Fokker-Planck equation
derived from the quantum master equation presented recently and shown to agree
very well with experiment [1]. For low damping, we find that the resulting
Wigner function yields the single-peaked oscillator position distribution and
recovers the appropriate energy distribution derived earlier using a classical
theory and verified experimentally [2]. For high damping, in contrast, we
predict a double-peaked position distribution, which we trace to an underlying
bistability induced by feedback. Unlike in cavity-based optomechanics,
stochastic processes play a major role in determining the bistable behavior. To
support our conclusions, we present analytical expressions as well as numerical
simulations using the truncated Wigner function approach. Our work opens up the
prospect of developing bistability-based devices, characterization of
phase-space dynamics, and investigation of the quantum-classical transition
using levitated nanoparticles.
|
1604.06767v2
|
2016-05-06
|
Multidimensional Thermoelasticity for Nonsimple Materials -- Well-Posedness and Long-Time Behavior
|
An initial-boundary value problem for the multidimensional type III
thermoelaticity for a nonsimple material with a center of symmetry is
considered. In the linear case, the well-posedness with and without
Kelvin-Voigt and/or frictional damping in the elastic part as well as the lack
of exponential stability in the elastically undamped case is proved. Further, a
frictional damping for the elastic component is shown to lead to the
exponential stability. A Cattaneo-type hyperbolic relaxation for the thermal
part is introduced and the well-posedness and uniform stability under a
nonlinear frictional damping are obtained using a compactness-uniqueness-type
argument. Additionally, a connection between the exponential stability and
exact observability for unitary $C_{0}$-groups is established.
|
1605.02049v1
|
2016-05-16
|
The Cauchy problem for the nonlinear damped wave equation with slowly decaying data
|
We study the Cauchy problem for the nonlinear damped wave equation and
establish the large data local well-posedness and small data global
well-posedness with slowly decaying initial data. We also prove that the
asymptotic profile of the global solution is given by a solution of the
corresponding parabolic problem, which shows that the solution of the damped
wave equation has the diffusion phenomena. Moreover, we show blow-up of
solution and give the estimate of the lifespan for a subcritical nonlinearity.
In particular, we determine the critical exponent for any space dimension.
|
1605.04616v2
|
2016-05-20
|
High-frequency behavior of FeN thin films fabricated by reactive sputtering
|
We investigated high-frequency behavior of FeN thin films prepared by
reactive sputtering through ferromagnetic resonance (FMR) and its relationship
with the static magnetic properties. The FMR was observed in the frequency
range from 2 to 18 GHz in the FeN films fabricated at proper nitrogen flow rate
(NFR). In those FeN thin films, a decrease of the saturation magnetization and
the corresponding decrease of the FMR frequency were observed as NFR was
increased during the deposition. The external field dependences of the FMR
frequencies were well fit to the Kittel formula and the Land\'e g-factors
determined from the fit were found to be very close to the free electron value.
The high-field damping parameters were almost insensitive to the growth
condition of NFR. However, the low-field damping parameters exhibited high
sensitivity to NFR very similar to the dependence of the hard-axis coercivity
on NFR, suggesting that extrinsic material properties such as impurities and
defect structures could be important in deciding the low-field damping
behavior.
|
1605.06179v1
|
2016-05-26
|
Thickness and temperature dependence of the magnetodynamic damping of pulsed laser deposited $\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ on (111)-oriented SrTi$\text{O}_3$
|
We have investigated the magnetodynamic properties of
$\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ (LSMO) films of thickness 10, 15
and 30 nm grown on (111)-oriented SrTi$\text{O}_3$ (STO) substrates by pulsed
laser deposition. Ferromagnetic resonance (FMR) experiments were performed in
the temperature range 100--300 K, and the magnetodynamic damping parameter
$\alpha$ was extracted as a function of both film thickness and temperature. We
found that the damping is lowest for the intermediate film thickness of 15 nm
with $\alpha \approx 2 \cdot 10^{-3}$, where $\alpha$ is relatively constant as
a function of temperature well below the Curie temperature of the respective
films.
|
1605.08195v2
|
2016-06-08
|
Effect of quantum noise on deterministic joint remote state preparation of a qubit state via a GHZ channel
|
Quantum secure communication brings a new direction for information security.
As an important component of quantum secure communication, deterministic joint
remote state preparation (DJRSP) could securely transmit a quantum state with
100\% success probability. In this paper, we study how the efficiency of DJRSP
is affected when qubits involved in the protocol are subjected to noise or
decoherence. Taking a GHZ based DJRSP scheme as an example, we study all types
of noise usually encountered in real-world implementations of quantum
communication protocols, i.e., the bit-flip, phase-flip (phase-damping),
depolarizing, and amplitude-damping noise. Our study shows that the fidelity of
the output state depends on the phase factor, the amplitude factor and the
noise parameter in the bit-flip noise, while the fidelity only depends on the
amplitude factor and the noise parameter in the other three types of noise. And
the receiver will get different output states depending on the first preparer's
measurement result in the amplitude-damping noise. Our results will be helpful
for improving quantum secure communication in real implementation.
|
1606.02484v2
|
2016-06-28
|
Radiation Damping by Thomson Scattering
|
Synchrotron radiation of relativistic electrons in storage rings naturally
leads to the process of damping of betatron oscillations. Damping time and
transverse beam emittance can be reduced by wigglers or undulators while the
beam parameters are still well defined by the common radiation integrals, based
on the properties of synchrotron radiation. However, the quantum excitation of
betatron oscillations in principle can be considerably reduced if an electron
radiation occurs due to the Thomson scattering in the periodic electromagnetic
field. After a brief introduction we compare radiation properties for different
cases and suggest the modification of the radiation integrals.
|
1606.08602v5
|
2016-06-29
|
Kinodynamic Motion Planning: A Novel Type Of Nonlinear, Passive Damping Forces And Advantages
|
This article extends the capabilities of the harmonic potential field
approach to planning to cover both the kinematic and dynamic aspects of a robot
motion. The suggested approach converts the gradient guidance field from a
harmonic potential to a control signal by augmenting it with a novel type of
damping forces called nonlinear, anisotropic, damping forces. The combination
of the two provides a signal that can both guide a robot and effectively manage
its dynamics. The kinodynamic planning signal inherits the guidance
capabilities of the harmonic gradient field. It can also be easily configured
to efficiently suppress the inertia-induced transients in the robot trajectory
without compromising the speed of operation. The approach works with
dissipative systems as well as systems acted on by external forces without
needing the full knowledge of the system dynamics. Theoretical developments and
simulation results are provided in this article.
