Spin motive forces and current fluctuations due to Brownian motion of domain walls

We compute the power spectrum of the noise in the current due to spin motive forces by a fluctuating domain wall. We find that the power spectrum of the noise in the current is colored, and depends on the Gilbert damping, the spin transfer torque parameter $\beta$, and the domain-wall pinning potential and magnetic anisotropy. We also determine the average current induced by the thermally-assisted motion of a domain wall that is driven by an external magnetic field. Our results suggest that measuring the power spectrum of the noise in the current in the presence of a domain wall may provide a new method for characterizing the current-to-domain-wall coupling in the system.Comment: Submitted to "Special issue: Caloritronics" in Solid State Communication

Spin-transfer mechanism for magnon-drag thermopower

We point out a relation between the dissipative spin-transfer-torque parameter $\beta$ and the contribution of magnon drag to the thermoelectric power in conducting ferromagnets. Using this result we estimate $\beta$ in iron at low temperatures, where magnon drag is believed to be the dominant contribution to the thermopower. Our results may be used to determine $\beta$ from magnon-drag-thermopower experiments, or, conversely, to infer the strength of magnon drag via experiments on spin transfer

Current-driven and field-driven domain walls at nonzero temperature

We present a model for the dynamics of current- and field-driven domain-wall lines at nonzero temperature. We compute thermally-averaged drift velocities from the Fokker-Planck equation that describes the nonzero-temperature dynamics of the domain wall. As special limits of this general description, we describe rigid domain walls as well as vortex domain walls. In these limits, we determine also depinning times of the domain wall from an extrinsic pinning potential. We compare our theory with previous theoretical and experimental work

Spin motive forces due to magnetic vortices and domain walls

We study spin motive forces, i.e, spin-dependent forces, and voltages induced by time-dependent magnetization textures, for moving magnetic vortices and domain walls. First, we consider the voltage generated by a one-dimensional field-driven domain wall. Next, we perform detailed calculations on field-driven vortex domain walls. We find that the results for the voltage as a function of magnetic field differ between the one-dimensional and vortex domain wall. For the experimentally relevant case of a vortex domain wall, the dependence of voltage on field around Walker breakdown depends qualitatively on the ratio of the so-called $\beta$-parameter to the Gilbert damping constant, and thus provides a way to determine this ratio experimentally. We also consider vortices on a magnetic disk in the presence of an AC magnetic field. In this case, the phase difference between field and voltage on the edge is determined by the $\beta$ parameter, providing another experimental method to determine this quantity.Comment: 8 pages, 9 figures, submitted to PR

Fluctuations of current-driven domain walls in the non-adiabatic regime

We outline a general framework to determine the effect of non-equilibrium fluctuations on driven collective coordinates, and apply it to a current-driven domain wall in a nanocontact. In this case the collective coordinates are the domain-wall position and its chirality, that give rise to momentum transfer and spin transfer, respectively. We determine the current-induced fluctuations corresponding to these processes and show that at small frequencies they can be incorporated by two separate effective temperatures. As an application, the average time to depin the domain wall is calculated and found to be lowered by current-induced fluctuations. It is shown that current-induced fluctuations play an important role for narrow domain walls, especially at low temperatures.Comment: More computations, explanations, and results include

Current-induced spin torques in III-V ferromagnetic semiconductors

We formulate a theory of current-induced spin torques in inhomogeneous III-V ferromagnetic semiconductors. The carrier spin-3/2 and large spin-orbit interaction, leading to spin non-conservation, introduce significant conceptual differences from spin torques in ferromagnetic metals. We determine the spin density in an electric field in the weak momentum scattering regime, demonstrating that the torque on the magnetization is intimately related to spin precession under the action of both the spin-orbit interaction and the exchange field characteristic of ferromagnetism. The spin polarization excited by the electric field is smaller than in ferromagnetic metals and, due to lack of angular momentum conservation, cannot be expressed in a simple closed vectorial form. Remarkably, scalar and spin-dependent scattering do not affect the result. We use our results to estimate the velocity of current-driven domain walls.Comment: 10 page

Youth’12 The Health and Wellbeing of Secondary School Students in New Zealand: Results for Young People Attracted to the Same Sex or Both Sexes

