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2021-06-10
|
Constraining extra dimensions using observations of black hole quasi-normal modes
|
The presence of extra dimensions generically modify the spacetime geometry of
a rotating black hole, by adding an additional hair, besides the mass $M$ and
the angular momentum $J$, known as the `tidal charge' parameter, $\beta$. In a
braneworld scenario with one extra spatial dimension, the extra dimension is
expected to manifest itself through -- (a) negative values of $\beta$, and (b)
modified gravitational perturbations. This in turn would affect the
quasi-normal modes of rotating black holes. We numerically solve the perturbed
gravitational field equations using the continued fractions method and
determine the quasi-normal mode spectra for the braneworld black hole. We find
that increasingly negative values of $\beta$ correspond to a diminishing
imaginary part of the quasi-normal mode, or equivalently, an increasing damping
time. Using the publicly available data of the properties of the remnant black
hole in the gravitational wave signal GW150914, we check for consistency
between the predicted values (for a given $\beta$) of the frequency and damping
time of the least-damped $\ell=2,m=2$ quasi-normal mode and measurements of
these quantities using other independent techniques. We find that it is highly
unlikely for the tidal charge, $\beta \lesssim -0.05$, providing a conservative
limit on the tidal charge parameter. Implications and future directions are
discussed.
|
2106.05558v2
|
2021-06-24
|
A Polarizable Water Potential Derived from a Model Electron Density
|
A new empirical potential for efficient, large scale molecular dynamics
simulation of water is presented. The HIPPO (Hydrogen-like Intermolecular
Polarizable POtential) force field is based upon the model electron density of
a hydrogen-like atom. This framework is used to derive and parameterize
individual terms describing charge penetration damped permanent electrostatics,
damped polarization, charge transfer, anisotropic Pauli repulsion, and damped
dispersion interactions. Initial parameter values were fit to Symmetry Adapted
Perturbation Theory (SAPT) energy components for ten water dimer
configurations, as well as the radial and angular dependence of the canonical
dimer. The SAPT-based parameters were then systematically refined to extend the
treatment to water bulk phases. The final HIPPO water model provides a balanced
representation of a wide variety of properties of gas phase clusters, liquid
water and ice polymorphs, across a range of temperatures and pressures. This
water potential yields a rationalization of water structure, dynamics and
thermodynamics explicitly correlated with an ab initio energy decomposition,
while providing a level of accuracy comparable or superior to previous
polarizable atomic multipole force fields. The HIPPO water model serves as a
cornerstone around which similarly detailed physics-based models can be
developed for additional molecular species.
|
2106.13116v3
|
2021-07-19
|
Long term behavior of 2D and 3D non-autonomous random convective Brinkman-Forchheimer equations driven by colored noise
|
The long time behavior of Wong-Zakai approximations of 2D as well as 3D
non-autonomous stochastic convective Brinkman-Forchheimer (CBF) equations with
non-linear diffusion terms on bounded and unbounded ($\mathbb{R}^d$ for
$d=2,3$) domains is discussed in this work. To establish the existence of
random pullback attractors, the concept of asymptotic compactness (AC) is used.
In bounded domains, AC is proved via compact Sobolev embeddings. In unbounded
domains, due to the lack of compact embeddings, the ideas of energy equations
and uniform tail estimates are exploited to prove AC. In the literature, CBF
equations are also known as \emph{Navier-Stokes equations (NSE) with damping},
and it is interesting to see that the modification in NSE by linear and
nonlinear damping provides better results than that available for NSE. The
presence of linear damping term helps to establish the results in the whole
domain $\mathbb{R}^d$. The nonlinear damping term supports to obtain better
results in 3D and also for a large class of nonlinear diffusion terms.
Moreover, we prove the existence of a unique random pullback attractor for
stochastic CBF equations with additive white noise. Finally, for additive as
well as multiplicative noise case, we establish the convergence of solutions
and upper semicontinuity of random pullback attractors for Wong-Zakai
approximations of stochastic CBF equations towards the random pullback
attractors for stochastic CBF equations when correlation time of colored noise
converges to zero.
|
2107.08890v1
|
2021-07-28
|
Queue-Channel Capacities with Generalized Amplitude Damping
|
The generalized amplitude damping channel (GADC) is considered an important
model for quantum communications, especially over optical networks. We make two
salient contributions in this paper apropos of this channel. First, we consider
a symmetric GAD channel characterized by the parameter $n=1/2,$ and derive its
exact classical capacity, by constructing a specific induced classical channel.
We show that the Holevo quantity for the GAD channel equals the Shannon
capacity of the induced binary symmetric channel, establishing at once the
capacity result and that the GAD channel capacity can be achieved without the
use of entanglement at the encoder or joint measurements at the decoder.
Second, motivated by the inevitable buffering of qubits in quantum networks, we
consider a generalized amplitude damping \emph{queue-channel} -- that is, a
setting where qubits suffer a waiting time dependent GAD noise as they wait in
a buffer to be transmitted. This GAD queue channel is characterized by
non-i.i.d. noise due to correlated waiting times of consecutive qubits. We
exploit a conditional independence property in conjunction with additivity of
the channel model, to obtain a capacity expression for the GAD queue channel in
terms of the stationary waiting time in the queue. Our results provide useful
insights towards designing practical quantum communication networks, and
highlight the need to explicitly model the impact of buffering.
|
2107.13486v1
|
2021-07-31
|
Damped inertial dynamics with vanishing Tikhonov regularization: strong asymptotic convergence towards the minimum norm solution
|
In a Hilbert space, we provide a fast dynamic approach to the hierarchical
minimization problem which consists in finding the minimum norm solution of a
convex minimization problem. For this, we study the convergence properties of
the trajectories generated by a damped inertial dynamic with Tikhonov
regularization. When the time goes to infinity, the Tikhonov regularization
parameter is supposed to tend towards zero, not too fast, which is a key
property to make the trajectories strongly converge towards the minimizer of
$f$ of minimum norm. According to the structure of the heavy ball method for
strongly convex functions, the viscous damping coefficient is proportional to
the square root of the Tikhonov regularization parameter. Therefore, it also
converges to zero, which will ensure rapid convergence of values. Precisely,
under a proper tuning of these parameters, based on Lyapunov's analysis, we
show that the trajectories strongly converge towards the minimizer of minimum
norm, and we provide the convergence rate of the values. We show a trade off
between the property of fast convergence of values, and the property of strong
convergence towards the minimum norm solution. This study improves several
previous works where this type of results was obtained under restrictive
hypotheses.
|
2108.00203v1
|
2021-08-13
|
Nonlinear modal testing of damped structures: Velocity feedback vs. phase resonance
|
In recent years, a new method for experimental nonlinear modal analysis has
been developed, which is based on the extended periodic motion concept. The
method is well suited to experimentally obtain amplitude-dependent modal
properties (modal frequency, damping ratio and deflection shape) for strongly
nonlinear systems. To isolate a nonlinear mode, the negative viscous damping
term of the extended periodic motion concept is approximated by ensuring phase
resonance between excitation and response. In this work, an alternative
approach to isolate a nonlinear mode is developed and analyzed: velocity
feedback. The accuracy of the extracted modal properties and robustness of
velocity feedback is first assessed by means of simulated experiments. The two
approaches phase resonance and velocity feedback are then compared in terms of
accuracy and experimental implementation effort. To this end, both approaches
are applied to an experimental specimen, which is a cantilevered beam
influenced by a strong dry friction nonlinearity. In this work, the discussion
is limited to single-point excitation. It is shown that a robust implementation
of velocity feedback requires the measurement of several response signals,
distributed over the structure. An advantage of velocity feedback is that no
controller is needed. The accuracy of the modal properties can, however, suffer
from imperfections of the excitation mechanism such as a phase lag due to
exciter-structure interactions or gyroscopic forces due to single-point
excitation.
|
2108.06189v1
|
2021-09-21
|
Double diffusion structure of logarithmically damped wave equations with a small parameter
|
We consider a wave equation with a nonlocal logarithmic damping depending on
a small parameter $\theta \in (0,1/2)$. This research is a counter part of that
was initiated by Charao-D'Abbicco-Ikehata considered in [5] for the large
parameter case $\theta \in (1/2,1)$. We study the Cauchy problem for this model
in the whole space for the small parameter case, and we obtain an asymptotic
profile and optimal estimates in time of solutions as time goes to infinity in
$L^2$-sense. An important discovery in this research is that in the one
dimensional case, we can present a threshold $\theta^{*} = 1/4$ of the
parameter $\theta$ such that the solution of the Cauchy problem decays with
some optimal rate for $\theta \in (0,\theta^{*})$, while the $L^2$-norm of the
corresponding solution blows up in infinite time for $\theta \in
[\theta^{*},1/2)$. The former (i.e., $\theta \in (0,\theta^{*})$ case)
indicates an usual diffusion phenomenon, while the latter (i.e., $\theta \in
[\theta^{*},1/2)$ case) implies, so to speak, a singular diffusion phenomenon.
Such a singular diffusion in the one dimensional case is a quite novel
phenomenon discovered through our new model produced by logarithmic damping
with a small parameter $\theta$.
|
2109.09944v2
|
2021-09-21
|
Non-intrusive Balancing Transformation of Highly Stiff Systems with Lightly-damped Impulse Response
|
Balanced truncation (BT) is a model reduction method that utilizes a
coordinate transformation to retain eigen-directions that are highly observable
and reachable. To address realizability and scalability of BT applied to highly
stiff and lightly-damped systems, a non-intrusive data-driven method is
developed for balancing discrete-time systems via the eigensystem realization
algorithm (ERA). The advantage of ERA for balancing transformation makes
full-state outputs tractable. Further, ERA enables balancing despite stiffness,
by eliminating computation of balancing modes and adjoint simulations. As a
demonstrative example, we create balanced ROMs for a one-dimensional reactive
flow with pressure forcing, where the stiffness introduced by the chemical
source term is extreme (condition number $10^{13}$), preventing analytical
implementation of BT. We investigate the performance of ROMs in prediction of
dynamics with unseen forcing inputs and demonstrate stability and accuracy of
balanced ROMs in truly predictive scenarios whereas without ERA, POD-Galerkin
and Least-squares Petrov-Galerkin projections fail to represent the true
dynamics. We show that after the initial transients under unit impulse forcing,
the system undergoes lightly-damped oscillations, which magnifies the influence
of sampling properties on predictive performance of the balanced ROMs. We
propose an output domain decomposition approach and couple it with tangential
interpolation to resolve sharp gradients at reduced computational costs.
|
2109.10408v2
|
2021-10-08
|
Site characterization at Treasure Island and Delaney Park downhole arrays by heterogeneous data assimilation
|
This article extends a recently proposed heterogeneous data assimilation
technique for site characterization to estimate compression and shear wave
velocity (Vp and Vs, respectively) and damping at Treasure Island and Delaney
Park downhole arrays. The adopted method is based on the joint inversion of
earthquake acceleration time series and experimental surface wave dispersion
data, and including physical constraints to improve the inverse problem's
well-posedness. We first use synthetic data at these two sites to refine the
proposed approach and then apply the refined algorithm to real data sets
available at the Treasure Island and Delaney Park downhole arrays. The joint
inversion results show that the estimated Vs and Vp profiles are in very good
agreement with measured profiles at these two sites. Our synthetic and real
data experiment results suggest that Vp estimation from inversion at downhole
arrays can be improved by integrating the water table depth information or the
higher modes of the Rayleigh wave dispersion data. Depending on the site
complexity, water table information can also help reduce uncertainties
associated with damping estimation. In the last part of this article, we
compare the performance of the inverted profiles to other methods used to
incorporate spatial variability and wave scattering effects in 1D ground
response analysis (GRA). The comparisons show that the joint inversion-based Vs
and Vp profiles and damping ratios estimated in this article can effectively
integrate the effects of spatial variability and wave scattering into 1D GRAs,
especially at the Delaney Park downhole array, which is classified as a poorly
modeled site using traditional 1D GRA.
|
2110.03849v1
|
2021-11-01
|
On the stochastic nature of Galactic cosmic-ray sources
|
The precision measurements of the spectra of cosmic ray nuclei and leptons in
recent years have revealed the existence of multiple features, such as the
spectral break at $\sim 300$ GV rigidity seen by PAMELA and AMS-02 and more
recently confirmed by DAMPE and CALET, the softening in the spectra of H and He
nuclei at $\sim 10$ TV reported by DAMPE, confirming previous hints by NUCLEON
and CREAM, a tiny change of slope at $\sim 40$ GeV in the electron spectrum,
revealed by AMS-02, and the large spectral break at $\sim$ TeV reported by
indirect (HESS, MAGIC and VERITAS) and direct (DAMPE, CALET) measurements of
the total (electrons+positrons) lepton spectrum. In all these cases, the
possibility has been suggested that these features might reflect the occasional
presence of a local cosmic ray source, inducing a noticeable reshaping of the
average expected spectra. All these proposals have to face the question of how
likely it is for such a source to exist, a question that we address here in a
quantitative way. We study the statistical properties of random distribution of
sources in space and time, and the effect of the spiral structure of our Galaxy
for both the spectra of light nuclei (p and He) and leptons (electrons and
positrons) in different energy regions.
|
2111.01171v2
|
2021-11-09
|
The In Situ Signature of Cyclotron Resonant Heating
|
The dissipation of magnetized turbulence is an important paradigm for
describing heating and energy transfer in astrophysical environments such as
the solar corona and wind; however, the specific collisionless processes behind
dissipation and heating remain relatively unconstrained by measurements. Remote
sensing observations have suggested the presence of strong temperature
anisotropy in the solar corona consistent with cyclotron resonant heating. In
the solar wind, in situ magnetic field measurements reveal the presence of
cyclotron waves, while measured ion velocity distribution functions have hinted
at the active presence of cyclotron resonance. Here, we present Parker Solar
Probe observations that connect the presence of ion-cyclotron waves directly to
signatures of resonant damping in observed proton-velocity distributions. We
show that the observed cyclotron wave population coincides with both flattening
in the phase space distribution predicted by resonant quasilinear diffusion and
steepening in the turbulent spectra at the ion-cyclotron resonant scale. In
measured velocity distribution functions where cyclotron resonant flattening is
weaker, the distributions are nearly uniformly subject to ion-cyclotron wave
damping rather than emission, indicating that the distributions can damp the
observed wave population. These results are consistent with active cyclotron
heating in the solar wind.
|
2111.05400v2
|
2021-11-10
|
Quantum amplitude damping for solving homogeneous linear differential equations: A noninterferometric algorithm
|
In contexts where relevant problems can easily attain configuration spaces of
enormous sizes, solving Linear Differential Equations (LDEs) can become a hard
achievement for classical computers; on the other hand, the rise of quantum
hardware can conceptually enable such high-dimensional problems to be solved
with a foreseeable number of qubits, whilst also yielding quantum advantage in
terms of time complexity. Nevertheless, in order to bridge towards experimental
realizations with several qubits and harvest such potential in a short-term
basis, one must dispose of efficient quantum algorithms that are compatible
with near-term projections of state-of-the-art hardware, in terms of both
techniques and limitations. As the conception of such algorithms is no trivial
task, insights on new heuristics are welcomed. This work proposes a novel
approach by using the Quantum Amplitude Damping operation as a resource, in
order to construct an efficient quantum algorithm for solving homogeneous LDEs.
