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Search Results: 1 - 10 of 62727 matches for " Yu-ichiro Matsushita "
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Interstitial Channels that Control Band Gaps and Effective Masses in Tetrahedrally Bonded Semiconductors
Yu-ichiro Matsushita,Atsushi Oshiyama
Physics , 2014, DOI: 10.1103/PhysRevLett.112.136403
Abstract: We find that electron states at the bottom of the conduction bands of covalent semiconductors are distributed mainly in the interstitial channels and that this floating nature leads to the band-gap variation and the anisotropic effective masses in various polytypes of SiC. We find that the channel length, rather than the hexagonality prevailed in the past, is the decisive factor for the band-gap variation in the polytypes. We also find that the floating nature causes two-dimensional electron and hole systems at the interface of different SiC polytypes and even one-dimensional channels near the inclined SiC surface.
Comparative study of hybrid functionals applied to structural and electronic properties of semiconductors and insulators
Yu-ichiro Matsushita,Kazuma Nakamura,Atsushi Oshiyama
Physics , 2011, DOI: 10.1103/PhysRevB.84.075205
Abstract: We present a systematic study that clarifies validity and limitation of current hybrid functionals in density functional theory for structural and electronic properties of various semiconductors and insulators. The three hybrid functionals, PBE0 by Perdew, Ernzerhof, and Becke, HSE by Heyd, Sucseria, and Ernzerhof, and a long-range corrected (LC) functional, are implemented in a well-established plane-wave-basis-set scheme combined with norm-conserving pseudopotentials, thus enabling us to assess applicability of each functional on equal footing to the properties of the materials. The materials we have examined in this paper range from covalent to ionic materials as well as a rare-gas solid whose energy gaps determined by experiments are in the range of 0.6 eV - 14.2 eV: i.e., Ge, Si, BaTiO$_3$, $\beta$-GaN, diamond, MgO, NaCl, LiCl, Kr, and LiF. We find that the calculated bulk moduli by the hybrid functionals show better agreement with the experiments than the generalized gradient approximation (GGA) provides, whereas the calculated lattice constants by the hybrid functionals and GGA show comparable accuracy. The calculated energy band gaps and the valence-band widths for the ten prototype materials show substantial improvement using the hybrid functional compared with GGA. In particular, it is found that the band gaps of the ionic materials as well as the rare-gas solid are well reproduced by the LC-hybrid functional, whereas those of covalent materials are well described by the HSE functional. We also examine exchange effects due to short-range and long-range components of the Coulomb interaction and propose an optimum recipe to the short-range and long-range separation in treating the exchange energy.
L1$_0$ stacked binaries as candidates for hard magnets: FePt, MnAl and MnGa
Yu-ichiro Matsushita,Galia Madjarova,C. Felser,S. Sharma,J. K. Dewhurst,E. K. U. Gross
Physics , 2015,
Abstract: A novel strategy of stacking binary magnets to enhance the magneto crystalline anisotropy is explored. This strategy is used in the search for hard magnets by studying FePt/MnGa and FePt/MnAl stacks. The choice of these binaries is motivated by the fact that they already possess large magneto crystalline anisotropy. Several possible alternative structures for these materials are explored in order to reduce the amount of Pt owing to its high cost.
Depletion of Glial Cell Line-Derived Neurotrophic Factor by Disuse Muscle Atrophy Exacerbates the Degeneration of Alpha Motor Neurons in Caudal Regions Remote from the Spinal Cord Injury  [PDF]
Yu-Ichiro Ohnishi, Koichi Iwatsuki, Toshiki Yoshimine
Neuroscience & Medicine (NM) , 2014, DOI: 10.4236/nm.2014.55025
Abstract: We have been previously reported that disuse muscle atrophy exacerbates both motor neuron (MN) degeneration in caudal regions remote from a spinal cord injury, and decrease in glial cell line-derived neurotrophic factor (GDNF) protein level in paralyzed muscle. In this study we found that disuse muscle atrophy exacerbated the decrease in GDNF protein level in the L4/5 spinal cord, which was not immunopositive for GDNF. Our results were consistent with the fact that in the lumbar spinal cord of rats with mid-thoracic contusion, GDNF expression was not detected, while expression of GDNF receptors (GFRα1 and RET) was. Our study showed that administration of exogenous recombinant GDNF into the atrophic muscle partially rescued α-MN degeneration in the L4/5 spinal cord. These results suggest that the depletion of GDNF protein by muscle atrophy exacerbates α-MN degeneration in caudal regions remote from the injury.
