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GaN grown via oxide vapor phase epitaxy (OVPE-GaN) can produce free-standing substrates with ultra-low resistivity because of the high doping concentration of oxygen. The bulk growth of OVPE-GaN is hindered by polycrystals generated during long-term growth. We have previously reported that thicker films can be grown by reducing the partial pressure of water vapor in the growth atmosphere with CH4. However, as CH4 is a dopant of carbon, a compensating acceptor, its addition may increase electrical resistance. In this study, we further investigated the effect of reducing water vapor partial pressure on polycrystals by combining Ga2O production (reaction of Ga and water vapor: a Ga–H2O system), which can reduce water vapor, with CH4 addition. However, CH4 addition to the Ga–H2O system increased polycrystal generation, possibly owing to the thermal decomposition of excess CH4. The properties of OVPE-GaN with CH4 addition were also evaluated. Although the CH4 addition resulted in high carbon doping, the carbon-doped OVPE-GaN maintained low resistivity. This is because the OVPE method involves three-dimensional growth with growth pits, and the growth pits leave behind low-resistivity high-oxygen-concentration regions. As the resistivity remains low even when CH4 is added in the OVPE method, both polycrystallization suppression and low resistivity can be achieved by selecting an appropriate CH4 flow rate. [ABSTRACT FROM AUTHOR]

Position-dependent three-dimensional reciprocal space mapping (RSM) by nanobeam x-ray diffraction (nanoXRD) was performed to reveal the strain fields produced around individual threading dislocations (TDs) in GaN substrates. The distribution and Burgers vector of TDs for the nanoXRD measurements were confirmed by prerequisite analysis of multi-photon excited photoluminescence and etch pit methods. The present results demonstrated that the nanoXRD can identify change in the lattice plane structure for all types of TDs, i.e., edge-, screw-, and mixed TDs with the Burgers vector of b = 1a, 1c and 1m + 1c. Strain tensor components related to edge and/or screw components of the TDs analyzed from the three-dimensional RSM data showed a nearly symmetrical strained region centered on the TD positions, which were in good agreements with simulation results based on the isotropic elastic theory using a particular Burgers vector. The present method is beneficial in that it allows non-destructive analysis of screw components of TDs that tend to contribute to leakage characteristics and are not routinely accessible by conventional structural analysis. These results indicate that nanoXRD could be a powerful way to reveal three-dimensional strain fields associated with arbitrary types of TDs in semiconductor materials, such as GaN and SiC. [ABSTRACT FROM AUTHOR]

The propagation behavior of threading dislocations (TDs) and the effects of Burgers vectors in hydride vapor phase epitaxy (HVPE) GaN bulk crystals generated on Na-flux-grown GaN and in a commercially available HVPE-grown GaN bulk crystal were investigated. Analyses based on chemical etching and transmission electron microscopy (TEM) revealed a close correlation between the etch pit sizes and the Burgers vector of these TDs. The existence of TDs with the unique Burgers vector b = 1m + 1c was observed for the first time ever using a large-angle convergent-beam electron diffraction technique and plan-view bright-field scanning TEM. Multi-photon excitation photoluminescence microscopy observations showed that TDs with b = 1c had a meandering morphology in contrast to the linear morphology of TDs with b = 1a, 1a + 1c, or 1m + 1c in both types of HVPE-grown GaN crystals. The inclinations of TDs with b = 1a and 1a + 1c in HVPE-grown GaN on Na-flux-grown GaN were greatly affected by large symmetrical hexagonal hillocks. The TDs with b = 1a were inclined in the slope directions of the hillock planes, while those with b = 1a + 1c were inclined in the a directions parallel or antiparallel to the a component in their Burgers vector. These inclinations were readily explained by the isotropic elastic theory of an individual TD. The hillocks were produced around pairs of parallel mixed TDs for which the a components were opposite to one another. This phenomenon was attributed to inclusions at the interface between the Na-flux-grown GaN substrate and the HVPE-grown layer. The origins of other TDs including unusual ones having b = 1m + 1c are also discussed herein. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to investigate the etiology of hearing loss (HL) based on the rate of its progression. Material and methods: Pure tone audiometry was conducted on 42,744 tests (9,269 cases) at Shinshu University Hospital between 2012 and 2022. Cases with unilateral HL, conductive HL, postoperative ear issues, functional hearing loss, and those with bilateral scaling-out at initial examination or lacking detailed data were excluded. A retrospective review was performed on 838 cases followed for over 5 years. Hearing progression was categorized as "Stable" (0-1 dB HL/year), "Slow progression" (1-3 dB HL/year), and "Fast progression" (>3 dB HL/year). Causes were classified as genetic, middle ear disease, Meniere's disease-related, other known causes, and unknown etiology. Results: Of the 838 cases, 302 were classified as "Stable", 402 as "Slow progression", and 134 as "Fast progression". Across all groups, unknown etiology was the predominant cause of HL, followed by genetic factors in Stable and Slow progression groups, and others in the Fast progression group. Regarding genetic etiology, the GJB2 and STRC genes were most prevalent in the Stable group, while genes such as SLC26A4 and CDH23 were identified across all groups. Conclusions: Regardless of progression rate, over half of bilateral HL cases had an unknown etiology. Genes such as GJB2 and STRC were identified to exhibit stable hearing, consistent with our findings. This study suggests that genes responsible for progressive HL manifest in an intermittent, rather than continuous, manner, highlighting the clinical utility of genetic testing, particularly in cases lacking long-term follow-up data. [ABSTRACT FROM AUTHOR]

Temporally- and spatially-resolved absorption and emission spectra were measured at various detection angles to examine NiO laser ablation at 266 nm. Ground states, excited states, lower lying states and other electronic states were differentiated from emission and absorption spectroscopy. Results show that excited Ni neutrals are produced mainly by the recombination of electrons and Ni+ ions.

