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Search Results: 1 - 10 of 901 matches for " Yosuke Mizuno "
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The Role of the Equation of State in Resistive Relativistic Magnetohydrodynamics
Yosuke Mizuno
Physics , 2013, DOI: 10.1088/0067-0049/205/1/7
Abstract: We have investigated the role of the equation of state in resistive relativistic magnetohydrodynamics using a newly developed resistive relativistic magnetohydrodynamic code. A number of numerical tests in one-dimension and multi-dimensions are carried out in order to check the robustness and accuracy of the new code. The code passes all the tests in situations involving both small and large uniform conductivities. Equations of state which closely approximate the single-component perfect relativistic gas are introduced. Results from selected numerical tests using different equations of state are compared. The main conclusion is that the choice of the equation of state as well as the value of the electric conductivity can result in considerable dynamical differences in simulations involving shocks, instabilities, and magnetic reconnection.
Enhancement of Brillouin Scattering Signal in Perfluorinated Graded-Index Polymer Optical Fibers
Yosuke Mizuno,Kentaro Nakamura
Applied Sciences , 2012, DOI: 10.3390/app2010046
Abstract: Perfluorinated graded-index polymer optical fibers (PFGI-POFs), fabricated by replacing the hydrogen atoms of standard polymethyl methacrylate-based POFs with fluorine atoms, have been extensively studied due to their relatively low propagation loss even at telecommunication wavelength. Recently, Brillouin scattering, which is one of the most significant nonlinear effects in optical fibers, has been successfully observed in PFGI-POFs at 1.55-μm wavelength. The Brillouin Stokes signal was, however, not large enough for practical applications or for detailed investigations of the Brillouin properties. In this paper, we review our recent work on Stokes signal enhancement. First, we induce stimulated Brillouin scattering based on the so-called pump-probe technique, and discuss its applicability to temperature sensors. Then, we investigate the influence of the core diameter and length of PFGI-POFs on Stokes signal, and observe the Brillouin linewidth narrowing effect. We believe our work is an important technological step toward the implementation of practical Brillouin-based devices and systems including distributed strain and temperature sensors.
Brillouin Scattering in Polymer Optical Fibers: Fundamental Properties and Potential Use in Sensors
Yosuke Mizuno,Kentaro Nakamura
Polymers , 2011, DOI: 10.3390/polym3020886
Abstract: We review the fundamental properties of Brillouin scattering in a perfluorinated graded-index polymer optical fiber (PFGI-POF) with 120 μm core diameter. The experiments were performed at 1.55 μm telecommunication wavelength. The Brillouin frequency shift (BFS) and the Brillouin bandwidth were 2.83 GHz and 105 MHz, respectively. The Brillouin gain coefficient was calculated to be 3.09 × 10 ?11 m/W, which was comparable to that of fused silica fibers. The Brillouin threshold power of the 100 m POF was estimated to be as high as 24 W, which can be, for practical applications, reduced by using POFs with smaller cores. These properties were compared with those of silica-based graded-index multi-mode fibers. We also investigated the BFS dependences on strain and temperature. They showed negative dependences with coefficients of ?121.8 MHz/% and ?4.09 MHz/K, respectively, which are ?0.2 and ?3.5 times as large as those in silica fibers. These BFS dependences indicate that the Brillouin scattering in PFGI-POFs can be potentially applied to high-accuracy temperature sensing with reduced strain sensitivity.
Alternative implementation of simplified Brillouin optical correlation-domain reflectometry
Neisei Hayashi,Yosuke Mizuno,Kentaro Nakamura
Physics , 2014,
Abstract: We developed an alternative configuration of simplified Brillouin optical correlation-domain reflectometry, which can overcome the drawbacks of the original configuration. This system uses, as reference light, the light that is Fresnel reflected at a partial reflection point artificially produced near an optical circulator. We show that the influence of the 0th correlation peak fixed at the partial reflection point can be suppressed by replacing the nearby fibers with other fibers having different Brillouin frequency shift values (here, multi-mode fibers are used). Finally, we demonstrate a distributed measurement for detecting a 1.46-m-long strained section with a high signal-to-noise ratio.
Brillouin scattering in multi-core optical fibers
Yosuke Mizuno,Neisei Hayashi,Kentaro Nakamura
Physics , 2014,
Abstract: We measure the Brillouin gain spectra in two cores (the central core and one of the outer cores) of a ~3-m-long, silica-based, 7-core multi-core fiber (MCF) with incident light of 1550 nm wavelength, and investigate the Brillouin frequency shift (BFS) and its dependence on strain and temperature. The BFSs of both the cores are ~10.92 GHz, and the strain- and temperature-dependence coefficients of the BFS in the central core are 484.8 MHz/% and 1.08 MHz/K, respectively, whereas those in the outer core are 516.9 MHz/% and 1.03 MHz/K. All of these values are not largely different from those in a silica single-mode fiber, which is expected because the cores are composed of the same material (silica). The difference in the BFS dependence of strain between the two cores may originate from the difference in structural deformation when strain is applied to the fiber, which is a unique characteristic to MCFs. The future prospect on distributed strain and temperature sensing based on Brillouin scattering in MCFs is finally presented.
