1,281 research outputs found
Positive Quantization in the Presence of a Variable Magnetic Field
Starting with a previously constructed family of coherent states, we
introduce the Berezin quantization for a particle in a variable magnetic field
and we show that it constitutes a strict quantization of a natural Poisson
algebra. The phase-space reinterpretation involves a magnetic version of the
Bargmann space and leads naturally to Berezin-Toeplitz operators.Comment: 15 page
Magnetic pseudodifferential operators with coefficients in C*-algebras
In previous articles, a magnetic pseudodifferential calculus and a family of
C*-algebras associated with twisted dynamical systems were introduced and the
connections between them have been established. We extend this formalism to
symbol classes of H\"ormander type with an x-behavior modelized by an abelian
C*-algebra. Some of these classes generate C*-algebras associated with the
twisted dynamical system. We show the relevance of these classes to the
spectral analysis of pseudodifferential operators with anisotropic symbols and
magnetic fields.Comment: 23 page
Mass-ratio dependent strong-field dissociation of artificial helium hydride isotopologues
We study the effect of the nuclear-mass ratio in a diatomic molecular ion on the dissociation dynamics in strong infrared laser pulses. A molecular ion is a charged system, in which the dipole moment depends on the reference point and therefore on the position of the nuclear center of mass, so that the laser-induced dynamics is expected to depend on the mass asymmetry. Whereas usually both the reduced mass and the mass ratio are varied when different isotopologues are compared, we fix the reduced mass and artificially vary the mass ratio in a model system. This allows us to separate effects related to changes in the resonance frequency, which is determined by the reduced mass, from those that arise due to the mass asymmetry. Numerical solutions of the time-dependent Schrödinger equation are compared with classical trajectory simulations. We find that at a certain mass ratio, vibrational excitation is strongly suppressed, which decreases the dissociation probability by many orders of magnitude
Recommended from our members
Magnitude of behavioral deficits varies with job-related chlorpyrifos exposure levels among Egyptian pesticide workers.
Chronic occupational exposure to organophosphorus pesticides (OPs) is consistently associated with deficits on behavioral tests when compared to unexposed comparison groups. However, a dose-response relationship has yet to be established, leading some to doubt an association between occupational OP exposure and behavioral deficits. Pesticide application teams in Egypt who are primarily exposed to one OP, chlorpyrifos (CPF), were recruited into a field assessment. Trail Making A and the more challenging Trail Making B tests were administered to 54 engineers (who supervise the pesticide application process, usually from the side of the field), 59 technicians (who guide the pesticide applicators in the field), 31 applicators (who mix and apply pesticides using knapsack sprayers), and 150 controls (who did not work in the fields) at two different times during the OP application season as well as immediately after applications had ended and 1.5 months later. All participants were males since only males work on pesticide application teams in Egypt. Urinary levels of 3,5,6-trichloro-2-pyridinol (TCPy), a specific metabolite of CPF, confirmed the pattern of lower to higher CPF exposures from engineers to technicians to applicators, and these were all greater than urinary metabolite levels in controls. A consistent relationship between job title and performance speed on the behavioral task was observed: Controls had the best (fastest) performance on Trail Making A and B tests throughout the application season, and applicators had significantly slower performance than engineers on Trail Making A (p = 0.015) and B (p = 0.003). However, individual urinary TCPy, blood acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) levels did not predict individual performance. This study identifies a dose-related effect based on job title, which serves as a surrogate for chronic exposure in that differing job titles exhibit varying group exposure levels. The results establish that chronic occupational exposure to chlorpyrifos is neurotoxic and suggest that the classic biomarkers of recent CPF exposure are not predictive of chronic exposure effects
Magnetic calculus and semiclassical trace formulas
The aim of these notes is to show how the magnetic calculus developed in
\cite{MP, IMP1, IMP2, MPR, LMR} permits to give a new information on the nature
of the coefficients of the expansion of the trace of a function of the magnetic
Schr\"odinger operator whose existence was established in \cite{HR2}
Semi- and Non-relativistic Limit of the Dirac Dynamics with External Fields
We show how to approximate Dirac dynamics for electronic initial states by
semi- and non-relativistic dynamics. To leading order, these are generated by
the semi- and non-relativistic Pauli hamiltonian where the kinetic energy is
related to and , respectively. Higher-order
corrections can in principle be computed to any order in the small parameter
v/c which is the ratio of typical speeds to the speed of light. Our results
imply the dynamics for electronic and positronic states decouple to any order
in v/c << 1.
