publicationDate
stringlengths 1
2.79k
| title
stringlengths 1
36.5k
⌀ | abstract
stringlengths 1
37.3k
⌀ | id
stringlengths 9
47
|
|---|---|---|---|
2017-06-16
|
Simulation of non-Pauli Channels
|
We consider the simulation of a quantum channel by two parties who share a
resource state and may apply local operations assisted by classical
communication (LOCC). One specific type of such LOCC is standard teleportation,
which is however limited to the simulation of Pauli channels. Here we show how
we can easily enlarge this class by means of a minimal perturbation of the
teleportation protocol, where we introduce noise in the classical communication
channel between the remote parties. By adopting this noisy protocol, we provide
a necessary condition for simulating a non-Pauli channel. In particular, we
characterize the set of channels that are generated assuming the Choi matrix of
an amplitude damping channel as a resource state. Within this set, we identify
a class of Pauli-damping channels for which we bound the two-way quantum and
private capacities.
|
1706.05384v2
|
2017-06-17
|
\emph{Ab initio} calculation of spin-orbit coupling for NV center in diamond exhibiting dynamic Jahn-Teller effect
|
Point defects in solids may realize solid state quantum bits. The spin-orbit
coupling in these point defects plays a key role in the magneto-optical
properties that determine the conditions of quantum bit operation. However,
experimental data and methods do not directly yield this highly important data,
particularly, for such complex systems where dynamic Jahn-Teller (DJT) effect
damps the spin-orbit interaction. Here, we show for an exemplary quantum bit,
nitrogen-vacancy (NV) center in diamond, that \emph{ab initio} supercell
density functional theory provide quantitative prediction for the spin-orbit
coupling damped by DJT. We show that DJT is responsible for the multiple
intersystem crossing rates of NV center at cryogenic temperatures. Our results
pave the way toward optimizing solid state quantum bits for quantum information
processing and metrology applications.
|
1706.05523v2
|
2017-06-20
|
Decoherence induced spin squeezing signatures in Greenberger-Horne-Zeilinger and W states
|
We reckon the behaviour of spin squeezing in tripartite unsqueezed maximally
entangled Green- berger-Horne-Zeilinger (GHZ) and W states under various
decoherence channels with Kitagawa- Ueda (KU) criteria. In order to search spin
squeezing sudden death (SSSD) and signatures of spin squeezing production we
use bit flip, phase flip, bit-phase-flip, amplitude damping, phase damping and
depolarization channels in the present study. In literature, the influence of
decoherence has been studied as a destroying element. On the contrary here we
investigate the positive aspect of decoherence, which produce spin squeezing in
unsqueezed GHZ and W states under certain channels. Our meticulous study shows
that GHZ state remain unsqueezed under aforementioned channels except
bit-phase-flip and depolarization channels. While all the decoherence channels
produce spin squeezing in W state. So we find, GHZ is more robust in comparison
to W state in the sense of spin squeezing production under decoherence. Most
importantly we find that none of the decoherence channel produce SSSD in any
one of the state.
|
1706.06273v2
|
2017-06-22
|
Adaptive recurrence quantum entanglement distillation for two-Kraus-operator channels
|
Quantum entanglement serves as a valuable resource for many important quantum
operations. A pair of entangled qubits can be shared between two agents by
first preparing a maximally entangled qubit pair at one agent, and then sending
one of the qubits to the other agent through a quantum channel. In this
process, the deterioration of entanglement is inevitable since the noise
inherent in the channel contaminates the qubit. To address this challenge,
various quantum entanglement distillation (QED) algorithms have been developed.
Among them, recurrence algorithms have advantages in terms of implementability
and robustness. However, the efficiency of recurrence QED algorithms has not
been investigated thoroughly in the literature. This paper put forth two
recurrence QED algorithms that adapt to the quantum channel to tackle the
efficiency issue. The proposed algorithms have guaranteed convergence for
quantum channels with two Kraus operators, which include phase-damping and
amplitude-damping channels. Analytical results show that the convergence speed
of these algorithms is improved from linear to quadratic and one of the
algorithms achieves the optimal speed. Numerical results confirm that the
proposed algorithms significantly improve the efficiency of QED.
|
1706.07461v1
|
2017-06-26
|
Landau Damping of Beam Instabilities by Electron Lenses
|
Modern and future particle accelerators employ increasingly higher intensity
and brighter beams of charged particles and become operationally limited by
coherent beam instabilities. Usual methods to control the instabilities, such
as octupole magnets, beam feedback dampers and use of chromatic effects, become
less effective and insufficient. We show that, in contrast, Lorentz forces of a
low-energy, a magnetically stabilized electron beam, or "electron lens", easily
introduces transverse nonlinear focusing sufficient for Landau damping of
transverse beam instabilities in accelerators. It is also important that,
unlike other nonlinear elements, the electron lens provides the frequency
spread mainly at the beam core, thus allowing much higher frequency spread
without lifetime degradation. For the parameters of the Future Circular
Collider, a single conventional electron lens a few meters long would provide
stabilization superior to tens of thousands of superconducting octupole
magnets.
|
1706.08477v1
|
2018-02-05
|
Intrinsic spin-orbit torque arising from Berry curvature in metallic-magnet/Cu-oxide interface
|
We report the observation of the intrinsic damping-like spin-orbit torque
(SOT) arising from the Berry curvature in metallic-magnet/CuO$_x$
heterostructures. We show that a robust damping-like SOT, an order of magnitude
larger than a field-like SOT, is generated in the heterostructure despite the
absence of the bulk spin-orbit effect in the CuO$_x$ layer. Furthermore, by
tuning the interface oxidation level, we demonstrate that the field-like SOT
changes drastically and even switches its sign, which originates from oxygen
modulated spin-dependent disorder. These results provide an important
information for fundamental understanding of the physics of the SOTs.
|
1802.01285v2
|
2018-02-12
|
Selective Phonon Damping in Topological Semimetals
|
Topological semimetals are characterized by their intriguing Fermi surfaces
(FSs) such as Weyl and Dirac points, or nodal FS, and their associated surface
states. Among them, topological crystalline semimetals, in the presence of
strong spin-orbit coupling, possess a nodal FS protected by non-symmorphic
lattice symmetries. In particular, it was theoretically proposed that
$\mathrm{SrIrO}_{3}$ exhibits a bulk nodal ring due to glide symmetries, as
well as flat two-dimensional surface states related to chiral and mirror
symmetries. However, due to the semimetallic nature of the bulk, direct
observation of these surface states is difficult. Here we study the effect of
flat-surface states on phonon modes for $\mathrm{SrIrO}_{3}$ side surfaces. We
show that particular phonon modes, based on mirror symmetry, have qualitatively
different damping mechanisms due to the surface states which could be used to
infer their existence. Experimental techniques for such measurements are also
discussed.
|
1802.04300v2
|
2018-02-14
|
Motion of interfaces for a damped hyperbolic Allen-Cahn equation
|
Consider the Allen-Cahn equation $u_t=\varepsilon^2\Delta u-F'(u)$, where $F$
is a double well potential with wells of equal depth, located at $\pm1$. There
are a lot of papers devoted to the study of the limiting behavior of the
solutions as the diffusion coefficient $\varepsilon\to0^+$, and it is well
known that, if the initial datum $u(\cdot,0)$ takes the values $+1$ and $-1$ in
the regions $\Omega_+$ and $\Omega_-$, then the "interface" connecting
$\Omega_+$ and $\Omega_-$ moves with normal velocity equal to the sum of its
principal curvatures, i.e. the interface moves by mean curvature flow.
This paper concerns with the motion of the inteface for a damped hyperbolic
Allen-Cahn equation, in a bounded domain of $\mathbb{R}^n$, for $n=2$ or $n=3$.
In particular, we focus the attention on radially simmetric solutions, studying
in detail the differences with the classic parabolic case, and we prove that,
under appropriate assumptions on the initial data $u(\cdot,0)$ and
$u_t(\cdot,0)$, the interface moves by mean curvature as $\varepsilon\to0^+$
also in the hyperbolic framework.
|
1802.05038v1
|
2018-02-23
|
Blow up of solutions for semilinear wave equations with noneffective damping
|
In this paper, we study the finite-time blow up of solutions to the following
semilinear wave equation with time-dependent damping \[ \partial_t^2u-\Delta
u+\frac{\mu}{1+t}\partial_tu=|u|^p \] in $\mathbb{R}_{+}\times\mathbb{R}^n$.
More precisely, for $0\leq\mu\leq 2,\mu \neq1$ and $n\geq 2$, there is no
global solution for $1<p<p_S(n+\mu)$, where $p_S(k)$ is the $k$-dimensional
Strauss exponent and a life-span of the blow up solution will be obtained. Our
work is an extension of \cite{IS}, where the authors proved a similar blow up
result with a larger range of $\mu$. However, we obtain a better life-span
estimate when $\mu\in(0,1)\cup(1,2)$ by using a different method.
|
1802.08403v2
|
2018-07-02
|
Global Existence of Solutions to the Compressible Euler Equations with Time-dependent Damping and Logarithmic State Equation
|
In mathematical physics, the pressure function is determined by the equation
of state. There are two existing barotropic state equations: the state equation
for polytropic gas with adiabatic index greater than or equal to 1 and the
state equation for generalized Chaplygin gas in cosmology. In this paper, a
logarithmic pressure is derived naturally with the coexistence of the two
existing state equations through an equivalent symmetric hyperbolic
transformation. On the study of the logarithmic pressure, global existence of
solutions with small initial data to the one-dimensional compressible Euler
equations with time-dependent damping is established.
|
1807.00550v2
|
2018-07-02
|
On wave equations of the $p$-Laplacian type with supercritical nonlinearities
|
This article focuses on a quasilinear wave equation of $p$-Laplacian type: \[
u_{tt} - \Delta_p u -\Delta u_t = f(u) \] in a bounded domain $\Omega \subset
\mathbb{R}^3$ with a sufficiently smooth boundary $\Gamma=\partial \Omega$
subject to a generalized Robin boundary condition featuring boundary damping
and a nonlinear source term. The operator $\Delta_p$, $2<p<3$, denotes the
classical $p$-Laplacian. The interior and boundary terms $f(u)$, $h(u)$ are
sources that are allowed to have a supercritical exponent, in the sense that
their associated Nemytskii operators are not locally Lipschitz from
$W^{1,p}(\Omega)$ into $L^2(\Omega)$ or $L^2(\Gamma)$. Under suitable
assumptions on the parameters we provide a rigorous proof of existence of a
local weak solution which can be extended globally in time, provided the
damping terms dominates the corresponding sources in an appropriate sense.
