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Search Results: 1 - 10 of 2846 matches for " Akira Uehara "
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Gauge Fields on Tachyon Matter
Akira Ishida,Shozo Uehara
Physics , 2002, DOI: 10.1016/S0370-2693(02)02542-X
Abstract: We study the rolling tachyon including the gauge fields in boundary string field theory. We show that there are no plane wave solutions for the gauge fields for large time. The disappearance of the plane wave solutions indicates that there are no excitations of the gauge fields on the tachyon matter, which is consistent with the Sen's conjecture.
Rolling down to D-brane and tachyon matter
Akira Ishida,Shozo Uehara
Physics , 2003, DOI: 10.1088/1126-6708/2003/02/050
Abstract: We investigate the spatially inhomogeneous decay of an unstable D-brane and construct an asymptotic solution which describes a codimension one D-brane and the tachyon matter in boundary string field theory. In this solution, the tachyon matter exists around the lower-dimensional D-brane.
Autoequivalences of derived categories on the minimal resolutions of $A_n$-singularities on surfaces
Akira Ishii,Hokuto Uehara
Mathematics , 2004,
Abstract: In this article, we study the group of autoequivalences of derived categories of coherent sheaves on the minimal resolution of $A_n$-singularities on surfaces. Our main result is to find generators of this group.
Chemical Phase Separation of Superconductive and Ferromagnetic Domains in
Takahiro Yamazaki,Akira Uehara,Katsuya Kozawa,Yoshihide Kimisima,Masatomo Uehara
Advances in Condensed Matter Physics , 2012, DOI: 10.1155/2012/902812
Abstract: Various ZnNyNi3?xCox compounds with differing Co content, x, were synthesized, and their magnetic properties were investigated. Uniform solid solutions could not be obtained at low Co content ( ); instead micrometer-scaled ferromagnetic ZnNyNi0.6Co2.4 domains formed embedded within a superconductive ZnNNi3 bulk, showing chemical phase separation of superconductive ZnNNi3 and ferromagnetic ZnNyNi0.6Co2.4. At intermediate levels of Co concentration ( ), this two-phase separation might persist, and the superconductive behavior was strongly suppressed in this composition region. Only at high Co concentration ( ) the uniform ferromagnetic solid solution ZnNyNi3?xCox (with most likely ) formed. The phase separation behavior is intrinsic to the system, reflecting the existence of a miscibility gap in ZnNyNi3?xCox for the samples with , and was shown not to be attributable to incomplete synthesis. In the two-phased samples, high-quality granular contact between the superconductor and ferromagnet has been realized, suggesting that the production of useful devices requiring high-quality contacts between superconductors and ferromagnets may be possible by making use of this two-phase situation. 1. Introduction He et al. discovered a new antiperovskite superconductor MgCNi3 that has a superconducting transition temperature ?K [1]. This compound has attracted attention in the context of the relationship between superconductivity and ferromagnetism, because the material includes large amounts of ferromagnetic Ni and has structural similarities with f.c.c. elemental Ni. Some researchers have supposed that the ferromagnetic correlation is associated with the superconductivity of MgCNi3. A theoretical calculation has pointed out that this compound is located near a ferromagnetic state and that the emergence of ferromagnetism may be induced by hole doping [2]. In order to reveal the superconducting gap symmetry and to clarify the microscopic origin of the superconductivity in MgCNi3, various types of experiments have been carried out [3–14]. However, a rigid consensus has not been obtained yet about the origin of superconductivity in MgCNi3. Stimulated by the discovery of MgCNi3, several new antiperovskite compounds have been synthesized including two new superconductors, CdCNi3 and ZnNNi3, and complementary theoretical studies have been performed, especially for these new superconductors [15–33]. In this study we synthesized and investigated the physical properties of the system composed of superconductive ZnNNi3 and ferromagnetic . ZnNNi3 is a superconductor with ?K
New anti-perovskite-type Superconductor ZnNyNi3
Masatomo Uehara,Akira Uehara,Katsuya Kozawa,Yoshihide Kimishima
Physics , 2008, DOI: 10.1143/JPSJ.78.033702
Abstract: We have synthesized a new superconductor ZnNyNi3 with Tc ~3 K. The crystal structure has the same anti-perovskite-type such as MgCNi3 and CdCNi3. As far as we know, this is the third superconducting material in Ni-based anti-perovskite series. For this material, superconducting parameters, lower-critical field Hc1(0), upper-critical field Hc2(0), coherence length x(0), penetration depth l(0), and Gintzburg -Landau parameter k(0) have been experimentally determined.
