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2016-05-02 | Three types of nonlinear resonances | We analyse different types of nonlinear resonances in a weakly damped Duffing
oscillator using bifurcation theory techniques. In addition to (i) odd
subharmonic resonances found on the primary branch of symmetric periodic
solutions with the forcing frequency and (ii) even subharmonic resonances due
to symmetry-broken periodic solutions that bifurcate off the primary branch and
also oscillate at the forcing frequency, we uncover (iii) novel resonance type
due to isolas of periodic solutions that are not connected to the primary
branch. These occur between odd and even resonances, oscillate at a fraction of
the forcing frequency, and give rise to a complicated resonance `curve' with
disconnected elements and high degree of multistability. We use bifurcation
continuation to compute resonance tongues in the plane of the forcing frequency
vs. the forcing amplitude for different but fixed values of the damping rate.
In this way, we demonstrate that identified here isolated resonances explain
the intriguing structure of "patchy tongues" observed for week damping and link
it to a seemingly unrelated phenomenon of "bifurcation superstructure"
described for moderate damping. | 1605.00858v2 |
2016-07-21 | The Noisy Oscillator : Random Mass and Random Damping | The problem of a linear damped noisy oscillator is treated in the presence of
two multiplicative sources of noise which imply a random mass and random
damping. The additive noise and the noise in the damping are responsible for an
influx of energy to the oscillator and its dissipation to the surrounding
environment. A random mass implies that the surrounding molecules not only
collide with the oscillator but may also adhere to it, thereby changing its
mass. We present general formulas for the first two moments and address the
question of mean and energetic stabilities. The phenomenon of stochastic
resonance, i.e. the expansion due to the noise of a system response to an
external periodic signal, is considered for separate and joint action of two
sources of noise and their characteristics. | 1607.06289v2 |
2016-08-09 | Optomechanical damping of a nanomembrane inside an optical ring cavity | We experimentally and theoretically investigate mechanical nanooscillators
coupled to the light in an optical ring resonator made of dielectric mirrors.
We identify an optomechanical damping mechanism that is fundamentally different
to the well known cooling in standing wave cavities. While, in a standing wave
cavity the mechanical oscillation shifts the resonance frequency of the cavity
in a ring resonator the frequency does not change. Instead the position of the
nodes is shifted with the mechanical excursion. We derive the damping rates and
test the results experimentally with a silicon-nitride nanomembrane. It turns
out that scattering from small imperfections of the dielectric mirror coatings
has to be taken into account to explain the value of the measured damping rate.
We extend our theoretical model and regard a second reflector in the cavity
that captures the effects of mirror back scattering. This model can be used to
also describe the situation of two membranes that both interact with the cavity
fields. This may be interesting for future work on synchronization of distant
oscillators that are coupled by intracavity light fields. | 1608.02799v1 |
2016-08-11 | Decay of geodesic acoustic modes due to the combined action of phase mixing and Landau damping | Geodesic acoustic modes (GAMs) are oscillations of the electric field whose
importance in tokamak plasmas is due to their role in the regulation of
turbulence. The linear collisionless damping of GAMs is investigated here by
means of analytical theory and numerical simulations with the global
gyrokinetic particle-in-cell code ORB5. The combined effect of the phase mixing
and Landau damping is found to quickly redistribute the GAM energy in
phase-space, due to the synergy of the finite orbit width of the passing ions
and the cascade in wave number given by the phase mixing. When plasma
parameters characteristic of realistic tokamak profiles are considered, the GAM
decay time is found to be an order of magnitude lower than the decay due to the
Landau damping alone, and in some cases of the same order of magnitude of the
characteristic GAM drive time due to the nonlinear interaction with an ITG
mode. In particular, the radial mode structure evolution in time is
investigated here and reproduced quantitatively by means of a dedicated initial
value code and diagnostics. | 1608.03447v1 |
2016-09-06 | JRSP of three-particle state via three tripartite GHZ class in quantum noisy channels | We present a scheme for joint remote state preparation (JRSP) of
three-particle state via three tripartite Greenberger-Horne-Zeilinger (GHZ)
entangled states as the quantum channel linking the parties. We use eight-qubit
mutually orthogonal basis vector as measurement point of departure. The
likelihood of success for this scheme has been found to be $1/8$. However, by
putting some special cases into consideration, the chances can be ameliorated
to $1/4$ and $1$. The effects of amplitude-damping noise, phase-damping noise
and depolarizing noise on this scheme have been scrutinized and the analytical
derivations of fidelities for the quantum noisy channels have been presented.
We found that for $0.55\leq\eta\leq1$, the states conveyed through depolarizing
channel lose more information than phase-damping channel while the information
loss through amplitude damping channel is most minimal. | 1609.01538v3 |
2016-09-22 | Damping of nonlinear standing kink oscillations: a numerical study | We aim to study the standing fundamental kink mode of coronal loops in the
nonlinear regime, investigating the changes in energy evolution in the
cross-section and oscillation amplitude of the loop which are related to
nonlinear effects, in particular to the development of the Kelvin-Helmholtz
instability (KHI). We run idea, high-resolution three-dimensional (3D)
magnetohydrodynamics (MHD) simulations, studying the influence of the initial
velocity amplitude and the inhomogeneous layer thickness. We model the coronal
loop as a straight, homogeneous magnetic flux tube with an outer inhomogeneous
layer, embedded in a straight, homogeneous magnetic field. We find that, for
low amplitudes which do not allow for the KHI to develop during the simulated
time, the damping time agrees with the theory of resonant absorption. However,
for higher amplitudes, the presence of KHI around the oscillating loop can
alter the loop's evolution, resulting in a significantly faster damping than
predicted by the linear theory in some cases. This questions the accuracy of
seismological methods applied to observed damping profiles, based on linear
theory. | 1609.06883v1 |
2016-09-28 | Nonlinear damping and dephasing in nanomechanical systems | We present a microscopic theory of nonlinear damping and dephasing of
low-frequency eigenmodes in nano- and micro-mechanical systems. The mechanism
of the both effects is scattering of thermally excited vibrational modes off
the considered eigenmode. The scattering is accompanied by energy transfer of
$2\hbar\omega_0$ for nonlinear damping and is quasieleastic for dephasing. We
develop a formalism that allows studying both spatially uniform systems and
systems with a strong nonuniformity, which is smooth on the typical wavelength
of thermal modes but not their mean free path. The formalism accounts for the
decay of thermal modes, which plays a major role in the nonlinear damping and
dephasing. We identify the nonlinear analogs of the Landau-Rumer,
thermoelastic, and Akhiezer mechanisms and find the dependence of the
relaxation parameters on the temperature and the geometry of a system. | 1609.08714v1 |
2016-09-24 | Parametric Landau damping of space charge modes | Landau damping is the mechanism of plasma and beam stabilization; it arises
through energy transfer from collective modes to the incoherent motion of
resonant particles. Normally this resonance requires the resonant particle's
frequency to match the collective mode frequency. We have identified an
important new damping mechanism, {\it parametric Landau damping}, which is
driven by the modulation of the mode-particle interaction. This reveals new
possibilities for stability control through manipulation of both particle and
mode-particle coupling spectra. We demonstrate the existence of parametric
Landau damping in a simulation of transverse coherent modes of bunched
accelerator beams with space charge. | 1609.09393v3 |
2016-12-13 | Continuous-variable entanglement generated with a hybrid PT-symmetric system | We study a proposal of generating macroscopic continuous-variable
entanglement with two coupled waveguides respectively carrying optical damping
and optical gain. Moreover, a squeezing element is added into one or both
waveguides. We show that quantum noise effect existing in the process is
essential to the degree of the generated entanglement. It will totally
eliminate the entanglement in the setup of adding the squeezing element into
the waveguide filled with optical damping material, but will not completely
damp the entanglement to zero in the other configurations of having the
squeezing element in the gain medium or in both gain and damping medium. The
degree of the generated continuous-variable entanglement is irrelevant to the
intensities of the input light in coherent states. Moreover, the relations
between the entanglement and system parameters are illustrated in terms of the
dynamical evolutions of the created continuous-variable entanglement. | 1612.03996v2 |
2017-01-08 | Decentralized Robust Control for Damping Inter-area Oscillations in Power Systems | As power systems become more and more interconnected, the inter-area
oscillations has become a serious factor limiting large power transfer among
different areas. Underdamped (Undamped) inter-area oscillations may cause
system breakup and even lead to large-scale blackout. Traditional damping
controllers include Power System Stabilizer (PSS) and Flexible AC Transmission
System (FACTS) controller, which adds additional damping to the inter-area
oscillation modes by affecting the real power in an indirect manner. However,
the effectiveness of these controllers is restricted to the neighborhood of a
prescribed set of operating conditions. In this paper, decentralized robust
controllers are developed to improve the damping ratios of the inter-area
oscillation modes by directly affecting the real power through the turbine
governing system. The proposed control strategy requires only local signals and
is robust to the variations in operation condition and system topology. The
effectiveness of the proposed robust controllers is illustrated by detailed
case studies on two different test systems. | 1701.02036v1 |
2017-01-18 | Ion beam test results of the Plastic Scintillator Detector of DAMPE | The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). DAMPE can detect electrons, photons and ions in a
wide energy range (5 GeV to 10 TeV) and ions up to iron (100GeV to 100 TeV).
Plastic Scintillator Detector (PSD) is one of the four payloads in DAMPE,
providing e/{\gamma} separation and charge identification up to Iron. An ion
beam test was carried out for the Qualification Model of PSD in CERN with
40GeV/u Argon primary beams. The Birk's saturation and charge resolution of PSD
were investigated. | 1701.04947v2 |
2017-01-18 | DAMPE space mission: first data | The DAMPE (DArk Matter Particle Explorer) satellite was launched on December
17, 2015 and started its data taking operation a few days later.
DAMPE has a large geometric factor ($\sim~0.3\ m^2\ sr$) and provides good
tracking, calorimetric and charge measurements for electrons, gammas rays and
nuclei. This will allow precise measurement of cosmic ray spectra from tens of
$GeV$ up to about $100\ TeV$. In particular, the energy region between $1-100\
TeV$ will be explored with higher precision compared to previous experiments.
The various subdetectors allow an efficient identification of the electron
signal over the large (mainly proton-induced) background. As a result, the
all-electron spectrum will be measured with excellent resolution from few $GeV$
up to few $TeV$, thus giving the opportunity to identify possible contribution
of nearby sources. A report on the mission goals and status is presented,
together with the on-orbit detector performance and the first data coming from
space. | 1701.05046v1 |
2017-01-25 | Control Allocation for Wide Area Coordinated Damping | In this work, a modal-based sparse control allocation (CA) is proposed for
coordinated and fault-tolerant wide-area damping controllers (WADCs). In our
proposed method, the supervisory CA only communicates with necessary actuators
to achieve the required damping performance and in case of actuator failures
(e.g., due to loss of communication or scheduling), capabilities of the
remaining actuators are fully used before the nominal performance is degraded.