Moreover, a blow-up result is proved for solutions with negative initial total
energy.
|
1807.00650v1
|
2018-06-30
|
Efficient $p$-multigrid method based on an exponential time discretization for compressible steady flows
|
An efficient multigrid framework is developed for the time marching of
steady-state compressible flows with a spatially high-order ($p$-order
polynomial) modal discontinuous Galerkin method. The core algorithm that based
on a global coupling, exponential time integration scheme provides strong
damping effects to accelerate the convergence towards the steady state, while
high-frequency, high-order spatial error modes are smoothed out with a
$s$-stage preconditioned Runge-Kutta method. Numerical studies show that the
exponential time integration substantially improves the damping and propagative
efficiency of Runge-Kutta time-stepping for use with the $p$-multigrid method,
yielding rapid and $p$-independent convergences to steady flows in both two and
three dimensions.
|
1807.01151v1
|
2018-07-04
|
Structural crossover in a model fluid exhibiting two length scales: repercussions for quasicrystal formation
|
We investigate the liquid state structure of the two-dimensional (2D) model
introduced by Barkan et al. [Phys. Rev. Lett. 113, 098304 (2014)], which
exhibits quasicrystalline and other unusual solid phases, focussing on the
radial distribution function $g(r)$ and its asymptotic decay $r\to\infty$. For
this particular model system, we find that as the density is increased there is
a structural crossover from damped oscillatory asymptotic decay with one
wavelength to damped oscillatory asymptotic decay with another distinct
wavelength. The ratio of these wavelengths is $\approx1.932$. Following the
locus in the phase diagram of this structural crossover leads directly to the
region where quasicrystals are found. We argue that identifying and following
such a crossover line in the phase diagram towards higher densities where the
solid phase(s) occur is a good strategy for finding quasicrystals in a wide
variety of systems. We also show how the pole analysis of the asymptotic decay
of equilibrium fluid correlations is intimately connected with the
non-equilibrium growth or decay of small amplitude density fluctuations in a
bulk fluid.
|
1807.01467v1
|
2018-07-04
|
Dirac's Method for the Two-Dimensional Damped Harmonic Oscillator in the Extended Phase Space
|
The system of two-dimensional damped harmonic oscillator is revisited in the
extended phase space. It is an old problem already addressed by many authors
that we present here in some fresh points of view and carry on smoothly a whole
discussion. We show that the system is singular. The classical Hamiltonian is
proportional to the first-class constraint. We pursue with the Dirac's
canonical quantization procedure by fixing the gauge and provide a reduced
phase space description of the system. As result the quantum system is simply
modeled by the original quantum Hamiltonian.
|
1807.01539v2
|
2018-07-05
|
Decay of approximate solutions for the damped semilinear wave equation on a bounded 1d domain
|
In this paper we study the long time behavior for a semilinear wave equation
with space-dependent and nonlinear damping term. After rewriting the equation
as a first order system, we define a class of approximate solutions that employ
tipical tools of hyperbolic systems of conservation laws, such as the Riemann
problem. By recasting the problem as a discrete-time nonhomogeneous system,
which is related to a probabilistic interpretation of the solution, we provide
a strategy to study its long-time behavior uniformly with respect to the mesh
size parameter $\Delta x=1/N\to 0$. The proof makes use of the Birkhoff
decomposition of doubly stochastic matrices and of accurate estimates on the
iteration system as $N\to\infty$.
Under appropriate assumptions on the nonlinearity, we prove the exponential
convergence in $L^\infty$ of the solution to the first order system towards a
stationary solution, as $t\to+\infty$, as well as uniform error estimates for
the approximate solutions.
|
1807.01968v3
|
2018-07-07
|
Axial Quasi-Normal Modes of Scalarized Neutron Stars with Realistic Equations of State
|
We compute the axial quasi-normal modes of static neutron stars in scalar
tensor theory. In particular, we employ various realistic equations of state
including nuclear, hyperonic and hybrid matter. We investigate the fundamental
curvature mode and compare the results with those of General Relativity. We
find that the frequency of the modes and the damping time are reduced for the
scalarized neutron stars. In addition, we confirm and extend the universal
relations for quasi-normal modes known in General Relativity to this wide range
of realistic equations of state for scalarized neutron stars and confirm the
universality of the scaled frequency and damping time in terms of the scaled
moment of inertia as well as compactness for neutron stars with and without
scalarization.
|
1807.02598v1
|
2018-07-09
|
DLA and sub-DLA metallicity evolution: A case study of absorbers towards Q0338-0005
|
The damped and sub-damped Lyman alpha systems (DLAs and sub-DLAs) traced in
absorption against bright background quasars represent the main reserve of
neutral hydrogen at high redshifts. We used the archival Very Large Telescope
(VLT) instrument Ultraviolet and Visual Echelle Spectrograph (UVES)
high-resolution data of Q0338-0005 (zem = 3.049) to study abundances of the DLA
(zabs = 2.2298) and sub-DLA (zabs =2.7457) along the line of sight. We
estimated column densities of HI and various elements present in the DLA and
sub-DLA through Voigt profile fitting. The DLA trough shows the Lyman alpha
emission from its host galaxy. We derive the metallicities of the DLA and
sub-DLA with [Zn/H] = -0.67 +/- 0.18 and [S/H] = -1.45 +/-0.17, respectively.
We compared our abundances of the DLA and sub-DLA with other high resolution
DLA and sub-DLA metallicities and find that both populations show an overall
increase of metallicity with decreasing redshift. However, sub-DLAs usually
have higher metallicities than the DLAs.
|
1807.04189v1
|
2018-07-19
|
Vibrational damping effects on electronic energy relaxation in molecular aggregates
|
Representation of molecular vibrational degrees of freedom by independent
harmonic oscillators, when describing electronic spectra or electronic
excitation energy transport, raises unfavourable effects as vibrational energy
relaxation becomes inaccessible. A standard theoretical description is extended
in this paper by including both electronic-phonon and vibrational-phonon
couplings. Using this approach we have simulated a model pigment-protein system
and have shown that intermode coupling leads to the quenching of pigment
vibrational modes, and to the redistribution of fluctuation spectral density
with respect to the electronic excitations. Moreover, new energy relaxation
pathways, opened by the vibrational-phonon interaction, allow to reach the
electronic excited state equilibrium quicker in the naturally occurring water
soluble chlorophyll binding protein (WSCP) aggregate, demonstrating the
significance that the damping of molecular vibrations has for the
intrarmolecular energy relaxation process rate.
|
1807.07314v1
|
2018-07-24
|
Role of stable modes in driven shear-flow turbulence
|
A linearly unstable, sinusoidal $E \times B$ shear flow is examined in the
gyrokinetic framework in both the linear and nonlinear regimes. In the linear
regime, it is shown that the eigenmode spectrum is nearly identical to
hydrodynamic shear flows, with a conjugate stable mode found at every unstable
wavenumber. In the nonlinear regime, turbulent saturation of the instability is
examined with and without the inclusion of a driving term that prevents
nonlinear flattening of the mean flow, and a scale-independent radiative
damping term that suppresses the excitation of conjugate stable modes. A simple
fluid model for how momentum transport and partial flattening of the mean flow
scale with the driving term is constructed, from which it is shown that, except
at high radiative damping, stable modes play an important role in the turbulent
state and yield significantly improved quantitative predictions when compared
with corresponding models neglecting stable modes.
|
1807.09280v1
|
2018-08-08
|
An application of $L^1$ estimates for oscillating integrals to parabolic like semi-linear structurally damped $σ$-evolution models
|
We study the following Cauchy problems for semi-linear structurally damped
$\sigma$-evolution models: \begin{equation*} u_{tt}+ (-\Delta)^\sigma u+ \mu
(-\Delta)^\delta u_t = f(u,u_t),\, u(0,x)= u_0(x),\, u_t(0,x)=u_1(x)
\end{equation*} with $\sigma \ge 1$, $\mu>0$ and $\delta \in
(0,\frac{\sigma}{2})$. Here the function $f(u,u_t)$ stands for the power
nonlinearities $|u|^{p}$ and $|u_t|^{p}$ with a given number $p>1$. We are
interested in investigating $L^{1}$ estimates for oscillating integrals in the
presentation of the solutions to the corresponding linear models with vanishing
right-hand sides by applying the theory of modified Bessel functions and
Fa\`{a} di Bruno's formula. By assuming additional $L^{m}$ regularity on the
initial data, we use $(L^{m}\cap L^{q})- L^{q}$ and $L^{q}- L^{q}$ estimates
with $q\in (1,\infty)$ and $m\in [1,q)$, to prove the global (in time)
existence of small data Sobolev solutions to the above semi-linear models from
suitable function spaces basing on $L^q$ spaces.
|
1808.02706v2
|
2018-08-09
|
Two-qubit state recovery from amplitude damping based on weak measurement
|
In the quantum control process, arbitrary pure or mixed initial states need
to be protected from amplitude damping through the noise channel using
measurements and quantum control. However, how to achieve it on a two-qubit
quantum system remains a challenge. In this paper, we propose a feed-forward
control approach to protect arbitrary two-qubit pure or mixed initial states
using the weak measurement. A feed-forward operation and measurements are used
before the noise channel, and afterwards a reversed operation and measurements
are applied to recover the state back to its initial state. In the case of
two-qubit pure states, we use the unravelling trick to describe the state of
the system in each step of the control procedure. For two-qubit mixed states, a
completely-positive trace-preserving (CPTP) map is implemented. Finally, the
fidelity and success probability are used to evaluate the effect of protection.
The complete recovery conditions for the measurement strengths are derived,
under which we achieve the optimal fidelity and the success probability of
recovering the initial pure or mixed states.
|
1808.03094v1
|
2018-08-10
|
Dynamical polarization and the optical response of silicene and related materials
|
We discuss the dynamical polarization, optical response in low-frequency
regime under in-plane polarized driving field of the silicene. The dynamical
polarization, dielectric function, and absorption of radiation in infrared
region are obtained and shown in the ${\bf q}\sim\omega$ space, and they are
distinguishing for the cases of chemical potential larger than the band gap and
smaller than the band gap. The optical properties of silicene and the related
group-V and group-VI materials: MoS$_{2}$ and black phosphorus are explored
through the first-principle study. The plasmon which damped into the
electron-hole pair in the single-particle excitation regime is also mentioned.
The spin/valley polarized electron-hole pairs can be formed through that way,
especially for the high-energy $\pi$-plasmon which begin to damp at the small
${\bf q}$-limit. The anisotropic effects induced by the warping structure or
charged impurity, and the anisotropic polarization induced by the polarized
incident light are also discussed. Our result exhibits the great potential in
the optoelectronic applications of the materials we discussed.
|
1808.03442v1
|
2018-08-19
|
Reconstruction algorithms for photoacoustic tomography in heterogenous damping media
|
In this article, we study several reconstruction methods for the inverse
source problem of photoacoustic tomography (PAT) with spatially variable sound
speed and damping. The backbone of these methods is the adjoint operators,
which we thoroughly analyze in both the $L^2$- and $H^1$-settings. They are
casted in the form of a nonstandard wave equation. We derive the well-pawedness
of the aforementioned wave equation in a natural functional space, and also
prove the finite speed of propagation. Under the uniqueness and visibility
condition, our formulations of the standard iterative reconstruction methods,
such as Landweber's and conjugate gradients (CG), achieve a linear rate of
convergence in either $L^2$- or $H^1$-norm. When the visibility condition is
not satisfied, the problem is severely ill-posed and one must apply a
regularization technique to stabilize the solutions. To that end, we study two
classes of regularization methods: (i) iterative, and (ii) variational
regularization. In the case of full data, our simulations show that the CG
method works best; it is very fast and robust. In the ill-posed case, the CG
method behaves unstably. Total variation regularization method (TV), in this
case, significantly improves the reconstruction quality.
|
1808.06176v1
|
2018-08-27
|
Landau damping of Alfvénic modes in stellarators
|
It is found that the presence of the so-called non-axisymmetric resonances of
wave-particle interaction in stellarators [which are associated with the lack
of axial symmetry of the magnetic configuration, Kolesnichenko et al., Phys.
Plasmas 9 (2002) 517] may have a strong stabilizing influence through Landau
mechanism on the Toroidicity-induced Alfv\'en Eigenmodes (TAE) and isomon modes
(Alfv\'enic modes with equal poloidal and toroidal mode numbers and frequencies
in the continuum region) destabilized by the energetic ions. These resonances
involve largest harmonics of the equilibrium magnetic field of stellarators and
lead to absorption of the mode energy by thermal ions in medium pressure
plasma, in which case the effect is large. On the other hand, at the high
pressure attributed to, e.g., a Helias reactor, thermal ions can interact also
with high frequency Alfv\'en gap modes [Helicity-induced Alfv\'en Eigenmodes
(HAE) and mirror-induced Alfv\'en Eigenmodes (MAE)], leading to a considerable
damping of these modes. Only resonances with passing particles are considered.
