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2006-05-19 | Energy Loss of Heavy Quarks from Asymptotically AdS Geometries | We investigate some universal features of AdS/CFT models of heavy quark
energy loss. In addition, as a specific example, we examine quark damping in
the spinning D3-brane solution dual to N=4 SU(N_c) super Yang-Mills at finite
temperature and R-charge chemical potential. | 0605191v2 |
2003-12-19 | Energy Decay of Damped Systems | We present a new and simple bound for the exponential decay of second order
systems using the spectral shift. This result is applied to finite matrices as
well as to partial differential equations of Mathematical Physics. The type of
the generated semigroup is shown to be bounded by the upper real part of the
numerical range of the underlying quadratic operator pencil. | 0312376v1 |
2004-04-06 | Bounds for contractive semigroups and second order systems | We derive a uniform bound for the difference of two contractive semigroups,
if the difference of their generators is form-bounded by the Hermitian parts of
the generators themselves. We construct a semigroup dynamics for second order
systems with fairly general operator coefficients and apply our bound to the
perturbation of the damping term. The result is illustrated on a dissipative
wave equation. As a consequence the exponential decay of some second order
systems is proved. | 0404120v1 |
2006-12-07 | Fractional Hamiltonian analysis of higher order derivatives systems | The fractional Hamiltonian analysis of 1+1 dimensional field theory is
investigated and the fractional Ostrogradski's formulation is obtained. The
fractional path integral of both simple harmonic oscillator with an
acceleration-squares part and a damped oscillator are analyzed. The classical
results are obtained when fractional derivatives are replaced with the integer
order derivatives. | 0612024v1 |
2000-02-23 | Two-frequency forced Faraday waves: Weakly damped modes and pattern selection | Recent experiments (Kudrolli, Pier and Gollub, 1998) on two-frequency
parametrically excited surface waves exhibit an intriguing "superlattice" wave
pattern near a codimension-two bifurcation point where both subharmonic and
harmonic waves onset simultaneously, but with different spatial wavenumbers.
The superlattice pattern is synchronous with the forcing, spatially periodic on
a large hexagonal lattice, and exhibits small-scale triangular structure.
Similar patterns have been shown to exist as primary solution branches of a
generic 12-dimensional $D_6\dot{+}T^2$-equivariant bifurcation problem, and may
be stable if the nonlinear coefficients of the bifurcation problem satisfy
certain inequalities (Silber and Proctor, 1998). Here we use the spatial and
temporal symmetries of the problem to argue that weakly damped harmonic waves
may be critical to understanding the stabilization of this pattern in the
Faraday system. We illustrate this mechanism by considering the equations
developed by Zhang and Vinals (1997, J. Fluid Mech. 336) for small amplitude,
weakly damped surface waves on a semi-infinite fluid layer. We compute the
relevant nonlinear coefficients in the bifurcation equations describing the
onset of patterns for excitation frequency ratios of 2/3 and 6/7. For the 2/3
case, we show that there is a fundamental difference in the pattern selection
problems for subharmonic and harmonic instabilities near the codimension-two
point. Also, we find that the 6/7 case is significantly different from the 2/3
case due to the presence of additional weakly damped harmonic modes. These
additional harmonic modes can result in a stabilization of the superpatterns. | 0002041v2 |
2000-05-18 | Environment-induced dynamical chaos | We examine the interplay of nonlinearity of a dynamical system and thermal
fluctuation of its environment in the ``physical limit'' of small damping and
slow diffusion in a semiclassical context and show that the trajectories of
c-number variables exhibit dynamical chaos due to the thermal fluctuations of
the bath. | 0005037v1 |
2003-02-12 | On Whitham theory for perturbed integrable equations | Whitham theory of modulations is developed for periodic waves described by
nonlinear wave equations integrable by the inverse scattering transform method
associated with $2\times2$ matrix or second order scalar spectral problems. The
theory is illustrated by derivation of the Whitham equations for perturbed
Korteweg-de Vries equation and nonlinear Schr\"odinger equation with linear
damping. | 0302027v1 |
2003-02-24 | Reverse Integration for Computing Stationary Points of Unstable Stiff Systems | Using existing, forward-in-time integration schemes, we demonstrate that it
is possible to compute unstable, saddle-type fixed points of stiff systems of
ODEs when the stable compenents are fast (i.e., rapidly damped) while the
unstable components are slow. The approach has implications for the reverse
(backward in time) integration of such stiff systems, and for the coarse
reverse integration of microscopic/stochastic simulations. | 0302055v1 |
2003-09-02 | Breather lattice and its stabilization for the modified Korteweg-de Vries equation | We obtain an exact solution for the breather lattice solution of the modified
Korteweg-de Vries (MKdV) equation. Numerical simulation of the breather lattice
demonstrates its instability due to the breather-breather interaction. However,
such multi-breather structures can be stabilized through the concurrent
application of ac driving and viscous damping terms. | 0309003v1 |
2003-12-19 | Existence of travelling waves in discrete sine-Gordon rings | We prove existence results for travelling waves in discrete, damped,
dc-driven sine-Gordon equations with periodic boundary conditions. | 0312042v5 |
2006-12-05 | Colliding Particles in Highly Turbulent Flows | We discuss relative velocities and the collision rate of small particles
suspended in a highly turbulent fluid. In the limit where the viscous damping
is very weak, we estimate the relative velocities using the Kolmogorov cascade
principle. | 0612008v2 |
1998-05-29 | Magnetic Faraday-Instability | In a magnetic fluid parametrically driven surface waves can be excited by an
external oscillating magnetic field. A static magnetic field changes the
restoring forces and damping coefficients of the various surface waves. This
property enables the excitation of both subharmonic and harmonic responses of
the standing waves. | 9806001v1 |
1999-06-08 | Electromagnetic modes in cold magnetized strongly coupled plasmas | The spectrum of electromagnetic waves propagating in a strongly coupled
magnetized fully ionized hydrogen plasma is found. The ion motion and damping
being neglected, the influence of the Coulomb coupling on the electromagnetic
spectrum is analyzed. | 9906016v1 |
2000-08-12 | The effects of the rotation in plasma | Electric and magnetic self-fields can exist in the rotating plasma. A
self-sustained rotation can be established in the plasma. The disturbed
distribution function of rotating plasma is derived from the Vlasov equation.
