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2022-12-21
|
Global existence and Blow-up for the 1D damped compressible Euler equations with time and space dependent perturbation
|
In this paper, we consider the 1D Euler equation with time and space
dependent damping term $-a(t,x)v$. It has long been known that when $a(t,x)$ is
a positive constant or $0$, the solution exists globally in time or blows up in
finite time, respectively. We prove that those results are invariant with
respect to time and space dependent perturbations. We suppose that the
coefficient $a$ satisfies the following condition $$ |a(t,x)- \mu_0| \leq
a_1(t) + a_2 (x), $$ where $\mu_0 \geq 0$ and $a_1$ and $a_2$ are integrable
functions with $t$ and $x$. Under this condition, we show the global existence
and the blow-up with small initial data, when $\mu_0 >0$ and $\mu=0$
respectively.
|
2212.11072v2
|
2023-02-13
|
A damped elastodynamics system under the global injectivity condition: Local wellposedness in $L^p$-spaces
|
The purpose of this paper is to model mathematically mechanical aspects of
cardiac tissues. The latter constitute an elastic domain whose total volume
remains constant. The time deformation of the heart tissue is modeled with the
elastodynamics equations dealing with the displacement field as main unknown.
These equations are coupled with a pressure whose variations characterize the
heart beat. This pressure variable corresponds to a Lagrange multiplier
associated with the so-called global injectivity condition. We derive the
corresponding coupled system with nonhomogeneous boundary conditions where the
pressure variable appears. For mathematical convenience a damping term is
added, and for a given class of strain energies we prove the existence of
local-in-time solutions in the context of the $L^p$-parabolic maximal
regularity.
|
2302.06327v2
|
2024-02-29
|
Quantum coherence and entanglement under the influence of decoherence
|
In this work, we delve into the dynamic traits of the relative entropy of
quantum coherence (REQC) as the quantum system interacts with the different
noisy channels, drawing comparisons with entanglement (concurrence). The
research results demonstrate the broader prevalence and stronger robustness of
the REQC as opposed to concurrence. It's worth noting that the bit flip channel
cannot uphold a constant nonzero frozen the REQC, besides, the concurrence
follows a pattern of temporary reduction to zero, followed by recovery after a
certain time span. More importantly, the REQC maintains its presence
consistently until reaching a critical threshold, whereas concurrence
experiences completely attenuation to zero under the influence of phase damping
and amplitude damping channels.
|
2402.19055v1
|
2003-07-01
|
Highly damped quasinormal modes of Kerr black holes
|
Motivated by recent suggestions that highly damped black hole quasinormal
modes (QNM's) may provide a link between classical general relativity and
quantum gravity, we present an extensive computation of highly damped QNM's of
Kerr black holes. We do not limit our attention to gravitational modes, thus
filling some gaps in the existing literature. The frequency of gravitational
modes with l=m=2 tends to \omega_R=2 \Omega, \Omega being the angular velocity
of the black hole horizon. If Hod's conjecture is valid, this asymptotic
behaviour is related to reversible black hole transformations. Other highly
damped modes with m>0 that we computed do not show a similar behaviour. The
real part of modes with l=2 and m<0 seems to asymptotically approach a constant
value \omega_R\simeq -m\varpi, \varpi\simeq 0.12 being (almost) independent of
a. For any perturbing field, trajectories in the complex plane of QNM's with
m=0 show a spiralling behaviour, similar to the one observed for
Reissner-Nordstrom (RN) black holes. Finally, for any perturbing field, the
asymptotic separation in the imaginary part of consecutive modes with m>0 is
given by 2\pi T_H (T_H being the black hole temperature). We conjecture that
for all values of l and m>0 there is an infinity of modes tending to the
critical frequency for superradiance (\omega_R=m) in the extremal limit.
Finally, we study in some detail modes branching off the so--called
``algebraically special frequency'' of Schwarzschild black holes. For the first
time we find numerically that QNM multiplets emerge from the algebraically
special Schwarzschild modes, confirming a recent speculation.
|
0307013v2
|
2019-10-15
|
Adversarial Examples for Models of Code
|
Neural models of code have shown impressive results when performing tasks
such as predicting method names and identifying certain kinds of bugs. We show
that these models are vulnerable to adversarial examples, and introduce a novel
approach for attacking trained models of code using adversarial examples. The
main idea of our approach is to force a given trained model to make an
incorrect prediction, as specified by the adversary, by introducing small
perturbations that do not change the program's semantics, thereby creating an
adversarial example. To find such perturbations, we present a new technique for
Discrete Adversarial Manipulation of Programs (DAMP). DAMP works by deriving
the desired prediction with respect to the model's inputs, while holding the
model weights constant, and following the gradients to slightly modify the
input code. We show that our DAMP attack is effective across three neural
architectures: code2vec, GGNN, and GNN-FiLM, in both Java and C#. Our
evaluations demonstrate that DAMP has up to 89% success rate in changing a
prediction to the adversary's choice (a targeted attack) and a success rate of
up to 94% in changing a given prediction to any incorrect prediction (a
non-targeted attack). To defend a model against such attacks, we empirically
examine a variety of possible defenses and discuss their trade-offs. We show
that some of these defenses can dramatically drop the success rate of the
attacker, with a minor penalty of 2% relative degradation in accuracy when they
are not performing under attack. Our code, data, and trained models are
available at https://github.com/tech-srl/adversarial-examples .
|
1910.07517v5
|
2020-02-14
|
Testing Physical Models for Cosmic Ray Transport Coefficients on Galactic Scales: Self-Confinement and Extrinsic Turbulence at GeV Energies
|
The microphysics of ~GeV cosmic ray (CR) transport on galactic scales remain
deeply uncertain, with almost all studies adopting simple prescriptions (e.g.
constant-diffusivity). We explore different physically-motivated, anisotropic,
dynamical CR transport scalings in high-resolution cosmological FIRE
simulations of dwarf and ~$L_{\ast}$ galaxies where scattering rates vary with
local plasma properties motivated by extrinsic turbulence (ET) or
self-confinement (SC) scenarios, with varying assumptions about e.g. turbulent
power spectra on un-resolved scales, Alfven-wave damping, etc. We
self-consistently predict observables including $\gamma$-rays ($L_{\gamma}$),
grammage, residence times, and CR energy densities to constrain the models. We
demonstrate many non-linear dynamical effects (not captured in simpler models)
tend to enhance confinement. For example, in multi-phase media, even allowing
arbitrary fast transport in neutral gas does not substantially reduce CR
residence times (or $L_{\gamma}$), as transport is rate-limited by the ionized
WIM and 'inner CGM' gaseous halo ($10^{4}-10^{6}$ K gas within 10-30 kpc), and
$L_{\gamma}$ can be dominated by trapping in small 'patches.' Most physical ET
models contribute negligible scattering of ~1-10 GeV CRs, but it is crucial to
account for anisotropy and damping (especially of fast modes) or else
scattering rates would violate observations. We show that the most
widely-assumed scalings for SC models produce excessive confinement by factors
>100 in the WIM and inner CGM, where turbulent and Landau damping dominate.
This suggests either a breakdown of quasi-linear theory used to derive the CR
transport parameters in SC, or that other novel damping mechanisms dominate in
intermediate-density ionized gas.
|
2002.06211v2
|
2021-06-11
|
Dynamics and Nonmonotonic Drag for Individually Driven Skyrmions
|
We examine the motion of an individual skyrmion driven through an assembly of
other skyrmions by a constant or increasing force in the absence of quenched
disorder. The skyrmion behavior is determined by the ratio of the damping and
Magnus terms, as expressed in terms of the intrinsic skyrmion Hall angle. For a
fixed driving force in the damping dominated regime, the effective viscosity
decreases monotonically with increasing skyrmion density, similar to what is
observed in overdamped systems where it becomes difficult for the driven
particle to traverse the surrounding medium at high densities. In contrast, in
the Magnus dominated regime the velocity dependence on the density is
nonmonotonic, and there is a regime in which the skyrmion moves faster with
increasing density, as well as a pronounced speed-up effect in which a skyrmion
traveling through a dense medium moves more rapidly than it would at low
densities or in the single particle limit. At higher densities, the effective
damping increases and the velocity decreases. The velocity-force curves in the
Magnus-dominated regime show marked differences from those in the
damping-dominated regimes. Under an increasing drive we find that there is a
threshold force for skyrmion motion which increases with density. Additionally,
the skyrmion Hall angle is drive dependent, starting near zero at the threshold
for motion and increasing with increasing drive before reaching a saturation
value, similar to the behavior found for skyrmions driven over quenched
disorder. We map dynamic phase diagrams showing the threshold for motion,
nonlinear flow, speed-up, and saturation regimes. We also find that in some
cases, increasing the density can reduce the skyrmion Hall angle while
producing a velocity boost, which could be valuable for applications.
|
2106.06093v1
|
2022-03-28
|
Composite Anderson acceleration method with dynamic window-sizes and optimized damping
|
In this paper, we propose and analyze a set of fully non-stationary Anderson
acceleration algorithms with dynamic window sizes and optimized damping.
Although Anderson acceleration (AA) has been used for decades to speed up
nonlinear solvers in many applications, most authors are simply using and
analyzing the stationary version of Anderson acceleration (sAA) with fixed
window size and a constant damping factor. The behavior and potential of the
non-stationary version of Anderson acceleration methods remain an open
question. Since most efficient linear solvers use composable algorithmic
components. Similar ideas can be used for AA to solve nonlinear systems. Thus
in the present work, to develop non-stationary Anderson acceleration
algorithms, we first propose two systematic ways to dynamically alternate the
window size $m$ by composition. One simple way to package sAA(m) with sAA(n) in
each iteration is applying sAA(m) and sAA(n) separately and then average their
results. It is an additive composite combination. The other more important way
is the multiplicative composite combination, which means we apply sAA(m) in the
outer loop and apply sAA(n) in the inner loop. By doing this, significant gains
can be achieved. Secondly, to make AA to be a fully non-stationary algorithm,
we need to combine these strategies with our recent work on the non-stationary
Anderson acceleration algorithm with optimized damping (AAoptD), which is
another important direction of producing non-stationary AA and nice performance
gains have been observed. Moreover, we also investigate the rate of convergence
of these non-stationary AA methods under suitable assumptions. Finally, our
numerical results show that some of these proposed non-stationary Anderson
acceleration algorithms converge faster than the stationary sAA method and they
may significantly reduce the storage and time to find the solution in many
cases.
|
2203.14627v1
|
2017-05-01
|
A note on the initial conditions within the effective field theory approach of cosmic acceleration
|
By using the effective field theory approach, we investigate the role of
initial condition for the dark energy or modified gravity models. In details,
we consider the constant and linear parametrization of the effective Newton
constant models. Firstly, under the adiabatic assumption, the correction from
the extra scalar degree of freedom in the beyond $\Lambda$CDM model is found to
be negligible. The dominant ingredient in this setup is the primordial
curvature perturbation originated from inflation mechanism, and the energy
budget of the matter components is not very crucial. Secondly, the
iso-curvature perturbation sourced by the extra scalar field is studied. For
the constant and linear model of the effective Newton constant, there is no
such kind of scalar mode exist. For the quadratic model, there is a non-trivial
one. However, the amplitude of the scalar field is damped away very fast on all
scales. Consequently, it could not support a reasonable structure formation.
