Tohoku University

About: Tohoku University is a education organization based out in Sendai, Japan. It is known for research contribution in the topics: Magnetization & Alloy. The organization has 72116 authors who have published 170791 publications receiving 3941714 citations. The organization is also known as: Tōhoku daigaku.

Neuronal activity in cortical motor areas related to ipsilateral, contralateral, and bilateral digit movements of the monkey

Abstract: 1. Single cell activity was studied in the precentral (PCM), premotor (PM), and supplementary (SMA) motor cortex of the monkey to compare magnitudes of activity changes in relation to ipsilateral, contralateral, and bilateral digit movements. 2. Three Japanese monkeys were trained to press a small key with the right or left hand, or with both hands, in accordance with visual instruction signals given 2.6-5.4 s before a visual movement-trigger signal. Great care was taken to train the animal to use only the required part of the limb. As a result of extensive training, electromyographic (EMG) studies revealed that muscle activities before the key press were limited to the digit and hand muscles of the limb instructed to move. No overt increase or decrease in activity was detectable in the proximal limb or body muscles in relation to the key-press movements or instructions. 3. Even though the movement was thus limited to distal forelimb, distinct ipsilateral relationships were observed in 8.2% of the task-related PCM neurons. They changed their activity before ipsilateral and bilateral (but not before contralateral) key press. 4. A majority of the neurons recorded from the digit area of PCM (mostly limited to the anterior bank of the central sulcus) exhibited a contralateral relationship; namely the activity increased or decreased before the onset of the contralateral and bilateral key-press movements. In most of them, the magnitudes of the activity changes before the contralateral and bilateral movements were similar. 5. In proximal limb and trunk areas of PCM and also in the somatosensory cortex, no neurons were found to exhibit distinct relations to any of the key-press movements. 6. In both SMA and PM, a number of neurons exhibited relationships of the type never or only rarely observed in the primary motor cortex. Thirty-seven percent of SMA and 62% of PM neurons exhibited premovement activity changes before all of the key-press movements. The movement-specific type of activity was observed in 28% of SMA and 16% of PM neurons. In these neurons, the activity changes were observed in relation to only one of the right or left key-press movements or exclusively in relation to the bilateral key press. Neuronal activity resembling the majority of the PCM neurons (contralateral type) was observed in 31% of SMA and 13% of PM neurons. 7. Instruction-induced changes in activity were more often found in the secondary than in the primary motor area.(ABSTRACT TRUNCATED AT 400 WORDS)

Training of working memory impacts structural connectivity.

Abstract: Working memory is the limited capacity storage system involved in the maintenance and manipulation of information over short periods of time. Individual capacity of working memory is associated with the integrity of white matter in the frontoparietal regions. It is unknown to what extent the integrity of white matter underlying the working memory system is plastic. Using voxel-based analysis (VBA) of fractional anisotropy (FA) measures of fiber tracts, we investigated the effect of working memory training on structural connectivity in an interventional study. The amount of working memory training correlated with increased FA in the white matter regions adjacent to the intraparietal sulcus and the anterior part of the body of the corpus callosum after training. These results showed training-induced plasticity in regions that are thought to be critical in working memory. As changes in myelination lead to FA changes in diffusion tensor imaging, a possible mechanism for the observed FA change is increased myelination after training. Observed structural changes may underlie previously reported improvement of working memory capacity, improvement of other cognitive functions, and altered functional activity following working memory training.

Magnetic Tunnel Junctions for Spintronic Memories and Beyond

Abstract: In this paper, recent developments in magnetic tunnel junctions (MTJs) are reported with their potential impacts on integrated circuits. MTJs consist of two metal ferromagnets separated by a thin insulator and exhibit two resistances, low (Rp) or high (Rap) depending on the relative direction of ferromagnet magnetizations, parallel (P) or antiparallel (AP), respectively. Tunnel magnetoresistance (TMR) ratios, defined as (Rap $Rp)/Rp as high as 361%, have been obtained in MTJs with Co40Fe40B20 fixed and free layers made by sputtering with an industry-standard exchange-bias structure and post deposition annealing at Ta = 400 degC. The corresponding output voltage swing DeltaV is over 500 mV, which is five times greater than that of the conventional amorphous Al-O-barrier MTJs. The highest TMR ratio obtained so far is 500% in a pseudospin-valve MTJ annealed at Ta = 475 degC, showing a high potential of the current material system. In addition to this high-output voltage swing, current-induced magnetization switching (CIMS) takes place at the critical current densities (JCO) on the order of 106 A/cm2 in these MgO-barrier MTJs. Furthermore, high antiferromagnetic coupling between the two CoFeB layers in a synthetic ferrimagnetic free layer has been shown to result in a high thermal-stability factor with a reduced JCO compared to single free-layer MTJs. The high TMR ratio enabled by the MgO-barrier MTJs, together with the demonstration of CIMS at a low JCO, allows development of not only scalable magnetoresistive random-access memory with feature sizes below 90 nm but also new memory-in-logic CMOS circuits that can overcome a number of bottlenecks in the current integrated-circuit architecture

Big-bang nucleosynthesis and gravitinos

Abstract: We derive big-bang nucleosynthesis (BBN) constraints on both unstable and stable gravitino taking account of recent progress in theoretical study of the BBN processes as well as observations of primordial light-element abundances In the case of unstable gravitino, we set the upper limit on the reheating temperature assuming that the primordial gravitinos are mainly produced by the scattering processes of thermal particles For stable gravitino, we consider B-ino, stau, and sneutrino as the next-to-the-lightest supersymmetric particle and obtain constraints on their properties Compared with the previous works, we improved the following points: (i) we use the most recent observational data, (ii) for gravitino production, we include contribution of the longitudinal component, and (iii) for the case with unstable long-lived stau, we estimate the bound-state effect of stau accurately by solving the Boltzmann equation