9,829 research outputs found
Finite Temperature Nuclear Response in Extended Random-Phase Approximation
The nuclear collective response at finite temperature is investigated for the
first time in the quantum framework of the small amplitude limit of the
extended TDHF approach, including a non-Markovian collision term. It is shown
that the collision width satisfies a secular equation. By employing a Skyrme
force, the isoscalar monopole, isovector dipole and isoscalar quadrupole
excitations in are calculated and important quantum features are
pointed out. The collisional damping due to decay into incoherent 2p-2h states
is small at low temperatures but increases rapidly at higher temperatures.Comment: 22 Latex pages including 9 figures. Phys. Rev. C (in press
Collective response of nuclei: Comparison between experiments and extended mean-field calculations
The giant monopole, dipole and quadrupole responses in Ca, Zr,
Sn and Pb are investigated using linear response treatment
based on a stochastic one-body transport theory. Effects of the coupling to
low-lying surface modes (coherent mechanism) and the incoherent mechanism due
to nucleon-nucleon collisions are included beyond the usual mean-field
description. We emphasize the importance of both mechanism in the fragmentation
and damping of giant resonance. Calculated spectra are compared with experiment
in terms of percentage of Energy-Weighted Sum-Rules in various energy regions.
We obtained reasonable agreement in all cases. A special attention as been
given to the fragmentation of the Giant Quadrupole Resonance in calcium and
lead. In particular, the equal splitting of the in Ca is
correctly reproduced. In addition, the appearance of fine structure in the
response Pb is partly described by the calculations in which the
coherent mechanism play an important role.Comment: 44 pages, 8 figures, submitted to Physical Review
Learning Recursive Segments for Discourse Parsing
Automatically detecting discourse segments is an important preliminary step
towards full discourse parsing. Previous research on discourse segmentation
have relied on the assumption that elementary discourse units (EDUs) in a
document always form a linear sequence (i.e., they can never be nested).
Unfortunately, this assumption turns out to be too strong, for some theories of
discourse like SDRT allows for nested discourse units. In this paper, we
present a simple approach to discourse segmentation that is able to produce
nested EDUs. Our approach builds on standard multi-class classification
techniques combined with a simple repairing heuristic that enforces global
coherence. Our system was developed and evaluated on the first round of
annotations provided by the French Annodis project (an ongoing effort to create
a discourse bank for French). Cross-validated on only 47 documents (1,445
EDUs), our system achieves encouraging performance results with an F-score of
73% for finding EDUs.Comment: published at LREC 201
Spectro-interferometric observations of interacting massive stars with VEGA/CHARA
We obtained spectro-interferometric observations in the visible of
Lyrae and Sgr using the instrument VEGA of the CHARA interferometric
array. For Lyrae, the dispersed fringe visibilities and differential
phases were obtained in spectral regions containing the H and HeI 6678
lines and the H and HeI 4921 lines. Whereas the source is unresolved in
the continuum, the source of the emission lines is resolved and the photocenter
of the bulk of the H emission exhibits offsets correlated with the
orbital phase. For Sgr, both the continuum and H sources are
resolved, but no clear binary signal is detected. The differential phase shift
across the line reveals that the bulk of the H emission is clearly
offset from the primary
Alien Registration- Denis, Philippe (Winslow, Kennebec County)
https://digitalmaine.com/alien_docs/16570/thumbnail.jp
Should you believe in the Shanghai ranking?
This paper proposes a critical analysis of the "Academic Ranking of World Universities", published every year by the Institute of Higher Education of the Jiao Tong University in Shanghai and more commonly known as the Shanghai ranking. After having recalled how the ranking is built, we first discuss the relevance of the criteria and then analyze the proposed aggregation method. Our analysis uses tools and concepts from Multiple Criteria Decision Making (MCDM). Our main conclusions are that the criteria that are used are not relevant, that the aggregation methodology is plagued by a number of major problems and that the whole exercise suffers from an insufficient attention paid to fundamental structuring issues. Hence, our view is that the Shanghai ranking, in spite of the media coverage it receives, does not qualify as a useful and pertinent tool to discuss the "quality" of academic institutions, let alone to guide the choice of students and family or to promote reforms of higher education systems. We outline the type of work that should be undertaken to oer sound alternatives to the Shanghai ranking.Shanghai ranking; multiple criteria decision analysis; evaluation models; higher education.
Comparison of two extraction methods for ergosterol determination in vegetal feeds
Ergosterol is the principal sterol of fungi in which it plays an essential role in cell membrane and other cellular constituents. This sterol is considered as a good marker of fungal contamination and of mycotoxin production. After validation of ergosterol quantification by HPLC-UV system (linearity range: 0.2 to 20.0 mg/ml, repeatability: 3.27%, between day precision: 4.75%), 2 extraction methods of ergosterol from 3 vegetal matrixes (maize, barley and wheat) were compared: the first one, normalized by the AFNOR, is based on solid phase extraction (SPE), while the other is based on liquid/liquid extraction (LLE). The LLE procedure allowed ergosterol extraction gains of around 20% for high initial sterol contents (3 to 5 mg/kg) in naturally contaminated matrixes or in spiked samples, and of 86% for low initial sterol contents (1-2 mg/kg) in maize. Moreover, the precision of ergosterol determination was comparable for the 2 methods even if it was slightly lower using LLE and was more affected by the initial ergosterol contents in vegetal matrix than by its nature. These results suggest that ergosterol contents in vegetal feeds would be underestimated with the official method (SPE) and emphasize the importance of the extraction step
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