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2015-10-23
|
Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet
|
Laser-induced magnetization precessional dynamics was investigated in
epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly
compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed,
the precession frequency for which exceeded 0.5 THz and originated from the
large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet.
The effective damping constant was approximately 0.03. The corresponding
effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable
to those of the similar Mn-Ga materials. The physical mechanisms for the
Gilbert damping and for the laser-induced excitation of the FMR mode were also
discussed in terms of the spin-orbit-induced damping and the laser-induced
ultrafast modulation of the magnetic anisotropy, respectively.
|
1510.06793v1
|
2017-04-11
|
CoFeAlB alloy with low damping and low magnetization for spin transfer torque switching
|
We investigate the effect of Al doping on the magnetic properties of the
alloy CoFeB. Comparative measurements of the saturation magnetization, the
Gilbert damping parameter $\alpha$ and the exchange constant as a function of
the annealing temperature for CoFeB and CoFeAlB thin films are presented. Our
results reveal a strong reduction of the magnetization for CoFeAlB in
comparison to CoFeB. If the prepared CoFeAlB films are amorphous, the damping
parameter $\alpha$ is unaffected by the Al doping in comparison to the CoFeB
alloy. In contrast, in the case of a crystalline CoFeAlB film, $\alpha$ is
found to be reduced. Furthermore, the x-ray characterization and the evolution
of the exchange constant with the annealing temperature indicate a similar
crystallization process in both alloys. The data proves the suitability of
CoFeAlB for spin torque switching properties where a reduction of the switching
current in comparison with CoFeB is expected.
|
1704.03326v1
|
2017-05-10
|
Negative mobility of a Brownian particle: strong damping regime
|
We study impact of inertia on directed transport of a Brownian particle under
non-equilibrium conditions: the particle moves in a one-dimensional periodic
and symmetric potential, is driven by both an unbiased time-periodic force and
a constant force, and is coupled to a thermostat of temperature T. Within
selected parameter regimes this system exhibits negative mobility, which means
that the particle moves in the direction opposite to the direction of the
constant force. It is known that in such a setup the inertial term is essential
for the emergence of negative mobility and it cannot be detected in the
limiting case of overdamped dynamics. We analyse inertial effects and show that
negative mobility can be observed even in the strong damping regime. We
determine the optimal dimensionless mass for the presence of negative mobility
and reveal three mechanisms standing behind this anomaly: deterministic
chaotic, thermal noise induced and deterministic non-chaotic. The last origin
has never been reported. It may provide guidance to the possibility of
observation of negative mobility for strongly damped dynamics which is of
fundamental importance from the point of view of biological systems, all of
which in situ operate in fluctuating environments.
|
1705.03661v1
|
2018-04-09
|
Damping and clustering into crowded environment of catalytic chemical oscillators
|
A system formed by a crowded environment of catalytic obstacles and complex
oscillatory chemical reactions is inquired. The obstacles are static spheres of
equal radius, which are placed in a random way. The chemical reactions are
carried out in a fluid following a multiparticle collision scheme where the
mass, energy and local momentum are conserved. Firstly, it is explored how the
presence of catalytic obstacles changes the oscillatory dynamics from a limit
cycle to a fix point reached after a damping. The damping is characterized by
the decay constant, which grows linearly with volume fraction for low values of
the mesoscale collision time and the catalytic reaction constant. Additionally,
it is shown that, although the distribution of obstacles is random, there are
regions in the system where the catalytic chemical reactions are favored. This
entails that in average the radius of gyrations of catalytic chemical reaction
does not match with the radius of gyration of obstacles, that is, clusters of
reactions emerge on the catalytic obstacles, even when the diffusion is
significant.
|
1804.03174v1
|
2018-10-09
|
The lifespan of solutions of semilinear wave equations with the scale-invariant damping in one space dimension
|
The critical constant of time-decaying damping in the scale-invariant case is
recently conjectured. It also has been expected that the lifespan estimate is
the same as for the associated semilinear heat equations if the constant is in
the \heat-like" domain. In this paper, we point out that this is not true if
the total integral of the sum of initial position and speed vanishes. In such a
case, we have a new type of the lifespan estimates which is closely related to
the non-damped case in shifted space dimensions.
|
1810.03780v2
|
2019-04-23
|
Ultrafast depinning of domain wall in notched antiferromagnetic nanostructures
|
The pinning and depinning of antiferromagnetic (AFM) domain wall is certainly
the core issue of AFM spintronics. In this work, we study theoretically the
N\'eel-type domain wall pinning and depinning at a notch in an
antiferromagnetic (AFM) nano-ribbon. The depinning field depending on the notch
dimension and intrinsic physical parameters are deduced and also numerically
calculated. Contrary to conventional conception, it is revealed that the
depinning field is remarkably dependent of the damping constant and the
time-dependent oscillation of the domain wall position in the weakly damping
regime benefits to the wall depinning, resulting in a gradual increase of the
depinning field up to a saturation value with increasing damping constant. A
one-dimensional model accounting of the internal dynamics of domain wall is
used to explain perfectly the simulated results. It is demonstrated that the
depinning mechanism of an AFM domain wall differs from ferromagnetic domain
wall by exhibiting a depinning speed typically three orders of magnitude faster
than the latter, suggesting the ultrafast dynamics of an AFM system.
|
1904.10197v2
|
2019-08-30
|
Magnetization reversal, damping properties and magnetic anisotropy of L10-ordered FeNi thin films
|
L10 ordered magnetic alloys such as FePt, FePd, CoPt and FeNi are well known
for their large magnetocrystalline anisotropy. Among these, L10-FeNi alloy is
economically viable material for magnetic recording media because it does not
contain rare earth and noble elements. In this work, L10-FeNi films with three
different strengths of anisotropy were fabricated by varying the deposition
process in molecular beam epitaxy system. We have investigated the
magnetization reversal along with domain imaging via magneto optic Kerr effect
based microscope. It is found that in all three samples, the magnetization
reversal is happening via domain wall motion. Further ferromagnetic resonance
(FMR) spectroscopy was performed to evaluate the damping constant and magnetic
anisotropy. It was observed that the FeNi sample with moderate strength of
anisotropy exhibits low value of damping constant ~ 4.9X10^-3. In addition to
this, it was found that the films possess a mixture of cubic and uniaxial
anisotropies.
|
1908.11761v1
|
2004-09-10
|
Constraint on the Squeeze Parameter of Inflaton from Cosmological Constant
|
The inflaton is highly likely to settle in a squeezed vacuum state after
inflation. The relic inflaton after inflation and reheating undergoes a damped
oscillatory motion and contributes to the effective cosmological constant. We
interpret the renormalized energy density from the squeezed vacuum state as an
effective cosmological constant. Using the recent observational data on the
cosmological constant, we find the constraint on the squeeze parameter of the
inflaton in the early universe.
|
0409044v1
|
2007-02-12
|
The Ucsd/Keck Damped Lya Abundance Database: A Decade of High Resolution Spectroscopy
|
We publish the Keck/HIRES and Keck/ESI spectra that we have obtained during
the first 10 years of Keck observatory operations. Our full sample includes 42
HIRES spectra and 39 ESI spectra along 65 unique sightlines providing abundance
measurements on ~85 damped Lya systems. The normalized data can be downloaded
from the journal or from our supporting website:
http://www.ucolick.org/~xavier/DLA/. The database includes all of the
sightlines that have been included in our papers on the chemical abundances,
kinematics, and metallicities of the damped Lya systems. This data has also
been used to argue for variations in the fine-structure constant. We present
new chemical abundance measurements for 10 damped Lya systems and a summary
table of high-resolution metallicity measurements (including values from the
literature) for 153 damped Lya systems at z>1.6. We caution, however, that this
metallicity sample (and all previous ones) is biased to higher N(HI) values
than a random sample.
|
0702325v1
|
1998-06-30
|
Structure and Spin Dynamics of La$_{0.85}$Sr$_{0.15}$MnO$_3$
|
Neutron scattering has been used to study the structure and spin dynamics of
La$_{0.85}$Sr$_{0.15}$MnO$_3$. The magnetic structure of this system is
ferromagnetic below T_C = 235 K. We see anomalies in the Bragg peak intensities
and new superlattice peaks consistent with the onset of a spin-canted phase
below T_{CA} = 205 K, which appears to be associated with a gap at q = (0, 0,
0.5) in the spin-wave spectrum. Anomalies in the lattice parameters indicate a
concomitant lattice distortion. The long-wavelength magnetic excitations are
found to be conventional spin waves, with a gapless (< 0.02 meV) isotropic
dispersion relation $E = Dq^2$. The spin stiffness constant D has a $T^{5/2}$
dependence at low T, and the damping at small q follows $q^4T^{2}$. An
anomalously strong quasielastic component, however, develops at small wave
vector above 200 K and dominates the fluctuation spectrum as T -> T_C. At
larger q, on the other hand, the magnetic excitations become heavily damped at
low temperatures, indicating that spin waves in this regime are not eigenstates
of the system, while raising the temperature dramatically increases the
damping. The strength of the spin-wave damping also depends strongly on the
symmetry direction in the crystal. These anomalous damping effects are likely
due to the itinerant character of the $e_g$ electrons.
|
9806381v1
|
2008-02-11
|
Eccentricity of masing disks in Active Galactic Nuclei
|
Observations of Keplerian disks of masers in NCG 4258 and other Seyfert
galaxies can be used to obtain geometric distance estimates and derive the
Hubble constant. The ultimate precision of such measurements could be limited
by uncertainties in the disk geometry. Using a time-dependent linear theory
model, we study the evolution of a thin initially eccentric disk under
conditions appropriate to sub-pc scales in Active Galactic Nuclei. The
evolution is controlled by a combination of differential precession driven by
the disk potential and propagating eccentricity waves that are damped by
viscosity. A simple estimate yields a circularization timescale of
approximately 10 Myr at 0.1 pc. Numerical solutions for the eccentricity
evolution confirm that damping commences on this timescale, but show that the
subsequent decay rate of the eccentricity depends upon the uncertain strength
of viscous damping of eccentricity. If eccentricity waves are important further
decay of the eccentricity can be slow, with full circularization requiring up
to 50 Myr for disks at radii of 0.1 pc to 0.2 pc. Observationally, this implies
that it is plausible that enough time has elapsed for the eccentricity of
masing disks to have been substantially damped, but that it may not be
justified to assume vanishing eccentricity. We predict that during the damping
phase the pericenter of the eccentric orbits describes a moderately tightly
wound spiral with radius.
|
0802.1524v1
|
2013-09-26
|
Non-Landau damping of magnetic excitations in systems with localized and itinerant electrons
|
We discuss the form of the damping of magnetic excitations in a metal near a
ferromagnetic instability. The paramagnon theory predicts that the damping term
should have the form $\Omega/\Gamma (q)$ with $\Gamma (q) \propto q$ (the
Landau damping). However, the experiments on uranium metallic compounds UGe$_2$
and UCoGe showed that $\Gamma (q)$ tends to a constant value at vanishing $q$.
