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2006-12-07
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On some peculiarities of electric field pulse propagation in electron Maxwellian plasma and its back response
|
In the spirit of continued study of general plasma wave properties we
investigated the boundary problem with the simplest form of electric field
pulse at the edge x=0 of half-infinite uniform plasma slab with Maxwellian
electron distribution function. In the case of longitudinal electric field
pulse its traveling velocity is essentially other than in the case of harmonic
waves; there is also no back response. In the case of transverse field pulse
there takes place the bimodal propagation rate of the non-damping fast pulse
signal and non-damping weak slow sign reversed pulse signals; some very weak
response (echo) arises with a time delay in the near coordinate zone of
formation of the asymptotical regime.
|
0612064v4
|
2007-01-30
|
Charge Fluctuation of Dust Grain and Its Impact on Dusty-Acoustic Wave Damping
|
We consider the influence of dust charge fluctuations on damping of the
dust-ion-acoustic waves. It is assumed that all grains have equal masses but
charges are not constant in time - they may fluctuate in time. The dust charges
are not really independent of the variations in the plasma potentials. All
modes will influence the charging mechanism, and feedback will lead to several
new interesting and unexpected phenomena. The charging of the grains depends on
local plasma characteristics. If the waves disturb these characteristic, then
charging of the grains is affected and the grain charge is modified, with a
resulting feedback on the wave mode. In the case considered here, when the
temperature of electrons is much greater than the temperature of the ions and
the temperature of electrons is not great enough for further ionization of the
ions, we show that attenuation of the acoustic wave depends only on one
phenomenological coefficient
|
0701336v1
|
1996-10-29
|
Bosonic Quantum Codes for Amplitude Damping
|
Traditional quantum error correction involves the redundant encoding of k
quantum bits using n quantum bits to allow the detection and correction of any
t bit error. The smallest general t=1 code requires n=5 for k=1. However, the
dominant error process in a physical system is often well known, thus inviting
the question: given a specific error model, can more efficient codes be
devised? We demonstrate new codes which correct just amplitude damping errors
which allow, for example, a t=1, k=1 code using effectively n=4.6. Our scheme
is based on using bosonic states of photons in a finite number of optical
modes. We present necessary and sufficient conditions for the codes, and
describe construction algorithms, physical implementation, and performance
bounds.
|
9610043v1
|
1997-01-16
|
Cooperative loss and decoherence in quantum computation and commuication
|
Cooperative effects in the loss (the amplitude damping) and decoherence (the
phase damping) of the qubits (two-state quantum systems) due to the inevitable
coupling to the same environment are investigated. It is found that the qubits
undergo the dissipation coherently in this case. In particular, for a special
kind of input states (called the coherence-preserving states), whose form
depends on the type of the coupling, loss and decoherence in quantum memory are
much reduced. Based on this phenomenon, a scheme by encoding the general input
states of the qubits into the corresponding coherence-preserving states is
proposed for reducing the cooperative loss and decoherence in quantum
computation or communication.
|
9701020v1
|
1997-03-22
|
Preserving coherence in quantum computation by pairing quantum bits
|
A scheme is proposed for protecting quantum states from both independent
decoherence and cooperative decoherence. The scheme operates by pairing each
qubit (two-state quantum system) with an ancilla qubit and by encoding the
states of the qubits into the corresponding coherence-preserving states of the
qubit-pairs. In this scheme, the amplitude damping (loss of energy) is
prevented as well as the phase damping (dephasing) by a strategy called the
free-Hamiltonian-elimination We further extend the scheme to include quantum
gate operations and show that loss and decoherence during the gate operations
can also be prevented.
|
9703040v2
|
1997-06-10
|
Perturbative expansions for the fidelities and spatially correlated dissipation of quantum bits
|
We construct generally applicable short-time perturbative expansions for some
fidelities, such as the input-output fidelity, the entanglement fidelity, and
the average fidelity. Successive terms of these expansions yield characteristic
times for the damping of the fidelities involving successive powers of the
Hamiltonian. The second-order results, which represent the damping rates of the
fidelities, are extensively discussed. As an interesting application of these
expansions, we use them to study the spatially-correlated dissipation of
quantum bits. Spatial correlations in the dissipation are described by a
correlation function. Explicit conditions are derived for independent
decoherence and for collective decoherence.
|
9706020v2
|
1998-05-27
|
Measurement Process In a Two-Barrier System
|
The description of a measuring process, such as that which occurs when a
quantum point contact (QPC) detector is influenced by a nearby external
electron which can take up two possible positions, provides a interesting
application of the method of quantum damping. We find a number of new effects,
due to the complete treatment of phases afforded by the formalism, although our
results are generally similiar to those of other treatments, particularly to
those of Buks et al.
These are effects depending on the phase shift in the detector, effects which
depend on the direction of the measuring current, and in addition to damping or
dissipative effects, an energy shift of the measured system. In particular, the
phase shift effect leads to the conclusion that there can be effects of
"observation" even when the two barriers in question pass the same current.
The nature of the current through the barriers and its statistics is
discussed, giving a description of correlations in the current due to
"measurement" and of the origin of "telegraphic" signals.
|
9805081v2
|
1998-10-06
|
Cumulant expansion for studying damped quantum solitons
|
The quantum statistics of damped optical solitons is studied using
cumulant-expansion techniques. The effect of absorption is described in terms
of ordinary Markovian relaxation theory, by coupling the optical field to a
continuum of reservoir modes. After introduction of local bosonic field
operators and spatial discretization pseudo-Fokker-Planck equations for
multidimensional s-parameterized phase-space functions are derived. These
partial differential equations are equivalent to an infinite set of ordinary
differential equations for the cumulants of the phase-space functions.
Introducing an appropriate truncation condition, the resulting finite set of
cumulant evolution equations can be solved numerically. Solutions are presented
in Gaussian approximation and the quantum noise is calculated, with special
emphasis on squeezing and the recently measured spectral photon-number
correlations [Spaelter et al., Phys. Rev. Lett. 81, 786 (1998)].
|
9810018v3
|
1999-02-10
|
Quantum noise in the position measurement of a cavity mirror undergoing Brownian motion
|
We perform a quantum theoretical calculation of the noise power spectrum for
a phase measurement of the light output from a coherently driven optical cavity
with a freely moving rear mirror. We examine how the noise resulting from the
quantum back action appears among the various contributions from other noise
sources. We do not assume an ideal (homodyne) phase measurement, but rather
consider phase modulation detection, which we show has a different shot noise
level. We also take into account the effects of thermal damping of the mirror,
losses within the cavity, and classical laser noise. We relate our theoretical
results to experimental parameters, so as to make direct comparisons with
current experiments simple. We also show that in this situation, the standard
Brownian motion master equation is inadequate for describing the thermal
damping of the mirror, as it produces a spurious term in the steady-state phase
fluctuation spectrum. The corrected Brownian motion master equation [L. Diosi,
Europhys. Lett. {\bf 22}, 1 (1993)] rectifies this inadequacy.
|
9902040v1
|
1999-10-05
|
Uncertainty, entropy and decoherence of the damped harmonic oscillator in the Lindblad theory of open quantum systems
|
In the framework of the Lindblad theory for open quantum systems, expressions
for the density operator, von Neumann entropy and effective temperature of the
damped harmonic oscillator are obtained. The entropy for a state characterized
by a Wigner distribution function which is Gaussian in form is found to depend
only on the variance of the distribution function. We give a series of
inequalities, relating uncertainty to von Neumann entropy and linear entropy.
We analyze the conditions for purity of states and show that for a special
choice of the diffusion coefficients, the correlated coherent states (squeezed
coherent states) are the only states which remain pure all the time during the
evolution of the considered system. These states are also the most stable under
evolution in the presence of the environment and play an important role in the
description of environment induced decoherence.
|
9910019v1
|
2000-06-07
|
Phenomenological approach to introduce damping effects on radiation field states
|
In this work we propose an approach to deal with radiation field states which
incorporates damping effects at zero temperature. By using some well known
results on dissipation of a cavity field state, obtained by standard ab-initio
methods, it was possible to infer through a phenomenological way the explicit
form for the evolution of the state vector for the whole system: the
cavity-field plus reservoir. This proposal turns out to be of extreme
convenience to account for the influence of the reservoir over the cavity
field.
To illustrate the universal applicability of our approach we consider the
attenuation effects on cavity-field states engineering. A proposal to maximize
the fidelity of the process is presented.
|
0006035v2
|
2001-09-28
|
Decoherence in trapped ions due to polarization of the residual background gas
|
We investigate the mechanism of damping and heating of trapped ions
associated with the polarization of the residual background gas induced by the
oscillating ions themselves. Reasoning by analogy with the physics of surface
electrons in liquid helium, we demonstrate that the decay of Rabi oscillations
observed in experiments on 9Be+ can be attributed to the polarization phenomena
investigated here. The measured sensitivity of the damping of Rabi oscillations
with respect to the vibrational quantum number of a trapped ion is also
predicted in our polarization model.
|
0109156v1
|
2002-06-18
|
Five Lectures On Dissipative Master Equations
|
1 First Lecture: Basics
1.1 Physical Derivation of the Master Equation
1.2 Some Simple Implications
1.3 Steady State
1.4 Action to the Left
2 Second Lecture: Eigenvalues and Eigenvectors of L
2.1 A Simple Case First
2.2 The General Case
3 Third Lecture: Completeness of the Damping Bases
3.1 Phase Space Functions
3.2 Completeness of the Eigenvectors of L
3.3 Positivity Conservation
3.4 Lindblad Form of Liouville Operators
4 Fourth Lecture: Quantum-Optical Applications
4.1 Periodically Driven Damped Oscillator
4.2 Conditional and Unconditional Evolution
4.3 Physical Signicance of Statistical Operators
5 Fifth Lecture: Statistics of Detected Atoms
5.1 Correlation Functions
5.2 Waiting Time Statistics
5.3 Counting Statistics
|
0206116v1
|
2002-10-02
|
Radiation damping and decoherence in quantum electrodynamics
|
The processes of radiation damping and decoherence in Quantum Electrodynamics
are studied from an open system's point of view. Employing functional
techniques of field theory, the degrees of freedom of the radiation field are
eliminated to obtain the influence phase functional which describes the reduced
dynamics of the matter variables. The general theory is applied to the dynamics
of a single electron in the radiation field. From a study of the wave packet
dynamics a quantitative measure for the degree of decoherence, the decoherence
function, is deduced. The latter is shown to describe the emergence of
decoherence through the emission of bremsstrahlung caused by the relative
motion of interfering wave packets. It is argued that this mechanism is the
most fundamental process in Quantum Electrodynamics leading to the destruction
of coherence, since it dominates for short times and because it is at work even
in the electromagnetic field vacuum at zero temperature. It turns out that
decoherence trough bremsstrahlung is very small for single electrons but
extremely large for superpositions of many-particle states.
|
0210013v1
|
2003-01-08
|
Dissipation, Emergent Quantization and Quantum Fluctuations
|
We review some aspects of the quantization of the damped harmonic oscillator.