Assessment of Cervical Screw Trajectory Using 3-Dimensional Software Planning  [PDF]
Yu-Ichiro Ohnishi, Koichi Iwatsuki, Toshiki Yoshimine
Open Journal of Modern Neurosurgery (OJMN) , 2015, DOI: 10.4236/ojmn.2015.51002
Abstract: Objective: It is important and helpful for surgeons to understand the correlation between spinal anatomy and screw trajectory before surgery. We aimed to assess a simple technique using 3D imaging software available on the hospital intranet for visual and quantitative feedback to prepare surgeons for an appropriate entry point and safe trajectory when placing cervical screws. Methods: A total of 59 cervical screws were inserted from C1 to T1 in 12 consecutive patients using this technique. First, a single CT optimal slice was selected from 3D CT images of the cervical spine to determine the intervals of bilateral entry points and lateral angle. Next, this 3D image was rotated to the lateral angle. Finally, bone was cut out on the entry point using subtractive manipulation, which removed the core of the pedicle or lateral mass. Screw trajectory was indicated, and surgeons could assess the correlation between surface landmarks, spinal anatomy, and screw trajectory. Posterior cervical fusion was performed using fluoroscopy. Postoperative outcomes and incidence of complications were retrospectively assessed. Results: One perforation (1.4%) was identified on postoperative CT images. No vascular injuries occurred. Differences in the intended entry point location and lateral angle of the screw from actual postoperative values were 1.49 ± 1.23 mm and 5.46 ± 4.46, respectively. Conclusions: A novel 3D CT imaging assessment underwent in cervical screw fixation. This technique is easily accessible on the hospital intranet and provides training in cervical screw placement for fellows. Surgeons can simulate screw placement and share surgical strategy.
Early Diagnosis of Spontaneous Spinal Epidural Hematoma with Echo-Planar Gradient-Echo T2*-Weighted MR Imaging  [PDF]
Koichi Iwatsuki, Toshiki Yoshimine, Yu-Ichiro Ohnishi, Koshi Ninomiya, Toshika Ohkawa, Kousuke Iwaisako
Neuroscience & Medicine (NM) , 2015, DOI: 10.4236/nm.2015.61004
Abstract:
Spontaneous spinal epidural hematoma (SSEH) is a rare idiopathic condition that leads to the acute onset of neurological deficits, which can have catastrophic consequences if not recognized early. It is important to make an early precise diagnosis. Spinal epidural hematoma has been increasingly recognized since the advent of magnetic resonance imaging (MRI). However, T1- and T2-weighted gradient-echo sequences are relatively less sensitive to the magnetic susceptibility effects of hemorrhage. Echo-planar gradient-echo T2*-weighted MR imaging (T2* MRI) is sensitive to these magnetic susceptibility effects and is commonly used for the detection of hemorrhage. We reported that the case of a 76-year-old man who presented with tetra paresis had an early diagnosis of spontaneous spinal epidural hematoma early diagnosed by T2* MRI.
