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1996-11-25 | Damping rates of hard momentum particles in a cold ultrarelativistic plasma | We compute the damping rates of one-particle excitations in a cold
ultrarelativistic plasma to leading order in the coupling constant e for three
types of interaction: Yukawa coupling to a massless scalar boson, QED and QCD.
Damping rates of charged particles in QED and QCD are of order e^3 mu, while
damping rates of other particles are of order e^4 mu or e^4 mu log(1/e). We
find that the damping rate of an electron or of a quark is constant far from
the Fermi surface, and decreases linearly with the excitation energy close to
the Fermi surface. This unusual behavior is attributed to the long-range
magnetic interactions. | 9611415v2 |
1999-09-24 | Gauge Invariance of Nonlinear Landau Damping Rate of Bose Excitations in Quark-Gluon Plasma | On the basis of the approximate dynamical equations describing the behavior
of quark-gluon plasma (QGP) in the semiclassical limit and Yang-Mills equation,
the kinetic equation for longitudinal waves (plasmons) is obtained. With the
Ward identities the gauge invariance of obtained nonlinear Landau damping rate
is proved. The physical mechanisms defining nonlinear scattering of a plasmon
by QGP particles are analyzed. The problem on a connection of nonlinear Landau
damping rate of longitudinal oscillations with damping rate, obtained in the
framework of hard thermal loops approximation, is considered. It is shown that
the gauge-dependent part of nonlinear Landau damping rate for the plasmons with
zero momentum vanishes on mass-shell. | 9909505v1 |
2005-07-16 | Sharp estimates for the number of degrees of freedom for the damped-driven 2D Navier--Stokes equations | We derive upper bounds for the number of asymptotic degrees (determining
modes and nodes) of freedom for the two-dimensional Navier--Stokes system and
Navier-Stokes system with damping. In the first case we obtain the previously
known estimates in an explicit form, which are larger than the fractal
dimension of the global attractor. However, for the Navier--Stokes system with
damping our estimates for the number of the determining modes and nodes are
comparable to the sharp estimates for the fractal dimension of the global
attractor. Our investigation of the damped-driven 2D Navier--Stokes system is
inspired by the Stommel--Charney barotropic model of ocean circulation where
the damping represents the Rayleigh friction. We remark that our results
equally apply to the Stommel--Charney model. | 0507327v1 |
2006-12-04 | A singular perturbation approach for choosing PageRank damping factor | The choice of the PageRank damping factor is not evident. The Google's choice
for the value c=0.85 was a compromise between the true reflection of the Web
structure and numerical efficiency. However, the Markov random walk on the
original Web Graph does not reflect the importance of the pages because it
absorbs in dead ends. Thus, the damping factor is needed not only for speeding
up the computations but also for establishing a fair ranking of pages. In this
paper, we propose new criteria for choosing the damping factor, based on the
ergodic structure of the Web Graph and probability flows. Specifically, we
require that the core component receives a fair share of the PageRank mass.
Using singular perturbation approach we conclude that the value c=0.85 is too
high and suggest that the damping factor should be chosen around 1/2. As a
by-product, we describe the ergodic structure of the OUT component of the Web
Graph in detail. Our analytical results are confirmed by experiments on two
large samples of the Web Graph. | 0612079v1 |
1998-10-26 | Microscopic Structure of Rotational Damping | The damping of collective rotational motion is studied microscopically,
making use of shell model calculations based on the cranked Nilsson deformed
mean-field and on residual two-body interactions, and focusing on the shape of
the gamma-gamma correlation spectra and on its systematic behavior. It is shown
that the spectral shape is directly related to the damping width of collective
rotation, \Gammarot, and to the spreading width of many-particle many-hole
configurations, \Gammamu. The rotational damping width is affected by the shell
structure, and is very sensitive to the position of the Fermi surface, besides
mass number, spin and deformation. This produces a rich variety of features in
the rotational damping phenomena. | 9810066v1 |
2004-07-25 | Rotational damping in a multi-$j$ shell particles-rotor model | The damping of collective rotational motion is investigated by means of
particles-rotor model in which the angular momentum coupling is treated exactly
and the valence nucleons are in a multi-$j$ shell mean-field. It is found that
the onset energy of rotational damping is around 1.1 MeV above yrast line, and
the number of states which form rotational band structure is thus limited. The
number of calculated rotational bands around 30 at a given angular momentum
agrees qualitatively with experimental data. The onset of rotational damping
takes place gradually as a function of excitation energy. It is shown that the
pairing correlation between valence nucleons has a significant effect on the
appearance of rotational damping. | 0407089v3 |
2001-07-19 | Manifold Damping of Transverse Wakefields in High Phase Advance Traveling Wave Structures and Local Damping of Dipole Wakefields in Standing Wave Accelerators | Operating the SLAC/KEK DDS (Damped Detuned Structure) X-band linacs at high
gradients (in excess of 70MV/m) has recently been found to be limited by the
accelerator structures breaking down and as a consequence severe damage occurs
to the cells which makes the structures inoperable. A series of recent
experiments at SLAC indicates that arcing in the structures is significantly
reduced if the group velocity of the accelerating mode is reduced and
additionally it has been discovered that reducing the length of the
accelerating structure also limits the number and intensity of breakdown events
[1]. However, in designing new accelerating structures care must be taken to
ensure that the beam-induced transverse wakefields do not cause the beam to
become unstable. Here, we report on damping transverse wakefields in two
different short structures: a 90cm traveling wave structure in which the
wakefield is coupled out to four attached manifolds and secondly, in a standing
wave structure in which a limited number of cells heavily damp down the
wakefield.
[1] C. Adolphsen, ROAA003, this conf. | 0107048v1 |
2002-06-28 | Manifold Damping Of Wakefields In High Phase Advance Linacs For The NLC | Earlier RDDS (Rounded Damped Detuned Structures) [1,2], designed, fabricated
and tested at SLAC, in collaboration with KEK, have been shown to damp
wakefields successfully. However, electrical breakdown has been found to occur
in these structures and this makes them inoperable at the desired gradient.
Recent results [3] indicate that lowering the group velocity of the
accelerating mode reduces electrical breakdown events. In order to preserve the
filling time of each structure a high synchronous phase advance (150 degrees as
opposed to 120 used in previous NLC designs) has been chosen. Here, damping of
the wakefield is analyzed. Manifold damping and interleaving of structure cell
frequencies is discussed. These wakefields impose alignment tolerances on the
cells and on the structure as a whole. Tolerance calculations are performed and
these are compared with analytic estimations. | 0206090v1 |
2006-06-30 | Nonlinear Damping of the LC Circuit using Anti-parallel Diodes | We investigate a simple variation of the series RLC circuit in which
anti-parallel diodes replace the resistor. This results in a damped harmonic
oscillator with a nonlinear damping term that is maximal at zero current and
decreases with an inverse current relation for currents far from zero. A set of
nonlinear differential equations for the oscillator circuit is derived and
integrated numerically for comparison with circuit measurements. The agreement
is very good for both the transient and steady-state responses. Unlike the
standard RLC circuit, the behavior of this circuit is amplitude dependent. In
particular for the transient response the oscillator makes a transition from
under-damped to over-damped behavior, and for the driven oscillator the
resonance response becomes sharper and stronger as drive source amplitude
increases. The equipment is inexpensive and common to upper level physics labs. | 0606261v1 |
1995-11-11 | A New Look at the Landau's Theory of Spreading and Damping of Waves in Collisionless Plasmas | The theory of plasma waves and Landau damping in Maxwellian plasmas, Landau's
``rule of pass around poles'' include doubtful statements, particularly related
to an artificial ``constructing'' of the dispersion equation, what should allow
the possibility of its solution otherwise not existing at all, and the
possibility of analytical continuations of corresponding very specific ruptured
functions in the one-dimensional Laplace transformation, used by Landau, what
is the base of his theory.
We represent, as an accessible variant, a more general alternative theory
based on a two-dimensional Laplace transformation, leading to an asymptotical
in time and space solution as a complicated superposition of coupled damping
and {\em non-damping \/} plane waves and oscillations with different dispersion
laws for every constituent mode. This theory naturally and very simply explains
paradoxes of the phenomenon of plasma echo. We propose for discussion a new
ideology of plasma waves (both electron and ion-acoustic waves) qualitatively
different from the traditional theory of Landau damping for non-collisional as
well as for low-collisional plasmas. | 9511001v1 |
2001-07-27 | Quantum limits of cold damping with optomechanical coupling | Thermal noise of a mirror can be reduced by cold damping. The displacement is
measured with a high-finesse cavity and controlled with the radiation pressure
of a modulated light beam. We establish the general quantum limits of noise in
cold damping mechanisms and we show that the optomechanical system allows to
reach these limits. Displacement noise can be arbitrarily reduced in a narrow
frequency band. In a wide-band analysis we show that thermal fluctuations are
reduced as with classical damping whereas quantum zero-point fluctuations are
left unchanged. The only limit of cold damping is then due to zero-point energy
of the mirror | 0107138v2 |
2005-05-20 | A symmetric treatment of damped harmonic oscillator in extended phase space | Extended phase space (EPS) formulation of quantum statistical mechanics
treats the ordinary phase space coordinates on the same footing and thereby
permits the definite the canonical momenta conjugate to these coordinates . The
extended lagrangian and extended hamiltonian are defined in EPS by the same
procedure as one does for ordinary lagrangian and hamiltonian. The combination
of ordinary phase space and their conjugate momenta exhibits the evolution of
particles and their mirror images together. The resultant evolution equation in
EPS for a damped harmonic oscillator, is such that the energy dissipated by the
actual oscillator is absorbed in the same rate by the image oscillator leaving
the whole system as a conservative system. We use the EPS formalism to obtain
the dual hamiltonian of a damped harmonic oscillator, first proposed by
Batemann, by a simple extended canonical transformations in the extended phase
space. The extended canonical transformations are capable of converting the
damped system of actual and image oscillators to an undamped one, and transform
the evolution equation into a simple form. The resultant equation is solved and
the eigenvalues and eigenfunctions for damped oscillator and its mirror image
are obtained. The results are in agreement with those obtained by Bateman. At
last, the uncertainty relation are examined for above system. | 0505147v1 |
2007-08-28 | Pattern formation in the damped Nikolaevskiy equation | The Nikolaevskiy equation has been proposed as a model for seismic waves,
electroconvection and weak turbulence; we show that it can also be used to
model transverse instabilities of fronts. This equation possesses a large-scale
"Goldstone" mode that significantly influences the stability of spatially
periodic steady solutions; indeed, all such solutions are unstable at onset,
and the equation exhibits so-called soft-mode turbulence. In many applications,
a weak damping of this neutral mode will be present, and we study the influence
of this damping on solutions to the Nikolaevskiy equation. We examine the
transition to the usual Eckhaus instability as the damping of the large-scale
mode is increased, through numerical calculation and weakly nonlinear analysis.
