publicationDate
stringlengths 1
2.79k
| title
stringlengths 1
36.5k
⌀ | abstract
stringlengths 1
37.3k
⌀ | id
stringlengths 9
47
|
|---|---|---|---|
2017-04-08
|
Improved Parameter Estimation Techniques for Induction Motors using Hybrid Algorithms
|
The performance of Newton-Raphson, Levenberg-Marquardt, Damped Newton-Raphson
and genetic algorithms are investigated for the estimation of induction motor
equivalent circuit parameters from commonly available manufacturer data. A new
hybrid algorithm is then proposed that combines the advantages of both descent
and natural optimisation algorithms. Through computer simulation, the hybrid
algorithm is shown to significantly outperform the conventional algorithms in
terms of convergence and squared error rates. All of the algorithms are tested
on a large data set of 6,380 IEC (50Hz) and NEMA (60Hz) motors.
|
1704.02424v1
|
2017-04-19
|
Fractional Herglotz Variational Principles with Generalized Caputo Derivatives
|
We obtain Euler-Lagrange equations, transversality conditions and a
Noether-like theorem for Herglotz-type variational problems with Lagrangians
depending on generalized fractional derivatives. As an application, we consider
a damped harmonic oscillator with time-depending mass and elasticity, and
arbitrary memory effects.
|
1704.05697v1
|
2017-04-24
|
Performance Evaluation of the Zero-Multipole Summation Method in Modern Molecular Dynamics Software
|
We evaluate the practical performance of the zero-multiple summation method
(ZMM), a method for approximately calculating electrostatic interactions in
molecular dynamics simulations. The performance of the ZMM is compared with
that of the smooth particle mesh Ewald method (SPME). Even though the ZMM uses
a larger cutoff distance than the SPME does, the performance of the ZMM is
found to be comparable to or better than that of the SPME. In particular, the
ZMM with quadrupole or octupole cancellation and no damping factor is an
excellent candidate for the fast calculation of electrostatic potentials.
|
1704.07071v1
|
2017-04-04
|
Gravity Induced Resonant Emission
|
The gravitational drift of ions relative to the electrons induces two type of
waves in magnetized plasma; ion acoustic (IO) waves and lower hybrid (LH)
waves. The IO waves induced by the gravity are damped by electromagnetic (EM)
waves leads to the formation of LH waves. For higher wave vector, these LH wave
results in to the resonant absorption and re-emission of EM waves, called as
gravity induced resonant emission (gire). A general formula has been derived
for gire frequency is convergence of all fundamental quantities.
|
1704.07225v1
|
2017-05-12
|
Controlling Multimode Optomechanical Interactions via Interference
|
We demonstrate optomechanical interference in a multimode system, in which an
optical mode couples to two mechanical modes. A phase-dependent
excitation-coupling approach is developed, which enables the observation of
constructive and destructive optomechanical interferences. The destructive
interference prevents the coupling of the mechanical system to the optical
mode, suppressing optically-induced mechanical damping. These studies establish
optomechanical interference as an essential tool for controlling the
interactions between light and mechanical oscillators.
|
1705.04722v1
|
2017-05-18
|
Band Gap Formation and Tunability in Stretchable Serpentine Interconnects
|
Serpentine interconnects are highly stretchable and frequently used in
flexible electronic systems. In this work, we show that the undulating geometry
of the serpentine interconnects will generate phononic band gaps to manipulate
elastic wave propagation. The interesting effect of `bands-sticking-together'
is observed. We further illustrate that the band structures of the serpentine
interconnects can be tuned by applying pre-stretch deformation. The discovery
offers a way to design stretchable and tunable phononic crystals by using
metallic interconnects instead of the conventional design with soft rubbers and
unfavorable damping.
|
1705.06658v2
|
2017-05-20
|
Dispersion and decay of collective modes in neutron star cores
|
We calculate the frequencies of collective modes of neutrons, protons and
electrons in the outer core of neutron stars. The neutrons and protons are
treated in a hydrodynamic approximation and the electrons are regarded as
collisionless. The coupling of the nucleons to the electrons leads to Landau
damping of the collective modes and to significant dispersion of the low-lying
modes. We investigate the sensitivity of the mode frequencies to the strength
of entrainment between neutrons and protons, which is not well characterized.
The contribution of collective modes to the thermal conductivity is evaluated.
|
1705.07357v2
|
2017-05-20
|
Biosensing using Functionally Graded Piezoelectric MEMS Resonators
|
Nonlinear dynamics of a two-side electro-statically actuated capacitive
micro-beam is studied. The piezoelectric actuation leads to the generation of
an axial force along the length of the micro-beam and this is used as a tuning
tool to shift the primary resonance of the micro-resonator. The governing
equation of motion is derived by minimization of the Hamiltonian and
generalized to the viscously damped systems. The periodic solutions in the
vicinity of the primary resonance are detected and their stability is
investigated. The basins of attraction conforming to three individual periodic
orbits are determined. The outcomes show that the higher the amplitude of the
periodic orbit, the smaller is the area of the attractor.
|
1705.08267v1
|
2017-05-24
|
X-Ray Amplification by Stimulated Brillouin Scattering
|
Plasma-based parametric amplification using stimulated Brillouin scattering
offers a route to coherent x-ray pulses orders-of-magnitude more intense than
those of the brightest available sources. Brillouin amplification permits
amplification of shorter wavelengths with lower pump intensities than Raman
amplification, which Landau and collisional damping limit in the x-ray regime.
Analytic predictions, numerical solutions of the three-wave coupling equations,
and particle-in-cell simulations suggest that Brillouin amplification in
solid-density plasmas will allow compression of current x-ray free electron
laser pulses to sub-femtosecond durations and unprecedented intensities.
|
1705.08599v2
|
2017-05-24
|
Long-lived mesoscopic entanglement between two damped infinite harmonic chains
|
We consider two chains, each made of $N$ independent oscillators, immersed in
a common thermal bath and study the dynamics of their mutual quantum
correlations in the thermodynamic, large-$N$ limit. We show that dissipation
and noise due to the presence of the external environment are able to generate
collective quantum correlations between the two chains at the mesoscopic level.
The created collective quantum entanglement between the two many-body systems
turns out to be rather robust, surviving for asymptotically long times even for
non vanishing bath temperatures.
|
1705.08648v1
|
2017-05-24
|
Effect of radiation damping on the Child-Langmuir law in open diodes
|
We present a microscopic derivation of the space charge limited current for
the motion of non-relativistic charged particles inside a parallel vacuum tube
diode taking into account the radiation reaction force. We study the space
charged limited current for two different limiting cases. Our results reveal
that in the low field regime the space charge current does not follow the
Child-Langmuir law, while in the high field regime the space charge current
follows the Child-Langmuir law with and effective electrostatic field, i.e. the
so called modified Child-Langmuir law.
|
1705.09567v2
|
2017-05-29
|
Deterministic preparation of highly non-classical macroscopic quantum states
|
We present a scheme to deterministically prepare non-classical quantum states
of a massive mirror including highly non-Gaussian states exhibiting sizeable
negativity of the Wigner function. This is achieved by exploiting the
non-linear light-matter interaction in an optomechanical cavity by driving the
system with optimally designed frequency patterns. Our scheme reveals to be
resilient against mechanical and optical damping, as well as mechanical thermal
noise and imperfections in the driving scheme. Our proposal thus opens a
promising route for table-top experiments to explore and exploit macroscopic
quantum phenomena.
|
1705.10334v2
|
2017-06-01
|
Nonlinear transport by vortex tangles in cuprate high-temperature superconductors
|
A unified model of vortex tangles is proposed to describe unconventional
transport in cuprate high-temperature superconductors, which not only captures
the fast vortices scenario at low density, but also predicts a novel mechanism
of core-core collisions in dense vortex fluid regime. The theory clarifies the
nature of vortex fluctuations being the quantum fluctuations of holes and then
resolves a discrepancy of two orders of magnitude of Anderson's damping model
$\hbar n_v$, with right prediction of the nonlinear field dependence of the
resistivity $\rho=\rho_n(B+B_T)/(B_0+B+B_T)$ and the Nernst effect, validated
by data of several samples. Consequently, Anderson's vortex tangles concept and
phase fluctuation scenario of pseudogap are verified quantitatively.
|
1706.00228v1
|
2017-06-16
|
Distributed Estimation of Oscillations in Power Systems: an Extended Kalman Filtering Approach
|
Online estimation of electromechanical oscillation parameters provides
essential information to prevent system instability and blackout and helps to
identify event categories and locations. We formulate the problem as a state
space model and employ the extended Kalman filter to estimate oscillation
frequencies and damping factors directly based on data from phasor measurement
units. Due to considerations of communication burdens and privacy concerns, a
fully distributed algorithm is proposed using diffusion extended Kalman filter.