We derive the exact action for a damped mechanical system in the frame of the
path integral formulation of the quantum Brownian motion problem developed by
Schwinger and by Feynman and Vernon. The doubling of the phase-space degrees of
freedom for dissipative systems and thermal field theories is discussed and the
doubled variables are related to quantum noise effects. The 't Hooft proposal,
according to which the loss of information due to dissipation in a classical
deterministic system manifests itself in the quantum features of the system, is
analyzed and the quantum spectrum of the harmonic oscillator is shown to be
originated from the dissipative character of the original classical
deterministic system.
|
0301031v1
|
2004-01-28
|
Bloch Equations and Completely Positive Maps
|
The phenomenological dissipation of the Bloch equations is reexamined in the
context of completely positive maps. Such maps occur if the dissipation arises
from a reduction of a unitary evolution of a system coupled to a reservoir. In
such a case the reduced dynamics for the system alone will always yield
completely positive maps of the density operator. We show that, for Markovian
Bloch maps, the requirement of complete positivity imposes some Bloch
inequalities on the phenomenological damping constants. For non-Markovian Bloch
maps some kind of Bloch inequalities involving eigenvalues of the damping basis
can be established as well. As an illustration of these general properties we
use the depolarizing channel with white and colored stochastic noise.
|
0401177v1
|
2004-02-12
|
Non-Markovian Quantum Trajectories Versus Master Equations: Finite Temperature Heat Bath
|
The interrelationship between the non-Markovian stochastic Schr\"odinger
equations and the corresponding non-Markovian master equations is investigated
in the finite temperature regimes. We show that the general finite temperature
non-Markovian trajectories can be used to derive the corresponding
non-Markovian master equations. A simple, yet important solvable example is the
well-known damped harmonic oscillator model in which a harmonic oscillator is
coupled to a finite temperature reservoir in the rotating wave approximation.
The exact convolutionless master equation for the damped harmonic oscillator is
obtained by averaging the quantum trajectories relying upon no assumption of
coupling strength or time scale. The master equation derived in this way
automatically preserves the positivity, Hermiticity and unity.
|
0402086v2
|
2005-04-27
|
Decoherence models and their effects on quantum maps and algorithms
|
In this work we study several models of decoherence and how different quantum
maps and algorithms react when perturbed by them. Following closely Ref. [1],
generalizations of the three paradigmatic one single qubit quantum channels
(these are the depolarizing channel, the phase damping channel and the
amplitude damping channel) for the case of an arbitrarily-sized
finite-dimensional Hilbert space are presented, as well as other types of noise
in phase space. More specifically, Grover's search algorithm's response to
decoherence is analyzed; together with those of a family of quantum versions of
chaotic and regular classical maps (the baker's map and the cat maps). A
relationship between how sensitive to decoherence a quantum map is and the
degree of complexity in the dynamics of its associated classical counterpart is
observed; resulting in a clear tendency to react the more decoherently the more
complex the associated classical dynamics is.
|
0504211v1
|
2005-09-22
|
Semiclassical quantization of non-Hamiltonian dynamical systems without memory
|
We propose a new method of quantization of a wide class of dynamical systems
that originates directly from the equations of motion. The method is based on
the correspondence between the classical and the quantum Poisson brackets,
postulated by Dirac. This correspondence applied to open (non-Hamiltonian)
systems allows one to point out the way of transition from the quantum
description based on the Lindblad equation to the dynamical description of
their classical analogs by the equations of motion and vice versa. As the
examples of using of the method we describe the procedure of the quantization
of three widely considered dynamical systems: 1) the harmonic oscillator with
friction, 2) the oscillator with a nonlinear damping that simulates the process
of the emergence of the limit cycle, and 3) the system of two periodic rotators
with a weak interaction that synchronizes their oscillations. We discuss a
possible application of the method for a description of quantum fluctuations in
Josephson junctions with a strong damping and for the quantization of open
magnetic systems with a dissipation and a pumping.
|
0509159v1
|
2005-11-15
|
Classical Phase Space Density for the Relativistic Hydrogen Atom
|
Quantum mechanics is considered to arise from an underlying classical
structure (``hidden variable theory'', ``sub-quantum mechanics''), where
quantum fluctuations follow from a physical noise mechanism. The stability of
the hydrogen ground state can then arise from a balance between Lorentz damping
and energy absorption from the noise. Since the damping is weak, the ground
state phase space density should predominantly be a function of the conserved
quantities, energy and angular momentum.
A candidate for this phase space density is constructed for ground state of
the relativistic hydrogen problem of a spinless particle. The first excited
states and their spherical harmonics are also considered in this framework. The
analytic expression of the ground state energy can be reproduced, provided
averages of certain products are replaced by products of averages. This
analysis puts forward that quantum mechanics may arise from an underlying
classical level as a slow variable theory, where each new quantum operator
relates to a new, well separated time interval.
|
0511144v1
|
2006-01-10
|
Quantum Brownian motion and the Third Law of thermodynamics
|
The quantum thermodynamic behavior of small systems is investigated in
presence of finite quantum dissipation. We consider the archetype cases of a
damped harmonic oscillator and a free quantum Brownian particle. A main finding
is that quantum dissipation helps to ensure the validity of the Third Law. For
the quantum oscillator, finite damping replaces the zero-coupling result of an
exponential suppression of the specific heat at low temperatures by a power-law
behavior. Rather intriguing is the behavior of the free quantum Brownian
particle. In this case, quantum dissipation is able to restore the Third Law:
Instead of being constant down to zero temperature, the specific heat now
vanishes proportional to temperature with an amplitude that is inversely
proportional to the ohmic dissipation strength. A distinct subtlety of finite
quantum dissipation is the result that the various thermodynamic functions of
the sub-system do not only depend on the dissipation strength but depend as
well on the prescription employed in their definition.
|
0601056v1
|
2006-03-13
|
Decoherence induced by a phase-damping reservoir
|
A phase damping reservoir composed by $N$-bosons coupled to a system of
interest through a cross-Kerr interaction is proposed and its effects on
quantum superpo sitions are investigated. By means of analytical calculations
we show that: i-) the reservoir induces a Gaussian decay of quantum coherences,
and ii-) the inher ent incommensurate character of the spectral distribution
yields irreversibility . A state-independent decoherence time and a master
equation are both derived an alytically. These results, which have been
extended for the thermodynamic limit, show that nondissipative decoherence can
be suitably contemplated within the EI D approach. Finally, it is shown that
the same mechanism yielding decoherence ar e also responsible for inducing
dynamical disentanglement.
|
0603109v2
|
2007-01-21
|
Casimir-Polder forces on excited atoms in the strong atom-field coupling regime
|
Based on macroscopic quantum electrodynamics in linear media, we develop a
general theory of the resonant Casimir-Polder force on an excited two-level
atom in the presence of arbitrary linear bodies, with special emphasis on the
strong-coupling regime where reabsorption of an emitted photon can give rise to
(vacuum) Rabi oscillations. We first derive a simple time-independent
expression for the force by using a dressed-state approximation. For initially
single-quantum excited atom-field systems we then study the dynamics of the
force by starting from the Lorentz force and evaluating its average as a
function of time. For strong atom-field coupling, we find that the force may
undergo damped Rabi oscillations. The damping is due to the decay of both the
atomic excitation and the field excitation, and both amplitude and mean value
of the oscillations depend on the chosen initial state.
|
0701151v2
|
2007-02-07
|
Protecting an optical qubit against photon loss
|
We consider quantum error-correction codes for multimode bosonic systems,
such as optical fields, that are affected by amplitude damping. Such a process
is a generalization of an erasure channel. We demonstrate that the most
accessible method of transforming optical systems with the help of passive
linear networks has limited usefulness in preparing and manipulating such
codes. These limitations stem directly from the recoverability condition for
one-photon loss. We introduce a three-photon code protecting against the first
order of amplitude damping, i.e. a single photon loss, and discuss its
preparation using linear optics with single-photon sources and conditional
detection. Quantum state and process tomography in the code subspace can be
implemented using passive linear optics and photon counting. An experimental
proof-of-principle demonstration of elements of the proposed quantum error
correction scheme for a one-photon erasure lies well within present
technological capabilites.
|
0702075v1
|
1995-02-03
|
Shock waves in the dissipative Toda lattice
|
We consider the propagation of a shock wave (SW) in the damped Toda lattice.
The SW is a moving boundary between two semi-infinite lattice domains with
different densities. A steadily moving SW may exist if the damping in the
lattice is represented by an ``inner'' friction, which is a discrete analog of
the second viscosity in hydrodynamics. The problem can be considered
analytically in the continuum approximation, and the analysis produces an
explicit relation between the SW's velocity and the densities of the two
phases. Numerical simulations of the lattice equations of motion demonstrate
that a stable SW establishes if the initial velocity is directed towards the
less dense phase; in the opposite case, the wave gradually spreads out. The
numerically found equilibrium velocity of the SW turns out to be in a very good
agreement with the analytical formula even in a strongly discrete case. If the
initial velocity is essentially different from the one determined by the
densities (but has the correct sign), the velocity does not significantly
alter, but instead the SW adjusts itself to the given velocity by sending
another SW in the opposite direction.
|
9502001v1
|
2007-04-04
|
An integral field spectroscopic survey for high redshift damped Lyman-alpha galaxies
|
We search for galaxy counterparts to damped Lyman-alpha absorbers (DLAs) at
z>2 towards nine quasars, which have 14 DLAs and 8 sub-DLAs in their spectra.
