publicationDate
stringlengths 1
2.79k
| title
stringlengths 1
36.5k
⌀ | abstract
stringlengths 1
37.3k
⌀ | id
stringlengths 9
47
|
|---|---|---|---|
2011-08-02
|
PHENIX Measurements of Higher-order Flow Harmonics in Au+Au collisions at Root_s = 200 GeV
|
Flow coefficients $v_n$ for $n$ = 2, 3, 4, characterizing the anisotropic
collective flow in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, are
presented. They indicate the expected growth of viscous damping for sound
propagation in the quark gluon plasma (QGP) produced in these collisions.
Hydrodynamical model comparisons which include the effects of initial state
geometry fluctuations, highlight the role of higher harmonics ($v_{n, n>2}$) as
a constraint for disentangling the effects of viscosity and initial conditions,
and suggest a small specific viscosity for the QGP. This viscosity is
compatible with that obtained via a newly proposed technique
\cite{Lacey:2011ug} which employs the relative magnitudes of $v_n$ to estimate
the viscosity, and the "viscous horizon" or length-scale which characterizes
the highest harmonic that survives viscous damping.
|
1108.0457v1
|
2011-08-10
|
Critical exponents of steady-state phase transitions in fermionic lattice models
|
We discuss reservoir induced phase transitions of lattice fermions in the
non-equilibrium steady state (NESS) of an open system with local reservoirs.
These systems may become critical in the sense of a diverging correlation
length upon changing the reservoir coupling. We here show that the transition
to a critical state is associated with a vanishing gap in the damping spectrum.
It is shown that although in linear systems there can be a transition to a
critical state there is no reservoir-induced quantum phase transition between
distinct phases with non-vanishing damping gap. We derive the static and
dynamical critical exponents corresponding to the transition to a critical
state and show that their possible values, defining universality classes of
reservoir-induced phase transitions are determined by the coupling range of the
independent local reservoirs. If a reservoir couples to N neighboring lattice
sites, the critical exponent can assume all fractions from 1 to 1/(N - 1).
|
1108.2263v5
|
2011-09-09
|
Observation of Spontaneous Brillouin Cooling
|
While radiation-pressure cooling is well known, the Brillouin scattering of
light from sound is considered an acousto-optical amplification-only process.
It was suggested that cooling could be possible in multi-resonance Brillouin
systems when phonons experience lower damping than light. However, this regime
was not accessible in traditional Brillouin systems since backscattering
enforces high acoustical frequencies associated with high mechanical damping.
Recently, forward Brillouin scattering in microcavities has allowed access to
low-frequency acoustical modes where mechanical dissipation is lower than
optical dissipation, in accordance with the requirements for cooling. Here we
experimentally demonstrate cooling via such a forward Brillouin process in a
microresonator. We show two regimes of operation for the Brillouin process:
acoustical amplification as is traditional, but also for the first time, a
Brillouin cooling regime. Cooling is mediated by an optical pump, and scattered
light, that beat and electrostrictively attenuate the Brownian motion of the
mechanical mode.
|
1109.2084v2
|
2011-09-14
|
Oscillations of simple networks
|
To describe the flow of a miscible quantity on a network, we introduce the
graph wave equation where the standard continuous Laplacian is replaced by the
graph Laplacian. This is a natural description of an array of inductances and
capacities, of fluid flow in a network of ducts and of a system of masses and
springs. The structure of the graph influences strongly the dynamics which is
naturally described using the basis of the eigenvectors. In particular, we show
that if two outer nodes are connected to a common third node with the same
coupling, then this coupling is an eigenvalue of the Laplacian. Assuming the
graph is forced and damped at specific nodes, we derive the amplitude
equations. These are analyzed for two simple non trivial networks: a tree and a
graph with a cycle. Forcing the network at a resonant frequency reveals that
damping can be ineffective if applied to the wrong node, leading to a
disastrous resonance and destruction of the network. These results could be
useful for complex physical networks and engineering networks like power grids.
|
1109.3071v2
|
2011-09-21
|
High-order explicit local time-stepping methods for damped wave equations
|
Locally refined meshes impose severe stability constraints on explicit
time-stepping methods for the numerical simulation of time dependent wave
phenomena. Local time-stepping methods overcome that bottleneck by using
smaller time-steps precisely where the smallest elements in the mesh are
located. Starting from classical Adams-Bashforth multi-step methods, local
time-stepping methods of arbitrarily high order of accuracy are derived for
damped wave equations. When combined with a finite element discretization in
space with an essentially diagonal mass matrix, the resulting time-marching
schemes are fully explicit and thus inherently parallel. Numerical experiments
with continuous and discontinuous Galerkin finite element discretizations
validate the theory and illustrate the usefulness of these local time-stepping
methods.
|
1109.4480v2
|
2011-09-21
|
Anisotropic critical magnetic fluctuations in the ferromagnetic superconductor UCoGe
|
We report neutron scattering measurements of critical magnetic excitations in
the weakly ferromagnetic superconductor UCoGe. The strong non-Landau damping of
the excitations we observe, although unusual has been found in another related
ferromagnet, UGe2 at zero pressure. However, we also find there is a
significant anisotropy of the magnetic correlation length in UCoGe that
contrasts with an almost isotropic length for UGe2. The values of the magnetic
correlation length and damping are found to be compatible with
superconductivity on small Fermi surface pockets. The anisotropy may be
important to explain why UCoGe is a superconductor at zero pressure while UGe2
is not.
|
1109.4541v1
|
2011-09-30
|
PT-symmetry, indefinite damping and dissipation-induced instabilities
|
With perfectly balanced gain and loss, dynamical systems with indefinite
damping can obey the exact PT-symmetry being marginally stable with a pure
imaginary spectrum. At an exceptional point where the symmetry is spontaneously
broken, the stability is lost via passing through a non-semisimple 1:1
resonance. In the parameter space of a general dissipative system, marginally
stable PT-symmetric ones occupy singularities on the boundary of the asymptotic
stability. To observe how the singular surface governs dissipation-induced
destabilization of the PT-symmetric system when gain and loss are not matched,
an extension of recent experiments with PT-symmetric LRC circuits is proposed.
|
1110.0018v2
|
2011-10-01
|
Electrical measurement of antivortex wall eigenfrequency
|
The dynamics of a ferromagnetic antivortex wall has been experimentally
studied in a magnetic nanostructure. Two different techniques have been used to
independently measure the eigenfrequency of an antivortex wall such as the
resonance excitation by sinusoidal microwave and the damped resonance
excitation induced by short voltage pulses. Direct observation of antivortex
wall nucleation has been measured in the frequency domain for the first time.
Electrical measurements of the antivortex dynamics in frequency domain reveal
the existence of multi-eigenmodes as well as nonlinear behaviors for large
excitation amplitudes. The time resolved measurements of the antivortex wall
show that the frequency of the damped gyration is similar to that of frequency
domain and coexistence of spin wave excitations.
|
1110.0113v1
|
2011-10-06
|
Comparative Wakefield Analysis of a First Prototype of a DDS Structure for CLIC Main Linac
|
A Damped Detuned Structure (DDS) for CLIC main linac has been proposed as an
alternative to the present baseline design which is based on heavy damping. A
first prototype, CLIC_DDS_A, for high power tests has been already designed and
is under construction. It is also foreseen to design a further prototype,
CLIC_DDS_B, to test both the wakefield suppression and high power performances.
Wakefield calculations for DDS are, in the early design stage, based on single
infinitely periodic cells. Though cell-to-cell interaction is taken into
account to calculate the wakefields, it is important to study full structure
properties using computational tools. In particular this is fundamental for
defining the input parameters for the HOM coupler that is crucial for the
performances of DDS. In the following a full analysis of wakefields and
impedances based on simulations conducted with finite difference based
electromagnetic computer code GdfidL will be presented.
|
1110.1207v1
|
2011-10-12
|
Nonlinear dynamic analysis of an optimal particle damper
|
We study the dynamical behavior of a single degree of freedom mechanical
system with a particle damper. The particle (granular) damping was optimized
for the primary system operating condition by using an appropriate gap size for
a prismatic enclosure. The particles absorb the kinetic energy of the vibrating
structure and convert it into heat through the inelastic collisions and
friction. This results in a highly nonlinear mechanical system. Considering
linear signal analysis, state space reconstruction, Poincar\'e sections and the
determination of maximal Lyapunov exponents, the motion of the granular system
inside the enclosure is characterized for a wide frequency range. With the
excitation frequency as control parameter, either regular and chaotic motion of
the granular bed are found and their influence on the damping is analyzed.
|
1110.2800v1
|
2011-10-14
|
Effect of Compton Scattering on the Electron Beam Dynamics at the ATF Damping Ring
|
Compton scattering provides one of the most promising scheme to obtain
polarized positrons for the next generation of $e^-$ -- $e^+$ colliders.
Moreover it is an attractive method to produce monochromatic high energy
polarized gammas for nuclear applications and X-rays for compact light sources.
In this framework a four-mirror Fabry-P\'erot cavity has been installed at the
Accelerator Test Facility (ATF - KEK, Tsukuba, Japan) and is used to produce an
intense flux of polarized gamma rays by Compton scattering
\cite{ipac-mightylaser}. For electrons at the ATF energy (1.28 GeV) Compton
scattering may result in a shorter lifetime due to the limited bucket
acceptance. We have implemented the effect of Compton scattering on a 2D
tracking code with a Monte-Carlo method. This code has been used to study the
longitudinal dynamics of the electron beam at the ATF damping ring, in
particular the evolution of the energy spread and the bunch length under
Compton scattering. The results obtained are presented and discussed. Possible
methods to observe the effect of Compton scattering on the ATF beam are
proposed.
|
1110.3241v1
|
2011-10-15
|
Atomistic spin dynamic method with both damping and moment of inertia effects included from first principles
|
We consider spin dynamics for implementation in an atomistic framework and we
address the feasibility of capturing processes in the femtosecond regime by
inclusion of moment of inertia. In the spirit of an {\it s-d} -like interaction
between the magnetization and electron spin, we derive a generalized equation
of motion for the magnetization dynamics in the semi-classical limit, which is
non-local in both space and time. Using this result we retain a generalized
Landau-Lifshitz-Gilbert equation, also including the moment of inertia, and
demonstrate how the exchange interaction, damping, and moment of inertia, all
can be calculated from first principles.
|
1110.3387v2
|
2011-10-24
|
CoB/Ni-Based Multilayer Nanowire with High-Speed Domain Wall Motion under Low Current Control
|
The spin-transfer torque motion of magnetic domain walls (DWs) in a
CoB/Ni-based nanowire driven by a low current density of
(1.12\pm0.8)\times10^{11} A m^{-2} has been observed indirectly by
magnetotransport measurements. A high DW velocity of 85\pm4 m/s at zero field
was measured at the threshold current density. Upon increasing the current
density to 2.6\times10^{11} A m^{-2}, the DW velocity increases to 197\pm16 m/s
before decreasing quickly in the high-current-density regime attributed to
nonadiabatic spin-transfer torque at a low damping factor and weak pinning. The
addition of B atoms to the Co layers decreased the magnitude of saturation
magnetization, Gilbert damping factor, and density of pinning sites, making the
CoB/Ni multilayer nanowire favorable for practical applications.