As the intended implementation involves performing Amplitude Damping
exclusively via a simple equivalent quantum circuit, our algorithm shall be
given by a gate-level quantum circuit (predominantly composed of elementary
2-qubit gates) and is particularly nonrestrictive in terms of connectivity
within and between some of its main quantum registers. We show that such an
open quantum system-inspired circuitry allows for constructing the real
exponential terms in the solution in a non-interferometric way; we also provide
a guideline for guaranteeing a lower bound on the probability of success for
each realization, by exploring the decay properties of the underlying quantum
operation.
|
2111.05646v2
|
2021-11-13
|
Attenuation of surface modes in granular media
|
In this work, an unconsolidated granular medium, made of silica microbeads,
is experimentally tested in a laboratory setting. The objective is to
investigate the attenuation mechanisms of vertically polarized seismic waves
traveling at the surface of unconsolidated substrates that are characterized by
power-law rigidity profiles. Both geometric spreading and material damping due
to skeletal dissipation are considered. An electromagnetic shaker is employed
to excite the granular medium between 300 and 550 Hz, generating linear modes
that are localized near the surface. A densely sampled section is recorded at
the surface using a laser vibrometer. The explicit solution of the geometric
attenuation law of Rayleigh-like waves in layered media is employed to
calculate the geometric spreading function of the vertically polarized surface
modes within the granular material. In accordance with recent studies, the
dynamics of these small-amplitude multi-modal linear waves can be analysed by
considering the granular medium as perfectly continuous and elastic. By
performing a non-linear regression analysis on particle displacements,
extracted from experimental velocity data, we determine the frequency-dependent
attenuation coefficients, which account for the material damping.
The findings of this work show that laboratory-scale physical models can be
used to study the geometric spreading of vertically polarized seismic waves
induced by the soil inhomogeneity and characterize the material damping of the
medium.
|
2111.07199v1
|
2021-11-15
|
The Interplay of Regularizing Factors in the Model of Upper Hybrid Oscillations of Cold Plasma
|
A one-dimensional nonlinear model of the so-called upper hybrid oscillations
in a magnetoactive plasma is investigated taking into account electron-ion
collisions. It is known that both the presence of an external magnetic field of
strength $ B_0 $ and a sufficiently large collisional factor $ \nu $ help
suppress the formation of a finite-dimensional singularity in a solution
(breaking of oscillations). Nevertheless, the suppression mechanism is
different: an external magnetic field increases the oscillation frequency, and
collisions tend to stabilize the medium and suppress oscillations. In terms of
the initial data and the coefficients $ B_0 $ and $ \nu $, we establish a
criterion for maintaining the global smoothness of the solution. Namely, for
fixed $ B_0 $ and $ \nu \ge 0 $ one can precisely divide the initial data into
two classes: one leads to stabilization to the equilibrium and the other leads
to the destruction of the solution in a finite time. Next, we examine the
nature of the stabilization. We show that for small $ B_0 $ an increase in the
intensity factor first leads to a change in the oscillatory behavior of the
solution to monotonic damping, which is then again replaced by oscillatory
damping. At large values of $ B_0 $, the solution is characterized by
oscillatory damping regardless of the value of the intensity factor $ \nu $.
|
2111.07826v3
|
2021-11-20
|
Excitation and Damping of Slow Magnetosonic Waves in Flaring Hot Coronal Loops: Effects of Compressive Viscosity
|
Slow magnetosonic waves associated with flares were observed in coronal loops
by SOHO/SUMER, SDO/AIA in various EUV bandpasses, and other instruments. The
excitation and damping of slow magnetosonic waves provides information on the
magnetic, temperature, and density structure of the loops. Recently, it was
found using 1.5D models that the thermal conduction is suppressed and
compressive viscosity is enhanced in hot (T>6 MK) flaring coronal loops. We
model the excitation and dissipation of slow magnetosonic waves in hot coronal
loops with realistic magnetic geometry, enhanced density, and temperature
(compared to background corona) guided by EUV observations using 3D MHD
visco-resistive model. The effects of compressive viscosity tensor component
along the magnetic field are included with classical and enhanced viscosity
coefficient values for the first time in 3D MHD coronal loop model. The waves
are excited by a velocity pulse at the footpoint of the loop at coronal lower
boundary. The modeling results demonstrate the excitation of the slow
magnetosonic waves and nonlinear coupling to other wave modes, such as the kink
and fast magnetosonic. We find significant leakage of the waves from the hot
coronal loops with small effect of viscous dissipation in cooler (6MK) loops,
and more significant effects of viscous dissipation in hotter (10.5MK) coronal
loops. Our results demonstrate that nonlinear 3D MHD models are required to
fully account for various wave couplings, damping, standing wave formation, and
viscous dissipation in hot flaring coronal loops. Our viscous 3D MHD code
provides a new tool for improved coronal seismology.
|
2111.10696v1
|
2021-12-22
|
Strong Stabilization of a 3D Potential Flow via a Weakly Damped von Karman Plate
|
The elimination of aeroelastic instability (resulting in sustained
oscillations of bridges, buildings, airfoils) is a central engineering and
design issue. Mathematically, this translates to strong asymptotic
stabilization of a 3D flow by a 2D elastic structure. The stabilization
(convergence to the stationary set) of a aerodynamic wave-plate model is
established here. A 3D potential flow on the half-space has a spatially-bounded
von Karman plate embedded in the boundary. The physical model, then, is a
Neumann wave equation with low regularity of coupling conditions. Motivated on
empirical observations, we examine if intrinsic panel damping can stabilize the
subsonic flow-plate system to a stationary point. Several partial results have
been established through partial regularization of the model. Without doing so,
classical approaches attempting to treat the given wave boundary data have
fallen short, owing to the failure of the Lopatinski condition (in the sense of
Kreiss, Sakamoto) and the associated regularity defect of the hyperbolic
Neumann mapping. Here, we operate on the panel model as in the engineering
literature with no regularization or modifications; we completely resolve the
question of stability by demonstrating that weak plate damping strongly
stabilizes system trajectories. This is accomplished by microlocalizing the
wave data (given by the plate) and observing an "anisotropic" a microlocal
compensation by the plate dynamics precisely where the regularity of the 3D
wave is compromsed (in the characteristic sector). Several additional stability
results for both wave and plate subsystems are established to "push" strong
stability of the plate onto the flow.
|
2112.12208v1
|
2021-12-28
|
Kinetic investigation of the planar Multipole Resonance Probe under arbitrary pressure
|
Active plasma resonance spectroscopy (APRS) refers to a class of plasma
diagnostic methods that use the ability of plasma to resonate at or near the
electron plasma frequency for diagnostic purposes. The planar multipole
resonance probe (pMRP) is an optimized realization of APRS. It has a
non-invasive structure and allows simultaneous measurement of the electron
density, electron temperature, and electron-neutral collision frequency.
Previous work has investigated the pMRP through the Drude model and
collision-less kinetic model. The Drude model misses important kinetic effects
such as collision-less kinetic damping. The collision-less kinetic model is
able to capture pure kinetic effects. However, it is only applicable to
low-pressure plasma. To further study the behavior of the pMRP, we develop a
collisional kinetic model in this paper, which applies to arbitrary pressure.
In this model, the kinetic equation is coupled to the Poisson equation under
the electrostatic approximation. The real part of the general admittance is
calculated to describe the spectral response of the probe-plasma system. Both
collision-less kinetic damping and collisional damping appear in the spectrum.
This model provides a possibility to calculate the electron density, electron
temperature, and electron-neutral collision frequency from the measurements.
|
2112.14190v2
|
2021-12-28
|
Metadamping in inertially amplified metamaterials: Trade-off between spatial attenuation and temporal attenuation
|
Metadamping is the phenomenon of either enhanced or diminished intrinsic
dissipation in a material stemming from the material's internal structural
dynamics. It has been previously shown that a locally resonant elastic
metamaterial may be designed to exhibit higher or lower dissipation compared to
a statically equivalent phononic crystal with the same amount of prescribed
damping. Here we reveal that even further dissipation, or alternatively further
reduction of loss, may be reached in an inertially amplified metamaterial that
is also statically equivalent and has the same amount of prescribed damping.
This is demonstrated by a passive configuration whereby an attenuation peak is
generated by the motion of a mass supported by an inclined lever arm. We
further show that by coupling this inertially amplified attenuation peak with
that of a local resonance attenuation peak, a trade-off between the intensity
of spatial attenuation versus temporal attenuation is realized for a range of
the inclination angles. Design for performance along this trade-off is
therefore possible by adjustment of the lever angle. These findings open the
way for highly expanding the Ashby space for stiffness-damping capacity or
stiffness-spatial attenuation capacity through design of the internal structure
of materials.
|
2112.14322v1
|
2022-01-10
|
Tidal erasure of stellar obliquities constrains the timing of hot Jupiter formation
|
Stars with hot Jupiters sometimes have high obliquities, which are possible
relics of hot Jupiter formation. Based on the characteristics of systems with
and without high obliquities, it is suspected that obliquities are tidally
damped when the star has a thick convective envelope, as is the case for
main-sequence stars cooler than ~6100K, and the orbit is within ~8 stellar
radii. A promising theory for tidal obliquity damping is the dissipation of
inertial waves within the star's convective envelope. Here, we consider the
implications of this theory for the timing of hot Jupiter formation.
Specifically, hot stars that currently lack a convective envelope possess one
during their pre-main sequence. We find that hot Jupiters orbiting within a
critical distance of ~0.02au from a misaligned main-sequence star lacking a
thick convective envelope must have acquired their tight orbits after a few
tens of millions of years in order to have retained their obliquities
throughout the pre-main-sequence. There are 4 known systems for which this
argument applies--XO-3b, Corot-3b, WASP-14b, and WASP-121b--subject to
uncertainties surrounding inertial wave dissipation. Moreover, we conclude that
a recently-identified overabundance of near-polar hot Jupiters is unlikely
sculpted by tides, instead reflecting their primordial configuration. Finally,
hot Jupiters arriving around cool stars after a few 100s of millions of years
likely find the host star rotating too slowly for efficient obliquity damping.
We predict that the critical effective temperature separating aligned and
misaligned stars should vary with metallicity, from 6300K to 6000K as [Fe/H]
varies from -0.3 to +0.3.
|
2201.03653v1
|
2022-01-22
|
Examining AGN UV/optical Variability Beyond the Simple Damped Random Walk
|
We present damped harmonic oscillator (DHO) light-curve modeling for a sample
of 12,714 spectroscopically confirmed quasars in the Sloan Digital Sky Survey
Stripe 82 region. DHO is a second-order continuous-time autoregressive
moving-average (CARMA) process, which can be fully described using four
independent parameters: a natural oscillation frequency ($\omega_{0}$), a
damping ratio ($\xi$), a characteristic perturbation timescale
($\tau_{\mathrm{perturb}}$), and an amplitude for the perturbing white noise
($\sigma_{\mathrm{\epsilon}}$). The asymptotic variability amplitude of a DHO
process is quantified by $\sigma_{\mathrm{DHO}}$ -- a function of $\omega_{0}$,
$\xi$, $\tau_{\mathrm{perturb}}$, and $\sigma_{\mathrm{\epsilon}}$. We find
that both $\tau_{\mathrm{perturb}}$ and $\sigma_{\mathrm{\epsilon}}$ follow
different dependencies with rest-frame wavelength ($\lambda_{\mathrm{RF}}$) on
either side of 2500 \AA, whereas $\sigma_{\mathrm{DHO}}$ follows a single
power-law relation with $\lambda_{\mathrm{RF}}$. After correcting for
wavelength dependence, $\sigma_{\mathrm{DHO}}$ exhibits anti-correlations with
both the Eddington ratio and the black hole mass, while
$\tau_{\mathrm{perturb}}$ -- with a typical value of days in the rest-frame --
shows an anti-correlation with the bolometric luminosity. Modeling AGN
variability as a DHO offers more insight into the workings of accretion disks
close to the supermassive black holes (SMBHs) at the center of AGN. The newly
discovered short-term variability (characterized by $\tau_{\mathrm{perturb}}$
and $\sigma_{\mathrm{\epsilon}}$) and its correlation with bolometric
luminosity pave the way for new algorithms that will derive fundamental
properties (e.g., Eddington ratio) of AGN using photometric data alone.
|
2201.08943v2
|
2022-02-06
|
Enhancing Perpendicular Magnetic Anisotropy in Garnet Ferrimagnet by Interfacing with Few-Layer WTe2
|
Engineering magnetic anisotropy in a ferro- or ferrimagnetic (FM) thin film
is crucial in spintronic device. One way to modify the magnetic anisotropy is
through the surface of the FM thin film. Here, we report the emergence of a
perpendicular magnetic anisotropy (PMA) induced by interfacial interactions in
a heterostructure comprised of a garnet ferrimagnet, Y3Fe5O12 (YIG), and the
low-symmetry, high spin orbit coupling (SOC) transition metal dichalcogenide,
WTe2. At the same time, we also observed an enhancement in Gilbert damping in
the WTe2 covered YIG area. Both the magnitude of interface-induced PMA and the
Gilbert damping enhancement have no observable WTe2 thickness dependence down
to single quadruple-layer, indicating that the interfacial interaction plays a
critical role. The ability of WTe2 to enhance the PMA in FM thin film, combined
with its previously reported capability to generate out-of-plane damping like
spin torque, makes it desirable for magnetic memory applications.