This method offers the advantages of modular design where WADC is initially
designed to achieve satisfactory damping without the detailed knowledge of
actuators. In the next step, CA is designed to manage actuator failures and
limitations without the need to redesign the nominal WADC. The proposed
approach is applied to a modified $286$-bus Western Electricity Coordinating
Council (WECC) system to verify the feasibility on a complex power system.
Simulation results indicate the effectiveness of the proposed method in
coordinating multiple actuators and building resiliency. | 1701.07456v1 |
2017-03-22 | Direct Measurement of Kramers Turnover with a Levitated Nanoparticle | Understanding the thermally activated escape from a metastable state is at
the heart of important phenomena such as the folding dynamics of proteins, the
kinetics of chemical reactions or the stability of mechanical systems. In 1940
Kramers calculated escape rates both in the high damping and the low damping
regime and suggested that the rate must have a maximum for intermediate
damping. This phenomenon, today known as the Kramers turnover, has triggered
important theoretical and numerical studies. However, to date there is no
direct and quantitative experimental verification of this turnover. Using a
nanoparticle trapped in a bi-stable optical potential we experimentally measure
the nanoparticle's transition rates for variable damping and directly resolve
the Kramers turnover. Our measurements are in agreement with an analytical
model that is free of adjustable parameters. | 1703.07699v2 |
2017-04-03 | Suppression of plasma echoes and Landau damping in Sobolev spaces by weak collisions in a Vlasov-Fokker-Planck equation | In this paper, we study Landau damping in the weakly collisional limit of a
Vlasov-Fokker-Planck equation with nonlinear collisions in the phase-space
$(x,v) \in \mathbb T_x^n \times \mathbb R^n_v$. The goal is four-fold: (A) to
understand how collisions suppress plasma echoes and enable Landau damping in
agreement with linearized theory in Sobolev spaces, (B) to understand how phase
mixing accelerates collisional relaxation, (C) to understand better how the
plasma returns to global equilibrium during Landau damping, and (D) to rule out
that collision-driven nonlinear instabilities dominate. We give an estimate for
the scaling law between Knudsen number and the maximal size of the perturbation
necessary for linear theory to be accurate in Sobolev regularity. We conjecture
this scaling to be sharp (up to logarithmic corrections) due to potential
nonlinear echoes in the collisionless model. | 1704.00425v2 |
2017-04-14 | Impulse-Based Hybrid Motion Control | The impulse-based discrete feedback control has been proposed in previous
work for the second-order motion systems with damping uncertainties. The
sate-dependent discrete impulse action takes place at zero crossing of one of
both states, either relative position or velocity. In this paper, the proposed
control method is extended to a general hybrid motion control form. We are
using the paradigm of hybrid system modeling while explicitly specifying the
state trajectories each time the continuous system state hits the guards that
triggers impulsive control actions. The conditions for a stable convergence to
zero equilibrium are derived in relation to the control parameters, while
requiring only the upper bound of damping uncertainties to be known. Numerical
examples are shown for an underdamped closed-loop dynamics with oscillating
transients, an upper bounded time-varying positive system damping, and system
with an additional Coulomb friction damping. | 1704.04372v5 |
2017-04-19 | Reliable channel-adapted error correction: Bacon-Shor code recovery from amplitude damping | We construct two simple error correction schemes adapted to amplitude damping
noise for Bacon-Shor codes and investigate their prospects for fault-tolerant
implementation. Both consist solely of Clifford gates and require far fewer
qubits, relative to the standard method, to achieve correction to a desired
order in the damping rate. The first, employing one-bit teleportation and
single-qubit measurements, needs only one fourth as many physical qubits, while
the second, using just stabilizer measurements and Pauli corrections, needs
only half. We show that existing fault-tolerance methods can be employed for
the latter, while the former can be made to avoid potential catastrophic errors
and can easily cope with damping faults in ancilla qubits. | 1704.05857v1 |
2017-04-30 | Comparison of dynamic mechanical properties of non-superheated and superheated A357 alloys | The influence of superheat treatment on the microstructure and dynamic
mechanical properties of A357 alloys has been investigated. The study of
microstructure was performed by the optical microscope. Dynamic mechanical
properties (storage modulus, loss modulus, and damping capacity) were measured
by the dynamic mechanical analyzer (DMA). Microstructure showed coarser and
angular eutectic Si particles with larger {\alpha}-Al dendrites in the
non-superheated A357 alloy. In contrast, finer and rounded eutectic Si
particles together with smaller and preferred oriented {\alpha}-Al dendrites
have been observed in the superheated A357 alloy. Dynamic mechanical properties
showed an increasing trend of loss modulus and damping capacity meanwhile a
decreasing trend of storage modulus at elevated temperatures for superheated
and non-superheated A357 alloys. The high damping capacity of superheated A357
has been ascribed to the grain boundary damping at elevated temperatures. | 1705.00350v1 |
2017-05-19 | Improving two - qubit state teleportation affected by amplitude damping noise based on choosing appropriate quantum channel | We consider two qubit teleportation via quantum channel affected by amplitude
damping noise. Addressing the same problem, X. Hu, Y. Gu, Q. Gong and G. Guo
[Phys. Rev. A 81, 054302, (2010)] recently showed that in presence of noise,
subjecting more qubits in quantum channel to amplitude damping can increase the
fidelity of teleportation protocol. However, in this paper, by making some
adjustments on quantum channel, we obtain teleportation fidelity which is even
higher than one in the case of X. Hu et al. Moreover, our strategy is simpler
than quantum distillation and compared to using weak measurement, it is
deterministic. Furthermore, explicit analysis of fidelity is provided, we show
that in general, choosing appropriate quantum channel enhances the ability of
teleportation better and negates the fact that more amplitude damping noise
more quality. | 1705.07064v2 |
2017-05-27 | Charge reconstruction study of the DAMPE Silicon-Tungsten Tracker with ion beams | The DArk Matter Particle Explorer (DAMPE) is one of the four satellites
within Strategic Pioneer Research Program in Space Science of the Chinese
Academy of Science (CAS). DAMPE can detect electrons, photons in a wide energy
range (5 GeV to 10 TeV) and ions up to iron (100GeV to 100 TeV).
Silicon-Tungsten Tracker (STK) is one of the four subdetectors in DAMPE,
providing photon-electron conversion, track reconstruction and charge
identification for ions. Ion beam test was carried out in CERN with 60GeV/u
Lead primary beams. Charge reconstruction and charge resolution of STK
detectors were investigated. | 1705.09791v1 |
2017-06-09 | Effect of oxygen plasma on nanomechanical silicon nitride resonators | Precise control of tensile stress and intrinsic damping is crucial for the
optimal design of nanomechanical systems for sensor applications and quantum
optomechanics in particular. In this letter we study the in uence of oxygen
plasma on the tensile stress and intrinsic damping of nanomechanical silicon
nitride resonators. Oxygen plasma treatments are common steps in micro and
nanofabrication. We show that oxygen plasma of only a few minutes oxidizes the
silicon nitride surface, creating several nanometer thick silicon dioxide
layers with a compressive stress of 1.30(16)GPa. Such oxide layers can cause a
reduction of the e ective tensile stress of a 50 nm thick stoichiometric
silicon nitride membrane by almost 50%. Additionally, intrinsic damping
linearly increases with the silicon dioxide lm thickness. An oxide layer of
1.5nm grown in just 10s in a 50W oxygen plasma almost doubled the intrinsic
damping. The oxide surface layer can be e ciently removed in bu ered HF. | 1706.02957v1 |
2017-07-03 | Quantum behaviour of pumped and damped triangular Bose Hubbard systems | We propose and analyse analogs of optical cavities for atoms using three-well
Bose-Hubbard models with pumping and losses. We consider triangular
configurations. With one well pumped and one damped, we find that both the
mean-field dynamics and the quantum statistics show a quantitative dependence
on the choice of damped well. The systems we analyse remain far from
equilibrium, preserving good coherence between the wells in the steady-state.
We find quadrature squeezing and mode entanglement for some parameter regimes
and demonstrate that the trimer with pumping and damping at the same well is
the stronger option for producing non-classical states. Due to recent
experimental advances, it should be possible to demonstrate the effects we
investigate and predict. | 1707.01000v1 |
2017-07-06 | Damping optimization of parameter dependent mechanical systems by rational interpolation | We consider an optimization problem related to semi-active damping of
vibrating systems. The main problem is to determine the best damping matrix
able to minimize influence of the input on the output of the system. We use a
minimization criteria based on the $\mathcal{H}_2$ system norm.
The objective function is non-convex and the associated optimization problem
typically requires a large number of objective function evaluations. We propose
an optimization approach that calculates `interpolatory' reduced order models,
allowing for significant acceleration of the optimization process.
In our approach, we use parametric model reduction (PMOR) based on the
Iterative Rational Krylov Algorithm, which ensures good approximations relative
to the $\mathcal{H}_2$ system norm, aligning well with the underlying damping
design objectives. For the parameter sampling that occurs within each PMOR
cycle, we consider approaches with predetermined sampling and approaches using
adaptive sampling, and each of these approaches may be combined with three
possible strategies for internal reduction. In order to preserve important
system properties, we maintain second-order structure, which through the use of
modal coordinates, allows for very efficient implementation.
The methodology proposed here provides a significant acceleration of the
optimization process; the gain in efficiency is illustrated in numerical
experiments. | 1707.01789v1 |
2017-07-08 | Nonlinear dynamics of damped DNA systems with long-range interactions | We investigate the nonlinear dynamics of a damped Peyrard-Bishop DNA model
taking into account long-range interactions with distance dependence |l|^-s on
the elastic coupling constant between different DNA base pairs. Considering
both Stokes and long-range hydrodynamical damping forces, we use the discrete
difference operator technique and show in the short wavelength modes that the
lattice equation can be governed by the complex Ginzburg-Landau equation. We
found analytically that the technique leads to the correct expression for the
breather soliton parameters. We found that the viscosity makes the amplitude of
the breather to damp out. We compare the approximate analytic results with
numerical simulations for the value s = 3 (dipole-dipole interactions). | 1707.02425v1 |
2017-08-05 | Dynamic Sensitivity Study of MEMS Capacitive Acceleration Transducer Based on Analytical Squeeze Film Damping and Mechanical Thermoelasticity Approaches | The dynamic behavior of a capacitive micro-electro-mechanical (MEMS)
accelerometer is evaluated by using a theoretical approach which makes use of a
squeeze film damping (SFD) model and ideal gas approach. The study investigates
the performance of the device as a function of the temperature, from 228 K to
398 K, and pressure, from 20 to 1000 Pa, observing the damping gas trapped
inside de mechanical transducer. Thermoelastic properties of the silicon bulk
are considered for the entire range of temperature. The damping gases
considered are Air, Helium and Argon. The global behavior of the system is
evaluated considering the electro-mechanical sensitivity (SEM) as the main
figure of merit in frequency domain. The results show the behavior of the main
mechanism losses of SFD, as well as the dynamic sensitivity of the MEMS
transducer system, and are in good agreement with experimental dynamic results
behavior. | 1708.01812v1 |
2017-09-01 | Scaling of the Rashba spin-orbit torque in magnetic domain walls | Spin-orbit torque in magnetic domain walls was investigated by solving the
Pauli-Schr\"{o}dinger equation for the itinerant electrons. The Rashba
interaction considered is derived from the violation of inversion symmetry at
interfaces between ferromagnets and heavy metals. In equilibrium, the Rashba
spin-orbit interaction gives rise to a torque corresponding to the
Dzyaloshinskii-Moriya interaction. When there is a current flowing, the
spin-orbit torque experienced by the itinerant electrons in short domain walls
has both field-like and damping-like components. However, when the domain wall
width is increased, the damping-like component, which is the counterpart of the
non-adiabatic spin transfer torque, decreases rapidly at the domain wall
center. In contrast to the non-adiabatic spin transfer torque, the damping-like
spin-orbit torque does not approach to zero far away from the domain wall
center, even in the adiabatic limit. The scattering of spin-up and spin-down
wave functions, which is caused by the Rashba spin-orbit interaction and the
spatial variation of magnetization profile in the domain wall, gives rise to
the finite damping-like spin-orbit torque. | 1709.00187v3 |
2017-09-12 | Temperature effects on MIPs in the BGO calorimeters of DAMPE | In this paper, we presented a study of temperature effects on BGO
calorimeters using proton MIP's collected in the first year operation of DAMPE.
