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Search Results: 1 - 10 of 1447 matches for " Ryo Ohashi "
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Lattice of Finite Group Actions on Prism Manifolds  [PDF]
John E. Kalliongis, Ryo Ohashi
Advances in Pure Mathematics (APM) , 2012, DOI: 10.4236/apm.2012.23022
Abstract: The set of finite group actions (up to equivalence) which operate on a prism manifold M, preserve a Heegaard Klein bottle and have a fixed orbifold quotient type, form a partially ordered set. We describe the partial ordering of these actions by relating them to certain sets of ordered pairs of integers. There are seven possible orbifold quotient types, and for any fixed quotient type we show that the partially ordered set is isomorphic to a union of distributive lattices of a certain type. We give necessary and sufficent conditions, for these partially ordered sets to be isomorphic and to be a union of Boolean algebras.
Hetero pairing and component-dependent pseudogap phenomena in an ultracold Fermi gas with mass imbalance
Ryo Hanai,Yoji Ohashi
Physics , 2014, DOI: 10.1103/PhysRevA.90.043622
Abstract: We investigate the superfluid phase transition and single-particle excitations in the BCS (Bareen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an ultracold Fermi gas with mass imbalance. In our recent paper [R. Hanai, et. al., Phys. Rev. A 88, 053621 (2013)], we showed that an extended $T$-matrix approximation (ETMA) can overcome the serious problem known in the ordinary (non-self-consistent) $T$-matrix approximation that it unphysically gives double-valued superfluid phase transition temperature $T_{\rm c}$ in the presence of mass imbalance. However, at the same time, the ETMA was also found to give the vanishing $T_{\rm c}$ in the weak-coupling and highly mass-imbalanced case. In this paper, we inspect the correctness of this ETMA result, using the self-consistent $T$-matrix approximation (SCTMA). We show that the vanishing $T_{\rm c}$ is an artifact of the ETMA, coming from an internal inconsistency of this theory. The superfluid phase transition actually always occurs, irrespective of the ratio of mass imbalance. We also apply the SCTMA to the pseudogap problem in a mass-imbalanced Fermi gas. We show that pairing fluctuations induce different pseudogap phenomena between the the light component and heavy component. We also point out that a $^6$Li-$^{40}$K mixture is a useful system for the realization of a hetero pairing state, as well as for the study of component-dependent pseudogap phenomena.
Strong-Coupling Effects and Single-Particle Properties in an Ultracold Fermi Gas with Mass Imbalance
Ryo Hanai,Yoji Ohashi
Physics , 2013,
Abstract: We investigate single-particle properties of a strongly interacting ultracold Fermi gas with mass imbalance. Using an extended $T$-matrix theory, we calculate the density of states, as well as the single-particle spectral weight, in the unitarity limit above the superfluid phase transition temperature $T_{\rm c}$. We show that the momentum regions where pairing fluctuations strongly affect single-particle excitations are different between light fermions and heavy fermions, reflecting the difference of the Pauli blocking effects between them. In addition, we obtain different pseudogap phenomena associated with pairing fluctuations in between the two components. Since the realization of a mass-imbalanced superfluid Fermi gas is an important challenge in this field, our results would contribute to the understanding of physical properties of the hetero-pairing state.
Development of a Retractor Holding Device to Reduce the Manpower in Total Hip Arthroplasty through Direct Anterior Approach  [PDF]
Hirotake Yo, Hirotsugu Ohashi, Ryo Sugama, Tessyu Ikawa
Open Journal of Orthopedics (OJO) , 2016, DOI: 10.4236/ojo.2016.62004
Abstract: Direct anterior approach (DAA) for total hip arthroplasty (THA) is a minimally invasive technique. In this approach, two assistants are necessary. We developed a retractor holding device called “Spider arm” to replace an assistant in the contra-lateral side. In this study, we investigated the usefulness of Spider arm in THA through direct anterior approach. 20 hips were operated without Spider arm and 21 hips were operated with Spider arm. The surgery time and the blood loss were compared. The cup position and leg length discrepancy were measured on radiography. There was no statistical significance between two groups in all parameters. No clinical complications were reported. With Spider arm, DAA-THA could be performed by two surgeons without deterioration of the surgery time and blood loss. The accuracy of cup position and leg length discrepancy was not affected. Spider arm can contribute to reducing the manpower in DAA-THA.
