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2022-03-15 | Search for gamma-ray line signals around the black hole at the galactic center with DAMPE observation | The adiabatic growth of a black hole (BH) may enhance the dark matter (DM)
density surrounding it, causing a spike in the DM density profile. The spike
around the supermassive BH at the center of the Milky Way may lead to a
dramatic enhancement of the gamma-ray flux of DM annihilation from the galactic
center (GC). In this work, we analyze the gamma-ray data of the innermost
region (i.e., the inner 1$^\circ$) of the GC to search for potential line-like
signals from the BH spike. Such line-like signals could be generated in the
process of DM particles annihilating into double photons. We adopt the
gamma-ray data from the Dark Matter Particle Explorer (DAMPE). Although the
DAMPE has a much smaller effective area than the Fermi-LAT, the gamma-ray line
search can benefit from its unprecedented high energy resolution. No
significant line-like signals are found in our analysis. We derive upper limits
on the cross section of the annihilation based on this non-detection. We find
that despite the DAMPE's small effective area for photon detection, we can
still place strong constraints on the cross section ($\left<\sigma
v\right>\lesssim10^{-27}\,{\rm cm^3\,s^{-1}}$) in the spike scenario due to the
very bright model-expected flux from the spike. Our results indicate that
either DM does not annihilate primarily through the $\gamma\gamma$ channel in
the mass range we considered or no sharp density spike is present at the GC. | 2203.08078v1 |
2022-03-15 | Optimal Damping with Hierarchical Adaptive Quadrature for Efficient Fourier Pricing of Multi-Asset Options in Lévy Models | Efficiently pricing multi-asset options is a challenging problem in
quantitative finance. When the characteristic function is available,
Fourier-based methods are competitive compared to alternative techniques
because the integrand in the frequency space often has a higher regularity than
that in the physical space. However, when designing a numerical quadrature
method for most Fourier pricing approaches, two key aspects affecting the
numerical complexity should be carefully considered: (i) the choice of damping
parameters that ensure integrability and control the regularity class of the
integrand and (ii) the effective treatment of high dimensionality. We propose
an efficient numerical method for pricing European multi-asset options based on
two complementary ideas to address these challenges. First, we smooth the
Fourier integrand via an optimized choice of the damping parameters based on a
proposed optimization rule. Second, we employ sparsification and
dimension-adaptivity techniques to accelerate the convergence of the quadrature
in high dimensions. The extensive numerical study on basket and rainbow options
under the multivariate geometric Brownian motion and some L\'evy models
demonstrates the advantages of adaptivity and the damping rule on the numerical
complexity of quadrature methods. Moreover, for the tested two-asset examples,
the proposed approach outperforms the COS method in terms of computational
time. Finally, we show significant speed-up compared to the Monte Carlo method
for up to six dimensions. | 2203.08196v4 |
2022-03-25 | Nonlinear damped spatially periodic breathers and the emergence of soliton-like rogue waves | The spatially periodic breather solutions (SPBs) of the nonlinear
Schr\"odinger equation, prominent in modeling rogue waves, are unstable. In
this paper we numerically investigate the effects of nonlinear dissipation and
higher order nonlinearities on the routes to stability of the SPBs in the
framework of the nonlinear damped higher order nonlinear Schr\"odinger
(NLD-HONLS) equation. The initial data used in the experiments are generated by
evaluating exact SPB solutions at time $T_0$. The number of instabilities of
the background Stokes wave and the damping strength are varied. The Floquet
spectral theory of the NLS equation is used to interpret and provide a
characterization of the perturbed dynamics in terms of nearby solutions of the
NLS equation. Significantly, as $T_0$ is varied, tiny bands of complex spectrum
are observed to pinch off in the Floquet decomposition of the NLD-HONLS data,
reflecting the breakup of the SPB into a waveform that is close to either a one
or two "soliton-like" structure. For wide ranges of $T_0$, i.e. for solutions
initialized in the early to middle stage of the development of the MI, all
rogue waves are observed to occur when the spectrum is close to a one or two
soliton-like state. When the solutions are initialized as the MI is saturating,
rogue waves also can occur after the spectrum has left a soliton-like state.
Other novel features arise due to nonlinear damping: enhanced asymmetry, two
timescales in the evolution of the spectrum and a delay in the growth of
instabilities due to frequency downshifting. | 2203.13488v2 |
2022-03-25 | Investigating the effect of noise channels on the quality of unitary t-designs | Unitary t-designs have a wide variety of applications in quantum information
theory, such as quantum data encryption and randomised benchmarking. However,
experimental realisations of t-designs are subject to noise. Here we
investigate the effect of noise channels on the quality of single-qubit
t-designs. The noise channels we study are bit flips, phase flips, bit and
phase flips, phase damping, amplitude damping, and depolarising noise. We
consider two noise models: the first has noise applied before the t-design
unitary operations, while the second has noise applied after the unitary
operations. We show that the single-qubit 1-design is affected only by
amplitude damping, while numeric results obtained for the 2-, 3-, 4-, and
5-designs suggest that a 2t-design is significantly more sensitive to noise
than a (2t-1)-design and that, with the exception of amplitude damping, a
(2t+1)-design is as sensitive to noise as a 2t-design. Numeric results also
reveal substantial variations in sensitivity to noise throughout the Bloch
sphere. In particular, t-designs appear to be most sensitive to noise when
acting on pure states and least sensitive to noise for the maximally mixed
state. For depolarising noise, we show that our two noise models are
equivalent, and for the other noise channels, numeric results obtained for the
model where noise is applied after the unitaries reflect the transformation of
the noise channel into a depolarising channel, an effect exploited in
randomised benchmarking with 2-designs. | 2203.13771v2 |
2022-04-25 | Geometrical aspects of contact mechanical systems and field theories | Many important theories in modern physics can be stated using differential
geometry. Symplectic geometry is the natural framework to deal with autonomous
Hamiltonian mechanics. This admits several generalizations for nonautonomous
systems, both regular and singular. Some of these extensions are the subject of
this thesis.
Recently there has been a growing interest in studying dissipative mechanical
systems from a geometric perspective using contact geometry. In this thesis we
review what has been done in this topic and go deeper, studying symmetries and
dissipated quantities of contact systems, and developing the Skinner-Rusk
formalism for these systems.
With regard to classical field theory, we introduce the notion of
k-precosymplectic manifold and use it to give a geometric description of
singular nonautonomous field theories. We also devise a constraint algorithm
for these systems.
Field theories with damping are described through a modification of the De
Donder-Weyl Hamiltonian field theory. This is achieved by combining contact
geometry and k-symplectic structures, resulting in the k-contact formalism. We
introduce two notions of dissipation laws, generalizing the concept of
dissipated quantity. These developments are also applied to Lagrangian field
theory. The Skinner-Rusk formulation for k-contact systems is described in
detail and we show how to recover the Lagrangian and Hamiltonian formalisms
from it.
Throughout the thesis we present several examples in mechanics and field
theory. The most remarkable mechanical examples are the damped harmonic
oscillator, the motion in a gravitational field with friction, the parachute
equation and the damped simple pendulum. In field theory, we study the damped
vibrating string, the Burgers' equation, the Klein-Gordon equation and its
relation with the telegrapher's equation, and the Maxwell's equations with
dissipation. | 2204.11537v1 |
2022-06-20 | Swinging a playground swing: torque controls for inducing sustained oscillations | Models of a playground swing have been studied since the 1960s. However, in
most of them, the position of the swinger is controlled directly. This
simplifies the problem but hides the mechanics of torques applied to keep the
swing moving in a regular pattern. This article studies these mechanics. Two
models of a swing with torques as controls that we consider are identical to
popular models of modern robotics: the Acrobot and reaction wheel pendulum.
However, the control task of sustaining the swing's regular oscillations by a
static feedback control is new and challenging, especially when damping in the
joint connecting the swing to the frame is considered. We develop two types of
controls to accomplish this task. One works for small damping and is based on
linearizing the undamped system by a suitable preliminary feedback control. The
other works for large damping. In the steady state, the resulting closed-loop
system describes a harmonically driven damped pendulum (a simple system known
for its complex behavior), including chaotic motion for some parameter values.
To address such complexities, we build free parameters into the controls, then
adjust them based on simulations to avoid chaos and achieve regular
oscillations that are seen on playgrounds. | 2206.09579v1 |
2022-07-01 | Frequency beating and damping of breathing oscillations of a harmonically trapped one-dimensional quasicondensate | We study the breathing (monopole) oscillations and their damping in a
harmonically trapped one-dimensional (1D) Bose gas in the quasicondensate
regime using a finite-temperature classical field approach. By characterising
the oscillations via the dynamics of the density profile's rms width over long
time, we find that the rms width displays beating of two distinct frequencies.
This means that 1D Bose gas oscillates not at a single breathing mode
frequency, as found in previous studies, but as a superposition of two distinct
breathing modes, one oscillating at frequency close to $\simeq\!\sqrt{3}\omega$
and the other at $\simeq\!2\omega$, where $\omega$ is the trap frequency. The
breathing mode at $\sim\!\sqrt{3}\omega$ dominates the beating at lower
temperatures, deep in the quasicondensate regime, and can be attributed to the
oscillations of the bulk of the density distribution comprised of particles
populating low-energy, highly-occupied states. The breathing mode at
$\simeq\!2\omega$, on the other hand, dominates the beating at higher
temperatures, close to the nearly ideal, degenerate Bose gas regime, and is
attributed to the oscillations of the tails of the density distribution
comprised of thermal particles in higher energy states. The two breathing modes
have distinct damping rates, with the damping rate of the bulk component being
approximately four times larger than that of the tails component. | 2207.00209v2 |
2022-07-29 | Coordinated control in multi-terminal VSC-HVDC systems to improve transient stability: Impact on electromechanical-oscillation damping | Multi-terminal high-voltage Direct Current technology based on Voltage-Source
Converter stations (VSC-MTDC) is expected to be one of the most important
contributors to the future of electric power systems. In fact, among other
features, it has already been shown how this technology can contribute to
improve transient stability in power systems by the use of supplementary
controllers. Along this line, this paper will investigate in detail how these
supplementary controllers may affect electromechanical oscillations, by means
of small-signal stability analysis. The paper analyses two control strategies
based on the modulation of active-power injections (P-WAF) and reactive-power
injections (Q-WAF) in the VSC stations. Both control strategies use global
signals of the frequencies of the VSC-MTDC system and they presented
significant improvements on transient stability. The paper will provide
guidelines for the design of these type of controllers to improve both, large-
and small-disturbance angle stability. Small-signal stability techniques (in
Matlab) will be used to assess electromechanical-oscillation damping, while
non-linear time domain simulation (in PSS/E) will be used to confirm the
results. Results will be illustrated in Nordic32A test system with an embedded
VSC-MTDC system. The paper analyses the impact of the controller gains and
communication latency on electromechanical-oscillation damping. The main
conclusion of the paper is that transient-stability-tailored supplementary
controllers in VSC-MTDC systems can be tuned to damp inter-area oscillations
too, maintaining their effectiveness for transient-stability improvement. | 2208.00083v1 |
2022-08-04 | Thermoelastic Damping in MEMS Gyroscopes at High Frequencies | Microelectromechanical systems (MEMS) gyroscopes are widely used, e.g. in
modern automotive and consumer applications, and require signal stability and
accuracy in rather harsh environmental conditions. In many use cases, device
reliability must be guaranteed under large external loads at high frequencies.