|
2202.02834v1
|
2022-04-21
|
Characterizing the $γ$-Ray Variability of Active Galactic Nuclei with Stochastic Process Method
|
The $\gamma$-ray astronomy in time domain has been by now progressed further
as the variabilities of Active Galactic Nuclei (AGNs) on different timescales
have been reported a lot. We study the $\gamma$-ray variabilities of 23 jetted
AGNs through applying a stochastic process method to the ~12.7 yr long-term
light curve (LC) obtained by Fermi-Large Area Telescope (Fermi-LAT). In this
method, the stochastically driven damped simple harmonic oscillator (SHO) and
the damped random walk (DRW) models are used to model the long-term LCs. Our
results show that the long-term variabilities of 23 AGNs can be characterized
well by both SHO and DRW models. However, the SHO model is restricted in the
over-damped mode and the parameters are poorly constrained. The SHO power
spectral densities (PSDs) are same as the typical DRW PSD. In the plot of the
rest-frame timescale that corresponds to the broken frequency in the PSD versus
black hole mass, the intrinsic $\gamma$-ray characteristic timescales of 23
AGNs occupy almost the same space with the optical variability timescales
obtained from the accretion disk emission. This suggests a connection between
the jet and the accretion disk. Same as the optical variability of AGN
accretion disk, the $\gamma$-ray timescale is also consistent with the thermal
timescale caused by the thermal instability in the standard accretion disk of
AGN.
|
2204.09987v1
|
2022-04-29
|
A fast point charge interacting with the screened Vlasov-Poisson system
|
We consider the long-time behavior of a fast, charged particle interacting
with an initially spatially homogeneous background plasma. The background is
modeled by the screened Vlasov-Poisson equations, whereas the interaction
potential of the point charge is assumed to be smooth. We rigorously prove the
validity of the \emph{stopping power theory} in physics, which predicts a
decrease of the velocity $V(t)$ of the point charge given by $\dot{V} \sim
-|V|^{-3} V$, a formula that goes back to Bohr (1915). Our result holds for all
initial velocities larger than a threshold value that is larger than the
velocity of all background particles and remains valid until (i) the particle
slows down to the threshold velocity, or (ii) the time is exponentially long
compared to the velocity of the point charge. The long-time behavior of this
coupled system is related to the question of Landau damping which has remained
open in this setting so far. Contrary to other results in nonlinear Landau
damping, the long-time behavior of the system is driven by the non-trivial
electric field of the plasma, and the damping only occurs in regions that the
point charge has already passed.
|
2205.00035v2
|
2022-05-06
|
Discovery of a coherent, wave-like velocity pattern for the Radcliffe Wave
|
Recently studies discovered that part of the Gould Belt belongs to a 2.7
kpc-long {coherent, thin} wave consisting of a chain of clouds, where a damped
undulation pattern has been identified from the spatial arrangement of the
clouds. We use the proper motions of Young Stellar Objects (YSOs) anchored
inside the clouds to study the kinematic structure of the Radcliffe Wave in
terms of $v_z$, and identify a damped, wave-like pattern from the $v_z$ space,
which we call "velocity undulation". We propose a new formalism based on the
Ensemble Empirical Mode Decomposition (EEMD) to determine the amplitude,
period, and phase of the undulation pattern, and find that the spatial and the
velocity undulation share an almost identical spatial frequency of about 1.5
kpc, and both are damped when measured from one side to the other. Measured for
the first cycle, they exhibit a phase difference of around $2\pi/3$. The
structure is oscillating around the midplane of the Milky Way disk with an
amplitude of $\sim\,130\,\pm\,20\,\rm pc$. The vertical extent of the Radcliffe
Wave exceeds the thickness of the molecular disk, suggesting that the
undulation of the undulation signature might originate from a perturbation,
e.g. the passage of a dwarf galaxy.
|
2205.03218v1
|
2022-05-17
|
Resolving the HI in Damped Lyman-α systems that power star-formation
|
Reservoirs of dense atomic gas (primarily hydrogen), contain approximately 90
percent of the neutral gas at a redshift of 3, and contribute to 2-3 percent of
the total baryons in the Universe. These damped Lyman-${\alpha}$ systems (so
called because they absorb Lyman-${\alpha}$ photons from within and from
background sources) have been studied for decades, but only through absorption
lines present in the spectra of background quasars and gamma-ray bursts. Such
pencil beams do not constrain the physical extent of the systems. Here, we
report integral-field spectroscopy of a bright, gravitationally lensed galaxy
at a redshift of 2.7 with two foreground damped Lyman-${\alpha}$ systems. These
systems are $>$ 238 $kpc^2$ in extent, with column densities of neutral
hydrogen varying by more than an order of magnitude on $<$ 3 kpc-scales. The
mean column densities are $10^{20.46}$ - $10^{20.84} cm^{-2}$ and the total
masses are $> 5.5 \times 10^{8}$ - $1.4 \times 10^{9} M_{\odot}$, showing that
they contain the necessary fuel for the next generation of star formation,
consistent with relatively massive, low-luminosity primeval galaxies at
redshifts $>$ 2.
|
2205.08554v1
|
2022-05-21
|
Accuracy of one-dimensional approximation in neutron star quasi-normal modes
|
Since the eigenfrequency of gravitational waves from cold neutron stars
becomes a complex number, where the real and imaginary parts respectively
correspond to an oscillation frequency and damping rate, one has to somehow
solve the eigenvalue problem concerning the eigenvalue in two-dimensional
parameter space. To avoid this bother, one sometimes adopts an approximation,
where the eigenvalue is in one-dimensional parameter space. In this study,
first, we show the accuracy of the zero-damping approximation, which is one of
the one-dimensional approximations, for the fundamental and 1st pressure modes.
But, this approximation is not applicable to the spacetime mode, because the
damping rate of the spacetime mode is generally comparable to the oscillation
frequency. Nevertheless, we find the empirical relation for the ratio of the
imaginary part to the real part of the eigenfrequency, which is expressed as a
function of the steller compactness almost independently of the adopted
equations of state for neutron star matter. Adopting this empirical relation,
one can express the eigenfrequency in terms of just the real part, i.e., the
problem to solve becomes an eigenvalue problem with a one-dimensional
eigenvalue. Then, we find that the frequencies are estimated with good accuracy
even with such approximations even for the 1st spacetime mode.
|
2205.10523v1
|
2022-06-02
|
Proximity of exoplanets to first-order mean-motion resonances
|
Planetary formation theories and, more specifically, migration models predict
that planets can be captured in mean-motion resonances (MMRs) during the disc
phase. The distribution of period ratios between adjacent planets shows an
accumulation in the vicinity of the resonance, which is not centred on the
nominal resonance but instead presents an offset slightly exterior to it. Here
we extend on previous works by thoroughly exploring the effect of different
disc and planet parameters on the resonance offset during the disc migration
phase. The dynamical study is carried out for several first-order MMRs and for
both low-mass Earth-like planets undergoing type-I migration and giant planets
evolving under type-II migration. We find that the offset varies with time
during the migration of the two-planet system along the apsidal corotation
resonance family. The departure from the nominal resonance increases for higher
planetary masses and stronger eccentricity damping. In the Earth to super-Earth
regime, we find offset values in agreement with the observations when using a
sophisticated modelling for the planet-disc interactions, where the damping
timescale depends on the eccentricity. This dependence causes a feedback which
induces an increase of the resonance offsets. Regarding giant planets, the
offsets of detected planet pairs are well reproduced with a classical
$K$-factor prescription for the planet-disc interactions when the eccentricity
damping rate remains low to moderate. In both regimes, eccentricities are in
agreement with the observations too. As a result, planet-disc interactions
provide a generic channel to generate the offsets found in the observations.
|
2206.00943v1
|
2022-06-03
|
Dynamical Instability in Multi-Orbiter Systems with Gas Friction
|
Closely-packed multi-planet systems are known to experience dynamical
instability if the spacings between the planets are too small. Such instability
can be tempered by the frictional forces acting on the planets from gaseous
discs. A similar situation applies to stellar-mass black holes embedded in AGN
discs around supermassive black holes. In this paper, we use $N$-body
integrations to evaluate how the frictional damping of orbital eccentricity
affects the growth of dynamical instability for a wide range of planetary
spacing and planet-to-star mass ratios. We find that the stability of a system
depends on the damping timescale $\tau$ relative to the zero-friction
instability growth timescale $t_{\rm inst}$. In a two-planet system, the
frictional damping can stabilise the dynamical evolution if $t_{\rm
inst}\gtrsim\tau$. With three planets, $t_{\rm inst} \gtrsim 10\tau - 100\tau$
is needed for stabilisation. When the separations between the planetary orbits
are sufficiently small, $t_{\rm inst}$ can be less than the synodic period
between the planets, which makes frictional stabilisation unlikely to occur. As
the orbital spacing increases, the instability timescale tends to grow
exponentially on average, but it can vary by a few orders of magnitude
depending on the initial orbital phases of the planets. In general, the stable
region (at large orbital spacings) and unstable region (at small orbital
spacings) are separated by a transition zone, in which the (in)stability of the
system is not guaranteed. We also devise a linear map to analyse the dynamical
instability of the "planet + test-mass" system, and we find qualitatively
similar results to the $N$-body simulations.
|
2206.01755v1
|
2022-08-15
|
Nonperturbative approach to interfacial spin-orbit torques induced by Rashba effect
|
Current-induced spin-orbit torque (SOT) in normal metal/ferromagnet (NM/FM)
bilayers bears great promise for technological applications, but the
microscopic origin of purely interfacial SOTs in ultra-thin systems is not yet
fully understood. Here, we show that a linear response theory with a
nonperturbative treatment of spin-dependent interactions and impurity
scattering potential predicts damping-like SOTs that are strictly absent in
perturbative approaches. The technique is applied to a two-dimensional
Rashba-coupled ferromagnet (the paradigmatic model of a NM/FM interface), where
higher-order scattering processes encoding skew scattering from nonmagnetic
impurities allow for current-induced spin polarization with nonzero components
along all spatial directions. This is in stark contrast to previous results of
perturbative methods (neglecting skew scattering), which predict a coplanar
spin-polarization locked perpendicular to the charge current as a result of
conventional Rashba-Edelstein effect. Furthermore, the angular dependence of
ensuing SOTs and their dependence upon the scattering potential strength is
analysed numerically. Simple analytic expressions for the
spin-density--charge-current response function, and related SOT efficiencies,
are obtained in the weak scattering limit. We find that the extrinsic
damping-like torques driven by impurity scattering reaches efficiencies of up
to 7% of the field-like (Rashba-Edelstein) torque. Our microscopic theory shows
that bulk phenomena, such as the spin Hall effect, are not a necessity in the
generation of the damping-like SOTs of the type observed in experiments on
ultra-thin systems.
|
2208.07296v1
|
2022-08-22
|
Plasma heating and nanoflare caused by slow-mode wave in a coronal loop
|
We present a detailed analysis of a reflecting intensity perturbation in a
large coronal loop that appeared as sloshing oscillation and lasted for at
least one and a half periods. The perturbation is initiated by a microflare at
one footpoint of the loop, propagates along the loop and is eventually
reflected at the remote footpoint where significant brightenings are observed
in all the AIA extreme-ultraviolet (EUV) channels. This unique observation
provides us with the opportunity to better understand not only the thermal
properties and damping mechanisms of the sloshing oscillation, but also the
energy transfer at the remote footpoint. Based on differential emission
measures (DEM) analysis and the technique of coronal seismology, we find that
1) the calculated local sound speed is consistent with the observed propagation
speed of the perturbation during the oscillation, which is suggestive of a slow
magnetoacoustic wave; 2) thermal conduction is the major damping mechanism of
the wave but additional damping mechanism such as anomalous enhancement of
compressive viscosity or wave leakage is also required to account for the rapid
decay of the observed waves; 3) the wave produced a nanoflare at the remote
footpoint, with a peak thermal energy of $\thicksim10^{24}-10^{25}$ erg. This
work provides a consistent picture of the magnetoacoustic wave propagation and
reflection in a coronal loop, and reports the first solid evidence of a
wave-induced nanoflare. The results reveal new clues for further simulation
studies and may help solving the coronal heating problem.
|
2208.10029v1
|
2022-09-07
|
AlH lines in the blue spectrum of Proxima Centauri
|
The recently-computed ExoMol line lists for isotopologues of AlH are used to
analyse the blue spectrum (4000-4500 {\AA}) of Proxima Cen (M5.5 V). Comparison
of the observed and computed spectra enables the identification of a large
number of 27AlH lines of the A1{\Pi} - X1{\Sigma}+ band system: the spectral
range covering 1-0, 0-0 and 1-1 bands is dominated by clearly resolved AlH
lines. We reveal the diffuse nature of transitions close to the dissociation
limit which appears in the form of increasingly wider(up to 5 {\AA}) and
shallower (up to the continuum confusion limit) AlH line profiles. The
predicted wavelengths of AlH diffuse lines are systematically displaced. The
effect broadening by pre-dissociation states on the line profiles is included
by increasing the radiative damping rate by up to 5 orders of magnitude. We
determine empirical values of damping rates for a number of the clean 0-0
Q-branch transitions by comparing the observed and synthetic stellar spectra.
We find excellent agreement between our damping rates and lifetimes available
in the literature. A comparison of 27Al1H ExoMol and REALH spectra shows that
the observed spectrum is better described by the ExoMol line list. A search for
26Al1H lines in the Proxima Cen spectrum does not reveal any notable features;
giving an upper limit of 27Al1H/26Al1H {>} 100.
|
2209.03037v2
|
2022-09-19
|
Semi-implicit Integration and Data-Driven Model Order Reduction in Structural Dynamics with Hysteresis
|
Structural damping is known to be approximately rate-independent in many
cases. Popular models for rate-independent dissipation are hysteresis models;
and a highly popular hysteresis model is the Bouc-Wen model. If such hysteretic
dissipation is incorporated in a refined finite element model, then the
mathematical model includes the usual structural dynamics equations along with
nonlinear nonsmooth ordinary differential equations for a large number of
internal hysteretic states at Gauss points, to be used within the virtual work
calculation for dissipation. For such systems, numerical integration becomes
difficult due to both the distributed non-analytic nonlinearity of hysteresis
as well as the very high natural frequencies in the finite element model. Here
we offer two contributions. First, we present a simple semi-implicit
integration approach where the structural part is handled implicitly based on
the work of Pich\'e, and where the hysteretic part is handled explicitly. A
cantilever beam example is solved in detail using high mesh refinement.
