Detection of anomalous Hall voltages in ultrahigh-mobility two-dimensional hole gases generated by optical spin orientation

By combining optical spin orientation and an externally applied longitudinal electric field, transverse charge accumulation has been detected in very high-mobility two-dimensional hole gases by measuring the transverse voltage drop across simple Hall devices. Our results indicate intrinsic band-structure (rather than extrinsic skew scattering) derived spin-orbit coupling as the underlying mechanism of this spin-polarized transport effect.This work was supported by the EPSRC.This is the author accepted manuscript. The final version was first published by APS at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.201406

Experimental progress towards probing the ground state of an electron-hole bilayer by low-temperature transport

Recently, it has been possible to design independently contacted electron-hole bilayers (EHBLs) with carrierdensities  cm2 in each layer and a separation of 10–20 nm in a GaAs/AlGaAs system. In these EHBLs,the interlayer interaction can be stronger than the intralayer interactions. Theoretical works have indicated thepossibility of a very rich phase diagram in EHBLs consisting of excitonic superfluid phases, charge densitywaves, and Wigner crystals. Experiments have revealed that the Coulomb drag on the hole layer shows strongnonmonotonic deviations from a behaviour expected for Fermi-liquids at low temperatures. Simultaneously,an unexpected insulating behaviour in the single-layer resistances (at a highly “metallic” regime with) also appears in both layers despite electron mobilities of above and hole mobilitiesover . Experimental data also indicates that the point of equal densities () is not special.Peer Reviewe

Scaling behavior of the directed percolation universality class

In this work we consider five different lattice models which exhibit continuous phase transitions into absorbing states. By measuring certain universal functions, which characterize the steady state as well as the dynamical scaling behavior, we present clear numerical evidence that all models belong to the universality class of directed percolation. Since the considered models are characterized by different interaction details the obtained universal scaling plots are an impressive manifestation of the universality of directed percolation.Comment: 24 pages, 7 figures, accepted for publication in Nuclear Physics

Streetsport: Supporting and facilitating the development of enhanced graduate attributes.

Streetsport is a programme that aims to exercise social innovation by reducing instances of youth crime and anti-social behaviour; whilst promoting health and wellbeing through sport, physical activity and creative endeavour. As a vehicle for delivery the initiative facilitates work based educational experiences that are embedded within disadvantaged communities; supporting the development of enhanced graduate attributes by way of collaborative teaching and learning support. Adopting a collaborative partnership model, the programme brings together multiple courses, students and stakeholders to work within communities resulting in activities that react and respond to local needs, interests and demand

Changes in calcium dynamics following the reversal of the sodium-calcium exchanger have a key role in AMPA receptor-mediated neurodegeneration via calpain activation in hippocampal neurons

Proteolytic cleavage of the Na(+)/Ca(2+) exchanger (NCX) by calpains impairs calcium homeostasis, leading to a delayed calcium overload and excitotoxic cell death. However, it is not known whether reversal of the exchanger contributes to activate calpains and trigger neuronal death. We investigated the role of the reversal of the NCX in Ca(2+) dynamics, calpain activation and cell viability, in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-stimulated hippocampal neurons. Selective overactivation of AMPA receptors caused the reversal of the NCX, which accounted for approximately 30% of the rise in intracellular free calcium concentration ([Ca(2+)](i)). The NCX reverse-mode inhibitor, 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea (KB-R7943), partially inhibited the initial increase in [Ca(2+)](i), and prevented a delayed increase in [Ca(2+)](i). In parallel, overactivation of AMPA receptors strongly activated calpains and led to the proteolysis of NCX3. KB-R7943 prevented calpain activation, cleavage of NCX3 and was neuroprotective. Silencing of NCX3 reduced Ca(2+) uptake, calpain activation and was neuroprotective. Our data show for the first time that NCX reversal is an early event following AMPA receptor stimulation and is linked to the activation of calpains. Since calpain activation subsequently inactivates NCX, causing a secondary Ca(2+) entry, NCX may be viewed as a new suicide substrate operating in a Ca(2+)-dependent loop that triggers cell death and as a target for neuroprotectio

Fatigue strength of common tibial intramedullary nail distal locking screws

Premature failure of either the nail and/or locking screws with unstable fracture patterns may lead to angulation, shortening, malunion, and IM nail migration. Up to thirty percent of all unreamed nail locking screws can break after initial weight bearing is allowed at 8–10 weeks if union has not occurred. The primary problem this presents is hardware removal during revision surgery. The purposes of our study was to evaluate the relative fatigue resistance of distal locking screws and bolts from representative manufacturers of tibial IM nail systems, and develop a relative risk assessment of screws and materials used. Evaluations included quantitative and qualitative measures of the relative performance of these screws

