647 research outputs found
Polarization correlations in the two--photon decay of hydrogen--like ions
Polarization properties of the photons emitted in the two-photon decay of
hydrogen-like ions are studied within the framework of the density matrix and
second-order perturbation theory. In particular, we derive the polarization
correlation function that gives the probability of the (two-photon) coincidence
measurement performed by polarization-sensitive detectors. Detailed
calculations of this function are performed for the
transition in neutral hydrogen as well as Xe and U ions. The
obtained results allow us to understand the influence of relativistic and
non-dipole effects on the polarization correlations in the bound-bound
two-photon transitions in heavy ions
Quantized form factor shift in the presence of free electron laser radiation
In electron scattering, the target form factors contribute significantly to
the diffraction pattern and carry information on the target electromagnetic
charge distribution. Here we show that the presence of electromagnetic
radiation, as intense as currently available in Free Electron Lasers, shifts
the dependence of the target form factors by a quantity that depends on the
number of photons absorbed or emitted by the electron as well as on the
parameters of the electromagnetic radiation. As example, we show the impact of
intense ultraviolet and soft X-ray radiation on elastic electron scattering by
Ne-like Argon ion and by Xenon atom. We find that the shift brought by the
radiation to the form factor is in the order of some percent. Our results may
open up a new avenue to explore matter with the assistance of laser
Analytical evaluation of atomic form factors: application to Rayleigh scattering
Atomic form factors are widely used for the characterization of targets and
specimens, from crystallography to biology. By using recent mathematical
results, here we derive an analytical expression for the atomic form factor
within the independent particle model constructed from nonrelativistic screened
hydrogenic wavefunctions. The range of validity of this analytical expression
is checked by comparing the analytically obtained form factors with the ones
obtained within the Hartee-Fock method. As an example, we apply our analytical
expression for the atomic form factor to evaluate the differential cross
section for Rayleigh scattering off neutral atoms.Comment: 7 pages, 1 figur
Effects of Single-Dose Prucalopride on Intestinal Hypomotility in Horses: Preliminary Observations
Abnormalities of gastrointestinal motility are often a challenge in horses; however, the use of prokinetic drugs in such conditions must be firmly established yet. For this reason we carried out a preliminary study on the effects of prucalopride on intestinal motor activity of horses with gut hypomotility.
The effect of prucalopride per os by oral dose syringe (2 mg/100 kg body weight) was assessed by abdominal ultrasound (evaluating duodenal, cecal, and colonic motor activity) in six horses with gut hypomotility. After administration of prucalopride, a significant increase of contractile activity was found in the duodenum at 30 minutes (p = 0.0005), 60 minutes (p = 0.01) and 90 minutes (p = 0.01), whereas in the cecum and in the left colon the increase was only present at 60 minutes (p = 0.03, and
p = 0.02, respectively). No changes from baseline heart and respiratory rate or behavior side effects were observed after administration of the drug and throughout the observation period. Prucalopride may be a useful adjunct to the therapeutic armamentary for treating hypomotile upper gut conditions of horses. Dosing information is however needed to establish its actual clinical efficacy and its proper effects on the large bowel in these animals
Phylogeography of the marbled crab Pachygrapsus marmoratus (Decapoda, Grapsidae) along part of the African Mediterranean coast reveals genetic homogeneity across the Siculo-Tunisian Strait versus heterogeneity across the Gibraltar Strait
We investigate the influence of previously postulated biogeographic barriers in the Mediterranean Sea on the population genetic structure of a highly dispersive and continuously distributed coastal species. In particular, we examine nuclear and mitochondrial genetic variation in the marbled crab, Pachygrapsus marmoratus, across part of the African Mediterranean coast in order to assess the influence of the Siculo-Tunisian Strait on its population genetic structure. Four polymorphic microsatellite loci were genotyped for 110 individuals, collected from eight locations covering parts of the Algerian, Tunisian and Libyan coasts. In addition, mtDNA corresponding to the Cox1 gene was sequenced for 80 samples. The corresponding results show contrasting patterns of genetic differentiation. While