|
1110.5112v3
|
2011-10-28
|
Stability of linear and non-linear lambda and tripod systems in the presence of amplitude damping
|
We present the stability analysis of the dark states in the adiabatic passage
for the linear and non-linear lambda and tripod systems in the presence of
amplitude damping (losses). We perform an analytic evaluation of the real parts
of eigenvalues of the corresponding Jacobians, the non-zero eigenvalues of
which are found from the quadratic characteristic equations, as well as by the
corresponding numerical simulations. For non-linear systems, we evaluate the
Jacobians at the dark states. Similarly to the linear systems, here we also
find the non-zero eigenvalues from the characteristic quadratic equations. We
reveal a common property of all the considered systems showing that the
evolution of the real parts of eigenvalues can be split into three stages. In
each of them the evolution of the stimulated Raman adiabatic passage (STIRAP)
is characterized by different effective dimension. This results in a possible
adiabatic reduction of one or two degrees of freedom.
|
1110.6379v2
|
2011-11-07
|
Control of Material Damping in High-Q Membrane Microresonators
|
We study the mechanical quality factors of bilayer aluminum/silicon-nitride
membranes. By coating ultrahigh-Q Si3N4 membranes with a more lossy metal, we
can precisely measure the effect of material loss on Q's of tensioned resonator
modes over a large range of frequencies. We develop a theoretical model that
interprets our results and predicts the damping can be reduced significantly by
patterning the metal film. Using such patterning, we fabricate Al-Si3N4
membranes with ultrahigh Q at room temperature. Our work elucidates the role of
material loss in the Q of membrane resonators and informs the design of hybrid
mechanical oscillators for optical-electrical-mechanical quantum interfaces.
|
1111.1703v2
|
2011-11-15
|
Thermodynamic anomaly of the free damped quantum particle: the bath perspective
|
A possible definition of the specific heat of open quantum systems is based
on the reduced partition function of the system. For a free damped quantum
particle, it has been found that under certain conditions, this specific heat
can become negative at low temperatures. In contrast to the conventional
approaches focusing on the system degree of freedom, here we concentrate on the
changes induced in the environment when the system is coupled to it. Our
analysis is carried out for an Ohmic environment consisting of harmonic
oscillators and allows to identify the mechanism by which the specific heat
becomes negative. Furthermore, the formal condition for the occurrence of a
negative specific heat is given a physical interpretation in terms of the total
mass of bath oscillators and the system mass.
|
1111.3594v2
|
2011-12-02
|
On the propagation of binary signals in damped mechanical systems of oscillators
|
In the present work, we explore efficient ways to transmit binary information
in discrete, semi-infinite chains of coupled oscillators using the process of
nonlinear supratransmission. A previous work showed that such transmission is
possible and, indeed, reliable under the idealistic condition when weak or no
damping is present. In this paper, we study a more realistic case and propose
the design of mechanical devices in order to avoid the loss of information,
consisting on the linear concatenation of several such mechanical systems. Our
results demonstrate that the loss of information can be minimized or avoided
using such physical structures.
|
1112.0585v1
|
2011-12-02
|
On the simulation of the energy transmission in the forbidden band-gap of a spatially discrete double sine-Gordon system
|
In this work, we present a numerical method to consistently approximate
solutions of a spatially discrete, double sine-Gordon chain which considers the
presence of external damping. In addition to the finite-difference scheme
employed to approximate the solution of the difference-differential equations
of the model under investigation, our method provides positivity-preserving
schemes to approximate the local and the total energy of the system, in such
way that the discrete rate of change of the total energy with respect to time
provides a consistent approximation of the corresponding continuous rate of
change. Simulations are performed, first of all, to assess the validity of the
computational technique against known qualitative solutions of coupled
sine-Gordon and coupled double sine-Gordon chains. Secondly, the method is used
in the investigation of the phenomenon of nonlinear transmission of energy in
double sine-Gordon systems; the qualitative effects of the damping coefficient
on the occurrence of the nonlinear process of supratransmission are briefly
determined in this work, too.
|
1112.0595v1
|
2011-12-11
|
Spin-polarized current effect on antiferromagnet magnetization in a ferromagnet - antiferromagnet nanojunction: Theory and simulation
|
Spin-polarized current effect is studied on the static and dynamic
magnetization of the antiferromagnet in a ferromagnet - antiferromagnet
nanojunction. The macrospin approximation is generalized to antiferromagnets.
Canted antiferromagnetic configuration and resulting magnetic moment are
induced by an external magnetic field. The resonance frequency and damping are
calculated, as well as the threshold current density corresponding to
instability appearance. A possibility is shown of generating low-damping
magnetization oscillations in terahertz range. The fluctuation effect is
discussed on the canted antiferromagnetic configuration. Numerical simulation
is carried out of the magnetization dynamics of the antiferromagnetic layer in
the nanojunction with spin-polarized current. Outside the instability range,
the simulation results coincide completely with analytical calculations using
linear approximation. In the instability range, undamped oscillations occur of
the longitudinal and transverse magnetization components.
|
1112.2362v1
|
2011-12-15
|
Analytic gas orbits in an arbitrary rotating galactic potential using the linear epicyclic approximation
|
A code, Epic5, has been developed which computes, in the two-dimensional
case, the initially circular orbits of guiding centra in an arbitrary
axisymmetric potential with an arbitrary, weak perturbing potential in solid
body rotation. This perturbing potential is given by its Fourier expansion. The
analytic solution solves the linear epicyclic approximation of the equations of
motion. To simulate the motion of interstellar matter and to damp the Lindblad
resonances, we have in these equations introduced a friction which is
proportional to the deviation from circular velocity. The corotation resonance
is also damped by a special parameter. The program produces, in just a few
seconds, orbital and density maps, as well as line of sight velocity maps for a
chosen orientation of the galaxy.
We test Epic5 by comparing its results with previous simulations and
observations from the literature, which gives satisfactory agreement. The aim
is that this program should be a useful complement to elaborate numerical
simulations. Particularly so are its abilities to quickly explore the parameter
space, to construct artificial galaxies, and to isolate various single agents
important for developing structure of interstellar matter in disc galaxies.
|
1112.3658v1
|
2011-12-23
|
Temperature gradient assisted magnetodynamics in a ferromagnetic nanowire
|
The dynamics of the low energy excitations in a ferromagnet is studied in
case a temperature gradient is coupled to the local magnetization. Due to the
different time scales of changing temperature and magnetization it is argued
that only the coupling between the spatially varying part of the temperature
field and the magnetization is relevant. Using variational principles the
evolution equation for the magnetic system is found which is strongly
influenced by the local temperature profile. The system offers damped spin wave
excitations where the strength of damping is determined by the magneto-thermal
coupling. Applying the model to nanowires it is demonstrated that the energy
spectrum is significantly affected by the boundary conditions as well as the
initial temperature distribution. In particular, the coupling between
temperature and magnetization is expected to be several orders stronger for the
open as for the isolated wire.
|
1112.5562v1
|
2012-01-04
|
A new candidate for probing Population III nucleosynthesis with carbon-enhanced damped Lyman-alpha systems
|
We report the identification of a very metal-poor damped Lyman-alpha system
(DLA) at z_abs = 3.067295 that is modestly carbon-enhanced, with an iron
abundance of ~1/700 solar ([Fe/H] = -2.84) and [C,O/Fe] ~ +0.6. Such an
abundance pattern is likely to be the result of nucleosynthesis by massive
stars. On the basis of 17 metal absorption lines, we derive a 2 sigma upper
limit on the DLA's kinetic temperature of T_DLA <= 4700 K, which is broadly
consistent with the range of spin temperature estimates for DLAs at this
redshift and metallicity. While the best-fitting abundance pattern shows the
expected hallmarks of Population III nucleosynthesis, models of high-mass
Population II stars can match the abundance pattern almost as well. We discuss
current limitations in distinguishing between these two scenarios and the
marked improvement in identifying the remnants of Population III stars expected
from the forthcoming generation of 30-metre class telescopes.
|
1201.1004v2
|
2012-01-06
|
Magnetic field decay with Hall drift in neutron star crusts
|
The dynamics of magnetic field decay with Hall drift is investigated.
Assuming that axisymmetric magnetic fields are located in a spherical crust
with uniform conductivity and electron number density, long-term evolution is
calculated up to Ohmic dissipation. The nonlinear coupling between poloidal and
toroidal components is explored in terms of their energies and helicity.
Nonlinear oscillation by the drift in strongly magnetized regimes is clear only
around the equipartition between two components. Significant energy is
transferred to the poloidal component when the toroidal component initially
dominates. However, the reverse is not true. Once the toroidal field is less
dominant, it quickly decouples due to a larger damping rate. The polar field at
the surface is highly distorted from the initial dipole during the Hall drift
timescale, but returns to the initial dipole in a longer dissipation timescale,
since it is the least damped one.
|
1201.1346v1
|
2012-01-06
|
Reversible Dissipative Processes, Conformal Motions and Landau Damping
|
The existence of a dissipative flux vector is known to be compatible with
reversible processes, provided a timelike conformal Killing vector (CKV)
$\chi^\alpha=\frac{V^\alpha}{T}$ (where $V^\alpha$ and $T$ denote the
four-velocity and temperature respectively) is admitted by the space-time. Here
we show that if a constitutive transport equation, either within the context of
standard irreversible thermodynamics or the causal Israel--Stewart theory, is
adopted, then such a compatibility also requires vanishing dissipative fluxes.
Therefore, in this later case the vanishing of entropy production generated by
the existence of such CKV is not actually associated to an imperfect fluid, but
to a non-dissipative one. We discuss also about Landau damping.
|
1201.1390v1
|
2012-01-19
|
Wave Leakage and Resonant Absorption in a Loop Embedded in a Coronal Arcade
|
We investigate the temporal evolution of impulsively generated perturbations
in a potential coronal arcade with an embedded loop. As the initial
configuration we consider a coronal loop, represented by a density enhancement,
which is unbounded in the ignorable direction of the arcade. The linearized
time-dependent magnetohydrodynamic equations have been numerically solved in
field-aligned coordinates and the time evolution of the initial perturbations
has been studied in the zero-beta approximation. For propagation constrained to
the plane of the arcade, the considered initial perturbations do not excite
trapped modes of the system. This weakness of the model is overcome by the
inclusion of wave propagation in the ignorable direction. The inclusion of
perpendicular propagation produces two main results. First, damping by wave
leakage is less efficient because the loop is able to act as a wave trap of
vertical oscillations. Second, the consideration of an inhomogeneous corona
enables the resonant damping of vertical oscillations and the energy transfer
from the interior of the loop to the external coronal medium.
|
1201.4042v1
|
2012-02-08
|
Evidence of Wave Damping at Low Heights in a Polar Coronal Hole
|
We have measured the widths of spectral lines from a polar coronal hole using
the Extreme Ultraviolet Imaging Spectrometer onboard Hinode. Polar coronal
holes are regions of open magnetic field and the source of the fast solar wind.