We use integral field spectroscopy to search for Ly-alpha emission line objects
at the redshifts of the absorption systems. Besides recovering two previously
confirmed objects, we find six statistically significant candidate Ly-alpha
emission line objects. The candidates are identified as having wavelengths
close to the DLA line where the background quasar emission is absorbed. In
comparison with the six currently known Ly-alpha emitting DLA galaxies the
candidates have similar line fluxes and line widths, while velocity offsets
between the emission lines and systemic DLA redshifts are larger. The impact
parameters are larger than 10 kpc, and lower column density systems are found
at larger impact parameters. Assuming that a single gas cloud extends from the
QSO line of sight to the location of the candidate emission line, we find that
the average candidate DLA galaxy is surrounded by neutral gas with an
exponential scale length of ~5 kpc.
|
0704.0654v1
|
2007-04-06
|
9.7 micrometer Silicate Absorption in a Damped Lyman-alpha Absorber at z=0.52
|
We report a detection of the 9.7 micrometer silicate absorption feature in a
damped Lyman-alpha (DLA) system at z_{abs} = 0.524 toward AO0235+164, using the
Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The feature
shows a broad shallow profile over about 8-12 micrometers in the absorber rest
frame and appears to be > 15 sigma significant in equivalent width. The feature
is fit reasonably well by the silicate absorption profiles for laboratory
amorphous olivine or diffuse Galactic interstellar clouds. To our knowledge,
this is the first indication of 9.7 micrometer silicate absorption in a DLA. We
discuss potential implications of this finding for the nature of the dust in
quasar absorbers. Although the feature is relatively shallow (tau_{9.7} =
0.08-0.09), it is about 2 times deeper than expected from extrapolation of the
tau_{9.7} vs. E(B-V) relation known for diffuse Galactic interstellar clouds.
Further studies of the 9.7 micrometer silicate feature in quasar absorbers will
open a new window on the dust in distant galaxies.
|
0704.0826v2
|
2007-04-17
|
Boolean network model predicts cell cycle sequence of fission yeast
|
A Boolean network model of the cell-cycle regulatory network of fission yeast
(Schizosaccharomyces Pombe) is constructed solely on the basis of the known
biochemical interaction topology. Simulating the model in the computer,
faithfully reproduces the known sequence of regulatory activity patterns along
the cell cycle of the living cell. Contrary to existing differential equation
models, no parameters enter the model except the structure of the regulatory
circuitry. The dynamical properties of the model indicate that the biological
dynamical sequence is robustly implemented in the regulatory network, with the
biological stationary state G1 corresponding to the dominant attractor in state
space, and with the biological regulatory sequence being a strongly attractive
trajectory. Comparing the fission yeast cell-cycle model to a similar model of
the corresponding network in S. cerevisiae, a remarkable difference in
circuitry, as well as dynamics is observed. While the latter operates in a
strongly damped mode, driven by external excitation, the S. pombe network
represents an auto-excited system with external damping.
|
0704.2200v1
|
2007-05-08
|
Optical dilution and feedback cooling of a gram-scale oscillator to 6.9 mK
|
We report on use of a radiation pressure induced restoring force, the optical
spring effect, to optically dilute the mechanical damping of a 1 gram suspended
mirror, which is then cooled by active feedback (cold damping). Optical
dilution relaxes the limit on cooling imposed by mechanical losses, allowing
the oscillator mode to reach a minimum temperature of 6.9 mK, a factor of
~40000 below the environmental temperature. A further advantage of the optical
spring effect is that it can increase the number of oscillations before
decoherence by several orders of magnitude. In the present experiment we infer
an increase in the dynamical lifetime of the state by a factor of ~200.
|
0705.1018v2
|
2007-05-14
|
Electron-muon heat conduction in neutron star cores via the exchange of transverse plasmons
|
We calculate the thermal conductivity of electrons and muons kappa_{e-mu}
produced owing to electromagnetic interactions of charged particles in neutron
star cores and show that these interactions are dominated by the exchange of
transverse plasmons (via the Landau damping of these plasmons in
nonsuperconducting matter and via a specific plasma screening in the presence
of proton superconductivity). For normal protons, the Landau damping strongly
reduces kappa_{e-mu} and makes it temperature independent. Proton
superconductivity suppresses the reduction and restores the Fermi-liquid
behavior kappa_{e-mu} ~ 1/T. Comparing with the thermal conductivity of
neutrons kappa_n, we obtain kappa_{e-mu}> kappa_n for T>2 GK in normal matter
and for any T in superconducting matter with proton critical temperatures
T_c>3e9 K. The results are described by simple analytic formulae.
|
0705.1963v1
|
2007-05-24
|
Measurement of Newtonian fluid slip using a torsional ultrasonic oscillator
|
The composite torsional ultrasonic oscillator, a versatile experimental
system, can be used to investigate slip of Newtonian fluid at a smooth surface.
A rigorous analysis of slip-dependent damping for the oscillator is presented.
Initially, the phenomenon of finite surface slip and the slip length are
considered for a half-space of Newtonian fluid in contact with a smooth,
oscillating solid surface. Definitions are revisited and clarified in light of
inconsistencies in the literature. We point out that, in general oscillating
flows, Navier's slip length b is a complex number. An intuitive velocity
discontinuity parameter of unrestricted phase is used to describe the effect of
slip on measurement of viscous shear damping. The analysis is applied to the
composite oscillator and preliminary experimental work for a 40 kHz oscillator
is presented. The Non-Slip Boundary Condition (NSBC) has been verified for a
hydrophobic surface in water to within ~60 nm of |b|=0 nm. Experiments were
carried out at shear rate amplitudes between 230 and 6800 /s, corresponding to
linear displacement amplitudes between 3.2 and 96 nm.
|
0705.3498v3
|
2007-06-05
|
Waves and instabilities in dissipative rotating superfluid neutron stars
|
We discuss wave propagation in rotating superfluid neutron star cores, taking
into account the vortex mediated mutual friction force. For models where the
two fluids co-rotate in the unperturbed state, our analysis clarifies the role
of chemical coupling and entrainment for sound and inertial waves. We also
investigate the mutual friction damping, providing results that demonstrate the
well-known fact that sound waves propagating along a vortex array are undamped.
We show that the same is not true for inertial waves, which are damped by the
mutual friction regardless of the propagation direction. We then include the
vortex tension, which arises due to local vortex curvature. Focussing on purely
transverse inertial waves, we derive the small correction that the tension
induces in the wave frequency. Finally, we allow for a relative linear flow in
the background (along the rotation axis). In this case we show how the mutual
friction coupling may induce a dynamical instability in the inertial waves. We
discuss the critical flow required for the instability to be present, its
physical interpretation and the possible relevance it may have for neutron star
physics.
|
0706.0672v1
|
2007-07-20
|
Dissipation-Scale Turbulence in the Solar Wind
|
We present a cascade model for turbulence in weakly collisional plasmas that
follows the nonlinear cascade of energy from the large scales of driving in the
MHD regime to the small scales of the kinetic Alfven wave regime where the
turbulence is dissipated by kinetic processes. Steady-state solutions of the
model for the slow solar wind yield three conclusions: (1) beyond the observed
break in the magnetic energy spectrum, one expects an exponential cut-off; (2)
the widely held interpretation that this dissipation range obeys power-law
behavior is an artifact of instrumental sensitivity limitations; and, (3) over
the range of parameters relevant to the solar wind, the observed variation of
dissipation range spectral indices from -2 to -4 is naturally explained by the
varying effectiveness of Landau damping, from an undamped prediction of -7/3 to
a strongly damped index around -4.
|
0707.3149v1
|
2007-08-09
|
An algorithm for detecting oscillatory behavior in discretized data: the damped-oscillator oscillator detector
|
We present a simple algorithm for detecting oscillatory behavior in discrete
data. The data is used as an input driving force acting on a set of simulated
damped oscillators. By monitoring the energy of the simulated oscillators, we
can detect oscillatory behavior in data. In application to in vivo deep brain
basal ganglia recordings, we found sharp peaks in the spectrum at 20 and 70 Hz.
The algorithm is also compared to the conventional fast Fourier transform and
circular statistics techniques using computer generated model data, and is
found to be comparable to or better than fast Fourier transform in test cases.
Circular statistics performed poorly in our tests.
|
0708.1341v1
|
2007-08-22
|
The dynamics of vortex generation in superfluid 3He-B
|
A profound change occurs in the stability of quantized vortices in externally
applied flow of superfluid 3He-B at temperatures ~ 0.6 Tc, owing to the rapidly
decreasing damping in vortex motion with decreasing temperature. At low damping
an evolving vortex may become unstable and generate a new independent vortex
loop. This single-vortex instability is the generic precursor to turbulence. We
investigate the instability with non-invasive NMR measurements on a rotating
cylindrical sample in the intermediate temperature regime (0.3 - 0.6) Tc. From
comparisons with numerical calculations we interpret that the instability
occurs at the container wall, when the vortex end moves along the wall in
applied flow.
|
0708.3003v2
|
2007-08-26
|
Geodesic plasma flows instabilities of Riemann twisted solar loops
|
Riemann and sectional curvatures of magnetic twisted flux tubes in Riemannian
manifold are computed to investigate the stability of the plasma astrophysical
tubes. The geodesic equations are used to show that in the case of thick
magnetic tubes, the curvature of planar (Frenet torsion-free) tubes have the
effect ct of damping the flow speed along the tube. Stability of geodesic flows
in the Riemannian twisted thin tubes (almost filaments), against constant
radial perturbations is investigated by using the method of negative sectional
curvature for unstable flows. No special form of the flow like Beltrami flows
is admitted, and the proof is general for the case of thin magnetic flux tubes.
In the magnetic equilibrium state, the twist of the tube is shown to display
also a damping effect on the toroidal velocity of the plasma flow. It is found
that for positive perturbations and angular speed of the flow, instability is
achieved, since the sectional Ricci curvature of the magnetic twisted tube
metric is negative. Solar flare production may appear from these geometrical
instabilities of the twisted solar loops.
|
0708.3473v1
|
2007-09-05
|
Phonon bottleneck in the low-excitation limit
|
The phonon-bottleneck problem in the relaxation of two-level systems (spins)
via direct phonon processes is considered numerically in the weak-excitation
limit where the Schroedinger equation for the spin-phonon system simplifies.
The solution for the relaxing spin excitation p(t), emitted phonons n_k(t),
etc. is obtained in terms of the exact many-body eigenstates. In the absence of
phonon damping Gamma_{ph} and inhomogeneous broadening, p(t) approaches the
bottleneck plateau p_\infty > 0 with strongly damped oscillations, the
frequency being related to the spin-phonon splitting Delta at the avoided
crossing. For any Gamma_{ph} > 0 one has p(t) -> 0 but in the case of strong
bottleneck the spin relaxation rate is much smaller than Gamma_{ph} and p(t) is
nonexponential. Inhomogeneous broadening exceeding Delta partially alleviates
the bottleneck and removes oscillations of p(t). The line width of emitted
phonons, as well as Delta, increase with the strength of the bottleneck, i.e.,
with the concentration of spins.
|
0709.0556v1
|
2007-09-13
|
Distribution of PageRank Mass Among Principle Components of the Web
|
We study the PageRank mass of principal components in a bow-tie Web Graph, as
a function of the damping factor c. Using a singular perturbation approach, we
show that the PageRank share of IN and SCC components remains high even for
very large values of the damping factor, in spite of the fact that it drops to
zero when c goes to one. However, a detailed study of the OUT component reveals
the presence ``dead-ends'' (small groups of pages linking only to each other)
that receive an unfairly high ranking when c is close to one. We argue that
this problem can be mitigated by choosing c as small as 1/2.
|
0709.2016v1
|
2007-10-02
|
Oscillating Starless Cores: The Nonlinear Regime
|
In a previous paper, we modeled the oscillations of a thermally-supported
(Bonnor-Ebert) sphere as non-radial, linear perturbations following a standard
analysis developed for stellar pulsations. The predicted column density
variations and molecular spectral line profiles are similar to those observed
in the Bok globule B68 suggesting that the motions in some starless cores may
be oscillating perturbations on a thermally supported equilibrium structure.
