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Search Results: 1 - 10 of 367 matches for " Asano "
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On the Tempo-Spatial Evolution of the Lower Ionospheric Perturbation for the 2016 Kumamoto Earthquakes from Comparisons of VLF Propagation Data Observed at Multiple Stations with Wave-Hop Theoretical Computations  [PDF]
Tomokazu Asano, Masashi Hayakawa
Open Journal of Earthquake Research (OJER) , 2018, DOI: 10.4236/ojer.2018.73010
Abstract:
There have been published many papers on VLF (very low frequency) characteristics to study seismo-ionospheric perturbations. Usually VLF records (amplitude and/or phase) are used to investigate mainly the temporal evolution of VLF propagation anomalies with special attention to one particular propagation path. The most important advantage of this paper is the simultaneous use of several propagation paths. A succession of earthquakes (EQs) happened in the Kumamoto area in Kyusyu Island; two strong foreshocks with magnitude of 6.5 and 6.4 on 14 April (UT) and the main shock with magnitude 7.3 on 15 April (UT). Because the EQ epicenters are not far from the VLF transmitter (with the call sign of JJI in Miyazaki prefecture), we can utilize simultaneously 8 observing stations of our network all over Japan. Together with the use of theoretical computations based on wave-hop theory, we try to trace both the temporal and spatial evolutions of the ionospheric perturbation associated with this succession of EQs. It is found that the ionospheric perturbation begins to appear about two weeks before the EQs, and this perturbation becomes most developed 5 - 3 days before the main shock. When the perturbation is most disturbed, the maximum change in vertical direction is depletion in the VLF effective ionospheric height of the order of 10 km, and its horizontal scale (or its radius) is about 1000 km. These spatio-temporal changes of the seismo-ionospheric perturbation will be investigated in details in the discus-sion, a comparison has made with the VLF characteristics of the 1995 Kobe with the same magnitude and of the same fault-type, and a brief discussion on the generation mechanism of seismo-ionospheric perturbation is finally made.
Endoscopic submucosal dissection and surgical treatment for gastrointestinal cancer
Michio Asano
World Journal of Gastrointestinal Endoscopy , 2012, DOI: 10.4253/wjge.v4.i10.438
Abstract: Endoscopic submucosal dissection (ESD) is widely used in Japan as a minimally invasive treatment for early gastric cancer. The application of ESD has expanded to the esophagus and colorectum. The indication criteria for endoscopic resection (ER) are established for each organ in Japan. Additional treatment, including surgery with lymph node dissection, is recommended when pathological examinations of resected specimens do not meet the criteria. Repeat ER for locally recurrent gastrointestinal tumors may be difficult because of submucosal fibrosis, and surgical resection is required in these cases. However, ESD enables complete resection in 82%-100% of locally recurrent tumors. Transanal endoscopic microsurgery (TEM) is a well-developed surgical procedure for the local excision of rectal tumors. ESD may be superior to TEM alone for superficial rectal tumors. Perforation is a major complication of ESD, and it is traditionally treated using salvage laparotomy. However, immediate endoscopic closure followed by adequate intensive treatment may avoid the need for surgical treatment for perforations that occur during ESD. A second primary tumor in the remnant stomach after gastrectomy or a tumor in the reconstructed organ after esophageal resection has traditionally required surgical treatment because of the technical difficulty of ER. However, ESD enables complete resection in 74%-92% of these lesions. Trials of a combination of ESD and laparoscopic surgery for the resection of gastric submucosal tumors or the performance of sentinel lymph node biopsy after ESD have been reported, but the latter procedure requires a careful evaluation of its clinical feasibility.
On a class of topological quantum field theories in three-dimensions
Masako Asano
Physics , 1995, DOI: 10.1142/S0217751X96002121
Abstract: We investigate the Chung-Fukuma-Shapere theory, or Kuperberg theory, of three-dimensional lattice topological field theory. We construct a functor which satisfies the Atiyah's axioms of topological quantum field theory by reformulating the theory as Turaev-Viro type state-sum theory on a triangulated manifold. The theory can also be extended to give a topological invariant of manifolds with boundary.
Stringy Cosmic Strings and Compactifications of F-theory
Masako Asano
Physics , 1997, DOI: 10.1016/S0550-3213(97)00377-5
Abstract: We construct stringy cosmic string solutions corresponding to compactifications of F-theory on several elliptic Calabi-Yau manifolds by solving the equations of motion of low energy effective action of ten dimensional type IIB superstring theory. Existence of such solutions supports the compactifications of F-theory.