The effectiveness of proposed algorithms is confirmed by both simulated and
real data collected during events in State Grid Jiangsu Electric Power Company.
|
1706.05355v1
|
2017-06-20
|
Relative and Mean Motions of Multi-Machine Power Systems in Classical Model
|
It is well-known that in an m-machine power system where each machine is
represented by a second-order differential equation, the Jacobian of the system
equation contains (m-1) pairs of conjugate eigenvalues and two real
eigenvalues, including at least one zero. This letter proves that under the
uniform damping condition, the dynamics associated with the two real
eigenvalues do not have any impact on the dynamics associated with those
complex eigenvalues. This conclusion is important to justify the use of the
relative motions or center-of-inertia (COI) coordinate to analyze the rotor
angle stability in a multi-machine power system.
|
1706.06226v1
|
2017-06-25
|
Influence of qubits' nonradiative decay into a common bath on the transport properties of microwave photons
|
We consider the influence of nonradiative damping of qubits on the microwave
transport of photons, propagating in an open one-dimensional microstrip line.
Within the framework of the formalism of a non-Hermitian Hamiltonian we
obtained the expressions for the transmission and reflection coefficients for
two qubits which explicitly account for the indirect interaction between qubits
due to nonradiative decay into common bath. It is shown that this interaction
leads to the results that are significantly different from those already known
|
1706.08028v2
|
2017-06-26
|
Complexity of the Regularized Newton Method
|
Newton's method for finding an unconstrained minimizer for strictly convex
functions, generally speaking, does not converge from any starting point.
We introduce and study the damped regularized Newton's method (DRNM). It
converges globally for any strictly convex function, which has a minimizer in
$R^n$.
Locally DRNM converges with a quadratic rate. We characterize the
neighborhood of the minimizer, where the quadratic rate occurs. Based on it we
estimate the number of DRNM's steps required for finding an $\varepsilon$-
approximation for the minimizer.
|
1706.08483v1
|
2018-02-02
|
Energy decay and global solutions for a damped free boundary fluid-elastic structure interface model with variable coefficients in elasticity
|
We cope with a free boundary fluid-structure interaction model. In the model,
the viscous incompressible fluid interacts with elastic body via the common
boundary. The motion of the fluid is governed by Navier-Stokes equations while
the displacement of elastic structure is described by variable coefficient wave
equations. The dissipation is placed on the common boundary between fluid and
elastic body. Given small initial data, the global existence of the solutions
of this system is proved and the exponential decay of solutions are obtained.
|
1802.00585v2
|
2018-06-30
|
Global Well-Posedness and Exponential Stability for Heterogeneous Anisotropic Maxwell's Equations under a Nonlinear Boundary Feedback with Delay
|
We consider an initial-boundary value problem for the Maxwell's system in a
bounded domain with a linear inhomogeneous anisotropic instantaneous material
law subject to a nonlinear Silver-Muller-type boundary feedback mechanism
incorporating both an instantaneous damping and a time-localized delay effect.
By proving the maximal monotonicity property of the underlying nonlinear
generator, we establish the global well-posedness in an appropriate Hilbert
space. Further, under suitable assumptions and geometric conditions, we show
the system is exponentially stable.
|
1807.00098v2
|
2018-07-05
|
Generalized Adiabatic Theorem and Strong-Coupling Limits
|
We generalize Kato's adiabatic theorem to nonunitary dynamics with an
isospectral generator. This enables us to unify two strong-coupling limits: one
driven by fast oscillations under a Hamiltonian, and the other driven by strong
damping under a Lindbladian. We discuss the case where both mechanisms are
present and provide nonperturbative error bounds. We also analyze the links
with the quantum Zeno effect and dynamics.
|
1807.02036v2
|
2018-07-13
|
Weighted $L^2-L^2$ estimate for wave equation and its applications
|
In this work we establish a weighted $L^2-L^2$ estimate for inhomogeneous
wave equation in 3-D, by introducing a Morawetz multiplier with weight of power
$s(1<s<2)$, and then integrating on the light cones and $t$ slice. With this
weighted $L^2-L^2$ estimate in hand, we may give a new proof of global
existence for small data Cauchy problem of semilinear wave equation with
supercritical power in 3-D. What is more, by combining the Huygens' principle
for wave equations in 3-D, the global existence for semilinear wave equation
with scale invariant damping in 3-D is established.
|
1807.05109v1
|
2018-07-14
|
Non-Markovianity through quantum coherence in an all-optical setup
|
We propose an all-optical experiment to quantify non-Markovianity in an open
quantum system through quantum coherence of a single quantum bit. We use an
amplitude damping channel implemented by an optical setup with an intense laser
beam simulating a single-photon polarization. The optimization over initial
states required to quantify non-Markovianity is analytically evaluated. The
experimental results are in a very good agreement with the theoretical
predictions.
|
1807.05378v2
|
2018-07-17
|
Energy decay for evolution equations with delay feedbacks
|
We study abstract linear and nonlinear evolutionary systems with single or
multiple delay feedbacks, illustrated by several concrete examples. In
particular, we assume that the operator associated with the undelayed part of
the system generates an exponentially stable semigroup and that the delay
damping coefficients are locally integrable in time. A step by step procedure
combined with Gronwall's inequality allows us to prove the existence and
uniqueness of solutions. Furthermore, under appropriate conditions we obtain
exponential decay estimates.
|
1807.06445v2
|
2018-07-31
|
Cooling of the rotation of a nanodiamond via the interaction with the electron spin of the contained NV-center
|
We propose a way to cool the rotation of a nanodiamond, which contains a
NV-center and is levitated by an optical tweezer.
Following the rotation of the particle, the NV-center electron spin
experiences varying external fields and so leads to spin-rotation coupling. By
optically pumping the electrons from a higher energy level to a lower level,
the rotation energy is dissipated. We give the analytical result for the
damping torque exerted on the nanodiamond, and evaluate the final cooling
temperature by the fluctuation-dissipation theorem. It's shown that the quantum
regime of the rotation can be reached with our scheme.
|
1807.11647v1
|
2018-08-02
|
Enhanced Attenuation Arising from Lattice Resonances in a Plasma Photonic Crystal
|
We describe the experimental verification of lattice resonances in
two-dimensional photonic crystals constructed from an array of gaseous plasma
columns. Enhancements are seen in the extinction of normal incidence transverse
electric electromagnetic waves when the localized surface plasmon modes of the
plasma columns are shifted into the vicinity of the photonic crystal Bragg
resonances. Simulations and experiments are in reasonable agreement and confirm
the appearance of a Fano-like profile with deep and broad extinction bands. The
broadening of the spectra as surface plasmon modes come into coincidence with
Bragg gaps suggest that the Bragg fields couple strongly into the radiating Mie
dipoles to drive enhanced damping of the photonic crystal resonance.
|
1808.00610v1
|
2018-08-10
|
On the compactness of weak solutions to the Navier-Stokes-Korteweg equations for capillary fluids
|
In this paper we consider the Navier-Stokes-Korteweg equations for a viscous
compressible fluid with capillarity effects in three space dimensions. We prove
compactness of finite energy weak solutions for large initial data. In contrast
with previous results regarding this system, vacuum regions are allowed in the
definition of weak solutions and no additional damping terms are considered.
The compactness is obtained by introducing suitable truncations of the velocity
field and the mass density at different scales and use only the a priori bounds
obtained by the energy and the BD entropy.
|
1808.03495v2
|
2018-08-10
|
Collision quenching in the ultrafast dynamics of plasmonic materials
|
We explore the nonlinear response of plasmonic materials driven by ultrashort
pulses of electromagnetic radiation with temporal duration of few femtoseconds
and high peak intensity. By developing the Fokker-Planck-Landau theory of
electron collisions, we solve analytically the collisional integral and derive
a novel set of hydrodynamical equations accounting for plasma dynamics at
ultrashort time scales. While in the limit of small light intensities we
recover the well established Drude model of plasmas, in the high intensity
limit we observe nonlinear quenching of collision-induced damping leading to
absorption saturation. Our results provide a general background to understand
electron dynamics in plasmonic materials with promising photonic applications
in the manipulation of plasma waves with reduced absorption at the femtosecond
time scale.
|
1808.03669v1
|
2018-08-11
|
Beam Breakup Mitigation by Ion Mobility in Plasma Acceleration
|
Moderate ion mobility provides a source of damping in the plasma wakefield
acceleration, which may serve as an effective remedy against the transverse
instability of the trailing bunch. Ion mobility in the fields of the driving
and trailing bunches is taken into account; the related effects are estimated
for the FACET-II parameters.
|
1808.03860v2
|
2018-08-22
|
Weak convergence of Euler-Maruyama's approximation for SDEs under integrability condition
|
This work establishes the weak convergence of Euler-Maruyama's approximation
for stochastic differential equations (SDEs) with singular drifts under the
integrability condition in lieu of the widely used growth condition. This
method is based on a skillful application of the dimension-free Harnack
inequality. Moreover, when the drifts satisfy certain regularity conditions,
the convergence rate is estimated. This method is also applicable when the
diffusion coefficients are degenerate. A stochastic damping Hamiltonian system
is studied as an illustrative example.