|
1606.09270v1
|
2016-07-20
|
Envelope equation for the linear and nonlinear propagation of an electron plasma wave, including the effects of Landau damping, trapping, plasma inhomogeneity, and the change in the state of wave
|
This paper addresses the linear and nonlinear three-dimensional propagation
of an electron wave in a collisionless plasma that may be inhomogeneous,
nonstationary, anisotropic and even weakly magnetized. The wave amplitude,
together with any hydrodynamic quantity characterizing the plasma (density,
temperature,...) are supposed to vary very little within one wavelength or one
wave period. Hence, the geometrical optics limit is assumed, and the wave
propagation is described by a first order differential equation. This equation
explicitly accounts for three-dimensional effects, plasma inhomogeneity, Landau
damping, and the collisionless dissipation and electron acceleration due to
trapping. It is derived by mixing results obtained from a direct resolution of
the Vlasov-Poisson system and from a variational formalism involving a nonlocal
Lagrangian density. In a one-dimensional situation, abrupt transitions are
predicted in the coefficients of the wave equation. They occur when the state
of the electron plasma wave changes, from a linear wave to a wave with trapped
electrons. In a three dimensional geometry, the transitions are smoother,
especially as regards the nonlinear Landau damping rate, for which a very
simple effective and accurate analytic expression is provided.
|
1607.05844v2
|
2016-09-02
|
Particle dynamics and Stochastic Resonance in Periodic potentials
|
We have studied the dynamics of a particle in a periodically driven
underdamped periodic potential. Recent studies have reported the occurrence of
Stochastic Resonance (SR) in such systems in the high frequency regime, using
input energy per period of external drive as a quantifier. The particle
trajectories in these systems can be in two dynamical states characterised by
their definite energy and phase relation with the external drive. SR is due to
the noise assisted transition of the particles between these two states. We
study the role of damping on the occurrence of SR. We show that a driven
underdamped periodic system exhibits SR only if the damping is below a
particular limit. To explain this we study the syatem in the deterministic
regime. The existence of the two dynamical states in the deterministic regime
is dependent on the amount of damping and the amplitude od external drive. We
also study the input energy distributions and phase difference of the response
amplitude with the external drive as afunction of the friction parameter.
|
1609.00678v1
|
2016-09-26
|
An efficient quantum algorithm for spectral estimation
|
We develop an efficient quantum implementation of an important signal
processing algorithm for line spectral estimation: the matrix pencil method,
which determines the frequencies and damping factors of signals consisting of
finite sums of exponentially damped sinusoids. Our algorithm provides a quantum
speedup in a natural regime where the sampling rate is much higher than the
number of sinusoid components. Along the way, we develop techniques that are
expected to be useful for other quantum algorithms as well - consecutive phase
estimations to efficiently make products of asymmetric low rank matrices
classically accessible and an alternative method to efficiently exponentiate
non-Hermitian matrices. Our algorithm features an efficient quantum-classical
division of labor: The time-critical steps are implemented in quantum
superposition, while an interjacent step, requiring only exponentially few
parameters, can operate classically. We show that frequencies and damping
factors can be obtained in time logarithmic in the number of sampling points,
exponentially faster than known classical algorithms.
|
1609.08170v1
|
2016-10-01
|
On the regularization of impact without collision: the Painlevé paradox and compliance
|
We consider the problem of a rigid body, subject to a unilateral constraint,
in the presence of Coulomb friction. We regularize the problem by assuming
compliance (with both stiffness and damping) at the point of contact, for a
general class of normal reaction forces. Using a rigorous mathematical
approach, we recover impact without collision (IWC) in both the inconsistent
and indeterminate Painlev\'e paradoxes, in the latter case giving an exact
formula for conditions that separate IWC and lift-off. We solve the problem for
arbitrary values of the compliance damping and give explicit asymptotic
expressions in the limiting cases of small and large damping, all for a large
class of rigid bodies.
|
1610.00143v2
|
2016-11-25
|
Bulk viscous corrections to screening and damping in QCD at high temperatures
|
Non-equilibrium corrections to the distribution functions of quarks and
gluons in a hot and dense QCD medium modify the "hard thermal loops" (HTL). The
HTLs determine the retarded, advanced, and symmetric (time-ordered) propagators
for gluons with soft momenta as well as the Debye screening and Landau damping
mass scales. We compute such corrections to a thermal as well as to a
non-thermal fixed point.The screening and damping mass scales are sensitive to
the bulk pressure and hence to (pseudo-) critical dynamical scaling of the bulk
viscosity in the vicinity of a second-order critical point. This could be
reflected in the properties of quarkonium bound states in the deconfined phase
and in the dynamics of soft gluon fields.
|
1611.08379v2
|
2016-12-07
|
Investigation of Stimulated Brillouin Scattering in Laser-Plasma Interactions
|
In this paper, we present our numerical simulation results on the Stimulated
Brillouin Scattering (SBS) with injection of an ordinary mode (O-mode)
electromagnetic wave (our pump wave) with frequencies 70 GHz and 110 GHz.
Solving the Fourier transformed Vlasov equation in the velocity space, creates
a profile for distribution function. Time evolution of the distribution
function is investigated as well. Considering an average density for plasma
fusion (n_{0} ~ 10^{19} m^{-3}), we gain a profile for density. Then
two-dimensional instability rate for SBS is obtained. So, the fluctuation of
distribution function affects density and again density affects instability
rate. Increasing the incident light wave frequency causes the instability
growth rate to decrease. Time evolution shows a clear damping for instability
rate since the pump wave's energy is absorbed in plasma (plasma heating).
Furthermore, changing Landau damping for ion acoustic waves (IAW) by changing
ion-to-electron temperature ratio is presented as well, because this damping is
more dominant in high temperatures.
|
1612.02214v1
|
2016-12-08
|
Damped spin-wave excitations in the itinerant antiferromagnet $γ$-Fe$_{0.7}$Mn$_{0.3}$
|
The collective spin-wave excitations in the antiferromagnetic state of
$\gamma$-Fe$_{0.7}$Mn$_{0.3}$ were investigated using the inelastic neutron
scattering technique. The spin excitations remain isotropic up to the high
excitation energy, ${\hbar\omega}= 78$ meV. The excitations gradually become
broad and damped above 40 meV. The damping parameter ${\gamma}$ reaches 110(16)
meV at ${\hbar\omega} = 78$ meV, which is much larger than that for other
metallic compounds, e.g., CaFe$_2$As$_2$ (24 meV),
La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ ($52-72$ meV), and Mn$_{90}$Cu$_{10}$ (88
meV). In addition, the spin-wave dispersion shows a deviation from the relation
$({\hbar\omega})^2 = c^2q^2 + {\Delta}^2$ above 40 meV. The group velocity
above this energy increases to 470(40) meV{\AA}, which is higher than that at
the low energies, $c = 226(5)$ meV{\AA}. These results could suggest that the
spin-wave excitations merge with the continuum of the individual particle-hole
excitations at 40 meV.
|
1612.02515v2
|
2016-12-09
|
How strong a logistic damping can prevent blow-up for the minimal Keller-Segel chemotaxis system?
|
In this paper, we study the minimal Keller-Segel model with a logistic source
and obtain quantitative and qualitative descriptions of the competition between
logistic damping and other ingredient, especially, chemotactic aggregation to
guarantee boundedness and convergence. More specifically, we establish how
precisely strong a logistic source can prevent blow-up, and then we obtain an
explicit relationship between logistic damping and other ingredient,
especially, chemotactic aggregation so that convergences are ensured and their
respective convergence rates are explicitly calculated out. Known results in
the literature are completed and refined.
