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2018-11-07 | Statistical complexity of the quasiperiodical damped systems | We consider the concept of statistical complexity to write the
quasiperiodical damped systems applying the snapshot attractors. This allows us
to understand the behaviour of these dynamical systems by the probability
distribution of the time series making a difference between the regular, random
and structural complexity on finite measurements. We interpreted the
statistical complexity on snapshot attractor and determined it on the
quasiperiodical forced pendulum. | 1811.02958v1 |
2018-12-13 | Rapid exponential stabilization of a 1-D transmission wave equation with in-domain anti-damping | We consider the problem of pointwise stabilization of a one-dimensional wave
equation with an internal spatially varying anti-damping term. We design a
feedback law based on the backstepping method and prove exponential stability
of the closed-loop system with a desired decay rate. | 1812.11035v1 |
2019-01-20 | Stationary Solutions of Damped Stochastic 2-dimensional Euler's Equation | Existence of stationary point vortices solution to the damped and
stochastically driven Euler's equation on the two dimensional torus is proved,
by taking limits of solutions with finitely many vortices. A central limit
scaling is used to show in a similar manner the existence of stationary
solutions with white noise marginals. | 1901.06744v1 |
2019-03-13 | Solar $p$-mode damping rates: insight from a 3D hydrodynamical simulation | Space-borne missions CoRoT and Kepler have provided a rich harvest of
high-quality photometric data for solar-like pulsators. It is now possible to
measure damping rates for hundreds of main-sequence and thousands of red-giant.
However, among the seismic parameters, mode damping rates remain poorly
understood and thus barely used for inferring the physical properties of stars.
Previous approaches to model mode damping rates were based on mixing-length
theory or a Reynolds-stress approach to model turbulent convection. While able
to grasp the main physics of the problem, those approaches are of little help
to provide quantitative estimates as well as a definitive answer on the
relative contribution of each physical mechanism. Our aim is thus to assess the
ability of 3D hydrodynamical simulations to infer the physical mechanisms
responsible for damping of solar-like oscillations. To this end, a solar
high-spatial resolution and long-duration hydrodynamical 3D simulation computed
with the ANTARES code allows probing the coupling between turbulent convection
and the normal modes of the simulated box. Indeed, normal modes of the
simulation experience realistic driving and damping in the super-adiabatic
layers of the simulation. Therefore, investigating the properties of the normal
modes in the simulation provides a unique insight into the mode physics. We
demonstrate that such an approach provides constraints on the solar damping
rates and is able to disentangle the relative contribution related to the
perturbation of the turbulent pressure, the gas pressure, the radiative flux,
and the convective flux contributions. Finally, we conclude that using the
normal modes of a 3D numerical simulation is possible and is potentially able
to unveil the respective role of the different physical mechanisms responsible
for mode damping provided the time-duration of the simulation is long enough. | 1903.05479v1 |
2019-04-15 | Carleman estimate for an adjoint of a damped beam equation and an application to null controllability | In this article we consider a control problem of a linear Euler-Bernoulli
damped beam equation with potential in dimension one with periodic boundary
conditions. We derive a new Carleman estimate for an adjoint of the equation
under consideration. Then using a well known duality argument we obtain
explicitly the control function which can be used to drive the solution
trajectory of the control problem to zero state. | 1904.07038v1 |
2019-05-01 | Dissipative structure and diffusion phenomena for doubly dissipative elastic waves in two space dimensions | In this paper we study the Cauchy problem for doubly dissipative elastic
waves in two space dimensions, where the damping terms consist of two different
friction or structural damping. We derive energy estimates and diffusion
phenomena with different assumptions on initial data. Particularly, we find the
dominant influence on diffusion phenomena by introducing a new threshold of
diffusion structure. | 1905.00257v1 |
2019-07-12 | Non-Existence of Periodic Orbits for Forced-Damped Potential Systems in Bounded Domains | We prove Lr-estimates on periodic solutions of periodically-forced,
linearly-damped mechanical systems with polynomially-bounded potentials. The
estimates are applied to obtain a non-existence result of periodic solutions in
bounded domains, depending on an upper bound on the gradient of the potential.
The results are illustrated on examples. | 1907.05778v1 |
2019-09-02 | On the inclusion of damping terms in the hyperbolic MBO algorithm | The hyperbolic MBO is a threshold dynamic algorithm which approximates
interfacial motion by hyperbolic mean curvature flow. We introduce a
generalization of this algorithm for imparting damping terms onto the equation
of motion. We also construct corresponding numerical methods, and perform
numerical tests. We also use our results to show that the generalized
hyperbolic MBO is able to approximate motion by the standard mean curvature
flow. | 1909.00552v1 |
2019-09-07 | Lindblad dynamics of the damped and forced quantum harmonic oscillator: General solution | The quantum dynamics of a damped and forced harmonic oscillator described by
a Lindblad master equation is analyzed. The master equation is converted into a
matrix-vector representation and the resulting non-Hermitian Schr\"odinger
equation is solved by Lie-algebraic techniques allowing the construction of the
general solution for the density operator. | 1909.03206v1 |
2019-11-01 | Convergence of a damped Newton's method for discrete Monge-Ampere functions with a prescribed asymptotic cone | We prove the convergence of a damped Newton's method for the nonlinear system
resulting from a discretization of the second boundary value problem for the
Monge-Ampere equation. The boundary condition is enforced through the use of
the notion of asymptotic cone. The differential operator is discretized based
on a partial discrete analogue of the subdifferential. | 1911.00260v2 |
2019-12-17 | Comment on "On the Origin of Frictional Energy Dissipation" | In their interesting study (Ref. [1]) Hu et al have shown that for a simple
"harmonium" solid model the slip-induced motion of surface atoms is close to
critically damped. This result is in fact well known from studies of
