12,183 research outputs found
Envelope-driven recollisions triggered by an elliptically polarized laser pulse
Increasing ellipticity usually suppresses the recollision probability
drastically. In contrast, we report on a recollision channel with large return
energy and a substantial probability, regardless of the ellipticity. The laser
envelope plays a dominant role in the energy gained by the electron, and in the
conditions under which the electron comes back to the core. We show that this
recollision channel eciently triggers multiple ionization with an elliptically
polarized pulse
Fractionalization of minimal excitations in integer quantum Hall edge channels
A theoretical study of the single electron coherence properties of Lorentzian
and rectangular pulses is presented. By combining bosonization and the Floquet
scattering approach, the effect of interactions on a periodic source of voltage
pulses is computed exactly. When such excitations are injected into one of the
channels of a system of two copropagating quantum Hall edge channels, they
fractionalize into pulses whose charge and shape reflects the properties of
interactions. We show that the dependence of fractionalization induced
electron/hole pair production in the pulses amplitude contains clear signatures
of the fractionalization of the individual excitations. We propose an
experimental setup combining a source of Lorentzian pulses and an Hanbury Brown
and Twiss interferometer to measure interaction induced electron/hole pair
production and more generally to reconstruct single electron coherence of these
excitations before and after their fractionalization.Comment: 18 pages, 10 figures, 1 tabl
Examples of derivation-based differential calculi related to noncommutative gauge theories
Some derivation-based differential calculi which have been used to construct
models of noncommutative gauge theories are presented and commented. Some
comparisons between them are made.Comment: 22 pages, conference given at the "International Workshop in honour
of Michel Dubois-Violette, Differential Geometry, Noncommutative Geometry,
Homology and Fundamental Interactions". To appear in a special issue of
International Journal of Geometric Methods in Modern Physic
Hydrodynamic lift of vesicles under shear flow in microgravity
The dynamics of a vesicle suspension in a shear flow between parallel plates
has been investigated under microgravity conditions, where vesicles are only
submitted to hydrodynamic effects such as lift forces due to the presence of
walls and drag forces. The temporal evolution of the spatial distribution of
the vesicles has been recorded thanks to digital holographic microscopy, during
parabolic flights and under normal gravity conditions. The collected data
demonstrates that vesicles are pushed away from the walls with a lift velocity
proportional to where is the shear rate,
the vesicle radius and its distance from the wall. This scaling as well
as the dependence of the lift velocity upon vesicle aspect ratio are consistent
with theoretical predictions by Olla [J. Phys. II France {\bf 7}, 1533--1540
(1997)].Comment: 6 pages, 8 figure
Abundance of local actions for the vacuum Einstein equations
We exhibit large classes of local actions for the vacuum Einstein equations.
In presence of fermions, or more generally of matter which couple to the
connection, these actions lead to inequivalent equations revealing an arbitrary
number of parameters. Even in the pure gravitational sector, any corresponding
quantum theory would depend on these parameters.Comment: 10 pages. Final version to appear in Letters in Mathematical Physic
Local methylthiolate adsorption geometry on Au(111) from photoemission core-level shifts
The local adsorption structure of methylthiolate in the ordered Au(111)-(√3×√3)R30° phase has been investigated using core-level-shift measurements of the surface and bulk components of the Au 4f7/2 photoelectron binding energy. The amplitude ratio of the core-level-shift components associated with surface Au atoms that are, and are not, bonded to the thiolate is found to be compatible only with the previously proposed Au-adatom-monothiolate moiety in which the thiolate is bonded atop Au adatoms in hollow sites, and not on an unreconstructed surface, or in Au-adatom-dithiolate species
Guiding-center motion for electrons in strong laser fields
We consider the dynamics of electrons in combined strong laser and Coulomb
fields. Under a timescale separation condition, we reduce this dynamics to a
guiding-center framework. More precisely, we derive a hierarchy of models for
the guiding-center dynamics based on averaging over the fast motion of the
electron using Lie transforms. The reduced models we obtain describe well the
different ionization channels, in particular, the conditions under which an
electron is rescattered by the ionic core or is directly ionized. The
comparison between these models highlights the models which are best suited for
a qualitative and quantitative agreement with the parent dynamics
Double-ionization mechanisms of magnesium driven by electron impact
We study double ionization of Mg by electron impact through the vantage point of classical mechanics. We consider all electron-electron correlations in a Coulomb four-body problem, where three electrons belong to the atom and the fourth electron causes the impact ionization. From our model we compute the double-ionization probability of Mg for impact energies from 15 to 125 eV. Double ionization occurs through eight double-ionization mechanisms, which we classify into four categories: inner shell capture, direct, delay, and ionized inner shell mechanisms. We show that delay and ionized inner shell mechanisms require electron-electron correlations among the four electrons, and are responsible for the second increase in the double-ionization probability. Furthermore, we show that our theoretical prediction about the relative prominence of certain double-ionization mechanisms is in agreement with experimental results on the relative prominence of non-first- over first-order mechanisms
Bipolar querying of valid-time intervals subject to uncertainty
Databases model parts of reality by containing data representing properties of real-world objects or concepts. Often, some of these properties are time-related. Thus, databases often contain data representing time-related information. However, as they may be produced by humans, such data or information may contain imperfections like uncertainties. An important purpose of databases is to allow their data to be queried, to allow access to the information these data represent. Users may do this using queries, in which they describe their preferences concerning the data they are (not) interested in. Because users may have both positive and negative such preferences, they may want to query databases in a bipolar way. Such preferences may also have a temporal nature, but, traditionally, temporal query conditions are handled specifically. In this paper, a novel technique is presented to query a valid-time relation containing uncertain valid-time data in a bipolar way, which allows the query to have a single bipolar temporal query condition
Absence of boron aggregates in superconducting silicon confirmed by atom probe tomography
Superconducting boron-doped silicon films prepared by gas immersion laser
doping (GILD) technique are analyzed by atom probe tomography. The resulting
three-dimensional chemical composition reveals that boron atoms are
incorporated into crystalline silicon in the atomic percent concentration
range, well above their solubility limit, without creating clusters or
precipitates at the atomic scale. The boron spatial distribution is found to be
compatible with local density of states measurements performed by scanning
tunneling spectroscopy. These results, combined with the observations of very
low impurity level and of a sharp two-dimensional interface between doped and
undoped regions show, that the Si:B material obtained by GILD is a well-defined
random substitutional alloy endowed with promising superconducting properties.Comment: 4 page
- …