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Search Results: 1 - 10 of 1883 matches for " Hajime Shibata "
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Orbital-dependent two-band superconductivity in MgB2
Takashi Yanagisawa,Hajime Shibata
Physics , 2003, DOI: 10.1143/JPSJ.72.1619
Abstract: We show that a two-band model with ${\bf k}$-dependent superconducting gaps well describes the transmission and optical conductivity measured for MgB$_2$ thin films. It is also shown that the two-band anisotropic model consistently describes the specific-heat jump and thermodynamic critical magnetic field $H_c$. A single-gap anisotropic model is shown to be insufficient to understand consistently optical and thermodynamic behaviors. In our model, the pairing symmetry in each band has an anisotropic characteristic which is determined almost uniquely; the superconducting gap in the $\sigma$-band has anisotropy in the ab-plane and the gap in the $\pi$-band has a prolate form exhibiting anisotropy in the c-direction. The anisotropy in the $\sigma$-band produces rather small effects on the physical properties compared to the anisotropy in the $\pi$-band.
Optical properties of unconventional superconductors
Takashi Yanagisawa,Hajime Shibata
Physics , 2004,
Abstract: The optical conductivity measurements give a powerful tool to investigate the nature of the superconducting gap for conventional and unconventional superconductors. In this article, first, general analyses of the optical conductivity are given stemmed from the Mattis-Bardeen formula for conventional BCS superconductors to unconventional anisotropic superconductors. Second, we discuss the reflectance-transmittance (R-T) method which has been proposed to measure far-infrared spectroscopy. The R-T method provides us precise measurements of the frequency-dependent conductivity. Third, the optical conductivity spectra of the electron-doped cuprate superconductor Nd_{2-x}Ce_xCuO_4 are investigated based on the anisotropic pairing model. It is shown that the behavior of optical conductivity is consistent with an anisotropic gap and is well explained by the formula for d-wave pairing in the far-infrared region. The optical properties of the multiband superconductor MgB_2, i n which the existence of superconductivity with relatively high-T_c (39K) was recently announced, is also examined to determine the symmetry of superconducting gaps.
Genetic Association between Akt1 Polymorphisms and Alzheimer's Disease in a Japanese Population
Nobuto Shibata,Tohru Ohnuma,Bolati Kuerban,Miwa Komatsu,Hajime Baba,Heii Arai
International Journal of Alzheimer's Disease , 2011, DOI: 10.4061/2011/762471
Abstract: A recent paper reported that Aβ oligomer causes neuronal cell death through the phosphatidylinositol-3-OH kinase (PI3K)-Akt-mTOR signaling pathway. Intraneuronal Aβ, a main pathological finding of Alzheimer's disease (AD), is also known as inhibiting activation of Akt. This study aims to investigate whether single nucleotide polymorphisms (SNPs) of the Akt1 gene are associated with AD. SNPs genotyped using TaqMan technology was analyzed using a case-control study design. Our case-control dataset consisted of 180 AD patients and 130 age-matched controls. Although two SNPs showed superficial positive, Hardy-Weinberg equilibrium (HWE) tests, and linkage disequilibrium (LD) analyses suggested that genetic regions of the gene are highly polymorphic. We failed to detect any synergetic association among Akt1 polymorphisms, Apolipoprotein E (APO E), and AD. Further genetic studies are needed to clarify the relationship between the Akt1 and AD. 1. Introduction The main pathological feature of Alzheimer’s disease (AD) is the senile plaque containing aggregated Amyloid β peptide (Aβ). Three genes have been identified as causative genes in familial AD; the amyloid precursor protein (APP), presenilin-1, and presenilin-2 genes. Apolipoprotein E (APO E) is recognized as a genetic risk factor for familial and sporadic AD [1]. In addition, variants of the sortilin-related receptor 1 (SORL1) gene have also been associated with the disease [1, 2]. The evidence from SORL1 suggested that intraneuronal Aβ is significant in early pathogenesis for AD. Recent findings showed that Aβ oligomer is more toxic for neuronal cell [3, 4]. There is widening recognition that the phosphatidylinositol-3-OH kinase (PI3K)-Akt-mTOR signaling pathway is directly affected by Aβ and especially Aβ oligomer modulate cell survival through PI3K-Akt pathway [3, 5–7]. An impaired insulin-mediated signal transduction is one of the pathological features of neurodegenerative diseases [8]. Epidemiological studies note that type II diabetes is risk factor for late-onset AD [9]. Insulin dysfunction might be associated with Aβ and tangles [10, 11]. Intraneuronal Aβ inhibits insulin receptors signaling in neurons by interfering with the association between Akt1 to preclude Akt1 activation [12]. In AD brains, level of PI3K-Akt-mTOR would be decreased [8]. Thus current reports revealed that the dysfunction of PI3K-Akt-mTOR system affect AD pathology [9]. Although genetic variability of PI3K has been reported to affect the risk for AD [13], there are few genetic researches about Akt and AD. In this study, the