The latter is accomplished using asymptotically consistent systems of coupled
amplitude equations. We find that there is a critical value of the damping
below which (for a given value of the supercriticality parameter) all periodic
steady states are unstable. The last solutions to lose stability lie in a cusp
close to the left-hand side of the marginal stability curve. | 0708.3735v1 |
2008-01-12 | Strong and weak coupling limits in optics of quantum well excitons | A transition between the strong (coherent) and weak (incoherent) coupling
limits of resonant interaction between quantum well (QW) excitons and bulk
photons is analyzed and quantified as a function of the incoherent damping rate
caused by exciton-phonon and exciton-exciton scattering. For confined QW
polaritons, a second, anomalous, damping-induced dispersion branch arises and
develops with increasing damping. In this case, the strong-weak coupling
transition is attributed to a critical damping rate, when the intersection of
the normal and damping-induced dispersion branches occurs. For the radiative
states of QW excitons, i.e., for radiative QW polaritons, the transition is
described as a qualitative change of the photoluminescence spectrum at grazing
angles along the QW structure. Furthermore, we show that the radiative
corrections to the QW exciton states with in-plane wavevector approaching the
photon cone are universally scaled by an energy parameter rather than diverge.
The strong-weak coupling transition rates are also proportional to the same
energy parameter. The numerical evaluations are given for a GaAs single quantum
well with realistic parameters. | 0801.1895v2 |
2008-01-22 | Damped Bloch Oscillations of Bose-Einstein Condensates in Disordered Potential Gradients | We investigate both experimentally and theoretically disorder induced damping
of Bloch oscillations of Bose-Einstein condensates in optical lattices. The
spatially inhomogeneous force responsible for the damping is realised by a
combination of a disordered optical and a magnetic gradient potential. We show
that the inhomogeneity of this force results in a broadening of the
quasimomentum spectrum, which in turn causes damping of the centre-of-mass
oscillation. We quantitatively compare the obtained damping rates to the
simulations using the Gross-Pitaevskii equation. Our results are relevant for
high precision experiments on very small forces, which require the observation
of a large number of oscillation cycles. | 0801.3437v2 |
2008-02-26 | Fractional Langevin Equation: Over-Damped, Under-Damped and Critical Behaviors | The dynamical phase diagram of the fractional Langevin equation is
investigated for harmonically bound particle. It is shown that critical
exponents mark dynamical transitions in the behavior of the system. Four
different critical exponents are found. (i) $\alpha_c=0.402\pm 0.002$ marks a
transition to a non-monotonic under-damped phase, (ii) $\alpha_R=0.441...$
marks a transition to a resonance phase when an external oscillating field
drives the system, (iii) $\alpha_{\chi_1}=0.527...$ and (iv)
$\alpha_{\chi_2}=0.707...$ marks transition to a double peak phase of the
"loss" when such an oscillating field present. As a physical explanation we
present a cage effect, where the medium induces an elastic type of friction.
Phase diagrams describing over-damped, under-damped regimes, motion and
resonances, show behaviors different from normal. | 0802.3777v1 |
2008-04-26 | Vibrational modes of metal nanoshells and bimetallic core-shell nanoparticles | We study theoretically spectrum of radial vibrational modes in composite
metal nanostructures such as bimetallic core-shell particles and metal
nanoshells with dielectric core in an environment. We calculate frequencies and
damping rates of fundamental (breathing) modes for these nanostructures along
with those of two higher-order modes. For metal nanoshells, we find that the
breathing mode frequency is always lower than the one for solid particles of
the same size, while the damping is higher and increases with reduction of the
shell thickness. We identify two regimes that can be characterized as weakly
damped and overdamped vibrations in the presence of external medium. For
bimetalllic particles, we find periodic dependence of frequency and damping
rate on the shell thickness with period determined by mode number. For both
types of nanostructures, the frequency of higher modes is nearly independent of
the environment, while the damping rate shows strong sensitivity to outside
medium. | 0804.4249v2 |
2008-09-26 | Damping of the baryon acoustic oscillations in the matter power spectrum as a probe of the growth factor | We investigate the damping of the baryon acoustic oscillations (BAO)
signature in the matter power spectrum due to the quasi-nonlinear clustering of
density perturbations. On the basis of the third order perturbation theory, we
construct a fitting formula of the damping in an analytic way. This
demonstrates that the damping is closely related with the growth factor and the
amplitude of the matter power spectrum. Then, we investigate the feasibility of
constraining the growth factor through a measurement of the damping of the BAO
signature. An extension of our formula including higher order corrections of
density perturbations is also discussed. | 0809.4538v2 |
2008-10-07 | Corotational Damping of Diskoseismic C-modes in Black Hole Accretion Discs | Diskoseismic c-modes in accretion discs have been invoked to explain
low-frequency variabilities observed in black-hole X-ray binaries. These modes
are trapped in the inner-most region of the disc and have frequencies much
lower than the rotation frequency at the disc inner radius. We show that
because the trapped waves can tunnel through the evanescent barrier to the
corotational wave zone, the c-modes are damped due to wave absorption at the
corotation resonance. We calculate the corotational damping rates of various
c-modes using the WKB approximation. The damping rate varies widely depending
on the mode frequency, the black hole spin parameter and the disc sound speed,
and is generally much less than 10% of the mode frequency. A sufficiently
strong excitation mechanism is needed to overcome this corotational damping and
make the mode observable. | 0810.1299v3 |
2008-10-10 | Non-standard conserved Hamiltonian structures in dissipative/damped systems : Nonlinear generalizations of damped harmonic oscillator | In this paper we point out the existence of a remarkable nonlocal
transformation between the damped harmonic oscillator and a modified Emden type
nonlinear oscillator equation with linear forcing, $\ddot{x}+\alpha
x\dot{x}+\beta x^3+\gamma x=0,$ which preserves the form of the time
independent integral, conservative Hamiltonian and the equation of motion.
Generalizing this transformation we prove the existence of non-standard
conservative Hamiltonian structure for a general class of damped nonlinear
oscillators including Li\'enard type systems. Further, using the above
Hamiltonian structure for a specific example namely the generalized modified
Emden equation $\ddot{x}+\alpha x^q\dot{x}+\beta x^{2q+1}=0$, where $\alpha$,
$\beta$ and $q$ are arbitrary parameters, the general solution is obtained
through appropriate canonical transformations. We also present the conservative
Hamiltonian structure of the damped Mathews-Lakshmanan oscillator equation. The
associated Lagrangian description for all the above systems is also briefly
discussed. | 0810.1819v2 |
2008-11-05 | R-matrix inner-shell electron-impact excitation of Fe$^{15+}$ including Auger-plus-radiation damping | We present results for the inner-shell electron-impact excitation of
Fe$^{15+}$ using the intermediate-coupling frame transformation {\it R}-matrix
approach in which Auger-plus-radiation damping has been included. The target
and close-coupling expansions are both taken to be the 134 levels belonging to
the configurations ${\rm 2s^22p^63}l$, ${\rm 2s^22p^53s3}l$, ${\rm
2s^22p^53p^2}$ and ${\rm 2s^22p^53p3d}$. The comparison of Maxwell-averaged
effective collision strengths with and without damping shows that the damping
reduction is about 30-40% for many transitions at low temperatures, but up to
80% for a few transitions. As a consequence, the results of previous Dirac
$R$-matrix calculations (Aggarwal and Keenan, 2008) overestimate the effective
collision strengths due to their omission of Auger-plus-radiation damping. | 0811.0750v1 |
2009-03-11 | An alternate design for CLIC main linac wakefield suppression | The present design of the main accelerating structure for CLIC is based on
heavy damping (WDS) with a Q of ~10. The wakefield suppression in this case
entails locating the damping materials in relatively close proximity to the
accelerating cells. Herein we present an alternate design for the main
accelerating structures. We detune the lowest dipole band by prescribing a
Gaussian distribution to the cell parameters and consider moderate damping
Q~500 to prevent the recoherence of the modes; in this case the damping
materials can be located at an extended distance from the accelerating
structure. The procedure to achieve a well-damped wakefield is described.
Results are presented elucidating the various designs including the current one
which is being developed to incorporate r.f. breakdown, pulse surface heating
and beam dynamics constraints. | 0903.1935v1 |
2009-04-17 | Revealing Sub-Surface Vibrational Modes by Atom-Resolved Damping Force Spectroscopy | We propose to use the damping signal of an oscillating cantilever in dynamic
atomic force microscopy as a noninvasive tool to study the vibrational
structure of the substrate. We present atomically resolved maps of damping in
carbon nanotube peapods, capable of identifying the location and packing of
enclosed Dy@C82 molecules as well as local excitations of vibrational modes
inside nanotubes of different diameter. We elucidate the physical origin of
damping in a microscopic model and provide quantitative interpretation of the
observations by calculating the vibrational spectrum and damping of Dy@C82
inside nanotubes with different diameters using ab initio total energy and
molecular dynamics calculations. | 0904.2666v1 |
2009-08-04 | Time domain detection of pulsed spin torque damping reduction | Combining multiple ultrafast spin torque impulses with a 5 nanosecond
duration pulse for damping reduction, we observe time-domain precession which
evolves from an initial 1 ns duration transient with changing precessional
amplitude to constant amplitude oscillations persisting for over 2 ns. These
results are consistent with relaxation of the transient trajectories to a
stable orbit with nearly zero damping. We find that in order to observe
complete damping cancellation and the transient behavior in a time domain
sampling measurement, a short duration, fast rise-time pulse is required to
cancel damping without significant trajectory dephasing. | 0908.0481v1 |
2009-10-02 | Damping of a nanomechanical oscillator strongly coupled to a quantum dot | We present theoretical and experimental results on the mechanical damping of
an atomic force microscope cantilever strongly coupled to a self-assembled InAs
quantum dot. When the cantilever oscillation amplitude is large, its motion
dominates the charge dynamics of the dot which in turn leads to nonlinear,
amplitude-dependent damping of the cantilever. We observe highly asymmetric
lineshapes of Coulomb blockade peaks in the damping that reflect the degeneracy
of energy levels on the dot, in excellent agreement with our strong coupling
theory. Furthermore, we predict that excited state spectroscopy is possible by
studying the damping versus oscillation amplitude, in analogy to varying the
amplitude of an ac gate voltage. | 0910.0308v1 |
2010-01-27 | The spatial damping of magnetohydrodynamic waves in a flowing partially ionised prominence plasma | Solar prominences are partially ionised plasmas displaying flows and
oscillations. These oscillations show time and spatial damping and, commonly,
have been explained in terms of magnetohydrodynamic (MHD) waves. We study the
spatial damping of linear non-adiabatic MHD waves in a flowing partially
ionised plasma, having prominence-like physical properties. We consider single
fluid equations for a partially ionised hydrogen plasma including in the energy
equation optically thin radiation, thermal conduction by electrons and
neutrals, and heating. Keeping the frequency real and fixed, we have solved the
obtained dispersion relations for the complex wavenumber, k, and have analysed
the behaviour of the damping length, wavelength and the ratio of the damping
length to the wavelength, versus period, for Alfven, fast, slow and thermal
waves. | 1001.4962v1 |
2010-03-04 | Internal dissipation of a polymer | The dynamics of flexible polymer molecules are often assumed to be governed
by hydrodynamics of the solvent. However there is considerable evidence that
internal dissipation of a polymer contributes as well. Here we investigate the
dynamics of a single chain in the absence of solvent to characterize the nature
of this internal friction. We model the chains as freely hinged but with
localized bond angles and 3-fold symmetric dihedral angles. We show that the
damping is close but not identical to Kelvin damping, which depends on the
first temporal and second spatial derivative of monomer position. With no
internal potential between monomers, the magnitude of the damping is small for
long wavelengths and weakly damped oscillatory time dependent behavior is seen
for a large range of spatial modes. When the size of the internal potential is
increased, such oscillations persist, but the damping becomes larger. However
underdamped motion is present even with quite strong dihedral barriers for long
enough wavelengths. | 1003.0944v2 |
2010-05-26 | Indirect Evidence for Lévy Walks in Squeeze Film Damping | Molecular flow gas damping of mechanical motion in confined geometries, and
its associated noise, is important in a variety of fields, including precision
measurement, gravitational wave detection, and MEMS devices. We used two
torsion balance instruments to measure the strength and distance-dependence of
`squeeze film' damping. Measured quality factors derived from free decay of
oscillation are consistent with gas particle superdiffusion in L\'evy walks and
inconsistent with those expected from traditional Gaussian random walk particle
motion. The distance-dependence of squeeze film damping observed in our
experiments is in agreement with a parameter-free Monte Carlo simulation. The
squeeze film damping of the motion of a plate suspended a distance d away from
a parallel surface scales with a fractional power between 1/d and 1/d^2. | 1005.4926v2 |
2010-05-28 | Gravitational wave asteroseismology with fast rotating neutron stars | We investigate damping and growth times of the f-mode for rapidly rotating
stars and a variety of different polytropic equations of state in the Cowling
approximation. We discuss the differences in the eigenfunctions of co- and
counterrotating modes and compute the damping times of the f-mode for several
EoS and all rotation rates up to the Kepler-limit. This is the first study of
the damping/growth time of this type of oscillations for fast rotating neutron
stars in a general relativistic framework. We use these frequencies and
damping/growth times to create robust empirical formulae which can be used for
gravitational wave asteroseismology. The estimation of the damping/growth time
is based on the quadrupole formula and our results agree very well with
Newtonian ones in the appropriate limit. | 1005.5228v3 |
2010-06-09 | Synchrotron oscillation damping due to beam-beam collisions | In DA{\Phi}NE, the Frascati e+/e- collider, the crab waist collision scheme
has been successfully implemented in 2008 and 2009. During the collision
operations for Siddharta experiment, an unusual synchrotron damping effect has
been observed. Indeed, with the longitudinal feedback switched off, the
positron beam becomes unstable with beam currents in the order of 200-300 mA.