The propagation of waves in rotating plasma differs from that in the usual
plasma. New terms for Landau damping appear. The local rotational behaviour may
become prevailing. | 0008039v1 |
2000-12-11 | An improved empirical equation for bunch lengthening in electron storage rings | In this paper we propose an improved empirical equation for the bunch
lengthening in electron storage rings. The comparisons are made between the
analytical and experimental results, and the agreements are quite well. This
improved equation can be equally applied to the case where a storage ring is
very resistive (such as the improved SLC damping rings) instead of inductive as
usual. | 0012020v2 |
2001-07-25 | Causal Classical Theory of Radiation Damping | It is shown how initial conditions can be appropriately defined for the
integration of Lorentz-Dirac equations of motion. The integration is performed
\QTR{it}{forward} in time. The theory is applied to the case of the motion of
an electron in an intense laser pulse, relevant to nonlinear Compton
scattering. | 0107062v1 |
2001-11-26 | Methods of Laser Cooling of Electron Beams in Storage Rings | Methods of enhanced laser cooling of particle beams in storage rings and
Robinson's damping criterion are discussed. The dynamics of amplitudes of
betatron oscillations and instantaneous orbits of electrons interacting with
laser beams being displaced in the radial direction is investigated. | 0111184v2 |
2002-04-17 | Soliton self-modulation of the turbulence amplitude and plasma rotation | The space-uniform amplitude envelope of the Ion Temperature Gradient driven
turbulence is unstable to small perturbations and evolves to nonuniform,
soliton-like modulated profiles. The induced poloidal asymmetry of the
transport fluxes can generate spontaneous poloidal spin-up of the tokamak
plasma. | 0204050v2 |
2002-05-06 | Delayed Equation for Charged Rigid Nonrelativistic Ball | Simple expression for self-force acting on radiating rigid charged ball is
derived (Sommerfeld ball). It is shown that appropriate delayed equation of
motion has solutions in general differ from that for Sommerfeld sphere - there
are no "radiationless" solutions, but there are oscillating without damping
solutions though self-force has nonzero value. | 0205012v1 |
2003-12-10 | Charge Fluctuation of Dust Grains and its Impact on Dusty Wave Propagation | In this paper we consider the influence of dust charge fluctuations on
damping of the dust-ion-acoustic waves. Fluid approximation of longitudinal
electrostatic waves in unmagnetized plasmas is considered. We show that for a
weak acoustic wave the attenuation depends on a phenomenological charging
coefficient. | 0312067v1 |
2004-09-03 | Relativistic electron beam acceleration by Compton scattering of lower-hybrid waves | It has been proved theoetically and numerically that the highly relativistic
electron beam can be accelerated efficiently via the Compton scattering induced
by nonlinear Landau and cyclotron damping of the lower-hybrid waves. | 0409024v1 |
1998-02-16 | Classical states via decoherence | The initial states which minimize the predictability loss for a damped
harmonic oscillator are identified as quasi-free states with a symmetry
dictated by the environment's diffusion coefficients. For an isotropic
diffusion in phase space, coherent states (or mixtures of coherent states) are
selected as the most stable ones. | 9802044v1 |
2000-01-08 | Quantum computation with mesoscopic superposition states | We present a strategy to engineer a simple cavity-QED two-bit universal
quantum gate using mesoscopic distinct quantum superposition states. The
dissipative effect on decoherence and amplitude damping of the quantum bits are
analyzed and the critical parameters are presented. | 0001018v1 |
2001-10-03 | Thermal and quantum noise in active systems | We present a quantum network approach to the treatment of thermal and quantum
fluctuations in measurement devices. The measurement is described as a
scattering process of input fluctuations towards output ones. We present the
results obtained with this method for the treatment of a cold damped capacitive
accelerometer. | 0110021v1 |
2001-11-24 | Deformed versus undeformed cat states encoding qubit | We study the possibility of exploiting superpositions of coherent states to
encode qubit. A comparison between the use of deformed and undeformed bosonic
algebra is made in connection with the amplitude damping errors. | 0111128v1 |
2002-11-05 | Unitary reduction of the Liouville equation relative to a two-level atom coupled to a bimodal lossy cavity | The Liouville equation of a two-level atom coupled to a degenerate bimodal
lossy cavity is unitarily and exactly reduced to two uncoupled Liouville
equations. The first one describes a dissipative Jaynes-Cummings model and the
other one a damped harmonic oscillator. Advantages related to the reduction
method are discussed. | 0211015v1 |
2003-11-10 | Cavity Assisted Nondestructive Laser Cooling of Atomic Qubits | We analyze two configurations for laser cooling of neutral atoms whose
internal states store qubits. The atoms are trapped in an optical lattice which
is placed inside a cavity. We show that the coupling of the atoms to the damped
cavity mode can provide a mechanism which leads to cooling of the motion
without destroying the quantum information. | 0311054v2 |
2003-11-19 | Noise enhancing the classical information capacity of a quantum channel | We present a simple model of quantum communication where a noisy quantum
channel may benefit from the addition of further noise at the decoding stage.
We demonstrate enhancement of the classical information capacity of an
amplitude damping channel, with a predetermined detection threshold, by the
addition of noise in the decoding measurement. | 0311126v1 |
2003-12-22 | Observation of Exceptional Points in Electronic Circuits | Two damped coupled oscillators have been used to demonstrate the occurrence
of exceptional points in a purely classical system. The implementation was
achieved with electronic circuits in the kHz-range. The experimental results
perfectly match the mathematical predictions at the exceptional point. A
discussion about the universal occurrence of exceptional points -- connecting
dissipation with spatial orientation -- concludes the paper. | 0312182v1 |
2004-08-01 | Remark on the additivity conjecture for the quantum depolarizing channel | We consider bistochastic quantum channels generated by unitary
representations of the discret group. The proof of the additivity conjecture
for the quantum depolarizing channel $\Phi$ based on the decreasing property of
the relative entropy is given. We show that the additivity conjecture is true
for the channel $\Xi =\Psi \circ \Phi $, where $\Psi $ is the phase damping. | 0408004v2 |
2005-03-26 | Markovian feedback to control continuous variable entanglement | We present a model to realize quantum feedback control of continuous variable
entanglement. It consists of two interacting bosonic modes subject to amplitude
damping and achieving entangled Gaussian steady state. The possibility to
greatly improve the degree of entanglement by means of Markovian (direct)
feedback is then shown. | 0503206v2 |
2005-04-12 | Generation of Werner states and preservation of entnglement in a noisy environment | We study the influence of noisy environment on the evolution of two-atomic
system in the presence of collective damping. Generation of Werner states as
asymptotic states of evolution is described. We also show that for some initial
states the amount of entanglement is preserved during the evolution. | 0504090v2 |
2005-04-25 | Dissipative dynamics of nondegenerate two-photon Jaynes-Cummings model | A nondegenerate two-photon Jaynes-Cummings model is investigated where the
leakage of photon through the cavity is taken into account. The effect of