A non-zero $\Gamma (0)$ is impossible in systems with one type of carriers
(either localized or itinerant) because it would violate the spin conservation.
It has been conjectured recently that a non-zero $\Gamma (q)$ in UGe$_2$ and
UCoGe may be due to the presence of both localized and itinerant electrons in
these materials, with ferromagnetism involving predominantly localized spins.
We present microscopic analysis of the damping of near-critical localized
excitations due to interaction with itinerant carriers. We show explicitly how
the presence of two types of electrons breaks the cancellation between the
contributions to $\Gamma (0)$ from self-energy and vertex correction insertions
into the spin polarization bubble and discuss the special role of the
Aslamazov-Larkin processes. We show that $\Gamma (0)$ increases with $T$ both
in the paramagnetic and ferromagnetic regions, but in-between it has a peak at
$T_c$. We compare our theory with the available experimental data.
|
1309.7065v3
|
2016-04-20
|
Nonlinear wave damping due to multi-plasmon resonances
|
For short wavelengths, it is well known that the linearized Wigner-Moyal
equation predicts wave damping due to wave-particle interaction, where the
resonant velocity shifted from the phase velocity by a velocity $v_q = \hbar
k/2m$. Here $\hbar$ is the reduced Planck constant, $k$ is the wavenumber and
$m$ is the electron mass. Going beyond linear theory, we find additional
resonances with velocity shifts $n v_q$, $n = 2, 3, \ldots$, giving rise to a
new wave-damping mechanism that we term \emph{multi-plasmon damping}, as it can
be seen as the simultaneous absorption (or emission) of multiple plasmon
quanta. Naturally this wave damping is not present in classical plasmas. For a
temperature well below the Fermi temperature, if the linear ($n = 1$) resonant
velocity is outside the Fermi sphere, the number of linearly resonant particles
is exponentially small, while the multi-plasmon resonances can be located in
the bulk of the distribution. We derive sets of evolution equations for the
case of two-plasmon and three-plasmon resonances for Langmuir waves in the
simplest case of a fully degenerate plasma. By solving these equations
numerically for a range of wave-numbers we find the corresponding damping
rates, and we compare them to results from linear theory to estimate the
applicability. Finally, we discuss the effects due to a finite temperature.
|
1604.05983v2
|
2017-10-30
|
Enhancement of intrinsic magnetic damping in defect-free epitaxial Fe3O4 thin films
|
We have investigated the magnetic damping of precessional spin dynamics in
defect-controlled epitaxial grown Fe$_3$O$_4$(111)/Yttria-stabilized Zirconia
(YSZ) nanoscale films by all-optical pump-probe measurements. The intrinsic
damping constant of the defect-free Fe$_3$O$_4$ film is found to be strikingly
larger than that of the as-grown Fe$_3$O$_4$ film with structural defects. We
demonstrate that the population of the first-order perpendicular standing spin
wave (PSSW) mode, which is exclusively observed in the defect-free film under
sufficiently high external magnetic fields, leads to the enhancement of the
magnetic damping of the uniform precession (Kittel) mode. We propose a physical
picture in which the PSSW mode acts as an additional channel for the extra
energy dissipation of the Kittel mode. The energy transfer from Kittel mode to
PSSW mode increases as in-plane magnetization precession becomes more uniform,
resulting in the unique intrinsic magnetic damping enhancement in the
defect-free Fe$_3$O$_4$ film.
|
1710.10938v2
|
2017-11-20
|
Spin Pumping in Ion-beam Sputtered Co_{2}FeAl/Mo Bilayers:Interfacial Gilbert Damping
|
The spin pumping mechanism and associated interfacial Gilbert damping are
demonstrated in ion-beam sputtered Co2FeAl (CFA) /Mo bilayer thin films
employing ferromagnetic resonance spectroscopy. The dependence of the net spin
current transportation on Mo layer thickness, 0 to 10 nm, and the enhancement
of the net effective Gilbert damping are reported. The experimental data has
been analyzed using spin pumping theory in terms of spin current pumped through
the ferromagnet /nonmagnetic metal interface to deduce the effective spin
mixing conductance and the spin-diffusion length, which are estimated to be
1.16(0.19)x10^19 m^-2 and 3.50(0.35)nm, respectively. The damping constant is
found to be 8.4(0.3)x10^-3 in the Mo(3.5nm) capped CFA(8nm) sample
corresponding to a ~42% enhancement of the original Gilbert damping
(6.0(0.3)x10^-3) in the uncapped CFA layer. This is further confirmed by
inserting a Cu dusting layer which reduces the spin transport across the CFA
/Mo interface. The Mo layer thickness dependent net spin current density is
found to lie in the range of 1-3 MAm^-2, which also provides additional
quantitative evidence of spin pumping in this bilayer thin film system.
|
1711.07455v1
|
2018-07-20
|
Another view on Gilbert damping in two-dimensional ferromagnets
|
A keen interest towards technological implications of spin-orbit driven
magnetization dynamics requests a proper theoretical description, especially in
the context of a microscopic framework, to be developed. Indeed, magnetization
dynamics is so far approached within Landau-Lifshitz-Gilbert equation which
characterizes torques on magnetization on purely phenomenological grounds.
Particularly, spin-orbit coupling does not respect spin conservation, leading
thus to angular momentum transfer to lattice and damping as a result. This
mechanism is accounted by the Gilbert damping torque which describes relaxation
of the magnetization to equilibrium. In this study we work out a microscopic
Kubo-St\v{r}eda formula for the components of the Gilbert damping tensor and
apply the elaborated formalism to a two-dimensional Rashba ferromagnet in the
weak disorder limit. We show that an exact analytical expression corresponding
to the Gilbert damping parameter manifests linear dependence on the scattering
rate and retains the constant value up to room temperature when no vibrational
degrees of freedom are present in the system. We argue that the methodology
developed in this paper can be safely applied to bilayers made of non- and
ferromagnetic metals, e.g., CoPt.
|
1807.07897v2
|
2022-06-08
|
Motion control with optimal nonlinear damping: from theory to experiment
|
Optimal nonlinear damping control was recently introduced for the
second-order SISO systems, showing some advantages over a classical PD feedback
controller. This paper summarizes the main theoretical developments and
properties of the optimal nonlinear damping controller and demonstrates, for
the first time, its practical experimental evaluation. An extended analysis and
application to more realistic (than solely the double-integrator) motion
systems are also given in the theoretical part of the paper. As comparative
linear feedback controller, a PD one is taken, with the single tunable gain and
direct compensation of the plant time constant. The second, namely
experimental, part of the paper includes the voice-coil drive system with
relatively high level of the process and measurement noise, for which the
standard linear model is first identified in frequency domain. The linear
approximation by two-parameters model forms the basis for designing the PD
reference controller, which fixed feedback gain is the same as for the optimal
nonlinear damping control. A robust sliding-mode based differentiator is used
in both controllers for a reliable velocity estimation required for the
feedback. The reference PD and the proposed optimal nonlinear damping
controller, both with the same single design parameter, are compared
experimentally with respect to trajectory tracking and disturbance rejection.
|
2206.03802v2
|
2023-07-12
|
Exponential stability of damped Euler-Bernoulli beam controlled by boundary springs and dampers
|
In this paper, the vibration model of an elastic beam, governed by the damped
Euler-Bernoulli equation
$\rho(x)u_{tt}+\mu(x)u_{t}$$+\left(r(x)u_{xx}\right)_{xx}=0$, subject to the
clamped boundary conditions $u(0,t)=u_x(0,t)=0$ at $x=0$, and the boundary
conditions $\left(-r(x)u_{xx}\right)_{x=\ell}=k_r u_x(\ell,t)+k_a
u_{xt}(\ell,t)$, $\left(-\left(r(x)u_{xx}\right)_{x}\right )_{x=\ell}$$=- k_d
u(\ell,t)-k_v u_{t}(\ell,t)$ at $x=\ell$, is analyzed. The boundary conditions
at $x=\ell$ correspond to linear combinations of damping moments caused by
rotation and angular velocity and also, of forces caused by displacement and
velocity, respectively. The system stability analysis based on well-known
Lyapunov approach is developed. Under the natural assumptions guaranteeing the
existence of a regular weak solution, uniform exponential decay estimate for
the energy of the system is derived. The decay rate constant in this estimate
depends only on the physical and geometric parameters of the beam, including
the viscous external damping coefficient $\mu(x) \ge 0$, and the boundary
springs $k_r,k_d \ge 0$ and dampers $k_a,k_v \ge 0$. Some numerical examples
are given to illustrate the role of the damping coefficient and the boundary
dampers.
|
2307.06170v2
|
2000-09-06
|
The Cosmological Evolution of Quasar Damped Lyman-Alpha Systems
|
We present results from an efficient, non-traditional survey to discover
damped Lyman-alpha (DLA) absorption-line systems with neutral hydrogen column
densities N(HI)>2x10^{20} atoms cm^{-2} and redshifts z<1.65. Contrary to
previous studies at higher redshift that showed a decrease in the cosmological
mass density of neutral gas in DLA absorbers, Omega_{DLA}, with time, our
results indicate that Omega_{DLA} is consistent with remaining constant from
redshifts z \approx 4 to z \approx 0.5. There is no evidence that Omega_{DLA}
is approaching the value at z=0. Other interesting results from the survey are
also presented.
|
0009098v1
|
2005-06-09
|
Phantom damping of matter perturbations
|
Cosmological scaling solutions are particularly important in solving the
coincidence problem of dark energy. We derive the equations of sub-Hubble
linear matter perturbations for a general scalar-field Lagrangian--including
quintessence, tachyon, dilatonic ghost condensate and k-essence--and solve them
analytically for scaling solutions. We find that matter perturbations are
always damped if a phantom field is coupled to dark matter and identify the
cases in which the gravitational potential is constant. This provides an
interesting possibility to place stringent observational constraints on scaling
dark energy models.
|
0506222v1
|
1995-02-10
|
The influence of structure disorder on mean atomic momentum fluctuations and a spin-wave spectrum
|
The relation between atomic momenta fluctuations and density fluctuations is
obtained in frames of mean-field approximation. Using two-time temperature
Green functions within Tyablikov approximation the equations for spin
excitation energy and damping are obtained. The asymptotics of energy and
damping in the long-wave limit are investigated and the anomalous behaviour of
spin-wave stiffness constant is discussed.
|
9502042v1
|
1999-01-19
|
Damping of Growth Oscillations
|
Computer simulations and scaling theory are used to investigate the damping
of oscillations during epitaxial growth on high-symmetry surfaces. The
crossover from smooth to rough growth takes place after the deposition of
(D/F)^\delta monolayers, where D and F are the surface diffusion constant and
the deposition rate, respectively, and the exponent \delta=2/3 on a
two-dimensional surface. At the transition, layer-by-layer growth becomes
desynchronized on distances larger than a layer coherence length proportional
l^2, where l is a typical distance between two-dimensional islands in the
submonolayer region of growth.
|
9901178v1
|
2000-03-27
|
Effect of memory and dynamical chaos in long Josephson junctions
|
A long Josephson junction in a constant external magnetic field and in the
presence of a dc bias current is investigated. It is shown that the system,
simulated by the sine-Gorgon equation, "remembers" a rapidly damping initial
perturbation and final asymptotic states are determined exactly with this
perturbation. Numerical solving of the boundary sine-Gordon problem and
calculations of Lyapunov indices show that this system has a memory even when
it is in a state of dynamical chaos, i.e., dynamical chaos does not destroy
initial information having a character of rapidly damping perturbation.
|
0003421v1
|
2003-09-24
|
Landau Damping in a 2D Electron Gas with Imposed Quantum Grid
|
Dielectric properties of semiconductor substrate with imposed two dimensional
(2D) periodic grid of quantum wires or nanotubes (quantum crossbars, QCB) are
studied. It is shown that a capacitive contact between QCB and semiconductor
substrate does not destroy the Luttinger liquid character of the long wave QCB
excitations. However, the dielectric losses of a substrate surface are
drastically modified due to diffraction processes on the QCB superlattice.
