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Search Results: 1 - 10 of 5658 matches for " Shin-ichiro Nagahiro "
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Bending-Filament Model for the Buckling and Coiling Instability of Viscous Fluid Rope
Shin-ichiro Nagahiro,Yoshinori Hayakawa
Physics , 2008, DOI: 10.1103/PhysRevE.78.025302
Abstract: A simple model is proposed for the buckling and coiling instability of a viscous "fluid rope" falling on a plane. By regarding a fluid rope as a one-dimensional flow, this model accounts for only the axial and shared viscous forces. Our model successfully reproduces several experiments with no adjustable parameters, such as the existence of three distinct coiling regimes reported in Phys. Rev. Lett. 93, 214502 (2004). Our model allows for the discussion of unsteady motion. An expression for the critical fall height at which the coiling frequency changes from a decrease to increase was phenomenologically derived. It was found that the coil-uncoil transition shows remarkable hysteresis only for weak gravity condition.
A theoretical and numerical approach to "magic angle" of stone skipping
Shin-ichiro Nagahiro,Yoshinori Hayakawa
Physics , 2004, DOI: 10.1103/PhysRevLett.94.174501
Abstract: We investigate oblique impacts of a circular disk and water surface. An experiment [ Clanet, C., Hersen, F. and Bocquet, L., Nature 427, 29 (2004) ] revealed that there exists a "magic angle" of 20 [deg.] between a disk face and water surface which minimize the required speed for ricochet. We perform 3-dimensional simulation of the water impacts using the Smoothed Particle Hydrodynamics (SPH) and analyze the results with an ordinal differential equation (ODE) model. Our simulation is in good agreement with the experiment. The analysis with the ODE model give us a theoretical insight for the ``magic angle" of stone skipping.
Collision of One-Dimensional Nonlinear Chains
Shin-ichiro Nagahiro,Yoshinori Hayakawa
Physics , 2002, DOI: 10.1103/PhysRevE.67.036609
Abstract: We investigate one-dimensional collisions of unharmonic chains and a rigid wall. We find that the coefficient of restitution (COR) is strongly dependent on the velocity of colliding chains and has a minimum value at a certain velocity. The relationship between COR and collision velocity is derived for low-velocity collisions using perturbation methods. We found that the velocity dependence is characterized by the exponent of the lowest unharmonic term of interparticle potential energy.
Negative pressure in shear thickening band of a dilatant fluid
Shin-ichiro Nagahiro,Hiizu Nakanishi
Physics , 2015,
Abstract: We perform experiments and numerical simulations to investigate spatial distribution of pressure in a sheared dilatant fluid of the Taylor-Couette flow under a constant external shear stress. In a certain range of shear stress, the flow undergoes the shear thickening oscillation around 20 Hz. The pressure measurement during the oscillation at the wall of the outer cylinder indicates that a localized negative pressure region rotates around the axis with the flow. The maximum negative pressure is close to the Laplace pressure of the grain radius and nearly independent of the applied shear stress. Simulations of a phenomenological model reveal that the thickened region is dominated by a negative pressure band, which extends along the tensile direction in the flow. Such shear thickening with negative pressure contradicts a naive picture of jamming mechanism, where thickening is expected in the compressing direction with the positive pressure.
New Neumerical Method to Calculate Time-Dependent Quantum Properties in Finite Temperature Based on the Heisenberg Equation of Motion  [PDF]
Shin-Ichiro Kondo
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.310190
Abstract: For the purpose of computer calculation to evaluate time-dependent quantum properties in finite temperature, we propose new numerical method expressed in the forms of simultaneous differential equations. At first we derive the equation of motion in finite temperature, which is found to be same expression as Heisenberg equation of motion except for the c-number. Based on this equation, we construct numerical method to estimate time-dependent physical properties in finite temperature precisely without using analytical procedures such as Keldysh formalism. Since our approach is so simple and is based on the simultaneous differential equations including no terms related to self-energies, computer programming can be easily performed. It is possible to estimate exact time-dependent physical properties, providing that Hamiltonian of the system is taken to be a one-electron picture. Furthermore, we refer to the application to the many body problem and it is numerically possible to calculate physical properties using Hartree Fock approximation. Our numerical method can be applied to the case even when perturbative Hamiltonians are newly introduced or Hamiltonian shows complex time-dependent behavior. In this article, at first, we derive the equation of motion in finite temperature. Secondly, for the purpose of verification and of exhibiting the usefulness, we show the derivation of gap equation of superconductivity and of sum rule of electrical conductivity and the application to the many body problem. Finally we apply this method to these two cases: the first case is most simplified resonance charge transfer neutralization of an ion and the second is the same process but impurity potential is newly introduced as perturbative Hamiltonian. Through both cases, it is found that neutralization process is not so sensitive to temperature, however, impurity potential as small as 10 meV strongly influences the neutralization of ion.