cavity damping on the mean photon number, atomic populations, field statistics
and both field and atomic squeezing is considered on the basis of master
equation in dressed-state approximation for initial coherent fields and excited
atom. | 0504184v1 |
2005-07-20 | A minimal coupling method for dissipative quantum systems | Quantum dynamics of a general dissipative system investigated by its coupling
to a Klein-Gordon type field as the environment by introducing a minimal
coupling method. As an example, the quantum dynamics of a damped three
dimensional harmonic oscillator investigated and some transition probabilities
indicating the way energy flows between the subsystems obtained. The quantum
dynamics of a dissipative two level system considered. | 0507195v1 |
2007-02-09 | Linear-optics manipulations of photon-loss codes | We discuss codes for protecting logical qubits carried by optical fields from
the effects of amplitude damping, i.e. linear photon loss. We demonstrate that
the correctability condition for one-photon loss imposes limitations on the
range of manipulations than can be implemented with passive linear-optics
networks. | 0702091v1 |
2007-08-27 | Band-Gap Engineering of Phononic Crystals: A Computational Survey of Two-Dimensional Systems | We present graphic results with high-levels of abstraction to desribe the
basic principles and rules of thumb for acoustic or phononic band-gap
engineering. We use these rules for developing an improved machien mount for
damping acoustic vibrations, a phononic lens and a frequency selective filter
in the acoustic regime. | 0708.3669v1 |
2007-09-01 | Comments on 'Controversy on a Dispersion Relation for MHD Waves' by Chandra and Kumthekar | We comment on the work by Chandra and Kumthekar (2007, henceforth CK) which
is questionable. In the derivation of dispersion relation, CK neither invoke
the concept of vector space nor do they follow the basic criterion for the
elimination of perturbation terms under which the damped magnetoacoustic waves
are derived. | 0709.0040v1 |
2007-09-17 | Intrinsic dissipation in cantilevers | We consider the effects of a velocity-independent friction force on
cantilever damping. It is shown that this dissipation mechanism causes
nonlinear effects in the cantilever vibrations. The size of the nonlinearity
increases with decreasing cantilever velocity. Our analysis makes it possible
to understand experiments [Stipe et al, PRL 87, 096801 (2001)] where an
amplitude dependence of the cantilever eigenfrequency and anomalous dissipation
was observed only at small amplitudes. | 0709.2582v1 |
2007-09-21 | Enhanced Optical Cooling of Particle Beams in Storage Rings | A method of enhanced optical cooling (EOC) based on nonlinear selective
interaction between particles and theirs amplified undulator radiation wavelets
(URW) in storage rings is discussed. It leads to non-exponential fast damping.
The selectivity is arranged by a moving screen located on the image plane of
the optical system projecting URW there. | 0709.3403v1 |
2007-10-26 | Vacuum - induced stationary entanglement in radiatively coupled three - level atoms | We consider a pair of three - level atoms interacting with a common vacuum
and analyze the process of entanglement production due to spontaneous emission.
We show that in the case of closely separated atoms, collective damping can
generate robust entanglement of the asymptotic states. | 0710.5048v2 |
2007-11-15 | $C^m$-theory of damped wave equations with stabilisation | The aim of this note is to extend the energy decay estimates from [J. Wirth,
J. Differential Equations 222 (2006) 487--514] to a broader class of
time-dependent dissipation including very fast oscillations. This is achieved
using stabilisation conditions on the coefficient in the spirit of [F.
Hirosawa, Math. Ann. 339/4 (2007) 819--839]. | 0711.2403v1 |
2008-04-21 | Resonant excitation amidst dephasing: An exact analytic solution | An exact analytic solution is presented for coherent resonant excitation of a
two-state quantum system driven by a time-dependent pulsed external field with
a hyperbolic-secant shape in the presence of dephasing. Analytic results are
derived for the amplitude and the phase shift of the damped Rabi oscillations. | 0804.3315v1 |
2008-05-06 | Logarithmic decay of hyperbolic equations with arbitrary boundary damping | In this paper, we study the logarithmic stability for the hyperbolic
equations by arbitrary boundary observation. Based on Carleman estimate, we
first prove an estimate of the resolvent operator of such equation. Then we
prove the logarithmic stability estimate for the hyperbolic equations without
any assumption on an observation subboundary. | 0805.0625v1 |
2008-07-14 | A z = 3 Lyman Alpha Blob Associated with a Damped Lyman Alpha System Proximate to its Background Quasar | We report on the discovery of a bright Lyman alpha blob associated with the
z=3 quasar SDSSJ124020.91+145535.6 which is also coincident with strong damped
Lyman alpha absorption from a foreground galaxy (a so-called proximate damped
Lyman alpha system; PDLA). The one dimensional spectrum acquired by the Sloan
Digital Sky Survey (SDSS) shows a broad Lyman alpha emission line with a FWHM ~
500 km/s and a luminosity of L_{Lya} = 3.9e43 erg/s superposed on the trough of
the PDLA. Mechanisms for powering this large Lyman alpha luminosity are
discussed. We argue against emission from HII regions in the PDLA galaxy since
this requires an excessive star-formation rate ~ 500 Msun/yr and would
correspond to the largest Lyman alpha luminosity ever measured from a damped
Lyman alpha system or starburst galaxy. We use a Monte Carlo radiative transfer
simulation to investigate the possibility that the line emission is fluorescent
recombination radiation from the PDLA galaxy powered by the ionizing flux of
the quasar, but find that the predicted Lyman alpha flux is several orders of
magnitude lower than observed. We conclude that the Lyman alpha emission is not
associated with the PDLA galaxy at all, but instead is intrinsic to the
quasar's host and similar to the extended Lyman alpha 'fuzz' which is detected
around many AGN. PDLAs are natural coronagraphs that block their background
quasar at Lyman alpha, and we discuss how systems similar to
SDSSJ124020.91+145535.6 might be used to image the neutral hydrogen in the PDLA
galaxy in silhouette against the screen of extended Lyman alpha emission from
the background quasar. | 0807.2271v1 |
2008-09-23 | Analysis of complete positivity conditions for quantum qutrit channels | We present an analysis of complete positivity (CP) constraints on qutrit
quantum channels that have a form of affine transformations of generalized
Bloch vector. For diagonal (damping) channels we derive conditions analogous to
the ones that in qubit case produce tetrahedron structure in the channel
parameter space. | 0809.3882v3 |
2008-10-28 | Excitation and damping of p-mode oscillations of alpha Cen B | This paper presents an analysis of observational data on the p-mode spectrum
of the star alpha Cen B and a comparison with theoretical computations of the
stochastic excitation and damping of the modes. We find that at frequencies >
4500 micro-Hz, the model damping rates appear to be too weak to explain the
observed shape of the power spectral density of alpha Cen B. The conclusion
rests on the assumption that most of the disagreement is due to problems
modelling the damping rates, not the excitation rates, of the modes. This
assumption is supported by a parallel analysis of BiSON Sun-as-a-star data, for
which it is possible to use analysis of very long timeseries to place tight
constraints on the assumption. The BiSON analysis shows that there is a similar
high-frequency disagreement between theory and observation in the Sun.
