345 research outputs found
M-lines characterization of selenide and telluride waveguides for mid-infrared interferometry
Nulling interferometry is an astronomical technique that combines equal
wavefronts to achieve a deep rejection ratio of an on-axis star, and that could
permit to detect Earth-like planets in the mid-infrared band 5 -- 20 microns.
Similarly to what is done in the near-infrared, high frequencies spatial
filtering of the incoming beams can be achieved using single-mode waveguides
operating in the mid-infrared. An appreciable reduction of the instrumental
complexity is also possible using integrated optics (IO) devices in this
spectral range. The relative lack of single-mode guided optics in the
mid-infrared has motivated the present technological study to demonstrate the
feasibility of dielectric waveguides functioning at longer wavelengths. We
propose to use selenide and telluride components to pursue the development of
more complex IO functions.Comment: accepted in OSA Optics Express, 11 pages, 4 figure
Transmission behaviors of single mode hollow metallic waveguides dedicated to mid-infrared nulling interferometry
This paper reports the characterization of hollow metallic waveguides (HMW)
to be used as single-mode wavefront filters for nulling interferometry in the
6-20 microns range. The measurements presented here were performed using both
single-mode and multimode conductive waveguides at 10.6 microns. We found
propagation losses of about 16dB/mm, which are mainly due to the theoretical
skin effect absorption in addition to the roughness of the waveguide metallic
walls. The input and output coupling efficiency of our samples has been
improved by adding tapers to minimize the impedance mismatch. A proper
distinction between propagation losses and coupling losses is presented.
Despite their elevate propagation losses, HMW show excellent spatial filtering
capabilities in a spectral range where photonics technologies are only
emerging.Comment: This paper was published in Optics Express and can be found at
http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-26-1800
HD139614: the interferometric case for a group-Ib pre-transitional young disk
The Herbig Ae star HD 139614 is a group-Ib object, which featureless SED
indicates disk flaring and a possible pre-transitional evolutionary stage. We
present mid- and near-IR interferometric results collected with MIDI, AMBER and
PIONIER with the aim of constraining the spatial structure of the 0.1-10 AU
disk region and assess its possible multi-component structure. A two-component
disk model composed of an optically thin 2-AU wide inner disk and an outer
temperature-gradient disk starting at 5.6 AU reproduces well the observations.
This is an additional argument to the idea that group-I HAeBe inner disks could
be already in the disk-clearing transient stage. HD 139614 will become a prime
target for mid-IR interferometric imaging with the second-generation instrument
MATISSE of the VLTI.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2014, 11 pages, 7 Figure
The Science Case for the Planet Formation Imager (PFI)
Among the most fascinating and hotly-debated areas in contemporary
astrophysics are the means by which planetary systems are assembled from the
large rotating disks of gas and dust which attend a stellar birth. Although
important work has already been, and is still being done both in theory and
observation, a full understanding of the physics of planet formation can only
be achieved by opening observational windows able to directly witness the
process in action. The key requirement is then to probe planet-forming systems
at the natural spatial scales over which material is being assembled. By
definition, this is the so-called Hill Sphere which delineates the region of
influence of a gravitating body within its surrounding environment. The Planet
Formation Imager project (PFI) has crystallized around this challenging goal:
to deliver resolved images of Hill-Sphere-sized structures within candidate
planet-hosting disks in the nearest star-forming regions. In this contribution
we outline the primary science case of PFI. For this purpose, we briefly review
our knowledge about the planet-formation process and discuss recent
observational results that have been obtained on the class of transition disks.
Spectro-photometric and multi-wavelength interferometric studies of these
systems revealed the presence of extended gaps and complex density
inhomogeneities that might be triggered by orbiting planets. We present
detailed 3-D radiation-hydrodynamic simulations of disks with single and
multiple embedded planets, from which we compute synthetic images at
near-infrared, mid-infrared, far-infrared, and sub-millimeter wavelengths,
enabling a direct comparison of the signatures that are detectable with PFI and
complementary facilities such as ALMA. From these simulations, we derive some
preliminary specifications that will guide the array design and technology
roadmap of the facility.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2014, Paper ID 9146-120, 13 pages, 3 Figure
Influenza Virus Segment Composition Influences Viral Stability in the Environment.
The transmission routes of Influenza A viruses (IAVs) submit virus particles to a wide range of environmental conditions that affect their transmission. In water, temperature, salinity, and pH are important factors modulating viral persistence in a strain-dependent manner, and the viral factors driving IAV persistence remain to be described. We used an innovative method based on a real-time cell system analysis to quantify viral decay in an environmental model. Thus, we identified the viral hemagglutinin (HA) and neuraminidase (NA) as the main proteins driving the environmental persistence by comparing the inactivation slopes of several reassortant viruses. We also introduced synonymous and non-synonymous mutations in the HA or in the NA that modulated IAV persistence. Our results demonstrate that HA stability and expression level, as well as calcium-binding sites of the NA protein, are molecular determinants of viral persistence. Finally, IAV particles could not trigger membrane fusion after environmental exposure, stressing the importance of the HA and the NA for environmental persistence
An infrared integrated optic astronomical beam combiner for stellar interferometry at 3-4 microns
Integrated-optic, astronomical, two-beam and three-beam, interferometric
combiners have been designed and fabricated for operation in the L band (3 - 4
microns) for the first time. The devices have been realized in
titanium-indiffused, x-cut lithium niobate substrates, and on-chip
electro-optic fringe scanning has been demonstrated. White light fringes were
produced in the laboratory using the two-beam combiner integrated with an
on-chip Y-splitter.Comment: This paper was published in Optics Express and is made available as
an electronic reprint with the permission of OSA. The paper can be found at
the following URL on the OSA website: http://www.opticsinfobase.org/oe.
