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Objectives: Studies of neurocognitively elite older adults, termed SuperAgers, have identified clinical predictors and neurobiological indicators of resilience against age-related neurocognitive decline. Despite rising rates of older persons living with HIV (PLWH), SuperAging (SA) in PLWH remains undefined. We aimed to establish neuropsychological criteria for SA in PLWH and examined clinically relevant correlates of SA. Methods: 734 PLWH and 123 HIV-uninfected participants between 50 and 64 years of age underwent neuropsychological and neuromedical evaluations. SA was defined as demographically corrected (i.e., sex, race/ethnicity, education) global neurocognitive performance within normal range for 25-year-olds. Remaining participants were labeled cognitively normal (CN) or impaired (CI) based on actual age. Chi-square and analysis of variance tests examined HIV group differences on neurocognitive status and demographics. Within PLWH, neurocognitive status differences were tested on HIV disease characteristics, medical comorbidities, and everyday functioning. Multinomial logistic regression explored independent predictors of neurocognitive status. Results: Neurocognitive status rates and demographic characteristics differed between PLWH (SA=17%; CN=38%; CI=45%) and HIV-uninfected participants (SA=35%; CN=55%; CI=11%). In PLWH, neurocognitive groups were comparable on demographic and HIV disease characteristics. Younger age, higher verbal IQ, absence of diabetes, fewer depressive symptoms, and lifetime cannabis use disorder increased likelihood of SA. SA reported increased independence in everyday functioning, employment, and health-related quality of life than non-SA. Conclusions: Despite combined neurological risk of aging and HIV, youthful neurocognitive performance is possible for older PLWH. SA relates to improved real-world functioning and may be better explained by cognitive reserve and maintenance of cardiometabolic and mental health than HIV disease severity. Future research investigating biomarker and lifestyle (e.g., physical activity) correlates of SA may help identify modifiable neuroprotective factors against HIV-related neurobiological aging. (JINS, 2019, 25, 507–519)
The deep subsurface of other planetary bodies is of special interest for robotic and human exploration. The subsurface provides access to planetary interior processes, thus yielding insights into planetary formation and evolution. On Mars, the subsurface might harbour the most habitable conditions. In the context of human exploration, the subsurface can provide refugia for habitation from extreme surface conditions. We describe the fifth Mine Analogue Research (MINAR 5) programme at 1 km depth in the Boulby Mine, UK in collaboration with Spaceward Bound NASA and the Kalam Centre, India, to test instruments and methods for the robotic and human exploration of deep environments on the Moon and Mars. The geological context in Permian evaporites provides an analogue to evaporitic materials on other planetary bodies such as Mars. A wide range of sample acquisition instruments (NASA drills, Small Planetary Impulse Tool (SPLIT) robotic hammer, universal sampling bags), analytical instruments (Raman spectroscopy, Close-Up Imager, Minion DNA sequencing technology, methane stable isotope analysis, biomolecule and metabolic life detection instruments) and environmental monitoring equipment (passive air particle sampler, particle detectors and environmental monitoring equipment) was deployed in an integrated campaign. Investigations included studying the geochemical signatures of chloride and sulphate evaporitic minerals, testing methods for life detection and planetary protection around human-tended operations, and investigations on the radiation environment of the deep subsurface. The MINAR analogue activity occurs in an active mine, showing how the development of space exploration technology can be used to contribute to addressing immediate Earth-based challenges. During the campaign, in collaboration with European Space Agency (ESA), MINAR was used for astronaut familiarization with future exploration tools and techniques. The campaign was used to develop primary and secondary school and primary to secondary transition curriculum materials on-site during the campaign which was focused on a classroom extra vehicular activity simulation.
Stormwater catch basins form part of artificial drainage systems in urban areas and can provide larval habitat for mosquito vector species of West Nile virus (WNv), such as Culex pipiens Linnaeus (Diptera: Culicidae). We evaluated the impact of management techniques and targeted applications of larvicide on larval populations of this potential WNv mosquito vector species in catch basins from the Lower Mainland of Vancouver and on Vancouver Island of British Columbia, Canada. A mixed effects logistic regression model described the relationship between larval presence and larvicide treatment while controlling for other parameters. Parameter estimates showed that larvicide treatment reduced the odds of larvae presence by a factor of ∼7.23. The model also revealed relationships between larval presence and water temperature and adjacent land use but larvicide treatment consistently reduced the presence of larvae regardless of these other factors. This knowledge can now be used to prioritise and target control efforts to most efficiently reduce WNv mosquito vector populations, and most effectively reduce the risk of WNv transmission to humans. A similar research strategy could be applied to emerging threats from other potential mosquito vectors of disease around the world, to help lower the incidence of mosquito-borne disease.