The sensitivity of the sensor to such external loads depends strongly on the
damping, or rather quality factor, of the high frequency mechanical modes of
the structure. In this paper, we investigate the influence of thermoelastic
damping on several high frequency modes by comparing finite element simulations
with measurements of the quality factor in an application-relevant temperature
range. We measure the quality factors over different temperatures in vacuum, to
extract the relevant thermoelastic material parameters of the polycrystalline
MEMS device. Our simulation results show a good agreement with the measured
quantities, therefore proving the applicability of our method for predictive
purposes in the MEMS design process. Overall, we are able to uniquely identify
the thermoelastic effects and show their significance for the damping of the
high frequency modes of an industrial MEMS gyroscope. Our approach is generic
and therefore easily applicable to any mechanical structure with many possible
applications in nano- and micromechanical systems. | 2208.02591v2 |
2022-08-02 | Motion of a parametrically driven damped coplanar double pendulum | We present the results of linear stability of a damped coplanar double
pendulum and its non-linear motion, when the point of suspension is vibrated
sinusoidally in the vertical direction with amplitude $a$ and frequency $\omega
$. A double pendulum has two pairs of Floquet multipliers, which have been
calculated for various driving parameters. We have considered the stability of
a double pendulum when it is in any of its possible stationary states: (i) both
pendulums are either vertically downward or upward and (ii) one pendulum is
downward, and the other is upward. The damping is considered to be
velocity-dependent, and the driving frequency is taken in a wide range. A
double pendulum excited from its stable state shows both periodic and chaotic
motion. The periodic motion about its pivot may be either oscillatory or
rotational. The periodic swings of a driven double pendulum may be either
harmonic or subharmonic for lower values of $a$. The limit cycles corresponding
to the normal mode oscillations of a double pendulum of two equal masses are
squeezed into a line in its configuration space. For unequal masses, the
pendulum shows multi-period swings for smaller values of $a$ and damping, while
chaotic swings or rotational motion at relatively higher values of $a$. The
parametric driving may lead to stabilization of a partially or fully inverted
double pendulum. | 2208.03292v2 |
2022-08-09 | Simultaneous measurements of unstable and stable Alfvén Eigenmodes in JET | In this paper, we report the novel experimental observation of both unstable
and stable Toroidicity-induced Alfv\'en Eigenmodes (TAEs) measured
simultaneously in a JET tokamak plasma. The three-ion-heating scheme
(D-DNBI-3He) is employed to accelerate deuterons to MeV energies, thereby
destabilizing TAEs with toroidal mode numbers n = 3-5, each decreasing in mode
amplitude. At the same time, the Alfv\'en Eigenmode Active Diagnostic
resonantly excites a stable n = 6 TAE with total normalized damping rate
$-\gamma/\omega_0 \approx$ 1%-4%. Hybrid kinetic-MHD modeling with codes NOVA-K
and MEGA both find eigenmodes with similar frequencies, mode structures, and
radial locations as in experiment. NOVA-K demonstrates good agreement with the
n = 3, 4, and 6 TAEs, matching the damping rate of the n = 6 mode within
uncertainties and identifying radiative damping as the dominant contribution.
Improved agreement is found with MEGA for all modes: the unstable n = 3-5 and
stable n = 2, 6 modes, with the latter two stabilized by higher intrinsic
damping and lower fast ion drive, respectively. While some discrepancies remain
to be resolved, this unique validation effort gives us confidence in TAE
stability predictions for future fusion devices. | 2208.05052v1 |
2022-09-24 | Deep Attentive Belief Propagation: Integrating Reasoning and Learning for Solving Constraint Optimization Problems | Belief Propagation (BP) is an important message-passing algorithm for various
reasoning tasks over graphical models, including solving the Constraint
Optimization Problems (COPs). It has been shown that BP can achieve
state-of-the-art performance on various benchmarks by mixing old and new
messages before sending the new one, i.e., damping. However, existing methods
of tuning a static damping factor for BP not only are laborious but also harm
their performance. Moreover, existing BP algorithms treat each variable node's
neighbors equally when composing a new message, which also limits their
exploration ability. To address these issues, we seamlessly integrate BP, Gated
Recurrent Units (GRUs), and Graph Attention Networks (GATs) within the
message-passing framework to reason about dynamic weights and damping factors
for composing new BP messages. Our model, Deep Attentive Belief Propagation
(DABP), takes the factor graph and the BP messages in each iteration as the
input and infers the optimal weights and damping factors through GRUs and GATs,
followed by a multi-head attention layer. Furthermore, unlike existing
neural-based BP variants, we propose a novel self-supervised learning algorithm
for DABP with a smoothed solution cost, which does not require expensive
training labels and also avoids the common out-of-distribution issue through
efficient online learning. Extensive experiments show that our model
significantly outperforms state-of-the-art baselines. | 2209.12000v1 |
2022-12-01 | Slack-based tunable damping leads to a trade-off between robustness and efficiency in legged locomotion | Animals run robustly in diverse terrain. This locomotion robustness is
puzzling because axon conduction velocity is limited to a few ten meters per
second. If reflex loops deliver sensory information with significant delays,
one would expect a destabilizing effect on sensorimotor control. Hence, an
alternative explanation describes a hierarchical structure of low-level
adaptive mechanics and high-level sensorimotor control to help mitigate the
effects of transmission delays. Motivated by the concept of an adaptive
mechanism triggering an immediate response, we developed a tunable physical
damper system. Our mechanism combines a tendon with adjustable slackness
connected to a physical damper. The slack damper allows adjustment of damping
force, onset timing, effective stroke, and energy dissipation. We characterize
the slack damper mechanism mounted to a legged robot controlled in open-loop
mode. The robot hops vertically and planar over varying terrains and
perturbations. During forward hopping, slack-based damping improves faster
perturbation recovery (up to 170%) at higher energetic cost (27%). The tunable
slack mechanism auto-engages the damper during perturbations, leading to a
perturbation-trigger damping, improving robustness at minimum energetic cost.
With the results from the slack damper mechanism, we propose a new functional
interpretation of animals' redundant muscle tendons as tunable dampers. | 2212.00475v1 |
2023-01-19 | Magnetoreological spring as element of vibration control system of dynamicly active equipment for biofuel production | The development of vibration protection systems that ensure efficiency and
safety in the operation of process equipment and pipelines is one of the main
tasks of controlling the dynamic state of machines. One of the effective
methods of vibration isolation of the equipment of these installations is the
use of vibration mounts. Today, both passive and active methods of
extinguishing are actively used. The combination of two methods of damping will
ensure the stability and adaptability of vibration protection systems to the
operating conditions of process equipment. The paper presents and investigates
the device of a hybrid vibration support, including a magnetorheological
spring, as an element of vibration damping. A distinctive feature of the
vibration mount is an extended range of performance and reduced wear rate of
the components. An analysis of the damping characteristics of a hybrid
vibration support in passive and active modes of operation is presented. A
simulation model of the vibration support under consideration has been
developed in the MATLAB Simulink simulation environment using the PIB
controller. The simulation results indicate the effectiveness of the use of
vibration damping systems with a magnetorheological spring in conjunction with
various technological equipment. | 2301.07911v1 |
2023-02-19 | Collective Quantum Approach to Surface Plasmon Resonance Effect | In this research we present a theory of the surface plasmon resonance (SPR)
effect based on the dual length-scale driven damped collective quantum
oscillations of the spill-out electrons in plasmonic material surface. The
metallic electron excitations are modeled using the Hermitian effective
Schr\"{o}dinger-Poisson system, whereas, the spill-out electron excitations are
modeled via the damped non-Hermitian effective Schr\"{o}dinger-Poisson system
adapted appropriately at the metal-vacuum interface. It is shows that, when
driven by external field, the system behaves like the driven damped oscillator
in wavenumber domain, quite analogous to the driven damped mechanical
oscillation in frequency domain, leading to the collective surface spill-out
electron excitation resonance. In this model the resonance occurs when the
wavenumber of the driving pseudoforce matches that of the surface plasmon
excitations which can be either due to single-electrons or collective effects.
Current theory of SPR is based on longitudinal electrostatic excitations of the
surface electrons, instead of the polariton excitation parallel to the
metal-dielectric or metal-vacuum surface. Current theory may also be extended
to use for the localized surface plasmon resonance (LSPR) in nanometer sized
metallic surfaces in non-planar geometry. A new equation of state (EoS) for the
plasmon electron number density in quantum plasmas is obtained which limits the
plasmonic effects in high-density low-temperature electron gas regime, due to
small transition probability of electrons to the plasmon energy band. | 2302.13974v1 |
2023-03-01 | Evolution of the eccentricity and inclination of low-mass planets subjected to thermal forces: a numerical study | By means of three dimensional, high resolution hydrodynamical simulations we
study the orbital evolution of weakly eccentric or inclined low-mass
protoplanets embedded in gaseous discs subject to thermal diffusion. We
consider both non-luminous planets, and planets that also experience the
radiative feedback from their own luminosity. We compare our results to
previous analytical work, and find that thermal forces (the contribution to the
disc's force arising from thermal effects) match those predicted by linear
theory within $\sim 20$%. When the planet's luminosity exceeds a threshold
found to be within $10$% of that predicted by linear theory, its eccentricity
and inclination grow exponentially, whereas these quantities undergo a strong
damping below this threshold. In this regime of low luminosity indeed, thermal
diffusion cools the surroundings of the planet and allows gas to accumulate in
its vicinity. It is the dynamics of this gas excess that contributes to damp
eccentricity and inclination. The damping rates obtained can be up to $h^{-1}$
times larger than those due to the resonant interaction with the disc, where
$h$ is the disc's aspect ratio. This suggests that models that incorporate
planet-disc interactions using well-known formulae based on resonant
wave-launching to describe the evolution of eccentricity and inclination
underestimate the damping action of the disc on the eccentricity and
inclination of low-mass planets by an order of magnitude. | 2303.00867v1 |
2023-03-13 | Discriminative sEMG-based features to assess damping ability and interpret activation patterns in lower-limb muscles of ACLR athletes | Objective: The main goal of the athletes who undergo anterior cruciate
ligament reconstruction (ACLR) surgery is a successful return-to-sport. At this
stage, identifying muscular deficits becomes important. Hence, in this study,
three discriminative features based on surface electromyographic signals (sEMG)
acquired in a dynamic protocol are introduced to assess the damping ability and
interpret activation patterns in lower-limb muscles of ACLR athletes. Methods:
The features include the median frequency of the power spectrum density (PSD),
the relative percentage of the equivalent damping or equivalent stiffness
derived from the median frequency, and the energy of the signals in the
time-frequency plane of the pseudo-Wigner-Ville distribution (PWVD). To
evaluate the features, 11 healthy and 11 ACLR athletes (6 months
post-reconstruction surgery) were recruited to acquire the sEMG signals from
the medial and the lateral parts of the hamstrings, quadriceps, and
gastrocnemius muscles in pre- and post-fatigue single-leg landings. Results: A
significant damping deficiency is observed in the hamstring muscles of ACLR
athletes by evaluating the proposed features. This deficiency indicates that
more attention should be paid to this muscle of ACLR athletes in
pre-return-to-sport rehabilitations. Conclusion: The quality of
electromyography-based pre-return-to-sport assessments on ACLR subjects depends
on the sEMG acquisition protocol, as well as the type and nature of the
extracted features. Hence, combinatorial application of both energy-based
features (derived from the PWVD) and power-based features (derived from the
PSD) could facilitate the assessment process by providing additional
biomechanical information regarding the behavior of the muscles surrounding the
knee. | 2303.06954v1 |
2023-03-28 | Search for damped oscillating structures from charged pion electromagnetic form factor data | The damped oscillating structures recently revealed by a three parametric
formula from the proton ``effective'' form factor data extracted of the
measured total cross section $\sigma^{bare}_{tot}(e^+e^-\to p\bar p)$ still
seem to have an unknown origin. The conjectures of their direct manifestation
of the quark-gluon structure of the proton indicate that they are not specific
only of the proton and neutron, but they have to be one's own, similar to other
hadrons.
Therefore, the oscillatory structures from the charged pion electromagnetic
form factor timelike data, extracted of the process $e^+e^-\to \pi^+ \pi^-$ are
investigated by using the same procedure as in the case of the proton.
The analysis shows the appearance of the oscillating structures in the
description of the charged pion electromagnetic form factor timelike data by
three parametric formula with a rather large value of $\chi^2/ndf$, while the
description of the data by the physically well-founded Unitary and Analytic
model has not revealed any damped oscillating structures.