Furthermore, our findings provide clues on how to produce blowup solutions
for KS chemotaxis models with logistic sources.
|
1612.03024v2
|
2016-12-28
|
Quantum coherence of two-qubit over quantum channels with memory
|
Using the axiomatic definition of the coherence measure, such as the $l_{1}$
norm and the relative entropy, we study the phenomena of two-qubit system
quantum coherence through quantum channels where successive uses of the
channels are memory. Different types of noisy channels with memory, such as
amplitude damping, phase-damping, and depolarizing channels effect on quantum
coherence have been discussed in detail. The results show that, quantum
channels with memory can efficiently protect coherence from noisy channels.
Particularly, as channels with perfect memory, quantum coherence is unaffected
by the phase damping as well as depolarizing channels. Besides, we also
investigate the cohering and decohering power of quantum channels with memory.
|
1612.08791v1
|
2017-01-04
|
Hamiltonian of mean force and a damped harmonic oscillator in an anisotropic medium
|
The quantum dynamics of a damped harmonic oscillator is investigated in the
presence of an anisotropic heat bath. The medium is modeled by a continuum of
three dimensional harmonic oscillators and anisotropic coupling is treated by
introducing tensor coupling functions. Starting from a classical Lagrangian,
the total system is quantized in the framework of the canonical quantization.
Following Fano technique, Hamiltonian of the system is diagonalized in terms of
creation and annihilation operators that are linear combinations of the basic
dynamical variables. Using the diagonalized Hamiltonian, the mean force
internal energy, free energy and entropy of the damped oscillator are
calculated.
|
1701.00964v2
|
2017-01-30
|
Quantization of energy and weakly turbulent profiles of the solutions to some damped second order evolution equations
|
We consider a second order equation with a linear "elastic" part and a
nonlinear damping term depending on a power of the norm of the velocity. We
investigate the asymptotic behavior of solutions, after rescaling them suitably
in order to take into account the decay rate and bound their energy away from
zero.We find a rather unexpected dichotomy phenomenon. Solutions with finitely
many Fouriercomponents are asymptotic to solutions of the linearized
equationwithout damping, and exhibit some sort of equipartition of theenergy
among the components. Solutions with infinitely manyFourier components tend to
zero weakly but not strongly. We showalso that the limit of the energy of
solutions depends only on thenumber of their Fourier components.The proof of
our results is inspired by the analysis of asimplified model which we devise
through an averaging procedure,and whose solutions exhibit the same asymptotic
properties as thesolutions to the original equation.
|
1701.08604v1
|
2017-02-15
|
Topological Properties of a Coupled Spin-Photon System Induced by Damping
|
We experimentally examine the topological nature of a strongly coupled
spin-photon system induced by damping. The presence of both spin and photonic
losses results in a non-Hermitian system with a variety of exotic phenomena
dictated by the topological structure of the eigenvalue spectra and the
presence of an exceptional point (EP), where the coupled spin-photon
eigenvectors coalesce. By controlling both the spin resonance frequency and the
spin-photon coupling strength we observe a resonance crossing for
cooperativities above one, suggesting that the boundary between weak and strong
coupling should be based on the EP location rather than the cooperativity.
Furthermore we observe dynamic mode switching when encircling the EP and
identify the potential to engineer the topological structure of coupled
spin-photon systems with additional modes. Our work therefore further
highlights the role of damping within the strong coupling regime, and
demonstrates the potential and great flexibility of spin-photon systems for
studies of non-Hermitian physics.
|
1702.04797v2
|
2017-02-22
|
Modified quantum-speed-limit bounds for open quantum dynamics in quantum channels
|
The minimal evolution time between two distinguishable states is of
fundamental interest in quantum physics. Very recently Mirkin et al. argue that
some most common quantum-speed-limit (QSL) bounds which depend on the actual
evolution time do not cleave to the essence of the QSL theory as they grow
indefinitely but the final state is reached at a finite time in a damped
Jaynes-Cummings (JC) model. In this paper, we thoroughly study this puzzling
phenomenon. We find the inconsistent estimates will happen if and only if the
limit of resolution of a calculation program is achieved, through which we
propose that the nature of the inconsistency is not a violation to the essence
of the QSL theory but an illusion caused by the finite precision in numerical
simulations. We also present a generic method to overcome the inconsistent
estimates and confirm its effectiveness in both amplitude-damping and
phase-damping channels. Additionally, we show special cases which may restrict
the QSL bound defined by "quantumness".
|
1702.06748v3
|
2017-03-07
|
Lower Bound and optimality for a nonlinearly damped Timoshenko system with thermoelasticity
|
In this paper, we consider a vibrating nonlinear Timoshenko system with
thermoelasticity with second sound. We first investigate the strong stability
of this system, then we devote our efforts to obtain the strong lower energy
estimates using Alabau--Boussouira's energy comparison principle introduced in
\cite{2} (see also \cite{alabau}). One of the main advantages of these results
is that they allows us to prove the optimality of the asymptotic results (as
$t\rightarrow \infty$) obtained in \cite{ali}. We also extend to our model the
nice results achieved in \cite{alabau} for the case of nonlinearly damped
Timoshenko system with thermoelasticity. The optimality of our results is also
investigated through some explicit examples of the nonlinear damping term. The
proof of our results relies on the approach in \cite{AB1, AB2}.
|
1703.02599v4
|
2017-03-08
|
A Parameterized Energy Correction Method for Electromagnetic Showers in BGO-ECAL of DAMPE
|
DAMPE is a space-based mission designed as a high energy particle detector
measuring cosmic-rays and $\gamma-$rays which was successfully launched on
Dec.17, 2015. The BGO electromagnetic calorimeter is one of the key
sub-detectors of DAMPE for energy measurement of electromagnetic showers
produced by $e^{\pm}/{\gamma}$. Due to energy loss in dead material and energy
leakage outside the calorimeter, the deposited energy in BGO underestimates the
primary energy of incident $e^{\pm}/{\gamma}$. In this paper, based on detailed
MC simulations, a parameterized energy correction method using the lateral and
longitudinal information of electromagnetic showers has been studied and
verified with data of electron beam test at CERN. The measurements of energy
linearity and resolution are significantly improved by applying this correction
method for electromagnetic showers.
