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2012-10-11 | Measurement of the damping of nuclear shell effect in the doubly magic $^{208}$Pb region | The damping of the nuclear shell effect with excitation energy has been
measured through an analysis of the neutron spectra following the triton
transfer in the $^7$Li induced reaction on $^{205}$Tl. The measured neutron
spectra demonstrate the expected large shell correction energy for the nuclei
in the vicinity of doubly magic $^{208}$Pb and a small value for $^{184}$W. A
quantitative extraction of the allowed values of the damping parameter
$\gamma$, along with those for the asymptotic nuclear level density parameter
$\tilde{a}$, has been made for the first time. | 1210.3213v2 |
2012-10-16 | Optimal control of laser plasma instabilities using Spike Trains of Uneven Duration and Delay (STUD pulses) for ICF and IFE | An adaptive method of controlling parametric instabilities in laser produced
plasmas is proposed. It involves fast temporal modulation of a laser pulse on
the fastest instability's amplification time scale, adapting to changing and
unknown plasma conditions. These pulses are comprised of on and off sequences
having at least one or two orders of magnitude contrast between them. Such
laser illumination profiles are called STUD pulses for Spike Trains of Uneven
Duration and Delay. The STUD pulse program includes scrambling the speckle
patterns spatially in between the laser spikes. The off times allow damping of
driven waves. The scrambling of the hot spots allows tens of damping times to
elapse before hot spot locations experience recurring high intensity spikes.
Damping in the meantime will have healed the scars of past growth. Another
unique feature of STUD pulses on crossing beams is that their temporal profiles
can be interlaced or staggered, and their interactions thus controlled with an
on-off switch and a dimmer. | 1210.4462v1 |
2012-10-28 | Mass Dependence of Instabilities of an Oscillator with Multiplicative and Additive Noise | We study the instabilities of a harmonic oscillator subject to additive and
dichotomous multiplicative noise, focussing on the dependance of the
instability threshold on the mass. For multiplicative noise in the damping, the
instability threshold is crossed as the mass is decreased, as long as the
smaller damping is in fact negative. For multiplicative noise in the stiffness,
the situation is more complicated and in fact the transition is reentrant for
intermediate noise strength and damping. For multiplicative noise in the mass,
the results depend on the implementation of the noise. One can take the
velocity or the momentum to be conserved as the mass is changed. In these cases
increasing the mass destabilizes the system. Alternatively, if the change in
mass is caused by the accretion/loss of particles to the Brownian particle,
these processes are asymmetric with momentum conserved upon accretion and
velocity upon loss. In this case, there is no instability, as opposed to the
other two implementations. We also study the distribution of the energy,
finding a power-law cutoff at a value which increases with time. | 1210.7433v1 |
2012-10-30 | Extending the Concept of Analog Butterworth Filter for Fractional Order Systems | This paper proposes the design of Fractional Order (FO) Butterworth filter in
complex w-plane (w=sq; q being any real number) considering the presence of
under-damped, hyper-damped, ultra-damped poles. This is the first attempt to
design such fractional Butterworth filters in complex w-plane instead of
complex s-plane, as conventionally done for integer order filters. Firstly, the
concept of fractional derivatives and w-plane stability of linear fractional
order systems are discussed. Detailed mathematical formulation for the design
of fractional Butterworth-like filter (FBWF) in w-plane is then presented.
Simulation examples are given along with a practical example to design the FO
Butterworth filter with given specifications in frequency domain to show the
practicability of the proposed formulation. | 1210.8194v3 |
2012-11-24 | Effects of Quantum Error Correction on Entanglement Sudden Death | We investigate the effects of error correction on non-local quantum coherence
as a function of time, extending the study by Sainz and Bj\"ork. We consider
error correction of amplitude damping, pure phase damping and combinations of
amplitude and phase damping as they affect both fidelity and quantum
entanglement. Initial two-qubit entanglement is encoded in arbitrary real
superpositions of both \Phi-type and \Psi-type Bell states. Our main focus is
on the possibility of delay or prevention of ESD (early stage decoherence, or
entanglement sudden death). We obtain the onset times for ESD as a function of
the state-superposition mixing angle. Error correction affects entanglement and
fidelity differently, and we exhibit initial entangled states for which error
correction increases fidelity but decreases entanglement, and vice versa. | 1211.5654v2 |
2012-12-04 | Polarization dependence of phonon influences in exciton-biexciton quantum dot systems | We report on a strong dependence of the phonon-induced damping of Rabi
dynamics in an optically driven exciton-biexciton quantum dot system on the
polarization of the exciting pulse. While for a fixed pulse intensity the
damping is maximal for linearly polarized excitation, it decreases with
increasing ellipticity of the polarization. This finding is most remarkable
considering that the carrier-phonon coupling is spin-independent. In addition
to simulations based on a numerically exact real-time path integral approach,
we present an analysis within a weak coupling theory that allows for analytical
expressions for the pertinent damping rates. We demonstrate that an efficient
coupling to the biexciton state is of central importance for the reported
polarization dependencies. Further, we discuss influences of various system
parameters and show that for finite biexciton binding energies Rabi scenarios
differ qualitatively from the widely studied two-level dynamics. | 1212.0642v1 |
2012-12-10 | Heat-induced damping modification in YIG/Pt hetero-structures | We experimentally demonstrate the manipulation of magnetization relaxation
utilizing a temperature difference across the thickness of an yttrium iron
garnet/platinum (YIG/Pt) hetero-structure: the damping is either increased or
decreased depending on the sign of the temperature gradient. This effect might
be explained by a thermally-induced spin torque on the magnetization
precession. The heat-induced variation of the damping is detected by microwave
techniques as well as by a DC voltage caused by spin pumping into the adjacent
Pt layer and the subsequent conversion into a charge current by the inverse
spin Hall effect. | 1212.2073v1 |
2012-12-13 | Surface plasmon polaritons in a semi-bounded degenerate plasma: role of spatial dispersion and collisions | Surface plasmon polaritons (SPPs) in a semi-bounded degenerate plasma (e.g.,
a metal) are studied using the quasiclassical mean-field kinetic model, taking
into account the spatial dispersion of the plasma (due to quantum degeneracy of
electrons) and electron-ion (electron-lattice, for metals) collisions. SPP
dispersion and damping are obtained in both retarded ($\omega/k_z\sim c$) and
non-retarded ($\omega/k_z\ll c$) regions, as well as in between. It is shown
that the plasma spatial dispersion significantly affects the properties of
SPPs, especially at short wavelengths (less than the collisionless skin depth,
$\lambda\lesssim c/\omega_{pe}$). Namely, the collisionless (Landau) damping of
SPPs (due to spatial dispersion) is comparable to the purely collisional
(Ohmic) damping (due to electron-lattice collisions) in a wide range of SPP
wavelengths, e.g., from $\lambda\sim20$ nm to $\lambda\sim0.8$ nm for SPP in
gold at T=293 K, and from $\lambda\sim400$ nm to $\lambda\sim0.7$ nm for SPPs
in gold at T=100 K. The spatial dispersion is also shown to affect, in a
qualitative way, the dispersion of SPPs at short wavelengths $\lambda\lesssim
c/\omega_{pe}$. | 1212.3040v1 |
2012-12-13 | Branching of quasinormal modes for nearly extremal Kerr black holes | We show that nearly extremal Kerr black holes have two distinct sets of
quasinormal modes, which we call zero-damping modes (ZDMs) and damped modes
(DMs). The ZDMs exist for all harmonic indices $l$ and $m \ge 0$, and their
frequencies cluster onto the real axis in the extremal limit. The DMs have
nonzero damping for all black hole spins; they exist for all counterrotating
modes ($m<0$) and for corotating modes with $0\leq \mu\lesssim \mu_c=0.74$ (in
the eikonal limit), where $\mu\equiv m/(l+1/2)$. When the two families coexist,
ZDMs and DMs merge to form a single set of quasinormal modes as the black hole
spin decreases. Using the effective potential for perturbations of the Kerr
spacetime, we give intuitive explanations for the absence of DMs in certain
areas of the spectrum and for the branching of the spectrum into ZDMs and DMs
at large spins. | 1212.3271v1 |
2012-12-31 | Effects of lateral device size and material properties on the ferromagnetic resonance response of spinwave eigen-modes in magnetic devices | We analyze the effects of lateral device size and magnetic material
parameters on the ferromagnetic resonance (FMR) response. Results presented are
directly relevant to widely used FMR experimental techniques for extracting
magnetic parameters from thin films, the results of which are often assumed to
carry over to corresponding nanometer-sized patterned devices. We show that
there can be significant variation in the FMR response with device size, and
that the extent of the variation depends on the magnetic material properties.
This explains, for example, why different experiments along these lines have
yielded different size-dependent trends from damping measurements. Observed
trends with increasing size and different material parameters are explained
through the evolution of three distinct eigen-modes, demonstrating the
respective roles of demagnetization and exchange. It is also shown that there
is a crossover of dominant eigen-modes in the response signal, accompanied by
conjugating edge-type modes, leading to evident effects in measured linewidth
and damping. Among the sizes considered, in higher saturation magnetization, we
observe as much as a 40% increase in apparent damping, due solely to device
size variation. | 1212.6835v1 |
2013-01-16 | Gain-tunable optomechanical cooling in a laser cavity | We study the optical cooling of the resonator mirror in a
cavity-optomechanical system that contains an optical gain medium. We find that
the optical damping rate is vanishingly small for an incoherently pumped laser
above threshold. In the presence of an external coherent drive however, the
optical damping rate can be enhanced substantially with respect to that of a
passive cavity. We show that the strength of the incoherent pump provides a
conduit to tune the damping rate and the minimum attainable phonon number with
the same radiation pressure force, and the latter can be lowered from that of a
passive cavity if the thermal contribution is nonnegligible. We also show that
the system can undergo a transition from the weak optomechanical coupling
regime to the strong optomechanical coupling regime as the incoherent pump
strength is varied. | 1301.3762v2 |
2013-01-18 | Adiabatic stability under semi-strong interactions: The weakly damped regime | We rigorously derive multi-pulse interaction laws for the semi-strong
interactions in a family of singularly-perturbed and weakly-damped
reaction-diffusion systems in one space dimension. Most significantly, we show
the existence of a manifold of quasi-steady N-pulse solutions and identify a
"normal-hyperbolicity" condition which balances the asymptotic weakness of the
linear damping against the algebraic evolution rate of the multi-pulses. Our
main result is the adiabatic stability of the manifolds subject to this normal
hyperbolicity condition. More specifically, the spectrum of the linearization
about a fixed N-pulse configuration contains essential spectrum that is
asymptotically close to the origin as well as semi-strong eigenvalues which
move at leading order as the pulse positions evolve. We characterize the
semi-strong eigenvalues in terms of the spectrum of an explicit N by N matrix,
and rigorously bound the error between the N-pulse manifold and the evolution
of the full system, in a polynomially weighted space, so long as the
semi-strong spectrum remains strictly in the left-half complex plane, and the
essential spectrum is not too close to the origin. | 1301.4466v1 |
2013-01-24 | Spin transport parameters in metallic multilayers determined by ferromagnetic resonance measurements of spin pumping | We measured spin transport in nonferromagnetic (NM) metallic multilayers from
the contribution to damping due to spin pumping from a ferromagnetic Co90Fe10
thin film. The multilayer stack consisted of NM1/NM2/Co90Fe10(2 nm)/NM2/NM3
with varying NM materials and thicknesses. Using conventional theory for one
dimensional diffusive spin transport in metals, we show that the effective
damping due to spin pumping can be strongly affected by the spin transport
properties of each NM in the multilayer, which permits the use of damping
measurements to accurately determine the spin transport properties of the
various NM layers in the full five-layer stack. We find that due to its high
electrical resistivity, amorphous Ta is a poor spin conductor, in spite of a
short spin-diffusion length of 1.0 nm, and that Pt is an excellent spin
conductor by virtue of its low electrical resistivity and a spin diffusion
length of only 0.5 nm. Spin Hall effect measurements may have underestimated
the spin Hall angle in Pt by assuming a much longer spin diffusion length. | 1301.5861v1 |
2013-02-11 | Low-damping epsilon-near-zero slabs: nonlinear and nonlocal optical properties | We investigate second harmonic generation, low-threshold multistability,
all-optical switching, and inherently nonlocal effects due to the free-electron
gas pressure in an epsilon-near-zero (ENZ) metamaterial slab made of
cylindrical, plasmonic nanoshells illuminated by TM-polarized light. Damping
compensation in the ENZ frequency region, achieved by using gain medium inside
the shells' dielectric cores, enhances the nonlinear properties. Reflection is
inhibited and the electric field component normal to the slab interface is
enhanced near the effective pseudo-Brewster angle, where the effective
\epsilon-near-zero condition triggers a non-resonant, impedance-matching
phenomenon. We show that the slab displays a strong effective, spatial
nonlocality associated with leaky modes that are mediated by the compensation
of damping. The presence of these leaky modes then induces further spectral and
angular conditions where the local fields are enhanced, thus opening new
windows of opportunity for the enhancement of nonlinear optical processes. | 1302.2392v1 |
2013-02-14 | A Matlab toolbox for fractional relaxation-oscillation equations | Stress relaxation and oscillation damping of complex viscoelastic media often
manifest history- and path-dependent physical behaviors and cannot accurately
be described by the classical models. Recent research found that fractional
derivative models can characterize such complex relaxation and damping.