High Resolution X-Ray Diffraction Analyses of (La,Sr)MnO3/ZnO/Sapphire(0001) Double Heteroepitaxial Films  [PDF]
Katsuhiko Inaba, Shintaro Kobayashi, Kenichi Uehara, Akira Okada, Sanapa Lakshmi Reddy, Tamio Endo
Advances in Materials Physics and Chemistry (AMPC) , 2013, DOI: 10.4236/ampc.2013.31A010
Abstract:

The epitaxial relationships of lattices and crystalline qualities of LSMO/ZnO/sapphire double-hetero systems were thoroughly analyzed using X-ray diffraction techniques with a modern high resolution XRD system. It was revealed that the epitaxial growth of the LSMO (110) phase was promoted under higher temperature accompanying the suppression of other competitive growth of the LSMO (001) and (111) phases. Supplying the plasma oxygen accelerated the suppression of the LSMO (111) phase. The complex epitaxial orientational relationships in these three growth modes were revealed from the precise analyses with the high resolution out-of-plane XRD and the in-plane XRD measurements, pole figure measurements, and reciprocal space mappings measurements, as [112ˉ](111)LSMO//[11ˉ00](0001)ZnO//[112ˉ0](0001)Sap, [110ˉ](111LSMO)//[11ˉ00](0001)Zno//[112ˉ0](0001)Sap, and [110](001)LSMO//[11ˉ00](0001)Zno//[112ˉ0](0001)Sap. The validity of this model for the epitaxial orientational relationships in LSMO/ZnO/sapphire double heteroepitaxial layers was confirmed identically with the data ana- lyses of the out-of-plane wide-range Reciprocal Space Mapping using the 2-dimensional X-ray detector.

Histological Findings of Bone Marrow Lesions on Magnetic Resonance Images in Patients with Varus Knee Osteoarthritis  [PDF]
Takehiko Sugita, Tomomaro Kawamata, Toshimi Aizawa, Akira Sasaki, Naohisa Miyatake, Takeshi Uehara
Open Journal of Orthopedics (OJO) , 2014, DOI: 10.4236/ojo.2014.412050
Abstract: Bone marrow lesions (BMLs) on magnetic resonance (MR) images in knee osteoarthritis patients are considered to predict the severity and progression of the disease. We evaluated the histological findings of BMLs on MR images of the subchondral area of the medial femoral condyle in varus osteoarthritic knees. In 24 patients with varus knee osteoarthritis who underwent total knee arthroplasty (TKA), sagittal T1- and T2-weighted MR images of the affected knee were acquired before TKA. During TKA, resected bone pieces from the distal medial femoral condyle were obtained. Sagittal specimens obtained from the center of the bone pieces were histologically examined. Twenty patients had BMLs. Histological findings of BMLs in the subchondral area showed various features, such as fibrovascular tissue, cyst formation, active bone remodeling with bone formation and bone resorption, and hyaline cartilage. BMLs were not found in four patients; histological findings of these patients showed normal bone marrow tissue with normal-thickness trabeculae. Subchondral bony end plate in knees with BMLs was usually thin or destroyed, while that without BMLs was thick or normal. The condition of the subchondral bony end plate would explain the differences in the severity and progression between patients with or without BMLs.
