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2011-02-24
|
Environment-assisted quantum Minority games
|
The effect of entanglement and correlated noise in a four-player quantum
Minority game is investigated. Different time correlated quantum memory
channels are considered to analyze the Nash equilibrium payoff of the 1st
player. It is seen that the Nash equilibrium payoff is substantially enhanced
due to the presence of correlated noise. The behaviour of damping channels
(amplitude damping and phase damping) is approximately similar. However,
bit-phase flip channel heavily influences the minority game as compared to
other channels in the presence of correlated noise. On the other hand, phase
flip channel has a symmetrical behaviour around 50% noise threshold. The
significant reduction in payoffs due to decoherence is well compensated due to
the presence of correlated noise. However, the Nash equilibrium of the game
does not change in the presence of noise. It is seen that in case of
generalized amplitude damping channel, entanglement plays a significant role at
lower level of decoherence. The channel has less dominant effects on the payoff
at higher values of decoherence. Furthermore, amplitude damping and generalized
amplitude damping channels have almost comparable effects at lower level of
decoherence $(p<0.5)$. Therefore, the game deserves careful study during its
implementation due to prominent role of noise for different channels.
|
1102.5056v2
|
2011-03-17
|
Viscous damping of r-modes: Large amplitude saturation
|
We analyze the viscous damping of r-mode oscillations of compact stars,
taking into account non-linear viscous effects in the large-amplitude regime.
The qualitatively different cases of hadronic stars, strange quark stars, and
hybrid stars are studied. We calculate the viscous damping times of r-modes,
obtaining numerical results and also general approximate analytic expressions
that explicitly exhibit the dependence on the parameters that are relevant for
a future spindown evolution calculation. The strongly enhanced damping of large
amplitude oscillations leads to damping times that are considerably lower than
those obtained when the amplitude dependence of the viscosity is neglected.
Consequently, large-amplitude viscous damping competes with the gravitational
instability at all physical frequencies and could stop the r-mode growth in
case this is not done before by non-linear hydrodynamic mechanisms.
|
1103.3521v2
|
2011-05-01
|
Viscous damping of nanobeam resonators: humidity, thermal noise and the paddling effect
|
The nanobeam resonator is the key mechanical component in the
nano-electromechanical system. In addition to its high frequency originating
from its low dimension, the performance is significantly influenced by the
circumstances, especially at nanoscale where a large surface area of the
material is exposed. Molecular dynamics simulations and theoretical analysis
are used for a quantitative prediction on the damping behavior, such as the
critical damping condition and lifetime, of nanobeam resonators that directly
maps the fluid-structure properties and interaction information into dynamical
behaviors. We show here how the humidity defines the critical damping condition
through viscous forces, marking the transition from under-damping to
over-damping regime at elevated humidity. Novel phenomena such as the thermal
fluctuation and paddling effects are also discussed.
|
1105.0139v1
|
2011-06-07
|
Damping by branching: a bioinspiration from trees
|
Man-made slender structures are known to be sensitive to high levels of
vibration, due to their flexibility, which often cause irreversible damage. In
nature, trees repeatedly endure large amplitudes of motion, mostly caused by
strong climatic events, yet with minor or no damage in most cases. A new
damping mechanism inspired by the architecture of trees is here identified and
characterized in the simplest tree-like structure, a Y-shape branched
structure. Through analytical and numerical analyses of a simple
two-degree-of-freedom model, branching is shown to be the key ingredient in
this protective mechanism that we call damping-by-branching. It originates in
the geometrical nonlinearities so that it is specifically efficient to damp out
large amplitudes of motion. A more realistic model, using flexible beam
approximation, shows that the mechanism is robust. Finally, two bioinspired
architectures are analyzed, showing significant levels of damping achieved via
branching with typically 30% of the energy being dissipated in one oscillation.
This concept of damping-by-branching is of simple practical use in the design
of slender flexible structures.
|
1106.1283v1
|
2011-11-29
|
Dispersion and damping of potential surface waves in a degenerate plasma
|
Potential (electrostatic) surface waves in plasma half-space with degenerate
electrons are studied using the quasi-classical mean-field kinetic model. The
wave spectrum and the collisionless damping rate are obtained numerically for a
wide range of wavelengths. In the limit of long wavelengths, the wave frequency
$\omega$ approaches the cold-plasma limit $\omega=\omega_p/\sqrt{2}$ with
$\omega_p$ being the plasma frequency, while at short wavelengths, the wave
spectrum asymptotically approaches the spectrum of zero-sound mode propagating
along the boundary. It is shown that the surface waves in this system remain
weakly damped at all wavelengths (in contrast to strongly damped surface waves
in Maxwellian electron plasmas), and the damping rate nonmonotonically depends
on the wavelength, with the maximum (yet small) damping occuring for surface
waves with wavelength of $\approx5\pi\lambda_{F}$, where $\lambda_{F}$ is the
Thomas-Fermi length.
|
1111.6723v1
|
2012-01-29
|
Smooth attractors of finite dimension for von Karman evolutions with nonlinear frictional damping localized in a boundary layer
|
In this paper dynamic von Karman equations with localized interior damping
supported in a boundary collar are considered. Hadamard well-posedness for von
Karman plates with various types of nonlinear damping are well-known, and the
long-time behavior of nonlinear plates has been a topic of recent interest.
Since the von Karman plate system is of "hyperbolic type" with critical
nonlinearity (noncompact with respect to the phase space), this latter topic is
particularly challenging in the case of geometrically constrained and nonlinear
damping. In this paper we first show the existence of a compact global
attractor for finite-energy solutions, and we then prove that the attractor is
both smooth and finite dimensional. Thus, the hyperbolic-like flow is
stabilized asymptotically to a smooth and finite dimensional set.
Key terms: dynamical systems, long-time behavior, global attractors,
nonlinear plates, nonlinear damping, localized damping
|
1201.6072v1
|
2012-06-15
|
Landau Damping in a Turbulent Setting
|
To address the problem of Landau damping in kinetic turbulence, the forcing
of the linearized Vlasov equation by a stationary random source is considered.
It is found that the time-asymptotic density response is dominated by resonant
particle interactions that are synchronized with the source. The energy
consumption of this response is calculated, implying an effective damping rate,
which is the main result of this paper. Evaluating several cases, it is found
that the effective damping rate can differ from the Landau damping rate in
magnitude and also, remarkably, in sign. A limit is demonstrated in which the
density and current become phase-locked, which causes the effective damping to
be negligible; this potentially resolves an energy paradox that arises in the
application of critical balance to a kinetic turbulence cascade.
|
1206.3415v4
|
2012-07-17
|
Asymptotic Dynamics of a Class of Coupled Oscillators Driven by White Noises
|
This paper is devoted to the study of the asymptotic dynamics of a class of
coupled second order oscillators driven by white noises. It is shown that any
system of such coupled oscillators with positive damping and coupling
coefficients possesses a global random attractor. Moreover, when the damping
and the coupling coefficients are sufficiently large, the global random
attractor is a one-dimensional random horizontal curve regardless of the
strength of the noises, and the system has a rotation number, which implies
that the oscillators in the system tend to oscillate with the same frequency
eventually and therefore the so called frequency locking is successful. The
results obtained in this paper generalize many existing results on the
asymptotic dynamics for a single second order noisy oscillator to systems of
coupled second order noisy oscillators. They show that coupled damped second
order oscillators with large damping have similar asymptotic dynamics as the
limiting coupled first order oscillators as the damping goes to infinite and
also that coupled damped second order oscillators have similar asymptotic
dynamics as their proper space continuous counterparts, which are of great
practical importance.
|
1207.3864v1
|
2013-10-29
|
Influence of sample geometry on inductive damping measurement methods
|
We study the precession frequency and effective damping of patterned
permalloy thin films of different geometry using integrated inductive test
structures. The test structures consist of coplanar wave guides fabricated onto
patterned permalloy stripes of different geometry. The width, length and
position of the permalloy stripe with respect to the center conductor of the
wave guide are varied. The precession frequency and effective damping of the
different devices is derived by inductive measurements in time and frequency
domain in in-plane magnetic fields. While the precession frequencies do not
reveal a significant dependence on the sample geometry we find a decrease of
the measured damping with increasing width of the permalloy centered underneath
the center conductor of the coplanar wave guide. We attribute this effect to an
additional damping contribution due to inhomogeneous line broadening at the
edges of the permalloy stripes which does not contribute to the inductive
signal provided the permalloy stripe is wider than the center conductor.
Consequences for inductive determination of the effective damping using such
integrated reference samples are discussed.
|
1310.7817v1
|
2014-03-13
|
The best decay rate of the damped plate equation in a square
|
In this paper we study the best decay rate of the solutions of a damped plate
equation in a square and with a homogeneous Dirichlet boundary conditions. We
show that the fastest decay rate is given by the supremum of the real part of
the spectrum of the infinitesimal generator of the underlying semigroup, if the
damping coefficient is in $L^\infty(\Omega).$ Moreover, we give some numerical
illustrations by spectral computation of the spectrum associated to the damped
plate equation. The numerical results obtained for various cases of damping are
in a good agreement with theoretical ones. Computation of the spectrum and
energy of discrete solution of damped plate show that the best decay rate is
given by spectral abscissa of numerical solution.
|
1403.3199v1
|
2014-04-02
|
Determination of the cross-field density structuring in coronal waveguides using the damping of transverse waves
|
Time and spatial damping of transverse magnetohydrodynamic (MHD) kink
oscillations is a source of information on the cross-field variation of the
plasma density in coronal waveguides. We show that a probabilistic approach to
the problem of determining the density structuring from the observed damping of
transverse oscillations enables us to obtain information on the two parameters
that characterise the cross-field density profile. The inference is performed
by computing the marginal posterior distributions for density contrast and
transverse inhomo- geneity length-scale using Bayesian analysis and damping
ratios for transverse oscillations under the assumption that damping is
produced by resonant absorption. The obtained distributions show that, for
damping times of a few oscillatory periods, low density contrasts and short
inho- mogeneity length scales are more plausible in explaining observations.
This means that valuable information on the cross-field density profile can be
obtained even if the inversion problem, with two unknowns and one observable,
is a mathematically ill-posed problem.
|
1404.0584v1
|
2014-04-05
|
Gilbert damping in noncollinear ferromagnets
|
The precession and damping of a collinear magnetization displaced from its
equilibrium are described by the Landau-Lifshitz-Gilbert equation. For a
noncollinear magnetization, it is not known how the damping should be
described. We use first-principles scattering theory to investigate the damping
in one-dimensional transverse domain walls (DWs) of the important ferromagnetic
alloy Ni$_{80}$Fe$_{20}$ and interpret the results in terms of phenomenological
models. The damping is found to depend not only on the magnetization texture
but also on the specific dynamic modes of Bloch and N\'eel DWs. Even in the
highly disordered Ni$_{80}$Fe$_{20}$ alloy, the damping is found to be
remarkably nonlocal.
|
1404.1488v2
|
2014-04-14
|
Distributed Approximate Message Passing for Compressed Sensing
|
In this paper, an efficient distributed approach for implementing the
approximate message passing (AMP) algorithm, named distributed AMP (DAMP), is
developed for compressed sensing (CS) recovery in sensor networks with the
sparsity K unknown. In the proposed DAMP, distributed sensors do not have to
use or know the entire global sensing matrix, and the burden of computation and
storage for each sensor is reduced. To reduce communications among the sensors,
a new data query algorithm, called global computation for AMP (GCAMP), is
proposed. The proposed GCAMP based DAMP approach has exactly the same recovery
solution as the centralized AMP algorithm, which is proved theoretically in the
paper. The performance of the DAMP approach is evaluated in terms of the
communication cost saved by using GCAMP. For comparison purpose, thresholding
algorithm (TA), a well known distributed Top-K algorithm, is modified so that
it also leads to the same recovery solution as the centralized AMP. Numerical
results demonstrate that the GCAMP based DAMP outperforms the Modified TA based
DAMP, and reduces the communication cost significantly.
|
1404.3766v2
|
2014-12-17
|
The most metal-rich damped Lyman alpha systems at z>1.5 I: The Data
|
We present HIRES observations for 30 damped Lyman alpha systems, selected on
the basis of their large metal column densities from previous, lower resolution
data. The measured metal column densities for Fe, Zn, S, Si, Cr, Mn, and Ni are
provided for these 30 systems. Combined with previously observed large metal
column density damped Lyman alpha systems, we present a sample of 44 damped
Lyman alpha systems observed with high resolution spectrographs (R~30000).