Finally, we study the importance of the setup of the scalar field starting
time. By setting different turn-on time, namely $a=10^{-2} $ and $a=10^{-7} $,
we compare the cosmic microwave background radiation temperature, lensing
deflection angle auto-correlation function as well as the matter power spectrum
in the constant and linear model. We find there is an order of
$\mathcal{O}(1\%)$ difference in the observable spectra for constant model,
while for the linear model, it is smaller than $\mathcal{O}(0.1\%)$.
|
1705.00502v1
|
2001-12-20
|
What is the manifestation of a "quasar" at z > 10^{10} ?
|
The process of forming an image of a cosmological point source (CPS) in
condition of high optical depth is considered accounting for all types of
interactions. It is shown that the energy conservation law causes the size of
this image which is keeping constant over all redshifts of the CPSs. This
effect must be taken into account for the consideration of the angular power
spectrum of the CMBR. In particular, distant point sources and small scale
fluctuations which were damping before recombination will contribute their
energy in the region of angular scale \theta_0 \approx 20'.
|
0112493v1
|
1994-12-17
|
The Crucial Formula for Determination of the Occurrence of the Non-Chaotic States in the rf-biased Nonlinear Oscillators
|
The crucial formulas to determine the non-chaotic states in the rf-biased
nonlinear oscillators are derived from the numerical experiments. The nature of
these formulas, which depends on symmetrical properties of the potential well,
in terms of the driven-frequency as a function of the damping constant k is
investigated. All these ones provide crucial guide posts to check which kinds
of solutions (simple or complicated) can be tailored in the dissipative
rf-biased nonlinear oscillators, respectively.
|
9412011v1
|
1995-03-17
|
Motion of heavy particles coupled to fermionic and bosonic environments in one dimension
|
Making use of a simple unitary transformation we change the hamiltonian of a
particle coupled to an one dimensional gas of bosons or fermions to a new form
from which the many body degrees of freedom can be easily traced out. The
effective dynamics of the particle allows us to compute its damping constant in
terms of the reflection coefficient of the interaction potential and the
occupation number of the environmental particles. We apply our results to a
delta repulsive potential.
|
9503089v2
|
2001-03-31
|
Stability of nonlinear stationary waves in composite superconductors
|
The thermomagnetic instability of the critical state in superconductors is
analysed with account of the dissipation and dispersion. The possibility is
demonstrated of the existance of a nonlinear shok wave describing the final
stage of the instability evolution in a superconductor. The structures possess
a finite-amplitude and propagate at a constant velocity. The apperance of these
structures is qualititively described and the wave propagation velocity is
estimated. The problem of nonlinear wave stability with respect to small
thermal and electromagnetic perturbations. It is shown that only damped
perturbations correspond to space-limited solutions.
|
0104007v1
|
2002-03-06
|
Deterministic ratchets: route to diffusive transport
|
The rectification efficiency of an underdamped ratchet operated in the
adiabatic regime increases according to a scaling current-amplitude curve as
the damping constant approaches a critical threshold; below threshold the
rectified signal becomes extremely irregular and eventually its time average
drops to zero. Periodic (locked) and diffusive (fully chaotic) trajectories
coexist on fine tuning the amplitude of the input signal. The transition from
regular to chaotic transport in noiseless ratchets is studied numerically.
|
0203129v1
|
2002-03-06
|
Stokes' Drift of linear Defects
|
A linear defect, viz. an elastic string, diffusing on a planar substrate
traversed by a travelling wave experiences a drag known as Stokes' drift. In
the limit of an infinitely long string, such a mechanism is shown to be
characterized by a sharp threshold that depends on the wave parameters, the
string damping constant and the substrate temperature. Moreover, the onset of
the Stokes' drift is signaled by an excess diffusion of the string center of
mass, while the dispersion of the drifting string around its center of mass may
grow anomalous.
|
0203131v1
|
2002-05-17
|
Long-Ranged Correlations in Sheared Fluids
|
The presence of long-ranged correlations in a fluid undergoing uniform shear
flow is investigated. An exact relation between the density autocorrelation
function and the density-mometum correlation function implies that the former
must decay more rapidly than $1/r$, in contrast to predictions of simple mode
coupling theory. Analytic and numerical evaluation of a non-perturbative
mode-coupling model confirms a crossover from $1/r$ behavior at ''small'' $r$
to a stronger asymptotic power-law decay. The characteristic length scale is
$\ell \approx \sqrt{\lambda_{0}/a}$ where $% \lambda_{0}$ is the sound damping
constant and $a$ is the shear rate.
|
0205366v1
|
2002-12-12
|
Disorder-induced rounding of certain quantum phase transitions
|
We study the influence of quenched disorder on quantum phase transitions in
systems with over-damped dynamics. For Ising order parameter symmetry disorder
destroys the sharp phase transition by rounding because a static order
parameter can develop on rare spatial regions. This leads to an exponential
dependence of the order parameter on the coupling constant. At finite
temperatures the static order on the rare regions is destroyed. This restores
the phase transition and leads to a double-exponential relation between
critical temperature and coupling strength. We discuss the behavior based on
Lifshitz-tail arguments and illustrate the results by simulations of a model
system.
|
0212305v1
|
2002-12-13
|
Scaling behavior of a nonlinear oscillator with additive noise, white and colored
|
We study analytically and numerically the problem of a nonlinear mechanical
oscillator with additive noise in the absence of damping. We show that the
amplitude, the velocity and the energy of the oscillator grow algebraically
with time. For Gaussian white noise, an analytical expression for the
probability distribution function of the energy is obtained in the long-time
limit. In the case of colored, Ornstein-Uhlenbeck noise, a self-consistent
calculation leads to (different) anomalous diffusion exponents. Dimensional
analysis yields the qualitative behavior of the prefactors (generalized
diffusion constants) as a function of the correlation time.
|
0212330v1
|
2003-06-13
|
Scaling of the magnetic response in doped antiferromagnets
|
A theory of the anomalous $\omega/T$ scaling of the dynamic magnetic response
in cuprates at low doping is presented. It is based on the memory function
representation of the dynamical spin suceptibility in a doped antiferromagnet
where the damping of the collective mode is constant and large, whereas the
equal-time spin correlations saturate at low $T$. Exact diagonalization results
within the t-J model are shown to support assumptions. Consequences, both for
the scaling function and the normalization amplitude, are well in agreement
with neutron scattering results.
|
0306366v2
|
2004-01-28
|
Microscopic mechanisms of magnetization reversal
|
Two principal scenarios of magnetization reversal are considered. In the
first scenario all spins perform coherent motion and an excess of magnetic
energy directly goes to a nonmagnetic thermal bath. A general dynamic equation
is derived which includes a tensor damping term similar to the
Bloch-Bloembergen form but the magnetization magnitude remains constant for any
deviation from equilibrium. In the second reversal scenario, the absolute value
of the averaged sample magnetization is decreased by a rapid excitation of
nonlinear spin-wave resonances by uniform magnetization precession. We have
developed an analytic k-space micromagnetic approach that describes this entire
reversal process in an ultra-thin soft ferromagnetic film for up to 90^{o}
deviation from equilibrium. Conditions for the occurrence of the two scenarios
are discussed.
|
0401590v1
|
2005-01-27
|
Current-induced macrospin vs spin-wave excitations in spin valves
|
The mode dependence of current-induced magnetic excitations in spin valves is
studied theoretically. The torque exerted on the magnetization by transverse
spin currents as well as the Gilbert damping constant are found to depend
strongly on the wave length of the excitation (spin wave). Analytic expressions
are presented for the critical currents that excite a selected spin wave. The
onset of macrospin (zero wavelength) vs finite wavelength instabilities depends
on the device parameters and the current direction, in agreement with recent
experimental findings.
|
0501672v3
|
2006-06-07
|
Ferromagnetic relaxation by magnon-induced currents
|
A theory for calculating spin wave relaxation times based on the
magnon-electron interaction is developed. The theory incorporates a thin film
geometry and is valid for a large range of magnon frequencies and wave vectors.