vibrational damping of atoms and molecules at surfaces. However, for real
practical cases the situation may be much more complex and the conclusions of
Hu et al invalid. | 1912.07799v1 |
2020-01-23 | Nonlinear inviscid damping for a class of monotone shear flows in finite channel | We prove the nonlinear inviscid damping for a class of monotone shear flows
in $T\times [0,1]$ for initial perturbation in Gevrey-$1/s$($s>2$) class with
compact support. The main idea of the proof is to use the wave operator of a
slightly modified Rayleigh operator in a well chosen coordinate system. | 2001.08564v1 |
2020-02-26 | Bistability in the dissipative quantum systems I: Damped and driven nonlinear oscillator | We revisit quantum dynamics of the damped and driven nonlinear oscillator. In
the classical case this system has two stationary solutions (the limit cycles)
in the certain parameter region, which is the origin of the celebrated
bistability phenomenon. The quantum-classical correspondence for the oscillator
dynamics is discussed in details. | 2002.11373v1 |
2020-04-08 | Scattering and asymptotic order for the wave equations with the scale-invariant damping and mass | We consider the linear wave equation with the time-dependent scale-invariant
damping and mass. We also treat the corresponding equation with the energy
critical nonlinearity. Our aim is to show that the solution scatters to a
modified linear wave solution and to obtain its asymptotic order. | 2004.03832v2 |
2020-04-24 | Infinite energy solutions for weakly damped quintic wave equations in $\mathbb{R}^3$ | The paper gives a comprehensive study of infinite-energy solutions and their
long-time behavior for semi-linear weakly damped wave equations in
$\mathbb{R}^3$ with quintic nonlinearities. This study includes global
well-posedness of the so-called Shatah-Struwe solutions, their dissipativity,
the existence of a locally compact global attractors (in the uniformly local
phase spaces) and their extra regularity. | 2004.11864v1 |
2020-07-30 | Delta shock solution to the generalized one-dimensional zero-pressure gas dynamics system with linear damping | In this paper, we propose a time-dependent viscous system and by using the
vanishing viscosity method we show the existence of delta shock solution for a
particular $2 \times 2$ system of conservation laws with linear damping. | 2007.15184v2 |
2020-08-06 | On global attractors for 2D damped driven nonlinear Schrödinger equations | Well-posedness and global attractor are established for 2D damped driven
nonlinear Schr\"odinger equation with almost periodic pumping in a bounded
region. The key role is played by a novel application of the energy equation. | 2008.02741v1 |
2020-08-30 | Influence of dissipation on extreme oscillations of a forced anharmonic oscillator | Dynamics of a periodically forced anharmonic oscillator (AO) with cubic
nonlinearity, linear damping, and nonlinear damping, is studied. To begin with,
the authors examine the dynamics of an AO. Due to this symmetric nature, the
system has two neutrally stable elliptic equilibrium points in positive and
negative potential-wells. Hence, the unforced system can exhibit both
single-well and double-well periodic oscillations depending on the initial
conditions. Next, the authors include nonlinear damping into the system. Then,
the symmetry of the system is broken instantly and the stability of the two
elliptic points is altered to result in stable focus and unstable focus in the
positive and negative potential-wells, respectively. Consequently, the system
is dual-natured and is either non-dissipative or dissipative, depending on
location in the phase space. Furthermore, when one includes a periodic external
forcing with suitable parameter values into the nonlinearly damped AO system
and starts to increase the damping strength, the symmetry of the system is not
broken right away, but it occurs after the damping reaches a threshold value.
As a result, the system undergoes a transition from double-well chaotic
oscillations to single-well chaos mediated through extreme events (EEs).
Furthermore, it is found that the large-amplitude oscillations developed in the
system are completely eliminated if one incorporates linear damping into the
system. The numerically calculated results are in good agreement with the
theoretically obtained results on the basis of Melnikov's function. Further, it
is demonstrated that when one includes linear damping into the system, this
system has a dissipative nature throughout the entire phase space of the
system. This is believed to be the key to the elimination of EEs. | 2008.13172v1 |
2020-09-18 | Vanishing viscosity limit for Riemann solutions to a $2 \times 2$ hyperbolic system with linear damping | In this paper, we propose a time-dependent viscous system and by using the
vanishing viscosity method we show the existence of %delta shock solution
solutions for the Riemann problem to a particular $2 \times 2$ system of
conservation laws with linear damping. | 2009.09041v1 |
2020-11-28 | A Smoluchowski-Kramers approximation for an infinite dimensional system with state-dependent damping | We study the validity of a Smoluchowski-Kramers approximation for a class of
wave equations in a bounded domain of $\mathbb{R}^n$ subject to a
state-dependent damping and perturbed by a multiplicative noise. We prove that
in the small mass limit the solution converges to the solution of a stochastic
quasilinear parabolic equation where a noise-induced extra drift is created. | 2011.14236v2 |
2020-12-13 | Uniform Stabilization of the Petrovsky-Wave Nonlinear coupled system with strong damping | This paper concerns the well-posedness and uniform stabilization of the
Petrovsky-Wave Nonlinear coupled system with strong damping. Existence of
global weak solutions for this problem is established by using the Galerkin
method. Meanwhile, under a clever use of the multiplier method, we estimate the
total energy decay rate. | 2012.07109v3 |
2021-03-24 | On the long-time statistical behavior of smooth solutions of the weakly damped, stochastically-driven KdV equation | This paper considers the damped periodic Korteweg-de Vries (KdV) equation in
the presence of a white-in-time and spatially smooth stochastic source term and
studies the long-time behavior of solutions. We show that the integrals of
motion for KdV can be exploited to prove regularity and ergodic properties of
invariant measures for damped stochastic KdV. First, by considering non-trivial
modifications of the integrals of motion, we establish Lyapunov structure by
proving that moments of Sobolev norms of solutions at all orders of regularity
are bounded globally-in-time; existence of invariant measures follows as an
immediate consequence. Next, we prove a weak Foias-Prodi type estimate for
damped stochastic KdV, for which the synchronization occurs in expected value.