These damped Lyman alpha systems probe the most chemically evolved systems at
redshifts greater than 1.5. We discuss the context of our sample with the
general damped Lyman alpha population, demonstrating that we are probing the
top 10% of metal column densities with our sample. In a companion paper, we
will present an analysis of the sample's elemental abundances in the context of
galactic chemical enrichment.
|
1412.5491v1
|
2015-02-16
|
Role of nonlinear anisotropic damping in the magnetization dynamics of topological solitons
|
The consequences of nonlinear anisotropic damping, driven by the presence of
Rashba spin-orbit coupling in thin ferromagnetic metals, are examined for the
dynamics of topological magnetic solitons such as domain walls, vortices, and
skyrmions. The damping is found to affect Bloch and N\'eel walls differently in
the steady state regime below Walker breakdown and leads to a monotonic
increase in the wall velocity above this transition for large values of the
Rashba coefficient. For vortices and skyrmions, a generalization of the damping
tensor within the Thiele formalism is presented. It is found that chiral
components of the damping affect vortex- and hedgehog-like skyrmions in
different ways, but the dominant effect is an overall increase in the
viscous-like damping.
|
1502.04695v2
|
2015-03-26
|
Transient nutations decay in diluted paramagnetic solids: a radiation damping mechanism
|
Here, a theory of the intensity and concentration dependent damping of
nutation signals observed by Boscaino et al. (Phys. Rev B 48, 7077 (1993);
Phys. Rev. A 59, 4087 (1999)) and by others in various two-level spin systems
is proposed. It is shown that in diluted paramagnetic solids contribution of
dipole-dipole interaction to the nutation decay is negligibly small. We
elaborated a cavity loss (radiation damping) mechanism that explains the
intensity- and concentration dependence of the damping. It is shown that
instead of ordinary Bloch's transverse T2 and longitudinal T1 damping
parameters the decay of transverse and longitudinal spin components in nutation
process are described by one and the same intensity-, concentration-,
frequency- and time dependent damping parameter.
|
1503.07641v2
|
2015-08-17
|
Increased magnetic damping of a single domain wall and adjacent magnetic domains detected by spin torque diode in a nanostripe
|
We use spin-torque resonance to probe simultaneously and separately the
dynamics of a magnetic domain wall and of magnetic domains in a nanostripe
magnetic tunnel junction. Thanks to the large associated resistance variations
we are able to analyze quantitatively the resonant properties of these single
nanoscale magnetic objects. In particular, we find that the magnetic damping of
both domains and domain walls is doubled compared to the damping value of their
host magnetic layer. We estimate the contributions to damping arising from
dipolar couplings between the different layers in the junction and from the
intralayer spin pumping effect. We find that they cannot explain the large
damping enhancement that we observe. We conclude that the measured increased
damping is intrinsic to large amplitudes excitations of spatially localized
modes or solitons such as vibrating or propagating domain walls
|
1508.04043v1
|
2016-02-22
|
Effects of Landau-Lifshitz-Gilbert damping on domain growth
|
Domain patterns are simulated by the Landau-Lifshitz-Gilbert (LLG) equation
with an easy-axis anisotropy. If the Gilbert damping is removed from the LLG
equation, it merely describes the precession of magnetization with a
ferromagnetic interaction. However, even without the damping, domains that look
similar to those of scalar fields are formed, and they grow with time. It is
demonstrated that the damping has no significant effects on domain growth laws
and large-scale domain structure. In contrast, small-scale domain structure is
affected by the damping. The difference in small-scale structure arises from
energy dissipation due to the damping.
|
1602.06673v3
|
2016-04-27
|
Influence of nonlocal damping on the field-driven domain wall motion
|
We derive the complete expression of nonlocal damping in noncollinear
magnetization due to the nonuniform spin current pumped by precessional
magnetization and incorporate it into a generalized Thiele equation to study
its effects on the dynamics of the transverse and vortex domain walls (DWs) in
ferromagnetic nanowires. We demonstrate that the transverse component of
nonlocal damping slows down the field-driven DW propagation and increases the
Walker breakdown field whereas it is neglected in many previous works in
literature. The experimentally measured DW mobility variation with the damping
tuned by doping with heavy rare-earth elements that had discrepancy from
micromagnetic simulation are now well understood with the nonlocal damping. Our
results suggest that the nonlocal damping should be properly included as a
prerequisite for quantitative studies of current-induced torques in
noncollinear magnetization.
|
1604.07971v2
|
2016-04-27
|
Damping of the Collective Amplitude Mode in Superconductors with Strong Electron-Phonon Coupling
|
We study the effect of strong electron-phonon interactions on the damping of
the Higgs amplitude mode in superconductors by means of non-equilibrium
dynamical mean-field simulations of the Holstein model. In contrast to the BCS
dynamics, we find that the damping of the Higgs mode strongly depends on the
temperature, becoming faster as the systen approaches the transition
temperature. The damping at low temperatures is well described by a power-law,
while near the transition temperature the damping shows exponential-like
behavior. We explain this crossover by a temperature-dependent quasiparticle
lifetime caused by the strong electron- phonon coupling, which smears the
superconducting gap edge and makes the relaxation of the Higgs mode into
quasiparticles more efficient at elevated temperatures. We also reveal that the
phonon dynamics can soften the Higgs mode, which results in a slower damping.
|
1604.08073v2
|
2016-05-29
|
Damped Infinite Energy Solutions of the 3D Euler and Boussinesq Equations
|
We revisit a family of infinite-energy solutions of the 3D incompressible
Euler equations proposed by Gibbon et al. [9] and shown to blowup in finite
time by Constantin [6]. By adding a damping term to the momentum equation we
examine how the damping coefficient can arrest this blowup. Further, we show
that similar infinite-energy solutions of the inviscid 3D Boussinesq system
with damping can develop a singularity in finite time as long as the damping
effects are insufficient to arrest the (undamped) 3D Euler blowup in the
associated damped 3D Euler system.
|
1605.08965v3
|
2016-06-14
|
Anomalous Damping of a Micro-electro-mechanical Oscillator in Superfluid $^3$He-B
|
The mechanical resonance properties of a micro-electro-mechanical oscillator
with a gap of 1.25 $\mu$m was studied in superfluid $^3$He-B at various
pressures. The oscillator was driven in the linear damping regime where the
damping coefficient is independent of the oscillator velocity. The quality
factor of the oscillator remains low ($Q\approx 80$) down to 0.1 $T_c$, 4
orders of magnitude less than the intrinsic quality factor measured in vacuum
at 4 K. In addition to the Boltzmann temperature dependent contribution to the
damping, a damping proportional to temperature was found to dominate at low
temperatures. We propose a multiple scattering mechanism of the surface Andreev
bound states to be a possible cause for the anomalous damping.
|
1606.04483v2
|
2016-12-16
|
Dynamics of cohering and decohering power under Markovian channels
|
In this paper, we investigate the cohering and decohering power for the
one-qubit Markovian channels with respect to coherence in terms of the
$l_{1}$-norm, the R$\acute{e}$nyi $\alpha$-relative entropy and the Tsallis
$\alpha$-relative entropy. In the case of $\alpha=2$, the cohering and
decohering power of the amplitude damping channel, the phase damping channel,
the depolarizing channel, and the flip channels under the three measures of
coherence are calculated analytically. The decohering power on the $x, y, z$
basis referring to the amplitude damping channel, the phase damping channel,
the flip channel for every measure we investigated is equal. This property also
happens in the cohering power of the phase damping channel, the depolarizing
channel, and the flip channels. However, the decohering power of the
depolarizing channel is independent to the reference basis, and the cohering
power of the amplitude damping channel on the $x, y$ basis is different to that
on the $z$ basis.
|
1612.05355v1
|
2017-01-19
|
Decoherence effects on multiplayer cooperative quantum games
|
We study the behavior of cooperative multiplayer quantum games [35,36] in the
presence of decoherence using different quantum channels such as amplitude
damping, depolarizing and phase damping. It is seen that the outcomes of the
games for the two damping channels with maximum values of decoherence reduce to
same value. However, in comparison to phase damping channel, the payoffs of
cooperators are strongly damped under the influence\ amplitude damping channel
for\ the lower values of decoherence parameter. In the case of depolarizing
channel, the game is a no-payoff game irrespective of the degree of
entanglement in the initial state for the larger values of decoherence
parameter. The decoherence gets the cooperators worse off.
|
1701.05342v1
|
2017-10-09
|
Resonant absorption of surface sausage and surface kink modes under photospheric conditions
|
We study the effect of resonant absorption of surface sausage and surface
kink modes under photospheric conditions where the slow surface sausage modes
undergo resonant damping in the slow continuum and the surface kink modes in
the slow and Alfv\'{e}n continua at the transitional layers. We use recently
derived analytical formulas to obtain the damping rate (time). By considering
linear density and linear pressure profiles for the transitional layers, we
show that resonant absorption in the slow continuum could be an efficient
mechanism for the wave damping of the slow surface sausage and slow surface
kink modes whilst the damping rate of the slow surface kink mode in the
Alfv\'{e}n continuum is weak. It is also found that the resonant damping of the
fast surface kink mode is much stronger than that of the slow surface kink
mode, showing a similar efficiency as under coronal conditions. It is worth to
notice that the slow body sausage and kink modes can also resonantly damp in
the slow continuum for those linear profiles.
|
1710.03350v2
|
2017-11-21
|
Nonexistence of global solutions of nonlinear wave equations with weak time-dependent damping related to Glassey conjecture
|
This work is devoted to the nonexistence of global-in-time energy solutions
of nonlinear wave equation of derivative type with weak time-dependent damping
in the scattering and scale invariant range. By introducing some multipliers to
absorb the damping term, we succeed in establishing the same upper bound of the
lifespan for the scattering damping as the non-damped case, which is a part of
so-called Glassey conjecture on nonlinear wave equations. We also study an
upper bound of the lifespan for the scale invariant damping with the same
method.
|
1711.07591v2
|
2018-01-03
|
Stabilisation of wave equations on the torus with rough dampings
|
For the damped wave equation on a compact manifold with {\em continuous}
dampings, the geometric control condition is necessary and sufficient for
{uniform} stabilisation. In this article, on the two dimensional torus, in the
special case where $a(x) = \sum\_{j=1}^N a\_j 1\_{x\in R\_j}$ ($R\_j$ are
polygons), we give a very simple necessary and sufficient geometric condition
for uniform stabilisation. We also propose a natural generalization of the
geometric control condition which makes sense for $L^\infty$ dampings. We show
that this condition is always necessary for uniform stabilisation (for any
compact (smooth) manifold and any $L^\infty$ damping), and we prove that it is
sufficient in our particular case on $\mathbb{T}^2$ (and for our particular
dampings).
|
1801.00983v2
|
2018-03-12
|
Optical Rotation of Levitated Spheres in High Vacuum
|
A circularly polarized laser beam is used to levitate and control the
rotation of microspheres in high vacuum. At low pressure, rotation frequencies
as high as 6 MHz are observed for birefringent vaterite spheres, limited by
centrifugal stresses. Due to the extremely low damping in high vacuum,
controlled optical rotation of amorphous SiO$_2$ spheres is also observed at
rates above several MHz. At $10^{-7}$ mbar, a damping time of $6\times10^4$ s
is measured for a $10\ \mu$m diameter SiO$_2$ sphere. No additional damping
mechanisms are observed above gas damping, indicating that even longer damping
times may be possible with operation at lower pressure. The controlled optical
rotation of microspheres at MHz frequencies with low damping, including for
materials that are not intrinsically birefringent, provides a new tool for
performing precision measurements using optically levitated systems.
|
1803.04297v1
|
2018-03-23
|
A conservation law with spatially localized sublinear damping
|
We consider a general conservation law on the circle, in the presence of a
sublinear damping. If the damping acts on the whole circle, then the solution
becomes identically zero in finite time, following the same mechanism as the
corresponding ordinary differential equation. When the damping acts only
locally in space, we show a dichotomy: if the flux function is not zero at the
origin, then the transport mechanism causes the extinction of the solution in
finite time, as in the first case. On the other hand, if zero is a
non-degenerate critical point of the flux function, then the solution becomes
extinct in finite time only inside the damping zone, decays algebraically
uniformly in space, and we exhibit a boundary layer, shrinking with time,
around the damping zone. Numerical illustrations show how similar phenomena may
be expected for other equations.
|
1803.08767v1
|
2019-03-06
|
Microwave magnon damping in YIG films at millikelvin temperatures
|
Magnon systems used in quantum devices require low damping if coherence is to
be maintained. The ferrimagnetic electrical insulator yttrium iron garnet (YIG)
has low magnon damping at room temperature and is a strong candidate to host
microwave magnon excitations in future quantum devices. Monocrystalline YIG
films are typically grown on gadolinium gallium garnet (GGG) substrates. In
this work, comparative experiments made on YIG waveguides with and without GGG
substrates indicate that the material plays a significant role in increasing
the damping at low temperatures. Measurements reveal that damping due to
temperature-peak processes is dominant above 1 K. Damping behaviour that we
show can be attributed to coupling to two-level fluctuators (TLFs) is observed
below 1 K. Upon saturating the TLFs in the substrate-free YIG at 20 mK,
linewidths of 1.4 MHz are achievable: lower than those measured at room
temperature.
|
1903.02527v3
|
2019-06-25
|
Conductivity-Like Gilbert Damping due to Intraband Scattering in Epitaxial Iron
|
Confirming the origin of Gilbert damping by experiment has remained a
challenge for many decades, even for simple ferromagnetic metals. In this
Letter, we experimentally identify Gilbert damping that increases with
decreasing electronic scattering in epitaxial thin films of pure Fe. This
observation of conductivity-like damping, which cannot be accounted for by
classical eddy current loss, is in excellent quantitative agreement with
theoretical predictions of Gilbert damping due to intraband scattering. Our
results resolve the longstanding question about a fundamental damping mechanism
and offer hints for engineering low-loss magnetic metals for cryogenic
spintronics and quantum devices.
|
1906.10326v2
|
2019-09-21
|
Stability for coupled waves with locally disturbed Kelvin-Voigt damping
|
We consider a coupled wave system with partial Kelvin-Voigt damping in the
interval (-1,1), where one wave is dissipative and the other does not. When the
damping is effective in the whole domain (-1,1) it was proven in H.Portillo
Oquendo and P.Sanez Pacheco, optimal decay for coupled waves with Kelvin-voigt
damping, Applied Mathematics Letters 67 (2017), 16-20. That the energy is
decreasing over the time with a rate equal to $t^{-\frac{1}{2}}$. In this
paper, using the frequency domain method we show the effect of the coupling and
the non smoothness of the damping coefficient on the energy decay. Actually, as
expected we show the lack of exponential stability, that the semigroup loses
speed and it decays polynomially with a slower rate then given in, H.Portillo
Oquendo and P.Sanez Pacheco, optimal decay for coupled waves with Kelvin-voigt
damping, Applied Mathematics Letters 67 (2017), 16-20, down to zero at least as
$t^{-\frac{1}{12}}$.
|
1909.09838v1
|
2020-06-30
|
Polynomial stabilization of non-smooth direct/indirect elastic/viscoelastic damping problem involving Bresse system
|
We consider an elastic/viscoelastic transmission problem for the Bresse
system with fully Dirichlet or Dirichlet-Neumann-Neumann boundary conditions.
