Influence of Processing Techniques on Copper Deep Levels Formation and on Photoconductivity in Silicon Doped Gallium Arsenide

Diffusion of copper in silicon doped gallium arsenide under different diffusion conditions is studied. Copper compensated silicon doped gallium arsenide (GaAs:Si:Cu) is used as switch material for bulk optically controlled semiconductor switch, and on-state photoconductivity of the switch is primarily due to the properties of the copper deep levels introduced in the material during diffusion. Gallium arsenide being a compound semiconductor, presence of vacancies and defects make the study of diffusion a complex process. The objective of the current research is twofold: a) to study the influence of diffusion conditions and processing techniques on copper deep level formation in silicon doped gallium arsenide (GaAs:Si) and b) to fabricate a switch material with high photoconductive gain so that low power semiconductor lasers can be used as the excitation source for closing the switch. Influence of different diffusion parameters, in particular, arsenic vapor pressure on the diffusion of copper and copper deep level formation in GaAs:Si is studied. Three different diffusion techniques, namely, closed tube diffusion, semi-closed tube diffusion, and leaky tube diffusion are used to diffuse copper in GaAs:Si. The diffusion of copper in GaAs is studied for the first time in the present work using the leaky tube diffusion technique, and the results show that it is the best among the three techniques studied, to diffuse copper to obtain high efficiency switch material. Photoinduced current transient spectroscopy (PICTS) and van der Pauw-Hall measurements are used to characterize the diffused samples. Various deep levels present in the diffused samples are identified and the variation of the characteristics of these levels with diffusion conditions is analyzed. PICTS spectra of GaAs:Si:Cu samples processed using different techniques are found to be strikingly different. Deep level structure at different depths from the surface of the GaAs:Si:Cu crystal annealed using the closed tube diffusion technique has been studied using the PICTS, and the results indicated the presence of a gradient in the copper related levels in the material. In leaky tube diffusion, the gradient effect is minimized by providing a source of copper on both surfaces of the sample and protecting the surfaces by silicon dioxide coating. Based on the characterization results, models for different copper related complexes have been identified, Vas CuGa VAs (arsenic vacancy is denoted as Vas and copper in gallium site is denoted as CuqJ and CuGa), and CuGa for CuB and CuA respectively. Photoconductivity of the GaAs:Si:Cu switches fabricated using the three different techniques is measured and found that switches fabricated using the leaky tube diffusion technique are the most efficient among the three. The efficiency of the leaky tube samples is high enough to use low power semiconductor laser diode as the excitation source

Molecular Pathways of Notch Signaling in Vascular Smooth Muscle Cells

Notch signaling in the cardiovascular system is important during embryonic development, vascular repair of injury, and vascular pathology in humans. The vascular smooth muscle cell (VSMC) expresses multiple Notch receptors throughout its life cycle, and responds to Notch ligands as a regulatory mechanism of differentiation, recruitment to growing vessels, and maturation. The goal of this review is to provide an overview of the current understanding of the molecular basis for Notch regulation of VSMC phenotype. Further, we will explore Notch interaction with other signaling pathways important in VSMC

Replacing home visits with telephone calls to support parents implementing a sleep management intervention : findings from a pilot study and implications for future research

Background - Resource constraints may inhibit the provision of appropriate interventions for children with neurodisabilities presenting with behavioural sleep problems. Telephone calls (TC), as opposed to home visits (HV), may be a more resource efficient means of supporting these families. Objective - To conduct a preliminary investigation exploring the feasibility and acceptability of replacing HV with TC to support parents implementing sleep management strategies and to gather evidence to inform the design and methods of a full trial. Methods - Parents referred to a sleep management intervention routinely delivered by a community paediatric team were alternately allocated to receive implementation support via HV (n = 7) or TC (n = 8). Activity logs recorded the frequency, duration and mode of support. Parents and practitioners were interviewed about their experiences of receiving/delivering the intervention. Results - Intervention drop-out was low, the frequency, number of contacts and intervention duration appeared comparable. Parents allocated TC received less contact time. Parents valued implementation support irrespective of delivery mode and practitioners reported that despite initial reservations, implementation support via TC appeared to work well. Conclusions - TC appears an acceptable and convenient mode of delivering sleep support, valued by both parents and practitioners. We recommend a full-scale trial to investigate effectiveness

The impact of increased food availability on reproduction in a long-distance migratory songbird: implications for environmental change?