By directly comparing MIP calibration constants used by DAMPE data production
pipe line, we found an experimental relation between temperature and signal
amplitudes of each BGO bar: a general deviation of -1.162%/$^{\circ}$C,and
-0.47%/$^{\circ}$C to -1.60%/$^{\circ}$C statistically for each detector
element. During 2016, DAMPE's temperature changed by about 7 degrees due to
solar elevation angle and the corresponding energy scale bias is about 8%. By
frequent MIP calibration operation, this kind of bias is eliminated to an
acceptable value. | 1709.03735v2 |
2017-09-28 | Universal and approximate relations for the gravitational-wave damping timescale of $f$-modes in neutron stars | Existing estimates of the gravitational-wave damping timescale of the
dominant quadrupole oscillation mode in the case of rapidly rotating stars are
based on using a Newtonian estimate for the energy of the mode, in combination
with the lowest-order post-Newtonian quadrupole formula for estimating the
gravitational-wave luminosity. We investigate a number of other choices for
estimating the gravitational-wave damping timescale in the nonrotating limit
and construct a highly accurate, empirically corrected formula that has a
maximum relative error of only 3% with respect to the perturbative result in
full general relativity. The expressions involved are sufficiently general to
be extended to the case of rapidly rotating stars. We also present a new
higher-order empirical relation for the gravitational-wave damping timescale of
quadrupole oscillations that is accurate in the whole range of expected values
for the compactness of neutron stars, without the need for involving the moment
of inertia. | 1709.10067v2 |
2017-10-09 | Time-dependent propagation speed vs strong damping for degenerate linear hyperbolic equations | We consider a degenerate abstract wave equation with a time-dependent
propagation speed. We investigate the influence of a strong dissipation, namely
a friction term that depends on a power of the elastic operator.
We discover a threshold effect. If the propagation speed is regular enough,
then the damping prevails, and therefore the initial value problem is
well-posed in Sobolev spaces. Solutions also exhibit a regularizing effect
analogous to parabolic problems. As expected, the stronger is the damping, the
lower is the required regularity.
On the contrary, if the propagation speed is not regular enough, there are
examples where the damping is ineffective, and the dissipative equation behaves
as the non-dissipative one. | 1710.03602v1 |
2017-10-31 | Improving mechanical sensor performance through larger damping | Mechanical resonances are used in a wide variety of devices; from smart phone
accelerometers to computer clocks and from wireless communication filters to
atomic force microscope sensors. Frequency stability, a critical performance
metric, is generally assumed to be tantamount to resonance quality factor (the
inverse of the linewidth and of the damping). Here we show that frequency
stability of resonant nanomechanical sensors can generally be made independent
of quality factor. At high bandwidths, we show that quality factor reduction is
completely mitigated by increases in signal to noise ratio. At low bandwidths,
strikingly, increased damping leads to better stability and sensor resolution,
with improvement proportional to damping. We confirm the findings by
demonstrating temperature resolution of 50 \mu K at 200 Hz bandwidth. These
results open the door for high performance ultrasensitive resonant sensors in
gaseous or liquid environments, single cell nanocalorimetry, nanoscale gas
chromatography, and atmospheric pressure nanoscale mass spectrometry. | 1710.11280v1 |
2017-11-30 | The electron-flavored Z'-portal dark matter and the DAMPE cosmic ray excess | The DAMPE experiment has recently reported strong indications for the
existence of an excess of high-energy electrons and positrons. If interpreted
in terms of the annihilation of dark matter, the DAMPE result restricts the
dark matter mass and possible annihilation channels to a few case. In this
paper we explain the DAMPE result with the electron-flavored $Z^\prime$-portal
fermionic dark matter. We show that the Dirac dark matter scenario is promising
to explain the excess via the process $\bar \chi \chi \to\mathbf{Z}'\to \bar e
e$. The reduced annihilation cross section is limited in a range of
$10^{-26}\sim 10^{-24}~{\rm cm^3 s^{-1}}$ to interpret the excess. | 1711.11182v2 |
2017-12-04 | DAMPE Electron-Positron Excess in Leptophilic $Z'$ model | Recently the DArk Matter Particle Explorer (DAMPE) has reported an excess in
the electron-positron flux of the cosmic rays which is interpreted as a dark
matter particle with the mass about $1.5$ TeV. We come up with a leptophilic
$Z'$ scenario including a Dirac fermion dark matter candidate which beside
explaining the observed DAMPE excess, is able to pass various
experimental/observational constraints including the relic density value from
the WMAP/Planck, the invisible Higgs decay bound at the LHC, the LEP bounds in
electron-positron scattering, the muon anomalous magnetic moment constraint,
Fermi-LAT data, and finally the direct detection experiment limits from the
XENON1t/LUX. By computing the electron-positron flux produced from a dark
matter with the mass about $1.5$ TeV we show that the model predicts the peak
observed by the DAMPE. | 1712.01239v4 |
2017-12-06 | Confronting the DAMPE Excess with the Scotogenic Type-II Seesaw Model | The DArk Matter Particle Explorer (DAMPE) has observed a tentative peak at
$E\sim1.4~\TeV$ in the cosmic-ray electron spectrum. In this paper, we
interpret this excess in the scotogenic type-II seesaw model. This model
extends the canonical type-II seesaw model with dark matter (DM) candidates and
a loop-induced vacuum expectation value of the triplet scalars, $v_\Delta$,
resulting in small neutrino masses naturally even for TeV scale triplet
scalars. Assuming a nearby DM subhalo, the DAMPE excess can be explained by DM
annihilating into a pair of triplet scalars which subsequently decay to charged
lepton final states. Spectrum fitting of the DAMPE excess indicates it
potentially favors the inverted neutrino mass hierarchy. We also discuss how to
evade associated neutrino flux in our model. | 1712.02021v3 |
2018-02-28 | Beliaev Damping in Spin-$\frac{1}{2}$ Interacting Bosons with Spin-Orbit Coupling | Beliaev damping provides one of the most important mechanisms for dissipation
of quasiparticles through beyond-mean-field effects at zero temperature. Here
we present the first analytical result of Beliaev damping in low-energy
excitations of spin-$\frac{1}{2}$ interacting bosons with equal Rashba and
Dresslhaus spin-orbit couplings. We identify novel features of Beliaev decay
rate due to spin-orbit coupling, in particular, it shows explicit dependence on
the spin-density interaction and diverges at the interaction-modified phase
boundary between the zero-momentum and plane-wave phases. This represents a
manifestation of the effect of spin-orbit coupling in the beyond-mean-field
regime, which by breaking Galilean invariance couples excitations in the
density- and spin-channels. By describing the Beliaev damping in terms of the
observable dynamic structure factors, our results allow direct experimental
access within current facilities. | 1802.10295v1 |
2018-03-03 | Universal stabilization of single-qubit states using a tunable coupler | We theoretically analyze a scheme for fast stabilization of arbitrary qubit
states with high fidelities, extending a protocol recently demonstrated
experimentally [Lu et al., Phys. Rev. Lett. 119, 150502 (2017)]. That
experiment utilized red and blue sideband transitions in a system composed of a
fluxonium qubit, a low-Q LC-oscillator, and a coupler enabling us to tune the
interaction between them. Under parametric modulations of the coupling
strength, the qubit can be steered into any desired pure or mixed single-qubit
state. For realistic circuit parameters, we predict that stabilization can be
achieved within 100 ns. By varying the ratio between the oscillator's damping
rate and the effective qubit-oscillator coupling strength, we can switch
between under-damped, critically-damped, and over-damped stabilization and find
optimal working points. We further analyze the effect of thermal fluctuations
and show that the stabilization scheme remains robust for realistic
temperatures. | 1803.01079v3 |
2018-04-30 | Wave-like blow-up for semilinear wave equations with scattering damping and negative mass term | In this paper we establish blow-up results and lifespan estimates for
semilinear wave equations with scattering damping and negative mass term for
subcritical power, which is the same as that of the corresponding problem
without mass term, and also the same as that of the corresponding problem
without both damping and mass term. For this purpose, we have to use the
comparison argument twice, due to the damping and mass term, in additional to a
key multiplier. Finally, we get the desired results by an iteration argument. | 1804.11073v3 |
2018-05-22 | Uniqueness of the Cauchy datum for the tempered-in-time response and conductivity operator of a plasma | We study the linear Vlasov equation with a given electric field $E \in
\mathcal{S}$, where $\mathcal{S}$ is the space of Schwartz functions. The
associated damped partial differential equation has a unique tempered solution,
which fixes the needed Cauchy datum. This tempered solution then converges to
the causal solution of the linear Vlasov equation when the damping parameter
goes to zero. This result allows us to define the plasma conductivity operator
$\sigma$, which gives the current density $j = \sigma (E)$ induced by the
electric field $E$. We prove that $\sigma$ is continuous from $\mathcal{S}$ to
its dual $\mathcal{S}^\prime$. We can treat rigorously the case of uniform
non-magnetized non-relativistic plasma (linear Landau damping) and the case of
uniform magnetized relativistic plasma (cyclotron damping). In both cases, we
demonstrate that the main part of the conductivity operator is a
pseudo-differential operator and we give its expression rigorously. This
matches the formal results widely used in the theoretical physics community. | 1805.08733v3 |
2018-05-26 | Stabilization for the wave equation with singular Kelvin-Voigt damping | We consider the wave equation with Kelvin-Voigt damping in a bounded domain.
The exponential stability result proposed by Liu and Rao or T\'ebou for that
system assumes that the damping is localized in a neighborhood of the whole or
a part of the boundary under some consideration. In this paper we propose to
deal with this geometrical condition by considering a singular Kelvin-Voigt
damping which is localized faraway from the boundary. In this particular case
it was proved by Liu and Liu the lack of the uniform decay of the energy.