From the obtained result on the most simple object of strong interactions,
one can conclude that damped oscillating structures received from the
``effective'' proton form factor data are probably generated by a utilization
of the improper three parametric formula which does not describe these data
with sufficient precision. | 2303.16681v1 |
2023-05-15 | Landau damping and the survival threshold | In this paper, we establish the large time asymptotic behavior of solutions
to the linearized Vlasov-Poisson system near general spatially homogenous
equilibria $\mu(\frac12|v|^2)$ with connected support on the whole space
$\RR^3_x \times \RR^3_v$, including those that are non-monotone. The problem
can be solved completely mode by mode for each spatial wave number, and their
longtime dynamics is intimately tied to the ``survival threshold'' of wave
numbers computed by $$\kappa_0^2 = 4\pi \int_0^\Upsilon \frac{u^2\mu(\frac12
u^2)}{\Upsilon^2-u^2} \;du$$ where $\Upsilon$ is the maximal speed of particle
velocities. It is shown that purely oscillatory electric fields exist and obey
a Klein-Gordon's type dispersion relation for wave numbers below the threshold,
thus confirming the existence of Langmuir's oscillatory waves known in the
physical literature. At the threshold, the phase velocity of these oscillatory
waves enters the range of admissible particle velocities, namely there are
particles that move at the same propagation speed of the waves. It is this
exact resonant interaction between particles and the oscillatory fields that
causes the waves to be damped, classically known as Landau damping. Landau's
law of decay is explicitly computed and is sensitive to the decaying rate of
the background equilibria. The faster it decays at the maximal velocity, the
weaker Landau damping is. Beyond the threshold, the electric fields are a
perturbation of those generated by the free transport dynamics and thus decay
rapidly fast due to the phase mixing mechanism. | 2305.08672v1 |
2023-06-04 | Large Dynamical Tide Amplitudes from Small Kicks at Pericenter | The effect of dynamical tide ``kicks" on eccentric binary orbits is
considered using the orbital mapping method. It is demonstrated that when mode
damping is negligible the mode amplitude will generically grow in time for all
values of orbital eccentricity and semi-major axis, even for small kicks
outside the regime exhibiting diffusive growth. The origin of the small-kick
growth is the change in kick size from orbit to orbit, an effect quadratic in
the mode amplitude. When damping of the mode is included, the growth is shut
off when the damping time is shorter than the growth time. Hence, in practice,
kicks of sufficient size and long mode damping times are required for
interesting levels of growth to occur. Application to the circularization of
hot Jupiters is discussed. Previous investigations found that diffusive growth
of the planetary f-mode in the large-kick regime would lead to rapid orbital
shrinkage, but upon exiting the diffusive regime at $e \sim 0.9$ the theory
would predict a large population of highly eccentric orbits. Simulations
presented here show that subsequent orbital evolution relying on the small-kick
regime may further decrease the eccentricity to $e \sim 0.2$ on timescales much
less than the Gyrs ages of these systems. | 2306.02382v1 |
2023-06-16 | Damping of MHD Turbulence in A Partially Ionized Medium | The coupling state between ions and neutrals in the interstellar medium plays
a key role in the dynamics of magnetohydrodynamic (MHD) turbulence, but is
challenging to study numerically. In this work, we investigate the damping of
MHD turbulence in a partially ionized medium using 3D two-fluid (ions+neutrals)
simulations generated with the AthenaK code. Specifically, we examine the
velocity, density, and magnetic field statistics of the two-fluid MHD
turbulence in different regimes of neutral-ion coupling. Our results
demonstrate that when ions and neutrals are strongly coupled, the velocity
statistics resemble those of single-fluid MHD turbulence. Both the velocity
structures and kinetic energy spectra of ions and neutrals are similar, while
their density structures can be significantly different. With an excess of
small-scale sharp density fluctuations in ions, the density spectrum in ions is
shallower than that of neutrals. When ions and neutrals are weakly coupled, the
turbulence in ions is more severely damped due to the ion-neutral collisional
friction than that in neutrals, resulting in a steep kinetic energy spectrum
and density spectrum in ions compared to the Kolmogorov spectrum. We also find
that the magnetic energy spectrum basically follows the shape of the kinetic
energy spectrum of ions, irrespective of the coupling regime. In addition, we
find large density fluctuations in ions and neutrals and thus spatially
inhomogeneous ionization fractions. As a result, the neutral-ion decoupling and
damping of MHD turbulence take place over a range of length scales. | 2306.10010v2 |
2023-07-24 | BGO quenching effect on spectral measurements of cosmic-ray nuclei in DAMPE experiment | The Dark Matter Particle Explorer (DAMPE) is a satellite-borne detector
designed to measure high energy cosmic-rays and $\gamma$-rays. As a key
sub-detector of DAMPE, the Bismuth Germanium Oxide (BGO) imaging calorimeter is
utilized to measure the particle energy with a high resolution. The nonlinear
fluorescence response of BGO for large ionization energy deposition, known as
the quenching effect, results in an under-estimate of the energy measurement
for cosmic-ray nuclei. In this paper, various models are employed to
characterize the BGO quenching factors obtained from the experimental data of
DAMPE. Applying the proper quenching model in the detector simulation process,
we investigate the tuned energy responses for various nuclei and compare the
results based on two different simulation softwares, i.e. GEANT4 and FLUKA. The
BGO quenching effect results in a decrease of the measured energy by
approximately $2.5\%$ ($5.7 \%$) for carbon (iron) at $\sim$10 GeV/n and $<1\%$
above 1 TeV/n, respectively. Accordingly, the correction of the BGO quenching
effect leads to an increase of the low-energy flux measurement of cosmic-ray
nuclei. | 2307.12629v1 |
2023-08-04 | Interplay of space charge, intrabeam scattering and synchrotron radiation in the Compact Linear Collider damping rings | Future ultra-low emittance rings for electron/positron colliders requiring
extremely high beam brightness can be limited by collective effects. In this
paper, the interplay of effects such as synchrotron radiation, intra-beam
scattering (IBS) and space charge in the vicinity of excited betatron
resonances is assessed. In this respect, two algorithms were developed to
simulate IBS and synchrotron radiation effects and integrated in the PyORBIT
tracking code, to be combined with its widely used space charge module. The
impact of these effects on the achievable beam parameters of the Compact Linear
Collider (CLIC) Damping Rings was studied, showing that synchrotron radiation
damping mitigates the adverse effects of IBS and space charge induced resonance
crossing. The studies include also a full dynamic simulation of the CLIC
damping ring cycle starting from the injection beam parameters. It is
demonstrated that a careful working point choice is necessary, in order to
accommodate the transition from a non-linear lattice induced detuning to a
space-charge dominated one and thereby avoid excessive losses and emittance
growth generated in the vicinity of strong resonances. | 2308.02196v3 |
2023-08-04 | Nonlinear wave damping by Kelvin-Helmholtz instability induced turbulence | Magnetohydrodynamic kink waves naturally form as a consequence of
perturbations to a structured medium, for example transverse oscillations of
coronal loops. Linear theory has provided many insights in the evolution of
linear oscillations, and results from these models are often applied to infer
information about the solar corona from observed wave periods and damping
times. However, simulations show that nonlinear kink waves can host the
Kelvin-Helmholtz instability (KHi) which subsequently creates turbulence in the
loop, dynamics which are beyond linear models. In this paper we investigate the
evolution of KHi-induced turbulence on the surface of a flux tube where a
non-linear fundamental kink-mode has been excited. We control our numerical
experiment so that we induce the KHi without exciting resonant absorption. We
find two stages in the KHi turbulence dynamics. In the first stage, we show
that the classic model of a KHi turbulent layer growing $\propto t$is
applicable. We adapt this model to make accurate predictions for damping of the
oscillation and turbulent heating as a consequence of the KHi dynamics. In the
second stage, the now dominant turbulent motions are undergoing decay. We find
that the classic model of energy decay proportional to $t^{-2}$ approximately
holds and provides an accurate prediction of the heating in this phase. Our
results show that we can develop simple models for the turbulent evolution of a
non-linear kink wave, but the damping profiles produced are distinct from those
of linear theory that are commonly used to confront theory and observations. | 2308.02217v2 |
2023-08-10 | JWST observations of galaxy damping wings during reionization interpreted with cosmological simulations | Spectra of the highest redshift galaxies taken with JWST are now allowing us
to see into the heart of the reionization epoch. Many of these observed
galaxies exhibit strong damping wing absorption redward of their Lyman-$\alpha$
emission. These observations have been used to measure the redshift evolution
of the neutral fraction of the intergalactic medium and sizes of ionized
bubbles. However, these estimates have been made using a simple analytic model
for the intergalactic damping wing. We explore the recent observations with
models of inhomogeneous reionization from the Sherwood-Relics simulation suite.
We carry out a comparison between the damping wings calculated from the
simulations and from the analytic model. We find that although the agreement is
good on the red side of the Lyman-$\alpha$ emission, there is a discrepancy on
the blue side due to residual neutral hydrogen present in the simulations,
which saturates the intergalactic absorption. For this reason, we find that it
is difficult to reproduce the claimed observations of large bubble sizes at z ~
7, which are driven by a detection of transmitted flux blueward of the
Lyman-$\alpha$ emission. We suggest instead that the observations can be
explained by a model with smaller ionized bubbles and larger intrinsic
Lyman-$\alpha$ emission from the host galaxy. | 2308.05800v1 |
2023-08-23 | Dynamics of pinned quantized vortices in superfluid $^4$He in a microelectromechanical oscillator | We numerically studied the vortex dynamics at zero temperature in superfluid
$^4$He confined between two parallel rough solid boundaries, one of which
oscillates in a shear mode. This study was motivated by the experimental work
by Barquist $et$ $al.$ which employed a microelectromechanical systems (MEMS)
oscillator operating in superfluid $^4$He at a near-zero temperature. Their
experiments suggest that the motion of the MEMS oscillator is damped by
quantized vortices. In our study, we postulated that this damping effect was
closely associated with vortex pinning phenomena and developed pinning models.
Our primary objective is to understand the vortex dynamics in the presence of
pinning and to provide insight into the experimental observations regarding the
damping mechanism. We confirmed that Kelvin waves were excited in the pinned
vortices when the oscillation frequency of the solid boundary matched with the
mode frequency of the Kelvin wave. Additionally, we examined the formation and
evolution of vortex tangles between the boundaries. The vortex tangle was
suppressed in the presence of pinning, while the absence of pinning allowed to
form well developed vortex tangle resulting in turbulence. Finally, by
evaluating the tension of pinned vortices we extracted the damping force acting
on the solid boundaries. | 2308.11942v2 |
2023-12-29 | Modeling polyelectrolyte hydration from a multi scale polarizable pseudo particle solvent coarse grained approach | We investigate the reliability of simulations of polyelectrolyte systems in
aqueous environments, simulations that are performed using an efficient multi
scale coarse grained polarizable pseudo-particle particle approach, denoted as
pppl, to model the solvent water, whereas the solutes are modeled using a
polarizable all atom force field. We focus our study on issues tied to two key
parameters of the pppl approach, namely the extension of the solvent domain SD
at the close vicinity of a solute (domain in which each solvent particle
corresponds to a single water molecule) and the magnitude of solute/solvent
short range polarization damping effects. To this end we built a new pppl
models from which we simulate NaCl aqueous solutions at the molar concentration
scale. We also re investigate the hydration of a hydrophobic polyelectrolyte
polymer that we showed in an earlier study [J Chem Phys, 114903 (155) 2021] to
evolve towards a counter intuitive globular form surrounded by a spherical
counter ion cloud along pppl-based simulations. Strong short range damping is
pivotal to simulate NaCl aqueous solutions. The extension of the domain SD (as
well as short range damping) has a weak effect on the conformation of the
polymer, but it plays a pivotal role to compute accurate solute/solvent
interaction energies. In all our results lead us to recommend to simulate
polyelectrolyte polymers as dissolved alone in pppl fluids (i.e. without
explicitly accounting for their counter ions) to investigate their behavior at
infinite dilution conditions, and to systematically consider strong
solute/solvent polarization short range damping to model charged species. | 2312.17580v1 |
2024-02-20 | The Fundamental Parameters of Astrophysical Plasma Turbulence and its Dissipation: Nonrelativistic Limit | A specific set of dimensionless plasma and turbulence parameters is
introduced to characterize the nature of turbulence and its dissipation in
weakly collisional space and astrophysical plasmas. Key considerations are
discussed for the development of predictive models of the turbulent plasma
heating that characterize the partitioning of dissipated turbulent energy
between the ion and electron species and between the perpendicular and parallel
degrees of freedom for each species. Identifying the kinetic physical
mechanisms that govern the damping of the turbulent fluctuations is a critical
first step in constructing such turbulent heating models. A set of ten general
plasma and turbulence parameters are defined, and reasonable approximations
along with the exploitation of existing scaling theories for
magnetohydrodynamic turbulence are used to reduce this general set of ten
parameters to just three parameters in the isotropic temperature case. A
critical step forward in this study is to identify the dependence of all of the
proposed kinetic mechanisms for turbulent damping in terms of the same set of
fundamental plasma and turbulence parameters. Analytical estimations of the
scaling of each damping mechanism on these fundamental parameters are
presented, and this information is synthesized to produce the first phase
diagram for the turbulent damping mechanisms as a function of driving scale and
ion plasma beta. | 2402.12829v1 |
2024-03-06 | Universality of pseudo-Goldstone damping near critical points | Recently, in studies of holographic models and hydrodynamics with spontaneous
breaking of approximate symmetries, it has been proposed that the damping of
pseudo-Goldstone modes at finite temperatures is universally constrained in the
way that $\Omega_{\varphi}/m_{\varphi}^2\simeq D_{\varphi}$ in the broken
phase, where $\Omega_{\varphi}$ and $m_{\varphi} $ are the relaxation rate at
zero wavenumber and the mass of pseudo-Goldstones, $D_{\varphi}$ is the
Goldstone diffusivity in the limit of purely spontaneous breaking. In this
paper, we investigate the pseudo-Goldstone damping in a purely relaxational
O($N$) model by performing the functional renormalization group calculations at
the full quantum and stochastic level within the Schwinger-Keldysh formalism.
