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2019-01-17
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Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures
|
We investigate the effect of capping layer (CAP) on the interfacial magnetic
anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
HfOx, or TaN). At room temperature (RT) the CAP materials influence the
effective magnitude of K_S, which is associated with a formation of interfacial
magnetic oxides. The dynamical dissipation parameters of Co are considerably
influenced by the CAP (especially MgO) while those of Py are not. This is
possibly due to an extra magnetic damping via spin-pumping process across the
Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
interfacial CoO. It is also observed that both anti-damping and field-like SOT
efficiencies vary marginally with the CAP in the thickness ranges we examined.
Our results reveal the crucial role of interfacial oxides on the perpendicular
magnetic anisotropy, magnetic damping, and SOTs.
|
1901.05777v1
|
2019-05-31
|
The amplitude of solar p-mode oscillations from three-dimensional convection simulations
|
The amplitude of solar p-mode oscillations is governed by stochastic
excitation and mode damping, both of which take place in the surface convection
zone. However, the time-dependent, turbulent nature of convection makes it
difficult to self-consistently study excitation and damping processes through
the use of traditional one-dimensional hydrostatic models. To this end, we
carried out \textit{ab initio} three-dimensional, hydrodynamical numerical
simulations of the solar atmosphere to investigate how p-modes are driven and
dissipated in the Sun. The description of surface convection in the simulations
is free from the tuneable parameters typically adopted in traditional
one-dimensional models. Mode excitation and damping rates are computed based on
analytical expressions whose ingredients are evaluated directly from the
three-dimensional model. With excitation and damping rates both available, we
estimate the theoretical oscillation amplitude and frequency of maximum power,
$\nu_{\max}$, for the Sun. We compare our numerical results with helioseismic
observations, finding encouraging agreement between the two. The numerical
method presented here provides a novel way to investigate the physical
processes responsible for mode driving and damping, and should be valid for all
solar-type oscillating stars.
|
1905.13397v2
|
2019-08-23
|
Damping enhancement in coherent ferrite/insulating-paramagnet bilayers
|
High-quality epitaxial ferrites, such as low-damping MgAl-ferrite (MAFO), are
promising nanoscale building blocks for all-oxide heterostructures driven by
pure spin current. However, the impact of oxide interfaces on spin dynamics in
such heterostructures remains an open question. Here, we investigate the spin
dynamics and chemical and magnetic depth profiles of 15-nm-thick MAFO
coherently interfaced with an isostructural $\approx$1-8-nm-thick overlayer of
paramagnetic CoCr$_2$O$_4$ (CCO) as an all-oxide model system. Compared to MAFO
without an overlayer, effective Gilbert damping in MAFO/CCO is enhanced by a
factor of $>$3, irrespective of the CCO overlayer thickness. We attribute this
damping enhancement to spin scattering at the $\sim$1-nm-thick chemically
disordered layer at the MAFO/CCO interface, rather than spin pumping or
proximity-induced magnetism. Our results indicate that damping in ferrite-based
heterostructures is strongly influenced by interfacial chemical disorder, even
if the thickness of the disordered layer is a small fraction of the ferrite
thickness.
|
1908.08629v2
|
2019-10-03
|
Many-body collision contributions to electron momentum damping rates in a plasma influenced by electron strong coupling
|
Experimental studies of electron-ion collision rates in an ultracold neutral
plasma (UNP) can be conducted through measuring the rate of electron plasma
oscillation damping. For sufficiently cold and dense conditions where strong
coupling influences are important, the measured damping rate was faster by 37\%
than theoretical expectations [W. Chen, C. Witte, and J. Roberts, Phys. Rev. E
\textbf{96}, 013203 (2017)]. We have conducted a series of numerical
simulations to isolate the primary source of this difference. By analyzing the
distribution of electron velocity changes due to collisions in a molecular
dynamics simulation, examining the trajectory of electrons with high deflection
angle in such simulations, and examining the oscillation damping rate while
varying the ratio of two-body to three-body electron-ion collision rates, we
have found that the difference is consistent with the effect due to many-body
collisions leading to bound electrons. This has implications for other
electron-ion collision related transport properties in addition to electron
oscillation damping.
|
1910.01707v1
|
2019-10-18
|
Escape of a forced-damped particle from weakly nonlinear truncated potential well
|
Escape from a potential well is an extreme example of transient behavior. We
consider the escape of the harmonically forced particle under viscous damping
from the benchmark truncated weakly nonlinear potential well. Main attention is
paid to most interesting case of primary 1:1 resonance. The treatment is based
on multiple-scales analysis and exploration of the slow-flow dynamics. Contrary
to Hamiltonian case described in earlier works, in the case with damping the
slow-flow equations are not integrable. However, if the damping is small
enough, it is possible to analyze the perturbed slow-flow equations. The effect
of the damping on the escape threshold is evaluated in the explicit analytic
form. Somewhat unexpectedly, the escape mechanisms in terms of the slow flow
are substantially different for the linear and weakly nonlinear cases.
|
1910.08545v1
|
2019-10-24
|
Topological damping Rashba spin orbit torque in ballistic magnetic domain walls
|
Rashba spin orbit torque derived from the broken inversion symmetry at
ferromagnet/heavy metal interfaces has potential application in spintronic
devices. In conventional description of the precessional and damping components
of the Rashba spin orbit torque in magnetization textures, the decomposition
coefficients are assumed to be independent of the topology of the underlying
structure. Contrary to this common wisdom, for Schr\"{o}dinger electrons
trespassing ballistically across a magnetic domain wall, we found that the
decomposition coefficient of the damping component is determined by the
topology of the domain wall. The resultant damping Rashba spin orbit torque is
protected by the topology of the underlying magnetic domain wall and robust
against small deviations from the ideal domain wall profile. Our identification
of a topological damping Rashba spin orbit torque component in magnetic domain
walls will help to understand experiments on current driven domain wall motion
in ferromagnet/heavy metal systems with broken inversion symmetry and to
facilitate its utilization in innovative device designs.
|
1910.10977v2
|
2019-11-02
|
Tuning Non-Gilbert-type damping in FeGa films on MgO(001) via oblique deposition
|
The ability to tailor the damping factor is essential for spintronic and
spin-torque applications. Here, we report an approach to manipulate the damping
factor of FeGa/MgO(001) films by oblique deposition. Owing to the defects at
the surface or interface in thin films, two-magnon scattering (TMS) acts as a
non-Gilbert damping mechanism in magnetization relaxation. In this work, the
contribution of TMS was characterized by in-plane angular dependent
ferromagnetic resonance (FMR). It is demonstrated that the intrinsic Gilbert
damping is isotropic and invariant, while the extrinsic mechanism related to
TMS is anisotropic and can be tuned by oblique deposition. Furthermore, the two
and fourfold TMS related to the uniaxial magnetic anisotropy (UMA) and
magnetocrystalline anisotropy were discussed. Our results open an avenue to
manipulate magnetization relaxation in spintronic devices.
|
1911.00728v1
|
2019-11-13
|
Dipole oscillations of fermionic superfluids along the BEC-BCS crossover in disordered potentials
|
We investigate dipole oscillations of ultracold Fermi gases along the BEC-BCS
crossover through disordered potentials. We observe a disorder-induced damping
of oscillations as well as a change of the fundamental Kohn-mode frequency. The
measurement results are compared to numerical density matrix renormalization
group calculations as well as to a three-dimensional simulation of
non-interacting fermions. Experimentally, we find a disorder-dependent damping,
which grows approximately with the second power of the disorder strength.
Moreover, we observe experimentally a change of oscillation frequency which
deviates from the expected behavior of a damped harmonic oscillator on a
percent level. While this behavior is qualitatively expected from the
theoretical models used, quantitatively the experimental observations show a
significantly stronger effect than predicted by theory. Furthermore, while the
frequency shift seems to scale differently with interaction strength in the BEC
versus BCS regime, the damping coefficient apparently decreases with the
strength of interaction, but not with the sign, which changes for BEC and BCS
type Fermi gases. This is surprising, as the dominant damping mechanisms are
expected to be different in the two regimes.
|
1911.05638v1
|
2020-02-07
|
Model of damping and anisotropy at elevated temperatures: application to granular FePt films
|
Understanding the damping mechanism in finite size systems and its dependence
on temperature is a critical step in the development of magnetic
nanotechnologies. In this work, nano-sized materials are modeled via atomistic
spin dynamics, the damping parameter being extracted from Ferromagnetic
Resonance (FMR) simulations applied for FePt systems, generally used for
heat-assisted magnetic recording media (HAMR). We find that the damping
increases rapidly close to Tc and the effect is enhanced with decreasing system
size, which is ascribed to scattering at the grain boundaries. Additionally,
FMR methods provide the temperature dependence of both damping and the
anisotropy, important for the development of HAMR. Semi-analytical calculations
show that, in the presence of a grain size distribution, the FMR linewidth can
decrease close to the Curie temperature due to a loss of inhomogeneous line
broadening. Although FePt has been used in this study, the results presented in
the current work are general and valid for any ferromagnetic material.
|
2002.02865v1
|
2020-04-06
|
Damping-like Torque in Monolayer 1T-TaS$_2$
|
A damping-like spin orbit torque (SOT) is a prerequisite for ultralow power
spin logic devices. Here, we report on the damping-like SOT in just one
monolayer of the conducting transition metal dichalcogenide (TMD) TaS$_2$
interfaced with a NiFe (Py) ferromagnetic layer. The charge-spin conversion
efficiency is found to be 0.25$\pm$0.03 and the spin Hall conductivity (2.63
$\times$ 10$^5$ $\frac{\hbar}{2e}$ $\Omega^{-1}$ m$^{-1}$) is found to be
superior to values reported for other TMDs. The origin of this large
damping-like SOT can be found in the interfacial properties of the TaS$_2$/Py
heterostructure, and the experimental findings are complemented by the results
from density functional theory calculations. The dominance of damping-like
torque demonstrated in our study provides a promising path for designing next
generation conducting TMD based low-powered quantum memory devices.
|
2004.02649v1
|
2020-05-15
|
Calibration and performance of the neutron detector onboard of the DAMPE mission
|
The DArk Matter Particle Explorer (DAMPE), one of the four space-based
scientific missions within the framework of the Strategic Pioneer Program on
Space Science of the Chinese Academy of Sciences, has been successfully
launched on Dec. 17th 2015 from Jiuquan launch center. One of the most
important scientific goals of DAMPE is to search for the evidence of dark
matter indirectly by measuring the spectrum of high energy cosmic-ray
electrons. The neutron detector, one of the four sub-payloads of DAMPE, is
designed to distinguish high energy electrons from hadron background by
measuring the secondary neutrons produced in the shower. In this paper, a
comprehensive introduction of the neutron detector is presented, including the
design, the calibration and the performance. The analysis with simulated data
and flight data indicates a powerful proton rejection capability of the neutron
detector, which plays an essential role for TeV electron identification of
DAMPE.
|
2005.07828v1
|
2020-05-16
|
Simultaneous observation of anti-damping and inverse spin Hall effect in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayer system
|
Manganites have shown potential in spintronics because they exhibit high spin
polarization. Here, by ferromagnetic resonance we have studied the damping
properties of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayers which are prepared by
oxide molecular beam epitaxy. The damping coefficient ($\alpha$) of
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) single layer is found to be 0.0104.
