publicationDate stringlengths 1 2.79k | title stringlengths 1 36.5k ⌀ | abstract stringlengths 1 37.3k ⌀ | id stringlengths 9 47 |
|---|---|---|---|
2009-09-22 | Ferroelectric Soft Mode in Pb(Mg1/3Nb2/3)O3 | Ferroelectric soft mode in Pb(Mg1/3Nb2/3)O3 (PMN) has been clearly resolved
by precision Raman scattering measurements for the first time. A polarization
direction of the incident laser was chosen along [110] in cubic configuration
in order to eliminate strong scattering components around 45 cm-1, which always
smeared the low-frequency spectra of PMN. The soft mode frequency omega_s
(=\sqrt{omega_0^2-gamma^2}) softens around 200 K, where omega_0 and gamma are a
harmonic frequency and a damping constant, respectively. The present result
evidenced that the origin of the polarizationthe in PMN is the soft mode. | 0909.3889v1 |
2010-07-20 | Nonlinear current response of an isolated system of interacting fermions | Nonlinear real-time response of interacting particles is studied on the
example of a one-dimensional tight-binding model of spinless fermions driven by
electric field. Using equations of motion and numerical methods we show that
for a non-integrable case at finite temperatures the major effect of
nonlinearity can be taken into account within the linear response formalism
extended by a renormalization of the kinetic energy due to the Joule heating.
On the other hand, integrable systems show on constant driving a different
universality with a damped oscillating current whereby the frequency is related
but not equal to the Bloch oscillations. | 1007.3383v1 |
2010-11-12 | Non-archimedean quantum cosmology and tachyonic inflation | We review the relevance of quantum rolling tachyons and corresponding
inflation scenario in the frame of the standard, $p$-adic and adelic
minisuperspace quantum cosmology. The field theory of tachyon matter proposed
by Sen in a zero-dimensional version suggested by Kar leads to a model of a
particle moving in a constant external field with quadratic damping. We
calculate the exact quantum propagator of the model, as well as, the vacuum
states and conditions necessary to construct an adelic generalization. In
addition we present an overview on several important cosmological models on
archimedean and nonarchimedean spaces. | 1011.2885v1 |
2012-07-08 | Non-monotonic behaviour of the superconducting order parameter in Nb/PdNi bilayers observed through point contact spectroscopy | Point contact spectroscopy measurements have been performed on Nb/PdNi
bilayers in which the thickness of the Nb layer, dNb, was kept constant to 40
nm while the thickness of PdNi, dPdNi, was changed from 2 nm to 9 nm. Features
related to the superconducting gap induced in the ferromagnet have been
observed in the dV/dI versus V curves. These structures show a non-monotonic
behaviour as a function of dPdNi as a consequence of the damped oscillatory
behaviour of the superconducting order parameter in the ferromagnetic layer. | 1207.1879v1 |
2013-02-26 | Modelling Fast-Alfvén Mode Conversion Using SPARC | We successfully utilise the SPARC code to model fast-Alfv\'en mode conversion
in the region $c_A \gg c_S$ via 3-D MHD numerical simulations of helioseismic
waves within constant inclined magnetic field configurations. This was achieved
only after empirically modifying the background density and gravitational
stratifications in the upper layers of our computational box, as opposed to
imposing a traditional Lorentz Force limiter, to ensure a manageable timestep.
We found that the latter approach inhibits the fast-Alfv\'en mode conversion
process by severely damping the magnetic flux above the surface. | 1302.6301v1 |
2013-06-29 | Perpendicular magnetization of Co20Fe50Ge30 films induced by MgO interface | Epitaxial growth of Co20Fe50Ge30 thin film on single crystal MgO (001)
substrate is reported. Structure characterization revealed (001)-oriented B2
order of CoFeGe well lattice matched with the MgO barrier. Perpendicular
magnetic anisotropy (PMA) was achieved in the MgO/CoFeGe/MgO structure with an
optimized magnetic anisotropy energy density (K) of 3 106 erg/cm3. The magnetic
anisotropy is found to depend strongly on the thickness of the MgO and CoFeGe
layers, indicating that the PMA of CoFeGe is contributed by the interfacial
anisotropy between CoFeGe and MgO. With reported low damping constant, CoFeGe
films are promising spintronic materials for achieving low switching current. | 1307.0104v1 |
2013-08-16 | Luminosity Upgrades for ILC | The possibility of increasing the luminosity for the ILC at Ecm < 350 GeV
centre-of-mass by increasing the beam power are considered. It will be shown
that an approximately constant luminosity can be achieved across the centre of
mass energy range (250-500 GeV) without exceeding the installed AC power for
500 GeV operation. Overall a factor of four in luminosity over the published
baseline could be achieved at 250 GeV resulting in 3*10**34 cm-2s-1. The
implications for the damping rings and positron source are also briefly
discussed. | 1308.3726v1 |
2014-09-01 | The co-existence of states in p53 dynamics driven by miRNA | The regulating mechanism of miRNA on p53 dynamics in p53-MDM2-miRNA model
network incorporating reactive oxygen species (ROS) is studied. The study shows
that miRNA drives p53 dynamics at various states, namely, stabilized states and
oscillating states (damped and sustain oscillation). We found the co-existence
of these states within certain range of the concentartion level of miRNA in the
system. This co-existence in p53 dynamics is the signature of the system's
survival at various states, normal, activated and apoptosis driven by a
constant concentration of miRNA. | 1409.1943v1 |
2014-12-04 | The fluctuation-dissipation relation in a resonantly driven quantum medium | We calculate the radiation noise level associated with the spontaneous
emission of a coherently driven medium. The significant field-induced
modification of relation between the noise power and damping constant in a
thermal reservoir is obtained. The nonlinear noise exchange between different
atomic frequencies leads to violation of standard relations dictated by the
fluctuation-dissipation theorem. | 1412.1646v3 |
2015-01-15 | Anomaly of the Internal Friction in the Helium Crystals Grown in the Burst-like Growth Mode | The internal friction in the crystals grown in two modes, namely, slow and
anomalously fast (burst-like growth) modes, is measured in the temperature
range 0.49-0.75K at a frequency of about 75kHz. An additional contribution to
the damping decrement and softening of the dynamic modulus are detected, and
their relaxation to equilibrium values at a time constant of about 3ms is
observed. Possible origins of this effect are discussed. | 1501.03739v1 |
2015-04-02 | Phase transition in p53 states induced by glucose | We present p53-MDM2-Glucose model to study spatio-temporal properties of the
system induced by glucose. The variation in glucose concentration level
triggers the system at different states, namely, oscillation death
(stabilized), sustain and damped oscillations which correspond to various
cellular states. The transition of these states induced by glucose is phase
transition like behaviour. We also found that the intrinsic noise in stochastic
system helps the system to stabilize more effectively. Further, the amplitude
of $p53$ dynamics with the variation of glucose concentration level follows
power law behaviour, $A_s(k)\sim k^\gamma$, where, $\gamma$ is a constant. | 1504.00431v1 |
2015-06-23 | The remarkable effectiveness of time-dependent damping terms for second order evolution equations | We consider a second order linear evolution equation with a dissipative term
multiplied by a time-dependent coefficient. Our aim is to design the
coefficient in such a way that all solutions decay in time as fast as possible.
We discover that constant coefficients do not achieve the goal, as well as
time-dependent coefficients that are too big. On the contrary, pulsating
coefficients which alternate big and small values in a suitable way prove to be
more effective.
Our theory applies to ordinary differential equations, systems of ordinary
differential equations, and partial differential equations of hyperbolic type. | 1506.06915v1 |
2015-07-02 | Global solutions for a supercritical drift-diffusion equation | We study the global existence of solutions to a one-dimensional
drift-diffusion equation with logistic term, generalizing the classical
parabolic-elliptic Keller-Segel aggregation equation arising in mathematical
biology. In particular, we prove that there exists a global weak solution, if
the order of the fractional diffusion $\alpha \in (1-c_1, 2]$, where $c_1>0$ is
an explicit constant depending on the physical parameters present in the
problem (chemosensitivity and strength of logistic damping). Furthermore, in
the range $1-c_2<\alpha\leq 2$ with $0<c_2<c_1$, the solution is globally
smooth. Let us emphasize that when $\alpha<1$, the diffusion is in the
supercritical regime. | 1507.00694v2 |
2015-10-26 | Variational Limits for Phase Precision in Linear Quantum Optical Metrology | We apply the variational method to obtain the universal and analytical lower
bounds for parameter precision in some noisy systems. We first derive a lower
bound for phase precision in lossy optical interferometry at non-zero
temperature. Then we consider the effect of both amplitude damping and phase
diffusion on phase-shift precision. At last, we extend the constant phase
estimation to the case of continuous fluctuating phase estimation, and find
that due to photon losses the corresponding mean square error transits from the
stochastic Heisenberg limit to the stochastic standard quantum limit as the
total photon flux increases. | 1510.07381v1 |
2016-02-26 | Correspondence between phasor transforms and frequency response function in RLC circuits | The analysis of RLC circuits is usually made by considering phasor transforms
of sinusoidal signals (characterized by constant amplitude, period and phase)
that allow the calculation of the AC steady state of RLC circuits by solving
simple algebraic equations. In this paper I try to show that phasor
representation of RLC circuits is analogue to consider the frequency response
function (commonly designated by FRF) of the total impedance of the circuit. In
this way I derive accurate expressions for the resonance and anti-resonance
frequencies and their corresponding values of impedances of the parallel and
series RLC circuits respectively, notwithstanding the presence of damping
effects. | 1602.08487v1 |
2016-05-02 | Undamped relativistic magnetoplasmons in lossy two-dimensional electron systems | We address electrodynamic effects in plasma oscillations of a lossy 2D
electron system whose dc 2D conductivity is comparable to the speed of light.