However, we show that the energy of the wave equation decreases logarithmically
to zero as time goes to infinity. Our method is based on the frequency domain
method. The main feature of our contribution is to write the resolvent problem
as a transmission system to which we apply a specific Carleman estimate. | 1805.10430v1 |
2018-06-01 | Fluctuation-damping of isolated, oscillating Bose-Einstein condensates | Experiments on the nonequilibrium dynamics of an isolated Bose-Einstein
condensate (BEC) in a magnetic double-well trap exhibit a puzzling divergence:
While some show dissipation-free Josephson oscillations, others find strong
damping. Such damping in isolated BECs cannot be understood on the level of the
coherent Gross-Pitaevskii dynamics. Using the Keldysh functional-integral
formalism, we describe the time-dependent system dynamics by means of a
multi-mode BEC coupled to fluctuations (single-particle excitations) beyond the
Gross-Pitaevskii saddle point. We find that the Josephson oscillations excite
an excess of fluctuations when the effective Josephson frequency,
$\tilde{\omega}_J$, is in resonance with the effective fluctuation energy,
$\tilde{\varepsilon}_m$, where both, $\tilde{\omega}_J$ and
$\tilde{\varepsilon}_m$, are strongly renormalized with respect to their
noninteracting values. Evaluating and using the model parameters for the
respective experiments describes quantitatively the presence or absence of
damping. | 1806.00376v2 |
2018-06-05 | Decoherence assisted spin squeezing generation in superposition of tripartite GHZ and W states | In the present paper, we study spin squeezing under decoherence in the
superposition of tripartite maximally entangled GHZ and W states. Here we use
amplitude damping, phase damping and depolarisation channel. We have
investigated the dynamics of spin squeezing with the interplay of superposition
and decoherence parameters with different directions of the mean spin vector.
We have found the mixture of GHZ and W states is robust against spin squeezing
generation for amplitude damping and phase damping channels for certain
directions of the mean spin vector. However, the depolarisation channel
performs well for spin squeezing generation and generates permanent spin
squeezing in the superposition of GHZ and W states. | 1806.01730v1 |
2018-07-31 | Dark Matter Particle Explorer observations of high-energy cosmic ray electrons plus positrons and their physical implications | The DArk Matter Particle Explorer (DAMPE) is a satellite-borne, high-energy
particle and $\gamma$-ray detector, which is dedicated to indirectly detecting
particle dark matter and studying high-energy astrophysics. The first results
about precise measurement of the cosmic ray electron plus positron spectrum
between 25 GeV and 4.6 TeV were published recently. The DAMPE spectrum reveals
an interesting spectral softening around $0.9$ TeV and a tentative peak around
$1.4$ TeV. These results have inspired extensive discussion. The detector of
DAMPE, the data analysis, and the first results are introduced. In particular,
the physical interpretations of the DAMPE data are reviewed. | 1807.11638v1 |
2018-08-08 | A Hybrid Dynamic-regenerative Damping Scheme for Energy Regeneration in Variable Impedance Actuators | Increasing research efforts have been made to improve the energy efficiency
of variable impedance actuators (VIAs) through reduction of energy consumption.
However, the harvesting of dissipated energy in such systems remains
underexplored. This study proposes a novel variable damping module design
enabling energy regeneration in VIAs by exploiting the regenerative braking
effect of DC motors. The proposed damping module uses four switches to combine
regenerative and dynamic braking, in a hybrid approach that enables energy
regeneration without reduction in the range of damping achievable. Numerical
simulations and a physical experiment are presented in which the proposed
module shows an optimal trade-off between task performance and energy
efficiency. | 1808.03143v1 |
2018-08-15 | $L^1$ estimates for oscillating integrals and their applications to semi-linear models with $σ$-evolution like structural damping | The present paper is a continuation of our recent paper \cite{DaoReissig}. We
will consider the following Cauchy problems for semi-linear structurally damped
$\sigma$-evolution models: \begin{equation*} u_{tt}+ (-\Delta)^\sigma u+ \mu
(-\Delta)^\delta u_t = f(u,u_t),\, u(0,x)= u_0(x),\, u_t(0,x)=u_1(x)
\end{equation*} with $\sigma \ge 1$, $\mu>0$ and $\delta \in
(\frac{\sigma}{2},\sigma]$. Our aim is to study two main models including
$\sigma$-evolution models with structural damping $\delta \in
(\frac{\sigma}{2},\sigma)$ and those with visco-elastic damping
$\delta=\sigma$. Here the function $f(u,u_t)$ stands for power nonlinearities
$|u|^{p}$ and $|u_t|^{p}$ with a given number $p>1$. We are interested in
investigating the global (in time) existence of small data solutions to the
above semi-linear models from suitable spaces basing on $L^q$ space by assuming
additional $L^{m}$ regularity on the initial data, with $q\in (1,\infty)$ and
$m\in [1,q)$. | 1808.05484v2 |
2018-09-26 | Permutation-invariant constant-excitation quantum codes for amplitude damping | The increasing interest in using quantum error correcting codes in practical
devices has heightened the need for designing quantum error correcting codes
that can correct against specialized errors, such as that of amplitude damping
errors which model photon loss. Although considerable research has been devoted
to quantum error correcting codes for amplitude damping, not so much attention
has been paid to having these codes simultaneously lie within the decoherence
free subspace of their underlying physical system. One common physical system
comprises of quantum harmonic oscillators, and constant-excitation quantum
codes can be naturally stabilized within them. The purpose of this paper is to
give constant-excitation quantum codes that not only correct amplitude damping
errors, but are also immune against permutations of their underlying modes. To
construct such quantum codes, we use the nullspace of a specially constructed
matrix based on integer partitions. | 1809.09801v4 |
2018-09-30 | Critical behavior of the damping rate of GHz acoustic phonons in SrTiO3 at the antiferrodistortive phase transition measured by time- and frequency-resolved Brillouin scattering | We determine the temperature dependent damping rate of longitudinal acoustic
phonons in SrTiO3 using frequency domain Brillouin scattering and time domain
Brillouin scattering. We investigate samples with (La,Sr)MnO3 and SrRuO3
capping layers, which result in compressive or tensile strain at the layer -
substrate interface, respectively. The different strain states lead to dif-
ferent domain structures in SrTiO3 that extend into the bulk of the SrTiO3
substrates and strongly affect the phonon propagation. Our experiments show
that the damping rate of acoustic phonons in the interfacial STO layer depends
strongly on the sample temperature and strain induced do- main structure. We
also show that the damping rate as function of temperature exhibits a critical
behavior close to the cubic-to-tetragonal phase transition of SrTiO3. | 1810.00381v1 |
2018-12-04 | Spin transport in a magnetic insulator with zero effective damping | Applications based on spin currents strongly profit from the control and
reduction of their effective damping and their transport properties. We here
experimentally observe magnon mediated transport of spin (angular) momentum
through a 13.4 nm thin yttrium iron garnet film with full control of the
magnetic damping via spin-orbit torque. Above a critical spin-orbit torque, the
fully compensated damping manifests itself as an increase of magnon
conductivity by almost two orders of magnitude. We compare our results to
theoretical expectations based on recently predicted current induced magnon
condensates and discuss other possible origins of the observed critical
behaviour. | 1812.01334v3 |
2019-01-10 | Data-Driven Online Optimization for Enhancing Power System Oscillation Damping | This paper reports an initial work on power system oscillation damping
improvement using a data-driven online optimization method. An online
oscillation damping optimization mod-el is proposed and formulated in a form
solvable by the data-driven method. Key issues in the online optimization
procedures, including the damping sensitivity identification method, its
compatibility with the dispatch plans, as well as other practical issues in
real large-scale system are discussed. Simulation results based on the 2-area
4-machine system, and the NETS-NYPS 68-bus system verify the feasibility and
efficiency of the proposed method. The results also show the capability of the
proposed method to bridge the gap between online data analysis and complex
optimization for power system dynamics. | 1901.03167v2 |
2019-01-15 | Continuum damping effects in nuclear collisions associated with twisted boundary conditions | The time-dependent Skyrme Hartree-Fock calculations have been performed to
study $^{24}$Mg +$^{24}$Mg collisions. The twisted boundary conditions, which
can avoid finite box-size effects of the employed 3D coordinate space, have
been implemented. The prolate deformed $^{24}$Mg has been set to different
orientations to study vibrations and rotations of the compound nucleus
$^{48}$Cr. Our time evolution results show continuum damping effects associated
with the twist-averaged boundary condition play a persistent role after the
fusion stage. In particular, a rotational damping in continuum is presented in
calculations of both twist-averaged and absorbing boundary conditions, in which
damping widths can be clearly extracted. It is unusual that the rotating
compound nucleus in continuum evolves towards spherical but still has a
considerable angular momentum. | 1901.04736v2 |
2019-03-07 | Investigating optically-excited THz standing spin waves using noncollinear magnetic bilayers | We investigate optically excited THz standing spin waves in noncollinear
magnetic bilayers. Using femtosecond laser-pulse excitation, a spin current is
generated in the first ferromagnetic (FM) layer, and flows through a conductive
spacer layer to be injected into the second (transverse) FM layer, where it
exerts a spin-transfer torque on the magnetization and excites higher-order
standing spin waves. We show that the noncollinear magnetic bilayer is a
convenient tool that allows easy excitation of THz spin waves, and can be used
to investigate the dispersion and thereby the spin wave stiffness parameter in
the thin-film regime. This is experimentally demonstrated using wedge-shaped Co
and CoB (absorption) layers. Furthermore, the damping of these THz spin waves
is investigated, showing a strong increase of the damping with decreasing
absorption layer thickness, much stronger than expected from interface spin
pumping effects. Additionally, a previously unseen sudden decrease in the
damping for the thinnest films is observed. A model for the additional damping
contribution incorporating both these observations is proposed. | 1903.02802v1 |
2019-03-14 | An analog simulation experiment to study free oscillations of a damped simple pendulum | The characteristics of drive-free oscillations of a damped simple pendulum
under sinusoidal potential force field differ from those of the damped harmonic
oscillations. The frequency of oscillation of a large amplitude simple pendulum
decreases with increasing amplitude. Many prototype mechanical simple pendulum
have been fabricated with precision and studied earlier in view of introducing
them in undergraduate physics laboratories. However, fabrication and
maintenance of such mechanical pendulum require special skill. In this work, we
set up an analog electronic simulation experiment to serve the purpose of
studying the force-free oscillations of a damped simple pendulum. We present
the details of the setup and some typical results of our experiment. The
experiment is simple enough to implement in undergraduate physics laboratories. | 1903.06162v1 |
2019-03-15 | Frictional Damping in Biomimetic Scale Beam Oscillations | Stiff scales adorn the exterior surfaces of fishes, snakes, and many
reptiles. They provide protection from external piercing attacks and control
over global deformation behavior to aid locomotion, slithering, and swimming
across a wide range of environmental condition. In this letter, we investigate
the dynamic behavior of biomimetic scale substrates for further understanding
the origins of the nonlinearity that involve various aspect of scales
interaction, sliding kinematics, interfacial friction, and their combination.