Compactification and Identification of Branes in the Kaluza-Klein monopole backgrounds
Masako Asano
Physics , 2000,
Abstract: We study the properties of branes in supergravity theory. We investigate a class of systems consisting of an M5-brane in the Kaluza-Klein monopole background with 1/4 supersymmetry in 11-dimensions. In the near core region of the KK-monopoles, the exact supergravity solution corresponding to each of these configurations is obtained. Then we argue the compactified 10-dimensional systems and suggest a way of unambiguous identification of branes in this background. Here the location of Dirac string type singularity accompanied by the D6-branes plays an important role. The method is essentially the same as that of (p,q)5-branes or (p,q)-strings within the 7-brane background in the IIB theory. We also argue the phenomena of D4-brane creation from D6-branes.
Spin Current in p-wave Superconducting Rings
Y. Asano
Physics , 2005, DOI: 10.1103/PhysRevB.72.092508
Abstract: A formula of the spin current in mesoscopic superconductors is derived from the mean-field theory of superconductivity. The spin flow is generated by the spatial fluctuations of $\vec{d}$ which represents a spin state of spin-triplet superconductors. We discuss a possibility of the circulating spin current in isolated p-wave superconducting rings at the zero magnetic field. The direction of the spin current depends on topological numbers which characterize the spatial configuration of $\vec{d}$ on the ring.
Disappearance of Ensemble-Averaged Josephson Current in Dirty SNS Junctions of d-wave Superconductors
Y. Asano
Physics , 2001, DOI: 10.1103/PhysRevB.64.014511
Abstract: We discuss the Josephson current in superconductor / dirty normal conductor / superconductor junctions, where the superconductors have $d_{x^2-y^2}$ pairing symmetry. The low-temperature behavior of the Josephson current depends on the orientation angle between the crystalline axis and the normal of the junction interface. We show that the ensemble-averaged Josephson current vanishes when the orientation angle is $\pi/4$ and the normal conductor is in the diffusive transport regime. The $d_{x^2-y^2}$-wave pairing symmetry is responsible for this fact.
Magnetoconductance Oscillations in Ballistic Semiconductor-Superconductor Junctions
Y. Asano
Physics , 1999, DOI: 10.1103/PhysRevB.61.1732
Abstract: The mechanism of the magnetoconductance oscillations in junctions of a ballistic semiconductor and a superconductor is discussed. The oscillations appear when both the normal and the Andreev reflection occur at the interface. The interplay between the classical cyclotron motion of a quasiparticle and the phase shift caused by the magnetic field is the origin of the conductance oscillations.
Usability of the NFW Galaxy Profile as a Cosmological Tool Estimated from 2-Image Gravitational Lens Systems
K. Asano
Physics , 1999, DOI: 10.1093/pasj/52.1.99
Abstract: The profile of Navarro, Frenk, and White (the NFW profile), which was derived from the {\it N}-body simulations of cold dark-matter halos, is a strong candidate for a galaxy or cluster profile. In order to check the usability of the NFW profile as a first approximation of a galaxy model, we studied the characteristic overdensity and scale radius of galaxies by reproducing the image positions and flux ratios of 2-image gravitational lens systems, under the following simple assumptions: the galaxies are spherically symmetric, and stars and external shear do not contribute to the gravitational lens. The scale radii of the lensing galaxies are smaller, and the characteristic overdensities are larger than the predicted value in the {\it N}-body simulations. These results indicate that our assumptions are overly simplified. It may be impossible to simply adopt the NFW profile, which does not include stars, to probe the cosmological parameters or the light propagation in an inhomogeneous universe and so on. If we adopt a softened isothermal profile to the lensing galaxies, the scale radii and the central matter densities agree with models which are derived from other observational results for early-type galaxies and which are independent of gravitational lensing. The isothermal sphere as a first approximation of a galaxy model has no serious problem.
Non-commutative branes in D-brane backgrounds
Masako Asano
Physics , 2001, DOI: 10.1142/S0217751X0201100X
Abstract: We study Myers world-volume effective action of coincident D-branes. We investigate a system of N_0 D0-branes in the geometry of Dp-branes with p=2 or p=4. The choice of coordinates can make the action simplified and tractable. For p=4, we show that a certain point-like D0-brane configuration solving equations of motion of the action can expand to form a fuzzy two-sphere without changing quantum numbers. We compare non-commutative D0-brane configurations with dual spherical D(6-p)-brane systems. We also discuss the relation between these configurations and giant gravitons in 11-dimensions.
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