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Search Results: 1 - 10 of 1970 matches for " Shintaro Aoki "
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Magnetization and phase transition induced by circularly polarized laser in quantum magnets
Shintaro Takayoshi,Hideo Aoki,Takashi Oka
Physics , 2013, DOI: 10.1103/PhysRevB.90.085150
Abstract: We theoretically predict a nonequilibrium phase transition in quantum spin systems induced by a laser, which provides a purely quantum-mechanical way of coherently controlling magnetization. Namely, when a circularly polarized laser is applied to a spin system, the magnetic component of a laser is shown to induce a magnetization normal to the plane of polarization, leading to an ultrafast phase transition. We first demonstrate this phenomenon numerically for an $S=1$ antiferromagnetic Heisenberg spin chain, where a new state emerges with magnetization perpendicular to the polarization plane of the laser in place of the topologically ordered Haldane state. We then elucidate its physical mechanism by mapping the system to an effective static model. The theory also indicates that the phenomenon should occur in general quantum spin systems with a magnetic anisotropy. The required laser frequency is in the terahertz range, with the required intensity being within a prospective experimental feasibility.
Phase diagram and pair Tomonaga-Luttinger liquid in a Bose-Hubbard model with flat bands
Shintaro Takayoshi,Hosho Katsura,Noriaki Watanabe,Hideo Aoki
Physics , 2013, DOI: 10.1103/PhysRevA.88.063613
Abstract: To explore superfluidity in flat-band systems, we consider a Bose-Hubbard model on a cross-linked ladder with $\pi$ flux, which has a flat band with a gap between the other band for noninteracting particles, where we study the effect of the on-site repulsion nonperturbatively. For low densities, we find exact degenerate ground states, each of which is a Wigner solid with nonoverlapping Wannier states on the flat band. At higher densities, the many-body system, when projected onto the lower flat band, can be mapped to a spin-chain model. This mapping enables us to reveal the existence of a Tomonaga-Luttinger liquid comprising it pairs of bosons. Interestingly, the high- and low- density regions have an overlap, where the two phases coexist.
Factors Associated with Excessive Daytime Sleepiness in Obstructive Sleep Apnea Syndrome under CPAP Treatment  [PDF]
Wataru Yamadera, Shintaro Chiba, Masayuki Iwashita, Ryo Aoki, Daisuke Harada, Miki Sato, Hiroto Moriwaki, Keita Obuchi, Motohiro Ozone, Seiji Nishino, Hiroshi Itoh, Kazuhiko Nakayama
International Journal of Clinical Medicine (IJCM) , 2012, DOI: 10.4236/ijcm.2012.33039
Abstract: The purpose of this study was to assess factors associated with subjective sleep evaluation, chiefly excessive daytime sleepiness (EDS) in obstructive sleep apnea syndrome (OSAS) adult outpatients under continuous positive airway pressure (CPAP) treatment. One thousand and forty-eight OSAS outpatients (mean age: 51.4% male: 90.5%) who were treated by CPAP were consecutively collected. Age, sex, CPAP compliance (CPAP usage as their device of nights with application-time of at least 4 hours per night objectively; %usage ≥ 4 h/d), and Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) of the patients showing EDS (Japanese version of the Epworth Sleepiness Scale; JESS ≥ 11) were compared cross-sectionally with those of the patients who did not show EDS (JESS < 11). Nineteen point two % of all patients showed EDS subjectively. Two hundred one patients were classified to an EDS(+) group and an 847 patients were classified to EDS(–) group. Age and global PSQI-J scores were significantly different between the two groups. Logistic regression showed that EDS was significantly associated with global PSQI-J scores, but not with age. Among PSQI-J components, overall sleep quality, duration of sleep, sleep disturbance, and day dysfunction due to sleepiness were significantly higher in the EDS(+) group. Especially, 19.4% of patient in the EDS(+) group reported actual sleep time during the past month to be less than 5 hours/day. Although functional relationship should be further evaluated, insufficient sleep is the main factor associated with EDS in the OSAS patients under CPAP treatment.
