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2013-10-25 | Voltage noise, switching rates, and multiple phase-slips in moderately damped Josephson junctions | We study the voltage noise properties including the switching rates and
statistics of phase-slips in moderately damped Josephson junctions using a
novel efficient numerical approach combining the matrix continued-fraction
method with the full counting statistics. By analyzing the noise results
obtained for the RCSJ model we identify different dominating components, namely
the thermal noise close to equilibrium (small current-bias regime), the shot
noise of (multiple) phase-slips in the intermediate range of biases and the
switching noise for yet higher bias currents. We extract thus far inaccessible
characteristic rates of phase-slips in the shot noise regime as well as the
escape and retrapping rates in the switching regime as functions of various
junction's parameters. The method can be extended and applied to other
experimentally relevant Josephson junction circuits. | 1310.6871v1 |
2013-11-06 | Analytical estimation of ATF beam halo distribution | In order to study the background status in the ATF2 beam line and the
interaction point (IP), this paper developed an analytical method to give the
estimation of ATF beam halo distribution based on K. Hirata and K. Yokoya's
theory. The equilibrium particle distribution of beam tail in ATF damping ring,
when each electron is being affected by, in addition to the synchrotron
radiation damping effects, several stochastic processes, such as beam-gas
scattring, beam-gas bremsstrahlung and intra-beam scattering, was presented.
This method is common and can be applied on other electron rings. | 1311.1267v3 |
2013-11-13 | Quantum turbulence in superfluids with wall-clamped normal component | In Fermi superfluids, like superfluid 3He, the viscous normal component can
be considered to be stationary with respect to the container. The normal
component interacts with the superfluid component via mutual friction which
damps the motion of quantized vortex lines and eventually couples the
superfluid component to the container. With decreasing temperature and mutual
friction the internal dynamics of the superfluid component becomes more
important compared to the damping and coupling effects from the normal
component. This causes profound changes in superfluid dynamics: the
temperature-dependent transition from laminar to turbulent vortex motion and
the decoupling from the reference frame of the container at even lower
temperatures. | 1311.3112v1 |
2013-11-19 | Protecting qutrit-qutrit entanglement by weak measurement and reversal | Entangled states in high dimensional systems are of great interest due to the
extended possibilities they provide in quantum information processing.
Recently, Sun et al. [Phys. Rev. A 82, 052323 (2010)] and Kim et al. [Nat.
Phys. 8, 117 (2012)] pointed out that weak measurement and quantum weak
measurement reversal can actively combat decoherence. We generalize their
studies from qubits to qutrits under amplitude damping decoherence. We find
that the qutrit-qutrit entanglement can be partially retrieved for certain
initial states when only weak measurement reversals are performed. However, we
can completely defeat amplitude damping decoherence for any initial states by
the combination of prior weak measurements and post optimal weak measurement
reversals. The experimental feasibility of our schemes is also discussed. | 1311.4692v2 |
2013-11-27 | Encapsulated formulation of the Selective Frequency Damping method | We present an alternative "encapsulated" formulation of the Selective
Frequency Damping method for finding unstable equilibria of dynamical systems,
which is particularly useful when analysing the stability of fluid flows. The
formulation makes use of splitting methods, which means that it can be wrapped
around an existing time-stepping code as a "black box". The method is first
applied to a scalar problem in order to analyse its stability and highlight the
roles of the control coefficient $\chi$ and the filter width $\Delta$ in the
convergence (or not) towards the steady-state. Then the steady-state of the
incompressible flow past a two-dimensional cylinder at $Re=100$, obtained with
a code which implements the spectral/hp element method, is presented. | 1311.7000v1 |
2013-12-02 | The spatial distribution of dark-matter-annihilation originated gamma-ray line signal | The GeV$-$TeV $\gamma-$ray line signal is the smoking gun signature of the
dark matter annihilation or decay. The detection of such a signal is one of the
main targets of some space-based telescopes, including Fermi-LAT and the
upcoming CALET, DAMPE and Gamma-400. An important feature of the
dark-matter-annihilation originated $\gamma-$ray line photons is their
concentration at the center of the Galaxy. So far no reliable $\gamma-$ray line
has been detected by Fermi-LAT and the upper limits on the cross section of
annihilation into $\gamma-$rays have been reported. We use these upper limits
to estimate the "maximal" number of $\gamma-$ray line photons detectable for
Fermi-LAT, DAMPE and Gamma-400 and then investigate the spatial distribution of
these photons. We show that usually the center of the distribution region will
be offset from the Galactic centre (Sgr A$^{\star}$) due to the limited
statistics. Such a result is almost independent of the dark matter distribution
models and renders the reconstruction of the dark matter distribution with the
$\gamma-$ray line signal very challenging for the foreseeable space-based
detectors. | 1312.0357v2 |
2013-12-03 | Inflationary Steps in the Planck Data | We extend and improve the modeling and analysis of large-amplitude, sharp
inflationary steps for second order corrections required by the precision of
the Planck CMB power spectrum and for arbitrary Dirac-Born-Infeld sound speed.
With two parameters, the amplitude and frequency of the resulting oscillations,
step models improve the fit by $\Delta \chi^2 = -11.4$. Evidence for
oscillations damping before the Planck beam scale is weak: damping only
improves the fit to $\Delta \chi^2 = -14.0$ for one extra parameter, if step
and cosmological parameters are jointly fit, in contrast to analyses which fix
the latter. Likewise, further including the sound speed as a parameter only
marginally improves the fit to $\Delta \chi^2 = -15.2$ but has interesting
implications for the lowest multipole temperature and polarization anisotropy.
Since chance features in the noise can mimic these oscillatory features, we
discuss tests from polarization power spectra, lensing reconstruction and
squeezed and equilateral bispectra that should soon verify or falsify their
primordial origin. | 1312.0946v1 |
2013-12-16 | Exploiting Intrinsic Triangular Geometry in Relativistic He3+Au Collisions to Disentangle Medium Properties | Recent results in d+Au and p+Pb collisions at RHIC and the LHC provide
evidence for collective expansion and flow of the created medium. We propose a
control set of experiments to directly compare particle emission patterns from
p+Au, d+Au, and He3+Au or t+Au collisions at the same sqrt(sNN). Using Monte
Carlo Glauber we find that a He3 or triton projectile, with a realistic
wavefunction description, induces a significant intrinsic triangular shape to
the initial medium and that, even with viscous damping, this survives into a
significant third order flow moment v3. By comparing systems with one, two, and
three initial hot spots, one can disentangle the effects from the initial
spatial distribution of the deposited energy and viscous damping. These are key
tools to answering the question of how small a droplet of matter is necessary
to form a quark-gluon plasma described by nearly inviscid hydrodynamics. | 1312.4565v2 |
2013-12-17 | Reversal time of the magnetization of magnetic nanoparticles at very low damping | The magnetization reversal time of ferromagnetic nanoparticles is
investigated in the very low damping regime. The energy-controlled diffusion
equation rooted in a generalization of the Kramers escape rate theory for point
Brownian particles in a potential to the magnetic relaxation of a macrospin,
yields the reversal time in closed integral form. The latter is calculated for
a nanomagnet with uniaxial anisotropy with a uniform field applied at an angle
to the easy axis and for a nanomagnet with biaxial anisotropy with the field
along the easy axis. The results completely agree with those yielded by
independent numerical and asymptotic methods. | 1312.4904v3 |
2013-12-18 | Quantum speed limit for arbitrary initial states | We investigate the generic bound on the minimal evolution time of the open
dynamical quantum system. This quantum speed limit time is applicable to both
mixed and pure initial states. We then apply this result to the damped
Jaynes-Cummings model and the Ohimc-like dephasing model starting from a
general time-evolution state. The bound of this time-dependent state at any
point in time can be found. For the damped Jaynes-Cummings model, the
corresponding bound first decreases and then increases in the Markovian
dynamics. While in the non-Markovian regime, the speed limit time shows an
interesting periodic oscillatory behavior. For the case of Ohimc-like dephasing
model, this bound would be gradually trapped to a fixed value. In addition, the
roles of the relativistic effects on the speed limit time for the observer in
non-inertial frames are discussed. | 1312.5071v1 |
2013-12-26 | Equilibrium of a Brownian particle in an inhomogeneous medium: An alternative approach | We look at the equilibrium of a Brownian particle in an inhomogeneous space
following the alternative approach proposed in ref.[1]. We consider a
coordinate dependent damping that makes the stochastic dynamics the one with
multiplicative noise. Here we show that the mapping to an additive noise gives
the equilibrium distribution of the generalized Langevin dynamics of a particle
with mass. The procedure does not need inclusion of any ad hoc current
cancelling term in the Langevin dynamics. The result shows a modified
Maxwell-Boltzmann distribution with a damping dependent amplitude. | 1312.7075v3 |
2014-01-22 | On Stability of Hyperbolic Thermoelastic Reissner-Mindlin-Timoshenko Plates | In the present article, we consider a thermoelastic plate of
Reissner-Mindlin-Timoshenko type with the hyperbolic heat conduction arising
from Cattaneo's law. In the absense of any additional mechanical dissipations,
the system is often not even strongly stable unless restricted to the
rotationally symmetric case, etc. We present a well-posedness result for the
linear problem under general mixed boundary conditions for the elastic and
thermal parts. For the case of a clamped, thermally isolated plate, we show an
exponential energy decay rate under a full damping for all elastic variables.
Restricting the problem to the rotationally symmetric case, we further prove
that a single frictional damping merely for the bending compoment is sufficient
for exponential stability. To this end, we construct a Lyapunov functional
incorporating the Bogovski\u{i} operator for irrotational vector fields which
we discuss in the appendix. | 1401.5669v1 |
2014-01-27 | Edge states in 2D lattices with hopping anisotropy and Chebyshev polynomials | Analytic technique based on Chebyshev polynomials is developed for studying
two-dimensional lattice ribbons with hopping anisotropy. In particular, the
tight-binding models on square and triangle lattice ribbons are investigated
with anisotropic nearest neighbouring hoppings. For special values of hopping
parameters the square lattice becomes topologically equivalent to a honeycomb
one either with zigzag or armchair edges. In those cases as well as for
triangle lattices we perform the exact analytic diagonalization of
tight-binding Hamiltonians in terms of Chebyshev polynomials. Deep inside the
edge state subband the wave functions exhibit exponential spatial damping which
turns into power-law damping at edge-bulk transition point. It is shown that
strong hopping anisotropy crashes down edge states, and the corresponding
critical conditions are found. | 1401.6770v2 |
2014-01-27 | Dynamical pattern formations in two dimensional fluid and Landau pole bifurcation | A phenomenological theory is proposed to analyze the asymptotic dynamics of
perturbed inviscid Kolmogorov shear flows in two dimensions. The phase diagram
provided by the theory is in qualitative agreement with numerical observations,
which include three phases depending on the aspect ratio of the domain and the
size of the perturbation: a steady shear flow, a stationary dipole, and four
traveling vortices. The theory is based on a precise study of the inviscid
damping of the linearized equation and on an analysis of nonlinear effects. In
particular, we show that the dominant Landau pole controlling the inviscid
damping undergoes a bifurcation, which has important consequences on the
asymptotic fate of the perturbation. | 1401.6865v1 |
2014-02-05 | On Linear Landau Damping for Relativistic Plasmas via Gevrey Regularity | We examine the phenomenon of Landau Damping in relativistic plasmas via a
study of the relativistic Vlasov-Poisson system (both on the torus and on
$\mathbb{R}^3$) linearized around a sufficiently nice, spatially uniform
kinetic equilibrium. We find that exponential decay of spatial Fourier modes is
impossible under modest symmetry assumptions. However, by assuming the
equilibrium and initial data are sufficiently regular functions of velocity for
a given wavevector (in particular that they exhibit a kind of Gevrey
regularity), we show that it is possible for the mode associated to this
wavevector to decay sub-exponentially if its magnitude exceeds a certain
critical size. We also give a heuristic argument why one should not expect such
rapid decay for modes with wavevectors below this threshold. | 1402.0992v2 |
2014-02-06 | Time dependent elastic response to a local shear transformation in amorphous solids | The elastic response of a two-dimensional amorphous solid to induced local
shear transformations, which mimic the elementary plastic events occurring in
deformed glasses, is investigated via Molecular Dynamics simulations. We show
that for different spatial realizations of the transformation, despite relative
fluctuations of order one, the long time equilibrium response averages out to
the prediction of the Eshelby inclusion problem for a continuum elastic medium.