However the LSMO/Pt bilayers exhibit decrease in $\alpha$ with increase in Pt
thickness. This decrease in the value of $\alpha$ is probably due to high
anti-damping like torque. Further, we have investigated the angle dependent
inverse spin Hall effect (ISHE) to quantify the spin pumping voltage from other
spin rectification effects such as anomalous Hall effect and anisotropic
magnetoresistance. We have observed high spin pumping voltage ($\sim$~20 $ \mu
V$). The results indicate that both anti-damping and spin pumping phenomena are
occuring simultaneously.
|
2005.07848v3
|
2020-07-25
|
Using a Lindbladian approach to model decoherence in two coupled nuclear spins via correlated phase-damping and amplitude damping noise channels
|
In this work, we studied the relaxation dynamics of coherences of different
order present in a system of two coupled nuclear spins. We used a previously
designed model for intrinsic noise present in such systems which considers the
Lindblad master equation for Markovian relaxation. We experimentally created
zero-, single- and double- quantum coherences in several two-spin systems and
performed a complete state tomography and computed state fidelity. We
experimentally measured the decay of zero- and double- quantum coherences in
these systems. The experimental data fitted well to a model that considers the
main noise channels to be a correlated phase damping channel acting
simultaneously on both spins in conjunction with a generalized amplitude
damping channel acting independently on both spins. The differential relaxation
of multiple-quantum coherences can be ascribed to the action of a correlated
phase damping channel acting simultaneously on both the spins.
|
2007.12972v1
|
2020-09-29
|
The effects of nonlinear damping on degenerate parametric amplification
|
This paper considers the dynamic response of a single degree of freedom
system with nonlinear stiffness and nonlinear damping that is subjected to both
resonant direct excitation and resonant parametric excitation, with a general
phase between the two. This generalizes and expands on previous studies of
nonlinear effects on parametric amplification, notably by including the effects
of nonlinear damping, which is commonly observed in a large variety of systems,
including micro- and nano-scale resonators. Using the method of averaging, a
thorough parameter study is carried out that describes the effects of the
amplitudes and relative phase of the two forms of excitation. The effects of
nonlinear damping on the parametric gain are first derived. The transitions
among various topological forms of the frequency response curves, which can
include isolae, dual peaks, and loops, are determined, and bifurcation analyses
in parameter spaces of interest are carried out. In general, these results
provide a complete picture of the system response and allow one to select drive
conditions of interest that avoid bistability while providing maximum amplitude
gain, maximum phase sensitivity, or a flat resonant peak, in systems with
nonlinear damping.
|
2009.14284v2
|
2020-11-10
|
Damped oscillators within the general theory of Casimir and van der Waals forces
|
It is demonstrated that the general theory of Casimir and van der Waals
forces describes the interaction-induced equilibrium thermodynamic potentials
of the damped harmonic oscillator bilinearly coupled to the environment. An
extended model for a damped oscillator is suggested along the lines of the
general theory of Casimir and van der Waals forces, and the corresponding
thermodynamic quantities obtained. While the original model involves a heat
bath consisting of a large number of free oscillators having infinitesimal
damping functions, the extended model allows any generally admissible frequency
and temperature dependent dissipative susceptibilities of the heat bath
constituents, influenced by the additional dissipative environmental channels
that are not directly linked to the system oscillator. Consequently, the
results obtained are applicable to the frequency and temperature dependent
damping function of the system oscillator.
|
2011.04960v2
|
2021-01-03
|
The effect of flow on resonant absorption of slow MHD waves in magnetic flux tubes
|
In this paper, we study kink and sausage oscillations in the presence of
longitudinal background flow. We study resonant absorption of the kink and
sausage modes in the slow continuum under magnetic pore conditions in the
presence of flow. we determine the dispersion relation then solve it
numerically, and find the frequencies and damping rates of the slow kink and
sausage surface modes. We also, obtain analytical solution for the damping rate
of the slow surface mode in the long wavelength limit. We show that in the
presence of plasma flow, resonance absorption can result in strong damping for
forward waves and can be considered as an efficient mechanism to justify the
extremely rapid damping of slow surface sausage waves observed in magnetic
pores. Also, the plasma flow reduces the efficiency of resonance absorption to
damp backward waves. Furthermore, for the pore conditions, the resonance
instability is avoided in our model.
|
2101.02064v1
|
2021-02-01
|
Blow-up and lifespan estimates for a damped wave equation in the Einstein-de Sitter spacetime with nonlinearity of derivative type
|
In this article, we investigate the blow-up for local solutions to a
semilinear wave equation in the generalized Einstein - de Sitter spacetime with
nonlinearity of derivative type. More precisely, we consider a semilinear
damped wave equation with a time-dependent and not summable speed of
propagation and with a time-dependent coefficient for the linear damping term
with critical decay rate. We prove in this work that the results obtained in a
previous work, where the damping coefficient takes two particular values $0$ or
$2$, can be extended for any positive damping coefficient. In the blow-up case,
the upper bound of the exponent of the nonlinear term is given, and the
lifespan estimate of the global existence time is derived as well.
|
2102.01137v2
|
2021-02-02
|
Analysis of Lower Hybrid Drift Waves in Kappa Distributions over Solar Atmosphere
|
Kappa distributions and with loss cone features have been frequently observed
with flares emissions with the signatures of Lower hybrid waves. We have
analysed the plasma with Kappa distributions and with loss cone features for
the drift wave instabilities in perpendicular propagation for Large flare and
Normal flare and Coronal condition . While analysing the growth/damping rate,
we understand that the growth of propagation of EM waves increases with kappa
distribution index for all the three cases. In comparing the propagation large
flare shows lesser growth in compared with the normal and the coronal plasmas.
When added the loss cone features to Kappa distributions, we find that the
damping of EM wave propagation takes place. The damping rate EM waves is
increases with perpendicular temperature and loss cone index l, in all the
three cases but damping is very high for large flare and then normal in
comparision with coronal condition. This shows that the lower hybrid damping
may be the source of coronal heating.
|
2102.01323v1
|
2021-02-25
|
Regularity and stability of the semigroup associated with some interacting elastic systems I: A degenerate damping case
|
In this paper, we examine regularity and stability issues for two damped
abstract elastic systems. The damping involves the average velocity and a
fractional power $\theta$, with $\theta$ in $[-1,1]$, of the principal
operator. The matrix operator defining the damping mechanism for the coupled
system is degenerate. First, we prove that for $\theta$ in $(1/2,1]$, the
underlying semigroup is not analytic, but is differentiable for $\theta$ in
$(0,1)$; this is in sharp contrast with known results for a single similarly
damped elastic system, where the semigroup is analytic for $\theta$ in
$[1/2,1]$; this shows that the degeneracy dominates the dynamics of the
interacting systems, preventing analyticity in that range. Next, we show that
for $\theta$ in $(0,1/2]$, the semigroup is of certain Gevrey classes. Finally,
we show that the semigroup decays exponentially for $\theta$ in $[0,1]$, and
polynomially for $\theta$ in $[-1,0)$. To prove our results, we use the
frequency domain method, which relies on resolvent estimates. Optimality of our
resolvent estimates is also established. Several examples of application are
provided.
|
2102.13217v4
|
2021-03-05
|
Existence and congruence of global attractors for damped and forced integrable and nonintegrable discrete nonlinear Schrödinger equations
|
We study two damped and forced discrete nonlinear Schr\"odinger equations on
the one-dimensional infinite lattice. Without damping and forcing they are
represented by the integrable Ablowitz-Ladik equation (AL) featuring non-local
cubic nonlinear terms, and its standard (nonintegrable) counterpart with local
cubic nonlinear terms (DNLS). The global existence of a unique solution to the
initial value problem for both, the damped and forced AL and DNLS, is proven.
It is further shown that for sufficiently close initial data, their
corresponding solutions stay close for all times. Concerning the asymptotic
behaviour of the solutions to the damped and forced AL and DNLS, for the former
a sufficient condition for the existence of a restricted global attractor is
established while it is shown that the latter possesses a global attractor.
