Abstract We present a new type of photovoltaic device where Gaussian superlattice is inserted in the i-region of a GaAs/GaInNAs p-i-n solar cell. A theoretical model is developed to study the performance of these devices. We establish a new criterion to calculate miniband widths in superlattice heterostructures in the presence of electric field. By optimizing miniband width, the spectral response of the cell in the energy region below the absorption edge of host material is significantly enhanced. Our results show that these devices could reach higher conversion efficiencies than the single-gap solar cell.

In order to understand the temporal dynamics of actinomycete communities of the rhizosphere of the desert plant Artemisia tridentata (sagebrush), two complementary methods were used. They were: (1) 16S rDNA-based PCR coupled with denaturing gradient gel electrophoresis (DGGE), and (2) an agar plate enumeration methodology in which three different media were used to quantify total bacteria, actinomycetes, and fungi. The objective of this research were: (1) to obtain a comprehensive picture of the structure of actinomycete populations, and (2) their dynamics in the rhizosphere of young and old sagebrush plants during two distinct seasons. PCR-DGGE analysis showed that actinomycete groups were less diverse in rhizosphere soils collected in winter than in bulk soils. On the other hand, rhizosphere soil of A. tridentata young plants (RSYP) collected in spring showed an enrichment of actinomycete diversity and/or selection of unique actinomycete populations. This was not the case with the actinomycete populations detected in the rhizosphere soil of old plants (RSOP) in the same season. In this later case, a shift in the dominant bands on PCR-DGGE gels was observed between seasons. Finally, the enumeration analysis showed that actinomycete counts tended to be higher in spring, while total bacteria counts were higher in winter. Although strong soil type effects were detected, more research in the unexplored environment of sagebrush rhizosphere is necessary.

Para comprender la dinámica estacional de las comunidades de actinomicetos en la rizosfera de la planta desértica Artemisia tridentata (sagebrush), se emplearon dos métodos complementarios: (1) PCR basado en el DNAr 16S acoplado con electroforesis de geles con gradientes desnaturalizantes (DGGE), y (2) la metodología de enumeración en placas de agar en la cual se utilizaron 3 medios diferentes para cuantificar bacterias totales, actinomicetos y hongos. Los objetivos de esta investigación fueron: (1) obtener una mayor comprensión de la estructura de las poblaciones de actinomicetos, y (2) determinar su dinámica en la rizosfera de plantas de sagebrush jóvenes y viejas en dos estaciones del año. El análisis de PCR-DGGE mostró que los grupos de actinomicetos fueron menos diversos en suelos obtenidos en invierno asociados a la rizosfera en comparación a aquellos que no estaban asociados. El efecto de la rizosfera para enriquecer la diversidad de actinomicetos y/o selección de poblaciones únicas de actinomicetos fue observado en suelos de rizosfera de planta joven (RSYP) obtenidos en primavera; dicho efecto fue menor en suelos rizosféricos de plantas viejas (RSOP) de la misma estación. En este último tipo de suelo, se observó un cambio en las bandas dominantes en geles de PCR-DGGE entre estaciones. Finalmente, el análisis de plaqueo mostró que el número de actinomicetos fue mayor en primavera, mientras que el de las bacterias totales fue mayor en invierno. Aún cuando se detectó un fuerte efecto del tipo de suelo, se generó información relevante que urge más investigación en el ambiente inexplorado de la rizosfera de sagebrush.

Vectorial transmission of Chagas disease has been strongly reduced in most parts of the Southern Cone countries of South America, except in the Gran Chaco region of Argentina, Bolivia, and Paraguay. Given periodical interruptions of the vector control programmes in the endemic region of the Gran Chaco of Argentina, the vectorial transmission of the disease has been increasing during the last years. From the beginning of 2004, the provincial Ministry of Health of La Rioja, Argentina, started a vector control programme to cover the rural houses of the Los Llanos area in the southwestern area of the Gran Chaco region. This article reports the result of a standardized entomological survey and insecticide application against Chagas disease vectors in the intra and peridomestic structures of the rural houses of Los Llanos. A total of 4062 houses were inspected, of which 46.8% were found to be infested by Triatoma infestans. Infestation by vector species other than T. infestans was less than 0.5%(T. eratyrusiformis and T. platensis). Intradomestic infestation was found in 27.2%, whereas peridomestic infestation was found in 39.3% of the houses. The lowest figure of intradomestic infestation was 6.6% (Department F Varela), and the highest value of intradomestic infestation was 45.1% (Department Independencia). In spite of the demonstrated success of vector control elsewhere, this study shows that the vector populations are susceptible to pyrethroid insecticides in the southern area of the Gran Chaco of Argentina, that there still are regions where rural houses show heavy infestation by T. infestans associated with big peridomestic structures and that the vectorial transmission of the Chagas disease will continue, unless a sustained and well organized vector control effort is installed in the region.

Breeding for high and low hypothermic responses to systemic administration of a serotonin1A (5-HT1A) receptor agonist (8-hydroxy-2-(di-n-propylamino)tetralin, 8-OH-DPAT) has resulted in high DPAT-sensitive (HDS) and low DPAT-sensitive (LDS) lines of rats, respectively. These lines also differ in several behavioral measures associated with stress. In the present microdialysis study we observed that basal 5-HT concentrations in the prefrontal cortex and dorsal hippocampus did not differ significantly between HDS and LDS rats. Thus, behavioral differences between the HDS and LDS lines might not be attributed to differences in basal 5-HT release. However, both lines had lower basal levels of 5-HT release than their randomly bred control group (random DPAT-sensitive, RDS) in the prefrontal cortex (mean ± SEM, pg/20 µl, was 3.0 ± 0.4 for LDS, 3.8 ± 0.3 for HDS and 6.4 ± 0.6 for RDS; F(2,59) = 5.8, P<0.005). The administration of (±)-fenfluramine (10 mg/kg) induced a greater increase in hippocampal 5-HT levels in HDS rats (500%) as compared with LDS (248%) or RDS (243%) rats (P<0.0001). There were no significant differences in the prefrontal cortex among lines, with a fenfluramine-induced 5-HT increase of about 900% in the three groups. This differential response to fenfluramine may be due to functional alterations of hippocampal 5-HT reuptake sites in the HDS line.