The developed theory is applied to various modes in the Wendelstein 7-X
stellarator and a Helias reactor, and to two TAE modes in the LHD helical
device.
|
1808.08862v1
|
2018-09-29
|
Uniform stabilization for the Klein-Gordon system in a inhomogeneous medium with locally distributed damping
|
We consider the Klein-Gordon system posed in an inhomogeneous medium with
smooth boundary subject to a local viscoelastic damping distributed around a
neighborhoodof the boundary according to the Geometric Control Condition. We
show that the energy of the system goes uniformly and exponentially to zero for
all initial data of finite energy taken in bounded sets of finite energy
phase-space. For this purpose, refined microlocal analysis arguments are
considered by exploiting ideas due to Burq and Gerard . By using sharp Carleman
estimates we prove a unique continuation property for coupled systems.
|
1810.00247v1
|
2018-10-09
|
Lévy-walk-like Langevin dynamics
|
Continuous time random walks and Langevin equations are two classes of
stochastic models for describing the dynamics of particles in the natural
world. While some of the processes can be conveniently characterized by both of
them, more often one model has significant advantages (or has to be used)
compared with the other one. In this paper, we consider the weakly damped
Langevin system coupled with a new subordinator|$\alpha$-dependent subordinator
with $1<\alpha<2$. We pay attention to the diffusion behaviour of the
stochastic process described by this coupled Langevin system, and find the
super-ballistic diffusion phenomena for the system with an unconfined potential
on velocity but sub-ballistic superdiffusion phenomenon with a confined
potential, which is like L\'{e}vy walk for long times. One can further note
that the two-point distribution of inverse subordinator affects mean square
displacement of this coupled weakly damped Langevin system in essential.
|
1810.04332v1
|
2018-10-18
|
Analysis of the controllability from the exterior of strong damping nonlocal wave equations
|
We make a complete analysis of the controllability properties from the
exterior of the (possible) strong damping wave equation with the fractional
Laplace operator subject to the nonhomogeneous Dirichlet type exterior
condition. In the first part, we show that if $0<s<1$, $\Omega\subset\RR^N$
($N\ge 1$) is a bounded Lipschitz domain and the parameter $\delta> 0$, then
there is no control function $g$ such that the following system
\begin{equation*} \begin{cases} u_{tt} + (-\Delta)^{s} u + \delta(-\Delta)^{s}
u_{t}=0 & \mbox{ in }\; \Omega\times(0,T),\\ u=g\chi_{\mathcal O\times (0,T)}
&\mbox{ in }\; (\Omc)\times (0,T) ,\\ u(\cdot,0) = u_0, u_t(\cdot,0) = u_1
&\mbox{ in }\; \Omega, \end{cases} \end{equation*} is exact or null
controllable at time $T>0$. In the second part, we prove that for every
$\delta\ge 0$ and $0<s<1$, the system is indeed approximately controllable for
any $T>0$ and $g\in \mathcal D(\mathcal O\times(0,T))$, where $\mathcal
O\subset\Omc$ is any non-empty open set.
|
1810.08060v1
|
2018-10-20
|
Memory-based mediated interactions between rigid particulate inclusions in viscoelastic environments
|
Many practically relevant materials combine properties of viscous fluids and
elastic solids to viscoelastic behavior. Our focus is on the induced dynamic
behavior of damped finite-sized particulate inclusions in such substances. We
explicitly describe history-dependent interactions that emerge between the
embedded particles. These interactions are mediated by the viscoelastic
surroundings. They result from the flows and distortions of the viscoelastic
medium when induced by the rigid inclusions. Both, viscoelastic environments of
terminal fluid-like flow or of completely reversible damped elastic behavior,
are covered. For illustration and to highlight the role of the formalism in
potential applications, we briefly address the relevant examples of dragging a
rigid sphere through a viscoelastic environment together with subsequent
relaxation dynamics, the switching dynamics of magnetic fillers in elastic gel
matrices, and the swimming behavior of active microswimmers in viscoelastic
solutions. The approach provides a basis for more quantitative and extended
investigations of these and related systems in the future.
|
1810.08832v1
|
2018-10-22
|
Dynamical instability towards finite-momentum pairing in quenched BCS superconducting phases
|
In this work we numerically investigate the fate of the
Bardeen-Cooper-Schrieffer (BCS) pairing in the presence of quenched phase under
Peierls substitution using time-dependent real space and momentum space
Bogoliubov-de Gennes equation methods and Anderson pseudospin representation
method. This kind of phase imprint can be realized by modulating electric field
in ultracold atoms and illumining of THz optical pump pulse in solids with
conventional and unconventional superconductors. In the case of weak phase
imprint, the BCS pairing is stable; while in the strong phase imprint,
instability towards finite-momentum pairing is allowed, in which the real space
and momentum space methods yield different results. In the pulsed gauge
potential, we find that this instability will not happen even with much
stronger vector potential. We also show that the uniform and staggered gauge
potentials yield different behaviors. While the staggered potential induces
transition from the BCS pairing to over-damped phase, the uniform gauge may
enhance the pairing and will not induce to the over-damped phase. These result
may shade light on the realization of finite momentum pairing, such as
Fulde-Ferrell-Larkin-Ovchinnikov phase with dynamical modulation.
|
1810.09125v1
|
2018-10-21
|
A note on a weakly coupled system of semi-linear visco-elastic damped $σ$-evolution models with different power nonlinearities and different $σ$ values
|
In this article, we prove the global (in time) existence of small data
solutions from energy spaces basing on $L^q$ spaces, with $q \in (1,\infty)$,
to the Cauchy problems for a weakly coupled system of semi-linear visco-elastic
damped $\sigma$-evolution models. Here we consider different power
nonlinearities and different $\sigma$ values in the comparison between two
single equations. To do this, we use $(L^m \cap L^q)- L^q$ and $L^q- L^q$
estimates, i.e., by mixing additional $L^m$ regularity for the data on the
basis of $L^q- L^q$ estimates for solutions, with $m \in [1,q)$, to the
corresponding linear Cauchy problems. In addition, allowing loss of decay and
the flexible choice of parameters $\sigma$, $m$ and $q$ bring some benefits to
relax the restrictions to the admissible exponents $p$.
|
1810.09664v1
|
2018-10-25
|
First-principles calculation of spin-orbit torque in a Co/Pt bilayer
|
The angular dependence of spin-orbit torque in a disordered Co/Pt bilayer is
calculated using a first-principles non-equilibrium Green's function formalism
with an explicit supercell averaging over Anderson disorder. In addition to the
usual dampinglike and fieldlike terms, the odd torque contains a sizeable
planar Hall-like term $(\mathbf{m\cdot
E})\mathbf{m}\times(\mathbf{z}\times\mathbf{m})$ whose contribution to
current-induced damping is consistent with experimental observations. The
dampinglike and planar Hall-like torquances depend weakly on disorder strength,
while the fieldlike torquance declines with increasing disorder. The torques
that contribute to damping are almost entirely due to spin-orbit coupling on
the Pt atoms, but the fieldlike torque does not require it.
|
1810.11003v2
|
2018-10-29
|
Optimal identification of non-Markovian environments for spin chains
|
Correlations of an environment are crucial for the dynamics of non-Markovian
quantum systems, which may not be known in advance. In this paper, we propose a
gradient algorithm for identifying the correlations in terms of time-varying
damping rate functions in a time-convolution-less master equation for spin
chains. By measuring time trace observables of the system, the identification
procedure can be formulated as an optimization problem. The gradient algorithm
is designed based on a calculation of the derivative of an objective function
with respect to the damping rate functions, whose effectiveness is shown in a
comparison to a differential approach for a two-qubit spin chain.
|
1810.11923v1
|
2018-10-29
|
Existence and uniqueness of dynamic evolutions for a one-dimensional debonding model with damping
|
In this paper we analyse a one-dimensional debonding model for a thin film
peeled from a substrate when viscosity is taken into account. It is described
by the weakly damped wave equation whose domain, the debonded region, grows
according to a Griffith's criterion. Firstly we prove that the equation admits
a unique solution when the evolution of the debonding front is assigned.
Finally we provide an existence and uniqueness result for the coupled problem
given by the wave equation together with Griffith's criterion.
|
1810.12006v3
|
2019-01-03
|
Calibration and Status of the 3D Imaging Calorimeter of DAMPE for Cosmic Ray Physics on Orbit
|
The DArk Matter Particle Explorer (DAMPE) developed in China was designed to
search for evidence of dark matter particles by observing primary cosmic rays
and gamma rays in the energy range from 5 GeV to 10 TeV. Since its launch in
December 2015, a large quantity of data has been recorded. With the data set
acquired during more than a year of operation in space, a precise
time-dependent calibration for the energy measured by the BGO ECAL has been
developed. In this report, the instrumentation and development of the BGO
Electromagnetic Calorimeter (BGO ECAL) are briefly described. The calibration
on orbit, including that of the pedestal, attenuation length, minimum ionizing
particle peak, and dynode ratio, is discussed, and additional details about the
calibration methods and performance in space are presented.
|
1901.00734v1
|
2019-01-08
|
Atom-only descriptions of the driven-dissipative Dicke model
|
We investigate how to describe the dissipative spin dynamics of the
driven-dissipative Dicke model, describing $N$ two-level atoms coupled to a
cavity mode, after adiabatic elimination of the cavity mode. To this end, we
derive a Redfield master equation which goes beyond the standard secular
approximation and large detuning limits. We show that the secular (or rotating
wave) approximation and the large detuning approximation both lead to
inadequate master equations, that fail to predict the Dicke transition or the
damping rates of the atomic dynamics. In contrast, the full Redfield theory
correctly predicts the phase transition and the effective atomic damping rates.
Our work provides a reliable framework to study the full quantum dynamics of
atoms in a multimode cavity, where a quantum description of the full model
becomes intractable.
|
1901.02473v2
|
2019-01-10
|
Stability and Controllability results for a Timoshenko system
|
In this paper, we study the indirect boundary stability and exact
controllability of a one-dimensional Timoshenko system. In the first part of
the paper, we consider the Timoshenko system with only one boundary fractional
damping. We first show that the system is strongly stable but not uniformly
stable. Hence, we look for a polynomial decay rate for smooth initial data.
Using frequency domain arguments combined with the multiplier method, we prove
that the energy decay rate depends on coefficients appearing in the PDE and on
the order of the fractional damping. Moreover, under the equal speed
propagation condition, we obtain the optimal polynomial energy decay rate. In
the second part of this paper, we study the indirect boundary exact
controllability of the Timoshenko system with mixed Dirichlet-Neumann boundary
conditions and boundary control. Using non-harmonic analysis, we first
establish a weak observability inequality, which depends on the ratio of the
waves propagation speeds. Next, using the HUM method, we prove that the system
is exactly controllable in appropriate spaces and that the control time can be
small.
|
1901.03303v2
|
2019-01-13
|
Dueling Dynamical Backaction in a Cryogenic Optomechanical Cavity
|
Dynamical backaction has proven to be a versatile tool in cavity
optomechanics, allowing for precise manipulation of a mechanical resonator's
motion using confined optical photons. In this work, we present measurements of
a silicon whispering-gallery-mode optomechanical cavity where backaction
originates from opposing radiation pressure and photothermal forces, with the
former dictating the optomechanical spring effect and the latter governing the
optomechanical damping. At high enough optical input powers, we show that the
photothermal force drives the mechanical resonator into self-oscillations for a
pump beam detuned to the lower-frequency side of the optical resonance,
contrary to what one would expect for a radiation-pressure-dominated
optomechanical device. Using a fully nonlinear model, we fit the hysteretic
response of the optomechanical cavity to extract its properties, demonstrating
that this non-sideband-resolved device exists in a regime where photothermal
damping could be used to cool its motion to the quantum ground state.
|
1901.03950v1
|
2019-01-22
|
Coupling between superfluid neutrons and superfluid protons in the elementary excitations of neutron star matter
|
Several phenomena occurring in neutron stars are affected by the elementary
excitations that characterize the stellar matter. In particular, low-energy
excitations can play a major role in the emission and propagation of neutrinos,
neutron star cooling and transport processes. In this paper, we consider the
elementary modes in the star region where both proton and neutron components
are superfluid.
