Efficient Electrical Spin Injection from a Magnetic Metal / Tunnel Barrier Contact into a Semiconductor

We report electrical spin injection from a ferromagnetic metal contact into a semiconductor light emitting diode structure with an injection efficiency of 30% which persists to room temperature. The Schottky barrier formed at the Fe/AlGaAs interface provides a natural tunnel barrier for injection of spin polarized electrons under reverse bias. These carriers radiatively recombine, emitting circularly polarized light, and the quantum selection rules relating the optical and carrier spin polarizations provide a quantitative, model-independent measure of injection efficiency. This demonstrates that spin injecting contacts can be formed using a widely employed contact methodology, providing a ready pathway for the integration of spin transport into semiconductor processing technology.Comment: 14 pages including 3 figures, version accepted by Applied Physics Letters - A. Hanbicki, et al. Appl. Phys. Lett. 80 (7), p.TBD (2002

Internal transitions of negatively charged magneto-excitons and many body effects in a two-dimensional electron gas

Spin-singlet and spin-triplet internal transitions of quasi-two-dimensional, negatively charged magneto-excitons (X-) and their evolution with excess electron density have been studied in GaAs/AlGaAs quantum-wells by optically detected resonance (ODR) spectroscopy. In the dilute electron limit, due to magnetic translational invariance, the ODR spectra are dominated by bound-to-continuum bands in contrast to the superficially similar negatively-charged-donor system D-, which exhibits strictly bound-to-bound transitions. With increasing excess electron density in the wells in the magnetic field region corresponding to Landau level filling factors nu < 2 the X- like transitions are blue-shifted; they are absent for nu > 2. The blue-shifted transitions are explained in terms of a new type of collective excitation -- magnetoplasmons bound to a mobile valence band hole, which demonstrates the many-body nature of "exciton-like" magnetoluminescence for nu < 2.Comment: 11 pages + 3 figures, final version accepted in PR

The impact of iron limitation on the physiology of the Antarctic diatom Chaetoceros simplex

Iron availability strongly governs the growth of Southern Ocean phytoplankton. To investigate how iron limitation affects photosynthesis as well as the uptake of carbon and iron in the Antarctic diatom Chaetoceros simplex, a combination of chlorophyll a fluorescence measurements and radiotracer incubations in the presence and absence of chemical inhibitors was conducted. Iron limitation in C. simplex led to a decline in growth rates, photochemical efficiency and structural changes in photosystem II (PSII), including a reorganisation of photosynthetic units in PSII and an increase in size of the functional absorption cross section of PSII. Iron-limited cells further exhibited a reduced plastoquinone pool and decreased photosynthetic electron transport rate, while non-photochemical quenching and relative xanthophyll pigment content were strongly increased, suggesting a photoprotective response. Additionally, iron limitation resulted in a strong decline in carbon fixation and thus the particulate organic carbon quotas. Inhibitor studies demonstrated that, independent of the iron supply, carbon fixation was dependent on internal, but not on extracellular carbonic anhydrase activity. Orthovanadate more strongly inhibited iron uptake in iron-limited cells, indicating that P-type ATPase transporters are involved in iron uptake. The stronger reduction in iron uptake by ascorbate in iron-limited cells suggests that the re-oxidation of iron is required before it can be taken up and further supports the presence of a high-affinity iron transport pathway. The measured changes to photosystem architecture and shifts in carbon and iron uptake strategies in C. simplex as a result of iron limitation provide evidence for a complex interaction of these processes to balance the iron requirements for photosynthesis and carbon demand for sustained growth in iron-limited waters. © 2014 The Author(s)

A national register for surveillance of inherited disorders: beta thalassaemia in the United Kingdom

OBJECTIVE: To demonstrate the value of a national register for surveillance of services for an inherited disorder. METHODS: Data from the United Kingdom Thalassaemia Register and the United Kingdom Register of Prenatal Diagnosis for Haemoglobin Disorders were combined in a database; these registers include all fetuses known to have been diagnosed with beta thalassaemia major, beta thalassaemia intermedia, or haemoglobin E/beta thalassaemia in the United Kingdom. Data were extracted to show outcomes (selective abortion or live birth) of all fetuses and the status of those born with a disorder (alive, dead, successful bone marrow transplant, or lost to follow-up) by parents' region of residence and ethnicity. FINDINGS: At the end of 1999 the register included 1074 patients, 807 of whom were alive and residing in the United Kingdom. A successful bone marrow transplant has been performed for 117 out of 581 (20%) patients born since 1975. Residents of Pakistani origin are now the main group at risk in the United Kingdom, replacing residents of Cypriot origin. This has led to a marked shift in the need for services from the south-east of England to the Midlands and the north of England. Despite the acceptability of prenatal diagnosis, the proportion of affected births remains 50% higher than would be expected, reflecting a widespread failure to deliver timely screening and counselling to carriers. Even though effective treatment is available the annual number of deaths is rising, indicating that better tolerated treatments are needed. CONCLUSION: A national diagnosis register is a powerful instrument for monitoring the treatment and prevention of inherited disorders and for highlighting correctable shortcomings. In view of the increasing possibilities for genetic screening there is a strong case for central funding for such databases within modern health services

