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Search Results: 1 - 10 of 325362 matches for " S. Miyashita "
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Dilution Effects on Ordering in the ${S=1/2}$ Heisenberg Antiferromagnet on the Square Lattice
J. Behre,S. Miyashita
Physics , 1993,
Abstract: The influence of dilution with non--magnetic impurities on the order in the ground state of the $S=1/2$ Heisenberg antiferromagnet is investigated by Quantum Monte Carlo simulations. Data of the spin correlation functions and thermodynamic properties for system sizes up to $L\times L=16\times16$ and for impurity concentrations up to $\delta=37.5\%$ are presented. In the low doping regime the correlation length shows similiar dependence on temperature as in the pure case. The staggered magnetization $\langle N_z^2(\delta)\rangle$ in the ground state which is the order parameter of the present model is estimated by extrapolating data at low temperatures. Impurity concentration dependence of $\langle N_z^2(\delta)\rangle$ is presented. $\langle N_z^2(\delta)\rangle$ decreases monotonically with impurity concentration and becomes very small around $\delta_c \sim 0.35$ which is much smaller than the classical percolation threshold.
Quantum Tunneling in Half-Integer Spin Systems
S. Miyashita,N. Nagaosa
Physics , 2001, DOI: 10.1143/PTP.106.533
Abstract: Motivated by the experimental observations of resonant tunnelings in the systems with half-integer spin, such as V$_{15}$ and Mn$_4$, we study the mechanism of adiabatic change of the magnetization in systems with the time-reversal symmetry. Within the time-reversal symmetric models, effects of several types of perturbations are investigated. Although tunneling between the ground states is suppressed in a simple Kramers doublet, we show that the nonadiabatic transition governed by the Landau-Zener-St\"uckelberg mechanism occurs in many cases due to the additional degeneracy of the ground state. We also found more general cases where LZS mechanism can not be applied directly even the system shows a kind of adiabatic change of the magnetization.
BaBar Results For Alpha: Measurement of CP-Violating Asymmetries in B^0 --> (rho pi)^0 Using a Time-Dependent Dalitz Plot Analysis
Tomonari S. Miyashita
Physics , 2013,
Abstract: Proceedings of CKM 2012, the 7th International Workshop on the CKM Unitarity Triangle, University of Cincinnati, USA, 28 September - 2 October 2012.
A microscopic mechanism for rejuvenation and memory effects in spin glasses
S. Miyashita,E. Vincent
Physics , 2001, DOI: 10.1007/s100510170128
Abstract: Aging in spin glasses (and in some other systems) reveals astonishing effects of `rejuvenation and memory' upon temperature changes. In this paper, we propose microscopic mechanisms (at the scale of spin-spin interactions) which can be at the origin of such phenomena. Firstly, we recall that, in a frustrated system, the effective average interaction between two spins may take different values (possibly with opposite signs) at different temperatures. We give simple examples of such situations, which we compute exactly. Such mechanisms can explain why new ordering processes (rejuvenation) seem to take place in spin glasses when the temperature is lowered. Secondly, we emphasize the fact that inhomogeneous interactions do naturally lead to a wide distribution of relaxation times for thermally activated flips. `Memory spots' spontaneously appear, in the sense that the flipping time of some spin clusters becomes extremely long when the temperature is decreased. Such memory spots are capable of keeping the memory of previous ordering at a higher temperature while new ordering processes occur at a lower temperature. After a qualitative discussion of these mechanisms, we show in the numerical simulation of a simplified example that this may indeed work. Our conclusion is that certain chaos-like phenomena may show up spontaneously in any frustrated and inhomogeneous magnetic system, without impeding the occurrence of memory effects.
The Modifications of Wagner’s Equation and Electrochemistry for the 21st Century  [PDF]
Tomofumi Miyashita
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.23022
Abstract: The use of samarium-doped ceria (SDC) electrolytes in SOFCs (solid oxide fuel cells) lowers the open circuit voltage (OCV) below the Nernst voltage (Vth). The OCV is calculated with Wagner’s equation which is included in NernstPlanck equation. Considering the separation of Boltzmann distribution, the fundamental basis of this topic is discussed. A constant voltage loss without leakage currents due to a mixed ionic and electronic conducting (MIEC) dense anode was explained. Only carrier species having sufficient energy to overcome the activation energy can contribute to current conduction, which is determined by incorporating a different constant in the definitions of chemical potential and electrical potential. This difference explains the results using dense MIEC anodes. This topic is not an isolated and minor topic, but of vital importance to electrochemical engineering for the 21st Century.