We argue that the perpendicular constant magnetic field B causes astonishing
features of magnetoplasma dynamics. We show that plasmon-polariton spectra can
be classified using a 'relativistic' phase diagram 2D conductivity divided by
the speed of light versus B. An extraordinarily low damping branch in
magnetoplasmon-polariton spectra emerges at two phases of this diagram. Some
magnetoplasmons at these phases are predicted to be undamped waves. | 1605.00430v2 |
2016-09-01 | Asymptotic for the perturbed heavy ball system with vanishing damping term | We investigate the long time behavior of solutions to the differential
equation $\ddot{x}(t)+\frac{c}{\left( t+1\right) ^{\alpha}}\dot{x}(t)+\nabla
\Phi\left( x(t)\right) =g(t),~t\geq0, $ where $c$ is nonnegative constant,
$\alpha\in\lbrack0,1[,$ $\Phi$ is a $C^{1}$ convex function on a Hilbert space
$\mathcal{H}$ and $g\in L^{1} (0,+\infty;\mathcal{H}).$ We obtain sufficient
conditions on the source term $g(t)$ ensuring the weak or the strong
convergence of any trajectory $x(t)$ as $t\rightarrow+\infty$ to a minimizer of
the function $\Phi$ if one exists. | 1609.00135v2 |
2016-09-19 | An entropic gradient structure for Lindblad equations and couplings of quantum systems to macroscopic models | We show that all Lindblad operators (i.e. generators of quantum semigroups)
on a finite-dimensional Hilbert space satisfying the detailed balance condition
with respect to the thermal equilibrium state can be written as a gradient
system with respect to the relative entropy.
We discuss also thermodynamically consistent couplings to macroscopic
systems, either as damped Hamiltonian systems with constant temperature or as
GENERIC systems. In particular we discuss the coupling of a quantum dot coupled
to macroscopic charge carriers. | 1609.05765v3 |
2016-10-25 | Quasi-flat plasmonic bands in twisted bilayer graphene | The charge susceptibility of twisted bilayer graphene is investigated in the
Dirac cone, respectively random-phase approximation. For small enough twist
angles $\theta\lesssim 2^\circ$ we find weakly Landau damped interband
plasmons, i.~e., collective excitonic modes which exist in the undoped
material, with an almost constant energy dispersion. In this regime, the loss
function can be described as a Fano resonance and we argue that these
excitations arise from the interaction of quasi-localised states with the
incident light field. These predictions can be tested by nano-infrared imaging
and possible applications include a "perfect" lens without the need of
left-handed materials. | 1610.07757v1 |
2016-12-31 | Dynamics of a spin-boson model with structured spectral density | We report the results of a study of the dynamics of a two-state system
coupled to an environment with peaked spectral density. An exact analytical
expression for the bath correlation function is obtained. Validity range of
various approximations to the correlation function for calculating the
population difference of the system are discussed as function of tunneling
splitting, oscillator frequency, coupling constant, damping rate and the
temperature of the bath. An exact expression for the population difference for
a limited range of parameters, is derived. | 1701.00122v1 |
2012-10-31 | Well-posedness of a Parabolic-hyperbolic Keller-Segel System in the Sobolev Space Framework | We study the global strong solutions to a 3-dimensional parabolic-hyperbolic
Keller-Segel model with initial data close to a stable equilibrium with
perturbations belonging to $L^2(\mathbb R^3)\times H^1(\mathbb{R}^3)$. We
obtain global well-posedness and decay property. Furthermore, if the mean value
of initial cell density is smaller than a suitabale constant, then the chemical
concentration decays exponentially to zero as $t$ goes to infinity. Proofs of
the main results are based on an application of Fourier analysis method to
uniform estimates for a linearized parabolic-hyperbolic system and also based
on the smoothing effect of the cell density as well as the damping effect of
the chemical concentration. | 1210.8214v1 |
2016-08-21 | Spin correlation functions and quasiparticle decay | We study one-dimensional anisotropic XXZ spin-$\frac12$ model with
ferromagnetic sign of the coupling and $z-z$ exchange constant $J_z = \Delta
J$, where $\Delta < 1$, and $J$ is the coupling within XY spin plane. We
calculate damping of low-energy excitations with $\omega \ll T $ due to their
scattering from thermal excitation bath with temperature $T \ll J$, taking into
account nonzero curvature of the excitation spectrum, $\epsilon(q) = u q +
\delta\epsilon(q)$. We calculate also longitudinal spin-spin correlation
function $\langle S^z(x,t)S^z(0,0) \rangle$ at $x \approx ut$ and find the
shape of the spreading "wave packet". | 1608.05937v1 |
2018-12-18 | Automation of the Cavendish Experiment to 'Weigh the Earth' | We describe a simple and inexpensive method for automating the data
collection in the well-known Cavendish torsion balance experiment to determine
the gravitational constant $G$. The method uses a linear array of
phototransistors and requires no moving parts. Multiplexers and a
data-acquisition device are used to sample the state of each phototransistor
sequentially. If the sampled phototransistor is illuminated by the laser spot,
the position and time are recorded to a data file. The recorded data does an
excellent job of capturing the damped harmonic oscillations. The resulting data
were analysed to extract an experimental value of $G$ that was within 5% of the
accepted value. | 1812.07644v1 |
2016-03-03 | Inspiral into Gargantua | We model the inspiral of a compact object into a more massive black hole
rotating very near the theoretical maximum. We find that once the body enters
the near-horizon regime the gravitational radiation is characterized by a
constant frequency, equal to (twice) the horizon frequency, with an
exponentially damped profile. This contrasts with the usual "chirping" behavior
and, if detected, would constitute a "smoking gun" for a near-extremal black
hole in nature. | 1603.01221v2 |
2019-09-11 | A fully space-time least-squares method for the unsteady Navier-Stokes system | We introduce and analyze a space-time least-squares method associated to the
unsteady Navier-Stokes system. Weak solution in the two dimensional case and
regular solution in the three dimensional case are considered. From any initial
guess, we construct a minimizing sequence for the least-squares functional
which converges strongly to a solution of the Navier-Stokes system. After a
finite number of iterates related to the value of the viscosity constant, the
convergence is quadratic. Numerical experiments within the two dimensional case
support our analysis. This globally convergent least-squares approach is
related to the damped Newton method when used to solve the Navier-Stokes system
through a variational formulation. | 1909.05034v1 |
2021-05-07 | Optomechanical amplification driven by interference of phonon-exciton and phonon-photon couplings | We study theoretically optomechanical damping and amplification spectra for
vibrations interacting with excitonic polaritons in a zero-dimensional
microcavity. We demonstrate, that the spectra strongly depend on the ratio of
the exciton-phonon and the photon-phonon coupling constants. The interference
between these couplings enables a situation when optomechanical gain exists
either only for a lower polaritonic resonance or only for an upper polaritonic
resonance. Our results provide insight in the optomechanical interactions in
various multi-mode systems, where several resonant oscillators, such as
photons, plasmons, or excitons are coupled to the same vibration mode. | 2105.03214v1 |
2019-07-16 | Theory of Skyrmionic Diffusion: Hidden Diffusion Coeffcients and Breathing Diffusion | Time evolution of the position-velocity correlation functions (PVCF) plays a
key role in a new formalism of Brownian motion. A system of differential
equations, which governs PVCF, is derived for magnetic Skyrmions on a
2-dimensional magnetic thin film with thermal agitation. In the formalism, a
new type of diffusion coeffcient is introduced which does not come out in the
usual diffusion equations. The mean-square displacement (MSD) is obtained from
the PVCF and found that it oscillates in time when the damping constant is
small. It is also shown, even for a structureless particle, that the famous
Ornstein-Fuerth formula should be corrected taking a proper initial value of
PVCF into account. | 1907.06926v1 |
2020-05-23 | Stability analysis of multi-term fractional-differential equations with three fractional derivatives | Necessary and sufficient stability and instability conditions are obtained
for multi-term homogeneous linear fractional differential equations with three
Caputo derivatives and constant coefficients. In both cases,
fractional-order-dependent as well as fractional-order-independent
characterisations of stability and instability properties are obtained, in
terms of the coefficients of the multi-term fractional differential equation.
The theoretical results are exemplified for the particular cases of the Basset
and Bagley-Torvik equations, as well as for a multi-term fractional
differential equation of an inextensible pendulum with fractional damping
terms, and for a fractional harmonic oscillator. | 2005.11486v1 |
2021-01-28 | Voltage Controlled Spin-Orbit Torque Switching in W/CoFeB/MgO | Voltage control of magnetism and spintronics have been highly desirable, but
rarely realized. In this work, we show voltage-controlled spin-orbit torque
(SOT) switching in W/CoFeB/MgO films with perpendicular magnetic anisotropy
(PMA) with voltage administered through SrTiO3 with a high dielectric constant.