Re-evaluation of cosmic ray cutoff terminology

The study of cosmic ray access to locations inside the geomagnetic field has evolved in a manner that has led to some misunderstanding and misapplication of the terminology originally developed to describe particle access. This paper presents what is believed to be a useful set of definitions for cosmic ray cutoff terminology for use in theoretical and experimental cosmic ray studies

Is There a Fundamental Line for Disk Galaxies?

We show that there are strong local correlations between metallicity, surface brightness, and dynamical mass-to-light ratio within M33, analogous to the fundamental line of dwarf galaxies identified by Prada & Burkert (2002). Using near-infrared imaging from 2MASS, the published rotation curve of M33, and literature measurements of the metallicities of HII regions and supergiant stars, we demonstrate that these correlations hold for points at radial distances between 140 pc and 6.2 kpc from the center of the galaxy. At a given metallicity or surface brightness, M33 has a mass-to-light ratio approximately four times as large as the Local Group dwarf galaxies; other than this constant offset, we see broad agreement between the M33 and dwarf galaxy data. We use analytical arguments to show that at least two of the three fundamental line correlations are basic properties of disk galaxies that can be derived from very general assumptions. We investigate the effect of supernova feedback on the fundamental line with numerical models and conclude that while feedback clearly controls the scatter in the fundamental line, it is not needed to create the fundamental line itself, in agreement with our analytical calculations. We also compare the M33 data with measurements of a simulated disk galaxy, finding that the simulation reproduces the trends in the data correctly and matches the fundamental line, although the metallicity of the simulated galaxy is too high, and the surface brightness is lower than that of M33.Comment: 14 pages, 14 figures (5 in color). Accepted for publication in Ap

InGaAs spin light emitting diodes measured in the Faraday and oblique Hanle geometries

InGaAs quantum well light emitting diodes (LED) with spin-injecting, epitaxial Fe contacts were fabricated using an in situ wafer transfer process where the semiconductor wafer was transferred under ultrahigh vacuum (UHV) conditions to a metals growth chamber to achieve a high quality interface between the two materials. The spin LED devices were measured optically with applied magnetic fields in either the Faraday or the oblique Hanle geometries in two experimental set-ups. Optical polarizations efficiencies of 4.5% in the Faraday geometry and 1.5% in the Hanle geometry are shown to be equivalent. The polarization efficiency of the electroluminescence is seen to decay as the temperature increases although the spin lifetime remains constant due to the influence of the D'yakonov–Perel' spin scattering mechanism in the quantum well.RM would like to acknowledge support from the EPSRC.This is the final version of the article. It first appeared from the Institute of Physics via https://doi.org/10.1088/0022-3727/49/16/16510

A functional correlate of severity in alternating hemiplegia of childhood

OBJECTIVE: Mutations in ATP1A3, the gene that encodes the α3 subunit of the Na(+)/K(+) ATPase, are the primary cause of alternating hemiplegia of childhood (AHC). Correlations between different mutations and AHC severity were recently reported, with E815K identified in severe and D801N and G947R in milder cases. This study aims to explore the molecular pathological mechanisms in AHC and to identify functional correlates for mutations associated with different levels of disease severity. METHODS: Human wild type ATP1A3, and E815K, D801N and G947R mutants were expressed in Xenopus laevis oocytes and Na(+)/K(+) ATPase function measured. Structural homology models of the human α3 subunit containing AHC mutations were created. RESULTS: The AHC mutations examined all showed similar levels of reduction in forward cycling. Wild type forward cycling was reduced by coexpression with any mutant, indicating dominant negative interactions. Proton transport was measured and found to be selectively impaired only in E815K. Homology modeling showed that D801 and G947 lie within or near known cation binding sites while E815 is more distal. Despite its effect on proton transport, E815K was also distant from the proposed proton transport route. INTERPRETATION: Loss of forward cycling and dominant negativity are common and likely necessary pathomechanisms for AHC. In addition, loss of proton transport correlated with severity of AHC. D801N and G947R are likely to directly disrupt normal Na(+)/K(+) binding while E815K may disrupt forward cycling and proton transport via allosteric mechanisms yet to be elucidated