The longitudinal instability is damped by bringing the positron beam in
collision with a high current electron beam (~2A). Besides, we have observed a
shift of \approx 600Hz in the residual synchrotron sidebands. Precise
measurements have been performed by using both a commercial spectrum analyzer
and the diagnostics capabilities of the DA{\Phi}NE longitudinal bunch-by-bunch
feedback. This damping effect has been observed in DA{\Phi}NE for the first
time during collisions with the crab waist scheme. Our explanation is that beam
collisions with a large crossing angle produce a longitudinal tune shift and a
longitudinal tune spread, providing Landau damping of synchrotron oscillations. | 1006.1783v1 |
2010-06-30 | Landau Damping of Baryon Structure Formation in the Post Reionization Epoch | It has been suggested by Chen and Lai that the proper description of the
large scale structure formation of the universe in the post-reionization era,
which is conventionally characterized via gas hydrodynamics, should include the
plasma collective effects in the formulation. Specifically, it is the combined
pressure from the baryon thermal motions and the residual long-range
electrostatic potentials resulted from the imperfect Debye shielding, that
fights against the gravitational collapse. As a result, at small-scales the
baryons would oscillate at the ion-acoustic, instead of the conventional
neutral acoustic, frequency. In this paper we extend and improve the Chen-Lai
formulation with the attention to the Landau damping of the ion-acoustic
oscillations. Since T_e \sim T_i in the post-reionization era, the ion acoustic
oscillations would inevitably suffer the Landau damping which severely
suppresses the baryon density spectrum in the regimes of intermediate and high
wavenumber k. To describe this Landau-damping phenomenon more appropriately, we
find it necessary to modify the filtering wavenumber k_f in our analysis. It
would be interesting if our predicted Landau damping of the ion-acoustic
oscillations can be observed at high redshifts. | 1006.5777v1 |
2010-07-12 | Passive damping of beam vibrations through distributed electric networks and piezoelectric transducers: prototype design and experimental validation | The aim of this work is two-fold: to design devices for passive electric
damping of structural vibrations by distributed piezoelectric transducers and
electric networks, and to experimentally validate the effectiveness of such a
damping concept. Two different electric networks are employed, namely a purely
resistive network and an inductive-resistive one. The presented devices can be
considered as distributed versions of the well-known resistive and resonant
shunt of a single piezoelectric transducer. The technicalfeasibility and
damping effectiveness of the proposed novel devices are assessed through the
construction of an experimental prototype. Experimental results are shown to be
in very good agreement with theoretical predictions. It is proved that the
presented technique allows for a substantial reduction in the inductances used
when compared with those required by the single resonant shunted transducer. In
particular, it is shown that the required inductance decreases when the number
of piezoelectric elements is increased. The electric networks are optimized in
order to reduce forced vibrations close to the first resonance frequency.
Nevertheless, the damping effectiveness for higher modes is experimentally
proved. As well as specific results, fundamental theoretical and experimental
considerations for passive distributed vibration control are provided. | 1007.1863v1 |
2010-07-23 | Highly-damped quasi-normal frequencies for piecewise Eckart potentials | Highly-damped quasi-normal frequencies are very often of the form omega_n =
(offset) + i n (gap). We investigate the genericity of this phenomenon by
considering a model potential that is piecewise Eckart (piecewise
Poeschl-Teller), and developing an analytic "quantization condition" for the
highly-damped quasi-normal frequencies. We find that this omega_n = (offset) +
i n (gap) behaviour is generic but not universal, with the controlling feature
being whether or not the ratio of the rates of exponential falloff in the two
asymptotic directions is a rational number. These observations are of direct
relevance to any physical situation where highly-damped quasi-normal modes
(damped modes) are important --- in particular (but not limited to) to black
hole physics, both theoretical and observational. | 1007.4039v2 |
2010-09-23 | Asymptotic Spectrum of Kerr Black Holes in the Small Angular Momentum Limit | We study analytically the highly damped quasinormal modes of Kerr black holes
in the small angular momentum limit. To check the previous analytic
calculations in the literature, which use a combination of radial and tortoise
coordinates, we reproduce all the results using the radial coordinate only.
According to the earlier calculations, the real part of the highly damped
quasinormal mode frequency of Kerr black holes approaches zero in the limit
where the angular momentum goes to zero. This result is not consistent with the
Schwarzschild limit where the real part of the highly damped quasinormal mode
frequency is equal to c^3 ln(3)/(8 pi G M). In this paper, our calculations
suggest that the highly damped quasinormal modes of Kerr black holes in the
zero angular momentum limit make a continuous transition from the Kerr value to
the Schwarzschild value. We explore the nature of this transition using a
combination of analytical and numerical techniques. Finally, we calculate the
highly damped quasinormal modes of the extremal case in which the topology of
Stokes/anti-Stokes lines takes a different form. | 1009.4632v2 |
2010-12-31 | Exact Tkachenko modes and their damping in the vortex lattice regime of rapidly rotating bosons | We have found an exact analytical solution of the Bogoliubov-de Gennes
equations for the Tkachenko modes of the vortex lattice in the lowest Landau
level (LLL) in the thermodynamic limit at any momenta and calculated their
damping rates. At finite temperatures both Beliaev and Landau damping leads to
momentum independent damping rates in the low-energy limit, which shows that at
sufficiently low energies Tkachenko modes become strongly damped. We then found
that the mean square fluctuations of the density grow logarithmically at large
distances, which indicates that the state is ordered in the vortex lattice only
on a finite (although exponentially large) distance scale and introduces a
low-momentum cut-off. Using this circumstance we showed that at finite
temperatures the one-body density matrix undergoes an exponential decay at
large distances. | 1101.0269v1 |
2011-01-20 | Decoherence and entanglement degradation of a qubit-qutrit system in non-inertial frames | We study the effect of decoherence on a qubit-qutrit system under the
influence of global, local and multilocal decoherence in non-inertial frames.
We show that the entanglement sudden death can be avoided in non-inertial
frames in the presence of amplitude damping, depolarizing and phase damping
channels. However, degradation of entanglement is seen due to Unruh effect. It
is shown that for lower level of decoherence, the depolarizing channel degrades
the entanglement more heavily as compared to the amplitude damping and phase
damping channels. However, for higher values of decoherence parameters,
amplitude damping channel heavily degrades the entanglement of the hybrid
system. Further more, no ESD is seen for any value of Rob's acceleration. | 1101.3986v1 |
2011-10-05 | Radiation damping in pulsed Gaussian beams | We consider the effects of radiation damping on the electron dynamics in a
Gaussian beam model of a laser field. For high intensities, i.e. with
dimensionless intensity a0 \gg 1, it is found that the dynamics divide into
three regimes. For low energy electrons (low initial {\gamma}-factor,
{\gamma}0) the radiation damping effects are negligible. At higher energies,
but still at 2{\gamma}0 < a0, the damping alters the final displacement and the
net energy change of the electron. For 2{\gamma}0 > a0 one is in a regime of
radiation reaction induced electron capture. This capture is found to be stable
with respect to the spatial properties of the electron beam and results in a
significant energy loss of the electrons. In this regime the plane wave model
of the laser field provides a good description of the dynamics, whereas for
lower energies the Gaussian beam and plane wave models differ significantly.
Finally the dynamics are considered for the case of an XFEL field. It is found
that the significantly lower intensities of such fields inhibits the damping
effects. | 1110.0996v1 |
2012-03-28 | Analysis of the absorbing layers for the weakly-compressible lattice Boltzmann schemes | It has been demonstrated that Lattice Boltzmann schemes (LBSs) are very
efficient for Computational AeroAcoustics (CAA). In order to handle the issue
of absorbing acoustic boundary conditions for LBS, three kinds of damping terms
are proposed and added into the right hand sides of the governing equations of
LBS. From the classical theory, these terms play an important role to absorb
and minimize the acoustic wave reflections from computational boundaries.
Meanwhile, the corresponding macroscopic equations with the damping terms are
recovered for analyzing the macroscopic behaviors of the these damping terms
and determining the critical absorbing strength. Further, in order to detect
the dissipation and dispersion behaviors, the linearized LBS with the damping
terms is derived and analyzed. The dispersive and dissipative properties are
explored in the wave-number spaces via the Von Neumann analysis. The related
damping strength critical values and the optimal absorbing term are addressed.