|
1808.07250v1
|
2018-09-30
|
Dynamic behaviour of a ring coupled boost converter system with passivity-based control
|
This paper discusses a dispersed generation system of multiple DC/DC
converters with DC power sources connected in a ring formulation. Here is
presented the analysis of the system based on the stored energy and passivity
characteristics of the system. Passivity Based Control (PBC), with its
energy-modifying and damping-injection technique, is applied to a ring coupled
converter system to stabilize itself at a desired DC voltage in the presence of
external disturbances. The numerical results reveal the effective application
of the control as a robust and flexible technique.
|
1810.00417v1
|
2018-10-08
|
Screening in the finite-temperature reduced Hartree-Fock model
|
We prove the existence of solutions of the reduced Hartree-Fock equations at
finite temperature for a periodic crystal with a small defect, and show total
screening of the defect charge by the electrons. We also show the convergence
of the damped self-consistent field iteration using Kerker preconditioning to
remove charge sloshing. As a crucial step of the proof, we define and study the
properties of the dielectric operator.
|
1810.03342v2
|
2018-10-17
|
A natural 4-parameter family of covariance functions for stationary Gaussian processes
|
A four-parameter family of covariance functions for stationary Gaussian
processes is presented. We call it 2Dsys. It corresponds to the general
solution of an autonomous second-order linear stochastic differential equation,
thus arises naturally from modelling. It covers underdamped and overdamped
systems, so it is proposed to use this family when one wishes to decide if a
time-series corresponds to stochastically forced damped oscillations or a
stochastically forced overdamped system.
|
1810.07738v1
|
2018-10-29
|
Nonlinear Semi-Classical 3D Quantum Spin
|
In an effort to provide an alternative method to represent a quantum spin, a
precise 3D nonlinear dynamics method is used. A two-sided torque function is
created to mimic the unique behavior of the quantum spin. A full 3D
representation of the magnetic field of a Stern-Gerlach device was used as in
the original experiment. Furthermore, the temporarily driven nonlinear damped
model exhibits chaos, but struggles to be consistent through azimuthal angles
in reproducing the quantum spin statistics.
|
1810.12424v1
|
2019-01-03
|
Ultrafast carrier relaxation and its Pauli drag in photo-enhanced melting of solids
|
Ultrafast light-matter interaction is a powerful tool for the study of
solids. Upon laser excitation, carrier multiplication and lattice acceleration
beyond thermal velocity can occur, as a result of far-from-equilibrium carrier
relaxation. The roles of electron-electron and electron-phonon scatterings are
identified by first-principles dynamic simulations, from which a unified phase
diagram emerges. It not only explains the experimentally-observed "inertial"
melting but also predicts abnormal damping by Pauli Exclusion Principle with a
new perspective on ultrahigh-intensity laser applications.
|
1901.00609v1
|
2019-01-04
|
Event-triggered damping stabilization of a linear wave equation
|
The paper addresses the design of an event-triggering mechanism for a partial
differential wave equation posed in a bounded domain. The wave equation is
supposed to be controlled through a first order time derivative term
distributed in the whole domain. Sufficient conditions based on the use of
suitable Lyapunov functional are proposed to guarantee that an event-triggered
distributed control still ensures the exponential stability of the closed-loop
system. Moreover, the designed event-triggering mechanism allows to avoid the
Zeno behavior. The 'existence and regularity' prerequisite properties of
solutions for the closed loop system are also proven.
|
1901.01009v1
|
2019-01-18
|
On Quantum Fields at High Temperature
|
Revisiting the fast fermion damping rate calculation in a thermalized QED
and/or QCD plasma at 4-loop order, focus is put on a peculiar perturbative
structure which has no equivalent at zero-temperature. Not surprisingly and in
agreement with previous $C^\star$-algebraic analyses, this structure renders
the use of thermal perturbation theory quite questionable.
|
1901.06338v2
|
2019-01-23
|
Global well-posedness for the Phan-Thein-Tanner model in critical Besov spaces without damping
|
In this paper, we mainly investigate the Cauchy problem for the
Phan-Thein-Tanner (PTT) model. The PPT model can be viewed as a Navier-Stokes
equations couple with a nonlinear transport system. This model is derived from
network theory for the polymeric fluid. We study about the global well
posedness of the PTT model in critical Besov spaces. When the initial data is a
small perturbation over around the equilibrium, we prove that the strong
solution in critical Besov spaces exists globally.
|
1901.08515v1
|
2019-01-27
|
Breaking optomechanical cooling limit by two drive fields on a membrane-in-middle system
|
We present a theoretical scheme for ground state cooling of a mechanical
resonator in a membrane-in-middle optomechanical system (OMS) driven by two
red-detuned drive fields. The details of dynamical evolution of OMS are
provided, and the effect of system conditions on cooling results are
systematically studied. Most importantly, the setups with two drives are found
to be capable of achieving better cooling results than the theoretical cooling
limit with single cavity. Even an improvement by one order of thermal phonon
number is possible with proper combination of the cavity damping rate and drive
intensity.
|
1901.09338v1
|
2019-04-03
|
Comparison of semiclassical and quantum models of a two-level atom-cavity QED system in the strong coupling regime
|
We present a numerical study comparing semiclassical and quantum models of a
damped, strongly interacting cavity QED system composed of a single two-level
atom interacting with a single quantized cavity mode driven externally by a
tunable monochromatic field. We compute the steady state transmission spectrum
of the coupled system under each model and show that in the strong coupling
regime, the two models yield starkly different results. The fully quantum
mechanical model of the system correctly yields the expected multiphoton
transmission spectra while the semiclassical approach results in a bistable
spectrum.
|
1904.02270v2
|
2019-04-04
|
Comparison between isothermal collision-streaming and finite-difference lattice Boltzmann models
|
We present here a comparison between collision-streaming and
finite-difference lattice Boltzmann (LB) models. This study provides a
derivation of useful formulae which help one to properly compare the simulation
results obtained with both LB models. We consider three physical problems: the
shock wave propagation, the damping of shear waves, and the decay of
Taylor-Green vortices, often used as benchmark tests. Despite the different
mathematical and computational complexity of the two methods, we show how the
physical results can be related to obtain relevant quantities.
|
1904.02471v1
|
2019-04-07
|
Remarks on decay effects of regularity loss type wave equations with structural damping terms
|
After GGH model was proposed by M. Ghisi, M. Gobbino and A. Haraux (2016), R.
Ikehata and S. Iyota (2018) showed decay estimates for the total energy of
solutions to GGH equations uniformly in the initial data. However, their
results imply that the total energy is bounded when the initial data belong to
the energy space. That is, whether it actually decays has not been known so
far. In this paper we report a positive answer to that question.
|
1904.03686v1
|
2019-04-18
|
Equilibrium properties and decoherence of an open harmonic oscillator
|
The equilibrium properties of an open harmonic oscillator are considered in
three steps: First the creation and destruction operators are generalized for
open dynamics and the creation operator is used to construct coherent states.
The second step consists of the introduction of the Heisenberg representation
where the dynamical decoherence can be identified without making reference to
the state of the system. Finally it is pointed out that the quantum
fluctuations generate non-continuous limit for infinitesimal system-environment
interactions and at the border of the under- and over-damped oscillator.
|
1904.08706v2
|
2019-04-18
|
Rellich, Gagliardo-Nirenberg, Trudinger and Caffarelli-Kohn-Nirenberg inequalities for Dunkl operators and applications
|
In this paper we obtain weighted higher order Rellich, weighted
Gagliardo-Nirenberg, Trudinger, Caffarelli-Kohn-Nirenberg inequalities and the
uncertainty principle for Dunkl operators. Moreover, we introduce an extension
of the classical Caffarelli-Kohn-Nirenberg inequalities. Furthermore, we give
an application of Gagliardo-Nirenberg inequality to the Cauchy problem for the
nonlinear damped wave equations for the Dunkl Laplacian.
|
1904.08725v2
|
2019-04-19
|
Axi-symmetrization near point vortex solutions for the 2D Euler equation
|
We prove a definitive theorem on the asymptotic stability of point vortex
solutions to the full Euler equation in 2 dimensions. More precisely, we show
that a small, Gevrey smooth, and compactly supported perturbation of a point
vortex leads to a global solution of the Euler equation in 2D, which converges
weakly as $t\to\infty$ to a radial profile with respect to the vortex. The
position of the point vortex, which is time dependent, stabilizes rapidly and
becomes the center of the final, radial profile. The mechanism that leads to
stabilization is mixing and inviscid damping.
