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Electron paramagnetic resonance (EPR) and infrared absorption are used to detect Ir4+ ions in β-Ga2O3 crystals. Mg and Fe doped crystals are investigated, and concentrations of Ir4+ ions greater than 1 × 1018 cm−3 are observed. The source of the unintentional deep iridium donors is the crucible used to grow the crystal. In the Mg-doped crystals, the Ir4+ ions provide compensation for the singly ionized Mg acceptors and thus contribute to the difficulties in producing p-type behavior. The Ir4+ ions replace Ga3+ ions at the Ga(2) sites, with the six oxygen neighbors forming a distorted octahedron. A large spin-orbit coupling causes these Ir4+ ions to have a low-spin (5d5, S = 1/2) ground state. The EPR spectrum consists of one broad line with a significant angular dependence. Principal values of the g matrix are 2.662, 1.815, and 0.541 (with principal axes near the crystal a, b, and c directions, respectively). Ionizing radiation at 77 K decreases the Ir4+ EPR signal in Mg-doped crystals and increases the signal in Fe-doped crystals. In addition to the EPR spectrum, the Ir4+ ions have an infrared absorption band representing a d-d transition within the t2g orbitals. At room temperature, this band peaks near 5153 cm−1 (1.94 μm) and has a width of 17 cm−1. The band is highly polarized: its intensity is maximum when the electric field E is parallel to the b direction in the crystal and is nearly zero when E is along the c direction. [ABSTRACT FROM AUTHOR]

Conditions created by the COVID-19 pandemic have impacted many aspects of medical practice. Responding to this crisis has required health systems to rapidly address a multitude of concerns, including workforce safety, staff redeployment, supply shortages and physical space restructuring. The pace of change created by new information and evolving conditions has proven challenging for traditionally-structured academic departments in medicine. Pandemic medicine requires a nimbleness in decisionmaking, clarity of communication and comprehensiveness of services that may demand a temporary rearrangement of leadership structure and clinical service delivery. Furthermore, the uncertain nature of a pandemic may require reinstitution and dissolution of services as demand sporadically either rises or falls. As the global medical community continues to respond to what may be multiple COVID-19 peaks stretching over months or years, it is important that approaches to preparation and management of the pandemic are shared to enable the identification of best practices and an effective response. With the availability of open access and free communication technologies, these strategies can be easily shared among the global anaesthesia community. The approach outlined here represents one way to organise leadership and streamline communication in order to reinvent an academic department to match the dynamic requirements of crisis conditions. We describe our experience in offering new services such as an airway team, COVID-19 simulation training and personal protective equipment testing, as well as our approach to evaluating the rapid flow of research findings related to SARS-CoV-2 and COVID-19. We summarise lessons learnt and our adaptation to what may be a "new normal" in anaesthesiology practice. [ABSTRACT FROM AUTHOR]

Scanning probe deep-level transient spectroscopy (SP-DLTS) is applied to cross-sectioned, fully processed, commercially sourced AlGaN/GaN Schottky barrier diodes (SBDs) and high electron mobility transistors (HEMTs) biased in situ. The SBD and HEMT structures had been specially designed to allow two- and three-terminal biasing after cross-sectioning. The cross-sectioning procedure exposes electrically active regions throughout the length and depth of the devices while also preserving electrical functionality. Spatially resolved SP-DLTS surface potential transients (SPTs) measured on the appropriately cross-sectioned faces of the devices reveal the presence of two traps in the GaN buffer layer which are shown to be consistent with traps detected in macroscopic deep-level transient spectroscopy measurements performed on an intact AlGaN/GaN SBD made at the same time as the HEMT device. This indicates that, for an appropriate cross-sectioning process, the cross-sectioned surface does not screen or mask defects in the bulk GaN from the probe tip. SP-DLTS maps collected over the cross-sectioned faces in active device regions also reveal the spatial variation in trapping-induced SPTs. These measurements demonstrate an avenue for exploring the energies, concentrations, and spatial distributions of traps located throughout GaN-based devices with potential applications to other material and device systems. [ABSTRACT FROM AUTHOR]

The article focuses on the construction of two-piece pharyngeal dental prostheses. These dentures are constructed as an anterior maxillary appliance and a posterior component that is attached to the anterior component. Impression procedures are designed for reproducing the anterior maxillary arch and to define the velum or its remaining parts in a relaxed position. The maxillary dental component consists of a sagittal guide channel, which is used as a sleeve for a straight section of stainless wrought iron alloy. For pharyngeal extensions that are not subject to strong forces, the sleeve may be formed in the denture base resin of the denture.

Reports on a study which discussed the stochastic model for crystal amorphous transition in low temperature molecular beam epitaxy silicon. Kinetic and stochastic model characteristics; Experimental details; Results.