We find that the line widths decrease at relatively low heights. Previous
observations have attributed such decreases to systematic effects, but we find
that such effects are too small to explain our results. We conclude that the
line narrowing is real. The non-thermal line widths are believed to be
proportional to the amplitude of Alfven waves propagating along these open
field lines. Our results suggest that Alfven waves are damped at unexpectedly
low heights in a polar coronal hole. We derive an estimate on the upper limit
for the energy dissipated between 1.1 and 1.3 solar radii and find that it is
enough to account for up to 70% of that required to heat the polar coronal hole
and accelerate the solar wind.
|
1202.1743v2
|
2012-02-14
|
The kinetic temperature in a damped Lyman-alpha absorption system in Q2206-199 - an example of the warm neutral medium
|
By comparing the widths of absorption lines from OI, SiII and FeII in the
redshift z=2.076 single-component damped Lyman alpha absorption system in the
spectrum of Q2206-199 we establish that these absorption lines arise in Warm
Neutral Medium gas at ~12000 +/- 3000K. This is consistent with thermal
equilibrium model estimates of ~ 8000K for the Warm Neutral Medium in galaxies,
but not with the presence of a significant cold component. It is also
consistent with, but not required by, the absence of CII* fine structure
absorption in this system. Some possible implications concerning abundance
estimates in narrow-line WNM absorbers are discussed.
|
1202.3012v1
|
2012-02-23
|
Eigenmodes of the damped wave equation and small hyperbolic subsets
|
We study stationary solutions of the damped wave equation on a compact and
smooth Riemannian manifold without boundary. In the high frequency limit, we
prove that a sequence of $\beta$-damped stationary solutions cannot be
completely concentrated in small neighborhoods of a small fixed hyperbolic
subset made of $\beta$-damped trajectories of the geodesic flow. The article
also includes an appendix (by S. Nonnenmacher and the author) where we
establish the existence of an inverse logarithmic strip without eigenvalues
below the real axis, under a pressure condition on the set of undamped
trajectories.
|
1202.5123v3
|
2012-03-04
|
Dissipation effects in random transverse-field Ising chains
|
We study the effects of Ohmic, super-Ohmic, and sub-Ohmic dissipation on the
zero-temperature quantum phase transition in the random transverse-field Ising
chain by means of an (asymptotically exact) analytical strong-disorder
renormalization-group approach. We find that Ohmic damping destabilizes the
infinite-randomness critical point and the associated quantum Griffiths
singularities of the dissipationless system. The quantum dynamics of large
magnetic clusters freezes completely which destroys the sharp phase transition
by smearing. The effects of sub-Ohmic dissipation are similar and also lead to
a smeared transition. In contrast, super-Ohmic damping is an irrelevant
perturbation; the critical behavior is thus identical to that of the
dissipationless system. We discuss the resulting phase diagrams, the behavior
of various observables, and the implications to higher dimensions and
experiments.
|
1203.0698v2
|
2012-03-22
|
Large Amplitude Longitudinal Oscillations in a Solar Filament
|
We have developed the first self-consistent model for the observed
large-amplitude oscillations along filament axes that explains the restoring
force and damping mechanism. We have investigated the oscillations of multiple
threads formed in long, dipped flux tubes through the thermal nonequilibrium
process, and found that the oscillation properties predicted by our simulations
agree with the observed behavior. We then constructed a model for the
large-amplitude longitudinal oscillations that demonstrates that the restoring
force is the projected gravity in the tube where the threads oscillate.
Although the period is independent of the tube length and the constantly
growing mass, the motions are strongly damped by the steady accretion of mass
onto the threads by thermal nonequilibrium. The observations and our model
suggest that a nearby impulsive event drives the existing prominence threads
along their supporting tubes, away from the heating deposition site, without
destroying them. The subsequent oscillations occur because the displaced
threads reside in magnetic concavities with large radii of curvature. Our model
yields a powerful seismological method for constraining the coronal magnetic
field and radius of curvature of dips. Furthermore, these results indicate that
the magnetic structure is most consistent with the sheared-arcade model for
filament channels.
|
1203.5027v1
|
2012-03-26
|
Analysis of the Energy Decay of a Degenerated Thermoelasticity System
|
In this paper, we study a system of thermoelasticity with a degenerated
second order operator in the Heat equation. We analyze the evolution of the
energy density of a family of solutions. We consider two cases: when the set of
points where the ellipticity of the Heat operator fails is included in a
hypersurface and when it is an open set. In the first case and under special
assumptions, we prove that the evolution of the energy density is the one of a
damped wave equation: propagation along the rays of geometric optic and damping
according to a microlocal process. In the second case, we show that the energy
density propagates along rays which are distortions of the rays of geometric
optic.
|
1203.5606v1
|
2012-03-26
|
Infinite Energy Solutions for Damped Navier-Stokes Equations in R2
|
We study the so-called damped Navier-Stokes equations in the whole 2D space.
The global well-posedness, dissipativity and further regularity of weak
solutions of this problem in the uniformly-local spaces are verified based on
the further development of the weighted energy theory for the Navier-Stokes
type problems. Note that any divergent free vector field $u_0\in
L^\infty(\mathbb R^2)$ is allowed and no assumptions on the spatial decay of
solutions as $|x|\to\infty$ are posed. In addition, applying the developed
theory to the case of the classical Navier-Stokes problem in R2, we show that
the properly defined weak solution can grow at most polynomially (as a quintic
polynomial) as time goes to infinity.
|
1203.5733v2
|
2012-03-28
|
Quantum-correlating power of local quantum channels
|
Quantum correlation can be created by local operations from a classically
correlated state. We define quantum-correlating power (QCP) of a local quantum
channel as the maximum amount of quantum correlation that can be created by the
channel. The quantum correlation that we discuss in this article is defined on
the left part of the bipartite state. We prove that for any local channel, the
optimal input state, which corresponds to the maximum quantum correlation in
the output state, must be a classical-classical state. Further, the
single-qubit channels with maximum QCP can be found in the class of rank-1
channels which take their optimal input states to rank-2 quantum-classical
states. The analytic expression for QCP of single-qubit amplitude damping
channel is obtained. Super-activation property of QCP, i.e., two zero-QCP
channels can consist a positive-QCP channel, is discussed for single-qubit
phase damping channels.
|
1203.6149v1
|
2012-04-12
|
On the sizes of z>2 Damped Lyman-alpha Absorbing Galaxies
|
Recently, the number of detected galaxy counterparts of z > 2 Damped
Lyman-alpha Absorbers in QSO spectra has increased substantially so that we
today have a sample of 10 detections. M{\o}ller et al. in 2004 made the
prediction, based on a hint of a luminosity-metallicity relation for DLAs, that
HI size should increase with increasing metallicity. In this paper we
investigate the distribution of impact parameter and metallicity that would
result from the correlation between galaxy size and metallicity. We compare our
observations with simulated data sets given the relation of size and
metallicity. The observed sample presented here supports the metallicity-size
prediction: The present sample of DLA galaxies is consistent with the model
distribution. Our data also show a strong relation between impact parameter and
column density of HI. We furthermore compare the observations with several
numerical simulations and demonstrate that the observations support a scenario
where the relation between size and metallicity is driven by feedback
mechanisms controlling the star-formation efficiency and outflow of enriched
gas.
|
1204.2833v1
|
2012-04-16
|
Quasi-normal modes, area spectra and multi-horizon spacetimes
|
We suggest an interpretation for the highly damped QNM frequencies of the
spherically symmetric multi-horizon spacetimes (Reissner-Nordstrom,
Schwarzschild-deSitter, Reissner-Nordstrom-deSitter) following Maggiore's
proposal about the link between the asymptotic QNM frequencies and the black
hole thermodynamics. We show that the behavior of the asymptotic frequencies is
easy to understand if one assumes that all of the horizons have the same
equispaced area spectra. The QNM analysis is then consistent with the choice of
the area spectra to be the one originally proposed for the black hole's horizon
by Bekenstein: A=8\pi n (in Planck units). The interpretation of the highly
damped QNM frequencies in the multi-horizon case is based on the similar
grounds as in the single horizon (Schwarzschild) case, but it has some new
features that are discussed in the paper.
|
1204.3566v2
|
2012-05-03
|
Explicit local time-stepping methods for time-dependent wave propagation
|
Semi-discrete Galerkin formulations of transient wave equations, either with
conforming or discontinuous Galerkin finite element discretizations, typically
lead to large systems of ordinary differential equations. When explicit time
integration is used, the time-step is constrained by the smallest elements in
the mesh for numerical stability, possibly a high price to pay. To overcome
that overly restrictive stability constraint on the time-step, yet without
resorting to implicit methods, explicit local time-stepping schemes (LTS) are
presented here for transient wave equations either with or without damping. In
the undamped case, leap-frog based LTS methods lead to high-order explicit LTS
schemes, which conserve the energy. In the damped case, when energy is no
longer conserved, Adams-Bashforth based LTS methods also lead to explicit LTS
schemes of arbitrarily high accuracy. When combined with a finite element
discretization in space with an essentially diagonal mass matrix, the resulting
time-marching schemes are fully explicit and thus inherently parallel.
Numerical experiments with continuous and discontinuous Galerkin finite element
discretizations validate the theory and illustrate the usefulness of these
local time-stepping methods.
|
1205.0654v2
|
2012-05-15
|
Molecular vibrations-induced quantum beats in two-dimensional electronic spectroscopy
|
Quantum beats in nonlinear spectroscopy of molecular aggregates are often
attributed to electronic phenomena of excitonic systems, while nuclear degrees
of freedom are commonly included into models as overdamped oscillations of bath
constituents responsible for dephasing. However, molecular systems are coupled
to various high-frequency molecular vibrations, which can cause the spectral
beats hardly distinguishable from those created by purely electronic
coherences. Models containing damped, undamped and overdamped vibrational modes
coupled to an electronic molecular transition are discussed in this paper in
context of linear absorption and two-dimensional electronic spectroscopy.
Analysis of different types of bath models demonstrates how do vibrations map
onto two-dimensional spectra and how the damping strength of the coherent
vibrational modes can be resolved from spectroscopic signals.
|
1205.3383v2
|
2012-05-16
|
Deuterium at high-redshift: Primordial abundance in the zabs = 2.621 damped Ly-alpha system towards CTQ247
|
The detection of neutral deuterium in the low-metallicity damped
Lyman-{\alpha} system at zabs = 2.621 towards the quasar CTQ247 is reported.