We find that, away from the critical temperature, the proposed relation is
always valid. When the temperature is very close to the critical value such
that the mass of the Higgs mode is comparable to the mass of the
pseudo-Goldstone modes, the pseudo-Goldstone damping displays a novel scaling
behavior that follows $\Omega_\varphi/m_\varphi^2\propto
m_{\varphi}^{\Delta_\eta}$ with a correction $\Delta_\eta$ controlled by the
critical universalities. Moreover, we study how the correction depends on the
value of $N$ and show that $\Delta_\eta \rightarrow 0$ when fluctuations are
infinitely suppressed in the large $N$ limit. In this case, the proposed
relation works even in the critical region. Finally, we match our results to
the dissipative sector of the pion dynamics near the chiral phase transition. | 2403.03503v2 |
1993-11-17 | Early Reionization in Cosmology | The cosmic microwave background (CMB) anisotropies have turned out to
represent one of the most stringent 'bottle necks' for scenarios of large scale
structure formation. As a possibility to relax this constraint, it has been
proposed that early reionization can damp CMB fluctuations on small scales due
to photon diffusion in the ionized plasma. As an example, I investigate the
recently proposed scenario with cold dark matter (CDM) and texture seeds.
There, an analysis of CMB anisotropies shows that early reionization is a
crucial ingredient for this scenario. Without damping, the small scale
anisotropies would dominate and exceed observed limits. In this paper I present
analytical and numerical results for the amount of damping due to early
reionization for CMB perturbations induced by a collapsing texture.
Furthermore, the spectral distortion of the CMB due to Compton scattering of
the hotter plasma electrons is calculated. Next I discuss the physical
processes which lead to a system of coupled ordinary differential equations for
the degree of ionization, the electron temperature and the evolution of the
ionizing radiation. | 9311039v1 |
1994-08-18 | The Damping and Excitation of Galactic Warps by Dynamical Friction | We investigate the dynamical interaction of galactic warps with the
surrounding dark matter halo, using analytic perturbation theory. A precessing
warp induces a density wake in the collisionless dark matter, which acts back
on the original warp, transferring energy and angular momentum between the warp
and halo (dynamical friction). In most cases dynamical friction damps the warp,
but in unusual circumstances (such as a halo that rotates in the same direction
as the precession of the warp, or a warp in the equatorial plane of an
axisymmetric prolate halo) friction can excite a warp. The damping/excitation
time is usually short compared to the Hubble time for realistic systems. Thus
most warps cannot be primordial; they must be maintained by some ongoing
excitation mechanism. | 9408068v1 |
1995-09-14 | Another Look at Gaussian Isocurvature Hot Dark Matter Models For Large- Scale Structure | We examine Gaussian isocurvature hot dark matter (massive neutrino) models
for large-scale structure in which the initial density perturbations are
produced in the baryons with a power--law spectrum $P_B(k) = Ak^{n_B}$. We
calculate the linearly-evolved power spectrum and cosmic microwave
fluctuations. We find that models with only isocurvature perturbations are
inconsistent with observations of damped Ly$\alpha$ systems and COBE
constraints on the power index. However, models which contain a mixture of
adiabatic and isocurvature perturbations can be made consistent with COBE,
galaxy surveys and damped Ly$\alpha$ systems.Isocurvature hot dark matter
models also produce a bias between baryons and neutrinos even in the linear
regime. We find that this ``natural bias'' can increase the baryon fraction in
small scale objects like damped Ly$\alpha$ systems, but it has no effect on
cluster scales. | 9509075v1 |
1995-10-16 | Star Formation and Chemical Evolution in Damped Lya Clouds | Using the redshift evolution of the neutral hydrogen density, as inferred
from observations of damped Ly$\alpha$ clouds, we calculate the evolution of
star formation rates and elemental abundances in the universe. For most
observables our calculations are in rough agreement with previous results based
on the instantaneous re-cycling approximation (IRA). However, for the key
metallicity tracer Zn, we find a better match to the observed abundance at high
redshift than that given by the constant-yield IRA model. We investigate
whether the redshift evolution of deuterium, depressions in the diffuse
extragalactic gamma-ray background, and measurement of the MeV neutrino
background may help determine if observational bias due to dust obscuration is
important. We also indicate how the importance of dust on the calculations can
be significantly reduced if correlations of the HI column density with
metallicity are present. The possibilities for measuring $q_o$ with
observations of elemental abundances in damped Ly$\alpha$ systems are
discussed. | 9510078v1 |
1995-12-12 | A radio Search for high redshift HI absorption | Ground based optical observations have yielded considerable information on
the statistics of damped-lyman alpha systems. In particular these systems are
known to be the dominant repository of the observed neutral gas at high
redshift. However, particularly at high redshift, there is the possibility that
optical observations could be biased due to the exclusion of damped-lyman alpha
systems that contain moderate to significant amounts of dust. Independent
observational constraints on the neutral hydrogen content at high redshifts and
the amount of dust in high redshift systems can be obtained from a radio search
against the bright lobes of distant radio galaxies (which is less affected by
the presence of dust in foreground damped-lyman alpha systems). We describe
here a pilot radio survey along the line of sight to a small sample of high
redshift radio galaxies, and also present some preliminary results. The survey
uses a novel observing mode at the WSRT which enables one to make sensitive
searches of a large redshift interval in a modest amount of telescope time. | 9512069v1 |
1996-01-26 | The chemical evolution of galaxies at high redshift | Observations of absorption lines in the spectra of distant QSOs offer a new
approach for tracking the evolution of normal galaxies from early epochs to the
present day. The damped Ly alpha systems are particularly suitable for
measuring the properties of what are likely to be the progenitors of
present-day luminous galaxies. We have recently concluded a long-term survey of
30 damped absorbers (including eight from the literature) aimed at measuring
the metallicity and dust content of the universe from redshift z = 3.39 to
0.69. The major conclusions are that the epoch of chemical enrichment in
galaxies may have begun at z = 2.5-3--corresponding to a look-back time of 14
Gyr--and that at z = 2 the typical metallicity was 1/15 of solar. There is
clear evidence for the presence of interstellar dust at z = 2, although several
high-redshift galaxies, particularly the most metal-poor, appear to be
essentially dust-free. We discuss the nature of the damped Ly alpha galaxies in
the light of these and other new results. | 9601153v1 |
1996-07-23 | A damped Ly-alpha candidate at z~0.1 toward Q 0439-433 | We report on the detection of a z_gal=0.101 galaxy projected on the sky at
4.2 arcsec (or 5.2 h^{-1} kpc for q_o=0.5) from the quasar Q 0439-433
(z_em=0.594). The HST spectrum of the quasar shows strong MgII, FeII, SiII,
AlII and CIV absorption lines at the same redshift as the galaxy. The
equivalent width ratios of the low ionization lines indicate that this system
is probably damped with a neutral hydrogen column density of
N_HI~10^{20}cm^{-2}. The CIV doublet presents a complex structure, and in
particular a satellite with a velocity v=1100km/s relative to the galaxy.
Additional HST and redshifted 21cm observations of this QSO-galaxy pair would
offer an ideal opportunity to study the morphology of a damped absorber and the
kinematics of the halo of a low-redshift galaxy. | 9607111v2 |
1997-08-11 | Dynamos with different formulations of a dynamic alpha-effect | We investigate the behaviour of $\alpha\Omega$ dynamos with a dynamic
$\alpha$, whose evolution is governed by the imbalance between a driving and a
damping term. We focus on truncated versions of such dynamo models which are
often studied in connection with solar and stellar variability. Given the
approximate nature of such models, it is important to study how robust they are
with respect to reasonable changes in the formulation of the driving and
damping terms. For each case, we also study the effects of changes of the
dynamo number and its sign, the truncation order and initial conditions. Our
results show that changes in the formulation of the driving term have important
consequences for the dynamical behaviour of such systems, with the detailed
nature of these effects depending crucially on the form of the driving term
assumed, the value and the sign of the dynamo number and the initial
conditions. On the other hand, the change in the damping term considered here
seems to produce little qualitative effect. | 9708093v1 |
1997-11-20 | ORT observations of the damped Lyman alpha system towards PKS 0201+113 | We report a deep radio search with the Ooty Radio Telescope (ORT) for the
redshifted 21 cm absorption line from the damped Lyman alpha system seen at
redshift 3.388 against the quasar PKS 0201+113. This is currently the most
distant system for which a detection of 21 cm absorption has been claimed. The
present observations have a sensitivity comparable to the earlier ones and
detect no statistically significant absorption. We use the non-detection to
place an upper limit of ~ 0.011 on the optical depth of the damped Lyman alpha
absorber. This corresponds to a lower limit of ~ 5600 K to the spin temperature
of the system. This is considerably higher than the previous upper limit of ~
1380 K. | 9711234v1 |
1998-01-28 | Dynamical Tide in Solar-Type Binaries | Circularization of late-type main-sequence binaries is usually attributed to
turbulent convection, while that of early-type binaries is explained by
resonant excitation of g modes. We show that the latter mechanism operates in
solar-type stars also and is at least as effective as convection, despite
inefficient damping of g modes in the radiative core. The maximum period at
which this mechanism can circularize a binary composed of solar-type stars in
10 Gyr is as low as 3 days, if the modes are damped by radiative diffusion only
and g-mode resonances are fixed; or as high as 6 days, if one allows for
evolution of the resonances and for nonlinear damping near inner turning
points. Even the larger theoretical period falls short of the observed
transition period by a factor two. | 9801289v1 |
1998-02-06 | Acoustic oscillations and viscosity | Using a simple thermo-hydrodynamic model that respects relativistic
causality, we revisit the analysis of qualitative features of acoustic
oscillations in the photon-baryon fluid. The growing photon mean free path
introduces transient effects that can be modelled by the causal generalization
of relativistic Navier-Stokes-Fourier theory. Causal thermodynamics provides a
more satisfactory hydrodynamic approximation to kinetic theory than the
quasi-stationary (and non-causal) approximations arising from standard
thermodynamics or from expanding the photon distribution to first order in the
Thomson scattering time. The causal approach introduces small corrections to
the dispersion relation obtained in quasi-stationary treatments. A dissipative
contribution to the speed of sound slightly increases the frequency of the
oscillations. The diffusion damping scale is slightly increased by the causal
corrections. Thus quasi-stationary approximations tend to over-estimate the
spacing and under-estimate the damping of acoustic peaks. In our simple model,
the fractional corrections at decoupling are $\gtrsim 10^{-3}$. | 9802074v2 |
2000-02-29 | Metallicity Evolution in the Early Universe | Observations of the damped Lya systems provide direct measurements on the
chemical enrichment history of neutral gas in the early universe. In this
Letter, we present new measurements for four damped Lya systems at high
redshift. Combining these data with [Fe/H] values culled from the literature,
we investigate the metallicity evolution of the universe from z~1.5-4.5.
Contrary to our expectations and the predictions of essentially every chemical
evolution model, the N(HI)-weighted mean [Fe/H] metallicity exhibits minimal
evolution over this epoch. For the individual systems, we report tentative
evidence for an evolution in the unweighted [Fe/H] mean and the scatter in
[Fe/H] with the higher redshift systems showing lower scatter and lower typical
[Fe/H] values. We also note that no damped Lya system has [Fe/H] < -2.7 dex.