|
1703.02821v2
|
2017-03-08
|
A GAMP Based Low Complexity Sparse Bayesian Learning Algorithm
|
In this paper, we present an algorithm for the sparse signal recovery problem
that incorporates damped Gaussian generalized approximate message passing
(GGAMP) into Expectation-Maximization (EM)-based sparse Bayesian learning
(SBL). In particular, GGAMP is used to implement the E-step in SBL in place of
matrix inversion, leveraging the fact that GGAMP is guaranteed to converge with
appropriate damping. The resulting GGAMP-SBL algorithm is much more robust to
arbitrary measurement matrix $\boldsymbol{A}$ than the standard damped GAMP
algorithm while being much lower complexity than the standard SBL algorithm. We
then extend the approach from the single measurement vector (SMV) case to the
temporally correlated multiple measurement vector (MMV) case, leading to the
GGAMP-TSBL algorithm. We verify the robustness and computational advantages of
the proposed algorithms through numerical experiments.
|
1703.03044v2
|
2017-03-28
|
Singularity formation for the 1D compressible Euler equation with variable damping coefficient
|
In this paper, we consider some blow-up problems for the 1D Euler equation
with time and space dependent damping. We investigate sufficient conditions on
initial data and the rate of spatial or time-like decay of the coefficient of
damping for the occurrence of the finite time blow-up. In particular, our
sufficient conditions ensure that the derivative blow-up occurs in finite time
with the solution itself and the pressure bounded. Our method is based on
simple estimates with Riemann invariants. Furthermore, we give sharp lower and
upper estimates of the lifespan of solutions, when initial data are small
perturbations of constant states.
|
1703.09821v3
|
2017-04-07
|
Underdamped stochastic harmonic oscillator
|
We investigate stationary states of the linear damped stochastic oscillator
driven by L\'evy noises. In the long time limit kinetic and potential energies
of the oscillator do not fulfill the equipartition theorem and their
distributions follow the power-law asymptotics. At the same time, partition of
the mechanical energy is controlled by the damping coefficient. We show that in
the limit of vanishing damping a stochastic analogue of the equipartition
theorem can be proposed, namely the statistical properties of potential and
kinetic energies attain distributions characterized by the same width. Finally,
we demonstrate that the ratio of instantaneous kinetic and potential energies
which signifies departure from the mechanical energy equipartition, follows
universal power-law asymptotics.
|
1704.02119v2
|
2017-04-13
|
Quantum behaviour of open pumped and damped Bose-Hubbard trimers
|
We propose and analyse analogs of optical cavities for atoms using three-well
inline Bose-Hubbard models with pumping and losses. With one well pumped and
one damped, we find that both the mean-field dynamics and the quantum
statistics show a qualitative dependence on the choice of damped well. The
systems we analyse remain far from equilibrium, although most do enter a
steady-state regime. We find quadrature squeezing, bipartite and tripartite
inseparability and entanglement, and states exhibiting the EPR paradox,
depending on the parameter regimes. We also discover situations where the
mean-field solutions of our models are noticeably different from the quantum
solutions for the mean fields. Due to recent experimental advances, it should
be possible to demonstrate the effects we predict and investigate in this
article.
|
1704.04021v1
|
2017-05-10
|
Negative mobility of a Brownian particle: strong damping regime
|
We study impact of inertia on directed transport of a Brownian particle under
non-equilibrium conditions: the particle moves in a one-dimensional periodic
and symmetric potential, is driven by both an unbiased time-periodic force and
a constant force, and is coupled to a thermostat of temperature T. Within
selected parameter regimes this system exhibits negative mobility, which means
that the particle moves in the direction opposite to the direction of the
constant force. It is known that in such a setup the inertial term is essential
for the emergence of negative mobility and it cannot be detected in the
limiting case of overdamped dynamics. We analyse inertial effects and show that
negative mobility can be observed even in the strong damping regime. We
determine the optimal dimensionless mass for the presence of negative mobility
and reveal three mechanisms standing behind this anomaly: deterministic
chaotic, thermal noise induced and deterministic non-chaotic. The last origin
has never been reported. It may provide guidance to the possibility of
observation of negative mobility for strongly damped dynamics which is of
fundamental importance from the point of view of biological systems, all of
which in situ operate in fluctuating environments.
|
1705.03661v1
|
2017-05-27
|
Power System Supplementary Damping Controllers in the Presence of Saturation
|
This paper presents the analysis and a method to design supplementary damping
controllers (SDCs) for synchronous generators considering the effects of
saturation limits. Usually such saturations of control signals are imposed in
order to enforce practical limitations such as component ratings. However, to
guarantee the stability in the presence of saturation limits, the state
trajectories must remain inside the domain of attraction (DA). In this paper,
the domain of attraction of a single-machine infinite-bus (SMIB) power system
with saturation nonlinearity is estimated and compared with the exact
description of the null controllable region. Then, state-feedback controllers
are designed to enlarge the DA. Our analysis shows that nonlinear effects of
saturation should be considered to guarantee stability and satisfactory
performance. Simulation results on a detailed nonlinear model of a synchronous
generator indicate that the DA enlarges with the proposed controller. The
results also indicate that Critical Clearing Time (CCT) and damping of the
system with saturation can be improved by the proposed method.
|
1705.09849v1
|
2017-05-26
|
Absence of Landau damping in driven three-component Bose-Einstein condensate in optical lattices
|
We explore the quantum many-body physics of a three-component Bose-Einstein
condensate (BEC) in an optical lattices driven by laser fields in $V$ and
$\Lambda$ configurations. We obtain exact analytical expressions for the energy
spectrum and amplitudes of elementary excitations, and discover symmetries
among them. We demonstrate that the applied laser fields induce a gap in the
otherwise gapless Bogoliubov spectrum. We find that Landau damping of the
collective modes above the energy of the gap is carried by laser-induced roton
modes and is considerably suppressed compared to the phonon-mediated damping
endemic to undriven scalar BECs.
|
1705.10199v2
|
2017-05-31
|
Low-energy modes of spin-imbalanced Fermi gases in BCS phase
|
The low-energy modes of a spin-imbalanced superfluid Fermi gas in the
Bardeen-Cooper-Schrieffer (BCS) side are studied. The gas is assumed to be
sufficiently dilute so that the pairing of atoms can be considered effective
only in s-wave between fermions of different internal state. The order
parameter at equilibrium is determined by the mean-field approximation, while
the properties of the collective modes are calculated within a Gaussian
approximation for the fluctuations of the order parameter. In particular we
investigate the effects of asymmetry between the populations of the two
different components and of temperature on the frequency and damping of
collective modes. It is found that the temperature does not much affect the
frequency and the damping of the modes, whereas an increase of the imbalance
shifts the frequency toward lower values and enhances the damping sensitively.
Besides the Bogoliubov-Anderson phonons, we observe modes at zero frequency for
finite values of the wave-number. These modes indicate that an instability
develops driving the system toward two separate phases, normal and superfluid.
|
1705.11162v1
|
2017-06-01
|
Global Stabilization of the Navier-Stokes-Voight and the damped nonlinear wave equations by finite number of feedback controllers
|
In this paper we introduce a finite-parameters feedback control algorithm for
stabilizing solutions of the Navier-Stokes-Voigt equations, the strongly damped
nonlinear wave equations and the nonlinear wave equation with nonlinear damping
term, the Benjamin-Bona-Mahony-Burgers equation and the KdV-Burgers equation.