We study the overall spectral functions of protons, neutrons and electrons on
the basis of the Coulomb and nuclear interactions.
This study is performed in the framework of the Random Phase Approximation,
generalized to superfluid systems. The formalism we use ensures that the
Generalized Ward's Identities are satisfied. We focus on the coupling between
neutrons and protons. On one hand this coupling results in collective modes
that involve simultaneously neutrons and protons, on the other hand it produces
a damping of the excitations. Both effects are especially visible in the
spectral functions of the different components of the matter. At high density
while the neutrons and protons tend to develop independent excitations, as
indicated by the spectral functions, the neutron-proton coupling still produces
a strong damping of the modes.
|
1901.07550v1
|
2019-03-30
|
Uncertainty damping in kinetic traffic models by driver-assist controls
|
In this paper, we propose a kinetic model of traffic flow with uncertain
binary interactions, which explains the scattering of the fundamental diagram
in terms of the macroscopic variability of aggregate quantities, such as the
mean speed and the flux of the vehicles, produced by the microscopic
uncertainty. Moreover, we design control strategies at the level of the
microscopic interactions among the vehicles, by which we prove that it is
possible to dampen the propagation of such an uncertainty across the scales.
Our analytical and numerical results suggest that the aggregate traffic flow
may be made more ordered, hence predictable, by implementing such control
protocols in driver-assist vehicles. Remarkably, they also provide a precise
relationship between a measure of the macroscopic damping of the uncertainty
and the penetration rate of the driver-assist technology in the traffic stream.
|
1904.00257v2
|
2019-04-01
|
Reduction of Kinetic Equations to Liénard-Levinson-Smith Form: Counting Limit Cycles
|
We have presented an unified scheme to express a class of system of equations
in two variables into a Li\'enard-Levinson-Smith (LLS) oscillator form. We have
derived the condition for limit cycle with special reference to Rayleigh and
Li\'enard systems for arbitrary polynomial functions of damping and restoring
force. Krylov-Boguliubov (K-B) method is implemented to determine the maximum
number of limit cycles admissible for a LLS oscillator atleast in the weak
damping limit. Scheme is illustrated by a number of model systems with single
cycle as well as the multiple cycle cases.
|
1904.00604v2
|
2019-04-02
|
Stability of the interface of an isotropic active fluid
|
We study the linear stability of an isotropic active fluid in three different
geometries: a film of active fluid on a rigid substrate, a cylindrical thread
of fluid, and a spherical fluid droplet. The active fluid is modeled by the
hydrodynamic theory of an active nematic liquid crystal in the isotropic phase.
In each geometry, we calculate the growth rate of sinusoidal modes of
deformation of the interface. There are two distinct branches of growth rates;
at long wavelength, one corresponds to the deformation of the interface, and
one corresponds to the evolution of the liquid crystalline degrees of freedom.
The passive cases of the film and the spherical droplet are always stable. For
these geometries, a sufficiently large activity leads to instability. Activity
also leads to propagating damped or growing modes. The passive cylindrical
thread is unstable for perturbations with wavelength longer than the
circumference. A sufficiently large activity can make any wavelength unstable,
and again leads to propagating damped or growing modes.
|
1904.01558v1
|
2019-04-04
|
Shear viscosity of classical fields in scalar theory
|
We investigate the shear viscosity of massless classical scalar fields in the
$\phi^4$ theory on a lattice by using the Green-Kubo formula. Based on the
scaling property of the classical field, the shear viscosity is represented
using a scaling function. Equilibrium expectation value of the time-correlation
function of the energy-momentum tensor is evaluated as the ensemble average of
the classical field configurations, whose time evolution is obtained by solving
the classical equation of motion starting from the initial condition in thermal
equilibrium. It is found that there are two distinct damping time scales in the
time-correlation function, which is found to show damped oscillation behavior
in the early stage around a slow monotonous decay with an exponential form, and
the slow decay part is found to dominate the shear viscosity in the massless
classical field theory. This kind of slow decay is also known to exist in the
molecular dynamics simulation, then it may be a generic feature of dense
matter.
|
1904.02419v3
|
2019-04-08
|
Study of Decoherence in Quantum Computers: A Circuit-Design Perspective
|
Decoherence of quantum states is a major hurdle towards scalable and reliable
quantum computing. Lower decoherence (i.e., higher fidelity) can alleviate the
error correction overhead and obviate the need for energy-intensive noise
reduction techniques e.g., cryogenic cooling. In this paper, we performed a
noise-induced decoherence analysis of single and multi-qubit quantum gates
using physics-based simulations. The analysis indicates that (i) decoherence
depends on the input state and the gate type. Larger number of $|1\rangle$
states worsen the decoherence; (ii) amplitude damping is more detrimental than
phase damping; (iii) shorter depth implementation of a quantum function can
achieve lower decoherence. Simulations indicate 20\% improvement in the
fidelity of a quantum adder when realized using lower depth topology. The
insights developed in this paper can be exploited by the circuit designer to
choose the right gates and logic implementation to optimize the system-level
fidelity.
|
1904.04323v1
|
2019-04-23
|
A novel undamped gapless plasmon mode in tilted type-II Dirac semimetal
|
We predict the existence of a novel long-lived gapless plasmon mode in a
type-II Dirac semimetal (DSM). This gapless mode arises from the out-of-phase
oscillations of the density fluctuations in the electron and the hole pockets
of a type-II DSM. It originates beyond a critical wave-vector along the
direction of the tilt axis, owing to the momentum separation of the electron
and hole pockets. A similar out-of-phase plasmon mode arises in other
multi-component charged fluids as well, but generally it is Landau damped and
lies within the particle-hole continuum. In the case of a type-II DSM, the open
Fermi surface prohibits low-energy finite momentum single-particle excitations,
creating a `gap' in the particle-hole continuum. The gapless plasmon mode lies
within this particle-hole continuum gap and, thus, it is protected from Landau
damping.
|
1904.10137v1
|
2019-04-25
|
Interplay between nonclassicality and $\mathcal{PT}$ symmetry in an effective two level system with open system effects
|
A three level atom in $\Lambda$ configuration is reduced to an effective two
level system, under appropriate conditions, and its $\mathcal{PT}$ symmetric
properties are investigated. This effective qubit system when subjected to a
beam-splitter type of interaction, it provides the scope of directly
(indirectly) probing the nonclassical properties of the output (input) state.
Here, we study nonclassical properties of the output state by using some well
known measures of nonclassical correlations like the measurement induced
disturbance, concurrence and negativity. The nonclassical features are found to
enhance in the $\mathcal{PT}$ symmetric (PTS) phase compared to the
$\mathcal{PT}$ symmetry broken (PTSB) phase. Further, the output ports of the
beam-splitter are subjected to different quantum noise channels, both
non-Markovian, e.g., random telegraph noise as well as Markovian, e.g., phase
damping, and amplitude damping noise. The application of noise channels is
found to decrease the degree of nonclassicality, though continuing to exhibit
distinct behavior in PTS and PTSB phases, with the dominant behavior appearing
in the former case.
|
1904.11181v1
|
2019-04-30
|
A Self-Adaptive Contractive Algorithm for Enhanced Dynamic Phasor Estimation
|
In this paper, a self-adaptive contractive (SAC) algorithm is proposed for
enhanced dynamic phasor estimation in the diverse operating conditions of
modern power systems. At a high-level, the method is composed of three stages:
parameter shifting, filtering and parameter unshifting. The goal of the first
stage is to transform the input signal phasor so that it is approximately
mapped to nominal conditions. The second stage provides estimates of the
phasor, frequency, rate of change of frequency (ROCOF), damping and rate of
change of damping (ROCOD) of the parameter shifted phasor by using a
differentiator filter bank (DFB). The final stage recovers the original signal
phasor parameters while rejecting misleading estimates. The most important
features of the algorithm are that it offers convergence guarantees in a set of
desired conditions, and also great harmonic rejection. Numerical examples,
including the IEEE C37.118.1 standard tests with realistic noise levels, as
well as fault conditions, validate the proposed algorithm.
|
1904.13328v1
|
2019-06-04
|
High frequency voltage-induced ferromagnetic resonance in magnetic tunnel junctions
|
Voltage-induced ferromagnetic resonance (V-FMR) in magnetic tunnel junctions
(MTJs) with a W buffer is investigated. Perpendicular magnetic anisotropy (PMA)
energy is controlled by both thickness of a CoFeB free layer deposited directly
on the W buffer and a post-annealing process at different temperatures. The PMA
energy as well as the magnetization damping are determined by analysing
field-dependent FMR signals in different field geometries. An optimized MTJ
structure enabled excitation of V-FMR at frequencies exceeding 30 GHz. The
macrospin modelling is used to analyse the field- and angular-dependence of the
V-FMR signal and to support experimental magnetization damping extraction.
|
1906.01301v1
|
2019-06-04
|
Late time approach to Hawking radiation: terms beyond leading order
|
Black hole evaporation is studied using wave packets for the modes. These
allow for approximate frequency and time resolution. The leading order late
time behavior gives the well known Hawking radiation that is independent of how
the black hole formed. The focus here is on the higher order terms and the rate
at which they damp at late times. Some of these terms carry information about
how the black hole formed. A general argument is given which shows that the
damping is significantly slower (power law) than what might be naively expected
from a stationary phase approximation (exponential). This result is verified by
numerical calculations in the cases of 2D and 4D black holes that form from the
collapse of a null shell.
|
1906.01735v2
|
2019-06-20
|
Time-sliced perturbation theory with primordial non-Gaussianity and effects of large bulk flows on inflationary oscillating features
|
We extend the formalism of time-sliced perturbation theory (TSPT) for
cosmological large-scale structure to include non-Gaussian initial conditions.
We show that in such a case the TSPT interaction vertices acquire new
contributions whose time-dependence factorizes for the Einstein-de Sitter
cosmology. The new formulation is free from spurious infrared (IR) enhancements
and reveals a clear IR structure of non-Gaussian vertices. We use the new
technique to study the evolution of oscillating features in primordial
statistics and show that they are damped due to non-linear effects of large
bulk flows. We derive the damping factors for the oscillating primordial power
spectrum and bispectrum by means of a systematic IR resummation of relevant
Feynman diagrams.
|
1906.08697v2
|
2019-06-21
|
Exponential damping induced by random and realistic perturbations
|
Given a quantum many-body system and the expectation-value dynamics of some
operator, we study how this reference dynamics is altered due to a perturbation
of the system's Hamiltonian. Based on projection operator techniques, we unveil
that if the perturbation exhibits a random-matrix structure in the eigenbasis
of the unperturbed Hamiltonian, then this perturbation effectively leads to an
exponential damping of the original dynamics. Employing a combination of
dynamical quantum typicality and numerical linked cluster expansions, we
demonstrate that our theoretical findings for random matrices can, in some
cases, be relevant for the dynamics of realistic quantum many-body models as
well. Specifically, we study the decay of current autocorrelation functions in
spin-$1/2$ ladder systems, where the rungs of the ladder are treated as a
perturbation to the otherwise uncoupled legs. We find a convincing agreement
between the exact dynamics and the lowest-order prediction over a wide range of
interchain couplings.
|
1906.09268v2
|
2019-06-27
|
Fast control of dissipation in a superconducting resonator
|
We report on fast tunability of an electromagnetic environment coupled to a
superconducting coplanar waveguide resonator. Namely, we utilize a
recently-developed quantum-circuit refrigerator (QCR) to experimentally
demonstrate a dynamic tunability in the total damping rate of the resonator up
to almost two orders of magnitude. Based on the theory it corresponds to a
change in the internal damping rate by nearly four orders of magnitude. The
control of the QCR is fully electrical, with the shortest implemented operation
times in the range of 10 ns. This experiment constitutes a fast active reset of
a superconducting quantum circuit. In the future, a similar scheme can
potentially be used to initialize superconducting quantum bits.
|
1906.11519v1
|
2019-06-28
|
Ground-state cooling of an magnomechanical resonator induced by magnetic damping
|
Quantum manipulation of mechanical resonators has been widely applied in
fundamental physics and quantum information processing. Among them, cooling the
mechanical system to its quantum ground state is regarded as a key step. In
this work, we propose a scheme which one can realize ground-state cooling of
resonator in a cavity magnomechanical system. The system consists of a
microwave cavity and a small ferromagnetic sphere, in which phonon-magnon
coupling and cavity photon-magnon coupling can be achieved via magnetostrictive
interaction and magnetic dipole interaction, respectively. After adiabatically
eliminating the cavity mode, an effective Hamiltonian which consists of magnon
and mechanical modes is obtained. Within experimentally feasible parameters, we
demonstrate that the ground-state cooling of the magnomechanical resonator can
be achieved by extra magnetic damping. Unlike optomechanical cooling,
magnomechanical interaction is utilized to realize the cooling of resonators.
