Tilted-wing-induced stress distribution in epitaxial lateral overgrown GaN

Epitaxial lateral overgrowth (ELO) is one of the most extensively studied techniques used to improve the mismatched heteroepitaxy of GaN on sapphire (-Al₂O₃) substrates. In this method, a mask is first deposited over the GaN seed layer and parallel windows are opened along a specific direction in the mask. GaN is grown vertically at the window position and then grows laterally along the mask surface (wing region). The adjacent GaN regions will coalesce to form a continuous film if enough growth time is used. The impact of the ELO of GaN on sapphire substrates using a SiO₂ mask is measured with the white beam synchrotron X-ray topography technique. The topography results show that the crystal planes in the laterally overgrown regions (wings) are tilted. The maximum wing tilt is about 0.36° at a fill factor of 0.5 (fill factor measures the window width relative to the window width plus SiO₂ mask width). High-resolution micro-Raman spectroscopy stress-mapping measurements, using Ar⁺ 488-nm laser excitation, indicate that the GaN epilayer is under compressive stress, as is expected from the growth conditions. The measured average compressive stress is about 460 MPa. Furthermore, a wave-like stress field is observed in the ELO GaN epilayer. The wave valley (low compressive stress region) is usually located at the coalesced region between two adjacent wings. In general, these coalesced regions exhibit about 60 MPa lower compressive stress than the average stress in the ELO epilayer. Voids formed by the tilted wings at the coalesced region are regarded as a possible reason for the lower compressive stress in the coalesced region.     

A simple one-dimensional model for the explanation and analysis ofGaAs MESFET behavior

The explanation of GaAs metal-semiconductor field effect transistor (MESFET) operation often involves the use of simplistic analytical formulae, which serve to obscure the more subtle physics of device action. The authors consider here a simple one-dimensional (1-D) model for GaAs MESFETs, which avoids more confusing numerical modeling schemes, yet still facilitates an analysis of the physical functionality of the device. The model takes into account current saturation due to either velocity saturation or channel pinch-off, the modulation of effective gate length and the series resistance of the regions beyond the gate. The results of the model have been compared to experimental data readily obtained from the literature, and the agreement has been shown to be good     

Cognitive processing of trauma cues in adults reporting repressed, recovered, or continuous memories of childhood sexual abuse.

Psychologically traumatized people exhibit delayed color naming of trauma words in the emotional Stroop task. Four groups of participants were asked to color name positive words, neutral words, and trauma words; these groups included 15 women who believed that they harbored repressed memories of childhood sexual abuse (CSA), 13 women who reported recovered memories of CSA, 15 women who had never forgotten their CSA, and 12 women who had never been abused. Repressed-memory participants exhibited patterns of interference indistinguishable from those of the nonabused control group participants. Irrespective of group membership, the severity of self-reported posttraumatic stress disorder symptoms was the only significant predictor of trauma-related interference, r(48)?=?.30?, p?     

Idiopathic thrombocytopenic purpura in a liver transplant recipient with previous primary biliary cirrhosis

The loss of immunotolerance has been implicated in the pathogenesis of both primary biliary cirrhosis (PBC) and idiopathic, immune-mediated thrombocytopenic purpura (ITP). An association between these two autoimmune diseases has been well described. We describe a 41-year-old woman in whom ITP developed 457 days after liver transplantation for PBC while receiving immunosuppressive medications sufficient to maintain allograft function. Our case report, the first to describe post-transplant ITP in association with PBC, demonstrates the persistence of the underlying immune dysregulation of PBC after transplantation. The practice of decreasing the dosage of immunosuppressive medication to maintenance levels after transplantation may unmask the effects of this defect in immunotolerance.     

Synergistic effect of glucose and prolactin on GLUT2 expression in cultured neonatal rat islets

We studied the synergistic effect of glucose and prolactin (PRL) on insulin secretion and GLUT2 expression in cultured neonatal rat islets. After 7 days in culture, basal insulin secretion (2.8 mM glucose) was similar in control and PRL-treated islets (1.84 +/- 0.06% and 2.08 +/- 0.07% of the islet insulin content, respectively). At 5.6 and 22 mM glucose, insulin secretion was significantly higher in PRL-treated than in control islets, achieving 1.38 +/- 0.15% and 3.09 +/- 0.21% of the islet insulin content in control and 2.43 +/- 0.16% and 4.31 +/- 0.24% of the islet insulin content in PRL-treated islets, respectively. The expression of the glucose transporter GLUT2 in B-cell membranes was dose-dependently increased by exposure of the islet to increasing glucose concentrations. This effect was potentiated in islets cultured for 7 days in the presence of 2 micrograms/ml PRL. At 5.6 and 10 mM glucose, the increase in GLUT2 expression in PRL-treated islets was 75% and 150% higher than that registered in the respective control. The data presented here indicate that insulin secretion, induced by different concentrations of glucose, correlates well with the expression of the B-cell-specific glucose transporter GLUT2 in pancreatic islets.     

Film-induced negative affect triggers overeating in restrained eaters.

We tested the effects of film-induced negative affect (i.e., exposure to a frightening film) in 60 women classified as either restrained or unrestrained eaters on the basis of their responses to the Revised Restraint Scale (C. P. Herman and J. Polivy, 1980). Exposure to the frightening film, in contrast to a neutral film, was associated with increases in anxiety, sadness, and anger. High restraint subjects exposed to the frightening film ate more than did equally restrained subjects exposed to a neutral film or low restraint subjects exposed to either film. Thus, negative affect triggered overeating among restrained eaters. Although unrestrained eaters exposed to the frightening film ate less than those who viewed the neutral film, this difference was not statistically significant. These results suggest that negative affect may prompt overeating in persons who attempt to restrict their caloric intake. (PsycINFO Database Record (c) 2010 APA, all rights reserved)