Aoyama Gakuin University

About: Aoyama Gakuin University is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Superconductivity & Thin film. The organization has 3494 authors who have published 6419 publications receiving 115648 citations. The organization is also known as: Aoyama gakuin daigaku.

Non-invasive measurement method for hardness in muscular tissues

Abstract: THERE IS no objective and quantitative non-invasive method to evaluate hardness of soft tissues, especially that of muscles. In usual clinical practice, hardness is evaluated only by palpation. To date, quantitative evaluation of muscle hardness has been performed on extracted muscles (MAsoN, 1978; HASAN and MASON, 1978). Despite various studies on non-invasive measurement methods to evaluate human muscle hardness, no widely accepted techniques have yet been developed. In the past, SCHADE (1926) and other researchers used such equipment as the elastometer or sclerometer for measuring the elasticity and hardness of skin and organs. However, such equipment could not provide objective and reproducible data. Later, other researchers tried to measure muscle hardness using the changes of resonance frequency associated with the changes of mechanical impedance. This was performed using vibration on the measuring site of the body (KATO et al., 1980). However, there were some problems with this method. For example, influences from the tonic vibration reflex of muscles, which are produced by the given vibration, are unavoidable. Also unavoidable are the errors made by improper contact of the measuring system with the body surface. I n the present study, we introduce an experimental model of a pressure/displacement transducer with a laser distance sensor, which has been developed for monitoring muscle hardness non-invasively and quantitatively. Muscle hardness can be calculated from the slope of the pressure/ displacement line which is recorded with our experimental equipment.

Spin gap and dynamics in Sr 14 − x Ca x Cu 24 O 41 comprising hole-doped two-leg spin ladders: Cu NMR study on single crystals

Abstract: We report comprehensive Cu NMR studies on single crystals of ${\mathrm{Sr}}_{14\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41},$ which contain simple ${\mathrm{CuO}}_{2}$ chains and two-leg ${\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ ladders. From measurements of the ${}^{63}\mathrm{Cu}$ NMR shift, it is clear that the spin gap in the ladders decreases with isovalent Ca substitution from $\ensuremath{\Delta}=550\ifmmode\pm\else\textpm\fi{}30$ K for ${\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ (Sr14) to $350\ifmmode\pm\else\textpm\fi{}30$ K, $280\ifmmode\pm\else\textpm\fi{}30$ K, and $270\ifmmode\pm\else\textpm\fi{}30$ K for $x=6$ (Ca6), $x=9$ (Ca9), and $x=11.5$ (Ca11.5), respectively. The exponential decrease of the nuclear spin-lattice relaxation rate ${1/T}_{1}$ below \ensuremath{\sim}130 K is consistent with the presence of the spin gap in the spin excitation spectrum. In the $T$ range higher than $\ensuremath{\sim}200$ K, we observed the following dependences: ${1/T}_{1}=\mathrm{const}$ and the square of Gaussian spin-echo decay time, ${T}_{2G}^{2}\ensuremath{\propto}T$ which are consistent with the scaling theory for the $S=1/2$ one-dimensional (1D) Heisenberg model. The value of ${T}_{2G}{/T}_{1}\sqrt{T}$ is compatible with the theoretical prediction of an exchange constant along the leg ${J}_{\ensuremath{\parallel}}\ensuremath{\sim}1800$ K for Ca6 and ${J}_{\ensuremath{\parallel}}\ensuremath{\sim}1500$ K for Ca9 and Ca11.5. A notable finding is that the magnitude of the spin gap remains nearly constant and characteristics of novel 1D-like spin dynamics are maintained in the content varying from Ca9 to Ca11.5. On the other hand, the charge transport changes with increasing Ca content so that the more conductive Ca11.5 exhibits pressure-induced superconductivity exceeding 3.5 GPa. We have found that ${T}_{2G}^{2}$, which is proportional to the inverse spin correlation length ${\ensuremath{\xi}}^{\ensuremath{-}1}$, deviates from a linear $T$ dependence upon cooling and is described by $A+BT\mathrm{exp}(\ensuremath{-}\ensuremath{\Delta}/T)$, regardless of the Ca substitution. We point out that the value of ${T}_{2G}^{2}(T=0)=A$ is proportional to the finite value of ${\ensuremath{\xi}}_{0}^{\ensuremath{-}1}=\ensuremath{\Delta}{/c}_{1D},$ where ${c}_{1D}=(\ensuremath{\pi}{/2)J}_{\ensuremath{\parallel}}$ is the spin-wave velocity. From the result that the values of ${A}^{\ensuremath{-}1}\ensuremath{\sim}{\ensuremath{\xi}}_{\mathrm{eff}}$ for Ca6, Ca9, and Ca11.5 are significantly reduced compared to that for Sr14, it is suggested that ${\ensuremath{\xi}}_{\mathrm{eff}}$ is dominated at low $T$ by an average distance $d$ among mobile holes obeying the relation ${\ensuremath{\xi}}_{\mathrm{eff}}\ensuremath{\sim}d={\ensuremath{\xi}}_{h}.$ From an estimate of ${\ensuremath{\xi}}_{0}/a\ensuremath{\sim}$ 5.2 for Sr14, where $a$ is the Cu-Cu distance along the leg, ${\ensuremath{\xi}}_{h}/a$ is obtained as $\ensuremath{\sim}3.5$, 2.3, and 2.0, and hole content $x$ as $\ensuremath{\sim}0.14$, 0.22, and 0.25 per ${\mathrm{Cu}}_{2}{\mathrm{O}}_{3}$ ladder for Ca6, Ca9, and Ca11.5, respectively. These values were consistent with $x=$ 0.14, 0.2, and 0.22 for Ca6, Ca9, and Ca11 estimated from the optical conductivity experiment by Osafune et al. [Phys. Rev. Lett. 78, 1980 (1997)]. The ${\mathrm{Sr}}_{14\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ compounds are thus hole-doped two-leg spin-ladder systems which reveal the metallic behavior dominated by the 1D-like spin dynamics at high $T$ and accompanied by the spin gap formation at low $T$. For Ca11.5, as the spin gap is formed upon cooling below $\ensuremath{\sim}180$ K, the resistivity increases in the direction perpendicular to the ladder, whereas the conductivity along the ladder remains metallic, followed by the localization of mobile holes in both directions below ${T}_{L}\ensuremath{\sim}60$ K. We point out that preformed pairs are confined in each ladder and localized below $\ensuremath{\sim}60$ K at an ambient pressure.

Fracture mechanism characterization of cross-ply carbon-fiber composites using acoustic emission analysis

Abstract: The sequence of microscopic fracture mechanisms in locally loaded cross-ply carbon-fiber composites was studied by analyzing acoustic emission (AE) signals in combination with the modal analysis of Lamb waves, using microscopic and ultrasonic examination of the specimen after load interruption. The first 70 AE events were analyzed, which were detected during the initial loading segment when the first sudden load drop and gradual load recovery were observed. Characteristics of the detected waves were compared with the S 0 - and A 0 -mode Lamb waves produced by a spot- or line-focused YAG laser. The internal damage progression of the composite specimen was determined to be the fiber fracture in the front lamina, transverse cracks in the mid-lamina, delamination and splitting.