Effect of temporal resolution on the estimation of left ventricular function by cardiac MR imaging

The aim of this study was to investigate the effect of temporal resolution on the estimation of left ventricular (LV) function by cardiac magnetic resonance (MR) imaging using a steady-state free precession (SSFP) sequence. Left ventricular function was assessed by cine MR imaging using a segmented SSFP sequence in 10 healthy volunteers. Views per segment (VPS) were set at 8 and 20, resulting in high and low true temporal resolution, respectively. Irrespective of VPS, images were reconstructed at 40 cardiac phases, providing high apparent temporal resolution. Data were analyzed using 40, 20 and 10 phases to simulate different apparent temporal resolutions. Increasing the cardiac phases used for analysis slightly decreased mean end-systolic volume (ESV) and slightly increased mean ejection fraction (EF). No substantial difference in estimates of end-diastolic volume (EDV) was found between VPSs of 8 and 20. Imaging with a VPS of 20 yielded a larger ESV and smaller EF than imaging with a VPS of 8 when 40 phases were used. In conclusion, low true temporal resolution causes overestimation of ESV and underestimation of EF. Improvement of apparent temporal resolution mildly reduces but does not eliminate the errors caused by low true temporal resolution.     

Electronic transport in fullerene C20 bridge assisted by molecular vibrations

The effect of molecular vibrations on electronic transport is investigated with the smallest fullerene C20 bridge, utilizing the Keldysh nonequilibrium Green's function techniques combined with the tight-binding molecular-dynamics method. Large discontinuous steps appear in the differential conductance when the applied bias voltage matches particular vibrational energies. The magnitude of the step is found to vary considerably with the vibrational mode and to depend on the local electronic states besides the strength of electron-vibration coupling. On the basis of this finding, a novel way to control the molecular motion by adjusting the gate voltage is proposed.     

Direct micropatterning of high dielectric BaTiO3 films by laser-induced pyrolysis with a nano-crystalline seeding technique

A direct patterning method of dielectric BaTiO₃ (BT) films is proposed, which applies laser-induced pyrolysis in combination with nano-crystalline seeding technique. A precursor solution of a BT complex alkoxide containing BT nano-crystalline particles with polyvinylpyrollidone (PVP) as dispersion stabilizer was spin-coated on Pt substrate. An Ar⁺ laser beam was focused and scanned on spin-coated BT films, which induced pyrolysis and crystallization of the films with spatial selectivity. Micropatterns were obtained by striping laser-unirradiated regions on the films with HCl aqueous solution. Raman spectra of the micropattern confirmed that the structures were tetragonal crystalline BT. Clear micropatterns with a line width of ca. 3 μm and an interval of 5 μm were formed at PVP concentrations of 25 and 50 kg/m³. The dielectric constant and dissipation factor of the film fabricated at a laser energy density of 27 MW/cm² and a scanning speed of 25 μm/s attained 76.2 and 0.07, respectively, for a measurement frequency of 100 kHz.     

Fermi-surface reconstruction without breakdown of Kondo screening at the quantum critical point

Motivated by recent Hall-effect experiment in YbRh(2)Si(2), we study ground state properties of a Kondo lattice model in a two-dimensional square lattice using variational Monte Carlo method. We show that there are two types of phase transition, an antiferromagnetic transition and a topological one (Fermi-surface reconstruction). In a wide region of parameters, these two transitions occur simultaneously without the breakdown of Kondo screening, accompanied by a discontinuous change of the Hall coefficient. This result is consistent with the experiment and gives a novel theoretical picture for the quantum critical point in heavy-fermion systems.     

Observation of magnetic order of Cu-moment aroundx=0.12 in La2−x Ba x CuO4 and La2−x sr x CuO4 by μ+SR

Zero field positive muon spin rotation method ( ⁺SR) is applied on La_2–x Sr _x CuO₄ around forx=0.12 at which the high-T _c superconductivity (SC) is suppressed. The magnetically ordered state of Cu-moments, which is not a spin glass state but an antiferromagnetic like state, appears below 15 K for 0.105x0.120. The magnetic phase boundary is very similar to the one of the La_2–x Ba _x CuO₄ in which the structural transition from the low temperature orthorhombic (LTO) phase to the low temperature tetragonal (LTT) phase is observed aroundx=0.12. The present study suggests that there is no big difference of the electronic state of the CuO₂ plane between the La-Ba system and the La-Sr system and that the magnetic ordering of Cu-moments plays an important role for the suppression of the high-T _c SC aroundx=0.12 in both of the systems, although the LTO-LTT structural transition has not been observed yet in the La-Sr system.     

Triviality of Hierarchical Ising Model¶in Four Dimensions

Existence of critical renormalization group trajectory for a hierarchical Ising model in 4 dimensions is shown. After 70 iterations of renormalization group transformations, the critical Ising model is mapped into a vicinity of the Gaussian fixed point. Convergence of the subsequent trajectory to the Gaussian fixed point is shown by power decay of the effective coupling constant. The analysis in the strong coupling regime is computer-aided and Newman's inequalities on truncated correlations are used to give mathematical rigor to the numerical bounds. In order to obtain a criterion for convergence to the Gaussian fixed point, characteristic functions and Newman's inequalities are systematically used. Received: 27 April 2000 / Accepted: 5 January 2001     

Enhanced photoinduced desorption from metal nanoparticles by photoexcitation of confined hot electrons using femtosecond laser pulses

Strong fluence dependence of photodesorption cross sections is observed in femtosecond laser photodesorption of NO from (NO)2 on silver nanoparticles, in contrast to femtosecond photodesorption on bulk metals. The time scale of excitation buildup is found to be equal or less than the pulse duration of ～100 fs; NO translational energies are independent of fluence and pulse duration. We propose a nanoparticle-specific nonlinear mechanism in which, due to confinement, strongly nonthermal hot-electron distributions are maintained during the femtosecond pulses, enhancing the normal desorption pathway.     

Experimental investigation on reversal of secondary Bjerknes force between two bubbles in ultrasonic standing wave

The direction of the secondary Bjerknes force between a free bubble and an attached bubble was experimentally investigated. The behavior of the two bubbles in an ultrasonic standing wave of 27 kHz was observed using an imaging system with a high-speed video camera. It was demonstrated experimentally that the direction of the force reversed at a specific separation distance between the two bubbles, which was defined as the threshold distance. The threshold distance changed with the radius of the attached bubble. In addition, a theoretical calculation was performed using a previously derived model that coupled the vibrations of two free bubbles [Ida, Phys. Lett. A 297, 210-217 (2002)]. The experiment data for the threshold distance qualitatively agreed with the theoretical predictions, except when the separation distance was very small. Then, it was discovered that the free bubble became trapped near the attached bubble when the separation distance between the two bubbles was very small. This indicated that a stable equilibrium point for the separation distance exists that cannot be predicted by the theoretical model.