However, to our best knowledge, easy-to-use numerical software is not available
for fractional relaxation-oscillation (FRO) equations. This paper is to
introduce an open source free Matlab toolbox which we developed in recent years
for numerical solution of the FRO equations. This FRO toolbox uses the
predictor-corrector approach for the discretization of time fractional
derivative, and non-expert users can accurately solve fractional
relaxation-oscillation equations via a friendly graphical user interface.
Compared with experimental data, our numerical experiments show that the FRO
toolbox is highly efficient and accurate to simulate viscoelastic stress
relaxation and damped vibration. This free toolbox will help promote the
research and practical use of fractional relaxation-oscillation equations. | 1302.3384v1 |
2013-03-11 | The Analysis of Long-Term Frequency and Damping Wandering in Buildings Using the Random Decrement Technique | The characterization and monitoring of buildings is an issue that has
attracted the interest of many sectors over the last two decades. With the
increasing use of permanent, continuous and real-time networks, ambient
vibrations can provide a simple tool for the identification of dynamic building
parameters. This study is focused on the long-term variation of frequency and
damping in several buildings, using the Random Decrement Technique (RDT). RDT
provides a fast, robust and accurate long-term analysis and improves the
reliability of frequency and damping measurements for structural health
monitoring. This reveals particularly useful information in finding out
precisely how far changes in modal parameters can be related to changes in
physical properties. This paper highlights the reversible changes of the
structure's dynamic parameters, correlated with external forces, such as
temperature and exposure to the sun. Contrasting behaviors are observed,
including correlation and anti-correlation with temperature variations. | 1303.2642v1 |
2013-03-21 | Optimizing atomic resolution of force microscopy in ambient conditions | Ambient operation poses a challenge to AFM because in contrast to operation
in vacuum or liquid environments, the cantilever dynamics change dramatically
from oscillating in air to oscillating in a hydration layer when probing the
sample. We demonstrate atomic resolution by imaging of the KBr(001) surface in
ambient conditions by frequency-modulation atomic force microscopy with a
cantilever based on a quartz tuning fork (qPlus sensor) and analyze both long-
and short-range contributions to the damping. The thickness of the hydration
layer increases with relative humidity, thus varying humidity enables us to
study the in uence of the hydration layer thickness on cantilever damping.
Starting with measurements of damping versus amplitude, we analyzed the signal
and the noise characteristics at the atomic scale. We then determined the
optimal amplitude which enabled us to acquire high-quality atomically resolved
images. | 1303.5204v2 |
2013-04-10 | Current Sheets and Collisionless Damping in Kinetic Plasma Turbulence | We present the first study of the formation and dissipation of current sheets
at electron scales in a wave-driven, weakly collisional, 3D kinetic turbulence
simulation. We investigate the relative importance of dissipation associated
with collisionless damping via resonant wave-particle interactions versus
dissipation in small-scale current sheets in weakly collisional plasma
turbulence. Current sheets form self-consistently from the wave-driven
turbulence, and their filling fraction is well correlated to the electron
heating rate. However, the weakly collisional nature of the simulation
necessarily implies that the current sheets are not significantly dissipated
via Ohmic dissipation. Rather, collisionless damping via the Landau resonance
with the electrons is sufficient to account for the measured heating as a
function of scale in the simulation, without the need for significant Ohmic
dissipation. This finding suggests the possibility that the dissipation of the
current sheets is governed by resonant wave-particle interactions and that the
locations of current sheets correspond spatially to regions of enhanced
heating. | 1304.2958v2 |
2013-04-23 | Existence and non-existence of breather solutions in damped and driven nonlinear lattices | We investigate the existence of spatially localised solutions, in the form of
discrete breathers, in general damped and driven nonlinear lattice systems of
coupled oscillators. Conditions for the exponential decay of the difference
between the maximal and minimal amplitudes of the oscillators are provided
which proves that initial non-uniform spatial patterns representing breathers
attain exponentially fast a spatially uniform state preventing the formation
and/or preservation of any breather solution at all. Strikingly our results are
generic in the sense that they hold for arbitrary dimension of the system, any
attractive interaction, coupling strength and on-site potential and general
driving fields. Furthermore, our rigorous quantitative results establish
conditions under which discrete breathers in general damped and driven
nonlinear lattices can exist at all and open the way for further research on
the emergent dynamical scenarios, in particular features of pattern formation,
localisation and synchronisation, in coupled cell networks. | 1304.6370v3 |
2013-06-21 | Inviscid damping and the asymptotic stability of planar shear flows in the 2D Euler equations | We prove asymptotic stability of shear flows close to the planar Couette flow
in the 2D inviscid Euler equations on $\Torus \times \Real$. That is, given an
initial perturbation of the Couette flow small in a suitable regularity class,
specifically Gevrey space of class smaller than 2, the velocity converges
strongly in L^2 to a shear flow which is also close to the Couette flow. The
vorticity is asymptotically driven to small scales by a linear evolution and
weakly converges as $t \rightarrow \pm\infty$. The strong convergence of the
velocity field is sometimes referred to as inviscid damping, due to the
relationship with Landau damping in the Vlasov equations. This convergence was
formally derived at the linear level by Kelvin in 1887 and it occurs at an
algebraic rate first computed by Orr in 1907; our work appears to be the first
rigorous confirmation of this behavior on the nonlinear level. | 1306.5028v3 |
2013-07-12 | Spin injection from topological insulator tunnel-coupled to metallic leads | We study theoretically helical edge states of 2D and 3D topological
insulators (TI) tunnel-coupled to metal leads and show that their transport
properties are strongly affected by contacts as the latter play a role of a
heat bath and induce damping and relaxation of electrons in the helical states
of TI. A simple structure that produces a pure spin current in the external
circuit is proposed. The current and spin current delivered to the external
circuit depend on relation between characteristic lengths: damping length due
to tunneling, contact length and, in case of 3D TI, mean free path and spin
relaxation length caused by momentum scattering. If the damping length due to
tunneling is the smallest one, then the electric and spin currents are
proportional to the conductance quantum in 2D TI, and to the conductance
quantum multiplied by the ratio of the contact width to the Fermi wavelength in
3D TI. | 1307.3333v1 |
2013-07-19 | Damping and non-linearity of a levitating magnet in rotation above a superconductor | We study the dissipation of moving magnets in levitation above a
superconductor. The rotation motion is analyzed using optical tracking
techniques. It displays a remarkable regularity together with long damping time
up to several hours. The magnetic contribution to the damping is investigated
in detail by comparing 14 distinct magnetic configurations, and points towards
amplitude-dependent dissipation mechanisms. The non-linear dynamics of the
mechanical rotation motion is also revealed and described with an effective
Duffing model. The obtained picture of the coupling of levitating magnets to
their environment sheds light on their potential as ultra-low dissipation
mechanical oscillators for high precision physics. | 1307.5155v1 |
2013-07-19 | Perfect squeezing by damping modulation in circuit quantum electrodynamics | Dissipation-driven quantum state engineering uses the environment to steer
the state of quantum systems and preserve quantum coherence in the steady
state. We show that modulating the damping rate of a microwave resonator
generates a vacuum squeezed state of arbitrary squeezing strength, thereby
constituting a mechanism allowing perfect squeezing. Given the recent
experimental realizations in circuit QED of a microwave resonator with a
tunable damping rate [Yin et al., Phys. Rev. Lett. 110, 107001 (2013)],
superconducting circuits are an ideal playground to implement this technique.
By dispersively coupling a qubit to the microwave resonator, it is possible to
obtain qubit-state dependent squeezing. | 1307.5311v2 |
2013-07-27 | Charge-carrier-induced frequency renormalization, damping and heating of vibrational modes in nanoscale junctions | In nanoscale junctions the interaction between charge carriers and the local
vibrations results in renormalization, damping and heating of the vibrational
modes. We here formulate a nonequilibrium Green's functions based theory to
describe such effects. Studying a generic junction model with an off-resonant
electronic level, we find a strong bias dependence of the frequency
renormalization and vibrational damping accompanied by pronounced nonlinear
vibrational heating in junctions with intermediate values of the coupling to
the leads. Combining our theory with ab-initio calculations we furthermore show
that the bias dependence of the Raman shifts and linewidths observed
experimentally in an OPV3 junction [D. Ward et al., Nature Nano. 6, 33 (2011)]
may be explained by a combination of dynamic carrier screening and molecular
charging. | 1307.7288v3 |
2013-07-30 | Phase retrapping in a pointlike $\varphi$ Josephson junction: the Butterfly effect | We consider a $\varphi$ Josephson junction, which has a bistable zero-voltage
state with the stationary phases $\psi=\pm\varphi$. In the non-zero voltage
state the phase "moves" viscously along a tilted periodic double-well
potential. When the tilting is reduced quasistatically, the phase is retrapped
in one of the potential wells. We study the viscous phase dynamics to determine
in which well ($-\varphi$ or $+\varphi$) the phase is retrapped for a given
damping, when the junction returns from the finite-voltage state back to
zero-voltage state. In the limit of low damping the $\varphi$ Josephson
junction exhibits a butterfly effect --- extreme sensitivity of the destination
well on damping. This leads to an impossibility to predict the destination
well. | 1307.8042v1 |
2013-08-10 | CESR Test Accelerator | The Cornell Electron Storage Ring (CESR) was reconfigured in 2008 as a test
accelerator to investigate the physics of ultra-low emittance damping rings.