We show that a DC voltage can significantly lower PMA by 45%, reduce switching
current by 23%, and increase the damping-like torque as revealed by the first
and second-harmonic measurements. These are characteristics that are
prerequisites for voltage-controlled and voltage-select SOT switching
spintronic devices. | 2101.12281v1 |
2021-03-14 | A note on damped wave equations with a nonlinear dissipation in non-cylindrical domains | In this paper, we study the large time behavior of a class of wave equation
with a nonlinear dissipation in non-cylindrical domains. The result we obtained
here relaxes the conditions for the nonlinear term coefficients (in precise,
that is $\beta(t)|u|^\rho u$) in \cite{alb} and \cite{ha} (which require
$\beta(t)$ to be a constant or $\beta(t)$ to be decreasing with time $t$) and
has less restriction for the defined regions. | 2103.09678v2 |
2022-04-17 | Optimizing Brownian heat engine with shortcut strategy | Shortcuts to isothermality provide a powerful method to speed up quasistatic
thermodynamic processes within finite-time manipulation. We employ the shortcut
strategy to design and optimize Brownian heat engines, and formulate a
geometric description of the energetics with the thermodynamic length. We
obtain a tight and reachable bound of the output power, which is reached by the
optimal protocol to vary the control parameters with a proper constant velocity
of the thermodynamic length. Our results generalize the previous optimization
in the highly underdamped and the overdamped regimes to the general-damped
situation, and are applicable for arbitrary finite-time cycles. | 2204.08015v2 |
2022-11-17 | Elucidating the thermal spike effect by using a coupled classical oscillator model | Atomic heating is a fundamental phenomenon governed by the thermal spike
effect during energetic deposition. This work presented another insight into
thermal spike using a coupled classical oscillator model instead of a typical
heat diffusion model. The temperature profile of deposited atoms was replaced
by oscillator amplitude as an energy descriptor. Solving associated partial
differential equations (PDEs)suggests the efficiency of energy transfer from
the coupled hot to cold oscillators essentially relies on the atomic distance r
and the spring constant k. The solution towards the damped wave equation
further emphasize that a localized thermal fluctuation during energy
propagation. | 2211.09357v1 |
2023-03-27 | Nonlinear inviscid damping for 2-D inhomogeneous incompressible Euler equations | We prove the asymptotic stability of shear flows close to the Couette flow
for the 2-D inhomogeneous incompressible Euler equations on $\mathbb{T}\times
\mathbb{R}$. More precisely, if the initial velocity is close to the Couette
flow and the initial density is close to a positive constant in the Gevrey
class 2, then 2-D inhomogeneous incompressible Euler equations are globally
well-posed and the velocity converges strongly to a shear flow close to the
Couette flow, and the vorticity will be driven to small scales by a linear
evolution and weakly converges as $t\to \infty$. To our knowledge, this is the
first global well-posedness result for the 2-D inhomogeneous incompressible
Euler equations. | 2303.14858v1 |
2023-08-05 | Dynamics of Skyrmion Contraction and Expansion in a Magnetic Film | Contraction and expansion of skyrmions in ferromagnetic films are
investigated. In centrosymmetric systems, the dynamics of a collapsing skyrmion
is driven by dissipation. The collapse time has a minimum on the damping
constant. In systems with broken inversion symmetry, the evolution of skyrmions
toward equilibrium size is driven by the Dzyaloshinskii-Moriya interaction.
Expressions describing the time dependence of the skyrmion size are derived and
their implications for skyrmion-based information processing are discussed. | 2308.02826v1 |
2024-01-15 | Two-Dimensional Electronic Spectroscopy for Three-Level Atoms with Electromagnetically Induced Transparency | Two-dimensional electronic spectroscopy (2DES) has high spectral resolution
and is a useful tool for studying atom dynamics. In this paper, we apply the
electromagnetically induced transparency (EIT) technique to 2DES in a
three-level atom, and find out that the number of peaks (troughs) will become
more due to the introduction of EIT. Also, the height of the peaks (the depth
of troughs) will change from constant to a damped oscillation. These findings
may help us obtain more information about the dynamics of excited states. | 2401.07424v1 |
2022-02-08 | Evolution of energy, momentum, and spin parameter in dark matter flow and integral constants of motion | N-body equations of motion in comoving system and expanding background are
reformulated in a transformed system with static background and fixed damping.
The energy and momentum evolution in dark matter flow are rigorously formulated
for both systems. The energy evolution in transformed system has a simple form
that is identical to the damped harmonic oscillator. The cosmic energy equation
can be easily derived in both systems. For entire N-body system, 1) combined
with the two-body collapse model (TBCM), kinetic and potential energy increase
linearly with time $t$ such that $K_p=\varepsilon_ut$ and
$P_y=-7\varepsilon_ut/5$, where $\varepsilon_u$ is a constant rate of energy
cascade; 2) an effective gravitational potential exponent $n_e=-10/7\ne-1$
($n_e=-1.38$ from simulation) can be identified due to surface energy of fast
growing halos; 3) the radial momentum $G\propto a^{3/2}$ and angular momentum
$H\propto a^{5/2}$, where $a$ is the scale factor. On halo scale, 1) halo
kinetic and potential energy can be modelled by two dimensionless constants
$\alpha_s^*$ and $\beta_s^*$. Both constants are independent of time and halo
mass; 2) both halo radial and angular momentum $\propto a^{3/2}$ and can be
modeled by two mass-dependent coefficients $\tau_s^*$ and $\eta_s^*$; 3) halo
spin parameter is determined by $\alpha_s^*$ and $\eta_s^*$ and decreases with
halo mass with derived values of 0.09 and 0.031 for small and large halos.
Finally, the radial and angular momentum are closely related to the integral
constants of motion $I_m$, i.e. the integral of velocity correlation or the
$m$th derivative of energy spectrum at long wavelength limit. On large scale,
angular momentum is negligible, $I_2$=0 reflects the conservation of linear
momentum, while $I_4$ reflects the fluctuation of radial momentum $G$. On halo
scale, $I_4$ is determined by both momentum that are comparable with each
other. | 2202.04054v2 |
1997-03-11 | Constraints on Galaxy Evolution and the Cosmological Constant From Damped Ly-alpha Absorbers | We use the existing catalog of Damped Lyman-Alpha (DLA) systems to place
constraints on the amount of evolution in the baryonic content of galaxies and
on the value of the cosmological constant. The density of cold gas at redshifts
z=3+-1 is obtained from the mean HI column density of DLAs per cosmological
path length. This path length per unit redshift is in turn a sensitive function
of the vacuum density parameter, Omega_v. We compare the total inferred mass of
cold gas at high redshifts to that observed in stars today for flat
cosmologies. We define "eta" to be net fraction of the baryonic content of
local galaxies which was expelled since z=3, and use Bayesian inference to
derive confidence regions in the (eta, Omega_v) plane. In all cosmologies we
find that eta<0.4 with at least 95% confidence if <25% of the current stellar
population formed before z=3. The most likely value of eta is negative,
implying a net increase by several tens of percent in the baryonic mass of
galaxies since z=3+-1. On the other hand, recent observations of high metal
abundances in the intracluster medium of rich clusters (Loewenstein & Mushotzky
1996) require that metal-rich gas be expelled from galaxies in an amount
approximately equal to the current mass in stars. Based on our results and the
low metallicity observed in DLAs at z>2, we infer that more than half of the
baryonic mass processed through galaxies must have been assembled and partly
expelled from galaxies after z=2. We expect our constraints to improve
considerably as the size of the DLA sample will increase with the forthcoming
Sloan Digital Sky Survey. | 9703076v1 |
1998-04-18 | Accretion in the Early Kuiper Belt I. Coagulation and Velocity Evolution | We describe planetesimal accretion calculations in the Kuiper Belt.
Our evolution code simulates planetesimal growth in a single annulus and
includes velocity evolution but not fragmentation. Test results match analytic
solutions and duplicate previous simulations at 1 AU.
In the Kuiper Belt, simulations without velocity evolution produce a single
runaway body with a radius of 1000 km on a time scale inversely proportional to
the initial mass in the annulus. Runaway growth occurs in 100 Myr for 10 earth
masses and an initial eccentricity of 0.001 in a 6 AU annulus centered at 35
AU. This mass is close to the amount of dusty material expected in a minimum
mass solar nebula extrapolated into the Kuiper Belt.