Finally, we prove the congruence of the restricted global AL attractor and the
DNLS attractor for dynamics ensuing from initial data contained in an
appropriate bounded subset in a Banach space.
|
2103.03533v1
|
2021-05-17
|
Dissipation of Oscillation Energy and Distribution of Damping Power in a Multimachine Power System: A Small-signal Analysis
|
This paper revisits the concept of damping torque in a multimachine power
system and its relation to the dissipation of oscillation energy in synchronous
machine windings. As a multimachine extension of an existing result on a
single-machine-infinite-bus (SMIB) system, we show that the total damping power
for a mode stemming from the interaction of electromagnetic torques and rotor
speeds is equal to the sum of average power dissipations in the generator
windings corresponding to the modal oscillation. Further, counter-intuitive to
the SMIB result, we demonstrate that, although the equality holds on an
aggregate, such is not the case for individual machines in an interconnected
system. To that end, distribution factors are derived for expressing the
average damping power of each generator as a linear combination of average
powers of modal energy dissipation in the windings of all machines in the
system. These factors represent the distribution of damping power in a
multimachine system. The results are validated on IEEE 4-machine and 16-machine
test systems.
|
2105.07618v2
|
2021-06-04
|
Imaging spin-wave damping underneath metals using electron spins in diamond
|
Spin waves in magnetic insulators are low-damping signal carriers that could
enable a new generation of spintronic devices. The excitation, control, and
detection of spin waves by metal electrodes is crucial for interfacing these
devices to electrical circuits. It is therefore important to understand
metal-induced damping of spin-wave transport, but characterizing this process
requires access to the underlying magnetic films. Here we show that spins in
diamond enable imaging of spin waves that propagate underneath metals in
magnetic insulators, and then use this capability to reveal a 100-fold increase
in spin-wave damping. By analyzing spin-wave-induced currents in the metal, we
derive an effective damping parameter that matches these observations well. We
furthermore detect buried scattering centers, highlighting the technique's
power for assessing spintronic device quality. Our results open new avenues for
studying metal - spin-wave interaction and provide access to interfacial
processes such as spin-wave injection via the spin-Hall effect.
|
2106.02508v2
|
2021-06-04
|
Inherent Non-Linear Damping in Resonators with Inertia Amplification
|
Inertia amplification is a mechanism coupling degrees of freedom within a
vibrating structure. Its goal is to achieve an apparent high dynamic mass and,
accordingly, a low resonance frequency. Such structures have been described for
use in locally resonant metamaterials and phononic crystals to lower the
starting frequency of a band gap without adding mass to the system. This study
shows that any non-linear kinematic coupling between translational or
rotational vibrations leads to the appearance of amplitude-dependent damping.
The analytical derivation of the equation of motion of a resonator with inertia
amplification creates insight in the damping process, and shows that the
vibration damping increases with its amplitude. The theoretical study is
validated by experimental evidence from two types of inertia-amplification
resonators. Finally, the importance of amplitude-dependent damping is
illustrated when the structure is used as a tuned mass damper for a cantilever
beam.
|
2106.02576v2
|
2021-06-30
|
On the effect of perturbations in first-order optimization methods with inertia and Hessian driven damping
|
Second-order continuous-time dissipative dynamical systems with viscous and
Hessian driven damping have inspired effective first-order algorithms for
solving convex optimization problems. While preserving the fast convergence
properties of the Nesterov-type acceleration, the Hessian driven damping makes
it possible to significantly attenuate the oscillations. To study the stability
of these algorithms with respect to perturbations, we analyze the behaviour of
the corresponding continuous systems when the gradient computation is subject
to exogenous additive errors. We provide a quantitative analysis of the
asymptotic behaviour of two types of systems, those with implicit and explicit
Hessian driven damping. We consider convex, strongly convex, and non-smooth
objective functions defined on a real Hilbert space and show that, depending on
the formulation, different integrability conditions on the perturbations are
sufficient to maintain the convergence rates of the systems. We highlight the
differences between the implicit and explicit Hessian damping, and in
particular point out that the assumptions on the objective and perturbations
needed in the implicit case are more stringent than in the explicit case.
|
2106.16159v2
|
2021-07-02
|
Anomalous Gilbert Damping and Duffing Features of the SFS {\boldmath $\varphi_0$} Josephson Junction
|
We demonstrate unusual features of phase dynamics, IV-characteristics and
magnetization dynamics of the $\varphi_0$ Josephson junction at small values of
spin-orbit interaction, ratio of Josephson to magnetic energy and Gilbert
damping. In particular, an anomalous shift of the ferromagnetic resonance
frequency with an increase of Gilbert damping is found. The ferromagnetic
resonance curves show the Duffing oscillator behaviour, reflecting the
nonlinear nature of Landau-Lifshitz-Gilbert (LLG) equation. Based on the
numerical analysis of each term in LLG equation we obtained an approximated
equation demonstrated both damping effect and Duffing oscillator features. The
resulting Duffing equation incorporates the Gilbert damping in a special way
across the dissipative term and the restoring force. A resonance method for the
determination of spin-orbit interaction in noncentrosymmetric materials which
play the role of barrier in $\varphi_0$ junctions is proposed.
|
2107.00982v3
|
2021-07-13
|
A new approach to the quantization of the damped harmonic oscillator
|
In this paper, a new approach for constructing Lagrangians for driven and
undriven linearly damped systems is proposed, by introducing a redefined time
coordinate and an associated coordinate transformation to ensure that the
resulting Lagrangian satisfies the Helmholtz conditions. The approach is
applied to canonically quantize the damped harmonic oscillator and although it
predicts an energy spectrum that decays at the same rate to previous models,
unlike those approaches it recovers the classical critical damping condition,
which determines transitions between energy eigenstates, and is therefore
consistent with the correspondence principle. It is also demonstrated how to
apply the procedure to a driven damped harmonic oscillator.
|
2107.05827v3
|
2021-10-26
|
Theory of sound attenuation in amorphous solids from nonaffine motions
|
We present a theoretical derivation of acoustic phonon damping in amorphous
solids based on the nonaffine response formalism for the viscoelasticity of
amorphous solids. The analytical theory takes into account the nonaffine
displacements in transverse waves and is able to predict both the ubiquitous
low-energy diffusive damping $\sim k^{2}$, as well as a novel contribution to
the Rayleigh damping $\sim k^{4}$ at higher wavevectors and the crossover
between the two regimes observed experimentally. The coefficient of the
diffusive term is proportional to the microscopic viscous (Langevin-type)
damping in particle motion (which arises from anharmonicity), and to the
nonaffine correction to the static shear modulus, whereas the Rayleigh damping
emerges in the limit of low anharmonicity, consistent with previous
observations and macroscopic models. Importantly, the $k^4$ Rayleigh
contribution derived here does not arise from harmonic disorder or elastic
heterogeneity effects and it is the dominant mechanism for sound attenuation in
amorphous solids as recently suggested by molecular simulations.
|
2110.13446v2
|
2021-11-21
|
Energy Transport in 1-Dimensional Oscillator Arrays With Hysteretic Damping
|
Energy transport in 1-dimensional oscillator arrays has been extensively
studied to date in the conservative case, as well as under weak viscous
damping. When driven at one end by a sinusoidal force, such arrays are known to
exhibit the phenomenon of supratransmission, i.e. a sudden energy surge above a
critical driving amplitude. In this paper, we study 1-dimensional oscillator
chains in the presence of hysteretic damping, and include nonlinear stiffness
forces that are important for many materials at high energies. We first employ
Reid's model of local hysteretic damping, and then study a new model of nearest
neighbor dependent hysteretic damping to compare their supratransmission and
wave packet spreading properties in a deterministic as well as stochastic
setting. The results have important quantitative differences, which should be
helpful when comparing the merits of the two models in specific engineering
applications.
|
2111.10816v3
|
2021-12-15
|
An Innovative Transverse Emittance Cooling Technique using a Laser-Plasma Wiggler
|
We propose an innovative beam cooling scheme based on laser driven plasma
wakefields to address the challenge of high luminosity generation for a future
linear collider. For linear colliders, beam cooling is realised by means of
damping rings equipped with wiggler magnets and accelerating cavities. This
scheme ensures systematic reduction of phase space volume through synchrotron
radiation emission whilst compensating for longitudinal momentum loss via an
accelerating cavity. In this paper, the concept of a plasma wiggler and its
effective model analogous to a magnetic wiggler are introduced; relation of
plasma wiggler characteristics with damping properties are demonstrated;
underpinning particle-in-cell simulations for laser propagation optimisation
are presented. The oscillation of transverse wakefields and resulting
sinusoidal probe beam trajectory are numerically demonstrated. The formation of
an order of magnitude larger effective wiggler field compared to conventional
wigglers is successfully illustrated. Potential damping ring designs on the
basis of this novel plasma-based technology are presented and performance in
terms of damping times and footprint was compared to an existing conventional
damping ring design.
|
2112.08163v1
|
2021-12-21
|
ISS-Based Robustness to Various Neglected Damping Mechanisms for the 1-D Wave PDE
|
This paper is devoted to the study of the robustness properties of the 1-D
wave equation for an elastic vibrating string under four different damping
mechanisms that are usually neglected in the study of the wave equation: (i)
friction with the surrounding medium of the string (or viscous damping), (ii)
thermoelastic phenomena (or thermal damping), (iii) internal friction of the
string (or Kelvin-Voigt damping), and (iv) friction at the free end of the
string (the so-called passive damper). The passive damper is also the simplest
boundary feedback law that guarantees exponential stability for the string. We
study robustness with respect to distributed inputs and boundary disturbances
in the context of Input-to-State Stability (ISS). By constructing appropriate
ISS Lyapunov functionals, we prove the ISS property expressed in various
spatial norms.
|
2112.11287v1
|
2022-01-20
|
Derivation of the linear Boltzmann equation from the damped quantum Lorentz gas with a general scatterer configuration
|
It is a fundamental problem in mathematical physics to derive macroscopic
transport equations from microscopic models. In this paper we derive the linear
Boltzmann equation in the low-density limit of a damped quantum Lorentz gas for
a large class of deterministic and random scatterer configurations. Previously
this result was known only for the single-scatterer problem on the flat torus,
and for uniformly random scatterer configurations where no damping is required.
The damping is critical in establishing convergence -- in the absence of
damping the limiting behaviour depends on the exact configuration under
consideration, and indeed, the linear Boltzmann equation is not expected to
appear for periodic and other highly ordered configurations.
|
2201.08229v2
|
2022-01-22
|
Effect of MagneticField on the Damping Behavior of a Ferrofluid based Damper
|
This paper is an extension of our earlier work where we had reported a proof
of concept for a ferrofluid based damper. The damper used ferrofluid as damping
medium and it was seen that damping efficiency of the damper changes on
application of magnetic field. The present paper deals with a systematic study
of the effect of magnetic field on the damping efficiency of the damper.