Finally, some benchmark problems are implemented to assess the theoretical
results. | 1203.6350v1 |
2012-04-11 | Formation of bremsstrahlung in an absorptive QED/QCD medium | The radiative energy loss of a relativistic charge in a dense, absorptive
medium can be affected significantly by damping phenomena. The effect is more
pronounced for large energies of the charge and/or large damping of the
radiation. This can be understood in terms of a competition between the
formation time of bremsstrahlung and a damping time scale. We discuss this
competition in detail for the absorptive QED and QCD medium, focusing on the
case in which the mass of the charge is large compared to the in-medium mass of
the radiation quanta. We identify the regions in energy and parameter space, in
which either coherence or damping effects are of major importance for the
radiative energy loss spectrum. We show that damping phenomena can lead to a
stronger suppression of the spectrum than coherence effects. | 1204.2469v2 |
2012-06-05 | Existence and exponential stability of a damped wave equation with dynamic boundary conditions and a delay term | In this paper we consider a multi-dimensional wave equation with dynamic
boundary conditions related to the Kelvin-Voigt damping and a delay term acting
on the boundary. If the weight of the delay term in the feedback is less than
the weight of the term without delay or if it is greater under an assumption
between the damping factor, and the difference of the two weights, we prove the
global existence of the solutions. Under the same assumptions, the exponential
stability of the system is proved using an appropriate Lyapunov functional.
More precisely, we show that even when the weight of the delay is greater than
the weight of the damping in the boundary conditions, the strong damping term
still provides exponential stability for the system. | 1206.1010v1 |
2012-08-27 | Analysis of the damped quantum search and its application to the one-dimensional Ising system | An analysis on the damped quantum search by exploring the rate at which the
target state is obtained. The results were compared with that of the classical
search since the standard Grover's algorithm does not give a convergent result
if the number of target state is unknown. For a large number of target states,
the classical and the damped quantum search give a similar result. However, for
intermediate values of the target size the damped quantum search gives a higher
probability of success than the classical search. Furthermore, we also made an
analysis on the average number of iterations needed to obtain at least one of
the target states. As the number of target states is reduced, the damped
quantum search gives a better result than the classical search. The results
coincide if the size of target state is comparable to the size of the sample. | 1208.5509v1 |
2012-10-20 | Radiative damping of surface plasmon resonance in spheroidal metallic nanoparticle embedded in a dielectric medium | The local field approach and kinetic equation method is applied to calculate
the surface plasmon radiative damping in a spheroidal metal nanoparticle
embedded in any dielectric media. The radiative damping of the surface plasmon
resonance as a function of the particle radius, shape, dielectric constant of
the surrounding medium and the light frequency is studied in detail. It is
found that the radiative damping grows quadratically with the particle radius
and oscillates with altering both the particle size and the dielectric constant
of a surrounding medium. Much attention is paid to the electron
surface-scattering contribution to the plasmon decay. All calculations of the
radiative damping are illustrated by examples on the Au and Na nanoparticles. | 1210.5647v1 |
2012-11-11 | Dissipation in relativistic superfluid neutron stars | We analyze damping of oscillations of general relativistic superfluid neutron
stars. To this aim we extend the method of decoupling of superfluid and normal
oscillation modes first suggested in [Gusakov & Kantor PRD 83, 081304(R)
(2011)]. All calculations are made self-consistently within the finite
temperature superfluid hydrodynamics. The general analytic formulas are derived
for damping times due to the shear and bulk viscosities. These formulas
describe both normal and superfluid neutron stars and are valid for oscillation
modes of arbitrary multipolarity. We show that: (i) use of the ordinary
one-fluid hydrodynamics is a good approximation, for most of the stellar
temperatures, if one is interested in calculation of the damping times of
normal f-modes; (ii) for radial and p-modes such an approximation is poor;
(iii) the temperature dependence of damping times undergoes a set of rapid
changes associated with resonance coupling of neighboring oscillation modes.
The latter effect can substantially accelerate viscous damping of normal modes
in certain stages of neutron-star thermal evolution. | 1211.2452v1 |
2013-03-07 | Universal damping behavior of dipole oscillations of one-dimensional ultracold gases induced by quantum phase slips | We study superflow decay via quantum phase slips in trapped one-dimensional
(1D) quantum gases through dipole oscillations induced by sudden displacement
of the trapping potential. We find the relation between the damping rate of the
dipole oscillation $G$ and the phase-slip nucleation rate $\Gamma$ as $G\propto
\Gamma/v$, where $v$ is the flow velocity. This relation allows us to show that
damping of 1D Bose gases in optical lattices, which has been extensively
studied in experiment, is due to quantum phase slips. It is also found that the
damping rate versus the flow velocity obeys the scaling formula for an impurity
potential even in the absence of an explicit impurity. We suggest that the
damping rate at a finite temperature exhibits a universal crossover behavior
upon changing the flow velocity. | 1303.1616v1 |
2013-07-16 | Blow-up of solutions to the one-dimensional semilinear wave equation with damping depending on time and space variables | In this paper, we give a small data blow-up result for the one-dimensional
semilinear wave equation with damping depending on time and space variables. We
show that if the damping term can be regarded as perturbation, that is,
non-effective damping in a certain sense, then the solution blows up in finite
time for any power of nonlinearity. This gives an affirmative answer for the
conjecture that the critical exponent agrees with that of the wave equation
when the damping is non-effective in one space dimension. | 1307.4260v2 |
2013-11-12 | Landau damping: paraproducts and Gevrey regularity | We give a new, simpler, proof of nonlinear Landau damping on T^d in
Gevrey-1/s regularity (s > 1/3) which matches the regularity requirement
predicted by the formal analysis of Mouhot and Villani in the original proof of
Landau damping [Acta Mathematica 2011]. Our proof combines in a novel way ideas
from the original proof of Landau damping and the proof of inviscid damping in
2D Euler [arXiv:1306.5028]. As in the work on 2D Euler, we use paraproduct
decompositions and controlled regularity loss to replace the Newton iteration
scheme employed in the original proof. We perform time-response estimates
adapted from the original proof to control the plasma echoes and couple them to
energy estimates on the distribution function in the style of the work on 2D
Euler. | 1311.2870v1 |
2014-02-26 | Comparison of methods for numerical calculation of continuum damping | Continuum resonance damping is an important factor in determining the
stability of certain global modes in fusion plasmas. A number of analytic and
numerical approaches have been developed to compute this damping, particularly
in the case of the toroidicity-induced shear Alfv\'en eigenmode. This paper
compares results obtained using an analytical perturbative approach with those
found using resistive and complex contour numerical approaches. It is found
that the perturbative method does not provide accurate agreement with reliable
numerical methods for the range of parameters examined. This discrepancy exists
even in the limit where damping approaches zero. When the perturbative
technique is implemented using a standard finite element method, the damping
estimate fails to converge with radial grid resolution. The finite elements
used cannot accurately represent the eigenmode in the region of the continuum
resonance, regardless of the number of radial grid points used. | 1402.6389v1 |
2014-05-16 | Quantum corrections to nonlinear ion acoustic wave with Landau damping | Quantum corrections to nonlinear ion acoustic wave with Landau damping have
been computed using Wigner equation approach. The dynamical equation governing
the time development of nonlinear ion acoustic wave with semiclassical quantum
corrections is shown to have the form of higher KdV equation which has higher
order nonlinear terms coming from quantum corrections, with the usual classical
and quantum corrected Landau damping integral terms.
The conservation of total number of ions is shown from the evolution
equation. The decay rate of KdV solitary wave amplitude due to presence of
Landau damping terms has been calculated assuming the Landau damping parameter
$\alpha_1 = \sqrt{{m_e}/{m_i}}$ to be of the same order of the quantum
parameter $Q = {\hbar^2}/({24 m^2 c^2_{s} L^2})$. The amplitude is shown to
decay very slowly with time as determined by the quantum factor $ Q$. | 1405.4107v1 |
2014-05-19 | Mesh Size and Damped Edge Effects in Micromagnetic Spin Wave Simulation | We have studied the dependence of spin wave dispersion on the characteristics
of the mesh used in a finite element micromagnetic simulation. It is shown that
the dispersion curve has a cut off at a frequency which is analytically
predictable. The frequency depends on the average mesh length used for the
simulation. Based on this, a recipe to effectively obtain the dispersion
relation has been suggested. In a separate study, spin wave reflections are
absorbed by introducing highly damped edges in the device. However, an abrupt
change in the damping parameter causes reflections. We compare damping profiles
and identify an exponential damping profile as causing significantly less
reflections. | 1405.4615v2 |
2014-07-08 | Fourier-Hermite spectral representation for the Vlasov-Poisson system in the weakly collisional limit | We study Landau damping in the 1+1D Vlasov-Poisson system using a
Fourier-Hermite spectral representation. We describe the propagation of free
energy in phase space using forwards and backwards propagating Hermite modes
recently developed for gyrokinetics [Schekochihin et al. (2014)]. The change in
the electric field corresponds to the net Hermite flux via a free energy
evolution equation. In linear Landau damping, decay in the electric field
corresponds to forward propagating Hermite modes; in nonlinear damping, the
initial decay is followed by a growth phase characterised by the generation of
backwards propagating Hermite modes by the nonlinear term. The free energy
content of the backwards propagating modes increases exponentially until
balancing that of the forward propagating modes. Thereafter there is no
systematic net Hermite flux, so the electric field cannot decay and the
nonlinearity effectively suppresses Landau damping. These simulations are
performed using the fully-spectral 5D gyrokinetics code SpectroGK [Parker et
al. 2014], modified to solve the 1+1D Vlasov-Poisson system. This captures
Landau damping via an iterated L\'enard-Bernstein collision operator or via
Hou-Li filtering in velocity space. Therefore the code is applicable even in
regimes where phase-mixing and filamentation are dominant. | 1407.1932v1 |
2014-08-14 | Particle Dynamics in Damped Nonlinear Quadrupole Ion Traps | We examine the motions of particles in quadrupole ion traps as a function of
damping and trapping forces, including cases where nonlinear damping or
nonlinearities in the electric field geometry play significant roles. In the
absence of nonlinearities, particles are either damped to the trap center or
ejected, while their addition brings about a rich spectrum of stable closed
particle trajectories. In three-dimensional (3D) quadrupole traps, the extended
orbits are typically confined to the trap axis, and for this case we present a
1D analysis of the relevant equation of motion. We follow this with an analysis
of 2D quadrupole traps that frequently show diamond-shaped closed orbits. For
both the 1D and 2D cases we present experimental observations of the calculated
trajectories in microparticle ion traps. We also report the discovery of a new
collective behavior in damped 2D microparticle ion traps, where particles
spontaneously assemble into a remarkable knot of overlapping, corotating
diamond orbits, self-stabilized by air currents arising from the particle
motion. | 1409.6262v1 |
2015-01-03 | Finite-Parameters Feedback Control for Stabilizing Damped Nonlinear Wave Equations | In this paper we introduce a finite-parameters feedback control algorithm for
stabilizing solutions of various classes of damped nonlinear wave equations.
