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Search Results: 1 - 10 of 795 matches for " Masao Sugawa "
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Relativistic electron beam acceleration by Compton scattering of lower-hybrid waves
Reiji Sugaya,Tsunehiro Maehara,Masao Sugawa
Physics , 2004,
Abstract: It has been proved theoetically and numerically that the highly relativistic electron beam can be accelerated efficiently via the Compton scattering induced by nonlinear Landau and cyclotron damping of the lower-hybrid waves.
Quasiconformal extension of strongly spirallike functions
Toshiyuki Sugawa
Mathematics , 2011,
Abstract: We show that a strongly $\lambda$-spirallike function of order $\alpha$ can be extended to a $\sin(\pi\alpha/2)$-quasiconformal automorphism of the complex plane for $-\pi/2<\lambda<\pi/2$ and $0<\alpha<1$ with $|\lambda|<\pi\alpha/2.$ In order to prove it, we provide several geometric characterizations of a strongly $\lambda$-spirallike domain of order $\alpha.$ We also give a concrete form of the mapping function of the standard strongly $\lambda$-spirallike domain $U_{\lambda,\alpha}$ of order $\alpha.$ A key tool of the present study is the notion of $\lambda$-argument, which was developed by Y. C. Kim and the author.
Spherical density of hyperbolic metric and uniform perfectness
Toshiyuki Sugawa
Mathematics , 2015,
Abstract: It is well known that a hyperbolic domain in the complex plane has uniformly perfect boundary precisely when the product of its hyperbolic density and the distance function to its boundary has a positive lower bound. We extend this characterization to a hyperbolic domain in the Riemann sphere in terms of the spherical metric.
Asset Pricing with Stochastic Habit Formation  [PDF]
Masao Nakagawa
Journal of Mathematical Finance (JMF) , 2012, DOI: 10.4236/jmf.2012.22018
Abstract: This paper examines optimal consumption/portfolio choices under stochastic habit formation in which it is uncertain how deep consumers would become in the habit of consuming in future. By extending Shroder and Skiadas [1] to stochastic habit formation, the optimization problem with stochastic habit forming preferences is transformed into that with simple time-additive preferences. Optimal portfolios are composed of the tangency portfolio and habit hedging portfolio. Resulting risk premia are characterized by consumption beta, which is proportionate to the covariance with consumption changes, and habit beta, defined by using the covariance with habit.
Novel Cathode Materials for Sodium Ion Batteries Derived from Layer Structured Titanate Cs2Ti5O11·(1 + x)H2O  [PDF]
Masao Ohashi
Materials Sciences and Applications (MSA) , 2018, DOI: 10.4236/msa.2018.96037
Abstract: A layer structured titanate Cs2Ti5O11·(1 + x)H2O (x = 0.70) has been prepared in a solid state reaction using Cs2CO3 and anatase type TiO2 at 900°C. Ion exchange reactions of Cs+ in the interlayer space were studied in aqueous solutions. The single phases of Li+, Na+ and H+ exchange products were obtained. The three kinds of resulting titanates were evaluated for use as the cathodes in rechargeable sodium batteries after dehydrations by heating at 200°C in a vacuum. The electrochemical measurements showed that they exhibited the reversible Na+ intercalation-deintercalation in a voltage range of 0.5 - 3.5 V or 0.7 - 4.0 V. The Li+ exchange product showed the best performance of the discharge-charge capacities in this study. The initial Na+ intercalation-deintercalation capacities of the Li2Ti5O11 were 120 mAh/g and 100 mAh/g; the amounts of Na+ correspond to 1.9 and 1.6 of the formula unit, respectively. The titanates are nontoxic, inexpensive and environmentally benign.
Ion Exchange of Layer-Structured Titanate CsxTi2-x/2Mgx/2O4 (x = 0.70) and Applications as Cathode Materials for Both Lithium- and Sodium-Ion Batteries  [PDF]
Masao Ohashi
Materials Sciences and Applications (MSA) , 2019, DOI: 10.4236/msa.2019.102012
Abstract: Cathode materials for rechargeable batteries have been extensively investigated. Sodium-ion batteries are emerging as alternatives to lithium-ion batteries. In this study, a novel cathode material for both lithium- and sodium-ion batteries has been derived from a layered crystal. Layer-structured titanate CsxTi2-x/2Mgx/2O4 (x = 0.70) with lepidocrocite (γ-FeOOH)-type structure has been prepared in a solid-state reaction from Cs2CO3, anatase-type TiO2, and MgO at 800°C. Ion-exchange reactions of Cs+ in the interlayer space were studied in aqueous solutions. The single phases of Li+, Na+, and H+ exchange products were obtained, and these were found to contain interlayer water. The interlayer water in the lithium ion-exchange product was removed by heating at 180°C in vacuum. The resulting titanate Li0.53H0.13Cs0.14Ti1.65Mg0.30O4 was evaluated for use as cathodes in both rechargeable lithium and sodium batteries. The Li+ intercalation-deintercalation capacities were found to be 151 mAh/g and 114 mAh/g, respectively, for the first cycle in the voltage range 1.0 - 3.5 V. The amounts of Li+ corresponded to 0.98 and 0.74 of the formula unit, respectively. The Na+ intercalation-deintercalation capacities were 91 mAh/g and 77 mAh/g, respectively, for the first cycle in the voltage range 0.70 - 3.5 V. The amounts of Na+ corresponded to 0.59 and 0.50 of the formula unit, respectively. The new cathode material derived from the layer-structured titanate is non-toxic, inexpensive, and environmentally benign.
Dual mean value problem for complex polynomials
Vladimir Dubinin,Toshiyuki Sugawa
Mathematics , 2009,
Abstract: We consider an extremal problem for polynomials, which is dual to the well-known Smale mean value problem. We give a rough estimate depending only on the degree.
Univalent functions with half-integral coefficients
Naoki Hiranuma,Toshiyuki Sugawa
Mathematics , 2012,
Abstract: B. Friedman found in his 1946 paper that the set of analytic univalent functions on the unit disk in the complex plane with integral Taylor coefficients consists of nine functions. In the present paper, we prove that the similar set obtained by replacing "integral" by "half-integral" consists of another twelve functions in addition to the nine. We also observe geometric properties of the twelve functions.
Coefficient estimates of analytic endomorphisms of the unit disk fixing a point with applications to concave functions
Rintaro Ohno,Toshiyuki Sugawa
Mathematics , 2015,
Abstract: In this note, we discuss the coefficient regions of analytic self-maps of the unit disk with a prescribed fixed point. As an application, we solve the Fekete-Szeg\H{o} problem for normalized concave functions with a prescribed pole in the unit disk.
On the second Hankel determinant of concave functions
Rintaro Ohno,Toshiyuki Sugawa
Mathematics , 2015,
Abstract: In the present paper, we will discuss the Hankel determinants $H(f) =a_2a_4-a_3^2$ of order 2 for normalized concave functions $f(z)=z+a_2z^2+a_3z^3+\dots$ with a pole at $p\in(0,1).$ Here, a meromorphic function is called concave if it maps the unit disk conformally onto a domain whose complement is convex. To this end, we will characterize the coefficient body of order 2 for the class of analytic functions $\varphi(z)$ on $|z|<1$ with $|\varphi|<1$ and $\varphi(p)=p.$ We believe that this is helpful for other extremal problems concerning $a_2, a_3, a_4$ for normalized concave functions with a pole at $p.$
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