We further illustrate the ground-state cooling can be effectively controlled by
the external magnetic field.
|
1906.12081v1
|
2019-06-30
|
Non-linear spin torque, pumping and cooling in superconductor/ferromagnet systems
|
We study the effects of the coupling between magnetization dynamics and the
electronic degrees of freedom in a heterostructure of a metallic nanomagnet
with dynamic magnetization coupled with a superconductor containing a steady
spin-splitting field. We predict how this system exhibits a non-linear spin
torque, which can be driven either with a temperature difference or a voltage
across the interface. We generalize this notion to arbitrary magnetization
precession by deriving a Keldysh action for the interface, describing the
coupled charge, heat and spin transport in the presence of a precessing
magnetization. We characterize the effect of superconductivity on the
precession damping and the anti-damping torques. We also predict the full
non-linear characteristic of the Onsager counterparts of the torque, showing up
via pumped charge and heat currents. For the latter, we predict a spin-pumping
cooling effect, where the magnetization dynamics can cool either the nanomagnet
or the superconductor.
|
1907.00424v2
|
2019-07-03
|
Wave-ice interaction in the North-West Barents Sea
|
The results of field work on drift ice during wave propagation are analyzed
and presented. The field work was performed in the Barents Sea, and the main
focus of the paper is on wave processes in the MIZ. A model of wave damping in
broken ice is formulated and applied to interpret the field work results. It is
confirmed that waves of higher frequencies are subjected to stronger damping
when they propagate below the ice. This reduces the frequency of most energetic
wave with increasing distance from the ice edge. Difference of wave spectra
measured in two relatively close locations within the MIZ is discussed. The
complicated geometry and dynamics of the MIZ in the North-West Barents Sea
allow waves from the Atlantic Ocean and south regions of the Barents Sea to
penetrate into different locations of the MIZ.
|
1907.02032v1
|
2019-07-03
|
Anisotropy of spin-transfer torques and Gilbert damping induced by Rashba coupling
|
Spin-transfer torques (STT), Gilbert damping (GD), and effective spin
renormalization (ESR) are investigated microscopically in a 2D Rashba
ferromagnet with spin-independent Gaussian white-noise disorder. Rashba
spin-orbit coupling induced anisotropy of these phenomena is thoroughly
analysed. For the case of two partly filled spin subbands, a remarkable
relation between the anisotropic STT, GD, and ESR is established. In the
absence of magnetic field and other torques on magnetization, this relation
corresponds to a current-induced motion of a magnetic texture with the
classical drift velocity of conduction electrons. Finally, we compute spin
susceptibility of the system and generalize the notion of spin-polarized
current.
|
1907.02041v3
|
2019-07-05
|
Nesterov's acceleration and Polyak's heavy ball method in continuous time: convergence rate analysis under geometric conditions and perturbations
|
In this article a family of second order ODEs associated to inertial gradient
descend is studied. These ODEs are widely used to build trajectories converging
to a minimizer $x^*$ of a function $F$, possibly convex. This family includes
the continuous version of the Nesterov inertial scheme and the continuous heavy
ball method. Several damping parameters, not necessarily vanishing, and a
perturbation term $g$ are thus considered. The damping parameter is linked to
the inertia of the associated inertial scheme and the perturbation term $g$ is
linked to the error that can be done on the gradient of the function $F$. This
article presents new asymptotic bounds on $F(x(t))-F(x^*)$ where $x$ is a
solution of the ODE, when $F$ is convex and satisfies local geometrical
properties such as {\L}ojasiewicz properties and under integrability conditions
on $g$. Even if geometrical properties and perturbations were already studied
for most ODEs of these families, it is the first time they are jointly studied.
All these results give an insight on the behavior of these inertial and
perturbed algorithms if $F$ satisfies some {\L}ojasiewicz properties especially
in the setting of stochastic algorithms.
|
1907.02710v1
|
2019-07-08
|
Role of Toll-Like Receptors in the interplay between pathogen and damage associated molecular patterns
|
Various theoretical studies have been carried out to infer relevant
protein-protein interactions among pathogens and their hosts. Such studies are
generally based on preferential attachment of bacteria / virus to their human
receptor homologs. We have analyzed 17 pathogenic species mainly belonging to
bacterial and viral pathogenic classes, with the aim to identify the
interacting human proteins which are targeted by both bacteria and virus
specifically. Our study reveals that the TLRs play a crucial role between the
pathogen-associated molecular patterns (PAMPs) and the damage associated
molecular patterns (DAMPS). PAMPs include bacterial lipopolysaccharides (LPs),
endotoxins, bacterial flagellin, lipoteichoic acid, peptidoglycan in bacterial
organisms and nucleic acid variants associated with viral organisms, whereas
DAMPs are associated with host biomolecules that perpetuate non-infectious
inflammatory responses. We found out the presence of SOD1 and SOD2 (superoxide
dismutase) is crucial, as it acts as an anti-oxidant and helps in eliminating
oxidative stress by preventing damage from reactive oxygen species. Hence, such
strategies can be used as new therapies for anti-inflammatory diseases with
significant clinical outcomes.
|
1907.03512v1
|
2019-07-15
|
Alternating Direction Method of Multipliers (ADMMs) Based Distributed Approach For Wide-Area Control
|
In this paper, an alternating direction method of multipliers based novel
distributed wide-area control architecture is proposed for damping the
interarea oscillations. In this approach, first, an interconnected power system
is divided into areas based on coherency grouping. Second, local processors are
assigned on each area that estimate a black-box transfer function model based
on Lagrange multipliers using measurements. These local area processors are
then used to estimate a global transfer function model of the power system
based on a consensus algorithm through a global processor. After convergence, a
transfer function residue corresponding to the interarea mode of interest is
derived, to determine optimal wide area control loop. Finally, a wide-area
damping controller is designed based on this information. The efficacy of the
controller is validated using two area and IEEE-39 bus test systems on
RTDS/RSCAD and MATLAB cosimulation platform.
|
1907.06340v1
|
2019-07-16
|
Coherency and Online Signal Selection Based Wide Area Control of Wind Integrated Power Grid
|
This paper introduces a novel method of designing wide area control (WAC)
based on a discrete linear quadratic regulator and Kalman filtering based
state-estimation that can be applied for real-time damping of interarea
oscillations of wind integrated power grid. The main advantages of the proposed
method are that the architecture provides online coherency grouping that
properly characterizes real-time changes in the power grid and online wide-area
signal selection based on residue method for proper selection of the WAC
signals. The proposed architecture can, thus, accurately monitors changes in
the power grid and select the appropriate control signal for more effectively
damping the interarea oscillation when compared to the conventional local
signal based power system stabilizers or offline based WAC designs. The
architecture is tested on a wind integrated two-area system and the IEEE 39 bus
system in order to show the capability of the proposed method.
|
1907.06846v1
|
2019-07-20
|
Magnon Bose-Einstein condensate and supercurrents over a wide temperature range
|
Magnon Bose-Einstein Condensates (BECs) and supercurrents are coherent
quantum phenomena, which appear on a macroscopic scale in parametrically
populated solid state spinsystems. One of the most fascinating and attractive
features of these processes is the possibility of magnon condensation and
supercurrent excitation even at room temperature. At the same time, valuable
information about a magnon BEC state, such as its lifetime, its formation
threshold, and coherency, is provided by experiments at various temperatures.
Here, we use Brillouin Light Scattering (BLS) spectroscopy for the
investigation of the magnon BEC dynamics in a single-crystal film of yttrium
iron garnet in a wide temperature range from 30 K to 380 K. By comparing the
BLS results with previous microwave measurements, we re-vealed the direct
relation between the damping of the condensed and the parametrically injected
magnons. The enhanced supercurrent dynamics was detected at 180 K near the
minimum of BEC damping.
|
1907.08805v1
|
2019-07-21
|
Explaining Retrocausality Phenomena in Quantum Mechanics using a Modified Variational Principle
|
A modified lagrangian with causal and retrocausal momenta was used to derive
a first causal wave equation and a second retrocausal wave equation using the
principle of least action. The retrocausal wave function obtained through this
method was found to be equivalent to the complex conjugate of the causal wave
function, thus leading to the conclusion that a retrocausal effect is already
implicit in quantum mechanics through the means of complex conjugation of the
wave function when computing the probability density for a particle. Lastly,
the same variational principle was employed with a fractionary langriangian,
(that is, containing fractional Riemann derivatives) to obtain a pair of
modified wave equations, one causal and other retrocausal, both of which
correspond to the differential equation of a damped oscillator in the free
particle (potential energy V=0) case. The solutions of this damped wave
equations remain to be explored.
|
1907.09688v3
|
2019-07-23
|
Global wellposedness to the $n$-dimensional compressible Oldroyd-B model without damping mechanism
|
The Cauchy problem of the compressible Oldroyd-B model without damping
mechanism in R^n$ with $n\ge2$ is considered. The lack of dissipation in
density and stress tensor in the model is compensated by exploiting an
intrinsic structure and introducing new quantities between density, velocity
and stress tensor. Therefore, global solutions to the system with small initial
data in critical Besov spaces are obtained. As a byproduct, optimal time decay
rates of the solutions are derived by using an energy estimation argument. The
results remain valid for the compressible viscoelastic system without the
`div-curl structure assumption and thus improve those given by Hu and Wang [ J.
Differential Equations, {\bf 250}, 1200--1231, 2011] and Qian and Zhang [Arch.
Ration. Mech. Anal., {\bf 198}, 835--868, 2010].
|
1907.09829v3
|
2019-10-02
|
Exponential stability for the nonlinear Schrödinger equation with locally distributed damping
|
In this paper, we study the defocusing nonlinear Schr\"{o}dinger equation
with a locally distributed damping on a smooth bounded domain as well as on the
whole space and on an exterior domain. We first construct approximate solutions
using the theory of monotone operators. We show that approximate solutions
decay exponentially fast in the $L^2$-sense by using the multiplier technique
and a unique continuation property. Then, we prove the global existence as well
as the $L^2$-decay of solutions for the original model by passing to the limit
and using a weak lower semicontinuity argument, respectively. The distinctive
feature of the paper is the monotonicity approach, which makes the analysis
independent from the commonly used Strichartz estimates and allows us to work
without artificial smoothing terms inserted into the main equation. We, in
addition, implement a precise and efficient algorithm for studying the
exponential decay established in the first part of the paper numerically. Our
simulations illustrate the efficacy of the proposed control design.
|
1910.00921v1
|
2019-10-07
|
Quantum mechanics at high redshift -- Modelling Damped Lyman-$α$ absorption systems
|
For around 100 years, hydrogen spectral modelling has been based on Voigt
profile fitting. The semi-classical Voigt profile is based on a 2-level atom
approximation. Whilst the Voigt profile is excellent for many circumstances,
the accuracy is insufficient for very high column density damped Lyman-$\alpha$
absorption systems. We have adapted the quantum-mechanical Kramers-Heisenberg
model to include thermal broadening, producing a new profile, the KHT profile.
