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Search Results: 1 - 10 of 1284 matches for " Kubota Minoru "
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Quantized vortex state in hcp solid 4He
Minoru Kubota
Physics , 2012, DOI: 10.1007/s10909-012-0653-0
Abstract: The quantized vortex state appearing in the recently discovered new states in hcp 4He since their discovery is discussed. Special attention is given to evidence for the vortex state as the vortex fluid (VF) state and its transition into the supersolid (SS) state. Its features are described. The historical expla- nations for the SS state in quantum solids such as solid 4He were based on the idea of Bose Einstein Condensation (BEC) of the imperfections such as va- cancies, interstitials and other possible excitations in the quantum solids which are expected because of the large zero-point motions. The SS state was proposed as a new state of matter in which real space ordering of the lattice structure of the solid coexists with the momentum space ordering of superfluidity. A new type of superconductors, since the discovery of the cuprate high Tc superconductors, HTSCs, has been shown to share a feature with the vortex state, involving the VF and vortex solid states. The high Tcs of these materials are being discussed in connection to the large fluctuations associated with some other phase transitions like the antiferromagnetic transition in addition to that of the low dimensionality. The supersolidity in the hcp solid 4He, in contrast to the new superconductors which have multiple degrees of freedom of the Cooper pairs with spin as well as angular momentum freedom, has a unique feature of possessing possibly only the momentum fluctuations and vortex ring excitations associated with the possible low dimensional fluctuations of the subsystem(s). The high onset temperature of the VF state can be understood by considering thermally excited low D quantized vortices and it may be necessary to seek low dimensional sub-systems in hcp He which are hosts for vortices.
Vortex Fluid State below an Onset Temperature T_0 of Solid 4He
Andrey Penzev,Yoshinori Yasuta,Minoru Kubota
Physics , 2007, DOI: 10.1103/PhysRevLett.101.065301
Abstract: Detailed studies of AC velocity Vac and temperature dependence of torsional oscillator responses of solid 4He are reported. A characteristic onset temperature T0 about 0.5 K is found, below which a significant Vac dependent change occurs in the energy dissipation for the sample at 32 bar. A Vac dependence of the non-classical rotational inertia fraction, NCRIF also appears below about T0. This value of T0 excludes the possible explanation of supersolid by liquid superfluidity in grain boundaries or other liquid related origins. The log(Vac) linear dependence was found in NCRIF. Furthermore, this linear slope changes in proportion to 1/T 2 for 40 < Vac < 400 micro-m/s, then crosses over to about 1/T for larger Vac. We discuss properties of the vortex fluid state proposed by Anderson above Tc, below T0.
Possible vortex fluid to supersolid transition in solid $^4$He below about 75 mK
Nobutaka Shimizu,Yoshinori Yasuta,Minoru Kubota
Physics , 2009,
Abstract: A detailed torsional oscillator (TO) study on a stable solid 4He sample at 49 bar with To = 0.5K, is reported to T below the dissipation peak at Tp . We find hysteretic behavior starting below Tc = about 75 mK, in period shift, as well as in dissipation, with changes of AC excitation amplitude Vac . The derived difference of non-linear rotational susceptibility DeltaNLRS(T)hys across the hysteresis loop under a systematic condition is analyzed as a function of Vac and T . We propose that DeltaN LRS(T)hys is proportional to non- classical rortational inertia fraction, NCRIF, and is actually the supersolid density rho_ss of the 3D supersolid state below Tc . rho_ss changes linearly with T down to about 60 mK and then increases much more steeply, and approaching a finite value towards T = 0. We find an AC velocity of 40 micrometer/s beyond which the hysteresis starts at T < Tc and a critical AC velocity, about 1 cm/s, above which rho_ss is completely destroyed. We discuss also the coherence length of the supersolid.