Non-equilibrium properties of a pumped-decaying Bose-condensed electron-hole gas in the BCS-BEC crossover region
Ryo Hanai,Peter B. Littlewood,Yoji Ohashi
Physics , 2015,
Abstract: We theoretically investigate a Bose-condensed exciton gas out of equilibrium. Within the framework of the combined BCS-Leggett strong-coupling theory with the non-equilibrium Keldysh formalism, we show how the Bose-Einstein condensation (BEC) of excitons is suppressed to eventually disappear, when the system is in the non-equilibrium steady state. The supply of electrons and holes from the bath is shown to induce quasi-particle excitations, leading to the partial occupation of the upper branch of Bogoliubov single-particle excitation spectrum. We also discuss how this quasi-particle induction is related to the suppression of exciton BEC, as well as the stability of the steady state.
Spin susceptibility and effects of inhomogeneous strong pairing fluctuations in a trapped ultracold Fermi gas
Hiroyuki Tajima,Ryo Hanai,Yoji Ohashi
Physics , 2015,
Abstract: We theoretically investigate magnetic properties of a unitary Fermi gas in a harmonic trap. Including strong pairing fluctuations within the framework of an extended $T$-matrix approximation (ETMA), as well as effects of a trap potential within the local density approximation (LDA), we calculate the local spin susceptibility $\chi(T,r)$ above the superfluid phase transition temperature $T_{\rm c}$. We show that the formation of preformed singlet Cooper pairs anomalously suppresses $\chi(T,r)$ in the trap center near $T_{\rm c}$. We also point out that, in the unitarity limit, the spin-gap temperature in a uniform Fermi gas can be evaluated from the observation of the spatial variation of $\chi(T,r)$. Since a real ultracold Fermi gas is always in a trap potential, our results would be useful for the study of how this spatial inhomogeneity affects thermodynamic properties of an ultracold Fermi gas in the BCS-BEC crossover region.
Activation and detection of HTLV-I Tax-specific CTLs by Epitope expressing Single-Chain Trimers of MHC Class I in a rat model
Takashi Ohashi, Mika Nagai, Hiroyuki Okada, Ryo Takayanagi, Hisatoshi Shida
Retrovirology , 2008, DOI: 10.1186/1742-4690-5-90
Abstract: We have established expression vectors which encode SCTs of rat MHC-I (RT1.Al) with Tax180-188 peptide. Human cell lines transfected with the established expression vectors were able to induce IFN-γ and TNF-α production by a Tax180-188-specific CTL line, 4O1/C8. We have further fused the C-terminus of SCTs to EGFP and established cells expressing SCT-EGFP fusion protein on the surface. By co-cultivating the cells with 4O1/C8, we have confirmed that the epitope-specific CTLs acquired SCT-EGFP fusion proteins and that these EGFP-possessed CTLs were detectable by flow cytometric analysis.We have generated a SCT of rat MHC-I linked to Tax epitope peptide, which can be applicable for the induction of Tax-specific CTLs in rat model systems of HTLV-I infection. We have also established a detection system of Tax-specific CTLs by using cells expressing SCTs fused with EGFP. These systems will be useful tools in understanding the role of HTLV-I specific CTLs in HTLV-I pathogenesis.Human T-cell leukemia virus type I (HTLV-I) is etiologically linked to adult T-cell leukemia (ATL) [1,2], a chronic progressive neurological disorder termed HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) [3,4], and various other human diseases [5-8]. ATL is a malignant lymphoproliferative disease affecting a subgroup of middle-aged HTLV-I carriers characterized by the presence of mature T cell phenotype [9]. HTLV-I genome contains a unique 3' region, designated as pX, which encodes the viral transactivator protein, Tax [10]. Because of its broad transactivation capabilities [11], it is speculated that Tax plays a central role in HTLV-I associated immortalization and transformation of T cells, which may lead to the development of ATL.Tax is also known as a major target protein recognized by cytotoxic T lymphocytes (CTL) of HTLV-I carriers [12]. It has been reported that the levels of HTLV-I-specific CTL are quite diverse among HTLV-I carriers and that ATL patients have impaired l
Excitation properties and effects of mass imbalance in the BCS-BEC crossover regime of an ultracold Fermi gas
Ryo Hanai,Takashi Kashimura,Ryota Watanabe,Daisuke Inotani,Yoji Ohashi