Particularly, we study the vibrational characteristics through an analytical
model and numerical investigations for the case of a simply supported scale
covered beam. Our results reveal for the first time that biomimetic scale beams
exhibit viscous damping behavior even when only Coulomb friction is postulated
for free vibrations. We anticipate and quantify the anisotropy in the damping
behavior with respect to curvature. We also find that unlike static pure
bending where friction increases bending stiffness, a corresponding increase in
natural frequency for the dynamic case does not arise for simply supported
beam. Since both scale geometry, distribution and interfacial properties can be
easily tailored, our study indicates a biomimetic strategy to design
exceptional synthetic materials with tailorable damping behavior. | 1903.06819v1 |
2019-04-08 | Damping control in viscoelastic beam dynamics | Viscoelasticity plays a key role in many practical applications and in
different reasearch fields, such as in seals, sliding-rolling contacts and
crack propagation. In all these contexts, a proper knowledge of the
viscoelastic modulus is very important. However, the experimental
characterization of the frequency dependent modulus, carried out through
different standard procedures, still presents some complexities, then possible
alternative approaches are desirable. For example, the experimental
investigation of viscoelastic beam dynamics would be challenging, especially
for the intrinsic simplicity of this kind of test. This is why, a deep
understanding of damping mechanisms in viscoelastic beams results to be a quite
important task to better predict their dynamics. With the aim to enlighten
damping properties in such structures, an analytical study of the transversal
vibrations of a viscoelastic beam is presented in this paper. Some
dimensionless parameters are defined, depending on the material properties and
the beam geometry, which enable to shrewdly design the beam dynamics. In this
way, by properly tuning such disclosed parameters, for example the
dimensionless beam length or a chosen material, it is possible to enhance or
suppress some resonant peaks, one at a time or more simultaneously. This is a
remarkable possibility to efficiently control damping in these structures, and
the results presented in this paper may help in elucidating experimental
procedures for the characterization of viscoelastic materials. | 1904.03875v1 |
2019-04-28 | On the Kolmogorov dissipation law in a damped Navier-Stokes equation | We consider here the Navier-Stokes equations in $\mathbb{R}^{3}$ with a
stationary, divergence-free external force and with an additional damping term
that depends on two parameters. We first study the well-posedness of weak
solutions for these equations and then, for a particular set of the damping
parameters, we will obtain an upper and lower control for the energy
dissipation rate $\varepsilon$ according to the Kolmogorov K41 theory. However,
although the behavior of weak solutions corresponds to the K41 theory, we will
show that in some specific cases the damping term introduced in the
Navier-Stokes equations could annihilate the turbulence even though the Grashof
number (which are equivalent to the Reynolds number) are large. | 1904.12382v1 |
2019-04-23 | Entanglement sudden death and birth effects in two qubits maximally entangled mixed states under quantum channels | In the present article, the robustness of entanglement in two qubits
maximally entangled mixed states (MEME) have been studied under quantum
decoherence channels. Here we consider bit flip, phase flip, bit-phase-flip,
amplitude damping, phase damping and depolarization channels. To quantify the
entanglement, the concurrence has been used as an entanglement measure. During
this study interesting results have been found for sudden death and birth of
entanglement under bit flip and bit-phase-flip channels. While amplitude
damping channel produces entanglement sudden death and does not allow re-birth
of entanglement. On the other hand, two qubits MEMS exhibit the robust
character against the phase flip, phase damping and depolarization channels.
The elegant behavior of all the quantum channels have been investigated with
varying parameter of quantum state MEMS in different cases. | 1904.12630v2 |
2019-05-24 | Multicomponent Dark Matter in the Light of CALET and DAMPE | In the light of the latest measurements on the total $e^+ + e^-$ flux by
CALET and DAMPE experiments, we revisit the multicomponent leptonically
decaying dark matter (DM) explanations to the cosmic-ray electron/positron
excesses observed previously. Especially, we use the single and
double-component DM models to explore the compatibility of the AMS-02 positron
fraction with the new CALET or DAMPE data. It turns out that neither single nor
double-component DM models are able to fit the AMS-02 positron fraction and
DAMPE total $e^+ + e^-$ flux data simultaneously. On the other hand, for the
combined AMS-02 and CALET dataset, both the single and double-component DM
models can provide reasonable fits. If we further take into the diffuse
$\gamma$-ray constraints from Fermi-LAT, only the double-component DM models
are allowed. | 1905.10136v3 |
2019-05-30 | Quantum dynamical speedup in correlated noisy channels | The maximal evolution speed of a quantum system can be represented by quantum
speed limit time (QSLT).We investigate QSLT of a two-qubit system passing
through a correlated channel (amplitude damping, phase damping, and
depolarizing).By adjusting the correlation parameter of channel and the initial
entanglement,a method to accelerate the evolution speed of the system for some
specific channels is proposed.It is shown that, in amplitude damping channel
and depolarizing channel,QSLT may be shortened in some cases by increasing
correlation parameter of the channel and initial entanglement, which are in
sharp contrast to phase damping channel.In particular, under depolarizing
channels, the transition from no-speedup evolution to speedup evolution for the
system can be realized by changing correlation strength of the channel. | 1905.12911v3 |
2019-07-01 | Probing superfluid $^4\mathrm{He}$ with high-frequency nanomechanical resonators down to $\mathrm{mK}$ temperatures | Superfluids, such as superfluid $^3\mathrm{He}$ and $^4\mathrm{He}$, exhibit
a broad range of quantum phenomena and excitations which are unique to these
systems. Nanoscale mechanical resonators are sensitive and versatile force
detectors with the ability to operate over many orders of magnitude in damping.
Using nanomechanical-doubly clamped beams of extremely high quality factors
($Q>10^6$), we probe superfluid $^4\mathrm{He}$ from the superfluid transition
temperature down to $\mathrm{mK}$ temperatures at frequencies up to $11.6 \,
\mathrm{MHz}$. Our studies show that nanobeam damping is dominated by
hydrodynamic viscosity of the normal component of $^4\mathrm{He}$ above
$1\,\mathrm{K}$. In the temperature range $0.3-0.8\,\mathrm{K}$, the ballistic
quasiparticles (phonons and rotons) determine the beams' behavior. At lower
temperatures, damping saturates and is determined either by magnetomotive
losses or acoustic emission into helium. It is remarkable that all these
distinct regimes can be extracted with just a single device, despite damping
changing over six orders of magnitude. | 1907.00970v1 |
2019-07-15 | Asymptotic profiles of solutions for regularity-loss type generalized thermoelastic plate equations and their applications | In this paper, we consider generalized thermoelastic plate equations with
Fourier's law of heat conduction. By introducing a threshold for decay
properties of regularity-loss, we investigate decay estimates of solutions
with/without regularity-loss in a framework of weighted $L^1$ spaces.
Furthermore, asymptotic profiles of solutions are obtained by using
representations of solutions in the Fourier space, which are derived by
employing WKB analysis. Next, we study generalized thermoelastic plate
equations with additional structural damping, and analysis the influence of
structural damping on decay properties and asymptotic profiles of solutions. We
find that the regularity-loss structure is destroyed by structural damping.
Finally, we give some applications of our results on thermoelastic plate
equations and damped Moore-Gibson-Thompson equation. | 1907.06344v1 |
2019-07-21 | Critical Thresholds in One Dimensional Damped Euler-Poisson Systems | This paper is concerned with the critical threshold phenomenon for one
dimensional damped, pressureless Euler-Poisson equations with electric force
induced by a constant background, originally studied in [S. Engelberg and H.
Liu and E. Tadmor, Indiana Univ. Math. J., 50:109--157, 2001]. A simple
transformation is used to linearize the characteristic system of equations,
which allows us to study the geometrical structure of critical threshold curves
for three damping cases: overdamped, underdamped and borderline damped through
phase plane analysis. We also derive the explicit form of these critical
curves. These sharp results state that if the initial data is within the
threshold region, the solution will remain smooth for all time, otherwise it
will have a finite time breakdown. Finally, we apply these general results to
identify critical thresholds for a non-local system subjected to initial data
on the whole line. | 1907.09039v1 |
2019-07-23 | Ignatyuk damping factor: A semiclassical formula | Data on nuclear level densities extracted from transmission data or gamma
energy spectrum store the basic statistical information about nuclei at various
temperatures. Generally this extracted data goes through model fitting using
computer codes like CASCADE. However, recently established semiclassical
methods involving no adjustable parameters to determine the level density
parameter for magic and semi-magic nuclei give a good agreement with the
experimental values. One of the popular ways to paramaterize the level density
parameter which includes the shell effects and its damping was given by
Ignatyuk. This damping factor is usually fitted from the experimental data on
nuclear level density and it comes around 0.05 $MeV^{-1}$. In this work we
calculate the Ignatyuk damping factor for various nuclei using semiclassical
methods. | 1907.09770v1 |
2019-08-13 | Dynamics of Riemann waves with sharp measure-controlled damping | This paper is concerned with locally damped semilinear wave equations defined
on compact Riemannian manifolds with boundary. We present a construction of
measure-controlled damping regions which are sharp in the sense that their
summed interior and boundary measures are arbitrarily small. The construction
of this class of open sets is purely geometric and allows us to prove a new
observability inequality in terms of potential energy rather than the usual one
with kinetic energy. A unique continuation property is also proved. Then, in
three-dimension spaces, we establish the existence of finite dimensional smooth
global attractors for a class of wave equations with nonlinear damping and
forces with critical Sobolev growth. In addition, by means of an obstacle
control condition, we show that our class of measure-controlled regions
satisfies the well-known geometric control condition (GCC). Therefore, many of
known results for the stabilization of wave equations hold true in the present
context. | 1908.04814v1 |
2019-08-15 | Sharp polynomial decay rates for the damped wave equation with Hölder-like damping | We study decay rates for the energy of solutions of the damped wave equation
on the torus. We consider dampings invariant in one direction and bounded above
and below by multiples of $x^{\beta}$ near the boundary of the support and show
decay at rate $1/t^{\frac{\beta+2}{\beta+3}}$. In the case where $W$ vanishes
exactly like $x^{\beta}$ this result is optimal by work of the second author.