Systematic or multiple reproduction or distribution to multiple locations via
electronic or other means is prohibited and is subject to penalties under la
Planet Formation Imager (PFI): Introduction and Technical Considerations
Complex non-linear and dynamic processes lie at the heart of the planet
formation process. Through numerical simulation and basic observational
constraints, the basics of planet formation are now coming into focus. High
resolution imaging at a range of wavelengths will give us a glimpse into the
past of our own solar system and enable a robust theoretical framework for
predicting planetary system architectures around a range of stars surrounded by
disks with a diversity of initial conditions. Only long-baseline interferometry
can provide the needed angular resolution and wavelength coverage to reach
these goals and from here we launch our planning efforts. The aim of the
"Planet Formation Imager" (PFI) project is to develop the roadmap for the
construction of a new near-/mid-infrared interferometric facility that will be
optimized to unmask all the major stages of planet formation, from initial dust
coagulation, gap formation, evolution of transition disks, mass accretion onto
planetary embryos, and eventual disk dispersal. PFI will be able to detect the
emission of the cooling, newly-formed planets themselves over the first 100
Myrs, opening up both spectral investigations and also providing a vibrant look
into the early dynamical histories of planetary architectures. Here we
introduce the Planet Formation Imager (PFI) Project
(www.planetformationimager.org) and give initial thoughts on possible facility
architectures and technical advances that will be needed to meet the
challenging top-level science requirements.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2014, Paper ID 9146-35, 10 pages, 2 Figure
Metagenomic survey of the microbiome of ancient Siberian permafrost and modern Kamchatkan cryosols
In the context of global warming, the melting of arctic permafrost raises the threat of a re-emergence of microorganisms some of which were shown to remain viable in ancient frozen soils for up to half a million years. In order to evaluate this risk, it is of interest to acquire a better knowledge of the composition of the microbial communities found in this understudied environment.
Here we present a metagenomics analysis of 12 soil samples from Russian Arctic and subarctic pristine areas: Chukotka, Yakutia, and Kamchatka, including 9 permafrost samples collected at various depths. These large datasets (9.2 1011 total bp) were assembled (525,313 contigs > 5kb), their encoded protein contents predicted, then used to perform taxonomical assignments of bacterial, archaeal, and eukaryotic organisms, as well as DNA viruses.
The various samples exhibited variable DNA contents and highly diverse taxonomic profiles showing no obvious relationship with their locations, depths or deposit ages. Bacteria represented the largely dominant DNA fraction (95%) in all samples, followed by archaea (3.2%), surprisingly little eukaryotes (0.5%), and viruses (0.4%).
Although no common taxonomic pattern was identified, the samples shared unexpected high frequencies of β-lactamase genes, almost 0.9 copy/bacterial genome. In addition of known environmental threats, the particularly intense warming of the Arctic might thus enhance the spread of bacterial antibiotic resistances, today's major challenge in public health. β-lactamases were also observed at high frequency in other types of soils, suggesting their general role in the regulation of bacterial populations
A model and typology of collaboration between professionals
Abstract Background: The new forms of organization of healthcare services entail the development of new clinical practices that are grounded in collaboration. Despite recent advances in research on the subject of collaboration, there is still a need for a better understanding of collaborative processes and for conceptual tools to help healthcare professionals develop collaboration amongst themselves in complex systems. This study draws on D'Amour's structuration model of collaboration to analyze healthcare facilities offering perinatal services in four health regions in the province of Quebec. The objectives are to: 1) validate the indicators of the structuration model of collaboration; 2) evaluate interprofessional and interorganizational collaboration in four health regions; and 3) propose a typology of collaboratio
Spodoptera frugiperda (Lepidoptera: Noctuidae) host-plant variants: two host strains or two distinct species?
International audienceThe moth Spodoptera frugiperda is a well-known pest of crops throughout the Americas, which consists of two strains adapted to different host-plants: the first feeds preferentially on corn, cotton and sorghum whereas the second is more associated with rice and several pasture grasses. Though morphologically indistinguishable, they exhibit differences in their mating behavior, pheromone compositions, and show development variability according to the host-plant. Though the latter suggest that both strains are different species, this issue is still highly controversial because hybrids naturally occur in the wild, not to mention the discrepancies among published results concerning mating success between the two strains. In order to clarify the status of the two host-plant strains of S. frugiperda, we analyze features that possibly reflect the level of post-zygotic isolation: (1) first generation (F1) hybrid lethality and sterility; (2) patterns of meiotic segregation of hybrids in reciprocal second generation (F2), as compared to the meiosis of the two parental strains. We found a significant reduction of mating success in F1 in one direction of the cross and a high level of microsatellite markers showing transmission ratio distortion in the F2 progeny. Our results support the existence of post-zygotic reproductive isolation between the two laboratory strains and are in accordance with the marked level of genetic differentiation that was recovered between individuals of the two strains collected from the field. Altogether these results provide additional evidence in favor of a sibling species status for the two strains
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