Atherosclerotic lesions tend to localize at curvatures and branches of the arterial system, where the local flow is often disturbed and irregular (e.g., flow separation, recirculation, complex flow patterns, and nonuniform shear stress distributions). The effects of such flow conditions on cultured human umbilical vein endothelial cells (HUVECs) were studied in vitro by using a vertical-step flow channel (VSF). Detailed shear stress distributions and flow structures have been computed by using the finite volume method in a general curvilinear coordinate system. HUVECs in the reattachment areas with low shear stresses were generally rounded in shape. In contrast, the cells under higher shear stresses were significantly elongated and aligned with the flow direction, even for those in the area with reversed flow. When HUVECs were subjected to shearing in VSF, their actin stress fibers reorganized in association with the morphological changes. The rate of DNA synthesis in the vicinity of the flow reattachment area was higher than that in the laminar flow area. These in vitro experiments have provided data for the understanding of the in vivo responses of endothelial cells under complex flow environments found in regions of prevalence of atherosclerotic lesions.

A novel experimental method of producing and observing the active motion of polymorphonuclear leukocytes (PMNs) using a micropipette technique has been recently developed (Usami et al., 1992). The present paper develops a quantitative theory for the chemoattractant gradients and cell locomotion observed in these experiments. In previous experimental methods (e.g., the Boyden chamber, the Zygmond chamber and the Dunn chamber) for study chemotaxis of leukocytes, fibroblasts, and PMNs, the exact nature of the concentration gradient of the chemoattractant is unknown. The cells may themselves modify the local gradient of the chemoattractant. In experiments using the micropipette, an internal source of chemoattractant provides well-defined boundary and initial conditions which allow the computation of the chemoattractant concentration gradient during the active locomotion of the PMNs. Since the cell completely fills the pipette lumen, convection is limited to the motion of the cells themselves. In coordinates moving with cell, it is assumed that diffusion is the only mechanism of mass transport of the chemoattractant (fMLP). Computations of the fMLP concentration during locomotion of the cell were carried out for a range of rates of fMLP binding by the receptors expressed on the front face of the cell membrane. The results show that the front face of the cell is subjected to increasing fMLP concentration during the cell motion. The sequence of events involve receptor binding of fMLP, signal transduction, polymerization of the cell cytoskeleton at the membrane of the front face, spatially dependent adhesion to the pipette wall, and localized contraction of the cytoskeleton. This sequence of events leads to the steady locomotion of the leukocytes in the micropipette. The computation of the distribution of the fMLP concentration during cell locomotion with constant velocity in micropipette experiments shows that the cell is exposed to increasing concentration of fMLP. This suggests that chemotaxis maybe induced by temporal gradient of an attractant.

Introduction: Ecological studies have suggested the protective effect of micro-dose lithium in drinking water against suicide, however, the association between body lithium level and suicide is unknown. Objectives: We aimed to compare body lithium levels between suicide and non-suicide fatalities. Methods: This cross-sectional study included 12 suicides and 16 non-suicides who were examined or dissected at the Tokyo Medical Examiner's Office from March 2018 to June 2021. The aqueous humor lithium concentration was measured twice using inductively coupled plasma mass spectrometry. Analysis of covariance (ANCOVA) was used to compare the lithium concentration between suicides and non-suicides. Mixed-effects model was conducted to account for all lithium concentration data. Results: The aqueous humor lithium concentration did not change after death (t (7)=-0.70, SE=0.03, 95% CI=[-0.09, 0.05], P=0.51, Cohen's d =0.01). The aqueous humor lithium concentration was lower in suicides (mean 0.50 μg/L (variance s2 0.04)) than in non-suicides (mean 0.92 μg/L (s2 0.07)) (t (26)=4.47, SE=0.09, 95% CI=[0.22 to 0.61], P<0.001, Cohen's d =1.71). The ANCOVA showed that death by suicide was significantly associated with lower lithium concentration (F (1, 24)=8.57, P=0.007), and the effect size was large (ηp2 =0.26). The random intercept model showed a significant effect of suicide on aqueous humor lithium concentration (b=-0.261, SE=0.102, 95% CI=[-0.471 to -0.051], t(24)=-2.568, P=0.017). Conclusions: The results of this study demonstrate that even micro-dose lithium is associated with suicide death. Clinical studies are warranted to examine the effects of micro-dose lithium on suicide prevention. Disclosure of Interest: None Declared [ABSTRACT FROM AUTHOR]