Strain-balanced type-II superlattices for efficient multi-junction solar cells.

Multi-junction solar cells made by assembling semiconductor materials with different bandgap energies have hold the record conversion efficiencies for many years and are currently approaching 50%. Theoretical efficiency limits make use of optimum designs with the right lattice constant-bandgap energy combination, which requires a 1.0-1.15 eV material lattice-matched to GaAs/Ge. Nevertheless, the lack of suitable semiconductor materials is hindering the achievement of the predicted efficiencies, since the only candidates were up to now complex quaternary and quinary alloys with inherent epitaxial growth problems that degrade carrier dynamics. Here we show how the use of strain-balanced GaAsSb/GaAsN superlattices might solve this problem. We demonstrate that the spatial separation of Sb and N atoms avoids the ubiquitous growth problems and improves crystal quality. Moreover, these new structures allow for additional control of the effective bandgap through the period thickness and provide a type-II band alignment with long carrier lifetimes. All this leads to a strong enhancement of the external quantum efficiency under photovoltaic conditions with respect to bulk layers of equivalent thickness. Our results show that GaAsSb/GaAsN superlattices with short periods are the ideal (pseudo)material to be integrated in new GaAs/Ge-based multi-junction solar cells that could approach the theoretical efficiency limit.

Nano-cones for broadband light coupling to high index substrates.

The moth-eye structure has been proposed several times as an antireflective coating to replace the standard optical thin films. Here, we experimentally demonstrate the feasibility of a dielectric moth-eye structure as an antireflective coating for high-index substrates, like GaAs. The fabricated photonic crystal has Si3N4 cones in a square lattice, sitting on top of a TiO2 index matching layer. This structure attains 1.4% of reflectance power losses in the operation spectral range of GaAs solar cells (440-870 nm), a 12.5% relative reduction of reflection power losses in comparison with a standard bilayer. The work presented here considers a fabrication process based on laser interference lithography and dry etching, which are compatible with solar cell devices. The experimental results are consistent with scattering matrix simulations of the fabricated structures. In a broader spectral range (400-1800 nm), the simulation estimates that the nanostructure also significantly outperforms the standard bilayer coating (3.1% vs. 4.5% reflection losses), a result of interest for multijunction tandem solar cells.

Broadband antireflective nano-cones for tandem solar cells.

Broadband solar cell antireflection coatings made of nano-cones are studied in square lattices of ZnS, TiO(2) and Si(3)N(4). In the best case, the spectrally integrated transmittance (accounting for both reflection and dielectric absorption losses) for direct solar radiation is 99 %, which represents a four-fold decrease in transmission losses in comparison to a standard antireflective coating bilayer. The dependence of the transmission as a function of nanostructure dimensions is studied, showing a wide maximum, thus leading to a high tolerance for manufacturing errors. This high transmittance is also robust against deviations from normal incidence. Our analysis suggests that the high transmittance is due not only to an effective gradual index effect, but is also due to light coupling to quasiguided modes in the photonic crystal leaking mostly towards the substrate.

Cholesterol degradation by Gordonia cholesterolivorans.

This paper reports physiological and genetic data about the type strain Gordonia cholesterolivorans, a strain that is able to degrade steroid compounds containing a long carbon side chain such as cholesterol (C(27)), cholestenone (C(27)), ergosterol (C(28)), and stigmasterol (C(29)). The length of the carbon side chain appears to be of great importance for this bacterium, as the strain is unable to grow using steroids with a shorter or nonaliphatic carbon side chain such as cholic acid (C(24)), progesterone (C(21)), testosterone, androsterone, 4-androstene-3,17-dione (all C(19)), and further steroids. This study also demonstrates that the degradation of cholesterol is a quite common feature of the genus Gordonia by comparing Gordonia cholesterolivorans with some other species of this genus (e.g., G. sihwensis, G. hydrophobica, G. australis, and G. neofelifaecis). Pyrosequencing of the genome of G. cholesterolivorans led to the identification of two conventional cholesterol oxidase genes on an 8-kb and a 12.8-kb genomic fragment with genetic organizations that are quite unique as compared to the genomes of other cholesterol-degrading bacteria sequenced so far. The identified two putative cholesterol oxidases of G. cholesterolivorans are both intracellularly acting enzymes of the class I type. Whereas one of these two cholesterol oxidases (ChoOx-1) shows high identity with an oxidoreductase of the opportunistic pathogen G. bronchialis and is not transcribed during growth with cholesterol, the other one (ChoOx-2) appears phylogenetically closer to cholesterol oxidases from members of the genus Rhodococcus and is transcribed constitutively. By using targeted gene disruption, a G. cholesterolivorans ChoOx-2 gene mutant strain that was unable to grow with steroids was obtained.

Interpretation of the approximate entropy using fixed tolerance values as a measure of amplitude variations in biomedical signals.