We demonstrate that by using suitable comparisons of theory and observation
it is possible to make inference on the dependence of the p-mode linewidths on
frequency, without directly measuring those linewidths, even though the alpha
Cen B dataset is only a few nights long. Use of independent measures from a
previous study of the alpha Cen B linewidths in two parts of its spectrum also
allows us to calibrate our linewidth estimates for the star. The resulting
calibrated linewidth curve looks similar to a frequency-scaled version of its
solar cousin, with the scaling factor equal to the ratio of the respective
acoustic cut-off frequencies of the two stars. The ratio of the frequencies at
which the onset of high-frequency problems is seen in both stars is also given
approximately by the same scaling factor. | 0810.5022v1 |
2008-11-03 | Equation of state for QCD matter in a quasiparticle model | A phenomenological QCD quasiparticle model provides a means to map lattice
QCD results to regions relevant for a variety of heavy-ion collision
experiments at larger baryon density. We report on effects of collectives modes
and damping on the equation of state. | 0811.0274v1 |
2009-01-14 | On the use of continuous wavelet analysis for modal identification | This paper reviews two different uses of the continuous wavelet transform for
modal identification purposes. The properties of the wavelet transform, mainly
energetic, allow to emphasize or filter the main information within measured
signals and thus facilitate the modal parameter identification especially when
mechanical systems exhibit modal coupling and/or relatively strong damping. | 0901.2000v1 |
2009-01-20 | Quasi-periodic motions in strongly dissipative forced systems | We consider a class of ordinary differential equations describing
one-dimensional systems with a quasi-periodic forcing term and in the presence
of large damping. We discuss the conditions to be assumed on the mechanical
force and the forcing term for the existence of quasi-periodic solutions which
have the same frequency vector as the forcing. | 0901.3009v1 |
2009-01-23 | On the regularity of global attractors | This note is focused on a novel technique in order to establish the
boundedness in more regular spaces for global attractors of dissipative
dynamical systems, without appealing to uniform-in-time estimates. As an
application of the abstract result, the semigroup generated by the strongly
damped wave equation $$u_{tt}-\Delta u_t-\Delta u+\phi(u)=f$$ with critical
nonlinearity is considered, whose attractor is shown to possess the optimal
regularity. | 0901.3607v1 |
2009-05-07 | On a Stochastic Wave Equation Driven by a Non-Gaussian Levy Process | This paper investigates a damped stochastic wave equation driven by a
non-Gaussian Levy noise. The weak solution is proved to exist and be unique.
Moreover we show the existence of a unique invariant measure associated with
the transition semigroup under mild conditions. | 0905.0992v1 |
2009-05-07 | Metal-Enriched Plasma in Protogalactic Halos: A Survey of N V Absorption in High-z Damped & Sub-Damped Lyman-alpha Systems | We continue our recent work to characterize the plasma content of
high-redshift damped and sub-damped Lyman-alpha systems (DLAs/sub-DLAs), which
represent multi-phase gaseous (proto)galactic disks and halos seen toward a
background source. We survey N V absorption in a sample of 91 DLAs and 18
sub-DLAs in the redshift range 1.67<z<4.28 with unblended coverage of the N V
doublet, using data from VLT/UVES, Keck/HIRES, and Keck/ESI. In DLAs, we find
eight secure N V detections, four marginal detections, and 79 non-detections.
The detection rate of N V in DLAs is therefore 13^{+5}_{-4}%. Two sub-DLA N V
detections are found among a sample of 18, at a similar detection rate of
11^{+15}_{-7}%. We show that the N V detection rate is a strong function of
metallicity, increasing by a factor of ~4 at [N/H]=[NI/HI]>-2.3. The N V and
CIV component b-value distributions in DLAs are statistically similar, but the
median b(N V) of 18 km/s is lower than the median b(O VI) of 25 km/s. Some ~20%
of the N V components have b<10 km/s and thus arise in warm photoionized plasma
at log (T/K)<4.92; local sources of ionizing radiation (as opposed to the
extragalactic background) are required to keep the cloud sizes physically
reasonable. The nature of the remaining ~80% of (broad) N V components is
unclear; models of radiatively-cooling collisionally-ionized plasma at
log(T/K)=5.2-5.4 are fairly successful in reproducing the observed integrated
high-ion column density ratios and the component line widths, but we cannot
rule out photoionization by local sources. Finally, we identify several unusual
DLAs with extremely low metallicity (<0.01 solar) but strong high-ion
absorption [log N(N V)>14 or log N(O VI)>14.2] that present challenges to
either galactic inflow or outflow models. | 0905.1042v2 |
2009-05-12 | Quantum measurement with chaotic apparatus | We study a dissipative quantum mechanical model of the projective measurement
of a qubit. We demonstrate how a correspondence limit, damped quantum
oscillator can realise chaotic-like or periodic trajectories that emerge in
sympathy with the projection of the qubit state, providing a model of the
measurement process. | 0905.1867v2 |
2009-06-12 | Tailoring the carrier mobility of semiconducting nanowires by remote dielectrics | The dielectric environment of thin semiconductor nanowires can affect the
charge transport properties inside the wire. In this work, it is shown that
Coulomb impurity scattering inside thin nanowires can be damped strongly by
coating the wire with a high-k dielectric. This will lead to an increase in the
mobility of free charges inside the wire. | 0906.2371v1 |
2009-10-22 | Modelling collisions in a relativistic plasma | Generalising the work of Lenard and Bernstein, we introduce a new, fully
relativistic model to describe collisional plasmas. Like the Fokker-Planck
operator, this equation represents velocity diffusion and conserves particle
number. However, unlike the Fokker-Planck operator it is linear in the
distribution function, and so more amenable to a fluid treatment. By taking
moments, we derive a new fluid model, and demonstrate the damping effects of
collisions on Langmuir waves. | 0910.4368v1 |
2009-11-24 | Non-Markovian master equation for a damped driven two-state system | We present a detailed microscopic derivation for a non-Markovian master
equation for a driven two-state system interacting with a general structured
reservoir. The master equation is derived using the time-convolutionless
projection operator technique in the limit of weak coupling between the
two-state quantum system and its environment. We briefly discuss the Markov
approximation, the secular approximation and their validity. | 0911.4600v1 |
2009-12-07 | Analyticity and Gevrey-class regularity for the second-grade fluid equations | We address the global persistence of analyticity and Gevrey-class regularity
of solutions to the two and three-dimensional visco-elastic second-grade fluid
equations. We obtain an explicit novel lower bound on the radius of analyticity
of the solutions to the second-grade fluid equations that does not vanish as
$t\to \infty$. Applications to the damped Euler equations are given. | 0912.1327v1 |
2010-02-15 | Analysis on Path Spaces over Riemmannian Manifolds with Boundary | By using Hsu's multiplicative functional for the Neumann heat equation, a
natural damped gradient operator is defined for the reflecting Brownian motion
on compact manifolds with boundary. This operator is linked to quasi-invariant
flows in terms of a integration by parts formula, which leads to the standard
log-Sobolev inequality for the associated Dirichlet form on the path space. | 1002.2887v1 |
2010-03-07 | Decay of Langmuir wave in dense plasmas and warm dense matter | The decays of the Langmuir waves in dense plasmas are computed using the
dielectric function theory widely used in the solid state physics.