Finally, we discuss the potential impact of small number statistics and dust on
our conclusions and consider the implications of these results on chemical
evolution in the early universe. | 0002513v3 |
2000-06-02 | Surveys for z > 3 Damped Lyman-alpha Absorption Systems | We have completed spectroscopic observations using LRIS on the Keck 1
telescope of 30 very high redshift quasars, 11 selected for the presence of
damped Ly-alpha absorption systems and 19 with redshifts z > 3.5 not previously
surveyed for absorption systems. We have surveyed an additional 10 QSOs with
the Lick 120'' and the Anglo-Australian Telescope. We have combined these with
previous data resulting in a statistical sample of 646 QSOs and 85 damped
Ly-alpha absorbers with column densities N(HI) >= 2 x 10^20 atoms/cm^2 covering
the redshift range 0.008 <= z <= 4.694. To make the data in our statistical
sample more readily available for comparison with scenarios from various
cosmological models, we provide tables that includes all 646 QSOs from our new
survey and previously published surveys. They list the minimum and maximum
redshift defining the redshift path along each line of sight, the QSO emission
redshift, and when an absorber is detected, the absorption redshift and
measured HI column density. [see the paper for the complete abstract] | 0006044v1 |
2000-06-21 | Constraints on the physical properties of the damped Ly-alpha system of Q0000-2619 at z = 3.054 | We present the detection of CII and CII* absorption in the z = 3.0543 damped
Ly-alpha system toward Q0000-2619. The derived population ratio implies a fine
structure excitation temperature between 19.6 and 21.6 K. The upper value sets
a strict upper limit on the CMB temperature at this redshift, which is
consistent with the predicted value of 11.05 K from standard cosmology. Under
the assumptions of an ionization degree ranging from 0 to 10%, a gas kinetic
temperature between 100 and 10000 K and a UV field with a Milky Way spectrum,
the density of the absorber is constrained to be between 0.7 and 40 cm^-3 and
the H-ionizing flux between 1 and 80 times the intensity of the Galactic UV
field. If the damped Ly-alpha system is assumed to be homogeneous, the
implication is that its size in the direction of the line of sight must be
between 1 and 100 pc. | 0006308v1 |
2001-04-10 | Damping scales of neutralino cold dark matter | The lightest supersymmetric particle, most likely the neutralino, might
account for a large fraction of dark matter in the Universe. We show that the
primordial spectrum of density fluctuations in neutralino cold dark matter
(CDM) has a sharp cut-off due to two damping mechanisms: collisional damping
during the kinetic decoupling of the neutralinos at about 30 MeV (for typical
neutralino and sfermion masses) and free streaming after last scattering of
neutralinos. The last scattering temperature is lower than the kinetic
decoupling temperature by one order of magnitude. The cut-off in the primordial
spectrum defines a minimal mass for CDM objects in hierarchical structure
formation. For typical neutralino and sfermion masses the first gravitationally
bound neutralino clouds have to have masses above 10^(-7) solar masses. | 0104173v2 |
2002-05-15 | Building the bridge between Damped Ly-alpha Absorbers and Lyman Break galaxies | In 2000, we started the program ``Building the Bridge between Damped Ly-alpha
Absorbers and Lyman-Break Galaxies: Ly-alpha Selection of Galaxies'' at the
European Southern Observatory's Very Large Telescope. This project is an
attempt to use Ly-alpha selection of high-z galaxies to bridge the gap between
absorption- and emission-selected galaxies by creating a large database of z=3
galaxies belonging to the abundant population of faint (R>25.5) galaxies probed
by the Damped Ly-alpha Absorbers (DLAs). Here we present the first results of
our program, namely the results from a deep Ly-alpha study of the field of the
z=2.85 DLA towards Q2138-4427. | 0205234v2 |
2002-05-23 | Constraining the strength of Dark Matter Interactions from Structure Formation | We discuss the damping of primordial dark matter fluctuations, taking into
account explicitly the interactions of dark matter - whatever their intensity -
both with itself and with other particle species. Relying on a general
classification of dark matter particle candidates, our analysis provides, from
structure formation, a new set of constraints on the dark matter particle mass
and interaction rates (in particular with photons and neutrinos).
This determines up to which cross sections the dark matter interactions may
effectively be disregarded, and when they start playing an essential role,
either through collisional damping or through an enhancement of the
free-streaming scale. It leads us to extend the notions of Cold, Warm and Hot
Dark Matter scenarios when dark matter interactions are no longer taken to be
negligible. It also suggests the possibility of new scenarios of Collisional
Warm Dark Matter, with moderate damping induced by dark matter interactions. | 0205406v1 |
2002-06-06 | A catalogue of damped Lyman alpha absorption systems and radio flux densities of the background quasars | We present a catalogue of the 322 damped Lyman alpha absorbers taken from the
literature. All damped Lyman alpha absorbers are included, with no selection on
redshift or quasar magnitude. Of these, 123 are candidates and await
confirmation using high resolution spectroscopy. For all 322 objects we
catalogue the radio properties of the background quasars, where known. Around
60 quasars have radio flux densities above 0.1 Jy and approximately half of
these have optical magnitudes brighter than V = 18. This compilation should
prove useful in several areas of extragalactic/cosmological research. | 0206091v1 |
2002-11-14 | Formation of small-scale structure in SUSY CDM | The lightest supersymmetric particle, most likely the lightest neutralino, is
one of the most prominent particle candidates for cold dark matter (CDM). We
show that the primordial spectrum of density fluctuations in neutralino CDM has
a sharp cut-off, induced by two different damping mechanisms. During the
kinetic decoupling of neutralinos, non-equilibrium processes constitute
viscosity effects, which damp or even absorb density perturbations in CDM.
After the last scattering of neutralinos, free streaming induces neutralino
flows from overdense to underdense regions of space. Both damping mechanisms
together define a minimal mass scale for perturbations in neutralino CDM,
before the inhomogeneities enter the nonlinear epoch of structure formation. We
find that the very first gravitationally bound neutralino clouds ought to have
masses above 10^{-6} solar masses, which is six orders of magnitude above the
mass of possible axion miniclusters. | 0211325v1 |
2002-12-09 | Galaxies at z=3 around Damped Ly-alpha Clouds | We are exploring the connection between damped Ly-alpha absorbers (DLAs) and
Lyman break galaxies (LBGs) using deep -- (5sigma)=26 m_{AB}-- broad band
imaging (UBVI) of four wide fields (0.25 sq. deg. each) obtained at the Kitt
Peak 4-m telescope with MOSAIC. Each field contains a damped system at z=3.
We want to address the nature of DLAs at high-redshifts: (1) Are they
embedded in much larger systems of galaxies? (2) How does the spatial
distribution of LBGs in 3D (space and redshift) correlate with the absorber?
Contrary to most previous DLA studies, we are not looking for the absorber, and
we do not rely on control fields because each of our fields is 40 Mpc
(co-moving) on a side. We present preliminary results in two of our fields. In
one case, we see an indication of an overdensity of galaxies on a scale of 5
Mpc. We discuss the possible implications and sources of contamination of our
results. | 0212206v1 |
2003-04-16 | Building Blocks in Hierarchical Clustering Scenarios and their Connection with Damped Ly$α$ Systems | We carried out a comprehensive analysis of the chemical properties of the
interstellar medium (ISM) and the stellar population (SP) of current normal
galaxies and their progenitors in a hierarchical clustering scenario. We
compared the results with observations of Damped Lyman-$\alpha$ systems (DLAs)
under the hypothesis that, at least, part of the observed DLAs could originate
in the building blocks of today normal galaxies. We used a hydrodynamical
cosmological code which includes star formation and chemical enrichment.
Galaxy-like objects are identified at $z=0$ and then followed back in time.
Random line-of-sights (LOS) are drawn through these structures in order to
mimic Damped Lyman $\alpha$ systems. We then analysed the chemical properties
of the ISM and SP along the LOS. We found that the progenitors of current
galaxies in the field with mean $L <0.5 L^* $ and virial circular velocity of
$100-250 {\rm km/sec}$ could be the associated DLA galaxies. For these systems
we detected a trend for $<L/L^*>$ to increase with redshift.(Abridged) | 0304303v2 |
2003-05-16 | The ESI/KeckII Damped Lya Abundance Database | This paper presents chemical abundance measurements for 37 damped Lya systems
at z>2.5 observed with the Echellette Spectrograph and Imager on the KeckII
telescope. We measure the HI column densities of these damped systems through
Voigt profile fits to their Lya profiles and we implement the apparent optical
depth method to determine ionic column densities. Figures and tables of all
relevant data are presented. A full analysis of the chemical enrichment history
described by these observations will be presented in a future paper. This
dataset is also valuable for efficiently planning future echelle observations
and for rough abundance pattern analyses. We aim to make this entire data set
public within three years of this publication. | 0305312v1 |
2003-10-28 | Chemical Abundances in the Damped Lya Systems | I introduce and review the data and analysis techniques used to measure
abundances in the damped Lya systems, quasar absorption-line systems associated
with galaxies in the early Universe. The observations and issues associated
with their abundance analysis are very similar to those of the Milky Way's
interstellar medium. We measure gas-phase abundances and are therefore subject
to the effects of differential depletion. I review the impact of dust depletion
and then present a summary of current results on the age-metallicity relation
derived from damped Lya systems and new results impacting theories of
nucleosynthesis in the early Universe. | 0310814v1 |
2004-12-14 | Radiative Effects on Particle Acceleration in Electromagnetic Dominated Outflows | Plasma outflows from gamma-ray bursts (GRB), pulsar winds, relativistic jets,
and ultra-intense laser targets radiate high energy photons. However, radiation
damping is ignored in conventional PIC simulations. In this letter, we study
the radiation damping effect on particle acceleration via Poynting fluxes in
two-and-half-dimensional particle-in-cell (PIC) plasma simulation of
electron-positron plasmas. Radiation damping force is self-consistently
calculated for each particle and reduces the net acceleration force. The
emitted radiation is peaked within a few degrees from the direction of Poynting
flux and strongly linear-polarized. | 0412310v3 |
2005-09-16 | Damped Lyman alpha Systems | Observations of damped Lyman alpha systems offer a unique window on the
neutral-gas reservoirs that gave rise to galaxies at high redshifts. This
review focuses on critical properties such as the H I and metal content of the
gas and on independent evidence for star formation. Together, these provide an
emerging picture of gravitationally bound objects in which accretion of gas
from the IGM replenishes gas consumed by star formation. Other properties such
as dust content, molecular content, ionized-gas content, gas kinematics, and
galaxy identifications are also reviewed. These properties point to a
multiphase ISM in which radiative and hydrodynamic feedback processes are
present. Numerical simulations and other types of models used to describe
damped Lyman alpha systems within the context of galaxy formation are also
discussed. | 0509481v2 |
2005-11-11 | Oscillation mode lifetimes in ksi Hydrae: Will strong mode damping limit asteroseismology of red giant stars? | We introduce a new method to measure frequency separations and mode lifetimes
of stochastically excited and damped oscillations, so-called solar-like
oscillations. Our method shows that velocity data of the red giant star ksi Hya
(Frandsen et al. 2002) support a large frequency separation between modes of
roughly 7 microHz. We also conclude that the data are consistent with a mode
lifetime of 2 days, which is so short relative to its pulsation period that
none of the observed frequencies are unambiguous. Hence, we argue that the
maximum asteroseismic output that can be obtained from these data is an average
large frequency separation, the oscillation amplitude and the average mode
lifetime. However, the significant discrepancy between the theoretical
calculations of the mode lifetime (Houdek & Gough 2002) and our result based on
the observations of ksi Hya, implies that red giant stars can help us better
understand the damping and driving mechanisms of solar-like p-modes by
convection. | 0511344v1 |
1996-12-14 | Nonlinear Landau damping in collisionless plasma and inviscid fluid | The evolution of an initial perturbation in Vlasov plasma is studied in the
intrinsically nonlinear long-time limit dominated by the effects of particle
trapping. After the possible transient linear exponential Landau damping, the
evolution enters into a universal regime with an algebraically damped electric
field, $E\propto1/t$. The trick used for the Vlasov equation is also applied to
the two-dimensional (2D) Euler equation. It is shown that the stream function
perturbation to a stable shear flow decays as $t^{-5/2}$ in the long-time
limit. These results imply a strong non-ergodicity of the fluid element motion,
which invalidates Gibbs-ensemble-based statistical theories of Vlasov and 2D
fluid turbulence. | 9612021v1 |
1998-03-05 | On how a joint interaction of two innocent partners (smooth advection & linear damping) produces a strong intermittency | Forced advection of passive scalar by a smooth $d$-dimensional incompressible
velocity in the presence of a linear damping is studied. Acting separately
advection and dumping do not lead to an essential intermittency of the steady
scalar statistics, while being mixed together produce a very strong
non-Gaussianity in the convective range: $q$-th (positive) moment of the
absolute value of scalar difference, $<|\theta (t;{\bf r})-\theta (t;0)|^{q}> $
is proportional to $r^{\xi_{q}}$, $\xi _{q}=\sqrt{d^{2}/4+\alpha dq/[
(d-1)D]}-d/2$, where $\alpha /D$ measures the rate of the damping in the units
of the stretching rate. Probability density function (PDF) of the scalar
difference is also found. | 9803007v1 |
1999-02-05 | Nonlinear Dynamics of A Damped Magnetic Oscillator | We consider a damped magnetic oscillator, consisting of a permanent magnet in
a periodically oscillating magnetic field. A detailed investigation of the
dynamics of this dissipative magnetic system is made by varying the field
amplitude $A$. As $A$ is increased, the damped magnetic oscillator, albeit
simple looking, exhibits rich dynamical behaviors such as symmetry-breaking
pitchfork bifurcations, period-doubling transitions to chaos,
symmetry-restoring attractor-merging crises, and saddle-node bifurcations
giving rise to new periodic attractors. Besides these familiar behaviors, a
cascade of ``resurrections'' (i.e., an infinite sequence of alternating
restabilizations and destabilizations) of the stationary points also occurs. It
is found that the stationary points restabilize (destabilize) through
alternating subcritical (supercritical) period-doubling and pitchfork
bifurcations. We also discuss the critical behaviors in the period-doubling
cascades. | 9902005v1 |
1996-09-03 | Mode damping in a commensurate monolayer solid | The normal modes of a commensurate monolayer solid may be damped by mixing
with elastic waves of the substrate. This was shown by B. Hall et al., Phys.