The science of instruction and training is founded on decades of research and practice. Moreover, the field continues to evolve as new theories, methods and practices emerge. A modern driver for this evolution has been the development of a vast array of instructional technologies. One of the newer technological advances is the use of virtual environments. This article considers how fundamental theories and findings from educational and training psychology may or may not apply in the world of virtual environments. In addition, apparent gaps are highlighted in the current knowledge base in order to foster ideas for future research. [ABSTRACT FROM AUTHOR]

The science of instruction and training is founded on decades of research and practice. Moreover, the field continues to evolve as new theories, methods and practices emerge. A modern driver for this evolution has been the development of a vast array of instructional technologies. One of the newer technological advances is the use of virtual environments. This article considers how fundamental theories and findings from educational and training psychology may or may not apply in the world of virtual environments. In addition, apparent gaps are highlighted in the current knowledge base in order to foster ideas for future research. [ABSTRACT FROM AUTHOR]

Employing exit-plane wave function (EPWF) reconstruction in high-resolution transmission electron microscopy (HRTEM), we have developed an approach to atomic scale compositional analysis of III-V semiconductor interfaces, especially suitable for analyzing quaternary heterostructures with intermixing in both cation and anion sub-lattices. Specifically, we use the focal-series reconstruction technique, which retrieves the complex-valued EPWF from a thru-focus series of HRTEM images. A study of interfaces in Al0.4Ga0.6As–GaAs and In0.25Ga0.75Sb–InAs heterostructures using focal-series reconstruction shows that change in chemical composition along individual atomic columns across an interface is discernible in the phase image of the reconstructed EPWF. To extract the interface composition profiles along the cation and anion sub-lattices, quantitative analysis of the phase image is performed using factorial analysis of correspondence. This enabled independent quantification of changes in the In–Ga and As–Sb contents across ultra-thin interfacial regions (approximately 0.6 nm wide) with true atomic resolution, in the In0.25Ga0.75Sb–InAs heterostructure. The validity of the method is demonstrated by analyzing simulated HRTEM images of an InAs–GaSb–InAs model structure with abrupt and graded interfaces. Our approach is general, permitting atomic-level compositional analysis of heterostructures with two species per sub-lattice, hitherto unfeasible with existing HRTEM methods. [ABSTRACT FROM AUTHOR]

The article discusses active portfolio management and examines a discussion of viewing portfolio construction as an optimization problem proposed by M. Barton Waring and Laurence B. Siegel. The author looks at assumptions made about the covariance structure of active return that are used in optimal portfolio structure. Using sensitivity analysis, the author finds that the degree of diversification in active returns and the sources of active return leads to variation in optimal portfolios. The author concludes that active portfolio management is made up of the level of active return, the volatility of active return, and the covariance structure of active return.

Developing neuronal populations undergo significant attrition by natural cell death. Dopaminergic neurons in the substantia nigra pars compacta undergo apoptosis during synaptogenesis. Following this time window, destruction of the anatomic target of dopaminergic neurons results in dopaminergic cell death but the morphology is no longer apoptotic. We describe ultrastructural changes that appear unique to dying embryonic dopaminergic neurons. In primary cultures of mesencephalon, death of dopaminergic neurons is triggered by activation of glutamate receptors sensitive to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and differs ultrastructurally from both neuronal apoptosis or typical excitotoxicity. AMPA causes morphological changes selectively in dopaminergic neurons, without affecting other neurons in the same culture dishes. Two hours after the onset of treatment swelling of Golgi complexes is apparent. At 3 h, dopaminergic neurons display loss of membrane asymmetry (coinciding with commitment to die), as well as nuclear membrane invagination, irregular aggregation of chromatin, and mitochondrial swelling. Nuclear changes continue to worsen until loss of cytoplasmic structures and cell death begins to occur after 12 h. These changes are different from those described in neurons undergoing either apoptosis or excitotoxic death, but are similar to ultrastructural changes observed in spontaneous death of dopaminergic neurons in the natural mutant weaver mouse. [ABSTRACT FROM AUTHOR]

Work was conducted on The University of Texas at Austin Prompt Gamma Activation Analysis Facility located on Beam Port 3 of the 1.1 MW Triga reactor at the Nuclear Engineering Teaching Laboratory. This effort required that the flux weighted detector efficiency be determined. Measurements of the neutron beam intensity as a function of spatial position over the target were conducted. In addition, the point-wise detector efficiency was mapped over the area where the neutron beam bus the sample. The flux-weighted efficiency was then calculated to match the sample geometry. This average efficiency was then utilized for quantitative analysis of the prompt gamma-ray spectra. [ABSTRACT FROM AUTHOR]

