99 research outputs found
Ultraviolet and soft X--ray photon--photon elastic scattering in an electron gas
We have considered the processes which lead to elastic scattering between two
far ultraviolet or X--ray photons while they propagate inside a solid, modeled
as a simple electron gas. The new ingredient, with respect to the standard
theory of photon--photon scattering in vacuum, is the presence of low--energy,
nonrelativistic electron--hole excitations. Owing to the existence of
two--photon vertices, the scattering processes in the metal are predominantly
of second order, as opposed to fourth order for the vacuum case. The main
processes in second order are dominated by exchange of virtual plasmons between
the two photons. For two photons of similar energy , this gives
rise to a cross section rising like up to maximum of around
~cm, and then decreasing like . The maximal cross
section is found for the photon wavevector , the Fermi surface
size, which typically means a photon energy in the keV range.
Possible experiments aimed at checking the existence of these rare but
seemingly measurable elastic photon--photon scattering processes are discussed,
using in particular intense synchrotron sources.Comment: 33 pages, TeX, Version 3.1, S.I.S.S.A. preprint 35/93/C
Two-photon final states in peripheral heavy ion collisions
We discuss processes leading to two photon final states in peripheral heavy
ion collisions at RHIC. Due to the large photon luminosity we show that the
continuum subprocess can be observed with a
large number of events. We study this reaction when it is intermediated by a
resonance made of quarks or gluons and discuss its interplay with the continuum
process, verifying that in several cases the resonant process ovewhelms the
continuum one. It is also investigated the possibility of observing a scalar
resonance (the meson) in this process. Assuming for the the
mass and total decay width values recently reported by the E791 Collaboration
we show that RHIC may detect this particle in its two photon decay mode if its
partial photonic decay width is of the order of the ones discussed in the
literature.Comment: 10 pages, 8 figure
Probing For New Physics and Detecting non linear vacuum QED effects using gravitational wave interferometer antennas
Low energy non linear QED effects in vacuum have been predicted since 1936
and have been subject of research for many decades. Two main schemes have been
proposed for such a 'first' detection: measurements of ellipticity acquired by
a linearly polarized beam of light passing through a magnetic field and direct
light-light scattering. The study of the propagation of light through an
external field can also be used to probe for new physics such as the existence
of axion-like particles and millicharged particles. Their existence in nature
would cause the index of refraction of vacuum to be different from unity in the
presence of an external field and dependent of the polarization direction of
the light propagating. The major achievement of reaching the project
sensitivities in gravitational wave interferometers such as LIGO an VIRGO has
opened the possibility of using such instruments for the detection of QED
corrections in electrodynamics and for probing new physics at very low
energies. In this paper we discuss the difference between direct birefringence
measurements and index of refraction measurements. We propose an almost
parasitic implementation of an external magnetic field along the arms of the
VIRGO interferometer and discuss the advantage of this choice in comparison to
a previously proposed configuration based on shorter prototype interferometers
which we believe is inadequate. Considering the design sensitivity in the
strain, for the near future VIRGO+ interferometer, of in the range 40 Hz Hz leads to a variable
dipole magnet configuration at a frequency above 20 Hz such that Tm/ for a `first' vacuum non linear QED detection
SYMBIOmatics: Synergies in Medical Informatics and Bioinformatics – exploring current scientific literature for emerging topics
Background: The SYMBIOmatics Specific Support Action (SSA) is "an information gathering and dissemination activity" that seeks "to identify synergies between the bioinformatics and the medical informatics" domain to improve collaborative progress between both domains (ref. to http://www.symbiomatics.org). As part of the project experts in both research fields will be identified and approached through a survey. To provide input to the survey, the scientific literature was analysed to extract topics relevant to both medical informatics and bioinformatics. Results: This paper presents results ofa systematic analysis of the scientific literature from medical informatics research and bioinformatics research. In the analysis pairs of words (bigrams) from the leading bioinformatics and medical informatics journals have been used as indication of existing and emerging technologies and topics over the period 2000-2005 ("recent") and 1990-1990 ("past"). We identified emerging topics that were equally important to bioinformatics and medical informatics in recent years such as microarray experiments, ontologies, open source, text mining and support vector machines. Emerging topics that evolved only in bioinformatics were system biology, protein interaction networks and statistical methods for microarray analyses, whereas emerging topics in medical informatics were grid technology and tissue microarrays. Conclusion: We conclude that although both fields have their own specific domains of interest, they share common technological developments that tend to be initiated by new developments in biotechnology and computer science
