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Search Results: 1 - 10 of 633 matches for " Rika Saikawa "
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Different Magnetic Resonance Imaging Manifestations of Diabetic Chorea in a Case with Hyperglycemia and Another One with Hypoglycemia  [PDF]
Hodaka Yamada, Rika Saikawa, Suzuki Daisuke, Yuko Matsumoto, Masashi Yoshida, Kazuo Hara
Case Reports in Clinical Medicine (CRCM) , 2018, DOI: 10.4236/crcm.2018.73019
Abstract: Diabetic chorea (DC) is a rare complication of diabetes. Here we describe two cases of DC; patient 1 was an 87-year-old woman with chronic kidney disease and was administered with sulphonylurea and dipeptidylpeptodase-4 inhibitor. She showed right side hemiballismus and head magnetic resonance imaging T1-weighted images revealed a high intensity area in the putamen and caudate nucleus. Patient 2 was a 51-year-old woman who was diagnosed with diabetic ketoacidosis. She showed right side hemiballism and multiple, small hyperintense regions in both the periventricular sides in diffusion weighted images. Based on the hemiballism, we concluded a diagnosis of DC in the diabetic patient, although the case presentation is rare or has atypical MRI findings.
Anisotropic pseudogap in the half-filling 2-d Hubbard model at finite T
T. Saikawa,A. Ferraz
Physics , 1998,
Abstract: We have studied the pseudogap formation in the single-particle spectra of the half-filling two-dimensional Hubbard model. Using a Green's function with the one-loop self-energy correction of the spin and charge fluctuations, we have numerically calculated the self-energy, the spectral function, and the density of states in the weak-coupling regime at finite temperature. Pseudogap formations have been observed in both the density of states and the spectral function at the Fermi level. The pseudogap in the spectral function is explained by the non-Fermi-liquid-like nature of the self-energy. The anomalous behavior in the self-energy is caused by both the strong antiferromagnetic spin fluctuation and the nesting condition on the non-interacting Fermi surface. In the present approximation, we find a logarithmic singularity in the integrand of the imaginary part of the self-energy. Concerning the energy dependence of the spectral function and the self-energy, two theorems are proved. They give a necessary condition in the self-energy to produce the pseudogap at the Fermi level. The pseudogap in the spectral function is highly momentum dependent on the Fermi surface. It opens initially in the $(\pm \pi,0)$, $(0,\pm \pi)$ regions as the normal state pseudogap observed in the high-$T_c$ superconductors and if the interaction is increased, it spreads to other Fermi surface sectors. The anisotropy of the pseudogap is produced by the low-energy enhancement of the spin excitation around ${\bf Q}=(\pi,\pi)$ and the flatness of the band dispersion around the saddle point.
Remnant Fermi surface in a pseudogap regime of the two-dimensional Hubbard model at finite temperature
Taiichiro Saikawa,Alvaro Ferraz
Physics , 1999,
Abstract: A precursor effect on the Fermi surface in the two-dimensional Hubbard model at finite temperatures near the antiferromagnetic instability is studied using three different itinerant approaches: the second order perturbation theory, the paramagnon theory (PT), and the two-particle self-consistent (TPSC) approach. In general, at finite temperature, the Fermi surface of the interacting electron systems is not sharply defined due to the broadening effects of the self-energy. In order to take account of those effects we consider the single-particle spectral function $A({\bf k},0)$ at the Fermi level, to describe the counterpart of the Fermi surface at T=0. We find that the Fermi surface is destroyed close to the pseudogap regime due to the spin-fluctuation effects in both PT and TPSC approaches. Moreover, the top of the effective valence band is located around ${\bf k}=(\pi/2,\pi/2)$ in agreement with earlier investigations on the single-hole motion in the antiferromagnetic background. A crossover behavior from the Fermi-liquid regime to the pseudogap regime is observed in the electron concentration dependence of the spectral function and the self-energy.
Study of gravitational radiation from cosmic domain walls
Masahiro Kawasaki,Ken'ichi Saikawa
Physics , 2011, DOI: 10.1088/1475-7516/2011/09/008
Abstract: In this paper, following the previous study, we evaluate the spectrum of gravitational wave background generated by domain walls which are produced if some discrete symmetry is spontaneously broken in the early universe. We apply two different methods to calculate the gravitational wave spectrum: One is to calculate the gravitational wave spectrum directly from numerical simulations, and another is to calculate it indirectly by estimating the unequal time anisotropic stress power spectrum of the scalar field. Both analysises indicate that the slope of the spectrum changes at two characteristic frequencies corresponding to the Hubble radius at the decay of domain walls and the width of domain walls, and that the spectrum between these two characteristic frequencies becomes flat or slightly red tilted. The second method enables us to evaluate the GW spectrum semi-analytically for the frequencies which can not be resolved in the finite box lattice simulations, but relies on the assumptions for the unequal time correlations of the source.
Evolution and thermalization of dark matter axions in the condensed regime
Ken'ichi Saikawa,Masahide Yamaguchi
Physics , 2012, DOI: 10.1103/PhysRevD.87.085010
Abstract: We discuss the possibility that dark matter axions form a Bose-Einstein condensate (BEC) due to the gravitational self-interactions. The formation of BEC occurs in the condensed regime, where the transition rate between different momentum states is large compared to the energy exchanged in the transition. The time evolution of the quantum state occupation number of axions in the condensed regime is derived based on the in-in formalism. We recover the expression for the thermalization rate due to self interaction of the axion field, which was obtained in the other literature. It is also found that the leading order contributions for interactions between axions and other species vanish, which implies that the axion BEC does not give any significant modifications on standard cosmological parameters.