This algorithm capitalizes on the fact that such infinite-dimensional
dissipative dynamical systems posses finite-dimensional long-time behavior
which is represented by, for instance, the finitely many determining parameters
of their long-time dynamics, such as determining Fourier modes, determining
volume elements, determining nodes , etc..The algorithm utilizes these finite
parameters in the form of feedback control to stabilize the relevant solutions.
For the sake of clarity, and in order to fix ideas, we focus in this work on
the case of low Fourier modes feedback controller, however, our results and
tools are equally valid for using other feedback controllers employing other
spatial coarse mesh interpolants.
|
1706.00162v1
|
2017-06-08
|
Realistic clocks for a Universe without time
|
There are a number of problematic features within the current treatment of
time in physical theories, including the "timelessness" of the Universe as
encapsulated by the Wheeler-DeWitt equation. This paper considers one
particular investigation into resolving this issue; a conditional probability
interpretation that was first proposed by Page and Wooters. Those authors
addressed the apparent timelessness by subdividing a faux Universe into two
entangled parts, "the clock" and "the remainder of the Universe", and then
synchronizing the effective dynamics of the two subsystems by way of
conditional probabilities. The current treatment focuses on the possibility of
using a (somewhat) realistic clock system; namely, a coherent-state description
of a damped harmonic oscillator. This clock proves to be consistent with the
conditional probability interpretation; in particular, a standard evolution
operator is identified with the position of the clock playing the role of time
for the rest of the Universe. Restrictions on the damping factor are determined
and, perhaps contrary to expectations, the optimal choice of clock is not
necessarily one of minimal damping.
|
1706.02531v1
|
2017-06-26
|
High $β$ Effects on Cosmic Ray Streaming in Galaxy Clusters
|
Diffuse, extended radio emission in galaxy clusters, commonly referred to as
radio halos, indicate the presence of high energy cosmic ray (CR) electrons and
cluster-wide magnetic fields. We can predict from theory the expected surface
brightness of a radio halo, given magnetic field and CR density profiles.
Previous studies have shown that the nature of CR transport can radically
effect the expected radio halo emission from clusters (Wiener et al. 2013).
Reasonable levels of magnetohydrodynamic (MHD) wave damping can lead to
significant CR streaming speeds. But a careful treatment of MHD waves in a high
$\beta$ plasma, as expected in cluster environments, reveals damping rates may
be enhanced by a factor of $\beta^{1/2}$. This leads to faster CR streaming and
lower surface brightnesses than without this effect. In this work we re-examine
the simplified, 1D Coma cluster simulations (with radial magnetic fields) of
Wiener et al. (2013) and discuss observable consequences of this high $\beta$
damping. Future work is required to study this effect in more realistic
simulations.
|
1706.08525v2
|
2017-07-02
|
Metastability of Kolmogorov flows and inviscid damping of shear flows
|
First, we consider Kolmogorov flow (a shear flow with a sinusoidal velocity
profile) for 2D Navier-Stokes equation on a torus. Such flows, also called bar
states, have been numerically observed as one type of metastable states in the
study of 2D turbulence. For both rectangular and square tori, we prove that the
non-shear part of perturbations near Kolmogorov flow decays in a time scale
much shorter than the viscous time scale. The results are obtained for both the
linearized NS equations with any initial vorticity in L^2, and the nonlinear NS
equation with initial L^2 norm of vorticity of the size of viscosity. In the
proof, we use the Hamiltonian structure of the linearized Euler equation and
RAGE theorem to control the low frequency part of the perturbation. Second, we
consider two classes of shear flows for which a sharp stability criterion is
known. We show the inviscid damping in a time average sense for non-shear
perturbations with initial vorticity in L^2. For the unstable case, the
inviscid damping is proved on the center space. Our proof again uses the
Hamiltonian structure of the linearized Euler equation and an instability index
theory recently developed by Lin and Zeng for Hamiltonian PDEs.
|
1707.00278v1
|
2017-08-30
|
Convergence to diffusion waves for solutions of Euler equations with time-depending damping on quadrant
|
This paper is concerned with the asymptotic behavior of the solution to the
Euler equations with time-depending damping on quadrant $(x,t)\in
\mathbb{R}^+\times\mathbb{R}^+$, \begin{equation}\notag \partial_t v
-
\partial_x u=0, \qquad \partial_t u
+
\partial_x p(v)
=\displaystyle
-\frac{\alpha}{(1+t)^\lambda} u, \end{equation} with null-Dirichlet boundary
condition or null-Neumann boundary condition on $u$. We show that the
corresponding initial-boundary value problem admits a unique global smooth
solution which tends time-asymptotically to the nonlinear diffusion wave.
Compared with the previous work about Euler equations with constant coefficient
damping, studied by Nishihara and Yang (1999, J. Differential Equations, 156,
439-458), and Jiang and Zhu (2009, Discrete Contin. Dyn. Syst., 23, 887-918),
we obtain a general result when the initial perturbation belongs to the same
space. In addition, our main novelty lies in the facts that the cut-off points
of the convergence rates are different from our previous result about the
Cauchy problem. Our proof is based on the classical energy method and the
analyses of the nonlinear diffusion wave.
|
1708.09127v1
|
2017-09-06
|
Linear gyrokinetic investigation of the geodesic acoustic modes in realistic tokamak configurations
|
Geodesic acoustic modes (GAMs) are studied by means of the gyrokinetic global
particle-in-cell code ORB5. Linear electromagnetic simulations in the low
electron beta limit have been performed, in order to separate acoustic and
Alfv\'enic time scales and obtain more accurate measurements. The dependence of
the frequency and damping rate on several parameters such as the safety factor,
the GAM radial wavenumber and the plasma elongation is studied. All simulations
have been performed with kinetic electrons with realistic electron/ion mass
ratio. Interpolating formulae for the GAM frequency and damping rate, based on
the results of the gyrokinetic simulations, have been derived. Using these
expressions, the influence of the temperature gradient on the damping rate is
also investigated. Finally, the results are applied to the study of a real
discharge of the ASDEX Upgrade tokamak.
|
1709.01818v1
|
2017-09-17
|
Further insights into the damping-induced self-recovery phenomenon
|
In a series of papers, D. E. Chang, et al., proved and experimentally
demonstrated a phenomenon they termed "damping-induced self-recovery". However,
these papers left a few questions concerning the observed phenomenon unanswered
- in particular, the effect of the intervening lubricant-fluid and its
viscosity on the recovery, the abrupt change in behaviour with the introduction
of damping, a description of the energy dynamics, and the curious occurrence of
overshoots and oscillations and its dependence on the control law. In this
paper we attempt to answer these questions through theory. In particular, we
derive an expression for the infinite-dimensional fluid-stool-wheel system,
that approximates its dynamics to that of the better understood
finite-dimensional case.
|
1709.05596v5
|
2017-09-19
|
An Improved Primal-Dual Interior Point Solver for Model Predictive Control
|
We propose a primal-dual interior-point (PDIP) method for solving quadratic
programming problems with linear inequality constraints that typically arise
form MPC applications. We show that the solver converges (locally)
quadratically to a suboptimal solution of the MPC problem. PDIP solvers rely on
two phases: the damped and the pure Newton phases. Compared to state-of-the-art
PDIP methods, our solver replaces the initial damped Newton phase (usually used
to compute a medium-accuracy solution) with a dual solver based on Nesterov's
fast gradient scheme (DFG) that converges with a sublinear convergence rate of
order O(1/k^2) to a medium-accuracy solution. The switching strategy to the
pure Newton phase, compared to the state of the art, is computed in the dual
space to exploit the dual information provided by the DFG in the first phase.
