Narrow emission linewidths of positioned InAs quantum dots grown on pre-patterned GaAs(100) substrates

We report photoluminescence measurements on a single layer of site-controlled InAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) on pre-patterned GaAs(100) substrates with a 15 nm re-growth buffer separating the dots from the re-growth interface. A process for cleaning the re-growth interface allows us to measure single dot emission linewidths of 80 μeV under non-resonant optical excitation, similar to that observed for self-assembled QDs. The dots reveal excitonic transitions confirmed by power dependence and fine structure splitting measurements. The emission wavelengths are stable, which indicates the absence of a fluctuating charge background in the sample and confirms the cleanliness of the re-growth interface.     

Amino acid enrichment and compositional changes among mammalian milk proteins and the resulting nutritional consequences

Milk is a hallmark of mammalian evolution: a unique food that has evolved with mammals. Despite the importance of this food, it is not known if variation in AA composition between different species is important to milk proteins or how it might affect the nutritional value of milk. As milk is the only food source for newborn mammals, it has long been speculated that milk proteins should be enriched in essential AA. However, no systematic analysis supports this assumption. Although many factors influence the overall nutritional value of milk, including total protein concentration, we focused here on the AA composition of milk proteins and investigated the possibility that selection drives compositional changes. We identified 9 major milk proteins present in 13 mammalian species and compared them with a large group of nonmilk proteins. Our results indicate heterogeneity in the AA composition of milk proteins, showing significant enrichment and depletion of certain AA in milk-specific proteins. Although high levels of particular AA appear to be consistently maintained, orthologous milk proteins display significant differences in AA composition across species, most notably among the caseins. Interspecies variation of milk composition is thought to be indicative of nutritional optimization to the requirements of the species. In accordance with this, our observations indicate that milk proteins may have adapted to the species-specific nutritional needs of the neonate.     

The stability and a.c. electrical characteristics of composites containing YBa2Cu3O7−x and alumina at elevated temperatures

Samples of a high-temperature superconductor YBa₂Cu₃O_7–x (orthorhombic phase) showed no significant weight loss in nitrogen up to 1173 K; however, differential thermal analysis measurements show that restructuring/decomposition begins around 1121 K. No reaction with alumina was found after prolonged heating at 1073 K. Electrical properties between 100 Hz and 1 MHz were generally stable at high temperatures, with little variation in properties at 1 MHz in inert and oxidizing atmospheres. Surface oxygen can be removed at high temperatures in flowing argon causing erratic electrical behaviour at lower frequencies and lower temperatures, which can be associated with changes in the oxygen content, x, and partial quenching to the high-temperature tetragonal phase. Stability and electrical tests after pretreatment of YBCO-alumina composites at 933 K in CO₂ or steam showed partial decomposition to BaCO₃, CuO and Y₂Cu₂O₅ and a phase transition from orthorhombic to tetragonal in the YBa₂Cu₃O_7–x . The original state could be retrieved by calcination in air at73 K.     

Evolution of GaAs quantum well excitons with excess electron density and magnetic field

We present an experimental study of excitonic optical transitions in GaAs quantum wells (QWs) as a function of their excess electron density and an applied magnetic field. There is a dramatic weakening of the neutral excitonic transitions (X) upon adding 10¹⁰ cm⁻² excess electrons to the QW, accompanied by strengthening of the transition due to the negatively-charged exciton (X⁻) to lower energy. Increasing the density further causes X to be completely quenched from the spectra, while X⁻ evolves smoothly into the Fermi-edge singularity. A qualitatively different evolution with an applied magnetic field is observed for X and X⁻, the former showing similar behaviour to that in undoped QWs. Assignment of the X⁻ transition is confirmed by its partial circular light polarization in excitation spectra taken at field, caused by the higher population of excess electrons in the lower energy spin state at low temperature. There is a large enhancement of the second electron binding energy with magnetic field, which stabilizes excited (spin-triplet) X⁻ states.     

Theory of mercury porosimetry hysteresis

Intrusion—extrusion hysteresis and energy conservation in mercury porosimetry can be explained thermodynamically. In a first intrusion—extrusion cycle, hysteresis is explained and work is shown to be conserved when the processes of mercury entrapment and contact angle changes are considered. In subsequent cycles, when mercury entrapment ceases, it can be shown that work is conserved and hysteresis can be explained by the use of the correct intrusion and extrusion contact angles.     