Rev. B 32, 4932 (1985), for perpendicular adsorbate vibrations in the presence
of an isotropic elastic medium. That work is generalized with an elastic
continuum theory of the response of modes of either parallel or perpendicular
polarization for a spherical adsorbate on a hexagonal substrate. The results
are applied to the discussion of computer simulations and inelastic atomic
scattering experiments for adsorbates on graphite. The extreme anisotropy of
the elastic behavior of the graphite leads to quite different wave vector
dependence of the damping for modes polarized perpendicular and parallel to the
substrate. A phenomenological extension of the elasticity theory of the
graphite to include bond-bending energies improves the description of substrate
modes with strong anomalous dispersion and enables a semi-quantitative account
of observed avoided crossings of the adlayer perpendicular vibration mode and
the substrate Rayleigh mode. | 9609032v1 |
1997-12-08 | Collective oscillations in superconductors revisited | In the recent paper Ohashi and Takada (OT) made statements that in the clean
limit considered by us (AV) in 1975, weakly damped collective oscillations in
superconductors do not exist due to the Landau damping and their spectrum
differs from that obtained in AV. In this Comment we would like to note that
these statements arise as a result of a misunderstanding of the term "clean"
case. OT considered the limit of frequencies larger, than elastic scattering
rate, meanwhile AV obtained weakly damped mode in the case when temperature is
larger than scattering rate, the frequencies being smaller (!) than elastic
scattering rate. All these problems were discussed in our review article in
1979 which was, presumably, unknown to OT. | 9712086v1 |
1999-01-11 | Vortex motion in superconducting YBCO inferred from the damping of the oscillations of a levitating magnetic microsphere | The damping of the oscillations of a small permanent magnet (spherical shape,
radius 0.1 mm) levitating between two parallel YBCO surfaces is measured as a
function of oscillation amplitude and temperature. The losses in the samples
(epitaxial thin films, bulk granular and bulk melt-textured) are analyzed in
terms of oscillating shielding currents flowing through trapped flux lines
whose motion gives rise to electric fields. We find dissipation to originate
from different mechanisms of flux dynamics. At small amplitudes there is a
linear regime described by a surface resistance varying from 10^-9 Ohm for bulk
samples down to 10^-13 Ohm for the thin films at low temperatures. With
increasing amplitude various nonlinear regimes are observed, firstly collective
pinning with diverging energy barriers, secondly in bulk samples above 85 K
hysteretic damping, and finally in thin films exponentially large losses which
can be described by pinning energies vanishing linearly at large currents. | 9901085v1 |
1999-10-07 | On the relative positions of the $2Δ$ peaks in Raman and tunneling spectra of d-wave superconductors | We study $B_{1g}$ Raman intensity $R(\Omega)$ and the density of states
$N(\omega)$ in isotropic 2D d-wave superconductors. For an ideal gas,
$R(\Omega)$ and $N(\omega)$ have sharp peaks at $\Omega =2\Delta$ and $\omega
=\Delta$, respectively, where $\Delta$ is the maximum value of the gap.
We study how the peak positions are affected by the fermionic damping due to
impurity scattering.
We show that while the damping generally shifts the peak positions to larger
frequencies, the peak in $R(\Omega)$ still occurs at almost twice the peak
position in $N(\omega)$ and therefore cannot account for the experimentally
observed downturn shift of the peak frequency in $R(\Omega)$ in underdoped
cuprates compared to twice that in $N(\omega)$. We also discuss how the
fermionic damping affects the dynamical spin susceptibility. | 9910090v1 |
2000-03-31 | Kinetic Theory of Collective Excitations and Damping in Bose-Einstein Condensed Gases | We calculate the frequencies and damping rates of the low-lying collective
modes of a Bose-Einstein condensed gas at nonzero temperature. We use a complex
nonlinear Schr\"odinger equation to determine the dynamics of the condensate
atoms, and couple it to a Boltzmann equation for the noncondensate atoms. In
this manner we take into account both collisions between
noncondensate-noncondensate and condensate-noncondensate atoms. We solve the
linear response of these equations, using a time-dependent gaussian trial
function for the condensate wave function and a truncated power expansion for
the deviation function of the thermal cloud. As a result, our calculation turns
out to be characterized by two dimensionless parameters proportional to the
noncondensate-noncondensate and condensate-noncondensate mean collision times.
We find in general quite good agreement with experiment, both for the
frequencies and damping of the collective modes. | 0003517v1 |
2000-09-01 | The broad Brillouin doublets and central peak of KTaO_3 | The incipient ferroelectric KTaO3 presents low-T Brillouin spectra
anomalies,e.g. a broad central peak (CP), and some additional Brillouin
doublets (BD), whose origin is interpreted in terms of phonon-density
fluctuation processes. A parameterisation from new extensive high-resolution
neutron-scattering measurements is used to show that hydrodynamic second sound
from high damping (compared to BD frequency) TA phonons may exist in the
crystal. Furthermore, low damping thermal phonons may scatter light through
two-phonon difference processes and appear on the Brillouin spectra either as a
sharp or a broader BD, depending on the phonon damping and group velocity . The
comparison between computed anisotropies and experimental measurements favours
the second process. | 0009012v1 |
2001-01-15 | Temperature Dependence of Damping and Frequency Shifts of the Scissors Mode of a trapped Bose-Einstein Condensate | We have studied the properties of the scissors mode of a trapped
Bose-Einstein condensate of $^{87}$Rb atoms at finite temperature. We measured
a significant shift in the frequency of the mode below the hydrodynamic limit
and a strong dependence of the damping rate as the temperature increased. We
compared our damping rate results to recent theoretical calculations for other
observed collective modes finding a fair agreement. From the frequency
measurements we deduce the moment of inertia of the gas and show that it is
quenched below the transition point, because of the superfluid nature of the
condensed gas. | 0101213v2 |
2001-03-16 | Gap Anisotropy and de Haas-van Alphen Effect in Type-II Superconductors | We present a theoretical study on the de Haas-van Alphen (dHvA) oscillation
in the vortex state of type-II superconductors, with a special focus on the
connection between the gap anisotropy and the oscillation damping. Numerical
calculations for three different gap structures clearly indicate that the
average gap along extremal orbits is relevant for the magnitude of the extra
damping, thereby providing a support for experimental efforts to probe gap
anisotropy through the dHvA signal. We also derive an analytic formula for the
extra damping which gives a good fit to the numerical results. | 0103336v3 |
2001-04-10 | Quantum phase transitions and collective modes in d-wave superconductors | Fluctuations near second-order quantum phase transitions in d-wave
superconductors can cause strong damping of fermionic excitations, as observed
in photoemission experiments. The damping of the gapless nodal quasiparticles
can arise naturally in the quantum-critical region of a transition with an
additional spin-singlet, zero momentum order parameter; we argue that the
transition to a d_x^2-y^2 + i d_xy pairing state is the most likely possibility
in this category. On the other hand, the gapped antinodal quasiparticles can be
strongly damped by the coupling to antiferromagnetic spin fluctuations arising
from the proximity to a Neel-ordered state. We review some aspects of the
low-energy field theories for both transitions and the corresponding
quantum-critical behavior. In addition, we discuss the spectral properties of
the collective modes associated with the proximity to a superconductor with
d_x^2-y^2 + i d_xy symmetry, and implications for experiments. | 0104176v1 |
2002-04-11 | Nonequilibrium relaxation in neutral BCS superconductors: Ginzburg-Landau approach with Landau damping in real time | We present a field-theoretical method to obtain consistently the equations of
motion for small amplitude fluctuations of the order parameter directly in real
time for a homogeneous, neutral BCS superconductor. This method allows to study
the nonequilibrium relaxation of the order parameter as an initial value
problem. We obtain the Ward identities and the effective actions for small
phase the amplitude fluctuations to one-loop order. Focusing on the
long-wavelength, low-frequency limit near the critical point, we obtain the
time-dependent Ginzburg-Landau effective action to one-loop order, which is
nonlocal as a consequence of Landau damping. The nonequilibrium relaxation of
the phase and amplitude fluctuations is studied directly in real time. The
long-wavelength phase fluctuation (Bogoliubov-Anderson-Goldstone mode) is
overdamped by Landau damping and the relaxation time scale diverges at the
critical point, revealing critical slowing down. | 0204239v2 |
2002-05-21 | Linear spin waves in a trapped Bose gas | An ultra-cold Bose gas of two-level atoms can be thought of as a spin-1/2
Bose gas. It supports spin-wave collective modes due to the exchange mean
field. Such collective spin oscillations have been observed in recent
experiments at JILA with ${}^{87}$Rb atoms confined in a harmonic trap. We
present a theory of the spin-wave collective modes based on the moment method
for trapped gases. In the collisionless and hydrodynamic limits, we derive
analytic expressions for the frequencies and damping rates of modes with dipole
and quadrupole symmetry. We find that the frequency for a given mode is given
by a temperature independent function of the peak density $n$, and falls off as
$1/n$. We also find that, to a very good approximation, excitations in the
radial and axial directions are decoupled. We compare our model to the
numerical integration of a one dimensional version of the kinetic equation and
find very good qualitative agreement. The damping rates, however, show the
largest deviation for intermediate densities, where one expects Landau damping
-- which is unaccounted for in our moment approach -- to play a significant
role. | 0205450v1 |
2002-08-02 | Landau damping of transverse quadrupole oscillations of an elongated Bose-Einstein condensate | We study the interaction between low-lying transverse collective oscillations
and thermal excitations of an elongated Bose-Einstein condensate by means of
perturbation theory. We consider a cylindrically trapped condensate and
calculate the transverse elementary excitations at zero temperature by solving
the linearized Gross-Pitaevskii equations in two dimensions. We use them to
calculate the matrix elements between thermal excited states coupled with the
quasi-2D collective modes. The Landau damping of transverse collective modes is
investigated as a function of temperature. At low temperatures, the damping
rate due to the Landau decay mechanism is in agreement with the experimental
data for the decay of the transverse quadrupole mode, but it is too small to
explain the slow experimental decay of the transverse breathing mode. The
reason for this discrepancy is discussed. | 0208047v1 |
2002-08-28 | Transverse modes of a cigar-shaped Bose-Einstein condensate | We discuss the collective modes in a harmonically trapped, highly-elongated
Bose condensed gas. The transverse breathing mode exhibits a number of
interesting features, such as the insensitivity of the condensate mode
frequency to the interaction strength, and the closeness of the frequency to
that of the non-condensed thermal cloud in the collisionless limit. Using
finite temperature simulations, we show that these features are responsible for
the very small damping rate observed experimentally. Our results for the
temperature dependence of the damping rate and frequency shift are in excellent
agreement with experiment. We also demonstrate that the unusually small damping
rate does not arise for the $m=2$ mode or for more isotropic trap potentials,
suggesting further possible experimental tests of our theory. | 0208567v1 |
2002-10-31 | Stationary quantum statistics of a non-Markovian atom laser | We present a steady state analysis of a quantum-mechanical model of an atom
laser. A single-mode atomic trap coupled to a continuum of external modes is
driven by a saturable pumping mechanism. In the dilute flux regime, where
atom-atom interactions are negligible in the output, we have been able to solve
this model without making the Born-Markov approximation. The more exact
treatment has a different effective damping rate and occupation of the lasing
mode, as well as a shifted frequency and linewidth of the output. We examine
gravitational damping numerically, finding linewidths and frequency shifts for
a range of pumping rates. We treat mean field damping analytically, finding a