We characterize the effects of the underlying dynamics on the propagation of
the elastic signal. A crossover from a propagative transmission in the case of
weakly-damped dynamics to a diffusive transmission for strong damping is
evidenced. In the latter case, the full time dependent elastic response is in
agreement with the theoretical prediction, obtained by solving the diffusion
equation for the displacement field in an elastic medium. | 1402.1474v1 |
2014-02-07 | A temperature dependent formation time approach for Υsuppression at LHC | We present here a model to describe the bottomonium suppression in Pb$+$Pb
collisions at Large Hadron Collider (LHC), at $\sqrt{s_{NN}}=2.76$ TeV by using
the quasi-particle model (QPM) equation of state (EOS) for the Quark-Gluon
Plasma (QGP) expanding under Bjorken's hydrodynamical expansion. The current
model includes the modification of the formation time based on the temperature
of QGP, color screening during bottomonium production, gluon induced
dissociation and collisional damping. The cold nuclear matter (CNM) effects and
decay of higher resonances of bottomonium have also been included in the
present work. The final suppression of the bottomonium states, at mid rapidity
is calculated as a function of centrality. The results compare closely with the
recent data at Large hadron Collider (LHC) in the mid rapidity region for
various centrality bins. {\nd \it Keywords } : Color screening, Gluonic
dissociation, Collisional damping, Survival probability, CNM effects\\ {\nd \it
PACS numbers } : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa | 1402.1560v5 |
2014-02-12 | A numerical comparison between degenerate parabolic and quasilinear hyperbolic models of cell movements under chemotaxis | We consider two models which were both designed to describe the movement of
eukaryotic cells responding to chemical signals. Besides a common standard
parabolic equation for the diffusion of a chemoattractant, like chemokines or
growth factors, the two models differ for the equations describing the movement
of cells. The first model is based on a quasilinear hyperbolic system with
damping, the other one on a degenerate parabolic equation. The two models have
the same stationary solutions, which may contain some regions with vacuum. We
first explain in details how to discretize the quasilinear hyperbolic system
through an upwinding technique, which uses an adapted reconstruction, which is
able to deal with the transitions to vacuum. Then we concentrate on the
analysis of asymptotic preserving properties of the scheme towards a
discretization of the parabolic equation, obtained in the large time and large
damping limit, in order to present a numerical comparison between the
asymptotic behavior of these two models. Finally we perform an accurate
numerical comparison of the two models in the time asymptotic regime, which
shows that the respective solutions have a quite different behavior for large
times. | 1402.2831v2 |
2014-02-13 | Surface Activity and Oscillation Amplitudes of Red Giants in Eclipsing Binaries | Among 19 red-giant stars belonging to eclipsing binary systems that have been
identified in Kepler data, 15 display solar-like oscillations. We study whether
the absence of mode detection in the remaining 4 is an observational bias or
possibly evidence of mode damping that originates from tidal interactions. A
careful analysis of the corresponding Kepler light curves shows that modes with
amplitudes that are usually observed in red giants would have been detected if
they were present. We observe that mode depletion is strongly associated with
short-period systems, in which stellar radii account for 16-24 % of the
semi-major axis, and where red-giant surface activity is detected. We suggest
that when the rotational and orbital periods synchronize in close binaries, the
red-giant component is spun up, so that a dynamo mechanism starts and generates
a magnetic field, leading to observable stellar activity. Pressure modes would
then be damped as acoustic waves dissipate in these fields. | 1402.3027v1 |
2014-02-18 | Cherenkov friction on a neutral particle moving parallel to a dielectric | Based on a fully relativistic framework and the assumption of local
equilibrium, we describe a simple mechanism of quantum friction for a particle
moving parallel to a dielectric. The Cherenkov effect explains how the bare
ground state becomes globally unstable and how fluctuations of the
electromagnetic field and the particle's dipole are converted into pairs of
excitations. Modelling the particle as a silver nano-sphere, we investigate the
spectrum of the force and its velocity dependence. We find that the damping of
the plasmon resonance in the silver particle has a relatively strong impact
near the Cherenkov threshold velocity. We also present an expansion of the
friction force near the threshold velocity for both damped and undamped
particles. | 1402.4518v1 |
2014-02-20 | Feed-forward control for quantum state protection against decoherence | We propose a novel scheme of feed-forward control and its reversal for
protecting quantum state against decoherence. Before the noise channel our
pre-weak measurement and feed-forward are just to change the protected state
into the state almost immune to the noise channel, and after the channel our
reversed operations and post-weak measurements are just to restore the
protected state. Unlike most previous state protection schemes, ours only
concerns the noise channel and does not care about the protected state. We show
that our scheme can effectively protect unknown states, nonorthogonal states
and entangled states against amplitude damping noise. Our scheme has dramatic
merits of protecting quantum states against heavy amplitude damping noise, and
can perfectly protect some specific nonorthogonal states in an almost
deterministic way, which might be found some applications in current quantum
communication technology. And it is most important that our scheme is
experimentally available with current technology. | 1402.4921v2 |
2014-02-25 | Elastic Anomalies Associated with the Antiferroelectric Phase Transitions of PbHfO3 Single Crystals | The temperature dependence of the elastic properties of antiferroelectric
PbHfO3 was investigated by Brillouin scattering. The two structural phase
transitions of antiferroelectric-antiferroelectric-paraelectric phases were
clearly identified by discontinuous changes in the acoustic mode frequencies
and the hypersonic damping. The substantial softening of the mode frequency
along with the remarkable increase in the acoustic damping observed in the
paraelectric phase indicated the formation of precursor noncentrosymmetric
(polar) clusters and their coupling to the acoustic waves. This was
corroborated by the observation of quasi-elastic central peaks, the intensity
of which grew upon cooling toward the Curie point. The obtained relaxation time
exhibited a slowing-down behavior, suggesting that the dynamics of precursor
clusters becomes more sluggish on approaching the phase transition temperature. | 1402.6175v1 |
2014-03-05 | Short-period pulsar oscillations following a glitch | Following a glitch, the crust and magnetized plasma in the outer core of a
neutron star are believed to rapidly establish a state of co-rotation within a
few seconds by process analogous to classical Ekman pumping. However, in ideal
magnetohydrodynamics, a final state of co-rotation is inconsistent with
conservation of energy of the system. We demonstrate that, after the Ekman-like
spin up is completed, magneto-inertial waves continue to propagate throughout
the star, exciting torsional oscillations in the crust and plasma. The crust
oscillation is irregular and quasi-periodic, with a dominant frequency of the
order of seconds. Crust oscillations commence after an Alfv\'en crossing time,
approximately half a minute at the magnetic pole, and are subsequently damped
by the electron viscosity over approximately an hour. In rapidly rotating
stars, the magneto-inertial spectrum in the core approaches a continuum, and
crust oscillations are damped by resonant absorption analogous to
quasi-periodic oscillations in magnetars. The oscillations predicted are
unlikely to be observed in timing data from existing radio telescopes, but may
be visible to next generation telescope arrays. | 1403.1046v2 |
2014-03-06 | On the damped oscillations of an elastic quasi-circular membrane in a two-dimensional incompressible fluid | We propose a procedure - partly analytical and partly numerical - to find the
frequency and the damping rate of the small-amplitude oscillations of a
massless elastic capsule immersed in a two-dimensional viscous incompressible
fluid. The unsteady Stokes equations for the stream function are decomposed
onto normal modes for the angular and temporal variables, leading to a
fourth-order linear ordinary differential equation in the radial variable. The
forcing terms are dictated by the properties of the membrane, and result into
jump conditions at the interface between the internal and external media. The
equation can be solved numerically, and an excellent agreement is found with a
fully-computational approach we developed in parallel. Comparisons are also
shown with the results available in the scientific literature for drops, and a
model based on the concept of embarked fluid is presented, which allows for a
good representation of the results and a consistent interpretation of the
underlying physics. | 1403.1423v1 |
2014-03-07 | The silicon matrix for the prototype for the Dark Matter Particle Explorer | A new generation detector for the high energy cosmic ray - the DAMPE(DArk
Matter Particle Explorer) is a satellite based project. Its main object is the
measurement of energy spectrum of cosmic ray nuclei from 100GeV to 100TeV, the
high energy electrons and gamma ray from 5GeV to 10TeV. A silicon matrix
detector described in this paper, is employed for the sea level cosmic ray
energy and position detection while the prototype testing of the DAMPE. This
matrix is composed by the 180 silicon PIN detectors, which covers an area of
32*20 cm2. The primary testing results are shown including MIPs energy spectrum
and the position sensitive map. | 1403.1679v2 |
2014-04-01 | Anomalies in the specific heat of a free damped particle: The role of the cutoff in the spectral density of the coupling | The properties of a dissipative system depend on the spectral density of the
coupling to the environment. Mostly, the dependence on the low-frequency
behavior is in the focus of interest. However, in order to avoid divergencies,
it is also necessary to suppress the spectral density of the coupling at high
frequencies. Interestingly, the very existence of this cutoff may lead to a
mass renormalization which can have drastic consequences for the thermodynamic
properties of the dissipative system. Here, we explore the role which the
cutoff in the spectral density of the coupling plays for a free damped particle
and we compare the effect of an algebraic cutoff with that of a sharp cutoff. | 1404.0254v1 |
2014-04-09 | Directly imaging damped Ly-alpha galaxies at z>2. II: Imaging and spectroscopic observations of 32 quasar fields | Damped Ly-alpha absorbers (DLAs) are a well-studied class of absorption line
systems, and yet the properties of their host galaxies remain largely unknown.