This estimate plays a crucial role throughout our subsequent analysis. As a
first novel application, we combine the Foias-Prodi estimate with the Lyapunov
structure to establish that invariant measures are supported on $C^\infty$
functions provided that the external driving forces belong to $C^\infty$. We
then establish ergodic properties of invariant measures, treating the regimes
of arbitrary damping and large damping separately. For arbitrary damping, we
demonstrate that the framework of `asymptotic coupling' can be implemented for
a compact proof of uniqueness of the invariant measure provided that
sufficiently many directions in phase space are stochastically forced. Our
proof is paradigmatic for SPDEs for which a weak Foias-Prodi type property
holds. Lastly, for large damping, we establish the existence of a spectral gap
with respect to a Wasserstein-like distance, and exponential mixing and
uniqueness of the invariant measure follows. | 2103.12942v2 |
2021-04-21 | On absorbing set for 3D Maxwell--Schrödinger damped driven equations in bounded region | We consider the 3D damped driven Maxwell--Schr\"odinger equations in a
bounded region under suitable boundary conditions. We establish new a priori
estimates, which provide the existence of global finite energy weak solutions
and bounded absorbing set. The proofs rely on the Sobolev type estimates for
magnetic Schr\"odinger operator. | 2104.10723v1 |
2021-06-23 | Pitt inequality for the linear structurally damped $σ$-evolution equations | This work is devoted to improve the time decay estimates for the solution and
some of its derivatives of the linear structurally damped $\sigma$-evolution
equations. The Pitt inequality is the main tool provided that the initial data
lies in some weighted spaces. | 2106.12342v1 |
2021-07-22 | Dimension estimates for the attractor of the regularized damped Euler equations on the sphere | We prove existence of the global attractor of the damped and driven
Euler--Bardina equations on the 2D sphere and on arbitrary domains on the
sphere
and give explicit estimates of its fractal dimension in terms of the physical
parameters. | 2107.10779v1 |
2021-09-22 | State-space representation of Matérn and Damped Simple Harmonic Oscillator Gaussian processes | Gaussian processes (GPs) are used widely in the analysis of astronomical time
series. GPs with rational spectral densities have state-space representations
which allow O(n) evaluation of the likelihood. We calculate analytic state
space representations for the damped simple harmonic oscillator and the
Mat\'ern 1/2, 3/2 and 5/2 processes. | 2109.10685v1 |
2021-10-21 | Stability properties of dissipative evolution equations with nonautonomous and nonlinear damping | In this paper, we obtain some stability results of (abstract) dissipative
evolution equations with a nonautonomous and nonlinear damping using the
exponential stability of the retrograde problem with a linear and autonomous
feedback and a comparison principle. We then illustrate our abstract statements
for different concrete examples, where new results are achieved. In a
preliminary step, we prove some well-posedness results for some nonlinear and
nonautonomous evolution equations. | 2110.11122v1 |
2021-11-23 | Logistic damping effect in chemotaxis models with density-suppressed motility | This paper is concerned with a parabolic-elliptic chemotaxis model with
density-suppressed motility and general logistic source in an $n$-dimensional
smooth bounded domain with Neumann boundary conditions. Under the minimal
conditions for the density-suppressed motility function, we explore how strong
the logistic damping can warrant the global boundedness of solutions, and
further establish the asymptotic behavior of solutions on top of the
conditions. | 2111.11669v1 |
2022-01-04 | Global existence and decay estimates for a viscoelastic plate equation with nonlinear damping and logarithmic nonlinearity | In this article, we consider a viscoelastic plate equation with a logarithmic
nonlinearity in the presence of nonlinear frictional damping term. Using the
the Faedo-Galerkin method we establish the global existence of the solution of
the problem and we also prove few general decay rate results. | 2201.00983v1 |
2022-01-20 | Long Time Decay of Leray Solution of 3D-NSE With Damping | In \cite{CJ}, the authors show that the Cauchy problem of the Navier-Stokes
equations with damping $\alpha|u|^{\beta-1}u(\alpha>0,\;\beta\geq1)$ has global
weak solutions in $L^2(\R^3)$. In this paper, we prove the uniqueness, the
continuity in $L^2$ for $\beta>3$, also the large time decay is proved for
$\beta\geq\frac{10}3$. Fourier analysis and standard techniques are used. | 2201.08427v1 |
2022-02-20 | On a non local non-homogeneous fractional Timoshenko system with frictional and viscoelastic damping terms | We are devoted to the study of a nonhomogeneous time-fractional Timoshenko
system with frictional and viscoelastic damping terms. We are concerned with
the well-posedness of the given problem. The approach relies on some
functional-analysis tools, operator theory, a prori estimates, and density
arguments. | 2202.09879v1 |
2022-04-05 | Large time behavior of solutions to nonlinear beam equations | In this note we analyze the large time behavior of solutions to a class of
initial/boundary problems involving a damped nonlinear beam equation. We show
that under mild conditions on the damping term of the equation of motions the
solutions of the dynamical problem converge to the solution of the stationary
problem. We also show that this convergence is exponential. | 2204.02151v1 |
2022-05-09 | Energy asymptotics for the strongly damped Klein-Gordon equation | We consider the strongly damped Klein Gordon equation for defocusing
nonlinearity and we study the asymptotic behaviour of the energy for periodic
solutions. We prove first the exponential decay to zero for zero mean
solutions. Then, we characterize the limit of the energy, when the time tends
to infinity, for solutions with small enough initial data and we finally prove
that such limit is not necessary zero. | 2205.04205v1 |
2022-06-07 | Asymptotic study of Leray Solution of 3D-NSE With Exponential Damping | We study the uniqueness, the continuity in $L^2$ and the large time decay for
the Leray solutions of the $3D$ incompressible Navier-Stokes equations with the
nonlinear exponential damping term $a (e^{b |u|^{\bf 2}}-1)u$, ($a,b>0$)
studied by the second author in \cite{J1}. | 2206.03138v1 |
2022-06-25 | Decay estimate in a viscoelastic plate equation with past history, nonlinear damping, and logarithmic nonlinearity | In this article, we consider a viscoelastic plate equation with past history,
nonlinear damping, and logarithmic nonlinearity. We prove explicit and general
decay rate results of the solution to the viscoelastic plate equation with past
history. Convex properties, logarithmic inequalities, and generalised Young's
inequality are mainly used to prove the decay estimate. | 2206.12561v1 |
2022-09-07 | Blow up and lifespan estimates for systems of semi-linear wave equations with dampings and potentials | In this paper, we consider the semi-linear wave systems with
power-nonlinearities and space-dependent dampings and potentials. We obtain the
blow-up regions for three types wave systems as well as the lifespan estimates. | 2209.02920v1 |
2022-12-14 | Gevrey regularity for the Euler-Bernoulli beam equation with localized structural damping | We study a Euler-Bernoulli beam equation with localized discontinuous
structural damping. As our main result, we prove that the associated
$C_0$-semigroup $(S(t))_{t\geq0}$ is of Gevrey class $\delta>24$ for $t>0$,
hence immediately differentiable. Moreover, we show that $(S(t))_{t\geq0}$ is
exponentially stable. | 2212.07110v1 |
2022-12-28 | On extended lifespan for 1d damped wave equation | In this manuscript, a sharp lifespan estimate of solutions to semilinear
classical damped wave equation is investigated in one dimensional case, when
the sum of initial position and speed is $0$ pointwisely. Especially, an
extension of lifespan is shown in this case. Moreover, existence of some global
solutions are obtained by a direct computation. | 2212.13845v1 |
2023-02-06 | Uniform stabilization of an acoustic system | We study the problem of stabilization for the acoustic system with a
spatially distributed damping. With imposing hypothesis on the structural
properties of the damping term, we identify exponential decay of solutions with
growing time. | 2302.02726v1 |
2023-05-22 | Fast energy decay for wave equation with a monotone potential and an effective damping | We consider the total energy decay of the Cauchy problem for wave equations