Four cases are considered: a classical plasma, a Maxwellian plasma, a
degenerate quantum plasma, and a partially degenerate plasma. The result is
considerably different from the conventional Landau damping theory. | 1003.1524v2 |
2010-05-20 | Cavity spin optodynamics | The dynamics of a large quantum spin coupled parametrically to an optical
resonator is treated in analogy with the motion of a cantilever in cavity
optomechanics. New spin optodynamic phenonmena are predicted, such as
cavity-spin bistability, optodynamic spin-precession frequency shifts, coherent
amplification and damping of spin, and the spin optodynamic squeezing of light. | 1005.3853v2 |
2011-02-21 | Noncommutative gauge theory and renormalisability | We review two different noncommutative gauge models generalizing approaches
which lead to renormalizable scalar quantum field theories. One of them
implements the crucial IR damping of the gauge field propagator in the
so-called ``soft breaking'' part. We discuss one-loop renormalisability. | 1102.4167v1 |
2011-04-10 | Stabilization of the wave equation with external force | We study the rate of decay of the energy functional of solutions of the wave
equation with localized damping and a external force. We prove that the decay
rates of the energy functional is determined from a forced differential
equation. | 1104.1808v3 |
2011-05-01 | Set, Reset, and Retention Times for Ionic and Filamentary Mem-Resistors | A dynamic systems model has previously been proposed for mem-resistors based
on a driven damped harmonic oscillator differential equation describing
electron and ionic depletion widths in a thin semiconductor film. This paper
derives equations for set, reset, and retention times based on the previously
proposed model. Keywords- mem-resistor, RRAM, ReRAM | 1105.0134v3 |
2011-07-30 | Ion-kinetic D'Angelo mode | An extension of hydrodynamic D'Angelo mode of inhomogeneous sheared plasma
flow along the magnetic field into the short-wavelength limit, where the
hydrodynamic treatment is not valid, has been considered. We find that D'Angelo
mode in this wavelength range is excited by inverse ion Landau damping and
becomes the shear flow driven ion-kinetic mode. | 1108.0093v1 |
2011-11-14 | Twist of fractional oscillations | Using the method of the Laplace transform, we consider fractional
oscillations. They are obtained by the time-clock randomization of ordinary
harmonic vibrations. In contrast to sine and cosine, the functions describing
the fractional oscillations exhibit a finite number of damped oscillations with
an algebraic decay. Their fractional differential equation is derived. | 1111.5298v1 |
2011-12-02 | On the transmission of binary bits in discrete Josephson-junction arrays | In this work, we use supratransmission and infratransmission in the
mathematical modeling of the propagation of digital signals in weakly damped,
discrete Josephson-junction arrays, using energy-based detection criteria. Our
results show an efficient and reliable transmission of binary information. | 1112.0589v1 |
2012-01-12 | Superconducting elliptical cavities | We give a brief overview of the history, state of the art, and future for
elliptical superconducting cavities. Principles of the cell shape optimization,
criteria for multi-cell structures design, HOM damping schemes and other
features are discussed along with examples of superconducting structures for
various applications. | 1201.2598v1 |
2012-02-19 | Cluster-based Superconducting Tunneling Networks | A 2D tunneling network consisting of nanoclusters placed on a surface is
studied. It is shown that such a network is capable of transferring large
supercurrent at high temperatures. For a realistic set of parameters the
damping is quite small, and the smallness is due to strong renormalization of
the capacitance of a cluster. The critical field also turns out to be lar | 1202.4132v1 |
2012-02-25 | Design of a Fractional Order Phase Shaper for Iso-damped Control of a PHWR under Step-back Condition | Phase shaping using fractional order (FO) phase shapers has been proposed by
many contemporary researchers as a means of producing systems with iso-damped
closed loop response due to a stepped variation in input. Such systems, with
the closed loop damping remaining invariant to gain changes can be used to
produce dead-beat step response with only rise time varying with gain. This
technique is used to achieve an active step-back in a Pressurized Heavy Water
Reactor (PHWR) where it is desired to change the reactor power to a
pre-determined value within a short interval keeping the power undershoot as
low as possible. This paper puts forward an approach as an alternative for the
present day practice of a passive step-back mechanism where the control rods
are allowed to drop during a step-back action by gravity, with release of
electromagnetic clutches. The reactor under a step-back condition is identified
as a system using practical test data and a suitable Proportional plus Integral
plus Derivative (PID) controller is designed for it. Then the combined plant is
augmented with a phase shaper to achieve a dead-beat response in terms of power
drop. The fact that the identified static gain of the system depends on the
initial power level at which a step-back is initiated, makes this application
particularly suited for using a FO phase shaper. In this paper, a model of a
nuclear reactor is developed for a control rod drop scenario involving rapid
power reduction in a 500MWe Canadian Deuterium Uranium (CANDU) reactor using
AutoRegressive Exogenous (ARX) algorithm. The system identification and reduced
order modeling are developed from practical test data. For closed loop active
control of the identified reactor model, the fractional order phase shaper
along with a PID controller is shown to perform better than the present Reactor
Regulating System (RRS) due to its iso-damped nature. | 1202.5657v1 |
2012-02-27 | Simple absorbing boundary conditions for wave simulations with Smoothed Particle Hydrodynamics | We study and implement a simple method, based on the Perfectly Matched Layer
approach, to treat non reflecting boundary conditions with the Smoothed
