Nonequilibrium electron spin polarization in a double quantum dot. Lande mechanism

In moderately strong magnetic fields, the difference in Lande g-factors in each of the dots of a coupled double quantum dot device may induce oscillations between singlet and triplet states of the entangled electron pair and lead to a nonequilibrium electron spin polarization. We will show that this polarization may partially survive the rapid inhomogeneous decoherence due to random nuclear magnetic fields.Comment: New version contains figures. New title better reflects the content of the pape

Yield Curve Shapes and the Asymptotic Short Rate Distribution in Affine One-Factor Models

We consider a model for interest rates, where the short rate is given by a time-homogenous, one-dimensional affine process in the sense of Duffie, Filipovic and Schachermayer. We show that in such a model yield curves can only be normal, inverse or humped (i.e. endowed with a single local maximum). Each case can be characterized by simple conditions on the present short rate. We give conditions under which the short rate process will converge to a limit distribution and describe the limit distribution in terms of its cumulant generating function. We apply our results to the Vasicek model, the CIR model, a CIR model with added jumps and a model of Ornstein-Uhlenbeck type

Enhanced external radiative efficiency for 20.8 efficient single-junction GaInP solar cells

We demonstrate 1.81 eV GaInP solar cells approaching the Shockley-Queisser limit with 20.8% solar conversion efficiency, 8% external radiative efficiency, and 80–90% internal radiative efficiency at one-sun AM1.5 global conditions. Optically enhanced voltage through photon recycling that improves light extraction was achieved using a back metal reflector. This optical enhancement was realized at one-sun currents when the non-radiative Sah-Noyce-Shockley junction recombination current was reduced by placing the junction at the back of the cell in a higher band gap AlGaInP layer. Electroluminescence and dark current-voltage measurements show the separate effects of optical management and non-radiative dark current reduction

The Cosmic Battery and the Inner Edge of the Accretion Disk

The Poynting-Robertson Cosmic Battery proposes that the innermost part of the accretion disk around a black hole is threaded by a large scale dipolar magnetic field generated in situ, and that the return part of the field diffuses outward through the accretion disk. This is different from the scenario that the field originates at large distances and is carried inward by the accretion flow. In view of the importance of large scale magnetic fields in regulating the processes of accretion and outflows, we study the stability of the inner edge of a magnetized disk in general relativity when the distribution of the magnetic field is the one predicted by the Poynting-Robertson Cosmic Battery. We found that as the field grows, the inner edge of the disk gradually moves outward. In a fast spinning black hole with a>0.8M the inner edge moves back in towards the black hole horizon as the field grows beyond some threshold value. In all cases, the inner part of the disk undergoes a dramatic structural change as the field approaches equipartition.Comment: 7 pages, 3 figures, accepted for publication in Monthly Notices of the RA

Novel Nonreciprocal Acoustic Effects in Antiferromagnets

The possible occurrence of nonreciprocal acoustic effects in antiferromagnets in the absence of an external magnetic field is investigated using both (i) a microscopic formulation of the magnetoelastic interaction between spins and phonons and (ii) symmetry arguments. We predict for certain antiferromagnets the existence of two new nonreciprocal (non-time invariant) effects: A boundary-condition induced nonreciprocal effect and the occurrence of transversal phonon modes propagating in opposite directions having different velocities. Estimates are given and possible materials for these effects to be observed are suggested.Comment: Euro. Phys. Lett. (in press

A Logic of Blockchain Updates

Blockchains are distributed data structures that are used to achieve consensus in systems for cryptocurrencies (like Bitcoin) or smart contracts (like Ethereum). Although blockchains gained a lot of popularity recently, there is no logic-based model for blockchains available. We introduce BCL, a dynamic logic to reason about blockchain updates, and show that BCL is sound and complete with respect to a simple blockchain model