However, the linear analysis is unable to address several questions, among them
the stability, and lifetime of the perturbations. In this paper we simulate the
oscillations using a three-dimensional numerical hydrodynamic code. We find
that the oscillations are damped predominantly by non-linear mode-coupling, and
the damping time scale is typically many oscillation periods, corresponding to
a few million years, and persisting over the inferred lifetime of gobules.
|
0710.0625v1
|
2007-10-08
|
Jet quenching parameter \hat q in the stochastic QCD vacuum with Landau damping
|
We argue that the radiative energy loss of a parton traversing the
quark-gluon plasma is determined by Landau damping of soft modes in the plasma.
Using this idea, we calculate the jet quenching parameter of a gluon. The
calculation is done in SU(3) quenched QCD within the stochastic vacuum model.
At the LHC-relevant temperatures, the result depends on the gluon condensate,
the vacuum correlation length, and the gluon Debye mass. Numerically, when the
temperature varies from T=T_c to T=900 MeV, the jet quenching parameter rises
from \hat q=0 to approximately 1.8 GeV^2/fm. We compare our results with the
predictions of perturbative QCD and other calculations.
|
0710.1540v2
|
2007-11-07
|
Tuning the effective coupling of an AFM lever to a thermal bath
|
Fabrication of Nano-Electro-Mechanical-Systems (NEMS) of high quality is
nowadays extremely efficient. These NEMS will be used as sensors and actuators
in integrated systems. Their use however raises questions about their interface
(actuation, detection, read out) with external detection and control systems.
Their operation implies many fundamental questions related to single particle
effects such as Coulomb blockade, light matter interactions such as radiation
pressure, thermal effects, Casimir forces and the coupling of nanosystems to
external world (thermal fluctuations, back action effect). Here we specifically
present how the damping of an oscillating cantilever can be tuned in two
radically different ways: i) through an electro-mechanical coupling in the
presence of a strong Johnson noise, ii) through an external feedback control of
thermal fluctuations which is the cold damping closely related to Maxwell's
demon. This shows how the interplay between MEMS or NEMS external control and
their coupling to a thermal bath can lead to a wealth of effects that are
nowadays extensively studied in different areas.
|
0711.1024v1
|
2007-12-11
|
Neutrino oscillations in a stochastic model for space-time foam
|
We study decoherence models for flavour oscillations in four-dimensional
stochastically fluctuating space times and discuss briefly the sensitivity of
current neutrino experiments to such models. We pay emphasis on demonstrating
the model dependence of the associated decoherence-induced damping coefficients
in front of the oscillatory terms in the respective transition probabilities
between flavours. Within the context of specific models of foam, involving
point-like D-branes and leading to decoherence-induced damping which is
inversely proportional to the neutrino energies, we also argue that future
limits on the relevant decoherence parameters coming from TeV astrophysical
neutrinos, to be observed in ICE-CUBE, are not far from theoretically expected
values with Planck mass suppression. Ultra high energy neutrinos from Gamma Ray
Bursts at cosmological distances can also exhibit in principle sensitivity to
such effects.
|
0712.1779v1
|
2008-01-21
|
Collective cyclotron motion of the relativistic plasma in graphene
|
We present a theory of the finite temperature thermo-electric response
functions of graphene, in the hydrodynamic regime induced by electron-electron
collisions. In moderate magnetic fields, the Dirac particles undergo a
collective cyclotron motion with a temperature-dependent relativistic cyclotron
frequency proportional to the net charge density of the Dirac plasma. In
contrast to the undamped cyclotron pole in Galilean-invariant systems (Kohn's
theorem), here there is a finite damping induced by collisions between the
counter-propagating particles and holes. This cyclotron motion shows up as a
damped pole in the frequency dependent conductivities, and should be readily
detectable in microwave measurements at room temperature. We also discuss the
large Nernst effect to be expected in graphene.
|
0801.2970v3
|
2008-01-25
|
Sound waves and solitons in hot and dense nuclear matter
|
Assuming that nuclear matter can be treated as a perfect fluid, we study the
propagation of perturbations in the baryon density. The equation of state is
derived from a relativistic mean field model, which is a variant of the
non-linear Walecka model. The expansion of the Euler and continuity equations
of relativistic hydrodynamics around equilibrium configurations leads to
differential equations for the density fluctuations. We solve them numerically
for linear and spherical perturbations and follow the time evolution of the
initial pulses. For linear perturbations we find single soliton solutions and
solutions with one or more solitons followed by radiation. Depending on the
equation of state a strong damping may occur. Spherical perturbations are
strongly damped and almost do not propagate. We study these equations also for
matter at finite temperature. Finally we consider the limiting case of shock
wave formation.
|
0801.3938v1
|
2008-01-28
|
Qualitative Analysis of Forced Response of Blisks With Friction Ring Dampers
|
A damping strategy for blisks (integrally bladed disks) of turbomachinery
involving a friction ring is investigated. These rings, located in grooves
underside the wheel of the blisks, are held in contact by centrifugal loads and
the energy is dissipated when relative motions between the ring and the disk
occur. A representative lumped parameter model of the system is introduced and
the steady-state nonlinear response is derived using a multi-harmonic balance
method combined with an AFT procedure where the friction force is calculated in
the time domain. Numerical simulations are presented for several damper
characteristics and several excitation configurations. From these results, the
performance of this damping strategy is discussed and some design guidelines
are given.
|
0801.4350v1
|
2008-01-29
|
Long Term Evolution of Magnetic Turbulence in Relativistic Collisionless Shocks
|
We study the long term evolution of magnetic fields generated by an initially
unmagnetized collisionless relativistic $e^+e^-$ shock. Our 2D particle-in-cell
numerical simulations show that downstream of such a Weibel-mediated shock,
particle distributions are approximately isotropic, relativistic Maxwellians,
and the magnetic turbulence is highly intermittent spatially, nonpropagating,
and decaying. Using linear kinetic theory, we find a simple analytic form for
these damping rates. Our theory predicts that overall magnetic energy decays
like $(\omega_p t)^{-q}$ with $q \sim 1$, which compares favorably with
simulations, but predicts overly rapid damping of short wavelength modes.
Magnetic trapping of particles within the magnetic structures may be the origin
of this discrepancy. We conclude that initially unmagnetized relativistic
shocks in electron-positron plasmas are unable to form persistent downstream
magnetic fields. These results put interesting constraints on synchrotron
models for the prompt and afterglow emission from GRBs.
|
0801.4583v1
|
2008-02-20
|
Mechanical mode dependence of bolometric back-action in an AFM microlever
|
Two back action (BA) processes generated by an optical cavity based detection
device can deeply transform the dynamical behavior of an AFM microlever: the
photothermal force or the radiation pressure. Whereas noise damping or
amplifying depends on optical cavity response for radiation pressure BA, we
present experimental results carried out under vacuum and at room temperature
on the photothermal BA process which appears to be more complex. We show for
the first time that it can simultaneously act on two vibration modes in
opposite direction: noise on one mode is amplified whereas it is damped on
another mode. Basic modeling of photothermal BA shows that dynamical effect on
mechanical mode is laser spot position dependent with respect to mode shape.
This analysis accounts for opposite behaviors of different modes as observed.
|
0802.2763v2
|
2008-02-21
|
Propagation of cosmic rays in the foam-like Universe
|
The model of a classical spacetime foam is considered, which consists of
static wormholes embedded in Minkowski spacetime. We examine the propagation of
particles in such a medium and demonstrate that a single thin ray undergoes a
specific damping in the density of particles depending on the traversed path
and the distribution of wormholes. The missing particles are scattered around
the ray. Wormholes was shown to form DM halos around point-like sources.
Therefore, the correlation predicted between the damping and the amount of DM
can be used to verify the topological nature of Dark Matter.
|
0802.3109v2
|
2008-02-21
|
Damping by slow relaxing rare earth impurities in Ni80Fe20
|
Doping NiFe by heavy rare earth atoms alters the magnetic relaxation
properties of this material drastically. We show that this effect can be well
explained by the slow relaxing impurity mechanism. This process is a
consequence of the anisotropy of the on site exchange interaction between the
4f magnetic moments and the conduction band. As expected from this model the
magnitude of the damping effect scales with the anisotropy of the exchange
interaction and increases by an order of magnitude at low temperatures. In
addition our measurements allow us to determine the relaxation time of the 4f
electrons as a function of temperature.
|
0802.3206v3
|
2008-03-11
|
Domain wall motion of magnetic nanowires under a static field
|
The propagation of a head-to-head magnetic domain-wall (DW) or a tail-to-tail
DW in a magnetic nanowire under a static field along the wire axis is studied.