Convergence is good for lower damping and a smoother hysteresis loop. For a
less smooth hysteresis loop and/or higher damping, convergence is observed to
be roughly linear on average. Encouragingly, the time step needed for stability
is much larger than the time period of the highest natural frequency of the
structural model. Subsequently, data from several simulations conducted using
the above semi-implicit method are used to construct reduced order models of
the system, where the structural dynamics is projected onto a small number of
modes and the number of hysteretic states is reduced significantly as well.
Convergence studies of error against the number of retained hysteretic states
show very good results.
|
2209.08765v2
|
2022-10-02
|
Reduction in turbulence-induced non-linear dynamic vibration using tuned liquid damper (TLD)
|
In the present research work, an attempt is made to develop a coupled
non-linear turbulence-structure-damper model in a finite volume-finite
difference (FV-FD) framework. Tuned liquid damper (TLD) is used as the
additional damping system along with inherent structural damping. Real-time
simulation of flow-excited bridge box girder or chimney section and the
vibration reduction using TLD can be performed using the developed model. The
turbulent flow field around a structure is modeled using an OpenFOAM transient
PISO solver, and the time-varying drag force is calculated. This force perturbs
the structure, causing the sloshing phenomena of the attached TLD, modeled
using shallow depth approximation, damping the flow-induced vibration of the
structure. The structural motion with and without the attached TLD is modeled
involving the FD-based Newmark-Beta method using in-house MATLAB codes. The TLD
is tuned with the vortex-shedding frequency of the low-Reynolds number flows,
and it is found to be reducing the structural excitation significantly. On the
other hand, the high-Reynolds number turbulent flow exhibits a broadband
excitation, for which by tuning the TLD with few frequencies obtained through
investigations, a good reduction in vibration is observed.
|
2210.00428v3
|
2022-10-17
|
Interpretations of the cosmic ray secondary-to-primary ratios measured by DAMPE
|
Precise measurements of the boron-to-carbon and boron-to-oxygen ratios by
DAMPE show clear hardenings around $100$ GeV/n, which provide important
implications on the production, propagation, and interaction of Galactic cosmic
rays. In this work we investigate a number of models proposed in literature in
light of the DAMPE findings. These models can roughly be classified into two
classes, driven by propagation effects or by source ones. Among these models
discussed, we find that the re-acceleration of cosmic rays, during their
propagation, by random magnetohydrodynamic waves may not reproduce sufficient
hardenings of B/C and B/O, and an additional spectral break of the diffusion
coefficient is required. The other models can properly explain the hardenings
of the ratios. However, depending on simplifications assumed, the models differ
in their quality in reproducing the data in a wide energy range. The models
with significant re-acceleration effect will under-predict low-energy
antiprotons but over-predict low-energy positrons, and the models with
secondary production at sources over-predict high-energy antiprotons. For all
models high-energy positron excess exists.
|
2210.09205v3
|
2022-10-19
|
Energy Dissipation in Synchronous Binary Asteroids
|
Synchronous binary asteroids can experience libration about their
tidally-locked equilibrium, which will result in energy dissipation. This is an
important topic to the Asteroid Impact and Deflection Assessment, where
excitation caused by the DART kinetic impact in the Didymos binary asteroid
system may be reduced through dissipation before Hera arrives to survey the
effects of the impact. We develop a numeric model for energy dissipation in
binary asteroids to explore how different system configurations affect the rate
of energy dissipation. We find tumbling within the synchronous state eliminates
a systematic trend in libration damping on short timescales (several years),
but not over long times (hundreds of years) depending on the material
conditions. Furthermore, damping of libration, eccentricity, and fluctuations
in the semimajor axis are primarily dependent on the stiffness of the
secondary, whereas the semimajor axis secular expansion rate is dictated by the
stiffness of the primary, as expected. Systems experiencing stable planar
libration in the secondary can see a noticeable reduction in libration
amplitude after only a few years depending on the stiffness of the secondary,
and thus dissipation should be considered during Hera's survey of Didymos. For
a very dissipative secondary undergoing stable libration, Hera may be able to
calculate the rate of libration damping in Dimorphos and therefore constrain
its tidal parameters.
|
2210.10877v1
|
2022-11-14
|
Heavily Damped Precessional Switching with Very Low Write-error Rate in Elliptical-cylinder Magnetic Tunnel Junction
|
Voltage-induced dynamic switching in magnetic tunnel junctions (MTJs) is a
writing technique for voltage-controlled magnetoresistive random access memory
(VCMRAM), which is expected to be an ultimate non-volatile memory with
ultra-low power consumption. In conventional dynamic switching, the width of
sub-nanosecond write voltage pulses must be precisely controlled to achieve a
sufficiently low write-error rate (WER). This very narrow tolerance of pulse
width is the biggest technical difficulty in developing VCMRAM. Heavily damped
precessional switching is a writing scheme for VCMRAM with a substantially high
tolerance of pulse width although the minimum WER has been much higher than
that of conventional dynamic switching with an optimum pulse width. In this
study, we theoretically investigate the effect of MTJ shape and the direction
of the applied magnetic field on the WER of heavily damped precessional
switching. The results show that the WER in elliptical-cylinder MTJ can be
several orders of magnitude smaller than that in usual circular-cylinder MTJ
when the external magnetic field is applied parallel to the minor axis of the
ellipse. The reduction in WER is due to the fact that the demagnetization field
narrows the component of the magnetization distribution perpendicular to the
plane direction immediately before the voltage is applied.
|
2211.07148v1
|
2022-11-19
|
Regularity to Timoshenko's System with Thermoelasticity of Type III with Fractional Damping
|
The article, presents the study of the regularity of two thermoelastic beam
systems defined by the Timoshenko beam model coupled with the heat conduction
of Green-Naghdiy theory of type III, both mathematical models are
differentiated by their coupling terms that arise as a consequence of the
constitutive laws initially considered. The systems presented in this work have
3 fractional dampings: $\mu_1(-\Delta)^\tau \phi_t$, $\mu_2(-\Delta)^\sigma
\psi_t$ and $K(-\Delta)^\xi \theta_t$, where $\phi,\psi$ and $\theta$ are
transverse displacement, rotation angle and empirical temperature of the bean
respectively and the parameters $(\tau,\sigma,\xi)\in [0,1]^3$. It is noted
that for values 0 and 1 of the parameter $\tau$, the so-called frictional or
viscous damping will be faced, respectively. The main contribution of this
article is to show that the corresponding semigroup
$S_i(t)=e^{\mathcal{B}_it}$, with $i=1,2$, is of Gevrey class
$s>\frac{r+1}{2r}$ for $r=\min \{\tau,\sigma,\xi\}$ for all
$(\tau,\sigma,\xi )\in R_{CG}:= (0, 1)^3$. It is also showed that
$S_1(t)=e^{\mathcal{B}_1t}$ is analytic in the region $R_{A_1}:=\{(\tau,\sigma,
\xi )\in [\frac{1}{2},1]^3\}$ and $S_2(t)=e^{\mathcal{B}_2t}$ is analytic in
the region $R_{A_2}:=\{(\tau,\sigma, \xi )\in [\frac{1}{2},1]^3/ \tau=\xi\}$.
|
2211.10816v2
|
2022-12-04
|
An Unsupervised Machine Learning Method for Electron--Proton Discrimination of the DAMPE Experiment
|
Galactic cosmic rays are mostly made up of energetic nuclei, with less than
$1\%$ of electrons (and positrons). Precise measurement of the electron and
positron component requires a very efficient method to reject the nuclei
background, mainly protons. In this work, we develop an unsupervised machine
learning method to identify electrons and positrons from cosmic ray protons for
the Dark Matter Particle Explorer (DAMPE) experiment. Compared with the
supervised learning method used in the DAMPE experiment, this unsupervised
method relies solely on real data except for the background estimation process.
As a result, it could effectively reduce the uncertainties from simulations.
For three energy ranges of electrons and positrons, 80--128 GeV, 350--700 GeV,
and 2--5 TeV, the residual background fractions in the electron sample are
found to be about (0.45 $\pm$ 0.02)$\%$, (0.52 $\pm$ 0.04)$\%$, and (10.55
$\pm$ 1.80)$\%$, and the background rejection power is about (6.21 $\pm$ 0.03)
$\times$ $10^4$, (9.03 $\pm$ 0.05) $\times$ $10^4$, and (3.06 $\pm$ 0.32)
$\times$ $10^4$, respectively. This method gives a higher background rejection
power in all energy ranges than the traditional morphological parameterization
method and reaches comparable background rejection performance compared with
supervised machine learning~methods.
|
2212.01843v1
|
2022-12-05
|
Stability of Cnoidal Waves for the Damped Nonlinear Schrödinger Equation
|
We consider the cubic nonlinear Schr\"odinger (NLS) equation with a linear
damping on the one dimensional torus and we investigate the stability of some
solitary wave profiles within the dissipative dynamics. The undamped cubic NLS
equation is well known to admit a family of periodic waves given by Jacobi
elliptic functions of cnoidal type. We show that the family of cnoidal waves is
orbitally stable. More precisely, by considering a sufficiently small
perturbation of a given cnoidal wave at initial time, the evolution will always
remain close (up to symmetries of the equation) to the cnoidal wave whose mass
is modulated according to the dissipative dynamics. This result extends the
concept of orbital stability to this non-Hamiltonian evolution. Since cnoidal
waves are not exact solutions to the damped NLS, the perturbation is forced
away from the family of solitary wave profiles. In order to control this
secular growth of the error, we find a first order approximation of the
solitary wave that takes into account the dissipative term. Then we use a
suitable, exponentially decreasing Lyapunov functional that controls the
$H^1$-norm of the perturbation around the approximated solitons.
|
2212.02195v2
|
2022-12-08
|
Strong photon-magnon coupling using a lithographically defined organic ferrimagnet
|
We demonstrate a hybrid quantum system composed of superconducting resonator
photons and magnons hosted by the organic-based ferrimagnet vanadium
tetracyanoethylene (V[TCNE]$_x$). Our work is motivated by the challenge of
scalably integrating an arbitrarily-shaped, low-damping magnetic system with
planar superconducting circuits, thus enabling a host of quantum magnonic
circuit designs that were previously inaccessible. For example, by leveraging
the inherent properties of magnons, one can enable nonreciprocal
magnon-mediated quantum devices that use magnon propagation rather than
electrical current. We take advantage of the properties of V[TCNE]$_x$, which
has ultra-low intrinsic damping, can be grown at low processing temperatures on
arbitrary substrates, and can be patterned via electron beam lithography. We
demonstrate the scalable, lithographically integrated fabrication of hybrid
quantum magnonic devices consisting of a thin-film superconducting resonator
coupled to a low-damping, thin-film V[TCNE]$_x$ microstructure. Our devices
operate in the strong coupling regime, with a cooperativity as high as 1181(44)
at T$\sim$0.4 K, suitable for scalable quantum circuit integration. This work
paves the way for the exploration of high-cooperativity hybrid magnonic quantum
devices in which magnonic circuits can be designed and fabricated as easily as
electrical wires.
|
2212.04423v1
|
2022-12-28
|
Scattering of the UHECR at small pitch angle by damped plasma waves
|
In spite a lot of theoretical and experimental effort that has been achieved
in ultra-high energy cosmic ray (UHECR) scattering research in last few
decades, some questions remain unanswered, or partially answered. Two of them,
that will be in the focus of this paper are: possible source of UHECRs and the
acceleration mechanism of cosmic rays beyond PeV energies. Small pitch-angle
scattering of UHECRs and possible confinement has been investigated using
quasilinear theory in order to analytically calculate pitch-angle Fokker-Planck
coefficient. CR particles resonantly interact with oblique low frequency damped
waves. We show that the resonance function is broadened due to damping effects
and this result is compared with the nonlinear broadening. Unlike the case of
purely parallel (or antiparallel) propagating waves in slab turbulence, the
presence of the compressive magnetic field component of oblique fast-mode waves
allows the cosmic ray particles to resonantly interact with these waves through
the n = 0 resonance, together with gyroresonance, which strongly influence the
Hillas limit. The derived results can be used to compute the parallel mean free
path for all forms of the turbulence spectrum; it has been applied on the
transport and propagation of CRs close to ultra-high energies in the Galaxy. An
accurate understanding of particle acceleration in astrophysical sources could
help to interpret eventual transition from Galactic to extragalactic origin of
cosmic rays, if any, and the shape of the UHECR spectrum at the highest
energies.
|
2212.13755v1
|
2023-02-02
|
Leveraging symmetry for an accurate spin-orbit torques characterization in ferrimagnetic insulators
|
Spin-orbit torques (SOTs) have emerged as an efficient means to electrically
control the magnetization in ferromagnetic heterostructures. Lately, an
increasing attention has been devoted to SOTs in heavy metal (HM)/magnetic
insulator (MI) bilayers owing to their tunable magnetic properties and
insulating nature. Quantitative characterization of SOTs in HM/MI
heterostructures are, thus, vital for fundamental understanding of charge-spin
interrelations and designing novel devices. However, the accurate determination
of SOTs in MIs have been limited so far due to small electrical signal outputs
and dominant spurious thermoelectric effects caused by Joule heating. Here, we
report a simple methodology based on harmonic Hall voltage detection and
macrospin simulations to accurately quantify the damping-like and field-like
SOTs, and thermoelectric contributions separately in MI-based systems.
