137 research outputs found
Feasibility study on extracting the gluon polarization in Di-Jet production in polarized pp collisions at RHIC
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009.Includes bibliographical references (p. 43).The STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is carrying out a spin physics program at is = 200 - 500 GeV to gain a deeper insight into the spin structure and dynamics of the proton. These studies provide fundamental tests of Quantum Chromodynamics (QCD). One of the main objectives of the STAR spin physics program is the determination of the polarized gluon distribution function through a measurement of the longitudinal double-spin asymmetry, ALL, for various processes. Di-Jet production is of particular interest since it allows a direct access of the underlying partonic kinematics, in particular the reconstruction of the gluon momentum fraction relative to the respective proton momentum. The main objective of this study is to examine to what extent the gluon polarization can be measured as a function of the gluon momentum fraction in leading-order perturbation theory. We propose a leading order method to extract the gluon polarization from ALL, and find that it transforms the problem into simply solving the quadratic formula.by Robert C. Haussman.S.B
Modellrechnungen zur ermittlung optimaler prĂŒfungs- und selektionssysteme fur reinzuchtpopulationen beim schwein
International audienc
Coulomb Correlations and Pseudo-gap Effects in a Pre-formed Pair Model for the Cuprates
We extend previous work on pre-formed pair models of superconductivity to
incorporate Coulomb correlation effects. For neutral systems, these models have
provided a useful scheme which interpolates between BCS and Bose Einstein
condensation with increasing coupling and thereby describes some aspects of
pseudo-gap phenomena. However, charge fluctuations (via the plasmon,
) significantly modify the collective modes and therefore the
interpolation behavior. We discuss the resulting behavior of the pseudo-gap and
thermodynamic quantities such as , and as a function of
.Comment: 4 pages RevTeX, 3 ps figures included (Submitted to Physical Review B
August 27, 1996
Quantifying Stock Price Response to Demand Fluctuations
We address the question of how stock prices respond to changes in demand. We
quantify the relations between price change over a time interval
and two different measures of demand fluctuations: (a) , defined as the
difference between the number of buyer-initiated and seller-initiated trades,
and (b) , defined as the difference in number of shares traded in buyer
and seller initiated trades. We find that the conditional expectations and of price change for a given or
are both concave. We find that large price fluctuations occur when demand is
very small --- a fact which is reminiscent of large fluctuations that occur at
critical points in spin systems, where the divergent nature of the response
function leads to large fluctuations.Comment: 4 pages (multicol fomat, revtex
Electron-hole correlation effects in the emission of light from quantum wires
We present a self-consistent treatment of the electron-hole correlations in
optically excited quantum wires within the ladder approximation, and using a
contact potential interaction. The limitations of the ladder approximation to
the excitonic low-density region are largely overcome by the introduction of
higher order correlations through self consistency. We show relevance of these
correlations in the low-temperature emission, even for high density relevant in
lasing, when large gain replaces excitonic absorption.Comment: 4 paes 3 figure
Effect of the Equivalence Between Topological and Electric Charge on the Magnetization of the Hall Ferromagnet
The dependence on temperature of the spin magnetization of a two-dimensional
electron gas at filling factor unity is studied. Using classical Monte Carlo
simulations we analyze the effect that the equivalence between topological and
electrical charge has on the the behavior of the magnetization. We find that at
intermediate temperatures the spin polarization increases in a thirty per cent
due to the Hartree interaction between charge fluctuations.Comment: 4 pages. Submitted to Phys.Rev.