The physical model consists of three wave equations coupled in certain pattern.
The system is damped directly or indirectly by global or local Kelvin-Voigt
damping. Actually, the number of the dampings, their nature of distribution
(locally or globally) and the smoothness of the damping coefficient at the
interface play a crucial role in the type of the stabilization of the
corresponding semigroup. Indeed, using frequency domain approach combined with
multiplier techniques and the construction of a new multiplier function, we
establish different types of energy decay rate (see the table of stability
results below). Our results generalize and improve many earlier ones in the
literature and in particular some studies done on the Timoshenko system with
Kelvin-Voigt damping.
|
2006.16595v2
|
2020-07-02
|
Uniformly-Damped Binomial Filters: Five-percent Maximum Overshoot Optimal Response Design
|
In this paper, the five-percent maximum overshoot design of uniformly-damped
binomial filters (transfer-functions) is introduced. First, the butterworth
filter response is represented as a damped-binomial filter response. To extend
the maximum-overshoot response of the second-order butterworth to higher
orders, the binomial theorem is extended to the uniformly-damped binomial
theorem. It is shown that the five-percent uniformly-damped binomial filter is
a compromise between the butterworth filter and the standard binomial filter,
with respect to the filter-approximation problem in the time and frequency
domain. Finally, this paper concludes that in applications of interest, such as
step-tracking, where both strong filtering and a fast, smooth
transient-response, with negligible overshoot are desired, the response of the
normalized five-percent uniformly-damped binomial form is a candidate
replacement for both the butterworth and standard binomial filter forms.
|
2007.00890v3
|
2020-09-17
|
Temperature Dependent Non-linear Damping in Palladium Nano-mechanical Resonators
|
Advances in nano-fabrication techniques has made it feasible to observe
damping phenomena beyond the linear regime in nano-mechanical systems. In this
work, we report cubic non-linear damping in palladium nano-mechanical
resonators. Nano-scale palladium beams exposed to a $H_2$ atmosphere become
softer and display enhanced Duffing non-linearity as well as non-linear damping
at ultra low temperatures. The damping is highest at the lowest temperatures of
$\sim 110\: mK$ and decreases when warmed up-to $\sim 1\textrm{ }K$. We
experimentally demonstrate for the first time a temperature dependent
non-linear damping in a nano-mechanical system below 1 K. It is consistent with
a predicted two phonon mediated non-linear Akhiezer scenario for ballistic
phonons with mean free path comparable to the beam thickness. This opens up new
possibilities to engineer non-linear phenomena at low temperatures.
|
2009.08324v1
|
2020-09-22
|
Sharp exponential decay rates for anisotropically damped waves
|
In this article, we study energy decay of the damped wave equation on compact
Riemannian manifolds where the damping coefficient is anisotropic and modeled
by a pseudodifferential operator of order zero. We prove that the energy of
solutions decays at an exponential rate if and only if the damping coefficient
satisfies an anisotropic analogue of the classical geometric control condition,
along with a unique continuation hypothesis. Furthermore, we compute an
explicit formula for the optimal decay rate in terms of the spectral abscissa
and the long-time averages of the principal symbol of the damping over
geodesics, in analogy to the work of Lebeau for the isotropic case. We also
construct genuinely anisotropic dampings which satisfy our hypotheses on the
flat torus.
|
2009.10832v2
|
2020-12-25
|
Information constraint in open quantum systems
|
We propose an effect called information constraint which is characterized by
the existence of different decay rates of signal strengths propagating along
opposite directions. It is an intrinsic property of a type of open quantum
system, which does not rely on boundary conditions. We define the value of
information constraint ($I_C$) as the ratio of different decay rates and derive
the analytical representation of $I_C$ for general quadratic Lindbladian
systems. Based on information constraint, we can provide a simple and elegant
explanation of chiral and helical damping, and get the local maximum points of
relative particle number for the periodical boundary system, consistent with
numerical calculations. Inspired by information constraint, we propose and
prove the correspondence between edge modes and damping modes. A new damping
mode called Dirac damping is constructed, and chiral/helical damping can be
regarded as a special case of Dirac damping.
|
2012.13583v3
|
2021-04-29
|
Non-linear damping of standing kink waves computed with Elsasser variables
|
In a previous paper, we computed the energy density and the non-linear energy
cascade rate for transverse kink waves using Elsasser variables. In this paper,
we focus on the standing kink waves, which are impulsively excited in coronal
loops by external perturbations. We present an analytical calculation to
compute the damping time due to the non-linear development of the
Kelvin-Helmholtz instability. The main result is that the damping time is
inversely proportional to the oscillation amplitude. We compare the damping
times from our formula with the results of numerical simulations and
observations. In both cases we find a reasonably good match. The comparison
with the simulations show that the non-linear damping dominates in the high
amplitude regime, while the low amplitude regime shows damping by resonant
absorption. In the comparison with the observations, we find a power law
inversely proportional to the amplitude $\eta^{-1}$ as an outer envelope for
our Monte Carlo data points.
|
2104.14331v1
|
2021-05-31
|
Revisiting the Plasmon Radiation Damping of Gold Nanorods
|
Noble metal nanoparticles have been utilized for a vast amount of optical
applications. For the applications that used metal nanoparticles as nanosensors
and optical labeling, larger radiation damping is preferred (higher optical
signal). To get a deeper knowledge about the radiation damping of noble metal
nanoparticles, we used gold nanorods with different geometry factors (aspect
ratios) as the model system to study. We investigated theoretically how the
radiation damping of a nanorod depends on the material, and shape of the
particle. Surprisingly, a simple analytical equation describes radiation
damping very accurately and allow to disentangle the maximal radiation damping
parameter for gold nanorod with resonance energy E_res around 1.81 eV (685 nm).
We found very good agreement with theoretical predictions and experimental data
obtained by single-particle spectroscopy. Our results and approaches may pave
the way for designing and optimizing gold nanostructure with higher optical
signal and better sensing performance.
|
2105.14873v1
|
2021-06-23
|
Bayesian evidence for a nonlinear damping model for coronal loop oscillations
|
Recent observational and theoretical studies indicate that the damping of
solar coronal loop oscillations depends on the oscillation amplitude. We
consider two mechanisms, linear resonant absorption and a nonlinear damping
model. We confront theoretical predictions from these models with observed data
in the plane of observables defined by the damping ratio and the oscillation
amplitude. The structure of the Bayesian evidence in this plane displays a
clear separation between the regions where each model is more plausible
relative to the other. There is qualitative agreement between the regions of
high marginal likelihood and Bayes factor for the nonlinear damping model and
the arrangement of observed data. A quantitative application to 101 loop
oscillation cases observed with SDO/AIA results in the marginal likelihood for
the nonlinear model being larger in the majority of them. The cases with
conclusive evidence for the nonlinear damping model outnumber considerably
those in favor of linear resonant absorption.
|
2106.12243v1
|
2021-07-13
|
Convergence of iterates for first-order optimization algorithms with inertia and Hessian driven damping
|
In a Hilbert space setting, for convex optimization, we show the convergence
of the iterates to optimal solutions for a class of accelerated first-order
algorithms. They can be interpreted as discrete temporal versions of an
inertial dynamic involving both viscous damping and Hessian-driven damping. The
asymptotically vanishing viscous damping is linked to the accelerated gradient
method of Nesterov while the Hessian driven damping makes it possible to
significantly attenuate the oscillations. By treating the Hessian-driven
damping as the time derivative of the gradient term, this gives, in discretized
form, first-order algorithms. These results complement the previous work of the
authors where it was shown the fast convergence of the values, and the fast
convergence towards zero of the gradients.
|
2107.05943v1
|
2021-12-13
|
Effect of interfacial damping on high-frequency surface wave resonance on a nanostrip-bonded substrate
|
Since surface acoustic waves (SAW) are often generated on substrates to which
nanostrips are periodically attached, it is very important to consider the
effect of interface between the deposited strip and the substrate surface,
which is an unavoidable issue in manufacturing. In this paper, we propose a
theoretical model that takes into account the interface damping and calculate
the dispersion relationships both for frequency and attenuation of SAW
resonance. This results show that the interface damping has an insignificant
effect on resonance frequency, but, interestingly, attenuation of the SAW can
decrease significantly in the high frequency region as the interface damping
increases. Using picosecond ultrasound spectroscopy, we confirm the validity of
our theory; the experimental results show similar trends both for resonant
frequency and attenuation in the SAW resonance. Furthermore, the resonant
behavior of the SAW is simulated using the finite element method, and the
intrinsic cause of interface damping on the vibrating system is discussed.
These findings strongly indicate the necessity of considering interfacial
damping in the design of SAW devices.
|
2112.06367v1
|
2021-12-13
|
Cosmic ray streaming in the turbulent interstellar medium
|
We study the streaming instability of GeV$-100~$GeV cosmic rays (CRs) and its
damping in the turbulent interstellar medium (ISM). We find that the damping of
streaming instability is dominated by ion-neutral collisional damping in weakly
ionized molecular clouds, turbulent damping in the highly ionized warm medium,
and nonlinear Landau damping in the Galactic halo. Only in the Galactic halo,
is the streaming speed of CRs close to the Alfv\'{e}n speed. Alfv\'{e}nic
turbulence plays an important role in both suppressing the streaming
instability and regulating the diffusion of streaming CRs via magnetic field
line tangling, with the effective mean free path of streaming CRs in the
observer frame determined by the Alfv\'{e}nic scale in super-Alfv\'{e}nic
turbulence. The resulting diffusion coefficient is sensitive to Alfv\'{e}n Mach
number, which has a large range of values in the multi-phase ISM.
Super-Alfv\'{e}nic turbulence contributes to additional confinement of
streaming CRs, irrespective of the dominant damping mechanism.
|
2112.06941v2
|
2022-05-27
|
Scalar field damping at high temperatures
|
The motion of a scalar field that interacts with a hot plasma, like the
inflaton during reheating, is damped, which is a dissipative process. At high
temperatures the damping can be described by a local term in the effective
equation of motion. The damping coefficient is sensitive to multiple
scattering. In the loop expansion its computation would require an all-order
resummation. Instead we solve an effective Boltzmann equation, similarly to the
computation of transport coefficients. For an interaction with another scalar
field we obtain a simple relation between the damping coefficient and the bulk
viscosity, so that one can make use of known results for the latter. The
numerical prefactor of the damping coefficient turns out to be rather large, of
order $ 10 ^ 4 $.
|
2205.14166v2
|
2022-09-13
|
Latest results from the DAMPE space mission
|
The DArk Matter Particle Explorer (DAMPE) is a space-based particle detector
launched on December 17th, 2015 from the Jiuquan Satellite Launch Center
(China). The main goals of the DAMPE mission are the study of galactic cosmic
rays (CR), the electron-positron energy spectrum, gamma-ray astronomy, and
indirect dark matter search. Among its sub-detectors, the deep calorimeter
makes DAMPE able to measure electrons and gamma-ray spectra up to 10 TeV, and
CR nuclei spectra up to hundreds of TeV, with unprecedented energy resolution.
This high-energy region is important in order to search for electron-positron
sources, for dark matter signatures in space, and to clarify CR acceleration
and propagation mechanisms inside our galaxy. A general overview of the DAMPE
experiment will be presented in this work, along with its main results and
ongoing activities.
|
2209.06014v1
|
2022-10-25
|
Microscopic structure of electromagnetic whistler wave damping by kinetic mechanisms in hot magnetized Vlasov plasmas
|
The kinetic damping mechanism of low frequency transverse perturbations
propagating parallel to the magnetic field in a magnetized warm electron plasma
is simulated by means of electromagnetic (EM) Vlasov simulations. The
short-time-scale damping of the electron magnetohydrodynamic whistler
perturbations and underlying physics of finite electron temperature effect on
its real frequency are recovered rather deterministically, and analyzed. The
damping arises from an interplay between a global (prevailing over entire
phase-space) and the more familiar resonant-electron-specific kinetic damping
mechanisms, both of which preserve entropy but operate distinctly by leaving
their characteristic signatures on an initially coherent finite amplitude
modification of the warm electron equilibrium distribution. The net damping
results from a deterministic thermalization, or phase-mixing process, largely
supplementing the resonant acceleration of electrons at shorter time scales,
relevant to short-lived turbulent EM fluctuations. A kinetic model for the
evolving initial transverse EM perturbation is presented and applied to
signatures of the whistler wave phase-mixing process in simulations.
|
2210.13764v1
|
2022-12-02
|
Equivalence between the energy decay of fractional damped Klein-Gordon equations and geometric conditions for damping coefficients
|
We consider damped $s$-fractional Klein--Gordon equations on $\mathbb{R}^d$,
where $s$ denotes the order of the fractional Laplacian. In the one-dimensional
case $d = 1$, Green (2020) established that the exponential decay for $s \geq
2$ and the polynomial decay of order $s/(4-2s)$ hold if and only if the damping
coefficient function satisfies the so-called geometric control condition. In
this note, we show that the $o(1)$ energy decay is also equivalent to these
conditions in the case $d=1$. Furthermore, we extend this result to the
higher-dimensional case: the logarithmic decay, the $o(1)$ decay, and the
thickness of the damping coefficient are equivalent for $s \geq 2$. In
addition, we also prove that the exponential decay holds for $0 < s < 2$ if and
only if the damping coefficient function has a positive lower bound, so in
particular, we cannot expect the exponential decay under the geometric control
condition.
|
2212.01029v4
|
2023-01-13
|
An artificially-damped Fourier method for dispersive evolution equations
|
Computing solutions to partial differential equations using the fast Fourier
transform can lead to unwanted oscillatory behavior. Due to the periodic nature
of the discrete Fourier transform, waves that leave the computational domain on
one side reappear on the other and for dispersive equations these are typically
high-velocity, high-frequency waves. However, the fast Fourier transform is a
very efficient numerical tool and it is important to find a way to damp these
oscillations so that this transform can still be used. In this paper, we
accurately model solutions to four nonlinear partial differential equations on
an infinite domain by considering a finite interval and implementing two
damping methods outside of that interval: one that solves the heat equation and
one that simulates rapid exponential decay. Heat equation-based damping is best
suited for small-amplitude, high-frequency oscillations while exponential decay
is used to damp traveling waves and high-amplitude oscillations. We demonstrate
significant improvements in the runtime of well-studied numerical methods when
adding in the damping method.
|
2301.05789v1
|
2023-03-07
|
Stabilization of the wave equation on larger-dimension tori with rough dampings
|
This paper deals with uniform stabilization of the damped wave equation. When
the manifold is compact and the damping is continuous, the geometric control
condition is known to be necessary and sufficient. In the case where the
damping is a sum of characteristic functions of polygons on a two-dimensional
torus, a result by Burq-G\'erard states that stabilization occurs if and only
if every geodesic intersects the interior of the damped region or razes damped
polygons on both sides. We give a natural generalization of their result to a
sufficient condition on tori of any dimension $d \geq 3$. In some particular
cases, we show that this sufficient condition can be weakened.
|
2303.03733v4
|
2023-07-10
|
The Characteristic Shape of Damping Wings During Reionization
|
Spectroscopic analysis of Ly$\alpha$ damping wings of bright sources at $z>6$
is a promising way to measure the reionization history of the universe.