During the approximately 40 days/year available for dedicated operation as a
test accelerator, specialized instrumentation is used to measure growth and
mitigation of the electron cloud, emittance growth due to electron cloud,
intra-beam scattering, and ions, and single and multi-bunch instabilities
generated by collective effects. The flexibility of the CESR guide field optics
and the integration of accelerator modeling codes with the control system have
made possible an extraordinary range of experiments. Findings at CesrTA with
respect to electron cloud effects, emittance tuning techniques, and beam
instrumentation for measuring electron cloud, beam sizes, and beam positions
are the basis for much of the design of the ILC damping rings as documented in
the ILC-Technical Design Report. The program has allowed the Cornell group to
cultivate the kind of talent and expertise that will be absolutely essential to
the final engineering design, and commissioning of the damping rings for a
linear collider. | 1308.2325v1 |
2013-09-09 | Characterization of the International Linear Collider damping ring optics | A method is presented for characterizing the emittance dilution and dynamic
aperture for an arbitrary closed lattice that includes guide field magnet
errors, multipole errors and misalignments. This method, developed and tested
at the Cornell Electron Storage Ring Test Accelerator (CesrTA), has been
applied to the damping ring lattice for the International Linear Collider
(ILC). The effectiveness of beam based emittance tuning is limited by beam
position monitor (BPM) measurement errors, number of corrector magnets and
their placement, and correction algorithm. The specifications for damping ring
magnet alignment, multipole errors, number of BPMs, and precision in BPM
measurements are shown to be consistent with the required emittances and
dynamic aperture. The methodology is then used to determine the minimum number
of position monitors that is required to achieve the emittance targets, and how
that minimum depends on the location of the BPMs. Similarly, the maximum
tolerable multipole errors are evaluated. Finally, the robustness of each BPM
configuration with respect to random failures is explored. | 1309.2248v3 |
2013-09-19 | Van der Waals Coefficients for the Alkali-metal Atoms in the Material Mediums | The damping coefficients for the alkali atoms are determined very accurately
by taking into account the optical properties of the atoms and three distinct
types of trapping materials such as Au (metal), Si (semi-conductor) and
vitreous SiO2 (dielectric). Dynamic dipole polarizabilities are calculated
precisely for the alkali atoms that reproduce the damping coefficients in the
perfect conducting medium within 0.2% accuracy. Upon the consideration of the
available optical data of the above wall materials, the damping coefficients
are found to be substantially different than those of the ideal conductor. We
also evaluated dispersion coefficients for the alkali dimers and compared them
with the previously reported values. These coefficients are fitted into a
ready-to-use functional form to aid the experimentalists the interaction
potentials only with the knowledge of distances. | 1309.4897v1 |
2013-10-13 | What the Timing of Millisecond Pulsars Can Teach us about Their Interior | The cores of compact stars reach the highest densities in nature and
therefore could consist of novel phases of matter. We demonstrate via a
detailed analysis of pulsar evolution that precise pulsar timing data can
constrain the star's composition, through unstable global oscillations
(r-modes) whose damping is determined by microscopic properties of the
interior. If not efficiently damped, these modes emit gravitational waves that
quickly spin down a millisecond pulsar. As a first application of this general
method, we find that ungapped interacting quark matter is consistent with both
the observed radio and x-ray data, whereas for ordinary nuclear matter some
additional enhanced damping mechanism is required. | 1310.3524v2 |
2013-11-28 | Conservative effects in spin-transfer-driven magnetization dynamics | It is shown that under appropriate conditions spin-transfer-driven
magnetization dynamics in a single-domain nanomagnet is conservative in nature
and admits a specific integral of motion, which is reduced to the usual
magnetic energy when the spin current goes to zero. The existence of this
conservation law is connected to the symmetry properties of the dynamics under
simultaneous inversion of magnetisation and time. When one applies an external
magnetic field parallel to the spin polarization, the dynamics is transformed
from conservative into dissipative. More precisely, it is demonstrated that
there exists a state function such that the field induces a monotone relaxation
of this function toward its minima or maxima, depending on the field
orientation. These results hold in the absence of intrinsic damping effects.
When intrinsic damping is included in the description, a competition arises
between field-induced and damping-induced relaxations, which leads to the
appearance of limit cycles, that is, of magnetization self-oscillations. | 1311.7344v1 |
2013-12-05 | The initial condition problems of damped quantum harmonic oscillator | We investigate the exact dynamics of the damped quantum harmonic oscillator
under the (un)correlated initial conditions. The master equation is generalized
to the cases of the arbitrary factorized state and/or Gaussian state. We show
that the variances of the factorized Gaussian state do not sensitively depend
on the initial oscillator-bath correlation, which however can remarkably affect
the mean values even at high temperature. We also illustrate that the
correlations among the factorized states still give rise to the initial dips
during the purity evolutions, which can be smoothed out by increasing the
amount of correlation to some extent. We finally study the effects of repeated
measurements on the time evolution of the damped oscillator analytically, which
are compared with the weak coupling results to indicate that they give rather
different transient behaviors even for an intermediate coupling. | 1312.1454v1 |
2013-12-13 | Optical variability of quasars: a damped random walk | A damped random walk is a stochastic process, defined by an exponential
covariance matrix that behaves as a random walk for short time scales and
asymptotically achieves a finite variability amplitude at long time scales.
Over the last few years, it has been demonstrated, mostly but not exclusively
using SDSS data, that a damped random walk model provides a satisfactory
statistical description of observed quasar variability in the optical
wavelength range, for rest-frame timescales from 5 days to 2000 days. The
best-fit characteristic timescale and asymptotic variability amplitude scale
with the luminosity, black hole mass, and rest wavelength, and appear
independent of redshift. In addition to providing insights into the physics of
quasar variability, the best-fit model parameters can be used to efficiently
separate quasars from stars in imaging surveys with adequate long-term
multi-epoch data, such as expected from LSST. | 1312.3966v1 |
2013-12-25 | Non-linear damping of visco-resistive Alfven waves in solar spicules | Interaction of Alfven waves with plasma inhomogeneities generates phase
mixing which can lead to dissipate Alfven waves and to heat the solar plasma.
Here we study the dissipation of Alfven waves by phase mixing due to viscosity
and resistivity variations with height. We also consider nonlinear
magnetohydrodynamic (MHD) equations in our theoretical model. Non-linear terms
of MHD equations include perturbed velocity, magnetic field, and density. To
investigate the damping of Alfven waves in a stratified atmosphere of solar
spicules, we solve the non-linear MHD equations in the x-z plane. Our
simulations show that the damping is enhanced due to viscosity and resistivity
gradients. Moreover, energy variations is influenced due to nonlinear terms in
MHD equations. | 1312.7866v1 |
2013-12-31 | A novel variability-based method for quasar selection: evidence for a rest frame ~54 day characteristic timescale | We compare quasar selection techniques based on their optical variability
using data from the Catalina Real-time Transient Survey (CRTS). We introduce a
new technique based on Slepian wavelet variance (SWV) that shows comparable or
better performance to structure functions and damped random walk models but
with fewer assumptions. Combining these methods with WISE mid-IR colors
produces a highly efficient quasar selection technique which we have validated
spectroscopically. The SWV technique also identifies characteristic timescales
in a time series and we find a characteristic rest frame timescale of ~54 days,
confirmed in the light curves of ~18000 quasars from CRTS, SDSS and MACHO data,
and anticorrelated with absolute magnitude. This indicates a transition between
a damped random walk and $P(f) \propto f^{-1/3}$ behaviours and is the first
strong indication that a damped random walk model may be too simplistic to
describe optical quasar variability. | 1401.1785v1 |
2014-02-09 | Manipulation of tripartite-to-bipartite entanglement localization under quantum noises and its application to entanglement distribution | This paper is to investigate the effects of quantum noises on entanglement
localization by taking an example of reducing a three-qubit
Greenberger-Horne-Zeilinger (GHZ) state to a two-qubit entangled state. We
consider, respectively, two types of quantum decoherence, i.e.,
amplitude-damping and depolarizing decoherence, and explore the best von
Neumann measurements on one of three qubits of the triple GHZ state for making
the amount of entanglement of the collapsed bipartite state be as large as
possible. The results indicate that different noises have different impacts on
entanglement localization, and that the optimal strategy for reducing a
three-qubit GHZ state to a two-qubit one via local measurements and classical
communications in the amplitude-damping case is different from that in the
noise-free case. We also show that the idea of entanglement localization could
be utilized to improve the quality of bipartite entanglement distributing
through amplitude-damping channels. These findings might shed a new light on
entanglement manipulations and transformations. | 1402.1914v2 |
2014-02-25 | Thermodynamic anomalies in the presence of dissipation: from the free particle to the harmonic oscillator | A free particle coupled to a heat bath can exhibit a number of thermodynamic
anomalies like a negative specific heat or reentrant classicality. These
low-temperature phenomena are expected to be modified at very low temperatures
where finite-size effects associated with the discreteness of the energy
spectrum become relevant. In this paper, we explore in which form the
thermodynamic anomalies of the free damped particle appear for a damped
harmonic oscillator. Since the discreteness of the oscillator's energy spectrum
is fully accounted for, the results are valid for arbitrary temperatures. As
expected, they are in agreement with the third law of thermodynamics and
indicate how the thermodynamic anomalies of the free damped particle can be
reconciled with the third law. Particular attention is paid to the transition
from the harmonic oscillator to the free particle when the limit of the
oscillator frequency to zero is taken. | 1402.6221v1 |
2014-02-26 | Magneto-elastic modes and lifetime of magnons in thin yttrium-iron garnet films | We calculate the effects of the spin-lattice coupling on the magnon spectrum
of thin ferromagnetic films consisting of the magnetic insulator yttrium-iron
garnet. The magnon-phonon hybridisation generates a characteristic minimum in
the spin dynamic structure factor which quantitatively agrees with recent
Brillouin light scattering experiments. We also show that at room temperature
the phonon contribution to the magnon damping exhibits a rather complicated
momentum dependence: In the exchange regime the magnon damping is dominated by
Cherenkov type scattering processes, while in the long-wavelength dipolar
regime these processes are subdominant and the magnon damping is two orders of
magnitude smaller. We supplement our calculations by actual measurements of the
magnon relaxation in the dipolar regime. Our theory provides a simple
explanation of a recent experiment probing the different temperatures of the
magnon and phonon gases in yttrium-iron garnet. | 1402.6575v2 |
2014-03-10 | Quantum Fisher Information of W States in Decoherence Channels | We study the quantum Fisher information (QFI) of W states analytically with
respect to SU(2) rotations in the basic decoherence channels i.e. depolarizing
(DPC), amplitude damping (ADC) and phase damping (PDC), and present the
interesting behavior of QFI of W states, especially when compared to that of
GHZ states [Ma et al., Phys. Rev. A, 84, 022302 (2011)]. We find that when