with a potential and an effective damping. We treat it in the whole
one-dimensional Euclidean space. Fast energy decay is established with the help
of potential. The proofs of main results rely on a multiplier method and
modified techniques adopted in [8]. | 2305.12666v1 |
2023-08-03 | Blow-up for semilinear wave equations with damping and potential in high dimensional Schwarzschild spacetime | In this work, we study the blow up results to power-type semilinear wave
equation in the high dimensional Schwarzschild spacetime, with damping and
potential terms. We can obtain the upper bound estimates of lifespan without
the assumption that the support of the initial date should be far away from the
black hole. | 2308.01691v1 |
2023-08-22 | Lifespan estimates for 1d damped wave equation with zero moment initial data | In this manuscript, a sharp lifespan estimate of solutions to semilinear
classical damped wave equation is investigated in one dimensional case when the
Fourier 0th moment of sum of initial position and speed is $0$. Especially, it
is shown that the behavior of lifespan changes with $p=3/2$ with respect to the
size of the initial data. | 2308.11113v1 |
2023-09-01 | Damped Euler system with attractive Riesz interaction forces | We consider the barotropic Euler equations with pairwise attractive Riesz
interactions and linear velocity damping in the periodic domain. We establish
the global-in-time well-posedness theory for the system near an equilibrium
state. We also analyze the large-time behavior of solutions showing the
exponential rate of convergence toward the equilibrium state as time goes to
infinity. | 2309.00210v1 |
2023-10-02 | The damped wave equation and associated polymer | Considering the damped wave equation with a Gaussian noise $F$ where $F$ is
white in time and has a covariance function depending on spatial variables, we
will see that this equation has a mild solution which is stationary in time
$t$. We define a weakly self-avoiding polymer with intrinsic length $J$
associated to this SPDE. Our main result is that the polymer has an effective
radius of approximately $J^{5/3}$. | 2310.01631v1 |
2023-10-17 | Indirect boundary stabilization for weakly coupled degenerate wave equations under fractional damping | In this paper, we consider the well-posedness and stability of a
one-dimensional system of degenerate wave equations coupled via zero order
terms with one boundary fractional damping acting on one end only. We prove
optimal polynomial energy decay rate of order $1/t^{(3-\tau)}$. The method is
based on the frequency domain approach combined with multiplier technique. | 2310.11174v1 |
2024-03-11 | Uniform estimates for solutions of nonlinear focusing damped wave equations | For a damped wave (or Klein-Gordon) equation on a bounded domain, with a
focusing power-like nonlinearity satisfying some growth conditions, we prove
that a global solution is bounded in the energy space, uniformly in time. Our
result applies in particular to the case of a cubic equation on a bounded
domain of dimension 3. | 2403.06541v1 |
1995-10-27 | A modified R1 X R1 method for helioseismic rotation inversions | We present an efficient method for two dimensional inversions for the solar
rotation rate using the Subtractive Optimally Localized Averages (SOLA) method
and a modification of the R1 X R1 technique proposed by Sekii (1993). The SOLA
method is based on explicit construction of averaging kernels similar to the
Backus-Gilbert method. The versatility and reliability of the SOLA method in
reproducing a target form for the averaging kernel, in combination with the
idea of the R1 X R1 decomposition, results in a computationally very efficient
inversion algorithm. This is particularly important for full 2-D inversions of
helioseismic data in which the number of modes runs into at least tens of
thousands. | 9510143v1 |
1997-10-22 | Globular Cluster Microlensing: Globular Clusters as Microlensing Targets | We investigate the possibility of using globular clusters as targets for
microlensing searches. Such searches will be challenging and require more
powerful telescopes than now employed, but are feasible in the 0 future.
Although expected event rates are low, we show that the wide variety of lines
of sight to globular clusters greatly enhances the ability to distinguish
between halo models using microlensing observations as compared to LMC/SMC
observations alone. | 9710251v1 |
2002-12-17 | An Intrinsic Baldwin Effect in the H-beta Broad Emission Line in the Spectrum of NGC 5548 | We investigate the possibility of an intrinsic Baldwin Effect (i.e.,nonlinear
emission-line response to continuum variations) in the broad H-beta emission
line of the active galaxy NGC 5548 using cross-correlation techniques to remove
light travel-time effects from the data. We find a nonlinear relationship
between the H-beta emission line and continuum fluxes that is in good agreement
with theoretical predictions. We suggest that similar analysis of multiple
lines might provide a useful diagnostic of physical conditions in the
broad-line region. | 0212379v1 |
2002-12-28 | Detecting supersymmetric dark matter in M31 with CELESTE ? | It is widely believed that dark matter exists within galaxies and clusters of
galaxies. Under the assumption that this dark matter is composed of the
lightest, stable supersymmetric particle, assumed to be the neutralino, the
feasibility of its indirect detection via observations of a diffuse gamma-ray
signal due to neutralino annihilation within M31 is examined. | 0212560v1 |
2003-03-18 | Model-Independent Reionization Observables in the CMB | We represent the reionization history of the universe as a free function in
redshift and study the potential for its extraction from CMB polarization
spectra. From a principal component analysis, we show that the ionization
history information is contained in 5 modes, resembling low-order Fourier modes
in redshift space. The amplitude of these modes represent a compact description
of the observable properties of reionization in the CMB, easily predicted given
a model for the ionization fraction. Measurement of these modes can ultimately
constrain the total optical depth, or equivalently the initial amplitude of
fluctuations to the 1% level regardless of the true model for reionization. | 0303400v1 |
2006-05-08 | Discovery of an Extended Halo of Metal-poor Stars in the Andromeda Spiral Galaxy | This paper has been withdrawn. Please see astro-ph/0502366. | 0605172v3 |
1995-01-02 | Dynamics of homogeneous magnetizations in strong transverse driving fields | Spatially homogeneous solutions of the Landau--Lifshitz--Gilbert equation are
analysed. The conservative as well as the dissipative case is considered
explicitly. For the linearly polarized driven Hamiltonian system we apply
canonical perturbation theory to uncover the main resonances as well as the
global phase space structure. In the case of circularly polarized driven
dissipative motion we present the complete bifurcation diagram including
bifurcations up to codimension three. | 9501002v1 |
2000-09-18 | Electronic properties of the degenerate Hubbard Model : A dynamical mean field approach | We have investigated electronic properties of the degenerate multi-orbital
Hubbard model, in the limit of large spatial dimension. A new local model,
including a doubly degenerate strongly correlated site has been introduced and
solved in the framework of the non-crossing approximation (NCA). Mott-Hubbard
transitions have been examined in details, including the calculation of Coulomb
repulsion critical values and electronic densities of states for any regime of
parameters. | 0009253v1 |
2001-01-11 | Theoretical and Experimental Approach to Spin Dynamics in Thin Magnetic Films | The Landau-Lifshitz (L-L) equation describing the time dependence of the
magnetisation vector is numerically integrated fully without any simplifying
assumptions in the time domain and the magnetisation time series obtained is
Fourier transformed (FFT) to yield the permeability spectrum up to 10 GHz. The
non linear results are compared to the experimental results obtained on
magnetic amorphous thin films of Co-Zr, Co-Zr-Re. We analyse our results with
the frequency response obtained directly from the Landau-Lifshitz equation as
well as with the second order Gilbert frequency response. | 0101154v1 |
2004-08-13 | Finite lattice size effect in the ground state phase diagram of quasi-two-dimensional magnetic dipolar dots array with perpendicular anisotropy | A prototype Hamiltonian for the generic patterned magnetic structures, of
dipolar interaction with perpendicular anisotropy, is investigated within the
finite-size framework by Landau-Lifshift-Gilbert classical spin dynamics.
