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Search Results: 1 - 10 of 2568 matches for " Akira Kohyama "
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Effects of Pressure during Preform Densification on SiC/SiC Composites  [PDF]
Naofumi Nakazato, Akira Kohyama, Yutaka Kohno
Open Journal of Inorganic Non-metallic Materials (OJINM) , 2013, DOI: 10.4236/ojinm.2013.31003

The nano-infiltration and transient eutectic-phase (NITE) method is one of the most attractive methods for fabrication of SiC and SiC/SiC composites. In the NITE method, preform densification is essential option for damage less near-net shaping technique. However, optimization of preform densification is insufficient yet. The objective of this study is to evaluate the effects of pressure during preform densification on SiC/SiC composites. The preform before preform densification has many pores in the inter-prepreg sheets. These pores were disappeared by preform densification. As the effects of pressure on preform, densification in the intra-fiber-bundle was improved due to increasing pressure. Flexural strength of the preforms with 1 MPa and 17 MPa indicated almost same value. The result suggested that increasing of pressure did not cause any change in fiber properties. In the effects of pressure on the composites, the composites with 17 MPa was exhibited improvement in bulk density and mechanical property, compared with that with 1 MPa.

Sleep, Serotonin, and Suicide  [PDF]
Jun Kohyama
Journal of Behavioral and Brain Science (JBBS) , 2012, DOI: 10.4236/jbbs.2012.24055
Abstract: The author hypothesizes that sleep loss associated with a decrease in serotonergic activity plays a significant role in attempted suicide. Recent research has emphasized the role of the economic recession on the occurrence of suicide, but with no attention paid to possible biological aspects. In this brief review, the association between sleep, the serotonergic system, and suicide is initially introduced. Then, with consideration of recent research, a hypothesis regarding the oc- currence of suicide is proposed. Finally, based on that hypothesis, three factors possibly germane to reducing suicides (sufficient sleep duration, activation of the serotonergic system, and activation of the prefrontal cortex) are discussed.
Capacity Limitations of Medical Services Provided by Pediatricians in Japan  [PDF]
Jun Kohyama
Open Journal of Pediatrics (OJPed) , 2014, DOI: 10.4236/ojped.2014.41014

The shortage of pediatricians has been identified as one of the largest social problems in Japan. This study aimed to compare the assumed ideal nighttime working conditions of pediatric hospitalists in Japan with the actual current situation. By using available data on the age-related numbers of pediatricians in Japan, we described the ideal working conditions for pediatric hospitalists in Japan. The ideal situation was then compared with the existing actual working conditions. Compared with the assumed ideal condition, current pediatric hospitalists are working in many hospitals with a few colleagues. To solve the current supply-demand mismatch on medical care for children during night, an involvement of non-pediatric physicians in the medical care of children during the night is indispensable. Also, parents in Japan need to know the limitations relating to the available capacity of pediatricians, and accept that their children can be cared for adequately by non-pediatric physicians, who have been trained to provide primary medical care to children.

High Frequency of a Single Nucleotide Substitution (c.-6-180T>G) of the Canine MDR1/ABCB1 Gene Associated with Phenobarbital-Resistant Idiopathic Epilepsy in Border Collie Dogs
Keijiro Mizukami,Akira Yabuki,Hye-Sook Chang,Mohammad Mejbah Uddin,Mohammad Mahbubur Rahman,Kazuya Kushida,Moeko Kohyama,Osamu Yamato
Disease Markers , 2013, DOI: 10.1155/2013/695918
Abstract: A single nucleotide substitution (c.-6-180T>G) associated with resistance to phenobarbital therapy has been found in the canine MDR1/ABCB1 gene in Border Collies with idiopathic epilepsy. In the present study, a PCR-restriction fragment length polymorphism assay was developed for genotyping this mutation, and a genotyping survey was carried out in a population of 472 Border Collies in Japan to determine the current allele frequency. The survey demonstrated the frequencies of the T/T wild type, T/G heterozygote, and G/G mutant homozygote to be 60.0%, 30.3%, and 9.8%, respectively, indicating that the frequency of the mutant G allele is extremely high (24.9%) in Border Collies. The results suggest that this high mutation frequency of the mutation is likely to cause a high prevalence of phenobarbital-resistant epilepsy in Border Collies. 1. Introduction Recently, a single nucleotide substitution associated with phenobarbital-resistant idiopathic epilepsy was found in Border Collies [1], which frequently present with severe epileptic seizures that are poorly controlled with antiepileptic drugs [2]. This polymorphic mutation is a substitution of thymine for guanine at intron 1 near the 5′-end of the canine MDR1/ABCB1 gene (c.-6-180T>G), where the most important promoter elements are located [3]. The mutation is not directly associated with the pathogenesis of idiopathic epilepsy, but it may create resistance to phenobarbital therapy in epileptic Border Collies [1]. However, the c.-6-180T>G mutation has been shown not to be a fully penetrant polymorphic mutation for phenobarbital nonresponsiveness because phenobarbital-resistant, idiopathically epileptic Border Collies in a previous case control study included a homozygous T/T wild-type dog [1]. On the basis of data from a relatively small cohort of Border Collies, it was hypothesized that the mutation might be related to an upregulation of the gene and an overexpression of P-glycoprotein (P-gp) encoded by the MDR1/ABCB1 gene. Therefore, further studies are required to understand the regulatory effect of the mutation and its potential clinical relevance. For these purposes, an accurate method of genotyping for the mutation should be developed, and the frequency of the mutation should be determined in a large, normal population of dogs. In the present study, a PCR-restriction fragment length polymorphism (RFLP) assay was developed in order to discriminate the genotypes of the mutation, and a genotyping survey was conducted in Japan by using samples from clinically healthy Border Collies in order to determine
Phase diagram of quark-antiquark and diquark condensates at finite temperature and density in the 3-dimensional Gross Neveu model
Kohyama, Hiroaki
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.77.045016
Abstract: We construct the phase diagrams of the quark-antiquark and diquark condensates at finite temperature and density in the 3D (dimensional) 2-flavor Gross Neveu model. We found that, in contrast to the case of the 4D Nambu Jona-Lasinio model, there is no region where the quark-antiquark and diquark condensates coexist. The phase diagrams obtained for some parameter region show similar structure with the 4D QCD phase diagram.
Early rising children are more active than late risers
Jun Kohyama
Neuropsychiatric Disease and Treatment , 2007,
Abstract: Jun KohyamaDepartment of Pediatrics, Tokyo Kita Shakai Hoken Hospital, Tokyo, JapanBackground: A low level of physical activity impacts mental as well as physical health. This study investigated the daily lifestyle habits that affect physical activity in young children.Methods: The relationship between physical activity, assessed by means of a Mini-Mitter Actiwatch device, and observed daily lifestyle habits was analyzed for 204 children, aged 12 to 40 months (average: 22.6 months), for whom 6-consecutive-day data from both the Actiwatch and sleep log were obtained.Results: An older age, male gender, and early waking time showed significant positive correlations with physical activity level. Multiple regression analysis revealed that these three variables were significant predictors of physical activity.Conclusion: Promoting an early rising time is suggested to be an important element of cultivating good health in young children.Keywords: physical activity, children, actigraphy, morning light
Effects of Preparation Conditions on the Microstructure and Properties of Hot Pressed SiC/SiC Composites