However, the theoretical interpretation of the damping wings is challenging due
to the inhomogeneous nature of the reionization process and the proximity
effect of bright sources. In this Letter, we analyze the damping wings arising
from the neutral patches in the radiative transfer cosmological simulation
suite Cosmic Reionization on Computers (CROC). We find that the damping wing
profile remains a tight function of volume-weighted neutral fraction $\left<
x_{\rm HI} \right>_{\rm v}$, especially when $\left< x_{\rm HI} \right>_{\rm
v}>0.5$, despite the patchy nature of reionization and the proximity effect.
This small scatter indicates that with a well-measured damping wing profile, we
could constrain the volume-weighted neutral fraction as precise as $\Delta
\left< x_{\rm HI} \right>_{\rm v} \lesssim 0.1$ in the first half of
reionization.
|
2307.04797v1
|
2023-07-17
|
Dissipation in solids under oscillatory shear: Role of damping scheme and sample thickness
|
We study dissipation as a function of sample thickness in solids under global
oscillatory shear applied to the top layer of the sample. Two types of damping
mechanism are considered: Langevin and Dissipative Particle Dynamics (DPD). In
the regime of low driving frequency, and under strain-controlled conditions, we
observe that for Langevin damping, dissipation increases with sample thickness,
while for DPD damping, it decreases. Under force-controlled conditions,
dissipation increases with sample thickness for both damping schemes. These
results can be physically understood by treating the solid as a one-dimensional
harmonic chain in the quasi-static limit, for which explicit equations (scaling
relations) describing dissipation as a function of chain length (sample
thickness) are provided. The consequences of these results, in particular
regarding the choice of damping scheme in computer simulations, are discussed.
|
2307.08413v1
|
2023-08-17
|
A low-rank algorithm for strongly damped wave equations with visco-elastic damping and mass terms
|
Damped wave equations have been used in many real-world fields. In this
paper, we study a low-rank solution of the strongly damped wave equation with
the damping term, visco-elastic damping term and mass term. Firstly, a
second-order finite difference method is employed for spatial discretization.
Then, we receive a second-order matrix differential system. Next, we transform
it into an equivalent first-order matrix differential system, and split the
transformed system into three subproblems. Applying a Strang splitting to these
subproblems and combining a dynamical low-rank approach, we obtain a low-rank
algorithm. Numerical experiments are reported to demonstrate that the proposed
low-rank algorithm is robust and accurate, and has second-order convergence
rate in time.
|
2308.08888v2
|
2023-10-30
|
Optimal backward uniqueness and polynomial stability of second order equations with unbounded damping
|
For general second order evolution equations, we prove an optimal condition
on the degree of unboundedness of the damping, that rules out finite-time
extinction. We show that control estimates give energy decay rates that
explicitly depend on the degree of unboundedness, and establish a dilation
method to turn existing control estimates for one propagator into those for
another in the functional calculus. As corollaries, we prove Schr\"odinger
observability gives decay for unbounded damping, weak monotonicity in damping,
and quantitative unique continuation and optimal propagation for fractional
Laplacians. As applications, we establish a variety of novel and explicit
energy decay results to systems with unbounded damping, including singular
damping, linearised gravity water waves and Euler--Bernoulli plates.
|
2310.19911v1
|
2023-11-27
|
Gilbert damping in two-dimensional metallic anti-ferromagnets
|
A finite spin life-time of conduction electrons may dominate Gilbert damping
of two-dimensional metallic anti-ferromagnets or anti-ferromagnet/metal
heterostructures. We investigate the Gilbert damping tensor for a typical
low-energy model of a metallic anti-ferromagnet system with honeycomb magnetic
lattice and Rashba spin-orbit coupling for conduction electrons. We distinguish
three regimes of spin relaxation: exchange-dominated relaxation for weak
spin-orbit coupling strength, Elliot-Yafet relaxation for moderate spin-orbit
coupling, and Dyakonov-Perel relaxation for strong spin-orbit coupling. We
show, however, that the latter regime takes place only for the in-plane Gilbert
damping component. We also show that anisotropy of Gilbert damping persists for
any finite spin-orbit interaction strength provided we consider no spatial
variation of the N\'eel vector. Isotropic Gilbert damping is restored only if
the electron spin-orbit length is larger than the magnon wavelength. Our theory
applies to MnPS3 monolayer on Pt or to similar systems.
|
2311.16268v2
|
2024-01-18
|
Real-space nonlocal Gilbert damping from exchange torque correlation applied to bulk ferromagnets and their surfaces
|
In this work we present an ab initio scheme based on linear response theory
of exchange torque correlation, implemented into the real-space
Korringa-Kohn-Rostoker (RS-KKR) framework to calculate diagonal elements of the
atomic-site-dependent intrinsic Gilbert damping tensor. The method is first
applied to bcc iron and fcc cobalt bulk systems. Beside reproducing earlier
results from the literature for those bulk magnets, the effect of the lattice
compression is also studied for Fe bulk, and significant changes for the
Gilbert damping are found. Furthermore, (001)-oriented surfaces of Fe and Co
are also investigated. It is found that the on-site Gilbert damping increases
in the surface atomic layer and decreases in the subsurface layer, and
approaches the bulk value moving further inside the magnets. Realistic atomic
relaxation of the surface layers enhances the identified effects. The
first-neighbor damping parameters are extremely sensitive to the surface
relaxation. Despite their inhomogeneity caused by the surface, the transverse
Gilbert damping tensor components remain largely insensitive to the
magnetization direction.
|
2401.09938v2
|
2024-03-12
|
Modulational instability of nonuniformly damped, broad-banded waves: applications to waves in sea-ice
|
This paper sets out to explore the modulational (or Benjamin-Feir)
instability of a monochromatic wave propagating in the presence of damping such
as that induced by sea-ice on the ocean surface. The fundamental wave motion is
modelled using the spatial Zakharov equation, to which either uniform or
non-uniform (frequency dependent) damping is added. By means of mode truncation
the spatial analogue of the classical Benjamin-Feir instability can be studied
analytically using dynamical systems techniques. The formulation readily yields
the free surface envelope, giving insight into the physical implications of
damping on the modulational instability. The evolution of an initially unstable
mode is also studied numerically by integrating the damped, spatial Zakharov
equation, in order to complement the analytical theory. This sheds light on the
effects of damping on spectral broadening arising from this instability.
|
2403.07425v1
|
2006-01-10
|
On the variation of the fine-structure constant: Very high resolution spectrum of QSO HE 0515-4414
|
We present a detailed analysis of a very high resolution (R\approx 112,000)
spectrum of the quasar HE 0515-4414 obtained using the High Accuracy Radial
velocity Planet Searcher (HARPS) mounted on the ESO 3.6 m telescope at the La
Silla observatory. The HARPS spectrum, of very high wavelength calibration
accuracy (better than 1 m\AA), is used to search for possible systematic
inaccuracies in the wavelength calibration of the UV Echelle Spectrograph
(UVES) mounted on the ESO Very Large Telescope (VLT). We have carried out
cross-correlation analysis between the Th-Ar lamp spectra obtained with HARPS
and UVES. The shift between the two spectra has a dispersion around zero of
\sigma\simeq 1 m\AA. This is well within the wavelength calibration accuracy of
UVES (i.e \sigma\simeq 4 m\AA). We show that the uncertainties in the
wavelength calibration induce an error of about, \Delta\alpha/\alpha\le
10^{-6}, in the determination of the variation of the fine-structure constant.
Thus, the results of non-evolving \Delta\alpha/\alpha reported in the
literature based on UVES/VLT data should not be heavily influenced by problems
related to wavelength calibration uncertainties. Our higher resolution spectrum
of the z_{abs}=1.1508 damped Lyman-\alpha system toward HE 0515-4414 reveals
more components compared to the UVES spectrum. Using the Voigt profile
decomposition that simultaneously fits the high resolution HARPS data and the
higher signal-to-noise ratio UVES data, we obtain,
\Delta\alpha/\alpha=(0.05\pm0.24)x10^{-5} at z_{abs}=1.1508. This result is
consistent with the earlier measurement for this system using the UVES spectrum
alone.
|
0601194v1
|
2008-09-08
|
The Impact of HI in Galaxies on 21-cm Intensity Fluctuations During the Reionisation Epoch
|
We investigate the impact of neutral hydrogen (HI) in galaxies on the
statistics of 21-cm fluctuations using analytic and semi-numerical modelling.
Following the reionisation of hydrogen the HI content of the Universe is
dominated by damped absorption systems (DLAs), with a cosmic density in HI that
is observed to be constant at a level equal to ~2% of the cosmic baryon density
from z~1 to z~5. We show that extrapolation of this constant fraction into the
reionisation epoch results in a reduction of 10-20% in the amplitude of 21-cm
fluctuations over a range of spatial scales. The assumption of a different
percentage during the reionisation era results in a proportional change in the
21-cm fluctuation amplitude. We find that consideration of HI in galaxies/DLAs
reduces the prominence of the HII region induced shoulder in the 21-cm power
spectrum (PS), and hence modifies the scale dependence of 21-cm fluctuations.
We also estimate the 21cm-galaxy cross PS, and show that the cross PS changes
sign on scales corresponding to the HII regions. From consideration of the
sensitivity for forthcoming low-frequency arrays we find that the effects of HI
in galaxies/DLAs on the statistics of 21-cm fluctuations will be significant
with respect to the precision of a PS or cross PS measurement. In addition,
since overdense regions are reionised first we demonstrate that the
cross-correlation between galaxies and 21-cm emission changes sign at the end
of the reionisation era, providing an alternative avenue to pinpoint the end of
reionisation. The sum of our analysis indicates that the HI content of the
galaxies that reionise the universe will need to be considered in detailed
modelling of the 21-cm intensity PS in order to correctly interpret
measurements from forthcoming low-frequency arrays.
|
0809.1271v1
|
2009-07-24
|
An Observational Determination of the Proton to Electron Mass Ratio in the Early Universe
|
In an effort to resolve the discrepancy between two measurements of the
fundamental constant mu, the proton to electron mass ratio, at early times in
the universe we reanalyze the same data used in the earlier studies. Our
analysis of the molecular hydrogen absorption lines in archival VLT/UVES
spectra of the damped Lyman alpha systems in the QSOs Q0347-383 and Q0405-443
yields a combined measurement of a (Delta mu)/mu value of (-7 +/- 8) x 10^{-6},
consistent with no change in the value of mu over a time span of 11.5
gigayears. Here we define (Delta mu) as (mu_z - mu_0) where mu_z is the value
of mu at a redshift of z and mu_0 is the present day value. Our null result is
consistent with the recent measurements of King et al. 2009, (Delta mu)/u =
(2.6 +/- 3.0) x 10^{-6}, and inconsistent with the positive detection of a
change in mu by Reinhold et al. 2006. Both of the previous studies and this
study are based on the same data but with differing analysis methods.
Improvements in the wavelength calibration over the UVES pipeline calibration
is a key element in both of the null results. This leads to the conclusion that
the fundamental constant mu is unchanged to an accuracy of 10^{-5} over the
last 80% of the age of the universe, well into the matter dominated epoch. This
limit provides constraints on models of dark energy that invoke rolling scalar
fields and also limits the parameter space of Super Symmetric or string theory
models of physics. New instruments, both planned and under construction, will
provide opportunities to greatly improve the accuracy of these measurements.
|
0907.4392v1
|
2009-07-31
|
A physical interpretation of the variability power spectral components in accreting neutron stars
|
We propose a physical framework for interpreting the characteristic
frequencies seen in the broad band power spectra from black hole and neutron
star binaries. We use the truncated disc/hot inner flow geometry, and assume
that the hot flow is generically turbulent. Each radius in the hot flow
produces fluctuations, and we further assume that these are damped on the
viscous frequency. Integrating over radii gives broad band continuum noise
power between low and high frequency breaks which are set by the viscous
timescale at the outer and inner edge of the hot flow, respectively.
Lense-Thirring (vertical) precession of the entire hot flow superimposes the
low frequency QPO on this continuum power.