Many populations of migratory songbirds are declining or shifting in distribution. This is likely due to environmental changes that alter factors such as food availability that may have an impact on survival and/or breeding success. We tested the impact of experimentally supplemented food on the breeding success over three years of northern wheatears (Oenanthe oenanthe), a species in decline over much of Europe. The number of offspring fledged over the season was higher for food-supplemented birds than for control birds. The mechanisms for this effect were that food supplementation advanced breeding date, which, together with increased resources, allowed further breeding attempts. While food supplementation did not increase the clutch size, hatching success or number of chicks fledged per breeding attempt, it did increase chick size in one year of the study. The increased breeding success was greater for males than females; males could attempt to rear simultaneous broods with multiple females as well as attempting second broods, whereas females could only increase their breeding effort via second broods. Multiple brooding is rare in the study population, but this study demonstrates the potential for changes in food availability to affect wheatear breeding productivity, primarily via phenotypic flexibility in the number of breeding attempts. Our results have implications for our understanding of how wheatears may respond to natural changes in food availability due to climate changes or changes in habitat management

GP Participation and Recruitment of Patients to RCTs: Lessons from Trials of Acupuncture and Exercise for Low Back Pain in Primary Care

The objective of this study was to identify factors associated with general practitioner (GP) participation and the recruitment of people to trials in primary care, based on data from two trials of interventions for treating chronic low back pain. The study was based on data from two randomized controlled trials (RCTs), one involving exercise, the other acupuncture, and subsequent reporting by GPs in a postal questionnaire. The exercise trial achieved 62% recruitment whereas the acupuncture trial achieved 100% recruitment. In both trials GPs most efficient at referring patients were those with a special interest in the subject area, and those known personally to the research team. A follow-up GP questionnaire found that both trials had maintained a high profile with over 80% of GPs, and successful recruitment strategies included project reminder letters, updates and personal contacts. Achieving target recruitment of patients in the acupuncture trial was aided by the deliberate application of lessons learned in the exercise trial, in particular the need to keep initial study entry criteria broad, with subsequent filtering undertaken by the study researcher. In addition the use of effective methods of maintaining the trial profile, the involvement of a GP advisor, the decision to maximize the recruitment of GPs early in the trial and the direct recruitment of interested individual GPs. The successful recruitment of patients to trials in primary care requires careful planning and continuous monitoring from the outset. Prior to starting recruitment, it is useful to identify previous trials in a similar environment in order to learn from their experience and optimize patient recruitment

A generalized precession parameter χp\chi_\mathrm{p} to interpret gravitational-wave data

Originally designed for waveform approximants, the effective precession parameter $\chi_\mathrm{p}$ is the most commonly used quantity to characterize spin-precession effects in gravitational-wave observations of black-hole binary coalescences. We point out that the current definition of $\chi_\mathrm{p}$ retains some, but not all, variations taking place on the precession timescale. We rectify this inconsistency and propose more general definitions that either fully consider or fully average those oscillations. Our generalized parameter $\chi_\mathrm{p}\in[0,2]$ presents an exclusive region $\chi_\mathrm{p}>1$ that can only be populated by binaries with two precessing spins. We apply our prescriptions to current LIGO/Virgo events and find that posterior distributions of $\chi_\mathrm{p}$ tend to show longer tails at larger values. This appears to be a generic feature, implying that (i) current $\chi_\mathrm{p}$ measurement errors might be underestimated, but also that (ii) evidence for spin precession in current data might be stronger than previously inferred. Among the gravitational-wave events released to date, that which shows the most striking behavior is GW190521.Comment: 12 pages, 6 figures, 1 table. Published in PRD. Software available at https://github.com/dgerosa/generalizedchi

Reducing Plasmodium falciparum malaria transmission in Africa: a model-based evaluation of intervention strategies.

BACKGROUND: Over the past decade malaria intervention coverage has been scaled up across Africa. However, it remains unclear what overall reduction in transmission is achievable using currently available tools. METHODS AND FINDINGS: We developed an individual-based simulation model for Plasmodium falciparum transmission in an African context incorporating the three major vector species (Anopheles gambiae s.s., An. arabiensis, and An. funestus) with parameters obtained by fitting to parasite prevalence data from 34 transmission settings across Africa. We incorporated the effect of the switch to artemisinin-combination therapy (ACT) and increasing coverage of long-lasting insecticide treated nets (LLINs) from the year 2000 onwards. We then explored the impact on transmission of continued roll-out of LLINs, additional rounds of indoor residual spraying (IRS), mass screening and treatment (MSAT), and a future RTS,S/AS01 vaccine in six representative settings with varying transmission intensity (as summarized by the annual entomological inoculation rate, EIR: 1 setting with low, 3 with moderate, and 2 with high EIRs), vector-species combinations, and patterns of seasonality. In all settings we considered a realistic target of 80% coverage of interventions. In the low-transmission setting (EIR approximately 3 ibppy [infectious bites per person per year]), LLINs have the potential to reduce malaria transmission to low levels (90%) or novel tools and/or substantial social improvements will be required, although considerable reductions in prevalence can be achieved with existing tools and realistic coverage levels. CONCLUSIONS: Interventions using current tools can result in major reductions in P. falciparum malaria transmission and the associated disease burden in Africa. Reduction to the 1% parasite prevalence threshold is possible in low- to moderate-transmission settings when vectors are primarily endophilic (indoor-resting), provided a comprehensive and sustained intervention program is achieved through roll-out of interventions. In high-transmission settings and those in which vectors are mainly exophilic (outdoor-resting), additional new tools that target exophagic (outdoor-biting), exophilic, and partly zoophagic mosquitoes will be required