Modifications on the ground state phase diagram are discussed with an emphasis
on the disappearance of continuous degeneracy in the ground state of in-plane
phase due to the finite lattice size effect. The symmetry-governed ground state
evolution upon the lattice size increase provides a critical insight into the
systematic transition to the infinite extreme. | 0408324v1 |
2004-10-01 | Current-spin coupling for ferromagnetic domain walls in fine wires | The coupling between a current and a domain wall is examined. In the presence
of a finite current and the absence of a potential which breaks the
translational symmetry, there is a perfect transfer of angular momentum from
the conduction electrons to the wall. As a result, the ground state is in
uniform motion. This remains the case when relaxation is accounted for. This is
described by, appropriately modified, Landau-Lifshitz-Gilbert equations. | 0410035v1 |
2004-12-17 | Hysteresis loops of magnetic thin films with perpendicular anisotropy | We model the magnetization of quasi two-dimensional systems with easy
perpendicular (z-)axis anisotropy upon change of external magnetic field along
z. The model is derived from the Landau-Lifshitz-Gilbert equation for
magnetization evolution, written in closed form in terms of the z component of
the magnetization only. The model includes--in addition to the external
field--magnetic exchange, dipolar interactions and structural disorder. The
phase diagram in the disorder/interaction strength plane is presented, and the
different qualitative regimes are analyzed. The results compare very well with
observed experimental hysteresis loops and spatial magnetization patterns, as
for instance for the case of Co-Pt multilayers. | 0412461v1 |
2006-01-11 | Relaxing-Precessional Magnetization Switching | A new way of magnetization switching employing both the spin-transfer torque
and the torque by a magnetic field is proposed. The solution of the
Landau-Lifshitz-Gilbert equation shows that the dynamics of the magnetization
in the initial stage of the switching is similar to that in the precessional
switching, while that in the final stage is rather similar to the relaxing
switching. We call the present method the relaxing-precessional switching. It
offers a faster and lower-power-consuming way of switching than the relaxing
switching and a more controllable way than the precessional switching. | 0601227v1 |
2006-04-01 | Magnetization reversal through synchronization with a microwave | Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a
circularly-polarized microwave can reverse the magnetization of a Stoner
particle through synchronization. In comparison with magnetization reversal
induced by a static magnetic field, it can be shown that when a proper
microwave frequency is used the minimal switching field is much smaller than
that of precessional magnetization reversal. A microwave needs only to overcome
the energy dissipation of a Stoner particle in order to reverse magnetization
unlike the conventional method with a static magnetic field where the switching
field must be of the order of magnetic anisotropy. | 0604013v1 |
2006-06-26 | Self Consistent NEGF-LLG Model for Spin-Torque Based Devices | We present here a self consistent solution of quantum transport, using the
Non Equilibrium Green's Function (NEGF) method, and magnetization dynamics,
using the Landau-Lifshitz-Gilbert (LLG) formulation. We have applied this model
to study current induced magnetic switching due to `spin torque' in a device
where the electronic transport is ballistic and the free magnetic layer is
sandwiched between two anti-parallel ferromagnetic contacts. The device shows
clear hysteretic current-voltage characteristics, at room temperature, with a
sharp transition between the bistable states and hence can be used as a
non-volatile memory. We show that the proposed design may allow reducing the
switching current by an order of magnitude. | 0606648v2 |
2006-07-25 | Thermally-Assisted Current-Driven Domain Wall Motion | Starting from the stochastic Landau-Lifschitz-Gilbert equation, we derive
Langevin equations that describe the nonzero-temperature dynamics of a rigid
domain wall. We derive an expression for the average drift velocity of the
domain wall as a function of the applied current, and find qualitative
agreement with recent magnetic semiconductor experiments. Our model implies
that at any nonzero temperature the average domain-wall velocity initially
varies linearly with current, even in the absence of non-adiabatic spin
torques. | 0607663v1 |
2006-09-08 | Large cone angle magnetization precession of an individual nanomagnet with dc electrical detection | We demonstrate on-chip resonant driving of large cone-angle magnetization
precession of an individual nanoscale permalloy element. Strong driving is
realized by locating the element in close proximity to the shorted end of a
coplanar strip waveguide, which generates a microwave magnetic field. We used a
microwave frequency modulation method to accurately measure resonant changes of
the dc anisotropic magnetoresistance. Precession cone angles up to $9^{0}$ are
determined with better than one degree of resolution. The resonance peak shape
is well-described by the Landau-Lifshitz-Gilbert equation. | 0609190v1 |
2006-12-30 | Low relaxation rate in a low-Z alloy of iron | The longest relaxation time and sharpest frequency content in ferromagnetic
precession is determined by the intrinsic (Gilbert) relaxation rate \emph{$G$}.
For many years, pure iron (Fe) has had the lowest known value of $G=\textrm{57
Mhz}$ for all pure ferromagnetic metals or binary alloys. We show that an
epitaxial iron alloy with vanadium (V) possesses values of $G$ which are
significantly reduced, to 35$\pm$5 Mhz at 27% V. The result can be understood
as the role of spin-orbit coupling in generating relaxation, reduced through
the atomic number $Z$. | 0701004v1 |
2004-09-07 | Distance properties of expander codes | We study the minimum distance of codes defined on bipartite graphs. Weight
spectrum and the minimum distance of a random ensemble of such codes are
computed. It is shown that if the vertex codes have minimum distance $\ge 3$,
the overall code is asymptotically good, and sometimes meets the
Gilbert-Varshamov bound.