Studies of recently isolated populations are useful because observed differences can often be attributed to current environmental variation. Two populations of the lizard Anolis lemurinus have been isolated on the islands of Cayo Menor and Cayo Mayor in the Cayos Cochinos Archipelago of Honduras for less than 15 000 y. We measured 12 morphometric and 10 habitat-use variables on 220 lizards across these islands in 2 y, 2008 and 2009. The goals of our study were (1) to explore patterns of sexual dimorphism, and (2) to test the hypothesis that differences in environment among islands may have driven divergence in morphology and habitat use despite genetic homogeneity among populations. Although we found no differences among sexes in habitat use, males had narrower pelvic girdles and longer toe pads on both islands. Between islands, males differed in morphology, but neither males nor females differed in habitat use. Our data suggest that either recent selection has operated differentially on males despite low genetic differentiation, or that they display phenotypic plasticity in response to environmental variation. We suggest that patterns may be driven by variation in intrapopulation density or differences in predator diversity among islands.
Tantalum, being a refractory metal, is sensitive to ambient impurities when forming a silicide. By introducing nitrogen and oxygen impurities into a tantalum-silicon system, interesting chemical and physical effects are observed in their subsequent reactions. Nitrogen and oxygen behave similarly in such a system. If initially present in Ta, they segregate into the still unreacted Ta as the silicide layer grows at a somewhat retarded rate. The same impurities, initially present in Si, are immobile in the form of stable compouis and suppress TaSi2 growth. The rare isotopes 15N and 18O are introduced bY implantation and Profiled by 15N(P,α)12C and 18O(P,α)15N nuclear reaction analyses, respectively. In addition, unintentionally incorporated 18O is checked by the 16O(d,α) 14N nuclear reaction. The results are explained in terms of the moving species Si, and of the chemical affinity, solubility and diffusivity of the impurities in their host lattice.
The use of spun-on liquids to form ohmic and Schottky barrier contacts on Si has been investigated. Two commercially available metallo-organic solutions containing Au or Pt were applied to Si substrates by spinning techniques. The Au or Pt contacts were then formed by annealing at 250°C or 450°C respectively. The metallurgical interactions between the spun-on Au or Pt layers and the Si substrate were investigated by MeV backscattering spectrometry and X-ray diffraction as a function of the annealing temperature. The resulting electrical characteristics were investigated with four point probe, I-V and C-V techniques. It was found that the spun-on Au or Pt films react with Si substrates at much higher temperatures than those deposited by vacuum evaporation. The diode characteristics of the spun-on Au films are comparable to those of evaporated Au films ( φB ∼0.85V, n ∼1.08), whereas diode characteristics of spunon Pt films show no linear region on the ln I-V curve. The application of spun-on Au also improves the bondability of Si chips on Mo headers.
ErSi2 contacts formed by reacting Er with single crystal silicon using conventional furnace heat treatment are dominated by pits. Recently rapid electron and laser beam heating have been used to form pit-free ErSi 2 layers on Si by reacting Er with the Si substrate. For this investigation we studied the electrical properties of erbium silicide/Si<p,100> contact prepared by thermal, laser and electron beam annealing. We prepared and annealed three types of samples; (I) Er(600Å)/Si<p,100>, (II) Si(100Å)/ Er(600Å)/Si<p,100> and (III) Si(900Å)/Er(600Å)/Si<p,100>.The barrier height of the pit-free thermal annealed samples (type III) was ∼0.78 eV. All laser and e-beam annealed samples were observed to be pit-free. The barrier heights for the laser annealed samples varied from ∼ 0.63 eV for type I samples to ∼ 0.77 eV for type III samples. The e-beam annealed samples gave barrier heights ∼ 0.71 eV (type I and II) and ∼ 0.77 eV for type III. The barrier heights of beam processed diodes shifted towards the 0.78 eV range upon post-annealing. We model these results in terms of defects created at the ErSi2-Si interface.