Multi-Junction Switching in Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$ Intrinsic Josephson Junctions
Hiromi Kashiwaya,Tetsuro Matsumoto,Hajime Shibata,Hiroshi Eisaki,Yoshiyuki Yoshida,Hiroshi Kambara,Shiro Kawabata,Satoshi Kashiwaya
Physics , 2010, DOI: 10.1143/APEX.3.043101
Abstract: We study the dynamics of multi-junction switching (MJS): several intrinsic Josephson junctions (IJJs) in an array switch to the finite voltage state simultaneously. The number of multi-switching junctions ($N$) was successfully tuned by changing the load resistance serially connected to an Bi$_2$Sr$_{1.6}$La$_{0.4}$CuO$_{6+\delta}$ IJJ array. The independence of the escape rates of $N$ in the macroscopic quantum tunneling regime indicates that MJS is a $successive$ switching process rather than a $collective$ process. The origin of MJS is explained by the gradient of a load curve and the relative magnitudes of the switching currents of quasiparticle branches in the current-voltage plane.
Anisotropic Optical Conductivity of Nd2-xCexCuO4 Thin Films
Takashi Yanagisawa,Shigeru Koikegami,Hajime Shibata,Shinji Kimura,Satoshi Kashiwaya,Akihito Sawa,Noritaka Matsubara,Koki Takita
Physics , 2002, DOI: 10.1143/JPSJ.70.2833
Abstract: Opticcal conductivity spectra $\sigma_1(\omega)$ of Nd2-xCexCuO4 thin films, measured by the reflectance-transmittance method (R-T method) which has been proposed to investigate far-infrared spectroscopy, are investigated based on the anisotropic pairing model. Precise measurements of the frequency-dependent conductivity enable us to examine quantitatively the nature of the superconducting gap through infrared properties in the electron-doped high-Tc superconductors. We show that the behavior of optical conductivity $\sigma_1$ is consistent with the anisotropic superconducting gap and is well explained by the formula for d-wave pairing in the low-energy regime of the far-infrared region. Our results suggest that the electron-doped cuprate superconductors Nd2-xCexCuO4 have nodes in the superconducting gap.
Two cases of juvenile hypertrophic cardiomyopathy presenting with marked bi-atrial enlargement on standard 12-lead electrocardiogram  [PDF]
Hajime Kataoka
Open Journal of Internal Medicine (OJIM) , 2012, DOI: 10.4236/ojim.2012.21007
Abstract: This report describes two cases of juvenile hypertrophic cardiomyopathy (HCM) in which prominent bi-atrial enlargement was observed on standard 12-lead electrocardiogram, suggesting inherent predis-position to extreme enlargement and/or hypertrophy may exist in atrial myocardium in juvenile HCM. Comparative study between juvenile and adult HCM patients using a large sample size is required to confirm this hypothesis.
Protective Effect of Ethanolamine on Hepatic Preneoplastic Alterations Induced by the Administration of N-Nitrosodiethylamine in Rats  [PDF]
Hajime Sasaki
Food and Nutrition Sciences (FNS) , 2017, DOI: 10.4236/fns.2017.810067
The effects of exogenously administered ethanolamine (Etn) on the N-nitrosodiethylamine (NDA)-induced formation of hepatic lesions in rats were investigated. Sprague-Dawley rats were intraperitoneally administered NDA (100 mg/kg body weight) at 7-day intervals, and the animals were allowed free access to water containing Etn (15 or 50 mg/L) for 35 days. NDA-induced hepatic lesions were assessed according to the number of nodules detectable on the liver surface, areas of clear cell foci observed on histopathological thin sections, hydroxyproline levels in liver homogenates, and blood biochemical marker levels. Compared with those from control rats that were not administered Etn, livers from Etn-exposed rats had significantly fewer surface nodules and smaller areas of clear cell foci, indicating that Etn prevented or delayed the formation of preneoplastic cell alterations. Hydroxyproline levels in livers were significantly lower in Etn-treated rats, indicating that the chemical prevented the formation of fibrotic alterations. The protective effects of Etn on NDA-induced hepatic lesions were demonstrated by changes in blood biochemical marker levels. These results suggest that Etn can protect against cellular alterations induced by a carcinogenic chemical, possibly by enhancing hepatic phospholipid synthesis.