Deterministic Parsing Model of the Compound Biological Effectiveness (CBE) Factor for Intracellular 10Boron Distribution in Boron Neutron Capture Therapy  [PDF]
Shintaro Ishiyama
Journal of Cancer Therapy (JCT) , 2014, DOI: 10.4236/jct.2014.514140

Purpose: In defining the biological effects of the 10B(n, α)7Li neutron capture reaction, we have previously developed a deterministic parsing model to determine the Compound Biological Effectiveness (CBE) factor in Borono-Phenyl-Alanine (BPA)-mediated Boron Neutron Capture Therapy (BNCT). In present paper, we demonstrate that the CBE factor is directly and unambiguously derivable by the new formula for any case of intracellular 10Boron (10B) distribution, which is founded on this model for tissues and tumor. Method: To determine the

Intra-Articular Giant Heterotopic Ossification following Total Knee Arthroplasty for Charcot Arthropathy
Arata Nakajima,Shintaro Tsuge,Yasuchika Aoki,Masato Sonobe,Yoshifumi Shibata,Yu Sasaki,Koichi Nakagawa
Case Reports in Orthopedics , 2013, DOI: 10.1155/2013/472378
Abstract: Although the Charcot arthropathy may be associated with serious complications, total knee arthroplasty (TKA) is the preferred choice of treatment by patients. This case report presents an 80-year-old man with intra-articular giant heterotopic ossification following loosening of femoral and tibial implants and femoral condylar fracture. He had undergone TKA because of Charcot neuropathy seven years ago and had been doing well since. Immediately after a left knee sprain, he became unable to walk. Because he had developed a skin ulcer on his left calf where methicillin-resistant Staphylococcus aureus was detected, we postponed revision surgery until the ulcer was completely healed. While waiting, intra-articular bony fragments grew larger and formed giant heterotopic ossified masses. Eventually, the patient underwent revision surgery, and two major ossified masses were carefully and successfully extirpated. It should be noted that intra-articular heterotopic giant ossification is a significant complication after TKA for neuropathic arthropathy. 1. Introduction Neuropathic arthropathy was described by Jean Martin Charcot (1825–1893) as the progressive destruction of bone and soft tissues in a patient with peripheral neuropathy. Charcot also noted the relationship between syphilis and severe arthropathy in 1868 [1]. Diabetes mellitus is currently the most common cause of Charcot arthropathy, especially of the foot and ankle. The diagnosis of Charcot arthropathy in the knee is rare. However, we can expect the increasing number of diabetic patients living longer due to improvements in medical treatment to show an increasing incidence of neuropathic arthropathy as a late effect of peripheral neuropathy. The optimal treatment for Charcot arthropathy of the knee is controversial. Some investigators [2–4] consider it as an absolute contraindication to total knee arthroplasty (TKA). Recently, however, several studies [5] have shown satisfactory results from TKA. In general, TKA for Charcot arthropathy is associated with high incidence of such serious complications as periprosthetic fractures, aseptic loosening, dislocation of the patella and tibiofemoral joint, and deep infection [6–8]. However, due to excellent functional recovery compared with conservative therapy and arthrodesis, TKA should not be contraindicated. We present a case report of an 80-year-old man with intra-articular, giant, heterotopic ossification and a femoral condylar fracture following loosening of femoral and tibial implants. To date, the occurrence of intra-articular, giant, heterotopic
Computation of Greeks Using Binomial Tree  [PDF]
Yoshifumi Muroi, Shintaro Suda
Journal of Mathematical Finance (JMF) , 2017, DOI: 10.4236/jmf.2017.73031
Abstract: This paper proposes a new efficient algorithm for the computation of Greeks for options using the binomial tree. We also show that Greeks for European options introduced in this article are asymptotically equivalent to the discrete version of Malliavin Greeks. This fact enables us to show that our Greeks converge to Malliavin Greeks in the continuous time model. The computation algorithm of Greeks for American options using the binomial tree is also given in this article. There are three advantageous points to use binomial tree approach for the computation of Greeks. First, mathematics is much simpler than using the continuous time Malliavin calculus approach. Second, we can construct a simple algorithm to obtain the Greeks for American options. Third, this algorithm is very efficient because one can compute the price and Greeks (delta, gamma, vega, and rho) at once. In spite of its importance, only a few previous studies on the computation of Greeks for American options exist, because performing sensitivity analysis for the optimal stopping problem is difficult. We believe that our method will become one of the popular ways to compute Greeks for options.