We test this model on the power spectra seen in the neutron star systems
(atolls) as these have the key advantage that the (upper) kHz QPO most likely
independently tracks the truncation radius. These show that this model can give
a consistent solution, with the truncation radius decreasing from 20-8 Rg while
the inner radius of the flow remains approximately constant at ~4.5 Rg i.e. 9.2
km. We use this very constrained geometry to predict the low frequency QPO from
Lense-Thirring precession of the entire hot flow from r_o to r_i. The simplest
assumption of a constant surface density in the hot flow matches the observed
QPO frequency to within 25 per cent. This match can be made even better by
considering that the surface density should become increasingly centrally
concentrated as the flow collapses into an optically thick boundary layer
during the spectral transition. The success of the model opens up the way to
use the broad band power spectra as a diagnostic of accretion flows in strong
gravity.
|
0907.5485v3
|
2010-07-15
|
Noncommutative Double Scalar Fields in FRW Cosmology as Cosmical Oscillators
|
We investigate effects of noncommutativity of phase space generated by two
scalar fields conformally coupled to curvature in FRW cosmology. We restrict
deformation of minisuperspace to noncommutativity between scalar fields and
between their canonical conjugate momenta. The investigation is carried out by
means of comparative analysis of mathematical properties of time evolution of
variables in classical model and wave function of universe in quantum level. We
find that impose of noncommutativity causes more ability in tuning time
solutions of scalar fields and hence, has important implications in evolution
of universe. We get that noncommutative parameter in momenta sector is the only
responsible parameter for noncommutative effects in flat universes. A
distinguishing feature of noncommutative solutions of scalar fields is that
they can be simulated with well known harmonic oscillators, depend on values of
spatial curvature. Namely free, forced and damped harmonic oscillators
corresponding to flat, closed and open universes. In this respect, we call them
cosmical oscillators. In closed universes, when noncommutative parameters are
small, cosmical oscillators have analogous effect with familiar beating effect
in sound phenomenon. The existence of non-zero constant potential does not
change solutions of scalar fields, but modifies scale factor. An interesting
feature of well behaved solutions of wave functions is that functional form of
its radial part is the same as commutative ones provided that given replacement
of constants, caused by noncommutative parameters, is performed. Further,
Noether theorem has been employed to explore effects of noncommutativity on
underlying symmetries in commutative frame. Two of six Noether symmetries of
flat universes, in general, are retained in noncommutative case, and one out of
three ones in non flat universes.
|
1007.2499v2
|
2011-06-07
|
Rhythms of Memory and Bits on Edge: Symbol Recognition as a Physical Phenomenon
|
Preoccupied with measurement, physics has neglected the need, before anything
can be measured, to recognize what it is that is to be measured. The
recognition of symbols employs a known physical mechanism. The elemental
mechanism-a damped inverted pendulum joined by a driven adjustable pendulum (in
effect a clock)-both recognizes a binary distinction and records a single bit.
Referred to by engineers as a "clocked flip-flop," this paired-pendulum
mechanism pervades scientific investigation. It shapes evidence by imposing
discrete phases of allowable leeway in clock readings; and it generates a
mathematical form of evidence that neither assumes a geometry nor assumes
quantum states, and so separates statements of evidence from further
assumptions required to explain that evidence, whether the explanations are
made in quantum terms or in terms of general relativity. Cleansed of
unnecessary assumptions, these expressions of evidence form a platform on which
to consider the working together of general relativity and quantum theory as
explanatory language for evidence from clock networks, such as the Global
Positioning System. Quantum theory puts Planck's constant into explanations of
the required timing leeway, while explanations of leeway also draw on the
theory of general relativity, prompting the question: does Planck's constant in
the timing leeway put the long known tension between quantum theory and general
relativity in a new light?
|
1106.1639v1
|
2014-12-17
|
Cosmology based on $f(R)$ gravity with ${\cal O}(1)$ eV sterile neutrino
|
We address the cosmological role of an additional ${\cal O}(1)$ eV sterile
neutrino in modified gravity models. We confront the present cosmological data
with predictions of the FLRW cosmological model based on a variant of $f(R)$
modified gravity proposed by one of the authors previously. This viable
cosmological model which deviation from general relativity with a cosmological
constant $\Lambda$ decreases as $R^{-2n}$ for large, but not too large values
of the Ricci scalar $R$ provides an alternative explanation of present dark
energy and the accelerated expansion of the Universe. Various up-to-date
cosmological data sets exploited include Planck CMB anisotropy, CMB lensing
potential, BAO, cluster mass function and Hubble constant measurements. We find
that the CMB+BAO constraints strongly the sum of neutrino masses from above.
This excludes values $\lambda\sim 1$ for which distinctive cosmological
features of the model are mostly pronounced as compared to the $\Lambda$CDM
model, since then free streaming damping of perturbations due to neutrino rest
masses is not sufficient to compensate their extra growth occurring in $f(R)$
gravity. Thus, we obtain $\lambda>8.2$ ($2\sigma$) with cluster systematics and
$\lambda>9.4$ ($2\sigma$) without that. In the latter case we find for the
sterile neutrino mass
$0.47\,\,\rm{eV}$$\,<\,$$m_{\nu,\,\rm{sterile}}$$\,<\,$$1\,\,\rm{eV}$
($2\sigma$) assuming the active neutrinos are massless, not significantly
larger than in the standard $\Lambda$CDM with the same data set:
$0.45\,\,\rm{eV}$$\,<\,$$m_{\nu,\,\rm{sterile}}$$\,<\,$$0.92\,\,\rm{eV}$
($2\sigma$). However, a possible discovery of a sterile neutrino with the mass
$m_{\nu,\,\rm{sterile}} \approx 1.5\,$eV motivated by various anomalies in
neutrino oscillation experiments would favor cosmology based on $f(R)$ gravity
rather than the $\Lambda$CDM model.
|
1412.5239v2
|
2021-07-09
|
Casimir densities induced by a sphere in the hyperbolic vacuum of de Sitter spacetime
|
Complete set of modes and the Hadamard function are constructed for a scalar
field inside and outside a sphere in (D+1)-dimensional de Sitter spacetime
foliated by negative constant curvature spaces. We assume that the field obeys
Robin boundary condition on the sphere. The contributions in the Hadamard
function induced by the sphere are explicitly separated and the vacuum
expectation values (VEVs) of the field squared and energy-momentum tensor are
investigated for the hyperbolic vacuum. In the flat spacetime limit the latter
is reduced to the conformal vacuum in the Milne universe and is different from
the maximally symmetric Bunch-Davies vacuum state. The vacuum energy-momentum
tensor has a nonzero off-diagonal component that describes the energy flux in
the radial direction. The latter is a purely sphere-induced effect and is
absent in the boundary-free geometry. Depending on the constant in Robin
boundary condition and also on the radial coordinate, the energy flux can be
directed either from the sphere or towards the sphere. At early stages of the
cosmological expansion the effects of the spacetime curvature on the
sphere-induced VEVs are weak and the leading terms in the corresponding
expansions coincide with those for a sphere in the Milne universe. The
influence of the gravitational field is essential at late stages of the
expansion. Depending on the field mass and the curvature coupling parameter,
the decay of the sphere-induced VEVs, as functions of the time coordinate, is
monotonic or damping oscillatory. At large distances from the sphere the
fall-off of the sphere-induced VEVs, as functions of the geodesic distance, is
exponential for both massless and massive fields.
|
2107.04376v1
|
2022-11-23
|
Lattice eddy simulation of turbulent flows
|
Kolmogorov's (1941) theory of self-similarity implies the universality of
small-scale eddies, and holds promise for a universal sub-grid scale model for
large eddy simulation. The fact is the empirical coefficient of a typical
sub-grid scale model varies from 0.1 to 0.2 in free turbulence and damps
gradually to zero approaching the walls. This work has developed a Lattice Eddy
Simulation method (LAES), in which the sole empirical coefficient is constant
(Cs=0.08). LAES assumes the fluid properties are stored in the nodes of a
typical CFD mesh, treats the nodes as lattices and makes analysis on one
specific lattice, i. To be specific, LAES express the domain derivative on that
lattice with the influence of nearby lattices. The lattices right next to i,
which is named as i+, "collide" with i, imposing convective effects on i. The
lattices right next to i+, which is named as i++, impose convective effects on
i+ and indirectly influence i. The influence is actually turbulent diffusion.
The derived governing equations of LAES look like the Navier-Stokes equations
and reduce to filtered Naiver-Stokes equations with the Smagorinsky sub-grid
scale model (Smagorinsky 1963) on meshes with isotropic cells. LAES yields
accurate predictions of turbulent channel flows at Re=180, 395, and 590 on very
coarse meshes and LAES with a constant Cs perform as well as the dynamic LES
model (Germano et al. 1991) does. Thus, this work has provided strong evidence
for Kolmogorov's theory of self-similarity.
|
2211.12810v1
|
2020-11-30
|
Role of Compressive Viscosity and Thermal Conductivity on the Damping of Slow Waves in the Coronal Loops With and Without Heating-Cooling Imbalance
|
In the present paper, we derive a new dispersion relation for slow
magnetoacoustic waves invoking the effect of thermal conductivity, compressive
viscosity, radiation and unknown heating term along with the consideration of
heating cooling imbalance from linearized MHD equations. We solve the general
dispersion relation to understand role of compressive viscosity and thermal
conductivity in damping of the slow waves in coronal loops with and without
heating cooling imbalance. We have analyzed wave damping for the range of loop
length $L$=50-500 Mm, temperature $T$=5-30 MK, and density
$\rho$=10$^{-11}$-10$^{-9}$ kg m$^{-3}$. It was found that inclusion of
compressive viscosity along with thermal conductivity significantly enhances
the damping of fundamental mode oscillations in shorter (e.g., $L$=50 Mm) and
super-hot ($T>$10 MK) loops. However, role of the viscosity in damping is
insignificant in longer (e.g., $L$=500 Mm) and hot loops (T$\leq$10 MK) where,
instead, thermal conductivity along with the presence of heating cooling
imbalance plays a dominant role. For the shorter loops at the super-hot regime
of the temperature, increment in loop density substantially enhances damping of
the fundamental modes due to thermal conductivity when the viscosity is absent,
however, when the compressive viscosity is added the increase in density
substantially weakens damping. Thermal conductivity alone is found to play a
dominant role in longer loops at lower temperatures (T$\leq$10 MK), while
compressive viscosity dominates in damping at super-hot temperatures ($T>$10
MK) in shorter loops. The predicted scaling law between damping time ($\tau$)
and wave period ($P$) is found to better match to observed SUMER oscillations
when heating cooling imbalance is taken into account in addition to thermal
conductivity and compressive viscosity for the damping of the fundamental slow
mode oscillations.
|
2011.14519v2
|
2013-10-23
|
Fundamental constants and high resolution spectroscopy
|
Absorption-line systems detected in high resolution quasar spectra can be
used to compare the value of dimensionless fundamental constants such as the
fine-structure constant, alpha, and the proton-to-electron mass ratio, mu =
m_p/m_e, as measured in remote regions of the Universe to their value today on
Earth. In recent years, some evidence has emerged of small temporal and also
spatial variations in alpha on cosmological scales which may reach a fractional
level of 10 ppm . We are conducting a Large Programme of observations with VLT
UVES to explore these variations. We here provide a general overview of the
Large Programme and report on the first results for these two constants,
discussed in detail in Molaro et al. and Rahmani et al. A stringent bound for
Delta(alpha)/Alpha is obtained for the absorber at_abs = 1.6919 towards HE
2217-2818. The absorption profile is complex with several very narrow features,
and is modeled with 32 velocity components. The relative variation in alpha in
this system is +1.3+-2.4_{stat}+-1.0_{sys} ppm if Al II lambda 1670AA and three
Fe II transitions are used, and +1.1+-2.6_{stat} ppm in a lightly different
analysis with only Fe II transitions used. The expectation at this sky position
of the recently-reported dipolar variation of alpha is (3.2--5.4)+-1.7 ppm
depending on dipole model. This constraint of Delta(alpha)/alpha at face value
is not supporting this expectation but is not inconsistent with it at the 3
sigma level. For the proton-to-electron mass ratio the analysis of the H_2
absorption lines of the z_{abs}~2.4018 damped Ly alpha system towards HE 0027-
1836 provides Delta(mu)/mu = (-7.6 +- 8.1_{stat} +- 6.3_{sys}) ppm which is
also consistent with a null variation. (abridged)
|
1310.6280v1
|
2012-10-26
|
A Measurement of the Cosmic Microwave Background Damping Tail from the 2500-square-degree SPT-SZ survey
|
We present a measurement of the cosmic microwave background (CMB) temperature
power spectrum using data from the recently completed South Pole Telescope
Sunyaev-Zel'dovich (SPT-SZ) survey. This measurement is made from observations
of 2540 deg$^2$ of sky with arcminute resolution at $150\,$GHz, and improves
upon previous measurements using the SPT by tripling the sky area. We report
CMB temperature anisotropy power over the multipole range $650<\ell<3000$. We
fit the SPT bandpowers, combined with the seven-year Wilkinson Microwave
Anisotropy Probe (WMAP7) data, with a six-parameter LCDM cosmological model and
find that the two datasets are consistent and well fit by the model. Adding SPT
measurements significantly improves LCDM parameter constraints; in particular,
the constraint on $\theta_s$ tightens by a factor of 2.7. The impact of
gravitational lensing is detected at $8.1\, \sigma$, the most significant
detection to date. This sensitivity of the SPT+WMAP7 data to lensing by
large-scale structure at low redshifts allows us to constrain the mean
curvature of the observable universe with CMB data alone to be
$\Omega_k=-0.003^{+0.014}_{-0.018}$. Using the SPT+WMAP7 data, we measure the
spectral index of scalar fluctuations to be $n_s=0.9623 \pm 0.0097$ in the LCDM
model, a $3.9\,\sigma$ preference for a scale-dependent spectrum with $n_s<1$.
