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Search Results: 1 - 10 of 45 matches for " Morikuni Tobita "
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Mesenchymal Stem Cells Isolated from Adipose and Other Tissues: Basic Biological Properties and Clinical Applications
Hakan Orbay,Morikuni Tobita,Hiroshi Mizuno
Stem Cells International , 2012, DOI: 10.1155/2012/461718
Abstract: Mesenchymal stem cells (MSCs) are adult stem cells that were initially isolated from bone marrow. However, subsequent research has shown that other adult tissues also contain MSCs. MSCs originate from mesenchyme, which is embryonic tissue derived from the mesoderm. These cells actively proliferate, giving rise to new cells in some tissues, but remain quiescent in others. MSCs are capable of differentiating into multiple cell types including adipocytes, chondrocytes, osteocytes, and cardiomyocytes. Isolation and induction of these cells could provide a new therapeutic tool for replacing damaged or lost adult tissues. However, the biological properties and use of stem cells in a clinical setting must be well established before significant clinical benefits are obtained. This paper summarizes data on the biological properties of MSCs and discusses current and potential clinical applications. 1. Introduction A stem cell is an undifferentiated cell with the capacity for multilineage differentiation and self-renewal without senescence. Totipotent stem cells (zygotes) can give rise to a full viable organism and pluripotent stem cells (embryonic stem (ES) cells) can differentiate into any cell type within in the human body. By contrast, trophoblasts are multipotent stem cells that can differentiate into some (e.g., mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs)), but not all, cell types. Adult tissues have specific stem cell niches, which supply replacement cells during normal cell turnover and tissue regeneration following injury [1–3]. The epidermis, hair, HSCs, and the gastrointestinal tract all present good examples of tissues with niches that contribute stem cells during normal cellular turnover [3]. The exact locations of these stem cell niches are poorly understood, but there is growing evidence suggesting a close relationship with pericytes [1, 4, 5] (Figure 1). MSCs have been isolated from adipose tissue [6], tendon [7], periodontal ligament [8], synovial membranes [9], trabecular bone [10], bone marrow [11], embryonic tissues [12], the nervous system [13], skin [14], periosteum [9], and muscle [15]. These adult stem cells were once thought to be committed cell lines that could give rise to only one type of cell, but are now known to have a much greater level of plasticity [16, 17]. Despite the vast variety of source tissues, MSCs show some common characteristics that support the hypothesis of a common origin [1, 18]. These characteristics are: fibroblast like shape in culture, multipotent differentiation, extensive proliferation
Symmetric inner-iteration preconditioning for rank-deficient least squares problems
Keiichi Morikuni
Mathematics , 2015,
Abstract: Stationary iterative methods with a symmetric splitting matrix are performed as inner-iteration preconditioning for Krylov subspace methods. We give a necessary and sufficient condition such that the inner-iteration preconditioning matrix is definite, and show that conjugate gradient (CG) method preconditioned by the inner iterations determines a solution of a symmetric and positive semidefinite linear system, and the minimal residual (MR) method preconditioned by the inner iterations determines a solution of a symmetric linear system including the singular case. These results are applied to the CG and MR-type methods such as the CGLS, LSMR, and CGNE methods preconditioned by inner iterations, and thus justify using these methods for solving least squares and minimum-norm solution problems those coefficient matrices are not necessarily of full rank. Thus, we complement the theory of these methods presented in [K. Morikuni and K. Hayami, SIAM J. Matrix Appl. Anal., 34 (2013), pp. 1-22], [K. Morikuni and K. Hayami, SIAM J. Matrix Appl. Anal., 36 (2015), pp. 225-250], and give bounds for these methods.
Inner-iteration preconditioning for singular linear systems
Keiichi Morikuni
Mathematics , 2015,
Abstract: Several steps of stationary iterative methods serve as inner-iteration preconditioning for solving linear systems of equations. We apply the preconditioner to the generalized minimal residual (GMRES) method and present theoretical justifications for using this approach including the singular case. We characterize classes of stationary iterative methods that can be used for inner-iteration preconditioning. Numerical experiments show that the successive overrelaxation (SOR) inner-iteration preconditioning is more robust and efficient compared to diagonal scaling for some test problems of large sparse singular linear systems.
Threshold Particle Diameters in Miniemulsion Reversible-Deactivation Radical Polymerization
Hidetaka Tobita
Polymers , 2011, DOI: 10.3390/polym3041944
Abstract: Various types of controlled/living radical polymerizations, or using the IUPAC recommended term, reversible-deactivation radical polymerization (RDRP), conducted inside nano-sized reaction loci are considered in a unified manner, based on the polymerization rate expression, R p = k p[M] K[ Interm]/[ Trap]. Unique miniemulsion polymerization kinetics of RDRP are elucidated on the basis of the following two factors: (1) A high single molecule concentration in a nano-sized particle; and (2) a significant statistical concentration variation among particles. The characteristic particle diameters below which the polymerization rate start to deviate significantly (1) from the corresponding bulk polymerization, and (2) from the estimate using the average concentrations, can be estimated by using simple equations. For stable-radical-mediated polymerization (SRMP) and atom-transfer radical polymerization (ATRP), an acceleration window is predicted for the particle diameter range, . For reversible-addition-fragmentation chain-transfer polymerization (RAFT), degenerative-transfer radical polymerization (DTRP) and also for the conventional nonliving radical polymerization, a significant rate increase occurs for . On the other hand, for ?the polymerization rate is suppressed because of a large statistical variation of monomer concentration among particles.