Relationship between the DW velocity and DW structure is obtained from the
energy consideration. The role of the energy dissipation in the field-driven DW
motion is clarified. Namely, a field can only drive a domain-wall propagating
along the field direction through the mediation of a damping. Without the
damping, DW cannot propagate along the wire. Contrary to the common wisdom, DW
velocity is, in general, proportional to the energy dissipation rate, and one
needs to find a way to enhance the energy dissipation in order to increase the
propagation speed. The theory provides also a nature explanation of the
wire-width dependence of the DW velocity and velocity oscillation beyond Walker
breakdown field.
|
0803.1531v1
|
2008-03-11
|
Equation of state for strongly interacting matter: collective effects, Landau damping and predictions for LHC
|
The equation of state (EOS) is of utmost importance for the description of
the hydrodynamic phase of strongly interacting matter in relativistic heavy-ion
collisions. Lattice QCD can provide useful information on the EOS, mainly for
small net baryon densities. The QCD quasiparticle model provides a means to map
lattice QCD results into regions relevant for a variety of experiments. We
report here on effects of collectives modes and damping on the EOS. Some
predictions for forthcoming heavy-ion collisions at LHC/ALICE are presented and
perspectives for deriving an EOS for FAIR/CBM are discussed.
|
0803.1571v1
|
2008-04-04
|
Spin-charge coupling in a band ferromagnet: magnon-energy reduction, anomalous softening, and damping
|
The effects of correlation-induced coupling between spin and charge
fluctuations on spin-wave excitations in a band ferromagnet are investigated by
including self-energy and vertex corrections within a systematic
inverse-degeneracy expansion scheme which explicitly preserves the Goldstone
mode. Arising from the scattering of a magnon into intermediate spin-excitation
states (including both magnon and Stoner excitations) accompanied with charge
fluctuations in the majority spin band, this spin-charge coupling results not
only in a substantial reduction of magnon energies but also in anomalous
softening and significant magnon damping for zone-boundary modes lying within
the Stoner gap. Our results are in good qualitative agreement with recent
spin-wave excitation measurements in colossal magneto-resistive manganites and
ferromagnetic ultrathin films of transition metals.
|
0804.0680v1
|
2008-05-07
|
Noise Analysis and Noise-based Optimization for Resonant MEMS Structures
|
This paper presents a detailed noise analysis and a noise-based optimization
procedure for resonant MEMS structures. A design for high sensitivity of MEMS
structures needs to take into account the noise shaping induced by damping
phenomena at micro scale. The existing literature presents detailed models for
the damping at microscale, but usually neglects them in the noise analysis
process, assuming instead a white spectrum approximation for the
mechano-thermal noise. The present work extends the implications of the complex
gas-solid interaction into the field of noise analysis for mechanical sensors,
and provides a semi-automatic procedure for behavioral macromodel extraction
and sensor optimization with respect to signal-to-noise ratio.
|
0805.0927v1
|
2008-05-07
|
Scaling crossovers in activated escape of nonequilibrium systems: a resonantly driven oscillator
|
The rate of metastable decay in nonequilibrium systems is expected to display
scaling behavior: i.e., the logarithm of the decay rate should scale as a power
of the distance to a bifurcation point where the metastable state disappears.
Recently such behavior was observed and some of the earlier predicted exponents
were found in experiments on several types of systems described by a model of a
modulated oscillator. Here we establish the range where different scaling
behavior is displayed and show how the crossover between different types of
scaling occurs. The analysis is done for a nonlinear oscillator with two
coexisting stable states of forced vibrations. Our numerical calculations,
based on the the instanton method allow the mapping of the entire parameter
range of bi-stability. We find the regions where the scaling exponents are 1 or
3/2, depending on the damping. The exponent 3/2 is found to extend much further
from the bifurcation then were it would be expected to hold as a result of an
over-damped soft mode. We also uncover a new scaling behavior with exponent of
$\approx$ 1.3 which extends, numerically, beyond the close vicinity of the
bifurcation point.
|
0805.0972v2
|
2008-05-07
|
Quantum Noise, Effective Temperature, and Damping in a Superconducting Single-Electron Transistor
|
We have directly measured the quantum noise of a superconducting
single-electron transistor (S-SET) embedded in a microwave resonator consisting
of a superconducting LC tank circuit. Using an effective bath description, we
find that the S-SET provides damping of the resonator modes proportional to its
differential conductance and has an effective temperature that depends strongly
on the S-SET bias conditions. In the vicinity of a double Cooper pair
resonance, when both resonances are red detuned the S-SET effective temperature
can be well below both the ambient temperature and the energy scale of the bias
voltage. When blue detuned, the S-SET shows negative differential conductivity,
|
0805.1037v1
|
2008-05-08
|
Adaptive Affinity Propagation Clustering
|
Affinity propagation clustering (AP) has two limitations: it is hard to know
what value of parameter 'preference' can yield an optimal clustering solution,
and oscillations cannot be eliminated automatically if occur. The adaptive AP
method is proposed to overcome these limitations, including adaptive scanning
of preferences to search space of the number of clusters for finding the
optimal clustering solution, adaptive adjustment of damping factors to
eliminate oscillations, and adaptive escaping from oscillations when the
damping adjustment technique fails. Experimental results on simulated and real
data sets show that the adaptive AP is effective and can outperform AP in
quality of clustering results.
|
0805.1096v1
|
2008-06-06
|
On the stability of shocks with particle pressure
|
We perform a linear stability analysis for corrugations of a Newtonian shock,
with particle pressure included, for an arbitrary diffusion coefficient. We
study first the dispersion relation for homogeneous media, showing that,
besides the conventional pressure waves and entropy/vorticity disturbances, two
new perturbation modes exist, dominated by the particles' pressure and damped
by diffusion. We show that, due to particle diffusion into the upstream region,
the fluid will be perturbed also upstream: we treat these perturbation in the
short wavelength (WKBJ) regime. We then show how to construct a corrugational
mode for the shock itself, one, that is, where the shock executes free
oscillations (possibly damped or growing) and sheds perturbations away from
itself: this global mode requires the new modes. Then, using the perturbed
Rankine-Hugoniot conditions, we show that this leads to the determination of
the corrugational eigenfrequency. We solve numerically the equations for the
eigenfrequency in the WKBJ regime for the models of Amato and Blasi (2005),
showing that they are stable. We then discuss the differences between our
treatment and previous work.
|
0806.1113v1
|
2008-06-17
|
Damping of Fast Magnetohydrodynamic Oscillations in Quiescent Filament Threads
|
High-resolution observations provide evidence about the existence of
small-amplitude transverse oscillations in solar filament fine structures.
These oscillations are believed to represent fast magnetohydrodynamic (MHD)
waves and the disturbances are seen to be damped in short timescales of the
order of 1 to 4 periods. In this Letter we propose that, due to the highly
inhomogeneous nature of the filament plasma at the fine structure spatial
scale, the phenomenon of resonant absorption is likely to operate in the
temporal attenuation of fast MHD oscillations. By considering transverse
inhomogeneity in a straight flux tube model we find that, for density
inhomogeneities typical of filament threads, the decay times are of a few
oscillatory periods only.
|
0806.2728v1
|
2008-06-27
|
Global attractor and asymptotic smoothing effects for the weakly damped cubic Schrödinger equation in $L^2(\T)$
|
We prove that the weakly damped cubic Schr\"odinger flow in $L^2(\T)$
provides a dynamical system that possesses a global attractor. The proof relies
on a sharp study of the behavior of the associated flow-map with respect to the
weak $ L^2(\T) $-convergence inspired by a previous work of the author.
Combining the compactness in $ L^2(\T) $ of the attractor with the approach
developed by Goubet, we show that the attractor is actually a compact set of $
H^2(\T) $. This asymptotic smoothing effect is optimal in view of the
regularity of the steady states.
|
0806.4578v3
|
2008-06-30
|
Thermal depinning of fluxons in discrete Josephson rings
|
We study the thermal depinning of single fluxons in rings made of Josephson
junctions. Due to thermal fluctuations a fluxon can be excited from its energy
minima and move through the array, causing a voltage across each junction. We
find that for the initial depinning, the fluxon behaves as a single particle
and follows a Kramers-type escape law. However, under some conditions this
single particle description breaks down. At low values of the discreteness
parameter and low values of the damping, the depinning rate is larger than the
single particle result would suggest. In addition, for some values of the
parameters the fluxon can undergo low-voltage diffusion before switching to the
high-voltage whirling mode. This type of diffusion is similar to phase
diffusion in a single junction, but occurs without frequency-dependent damping.
We study the switching to the whirling state as well.
|
0806.4828v1
|
2008-07-03
|
Dependence of the decoherence of polarization states in phase-damping channels on the frequency spectrum envelope of photons
|
We consider the decoherence of photons suffering in phase-damping channels.
By exploring the evolutions of single-photon polarization states and two-photon
polarization-entangled states, we find that different frequency spectrum
envelopes of photons induce different decoherence processes. A white frequency
spectrum can lead the decoherence to an ideal Markovian process. Some color
frequency spectrums can induce asymptotical decoherence, while, some other
color frequency spectrums can make coherence vanish periodically with variable
revival amplitudes. These behaviors result from the non-Markovian effects on
the decoherence process, which may give rise to a revival of coherence after
complete decoherence.
|
0807.0536v3
|
2008-07-17
|
Planetary Migration in Resonance, the question of the Eccentricities : Les Houches contribution
|
The formation of resonant planets pairs in exoplanetary systems involves
planetary migration inside the protoplanetary disc : an inwards migrating outer
planet captures in Mean Motion Resonance an inner planet. During the migration
of the resonant pair of planets, the eccentricities are expected to rise
excessively, if no damping mechanism is applied on the inner planet. We express
the required damping action to match the observations, and we show that the
inner disk can play this role. This result applies for instance to the system
GJ 876 : we reproduce the observed orbital elements through a fully
hydrodynamical simulation of the evolution of the resonant planets.
|
0807.2828v2
|
2008-07-18
|
Heavily Damped Motion of One-Dimensional Bose Gases in an Optical Lattice
|
We study the dynamics of strongly correlated one-dimensional Bose gases in a
combined harmonic and optical lattice potential subjected to sudden
displacement of the confining potential. Using the time-evolving block
decimation method, we perform a first-principles quantum many-body simulation
of the experiment of Fertig {\it et al.} [Phys. Rev. Lett. {\bf 94}, 120403
(2005)] across different values of the lattice depth ranging from the
superfluid to the Mott insulator regimes. We find good quantitative agreement
with this experiment: the damping of the dipole oscillations is significant
even for shallow lattices, and the motion becomes overdamped with increasing
lattice depth as observed. We show that the transition to overdamping is
attributed to the decay of superfluid flow accelerated by quantum fluctuations,
which occurs well before the emergence of Mott insulator domains.
|
0807.2898v2
|
2008-07-21
|
Mutual friction in a cold color flavor locked superfluid and r-mode instabilities in compact stars
|
Dissipative processes acting in rotating neutron stars are essential in
preventing the growth of the r-mode instability. We estimate the damping time
of r-modes of an hypothetical compact quark star made up by color flavor locked
quark matter at a temperature $T \lesssim 0.01$ MeV. The dissipation that we
consider is due to the the mutual friction force between the normal and the
superfluid component arising from the elastic scattering of phonons with
quantized vortices. This process is the dominant one for temperatures $T
\lesssim 0.01$ MeV where the mean free path of phonons due to their
self-interactions is larger than the radius of the star and they can be
described as an ideal bosonic gas. We find that r-modes oscillations are
efficiently damped by this mechanism for pulsars rotating at frequencies of the
order of 1 Hz at most. Our analysis rules out the possibility that cold pulsars
rotating at higher frequencies are entirely made up by color flavor locked
quark matter.
