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Search Results: 1 - 10 of 130 matches for " Naohisa Yahagi "
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What are the latest developments in colorectal endoscopic submucosal dissection?
Toshio Uraoka,Yutaka Saito,Naohisa Yahagi
World Journal of Gastrointestinal Endoscopy , 2012, DOI: 10.4253/wjge.v4.i7.296
Abstract: Endoscopic submucosal dissection (ESD) enables direct submucosal dissection so that even large early-stage gastrointestinal tumors can be resected en bloc. ESD has recently been applied to the colorectum since it was originally developed for use in the stomach. However, colorectal ESD is technically more difficult with an increased risk of perforation compared with gastric ESD. In addition, this procedure is seldom performed in Western countries. Consequently, further technical advances and the availability of a suitable clinical training system are required for the extensive use of colorectal ESD. In this topic highlight, we review the most recent developments in colorectal ESD.
Effects of Nonuniform Outflow and Buoyancy on Drag Coefficient Acting on a Spherical Particle  [PDF]
Mariko Watanabe, Joji Yahagi
Journal of Flow Control, Measurement & Visualization (JFCMV) , 2017, DOI: 10.4236/jfcmv.2017.54008
Abstract: Pyrolysis gas jets out from the surface of a solid fuel particle when heated. This study experimentally observes the occurrence of gas jetsfrom heated solid fuel particles. Results reveal a local gas jet occurs from the particle’s surface when its temperature reaches the point at which a pyrolysis reaction occurs. To investigate the influence of the gas jet on particle motion, a numerical simulation of the uniform flow around a spherical particle with a nonuniform outflow or high surface temperature is conducted, and the drag force acting on the spherical particle is estimated. In the numerical study, the magnitude of the outflow velocity, direction of outflow, and Rayleigh number,?i.e., particle surface temperature, are altered, and outflow velocities and the Rayleigh number are set based on the experiment. The drag coefficient is found to decrease when an outflow occurs in the direction against the mainstream; this drag coefficient at a higher Rayleigh number is slightly higher than that at a Rayleigh number of zero.
Usefulness and safety of 0.4% sodium hyaluronate solution as a submucosal fluid "cushion" for endoscopic resection of colorectal mucosal neoplasms: A prospective multi-center open-label trial
Shoji Hirasaki, Takahiro Kozu, Hironori Yamamoto, Yasushi Sano, Naohisa Yahagi, Tsuneo Oyama, Tadakazu Shimoda, Kentaro Sugano, Hisao Tajiri, Takao Takekoshi, Daizo Saito
BMC Gastroenterology , 2009, DOI: 10.1186/1471-230x-9-1
Abstract: A prospective multi-center open-label study was designed. A total of 41 patients with 5–20 mm neoplastic lesions localized in the colorectal mucosa at six referral hospitals in Japan in a single year period from December 2002 to November 2003 were enrolled and underwent endoscopic resection with SH. The usefulness of 0.4% SH was assessed by the en bloc complete resection and the formation and maintenance of mucosal lesion-lifting during endoscopic resection. Safety was evaluated by analyzing adverse events during the study period.The usefulness rate was high (82.5%; 33/40). The following secondary outcome measures were noted: 1) steepness of mucosal lesion-lifting, 75.0% (30/40); 2) intraoperative complications, 10.0% (4/40); 3) time required for mucosal resection, 6.7 min; 4) volume of submucosal injection, 6.8 mL and 5) ease of mucosal resection, 87.5% (35/40). Two adverse events of bleeding potentially related to 0.4% SH were reported.Using 0.4% SH solution enabled sufficient lifting of a colorectal intramucosal lesion during endoscopic resection, reducing the need for additional injections and the risk of perforation. Therefore, 0.4% SH may contribute to the reduction of complications and serve as a promising submucosal injection solution due to its potentially superior safety in comparison to normal saline solution.The incidence of colorectal neoplasm in Japan is high, and the number of patients with colorectal neoplasm is steadily increasing. The chances of treating colorectal mucosal lesion with endoscopy have increased [1-3]. Depending on techniques and equipment, endoscopic resection of the colon includes polypectomy, endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD) in the colon. Focusing on the physiochemical properties of sodium hyaluronate (SH), Yamamoto et al. developed a technique known as EMR using sodium hyaluronate (EMRSH), and reported that when SH was injected into the submucosal layer during EMR, mucosal lesions could
N-Body Code with Adaptive Mesh Refinement
Hideki Yahagi,Yuzuru Yoshii
Physics , 2001, DOI: 10.1086/322457
Abstract: We have developed a simulation code with the techniques which enhance both spatial and time resolution of the PM method for which the spatial resolution is restricted by the spacing of structured mesh. The adaptive mesh refinement (AMR) technique subdivides the cells which satisfy the refinement criterion recursively. The hierarchical meshes are maintained by the special data structure and are modified in accordance with the change of particle distribution. In general, as the resolution of the simulation increases, its time step must be shortened and more computational time is required to complete the simulation. Since the AMR enhances the spatial resolution locally, we reduce the time step locally also, instead of shortening it globally. For this purpose we used a technique of hierarchical time steps (HTS) which changes the time step, from particle to particle, depending on the size of the cell in which particles reside. Some test calculations show that our implementation of AMR and HTS is successful. We have performed cosmological simulation runs based on our code and found that many of halo objects have density profiles which are well fitted to the universal profile proposed by Navarro, Frenk, & White (1996) over the entire range of their radius.
