The recent discovery of a new and intense solar flare radiation spectral component with a maximum in the terahertz range has raised a great deal of interest. The origin of this component is still unknown, constituting a problem that goes beyond the application of canonical models used to describe the well-known microwave spectrum. In this work, we present preliminary results on the investigation of a possible contribution from electron-positron pairs produced in a Drell-Yan process to the emission of the terahertz component observed in solar flares.

In this work we calculate the J/psi production in the initial stage of proton-proton, proton-nucleus and nucleus-nucleus collisions at RHIC and LHC energies, taking into account the high parton density regime of QCD, where the physics of parton saturation is expected to be dominant. We perform a quantitative analysis of the xF distributions in these collisions with the Color Glass Condensate (CGC) approach. The ratio between distributions with or without saturated gluons shows that this mechanism produces a suppression on the J/psi yield in the forward region and presents a dip in intermediate values of xF, which is visible only at LHC energies.

In this work we use the IGM, a model that describes well the energy flux in hadronic collisions, to study the leading particle spectrum when saturation effects on the gluon distribution function are included. The leading particle spectrum is calculated for several center of mass energies (<FONT FACE=Symbol>Ö</FONT>s). In the very high energy limit we compare our results with the predictions made in a recent paper, which also addresses the same problem.

The D*Dpi form factor is evaluated at low and moderate Q² in a hadronic loop model, for off-shell D mesons. The results contain arbitrary constants, which are fixed so as to match a previous QCD sum rule calculation valid at higher Q². The form factor obtained in this way is used to extract the coupling constant, which is in very good agreement with the experimental value.

O trabalho foi realizado com o objetivo de avaliar a influência da peletização de sementes de três cultivares de sorgo (Sorghum bicolor (L.) Moench), cv. BRS 701, BRS 304 e BRS 601, com calcário e com termofosfato magnesiano, na absorção de P e de K. Sementes peletizadas e não peletizadas foram colocadas para germinar, por oito dias, em temperatura ambiente. Após este período, oito plântulas com crescimento uniforme (parte aérea e raiz) foram distribuídas em vasos que continham solução nutritiva completa de Hoagland. Após 20 dias, iniciou-se a determinação da absorção de fósforo e de potássio por meio da depleção desses nutrientes na solução nutritiva. Os resultados permitiram concluir que o tipo de revestimento das sementes influenciou, de modo distinto, o crescimento de cada cultivar de sorgo. A absorção de P e de K e o total absorvido também foram influenciados pelo revestimento das sementes em virtude do aumento no crescimento inicial das plântulas. De modo geral, independentemente do tipo de revestimento das sementes, houve maior absorção de fósforo e de potássio quando as sementes foram peletizadas. A taxa de absorção de fósforo aumentou com o peso da matéria seca do sistema radicular e com o peso da matéria seca da parte aérea, mas, neste caso, até o limite de 3,5 µmol planta-1 h-1 de P. Taxas de absorção acima deste valor não estiveram associadas ao aumento do peso da matéria seca da parte aérea.

The aim of this work was to evaluate the influence of seed pelleting with lime and with 'Magnesian Thermophosphate' on ionic absorption of three sorghum genotypes (Sorghum bicolor (L.) Moench), cv BRS 701, BRS 304 e BRS 601. Pelletized and non-pelletized seeds were germinated during eight days at room temperature. After this period, eight plants with uniform root and shoot development, from each treatment, were transferred to a Hoagland solution. Phosphorus and potassium absorption parameters were determined after 20 days. Phosphorus and potassium uptakes varied among sorghum genotypes and were influenced by the compound used in the pelletization, which affected initial plant growth. Phosphorus absorption rate showed positive correlation with the dry matter of the root system and with shoot dry matter up to 3.5 µmol P plant-1 h-1 of P. Absorption rates higher than this value did not show significant correlation with shoot dry matter.