initially pure W states are under decoherence, i) DPC: as decoherence starts
and increases, QFI smoothly decays; ii) ADC: just as decoherence starts, QFI
exhibits a sudden drop to the shot noise level and as decoherence increases,
QFI continues to decrease to zero and then increases back to the shot noise
level; iii) PDC: just as decoherence starts, a sudden death of QFI occurs and
QFI remains zero for any rate of decoherence, therefore W states in phase
damping channel do not provide phase sensitivity. We also find that, on the
contrary to GHZ states, pure or decohered W states are not sensitive with
respect to rotations in z direction and the sensitivities with respect to
rotations in x and y directions are equal to each other, implying no sudden
change points of QFI due to competition between directions. | 1403.2376v1 |
2014-03-14 | Silk damping at a redshift of a billion: a new limit on small-scale adiabatic perturbations | We study the dissipation of small-scale adiabatic perturbations at early
times when the Universe is hotter than T ~ 0.5 keV. When the wavelength falls
below the damping scale 1/kD, the acoustic modes diffuse and thermalize,
causing entropy production. Before neutrino decoupling, kD is primarily set by
the neutrino shear viscosity, and we study the effect of acoustic damping on
the relic neutrino number, primordial nucleosynthesis, dark-matter freeze-out,
and baryogenesis. This sets a new limit on the amplitude of primordial
fluctuations of DeltaR^2 < 0.007 at 10^4/Mpc< k < 10^5/Mpc and a model
dependent limit of DeltaR^2 < 0.3 at k < 10^{20-25}/Mpc. | 1403.3697v1 |
2014-06-02 | CMB $μ$ distortion from primordial gravitational waves | We propose a new mechanism of generating the $\mu$ distortion in cosmic
microwave background (CMB) originated from primordial gravitational waves. Such
$\mu$ distortion is generated by the damping of the temperature anisotropies
through the Thomson scattering, even on scales larger than that of Silk
damping. This mechanism is in sharp contrast with that from the primordial
curvature (scalar) perturbations, in which the temperature anisotropies mainly
decay by Silk damping effects. We estimate the size of the $\mu$ distortion
from the new mechanism, which can be used to constrain the amplitude of
primordial gravitational waves on smaller scales independently from the CMB
anisotropies, giving more wide-range constraint on their spectral index by
combining the amplitude from the CMB anisotropies. | 1406.0451v2 |
2014-06-04 | Self-organized escape processes of linear chains in nonlinear potentials | An enhancement of localized nonlinear modes in coupled systems gives rise to
a novel type of escape process. We study a spatially one dimensional set-up
consisting of a linearly coupled oscillator chain of $N$ mass-points situated
in a metastable nonlinear potential. The Hamilton-dynamics exhibits breather
solutions as a result of modulational instability of the phonon states. These
breathers localize energy by freezing other parts of the chain. Eventually this
localised part of the chain grows in amplitude until it overcomes the critical
elongation characterized by the transition state. Doing so, the breathers
ignite an escape by pulling the remaining chain over the barrier. Even if the
formation of singular breathers is insufficient for an escape, coalescence of
moving breathers can result in the required concentration of energy. Compared
to a chain system with linear damping and thermal fluctuations the breathers
help the chain to overcome the barriers faster in the case of low damping. With
larger damping, the decreasing life time of the breathers effectively inhibits
the escape process. | 1406.0938v1 |
2014-06-08 | Dissipation-driven squeezed and sub-Poissonian mechanical states in quadratic optomechanical systems | In this work we study an optomechanical system in which there is a purely
quadratic optomechanical coupling between the optical and mechanical modes. The
optical mode is pumped by three coherent fields and the mechanical mode is
parametrically driven. We show that if the frequencies and amplitudes of both
optical and mechanical drivings are properly chosen, the optomechanical
interaction gives rise to an effective interaction, which, in the presence of
optical damping and in the absence of mechanical damping, has the squeezed
vacuum state and the squeezed one phonon state as dark states of the dynamics.
These states are well known for presenting quadrature squeezing and
sub-Poissonian statistics. However, even in the presence of mechanical damping
it is possible to find steady states with large degrees of quadrature squeezing
or strong sub-Poissonian statistics. Furthermore, we find a counter-intuitive
behavior in which a nonzero temperature of the mechanical environment allows
the observation of mechanical states with more pronounced sub-Poissonian
statistics. | 1406.1987v3 |
2014-06-13 | Frequency-dependent damping in propagating slow magneto-acoustic waves | Propagating slow magneto-acoustic waves are often observed in polar plumes
and active region fan loops. The observed periodicities of these waves range
from a few minutes to few tens of minutes and their amplitudes were found to
decay rapidly as they travel along the supporting structure. Previously,
thermal conduction, compressive viscosity, radiation, density stratification,
and area divergence, were identified to be some of the causes for change in the
slow wave amplitude. Our recent studies indicate that the observed damping in
these waves is frequency dependent. We used imaging data from SDO/AIA, to study
this dependence in detail and for the first time from observations we attempted
to deduce a quantitative relation between damping length and frequency of these
oscillations. We developed a new analysis method to obtain this relation. The
observed frequency dependence does not seem to agree with the current linear
wave theory and it was found that the waves observed in the polar regions show
a different dependence from those observed in the on-disk loop structures
despite the similarity in their properties. | 1406.3565v1 |
2014-06-24 | On finite density effects on cosmic reheating and moduli decay and implications for Dark Matter production | We study the damping of an oscillating scalar field in a
Friedmann-Robertson-Walker spacetime by perturbative processes, taking into
account the finite density effects that interactions with the plasma of decay
products have on the damping rate. The scalar field may be identified with the
inflaton, in which case this process leads to the reheating of the universe
after inflation. It can also resemble a modulus that dominates the energy
density of the universe at later times. We find that the finite density
corrections to the damping rate can have a drastic effect on the thermal
history and considerably increase both, the maximal temperature in the early
universe and the reheating temperature at the onset of the radiation dominated
era. As a result abundance of some Dark Matter candidates may be considerably
larger than previously estimated. We give improved analytic estimates for the
maximal and the reheating temperatures and confirm them numerically in a simple
model. | 1406.6243v2 |
2014-08-13 | Probing dense matter in compact star cores with radio pulsar data | Astrophysical observations of compact stars provide, in addition to collider
experiments, the other big source of information on matter under extreme
conditions. The largest and most precise data set about neutron stars is the
timing data of radio pulsars. We show how this unique data can be used to learn
about the ultra-dense matter in the compact star interior. The method relies on
astro-seismology based on special global oscillation modes (r-modes) that emit
gravitational waves. They would prevent pulsars from spinning with their
observed high frequencies, unless the damping of these modes, determined by the
microscopic properties of matter, can prevent this. We show that for each form
of matter there is a distinct region in a frequency/spindown-rate diagram where
r-modes can be present. We find that stars containing ungapped quark matter are
consistent with both the observed radio and x-ray data, whereas, even when
taking into account the considerable uncertainties, neutron star models with
standard viscous damping are inconsistent with both data sets and additional
damping mechanisms would be required. | 1408.3152v1 |
2014-09-04 | A numerical study of the pull-in instability in some free boundary models for MEMS | In this work we numerically compute the bifurcation curve of stationary
solutions for the free boundary problem for MEMS in one space dimension. It has
a single turning point, as in the case of the small aspect ratio limit. We also
find a threshold for the existence of global-in-time solutions of the evolution
equation given by either a heat or a damped wave equation. This threshold is
what we term the dynamical pull-in value: it separates the stable operation
regime from the touchdown regime. The numerical calculations show that the
dynamical threshold values for the heat equation coincide with the static
values. For the damped wave equation the dynamical threshold values are smaller
than the static values. This result is in agreement with the observations
reported for a mass-spring system studied in the engineering literature. In the
case of the damped wave equation, we also show that the aspect ratio of the
device is more important than the inertia in the determination of the pull-in
value. | 1409.1291v2 |
2014-09-15 | Direct path from microscopic mechanics to Debye shielding, Landau damping, and wave-particle interaction | The derivation of Debye shielding and Landau damping from the $N$-body
description of plasmas is performed directly by using Newton's second law for
the $N$-body system. This is done in a few steps with elementary calculations
using standard tools of calculus, and no probabilistic setting. Unexpectedly,
Debye shielding is encountered together with Landau damping. This approach is
shown to be justified in the one-dimensional case when the number of particles
in a Debye sphere becomes large. The theory is extended to accommodate a
correct description of trapping and chaos due to Langmuir waves. Shielding and
collisional transport are found to be two related aspects of the repulsive
deflections of electrons, in such a way that each particle is shielded by all
other ones while keeping in uninterrupted motion. | 1409.4323v1 |
2014-09-19 | Damping of metallized bilayer nanomechanical resonators at room temperature | We investigate the influence of gold thin-films subsequently deposited on a
set of initially bare, doubly clamped, high-stress silicon nitride string
resonators at room temperature. Analytical expressions for resonance frequency,
quality factor and damping for both in- and out-of-plane flexural modes of the
bilayer system are derived, which allows for the determination of effective
elastic parameters of the composite structure from our experimental data. We
find the inverse quality factor to scale linearly with the gold film thickness,
indicating that the overall damping is governed by losses in the metal.
Correspondingly, the mechanical linewidth increases by more than one order of
magnitude compared to the bare silicon nitride string resonator. Furthermore,
we extract mechanical quality factors of the gold film for both flexural modes
and show that they can be enhanced by complete deposition of the metal in a
single step, suggesting that surface and interface losses play a vital role in
metal thin-films. | 1409.5670v1 |
2014-10-09 | Non-Fermi-liquid behavior and anomalous suppression of Landau damping in layered metals close to ferromagnetism | We analyse the low-energy physics of nearly ferromagnetic metals in two
spatial dimensions using the functional renormalization group technique. We
find a new low-energy fixed point, at which the fermionic (electron-like)
excitations are non-Fermi-liquid ($z_f = 13/10$) and the magnetic fluctuations
exhibit an anomalous Landau damping whose rate vanishes as $\Gamma_{\bf q} \sim
\vert {\bf q} \vert^{3/5}$ in the low-$\vert {\bf q} \vert$ limit. We discuss
this renormalization of the Landau-damping exponent, which is the major novel
prediction of our work, and highlight the possible link between that
renormalization and neutron-scattering data on UGe$_2$ and related compounds.
Implications of our analysis for YFe$_2$Al$_{10}$ are also discussed. | 1410.2539v3 |
2014-10-09 | Special mean motion resonance pairs: Mimas-Tethys and Titan-Hyperion | Five pairs of large solar system satellites occupy first order mean-motion
resonances (MMRs). Among these, the pairs of Mimas-Tethys and Titan-Hyperion
are special. They are located much deeper in resonance than the others and
their critical arguments librate with much greater amplitudes. These
characteristics are traced to the insignificant damping, over $\Gyr$
timescales, of Mimas's orbital inclination and Hyperion's orbital eccentricity.
