S-, P-, and D-wave resonances in positronium-lithium-atom scattering

We investigate ortho-positronium-lithium-atom (Ps-Li) scattering using static-exchange and three-Ps-state coupled-channel calculations. The present three-PS-state scheme, while closely agreeing with the resonance and binding energies in the Ps-H system, predicts S-, P-, and D-wave resonances at 4.25 eV, 4.9 eV, and, 5.25 eV. respectively, in the electronic spin-singlet channel of Ps-Li scattering. The present calculation also yields a Ps-Li binding in this attractive singlet channel with an approximate binding energy of 0.218 eV, which is in adherence with the recent findings of a chemically stable PsLi system using stocastic variational and quantum Monte Carlo calculations. We further report elastic, Ps(2s)-, and Ps(2p)-excitation cross sections at low to medium energies (0.068-30 eV).

Low-energy correlations in the positronium-hydrogen-atom system

Employing a nonlocal model potential for electron exchange we study positronium-hydrogen-atom (Ps-H) scattering using a five-state coupled-channel model allowing for Ps(2s,2p)H(1s) and Ps(1s)H(2s,2p) excitations. We find remarkable correlations among S-wave Ps-H binding energy, scattering length, effective range, and resonance energy in the electronic singlet state. Using these correlations we predict fairly accurate values of singlet Ps-H scattering length (3.50a0) and effective range (1.65a0).

Variational calculation of positronium-helium-atom scattering length

A basis-set calculation scheme for S-waves Ps-He elastic scattering below the lowest inelastic threshold was formulated using a variational expression for the transition matrix. The scheme was illustrated numerically by calculating the scattering length in the electronic doublet state: a=1.0±0.1 a.u.

Cobertura da cultura da soja pela calda fungicida em função, de pontas de pulverização e volumes de aplicação

The goal of this research was to evaluate two tips of spraying nozzles (hollow cone nozzle and two flat fan nozzle annexed to a nozzle body DUO) and three spray volumes (100, 150 and 200 dm3 ha-1), whose application was for the control of the Asian soybean rust. An area of 288 m 2 was used, with a randomized blocks design in a factorial 2×3 with 4 repetitions, total of 24 experimental parcels of 12 m2. For the spraying with hydraulical nozzles a costal spray of constant pressure kept by C02 compressed with bar of 2 m was used. The analysis of the covering percentage was carried through by means of the use of hidro-sensible paper, that was placed in three position of the plant what it represents, in height, the third superior, average and inferior of the canopy. For both the third no interaction between the evaluated factors, was found and meither difference statistics between the spraying tips and the volumes. In absolute values the twin flat fan nozzle DUO presented minimum difference of covering in relation to the hollow cone nozzle, and for the spray volume of 200 dm3 ha -1 presented greater covering percentage.

Los mercados en el Istmo Centroamericano y México: ¿qué ha pasado con la competencia?

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El sector financiero en América Latina: ha llegado la hora de consolidar el marco institucional

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Los mercados en el Istmo Centroamericano y México: ¿qué ha pasado con la competencia?

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La familia desde la cultura. ¿Qué ha cambiado en América Latina?

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Pueblos indígenas de América Latina: políticas y programas de salud, ¿cuánto y cómo se ha avanzado? Informe del Seminario-Taller

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Air-assistance in spray booms which have different spray volumes and nozzle types for chemically controlling spodoptera frugiperda on corn

The study aimed to evaluate the performance of air assistance in spray booms using different types of nozzles and spray volumes. We took into account spray deposits, fall armyworm control and crop corn performance in a narrow row cropping system. The experiment was carried out at the experimental area of Sao Paulo State University, Botucatu/SP, Brazil, during the 2008/2009 agricultural season, in randomized blocks with a factorial scheme (2×2+1) and four replications. Two spray nozzles (flat fan nozzle and hollow cone nozzle) were tested, combined with two air assistance levels in the spray boom (with and without air assistance) and a treatment control. In the experimental spraying, Spinosad insecticide was sprayed in amounts of 48 g active substance (a.s.)/ha. The air assistance in the spray boom increased the spray deposits in the V 4 growth stage of the corn plants. Moreover, the application of this technology showed higher efficiency on fall armyworm control, reaching a 100% level 15 days after spraying, in the V 10 growth stage of the plants. The hollow cone nozzle increased the spray deposit level on the corn plants compared with the flat fan nozzle, at growth stage V 4. However, the flat fan nozzle, combined with air assistance technology, was more effective for controlling fall armyworm in the same growth stage (V 4), although the hollow cone nozzle increased the deposit levels on the plants. All the technologies tested in the study promoted a reduction of plant damage from fall armyworm attack. Corn productivity is directly related to the control efficiency of fall armyworm.