Transplantation of Olfactory Mucosa as a Scaffold for Axonal Regeneration Following Spinal Cord Contusion in Rats  [PDF]
Koichi Iwatsuki, Toshiki Yoshimine, Yoshiyuki Sankai, Masao Umegaki, Yu-Ichiro Ohnishi, Masahiro Ishihara, Takashi Moriwaki, Noriko Oda
Neuroscience & Medicine (NM) , 2013, DOI: 10.4236/nm.2013.42018
Abstract:

Object: The inability of the spinal cord to regenerate after SCI is due to the extremely limited regenerative capacity of most central nervous system (CNS) axons, along with the hostile environment of the adult CNS, which does not support axonal growth. It seems that for successful axonal regeneration to take place, a supportive local environment is required after the injury. We have previously reported that transplantation of the olfactory mucosa is effective in restoring functional recovery in rats following spinal cord transaction. In this study, we examined histological features of olfactory mucosa grafts in rats subjected to a spinal cord contusion protocol. Respiratory mucosa was utilized as a control, as we have previously found that respiratory mucosa does not support neuronal generation. Methods: The rats spinal cords were crash-injured by dropping a 10-g metal rod from a height of 7.5 cm, and a couple of weeks later, the injury sites were exposed, and both olfactory and respiratory mucosae were inserted into the posterior sulcuses of the spinal cord. The each number of olfactory and mucosa transplanted rats were five. The Basso, Beattie, and Bresnahan (BBB) score was observed. Immunohistochemical study for neurofilament was performed. Results: Olfactory mucosa transplanted rats following spinal cord injury can support at least partial hind limb motor recovery compared with respiratory mucosa transplanted rats and we identified numerous axons surrounding the transplanted olfactory mucosa cells, and penetrating the olfactory mucosa at the transplant site. Conclusion: Olfactory mucosa might be a suitable scaffold for axonal regeneration.

Involuntary muscle spasm expressed as motor evoked potential after olfactory mucosa autograft in patients with chronic spinal cord injury and complete paraplegia  [PDF]
Koichi Iwatsuki, Toshiki Yoshimine, Yoshiyuki Sankai, Fumihiro Tajima, Masao Umegaki, Yu-Ichiro Ohnishi, Masahiro Ishihara, Koshi Ninomiya, Takashi Moriwaki
Journal of Biomedical Science and Engineering (JBiSE) , 2013, DOI: 10.4236/jbise.2013.69111
Abstract: Object: The efficacy of olfactory mucosa autograft (OMA) for chronic spinal cord injury has been reported. New activity in response to voluntary effort has been documented by electromyography (EMG), but the emergence of motor evoked potential (MEP) reflecting electrophysiological conductivity in the central nervous system, including the corticospinal pathway, after OMA, and the best indications for OMA, have not been clarified. Here, we report the emergence of MEPs after OMA and offer recom-mendations for appropriate indications based on the presence of involuntary muscle spasm (IMS). We used analysis of MEP to examine the efficacy of OMA for patients with complete paraplegia due to chronic spinal cord injury. To clarify the indications for OMA, we investigated the association of IMS and efficacy of OMA. Methods: Four patients, 3 men and 1 woman, were enrolled. The mean age of the cases was 30.3 ± 9.5 years (range, 19 to 40 years). All 4 cases were American Spinal Injury Association (ASISA) grade A. The mean duration from injury to OMA was 95.8 ± 68.2 months (range, 17 to 300 months). Samples of olfactory mucosa were removed, cut into smaller pieces, and grafted into the sites of spinal cord lesions after laminectomy. Postoperative subcutaneous fluid collection, postoperative meningitis, postoperative nosebleed, postoperative infection in the nasal cavity, impaired olfaction, neoplastic tissue overgrowth at the autograft site, new sensory disturbance, and involuntary muscle spasm were investigated as safety issues. Improvements in ASIA grade, variations in ASIA scores, EMG, SSEP, and improved urological function were evaluated as efficacy indicators. Results: There were no serious adverse events in this series. In 2 of the 4 cases, an improvement in motor