Vortex Fluid Relaxation Model for Torsional Oscillation Responses of Solid 4He
Sergey K. Nemirovskii,Nobutaka Shimizu,Yoshinori Yasuta,Minoru Kubota
Physics , 2009,
Abstract: A phenomenological model is developed to explain a new set of detailed torsional oscillator data for hcp 4He. The model is based on Anderson's idea of the vortex fluid (vortex tangle) in solid 4He. Utilizing a well-studied treatment of dynamics of quantized vortices we describe how the "local superfluid component" is involved in rotation (torsional oscillation) via a polaried vortices tangle. The polarization in the tangle appears both due to aligning the remnant or thermal vortices and due to penetration of additional vortices into volume. Both are supposed to occur in a relaxation manner, and the inverse full relaxation time tau^-1 is the sum of them. One of them is found to change linearly with respect to the rim velocity Vac. The developed approach explains the behavior of both NLRS and Delta Q^-1 seen in the experiment. We reproduce not only the unique Vac dependence, but also obtain new information about the vortices tangle, for example, a divergence in tau at extrapolated T ~ 30 mK.
Continuous Vagus Nerve Monitoring during Carotid Endarterectomy  [PDF]
Tamaki Tomonori, Kubota Minoru, Node Yoji, Morita Akio
Open Journal of Modern Neurosurgery (OJMN) , 2017, DOI: 10.4236/ojmn.2017.71001
Abstract: Backgrounds: Injury to the vagus nerve or one of its branches during carotid endarterectomy can result in vocal fold paralysis but the exact mechanism of injury responsible for vocal fold paralysis after carotid endarterectomy is unclear. Aims: This study was performed to identify potential predictors of vagus nerve injury and obtain feedback by application of intraoperative continuous vagus nerve monitoring. Materials and Methods: Seventy-four patients undergoing carotid endarterectomy were enrolled. A new vagus nerve electrode was designed for less invasive continuous vagus nerve stimulation and monitoring of the vocal fold electromyogram without disturbing the surgical procedure. The device was rectangular (13 mm × 9 mm), with two small round electrodes set on a flexible silicon plate and tube. The electrode was fully implantable during carotid endarterectomy and was positioned at the most distal site of the vagus nerve by suturing to the connective tissue without nerve dissection. All patients underwent laryngoscopy to assess postoperative vocal fold and pharyngeal wall palsy at one week after carotid endarterectomy. Results: Sudden loss of the vocal fold electromyogram was noted in two patients (during plaque removal and during arterial wall suture in one each). In these two patients, incomplete vocal fold and pharyngeal palsy was confirmed by laryngoscopy. The cause of vagus nerve injury may have been traction at the time of distal internal carotid artery manipulation. The vocal fold electromyogram remained normal during the operation in the other 72 patients. However laryngoscopy revealed postoperative vocal fold and pharyngeal palsy in six patients. These findings suggested that delayed vagus nerve injury can occur after carotid endarterectomy. Conclusion: The continuous vagus nerve monitoring may be worthwhile for elucidating the mechanism of vagus nerve injury related to carotid endarterectomy.
Minimum Wage, Public Investment, Economic Growth  [PDF]
Minoru Watanabe
Theoretical Economics Letters (TEL) , 2013, DOI: 10.4236/tel.2013.35048
Abstract: This paper considers the relationship between economic growth and minimum wage. Minimum wage helps reduce poverty and maintain a minimum standard of living. However, it is also claimed that minimum wage has a negative effect on employment and GDP. This paper develops a simple two-period overlapping generation model with three economic policies, minimum wage, unemployment benefit, and public investment that improves labor productivity. The government imposes tax on firms to finance public capital and unemployment benefit under a balanced budget. We show that economic growth is promoted with an increase in minimum wage and the ratio of public investment to tax revenue.