For high conductivity metals such as permalloy, the wave vector dependent
damping constant approaches values as high as 0.2, showing the large magnitude
of the effect, and can dominate experimentally observed relaxation.
|
0606197v1
|
1999-12-01
|
Brane-world cosmology
|
A simple model of the brane-world cosmology has been proposed, which is
characterized by four parameters, the bulk cosmological constant, the spatial
curvature of the universe, the radiation strength arising from bulk space-time
and the breaking parameter of $Z_2$-symmetry. The bulk space-time is assumed to
be locally static five-dimensional analogue of the Schwarzschild-anti-de Sitter
space-time, and then the location of three-brane is determined by metric
junction. The resulting Friedmann equation recovers standard cosmology, and a
new term arises if the assumption $Z_2$-symmetry is dropped, which behaves as
cosmological term in the early universe, next turns to negative curvature term,
and finally damps rapidly.
|
9912002v1
|
2003-01-05
|
On non-Riemannian geometry of superfluids
|
The Gross-Pitaevski (GP) equation describing helium superfluids is extended
to non-Riemannian spacetime background where torsion is shown to induce the
splitting in the potential energy of the flow. A cylindrically symmetric
solution for Minkowski background with constant torsion is obtained which shows
that torsion induces a damping on the superfluid flow velocity. The Sagnac
phase shift is computed from the superfluid flow velocity obtained from the
solution of GP equations.
|
0301013v1
|
2003-04-28
|
Sphaleron relaxation temperatures
|
The transition of sphaleron processes from non-equilibrium to thermal
equilibrium in the early Universe is examined in detail. The relations between
the damping rates and frequencies of the weak and QCD sphaleron degeneracy
parameters are determined in general form and the respective relaxation
temperatures are calculated in specific scenarios. It is pointed out that the
gauge coupling constants running with energy produces strong and weak sphaleron
rates closer to each other at very high temperatures and makes them larger in
supersymmetric models than in the standard model case.
|
0304263v4
|
2006-08-10
|
Effects of Cosmic Strings on Free Streaming
|
We study the effect of free streaming in a universe with cosmic strings with
time-varying tension as well as with constant tension. Although current
cosmological observations suggest that fluctuation seeded by cosmic strings
cannot be the primary source of cosmic density fluctuation, some contributions
from them are still allowed. Since cosmic strings actively produce isocurvature
fluctuation, the damping of small scale structure via free streaming by dark
matter particles with large velocity dispersion at the epoch of
radiation-matter equality is less efficient than that in models with
conventional adiabatic fluctuation. We discuss its implications to the
constraints on the properties of particles such as massive neutrinos and warm
dark matter.
|
0608115v1
|
2006-10-26
|
QCD traveling waves beyond leading logarithms
|
We derive the asymptotic traveling-wave solutions of the nonlinear
1-dimensional Balitsky-Kovchegov QCD equation for rapidity evolution in
momentum-space, with 1-loop running coupling constant and equipped with the
Balitsky-Kovchegov-Kuraev-Lipatov kernel at next-to-leading logarithmic
accuracy, conveniently regularized by different resummation schemes. Traveling
waves allow to define "universality classes" of asymptotic solutions, i.e.
independent of initial conditions and of the nonlinear damping. A dependence on
the resummation scheme remains, which is analyzed in terms of geometric scaling
properties.
|
0610354v3
|
1999-12-20
|
$Λ$-symmetry and background independence of noncommutative gauge theory on $\mathbb R^n$
|
Background independence of noncommutative Yang-Mills theory on $\mathbb R^n$
is discussed. The quantity $\theta \hat F \theta - \theta$ is found to be
background dependent at subleading order, and it becomes background independent
only when the ordinary gauge field strength $F$ is constant. It is shown that,
at small values of $B$, the noncommutative Dirac-Born-Infeld action possesses
$\Lambda$-symmetry at least to subleading order in $\theta$ if $F$ damps fast
enough at infinity.
|
9912174v2
|
1998-10-18
|
Simulation and analysis of electron cyclotron resonance discharges
|
We describe in detail the method for Particle-in cell/Monte-Carlo simulation
of electron cyclotron resonance (ECR) discharges. In the simulation, electric
and magnetic fields are obtained by solving Maxwell equations, and electrons
and ions are accelerated by solving equations of motion. We consider two
different cases: (i) propagation of electromagnetic wave in the presence of a
constant external magnetic field; (ii) propagation of electromagnetic wave in
the presence of a linearly decreasing magnetic field which corresponds to a
realistic ECR discharge. The simulation results indicate that at the resonance
layer, the electrons are heated by the electromagnetic wave, and the incoming
wave amplitude is pronouncedly damped, with the wave hardly propagating through
the ECR layer.
|
9810033v1
|
2003-08-30
|
Squeezed States of the Generalized Minimum Uncertainty State for the Caldirola-Kanai Hamiltonian
|
We show that the ground state of the well-known pseudo-stationary states for
the Caldirola-Kanai Hamiltonian is a generalized minimum uncertainty state,
which has the minimum allowed uncertainty $\Delta q \Delta p = \hbar
\sigma_0/2$, where $\sigma_0 (\geq 1)$ is a constant depending on the damping
factor and natural frequency. The most general symmetric Gaussian states are
obtained as the one-parameter squeezed states of the pseudo-stationary ground
state. It is further shown that the coherent states of the pseudo-stationary
ground state constitute another class of the generalized minimum uncertainty
states.
|
0309003v1
|
2004-03-31
|
Quantum and Thermal Corrections to a Classically Chaotic Dissipative System
|
The effects of quantum and thermal corrections on the dynamics of a damped
nonlinearly kicked harmonic oscillator are studied. This is done via the
Quantum Langevin Equation formalism working on a truncated moment expansion of
the density matrix of the system. We find that the type of bifurcations present
in the system change upon quantization and that chaotic behavior appears for
values of the nonlinear parameter that are far below the chaotic threshold for
the classical model. Upon increase of temperature or Planck's constant,
bifurcation points and chaotic thresholds are shifted towards lower values of
the nonlinear parameter. There is also an anomalous reverse behavior for low
values of the cutoff frequency.
|
0404001v1
|
2005-06-22
|
A degenerate three-level laser with a parametric amplifier
|
The aim of this paper is to study the squeezing and statistical properties of
the light produced by a degenerate three-level laser whose cavity contains a
degenerate parametric amplifier. In this quantum optical system the top and
bottom levels of the three-level atoms injected into the laser cavity are
coupled by the pump mode emerging from the parametric amplifier. For a linear
gain coefficient of 100 and for a cavity damping constant of 0.8, the maximum
intracavity squeezing is found at steady state and at threshold to be 93%.
|
0506178v3
|
2007-08-21
|
Dimer diffusion in a washboard potential
|
The transport of a dimer, consisting of two Brownian particles bounded by a
harmonic potential, moving on a periodic substrate is investigated both
numerically and analytically. The mobility and diffusion of the dimer center of
mass present distinct properties when compared with those of a monomer under
the same transport conditions. Both the average current and the diffusion
coefficient are found to be complicated non-monotonic functions of the driving
force. The influence of dimer equilibrium length, coupling strength and damping
constant on the dimer transport properties are also examined in detail.
|
0708.2858v2
|
2007-09-13
|
Spin polarization in biased Rashba-Dresselhaus two-dimensional electron systems
|
Based on spin-charge coupled drift-diffusion equations, which are derived
from kinetic equations for the spin-density matrix in a rigorous manner, the
electric-field-induced nonequilibrium spin polarization is treated for a
two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit
coupling. Most emphasis is put on the consideration of the field-mediated spin
dynamics for a model with equal Rashba and Dresselhaus coupling constants, in
which the spin relaxation is strongly suppressed. Weakly damped
electric-field-induced spin excitations are identified, which remind of
space-charge waves in crystals.
|
0709.2054v1
|
2007-12-31
|
Quantum mechanics of the closed collapsing Universe
|
Two approaches to quantization of Freedman's closed Universe are compared. In
the first approach, the Shrodinger's norm of the wave function of Universe is
used, and in the second approach, the Klein-Gordon's norm is used. The second
one allows building the quasi-Heisenberg operators as functions of time and
finding their average values. It is shown that the average value of the
Universe scale factor oscillates with damping and approaches to some constant
value at the end of the Universe evolution.
|
0801.0212v1
|
2008-04-08
|
Quantum Cosmology and Tachyons
|
We discuss the relevance of the classical and quantum rolling tachyons
inflation in the frame of the standard, p-adic and adelic minisuperspace
quantum cosmology. The field theory of tachyon matter proposed by Sen in a
zero-dimensional version suggested by Kar leads to a model of a particle moving
in a constant external field with quadratic damping. We calculate the exact
quantum propagator of the model, as well as, the vacuum states and conditions
necessary to construct an adelic generalization.
|
0804.1328v1
|
2008-04-24
|
Confined gravitational waves for chiral matter with heat
|
The GR wave self-heating of geodesic massive bodies with constant
thermo-gravimechanical energies increases the brightness-to-charge ratio along
spiral radial transitions in the energy-to-energy gravitation. Paired confined
gravitons locally warm accelerated matter that suggests the thermodynamical
origin of electromagnetic outbursts with oscillating Wien's displacements.
Damping of orbital periods by chiral GR waves is more efficient for neutron
stars around giant companions than for binary pulsars.
|
0804.3820v3
|
2008-05-08
|
Dislocations in cubic crystals described by discrete models
|
Discrete models of dislocations in cubic crystal lattices having one or two
atoms per unit cell are proposed. These models have the standard linear
anisotropic elasticity as their continuum limit and their main ingredients are
the elastic stiffness constants of the material and a dimensionless periodic
function that restores the translation invariance of the crystal and influences
the dislocation size. For these models, conservative and damped equations of
motion are proposed. In the latter case, the entropy production and
thermodynamic forces are calculated and fluctuation terms obeying the
fluctuation-dissipation theorem are added. Numerical simulations illustrate
static perfect screw and 60$^\circ$ dislocations for GaAs and Si.
|
0805.1221v1
|
2008-07-21
|
The Analysis of Rotated Vector Field for the Pendulum
|
The pendulum, in the presence of linear dissipation and a constant torque, is
a non-integrable, nonlinear differential equation. In this paper, using the
idea of rotated vector fields, derives the relation between the applied force
$\beta$ and the periodic solution, and a conclusion that the critical value of
$\beta$ is a fixed one in the over damping situation. These results are of
practical significance in the study of charge-density waves in physics.
|
0807.3288v2
|
2008-08-01
|
Electric-field driven long-lived spin excitations on a cylindrical surface with spin-orbit interaction
|
Based on quantum-kinetic equations, coupled spin-charge drift-diffusion
equations are derived for a two-dimensional electron gas on a cylindrical
surface. Besides the Rashba and Dresselhaus spin-orbit interaction, the elastic
scattering on impurities, and a constant electric field are taken into account.