|
0807.3264v2
|
2008-07-23
|
Dynamical Backaction of Microwave Fields on a Nanomechanical Oscillator
|
We measure the response and thermal motion of a high-Q nanomechanical
oscillator coupled to a superconducting microwave cavity in the
resolved-sideband regime where the oscillator's resonance frequency exceeds the
cavity's linewidth. The coupling between the microwave field and mechanical
motion is strong enough for radiation pressure to overwhelm the intrinsic
mechanical damping. This radiation-pressure damping cools the fundamental
mechanical mode by a factor of 5 below the thermal equilibrium temperature in a
dilution refrigerator to a phonon occupancy of 140 quanta.
|
0807.3585v3
|
2008-07-28
|
Shear Viscosity of the outer crust of Neutron stars: Ion Contribution
|
The shear viscosity of the crust might have a damping effect on the amplitude
of r-modes of rotating neutron stars. This damping has implications for the
emission of gravitational waves. We calculate the contribution to the shear
viscosity coming from the ions using both semi-analytical methods, that
consider binary collisions, and Molecular Dynamics simulations. We compare
these results with the contribution coming from electrons. We study how the
shear viscosity depends on density for conditions of interest in neutron star
envelopes and outer crusts. In the low density limit, we find good agreement
between results of our molecular dynamics simulations and classical
semi-analytic calculations.
|
0807.4353v2
|
2008-07-28
|
Unusual decoherence in qubit measurements with a Bose-Einstein condensate
|
We consider an electrostatic qubit located near a Bose-Einstein condensate
(BEC) of noninteracting bosons in a double-well potential, which is used for
qubit measurements. Tracing out the BEC variables we obtain a simple analytical
expression for the qubit's density-matrix. The qubit's evolution exhibits a
slow ($\propto1/\sqrt{t}$) damping of the qubit's coherence term, which however
turns to be a Gaussian one in the case of static qubit. This stays in contrast
to the exponential damping produced by most classical detectors. The
decoherence is, in general, incomplete and strongly depends on the initial
state of the qubit.
|
0807.4440v2
|
2008-08-03
|
Superradiant Instability of Five-Dimensional Rotating Charged AdS Black Holes
|
We study the instability of small AdS black holes with two independent
rotation parameters in minimal five-dimensional gauged supergravity to massless
scalar perturbations. We analytically solve the Klein-Gordon equation for
low-frequency perturbations in two regions of the spacetime of these black
holes: namely, in the region close to the horizon and in the far-region. By
matching the solutions in an intermediate region, we calculate the frequency
spectrum of quasinormal modes. We show that in the regime of superradiance only
the modes of even orbital quantum number undergo negative damping, resulting in
exponential growth of the amplitude. That is, the black holes become unstable
to these modes. Meanwhile, the modes of odd orbital quantum number do not
undergo any damping, oscillating with frequency-shifts. This is in contrast
with the case of four-dimensional small Kerr-AdS black holes which exhibit the
instability to all modes of scalar perturbations in the regime of
superradiance.
|
0808.0280v3
|
2008-08-15
|
Collective excitations in two-dimensional antiferromagnet in strong magnetic field
|
We discuss spin-$\frac12$ two-dimensional (2D) Heisenberg antiferromagnet
(AF) on a square lattice at T=0 in strong magnetic field H near its saturation
value $H_c$. A perturbation approach is proposed to obtain spectrum of magnons
with momenta not very close to AF vector in the leading order in small
parameter $(H_c-H)/H_c$. We find that magnons are well-defined quasi-particles
at $H>0.9H_c$ although the damping is quite large near the zone boundary. A
characteristic rotonlike local minimum in the spectrum is observed at ${\bf
k}=(\pi,0)$ accompanied by decrease of the damping near $(\pi,0)$. The
suggested approach can be used in discussion of short-wavelength excitations in
other 2D Bose gases of particles or quasi-particles.
|
0808.2127v3
|
2008-08-26
|
Nonlinear regularization techniques for seismic tomography
|
The effects of several nonlinear regularization techniques are discussed in
the framework of 3D seismic tomography. Traditional, linear, $\ell_2$ penalties
are compared to so-called sparsity promoting $\ell_1$ and $\ell_0$ penalties,
and a total variation penalty. Which of these algorithms is judged optimal
depends on the specific requirements of the scientific experiment. If the
correct reproduction of model amplitudes is important, classical damping
towards a smooth model using an $\ell_2$ norm works almost as well as
minimizing the total variation but is much more efficient. If gradients (edges
of anomalies) should be resolved with a minimum of distortion, we prefer
$\ell_1$ damping of Daubechies-4 wavelet coefficients. It has the additional
advantage of yielding a noiseless reconstruction, contrary to simple $\ell_2$
minimization (`Tikhonov regularization') which should be avoided. In some of
our examples, the $\ell_0$ method produced notable artifacts. In addition we
show how nonlinear $\ell_1$ methods for finding sparse models can be
competitive in speed with the widely used $\ell_2$ methods, certainly under
noisy conditions, so that there is no need to shun $\ell_1$ penalizations.
|
0808.3472v3
|
2008-09-09
|
Process tomography of field damping and measurement of Fock state lifetimes by quantum non-demolition photon counting in a cavity
|
The relaxation of a quantum field stored in a high-$Q$ superconducting cavity
is monitored by non-resonant Rydberg atoms. The field, subjected to repetitive
quantum non-demolition (QND) photon counting, undergoes jumps between photon
number states. We select ensembles of field realizations evolving from a given
Fock state and reconstruct the subsequent evolution of their photon number
distributions. We realize in this way a tomography of the photon number
relaxation process yielding all the jump rates between Fock states. The damping
rates of the $n$ photon states ($0\leq n \leq 7$) are found to increase
linearly with $n$. The results are in excellent agreement with theory including
a small thermal contribution.
|
0809.1511v1
|
2008-10-01
|
Excitation of trapped oscillations in discs around black holes
|
High-frequency quasi-periodic oscillations detected in the light curves of
black hole candidates can, according to one model, be identified with
hydrodynamic oscillations of the accretion disc. We describe a non-linear
coupling mechanism, suggested by Kato, through which inertial waves trapped in
the inner regions of accretion discs around black holes are excited. Global
warping and/or eccentricity of the disc have a fundamental role in this
coupling: they combine with trapped modes, generating negative energy waves,
that are damped as they approach the inner edge of the disc or their corotation
resonance. As a result of this damping, inertial oscillations are amplified. We
calculate the resulting eigenfunctions and their growth rates.
|
0810.0116v1
|
2008-10-09
|
Atomistic spin dynamics of the CuMn spin glass alloy
|
We demonstrate the use of Langevin spin dynamics for studying dynamical
properties of an archetypical spin glass system. Simulations are performed on
CuMn (20% Mn) where we study the relaxation that follows a sudden quench of the
system to the low temperature phase. The system is modeled by a Heisenberg
Hamiltonian where the Heisenberg interaction parameters are calculated by means
of first-principles density functional theory. Simulations are performed by
numerically solving the Langevin equations of motion for the atomic spins. It
is shown that dynamics is governed, to a large degree, by the damping parameter
in the equations of motion and the system size. For large damping and large
system sizes we observe the typical aging regime.
|
0810.1645v1
|
2008-10-20
|
On the Existence of Exponentially Decreasing Solutions of the Nonlinear Landau Damping Problem
|
In this paper we prove the existence of a large class of periodic solutions
of the Vlasov-Poisson in one space dimension that decay exponentially as t goes
to infinity. The exponential decay is well known for the linearized version of
the Landau damping problem and it has been proved in [4] for a class of
solutions of the Vlasov-Poisson system that behaves asymptotically as free
streaming solutions and are sufficiently flat in the space of velocities. The
results in this paper enlarge the class of possible asymptotic limits,
replacing the fatness condition in [4] by a stability condition for the
linearized problem.
|
0810.3456v2
|
2008-10-22
|
Thermal (in)stability of type I collagen fibrils
|
We measured Young's modulus at temperatures ranging from 20 to 100 ^{\circ}$C
for a collagen fibril taken from rat's tendon. The hydration change under
heating and the damping decrement were measured as well. At physiological
temperatures $25-45^{\circ}$C Young's modulus decreases, which can be
interpreted as instability of collagen. For temperatures between
$45-80^{\circ}$C Young's modulus first stabilizes and then increases with
decreasing the temperature. The hydrated water content and the damping
decrement have strong maxima in the interval $70-80^{\circ}$C indicating on
complex inter-molecular structural changes in the fibril. All these effects
disappear after heat-denaturating the sample at $120^\circ$C. Our main result
is a five-stage mechanism by which the instability of a single collagen at
physiological temperatures is compensated by the interaction between collagen
molecules within the fibril.
|
0810.4172v1
|
2008-11-03
|
Ion thermal effects in oscillating multi-ion plasma sheath theory
|
The effects of ion temperature are discussed in a two-ion electron plasma and
for a model applicable to the oscillating sheath theory that has recently been
much in the focus of researchers. The differences between the fluid and kinetic
models have been pointed out, as well as the differences between the
approximative kinetic description (which involves the expansion of the plasma
dispersion function), and the exact kinetic description. It is shown that the
approximative kinetic description, first, can not describe the additional
acoustic mode which naturally exists in the plasma with an additional ion
population with a finite temperature, and, second, it yields an inaccurate
Landau damping of the bulk ion acoustic mode. The reasons for these two
failures are described. In addition to this, a fluid model is presented that is
capable of capturing both of these features that are missing in the
approximative kinetic description, i.e., two (fast and slow) ion acoustic
modes, and the corresponding Landau damping of both modes.
|
0811.0251v1
|
2008-12-01
|
Self-Diffusion in 2D Dusty Plasma Liquids: Numerical Simulation Results
|
We perform Brownian dynamics simulations for studying the self-diffusion in
two-dimensional (2D) dusty plasma liquids, in terms of both mean-square
displacement and velocity autocorrelation function (VAF). Super-diffusion of
charged dust particles has been observed to be most significant at infinitely
small damping rate $\gamma$ for intermediate coupling strength, where the
long-time asymptotic behavior of VAF is found to be the product of $t^{-1}$ and
$\exp{(-\gamma t)}$. The former represents the prediction of early theories in
2D simple liquids and the latter the VAF of a free Brownian particle. This
leads to a smooth transition from super-diffusion to normal diffusion, and then
to sub-diffusion with an increase of the damping rate. These results well
explain the seemingly contradictory scattered in recent classical molecular
dynamics simulations and experiments of dusty plasmas.
