Structural perfection in poorly lattice matched heterostructures

Continuum elastic theory is applied to the formation of misfit dislocations and point defects in strained layer structures. Explicit calculations of the energies of misfit dislocations in the double‐ and single‐kink geometries yield line tensions below which strained films are stable with respect to defect formation. Our results yield a mismatch‐dependent stability limit which, in the double kink case, differs from the Matthews–Blakeslee model by a geometrical factor and by the addition of a stress term associated with climb of the misfit dislocation. While our calculations yield equilibrium stability limits which may not correspond to observed critical thicknesses, the calculated stresses may be applied to descriptions of the kinetics of strain relief in films grown beyond these limits. Last, calculations of strain‐related contributions to the free energy of formation of point defects suggest a contribution │ΔG_(strain)│ ≃0.25 eV for a 5% lattice mismatch. This suggests a means of suppressing or enhancing the formation of vacancies or interstitials in semiconductors favoring these defects

Oceanic wave measurement system

An oceanic wave measured system is disclosed wherein wave height is sensed by a barometer mounted on a buoy. The distance between the trough and crest of a wave is monitored by sequentially detecting positive and negative peaks of the output of the barometer and by combining (adding) each set of two successive half cycle peaks. The timing of this measurement is achieved by detecting the period of a half cycle of wave motion

Health chatbots acceptability moderated by perceived stigma and severity: A cross-sectional survey

Background: Chatbots and virtual voice assistants are increasingly common in primary care without sufficient evidence for their feasibility and effectiveness. We aimed to assess how perceived stigma and severity of various health issues are associated with the acceptability for three sources of health information and consultation: an automated chatbot, a General Practitioner (GP), or a combination of both. Methods: Between May and June 2019, we conducted an online study, advertised via Facebook, for UK citizens. It was a factorial simulation experiment with three within-subject factors (perceived health issue stigma, severity, and consultation source) and six between-subject covariates. Acceptability rating for each consultation source was the dependant variable. A single mixed-model ANOVA was performed. Results: Amongst 237 participants (65% aged over 45 years old, 73% women), GP consultations were seen as most acceptable, followed by GP-chatbot service. Chatbots were seen least acceptable as a consultation source for severe health issues, while the acceptability was significantly higher for stigmatised health issues. No associations between participants’ characteristics and acceptability were found. Conclusions: Although healthcare professionals are perceived as the most desired sources of health information, chatbots may be useful for sensitive health issues in which disclosure of personal information is challenging. However, chatbots are less acceptable for health issues of higher severity and should not be recommended for use within that context. Policymakers and digital service designers need to recognise the limitations of health chatbots. Future research should establish a set of health topics most suitable for chatbot-led interventions and primary healthcare services

Periodic point data detects subdynamics in entropy rank one

A framework for understanding the geometry of continuous actions of Z^d was developed by Boyle and Lind using the notion of expansive behaviour along lower-dimensional subspaces. For algebraic Zd-actions of entropy rank one, the expansive subdynamics are readily described in terms of Lyapunov exponents. Here we show that periodic point counts for elements of an entropy rank-one action determine the expansive subdynamics. Moreover, the finer structure of the non-expansive set is visible in the topological and smooth structure of a set of functions associated to the periodic point data

A dichotomy in orbit growth for commuting automorphisms

We consider asymptotic orbit-counting problems for certain expansive actions by commuting automorphisms of compact groups. A dichotomy is found between systems with asymptotically more periodic orbits than the topological entropy predicts, and those for which there is no excess of periodic orbits

Structure of CdTe/ZnTe superlattices

The structure of CdTe/ZnTe superlattices has been analyzed through θ/2θ x‐ray diffraction, photoluminescence, and in situ reflection high‐energy electron diffraction (RHEED) measurements. Samples are found to break away from Cd_(x)Zn_(1−x)Te buffer layers as a consequence of the 6% lattice mismatch in this system. However, defect densities in these superlattices are seen to drop dramatically away from the buffer layer interface, accounting for the intense photoluminescence and high‐average strain fields seen in each of our samples. Observed variations in residual strains suggest that growth conditions play a role in forming misfit defects. This could explain discrepancies with calculated values of critical thickness based on models which neglect growth conditions. Photoluminescence spectra reveal that layer‐to‐layer growth proceeded with single monolayer uniformity, suggesting highly reproducible growth. Our results give hope for relatively defect‐free Cd_(x)Zn_(1−x)Te/Cd_(y)Zn_(1−y)Te superlattices with the potential for applications to optoelectronics offered by intense visible light emitters

Migrant workers’ exercise of agency during the COVID-19 pandemic in the UK: resilience, reworking and resistance

Drawing on qualitative data, we apply Katz’s conceptual framework of agency as resilience, reworking and resistance practices to theorise UK migrant workers’ responses to worsened employment conditions, stress of unemployment and reduced incomes during the pandemic. We draw attention to the range of micro practices they adopted to survive and rework existing conditions to their advantage - actions which rarely feature in academic writing, yet which recognise those who do not ‘resist’ as conscious agents who exercise power. Meanwhile, although outright oppositional responses to deteriorating employment conditions are rare, we demonstrate the nature of workplace union representation as a central factor in resisting managerial control. We extend Katz’s framework by considering the ‘how’ and ‘why’ behind migrant workers’ responses, to understand better their dynamic choices of resilience, reworking and resistance practices in the chaotic circumstances of the pandemic

Type II superlattices for infrared detectors and devices

Superlattices consisting of combinations of III-V semiconductors with type II band alignments are of interest for infrared applications because their energy gaps can be made smaller than those of any 'natural' III-V compounds. Specifically, it has been demonstrated that both InSb/InAsxSb1-x superlattices and Ga1-xInxSb/InAs superlattices can possess energy gaps in the 8-14 mu m range. The efforts have focused on the Ga1-xInxSb/InAs system because of its extreme broken gap band alignment, which results in narrow energy gaps for very short superlattice periods. The authors report the use of in situ chemical doping of Ga1-xInxSb/InAs superlattices to fabricate p-n photodiodes. These diodes display a clear photovoltaic response with a threshold near 12 mu m. They have also attained outstanding structural quality in Ga1-xInxSb/InAs superlattices grown on radiatively heated GaSb substrates. Cross-sectional transmission electron microscope images of these superlattices display no dislocations, while high resolution X-ray diffraction scans reveal sharp high-order superlattice satellites and strong Pendellosung fringes