Zn(O, S) layers for chalcoyprite solar cells sputtered from a single target

A simplified Cu(In, Ga)(S, Se)2/Zn(O, S)/ZnO:Al stack for chalcopyrite thin- film solar cells is proposed. In this stack the Zn(O, S) layer combines the roles of the traditional CdS buffer and undoped ZnO layers. It will be shown that Zn(O, S) films can be sputtered in argon atmosphere from a single mixed target without substrate heating. The photovoltaic performance of the simplified stack matches that of the conventional approach. Replacing the ZnO target with a ZnO/ZnS target may therefore be sufficient to omit the CdS buffer layer and avoid the associated complexity, safety and recycling issues, and to lower production cost

Anaemia prevalence and nutrient intake among women in peri-urban settlements in Accra, Ghana

Anaemia among women is a major public health concern globally. In developing countries, nutritional anaemia may be due to poor bioavailability of dietary iron, haemoglobinopathies, or intestinal parasites. The study objectives were to determine the prevalence of anaemia and current nutrient intakes essential to erythropoiesis among women of reproductive age (WRA) in peri-urban settlements in the Ga-East Municipality, Accra, Ghana. This cross-sectional study assessed the nutrient intake, sickling and haemoglobin levels of 134 women aged 15-49 years enrolled in a peanut-based field trial at baseline. A pretested semi-quantitative food frequency questionnaire was used to assess energy and nutrient intake using the Food Processor (ESHA) software. Whole blood was used to determine full blood count using the haematology automated analyser. Sickling was determined by blood staining. Anaemia was classified based on recommended cut-offs. Chi-square analysis was used as a test of independence between anaemia and age groups. Linear regression was used to determine predictors of haemoglobin concentration. The mean age of the women was 29 ± 8 years. The mean total caloric intake was 2315 ± 915 kcal, whilst protein and fat intakes were 67 ± 27g and 68± 30g, respectively. Almost three-quarters of the women met the recommended dietary allowance (RDA) for iron and vitamin C. However, only a third met the RDA for fat, and about two-thirds met their needs for energy and protein. None of the women met the RDA for folate which is integral for haem formation. Also 17% (23/134) of the women were sickle cell anaemia positive. Mean haemoglobin concentration was 12.1 ± 1.8 g/dL. Mild, moderate and severe anaemia due to iron deficiency was present in 35.8%, 6.7% and 1.5%, of the women respectively. All categories of anaemia was present in 44% of the women. Anaemia, prevalence increased during the early stages of the reproductive age (15-29 years) and declined towards the end of the reproductive age period (40-49 years). An increase in age of one year was significantly associated with a 0.056 g/dL rise in haemoglobin level (p=0.014). Anaemia due to iron deficiency exists as a public health problem among women in peri-urban settlements in the Ga-East Municipality, Accra, Ghana. Dietary diversity to include green leafy vegetables which are rich in folate and pro-vitamin A may reduce the current level of prevalence.Key words: Anaemia, Nutrients, Peri-urban, Women, RDA, sickling test, Food Processor softwar

Anisotropic spin freezing in the S=1/2 zigzag ladder compound SrCuO2

Using magnetic neutron scattering we characterize an unusual low temperature phase in orthorhombic SrCuO2. The material contains zigzag spin ladders formed by pairs of S=1/2 chains (J=180 meV) coupled through a weak frustrated interaction |J'|<0.1J. At T<Tc1=5.0(4)K an elastic peak develops in a gapless magnetic excitation spectrum indicating spin freezing on a time scale larger than 200 picoseconds. While the frozen state has long range commensurate antiferromagnetic order along the chains with the correlation length exceeding 200 lattice periods along the c-axis and a substantial correlation length of 60(25) spacings along the a-axis perpendicular to the zigzag plane, only 2 lattice units are correlated along the b-axis which is the direction of the frustrated interactions. The frozen magnetic moment of each Cu ion is very small, 0.033(7) Bohr magneton even at T=0.35K, and has unusual temperature dependence with a cusp at Tc2=1.5K reminiscent of a phase transition. We argue that slow dynamics of stripe-like cooperative magnetic defects in tetragonal a-c planes yield this anisotropic frozen state.Comment: 4 pages, LaTeX, submitted to PR