From the solution of the drift-diffusion equations, a long-lived spin
excitation is identified for spins coupled to the Rashba term on a cylinder
with a given radius. The electric-field driven weakly damped spin waves are
manifest in the components of the magnetization and have the potential for
non-ballistic spin-device applications.
|
0808.0069v1
|
2009-09-22
|
Ferroelectric Soft Mode in Pb(Mg1/3Nb2/3)O3
|
Ferroelectric soft mode in Pb(Mg1/3Nb2/3)O3 (PMN) has been clearly resolved
by precision Raman scattering measurements for the first time. A polarization
direction of the incident laser was chosen along [110] in cubic configuration
in order to eliminate strong scattering components around 45 cm-1, which always
smeared the low-frequency spectra of PMN. The soft mode frequency omega_s
(=\sqrt{omega_0^2-gamma^2}) softens around 200 K, where omega_0 and gamma are a
harmonic frequency and a damping constant, respectively. The present result
evidenced that the origin of the polarizationthe in PMN is the soft mode.
|
0909.3889v1
|
2010-07-20
|
Nonlinear current response of an isolated system of interacting fermions
|
Nonlinear real-time response of interacting particles is studied on the
example of a one-dimensional tight-binding model of spinless fermions driven by
electric field. Using equations of motion and numerical methods we show that
for a non-integrable case at finite temperatures the major effect of
nonlinearity can be taken into account within the linear response formalism
extended by a renormalization of the kinetic energy due to the Joule heating.
On the other hand, integrable systems show on constant driving a different
universality with a damped oscillating current whereby the frequency is related
but not equal to the Bloch oscillations.
|
1007.3383v1
|
2010-11-12
|
Non-archimedean quantum cosmology and tachyonic inflation
|
We review the relevance of quantum rolling tachyons and corresponding
inflation scenario in the frame of the standard, $p$-adic and adelic
minisuperspace quantum cosmology. The field theory of tachyon matter proposed
by Sen in a zero-dimensional version suggested by Kar leads to a model of a
particle moving in a constant external field with quadratic damping. We
calculate the exact quantum propagator of the model, as well as, the vacuum
states and conditions necessary to construct an adelic generalization. In
addition we present an overview on several important cosmological models on
archimedean and nonarchimedean spaces.
|
1011.2885v1
|
2011-04-15
|
Lagrangian approach and dissipative magnetic systems
|
A Lagrangian is introduced which includes the coupling between magnetic
moments $\mathbf{m}$ and the degrees of freedom $\boldsymbol{\sigma}$ of a
reservoir. In case the system-reservoir coupling breaks the time reversal
symmetry the magnetic moments perform a damped precession around an effective
field which is self-organized by the mutual interaction of the moments. The
resulting evolution equation has the form of the Landau-Lifshitz-Gilbert
equation. In case the bath variables are constant vector fields the moments
$\mathbf{m}$ fulfill the reversible Landau-Lifshitz equation. Applying
Noether's theorem we find conserved quantities under rotation in space and
within the configuration space of the moments.
|
1104.3002v1
|
2011-07-04
|
Minimization of the Switching Time of a Synthetic Free Layer in Thermally Assisted Spin Torque Switching
|
We theoretically studied the thermally assisted spin torque switching of a
synthetic free layer and showed that the switching time is minimized if the
condition H_J=|H_s|/(2 alpha) is satisfied, where H_J, H_s and alpha are the
coupling field of two ferromagnetic layers, the amplitude of the spin torque,
and the Gilbert damping constant. We also showed that the coupling field of the
synthetic free layer can be determined from the resonance frequencies of the
spin-torque diode effect.
|
1107.0753v2
|
2012-07-08
|
Non-monotonic behaviour of the superconducting order parameter in Nb/PdNi bilayers observed through point contact spectroscopy
|
Point contact spectroscopy measurements have been performed on Nb/PdNi
bilayers in which the thickness of the Nb layer, dNb, was kept constant to 40
nm while the thickness of PdNi, dPdNi, was changed from 2 nm to 9 nm. Features
related to the superconducting gap induced in the ferromagnet have been
observed in the dV/dI versus V curves. These structures show a non-monotonic
behaviour as a function of dPdNi as a consequence of the damped oscillatory
behaviour of the superconducting order parameter in the ferromagnetic layer.
|
1207.1879v1
|
2012-10-31
|
Well-posedness of a Parabolic-hyperbolic Keller-Segel System in the Sobolev Space Framework
|
We study the global strong solutions to a 3-dimensional parabolic-hyperbolic
Keller-Segel model with initial data close to a stable equilibrium with
perturbations belonging to $L^2(\mathbb R^3)\times H^1(\mathbb{R}^3)$. We
obtain global well-posedness and decay property. Furthermore, if the mean value
of initial cell density is smaller than a suitabale constant, then the chemical
concentration decays exponentially to zero as $t$ goes to infinity. Proofs of
the main results are based on an application of Fourier analysis method to
uniform estimates for a linearized parabolic-hyperbolic system and also based
on the smoothing effect of the cell density as well as the damping effect of
the chemical concentration.
|
1210.8214v1
|
2013-02-26
|
Modelling Fast-Alfvén Mode Conversion Using SPARC
|
We successfully utilise the SPARC code to model fast-Alfv\'en mode conversion
in the region $c_A \gg c_S$ via 3-D MHD numerical simulations of helioseismic
waves within constant inclined magnetic field configurations. This was achieved
only after empirically modifying the background density and gravitational
stratifications in the upper layers of our computational box, as opposed to
imposing a traditional Lorentz Force limiter, to ensure a manageable timestep.
We found that the latter approach inhibits the fast-Alfv\'en mode conversion
process by severely damping the magnetic flux above the surface.
|
1302.6301v1
|
2013-03-12
|
Thermally excited spin waves in a nano-structure: thermal gradient vs. constant temperature
|
Using micromagnetic simulations, we have investigated spin dynamics in a
nanostructure in the presence of thermal fluctuations. In particular, we have
studied the effects of a uniform temperature and of a uniform thermal gradient.
In both cases, the stochastic field leads to an increase of the precession
angle of the magnetization, and to a mild decreas of the linewidth of the
resonance peaks. Our results indicate that the Gilbert damping parameter plays
the role of control parameter for the amplification of spin waves.
|
1303.2895v1
|
2013-06-29
|
Perpendicular magnetization of Co20Fe50Ge30 films induced by MgO interface
|
Epitaxial growth of Co20Fe50Ge30 thin film on single crystal MgO (001)
substrate is reported. Structure characterization revealed (001)-oriented B2
order of CoFeGe well lattice matched with the MgO barrier. Perpendicular
magnetic anisotropy (PMA) was achieved in the MgO/CoFeGe/MgO structure with an
optimized magnetic anisotropy energy density (K) of 3 106 erg/cm3. The magnetic
anisotropy is found to depend strongly on the thickness of the MgO and CoFeGe
layers, indicating that the PMA of CoFeGe is contributed by the interfacial
anisotropy between CoFeGe and MgO. With reported low damping constant, CoFeGe
films are promising spintronic materials for achieving low switching current.
|
1307.0104v1
|
2013-08-16
|
Luminosity Upgrades for ILC
|
The possibility of increasing the luminosity for the ILC at Ecm < 350 GeV
centre-of-mass by increasing the beam power are considered. It will be shown
that an approximately constant luminosity can be achieved across the centre of
mass energy range (250-500 GeV) without exceeding the installed AC power for
500 GeV operation. Overall a factor of four in luminosity over the published
baseline could be achieved at 250 GeV resulting in 3*10**34 cm-2s-1. The
implications for the damping rings and positron source are also briefly
discussed.
|
1308.3726v1
|
2014-09-01
|
The co-existence of states in p53 dynamics driven by miRNA
|
The regulating mechanism of miRNA on p53 dynamics in p53-MDM2-miRNA model
network incorporating reactive oxygen species (ROS) is studied. The study shows
that miRNA drives p53 dynamics at various states, namely, stabilized states and
oscillating states (damped and sustain oscillation). We found the co-existence
of these states within certain range of the concentartion level of miRNA in the
system. This co-existence in p53 dynamics is the signature of the system's
survival at various states, normal, activated and apoptosis driven by a
constant concentration of miRNA.
|
1409.1943v1
|
2014-12-04
|
The fluctuation-dissipation relation in a resonantly driven quantum medium
|
We calculate the radiation noise level associated with the spontaneous
emission of a coherently driven medium. The significant field-induced
modification of relation between the noise power and damping constant in a
thermal reservoir is obtained. The nonlinear noise exchange between different
atomic frequencies leads to violation of standard relations dictated by the
fluctuation-dissipation theorem.
|
1412.1646v3
|
2015-01-15
|
Anomaly of the Internal Friction in the Helium Crystals Grown in the Burst-like Growth Mode
|
The internal friction in the crystals grown in two modes, namely, slow and
anomalously fast (burst-like growth) modes, is measured in the temperature
range 0.49-0.75K at a frequency of about 75kHz. An additional contribution to
the damping decrement and softening of the dynamic modulus are detected, and
their relaxation to equilibrium values at a time constant of about 3ms is
observed. Possible origins of this effect are discussed.
|
1501.03739v1
|
2015-04-02
|
Phase transition in p53 states induced by glucose
|
We present p53-MDM2-Glucose model to study spatio-temporal properties of the
system induced by glucose. The variation in glucose concentration level
triggers the system at different states, namely, oscillation death
(stabilized), sustain and damped oscillations which correspond to various
cellular states. The transition of these states induced by glucose is phase
transition like behaviour. We also found that the intrinsic noise in stochastic
system helps the system to stabilize more effectively. Further, the amplitude
of $p53$ dynamics with the variation of glucose concentration level follows
power law behaviour, $A_s(k)\sim k^\gamma$, where, $\gamma$ is a constant.
|
1504.00431v1
|
2015-06-23
|
The remarkable effectiveness of time-dependent damping terms for second order evolution equations
|
We consider a second order linear evolution equation with a dissipative term
multiplied by a time-dependent coefficient. Our aim is to design the
coefficient in such a way that all solutions decay in time as fast as possible.
We discover that constant coefficients do not achieve the goal, as well as
time-dependent coefficients that are too big. On the contrary, pulsating
coefficients which alternate big and small values in a suitable way prove to be
more effective.