Prompt gamma activation analysis (PGAA) is a common technique for the identification of hydrogen and the measurement of hydrogen concentrations within a material. Carbon fiber reinforced epoxy matrix composites are materials that are known to absorb water. The experiments described herein demonstrate the feasibility of using PGAA to detect water absorption and desorption and show that PGAA measurements of hydrogen concentration are more sensitive to water absorption than gravimetric measurements. Hydrogen concentration measurements are made using PGAA after calibration with a boric acid solution sample. Relative changes in PGAA measurements generally agree with values expected based on gravimetric measurements. [ABSTRACT FROM AUTHOR]

An image simulation study is performed to investigate the applicability of exit-plane wave function (EPWF) images for an atomic-level compositional mapping of interfaces in the GaAs–AlAs system. A simple procedure for quantifying the composition across an interface, which is based on the method of factorial analysis of correspondence is proposed. A test of this procedure on a simulated EPWF-phase image of Al0.4Ga0.6As/GaAs/Al0.4Ga0.6As structure, with an atomically abrupt interface on one side and a graded interface on the other, yields profiles which mimic the model-profiles. [ABSTRACT FROM AUTHOR]

The use of light-weight, high-strength composite materials in motors, generators, and energy storage devices has become common as a means to maximize energy density. To ensure reliability, non-destructive and destructive evaluation techniques have been employed to measure the mechanical properties of fabricated components. In carbon fiber-reinforced, polymer matrix composites, mechanical strength is primarily derived from the fiber volume fraction. Due to the lack of a nondestructive method, common techniques for fiber volume determination are currently destructive. In this investigation, a non-destructive method for the measurement of the fiber volume fraction of carbon fiber-reinforced, polymer matrix composites has been developed using cold neutron prompt gamma activation analysis (PGAA). Fiber volume determination is accomplished in this technique by measuring and comparing the carbon and hydrogen content in a given sample (or samples). PGAA is a nuclear analytical technique performed by exposing a sample to neutron radiation. PGAA measurements are non-destructive and can be performed without chemical preparation of the sample. Fiber volumes of several composite coupons have been determined relative to standard samples of known fiber volume and measurements are in good agreement with values predicted by acid digestion tests. Fiber volume measurement using PGAA can potentially be applied to any composite material where the contents of the matrix and reinforcement differ. The technique can also be spatially sensitive, with resolution limited by the dimensions of the neutron beam that is used. [ABSTRACT FROM AUTHOR]

Surface dynamics dominate the temporal variation of reflection high energy electron diffraction (RHEED) intensity in the low temperature molecular beam epitaxy (MBE) of (100) gallium arsenide (GaAs). A rate equation model is proposed which includes the presence and dynamics of a physisorbed arsenic (PA) layer riding the growth surface. Using the results of the temporal evolution of the surface, the RHEED intensity is computed based on kinematical theory of electron diffraction with an As-As interplanar distance of 2.48 Å for the physisorbed As layer and a (100) Ga-As crystalline interplanar distance of 1.41 Å. The model results show ROs at low and high temperatures but not in the intermediate range of 300–450°C which is in good agreement with experiments. At low temperatures, the surface is covered by the PA layer whose vertical distribution across the layers depends upon that of the underlying crystalline surface. Thus a temporal variation of the step density of the crystalline GaAs surface results in step density variation of the PA layer which, in turn, yields ROs. Since the height of the PA layer is uniformly 2.48Å in this case, the RHEED beam sees a step height equal to the GaAs interplanar distance of 1.41Å, and the specular intensity of the RHEED beam will respond to the temporal variations in the underlying GaAs surface, yielding ROs if the growth is layer-by-layer. At high temperatures the crystalline GaAs is exposed to the RHEED beam due to evaporation of PA layer and the ROs appear due to periodic step density oscillations with a step height of 1.41Å which is the Ga-As crystalline interplanar distance. At intermediate temperatures, the partial coverage of the surface by the PA layer and crystalline GaAs, coupled with very different interplanar distances in these layers, results in a complete destructive interference of the RHEED intensity. The RO dependence on the As BEP is also presented and discussed. [ABSTRACT FROM AUTHOR]

Employing the focal-series reconstruction technique in high-resolution transmission electron microscopy, we obtained true atomic resolution images of interfacial disorder within cation and anion sublattices across interfaces in an InGaSb/InAs heterostructure. This enabled independent quantitative mapping of changes in the In–Ga and As–Sb contents across interfacial regions ∼0.6 nm in width. A comparison of the cation and anion sublattice images revealed that intermixing at the InGaSb-on-InAs interface is confined to the In–Ga sublattice. Also, atomic scale roughness within the As–Sb sublattice of the InAs-on-InGaSb interface was discerned. This approach is general, permitting atomic-scale compositional analysis of heterointerfaces with two species per sublattice. [ABSTRACT FROM AUTHOR]