To investigate the origin of these systems, we have conducted an imaging survey
of 32 quasar fields with intervening DLAs between z~1.9-3.8, leveraging a
technique that allows us to image galaxies at any small angular separation from
the background quasars. In this paper, we present the properties of the
targeted DLA sample, new imaging observations of the quasar fields, and the
analysis of new and archival spectra of the background quasars. | 1404.2599v2 |
2014-04-13 | Homotopy invariants methods in the global dynamics of strongly damped wave equation | We are interested in the following differential equation $\ddot u(t) = -A
u(t) - c A \dot u(t) + \lambda u(t) + F(u(t))$ where $c > 0$ is a damping
factor, $A$ is a sectorial operator and $F$ is a continuous map. We consider
the situation where the equation is at resonance at infinity, which means that
$\lambda$ is an eigenvalue of $A$ and $F$ is a bounded map. We provide
geometrical conditions for the nonlinearity $F$ and determine the Conley index
of the set $K_\infty$, that is the union of the bounded orbits of this
equation. | 1404.3429v3 |
2014-04-14 | Low-distance Surface Codes under Realistic Quantum Noise | We study the performance of distance-three surface code layouts under
realistic multi-parameter noise models. We first calculate their thresholds
under depolarizing noise. We then compare a Pauli-twirl approximation of
amplitude and phase damping to amplitude and phase damping. We find the
approximate channel results in a pessimistic estimate of the logical error
rate, indicating the realistic threshold may be higher than previously
estimated. From Monte-Carlo simulations, we identify experimental parameters
for which these layouts admit reliable computation. Due to its low resource
cost and superior performance, we conclude that the 17-qubit layout should be
targeted in early experimental implementations of the surface code. We find
that architectures with gate times in the 5-40 ns range and T1 times of at
least 1-2 us range will exhibit improved logical error rates with a 17-qubit
surface code encoding. | 1404.3747v3 |
2014-04-21 | Phase conversion dissipation in multicomponent compact stars | We propose a mechanism for the damping of density oscillations in
multicomponent compact stars. The mechanism is the periodic conversion between
different phases, i.e., the movement of the interface between them, induced by
pressure oscillations in the star. The damping grows nonlinearly with the
amplitude of the oscillation. We study in detail the case of r-modes in a
hybrid star with a sharp interface, and we find that this mechanism is powerful
enough to saturate the r-mode at very low saturation amplitude, of order
$10^{-10}$, and is therefore likely to be the dominant r-mode saturation
mechanism in hybrid stars with a sharp interface. | 1404.5279v4 |
2014-04-29 | Quasi-normal modes of superfluid neutron stars | We study non-radial oscillations of neutron stars with superfluid baryons, in
a general relativistic framework, including finite temperature effects. Using a
perturbative approach, we derive the equations describing stellar oscillations,
which we solve by numerical integration, employing different models of nucleon
superfluidity, and determining frequencies and gravitational damping times of
the quasi-normal modes. As expected by previous results, we find two classes of
modes, associated to superfluid and non-superfluid degrees of freedom,
respectively. We study the temperature dependence of the modes, finding that at
specific values of the temperature, the frequencies of the two classes of
quasi-normal modes show avoided crossings, and their damping times become
comparable. We also show that, when the temperature is not close to the avoided
crossings, the frequencies of the modes can be accurately computed by
neglecting the coupling between normal and superfluid degrees of freedom. Our
results have potential implications on the gravitational wave emission from
neutron stars. | 1404.7512v1 |
2014-05-27 | Nonequilibrium dynamical mean-field theory for bosonic lattice models | We develop the nonequilibrium extension of bosonic dynamical mean field
theory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity
solver. In contrast to Gutzwiller mean-field theory and strong coupling
perturbative approaches, nonequilibrium BDMFT captures not only dynamical
transitions, but also damping and thermalization effects at finite temperature.
We apply the formalism to quenches in the Bose-Hubbard model, starting both
from the normal and Bose-condensed phases. Depending on the parameter regime,
one observes qualitatively different dynamical properties, such as rapid
thermalization, trapping in metastable superfluid or normal states, as well as
long-lived or strongly damped amplitude oscillations. We summarize our results
in non-equilibrium "phase diagrams" which map out the different dynamical
regimes. | 1405.6941v2 |
2014-05-28 | Electronic control of the spin-wave damping in a magnetic insulator | It is demonstrated that the decay time of spin-wave modes existing in a
magnetic insulator can be reduced or enhanced by injecting an in-plane dc
current, $I_\text{dc}$, in an adjacent normal metal with strong spin-orbit
interaction. The demonstration rests upon the measurement of the ferromagnetic
resonance linewidth as a function of $I_\text{dc}$ in a 5~$\mu$m diameter
YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope
(MRFM). Complete compensation of the damping of the fundamental mode is
obtained for a current density of $\sim 3 \cdot 10^{11}\text{A.m}^{-2}$, in
agreement with theoretical predictions. At this critical threshold the MRFM
detects a small change of static magnetization, a behavior consistent with the
onset of an auto-oscillation regime. | 1405.7415v1 |
2014-06-16 | Study on FPGA SEU Mitigation for Readout Electronics of DAMPE BGO Calorimeter | The BGO calorimeter, which provides a wide measurement range of the primary
cosmic ray spectrum, is a key sub-detector of Dark Matter Particle Explorer
(DAMPE). The readout electronics of calorimeter consists of 16 pieces of Actel
ProASIC Plus FLASH-based FPGA, of which the design-level flip-flops and
embedded block RAMs are single event upset (SEU) sensitive in the harsh space
environment. Therefore to comply with radiation hardness assurance (RHA), SEU
mitigation methods, including partial triple modular redundancy (TMR), CRC
checksum, and multi-domain reset are analyzed and tested by the heavy-ion beam
test. Composed of multi-level redundancy, a FPGA design with the
characteristics of SEU tolerance and low resource consumption is implemented
for the readout electronics. | 1406.3928v1 |
2014-06-18 | Damping of glacial-interglacial cycles from anthropogenic forcing | Climate variability over the past million years shows a strong
glacial-interglacial cycle of ~100,000 years as a combined result of
Milankovitch orbital forcing and climatic resonance. It has been suggested that
anthropogenic contributions to radiative forcing may extend the length of the
present interglacial, but the effects of anthropogenic forcing on the
periodicity of glacial-interglacial cycles has received little attention. Here
I demonstrate that moderate anthropogenic forcing can act to damp this 100,000
year cycle and reduce climate variability from orbital forcing. Future changes
in solar insolation alone will continue to drive a 100,000 year climate cycle
over the next million years, but the presence of anthropogenic warming can
force the climate into an ice-free state that only weakly responds to orbital
forcing. Sufficiently strong anthropogenic forcing that eliminates the
glacial-interglacial cycle may serve as an indication of an epoch transition
from the Pleistocene to the Anthropocene. | 1406.4728v1 |
2014-06-27 | Magnetoplasmons of the tilted-anisotropic Dirac cone material $α-$(BEDT-TTF)$_2$I$_3$ | We study the collective modes of a low-energy continuum model of the
quasi-two-dimensional electron liquid in a layer of the organic compound
$\alpha-$(BEDT-TTF)$_2$I$_3$ in a perpendicular magnetic field. As testified by
zero magnetic field transport experiments and \textit{ab initio} theory, this
material hosts both massless and massive low-energy carriers, the former being
described by tilted and anisotropic Dirac cones. The polarizability of these
cones is anisotropic, and two sets of magnetoplasmon modes occur between any
two cyclotron resonances. We show that the tilt of the cones causes a unique
intervalley damping effect: the upper hybrid mode of one cone is damped by the
particle-hole continuum of the other cone in generic directions. We analyse how
the presence of massive carriers affects the response of the system, and
demonstrate how doping can tune $\alpha-$(BEDT-TTF)$_2$I$_3$ between regimes of
isotropic and anisotropic screening. | 1406.7081v2 |
2014-06-30 | Collective Coordinates Theory for Discrete Soliton Ratchets in the sine-Gordon Model | A collective coordinate theory is develop for soliton ratchets in the damped
discrete sine-Gordon model driven by a biharmonic force. An ansatz with two
collective coordinates, namely the center and the width of the soliton, is
assumed as an approximated solution of the discrete non-linear equation. The
evolution of these two collective coordinates, obtained by means of the
Generalized Travelling Wave Method, explains the mechanism underlying the
soliton ratchet and captures qualitatively all the main features of this
phenomenon. The theory accounts for the existence of a non-zero depinning
threshold, the non-sinusoidal behaviour of the average velocity as a function
of the difference phase between the harmonics of the driver, the non-monotonic
dependence of the average velocity on the damping and the existence of
non-transporting regimes beyond the depinning threshold. In particular it
provides a good description of the intriguing and complex pattern of subspaces
corresponding to different dynamical regimes in parameter space. | 1406.7656v1 |
2014-07-04 | Temperature Dependent Ferromagnetic Resonance via the Landau-Lifshitz-Bloch Equation: Application to FePt | Using the Landau-Lifshitz-Bloch (LLB) equation for ferromagnetic materials,
we derive analytic expressions for temperature dependent absorption spectra as
probed by ferromagnetic resonance (FMR). By analysing the resulting
expressions, we can predict the variation of the resonance frequency and
damping with temperature and coupling to the thermal bath. We base our
calculations on the technologically relevant L1$_0$ FePt, parameterised from
atomistic spin dynamics simulations, with the Hamiltonian mapped from ab-initio
parameters. By constructing a multi-macrospin model based on the LLB equation
and exploiting GPU acceleration we extend the study to investigate the effects
on the damping and resonance frequency in ${\mu}$m sized structures. | 1407.1174v1 |
2014-07-07 | Composition variation and underdamped mechanics near membrane proteins and coats | We study the effect of membrane proteins on the shape, composition and
thermodynamic stability of the surrounding membrane. When the coupling between
membrane composition and curvature is strong enough the nearby composition and
shape both undergo a transition from over-damped to under-damped spatial
variation, well before the membrane becomes unstable in the bulk. This
transition is associated with a change in the sign of the thermodynamic energy
and hence has the unusual features that it can favour the early stages of coat
assembly necessary for vesiculation (budding), while suppressing the activity
of mechanosensitive membrane channels and transporters. Our results also
suggest an approach to obtain physical parameters that are otherwise difficult
to measure. | 1407.1672v2 |
2014-07-11 | Evidence for Wave Heating of the Quiet Sun Corona | We have measured the energy and dissipation of Alfvenic waves in the quiet
Sun. A magnetic field was used to infer the location and orientation of the
magnetic field lines along which the waves are expected to travel. The waves
were measured using spectral lines to infer the wave amplitude. The waves cause
a non-thermal broadening of the spectral lines, which can be expressed as a
non-thermal velocity v_nt. By combining the spectroscopic measurements with
this magnetic field model we were able to trace the variation of v_nt along the
magnetic field. At the footpoints of the quiet Sun loops we find that waves
inject an energy flux in the range of 1.2-5.2 x 10^5 erg cm^-2 s^-1. At the
minimum of this range, this amounts to more than 80% of the energy needed to
heat the quiet Sun. We also find that these waves are dissipated over a region
centered on the top of the loops. The position along the loop where the damping
begins is strongly correlated with the length of the loop, implying that the
damping mechanism depends on the global loop properties rather than on local
collisional dissipation. | 1407.3250v1 |
2014-07-16 | Nonresonant high frequency excitation of mechanical vibrations in graphene based nanoresonator | We theoretically analyse the dynamics of a suspended graphene membrane which
is in tunnel contact with grounded metallic electrodes and subjected to
ac-electrostatic potential induced by a gate electrode. It is shown that for
such system the retardation effects in the electronic subsystem generate an
effective pumping for the relatively slow mechanical vibrations if the driving
frequency exceeds the inverse charge relax- ation time. Under this condition
there is a critical value of the driving voltage ampli- tude above which the
pumping overcomes the intrinsic damping of the mechanical resonator leading to
a mechanical instability. This nonresonant instability is saturated by
nonlinear damping and the system exhibits self-sustained oscillations of
relatively large amplitude. | 1407.4278v2 |
2014-07-21 | Non-Markovian dynamics of open quantum systems without rotating wave approximation | We study the non-Markovian dynamics of a damped oscillator coupled with a
reservoir. We present exact formulas for the oscillator's evolution directly
from the BCH formula by series expansion with neither Markovian nor rotating
wave approximation (RWA). Based on these, we show the existence of the
non-Markovian feature of the system's evolution for the damped oscillator. By
numerical simulation we find that the non-Markovian feature exists within a
wide range of the coupling strength, even when the coupling strength is very
small. To this problem, prior art results have assumed RWA and the existence of
non-Markovian feature was found when the system-reservoir coupling is strong
enough. However, as we show, given such a strong coupling, the original
Hamiltonian without RWA is actually not physical. Therefore, our exact study
here has thoroughly concluded the issue of non-Markovian feature. | 1407.5359v2 |
2014-07-23 | Global Existence of Smooth Solutions and Convergence to Barenblatt Solutions for the Physical Vacuum Free Boundary Problem of Compressible Euler Equations with Damping | For the physical vacuum free boundary problem with the sound speed being
$C^{{1}/{2}}$-H$\ddot{\rm o}$lder continuous near vacuum boundaries of the
one-dimensional compressible Euler equations with damping, the global existence
of the smooth solution is proved, which is shown to converge to the Barenblatt
self-similar solution for the the porous media equation with the same total
mass when the initial data is a small perturbation of the Barenblatt solution.