Absent that, these resonances would not survive. Instead their librations would
be overstable and escape from resonance would occur on the relevant damping
time. Unlike the aforementioned MMRs, those involving Enceladus-Dione,
Io-Europa, and Europa-Ganymede are limited by eccentricity damping. They must
either remain at the shallow depths they currently occupy, or, if they venture
deeper, retreat after a limited time. The latter seems almost certain for
Enceladus-Dione and quite likely for the others, We examine the MMRs involving
Mimas-Tethys and Titan-Hyperion under the assumption that they formed as a
result of convergent migration. Capture probabilities are $\sim 6\%$ for the
former and $100\%$ for the latter. The possibility of collisional excitation of
their large librations is investigated but largely discounted. | 1410.2648v1 |
2014-11-13 | Stability and bifurcation for the Kuramoto model | We study the mean-field limit of the Kuramoto model of globally coupled
oscillators. By studying the evolution in Fourier space and understanding the
domain of dependence, we show a global stability result. Moreover, we can
identify function norms to show damping of the order parameter for velocity
distributions and perturbations in $\mathcal{W}^{n,1}$ for $n > 1$. Finally,
for sufficiently regular velocity distributions we can identify exponential
decay in the stable case and otherwise identify finitely many eigenmodes. For
these eigenmodes we can show a center-unstable manifold reduction, which gives
a rigorous tool to obtain the bifurcation behaviour. The damping is similar to
Landau damping for the Vlasov equation. | 1411.3752v3 |
2014-11-26 | A singular finite element technique for calculating continuum damping of Alfvén eigenmodes | Damping due to continuum resonances can be calculated using dissipation-less
ideal magnetohydrodynamics (MHD) provided that the poles due to these
resonances are properly treated. We describe a singular finite element
technique for calculating the continuum damping of Alfv\'{e}n waves. A
Frobenius expansion is used to determine appropriate finite element basis
functions on an inner region surrounding a pole due to the continuum resonance.
The location of the pole due to the continuum resonance and mode frequency are
calculated iteratively using a Galerkin method. This method is used to find the
complex frequency and mode structure of a toroidicity-induced Alfv\'{e}n
eigenmode (TAE) in a large aspect ratio circular tokamak and are shown to agree
closely with a complex contour technique. | 1411.7111v1 |
2014-11-26 | Energy decay for a locally undamped wave equation | We study the decay rate for the energy of solutions of a damped wave equation
in a situation where the Geometric Control Condition is violated. We assume
that the set of undamped trajectories is a flat torus of positive codimension
and that the metric is locally flat around this set. We further assume that the
damping function enjoys locally a prescribed homogeneity near the undamped set
in traversal directions. We prove a sharp decay estimate at a polynomial rate
that depends on the homogeneity of the damping function. Our method relies on a
refined microlocal analysis linked to a second microlocalization procedure to
cut the phase space into tiny regions respecting the uncertainty principle but
way too small to enter a standard semi-classical analysis localization. Using a
multiplier method, we obtain the energy estimates in each region and we then
patch the microlocal estimates together. | 1411.7271v1 |
2014-12-05 | Entanglement Dynamics of Quantum Oscillators Nonlinearly Coupled to Thermal Environments | We study the asymptotic entanglement of two quantum harmonic oscillators
nonlinearly coupled to an environment. Coupling to independent baths and a
common bath are investigated. Numerical results obtained using the
Wangsness-Bloch-Redfield method are supplemented by analytical results in the
rotating wave approximation. The asymptotic negativity as function of
temperature, initial squeezing and coupling strength, is compared to results
for systems with linear system-reservoir coupling. We find that due to the
parity conserving nature of the coupling, the asymptotic entanglement is
considerably more robust than for the linearly damped cases. In contrast to
linearly damped systems, the asymptotic behavior of entanglement is similar for
the two bath configurations in the nonlinearly damped case. This is due to the
two-phonon system-bath exchange causing a supression of information exchange
between the oscillators via the bath in the common bath configuration at low
temperatures. | 1412.1999v1 |
2014-12-08 | The dispersion modification of electrostatic geodesic acoustic mode by electron geodesic drift current | The past studies treated the perturbed distribution of circulating electrons
as adiabatic one when studying the dispersion relation of electrostatic
geodesic acoustic mode(GAM). In this paper, the flow of electron geodesic
current (FEGC) is added to modify this adiabatic distribution. Based on the
drift kinetic theory, it is found that FEGC obviously increases the magnitude
of the standard GAM's frequency and reduces its damping rate. The increase of
frequency results from the contribution of FEGC to the radial flow. The reason
for the reduction of damping rate is that when the effect of FEGC counts, the
new resonant velocity becomes much larger than ions thermal velocity with
equilibrium distribution obeying Maxwellian distribution, compared with
unmodified Landau resonant velocity. Especially, FEGC changes the characters of
the frequency and damping rate of low-frequency GAM as functions of safety
factor $q$ . | 1412.2481v1 |
2014-12-10 | Alfvenic Turbulence Beyond the Ambipolar Diffusion Scale | We investigate the nature of the Alfv\'enic turbulence cascade in two fluid
MHD simulations in order to determine if turbulence is damped once the ion and
neutral species become decoupled at a critical scale called the ambipolar
diffusion scale (L$_{AD}$). Using mode decomposition to separate the three
classical MHD modes, we study the second order structure functions of the
Alfv\'en mode velocity field of both neutrals and ions in the reference frame
of the local magnetic field. On scales greater than L$_{AD}$ we confirm that
two fluid turbulence strongly resembles single fluid MHD turbulence. Our
simulations show that the behavior of two fluid turbulence becomes more complex
on scales less than L$_{AD}$. We find that Alfvenic turbulence can exist past
L$_{AD}$ when the turbulence is globally super-Alfv\'enic, with the ions and
neutrals forming separate cascades once decoupling has taken place. When
turbulence is globally sub-Alfvenic and hence strongly anisotropic with a large
separation between the parallel and perpendicular decoupling scales, turbulence
is damped at L$_{AD}$. We also find that the power spectrum of the kinetic
energy in the damped regime is consistent with a $k^{-4}$ scaling (in agreement
with the predictions of Lazarian, Vishniac & Cho 2004). | 1412.3452v1 |
2015-01-19 | Linear wave action decay entailed by Landau damping in inhomogeneous, nonstationary and anisotropic plasma | This paper addresses the linear propagation of an electron wave in a
collisionless, inhomogeneous, nonstationary and anisotropic plasma. The plasma
is characterized by its distribution function, $f_H$, at zero order in the wave
amplitude. This distribution function, from which are derived all the
hydrodynamical quantities, may be chosen arbitrarily, provided that it solves
Vlasov equation. Then, from the linearized version of the electrons equation of
motion, and from Gauss law, is derived an envelope equation for the wave
amplitude, assumed to evolve over time and space scales much larger than the
oscillation periods of the wave. The envelope equation may be cast into an
equation for the the wave action, derived from Whitham's variational principle,
that demonstrates the action decay due to Landau damping. Moreover, the Landau
damping rate is derived at first order in the variations of the wave number and
frequency. As briefly discussed, this paper generalizes numerous previous works
on the subject, provides a theoretical basis for heuristic arguments regarding
the action decay, and also addresses the propagation of an externally driven
wave. | 1501.04485v1 |
2015-01-23 | Response solutions for quasi-periodically forced, dissipative wave equations | We consider several models of nonlinear wave equations subject to very strong
damping and quasi-periodic external forcing. This is a singular perturbation,
since the damping is not the highest order term. We study the existence of
response solutions (i.e., quasi-periodic solutions with the same frequency as
the forcing). Under very general non-resonance conditions on the frequency, we
show the existence of asymptotic expansions of the response solution; moreover,
we prove that the response solution indeed exists and depends analytically on
$\varepsilon$ (where $\varepsilon$ is the inverse of the coefficient
multiplying the damping) for $\varepsilon$ in a complex domain, which in some
cases includes disks tangent to the imaginary axis at the origin. In other
models, we prove analyticity in cones of aperture $\pi/2$ and we conjecture it
is optimal. These results have consequences for the asymptotic expansions of
the response solutions considered in the literature. The proof of our results
relies on reformulating the problem as a fixed point problem, constructing an
approximate solution and studying the properties of iterations that converge to
the solutions of the fixed point problem. | 1501.05979v1 |
2015-01-30 | A large-scale magnetic shield with 10^6 damping at mHz frequencies | We present a magnetically shielded environment with a damping factor larger
than one million at the mHz frequency regime and an extremely low field and
gradient over an extended volume. This extraordinary shielding performance
represents an improvement of the state of the art in damping the difficult
regime of very low-frequency distortions by more than an order of magnitude.
This technology enables a new generation of high precision measurements in
fundamental physics and metrology, including searches for new physics far
beyond the reach of accelerator-based experiments. We discuss the technical
realization of the shield with its improvements in design. | 1501.07861v4 |
2015-02-01 | A Study on the Impact of Wind Generation on the Stability of Electromechanical Oscillations | Wind is becoming an increasingly significant source of energy in modern power
generation. Amongst existing technologies, Variable Speed Wind Turbines (VSWT)
equipped with Double Fed Induction Generators (DFIG) is widely deployed.
Consequently, power systems are now experiencing newer power flow patterns and
operating conditions. This paper investigates the impact of a DFIG based Wind
Farm (WF) on the stability of electromechanical oscillations. This is achieved
by performing modal analysis to evaluate the stability of a two-area power
network when subjected to different wind penetration levels and different
geographical installed locations. The approach via eigenvalues analysis
involves the design of voltage and Supplementary Damping Controllers (SDCs)
that contribute to network damping. The effect of Power System Stabilizer (PSS)
is also examined for several network conditions. Simulations demonstrate a
damping improvement up to 933% when the control systems are activated and the
system operates with 25% wind integration. | 1502.00215v1 |
2015-02-16 | Biomimetic Staggered Composites with Highly Enhanced Energy Dissipation: Design, Modeling, and Test | We investigate the damping enhancement in a class of biomimetic staggered
composites via a combination of design, modeling, and experiment. In total,
three kinds of staggered composites are designed by mimicking the structure of
bone and nacre. These composite designs are realized by 3D printing a rigid
plastic and a viscous elastomer simultaneously. Greatly-enhanced energy
dissipation in the designed composites is observed from both the experimental
results and theoretical prediction. The designed polymer composites have loss
modulus up to ~500 MPa, higher than most of the existing polymers. In addition,
their specific loss modulus (up to 0.43 $Km^2/s^2$) is among the highest of
damping materials. The damping enhancement is attributed to the large shear
deformation of the viscous soft matrix and the large strengthening effect from
the rigid inclusion phase. | 1502.04568v1 |
2015-03-02 | DAMPE silicon tracker on-board data compression algorithm | The Dark Matter Particle Explorer (DAMPE) is an upcoming scientific satellite
mission for high energy gamma-ray, electron and cosmic rays detection. The
silicon tracker (STK) is a sub detector of the DAMPE payload with an excellent
position resolution (readout pitch of 242um), which measures the incident
direction of particles, as well as charge. The STK consists 12 layers of
Silicon Micro-strip Detector (SMD), equivalent to a total silicon area of
6.5m$^2$. The total readout channels of the STK are 73728, which leads to a
huge amount of raw data to be dealt. In this paper, we focus on the on-board
data compression algorithm and procedure in the STK, which was initially
verified by cosmic-ray measurements. | 1503.00415v1 |
2015-03-08 | MHD Seismology of a loop-like filament tube by observed kink waves | We report and analyze the observational evidence of global kink oscillations
in a solar filament as observed in H alpha by National Solar Observatory
(NSO)/Global Oscillation Network Group (GONG) instrument. An M1.1-class flare
in active region 11692 on 2013 March 15 induced a global kink mode in the
filament lying in the south-west of AR11692.We find periods of about 61 - 67
minutes and damping times of 92 - 117 minutes at three vertical slice positions
chosen in and around the filament apex. We find that the waves are damped. From
the observed global kink mode period and damping time scale using the theory of
resonant absorption we perform prominence seismology. We estimate a lower
cut-off value for the inhomogeneity length-scale to be around 0.34 - 0.44 times
the radius of the filament cross-section. | 1503.02281v1 |
2015-03-13 | Comparison of spin-orbit torques and spin pumping across NiFe/Pt and NiFe/Cu/Pt interfaces | We experimentally investigate spin-orbit torques and spin pumping in NiFe/Pt
bilayers with direct and interrupted interfaces. The damping-like and
field-like torques are simultaneously measured with spin-torque ferromagnetic
resonance tuned by a dc bias current, whereas spin pumping is measured
electrically through the inverse spin Hall effect using a microwave cavity.
