45,317 research outputs found
Moduli Stabilization with the String Higgs Effect
We review the notion of the Higgs effect in the context of string theory. We
find that by including this effect in time dependent backgrounds, one is led to
a natural mechanism for stabilizing moduli at points of enhanced gauge
symmetry. We consider this mechanism for the case of the radion (size of the
extra dimensions) and find that as decompactification of the large spatial
dimensions takes place the radion will remain stabilized at the self dual
radius. We discuss how this mechanism can be incorporated into models of string
cosmology and brane inflation to resolve some outstanding problems. We also
address some issues regarding which string states should be included when
constructing low energy actions in string cosmology.Comment: 20 pages, references added, typos correcte
Inversion of stellar fundamental parameters from Espadons and Narval high-resolution spectra
The general context of this study is the inversion of stellar fundamental
parameters from high-resolution Echelle spectra. We aim indeed at developing a
fast and reliable tool for the post-processing of spectra produced by Espadons
and Narval spectropolarimeters. Our inversion tool relies on principal
component analysis. It allows reduction of dimensionality and the definition of
a specific metric for the search of nearest neighbours between an observed
spectrum and a set of observed spectra taken from the Elodie stellar library.
Effective temperature, surface gravity, total metallicity and projected
rotational velocity are derived. Various tests presented in this study, and
done from the sole information coming from a spectral band centered around the
Mg I b-triplet and with spectra from FGK stars are very promising.Comment: 13 pages, 8 figures (accepted A&A). arXiv admin note: text overlap
with arXiv:1401.108
Present state of knowledge of the upper atmosphere 1988: An assessment report
This document was issued in response to the Clean Air Act Amendments of 1977, Public Law 95-95, mandating that NASA and other key agencies submit biennial reports to Congress and EPA. NASA is to report on the state of our knowledge of the upper atmosphere, particularly the stratosphere. This is the sixth ozone assessment report submitted to Congress and the concerned regulatory agencies. Part 1 contains an outline of the NASA Upper Atmosphere Research Program and summaries of the research efforts supported during the last two years. An assessment is presented of the state of knowledge as of March 15, 1988 when the Ozone Trends Panel, organized by NASA and co-sponsored by the World Meteorological Organization, NOAA, FAA and the United Nations Environment Program released an executive summary of its findings from a critical in-depth study involving over 100 scientists from 12 countries. Chapter summaries of the International Ozone Trends Panel Report form the major part of this report. Two other sections are Model Predictions of Future Ozone Change and Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling. Each of these sections and the report in its entirety were peer reviewed
Neurohormonal modulation of the Limulus heart: amine actions on neuromuscular transmission and cardiac muscle
The responses of Limulus cardiac neuromuscular junctions and cardiac muscle cells to four endogenous amines were determined in order to identify the cellular targets underlying amine modulation of heartbeat amplitude. The amines increased the amplitude of the Limulus heartbeat, with dopamine (DA) being more potent than octopamine, epinephrine or norepinephrine. The effect of DA on heartbeat amplitude was not blocked by phentolamine. DA enhanced the contractility of deganglionated heart muscle, with time course and dose-dependence similar to its effect on the intact heart. The amines also enhanced neuromuscular transmission, with time course and dose-dependence similar to their effects upon the intact heart. The amplitude of unitary excitatory junction potentials (EJPs) and frequency of miniature excitatory junction potentials (mEJPs) were increased by DA, while mEJP amplitude was unchanged. Thus DA, and probably the other amines, had a presynaptic effect. Combined actions upon cardiac muscle and cardiac neuromuscular transmission account for the ability of these amines to increase the amplitude of the Limulus heartbeat
Comparison of predictive scores of symptomatic intracerebral haemorrhage after stroke thrombolysis in a single centre
Peer reviewedPublisher PD
Letter from J. T. J. Watson to B. R. Colson
Letter from J. T. J. Watson to B. R. Colson. The two-page typewritten note is on Highland Home College letterhead and is dated 2 June 1913
Gamma-Ray Bursts observed by XMM-Newton
Analysis of observations with XMM-Newton have made a significant contribution
to the study of Gamma-ray Burst (GRB) X-ray afterglows. The effective area,
bandpass and resolution of the EPIC instrument permit the study of a wide
variety of spectral features. In particular, strong, time-dependent, soft X-ray
emission lines have been discovered in some bursts. The emission mechanism and
energy source for these lines pose major problems for the current generation of
GRB models. Other GRBs have intrinsic absorption, possibly related to the
environment around the progenitor, or possible iron emission lines similar to
those seen in GRBs observed with BeppoSAX. Further XMM-Newton observations of
GRBs discovered by the Swift satellite should help unlock the origin of the GRB
phenomenon over the next few years.Comment: To appear in proceedings of the "XMM-Newton EPIC Consortium meeting,
Palermo, 2003 October 14-16", published in Memorie della Societa Astronomica
Italian
Defining the gap between research and practice in public relations programme evaluation - towards a new research agenda
The current situation in public relations programme evaluation is neatly summarized by McCoy who commented that 'probably the most common buzzwords in public relations in the last ten years have been evaluation and accountability' (McCoy 2005, 3). This paper examines the academic and practitioner-based literature and research on programme evaluation and it detects different priorities and approaches that may partly explain why the debate on acceptable and agreed evaluation methods continues. It analyses those differences and proposes a research agenda to bridge the gap and move the debate forward
Optimization by nonhierarchical asynchronous decomposition
Large scale optimization problems are tractable only if they are somehow decomposed. Hierarchical decompositions are inappropriate for some types of problems and do not parallelize well. Sobieszczanski-Sobieski has proposed a nonhierarchical decomposition strategy for nonlinear constrained optimization that is naturally parallel. Despite some successes on engineering problems, the algorithm as originally proposed fails on simple two dimensional quadratic programs. The algorithm is carefully analyzed for quadratic programs, and a number of modifications are suggested to improve its robustness
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