The pointwise convergence with a rate of density, the convergence rate of
velocity in supereme norm and the precise expanding rate of the physical vacuum
boundaries are also given. The proof is based on a construction of higher-order
weighted functionals with both space and time weights capturing the behavior of
solutions both near vacuum states and in large time, an introduction of a new
ansatz, higher-order nonlinear energy estimates and elliptic estimates. | 1407.6111v2 |
2014-07-24 | Decay of dark and bright plasmonic modes in a metallic nanoparticle dimer | We develop a general quantum theory of the coupled plasmonic modes resulting
from the near-field interaction between localized surface plasmons in a
heterogeneous metallic nanoparticle dimer. In particular, we provide analytical
expressions for the frequencies and decay rates of the bright and dark
plasmonic modes. We show that, for sufficiently small nanoparticles, the main
decay channel for the dark plasmonic mode, which is weakly coupled to light
and, hence, immune to radiation damping, is of nonradiative origin and
corresponds to Landau damping, i.e., decay into electron-hole pairs. | 1407.6569v2 |
2014-07-29 | Reproducing the Kinematics of Damped Lyman-alpha Systems | We examine the kinematic structure of Damped Lyman-alpha Systems (DLAs) in a
series of cosmological hydrodynamic simulations using the AREPO code. We are
able to match the distribution of velocity widths of associated low ionisation
metal absorbers substantially better than earlier work. Our simulations produce
a population of DLAs dominated by halos with virial velocities around 70 km/s,
consistent with a picture of relatively small, faint objects. In addition, we
reproduce the observed correlation between velocity width and metallicity and
the equivalent width distribution of SiII. Some discrepancies of moderate
statistical significance remain; too many of our spectra show absorption
concentrated at the edge of the profile and there are slight differences in the
exact shape of the velocity width distribution. We show that the improvement
over previous work is mostly due to our strong feedback from star formation and
our detailed modelling of the metal ionisation state. | 1407.7858v2 |
2014-07-31 | Plasmons in finite spherical ionic systems | The challenging question on possible plasmon type excitations in finite ionic
systems is discussed. The related theoretical model is formulated and developed
in order to describe surface and volume plasmons of ion liquid in finite
electrolyte systems. The irradiation of ionic surface plasmon fluctuations is
studied in terms of the Lorentz friction of oscillating charges. The
attenuation of surface plasmons in the ionic sphere is calculated and minimized
with respect to the sphere size. Various regimes of approximation for
description of size effect for damping of ionic plasmons are determined and a
cross-over in damping size-dependence is demonstrated. The most convenient
dimension of finite electrolyte system for energy and information transfer by
usage of ionic dipole plasmons is determined. The overall shift of size effect
to micrometer scale for ions in comparison to nanometer scale for electrons in
metals is found and by several orders red shift of plasmonic resonances in ion
systems is predicted in a wide range of variation depending of ion system
parameters. This convenient opportunity of tuning of resonances differs ionic
plasmons from plasmons in metals where electron concentration was firmly fixed. | 1407.8369v2 |
2014-08-04 | Collective Dynamics of Interacting Particles in Unsteady Flows | We use the Fokker-Planck equation and its moment equations to study the
collective behavior of interacting particles in unsteady one-dimensional flows.
Particles interact according to a long-range attractive and a short-range
repulsive potential field known as Morse potential. We assume Stokesian drag
force between particles and their carrier fluid, and find analytic
single-peaked traveling solutions for the spatial density of particles in the
catastrophic phase. In steady flow conditions the streaming velocity of
particles is identical to their carrier fluid, but we show that particle
streaming is asynchronous with an unsteady carrier fluid. Using linear
perturbation analysis, the stability of traveling solutions is investigated in
unsteady conditions. It is shown that the resulting dispersion relation is an
integral equation of the Fredholm type, and yields two general families of
stable modes: singular modes whose eigenvalues form a continuous spectrum, and
a finite number of discrete global modes. Depending on the value of drag
coefficient, stable modes can be over-damped, critically damped, or decaying
oscillatory waves. The results of linear perturbation analysis are confirmed
through the numerical solution of the fully nonlinear Fokker-Planck equation. | 1408.0558v1 |
2014-08-13 | Correlated decay of triplet excitations in the Shastry-Sutherland compound SrCu$_2$(BO$_3$)$_2$ | The temperature dependence of the gapped triplet excitations (triplons) in
the 2D Shastry-Sutherland quantum magnet SrCu$_2$(BO$_3$)$_2$ is studied by
means of inelastic neutron scattering. The excitation amplitude rapidly
decreases as a function of temperature while the integrated spectral weight can
be explained by an isolated dimer model up to 10~K. Analyzing this anomalous
spectral line-shape in terms of damped harmonic oscillators shows that the
observed damping is due to a two-component process: one component remains sharp
and resolution limited while the second broadens. We explain the underlying
mechanism through a simple yet quantitatively accurate model of correlated
decay of triplons: an excited triplon is long-lived if no thermally populated
triplons are near-by but decays quickly if there are. The phenomenon is a
direct consequence of frustration induced triplon localization in the
Shastry--Sutherland lattice. | 1408.3135v1 |
2014-08-20 | Enhanced dissipation and inviscid damping in the inviscid limit of the Navier-Stokes equations near the 2D Couette flow | In this work we study the long time, inviscid limit of the 2D Navier-Stokes
equations near the periodic Couette flow, and in particular, we confirm at the
nonlinear level the qualitative behavior predicted by Kelvin's 1887 linear
analysis. At high Reynolds number Re, we prove that the solution behaves
qualitatively like 2D Euler for times t \lesssim Re^(1/3), and in particular
exhibits inviscid damping (e.g. the vorticity weakly approaches a shear flow).
For times t \gtrsim Re^(1/3), which is sooner than the natural dissipative time
scale O(Re), the viscosity becomes dominant and the streamwise dependence of
the vorticity is rapidly eliminated by an enhanced dissipation effect.
Afterward, the remaining shear flow decays on very long time scales t \gtrsim
Re back to the Couette flow. When properly defined, the dissipative
length-scale in this setting is L_D \sim Re^(-1/3), larger than the scale L_D
\sim Re^(-1/2) predicted in classical Batchelor-Kraichnan 2D turbulence theory.