Particles Hydrodynamics numerical algorithm. The method is based on the concept
of physical damping. We illustrate how it works in the case of 1D and 2D time
dependent waves propagating in a finite domain. | 1202.5893v1 |
2012-07-22 | Singularity and existence to a wave system of nematic liquid crystals | In this paper, we prove the global existence and singularity formation for a
wave system from modelling nematic liquid crystals in one space dimension. In
our model, although the viscous damping term is included, the solution with
smooth initial data still has gradient blowup in general, even when the initial
energy is arbitrarily small. | 1207.5190v1 |
2012-07-26 | Upsilon Suppression in PbPb Collisions at sqrt(s_NN) = 2.76 TeV | We suggest that the combined effect of screening, gluon-induced dissociation,
collisional damping, and reduced feed-down explains most of the sequential
suppression of Y(nS) states that has been observed in PbPb relative to pp
collisions at sqrt(s_NN) = 2.76 TeV. The suppression is thus a clear, albeit
indirect, indication for the presence of a qgp. | 1207.6227v1 |
2012-09-08 | Local energy decay for the wave equation with nonlinear time dependent damping | This paper addresses a wave equation on a exterior domain in R^{d}(d odd)
with nonlinear time dependent dissipation. Under a microlocal geometric
condition we prove that the decay rates of the local energy functional are
obtained by solving a nonlinear non-autonomous differential equation. | 1209.1733v1 |
2012-12-28 | Turbulence-Induced Instabilities in EP and QGP | Polarization properties of turbulent stochastically inhomogeneous
ultrarelativistic QED plasma are studied. It is shown that the sign of
nonlinear turbulent Landau damping corresponds to an instability of the
spacelike modes and, for sufficiently large turbulent fields, to an actual
instability of a system. | 1212.6555v1 |
2013-02-26 | Spin Mixing in Spinor Fermi Gases | We study a spinor fermionic system under the effect of spin-exchange
interaction. We focus on the interplay between the spin-exchange interaction
and the effective quadratic Zeeman shift. We examine the static and the dynamic
properties of both two- and many-body system. We find that the spin-exchange
interaction induces coherent Rabi oscillation in the two-body system, but the
oscillation is quickly damped when the system is extended to the many-body
case. | 1302.6549v1 |
2013-03-12 | Damped jump-telegraph processes | We study a one-dimensional Markov modulated random walk with jumps. It is
assumed that amplitudes of jumps as well as a chosen velocity regime are random
and depend on a time spent by the process at a previous state of the underlying
Markov process.
Equations for the distribution and equations for its moments are derived. We
characterise the martingale distributions in terms of observable proportions
between jump and velocity regimes. | 1303.2796v1 |
2013-03-14 | Drag and Diffusion coefficients in extreme scenarios of temperature and chemical potential | A comparative study of high and zero temperature plasma for the case of
damping rate, drag and diffusion coefficients have been presented. In each of
these quantities, it is revealed how the magnetic interaction dominates over
the electric one at zero temperature unlike what happens at high temperature. | 1303.3353v1 |
2013-05-19 | On Collective Properties of Turbulent QED Plasma | Polarization properties of turbulent stochastically inhomogeneous
ultrarelativistic QED plasma are studied. It is shown that the sign of
nonlinear turbulent Landau damping corresponds to an instability of the
spacelike modes and, for sufficiently large turbulent fields, to an actual
instability of a system. Modification of plasmon dispersion relations due to
turbulent effects are studied. | 1305.4414v1 |
2013-06-17 | Uniformly polynomially stable approximations for a class of second order evolution equations | In this paper we study time semi-discrete approximations of a class of
polynomially stable infinite dimensional systems modeling the damped
vibrations. We prove that adding a suitable numerical viscosity term in the
numerical scheme, one obtains approximations that are uniformly polynomially
stable with respect to the discretization parameter. | 1306.3807v1 |
2013-08-21 | Overstable Librations can account for the Paucity of Mean Motion Resonances among Exoplanet Pairs | We assess the multi-planet systems discovered by the Kepler satellite in
terms of current ideas about orbital migration and eccentricity damping due to
planet-disk interactions. Our primary focus is on mean motion resonances. Only
a few percent of planet pairs are in close proximity to a resonance. However,
predicted migration rates (parameterized by $\tau_n=n/{|\dot n|}$) imply that
during convergent migration most planets would have been captured into first
order resonances. Eccentricity damping (parameterized by $\tau_e=e/{|\dot e|}$)
offers a plausible resolution. Estimates suggest $\tau_e/\tau_n\sim (h/a)^2\sim
10^{-2}$, where $h/a$ is the ratio of disk thickness to radius. Together,
eccentricity damping and orbital migration give rise to an equilibrium
eccentricity, $e_{eq}\sim(\tau_e/\tau_n)^{1/2}$. Capture is permanent provided
$e_{eq}\lesssim \mu^{1/3}$, where $\mu$ denotes the planet to star mass ratio.
But for $e_{eq}\gtrsim \mu^{1/3}$, capture is only temporary because librations
around equilibrium are overstable and lead to passage through resonance on
timescale $\tau_e$. Most Kepler planet pairs have $e_{eq}>\mu^{1/3}$. Since
$\tau_n>> \tau_e$ is the timescale for migration between neighboring
resonances, only a modest percentage of pairs end up trapped in resonances
after the disk disappears. Planet pairs close to a mean motion resonance
typically exhibit period ratios 1-2% larger than those for exact resonance. The
direction of this shift undoubtedly reflects the same asymmetry that requires
convergent migration for resonance capture. Permanent resonance capture at
these separations from exact resonance would demand $\mu
(\tau_n/\tau_e)^{1/2}\gtrsim 0.01$, a value that estimates of $\mu$ from
transit data and $(\tau_e/\tau_n)^{1/2}$ from theory are insufficient to match.