Results of these studies are reported. It is seen that damping ratio varies
linearly with magnetic field ({\zeta} / H = 0.028 per kG) for magnetic field in
range of 0.0 to 4.5 kG. It may be mentioned that ferrofluid is different from
magnetorheological fluid even though both of them are magnetic field-responsive
fluids. The ferrofluid-dampers are better suited than MR Fluid-dampers for
their use in automobiles.
|
2201.09027v1
|
2022-01-28
|
Machine learning-based method of calorimeter saturation correction for helium flux analysis with DAMPE experiment
|
DAMPE is a space-borne experiment for the measurement of the cosmic-ray
fluxes at energies up to around 100 TeV per nucleon. At energies above several
tens of TeV, the electronics of DAMPE calorimeter would saturate, leaving
certain bars with no energy recorded. In the present work we discuss the
application of machine learning techniques for the treatment of DAMPE data, to
compensate the calorimeter energy lost by saturation.
|
2201.12185v3
|
2022-03-10
|
Accelerated gradient methods combining Tikhonov regularization with geometric damping driven by the Hessian
|
In a Hilbert setting, for convex differentiable optimization, we consider
accelerated gradient dynamics combining Tikhonov regularization with
Hessian-driven damping. The Tikhonov regularization parameter is assumed to
tend to zero as time tends to infinity, which preserves equilibria. The
presence of the Tikhonov regularization term induces a strong convexity
property which vanishes asymptotically. To take advantage of the exponential
convergence rates attached to the heavy ball method in the strongly convex
case, we consider the inertial dynamic where the viscous damping coefficient is
taken proportional to the square root of the Tikhonov regularization parameter,
and therefore also converges towards zero. Moreover, the dynamic involves a
geometric damping which is driven by the Hessian of the function to be
minimized, which induces a significant attenuation of the oscillations. Under
an appropriate tuning of the parameters, based on Lyapunov's analysis, we show
that the trajectories have at the same time several remarkable properties: they
provide fast convergence of values, fast convergence of gradients towards zero,
and strong convergence to the minimum norm minimizer. This study extends a
previous paper by the authors where similar issues were examined but without
the presence of Hessian driven damping.
|
2203.05457v2
|
2022-04-01
|
On the Importance of High-Frequency Damping in High-Order Conservative Finite-Difference Schemes for Viscous Fluxes
|
This paper discusses the importance of high-frequency damping in high-order
conservative finite-difference schemes for viscous terms in the Navier-Stokes
equations. Investigating nonlinear instability encountered in a high-resolution
viscous shock-tube simulation, we have discovered that a modification to the
viscous scheme rather than the inviscid scheme resolves a problem with spurious
oscillations around shocks. The modification introduces a term responsible for
high-frequency damping that is missing in a conservative high-order viscous
scheme. The importance of damping has been known for schemes designed for
unstructured grids. However, it has not been recognized well in very high-order
difference schemes, especially in conservative difference schemes. Here, we
discuss how it is easily missed in a conservative scheme and how to improve
such schemes by a suitably designed damping term.
|
2204.00393v1
|
2022-06-20
|
Stability and Damping in the Disks of Massive Galaxies
|
After their initial formation, disk galaxies are observed to be rotationally
stable over periods of >6 Gyr, implying that any large velocity disturbances of
stars and gas clouds are damped rapidly on the timescale of their rotation.
However, it is also known that despite this damping, there must be a degree of
random local motion to stabilize the orbits against degenerate collapse. A
mechanism for such damping is proposed by a combination of inter-stellar
gravitational interactions, and interactions with the Oort clouds and exo-Oort
objects associated with each star. Analysis of the gravitational interactions
between two stars is a three-body problem, because the stars are also in orbit
round the large virtual mass of the galaxy. These mechanisms may produce rapid
damping of large perturbations within a time period that is short on the scale
of observational look-back time, but long on the scale of the disk rotational
period for stars with small perturbations. This mechanism may also account for
the locally observed mean perturbations in the Milky Way of 8-15~km/s for
younger stars and 20-30~km/s for older stars.
|
2206.09671v2
|
2022-08-25
|
The Effect of Frequency Droop Damping on System Parameters and Battery Sizing During Load Change Condition
|
Inverter-based resources (IBR) have been widely studied for their advantages
on the current power systems. This increase in the penetration of renewable
energy has raised some concerns about the stability of the existing grid.
Historically, power systems are dominated by synchronous generators that can
easily react to system instability due to high inertia and damping
characteristics. However, with IBR, the control of the inverter plays a crucial
role in contributing to the system stability and enhancing the functionality of
the inverters. One of these novel control methods is droop control. Droop
characteristics are used to control voltage, frequency, and active and reactive
power. This paper presents the impact of frequency droop damping on system
frequency, real power, and the rate of change of frequency with distributed
energy resources. Also, battery sizing is suggested based on the results. The
results also show the need for optimal selection for the frequency droop
damping to fulfill the appropriate battery size in terms of cost and
performance. The simulations are carried out in an electromagnetic transient
program (EMTP)
|
2208.12291v1
|
2022-09-15
|
Superfluid $^4$He as a rigorous test bench for different damping models in nanoelectromechanical resonators
|
We have used nanoelectromechanical resonators to probe superfluid $^4$He at
different temperature regimes, spanning over four orders of magnitude in
damping. These regimes are characterized by the mechanisms which provide the
dominant contributions to damping and the shift of the resonance frequency:
tunneling two level systems at the lowest temperatures, ballistic phonons and
rotons at few hundred mK, and laminar drag in the two-fluid regime below the
superfluid transition temperature as well as in the normal fluid. Immersing the
nanoelectromechanical resonators in fluid increases their effective mass
substantially, decreasing their resonance frequency. Dissipationless superflow
gives rise to a unique possibility to dramatically change the mechanical
resonance frequency in situ, allowing rigorous tests on different damping
models in mechanical resonators. We apply this method to characterize tunneling
two-level system losses and magnetomotive damping in the devices.
|
2209.07229v2
|
2022-10-16
|
Magnetic damping anisotropy in the two-dimensional van der Waals material Fe$_3$GeTe$_2$ from first principles
|
Magnetization relaxation in the two-dimensional itinerant ferromagnetic van
der Waals material Fe$_3$GeTe$_2$, below the Curie temperature, is
fundamentally important for applications to low-dimensional spintronics
devices. We use first-principles scattering theory to calculate the
temperature-dependent Gilbert damping for bulk and single-layer Fe$_3$GeTe$_2$.
The calculated damping frequency of bulk Fe$_3$GeTe$_2$ increases monotonically
with temperature because of the dominance of resistivitylike behavior. By
contrast, a very weak temperature dependence is found for the damping frequency
of a single layer, which is attributed to strong surface scattering in this
highly confined geometry. A systematic study of the damping anisotropy reveals
that orientational anisotropy is present in both bulk and single-layer
Fe3GeTe2. Rotational anisotropy is significant at low temperatures for both the
bulk and a single layer and is gradually diminished by temperature-induced
disorder. The rotational anisotropy can be significantly enhanced by up to 430%
in gated single-layer Fe$_3$GeTe$_2$.
|
2210.08429v1
|
2022-11-08
|
On the injection scale of the turbulence in the partially ionized very local interstellar medium
|
The cascade of magnetohydrodynamic (MHD) turbulence is subject to ion-neutral
collisional damping and neutral viscous damping in the partially ionized
interstellar medium. By examining the damping effects in the warm and partially
ionized local interstellar medium, we find that the interstellar turbulence is
damped by neutral viscosity at $\sim 261$ au and cannot account for the
turbulent magnetic fluctuations detected by Voyager 1 and 2. The MHD turbulence
measured by Voyager in the very local interstellar medium (VLISM) should be
locally injected in the regime where ions are decoupled from neutrals for its
cascade to survive the damping effects. With the imposed ion-neutral decoupling
condition, and the strong turbulence condition for the observed Kolmogorov
magnetic energy spectrum, we find that the turbulence in the VLISM is
sub-Alfv\'{e}nic, and its largest possible injection scale is $\sim 194$ au.
|
2211.04496v1
|
2022-12-11
|
The overtone level spacing of a black hole quasinormal frequencies: a fingerprint of a local $SL(2,\mathbb{R})$ symmetry
|
The imaginary part of the quasinormal frequencies spectrum for a static and
spherically symmetric black hole is analytically known to be equally spaced,
both for the highly damped and the weakly damped families of quasinormal modes.
Some interesting attempts have been made in the last twenty years to understand
in simple ways this level spacing for the only case of highly damped
quasinormal frequencies. Here, we show that the overtone level spacing, for
both the highly damped and weakly damped families of quasinormal modes, can
simply be understood as a fingerprint of a hidden local $SL(2,\mathbb{R})$
symmetry, near different regions of the black hole spacetime, i.e. the
near-horizon and the near-photon sphere regions.
|
2212.05538v1
|
2022-12-15
|
Formation of shifted shock for the 3D compressible Euler equations with time-dependent damping
|
In this paper, we show the shock formation to the compressible Euler
equations with time-dependent damping $\frac{a\p u}{(1+t)^{\lam}}$ in three
spatial dimensions without any symmetry conditions. It's well-known that for
$\lam>1$, the damping is too weak to prevent the shock formation for suitably
large data. However, the classical results only showed the finite existence of
the solution. Follow the work by D.Christodoulou in\cite{christodoulou2007},
starting from the initial isentropic and irrotational short pulse data, we show
the formation of shock is characterized by the collapse of the characteristic
hypersurfaces and the vanishing of the inverse foliation density function
$\mu$, at which the first derivatives of the velocity and the density blow up,
and the lifespan $T_{\ast}(a,\lam)$ is exponentially large. Moreover, the
damping effect will shift the time of shock formation $T_{\ast}$. The methods
in the paper can also be extended to the Euler equations with general
time-decay damping.
|
2212.07828v1
|
2023-01-15
|
Damped-driven system of bouncing droplets leading to deterministic diffusive behavior
|
Damped-driven systems are ubiquitous in science, however the damping and
driving mechanisms are often quite convoluted. This manuscript presents an
experimental and theoretical investigation of a fluidic droplet on a vertically
vibrating fluid bath as a damped-driven system. We study a fluidic droplet in
an annular cavity with the fluid bath forced above the Faraday wave threshold.