Effects of Pitavastatin on the Intima-Media Thickness of the Carotid Artery in Patients with Ischemic Stroke: The Pitavastatin Efficacy Study on Surrogate Markers and Imaging for Stroke (PESSMIST)  [PDF]
Yasushi Shibata
World Journal of Neuroscience (WJNS) , 2014, DOI: 10.4236/wjns.2014.44034

Pitavastatin is a strong statin that was developed in Japan. The clinical impact of pitavastatin treatment in patients with ischemic stroke has not been reported. We conducted a prospective, open label, clinical case-control study to determine the secondary preventive effects of pitavastatin for patients with cerebral infarction and hyperlipidemia. The pitavastatin group included 20 Japanese patients diagnosed with cerebral infarction and hyperlipidemia without previous statin intake. The control group included 22 patients diagnosed with cerebral infarction without hyperlipidemia. The pitavastatin group of patients received 2 mg of pitavastatin once a day after dinner. The mean age of the patients was 69.3 and 75.5 years for the pitavastatin and control groups, respectively, and the age of the pitavastatin group was significantly younger than that of the control group (P < 0.05). The serum TCho and LDL-C levels significantly decreased two months after the initiation of pitavastatin treatment. The mean and maximum intima-media thickness (IMT) also decreased after the initiation of pitavastatin. The mean and maximum IMT did not show any significant changes in the control group. The change of IMT %/year was less than zero for the pitavastatin group, and was almost zero or higher for the control group. Pitavastatin showed beneficial effects by improving the surrogate makers of stroke. These surrogate makers were effective to evaluate the efficacy of pitavastatin to prevent secondary stroke. Although a prospective randomized study is required to elucidate the long-term effects of pitavastatin, the current study suggests that pitavastatin may be effective to prevent secondary stroke in patients with stroke and hyperlipidemia.

Effect of Silver-Loaded Zeolite on the Susceptibility of Escherichia Coli Against Antibiotics  [PDF]
Yoshihiro Inoue, Hajime Hamashima
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2012, DOI: 10.4236/jbnb.2012.31015
Abstract: We investigated the effect of silver-loaded zeolite (Ag-Z) on antibacterial activity of some antibiotics against Es-cherichia coli against antibiotics. We treated the bacterial suspension of E. coli by Ag-Z to be the level which the decrease of viable cell count was not observed. Susceptibility test of E. coli treated with Ag-Z was carried out against four antibiotics with different mode of action. Apparent increase in susceptibility was found in the case of rifampicin, not in others. The result suggests that application of Ag-Z to ward environment might give a good outcome at the treatment with rifampicin and at the treatment for pathogenic microbe spread through the air, such as tubercle bacilli.
Electrochemical Analysis of the Redox State of Silver Contained in Antibacterial Material  [PDF]
Yoshihiro Inoue, Hajime Hamashima
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2012, DOI: 10.4236/jbnb.2012.32019
Abstract: Introduction of silver into some inorganic material causes the resulting mixture to have antibacterial activity. Here, we investigated the role of silver in the bactericidal activity of silver-loaded zeolite, by measuring the effects of silver-loaded zeolite on Escherichia coli cell viability under conditions in which the oxidation state of the silver was controlled electrochemically. Bactericidal activity was observed when the sweeping voltage between 0 and 0.7 V was applied to the silver electrode. When nitrogen gas bubbling or reactive oxygen scavengers were added to the experimental system, bactericidal activity decreased. These results indicated that the redox cycle, Ag0 <—> Ag+, caused the dissolved oxygen to form reactive oxygen species.
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