Using a high signal-to-noise and high spectral resolution (R = 60000) spectrum
from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we
precisely measure the deuterium-to-oxygen ratio log N(DI)/N(OI) = 0.74+/-0.04,
as well as the overall oxygen abundance, log N(OI)/N(HI)=-5.29+/-0.10 (or
equivalently [O/H]=-1.99+/-0.10 with respect to the solar value). Assuming
uniform metallicity throughout the system, our measurement translates to (D/H)
= (2.8+0.8 -0.6)x10^-5. This ratio is consistent within errors (<0.4sigma) with
the primordial ratio, (D/H)p = (2.59+/-0.15)x10^-5, predicted by standard
Big-Bang Nucleosynthesis using the WMAP7 value of the cosmological density of
baryons (100 Omega_b h^2 = 2.249+/-0.056). The DI absorption lines are observed
to be broader than the OI absorption lines. From a consistent fit of the
profiles we derive the turbulent broadening to be 5.2 km/s and the temperature
of the gas to be T = 8800+/-1500 K, corresponding to a warm neutral medium.
|
1205.3777v1
|
2012-05-23
|
Global existence for a damped wave equation and convergence towards a solution of the Navier-Stokes problem
|
In two and three space dimensions, and under suitable assumptions on the
initial data, we show global existence for a damped wave equation which
approaches, in some sense, the Navier-Stokes problem. The proofs are based on a
refined energy method. In this paper, we improve the results in two papers by
Y. Brenier, R. Natalini and M. Puel and by M. Paicu and G. Raugel. We relax the
regularity of the initial data of the former, even though we still use energy
methods as a principal tool. Regarding the second paper, the improvement
consists in the simplicity of the proofs since we do not use any Strichartz
estimate and in requiring less regularity for the convergence to the
Navier-Stokes problem. Indeed, the convergence result we obtain is near-optimal
regularity.
|
1205.5166v2
|
2012-05-24
|
Modelling the Propagation of a Weak Fast-Mode MHD Shock Wave near a 2D Magnetic Null Point Using Nonlinear Geometrical Acoustics
|
We present the results of analytical modelling of fast-mode
magnetohydrodynamic wave propagation near a 2D magnetic null point. We consider
both a linear wave and a weak shock and analyse their behaviour in cold and
warm plasmas. We apply the nonlinear geometrical acoustics method based on the
Wentzel-Kramers-Brillouin approximation. We calculate the wave amplitude, using
the ray approximation and the laws of solitary shock wave damping. We find that
a complex caustic is formed around the null point. Plasma heating is
distributed in space and occurs at a caustic as well as near the null point due
to substantial nonlinear damping of the shock wave. The shock wave passes
through the null point even in a cold plasma. The complex shape of the wave
front can be explained by the caustic pattern.
|
1205.5327v1
|
2012-05-31
|
Quasinormal modes for the scattering on a naked Reissner-Nordstrom singularity
|
What should be the quasinormal modes associated with a spacetime that
contains a naked singularity instead of a black hole? In the present work we
address this problem by studying the scattering of scalar fields on a curved
background described by a Reissner-Nordstr\"om spacetime with $|q| > m$. We
show that there is a qualitative difference between cases with $1 < q^2/m^2
\lesssim 9/8$ and cases with $q^2/m^2 \gtrsim 9/8$. We discuss the necessary
conditions for the well-posedness of the problem, and present results for the
low damped modes in the low $l$ and large $l$ limit. We also consider the
asymptotically highly damped quasinormal modes. We present strong evidence that
such modes are absent in the case of a naked Reissner-Nordstr\"om singularity,
corroborating recent conjectures relating them to classical and quantum
properties of horizons.
|
1206.0037v3
|
2012-06-06
|
Perturbation theory for very long-range potentials
|
Systems with very long-range interactions (that decay at large distances like
$U(r)\sim r^{-l}$ with $l\le d$ where $d$ is the space dimensionality) are
difficult to study by conventional statistical mechanics perturbation methods.
Examples of these systems are gravitational and charged (non-electroneutral).
In this work we propose two alternative methodologies to avoid these
difficulties and capture some of the properties of the original potential. The
first one consists in expressing the original potential in terms of a finite
sum of hard-core Yukawa potentials. In the second one, the potential is
rewritten as a damped potential, using a damping function with a parameter that
controls the range of the interaction. These new potentials, which mimic the
original one, can now be treated by conventional statistical mechanics methods.
|
1206.2211v2
|
2012-06-10
|
Comments on "Plasma oscillations and nonextensive statistics"
|
The paper, authored by J. A. S. Lima et al, was published in Phys. Rev. E in
2000 has discussed the dispersion relation and Landau damping of Langmuir wave
in the context of the nonextensive statistics proposed by Tsallis. It has been
cited by many authors because the dispersion relation in Tsallis formalism
present a good fit to the experimental data when q<1, while the classical
result based on Maxwellian distribution only provides a crude description.
However, the results obtained in this paper are problematic. In this comments
on the paper we shall derive the correct analytic formulas both for the
dispersion relation and Landau damping in Tsallis formalism. We hope that this
comments will be useful in providing the correct results.
|
1206.2345v1
|
2012-06-25
|
Ideal MHD Ballooning modes, shear flow and the stable continuum
|
There is a well established theory of Ballooning modes in a toroidal plasma.
The cornerstone of this is a local eigenvalue lambda on each magnetic surface -
which also depends on the ballooning phase angle k. In stationary plasmas
lambda(k) is required only near its maximum, but in rotating plasmas its
average over k is required. Unfortunately in many case lambda(k) does not exist
for some range of k, because the spectrum there contains only a stable
continuum. This limits the application of the theory, and raises the important
question of whether this "stable interval" gives rise to significant damping.
This question is re-examined using a new, simplified, model - which leads to
the conclusion that there is no appreciable damping at small shear flow. In
particular, therefore, a small shear flow should not affect Ballooning mode
stability boundaries.
|
1206.5855v2
|
2012-06-26
|
A Numerical Perspective on Hartree-Fock-Bogoliubov Theory
|
The method of choice for describing attractive quantum systems is
Hartree-Fock-Bogoliubov (HFB) theory. This is a nonlinear model which allows
for the description of pairing effects, the main explanation for the
superconductivity of certain materials at very low temperature. This paper is
the first study of Hartree-Fock-Bogoliubov theory from the point of view of
numerical analysis. We start by discussing its proper discretization and then
analyze the convergence of the simple fixed point (Roothaan) algorithm.
Following works by Canc\`es, Le Bris and Levitt for electrons in atoms and
molecules, we show that this algorithm either converges to a solution of the
equation, or oscillates between two states, none of them being a solution to
the HFB equations. We also adapt the Optimal Damping Algorithm of Canc\`es and
Le Bris to the HFB setting and we analyze it. The last part of the paper is
devoted to numerical experiments. We consider a purely gravitational system and
numerically discover that pairing always occurs. We then examine a simplified
model for nucleons, with an effective interaction similar to what is often used
in nuclear physics. In both cases we discuss the importance of using a damping
algorithm.
|
1206.6081v1
|
2012-06-27
|
Dynamics of zonal flow-like structures in the edge of the TJ-II stellarator
|
The dynamics of fluctuating electric field structures in the edge of the
TJ-II stellarator, that display zonal flow-like traits, is studied. These
structures have been shown to be global and affect particle transport
dynamically [J.A. Alonso et al., Nucl. Fus. 52 063010 (2012)]. In this article
we discuss possible drive (Reynolds stress) and damping (Neoclassical
viscosity, geodesic transfer) mechanisms for the associated ExB velocity. We
show that: (a) while the observed turbulence-driven forces can provide the
necessary perpendicular acceleration, a causal relation could not be firmly
established, possibly because of the locality of the Reynolds stress
measurements, (b) the calculated neoclassical viscosity and damping times are
comparable to the observed zonal flow relaxation times, and (c) although an
accompanying density modulation is observed to be associated to the zonal flow,
it is not consistent with the excitation of pressure side-bands, like those
present in geodesic acoustic oscillations, caused by the compression of the ExB
flow field.
|
1206.6191v1
|
2012-07-13
|
Decay of capillary wave turbulence
|
We report on the observation of freely decaying capillary wave turbulence on
the surface of a fluid. The capillary wave turbulence spectrum decay is found
to be self-similar in time with the same power law exponent than the one found
in the stationary regime, in agreement with weak turbulence predictions. The
amplitude of all Fourier modes are found to decrease exponentially with time at
the same damping rate. The longest wavelengths involved in the system are shown
to be damped by viscous surface boundary layer. These long waves play the role
of an energy source during the decay that sustains nonlinear interactions to
keep capillary waves in a wave turbulent state.
|
1207.3228v1
|
2012-07-17
|
Holographic Superfluids and the Dynamics of Symmetry Breaking
|
We explore the far from equilibrium response of a holographic superfluid
using the AdS/CFT correspondence. We establish the dynamical phase diagram
corresponding to quantum quenches of the order parameter source field. We find
three distinct regimes of behaviour that are related to the spectrum of black
hole quasi-normal modes. These correspond to damped oscillations of the order
parameter, and over-damped approaches to the superfluid and normal states. The
presence of three regimes, which includes an emergent dynamical temperature
scale, is argued to occur more generally in time-reversal invariant systems
that display continuous symmetry breaking.
|
1207.4194v2
|
2012-07-26
|
Generic Mechanism of Optimal Energy Transfer Efficiency: A Scaling Theory of the Mean First Passage Time in Exciton Systems
|
An asymptotic scaling theory is presented using the conceptual basis of
trapping-free subspace (i.e., orthogonal subspace) to establish the generic
mechanism of optimal efficiency of excitation energy transfer (EET) in
light-harvesting systems. Analogous to Kramers' turnover in classical rate
theory, the enhanced efficiency in the weak damping limit and the suppressed
efficiency in the strong damping limit define two asymptotic scaling regimes,
which are interpolated to predict the functional form of optimal efficiency of
the trapping-free subspace. In the presence of static disorder, the scaling law
of transfer time with respect to dephasing rate changes from linear to square
root, suggesting a weaker dependence on the environment. Though formulated in
the context of EET, the analysis and conclusions apply in general to open
quantum processes, including electron transfer, fluorescence emission, and heat
conduction.
|
1207.6197v1
|
2012-07-27
|
Dissipative and Non-dissipative Single-Qubit Channels: Dynamics and Geometry
|
Single-qubit channels are studied under two broad classes: amplitude damping
channels and generalized depolarizing channels. A canonical derivation of the
Kraus representation of the former, via the Choi isomorphism is presented for
the general case of a system's interaction with a squeezed thermal bath. This
isomorphism is also used to characterize the difference in the geometry and
rank of these channel classes. Under the isomorphism, the degree of decoherence
is quantified according to the mixedness or separability of the Choi matrix.
Whereas the latter channels form a 3-simplex, the former channels do not form a
convex set as seen from an ab initio perspective. Further, where the rank of
generalized depolarizing channels can be any positive integer upto 4, that of
amplitude damping ones is either 2 or 4. Various channel performance parameters
are used to bring out the different influences of temperature and squeezing in
dissipative channels. In particular, a noise range is identified where the
distinguishability of states improves inspite of increasing decoherence due to
environmental squeezing.
|
1207.6519v1
|
2012-07-27
|
Phonon Effects on Population Inversion in Quantum Dots: Resonant, Detuned and Frequency-swept Excitations
|
The effect of acoustic phonons on different light-induced excitations of a
semiconductor quantum dot is investigated. Resonant excitation of the quantum
dot leads to Rabi oscillations, which are damped due to the phonon interaction.