QCB-substrate interaction results in additional Landau damping regions of the
substrate plasmons. Their existence, form and the density of losses are
strongly sensitive to the QCB lattice constant.
|
0309546v2
|
2005-11-05
|
Ratchet Effect in Magnetization Reversal of Stoner Particles
|
A new strategy is proposed aimed at substantially reducing the minimal
magnetization switching field for a Stoner particle. Unlike the normal method
of applying a static magnetic field which must be larger than the magnetic
anisotropy, a much weaker field, proportional to the damping constant in the
weak damping regime, can be used to switch the magnetization from one state to
another if the field is along the motion of the magnetization. The concept is
to constantly supply energy to the particle from the time-dependent magnetic
field to allow the particle to climb over the potential barrier between the
initial and the target states.
|
0511135v1
|
1994-09-12
|
Fermion damping rate in a hot medium
|
In principle every excitation acquires a finite lifetime in a hot system.
This nonzero spectral width is calculated self-consistently for massive
fermions coupled to massless scalar, vector and pseudoscalar bosons. It is
shown that the self-consistent summation of the corresponding Fock diagram for
fermions eliminates all infrared divergences although the bosons are not
screened at all. Our solutions for the fermion damping rate are analytical in
the coupling constant, but not analytical in the temperature parameter around
T=0.
|
9409280v2
|
2004-02-06
|
Critical Behavior of Damping Rate for Plasmon with Finite Momentum in φ^4 Theory
|
Applying thermal renormalization group (TRG) equations to $\phi^4$ theory
with spontaneous breaking symmetry, we investigate the critical behavior of the
damping rate for the plasmons with finite momentum at the symmetry-restoring
phase transition. From the TRG equation the IR cutoff provided by the external
momentum leads to that the momentum-dependent coupling constant stops running
in the critical region. As the result, the critical slowing down phenomenon
reflecting the inherently IR effect doesn't take place at the critical point
for the plasmon with finite external momentum.
|
0402069v2
|
2006-11-26
|
On the Lagrangian and Hamiltonian description of the damped linear harmonic oscillator
|
Using the modified Prelle- Singer approach, we point out that explicit time
independent first integrals can be identified for the damped linear harmonic
oscillator in different parameter regimes. Using these constants of motion, an
appropriate Lagrangian and Hamiltonian formalism is developed and the resultant
canonical equations are shown to lead to the standard dynamical description.
Suitable canonical transformations to standard Hamiltonian forms are also
obtained. It is also shown that a possible quantum mechanical description can
be developed either in the coordinate or momentum representations using the
Hamiltonian forms.
|
0611048v1
|
2005-02-10
|
Modulational instabilities in Josephson oscillations of elongated coupled condensates
|
We study the Josephson oscillations of two coupled elongated condensates.
Linearized calculations show that the oscillating mode uniform over the length
of the condensates (uniform Josephson mode) is unstable : modes of non zero
longitudinal momentum grow exponentially. In the limit of strong atom
interactions, we give scaling laws for the instability time constant and
unstable wave vectors. Beyond the linearized approach, numerical calculations
show a damped recurrence behavior : the energy in the Josephson mode presents
damped oscillations. Finally, we derive conditions on the confinement of the
condensates to prevent instabilities.
|
0502050v3
|
2007-10-04
|
Activation of additional energy dissipation processes in the magnetization dynamics of epitaxial chromium dioxide films
|
The precessional magnetization dynamics of a chromium dioxide$(100)$ film is
examined in an all-optical pump-probe setup. The frequency dependence on the
external field is used to extract the uniaxial in-plane anisotropy constant.
The damping shows a strong dependence on the frequency, but also on the laser
pump fluency, which is revealed as an important experiment parameter in this
work: above a certain threshold further channels of energy dissipation open and
the damping increases discontinuously. This behavior might stem from spin-wave
instabilities.
|
0710.0986v2
|
2009-02-03
|
Freezing of spin dynamics in underdoped cuprates
|
The Mori's memory function approach to spin dynamics in doped
antiferromagnetic insulator combined with the assumption of temperature
independent static spin correlations and constant collective mode damping leads
to w/T scaling in a broad range. The theory involving a nonuniversal scaling
parameter is used to analyze recent inelastic neutron scattering results for
underdoped cuprates. Adopting modified damping function also the emerging
central peak in low-doped cuprates at low temperatures can be explained within
the same framework.
|
0902.0546v1
|
2010-04-26
|
Entanglement of a two-particle Gaussian state interacting with a heat bath
|
The effect of a thermal reservoir is investigated on a bipartite Gaussian
state. We derive a pre-Lindblad master equation in the non-rotating wave
approximation for the system. We then solve the master equation for a bipartite
harmonic oscillator Hamiltonian with entangled initial state. We show that for
strong damping the loss of entanglement is the same as for freely evolving
particles. However, if the damping is small, the entanglement is shown to
oscillate and eventually tend to a constant nonzero value.
|
1004.4515v2
|
2011-04-06
|
Relativistic magnetic reconnection at X-type neutral points
|
Relativistic effects in the oscillatory damping of magnetic disturbances near
two-dimensional X-points are investigated. By taking into account displacement
current, we study new features of extremely magnetized systems, in which the
Alfv\'en velocity is almost the speed of light. The frequencies of the
least-damped mode are calculated using linearized relativistic MHD equations
for wide ranges of the Lundquist number S and the magnetization parameter
$\sigma$. These timescales approach constant values in the large resistive
limit: the oscillation time becomes a few times the light crossing time,
irrespective of $\sigma$, and the decay time is proportional to $\sigma$ and
therefore is longer for a highly magnetized system.
|
1104.1003v1
|
2011-11-08
|
The entropy of large black holes in loop quantum gravity: A combinatorics/analysis approach
|
The issue of a possible damping of the entropy periodicity for large black
holes in Loop Quantum Gravity is highly debated. Using a combinatorics/analysis
approach, we give strong arguments in favor of this damping, at least for
prescriptions where the projection constraint is not fully implemented. This
means that black holes in loop gravity exhibit an asymptotic Bekenstein-Hawking
behavior, provided that a consistent choice of the Immirzi constant is made.
|
1111.1975v1
|
2013-04-04
|
Pais-Uhlenbeck Oscillator with a Benign Friction Force
|
It is shown that the Pais-Uhlenbeck oscillator with damping, considered by
Nesterenko, is a special case of a more general oscillator that has not only a
first order, but also a third order friction term. If the corresponding damping
constants, \alpha\ and \beta, are both positive and below certain critical
values, then the system is stable. In particular, if \alpha = - \beta, then we
have the unstable Nesterenko's oscillator
|
1304.1325v2
|
2014-12-05
|
Exponential dephasing of oscillators in the Kinetic Kuramoto Model
|
We study the kinetic Kuramoto model for coupled oscillators with coupling
constant below the synchronization threshold. We manage to prove that, for any
analytic initial datum, if the interaction is small enough, the order parameter
of the model vanishes exponentially fast, and the solution is asymptotically
described by a free flow. This behavior is similar to the phenomenon of Landau
damping in plasma physics. In the proof we use a combination of techniques from
Landau damping and from abstract Cauchy-Kowalewskaya theorem.
|
1412.1923v1
|
2014-12-23
|
Selftrapping triggered by losses in cavity QED
|
In a coupled cavity QED network model, we study the transition from a
localized super fluid like state to a delocalized Mott insulator like state,
triggered by losses. Without cavity losses, the transition never takes place.
Further, if one measures the quantum correlations between the polaritons via
the negativity, we find a critical cavity damping constant, above which the
negativity displays a single peak in the same time region where the transition
takes place. Additionally, we identify two regions in the parameter space,
where below the critical damping, oscillations of the initial localized state
are observed along with a multipeaked negativity, while above the critical
value, the oscillations die out and the transition is witnessed by a neat
single peaked negativity.
|
1412.7495v1
|
2015-11-19
|
Periodic damping gives polynomial energy decay
|
Let $u$ solve the damped Klein--Gordon equation $$ \big( \partial_t^2-\sum
\partial_{x_j}^2 +m \text{Id} +\gamma(x) \partial_t \big) u=0 $$ on
$\mathbb{R}^n$ with $m>0$ and $\gamma\geq 0$ bounded below on a $2 \pi
\mathbb{Z}^n$-invariant open set by a positive constant. We show that the
energy of the solution $u$ decays at a polynomial rate. This is proved via a
periodic observability estimate on $\mathbb{R}^n.$
|
1511.06144v5
|
2016-06-08
|
Energy Decay in a Wave Guide with Dissipation at Infinity
|
We prove local and global energy decay for the wave equation in a wave guide
with damping at infinity. More precisely, the absorption index is assumed to
converge slowly to a positive constant, and we obtain the diffusive phenomenon
typical for the contribution of low frequencies when the damping is effective
at infinity. On the other hand, the usual Geometric Control Condition is not
necessarily satisfied so we may have a loss of regularity for the contribution
of high frequencies. Since our results are new even in the Euclidean space, we
also state a similar result in this case.