The class of initial data we study is the sum of a sufficiently smooth function
and a small (with respect to Re^(-1)) $L^2$ function. | 1408.4754v1 |
2014-09-01 | Dynamical symmetries and crossovers in a three-spin system with collective dissipation | We consider the non-equilibrium dynamics of a simple system consisting of
interacting spin-$1/2$ particles subjected to a collective damping. The model
is close to situations that can be engineered in hybrid electro/opto-mechanical
settings. Making use of large-deviation theory, we find a Gallavotti-Cohen
symmetry in the dynamics of the system as well as evidence for the coexistence
of two dynamical phases with different activity levels. We show that additional
damping processes smoothen out this behavior. Our analytical results are backed
up by Monte Carlo simulations that reveal the nature of the trajectories
contributing to the different dynamical phases. | 1409.0422v2 |
2014-09-02 | Controlled bidirectional remote state preparation in noisy environment: A generalized view | It is shown that a realistic, controlled bidirectional remote state
preparation is possible using a large class of entangled quantum states having
a particular structure. Existing protocols of probabilistic, deterministic and
joint remote state preparation are generalized to obtain the corresponding
protocols of controlled bidirectional remote state preparation (CBRSP). A
general way of incorporating the effects of two well known noise processes, the
amplitude-damping and phase-damping noise, on the probabilistic CBRSP process
is studied in detail by considering that noise only affects the travel qubits
of the quantum channel used for the probabilistic CBRSP process. Also indicated
is how to account for the effect of these noise channels on deterministic and
joint remote state CBRSP protocols. | 1409.0833v1 |
2014-09-07 | The Effects of Long Pulse Durations and Radiation Damping in Selective Inversion Recovery Experiments | Long pulse durations necessary in selective inversion recovery (SIR)
experiments along with radiation damping (RD) introduce difficulties in
quantitative nuclear magnetic resonance measurements, such as those that allow
for the determination of a sample's characteristics, including the rates that
govern magnetization transfer. Because of these influences, the assumption of
perfect inversion is invalid. In this work, we present data that demonstrates
that long pulse durations as well as RD cause difficulties in SIR experiments
performed on simple one-spin systems, indicating that they will be problematic
for multiple-spin systems as well. These results emphasize the importance of
understanding the evolution of magnetization for all time points throughout an
experiment used in quantitative NMR measurements. Furthermore, experimental
parameters must be chosen carefully and understood completely. | 1409.2136v2 |
2014-09-19 | Angular dependence of spin-orbit spin transfer torques | In ferromagnet/heavy metal bilayers, an in-plane current gives rise to
spin-orbit spin transfer torque which is usually decomposed into field-like and
damping-like torques. For two-dimensional free-electron and tight-binding
models with Rashba spin-orbit coupling, the field-like torque acquires
nontrivial dependence on the magnetization direction when the Rashba spin-orbit
coupling becomes comparable to the exchange interaction. This nontrivial
angular dependence of the field-like torque is related to the Fermi surface
distortion, determined by the ratio of the Rashba spin-orbit coupling to the
exchange interaction. On the other hand, the damping-like torque acquires
nontrivial angular dependence when the Rashba spin-orbit coupling is comparable
to or stronger than the exchange interaction. It is related to the combined
effects of the Fermi surface distortion and the Fermi sea contribution. The
angular dependence is consistent with experimental observations and can be
important to understand magnetization dynamics induced by spin-orbit spin
transfer torques | 1409.5600v1 |
2014-10-01 | Non-linear collisionless damping of Weibel turbulence in relativistic blast waves | The Weibel/filamentation instability is known to play a key role in the
physics of weakly magnetized collisionless shock waves. From the point of view
of high energy astrophysics, this instability also plays a crucial role because
its development in the shock precursor populates the downstream with a
small-scale magneto-static turbulence which shapes the acceleration and
radiative processes of suprathermal particles. The present work discusses the
physics of the dissipation of this Weibel-generated turbulence downstream of
relativistic collisionless shock waves. It calculates explicitly the
first-order non-linear terms associated to the diffusive nature of the particle
trajectories. These corrections are found to systematically increase the
damping rate, assuming that the scattering length remains larger than the
coherence length of the magnetic fluctuations. The relevance of such
corrections is discussed in a broader astrophysical perspective, in particular
regarding the physics of the external relativistic shock wave of a gamma-ray
burst. | 1410.0146v1 |
2014-10-10 | The Fate of Scattered Planets | As gas giant planets evolve, they may scatter other planets far from their
original orbits to produce hot Jupiters or rogue planets that are not
gravitationally bound to any star. Here, we consider planets cast out to large
orbital distances on eccentric, bound orbits through a gaseous disk. With
simple numerical models, we show that super-Earths can interact with the gas
through dynamical friction to settle in the remote outer regions of a planetary
system. Outcomes depend on planet mass, the initial scattered orbit, and the
evolution of the time-dependent disk. Efficient orbital damping by dynamical
friction requires planets at least as massive as the Earth. More massive,
longer-lived disks damp eccentricities more efficiently than less massive,
short-lived ones. Transition disks with an expanding inner cavity can
circularize orbits at larger distances than disks that experience a global
(homologous) decay in surface density. Thus, orbits of remote planets may
reveal the evolutionary history of their primordial gas disks. A remote planet
with an orbital distance ~100 AU from the Sun is plausible and might explain
correlations in the orbital parameters of several distant trans-Neptunian
objects. | 1410.2816v1 |
2014-10-13 | Unified Theory of Inertial Granular Flows and Non-Brownian Suspensions | Rheological properties of dense flows of hard particles are singular as one
approaches the jamming threshold where flow ceases, both for aerial granular
flows dominated by inertia, and for over-damped suspensions. Concomitantly, the
lengthscale characterizing velocity correlations appears to diverge at jamming.
Here we introduce a theoretical framework that proposes a tentative, but
potentially complete scaling description of stationary flows. Our analysis,
which focuses on frictionless particles, applies {\it both} to suspensions and
inertial flows of hard particles. We compare our predictions with the empirical
literature, as well as with novel numerical data. Overall we find a very good
agreement between theory and observations, except for frictional inertial flows
whose scaling properties clearly differ from frictionless systems. For
over-damped flows, more observations are needed to decide if friction is a
relevant perturbation or not. Our analysis makes several new predictions on
microscopic dynamical quantities that should be accessible experimentally. | 1410.3535v3 |
2014-10-22 | Landau damping in the Kuramoto model | We consider the Kuramoto model of globally coupled phase oscillators in its
continuum limit, with individual frequencies drawn from a distribution with
density of class $C^n$ ($n\geq 4$). A criterion for linear stability of the
uniform stationary state is established which, for basic examples of frequency
distributions, is equivalent to the standard condition on the coupling strength
in the literature. We prove that, under this criterion, the Kuramoto order
parameter, when evolved under the full nonlinear dynamics, asymptotically
vanishes (with polynomial rate $n$) for every trajectory issued from
sufficiently small $C^n$ perturbation. The proof uses techniques from the
Analysis of PDEs and closely follows recent proofs of the nonlinear Landau
damping in the Vlasov equation and Vlasov-HMF model. | 1410.6006v1 |
2014-10-30 | Global Solutions to the Gas-Vacuum Interface Problem of Isentropic Compressible Inviscid Flows with Damping in Spherically Symmetric Motions and Physical Vacuum | For the physical vacuum free boundary problem with the sound speed being
$C^{{1}/{2}}$-H$\ddot{\rm o}$lder continuous near vacuum boundaries of the
three-dimensional compressible Euler equations with damping, the global
existence of spherically symmetric smooth solutions is proved, which are shown
to converge to Barenblatt self-similar solutions of the porous media equation
with the same total masses when initial data are small perturbations of
Barenblatt solutions. The pointwise convergence with a rate of density, the
convergence rate of velocity in supreme norm and the precise expanding rate of
physical vacuum boundaries are also given by constructing nonlinear functionals
with space-time weights featuring the behavior of solutions in large time and
near the vacuum boundary and the center of symmetry, the nonlinear energy
estimates and elliptic estimates. | 1410.8471v1 |
2014-11-03 | Monami as an oscillatory hydrodynamic instability in a submerged sea grass bed | The onset of monami ~-- the synchronous waving of sea grass beds driven by a
steady flow -- is modeled as a linear instability of the flow. Unlike previous
works, our model considers the drag exerted by the grass in establishing the
steady flow profile, and in damping out perturbations to it. We find two
distinct modes of instability, which we label Mode 1 and Mode 2. Mode 1 is
closely related to Kelvin-Helmholtz instability modified by vegetation drag,
whereas Mode 2 is unrelated to Kelvin-Helmholtz and arises from an interaction
between the flow in the vegetated and unvegetated layers. The vegetation
damping, according to our model, leads to a finite threshold flow for both
these modes. Experimental observations for the onset and frequency of waving
compare well with model predictions for the instability onset criteria and the
imaginary part of the complex growth rate respectively, but experiments lie in
a parameter regime where the two modes can not be distinguished. % The
inclusion of vegetation drag differentiates our mechanism from the previous
linear stability analyses of monami. | 1411.0365v2 |
2014-11-12 | Dependence of the Efficiency of Spin Hall Torque on the Transparency of Pt-Ferromagnetic Layer Interfaces | We report that spin current transport across Pt-ferromagnet (FM) interfaces
is strongly dependent on the type and the thickness of the FM layer and on
post-deposition processing protocols. By employing both harmonic voltage
measurements and spin-torque ferromagnetic resonance measurements, we find that
the efficiency of the Pt spin Hall effect in exerting a damping-like spin
torque on the FM ranges from < 0.05 to > 0.10 under different interfacial
conditions. We also show that the temperature dependence of the spin torque
efficiencies for both the damping-like torque and field-like torque is
dependent upon the details of the Pt-FM interface. The "internal" spin Hall
angle of the Pt thin films used in this study, after taking the interfacial
spin transmission factor into account, is estimated to be ~ 0.20. This suggests
that a careful engineering of Pt-FM interfaces can improve the spin-Hall-torque
efficiency of Pt-based spintronic devices. | 1411.3379v1 |
2014-11-13 | Transverse dynamical magnetic susceptibilities from regular static density functional theory: Evaluation of damping and g-shifts of spin-excitations | The dynamical transverse magnetic Kohn-Sham susceptibility calculated within
time-dependent density functional theory shows a fairly linear behavior for a
finite energy window. This observation is used to propose a scheme where the
computation of this quantity is greatly simplified. Regular simulations based
on static density functional theory can be used to extract the dynamical
behavior of the magnetic response function. Besides the ability to calculate
elegantly damping of magnetic excitations, we derive along the way useful
equations giving the main characteristics of these excitations: effective
$g$-factors and the resonance frequencies that can be accessed experimentally
using inelastic scanning tunneling spectroscopy or spin-polarized electron
energy loss spectroscopy. | 1411.3630v1 |
2014-11-17 | Decoherence Effects on the Non-locality of Symmetric States | The observation of the non-local properties of multipartite entangled states
is of great importance for quantum information protocols. Such properties,
however, are fragile and may not be observed in the presence of decoherence
exhibited by practical physical systems. In this work, we investigate the
robustness of the non-locality of symmetric states experiencing phase and
amplitude damping, using suitable Bell inequalities based on an extended
version of Hardy's paradox. We derive thresholds for observing non-locality in
terms of experimental noise parameters, and demonstrate the importance of the
choice of the measurement bases for optimizing the robustness. For $W$ states,
in the phase damping case, we show that this choice can lead to a trade-off
between obtaining a high violation of the non-local test and optimal robustness
thresholds; we also show that in this setting the non-locality of $W$ states is
particularly robust for a large number of qubits. Furthermore, we apply our
techniques to the discrimination of symmetric states belonging to different
entanglement classes, thus illustrating their usefulness for a wide range of
practical quantum information applications. | 1411.4489v1 |
2014-11-22 | Quantification of the spin-Hall anti-damping torque with a resonance spectrometer | We present a simple technique using a cavity-based resonance spectrometer to
quantify the anti-damping torque due to the spin Hall effect. Modification of
ferromagnetic resonance is observed as a function of small DC current in
sub-mm-wide strips of bilayers, consisting of magnetically soft FeGaB and
strong spin-Hall metal Ta. From the detected current-induced linewidth change,
we obtain an effective spin Hall angle of 0.08-0.09 independent of the magnetic
layer thickness. Our results demonstrate that a sensitive resonance
spectrometer can be a general tool to investigate spin Hall effects in various
material systems, even those with vanishingly low conductivity and
magnetoresistance. | 1411.6166v1 |
2014-11-28 | Quantifying entanglement of a two-qubit system via measurable and invariant moments of its partially transposed density matrix | We describe a direct method to determine the negativity of an arbitrary
two-qubit state in experiments. The method is derived by analyzing the relation
between the purity, negativity, and a universal entanglement witness for
two-qubit entanglement. We show how the negativity of a two-qubit state can be
calculated from just three experimentally accessible moments of the partially
transposed density matrix of a two-photon state. Moreover, we show that the
negativity can be given as a function of only six invariants, which are linear
combinations of nine invariants from the complete set of 21 fundamental and
independent two-qubit invariants. We analyze the relation between these moments
and the concurrence for some classes of two-qubit states (including the X
states, as well as pure states affected by the amplitude-damping and
phase-damping channels). We also discuss the possibility of using the universal
entanglement witness as an entanglement measure for various classes of
two-qubit states. Moreover, we analyze how noise affects the estimation of
entanglement via this witness. | 1411.7977v2 |
2014-12-05 | Adaptive Damping and Mean Removal for the Generalized Approximate Message Passing Algorithm | The generalized approximate message passing (GAMP) algorithm is an efficient
method of MAP or approximate-MMSE estimation of $x$ observed from a noisy
version of the transform coefficients $z = Ax$. In fact, for large zero-mean
i.i.d sub-Gaussian $A$, GAMP is characterized by a state evolution whose fixed
points, when unique, are optimal. For generic $A$, however, GAMP may diverge.