Experiments on the archetypical Bi-doped YIG/Pt heterostructure using the
developed method yield precise values for the field-like and damping-like SOTs,
reaching -0.14 and -0.15 mT per 1.7x$10^{ 11}$ A/$m^2$, respectively. We
further reveal that current-induced Joule heating changes the spin transparency
at the interface, reducing the spin Hall magnetoresistance and damping-like
SOT, simultaneously. These results and the devised method can be beneficial for
fundamental understanding of SOTs in MI-based heterostructures and designing
new devices where accurate knowledge of SOTs is necessary.
|
2302.01141v2
|
2022-12-31
|
Genuine three qubit Einstein-Podolsky-Rosen steering under decoherence: Revealing hidden genuine steerability via pre-processing
|
The behaviour of genuine EPR steering of three qubit states under various
environmental noises is investigated. In particular, we consider the two
possible steering scenarios in the tripartite setting: (1 -> 2), where Alice
demonstrates genuine steering to Bob-Charlie, and (2 -> 1), where Alice-Bob
together demonstrates genuine steering to Charlie. In both these scenarios, we
analyze the genuine steerability of the generalized Greenberger-Horne-Zeilinger
(gGHZ) states or the W-class states under the action of noise modeled by
amplitude damping (AD), phase flip (PF), bit flip (BF), and phase damping (PD)
channels. In each case, we consider three different interactions with the noise
depending upon the number of parties undergoing decoherence. We observed that
the tendency to demonstrate genuine steering decreases as the number of parties
undergoing decoherence increases from one to three. We have observed several
instances where the genuine steerability of the state revives after collapsing
if one keeps on increasing the damping. However, the hidden genuine
steerability of a state cannot be revealed solely from the action of noise. So,
the parties having a characterized subsystem, perform local pre-processing
operations depending upon the steering scenario and the state shared with the
dual intent of revealing hidden genuine steerability or enhancing it.
|
2302.02987v1
|
2023-02-20
|
Optimal energy harvesting efficiency from vortex-induced vibration of a circular cylinder under flow
|
This work applies a combined approach a reduced-order model (ROM) together
with experiments and direct numerical simulations to investigate the optimal
efficiency of fluid-flow energy harvesting from transverse vortex-induced
vibration (VIV) of a circular cylinder. High resolution efficiency maps were
predicted over wide ranges of flow reduced velocities and structural damping
ratios, and the maximum efficiency and optimal settings of damping ratio and
reduced velocity were then examined for different mass ratios and Reynolds
numbers. Efficiencies predicted by the ROM were also validated against either
experiments or direct simulations. The present work indicates that: (i) the
maximum efficiency is controlled by both the incoming reduced velocity and the
product of mass ratio and structural damping ratio, which is similar to the
maximum amplitude of VIV; (ii) the maximum efficiency at a relatively high
Reynolds number ($Re \approx 6 \times 10^3$) in subcritical regime is higher
than that of a low Reynolds number ($Re = 150$) in laminar regime; (iii) the
energy harvesting efficiency from VIV of a circular cylinder with a low mass
ratio is more robust than that with a high mass ratio. This finding suggests
that the VIV harvester performs better in water than in air.
|
2302.09975v1
|
2023-04-12
|
Liouvillian exceptional points in continuous variable system
|
The Liouvillian exceptional points for a quantum Markovian master equation of
an oscillator in a generic environment are obtained. They occur at the points
when the modified frequency of the oscillator vanishes, whereby the eigenvalues
of the Liouvillian become real. In a generic system there are two parameters
that modify the oscillator's natural frequency. One of the parameters can be
the damping rate. The exceptional point then corresponds to critical damping of
the oscillator. This situation is illustrated by the Caldeira--Leggett (CL)
equation and the Markovian limit of the Hu--Paz--Zhang (HPZ) equation. The
other parameter changes the oscillator's effective mass whereby the exceptional
point is reached in the limit of extremely heavy oscillator. This situation is
illustrated by a modified form of the Kossakowski--Lindblad (KL) equation. The
eigenfunctions coalesce at the exceptional points and break into subspaces
labelled by a natural number $N$. In each of the $N$-subspace, there is a
$(N+1)$-fold degeneracy and the Liouvillian has a Jordan block structure of
order-$(N+1)$. We obtain the explicit form of the generalized eigenvectors for
a few Liouvillians. Because of the degeneracies, there is a freedom of choice
in the generalized eigenfunctions. This freedom manifests itself as an
invariance in the Jordan block structure under a similarity transformation
whose form is obtained. We compare the relaxation of the first excited state of
an oscillator in the underdamped region, critically damped region which
corresponds to the exceptional point, and overdamped region using the
generalized eigenvectors of the CL equation.
|
2304.05792v2
|
2023-04-13
|
Network-Reconfiguration-Aware Power Oscillation Damping Controller for Newly Commissioned Converter-Interfaced Power Plants
|
In recent years, transmission system operators have started requesting
converter-interfaced generators (CIGs) to participate in grid services such as
power oscillation damping (POD). As power systems are prone to topology changes
because of connection and disconnection of generators and electrical lines, one
of the most important requirements in the POD controller design is to account
for these changes and to deal with them by using either adaptive or robust
approaches. The robust approach is usually preferred by system operators
because of the fixed structure of the controller. In this paper, a procedure to
design POD controllers for CIG-based power plants that takes into consideration
all possible network configurations is presented. This procedure is based on
frequency-response techniques, so it is suitable for the commissioning in newly
installed power plants, even in those cases when a detailed small-signal model
of the system is not available. This procedure can be used to damp critical
system modes by using active power, reactive power, or both power components
simultaneously. The proposed procedure is applied to the design of the POD
controller for a CIG-based power plant connected to the IEEE 39 Bus system.
Simulations performed in Matlab and SimPowerSystems are used to validate the
proposed design procedure.
|
2304.06555v1
|
2023-06-13
|
Particle-resolved study of the onset of turbulence
|
The transition from laminar to turbulent flow is an immensely important topic
that is still being studied. Here we show that complex plasmas, i.e.,
microparticles immersed in a low temperature plasma, make it possible to study
the particle-resolved onset of turbulence under the influence of damping, a
feat not possible with conventional systems. We performed three-dimensional
(3D) molecular dynamics (MD) simulations of complex plasmas flowing past an
obstacle and observed 3D turbulence in the wake and fore-wake region of this
obstacle. We found that we could reliably trigger the onset of turbulence by
changing key parameters such as the flow speed and particle charge, which can
be controlled in experiments, and show that the transition to turbulence
follows the conventional pathway involving the intermittent emergence of
turbulent puffs. The power spectra for fully developed turbulence in our
simulations followed the -5/3 power law of Kolmogorovian turbulence in both
time and space. We demonstrate that turbulence in simulations with damping
occurs after the formation of shock fronts, such as bow shocks and Mach cones.
By reducing the strength of damping in the simulations, we could trigger a
transition to turbulence in an undamped system. This work opens the pathway to
detailed experimental and simulation studies of the onset of turbulence on the
level of the carriers of the turbulent interactions, i.e., the microparticles.
|
2306.07711v1
|
2023-07-10
|
Vibroacoustic simulations of acoustic damping materials using a fictitious domain approach
|
The numerical investigation of acoustic damping materials, such as foams,
constitutes a valuable enhancement to experimental testing. Typically, such
materials are modeled in a homogenized way in order to reduce the computational
effort and to circumvent the need for a computational mesh that resolves the
complex micro-structure. However, to gain detailed insight into the acoustic
behavior, e.g., the transmittance of noise, such fully resolved models are
mandatory. The meshing process can still be avoided by using a ficticious
domain approach. We propose the finite cell method, which combines the
ficticious domain approach with high-order finite elements and resolves the
complex geometry using special quadrature rules. In order to take into account
the fluid-filled pores of a typical damping material, a coupled vibroacoustic
problem needs to be solved. To this end, we construct two separate finite cell
discretizations and prescribe coupling conditions at the interface in the usual
manner. The only difference to a classical boundary fitted approach to
vibroacoustics is that the fluid-solid interface is immersed into the
respective discretization and does not correspond to the element boundaries.
The proposed enhancement of the finite cell method for vibroacoustics is
verified based on a comparison with commercial software and used within an
exemplary application.
|
2307.04624v1
|
2023-07-12
|
A coupled rate-dependent/rate-independent system for adhesive contact in Kirchhoff-Love plates
|
We perform a dimension reduction analysis for a coupled
rate-dependent/rate-independent adhesive-contact model in the setting of
visco-elastodynamic plates. We work with a weak solvability notion inspired by
the theory of (purely) rate-independent processes, and accordingly term the
related solutions `Semistable Energetic'. For Semistable Energetic solutions,
the momentum balance holds in a variational sense, whereas the flow rule for
the adhesion parameter is replaced by a semi-stability condition coupled with
an energy-dissipation inequality. Prior to addressing the dimension reduction
analysis, we show that Semistable Energetic solutions to the three-dimensional
damped adhesive contact model converge, as the viscosity term tends to zero, to
three-dimensional Semistable Energetic solutions for the undamped corresponding
system. We then perform a dimension reduction analysis, both in the case of a
vanishing viscosity tensor (leading, in the limit, to an undamped model), and
in the complementary setting in which the damping is assumed to go to infinity
as the thickness of the plate tends to zero. In both regimes, the presence of
adhesive contact yields a nontrivial coupling of the in-plane and out-of-plane
contributions. In the undamped scenario we obtain in the limit an
energy-dissipation inequality and a semistability condition. In the damped
case, instead, we achieve convergence to an enhanced notion of solution,
fulfilling an energy-dissipation balance.
|
2307.06327v1
|
2023-08-16
|
Large time asymptotics for partially dissipative hyperbolic systems without Fourier analysis: application to the nonlinearly damped p-system
|
A new framework to obtain time-decay estimates for partially dissipative
hyperbolic systems set on the real line is developed. Under the classical
Shizuta-Kawashima (SK) stability condition, equivalent to the Kalman rank
condition in control theory, the solutions of these systems decay exponentially
in time for high frequencies and polynomially for low ones. This allows to
derive a sharp description of the space-time decay of solutions for large time.
However, such analysis relies heavily on the use of the Fourier transform that
we avoid here, developing the "physical space version" of the hyperbolic
hypocoercivity approach introduced by Beauchard and Zuazua, to prove new
asymptotic results in the linear and nonlinear settings. The new physical space
version of the hyperbolic hypocoercivity approach allows to recover the natural
heat-like time-decay of solutions under sharp rank conditions, without
employing Fourier analysis or $L^1$ assumptions on the initial data. Taking
advantage of this Fourier-free framework, we establish new enhanced time-decay
estimates for initial data belonging to weighted Sobolev spaces. These results
are then applied to the nonlinear compressible Euler equations with linear
damping. We also prove the logarithmic stability of the nonlinearly damped
$p$-system.
|
2308.08280v2
|
2023-08-28
|
The Effects of Non-Equilibrium Velocity Distributions on Alfvén Ion-Cyclotron Waves in the Solar Wind
|
In this work, we investigate how the complex structure found in solar wind
proton velocity distribution functions (VDFs), rather than the commonly assumed
two-component bi-Maxwellian structure, affects the onset and evolution of
parallel-propagating microinstabilities. We use the Arbitrary Linear Plasma
Solver (ALPS), a numerical dispersion solver, to find the real frequencies and
growth/damping rates of the Alfv\'en modes calculated for proton VDFs extracted
from Wind spacecraft observations of the solar wind. We compare this wave
behavior to that obtained by applying the same procedure to core-and-beam
bi-Maxwellian fits of the Wind proton VDFs. We find several significant
differences in the plasma waves obtained for the extracted data and
bi-Maxwellian fits, including a strong dependence of the growth/damping rate on
the shape of the VDF. By application of the quasilinear diffusion operator to
these VDFs, we pinpoint resonantly interacting regions in velocity space where
differences in VDF structure significantly affect the wave growth and damping
rates. This demonstration of the sensitive dependence of Alfv\'en mode behavior
on VDF structure may explain why the Alfv\'en ion-cyclotron instability
thresholds predicted by linear theory for bi-Maxwellian models of solar wind
proton background VDFs do not entirely constrain spacecraft observations of
solar wind proton VDFs, such as those made by the Wind spacecraft.
|
2308.14944v1
|
2023-08-31
|
Search for the gamma-ray spectral lines with the DAMPE and the Fermi-LAT observations
|
Weakly interacting massive particles, as a major candidate of dark matter
(DM), may directly annihilate or decay into high-energy photons, producing
monochromatic spectral lines in the gamma-ray band. These spectral lines, if
detected, are smoking-gun signatures for the existence of new physics. Using
the 5 years of DAMPE and 13 years of Fermi-LAT data, we search for line-like
signals in the energy range of 3 GeV to 1 TeV from the Galactic halo. Different
regions of interest are considered to accommodate different DM density
profiles. We do not find any significant line structure, and the previously
reported line-like feature at $\sim$133 GeV is also not detected in our
analysis. Adopting a local DM density of $\rho_{\rm local}=0.4\,{\rm
GeV\,cm^{-3}}$, we derive 95% confidence level constraints on the
velocity-averaged cross-section of $\langle{\sigma v}\rangle_{\gamma\gamma}
\lesssim 4 \times 10^{-28}\,{\rm cm^{3}\,s^{-1}}$ and the decay lifetime of
$\tau_{\gamma\nu} \gtrsim 5 \times 10^{29}\,{\rm s}$ at 100 GeV, achieving the
strongest constraints to date for the line energies of 6-660 GeV. The
improvement stems from the longer Fermi-LAT data set used and the inclusion of
DAMPE data in the analysis. The simultaneous use of two independent data sets
could also reduce the systematic uncertainty of the search.
|
2308.16762v1
|
2023-09-06
|
Strong magnon-magnon coupling in an ultralow damping all-magnetic-insulator heterostructure
|
Magnetic insulators such as yttrium iron garnets (YIGs) are of paramount
importance for spin-wave or magnonic devices as their ultralow damping enables
ultralow power dissipation that is free of Joule heating, exotic magnon quantum
state, and coherent coupling to other wave excitations. Magnetic insulator
heterostructures bestow superior structural and magnetic properties and house
immense design space thanks to the strong and engineerable exchange interaction
between individual layers. To fully unleash their potential, realizing low
damping and strong exchange coupling simultaneously is critical, which often
requires high quality interface. Here, we show that such a demand is realized
in an all-insulator thulium iron garnet (TmIG)/YIG bilayer system. The ultralow
dissipation rates in both YIG and TmIG, along with their significant spin-spin
interaction at the interface, enable strong and coherent magnon-magnon coupling
with a benchmarking cooperativity value larger than the conventional
ferromagnetic metal-based heterostructures. The coupling strength can be tuned
by varying the magnetic insulator layer thickness and magnon modes, which is
consistent with analytical calculations and micromagnetic simulations. Our
results demonstrate TmIG/YIG as a novel platform for investigating hybrid
magnonic phenomena and open opportunities in magnon devices comprising
all-insulator heterostructures.
|
2309.03116v1
|
2023-09-14
|
A new break near 10 TeV in the energy spectrum of protons according to data from space-based instruments: astrophysical interpretation
|
Recent experimental data from space-based instruments of the DAMPE and CALET
collaborations have shown that the energy spectrum of protons has a new
feature, a break in the $\sim 10$ TeV region. In this energy range, the
spectrum index of the observed particles varies from $-2.6$ to $-2.9$.