|
1606.02549v2
|
2016-07-06
|
Asymptotic profiles of solutions for structural damped wave equations
|
In this paper, we obtain several asymptotic profiles of solutions to the
Cauchy problem for structurally damped wave equations $\partial_{t}^{2} u -
\Delta u + \nu (-\Delta)^{\sigma} \partial_{t} u=0$, where $\nu >0$ and $0<
\sigma \le1$. Our result is the approximation formula of the solution by a
constant multiple of a special function as $t \to \infty$, which states that
the asymptotic profiles of the solutions are classified into $5$ patterns
depending on the values $\nu$ and $\sigma$.
|
1607.01839v1
|
2018-01-19
|
Robust integral action of port-Hamiltonian systems
|
Interconnection and damping assignment, passivity-based control (IDA-PBC) has
proven to be a successful control technique for the stabilisation of many
nonlinear systems. In this paper, we propose a method to robustify a system
which has been stabilised using IDA-PBC with respect to constant, matched
disturbances via the addition of integral action. The proposed controller
extends previous work on the topic by being robust against the damping of the
system, a quantity which may not be known in many applications.
|
1801.06279v1
|
2018-04-10
|
Motion of a superconducting loop in an inhomogeneous magnetic field: a didactic experiment
|
We present an experiment conductive to an understanding of both Faraday's law
and the properties of the superconducting state. It consists in the analysis of
the motion of a superconducting loop moving under the influence of gravity in
an inhomogeneous horizontal magnetic field. Gravity, conservation of magnetic
flux, and friction combine to give damped harmonic oscillations. The measured
frequency of oscillation and the damping constant as a function of the magnetic
field strength (the only free parameter) are in good agreement with the
theoretical model.
|
1804.03553v1
|
2019-09-11
|
Remark on global existence of solutions to the 1D compressible Euler equation with time-dependent damping
|
In this paper, we consider the 1D compressible Euler equation with the
damping coefficient $\lambda/(1+t)^{\mu}$. Under the assumption that $0\leq \mu
<1$ and $\lambda >0$ or $\mu=1$ and $\lambda > 2$, we prove that solutions
exist globally in time, if initial data are small $C^1$ perturbation near
constant states. In particular, we remove the conditions on the limit
$\lim_{|x| \rightarrow \infty} (u (0,x), v (0,x))$, assumed in previous
results.
|
1909.05683v1
|
2020-10-18
|
Classical limit of quantum mechanics for damped driven oscillatory systems: Quantum-classical correspondence
|
The investigation of quantum-classical correspondence may lead to gain a
deeper understanding of the classical limit of quantum theory. We develop a
quantum formalism on the basis of a linear-invariant theorem, which gives an
exact quantum-classical correspondence for damped oscillatory systems that are
perturbed by an arbitrary force. Within our formalism, the quantum trajectory
and expectation values of quantum observables are precisely coincide with their
classical counterparts in the case where we remove the global quantum constant
h from their quantum results. In particular, we illustrate the correspondence
of the quantum energy with the classical one in detail.
|
2010.08971v1
|
2020-12-28
|
An efficient method for approximating resonance curves of weakly-damped nonlinear mechanical systems
|
A method is presented for tracing the locus of a specific peak in the
frequency response under variation of a parameter. It is applicable to
periodic, steady-state vibrations of harmonically forced nonlinear mechanical
systems. It operates in the frequency domain and its central idea is to assume
a constant phase lag between forcing and response. The method is validated for
a two-degree-of-freedom oscillator with cubic spring and a bladed disk with
shroud contact. The method provides superior computational efficiency, but is
limited to weakly-damped systems. Finally, the capability to reveal isolated
solution branches is highlighted.
|
2012.14458v1
|
2021-02-04
|
Global existence results for semi-linear structurally damped wave equations with nonlinear convection
|
In this paper, we consider the Cauchy problem for semi-linear wave equations
with structural damping term $\nu (-\Delta)^2 u_t$, where $\nu >0$ is a
constant. As being mentioned in [8,10], the linear principal part brings both
the diffusion phenomenon and the regularity loss of solutions. This implies
that, for the nonlinear problems, the choice of solution spaces plays an
important role to obtain global solutions with sharp decay properties in time.
Our main purpose of this paper is to prove the global (in time) existence of
solutions for the small data and their decay properties for the supercritical
nonlinearities.
|
2102.02445v2
|
2021-04-12
|
The pressureless damped Euler-Riesz equations
|
In this paper, we analyze the pressureless damped Euler-Riesz equations posed
in either $\mathbb{R}^d$ or $\mathbb{T}^d$. We construct the global-in-time
existence and uniqueness of classical solutions for the system around a
constant background state. We also establish large-time behaviors of classical
solutions showing the solutions towards the equilibrium as time goes to
infinity. For the whole space case, we first show the algebraic decay rate of
solutions under additional assumptions on the initial data compared to the
existence theory. We then refine the argument to have the exponential decay
rate of convergence even in the whole space. In the case of the periodic
domain, without any further regularity assumptions on the initial data, we
provide the exponential convergence of solutions.
|
2104.05153v1
|
2021-05-20
|
On the the critical exponent for the semilinear Euler-Poisson-Darboux-Tricomi equation with power nonlinearity
|
In this note, we derive a blow-up result for a semilinear generalized Tricomi
equation with damping and mass terms having time-dependent coefficients. We
consider these coefficients with critical decay rates. Due to this threshold
nature of the time-dependent coefficients (both for the damping and for the
mass), the multiplicative constants appearing in these lower-order terms
strongly influence the value of the critical exponent, determining a
competition between a Fujita-type exponent and a Strauss-type exponent.
|
2105.09879v2
|
2022-04-04
|
Exponential ergodicity for damping Hamiltonian dynamics with state-dependent and non-local collisions
|
In this paper, we investigate the exponential ergodicity in a
Wasserstein-type distance for a damping Hamiltonian dynamics with
state-dependent and non-local collisions, which indeed is a special case of
piecewise deterministic Markov processes while is very popular in numerous
modelling situations including stochastic algorithms. The approach adopted in
this work is based on a combination of the refined basic coupling and the
refined reflection coupling for non-local operators. In a certain sense, the
main result developed in the present paper is a continuation of the counterpart
in \cite{BW2022} on exponential ergodicity of stochastic Hamiltonian systems
with L\'evy noises and a complement of \cite{BA} upon exponential ergodicity
for Andersen dynamics with constant jump rate functions.
|
2204.01372v1
|
2022-06-17
|
On energy-stable and high order finite element methods for the wave equation in heterogeneous media with perfectly matched layers
|
This paper presents a stable finite element approximation for the acoustic
wave equation on second-order form, with perfectly matched layers (PML) at the
boundaries. Energy estimates are derived for varying PML damping for both the
discrete and the continuous case. Moreover, a priori error estimates are
derived for constant PML damping. Most of the analysis is performed in Laplace
space. Numerical experiments in physical space validate the theoretical
results.
|
2206.08507v1
|
2022-12-27
|
Stabilization of the Kawahara-Kadomtsev-Petviashvili equation with time-delayed feedback
|
Results of stabilization for the higher order of the Kadomtsev-Petviashvili
equation are presented in this manuscript. Precisely, we prove with two
different approaches that under the presence of a damping mechanism and an
internal delay term (anti-damping) the solutions of the
Kawahara-Kadomtsev-Petviashvili equation are locally and globally exponentially
stable. The main novelty is that we present the optimal constant, as well as
the minimal time, that ensures that the energy associated with this system goes
to zero exponentially.
|
2212.13552v1
|
2014-10-20
|
Frequency-dependent attenuation and elasticity in unconsolidated earth materials: effect of damping
|
We use the Discrete Element Method (DEM) to understand the underlying
attenuation mechanism in granular media, with special applicability to the
measurements of the so-called effective mass developed earlier. We consider
that the particles interact via Hertz-Mindlin elastic contact forces and that
the damping is describable as a force proportional to the velocity difference
of contacting grains. We determine the behavior of the complex-valued normal
mode frequencies using 1) DEM, 2) direct diagonalization of the relevant
matrix, and 3) a numerical search for the zeros of the relevant determinant.
All three methods are in strong agreement with each other. The real and the
imaginary parts of each normal mode frequency characterize the elastic and the
dissipative properties, respectively, of the granular medium. We demonstrate
that, as the interparticle damping, $\xi$, increases, the normal modes exhibit
nearly circular trajectories in the complex frequency plane and that for a
given value of $\xi$ they all lie on or near a circle of radius $R$ centered on
the point $-iR$ in the complex plane, where $R\propto 1/\xi$. We show that each
normal mode becomes critically damped at a value of the damping parameter $\xi
\approx 1/\omega_n^0$, where $\omega_n^0$ is the (real-valued) frequency when
there is no damping. The strong indication is that these conclusions carry over
to the properties of real granular media whose dissipation is dominated by the
relative motion of contacting grains. For example, compressional or shear waves
in unconsolidated dry sediments can be expected to become overdamped beyond a
critical frequency, depending upon the strength of the intergranular damping
constant.
|
1410.5484v2
|
2018-09-13
|
Active Damping of a DC Network with a Constant Power Load: An Adaptive Passivity-based Control Approach
|
This paper proposes a nonlinear, adaptive controller to increase the
stability margin of a direct-current (DC) small-scale electrical network
containing a constant power load, whose value is unknown. Due to their negative
incremental impedance, constant power loads are known to reduce the effective
damping of a network, leading to voltage oscillations and even to network
collapse. To tackle this problem, we consider the incorporation of a controlled
DC-DC power converter between the feeder and the constant power load. The
design of the control law for the converter is based on the use of standard
Passivity-Based Control and Immersion and Invariance theories. The good
performance of the controller is evaluated with numerical simulations.
|
1809.04920v1
|
2018-10-29
|
A Graceful Exit for the Cosmological Constant Damping Scenario
|
We present a broad and simple class of scalar-tensor scenarios that
successfully realize dynamical damping of the effective cosmological constant,
therefore providing a viable dynamical solution to the fine-tuning or "old"
cosmological constant problem. In contrast to early versions of this approach,
pioneered in the works of A. Dolgov in the 1980es, these do not suffer from
unacceptable variations of Newton's constant, as one aims at a small but
strictly positive (rather than zero) late-time curvature. In our approach, the
original fine-tuning issue is traded for a hierarchy of couplings, and we
further suggest a way to naturally generate this hierarchy based on fermion
condensation and softly broken field shift symmetry.
|
1810.12336v2
|
2020-10-01
|
Avoiding coherent errors with rotated concatenated stabilizer codes
|
Coherent errors, which arise from collective couplings, are a dominant form
of noise in many realistic quantum systems, and are more damaging than oft
considered stochastic errors. Here, we propose integrating stabilizer codes
with constant-excitation codes by code concatenation. Namely, by concatenating
an $[[n,k,d]]$ stabilizer outer code with dual-rail inner codes, we obtain a
$[[2n,k,d]]$ constant-excitation code immune from coherent phase errors and
also equivalent to a Pauli-rotated stabilizer code. When the stabilizer outer
code is fault-tolerant, the constant-excitation code has a positive
fault-tolerant threshold against stochastic errors. Setting the outer code as a
four-qubit amplitude damping code yields an eight-qubit constant-excitation
code that corrects a single amplitude damping error, and we analyze this code's
potential as a quantum memory.