La apertura comercial ¿ha creado paraísos de contaminadores en América Latina?

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Dynamics and Conformational Studies of TOAC Spin Labeled Analogues of Ctx(Ile21)-Ha Peptide from Hypsiboas albopunctatus

Antimicrobial peptides (AMPs) isolated from several organisms have been receiving much attention due to some specific features that allow them to interact with, bind to, and disrupt cell membranes. The aim of this paper was to study the interactions between a membrane mimetic and the cationic AMP Ctx(Ile21)-Ha as well as analogues containing the paramagnetic amino acid 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) incorporated at residue positions n = 0, 2, and 13. Circular dichroism studies showed that the peptides, except for [TOAC13]Ctx(Ile21)-Ha, are unstructured in aqueous solution but acquire different amounts of α-helical secondary structure in the presence of trifluorethanol and lysophosphocholine micelles. Fluorescence experiments indicated that all peptides were able to interact with LPC micelles. In addition, Ctx(Ile21)-Ha and [TOAC13]Ctx(Ile21)-Ha peptides presented similar water accessibility for the Trp residue located near the N-terminal sequence. Electron spin resonance experiments showed two spectral components for [TOAC0]Ctx(Ile21)-Ha, which are most likely due to two membrane-bound peptide conformations. In contrast, TOAC2 and TOAC13 derivatives presented a single spectral component corresponding to a strong immobilization of the probe. Thus, our findings allowed the description of the peptide topology in the membrane mimetic, where the N-terminal region is in dynamic equilibrium between an ordered, membrane-bound conformation and a disordered, mobile conformation; position 2 is most likely situated in the lipid polar head group region, and residue 13 is fully inserted into the hydrophobic core of the membrane. © 2013 Vicente et al.

Assembling a xylanase-lichenase chimera through all-atom molecular dynamics simulations

Multifunctional enzyme engineering can improve enzyme cocktails for emerging biofuel technology. Molecular dynamics through structure-based models (SB) is an effective tool for assessing the tridimensional arrangement of chimeric enzymes as well as for inferring the functional practicability before experimental validation. This study describes the computational design of a bifunctional xylanase-lichenase chimera (XylLich) using the xynA and bglS genes from Bacillus subtilis. In silico analysis of the average solvent accessible surface area (SAS) and the root mean square fluctuation (RMSF) predicted a fully functional chimera, with minor fluctuations and variations along the polypeptide chains. Afterwards, the chimeric enzyme was built by fusing the xynA and bglS genes. XylLich was evaluated through small-angle X-ray scattering (SAXS) experiments, resulting in scattering curves with a very accurate fit to the theoretical protein model. The chimera preserved the biochemical characteristics of the parental enzymes, with the exception of a slight variation in the temperature of operation and the catalytic efficiency (k cat/Km). The absence of substantial shifts in the catalytic mode of operation was also verified. Furthermore, the production of chimeric enzymes could be more profitable than producing a single enzyme separately, based on comparing the recombinant protein production yield and the hydrolytic activity achieved for XylLich with that of the parental enzymes. © 2013 Elsevier B.V. All rights reserved.

Desigualdad de los ingresos en el Brasil. ¿Qué ha cambiado en los últimos años?

En este estudio se presentan datos empíricos que permiten evaluar la repercusión de diversas variables socioeconómicas y políticas en distintas formas de medir la desigualdad de los ingresos en las 27 unidades de la República Federativa del Brasil entre 1999 y 2008. La experiencia brasileña resulta útil para entender las políticas relativas a la desigualdad de los ingresos en los países en desarrollo. Los resultados indican que el progreso observado durante el período analizado se debe a la combinación de una mayor apertura comercial, el desarrollo tecnológico y financiero, la reducción de la tasa de desempleo, la puesta en práctica de políticas sociales con efecto directo en las familias más pobres y la implementación de mecanismos contra la corrupción.