|
1904.09170v1
|
2019-04-21
|
Quantum state preparation for coupled period tripling oscillators
|
We investigate the quantum transition to a correlated state of coupled
oscillators in the regime where they display period tripling in response to a
drive at triple the eigenfrequency. Correlations are formed between the
discrete oscillation phases of individual oscillators. The evolution toward the
ordered state is accompanied by the transient breaking of the symmetry between
seemingly equivalent configurations. We attribute this to the nontrivial
geometric phase that characterizes period tripling. We also show that the
Wigner distribution of a single damped quantum oscillator can display a minimum
at the classically stable zero-amplitude state.
|
1904.09628v1
|
2019-04-28
|
Quantum noise in the spin transfer torque effect
|
Describing the microscopic details of the interaction of magnets and
spin-polarized currents is key to achieve control of such systems at the
microscopic level. Here we discuss a description based on the Keldysh
technique, casting the problem in the language of open quantum systems. We
reveal the origin of noise in the presence of both field-like and damping like
terms in the equation of motion arising from spin conductance.
|
1904.12372v1
|
2019-06-03
|
Magnon-phonon interactions in magnetic insulators
|
We address the theory of magnon-phonon interactions and compute the
corresponding quasi-particle and transport lifetimes in magnetic insulators
with focus on yttrium iron garnet at intermediate temperatures from anisotropy-
and exchange-mediated magnon-phonon interactions, the latter being derived from
the volume dependence of the Curie temperature. We find in general weak effects
of phonon scattering on magnon transport and the Gilbert damping of the
macrospin Kittel mode. The magnon transport lifetime differs from the
quasi-particle lifetime at shorter wavelengths.
|
1906.01042v1
|
2019-06-17
|
Time discretization of an initial value problem for a simultaneous abstract evolution equation applying to parabolic-hyperbolic phase-field systems
|
This article deals with a simultaneous abstract evolution equation. This
includes a parabolic-hyperbolic phase-field system as an example which consists
of a parabolic equation for the relative temperature coupled with a semilinear
damped wave equation for the order parameter. Although a time discretization of
an initial value problem for an abstract evolution equation has been studied,
time discretizations of initial value problems for simultaneous abstract
evolution equations seem to be not studied yet. In this paper we focus on a
time discretization of a simultaneous abstract evolution equation applying to
parabolic-hyperbolic phase-field systems. Moreover, we can establish an error
estimate for the difference between continuous and discrete solutions.
|
1906.06887v1
|
2019-06-20
|
Low-cost ultrasonic distance measurement in a mechanical resonance experiment
|
We present a low-cost, dual-probe position sensor in a mechanical resonance
experiment suitable for deployment in large lab courses with multiple stations.
The motion of the two ends of a driven, damped spring oscillator is recorded
with US-100 ultrasonic distance sensors and ESP8266 microcontrollers. Sensor
lag is compensated via a modified Savitzky-Golay filter. Data is downloaded to
a computer via Wi-Fi in a format suitable for analysis in Logger Pro. Due to
the simple and fast data acquisition process, students can gather sufficient
data to plot curves of the amplitude and phase lag as a function of driving
frequency.
|
1906.08778v1
|
2019-06-25
|
Finite-Dimensional Controllers for Robust Regulation of Boundary Control Systems
|
We study the robust output regulation of linear boundary control systems by
constructing extended systems. The extended systems are established based on
solving static differential equations under two new conditions. We first
consider the abstract setting and present finite-dimensional reduced order
controllers. The controller design is then used for particular PDE models:
high-dimensional parabolic equations and beam equations with Kelvin-Voigt
damping. Numerical examples will be presented using Finite Element Method.
|
1906.10345v3
|
2019-07-06
|
Angle-resolved broadband ferromagnetic resonance apparatus enabled through a spring-loaded sample mounting manipulator
|
Broadband ferromagnetic resonance is a useful technique to determine the
magnetic anisotropy and study the magnetization dynamics of magnetic thin
films. We report a spring-loaded sample loading manipulator for reliable sample
mounting and rotation. The manipulator enables maximum signal, enhances system
stability and is particularly useful for fully automated in-plane-field
angle-resolved measurements. This angle-resolved broadband ferromagnetic
resonance apparatus provides a viable method to study anisotropic damping and
weak magnetic anisotropies, both vital for fundamental research and
applications.
|
1907.03097v1
|
2019-07-23
|
Trees and Islands -- Machine learning approach to nuclear physics
|
We implement machine learning algorithms to nuclear data. These algorithms
are purely data driven and generate models that are capable to capture
intricate trends. Gradient boosted trees algorithm is employed to generate a
trained model from existing nuclear data, which is used for prediction for data
of damping parameter, shell correction energies, quadrupole deformation,
pairing gaps, level densities and giant dipole resonance for large number of
nuclei. We, in particular, predict level density parameter for superheavy
elements which is of great current interest. The predictions made by the
machine learning algorithm is found to have standard deviation from 0.00035 to
0.73.
|
1907.09764v1
|
2019-07-31
|
Multiple Energy Storage Rings
|
Energy recovery linacs have been studied and developed over a number of
decades. In the standard arrangement there is a separate particle source and
particle beam dump. In this paper, a new arrangement is explored where the
energy recovery linac is used as an energy source in a storage ring which has
multiple beam energies. Several interesting topologies for the multiple beam
energies are shown schematically. Possible energy equilibria with and without
radiation damping are discussed. This idea may have applications to the problem
of electron cooling.
|
1907.13461v1
|
2019-10-07
|
Quasiclassical nonlinear plasmon resonance in graphene
|
Electrons in graphene behave like relativistic Dirac particles which can
reduce velocity of light by two orders of magnitude in the form of
plasmon-polaritons. Here we show how these properties lead to a peculiar
nonlinear plasmon response in the quasiclassical regime of terahertz
frequencies. On one hand we show how interband plasmon damping is suppressed by
the relativistic Klein tunneling effect. On the other hand we demonstrate huge
enhancement of the nonlinear intraband response when plasmon velocity
approaches the resonance with the electron Fermi velocity. This extreme
sensitivity on the plasmon intensity could be used for new terahertz
technologies.
|
1910.03017v2
|
2019-10-18
|
Square-integrable eigenfunctions in quantizing the Bateman oscillator model
|
In a recent paper [Phys. Lett. A 383 (2019) 2836; arXiv:1906.05121
[quant-ph]], Bagarello, Gargano, and Roccati have claimed that no
square-integrable vacuum exists in quantizing the Bateman oscillator model. In
this paper, we rebut their claim by actually deriving the square-integrable
vacuum eigenfunction using a common procedure. We see that no problems occur in
quantizing the Bateman oscillator model.
|
1910.08271v1
|
2019-10-25
|
A damped forward-backward algorithm for stochastic generalized Nash equilibrium seeking
|
We consider a stochastic generalized Nash equilibrium problem (GNEP) with
expected-value cost functions. Inspired by Yi and Pavel (Automatica, 2019), we
propose a distributed GNE seeking algorithm by exploiting the forward-backward
operator splitting and a suitable preconditioning matrix. Specifically, we
apply this method to the stochastic GNEP, where, at each iteration, the
expected value of the pseudo-gradient is approximated via a number of random
samples. Our main contribution is to show almost sure convergence of our
proposed algorithm if the sample size grows large enough.
|
1910.11776v2
|
2019-10-27
|
Phase slip statistics of a single isolated flux-biased superconducting ring
|
We describe measurements of the thermally-activated transitions between
fluxoid states of a single isolated superconducting ring. We compare these
measurements with theoretical predictions in which all of the relevant
parameters are determined via independent characterization of the same ring.
This no-free-parameters comparison shows qualitative agreement over a wide
range of temperatures. We discuss possible origins for the remaining
discrepancies between the data and theory, in particular the choice of model
for the superconducting order parameter's damping.
|
1910.12296v3
|
2019-10-28
|
Reply to Comment on "A no-go result for the quantum damped harmonic oscillator"
|
In a recent paper, \cite{deguchi}, Deguchi and Fujiwara claim that our
results in \cite{BGR} are wrong, and compute what they claim is the square
integrable vacuum of their annihilation operators. In this brief note, we show
that their vacuum is indeed not a vacuum, and we try to explain what is behind
their mistake. We also consider a very simple example clarifying the core of
the problem.
|
1910.12561v1
|
2019-11-30
|
Robustness Evaluation of the Butterfly Optimization Algorithm on a Control System
|
In this paper, the Butterfly Optimization Algorithm (BOA) proposed by [1] is
adopted to optimize the parameters of a designed Lead-Lad Controller so as to
obtain a stabilized control system. Numerical analysis was carried out for BOA
on the control problem and the results are compared to those obtained from the
well known Genetic Algorithm (GA) and Differential Evolution (DE) Algorithm.
