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Search Results: 1 - 10 of 51 matches for " Naokazu Ibuki "
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Monophasic Primary Renal Synovial Sarcoma Accompanied With a Hemorrhagic Cyst
Takeshi Nishida,Teruo Inamoto,Hiroshi Uehara,Naokazu Ibuki
Urology Journal , 2011,
Predictors of Success for Stone Fragmentation and Stone-Free Rate After Extracorporeal Shockwave Lithotripsy in the Treatment of Upper Urinary Tract Stones
Kiyoshi Takahara,Naokazu Ibuki,Teruo Inamoto,Hayahito Nomi
Urology Journal , 2012,
Abstract: PURPOSE: To evaluate factors affecting the success rate of stone fragmentation and stone-free rate after extracorporeal shockwave lithotripsy (SWL) in treatment of upper urinary tract stones. MATERIALS AND METHODS: A total of 121 patients with upper urinary tract calculi underwent SWL treatment. RESULTS: Success rate of stone fragmentation after SWL was 73.6% (89/121). In 89 patients who had success of breaking stones, 71 patients were followed up for the assessment of stone-free status, of whom 51 (71.8%) patients were stone-free at 3-month follow-up. Among four prognostic factors, including body mass index (BMI), stone size, stone position, and hydronephrosis, BMI and stone position had a significant impact on the success rate of stone fragmentation (P = .04 and U1: P = .0108, respectively). Among five prognostic factors of BMI, stone size, stone position, hydronephrosis, and times of SWL treatments, stone size was the only factor with significant impact on the stone-free rate (middle: P = .0229). CONCLUSION: Our study suggests that stone fragmentation and stone-free rate after SWL treatment for upper urinary tract stones can be predicted.
Quantum Hall Systems Studied by the Density Matrix Renormalization Group Method
Naokazu Shibata
Physics , 2009,
Abstract: The ground-state and low-energy excitations of quantum Hall systems are studied by the density matrix renormalization group (DMRG) method. From the ground-state pair correlation functions and low-energy excitions, the ground-state phase diagram is determined, which consists of incompressible liquid states, Fermi liquid type compressible liquid states, and many kinds of CDW states called stripe, bubble and Wigner crystal. The spin transition and the domain formation are studied at v=2/3. The evolution from composite fermion liquid state to an excitonic state in bilayer systems is investigated at total filling factor v=1.
Application of the density matrix renormalization group method to finite temperatures and two-dimensional systems
Naokazu Shibata
Physics , 2003, DOI: 10.1088/0305-4470/36/37/201
Abstract: The density matrix renormalization group (DMRG) method and its applications to finite temperatures and two-dimensional systems are reviewed. The basic idea of the original DMRG method, which allows precise study of the ground state properties and low-energy excitations, is presented for models which include long-range interactions. The DMRG scheme is then applied to the diagonalization of the quantum transfer matrix for one-dimensional systems, and a reliable algorithm at finite temperatures is formulated. Dynamic correlation functions at finite temperatures are calculated from the eigenvectors of the quantum transfer matrix with analytical continuation to the real frequency axis. An application of the DMRG method to two-dimensional quantum systems in a magnetic field is demonstrated and reliable results for quantum Hall systems are presented.
Ion clusters and ion-water potentials in MD-simulations
Ph. A. Bopp,K. Ibuki
Physics , 2012, DOI: 10.5488/CMP.15.23001
Abstract: A well known, if little documented, problem in many molecular simulations of aqueous ionic solutions at finite concentrations is that unrealistic cation-cation associations are frequently found. One might suspect a defect in the ion-ion interaction potentials, about which not much is known. However, we show that this phenomenon can also be traced to the fact that, in the pair-potential approximation, the cation-water potentials are too deep compared with the other ones and we investigate this phenomenon in some detail. We then attempt to draw some general conclusions.
