15,988 research outputs found
Nonlinear gyrotropic vortex dynamics in ferromagnetic dots
The quasistationary and transient (nanosecond) regimes of nonlinear vortex dynamics in a soft magnetic dot driven by an oscillating external field are studied. We derive a nonlinear dynamical system of equations for the vortex core position and phase, assuming that the main source of nonlinearity comes from the magnetostatic energy. In the stationary regime, we demonstrate the occurrence of a fold-over bifurcation and calculate analytically the resonant nonlinear vortex frequencies as a function of the amplitude and frequency of the applied driving field. In the transient regime, we show that the vortex core dynamics are described by an oscillating trajectory radius. The resulting dynamics contain multiple frequencies with amplitude decaying in time. Finally, we evaluate the ranges of the system parameters leading to a vortex core instability (core polarization reversal)
Block freeze-concentration of coffee extract: Effect of freezing and thawing stages on solute recovery and bioactive compounds
Coffee extract was freeze-concentrated using the total block technique. The effects of four parameters
were evaluated: the initial coffee mass fraction (5 and 15% w/w), the cooling temperature ( 10 and
20 C), the heating temperature (20 and 40 C) and the freezing direction (parallel and counter-flow
to the thawing direction). The solid concentration was measured during the thawing stage to quantify
the solute recovery and the concentration index for one stage of freeze concentration. The coffee mass
fraction, the freezing direction and the cooling temperature significantly influenced the solute recovery.
A concentration index between 1 and 2.3 was obtained in one cycle. The effect of block freeze concentration
on the bioactive compound concentration and the antioxidant activity was measured. The coffee bioactive
compounds were distributed in proportion to the total solid content in the ice and liquid.
Therefore, block freeze concentration is an effective technique to preserve functional properties of coffee
extracts.Postprint (published version
Bayesian optimization for the inverse scattering problem in quantum reaction dynamics
We propose a machine-learning approach based on Bayesian optimization to
build global potential energy surfaces (PES) for reactive molecular systems
using feedback from quantum scattering calculations. The method is designed to
correct for the uncertainties of quantum chemistry calculations and yield
potentials that reproduce accurately the reaction probabilities in a wide range
of energies. These surfaces are obtained automatically and do not require
manual fitting of the {\it ab initio} energies with analytical functions. The
PES are built from a small number of {\it ab initio} points by an iterative
process that incrementally samples the most relevant parts of the configuration
space. Using the dynamical results of previous authors as targets, we show that
such feedback loops produce accurate global PES with 30 {\it ab initio}
energies for the three-dimensional H + H H + H reaction
and 290 {\it ab initio} energies for the six-dimensional OH + H
HO + H reaction. These surfaces are obtained from 360
scattering calculations for H and 600 scattering calculations for OH.
We also introduce a method that quickly converges to an accurate PES without
the {\it a priori} knowledge of the dynamical results. By construction, our
method illustrates the lowest number of potential energy points (i.e. the
minimum information) required for the non-parametric construction of global PES
for quantum reactive scattering calculations.Comment: 9 pages, 8 figure
Finite-size scaling for the left-current correlator with non-degenerate quark masses
We study the volume dependence of the left-current correlator with
non-degenerate quark masses to next-to-leading order in the chiral expansion.
We consider three possible regimes: all quark masses are in the
-regime, all are in the -regime and a mixed-regime where the
lighest quark masses satisfy while the heavier . These results can be used to match lattice QCD and the Chiral
Effective Theory in a large but finite box in which the Compton wavelength of
the lightest pions is of the order of the box size. We consider both the full
and partially-quenched results.Comment: 27 pages, 4 figure
Asteroseismology of delta Scuti stars in open clusters: Praesepe
The present paper provides a general overview of the asteroseismic potential
of delta Scuti stars in clusters, in particular focusing on convection
diagnostics. We give a summarise of the last results obtained by the authors
for the Praesepe cluster of which five delta Scuti stars are analysed. In that
work, linear analysis is confronted with observations, using refined
descriptions for the effects of rotation on the determination of the global
stellar parameters and on the adiabatic oscillation frequency computations. A
single, complete, and coherent solution for all the selected stars is found,
which lead the authors to find important restrictions to the convection
description for a certain range of effective temperatures. Furthermore, the
method used allowed to give an estimate of the global parameters of the
selected stars and constrain the cluster.Comment: 6 pages, 1 figure. Accepted for publication in Communications in
Asteroseismolog
Reducing Residual-Mass Effects for Domain-Wall Fermions
It has been suggested to project out a number of low-lying eigenvalues of the
four-dimensional Wilson--Dirac operator that generates the transfer matrix of
domain-wall fermions in order to improve simulations with domain-wall fermions.
We investigate how this projection method reduces the residual chiral
symmetry-breaking effects for a finite extent of the extra dimension. We use
the standard Wilson as well as the renormalization--group--improved gauge
action. In both cases we find a substantially reduced residual mass when the
projection method is employed. In addition, the large fluctuations in this
quantity disappear.Comment: 18 pages, 10 figures, references updated, comments adde
Classification of Digital Systems Users
Repasamos las categorías más utilizadas para aludir a las características de las personas que utilizan algún tipo de sistema digital, ya sea por su grado de participación en la comunicación global y en los sistemas web -1.0 o 2.0-; por la actitud que toman ante el contenido digital -consumidores o productores-; por su intermitencia en el mundo digital -residentes o visitantes-; o por el momento histórico en el que nacieron -nativos digitales o inmigrantes digitales-, con el propósito de reflexionar sobre los cambios y las consecuencias que han impulsado los recursos y las herramientas digitales.The present work reviews the most common classifications of digital system users, either due to: their degree of involvement in the global communication via web: users 1.0 or 2.0; their attitude when interacting with digital content: consumers and producers; their constant or intermittent presence in the digital world: resident and visitors; or even due to their generational character: digital natives and digital immigrants; with the purpose of reflecting on the changes and the consequences that digital resources and digital tools have caused.Ministerio de Economía y Competitividad (España) EDU2011-28381; 2012-14Gobierno catalán AGAUR 2009 SGR 80
Constant of Motion for several one-dimensional systems and outlining the problem associated with getting their Hamiltonians
The constants of motion of the following systems are deduced: a relativistic
particle with linear dissipation, a no-relativistic particle with a time
explicitly depending force, a no-relativistic particle with a constant force
and time depending mass, and a relativistic particle under a conservative force
with position depending mass. The problem of getting the Hamiltonian for these
systems is determined by getting the velocity as an explicit function of
position and generalized linear momentum, and this problem can be solved a
first approximation for the first above system.Comment: 15 pages, Te
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