|
0812.0338v3
|
2008-12-11
|
Reduced nonlinear description of Farley-Buneman instability
|
In the study on nonlinear wave-wave processes in an ionosphere and a
magnetosphere usually the main attention is paid to investigation of plasma
turbulence at well developed stage, when the wide spectrum of plasma wave is
present. On the other side, it is well known that even if the number of
cooperating waves remains small due to a competition of processes of their
instability and attenuation, the turbulence appears in the result of their
stochastic behavior. The regimes of nonlinear dynamics of low frequency waves
excited due to Farley-Buneman instability in weakly ionized and inhomogeneous
ionospheric plasma in the presence of electric current perpendicular to ambient
magnetic field are considered. The problem is essentially three dimensional and
difficult for full numerical simulation, but the strong collisional damping of
waves allow to assume that in this case a perturbed state of plasma can be
described as finite set of interacting waves, some of which are unstable and
other strongly damping. The proposed nonlinear model allow to make full study
of nonlinear stabilization, conditions of stochasticity and to consider the
different regimes and properties of few mode plasma turbulence.
|
0812.2182v1
|
2008-12-16
|
Reconstructing Baryon Oscillations: A Lagrangian Theory Perspective
|
Recently Eisenstein and collaborators introduced a method to `reconstruct'
the linear power spectrum from a non-linearly evolved galaxy distribution in
order to improve precision in measurements of baryon acoustic oscillations. We
reformulate this method within the Lagrangian picture of structure formation,
to better understand what such a method does, and what the resulting power
spectra are. We show that reconstruction does not reproduce the linear density
field, at second order. We however show that it does reduce the damping of the
oscillations due to non-linear structure formation, explaining the improvements
seen in simulations. Our results suggest that the reconstructed power spectrum
is potentially better modeled as the sum of three different power spectra, each
dominating over different wavelength ranges and with different non-linear
damping terms. Finally, we also show that reconstruction reduces the
mode-coupling term in the power spectrum, explaining why mis-calibrations of
the acoustic scale are reduced when one considers the reconstructed power
spectrum.
|
0812.2905v3
|
2009-01-28
|
Location- and observation time-dependent quantum-tunneling
|
We investigate quantum tunneling in a translation invariant chain of
particles. The particles interact harmonically with their nearest neighbors,
except for one bond, which is anharmonic. It is described by a symmetric double
well potential. In the first step, we show how the anharmonic coordinate can be
separated from the normal modes. This yields a Lagrangian which has been used
to study quantum dissipation. Elimination of the normal modes leads to a
nonlocal action of Caldeira-Leggett type. If the anharmonic bond defect is in
the bulk, one arrives at Ohmic damping, i.e. there is a transition of a
delocalized bond state to a localized one if the elastic constant exceeds a
critical value $C_{crit}$. The latter depends on the masses of the bond defect.
Superohmic damping occurs if the bond defect is in the site $M$ at a finite
distance from one of the chain ends. If the observation time $T$ is smaller
than a characteristic time $\tau_M \sim M$, depending on the location M of the
defect, the behavior is similar to the bulk situation. However, for $T \gg
\tau_M$ tunneling is never suppressed.
|
0901.4518v1
|
2009-02-16
|
Plasmon excitations in homogeneous neutron star matter
|
We study the possible collective plasma modes which can affect neutron-star
thermodynamics and different elementary processes in the baryonic density range
between nuclear saturation ($\rho_0$) and $3\rho_0$. In this region, the
expected constituents of neutron-star matter are mainly neutrons, protons,
electrons and muons ($npe\mu$ matter), under the constraint of beta
equilibrium. The elementary plasma excitations of the $pe\mu$ three-fluid
medium are studied in the RPA framework. We emphasize the relevance of the
Coulomb interaction among the three species, in particular the interplay of the
electron and muon screening in suppressing the possible proton plasma mode,
which is converted into a sound-like mode. The Coulomb interaction alone is
able to produce a variety of excitation branches and the full spectral function
shows a rich structure at different energy. The genuine plasmon mode is pushed
at high energy and it contains mainly an electron component with a substantial
muon component, which increases with density. The plasmon is undamped for not
too large momentum and is expected to be hardly affected by the nuclear
interaction. All the other branches, which fall below the plasmon, are damped
or over-damped.
|
0902.2552v2
|
2009-02-27
|
Monogamy Inequality and Residual Entanglement of Three Qubits under Decoherence
|
Exploring an analytical expression for the convex roof of the pure state
squared concurrence for rank 2 mixed states the entanglement of a system of
three particles under decoherence is studied, using the monogamy inequality for
mixed states and the residual entanglement obtained from it. The monogamy
inequality is investigated both for the concurrence and the negativity in the
case of local independent phase damping channel acting on generalized GHZ
states of three particles and the local independent amplitude damping channel
acting on generalized W state of three particles. It is shown that the
bipartite entanglement between one qubit and the rest has a qualitative similar
behavior to the entanglement between individual qubits, and that the residual
entanglement in terms of the negativity cannot be a good entanglement measure
for mixed states, since it can increase under local decoherence.
|
0903.0019v2
|
2009-03-12
|
X-band crab cavities for the CLIC beam delivery system
|
The CLIC machine incorporates a 20 mrad crossing angle at the IP to aid the
extraction of spent beams. In order to recover the luminosity lost through the
crossing angle a crab cavity is proposed to rotate the bunches prior to
collision. The crab cavity is chosen to have the same frequency as the main
linac (11.9942 GHz) as a compromise between size, phase stability requirements
and beam loading. It is proposed to use a HE11 mode travelling wave structure
as the CLIC crab cavity in order to minimise beam loading and mode separation.
The position of the crab cavity close to the final focus enhances the effect of
transverse wake-fields so effective wake-field damping is required. A damped
detuned structure is proposed to suppress and de-cohere the wake-field hence
reducing their effect. Design considerations for the CLIC crab cavity will be
discussed as well as the proposed high power testing of these structures at
SLAC.
|
0903.2116v1
|
2009-03-16
|
Regularity of invariant sets in semilinear damped wave equations
|
Under fairly general assumptions, we prove that every compact invariant
subset $\mathcal I$ of the semiflow generated by the semilinear damped wave
equation \epsilon u_{tt}+u_t+\beta(x)u-\sum_{ij}(a_{ij}
(x)u_{x_j})_{x_i}&=f(x,u),&& (t,x)\in[0,+\infty[\times\Omega,
u&=0,&&(t,x)\in[0,+\infty[\times\partial\Omega in $H^1_0(\Omega)\times
L^2(\Omega)$ is in fact bounded in $D(\mathbf A)\times H^1_0(\Omega)$. Here
$\Omega$ is an arbitrary, possibly unbounded, domain in $\R^3$, $\mathbf A
u=\beta(x)u-\sum_{ij}(a_{ij}(x)u_{x_j})_{x_i}$ is a positive selfadjoint
elliptic operator and $f(x,u)$ is a nonlinearity of critical growth. The
nonlinearity $f(x,u)$ needs not to satisfy any dissipativeness assumption and
the invariant subset $\mathcal I$ needs not to be an an attractor.
|
0903.2782v1
|
2009-03-20
|
Hawking-Unruh radiation as irreversible consequence of radiative action in dynamics
|
Hawking-Unruh thermal state of warm surrounding field encountered in
non-inertial frames is shown to be a real phenomenon, a marker of nonstationary
dynamic evolutions. In accelerated motion of a charged particle it is shown
that the recoiled damping effect of Larmor radiation relaxation leads to
distinctive thermal power, which is akin to that of Hawking-Unruh radiation
from warm surrounding field of the accelerated charge. The damping effect from
recoil-momentum of transverse electromagnetic field is worked out by
considering torque imparted to the inherently existing angular evolution of
spherically polarized vacuum field around the point-like charged particle in
acceleration. Hawking-Unruh effects is generally noted to be a universal marker
of decoherence in evolution in all scales of microscopic, macroscopic and
megascopic systems. Besides detailing the case of electrodynamics, the various
efficacies of H-U relaxation are considered in the nonstationary evolutions.
|
0903.3529v2
|
2009-03-25
|
The covering factor of high redshift damped Lyman-$α$ systems
|
We have used the Very Long Baseline Array to image 18 quasars with foreground
damped Lyman-$\alpha$ systems (DLAs) at 327, 610 or 1420 MHz, to measure the
covering factor $f$ of each DLA at or near its redshifted HI 21cm line
frequency. Including six systems from the literature, we find that none of 24
DLAs at $0.09 < z < 3.45$ has an exceptionally low covering factor, with $f
\sim 0.45 - 1$ for the 14 DLAs at $z > 1.5$, $f \sim 0.41 - 1$ for the 10
systems at $z < 1$, and consistent covering factor distributions in the two
sub-samples. The observed paucity of detections of HI 21cm absorption in
high-$z$ DLAs thus cannot be explained by low covering factors and is instead
likely to arise due to a larger fraction of warm HI in these absorbers.
|
0903.4483v1
|
2009-04-15
|
Size dependent Acoustic Phonon Dynamics of CdTe0.68Se0.32 Nanoparticles in Borosilicate glass
|
Low frequency acoustic vibration and phonon linewidth for CdTe0.68Se0.32
nanoparticle embedded in borosilicate glass are calculated using two different
approaches by considering the elastic continuum model and fixed boundary
condition. The presence of medium significantly affects the phonon peaks and
results into the broadening of the modes. The linewidth is found to depend
inversely on the size, similar to that reported experimentally. The damping
time and quality factor have also been calculated. The damping time that is of
the order of picoseconds decreases with the decrease in size. High value of
quality factor for l=2 normal mode suggests the less loss of energy for this
mode.
|
0904.2278v1
|
2009-04-19
|
Incorporating Human Body Mass in Standards of Helmet Impact Protection against Traumatic Brain Injury
|
Impact induced traumatic brain injury (ITBI) describes brain injury from head
impact not necessarily accompanied by skull fracture. For sufficiently abrupt
head impact decelerations, ITBI results from brain tissue stress incurred as
the brain crashes into the inside of the skull wall, displacing the surrounding
cerebral spinal fluid (CSF). Proper helmet cushioning can damp the impact force
and reduce ITBI. But force is mass times acceleration and commonly used helmet
blunt impact standards are based only on acceleration thresholds. Here I show
how this implies that present standards overestimate the minimum acceleration
onset for ITBI by implicitly assuming that the brain is mechanically decoupled
from the body. I quantify how an arbitrary orientation of the body with respect
to impact direction increases the effective mass that should be used in
calculating the required damping force and injury threshold accelerations. I
suggest a practical method to incorporate the body mass and impact angle into
ITBI helmet standards and provide direction for further work.
|
0904.2856v1
|
2009-04-21
|
Type II migration of planets on eccentric orbits
|
The observed extrasolar planets possess both large masses (with a median M
sin i of 1.65 MJ) and a wide range in orbital eccentricity (0 < e < 0.94). As
planets are thought to form in circumstellar disks, one important question in
planet formation is determining whether, and to what degree, a gaseous disk
affects an eccentric planet's orbit. Recent studies have probed the interaction
between a disk and a terrestrial planet on an eccentric orbit, and the
interaction between a disk and a gas giant on a nearly circular orbit, but
little is known about the interaction between a disk and an eccentric gas
giant. Such a scenario could arise due to scattering while the disk is still
present, or perhaps through planet formation via gravitational instability. We
fill this gap with simulations of eccentric, massive (gap-forming) planets in
disks using the hydrodynamical code FARGO. Although the long-term orbital
evolution of the planet depends on disk properties, including the boundary
conditions used, the disk always acts to damp eccentricity when the planet is
released into the disk. This eccentricity damping takes place on a timescale of
40 years, 15 times faster than the migration timescale.
|
0904.3336v1
|
2009-05-13
|
J-transform applied to the detection of Gravitational Waves: preliminary results
|
We propose to apply to the detection of Gravitational Waves a new method
developed for the spectral analysis of noisy time-series of damped oscillators.