Removing the damped Newton phase has the additional advantage that our solver
saves the computational effort required by backtracking line search. The
effectiveness of the proposed solver is demonstrated on a 2-dimensional
discrete-time unstable system and on an aerospace application.
|
1709.06362v1
|
2017-09-22
|
Nonlinear stage of Benjamin-Feir instability in forced/damped deep water waves
|
We study a three-wave truncation of a recently proposed damped/forced
high-order nonlinear Schr\"odinger equation for deep-water gravity waves under
the effect of wind and viscosity. The evolution of the norm (wave-action) and
spectral mean of the full model are well captured by the reduced dynamics.
Three regimes are found for the wind-viscosity balance: we classify them
according to the attractor in the phase-plane of the truncated system and to
the shift of the spectral mean. A downshift can coexist with both net forcing
and damping, i.e., attraction to period-1 or period-2 solutions. Upshift is
associated with stronger winds, i.e., to a net forcing where the attractor is
always a period-1 solution. The applicability of our classification to
experiments in long wave-tanks is verified.
|
1709.07850v2
|
2017-09-27
|
On long-time asymptotics for viscous hydrodynamic models of collective behavior with damping and nonlocal interactions
|
Hydrodynamic systems arising in swarming modelling include nonlocal forces in
the form of attractive-repulsive potentials as well as pressure terms modelling
strong local repulsion. We focus on the case where there is a balance between
nonlocal attraction and local pressure in presence of confinement in the whole
space. Under suitable assumptions on the potentials and the pressure functions,
we show the global existence of weak solutions for the hydrodynamic model with
viscosity and linear damping. By introducing linear damping in the system, we
ensure the existence and uniqueness of stationary solutions with compactly
supported density, fixed mass and center of mass. The associated velocity field
is zero in the support of the density. Moreover, we show that global weak
solutions converge for large times to the set of these stationary solutions in
a suitable sense. In particular cases, we can identify the limiting density
uniquely as the global minimizer of the free energy with the right mass and
center of mass.
|
1709.09290v2
|
2017-09-28
|
Landau Damping with Electron Lenses in Space-Charge Dominated Beams
|
Progress on the Intensity Frontier of high energy physics critically depends
on record high intensity charged particles accelerators. Beams in such machines
become operationally limited by coherent beam instabilities, particularly
enhanced in the regime of strong space charge (SC). Usual methods to control
the instabilities, such as octupole magnets, beam feedback dampers and
employment of chromatic effects, become less effective and insufficient. In [1]
it was proposed to employ electron lenses for introduction of sufficient spread
in particle oscillation frequencies needed for beam stabilization and in [2] it
was shown that electron lenses are uniquely effective for Landau damping of
transverse beam instabilities in high energy particle accelerators and their
employment does not compromise incoherent (single particle) stability, dynamic
aperture and the beam lifetime. Here we consider an important issue of
effectiveness of the Landau damping with electron lenses in space-charge
dominated beams and demonstrate that the desired stability can be assured with
proper choice of the electron beam parameters and current distributions.
|
1709.10020v1
|
2017-10-13
|
Hydrodynamic-to-ballistic crossover in Dirac fluid
|
We develop an exactly solvable classical kinetic model of transport in Dirac
materials accounting for strong electron-electron (e-e) and electron-hole (e-h)
collisions. We use this model to track the evolution of graphene conductivity
and properties of its collective excitations across the
hydrodynamic-to-ballistic crossover. We find the relaxation rate of electric
current by e-e collisions that is possible due to the lack of Galilean
invariance, and introduce a universal numerical measure of this non-invariance
in arbitrary dimension. We find the two branches of collective excitations in
the Dirac fluid: plasmons and electron-hole sound. The sound waves have small
viscous damping at the neutrality point both in the hydrodynamic and ballistic
regimes, but acquire large damping due to e-h friction even at slight doping.
On the contrary, plasmons acquire strong frictional damping at the neutrality
point and become well-defined in doped samples.
|
1710.05054v3
|
2017-10-13
|
The second hyperpolarizability of systems described by the space-fractional Schrodinger equation
|
The static second hyperpolarizability is derived from the space-fractional
Schr\"{o}dinger equation in the particle-centric view. The Thomas-Reiche-Kuhn
sum rule matrix elements and the three-level ansatz determines the maximum
second hyperpolarizability for a space-fractional quantum system. The total
oscillator strength is shown to decrease as the space-fractional parameter
$\alpha$ decreases, which reduces the optical response of a quantum system in
the presence of an external field. This damped response is caused by the
wavefunction dependent position and momentum commutation relation. Although the
maximum response is damped, we show that the one-dimensional quantum harmonic
oscillator is no longer a linear system for $\alpha \neq 1$, where the second
hyperpolarizability becomes negative before ultimately damping to zero at the
lower fractional limit of $\alpha \rightarrow 1/2$.
|
1710.05099v2
|
2017-11-01
|
Tunable magnetization relaxation of Fe_{2}Cr_{1-x}Co_{x}Si half-metallic Heusler alloys by band structure engineering
|
We report a systematic investigation on the magnetization relaxation
properties of iron-based half-metallic Heusler alloy
Fe$_{2}$Cr$_{1-x}$Co_${x}$Si (FCCS) thin films using broadband angular-resolved
ferromagnetic resonance. Band structure engineering through Co doping (x)
demonstrated by first-principles calculations is shown to tune the intrinsic
magnetic damping over an order of magnitude, namely 0.01-0.0008. Notably, the
intrinsic damping constants for samples with high Co concentration are among
the lowest reported for Heusler alloys and even comparable to magnetic
insulator yttrium iron garnet. Furthermore, a significant reduction of both
isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys
was found in the FCCS films with x=0.5-0.75, which is of particular importance
for applications. These results demonstrate a practical recipe to tailor
functional magnetization for Heusler alloy-based spintronics at room
temperature
|
1711.00406v1
|
2017-11-08
|
Bulk viscous corrections to screening and damping in the deconfined phase at high temperature
|
Non-equilibrium corrections in a hot QCD medium modify the "hard thermal
loops" (HTL) which determine the resummed propagators for gluons with soft
momenta as well as the Debye screening and Landau damping mass scales. We focus
on bulk viscous corrections to a thermal fixed point. The screening and damping
mass scales are sensitive to the bulk pressure and perhaps to (pseudo-)
critical dynamical scaling of the bulk viscosity in the vicinity of a
second-order critical point. This would affect the properties of quarkonium
bound states in the deconfined phase.