When the excitation frequency is detuned, an occupation can only occur due to
phonon absorption or emission processes. For frequency-swept excitations a
population inversion is achieved through adiabatic rapid passage, but the
inversion is also damped by phonons. For all three scenarios the influence of
the phonons depends non-monotonically on the pulse area.
|
1207.6660v2
|
2012-07-28
|
Ultrafast optical control of magnetization in EuO thin films
|
All-optical pump-probe detection of magnetization precession has been
performed for ferromagnetic EuO thin films at 10 K. We demonstrate that the
circularly-polarized light can be used to control the magnetization precession
on an ultrafast time scale. This takes place within the 100 fs duration of a
single laser pulse, through combined contribution from two nonthermal
photomagnetic effects, i.e., enhancement of the magnetization and an inverse
Faraday effect. From the magnetic field dependences of the frequency and the
Gilbert damping parameter, the intrinsic Gilbert damping coefficient is
evaluated to be {\alpha} \approx 3\times10^-3.
|
1207.6686v1
|
2012-08-07
|
Observation of Coherent Helimagnons and Gilbert damping in an Itinerant Magnet
|
We study the magnetic excitations of itinerant helimagnets by applying
time-resolved optical spectroscopy to Fe0.8Co0.2Si. Optically excited
oscillations of the magnetization in the helical state are found to disperse to
lower frequency as the applied magnetic field is increased; the fingerprint of
collective modes unique to helimagnets, known as helimagnons. The use of
time-resolved spectroscopy allows us to address the fundamental magnetic
relaxation processes by directly measuring the Gilbert damping, revealing the
versatility of spin dynamics in chiral magnets. (*These authors contributed
equally to this work)
|
1208.1462v1
|
2012-08-08
|
Mechanism of collisionless sound damping in dilute Bose gas with condensate
|
We develop a microscopic theory of sound damping due to Landau mechanism in
dilute gas with Bose condensate. It is based on the coupled evolution equations
of the parameters describing the system. These equations have been derived in
earlier works within a microscopic approach which employs the
Peletminskii-Yatsenko reduced description method for quantum many-particle
systems and Bogoliubov model for a weakly nonideal Bose gas with a separated
condensate. The dispersion equations for sound oscillations were obtained by
linearization of the mentioned evolution equations in the collisionless
approximation. They were analyzed both analytically and numerically. The
expressions for sound speed and decrement rate were obtained in high and low
temperature limiting cases. We have shown that at low temperature the
dependence of the obtained quantities on temperature significantly differs from
those obtained by other authors in the semi-phenomenological approaches.
Possible effects connected with non-analytic temperature dependence of
dispersion characteristics of the system were also indicated.
|
1208.1653v2
|
2012-08-17
|
Detection of domain wall eigenfrequency in infinity-shaped magnetic nanostructures
|
The dynamics of a magnetic infinity-shaped nanostructure has been
experimentally studied by two different techniques such as the sinusoidal
resonance excitation and the damped short pulse excitation to measure the
eigenfrequency of domain walls. Direct observation of the magnetic domain wall
nucleation has been measured in the frequency domain. Electrical measurements
of the domain wall dynamics in the frequency domain reveal the existence of
multi-eigenmodes for large excitation amplitudes. The time-resolved
measurements show that the frequency of the damped gyration is similar to that
of the frequency domain and coexistence of spin wave excitations.
|
1208.3527v1
|
2012-08-21
|
Stress field and spin axis relaxation for inelastic triaxial ellipsoids
|
A compact formula for the stress tensor inside a self-gravitating, triaxial
ellipsoid in an arbitrary rotation state is given. It contains no singularity
in the incompressible medium limit. The stress tensor and the quality factor
model are used to derive a solution for the energy dissipation resulting in the
damping (short axis mode) or excitation (long axis) of wobbling. In the limit
of an ellipsoid of revolution, we compare our solution with earlier ones and
show that, with appropriate corrections, the differences in damping times
estimates are much smaller than it has been claimed.
This version implements corrections of misprints found in the MNRAS published
text.
|
1208.4283v2
|
2012-08-22
|
On unorthodox solutions of the Bloch equations
|
A systematic, rigorous, and complete investigation of the Bloch equations in
time-harmonic driving classical field is performed. Our treatment is unique in
that it takes full advantage of the partial fraction decomposition over real
number field, which makes it possible to find and classify all analytic
solutions. Torrey's analytic solution in the form of exponentially damped
harmonic oscillations [Phys. Rev. {\bf 76}, 1059 (1949)] is found to dominate
the parameter space, which justifies its use at numerous occasions in magnetic
resonance and in quantum optics of atoms, molecules, and quantum dots. The
unorthodox solutions of the Bloch equations, which do not have the form of
exponentially damped harmonic oscillations, are confined to rather small
detunings $\delta^2\lesssim (\gamma-\gamma_t)^2/27$ and small field strengths
$\Omega^2\lesssim 8 (\gamma-\gamma_t)^2/27$, where $\gamma$ and $\gamma_t$
describe decay rates of the excited state (the total population relaxation
rate) and of the coherence, respectively. The unorthodox solutions being
readily accessible experimentally are characterized by rather featureless time
dependence.
|
1208.5736v1
|
2012-08-29
|
Optically mediated nonlinear quantum optomechanics
|
We consider theoretically the optomechanical interaction of several
mechanical modes with a single quantized cavity field mode for linear and
quadratic coupling. We focus specifically on situations where the optical
dissipation is the dominant source of damping, in which case the optical field
can be adiabatically eliminated, resulting in effective multimode interactions
between the mechanical modes. In the case of linear coupling, the coherent
contribution to the interaction can be exploited e.g. in quantum state swapping
protocols, while the incoherent part leads to significant modifications of cold
damping or amplification from the single-mode situation. Quadratic coupling can
result in a wealth of possible effective interactions including the analogs of
second-harmonic generation and four-wave mixing in nonlinear optics, with
specific forms depending sensitively on the sign of the coupling. The
cavity-mediated mechanical interaction of two modes is investigated in two
limiting cases, the resolved sideband and the Doppler regime. As an
illustrative application of the formal analysis we discuss in some detail a
two-mode system where a Bose-Einstein condensate is optomechanically linearly
coupled to the moving end mirror of a Fabry-P\'erot cavity.
|
1208.5821v1
|
2012-08-31
|
Spectrums of Black Hole in de Sitter Spacetime with Highly Damped Quasinormal Modes: High Overtone Case
|
Motivated by recent physical interpretation on quasinormal modes presented by
Maggiore, the adiabatic quantity method given by Kunstatter is used to
calculate the spectrums of a non-extremal Schwarzschild de Sitter black hole in
this paper, as well as electrically charged case. According to highly damped
Konoplya and Zhidenko's numerical observational results for high overtone
modes\cite{Konoplya}, we found that the asymptotic non-flat spacetime structure
leads two interesting facts as followings: (i) near inner event horizon, the
area and entropy spectrums, which are given by $A_{en} = 8 n_1 \pi \hbar$,
$S_{en} = 2\pi n_1\hbar$, are equally spaced accurately. (ii) However, near
outer cosmological horizon the spectrums, which are in the form of $A_{cn} = 16
n_2 \pi \hbar - \sqrt{\frac{48\pi}{\Lambda}A_{cn} - 3 A_{cn}^2}$, $S_{cn} = 4
\pi n_2 \hbar - \sqrt{\frac{3\pi}{\Lambda}A_{cn} - 3/16 A_{cn}^2}$, are not
markedly equidistant. Finally, we also discuss the electrically charged case
and find the black holes in de Sitter spacetime have similar quantization
behavior no matter with or without charge.
|
1208.6485v1
|
2012-09-10
|
Rapid ramps across the BEC-BCS crossover: a novel route to measuring the superfluid gap
|
We investigate the response of superfluid Fermi gases to rapid changes of the
three-dimensional s-wave scattering length a by solving the time-dependent
Bogoliubov-de Gennes equations. In general the magnitude of the order parameter
|\Delta| performs oscillations, which are sometimes called the "Higgs" mode,
with the angular frequency 2 \Delta_{gap}/ \hbar, where \Delta_{gap} is the gap
in the spectrum of fermionic excitations. Firstly, we excite the oscillations
with a linear ramp of 1/a and study the evolution of |\Delta|. Secondly, we
continously drive the system with a sinusoidal modulation of 1/a. In the first
case, the oscillations in |\Delta| damp according to a power law. In the second
case, the continued driving causes revivals in the oscillations. In both cases,
the excitation of the oscillations causes a reduction in the time-averaged
value of |\Delta|. We propose two experimental protocols, based around the two
approaches, to measure the frequency and damping of the oscillations, and hence
\Delta_{gap}.
|
1209.2025v1
|
2012-09-12
|
Loss of Landau Damping for Bunch Oscillations
|
Conditions for the existence, uniqueness and stability of self-consistent
bunch steady states are considered. For the existence and uniqueness problems,
simple algebraic criteria are derived for both the action and Hamiltonian
domain distributions. For the stability problem, van Kampen theory is used. The
onset of a discrete van Kampen mode means the emergence of a coherent mode
without any Landau damping; thus, even a tiny couple-bunch or multi-turn wake
is sufficient to drive the instability. The method presented here assumes an
arbitrary impedance, RF shape, and beam distribution function. Available areas
on the intensity-emittance plane are shown for resistive wall wake and single
harmonic, bunch shortening and bunch lengthening RF configurations. Thresholds
calculated for the Tevatron parameters and impedance model are in agreement
with the observations. These thresholds are found to be extremely sensitive to
the small-argument behaviour of the bunch distribution function. Accordingly, a
method to increase the LLD threshold is suggested. This article summarizes and
extends recent author's publications.
|
1209.2715v1
|
2012-09-17
|
Generalized fluctuation-dissipation relation and statistics for the equilibrium of a system with conformation dependent damping
|
Liouville's theorem, based on the Hamiltonian flow (micro-canonical ensemble)
for a many particle system, indicates that the (stationary) equilibrium
probability distribution is a function of the Hamiltonian. A canonical ensemble
corresponds to a micro-canonical one at thermodynamic limit. On the contrary,
the dynamics of a single Brownian particle (BP) being explicitly
non-Hamiltonian with a force and damping term in it and at the other extreme to
thermodynamic limit admits the Maxwell-distribution (MD) for its velocity and
Boltmann-distribution (BD) for positions (when in a potential). This is due to
the fluctuation-dissipation relation (FDR), as was first introduced by
Einstein, which forces the Maxwell distribution to the Brownian particles. For
a structureless BP, that, this theory works is an experimentally verified fact
over a century now. Considering a structured Brownian particle we will show
that the BD and MD fails to ensure equilibrium. We will derive a generalized
FDR on the basis of the demand of zero current on inhomogeneous space. Our FDR
and resulting generalized equilibrium distributions recover the standard ones
at appropriate limits.