The purpose of this work is to establish the local sources's position and age
that determine this break, the index of the proton generation spectrum in them,
as well as the astrophysical interpretation of the results obtained in the
DAMPE and CALET experiments.
Within the framework of the model of nonclassical diffusion of cosmic rays
developed by the authors, which has break due to the propagation of particles
in a sharply inhomogeneous (fractal type) galactic medium, it is shown that
break in this energy range is formed by tevatron located at a distance of $\sim
120$ pc from the Earth. These source, whose age is $\sim 5 \cdot 10^5$ years,
generate particles with a spectrum index $\sim 2.7$.
The power-law behavior of the proton spectrum before and after the break,
soft spectrum of particles generation in the source, first obtained in the
DAMPE and CALET experiments, should be considered as an indication of the need
to revise the standard paradigm accepted today about the sources of cosmic
rays, mechanisms of particle acceleration in them and particles propagation in
the Galaxy.
|
2309.07420v1
|
2023-11-06
|
Phase mixing of propagating Alfv{é}n waves in a single-fluid partially ionized solar plasma
|
Phase mixing of Alfven waves is one of the most promising mechanisms for
heating of the solar atmosphere. The damping of waves in this case requires
small transversal scales, relative to the magnetic field direction. Here this
requirement is achieved by considering a transversal inhomogeneity in the
equilibrium plasma density profile. Using a single fluid approximation of a
partially ionized chromospheric plasma we study the effectiveness of the
damping of phase mixed shear Alfven waves and investigate the effect of varying
the ionization degree on the dissipation of waves. Our results show that the
dissipation length of shear Alfven waves strongly depends on the ionization
degree of the plasma, but more importantly, in a partially ionized plasma, the
damping length of shear Alfven waves is several orders of magnitude shorter
than in the case of a fully ionized plasma, providing evidence that phase
mixing could be a large contributor to heating the solar chromosphere. The
effectiveness of phase mixing is investigated for various ionization degrees,
ranging from very weakly to very strongly ionized plasmas. Our results show
that phase mixed propagating Alfven waves in a partially ionized plasma with
ionization degrees in the range 0.518 to 0.657, corresponding to heights of
1916 to 2150 km above the solar surface, can provide sufficient heating to
balance chromospheric radiative losses in the quiet Sun.
|
2311.02989v1
|
2023-11-15
|
Damped Proximal Augmented Lagrangian Method for weakly-Convex Problems with Convex Constraints
|
We give a damped proximal augmented Lagrangian method (DPALM) for solving
problems with a weakly-convex objective and convex linear/nonlinear
constraints. Instead of taking a full stepsize, DPALM adopts a damped dual
stepsize to ensure the boundedness of dual iterates. We show that DPALM can
produce a (near) $\vareps$-KKT point within $O(\vareps^{-2})$ outer iterations
if each DPALM subproblem is solved to a proper accuracy. In addition, we
establish overall iteration complexity of DPALM when the objective is either a
regularized smooth function or in a regularized compositional form. For the
former case, DPALM achieves the complexity of
$\widetilde{\mathcal{O}}\left(\varepsilon^{-2.5} \right)$ to produce an
$\varepsilon$-KKT point by applying an accelerated proximal gradient (APG)
method to each DPALM subproblem. For the latter case, the complexity of DPALM
is $\widetilde{\mathcal{O}}\left(\varepsilon^{-3} \right)$ to produce a near
$\varepsilon$-KKT point by using an APG to solve a Moreau-envelope smoothed
version of each subproblem. Our outer iteration complexity and the overall
complexity either generalize existing best ones from unconstrained or
linear-constrained problems to convex-constrained ones, or improve over the
best-known results on solving the same-structured problems. Furthermore,
numerical experiments on linearly/quadratically constrained non-convex
quadratic programs and linear-constrained robust nonlinear least squares are
conducted to demonstrate the empirical efficiency of the proposed DPALM over
several state-of-the art methods.
|
2311.09065v1
|
2023-12-07
|
Nonlinear aspects of stochastic particle acceleration
|
In turbulent magnetized plasmas, charged particles can be accelerated to high
energies through their interactions with the turbulent motions. As they do so,
they draw energy from the turbulence, possibly up to the point where they start
modifying the turbulent cascade. Stochastic acceleration then enters a
nonlinear regime because turbulence damping back-reacts in turn on the
acceleration process. This article develops a phenomenological model to examine
this situation in detail and to explore its consequences for the particle and
turbulent energy spectra. We determine a criterion that specifies the threshold
of nonthermal particle energy density and the characteristic momentum beyond
which back-reaction becomes effective. Once the back-reaction sets in, the
turbulence cascade becomes damped below a length scale that keeps increasing in
time. The accelerated particle momentum distribution develops a near power-law
of the form ${\rm d}n/{\rm d}p\propto p^{-s}$ with $s\sim2$ beyond the momentum
at which back-reaction first sets in. At very high energies, where the
gyroradius of accelerated particles becomes comparable to the outer scale of
the turbulence, the energy spectrum can display an even harder spectrum with
$s\sim 1.3-1.5$ over a short segment. The low-energy part of the spectrum,
below the critical momentum, is expected to be hard ($s\sim 1$ or harder), and
shaped by any residual acceleration process in the damped region of the
turbulence cascade. This characteristic broken power-law shape with $s\sim 2$
at high energies may find phenomenological applications in various high-energy
astrophysical contexts.
|
2312.04443v2
|
2023-12-12
|
Circularization in the damped Kepler problem
|
In this paper, we revisit the damped Kepler problem within a general family
of nonlinear damping forces with magnitude $\delta \vert u\vert^{\beta}\vert
\dot u\vert^{\alpha+1}$, depending on three parameters $\delta>0,\alpha\ge 0$
and $\beta\ge 0$, and address the general question of circularization whereby
orbits tend to become more circular as they approach the sun. Our approach is
based on dynamical systems theory, using blowup and desingularization as our
main technical tools. We find that $\gamma=\alpha+2\beta-3$ is an important
quantity, with the special case $\gamma=0$ separating circularization
($-3<\gamma<0$) where the eccentricity converges to zero, i.e. $e(t)\rightarrow
0$ as $u(t)\rightarrow 0$, from cases ($\gamma>0$) where $e(t)\rightarrow 1$ as
$u(t)\rightarrow 0$, both on open sets of initial conditions. We find that
circularization for $-3<\gamma<0$ occurs due to asymptotic stability of a
zero-Hopf equilibrium point (i.e., the eigenvalues are $\pm i \omega,0$) of a
three-dimensional reduced problem (which is analytic in the blowup
coordinates). The attraction is therefore not hyperbolic and in particular not
covered by standard dynamical systems theory. Instead we use recent results on
normal forms of the zero-Hopf to locally bring the system into a form where the
stability can be addressed directly. We believe that our approach can be used
to describe unbounded solutions.
|
2312.07249v1
|
2023-12-21
|
Annealing reduces Si$_3$N$_4$ microwave-frequency dielectric loss in superconducting resonators
|
The dielectric loss of silicon nitride (Si$_3$N$_4$) limits the performance
of microwave-frequency devices that rely on this material for sensing, signal
processing, and quantum communication. Using superconducting resonant circuits,
we measure the cryogenic loss tangent of either as-deposited or
high-temperature annealed stoichiometric Si$_3$N$_4$ as a function of drive
strength and temperature. The internal loss behavior of the electrical
resonators is largely consistent with the standard tunneling model of two-level
systems (TLS), including damping caused by resonant energy exchange with TLS
and by the relaxation of non-resonant TLS. We further supplement the TLS model
with a self-heating effect to explain an increase in the loss observed in
as-deposited films at large drive powers. Critically, we demonstrate that
annealing remedies this anomalous power-induced loss, reduces the
relaxation-type damping by more than two orders of magnitude, and reduces the
resonant-type damping by a factor of three. Employing infrared absorption
spectroscopy, we find that annealing reduces the concentration of hydrogen in
the Si$_3$N$_4$, suggesting that hydrogen impurities cause substantial
dissipation.
|
2312.13504v1
|
2023-12-31
|
Molecular Hybridization Induced Antidamping and Sizable Enhanced Spin-to-Charge Conversion in Co20Fe60B20/$β$-W/C60 Heterostructures
|
Development of power efficient spintronics devices has been the compelling
need in the post-CMOS technology era. The effective tunability of
spin-orbit-coupling (SOC) in bulk and at the interfaces of hybrid materials
stacking is a prerequisite for scaling down the dimension and power consumption
of these devices. In this work, we demonstrate the strong chemisorption of C60
molecules when grown on the high SOC $\beta$-W layer. The parent CFB/$\beta$-W
bilayer exhibits large spin-to-charge interconversion efficiency, which can be
ascribed to the interfacial SOC observed at the Ferromagnet/Heavy metal
interface. Further, the adsorption of C60 molecules on $\beta$-W reduces the
effective Gilbert damping by $\sim$15% in the CFB/$\beta$-W/C60
heterostructures. The anti-damping is accompanied by a gigantic $\sim$115%
enhancement in the spin-pumping induced output voltage owing to the molecular
hybridization. The non-collinear Density Functional Theory calculations confirm
the long-range enhancement of SOC of $\beta$-W upon the chemisorption of C60
molecules, which in turn can also enhance the SOC at the CFB/$\beta$-W
interface in CFB/$\beta$-W/C60 heterostructures. The combined amplification of
bulk as well interfacial SOC upon molecular hybridization stabilizes the
anti-damping and enhanced spin-to-charge conversion, which can pave the way for
the fabrication of power efficient spintronics devices.
|
2401.00486v1
|
2024-01-11
|
Instability windows of relativistic r-modes
|
The detectability of the gravitational-wave signal from $r$-modes depends on
the interplay between the amplification of the mode by the CFS instability and
its damping due to dissipative mechanisms present in the stellar matter. The
instability window of $r$-modes describes the region of stellar parameters
(angular velocity, $\Omega$, and redshifted stellar temperature, $T^\infty$),
for which the mode is unstable. In this study, we reexamine this problem in
nonbarotropic neutron stars, taking into account the previously overlooked
nonanalytic behavior (in $\Omega$) of relativistic $r$-modes and enhanced
energy dissipation resulting from diffusion in superconducting stellar matter.
We demonstrate that at slow rotation rates, relativistic $r$-modes exhibit
weaker amplification by the CFS instability compared to Newtonian ones.
However, their dissipation through viscosity and diffusion is significantly
more efficient. In rapidly rotating neutron stars within the framework of
general relativity, the amplification of $r$-modes by the CFS mechanism and
their damping due to shear viscosity become comparable to those predicted by
Newtonian theory. In contrast, the relativistic damping of the mode by
diffusion and bulk viscosity remains significantly stronger than in the
nonrelativistic case. Consequently, account for diffusion and general
relativity leads to a substantial modification of the $r$-mode instability
window compared to the Newtonian prediction. This finding is important for the
interpretation of observations of rotating neutron stars, as well as for
overall understanding of $r$-mode physics.
|
2401.06200v1
|
2024-02-06
|
The fermion self-energy and damping rate in a hot magnetized plasma
|
We derive a general expression for the fermion self-energy in a hot
magnetized plasma by using the Landau-level representation. In the one-loop
approximation, the Dirac structure of the self-energy is characterized by five
different functions that depend on the Landau-level index $n$ and the
longitudinal momentum $p_z$. We derive general expressions for all five
functions and obtain closed-form expressions for their imaginary parts. The
latter receive contributions from three types of on-shell processes, which are
interpreted in terms of Landau-level transitions, accompanied by a single
photon (gluon) emission or absorption. By making use of the imaginary parts of
the self-energy functions, we also derive the Landau-level dependent fermion
damping rates $\Gamma_{n}(p_z)$ and study them numerically in a wide range of
model parameters. We also demonstrate that the two-spin degeneracy of the
Landau levels is lifted by the one-loop self-energy corrections. While the spin
splitting of the damping rates is small, it may be important for some spin and
chiral effects. We argue that the general method and the numerical results for
the rates can have interesting applications in heavy-ion physics, astrophysics,
and cosmology, where strongly magnetized QED or QCD plasmas are ubiquitous.
|
2402.04307v2
|
2024-04-02
|
A new gap in the critical exponent for semi-linear structurally damped evolution equations
|
Our aim in this paper is to discuss the critical exponent in semi-linear
structurally damped wave and beam equations with additional dispersion term.
The special model we have in mind is $$
u_{tt}(t,x)+(-\Delta)^{\sigma}u(t,x)+(-\Delta)^{2\delta}u(t,x)+2(-\Delta)^{\delta}u_{t}(t,x)=\left|u(t,x)\right|
^{p} $$ where the initial displacement $u(0,x)=u_{0}(x)$, the initial velocity
$u_{t}(0,x)=u_{1}(x)$ and the parameters $ t\in [0,\infty)$, $x\in
\mathbb{R}^{n}$, $\sigma\geq 1$, $\delta\in(0,\frac{\sigma}{2})$, $p>1$. The
solution to the linear equation at low frequency region involves an interplay
of diffusion and oscillation phenomena represented by a real-complex Fourier
multiplier of the form $$m(t,\xi)=\frac{e^{-|\xi|^{2\delta}t\pm
i|\xi|^{\sigma}t}}{2i|\xi|^{\sigma}}, \ \ \xi\in \mathbb{R}^{n}, \ \
i=\sqrt{-1}.$$ The scaling argument shows that the diffusive part leads to
faster decay rates compared to the oscillatory one. This interplay creates a
new gap in the critical exponent between the blow up (in finite time) result
when $1<p<1+\frac{4\delta}{n-2\delta}$ (sub-critical case) and the global (in
time) existence result when $p>1+\frac{\sigma+2\delta}{n-\sigma}$
(super-critical case). We leave an open to show if this gap will be closed at
least in low or high space dimensions because, to the best of authors
knowledge, the necessary Fourier multiplier that leads to the sub-critical case
does not explicitly appear in $m(t,\xi)$.
|
2404.01544v1
|
2024-04-10
|
Quantum algorithms to simulate quadratic classical Hamiltonians and optimal control
|
Simulation of realistic classical mechanical systems is of great importance
to many areas of engineering such as robotics, dynamics of rotating machinery
and control theory. In this work, we develop quantum algorithms to estimate
quantities of interest such as the kinetic energy in a given classical
mechanical system in the presence of friction or damping as well as forcing or
source terms, which makes the algorithm of practical interest. We show that for
such systems, the quantum algorithm scales polynomially with the logarithm of
the dimension of the system. We cast this problem in terms of Hamilton's
equations of motion (equivalent to the first variation of the Lagrangian) and
solve them using quantum algorithms for differential equations. We then
consider the hardness of estimating the kinetic energy of a damped coupled
oscillator system. We show that estimating the kinetic energy at a given time
of this system to within additive precision is BQP hard when the strength of
the damping term is bounded by an inverse polynomial in the number of qubits.