Specifically, stabilization the zero steady state solution of initial boundary
value problems for nonlinear weakly and strongly damped wave equations,
nonlinear wave equation with nonlinear damping term and some related nonlinear
wave equations, introducing a feedback control terms that employ parameters,
such as, finitely many Fourier modes, finitely many volume elements and
finitely many nodal observables and controllers. In addition, we also establish
the stabilization of the zero steady state solution to initial boundary value
problem for the damped nonlinear wave equation with a controller acting in a
proper subdomain. Notably, the feedback controllers proposed here can be
equally applied for stabilizing other solutions of the underlying equations. | 1501.00556v1 |
2015-06-26 | A Universal Damping Mechanism of Quantum Vibrations in Deep Sub-Barrier Fusion Reactions | We demonstrate the damping of quantum octupole vibrations near the touching
point when two colliding nuclei approach each other in the mass-asymmetric
$^{208}$Pb + $^{16}$O system, for which the strong fusion hindrance was clearly
observed. We, for the first time, apply the random-phase approximation method
to the heavy-mass asymmetric di-nuclear system to calculate the transition
strength $B$(E3) as a function of the center-of-mass distance. The obtained
$B$(E3) strengths are substantially damped near the touching point, because the
single-particle wave functions of the two nuclei strongly mix with each other
and a neck is formed. The energy-weighted sums of $B$(E3) are also strongly
correlated with the damping factor which is phenomenologically introduced in
the standard coupled-channel calculations to reproduce the fusion hindrance.
This strongly indicates that the damping of the quantum vibrations universally
occurs in the deep sub-barrier fusion reactions. | 1506.07963v1 |
2015-07-28 | Phenomenology of chiral damping in noncentrosymmetric magnets | A phenomenology of magnetic chiral damping is proposed in the context of
magnetic materials lacking inversion symmetry breaking. We show that the
magnetic damping tensor adopts a general form that accounts for a component
linear in magnetization gradient in the form of Lifshitz invariants. We propose
different microscopic mechanisms that can produce such a damping in
ferromagnetic metals, among which spin pumping in the presence of anomalous
Hall effect and an effective "$s$-$d$" Dzyaloshinskii-Moriya antisymmetric
exchange. The implication of this chiral damping in terms of domain wall motion
is investigated in the flow and creep regimes. These predictions have major
importance in the context of field- and current-driven texture motion in
noncentrosymmetric (ferro-, ferri-, antiferro-)magnets, not limited to metals. | 1507.07762v1 |
2015-08-06 | Phenomenological description of the nonlocal magnetization relaxation in magnonics, spintronics, and domain-wall dynamics | A phenomenological equation called Landau-Lifshitz-Baryakhtar (LLBar)
equation, which could be viewed as the combination of Landau-Lifshitz (LL)
equation and an extra "exchange damping" term, was derived by Baryakhtar using
Onsager's relations. We interpret the origin of this "exchange damping" as
nonlocal damping by linking it to the spin current pumping. The LLBar equation
is investigated numerically and analytically for the spin wave decay and domain
wall motion. Our results show that the lifetime and propagation length of
short-wavelength magnons in the presence of nonlocal damping could be much
smaller than those given by LL equation. Furthermore, we find that both the
domain wall mobility and the Walker breakdown field are strongly influenced by
the nonlocal damping. | 1508.01478v1 |
2016-01-05 | Vlasov Simulations of Electron-Ion Collision Effects on Damping of Electron Plasma Waves | Collisional effects can play an essential role in the dynamics of plasma
waves by setting a minimum damping rate and by interfering with wave-particle
resonances. Kinetic simulations of the effects of electron-ion pitch angle
scattering on Electron Plasma Waves (EPWs) are presented here. In particular,
the effects of such collisions on the frequency and damping of small-amplitude
EPWs for a range of collision rates and wave phase velocities are computed and
compared with theory. Both the Vlasov simulations and linear kinetic theory
find the direct contribution of electron-ion collisions to wave damping is
about a factor of two smaller than is obtained from linearized fluid theory. To
our knowledge, this simple result has not been published before.
Simulations have been carried out using a grid-based (Vlasov) approach, based
on a high-order conservative finite difference method for discretizing the
Fokker-Planck equation describing the evolution of the electron distribution
function. Details of the implementation of the collision operator within this
framework are presented. Such a grid-based approach, which is not subject to
numerical noise, is of particular interest for the accurate measurements of the
wave damping rates. | 1601.01002v1 |
2016-02-13 | The effect of orbital damping during planet migration on the Inclination and Eccentricity Distributions of Neptune Trojans | We explore planetary migration scenarios for formation of high inclination
Neptune Trojans (NTs) and how they are affected by the planetary migration of
Neptune and Uranus. If Neptune and Uranus's eccentricity and inclination were
damped during planetary migration, then their eccentricities and inclinations
were higher prior and during migration than their current values. Using test
particle integrations we study the stability of primordial NTs, objects that
were initially Trojans with Neptune prior to migration. We also study
Trans-Neptunian objects captured into resonance with Neptune and becoming NTs
during planet migration. We find that most primordial NTs were unstable and
lost if eccentricity and inclination damping took place during planetary
migration. With damping, secular resonances with Neptune can increase a low
eccentricity and inclination population of Trans-Neptunian objects increasing
the probability that they are captured into 1:1 resonance with Neptune,
becoming high inclination NTs. We suggest that the resonant trapping scenario
is a promising and more effective mechanism explaining the origin of NTs that
is particularly effective if Uranus and Neptune experienced eccentricity and
inclination damping during planetary migration. | 1602.04303v1 |
2016-03-08 | Damping of the Higgs and Nambu-Goldstone modes of superfluid Bose gases at finite temperatures | We study collective modes of superfluid Bose gases in optical lattices at
commensurate fillings. We focus on the vicinity of the quantum phase transition
to the Mott insulator, where there exists the Higgs amplitude mode in addition
to the Nambu-Goldstone phase mode associated with the spontaneous U(1) symmetry
breaking. We analyze finite-temperature effects on the damping of the
collective modes by using an effective spin-1 model and the field theoretical
methods based on the finite-temperature Green's function. We calculate the
damping rates up to 1-loop order and evaluate them analytically and
numerically. We show that the damping rate of the Higgs mode increases with
increasing the temperature but it remains underdamped up to a typical
temperature achieved in experiments. Moreover, we find that the Nambu-Goldstone
mode attenuates via a Landau damping process resulting from interactions with
the Higgs mode and it can be overdamped at the typical temperature in a certain
parameter region. | 1603.02395v1 |
2016-04-12 | Offline software for the DAMPE experiment | A software system has been developed for the DArk Matter Particle Explorer
(DAMPE) mission, a satellite-based experiment. The DAMPE software is mainly
written in C++ and steered using Python script. This article presents an
overview of the DAMPE offline software, including the major architecture design
and specific implementation for simulation, calibration and reconstruction. The
whole system has been successfully applied to DAMPE data analysis, based on
which some results from simulation and beam test experiments are obtained and
presented. | 1604.03219v6 |
2016-04-18 | Stabilization of Damped Waves on Spheres and Zoll Surfaces of Revolution | We study the strong stabilization of wave equations on some sphere-like
manifolds, with rough damping terms which do not satisfy the geometric control
condition posed by Rauch-Taylor and Bardos-Lebeau-Rauch. We begin with an
unpublished result of G. Lebeau, which states that on S^d , the indicator
function of the upper hemisphere strongly stabilizes the damped wave equation,
even though the equators, which are geodesics contained in the boundary of the
upper hemisphere, do not enter the damping region. Then we extend this result
on dimension 2, to Zoll surfaces of revolution, whose geometry is similar to
that of S^2 . In particular, geometric objects such as the equator, and the
hemi-surfaces are well defined. Our result states that the indicator function
of the upper hemi-surface strongly stabilizes the damped wave equation, even
though the equator, as a geodesic, does not enter the upper hemi-surface
either. | 1604.05218v2 |
2016-07-25 | Damping of parametrically excited magnons in the presence of the longitudinal spin Seebeck effect | The impact of the longitudinal spin Seebeck effect (LSSE) on the magnon
damping in magnetic-insulator/nonmagnetic-metal bilayers was recently discussed
in several reports. However, results of those experiments can be blurred by
multimode excitation within the measured linewidth. In order to avoid possible
intermodal interference, we investigated the damping of a single magnon group
in a platinum covered Yttrium Iron Garnet (YIG) film by measurement of the
threshold of its parametric excitation. Both dipolar and exchange spin-wave
branches were probed. It turned out that the LSSE-related modification of
spin-wave damping in a micrometer-thick YIG film is too weak to be observed in
the entire range of experimentally accessible wavevectors. At the same time,
the change in the mean temperature of the YIG layer, which can appear by
applying a temperature gradient, strongly modifies the damping value. | 1607.07274v1 |
2016-07-27 | Frequency dispersion of small-amplitude capillary waves in viscous fluids | This work presents a detailed study of the dispersion of capillary waves with
small amplitude in viscous fluids using an analytically derived solution to the
initial value problem of a small-amplitude capillary wave as well as direct
numerical simulation. A rational parametrization for the dispersion of
capillary waves in the underdamped regime is proposed, including predictions
for the wavenumber of critical damping based on a harmonic oscillator model.
The scaling resulting from this parametrization leads to a self-similar
solution of the frequency dispersion of capillary waves that covers the entire
underdamped regime, which allows an accurate evaluation of the frequency at a
given wavenumber, irrespective of the fluid properties. This similarity also
reveals characteristic features of capillary waves, for instance that critical
damping occurs when the characteristic timescales of dispersive and dissipative
mechanisms are balanced. In addition, the presented results suggest that the
widely adopted hydrodynamic theory for damped capillary waves does not
accurately predict the dispersion when viscous damping is significant and a new
definition of the damping rate, which provides consistent accuracy in the
underdamped regime, is presented. | 1607.08266v1 |
2016-10-18 | On the stability of the Bresse system with frictional damping | In this paper, we consider the Bresse system with frictional damping terms
and prove some optimal decay results for the $L^2$-norm of the solution and its
higher order derivatives. In fact, if we consider just one damping term acting
on the second equation of the solution, we show that the solution does not
decay at all. On the other hand, by considering one damping term alone acting
on the third equation, we show that this damping term is strong enough to
stabilize the whole system. In this case, we found a completely new stability
number that depends on the parameters in the system.