DONG Shao-Ming,DING Yu-Sheng,JIANG Dong-Liang,KOHYAMA Akira,

无机材料学报 , 2005,
Abstract: 采用纳米SiC和亚微米SiC粉料作为基体形成原料,通过热压烧结技术制备了SiC/SiC复合材料.研究了粉料颗粒、烧结温度、烧结压力对复合材料显微结构和各种性能的影响.结果显示,采用纳米碳化硅粉体可有效降低烧结温度,促进复合材料的致密化过程,在1780℃、20MPa条件下可获得性能优良的复合材料.而采用亚微米SiC粉体,复合材料的致密化过程需要较高的温度,但随着密度的增加,基体与纤维之间的作用力增强,不利于性能的提高.
Analytical Study on the Sunyaev-Zeldovich Effect for Clusters of Galaxies
Satoshi Nozawa,Yasuharu Kohyama
Physics , 2009, DOI: 10.1103/PhysRevD.79.083005
Abstract: Starting from a covariant formalism of the Sunyaev-Zeldovich effect for the thermal and non-thermal distributions, we derive the frequency redistribution function identical to Wright's method assuming the smallness of the photon energy (in the Thomson limit). We also derive the redistribution function in the covariant formalism in the Thomson limit. We show that two redistribution functions are mathematically equivalent in the Thomson limit which is fully valid for the cosmic microwave background photon energies. We will also extend the formalism to the kinematical Sunyaev-Zeldovich effect. With the present formalism we will clarify the situation for the discrepancy existed in the higher order terms of the kinematical Sunyaev-Zeldovich effect.
Relativistic corrections to the Kompaneets equation
Satoshi Nozawa,Yasuharu Kohyama
Physics , 2014, DOI: 10.1016/j.astropartphys.2014.07.008
Abstract: We study the Sunyaev-Zeldovich effect for clusters of galaxies. We explore the relativistic corrections to the Kompaneets equation in terms of two different expansion approximation schemes, namely, the Fokker-Planck expansion approximation and delta function expansion approximation. We show that two expansion approximation formalisms are equivalent under the Thomson approximation, which is extremely good approximation for the CMB photon energies. This will clarify the situation for existing theoretical methods to analyse observation data.
Analytical studies on the Sunyaev-Zeldovich effect in the cluster of galaxies for three Lorentz frames II: single integral formula
Satoshi Nozawa,Yasuharu Kohyama
Physics , 2014, DOI: 10.1093/mnras/stu815
Abstract: We study the Sunyaev-Zeldovich effect for clusters of galaxies. The Boltzmann equations for the cosmic microwave background photon distribution function are studied in three Lorentz frames. We extend the previous work and derive analytic expressions for the integrated photon redistribution functions over the photon frequency. We also derive analytic expressions in the power series expansion approximation. By combining two formulas, we offer a simple and accurate tool to analyse observation data. These formulas are applicable to the non-thermal electron distributions as well as the standard thermal distribution. The Boltzmann equation is reduced to a single integral form of the electron velocity.
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