|
2010.00538v2
|
2023-05-17
|
Material Parameters for Faster Ballistic Switching of an In-plane Magnetized Nanomagnet
|
High-speed magnetization switching of a nanomagnet is necessary for faster
information processing. The ballistic switching by a pulsed magnetic filed is a
promising candidate for the high-speed switching. It is known that the
switching speed of the ballistic switching can be increased by increasing the
magnitude of the pulsed magnetic field. However it is difficult to generate a
strong and short magnetic field pulse in a small device. Here we explore
another direction to achieve the high-speed ballistic switching by designing
material parameters such as anisotropy constant, saturation magnetization, and
the Gilbert damping constant. We perform the macrospin simulations for the
ballistic switching of in-plane magnetized nano magnets with varying material
parameters. The results are analyzed based on the switching dynamics on the
energy density contour. We show that the pulse width required for the ballistic
switching can be reduced by increasing the magnetic anisotropy constant or by
decreasing the saturation magnetization. We also show that there exists an
optimal value of the Gilbert damping constant that minimizes the pulse width
required for the ballistic switching.
|
2305.10111v1
|
1995-05-17
|
GRAVITATIONAL LENSING OF QUASARS BY THEIR DAMPED LYMAN-ALPHA ABSORBERS
|
Damped Lyman-alpha absorbers are believed to be associated with galactic
disks. We show that gravitational lensing can therefore affect the statistics
of these systems. First, the magnification bias due to lensing raises faint
QSOs above a given magnitude threshold and thereby enhances the probability for
observing damped absorption systems. Second, the bending of light rays from the
source effectively limits the minimum impact parameter of the line-of-sight
relative to the center of the absorber, thus providing an upper cut-off to the
observed neutral hydrogen (HI) column density. The combination of these effects
yields a pronounced peak in the observed abundance of absorbers with high
column densities (>2*10^{21} cm^{-2}) and low redshifts (z<1). The inferred
value of the cosmological density parameter of neutral hydrogen, Omega_{HI},
increases with increasing redshift and luminosity of the sources even if the
true HI density remains constant. This trend resembles the observed evolution
of Omega_{HI}(z). Damped Lyman-alpha absorbers with column densities >10^{21}
cm^{-2} and redshifts 0.5<z<1 are reliable flags for lensed QSOs with a close
pair of images separated by 0.3 arcsec. Detection of these gravitational
lensing signatures with the Hubble Space Telescope can be used to constrain the
depth of the absorber potential-wells and the cosmological constant.
|
9505078v1
|
2000-06-01
|
Crust-core coupling and r-mode damping in neutron stars: a toy model
|
R-modes in neutron stars with crusts are damped by viscous friction at the
crust-core boundary. The magnitude of this damping, evaluated by Bildsten and
Ushomirsky (BU) under the assumption of a perfectly rigid crust, sets the
maximum spin frequency for a neutron star spun up by accretion in a Low-Mass
X-ray binary (LMXB). In this paper we explore the mechanical coupling between
the core r-modes and the elastic crust, using a toy model of a constant density
neutron star with a constant shear modulus crust. We find that, at spin
frequencies in excess of ~50 Hz, the r-modes strongly penetrate the crust. This
reduces the relative motion (slippage) between the crust and the core compared
to the rigid crust limit. We therefore revise down, by as much as a factor of
10^2-10^3, the damping rate computed by BU, significantly reducing the maximal
possible spin frequency of neutron star with a solid crust. The dependence of
the crust-core slippage on the spin frequency is complicated, and is very
sensitive to the physical thickness of the crust. If the crust is sufficiently
thick, the curve of the critical spin frequency for the onset of the r-mode
instability becomes multi-valued for some temperatures; this is related to the
avoided crossings between the r-mode and the higher-order torsional modes in
the crust. The critical frequencies are comparable to the observed spins of
neutron stars in LMXBs and millisecond pulsars.
|
0006028v1
|
2006-06-15
|
Purity and decoherence in the theory of a damped harmonic oscillator
|
For the generalized master equations derived by Karrlein and Grabert for the
microscopic model of a damped harmonic oscillator, the conditions for purity of
states are written, in particular for different initial conditions and
different types of damping, including Ohmic, Drude and weak coupling cases,
Agarwal and Weidlich-Haake models. It is shown that the states which remain
pure are the squeezed states with constant in time variances. For pure states,
the generalized nonlinear Schr\" odinger-type equations corresponding to these
master equations are also obtained. Then the condition for purity of states of
a damped harmonic oscillator is considered in the framework of Lindblad theory
for open quantum systems. For a special choice of the environment coefficients,
the correlated coherent states with constant variances and covariance are shown
to be the only states which remain pure all the time during the evolution of
the considered system. In Karrlein-Grabert and Lindblad models, as well as in
the considered particular models, the expressions of the rate of entropy
production is written and it is shown that the states which preserve their
purity in time are also the states which minimize the entropy production and,
therefore, they are the most stable ones under evolution in the presence of the
environment and play an important role in the description of decoherence
phenomenon.
|
0606134v1
|
2012-10-02
|
Coherence and Stimulated Emission in the Tavis-Cummings Model: A Quantum Description of the Free Induction Signal and Radiation Damping in Magnetic Resonance
|
We numerically solve the Liouville equation for the Tavis Cummings model of
multiple spins coupled to a lossless single mode cavity, starting from an
initial condition with small numbers of fully polarized spins tipped by a
specified angle, and the cavity in its ground Fock state. Time evolution of the
magnetizations and cavity states, following small to medium nutation by a
classical field, yields a microscopic quantum mechanical picture of radiation
damping in magnetic resonance, and the formation of the free induction signal,
that is, the transfer of Zeeman energy, via spin coherence, to cavity
coherence. Although the motion of the Bloch vector is nonclassical, our quantum
description is related to the macroscopic picture of NMR reception, by showing
the close relationship between the usual radiation damping constant, and the
quantum mechanical Rabi nutation frequency (as enhanced by cavity coupling and
stimulated emission.) That is, each is the product, of a nutation rate per
oscillator current, and a current. Although the current in the damping constant
is explicitly limited by cavity losses, which do not enter the formula for the
Rabi frequency, we nonetheless show (in an appendix) how these losses can be
introduced into our problem by means of a master equation. Numerical solution
of the classical Bloch-Kirchhoff equations reinforces the conclusion that the
strength of the free induction
|
1210.0868v2
|
2016-11-28
|
First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO
|
Interferometric gravitational wave detectors operate with high optical power
in their arms in order to achieve high shot-noise limited strain sensitivity. A
significant limitation to increasing the optical power is the phenomenon of
three-mode parametric instabilities, in which the laser field in the arm
cavities is scattered into higher order optical modes by acoustic modes of the
cavity mirrors. The optical modes can further drive the acoustic modes via
radiation pressure, potentially producing an exponential buildup. One proposed
technique to stabilize parametric instability is active damping of acoustic
modes. We report here the first demonstration of damping a parametrically
unstable mode using active feedback forces on the cavity mirror. A 15,538 Hz
mode that grew exponentially with a time constant of 182 sec was damped using
electro-static actuation, with a resulting decay time constant of 23 sec. An
average control force of 0.03 nNrms was required to maintain the acoustic mode
at its minimum amplitude.
|
1611.08997v1
|
2021-07-28
|
Evolution of a Mode of Oscillation Within Turbulent Accretion Disks
|
We investigate the effects of subsonic turbulence on a normal mode of
oscillation [a possible origin of the high-frequency quasi-periodic
oscillations (HFQPOs) within some black hole accretion disks]. We consider
perturbations of a time-dependent background (steady state disk plus
turbulence), obtaining an oscillator equation with stochastic damping, (mildly)
nonlinear restoring, and stochastic driving forces. The (long-term) mean values
of our turbulent functions vanish. In particular, turbulence does not damp the
oscillation modes, so `turbulent viscosity' is not operative. However, the
frequency components of the turbulent driving force near that of the mode can
produce significant changes in the amplitude of the mode. Even with an
additional (phenomenological constant) source of damping, this leads to an
eventual `blowout' (onset of effects of nonlinearity) if the turbulence is
sufficiently strong or the damping constant is sufficiently small. The
infrequent large increases in the energy of the mode could be related to the
observed low duty cycles of the HFQPOs. The width of the peak in the power
spectral density (PSD) is proportional to the amount of nonlinearity. A
comparison with observed continuum PSDs indicates the conditions required for
visibility of the mode.
|
2107.13546v1
|
2001-02-06
|
Decay of cosmological constant as Bose condensate evaporation
|
We consider the process of decay of symmetric vacuum state as evaporation of
a Bose condensate of physical Higgs particles, defined over asymmetric vacuum
state. Energy density of their selfinteraction is identified with cosmological
constant $\Lambda$ in the Einstein equation. $\Lambda$ decay then provides
dynamical realization of spontaneous symmetry breaking. The effective mechanism
is found for damping of coherent oscillations of a scalar field, leading to
slow evaporation regime as the effective mechanism for $\Lambda$ decay
responsible for inflation without special fine-tuning of the microphysical
parameters. This mechanism is able to incorporate reheating, generation of
proper primordial fluctuations, and nonzero cosmological constant today.
|
0102094v2
|
2003-07-12
|
Time-variability of the fine-structure constant expected from the Oklo constraint and the QSO absorption lines
|
The data from the QSO absorption lines indicating a nonzero time-variability
of the fine-structure constant has been re-analyzed on the basis of a
"damped-oscillator" fit, as motivated by the same type of behavior of a scalar
field, dilaton, which mimics a cosmological constant to understand the
accelerating universe. We find nearly as good fit to the latest data as the
simple weighted mean. In this way, we offer a way to fit the more stringent
result from the Oklo phenomenon, as well.
|
0307263v2
|
1996-01-30
|
Role of a "Local" Cosmological Constant in Euclidean Quantum Gravity
|
In 4D non-perturbative Regge calculus a positive value of the effective
cosmological constant characterizes the collapsed phase of the system. If a
local term of the form $S'=\sum_{h \epsilon \{h_1,h_2,...\} } \lambda_h V_h$ is
added to the gravitational action, where $\{h_1,h_2,...\}$ is a subset of the
hinges and $\{\lambda_h\}$ are positive constants, one expects that the volumes
$V_{h_1}$, $V_{h_2}$, ... tend to collapse and that the excitations of the
lattice propagating through the hinges $\{h_1,h_2,...\}$ are damped. We study
the continuum analogue of this effect. The additional term $S'$ may represent
the coupling of the gravitational field to an external Bose condensate.