Plausible alternatives involve eccentricity damping during or after disk
dispersal. (Abridged) | 1308.4688v2 |
2013-08-30 | Nested Head-Tail Vlasov Solver | Nested Head-Tail (NHT) is a Mathematica-based Vlasov solver for transverse
oscillations in multi-bunch beams. It takes into account azimuthal, radial,
coupled-bunch and beam-beam degrees of freedom, single- and inter-bunch dipole
wakes, an arbitrary damper, beam-beam effects and Landau damping. | 1309.0044v3 |
2013-09-24 | Attractors for damped quintic wave equations in bounded domains | The dissipative wave equation with a critical quintic nonlinearity in smooth
bounded three dimensional domain is considered. Based on the recent extension
of the Strichartz estimates to the case of bounded domains, the existence of a
compact global attractor for the solution semigroup of this equation is
established. Moreover, the smoothness of the obtained attractor is also shown. | 1309.6272v1 |
2013-09-30 | Harmonic oscillator: an analysis via Fourier series | The Fourier series method is used to solve the homogeneous equation governing
the motion of the harmonic oscillator. It is shown that the general solution to
the problem can be found in a surprisingly simple way for the case of the
simple harmonic oscillator. It is also shown that the damped harmonic
oscillator is susceptible to the analysis. | 1309.7918v1 |
2013-10-01 | Observations and predictions at CesrTA, and outlook for ILC | In this paper, we will describe some of the recent experimental measurements
[1, 2, 3] performed at CESRTA [4], and the supporting simulations, which probe
the interaction of the electron cloud with the stored beam. These experiments
have been done over a wide range of beam energies, emittances, bunch currents,
and fill patterns, to gather sufficient information to be able to fully
characterize the beam-electron-cloud interaction and validate the simulation
programs. The range of beam conditions is chosen to be as close as possible to
those of the ILC damping ring, so that the validated simulation programs can be
used to predict the performance of these rings with regard to electroncloud-
related phenomena. Using the new simulation code Synrad3D to simulate the
synchrotron radiation environment, a vacuum chamber design has been developed
for the ILC damping ring which achieves the required level of photoelectron
suppression. To determine the expected electron cloud density in the ring, EC
buildup simulations have been done based on the simulated radiation environment
and on the expected performance of the ILC damping ring chamber mitigation
prescriptions. The expected density has been compared with analytical estimates
of the instability threshold, to verify that the ILC damping ring vacuum
chamber design is adequate to suppress the electron cloud single-bunch
head-tail instability. | 1310.0261v1 |
2013-10-21 | A Critical History of Renormalization | The history of renormalization is reviewed with a critical eye, starting with
Lorentz's theory of radiation damping, through perturbative QED with Dyson,
Gell-Mann & Low, and others, to Wilson's formulation and Polchinski's
functional equation, and applications to "triviality", and dark energy in
cosmology. | 1310.5533v1 |
2013-10-27 | Fundamental limitations of half-metallicicity in spintronic materials | Zero-point spin fluctuations are shown to strongly influence the ground state
of ferromagnetic metals and to impose limitations for the fully spin polarized
state assumed in half-metallic ferromagnets, which may influence their
applications in spintronics. This phenomenon leads to the low-frequency Stoner
excitations and cause strong damping and softening of magnons in
magnetoresistive manganites observed experimentally. | 1310.7174v1 |
2013-12-13 | Probing Intergalactic Neutral Hydrogen by the Lyman Alpha Red Damping Wing of Gamma-Ray Burst 130606A Afterglow Spectrum at z = 5.913 | The unprecedentedly bright optical afterglow of GRB 130606A located by Swift
at a redshift close to the reionization era (z = 5.913) provides a new
opportunity to probe the ionization status of intergalactic medium (IGM). Here
we present an analysis of the red Ly alpha damping wing of the afterglow
spectrum taken by Subaru/FOCAS during 10.4-13.2 hr after the burst. We find
that the minimal model including only the baseline power-law and HI absorption
in the host galaxy does not give a good fit, leaving residuals showing concave
curvature in 8400-8900 A with an amplitude of about 0.6% of the flux. Such a
curvature in the short wavelength range cannot be explained either by
extinction at the host with standard extinction curves, intrinsic curvature of
afterglow spectra, or by the known systematic uncertainties in the observed
spectrum. The red damping wing by intervening HI gas outside the host can
reduce the residual by about 3 sigma statistical significance. We find that a
damped Ly alpha system is not favored as the origin of this intervening HI
absorption, from the observed Ly beta and metal absorption features. Therefore
absorption by diffuse IGM remains as a plausible explanation. A fit by a simple
uniform IGM model requires HI neutral fraction of f_HI ~ 0.1-0.5 depending on
the distance to the GRB host, implying high f_HI IGM associated with the
observed dark Gunn-Peterson (GP) troughs. This gives a new evidence that the
reionization is not yet complete at z ~ 6. | 1312.3934v3 |
2014-02-01 | Effects of stellar flybys on planetary systems: 3D modeling of the circumstellar disks damping effects | Stellar flybys in star clusters are suspected to affect the orbital
architecture of planetary systems causing eccentricity excitation and orbital
misalignment between the planet orbit and the equatorial plane of the star. We
explore whether the impulsive changes in the orbital elements of planets,
caused by an hyperbolic stellar flyby, can be fully damped by the circumstellar
disk surrounding the star. The time required to disperse stellar clusters is in
fact comparable to circumstellar disk's lifetime. We have modelled in 3D a
system made of a solar type star surrounded by a low density disk with a giant
planet embedded in it approached on a hyperbolic encounter trajectory by a
second star, of similar mass and with its own disk. We focus on extreme
configurations where a very deep stellar flyby perturbs a Jovian planet on an
external orbit. This allows to test in full the ability of the disk to erase
the effects of the stellar encounter. We find that the amount of mass lost by
the disk during the stellar flyby is less than in 2D models where a single disk
was considered due to the mass exchange between the two disks at the encounter.
The damping in eccentricity is slightly faster than in 2D models and it occurs
on timescales of the order of a few kyr. The only trace of the flyby left in
the planet system, after about 10^4 yr, is a small misalignment, lower than 9
degrees, between the star equatorial plane and the planet orbit. In a realistic
model based on 3D simulations of star--planet--disk interactions, we find that
stellar flybys cannot excite significant eccentricities and inclinations of
planets in stellar clusters. The circumstellar disks hosting the planets damp
on a short timescale all the step changes in the two orbital parameters
produced during any stellar encounter. All records of past encounters are
erased. | 1402.0077v1 |
2014-02-21 | Damping of electron Zitterbewegung in carbon nanotubes | Zitterbewegung (ZB, trembling motion) of electrons in semiconductor carbon
nanotubes is described taking into account dephasing processes. The density
matrix formalism is used for the theory. Differences between decay of ZB
oscillations due to electron localization and that due to dephasing are
discussed. | 1402.5393v1 |
2014-04-18 | Exponential mixing for the white - forced damped nonlinear wave equation | The paper is devoted to studying the stochastic nonlinear wave (NLW) equation
in a bounded domain D $\subset$ R3. We show that the Markov process associated
with the flow of solution has a unique stationary measure $\mu$, and the law of
any solution converges to $\mu$ with exponential rate in the dual-Lipschitz
norm | 1404.4697v1 |
2014-04-22 | A unique continuation result for the plate equation and an application | In this paper, we prove the unique continuation property for the weak
solution of the plate equation with non-smooth coefficients. Then, we apply
this result to study the global attractor for the semilinear plate equation
with a localized damping. | 1404.5586v3 |
2014-05-13 | Magneto-seismological insights into the penumbral chromosphere and evidence for wave damping in spicules | The observation of propagating magneto-hydrodynamic kink waves in magnetic
structures and measurement of their properties (amplitude, phase speed) can be
used to diagnose the plasma conditions in the neighbourhood of the magnetic
structure via magneto-seismology (MS). We aim to reveal properties of the
chromosphere/Transition Region above the sunspot penumbra using this technique.