Almost four percent (3.8%) of young people reported being attracted to others of the same sex or both sexes in Youth’12. This proportion is comparable to that found in the previous surveys conducted in 2001 and 2007, suggesting that over the past 11 years there has been no change in relation to the number of New Zealand secondary school students who are same/both-sex attracted. Furthermore these young people are ethnically, geographically, and socially diverse, and attend schools from around the country. In 2012, the majority (53.1%) of same/both-sex attracted young people had ‘come out’ (i.e. told people close to them about their sexuality) whilst 31.3% of same/both-sex attracted students had come out in 2001. However, in Youth’12 only 14.4% of these young people said that they could easily talk to their family about their sexuality. Most same/both-sex attracted students reported feeling positive towards school and described caring relationships with their parents and friends. Same/both-sex attracted students were also generous with their time in that they were more likely (than their opposite-sex attracted counterparts) to work as volunteers in their communities. Although most same/both-sex attracted students are doing well, there are significant and harmful disparities when these students are compared to their opposite-sex attracted peers. Same/both-sex attracted young people are often exposed to environments that are challenging and discriminatory, and this in turn affects their wellbeing. For example, same/both-sex attracted youth are more likely to be bullied, be physically harmed, and to be afraid that someone would hurt or bother them at school. Furthermore, 59.4% of same/both-sex attracted students had deliberately self-harmed, 41.3% had significant depressive symptoms, 18.3% had attempted suicide in the last 12 months, and 35.7% had difficulty getting help for their emotional concerns. These mental health issues have not improved since 2001, and worryingly the proportion of same/both-sex attracted students experiencing significant depressive symptoms has increased from 27.0% in 2001 to 41.3% in 2012, while the proportion of opposite-sex attracted students with these symptoms has remained fairly constant (9.5% in 2007 and 11.4% in 2001 and 2012). This suggests that poor progress is being made in terms of addressing mental health concerns. Overall this report highlights that while many same/both-sex attracted students are doing well, in comparison to opposite-sex attracted students, same/both-sex attracted young people continue to experience compromised health and wellbeing. Evidence from international studies suggest that reducing these disparities must focus on creating safe and nurturing environments which build upon the young person’s strengths and assets, and refrains from problematising (or pathologising) same/both-sex attracted young people

La interacción de procesos hidrológicos, químicos y microbiológicos en la formación de películas flotantes ricas en hierro en ambientes acuáticos de pH circumneutro

17 páginas.-- 3 figuras.-- 4 tablas.-- 53 referencias.-- Postprint (Versión editorial)[EN]: The direct contribution of microbial activity to the formation of iron-oxide minerals is difficult to prove in wetlands due to the high reactivity of solid iron phases with different compounds and the variety of redox processes that may occur at each oxic-anoxic boundary. Here, we propose an explanation for the formation of iron-oxide films in wetlands and groundwater seepage areas fed by sandy aquifers based on the interaction of hydrological, chemical and microbiological processes under circumneutral conditions. The presence of a floating iron-oxide film was found to create a boundary at the air-water interface that maintains a suboxic and slightly acidic environment below the film compared with the environments obtained in other free-film wetland areas. The water trapped below this film had an average pH of 6.1, was particularly poor in O2, HCO–3, Na+, Ca2+, Mg2+, K+, and Tot-S, and has high concentrations of Tot-P, Tot-Fe, NH+4 and Zn. The formation of a floating iron-oxide film was reproduced under anaerobic conditions after progressive enrichment through the incubation of natural sediment samples in the laboratory. Heterotrophic bacteria belonging to the genus Enterobacter were the dominant bacteria in the enrichments that resulted in the formation of a floating iron-oxide film. The X-ray diffraction patterns showed that the presence of two-line ferrihydrite was common to the iron-oxide films collected in both the natural environment and the laboratory cultures, whereas other iron-oxides (goethite and low-crystalline lepidocrocite) were observed only in the natural environment. This study highlights the role of ubiquitous bacteria, which are generally considered unimportant participants in iron-transformation processes in the environment, and the contribution of both biological and non-biological processes to iron oxidation in natural systems under circumneutral conditions.[ES]: En los humedales, es difícil probar que la actividad microbiana sea la responsable de la formación de óxido de hierro mineral debido, tanto a la gran reactividad del hierro en fase sólida con diferentes sustancias, como a la variedad de procesos redox que pueden ocurrir en cada interfase óxica-anóxica. El presente trabajo propone una explicación, basada en la interacción de procesos hidrológicos, químicos y microbiológicos en condiciones circumneutras, para explicar la formación de un film de óxido de hierro en humedales y manaderos donde aflora agua subterránea proveniente de acuíferos de arenas silíceas. Además, la presencia de un film de óxido de hierro que flota sobre la interfase agua-aire genera condiciones subóxicas y ligeramente ácidas en el agua que queda atrapada debajo, y que son muy distintas a otras zonas libres de film en el mismo humedal. Este agua atrapada bajo el film se caracterizó por presentar un pH medio de 6.1, una menor concentración de O2, HCO–3, Na+, Ca2+, Mg2+, K+, y S total, pero una mayor riqueza en P total, Fe total, NH+4 y Zn. La formación de un film flotante de óxido de hierro se reprodujo en el laboratorio, en condiciones anaeróbicas, tras el enriquecimiento progresivo de las muestras del sedimento natural que habían sido incubadas. En dichos enriquecimientos, donde se produjeron films flotantes de óxido de hierro, la bacteria dominante perteneció al género Enterobacter. Mediante difracción por rayos X, se encontró ferrihidrita con estructura en doble cadena, tanto en el film de muestras naturales como de cultivos de laboratorio. Además se encontraron otros tipos de óxidos minerales (goetita y lepidocrocita de pobre cristalización) sólo en las muestras naturales de film. El presente estudio muestra la relevancia de bacterias ubicuas, hasta ahora consideradas sin importancia en procesos naturales de transformación del hierro, y la participación tanto de procesos bióticos como abióticos en la oxidación del hierro en sistemas naturales sometidos a condiciones circumneutras.We are grateful to Han Golterman for his support and suggestions. We thank Lotte Fleskens and Christien van der Zwart for collaborating with the sediment collection and P-fractionation at the laboratory. This study was partially supported by the Spanish Ministry of Education and Science (CGL2004-03927-C02-01/BOS)Peer reviewe