Our theory applies to ordinary differential equations, systems of ordinary
differential equations, and partial differential equations of hyperbolic type.
|
1506.06915v1
|
2015-07-02
|
Global solutions for a supercritical drift-diffusion equation
|
We study the global existence of solutions to a one-dimensional
drift-diffusion equation with logistic term, generalizing the classical
parabolic-elliptic Keller-Segel aggregation equation arising in mathematical
biology. In particular, we prove that there exists a global weak solution, if
the order of the fractional diffusion $\alpha \in (1-c_1, 2]$, where $c_1>0$ is
an explicit constant depending on the physical parameters present in the
problem (chemosensitivity and strength of logistic damping). Furthermore, in
the range $1-c_2<\alpha\leq 2$ with $0<c_2<c_1$, the solution is globally
smooth. Let us emphasize that when $\alpha<1$, the diffusion is in the
supercritical regime.
|
1507.00694v2
|
2015-07-24
|
Boosting Domain Wall Propagation by Notches
|
We report a counter-intuitive finding that notches in an otherwise
homogeneous magnetic nanowire can boost current-induced domain wall (DW)
propagation. DW motion in notch-modulated wires can be classified into three
phases: 1) A DW is pinned around a notch when the current density is below the
depinning current density. 2) DW propagation velocity is boosted by notches
above the depinning current density and when non-adiabatic spin-transfer torque
strength $\beta$ is smaller than the Gilbert damping constant $\alpha$. The
boost can be manyfold. 3) DW propagation velocity is hindered when $\beta >
\alpha$. The results are explained by using the Thiele equation.
|
1507.06748v1
|
2015-10-26
|
Variational Limits for Phase Precision in Linear Quantum Optical Metrology
|
We apply the variational method to obtain the universal and analytical lower
bounds for parameter precision in some noisy systems. We first derive a lower
bound for phase precision in lossy optical interferometry at non-zero
temperature. Then we consider the effect of both amplitude damping and phase
diffusion on phase-shift precision. At last, we extend the constant phase
estimation to the case of continuous fluctuating phase estimation, and find
that due to photon losses the corresponding mean square error transits from the
stochastic Heisenberg limit to the stochastic standard quantum limit as the
total photon flux increases.
|
1510.07381v1
|
2016-02-26
|
Correspondence between phasor transforms and frequency response function in RLC circuits
|
The analysis of RLC circuits is usually made by considering phasor transforms
of sinusoidal signals (characterized by constant amplitude, period and phase)
that allow the calculation of the AC steady state of RLC circuits by solving
simple algebraic equations. In this paper I try to show that phasor
representation of RLC circuits is analogue to consider the frequency response
function (commonly designated by FRF) of the total impedance of the circuit. In
this way I derive accurate expressions for the resonance and anti-resonance
frequencies and their corresponding values of impedances of the parallel and
series RLC circuits respectively, notwithstanding the presence of damping
effects.
|
1602.08487v1
|
2016-03-03
|
Inspiral into Gargantua
|
We model the inspiral of a compact object into a more massive black hole
rotating very near the theoretical maximum. We find that once the body enters
the near-horizon regime the gravitational radiation is characterized by a
constant frequency, equal to (twice) the horizon frequency, with an
exponentially damped profile. This contrasts with the usual "chirping" behavior
and, if detected, would constitute a "smoking gun" for a near-extremal black
hole in nature.
|
1603.01221v2
|
2016-05-02
|
Undamped relativistic magnetoplasmons in lossy two-dimensional electron systems
|
We address electrodynamic effects in plasma oscillations of a lossy 2D
electron system whose dc 2D conductivity is comparable to the speed of light.
We argue that the perpendicular constant magnetic field B causes astonishing
features of magnetoplasma dynamics. We show that plasmon-polariton spectra can
be classified using a 'relativistic' phase diagram 2D conductivity divided by
the speed of light versus B. An extraordinarily low damping branch in
magnetoplasmon-polariton spectra emerges at two phases of this diagram. Some
magnetoplasmons at these phases are predicted to be undamped waves.
|
1605.00430v2
|
2016-08-21
|
Spin correlation functions and quasiparticle decay
|
We study one-dimensional anisotropic XXZ spin-$\frac12$ model with
ferromagnetic sign of the coupling and $z-z$ exchange constant $J_z = \Delta
J$, where $\Delta < 1$, and $J$ is the coupling within XY spin plane. We
calculate damping of low-energy excitations with $\omega \ll T $ due to their
scattering from thermal excitation bath with temperature $T \ll J$, taking into
account nonzero curvature of the excitation spectrum, $\epsilon(q) = u q +
\delta\epsilon(q)$. We calculate also longitudinal spin-spin correlation
function $\langle S^z(x,t)S^z(0,0) \rangle$ at $x \approx ut$ and find the
shape of the spreading "wave packet".
|
1608.05937v1
|
2016-09-01
|
Asymptotic for the perturbed heavy ball system with vanishing damping term
|
We investigate the long time behavior of solutions to the differential
equation $\ddot{x}(t)+\frac{c}{\left( t+1\right) ^{\alpha}}\dot{x}(t)+\nabla
\Phi\left( x(t)\right) =g(t),~t\geq0, $ where $c$ is nonnegative constant,
$\alpha\in\lbrack0,1[,$ $\Phi$ is a $C^{1}$ convex function on a Hilbert space
$\mathcal{H}$ and $g\in L^{1} (0,+\infty;\mathcal{H}).$ We obtain sufficient
conditions on the source term $g(t)$ ensuring the weak or the strong
convergence of any trajectory $x(t)$ as $t\rightarrow+\infty$ to a minimizer of
the function $\Phi$ if one exists.
|
1609.00135v2
|
2016-09-19
|
An entropic gradient structure for Lindblad equations and couplings of quantum systems to macroscopic models
|
We show that all Lindblad operators (i.e. generators of quantum semigroups)
on a finite-dimensional Hilbert space satisfying the detailed balance condition
with respect to the thermal equilibrium state can be written as a gradient
system with respect to the relative entropy.
We discuss also thermodynamically consistent couplings to macroscopic
systems, either as damped Hamiltonian systems with constant temperature or as
GENERIC systems. In particular we discuss the coupling of a quantum dot coupled
to macroscopic charge carriers.
|
1609.05765v3
|
2016-10-25
|
Quasi-flat plasmonic bands in twisted bilayer graphene
|
The charge susceptibility of twisted bilayer graphene is investigated in the
Dirac cone, respectively random-phase approximation. For small enough twist
angles $\theta\lesssim 2^\circ$ we find weakly Landau damped interband
plasmons, i.~e., collective excitonic modes which exist in the undoped
material, with an almost constant energy dispersion. In this regime, the loss
function can be described as a Fano resonance and we argue that these
excitations arise from the interaction of quasi-localised states with the
incident light field. These predictions can be tested by nano-infrared imaging
and possible applications include a "perfect" lens without the need of
left-handed materials.
|
1610.07757v1
|
2016-12-31
|
Dynamics of a spin-boson model with structured spectral density
|
We report the results of a study of the dynamics of a two-state system
coupled to an environment with peaked spectral density. An exact analytical
expression for the bath correlation function is obtained. Validity range of
various approximations to the correlation function for calculating the
population difference of the system are discussed as function of tunneling
splitting, oscillator frequency, coupling constant, damping rate and the
temperature of the bath. An exact expression for the population difference for
a limited range of parameters, is derived.
|
1701.00122v1
|
2018-12-18
|
Automation of the Cavendish Experiment to 'Weigh the Earth'
|
We describe a simple and inexpensive method for automating the data
collection in the well-known Cavendish torsion balance experiment to determine
the gravitational constant $G$. The method uses a linear array of
phototransistors and requires no moving parts. Multiplexers and a
data-acquisition device are used to sample the state of each phototransistor
sequentially. If the sampled phototransistor is illuminated by the laser spot,
the position and time are recorded to a data file. The recorded data does an
excellent job of capturing the damped harmonic oscillations. The resulting data
were analysed to extract an experimental value of $G$ that was within 5% of the
accepted value.
|
1812.07644v1
|
2019-07-16
|
Theory of Skyrmionic Diffusion: Hidden Diffusion Coeffcients and Breathing Diffusion
|
Time evolution of the position-velocity correlation functions (PVCF) plays a
key role in a new formalism of Brownian motion. A system of differential
equations, which governs PVCF, is derived for magnetic Skyrmions on a
2-dimensional magnetic thin film with thermal agitation. In the formalism, a
new type of diffusion coeffcient is introduced which does not come out in the
usual diffusion equations. The mean-square displacement (MSD) is obtained from
the PVCF and found that it oscillates in time when the damping constant is
small. It is also shown, even for a structureless particle, that the famous
Ornstein-Fuerth formula should be corrected taking a proper initial value of
PVCF into account.
|
1907.06926v1
|
2019-09-11
|
A fully space-time least-squares method for the unsteady Navier-Stokes system
|
We introduce and analyze a space-time least-squares method associated to the
unsteady Navier-Stokes system. Weak solution in the two dimensional case and
regular solution in the three dimensional case are considered. From any initial
guess, we construct a minimizing sequence for the least-squares functional
which converges strongly to a solution of the Navier-Stokes system. After a
finite number of iterates related to the value of the viscosity constant, the
convergence is quadratic. Numerical experiments within the two dimensional case
support our analysis. This globally convergent least-squares approach is
related to the damped Newton method when used to solve the Navier-Stokes system
through a variational formulation.
|
1909.05034v1
|
2020-01-17
|
Fermi Level Controlled Ultrafast Demagnetization Mechanism in Half-Metallic Heusler Alloy
|
The electronic band structure-controlled ultrafast demagnetization mechanism
in Co2FexMn1-xSi Heusler alloy is underpinned by systematic variation of
composition. We find the spin-flip scattering rate controlled by spin density
of states at Fermi level is responsible for non-monotonic variation of
ultrafast demagnetization time ({\tau}M) with x with a maximum at x = 0.4.
Furthermore, Gilbert damping constant exhibits an inverse relationship with
{\tau}M due to the dominance of inter-band scattering mechanism. This
establishes a unified mechanism of ultrafast spin dynamics based on Fermi level
position.
|
2001.06217v1
|
2020-05-23
|
Stability analysis of multi-term fractional-differential equations with three fractional derivatives
|
Necessary and sufficient stability and instability conditions are obtained
for multi-term homogeneous linear fractional differential equations with three
Caputo derivatives and constant coefficients. In both cases,
fractional-order-dependent as well as fractional-order-independent
characterisations of stability and instability properties are obtained, in
terms of the coefficients of the multi-term fractional differential equation.