Stability conditions on $A_n$-singularities
Akira Ishii,Kazushi Ueda,Hokuto Uehara
Mathematics , 2006,
Abstract: We study the spaces of locally-finite stability conditions on the derived categories of coherent sheaves on the minimal resolutions of $A_n$-singularities supported at the exceptional sets. Our main theorem is that they are connected and simply-connected. The proof is based on the study of spherical objects in math.AG/0409151 and the homological mirror symmetry for $A_n$-singularities.
Stress-induced hemorrhagic gastric ulcer after successful Helicobacter pylori eradication: two case reports
Mitsuru Moriya, Akira Uehara, Toshikatsu Okumura, Mitsuaki Miyamoto, Yutaka Kohgo
Journal of Medical Case Reports , 2011, DOI: 10.1186/1752-1947-5-252
Abstract: We report the cases of a 47-year-old Japanese man and a 69-year-old Japanese man who developed psychological stress-induced hemorrhagic gastric ulcers, in both of whom Helicobacter pylori had been successfully eradicated.Our cases strongly suggest that not only physical but also psychological stress is still an important pathogenic factor for peptic ulceration and accordingly that physicians should pay attention to the possible presence of psychological stress in the management of patients with peptic ulcers.Since Selye [1] reported that stress induces gastrointestinal ulcers, stress has been a major pathogenic factor for peptic ulceration. It is now well-documented, however, that Helicobacter pylori (Hp) infection is a major cause of peptic ulcers and that Hp eradication drastically reduces ulcer recurrence, thereby understating or even excluding the importance of stress in ulcer formation.On the other hand, there is increasing evidence that peptic ulcers can occur even in patients without chronic Hp infection or the use of non-steroidal anti-inflammatory drugs (NSAIDs). Chen et al. [2] examined 32 non-Hp and non-NSAID duodenal ulcer cases and reported that 15.6% of the cases were closely associated with psychophysical stress. In 2009, Wong et al. [3] revealed that patients with Hp-negative idiopathic bleeding ulcers, in the pathogenesis of which mental stress might play an important role, had a high risk of mortality and recurrent bleeding.Along these lines, we report the cases of two patients with psychological stress-induced hemorrhagic gastric ulcers in whom Hp had been successfully eradicated. This case report surely provides clinically important information that psychological stress should also be considered in the management of patients with gastric ulcers.A 47-year-old Japanese man had been admitted to the hospital for hematemesis and tarry stools 14 years ago. He had a medical history of gastric ulcer and had received Hp eradication therapy two years befor
Synthesis and characterisation of some metal complexes of hybrid phosphorus-nitrogenligands: the crystal structure of 1-(diphenylphosphino)-2-(2-pyridyl)ethane cobalt(II) chloride
Peter T. Ndifon, Moise O. Agwara, Yoshihito Hayashi, Akira Uehara
Bulletin of the Chemical Society of Ethiopia , 2008,
Abstract: Some iron(II), cobalt(II) and copper(II) complexes of the hybrid ligand 1-(diphenylphosphino)-2-(2-pyridyl)ethane (dppe) and diphenyl-2-pyridylphosphine (dppp) have been synthesised and characterised. Analyses suggest tetrahedral structures in which the metal atoms are bonded to two chlorine atoms and to both phosphorus and nitrogen atoms for 1-(diphenylphosphino)-2-(2-pyridyl)ethane on one hand and on the other hand, bonding is through the nitrogen atoms of two molecules of diphenyl-2-pyridylphosphine, which acts as a monodentate ligand. The crystal structure of 1-(diphenylphosphino)-2-(2-pyridyl)ethane cobalt(II) chloride shows a pseudo-tetrahedral structure in which the aminophosphine is bonded to the cobalt centre through both the phosphorus and nitrogen atoms, forming a 6-membered ring. KEY WORDS: Aminophosphines, Metal complexes, Cobalt(II) complex, Crystal structure Bull. Chem. Soc. Ethiop. 2008, 22(2), 253-260.
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