Hypothesis of Conservation of Particle Number  [PDF]
Kozo Aoki
Open Journal of Microphysics (OJM) , 2011, DOI: 10.4236/ojm.2011.11001
Abstract: As for several nuclear reactions, the electroweak interaction is simply explained by a law of conservation of particle number. We find that the positron and electron consist of the three fundamental particles, and , respectively. Furthermore, the members of the second and third generations quark composites consist of the first generation quark and the neutrino of fundamental particles. The particle and its anti- particle pair(or neutrino and its antineutrino pair) have to be an energy quantum (or a photon). The minimum Higgs boson (called “God particle”) might be a neutral pion. The fundamental particles are simply up and down quark, neutrino, muon-neutrino, and those anti-particles.
Second Thoughts about the τ-θ Puzzle  [PDF]
Kozo Aoki
Open Journal of Microphysics (OJM) , 2012, DOI: 10.4236/ojm.2012.23006
Abstract: The new parity value of π0 was determined according to the hypothesis of conservation of particle number. The theo-retical pentaquark proton’s parity value was also determined, and it was found that the conservation of parity is account nicely for the τ-θ puzzle.
Variation of Inner Radius of Dust Torus in NGC4151
Shintaro Koshida,Yuzuru Yoshii,Yukiyasu Kobayashi,Takeo Minezaki,Yu Sakata,Shota Sugawara,Keigo Enya,Masahiro Suganuma,Hiroyuki Tomita,Tsutomu Aoki,Bruce A. Peterson
Physics , 2009, DOI: 10.1088/0004-637X/700/2/L109
Abstract: The long-term optical and near infrared monitoring observations for a type 1 act ive galactic nucleus NGC 4151 were carried out for six years from 2001 to 2006 b y using the MAGNUM telescope, and delayed response of flux variations in the $K(2.2\mu m)$ band to those in the $V(0.55\mu m)$ band was clearly detected. Based on cross correlation analysis, we precisely measured a lag time $\Delta t$ for eight separate periods, and we found that $\Delta t$ is not constant changing be tween 30 and 70 days during the monitoring period. Since $\Delta t$ is the ligh t travel time from the central energy source out to the surrounding dust torus, this is the first convincing evidence that the inner radius of dust torus did ch ange in an individual AGN. In order to relate such a change of $\Delta t$ with a change of AGN luminosity $L$, we presented a method of taking an average of th e observed $V$-band fluxes that corresponds to the measured value of $\Delta t$, and we found that the time-changing track of NGC 4151 in the $\Delta t$ versus $L$ diagram during the monitoring period deviates from the relation of $\Delta t \propto L^{0.5}$ expected from dust reverberation. This result, combined with t he elapsed time from period to period for which $\Delta t$ was measured, indicat es that the timescale of dust formation is about one year, which should be taken into account as a new constraint in future studies of dust evolution in AGNs.
Long-Term Optical Continuum Color Variability of Nearby Active Galactic Nuclei
Yu Sakata,Takeo Minezaki,Yuzuru Yoshii,Yukiyasu Kobayashi,Shintaro Koshida,Tsutomu Aoki,Keigo Enya,Hiroyuki Tomita,Masahiro Suganuma,Yuka Katsuno Uchimoto,Shota Sugawara
Physics , 2010, DOI: 10.1088/0004-637X/711/1/461
Abstract: We examine whether the spectral energy distribution of optical continuum emission of active galactic nuclei (AGNs) changes during flux variation, based on accurate and frequent monitoring observations of 11 nearby Seyfert galaxies and QSOs carried out in the B, V, and I bands for seven years by the MAGNUM telescope. The multi-epoch flux data in any two different bands obtained on the same night show a very tight linear flux to flux relationship for all target AGNs. The flux of the host galaxy within the photometric aperture is carefully estimated by surface brightness fitting to available high-resolution HST images and MAGNUM images. The flux of narrow emission lines in the photometric bands is also estimated from available spectroscopic data. We find that the non-variable component of the host galaxy plus narrow emission lines for all target AGNs is located on the fainter extension of the linear regression line of multi-epoch flux data in the flux to flux diagram. This result strongly indicates that the spectral shape of AGN continuum emission in the optical region does not systematically change during flux variation. The trend of spectral hardening that optical continuum emission becomes bluer as it becomes brighter, which has been reported by many studies, is therefore interpreted as the domination of the variable component of the nearly constant spectral shape of an AGN as it brightens over the non-variable component of the host galaxy plus narrow lines, which is usually redder than AGN continuum emission.
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