Spin-orbit fields in asymmetric (001)-oriented GaAs/AlxGa 1-xAs quantum wells

We measure simultaneously the in-plane electron g factor and spin-relaxation rate in a series of undoped inversion-asymmetric (001)-oriented GaAs/AlGaAs quantum wells by spin-quantum beat spectroscopy. In combination the two quantities reveal the absolute values of both the Rashba and the Dresselhaus coefficients and prove that the Rashba coefficient can be negligibly small despite huge conduction-band potential gradients which break the inversion symmetry. The negligible Rashba coefficient is a consequence of the "isomorphism" of conduction- and valence-band potentials in quantum systems where the asymmetry is solely produced by alloy variations. © 2011 American Physical Society

Effect of symmetry reduction on the spin dynamics of (001)-oriented GaAs quantum wells

Spin quantum beat spectroscopy is employed to investigate the in-plane anisotropy of the spin dynamics in (001) GaAs/AlGaAs quantum wells induced by an external electric field. This technique allows the anisotropy of the spin relaxation rate Γs and the electron Landé g factor g* to be measured simultaneously. The measurements are compared to similar data from (001) GaAs/AlGaAs quantum wells with applied shear strain and asymmetric barrier growth. All of these operations act to reduce the symmetry compared to that of a symmetric (001) quantum well in an identical manner (D2d → C2v). However, by looking at the anisotropy of both Γs and g* simultaneously we show that the microscopic actions of these symmetry breaking operations are very different. The experiments attest that although symmetry arguments are a very useful tool to identify the allowed spin dependent properties of a material system, only a microscopic approach reveals if allowed anisotropies will manifest. © 2013 American Physical Society

Nonlinear birefringence and time-resolved Kerr measurement of spin lifetimes in (110) GaAs/AlyGa1-yAs quantum wells

We report a study of the nonlinear birefringence in undoped (110)-oriented GaAs/AlGaAs quantum wells using time-resolved pump-probe Kerr spectroscopy. Due to the optical anisotropy of the (110) quantum well plane, photoexcited carriers can give rise to a nonlinear birefringence and so cause probe polarization rotation independent of the pump polarization, i.e., independent of spin orientation. We develop a methodology for accurate determination of electron-spin lifetimes using the Kerr technique which takes account of this phenomenon and present room-temperature measurements of wavelength and power density dependence of the spin-relaxation rate.<br/

Reducing bias in trials due to reactions to measurement: experts produced recommendations informed by evidence

Objective: This study (MEasurement Reactions In Trials) aimed to produce recommendations on how best to minimize bias from measurement reactivity (MR) in randomized controlled trials of interventions to improve health. Study design and setting: The MERIT study consisted of: (1) an updated systematic review that examined whether measuring participants had effects on participants’ health-related behaviors, relative to no-measurement controls, and three rapid reviews to identify: (i) existing guidance on MR; (ii) existing systematic reviews of studies that have quantified the effects of measurement on behavioral or affective outcomes; and (iii) studies that have investigated the effects of objective measurements of behavior on health-related behavior; (2) a Delphi study to identify the scope of the recommendations; and (3) an expert workshop in October 2018 to discuss potential recommendations in groups. Results: Fourteen recommendations were produced by the expert group to: (1) identify whether bias is likely to be a problem for a trial; (2) decide whether to collect data about whether bias is likely to be a problem; (3) design trials to minimize the likelihood of this bias. Conclusion: These recommendations raise awareness of how and where taking measurements can produce bias in trials, and are thus helpful for trial design

A Steady-Hand Robotic System for Microsurgical Augmentation

: This paper reports the development of a robotic system designed to extend a human&apos;s ability to perform small-scale (sub-millimeter) manipulation tasks requiring human judgement, sensory integration and hand-eye coordination. Our novel approach, which we call &quot;steady hand&quot; micromanipulation, is for tools to be held simultaneously both by the operator&apos;s hand and a specially designed actively controlled robot arm. The robot&apos;s controller senses forces exerted by the operator on the tool and by the tool on the environment, and uses this information in various control modes to provide smooth, tremor-free precise positional control and force scaling. Our goal is to develop a manipulation system with the precision and sensitivity of a machine, but with the manipulative transparency and immediacy of hand-held tools for tasks characterized by compliant or semi-rigid contacts with the environment. 1. Introduction This paper describes the first steps in an ongoing development of a robotic assi..

A comprehensive neuropsychiatric study of elderly twins: The Older Australian Twins Study

The Older Australian Twins Study (OATS) was recently initiated to investigate genetic and environmental factors and their associations and interactions in healthy brain ageing and ageing-related neurocognitive disorders. The study extends the classic MZ-DZ design to include one or two equivalently aged siblings for each twin pair and utilizes the rich resources of the Australian Twin Registry. The study has a number of distinguishing features including comprehensive psychiatric, neuropsychological, cardiovascular, metabolic, and neuroimaging assessments, a longitudinal design and links with a brain donor program. The study measures many behavioral and environmental factors, but in particular lifetime physical and mental activity, physical and psychological trauma, loss of parent early in life, later losses and life events, early-life socioeconomic environment, alcohol and drug use, occupational exposure, and nutrition. It also includes comprehensive cardiovascular assessment, blood biochemistry, genetics and proteomics. The socio-demographic and health data on the first 172 pairs of twins participating in this study are presented. Prevalence of mild cognitive impairment is 12.8% and of dementia 1.5% in the sample. The target sample size is 1000, with at least 400 pairs of twins aged 65-90 years. The cohort will be assessed every two years, with in-depth assessments being repeated. OATS offers an excellent opportunity for collaboration with other similar studies as well as researchers who share the same interests