Separation of long DNA chains using non-uniform electric field: a numerical study
Shin-ichiro Nagahiro,Satoyuki Kawano,Hidetoshi Kotera
Physics , 2006, DOI: 10.1103/PhysRevE.75.011902
Abstract: We study migration of DNA molecules through a microchannel with a series of electric traps controlled by an ac electric field. We describe the motion of DNA based on Brownian dynamics simulations of a beads-spring chain. Our simulation demonstrates that the chain captured by an electrode escapes from the binding electric field due to thermal fluctuation. We find that the mobility of chain would depend on the chain length; the mobility sharply increases when the length of a chain exceeds a critical value, which is strongly affected by the amplitude of the applied ac field. Thus we can adjust the length regime, in which this microchannel well separates DNA molecules, without changing the structure of the channel. We also present a theoretical insight into the relation between the critical chain length and the field amplitude.
Experimental observation of shear thickening oscillation
Shin-ichiro Nagahiro,Hiizu Nakanishi,Namiko Mitarai
Physics , 2012, DOI: 10.1209/0295-5075/104/28002
Abstract: We report experimental observation of the shear thickening oscillation, i.e. the spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluid. The shear thickening oscillation is caused by the interplay between the fluid dynamics and the shear thickening, and has been predicted theoretically by the present authors using a phenomenological fluid dynamics model for the dilatant fluid, but never been reported experimentally. Using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width, we observed strong vibrations of the frequency around 20 Hz, which is consistent with our theoretical prediction.
Fluid dynamics of dilatant fluid
Hiizu Nakanishi,Shin-ichiro Nagahiro,Namiko Mitarai
Physics , 2011, DOI: 10.1103/PhysRevE.85.011401
Abstract: Dense mixture of granules and liquid often shows a sever shear thickening and is called a dilatant fluid. We construct a fluid dynamics model for the dilatant fluid by introducing a phenomenological state variable for a local state of dispersed particles. With simple assumptions for an equation of the state variable, we demonstrate that the model can describe basic features of the dilatant fluid such as the stress-shear rate curve that represents discontinuous severe shear thickening, hysteresis upon changing shear rate, instantaneous hardening upon external impact. Analysis of the model reveals that the shear thickening fluid shows an instability in a shear flow for some regime and exhibits {\it the shear thickening oscillation}, i.e. the oscillatory shear flow alternating between the thickened and the relaxed states. Results of numerical simulations are presented for one and two-dimensional systems.
Joint Operation of Atomic Force Microscope and Advanced Laser Confocal Microscope for Observing Surface Processes in a Protein Crystal  [PDF]
Shin-ichiro Yanagiya, Nobuo Goto
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2012, DOI: 10.4236/jsemat.2012.223032
Abstract: We demonstrated the insitu observation of a moving atomic force microscope (AFM) cantilever using a laser confocal microscope combined with a differential interference microscope (LCM-DIM). The AFM cantilever scanned or indented the {110} surface of a hen egg-white lysozyme crystal in a supersaturated solution. Using a soft cantilever, we could observe the step growth with high time resolution by LCM-DIM and perform quantitative measurements of the step height by AFM simultaneously. In addition, a hard cantilever was used with LCM-DIM to observe the dynamics of crystal surface scratching and indentation. In the supersaturated solution, the small steps generated from the scratched line aggregated to macro steps, and subsequently flattened the surface.
Degradation of Aqueous 2,6-Dibromophenol Solution by In-Liquid Dielectric Barrier Microplasma  [PDF]
Shin-Ichiro Kojima, Keiko Katayama-Hirayama, Tetsuya Akitsu
World Journal of Engineering and Technology (WJET) , 2016, DOI: 10.4236/wjet.2016.43042
Abstract: Degradation of 2,6-dibromophenol (2,6-DBP) in the aqueous solution was studied using dielectric barrier discharge in micro-bubbles. Experimental comparison of working gas Ar, N2, O2, and air showed that oxygen and air plasma efficiently decomposed 2,6-DBP to bromide ion, and inorganic carbon. The molecular orbital model was applied in the analysis of the degradation in electrophilic, nucleophilic, and radical reactions.
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