Hinode observed a sunspot as it was crossing the limb, providing a unique side
on view of the sunspot atmosphere. The presence of large spicule-like jets is
evident in \ion{Ca}{II} H images. The jets are found to support transverse wave
motions that displace the central axis, which can be interpreted as a kink
wave. The properties of a wave event are measured and used to determine the
magnetic and density stratification along the structure. We also measure the
width of the spicule and the intensity profile along the structure. The
measured wave properties reveal an initial rapid increase in amplitude with
height above the solar surface, followed by a decrease in amplitude. The MS
inversion suggests this initial increase corresponds to large changes in
density and magnetic field strength. In addition, we provide the first
measurements of spicule width with height, which confirm that the spicule under
goes rapid expansion. The measured expansion shows good agreement with the
results from the MS. The observed variations in plasma parameters are suggested
to be partly due to the presence of a gravitational stratified, ambient
atmosphere. Combining width measurements with phase speed measurements implies
the observed decrease in wave amplitude at greater heights can be explained by
wave damping. Hence, we provide the first direct evidence of wave damping in
chromospheric spicules and the quality factor of the damping is found to be
significantly smaller than estimated coronal values. | 1405.3203v1 |
2014-05-27 | Interior feedback stabilization of wave equations with dynamic boundary delay | In this paper we consider an interior stabilization problem for the wave
equation with dynamic boundary delay.We prove some stability results under the
choice of damping operator. The proof of the main result is based on a
frequency domain method and combines a contradiction argument with the
multiplier technique to carry out a special analysis for the resolvent. | 1405.6865v2 |
2014-07-11 | Remark on stabilization of second order evolution equations by unbounded dynamic feedbacks and applications | In this paper we consider second order evolution equations with unbounded
dynamic feedbacks. Under a regularity assumption we show that observability
properties for the undamped problem imply decay estimates for the damped
problem. We consider both uniform and non uniform decay properties. | 1407.3070v1 |
2014-09-11 | Eliminating flutter for clamped von Karman plates immersed in subsonic flows | We address the long-time behavior of a non-rotational von Karman plate in an
inviscid potential flow. The model arises in aeroelasticity and models the
interaction between a thin, nonlinear panel and a flow of gas in which it is
immersed [6, 21, 23]. Recent results in [16, 18] show that the plate component
of the dynamics (in the presence of a physical plate nonlinearity) converge to
a global compact attracting set of finite dimension; these results were
obtained in the absence of mechanical damping of any type. Here we show that,
by incorporating mechanical damping the full flow-plate system, full
trajectories---both plate and flow---converge strongly to (the set of)
stationary states. Weak convergence results require "minimal" interior damping,
and strong convergence of the dynamics are shown with sufficiently large
damping. We require the existence of a "good" energy balance equation, which is
only available when the flows are subsonic. Our proof is based on first showing
the convergence properties for regular solutions, which in turn requires
propagation of initial regularity on the infinite horizon. Then, we utilize the
exponential decay of the difference of two plate trajectories to show that full
flow-plate trajectories are uniform-in-time Hadamard continuous. This allows us
to pass convergence properties of smooth initial data to finite energy type
initial data. Physically, our results imply that flutter (a non-static end
behavior) does not occur in subsonic dynamics. While such results were known
for rotational (compact/regular) plate dynamics [14] (and references therein),
the result presented herein is the first such result obtained for
non-regularized---the most physically relevant---models. | 1409.3308v5 |
2014-12-15 | Optomechanical laser cooling with mechanical modulations | We theoretically study the laser cooling of cavity optomechanics when the
mechanical resonance frequency and damping depend on time. In the regime of
weak optomechanical coupling we extend the theory of laser cooling using an
adiabatic approximation. We discuss the modifications of the cooling dynamics
and compare it with numerical simulations in a wide range of modulation
frequencies. | 1412.4497v1 |
2015-03-08 | An Analytical Formulation of Power System Oscillation Frequency | This letter proposes an analytical approach to formulate the power system
oscillation frequency under a large disturbance. A fact is revealed that the
oscillation frequency is only the function of the oscillation amplitude when
the system's model and operating condition are fixed. Case studies also show
that this function is damping-insensitive and could be applied to an inter-area
model of a multi-machine power system. | 1503.07554v1 |
2015-04-07 | Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque | Spin-orbit effects [1-4] have the potential of radically changing the field
of spintronics by allowing transfer of spin angular momentum to a whole new
class of materials. In a seminal letter to Nature [5], Kajiwara et al. showed
that by depositing Platinum (Pt, a normal metal) on top of a 1.3 $\mu$m thick
Yttrium Iron Garnet (YIG, a magnetic insulator), one could effectively transfer
spin angular momentum through the interface between these two different
materials. The outstanding feature was the detection of auto-oscillation of the
YIG when enough dc current was passed in the Pt. This finding has created a
great excitement in the community for two reasons: first, one could control
electronically the damping of insulators, which can offer improved properties
compared to metals, and here YIG has the lowest damping known in nature;
second, the damping compensation could be achieved on very large objects, a
particularly relevant point for the field of magnonics [6,7] whose aim is to
use spin-waves as carriers of information. However, the degree of coherence of
the observed auto-oscillations has not been addressed in ref. [5]. In this
work, we emphasize the key role of quasi-degenerate spin-wave modes, which
increase the threshold current. This requires to reduce both the thickness and
lateral size in order to reach full damping compensation [8] , and we show
clear evidence of coherent spin-orbit torque induced auto-oscillation in
micron-sized YIG discs of thickness 20 nm. | 1504.01512v1 |
2015-05-01 | Periodic solutions for nonlinear hyperbolic evolution systems | We shall deal with the periodic problem for nonlinear perturbations of
abstract hyperbolic evolution equations generating an evolution system of
contractions. We prove an averaging principle for the translation along
trajectories operator associated to the nonlinear evolution system, expressed
in terms of the topological degree. The abstract results shall be applied to
the damped hyperbolic partial differential equation. | 1505.00150v1 |
2015-05-28 | Moore-Gibson-Thompson equation with memory, part I: exponential decay of energy | We are interested in the Moore-Gibson-Thompson(MGT) equation with memory
\begin{equation}\nonumber \tau u_{ttt}+ \alpha u_{tt}+c^2\A u+b\A u_t
-\int_0^tg(t-s)\A w(s)ds=0. \end{equation} We first classify the memory into
three types. Then we study how a memory term creates damping mechanism and how
the memory causes energy decay. | 1505.07523v1 |
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