Interactions involving multiple discrete atomic levels and continuum terms, not
accounted for in the Voigt model, generate asymmetries in the Lyman line wings.
If not modelled, this can lead to significant systematics in parameter
estimation when modelling real data. There are important ramifications in
particular for measurements of the primordial deuterium abundance. However, the
KHT model is complicated. We therefore present a simplified formulation based
on Taylor series expansions and look-up tables, quantifying the impact of the
approximations made. The KHT profile has been implemented within the
widely-used VPFIT code.
|
1910.02913v2
|
2019-10-12
|
Almost Global Solutions to the Three-dimensional Isentropic Inviscid Flows with Damping in Physical Vacuum Around Barenlatt Solutions
|
For the three-dimensional vacuum free boundary problem with physical
singularity that the sound speed is $C^{ {1}/{2}}$-H$\ddot{\rm o}$lder
continuous across the vacuum boundary of the compressible Euler equations with
damping, without any symmetry assumptions, we prove the almost global existence
of smooth solutions when the initial data are small perturbations of the
Barenblatt self-similar solutions to the corresponding porous media equations
simplified via Darcy's law. It is proved that if the initial perturbation is of
the size of $\epsilon$, then the existing time for smooth solutions is at least
of the order of $\exp(\epsilon^{-2/3})$. The key issue for the analysis is the
slow {\em sub-linear} growth of vacuum boundaries of the order of
$t^{1/(3\gamma-1)}$, where $\gamma>1$ is the adiabatic exponent for the gas.
This is in sharp contrast to the currently available global-in-time existence
theory of expanding solutions to the vacuum free boundary problems with
physical singularity of compressible Euler equations for which the expanding
rate of vacuum boundaries is linear. The results obtained in this paper is
closely related to the open question in multiple dimensions since T.-P. Liu's
construction of particular solutions in 1996 .
|
1910.05516v1
|
2019-10-15
|
Nonlocal quantum correlations under amplitude damping decoherence
|
Different nonlocal quantum correlations of entanglement, steering and Bell
nonlocality are defined with the help of local hidden state (LHS) and local
hidden variable (LHV) models. Considering their unique roles in quantum
information processing, it is of importance to understand the individual
nonlocal quantum correlation as well as their relationship. Here, we
investigate the effects of amplitude damping decoherence on different nonlocal
quantum correlations. In particular, we have theoretically and experimentally
shown that the entanglement sudden death phenomenon is distinct from those of
steering and Bell nonlocality. In our scenario, we found that all the initial
states present sudden death of steering and Bell nonlocality, while only some
of the states show entanglement sudden death. These results suggest that the
environmental effect can be different for different nonlocal quantum
correlations, and thus, it provides distinct operational interpretations of
different quantum correlations.
|
1910.06483v1
|
2019-10-17
|
The linearly damped nonlinear Schrödinger equation with localized driving: spatiotemporal decay estimates and the emergence of extreme wave events
|
We prove spatiotemporal algebraically decaying estimates for the density of
the solutions of the linearly damped nonlinear Schr\"odinger equation with
localized driving, when supplemented with vanishing boundary conditions. Their
derivation is made via a scheme, which incorporates suitable weighted Sobolev
spaces and a time-weighted energy method. Numerical simulations examining the
dynamics (in the presence of physically relevant examples of driver types and
driving amplitude/linear loss regimes), showcase that the suggested decaying
rates, are proved relevant in describing the transient dynamics of the
solutions, prior their decay: they support the emergence of waveforms
possessing an algebraic space-time localization (reminiscent of the Peregrine
soliton) as first events of the dynamics, but also effectively capture the
space-time asymptotics of the numerical solutions.
|
1910.08425v2
|
2019-10-24
|
Gapless and gapped holographic phonons
|
We study a holographic model where translations are both spontaneously and
explicitly broken, leading to the presence of (pseudo)-phonons in the spectrum.
The weak explicit breaking is due to two independent mechanisms: a small source
for the condensate itself and additional linearly space-dependent marginal
operators. The low energy dynamics of the model is described by Wigner crystal
hydrodynamics. In absence of a source for the condensate, the phonons remain
gapless, but momentum is relaxed. Turning on a source for the condensate damps
and pins the phonons. Finally, we verify that the universal relation between
the phonon damping rate, mass and diffusivity reported in arXiv:1812.08118
continues to hold in this model for weak enough explicit breaking.
|
1910.11330v2
|
2019-12-02
|
Boundary input-to-state stabilization of a damped Euler-Bernoulli beam in the presence of a state-delay
|
This paper is concerned with the point torque boundary feedback stabilization
of a damped Euler-Bernoulli beam model in the presence of a time-varying
state-delay. First, a finite-dimensional truncated model is derived by spectral
reduction. Then, for a given stabilizing state-feedback of the delay-free
truncated model, an LMI-based sufficient condition on the maximum amplitude of
the state-delay is employed to guarantee the stability of the closed-loop
state-delayed truncated model. Second, we assess the exponential stability of
the resulting closed-loop infinite-dimensional system under the assumption that
the number of modes of the original infinite-dimensional system captured by the
truncated model has been selected large enough. Finally, we consider in our
control design the possible presence of a distributed perturbation, as well as
additive boundary perturbations in the control inputs. In this case, we derive
for the closed-loop system an exponential input-to-state estimate with fading
memory of the distributed and boundary disturbances.
|
1912.01117v1
|
2019-12-03
|
The noise fluxes produced by the degree of first-order temporal coherence in a single mode class-A laser amplifier
|
The noise feature of a single mode class-A laser is investigated in the
presence (amplifier) and absence (free-running) of an input signal. The
Maxwell-Bloch equations of motion have been solved after adding the cavity
Langevin force to calculate fluctuations that imposed to the atomic population
inversion and the amplitude and phase of cavity electric field. The correlation
function of these fluctuations is then used to derive the spontaneous emission,
amplitude, and phase noise fluxes in the below and above-threshold states. The
bandwidth of noise fluxes is not only adjusted by the amplitude and frequency
detuning of input signal, but also by the laser pumping and cavity damping
rates. On the other hand, the degree of first-order temporal coherence (DFOTC)
is turned out as the correlation function of the amplitude fluctuation so that
its Fourier transform led to the amplitude noise flux. The coherence time plays
a dual role in order that it is equal to the damping rate invers of DFOTC and
at the same time has an uncertainty relation with the bandwidth of amplitude
noise flux. Finally, the flux conservation requires a balance between the input
pumping noise flux and the output amplitude and spontaneous emission noise
fluxes.
|
1912.01485v1
|
2019-12-05
|
A Fast Implementation for the Canonical Polyadic Decomposition
|
A new implementation of the canonical polyadic decomposition (CPD) is
presented. It features lower computational complexity and memory usage than the
available state of art implementations available. The CPD of tensors is a
challenging problem which has been approached in several manners. Alternating
least squares algorithms were used for a long time, but they convergence
properties are limited. Nonlinear least squares (NLS) algorithms - more
precisely, damped Gauss-Newton (dGN) algorithms - are much better in this
sense, but they require inverting large Hessians, and for this reason there is
just a few implementations using this approach. In this paper, we propose a
fast dGN implementation to compute the CPD. In this paper, we make the case to
always compress the tensor, and propose a fast damped Gauss-Newton
implementation to compute the canonical polyadic decomposition.
|
1912.02366v1
|
2019-12-05
|
Damping of spinful excitons in LaCoO$_3$ by thermal fluctuations: Theory and experiment
|
We present Co $L_3$-edge resonant inelastic x-ray scattering (RIXS) of bulk
LaCoO$_3$ across the thermally-induced spin-state crossover around 100~K. Owing
to a high energy resolution of 25~meV, we observe unambiguously the dispersion
of the intermediate-spin (IS) excitations in the low temperature regime.
Approaching the intermediate temperature regime, the IS excitations are damped
and the bandwidth is reduced. The observed behavior can be well described by a
model of mobile IS excitons with strong attractive interaction, which we solve
using dynamical mean-field theory for hard-core bosons. Our results provide a
detailed mechanism of how high-spin (HS) and IS excitations interact to
establish the physical properties of cobaltite perovskites.
|
1912.02564v3
|
2019-12-09
|
High Frequency Sound in a Unitary Fermi Gas
|
We present an experimental and theoretical study of the phonon mode in a
unitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation
spectra at a momentum of approximately half the Fermi momentum, both above and
below the superfluid critical temperature $T_\mathrm{c}$. Below $T_\mathrm{c}$,
the dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by
gradients in the phase of the superfluid order parameter. The temperature
dependence of the BA phonon is consistent with a theoretical model based on the
quasiparticle random phase approximation in which the dominant damping
mechanism is via collisions with thermally excited quasiparticles. As the
temperature is increased above $T_\mathrm{c}$, the phonon evolves into a
strongly damped collisional mode, accompanied by an abrupt increase in spectral
width. Our study reveals strong similarities between sound propagation in the
unitary Fermi gas and liquid helium.
|
1912.03830v1
|
2019-12-11
|
Quasinormal Modes of Charged Fields in Reissner-Nordstrom Backgrounds by Borel-Pade Summation of Bender-Wu Series
|
We extend recent work of Hatsuda on the computation of quasinormal mode
frequencies via analytic continuation of bound state energies and Borel-Pade
resummation of the Bender-Wu perturbation series to the case of charged fields
in the background of Reissner-Nordstrom black holes. We compare the quasinormal
mode frequencies obtained in this manner to calculations using Leaver's method
of continued fractions, and find good agreement for damped modes (DMs) with
imaginary part remaining finite in the extremal limit. We also present
numerical evidence that the frequencies of certain zero-damped modes (ZDMs)
with imaginary part tending to zero in the extremal limit can be computed when
constructing the Bender-Wu expansion about a peak of the potential inside the
outer horizon of the black hole.
|
1912.05553v2
|
2019-12-19
|
On twin peak quasi-periodic oscillations resulting from the interaction between discoseismic modes and turbulence in accretion discs around black holes
|
Given the peculiar and (in spite of many efforts) unexplained quasi-periodic
oscillation (QPO) twin peak phenomena in accretion disc PSD observations, the
present exploratory analytical article tries to inquire deeper into the
relationship between discoseismic modes and the underlying driving turbulence
in order to assess its importance. We employ a toy model in the form of a
Gaussian white noise driven damped harmonic oscillator with stochastic
frequency. This oscillator represents the discoseismic mode. (Stochastic
damping was also considered, but interestingly found to be less relevant for
the case at hand.) In the context of this model, we find that turbulence
interacts with disc oscillations in interesting ways. In particular, the
stochastic part in the oscillator frequency behaves as a separate driving
agent. This gives rise to 3:2 twin peaks for some values of the physical
parameters, which we find. We conclude with the suggestion that the study of
turbulence be brought to the forefront of disc oscillation dynamics, as opposed
to being a mere background feature. This change of perspective carries
immediate observable consequences, such as considerably shifting the values of
the (discoseismic) oscillator frequencies.