Simulations with velocity evolution produce runaway growth on a wide range of
time scales. Dynamical friction and viscous stirring increase particle
velocities in models with large (8 km radius) initial bodies. This velocity
increase delays runaway growth by a factor of two compared to models without
velocity evolution. In contrast, collisional damping dominates over dynamical
friction and viscous stirring in models with small (80--800 m radius) initial
bodies. Collisional damping decreases the time scale to runaway growth by
factors of 4--10 relative to constant velocity calculations. Simulations with
minimum mass solar nebulae, 10 earth masses, reach runaway growth on time
scales of 20-40 Myr with 80 m initial bodies, 50-100 Myr with 800 m bodies, and
75-250 Myr for 8 km initial bodies. These growth times vary linearly with the
mass of the annulus but are less sensitive to the initial eccentricity than
constant velocity models. | 9804185v1 |
1998-04-28 | Gravity-Modes in ZZ Ceti Stars: I.Quasiadiabatic Analysis of Overstability | We analyze the stability of g-modes in variable white dwarfs with hydrogen
envelopes. In these stars, the radiative layer contributes to mode damping
because its opacity decreases upon compression and the amplitude of the
Lagrangian pressure perturbation increases outward. The overlying convective
envelope is the seat of mode excitation because it acts as an insulating
blanket with respect to the perturbed flux that enters it from below. A crucial
point is that the convective motions respond to the instantaneous pulsational
state. Driving exceeds damping by as much as a factor of two provided
$\omega\tau_c\geq 1$, where $\omega$ is the radian frequency of the mode and
$\tau_c\approx 4\tau_{th}$ with $\tau_{th}$ being the thermal time constant
evaluated at the base of the convective envelope. As a white dwarf cools, its
convection zone deepens, and modes of lower frequency become overstable.
However, the deeper convection zone impedes the passage of flux perturbations
from the base of the convection zone to the photosphere. Thus the photometric
variation of a mode with constant velocity amplitude decreases. These factors
account for the observed trend that longer period modes are found in cooler
DAVs. The linear growth time, ranging from hours for the longest period
observed modes ($P\approx 20$ minutes) to thousands of years for those of
shortest period ($P\approx 2 $ minutes), probably sets the time-scale for
variations of mode amplitude and phase. This is consistent with observations
showing that longer period modes are more variable than shorter period ones.
Our investigation confirms many results obtained by Brickhill in his pioneering
studies of ZZ Cetis. | 9804305v1 |
2004-12-21 | Cosmochemistry, Cosmology and Fundamental Constants: High-Resolution Spectroscopy of Damped Lyman-Alpha Systems | Spectroscopy of QSO absorption lines provides essential observational input
for the study of nucleosynthesis and chemical evolution of galaxies at high
redshift. But new observations may indicate that present chemical abundance
data are biased due to deficient spectral resolution and unknown selection
effects: Recent high-resolution spectra reveal the hitherto unperceived
chemical nonuniformity of a molecule-bearing damped Lyman-alpha (DLA) system,
and the still ongoing H/ESO DLA survey produces convincing evidence for the
effect of dust attenuation. We present a revised analysis of the moleculecular
hydrogen-bearing DLA complex toward the QSO HE 0515-4414 showing nonuniform
differential depletion of chemical elements onto dust grains, and introduce the
H/ESO DLA survey and its implications. Conclusively, we aim at starting an
unbiased chemical abundance database established on high-resolution
spectroscopic observations. New data to probe the temperature-redshift relation
predicted by standard cosmology and to test the constancy of fundamental
constants will be potential spin-offs. | 0412552v4 |
2014-02-15 | Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt | We report on an experimental study on the spin-waves relaxation rate in two
series of nanodisks of diameter $\phi=$300, 500 and 700~nm, patterned out of
two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser
deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance
force microscope, we measure precisely the ferromagnetic resonance linewidth of
each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth
in the nanostructure is sensibly smaller than the one measured in the extended
film. Analysis of the frequency dependence of the spectral linewidth indicates
that the improvement is principally due to the suppression of the inhomogeneous
part of the broadening due to geometrical confinement, suggesting that only the
homogeneous broadening contributes to the linewidth of the nanostructure. For
the bare YIG nano-disks, the broadening is associated to a damping constant
$\alpha = 4 \cdot 10^{-4}$. A 3 fold increase of the linewidth is observed for
the series with Pt cap layer, attributed to the spin pumping effect. The
measured enhancement allows to extract the spin mixing conductance found to be
$G_{\uparrow \downarrow}= 1.55 \cdot 10^{14}~ \Omega^{-1}\text{m}^{-2}$ for our
YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the
design of YIG based nanostructures with optimized magnetic losses. | 1402.3630v1 |
2016-01-28 | Automatic calibration of damping layers in finite element time domain simulations | Matched layers are commonly used in numerical simulations of wave propagation
to model (semi-)infinite domains. Attenuation functions describe the damping in
layers, and provide a matching of the wave impedance at the interface between
the domain of interest and the absorbing region. Selecting parameters in the
attenuation functions is non-trivial. In this work, an optimisation procedure
for automatically calibrating matched layers is presented. The procedure is
based on solving optimisation problems constrained by partial differential
equations with polynomial and piecewise-constant attenuation functions. We show
experimentally that, for finite element time domain simulations,
piecewise-constant attenuation function are at least as efficient as quadratic
attenuation functions. This observation leads us to introduce consecutive
matched layers as an alternative to perfectly matched layers, which can easily
be employed for problems with arbitrary geometries. Moreover, the use of
consecutive matched layers leads to a reduction in computational cost compared
to perfectly matched layers. Examples are presented for acoustic, elastodynamic
and electromagnetic problems. Numerical simulations are performed with the
libraries FEniCS/DOLFIN and dolfin-adjoint, and the computer code to reproduce
all numerical examples is made freely available. | 1601.07941v1 |
2018-06-04 | Environment induced Symmetry Breaking of the Oscillation-Death State | We investigate the impact of a common external system, which we call a common
environment, on the Oscillator Death (OD) states of a group of Stuart-Landau
oscillators. The group of oscillators yield a completely symmetric OD state
when uncoupled to the external system, i.e. the two OD states occur with equal
probability. However, remarkably, when coupled to a common external system this
symmetry is significantly broken. For exponentially decaying external systems,
the symmetry breaking is very pronounced for low environmental damping and
strong oscillator-environment coupling. This is evident through the sharp
transition from the symmetric to asymmetric state occurring at a critical
oscillator-environment coupling strength and environmental damping rate.
Further, we consider time-varying connections to the common external
environment, with a fraction of oscillator-environment links switching on and
off. Interestingly, we find that the asymmetry induced by environmental
coupling decreases as a power law with increase in fraction of such on-off
connections. The suggests that blinking oscillator-environment links can
restore the symmetry of the OD state. Lastly, we demonstrate the generality of
our results for a constant external drive, and find marked breaking of symmetry
in the OD states there as well. When the constant environmental drive is large,
the asymmetry in the OD states is very large, and the transition between the
symmetric and asymmetric state with increasing oscillator-environment coupling
is very sharp. So our results demonstrate an environmental coupling-induced
mechanism for the prevalence of certain OD states in a system of oscillators,
and suggests an underlying process for obtaining certain states preferentially
in ensembles of oscillators with environment-mediated coupling. | 1806.01653v1 |
2017-06-23 | Characteristics of a magneto-optical trap of molecules | We present the properties of a magneto-optical trap (MOT) of CaF molecules.