|
1711.03072v1
|
2017-11-29
|
A model explaining neutrino masses and the DAMPE cosmic ray electron excess
|
We propose a flavored $U(1)_{e\mu}$ neutrino mass and dark matter~(DM) model
to explain the recent DArk Matter Particle Explorer (DAMPE) data, which feature
an excess on the cosmic ray electron plus positron flux around 1.4 TeV. Only
the first two lepton generations of the Standard Model are charged under the
new $U(1)_{e\mu}$ gauge symmetry. A vector-like fermion $\psi$, which is our DM
candidate, annihilates into $e^{\pm}$ and $\mu^{\pm}$ via the new gauge boson
$Z'$ exchange and accounts for the DAMPE excess. We have found that the data
favors a $\psi$ mass around 1.5~TeV and a $Z'$ mass around 2.6~TeV, which can
potentially be probed by the next generation lepton colliders and DM direct
detection experiments.
|
1711.10995v2
|
2017-11-29
|
Electrophilic dark matter with dark photon: from DAMPE to direct detection
|
The electron-positron excess reported by the DAMPE collaboration recently may
be explained by an electrophilic dark matter (DM). A standard model singlet
fermion may play the role of such a DM when it is stablized by some symmetries,
such as a dark $U(1)_X^{}$ gauge symmetry, and dominantly annihilates into the
electron-positron pairs through the exchange of a scalar mediator. The model,
with appropriate Yukawa couplings, can well interpret the DAMPE excess. Naively
one expects that in this type of models the DM-nucleon cross section should be
small since there is no tree-level DM-quark interactions. We however find that
at one-loop level, a testable DM-nucleon cross section can be induced for
providing ways to test the electrophilic model. We also find that a $U(1)$
kinetic mixing can generate a sizable DM-nucleon cross section although the
$U(1)_X^{}$ dark photon only has a negligible contribution to the DM
annihilation. Depending on the signs of the mixing parameter, the dark photon
can enhance/reduce the one-loop induced DM-nucleon cross section.
|
1711.11000v2
|
2017-11-30
|
Leptophilic dark matter in gauged $U(1)_{L_e-L_μ}$ model in light of DAMPE cosmic ray $e^+ + e^-$ excess
|
Motivated by the very recent cosmic-ray electron+positron excess observed by
DAMPE collaboration, we investigate a Dirac fermion dark matter (DM) in the
gauged $L_e - L_\mu$ model. DM interacts with the electron and muon via the
$U(1)_{e-\mu}$ gauge boson $Z^{'}$. The model can explain the DAMPE data well.
Although a non-zero DM-nucleon cross section is only generated at one loop
level and there is a partial cancellation between $Z^{'}ee$ and $Z^{'}\mu\mu$
couplings, we find that a large portion of $Z^{'}$ mass is ruled out from
direct DM detection limit leaving the allowed $Z^{'}$ mass to be close to two
times of the DM mass. Implications for $pp \to Z^{'} \to 2\ell$ and $pp \to
2\ell + Z^{'}$ , and muon $g-2$ anomaly are also studied.
|
1711.11563v3
|
2017-12-03
|
Explaining the DAMPE $e^+ e^-$ excess using the Higgs triplet model with a vector dark matter
|
We explain the $e^+ e^-$ excess observed by the DAMPE Collaboration using a
dark matter model based upon the Higgs triplet model and an additional hidden
$SU(2)_X$ gauge symmetry. Two of the $SU(2)_X$ gauge bosons are stable due to a
residual discrete symmetry and serve as the dark matter candidate. We search
the parameter space for regions that can explain the observed relic abundance,
and compute the flux of $e^+ e^-$ coming from a nearby dark matter subhalo.
With the inclusion of background cosmic rays, we show that the model can render
a good fit to the entire energy spectrum covering the AMS-02, Fermi-LAT and
DAMPE data.
|
1712.00793v2
|
2017-12-06
|
Explain DAMPE Results by Dark Matter With Hierarchical Lepton-Specific Yukawa Interactions
|
We propose to interpret the DAMPE electron excess at 1.5 TeV through scalar
or Dirac fermion dark matter (DM) annihilation with doubly charged scalar
mediators that have lepton-specific Yukawa couplings. Hierarchy of such
lepton-specific Yukawa couplings is generated through the Froggatt-Nielsen
mechanism, so that the dark matter annihilation products can be dominantly
electrons. Stringent constraints from LEP2 on intermediate vector boson
production can be evaded in our scenarios. In the case of scalar DM, we discuss
one scenario with DM annihilating directly to leptons and the other scenario
with DM annihilating to scalar mediators followed by their decays. We also
discuss the Breit-Wigner resonant enhancement and the Sommerfeld enhancement in
case that the s-wave annihilation process is small or helicity suppressed. With
both types of enhancement, constraints on the parameters can be relaxed and new
ways for model building will be open in explaining the DAMPE results.
|
1712.02381v3
|
2017-12-08
|
Kinetic damping in the spectra of the spherical impedance probe
|
The impedance probe is a measurement device to measure plasma parameter like
electron density. It consists of one electrode connected to a network analyzer
via a coaxial cable and is immersed into a plasma. A bias potential superposed
with an alternating potential is applied to the electrode and the response of
the plasma is measured. Its dynamical interaction with the plasma in
electrostatic, kinetic description can be modeled in an abstract notation based
on functional analytic methods. These methods provide the opportunity to derive
a general solution, which is given as the response function of the probe-plasma
system. It is defined by the matrix elements of the resolvent of an appropriate
dynamical operator. Based on the general solution a residual damping for
vanishing pressure can be predicted and can only be explained by kinetic
effects. Within this manuscript an explicit response function of the spherical
impedance probe is derived. Therefore, the resolvent is determined by its
algebraic representation based on an expansion in orthogonal basis functions.