Insertion of an atomically thin Cu dusting layer at the interface reduces the
damping-like torque, field-like torque, and spin pumping by nearly the same
factor of ~1.4. This finding confirms that the observed spin-orbit torques
predominantly arise from diffusive transport of spin current generated by the
spin Hall effect. We also find that spin-current scattering at the NiFe/Pt
interface contributes to additional enhancement in magnetization damping that
is distinct from spin pumping. | 1503.04104v3 |
2015-03-24 | Global weak solutions to compressible quantum Navier-Stokes equations with damping | The global-in-time existence of weak solutions to the barotropic compressible
quantum Navier-Stokes equations with damping is proved for large data in three
dimensional space. The model consists of the compressible Navier-Stokes
equations with degenerate viscosity, and a nonlinear third-order differential
operator, with the quantum Bohm potential, and the damping terms. The global
weak solutions to such system is shown by using the Faedo-Galerkin method and
the compactness argument. This system is also a very important approximated
system to the compressible Navier-Stokes equations. It will help us to prove
the existence of global weak solutions to the compressible Navier-Stokes
equations with degenerate viscosity in three dimensional space. | 1503.06894v4 |
2015-03-30 | Suppression of Spin Pumping Between Ni$_{80}$Fe$_{20}$ and Cu by a Graphene Interlayer | We compare ferromagnetic resonance measurements of Permalloy
Ni$_{80}$Fe$_{20}$ (Py) films sputtered onto Cu(111) films with and without a
graphene (Gr) interlayer grown by chemical vapor deposition before Py
deposition. A two-angle sputtering method ensured that neither Gr nor Py was
degraded by the sample preparation process. We find the expected damping
enhancement from spin pumping for the Py/Cu case and no detectable enhancement
for the Py/Gr/Cu case. Since damping is sensitive to effects other than spin
pumping, we used magnetometry to verify that differences in Py magnetostatic
properties are not responsible for the difference in damping. We attribute the
suppression of spin pumping in Py/Gr/Cu to the large contact resistance of the
Gr/Cu interface. | 1503.08777v1 |
2015-04-02 | Protecting the $\sqrt{SWAP}$ operation from general and residual errors by continuous dynamical decoupling | We study the occurrence of errors in a continuously decoupled two-qubit state
during a $\sqrt{SWAP}$ quantum operation under decoherence. We consider a
realization of this quantum gate based on the Heisenberg exchange interaction,
which alone suffices for achieving universal quantum computation. Furthermore,
we introduce a continuous-dynamical-decoupling scheme that commutes with the
Heisenberg Hamiltonian to protect it from the amplitude damping and dephasing
errors caused by the system-environment interaction. We consider two
error-protection settings. One protects the qubits from both amplitude damping
and dephasing errors. The other features the amplitude damping as a residual
error and protects the qubits from dephasing errors only. In both settings, we
investigate the interaction of qubits with common and independent environments
separately. We study how errors affect the entanglement and fidelity for
different environmental spectral densities. | 1504.00592v1 |
2015-04-07 | Damped Oscillating Dark Energy: Ideal Fluid and Scalar-Tensor description | In this paper, we study damped oscillating form of dark energy for explaining
dynamics of universe. First of all, we consider universe is filled with an
ideal fluid which has damped oscillating dark energy in terms of this case we
calculate several physical quantities such as Hubble parameter, acceleration
parameter, energy density, pressure and others for dark energy, dark
energy-matter coupling and non-coupling cases. Secondly, we consider as
universe is filled with scalar field instead of an ideal fluid we obtain these
physical quantities in terms of scalar potential and kinetic term for the same
cases in scalar-tensor formalism. Finally, we show that ideal fluid description
and scalar-tensor description of dark energy give mathematically equivalent
results for this EoS parameter, even if they haven't same physical meaning. | 1504.01509v2 |
2015-04-17 | Temperature-dependent Plasmons and Their Damping Rates for Graphene with a Finite Energy Bandgap | We obtained numerical and closed-form analytic expressions for
finite-temperature plasmon dispersion relations for intrinsic graphene in the
presence of a finite energy gap in the energy spectrum. The calculations were
carried out using the random-phase approximation. The analytic results have
been derived in the high temperature regime and long-wavelength limit. We have
found that the plasmon damping rate decreases in the presence of a band gap.
Our method of calculation could also be applied to silicene and other buckled
honeycomb lattice structures. The finite-temperature plasmon dispersion
relations are presented when a single graphene layer is Coulomb coupled to a
semi infinite conductor. Both cases of gapless and gapped monolayer graphene
have been investigated when a thick substrate is in their proximity. Both the
plasmon excitation frequency and damping rate are linear functions of the
in-plane wave vector in the long wavelength limit when a monolayer interacts
with a conducting substrate which is not the case for free-standing pristine or
gapped graphene. | 1504.04552v1 |
2015-05-09 | Existence, general decay and blow-up of solutions for a viscoelastic Kirchhoff equation with Balakrishnan-Taylor damping and dynamic boundary conditions | Our aim in this article is to study a nonlinear viscoelastic Kirchhoff
equation with strong damping, Balakrishnan-Taylor damping, nonlinear source and
dynamical boundary condition. Firstly, we prove the local existence of
solutions by using the Faedo-Galerkin approximation method combined with a
contraction mapping theorem. We then prove that if the initial data enter into
the stable set, the solution globally exists, and if the initial data enter
into the unstable set, the solution blows up in a finite time. Moreover, we
obtain a general decay result of the energy, from which the usual exponential
and polynomial decay rates are only special cases. | 1505.02220v3 |
2015-06-03 | Migration of two massive planets into (and out of) first order mean motion resonances | We consider the dynamical evolution of two planets orbiting in the vicinity
of a first order mean motion reso- nance while simultaneously undergoing
eccentricity damping and convergent migration. Following Goldreich &
Schlichting (2014), we include a coupling between the dissipative semimajor
axis evolution and the damping of the eccentricities. In agreement with past
studies, we find that this coupling can lead to overstability of the resonance
and that for a certain range of parameters capture into resonance is only
temporary. Using a more general model, we show that whether overstable motion
can occur depends in a characteristic way on the mass ratio between the two
planets as well as their relative eccentricity damping timescales. Moreover, we
show that even when escape from resonance does occur, the timescale for escape
is long enough such at any given time a pair of planets is more likely to be
found in a resonance rather than migrating between them. Thus, we argue that
overstability of resonances cannot singlehandedly reconcile convergent
migration with the observed lack of Kepler planet pairs found near resonances.
However, it is possible that overstable motion in combination with other
effects such as large scale orbital instability could produce the observed
period ratio distribution. | 1506.01382v1 |
2015-06-12 | Linear inviscid damping for monotone shear flows in a finite periodic channel, boundary effects, blow-up and critical Sobolev regularity | In a previous article, \cite{Zill3}, we have established linear inviscid
damping for a large class of monotone shear flows in a finite periodic channel
and have further shown that boundary effects asymptotically lead to the
formation of singularities of derivatives of the solution. As the main results
of this article, we provide a detailed description of the singularity formation
and establish stability in all sub-critical fractional Sobolev spaces and
blow-up in all super-critical spaces. Furthermore, we discuss the implications
of the blow-up to the problem of nonlinear inviscid damping in a finite
periodic channel, where high regularity would be essential to control nonlinear
effects. | 1506.04010v1 |
2015-06-12 | Nonlinear damped partial differential equations and their uniform discretizations | We establish sharp energy decay rates for a large class of nonlinearly
first-order damped systems, and we design discretization schemes that inherit
of the same energy decay rates, uniformly with respect to the space and/or time
discretization parameters, by adding appropriate numerical viscosity terms. Our
main arguments use the optimal-weight convexity method and uniform
observability inequalities with respect to the discretization parameters. We
establish our results, first in the continuous setting, then for space
semi-discrete models, and then for time semi-discrete models. The full
discretization is inferred from the previous results. Our results cover, for
instance, the Schr\"odinger equation with nonlinear damping, the nonlinear wave
equation, the nonlinear plate equation, as well as certain classes of equations
with nonlocal terms. | 1506.04163v2 |
2015-06-17 | Landau Damping of Electrostatic Waves in Arbitrarily Degenerate Quantum Plasmas | We carry out a systematic study of the dispersion relation for linear
electrostatic waves in an arbitrarily degenerate quantum electron plasma. We
solve for the complex frequency spectrum for arbitrary values of wavenumber $k$
and level of degeneracy $\mu$. Our finding is that for large $k$ and high $\mu$
the real part of the frequency $\omega_{r}$ grows linearly with $k$ and scales
with $\mu$ only because of the scaling of the Fermi energy. In this regime the
relative Landau damping rate $\gamma/\omega_{r}$ becomes independent of $k$ and
varies inversly with $\mu$. Thus, damping is weak but finite at moderate levels
of degeneracy for short wavelengths. | 1506.05494v2 |
2015-06-25 | Simultaneous Interconnection and Damping Assignment Passivity-based Control of Mechanical Systems Using Generalized Forces | To extend the realm of application of the well known controller design
technique of interconnection and damping assignment passivity-based control
(IDA-PBC) of mechanical systems two modifications to the standard method are
presented in this article. First, similarly to [1], it is proposed to avoid the
splitting of the control action into energy-shaping and damping injection
terms, but instead to carry them out simultaneously. Second, motivated by [2],
we propose to consider the inclusion of generalised forces, going beyond the
gyroscopic ones used in standard IDA-PBC. It is shown that several new
controllers for mechanical systems designed invoking other (less systematic
procedures) that do not satisfy the conditions of standard IDA-PBC, actually
belong to this new class of SIDA-PBC. | 1506.07679v1 |
2015-07-20 | Bifurcation of the quasinormal spectrum and Zero Damped Modes for rotating dilatonic black holes | It has been recently found that for the near extremal Kerr black holes
appearing of Zero Damped Modes (accompanied by qusinormal mode branching)
signifies about inapplicability of the regime of small perturbations and the
onset of turbulence. Here we show that this phenomena is not limited by Kerr or
Kerr-Newman solutions only, but also takes place for rotating dilatonic black
holes for which we have found Zero Damped Modes both numerically and
analytically. We have also shown that, contrary to recent claims, there is no
instability of a charged massive scalar field in the background of the rotating
dilatonic black hole under physically adequate boundary conditions. Analytic
expression for dominant quasinormal frequencies is deduced in the regime of
large coupling qQ, where q and Q are the field and black hole charges
respectively. | 1507.05649v1 |
2015-07-24 | Effect of Landau damping on alternative ion-acoustic solitary waves in a magnetized plasma consisting of warm adiabatic ions and non-thermal electrons | Bandyopadhyay and Das [Phys. Plasmas, 9, 465-473, 2002] have derived a
nonlinear macroscopic evolution equation for ion acoustic wave in a magnetized
plasma consisting of warm adiabatic ions and non-thermal electrons including
the effect of Landau damping. In that paper they have also derived the
corresponding nonlinear evolution equation when coefficient of the nonlinear
term of the above mentioned macroscopic evolution equation vanishes, the
nonlinear behaviour of the ion acoustic wave is described by a modified
macroscopic evolution equation. But they have not considered the case when the
coefficient is very near to zero. This is the case we consider in this paper
and we derive the corresponding evolution equation including the effect of
Landau damping. Finally, a solitary wave solution of this macroscopic evolution
is obtained, whose amplitude is found to decay slowly with time. | 1507.06733v1 |
2015-08-05 | Quantum discord protection from amplitude damping decoherence | Entanglement is known to be an essential resource for many quantum
information processes. However, it is now known that some quantum features may
be acheived with quantum discord, a generalized measure of quantum correlation.