mtDNA results revealed a homogeneous haplotype composition in our study area, microsatellite data depicted genetic differentiation among populations, but not associated with any geographic barrier. This pattern, already recorded for this species from different geographic regions, may hint at the involvement of a complex series of abiotic and biotic factors in determining genetic structure. Demographic history reconstruction, inferred from mtDNA data, supports demographic and spatial expansion for the North African metapopulation dating back to the Mid-Pleistocene and following an historical bottleneck. Comparison of these African mitochondrial sequences with new sequences from a Turkish population and previously published sequences revealed a weak but significant separation of Atlantic and Mediterranean populations across the Gibraltar Strait, which was not recorded in previous studies of this grapsid species
Eddy Covariance flux errors due to random and systematic timing errors during data acquisition
Modern eddy covariance (EC) systems collect
high-frequency data (10–20 Hz) via digital outputs of instru ments. This is an important evolution with respect to the tra ditional and widely used mixed analog/digital systems, as
fully digital systems help overcome the traditional limita tions of transmission reliability, data quality, and complete ness of the datasets
Gap modification of atomically thin boron nitride by phonon mediated interactions
A theory is presented for the modification of bandgaps in atomically thin
boron nitride (BN) by attractive interactions mediated through phonons in a
polarizable substrate, or in the BN plane. Gap equations are solved, and gap
enhancements are found to range up to 70% for dimensionless electron-phonon
coupling \lambda=1, indicating that a proportion of the measured BN bandgap may
have a phonon origin
Importance of Spin-Orbit Interaction for the Electron Spin Relaxation in Organic Semiconductors
Despite the great interest organic spintronics has recently attracted, there is only a partial understanding of the fundamental physics behind electron spin relaxation in organic semiconductors. Mechanisms based on hyperfine interaction have been demonstrated, but the role of the spin-orbit interaction remains elusive. Here, we report muon spin spectroscopy and time-resolved photoluminescence measurements on two series of molecular semiconductors in which the strength of the spin-orbit interaction has been systematically modified with a targeted chemical substitution of different atoms at a particular molecular site. We find that the spin-orbit interaction is a significant source of electron spin relaxation in these materials
Discovery of Lebambromyia in Myanmar cretaceous amber: phylogenetic and biogeographic implications (Insecta, Diptera, Phoroidea)
Lebambromyia sacculifera sp. nov. is described from Late Cretaceous amber from Myan-mar, integrating traditional observation techniques and X-ray phase contrast microtomography. Lebambromyia sacculifera is the second species of Lebambromyia after L. acrai Grimaldi and Cumming, described from Lebanese amber (Early Cretaceous), and the first record of this taxon from Myanmar amber, considerably extending the temporal and geographic range of this genus. The new specimen bears a previously undetected set of phylogenetically relevant characters such as a postpedicel sacculus and a prominent clypeus, which are shared with Ironomyiidae and Eumuscomorpha. Our cladistic analyses confirmed that Lebambromyia represented a distinct monophyletic lineage related to Platypezidae and Ironomyiidae, though its affinities are strongly influenced by the interpretation and coding of the enigmatic set of features characterizing these fossil flies
On the Munn-Silbey approach to polaron transport with off-diagonal coupling
Improved results using a method similar to the Munn-Silbey approach have been
obtained on the temperature dependence of transport properties of an extended
Holstein model incorporating simultaneous diagonal and off-diagonal
exciton-phonon coupling. The Hamiltonian is partially diagonalized by a
canonical transformation, and optimal transformation coefficients are
determined in a self-consistent manner. Calculated transport properties exhibit
substantial corrections on those obtained previously by Munn and Silbey for a
wide range of temperatures thanks to a numerically exact evaluation and an
added momentum-dependence of the transformation matrix. Results on the
diffusion coefficient in the moderate and weak coupling regime show distinct
band-like and hopping-like transport features as a function of temperature.Comment: 12 pages, 6 figures, accpeted in Journal of Physical Chemistry B:
Shaul Mukamel Festschrift (2011
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