|
9601160v1
|
1999-07-12
|
General considerations of the cosmological constant and the stabilization of moduli in the brane-world picture
|
We argue that the brane-world picture with matter-fields confined to 4-d
domain walls and with gravitational interactions across the bulk disallows
adding an arbitrary constant to the low-energy, 4-d effective theory -- which
finesses the usual cosmological constant problem. The analysis also points to
difficulties in stabilizing moduli fields; as an alternative, we suggest
scenarios in which the moduli motion is heavily damped by various cosmological
mechanisms and varying ultra-slowly with time.
|
9907080v1
|
2007-06-03
|
A class of series acceleration formulae for Catalan's constant
|
In this note, we develop transformation formulae and expansions for the log
tangent integral, which are then used to derive series acceleration formulae
for certain values of Dirichlet L-functions, such as Catalan's constant. The
formulae are characterized by the presence of an infinite series whose general
term consists of a linear recurrence damped by the central binomial coefficient
and a certain quadratic polynomial. Typically, the series can be expressed in
closed form as a rational linear combination of Catalan's constant and pi times
the logarithm of an algebraic unit.
|
0706.0356v1
|
2017-09-21
|
Low Gilbert Damping Constant in Perpendicularly Magnetized W/CoFeB/MgO Films with High Thermal Stability
|
Perpendicular magnetic materials with low damping constant and high thermal
stability have great potential for realizing high-density, non-volatile, and
low-power consumption spintronic devices, which can sustain operation
reliability for high processing temperatures. In this work, we study the
Gilbert damping constant ({\alpha}) of perpendicularly magnetized W/CoFeB/MgO
films with a high perpendicular magnetic anisotropy (PMA) and superb thermal
stability. The {\alpha} of these PMA films annealed at different temperatures
is determined via an all-optical Time-Resolved Magneto-Optical Kerr Effect
method. We find that {\alpha} of these W/CoFeB/MgO PMA films decreases with
increasing annealing temperature, reaches a minimum of {\alpha} = 0.016 at an
annealing temperature of 350 {\deg}C, and then increases to 0.024 after
post-annealing at 400 {\deg}C. The minimum {\alpha} observed at 350 {\deg}C is
rationalized by two competing effects as the annealing temperature becomes
higher: the enhanced crystallization of CoFeB and dead-layer growth occurring
at the two interfaces of the CoFeB layer. We further demonstrate that {\alpha}
of the 400 {\deg}C-annealed W/CoFeB/MgO film is comparable to that of a
reference Ta/CoFeB/MgO PMA film annealed at 300 {\deg}C, justifying the
enhanced thermal stability of the W-seeded CoFeB films.
|
1709.07483v1
|
2022-09-21
|
Performance enhancement of a spin-wave-based reservoir computing system utilizing different physical conditions
|
The authors have numerically studied how to enhance reservoir computing
performance by thoroughly extracting their spin-wave device potential for
higher-dimensional information generation. The reservoir device has a 1-input
exciter and 120-output detectors on the top of a continuous magnetic garnet
film for spin-wave transmission. For various nonlinear and fading-memory
dynamic phenomena distributing in the film space, small in-plane magnetic
fields were used to prepare stripe domain structures and various damping
constants at the film sides and bottom were explored. The ferromagnetic
resonant frequency and relaxation time of spin precession clearly characterized
the change in spin dynamics with the magnetic field and damping constant. The
common input signal for reservoir computing was a 1 GHz cosine wave with random
6-valued amplitude modulation. A basic 120-dimensional reservoir output vector
was obtained from time-series signals at the 120 output detectors under each of
the three magnetic field conditions. Then, 240- and 360-dimensional reservoir
output vectors were also constructed by concatenating two and three basic ones,
respectively. In nonlinear autoregressive moving average (NARMA) prediction
tasks, the computational performance was enhanced as the dimension of the
reservoir output vector becomes higher and a significantly low prediction error
was achieved for the 10th-order NARMA using the 360-dimensional vector and
optimum damping constant. The results are clear evidence that the collection of
diverse output signals efficiently increases the dimensionality effective for
reservoir computing, i.e., reservoir-state richness. This paper demonstrates
that performance enhancement through various configuration settings is a
practical approach for on-chip reservoir computing devices with small numbers
of real output nodes.
|
2209.10123v1
|
2000-06-09
|
Random values of the cosmological constant
|
One way that an anthropic selection mechanism may be manifest in a physical
theory involves multiple domains in the universe with different values of the
physical parameters. If this mechanism is to be relevant for understanding the
small observed value of the cosmological constant, it may involve a mechanism
by which some contributions to the cosmological constant can be fixed at a
continuous range of values in the different domains. I study the properties of
four possible mechanisms, including the possibility of the Hubble damping of a
scalar field with an extremely flat potential. Another interesting possibility
involves fixed random values of non-dynamical form fields, and a cosmological
mechanism is suggested. This case raises the possibility of anthropic selection
of other parameters in addition. Further requirements needed for a consistent
cosmology are discussed.
|
0006088v2
|
2013-05-11
|
Dividing Line between Quantum and Classical Trajectories: Bohmian Time Constant
|
This work proposes an answer to a challenge posed by Bell on the lack of
clarity in regards to the line between the quantum and classical regimes in a
measurement problem. To this end, a generalized logarithmic nonlinear
Schr\"odinger equation is proposed to describe the time evolution of a quantum
dissipative system under continuous measurement. Within the Bohmian mechanics
framework, a solution to this equation reveals a novel result: it displays a
time constant which should represent the dividing line between the quantum and
classical trajectories. It is shown that continuous measurements and damping
not only disturb the particle but compel the system to converge in time to a
Newtonian regime. While the width of the wave packet may reach a stationary
regime, its quantum trajectories converge exponentially in time to classical
trajectories. In particular, it is shown that damping tends to suppress further
quantum effects on a time scale shorter than the relaxation time of the system.
If the initial wave packet width is taken to be equal to 2.8 10^{-15} m (the
approximate size of an electron), the Bohmian time constant is found to have an
upper limit, i. e., ${\tau_{B\max}} = {10^{- 26}}s$.
|
1305.2517v2
|
2014-08-20
|
Building accurate initial models using gain functions for waveform inversion in the Laplace domain
|
We suggest an initial model building technique using time gain functions in
the Laplace domain. Applying the gain expressed as a power of time is
equivalent to taking the partial derivative of the Laplace-domain wavefield
with respect to a damping constant. We construct an objective function, which
minimizes the logarithmic differences between the gained field data and the
partial derivative of the modeled data with respect to the damping constant. We
calculate the modeled wavefield, the partial derivative wavefield, and the
gradient direction in the Laplace domain using the analytic Green's function
starting from a constant velocity model. This is an efficient method to
generate an accurate initial model for a following Laplace-domain inversion.
Numerical examples using two marine field datasets confirm that a starting
model updated once from a scratch using the gradient direction calculated with
the proposed method can be successfully used for a subsequent Laplace-domain
inversion.
|
1408.5872v1
|
1995-10-16
|
Star Formation and Chemical Evolution in Damped Lya Clouds
|
Using the redshift evolution of the neutral hydrogen density, as inferred
from observations of damped Ly$\alpha$ clouds, we calculate the evolution of
star formation rates and elemental abundances in the universe. For most
observables our calculations are in rough agreement with previous results based
on the instantaneous re-cycling approximation (IRA). However, for the key
metallicity tracer Zn, we find a better match to the observed abundance at high
redshift than that given by the constant-yield IRA model. We investigate
whether the redshift evolution of deuterium, depressions in the diffuse
extragalactic gamma-ray background, and measurement of the MeV neutrino
background may help determine if observational bias due to dust obscuration is
important. We also indicate how the importance of dust on the calculations can
be significantly reduced if correlations of the HI column density with
metallicity are present. The possibilities for measuring $q_o$ with
observations of elemental abundances in damped Ly$\alpha$ systems are
discussed.
|
9510078v1
|
2003-03-27
|
Oscillatory wave fronts in chains of coupled nonlinear oscillators
|
Wave front pinning and propagation in damped chains of coupled oscillators
are studied. There are two important thresholds for an applied constant stress
$F$: for $|F|<F_{cd}$ (dynamic Peierls stress), wave fronts fail to propagate,
for $F_{cd} < |F| < F_{cs}$ stable static and moving wave fronts coexist, and
for $|F| > F_{cs}$ (static Peierls stress) there are only stable moving wave
fronts. For piecewise linear models, extending an exact method of Atkinson and
Cabrera's to chains with damped dynamics corroborates this description. For
smooth nonlinearities, an approximate analytical description is found by means
of the active point theory. Generically for small or zero damping, stable wave
front profiles are non-monotone and become wavy (oscillatory) in one of their
tails.
|
0303576v1
|
2003-07-22
|
Classical dynamics of a nano-mechanical resonator coupled to a single-electron transistor
|
We analyze the dynamics of a nano-mechanical resonator coupled to a
single-electron transistor (SET) in the regime where the resonator behaves
classically. A master equation is derived describing the dynamics of the
coupled system which is then used to obtain equations of motion for the average
charge state of the SET and the average position of the resonator. We show that
the action of the SET on the resonator is very similar to that of a thermal
bath, as it leads to a steady-state probability-distribution for the resonator
which can be described by mean values of the resonator position, a renormalized
frequency, an effective temperature and an intrinsic damping constant.