We model the droplet as a kinematic point particle in air and as inelastic
collisions during impact with the bath. In both experiments and the model the
droplet is observed to chaotically change velocity with a Gaussian
distribution. Finally, the statistical distributions from experiments and
theory are analyzed. Incredibly, this simple deterministic interaction of
damping and driving of the droplet leads to more complex Brownian-like and
Levy-like behavior.
|
2301.06041v2
|
2023-03-01
|
Generation of intraparticle quantum correlations in amplitude damping channel and its robustness
|
Quantum correlations between two or more different degrees of freedom of the
same particle is sometimes referred to as intraparticle entanglement. In this
work, we study these intra-particle correlations between two different degrees
of freedom under various decoherence channels viz. amplitude damping,
depolarising and phase damping channels. We observe a unique feature of the
amplitude damping channel, wherein entanglement is shown to arise starting from
separable states. In case of non maximally entangled input states, in addition
to entanglement sudden death, the creation of entanglement is also observed,
having an asymptotic decay over a long time. These counter-intuitive behaviours
arise due to the subtle interplay of channel and input state parameters, and
are not seen for interparticle entanglement without consideration of
non-Markovian noise. It is also not observed for maximally entangled input
states. Furthermore, investigation of entanglement evolution in phase damping
and depolarizing channels shows its robustness against decoherence as compared
to interparticle entanglement.
|
2303.01238v1
|
2023-03-07
|
Electrically tunable Gilbert damping in van der Waals heterostructures of two-dimensional ferromagnetic metals and ferroelectrics
|
Tuning the Gilbert damping of ferromagnetic (FM) metals via a nonvolatile way
is of importance to exploit and design next-generation novel spintronic
devices. Through systematical first-principles calculations, we study the
magnetic properties of the van der Waals heterostructure of two-dimensional FM
metal CrTe2 and ferroelectric (FE) In2Te3 monolayers. The ferromagnetism of
CrTe2 is maintained in CrTe2/In2Te3 and its magnetic easy axis can be switched
from in-plane to out-of-plane by reversing the FE polarization of In2Te3.
Excitingly, we find that the Gilbert damping of CrTe2 is tunable when the FE
polarization of In2Te3 is reversed from upward to downward. By analyzing the
k-dependent contributions to the Gilbert damping, we unravel that such
tunability results from the changed intersections between the bands of CrTe2
and Fermi level on the reversal of the FE polarizations of In2Te3 in
CrTe2/In2Te3. Our work provides an appealing way to electrically tailor Gilbert
dampings of two-dimensional FM metals by contacting them with ferroelectrics.
|
2303.03852v1
|
2023-03-16
|
Quantum Brownian Motion in the Caldeira-Leggett Model with a Damped Environment
|
We model a quantum system coupled to an environment of damped harmonic
oscillators by following the approach of Caldeira-Leggett and adopting the
Caldirola-Kanai Lagrangian for the bath oscillators. In deriving the master
equation of the quantum system of interest (a particle in a general potential),
we show that the potential is modified non-trivially by a new inverted harmonic
oscillator term, induced by the damping of the bath oscillators. We analyze
numerically the case of a particle in a double-well potential, and find that
this modification changes both the rate of decoherence at short times and the
well-transfer probability at longer times. We also identify a simple rescaling
condition that keeps the potential fixed despite changes in the environmental
damping. Here, the increase of environmental damping leads to a slowing of
decoherence.
|
2303.09516v1
|
2023-03-22
|
A Numerical Study of Landau Damping with PETSc-PIC
|
We present a study of the standard plasma physics test, Landau damping, using
the Particle-In-Cell (PIC) algorithm. The Landau damping phenomenon consists of
the damping of small oscillations in plasmas without collisions. In the PIC
method, a hybrid discretization is constructed with a grid of finitely
supported basis functions to represent the electric, magnetic and/or
gravitational fields, and a distribution of delta functions to represent the
particle field. Approximations to the dispersion relation are found to be
inadequate in accurately calculating values for the electric field frequency
and damping rate when parameters of the physical system, such as the plasma
frequency or thermal velocity, are varied. We present a full derivation and
numerical solution for the dispersion relation, and verify the PETSC-PIC
numerical solutions to the Vlasov-Poisson for a large range of wave numbers and
charge densities.
|
2303.12620v1
|
2023-04-07
|
Shifted shock formation for the 3D compressible Euler equations with damping and variation of the vorticity
|
In this paper, we consider the shock formation problem for the
3-dimensional(3D) compressible Euler equations with damping inspired by the
work \cite{BSV3Dfulleuler}. It will be shown that for a class of large data,
the damping can not prevent the formation of point shock, and the damping
effect shifts the shock time and the wave amplitude while the shock location
and the blow up direction remain the same with the information of this point
shock being computed explicitly. Moreover, the vorticity is concentrated in the
non-blow-up direction, which varies exponentially due to the damping effect.
Our proof is based on the estimates for the modulated self-similar variables
and lower bounds for the Lagrangian trajectories.
|
2304.03506v2
|
2023-07-05
|
Bayesian evidence for two slow-wave damping models in hot coronal loops
|
We compute the evidence in favour of two models, one based on field-aligned
thermal conduction alone and another that includes thermal misbalance as well,
in explaining the damping of slow magneto-acoustic waves in hot coronal loops.
Our analysis is based on the computation of the marginal likelihood and the
Bayes factor for the two damping models. We quantify their merit in explaining
the apparent relationship between slow mode periods and damping times, measured
with SOHO/SUMER in a set of hot coronal loops. The results indicate evidence in
favour of the model with thermal misbalance in the majority of the sample, with
a small population of loops for which thermal conduction alone is more
plausible. The apparent possibility of two different regimes of slow-wave
damping, if due to differences between the loops of host active regions and/or
the photospheric dynamics, may help with revealing the coronal heating
mechanism.
|
2307.02439v1
|
2023-07-24
|
From characteristic functions to multivariate distribution functions and European option prices by the damped COS method
|
We provide a unified framework for the computation of the distribution
function and the computation of prices of financial options from the
characteristic function of some density by the COS method. The classical COS
method is numerically very efficient in one-dimension but cannot deal very well
with certain financial options in general dimensions. Therefore, we introduce
the damped COS method which can handle a large class of integrands very
efficiently. We prove the convergence of the (damped) COS method and study its
order of convergence. The (damped) COS method converges exponentially if the
characteristic function decays exponentially. To apply the (damped) COS method,
one has to specify two parameters: a truncation range for the multivariate
density and the number of terms to approximate the truncated density by a
cosine series. We provide an explicit formula for the truncation range and an
implicit formula for the number of terms. Numerical experiments up to five
dimensions confirm the theoretical results.
|
2307.12843v6
|
2023-07-26
|
A Nonlinear Damped Metamaterial: Wideband Attenuation with Nonlinear Bandgap and Modal Dissipation
|
In this paper, we incorporate the effect of nonlinear damping with the
concept of locally resonant metamaterials to enable vibration attenuation
beyond the conventional bandgap range. The proposed design combines a linear
host cantilever beam and periodically distributed inertia amplifiers as
nonlinear local resonators. The geometric nonlinearity induced by the inertia
amplifiers causes an amplitude-dependent nonlinear damping effect. Through the
implementation of both modal superposition and numerical harmonic methods the
finite nonlinear metamaterial is accurately modelled. The resulting nonlinear
frequency response reveals the bandgap is both amplitude-dependent and
broadened. Furthermore, the modal frequencies are also attenuated due to the
nonlinear damping effect. The theoretical results are validated experimentally.
By embedding the nonlinear damping effect into locally resonant metamaterials,
wideband attenuation of the proposed metamaterial is achieved, which opens new
possibilities for versatile metamaterials beyond the limit of their linear
counterparts.
|
2307.14165v2
|
2023-07-28
|
Premature jump-down mimicks nonlinear damping in nanoresonators
|
Recent experiments on nano-resonators in a bistable regime use the
`jump-down' point between states to infer mechanical properties of the membrane
or a load, but often suggest the presence of some nonlinear damping. Motivated
by such experiments, we develop a mechanical model of a membrane subject to a
uniform, oscillatory load and linear damping. We solve this model numerically
and compare its jump-down behaviour with standard asymptotic predictions for a
one-dimensional Duffing oscillator with strain stiffening. We show that the
axisymmetric, but spatially-varying, problem can be mapped to the Duffing
problem with coefficients determined rationally from the model's Partial
Differential Equations. However, we also show that jump-down happens earlier
than expected (i.e.~at lower frequency, and with a smaller oscillation
amplitude). Although this premature jump-down is often interpreted as the
signature of a nonlinear damping in experiments, its appearance in numerical
simulations with only linear damping suggests instead that indicate that the
limitations of asymptotic results may, at least sometimes, be the cause. We
therefore suggest that care should be exercised in interpreting the results of
nano-resonator experiments.
|
2307.15656v1
|
2023-09-22
|
Long time energy averages and a lower resolvent estimate for damped waves
|
We consider the damped wave equation on a compact manifold. We propose
different ways of measuring decay of the energy (time averages of lower energy
levels, decay for frequency localized data...) and exhibit links with resolvent
estimates on the imaginary axis. As an application we prove a universal
logarithmic lower resolvent bound on the imaginary axis for the damped wave
operator when the Geometric Control Condition (GCC) is not satisfied. This is
to be compared to the uniform boundedness of the resolvent on that set when GCC
holds. The proofs rely on (i) various (re-)formulations of the damped wave
equation as a conservative hyperbolic part perturbed by a lower order damping
term;(ii) a "Plancherel-in-time" argument as in classical proofs of the
Gearhart-Huang-Pr{\"u}ss theorem; and (iii) an idea of Bony-Burq-Ramond of
propagating a coherent state along an undamped trajectory up to Ehrenfest time.
|
2309.12709v1
|
2023-10-11
|
Damping Density of an Absorptive Shoebox Room Derived from the Image-Source Method
|
The image-source method is widely applied to compute room impulse responses
(RIRs) of shoebox rooms with arbitrary absorption. However, with increasing RIR
lengths, the number of image sources grows rapidly, leading to slow
computation. In this paper, we derive a closed-form expression for the damping
density, which characterizes the overall multi-slope energy decay. The
omnidirectional energy decay over time is directly derived from the damping
density. The resulting energy decay model accurately matches the late
reverberation simulated via the image-source method. The proposed model allows
the fast stochastic synthesis of late reverberation by shaping noise with the
energy envelope. Simulations of various wall damping coefficients demonstrate
the model's accuracy. The proposed model consistently outperforms the energy
decay prediction accuracy compared to a state-of-the-art approximation method.