Performance and risk of citrus fruits in Valencia
[EN] The purpose of this paper is to outline and adapt Sharpe's model to the agricultural activities as well as to measure the performance of crops when yield and risk are considered. The model is applied to the main varieties of citrus fruits in Valencia. For them, systematic and specific risks are measured and the yield-Ăndex elasticities are quantified. Applying performance rates, we determine the economic yields of citrus varieties in the 1985-1997 period. In the same way, we focus on its management based on the previously outlines criteria.[ES] En este trabajo se presenta el modelo de Sharpe adaptado al campo de la producciĂłn agraria asĂ como los mĂ©todos de medida de los resultados econĂłmicos de los cultivos cuando se consideran rentabilidad y riesgo. El modelo se ha aplicado a las principales variedades de cĂtricos en la Comunidad Valenciana. Para ellas se cuantifica la importancia del riesgo de los rendimientos, descomponiendo el riesgo total en riesgo sistemĂĄtico y especĂfico. Mediante la aplicaciĂłn de los Ăndices de resultados se determina el rendimiento de las variedades de cĂtricos en el perĂodo 1985-1997. De la misma forma se procede a una ordenaciĂłn de las mismas en base a los criterios anteriormente expuestos.Ahmed El Kamel, H.; GarcĂa Alvarez-Coque, JM. (2001). Resultados econĂłmicos y riesgo en los cĂtricos de la Comunidad Valenciana. EconomĂa Agraria y Recursos Naturales - Agricultural and Resource Economics. 1(1):95-114. https://doi.org/10.7201/earn.2001.01.05SWORD951141
Ătude de la variabilitĂ© agromorphologique de la collection nationale de mils locaux du SĂ©nĂ©gal
Objectif : Le mil est la premiĂšre culture vivriĂšre au SĂ©nĂ©gal. Il joue un rĂŽle capital dans la vie des populations rurales qui en dĂ©pendent pour leur survie (STAT/FAO/SENEGAL, 2010). Il est cultivĂ© sur plus 60% des terres arables. Les variĂ©tĂ©s locales Ă©taient les plus utilisĂ©es mais depuis quelques annĂ©es leur survie est menacĂ©e par l'introduction des variĂ©tĂ©s amĂ©liorĂ©es.Methodology et application des rĂ©sultats : Pour Ă©viter l'Ă©rosion gĂ©nĂ©tique, des missions de collecte ont Ă©tĂ©Â organisĂ©es en 1994 et 2006 dans les principales zones de culture du mil. Le matĂ©riel collectĂ© est caractĂ©risĂ©Â pour faciliter leur utilisation dans les programmes de crĂ©ation variĂ©tale. L'objectif du prĂ©sent travail est caractĂ©riser le germoplasme national mil du SĂ©nĂ©gal pour les rendre utilisables par les sĂ©lectionneurs pour la crĂ©ation de nouvelles variĂ©tĂ©s hautement productives pour l'augmentation de la production cĂ©rĂ©aliĂšre et l'atteinte de la sĂ©curitĂ© alimentaire. Pour caractĂ©riser les accessions, 12 variables sĂ©lectionnĂ©es Ă partir du Descripteur du mil IPGRI/ICRISAT, 1993 ont Ă©tĂ© utilisĂ©es. Un dispositif expĂ©rimental en blocs complets randomisĂ©s avec 3 rĂ©pĂ©titions a Ă©tĂ© choisi et les sites d'essais Ă©taient Bambey, Nioro et Darou pendant les hivernages 2011 et 2012. Les analyses descriptives ou qualitatives ; statistiques simples (ANOVA) ; de la diversitĂ© (phĂ©nologique ; gĂ©nĂ©tique avec la mĂ©thode de la classification ascendante (CAH), avec les composantes principales (ACP) et l'analyse factorielle discriminante (AFD)) ont Ă©tĂ© rĂ©alisĂ©es avec les logiciels Genstat Discovery4 et R. Les analyses descriptives ont montrĂ© l'existence d'une grande variabilitĂ© entre les accessions pour les caractĂšres qualitatifs comme l'architecture de l'Ă©pi et la couleur des grains. Les analyses statistiques simples (ANOVA) ont montrĂ© qu'il existe une diffĂ©rence hautement significative entre les entrĂ©es et les sites. Cependant, les interactions Ă©taient non significatives Ă l'exception de la floraison, de l'indice de rĂ©colte et des rendements en grains et en matiĂšre sĂšche. Les analyses de la diversitĂ© phĂ©nologique a permis de classer les variĂ©tĂ©s en trois groupes selon le cycle vĂ©gĂ©tatif (G1 des variĂ©tĂ©s extra-prĂ©coces, G2 des cycles courts et G3 des cycles longs). La classification ascendante hiĂ©rarchique (CAH) suivant la mĂ©thode de Ward a permis d'identifier la valeur des axes et les compositions des 3 groupes y dĂ©coulant (le groupe G1 compte 106 accessions, le G2 compte 129 accessions et le G3 compte 8 accessions) et de tracer le dendrogramme de filiations. L'analyse de la diversitĂ©Â gĂ©nĂ©tique par les composantes principales (ACP) a permis de dĂ©terminer la position des accessions par rapport aux axes expliquant les variabilitĂ©s inter-accessions. L'analyse de la diversitĂ© gĂ©nĂ©tique par la mĂ©thode factorielle discriminante a permis de dĂ©terminer la structuration de la diversitĂ© agromorphologique et la reprĂ©sentation graphique des accessions suivant un plan factoriel. Les groupes ainsi formĂ©s seront convertis en des entitĂ©s hĂ©tĂ©rotiques constituĂ©es de pools de gĂšnes diffĂ©rents oĂč les sĂ©lectionneurs et autres scientifiques vont puiser pour crĂ©er des variĂ©tĂ©s hautement productives et rĂ©sistantes aux stress bio et abiotiques afin de nourrir les populations et de lutter contre la faim et la malnutrition
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