Gastric Cancer: Current Status of Diagnosis and Treatment
Tsunehiro Takahashi,Yoshiro Saikawa,Yuko Kitagawa
Cancers , 2013, DOI: 10.3390/cancers5010048
Abstract: Gastric cancer is the second leading cause of death from malignant disease worldwide and most frequently discovered in advanced stages. Because curative surgery is regarded as the only option for cure, early detection of resectable gastric cancer is extremely important for good patient outcomes. Therefore, noninvasive diagnostic modalities such as evolutionary endoscopy and positron emission tomography are utilized as screening tools for gastric cancer. To date, early gastric cancer is being treated using minimally invasive methods such as endoscopic treatment and laparoscopic surgery, while in advanced cancer it is necessary to consider multimodality treatment including chemotherapy, radiotherapy, and surgery. Because of the results of large clinical trials, surgery with extended lymphadenectomy could not be recommended as a standard therapy for advanced gastric cancer. Recent clinical trials had shown survival benefits of adjuvant chemotherapy after curative resection compared with surgery alone. In addition, recent advances of molecular targeted agents would play an important role as one of the modalities for advanced gastric cancer. In this review, we summarize the current status of diagnostic technology and treatment for gastric cancer.
Chronic thromboembolic pulmonary hypertension related to hemangiolymphangioma  [PDF]
Tsuneyuki Nakamura, Keita Tamanuki, Giyo Ko, Masato Oguri, Chisato Akita, Chika Kitaoka, Toshimi Nakamura, Yutaka Saikawa
Case Reports in Clinical Medicine (CRCM) , 2014, DOI: 10.4236/crcm.2014.31009
Abstract:

Hemangiolymphangioma (HL) is a congenital anomaly and histologically benign tumor, which was composed of both the lymphatic and the blood vessels. We report an adult case of HL complicated by chronic thromboembolic pulmonary hypertension (CTEPH) in a 20-year-old female. Gastrointestinal bleeding scintigraphy and operative findings elucidate a close relationship between CTEPH and residual HL. This case indicates that HL survivors with remaining left-to-right shunt might lead to CTEPH during the long-term follow-up.

Gravitational Waves from Collapsing Domain Walls
Takashi Hiramatsu,Masahiro Kawasaki,Ken'ichi Saikawa
Physics , 2010, DOI: 10.1088/1475-7516/2010/05/032
Abstract: We study the production of gravitational waves from cosmic domain walls created during phase transition in the early universe. We investigate the process of formation and evolution of domain walls by running three dimensional lattice simulations. If we introduce an approximate discrete symmetry, walls become metastable and finally disappear. We calculate the spectrum of gravitational waves produced by collapsing metastable domain walls. Extrapolating the numerical results, we find the signal of gravitational waves produced by domain walls whose energy scale is around 10^10-10^12GeV will be observable in the next generation gravitational wave interferometers.
On the estimation of gravitational wave spectrum from cosmic domain walls
Takashi Hiramatsu,Masahiro Kawasaki,Ken'ichi Saikawa
Physics , 2013, DOI: 10.1088/1475-7516/2014/02/031
Abstract: We revisit the production of gravitational waves from unstable domain walls analyzing their spectrum by the use of field theoretic lattice simulations with grid size $1024^3$, which is larger than the previous study. We have recognized that there exists an error in the code used in the previous study, and the correction of the error leads to the suppression of the spectrum of gravitational waves at high frequencies. The peak of the spectrum is located at the scale corresponding to the Hubble radius at the time of the decay of domain walls, and its amplitude is consistent with the naive estimation based on the quadrupole formula. Using the numerical results, the magnitude and the peak frequency of gravitational waves at the present time are estimated. It is shown that for some choices of parameters the signal of gravitational waves is strong enough to be probed in the future gravitational wave experiments.
The 2-site Hubbard and t-J models
Adolfo Avella,Ferdinando Mancini,Taiichiro Saikawa
Physics , 2001, DOI: 10.1140/epjb/e2004-00002-8
Abstract: The fermionic and bosonic sectors of the 2-site Hubbard model have been exactly solved by means of the equation of motion and Green's function formalism. The exact solution of the t-J model has been also reported to investigate the low-energy dynamics. We have successfully searched for the exact eigenoperators, and the corresponding eigenenergies, having in mind the possibility to use them as an operatorial basis on the lattice. Many local, single-particle, thermodynamical and response properties have been studied as functions of the external parameters and compared between the two models and with some numerical and exact results. It has been shown that the 2-site Hubbard model already contains the most relevant energy scales of the Hubbard model: the local Coulomb interaction $U$ and the spin-exchange one $J=\frac{4t^2}U$. As a consequence of this, for some relevant properties (kinetic energy, double occupancy, energy, specific heat and entropy) and as regards the metal-insulator transition issue, it has resulted possible to almost exactly mime the behavior of larger systems, sometimes using a higher temperature to get a comparable level spacing. The 2-site models have been also used as toy models to test the efficiency of the Green's function formalism for composite operators. The capability to reproduce the exact solutions, obtained by the exact diagonalization technique, gives a firm ground to the approximate treatments based on this formalism.
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