Physics , 2013, DOI: 10.1103/PhysRevA.88.053621
Abstract: We investigate single-particle properties of a mass-imbalanced Fermi gas in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover region. In the presence of mass imbalance, we point out that the ordinary $T$-matrix approximation, which has been extensively used to clarify various BCS-BEC crossover physics in the mass-balanced case, unphysically gives a double-valued solution in terms of the superfluid phase transition temperature $T_{\rm c}$ in the crossover region. To overcome this serious problem, we include higher order strong-coupling corrections beyond the $T$-matrix level. Using this extended $T$-matrix theory, we calculate single-particle excitations in the normal state above $T_{\rm c}$. The so-called pseudogap phenomena originating from pairing fluctuations are shown to be different between the light mass component and heavy mass component, which becomes more remarkable at higher temperatures. Since Fermi condensates with hetero-Cooper pairs have recently been discussed in various fields, such as exciton (polariton) condensates, as well as color superconductivity, our results would be useful for the further development of Fermi superfluid physics, beyond the conventional superfluid state with homo-Cooper pairs.
Triplet pair amplitude in a trapped $s$-wave superfluid Fermi gas with broken spin rotation symmetry
Yuki Endo,Daisuke Inotani,Ryo Hanai,Yoji Ohashi
Physics , 2015, DOI: 10.1103/PhysRevA.92.023610
Abstract: We investigate the possibility that the broken spatial inversion symmetry by a trap potential induces a spin-triplet Cooper-pair amplitude in an $s$-wave superfluid Fermi gas. Being based on symmetry considerations, we clarify that this phenomenon may occur, when a spin rotation symmetry of the system is also broken. We also numerically confirm that a triplet pair amplitude is really induced under this condition, using a simple model. Our results imply that this phenomenon is already present in a trapped $s$-wave superfluid Fermi gas with spin imbalance. As an interesting application of this phenomenon, we point out that one may produce a $p$-wave superfluid Fermi gas, by suddenly changing the $s$-wave pairing interaction to a $p$-wave one by using the Feshbach resonance technique. Since a Cooper pair is usually classified into the spin-singlet (and even-parity) state and the spin-triplet (and odd-parity) state, our results would be useful in considering how to mix them with each other in a superfluid Fermi gas. Such admixture has recently attracted much attention in the field of non-centrosymmetric superconductivity, so that our results would also contribute to the further development of this research field, on the viewpoint of cold Fermi gas physics.
Specific heat and effects of pairing fluctuations in the BCS-BEC crossover regime of an ultracold Fermi gas
Pieter van Wyk,Hiroyuki Tajima,Ryo Hanai,Yoji Ohashi
Physics , 2015,
Abstract: We investigate the specific heat at constant volume $C_V$ in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an ultracold Fermi gas above the superfluid phase transition temperature $T_{\rm c}$. Within the framework of the strong-coupling theory developed by Nozi\`eres and Schmitt-Rink, we show that this thermodynamic quantity is sensitive to the stability of preformed Cooper pairs. That is, while $C_V(T\gesim T_{\rm c})$ in the unitary regime is remarkably enhanced by {\it metastable} preformed Cooper pairs or pairing fluctuations, it is well described by that of an ideal Bose gas of long-lived {\it stable} molecules in the strong-coupling BEC regime. Using these results, we identify the region where the system may be viewed as an almost ideal Bose gas of stable pairs, as well as the pseudogap regime where the system is dominated by metastable preformed Cooper pairs, in the phase diagram of an ultracold Fermi gas with respect to the strength of a pairing interaction and the temperature. We also show that the calculated specific heat agrees with the recent experiment on a $^6$Li unitary Fermi gas. Since the formation of preformed Cooper pairs is a crucial key in the BCS-BEC crossover phenomenon, our results would be helpful in considering how fluctuating preformed Cooper pairs appear in a Fermi gas, to eventually become stable, as one passes through the BCS-BEC crossover region.
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