Gender differences and laterality in maximal handgrip strength and controlled force exertion in young adults  [PDF]
Hiroshi Kubota, Shinichi Demura
Health (Health) , 2011, DOI: 10.4236/health.2011.311115
Abstract: This study examines gender differences and laterality in maximal handgrip strength and controlled force exertion (CFE) in young adults. The subjects were 75 healthy young males (mean age 19.6 ± 1.6 yrs.) and 50 healthy young females (mean age 20.9 ± 1.9 yrs.). Maximal handgrip strength was measured twice. The subjects performed the CFE test three times after one practice trial. They matched their handgrip strengths to the demand values, which constantly changed and ranged from 5 to 25% of maximal handgrip strength. The difference between the demand value and the grip exertion value was used as an estimate of CFE. Maximal handgrip strength was significantly larger in males than in females in both the dominant and non-dominant hands, and was significantly larger in the dominant hand in both males and females. Insignificant gender differences were found in CFE of both hands. CFE was significantly superior in the dominant hand in both genders. In conclusions, gender differences are present in maximal handgrip strength of the dominant and non-dominant hands in young adults, but not in CFE of both hands. Laterality exists in maximal handgrip strength and in CFE for both genders.
Role on Moment of Inertia and Vortex Dynamics for a Thin Rotating Plate  [PDF]
Yoshihiro Kubota, Osamu Mochizuki
World Journal of Mechanics (WJM) , 2013, DOI: 10.4236/wjm.2013.36028

In this study, we focused on the lift generation with a thin rotating plate. The objective of this study is to understand the appropriate shape and the role of vortex for rotating thin plate. We determined the shape of the plate through free-flight tests of paper strips and investigated the aerodynamic characteristics of the rotating plate with the selected shape. The rectangular plate with an aspect ratio 7 was relevant from moment of inertia and bending stress. An endplate on a wing tip increased the stability on the lateral vortex structure behind the rotating plate. Velocity field measurement by Particle Image Velocimetry (PIV) showed that the lift force was generated twice in a rotating cycle.

Numerical Investigation of Aerodynamic Characteristics by a Rotating Thin Plate  [PDF]
Yoshihiro Kubota, Osamu Mochizuki
World Journal of Mechanics (WJM) , 2015, DOI: 10.4236/wjm.2015.53005
Abstract: In this study, we use a thin rotating plate to generate propulsion and lift for a paper plate. And the thin plate rotates along the spanwise axis. We numerically determine the influence on aerodynamic characteristics with a rotational velocity of the thin plate. The rotational velocity is obtained with spin parameter which is the ratio of the peripheral speed of the plate to the main flow velocity. And the numerical simulations based on the discrete vortex method show that the autorotation mode of the plate in a uniform flow appears naturally when the spin parameter is unity. Vortex formed from the backward-rotating edge is weaker than those generated from the forward-rotating edge of thin plate. The maximum lift generated at S = 0.75 if S < 1. The negative moment becomes negative for the nondimensional rotating speed S ≤ 1.75. The most negative moment appears when S = 1; at that time, autorotation occurs naturally.
Splash Formation Due to a Frog Diving into Water  [PDF]
Yoshihiro Kubota, Osamu Mochizuki
World Journal of Mechanics (WJM) , 2015, DOI: 10.4236/wjm.2015.57014
Abstract: Herein, we present the results of our experimental investigation of splashes formed by a frog diving into water from the ground or from a leaf and the accompanying sound generated by the impact of the frog on the water. The experiments are performed by visualizing the flow with a high-speed camera. In addition, we used physical models comprising hydrophilic bodies made from hydrogel or acrylic resin to experimentally study how hydrophilicity affects the splash. In these experiments, we use the degree of swelling to define the hydrophilicity degree. The results show that different splashes are caused by the increase in water-film velocity upon an increase in hydrophilicity. For a body with strong hydrophilicity, at a relatively high film velocity, the water film forms when the body impacts the water surface separates from the body surface. In addition, an aircavity forms when the film separates from the body. We empirically examine the relation between the hydrophilicity degree and film velocity. The results indicate that increased hydrophilicity does not reduce the splash. Therefore, we conclude that reducing of the formation of water from the biomimetic point of view is related to the shape of body.
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