Risk of stroke and bleeding in relation to hypertension in anticoagulated patients with atrial fibrillation: a meta-analysis of randomised controlled trials.

Background and purpose Hypertension is common in patients with atrial fibrillation (AF) and carries an additional risk for complications, most notably stroke and bleeding. We assessed the history of hypertension, level of blood pressure control, and an interaction with the choice of oral anticoagulants on clinical outcomes. Methods We performed a systematic review and meta-analysis of studies that randomised patients to novel oral anticoagulants (NOACs) or vitamin K antagonists (VKAs) and reported outcomes stratified by presence of hypertension. Collected outcomes were: ischaemic stroke or systemic embolism (SE), haemorrhagic stroke, intracranial haemorrhage and major bleeding. Log adjusted hazard ratios (HR) and corresponding standard error were calculated, and HRs were compared using Mantel-Haenszel random effects. Quality of the evidence was assessed with Cochrane risk of bias tool. Results Five high-quality studies were eligible, including 71.527 participants who received NOACs (apixaban, dabigatran, edoxaban, rivaroxaban) or VKAs, with median follow-up of 1.8-2.8 years. Compared with patients without hypertension, those with hypertension had higher adjusted risk for ischaemic stroke/SE (HR: 1.25, 95%-CI:1.09, 1.43) and haemorrhagic stroke (HR:1.98, 1.24-3.16). On a continuous scale, the risk of ischaemic stroke/SE increased 6-7% per 10 mmHg increase in systolic blood pressure. No interactions were found between the efficacy or safety of NOACs versus VKAs in the presence or absence of hypertension. In both groups, the use of NOACs led to a lower risk of ischaemic stroke/SE, haemorrhagic stroke and intracranial haemorrhage compared with patients that used VKAs. Conclusions Adequate blood pressure management is vital to optimally reduce the risk of stroke in patients with atrial fibrillation. The benefits of NOACs over VKAs, also apply to patients with elevated blood pressure

Validating risk models versus age alone for atrial fibrillation in a young Dutch population cohort:should atrial fibrillation risk prediction be expanded to younger community members?

BACKGROUND: Advancing age is the primary selection criterion for community screening for atrial fibrillation (AF), with selection often restricted to those aged ≥65 years. If multivariable models were shown to have considerable additional value over age alone in predicting AF risk among younger individuals, AF screening could be expanded to patients with lower age, but with high AF risk as per a validated risk model. METHODS: We validated risk models CHARGE-AF (Cohorts for Heart and Aging Research in Genomic Epidemiology model for AF) and FHS-AF (Framingham Heart Study model for AF), and risk scores CHA(2)DS(2)-VASc and CHA(2)DS(2)-VA, and presented their predictive abilities for 5-year and 10-year AF risk versus that of age alone in a young Dutch population cohort (PREVEND) free from AF at baseline. We assessed discrimination by the C-statistic and calibration by the calibration plot and stratified Kaplan-Meier plot using survey-weighted Cox models. RESULTS: During 5-year and 10-year follow-up there were n=98 (2.46/1000 person-years) and n=249 (3.29/1000 person-years) new AF cases, respectively, among 8265 participants with mean age 49±13 years. CHARGE-AF and FHS-AF both showed good discrimination for 5-year and 10-year AF (C-statistic range 0.83–0.86) with accurate calibration for 5-year AF, but overestimation of 10-year AF risk in highest-risk individuals. CHA(2)DS(2)-VASc and CHA(2)DS(2)-VA relatively underperformed. Age alone showed similar discrimination to that of CHARGE-AF and FHS-AF both in the overall, young PREVEND cohort and in subgroups for lower age and lower stroke risk. CONCLUSION: Multivariable models accurately discriminate for 5-year and 10-year AF risk among young European community-dwelling individuals. However, their additional discriminatory value over age alone was limited. Selection strategies for primary AF screening using multivariable models should not be expanded to younger individuals