16,723 research outputs found
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
Adiabatic Charge Pumping through Quantum Dots in the Coulomb Blockade Regime
We investigate the influence of the Coulomb interaction on the adiabatic
pumping current through quantum dots. Using nonequilibrium Green's functions
techniques, we derive a general expression for the current based on the
instantaneous Green's function of the dot. We apply this formula to study the
dependence of the charge pumped per cycle on the time-dependent pumping
potentials. The possibility of charge quantization in the presence of a finite
Coulomb repulsion energy is investigated in the light of recent experiments.Comment: 11 pages, 10 figure
Non-adiabatic Electron Pumping through Interacting Quantum Dots
We study non-adiabatic charge pumping through single-level quantum dots
taking into account Coulomb interactions. We show how a truncated set of
equations of motion can be propagated in time by means of an auxiliary-mode
expansion. This formalism is capable of treating the time-dependent electronic
transport for arbitrary driving parameters. We verify that the proposed method
describes very precisely the well-known limit of adiabatic pumping through
quantum dots without Coulomb interactions. As an example we discuss pumping
driven by short voltage pulses for various interaction strengths. Such finite
pulses are particular suited to investigate transient non-adiabatic effects,
which may be also important for periodic drivings, where they are much more
difficult to reveal.Comment: 11 pages, 4 figure
On the continuum limit of fermionic topological charge in lattice gauge theory
It is proved that the fermionic topological charge of SU(N) lattice gauge
fields on the 4-torus, given in terms of a spectral flow of the Hermitian
Wilson--Dirac operator, or equivalently, as the index of the Overlap Dirac
operator, reduces to the continuum topological charge in the classical
continuum limit when the parameter is in the physical region .Comment: latex, 18 pages. v2: Several comments added. To appear in J.Math.Phy
Prevalencia del pie plano en niños y niñas en las edades de 9 a 12 años
El objetivo de este estudio, consiste en definir mediante huella plantar, el tipo de pie que se tiene en una escuela primaria con niños de 4º, 5º y 6º, entre las edades de 9 a 12 años. Se les tomo la huella plantar con un tipo de pintura de fácil disolución, para que de esa forma, los niño no tuvieran mayor problema a la hora de limpiarse o lavarse los pies. La cantidad de pie plano, que pensando que se encontrarÃa en mayor cantidad, no lo fue del todo asÃ, se encontraron más pies normales y cavos entre las huellas plantares. Los alumnos de 6º año, arrojaron la mayor cantidad de pie plano, en particular los hombres, las mujeres de 5º grado dieron la mayor cantidad de pie cavo, mientras los hombres de 4º grado arrojaron el mayor tipo de pie normal
- …