7,143 research outputs found
Existence criteria for stabilization from the scaling behaviour of ionization probabilities
We provide a systematic derivation of the scaling behaviour of various
quantities and establish in particular the scale invariance of the ionization
probability. We discuss the gauge invariance of the scaling properties and the
manner in which they can be exploited as consistency check in explicit
analytical expressions, in perturbation theory, in the Kramers-Henneberger and
Floquet approximation, in upper and lower bound estimates and fully numerical
solutions of the time dependent Schroedinger equation. The scaling invariance
leads to a differential equation which has to be satisfied by the ionization
probability and which yields an alternative criterium for the existence of
atomic bound state stabilization.Comment: 12 pages of Latex, one figur
Stabilization not for certain and the usefulness of bounds
Stabilization is still a somewhat controversial issue concerning its very
existence and also the precise conditions for its occurrence. The key quantity
to settle these questions is the ionization probability, for which hitherto no
computational method exists which is entirely agreed upon. It is therefore very
useful to provide various consistency criteria which have to be satisfied by
this quantity, whose discussion is the main objective of this contribution. We
show how the scaling behaviour of the space leads to a symmetry in the
ionization probability, which can be exploited in the mentioned sense.
Furthermore, we discuss how upper and lower bounds may be used for the same
purpose. Rather than concentrating on particular analytical expressions we
obtained elsewhere for these bounds, we focus in our discussion on the general
principles of this method. We illustrate the precise working of this procedure,
its advantages, shortcomings and range of applicability. We show that besides
constraining possible values for the ionization probability these bounds, like
the scaling behaviour, also lead to definite statements concerning the physical
outcome. The pulse shape properties which have to be satitisfied for the
existence of asymptotical stabilization is the vanishing of the total classical
momentum transfer and the total classical displacement and not smoothly
switched on and off pulses. Alternatively we support our results by general
considerations in the Gordon-Volkov perturbation theory and explicit studies of
various pulse shapes and potentials including in particular the Coulomb- and
the delta potential.Comment: 12 pages Late
Multielectron corrections in molecular high-order harmonic generation for different formulations of the strong-field approximation
We make a detailed assessment of which form of the dipole operator to use in
calculating high order harmonic generation within the framework of the strong
field approximation, and look specifically at the role the form plays in the
inclusion of multielectron effects perturbatively with regard to the
contributions of the highest occupied molecular orbital. We focus on how these
corrections affect the high-order harmonic spectra from aligned homonuclear and
heteronuclear molecules, exemplified by and CO, respectively,
which are isoelectronic. We find that the velocity form incorrectly finds zero
static dipole moment in heteronuclear molecules. In contrast, the length form
of the dipole operator leads to the physically expected non-vanishing
expectation value for the dipole operator in this case. Furthermore, the so
called "overlap" integrals, in which the dipole matrix element is computed
using wavefunctions at different centers in the molecule, are prominent in the
first-order multielectron corrections for the velocity form, and should not be
ignored. Finally, inclusion of the multielectron corrections has very little
effect on the spectrum. This suggests that relaxation, excitation and the
dynamic motion of the core are important in order to describe multielectron
effects in molecular high-order high harmonic generation.Comment: Figures 2 and 4 have been simplified in order to fulfil the size
requirements of arXiv; in the new version references have been adde
Quantum erasure in the presence of a thermal bath: the effects of system-environment microscopic correlations
We investigate the role of the environment in a quantum erasure setup in the
cavity quantum electrodynamics domain. Two slightly different schemes are
analyzed. We show that the effects of the environment vary when a scheme is
exchanged for another. This can be used to estimate the macroscopic parameters
related to the system-environment microscopic correlations.Comment: 10 pages, 2 figure
Relationships between nutrient composition of flowers and fruit quality in orange trees grown in calcareous soil
To determine if flower nutrient composition can be used to predict fruit quality, a field experiment was conducted over three seasons (1996-1999) in a commercial orange orchard (Citrus sinensis (L.) Osbeck cv. 'Valencia Late', budded on Troyer citrange rootstock) established on a calcareous soil in southern Portugal. Flowers were collected from 20 trees during full bloom in April and their nutrient composition determined, and fruits were harvested the following March and their quality evaluated. Patterns of covariation in flower nutrient concentrations and in fruit quality variables were evaluated by principal component analysis. Regression models relating fruit quality variables to flower nutrient composition were developed by stepwise selection procedures. The predictive power of the regression models was evaluated with an independent data set. Nutrient composition of flowers at full bloom could be used to predict the fruit quality variables fresh fruit mass and maturation index in the following year. Magnesium, Ca and Zn concentrations measured in flowers were related to fruit fresh mass estimations and N, P, Mg and Fe concentrations were related to fruit maturation index. We also established reference values for the nutrient composition of flowers based on measurements made in trees that produced large (> 76 mm in diameter) fruit.info:eu-repo/semantics/publishedVersio
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