In this paper, we study how quantum discord, or more specifically, the measures
of entropic discord and geometric discord are affected by the influence of
amplitude damping decoherence. We also show that a protocol deploying weak
measurement and quantum measurement reversal can effectively protect quantum
discord from amplitude damping decoherence, enabling to distribute quantum
correlation between two remote parties in a noisy environment. | 1508.00972v1 |
2015-09-03 | Stability analysis of degenerately-damped oscillations | Presented here is a study of well-posedness and asymptotic stability of a
"degenerately damped" PDE modeling a vibrating elastic string. The coefficient
of the damping may vanish at small amplitudes thus weakening the effect of the
dissipation. It is shown that the resulting dynamical system has strictly
monotonically decreasing energy and uniformly decaying lower-order norms,
however, is not uniformly stable on the associated finite-energy space. These
theoretical findings were motivated by numerical simulations of this model
using a finite element scheme and successive approximations. A description of
the numerical approach and sample plots of energy decay are supplied. In
addition, for certain initial data the solution can be determined in closed
form up to a dissipative nonlinear ordinary differential equation. Such
solutions can be used to assess the accuracy of the numerical examples. | 1509.00917v1 |
2015-09-27 | On the well-posedness and asymptotic behavior of the generalized KdV-Burgers equation | In this paper we are concerned with the well-posedness and the exponential
stabilization of the generalized Korteweg-de Vries Burgers equation, posed on
the whole real line, under the effect of a damping term. Both problems are
investigated when the exponent p in the nonlinear term ranges over the interval
$[1,5)$. We first prove the global well-posedness in $H^s(R)$, for $0 \leq s
\leq 3$ and $1 \leq p < 2$, and in $H^3(R)$, when $p \geq 2$. For $2 \leq p <
5$, we prove the existence of global solutions in the $L^2$-setting. Then, by
using multiplier techniques combined with interpolation theory, the exponential
stabilization is obtained for a indefinite damping term and $1 \leq p < 2$.
Under the effect of a localized damping term the result is obtained when $2
\leq p < 5$. Combining multiplier techniques and compactness arguments it is
shown that the problem of exponential decay is reduced to prove the unique
continuation property of weak solutions | 1509.08148v1 |
2015-10-11 | Error estimates of finite element method for semi-linear stochastic strongly damped wave equation | In this paper, we consider a semi-linear stochastic strongly damped wave
equation driven by additive Gaussian noise. Following a semigroup framework, we
establish existence, uniqueness and space-time regularity of a mild solution to
such equation. Unlike the usual stochastic wave equation without damping, the
underlying problem with space-time white noise (Q = I) allows for a mild
solution with a positive order of regularity in multiple spatial dimensions.
Further, we analyze a spatio-temporal discretization of the problem, performed
by a standard finite element method in space and a well-known linear implicit
Euler scheme in time. The analysis of the approximation error forces us to
significantly enrich existing error estimates of semidiscrete and fully
discrete finite element methods for the corresponding linear deterministic
equation. The main results show optimal convergence rates in the sense that the
orders of convergence in space and in time coincide with the orders of the
spatial and temporal regularity of the mild solution, respectively. Numerical
examples are finally included to confirm our theoretical findings. | 1510.03028v1 |
2015-11-10 | A study of energy correction for the electron beam data in the BGO ECAL of the DAMPE | The DArk Matter Particle Explorer (DAMPE) is an orbital experiment aiming at
searching for dark matter indirectly by measuring the spectra of photons,
electrons and positrons originating from deep space. The BGO electromagnetic
calorimeter is one of the key sub-detectors of the DAMPE, which is designed for
high energy measurement with a large dynamic range from 5 GeV to 10 TeV. In
this paper, some methods for energy correction are discussed and tried, in
order to reconstruct the primary energy of the incident electrons. Different
methods are chosen for the appropriate energy ranges. The results of Geant4
simulation and beam test data (at CERN) are presented. | 1511.02998v1 |
2015-11-10 | Quantum Fisher and Skew information for Unruh accelerated Dirac qubit | We develop a Bloch vector representation of Unruh channel for a Dirac field
mode. This is used to provide a unified, analytical treatment of quantum Fisher
and Skew information for a qubit subjected to the Unruh channel, both in its
pure form as well as in the presence of experimentally relevant external noise
channels. The time evolution of Fisher and Skew information is studied along
with the impact of external environment parameters such as temperature and
squeezing. The external noises are modelled by both purely dephasing phase
damping as well as the squeezed generalized amplitude damping channels. An
interesting interplay between the external reservoir temperature and squeezing
on the Fisher and Skew information is observed, in particular, for the action
of the squeezed generalized amplitude damping channel. It is seen that for some
regimes, squeezing can enhance the quantum information against the
deteriorating influence of the ambient environment. Similar features are also
observed for the analogous study of Skew information, highlighting the similar
origin of the Fisher and Skew information. | 1511.03029v1 |
2015-11-23 | Detection of high frequency oscillations and damping from multi-slit spectroscopic observations of the corona | During the total solar eclipse of 11 July 2010, multi-slit spectroscopic
observations of the solar corona were performed from Easter Island, Chile. To
search for high-frequency waves, observations were taken at a high cadence in
the green line at 5303 A due to [Fe xiv] and the red line at 6374 A due to [Fe
x]. The data are analyzed to study the periodic variations in the intensity,
Doppler velocity and line width using wavelet analysis. The data with high
spectral and temporal resolution enabled us to study the rapid dynamical
changes within coronal structures. We find that at certain locations each
parameter shows significant oscillation with periods ranging from 6 - 25 s. For
the first time, we could detect damping of high-frequency oscillations with
periods of the order of 10 s. If the observed damped oscillations are due to
magnetohydrodynamic (MHD) waves then they can contribute significantly in the
heating of the corona. From a statistical study we try to characterize the
nature of the observed oscillations while looking at the distribution of power
in different line parameters. | 1511.07160v1 |
2015-11-26 | Uniform exponential stability of Galerkin approximations for damped wave systems | We consider the numerical approximation of linear damped wave systems by
Galerkin approximations in space and appropriate time-stepping schemes. Based
on a dissipation estimate for a modified energy, we prove exponential decay of
the physical energy on the continuous level provided that the damping is
effective everywhere in the domain. The methods of proof allow us to analyze
also a class of Galerkin approximations based on a mixed variational
formulation of the problem. Uniform exponential stability can be guaranteed for
these approximations under a general compatibility condition on the
discretization spaces. As a particular example, we discuss the discretization
by mixed finite element methods for which we obtain convergence and uniform
error estimates under minimal regularity assumptions. We also prove
unconditional and uniform exponential stability for the time discretization by
certain one-step methods. The validity of the theoretical results as well as
the necessity of some of the conditions required for our analysis are
demonstrated in numerical tests. | 1511.08341v1 |
2015-12-01 | Epitaxial patterning of nanometer-thick Y3Fe5O12 films with low magnetic damping | Magnetic insulators such as yttrium iron garnet, Y3Fe5O12, with extremely low
magnetic damping have opened the door for low power spin-orbitronics due to
their low energy dissipation and efficient spin current generation and
transmission. We demonstrate reliable and efficient epitaxial growth and
nanopatterning of Y3Fe5O12 thin-film based nanostructures on insulating
Gd3Ga5O12 substrates. In particular, our fabrication process is compatible with
conventional sputtering and liftoff, and does not require aggressive ion
milling which may be detrimental to the oxide thin films. Structural and
magnetic properties indicate good qualities, in particular low magnetic damping
of both films and patterned structures. The dynamic magnetic properties of the
nanostructures are systematically investigated as a function of the lateral
dimension. By comparing to ferromagnetic nanowire structures, a distinct edge
mode in addition to the main mode is identified by both experiments and
simulations, which also exhbits cross-over with the main mode upon varying the
width of the wires. The non-linear evolution of dynamic modes over
nanostructural dimensions highlights the important role of size confinement to
their material properties in magnetic devices where Y3Fe5O12 nanostructures
serve as the key functional component. | 1512.00286v1 |
2015-12-03 | Probing Bogoliubov quasiparticles in superfluid $^3$He with a 'vibrating-wire like' MEMS device | We have measured the interaction between superfluid $^3$He-B and a
micro-machined goalpost-shaped device at temperatures below $0.2\,T_c$. The
measured damping follows well the theory developed for vibrating wires, in
which the Andreev reflection of quasiparticles in the flow field around the
moving structure leads to a nonlinear frictional force. At low velocities the
damping force is proportional to velocity while it tends to saturate for larger
excitations. Above a velocity of 2.6$\,$mms$^{-1}$ the damping abruptly
increases, which is interpreted in terms of Cooper-pair breaking.