Multi-Locus Phylogeographic and Population Genetic Analysis of Anolis carolinensis: Historical Demography of a Genomic Model Species
The green anole (Anolis carolinensis) has been widely used as an animal model in physiology and neurobiology but has recently emerged as an important genomic model. The recent sequencing of its genome has shed new light on the evolution of vertebrate genomes and on the process that govern species diversification. Surprisingly, the patterns of genetic diversity within natural populations of this widespread and abundant North American lizard remain relatively unknown. In the present study, we use 10 novel nuclear DNA sequence loci (N = 62 to 152) and one mitochondrial locus (N = 226) to delimit green anole populations and infer their historical demography. We uncovered four evolutionarily distinct and geographically restricted lineages of green anoles using phylogenetics, Bayesian clustering, and genetic distance methods. Molecular dating indicates that these lineages last shared a common ancestor ∼2 million years ago. Summary statistics and analysis of the frequency distributions of DNA polymorphisms strongly suggest range-wide expansions in population size. Using Bayesian Skyline Plots, we inferred the timing of population size expansions, which differ across lineages, and found evidence for a relatively recent and rapid westward expansion of green anoles across the Gulf Coastal Plain during the mid-Pleistocene. One surprising result is that the distribution of genetic diversity is not consistent with a latitudinal shift caused by climatic oscillations as is observed for many co-distributed taxa. This suggests that the most recent Pleistocene glacial cycles had a limited impact on the geographic distribution of the green anole at the northern limits of its range
Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients
HIBISCUS: Hydroxychloroquine for the secondary prevention of thrombotic and obstetrical events in primary antiphospholipid syndrome
The relapse rate in antiphospholipid syndrome (APS) remains high, i.e. around 20%-21% at 5 years in thrombotic APS and 20-28% in obstetrical APS [2, 3]. Hydroxychloroquine (HCQ) appears as an additional therapy, as it possesses immunomodulatory and anti-thrombotic various effects [4-16]. Our group recently obtained the orphan designation of HCQ in antiphospholipid syndrome by the European Medicine Agency. Furthermore, the leaders of the project made the proposal of an international project, HIBISCUS, about the use of Hydroxychloroquine in secondary prevention of obstetrical and thrombotic events in primary APS. This study has been launched in several countries and at now, 53 centers from 16 countries participate to this international trial. This trial consists in two parts: a retrospective and a prospective study. The French part of the trial in thrombosis has been granted by the French Minister of Health in December 2015 (the academic trial independent of the pharmaceutical industry PHRC N PAPIRUS) and is coordinated by one of the members of the leading consortium of HIBISCUS
Risk factors of highly pathogenic avian influenza H5N1 occurrence at the village and farm levels in the Red River Delta region in Vietnam
A case-control study at both village and farm levels was designed to investigate risk factors for highly pathogenic avian influenza H5N1 during the 2007 outbreaks in one province of Northern Vietnam. Data related to human and natural environments, and poultry production systems were collected for 19 case and 38 unmatched control villages and 19 pairs of matched farms. Our results confirmed the role of poultry movements and trading activities. In particular, our models found that higher number of broiler flocks in the village increased the risk (OR=1.49, 95% CI: 1.12-1.96), as well as the village having at least one poultry trader (OR=11.53, 95% CI: 1.34-98.86). To a lesser extent, in one of our two models, we also identified that increased density of ponds and streams, commonly used for waterfowl production, and greater number of duck flocks in the village also increased the risk. The higher percentage of households keeping poultry, as an indicator of households keeping backyard poultry in our study population, was a protective factor (OR=0.95, 95% CI: 0.91-0.98). At the farm level, three risk factors at the 5% level of type I error were identified by univariate analysis: a greater total number of birds (P=0.006), increase in the number of flocks having access to water (P=0.027) and a greater number of broiler flocks in the farm (P=0.049). Effect of vaccination implementation (date and doses) was difficult to investigate because of a poor recording system. Some protective or risk factors with limited effect may not have been identified owing to our limited sample size. Nevertheless, our results provide a better understanding of local transmission mechanisms of HPAI H5N1 in one province of the Red River Delta region in Vietnam and highlight the need to reduce at-risk trading and production practices
- …