The paper elaborates on the proposed damping density's applicability to
modeling multi-sloped sound energy decay, predicting reverberation time in
non-diffuse sound fields, and fast frequency-dependent RIR synthesis.
|
2310.07363v1
|
2023-10-14
|
Exploring Damping Effect of Inner Control Loops for Grid-Forming VSCs
|
This paper presents an analytical approach to explore the damping effect of
inner loops on grid-forming converters. First, an impedance model is proposed
to characterize the behaviors of inner loops, thereby illustrating their
influence on output impedance shaping. Then, based on the impedance
representation, the complex torque coefficient method is employed to assess the
contribution of inner loops to system damping. The interactions among inner
loops, outer loops, and the ac grid are analyzed. It reveals that inner loops
shape the electrical damping torque coefficient and consequently influence both
synchronous and sub-synchronous oscillation modes. The virtual admittance and
current control-based inner-loop scheme is employed to illustrate the proposed
analytical approach. The case study comprises the analysis of impedance
profiles, the analysis of damping torque contributed by inner loops under
various grid strengths, and the comparison between dq-frame and
{\alpha}\b{eta}-frame realizations of inner loops. Finally, simulation and
experimental tests collaborate with theoretical approaches and findings.
|
2310.09660v1
|
2023-10-24
|
Frictional weakening of a granular sheared layer due to viscous rolling revealed by Discrete Element Modeling
|
Considering a 3D sheared granular layer modeled with discrete elements, it is
well known the rolling resistance significantly influences the mechanical
behavior. Even if the rolling resistance role has been deeply investigated as
it is commonly used to represent the the roughness of the grains and the
interparticle locking, the role of rolling viscous damping coefficient has been
largely overlooked so far. This parameter is rarely used or only to dissipate
the energy and to converge numerically. This paper revisits the physical role
of those coefficients with a parametric study of the rolling friction and the
rolling damping for a sheared layer at different shear speeds and different
confinement pressures. It has been observed that the damping coefficient
induces a frictional weakening. Hence, competition between the rolling
resistance and the rolling damping occurs. Angular resistance aims to avoid
grains rolling, decreasing the difference between the angular velocities of
grains. Whereas, angular damping acts in the opposite, avoiding a change in the
difference between the angular velocities of grains. In consequence, grains
keep rolling and the sample strength decreases. This effect must be considered
to not overestimate the frictional response of a granular layer.
|
2310.15945v1
|
2023-12-12
|
Coordination of Damping Controllers: A Data-Informed Approach for Adaptability
|
This work proposes a data-informed approach for an adaptable coordination of
damping controllers. The novel concept of coordination is based on minimizing
the Total Action, a single metric that measures the system's dynamic response
post-disturbance. This is a performance measure based on the physics of the
power system, which encapsulates the oscillation energy related to synchronous
generators. Deep learning theory is used to propose a Total Action function
approximator, which captures the relationship between the system wide-area
measurements, the status of damping controllers, and the conditions of the
disturbance. By commissioning the switching status (on/off) of damping
controllers in real-time, the oscillation energy is reduced, enhancing the
power system stability. The concept is tested in the Western North America
Power System (wNAPS) and compared with a model-based approach for the
coordination of damping controllers. The data-informed coordination outperforms
the model-based approach, demonstrating exceptional adaptability and
performance to handle multi-modal events. The proposed scheme shows outstanding
reductions in low-frequency oscillations even under various operating
conditions, fault locations, and time delay considerations.
|
2312.07739v1
|
2024-01-26
|
Efficient Control of Magnetization Dynamics Via W/CuO$_\text{x}$ Interface
|
Magnetization dynamics, which determine the speed of magnetization switching
and spin information propagation, play a central role in modern spintronics.
Gaining its control will satisfy the different needs of various spintronic
devices. In this work, we demonstrate that the surface oxidized Cu
(CuO$_\text{x}$) can be employed for the tunability of magnetization dynamics
of ferromagnet (FM)/heavy metal (HM) bilayer system. The capping CuO$_\text{x}$
layer in CoFeB/W/CuO$_\text{x}$ trilayer reduces the magnetic damping value in
comparison with the CoFeB/W bilayer. The magnetic damping even becomes lower
than that of the CoFeB/CuO$_\text{x}$ by ~ 16% inferring the stabilization of
anti-damping phenomena. Further, the reduction in damping is accompanied by a
very small reduction in the spin pumping-induced output DC voltage in the
CoFeB/W/CuO$_\text{x}$ trilayer. The simultaneous observation of anti-damping
and spin-to-charge conversion can be attributed to the orbital Rashba effect
observed at the HM/CuO$_\text{x}$ interface. Our experimental findings
illustrate that the cost-effective CuO$_\text{x}$ can be employed as an
integral part of modern spintronics devices owing to its rich underneath
spin-orbital physics.
|
2401.14708v1
|
2024-02-08
|
The stability analysis based on viscous theory of Faraday waves in Hele-Shaw cells
|
The linear instability of Faraday waves in Hele-Shaw cells is investigated
with consideration of the viscosity of fluids after gap-averaging the governing
equations due to the damping from two lateral walls and the dynamic behavior of
contact angle. A new hydrodynamic model is thus derived and solved
semi-analytically. The contribution of viscosity to critical acceleration
amplitude is slight compared to other factors associated with dissipation, and
the potential flow theory is sufficient to describe onset based on the present
study, but the rotational component of velocity can change the timing of onset
largely, which paradoxically comes from the viscosity. The model degenerates
into a novel damped Mathieu equation if the viscosity is dropped with two
damping terms referring to the gap-averaged damping and dissipation from
dynamic contact angle, respectively. The former increases when the gap size
decreases, and the latter grows as frequency rises. When it comes to the
dispersion relation of Faraday waves, an unusual detuning emerges due to the
imaginary part of the gap-averaged damping.
|
2402.05505v2
|
2024-04-08
|
Stability Enhancement of LCL-Type Grid-Following Inverters Using Capacitor Voltage Active Damping
|
An LCL filter offers superior attenuation for high-frequency harmonics for
three-phase grid-following inverters compared to LC and L filters. However, it
also introduces an inherent resonance peak, which can lead to power quality
issues or even instability of the inverter control system. Active damping (AD)
is widely employed to effectively mitigate this resonance. Capacitor voltage
feedback (CVF) and capacitor current feedback (CCF) are effective AD methods
for LCL resonance damping. CVF is preferred due to its lower sensor requirement
compared to CCF. However, a derivative term appears in the active damping loop,
which introduces high-frequency noise into the system. This paper proposes a
noise-immune approach by replacing the derivative term with a discrete function
suitable for digital implementation. The LCL resonance can be damped
effectively, resulting in enhanced stability of the inverter control system.
Simulation results verify the proposed effectiveness of the method with grid
inductance variation and weak grid conditions
|
2404.05640v1
|
2024-04-10
|
Chemical Interface Damping by Electrochemical Gold Oxidation
|
Chemical interface damping is a change in the effective collision frequency
of conduction band electrons in metal originating from a chemical change of the
metal interface. In this work, we present in-situ ellipsometric measurements
that reveal the chemical interface damping effect from electrochemical
oxidation of single crystal and polycrystalline gold films. We observe an
increase in collision frequency of up to 21 meV for single-crystalline gold. To
compare to results obtained with thiols and metal-oxides on gold nanoparticles,
we normalize the collision frequency by the electron mean free path to the
surface of the structure. We show that electrochemical gold oxidation provides
a stronger effect on collision frequency than these coatings. Similar
ellipsometric experiments have previously been conducted to investigate the
optical properties of gold oxide, but without taking chemical interface damping
into account. The change in reflection from oxidation of gold was solely
attributed to the oxide coating. We also show that the chemical interface
damping effect saturates at a larger effective oxide thickness, which is
attributed to the stabilization of the gold-oxide interface.
|
2404.06799v1
|
1996-09-10
|
The Damping Tail of CMB Anisotropies
|
By decomposing the damping tail of CMB anisotropies into a series of transfer
functions representing individual physical effects, we provide ingredients that
will aid in the reconstruction of the cosmological model from small-scale CMB
anisotropy data. We accurately calibrate the model-independent effects of
diffusion and reionization damping which provide potentially the most robust
information on the background cosmology. Removing these effects, we uncover
model-dependent processes such as the acoustic peak modulation and
gravitational enhancement that can help distinguish between alternate models of
structure formation and provide windows into the evolution of fluctuations at
various stages in their growth.
|
9609079v1
|
1997-09-16
|
Lyman-alpha emission as a tool to study high redshift damped systems
|
We report a quantitative study of the escape of Lyman-alpha photons from an
inhomogeneous optically thick medium that mimics the structure of damped
Lyman-alpha absorbers. Modeling the optically thick disk with 3 components
(massive stars and HII regions, dust, and neutral hydrogen), we study the
resulting emission line profile that may arise near the extended damped
absorption profile.
|
9709150v1
|
1997-10-17
|
The chemical evolution of galaxies causing damped Ly$α$ absorption
|
We have compiled all available data on chemical abundances in damped Lyman
alpha absorption systems for comparison with results from our combined chemical
and spectrophotometric galaxy evolution models. Preliminary results from
chemically consistent calculations are in agreement with observations of damped
Ly$\alpha$ systems.