The theoretical results are exemplified for the particular cases of the Basset
and Bagley-Torvik equations, as well as for a multi-term fractional
differential equation of an inextensible pendulum with fractional damping
terms, and for a fractional harmonic oscillator.
|
2005.11486v1
|
2021-01-28
|
Voltage Controlled Spin-Orbit Torque Switching in W/CoFeB/MgO
|
Voltage control of magnetism and spintronics have been highly desirable, but
rarely realized. In this work, we show voltage-controlled spin-orbit torque
(SOT) switching in W/CoFeB/MgO films with perpendicular magnetic anisotropy
(PMA) with voltage administered through SrTiO3 with a high dielectric constant.
We show that a DC voltage can significantly lower PMA by 45%, reduce switching
current by 23%, and increase the damping-like torque as revealed by the first
and second-harmonic measurements. These are characteristics that are
prerequisites for voltage-controlled and voltage-select SOT switching
spintronic devices.
|
2101.12281v1
|
2021-03-14
|
A note on damped wave equations with a nonlinear dissipation in non-cylindrical domains
|
In this paper, we study the large time behavior of a class of wave equation
with a nonlinear dissipation in non-cylindrical domains. The result we obtained
here relaxes the conditions for the nonlinear term coefficients (in precise,
that is $\beta(t)|u|^\rho u$) in \cite{alb} and \cite{ha} (which require
$\beta(t)$ to be a constant or $\beta(t)$ to be decreasing with time $t$) and
has less restriction for the defined regions.
|
2103.09678v2
|
2021-05-07
|
Optomechanical amplification driven by interference of phonon-exciton and phonon-photon couplings
|
We study theoretically optomechanical damping and amplification spectra for
vibrations interacting with excitonic polaritons in a zero-dimensional
microcavity. We demonstrate, that the spectra strongly depend on the ratio of
the exciton-phonon and the photon-phonon coupling constants. The interference
between these couplings enables a situation when optomechanical gain exists
either only for a lower polaritonic resonance or only for an upper polaritonic
resonance. Our results provide insight in the optomechanical interactions in
various multi-mode systems, where several resonant oscillators, such as
photons, plasmons, or excitons are coupled to the same vibration mode.
|
2105.03214v1
|
2022-04-17
|
Optimizing Brownian heat engine with shortcut strategy
|
Shortcuts to isothermality provide a powerful method to speed up quasistatic
thermodynamic processes within finite-time manipulation. We employ the shortcut
strategy to design and optimize Brownian heat engines, and formulate a
geometric description of the energetics with the thermodynamic length. We
obtain a tight and reachable bound of the output power, which is reached by the
optimal protocol to vary the control parameters with a proper constant velocity
of the thermodynamic length. Our results generalize the previous optimization
in the highly underdamped and the overdamped regimes to the general-damped
situation, and are applicable for arbitrary finite-time cycles.
|
2204.08015v2
|
2022-11-17
|
Elucidating the thermal spike effect by using a coupled classical oscillator model
|
Atomic heating is a fundamental phenomenon governed by the thermal spike
effect during energetic deposition. This work presented another insight into
thermal spike using a coupled classical oscillator model instead of a typical
heat diffusion model. The temperature profile of deposited atoms was replaced
by oscillator amplitude as an energy descriptor. Solving associated partial
differential equations (PDEs)suggests the efficiency of energy transfer from
the coupled hot to cold oscillators essentially relies on the atomic distance r
and the spring constant k. The solution towards the damped wave equation
further emphasize that a localized thermal fluctuation during energy
propagation.
|
2211.09357v1
|
2023-03-27
|
Nonlinear inviscid damping for 2-D inhomogeneous incompressible Euler equations
|
We prove the asymptotic stability of shear flows close to the Couette flow
for the 2-D inhomogeneous incompressible Euler equations on $\mathbb{T}\times
\mathbb{R}$. More precisely, if the initial velocity is close to the Couette
flow and the initial density is close to a positive constant in the Gevrey
class 2, then 2-D inhomogeneous incompressible Euler equations are globally
well-posed and the velocity converges strongly to a shear flow close to the
Couette flow, and the vorticity will be driven to small scales by a linear
evolution and weakly converges as $t\to \infty$. To our knowledge, this is the
first global well-posedness result for the 2-D inhomogeneous incompressible
Euler equations.
|
2303.14858v1
|
2023-08-05
|
Dynamics of Skyrmion Contraction and Expansion in a Magnetic Film
|
Contraction and expansion of skyrmions in ferromagnetic films are
investigated. In centrosymmetric systems, the dynamics of a collapsing skyrmion
is driven by dissipation. The collapse time has a minimum on the damping
constant. In systems with broken inversion symmetry, the evolution of skyrmions
toward equilibrium size is driven by the Dzyaloshinskii-Moriya interaction.
Expressions describing the time dependence of the skyrmion size are derived and
their implications for skyrmion-based information processing are discussed.
|
2308.02826v1
|
2024-01-15
|
Two-Dimensional Electronic Spectroscopy for Three-Level Atoms with Electromagnetically Induced Transparency
|
Two-dimensional electronic spectroscopy (2DES) has high spectral resolution
and is a useful tool for studying atom dynamics. In this paper, we apply the
electromagnetically induced transparency (EIT) technique to 2DES in a
three-level atom, and find out that the number of peaks (troughs) will become
more due to the introduction of EIT. Also, the height of the peaks (the depth
of troughs) will change from constant to a damped oscillation. These findings
may help us obtain more information about the dynamics of excited states.
|
2401.07424v1
|
2022-02-08
|
Evolution of energy, momentum, and spin parameter in dark matter flow and integral constants of motion
|
N-body equations of motion in comoving system and expanding background are
reformulated in a transformed system with static background and fixed damping.
The energy and momentum evolution in dark matter flow are rigorously formulated
for both systems. The energy evolution in transformed system has a simple form
that is identical to the damped harmonic oscillator. The cosmic energy equation
can be easily derived in both systems. For entire N-body system, 1) combined
with the two-body collapse model (TBCM), kinetic and potential energy increase
linearly with time $t$ such that $K_p=\varepsilon_ut$ and
$P_y=-7\varepsilon_ut/5$, where $\varepsilon_u$ is a constant rate of energy
cascade; 2) an effective gravitational potential exponent $n_e=-10/7\ne-1$
($n_e=-1.38$ from simulation) can be identified due to surface energy of fast
growing halos; 3) the radial momentum $G\propto a^{3/2}$ and angular momentum
$H\propto a^{5/2}$, where $a$ is the scale factor. On halo scale, 1) halo
kinetic and potential energy can be modelled by two dimensionless constants
$\alpha_s^*$ and $\beta_s^*$. Both constants are independent of time and halo
mass; 2) both halo radial and angular momentum $\propto a^{3/2}$ and can be
modeled by two mass-dependent coefficients $\tau_s^*$ and $\eta_s^*$; 3) halo
spin parameter is determined by $\alpha_s^*$ and $\eta_s^*$ and decreases with
halo mass with derived values of 0.09 and 0.031 for small and large halos.
Finally, the radial and angular momentum are closely related to the integral
constants of motion $I_m$, i.e. the integral of velocity correlation or the
$m$th derivative of energy spectrum at long wavelength limit. On large scale,
angular momentum is negligible, $I_2$=0 reflects the conservation of linear
momentum, while $I_4$ reflects the fluctuation of radial momentum $G$. On halo
scale, $I_4$ is determined by both momentum that are comparable with each
other.
|
2202.04054v2
|
1997-03-11
|
Constraints on Galaxy Evolution and the Cosmological Constant From Damped Ly-alpha Absorbers
|
We use the existing catalog of Damped Lyman-Alpha (DLA) systems to place
constraints on the amount of evolution in the baryonic content of galaxies and
on the value of the cosmological constant. The density of cold gas at redshifts
z=3+-1 is obtained from the mean HI column density of DLAs per cosmological
path length. This path length per unit redshift is in turn a sensitive function
of the vacuum density parameter, Omega_v. We compare the total inferred mass of
cold gas at high redshifts to that observed in stars today for flat
cosmologies. We define "eta" to be net fraction of the baryonic content of
local galaxies which was expelled since z=3, and use Bayesian inference to
derive confidence regions in the (eta, Omega_v) plane. In all cosmologies we
find that eta<0.4 with at least 95% confidence if <25% of the current stellar
population formed before z=3. The most likely value of eta is negative,
implying a net increase by several tens of percent in the baryonic mass of
galaxies since z=3+-1. On the other hand, recent observations of high metal
abundances in the intracluster medium of rich clusters (Loewenstein & Mushotzky
1996) require that metal-rich gas be expelled from galaxies in an amount
approximately equal to the current mass in stars. Based on our results and the
low metallicity observed in DLAs at z>2, we infer that more than half of the
baryonic mass processed through galaxies must have been assembled and partly
expelled from galaxies after z=2. We expect our constraints to improve
considerably as the size of the DLA sample will increase with the forthcoming
Sloan Digital Sky Survey.
|
9703076v1
|
1998-04-18
|
Accretion in the Early Kuiper Belt I. Coagulation and Velocity Evolution
|
We describe planetesimal accretion calculations in the Kuiper Belt.
Our evolution code simulates planetesimal growth in a single annulus and
includes velocity evolution but not fragmentation. Test results match analytic
solutions and duplicate previous simulations at 1 AU.
In the Kuiper Belt, simulations without velocity evolution produce a single
runaway body with a radius of 1000 km on a time scale inversely proportional to
the initial mass in the annulus. Runaway growth occurs in 100 Myr for 10 earth
masses and an initial eccentricity of 0.001 in a 6 AU annulus centered at 35
AU. This mass is close to the amount of dusty material expected in a minimum
mass solar nebula extrapolated into the Kuiper Belt.