Constructive families of expander codes are presented whose minimum distance
asymptotically exceeds the product bound for all code rates between 0 and 1. | 0409010v1 |
1996-06-11 | Radiative corrections to $e^+e^-\to H^+ H^-$ | We study the 1-loop corrections to the charged Higgs production both in the
Minimal Supersymmetric Standard Model (MSSM) and in a more general type II
two-Higgs-doublet model (THDM-II). We consider the full set of corrections
(including soft photon contributions as well as box diagrams), and define a
parametrization that allows a comparison between the two models. Besides the
soft photon radiation there can be prominent model-dependent effects. | 9606300v1 |
1997-05-15 | Analytic constraints from electroweak symmetry breaking in the MSSM | We report on how a straightforward (albeit technically involved) analytic
study of the 1-loop effective potential in the Minimal Supersymmetric Standard
Model, modifies the usual electroweak symmetry breaking conditions involving
$\tan \beta$ and the other free parameters of the model. The study implies new
constraints which (in contrast with the existing ones like $1 \leq \tan \beta
\leq m_t/m_b$) are fully model-independent and exclude more restrictively a
region around $\tan \beta \sim 1$. Further results of this study will be only
touched upon here. | 9705330v1 |
1998-10-01 | Extracting chargino/neutralino mass parameters from physical observables | I report on two papers, hep-ph/9806279 and hep-ph/9807336, where
complementary strategies are proposed for the determination of the
chargino/neutralino sector parameters, $M_1, M_2, \mu $ and $\tan \beta$, from
the knowledge of some physical observables. This determination and the
occurrence of possible ambiguities are studied as far as possible analytically
within the context of the unconstrained MSSM, assuming however no CP-violation. | 9810214v1 |
1999-12-28 | Associated H$^{-}$ W$^{+}$ Production in High Energy $e^+e^-$ Collisions | We study the associated production of charged Higgs bosons with $W$ gauge
bosons in high energy $e^+ e^-$ collisions at the one loop level. We present
the analytical results and give a detailed discussion for the total cross
section predicted in the context of a general Two Higgs Doublet Model (THDM). | 9912527v2 |
2001-03-25 | Comment on ``Infrared Fixed Point Structure in Minimal Supersymmetric Standard Model with Baryon and Lepton Number Violation" | We reconsider the Infrared Quasi Fixed Points which were studied recently in
the literature in the context of the Baryon and Lepton number violating Minimal
Supersymmetric Standard Model (hep-ph/0011274). The complete analysis requires
further care and reveals more structure than what was previously shown. The
formalism we develop here is quite general, and can be readily applied to a
large class of models. | 0103270v1 |
1991-11-21 | "the Instability of String-Theoretic Black Holes" | It is demonstrated that static, charged, spherically--symmetric black holes
in string theory are classically and catastrophically unstable to linearized
perturbations in four dimensions, and moreover that unstable modes appear for
arbitrarily small positive values of the charge. This catastrophic classical
instability dominates and is distinct from much smaller and less significant
effects such as possible quantum mechanical evaporation. The classical
instability of the string--theoretic black hole contrasts sharply with the
situation which obtains for the Reissner--Nordstr\"om black hole of general
relativity, which has been shown by Chandrasekhar to be perfectly stable to
linearized perturbations at the event horizon. | 9111042v1 |
1997-12-09 | The combinatorics of biased riffle shuffles | This paper studies biased riffle shuffles, first defined by Diaconis, Fill,
and Pitman. These shuffles generalize the well-studied Gilbert-Shannon-Reeds
shuffle and convolve nicely. An upper bound is given for the time for these
shuffles to converge to the uniform distribution; this matches lower bounds of
Lalley. A careful version of a bijection of Gessel leads to a generating
function for cycle structure after one of these shuffles and gives new results
about descents in random permutations. Results are also obtained about the
inversion and descent structure of a permutation after one of these shuffles. | 9712240v1 |
2000-08-16 | Homotopies and automorphisms of crossed modules of groupoids | We give a detailed description of the structure of the actor 2-crossed module
related to the automorphisms of a crossed module of groupoids. This generalises
work of Brown and Gilbert for the case of crossed modules of groups, and part
of this is needed for work on 2-dimensional holonomy to be developed elsewhere
(see math.DG/0009082). | 0008117v2 |
2005-06-14 | Transitive and Self-dual Codes Attaining the Tsfasman-Vladut-Zink Bound | We introduce - as a generalization of cyclic codes - the notion of transitive
codes, and we show that the class of transitive codes is asymptotically good.