Quantum Jarzynski equalities for the energy costs of the information processes
Yohei Morikuni,Hiroyasu Tajima
Physics , 2013,
Abstract: We present quantum versions of the Jarzynski equality for the energy costs of information processes, namely the measurement and the information erasure. We also obtain inequalities for the energy costs of the information processes, using the Jensen inequality. The inequalities include Sagawa and Ueda's inequalities [Phys. Rev. Lett. 102, 250602 (2009)] as a special case.
Quantum Jarzynski-Sagawa-Ueda relations
Yohei Morikuni,Hal Tasaki
Statistics , 2010, DOI: 10.1007/s10955-011-0153-7
Abstract: We consider a (small) quantum mechanical system which is operated by an external agent, who changes the Hamiltonian of the system according to a fixed scenario. In particular we assume that the agent (who may be called a demon) performs measurement followed by feedback, i.e., it makes a measurement of the system and changes the protocol according to the outcome. We extend to this setting the generalized Jarzynski relations, recently derived by Sagawa and Ueda for classical systems with feedback. One of the two relations by Sagawa and Ueda is derived here in error-free quantum processes, while the other is derived only when the measurement process involves classical errors. The first relation leads to a second law which takes into account the efficiency of the feedback.
Traffic Flow Merging and Bifurcating at Junction on Two-Lane Highway  [PDF]
Kazuhiro Tobita, Yuichi Naito, Takashi Nagatani
World Journal of Mechanics (WJM) , 2012, DOI: 10.4236/wjm.2012.24025
Abstract: In this paper we study the traffic states and jams in vehicular traffic merging and bifurcating at a junction on a two-lane highway. The two-lane traffic model for the vehicular motion at the junction is presented where a jam occurs frequently due to merging, lane changing, and bifurcating. The traffic flow is called the weaving. At the weaving section, vehicles slow down and then move aside on the other lane for changing their direction. We derive the fundamental diagrams (flow-density diagrams) for the weaving traffic flow. The traffic states vary with the density, slowdown speed, and the fraction of vehicles changing the lane. The dynamical phase transitions occur. It is shown that the fundamental diagrams depend highly on the traffic states.
Traffic Behavior in CA Model of Vehicular Traffic through a Series of Signals
Kazuhiro Tobita,Takashi Nagatani
Discrete Dynamics in Nature and Society , 2012, DOI: 10.1155/2012/812969
Abstract:
Traffic Behavior in CA Model of Vehicular Traffic through a Series of Signals
Kazuhiro Tobita,Takashi Nagatani
Discrete Dynamics in Nature and Society , 2012, DOI: 10.1155/2012/812969
Abstract: We study the traffic states and fundamental diagram of vehicular traffic controlled by a series of traffic lights using a deterministic cellular automaton (CA) model. The CA model is not described by a set of rules but is given by a difference equation. The vehicular traffic varies highly with both signal’s characteristics and vehicular density. The dependence of fundamental diagram on the signal’s characteristics is derived. At a low value of cycle time, the fundamental diagram displays the typical trapezoid, while it shows a triangle at a high value of cycle time. The dynamic transitions among distinct traffic states depend greatly on the signal’s characteristics. The dependence of the transition points on the cycle time split and offset time is found. 1. Introduction Mobility is nowadays one of the most significant ingredients of a modern society. Recently, transportation problems have attracted much attention in the fields of physics [1–4]. Physics and other sciences meet at the frontier area of interdisciplinary research. The traffic flow, pedestrian flow, and bus-route problem have been studied from a point of view of statistical mechanics and nonlinear dynamics [5–7]. The interesting dynamic behaviors have been found in the transportation system. The jams, chaos, and pattern formation are typical signatures of the complex behavior of transportation [8, 9]. The cellular automaton (CA) model has been used extensively for the traffic dynamics [1, 3]. The CA model for traffic flow is a typical system of discrete dynamics. The traffic light is an essential element for managing the transportation network. In urban traffic, vehicles are controlled by traffic lights to give priority for a road because the city traffic networks often exceed the capacity and one avoids a collision between vehicles. Brockfeld et al. have studied optimizing traffic lights for city traffic by using a CA traffic model [10]. They have clarified the effect of signal control strategy on vehicular traffic. Also, they have shown that the city traffic controlled by traffic lights can be reduced to a simpler problem of a single-lane roadway. D. W. Huang and W. N. Huang have studied the traffic flow controlled by signals on a single-lane roadway by using Nagel-Schreckenberg model [11]. Sasaki and Nagatani have investigated the traffic flow on a single-lane roadway with traffic lights by using the optimal velocity model [12]. They have derived the relationship between the road capacity and jamming transition. Until now, one has studied the periodic traffic controlled by a few traffic
On coherence lengths of wave packets
Kenzo Ishikawa,Yutaka Tobita
Physics , 2009, DOI: 10.1143/PTP.122.1111
Abstract: Coherence lengths of one particle states described by quantum wave functions are studied. We show that one particle states in various situations are not described by simple plane waves but are described by wave packets that are superpositions of plane waves. Wave packet is an approximate eigenstate of the free Hamiltonian and has a finite spatial size which we call the coherence length. The coherence lengths in the coordinate space and in the momentum space are studied in the present paper. We investigate several mechanisms of forming wave packets, stabilities of wave packets, and transformations of wave packets.
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