|
9710193v1
|
1998-01-26
|
Are Damped Lyman alpha Systems Rotating Disks ?
|
We report on high spectral resolution observations of five damped Lyman alpha
systems whose line velocity profiles and abundances are analyzed. By combining
these data with information from the literature, we study the kinematics of the
low and high ionization phases of damped systems and discuss the possibility
that part of the motions is due to rotation.
|
9801243v1
|
2001-10-29
|
Damping of inhomogeneities in neutralino dark matter
|
The lightest supersymmetric particle, most likely the neutralino, might
account for a large fraction of dark matter in the Universe. We show that the
primordial spectrum of density fluctuations in neutralino cold dark matter
(CDM) has a sharp cut-off due to two damping mechanisms: collisional damping
during the kinetic decoupling of the neutralinos at O(10 MeV) and free
streaming after last scattering of neutralinos. The cut-off in the primordial
spectrum defines a minimal mass for CDM objects in hierarchical structure
formation. For typical neutralino and sfermion masses the first gravitationally
bound neutralino clouds have masses above 10^(-6) M_\odot.
|
0110601v1
|
2002-08-03
|
Adiabatic Index of Dense Matter and Damping of Neutron Star Pulsations
|
The adiabatic index Gamma_1 for perturbations of dense matter is studied
under various physical conditions which can prevail in neutron star cores. The
dependence of Gamma_1 on the composition of matter (in particular, on the
presence of hyperons), on the stellar pulsation amplitude, and on the baryon
superfluidity is analyzed. Timescales of damping of stellar pulsations are
estimated at different compositions, temperatures, and pulsation amplitudes.
Damping of pulsations by bulk viscosity in the neutron-star cores can prevent
the stars to pulsate with relative amplitudes > (1-15)% (depending on the
composition of matter).
|
0208078v1
|
2003-01-07
|
Damping of Neutron Star Shear Modes by Superfluid Friction
|
The forced motion of superfluid vortices in shear oscillations of rotating
solid neutron star matter produces damping of the mode. A simple model of the
unpinning and repinning processes is described, with numerical calculations of
the consequent energy decay times. These are of the order of 1 s or more for
typical anomalous X-ray pulsars but become very short for the general
population of radio pulsars. The superfluid friction processes considered here
may also be significant for the damping of r-modes in rapidly rotating neutron
stars.
|
0301112v1
|
2005-04-25
|
Radiative Effect on Particle Acceleration via Relativistic Electromagnetic Expansion
|
The radiation damping effect on the diamagnetic relativistic pulse
accelerator (DRPA) is studied in two-and-half dimensional Particle-in-Cell
(PIC) simulation with magnetized electron-positron plasmas. Self-consistently
solved radiation damping force converts particle energy to radiation energy.
The DRPA is still robust with radiation, and the Lorentz factor of the most
high energy particles reach more than two thousand before they decouple from
the electromagnetic pulse. Resulted emitted power from the pulse front is lower
in the radiative case than the estimation from the non-radiative case due to
the radiation damping. The emitted radiation is strongly linearly polarized and
peaked within few degrees from the direction of Poynting flux.
|
0504561v1
|
1999-05-06
|
Collective and chaotic motion in self-bound many-body systems
|
We investigate the interplay of collective and chaotic motion in a classical
self-bound N-body system with two-body interactions. This system displays a
hierarchy of three well separated time scales that govern the onset of chaos,
damping of collective motion and equilibration. Comparison with a mean-field
problem shows that damping is mainly due to dephasing. The Lyapunov exponent,
damping and equilibration rates depend mildly on the system size N.
|
9905007v2
|
1997-05-12
|
Damping of Oscillations in Layer-by-Layer Growth
|
We present a theory for the damping of layer-by-layer growth oscillations in
molecular beam epitaxy. The surface becomes rough on distances larger than a
layer coherence length which is substantially larger than the diffusion length.
The damping time can be calculated by a comparison of the competing roughening
and smoothening mechanisms. The dependence on the growth conditions,
temperature and deposition rate, is characterized by a power law. The
theoretical results are confirmed by computer simulations.
|
9705100v1
|
1999-09-17
|
Thermoelastic Damping in Micro- and Nano-Mechanical Systems
|
The importance of thermoelastic damping as a fundamental dissipation
mechanism for small-scale mechanical resonators is evaluated in light of recent
efforts to design high-Q micrometer- and nanometer-scale electro-mechanical
systems (MEMS and NEMS). The equations of linear thermoelasticity are used to
give a simple derivation for thermoelastic damping of small flexural vibrations
in thin beams. It is shown that Zener's well-known approximation by a
Lorentzian with a single thermal relaxation time slightly deviates from the
exact expression.
|
9909271v1
|
2000-10-01
|
Super-Radiance and the Unstable Photon Oscillator
|
If the damping of a simple harmonic oscillator from a thermally random force
is sufficiently strong, then the oscillator may become unstable. For a photon
oscillator (radiatively damped by electric dipole moments), the instability
leads to a low temperature Hepp-Lieb-Preparata super-radiant phase transition.
The stable oscillator regime is described by the free energy of the
conventional Casimir effect. The unstable (strongly damped) oscillator has a
free energy corresponding to Dicke super-radiance.
|
0010013v1
|
2001-08-07
|
Non-damped Acoustic Plasmon and Superconductivity in Single Wall Carbon Nanotubes
|
We show that non-damped acoustic plasmons exist in single wall carbon
nanotubes (SWCNT) and propose that the non-damped acoustic plasmons may mediate
electron-electron attraction and result in superconductivity in the SWCNT. The
superconducting transition temperature Tc for the SWCNT (3,3) obtained by this
mechanism agrees with the recent experimental result (Z. K. Tang et al, Science
292, 2462(2001)). We also show that it is possible to get higher Tc up to 99 K
by doping the SWCNT (5,5).
|
0108124v2
|
2001-10-11
|
Enhanced Gilbert Damping in Thin Ferromagnetic Films
|
Using a scattering matrix approach, the precession of the magnetization of a
ferromagnet is shown to transfer spins into adjacent normal metal layers. This
``pumping'' of spins slows down the precession corresponding to an enhanced
Gilbert damping factor in the Landau-Lifshitz equation. The damping is
expressed in terms of the scattering matrix of the ferromagnet-normal metal
interface, which is accessible to model and first-principles calculations. Our
estimates for permalloy thin films explain the trends observed in recent
experiments.
|
0110247v2
|
2001-12-16
|
The Damping of the Bose-Condensate Oscillations in a Trap at Zero Temperature
|
We discuss an existence of the damping for the radial condensate oscillations
in a cylindric trap at zero temperature. The damping is a result of the
parametric resonance leading to energy transfer from the coherent condensate
oscillations to the longitudinal sound waves within a finite frequency
interval. The parametric resonance is due to the oscillations of the sound
velocity. The triggering amplitudes at zero temperature are associated with the
zero-point oscillations.
|
0112292v1
|
2002-02-11
|
Radiation Induced Landau-Lifshitz-Gilbert Damping in Ferromagnets
|
The Landau-Lifshitz-Gilbert damping coefficient employed in the analysis of
spin wave ferromagnetic resonance is related to the electrical conductivity of
the sample. The changing magnetization (with time) radiates electromagnetic
fields. The electromagnetic energy is then absorbed by the sample and the
resulting heating effect describes magnetic dissipative damping. The
ferromagnetic resonance relaxation rate theoretically depends on the geometry
(shape and size) of the sample as well as temperature in agreement with
experiment.
|
0202181v1
|
2002-06-13
|
Beliaev damping of quasi-particles in a Bose-Einstein condensate
|
We report a measurement of the suppression of collisions of quasi-particles
with ground state atoms within a Bose-Einstein condensate at low momentum.
These collisions correspond to Beliaev damping of the excitations, in the
previously unexplored regime of the continuous quasi-particle energy spectrum.
We use a hydrodynamic simulation of the expansion dynamics, with the Beliaev
damping cross-section, in order to confirm the assumptions of our analysis.
|
0206234v1
|
2002-06-28
|
Accidental suppression of Landau damping of the transverse breathing mode in elongated Bose-Einstein condensates
|
We study transverse radial oscillations of an elongated Bose-Einstein
condensate using finite temperature simulations, in the context of a recent
experiment at ENS. We demonstrate the existence of a mode corresponding to an
in-phase collective oscillation of both the condensate and thermal cloud.
Excitation of this mode accounts for the very small damping rate observed
experimentally, and we find excellent quantitative agreement between experiment
and theory. In contrast to other condensate modes, interatomic collisions are
found to be the dominant damping mechanism in this case.
|
0206582v1
|
2004-04-19
|
Nonlinear response of superparamagnets with finite damping: an analytical approach
|
The strongly damping-dependent nonlinear dynamical response of classical
superparamagnets is investigated by means of an analytical approach. Using
rigorous balance equations for the spin occupation numbers a simple approximate
expression is derived for the nonlinear susceptibility. The results are in good
agreement with those obtained from the exact (continued-fraction) solution of
the Fokker-Planck equation. The formula obtained could be of assistance in the
modelling of the experimental data and the determination of the damping
coefficient in superparamagnets.
|
0404445v1
|
2004-09-24
|
Minimal field requirement in precessional magnetization switching
|
We investigate the minimal field strength in precessional magnetization
switching using the Landau-Lifshitz-Gilbert equation in under-critically damped
systems. It is shown that precessional switching occurs when localized
trajectories in phase space become unlocalized upon application of field
pulses. By studying the evolution of the phase space, we obtain the analytical
expression of the critical switching field in the limit of small damping for a
magnetic object with biaxial anisotropy. We also calculate the switching times
for the zero damping situation. We show that applying field along the medium
axis is good for both small field and fast switching times.