In addition, we prove the optimality of the results by using eigenvalues
expansions. Our obtained results have been proved under some assumptions on the
wave speeds of the three equations in the Bresse system. | 1610.05500v2 |
2017-01-12 | Blow-up for semilinear wave equations with the scale invariant damping and super-Fujita exponent | The blow-up for semilinear wave equations with the scale invariant damping
has been well-studied for sub-Fujita exponent. However, for super-Fujita
exponent, there is only one blow-up result which is obtained in 2014 by
Wakasugi in the case of non-effective damping. In this paper we extend his
result in two aspects by showing that: (I) the blow-up will happen for bigger
exponent, which is closely related to the Strauss exponent, the critical number
for non-damped semilinear wave equations; (II) such a blow-up result is
established for a wider range of the constant than the known non-effective one
in the damping term. | 1701.03232v3 |
2017-02-17 | Transition of multi-diffusive states in a biased periodic potential | We study a frequency-dependent damping model of hyper-diffusion within the
generalized Langevin equation. The model allows for the colored noise defined
by its spectral density, assumed to be proportional to $\omega^{\delta-1}$ at
low frequencies with $0<\delta<1$ (sub-Ohmic damping) or $1<\delta<2$
(super-Ohmic damping), where the frequency-dependent damping is deduced from
the noise by means of the fluctuation-dissipation theorem. It is shown that for
super-Ohmic damping and certain parameters, the diffusive process of the
particle in a titled periodic potential undergos sequentially four
time-regimes: thermalization, hyper-diffusion, collapse and asymptotical
restoration. For analysing transition phenomenon of multi-diffusive states, we
demonstrate that the first exist time of the particle escaping from the locked
state into the running state abides by an exponential distribution. The concept
of equivalent velocity trap is introduced in the present model, moreover,
reformation of ballistic diffusive system is also considered as a marginal
situation, however there does not exhibit the collapsed state of diffusion. | 1702.05370v1 |
2017-09-27 | Wave turbulence in vibrating plates : the effect of damping | The effect of damping in the wave turbulence regime for thin vibrating plates
is studied. An experimental method, allowing measurements of dissipation in the
system at all scales, is first introduced. Practical experimental devices for
increasing the dissipation are used. The main observable consequence of
increasing the damping is a significant modification in the slope of the power
spectral density, so that the observed power laws are not in a pure inertial
regime. However, the system still displays a turbulent behavior with a cut-off
frequency that is determined by the injected power which does not depend on
damping. By using the measured damping power-law in numerical simulations,
similar conclusions are drawn out. | 1709.09438v1 |
2017-11-02 | Vibration Damping of Carbon Nanotube Assembly Materials | Vibration reduction is of great importance in various engineering
applications, and a material that exhibits good vibration damping along with
high strength and modulus has become more and more vital. Owing to the superior
mechanical property of carbon nanotube (CNT), new types of vibration damping
material can be developed. This paper presents recent advancements, including
our progresses, in the development of high-damping macroscopic CNT assembly
materials, such as forests, gels, films, and fibers. In these assemblies,
structural deformation of CNTs, zipping and unzipping at CNT connection nodes,
strengthening and welding of the nodes, and sliding between CNTs or CNT bundles
are playing important roles in determining the viscoelasticity, and elasticity
as well. Towards the damping enhancement, strategies for micro-structure and
interface design are also discussed. | 1711.00623v1 |
2017-12-05 | Dark Matter Annihilation from Nearby Ultra-compact Micro Halos to Explain the Tentative Excess at ~1.4 TeV in DAMPE data | The tentative 1.4 TeV excess in the $e^+e^-$ spectrum measured by The DArk
Matter Particle Explorer (DAMPE) motivates the possible existence of one or
more local dark matter concentrated regions. In particular, Ultra-compact Micro
Halos (UCMHs) seeded by large density perturbations in the early universe,
allocated within ~0.3 kpc from the solar system, could provide the potential
source of electrons and positrons produced from dark matter annihilation,
enough to explain the DAMPE signal. Here we consider a UCMH with density
profile assuming radial in-fall and explore the preferred halo parameters to
explain the 1.4 TeV "DAMPE excess". We find that typical parameter space of
UCMHs can easily explain the "DAMPE excess" with usual thermal-averaged
annihilation cross section of WIMP. The fraction of dark matter stored in such
UCMHs in the Galactic-scale halo can be reduced to as small as $O(10^{-5})$,
well within the current cosmological and astrophysical constraints. | 1712.01724v2 |
2017-12-21 | A new charge reconstruction algorithm for the DAMPE silicon microstrip detector | The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within the Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). The Silicon-Tungsten Tracker (STK), which is composed
of 768 singled-sided silicon microstrip detectors, is one of the four
subdetectors in DAMPE, providing track reconstruction and charge identification
for relativistic charged particles. The charge response of DAMPE silicon
microstrip detectors is complicated, depending on the incident angle and impact
position. A new charge reconstruction algorithm for the DAMPE silicon
microstrip detector is introduced in this paper. This algorithm can correct the
complicated charge response, and was proved applicable by the ion test beam. | 1712.08011v1 |
2018-01-23 | The dominancy of damping like torque for the current induced magnetization switching in Pt/Co/W multilayers | Two classes of spin-orbit coupling (SOC) mechanisms have been considered as
candidate sources for the spin orbit torque (SOT): the spin Hall Effect (SHE)
in heavy metals with strong SOC and the Rashba effect arising from broken
inversion symmetry at material surfaces and interfaces. In this work, we have
investigated the SOT in perpendicularly magnetized Pt/Co/W films, which is
compared with the results in Pt/Co/AlOx films. Theoretically, in the case of
the asymmetric structure of trilayers with opposite sign of spin Hall angle,
both damping like torque and field like torque due to the SHE and the Rashba
effect will be enhanced. Using the harmonic measurements, we have characterized
the effective fields corresponding to the damping like torque and the field
like torque, but we have found the dominancy of damping like torque in the
Pt/Co/W films. It is much different from the results in the Pt/Co/AlOx films,
in which both the damping like torque and the field like torque are strong. | 1801.07408v1 |
2018-02-20 | The damped wave equation with unbounded damping | We analyze new phenomena arising in linear damped wave equations on unbounded
domains when the damping is allowed to become unbounded at infinity. We prove
the generation of a contraction semigroup, study the relation between the
spectra of the semigroup generator and the associated quadratic operator
function, the convergence of non-real eigenvalues in the asymptotic regime of
diverging damping on a subdomain, and we investigate the appearance of
essential spectrum on the negative real axis. We further show that the presence
of the latter prevents exponential estimates for the semigroup and turns out to
be a robust effect that cannot be easily canceled by adding a positive
potential. These analytic results are illustrated by examples. | 1802.07026v1 |
2018-05-29 | Enhancing precision of damping rate by PT symmetric Hamiltonian | We utilize quantum Fisher information to investigate the damping parameter
precision of a dissipative qubit. PT symmetric non-Hermitian Hamiltonian is
used to enhance the parameter precision in two models: one is direct PT
symmetric quantum feedback; the other is that the damping rate is encoded into
a effective PT symmetric non-Hermitian Hamiltonian conditioned on the absence
of decay events. We find that compared with the case without feedback and with
Hermitian quantum feedback, direct PT symmetric non-Hermitan quantum feedback
can obtain better precision of damping rate. And in the second model the result
shows that the uncertainty of damping rate can be close to 0 at the exceptional
point. We also obtain that non-maximal multiparticle entanglement can improve
the precision to reach Heisenberg limit. | 1805.11216v1 |
2018-05-31 | Damping Effect on PageRank Distribution | This work extends the personalized PageRank model invented by Brin and Page
to a family of PageRank models with various damping schemes. The goal with
increased model variety is to capture or recognize a larger number of types of
network activities, phenomena and propagation patterns. The response in
PageRank distribution to variation in damping mechanism is then characterized
analytically, and further estimated quantitatively on 6 large real-world link
graphs. The study leads to new observation and empirical findings. It is found
that the difference in the pattern of PageRank vector responding to parameter
variation by each model among the 6 graphs is relatively smaller than the
difference among 3 particular models used in the study on each of the graphs.
This suggests the utility of model variety for differentiating network
activities and propagation patterns. The quantitative analysis of the damping
mechanisms over multiple damping models and parameters is facilitated by a
highly efficient algorithm, which calculates all PageRank vectors at once via a
commonly shared, spectrally invariant subspace. The spectral space is found to
be of low dimension for each of the real-world graphs. | 1806.00127v1 |
2018-08-10 | Relativistic charge solitons created due to nonlinear Landau damping: A candidate for explaining coherent radio emission in pulsars | A potential resolution for the generation of coherent radio emission in
pulsar plasma is the existence of relativistic charge solitons, which are
solutions of nonlinear Schr\"{o}dinger equation (NLSE). In an earlier study,
Melikidze et al. (2000) investigated the nature of these charge solitons;
however, their analysis ignored the effect of nonlinear Landau damping, which
is inherent in the derivation of the NLSE in the pulsar pair plasma. In this
paper we include the effect of nonlinear Landau damping and obtain solutions of
the NLSE by applying a suitable numerical scheme. We find that for reasonable
parameters of the cubic nonlinearity and nonlinear Landau damping, soliton-like
intense pulses emerge from an initial disordered state of Langmuir waves and
subsequently propagate stably over sufficiently long times, during which they
are capable of exciting the coherent curvature radiation in pulsars. We
emphasize that this emergence of {\em stable} intense solitons from a
disordered state does not occur in a purely cubic NLSE; thus, it is {\em
caused} by the nonlinear Landau damping. | 1808.03657v1 |
2018-11-21 | Super Damping of Mechanical Vibrations | We report the phenomenon of coherent super decay, where a linear sum of
several damped oscillators can collectively decay much faster than the
individual ones in the first stage, followed by stagnating ones after more than
90 percent of the energy has already been dissipated. The parameters of the
damped oscillators for CSD are determined by the process of response function
decomposition, which is to use several slow decay response functions to
approximate the response function of a fast decay reference resonator. Evidence
established in experiments and in finite element simulations not only strongly
supported the numerical investigations, but also uncovered an unexplored region
of the tuned mass damper parameter space where TMDs with total mass less than
0.2 percent of a primary free body can damp its first resonance up to a damping
ratio of 4.6 percent. Our findings also shed light onto the intriguing
underline connections between complex functions with different singular points. | 1811.08621v2 |
2018-11-29 | Flowing fibers as a proxy of turbulence statistics | The flapping states of a flexible fiber fully coupled to a three-dimensional
turbulent flow are investigated via state-of-the-art numerical methods. Two
distinct flapping regimes are predicted by the phenomenological theory recently
proposed by Rosti et al. [Phys. Rev. Lett. 121, 044501, 2018]: the under-damped
regime, where the elasticity strongly affects the fiber dynamics, and the
over-damped regime, where the elastic effects are strongly inhibited. In both
cases we can identify a critical value of the bending rigidity of the fiber by
a resonance condition, which further provides a distinction between different
flapping behaviors, especially in the under-damped case. We validate the theory
by means of direct numerical simulations and find that, both for the
over-damped regime and for the under-damped one, fibers are effectively slaved
to the turbulent fluctuations and can therefore be used as a proxy to measure
various two-point statistics of turbulence. Finally, we show that this holds
true also in the case of a passive fiber, without any feedback force on the
fluid. | 1811.12023v2 |
2018-11-29 | The Lugiato-Lefever equation with nonlinear damping caused by two photon absorption | In this paper we investigate the effect of nonlinear damping on the
Lugiato-Lefever equation $$ \i \partial_t a = -(\i-\zeta) a - da_{xx}
-(1+\i\kappa)|a|^2a +\i f $$ on the torus or the real line. For the case of the
torus it is shown that for small nonlinear damping $\kappa>0$ stationary
spatially periodic solutions exist on branches that bifurcate from constant
solutions whereas all nonconstant solutions disappear when the damping
parameter $\kappa$ exceeds a critical value. These results apply both for
normal ($d<0$) and anomalous ($d>0$) dispersion. For the case of the real line
we show by the Implicit Function Theorem that for small nonlinear damping
$\kappa>0$ and large detuning $\zeta\gg 1$ and large forcing $f\gg 1$ strongly
localized, bright solitary stationary solutions exists in the case of anomalous
dispersion $d>0$. These results are achieved by using techniques from
bifurcation and continuation theory and by proving a convergence result for
solutions of the time-dependent Lugiato-Lefever equation. | 1811.12200v3 |
2018-11-26 | Linear Theory of Electron-Plasma Waves at Arbitrary Collisionality | The dynamics of electron-plasma waves are described at arbitrary
collisionality by considering the full Coulomb collision operator. The
description is based on a Hermite-Laguerre decomposition of the velocity
dependence of the electron distribution function. The damping rate, frequency,
and eigenmode spectrum of electron-plasma waves are found as functions of the
collision frequency and wavelength. A comparison is made between the
collisionless Landau damping limit, the Lenard-Bernstein and Dougherty
collision operators, and the electron-ion collision operator, finding large
deviations in the damping rates and eigenmode spectra. A purely damped entropy
mode, characteristic of a plasma where pitch-angle scattering effects are
dominant with respect to collisionless effects, is shown to emerge numerically,
and its dispersion relation is analytically derived. It is shown that such a
mode is absent when simplified collision operators are used, and that
like-particle collisions strongly influence the damping rate of the entropy
mode. | 1811.12855v2 |
2019-01-17 | Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures | We investigate the effect of capping layer (CAP) on the interfacial magnetic
anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
HfOx, or TaN). At room temperature (RT) the CAP materials influence the
effective magnitude of K_S, which is associated with a formation of interfacial
magnetic oxides. The dynamical dissipation parameters of Co are considerably
influenced by the CAP (especially MgO) while those of Py are not. This is
possibly due to an extra magnetic damping via spin-pumping process across the
Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
interfacial CoO. It is also observed that both anti-damping and field-like SOT
efficiencies vary marginally with the CAP in the thickness ranges we examined.