We study the process of loading the MOT from a decelerated buffer-gas-cooled
beam, and how best to slow this molecular beam in order to capture the most
molecules. We determine how the number of molecules, the photon scattering
rate, the oscillation frequency, damping constant, temperature, cloud size and
lifetime depend on the key parameters of the MOT, especially the intensity and
detuning of the main cooling laser. We compare our results to analytical and
numerical models, to the properties of standard atomic MOTs, and to MOTs of SrF
molecules. We load up to $2 \times 10^4$ molecules, and measure a maximum
scattering rate of $2.5 \times 10^6$ s$^{-1}$ per molecule, a maximum
oscillation frequency of 100 Hz, a maximum damping constant of 500 s$^{-1}$,
and a minimum MOT rms radius of 1.5 mm. A minimum temperature of 730 $\mu$K is
obtained by ramping down the laser intensity to low values. The lifetime,
typically about 100 ms, is consistent with a leak out of the cooling cycle with
a branching ratio of about $6 \times 10^{-6}$. The MOT has a capture velocity
of about 11 m/s. | 1706.07848v1 |
2015-12-08 | Critical exponents for the cloud-crystal phase transition of charged particles in a Paul Trap | It is well known that charged particles stored in a Paul trap, one of the
most versatile tools in atomic and molecular physics, may undergo a phase
transition from a disordered cloud state to a geometrically well-ordered
crystalline state (the Wigner crystal). In this paper we show that the average
lifetime $\bar\tau_m$ of the metastable cloud state preceding the cloud
$\rightarrow$ crystal phase transition follows a powerlaw, $\bar\tau_m \sim
(\gamma-\gamma_c)^{-\beta}$, $\gamma>\gamma_c$, where $\gamma_c$ is the
critical value of the damping constant $\gamma$ at which the cloud
$\rightarrow$ crystal phase transition occurs. The critical exponent $\beta$
depends on the trap control parameter $q$, but is independent of the number of
particles $N$ stored in the trap and the trap control parameter $a$, which
determines the shape (oblate, prolate, or spherical) of the cloud. For
$q=0.15,0.20$, and $0.25$, we find $\beta=1.20\pm 0.03$, $\beta=1.61\pm 0.09$,
and $\beta=2.38\pm 0.12$, respectively. In addition we find that for given $a$
and $q$, the critical value $\gamma_c$ of the damping scales approximately like
$\gamma_c=C \ln [ \ln (N)] + D$ as a function of $N$, where $C$ and $D$ are
constants. Beyond their relevance for Wigner crystallization of nonneutral
plasmas in Paul traps and mini storage rings, we conjecture that our results
are also of relevance for the field of crystalline beams. | 1512.02534v1 |
2006-02-20 | Fluctuation theorem applied to the Nosé-Hoover thermostated Lorentz gas | We present numerical evidence supporting the validity of the Gallavotti-Cohen
Fluctuation Theorem applied to the driven Lorentz gas with Nos\'e-Hoover
thermostating. It is moreover argued that the asymptotic form of the
fluctuation formula is independent of the amplitude of the driving force, in
the limit where it is small. | 0602458v1 |
1997-12-28 | Model-independent $\tan β$ bounds in the MSSM | We demonstrate, through the study of the one-loop effective potential in the
MSSM, the existence of fully model-independent lower and upper theoretical
bounds on $\tan \beta$. We give their general analytic form and illustrate some
of their implications. | 9712529v1 |
2006-12-26 | Very Light Gravitino Dark Matter | We address the question of dark matter in the context of gauge mediated
supersymmetry breaking models. In contrast with mSUGRA scenarios, the messenger
of the susy breaking to the visible sector can play an important role allowing
a relic gravitino in the $\sim {keV}$ to $10 {MeV}$ mass range to account for
the cold dark matter in the Universe. | 0612331v1 |
2004-09-15 | Characterizing rigid simplicial actions on trees | We extend Forester's rigidity theorem so as to give a complete
characterization of rigid group actions on trees (an action is rigid if it is
the only reduced action in its deformation space, in particular it is invariant
under automorphisms preserving the set of elliptic subgroups). | 0409245v1 |
2005-12-14 | Efficient Construction of Photonic Quantum Computational Clusters | We demonstrate a method of creating photonic two-dimensional cluster states
that is considerably more efficient than previously proposed approaches. Our
method uses only local unitaries and type-I fusion operations. The increased
efficiency of our method compared to previously proposed constructions is
obtained by identifying and exploiting local equivalence properties inherent in
cluster states. | 0512110v1 |
2007-10-26 | The dark matter as a light gravitino | We address the question of gravitino dark matter in the context of gauge
mediated supersymmetry breaking models. A special emphasis is put on the role
played by the MSSM singlet messenger in the case of SO(10) grand unification. | 0710.5121v1 |
2008-03-05 | Innovative Weak Formulation for The Landau-Lifshitz-Gilbert Equations | A non-conventional finite element formalism is proposed to solve the dynamic
Landau-Lifshitz-Gilbert micromagnetic equations. Two bidimensional test
problems are treated to estimate the validity and the accuracy of this finite
element approach | 0803.0599v1 |
2008-10-27 | The profile of bubbling solutions of a class of fourth order geometric equations on 4-manifolds | We study a class of fourth order geometric equations defined on a
4-dimensional compact Riemannian manifold which includes the Q-curvature
equation. We obtain sharp estimates on the difference near the blow-up points
between a bubbling sequence of solutions and the standard bubble. | 0810.4879v1 |
2009-03-02 | Asymptotic Improvement of the Binary Gilbert-Varshamov Bound on the Code Rate | We compute the code parameters for binary linear codes obtained by greedy
constructing the parity check matrix. Then we show that these codes improve the
Gilbert-Varshamov (GV) bound on the code size and rate. This result counter
proves the conjecture on the asymptotical exactness of the binary GV bound. | 0903.0302v2 |
2009-11-16 | The Independent Chip Model and Risk Aversion | We consider the Independent Chip Model (ICM) for expected value in poker
tournaments. Our first result is that participating in a fair bet with one
other player will always lower one's expected value under this model. Our
second result is that the expected value for players not participating in a
fair bet between two players always increases. We show that neither result
necessarily holds for a fair bet among three or more players. | 0911.3100v1 |
2011-03-29 | Statistical properties of $r$-adic processes and their connections to families of popular fractal curves | Results concerning the statists of $r$-adic processes and their fractal
properties are reviewed. The connection between singular eigenstates of the
statistical evolution of such processes and popular fractal curves is
emphasized. | 1103.5683v1 |
2011-05-09 | Global Solvability of the Cauchy Problem for the Landau-Lifshitz-Gilbert Equation in Higher Dimensions | We prove existence, uniqueness and asymptotics of global smooth solutions for
the Landau-Lifshitz-Gilbert equation in dimension $n \ge 3$, valid under a
smallness condition of initial gradients in the $L^n$ norm. The argument is
based on the method of moving frames that produces a covariant complex
Ginzburg-Landau equation, and a priori estimates that we obtain by the method
of weighted-in-time norms as introduced by Fujita and Kato. | 1105.1597v1 |
2012-03-28 | Fibonacci numbers in phyllotaxis : a simple model | A simple model is presented which explains the occurrence of high order
Fibonacci number parastichies in asteracae flowers by two distinct steps. First
low order parastichies result from the fact that a new floret, at its
appearance is repelled by two former ones, then, in order to accommodate for
the increase of the radius, parastichies numbers have to evolve and can do it
only by applying the Fibonacci recurrence formula. | 1203.6257v1 |
2014-02-19 | Ordered groupoids and the holomorph of an inverse semigroup | We present a construction for the holomorph of an inverse semigroup, derived
from the cartesian closed structure of the category of ordered groupoids. We
compare the holomorph with the monoid of mappings that preserve the ternary
heap operation on an inverse semigroup: for groups these two constructions
coincide. We present detailed calculations for semilattices of groups and for
the polycyclic monoids. | 1402.4592v1 |
2014-11-01 | Functorial Zeta Integrals | The functional equation for nonarchimedean Rankin-Selberg local Euler factors
was proved by Jacquet, Piatetski-Shapiro, and Shalika in 1983. In this
expository note we translate the original proof into the purely functorial
language of parabolic induction-restriction of Bernstein-Zelevinsky. This new
language gives a clearer presentation of the ideas, and works over arbitrary
fields with characteristic not equal to the residue characteristic. | 1411.0148v1 |
2016-02-17 | Dispersion and Scaling Law of Dynamic Hysteresis Based on the Landau-Lifshitz-Gilbert Model | Hysteresis dispersion under a varying external field Hex is investigated
through numerical simulations based on the Landau-Lifshitz-Gilbert (LLG)
equation, indicating the energy dissipation can be determined by W({\eta}) = A
(f, H0). A linear relation between area of hysteresis and magnitude of external
field is discovered. Evolution of hysteresis is also investigated under
oscillating external field. | 1602.05375v1 |
2017-02-21 | Cohomology and extensions of ordered groupoids | We adapt and generalise results of Loganathan on the cohomology of inverse
semigroups to the cohomology of ordered groupoids. We then derive a five-term
exact sequence in cohomology from an extension of ordered groupoids, and show
that this sequence leads to a classification of extensions by a second
cohomology group. Our methods use structural ideas in cohomology as far as
possible, rather than computation with cocycles. | 1702.06333v1 |
2017-05-11 | Two Gilbert-Varshamov Type Existential Bounds for Asymmetric Quantum Error-Correcting Codes | In this note we report two versions of Gilbert-Varshamov type existential
bounds for asymmetric quantum error-correcting codes. | 1705.04087v2 |
2017-09-21 | Self-Dual Codes better than the Gilbert--Varshamov bound | We show that every self-orthogonal code over $\mathbb F_q$ of length $n$ can
be extended to a self-dual code, if there exists self-dual codes of length $n$.