From the Pad\'e Approximations of the time-series Z-transform, a Jacobi
Matrix (J-Matrix) is constructed. We show that the J-Matrix has bound states
with eigenvalues strictly inside the unit circle. Each bound state can be
identified with one precise damped oscillator. Beside these bound states, there
is an essential spectrum sitting on the unit circle which represents the noise.
In this picture, signal and noise are clearly separated and identified in the
complex plane. Furthermore, we show that the J-transform enjoys the exceptional
feature of lossless undersampling. We take advantage of the above properties of
the J-transform to develop a procedure for the search of Gravitational Wave
bursts in interferometric data series such as those of LIGO and VIRGO projects.
Successful application of our procedure to simulated data having a poor signal
to noise ratio, highlights the power of our method.
|
0905.2000v1
|
2009-05-25
|
Non-Markovian dynamics of a biased qubit coupled to a structured bath
|
A new analytical approach, beyond rotating wave approximation, based on
unitary transformations and the non-Markovian master equation for the density
operator, is applied to treat the biased spin boson model with a Lorentzian
structured bath for arbitrary detunings at zero temperature. Compared to zero
bias, we find that the dynamics demonstrates two more damping oscillation
frequencies and one additional relaxation frequency for non-zero bias, where
one of the damping oscillation frequencies is a new effect. Analytical
expressions for the non-Markovian dynamics and the corresponding spectrum, the
localized-delocalized transition point, the coherent-incoherent transition
point, the analytical ground energy, the renormalized tunneling factor and the
susceptibility are determined. The sum rule and the Shiba relation are checked
in the coherent regime.
|
0905.3965v3
|
2009-05-28
|
A black box method for solving the complex exponentials approximation problem
|
A common problem, arising in many different applied contexts, consists in
estimating the number of exponentially damped sinusoids whose weighted sum best
fits a finite set of noisy data and in estimating their parameters. Many
different methods exist to this purpose. The best of them are based on
approximate Maximum Likelihood estimators, assuming to know the number of
damped sinusoids, which can then be estimated by an order selection procedure.
As the problem can be severely ill posed, a stochastic perturbation method is
proposed which provides better results than Maximum Likelihood based methods
when the signal-to-noise ratio is low. The method depends on some
hyperparameters which turn out to be essentially independent of the
application. Therefore they can be fixed once and for all, giving rise to a
black box method.
|
0905.4602v2
|
2009-06-10
|
GALEX Discovery of a Damped Ly-alpha System at Redshift z = 1
|
We report the first discovery of a QSO damped Ly-alpha (DLA) system by the
GALEX satellite. The system was initially identified as an MgII absorption-line
system (z_abs=1.028) in the spectrum of SDSS QSO J0203-0910 (z_em=1.58). The
presence of unusually strong absorption due to metal lines of ZnII, CrII, MnII,
and FeII clearly suggested that it might be a DLA system with N{HI} > 2 x 10^20
atoms cm^-2. Follow-up GALEX NUV grism spectroscopy confirms the system
exhibits a DLA absorption line, with a measured HI column density of N{HI} =
1.50+/-0.45 x 10^21 atoms cm^-2. By combining the GALEX N{HI} determination
with the SDSS spectrum measurements of unsaturated metal-line absorption due to
ZnII, which is generally not depleted onto grains, we find that the system's
neutral-gas-phase metal abundance is [Zn/H] = -0.69+/-0.22, or ~20% solar. By
way of comparison, although this system has one of the largest Zn^+ column
densities, its metal abundances are comparable to other DLAs at z~1.
Measurements of the abundances of Cr, Fe, and Mn help to further pin down the
evolutionary state of the absorber.
|
0906.2018v1
|
2009-06-11
|
Longitudinal Stability of Recycler Bunches; Part I: Thresholds for Loss of Landau Damping
|
We examine the stability of intense flat bunches in barrier buckets used in
the Recycler. We consider some common stationary distributions and show that
they would be unstable against rigid dipole oscillations. We then discuss an
analytical model for the line density that best describes measured bunch
profiles. We include space charge in this model to predict the bunch intensity
at which Landau damping would be lost. The dependence of this threshold on the
bunch length is studied and related to the results of an experimental study
with shorter bunch lengths. The threshold for the microwave instability is
estimated. These studies will be followed by more detailed numerical studies.
|
0906.2188v1
|
2009-06-15
|
Regge poles of the Schwarzschild black hole: a WKB approach
|
We provide simple and accurate analytical expressions for the Regge poles of
the Schwarzschild black hole. This is achieved by using third-order WKB
approximations to solve the radial wave equations for spins 0, 1 and 2. These
results permit us to obtain analytically the dispersion relation and the
damping of the "surface waves" lying on the photon sphere of the Schwarzschild
black hole and which generate the weakly damped quasinormal modes of its
spectrum. Our results could be helpful in order to simplify considerably the
description of wave scattering from the Schwarzschild black hole as well as the
analysis of the gravitational radiation created in many black hole processes.
Furthermore, the existence of dispersion relations for the photons propagating
close to the photon sphere could have also important consequences in the
context of gravitational lensing.
|
0906.2601v3
|
2009-06-30
|
Cooling a magnetic resonance force microscope via the dynamical back-action of nuclear spins
|
We analyze the back-action influence of nuclear spins on the motion of the
cantilever of a magnetic force resonance microscope. We calculate the
contribution of nuclear spins to the damping and frequency shift of the
cantilever. We show that, at the Rabi frequency, the energy exchange between
the cantilever and the spin system cools or heats the cantilever depending on
the sign of the high-frequency detuning. We also show that the spin noise leads
to a significant damping of the cantilever motion.
|
0906.5420v2
|
2009-07-03
|
Magnetic interference patterns in long disordered Josephson junctions
|
We study a diffusive superconductor - normal metal - superconductor (SNS)
junction in an external magnetic field. In the limit of a long junction, we
find that the form of the dependence of the Josephson current on the field and
on the length of the junction depends on the ratio between the junction width
and the length associated with the magnetic field. A certain critical ratio
between these two length scales separates two different regimes. In narrow
junctions, the critical current exhibits a pure decay as a function of the
junction length or of the magnetic field. In wide junctions, the critical
current exhibits damped oscillations as a function of the same parameters. This
damped oscillating behavior differs from the Fraunhofer pattern typical for
short or tunnel junctions. In wide and long junctions, superconducting pair
correlations and supercurrent are localized along the edges of the junction.
|
0907.0632v3
|
2009-07-12
|
Symmetries shape the current in ratchets induced by a bi-harmonic force
|
Equations describing the evolution of particles, solitons, or localized
structures, driven by a zero-average, periodic, external force, and invariant
under time reversal and a half-period time shift, exhibit a ratchet current
when the driving force breaks these symmetries. The bi-harmonic force
$f(t)=\epsilon_1\cos(q \omega t+\phi_1)+\epsilon_2\cos(p\omega t+\phi_2)$ does
it for almost any choice of $\phi_{1}$ and $\phi_{2}$, provided $p$ and $q$ are
two co-prime integers such that $p+q$ is odd. It has been widely observed, in
experiments in Josephson-junctions, photonic crystals, etc., as well as in
simulations, that the ratchet current induced by this force has the shape
$v\propto\epsilon_1^p\epsilon_2^q\cos(p \phi_{1} - q \phi_{2} + \theta_0)$ for
small amplitudes, where $\theta_0$ depends on the damping ($\theta_0=\pi/2$ if
there is no damping, and $\theta_0=0$ for overdamped systems). We rigorously
prove that this precise shape can be obtained solely from the broken symmetries
of the system and is independent of the details of the equation describing the
system.
|
0907.2029v2
|
2009-07-21
|
AFM Dissipation Topography of Soliton Superstructures in Adsorbed Overlayers
|
In the atomic force microscope, the nanoscale force topography of even
complex surface superstructures is extracted by the changing vibration
frequency of a scanning tip. An alternative dissipation topography with similar
or even better contrast has been demonstrated recently by mapping the
(x,y)-dependent tip damping but the detailed damping mechanism is still
unknown. Here we identify two different tip dissipation mechanisms: local
mechanical softness and hysteresis. Motivated by recent data, we describe both
of them in a onedimensional model of Moire' superstructures of incommensurate
overlayers. Local softness at "soliton" defects yields a dissipation contrast
that can be much larger than the corresponding density or corrugation contrast.
At realistically low vibration frequencies, however, a much stronger and more
effective dissipation is caused by the tip-induced nonlinear jumping of the
soliton, naturally developing bistability and hysteresis. Signatures of this
mechanism are proposed for experimental identification.
|
0907.3585v4
|
2009-07-24
|
Harmonic damped oscillators with feedback. A Langevin study
|
We consider a system in direct contact with a thermal reservoir and which, if
left unperturbed, is well described by a memory-less equilibrium Langevin
equation of the second order in the time coordinate. In such conditions, the
strength of the noise fluctuations is set by the damping factor, in accordance
with the Fluctuation and Dissipation theorem. We study the system when it is
subject to a feedback mechanism, by modifying the Langevin equation
accordingly. Memory terms now arise in the time evolution, which we study in a
non-equilibrium steady state. Two types of feedback schemes are considered, one
focusing on time shifts and one on phase shifts, and for both cases we evaluate
the power spectrum of the system's fluctuations. Our analysis finds application
in feedback cooled oscillators, such as the Gravitational Wave detector AURIGA.
|
0907.4309v1
|
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