Empirical Relations about the Number of Dimensions in Theoretical Physics with the Concept of Common and Unshared Dimensions  [PDF]
Tomofumi Miyashita
Journal of Modern Physics (JMP) , 2010, DOI: 10.4236/jmp.2010.12021
Abstract: How many dimensions are there in the universe? Currently, there is confusion about the number of dimensions in the universe. Empirical relations about the number of dimensions in theoretical physics with the concept of common space- time 4 dimensions and unshared dimensions are described in this report.
Quantum Physics Can Be Understood in Terms of Classical Thermodynamics  [PDF]
Tomofumi Miyashita
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.21005
Abstract: Quantum physics can be understood in terms of classical thermodynamics, which is already considered to be a complete field. However, inconsistencies in classical thermodynamics have been discovered in the area of solid-oxide fuel cells (SOFCs). The use of samarium-doped ceria (SDC) electrolytes in SOFCs lowers the open-circuit voltage (OCV) below the Nernst voltage (Vth). The low OCV is calculated with Wagner’s equation, included in the Nernst-Planck equation, which is based on the first and second thermodynamic laws. Experimental and theoretical limitations of Wagner’s equation have been discovered. Considering the separation of the Boltzmann distribution and Maxwell’s Demon, only carrier species having sufficient energy to overcome the activation energy can contribute to current conduction, as determined by incorporating different constants in the definitions of the chemical and electrical potentials. This means that an additional thermodynamic law is needed. Furthermore, quantum physics can be explained by the additional thermodynamic law.
The Clinical Application of Ambulatory Blood Pressure Monitoring in Pediatrics  [PDF]
Yosuke Miyashita
International Journal of Clinical Medicine (IJCM) , 2011, DOI: 10.4236/ijcm.2011.25111
Abstract: Management of hypertension (HTN) largely relies on proper and accurate measurement of blood pressure (BP). Even following the criteria for HTN diagnosis defined in the Fourth report on high BP in children and adolescents, inaccurate diagnosis and misdiagnosis can occur with white coat effect and masked HTN. The use of Ambulatory Blood Pressure Monitoring (ABPM) has been increasing in pediatrics in the last 20 years. The main use of ABPM is to differentiate between sustained HTN and white coat HTN in patients who have elevated casual BP measurements and to detect masked HTN in high risk patients. ABPM is most useful in patients with casual BP within 20% of the 95th percentile for age, gender, and height. This report will highlight the use of ABPM in the evaluation of elevated BP and management of HTN in pediatrics. The discussion includes a review of various non-invasive BP measuring techniques, a description of ABPM and ABPM-unique data and diagnoses, updated ABPM clinical data more specific to pediatrics, its use in HTN clinical trials, and future outlook and direction of ABPM in pediatrics.
Bell’s Non-Locality Theorem Can Be Understood in Terms of Classical Thermodynamics  [PDF]
Tomofumi Miyashita
Journal of Modern Physics (JMP) , 2017, DOI: 10.4236/jmp.2017.81008
Abstract: Bell’s non-locality theorem can be understood in terms of classical thermodynamics, which is already considered to be a complete field. However, inconsistencies in classical thermodynamics have been discovered in the area of solid-oxide fuel cells (SOFCs). The use of samarium-doped ceria electrolytes in SOFCs lowers the open-circuit voltage (OCV) to less than the Nernst voltage. This low OCV has been explained by Wagner’s equation, which is based on chemical equilibrium theory. However, Wagner’s equation is insufficient to explain the low OCV, which should be explained by fluctuation and dissipation theorems. Considering the separation of the Boltzmann distribution and Maxwell’s demon, only carrier species with sufficient energy to overcome the activation energy can contribute to current conduction, as determined by incorporating different constants into the definitions of the chemical and electrical potentials. Then, an energy loss equal to the activation energy will occur because of the interactions between ions and electrons. This energy loss means that an additional thermodynamic law based on an advanced model of Maxwell’s demon is needed. In this report, the zero-point energy can be explained by this additional ther-modynamic law, as can Bell’s non-locality theorem.
Empirical Relation of the Fine-Structure Constant with the Transference Number Concept  [PDF]
Tomofumi Miyashita
Journal of Modern Physics (JMP) , 2018, DOI: 10.4236/jmp.2018.913149
Abstract: The fine-structure constant of 1/137 is puzzling and has never been fully explained. When the interaction coefficient is 1/137, the transference number should be 136/137. With the transference number concept, we noticed that we must examine the constant of 1/136 instead of 1/137 to discover an empirical relationship in which the fine-structure constant is related to the mass ratio of electrons and quarks. Then, the physical meaning of this empirical relationship is discussed.
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