function below the level of injury was recognized. In one, the motor score was 50 until 16 weeks after surgery, and it increased to 52 from 20 weeks after surgery. In the other, the motor score was 50 until 20 weeks after surgery, and it increased to 52 at 24 weeks after surgery with a further increase to 54 at 48 weeks after surgery. The emergence of MEP was recognized in the latter case at 96 weeks after surgery. The other 2 cases had no improvement in ASIA motor score. Both of these cases who showed improvements in the ASIA motor scores exhibited relative IMS compared with those who had no ASIA motor score recovery. Conclusions: We recognized the emergence of MEPs in a case with complete paraplegia due to chronic spinal cord injury after OMA. IMS
Study of the Long-Term X-Ray Variability of a Possible Quasar RX J0957.9+6903 with ASCA
Yu-ichiro Ezoe,Naoko Iyomoto,Kazuo Makishima
Physics , 2000, DOI: 10.1093/pasj/53.1.69
Abstract: Long-term variability and spectral properties of a possible quasar, RX J0957.9+6903, were studied, utilizing 16 ASCA observations spanning 5.5 years. The average 0.7--10 keV spectrum of RX J0957.9+6903 is well represented by a power-law continuum of photon index 1.58 $\pm$ 0.03, and an absorption column of $\sim$ 1$\times{\rm 10}^{21}$ ${\rm cm}^{-2}$. The 2--10 keV flux of RX J0957.9+6903 varied by a factor of four over the period of six years, around a mean of $\sim$ 8.8$\times {\rm 10}^{-12}$ erg ${\rm s}^{-1}$ ${\rm cm}^{-2}$. Peak to peak variability within each observation was less than 25% on $\sim$ 1 day time scale. These properties support the classification of RX J0957.9+6903 as a quasar. The power spectrum density (PSD) was estimated in a "forward" manner, over a frequency range of $10^{-8.2}$--$10^{-4.3}$ Hz, by utilizing the structure function method and Monte-Carlo simulation assuming a broken power-law type PSD. Then, the break frequency $f_{\rm b}$ of the PSD of RX J0957.9+6903 has been constrained as 1/$f_{\rm b}$ = $1600^{+\infty}_{-1100}$ days, and the logarithmic slope of the high-frequency region of the PSD as $\alpha$ = $-$1.55 $\pm$ 0.2. A comparison of the estimated PSDs is made between RX J0957.9+6903 and the M81 nucleus, observed in the same field of view.
General Relativistic Ray-Tracing Method for Estimating the Energy and Momentum Deposition by Neutrino Pair Annihilation in Collapsars
Seiji Harikae,Kei Kotake,Tomoya Takiwaki,Yu-ichiro Sekiguchi
Physics , 2010, DOI: 10.1088/0004-637X/720/1/614
Abstract: Bearing in mind the application to the collapsar models of gamma-ray bursts (GRBs), we develop a numerical scheme and code for estimating the deposition of energy and momentum due to the neutrino pair annihilation ($\nu + {\bar \nu} \rightarrow e^{-} + e^{+}$) in the vicinity of accretion tori around a Kerr black hole. Our code is designed to solve the general relativistic neutrino transfer by a ray-tracing method. To solve the collisional Boltzmann equation in curved spacetime, we numerically integrate the so-called rendering equation along the null geodesics. For the neutrino opacity, the charged-current $\beta$-processes are taken into account, which are dominant in the vicinity of the accretion tori. The numerical accuracy of the developed code is certificated by several tests, in which we show comparisons with the corresponding analytic solutions. Based on the hydrodynamical data in our collapsar simulation, we estimate the annihilation rates in a post-processing manner. Increasing the Kerr parameter from 0 to 1, it is found that the general relativistic effect can increase the local energy deposition rate by about one order of magnitude, and the net energy deposition rate by several tens of percents. After the accretion disk settles into a stationary state (typically later than $\sim 9$ s from the onset of gravitational collapse), we point out that the neutrino-heating timescale in the vicinity of the polar funnel region can be shorter than the dynamical timescale. Our results suggest the neutrino pair annihilation has a potential importance equal to the conventional magnetohydrodynamic mechanism for igniting the GRB fireballs.
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