|
1912.09527v1
|
2019-12-28
|
Non-linear damping of superimposed primordial oscillations on the matter power spectrum in galaxy surveys
|
Galaxy surveys are an important probe for superimposed oscillations on the
primordial power spectrum of curvature perturbations, which are predicted in
several theoretical models of inflation and its alternatives. In order to
exploit the full cosmological information in galaxy surveys it is necessary to
study the matter power spectrum to fully non-linear scales. We therefore study
the non-linear clustering in models with superimposed linear and logarithmic
oscillations to the primordial power spectrum by running high-resolution
dark-matter-only N-body simulations. We fit a Gaussian envelope for the
non-linear damping of superimposed oscillations in the matter power spectrum to
the results of the N-body simulations for $k \lesssim 0.6\ h/$Mpc at $0 \leq z
\leq 5$ with an accuracy below the percent. We finally use this fitting formula
to forecast the capabilities of future galaxy surveys, such as Euclid and
Subaru, to probe primordial oscillation down to non-linear scales alone and in
combination with the information contained in CMB anisotropies.
|
1912.12499v3
|
2020-03-01
|
Optimal Oscillation Damping Control of cable-Suspended Aerial Manipulator with a Single IMU Sensor
|
This paper presents a design of oscillation damping control for the
cable-Suspended Aerial Manipulator (SAM). The SAM is modeled as a double
pendulum, and it can generate a body wrench as a control action. The main
challenge is the fact that there is only one onboard IMU sensor which does not
provide full information on the system state. To overcome this difficulty, we
design a controller motivated by a simplified SAM model. The proposed
controller is very simple yet robust to model uncertainties. Moreover, we
propose a gain tuning rule by formulating the proposed controller in the form
of output feedback linear quadratic regulation problem. Consequently, it is
possible to quickly dampen oscillations with minimal energy consumption. The
proposed approach is validated through simulations and experiments.
|
2003.00472v1
|
2020-03-06
|
Accelerating the Convergence of Higher-Order Coupled Cluster Methods II: Coupled Cluster $Λ$ Equations and Dynamic Damping
|
The method of sub-iteration, which was previously applied to the higher-order
coupled cluster amplitude equations, is extended to the case of the coupled
cluster $\Lambda$ equations. The sub-iteration procedure for the $\Lambda$
equations is found to be highly similar to that for the amplitude equations,
and to exhibit a similar improvement in rate of convergence relative to
extrapolation of all $\hat{T}$ or $\hat{\Lambda}$ amplitudes using DIIS. A
method of dynamic damping is also presented which is found to effectively
recover rapid convergence in the case of oscillatory behavior in the amplitude
or $\Lambda$ equations. Together, these techniques allow for the convergence of
both the amplitude and $\Lambda$ equations necessary for the calculation of
analytic gradients and properties of higher-order coupled cluster methods
without the high memory or disk I/O cost of full DIIS extrapolation.
|
2003.03455v1
|
2020-03-09
|
Forces between Silica Particles in Isopropanol Solutions of 1:1 Electrolytes
|
Interactions between silica surfaces across isopropanol solutions are
measured with colloidal probe technique based on atomic force microscope. In
particular, the influence of 1:1 electrolytes on the interactions between
silica particles is investigated. A plethora of different forces are found in
these systems. Namely, van der Waals, double-layer, attractive non-DLVO,
repulsive solvation, and damped oscillatory interactions are observed. The
measured decay length of the double-layer repulsion is substantially larger
than Debye lengths calculated from nominal salt concentrations. These
deviations are caused by pronounced ion pairing in alcohol solutions. At
separation below 10 nm, additional attractive and repulsive non-DLVO forces are
observed. The former are possibly caused by charge heterogeneities induced by
strong ion adsorption, whereas the latter originate from structuring of
isopropanol molecules close to the surface. Finally, at increased
concentrations the transition from monotonic to damped oscillatory interactions
is uncovered.
|
2003.04058v2
|
2020-03-13
|
Energy localization and transfer in autoresonant weakly dissipative anharmonic chains
|
In this work, we develop an analytical framework to explain the influence of
dissipation and detuning parameters on the emergence and stability of
autoresonance in a strongly nonlinear weakly damped chain subjected to harmonic
forcing with a slowly-varying frequency. Using the asymptotic procedures, we
construct the evolutionary equations, which describe the behavior of the array
under the condition of 1:1 resonance and then approximately compute the slow
amplitudes and phases as well as the duration of autoresonance. It is shown
that, in contrast to autoresonance in a non-dissipative chain with unbounded
growth of energy, the energy in a weakly damped array being initially at rest
is growing only in a bounded time interval up to an instant of simultaneous
escape from resonance of all autoresonant oscillators. Analytical conditions of
the emergence and stability of autoresonance are confirmed by numerical
simulations.
|
2003.06346v1
|
2020-03-13
|
Photon and Phonon Spectral-Functions for Continuum Quantum Optomechanics
|
We study many-particle phenomena of propagating multi-mode photons and
phonons interacting through Brillouin scattering-type Hamiltonian in nanoscale
waveguides. We derive photon and phonon retarded Green's functions and extract
their spectral functions in applying the factorization approximation of the
mean-field theory. The real part of the self-energy provides renormalization
energy shifts for the photons and the phonons. Besides the conventional leaks,
the imaginary part gives effective photon and phonon damping rates induced due
to many-particle phenomena. The results extend the simple spectral functions of
quantum optomechanics into continuum quantum optomechanics. We present the
influence of thermal phonons on the photon effective damping rates, and
consider cases of specific photon fields to be excited within the waveguide and
which are of importance for phonon cooling scenarios.
|
2003.06355v1
|
2020-03-13
|
Surface waves in a collisional quark-gluon plasma
|
Surface waves propagating in the semi-bounded collisional hot QCD medium
(quark-gluon plasma) are considered. To investigate the effect of collisions as
damping and non-ideality factor, the longitudinal and transverse dielectric
functions of the quark-gluon plasma are used within the Bhatnagar-Gross-Krook
(BGK) approach. The results were obtained both analytically and numerically in
the long wavelength limit. First of all, collisions lead to smaller values of
surface wave frequency and their stronger damping. Secondly, the results show
that non-ideality leads to the appearance of a new branch of surface waves
compared to the collisionless case. The relevance of the surface excitations
(waves) for the QGP realized in experiments is discussed.
|
2003.06373v2
|
2020-03-18
|
Finite time extinction for the strongly damped nonlinear Schr{ö}dinger equation in bounded domains
|
We prove the \textit{finite time extinction property} $(u(t)\equiv 0$ on
$\Omega$ for any $t\ge T_\star,$ for some $T_\star>0)$ for solutions of the
nonlinear Schr\"{o}dinger problem ${\rm i} u_t+\Delta u+a|u|^{-(1-m)}u=f(t,x),$
on a bounded domain $\Omega$ of $\mathbb{R}^N,$ $N\le 3,$ $a\in\mathbb{C}$ with
$\Im(a)>0$ (the damping case) and under the crucial assumptions $0<m<1$ and the
dominating condition $2\sqrt m\,\Im(a)\ge(1-m)|\Re(a)|.$ We use an energy
method as well as several a priori estimates to prove the main conclusion. The
presence of the non-Lipschitz nonlinear term in the equation introduces a lack
of regularity of the solution requiring a study of the existence and uniqueness
of solutions satisfying the equation in some different senses according to the
regularity assumed on the data.
|
2003.08105v2
|
2020-03-19
|
Challenge for describing the cluster states starting with realistic interaction
|
We aim to describe the cluster states of nuclear systems starting with a
realistic interaction, which is a challenge of modern nuclear theories. Here,
the short-range correlation of realistic interaction is treated by employing
the damping factor, and the resultant interaction can be applied to the cluster
structure of light nuclei. We start with a realistic interaction (G3RS) and
transform it in this way, and the $\alpha$-$\alpha$ energy curve is compared
with the results of phenomenological interactions. The attractive effect
between two $\alpha$'s is found to be not enough even with a damping factor for
the short-range repulsion, and the necessity of a finite-range three-body term
is discussed. With this three-body term, the resonance energy of the ground
state and the scattering phase shift of two $\alpha$'s can be reproduced. Also,
the binding energy of $^{16}$O from the four $\alpha$ threshold is reasonably
reproduced. The linear-chain structure of three and four $\alpha$ clusters in
$^{12}$C and $^{16}$O are calculated with this interaction and compared with
the results of the conventional approaches including the density functional
theories.
|
2003.08546v1
|
2020-03-20
|
Large Deflections of A Structurally Damped Panel in A Subsonic Flow
|
The large deflections of panels in subsonic flow are considered.
Specifically, a fully clamped von Karman plate accounting for both rotational
inertia in plate filaments and structural damping of square root type is
considered. The panel is taken to be embedded in the boundary of a linear,
subsonic potential flow on the positive halfspace in $\mathbb R^3$. Solutions
are constructed via a semigroup approach despite the lack of natural
dissipativity associated to the generator of the linear dynamics. The
flow-plate dynamics are then reduced---via an explicit Neumann-to-Dirichlet
(downwash-to-pressure) solver for the flow---to a memory-type dynamical system
for the plate. For the non-conservative plate dynamics, a global attractor is
explicitly constructed via Lyapunov and quasi-stability methods. Finally, it is
shown that via the compactness of the attractor and finiteness of the
dissipation integral, that all trajectories converge strongly to the set of
stationary states.
|
2003.09232v1
|
2020-03-24
|
Pulsed RF Schemes for Tearing Mode Stabilization
|
The RF stabilization of tearing modes with current condensation has the
potential to increase stabilization efficiency and loosen power localization
requirements. Such benefits stem from the cooperative feedback between the RF
deposition and resulting island temperature perturbation governed by diffusion.
A self consistent treatment of the damping of an rf ray as it traverses the
island shows that low damping scenarios can require unfavorably high powers to
overcome initial power leakage and effectively capitalize on the nonlinear
effect. In this work it is demonstrated that for such regimes,modulated
stabilization schemes can achieve significant improvements in heating and
current drive contributions to stabilization for the same average power as a
continuous wave scheme. The impact of modulation frequency and duty cycle on
the performance is explored, the results of which suggest modulation strategies
in which the pulsing periods are kept on the order of a diffusive time.
|
2003.10896v1
|
2020-03-24
|
Detecting Multiple DLAs per Spectrum in SDSS DR12 with Gaussian Processes
|
We present a revised version of our automated technique using Gaussian
processes (GPs) to detect Damped Lyman-$\alpha$ absorbers (DLAs) along quasar
(QSO) sightlines. The main improvement is to allow our Gaussian process
pipeline to detect multiple DLAs along a single sightline. Our DLA detections
are regularised by an improved model for the absorption from the Lyman-$\alpha$
forest which improves performance at high redshift. We also introduce a model
for unresolved sub-DLAs which reduces mis-classifications of absorbers without
detectable damping wings. We compare our results to those of two different
large-scale DLA catalogues and provide a catalogue of the processed results of
our Gaussian process pipeline using 158 825 Lyman-$\alpha$ spectra from SDSS
data release 12. We present updated estimates for the statistical properties of
DLAs, including the column density distribution function (CDDF), line density
($dN/dX$), and neutral hydrogen density ($\Omega_{\textrm{DLA}}$).
|
2003.11036v2
|
2020-03-28
|
Quantum speed limit based on the bound of Bures angle
|
In this paper, we investigate the unified bound of quantum speed limit time
in open systems based on the modified Bures angle. This bound is applied to the
damped Jaynes-Cummings model and the dephasing model, and the analytical
quantum speed limit time is obtained for both models. As an example, the
maximum coherent qubit state with white noise is chosen as the initial states
for the damped Jaynes-Cummings model. It is found that the quantum speed limit
time in both the non-Markovian and the Markovian regimes can be decreased by
the white noise compared with the pure state. In addition, for the dephasing
model, we find that the quantum speed limit time is not only related to the
coherence of initial state and non-Markovianity, but also dependent on the
population of initial excited state.