Simulations with velocity evolution produce runaway growth on a wide range of
time scales. Dynamical friction and viscous stirring increase particle
velocities in models with large (8 km radius) initial bodies. This velocity
increase delays runaway growth by a factor of two compared to models without
velocity evolution. In contrast, collisional damping dominates over dynamical
friction and viscous stirring in models with small (80--800 m radius) initial
bodies. Collisional damping decreases the time scale to runaway growth by
factors of 4--10 relative to constant velocity calculations. Simulations with
minimum mass solar nebulae, 10 earth masses, reach runaway growth on time
scales of 20-40 Myr with 80 m initial bodies, 50-100 Myr with 800 m bodies, and
75-250 Myr for 8 km initial bodies. These growth times vary linearly with the
mass of the annulus but are less sensitive to the initial eccentricity than
constant velocity models.
|
9804185v1
|
1998-04-28
|
Gravity-Modes in ZZ Ceti Stars: I.Quasiadiabatic Analysis of Overstability
|
We analyze the stability of g-modes in variable white dwarfs with hydrogen
envelopes. In these stars, the radiative layer contributes to mode damping
because its opacity decreases upon compression and the amplitude of the
Lagrangian pressure perturbation increases outward. The overlying convective
envelope is the seat of mode excitation because it acts as an insulating
blanket with respect to the perturbed flux that enters it from below. A crucial
point is that the convective motions respond to the instantaneous pulsational
state. Driving exceeds damping by as much as a factor of two provided
$\omega\tau_c\geq 1$, where $\omega$ is the radian frequency of the mode and
$\tau_c\approx 4\tau_{th}$ with $\tau_{th}$ being the thermal time constant
evaluated at the base of the convective envelope. As a white dwarf cools, its
convection zone deepens, and modes of lower frequency become overstable.
However, the deeper convection zone impedes the passage of flux perturbations
from the base of the convection zone to the photosphere. Thus the photometric
variation of a mode with constant velocity amplitude decreases. These factors
account for the observed trend that longer period modes are found in cooler
DAVs. The linear growth time, ranging from hours for the longest period
observed modes ($P\approx 20$ minutes) to thousands of years for those of
shortest period ($P\approx 2 $ minutes), probably sets the time-scale for
variations of mode amplitude and phase. This is consistent with observations
showing that longer period modes are more variable than shorter period ones.
Our investigation confirms many results obtained by Brickhill in his pioneering
studies of ZZ Cetis.
|
9804305v1
|
2004-12-21
|
Cosmochemistry, Cosmology and Fundamental Constants: High-Resolution Spectroscopy of Damped Lyman-Alpha Systems
|
Spectroscopy of QSO absorption lines provides essential observational input
for the study of nucleosynthesis and chemical evolution of galaxies at high
redshift. But new observations may indicate that present chemical abundance
data are biased due to deficient spectral resolution and unknown selection
effects: Recent high-resolution spectra reveal the hitherto unperceived
chemical nonuniformity of a molecule-bearing damped Lyman-alpha (DLA) system,
and the still ongoing H/ESO DLA survey produces convincing evidence for the
effect of dust attenuation. We present a revised analysis of the moleculecular
hydrogen-bearing DLA complex toward the QSO HE 0515-4414 showing nonuniform
differential depletion of chemical elements onto dust grains, and introduce the
H/ESO DLA survey and its implications. Conclusively, we aim at starting an
unbiased chemical abundance database established on high-resolution
spectroscopic observations. New data to probe the temperature-redshift relation
predicted by standard cosmology and to test the constancy of fundamental
constants will be potential spin-offs.
|
0412552v4
|
2014-02-15
|
Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt
|
We report on an experimental study on the spin-waves relaxation rate in two
series of nanodisks of diameter $\phi=$300, 500 and 700~nm, patterned out of
two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser
deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance
force microscope, we measure precisely the ferromagnetic resonance linewidth of
each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth
in the nanostructure is sensibly smaller than the one measured in the extended
film. Analysis of the frequency dependence of the spectral linewidth indicates
that the improvement is principally due to the suppression of the inhomogeneous
part of the broadening due to geometrical confinement, suggesting that only the
homogeneous broadening contributes to the linewidth of the nanostructure. For
the bare YIG nano-disks, the broadening is associated to a damping constant
$\alpha = 4 \cdot 10^{-4}$. A 3 fold increase of the linewidth is observed for
the series with Pt cap layer, attributed to the spin pumping effect. The
measured enhancement allows to extract the spin mixing conductance found to be
$G_{\uparrow \downarrow}= 1.55 \cdot 10^{14}~ \Omega^{-1}\text{m}^{-2}$ for our
YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the
design of YIG based nanostructures with optimized magnetic losses.
|
1402.3630v1
|
2015-12-08
|
Critical exponents for the cloud-crystal phase transition of charged particles in a Paul Trap
|
It is well known that charged particles stored in a Paul trap, one of the
most versatile tools in atomic and molecular physics, may undergo a phase
transition from a disordered cloud state to a geometrically well-ordered
crystalline state (the Wigner crystal). In this paper we show that the average
lifetime $\bar\tau_m$ of the metastable cloud state preceding the cloud
$\rightarrow$ crystal phase transition follows a powerlaw, $\bar\tau_m \sim
(\gamma-\gamma_c)^{-\beta}$, $\gamma>\gamma_c$, where $\gamma_c$ is the
critical value of the damping constant $\gamma$ at which the cloud
$\rightarrow$ crystal phase transition occurs. The critical exponent $\beta$
depends on the trap control parameter $q$, but is independent of the number of
particles $N$ stored in the trap and the trap control parameter $a$, which
determines the shape (oblate, prolate, or spherical) of the cloud. For
$q=0.15,0.20$, and $0.25$, we find $\beta=1.20\pm 0.03$, $\beta=1.61\pm 0.09$,
and $\beta=2.38\pm 0.12$, respectively. In addition we find that for given $a$
and $q$, the critical value $\gamma_c$ of the damping scales approximately like
$\gamma_c=C \ln [ \ln (N)] + D$ as a function of $N$, where $C$ and $D$ are
constants. Beyond their relevance for Wigner crystallization of nonneutral
plasmas in Paul traps and mini storage rings, we conjecture that our results
are also of relevance for the field of crystalline beams.
|
1512.02534v1
|
2016-01-28
|
Automatic calibration of damping layers in finite element time domain simulations
|
Matched layers are commonly used in numerical simulations of wave propagation
to model (semi-)infinite domains. Attenuation functions describe the damping in
layers, and provide a matching of the wave impedance at the interface between
the domain of interest and the absorbing region. Selecting parameters in the
attenuation functions is non-trivial. In this work, an optimisation procedure
for automatically calibrating matched layers is presented. The procedure is
based on solving optimisation problems constrained by partial differential
equations with polynomial and piecewise-constant attenuation functions. We show
experimentally that, for finite element time domain simulations,
piecewise-constant attenuation function are at least as efficient as quadratic
attenuation functions. This observation leads us to introduce consecutive
matched layers as an alternative to perfectly matched layers, which can easily
be employed for problems with arbitrary geometries. Moreover, the use of
consecutive matched layers leads to a reduction in computational cost compared
to perfectly matched layers. Examples are presented for acoustic, elastodynamic
and electromagnetic problems. Numerical simulations are performed with the
libraries FEniCS/DOLFIN and dolfin-adjoint, and the computer code to reproduce
all numerical examples is made freely available.
|
1601.07941v1
|
2017-06-23
|
Characteristics of a magneto-optical trap of molecules
|
We present the properties of a magneto-optical trap (MOT) of CaF molecules.
We study the process of loading the MOT from a decelerated buffer-gas-cooled
beam, and how best to slow this molecular beam in order to capture the most
molecules. We determine how the number of molecules, the photon scattering
rate, the oscillation frequency, damping constant, temperature, cloud size and
lifetime depend on the key parameters of the MOT, especially the intensity and
detuning of the main cooling laser. We compare our results to analytical and
numerical models, to the properties of standard atomic MOTs, and to MOTs of SrF
molecules. We load up to $2 \times 10^4$ molecules, and measure a maximum
scattering rate of $2.5 \times 10^6$ s$^{-1}$ per molecule, a maximum
oscillation frequency of 100 Hz, a maximum damping constant of 500 s$^{-1}$,
and a minimum MOT rms radius of 1.5 mm. A minimum temperature of 730 $\mu$K is
obtained by ramping down the laser intensity to low values. The lifetime,
typically about 100 ms, is consistent with a leak out of the cooling cycle with
a branching ratio of about $6 \times 10^{-6}$. The MOT has a capture velocity
of about 11 m/s.
|
1706.07848v1
|
2018-06-04
|
Environment induced Symmetry Breaking of the Oscillation-Death State
|
We investigate the impact of a common external system, which we call a common
environment, on the Oscillator Death (OD) states of a group of Stuart-Landau
oscillators. The group of oscillators yield a completely symmetric OD state
when uncoupled to the external system, i.e. the two OD states occur with equal
probability. However, remarkably, when coupled to a common external system this
symmetry is significantly broken. For exponentially decaying external systems,
the symmetry breaking is very pronounced for low environmental damping and
strong oscillator-environment coupling. This is evident through the sharp
transition from the symmetric to asymmetric state occurring at a critical
oscillator-environment coupling strength and environmental damping rate.
Further, we consider time-varying connections to the common external
environment, with a fraction of oscillator-environment links switching on and
off. Interestingly, we find that the asymmetry induced by environmental
coupling decreases as a power law with increase in fraction of such on-off
connections. The suggests that blinking oscillator-environment links can
restore the symmetry of the OD state. Lastly, we demonstrate the generality of
our results for a constant external drive, and find marked breaking of symmetry
in the OD states there as well. When the constant environmental drive is large,
the asymmetry in the OD states is very large, and the transition between the
symmetric and asymmetric state with increasing oscillator-environment coupling
is very sharp. So our results demonstrate an environmental coupling-induced
mechanism for the prevalence of certain OD states in a system of oscillators,
and suggests an underlying process for obtaining certain states preferentially
in ensembles of oscillators with environment-mediated coupling.
|
1806.01653v1
|
2020-10-15
|
Spin injection characteristics of Py/graphene/Pt by gigahertz and terahertz magnetization dynamics driven by femtosecond laser pulse
|
Spin transport characteristics of graphene has been extensively studied so
far. The spin transport along c-axis is however reported by rather limited
number of papers. We have studied spin transport characteristics through
graphene along c-axis with permalloy(Py)/graphene(Gr)/Pt by gigahertz (GHz) and
terahertz (THz) magnetization dynamics driven by femtosecond laser pulses. The
relatively simple sample structure does not require electrodes on the sample.