Using a family of Galois towers of algebraic function fields we show that over
any nonprime field $\mathbb F_q$, with $q\geq 64$, except possibly $q=125$,
there are self-dual codes better than the asymptotic Gilbert--Varshamov bound. | 1709.07221v1 |
2018-10-12 | A convex approach to the Gilbert-Steiner problem | We describe a convex relaxation for the Gilbert-Steiner problem both in $R^d$
and on manifolds, extending the framework proposed in [9], and we discuss its
sharpness by means of calibration type arguments. The minimization of the
resulting problem is then tackled numerically and we present results for an
extensive set of examples. In particular we are able to address the Steiner
tree problem on surfaces. | 1810.05417v1 |
2020-03-13 | 3D Stochastic Landau-Lifshitz-Gilbert Equations coupled with Maxwell's Equations with full energy | We consider 3D stochastic Landau-Lifshitz-Gilbert equations coupled with the
Maxwell equations with the full energy. We have proved the existence and some
further regularities of the weak solution. | 2003.06091v4 |
2016-06-06 | Proof of tightness of Varshamov - Gilbert bound for binary codes | We prove tightness of right logarithmic asymptotic of Varshamov- Gilbert
bound for linear binary codes We find general asymptotic coding bound for
linear codes | 1606.01592v5 |
2018-11-09 | Finslerian metrics locally conformally $R$-Einstein | Let $R$ be the $hh$-curvature associated with the Chern connection or the
Cartan connection. Adopting the pulled-back tangent bundle approach to the
Finslerian Geometry, an intrinsic characterization of $R$-Einstein metrics is
given. Finslerian metrics which are locally conformally $R$-Einstein are
classified. | 1811.04077v3 |
2019-02-05 | Harmonic maps with prescribed singularities and applications in general relativity | This paper presents a general existence and uniqueness result for harmonic
maps with prescribed singularities into non-positively curved targets, and
surveys a number of applications to general relativity. It is based on a talk
delivered by the author at The 11th Mathematical Society of Japan Seasonal
Institute, The Role of Metrics in the Theory of Partial Differential Equations. | 1902.01576v2 |
2021-12-09 | Induced Semi-Riemannian structures on null submanifolds | In this paper, we induce a semi-Riemannian metric on the $r$-null
submanifold. We establish the links between the null geometry and basics
invariants of the associated semi-Riemannian geometry on $r$-null submanifold
and semi-Riemannian constructed from a semi-Riemannian ambient. | 2112.07348v1 |
2022-04-12 | How to design a network architecture using capacity planning | Building a network architecture must answer to organization needs, but also
to two major elements which are the need for dependability and performance. By
performance, we must understand the ability to meet an immediate need and the
ability to scale without reducing the performance of the whole as new elements
are added to the network infrastructure. This last point is covered by Capacity
Planning domain. | 2204.05916v2 |
2022-07-31 | Moduli of Representations of Skewed-Gentle Algebras | We prove irreducible components of moduli spaces of semistable
representations of skewed-gentle algebras, and more generally, clannish
algebras, are isomorphic to products of projective spaces. This is achieved by
showing irreducible components of varieties of representations of clannish
algebras can be viewed as irreducible components of skewed-gentle algebras,
which we show are always normal. The main theorem generalizes an analogous
result for moduli of representations of special biserial algebras proven by
Carroll-Chindris-Kinser-Weyman. | 2208.00336v1 |
2022-08-01 | iOCR: Informed Optical Character Recognition for Election Ballot Tallies | The purpose of this study is to explore the performance of Informed OCR or
iOCR. iOCR was developed with a spell correction algorithm to fix errors
introduced by conventional OCR for vote tabulation. The results found that the
iOCR system outperforms conventional OCR techniques. | 2208.00865v1 |
2023-03-13 | Adaptive mesh refinement for the Landau-Lifshitz-Gilbert equation | We propose a new adaptive algorithm for the approximation of the
Landau-Lifshitz-Gilbert equation via a higher-order tangent plane scheme. We
show that the adaptive approximation satisfies an energy inequality and
demonstrate numerically, that the adaptive algorithm outperforms uniform
approaches. | 2303.07463v1 |
2023-05-08 | Evaluation of the Gilbert-Varshamov Bound using Multivariate Analytic Combinatorics | Analytic combinatorics in several variables refers to a suite of tools that
provide sharp asymptotic estimates for certain combinatorial quantities. In
this paper, we apply these tools to determine the Gilbert-Varshamov (GV) bound
for the sticky insertion and the constrained-synthesis channel. | 2305.04439v1 |
2023-12-11 | Matrix Formulae and Skein Relations for Quasi-cluster Algebras | In this paper, we give matrix formulae for non-orientable surfaces that
provide the Laurent expansion for quasi-cluster variables, generalizing the
orientable surface matrix formulae by Musiker-Williams. We additionally use our
matrix formulas to prove the skein relations for the elements in the
quasi-cluster algebra associated to curves on the non-orientable surface. | 2312.06148v1 |
1995-06-12 | The small-scale clustering power spectrum and relativistic decays | We present constraints on decaying-particle models in which an enhanced
relativistic density allows an $\Omega=1$ Cold Dark Matter universe to be
reconciled with acceptable values for the Hubble constant. Such models may
contain extra small-scale power, which can have important consequences for
enhanced object formation at high redshifts. Small-scale galaxy clustering and
abundances of high-redshift damped Lyman-$\alpha$ absorption clouds give a
preferred range for the mass of any such decaying particle of 2 to 30 keV and a
lifetime of 0.5 to 100 years for models with a high Hubble constant ($h>0.75$).
A lower Hubble constant, $h \simeq 0.5$, weakens the constraint to $0.5< m <
30$ keV, $0.2 < \tau < 500$ years. In permitted versions of the model,
reionization occurs at redshifts $\sim 10-200$, and this feature may be of
importance in understanding degree-scale CMB anisotropies. | 9506075v1 |
2003-10-21 | Photon mass and cosmological constant bounds from spacetime torsion | Photon mass and Cartan contortion bounds recently obtained from tiny Lorentz
violation observations in cosmology are used to find a limit of ${\lambda}\le
10^{-4}{\alpha}$ for the massive photon-torsion dimensionless coupling. Here
${\alpha}$ represents the fine-structure constant. A gauge invariant Proca
electrodynamics in spacetime endowed with torsion in de Sitter spacetime is
used to obtain an upper bound for the present value of the cosmological
constant given by ${\Lambda}\le 10^{-56} cm^{-2}$. This result is obtained in
regions of the universe where the photons are massless. A relation between the
contortion, photon mass and the radius of the universe is obtained. The Proca
electrodynamics with torsion and the radius of the universe allow us to place
more stringent bounds for the photon mass of $m_{\gamma}{\le} 10^{-44} GeV$
which is only two orders of magnitude lower than the astronomical bounds given
by the PARTICLE DATA GROUP (PDG). We also show that charge is locally conserved
in de Sitter spacetime with torsion and that plane waves are shown to be
damping by contortion inhomogeneities while dispersion is isotropic and
therefore Proca-Cartan photons do not violate Lorentz invariance. | 0310595v1 |
2002-09-28 | Strongly Localized State of a Photon at the Intersection of the Phase Slips in 2D Photonic Crystal with Low Contrast of Dielectric Constant | Two-dimensional photonic crystal with a rectangular symmetry and low contrast
(< 1) of the dielectric constant is considered. We demonstrate that, despite
the {\em absence} of a bandgap, strong localization of a photon can be achieved
for certain ``magic'' geometries of a unit cell by introducing two $\pi/2$
phase slips along the major axes. Long-living photon mode is bound to the
intersection of the phase slips. We calculate analytically the lifetime of this
mode for the simplest geometry -- a square lattice of cylinders of a radius,
$r$. We find the magic radius, $r_c$, of a cylinder to be 43.10 percent of the
lattice constant. For this value of $r$, the quality factor of the bound mode
exceeds $10^6$. Small ($\sim 1%$) deviation of $r$ from $r_c$ results in a
drastic damping of the bound mode. | 0209657v1 |
2006-06-13 | Spontaneously Induced Gravity: From Rippled Dark Matter to Einstein Corpuscles | Suppose General Relativity, provocatively governed by a dimensional coupling
constant, is a spontaneously induced theory of Gravity. Invoking Zee's
mechanism, we represent the reciprocal Newton constant by a Brans Dicke scalar
field, and let it damped oscillating towards its General Relativistic VEV. The
corresponding cosmological evolution, in the Jordan frame, averagely resembles
the familiar dark radiation -> dark matter -> dark energy domination sequence.
The fingerprints of the theory are fine ripples, hopefully testable, in the FRW
scale factor; they die away at the strict General Relativity limit. Also
derived is the spherically symmetric static configuration associated with
spontaneously induced General Relativity. At the stiff scalar potential limit,
the exterior Schwarzschild solution is recovered. However, due to level
crossing at the would have been horizon, it now connects with a novel dark core
characterized by a locally varying Newton constant. The theory further predicts
light Einstein-style gravitational corpuscles (elementary particles?) which
become point-like at the GR-limit. | 0606058v1 |
2000-03-16 | Quantum Field Theory Solution to The Gauge Hierarchy And Cosmological Constant Problems | A quantum field theory formalism is reviewed that leads to a self-consistent,
finite quantum gravity, Yang-Mills and Higgs theory, which is unitary and gauge
invariant to all orders of perturbation theory. The gauge hierarchy problem is
solved due to the exponential damping of the Higgs self-energy loop graph for
energies greater than a scale $\Lambda_H\leq 1$ TeV. The cosmological constant
problem is solved by introducing a fundamental quantum gravity scale,
$\Lambda_G\leq 10^{-4}$ eV, above which the virtual contributions to the vacuum
energy density coupled to gravity are exponentially suppressed, yielding an
observationally acceptable value for the particle physics contribution to the
cosmological constant. Classical Einstein gravity retains its causal behavior
as well as the standard agreement with observational data. Possible
experimental tests of the onset of quantum nonlocality at short distances are
considered. | 0003171v2 |
2007-06-12 | Simple Combined Model for Nonlinear Excitations in DNA | We propose a new simple model for DNA denaturation bases on the pendulum
model of Englander\cite{A1} and the microscopic model of Peyrard {\it et
al.},\cite{A3} so called "combined model". The main parameters of our model
are: the coupling constant $k$ along each strand, the mean stretching $y^\ast$
of the hydrogen bonds, the ratio of the damping constant and driven force
$\gamma/F$. We show that both the length $L$ of unpaired bases and the velocity
$v$ of kinks depend on not only the coupling constant $k$ but also the
temperature $T$. Our results are in good agreement with previous works. | 0706.1683v1 |
2010-11-28 | Energy release from hadron-quark phase transition in neutron stars and the axial $w$-mode of gravitational waves | Describing the hyperonic and quark phases of neutron stars with an isospin-
and momentum-dependent effective interaction for the baryon octet and the MIT
bag model, respectively, and using the Gibbs conditions to construct the mixed
phase, we study the energy release due to the hadron-quark phase transition.
