382 research outputs found
Participation de la Section de Phytopharmacie de la Division de DĂ©fense des Cultures de l'IRAT aux recherches de lutte chimique antiacridienne de l'OICMA
High-contrast imaging of Sirius~A with VLT/SPHERE: Looking for giant planets down to one astronomical unit
Sirius has always attracted a lot of scientific interest, especially after
the discovery of a companion white dwarf at the end of the 19th century. Very
early on, the existence of a potential third body was put forward to explain
some of the observed properties of the system. We present new coronagraphic
observations obtained with VLT/SPHERE that explore, for the very first time,
the innermost regions of the system down to 0.2" (0.5 AU) from Sirius A. Our
observations cover the near-infrared from 0.95 to 2.3 m and they offer the
best on-sky contrast ever reached at these angular separations. After detailing
the steps of our SPHERE/IRDIFS data analysis, we present a robust method to
derive detection limits for multi-spectral data from high-contrast imagers and
spectrographs. In terms of raw performance, we report contrasts of 14.3 mag at
0.2", ~16.3 mag in the 0.4-1.0" range and down to 19 mag at 3.7". In physical
units, our observations are sensitive to giant planets down to 11 at
0.5 AU, 6-7 in the 1-2 AU range and ~4 at 10 AU. Despite
the exceptional sensitivity of our observations, we do not report the detection
of additional companions around Sirius A. Using a Monte Carlo orbital analysis,
we show that we can reject, with about 50% probability, the existence of an 8
planet orbiting at 1 AU. In addition to the results presented in the
paper, we provide our SPHERE/IFS data reduction pipeline at
http://people.lam.fr/vigan.arthur/ under the MIT license.Comment: 16 pages, 10 figures, accepted for publication in MNRA
Oxalate found in wood cell wall during incipient brown rot degradation
Brown rot fungi are a marvel and an enigma of Nature. They are capable of depolymerizing holocellulose within wood cell walls without significantly ineralizing lignin. The exact details behind this feat remain unknown, but a staggered mechanism has been identified: 1) an initial step characterized by oxidative degradation of the wood cell wall biopolymers and hypothesized to involve transport of Fe3+ chelated by oxalate into the cell wall, and 2) a second degradation step dominated by hydrolytic enzymes, primarily endoglucanase activity. We subjected spruce wood (Picea abies) to Rhodonia placenta and isolated xylem tissue in the initial stage of degradation. Confocal Raman microscopy revealed oxalate accumulation in the secondary cell wall of a tracheid having fungal hyphae within the lumen. This observation is the first in situ verification of oxalate accumulation within the cell wall during the first step of brown rot degradation.publishedVersio
Approaches to Studying: A Cross-Sectional Comparison of Occupational Therapy Students in Six Education Programs in Norway
Studentsâ approaches to studying have been associated with their academic performance. Although previous research suggests that the cultural and educational context may influence approaches to studying, few studies have investigated differences in study approaches across education programs. The aim of this study was to examine whether approaches to studying differed among occupational therapy students enrolled in six different educational programs in Norway. From a population of 308 students, 187 first-year occupational therapy students in six educational programs in Norway were recruited. The students provided their sociodemographic information and completed the Approaches and Study Skills Inventory for Students (ASSIST), and group differences were analyzed with Chi-square tests and one-way analyses of variance. Scores on the deep and surface approach scales did not differ significantly among the students in the six educational programs, while there was an overall difference in scores on the strategic approach scale. Group differences regarding the subscales were minor, and only a few of the pairwise differences reached statistical significance. Differences at the education program level appear not to be important for the interpretation of differences in study approaches among students
Perceptions of Assessment in Norwegian Occupational Therapy Students
In addition to securing minimum standards of learning among students, assessment is increasingly used as a tool to improve studentsâ learning. Assessment quality is measured as part of the Course Experience Questionnaire; however, the original âappropriate assessmentâ scale has demonstrated ambiguous psychometric properties. The current study aimed to gain knowledge about occupational therapy studentsâ perceptions of assessment, and this was achieved by examining the factor structure and internal consistency of the six items on the âappropriate assessmentâ scale. Students from six Norwegian universities (n = 187, response rate 61.3 %) completed the scale and reported demographic information. The factor structure of the scale was assessed with Principal Components Analysis and Parallel Analysis, and internal consistency was assessed with Cronbachâs α and mean inter-item correlations. Three factors were extracted from the data: Factor 1 (three items, α = 0.51) is concerned with the content of assessment. Factor 2 (two items, α = 0.62) is concerned with the context of assessment. Finally, Factor 3 (one item) is concerned with the feedback to students following assessment. In view of the item mean scores, feedback in particular appears to be an area of improvement for the occupational therapy programs, as well as a venue for further research
Small scale structure in diffuse molecular gas from repeated FUSE and visible spectra of HD 34078
We present preliminary results from an ongoing program devoted to a study of
small scale structure in the spatial distribution of molecular gas. Our work is
based on multi-epoch FUSE and visible observations of HD34078. A detailed
comparison of H2, CH and CH+ absorption lines is performed. No short term
variations are seen (except for highly excited H2) but long-term changes in
N(CH) are clearly detected when comparing our data to spectra taken about 10
years ago.Comment: 4 pages, 2 figures, To appear in the Proceedings of the XVII IAP
Colloquium "Gaseous Matter in Galaxies and Intergalactic Space
Deuterium toward the WD0621-376 sight line: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission
Far Ultraviolet Spectroscopic Explorer observations are presented for
WD0621-376, a DA white dwarf star in the local interstellar medium (LISM) at a
distance of about 78 pc. The data have a signal-to-noise ratio of about 20-40
per 20 km/s resolution element and cover the wavelength range 905-1187 \AA.
LISM absorption is detected in the lines of D I, C II, C II*, C III, N I, N II,
N III, O I, Ar I, and Fe II. This sight line is partially ionized, with an
ionized nitrogen fraction of > 0.23. We determine the ratio (2). Assuming a standard interstellar
oxygen abundance, we derive . Using the
value of N(H I) derived from EUVE data gives a similar D/H ratio. The D I/N I
ratio is (2).Comment: accepted for publication in the ApJ
UVMag: stellar formation, evolution, structure and environment with space UV and visible spectropolarimetry
Important insights into the formation, structure, evolution and environment
of all types of stars can be obtained through the measurement of their winds
and possible magnetospheres. However, this has hardly been done up to now
mainly because of the lack of UV instrumentation available for long periods of
time. To reach this aim, we have designed UVMag, an M-size space mission
equipped with a high-resolution spectropolarimeter working in the UV and
visible spectral range. The UV domain is crucial in stellar physics as it is
very rich in atomic and molecular lines and contains most of the flux of hot
stars. Moreover, covering the UV and visible spectral domains at the same time
will allow us to study the star and its environment simultaneously. Adding
polarimetric power to the spectrograph will multiply tenfold the capabilities
of extracting information on stellar magnetospheres, winds, disks, and magnetic
fields. Examples of science objectives that can be reached with UVMag are
presented for pre-main sequence, main sequence and evolved stars. They will
cast new light onto stellar physics by addressing many exciting and important
questions. UVMag is currently undergoing a Research and Technology study and
will be proposed at the forthcoming ESA call for M-size missions. This
spectropolarimeter could also be installed on a large UV and visible
observatory (e.g. NASA's LUVOIR project) within a suite of instruments.Comment: Accepted in ApSS's special volume on UV astronom
- âŠ