memory function for the Thomas-Fermi regime. The occupation and linewidth are
found to have a nonlinear scaling behavior which has implications for the
stability of atom lasers. | 0210688v1 |
2003-03-23 | Damping of micromechanical structures by paramagnetic relaxation | We find that the damping of micromechanical cantilevers is sensitive to the
relaxation dynamics of paramagnetic ions contained within the levers. We
measure cantilevers containing paramagnetic Mn ions as a function of
temperature, magnetic field, and the vibrational mode of the lever and find
that the levers damping is strongly enhanced by the interplay between the
motion of the lever, the ions magnetic anisotropy, and the ratio of the ions
longitudinal relaxation rate to the resonance frequency of the cantilever. This
enhancement can improve the levers ability to probe the relaxation behavior of
paramagnetic or superparamagetic systems; it may also represent a previously
unrecognized source of intrinsic dissipation in micromechanical structures. | 0303489v1 |
2003-03-27 | Oscillatory wave fronts in chains of coupled nonlinear oscillators | Wave front pinning and propagation in damped chains of coupled oscillators
are studied. There are two important thresholds for an applied constant stress
$F$: for $|F|<F_{cd}$ (dynamic Peierls stress), wave fronts fail to propagate,
for $F_{cd} < |F| < F_{cs}$ stable static and moving wave fronts coexist, and
for $|F| > F_{cs}$ (static Peierls stress) there are only stable moving wave
fronts. For piecewise linear models, extending an exact method of Atkinson and
Cabrera's to chains with damped dynamics corroborates this description. For
smooth nonlinearities, an approximate analytical description is found by means
of the active point theory. Generically for small or zero damping, stable wave
front profiles are non-monotone and become wavy (oscillatory) in one of their
tails. | 0303576v1 |
2003-06-03 | Local Relaxation and Collective Stochastic Dynamics | Damping and thermal fluctuations have been introduced to collective normal
modes of a magnetic system in recent modeling of dynamic thermal magnetization
processes. The connection between this collective stochastic dynamics and
physical local relaxation processes is investigated here. A system of two
coupled magnetic grains embedded in two separate oscillating thermal baths is
analyzed with no \QTR{it}{a priori} assumptions except that of a Markovian
process. It is shown explicitly that by eliminating the oscillating thermal
bath variables, collective stochastic dynamics occurs in the normal modes of
the magnetic system. The grain interactions cause local relaxation to be felt
by the collective system and the dynamic damping to reflect the system
symmetry. This form of stochastic dynamics is in contrast to a common
phenomenological approach where a thermal field is added independently to the
dynamic equations of each discretized cell or interacting grain. The dependence
of this collective stochastic dynamics on the coupling strength of the magnetic
grains and the relative local damping is discussed. | 0306047v1 |
2003-07-22 | Classical dynamics of a nano-mechanical resonator coupled to a single-electron transistor | We analyze the dynamics of a nano-mechanical resonator coupled to a
single-electron transistor (SET) in the regime where the resonator behaves
classically. A master equation is derived describing the dynamics of the
coupled system which is then used to obtain equations of motion for the average
charge state of the SET and the average position of the resonator. We show that
the action of the SET on the resonator is very similar to that of a thermal
bath, as it leads to a steady-state probability-distribution for the resonator
which can be described by mean values of the resonator position, a renormalized
frequency, an effective temperature and an intrinsic damping constant.
Including the effects of extrinsic damping and finite temperature, we find that
there remain experimentally accessible regimes where the intrinsic damping of
the resonator still dominates its behavior. We also obtain the average current
through the SET as a function of the coupling to the resonator. | 0307528v1 |
2003-10-09 | Direct measurement of molecular stiffness and damping in confined water layers | We present {\em direct} and {\em linear} measurements of the normal stiffness
and damping of a confined, few molecule thick water layer. The measurements
were obtained by use of a small amplitude (0.36 $\textrm{\AA}$), off-resonance
Atomic Force Microscopy (AFM) technique. We measured stiffness and damping
oscillations revealing up to 7 layers separated by 2.56 $\pm$ 0.20
$\textrm{\AA}$. Relaxation times could also be calculated and were found to
indicate a significant slow-down of the dynamics of the system as the confining
separation was reduced. We found that the dynamics of the system is determined
not only by the interfacial pressure, but more significantly by solvation
effects which depend on the exact separation of tip and surface. Thus `
solidification\rq seems to not be merely a result of pressure and confinement,
but depends strongly on how commensurate the confining cavity is with the
molecule size. We were able to model the results by starting from the simple
assumption that the relaxation time depends linearly on the film stiffness. | 0310219v1 |
2004-03-08 | Mean-field magnetization relaxation in conducting ferromagnets | Collective ferromagnetic motion in a conducting medium is damped by the
transfer of the magnetic moment and energy to the itinerant carriers. We
present a calculation of the corresponding magnetization relaxation as a
linear-response problem for the carrier dynamics in the effective exchange
field of the ferromagnet. In electron systems with little intrinsic spin-orbit
interaction, a uniform magnetization motion can be formally eliminated by going
into the rotating frame of reference for the spin dynamics. The ferromagnetic
damping in this case grows linearly with the spin-flip rate when the latter is
smaller than the exchange field and is inversely proportional to the spin-flip
rate in the opposite limit. These two regimes are analogous to the
"spin-pumping" and the "breathing Fermi-surface" damping mechanisms,
respectively. In diluted ferromagnetic semiconductors, the hole-mediated
magnetization can be efficiently relaxed to the itinerant-carrier degrees of
freedom due to the strong spin-orbit interaction in the valence bands. | 0403224v2 |
2004-04-05 | Low-temperature specific heat of real crystals: Possibility of leading contribution of optical and short-wavelength acoustical vibrations | We point out that the repeatedly reported glass-like properties of
crystalline materials are not necessarily associated with localized (or
quasilocalized) excitations. In real crystals, optical and short-wavelength
acoustical vibrations remain damped due to defects down to zero temperature. If
such a damping is frequency-independent, e.g. due to planar defects or charged
defects, these optical and short-wavelength acoustical vibrations yield a
linear-in-$T$ contribution to the low-temperature specific heat of the crystal
lattices. At low enough temperatures such a contribution will prevail over that
of the long-wavelength acoustical vibrations (Debye contribution). The
crossover between the linear and the Debye regime takes place at $T^* \propto
\sqrt N$, where $N$ is the concentration of the defects responsible for the
damping. Estimates show that this crossover could be observable. | 0404063v4 |
2004-04-20 | Decoherence processes during active manipulation of excitonic qubits in semiconductor quantum dots | Using photoluminescence spectroscopy, we have investigated the nature of Rabi
oscillation damping during active manipulation of excitonic qubits in
self-assembled quantum dots. Rabi oscillations were recorded by varying the
pulse amplitude for fixed pulse durations between 4 ps and 10 ps. Up to 5
periods are visible, making it possible to quantify the excitation dependent
damping. We find that this damping is more pronounced for shorter pulse widths
and show that its origin is the non-resonant excitation of carriers in the
wetting layer, most likely involving bound-to-continuum and continuum-to-bound
transitions. | 0404465v1 |
2004-07-29 | From subdiffusion to superdiffusion of particles on solid surfaces | We present a numerical and partially analytical study of classical particles
obeying a Langevin equation that describes diffusion on a surface modeled by a
two dimensional potential. The potential may be either periodic or random.
Depending on the potential and the damping, we observe superdiffusion,
large-step diffusion, diffusion, and subdiffusion. Superdiffusive behavior is
associated with low damping and is in most cases transient, albeit often long.
Subdiffusive behavior is associated with highly damped particles in random
potentials. In some cases subdiffusive behavior persists over our entire
simulation and may be characterized as metastable. In any case, we stress that
this rich variety of behaviors emerges naturally from an ordinary Langevin
equation for a system described by ordinary canonical Maxwell-Boltzmann
statistics. | 0407781v1 |
2004-08-18 | Theory of Magnetic Polaron | The concept of magnetic polaron is analysed and developed to elucidate the
nature of itinerant charge carrier states in magnetic semiconductors and
similar complex magnetic materials. By contrasting the scattering and bound
states of carriers within the $s-d$ exchange model, the nature of bound states
at finite temperatures is clarified. The free magnetic polaron at certain
conditions is realized as a bound state of the carrier (electron or hole) with
the spin wave. Quite generally, a self-consistent theory of a magnetic polaron
is formulated within a nonperturbative many-body approach, the Irreducible
Green Functions (IGF) method which is used to describe the quasiparticle
many-body dynamics at finite temperatures. Within the above many-body approach
we elaborate a self-consistent picture of dynamic behavior of two interacting
subsystems, the localized spins and the itinerant charge carriers. In
particular, we show that the relevant generalized mean fields emerges naturally
within our formalism. At the same time, the correct separation of elastic
scattering corrections permits one to consider the damping effects (inelastic
scattering corrections) in the unified and coherent fashion. The damping of
magnetic polaron state, which is quite different from the damping of the
scattering states, finds a natural interpretation within the present
self-consistent scheme. | 0408404v2 |
2004-09-27 | Dephasing and delay time fluctuations in the chaotic scattering of a quantum particle weakly coupled to a complicated background | Effect of a complicated many-body environment is analyzed on the chaotic
motion of a quantum particle in a mesoscopic ballistic structure. The dephasing
and absorption phenomena are treated on the same footing in the framework of a
schematic microscopic model. The single-particle doorway resonance states
excited in the structure via an external channel are damped not only because of
the escape onto such channels but also due to ulterior population of the
long-lived background states. The transmission through the structure is
presented as an incoherent sum of the flow formed by the interfering damped
doorway resonances and the retarded flow of the particles reemitted by the
environment. The resulting internal damping as well as the dephasing rate are
uniquely expressed in terms of the spreading width which controls the coupling
to the background. The formation of the long-lived fine-structure resonances
strongly enhances delay time fluctuations thus broadening the delay time
distribution. | 0409690v1 |
2005-01-18 | Damping effects and the metal-insulator transition in the two-dimensional electron gas | The damping of single-particle degrees of freedom in strongly correlated
two-dimensional Fermi systems is analyzed. Suppression of the scattering
amplitude due to the damping effects is shown to play a key role in preserving
the validity of the Landau-Migdal quasiparticle picture in a region of a phase
transition, associated with the divergence of the quasiparticle effective mass.
The results of the analysis are applied to elucidate the behavior of the
conductivity $\sigma(T)$ of the two-dimensional dilute electron gas in the
density region where it undergoes a metal-insulator transition. | 0501427v2 |
2005-04-17 | Dynamics of thermoelastic thin plates: A comparison of four theories | Four distinct theories describing the flexural motion of thermoelastic thin
plates are compared. The theories are due to Chadwick, Lagnese and Lions,
Simmonds, and Norris. Chadwick's theory requires a 3D spatial equation for the
temperature but is considered the most accurate as the others are derivable
from it by different approximations. Attention is given to the damping of
flexural waves. Analytical and quantitative comparisons indicate that the
Lagnese and Lions model with a 2D temperature equation captures the essential
features of the thermoelastic damping, but contains systematic inaccuracies.