Moreover, the frequency and damping time of the first axial $w$-mode of
gravitational waves are studied for both hyperonic and hybrid stars. We find
that the energy release is much more sensitive to the bag constant than the
density dependence of the nuclear symmetry energy. Also, the frequency of the
$w$-mode is found to be significantly different with or without the
hadron-quark phase transition and depends strongly on the value of the bag
constant. Effects of the density dependence of the nuclear symmetry energy
become, however, important for large values of the bag constant that lead to
higher hadron-quark transition densities. | 1011.6073v1 |
2012-06-05 | Effects of Variable Newton Constant During Inflation | In this paper the effects of time-dependent Newton constant G during
inflation are studied. We present the formalism of curvature perturbations in
an inflationary system with a time-dependent Newton constant. As an example we
consider a toy model in which G undergoes a sudden change during inflation. By
imposing the appropriate matching conditions the imprints of this sharp change
in G on curvature perturbation power spectrum are studied. We show that if G
increases (decreases) during the transition the amplitude of curvature
perturbations on large scales decreases (increases). In our model with a sudden
change in G a continuous sinusoidal modulations on curvature power spectrum is
induced. However, in a realistic scenario in which the change in G has some
finite time scale we expect these sinusoidal modulations to be damped on short
scales. The generated features may be used to explain the observed glitches on
CMB power spectrum. This puts a bound on $\Delta G$ during inflation of roughly
the same order as current bounds on $\Delta G$ during the entire observed age
of the universe. | 1206.0903v2 |
2013-09-05 | Spherical steady accretion flows -- dependence on the cosmological constant, exact isothermal solutions and applications to cosmology | We investigate spherical, isothermal and polytropic steady accretion models
in the presence of the cosmological constant. Exact solutions are found for
three classes of isothermal fluids, assuming the test gas approximation. The
cosmological constant damps the mass accretion rate and - above certain limit -
completely stops the steady accretion onto black holes. A "homoclinic-type"
accretion flow of polytropic gas has been discovered in AdS spacetimes in the
test-gas limit. These results can have cosmological connotation, through the
Einstein--Straus vacuole model of embedding local structures into
Friedman-Lemaitre-Robertson-Walker spacetimes. In particular one infers that
steady accretion would not exist in the late phases of the Penrose's scenario
of the evolution of the Universe, known as the Weyl curvature hypothesis. | 1309.1252v1 |
2014-07-02 | Basins of attraction in forced systems with time-varying dissipation | We consider dissipative periodically forced systems and investigate cases in
which having information as to how the system behaves for constant dissipation
may be used when dissipation varies in time before settling at a constant final
value. First, we consider situations where one is interested in the basins of
attraction for damping coefficients varying linearly between two given values
over many different time intervals: we outline a method to reduce the
computation time required to estimate numerically the relative areas of the
basins and discuss its range of applicability. Second, we observe that
sometimes very slight changes in the time interval may produce abrupt large
variations in the relative areas of the basins of attraction of the surviving
attractors: we show how comparing the contracted phase space at a time after
the final value of dissipation has been reached with the basins of attraction
corresponding to that value of constant dissipation can explain the presence of
such variations. Both procedures are illustrated by application to a pendulum
with periodically oscillating support. | 1407.0556v1 |
2017-12-21 | An Adaptive Passivity-Based Controller of a Buck-Boost Converter With a Constant Power Load | This paper addresses the problem of regulating the output voltage of a DC-DC
buck-boost converter feeding a constant power load,which is a problem of
current practical interest. Designing a stabilising controller is theoretically
challenging because its average model is a bilinear second order system that,
due to the presence of the constant power load,is non- minimum phase with
respect to both states.Moreover,to design a high performance controller, the
knowledge of the extracted load power, which is difficult to measure in
industrial applications, is required. In this paper, an adaptive
interconnection and damping assignment passivity based control that
incorporates the immersion and invariance parameter estimator for the load
power is proposed to solve the problem. Some detailed simulations are provided
to validate the transient behaviour of the proposed controller and compare it
with the performance of a classical PD scheme. | 1712.07792v1 |
2023-08-03 | Quasinormal modes of the spherical bumblebee black holes with a global monopole | The bumblebee model is an extension of the Einstein-Maxwell theory that
allows for the spontaneous breaking of the Lorentz symmetry of the spacetime.
In this paper, we study the quasinormal modes of the spherical black holes in
this model that are characterized by a global monopole. We analyze the two
cases with a vanishing cosmological constant or a negative one (the anti-de
Sitter case). We find that the black holes are stable under the perturbation of
a massless scalar field. However, both the Lorentz symmetry breaking and the
global monopole have notable impacts on the evolution of the perturbation. The
Lorentz symmetry breaking may prolong or shorten the decay of the perturbation
according to the sign of the breaking parameter. The global monopole, on the
other hand, has different effects depending on whether a nonzero cosmological
constant presences: it reduces the damping of the perturbations for the case
with a vanishing cosmological constant, but has little influence for the
anti-de Sitter case. | 2308.01575v1 |
2009-08-12 | Linear Fractionally Damped Oscillator | In this paper the linearly damped oscillator equation is considered with the
damping term generalized to a Caputo fractional derivative. The order of the
derivative being considered is 0 less than or equal to nu which is less than or
equal to 1 . At the lower end, nu = 0, the equation represents an un-damped
oscillator and at the upper end, nu = 1, the ordinary linearly damped
oscillator equation is recovered. A solution is found analytically and a
comparison with the ordinary linearly damped oscillator is made. It is found
that there are nine distinct cases as opposed to the usual three for the
ordinary equation (damped, over-damped, and critically damped). For three of
these cases it is shown that the frequency of oscillation actually increases
with increasing damping order before eventually falling to the limiting value
given by the ordinary damped oscillator equation. For the other six cases the
behavior is as expected, the frequency of oscillation decreases with increasing
order of the derivative (damping term). | 0908.1683v1 |
2015-04-28 | Nearly Optimal Deterministic Algorithm for Sparse Walsh-Hadamard Transform | For every fixed constant $\alpha > 0$, we design an algorithm for computing
the $k$-sparse Walsh-Hadamard transform of an $N$-dimensional vector $x \in
\mathbb{R}^N$ in time $k^{1+\alpha} (\log N)^{O(1)}$. Specifically, the
algorithm is given query access to $x$ and computes a $k$-sparse $\tilde{x} \in
\mathbb{R}^N$ satisfying $\|\tilde{x} - \hat{x}\|_1 \leq c \|\hat{x} -
H_k(\hat{x})\|_1$, for an absolute constant $c > 0$, where $\hat{x}$ is the
transform of $x$ and $H_k(\hat{x})$ is its best $k$-sparse approximation. Our
algorithm is fully deterministic and only uses non-adaptive queries to $x$
(i.e., all queries are determined and performed in parallel when the algorithm
starts).
An important technical tool that we use is a construction of nearly optimal
and linear lossless condensers which is a careful instantiation of the GUV
condenser (Guruswami, Umans, Vadhan, JACM 2009). Moreover, we design a
deterministic and non-adaptive $\ell_1/\ell_1$ compressed sensing scheme based
on general lossless condensers that is equipped with a fast reconstruction
algorithm running in time $k^{1+\alpha} (\log N)^{O(1)}$ (for the GUV-based
condenser) and is of independent interest. Our scheme significantly simplifies
and improves an earlier expander-based construction due to Berinde, Gilbert,
Indyk, Karloff, Strauss (Allerton 2008).
Our methods use linear lossless condensers in a black box fashion; therefore,
any future improvement on explicit constructions of such condensers would
immediately translate to improved parameters in our framework (potentially
leading to $k (\log N)^{O(1)}$ reconstruction time with a reduced exponent in
the poly-logarithmic factor, and eliminating the extra parameter $\alpha$).
