836 research outputs found
Optical properties of tungsten thin films perforated with a bidimensional array of subwavelength holes
We present a theorical investigation of the optical transmission of a
dielectric grating carved in a tungsten layer. For appropriate wavelengths
tungsten shows indeed a dielectric behaviour. Our numerical simulations leads
to theoretical results similar to those found with metallic systems studied in
earlier works. The interpretation of our results rests on the idea that the
transmission is correlated with the resonant response of eigenmodes coupled to
evanescent diffraction orders.Comment: 4 pages, 3 figure
The catalog of radial velocity standard stars for the Gaia RVS: status and progress of the observations
A new full-sky catalog of Radial Velocity standard stars is being built for
the determination of the Radial Velocity Zero Point of the RVS on board of
Gaia. After a careful selection of 1420 candidates matching well defined
criteria, we are now observing all of them to verify that they are stable
enough over several years to be qualified as reference stars. We present the
status of this long-term observing programme on three spectrographs : SOPHIE,
NARVAL and CORALIE, complemented by the ELODIE and HARPS archives. Because each
instrument has its own zero-point, we observe intensively IAU RV standards and
asteroids to homogenize the radial velocity measurements. We can already
estimate that ~8% of the candidates have to be rejected because of variations
larger than the requested level of 300 m/s.Comment: Proceedings of SF2A2010, S. Boissier, M. Heydari-Malayeri, R. Samadi
and D. Valls-Gabaud (eds), 3 pages, 2 figure
Gene flow estimation with microsatellites in a Malagasy seed orchard of Eucalyptus grandis
International audienceEucalyptus grandis has a mixed-mating repro- ductive system. Malagasy Eucalyptus seed orchards were established 15 years ago with two aims both based on panmixia: open-pollinated seed production and genetic improvement. The panmixia hypothesis has never been confirmed in the seed orchard. From a seedling seed- orchard stand comprising 349 trees and using data obtained with six selected microsatellite markers, pater- nity analysis was performed for 724 offspring collected on 30 adult trees. Paternity assignment, based on exclu- sion procedures and likelihood-ratio method, was achieved with high accuracy; the exclusion probability value was 0.997. The outcrossing rate was very high (96.7%). More than 50% of potential male trees (199 out of 349) in the seed orchard contributed to pollination for 440 offspring of 30 progenies (8.6% of the basic population). The pollination rate from outside the seed orchard was high (39.2%), but might be due to the small size of this seed orchard. This study showed that "panmixia-like pollination" can be assume
Optical structure and function of the white filamentary hair covering the edelweiss bracts
The optical properties of the inflorescence of the high-altitude
''Leontopodium nivale'' subsp. ''alpinum'' (edelweiss) is investigated, in
relation with its submicrometer structure, as determined by scanning electron
microscopy. The filaments forming the hair layer have been found to exhibit an
internal structure which may be one of the few examples of a photonic structure
found in a plant. Measurements of light transmission through a self-supported
layer of hair pads taken from the bracts supports the idea that the wooly layer
covering the plant absorbs near-ultraviolet radiation before it reaches the
cellular tissue. Calculations based on a photonic-crystal model provides
insight on the way radiation can be absorbed by the filamentary threads.Comment: 9 pages, 13 figures. Published pape
Simulation of actively controlled spacecraft with flexible appendages
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76688/1/AIAA-25388-716.pd
Nonlinear Blind Parameter Estimation
This note deals with parameter estimation of nonlinear continuous-time models when the input signals of the corresponding system are not measured. The contribution of the note is to show that, with simple priors about the unknown input signals and using derivatives of the output signals, one can perform the estimation procedure. As an illustration, we consider situations where the simple priors, e.g., independence or Gaussianity of the unknown inputs, is assumed
Novel psychrophiles and exopolymers from permafrost thaw lake sediments
Thermokarst lakes are one of the most abundant types of microbial ecosystems in the circumpolar North. These shallow basins are formed by the thawing and collapse of ice-rich permafrost, with subsequent filling by snow and ice melt. Until now, permafrost thaw lakes have received little attention for isolation of microorganisms by culture-based analysis. The discovery of novel psychrophiles and their biomolecules makes these extreme environments suitable sources for the isolation of new strains, including for potential biotechnological applications. In this study, samples of bottom sediments were collected from three permafrost thaw lakes in subarctic Québec, Canada. Their diverse microbial communities were characterized by 16S rRNA gene amplicon analysis, and subsamples were cultured for the isolation of bacterial strains. Phenotypic and genetic characterization of the isolates revealed affinities to the genera Pseudomonas, Paenibacillus, Acinetobacter, Staphylococcus and Sphingomonas. The isolates were then evaluated for their production of extracellular enzymes and exopolymers. Enzymes of potential biotechnological interest included α and β-glucosidase, α and β-maltosidase, β-xylosidase and cellobiohydrolase. One isolate, Pseudomonas extremaustralis strain 2ASCA, also showed the capability to produce, in the loosely bound cell fraction, a levan-type polysaccharide with a yield of 613 mg/L of culture, suggesting its suitability as a candidate for eco-sustainable alternatives to commercial polymers
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