In this paper, we propose adaptive damping and mean-removal strategies that aim
to prevent divergence. Numerical results demonstrate significantly enhanced
robustness to non-zero-mean, rank-deficient, column-correlated, and
ill-conditioned $A$. | 1412.2005v1 |
2014-12-14 | An adaptive selective frequency damping method | The selective frequency damping (SFD) method is an alternative to classical
Newton's method to obtain unstable steady-state solutions of dynamical systems.
However this method has two main limitations: it does not converge for
arbitrary control parameters; and when it does converge, the time necessary to
reach the steady-state solution may be very long. In this paper we present an
adaptive algorithm to address these two issues. We show that by evaluating the
dominant eigenvalue of a "partially converged" steady flow, we can select a
control coefficient and a filter width that ensure an optimum convergence of
the SFD method. We apply this adaptive method to several classical test cases
of computational fluid dynamics and we show that a steady-state solution can be
obtained without any a priori knowledge of the flow stability properties. | 1412.4372v1 |
2014-12-23 | Photoacoustic elastic oscillation and characterization | Photoacoustic imaging and sensing have been studied extensively to probe the
optical absorption of biological tissue in multiple scales ranging from large
organs to small molecules. However, its elastic oscillation characterization is
rarely studied and has been an untapped area to be explored. In literature,
photoacoustic signal induced by pulsed laser is commonly modelled as a bipolar
"N-shape" pulse from an optical absorber. In this paper, the photoacoustic
damped oscillation is predicted and modelled by an equivalent mass-spring
system by treating the optical absorber as an elastic oscillator. The
photoacoustic simulation incorporating the proposed oscillation model shows
better agreement with the measured signal from an elastic phantom, than
conventional photoacoustic simulation model. More interestingly, the
photoacoustic damping oscillation effect could potentially be a useful
characterization approach to evaluate biological tissue's mechanical properties
in terms of relaxation time, peak number and ratio beyond optical absorption
only, which is experimentally demonstrated in this paper. | 1412.7284v1 |
2015-01-08 | Landau Damping of Geodesic Acoustic Mode in Toroidally Rotating Tokamaks | Geodesic acoustic mode (GAM) is analyzed by using modified gyro-kinetic (MGK)
equation applicable to low-frequency microinstabilities in a rotating
axisymmetric plasma. Dispersion relation of GAM in the presence of arbitrary
Mach number is analytically derived. Toroidal rotation plays the same effects
on the GAM regardless of the orientation of equilibrium flow. It is shown that
the toroidal Mach number $M$ increases the GAM frequency and dramatically
decreases the Landau damping rate. The valid of classical gyro-kinetic (CGK)
equation is also examined. For zero electron temperature, CGK is identical with
MGK. For non-zero electron temperature, CGK gives the same real frequency of
GAM as MGK but induces an instability with a growth rate proportional to
$M^3/q$, where $q$ is the safety factor. | 1501.01750v2 |
2015-01-17 | Applications of quantum cryptographic switch: Various tasks related to controlled quantum communication can be performed using Bell states and permutation of particles | Recently, several aspects of controlled quantum communication (e.g.,
bidirectional controlled state teleportation, controlled quantum secure direct
communication, controlled quantum dialogue, etc.) have been studied using
$n$-qubit ($n\geq3$) entanglement. Specially, a large number of schemes for
bidirectional controlled state teleportation are proposed using $m$-qubit
entanglement ($m\in\{5,6,7\}$). Here, we propose a set of protocols to
illustrate that it is possible to realize all these tasks related to controlled
quantum communication using only Bell states and permutation of particles
(PoP). As the generation and maintenance of a Bell state is much easier than a
multi-partite entanglement, the proposed strategy has a clear advantage over
the existing proposals. Further, it is shown that all the schemes proposed here
may be viewed as applications of the concept of quantum cryptographic switch
which was recently introduced by some of us. The performances of the proposed
protocols as subjected to the amplitude damping and phase damping noise on the
channels are also discussed. | 1501.04187v1 |
2015-02-06 | pQCD approach to Charmonium regeneration in QGP at the LHC | We analyze the applicability of perturbative QCD (pQCD) approach to the issue
of $J/\psi$ recombination at the Large Hadron Collider (LHC), and calculate the
recombination cross section for $c\bar{c}$ recombination to form $J/\psi$ as a
function of temperature. The charmonium wavefunction is obtained by employing a
temperature dependent phenomenological potential between the $c\bar{c}$ pair.
The temperature dependent formation time of charmonium is also employed in the
current work. A set of coupled rate equations is established which incorporates
color screening, gluonic dissociation, collisional damping and recombination of
uncorrelated $c\bar{c}$ pair in the quark-gluon plasma (QGP) medium. The final
$J/\psi$ suppression, thus determined as a function of centrality is compared
with the ALICE experimental data at both mid and forward rapidity and CMS
experimental data at mid rapidity obtained from the Large Hadron Collider (LHC)
at center of mass energy $\sqrt{s_{NN}} = 2.76$ TeV.
Keywords : Color screening, Recombination, Gluonic dissociation, Collisional
damping, Survival probability, pQCD, Charmonium
PACS numbers : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa | 1502.01790v2 |
2015-02-06 | Biological control via "ecological" damping: An approach that attenuates non-target effects | In this work we develop and analyze a mathematical model of biological
control to prevent or attenuate the explosive increase of an invasive species
population in a three-species food chain. We allow for finite time blow-up in
the model as a mathematical construct to mimic the explosive increase in
population, enabling the species to reach "disastrous" levels, in a finite
time. We next propose various controls to drive down the invasive population
growth and, in certain cases, eliminate blow-up. The controls avoid chemical
treatments and/or natural enemy introduction, thus eliminating various
non-target effects associated with such classical methods. We refer to these
new controls as "ecological damping", as their inclusion dampens the invasive
species population growth. Further, we improve prior results on the regularity
and Turing instability of the three-species model that were derived in earlier
work. Lastly, we confirm the existence of spatio-temporal chaos. | 1502.02010v1 |
2015-02-11 | On the mass determination in liquid utilizing measurement of only the fundamental flexural resonances of the micro-/nanomechanical based mass sensors | Micro-/nanomechanical mass sensors are capable to quantitatively determine
molecule mass from only first three (two) measured cantilever (bridge) resonant
frequencies. However, in liquid solutions that are relevant to most of the
biological systems, the mass determination is challenging because the Q-factor
due to fluid damping decreases and, as a result, usually just the fundamental
resonant frequencies can be correctly identified. Moreover, for higher modes
the resonance coupling, noise and internal damping have been proven to strongly
affect the measured resonant frequencies and, correspondingly, the accuracy of
the estimated masses. Here, we derive the easy accessible expressions enabling
the quantitative mass(es) determination just from the fundamental resonant
frequencies of the micro/nanomechanical mass sensor under intentionally applied
axial tension, which can be easily created and controlled by the electrostatic
or magnetostatic forces. We also show that typically achievable force
resolution has a negligible impact on the mass determination and the mass
sensitivity. | 1502.03232v1 |
2015-02-13 | A Dynamical Model of Plasma Turbulence in the Solar Wind | A dynamical approach, rather than the usual statistical approach, is taken to
explore the physical mechanisms underlying the nonlinear transfer of energy,
the damping of the turbulent fluctuations, and the development of coherent
structures in kinetic plasma turbulence. It is argued that the linear and
nonlinear dynamics of Alfven waves are responsible, at a very fundamental
level, for some of the key qualitative features of plasma turbulence that
distinguish it from hydrodynamic turbulence, including the anisotropic cascade
of energy and the development of current sheets at small scales. The first
dynamical model of kinetic turbulence in the weakly collisional solar wind
plasma that combines self-consistently the physics of Alfven waves with the
development of small-scale current sheets is presented and its physical
implications are discussed. This model leads to a simplified perspective on the
nature of turbulence in a weakly collisional plasma: the nonlinear interactions
responsible for the turbulent cascade of energy and the formation of current
sheets are essentially fluid in nature, while the collisionless damping of the
turbulent fluctuations and the energy injection by kinetic instabilities are
essentially kinetic in nature. | 1502.04109v1 |
2015-03-19 | Vertical Oscillations of Fluid and Stellar Disks | A satellite galaxy or dark matter subhalo that passes through a stellar disk
may excite coherent oscillations in the disk perpendicular to its plane. We
determine the properties of these modes for various self-gravitating plane
symmetric systems (Spitzer sheets) using the matrix method of Kalnajs. In
particular, we find an infinite series of modes for the case of a barotropic
fluid. In general, for a collisionless system, there is a double series of
modes, which include normal modes and/or Landau-damped oscillations depending
on the phase space distribution function of the stars. Even Landau-damped
oscillations may decay slowly enough to persist for several hundred Myr. We
discuss the implications of these results for the recently discovered vertical
perturbations in the kinematics of solar neighborhood stars and for broader
questions surrounding secular phenomena such as spiral structure in disk
galaxies. | 1503.05741v1 |
2015-03-24 | Linearized nonequilibrium dynamics in nonconformal plasma | We investigate the behaviour of the lowest nonhydrodynamic modes in a class
of holographic models which exhibit an equation of state closely mimicking the
one determined from lattice QCD. We calculate the lowest quasinormal mode
frequencies for a range of scalar self-interaction potentials and find that the
damping of the quasinormal modes at the phase transition/crossover falls off by
a factor of around two from conformality after factoring out standard conformal
temperature dependence. The damping encoded in the imaginary part of the
frequencies turns out to be correlated with the speed of sound and is basically
independent of the UV details of the model. We also find that the dynamics of
the nonhydrodynamic degrees of freedom remains ultralocal, even to a higher
degree, as we deviate from conformality. These results indicate that the role
of nonhydrodynamic degrees of freedom in the vicinity of the crossover
transition may be enhanced. | 1503.07149v1 |
2015-03-25 | The Conversion of CESR to Operate as the Test Accelerator, CesrTA, Part 1: Overview | Cornell's electron/positron storage ring (CESR) was modified over a series of
accelerator shutdowns beginning in May 2008, which substantially improves its
capability for research and development for particle accelerators. CESR's
energy span from 1.8 to 5.6 GeV with both electrons and positrons makes it
ideal for the study of a wide spectrum of accelerator physics issues and
instrumentation related to present light sources and future lepton damping
rings. Additionally a number of these are also relevant for the beam physics of
proton accelerators. This paper outlines the motivation, design and conversion
of CESR to a test accelerator, CesrTA, enhanced to study such subjects as low
emittance tuning methods, electron cloud (EC) effects, intra-beam scattering,
fast ion instabilities as well as general improvements to beam instrumentation.
