Theory and laboratory tests of the multi-stage phase mask coronagraph

A large number of coronagraphs have been proposed to overcome the ratio that exists between the star and its planet. The planet finder of the Extremely Large Telescope, which is called EPICS, will certainly need a more efficient coronagraph than the ones that have been developed so far. We propose to use a combination of chromatic Four Quadrant Phase Mask coronagraph to achromatize the dephasing of the device while maintaining a high rejection performance. After describing this multi-stage FQPM coronagraph, we show preliminary results of a study on its capabilities in the framework of the EPICS instrument, the planet finder of the European Extremely Large Telescope. Eventually, we present laboratory tests of a rough prototype of a multi-stage four-quadrant phase mask. On one hand, we deduce from our laboratory data that a detection at the 10^-10 level is feasible in monochromatic light. On the other hand, we show the detection of a laboratory companion fainter than 10^-8 with a spectral bandwidth larger than 20%.Comment: 9 pages, 9 figures, To appear in SPIE proceeding- conference 7015 held in Marseille in June 200

Dialogue Journal Writing in a Foreign Language Classroom: Assessing Communicative Competence and Proficiency.

This research studied dialogue journal writing, as it occurred between a teacher and twenty-one students in a French III high school. Results on attitude questionnaire indicated that dialogue journals helped students overcome their fear of the written form and increase their self-confidence and willingness to write. By demystifying the writing process, writing in their dialogue journals helped these students develop positive attitudes. The results on writing proficiency pre and post-tests indicated that students performed as well or better than students after four years of a foreign language in a high school setting or four semesters of college instruction. The dialogue journals served as a bridge to other kinds of writing such as the topics in the writing proficiency test. To arrive at characteristics of good language communicators, three independent measures were used: (1) holistic assessment of communicative competence of the dialogue journals, (2) results on a proficiency writing test, (3) analysis of the dialogue journals based on Gutstein\u27s (1987) model of communicative competence (quantity, coherence, topical appropriateness, functionality, and interactional awareness). The relationship among these three measures were seen to be indicative of student communicative competence in dialogue journal writing. The results of both the proficiency writing post-test and the holistic ranking showed a high correlation with the following characteristics of good language communicators: quantity (the total number of words), interactional awareness (percentage of answered questions), grammar (percentage of correct verb conjugation and tense/mood), and the function of analyzing, evaluating, and reflecting. The holistic ranking also showed the following characteristics of a good language communicator: the function of reporting personal facts, the function of requesting general information, the function of request for opinions, the range of language functions used, the miscellaneous topic domain, the range of topic categories written about. The best predictors for the holistic ranking of the dialogue journals were the total number of functions used and the total number of words written. The best predictor for the results on the proficiency writing post-test was the percentage of correct usage of tense/mood verbs. These findings provide support for the inclusion of dialogue journals in the foreign language classroom

Generalized Spectral Analysis of Planar Lines on Layered Media Including Uniaxial and Biaxial Dielectric Substrates

In this paper the spectral-domain analysis (SDA) is generalized in order to compute the dispersive properties of a wide variety of planar and quasi-planar transmission lines (microstrips and finlines) printed on a stratified dielectric medium. Uniaxial and biaxial dielectric anisotropy can be easily manipulated due to the definition of a “transverse propagation matrix” characterizing each dielectric layer. The whole boundary value problem is reduced to two simpler problems involving only one or two dielectrics. Then, the spectral dyadic Green’s function is derived via a recurrence algorithm. The dispersion equation is derived by using the Ritz-Galerkin method. The numerical convergence is substantially improved taking into account the asymptotic behavior of the series. A number of illustrative examples have been included to emphasize the power of the method

Polarimétrie à HERA

TRANSPARENTS CDRO

Usability Testing of the North Carolina Digital Heritage Center's Website, DigitalNC.org