|
2003.12758v1
|
2020-03-31
|
First-principles study of ultrafast dynamics of Dirac plasmon in graphene
|
Exploring low-loss two-dimensional plasmon modes is considered central for
achieving light manipulation at the nanoscale and applications in plasmonic
science and technology. In this context, pump-probe spectroscopy is a powerful
tool for investigating these collective modes and the corresponding energy
transfer processes. Here, I present a first-principles study on non-equilibrium
Dirac plasmon in graphene, wherein damping channels under ultrafast conditions
are still not fully explored. The laser-induced blueshift of plasmon energy is
explained in terms of thermal increase of the electron-hole pair concentration
in the intraband channel. Interestingly, while damping pathways of the
equilibrium graphene plasmon are entirely ruled by scatterings with acoustic
phonons, the photoinduced plasmon predominantly transfers its energy to the
strongly coupled hot optical phonons, which explains the
experimentally-observed tenfold increase of the plasmon linewidth. The present
study paves the way for an in-depth theoretical comprehension of plasmon
temporal dynamics in novel two-dimensional systems and heterostructures.
|
2003.14074v2
|
2020-03-31
|
Parametric analysis of COVID-19 expansion in European countries in the period of February to June 2020
|
The data on number of registered cases of COVID-19 disease in twenty European
countries is analyzed by the least-squares fitting procedure with generic
analytic functions. Three regimes of the expansion of the disease are
identified and quantified -- early exponential expansion, damped exponential,
and linear expansion. Differences among countries in the early expansion period
are quantified. The velocity of the expansion in the exponential regime lies
within one standard deviation from the average value for 11 countries. The
number of infected individuals at the initial time is excessively high for
Italy, 7 standard deviations from the average value.
Method for predicting the expansion based on extrapolation in the parametric
space is presented. One-week predictions based on extrapolations have average
precision of 18% and 29% during the later period of the damped exponential
expansion for the case of Italy and Czechia, respectively. The method based on
extrapolations in the parametric space may provide an elementary method to
quantify the impact of restrictive measures on the spreading of the disease.
|
2003.14283v2
|
2020-08-13
|
Using Machine Learning to Find Ghostly Damped Ly$α$ Systems in SDSS DR14
|
We report the discovery of 59 new ghostly absorbers from the Sloan Digital
Sky Survey (SDSS) Data Release 14 (DR14). These absorbers, with $z_{\rm
abs}$$\sim$$z_{\rm QSO}$, reveal no Ly$\alpha$ absorption, and they are mainly
identified through the detection of strong metal absorption lines in the
spectra. The number of previously known such systems is 30. The new systems are
found with the aid of machine learning algorithms. The spectra of 41 (out of
total of 89) absorbers also cover the Ly$\beta$ spectral region. By fitting the
damping wings of the Ly$\beta$ absorption in the stacked spectrum of 21 (out of
41) absorbers with relatively stronger Ly$\beta$ absorption, we measured an HI
column density of log$N$(HI)=21.50. This column density is 0.5dex higher than
that of the previous work. We also found that the metal absorption lines in the
stacked spectrum of the 21 ghostly absorbers with stronger Ly$\beta$ absorption
have similar properties as those in the stacked spectrum of the remaining
systems. These circumstantial evidence strongly suggest that the majority of
our ghostly absorbers are indeed DLAs.
|
2008.05910v1
|
2020-08-15
|
$L^1$-convergence to generalized Barenblatt solution for compressible Euler equations with time-dependent damping
|
The large time behavior of entropy solution to the compressible Euler
equations for polytropic gas (the pressure $p(\rho)=\kappa\rho^{\gamma},
\gamma>1$) with time dependent damping like $-\frac{1}{(1+t)^\lambda}\rho u$
($0<\lambda<1$) is investigated. By introducing an elaborate iterative method
and using the intensive entropy analysis, it is proved that the $L^\infty$
entropy solution of compressible Euler equations with finite initial mass
converges strongly in the natural $L^1$ topology to a fundamental solution of
porous media equation (PME) with time-dependent diffusion, called by
generalized Barenblatt solution. It is interesting that the $L^1$ decay rate is
getting faster and faster as $\lambda$ increases in $(0,
\frac{\gamma}{\gamma+2}]$, while is getting slower and slower in $[
\frac{\gamma}{\gamma+2}, 1)$.
|
2008.06704v1
|
2020-08-21
|
Structure preserving algorithms for simulation of linearly damped acoustic systems
|
Energy methods for constructing time-stepping algorithms are of increased
interest in application to nonlinear problems, since numerical stability can be
inferred from the conservation of the system energy. Alternatively, symplectic
integrators may be constructed that preserve the symplectic form of the system.
This methodology has been established for Hamiltonian systems, with numerous
applications in engineering problems. In this paper an extension of such
methods to non-conservative acoustic systems is presented. Discrete
conservation laws, equivalent to that of energy-conserving schemes, are derived
for systems with linear damping, incorporating the action of external forces.
Furthermore the evolution of the symplectic structure is analysed in the
continuous and the discrete case. Existing methods are examined and novel
methods are designed using a lumped oscillator as an elemental model. The
proposed methodology is extended to the case of distributed systems and
exemplified through a case study of a vibrating string bouncing against a rigid
obstacle.
|
2008.09479v1
|
2020-08-24
|
The move from Fujita to Kato type exponent for a class of semilinear evolution equations with time-dependent damping
|
In this paper, we derive suitable optimal $L^p-L^q$ decay estimates, $1\leq
p\leq 2\leq q\leq \infty$, for the solutions to the $\sigma$-evolution
equation, $\sigma>1$, with scale-invariant time-dependent damping and power
nonlinearity~$|u|^p$, \[ u_{tt}+(-\Delta)^\sigma u + \frac{\mu}{1+t} u_t=
|u|^{p}, \] where $\mu>0$, $p>1$. The critical exponent $p=p_c$ for the global
(in time) existence of small data solutions to the Cauchy problem is related to
the long time behavior of solutions, which changes accordingly $\mu \in (0, 1)$
or $\mu>1$. Under the assumption of small initial data in $L^1\cap L^2$, we
find the critical exponent \[ p_c=1+ \max
\left\{\frac{2\sigma}{[n-\sigma+\sigma\mu]_+}, \frac{2\sigma}{n} \right\}
=\begin{cases} 1+ \frac{2\sigma}{[n-\sigma+\sigma\mu]_+}, \quad \mu \in (0,
1)\\ 1+ \frac{2\sigma}{n}, \quad \mu>1. \end{cases} \]
For $\mu>1$ it is well known as Fujita type exponent, whereas for $\mu \in
(0, 1)$ one can read it as a shift of Kato exponent.
|
2008.10374v1
|
2020-09-01
|
On the decay in $W^{1,\infty}$ for the 1D semilinear damped wave equation on a bounded domain
|
In this paper we study a semilinear wave equation with nonlinear,
time-dependent damping in one space dimension. For this problem, we prove a
well-posedness result in $W^{1,\infty}$ in the space-time domain $(0,1)\times
[0,+\infty)$. Then we address the problem of the time-asymptotic stability of
the zero solution and show that, under appropriate conditions, the solution
decays to zero at an exponential rate in the space $W^{1,\infty}$. The proofs
are based on the analysis of the corresponding semilinear system for the first
order derivatives, for which we show a contractive property of the invariant
domain.
|
2009.00731v2
|
2020-09-08
|
Nanomechanical damping via electron-assisted relaxation of two-level systems
|
We report on measurements of dissipation and frequency noise at millikelvin
temperatures of nanomechanical devices covered with aluminum. A clear excess
damping is observed after switching the metallic layer from superconducting to
the normal state with a magnetic field. Beyond the standard model of internal
tunneling systems coupled to the phonon bath, here we consider the relaxation
to the conduction electrons together with the nature of the mechanical
dispersion laws for stressed/unstressed devices. With these key ingredients, a
model describing the relaxation of two-level systems inside the structure due
to interactions with electrons and phonons with well separated timescales
captures the data. In addition, we measure an excess 1/f-type frequency noise
in the normal state, which further emphasizes the impact of conduction
electrons.
|
2009.03804v3
|
2020-09-10
|
Inclination damping on Callisto
|
Callisto is thought to possess a subsurface ocean, which will dissipate
energy due to obliquity tides. This dissipation should have damped any
primordial inclination within 1 Gyr - and yet Callisto retains a present-day
inclination. We argue that Callisto's inclination and eccentricity were both
excited in the relatively recent past (~0.3 Gyr). This excitation occurred as
Callisto migrated outwards according to the "resonance-locking" model and
passed through a 2:1 mean-motion resonance with Ganymede. Ganymede's orbital
elements were likewise excited by the same event. To explain the present-day
orbital elements we deduce a solid-body tidal k2/Q~0.05 for Callisto and a
significantly lower value for Ganymede.
|
2009.05002v1
|
2020-09-25
|
Sound in a system of chiral one-dimensional fermions
|
We consider a system of one-dimensional fermions moving in one direction,
such as electrons at the edge of a quantum Hall system. At sufficiently long
time scales the system is brought to equilibrium by weak interactions between
the particles, which conserve their total number, energy, and momentum. Time
evolution of the system near equilibrium is described by hydrodynamics based on
the three conservation laws. We find that the system supports three sound
modes. In the low temperature limit one mode is a pure oscillation of particle
density, analogous to the ordinary sound. The other two modes involve
oscillations of both particle and entropy densities. In the presence of
disorder, the first sound mode is strongly damped at frequencies below the
momentum relaxation rate, whereas the other two modes remain weakly damped.
|
2009.12364v1
|
2020-09-30
|
Dynamical properties of a driven dissipative dimerized $S = 1/2$ chain
|
We consider the dynamical properties of a gapped quantum spin system coupled
to the electric field of a laser, which drives the resonant excitation of
specific phonon modes that modulate the magnetic interactions. We deduce the
quantum master equations governing the time-evolution of both the lattice and
spin sectors, by developing a Lindblad formalism with bath operators providing
an explicit description of their respective phonon-mediated damping terms. We
investigate the nonequilibrium steady states (NESS) of the spin system
established by a continuous driving, delineating parameter regimes in driving
frequency, damping, and spin-phonon coupling for the establishment of
physically meaningful NESS and their related non-trivial properties. Focusing
on the regime of generic weak spin-phonon coupling, we characterize the NESS by
their frequency and wave-vector content, explore their transient and relaxation
behavior, and discuss the energy flow, the system temperature, and the critical
role of the type of bath adopted. Our study lays a foundation for the
quantitative modelling of experiments currently being designed to control
coherent many-body spin states in quantum magnetic materials.
|
2009.14805v2
|
2020-10-02
|
Parametric instability in a free evolving warped protoplanetary disc
|
Warped accretion discs of low viscosity are prone to hydrodynamic instability
due to parametric resonance of inertial waves as confirmed by local
simulations. Global simulations of warped discs, using either smoothed particle
hydrodynamics (SPH) or grid-based codes, are ubiquitous but no such instability
has been seen. Here we utilize a hybrid Godunov-type Lagrangian method to study
parametric instability in global simulations of warped Keplerian discs at
unprecedentedly high resolution (up to 120 million particles). In the global
simulations, the propagation of the warp is well described by the linear
bending-wave equations before the instability sets in. The ensuing turbulence,
captured for the first time in a global simulation, damps relative orbital
inclinations and leads to a decrease in the angular momentum deficit. As a
result, the warp undergoes significant damping within one bending-wave crossing
time. Observed protoplanetary disc warps are likely maintained by companions or
aftermath of disc breaking.
|
2010.00862v2
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.