Our results reveal the crucial role of interfacial oxides on the perpendicular
magnetic anisotropy, magnetic damping, and SOTs. | 1901.05777v1 |
2019-05-31 | The amplitude of solar p-mode oscillations from three-dimensional convection simulations | The amplitude of solar p-mode oscillations is governed by stochastic
excitation and mode damping, both of which take place in the surface convection
zone. However, the time-dependent, turbulent nature of convection makes it
difficult to self-consistently study excitation and damping processes through
the use of traditional one-dimensional hydrostatic models. To this end, we
carried out \textit{ab initio} three-dimensional, hydrodynamical numerical
simulations of the solar atmosphere to investigate how p-modes are driven and
dissipated in the Sun. The description of surface convection in the simulations
is free from the tuneable parameters typically adopted in traditional
one-dimensional models. Mode excitation and damping rates are computed based on
analytical expressions whose ingredients are evaluated directly from the
three-dimensional model. With excitation and damping rates both available, we
estimate the theoretical oscillation amplitude and frequency of maximum power,
$\nu_{\max}$, for the Sun. We compare our numerical results with helioseismic
observations, finding encouraging agreement between the two. The numerical
method presented here provides a novel way to investigate the physical
processes responsible for mode driving and damping, and should be valid for all
solar-type oscillating stars. | 1905.13397v2 |
2019-10-03 | Many-body collision contributions to electron momentum damping rates in a plasma influenced by electron strong coupling | Experimental studies of electron-ion collision rates in an ultracold neutral
plasma (UNP) can be conducted through measuring the rate of electron plasma
oscillation damping. For sufficiently cold and dense conditions where strong
coupling influences are important, the measured damping rate was faster by 37\%
than theoretical expectations [W. Chen, C. Witte, and J. Roberts, Phys. Rev. E
\textbf{96}, 013203 (2017)]. We have conducted a series of numerical
simulations to isolate the primary source of this difference. By analyzing the
distribution of electron velocity changes due to collisions in a molecular
dynamics simulation, examining the trajectory of electrons with high deflection
angle in such simulations, and examining the oscillation damping rate while
varying the ratio of two-body to three-body electron-ion collision rates, we
have found that the difference is consistent with the effect due to many-body
collisions leading to bound electrons. This has implications for other
electron-ion collision related transport properties in addition to electron
oscillation damping. | 1910.01707v1 |
2019-10-18 | Escape of a forced-damped particle from weakly nonlinear truncated potential well | Escape from a potential well is an extreme example of transient behavior. We
consider the escape of the harmonically forced particle under viscous damping
from the benchmark truncated weakly nonlinear potential well. Main attention is
paid to most interesting case of primary 1:1 resonance. The treatment is based
on multiple-scales analysis and exploration of the slow-flow dynamics. Contrary
to Hamiltonian case described in earlier works, in the case with damping the
slow-flow equations are not integrable. However, if the damping is small
enough, it is possible to analyze the perturbed slow-flow equations. The effect
of the damping on the escape threshold is evaluated in the explicit analytic
form. Somewhat unexpectedly, the escape mechanisms in terms of the slow flow
are substantially different for the linear and weakly nonlinear cases. | 1910.08545v1 |
2020-02-07 | Model of damping and anisotropy at elevated temperatures: application to granular FePt films | Understanding the damping mechanism in finite size systems and its dependence
on temperature is a critical step in the development of magnetic
nanotechnologies. In this work, nano-sized materials are modeled via atomistic
spin dynamics, the damping parameter being extracted from Ferromagnetic
Resonance (FMR) simulations applied for FePt systems, generally used for
heat-assisted magnetic recording media (HAMR). We find that the damping
increases rapidly close to Tc and the effect is enhanced with decreasing system
size, which is ascribed to scattering at the grain boundaries. Additionally,
FMR methods provide the temperature dependence of both damping and the
anisotropy, important for the development of HAMR. Semi-analytical calculations
show that, in the presence of a grain size distribution, the FMR linewidth can
decrease close to the Curie temperature due to a loss of inhomogeneous line
broadening. Although FePt has been used in this study, the results presented in
the current work are general and valid for any ferromagnetic material. | 2002.02865v1 |
2020-04-06 | Damping-like Torque in Monolayer 1T-TaS$_2$ | A damping-like spin orbit torque (SOT) is a prerequisite for ultralow power
spin logic devices. Here, we report on the damping-like SOT in just one
monolayer of the conducting transition metal dichalcogenide (TMD) TaS$_2$
interfaced with a NiFe (Py) ferromagnetic layer. The charge-spin conversion
efficiency is found to be 0.25$\pm$0.03 and the spin Hall conductivity (2.63
$\times$ 10$^5$ $\frac{\hbar}{2e}$ $\Omega^{-1}$ m$^{-1}$) is found to be
superior to values reported for other TMDs. The origin of this large
damping-like SOT can be found in the interfacial properties of the TaS$_2$/Py
heterostructure, and the experimental findings are complemented by the results
from density functional theory calculations. The dominance of damping-like
torque demonstrated in our study provides a promising path for designing next
generation conducting TMD based low-powered quantum memory devices. | 2004.02649v1 |
2020-05-15 | Calibration and performance of the neutron detector onboard of the DAMPE mission | The DArk Matter Particle Explorer (DAMPE), one of the four space-based
scientific missions within the framework of the Strategic Pioneer Program on
Space Science of the Chinese Academy of Sciences, has been successfully
launched on Dec. 17th 2015 from Jiuquan launch center. One of the most
important scientific goals of DAMPE is to search for the evidence of dark
matter indirectly by measuring the spectrum of high energy cosmic-ray
electrons. The neutron detector, one of the four sub-payloads of DAMPE, is
designed to distinguish high energy electrons from hadron background by
measuring the secondary neutrons produced in the shower. In this paper, a
comprehensive introduction of the neutron detector is presented, including the
design, the calibration and the performance. The analysis with simulated data
and flight data indicates a powerful proton rejection capability of the neutron
detector, which plays an essential role for TeV electron identification of
DAMPE. | 2005.07828v1 |
2020-07-16 | Linearized wave-damping structure of Vlasov-Poisson in $\mathbb R^3$ | In this paper we study the linearized Vlasov-Poisson equation for localized
disturbances of an infinite, homogeneous Maxwellian background distribution in
$\mathbb R^3_x \times \mathbb R^3_v$. In contrast with the confined case
$\mathbb T^d _x \times \mathbb R_v ^d$, or the unconfined case $\mathbb R^d_x
\times \mathbb R^d_v$ with screening, the dynamics of the disturbance are not
scattering towards free transport as $t \to \pm \infty$: we show that the
electric field decomposes into a very weakly-damped Klein-Gordon-type evolution
for long waves and a Landau-damped evolution. The Klein-Gordon-type waves
solve, to leading order, the compressible Euler-Poisson equations linearized
about a constant density state, despite the fact that our model is
collisionless, i.e. there is no trend to local or global thermalization of the
distribution function in strong topologies. We prove dispersive estimates on
the Klein-Gordon part of the dynamics. The Landau damping part of the electric
field decays faster than free transport at low frequencies and damps as in the
confined case at high frequencies; in fact, it decays at the same rate as in
the screened case. As such, neither contribution to the electric field behaves
as in the vacuum case. | 2007.08580v1 |
2020-07-25 | Using a Lindbladian approach to model decoherence in two coupled nuclear spins via correlated phase-damping and amplitude damping noise channels | In this work, we studied the relaxation dynamics of coherences of different
order present in a system of two coupled nuclear spins. We used a previously
designed model for intrinsic noise present in such systems which considers the
Lindblad master equation for Markovian relaxation. We experimentally created
zero-, single- and double- quantum coherences in several two-spin systems and
performed a complete state tomography and computed state fidelity. We
experimentally measured the decay of zero- and double- quantum coherences in
these systems. The experimental data fitted well to a model that considers the
main noise channels to be a correlated phase damping channel acting
simultaneously on both spins in conjunction with a generalized amplitude
damping channel acting independently on both spins. The differential relaxation
of multiple-quantum coherences can be ascribed to the action of a correlated
phase damping channel acting simultaneously on both the spins. | 2007.12972v1 |
2020-09-29 | The effects of nonlinear damping on degenerate parametric amplification | This paper considers the dynamic response of a single degree of freedom
system with nonlinear stiffness and nonlinear damping that is subjected to both
resonant direct excitation and resonant parametric excitation, with a general
phase between the two. This generalizes and expands on previous studies of
nonlinear effects on parametric amplification, notably by including the effects
of nonlinear damping, which is commonly observed in a large variety of systems,
including micro- and nano-scale resonators. Using the method of averaging, a
thorough parameter study is carried out that describes the effects of the
amplitudes and relative phase of the two forms of excitation. The effects of
nonlinear damping on the parametric gain are first derived. The transitions
among various topological forms of the frequency response curves, which can
include isolae, dual peaks, and loops, are determined, and bifurcation analyses
in parameter spaces of interest are carried out. In general, these results
provide a complete picture of the system response and allow one to select drive
conditions of interest that avoid bistability while providing maximum amplitude
gain, maximum phase sensitivity, or a flat resonant peak, in systems with
nonlinear damping. | 2009.14284v2 |
2020-11-10 | Damped oscillators within the general theory of Casimir and van der Waals forces | It is demonstrated that the general theory of Casimir and van der Waals
forces describes the interaction-induced equilibrium thermodynamic potentials
of the damped harmonic oscillator bilinearly coupled to the environment. An
extended model for a damped oscillator is suggested along the lines of the
general theory of Casimir and van der Waals forces, and the corresponding
thermodynamic quantities obtained. While the original model involves a heat
bath consisting of a large number of free oscillators having infinitesimal
damping functions, the extended model allows any generally admissible frequency
and temperature dependent dissipative susceptibilities of the heat bath
constituents, influenced by the additional dissipative environmental channels
that are not directly linked to the system oscillator. Consequently, the
results obtained are applicable to the frequency and temperature dependent
damping function of the system oscillator. | 2011.04960v2 |
2021-01-03 | The effect of flow on resonant absorption of slow MHD waves in magnetic flux tubes | In this paper, we study kink and sausage oscillations in the presence of
longitudinal background flow. We study resonant absorption of the kink and
sausage modes in the slow continuum under magnetic pore conditions in the
presence of flow. we determine the dispersion relation then solve it
numerically, and find the frequencies and damping rates of the slow kink and
sausage surface modes. We also, obtain analytical solution for the damping rate
of the slow surface mode in the long wavelength limit. We show that in the
presence of plasma flow, resonance absorption can result in strong damping for
forward waves and can be considered as an efficient mechanism to justify the
extremely rapid damping of slow surface sausage waves observed in magnetic
pores. Also, the plasma flow reduces the efficiency of resonance absorption to
damp backward waves. Furthermore, for the pore conditions, the resonance
instability is avoided in our model. | 2101.02064v1 |
2021-02-02 | Analysis of Lower Hybrid Drift Waves in Kappa Distributions over Solar Atmosphere | Kappa distributions and with loss cone features have been frequently observed
with flares emissions with the signatures of Lower hybrid waves. We have
analysed the plasma with Kappa distributions and with loss cone features for
the drift wave instabilities in perpendicular propagation for Large flare and
Normal flare and Coronal condition . While analysing the growth/damping rate,
we understand that the growth of propagation of EM waves increases with kappa
distribution index for all the three cases. In comparing the propagation large
flare shows lesser growth in compared with the normal and the coronal plasmas.