Including the effects of extrinsic damping and finite temperature, we find that
there remain experimentally accessible regimes where the intrinsic damping of
the resonator still dominates its behavior. We also obtain the average current
through the SET as a function of the coupling to the resonator.
|
0307528v1
|
2006-05-16
|
Collective mode damping and viscosity in a 1D unitary Fermi gas
|
We calculate the damping of the Bogoliubov-Anderson mode in a one-dimensional
two-component attractive Fermi gas for arbitrary coupling strength within a
quantum hydrodynamic approach. Using the Bethe-Ansatz solution of the 1D
BCS-BEC crossover problem, we derive analytic results for the viscosity
covering the full range from a Luther-Emery liquid of weakly bound pairs to a
Lieb-Liniger gas of strongly bound bosonic dimers. At the unitarity point, the
system is a Tonks-Girardeau gas with a universal constant $\alpha_{\zeta}=0.38$
in the viscosity $\zeta=\alpha_{\zeta}\hbar n$ for T=0. For the trapped case,
we calculate the Q-factor of the breathing mode and show that the damping
provides a sensitive measure of temperature in 1D Fermi gases.
|
0605413v2
|
2006-06-09
|
Spin wave dynamics and the determination of intrinsic Gilbert damping in locally-excited Permalloy thin films
|
Time-resolved scanning Kerr effect microscopy has been used to study
magnetization dynamics in Permalloy thin films excited by transient magnetic
pulses generated by a micrometer-scale transmission line structure. The results
are consistent with magnetostatic spin wave theory and are supported by
micromagnetic simulations. Magnetostatic volume and surface spin waves are
measured for the same specimen using different bias field orientations and can
be accurately calculated by k-space integrations over all excited plane wave
components. A single damping constant of Gilbert form is sufficient to describe
both scenarios. The nonuniform pulsed field plays a key role in the spin wave
dynamics, with its Fourier transform serving as a weighting function for the
participating modes. The intrinsic Gilbert damping parameter $\alpha$ is most
conveniently measured when the spin waves are effectively stationary.
|
0606235v3
|
1996-03-14
|
Dissipation and Topologically Massive Gauge Theories in Pseudoeuclidean Plane
|
In the pseudo-euclidean metrics Chern-Simons gauge theory in the infrared
region is found to be associated with dissipative dynamics. In the infrared
limit the Lagrangian of 2+1 dimensional pseudo-euclidean topologically massive
electrodynamics has indeed the same form of the Lagrangian of the damped
harmonic oscillator. On the hyperbolic plane a set of two damped harmonic
oscillators, each other time-reversed, is shown to be equivalent to a single
undamped harmonic oscillator. The equations for the damped oscillators are
proven to be the same as the ones for the Lorentz force acting on two particles
carrying opposite charge in a constant magnetic field and in the electric
harmonic potential. This provides an immediate link with Chern-Simons-like
dynamics of Bloch electrons in solids propagating along the lattice plane with
hyperbolic energy surface. The symplectic structure of the reduced theory is
finally discussed in the Dirac constrained canonical formalism.
|
9603092v1
|
2002-02-12
|
Landau Damping and Coherent Structures in Narrow-Banded 1+1 Deep Water Gravity Waves
|
We study the nonlinear energy transfer around the peak of the spectrum of
surface gravity waves by taking into account nonhomogeneous effects. In the
narrow-banded approximation the kinetic equation resulting from a
nonhomogeneous wave field is a Vlasov-Poisson type equation which includes at
the same time the random version of the Benjamin-Feir instability and the
Landau damping phenomenon. We analytically derive the values of the Phillips'
constant $\alpha$ and the enhancement factor $\gamma$ for which the
narrow-banded approximation of the JONSWAP spectrum is unstable. By performing
numerical simulations of the nonlinear Schr\"{o}dinger equation we check the
validity of the prediction of the related kinetic equation. We find that the
effect of Landau damping is to suppress the formation of coherent structures.
The problem of predicting freak waves is briefly discussed.
|
0202026v1
|
2006-07-31
|
Nonadiabatic Transitions for a Decaying Two-Level-System: Geometrical and Dynamical Contributions
|
We study the Landau-Zener Problem for a decaying two-level-system described
by a non-hermitean Hamiltonian, depending analytically on time. Use of a
super-adiabatic basis allows to calculate the non-adiabatic transition
probability P in the slow-sweep limit, without specifying the Hamiltonian
explicitly. It is found that P consists of a ``dynamical'' and a
``geometrical'' factors. The former is determined by the complex adiabatic
eigenvalues E_(t), only, whereas the latter solely requires the knowledge of
\alpha_(+-)(t), the ratio of the components of each of the adiabatic
eigenstates. Both factors can be split into a universal one, depending only on
the complex level crossing points, and a nonuniversal one, involving the full
time dependence of E_(+-)(t). This general result is applied to the
Akulin-Schleich model where the initial upper level is damped with damping
constant $\gamma$. For analytic power-law sweeps we find that Stueckelberg
oscillations of P exist for gamma smaller than a critical value gamma_c and
disappear for gamma > gamma_c. A physical interpretation of this behavior will
be presented by use of a damped harmonic oscillator.
|
0607221v1
|
2007-06-01
|
The geometrical quantity in damped wave equations on a square
|
The energy in a square membrane $\Omega$ subject to constant viscous damping
on a subset $\omega\subset \Omega$ decays exponentially in time as soon as
$\omega$ satisfies a geometrical condition known as the "Bardos-Lebeau-Rauch"
condition. The rate $\tau(\omega)$ of this decay satisfies $\tau(\omega)= 2
\min(-\mu(\omega), g(\omega))$ (see Lebeau [Math. Phys. Stud. 19 (1996)
73-109]). Here $\mu(\omega)$ denotes the spectral abscissa of the damped wave
equation operator and $g(\omega)$ is a number called the geometrical quantity
of $\omega$ and defined as follows. A ray in $\Omega$ is the trajectory
generated by the free motion of a mass-point in $\Omega$ subject to elastic
reflections on the boundary. These reflections obey the law of geometrical
optics. The geometrical quantity $g(\omega)$ is then defined as the upper limit
(large time asymptotics) of the average trajectory length. We give here an
algorithm to compute explicitly $g(\omega)$ when $\omega$ is a finite union of
squares.
|
0706.0172v1
|
2009-10-14
|
Constraint on the growth factor of the cosmic structure from the damping of the baryon acoustic oscillation signature
|
We determine a constraint on the growth factor by measuring the damping of
the baryon acoustic oscillations in the matter power spectrum using the Sloan
Digital Sky Survey luminous red galaxy sample. The damping of the BAO is
detected at the one sigma level. We obtain \sigma_8D_1(z=0.3) =
0.42^{+0.34}_{-0.28} at the 1\sigma statistical level, where \sigma_8 is the
root mean square overdensity in a sphere of radius 8h^{-1}Mpc and D_1(z) is the
growth factor at redshift z. The above result assumes that other parameters are
fixed and the cosmology is taken to be a spatially flat cold dark matter
universe with the cosmological constant.
|
0910.2513v1
|
2011-02-04
|
A symmetry trip from Caldirola to Bateman damped systems
|
For the Caldirola-Kanai system, describing a quantum damped harmonic
oscillator, a couple of constant-of-motion operators generating the Heisenberg
algebra can be found. The inclusion of the standard time evolution symmetry in
this algebra for damped systems, in a unitary manner, requires a non-trivial
extension of this basic algebra and hence the physical system itself.
Surprisingly, this extension leads directly to the so-called Bateman's dual
system, which now includes a new particle acting as an energy reservoir. The
group of symmetries of the dual system is presented, as well as a quantization
that implies, in particular, a first-order Schr\"odinger equation. The usual
second-order equation and the inclusion of the original Caldirola-Kanai model
in Bateman's system are also discussed.
|
1102.0990v1
|
2011-03-08
|
Steady states of the parametric rotator and pendulum
|
We discuss several steady-state rotation and oscillation modes of the planar
parametric rotator and pendulum with damping. We consider a general elliptic
trajectory of the suspension point for both rotator and pendulum, for the
latter at an arbitrary angle with gravity, with linear and circular
trajectories as particular cases. We treat the damped, non-linear equation of
motion of the parametric rotator and pendulum perturbatively for small
parametric excitation and damping, although our perturbative approach can be
extended to other regimes as well. Our treatment involves only ordinary
second-order differential equations with constant coefficients, and provides
numerically accurate perturbative solutions in terms of elementary functions.
Some of the steady-state rotation and oscillation modes studied here have not
been discussed in the previous literature. Other well-known ones, such as
parametric resonance and the inverted pendulum, are extended to elliptic
parametric excitation tilted with respect to gravity. The results presented
here should be accessible to advanced undergraduates, and of interest to
graduate students and specialists in the field of non-linear mechanics.
|
1103.1413v1
|
2011-06-17
|
Controlling Excitations Inversion of a Cooper Pair Box Interacting with a Nanomechanical Resonator
|
We investigate the action of time dependent detunings upon the excitation
inversion of a Cooper pair box interacting with a nanomechanical resonator. The
method employs the Jaynes-Cummings model with damping, assuming different decay
rates of the Cooper pair box and various fixed and t-dependent detunings. It is
shown that while the presence of damping plus constant detunings destroy the
collapse/revival effects, convenient choices of time dependent detunings allow
one to reconstruct such events in a perfect way. It is also shown that the mean
excitation of the nanomechanical resonator is more robust against damping of
the Cooper pair box for convenient values of t-dependent detunings.
|
1106.3379v1
|
2011-07-24
|
Traveling kinks in cubic nonlinear Ginzburg-Landau equations
|
Nonlinear cubic Euler-Lagrange equations of motion in the traveling variable
are usually derived from Ginzburg-Landau free energy functionals frequently
encountered in several fields of physics. Many authors considered in the past
damped versions of such equations with the damping term added by hand
simulating the friction due to the environment. It is known that even in this
damped case kink solutions can exist. By means of a factorization method, we
provide analytic formulas for several possible kink solutions of such equations
of motion in the undriven and constant field driven cases, including the
recently introduced Riccati parameter kinks which were not considered
previously in such a context. The latter parameter controls the delay of the
switching stage of the kinks
|
1107.4773v4
|
2011-12-02
|
An energy-based computational method in the analysis of the transmission of energy in a chain of coupled oscillators
|
In this paper we study the phenomenon of nonlinear supratransmission in a
semi-infinite discrete chain of coupled oscillators described by modified
sine-Gordon equations with constant external and internal damping, and subject
to harmonic external driving at the end. We develop a consistent and
conditionally stable finite-difference scheme in order to analyze the effect of
damping in the amount of energy injected in the chain of oscillators; numerical
bifurcation analyses to determine the dependence of the amplitude at which
supratransmission first occurs with respect to the frequency of the driving
oscillator are carried out in order to show the consequences of damping on
harmonic phonon quenching and the delay of appearance of critical amplitude.
|
1112.0581v1
|
2014-08-25
|
Spin-Scattering Rates in Metallic Thin Films Measured by Ferromagnetic Resonance Damping Enhanced by Spin-Pumping
|
We determined the spin-transport properties of Pd and Pt thin films by
measuring the increase in ferromagnetic resonance damping due to spin-pumping
in ferromagnetic (FM)-nonferromagnetic metal (NM) multilayers with varying NM
thicknesses. The increase in damping with NM thickness depends strongly on both
the spin- and charge-transport properties of the NM, as modeled by diffusion
equations that include both momentum- and spin-scattering parameters. We use
the analytical solution to the spin-diffusion equations to obtain
spin-diffusion lengths for Pt and Pd. By measuring the dependence of
conductivity on NM thickness, we correlate the charge- and spin-transport
parameters, and validate the applicability of various models for
momentum-scattering and spin-scattering rates in these systems: constant,
inverse-proportional (Dyakanov-Perel), and linear-proportional (Elliot-Yafet).