We then consider the problem of designing optimal control of classical systems,
which can be cast as the second variation of the Lagrangian. In this direction,
we first consider the Riccati equation, which is a nonlinear differential
equation ubiquitous in control theory. We give an efficient quantum algorithm
to solve the Riccati differential equation well into the nonlinear regime. To
our knowledge, this is the first example of any nonlinear differential equation
that can be solved when the strength of the nonlinearity is asymptotically
greater than the amount of dissipation. We then show how to use this algorithm
to solve the linear quadratic regulator problem, which is an example of the
Hamilton-Jacobi-Bellman equation.
|
2404.07303v1
|
1999-07-23
|
Autoregressive model of 1/f noise
|
An analytically solvable model is proposed exhibiting 1/f spectrum in any
desirably wide range of frequency (but excluding the point f=0). The model
consists of pulses whose recurrence times obey an autoregressive process with
very small damping.
|
9907008v1
|
1996-08-22
|
Evolution of Neutral Gas at High Redshift -- Implications for the Epoch of Galaxy Formation
|
Though observationally rare, damped Lya absorption systems dominate the mass
density of neutral gas in the Universe. Eleven high redshift damped Lya systems
covering 2.8<z<4.4 were discovered in 26 QSOs from the APM z>4 QSO Survey,
extending these absorption system surveys to the highest redshifts currently
possible. Combining our new data set with previous surveys we find that the
cosmological mass density in neutral gas, omega_g, does not rise as steeply
prior to z~2 as indicated by previous studies. There is evidence in the
observed omega_g for a flattening at z~2 and a possible turnover at z~3. When
combined with the decline at z>3.5 in number density per unit redshift of
damped systems with column densities log N(HI)>21 atoms cm^-2, these results
point to an epoch at z>3 prior to which the highest column density damped
systems are still forming. We find that over the redshift range 2<z<4 the total
mass in neutral gas is marginally comparable with the total visible mass in
stars in present day galaxies. However, if one considers the total mass visible
in stellar disks alone, ie excluding galactic bulges, the two values are
comparable. We are observing a mass of neutral gas comparable to the mass of
visible disk stars. Lanzetta, Wolfe & Turnshek (1995) found that omega_g(z~3.5)
was twice omega_g(z~2), implying a much larger amount of star formation must
have taken place between z=3.5 and z=2 than is indicated by metallicity
studies. This created a `cosmic G-dwarf problem'. The more gradual evolution of
omega_g we find alleviates this. These results have profound implications for
theories of galaxy formation.
|
9608147v1
|
1997-07-14
|
Damped Lyman-alpha Absorption Associated with an Early-Type Galaxy at Redshift z = 0.16377
|
We report new HST and ground-based observations of a damped Lyman-alpha
absorption system toward the QSO 0850+4400. The redshift of the absorption
system is z = 0.163770 and the neutral hydrogen column density of the
absorption system is log N = 19.81 cm**-2. The absorption system is by far the
lowest redshift confirmed damped Lyman-alpha absorption system yet identified,
which provides an unprecedented opportunity to examine the nature, impact
geometry, and kinematics of the absorbing galaxy in great detail. The
observations indicate that the absorption system is remarkable in three
respects: First, the absorption system is characterized by weak metal
absorption lines and a low metal abundance, possibly less than 4% of the solar
metal abundance. This cannot be explained as a consequence of dust, because the
neutral hydrogen column density of the absorption system is far too low for
obscuration by dust to introduce any significant selection effects. Second, the
absorption system is associated with a moderate-luminosity early-type S0
galaxy, although the absorption may actually arise in one of several very faint
galaxies detected very close to the QSO line of sight. Third, the absorbing
material moves counter to the rotating galaxy disk, which rules out the
possibility that the absorption arises in a thin or thick co-rotating gaseous
disk. These results run contrary to the expectation that low-redshift damped
Lyman-alpha absorption systems generally arise in the gas- and metal-rich inner
parts of late-type spiral galaxies. We suggest instead that mounting evidence
indicates that low-redshift galaxies of a variety of morphological types may
contain significant quantities of low metal abundance gas at large
galactocentric distances.
|
9707157v1
|
1997-08-27
|
Reionization of the Intergalactic Medium and the Damping Wing of the Gunn-Peterson Trough
|
Observations of high-redshift quasars show that the IGM must have been
reionized at some redshift $z>5$. If a source of radiation could be observed at
the rest-frame Lya wavelength, at a sufficiently high redshift where some of
the IGM in the line-of-sight was not yet reionized, the Gunn-Peterson trough
should be present. Longward of the Lya wavelength, a damping wing should be
observed caused by the neutral IGM whose absorption profile can be predicted.
Measuring the shape of this damping wing would provide irrefutable evidence of
the observation of the IGM before reionization, and a determination of the
density of the neutral IGM. This measurement might be hindered by the possible
presence of a dense absorption system associated with the source.
Shortward of the \lya wavelength, absorption should be seen from the patchy
structure of the IGM in the process of reionization. We show that a complete
Gunn-Peterson trough is most likely to continue to be observed through the
epoch where the IGM is partially ionized. The damping wings of the neutral
patches should overlap if the proper pathlength through an ionized region is
less than 1 h^{-1} Mpc; even in larger ionized regions, the characteristic
background intensity should be low enough to yield a very high optical depth
due to the residual neutral fraction, although occasionally some flux may be
transmitted through large, underdense voids within an ionized region. The case
of the HeII reionization is also discussed, and we argue that helium was
already doubly ionized by z=3 throughout the IGM.
The recently discovered afterglows of gamma-ray bursts might soon be observed
at very high redshifts. Their featureless continuum spectrum and high
luminosities make them ideal sources for studying absorption by the IGM.
|
9708253v1
|
1997-09-16
|
On the nature of z(abs) ~ z(em) damped absorbers in quasar spectra
|
We present spectroscopic observations of the damped Ly-alpha absorber at
redshift z=1.9342 seen in the spectrum of the quasar Q0151+048A. The redshift
of the absorber is greater than the redshift of the quasar, so the system
resembles the z(abs) ~ z(em) damped absorber at z=2.81 towards the quasar
PKS0528-250. We have previously reported the detection of Ly-alpha emission
from the latter absorber, one of only two damped absorbers for which Ly-alpha
emission has unambiguously been detected. The resemblance between the
PKS0528-250 and Q0151+048A systems is made closer by the detection of a weak
emission feature in the trough of the Q0151+048A absorber. This leads us to
consider whether these z(abs) ~ z(em) DLA absorbers are different objects to
the intervening DLA absorbers. Two possibilities are examined and rejected.
Firstly the Q0151+048A and PKS0528-250 z(abs) ~ z(em) absorbers appear to be
unrelated to the intrinsic absorbers (i.e. gas close to the quasar nucleus,
ejected by the quasar), as intrinsic absorbers are of higher metallicity, have
higher ionisation parameter, and show complex absorption profiles. Secondly
these two DLA absorbers cannot be equated with the gaseous disks of the quasar
host galaxies, as the absorber redshifts differ significantly from the quasar
systemic redshifts. It is likely, then, that intrinsically the z(abs) ~ z(em)
DLA absorbers are the same as the intervening DLA absorbers, so that
peculiarities in some of the z(abs) ~ z(em) absorbers can be ascribed to their
different environment i.e. proximity to the quasar, or membership of the same
cluster as the quasar. We point out that the proximity effect may play some
role, by reducing the Ly-alpha forest line blanketing of any Ly-alpha emission
line from z(abs) ~ z(em) absorbers.
|
9709160v1
|
1998-01-15
|
A HST Spectroscopic study of QSOs with intermediate redshift damped Lyman-alpha systems
|
We present HST spectra for a sample of six QSOs with intermediate redshift
(z_a < 1) damped Ly-alpha systems. These observations aim at measuring the HI
column density and detect metal lines in order to investigate the metal
enrichment of the gas, as well as the presence of neutral species, molecules
and dust. All systems selected on the basis of 21 cm absorption and/or strong
FeII lines relative to MgII ones turn out to have N(HI) larger than 10^20 cm-2.
It appears that although the scatter of metallicities is as large at z_a<1 as
at high redshift, an increasing proportion of systems with metallicities ~ 30%
solar are found when going at lower redshifts. Our results suggest that
available observations may be biased against dust-rich absorbers. Further, when
all available measurements of N(HI) and [Zn/H] are considered, a clear
deficiency of systems with large N(HI) and high metallicity is apparent. We
conclude that dust extinction causes a preferential selection of QSOs with
intervening gas relatively poor in metals, dust and molecules. As a
consequence, the high end of the HI column density distribution (and hence
Omega_g, the contribution of neutral gas to the cosmological mass density) is
probably more heavily underestimated than previously thought, especially at low
redshift. Such a bias could also explain the high incidence of non-spiral
morphologies in our sample. We stress that observation of a larger sample of
low z damped Ly-alpha systems as well as surveys of damped Ly-alpha systems in
fainter QSOs would give a more representative view of the true diversity of
absorber properties and should help to probe the denser phases of the
interstellar medium in distant galaxies.
|
9801146v1
|
1998-06-15
|
On the kinematics of damped Lyman-alpha systems
|
We report on high spectral resolution observations of five damped Ly-alpha
absorbers. Line velocity profiles and heavy element abundances are discussed.
Nitrogen is found to have abundances less than silicon in the systems toward Q
0347-383, Q 0913+072, and Q 1213+093. The absorber toward Q 0913+072 is the
most metal-deficient damped system known, with [Fe/H] < -3.2. The simple
kinematical structure of the metal absorptions makes this system ideal to
discuss the [O/Si] and [N/O] ratios. We find [O/H] ~ -2.7 and -2.7 < [Si/H] <
-2.2. By combining these data with information gathered in the literature, we
study the kinematics of the low and high ionization phases in a sample of 26
damped Ly-alpha systems in the redshift range 1.17-4.38. We note a strong
correlation between the velocity broadenings of the SiII,1808 and FeII,1608
lines whatever the line optical depth, implying that the physical conditions
are quite homogeneous in the sample. Statistically this shows that large
variations of abundance ratios and thus large variations of depletion into dust
grains are unlikely. The velocity broadening of the absorption lines, Delta V,
is correlated with the asymmetry of the lines for Delta V < 150 km/s. The
broader the line the more asymmetric it is, as expected in case rotation
dominates the line broadening. However this correlation does not hold for
larger Delta V suggesting that evidence for rotational motions is restricted to
velocity broadenings Delta V < 150 km/s. The systems with Delta V > 200 km/s
are peculiar with kinematics consistent with random motions. They show
sub-systems as those expected if the objects are in the process of merging
(abridged).
|
9806202v1
|
1999-10-07
|
Si and Mn Abundances in Damped Lya Systems with Low Dust Content
|
We have measured the abundances of Zn, Si, Mn, Cr, Fe, and Ni in three damped
Lyman alpha systems at redshifts z < 1 from high resolution echelle spectra of
QSOs recorded with the Keck I telescope. In all three cases the abundances of
Cr, Fe, and Ni relative to Zn indicate low levels of dust depletions. We
propose that when the proportion of refractory elements locked up in dust
grains is less than about 50 percent, it is plausible to assume an
approximately uniform level of depletion for all grain constituents and, by
applying a small dust correction, recover the intrisic abundances of Si and Mn.