The SPT measurement of the CMB damping tail helps break the degeneracy that
exists between the tensor-to-scalar ratio $r$ and $n_s$ in large-scale CMB
measurements, leading to an upper limit of $r<0.18$ (95%,C.L.) in the LCDM+$r$
model. Adding low-redshift measurements of the Hubble constant ($H_0$) and the
baryon acoustic oscillation (BAO) feature to the SPT+WMAP7 data leads to
further improvements. The combination of SPT+WMAP7+$H_0$+BAO constrains
$n_s=0.9538 \pm 0.0081$ in the LCDM model, a $5.7\,\sigma$ detection of $n_s <
1$, ... [abridged]
|
1210.7231v2
|
1993-06-22
|
Weakly Damped Modes in Star Clusters and Galaxies
|
A perturber may excite a coherent mode in a star cluster or galaxy. If the
stellar system is stable, it is commonly assumed that such a mode will be
strongly damped and therefore of little practical consequence other than
redistributing momentum and energy deposited by the perturber. This paper
demonstrates that this assumption is false; weakly damped modes exist and may
persist long enough to have observable consequences. To do this, a method for
investigating the dispersion relation for spherical stellar systems and for
locating weakly damped modes in particular is developed and applied to King
models of varying concentration. This leads to the following remarkable result:
King models exhibit {\it very} weakly damped $m=1$ modes over a wide range of
concentration ($0.67\le c\le1.5$ have been examined). The predicted damping
time is tens to hundreds of crossing times. This mode causes the peak density
to shift from and slowly revolve about the initial center. The existence of the
mode is supported by n-body simulation. Higher order modes and possible
astronomical consequences are discussed. Weakly damped modes, for example, may
provide a natural explanation for observed discrepancies between density and
kinematic centers in galaxies, the location of velocity cusps due to massive
black holes, and $m=1$ disturbances of disks embedded in massive halos.
Gravitational shocking may excite the $m=1$ mode in globular clusters, which
could modify their subsequent evolution and displace the positions of exotic
remnants.
|
9306020v1
|
1997-12-03
|
On the Evolution of Damped Lyman Alpha Systems to Galactic Disks
|
The mean metallicity of the thick disk of the Galaxy is 0.5 dex higher than
that of the damped Lyman alpha systems. This has been interpreted to argue that
stars in the former do not arise out of gas in the latter. Using new
metallicity and H I column-density data we show the metal-rich damped systems
do contain sufficient baryons at the thick-disk metallicity to account for the
stellar masses of thick disks. Comparing our kinematic data with the
metallicities we show that damped Lyman alpha systems exhibiting the largest
profile velocity widths span a narrow range of high metallicities, while
systems with small velocity widths span a wider range of metallicities. This is
naturally explained by passage of the damped Lyman alpha sightlines through
rapidly rotating disks with negative radial gradients in metallicity. The
systematically lower N(H I) of systems with high velocity widths indicates (a)
the gaseous disks have centrally located holes, and (b) an apparent
inconsistency with the protogalactic clump model for damped Lyman alpha
systems. The higher metallicity of systems with low N(H I) further implies that
stars rather than gas dominate the baryonic content of the most metal-rich
damped systems.
|
9712050v1
|
1998-10-23
|
Chemical Abundances of the Damped Lya Systems at z>1.5
|
We present chemical abundance measurements for 19 damped lya systems observed
with HIRES on the 10m W.M. Keck Telescope. Our principal goal is to investigate
the abundance patterns of the damped systems and thereby determine the
underlying physical processes which dominate their chemical evolution. We place
particular emphasis on gauging the relative importance of two complementary
effects often invoked to explain the damped lya abundances: (1) nucleosynthetic
enrichment from Type II supernovae and (2) an ISM-like dust depletion pattern.
Similar to the principal results of Lu et al. (1996), our observations lend
support both for dust depletion and Type II SN enrichment. Specifically, the
observed overabundance of Zn/Fe and underabundance of Ni/Fe relative to solar
abundances suggest significant dust depletion within the damped lya systems.
Meanwhile, the relative abundances of Al, Si, and Cr vs. Fe are consistent with
both dust depletion and Type II supernova enrichment. Our measurements of Ti/Fe
and the Mn/Fe measurements from Lu et al. (1996), however, cannot be explained
by dust depletion and indicate an underlying Type II SN pattern. Finally, the
observed values of [S/Fe] are inconsistent with the combined effects of dust
depletion and the nucleosynthetic yields expected for Type II supernovae. This
last result emphasizes the need for another physical process to explain the
damped lya abundance patterns.
We also examine the metallicity of the damped lya systems both with respect
to Zn/H and Fe/H. Our results confirm previous surveys by Pettini and
collaborators, i.e., [<Zn/H>] = -1.15 +/- 0.15 dex. [abridged]
|
9810381v1
|
2002-04-03
|
The role of damped Alfven waves on magnetospheric accretion models of young stars
|
We examine the role of Alfven wave damping in heating the plasma in the
magnetic funnels of magnetospheric accretion models of young stars. We study
four different damping mechanisms of the Alfven waves: nonlinear, turbulent,
viscous-resistive and collisional. Two different possible origins for the
Alfven waves are discussed: 1) Alfven waves generated at the surface of the
star by the shock produced by the infalling matter; and 2) Alfven waves
generated locally in the funnel by the Kelvin-Helmholtz instability. We find
that, in general, the damping lengths are smaller than the tube length. Since
thermal conduction in the tube is not efficient, Alfven waves generated only at
the star's surface cannot heat the tube to the temperatures necessary to fit
the observations. Only for very low frequency Alfven waves ~10^{-5} the ion
cyclotron frequency, is the viscous-resistive damping length greater than the
tube length. In this case, the Alfven waves produced at the surface of the star
are able to heat the whole tube. Otherwise, local production of Alfven waves is
required to explain the observations. The turbulence level is calculated for
different frequencies for optically thin and thick media. We find that
turbulent velocities varies greatly for different damping mechanisms, reaching
\~100 km s^{-1} for the collisional damping of small frequency waves.
|
0204056v1
|
2009-09-19
|
Resonantly Damped Kink Magnetohydrodynamic Waves in a Partially Ionized Filament Thread
|
Transverse oscillations of solar filament and prominence threads have been
frequently reported. These oscillations have the common features of being of
short period (2-10 min) and being damped after a few periods. Kink
magnetohydrodynamic (MHD) wave modes have been proposed as responsible for the
observed oscillations, whereas resonant absorption in the Alfven continuum and
ion-neutral collisions are the best candidates to be the damping mechanisms.
Here, we study both analytically and numerically the time damping of kink MHD
waves in a cylindrical, partially ionized filament thread embedded in a coronal
environment. The thread model is composed of a straight and thin, homogeneous
filament plasma, with a transverse inhomogeneous transitional layer where the
plasma physical properties vary continuously from filament to coronal
conditions. The magnetic field is homogeneous and parallel to the thread axis.
We find that the kink mode is efficiently damped by resonant absorption for
typical wavelengths of filament oscillations, the damping times being
compatible with the observations. Partial ionization does not affect the
process of resonant absorption, and the filament plasma ionization degree is
only important for the damping for wavelengths much shorter than those
observed. To our knowledge, this is the first time that the phenomenon of
resonant absorption is studied in a partially ionized plasma.
|
0909.3599v1
|
2009-10-15
|
Time damping of non-adiabatic magnetohydrodynamic waves in a partially ionized prominence plasma: Effect of helium
|
Prominences are partially ionized, magnetized plasmas embedded in the solar
corona. Damped oscillations and propagating waves are commonly observed. These
oscillations have been interpreted in terms of magnetohydrodynamic (MHD) waves.
Ion-neutral collisions and non-adiabatic effects (radiation losses and thermal
conduction) have been proposed as damping mechanisms. We study the effect of
the presence of helium on the time damping of non-adiabatic MHD waves in a
plasma composed by electrons, protons, neutral hydrogen, neutral helium (He I),
and singly ionized helium (He II) in the single-fluid approximation. The
dispersion relation of linear non-adiabatic MHD waves in a homogeneous,
unbounded, and partially ionized prominence medium is derived. The period and
the damping time of Alfven, slow, fast, and thermal waves are computed. A
parametric study of the ratio of the damping time to the period with respect to
the helium abundance is performed. The efficiency of ion-neutral collisions as
well as thermal conduction is increased by the presence of helium. However, if
realistic abundances of helium in prominences (~10%) are considered, this
effect has a minor influence on the wave damping. The presence of helium can be
safely neglected in studies of MHD waves in partially ionized prominence
plasmas.
|
0910.2883v1
|
2009-12-21
|
The effect of longitudinal flow on resonantly damped kink oscillations
|
The most promising mechanism acting towards damping the kink oscillations of
coronal loops is resonant absorption. In this context most of previous studies
neglected the effect of the obvious equilibrium flow along magnetic field
lines. The flows are in general sub-Alfv\'enic and hence comparatively slow.
Here we investigate the effect of an equilibrium flow on the resonant
absorption of linear kink MHD waves in a cylindrical magnetic flux tube with
the aim of determining the changes in the frequency of the forward and backward
propagating waves and in the modification of the damping times due to the flow.
A loop model with both the density and the longitudinal flow changing in the
radial direction is considered. We use the thin tube thin boundary (TTTB)
approximation in order to calculate the damping rates. The full resistive
eigenvalue problem is also solved without assuming the TTTB approximation.
Using the small ratio of flow and Alfv\'en speeds we derive simple analytical
expressions to the damping rate. The analytical expressions are in good
agreement with the resistive eigenmode calculations. Under typical coronal
conditions the effect of the flow on the damped kink oscillations is small when
the characteristic scale of the density layer is similar or smaller than the
characteristic width of the velocity layer. However, in the opposite situation
the damping rates can be significantly altered, specially for the backward
propagating wave which is undamped while the forward wave is overdamped.
|
0912.4136v1
|
2010-07-12
|
Seismology of Standing Kink Oscillations of Solar Prominence Fine Structures
|
We investigate standing kink magnetohydrodynamic (MHD) oscillations in a
prominence fine structure modeled as a straight and cylindrical magnetic tube
only partially filled with the prominence material, and with its ends fixed at
two rigid walls representing the solar photosphere. The prominence plasma is
partially ionized and a transverse inhomogeneous transitional layer is included
between the prominence thread and the coronal medium. Thus, ion-neutral
collisions and resonant absorption are the considered damping mechanisms.
Approximate analytical expressions of the period, the damping time, and their
ratio are derived for the fundamental mode in the thin tube and thin boundary
approximations. We find that the dominant damping mechanism is resonant
absorption, which provides damping ratios in agreement with the observations,
whereas ion-neutral collisions are irrelevant for the damping. The values of
the damping ratio are independent of both the prominence thread length and its
position within the magnetic tube, and coincide with the values for a tube
fully filled with the prominence plasma. The implications of our results in the
context of the MHD seismology technique are discussed, pointing out that the
reported short-period (2 - 10 min) and short-wavelength (700 - 8,000 km) thread
oscillations may not be consistent with a standing mode interpretation and
could be related to propagating waves. Finally, we show that the inversion of
some prominence physical parameters, e.g., Alfv\'en speed, magnetic field
strength, transverse inhomogeneity length-scale, etc., is possible using
observationally determined values of the period and damping time of the
oscillations along with the analytical approximations of these quantities.
|
1007.1959v2
|
2012-10-30
|
Mode- and size-dependent Landau-Lifshitz damping in magnetic nanostructures: Evidence for non-local damping
|
We demonstrate a strong dependence of the effective damping on the nanomagnet
size and the particular spin-wave mode that can be explained by the theory of
intralayer transverse-spin-pumping. The effective Landau-Lifshitz damping is
measured optically in individual, isolated nanomagnets as small as 100 nm. The
measurements are accomplished by use of a novel heterodyne magneto-optical
microwave microscope with unprecedented sensitivity. Experimental data reveal
multiple standing spin-wave modes that we identify by use of micromagnetic
modeling as having either localized or delocalized character, described
generically as end- and center-modes. The damping parameter of the two modes
depends on both the size of the nanomagnet as well as the particular spin-wave
mode that is excited, with values that are enhanced by as much as 40% relative
to that measured for an extended film. Contrary to expectations based on the ad
hoc consideration of lithography-induced edge damage, the damping for the
end-mode decreases as the size of the nanomagnet decreases. The data agree with
the theory for damping caused by the flow of intralayer transverse
spin-currents driven by the magnetization curvature. These results have serious
implications for the performance of nanoscale spintronic devices such as
spin-torque-transfer magnetic random access memory.
|
1210.8118v3
|
2012-11-21
|
Kinetic theory of surface plasmon polariton in semiconductor nanowires
|
Based on the semiclassical model Hamiltonian of the surface plasmon polariton
and the nonequilibrium Green-function approach, we present a microscopic
kinetic theory to study the influence of the electron scattering on the
dynamics of the surface plasmon polariton in semiconductor nanowires. The
damping of the surface plasmon polariton originates from the resonant
absorption by the electrons (Landau damping), and the corresponding damping
exhibits size-dependent oscillations and distinct temperature dependence
without any scattering. The scattering influences the damping by introducing a
broadening and a shifting to the resonance. To demonstrate this, we investigate
the damping of the surface plasmon polariton in InAs nanowires in the presence
of the electron-impurity, electron-phonon and electron-electron Coulomb
scatterings. The main effect of the electron-impurity and electron-phonon
scatterings is to introduce a broadening, whereas the electron-electron Coulomb
scattering can not only cause a broadening, but also introduce a shifting to
the resonance. For InAs nanowires under investigation, the broadening due to
the electron-phonon scattering dominates. As a result, the scattering has a
pronounced influence on the damping of the surface plasmon polariton: The
size-dependent oscillations are smeared out and the temperature dependence is
also suppressed in the presence of the scattering. These results demonstrate
the the important role of the scattering on the surface plasmon polariton
damping in semiconductor nanowires.