Simplified configuration of Brillouin optical correlation-domain reflectometry
Neisei Hayashi,Yosuke Mizuno,Kentaro Nakamura
Physics , 2014,
Abstract: We develop a simple and cost-efficient configuration of Brillouin optical correlation-domain reflectometry (BOCDR), the setup of which does not include an additional reference path used in standard BOCDR systems. The Fresnel-reflected light from an open end of a sensing fiber is used as reference light. The limitations of spatial resolution, measurement range, and their ratio are theoretically clarified, and then a distributed strain measurement with a < 100-mm spatial resolution and a 4.1-m measurement range is demonstrated with a high signal-to-noise ratio.
Fiber-Optic Interferometry Using Narrowband Light Source and Electrical Spectrum Analyzer: Influence on Brillouin Measurement
Yosuke Mizuno,Neisei Hayashi,Kentaro Nakamura
Physics , 2014, DOI: 10.1109/JLT.2014.2365187
Abstract: We observe an interference pattern using a simple fiber-optic interferometer consisting of an electrical spectrum analyzer and a narrowband light source, which is commonly employed for observing the Brillouin gain spectrum. This interference pattern expands well beyond the frequency range corresponding to the Brillouin frequency shift in silica fibers (approximately 11 GHz at 1550 nm). Using both silica single-mode and polymer optical sensing fibers, we then experimentally prove that the distinctive noise in a self-heterodyne-based Brillouin measurement with an unoptimized polarization state originates from the interference between the reference light and the Fresnel-reflected light. This noise can be almost completely suppressed by employing a delay line that is longer than the coherence length of the light source and by artificially applying a high loss near the open end of the sensing fiber.
Hepatic Sinusoidal Obstruction Syndrome without Preceding Medical Events  [PDF]
Yukino Kawanami, Riko Kitazawa, Ryuma Haraguchi, Yasuo Ueda, Yukiko Nishi, Kanazu Ariyasu, Yosuke Mizuno, Sohei Kitazawa
Case Reports in Clinical Medicine (CRCM) , 2016, DOI: 10.4236/crcm.2016.53019
Abstract: Sinusoidal obstruction syndrome (SOS) is one of the severe complications of radiation, anticancer chemotherapy and immunosuppressive agents for transplantation. Autopsy of a case of rapidly progressive, uncontrollable severe ascites, without apparent signs of preceding drug toxicity, revealed a tensely enlarged liver and spleen, and 3000 ml of ascites attributed to secondary portal hypertension. Histopathological analysis disclosed sinusoidal endothelial damage and fibrous expansion from central veins. All the foregoing indicated hepatic SOS that needs to be included in the differential diagnosis of progressive ascites in patients without an apparent history of malignancy or transplantation.
Spin-dependent transport properties in GaMnAs-based spin hot-carrier transistors
Yosuke Mizuno,Shinobu Ohya,Pham Nam Hai,Masaaki Tanaka
Physics , 2007,
Abstract: We have investigated the spin-dependent transport properties of GaMnAs-based three-terminal semiconductor spin hot-carrier transistor (SSHCT) structures. The emitter-base bias voltage VEB dependence of the collector current IC, emitter current IE, and base current IB shows that the current transfer ratio alpha (= IC / IE) and the current gain beta (= IC / IB) are 0.8-0.95 and 1-10, respectively, which means that GaMnAs-based SSHCTs have current amplifiability. In addition, we observed an oscillatory behavior of the tunneling magnetoresistance (TMR) ratio with the increasing bias, which can be explained by the resonant tunneling effect in the GaMnAs quantum well.
Spatial Growth of the Current-Driven Instability in Relativistic Jets
Yosuke Mizuno,Philip E. Hardee,Ken-Ichi Nishikawa
Physics , 2014, DOI: 10.1088/0004-637X/784/2/167
Abstract: We have investigated the influence of velocity shear and a radial density profile on the spatial development of the current driven kink instability along helically magnetized relativistic jets via three-dimensional relativistic magnetohydrodynamic simulations. In this study, we use a non-periodic computational box, the jet flow is initially established across the computational grid, and a precessional perturbation at the inlet triggers growth of the kink instability. If the velocity shear radius is located inside the characteristic radius of the helical magnetic field, a static non-propagating current driven kink is excited as the perturbation propagates down the jet. Temporal growth disrupts the initial flow across the computational grid not too far from the inlet. On the other hand, if the velocity shear radius is outside the characteristic radius of the helical magnetic field, the kink is advected with the flow and grows spatially down the jet. In this case flow is maintained to much larger distances from the inlet. The effect of different radial density profiles is more subtle. When the density increases with radius, the kink appears to saturate by the end of the simulation without apparent disruption of the helical twist. This behavior suggests that relativistic jets consisting of a tenuous spine surrounded by a denser medium with a velocity shear radius outside the radius of maximum toroidal magnetic field have a relatively stable configuration.
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