To decide whether to get semi- or non-relativistic effective dynamics, one
needs to choose a scaling for the kinetic momentum operator. Then the effective
dynamics are derived using space-adiabatic perturbation theory by Panati et. al
with the novel input of a magnetic pseudodifferential calculus adapted to
either the semi- or non-relativistic scaling.Comment: 42 page
The effect of dressing on high-order harmonic generation in vibrating H molecules
We develop the strong-field approximation for high-order harmonic generation
in hydrogen molecules, including the vibrational motion and the laser-induced
coupling of the lowest two Born-Oppenheimer states in the molecular ion that is
created by the initial ionization of the molecule. We show that the field
dressing becomes important at long laser wavelengths (m),
leading to an overall reduction of harmonic generation and modifying the ratio
of harmonic signals from different isotopes.Comment: 23 pages, 11 figures, submitted to PR
Computational Controversy
Climate change, vaccination, abortion, Trump: Many topics are surrounded by
fierce controversies. The nature of such heated debates and their elements have
been studied extensively in the social science literature. More recently,
various computational approaches to controversy analysis have appeared, using
new data sources such as Wikipedia, which help us now better understand these
phenomena. However, compared to what social sciences have discovered about such
debates, the existing computational approaches mostly focus on just a few of
the many important aspects around the concept of controversies. In order to
link the two strands, we provide and evaluate here a controversy model that is
both, rooted in the findings of the social science literature and at the same
time strongly linked to computational methods. We show how this model can lead
to computational controversy analytics that have full coverage over all the
crucial aspects that make up a controversy.Comment: In Proceedings of the 9th International Conference on Social
Informatics (SocInfo) 201
LCAA, a Novel Factor Required for Magnesium Protoporphyrin Monomethylester Cyclase Accumulation and Feedback Control of Aminolevulinic Acid Biosynthesis in Tobacco
Low Chlorophyll Accumulation A (LCAA) antisense plants were obtained from a screen for genes whose partial down-regulation results in a strong chlorophyll deficiency in tobacco (Nicotiana tabacum). The LCAA mutants are affected in a plastid-localized protein of unknown function, which is conserved in cyanobacteria and all photosynthetic eukaryotes. They suffer from drastically reduced light-harvesting complex (LHC) contents, while the accumulation of all other photosynthetic complexes per leaf area is less affected. As the disturbed accumulation of LHC proteins could be either attributable to a defect in LHC biogenesis itself or to a bottleneck in chlorophyll biosynthesis, chlorophyll synthesis rates and chlorophyll synthesis intermediates were measured. LCAA antisense plants accumulate magnesium (Mg) protoporphyrin monomethylester and contain reduced protochlorophyllide levels and a reduced content of CHL27, a subunit of the Mg protoporphyrin monomethylester cyclase. Bimolecular fluorescence complementation assays confirm a direct interaction between LCAA and CHL27. 5-Aminolevulinic acid synthesis rates are increased and correlate with an increased content of glutamyl-transfer RNA reductase. We suggest that LCAA encodes an additional subunit of the Mg protoporphyrin monomethylester cyclase, is required for the stability of CHL27, and contributes to feedback-control of 5-aminolevulinic acid biosynthesis, the rate-limiting step of chlorophyll biosynthesis
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