Charge pumping in magnetic tunnel junctions: Scattering theory

We study theoretically the charge transport pumped by magnetization dynamics through epitaxial FIF and FNIF magnetic tunnel junctions (F: Ferromagnet, I: Insulator, N: Normal metal). We predict a small but measurable DC pumping voltage under ferromagnetic resonance conditions for collinear magnetization configurations, which may change sign as function of barrier parameters. A much larger AC pumping voltage is expected when the magnetizations are at right angles. Quantum size effects are predicted for an FNIF structure as a function of the normal layer thickness.Comment: 4 pages, 3 figures. to be published on Physical Review B Rapid Communicatio

Sensitivity of spin-torque diodes for frequency-tunable resonant microwave detection

We calculate the efficiency with which magnetic tunnel junctions can be used as resonant detectors of incident microwave radiation via the spin-torque diode effect. The expression we derive is in good agreement with the sensitivities we measure for MgO-based magnetic tunnel junctions with an extended (unpatterned) magnetic pinned layer. However, the measured sensitivities are reduced below our estimate for a second set of devices in which the pinned layer is a patterned synthetic antiferromagnet (SAF). We suggest that this reduction may be due to an undesirable coupling between the magnetic free layer and one of the magnetic layers within the etched SAF. Our calculations suggest that optimized tunnel junctions should achieve sensitivities for resonant detection exceeding 10,000 mV/mW.Comment: 17 pages, 2 figure

Raft-derived tau-associated vesicles

Aims: Neurofibrillary tangles (NFTs), a cardinal pathological feature of neurodegenerative disorders, such as Alzheimer's disease (AD) are primarily composed of hyper‐phosphorylated tau protein. Recently, several other molecules, including flotillin‐1, phosphatidylinositol‐4,5‐bisphosphate [PtdIns(4,5)P2] and cyclin‐dependent kinase 5 (CDK5), have also been revealed as constituents of NFTs. Flotillin‐1 and PtdIns(4,5)P2 are considered markers of raft microdomains, whereas CDK5 is a tau kinase. Therefore, we hypothesized that NFTs have a relationship with raft domains and the tau phosphorylation that occurs within NFTs. Methods: We investigated six cases of AD, six cases of other neurodegenerative diseases with NFTs and three control cases. We analysed the PtdIns(4,5)P2‐immunopositive material in detail, using super‐resolution microscopy and electron microscopy to elucidate its pattern of expression. We also investigated the spatial relationship between the PtdIns(4,5)P2‐immunopositive material and tau kinases through double immunofluorescence analysis. Results: Pretangles contained either paired helical filaments (PHFs) or PtdIns(4,5)P2‐immunopositive small vesicles (approximately 1 μm in diameter) with nearly identical topology to granulovacuolar degeneration (GVD) bodies. Various combinations of these vesicles and GVD bodies, the latter of which are pathological hallmarks observed within the neurons of AD patients, were found concurrently in neurons. These vesicles and GVD bodies were both immunopositive not only for PtdIns(4,5)P2, but also for several tau kinases such as glycogen synthase kinase‐3β and spleen tyrosine kinase. Conclusions: These observations suggest that clusters of raft‐derived vesicles that resemble GVD bodies are substructures of pretangles other than PHFs. These tau kinase‐bearing vesicles are likely involved in the modification of tau protein and in NFT formation

Induced sensorimotor brain plasticity controls pain in phantom limb patients

The cause of pain in a phantom limb after partial or complete deafferentation is an important problem. A popular but increasingly controversial theory is that it results from maladaptive reorganization of the sensorimotor cortex, suggesting that experimental induction of further reorganization should affect the pain, especially if it results in functional restoration. Here we use a brain-machine interface (BMI) based on real-time magnetoencephalography signals to reconstruct affected hand movements with a robotic hand. BMI training induces significant plasticity in the sensorimotor cortex, manifested as improved discriminability of movement information and enhanced prosthetic control. Contrary to our expectation that functional restoration would reduce pain, the BMI training with the phantom hand intensifies the pain. In contrast, BMI training designed to dissociate the prosthetic and phantom hands actually reduces pain. These results reveal a functional relevance between sensorimotor cortical plasticity and pain, and may provide a novel treatment with BMI neurofeedback.This research was conducted under the ‘Development of BMI Technologies for Clinical Application’ of SRPBS by MEXT and AMED. This research was also supported in part by JST PRESTO; JSPS KAKENHI JP24700419, JP26560467, JP22700435, JP26242088, JP26282165, JP15H05710 and JP15H05920; Brain/MINDS and SICP from AMED; ImPACT; Ministry of Health, Labor, and Welfare (18261201); and the Japan Foundation of Aging and Health

Distribution of the magnetization reversal duration in sub-ns spin-transfer switching

We study the distribution of switching times in spin-transfer switching induced by sub-ns current pulses in pillar-shaped spin-valves. The pulse durations leading to switching follow a comb-like distribution, multiply-peaked at a few most probable, regularly spaced switching durations. These durations reflect the precessional nature of the switching, which occurs through a fluctuating integer number of precession cycles. This can be modeled considering the thermal variance of the initial magnetization orientations and the occurrence of vanishing total torque in the possible magnetization trajectories. Biasing the spin-valve with a hard axis field prevents some of these occurrences, and can provide an almost perfect reproducibility of the switching duration.Comment: submitted to PR

Study of the Proton Single-Particle Strengths in 19F and Proton Shell Closure of 18O through the 18O(d, n)19F Reaction

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