The proof uses a version of the Morawetz multiplier method. | 1908.05631v3 |
2019-08-26 | Revisiting the Coulomb-Damped Harmonic Oscillator | The force of dry friction is studied extensively in introductory physics but
its effect on oscillations is hardly ever mentioned. Instead, to provide a
mathematically tractable introduction to damping, virtually all authors adopt a
viscous resistive force. While exposure to linear damping is of paramount
importance to the student of physics, the omission of Coulomb damping might
have a negative impact on the way the students conceive of the subject. In the
paper, we propose to approximate the action of Coulomb friction on a harmonic
oscillator by a sinusoidal resistive force whose amplitude is the model's only
free parameter. We seek the value of this parameter that yields the best fit
and obtain a closed-form analytic solution, which is shown to nicely fit the
numerical one. | 1908.10363v1 |
2019-09-21 | Resonant absorption of kink oscillations in coronal flux tubes with continuous magnetic twist | There are observational evidences for the existence of twisted magnetic field
in the solar corona. Here, we have investigated resonant damping of the
magnetohydrodynamic (MHD) kink waves in magnetic flux tubes. A realistic model
of the tube with continuous magnetic twist and radially inhomogeneous density
profile has been considered. We have obtained the dispersion relation of the
kink wave using the solution to the linear MHD equations outside the density
inhomogeneity and the appropriate connection formula to the solutions across
the thin transitional boundary layer. The dependence of the oscillation
frequency and damping rate of the waves on the twist parameter and longitudinal
wavenumber has been investigated. For the flux tube parameters considered in
this paper, we obtain rapid damping of the kink waves comparable to the
observations. In order to justify this rapid damping, depending on the sign of
the azimuthal kink mode number, $m=+1$ or $m=-1$, the background magnetic field
must have left handed or right handed twisted profile, respectively. For the
model considered here, the resonant absorption occurs only when the twist
parameter is in a range specified by the density contrast. | 1909.09787v1 |
2019-10-22 | Controlled nonlinear magnetic damping in spin-Hall nano-devices | Large-amplitude magnetization dynamics is substantially more complex compared
to the low-amplitude linear regime, due to the inevitable emergence of
nonlinearities. One of the fundamental nonlinear phenomena is the nonlinear
damping enhancement, which imposes strict limitations on the operation and
efficiency of magnetic nanodevices. In particular, nonlinear damping prevents
excitation of coherent magnetization auto-oscillations driven by the injection
of spin current into spatially extended magnetic regions. Here, we propose and
experimentally demonstrate that nonlinear damping can be controlled by the
ellipticity of magnetization precession. By balancing different contributions
to anisotropy, we minimize the ellipticity and achieve coherent magnetization
oscillations driven by spatially extended spin current injection into a
microscopic magnetic disk. Our results provide a novel route for the
implementation of efficient active spintronic and magnonic devices driven by
spin current. | 1910.09801v1 |
2019-10-24 | The lifespan of solutions of semilinear wave equations with the scale-invariant damping in two space dimensions | In this paper, we study the initial value problem for semilinear wave
equations with the time-dependent and scale-invariant damping in two
dimensions. Similarly to the one dimensional case by Kato, Takamura and Wakasa
in 2019, we obtain the lifespan estimates of the solution for a special
constant in the damping term, which are classified by total integral of the sum
of the initial position and speed. The key fact is that, only in two space
dimensions, such a special constant in the damping term is a threshold between
"wave-like" domain and "heat-like" domain. As a result, we obtain a new type of
estimate especially for the critical exponent. | 1910.11692v2 |
2019-11-05 | Exceptional points in dissipatively coupled spin dynamics | We theoretically investigate dynamics of classical spins exchange-coupled
through an isotropic medium. The coupling is treated at the adiabatic level of
the medium's response, which mediates a first-order in frequency dissipative
interaction along with an instantaneous Heisenberg exchange. The resultant
damped spin precession yields exceptional points (EPs) in the coupled spin
dynamics, which should be experimentally accessible with the existing magnetic
heterostructures. In particular, we show that an EP is naturally approached in
an antiferromagnetic dimer by controlling local damping, while the same is
achieved by tuning the dissipative coupling between spins in the ferromagnetic
case. Extending our treatment to one-dimensional spin chains, we show how EPs
can emerge within the magnonic Brillouin zone by tuning the dissipative
properties. The critical point, at which an EP pair emerges out of the
Brillouin zone center, realizes a gapless Weyl point in the magnon spectrum.
Tuning damping beyond this critical point produces synchronization (level
attraction) of magnon modes over a finite range of momenta, both in ferro- and
antiferromagnetic cases. We thus establish that damped magnons can generically
yield singular points in their band structure, close to which their kinematic
properties, such as group velocity, become extremely sensitive to the control
parameters. | 1911.01619v2 |
2019-11-08 | Influence of Sensor Feedback Limitations on Power Oscillation Damping and Transient Stability | Fundamental sensor feedback limitations for improving rotor angle stability
using local frequency or phase angle measurement are derived. Using a
two-machine power system model, it is shown that improved damping of inter-area
oscillations must come at the cost of reduced transient stability margins,
regardless of the control design method. The control limitations stem from that
the excitation of an inter-area mode by external disturbances cannot be
estimated with certainty using local frequency information. The results are
validated on a modified Kundur four-machine two-area test system where the
active power is modulated on an embedded high-voltage dc link. Damping control
using local phase angle measurements, unavoidably leads to an increased rotor
angle deviation following certain load disturbances. For a highly stressed
system, it is shown that this may lead to transient instability. The
limitations derived in the paper may motivate the need for wide-area
measurements in power oscillation damping control. | 1911.03342v3 |
2019-11-12 | Non-uniform Stability of Damped Contraction Semigroups | We investigate the stability properties of strongly continuous semigroups
generated by operators of the form $A-BB^\ast$, where $A$ is a generator of a
contraction semigroup and $B$ is a possibly unbounded operator. Such systems
arise naturally in the study of hyperbolic partial differential equations with
damping on the boundary or inside the spatial domain. As our main results we
present general sufficient conditions for non-uniform stability of the
semigroup generated by $A-BB^\ast$ in terms of selected observability-type
conditions of the pair $(B^\ast,A)$. We apply the abstract results to obtain
rates of energy decay in one-dimensional and two-dimensional wave equations, a
damped fractional Klein--Gordon equation and a weakly damped beam equation. | 1911.04804v3 |
2020-01-31 | Dynamo in weakly collisional nonmagnetized plasmas impeded by Landau damping of magnetic fields | We perform fully kinetic simulations of flows known to produce dynamo in
magnetohydrodynamics (MHD), considering scenarios with low Reynolds number and
high magnetic Prandtl number, relevant for galaxy cluster scale fluctuation
dynamos. We find that Landau damping on the electrons leads to a rapid decay of
magnetic perturbations, impeding the dynamo. This collisionless damping process
operates on spatial scales where electrons are nonmagnetized, reducing the
range of scales where the magnetic field grows in high magnetic Prandtl number
fluctuation dynamos. When electrons are not magnetized down to the resistive
scale, the magnetic energy spectrum is expected to be limited by the scale
corresponding to magnetic Landau damping or, if smaller, the electron
gyroradius scale, instead of the resistive scale. In simulations we thus
observe decaying magnetic fields where resistive MHD would predict a dynamo. | 2001.11929v2 |
2020-03-05 | Sound propagation and quantum limited damping in a two-dimensional Fermi gas | Strongly interacting two-dimensional Fermi systems are one of the great
remaining challenges in many-body physics due to the interplay of strong local
correlations and enhanced long-range fluctuations. Here, we probe the
thermodynamic and transport properties of a 2D Fermi gas across the BEC-BCS
crossover by studying the propagation and damping of sound modes. We excite
particle currents by imprinting a phase step onto homogeneous Fermi gases
trapped in a box potential and extract the speed of sound from the frequency of
the resulting density oscillations. We measure the speed of sound across the
BEC-BCS crossover and compare the resulting dynamic measurement of the equation
of state both to a static measurement based on recording density profiles and
to Quantum Monte Carlo calculations and find reasonable agreement between all
three. We also measure the damping of the sound mode, which is determined by
the shear and bulk viscosities as well as the thermal conductivity of the gas.
We find that the damping is minimal in the strongly interacting regime and the
diffusivity approaches the universal quantum bound $\hbar/m$ of a perfect
fluid. | 2003.02713v1 |
2020-03-09 | Proof-of-principle direct measurement of Landau damping strength at the Large Hadron Collider with an anti-damper | Landau damping is an essential mechanism for ensuring collective beam
stability in particle accelerators. Precise knowledge of how strong Landau
damping is, is key to making accurate predictions on beam stability for
state-of-the-art high energy colliders. In this paper we demonstrate an
experimental procedure that would allow quantifying the strength of Landau
damping and the limits of beam stability using an active transverse feedback as
a controllable source of beam coupling impedance. In a proof-of-principle test
performed at the Large Hadron Collider stability diagrams for a range of Landau
Octupole strengths have been measured. In the future, the procedure could
become an accurate way of measuring stability diagrams throughout the machine
cycle. | 2003.04383v1 |
2020-03-19 | An inverse-system method for identification of damping rate functions in non-Markovian quantum systems | Identification of complicated quantum environments lies in the core of
quantum engineering, which systematically constructs an environment model with
the aim of accurate control of quantum systems. In this paper, we present an
inverse-system method to identify damping rate functions which describe
non-Markovian environments in time-convolution-less master equations. To access
information on the environment, we couple a finite-level quantum system to the
environment and measure time traces of local observables of the system. By
using sufficient measurement results, an algorithm is designed, which can
simultaneously estimate multiple damping rate functions for different
dissipative channels. Further, we show that identifiability for the damping
rate functions corresponds to the invertibility of the system and a necessary
condition for identifiability is also given. The effectiveness of our method is
shown in examples of an atom and three-spin-chain non-Markovian systems. | 2003.08617v1 |
2020-04-23 | Damping of gravitational waves in 2-2-holes | A 2-2-hole is an explicit realization of a horizonless object that can still
very closely resemble a BH. An ordinary relativistic gas can serve as the
matter source for the 2-2-hole solution of quadratic gravity, and this leads to
a calculable area-law entropy. Here we show that it also leads to an estimate
of the damping of a gravitational wave as it travels to the center of the
2-2-hole and back out again. We identify two frequency dependent effects that
greatly diminish the damping. Spinning 2-2-hole solutions are not known, but we
are still able to consider some spin dependent effects. The frequency and spin
dependence of the damping helps to determine the possible echo resonance signal
from the rotating remnants of merger events. It also controls the fate of the
ergoregion instability. | 2004.11285v3 |
2020-05-04 | Plasmon damping in electronically open systems | Rapid progress in electrically-controlled plasmonics in solids poses a
question about effects of electronic reservoirs on the properties of plasmons.
We find that plasmons in electronically open systems [i.e. in (semi)conductors
connected to leads] are prone to an additional damping due to charge carrier
penetration into contacts and subsequent thermalization. We develop a theory of
such lead-induced damping based on kinetic equation with self-consistent
electric field, supplemented by microscopic carrier transport at the
interfaces. The lifetime of plasmon in electronically open ballistic system
appears to be finite, order of conductor length divided by carrier Fermi
(thermal) velocity. The reflection loss of plasmon incident on the contact of
semi-conductor and perfectly conducting metal also appears to be finite, order
of Fermi velocity divided by wave phase velocity. Recent experiments on
plasmon-assisted photodetection are discussed in light of the proposed
lead-induced damping phenomenon. | 2005.01680v1 |
2020-05-06 | Helical damping and anomalous critical non-Hermitian skin effect | Non-Hermitian skin effect and critical skin effect are unique features of
non-Hermitian systems. In this Letter, we study an open system with its
dynamics of single-particle correlation function effectively dominated by a
non-Hermitian damping matrix, which exhibits $\mathbb{Z}_2$ skin effect, and
uncover the existence of a novel phenomenon of helical damping. When adding
perturbations that break anomalous time reversal symmetry to the system, the
critical skin effect occurs, which causes the disappearance of the helical
damping in the thermodynamic limit although it can exist in small size systems.