Finally, by allowing the algorithm to use randomness, while still using
non-adaptive queries, the running time of the algorithm can be improved to
$\tilde{O}(k \log^3 N)$. | 1504.07648v1 |
2019-05-31 | Balancing spreads of influence in a social network | The personalization of our news consumption on social media has a tendency to
reinforce our pre-existing beliefs instead of balancing our opinions. This
finding is a concern for the health of our democracies which rely on an access
to information providing diverse viewpoints. To tackle this issue from a
computational perspective, Garimella et al. (NIPS'17) modeled the spread of
these viewpoints, also called campaigns, using the well-known independent
cascade model and studied an optimization problem that aims at balancing
information exposure in a social network when two opposing campaigns propagate
in the network. The objective in their $NP$-hard optimization problem is to
maximize the number of people that are exposed to either both or none of the
viewpoints. For two different settings, one corresponding to a model where
campaigns spread in a correlated manner, and a second one, where the two
campaigns spread in a heterogeneous manner, they provide constant ratio
approximation algorithms. In this paper, we investigate a more general
formulation of this problem. That is, we assume that $\mu$ different campaigns
propagate in a social network and we aim to maximize the number of people that
are exposed to either $\nu$ or none of the campaigns, where $\mu\ge\nu\ge2$. We
provide dedicated approximation algorithms for both the correlated and
heterogeneous settings. Interestingly, for the heterogeneous setting with
$\nu\ge 3$, we give a reduction leading to several approximation hardness
results. Maybe most importantly, we obtain that the problem cannot be
approximated within a factor of $n^{-g(n)}$ for any $g(n)=o(1)$ assuming
Gap-ETH, denoting with $n$ the number of nodes in the social network. For $\nu
\ge 4$, there is no $n^{-\epsilon}$-approximation algorithm if a certain class
of one-way functions exists, where $\epsilon > 0$ is a given constant which
depends on $\nu$. | 1906.00074v1 |
2012-09-11 | The Panchromatic Hubble Andromeda Treasury II. Tracing the Inner M31 Halo with Blue Horizontal Branch Stars | We attempt to constrain the shape of M31's inner stellar halo by tracing the
surface density of blue horizontal branch (BHB) stars at galactocentric
distances ranging from 2 kpc to 35 kpc. Our measurements make use of resolved
stellar photometry from a section of the Panchromatic Hubble Andromeda Treasury
(PHAT) survey, supplemented by several archival Hubble Space Telescope
observations. We find that the ratio of BHB to red giant stars is relatively
constant outside of 10 kpc, suggesting that the BHB is as reliable a tracer of
the halo population as the red giant branch. In the inner halo, we do not
expect BHB stars to be produced by the high metallicity bulge and disk, making
BHB stars a good candidate to be a reliable tracer of the stellar halo to much
smaller galactocentric distances. If we assume a power-law profile r^(-\alpha)
for the 2-D projected surface density BHB distribution, we obtain a
high-quality fit with a 2-D power-law index of \alpha=2.6^{+0.3}_{-0.2} outside
of 3 kpc, which flattens to \alpha<1.2 inside of 3 kpc. This slope is
consistent with previous measurements but is anchored to a radial baseline that
extends much farther inward. Finally, assuming azimuthal symmetry and a
constant mass-to-light ratio, the best-fitting profile yields a total halo
stellar mass of 2.1^{+1.7}_{-0.4} x 10^9 M_sun. These properties are comparable
with both simulations of stellar halo formation formed by satellite disruption
alone, and with simulations that include some in situ formation of halo stars. | 1209.2416v1 |
2004-05-06 | On a theorem of Kac and Gilbert | We prove a general operator theoretic result that asserts that many
multiplicity two selfadjoint operators have simple singular spectrum. | 0405110v1 |
2011-01-05 | Beating the Gilbert-Varshamov Bound for Online Channels | In the online channel coding model, a sender wishes to communicate a message
to a receiver by transmitting a codeword x =(x_1,...,x_n) in {0,1}^n bit by bit
via a channel limited to at most pn corruptions. The channel is online in the
sense that at the ith step the channel decides whether to flip the ith bit or
not and its decision is based only on the bits transmitted so far, i.e.,
(x_1,...,x_i). This is in contrast to the classical adversarial channel in
which the corruption is chosen by a channel that has full knowledge on the sent
codeword x. The best known lower bound on the capacity of both the online
channel and the classical adversarial channel is the well-known
Gilbert-Varshamov bound. In this paper we prove a lower bound on the capacity
of the online channel which beats the Gilbert-Varshamov bound for any positive
p such that H(2p) < 0.5 (where H is the binary entropy function). To do so, we
prove that for any such p, a code chosen at random combined with the nearest
neighbor decoder achieves with high probability a rate strictly higher than the
Gilbert-Varshamov bound (for the online channel). | 1101.1045v1 |
2014-11-25 | From heavy-tailed Boolean models to scale-free Gilbert graphs | Define the scale-free Gilbert graph based on a Boolean model with
heavy-tailed radius distribution on the $d$-dimensional torus by connecting two
centers of balls by an edge if at least one of the balls contains the center of
the other. We investigate two asymptotic properties of this graph as the size
of the torus tends to infinity. First, we determine the tail index associated
with the asymptotic distribution of the sum of all power-weighted incoming and
outgoing edge lengths at a randomly chosen vertex. Second, we study the
behavior of chemical distances on scale-free Gilbert graphs and show the
existence of different regimes depending on the tail index of the radius
distribution. Despite some similarities to long-range percolation and
ultra-small scale-free geometric networks, scale-free Gilbert graphs are
actually more closely related to fractal percolation and this connection gives
rise to different scaling limits. We also propose a modification of the graph,
where the total number of edges can be reduced substantially at the cost of
introducing a logarithmic factor in the chemical distances. | 1411.6824v1 |
2017-05-09 | Gilbert's disc model with geostatistical marking | We study a variant of Gilbert's disc model, in which discs are positioned at
the points of a Poisson process in $\mathbb{R}^2$ with radii determined by an
underlying stationary and ergodic random field
$\varphi:\mathbb{R}^2\to[0,\infty)$, independent of the Poisson process. When
the random field is independent of the point process one often talks about
'geostatistical marking'. We examine how typical properties of interest in
stochastic geometry and percolation theory, such as coverage probabilities and
the existence of long-range connections, differ between Gilbert's model with
radii given by some random field and Gilbert's model with radii assigned
independently, but with the same marginal distribution. Among our main
observations we find that complete coverage of $\mathbb{R}^2$ does not
necessarily happen simultaneously, and that the spatial dependence induced by
the random field may both increase as well as decrease the critical threshold
for percolation. | 1705.03337v2 |
2019-01-30 | Is the mailing Gilbert-Steiner problem convex? | A convexification of the mailing version of the finite Gilbert problem for
optimal networks is introduced. It is ia convex functional on the set of
probability measures subject to the Wasserstein $p-$ metric. The minimizer of
this convex functional is a measure supported in a graph. If this graph is a
tree (i.e contains no cycles) then this tree is also a minimum of the
corresponding mailing Gilbert problem. A numerical algorithm for the
implementation of the convexified Gilbert-mailing problem is also suggested,
based on entropic regularization. | 1901.10924v4 |
2016-03-16 | Recent Results from SPLASH: Chemical Abundances and Kinematics of Andromeda's Stellar Halo | Large scale surveys of Andromeda's resolved stellar populations have
revolutionized our view of this galaxy over the past decade. The combination of
large-scale, contiguous photometric surveys and pointed spectroscopic surveys
has been particularly powerful for discovering substructure and disentangling
the structural components of Andromeda. The SPLASH (Spectroscopic and
Photometric Landscape of Andromeda's Stellar Halo) survey consists of broad-
and narrow-band imaging and spectroscopy of red giant branch stars in lines of
sight ranging in distance from 2 kpc to more than 200 kpc from Andromeda's
center. The SPLASH data reveal a power-law surface brightness profile extending
to at least two-thirds of Andromeda's virial radius (Gilbert et al. 2012), a
metallicity gradient extending to at least 100 kpc from Andromeda's center
(Gilbert et al. 2014), and evidence of a significant population of heated disk
stars in Andromeda's inner halo (Dorman et al. 2013). We are also using the
velocity distribution of halo stars to measure the tangential motion of
Andromeda (Beaton et al., in prep). | 1603.05160v1 |
2019-11-06 | Phase transitions for chase-escape models on Gilbert graphs | We present results on phase transitions of local and global survival in a
two-species model on Gilbert graphs. At initial time there is an infection at
the origin that propagates on the Gilbert graph according to a continuous-time
nearest-neighbor interacting particle system. The Gilbert graph consists of
susceptible nodes and nodes of a second type, which we call white knights. The
infection can spread on susceptible nodes without restriction. If the infection
reaches a white knight, this white knight starts to spread on the set of
infected nodes according to the same mechanism, with a potentially different
rate, giving rise to a competition of chase and escape. We show
well-definedness of the model, isolate regimes of global survival and
extinction of the infection and present estimates on local survival. The proofs
rest on comparisons to the process on trees, percolation arguments and
finite-degree approximations of the underlying random graphs. | 1911.02622v2 |
2019-12-13 | Distance between Bound Entangled States from Unextendible Product Bases and Separable States | We discuss the use of the Gilbert algorithm to tailor entanglement witnesses
for unextendibleproduct basis bound entangled states (UPB BE states). The
method relies on the fact that an optimalentanglement witness is given by a
plane perpendicular to a line between the reference state, entanglementof which
is to be witnessed, and its closest separable state (CSS). The Gilbert
algorithm finds anapproximation of CSS. In this article, we investigate if this
approximation can be good enough toyield a valid entanglement witness. We
compare witnesses found with Gilbert algorithm and those givenby
Bandyopadhyay-Ghosh-Roychowdhury (BGR) construction. This comparison allows us
to learnabout the amount of entanglement and we find a relationship between it
and a feature of the constructionof UPB BE states, namely the size of their
central tile. We show that in most studied cases, witnessesfound with the
Gilbert algorithm in this work are more optimal than ones obtained by
Bandyopadhyay,Ghosh, and Roychowdhury. This result implies the increased
tolerance to experimental imperfections ina realization of the state. | 1912.06569v2 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.