The North Carolina Digital Heritage Center's website, DigitalNC.org, has provided access to digitized cultural heritage materials from many small North Carolinian museums and libraries since its inception in 2003. The current website has been in use since that time, and is in sore need of usability analysis prior to a major redesign effort. The current DigitalNC.org site design is the only way for contributing institutions and researchers to access the digitized materials online, making access and use of the website via its design of paramount importance to the NCDHC's mission. No data has been collected about the usability of the site thus far. This usability study will help to collect data to inform a user-centered redesign of the current DigitalNC.org site. Furthermore, data collected will provide quantitative information to help create a hierarchy of priority for any perceived issues with the current interface. This study was designed using guidelines developed by Jakob Nielsen and Steve Krug. The guidelines developed by these two usability experts were used in this case because they are intended to be implemented in instances when usability testing needs to be inexpensive, iterative, and lean.Master of Science in Information Scienc

Multi-stage four-quadrant phase mask: achromatic coronagraph for space-based and ground-based telescopes

Less than 3% of the known exoplanets were directly imaged for two main reasons. They are angularly very close to their parent star, which is several magnitudes brighter. Direct imaging of exoplanets thus requires a dedicated instrumentation with large telescopes and accurate wavefront control devices for high-angular resolution and coronagraphs for attenuating the stellar light. Coronagraphs are usually chromatic and they cannot perform high-contrast imaging over a wide spectral bandwidth. That chromaticity will be critical for future instruments. Enlarging the coronagraph spectral range is a challenge for future exoplanet imaging instruments on both space-based and ground-based telescopes. We propose the multi-stage four-quadrant phase mask that associates several monochromatic four-quadrant phase mask coronagraphs in series. Monochromatic device performance has already been demonstrated and the manufacturing procedures are well-under control since their development for previous instruments on VLT and JWST. The multi-stage implementation simplicity is thus appealing. We present the instrument principle and we describe the laboratory performance for large spectral bandwidths and for both pupil shapes for space- (off-axis telescope) and ground-based (E-ELT) telescopes. The multi-stage four-quadrant phase mask reduces the stellar flux over a wide spectral range (30%) and it is a very good candidate to be associated with a spectrometer for future exoplanet imaging instruments in ground- and space-based observatories.Comment: 7 pages, 11 figures, 4 tables, accepted in A&

On the abundance of Lithium in T Coronae Borealis

We have obtained high resolution echelle spectroscopy of the recurrent nova T CrB. We find that the surface lithium abundance in T CrB is signifcantly enhanced compared to field M giants, where it is not detectable. We offer possible explanations for this in terms of either a delay in the onset of convection in the giant star, enhanced coronal activity due to star-spots or the enhancement of Li resulting from the nova explosion(s).Comment: 3 pages, 1 figure (a and b), accepted by MNRA

Tohoku-Hiroshima-Nagoya planetary spectra library: A method for characterizing planets in the visible to near infrared

There has not been a comprehensive framework for comparing spectral data from different planets.Such a framework is needed for the study of extrasolar planets and objects within the solar system. We have undertaken observations to compile a library of planet spectra for all planets, some moons, and some dwarf planets in the solar system to study their general spectroscopic and photometric natures. During May and November of 2008, we acquired spectra for the planets using TRISPEC, which is capable of simultaneous three-band spectroscopy in a wide wavelength range of 0.45 - 2.5 microns with low resolving power (lambda-over-Delta-lambda is 140 - 360). Patterns emerge from comparing the spectra. Analyzing their general spectroscopic and photometric natures, we show that it is possible to distinguish between gas planets, soil planets and ice planets. These methods can be applied to extrasolar observations using low resolution spectrography or broad-band filters. The present planet spectral library is the first library to contain observational spectra for all of the solar system planets, based on simultaneous observations in visible and near infrared wavelengths. This library will be a useful reference for analyzing extrasolar planet spectra, and for calibrating planetary data sets.Comment: 11 pages, 6 figures, Accepted on 28/08/2009 to appear in Section 10. Planets and planetary systems of Astronomy and Astrophysic