|
1209.3654v3
|
2012-09-17
|
Nonlinear emission of spin-wave caustics from an edge mode of a micro-structured Co2Mn0.6Fe0.4Si waveguide
|
Magnetic Heusler materials with very low Gilbert damping are expected to show
novel magnonic transport phenomena. We report nonlinear generation of higher
harmonics leading to the emission of caustic spin-wave beams in a low-damping,
micro-structured Co2Mn0.6Fe0.4Si Heusler waveguide. The source for the higher
harmonic generation is a localized edge mode formed by the strongly
inhomogeneous field distribution at the edges of the spin-wave waveguide. The
radiation characteristics of the propagating caustic waves observed at twice
and three times the excitation frequency are described by an analytical
calculation based on the anisotropic dispersion of spin waves in a magnetic
thin film.
|
1209.3669v2
|
2012-09-20
|
High Resolution BPM Upgrade for the ATF Damping Ring at KEK
|
A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility
(ATF) damping ring has been accomplished, carried out by a KEK/FNAL/SLAC
collaboration under the umbrella of the global ILC R&D effort. The upgrade
consists of a high resolution, high reproducibility read-out system, based on
analog and processing, and also implements a new automatic gain error
correction schema. The technical concept and realization as well as results of
beam studies are presented.
|
1209.4569v1
|
2012-09-23
|
Ion Landau Damping on Drift Tearing Modes
|
Kinetic treatments of drift-tearing modes that match an inner resonant layer
solution to an external MHD region solution, characterised by
$\Delta^{\prime}$, fail to properly match the ideal MHD boundary condition on
the parallel electric field, $E_{\parallel}.$ In this paper we demonstrate how
consideration of ion sound and ion Landau damping effects achieves this and
place the theory on a firm footing. As a consequence, these effects contribute
quite significantly to the critical value of $\Delta^{\prime}$ for instability
of drift-tearing modes and play a key role in determining the minimum value for
this threshold.
|
1209.5054v3
|
2012-09-26
|
Inverse Energy Cascade in Forced 2D Quantum Turbulence
|
We demonstrate an inverse energy cascade in a minimal model of forced 2D
quantum vortex turbulence. We simulate the Gross-Pitaevskii equation for a
moving superfluid subject to forcing by a stationary grid of obstacle
potentials, and damping by a stationary thermal cloud. The forcing injects
large amounts of vortex energy into the system at the scale of a few healing
lengths. A regime of forcing and damping is identified where vortex energy is
efficiently transported to large length scales via an inverse energy cascade
associated with the growth of clusters of same-circulation vortices, a
Kolmogorov scaling law in the kinetic energy spectrum over a substantial
inertial range, and spectral condensation of kinetic energy at the scale of the
system size. Our results provide clear evidence that the inverse energy cascade
phenomenon, previously observed in a diverse range of classical systems, can
also occur in quantum fluids.
|
1209.5824v2
|
2012-09-27
|
Comparison of non-Markovianity criteria in a qubit system under random external fields
|
We give the map representing the evolution of a qubit under the action of
non-dissipative random external fields. From this map we construct the
corresponding master equation that in turn allows us to phenomenologically
introduce population damping of the qubit system. We then compare, in this
system, the time-regions when non-Markovianity is present on the basis of
different criteria both for the non-dissipative and dissipative case. We show
that the adopted criteria agree both in the non-dissipative case and in the
presence of population damping.
|
1209.6331v2
|
2012-10-01
|
Gravitational Coleman-Weinberg Potential and It's Finite Temperature Counterpart
|
Coleman-Weinberg (CW) phenomena for the case of gravitons minimally coupled
to massless scalar field is studied. The one loop effect completely vanishes if
there is no self interaction term present in the matter sector. The one loop
effective potential is shown to develop an instability in the form of acquiring
an imaginary part, which can be traced to the tachyonic pole in the graviton
propagator. The finite temperature counterpart of this CW potential is computed
to study the behaviour of the potential in the high and low temperature regimes
with respect to the typical energy scale of the theory. Finite temperature
contribution to the imaginary part of gravitational CW potential exhibits a
damped oscillatory behaviour; all thermal effects are damped out as the
temperature vanishes, consistent with the zero-temperature result. Possibility
of symmetry restoration at high temperature is also depicted.
|
1210.0497v4
|
2012-10-09
|
Analytic approximate seismology of propagating MHD waves in the solar corona
|
Observations show that propagating magnetohydrodynamic (MHD) waves are
ubiquitous in the solar atmosphere. The technique of MHD seismology uses the
wave observations combined with MHD wave theory to indirectly infer physical
parameters of the solar atmospheric plasma and magnetic field. Here we present
an analytical seismological inversion scheme for propagating MHD waves. This
scheme uses in a consistent manner the observational information on wavelengths
and damping lengths, along with observed values of periods or phase velocities,
and is based on approximate asymptotic expressions for the theoretical values
of wavelengths and damping lengths. The applicability of the inversion scheme
is discussed and an example is given.
|
1210.2689v1
|
2012-10-12
|
Reversal of magnetization of a single-domain magnetic particle by the ac field of time-dependent frequency
|
We report numerical and analytical studies of the reversal of the magnetic
moment of a single-domain magnetic particle by a circularly polarized ac field
of time-dependent frequency. For the time-linear frequency sweep, the phase
diagrams are computed that illustrate the dependence of the reversal on the
frequency sweep rate v, the amplitude of the ac field h, the magnetic
anisotropy field d, and the damping parameter alpha. It is shown that the most
efficient magnetization reversal requires a non-linear time dependence of the
frequency, omega(t), for which an exact analytical formula is derived with
account of damping. The necessary condition of the reversal is h > alpha d.
Implementation of a small-scale magnetization reversal is proposed in which a
nanomagnet is electromagnetically coupled to two weak superconducting links
controlled by the voltage. Dynamics of such a system is analyzed with account
of the back effect of the magnet on the superconducting links.
|
1210.3530v1
|
2012-10-18
|
SDO/AIA Observations of Large-Amplitude Longitudinal Oscillations in a Solar Filament
|
We present the first \emph{Solar Dynamics Observatory}/Atmospheric Imaging
Assembly observations of the large-amplitude longitudinal (LAL) oscillations in
the south and north parts (SP and NP) of a solar filament on 2012 April 7. Both
oscillations are triggered by flare activities close to the filament. The
period varies with filamentary threads, ranging from 44 to 67 min. The
oscillations of different threads are out of phase, and their velocity
amplitudes vary from 30 to 60 km s$^{-1}$, with a maximum displacement of about
25 Mm. The oscillations of the SP repeat for about 4 cycles without any
significant damping and then a nearby C2.4 flare causes the transition from the
LAL oscillations of the filament to its later eruption. The filament eruption
is also associated with a coronal mass ejection and a B6.8 flare. However, the
oscillations of the NP damp with time and die out at last. Our observations
show that the activated part of the SP repeatedly shows a helical motion. This
indicates that the magnetic structure of the filament is possibly modified
during this process. We suggest that the restoring force is the coupling of the
magnetic tension and gravity.
|
1210.5110v1
|
2012-10-31
|
The Kerr medium as an {\sf SU(2)} system
|
The Kerr medium in the presence of damping and associated with SU(1,1)
symmetry, is solved using the techniques of Thermo field Dynamics (TFD).These
TFD techniques, well studied earlier (Chaturvedi and Srinivasan, 1991), help us
to exactly solve the Kerr medium as a spin damped system associated with SU(2)
symmetry. Using TFD, the association with SU(2) is exploited to express the
dynamics of the system as a Schrodinger-like equation, whose solution is
obtained using the appropriate disentanglement theorem. These considerations
are extended to a system with multi-mode coupled nonlinear oscillators."
|
1210.8240v1
|
2012-11-02
|
Dynamic Spin Injection into Chemical Vapor Deposited Graphene
|
We demonstrate dynamic spin injection into chemical vapor deposition (CVD)
grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic
resonance measurements at room temperature reveal a strong enhancement of the
Gilbert damping at the Py/graphene interface, exceeding that observed in even
Py/platinum interfaces. Similar results are also shown on Co/graphene layers.
This enhancement in the Gilbert damping is understood as the consequence of
spin pumping at the interface driven by magnetization dynamics. Our
observations suggest a strong enhancement of spin-orbit coupling in CVD
graphene, in agreement with earlier spin valve measurements.
|
1211.0492v1
|
2012-12-06
|
A simple and effective Verlet-type algorithm for simulating Langevin dynamics
|
We present a revision to the well known Stormer-Verlet algorithm for
simulating second order differential equations. The revision addresses the
inclusion of linear friction with associated stochastic noise, and we
analytically demonstrate that the new algorithm correctly reproduces diffusive
behavior of a particle in a flat potential. For a harmonic oscillator, our
algorithm provides the exact Boltzmann distribution for any value of damping,
frequency, and time step for both underdamped and over damped behavior within
the usual the stability limit of the Verlet algorithm. Given the structure and
simplicity of the method we conclude this approach can trivially be adapted for
contemporary applications, including molecular dynamics with extensions such as
molecular constraints.
|
1212.1244v4
|
2012-12-10
|
Shear viscosity and the r-mode instability window in superfluid neutron stars
|
We analyze how recent computations of the shear viscosity $\eta$ in the core
of superfluid neutron stars affect the r-mode instability window. We first
analyze the contribution of superfluid phonons to the viscosity, both in their
hydrodynamical and ballistic regime. We also consider the recent computation of
$\eta$ arising from the collisions of electrons with electrons and protons by
Shternin and Yakovlev, and discuss how the interactions among superfluid
phonons and electrons might contribute to the shear viscosity. For assessing
the r-mode instability window we compare the shear viscosity due to phonons in
the hydrodynamical regime with respect to the shear viscosity due to electron
collisions. Only at high temperatures the superfluid phonon contribution to
$\eta$ starts to dominate the process of r-mode damping. While our results for
the instability window are preliminary, as other dissipative processes should
be taken into account as well, they differ from previous evaluations of the
r-mode damping due to the shear viscosity in superfluid neutron stars.
|
1212.2075v2
|
2012-12-12
|
The operator sum-difference representation for quantum maps: application to the two-qubit amplitude damping channel
|
On account of the Abel-Galois no-go theorem for the algebraic solution to
quintic and higher order polynomials, the eigenvalue problem and the associated
characteristic equation for a general noise dynamics in dimension $d$ via the
Choi-Jamiolkowski approach cannot be solved in general via radicals. We provide
a way around this impasse by decomposing the Choi matrix into simpler, not
necessarily positive, Hermitian operators that are diagonalizable via radicals,
which yield a set of `positive' and `negative' Kraus operators. The price to
pay is that the sufficient number of Kraus operators is $d^4$ instead of $d^2$,
sufficient in the Kraus representation. We consider various applications of the
formalism: the Kraus repesentation of the 2-qubit amplitude damping channel,
the noise resulting from a 2-qubit system interacting dissipatively with a
vacuum bath; defining the maximally dephasing and purely dephasing components
of the channel in the new representation, and studying their entanglement
breaking and broadcast properties.
|
1212.2780v1
|
2012-12-13
|
Efficiency improvement of the frequency-domain BEM for rapid transient elastodynamic analysis
|
The frequency-domain fast boundary element method (BEM) combined with the
exponential window technique leads to an efficient yet simple method for
elastodynamic analysis. In this paper, the efficiency of this method is further
enhanced by three strategies. Firstly, we propose to use exponential window
with large damping parameter to improve the conditioning of the BEM matrices.