Refractory metal silicides have been shown to form stable Schottky barriers on GaAs up to an annealing temperature of ∼850°C. In this study, the metallurgical and electrical stability of near noble metal (Pd and Pt) silicide contacts to GaAs have been investigated. It is observed that Pd and Pt silicides are metallurgically more stable than Pd and Pt alone on GaAs. A correlation between the stability of silicide contacts and the heat of formation of the silicides normalized to per metal atom is found, thus allowing the prediction of contact stability of other silicides on GaAs. We have also investigated the feasibility of using solid-phase epitaxy (SPE) to grow a highly doped Ge epitaxial layer on GaAs to form a non-alloyed ohmic contact. This approach of forming a Ge/GaAs heterojunction alleviates the high vacuum requirement of MBE techniques. Our preliminary results indicate that relatively low contact resistivities can be obtained by SPE using the Ge-Sb-Pd system.
Qualitatively, the basic principles behind the operation of OLEDs are well established. In order to optimize device parameters such as power efficiency and operating voltage, to explore the limits of performance and to understand changes in the electrical properties as diodes age, it is necessary to develop a quantitative understanding of each of the relevant processes: injection of electrons and holes at the cathode and anode, charge transport, recombination and exciton formation, and emission. In this paper, we summarize our experimental, theoretical and numerical studies to address these issues.
New and emerging process technologies such as Damascene interconnect, metal gate and metal silicide processes are creating metal contamination control challenges for current and future generations of integrated circuits. In this work, we studied the contamination of oxidized silicon wafers by several metals of industrial importance including copper, cobalt, sodium, iron and nickel. Contamination was applied by spin-coating in a range from 20ppb to 500 ppb. Such levels are representative of exposure challenges induced during chemical processes such as CMP (chemical mechanical planarization) cleans. Solvated contamination ions were driven into the oxide layer by corona temperature stress (CTS). The concentrations of metallic species incorporated within the oxide by CTS were quantified using VPD-ICPMS (vapor phase decomposition) and SIMS (secondary ion mass spectrometry) surface analysis techniques. Noncontact COCOS (Corona Oxide Characterization of Semiconductor) methods were employed to measure the electrical properties and reliability of nascent and contaminated oxide/silicon structures. We show that in the absence of significant signals from the surface analysis techniques the COCOS methods show signatures of the metallic contamination in the measurement results.
Ab Initio calculations of various configurations of In2Se3 compounds are used to gain insight into the transition from crystalline to amorphous phase. The structures considered are based on wurzite structures with 1/3 of indium sites vacant as observed experimentally. From extensive calculations for possible vacancy configurations in In2Se3 compounds, predictions based on the local coordination of In/Se atoms are made for the energetically favorable vacancy ordering structures. Results indicate that in the most stable In vacancy configurations, Se atoms have coordination of either 2 or 3 (In atoms have coordination of 4). Other coordinations lead to significantly higher formation energies. Results from analyzing the total energy and electronic structure of a range of off-stoichiometry, including vacancies, interstitials and anti-site, configurations, suggest that the energetically most favorable way to form In-rich material is via incorporation of Se vacancies, while Se occupying a vacant site is the most favorable for formation of Se-rich phase. Based on these calculations, predictions are made on how stoichiometry deviations impact structural evolution during phase change.
Titanium nitride (TiN) is a candidate material for hard and wear resistant coatings on metallic substrates such as titanium (Ti), stainless steel and aluminum. Coating processes include chemical vapor deposition, ion implantation, plasma and thermal nitriding under vacuum and controlled environments. The motivation for the present research is to develop a laser plasma process for high rate formation of TiN coatings on Ti substrates at near-atmospheric pressures. Laser induced plasma generated by a pulsed CO2 laser was used to excite a Ti substrate. The species in the vapor plume were characterized by optical emission spectroscopy. Spatially and temporally resolved spectral characterization was performed as a function of laser power, position of the substrate relative to the focal plane, pulse parameters, and shielding gases. These experiments are a first step in understanding laser assisted plasma deposition of nitride/oxy-nitride coatings on titanium metal under atmospheric conditions. Results indicate a window of optimal process parameters for developing titanium nitride coatings.