Interestingly, this critical velocity is significantly lower than reported with
other mechanical probes immersed in superfluid $^3$He. Furthermore, we report
on a nonlinear resonance shape for large motion amplitudes that we interpret as
an inertial effect due to quasiparticle friction, but other mechanisms could
possibly be invoked as well. | 1512.01033v1 |
2016-01-03 | Event-triggered Communication in Wide-area Damping Control: A Limited Output Feedback Based Approach | A conceptual design methodology is proposed for event-triggered based power
system wide area damping controller. The event-triggering mechanism is adopted
to reduce the communication burden between origin of the remote signal and the
wide area damping controller (WADC) location. The remote signal is transmitted
to the WADC only when an event-triggering condition based on a predefined
system output, is satisfied. The triggering condition is derived from a
stability criterion, and is monitored continuously by a separate
event-monitoring unit located at the origin of the remote signal. The stability
of the resulting closed loop system is guaranteed via the input-to-state
stability (ISS) technique. The proposed event triggered WADC (ET-WADC) is
implemented on two typical test power systems - two area four machine and IEEE
39 bus 10 machine. The validation of proposed mechanism is carried out through
non-linear simulation studies on MATLAB/Simulink platform. The numerical
results show the efficacy of the controller in managing the communication
channel usage without compromising the stated system stability objectives. | 1601.00255v1 |
2016-01-05 | Lie transformation method on quantum state evolution of a general time-dependent driven and damped parametric oscillator | A variety of dynamics in nature and society can be approximately treated as a
driven and damped parametric oscillator. An intensive investigation of this
time-dependent model from an algebraic point of view provides a consistent
method to resolve the classical dynamics and the quantum evolution in order to
understand the time-dependent phenomena that occur not only in the macroscopic
classical scale for the synchronized behaviors but also in the microscopic
quantum scale for a coherent state evolution. By using a Floquet
U-transformation on a general time-dependent quadratic Hamiltonian, we exactly
solve the dynamic behaviors of a driven and damped parametric oscillator to
obtain the optimal solutions by means of invariant parameters of $K$s to
combine with Lewis-Riesenfeld invariant method. This approach can discriminate
the external dynamics from the internal evolution of a wave packet by producing
independent parametric equations that dramatically facilitate the parametric
control on the quantum state evolution in a dissipative system. In order to
show the advantages of this method, several time-dependent models proposed in
the quantum control field are analyzed in details. | 1601.00727v3 |
2016-02-19 | Distinctive response of many-body localized systems to strong electric field | We study systems which are close to or within the many-body localized (MBL)
regime and are driven by strong electric field. In the ergodic regime, the
disorder extends applicability of the equilibrium linear--response theory to
stronger drivings, whereas the response of the MBL systems is very distinctive,
revealing currents with damped oscillations. The oscillation frequency is
independent of driving and the damping is not due to heating but rather due to
dephasing. The details of damping depend on the system's history reflecting
nonergodicity of the MBL phase, while the frequency of the oscillations remains
a robust hallmark of localization. We show that the distinctive characteristic
of the driven MBL phase is also a logarithmic increase of the energy and the
polarization with time. | 1602.06055v1 |
2016-02-24 | Pressure of a gas of underdamped active dumbbells | The pressure exerted on a wall by a gas at equilibrium does not depend on the
shape of the confining potential defining the wall. In contrast, it has been
shown recently [A.P. Solon et al., Nat. Phys. 11, 673 (2015)] that a gas of
overdamped active particles exerts on a wall a force that depends on the
confining potential, resulting in a net force on an asymmetric wall between two
chambers at equal densities. Here, considering a model of underdamped
self-propelled dumbbells in two dimensions, we study how the behavior of the
pressure depends on the damping coefficient of the dumbbells, thus exploring
inertial effects. We find in particular that the force exerted on a moving wall
between two chambers at equal density continuously vanishes at low damping
coefficient, and exhibits a complex dependence on the damping coefficient at
low density, when collisions are scarce. We further show that this behavior of
the pressure can to a significant extent be understood in terms of the
trajectories of individual particles close to and in contact with the wall. | 1602.07420v1 |
2016-03-07 | Optimal Load and Stiffness for Displacement-Constrained Vibration Energy Harvesters | The power electronic interface to a vibration energy harvester not only
provides ac-dc conversion, but can also set the electrical damping to maximize
output power under displacement-constrained operation. This is commonly
exploited for linear two-port harvesters by synchronous switching to realize a
Coulomb-damped resonant generator, but has not been fully explored when the
harvester is asynchronously switched to emulate a resistive load. In order to
understand the potential of such an approach, the optimal values of load
resistance and other control parameters need to be known. In this paper we
determine analytically the optimal load and stiffness of a harmonically driven
two-port harvester with displacement constraints. For weak-coupling devices, we
do not find any benefit of load and stiffness adjustment beyond maintaining a
saturated power level. For strong coupling we find that the power can be
optimized to agree with the velocity damped generator beyond the first critical
force for displacement-constrained operation. This can be sustained up to a
second critical force, determined by a resonator figure-of-merit, at which the
power ultimately levels out. | 1603.01909v1 |
2016-03-22 | Generation and protection of steady-state quantum correlations due to quantum channels with memory | We have proposed a scheme of the generation and preservation of two-qubit
steady state quantum correlations through quantum channels where successive
uses of the channels are correlated. Different types of noisy channels with
memory, such as amplitude damping, phase-damping, and depolarizing channels
have been taken into account. Some analytical or numerical results are
presented. The effect of channels with memory on dynamics of quantum
correlations has been discussed in detail. The results show that, steady state
entanglement between two independent qubits without entanglement subject to
amplitude damping channel with memory can be generated. Besides, we compare the
dynamics of entanglement with that of quantum discord when a two-qubit system
is prepared in an entangled state. We show that entanglement dynamics suddenly
disappears, while quantum discord displays only in the asymptotic limit.
Two-qubit quantum correlations can be preserved at a long time in the limit of
$\mu\rightarrow1$. | 1603.06676v2 |
2016-03-31 | Recovery of time-dependent damping coefficients and potentials appearing in wave equations from partial data | We consider the inverse problem of determining a time-dependent damping
coefficient $a$ and a time-dependent potential $q$, appearing in the wave
equation $\partial_t^2u-\Delta_x u+a(t,x)\partial_tu+q(t,x)u=0$ in
$Q=(0,T)\times\Omega$, with $T>0$ and $\Omega$ a $ \mathcal C^2$ bounded domain
of $\mathbb R^n$, $n\geq2$, from partial observations of the solutions on
$\partial Q$. More precisely, we look for observations on $\partial Q$ that
allow to determine uniquely a large class of time-dependent damping
coefficients $a$ and time-dependent potentials $q$ without involving an
important set of data. We prove global unique determination of $a\in
W^{1,p}(Q)$, with $p>n+1$, and $q\in L^\infty(Q)$ from partial observations on
$\partial Q$. | 1603.09600v2 |
2016-04-22 | Feedback-induced Bistability of an Optically Levitated Nanoparticle: A Fokker-Planck Treatment | Optically levitated nanoparticles have recently emerged as versatile
platforms for investigating macroscopic quantum mechanics and enabling
ultrasensitive metrology. In this article we theoretically consider two damping
regimes of an optically levitated nanoparticle cooled by cavityless parametric
feedback. Our treatment is based on a generalized Fokker-Planck equation
derived from the quantum master equation presented recently and shown to agree
very well with experiment [1]. For low damping, we find that the resulting
Wigner function yields the single-peaked oscillator position distribution and
recovers the appropriate energy distribution derived earlier using a classical
theory and verified experimentally [2]. For high damping, in contrast, we
predict a double-peaked position distribution, which we trace to an underlying
bistability induced by feedback. Unlike in cavity-based optomechanics,
stochastic processes play a major role in determining the bistable behavior. To
support our conclusions, we present analytical expressions as well as numerical
simulations using the truncated Wigner function approach. Our work opens up the
prospect of developing bistability-based devices, characterization of
phase-space dynamics, and investigation of the quantum-classical transition
using levitated nanoparticles. | 1604.06767v2 |
2016-05-06 | Multidimensional Thermoelasticity for Nonsimple Materials -- Well-Posedness and Long-Time Behavior | An initial-boundary value problem for the multidimensional type III
thermoelaticity for a nonsimple material with a center of symmetry is
considered. In the linear case, the well-posedness with and without
Kelvin-Voigt and/or frictional damping in the elastic part as well as the lack
of exponential stability in the elastically undamped case is proved. Further, a
frictional damping for the elastic component is shown to lead to the
exponential stability. A Cattaneo-type hyperbolic relaxation for the thermal
part is introduced and the well-posedness and uniform stability under a
nonlinear frictional damping are obtained using a compactness-uniqueness-type
argument. Additionally, a connection between the exponential stability and
exact observability for unitary $C_{0}$-groups is established. | 1605.02049v1 |
2016-05-16 | The Cauchy problem for the nonlinear damped wave equation with slowly decaying data | We study the Cauchy problem for the nonlinear damped wave equation and
establish the large data local well-posedness and small data global
well-posedness with slowly decaying initial data. We also prove that the
asymptotic profile of the global solution is given by a solution of the
corresponding parabolic problem, which shows that the solution of the damped
wave equation has the diffusion phenomena. Moreover, we show blow-up of
solution and give the estimate of the lifespan for a subcritical nonlinearity.
In particular, we determine the critical exponent for any space dimension. | 1605.04616v2 |
2016-05-20 | High-frequency behavior of FeN thin films fabricated by reactive sputtering | We investigated high-frequency behavior of FeN thin films prepared by
reactive sputtering through ferromagnetic resonance (FMR) and its relationship
with the static magnetic properties. The FMR was observed in the frequency
range from 2 to 18 GHz in the FeN films fabricated at proper nitrogen flow rate
(NFR). In those FeN thin films, a decrease of the saturation magnetization and
the corresponding decrease of the FMR frequency were observed as NFR was
increased during the deposition. The external field dependences of the FMR
frequencies were well fit to the Kittel formula and the Land\'e g-factors
determined from the fit were found to be very close to the free electron value.
The high-field damping parameters were almost insensitive to the growth
condition of NFR. However, the low-field damping parameters exhibited high
sensitivity to NFR very similar to the dependence of the hard-axis coercivity
on NFR, suggesting that extrinsic material properties such as impurities and
defect structures could be important in deciding the low-field damping
behavior. | 1605.06179v1 |
2016-06-08 | Effect of quantum noise on deterministic joint remote state preparation of a qubit state via a GHZ channel | Quantum secure communication brings a new direction for information security.
As an important component of quantum secure communication, deterministic joint
remote state preparation (DJRSP) could securely transmit a quantum state with
100\% success probability. In this paper, we study how the efficiency of DJRSP
is affected when qubits involved in the protocol are subjected to noise or
decoherence. Taking a GHZ based DJRSP scheme as an example, we study all types
of noise usually encountered in real-world implementations of quantum
communication protocols, i.e., the bit-flip, phase-flip (phase-damping),
depolarizing, and amplitude-damping noise. Our study shows that the fidelity of
the output state depends on the phase factor, the amplitude factor and the
noise parameter in the bit-flip noise, while the fidelity only depends on the
amplitude factor and the noise parameter in the other three types of noise. And
the receiver will get different output states depending on the first preparer's
measurement result in the amplitude-damping noise. Our results will be helpful
for improving quantum secure communication in real implementation. | 1606.02484v2 |
2016-06-28 | Radiation Damping by Thomson Scattering | Synchrotron radiation of relativistic electrons in storage rings naturally
leads to the process of damping of betatron oscillations. Damping time and
transverse beam emittance can be reduced by wigglers or undulators while the
beam parameters are still well defined by the common radiation integrals, based
on the properties of synchrotron radiation. However, the quantum excitation of
betatron oscillations in principle can be considerably reduced if an electron
radiation occurs due to the Thomson scattering in the periodic electromagnetic
field. After a brief introduction we compare radiation properties for different
cases and suggest the modification of the radiation integrals. | 1606.08602v5 |
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