These are attributable to the approximation for the first moment of the
temperature used in deriving the Lagnese and Lions equation. Simmonds' model
with an explicit formula for temperature in terms of plate deflection is the
simplest of all but is accurate only at low frequency, where the damping is
linearly proportional to the frequency. It is shown that the Norris model,
which is almost as simple as Simmond's, is as accurate as the more precise but
involved theory of Chadwick. | 0504412v1 |
2005-04-29 | Probing temperature and damping rates in Bose-Einstein condensates using ultraslow light experiments | We propose a method to probe Landau and Beliaev processes in dilute trapped
atomic condensates with a multiple state structure using ultraslow light
experimental configurations. Under certain conditions, damping rates from these
collisional processes are directly proportional to the dephasing rates, making
it possible to determine damping rates through measurement of the dephasing. In
the ultraslow light systems we consider, Landau decay rates are enhanced at low
momenta, which allows one to distinguish between Landau-dominated and
Beliaev-dominated regimes at the same temperature. Furthermore, the enhancement
of Landau rates potentially provides a way to measure low temperatures ($T \ll
T_c$) in dilute condensates more accurately than current methods permit. | 0504784v2 |
2005-05-23 | Anharmonic vs. relaxational sound damping in glasses: I. Brillouin scattering from densified silica | This series discusses the origin of sound damping and dispersion in glasses.
In particular, we address the relative importance of anharmonicity versus
thermally activated relaxation. In this first article, Brillouin-scattering
measurements of permanently densified silica glass are presented. It is found
that in this case the results are compatible with a model in which damping and
dispersion are only produced by the anharmonic coupling of the sound waves with
thermally excited modes. The thermal relaxation time and the unrelaxed velocity
are estimated. | 0505558v3 |
2005-05-23 | Anharmonic vs. relaxational sound damping in glasses: II. Vitreous silica | The temperature dependence of the frequency dispersion in the sound velocity
and damping of vitreous silica is reanalyzed. Thermally activated relaxation
accounts for the sound attenuation observed above 10 K at sonic and ultrasonic
frequencies. Its extrapolation to the hypersonic regime reveals that the
anharmonic coupling to the thermal bath becomes important in
Brillouin-scattering measurements. At 35 GHz and room temperature, the damping
due to this anharmonicity is found to be nearly twice that produced by
thermally activated relaxation. The analysis also reveals a sizeable velocity
increase with temperature which is not related with sound dispersion. This
suggests that silica experiences a gradual structural change that already
starts well below room temperature. | 0505560v2 |
2005-06-06 | Heat Bath Approach to Landau Damping and Pomeranchuk Quantum Critical Points | We study the problem of the damping of collective modes close to a
Pomeranchuk quantum critical point in a Fermi liquid. In analogy with problems
in dissipative open quantum systems, we derive the Landau damping of a Fermi
liquid by integrating out a macroscopic number of degrees of freedom from a
generating functional. Being a reformulation of the linearized Boltzmann
equation this approach reproduces well-known results from the theory of Fermi
liquids. We also study the Bethe-Salpeter equations within the Landau theory
and discuss the implications of these results on quantum phase transitions of
the Pomeranchuk type and its dynamical exponent, z. We apply our results to the
electronic nematic instability and find z=3 in the collisionless limit. | 0506146v3 |
2005-07-01 | Measurement of Dissipation of a Three-Level rf SQUID Qubit | The dissipation-induced relaxation (T_1) time of a macroscopic quantum system
- a \{lambda}-type three-level rf SQUID flux qubit weakly coupled to control
and readout circuitry (CRC) - is investigated via time-domain measurement. The
measured interwell relaxation time of the qubit's first excited state,
T_1=3.45+/-0.06 \{mu}s, corresponds to an effective damping resistance of the
flux qubit R=1.6+/-0.1 M\{omega} which is much lower than the intrinsic
quasiparticle resistance of the Josephson tunnel junction. An analysis of the
system shows that although the CRC is very weakly coupled to the qubit it is
the primary source of damping. This type of damping can be significantly
reduced by the use of more sophisticated circuit design to allow coherent
manipulation of qubit states. | 0507008v1 |
2005-09-19 | Interaction effects on magnetooscillations in a two-dimensional electron gas | Motivated by recent experiments, we study the interaction corrections to the
damping of magnetooscillations in a two-dimensional electron gas (2DEG). We
identify leading contributions to the interaction-induced damping which are
induced by corrections to the effective mass and quantum scattering time. The
damping factor is calculated for Coulomb and short-range interaction in the
whole range of temperatures, from the ballistic to the diffusive regime. It is
shown that the dominant effect is that of the renormalization of the effective
electron mass due to the interplay of the interaction and impurity scattering.
The results are relevant to the analysis of experiments on magnetooscillations
(in particular, for extracting the value of the effective mass) and are
expected to be useful for understanding the physics of a high-mobility 2DEG
near the apparent metal-insulator transition. | 0509463v2 |
2005-12-20 | Damping of zero sound in Luttinger liquids | We calculate the damping gamma_q of collective density oscillations (zero
sound) in a one-dimensional Fermi gas with dimensionless forward scattering
interaction F and quadratic energy dispersion k^2 / 2 m at zero temperature.
For wave-vectors | q| /k_F small compared with F we find to leading order
gamma_q = v_F^{-1} m^{-2} Y (F) | q |^3, where v_F is the Fermi velocity, k_F
is the Fermi wave-vector, and Y (F) is proportional to F^3 for small F. We also
show that zero-sound damping leads to a finite maximum proportional to |k - k_F
|^{-2 + 2 eta} of the charge peak in the single-particle spectral function,
where eta is the anomalous dimension. Our prediction agrees with photoemission
data for the blue bronze K_{0.3}MoO_3. | 0512494v4 |
2006-04-11 | Damping and dispersion of oscillating modes of a multicomponent ionic mixture in a magnetic field | The collective-mode spectrum of a multicomponent magnetized ionic mixture for
small wave number k is studied with the use of magnetohydrodynamics and formal
kinetic theory. Apart from the usual thermal and diffusive modes, the spectrum
contains a set of four oscillating modes. By evaluating the k^2 contributions
to the eigenfrequencies, the damping and the dispersion of these oscillating
modes are determined. The long-range nature of the Coulomb interactions is
shown to imply that Burnett terms with higher-order gradients in the linear
phenomenological laws have to be taken into account in order to obtain a full
description of all damping and dispersion effects. | 0604272v1 |
2006-05-16 | Collective mode damping and viscosity in a 1D unitary Fermi gas | We calculate the damping of the Bogoliubov-Anderson mode in a one-dimensional
two-component attractive Fermi gas for arbitrary coupling strength within a
quantum hydrodynamic approach. Using the Bethe-Ansatz solution of the 1D
BCS-BEC crossover problem, we derive analytic results for the viscosity
covering the full range from a Luther-Emery liquid of weakly bound pairs to a
Lieb-Liniger gas of strongly bound bosonic dimers. At the unitarity point, the
system is a Tonks-Girardeau gas with a universal constant $\alpha_{\zeta}=0.38$
in the viscosity $\zeta=\alpha_{\zeta}\hbar n$ for T=0. For the trapped case,
we calculate the Q-factor of the breathing mode and show that the damping
provides a sensitive measure of temperature in 1D Fermi gases. | 0605413v2 |
2006-07-06 | Low energy theory of a single vortex and electronic quasiparticles in a d-wave superconductor | We highlight the properties of a simple model (contained in our recent work)
of the quantum dynamics of a single point vortex interacting with the nodal
fermionic quasiparticles of a d-wave superconductor. We describe the
renormalization of the vortex motion by the quasiparticles: at T=0, the
quasiparticles renormalize the vortex mass and introduce only a weak sub-Ohmic
damping. Ohmic (or `Bardeen-Stephen' damping) appears at T>0, with the damping
co-efficient vanishing ~ T^2 with a universal prefactor. Conversely, quantum
fluctuations of the vortex renormalize the quasiparticle spectrum. A point
vortex oscillating in a harmonic pinning potential has no zero-bias peak in the
electronic local density of states (LDOS), but has small satellite features at
an energy determined by the pinning potential. These are proposed as the origin
of sub-gap LDOS peaks observed in scanning tunneling microscopic studies of the
LDOS near a vortex. | 0607137v2 |
2005-08-23 | Investigations of Process Damping Forces in Metal Cutting | Using finite element software developed for metal cutting by Third Wave
Systems we investigate the forces involved in chatter, a self-sustained
oscillation of the cutting tool. The phenomena is decomposed into a vibrating
tool cutting a flat surface work piece, and motionless tool cutting a work
piece with a wavy surface. While cutting the wavy surface, the shearplane was
seen to oscillate in advance of the oscillation of the depth of cut, as were
the cutting, thrust, and shear plane forces. The vibrating tool was used to
investigate process damping through the interaction of the relief face of the
tool and the workpiece. Crushing forces are isolated and compared to the
contact length between the tool and workpiece. We found that the wavelength
dependence of the forces depended on the relative size of the wavelength to the
length of the relief face of the tool. The results indicate that the damping
force from crushing will be proportional to the cutting speed for short tools,
and inversely proportional for long tools. | 0508102v1 |
1999-09-27 | R-Modes in Superfluid Neutron Stars | The analogs of r-modes in superfluid neutron stars are studied here. These
modes, which are governed primarily by the Coriolis force, are identical to
their ordinary-fluid counterparts at the lowest order in the small
angular-velocity expansion used here. The equations that determine the next
order terms are derived and solved numerically for fairly realistic superfluid
neutron-star models. The damping of these modes by superfluid ``mutual
friction'' (which vanishes at the lowest order in this expansion) is found to
have a characteristic time-scale of about 10^4 s for the m=2 r-mode in a
``typical'' superfluid neutron-star model. This time-scale is far too long to
allow mutual friction to suppress the recently discovered gravitational
radiation driven instability in the r-modes. However, the strength of the
mutual friction damping depends very sensitively on the details of the
neutron-star core superfluid. A small fraction of the presently acceptable
range of superfluid models have characteristic mutual friction damping times
that are short enough (i.e. shorter than about 5 s) to suppress the
gravitational radiation driven instability completely. | 9909084v1 |
2001-02-08 | Cyclotron damping and Faraday rotation of gravitational waves | We study the propagation of gravitational waves in a collisionless plasma
with an external magnetic field parallel to the direction of propagation. Due
to resonant interaction with the plasma particles the gravitational wave
experiences cyclotron damping or growth, the latter case being possible if the
distribution function for any of the particle species deviates from
thermodynamical equilibrium. Furthermore, we examine how the damping and
dispersion depends on temperature and on the ratio between the cyclotron- and
gravitational wave frequency. The presence of the magnetic field leads to
different dispersion relations for different polarizations, which in turn imply
Faraday rotation of gravitational waves. | 0102031v2 |
2007-02-07 | Relativistic r-modes and shear viscosity | We derive the relativistic equations for stellar perturbations, including in
a consistent way shear viscosity in the stress-energy tensor, and we
numerically integrate our equations in the case of large viscosity. We consider
the slow rotation approximation, and we neglect the coupling between polar and
axial perturbations. In our approach, the frequency and damping time of the
emitted gravitational radiation are directly obtained. We find that,
approaching the inviscid limit from the finite viscosity case, the continuous
spectrum is regularized. Constant density stars, polytropic stars, and stars
with realistic equations of state are considered. In the case of constant
density stars and polytropic stars, our results for the viscous damping times
agree, within a factor two, with the usual estimates obtained by using the
eigenfunctions of the inviscid limit. For realistic neutron stars, our
numerical results give viscous damping times with the same dependence on mass
and radius as previously estimated, but systematically larger of about 60%. | 0702040v1 |
2000-08-18 | Fabrication Process of Rounded Damped Detuned Structure | Following the successful design and fabrication of Damped Detuned Structures
(DDS), the JLC/NLC linear collider project advanced to Rounded Damped Detuned
Structures (RDDS) with curved cross section of the cavity shape for increased
shunt impedance. Various advanced techniques for fabricating RDDS1 disks
comparing to those for DDS were established to satisfy the dimension accuracy
of +-1 micron over the entire surface made by ultra-precision turning. These
disks were assembled with almost the same stacking and bonding jigs and
processes as those of DDS3 assembly. In consequence, the assembly showed little
disk-to-disk misalignment within 1 micron before and after the process. Though,
it had 200 micron smooth bowing, which was subsequently corrected as DDS3, and
flares at both ends. | 0008034v1 |
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