|
1211.5055v2
|
2013-11-12
|
Damping filter method for obtaining spatially localized solutions
|
Spatially localized structures are key components of turbulence and other
spatio-temporally chaotic systems. From a dynamical systems viewpoint, it is
desirable to obtain corresponding exact solutions, though their existence is
not guaranteed. A damping filter method is introduced to obtain variously
localized solutions, and adopted into two typical cases. This method introduces
a spatially selective damping effect to make a good guess at the exact
solution, and we can obtain an exact solution through a continuation with the
damping amplitude. First target is a steady solution to Swift-Hohenberg
equation, which is a representative of bi-stable systems in which localized
solutions coexist, and a model for span-wisely localized cases. Not only
solutions belonging to the well-known snaking branches but also those belonging
to an isolated branch known as "isolas" are found with a continuation paths
between them in phase space extended with the damping amplitude. This indicates
that this spatially selective excitation mechanism has an advantage in
searching spatially localized solutions. Second target is a spatially localized
traveling-wave solution to Kuramoto-Sivashinsky equation, which is a model for
stream-wisely localized cases. Since the spatially selective damping effect
breaks Galilean and translational invariances, the propagation velocity cannot
be determined uniquely while the damping is active, and a singularity arises
when these invariances are recovered. We demonstrate that this singularity can
be avoided by imposing a simple condition, and a localized traveling-wave
solution is obtained with a specific propagation speed.
|
1311.2792v2
|
2014-09-19
|
Highly confined low-loss plasmons in graphene-boron nitride heterostructures
|
Graphene plasmons were predicted to possess ultra-strong field confinement
and very low damping at the same time, enabling new classes of devices for deep
subwavelength metamaterials, single-photon nonlinearities, extraordinarily
strong light-matter interactions and nano-optoelectronic switches. While all of
these great prospects require low damping, thus far strong plasmon damping was
observed, with both impurity scattering and many-body effects in graphene
proposed as possible explanations. With the advent of van der Waals
heterostructures, new methods have been developed to integrate graphene with
other atomically flat materials. In this letter we exploit near-field
microscopy to image propagating plasmons in high quality graphene encapsulated
between two films of hexagonal boron nitride (h-BN). We determine dispersion
and particularly plasmon damping in real space. We find unprecedented low
plasmon damping combined with strong field confinement, and identify the main
damping channels as intrinsic thermal phonons in the graphene and dielectric
losses in the h-BN. The observation and in-depth understanding of low plasmon
damping is the key for the development of graphene nano-photonic and
nano-optoelectronic devices.
|
1409.5674v1
|
2015-09-02
|
Energy Dependence of Synchrotron X-Ray Rims in Tycho's Supernova Remnant
|
Several young supernova remnants exhibit thin X-ray bright rims of
synchrotron radiation at their forward shocks. Thin rims require strong
magnetic field amplification beyond simple shock compression if rim widths are
only limited by electron energy losses. But, magnetic field damping behind the
shock could produce similarly thin rims with less extreme field amplification.
Variation of rim width with energy may thus discriminate between competing
influences on rim widths. We measured rim widths around Tycho's supernova
remnant in 5 energy bands using an archival 750 ks Chandra observation. Rims
narrow with increasing energy and are well described by either loss-limited or
damped scenarios, so X-ray rim width-energy dependence does not uniquely
specify a model. But, radio counterparts to thin rims are not loss-limited and
better reflect magnetic field structure. Joint radio and X-ray modeling favors
magnetic damping in Tycho's SNR with damping lengths ~1--5% of remnant radius
and magnetic field strengths ~50--400 $\mu$G assuming Bohm diffusion. X-ray rim
widths are ~1% of remnant radius, somewhat smaller than inferred damping
lengths. Electron energy losses are important in all models of X-ray rims,
suggesting that the distinction between loss-limited and damped models is
blurred in soft X-rays. All loss-limited and damping models require magnetic
fields $\gtrsim$ 20 $\mu$G, affirming the necessity of magnetic field
amplification beyond simple compression.
|
1509.00877v1
|
2016-02-02
|
Forward Modelling of Propagating Slow Waves in Coronal Loops and Their Frequency-Dependent Damping
|
Propagating slow waves in coronal loops exhibit a damping which depends upon
the frequency of the waves. In this study we aim to investigate the
relationship of the damping length (L$_d$) with the frequency of the
propagating wave. We present a 3-D coronal loop model with uniform density and
temperature and investigate the frequency dependent damping mechanism for the
four chosen wave periods. We include the thermal conduction to damp the waves
as they propagate through the loop. The numerical model output has been forward
modelled to generate synthetic images of SDO/AIA 171 \r{A} and 193 \r{A}
channels. The use of forward modelling, which incorporates the atomic emission
properties into the intensity images, allows us to directly compare our results
with the real observations. The results show that the damping lengths vary
linearly with the periods. We also measure the contributions of the emission
properties on the damping lengths by using density values from the simulation.
In addition to that} we have also calculated the theoretical dependence of
L$_d$ with wave periods and showed that it is consistent with the results we
obtained from the numerical modelling and earlier observations.
|
1602.00787v1
|
2016-05-11
|
Damping of prominence longitudinal oscillations due to mass accretion
|
We study the damping of longitudinal oscillations of a prominence thread
caused by the mass accretion. In this model we considered a thin curved
magnetic tube filled with the plasma. The parts of the tube at the two sides of
the thread are filled with hot rarefied plasma. We assume that there are flows
of rarefied plasma toward the thread caused by the plasma evaporation at the
magnetic tube footpoints. Our main assumption is that the hot plasma is
instantaneously accommodated by the thread when it arrives at the thread, and
its temperature and density become equal to those of the thread. Then we derive
the system of ordinary differential equations describing the thread dynamics.
We consider linear and nonlinear oscillation. The nonlinearity reduces the
damping time, however this reduction is small. The damping time is inversely
proportional to the accretion rate. We also obtain that the oscillation periods
decrease with time. However even for the largest initial oscillation amplitude
considered in our article the period reduction does not exceed 20%. We conclude
that the mass accretion can damp the motion of the threads rapidly. Thus, this
mechanism can explain the observed strong damping of large-amplitude
longitudinal oscillations. In addition, the damping time can be used to
determine the mass accretion rate and indirectly the coronal heating.
|
1605.03376v1
|
2016-11-17
|
Inductive detection of field-like and damping-like AC inverse spin-orbit torques in ferromagnet/normal metal bilayers
|
Functional spintronic devices rely on spin-charge interconversion effects,
such as the reciprocal processes of electric field-driven spin torque and
magnetization dynamics-driven spin and charge flow. Both damping-like and
field-like spin-orbit torques have been observed in the forward process of
current-driven spin torque and damping-like inverse spin-orbit torque has been
well-studied via spin pumping into heavy metal layers. Here we demonstrate that
established microwave transmission spectroscopy of ferromagnet/normal metal
bilayers under ferromagnetic resonance can be used to inductively detect the AC
charge currents driven by the inverse spin-charge conversion processes. This
technique relies on vector network analyzer ferromagnetic resonance (VNA-FMR)
measurements. We show that in addition to the commonly-extracted spectroscopic
information, VNA-FMR measurements can be used to quantify the magnitude and
phase of all AC charge currents in the sample, including those due to spin
pumping and spin-charge conversion. Our findings reveal that
Ni$_{80}$Fe$_{20}$/Pt bilayers exhibit both damping-like and field-like inverse
spin-orbit torques. While the magnitudes of both the damping-like and
field-like inverse spin-orbit torque are of comparable scale to prior reported
values for similar material systems, we observed a significant dependence of
the damping-like magnitude on the order of deposition. This suggests interface
quality plays an important role in the overall strength of the damping-like
spin-to-charge conversion.
|
1611.05798v2
|
2017-01-04
|
Controlling plasmon modes and damping in buckled two-dimensional material open systems
|
Full ranges of both hybrid plasmon-mode dispersions and their damping are
studied systematically by our recently developed mean-field theory in open
systems involving a conducting substrate and a two-dimensional (2D) material
with a buckled honeycomb lattice, such as silicene, germanene, and a group
\rom{4} dichalcogenide as well. In this hybrid system, the single plasmon mode
for a free-standing 2D layer is split into one acoustic-like and one
optical-like mode, leading to a dramatic change in the damping of plasmon
modes. In comparison with gapped graphene, critical features associated with
plasmon modes and damping in silicene and molybdenum disulfide are found with
various spin-orbit and lattice asymmetry energy bandgaps, doping types and
levels, and coupling strengths between 2D materials and the conducting
substrate. The obtained damping dependence on both spin and valley degrees of
freedom is expected to facilitate measuring the open-system dielectric property
and the spin-orbit coupling strength of individual 2D materials. The unique
linear dispersion of the acoustic-like plasmon mode introduces additional
damping from the intraband particle-hole modes which is absent for a
free-standing 2D material layer, and the use of molybdenum disulfide with a
large bandgap simultaneously suppresses the strong damping from the interband
particle-hole modes.
|
1701.01084v1
|
2017-04-05
|
Stimulated Brillouin scattering behaviors in different species ignition hohlraum plasmas in high-temperature and high-density region
|
The presence of multiple ion species can add additional branches to the IAW
dispersion relation and change the Landau damping significantly. Different IAW
modes excited by stimulated Brillouin scattering (SBS) and different SBS
behaviors in several typical ignition hohlraum plasmas in the high-temperature
and high-density region have been researched by Vlasov-Maxwell simulation. The
slow mode in HeH or CH plasmas is the least damped mode and will be excited in
SBS, while the fast mode in AuB plasmas is the least damped mode and will be
excited in SBS. Due to strong Landau damping, the SBS in H or HeH plasmas is
strong convective instability, while the SBS in AuB plasmas is absolute
instability due to the weak Landau damping. However, although the SBS in CH
plasmas is weak convective instability in the linear theory, the SBS will
transform into absolute instability due to decreasing linear Landau damping by
particles trapping. These results give a detail research of the IAW modes
excitation and the properties of SBS in different species plasmas, thus
providing the possibility of controlling SBS by increasing the linear Landau
damping of the IAW by changing ion species.
|
1704.02317v1
|
2017-06-29
|
Resonant Absorption of Axisymmetric Modes in Twisted Magnetic Flux Tubes
|
It has been shown recently that magnetic twist and axisymmetric MHD modes are
ubiquitous in the solar atmosphere and therefore, the study of resonant
absorption for these modes have become a pressing issue as it can have
important consequences for heating magnetic flux tubes in the solar atmosphere
and the observed damping. In this investigation, for the first time, we
calculate the damping rate for axisymmetric MHD waves in weakly twisted
magnetic flux tubes. Our aim is to investigate the impact of resonant damping
of these modes for solar atmospheric conditions. This analytical study is based
on an idealized configuration of a straight magnetic flux tube with a weak
magnetic twist inside as well as outside the tube. By implementing the
conservation laws derived by \cite{Sakurai:1991aa} and the analytic solutions
for weakly twisted flux tubes obtained recently by \cite{Giagkiozis:2015apj},
we derive a dispersion relation for resonantly damped axisymmetric modes in the
spectrum of the Alfv\'{e}n continuum. We also obtain an insightful analytical
expression for the damping rate in the long wavelength limit. Furthermore, it
shown that both the longitudinal magnetic field and the density, which are
allowed to vary continuously in the inhomogeneous layer, have a significant
impact on the damping time. Given the conditions in the solar atmosphere,
resonantly damped axisymmetric modes are highly likely to be ubiquitous and
play an important role in energy dissipation.
We also suggest that given the character of these waves, it is likely that
they have already been observed in the guise of Alfv\'{e}n waves.
|
1706.09665v1
|
2017-08-16
|
Damping of an oscillating scalar field indirectly coupled to a thermal bath
|
The damping process of a homogeneous oscillating scalar field that indirectly
interacts with a thermal bath through a mediator field is investigated over a
wide range of model parameters. We consider two types of mediator fields, those
that can decay to the thermal bath and those that are individually stable but
pair annihilate. The former case has been extensively studied in the literature
by treating the damping as a local effect after integrating out the assumed
close-to-equilibrium mediator field. The same approach does not apply if the
mediator field is stable and freezes out of equilibrium. To account for the
latter case, we adopt a non-local description of damping that is only
meaningful when we consider full half-oscillations of the field being damped.
The damping rates of the oscillating scalar field and the corresponding heating
rate of the thermal bath in all bulk parameter regions are calculated in both
cases, corroborating previous results in the direct decay case. Using the
obtained results, the time it takes for the amplitude of the scalar field to be
substantially damped is estimated.
|
1708.04865v2
|
2018-09-14
|
Continuous and discrete damping reduction for systems with quadratic interaction
|
We study the connection between Lagrangian and Hamiltonian descriptions of
closed/open dynamics, for a collection of particles with quadratic interaction
(closed system) and a sub-collection of particles with linear damping (open
system). We consider both continuous and discrete versions of mechanics. We
define the Damping Reduction as the mapping from the equations of motion of the
closed system to those of the open one. As variational instruments for the
obtention of these equations we use the Hamilton's principle (closed dynamics)
and Lagrange-d'Alembert principle (open dynamics). We establish the
commutativity of the branches Legendre transform + Damping Reduction and
Damping Reduction+Legendre transform, where the Legendre transform is the usual
mapping between Lagrangian and Hamiltonian mechanics. At a discrete level, this
commutativity provides interesting insight about the resulting integrators.