While the initial studies of CesrTA focussed on questions related to the
International Linear Collider (ILC) damping ring design, CesrTA is a very
flexible storage ring, capable of studying a wide range of accelerator physics
and instrumentation questions. This paper contains the outline and the basis
for a set of papers documenting the reconfiguration of the storage ring and the
associated instrumentation required for the studies described above. Further
details may be found in these papers. | 1503.07451v2 |
2015-04-10 | Fission barrier, damping of shell correction and neutron emission in the fission of A$\sim$200 | Decay of $^{210}$Po compound nucleus formed in light and heavy-ion induced
fusion reactions has been analyzed simultaneously using a consistent
prescription for fission barrier and nuclear level density incorporating shell
correction and its damping with excitation energy. Good description of all the
excitation functions have been achieved with a fission barrier of 21.9 $\pm$
0.2 MeV. For this barrier height, the predicted statistical pre-fission
neutrons in heavy-ion fusion-fission are much smaller than the experimental
values, implying the presence of dynamical neutrons due to dissipation even at
these low excitation energies ($\sim$ 50~MeV) in the mass region A $\sim$ 200.
When only heavy-ion induced fission excitation functions and the pre-fission
neutron multiplicities are included in the fits, the deduced best fit fission
barrier depends on the assumed fission delay time during which dynamical
neutrons can be emitted. A fission delay of (0.8 $\pm$ 0.1 )$\times 10^{-19}$ s
has been estimated corresponding to the above fission barrier height assuming
that the entire excess neutrons over and above the statistical model
predictions are due to the dynamics. The present observation has implication on
the study of fission time scale/ nuclear viscosity using neutron emission as a
probe. | 1504.02599v1 |
2015-04-10 | Enhancement of the Anti-Damping Spin Torque Efficacy of Platinum by Interface Modification | We report a strong enhancement of the efficacy of the spin Hall effect (SHE)
of Pt for exerting anti-damping spin torque on an adjacent ferromagnetic layer
by the insertion of $\approx$ 0.5 nm layer of Hf between a Pt film and a thin,
< 2 nm, Fe$_{60}$Co$_{20}$B$_{20}$ ferromagnetic layer. This enhancement is
quantified by measurement of the switching current density when the
ferromagnetic layer is the free electrode in a magnetic tunnel junction. The
results are explained as the suppression of spin pumping through a substantial
decrease in the effective spin-mixing conductance of the interface, but without
a concomitant reduction of the ferromagnet\' s absorption of the SHE generated
spin current. | 1504.02806v1 |
2015-04-21 | Effect of assortative mixing in the second-order Kuramoto model | In this paper we analyze the second-order Kuramoto model presenting a
positive correlation between the heterogeneity of the connections and the
natural frequencies in scale-free networks. We numerically show that
discontinuous transitions emerge not just in disassortative but also in
assortative networks, in contrast with the first-order model. We also find that
the effect of assortativity on network synchronization can be compensated by
adjusting the phase damping. Our results show that it is possible to control
collective behavior of damped Kuramoto oscillators by tuning the network
structure or by adjusting the dissipation related to the phases movement. | 1504.05447v1 |
2015-04-27 | Controlled merging and annihilation of localized dissipative structures in an AC-driven damped nonlinear Schrödinger system | We report studies of controlled interactions of localized dissipative
structures in a system described by the AC-driven damped nonlinear
Schr\"odinger equation. Extensive numerical simulations reveal a diversity of
interaction scenarios that are governed by the properties of the system driver.
In our experiments, performed with a nonlinear optical Kerr resonator, the
phase profile of the driver is used to induce interactions on demand. We
observe both merging and annihilation of localized structures, i.e.,
interactions governed by the dissipative, out-of-equilibrium nature of the
system. | 1504.07231v1 |
2015-04-29 | Wide-Range Tunable Dynamic Property of Carbon Nanotube-Based Fibers | Carbon nanotube (CNT) fiber is formed by assembling millions of individual
tubes. The assembly feature provides the fiber with rich interface structures
and thus various ways of energy dissipation, as reflected by the non-zero loss
tangent (>0.028--0.045) at low vibration frequencies. A fiber containing
entangled CNTs possesses higher loss tangents than a fiber spun from aligned
CNTs. Liquid densification and polymer infiltration, the two common ways to
increase the interfacial friction and thus the fiber's tensile strength and
modulus, are found to efficiently reduce the damping coefficient. This is
because the sliding tendency between CNT bundles can also be well suppressed by
the high packing density and the formation of covalent polymer cross-links
within the fiber. The CNT/bismaleimide composite fiber exhibited the smallest
loss tangent, nearly as the same as that of carbon fibers. At a higher level of
the assembly structure, namely a multi-ply CNT yarn, the inter-fiber friction
and sliding tendency obviously influence the yarn's damping performance, and
the loss tangent can be tuned within a wide range, as similar to carbon fibers,
nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow
new applications ranging from high quality factor materials to dissipative
systems. | 1504.07881v1 |
2015-05-10 | Effects of electron drift on the collisionless damping of kinetic Alfvén waves in the solar wind | The collisionless dissipation of anisotropic Alfv\'enic turbulence is a
promising candidate to solve the solar wind heating problem. Extensive studies
examined the kinetic properties of Alfv\'en waves in simple Maxwellian or
bi-Maxwellian plasmas. However, the observed electron velocity distribution
functions in the solar wind are more complex. In this study, we analyze the
properties of kinetic Alfv\'en waves in a plasma with two drifting electron
populations. We numerically solve the linearized Maxwell-Vlasov equations and
find that the damping rate and the proton-electron energy partition for kinetic
Alfv\'en waves are significantly modified in such plasmas, compared to plasmas
without electron drifts. We suggest that electron drift is an important factor
to take into account when considering the dissipation of Alfv\'enic turbulence
in the solar wind or other $\beta \sim 1$ astrophysical plasmas. | 1505.02328v1 |
2015-05-13 | The effect of a reversible shear transformation on plastic deformation of an amorphous solid | Molecular dynamics simulations are performed to investigate the plastic
response of a model glass to a local shear transformation in a quiescent
system. The deformation of the material is induced by a spherical inclusion
that is gradually strained into an ellipsoid of the same volume and then
reverted back into the sphere. We show that the number of cage-breaking events
increases with increasing strain amplitude of the shear transformation. The
results of numerical simulations indicate that the density of cage jumps is
larger in the cases of weak damping or slow shear transformation. Remarkably,
we also found that, for a given strain amplitude, the peak value of the density
profiles is a function of the ratio of the damping coefficient and the time
scale of the shear transformation. | 1505.03488v1 |
2015-05-14 | Local large deviations principle for occupation measures of the damped nonlinear wave equation perturbed by a white noise | We consider the damped nonlinear wave (NLW) equation driven by a spatially
regular white noise. Assuming that the noise is non-degenerate in all Fourier
modes, we establish a large deviations principle (LDP) for the occupation
measures of the trajectories. The lower bound in the LDP is of a local type,
which is related to the weakly dissipative nature of the equation and seems to
be new in the context of randomly forced PDE's. The proof is based on an
extension of methods developed in \cite{JNPS-2012} and \cite{JNPS-2014} in the
case of kick forced dissipative PDE's with parabolic regularisation property
such as, for example, the Navier-Stokes system and the complex Ginzburg-Landau
equations. We also show that a high concentration towards the stationary
measure is impossible, by proving that the rate function that governs the LDP
cannot have the trivial form (i.e., vanish on the stationary measure and be
infinite elsewhere). | 1505.03686v1 |
2015-05-19 | Undamped nonequilibrium dynamics of a nondegenerate Bose gas in a 3D isotropic trap | We investigate anomalous damping of the monopole mode of a non-degenerate 3D
Bose gas under isotropic harmonic confinement as recently reported by the JILA
TOP trap experiment [D. S. Lob- ser, A. E. S. Barentine, E. A. Cornell, and H.
J. Lewandowski (in preparation)]. Given a realistic confining potential, we
develop a model for studying collective modes that includes the effects of
anharmonic corrections to a harmonic potential. By studying the influence of
these trap anharmonicities throughout a range of temperatures and collisional
regimes, we find that the damping is caused by the joint mechanisms of
dephasing and collisional relaxation. Furthermore, the model is complimented by
Monte Carlo simulations which are in fair agreement with data from the JILA
experiment. | 1505.04841v1 |
2015-05-21 | Control and stabilization of degenerate wave equations | We study a wave equation in one space dimension with a general diffusion
coefficient which degenerates on part of the boundary. Degeneracy is measured
by a real parameter $\mu_a>0$. We establish observability inequalities for
weakly (when $\mu_a \in [0,1[$) as well as strongly (when $\mu_a \in [1,2[$)
degenerate equations. We also prove a negative result when the diffusion
coefficient degenerates too violently (i.e. when $\mu_a>2$) and the blow-up of
the observability time when $\mu_a$ converges to $2$ from below. Thus, using
the HUM method we deduce the exact controllability of the corresponding
degenerate control problem when $\mu_a \in [0,2[$. We conclude the paper by
studying the boundary stabilization of the degenerate linearly damped wave
equation and show that a suitable boundary feedback stabilizes the system
exponentially. We extend this stability analysis to the degenerate nonlinearly
boundary damped wave equation, for an arbitrarily growing nonlinear feedback
close to the origin. This analysis proves that the degeneracy does not affect
the optimal energy decay rates at large time. We apply the optimal-weight
convexity method of \cite{alaamo2005, alajde2010} together with the results of
the previous section, to perform this stability analysis. | 1505.05720v1 |
2015-05-23 | Existence, blow-up and exponential decay of solutions for a porous-elastic system with damping and source terms | In this paper we consider a porous-elastic system consisting of nonlinear
boundary/interior damping and nonlinear boundary/interior sources. Our interest
lies in the theoretical understanding of the existence, finite time blow-up of
solutions and their exponential decay using non-trivial adaptations of
well-known techniques. First, we apply the conventional Faedo-Galerkin method
with standard arguments of density on the regularity of initial conditions to
establish two local existence theorems of weak solutions. Moreover, we detail
the uniqueness result in some specific cases. In the second theme, we prove
that any weak solution possessing negative initial energy has the latent
blow-up in finite time. Finally, we obtain the so-called exponential decay
estimates for the global solution under the construction of a suitable Lyapunov
functional. In order to corroborate our theoretical decay, a numerical example
is provided. | 1505.06373v2 |
2015-05-26 | Quantum Particle Motion in Absorbing Harmonic Trap | The motivation of this work is to get an additional insight into the
irreversible energy dissipation on the quantum level. The presented examination
procedure is based on the Feynman path integral method that is applied and
widened towards the calculation of the kernel of a quantum mechanical damped
oscillator. Here, it is shown that the energy loss of the oscillator can be
generated by the introduced harmonic complex potential. The related damped wave
function, however, does not pertain to the probability meaning as it is usual
in the case of complex absorbing potentials. This decrease of the wave function
is evaluated, moreover, the energy dissipation and the measure the
irreversibility are expressed. | 1505.06874v1 |
2015-06-03 | Non-uniqueness of Admissible Weak Solutions to Compressible Euler Systems with Source Terms | We consider admissible weak solutions to the compressible Euler system with
source terms, which include rotating shallow water system and the Euler system
with damping as special examples. In the case of anti-symmetric sources such as
rotations, for general piecewise Lipschitz initial densities and some suitably
constructed initial momentum, we obtain infinitely many global admissible weak
solutions. Furthermore, we construct a class of finite-states admissible weak
solutions to the Euler system with anti-symmetric sources. Under the additional
smallness assumption on the initial densities, we also obtain multiple
global-in-time admissible weak solutions for more general sources including
damping. The basic framework are based on the convex integration method
developed by De~Lellis and Sz\'{e}kelyhidi \cite{dLSz1,dLSz2} for the Euler
system. One of the main ingredients of this paper is the construction of
specified localized plane wave perturbations which are compatible with a given
source term. | 1506.01103v1 |
2015-06-03 | The effect of perpendicular electric field on Temperature-induced plasmon excitations for intrinsic silicene | We use the tight-binding model and the random-phase approximation to
investigate the intrinsic plasmon in silicene. At finite temperatures, an
undamped plasmon is generated from the interplay between the intraband and the
interband-gap transitions. The extent of the plasmon existence range in terms
of momentum and temperature, which is dependent on the size of
single-particle-excitation gap, is further tuned by applying a perpendicular
electric field. The plasmon becomes damped in the interband-excitation region.