A new method for the quantification of amplitude variations in biomedical signals through moving approximate entropy is presented. Unlike the usual method to calculate the approximate entropy (ApEn), in which the tolerance value (r) varies based on the standard deviation of each moving window, in this work ApEn has been computed using a fixed value of r. We called this method, moving approximate entropy with fixed tolerance values: ApEn(f). The obtained results indicate that ApEn(f) allows determining amplitude variations in biomedical data series. These amplitude variations are better determined when intermediate values of tolerance are used. The study performed in diaphragmatic mechanomyographic signals shows that the ApEn(f) curve is more correlated with the respiratory effort than the standard RMS amplitude parameter. Furthermore, it has been observed that the ApEn(f) parameter is less affected by the existence of impulsive, sinusoidal, constant and Gaussian noises in comparison with the RMS amplitude parameter.

Efficacy of methylprednisolone in controlling complications after impacted lower third molar surgical extraction.

INTRODUCTION: Impacted third molar extraction causes considerable swelling in the days immediately following surgery. The aim of the present investigation was to evaluate the efficacy of methylprednisolone as a single 40-mg intramuscular dose in controlling the complications of impacted lower third molar surgical removal. MATERIALS AND METHODS: Thirty-five patients were evaluated within the framework of a consecutive sampling and double-blind study with intrasubject measurements. Extraction comprised ostectomy with tooth sectioning of both lower third molars under local anesthesia. The study group received 40 mg of methylprednisolone injected into the gluteal region, while the controls received no such medication. In each individual one molar was randomly assigned to the study group and the other to the control series - with extraction of the two teeth being spaced 1 month apart. Evaluations were made of postoperative pain, trismus and swelling, and measurements were obtained for oral aperture and various distances (tragus-lip commissure, gonion-lip commissure and gonion-external canthus of the eye) before surgery and 2-7 days after extraction. Statistical correlations were made based on the Student t-test for the comparison of means of related samples. RESULTS: A statistically and clinically significant association was observed 2 days after surgery between methylprednisolone administration and increased oral aperture and diminished facial swelling. Likewise, less pain was recorded in the study group 6 h after surgery. CONCLUSION: The results confirm the efficacy of methylprednisolone in providing a more comfortable postoperative course after surgical extraction of impacted lower third molars.

Further studies on RpoS in enterobacteria: identification of rpoS in Enterobacter cloacae and Kluyvera cryocrescens.

RpoS, the alternative sigma factor sigma(s), is important for bacterial survival under extreme conditions. Many enterobacteria are opportunistic human pathogens and their ability to survive in a changing environment could be an essential step for their virulence. To determine the presence of this gene in enteric bacteria, an Escherichia coli rpoS probe was constructed and used to detect the presence of this gene in different species. A gene homologous to rpoS was found in Citrobacter amalonaticus, Enterobacter cloacae, Klebsiella planticola, Kluyvera cryocrescens, Serratia rubidaea, Shigella sonnei, and Yersinia ruckeri. Providencia stuartii and Proteus vulgaris were the only tested enterobacteria that did not show any signal with the E. coli rpoS probe or that did not lead to amplification of an rpoS fragment using specific primers. The rpoS gene from E. cloacae and from K. cryocrescens was cloned and sequenced and a mutant allele was constructed in E. cloacae. Survival rates under different harsh conditions were followed in order to determine the effect of rpoS inactivation in exponential- and stationary-phase cells of both strains. E. cloacae rpoS mutants were more sensitive to extreme pH, high osmolarity, and high temperature than the wild-type.

Significant rise in plasma insulin after electroconvulsive therapy.

The effect of ECT on insulin plasma levels was studied in 10 single treatments in five patients suffering from DSM III-diagnosed schizophrenia. The treatments were chosen from early, middle and late ordinal positions. A significant rise was found 10, 20 and 30 min after an effective electrical stimulus. Values returned to normal in all cases at 60 min. The rise at 10 min occurred in all treatments, irrespective of ordinal position, but an incidental finding was that the higher the ordinal position of a given treatment, the higher the peak of insulin.

[Treatment of male infertility with clomiphene citrate (author's transl)]. / Tratamiento de la infertilidad masculina con citrato de clomifeno.

Ninety unselected male patients with infertility were treated with clomiphene citrate, 25 mg/day, taken on 20 consecutive days each month for a period of 3 to 12 months. The patients were divided into two groups according to sperm counts. In 39 cases of oligozoospermia with sperm counts above 10 million/ml, six pregnancies were obtained (15.4%) while a significant improvement of sperm counts occurred in 22 cases (56.4%). On the other hand, in 51 cases with azoospermia or oligozoospermia below 10 million/ml only three pregnancies occurred (5.9%) and two patients (3.9%) had significantly improved sperm counts. The indications and form of administration of clomiphene citrate are commented upon.

[Effect of the thyroid in the development of intestinal hydroxylases]. / Influencia del tiroides en el desarrollo de las hidrolasas intestinales

The authors studied the saccharidase levels in the intestines of rats during the perinatal period. Sucrase and maltase values increase with advancing time, while lactase values decrease also age-dependently. The thyroid gland has a decisive role in the intestinal maturation of fats. In an assessment of circulating blood thyroxin levels, the authors found that the amount of thyroxin at birth is practically undetectable (less than 0,05 mug/100 ml expressed in iodine), rapidly increasing up to adult levels (3,8 mug/100 ml) 22 days after birth.