BOA performs better in terms of eigenvalue analysis but similar to GA and DE in
terms of optimizing the minimum damping coefficient for the control system
|
1912.00185v1
|
2019-12-05
|
Blow up for small-amplitude semilinear wave equations with mixed nonlinearities on asymptotically Euclidean manifolds
|
In this work, we investigate the problem of finite time blow up as well as
the upper bound estimates of lifespan for solutions to small-amplitude
semilinear wave equations with mixed nonlinearities $a |u_t|^p+b |u|^q$, posed
on asymptotically Euclidean manifolds, which is related to both the Strauss
conjecture and Glassey conjecture. In some cases, we obtain existence results,
where the lower bound of the lifespan agrees with the upper bound in order. In
addition, our results apply for semilinear damped wave equations, when the
coefficient of the dissipation term is integrable (without sign condition) and
space-independent.
|
1912.02561v1
|
2019-12-13
|
On an existence theory for a fluid-beam problem encompassing possible contacts
|
In this paper we consider a coupled system of pdes modelling the interaction
between a two--dimensional incompressible viscous fluid and a one--dimensional
elastic beam located on the upper part of the fluid domain boundary. We design
a functional framework to define weak solutions in case of contact between the
elastic beam and the bottom of the fluid cavity. We then prove that such
solutions exist globally in time regardless a possible contact by approximating
the beam equation by a damped beam and letting this additional viscosity
vanish.
|
1912.06396v1
|
2019-12-16
|
Performance and error modeling of Deutsch's algorithm in IBM Q
|
The performance of quantum computers today can be studied by analyzing the
effect of errors in the result of simple quantum algorithms. The modeling and
characterization of these errors is relevant to correct them, for example, with
quantum correcting codes. In this article we characterize the error of the five
qubits quantum computer ibmqx4 (IBM Q), using a Deutsch algorithm and modeling
the error by Generalized Amplitude Damping (GAD) and a unitary misalignment
operation.
Keywords: Quantum Deutsch's algorithm, Quantum error models, IBM Quantum
Experience
|
1912.07486v1
|
2019-12-17
|
Global cosmic string networks as a function of tension
|
We investigate the properties of global cosmic string networks as a function
of the ratio of string tension to Goldstone-field coupling, and as a function
of the Hubble damping strength. Our results show unambiguously that the string
density is sensitive to this ratio. We also find that existing semi-analytical
(one-scale) models must be missing some important aspect of the network
dynamics. Our results point the way towards improving such models.
|
1912.08058v2
|
2019-12-20
|
Exact Model Reduction and Fast Forced Response Calculation in High-Dimensional Nonlinear Mechanical Systems
|
We show how spectral submanifold (SSM) theory can be used to extract
forced-response curves, including isolas, without any numerical simulation in
high-degree-of-freedom, periodically forced mechanical systems. We use
multivariate recurrence relations to construct the SSMs, achieving a major
speed-up relative to earlier autonomous SSM algorithms. The increase in
computational efficiency promises to close the current gap between studying
lower-dimensional academic examples and analyzing larger systems obtained from
finite-element modeling, as we illustrate on a discretization of a
damped-forced beam model.
|
1912.11399v1
|
2019-12-24
|
Enstrophy dissipation and vortex thinning for the incompressible 2D Navier-Stokes equations
|
By direct numerical simulation to the two-dimensional Navier-Stokes equations
with small-scale forcing and large-scale damping, Xiao-Wan-Chen-Eyink (2009)
found an evidence that inverse energy cascade may proceed with the vortex
thinning mechanism. On the other hand, Alexakis-Doering (2006) calculated upper
bound of the bulk averaged enstrophy dissipation rate of the steady-state two
dimensional turbulence. {In this paper, we show that vortex thinning induces
enhanced dissipation with strictly slower vanishing order of the enstrophy
dissipation than $Re^{-1}$.}
|
1912.11479v2
|
2019-12-26
|
Bifurcation analysis of a density oscillator using two-dimensional hydrodynamic simulation
|
A density oscillator exhibits limit-cycle oscillations driven by the density
difference of the two fluids. We performed two-dimensional hydrodynamic
simulations with a simple model, and reproduced the oscillatory flow observed
in experiments. As the density difference is increased as a bifurcation
parameter, a damped oscillation changes to a limit-cycle oscillation through a
supercritical Hopf bifurcation. We estimated the critical density difference at
the bifurcation point and confirmed that the period of the oscillation remains
finite even around the bifurcation point.
|
1912.11806v2
|
2019-12-31
|
Neutrino evolution and quantum decoherence
|
Neutrino interactions with an external environment can in influence the
neutrino oscillation pattern and the oscillations can be damped as a result of
the neutrino quantum decoherence. In particular, the quantum decoherence of
neutrino states engendered by the neutrino radiative decay accounting for the
nonstandard interactions (NSI) leads to the suppression of flavor neutrino
oscillations in the solar neutrino fluxes.
|
1912.13311v1
|
2020-03-02
|
Optimal transport: discretization and algorithms
|
This chapter describes techniques for the numerical resolution of optimal
transport problems. We will consider several discretizations of these problems,
and we will put a strong focus on the mathematical analysis of the algorithms
to solve the discretized problems. We will describe in detail the following
discretizations and corresponding algorithms: the assignment problem and
Bertsekas auction's algorithm; the entropic regularization and Sinkhorn-Knopp's
algorithm; semi-discrete optimal transport and Oliker-Prussner or damped
Newton's algorithm, and finally semi-discrete entropic regularization. Our
presentation highlights the similarity between these algorithms and their
connection with the theory of Kantorovich duality.
|
2003.00855v1
|
2020-03-03
|
Preconditioning mixed finite elements for tide models
|
We describe a fully discrete mixed finite element method for the linearized
rotating shallow water model, possibly with damping. While Crank-Nicolson
time-stepping conserves energy in the absence of drag or forcing terms and is
not subject to a CFL-like stability condition, it requires the inversion of a
linear system at each step. We develop weighted-norm preconditioners for this
algebraic system that are nearly robust with respect to the physical and
discretization parameters in the system. Numerical experiments using Firedrake
support the theoretical results.
|
2003.01632v1
|
2020-03-12
|
Geometry-aware Dynamic Movement Primitives
|
In many robot control problems, factors such as stiffness and damping
matrices and manipulability ellipsoids are naturally represented as symmetric
positive definite (SPD) matrices, which capture the specific geometric
characteristics of those factors. Typical learned skill models such as dynamic
movement primitives (DMPs) can not, however, be directly employed with
quantities expressed as SPD matrices as they are limited to data in Euclidean
space.
In this paper, we propose a novel and mathematically principled framework
that uses Riemannian metrics to reformulate DMPs such that the resulting
formulation can operate with SPD data in the SPD manifold. Evaluation of the
approach demonstrates that beneficial properties of DMPs such as change of the
goal during operation apply also to the proposed formulation.
|
2003.06061v1
|
2020-03-16
|
Extreme Hawking Radiation
|
Modeling the collapse of an extreme Reissner-Nordstr\"om (ERN) black hole by
solving the corresponding moving mirror model for the trajectory that
asymptotically approaches uniform acceleration, we obtain the non-zero beta
coefficients for all times. Finite energy is emitted, the radiation spectra is
non-thermal (non-steady / not Planck), soft particles characterize the
evaporation, and particle production at ultra-late times is damped.
Entanglement entropy diverges with no Page curve turn-over, demonstrating
non-thermal information loss. The radiation obeys time-reversal symmetry.
|
2003.07016v1
|
2020-03-23
|
Mixed boundary valued problem for linear and nonlinear wave equations in domains with fractal boundaries
|
The weak well-posedness, with the mixed boundary conditions, of the strongly
damped linear wave equation and of the non linear Westervelt equation is proved
in the largest natural class of Sobolev admissible non-smooth domains. In the
framework of uniform domains in R^2 or R^3 we also validate the approximation
of the solution of the Wester-velt equation on a fractal domain by the
solutions on the prefractals using the Mosco convergence of the corresponding
variational forms.
|
2003.10134v2
|
2020-08-02
|
Partially Coherent Direct Sum Channels
|
We introduce Partially Coherent Direct Sum (PCDS) quantum channels, as a
generalization of the already known Direct Sum quantum channels. We derive
necessary and sufficient conditions to identify the subset of those maps which
are degradable, and provide a simplified expression for their quantum
capacities. Interestingly, the special structure of PCDS allows us to extend
the computation of the quantum capacity formula also for quantum channels which
are explicitly not degradable (nor antidegradable). We show instances of
applications of the results to dephasing channels, amplitude damping channels
and combinations of the two.
|
2008.00494v4
|
2020-08-05
|
Time scales in the thermal dynamics of magnetic dipolar clusters
|
The collective behavior of thermally active structures offers clues on the
emergent degrees of freedom and the physical mechanisms that determine the low
energy state of a variety of systems. Here, the thermally active dynamics of
magnetic dipoles at square plaquettes is modeled in terms of Brownian
oscillators in contact with a heat bath. Solution of the Langevin equation for
a set of interacting x-y dipoles allows the identification of the time scales
and correlation length that reveal how interactions, temperature, damping and
inertia may determine the frequency modes of edge and bulk magnetic mesospins
in artificial dipolar systems.
