Unambiguous determination of spin dephasing times in ZnO

Time-resolved magneto-optics is a well-established optical pump probe technique to generate and to probe spin coherence in semiconductors. By this method, spin dephasing times T_2^* can easily be determined if their values are comparable to the available pump-probe-delays. If T_2^* exceeds the laser repetition time, however, resonant spin amplification (RSA) can equally be used to extract T_2^*. We demonstrate that in ZnO these techniques have several tripping hazards resulting in deceptive values for T_2^* and show how to avoid them. We show that the temperature dependence of the amplitude ratio of two separate spin species can easily be misinterpreted as a strongly temperature dependent T_2^* of a single spin ensemble, while the two spin species have T_2^* values which are nearly independent of temperature. Additionally, consecutive pump pulses can significantly diminish the spin polarization, which remains from previous pump pulses. While this barely affects T_2^* values extracted from delay line scans, it results in seemingly shorter T_2^* values in RSA.Comment: 11 pages, 10 figure

Self-assembly of ordered wurtzite/rock salt heterostructures—A new view on phase separation in MgxZn1−xO

The self-assembled formation of ordered, vertically stacked rocksalt/wurtzite Mg x Zn 1−xO heterostructures by planar phase separation is shown. These heterostructures form quasi “natural” two-dimensional hetero-interfaces between the different phases upon annealing of MgO-oversaturated wurtzite Mg x Zn 1−xO layers grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. The optical absorption spectra show a red shift simultaneous with the appearance of a cubic phase upon annealing at temperatures between 900 °C and 1000 °C. Transmission electron microscopy reveals that these effects are caused by phase separation leading to the formation of a vertically ordered rock salt/wurtzite heterostructures. To explain these observations, we suggest a phase separation epitaxy model that considers this process being initiated by the formation of a cubic (Mg,Zn)Al2O4 spinel layer at the interface to the sapphire substrate, acting as a planar seed for the epitaxial precipitation of rock salt Mg x Zn 1−xO. The equilibrium fraction x of magnesium in the resulting wurtzite (rock salt) layers is approximately 0.15 (0.85), independent of the MgO content of the as-grown layer and determined by the annealing temperature. This model is confirmed by photoluminescence analysis of the resulting layer systems after different annealing temperatures. In addition, we show that the thermal annealing process results in a significant reduction in the density of edge- and screw-type dislocations, providing the possibility to fabricate high quality templates for quasi-homoepitaxial growth

Potential antiproteolytic effects of L-leucine: observations of in vitro and in vivo studies

The purpose of present review is to describe the effect of leucine supplementation on skeletal muscle proteolysis suppression in both in vivo and in vitro studies. Most studies, using in vitro methodology, incubated skeletal muscles with leucine with different doses and the results suggests that there is a dose-dependent effect. The same responses can be observed in in vivo studies. Importantly, the leucine effects on skeletal muscle protein synthesis are not always connected to the inhibition of skeletal muscle proteolysis. As a matter of fact, high doses of leucine incubation can promote suppression of muscle proteolysis without additional effects on protein synthesis, and low leucine doses improve skeletal muscle protein ynthesis but have no effect on skeletal muscle proteolysis. These research findings may have an important clinical relevancy, because muscle loss in atrophic states would be reversed by specific leucine supplementation doses. Additionally, it has been clearly demonstrated that leucine administration suppresses skeletal muscle proteolysis in various catabolic states. Thus, if protein metabolism changes during different atrophic conditions, it is not surprising that the leucine dose-effect relationship must also change, according to atrophy or pathological state and catabolism magnitude. In conclusion, leucine has a potential role on attenuate skeletal muscle proteolysis. Future studies will help to sharpen the leucine efficacy on skeletal muscle protein degradation during several atrophic states

Steroids in kidney transplant patients

Any evaluation of steroids in kidney transplantation is hampered by individual variability in metabolism, the lack of clinically available steroid blood levels, and overall little attention to steroid exposure. Many feel that steroids were an essential part of chronic immunosuppression in past decades but may no longer be necessary in low-risk populations when our newer and more potent drugs are used. Potential differences in long-term outcome will be unapparent in short-term antibody induction studies in low-risk patients, particularly with low on steroid doses, as may have happened in the recent, well-done Astellas trial. In many studies, the evidence for the superiority of mycophenolate (MMF) and tacrolimus (TAC) was not as strong as the evidence for the benefit of steroids in the Canadian cyclosporine study. As the practice of steroid withdrawal has increased, we have not seen the improvement in long-term graft survival that many expected with our newer agents. Steroids have immunosuppressive effects even in doses that are low by historic standards, and side effects may not justify their abandonment

Evaluation of Jatropha macrocarpa as an oil crop for biodiesel production in arid lands of the Dry Chaco, Argentina

Jatropha macrocarpa grows naturally in arid environments of the Dry Chaco, northwestern Argentina, where freezing winters make impossible the cultivation of other species of the genus Jatropha. This article is the first report of J. macrocarpa seed productivity aimed to quantify the reproductive performance and seed oil characteristics at different stages of fruit ripening. In addition, J. macrocarpa is evaluated as a new oil crop for biodiesel. Fruits from natural populations near La Rioja city were hand-harvested during the 2007/8 reproductive season and classified according to 7 fruit sizes, from the smallest fruits (G1) to the largest (G7 or mature). Total seed production averaged 87 ± 8 g plant-1 throughout the growing season. Explosive dehiscence of mature fruits produced 46% of total seed loss. Mature fruits produced individual seeds of 550 ± 7 mg with a medium-to-high seed oil concentration ranging from 36 to 40%, and biomass allocation to seeds was 36% of total fruit biomass. Fruits harvested early, at the G6 stage, were lighter and had a significantly less oil concentration. Main fatty acids in mature seeds included linoleic (50%), oleic (32%), palmitic (8.5%) and stearic (7%) acids. Biodiesel quality parameters indicated only slight differences for cetane number and iodine value with respect to European normative requirements. The acceptable oil content of J. macrocarpa shows promise to be used for biodiesel production. However, the low productivity per plant and the explosive fruit dehiscence need to be corrected substantially by breeding.Fil: Wassner, Diego Fernan. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cultivos Industriales; Argentina. Biogreenoil Argentina; ArgentinaFil: Larran, A.. Biogreenoil Argentina; ArgentinaFil: Rondanini, Deborah Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentin