Current driven magnetization dynamics in helical spin density waves

A mechanism is proposed for manipulating the magnetic state of a helical spin density wave using a current. In this paper, we show that a current through a bulk system with a helical spin density wave induces a spin transfer torque, giving rise to a rotation of the order parameter.The use of spin transfer torque to manipulate the magnetization in bulk systems does not suffer from the obstacles seen for magnetization reversal using interface spin transfer torque in multilayered systems. We demonstrate the effect by a quantitative calculation of the current induced magnetization dynamics of Erbium. Finally we propose a setup for experimental verification.Comment: In the previous version of this paper was a small numerical mistake made when evaluating equation 3 and 9. The number of digits given in the calculation of the torque current tensor is reduced to better represent the accuracy of the calculation. A slightly modified paper have been published in Phys. Rev. Lett. 96, 256601 (2006) 4 pages 3 figure

The function of ‘functional’: a mixed methods investigation

OBJECTIVE: The term 'functional' has a distinguished history, embodying a number of physiological concepts, but has increasingly come to mean 'hysterical'. The DSM-V working group proposes to use 'functional' as the official diagnostic term for medically unexplained neurological symptoms (currently known as 'conversion disorder'). This study aimed to explore the current neurological meanings of the term and to understand its resilience. DESIGN: Mixed methods were used, first interviewing the neurologists in a large UK region and then surveying all neurologists in the UK on their use of the term. RESULTS: The interviews revealed four dominant uses--'not organic', a physical disability, a brain disorder and a psychiatric problem--as well as considerable ambiguity. Although there was much dissatisfaction with the term, the ambiguity was also seen as useful when engaging with patients. The survey confirmed these findings, with a majority adhering to a strict interpretation of 'functional' to mean only 'not organic', but a minority employing it to mean different things in different contexts - and endorsing the view that 'functional' would one day be a neurological construct again. CONCLUSIONS: 'Functional' embodies real divisions in neurologists' conceptualisation of unexplained symptoms and, perhaps, between those of patients and neurologists: its diversity of meanings allows it to be a common term while meaning different things to different people, or at different times, and thus conceal some of the conflict in a particularly contentious area. This flexibility may help explain the term's longevity

Headache in 25 consecutive patients with atrial septal defects before and after percutaneous closure – a prospective case series

In contrast to patent foramen ovale, that is highly prevalent in the general population, atrial septal defect (ASD) is a rare congenital heart defect. The effect of ASD closure on headache and migraine remains a matter of controversy. The objectives of the study were (i) to determine headache prevalence in consecutive patients with ASD scheduled for percutaneous closure for cardiologic indications, using the classification of the International Headache Society and (ii) to compare headache characteristics before and after closure of ASD. In this observational case series no a priori power analysis was performed. Twenty-five consecutive patients were prospectively included over 27 months. Median duration of follow-up was 12 months, [Interquartile range 0]. Prevalence of active headache seemed to be increased compared to the general population: Any headaches 88% (95% confidence interval 70-96), migraine without aura 28% (14-48), migraine with aura 16% (6-35). After ASD closure, we observed a slightly lower headache frequency (median frequency 1.0 [2.6] vs. 0.3 [1.5] headaches per month; p=0.067). In patients with ongoing headaches, a significant decrease in headache intensity (median VAS 7 [3] vs. 5 [4]; p=0.036) was reported. Three patients with migraine with aura before the intervention reported no migraine with aura attacks at followup, two of them reported ongoing tension-type headache, one migraine without aura. In summary, this prospective observational study confirms the high prevalence of headache, particularly migraine, in ASD patients and suggests a possible small beneficial effect of ASD closure

Spin Transfer Torques in MnSi at Ultra-low Current Densities

Spin manipulation using electric currents is one of the most promising directions in the field of spintronics. We used neutron scattering to observe the influence of an electric current on the magnetic structure in a bulk material. In the skyrmion lattice of MnSi, where the spins form a lattice of magnetic vortices similar to the vortex lattice in type II superconductors, we observe the rotation of the diffraction pattern in response to currents which are over five orders of magnitude smaller than those typically applied in experimental studies on current-driven magnetization dynamics in nanostructures. We attribute our observations to an extremely efficient coupling of inhomogeneous spin currents to topologically stable knots in spin structures

Impact of paternal deployment to the conflicts in Iraq and Afghanistan and paternal post-traumatic stress disorder on the children of military fathers

Background Little is known about the social and emotional well-being of children whose fathers have been deployed to the conflicts in Iraq/ Afghanistan or who have post-traumatic stress disorder (PTSD). Aims To examine the emotional and behavioural well-being of children whose fathers are or have been in the UK armed forces, in particular the effects of paternal deployment to the conflicts in Iraq or Afghanistan and paternal PTSD. Method Fathers who had taken part in a large tri-service cohort and had children aged 3–16 years were asked about the emotional and behavioural well-being of their child(ren) and assessed for symptoms of PTSD via online questionnaires and telephone interview. Results In total, 621 (67%) fathers participated, providing data on 1044 children. Paternal deployment to Iraq or Afghanistan was not associated with childhood emotional and behavioural difficulties. Paternal probable PTSD were associated with child hyperactivity. This finding was limited to boys and those under 11 years of age. Conclusions This study showed that adverse childhood emotional and behavioural well-being was not associated with paternal deployment but was associated with paternal probable PTSD

Coherent Pair Production by Photons in the 20-170 GeV Energy Range Incident on Crystals and Birefringence

The cross section for coherent pair production by linearly polarised photons in the 20-170 GeV energy range was measured for photon aligned incidence on ultra-high quality diamond and germanium crystals. The theoretical description of coherent bremsstrahlung and coherent pair production phenomena is an area of active theoretical debate and development. However, under our experimental conditions, the theory predicted the combined cross section and polarisation experimental observables very well indeed. In macroscopic terms, our experiment measured a birefringence effect in pair production in a crystal. This study of this effect also constituted a measurement of the energy dependent linear polarisation of photons produced by coherent bremsstrahlung in aligned crystals. New technologies for manipulating high energy photon beams can be realised based on an improved understanding of QED phenomena at these energies. In particular, this experiment demonstrates an efficient new polarimetry technique. The pair production measurements were done using two independent methods simultaneously. The more complex method using a magnet spectrometer showed that the simpler method using a multiplicity detector was also viable.Comment: 10 pages, 13 figures, 1 table, REVTeX4 two column, Version for publicatio

Linear to Circular Polarisation Conversion using Birefringent Properties of Aligned Crystals for Multi-GeV Photons

We present the first experimental results on the use of a thick aligned Si crystal acting as a quarter wave plate to induce a degree of circular polarisation in a high energy linearly polarised photon beam. The linearly polarised photon beam is produced from coherent bremsstrahlung radiation by 178 GeV unpolarised electrons incident on an aligned Si crystal, acting as a radiator. The linear polarisation of the photon beam is characterised by measuring the asymmetry in electron-positron pair production in a Ge crystal, for different crystal orientations. The Ge crystal therefore acts as an analyser. The birefringence phenomenon, which converts the linear polarisation to circular polarisation, is observed by letting the linearly polarised photons beam pass through a thick Si quarter wave plate crystal, and then measuring the asymmetry in electron-positron pair production again for a selection of relative angles between the crystallographic planes of the radiator, analyser and quarter wave plate. The systematics of the difference between the measured asymmetries with and without the quarter wave plate are predicted by theory to reveal an evolution in the Stokes parameters from which the appearance of a circularly polarised component in the photon beam can be demonstrated. The measured magnitude of the circularly polarised component was consistent with the theoretical predictions, and therefore is in indication of the existence of the birefringence effect.Comment: 12 pages, 12 figures, 1 table, REVTeX4 two column, Version for publicatio