We use this approach on a small sample of damped systems for which it is
appropriate, with the aim of comparing the metallicity dependence of the ratios
[Si/Fe] and [Mn/Fe] with analogous measurements in Milky Way stars. The main
conclusion is that the relative abundances of both elements in distant galaxies
are broadly in line with expectations based on Galactic data. Si displays a
mild enhancement at low metallicities, as expected for an alpha-capture
element, but there are also examples of near-solar [Si/Fe] at [Fe/H] < -1. The
underabundance of Mn at low metallicities is possibly even more pronounced than
that in metal-poor stars, and no absorption system has yet been found where
[Mn/Fe] is solar. The heterogeneous chemical properties of damped Lyman alpha
systems, evident even from this limited set of measurements, provide further
support for the conclusion from imaging studies that a varied population of
galaxies gives rise to this class of QSO absorbers.
|
9910131v1
|
1999-11-23
|
On the orbital evolution and growth of protoplanets embedded in a gaseous disc
|
We present a new computation of the linear tidal interaction of a
protoplanetary core with a thin gaseous disc in which it is fully embedded. For
the first time a discussion of the orbital evolution of cores with eccentricity
(e) significantly larger than the gas-disc scale height to radius ratio (H/r)
is given. We find that the direction of orbital migration reverses for
e>1.1H/r. This occurs as a result of the orbital crossing of resonances in the
disc that do not overlap the orbit when the eccentricity is very small. Simple
expressions giving approximate fits to the eccentricity damping rate and the
orbital migration rate are presented. We go on to calculate the rate of
increase of the mean eccentricity for a system of protoplanetary cores due to
dynamical relaxation. By equating the eccentricity damping time-scale with the
dynamical relaxation time-scale we deduce that an equilibrium between
eccentricity damping and excitation through scattering is attained on a 10^3 to
10^4 yr time-scale, at 1au. The equilibrium thickness of the protoplanet
distribution is such that it is generally well confined within the gas disc. By
use of a three dimensional N-body code we simulate the evolution of a system of
protoplanetary cores, incorporating our eccentricity damping and migration
rates. Assuming that collisions lead to agglomeration, we find that the
vertical confinement of the protoplanet distribution permits cores to build up
from 0.1 to 1 earth mass in only ~10^4 yr, within 1au. The time-scale required
to achieve this is comparable to the migration time-scale. We deduce that it is
not possible to build up a massive enough core to form a gas giant planet
before orbital migration ultimately results in the preferential delivery of all
such bodies to the neighbourhood of the central star. [Abridged]
|
9911431v1
|
1999-12-14
|
Finding typical high redshift galaxies with the NOT
|
We present results from an ongoing search for galaxy counterparts of a
subgroup of Quasar Absorption Line Systems called Damped Ly-alpha Absorbers
(DLAs). DLAs have several characteristics that make them prime candidates for
being the progenitors of typical present day galaxies.
|
9912278v1
|
2000-10-21
|
UVES observations of QSO 0000-2620: Argon and Phosphorus abundances in the dust-free damped Ly-alpha system at zabs = 3.3901
|
The UV resonance transitions of neutral argon ArI 1066 A, and of singly
ionized phosphorus PII 963 A, originated in the damped Ly_alpha system (DLA) at
zabs = 3.3901 towards QSO 0000--2620 have been detected by means of the UVES
spectrograph at the 8.2m ESO KUEYEN telescope. So far, this is the first
measurement of ArI, and the second of PII, ever performed in damped galaxies
and in high redshift objects. This DLA is well known for having one of the
lowest metal abundances and dust content, and the lowest fractional abundance
of molecular hydrogen H_2. The measured Ar abundance is [Ar/H] = - 1.91 (+/-
0.09) which is equal to the abundances of the other alpha-chain elements (O, S
and Si). The similarity of the Ar abundance with the other alpha-chain elements
implies the absence of significant photoionization by either UV background or
stellar sources along the sightline throughout the damped Ly_alpha system. Both
log(Ar/O) and log(Ar/S) ratios are found close to those measured in the
extragalactic HII regions and in blue compact galaxies where O is more abundant
by at least one order of magnitude. This strengthens the universality of the
Ar/O and Ar/S ratios and lends support to the existence of a universal IMF. The
abundance of the non-refractory element phosphorus [P/H] = - 2.31 (+/- 0.10)
confirms the low amount of chemical evolution in the DLA. This is the
measurement of P in the most metal-poor material and shows a subsolar [P/Fe] =
--0.27 value. The measured ratios [P/Si] = - 0.40 (+/- 0.13) and [P/S] = - 0.33
(+/- 0.13) provide evidence for a mild odd-even effect. Finally, a stringent
upper limit to the population of the 3P_1 level in the ground state of OI is
derived, which provides a lower limit to the physical dimensions of the zabs =
3.3901 system of L > 7 pc.
|
0010434v1
|
2001-09-21
|
Coincidences of high density peaks in UVES spectra of QSO pairs
|
We present preliminary results of an investigation of the clustering
properties of high matter density peaks between redshift ~2 and ~3, as traced
by Lyman limit and Damped Ly-alpha systems in spectra of close QSO pairs and
groups.
|
0109373v1
|
2002-01-31
|
Electron impact excitation of helium-like oxygen up to n = 4 levels including radiation damping
|
The primary X-ray diagnostic lines in He-like ions are mainly excited by
electron impact from the ground level to the n = 2 levels, but at high
temperatures n > 2 levels are also excited. In order to describe the atomic
processes more completely collision strengths are computed for OVII including
for the first time all of the following: (i) relativistic fine structure, (ii)
levels up to the n = 4, and (iii) radiation damping of autoionizing resonances.
The calculations are carried out using the Breit-Pauli R-matrix (BPRM) method
with a 31-level eigenfunction expansion. Resonance structures in collision
strengths are delineated in detail up to the n = 4 thresholds. For highly
charged He-like ions radiation damping of autoionizing resonances is known to
be significant. We investigate this effect in detail and find that while
resonances are discernibly damped radiatively as the series limit n --> infty
is approached from below, the overall effect on effective cross sections and
rate coefficients is found to be very small. Collision strengths for the
principal lines important in X-ray plasma diagnostics, w,x,y and z,
corresponding to the 4 transitions to the ground level 1s^2 (^1S_0) <-- 1s2p
(^1P^o_1), 1s2p (^3P^o_2), 1s2p (^3P^o_1), 1s2s (^3S_1), are explicitly shown.
It is found that the effective collision strength of the forbidden z-line is up
to a factor of 4 higher at T < 10^6 K than previous values. This is likely to
be of considerable importance in the diagnostics of photoionized astrophysical
plasmas. Significant differences are also found with previous works for several
other transitions. This work is carried out as part of the Iron Project-RmaX
Network.
|
0201535v1
|
2002-12-07
|
Improved Bounds on Violation of the Strong Equivalence Principle
|
I describe a unique, 20-year-long timing program for the binary pulsar
B0655+64, the stalwart control experiment for measurements of gravitational
radiation damping in relativistic neutron-star binaries. Observed limits on
evolution of the B0655+64 orbit provide new bounds on the existence of dipolar
gravitational radiation, and hence on violation of the Strong Equivalence
Principle.
|
0212180v1
|
2006-01-23
|
Bulk viscosity of a gas of neutrinos and coupled scalar particles, in the era of recombination
|
Bulk viscosity may serve to damp sound waves in a system of neutrinos coupled
to very light scalar particles, in the era after normal neutrino decoupling but
before recombination. We calculate the bulk viscosity parameter in a minimal
scheme involving the coupling of the two systems. We add some remarks on the
bulk viscosity of a system of fully ionized hydrogen plus photons.
|
0601525v1
|
2006-09-28
|
Turbulent Comptonization in Relativistic Accretion Disks
|
Turbulent Comptonization, a potentially important damping and radiation
mechanism in relativistic accretion flows, is discussed. Particular emphasis is
placed on the physical basis, relative importance, and thermodynamics of
turbulent Comptonization. The effects of metal-absorption opacity on the
spectral component resulting from turbulent Comptonization is considered as
well.
|
0609797v1
|
1994-05-16
|
Bifurcations of two coupled classical spin oscillators
|
Two classical, damped and driven spin oscillators with an isotropic exchange
interaction are considered. They represent a nontrivial physical system whose
equations of motion are shown to allow for an analytic treatment of local
codimension 1 and 2 bifurcations. In addition, numerical results are presented
which exhibit a Feigenbaum route to chaos.
|
9405011v1
|
1998-04-02
|
The Decay Properties of the Finite Temperature Density Matrix in Metals
|
Using ordinary Fourier analysis, the asymptotic decay behavior of the density
matrix F(r,r') is derived for the case of a metal at a finite electronic
temperature. An oscillatory behavior which is damped exponentially with
increasing distance between r and r' is found. The decay rate is not only
determined by the electronic temperature, but also by the Fermi energy. The
theoretical predictions are confirmed by numerical simulations.
|
9804013v1
|
1998-12-02
|
Dissipative properties of vibrated granular materials
|
We investigate collective dissipative properties of vibrated granular
materials by means of molecular dynamics simulations. Rates of energy losses
indicate three different regimes or "phases"in the amplitude-frequency plane of
the external forcing, namely, solid, convective, and gas-like regimes. The
behavior of effective damping decrement in the solid regime is glassy.
Practical applications are dicussed.
|
9812036v1
|
1999-01-14
|
Spin dynamics in the generalized ferromagnetic Kondo model for manganites
|
Dynamical spin susceptibility is calculated for the generalized ferromagnetic
Kondo model which describes itinerant $e_{g}$ electrons interacting with
localized $t_{2g}$ electrons with antiferromagnetic coupling. The calculations
done in the mean field approximation show that the spin-wave spectrum of the
system in ferromagnetic state has two branches, acoustic and optic ones.
Self-energy corrections to the spectrum are considered and the acoustic
spin-wave damping is evaluated.
|
9901141v1
|
1999-10-01
|
Properties of excitations in systems with a spinor Bose-Einstein condensate
|
General theory in case of homogenous Bose-Einstein condensed systems with
spinor condensate is presented for the correlation functions of density and
spin fluctuations and for the one-particle propagators as well. The random
phase approximation is investigated and the damping of the modes is given in
the intermediate temperature region. It is shown that the collective and the
one-particle excitation spectra do not coincide fully.
|
9910010v1
|
2001-07-16
|
Anomalous Levy decoherence
|
We investigate the decoherence of a small quantum system weakly coupled to a
complex, chaotic environment when the dynamics is not Gaussian but Levy
anomalous. By studying the time dependence of the linear entropy and the
damping of the interference of two Gaussian wave packets in the Wigner
representation, we show that the decoherence time for a quantum Levy stable
process is always smaller than for Gaussian diffusion.
|
0107344v1
|
2002-03-06
|
Effect of electron-phonon interaction on the shift and attenuation of optical phonons
|
Using the Boltzmann equation for electrons in metals, we show that the
optical phonons soften and have a dispersion due to screening in agreement with
the results reported recently [M. Reizer, Phys. Rev. B {\bf 61}, 40 (2000)].
Additional phonon damping and frequency shift arise when the electron--phonon
interaction is properly included.
|
0203112v1
|
2002-04-09
|
Spatial resolution of spin waves in an ultra-cold gas
|
We present the first spatially resolved images of spin waves in a gas. The
complete longitudinal and transverse spin field as a function of time and space
is reconstructed. Frequencies and damping rates for a standing-wave mode are
extracted and compared with theory.
|
0204182v1
|
2002-08-14
|
Three-wave mixing of Bogoliubov quasi-particles in a Bose condensate
|
A dressed basis is used to calculate the dynamics of three-wave mixing
between Bogoliubov quasi-particles in a Bose condensate. Due to the observed
oscillations between different momenta modes, an energy splitting, analogous to
the optical Mollow triplet, appears in the Beliaev damping spectrum of the
excitations from the oscillating modes.
|
0208283v2
|
2002-11-08
|
Reply on ``Fluctuation-dissipation considerations for phenomenological damping models for ferromagnetic thin films'' [N. Smith, J. Appl. Phys. \bf{92}, 3877 (2002)]
|
We show that the critique of our recent papers presented in the
abovementioned paper (NS) appeals to an incorrect mathematical analogy between
electrical circuits and linear magnetization dynamics, improperly uses
classical concepts of normal modes and basic equations, gives inconsistent
results and therefore comes to incorrect conclusions.
|
0211147v1
|
2003-02-04
|
Squeezing and temperature measurement in Bose-Einstein Condensates
|
In this paper we discuss the presence of temperature-dependent squeezing in
the collective excitations of trapped Bose-Einstein condensates, based on a
recent theory of quasiparticle damping. A new scheme to measure temperature
below the critical temperature is also considered.
|
0302068v1
|
2003-03-12
|
Time-Dependent Dynamics of the Bose-Fermi Mixed Condensed System
|
We study the monopole oscillation in the bose-fermi mixed condensed system by
performing the time-dependent Gross-Pitaevsky (GP) and Vlasov equations. We
find that the big damping exists for the fermion oscillation in the mixed
system even at zero temperature
|
0303216v1
|
2005-10-06
|
Thermal processes induced in carbon nanotubes by attosecond laser pulses
|
In this paper the heat transport in carbon nanotubes is investigated. When
the dimension of the structure is of the order of the de Broglie wave length
the transport phenomena must be analyzed within quantum mechanics. In this
paper we developed the Dirac type thermal equation. The solution of the
equation the temperature fields for electrons can be damped or can oscillate
depending on the dynamics of the scattering.
|
0510141v1
|
2006-08-22
|
Simulation of stress-impedance effects in low magnetostrictive films
|
A theoretical study of stress-impedance effect based on the solution of
Landau-Lifsitz-Gilbert equation has been carried out. The results show that
stress impedance effects depend largely on several extrinsic (external bias
field, external frequency) and intrinsic (orientation and magnitude of uniaxial
anisotropy, damping) parameters.
|
0608488v1
|
2006-09-05
|
Lifetimes of electrons in the Shockley surface state band of Ag(111)
|
We present a theoretical many-body analysis of the electron-electron (e-e)
inelastic damping rate $\Gamma$ of electron-like excitations in the Shockley
surface state band of Ag(111). It takes into account ab-initio band structures
for both bulk and surface states. $\Gamma$ is found to increase more rapidly as
a function of surface state energy E than previously reported, thus leading to
an improved agreement with experimental data.
|
0609080v1
|
2006-09-28
|
Transition-Event Durations in One Dimensional Activated Processes
|
Despite their importance in activated processes, transition-event durations
-- which are much shorter than first passage times -- have not received a
complete theoretical treatment. We therefore study the distribution of
durations of transition events over a barrier in a one-dimensional system
undergoing over-damped Langevin dynamics.
|
0609741v1
|
2007-01-08
|
Coefficient of restitution for viscoelastic disks
|
The dissipative collision of two identical viscoelastic disks is studied. By
using a known law for the elastic part of the interaction force and the
viscoelastic damping model an analytical solution for the coefficient of
restitution shall be given. The coefficient of restitution depends
significantly on the impact velocity. It approaches one for small velocities
and decreases for increasing velocities.
|
0701142v1
|
2007-01-09
|
Enhanced Weiss oscillations in graphene
|
The magneto-conductivity of a single graphene layer where the electrons are
described by the Dirac Hamiltonian weakly modulated by a periodic potential is
calculated. It is shown that Weiss oscillations periodic in the inverse
magnetic field appear, that are more pronounced and less damped with the
increment of temperature as compared with the same oscillations in a typical
two-dimensional electron system with a standard parabolic energy spectrum.
|
0701175v1
|
2007-03-15
|
A new electromagnetic mode in graphene
|
A new, weakly damped, {\em transverse} electromagnetic mode is predicted in
graphene. The mode frequency $\omega$ lies in the window
$1.667<\hbar\omega/\mu<2$, where $\mu$ is the chemical potential, and can be
tuned from radiowaves to the infrared by changing the density of charge
carriers through a gate voltage.
|
0703406v1
|
1997-04-01
|
Controversies in the History of the Radiation Reaction problem in General Relativity
|
This paper examines the historical controversy over whether gravitationally
bound systems, such as binary stars, experienced orbital damping due to the
emission of gravitational radiation, focusing especially on the period of the
1950s, but also discussing the work of Einstein and Rosen in the 1930s on
cylindrical gravitational waves and the later quadrupole formula controversy.
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9704002v1
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