Even more, transitive codes attain the Tsfasman-Vladut-Zink bound over F_q, for
all aquares q=l^2. We also show that self-orthogonal and self-dual codes attain
the Tsfasman-Vladut-Zink bound, thus improving previous results about self-dual
codes attaining the Gilbert-Varshamov bound. The main tool is a new
asymptotically optimal tower (E_n) of function fields over F_q where all
extensions E_n/E_0 are Galois. | 0506264v1 |
2005-09-01 | Counting unlabelled toroidal graphs with no K33-subdivisions | We provide a description of unlabelled enumeration techniques, with complete
proofs, for graphs that can be canonically obtained by substituting 2-pole
networks for the edges of core graphs. Using structure theorems for toroidal
and projective-planar graphs containing no K33-subdivisions, we apply these
techniques to obtain their unlabelled enumeration. | 0509004v2 |
2006-05-19 | Deformation spaces of trees | Let G be a finitely generated group. Two simplicial G-trees are said to be in
the same deformation space if they have the same elliptic subgroups (if H fixes
a point in one tree, it also does in the other). Examples include
Culler-Vogtmann's outer space, and spaces of JSJ decompositions. We discuss
what features are common to trees in a given deformation space, how to pass
from one tree to all other trees in its deformation space, and the topology of
deformation spaces. In particular, we prove that all deformation spaces are
contractible complexes. | 0605545v2 |
1999-10-12 | Uniform spectral properties of one-dimensional quasicrystals, III. $α$-continuity | We study the spectral properties of discrete one-dimensional Schr\"odinger
operators with Sturmian potentials. It is shown that the point spectrum is
always empty. Moreover, for rotation numbers with bounded density, we establish
purely $\alpha$-continuous spectrum, uniformly for all phases. The proofs rely
on the unique decomposition property of Sturmian potentials, a
mass-reproduction technique based upon a Gordon-type argument, and on the
Jitomirskaya-Last extension of the Gilbert-Pearson theory of subordinacy. | 9910017v1 |
2003-08-18 | Vector Coherent States on Clifford algebras | The well-known canonical coherent states are expressed as an infinite series
in powers of a complex number $z$ together with a positive sequence of real
numbers $\rho(m)=m$. In this article, in analogy with the canonical coherent
states, we present a class of vector coherent states by replacing the complex
variable $z$ by a real Clifford matrix. We also present another class of vector
coherent states by simultaneously replacing $z$ by a real Clifford matrix and
$\rho(m)$ by a real matrix. As examples, we present vector coherent states on
quaternions and octonions with their real matrix representations. | 0308020v2 |
2007-01-12 | Non-equilibrium Lorentz gas on a curved space | The periodic Lorentz gas with external field and iso-kinetic thermostat is
equivalent, by conformal transformation, to a billiard with expanding
phase-space and slightly distorted scatterers, for which the trajectories are
straight lines. A further time rescaling allows to keep the speed constant in
that new geometry. In the hyperbolic regime, the stationary state of this
billiard is characterized by a phase-space contraction rate, equal to that of
the iso-kinetic Lorentz gas. In contrast to the iso-kinetic Lorentz gas where
phase-space contraction occurs in the bulk, the phase-space contraction rate
here takes place at the periodic boundaries. | 0701024v1 |
2006-02-23 | Equivalence of two mathematical forms for the bound angular momentum of the electromagnetic field | It is shown that the mathematical form, obtained in a recent paper, for the
angular momentum of the electromagnetic field in the vicinity of electric
charge is equivalent to another form obtained previously by Cohen-Tannoudji,
Dupont-Roc and Gilbert. In this version of the paper an improved derivation is
given. | 0602157v3 |
2006-10-13 | Senescence Can Explain Microbial Persistence | It has been known for many years that small fractions of persister cells
resist killing in many bacterial colony-antimicrobial confrontations. These
persisters are not believed to be mutants. Rather it has been hypothesized that
they are phenotypic variants. Current models allow cells to switch in and out
of the persister phenotype. Here we suggest a different explanation, namely
senescence, for persister formation. Using a mathematical model including age
structure, we show that senescence provides a natural explanation for
persister-related phenomena including the observations that persister fraction
depends on growth phase in batch culture and dilution rate in continuous
culture. | 0610026v1 |
2002-12-30 | Dark propagation modes in optical lattices | We examine the stimulated light scattering onto the propagation modes of a
dissipative optical lattice. We show that two different pump-probe
configurations may lead to the excitation, via different mechanisms, of the
same mode. We found that in one configuration the scattering on the propagation
mode results in a resonance in the probe transmission spectrum while in the
other configuration no modification of the scattering spectrum occurs, i.e. the
mode is dark. A theoretical explanation of this behaviour is provided. | 0212157v1 |
2003-09-29 | Phase-control of directed diffusion in a symmetric optical lattice | We demonstrate the phenomenon of directed diffusion in a symmetric periodic
potential. This has been realized with cold atoms in a one-dimensional
dissipative optical lattice. The stochastic process of optical pumping leads to
a diffusive dynamics of the atoms through the periodic structure, while a
zero-mean force which breaks the temporal symmetry of the system is applied by
phase-modulating one of the lattice beams. The atoms are set into directed
motion as a result of the breaking of the temporal symmetry of the system. | 0309208v1 |
2003-09-29 | Synchronization of Hamiltonian motion and dissipative effects in optical lattices: Evidence for a stochastic resonance | We theoretically study the influence of the noise strength on the excitation
of the Brillouin propagation modes in a dissipative optical lattice. We show
that the excitation has a resonant behavior for a specific amount of noise
corresponding to the precise synchronization of the Hamiltonian motion on the
optical potential surfaces and the dissipative effects associated with optical
pumping in the lattice. This corresponds to the phenomenon of stochastic
resonance. Our results are obtained by numerical simulations and correspond to
the analysis of microscopic quantities (atomic spatial distributions) as well
as macroscopic quantities (enhancement of spatial diffusion and pump-probe
spectra). We also present a simple analytical model in excellent agreement with
the simulations. | 0309210v1 |
2006-06-23 | Playing Quantum Physics Jeopardy with zero-energy eigenstates | We describe an example of an exact, quantitative Jeopardy-type quantum
mechanics problem. This problem type is based on the conditions in
one-dimensional quantum systems that allow an energy eigenstate for the
infinite square well to have zero curvature and zero energy when suitable Dirac
delta functions are added. This condition and its solution are not often
discussed in quantum mechanics texts and have interesting pedagogical
consequences. | 0606196v1 |
2006-10-18 | Subsystem Codes | We investigate various aspects of operator quantum error-correcting codes or,
as we prefer to call them, subsystem codes. We give various methods to derive
subsystem codes from classical codes. We give a proof for the existence of
subsystem codes using a counting argument similar to the quantum
Gilbert-Varshamov bound. We derive linear programming bounds and other upper
bounds. We answer the question whether or not there exist
[[n,n-2d+2,r>0,d]]<sub>q</sub> subsystem codes. Finally, we compare stabilizer
and subsystem codes with respect to the required number of syndrome qudits. | 0610153v1 |
2007-05-14 | The dynamical response to the node defect in thermally activated remagnetization of magnetic dot array | The influence of nonmagnetic central node defect on dynamical properties of
regular square-shaped 5 x 5 segment of magnetic dot array under the thermal
activation is investigated via computer simulations. Using stochastic
Landau-Lifshitz-Gilbert equation we simulate hysteresis and relaxation
processes. The remarkable quantitative and qualitative differences between
magnetic dot arrays with nonmagnetic central node defect and magnetic dot
arrays without defects have been found. | 0705.1889v1 |
2007-05-18 | Steady-state conduction in self-similar billiards | The self-similar Lorentz billiard channel is a spatially extended
deterministic dynamical system which consists of an infinite one-dimensional
sequence of cells whose sizes increase monotonically according to their
indices. This special geometry induces a nonequilibrium stationary state with
particles flowing steadily from the small to the large scales. The
corresponding invariant measure has fractal properties reflected by the
phase-space contraction rate of the dynamics restricted to a single cell with
appropriate boundary conditions. In the near-equilibrium limit, we find
numerical agreement between this quantity and the entropy production rate as
specified by thermodynamics. | 0705.2758v1 |
2007-06-04 | Generation of microwave radiation in planar spin-transfer devices | Current induced precession states in spin-transfer devices are studied in the
case of large easy plane anisotropy (present in most experimental setups). It
is shown that the effective one-dimensional planar description provides a
simple qualitative understanding of the emergence and evolution of such states.
