Sporopollenin, a natural copolymer, is robust under high hydrostatic pressure

Lycopodium sporopollenin, a natural copolymer, shows exceptional stability under high hydrostatic pressures (10 GPa) as determined by in situ high pressure synchrotron source FTIR spectroscopy. This stability is evaluated in terms of the component compounds of the sporopollenin: p-coumaric acid, phloretic acid, ferulic acid, and palmitic and sebacic acids, which represent the additional n-acid and ndiacid components. This high stability is attributed to interactions between these components, rather than the exceptional stability of any one molecular component. We propose a biomimetic solution for the creation of polymer materials that can withstand high pressures for a multitude of uses in aeronautics, vascular autografts, ballistics and light-weight protective materials

Muon Spin Relaxation Studies of Superconductivity in a Crystalline Array of Weakly Coupled Metal Nanoparticles

We report Muon Spin Relaxation studies in weak transverse fields of the superconductivity in the metal cluster compound, Ga$\_{84}$[N(SiMe$\_{3}$)$\_{2}$]$\_{20}$-Li$\_{6}$Br$\_{2}$(thf)$\_{20}\cdot$2toluene. The temperature and field dependence of the muon spin relaxation rate and Knight shift clearly evidence type II bulk superconductivity below $T\_{\text{c}}\approx7.8$ K, with $B\_{\text{c1}}\approx 0.06$ T, $B\_{\text{c2}}\approx 0.26$ T, $\kappa\sim 2$ and weak flux pinning. The data are well described by the s-wave BCS model with weak electron-phonon coupling in the clean limit. A qualitative explanation for the conduction mechanism in this novel type of narrow band superconductor is presented.Comment: 4 figures, 5 page

Tasas de dispersión y supervivencia de adultos y juveniles del rabijunco colirrojo (Phaethon rubricauda) expuestas a contaminantes potenciales

Annual survival and dispersal rates of adult and juvenile red–tailed tropicbirds were examined in connection with exposure to heavy metals. From 1990–2000 the incineration of a U.S. stockpile of chemical weapons stored at Johnston Atoll exposed nesting tropicbirds to increased levels of human disturbance, smoke stack emissions and potential leaks. Using a multi–state mark–recapture modeling approach, birds nesting in this site (downwind of the plant) were compared to those nesting in a reference site (upwind of the plant) with less human disturbance, no exposure to smoke stack emissions or other potential incineration emissions. We did not find any difference in survival of adults or juveniles when comparing the two sites. Adult breeding dispersal rates did not differ between the sites but we did find differences in the age–specific natal dispersal rates. Birds fledged from downwind areas were less likely to return to their natal area to nest and more likely to immigrate to the upwind area than vice–versa. This asymmetry in emigration rates is believed to be due to differing vegetation densities and has implications for vegetation management in relation to tropicbird nest success and population size.Se examinaron las tasas de dispersión y de supervivencia anual de adultos y jóvenes de los rabijuncos colirrojos en relación a la exposición a metales pesados. Entre los años 1990 y 2000, la incineración de un arsenal de armas químicas del ejército de Estados Unidos almacenadas en Johnston Atoll expuso a las aves del trópico que anidaban en la zona a niveles más elevados de perturbaciones antrópicas/contaminación humana, emisiones procedentes de chimeneas y fugas potenciales. Se comparó las aves nidificantes en este lugar (a favor del viento de la planta) mediante modelos de captura–recaptura de multiestados, con las que anidaban en un emplazamiento de referencia (en cuyo caso la planta quedaba situada en contra del viento), caracterizado por menos perturbaciones antrópicas y ninguna exposición a emisiones procedentes de chimeneas ni a ningún otro tipo de emisiones potenciales de incineración. Al comparar ambos emplazamientos, no se halló ninguna diferencia en cuanto a la supervivencia de las aves adultas o jóvenes. Las tasas de dispersión reproductiva de los adultos no difirieron entre los emplazamientos; en cambio, sí que se observaron diferencias en las tasas de dispersión natal por edades. Las aves jóvenes que abandonaron las áreas situadas a favor del viento era menos probable que regresaran a su área natal para anidar y más probable que inmigraran al área situada en contra del viento. Se considera que esta asimetría en las tasas de emigración obedece a las diferentes densidades de vegetación, repercutiendo en la gestión de la vegetación con respecto al éxito de los nidos de las aves del trópico y el tamaño poblacional