Relapse as a nonlinear dynamic system: Application to patients with alcohol use disorders.

Understanding the relapse process is one of the most important issues in addictive behaviors research. To date, most studies have taken a linear approach toward predicting relapse based on risk factors. Nonlinear dynamical systems theory can be used to describe processes that are not adequately modeled using a linear approach. In particular, the authors propose that catastrophe theory, a subset of nonlinear dynamical systems theory, can be used to describe the relapse process in addictive behaviors. Two small prospective studies using 6-month follow-ups of patients with alcohol use disorders (inpatient, n=51; outpatient, n=43) illustrate how cusp catastrophe theory may be used to predict relapse. Results from these preliminary studies indicate that a cusp catastrophe model has more predictive utility than traditional linear models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of human beta2-microglobulin on major histocompatibility complex I peptide loading and the engineering of a high affinity variant. Implications for peptide-based vaccines

The ability to directly load cell surface major histocompatibility complex (MHC) class I molecules with peptides provides a potentially powerful approach toward the development of vaccines to generate cell-mediated immunity. We demonstrate that exogenous beta2-microglobulin (beta2m) stabilizes human cell surface MHC I molecules and facilitates their loading with exogenous peptides. Additionally, using three-dimensional crystal structures and known interaction sites between MHC I heavy chains and beta2m, we engineered variants of human beta2m (hbeta2m) with a single serine substitution at residue 55. This alteration was predicted to promote hydrophobic interactions at the MHC I heavy chain/beta2m interface and displace an ordered water molecule. Compared with hbeta2m, the serine to valine substitution at residue 55 had improved ability to bind to cell surface HLA-A1, HLA-A2, and HLA-A3 molecules, facilitate exogenous peptide loading, and promote recognition by peptide-specific T cells. The inclusion of hbeta2m or higher affinity variants when pulsing cells with MHC-restricted peptides increases the efficiency of peptide loading 50-80-fold. Therefore, the inclusion of hbeta2m in peptide-based vaccines may increase cell surface antigen densities above thresholds that allow recognition of peptide antigens by the immune system, particularly for cryptic, subdominant, or marginally antigenic peptides.     

A comprehensive review of sedative and analgesic agents

Transforming growth factor-beta proteins are key regulators of cellular growth and differentiation. To understand the role of TGF-beta in colonic tumour progression, 47 paraffin embedded samples from colonic tumours (13 adenomas, and 34 adenocarcinomas) were studied. Gene mutations in the region coding for the active protein were studied by PCR SSCP analysis of exons 5, 6, and 7. TGF-beta1 mRNA expression and localization were studied by NISH using cDNA probes generated by RT-PCR. Protein distribution was investigated by immunohistochemistry using antibodies against both intracellular and extracellular forms. Three mutations were found: one in exon 5 (Dukes C) and two in exon 7 (Dukes C and A). TGF-beta1 mRNA was observed in 9 (69%) of 13 adenomas and in 30 (88%) of 34 adenocarcinomas. Levels of TGF-beta1 mRNA and proteins were higher in colorectal carcinomas than in colorectal adenomas. Tubular adenomas associated with dysplasia showed greater expression of TGF-beta1 than adenomas without dysplasia and than non-neoplastic colonic mucosa. In dysplasia and cancer, epithelial neoplastic cells and stromal cells were positive for TGF-beta1. In normal tissue endothelial cells and granulocytes sporadically showed immunoreactivity for TGF-beta1, whereas epithelial cells were all negative. The three mutations in TGF-beta1 exons 5, 6 and 7 found in colorectal adenocarcinomas suggest that TGF-beta1 mutation may play a role in colorectal carcinogenesis and that the presence of the mutant form contributes to the transformed state. Our two other findings, the loss of staining gradient in normal colonic mucosa and the higher levels of TGF-beta1 mRNA and proteins in colorectal carcinomas than in colorectal adenomas, indicate that the de-regulation of TGF-beta1 expression may occur as an early event in colorectal carcinogenesis. Although TGF-beta1 expression is generally a reflection of cellular differentiation, tumour grade is not associated with TGF-beta1 mRNA expression. Beside being present in the epithelial cells of the colonic tumours, TGF-beta1 mRNA also occurred in the stroma: its localization in the macrophages adjacent to tumour strongly suggests that TGF-beta1 could be secreted by macrophages. This hypothesis should lead to new therapeutic strategies for colorectal carcinoma.