The graphene layer was prepared by chemical vapor deposition and transferred on
Pt film. The quality of graphene layer was characterized by Raman microscopy.
Time resolved magneto-optical Kerr effect is used to characterize gigahertz
magnetization dynamics. Magnetization precession is clearly observed both for
Pt/Py and Pt/Gr/Py. The Gilbert damping constant of Pt/Py was 0.015, indicates
spin pumping effect from Py to Pt. The Gilbert damping constant of Pt/Gr/Py is
found to be 0.011, indicates spin injection is blocked by graphene layer. We
have also performed the measurement of THz emission for Pt/Py and Pt/Gr/Py.
While the THz emission is clearly observed for Pt/Py, a strong reduction of THz
emission is observed for Pt/Gr/Py. With these two different experiments, and
highly anisotropic resistivity of graphite, we conclude that the vertical spin
transport is strongly suppressed by the graphene layer.
|
2010.07694v1
|
2023-05-16
|
Non-Hermitian Casimir Effect of Magnons
|
There has been a growing interest in non-Hermitian quantum mechanics. The key
concepts of quantum mechanics are quantum fluctuations. Quantum fluctuations of
quantum fields confined in a finite-size system induce the zero-point energy
shift. This quantum phenomenon, the Casimir effect, is one of the most striking
phenomena of quantum mechanics in the sense that there are no classical analogs
and has been attracting much attention beyond the hierarchy of energy scales,
ranging from elementary particle physics to condensed matter physics, together
with photonics. However, the non-Hermitian extension of the Casimir effect and
the application to spintronics have not yet been investigated enough, although
exploring energy sources and developing energy-efficient nanodevices are its
central issues. Here we fill this gap. By developing a magnonic analog of the
Casimir effect into non-Hermitian systems, we show that this non-Hermitian
Casimir effect of magnons is enhanced as the Gilbert damping constant (i.e.,
the energy dissipation rate) increases. When the damping constant exceeds a
critical value, the non-Hermitian Casimir effect of magnons exhibits an
oscillating behavior, including a beating one, as a function of the film
thickness and is characterized by the exceptional point. Our result suggests
that energy dissipation serves as a key ingredient of Casimir engineering.
|
2305.09231v1
|
1995-06-12
|
The small-scale clustering power spectrum and relativistic decays
|
We present constraints on decaying-particle models in which an enhanced
relativistic density allows an $\Omega=1$ Cold Dark Matter universe to be
reconciled with acceptable values for the Hubble constant. Such models may
contain extra small-scale power, which can have important consequences for
enhanced object formation at high redshifts. Small-scale galaxy clustering and
abundances of high-redshift damped Lyman-$\alpha$ absorption clouds give a
preferred range for the mass of any such decaying particle of 2 to 30 keV and a
lifetime of 0.5 to 100 years for models with a high Hubble constant ($h>0.75$).
A lower Hubble constant, $h \simeq 0.5$, weakens the constraint to $0.5< m <
30$ keV, $0.2 < \tau < 500$ years. In permitted versions of the model,
reionization occurs at redshifts $\sim 10-200$, and this feature may be of
importance in understanding degree-scale CMB anisotropies.
|
9506075v1
|
2003-10-21
|
Photon mass and cosmological constant bounds from spacetime torsion
|
Photon mass and Cartan contortion bounds recently obtained from tiny Lorentz
violation observations in cosmology are used to find a limit of ${\lambda}\le
10^{-4}{\alpha}$ for the massive photon-torsion dimensionless coupling. Here
${\alpha}$ represents the fine-structure constant. A gauge invariant Proca
electrodynamics in spacetime endowed with torsion in de Sitter spacetime is
used to obtain an upper bound for the present value of the cosmological
constant given by ${\Lambda}\le 10^{-56} cm^{-2}$. This result is obtained in
regions of the universe where the photons are massless. A relation between the
contortion, photon mass and the radius of the universe is obtained. The Proca
electrodynamics with torsion and the radius of the universe allow us to place
more stringent bounds for the photon mass of $m_{\gamma}{\le} 10^{-44} GeV$
which is only two orders of magnitude lower than the astronomical bounds given
by the PARTICLE DATA GROUP (PDG). We also show that charge is locally conserved
in de Sitter spacetime with torsion and that plane waves are shown to be
damping by contortion inhomogeneities while dispersion is isotropic and
therefore Proca-Cartan photons do not violate Lorentz invariance.
|
0310595v1
|
2002-09-28
|
Strongly Localized State of a Photon at the Intersection of the Phase Slips in 2D Photonic Crystal with Low Contrast of Dielectric Constant
|
Two-dimensional photonic crystal with a rectangular symmetry and low contrast
(< 1) of the dielectric constant is considered. We demonstrate that, despite
the {\em absence} of a bandgap, strong localization of a photon can be achieved
for certain ``magic'' geometries of a unit cell by introducing two $\pi/2$
phase slips along the major axes. Long-living photon mode is bound to the
intersection of the phase slips. We calculate analytically the lifetime of this
mode for the simplest geometry -- a square lattice of cylinders of a radius,
$r$. We find the magic radius, $r_c$, of a cylinder to be 43.10 percent of the
lattice constant. For this value of $r$, the quality factor of the bound mode
exceeds $10^6$. Small ($\sim 1%$) deviation of $r$ from $r_c$ results in a
drastic damping of the bound mode.
|
0209657v1
|
2006-06-13
|
Spontaneously Induced Gravity: From Rippled Dark Matter to Einstein Corpuscles
|
Suppose General Relativity, provocatively governed by a dimensional coupling
constant, is a spontaneously induced theory of Gravity. Invoking Zee's
mechanism, we represent the reciprocal Newton constant by a Brans Dicke scalar
field, and let it damped oscillating towards its General Relativistic VEV. The
corresponding cosmological evolution, in the Jordan frame, averagely resembles
the familiar dark radiation -> dark matter -> dark energy domination sequence.
The fingerprints of the theory are fine ripples, hopefully testable, in the FRW
scale factor; they die away at the strict General Relativity limit. Also
derived is the spherically symmetric static configuration associated with
spontaneously induced General Relativity. At the stiff scalar potential limit,
the exterior Schwarzschild solution is recovered. However, due to level
crossing at the would have been horizon, it now connects with a novel dark core
characterized by a locally varying Newton constant. The theory further predicts
light Einstein-style gravitational corpuscles (elementary particles?) which
become point-like at the GR-limit.
|
0606058v1
|
2000-03-16
|
Quantum Field Theory Solution to The Gauge Hierarchy And Cosmological Constant Problems
|
A quantum field theory formalism is reviewed that leads to a self-consistent,
finite quantum gravity, Yang-Mills and Higgs theory, which is unitary and gauge
invariant to all orders of perturbation theory. The gauge hierarchy problem is
solved due to the exponential damping of the Higgs self-energy loop graph for
energies greater than a scale $\Lambda_H\leq 1$ TeV. The cosmological constant
problem is solved by introducing a fundamental quantum gravity scale,
$\Lambda_G\leq 10^{-4}$ eV, above which the virtual contributions to the vacuum
energy density coupled to gravity are exponentially suppressed, yielding an
observationally acceptable value for the particle physics contribution to the
cosmological constant. Classical Einstein gravity retains its causal behavior
as well as the standard agreement with observational data. Possible
experimental tests of the onset of quantum nonlocality at short distances are
considered.
|
0003171v2
|
2007-06-12
|
Simple Combined Model for Nonlinear Excitations in DNA
|
We propose a new simple model for DNA denaturation bases on the pendulum
model of Englander\cite{A1} and the microscopic model of Peyrard {\it et
al.},\cite{A3} so called "combined model". The main parameters of our model
are: the coupling constant $k$ along each strand, the mean stretching $y^\ast$
of the hydrogen bonds, the ratio of the damping constant and driven force
$\gamma/F$. We show that both the length $L$ of unpaired bases and the velocity
$v$ of kinks depend on not only the coupling constant $k$ but also the
temperature $T$. Our results are in good agreement with previous works.
|
0706.1683v1
|
2010-11-28
|
Energy release from hadron-quark phase transition in neutron stars and the axial $w$-mode of gravitational waves
|
Describing the hyperonic and quark phases of neutron stars with an isospin-
and momentum-dependent effective interaction for the baryon octet and the MIT
bag model, respectively, and using the Gibbs conditions to construct the mixed
phase, we study the energy release due to the hadron-quark phase transition.
Moreover, the frequency and damping time of the first axial $w$-mode of
gravitational waves are studied for both hyperonic and hybrid stars. We find
that the energy release is much more sensitive to the bag constant than the
density dependence of the nuclear symmetry energy. Also, the frequency of the
$w$-mode is found to be significantly different with or without the
hadron-quark phase transition and depends strongly on the value of the bag
constant. Effects of the density dependence of the nuclear symmetry energy
become, however, important for large values of the bag constant that lead to
higher hadron-quark transition densities.
|
1011.6073v1
|
2011-11-18
|
Charge and Spin Transport in Magnetic Tunnel Junctions: Microscopic Theory
|
We study the charge and spin currents passing through a magnetic tunnel
junction (MTJ) on the basis of a tight-binding model. The currents are
evaluated perturbatively with respect to the tunnel Hamiltonian. The charge
current has the form $A[\bm M_1(t)\times\dot{\bm M}_1(t)]\cdot\bm M_2+B\dot{\bm
M}_1(t)\cdot\bm M_2$, where $\bm M_1(t)$ and $\bm M_2$ denote the directions of
the magnetization in the free layer and fixed layer, respectively. The constant
$A$ vanishes when one or both layers are insulators, {while the constant $B$
disappears when both layers are insulators or the same ferromagnets.} The first
term in the expression for charge current represents dissipation driven by the
effective electric field induced by the dynamic magnetization. In addition,
from an investigation of the spin current, we obtain the microscopic expression
for the enhanced Gilbert damping constant $\varDelta \alpha$. We show that
$\varDelta\alpha$ is proportional to the tunnel conductance and depends on the
bias voltage.
|
1111.4295v2
|
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