We also demonstrate the existence of anomalous critical skin effect when we
couple two identical systems with $\mathbb{Z}_2$ skin effect. With the help of
non-Bloch band theory, we unveil that the change of generalized Brillouin zone
equation is the necessary condition of critical skin effect. | 2005.02617v1 |
2020-05-16 | Gravitational Landau Damping for massive scalar modes | We establish the possibility of Landau damping for gravitational scalar waves
which propagate in a non-collisional gas of particles. In particular, under the
hypothesis of homogeneity and isotropy, we describe the medium at the
equilibrium with a J\"uttner-Maxwell distribution, and we analytically
determine the damping rate from the Vlasov equation. We find that damping
occurs only if the phase velocity of the wave is subluminal throughout the
propagation within the medium. Finally, we investigate relativistic media in
cosmological settings by adopting numerical techniques. | 2005.08010v4 |
2020-05-21 | On Strong Feller Property, Exponential Ergodicity and Large Deviations Principle for Stochastic Damping Hamiltonian Systems with State-Dependent Switching | This work focuses on a class of stochastic damping Hamiltonian systems with
state-dependent switching, where the switching process has a countably infinite
state space. After establishing the existence and uniqueness of a global weak
solution via the martingale approach under very mild conditions, the paper next
proves the strong Feller property for regime-switching stochastic damping
Hamiltonian systems by the killing technique together with some resolvent and
transition probability identities. The commonly used continuity assumption for
the switching rates $q_{kl}(\cdot)$ in the literature is relaxed to
measurability in this paper. Finally the paper provides sufficient conditions
for exponential ergodicity and large deviations principle for regime-switching
stochastic damping Hamiltonian systems. Several examples on regime-switching
van der Pol and (overdamped) Langevin systems are studied in detail for
illustration. | 2005.10730v1 |
2020-06-14 | Bulk Viscous Damping of Density Oscillations in Neutron Star Mergers | In this paper, we discuss the damping of density oscillations in dense
nuclear matter in the temperature range relevant to neutron star mergers. This
damping is due to bulk viscosity arising from the weak interaction ``Urca''
processes of neutron decay and electron capture. The nuclear matter is modelled
in the relativistic density functional approach. The bulk viscosity reaches a
resonant maximum close to the neutrino trapping temperature, then drops rapidly
as temperature rises into the range where neutrinos are trapped in neutron
stars. We investigate the bulk viscous dissipation timescales in a post-merger
object and identify regimes where these timescales are as short as the
characteristic timescale $\sim$10 ms, and, therefore, might affect the
evolution of the post-merger object. Our analysis indicates that bulk viscous
damping would be important at not too high temperatures of the order of a few
MeV and densities up to a few times saturation density. | 2006.07975v2 |
2020-06-15 | Exact solutions of a damped harmonic oscillator in a time dependent noncommutative space | In this paper we have obtained the exact eigenstates of a two dimensional
damped harmonic oscillator in time dependent noncommutative space. It has been
observed that for some specific choices of the damping factor and the time
dependent frequency of the oscillator, there exists interesting solutions of
the time dependent noncommutative parameters following from the solutions of
the Ermakov-Pinney equation. Further, these solutions enable us to get exact
analytic forms for the phase which relates the eigenstates of the Hamiltonian
with the eigenstates of the Lewis invariant. We then obtain expressions for the
matrix elements of the coordinate operators raised to a finite arbitrary power.
From these general results we then compute the expectation value of the
Hamiltonian. The expectation values of the energy are found to vary with time
for different solutions of the Ermakov-Pinney equation corresponding to
different choices of the damping factor and the time dependent frequency of the
oscillator. | 2006.08611v1 |
2020-06-16 | Enhancing nonlinear damping by parametric-direct internal resonance | Mechanical sources of nonlinear damping play a central role in modern
physics, from solid-state physics to thermodynamics. The microscopic theory of
mechanical dissipation [M. I . Dykman, M. A. Krivoglaz, Physica Status Solidi
(b) 68, 111 (1975)] suggests that nonlinear damping of a resonant mode can be
strongly enhanced when it is coupled to a vibration mode that is close to twice
its resonance frequency. To date, no experimental evidence of this enhancement
has been realized. In this letter, we experimentally show that nanoresonators
driven into parametric-direct internal resonance provide supporting evidence
for the microscopic theory of nonlinear dissipation. By regulating the drive
level, we tune the parametric resonance of a graphene nanodrum over a range of
40-70 MHz to reach successive two-to-one internal resonances, leading to a
nearly two-fold increase of the nonlinear damping. Our study opens up an
exciting route towards utilizing modal interactions and parametric resonance to
realize resonators with engineered nonlinear dissipation over wide frequency
range. | 2006.09364v3 |
2020-06-22 | Blow-up for wave equation with the scale-invariant damping and combined nonlinearities | In this article, we study the blow-up of the damped wave equation in the
\textit{scale-invariant case} and in the presence of two nonlinearities. More
precisely, we consider the following equation: $$u_{tt}-\Delta
u+\frac{\mu}{1+t}u_t=|u_t|^p+|u|^q, \quad \mbox{in}\ \R^N\times[0,\infty), $$
with small initial data.\\ For $\mu < \frac{N(q-1)}{2}$ and $\mu \in (0,
\mu_*)$, where $\mu_*>0$ is depending on the nonlinearties' powers and the
space dimension ($\mu_*$ satisfies $(q-1)\left((N+2\mu_*-1)p-2\right) = 4$), we
prove that the wave equation, in this case, behaves like the one without
dissipation ($\mu =0$). Our result completes the previous studies in the case
where the dissipation is given by $\frac{\mu}{(1+t)^\beta}u_t; \ \beta >1$
(\cite{LT3}), where, contrary to what we obtain in the present work, the effect
of the damping is not significant in the dynamics. Interestingly, in our case,
the influence of the damping term $\frac{\mu}{1+t}u_t$ is important. | 2006.12600v1 |
2020-07-10 | Decentralized Frequency Control using Packet-based Energy Coordination | This paper presents a novel frequency-responsive control scheme for
demand-side resources, such as electric water heaters. A frequency-dependent
control law is designed to provide damping from distributed energy resources
(DERs) in a fully decentralized fashion. This local control policy represents a
frequency-dependent threshold for each DER that ensures that the aggregate
response provides damping during frequency deviations. The proposed
decentralized policy is based on an adaptation of a packet-based DER
coordination scheme where each device send requests for energy access (also
called an "energy packet") to an aggregator. The number of previously accepted
active packets can then be used a-priori to form an online estimate of the
aggregate damping capability of the DER fleet in a dynamic power system. A
simple two-area power system is used to illustrate and validate performance of
the decentralized control policy and the accuracy of the online damping
estimating for a fleet of 400,000 DERs. | 2007.05624v1 |
2020-07-30 | Origin of micron-scale propagation lengths of heat-carrying acoustic excitations in amorphous silicon | The heat-carrying acoustic excitations of amorphous silicon are of interest
because their mean free paths may approach micron scales at room temperature.
Despite extensive investigation, the origin of the weak acoustic damping in the
heat-carrying frequencies remains a topic of debate. Here, we report
measurements of the thermal conductivity mean free path accumulation function
in amorphous silicon thin films from 60 - 315 K using transient grating
spectroscopy. With additional picosecond acoustics measurements and considering
the known frequency-dependencies of damping mechanisms in glasses, we
reconstruct the mean free paths from $\sim 0.1-3$ THz. The mean free paths are
independent of temperature and exhibit a Rayleigh scattering trend over most of
this frequency range. The observed trend is inconsistent with the predictions
of numerical studies based on normal mode analysis but agrees with diverse
measurements on other glasses. The micron-scale MFPs in amorphous Si arise from
the absence of anharmonic or two-level system damping in the sub-THz
frequencies, leading to heat-carrying acoustic excitations with
room-temperature damping comparable to that of other glasses at cryogenic
temperatures. | 2007.15777v2 |
2020-08-06 | Quantum sensing of open systems: Estimation of damping constants and temperature | We determine quantum precision limits for estimation of damping constants and
temperature of lossy bosonic channels. A direct application would be the use of
light for estimation of the absorption and the temperature of a transparent
slab. Analytic lower bounds are obtained for the uncertainty in the estimation,
through a purification procedure that replaces the master equation description
by a unitary evolution involving the system and ad hoc environments. For zero
temperature, Fock states are shown to lead to the minimal uncertainty in the
estimation of damping, with boson-counting being the best measurement
procedure. In both damping and temperature estimates, sequential
pre-thermalization measurements, through a stream of single bosons, may lead to
huge gain in precision. | 2008.02728v1 |
2020-08-07 | Quantifying the evidence for resonant damping of coronal waves with foot-point wave power asymmetry | We use Coronal Multi-channel Polarimeter (CoMP) observations of propagating
waves in the solar corona and Bayesian analysis to assess the evidence of
models with resonant damping and foot-point wave power asymmetries. Two nested
models are considered. The reduced model considers resonant damping as the sole
cause of the measured discrepancy between outward and inward wave power. The
larger model contemplates an extra source of asymmetry with origin at the
foot-points. We first compute probability distributions of parameters
conditional on the models and the observed data. The obtained constraints are
then used to calculate the evidence for each model in view of data. We find
that we need to consider the larger model to explain CoMP data and to
accurately infer the damping ratio, hence, to better assess the possible
contribution of the waves to coronal heating. | 2008.03004v1 |
2020-08-22 | Sound damping in frictionless granular materials: The interplay between configurational disorder and inelasticity | We numerically investigate sound damping in a model of granular materials in
two dimensions. We simulate evolution of standing waves in disordered
frictionless disks and analyze their damped oscillations by velocity
autocorrelation functions and power spectra. We control the strength of
inelastic interactions between the disks in contact to examine the effect of
energy dissipation on sound characteristics of disordered systems. Increasing
the strength of inelastic interactions, we find that (i) sound softening
vanishes and (ii) sound attenuation due to configurational disorder, i.e. the
Rayleigh scattering at low frequencies and disorder-induced broadening at high
frequencies, is completely dominated by the energy dissipation. Our findings
suggest that sound damping in granular media is determined by the interplay
between elastic heterogeneities and inelastic interactions. | 2008.09760v1 |
2020-09-27 | Squeezed comb states | Continuous-variable codes are an expedient solution for quantum information
processing and quantum communication involving optical networks. Here we
characterize the squeezed comb, a finite superposition of equidistant squeezed
coherent states on a line, and its properties as a continuous-variable encoding
choice for a logical qubit. The squeezed comb is a realistic approximation to
the ideal code proposed by Gottesman, Kitaev, and Preskill [Phys. Rev. A 64,
012310 (2001)], which is fully protected against errors caused by the
paradigmatic types of quantum noise in continuous-variable systems: damping and
diffusion. This is no longer the case for the code space of finite squeezed
combs, and noise robustness depends crucially on the encoding parameters. We
