Hideaki Sakai 교수

For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered an

We report a ferroelectric transition driven by the off-centering of magnetic Mn(4+) ions in antiferromagnetic Mott insulators Sr(1-x)Ba(x)MnO(3) with a perovskite structure. As x increases, the perovskite lattice shows the typical soft-mode dynamics, as revealed by the momentum-resolved inelastic x-ray scattering and far-infrared spectroscopy, and the ferroelectricity shows up for x ≥ 0.45. The observed polarization is comparable to that for a prototypical ferroelectric BaTiO(3). We further demo

Abstract The mechanism controlling the disappearance of osteoclasts from bone surfaces after bone resorption in vivo is largely unknown. This is because there is no suitable experimental system to trace the final fate of osteoclasts. Here, we used an experimental model of tooth movement in rats to show that preexisting osteoclasts disappeared from the bone surface through apoptosis during a force-induced rapid shift from bone resorption to formation. On the distal alveolar bone surface of the ma

The transradial approach (TRA) has been used for diagnostic and interventional cardiology. It has not previously been determined how many times the same radial artery can be cannulated without complications. A total of 812 patients (502 men and 310 women) underwent angiography or angioplasty via the TRA between 1997 and 1999 at our institution with a total of 1,438 procedures. Sheaths were 5 (55%) or 6 Fr (45%). Dropout rates of 3.5% and 7.9% were found at the second TRA attempt in the men and t

We derive autocorrelations of a chaos arising from a simple nonlinear deterministic difference equation. The resulting autocorrelations are identical with those of a stochastic first-order autoregressive process.

The enzyme activity of lysosomal cysteine proteinases in vital rabbit osteoclasts and mouse osteoclast-like cells was visualized with Z-Leu-Arg-4-methoxy-beta-naphthylamide (Z-LR-MNA) as the enzyme substrate. The MNA liberated by proteolysis forms a fluorescent insoluble Schiff-base product in the presence of 5-nitrosalicylaldehyde. Many small fluorescent particles, endproducts of the Z-LR-MNA hydrolysis, were observed in proximity to the bone surface underneath the actively resorbing osteoclast

Recently, Pagano has found a one-to-one relationship between multivariate autoregression and scalar periodic autoregressions, and derived a set of fundamental Yule-Walker (YW) type equations for estimating the parameters of the periodic autoregressions. In this paper, we first obtain a Levinson-type recursive algorithm for solving the above mentioned YW equations. Then using this recursion we show a circular lattice structure of the process. This enables us to obtain a Burg-type algorithm which

Ferroelectrics with spontaneous electric polarization play an essential role in today's device engineering, such as capacitors and memories. Their physical properties are further enriched by suppressing the long-range polar order, as exemplified by quantum paraelectrics with giant piezoelectric and dielectric responses at low temperatures. Likewise in metals, a polar lattice distortion has been theoretically predicted to give rise to various unusual physical properties. However, to date, a "ferr

Statistical analysis is performed for Pisarenko's method of sinusoidal frequency estimation by using the periodogram technique. Under the assumption that the data consist of several sinusoids plus white noise, we give an asymptotic expression of the error variance of the sinusoidal frequency estimator. Also, a modified method is proposed. This is computationally efficient but the statistical property is not improved. We also present simulation results and compare them to the theoretical ones. La

Abstract The problem of estimating parameters of an autoregressive process based on the data corrupted by unknown white noise is considered. We shall mainly discuss two methods, the one based on the Yule–Walker equations and the other based on the modified least-squares estimation previously proposed by Sagara and Wada. The latter is based on the fact that a consistent estimator may be obtained by compensating an asymptotic bias on the least-squares estimator. An asymptotic expression of the err

This paper investigates several statistical properties of the autoregressive (AR) spectral analysis method by using the periodogram technique recently devised by the author. When the data are made up of several sinusoids contaminated by stationary noise, the asymptotic variances of the AR spectral estimator are given. It is shown numerically that the behavior of the variances is similar to Kromer and Berk's earlier result for stationary processes. As for frequency measurement accuracies, the sta

Single crystals of electron-doped ${\text{SrMnO}}_{3}$ with a cubic perovskite structure have been systematically investigated as the most canonical (orbital-degenerate) double-exchange system, whose ground states have been still theoretically controversial. With only $1--2\text{ }\mathrm{%}$ electron doping by Ce substitution for Sr, a $G$-type antiferromagnetic metal with a tiny spin canting in a cubic lattice shows up as the ground state, where the Jahn-Teller polarons with heavy mass are lik

Following determination of the first crystal structure of the reaction center of Rhodopseudomonas viridis, a membrane protein, by X-ray crystal structure analysis at 3.0 A resolution, 18 X-ray crystal structures and two electron crystal structures of membrane proteins have been obtained at higher than 3.5 A resolution. Besides these integral membrane protein structures, three crystal structures of water-soluble proteins, which can enter membranes, have been determined by X-ray crystallography at

Unconventional features of relativistic Dirac/Weyl quasiparticles in topological materials are most evidently manifested in the two-dimensional quantum Hall effect (QHE), whose variety is further enriched by their spin and/or valley polarization. Although its extension to three dimensions has been long sought and inspired theoretical proposals, material candidates have been lacking. Here, we have discovered valley-contrasting spin-polarized Dirac fermions in a multilayer form in the bulk antifer