Curvature Dependent Diffusion Flow on Surface with Thickness
Naohisa Ogawa
Physics , 2009, DOI: 10.1103/PhysRevE.81.061113
Abstract: Particle diffusion in a two dimensional curved surface embedded in $R_3$ is considered. In addition to the usual diffusion flow, we find a new flow with an explicit curvature dependence. New diffusion equation is obtained in $\epsilon$ (thickness of surface) expansion. As an example, the surface of elliptic cylinder is considered, and curvature dependent diffusion coefficient is calculated.
A Note on the scale symmetry and Noether current
Naohisa Ogawa
Physics , 1998,
Abstract: Usually we consider the symmetry of action as the symmetry of the theory, however, in the Keplar problem the scaling symmetry existing in equa tion of motion is not the ones for action. It changes the multiplicative c onstant of action and the time boundary. In such a case that the scale tran sformation does not leave the action invariant but keeping the equation inva riant, the following statement is proved. The time integration of Lagrangian is explicitly performed and the action ca n be expressed by the difference of formal (non-conserved) Noether charges a t time boundaries. In field theory the action can be expressed by the bound ary integration of the formal Noether current.
Quantum Mechanical Embedding of Spinning Particle and Induced Spin-connection
Naohisa Ogawa
Physics , 1997, DOI: 10.1142/S0217732397001618
Abstract: This paper introduces the way of the embedding of spinning particle quantum mechanically. Schr\"odinger equation on its submanifold obtains the gauge field as spin connection, and it reduces to the ones obtained by Ohnuki and Kitakado when we consider $S^2$ in $R^3$. PACS numbers: 03.65
Pedagogical Introduction to Hamiltonian BRST formalism
Naohisa Ogawa
Physics , 1997,
Abstract: Hamiltonian BRST formalism (FV formalism) includes many auxiliary fields without explanation. Its path-integration has a simple form by using BRST charge, but its construction is quite mechanically and hard to understand physical meaning. In this paper we perform the phase space path-integral with requiring BRST invariance for action and measure, and show that the resultant form is equivalent to the Hamiltonian BRST (FV) formalism in gravitational theory. This explains why so many auxiliary fields are necessary to be introduced. We also find the gauge fixing is automatically done by requiring the BRST invariance of the path-integral measure. This is a pedagogical introduction to Hamiltonian BRST formalism.
Embedding of Relativistic Particles and Spinor Natural-Frame
Naohisa Ogawa
Physics , 1997,
Abstract: Embedding of Klein-Gordon and Dirac particle onto Riemannian submanifold in higher dimensional Minkowski space is given by using Hamiltonian BRST formalism. Up to the ordering and quantum potential term induced by embedding, obtained K-G equation is the usual one in Riemannian space, instead, the obtained Dirac equation is essentially different from the usual well known form using vierbein. The requirement of equivalence between two Dirac equations gives the property of natural-frame for spinor.
Diffusion in a Curved Tube
Naohisa Ogawa
Physics , 2011, DOI: 10.1016/j.physleta.2013.07.054
Abstract: The diffusion of particles in confining walls forming a tube is discussed. Such a transport phenomenon is observed in biological cells and porous media. We consider the case in which the tube is winding with curvature and torsion, and the thickness of the tube is sufficiently small compared with its curvature radius. We discuss how geomerical quantities appear in a quasi-one-dimensional diffusion equation.
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