analyze finite squeezed comb states in phase space, highlighting their
complicated interference features and characterizing their dynamics when
exposed to amplitude damping and Gaussian diffusion noise processes. We find
that squeezed comb state are more suitable and less error-prone when exposed to
damping, which speaks against standard error correction strategies that employ
linear amplification to convert damping into easier-to-describe isotropic
diffusion noise. | 2009.12888v2 |
2020-11-16 | Switchable Damping for a One-Particle Oscillator | The possibility to switch the damping rate for a one-electron oscillator is
demonstrated, for an electron that oscillates along the magnetic field axis in
a Penning trap. Strong axial damping can be switched on to allow this
oscillation to be used for quantum nondemolition detection of the cyclotron and
spin quantum state of the electron. Weak axial damping can be switched on to
circumvent the backaction of the detection motion that has limited past
measurements. The newly developed switch will reduce the linewidth of the
cyclotron transition of one-electron by two orders of magnitude. | 2011.08136v2 |
2020-11-17 | Challenging an experimental nonlinear modal analysis method with a new strongly friction-damped structure | In this work, we show that a recently proposed method for experimental
nonlinear modal analysis based on the extended periodic motion concept is well
suited to extract modal properties for strongly nonlinear systems (i.e. in the
presence of large frequency shifts, high and nonlinear damping, changes of the
mode shape, and higher harmonics). To this end, we design a new test rig that
exhibits a large extent of friction-induced damping (modal damping ratio up to
15 %) and frequency shift by 36 %. The specimen, called RubBeR, is a
cantilevered beam under the influence of dry friction, ranging from full stick
to mainly sliding. With the specimen's design, the measurements are well
repeatable for a system subjected to dry frictional force. Then, we apply the
method to the specimen and show that single-point excitation is sufficient to
track the modal properties even though the deflection shape changes with
amplitude. Computed frequency responses using a single nonlinear-modal
oscillator with the identified modal properties agree well with measured
reference curves of different excitation levels, indicating the modal
properties' significance and accuracy. | 2011.08527v1 |
2020-11-27 | Thermal damping of Weak Magnetosonic Turbulence in the Interstellar Medium | We present a generic mechanism for the thermal damping of compressive waves
in the interstellar medium (ISM), occurring due to radiative cooling. We solve
for the dispersion relation of magnetosonic waves in a two-fluid (ion-neutral)
system in which density- and temperature-dependent heating and cooling
mechanisms are present. We use this dispersion relation, in addition to an
analytic approximation for the nonlinear turbulent cascade, to model
dissipation of weak magnetosonic turbulence. We show that in some ISM
conditions, the cutoff wavelength for magnetosonic turbulence becomes tens to
hundreds of times larger when the thermal damping is added to the regular
ion-neutral damping. We also run numerical simulations which confirm that this
effect has a dramatic impact on cascade of compressive wave modes. | 2011.13879v3 |
2021-02-10 | WAMS-Based Model-Free Wide-Area Damping Control by Voltage Source Converters | In this paper, a novel model-free wide-area damping control (WADC) method is
proposed, which can achieve full decoupling of modes and damp multiple critical
inter-area oscillations simultaneously using grid-connected voltage source
converters (VSCs). The proposed method is purely measurement based and requires
no knowledge of the network topology and the dynamic model parameters. Hence,
the designed controller using VSCs can update the control signals online as the
system operating condition varies. Numerical studies in the modified IEEE
68-bus system with grid-connected VSCs show that the proposed method can
estimate the system dynamic model accurately and can damp inter-area
oscillations effectively under different working conditions and network
topologies. | 2102.05494v1 |
2021-04-08 | Fast optimization of viscosities for frequency-weighted damping of second-order systems | We consider frequency-weighted damping optimization for vibrating systems
described by a second-order differential equation. The goal is to determine
viscosity values such that eigenvalues are kept away from certain undesirable
areas on the imaginary axis. To this end, we present two complementary
techniques. First, we propose new frameworks using nonsmooth constrained
optimization problems, whose solutions both damp undesirable frequency bands
and maintain stability of the system. These frameworks also allow us to weight
which frequency bands are the most important to damp. Second, we also propose a
fast new eigensolver for the structured quadratic eigenvalue problems that
appear in such vibrating systems. In order to be efficient, our new eigensolver
exploits special properties of diagonal-plus-rank-one complex symmetric
matrices, which we leverage by showing how each quadratic eigenvalue problem
can be transformed into a short sequence of such linear eigenvalue problems.
The result is an eigensolver that is substantially faster than standard
techniques. By combining this new solver with our new optimization frameworks,
we obtain our overall algorithm for fast computation of optimal viscosities.
The efficiency and performance of our new methods are verified and illustrated
on several numerical examples. | 2104.04035v1 |
2021-04-12 | Slow periodic oscillation without radiation damping: New evolution laws for rate and state friction | The dynamics of sliding friction is mainly governed by the frictional force.
Previous studies have shown that the laboratory-scale friction is well
described by an empirical law stated in terms of the slip velocity and the
state variable. The state variable represents the detailed physicochemical
state of the sliding interface. Despite some theoretical attempts to derive
this friction law, there has been no unique equation for time evolution of the
state variable. Major equations known to date have their own merits and
drawbacks. To shed light on this problem from a new aspect, here we investigate
the feasibility of periodic motion without the help of radiation damping.
Assuming a patch on which the slip velocity is perturbed from the rest of the
sliding interface, we prove analytically that three major evolution laws fail
to reproduce stable periodic motion without radiation damping. Furthermore, we
propose two new evolution equations that can produce stable periodic motion
without radiation damping. These two equations are scrutinized from the
viewpoint of experimental validity and the relevance to slow earthquakes. | 2104.05398v2 |
2021-04-27 | Absence of a boson peak in anharmonic phonon models with Akhiezer-type damping | In a recent article M. Baggioli and A. Zaccone (Phys. Rev. Lett. {\bf 112},
145501 (2019)) claimed that an anharmonic damping, leading to a sound
attenuation proportional to $\omega^2$ (Akhiezer-type damping) would imply a
boson peak, i.e.\ a maximum in the vibrational density of states, divided by
the frequency squared (reduced density of states). This would apply both to
glasses and crystals.Here we show that this is not the case. In a
mathematically correct treatment of the model the reduced density of states
monotonously decreases, i.e.\ there is no boson peak. We further show that the
formula for the would-be boson peak, presented by the authors, corresponds to a
very short one-dimensional damped oscillator system. The peaks they show
correspond to resonances, which vanish in the thermodynamic limit. | 2104.13076v1 |
2021-05-03 | Damping and polarization rates in near equilibrium state | The collision terms in spin transport theory are analyzed in Kadanoff-Baym
formalism for systems close to equilibrium. The non-equilibrium fluctuations in
spin distribution include both damping and polarization, with the latter
arising from the exchange between orbital and spin angular momenta. The damping
and polarization rates or the relaxation times are expressed in terms of
various Dirac components of the self-energy. Unlike the usually used
Anderson-Witting relaxation time approximation assuming a single time scale for
different degrees of freedom, the polarization effect is induced by the thermal
vorticity and its time scale of thermalization is different from the damping.
The numerical calculation in the Nambu--Jona-Lasinio model shows that, charge
is thermalized earlier and spin is thermalized later. | 2105.00915v1 |
2021-06-07 | Voltage-control of damping constant in magnetic-insulator/topological-insulator bilayers | The magnetic damping constant is a critical parameter for magnetization
dynamics and the efficiency of memory devices and magnon transport. Therefore,
its manipulation by electric fields is crucial in spintronics. Here, we
theoretically demonstrate the voltage-control of magnetic damping in ferro- and
ferrimagnetic-insulator (FI)/topological-insulator (TI) bilayers. Assuming a
capacitor-like setup, we formulate an effective dissipation torque induced by
spin-charge pumping at the FI/TI interface as a function of an applied voltage.
By using realistic material parameters, we find that the effective damping for
a FI with 10nm thickness can be tuned by one order of magnitude under the
voltage with 0.25V. Also, we provide perspectives on the voltage-induced
modulation of the magnon spin transport on proximity-coupled FIs. | 2106.03332v1 |
2021-05-14 | Exact solution of damped harmonic oscillator with a magnetic field in a time dependent noncommutative space | In this paper we have obtained the exact eigenstates of a two dimensional
damped harmonic oscillator in the presence of an external magnetic field
varying with respect to time in time dependent noncommutative space. It has
been observed that for some specific choices of the damping factor, the time
dependent frequency of the oscillator and the time dependent external magnetic
field, there exists interesting solutions of the time dependent noncommutative
parameters following from the solutions of the Ermakov-Pinney equation.
Further, these solutions enable us to get exact analytic forms for the phase
which relates the eigenstates of the Hamiltonian with the eigenstates of the
Lewis invariant. Then we compute the expectation value of the Hamiltonian. The
expectation values of the energy are found to vary with time for different
solutions of the Ermakov-Pinney equation corresponding to different choices of
the damping factor, the time dependent frequency of the oscillator and the time
dependent applied magnetic field. We also compare our results with those in the
absence of the magnetic field obtained earlier. | 2106.05182v1 |
2021-06-21 | Self-stabilization of light sails by damped internal degrees of freedom | We consider the motion of a light sail that is accelerated by a powerful
laser beam. We derive the equations of motion for two proof-of-concept sail
designs with damped internal degrees of freedom. Using linear stability
analysis we show that perturbations of the sail movement in all lateral degrees
of freedom can be damped passively. This analysis also shows complicated
behaviour akin to that associated with exceptional points in PT-symmetric
systems in optics and quantum mechanics. The excess heat that is produced by
the damping mechanism is likely to be substantially smaller than the expected
heating due to the partial absorption of the incident laser beam by the sail. | 2106.10961v1 |
2021-07-14 | Determining the source of phase noise: Response of a driven Duffing oscillator to low-frequency damping and resonance frequency fluctuations | We present an analytical calculation of the response of a driven Duffing
oscillator to low-frequency fluctuations in the resonance frequency and
damping. We find that fluctuations in these parameters manifest themselves
distinctively, allowing them to be distinguished. In the strongly nonlinear
regime, amplitude and phase noise due to resonance frequency fluctuations and
amplitude noise due to damping fluctuations are strongly attenuated, while the
transduction of damping fluctuations into phase noise remains of order $1$. We
show that this can be seen by comparing the relative strengths of the amplitude
fluctuations to the fluctuations in the quadrature components, and suggest that
this provides a means to determine the source of low-frequency noise in a
driven Duffing oscillator. | 2107.06879v1 |
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