Ocorrência de fotossensibilização em equinos mantidos em pastagem de Brachiaria humidicola.

bitstream/item/138780/1/COT-40.pdfCNPGC

Problemas com cavalos em pastagens de humidicola.

bitstream/item/138777/1/COT-37.pdfCNPGC

Chiral two-loop pion-pion scattering parameters from crossing-symmetric constraints

Constraints on the parameters in the one- and two-loop pion-pion scattering amplitudes of standard chiral perturbation theory are obtained from explicitly crossing-symmetric sum rules. These constraints are based on a matching of the chiral amplitudes and the physical amplitudes at the symmetry point of the Mandelstam plane. The integrals over absorptive parts appearing in the sum rules are decomposed into crossing-symmetric low- and high-energy components and the chiral parameters are finally related to high-energy absorptive parts. A first application uses a simple model of these absorptive parts. The sensitivity of the results to the choice of the energy separating high and low energies is examined with care. Weak dependence on this energy is obtained as long as it stays below ~560 MeV. Reliable predictions are obtained for three two-loop parameters.Comment: 23 pages, 4 figures in .eps files, Latex (RevTex), our version of RevTex runs under Latex2.09, submitted to Phys. Rev. D,minor typographical corrections including the number at the end of the abstract, two sentences added at the end of Section 5 in answer to a referee's remar

Adensamentos periódicos do rebanho bovino de corte no Pantanal e seus reflexos na eficiência reprodutiva: um relato.

Os adensamentos consistem em promover, periodicamente, rodeios (agrupar o rebanho de cria), sob a hipótese de que a aproximação de touros e vacas conduz a um maior índice de prenhez. Este trabalho teve como objetivo relatar a experiência de um estudo realizado para averiguar se essa pratica tem, efetivamente, o efeito esperado, bem como relatar as dificuldades encontradas. Foi conduzido numa propriedade particular representativa do Pantanal de Rio Verde de Mato Grosso, MS, no período de 1987 a 1990. Utilizaram-se 766 vacas neloradas e 46 touros da raça Nelore, mantidos em duas invernadas (pastagem nativa) de, aproximadamente, 1.500 hectares cada, cuja lotação foi de 3 hectares/unidade animal e a relação touro/vaca foi de 1:16. O ensaio envolveu dois tratamentos (T1 e T2). O T1 obedeceu ao manejo tradicional da região (testemunha). No T2, o rebanho foi submetido a adensamentos a cada 21 dias, durante a estação de monta (setembro a março). O adensamento consistiu em levar todo o gado para um piquete a parte, com 19 hectares, mantendo-o por 48 horas. Os resultados obtidos não são conclusivos por falta de controle das condições experimentais. Discutem-se as dificuldades encontradas nesse ensaio, bem como são apresentadas sugestões para futuros trabalhos a serem conduzidos na região.bitstream/item/139369/1/cir-tec-28.pd

Pion propagation in real time field theory at finite temperature

We describe how the thermal counterpart of a vacuum two-point function may be obtained in the real time formalism in a simple way by using directly the $2\times 2$ matrices that different elements acquire in this formalism. Using this procedure we calculate the analytic (single component) thermal amplitude for the pion pole term in the ensemble average of two axial-vector currents to two loops in chiral perturbation theory. The general expressions obtained for the effective mass and decay constants of the pion are evaluated in the chiral and the nonrelativistic limits. We also investigate the effect of massive states on these effective parameters.Comment: 17 pages TeX and 9 eps figure