Secondly, the frequency domain windowing technique is introduced to alleviate
the severe Gibbs oscillations in time-domain responses caused by large damping
parameters. Thirdly, a solution extrapolation scheme is applied to obtain
better initial guesses for solving the sequential linear systems in the
frequency domain. Numerical results of three typical examples with the problem
size up to 0.7 million unknowns clearly show that the first and third
strategies can significantly reduce the computational time. The second strategy
can effectively eliminate the Gibbs oscillations and result in accurate
time-domain responses.
|
1212.3032v2
|
2012-12-16
|
Decay of the solution to the bipolar Euler-Poisson system with damping in $\mathbb{R}^3$
|
We construct the global solution to the Cauchy's problem of the bipolar
Euler-Poisson equations with damping in $\mathbb{R}^3$ when $H^3$ norm of the
initial data is small. If further, the $\dot{H}^{-s}$ norm ($0\leq s<3/2)$ or
$\dot{B}_{2,\infty}^{-s}$ norm ($0<s\leq3/2$) of the initial data is bounded,
we give the optimal decay rates of the solution. As a byproduct, the decay
results of the $L^p-L^2$ ($1\leq p\leq2$) type hold without the smallness of
the $L^p$ norm of the initial data. In particular, we deduce that
$\|\nabla^k(\rho_1-\rho_2)\|_{L^2} \sim(1+t)^{-5/4-\frac{k}{2}}$ and
$\|\nabla^k(\rho_i-\bar{\rho},u_i,\nabla\phi)\|_{L^2}
\sim(1+t)^{-3/4-\frac{k}{2}}$. We improve the decay results in Li and Yang
\cite{Li3}(\emph{J.Differential Equations} 252(2012), 768-791), where they
showed the decay rates as $\|\nabla^k(\rho_i-\bar{\rho})\|_{L^2}
\sim(1+t)^{-3/4-\frac{k}{2}}$ and $\|\nabla^k(u_i,\nabla\phi)\|_{L^2}
\sim(1+t)^{-1/4-\frac{k}{2}}$, when the $H^3\cap L^1$ norm of the initial data
is small. Our analysis is motivated by the technique developed recently in Guo
and Wang \cite{Guo}(\emph{Comm. Partial Differential Equations} 37(2012),
2165-2208) with some modifications.
|
1212.3754v2
|
2012-12-24
|
Effects of kappa distribution function on Landau damping in electrostatic Vlasov simulation
|
Effects of non-thermal high-energy electrons on Langmuir wave-particle
interaction are investigated by an initial value approach. A Vlasov-Poisson
simulation is employed which is based on the splitting scheme by Cheng and
Knorr [Cheng, C.Z. and G. Knorr, 1976: J. Comput. Phys. 22, 330-351.]. The
kappa distribution function is taken as an example of non-thermal electrons.
The modification is manifested as an increase in the Landau damping rate and a
decrease in the real frequency for a long wavelength limit. A part of the
analyses by the modified plasma dispersion function [Summers, D. and
R.M.Thorne, 1991: Phys. Fluids, B 3, 1835-1847.] is reproduced for $\kappa =
2,3$ and 6. The dispersion relation from the initial value simulation and the
plasma dispersion function compare favorably.
|
1212.5872v1
|
2012-12-26
|
Anomalous dynamic back-action in interferometers
|
We analyze the dynamic optomechanical back-action in signal-recycled
Michelson and Michelson-Sagnac interferometers that are operated off dark port.
We show that in this case --- and in contrast to the well-studied canonical
form of dynamic back-action on dark port --- optical damping in a
Michelson-Sagnac interferometer acquires a non-zero value on cavity resonance,
and additional stability/instability regions on either side of the resonance,
revealing new regimes of cooling/heating of micromechanical oscillators. In a
free-mass Michelson interferometer for a certain region of parameters we
predict a stable single-carrier optical spring (positive spring and positive
damping), which can be utilized for the reduction of quantum noise in
future-generation gravitational-wave detectors.
|
1212.6242v2
|
2013-01-01
|
A scattering approach to some aspects of the Schwarzschild Black Hole
|
In this paper, we consider a massless field, with spin j, in interaction with
a Schwarzschild black hole in four dimensions, focusing mainly our study on the
s-wave scattering. First, using a Fourier analysis, we show that one can have a
simple and natural description of the Physics near the event horizon without
using any conformal field approaches. Then, within the same "scattering
picture", we derive analytically the imaginary part of the highly damped
quasinormal complex frequencies and, as a natural consequence of our analysis,
we show that thermal effects and in particular Hawking radiation, can be
understood through the scattering of an ingoing s-wave by the non null barrier
of the Regge-Wheeler potential associated with the Schwarzschild black hole.
Finally, with the help of the well-known expression of the highly damped
quasinormal complex frequencies, we propose a heuristic extension of the
"tripled Pauli statistics" suggested by Motl, some years ago.
|
1301.0108v1
|
2013-01-02
|
Memory models of adaptive behaviour
|
Adaptive response to a varying environment is a common feature of biological
organisms. Reproducing such features in electronic systems and circuits is of
great importance for a variety of applications. Here, we consider memory models
inspired by an intriguing ability of slime molds to both memorize the period of
temperature and humidity variations, and anticipate the next variations to
come, when appropriately trained. Effective circuit models of such behavior are
designed using i) a set of LC-contours with memristive damping, and ii) a
single memcapacitive system-based adaptive contour with memristive damping. We
consider these two approaches in detail by comparing their results and
predictions. Finally, possible biological experiments that would discriminate
between the models are discussed. In this work, we also introduce an effective
description of certain memory circuit elements.
|
1301.0209v2
|
2013-01-03
|
Collective modes of a two-dimensional spin-1/2 Fermi gas in a harmonic trap
|
We derive analytical expressions for the frequency and damping of the lowest
collective modes of a two-dimensional Fermi gas using kinetic theory. For
strong coupling, we furthermore show that pairing correlations overcompensate
the effects of Pauli blocking on the collision rate for a large range of
temperatures, resulting in a rate which is larger than that of a classical gas.
Our results agree well with experimental data, and they recover the observed
cross-over from collisionless to hydrodynamic behaviour with increasing
coupling for the quadruple mode. Finally, we show that a trap anisotropy within
the experimental bounds results in a damping of the breathing mode which is
comparable to what is observed, even for a scale invariant system.
|
1301.0358v2
|
2013-01-09
|
Synthesis of new neutron-rich heavy nuclei: An experimentalist's view
|
I attempt to experimentally evaluate the prospects of synthesizing new
neutron- rich superheavy nuclei. I consider three possible synthetic paths to
neutron- rich superheavy nuclei: (a) the use of neutron-rich radioactive beams.
(b) the use of damped collisions and (c) the use of multi-nucleon transfer
reactions. I consider the prospects of synthesizing new n-rich isotopes of
Rf-Bh using light n-rich radioactive beams and targeted beams from ReA3, FRIB
and SPIRAL2. For the damped collision path, I present the results of a study of
a surrogate reaction, 160Gd + 186W. These data indicate the formation of Au
(trans-target) fragments and the depletion of yields of target-like fragments
by fission and fragment emission. The data are compared to predictions of
Zagrebaev and Greiner. For the multi-nucleon transfer reactions, the results of
a study of the 136Xe + 208Pb reaction are discussed. I consider the possibility
of multi-nucleon transfer reactions with radioactive beams.
|
1301.1759v1
|
2013-01-10
|
First-principles calculation of the Gilbert damping parameter via the linear response formalism with application to magnetic transition-metals and alloys
|
A method for the calculations of the Gilbert damping parameter $\alpha$ is
presented, which based on the linear response formalism, has been implemented
within the fully relativistic Korringa-Kohn-Rostoker band structure method in
combination with the coherent potential approximation alloy theory. To account
for thermal displacements of atoms as a scattering mechanism, an alloy-analogy
model is introduced. This allows the determination of $\alpha$ for various
types of materials, such as elemental magnetic systems and ordered magnetic
compounds at finite temperature, as well as for disordered magnetic alloys at
$T = 0$ K and above. The effects of spin-orbit coupling, chemical and
temperature induced structural disorder are analyzed. Calculations have been
performed for the 3$d$ transition-metals bcc Fe, hcp Co, and fcc Ni, their
binary alloys bcc Fe$_{1-x}$Co$_{x}$, fcc Ni$_{1-x}$Fe$_x$, fcc
Ni$_{1-x}$Co$_x$ and bcc Fe$_{1-x}$V$_{x}$, and for 5d impurities in
transition-metal alloys. All results are in satisfying agreement with
experiment.
|
1301.2114v1
|
2013-01-13
|
Entanglement dynamics of non-inertial observers in a correlated environment
|
Effect of decoherence and correlated noise on the entanglement of X-type
state of the Dirac fields in the non-inertial frame is investigated. A two
qubit X-state is considered to be shared between the partners where Alice is in
inertial frame and Rob in an accelerated frame. The concurrence is used to
quantify the entanglement of the X-state system influenced by time correlated
amplitude damping, depolarizing and bit flip channels. It is seen that
amplitude damping and bit flip channels heavily influence the entanglement of
the system as compared to the depolarizing channel. It is found possible to
avoid entanglement sudden death (ESD) for all the channels under consideration
for {\mu}>0.75 for any type of initial state. No ESD behaviour is seen for
depolarizing channel in the presence of correlated noise for entire range of
decoherence parameter p and Rob's acceleration r. It is also seen that the
effect of environment is much stronger than that of acceleration of the
accelerated partner. Furthermore, it is investigated that correlated noise
compensates the loss of entanglement caused by the Unruh effect.
|
1301.2759v1
|
2013-01-13
|
Decoherence and multipartite entanglement of non-inertial observers
|
Decoherence effect on multipartite entanglement in non-inertial frames is
investigated. GHZ state is considered to be shared between the partners with
one partner in inertial frame whereas the other two in accelerated frames.
One-tangle and {\pi}-tangles are used to quantify the entanglement of the
multipartite system influenced by phase damping and phase flip channels. It is
seen that for phase damping channel, entanglement sudden death (ESD) occurs for
p>0.5 in the infinite acceleration limit. On the other hand, in case of phase
flip channel, ESD behaviour happens around 50% decoherence. It is also seen
that entanglement sudden birth (ESB) does occur in case of phase flip channel.