Ground state phase diagram of 2D electrons in high magnetic field
Naokazu Shibata,Daijiro Yoshioka
Physics , 2003, DOI: 10.1016/j.physe.2003.11.228
Abstract: The ground state phase diagram of two-dimensional electrons in high magnetic field is studied by the density matrix renormalization group (DMRG) method. The low energy excitations and pair correlation functions in Landau levels of N=0,1,2 are calculated for wide range of fillings. The obtained results for systems with up to 25 electrons confirm the existence of various electronic states in quantum Hall systems. The ground state phase diagram for N=0,1,2 consisting of incompressible liquids, compressible liquids, charge density waves called stripe, bubble and Wigner crystal is determined.
Domain Formation in v=2/3 Fractional Quantum Hall Systems
Naokazu Shibata,Kentaro Nomura
Physics , 2007, DOI: 10.1143/JPSJ.76.103711
Abstract: We study the domain formation in the v=2/3 fractional quantum Hall systems basing on the density matrix renormalization group (DMRG) analysis. The ground-state energy and the pair correlation functions are calculated for various spin polarizations. The results confirm the domain formation in partially spin polarized states, but the presence of the domain wall increases the energy of partially spin polarized states and the ground state is either spin unpolarized state or fully spin polarized state depending on the Zeeman energy. We expect coupling with external degrees of freedom such as nuclear spins is important to reduce the energy of partially spin polarized state.
Fractional Quantum Hall Effects in Graphene and Its Bilayer
Naokazu Shibata,Kentaro Nomura
Physics , 2009, DOI: 10.1143/JPSJ.78.104708
Abstract: Single-layer and Bilayer of graphene are new classes of two-dimensional electron systems with unconventional band structures and valley degrees of freedom. The ground states and excitations in the integer and fractional quantum Hall regimes are investigated on torus and spherical geometries with the use of the density matrix renormalization group (DMRG) method. At nonzero Landau level indices, the ground states at effective filling factors 1, 1/3, 2/3 and 2/5 are valley polarized both in single-layer and bilayer graphenes. We examine the elementary charge excitations which could couple with the valley degrees of freedom (so called valley skyrmions). The excitation gaps are calculated and extrapolated to the thermodynamic limit. The largest excitation gap at effective filling 1/3 is obtained in bilayer graphene, which is a good candidate for experimental observation of fractional quantum Hall effect.
Stability of the Excitonic Phase in Bilayer Quantum Hall Systems at Total Filling One -- Effects of Finite Well Width and Pseudopotentials --
Daijiro Yoshioka,Naokazu Shibata
Physics , 2010, DOI: 10.1143/JPSJ.79.064717
Abstract: The ground state of a bilayer quantum Hall system at $\nu_{\rm T}=1$ with model pseudopotential is investigated by the DMRG method. Firstly, pseudopotential parameters appropriate for the system with finite layer thickness are derived, and it is found that the finite thickness makes the excitonic phase more stable. Secondly, a model, where only a few pseudopotentials with small relative angular momentum have finite values, is studied, and it is clarified how the excitonic phase is destroyed as intra-layer pseudopotential becomes larger. The importance of the intra-layer repulsive interaction at distance twice of the magnetic length for the destruction of the excitonic phase is found.
Real Space Effective Interaction and Phase Transition in the Lowest Landau Level
Naokazu Shibata,Daijiro Yoshioka
Physics , 2004, DOI: 10.1143/JPSJ.73.2169
Abstract: The transition between the stripe state and the liquid state in a high magnetic field is studied by the density-matrix renormalization-group (DMRG) method. Systematic analysis on the ground state of two-dimensional electrons in the lowest Landau level shows that the transition from the stripe state to the liquid state at v=3/8 is caused by a reduction of repulsive interaction around r=3. The same reduction of the interaction also stabilizes the incompressible liquid states at v=1/3 and 2/5, which shows a similarity between the two liquid states at v=3/8 and 1/3. It is also shown that the strong short-range interaction around r=1 in the lowest Landau level makes qualitatively different stripe correlations compared with that in higher Landau levels.
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