More concretely, Discrete Damping Reduction yields particular numerical schemes
for linearly damped systems which are not symplectic anymore, but preserve some
of the features of their symplectic counterparts from which they proceed (for
instance the semi-implicitness in some cases). The theoretical results are
illustrated with the examples of the heat bath and transmission lines. In the
latter case some simulations are displayed, showing a better performance of the
integrators with variational origin.
|
1809.05532v1
|
2020-05-31
|
Optimal decay rates of the compressible Euler equations with time-dependent damping in $\mathbb R^n$: (II) over-damping case
|
This paper is concerned with the multi-dimensional compressible Euler
equations with time-dependent over-damping of the form
$-\frac{\mu}{(1+t)^\lambda}\rho\boldsymbol u$ in $\mathbb R^n$, where $n\ge2$,
$\mu>0$, and $\lambda\in[-1,0)$. This continues our previous work dealing with
the under-damping case for $\lambda\in[0,1)$. We show the optimal decay
estimates of the solutions such that for $\lambda\in(-1,0)$ and $n\ge2$,
$\|\rho-1\|_{L^2(\mathbb R^n)}\approx(1+t)^{-\frac{1+\lambda}{4}n}$ and
$\|\boldsymbol u\|_{L^2(\mathbb R^n)}\approx
(1+t)^{-\frac{1+\lambda}{4}n-\frac{1-\lambda}{2}}$, which indicates that a
stronger damping gives rise to solutions decaying optimally slower. For the
critical case of $\lambda=-1$, we prove the optimal logarithmical decay of the
perturbation of density for the damped Euler equations such that
$\|\rho-1\|_{L^2(\mathbb R^n)}\approx |\ln(e+t)|^{-\frac{n}{4}}$ and
$\|\boldsymbol u\|_{L^2(\mathbb R^n)}\approx
(1+t)^{-1}\cdot|\ln(e+t)|^{-\frac{n}{4}-\frac{1}{2}}$ for $n\ge7$. The
over-damping effect reduces the decay rates of the solutions to be slow, which
causes us some technical difficulty in obtaining the optimal decay rates by the
Fourier analysis method and the Green function method. Here, we propose a new
idea to overcome such a difficulty by artfully combining the Green function
method and the time-weighted energy method.
|
2006.00403v1
|
2020-07-07
|
Nonlinear viscoelastic isolation for seismic vibration mitigation
|
The aim of this paper is to assess the effectiveness of nonlinear
viscoelastic damping in controlling base-excited vibrations. Specifically, the
focus is on investigating the robustness of the nonlinear base isolation
performance in controlling the system response due to a wide set of possible
excitation spectra. The dynamic model is derived to study a simple structure
whose base isolation is provided via a Rubber-Layer Roller Bearing (RLRB)
(rigid cylinders rolling on rigid plates with highly damping rubber coatings)
equipped with a nonlinear cubic spring, thus presenting both nonlinear damping
and stiffness. We found that, under periodic loading, due to the non-monotonic
bell-shaped viscoelastic damping arising from the viscoelastic rolling
contacts, different dynamic regimes occur mostly depending on whether the
damping peak is overcome or not. Interestingly, in the former case, poorly
damped self-excited vibrations may be triggered by the steep damping decrease.
Moreover, in order to investigate the robustness of the isolation performance,
we consider a set of real seismic excitations, showing that tuned nonlinear
RLRB provide loads isolation in a wider range of excitation spectra, compared
to generic linear isolators. This is peculiarly suited for applications (such
as seismic and failure engineering) in which the specific excitation spectrum
is unknown a priori, and blind design on statistical data has to be employed.
|
2007.04378v1
|
2021-01-20
|
Damped perturbations in stellar systems: Genuine modes and Landau-damped waves
|
This research was stimulated by the recent studies of damping solutions in
dynamically stable spherical stellar systems. Using the simplest model of the
homogeneous stellar medium, we discuss nontrivial features of stellar systems.
Taking them into account will make it possible to correctly interpret the
results obtained earlier and will help to set up decisive numerical experiments
in the future. In particular, we compare the initial value problem versus the
eigenvalue problem. It turns out that in the unstable regime, the Landau-damped
waves can be represented as a superposition of van Kampen modes {\it plus} a
discrete damped mode, usually ignored in the stability study. This mode is a
solution complex conjugate to the unstable Jeans mode. In contrast, the
Landau-damped waves are not genuine modes: in modes, eigenfunctions depend on
time as $\exp (-{\rm i} \omega t)$, while the waves do not have eigenfunctions
on the real $v$-axis at all. However, `eigenfunctions' on the complex
$v$-contours do exist. Deviations from the Landau damping are common and can be
due to singularities or cut-off of the initial perturbation above some fixed
value in the velocity space.
|
2101.08287v2
|
2021-03-10
|
Dynamical Pose Estimation
|
We study the problem of aligning two sets of 3D geometric primitives given
known correspondences. Our first contribution is to show that this primitive
alignment framework unifies five perception problems including point cloud
registration, primitive (mesh) registration, category-level 3D registration,
absolution pose estimation (APE), and category-level APE. Our second
contribution is to propose DynAMical Pose estimation (DAMP), the first general
and practical algorithm to solve primitive alignment problem by simulating
rigid body dynamics arising from virtual springs and damping, where the springs
span the shortest distances between corresponding primitives. We evaluate DAMP
in simulated and real datasets across all five problems, and demonstrate (i)
DAMP always converges to the globally optimal solution in the first three
problems with 3D-3D correspondences; (ii) although DAMP sometimes converges to
suboptimal solutions in the last two problems with 2D-3D correspondences, using
a scheme for escaping local minima, DAMP always succeeds. Our third
contribution is to demystify the surprising empirical performance of DAMP and
formally prove a global convergence result in the case of point cloud
registration by charactering local stability of the equilibrium points of the
underlying dynamical system.
|
2103.06182v3
|
2021-04-13
|
Apparent nonlinear damping triggered by quantum fluctuations
|
Nonlinear damping, the change in damping rate with the amplitude of
oscillations plays an important role in many electrical, mechanical and even
biological oscillators. In novel technologies such as carbon nanotubes,
graphene membranes or superconducting resonators, the origin of nonlinear
damping is sometimes unclear. This presents a problem, as the damping rate is a
key figure of merit in the application of these systems to extremely precise
sensors or quantum computers. Through measurements of a superconducting
resonator, we show that from the interplay of quantum fluctuations and the
nonlinearity of a Josephson junction emerges a power-dependence in the
resonator response which closely resembles nonlinear damping. The phenomenon
can be understood and visualized through the flow of quasi-probability in phase
space where it reveals itself as dephasing. Crucially, the effect is not
restricted to superconducting circuits: we expect that quantum fluctuations or
other sources of noise give rise to apparent nonlinear damping in systems with
a similar conservative nonlinearity, such as nano-mechanical oscillators or
even macroscopic systems.
|
2104.06464v2
|
2023-07-26
|
Improving frequency response with synthetic damping available from fleets of distributed energy resources
|
With the increasing use of renewable generation in power systems, responsive
resources will be necessary to support primary frequency control in future
low-inertia/under-damped power systems. Flexible loads can provide
fast-frequency response services if coordinated effectively. However, practical
implementations of such synthetic damping services require both effective local
sensing and control at the device level and an ability to accurately estimate
online and predict the available synthetic damping from a fleet. In addition,
the inherent trade-off between a fleet being available for fast frequency
response while providing other ancillary services needs to be characterized. In
this context, the manuscript presents a novel, fully decentralized,
packet-based controller for diverse flexible loads that dynamically prioritizes
and interrupts loads to engender synthetic damping suitable for primary
frequency control. Moreover, the packet-based control methodology is shown to
accurately characterize the available synthetic damping in real-time, which is
useful to aggregators and system operators. Furthermore, spectral analysis of
historical frequency regulation data is used to produce a probabilistic bound
on the expected available synthetic damping for primary frequency control from
a fleet and the trade-off from concurrently providing secondary frequency
control services. Finally, numerical simulation on IEEE test networks
demonstrates the effectiveness of the proposed methodology.
|
2307.14498v1
|
2023-12-11
|
Possible Contamination of the Intergalactic Medium Damping Wing in ULAS J1342+0928 by Proximate Damped Ly$α$ Absorption
|
The red damping wing from neutral hydrogen in the intergalactic medium is a
smoking-gun signal of ongoing reionization. One potential contaminant of the
intergalactic damping wing signal is dense gas associated with foreground
galaxies, which can give rise to proximate damped Ly$\alpha$ absorbers. The
Ly$\alpha$ imprint of such absorbers on background quasars is indistinguishable
from the intergalactic medium within the uncertainty of the intrinsic quasar
continuum, and their abundance at $z\gtrsim7$ is unknown. Here we show that the
complex of low-ionization metal absorption systems recently discovered by deep
JWST/NIRSpec observations in the foreground of the $z=7.54$ quasar
ULAS~J1342$+$0928 can potentially reproduce the quasar's spectral profile close
to rest-frame Ly$\alpha$ without invoking a substantial contribution from the
intergalactic medium, but only if the absorbing gas is extremely metal-poor
($[{\rm O}/{\rm H}]\sim-3.5$). Such a low oxygen abundance has never been
observed in a damped Ly$\alpha$ absorber at any redshift, but this possibility
still complicates the interpretation of the spectrum. Our analysis highlights
the need for deep spectroscopy of high-redshift quasars with JWST or ELT to
"purify" damping wing quasar samples, an exercise which is impossible for much
fainter objects like galaxies.
|
2312.06747v1
|
2024-02-13
|
Forecasts for Constraining Lorentz-violating Damping of Gravitational Waves from Compact Binary Inspirals
|
Violation of Lorentz symmetry can result in two distinct effects in the
propagation of the gravitational waves (GWs). One is a modified dispersion
relation and another is a frequency-dependent damping of GWs. While the former
has been extensively studied in the literature, in this paper we concentrate on
the frequency-dependent damping effect that arises from several specific
Lorentz-violating theories, such as spatial covariant gravities,
Ho\v{r}ava-Lifshitz gravities, etc. This Lorentz-violating damping effect
changes the damping rate of GWs at different frequencies and leads to an
amplitude correction to the GW waveform of compact binary inspiral systems.
With this modified waveform, we then use the Fisher information matrix to
investigate the prospects of constraining the Lorentz-violating damping effect
with GW observations. We consider both ground-based and space-based GW
detectors, including the advanced LIGO, Einstein Telescope, Cosmic Explorer
(CE), Taiji, TianQin, and LISA. Our results indicate that the ground-based
detectors in general give tighter constraints than those from the space-based
detectors. Among the considered three ground-based detectors, CE can give the
tightest constraints on the Lorentz-violating damping effect, which improves
the current constraint from LIGO-Virgo-KAGRA events by about 8 times.
|
2402.08240v2
|
2024-03-13
|
Thermal Hall effect incorporating magnon damping in localized spin systems
|
We propose a theory for thermal Hall transport mediated by magnons to address
the impact of their damping resulting from magnon-magnon interactions in
insulating magnets. This phenomenon is anticipated to be particularly
significant in systems characterized by strong quantum fluctuations,
exemplified by spin-1/2 systems. Employing a nonlinear flavor-wave theory, we
analyze a general model for localized electron systems and develop a
formulation for thermal conductivity based on a perturbation theory, utilizing
bosonic Green's functions with a nonzero self-energy. We derive the expression
of the thermal Hall conductivity incorporating magnon damping. To demonstrate
the applicability of the obtained representation, we adopt it to two $S=1/2$
quantum spin models on a honeycomb lattice. In calculations for these systems,
we make use of the self-consistent imaginary Dyson equation approach at finite
temperatures for evaluating the magnon damping rate. In both systems, the
thermal Hall conductivity is diminished due to the introduction of magnon
damping over a wide temperature range. This effect arises due to the smearing
of magnon spectra with nonzero Berry curvatures. We also discuss the relation
to the damping of chiral edge modes of magnons. Our formulation can be applied
to various localized electron systems as we begin with a general Hamiltonian
for these systems. Our findings shed light on a new aspect of topological
magnonics emergent from many-body effects and will stimulate further
investigations on the impact of magnon damping on topological phenomena.
|
2403.08478v1
|
2024-04-02
|
A recipe for eccentricity and inclination damping for partial gap opening planets in 3D disks
|
In a previous paper we showed that, like the migration speed, the
eccentricity damping efficiency is modulated linearly by the depth of the
partial gap a planet carves in the disk surface density profile, resulting in
less efficient $e$-damping compared to the prescription commonly used in
population synthesis works. Here, we extend our analysis to 3D, refining our
$e$-damping formula and studying how the inclination damping efficiency is also
affected. We perform high resolution 3D locally isothermal hydrodynamical
simulations of planets with varying masses embedded in disks with varying
aspect ratios and viscosities. We extract the gap profile and orbital damping
timescales for fixed eccentricities and inclinations up to the disk scale
height. The limit in gap depths below which vortices appear, in the
low-viscosity case, happens roughly at the transition between classical type-I
and type-II migration regimes. The orbital damping timescales can be described
by two linear trends with a break around gap depths $\sim80\%$ and with slopes
and intercepts depending on the eccentricity and inclination. These trends are
understood on physical grounds and are reproduced by simple fitting formulas
whose error is within the typically uncertainty of type-I torque formulas.
Thus, our recipes for the gap depth and orbital damping efficiencies yield a
simple description for planet-disk interactions to use in N-body codes in the
case of partial gap opening planets that is consistent with high-resolution 3D
hydro-simulations. Finally, we show examples of how our novel orbital damping
prescription can affect the outcome of population synthesis experiments.
|
2404.02247v1
|
2009-08-21
|
Surface Alfven Wave Damping in a 3D Simulation of the Solar Wind
|
Here we investigate the contribution of surface Alfven wave damping to the
heating of the solar wind in minima conditions. These waves are present in
regions of strong inhomogeneities in density or magnetic field (e. g., the
border between open and closed magnetic field lines). Using a 3-dimensional
Magnetohydrodynamics (MHD) model, we calculate the surface Alfven wave damping
contribution between 1-4 solar radii, the region of interest for both
acceleration and coronal heating. We consider waves with frequencies lower than
those that are damped in the chromosphere and on the order of those dominating
the heliosphere. In the region between open and closed field lines, within a
few solar radii of the surface, no other major source of damping has been
suggested for the low frequency waves we consider here. This work is the first
to study surface Alfven waves in a 3D environment without assuming a priori a
geometry of field lines or magnetic and density profiles. We determine that
waves with frequencies >2.8x10^-4 Hz are damped between 1-4 solar radii. In
quiet sun regions, surface Alfven waves are damped at further distances
compared to active regions, thus carrying additional wave energy into the
corona. We compare the surface Alfven wave contribution to the heating by a
variable polytropic index and find that it an order of magnitude larger than
needed for quiet sun regions. For active regions the contribution to the
heating is twenty percent. As it has been argued that a variable gamma acts as
turbulence, our results indicate that surface Alfven wave damping is comparable
to turbulence in the lower corona. This damping mechanism should be included
self consistently as an energy driver for the wind in global MHD models.
|
0908.3146v1
|
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