NaAlSi: a self-doped semimetallic superconductor with free electrons and covalent holes

The layered ternary sp conductor NaAlSi, possessing the iron-pnictide "111" crystal structure, superconducts at 7 K. Using density functional methods, we show that this compound is an intrinsic (self-doped) low-carrier-density semimetal with a number of unusual features. Covalent Al-Si valence bands provide the holes, and free-electron-like Al 3s bands, which propagate in the channel between the neighboring Si layers, dip just below the Fermi level to create the electron carriers. The Fermi level (and therefore the superconducting carriers) lies in a narrow and sharp peak within a pseudogap in the density of states. The small peak arises from valence bands which are nearly of pure Si, quasi-two-dimensional, flat, and coupled to Al conduction bands. Isostructural NaAlGe, which is not superconducting above 1.6 K, has almost exactly the same band structure except for one missing piece of small Fermi surface. Certain deformation potentials induced by Si and Na displacements along the c-axis are calculated and discussed. It seems likely that the mechanism of pairing is related to that of several other lightly doped two-dimensional nonmagnetic semiconductors (TiNCl, ZrNCl, HfNCl), which is not well understood but apparently not of phonon origin.Comment: 9 pages, 7 figures, 1 tabl

Exercise training to improve brain health in older people living with HIV: Study protocol for a randomized controlled trial

BACKGROUND: With the advent of antiretrovirals, people living with HIV are living near-normal lifespans. However, people living with HIV are at greater risk of experiencing cognitive impairment and reduced brain integrity despite well-controlled viremia. A robust literature supports exercise interventions as a method of improving cognition and structural brain integrity in older individuals without HIV. The effects of exercise on cardiometabolic, neurocognitive, and neural structures in middle-aged to older people living with HIV are less well known, with few prospective studies examining these measures. OBJECTIVE: This prospective randomized clinical trial will examine the effects of a 6-month exercise training intervention compared to a 6-month stretching intervention (control) on cardiorespiratory fitness, physical function and strength, cognition, and neuroimaging measures of brain volumes and cerebral blood flow in people living with HIV. METHODS: Sedentary middle-aged to older people living with HIV (ages≥40; n=150) with undetectable HIV viral load (\u3c20 copies/mL) will be enrolled in the study. At the baseline and final visit, fasting plasma lipid, insulin, glucose, and brain neurotrophic factor concentrations; cardiorespiratory fitness; cognitive performance; brain volumes; and cerebral blood flow via a magnetic resonance imaging scan will be measured. Participants will be randomized in a 2:1 ratio to either the exercise or control stretching intervention. All participants will complete their assigned programs at a community fitness center 3 times a week for 6 months. A professional fitness trainer will provide personal training guidance at all sessions for individuals enrolled in both arms. Individuals randomized to the exercise intervention will perform endurance and strength training exercises, while those randomized to the control intervention will perform stretches to increase flexibility. A midpoint visit (at 3 months) will assess cognitive performance, and at the end point visit, subjects will undergo cardiorespiratory fitness and cognition testing, and a magnetic resonance imaging scan. Physical activity throughout the duration of the trial will be recorded using an actigraph. RESULTS: Recruitment and data collection are complete as of December 2020. Data processing, cleaning, and organization are complete as of December 2021. Data analysis began in January 2022, with the publication of study results for primary aims 1 and 2 expected by early 2023. CONCLUSIONS: This study will investigate the effects of a 6-month aerobic and resistance exercise training intervention to improve cardiometabolic risk factors, cognitive performance, cerebral structure, and blood flow in sedentary people living with HIV. Results will inform clinicians and patients of the potential benefits of a structured aerobic exercise training program on the cognitive, functional, and cardiometabolic health status of older people living with HIV. Assessment of compliance will inform the development and implementation of future exercise programs for people living with HIV. TRIAL REGISTRATION: ClinicalTrials.gov NCT02663934; https://clinicaltrials.gov/ct2/show/NCT02663934. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/41421

P and S velocity sturcture of the crust and the upper mantle beneath Central Java from local tomography inversion

Here we present the results of local source tomographic inversion beneath central Java. The data set was collected by a temporary seismic network. More than 100 stations were operated for almost half a year. About 13,000 P and S arrival times from 292 events were used to obtain three-dimensional (3-D) Vp, Vs, and Vp/Vs models of the crust and the mantle wedge beneath central Java. Source location and determination of the 3-D velocity models were performed simultaneously based on a new iterative tomographic algorithm, LOTOS-06. Final event locations clearly image the shape of the subduction zone beneath central Java. The dipping angle of the slab increases gradually from almost horizontal to about 70°. A double seismic zone is observed in the slab between 80 and 150 km depth. The most striking feature of the resulting P and S models is a pronounced low-velocity anomaly in the crust, just north of the volcanic arc (Merapi-Lawu anomaly (MLA)). An algorithm for estimation of the amplitude value, which is presented in the paper, shows that the difference between the fore arc and MLA velocities at a depth of 10 km reaches 30% and 36% in P and S models, respectively. The value of the Vp/Vs ratio inside the MLA is more than 1.9. This shows a probable high content of fluids and partial melts within the crust. In the upper mantle we observe an inclined low-velocity anomaly which links the cluster of seismicity at 100 km depth with MLA. This anomaly might reflect ascending paths of fluids released from the slab. The reliability of all these patterns was tested thoroughly

Environmental surveying and surveillance

© Springer International Publishing AG 2018. In this section, we discuss the quantitative and qualitative data that could be collected using GNSS satellites, and in so doing, attempt to answer the question “what can GNSS satellites deliver that are of use to environmental monitoring?” The observed parameters necessary for environmental monitoring vary, depending upon the indicators being assessed. Some are physical variables such as changes in soil patterns, vegetation, rainfall, water levels, temperature, deforestation, solar and UV radiation. Others are chemical variables, e.g., pH, salinity, nutrients, metals, pesticides, while others are biological variables, e.g., species types, ecosystem health, and indicator species