Lifetimes of Confined Acoustic Phonons in Ultra-Thin Silicon Membranes

We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultra-thin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from \sim 4.7 ns to 5 ps with decreasing membrane thickness from \sim 194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic surface roughness scattering including a wavelength-dependent specularity. Our results provide insight to understand some of the limits of nanomechanical resonators and thermal transport in nanostructures

Viral metacommunities associated to bats and rodents at different spatial scales

One of the main goals of community ecology is to measure the relative importance of environmental filters to understand patterns of species distribution at different temporal and spatial scales. Likewise, the identification of factors that shape symbiont metacommunity structures is important in disease ecology because resulting structures drive disease transmission. We tested the hypothesis that distributions of virus species and viral families from rodents and bats are defined by shared responses to host phylogeny and host functional characteristics, shaping the viral metacommunity structures at four spatial scales (Continental, Biogeographical, Zoogeographical, and Regional). The contribution of host phylogeny and host traits to the metacommunity of viruses at each spatial scale was calculated using a redundant analysis of canonical ordering (RDA). For rodents, at American Continental scale the coherence of viral species metacommunity increased while the spatial scale decreased and Quasi-Clementsian structures were observed. This pattern suggests a restricted distribution of viruses through their hosts, while in the Big Mass (Europe, Africa, and Asia), the coherence decreased as spatial scale decreased. Viral species metacommunities associated with bats was dominated by random structures along all spatial scales. We suggest that this random pattern is a result of the presence of viruses with high occupancy range such as rabies (73%) and coronavirus (27%), that disrupt such structures. At viral family scale, viral metacommunities associated with bats showed coherent structures, with the emergence of Quasi- Clementsian and Checkerboard structures. RDA analysis indicates that the assemblage of viral diversity associated with rodents and bats responds to phylogenetic and functional characteristics, which alternate between spatial scales. Several of these variations could be subject to the spatial scale, in spite of this, we could identify patterns at macro ecological scale. The application of metacommunity theory at symbiont scales is particularly useful for large-scale ecological analysis. Understanding the rules of host-virus association can be useful to take better decisions in epidemiological surveillance, control and even predictions of viral distribution and dissemination

Effect of a heterotrimeric G protein α subunit on conidia germination, stress response, and roquefortine C production in Penicillium roqueforti

Summary. Heterotrimeric G protein signaling regulates many processes in fungi, such as development, pathogenicity, and secondary metabolite biosynthesis. For example, the Gα subunit Pga1 from Penicillium chrysogenum regulates conidiation and secondary metabolite production in this fungus. The dominant activating allele, pga1G42R, encoding a constitutively active Pga1 Gα subunit, was introduced in Penicillium roqueforti by transformation, resulting in a phenotype characterized by low sporulation and slow growth. In this work, the effect of the constitutively active Pga1G42R Gα subunit on conidial germination, stress tolerance, and roquefortine C production of P. roqueforti was studied. Pga1G42R triggered germination in the absence of a carbon source, in addition to negatively regulating thermal and osmotic stress tolerance. The presence of the Pga1G42R Gα subunit also had an important effect on roquefortine C biosynthesis, increasing production and maintaining high levels of the mycotoxin throughout a culture period of 30 days. Together, the results suggest that G protein-mediated signaling participates in the regulation of these three processes in P. roqueforti. [Int Microbiol 2009; 12(2):123-129

Ullucus tuberosus Caldas: colección de germoplasma de ullucu conservada en el Centro Internacional de la Papa (CIP).

El presente catálogo contiene información pasaporte, datos de caracterización morfológica y ploidía para 432 accesiones de ulluco mantenidas en el banco de germoplasma del CIP. Para ilustrar mejor los datos de caracterización morfológica, cada accesión está acompañada de un set de fotografías que incluye la parte aérea de la planta, los tubérculos, las flores y una muestra lista para herborizar conformada por un tallo con sus hojas y flores. La información pasaporte es complementada con mapas ilustrados que muestran el lugar de colecta de cada accesión

A Genetic Programming infrastructure profiting from public computation resources

In this article an experience of the utilization of PRC (Public Resource Computation) in research projects that needs large quantities of CPU time is presented. We have developed a distributed architecture based on middleware BOINC and LilGP Genetic Programming tool. In order to run LilGP applications under BOINC platforms, some core LilGP functions has been adapted to BOINC requirements. We have used a classic GP problem known as the artificial ANT in Santa Fe Trail. Some computers from a classroom were used acting as clients, proving that they can be used for scientific computation in conjunction with their primary uses

Una Herramienta de Programación Genética Paralela que Aprovecha Recursos Públicos de Computación

Éste artículo presenta una primera implementación de una herramienta genérica de programación genética capaz de aprovechar recursos públicos de computación. Dadas las altas necesidades de recursos de computación requeridos por los algoritmos evolutivos, la aplicación del paralelismo ha sido habitual recientemente, aunque las herramientas paralelas requieren infraestructuras costosas para su aprovechamiento. El modelo que se presenta en este artículo, permite utilizar computadores distribuidos en Internet, cuyos usuarios ceden altruistamente para colaborar en proyectos de investigación. El proceso de donación de recursos es simple e inmediato por parte del usuario, afectando solamente a los ciclos de CPU que no son consumidos por el propio usuario. Se estudia la mejora de las prestaciones obtenidas gracias al uso de estos recursos en Programación Genética Distribuida

Differential protection induced by immunization with variable doses of a Leishmania antigenic extract against Leishmania amazonensis.

Experimental vaccines have been developed to protect against leishmaniasis using the BALB/c mice model immunized with different immunogens, but an effective vaccine still does not exist. To determine factors inherent to immunogens that might abrogate vaccine-induced efficacy, our research sought to investigate the impact of immunization using variable doses (low, medium and high) of a known soluble Leishmania antigenic extracts (SLA), associated or not with alum, in order to determine the best dose of this vaccine immunogen able to induce the best level of protection in BALB/c mice against L. amazonensis infection. This work shows that the immunization´ model using a high inoculum (100 µg) of SLA results in the best level of protection against challenge. These mice presented significant reductions in the footpad swelling and parasite load; high levels of IFN-γ and IL-12, and low levels of IL-4, IL-10, TGF-β and Leishmania-specific IgG and IgE antibodies. Mice immunized with 50 µg of SLA present intermediate results of protection; on the other hand, mice immunized with 1 µg showed the worst results. Considering all the elements, it could be concluded that the model employing a high dose of SLA in BALB/c mice can bring about the development of a protective immune response in the animals, thus allowing for the protection against the disease. In addition, we understand that the definition of an ideal dose for each vaccine candidate appears to be fundamental to determining the phenotype of resistance and/or susceptibility in murine models to study leishmaniasis