We confirm previous reports that the spin-scattering time can be shorter than
the momentum scattering time in Pt, and the Dyakanov-Perel-like model is the
best fit to the data.
|
1408.5921v2
|
2015-02-05
|
Nonlinear analysis of magnetization dynamics excited by spin Hall effect
|
We investigate the possibility of exciting self-oscillation in a
perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear
analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-oscillation
state, the energy supplied by the spin torque during a precession on a constant
energy curve should equal the dissipation due to damping. Also, the current to
balance the spin torque and the damping torque in the self-oscillation state
should be larger than the critical current to destabilize the initial state. We
find that the second condition in the spin Hall system is not satisfied by
deriving analytical solutions of the energy supplied by the spin transfer
effect and the dissipation due to the damping from the nonlinear LLG equation.
This indicates that the self-oscillation of a perpendicular ferromagnet cannot
be excited solely by the spin Hall torque.
|
1502.01420v2
|
2015-04-09
|
Periodic-coefficient damping estimates, and stability of large-amplitude roll waves in inclined thin film flow
|
A technical obstruction preventing the conclusion of nonlinear stability of
large-Froude number roll waves of the St. Venant equations for inclined thin
film flow is the "slope condition" of Johnson-Noble-Zumbrun, used to obtain
pointwise symmetrizability of the linearized equations and thereby
high-frequency resolvent bounds and a crucial H s nonlinear damping estimate.
Numerically, this condition is seen to hold for Froude numbers 2 \textless{} F
3.5, but to fail for 3.5 F. As hydraulic engineering applications typically
involve Froude number 3 F 5, this issue is indeed relevant to practical
considerations. Here, we show that the pointwise slope condition can be
replaced by an averaged version which holds always, thereby completing the
nonlinear theory in the large-F case. The analysis has potentially larger
interest as an extension to the periodic case of a type of weighted
"Kawashima-type" damping estimate introduced in the asymptotically-constant
coefficient case for the study of stability of large-amplitude viscous shock
waves.
|
1504.02292v1
|
2015-05-08
|
Existence and general stabilization of the Timoshenko system with a thermo-viscoelastic damping and a delay term in the internal feedback
|
In this paper, we consider a Timoshenko system with a thermo-viscoelastic
damping and a delay term in the internal feedback together with initial datum
and boundary conditions of Dirichlet type, where g is a positive non-increasing
relaxation function and {\mu}1, {\mu}2 are positive constants. Under an
hypothesis between the weight of the delay term in the feedback and the the
weight of the friction damping term, using the Faedo-Galerkin approximations
together with some energy estimates, we prove the global existence of the
solutions. Then, by introducing appropriate Lyapunov functionals, under the
imposed constrain on the weights of the two feedbacks and the coefficients, we
establish the general energy decay result from which the exponential and
polynomial types of decay are only special cases.
|
1505.01899v1
|
2016-03-25
|
Large spin pumping effect in antisymmetric precession of Ni$_{79}$Fe$_{21}$/Ru/Ni$_{79}$Fe$_{21}$
|
In magnetic trilayer structures, a contribution to the Gilbert damping of
ferromagnetic resonance arises from spin currents pumped from one layer to
another. This contribution has been demonstrated for layers with weakly
coupled, separated resonances, where magnetization dynamics are excited
predominantly in one layer and the other layer acts as a spin sink. Here we
show that trilayer structures in which magnetizations are excited
simultaneously, antisymmetrically, show a spin-pumping effect roughly twice as
large. The antisymmetric (optical) mode of antiferromagnetically coupled
Ni$_{79}$Fe$_{21}$(8nm)/Ru/Ni$_{79}$Fe$_{21}$(8nm) trilayers shows a Gilbert
damping constant greater than that of the symmetric (acoustic) mode by an
amount as large as the intrinsic damping of Py ($\Delta
\alpha\simeq\textrm{0.006}$). The effect is shown equally in field-normal and
field-parallel to film plane geometries over 3-25 GHz. The results confirm a
prediction of the spin pumping model and have implications for the use of
synthetic antiferromagnets (SAF)-structures in GHz devices.
|
1603.07977v1
|
2016-05-26
|
Thickness and temperature dependence of the magnetodynamic damping of pulsed laser deposited $\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ on (111)-oriented SrTi$\text{O}_3$
|
We have investigated the magnetodynamic properties of
$\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ (LSMO) films of thickness 10, 15
and 30 nm grown on (111)-oriented SrTi$\text{O}_3$ (STO) substrates by pulsed
laser deposition. Ferromagnetic resonance (FMR) experiments were performed in
the temperature range 100--300 K, and the magnetodynamic damping parameter
$\alpha$ was extracted as a function of both film thickness and temperature. We
found that the damping is lowest for the intermediate film thickness of 15 nm
with $\alpha \approx 2 \cdot 10^{-3}$, where $\alpha$ is relatively constant as
a function of temperature well below the Curie temperature of the respective
films.
|
1605.08195v2
|
2017-03-28
|
Singularity formation for the 1D compressible Euler equation with variable damping coefficient
|
In this paper, we consider some blow-up problems for the 1D Euler equation
with time and space dependent damping. We investigate sufficient conditions on
initial data and the rate of spatial or time-like decay of the coefficient of
damping for the occurrence of the finite time blow-up. In particular, our
sufficient conditions ensure that the derivative blow-up occurs in finite time
with the solution itself and the pressure bounded. Our method is based on
simple estimates with Riemann invariants. Furthermore, we give sharp lower and
upper estimates of the lifespan of solutions, when initial data are small
perturbations of constant states.
|
1703.09821v3
|
2017-08-30
|
Convergence to diffusion waves for solutions of Euler equations with time-depending damping on quadrant
|
This paper is concerned with the asymptotic behavior of the solution to the
Euler equations with time-depending damping on quadrant $(x,t)\in
\mathbb{R}^+\times\mathbb{R}^+$, \begin{equation}\notag \partial_t v
-
\partial_x u=0, \qquad \partial_t u
+
\partial_x p(v)
=\displaystyle
-\frac{\alpha}{(1+t)^\lambda} u, \end{equation} with null-Dirichlet boundary
condition or null-Neumann boundary condition on $u$. We show that the
corresponding initial-boundary value problem admits a unique global smooth
solution which tends time-asymptotically to the nonlinear diffusion wave.
Compared with the previous work about Euler equations with constant coefficient
damping, studied by Nishihara and Yang (1999, J. Differential Equations, 156,
439-458), and Jiang and Zhu (2009, Discrete Contin. Dyn. Syst., 23, 887-918),
we obtain a general result when the initial perturbation belongs to the same
space. In addition, our main novelty lies in the facts that the cut-off points
of the convergence rates are different from our previous result about the
Cauchy problem. Our proof is based on the classical energy method and the
analyses of the nonlinear diffusion wave.
|
1708.09127v1
|
2017-11-01
|
Tunable magnetization relaxation of Fe_{2}Cr_{1-x}Co_{x}Si half-metallic Heusler alloys by band structure engineering
|
We report a systematic investigation on the magnetization relaxation
properties of iron-based half-metallic Heusler alloy
Fe$_{2}$Cr$_{1-x}$Co_${x}$Si (FCCS) thin films using broadband angular-resolved
ferromagnetic resonance. Band structure engineering through Co doping (x)
demonstrated by first-principles calculations is shown to tune the intrinsic
magnetic damping over an order of magnitude, namely 0.01-0.0008. Notably, the
intrinsic damping constants for samples with high Co concentration are among
the lowest reported for Heusler alloys and even comparable to magnetic
insulator yttrium iron garnet. Furthermore, a significant reduction of both
isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys
was found in the FCCS films with x=0.5-0.75, which is of particular importance
for applications. These results demonstrate a practical recipe to tailor
functional magnetization for Heusler alloy-based spintronics at room
temperature
|
1711.00406v1
|
2018-01-23
|
The effect of liquid on the vibrational intensity of a wineglass at steady state resonance
|
As a liquid is inserted into a wineglass, the natural frequency of the
wineglass decreases. This phenomenon, known as pitch lowering, is well
explained in past papers. However, previous literature have not yet mentioned
that pitch lowering also reduces the resonance intensity of a wineglass. Thus,
this present paper aims to extend the body of research on this topic by
describing the relationship between pitch lowering and its effect on resonation
intensity. To do so, we identify the vibrating wineglass wall as a damped
harmonic oscillator, derive a theoretical model, and find that the resonance
intensity of the wineglass is proportional to the square of its natural
frequency, under the assumption that damping stays constant. However, our
experiments showed the coefficient of damping to increase with respect to the
amount of liquid, which caused the data to deviate from its theoretical
predictions. We conclude by discussing the accuracy and limitation of our
proposed model.
|
1801.07514v5
|
2018-04-11
|
A global existence result for a semilinear wave equation with scale-invariant damping and mass in even space dimension
|
In the present article a semilinear wave equation with scale-invariant
damping and mass is considered. The global (in time) existence of radial
symmetric solutions in even spatial dimension $n$ is proved using weighted
$L^\infty-L^\infty$ estimates, under the assumption that the multiplicative
constants, which appear in the coefficients of damping and of mass terms,
fulfill an interplay condition which yields somehow a "wave-like" model. In
particular, combining this existence result with a recently proved blow-up
result, a suitable shift of Strauss exponent is proved to be the critical
exponent for the considered model. Moreover, the still open part of a
conjecture done by D'Abbicco - Lucente - Reissig is proved to be true in the
massless case.
|
1804.03978v1
|
2018-12-21
|
Reply to the Comment on "Negative Landau damping in bilayer graphene"
|
Here we address the concerns of Svintsov and Ryzhii [arXiv:1812.03764] on our
article on negative Landau damping in graphene [Phys. Rev. Lett. 119, 133901
(2017)]. We prove that due to the differences between the kinetic and canonical
momenta, the conductivity of drift-current biased graphene is ruled by a
Galilean transformation when the electron-electron interactions predominate and
force the electron gas to move with constant velocity, similar to a moving
medium. Furthermore, it is shown that the nonlocal effects in graphene neither
preclude a negative Landau damping nor the emergence of instabilities in
graphene platforms.
|
1812.09103v3
|
2018-12-30
|
Smooth, Time-invariant Regulation of Nonholonomic Systems via Energy Pumping-and-Damping
|
In this paper we propose an energy pumping-and-damping technique to regulate
nonholonomic systems described by kinematic models. The controller design
follows the widely popular interconnection and damping assignment
passivity-based methodology, with the free matrices partially structured. Two
asymptotic regulation objectives are considered: drive to zero the state or
drive the systems total energy to a desired constant value. In both cases, the
control laws are smooth, time-invariant, state-feedbacks. For the nonholonomic
integrator we give an almost global solution for both problems, with the
objectives ensured for all system initial conditions starting outside a set
that has zero Lebesgue measure and is nowhere dense. For the general case of
higher-order nonholonomic systems in chained form, a local stability result is
given. Simulation results comparing the performance of the proposed controller
with other existing designs are also provided.
|
1812.11538v2
|
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