|
2008.01891v2
|
2020-08-06
|
Plasmonic nonreciprocity driven by band hybridization in moiré materials
|
We propose a new current-driven mechanism for achieving significant plasmon
dispersion nonreciprocity in systems with narrow, strongly hybridized electron
bands. The magnitude of the effect is controlled by the strength of
electron-electron interactions $\alpha$, which leads to its particular
prominence in moir\'e materials, characterized by $\alpha \gg 1$. Moreover,
this phenomenon is most evident in the regime where Landau damping is quenched
and plasmon lifetime is increased. The synergy of these two effects holds a
great promise for novel optoelectronic applications of moir\'e materials.
|
2008.02804v1
|
2022-01-12
|
Light and microwave driven spin pumping across FeGaB-BiSb interface
|
3-D topological insulators (TI) with large spin Hall conductivity have
emerged as potential candidates for spintronic applications. Here, we report
spin to charge conversion in bilayers of amorphous ferromagnet (FM)
Fe_{78}Ga_{13}B_{9} (FeGaB) and 3-D TI Bi_{85}Sb_{15} (BiSb) activated by two
complementary techniques: spin pumping and ultrafast spin-current injection. DC
magnetization measurements establish the soft magnetic character of FeGaB
films, which remains unaltered in the heterostructures of FeGaB-BiSb. Broadband
ferromagnetic resonance (FMR) studies reveal enhanced damping of precessing
magnetization and large value of spin mixing conductance (5.03 x 10^{19}
m^{-2}) as the spin angular momentum leaks into the TI layer. Magnetic field
controlled bipolar dc voltage generated across the TI layer by inverse spin
Hall effect is analyzed to extract the values of spin Hall angle and spin
diffusion length of BiSb. The spin pumping parameters derived from the
measurements of the femtosecond light-pulse-induced terahertz emission are
consistent with the result of FMR. Kubo-Bastin formula and tight-binding model
calculations shed light on the thickness-dependent spin-Hall conductivity of
the TI films, with predictions that are in remarkable agreement with the
experimental data. Our results suggest that room temperature deposited
amorphous and polycrystalline heterostructures provide a promising platform for
creating novel spin orbit torque devices.
|
2201.04686v1
|
2024-03-21
|
Picotesla-sensitivity microcavity optomechanical magnetometry
|
Cavity optomechanical systems have enabled precision sensing of magnetic
fields, by leveraging the optical resonance-enhanced readout and mechanical
resonance-enhanced response. Previous studies have successfully achieved
scalable and reproducible microcavity optomechanical magnetometry (MCOM) by
incorporating Terfenol-D thin films into high-quality ($Q$) factor whispering
gallery mode (WGM) microcavities. However, the sensitivity was limited to 585
pT/Hz$^{1/2}$, over 20 times inferior to those using Terfenol-D particles. In
this work, we propose and demonstrate a high-sensitivity and scalable MCOM
approach by sputtering a FeGaB thin film onto a high-$Q$ SiO$_2$ WGM microdisk.
Theoretical studies are conducted to explore the magnetic actuation constant
and noise-limited sensitivity by varying the parameters of the FeGaB film and
SiO$_2$ microdisk. Multiple magnetometers with different radii are fabricated
and characterized. By utilizing a microdisk with a radius of 355 $\mu$m and a
thickness of 1 $\mu$m, along with a FeGaB film with a radius of 330 $\mu$m and
a thickness of 1.3 $\mu$m, we have achieved a remarkable peak sensitivity of
1.68 pT/Hz$^{1/2}$ at 9.52 MHz. This represents a significant improvement of
over two orders of magnitude compared with previous studies employing sputtered
Terfenol-D film. Notably, the magnetometer operates without a bias magnetic
field, thanks to the remarkable soft magnetic properties of the FeGaB film.
Furthermore, as a proof-of-concept, we have demonstrated the real-time
measurement of a pulsed magnetic field simulating the corona current in a
high-voltage transmission line using our developed magnetometer. These
high-sensitivity magnetometers hold great potential for various applications,
such as magnetic induction tomography and corona current monitoring.
|
2403.14301v1
|
2015-08-28
|
Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching
|
Electric-field modulation of magnetism in strain-mediated multiferroic
heterostructures is considered a promising scheme for enabling memory and
magnetic microwave devices with ultralow power consumption. However, it is not
well understood how electric-field-induced strain influences magnetic
relaxation, an important physical process for device applications. Here we
investigate resonant magnetization dynamics in ferromagnet/ferrolectric
multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct
strain states provided by electric-field-induced ferroelectric phase
transition. The strain not only modifies magnetic anisotropy but also magnetic
relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic
Gilbert damping by electric field, which is attributed to strain-induced tuning
of spin-orbit coupling. By contrast, a small but measurable change in extrinsic
linewidth broadening is attributed to inhomogeneous ferroelastic domain
switching during the phase transition of the PMN-PT substrate.
|
1508.07290v2
|
2022-01-11
|
Resonant Precession of Magnetization and Precession -- Induced DC voltages in FeGaB Thin Films
|
Measurements of frequency dependent ferromagnetic resonance (FMR) and spin
pumping driven dc voltage (V_{dc}) are reported for amorphous films of
Fe_{78}Ga_{13}B_{9} (FeGaB) alloy to address the phenomenon of self-induced
inverse spin Hall effect (ISHE) in plain films of metallic ferromagnets. The
V_{dc} signal, which is antisymmetric on field reversal, comprises of symmetric
and asymmetric Lorentzians centered around the resonance field. Dominant role
of thin film size effects is seen in setting the magnitude of static
magnetization, V_{dc} and dynamics of magnetization precession in thinner films
(\leq 8 nm). The film thickness dependence of magnetization parameters
indicates the presence of a magnetically disordered region at the
film-substrate interface, which may promote preferential flow of spins
generated by the precessing magnetization towards the substrate. However, the
V_{dc} signal also draws contributions from rectification effects of a \approx
0.4 \% anisotropic magnetoresistance and a large (\approx 54 n\Omega.m)
anomalous Hall resistivity (AHR) of these films which ride over the effect of
spin-orbit coupling driven spin-to-charge conversion near the film-substrate
interface. We have addressed these data in the framework of the existing
theories of electrodynamics of a ferromagnetic film subjected to
radio-frequency field in a coplanar waveguide geometry. Our estimation of the
self-induced ISHE for the sample with 54 n\Omega.m AHR shows that it may
contribute significantly (\approx 90\%) to the measured symmetric voltage. This
study is expected to be very useful for fully understanding the spin pumping
induced dc voltages in metallic ferromagnets with disordered interfaces and
large anomalous Hall effect.
|
2201.03739v1
|
2014-11-22
|
Quantification of the spin-Hall anti-damping torque with a resonance spectrometer
|
We present a simple technique using a cavity-based resonance spectrometer to
quantify the anti-damping torque due to the spin Hall effect. Modification of
ferromagnetic resonance is observed as a function of small DC current in
sub-mm-wide strips of bilayers, consisting of magnetically soft FeGaB and
strong spin-Hall metal Ta. From the detected current-induced linewidth change,
we obtain an effective spin Hall angle of 0.08-0.09 independent of the magnetic
layer thickness. Our results demonstrate that a sensitive resonance
spectrometer can be a general tool to investigate spin Hall effects in various
material systems, even those with vanishingly low conductivity and
magnetoresistance.
|
1411.6166v1
|
2021-12-10
|
Enhanced Planar Antenna Efficiency Through Magnetic Thin-Films
|
This work proposes to use magnetic material as the substrate of planar
antennas to overcome the platform effect caused by the conducting ground plane.
The upper bound of the radiation efficiency of an electric-current-driven
low-profile antenna is theoretically derived, which is inversely proportional
to the Gilbert damping factor of the magnetic material. Meanwhile, the
improvement of radiation due to the use of magnetic material is demonstrated by
a three-dimensional (3D) multiphysics and multiscale time-domain model. The
simulation results match the theoretical derivation, showing 25% radiation
efficiency from a planar antenna backed by a FeGaB thin film with 2.56 um
thickness. Furthermore, for conductive ferromagnetic materials, it is shown
that the eddy current loss can be well suppressed by laminating the thin film
into multiple layers. The radiation efficiency of the modeled antenna with a
conductive ferromagnetic substrate is improved from 2.2% to 11.8% by dividing
the substrate into 10 layers, with a ferromagnetic material fill factor of 93%.
|
2201.04932v1
|
2017-09-29
|
Non-local Gilbert damping tensor within the torque-torque correlation model
|
An essential property of magnetic devices is the relaxation rate in magnetic
switching which depends strongly on the damping in the magnetisation dynamics.