|
0409671v1
|
2005-03-03
|
Collapse of thermal activation in moderately damped Josephson junctions
|
We study switching current statistics in different moderately damped
Josephson junctions: a paradoxical collapse of the thermal activation with
increasing temperature is reported and explained by interplay of two
conflicting consequences of thermal fluctuations, which can both assist in
premature escape and help in retrapping back into the stationary state. We
analyze the influence of dissipation on the thermal escape by tuning the
damping parameter with a gate voltage, magnetic field, temperature and an
in-situ capacitor.
|
0503067v1
|
2006-01-10
|
Voltage dependence of Landau-Lifshitz-Gilbert damping of a spin in a current driven tunnel junction
|
We present a theory of Landau-Lifshitz-Gilbert damping $\alpha$ for a
localized spin ${\vec S}$ in the junction coupled to the conduction electrons
in both leads under an applied volatege $V$. We find the voltage dependence of
the damping term reflecting the energy dependence of the density of states. We
find the effect is linear in the voltage and cotrolled by particle-hole
asymmetry of the leads.
|
0601185v1
|
2006-03-13
|
Universal features of the defect-induced damping of lattice vibrations
|
It is shown that any defect gives an Ohmic contribution to the damping of any
normal mode of the crystal lattice with nonzero wavevector which does not
vanish at zero temperature. This explains the large phason damping observed at
low temperatures in incommensurate phases, and might be a key factor to
understand the linear-in-$T$ specific heat observed in a number of real
dielectrics at low enough temperatures.
|
0603343v2
|
2006-04-25
|
Spin Precession and Avalanches
|
In many magnetic materials, spin dynamics at short times are dominated by
precessional motion as damping is relatively small. In the limit of no damping
and no thermal noise, we show that for a large enough initial instability, an
avalanche can transition to an ergodic phase where the state is equivalent to
one at finite temperature, often above that for ferromagnetic ordering. This
dynamical nucleation phenomenon is analyzed theoretically. For small finite
damping the high temperature growth front becomes spread out over a large
region. The implications for real materials are discussed.
|
0604563v1
|
2007-02-11
|
Non-Markovian coherence dynamics of driven spin boson model: damped quantum beat or large amplitude coherence oscillation
|
The dynamics of driven spin boson model is studied analytically by means of
the perturbation approach based on a unitary transformation. We gave the
analytical expression for the population difference and coherence of the two
level system. The results show that in the weak driven case, the population
difference present damped coherent oscillation (single or double frequency) and
the frequencies depend on the initial state. The coherence exhibit damped
oscillation with Rabi frequency. When driven field is strong enough, the
population difference exhibit undamped large-amplitude coherent oscillation.
The results easily return to the two extreme cases without dissipation or
without periodic driven.
|
0702268v1
|
2005-05-10
|
Highly Damped Quasinormal Modes of Generic Single Horizon Black Holes
|
We calculate analytically the highly damped quasinormal mode spectra of
generic single-horizon black holes using the rigorous WKB techniques of
Andersson and Howls\cite{Andersson}. We thereby provide a firm foundation for
previous analysis, and point out some of their possible limitations. The
numerical coefficient in the real part of the highly damped frequency is
generically determined by the behavior of coupling of the perturbation to the
gravitational field near the origin, as expressed in tortoise coordinates. This
fact makes it difficult to understand how the famous $ln(3)$ could be related
to the quantum gravitational microstates near the horizon.
|
0505044v1
|
2006-05-01
|
Stability and quasinormal modes of the massive scalar field around Kerr black holes
|
We find quasinormal spectrum of the massive scalar field in the background of
the Kerr black holes. We show that all found modes are damped under the
quasinormal modes boundary conditions when $\mu M$ is not large, thereby
implying stability of the massive scalar field. This complements the region of
stability determined by the Beyer inequality for large masses of the field. We
show that, similar to the case of a non-rotating black holes, the massive term
of the scalar field does not contribute in the regime of high damping. Thereby,
the high damping asymptotic should be the same as for the massless scalar
field.
|
0605013v1
|
1993-02-09
|
Damping rates for moving particles in hot QCD
|
Using a program of perturbative resummation I compute the damping rates for
fields at nonzero spatial momentum to leading order in weak coupling in hot
$QCD$. Sum rules for spectral densities are used to simplify the calculations.
For massless fields the damping rate has an apparent logarithmic divergence in
the infrared limit, which is cut off by the screening of static magnetic fields
(``magnetic mass''). This demonstrates how at high temperature even
perturbative quantities are sensitive to nonperturbative phenomenon.
|
9302242v1
|
1994-04-21
|
Is \lq\lq Heavy Quark Damping Rate Puzzle'' in Hot QCD Really the Puzzle?
|
Within the framework of perturbative resummation scheme of Pisarski and
Braaten, the decay- or damping-rate of a moving heavy quark (muon) to leading
order in weak coupling in hot QCD (QED) is examined. Although, as is well
known, the conventionally-defined damping rate diverges logarithmically at the
infrared limit, shown is that no such divergence appears in the physically
measurable decay rate. The cancellation occurs between the contribution from
the \lq\lq real'' decay diagram and the contribution from the diagrams with
\lq\lq thermal radiative correction''.
|
9404318v1
|
1996-01-12
|
Damping Rate of a Scalar Particle in Hot Scalar QED
|
In contrast to the damping of partons in a quark-gluon plasma, the damping of
a scalar particle in a hot scalar QED plasma can be calculated to leading order
for the whole momentum range using the Braaten-Pisarski method. In this way the
evolution of the logarithmic infrared singularity caused by the exchange of a
transverse photon from soft to hard momenta can be studied.
|
9601254v1
|
1996-09-17
|
Damping Rate of Quasiparticles in Degenerate Ultrarelativistic Plasmas
|
We compute the damping rate of a fermion in a dense relativistic plasma at
zero temperature. Just above the Fermi sea, the damping rate is dominated by
the exchange of soft magnetic photons (or gluons in QCD) and is proportional to
$(E-\mu)$, where E is the fermion energy and $\mu$ the chemical potential. We
also compute the contribution of soft electric photons and of hard photons. As
in the nonrelativistic case, the contribution of longitudinal photons is
proportional to $(E-\mu)^2$, and is thus non leading in the relativistic case.
|
9609369v1
|
1997-05-28
|
Classical Statistical Mechanics and Landau Damping
|
We study the retarded response function in scalar $\phi^4$-theory at finite
temperature. We find that in the high-temperature limit the imaginary part of
the self-energy is given by the classical theory to leading order in the
coupling. In particular the plasmon damping rate is a purely classical effect
to leading order, as shown by Aarts and Smit. The dominant contribution to
Landau damping is given by the propagation of classical fields in a heat bath
of non-interacting fields.
|
9705452v1
|
1997-12-01
|
A potential infrared problem with the damping rates for gluons with soft momentum in hot QCD
|
We calculate the damping rate $\gamma_l$ for longitudinal gluons with zero
momentum in finite high temperature QCD and show that some of its contributing
terms are infrared divergent. This is in contrast with the expectation that
this damping rate is to be equal to the corresponding one $\gamma_t$ for
transverse gluons which is known to be finite. Our calculation was motivated by
the fact that similar divergent terms occur when we calculated in a previous
work $\gamma_t$ to order $ p^2$, p being the momentum of the gluon. After we
present our results, we briefly discuss them.
|
9712210v1
|
1998-04-21
|
The Plasmon Damping Rate for T -> T_C
|
The plasmon damping rate in scalar field theory is computed close to the
critical temperature. It is shown that the divergent result obtained in
perturbation theory is a consequence of neglecting the thermal renormalization
of the coupling. Taking this effect into account, a vanishing damping rate is
obtained, leading to the critical slowing down of the equilibration process.
|
9804351v2
|
1998-10-06
|
Self-consistent Study on Color Transport in the Quark Gluon Plasma at Finite Chemical Potential
|
We calculate the relaxation time self-consistently to study the damping of
collective color modes and the color conductivity in a QGP by deriving
self-consistent equations for the damping rates of gluons and quarks to leading
order QCD by TFD including a chemical potential for quarks. We show that the
damping rates are not sensitive to the chemical potential whereas color
conductivity is enhanced considerably.
|
9810256v1
|
1999-02-19
|
The problem of nonlinear Landau damping in quark-gluon plasma
|
On the basis of the semiclassical equations for quark-gluon plasma (QGP) and
Yang-Mills equation, the generalized kinetic equation for waves with regard to
its interaction is obtained. The physical mechanisms defining nonlinear
scattering of a plasmon by QGP particles are analysed. The problem on a
connection of nonlinear Landau damping rate of longitudinal oscillation with
damping rate, obtained on the basis of hard thermal loops approximation, is
considered.
|
9902397v2
|
1999-07-21
|
A Slavnov-Taylor identity and equality of damping rates for static transverse and longitudinal gluons in hot QCD
|
A Slavnov-Taylor identity is derived for the gluon polarization tensor in hot
QCD. We evaluate its implications for damping of gluonic modes in the plasma.
Applying the identity to next to the leading order in hard-thermal-loop
resummed perturbation theory, we derive the expected equality of damping rates
for static transverse and longitudinal (soft) gluons. This is of interest also
in view of deviating recent reports of $\gamma_t(p=0)\neq\gamma_l(p=0)$ based
on a direct calculation of $\gamma_l(p=0)$.
|
9907439v1
|
2000-09-15
|
Fermion Damping Rate Effects in Cold Dense Matter
|
We review the non-Fermi or marginal liquid behavior of a relativistic QED
plasma. In this medium a quasiparticle has a damping rate that depends linearly
on the distance between its energy and the Fermi surface. We stress that this
dependence is due to the long-range character of the magnetic interactions in
the medium. Finally, we study how the quark damping rate modifies the gap
equation of color superconductivity, reducing the value of the gap at the Fermi
surface.
|
0009182v1
|
2001-07-19
|
Photon Damping Caused by Electron-Positron Pair Production in a Strong Magnetic Field
|
Damping of an electromagnetic wave in a strong magnetic field is analyzed in
the kinematic region near the threshold of electron-positron pair production.
Damping of the electromagnetic field is shown to be noticeably nonexponential
in this region. The resulting width of the photon $\gamma \to e^+ e^-$ decay is
considerably smaller than previously known results.
|
0107217v1
|
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