Furthermore, it is seen that effect of environment on multipartite entanglement
is much stronger than that of the acceleration of non-inertial frames.
|
1301.2765v2
|
2013-01-18
|
Current induced torques and interfacial spin-orbit coupling: Semiclassical Modeling
|
In bilayer nanowires consisting of a ferromagnetic layer and a non-magnetic
layer with strong spin-orbit coupling, currents create torques on the
magnetization beyond those found in simple ferromagnetic nanowires. The
resulting magnetic dynamics appear to require torques that can be separated
into two terms, damping-like and field-like. The damping-like torque is
typically derived from models describing the bulk spin Hall effect and the spin
transfer torque, and the field-like torque is typically derived from a Rashba
model describing interfacial spin-orbit coupling. We derive a model based on
the Boltzmann equation that unifies these approaches. We also consider an
approximation to the Boltzmann equation, the drift-diffusion model, that
qualitatively reproduces the behavior, but quantitatively fails to reproduce
the results. We show that the Boltzmann equation with physically reasonable
parameters can match the torques for any particular sample, but in some cases,
it fails to describe the experimentally observed thickness dependences.
|
1301.4513v1
|
2013-01-25
|
Driven skyrmions and dynamical transitions in chiral magnets
|
We study the dynamics of skyrmions in chiral magnets in the presence of a
spin polarized current. The motion of skyrmions in the ferromagnetic background
excites spin waves and contributes to additional damping. At a large current,
the spin wave spectrum becomes gapless and skyrmions are created dynamically
from the ferromagnetic state. At an even higher current, these skyrmions are
strongly deformed due to the damping and become unstable at a threshold
current, leading to a chiral liquid. We show how skyrmions can be created by
increasing the current in the magnetic spiral state. We then construct a
dynamic phase diagram for a chiral magnet with a current. The instability
transitions between different states can be observed as experimentally clear
signatures in the transport measurements, such as jumps and hysteresis.
|
1301.5963v2
|
2013-02-13
|
Entanglement of Tripartite States with Decoherence in Noninertial frames
|
The one-tangle and {\pi}-tangle are used to quantify the entanglement of a
tripartite GHZ state in noninertial frames when the system interacts with a
noisy environment in the form of phase damping, phase flip and bit flip
channel. It is shown that the two-tangles behave as a closed system. The
one-tangle and {\pi}-tangle have different behaviors in the three channel. In
the case of phase damping channel, depending on the kind of coupling, the
sudden death of both one-tangle and {\pi}-tangle may or may not happen. Whereas
in the case of phase flip channel the sudden death cannot be avoided. The
effect of decoherence may be ignored in the limit of infinite acceleration when
the system interacts with a bit flip channel. Furthermore, a sudden rebirth of
the one-tangle and {\pi}-tangle occur in the case of phase flip channel that
may be delayed when collective coupling is switched on.
|
1302.3005v1
|
2013-02-17
|
Global existence and exponential growth for a viscoelastic wave equation with dynamic boundary conditions
|
The goal of this work is to study a model of the wave equation with dynamic
boundary conditions and a viscoelastic term. First, applying the Faedo-Galerkin
method combined with the fixed point theorem, we show the existence and
uniqueness of a local in time solution. Second, we show that under some
restrictions on the initial data, the solution continues to exist globally in
time. On the other hand, if the interior source dominates the boundary damping,
then the solution is unbounded and grows as an exponential function. In
addition, in the absence of the strong damping, then the solution ceases to
exist and blows up in finite time.
|
1302.4036v1
|
2013-02-22
|
Mixing of blackbodies: Increasing our view of inflation to 17 e-folds with spectral distortions from Silk damping
|
Silk damping in the early Universe, before and during recombination, erases
anisotropies in the cosmic microwave background (CMB) on small scales. This
power, which disappears from anisotropies, appears in the monopole as y-type,
i-type and \mu-type distortions. The observation of the CMB spectral
distortions will thus make available to us the information about the primordial
power spectrum on scales corresponding to the comoving wavenumbers $8< k < 10^4
Mpc^{-1}$ increasing our total view of inflation, when combined with CMB
anisotropies, to span 17 e-folds. These distortions can be understood simply as
mixing of blackbodies of different temperatures and the subsequent
comptonization of the resulting distortions.
|
1302.5633v1
|
2013-02-26
|
Tenfold reduction of Brownian noise in optical interferometry
|
Thermally induced fluctuations impose a fundamental limit on precision
measurement. In optical interferometry, the current bounds of stability and
sensitivity are dictated by the excess mechanical damping of the
high-reflectivity coatings that comprise the cavity end mirrors. Over the
preceding decade, the mechanical loss of these amorphous multilayer reflectors
has at best been reduced by a factor of two. Here we demonstrate a new paradigm
in optical coating technology based on direct-bonded monocrystalline
multilayers, which exhibit both intrinsically low mechanical loss and high
optical quality. Employing these "crystalline coatings" as end mirrors in a
Fabry-P\'erot cavity, we obtain a finesse of 150,000. More importantly, at room
temperature, we observe a thermally-limited noise floor consistent with a
tenfold reduction in mechanical damping when compared with the best dielectric
multilayers. These results pave the way for the next generation of
ultra-sensitive interferometers, as well as for new levels of laser stability.
|
1302.6489v1
|
2013-03-01
|
Quantum error correction and detection: quantitative analysis of a coherent-state amplitude damping code
|
We re-examine a non-Gaussian quantum error correction code designed to
protect optical coherent-state qubits against errors due to an amplitude
damping channel. We improve on a previous result [Phys. Rev. A 81, 062344
(2010)] by providing a tighter upper bound on the performance attained when
considering realistic assumptions which constrain the operation of the gates
employed in the scheme. The quantitative characterization is performed through
measures of fidelity and concurrence, the latter obtained by employing the code
as an entanglement distillation protocol. We find that, when running the code
in fully-deterministic error correction mode, direct transmission can only be
beaten for certain combinations of channel and input state parameters, whereas
in error detection mode, the usage of higher repetition encodings remains
beneficial throughout.
|
1303.0273v2
|
2013-03-04
|
Transverse oscillations in solar spicules induced by propagating Alfvenic pulses
|
The excitation of Alfvenic waves in the solar spicules due to the localized
Alfvenic pulse is investigated. A set of incompressible MHD equations in two
dimensional $x-z$ plane with steady flows and sheared magnetic fields is
solved. Stratification due to gravity and transition region between
chromosphere and corona are taken into account. An initially localized Alfvenic
pulse launched below the transition region can penetrate from transition region
into the corona. We show that the period of transversal oscillations is in
agreement with those observed in spicules. Moreover, it is found that the
excited Alfvenic waves spread during propagation along the spicule length, and
suffer efficient damping of the oscillations amplitude. The damping time of
transverse oscillations elongated with decrease in k_b values.
|
1303.0833v1
|
2013-03-04
|
Tidal damping of the mutual inclination in hierachical systems
|
Hierarchical two-planet systems, in which the inner body's semi-major axis is
between 0.1 and 0.5 AU, usually present high eccentricity values, at least for
one of the orbits. As a result of the formation process, one may expect that
planetary systems with high eccentricities also have high mutual inclinations.
However, here we show that tidal effects combined with gravitational
interactions damp the initial mutual inclination to modest values in timescales
that are shorter than the age of the system. This effect is not a direct
consequence of tides on the orbits, but it results from a secular forcing of
the inner planet's flattening. We then conclude that these hierarchical
planetary systems are unlikely to present very high mutual inclinations, at
least as long as the orbits remain outside the Lidov-Kozai libration areas. The
present study can also be extended to systems of binary stars and to
planet-satellite systems.
|
1303.0864v2
|
2013-03-05
|
Anomalous velocity distributions in active Brownian suspensions
|
Large scale simulations and analytical theory have been combined to obtain
the non-equilibrium velocity distribution, $f(v)$, of randomly accelerated
particles in suspension. The simulations are based on an event-driven
algorithm, generalised to include friction. They reveal strongly anomalous but
largely universal distributions which are independent of volume fraction and
collision processes, which suggests a one-particle model should capture all the
essential features. We have formulated this one-particle model and solved it
analytically in the limit of strong damping, where we find that $f(v)$ decays
as $1/v$ for multiple decades, eventually crossing over to a Gaussian decay for
the largest velocities. Many particle simulations and numerical solution of the
one-particle model agree for all values of the damping.
|
1303.0996v3
|
2013-03-07
|
Quantum critical metals in $d=3+1$
|
We study the problem of disorder-free metals near a continuous Ising nematic
quantum critical point in $d=3+1$ dimensions. We begin with perturbation theory
in the `Yukawa' coupling between the electrons and undamped bosons (nematic
order parameter fluctuations) and show that the perturbation expansion breaks
down below energy scales where the bosons get substantially Landau damped.
Above this scale however, we find a regime in which low-energy fermions obtain
an imaginary self-energy that varies linearly with frequency, realizing the
`marginal Fermi liquid' phenomenology\cite{Varma}. We discuss a large N theory
in which the marginal Fermi liquid behavior is enhanced while the role of
Landau damping is suppressed, and show that quasiparticles obtain a decay rate
parametrically larger than their energy.
|
1303.1587v2
|
2013-03-08
|
Ultra High Energy Electrons Powered by Pulsar Rotation
|
A new mechanism of particle acceleration to ultra high energies, driven by
the rotational slow down of a pulsar (Crab pulsar, for example), is explored.
The rotation, through the time dependent centrifugal force, can very
efficiently excite unstable Langmuir waves in the e-p plasma of the star
magnetosphere via a parametric process. These waves, then, Landau damp on
electrons accelerating them in the process. The net transfer of energy is
optimal when the wave growth and the Landau damping times are comparable and
are both very short compared to the star rotation time. We show, by detailed
calculations, that these are precisely the conditions for the parameters of the
Crab pulsar. This highly efficient route for energy transfer allows the
electrons in the primary beam to be catapulted to multiple TeV ($\sim 100$ TeV)
and even PeV energy domain. It is expected that the proposed mechanism may,
partially, unravel the puzzle of the origin of ultra high energy cosmic ray
electrons.
|
1303.2093v1
|
2013-04-01
|
Fidelity of remote state preparation can be enhanced by local operation
|
Remote state preparation (RSP) is a quantum information protocol which allows
preparing a quantum state at a distant location with the help of a preshared
nonclassical resource state and a classical channel. The efficiency of
successfully doing this task can be represented by the RSP-fidelity of the
resource state. In this paper, we study the influence on the RSP-fidelity by
applying certain local operations on the resource state. We prove that
RSP-fidelity does not increase for any unital local operation. However, for
nonunital local operation, such as local amplitude damping channel, we find
that some resource states can be enhanced to increase the RSP-fidelity. We give
the optimal parameter of symmetric local amplitude damping channel for
enhancing Bell-diagonal resource states. In addition, we show RSP-fidelity can
suddenly change or even vanish at instant under local decoherence.
|
1304.0283v1
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.