When added the loss cone features to Kappa distributions, we find that the
damping of EM wave propagation takes place. The damping rate EM waves is
increases with perpendicular temperature and loss cone index l, in all the
three cases but damping is very high for large flare and then normal in
comparision with coronal condition. This shows that the lower hybrid damping
may be the source of coronal heating. | 2102.01323v1 |
2021-02-25 | Regularity and stability of the semigroup associated with some interacting elastic systems I: A degenerate damping case | In this paper, we examine regularity and stability issues for two damped
abstract elastic systems. The damping involves the average velocity and a
fractional power $\theta$, with $\theta$ in $[-1,1]$, of the principal
operator. The matrix operator defining the damping mechanism for the coupled
system is degenerate. First, we prove that for $\theta$ in $(1/2,1]$, the
underlying semigroup is not analytic, but is differentiable for $\theta$ in
$(0,1)$; this is in sharp contrast with known results for a single similarly
damped elastic system, where the semigroup is analytic for $\theta$ in
$[1/2,1]$; this shows that the degeneracy dominates the dynamics of the
interacting systems, preventing analyticity in that range. Next, we show that
for $\theta$ in $(0,1/2]$, the semigroup is of certain Gevrey classes. Finally,
we show that the semigroup decays exponentially for $\theta$ in $[0,1]$, and
polynomially for $\theta$ in $[-1,0)$. To prove our results, we use the
frequency domain method, which relies on resolvent estimates. Optimality of our
resolvent estimates is also established. Several examples of application are
provided. | 2102.13217v4 |
2021-03-05 | Existence and congruence of global attractors for damped and forced integrable and nonintegrable discrete nonlinear Schrödinger equations | We study two damped and forced discrete nonlinear Schr\"odinger equations on
the one-dimensional infinite lattice. Without damping and forcing they are
represented by the integrable Ablowitz-Ladik equation (AL) featuring non-local
cubic nonlinear terms, and its standard (nonintegrable) counterpart with local
cubic nonlinear terms (DNLS). The global existence of a unique solution to the
initial value problem for both, the damped and forced AL and DNLS, is proven.
It is further shown that for sufficiently close initial data, their
corresponding solutions stay close for all times. Concerning the asymptotic
behaviour of the solutions to the damped and forced AL and DNLS, for the former
a sufficient condition for the existence of a restricted global attractor is
established while it is shown that the latter possesses a global attractor.
Finally, we prove the congruence of the restricted global AL attractor and the
DNLS attractor for dynamics ensuing from initial data contained in an
appropriate bounded subset in a Banach space. | 2103.03533v1 |
2021-05-17 | Dissipation of Oscillation Energy and Distribution of Damping Power in a Multimachine Power System: A Small-signal Analysis | This paper revisits the concept of damping torque in a multimachine power
system and its relation to the dissipation of oscillation energy in synchronous
machine windings. As a multimachine extension of an existing result on a
single-machine-infinite-bus (SMIB) system, we show that the total damping power
for a mode stemming from the interaction of electromagnetic torques and rotor
speeds is equal to the sum of average power dissipations in the generator
windings corresponding to the modal oscillation. Further, counter-intuitive to
the SMIB result, we demonstrate that, although the equality holds on an
aggregate, such is not the case for individual machines in an interconnected
system. To that end, distribution factors are derived for expressing the
average damping power of each generator as a linear combination of average
powers of modal energy dissipation in the windings of all machines in the
system. These factors represent the distribution of damping power in a
multimachine system. The results are validated on IEEE 4-machine and 16-machine
test systems. | 2105.07618v2 |
2021-06-04 | Imaging spin-wave damping underneath metals using electron spins in diamond | Spin waves in magnetic insulators are low-damping signal carriers that could
enable a new generation of spintronic devices. The excitation, control, and
detection of spin waves by metal electrodes is crucial for interfacing these
devices to electrical circuits. It is therefore important to understand
metal-induced damping of spin-wave transport, but characterizing this process
requires access to the underlying magnetic films. Here we show that spins in
diamond enable imaging of spin waves that propagate underneath metals in
magnetic insulators, and then use this capability to reveal a 100-fold increase
in spin-wave damping. By analyzing spin-wave-induced currents in the metal, we
derive an effective damping parameter that matches these observations well. We
furthermore detect buried scattering centers, highlighting the technique's
power for assessing spintronic device quality. Our results open new avenues for
studying metal - spin-wave interaction and provide access to interfacial
processes such as spin-wave injection via the spin-Hall effect. | 2106.02508v2 |
2021-06-04 | Inherent Non-Linear Damping in Resonators with Inertia Amplification | Inertia amplification is a mechanism coupling degrees of freedom within a
vibrating structure. Its goal is to achieve an apparent high dynamic mass and,
accordingly, a low resonance frequency. Such structures have been described for
use in locally resonant metamaterials and phononic crystals to lower the
starting frequency of a band gap without adding mass to the system. This study
shows that any non-linear kinematic coupling between translational or
rotational vibrations leads to the appearance of amplitude-dependent damping.
The analytical derivation of the equation of motion of a resonator with inertia
amplification creates insight in the damping process, and shows that the
vibration damping increases with its amplitude. The theoretical study is
validated by experimental evidence from two types of inertia-amplification
resonators. Finally, the importance of amplitude-dependent damping is
illustrated when the structure is used as a tuned mass damper for a cantilever
beam. | 2106.02576v2 |
2021-06-30 | On the effect of perturbations in first-order optimization methods with inertia and Hessian driven damping | Second-order continuous-time dissipative dynamical systems with viscous and
Hessian driven damping have inspired effective first-order algorithms for
solving convex optimization problems. While preserving the fast convergence
properties of the Nesterov-type acceleration, the Hessian driven damping makes
it possible to significantly attenuate the oscillations. To study the stability
of these algorithms with respect to perturbations, we analyze the behaviour of
the corresponding continuous systems when the gradient computation is subject
to exogenous additive errors. We provide a quantitative analysis of the
asymptotic behaviour of two types of systems, those with implicit and explicit
Hessian driven damping. We consider convex, strongly convex, and non-smooth
objective functions defined on a real Hilbert space and show that, depending on
the formulation, different integrability conditions on the perturbations are
sufficient to maintain the convergence rates of the systems. We highlight the
differences between the implicit and explicit Hessian damping, and in
particular point out that the assumptions on the objective and perturbations
needed in the implicit case are more stringent than in the explicit case. | 2106.16159v2 |
2021-07-13 | A new approach to the quantization of the damped harmonic oscillator | In this paper, a new approach for constructing Lagrangians for driven and
undriven linearly damped systems is proposed, by introducing a redefined time
coordinate and an associated coordinate transformation to ensure that the
resulting Lagrangian satisfies the Helmholtz conditions. The approach is
applied to canonically quantize the damped harmonic oscillator and although it
predicts an energy spectrum that decays at the same rate to previous models,
unlike those approaches it recovers the classical critical damping condition,
which determines transitions between energy eigenstates, and is therefore
consistent with the correspondence principle. It is also demonstrated how to
apply the procedure to a driven damped harmonic oscillator. | 2107.05827v3 |
2021-11-21 | Energy Transport in 1-Dimensional Oscillator Arrays With Hysteretic Damping | Energy transport in 1-dimensional oscillator arrays has been extensively
studied to date in the conservative case, as well as under weak viscous
damping. When driven at one end by a sinusoidal force, such arrays are known to
exhibit the phenomenon of supratransmission, i.e. a sudden energy surge above a
critical driving amplitude. In this paper, we study 1-dimensional oscillator
chains in the presence of hysteretic damping, and include nonlinear stiffness
forces that are important for many materials at high energies. We first employ
Reid's model of local hysteretic damping, and then study a new model of nearest
neighbor dependent hysteretic damping to compare their supratransmission and
wave packet spreading properties in a deterministic as well as stochastic
setting. The results have important quantitative differences, which should be
helpful when comparing the merits of the two models in specific engineering
applications. | 2111.10816v3 |
2021-12-15 | An Innovative Transverse Emittance Cooling Technique using a Laser-Plasma Wiggler | We propose an innovative beam cooling scheme based on laser driven plasma
wakefields to address the challenge of high luminosity generation for a future
linear collider. For linear colliders, beam cooling is realised by means of
damping rings equipped with wiggler magnets and accelerating cavities. This
scheme ensures systematic reduction of phase space volume through synchrotron
radiation emission whilst compensating for longitudinal momentum loss via an
accelerating cavity. In this paper, the concept of a plasma wiggler and its
effective model analogous to a magnetic wiggler are introduced; relation of
plasma wiggler characteristics with damping properties are demonstrated;
underpinning particle-in-cell simulations for laser propagation optimisation
are presented. The oscillation of transverse wakefields and resulting
sinusoidal probe beam trajectory are numerically demonstrated. The formation of
an order of magnitude larger effective wiggler field compared to conventional
wigglers is successfully illustrated. Potential damping ring designs on the
basis of this novel plasma-based technology are presented and performance in
terms of damping times and footprint was compared to an existing conventional
damping ring design. | 2112.08163v1 |
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