This allows to compute an approximated response function and its corresponding
spectra. These spectra show additional damping due to kinetic effects and are
in good agreement with former kinetically determined spectra.
|
1712.03126v1
|
2017-12-14
|
DAMPE squib? Significance of the 1.4 TeV DAMPE excess
|
We present a Bayesian and frequentist analysis of the DAMPE charged cosmic
ray spectrum. The spectrum, by eye, contained a spectral break at about 1 TeV
and a monochromatic excess at about 1.4 TeV. The break was supported by a Bayes
factor of about $10^{10}$ and we argue that the statistical significance was
resounding. We investigated whether we should attribute the excess to dark
matter annihilation into electrons in a nearby subhalo. We found a local
significance of about $3.6\sigma$ and a global significance of about
$2.3\sigma$, including a two-dimensional look-elsewhere effect by simulating
1000 pseudo-experiments. The Bayes factor was sensitive to our choices of
priors, but favoured the excess by about 2 for our choices. Thus, whilst
intriguing, the evidence for a signal is not currently compelling.
|
1712.05089v1
|
2017-12-15
|
Radiative Seesaw Model and DAMPE Excess from Leptophilic Gauge Symmetry
|
In the light of the $e^{+}+e^{-}$ excess observed by DAMPE experiment, we
propose an anomaly-free radiative seesaw model with an alternative leptophilic
$U(1)_X$ gauge symmetry. In the model, only right-handed leptons are charged
under $U(1)_X$ symmetry. The tiny Dirac neutrino masses are generated at
one-loop level and charged leptons acquire masses though the type-I seesaw-like
mechanism with heavy intermediate fermions. In order to cancel the anomaly,
irrational $U(1)_{X}$ charge numbers are assigned to some new particles. After
the spontaneous breaking of $U(1)_{X}$ symmetry, the dark $Z_{2}$ symmetry
could appear as a residual symmetry such that the stability of inert particles
with irrational charge numbers are guaranteed, naturally leading to stable DM
candidates. We show that the Dirac fermion DM contained in the model can
explain the DAMPE excess. Meanwhile, experimental constraints from DM relic
density, direct detection, LEP and anomalous magnetic moments are satisfied.
|
1712.05722v2
|
2017-12-19
|
Damping of Josephson oscillations in strongly correlated one-dimensional atomic gases
|
We study Josephson oscillations of two strongly correlated one-dimensional
bosonic clouds separated by a localized barrier. Using a quantum-Langevin
approach and the exact Tonks-Girardeau solution in the impenetrable-boson
limit, we determine the dynamical evolution of the particle-number imbalance,
displaying an effective damping of the Josephson oscillations which depends on
barrier height, interaction strength and temperature. We show that the damping
originates from the quantum and thermal fluctuations intrinsically present in
the strongly correlated gas. Thanks to the density-phase duality of the model,
the same results apply to particle-current oscillations in a one-dimensional
ring where a weak barrier couples different angular momentum states.
|
1712.06949v2
|
2017-12-21
|
The gluon condensation effects in the DAMPE cosmic ray spectrum of electrons and positrons
|
Gluons dominate the proton behavior at high energy collisions, they can be
condensed at ultra high energy. The collisions of the accelerated high energy
protons with interplanetary matter in cosmic rays will produce a huge number of
secondary particles at the gluon condensate energy region, which break the
primary power-law of cosmic rays. The above predictions seem to be consistent
with the recent DAMPE data concerning the electron plus positron spectra. We
find that the smoothly broken power-law at $\sim 0.9 TeV$ and $3\sim 4 TeV$ in
the DAMPE data can be understood as the gluon condensation effects in proton.
|
1712.07868v2
|
2017-12-22
|
Low-momentum dynamic structure factor of a strongly interacting Fermi gas at finite temperature: The Goldstone phonon and its Landau damping
|
We develop a microscopic theory of dynamic structure factor to describe the
Bogoliubov-Anderson-Goldstone phonon mode and its damping rate in a strongly
interacting Fermi gas at finite temperature. It is based on a density
functional approach - the so-called superfluid local density approximation. The
accuracy of the theory is quantitatively examined by comparing the theoretical
predictions with the recent experimental measurements for the local dynamic
structure factor of a nearly homogeneous unitary Fermi gas at low transferred
momentum {[}S. Hoinka \textit{et al.}, Nat. Phys. \textbf{13}, 943 (2017){]},
without any free parameters. We calculate the dynamic structure factor as
functions of temperature and transferred momentum, and determine the
temperature evolution of the phonon damping rate, by considering the dominant
decay process of the phonon mode via scatterings off fermionic quasiparticles.
These predictions can be confronted with future Bragg scattering experiments on
a unitary Fermi gas near the superfluid transition.
|
1712.08318v1
|
2017-12-22
|
A brief summary of nonlinear echoes and Landau damping
|
In this expository note we review some recent results on Landau damping in
the nonlinear Vlasov equations, focusing specifically on the recent
construction of nonlinear echo solutions by the author [arXiv:1605.06841] and
the associated background. These solutions show that a straightforward
extension of Mouhot and Villani's theorem on Landau damping to Sobolev spaces
on $\mathbb T^n_x \times \mathbb R^n_v $ is impossible and hence emphasize the
subtle dependence on regularity of phase mixing problems. This expository note
is specifically aimed at mathematicians who study the analysis of PDEs, but not
necessarily those who work specifically on kinetic theory. However, for the
sake of brevity, this review is certainly not comprehensive.
|
1712.08498v1
|
2017-12-28
|
Coherence evolution in two-qubit system going through amplitude damping channel
|
In this paper, we analyze the evolution of quantum coherence in a two-qubit
system going through the amplitude damping channel. After they have gone
through this channel many times, we analyze the systems with respect to the
coherence of their output states. When only one subsystem goes through the
channel, frozen coherence occurs if and only if this subsystem is incoherent
and an auxiliary condition is satisfied for the other subsystem. When two
subsystems go through this quantum channel, quantum coherence can be frozen if
and only if the two subsystems are both incoherent. We also investigate the
evolution of coherence for maximally incoherent-coherent states and derive an
equation for the output states after one or two subsystems have gone through
the amplitude damping channel.
|
1712.09769v1
|
2018-01-09
|
Balanced Truncation Model Reduction of a Nonlinear Cable-Mass PDE System with Interior Damping
|
We consider model order reduction of a nonlinear cable-mass system modeled by
a 1D wave equation with interior damping and dynamic boundary conditions. The
system is driven by a time dependent forcing input to a linear mass-spring
system at one boundary. The goal of the model reduction is to produce a low
order model that produces an accurate approximation to the displacement and
velocity of the mass in the nonlinear mass-spring system at the opposite
boundary. We first prove that the linearized and nonlinear unforced systems are
well-posed and exponentially stable under certain conditions on the damping
parameters, and then consider a balanced truncation method to generate the
reduced order model (ROM) of the nonlinear input-output system. Little is known
about model reduction of nonlinear input-output systems, and so we present
detailed numerical experiments concerning the performance of the nonlinear ROM.
We find that the ROM is accurate for many different combinations of model
parameters.
|
1801.02792v1
|
2018-01-18
|
Analytic solutions to various dissipation models of the simple and driven quantum harmonic oscillator
|
We obtain analytic solutions to various models of dissipation of the quantum
harmonic oscillator, employing a simple method in the Wigner function Fourier
transform description of the system; and study as an exemplification, the
driven open quantum harmonic oscillator. The environmental models we use are
based on optical master equations for the zero and finite temperature bath and
whose open dynamics are described by a Lindblad master equation, and also we
use the Caldeira-Leggett model for the high temperature limit, in the the under
damped an the over damped case. Under the Wigner Fourier transform or chord
function as it has been called, it becomes particularly simple to solve the
dynamics of the open oscillator in the sense that the dynamics of the system
are reduced to the application of an evolution matrix related to the damped
motion of the oscillator.
|
1801.05943v1
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.