It was recently measured that damping depends on the magnetic texture and,
consequently, is a non-local quantity. The damping enters the
Landau-Lifshitz-Gilbert equation as the phenomenological Gilbert damping
parameter $\alpha$, that does not, in a straight forward formulation, account
for non-locality. Efforts were spent recently to obtain Gilbert damping from
first principles for magnons of wave vector $\mathbf{q}$. However, to the best
of our knowledge, there is no report about real space non-local Gilbert damping
$\alpha_{ij}$. Here, a torque-torque correlation model based on a tight binding
approach is applied to the bulk elemental itinerant magnets and it predicts
significant off-site Gilbert damping contributions, that could be also
negative. Supported by atomistic magnetisation dynamics simulations we reveal
the importance of the non-local Gilbert damping in atomistic magnetisation
dynamics. This study gives a deeper understanding of the dynamics of the
magnetic moments and dissipation processes in real magnetic materials. Ways of
manipulating non-local damping are explored, either by temperature, material's
doping or strain.
|
1709.10365v1
|
2016-02-23
|
Experimental Investigation of Temperature-Dependent Gilbert Damping in Permalloy Thin Films
|
The Gilbert damping of ferromagnetic materials is arguably the most important
but least understood phenomenological parameter that dictates real-time
magnetization dynamics. Understanding the physical origin of the Gilbert
damping is highly relevant to developing future fast switching spintronics
devices such as magnetic sensors and magnetic random access memory. Here, we
report an experimental study of temperature-dependent Gilbert damping in
permalloy (Py) thin films of varying thicknesses by ferromagnetic resonance.
From the thickness dependence, two independent contributions to the Gilbert
damping are identified, namely bulk damping and surface damping. Of particular
interest, bulk damping decreases monotonically as the temperature decreases,
while surface damping shows an enhancement peak at the temperature of ~50 K.
These results provide an important insight to the physical origin of the
Gilbert damping in ultrathin magnetic films.
|
1602.07325v1
|
2019-02-22
|
Strongly Enhanced Gilbert Damping in 3d Transition Metal Ferromagnet Monolayers in Contact with Topological Insulator Bi2Se3
|
Engineering Gilbert damping of ferromagnetic metal films is of great
importance to exploit and design spintronic devices that are operated with an
ultrahigh speed. Based on scattering theory of Gilbert damping, we extend the
torque method originally used in studies of magnetocrystalline anisotropy to
theoretically determine Gilbert dampings of ferromagnetic metals. This method
is utilized to investigate Gilbert dampings of 3d transition metal ferromagnet
iron, cobalt and nickel monolayers that are contacted by the prototypical
topological insulator Bi2Se3. Amazingly, we find that their Gilbert dampings
are strongly enhanced by about one order in magnitude, compared with dampings
of their bulks and free-standing monolayers, owing to the strong spin-orbit
coupling of Bi2Se3. Our work provides an attractive route to tailoring Gilbert
damping of ferromagnetic metallic films by putting them in contact with
topological insulators.
|
1902.08700v1
|
2018-08-20
|
Gilbert damping of [Co/Pd]n/Py multilayer thin films
|
Understanding the Gilbert damping in exchange-coupled multilayer materials is
particularly important to develop future fast switching spintronics devices.
Here, we report an experimental investigation of temperature-dependent Gilbert
damping in [Co/Pd]n/Py multilayer films of varying the number of Co/Pd
repetitions by ferromagnetic resonance. The results demonstrate that three
independent contributions to the Gilbert damping are identified, namely the
intrinsic Gilbert damping, the inhomogeneous linewidth broadening and the
two-magnon scattering contribution. Of particular interest, the two-magnon
scattering intensity increases as the enlargement of number repetitions of
Co/Pd due to the larger pinning effect at the interface between Py and the
Co/Pd layers. The Gilbert damping increases monotonically as the temperature
decreases from 300K to 50K. Our findings open the door to comprehend the
physical origin of the Gilbert damping in ultrathin exchange-coupled multilayer
films.
|
1808.06515v2
|
2007-08-24
|
Enhancement of the Gilbert damping constant due to spin pumping in noncollinear ferromagnet/nonmagnet/ferromagnet trilayer systems
|
We analyzed the enhancement of the Gilbert damping constant due to spin
pumping in non-collinear ferromagnet / non-magnet / ferromagnet trilayer
systems. We show that the Gilbert damping constant depends both on the
precession angle of the magnetization of the free layer and on the direction of
the magntization of the fixed layer. We find the condition to be satisfied to
realize strong enhancement of the Gilbert damping constant.
|
0708.3323v1
|
2017-06-14
|
Temperature-dependent Gilbert damping of Co2FeAl thin films with different degree of atomic order
|
Half-metallicity and low magnetic damping are perpetually sought for in
spintronics materials and full Heusler alloys in this respect provide
outstanding properties. However, it is challenging to obtain the well-ordered
half-metallic phase in as-deposited full Heusler alloys thin films and theory
has struggled to establish a fundamentals understanding of the temperature
dependent Gilbert damping in these systems. Here we present a study of the
temperature dependent Gilbert damping of differently ordered as-deposited
Co2FeAl full Heusler alloy thin films. The sum of inter- and intraband electron
scattering in conjunction with the finite electron lifetime in Bloch states
govern the Gilbert damping for the well-ordered phase in contrast to the
damping of partially-ordered and disordered phases which is governed by
interband electronic scattering alone. These results, especially the ultralow
room temperature intrinsic damping observed for the well-ordered phase provide
new fundamental insights to the physical origin of the Gilbert damping in full
Heusler alloy thin films.
|
1706.04670v2
|
2023-11-27
|
Gilbert damping in two-dimensional metallic anti-ferromagnets
|
A finite spin life-time of conduction electrons may dominate Gilbert damping
of two-dimensional metallic anti-ferromagnets or anti-ferromagnet/metal
heterostructures. We investigate the Gilbert damping tensor for a typical
low-energy model of a metallic anti-ferromagnet system with honeycomb magnetic
lattice and Rashba spin-orbit coupling for conduction electrons. We distinguish
three regimes of spin relaxation: exchange-dominated relaxation for weak
spin-orbit coupling strength, Elliot-Yafet relaxation for moderate spin-orbit
coupling, and Dyakonov-Perel relaxation for strong spin-orbit coupling. We
show, however, that the latter regime takes place only for the in-plane Gilbert
damping component. We also show that anisotropy of Gilbert damping persists for
any finite spin-orbit interaction strength provided we consider no spatial
variation of the N\'eel vector. Isotropic Gilbert damping is restored only if
the electron spin-orbit length is larger than the magnon wavelength. Our theory
applies to MnPS3 monolayer on Pt or to similar systems.
|
2311.16268v2
|
2008-07-31
|
Scattering Theory of Gilbert Damping
|
The magnetization dynamics of a single domain ferromagnet in contact with a
thermal bath is studied by scattering theory. We recover the
Landau-Liftshitz-Gilbert equation and express the effective fields and Gilbert
damping tensor in terms of the scattering matrix. Dissipation of magnetic
energy equals energy current pumped out of the system by the time-dependent
magnetization, with separable spin-relaxation induced bulk and spin-pumping
generated interface contributions. In linear response, our scattering theory
for the Gilbert damping tensor is equivalent with the Kubo formalism.
|
0807.5009v1
|
2024-01-18
|
Real-space nonlocal Gilbert damping from exchange torque correlation applied to bulk ferromagnets and their surfaces
|
In this work we present an ab initio scheme based on linear response theory
of exchange torque correlation, implemented into the real-space
Korringa-Kohn-Rostoker (RS-KKR) framework to calculate diagonal elements of the
atomic-site-dependent intrinsic Gilbert damping tensor. The method is first
applied to bcc iron and fcc cobalt bulk systems. Beside reproducing earlier
results from the literature for those bulk magnets, the effect of the lattice
compression is also studied for Fe bulk, and significant changes for the
Gilbert damping are found. Furthermore, (001)-oriented surfaces of Fe and Co
are also investigated. It is found that the on-site Gilbert damping increases
in the surface atomic layer and decreases in the subsurface layer, and
approaches the bulk value moving further inside the magnets. Realistic atomic
relaxation of the surface layers enhances the identified effects. The
first-neighbor damping parameters are extremely sensitive to the surface
relaxation. Despite their inhomogeneity caused by the surface, the transverse
Gilbert damping tensor components remain largely insensitive to the
magnetization direction.
|
2401.09938v2
|
2007-06-12
|
Gilbert and Landau-Lifshitz damping in the presense of spin-torque
|
A recent article by Stiles et al. (cond-mat/0702020) argued in favor of the
Landau-Lifshitz damping term in the micromagnetic equations of motion over that
of the more commonly accepted Gilbert damping form. Much of their argument
revolved around spin-torque driven domain wall motion in narrow magnetic wires,
since the presence of spin-torques can more acutely draw a distinction between
the two forms of damping. In this article, the author uses simple arguments and
examples to offer an alternative point of view favoring Gilbert.
