3,633 research outputs found
Pion Generalized Parton Distributions within a fully covariant constituent quark model
We extend the investigation of the Generalized Parton Distribution for a
charged pion within a fully covariant constituent quark model, in two respects:
(i) calculating the tensor distribution and (ii) adding the treatment of the
evolution, needed for achieving a meaningful comparison with both the
experimental parton distribution and the lattice evaluation of the so-called
generalized form factors. Distinct features of our phenomenological covariant
quark model are: (i) a 4D Ansatz for the pion Bethe-Salpeter amplitude, to be
used in the Mandelstam formula for matrix elements of the relevant current
operators, and (ii) only two parameters, namely a quark mass assumed to hold
MeV and a free parameter fixed through the value of the pion decay
constant. The possibility of increasing the dynamical content of our covariant
constituent quark model is briefly discussed in the context of the Nakanishi
integral representation of the Bethe-Salpeter amplitude.Comment: Pages 20, figure 11 and table 8. Minor changes. To be published in
EPJ
Four wave mixing oscillation in a semiconductor microcavity: Generation of two correlated polariton populations
We demonstrate a novel kind of polariton four wave mixing oscillation. Two
pump polaritons scatter towards final states that emit two beams of equal
intensity, separated both spatially and in polarization with respect to the
pumps. The measurement of the intensity fluctuations of the emitted light
demonstrates that the final states are strongly correlated.Comment: 5 pages, 5 figures In this strongly revised version several new
experimental data are adde
English Speakers Learning Spanish: Perception Issues Regarding Vowels and Stress
The present pilot study examines both the perception of Spanish vowels /a, e, o/ in word – final position and the perception of final and penultimate stress of words ending in those vowels by beginner American English learners of Spanish. Seventeen English speakers and seven native Spanish speakers participated in this study. The English speakers were exposed to 90 hours of Spanish lessons during a three–week course in Mar del Plata, Argentina, a Spanish speaking country. Participants’ perception was assessed by pretest and posttest, which consisted of identification tasks with nonce words. The study yielded these results: (a) native English-speaking participants perceived Spanish vowels like native Spanish-speaking participants after a three-week language course; (b) Initially, English speakers received lower scores in the perception of stress than did Spanish speakers who served as a comparison (control) group; c) Three weeks after exposure to the language, the English speaking students performed like Spanish speakers in the perception of penultimate stress but not in the perception of final stress. The article concludes that vowel perception is not a problem for English speakers learning Spanish while the perception of stress contrasts is a difficult challenge. More emphasis should be given to stress perception in Spanish programs for English speakers, as stress contrasts, together with vowels, are key to interpreting the meaning of a verb in the Spanish verbal morphology system
The sentiment analysis of tweets as a new tool to measure public perception of male erectile and ejaculatory dysfunctions
Twitter is a social network based on "tweets," short messages of up to 280 characters. Social media has been investigated in health care research to ascertain positive or negative feelings associated with several conditions but never in sexual medicin
Temperature dependence of the zero point kinetic energy in ice and water above room temperature
By means of Deep Inelastic Neutron Scattering we determined the temperature dependence of the proton kinetic energy in polycrystalline ice Ih between 5 K and 271 K. We compare our results with predictions form Path Integral quantum simulations and semiclassical quasi-harmonic models with phase-dependent frequencies. The latter show the best agreement with the experiment if the librational contribution is properly taken into account. The kinetic energy increase with temperature in ice is also found to be approximately a factor ∼ 5 smaller than in the case of liquid water above room temperature, highlighting the role played by anharmonic quantum fluctuations in the two phases
Microstability analysis of pellet fuelled discharges in MAST
Reactor grade plasmas are likely to be fuelled by pellet injection. This
technique transiently perturbs the profiles, driving the density profile hollow
and flattening the edge temperature profile. After the pellet perturbation, the
density and temperature profiles relax towards their quasi-steady-state shape.
Microinstabilities influence plasma confinement and will play a role in
determining the evolution of the profiles in pellet fuelled plasmas. In this
paper we present the microstability analysis of pellet fuelled H-mode MAST
plasmas. Taking advantage of the unique capabilities of the MAST Thomson
scattering system and the possibility of synchronizing the eight lasers with
the pellet injection, we were able to measure the evolution of the post-pellet
electron density and temperature profiles with high temporal and spatial
resolution. These profiles, together with ion temperature profiles measured
using a charge exchange diagnostic, were used to produce equilibria suitable
for microstability analysis of the equilibrium changes induced by pellet
injection. This analysis, carried out using the local gyrokinetic code GS2,
reveals that the microstability properties are extremely sensitive to the rapid
and large transient excursions of the density and temperature profiles, which
also change collisionality and beta e significantly in the region most strongly
affected by the pellet ablation.Comment: 21 pages, 10 figures. This is an author-created, un-copyedited
version of an article submitted for publication in Plasma Physics and
Controlled Fusion. IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Dependence of the location of the Martian magnetic lobes on the interplanetary magnetic field direction: Observations from Mars Global Surveyor
We use magnetometer data from the Mars Global Surveyor (MGS) spacecraft during portions of the premapping orbits of the mission to study the variability of the Martian-induced magnetotail as a function of the orientation of the interplanetary magnetic field (IMF). The time spent by MGS in the magnetotail lobes during periods with positive solar wind flow-aligned IMF component B IMF suggests that their location as well as the position of the central polarity reversal layer (PRL) are displaced in the direction antiparallel to the IMF cross-flow component B IMF. Analogously, in the cases where B IMF is negative, IMF the lobes are displaced in the direction of B ⟂ . This behavior is compatible with a previously published analytical model of the IMF draping, where for the first time, the displacement of a complementary reversal layer (denoted as IPRL for inverse polarity reversal layer) is deduced from first principles.Fil: Romanelli, Norberto Julio. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Bertucci, Cesar. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Gomez, Daniel Osvaldo. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Mazelle, C.. Université Paul Sabatier; Franci
From Manaus to Maputo: Toward a Public Health and Biodiversity Framework
The linkages between human health, biodiversity, ecosystems, and the life-supporting services that they provide are varied and complex. The traditional neglect of this nexus by policy-makers perpetuates threats posed to ecosystems with potentially critical impacts on global health. The Convention on Biological Diversity and the World Health Organization recently co-convened two regional workshops on these intricate but vital linkages. From discussions held with policy-makers and experts in the biodiversity and health sectors, spanning some 50 countries in Africa and the Americas, we derive a broad framework for the development of national and regional public health and biodiversity strategies relevant to strategic planning processes in the emerging post-2015 development context
Quantum Mechanical Search and Harmonic Perturbation
Perturbation theory in quantum mechanics studies how quantum systems interact
with their environmental perturbations. Harmonic perturbation is a rare special
case of time-dependent perturbations in which exact analysis exists. Some
important technology advances, such as masers, lasers, nuclear magnetic
resonance, etc., originated from it. Here we add quantum computation to this
list with a theoretical demonstration. Based on harmonic perturbation, a
quantum mechanical algorithm is devised to search the ground state of a given
Hamiltonian. The intrinsic complexity of the algorithm is continuous and
parametric in both time T and energy E. More precisely, the probability of
locating a search target of a Hamiltonian in N-dimensional vector space is
shown to be 1/(1+ c N E^{-2} T^{-2}) for some constant c. This result is
optimal. As harmonic perturbation provides a different computation mechanism,
the algorithm may suggest new directions in realizing quantum computers.Comment: 6 pages, 4 figures, revtex
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