25 research outputs found
Transversity distributions in the nucleon in the large-N_c limit
We compute the quark and antiquark transversity distributions in the nucleon
at a low normalization point of 600 MeV in the large- limit, where the
nucleon can be described as a soliton of an effective chiral theory (chiral
quark-soliton model). The flavor-nonsinglet distributions, and , appear in leading order
of the -expansion, while the flavor-singlet distributions, and , are non-zero only in
next-to-leading order. The transversity quark and antiquark distributions are
found to be significantly different from the longitudinally polarized
distributions and , respectively, in contrast to the prediction of the naive
non-relativistic quark model. We show that this affects the predictions for the
spin asymmetries in Drell-Yan pair production in transversely polarized pp and
ppbar collisions.Comment: 45 pages, 16 figure
Simulation of dimensionality effects in thermal transport
The discovery of nanostructures and the development of growth and fabrication
techniques of one- and two-dimensional materials provide the possibility to
probe experimentally heat transport in low-dimensional systems. Nevertheless
measuring the thermal conductivity of these systems is extremely challenging
and subject to large uncertainties, thus hindering the chance for a direct
comparison between experiments and statistical physics models. Atomistic
simulations of realistic nanostructures provide the ideal bridge between
abstract models and experiments. After briefly introducing the state of the art
of heat transport measurement in nanostructures, and numerical techniques to
simulate realistic systems at atomistic level, we review the contribution of
lattice dynamics and molecular dynamics simulation to understanding nanoscale
thermal transport in systems with reduced dimensionality. We focus on the
effect of dimensionality in determining the phononic properties of carbon and
semiconducting nanostructures, specifically considering the cases of carbon
nanotubes, graphene and of silicon nanowires and ultra-thin membranes,
underlying analogies and differences with abstract lattice models.Comment: 30 pages, 21 figures. Review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
Calculations of binding energies and masses of heavy quarkonia using renormalon cancellation
We use various methods of Borel integration to calculate the binding ground
energies and masses of b-bbar and t-tbar quarkonia. The methods take into
account the leading infrared renormalon structure of the hard+soft part of the
binding energies E(s), and of the corresponding quark pole masses m_q, where
the contributions of these singularities in M(s) = 2 m_q + E(s) cancel.
Beforehand, we carry out the separation of the binding energy into its
hard+soft and ultrasoft parts. The resummation formalisms are applied to
expansions of m_q and E(s) in terms of quantities which do not involve
renormalon ambiguity, such as MSbar quark mass, and alpha_s. The
renormalization scales are different in calculations of m_q, E(s) and E(us).
The MSbar mass of b quark is extracted, and the binding energies of t-tbar and
the peak (resonance) energies for (t+tbar) production are obtained.Comment: 23 pages, 8 double figures, revtex4; the version to appear in
Phys.Rev.D; extended discussion between Eqs.(25) and (26); the paragraph
between Eqs.(32) and (33) is new and explains the numerical dependence of the
residue parameter on the factorization scale; several new references were
added; acknowledgments were modified; the numerical results are unchange
Burden and risk factors for Pseudomonas aeruginosa community-acquired pneumonia:a Multinational Point Prevalence Study of Hospitalised Patients
Pseudornonas aeruginosa is a challenging bacterium to treat due to its intrinsic resistance to the antibiotics used most frequently in patients with community-acquired pneumonia (CAP). Data about the global burden and risk factors associated with P. aeruginosa-CAP are limited. We assessed the multinational burden and specific risk factors associated with P. aeruginosa-CAP.
We enrolled 3193 patients in 54 countries with confirmed diagnosis of CAP who underwent microbiological testing at admission. Prevalence was calculated according to the identification of P. aeruginosa. Logistic regression analysis was used to identify risk factors for antibiotic-susceptible and antibiotic-resistant P. aeruginosa-CAP.
The prevalence of P. aeruginosa and antibiotic-resistant P. aeruginosa-CAP was 4.2% and 2.0%, respectively. The rate of P. aeruginosa CAP in patients with prior infection/colonisation due to P. aeruginosa and at least one of the three independently associated chronic lung diseases (i.e. tracheostomy, bronchiectasis and/or very severe chronic obstructive pulmonary disease) was 67%. In contrast, the rate of P. aeruginosa-CAP was 2% in patients without prior P. aeruginosa infection/colonisation and none of the selected chronic lung diseases. The multinational prevalence of P. aeruginosa-CAP is low.
The risk factors identified in this study may guide healthcare professionals in deciding empirical antibiotic coverage for CAP patients
Studies on the heavy minerals of some soils under Casuarina equisetifolia plantations in India
Utilización de compost agotado de champiñón como capa de coberturas en nuevos ciclos de producción Using spent mushroom substrate as casing layers in new growing cycles
El objetivo de este trabajo fue evaluar el comportamiento agronómico de seis mezclas de cobertura, elaboradas a partir de sustrato postcultivo del champiñón Agaricus bisporus, en nuevos ciclos de cultivo. Los resultados obtenidos mostraron la viabilidad de la reintroducción del sustrato en nuevos ciclos de cultivo, ya sea como material de base único, si se somete a un proceso de lavado para eliminar sales solubles, o bien mezclado con otros materiales de baja conductividad, como es el caso de la turba rubia o la fibra de coco. Se destacan los altos valores de eficiencia biológica registrados, que llegaron hasta los 100 kg kg-1 de compost, similares a los proporcionados por los testigos, y los altos valores relativos observados (con respecto a los testigos) en el contenido en materia seca de los carpóforos cosechados con algunas de las nuevas coberturas elaboradas. Esta reutilización del compost constituye una alternativa interesante, con vistas a reemplazar a las tierras y a los sustratos orgánicos utilizados habitualmente como cobertura, con la doble ventaja de disminuir los costos de elaboración y el impacto ambiental.<br>The objective of this work was to evaluate the agronomic behaviour of six mixtures of casing, prepared from spent mushroom substrate (SMS), in new production cycles of Agaricus bisporus. The results obtained showed the feasibility of reuse of the SMS in new cultivation cycles when used alone by submitting it to a washing process to remove soluble salts, or mixed with other materials of low conductivity, such as Sphagnum peat or coconut fiber pith. The high values of biological efficiency recorded up to 100 kg kg-1 compost, similar to that of the controls, and the same high values observed in the dry matter content of the mushrooms harvested with some of the new casing layers prepared must be highlighted. The suggested use for SMS is an important alternative to consider, in order to replace soils and other organic substrates typically used as casing, with the added advantages of lowering the production costs and decreasing the environmental impact