Constraint on intergalactic dust from thermal history of intergalactic medium     

Akio K. Inoue †  Hideyuki Kamaya 《Monthly notices of the Royal Astronomical Society》2003,341(3):L7-L11

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Merged binary white dwarf evolution: rapidly accreting carbon–oxygen white dwarfs and the progeny of extreme helium stars     

Hideyuki Saio  C. Simon Jeffery 《Monthly notices of the Royal Astronomical Society》2002,333(1):121-132

We have examined the evolution of merged low-mass double white dwarfs that become luminous helium stars. We have approximated the merging process by the rapid accretion of matter, consisting mostly of helium, on to a carbon–oxygen (CO) white dwarf. After a certain mass is accumulated, a helium shell flash occurs, the radius and luminosity increase and the star becomes a yellow giant. Mass accretion is stopped artificially when the total mass reaches a pre-determined value. When the mass above the helium-burning shell becomes small enough, the star evolves blueward almost horizontally in the Hertzsprung–Russell diagram. The theoretical models for the merger of a 0.6-M_⊙ CO white dwarf with a 0.3-M_⊙ He white dwarf agree very well with the observed locations of extreme helium stars in the  log  T _eff–log  g   diagram, with their observed rates of blueward evolution, and with luminosities and masses obtained from their pulsations. Together with predicted merger rates for  CO+He  white dwarf pairs, the evolutionary time-scales are roughly consistent with the observed numbers of extreme helium stars. Predicted surface carbon and oxygen abundances can be consistent with the observed values if carbon and oxygen produced in the helium shell during a previous asymptotic giant branch phase are assumed to exist in the helium zone of the initial CO white dwarfs. These results establish the  CO+He  white dwarf merger as the best, if not only, viable model for the creation of extreme helium stars and, by association, the majority of R Coronae Borealis stars.  相似文献   

Experimental and numerical analysis of container stack dynamics using a scaled model test     

Vinicius Aguiar de Souza  Levent Kirkayak  Katsuyuki Suzuki  Hideyuki Ando  Hidetoshi Sueoka 《Ocean Engineering》2012

This paper describes an approach to simulate a seven-tier stack consisting of scaled model of a 20 ft ISO freight container and its linking connectors, denominated twist locks, subjected to dynamical load induced by its base. The physical (dimensions, mass, and moments of inertia) and structural (longitudinal, transversal and torsional stiffness) characteristics of the scaled models were decided based on two dimensionless numbers: ratios between gravity force and inertia force, and elastic force divided by inertia force, through experimental and numerical analysis. A series of experiments with controlled parameters were performed using a shaking table test to understand the effects of each variable in the container stack dynamics and present enough data to validate the numerical model. The results of this study indicate that the numerical model built is a promising tool for further study. Moreover, the model is able to predict conditions close to real situations faced by container stacks while storage on a ship's deck.  相似文献   

Installation of ocean bottom bases for observation of seafloor crustal movement     

Hiromi Fujimoto  Jiro Segawa  Toshio Furuta  Hideyuki Murakami 《Marine Geodesy》2013,36(3-4):177-184

Abstract

Ocean bottom bases (OBBs) have been installed on both sides of the axis of the Sagami Trough east of the Izu Peninsula, central Japan, as the first step toward long‐term geodetic and geophysical observations at the plate boundary (subduction zone). The OBB is a platform for seafloor measurements; otherwise it is difficult to find an appropriate place for precise seafloor measurements in the subduction zones. It is made of a nonmagnetic concrete block of size 1100 × 1100 × 500 mm. It was lowered from a ship using a winch wire and installed on a predetermined place with its position being monitored by an acoustic transponder system and a 30‐kHz bottom pinger with an accuracy of about 2 m.

It was confirmed later during the divings on board the submersible Shinkai 2000 that the OBB was installed on a flat mud bottom in normal condition. No change has been recognized in the installation condition in 3 years; the OBB is stable enough to be used for acoustic range measurements on the seafloor as well as for several geophysical measurements.

The resolution of seafloor range measurement can be improved by two orders by using phase measurement techniques with the aid of pulse compression. Precise acoustic range measurement of the order of 10^?5 is feasible under the following conditions: two‐way measurements between the two OBBs installed on the slope facing each other with angles larger than 1.5°. Correction is necessary for the effect of long‐term temperature variation.  相似文献   

How to drive roAp stars     

Alfred Gautschy  Hideyuki Saio  & Housi Harzenmoser 《Monthly notices of the Royal Astronomical Society》1998,301(1):31-41

Rapidly oscillating Ap stars constitute a unique class of pulsators with which to study non-radial oscillations under some — even for stars — unusual physical conditions. These stars are chemically peculiar, they have strong magnetic fields and they often pulsate in several high-order acoustic modes simultaneously. We discuss here an excitation mechanism for short-period oscillation modes based on the classical κ mechanism. We particularly stress the conditions that must be fulfilled for successful driving. Specifically, we discuss the roles of the chemical peculiarity and strong magnetic field on the oscillation modes and what separates these pulsators from δ Scuti and Am-type stars.  相似文献   

Sequential forecasting of the surface and subsurface conditions in the Japan Sea   总被引：1，自引：0，他引：1  

Naoki Hirose  Hideyuki Kawamura  Ho Jin Lee  Jong-Hwan Yoon 《Journal of Oceanography》2007,63(3):467-481

This study estimates a realistic change of the Japan Sea by assimilating satellite measurements into an eddy-resolving circulation model. Suboptimal but feasible assimilation schemes of approximate filtering and nudging play essential roles in the system. The sequential update of error covariance significantly outperforms the asymptotic covariance in the sequential assimilation due to the irregular sampling patterns from multiple altimeter satellites. The best estimates show an average rms difference of only 1.2°C from the radiometer data, and also explain about half of the sea level variance measured by the altimeter observation. The subsurface conditions associated with the mesoscale variabilities are also improved, especially in the Tsushima Warm Current region. It is demonstrated that the forecast limit strongly depends on variable, depth, and location.  相似文献   

Projections of glacier change in the Altai Mountains under twenty-first century climate scenarios     

Yong Zhang  Hiroyuki Enomoto  Tetsuo Ohata  Hideyuki Kitabata  Tsutomu Kadota  Yukiko Hirabayashi 《Climate Dynamics》2016,47(9-10):2935-2953

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On the possibility of observing the double emission line feature of H₂ and HD from primordial molecular cloud cores     

Hideyuki Kamaya  Joseph Silk 《Monthly notices of the Royal Astronomical Society》2003,339(4):1256-1264

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Observing baryonic dark matter with ALMA     

Hideyuki Kamaya  Joseph Silk 《Monthly notices of the Royal Astronomical Society》2002,335(3):L62-L66

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Comments on a dwarf elliptical galaxy with warm interstellar medium     

Hideyuki Kamaya 《Astrophysics and Space Science》2014,350(1):313-316

Recent observations show the evidence of warm ionized interstellar medium (WIM) in some dwarf elliptical galaxies (dEs). The presence of WIM should be accounted for since diffuse plasma in dE is easy to escape owing to galactic wind during the star-burst epoch and ram pressure of intra-cluster medium. In this paper, we present a possible scenario of origin of dE with WIM. By estimating time-scale of ram pressure stripping of interstellar medium, we find dE with WIM is able to emerge when a field dwarf galaxy enters into a cluster of galaxies. Then, the author suggests that low surface brightness galaxies and blue compact dwarf galaxies can be a precursor of dE with WIM.  相似文献