2,838 research outputs found
The spatial damping of magnetohydrodynamic waves in a flowing partially ionised prominence plasma
Solar prominences are partially ionised plasmas displaying flows and
oscillations. These oscillations show time and spatial damping and, commonly,
have been explained in terms of magnetohydrodynamic (MHD) waves. We study the
spatial damping of linear non-adiabatic MHD waves in a flowing partially
ionised plasma, having prominence-like physical properties. We consider single
fluid equations for a partially ionised hydrogen plasma including in the energy
equation optically thin radiation, thermal conduction by electrons and
neutrals, and heating. Keeping the frequency real and fixed, we have solved the
obtained dispersion relations for the complex wavenumber, k, and have analysed
the behaviour of the damping length, wavelength and the ratio of the damping
length to the wavelength, versus period, for Alfven, fast, slow and thermal
waves.Comment: 28 pages, 9 figure
Supervised Topical Key Phrase Extraction of News Stories using Crowdsourcing, Light Filtering and Co-reference Normalization
Fast and effective automated indexing is critical for search and personalized
services. Key phrases that consist of one or more words and represent the main
concepts of the document are often used for the purpose of indexing. In this
paper, we investigate the use of additional semantic features and
pre-processing steps to improve automatic key phrase extraction. These features
include the use of signal words and freebase categories. Some of these features
lead to significant improvements in the accuracy of the results. We also
experimented with 2 forms of document pre-processing that we call light
filtering and co-reference normalization. Light filtering removes sentences
from the document, which are judged peripheral to its main content.
Co-reference normalization unifies several written forms of the same named
entity into a unique form. We also needed a "Gold Standard" - a set of labeled
documents for training and evaluation. While the subjective nature of key
phrase selection precludes a true "Gold Standard", we used Amazon's Mechanical
Turk service to obtain a useful approximation. Our data indicates that the
biggest improvements in performance were due to shallow semantic features, news
categories, and rhetorical signals (nDCG 78.47% vs. 68.93%). The inclusion of
deeper semantic features such as Freebase sub-categories was not beneficial by
itself, but in combination with pre-processing, did cause slight improvements
in the nDCG scores.Comment: In 8th International Conference on Language Resources and Evaluation
(LREC 2012
Smoothing Proximal Gradient Method for General Structured Sparse Learning
We study the problem of learning high dimensional regression models
regularized by a structured-sparsity-inducing penalty that encodes prior
structural information on either input or output sides. We consider two widely
adopted types of such penalties as our motivating examples: 1) overlapping
group lasso penalty, based on the l1/l2 mixed-norm penalty, and 2) graph-guided
fusion penalty. For both types of penalties, due to their non-separability,
developing an efficient optimization method has remained a challenging problem.
In this paper, we propose a general optimization approach, called smoothing
proximal gradient method, which can solve the structured sparse regression
problems with a smooth convex loss and a wide spectrum of
structured-sparsity-inducing penalties. Our approach is based on a general
smoothing technique of Nesterov. It achieves a convergence rate faster than the
standard first-order method, subgradient method, and is much more scalable than
the most widely used interior-point method. Numerical results are reported to
demonstrate the efficiency and scalability of the proposed method.Comment: arXiv admin note: substantial text overlap with arXiv:1005.471
Description of He tetramer bound and scattering states
Faddeev-Yakubovski equations are solved numerically for 4He tetramer and
trimer states using realistic helium-helium interaction models. We describe the
properties of ground and excited states, and we discuss with a special emphasis
the 4He-4He3 low energy scattering
Testing Non-local Nucleon-Nucleon Interactions in the Four-Nucleon Systems
The Faddeev-Yakubovski equations are solved in configuration space for the -particle and n-H continuum states. We test the ability of nonlocal
nucleon-nucleon interaction models to describe 3N and 4N systems.Comment: 16 pages, 6 figure
The Anatomy of Subjective Well-Being
Subjective Well-Being has increasingly been studied by several economists. This paper fits in that literature but takes into account that there are different aspects of life such as health, financial situation, and job. We call them domains. In this paper, we consider Subjective Well-Being as a composite of various domain satisfactions (DS). We postulate a two -layer model where individual Subjective Well-Being is explained by individual subjective domain satisfactions with respect to job, finance, health, leisure, housing, and environment. We distinguish between long -term and short - term effects. Next, we explain domain satisfactions and Subjective Well-Being by objectively measurable variables such as income. We estimate a model for the GS and DS equations with individual random effects and fix time effects.Subjective Well-Being, satisfaction measurement, qualitative regressors, health satisfaction, job satisfaction
Nuclear models on a lattice
We present the first results of a quantum field approach to nuclear models
obtained by lattice techniques. Renormalization effects for fermion mass and
coupling constant in case of scalar and pseudoscalar interaction lagrangian
densities are discussed.Comment: 4 pages - 7 figures ; Invited talk to QCD 05: 12th International QCD
Conference, 4-9 Jul 2005, Montpellier, France ; To appear in Nucl. Phys. B
(Proc. Suppl.
Periodicities in sunspot activity during solar cycle 23
The data of sunspot numbers, sunspot areas and solar flare index during cycle
23 are analyzed to investigate the intermediate-term periodicities. Power
spectral analysis has been performed separately for the data of the whole disk,
northern and southern hemispheres of the Sun. Several significant midrange
periodicities (175, 133, 113, 104, 84, 63 days) are detected in sunspot
activity. Most of the periodicities in sunspot numbers generally agree with
those of sunspot areas during the solar cycle 23. The study reveals that the
periodic variations in the northern and southern hemispheres of the Sun show a
kind of asymmetrical behavior. Periodicities of 175 days and 133
days are highly significant in the sunspot data of northern hemisphere showing
consistency with the findings of Lean (1990) during solar cycles 12-21. On the
other hand, southern hemisphere shows a strong periodicity of about 85 days in
terms of sunspot activity. The analysis of solar flare index data of the same
time interval does not show any significant peak. The different periodic
behavior of sunspot and flare activity can be understood in the light of
hypothesis proposed by Ballester et al. (2002), which suggests that during
cycle 23, the periodic emergence of magnetic flux partly takes place away from
developed sunspot groups and hence may not necessarily increase the magnetic
complexity of sunspot groups that leads to the generation of flares.Comment: 4 pages, 4 figure
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