Switching boundaries are found analytically for the collinear device and the
spin-flip transistor. The latter can generate microwave oscillations at zero
external magnetic field without either special functional form of spin-transfer
torque, or ``field-like'' terms, if Gilbert constant corresponds to the
overdamped planar regime. | 0706.0529v1 |
2007-12-26 | Mass and angular-momentum inequalities for axi-symmetric initial data sets. II. Angular-momentum | We extend the validity of Dain's angular-momentum inequality to maximal,
asymptotically flat, initial data sets on a simply connected manifold with
several asymptotically flat ends which are invariant under a U(1) action and
which admit a twist potential. | 0712.4064v2 |
2008-01-28 | TER: A Robot for Remote Ultrasonic Examination: Experimental Evaluations | This chapter:
o Motivates the clinical use of robotic tele-echography
o Introduces the TER system
o Describes technical and clinical evaluations performed with TER | 0801.4355v1 |
2008-03-14 | Spin-torque shot noise in magnetic tunnel junctions | Spin polarized current may transfer angular momentum to a ferromagnet,
resulting in a spin-torque phenomenon. At the same time the shot noise,
associated with the current, leads to a non-equilibrium stochastic force acting
on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert
equation for a magnetization of a ''free'' ferromagnetic layer in contact with
a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and
show that the non-equilibrium noise yields to a non-monotonous dependence of
the precession spectrum linewidth on the current. | 0803.2101v1 |
2008-04-07 | Paired Orbitals for Different Spins equations | Eigenvalue-type equations for Lowdin-Amos-Hall spin-paired (corresponding)
orbitals are developed to provide an alternative to the standard spin-polarized
Hartree-Fock or Kohn-Sham equations. Obtained equations are non-canonical
unrestricted Hartree-Fock-type equations in which non-canonical orbitals are
fixed to be biorthogonal spin-paired orbitals. To derive paired orbitals for
different spins (PODS) equations there has been applied Adams-Gilbert
localizing operator approach. PODS equations are especially useful for
treatment of the broken-symmetry solutions for antiferromagnetic materials. | 0804.0967v1 |
2008-04-26 | Spin-torque oscillator based on tilted magnetization of the fixed layer | The spin torque oscillator (STO), where the magnetization of the fixed layer
is tilted out of the film plane, is capable of strong microwave signal
generation in zero magnetic field. Through numerical simulations of the
Landau-Lifshitz-Gilbert-Slonczewski equations, within a macro-spin
approximation, we study the microwave signal generation as a function of drive
current for two realistic tilt angles. The tilt magnetization of the fixed
layer can be achieved by using a material with high out-of-plane
magnetocrystalline anisotropy, such as L10 FePt. | 0804.4213v1 |
2008-07-11 | Superconductivity up to 29 K in SrFe2As2 and BaFe2As2 at high pressures | We report the discovery of superconductivity at high pressure in SrFe2As2 and
BaFe2As2. The superconducting transition temperatures are up to 27 K in
SrFe2As2 and 29 K in BaFe2As2, making these the highest pressure-induced
superconducting materials discovered thus far. | 0807.1896v2 |
2008-07-14 | An Adaptive Entanglement Distillation Scheme Using Quantum Low Density Parity Check Codes | Quantum low density parity check (QLDPC) codes are useful primitives for
quantum information processing because they can be encoded and decoded
efficiently. Besides, the error correcting capability of a few QLDPC codes
exceeds the quantum Gilbert-Varshamov bound. Here, we report a numerical
performance analysis of an adaptive entanglement distillation scheme using
QLDPC codes. In particular, we find that the expected yield of our adaptive
distillation scheme to combat depolarization errors exceed that of Leung and
Shor whenever the error probability is less than about 0.07 or greater than
about 0.28. This finding illustrates the effectiveness of using QLDPC codes in
entanglement distillation. | 0807.2122v1 |
2008-07-16 | Analytical solution of the equation of motion for a rigid domain wall in a magnetic material with perpendicular anisotropy | This paper reports the solution of the equation of motion for a domain wall
in a magnetic material which exhibits high magneto-crystalline anisotropy.
Starting from the Landau-Lifschitz-Gilbert equation for field-induced motion,
we solve the equation to give an analytical expression, which specifies the
domain wall position as a function of time. Taking parameters from a Co/Pt
multilayer system, we find good quantitative agreement between calculated and
experimentally determined wall velocities, and show that high field uniform
wall motion occurs when wall rigidity is assumed. | 0807.2604v3 |
2008-07-16 | A graphical extension for the Windows version of the Parallel Finite Element Micromagnetics Package (MagParExt) | In the current paper we present a graphical user interface useful for
settings input parameter of the Windows precompiled binaries for the Parallel
Finite Element Micromagnetics Package (MagPar). The Package is used for
magnetization dynamics analysis on a base of the Landau-Lifshitz-Gilbert (LLG)
equation. In an available version of the MagPar package there are several text
files which control simulations. Presented here graphical extension (MagParExt)
enables easy preparation of input and output data, stored in text files, and
additionally, direct and fast creation of figures obtained from dependencies
between simulated physical quantities. | 0807.2655v1 |
2008-08-17 | Attempt frequency of magnetization in nanomagnets with thin-film geometry | Solving the stochastic Landau-Lifshitz-Gilbert equation numerically, we
investigate the effect of the potential landscape on the attempt frequency of
magnetization in nanomagnets with the thin-film geometry. Numerical estimates
of the attempt frequency are analyzed in comparison with theoretical
predictions from the Fokker-Planck equation for the Neel-Brown model. It is
found that for a nanomagnet with the thin-film geometry, theoretically
predicted values for the universal case are in excellent agreement with
numerical estimates. | 0808.2281v1 |
2008-08-30 | Path integral study of the role of correlation in exchange coupling of spins in double quantum dots and optical lattices | We explore exchange coupling of a pair of spins in a double dot and in an
optical lattice. Our algorithm uses the frequency of exchanges in a bosonic
path integral, evaluated with Monte Carlo. This algorithm is simple enough to
be a "black box" calculator, yet gives insights into the role of correlation
through two-particle probability densities, visualization of instantons, and
pair correlation functions. We map the problem to Hubbard model and see that
exchange and correlation renormalize the effective parameters, dramatically
lowering U at larger separations. | 0809.0038v1 |
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