The density and peculiar velocity fields of nearby galaxies

We review the quantitative science that can be and has been done with redshift and peculiar velocity surveys of galaxies in the nearby universe. After a brief background setting the cosmological context for this work, the first part of this review focuses on redshift surveys. The practical issues of how redshift surveys are carried out, and how one turns a distribution of galaxies into a smoothed density field, are discussed. Then follows a description of major redshift surveys that have been done, and the local cosmography out to 8,000 km/s that they have mapped. We then discuss in some detail the various quantitative cosmological tests that can be carried out with redshift data. The second half of this review concentrates on peculiar velocity studies, beginning with a thorough review of existing techniques. After discussing the various biases which plague peculiar velocity work, we survey quantitative analyses done with peculiar velocity surveys alone, and finally with the combination of data from both redshift and peculiar velocity surveys. The data presented rule out the standard Cold Dark Matter model, although several variants of Cold Dark Matter with more power on large scales fare better. All the data are consistent with the hypothesis that the initial density field had a Gaussian distribution, although one cannot rule out broad classes of non-Gaussian models. Comparison of the peculiar velocity and density fields constrains the Cosmological Density Parameter. The results here are consistent with a flat universe with mild biasing of the galaxies relative to dark matter, although open universe models are by no means ruled out.Comment: In press, Physics Reports. 153 pages. gzip'ed postscript of text plus 20 embedded figures. Also available via anonymous ftp at ftp://eku.ias.edu/pub/strauss/review/physrep.p

Treatment of diaphyseal non-unions of the ulna and radius

Non-unions of the forearm often cause severe dysfunction of the forearm as they affect the interosseus membrane, elbow and wrist. Treatment of these non-unions can be challenging due to poor bone stock, broken hardware, scarring and stiffness due to long-term immobilisation. We retrospectively reviewed a large cohort of forearm non-unions treated by using a uniform surgical approach during a period of 33 years (1975-2008) in a single trauma centre. All non-unions were managed following the AO-principles of compression plate fixation and autologous bone grafting if needed. The study cohort consisted of 47 patients with 51 non-unions of the radius and/or ulna. The initial injury was a fracture of the diaphyseal radius and ulna in 22 patients, an isolated fracture of the diaphyseal ulna in 13, an isolated fracture of the diaphyseal radius in 5, a Monteggia fracture in 5, and a Galeazzi fracture-dislocation of the forearm in 2 patients. Index surgery for non-union consisted of open reduction and plate fixation in combination with a graft in 30 cases (59%), open reduction and plate fixation alone in 14 cases (27%), and only a graft in 7 cases (14%). The functional result was assessed in accordance to the system used by Anderson and colleagues. Average follow-up time was 75 months (range 12-315 months). All non-unions healed within a median of 7 months. According to the system of Anderson and colleagues, 29 patients (62%) had an excellent result, 8 (17%) had a satisfactory result, and 10 (21%) had an unsatisfactory result. Complications were seen in six patients (13%). Our results show that treatment of diaphyseal forearm non-unions using classic techniques of compression plating osteosynthesis and autologous bone grafting if needed will lead to a high union rate (100% in our series). Despite clinical and radiographic bone healing, however, a substantial subset of patients will have a less than optimal functional outcom

A Common Ca2+-Driven Interdomain Module Governs Eukaryotic NCX Regulation

Na+/Ca2+ exchanger (NCX) proteins mediate Ca2+-fluxes across the cell membrane to maintain Ca2+ homeostasis in many cell types. Eukaryotic NCX contains Ca2+-binding regulatory domains, CBD1 and CBD2. Ca2+ binding to a primary sensor (Ca3-Ca4 sites) on CBD1 activates mammalian NCXs, whereas CALX, a Drosophila NCX ortholog, displays an inhibitory response to regulatory Ca2+. To further elucidate the underlying regulatory mechanisms, we determined the 2.7 Å crystal structure of mammalian CBD12-E454K, a two-domain construct that retains wild-type properties. In conjunction with stopped-flow kinetics and SAXS (small-angle X-ray scattering) analyses of CBD12 mutants, we show that Ca2+ binding to Ca3-Ca4 sites tethers the domains via a network of interdomain salt-bridges. This Ca2+-driven interdomain switch controls slow dissociation of “occluded” Ca2+ from the primary sensor and thus dictates Ca2+ sensing dynamics. In the Ca2+-bound conformation, the interdomain angle of CBD12 is very similar in NCX and CALX, meaning that the interdomain distances cannot account for regulatory diversity in NCX and CALX. Since the two-domain interface is nearly identical among eukaryotic NCXs, including CALX, we suggest that the Ca2+-driven interdomain switch described here represents a general mechanism for initial conduction of regulatory signals in NCX variants