A low damped zone is created by the field-induced spin split. The
field-dependent plasmon spectrum shows a strong tunability in plasmon intensity
and spectral bandwidth. This could make silicene a very suitable candidate for
plasmonic applications. | 1506.01140v1 |
2015-06-09 | Transport Barrier generation at the interface of regions with different zonal flows dynamics | A novel and generic understanding of spontaneous generation of transport
barriers and zonation regimes in turbulent self-organization is presented. It
associates the barrier onset to the development of a spectral gap between large
scale flows and turbulence modes leading to a zonation regime. A robust barrier
builds-up at the interface of such a region and a neighboring one with reduced
zonal flow generation. This more complex and generic transition paradigm could
fit the numerous and sometimes conflicting observations as in fusion plasma
experiments. Barrier relaxation by bursts of turbulence regenerate the zonal
flows that are eroded by viscous (collisional-like) damping. The duration of
the quiescent phase between the quasi-periodic relaxation events is governed by
this damping process, hence the barrier collision frequency for fusion plasmas. | 1506.02942v2 |
2015-06-11 | Fighting noise with noise in realistic quantum teleportation | We investigate how the efficiency of the quantum teleportation protocol is
affected when the qubits involved in the protocol are subjected to noise or
decoherence. We study all types of noise usually encountered in real world
implementations of quantum communication protocols, namely, the bit flip, phase
flip (phase damping), depolarizing, and amplitude damping noise. Several
realistic scenarios are studied in which a part or all of the qubits employed
in the execution of the quantum teleportation protocol are subjected to the
same or different types of noise. We find noise scenarios not yet known in
which more noise or less entanglement lead to more efficiency. Furthermore, we
show that if noise is unavoidable it is better to subject the qubits to
different noise channels in order to obtain an increase in the efficiency of
the protocol. | 1506.03803v2 |
2015-07-08 | Low-Dimensional Stochastic Projected Gross-Pitaevskii Equation | We present reduced-dimensional stochastic projected Gross-Pitaevskii
equations describing regimes of confinement and temperature where a 1D or 2D
superfluid is immersed in a 3D thermal cloud. The projection formalism provides
both a formally rigorous and physically natural way to effect the dimensional
reduction. The 3D form of the number-damping (growth) terms is unchanged by the
dimensional reduction. Projection of the energy-damping (scattering) terms
leads to modified stochastic equations of motion describing energy exchange
with the thermal reservoir. The regime of validity of the dimensional reduction
is investigated via variational analysis. Paying particular attention to 1D, we
validate our variational treatment by comparing numerical simulations of a
trapped oblate system in 3D with the 1D theory, and establish a consistent
choice of cutoff for the 1D theory. We briefly discuss the scenario involving
two-components with different degeneracy, suggesting that a wider regime of
validity exists for systems in contact with a buffer-gas reservoir. | 1507.02023v2 |
2015-07-08 | Low-emittance storage rings | The effects of synchrotron radiation on particle motion in storage rings are
discussed. In the absence of radiation, particle motion is symplectic, and the
beam emittances are conserved. The inclusion of radiation effects in a
classical approximation leads to emittance damping: expressions for the damping
times are derived. Then, it is shown that quantum radiation effects lead to
excitation of the beam emittances. General expressions for the equilibrium
longitudinal and horizontal (natural) emittances are derived. The impact of
lattice design on the natural emittance is discussed, with particular attention
to the special cases of FODO, achromat, and TME style lattices. Finally, the
effects of betatron coupling and vertical dispersion (generated by magnet
alignment and lattice tuning errors) on the vertical emittance are considered. | 1507.02213v1 |
2015-07-09 | Controlling the stability of steady states in continuous variable quantum systems | For the paradigmatic case of the damped quantum harmonic oscillator we
present two measurement-based feedback schemes to control the stability of its
fixed point. The first scheme feeds back a Pyragas-like time-delayed reference
signal and the second uses a predetermined instead of time-delayed reference
signal. We show that both schemes can reverse the effect of the damping by
turning the stable fixed point into an unstable one. Finally, by taking the
classical limit $\hbar\rightarrow0$ we explicitly distinguish between inherent
quantum effects and effects, which would be also present in a classical noisy
feedback loop. In particular, we point out that the correct description of a
classical particle conditioned on a noisy measurement record is given by a
non-linear stochastic Fokker-Planck equation and not a Langevin equation, which
has observable consequences on average as soon as feedback is considered. | 1507.02538v1 |
2015-07-14 | WIMP isocurvature perturbation and small scale structure | The adiabatic perturbation of dark matter is damped during the kinetic
decoupling due to the collision with relativistic component on sub-horizon
scales. However the isocurvature part is free from damping and could be large
enough to make a substantial contribution to the formation of small scale
structure. We explicitly study the weakly interacting massive particles as dark
matter with an early mater dominated period before radiation domination and
show that the isocurvature perturbation is generated during the phase
transition and leaves imprint in the observable signatures for small scale
structure. | 1507.03871v2 |
2015-07-17 | Pairwise quantum discord for a symmetric multi-qubit system in different types of noisy channels | We study the pairwise quantum discord (QD) for a symmetric multi-qubit system
in different types of noisy channels, such as phase-flip, amplitude damping,
phase-damping, and depolarizing channels. Using the QD and geometric measure of
quantum discord (GMQD) to quantify quantum correlations, some analytical or
numerical results are presented. The results show that, the dynamics of the
pairwise QD is related to the number of spin particles $N$ as well as initial
parameter $\theta$ of the one-axis twisting collective state. With the number
of spin particles $N$ increasing, the amount of the pairwise QD increases.
However, when the amount of the pairwise QD arrives at a stable maximal value,
the pairwise QD is independence of the number of spin particles $N$ increasing.
The behavior of the pairwise QD is symmetrical during a period $0\leq \theta
\leq 2\pi$. Moreover, we compare the pairwise QD dynamics with the GMQD for a
symmetric multi-qubit system in different types of noisy channels. | 1507.04826v1 |
2015-07-20 | Landau damping effects in the synchronization of conformist and contrarian oscillators | Two decades ago, a phenomenon resembling Landau damping was described in the
synchronization of globally coupled oscillators: the evidence of a regime where
the order parameter decays when linear theory predicts neutral stability for
the incoherent state. We here show that such an effect is far more generic, as
soon as phase oscillators couple to their mean field according to their natural
frequencies, being then grouped into two distinct populations of conformists
and contrarians. We report the analytical solution of this latter situation,
which allows determining the critical coupling strength and the stability of
the incoherent state, together with extensive numerical simulations that fully
support all theoretical predictions. The relevance of our results is discussed
in relationship to collective phenomena occurring in polarized social systems. | 1507.05383v1 |
2015-07-28 | Attractors for Strongly Damped Wave Equations with Nonlinear Hyperbolic Dynamic Boundary Conditions | We establish the well-posedness of a strongly damped semilinear wave equation
equipped with nonlinear hyperbolic dynamic boundary conditions. Results are
carried out with the presence of a parameter distinguishing whether the
underlying operator is analytic, $\alpha>0$, or only of Gevrey class,
$\alpha=0$. We establish the existence of a global attractor for each
$\alpha\in[0,1],$ and we show that the family of global attractors is
upper-semicontinuous as $\alpha\rightarrow0.$ Furthermore, for each
$\alpha\in[0,1]$, we show the existence of a weak exponential attractor. A weak
exponential attractor is a finite dimensional compact set in the weak topology
of the phase space. This result insures the corresponding global attractor also
possess finite fractal dimension in the weak topology; moreover, the dimension
is independent of the perturbation parameter $\alpha$. In both settings,
attractors are found under minimal assumptions on the nonlinear terms. | 1507.07971v1 |
2015-07-29 | Neimark--Sacker bifurcation and evidence of chaos in a discrete dynamical model of walkers | Bouncing droplets on a vibrating fluid bath can exhibit wave-particle
behavior, such as being propelled by interacting with its own wave field. These
droplets seem to walk across the bath, and thus are dubbed walkers. Experiments
have shown that walkers can exhibit exotic dynamical behavior indicative of
chaos. While the integro-differential models developed for these systems agree
well with the experiments, they are difficult to analyze mathematically. In
recent years, simpler discrete dynamical models have been derived and studied
numerically. The numerical simulations of these models show evidence of exotic
dynamics such as period doubling bifurcations, Neimark--Sacker (N--S)
bifurcations, and even chaos. For example, in [Gilet, PRE 2014], based on
simulations Gilet conjectured the existence of a supercritical N-S bifurcation
as the damping factor in his one-dimensional path model. We prove Gilet's
conjecture and more; in fact, both supercritical and subcritical (N-S)
bifurcations are produced by separately varying the damping factor and
wave-particle coupling for all eigenmode shapes. Then we compare our
theoretical results with some previous and new numerical simulations, and find
complete qualitative agreement. Furthermore, evidence of chaos is shown by
numerically studying a global bifurcation. | 1507.08057v2 |
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