|
0706.1736v1
|
2008-04-04
|
Inhomogeneous Gilbert damping from impurities and electron-electron interactions
|
We present a unified theory of magnetic damping in itinerant electron
ferromagnets at order $q^2$ including electron-electron interactions and
disorder scattering. We show that the Gilbert damping coefficient can be
expressed in terms of the spin conductivity, leading to a Matthiessen-type
formula in which disorder and interaction contributions are additive. In a weak
ferromagnet regime, electron-electron interactions lead to a strong enhancement
of the Gilbert damping.
|
0804.0820v2
|
2006-12-01
|
Gilbert damping and spin Coulomb drag in a magnetized electron liquid with spin-orbit interaction
|
We present a microscopic calculation of the Gilbert damping constant for the
magnetization of a two-dimensional spin-polarized electron liquid in the
presence of intrinsic spin-orbit interaction. First we show that the Gilbert
constant can be expressed in terms of the auto-correlation function of the
spin-orbit induced torque. Then we specialize to the case of the Rashba
spin-orbit interaction and we show that the Gilbert constant in this model is
related to the spin-channel conductivity. This allows us to study the Gilbert
damping constant in different physical regimes, characterized by different
orderings of the relevant energy scales -- spin-orbit coupling, Zeeman
coupling, momentum relaxation rate, spin-momentum relaxation rate, spin
precession frequency -- and to discuss its behavior in various limits.
Particular attention is paid to electron-electron interaction effects,which
enter the spin conductivity and hence the Gilbert damping constant via the spin
Coulomb drag coefficient.
|
0612015v1
|
2021-01-07
|
Mechanisms behind large Gilbert damping anisotropies
|
A method with which to calculate the Gilbert damping parameter from a
real-space electronic structure method is reported here. The anisotropy of the
Gilbert damping with respect to the magnetic moment direction and local
chemical environment is calculated for bulk and surfaces of Fe$_{50}$Co$_{50}$
alloys from first principles electronic structure in a real space formulation.
The size of the damping anisotropy for Fe$_{50}$Co$_{50}$ alloys is
demonstrated to be significant. Depending on details of the simulations, it
reaches a maximum-minimum damping ratio as high as 200%. Several microscopic
origins of the strongly enhanced Gilbert damping anisotropy have been examined,
where in particular interface/surface effects stand out, as do local
distortions of the crystal structure. Although theory does not reproduce the
experimentally reported high ratio of 400% [Phys. Rev. Lett. 122, 117203
(2019)], it nevertheless identifies microscopic mechanisms that can lead to
huge damping anisotropies.
|
2101.02794v2
|
2018-08-13
|
Gilbert damping phenomenology for two-sublattice magnets
|
We present a systematic phenomenological description of Gilbert damping in
two-sublattice magnets. Our theory covers the full range of materials from
ferro- via ferri- to antiferromagnets. Following a Rayleigh dissipation
functional approach within a Lagrangian classical field formulation, the theory
captures intra- as well as cross-sublattice terms in the Gilbert damping,
parameterized by a 2$\times$2 matrix. When spin-pumping into an adjacent
conductor causes dissipation, we obtain the corresponding Gilbert damping
matrix in terms of the interfacial spin-mixing conductances. Our model
reproduces the experimentally observed enhancement of the ferromagnetic
resonance linewidth in a ferrimagnet close to its compensation temperature
without requiring an increased Gilbert parameter. It also predicts new
contributions to damping in an antiferromagnet and suggests the resonance
linewidths as a direct probe of the sublattice asymmetry, which may stem from
boundary or bulk.
|
1808.04385v2
|
2021-07-02
|
Anomalous Gilbert Damping and Duffing Features of the SFS {\boldmath $\varphi_0$} Josephson Junction
|
We demonstrate unusual features of phase dynamics, IV-characteristics and
magnetization dynamics of the $\varphi_0$ Josephson junction at small values of
spin-orbit interaction, ratio of Josephson to magnetic energy and Gilbert
damping. In particular, an anomalous shift of the ferromagnetic resonance
frequency with an increase of Gilbert damping is found. The ferromagnetic
resonance curves show the Duffing oscillator behaviour, reflecting the
nonlinear nature of Landau-Lifshitz-Gilbert (LLG) equation. Based on the
numerical analysis of each term in LLG equation we obtained an approximated
equation demonstrated both damping effect and Duffing oscillator features. The
resulting Duffing equation incorporates the Gilbert damping in a special way
across the dissipative term and the restoring force. A resonance method for the
determination of spin-orbit interaction in noncentrosymmetric materials which
play the role of barrier in $\varphi_0$ junctions is proposed.
|
2107.00982v3
|
2023-03-07
|
Electrically tunable Gilbert damping in van der Waals heterostructures of two-dimensional ferromagnetic metals and ferroelectrics
|
Tuning the Gilbert damping of ferromagnetic (FM) metals via a nonvolatile way
is of importance to exploit and design next-generation novel spintronic
devices. Through systematical first-principles calculations, we study the
magnetic properties of the van der Waals heterostructure of two-dimensional FM
metal CrTe2 and ferroelectric (FE) In2Te3 monolayers. The ferromagnetism of
CrTe2 is maintained in CrTe2/In2Te3 and its magnetic easy axis can be switched
from in-plane to out-of-plane by reversing the FE polarization of In2Te3.
Excitingly, we find that the Gilbert damping of CrTe2 is tunable when the FE
polarization of In2Te3 is reversed from upward to downward. By analyzing the
k-dependent contributions to the Gilbert damping, we unravel that such
tunability results from the changed intersections between the bands of CrTe2
and Fermi level on the reversal of the FE polarizations of In2Te3 in
CrTe2/In2Te3. Our work provides an appealing way to electrically tailor Gilbert
dampings of two-dimensional FM metals by contacting them with ferroelectrics.
|
2303.03852v1
|
2015-08-28
|
The inviscid limit for the Landau-Lifshitz-Gilbert equation in the critical Besov space
|
We prove that in dimensions three and higher the Landau-Lifshitz- Gilbert
equation with small initial data in the critical Besov space is globally
wellposed in a uniform way with respect to the Gilbert damping parameter. Then
we show that the global solution converges to that of the Schrodinger maps in
the natural space as the Gilbert damping term vanishes. The proof is based on
some studies on the derivative Ginzburg-Landau equations.
|
1508.07118v3
|
2023-09-20
|
Evaluating Gilbert Damping in Magnetic Insulators from First Principles
|
Magnetic damping has a significant impact on the performance of various
magnetic and spintronic devices, making it a long-standing focus of research.
The strength of magnetic damping is usually quantified by the Gilbert damping
constant in the Landau-Lifshitz-Gilbert equation. Here we propose a
first-principles based approach to evaluate the Gilbert damping constant
contributed by spin-lattice coupling in magnetic insulators. The approach
involves effective Hamiltonian models and spin-lattice dynamics simulations. As
a case study, we applied our method to Y$_3$Fe$_5$O$_{12}$, MnFe$_2$O$_4$ and
Cr$_2$O$_3$. Their damping constants were calculated to be $0.8\times10^{-4}$,
$0.2\times10^{-4}$, $2.2\times 10^{-4}$, respectively at a low temperature. The
results for Y$_3$Fe$_5$O$_{12}$ and Cr$_2$O$_3$ are in good agreement with
experimental measurements, while the discrepancy in MnFe$_2$O$_4$ can be
attributed to the inhomogeneity and small band gap in real samples. The
stronger damping observed in Cr$_2$O$_3$, compared to Y$_3$Fe$_5$O$_{12}$,
essentially results from its stronger spin-lattice coupling. In addition, we
confirmed a proportional relationship between damping constants and the
temperature difference of subsystems, which had been reported in previous
studies. These successful applications suggest that our approach serves as a
promising candidate for estimating the Gilbert damping constant in magnetic
insulators.
|
2309.11152v1
|
2019-06-25
|
Conductivity-Like Gilbert Damping due to Intraband Scattering in Epitaxial Iron
|
Confirming the origin of Gilbert damping by experiment has remained a
challenge for many decades, even for simple ferromagnetic metals. In this
Letter, we experimentally identify Gilbert damping that increases with
decreasing electronic scattering in epitaxial thin films of pure Fe. This
observation of conductivity-like damping, which cannot be accounted for by
classical eddy current loss, is in excellent quantitative agreement with
theoretical predictions of Gilbert damping due to intraband scattering. Our
results resolve the longstanding question about a fundamental damping mechanism
and offer hints for engineering low-loss magnetic metals for cryogenic
spintronics and quantum devices.
|
1906.10326v2
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.