The Galactic IMF: origin in the combined mass distribution functions of dust grains and gas clouds

We present here a theoretical model to account for the stellar IMF as a result of the composite behaviour of the gas and dust distribution functions. Each of these has previously been modelled and the models tested against observations. The model presented here implies a relation between the characteristic size of the dust grains and the characteristic final mass of the stars formed within the clouds containing the grains, folded with the relation between the mass of a gas cloud and the characteristic mass of the stars formed within it. The physical effects of dust grain size are due to equilibrium relations between the efficiency of grains in cooling the clouds, which is a falling function of grain size, and the efficiency of grains in catalyzing the production of molecular hydrogen, which is a rising function of grain size. We show that folding in the effects of grain distribution can yield a reasonable quantitative account of the IMF, while gas cloud mass function alone cannot do so.Comment: 8 pages, 6 figures, MNRAS accepted for publicatio

A new chemo-evolutionary population synthesis model for early-type galaxies. I: Theoretical basis

We have developed a new stellar population synthesis model designed to study early-type galaxies. It provides optical and near-infrared colors, and line indices for 25 absorption lines. It can synthesize single age, single metallicity stellar populations or follow the galaxy through its evolution from an initial gas cloud to the present time. The model incorporates the new isochrones of the Padova group and the latest stellar spectral libraries. The model has been extensively compared with previous ones in the literature to establish its accuracy as well as the accuracy of this kind of models in general. Using the evolutionary version of the model we find that we cannot fit the most metal-rich elliptical galaxies if we keep the IMF constant and do not allow infall of gas. We do however reproduce the results of Arimoto \& Yoshii (1986) for the evolution of the gas, and produce colors, and, for the first time with this type of models, absorption line-strengths. It is in fact possible to fit the data for the elliptical galaxies by varying the IMF with time. Our numerical model is in good broad agreement with the analytical 'simple model'. In the present paper we describe the model, and compare a few key observables with new data for three early-type {\em standard} galaxies. However the data, as well as our fits, will be discussed in much more detail in a second paper (Vazdekis {\it et al.} 1996), where some conclusions will be drawn about elliptical galaxies on the basis of this model.Comment: 37 pages; includes 8 tables and 23 figures, accepted by the Astrophysical Journal Supplement. Fig. 11, can be obtained from http://www.astro.rug.nl/~peletier/paper1.htm

Monitoreo de plagas y enfermedades presentes en el cultivo de cártamo (Carthamus tinctorius L.) del sudoeste chaqueño

El cultivo del cártamo (Carthamus tinctorius L.) representa una buena alternativa como cultivo de invierno en el norte argentino. Las provincias con mayor incidencia en la producción nacional son: Salta, Chaco y Santiago del Estero. En el sudoeste chaqueño se plantea ésta especie como una alternativa productiva no estival adaptada a las condiciones semiáridas (inverno - primaveral) por su resistencia a la sequía. Contar con información local sobre las plagas que afectan a esta oleaginosa, es esencial para optimizar el rendimiento por lo que en este trabajo se planteó evaluar los artrópodos que afectan al cultivo de cártamo y los agentes causales de las enfermedades en su relación con el estado fenológico del cultivo. Se puede concluir que el cultivo es afectado por insectos plagas en la etapa vegetativa, pertenecientes a los órdenes Hemiptera (Uroleucon y Athaumastus), Coleoptera (Diabrotica); Thysanoptera (Trips), Diptera (Melanagromyza) y Lepidoptera (Helicoverpa), mientras que en la etapa reproductiva solo se vio afectado por Melanagromyza cunctanoides. Con respecto a las enfermedades observadas durante el desarrollo del cultivo en estudio, se observó en el estrato inferior de las plantas, uredosoros y uredosporas coincidentes con Puccinia carthami agente causal de la roya del cártamo y también conidios y conidióforos correspondientes a Alternaria sp.EEA Las BreñasFil: Esquivel, Cristian E. Arrocera Adeco Agropecuaria; ArgentinaFil: Casuso, Violeta Macarena. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Las Breñas; ArgentinaFil: Tarrago, Jose Ramon. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Cátedra de Terapéutica Vegetal; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Las Breñas; Argentin

Nanoscale electrical conductivity of the purple membrane monolayer

Nanoscale electron transport through the purple membrane monolayer, a two-dimensional crystal lattice of the transmembrane protein bacteriorhodopsin, is studied by conductive atomic force microscopy. We demonstrate that the purple membrane exhibits nonresonant tunneling transport, with two characteristic tunneling regimes depending on the applied voltage (direct and Fowler-Nordheim). Our results show that the purple membrane can carry significant current density at the nanometer scale, several orders of magnitude larger than previously estimated by macroscale measurements

Monitoreo de plagas y enfermedades presentes en el cultivo de cártamo (Carthamus tinctorius L.) del sudoeste chaqueño

El cultivo del cártamo (Carthamus tinctorius L.) representa una buena alternativa como cultivo de invierno en el norte argentino. Las provincias con mayor incidencia en la producción nacional son: Salta, Chaco y Santiago del Estero. En el sudoeste chaqueño se plantea ésta especie como una alternativa productiva no estival adaptada a las condiciones semiáridas (inverno - primaveral) por su resistencia a la sequía. Contar con información local sobre las plagas que afectan a esta oleaginosa, es esencial para optimizar el rendimiento por lo que en este trabajo se planteó evaluar los artrópodos que afectan al cultivo de cártamo y los agentes causales de las enfermedades en su relación con el estado fenológico del cultivo. Se puede concluir que el cultivo es afectado por insectos plagas en la etapa vegetativa, pertenecientes a los órdenes Hemiptera (Uroleucon y Athaumastus), Coleoptera (Diabrotica); Thysanoptera (Trips), Diptera (Melanagromyza) y Lepidoptera (Helicoverpa), mientras que en la etapa reproductiva solo se vio afectado por Melanagromyza cunctanoides. Con respecto a las enfermedades observadas durante el desarrollo del cultivo en estudio, se observó en el estrato inferior de las plantas, uredosoros y uredosporas coincidentes con Puccinia carthami agente causal de la roya del cártamo y también conidios y conidióforos correspondientes a Alternaria sp

The Retroviral Restriction Ability of SAMHD1, but Not Its Deoxynucleotide Triphosphohydrolase Activity, Is Regulated by Phosphorylation

SummarySAMHD1 is a cellular enzyme that depletes intracellular deoxynucleoside triphosphates (dNTPs) and inhibits the ability of retroviruses, notably HIV-1, to infect myeloid cells. Although SAMHD1 is expressed in both cycling and noncycling cells, the antiviral activity of SAMHD1 is limited to noncycling cells. We determined that SAMHD1 is phosphorylated on residue T592 in cycling cells but that this phosphorylation is lost when cells are in a noncycling state. Reverse genetic experiments revealed that SAMHD1 phosphorylated on residue T592 is unable to block retroviral infection, but this modification does not affect the ability of SAMHD1 to decrease cellular dNTP levels. SAMHD1 contains a target motif for cyclin-dependent kinase 1 (cdk1) (592TPQK595), and cdk1 activity is required for SAMHD1 phosphorylation. Collectively, these findings indicate that phosphorylation modulates the ability of SAMHD1 to block retroviral infection without affecting its ability to decrease cellular dNTP levels