Optical probing of spin polarization of electrons in quantum dot edge channels

We propose an optical method for the investigation of the quantum dot edge channels by utilizing circularly polarized photoluminescence in the integer-quantum-Hall-effect regime. One of the advantages of our method is that the degree of the spin-polarization of the electrons in the inner- and outer-compressible liquids can be probed separately. The observed polarized photoluminescence spectra can be explained by the calculated electron spin-dependent optical transition probabilities based on the local-spin density approximation.     

Observation of radiative B-->phi K gamma decays

The radiative decay B-->phi K gamma is observed for the first time. The branching fraction for the charged B--->phi K- gamma decay mode is measured to be B(B--->phi K- gamma)=(3.4+/-0.9+/-0.4)x10(-6). The photon energy distribution for the B--->phi K- gamma decay is presented. The signal for the neutral B(0)-->phi K(0)gamma decay mode is not statistically significant and an upper limit, B(B(0)-->phi K(0)gamma)<8.3x10(-6) at 90% C.L., is set. The analysis is based on a data set of 90 fb(-1) collected by the Belle experiment at the e(+)e(-) asymmetric collider KEKB.     

Measurement of branching fractions for B-->eta(c)K(*) decays

We report measurements of branching fractions for charged and neutral B-->eta(c)K decays where the eta(c) meson is reconstructed in the K(0)(S)K+/-pi(-/+), K+K-pi(0), K(*0)K-pi(+), and pp; decay channels. The neutral B0 channel is a CP eigenstate and can be used to measure the CP violation parameter sin(2phi(1). We also report the first observation of the B0-->eta(c)K(*0) mode. The results are based on an analysis of 29.1 fb(-1) of data collected by the Belle detector at KEKB.     

Noise-driven switching and chaotic itinerancy among dynamic states in a three-mode intracavity second-harmonic generation laser operating on a Lambda transition

We studied the antiphase self-pulsation in a globally coupled three-mode laser operating in different optical spectrum configurations. We observed locking of modal pulsation frequencies, quasiperiodicity, clustering behaviors, and chaos, resulting from the nonlinear interaction among modes. The robustness of [p:q:r] three-frequency locking states and quasiperiodic oscillations against residual noise has been examined by using joint time-frequency analysis of long-term experimental time series. Two sharply antithetical types of switching behaviors among different dynamic states were observed during temporal evolutions; noise-driven switching and self-induced switching, which manifests itself in chaotic itinerancy. The modal interplay behind observed behaviors was studied by using the statistical dynamic quantity of the information circulation. Well-organized information flows among modes, which correspond to the number of degeneracies of modal pulsation frequencies, were found to be established in accordance with the inherent antiphase dynamics. Observed locking behaviors, quasiperiodic motions, and chaotic itinerancy were reproduced by numerical simulation of the model equations.     

Effects of fine fuel droplets on a laminar flame stabilized in a partially prevaporized spray stream

A partially prevaporized spray burner was developed to investigate the interaction between fuel droplets and a flame. Monodispersed partially prevaporized ethanol sprays with narrow diameter distribution were generated by the condensation method using rapid pressure reduction of a saturated ethanol vapor–air mixture. A tilted flat flame was stabilized at the nozzle exit using a hot wire. Particle tracking velocimetry (PTV) was applied to measurements of the droplet velocity; the laminar burning velocity was obtained from gas velocity derived from the droplet velocity. Observations were made of flames in partially prevaporized spray streams with mean droplet diameters of 7 μm and the liquid equivalence ratios of 0.2; the total equivalence ratio was varied. In all cases, a sharp vaporization plane was observed in front of the blue flame. Flame oscillation was observed on the fuel-rich side. At strain rates under 50 s⁻¹, the change in the burning velocity with the strain rate is small in fuel-lean spray streams. In spray streams of 0.7 and 0.8 in the total equivalence ratio, burning velocity increases with strain rates of greater than 50 s⁻¹. However, in spray streams with 0.9 and 1.0 in the total equivalence ratio, burning velocity decreases as the strain rate increases. At strain rates greater than 80 s⁻¹, burning velocity decreases with an increased gas equivalence ratio. The effect of mean droplet diameter, and the entry length of droplets into a flame on the laminar burning velocity, were also investigated to interpret the effect of the strain rate on the laminar burning velocity of partially prevaporized sprays.     

Photoluminescence measurements in Be-δ-doped back-gated quantum well

We measured the photoluminescence (PL) spectra of a two-dimensional electron system induced in a Be-δ-doped GaAs/AlGaAs quantum well (QW) with a back gate. The electron density is controlled by means of the back-gate voltage. We estimated the electron density using the magneto-optical method and the PL linewidth, and also by undertaking transport measurements. We show that a uniform 2DES as large as 1 mm² is induced by the back-gate operation from 2.5 × 10¹⁰ cm⁻². This experiment indicates that optical measurement with a back-gated QW is advantageous for studying the low-density 2DES.     

<Superscript>119</Superscript>Sn Mössbauer studies on ferromagnetic and photocatalytic Sn–TiO<Subscript>2</Subscript> nanocrystals

Diluted Sn doped TiO₂ nanocrystals (Sn/Ti ratio: x ≤ 1.37 %) were synthesized by a simple hydrothermal method using pure reagents without any surfactant and dispersant material. The XRD of these samples showed an anatase phase, anatase and rutile mixed phases, and a rutile phase of TiO₂ and SnO₂ with the increase of Sn dopant concentrations. ¹¹⁹Sn Mössbauer spectra gave the broad peaks, which were decomposed into doublets and sextets because almost all these samples showed magnetic hysteresis even at room temperature. The titanium oxides doped with x ≤ 0.12 % showed the relatively large magnetic hysteresis and high photocatalytic activity. Mössbauer spectra of samples doped with x > 0.3 % were analyzed by one doublet and two sextets although the samples showed weak ferromagnetism. Three kinds of Sn species may be distinguished as Sn ⁴⁺ substituted TiO₂ and two different magnetic arrangements of Sn doped TiO₂: one with more oxygen defects and other at the interface of TiO₂ and precipitated SnO₂ containing Ti atoms. The correlation between various amounts of Sn sites and photocatalytic activity and/ or magnetic property was discussed.     

Retention Behavior of Nucleic Acid Bases and Purine Derivatives on Titania

The retention of nucleic acid bases and purine derivatives on titania was studied using a 0.4 mM acetic acid–sodium acetate buffer (pH 6.0) and 70% aqueous methanol as mobile phases. We observed that the retention strength of tested analytes on titania was dependent on the structural differences between pyrimidine and purine skeletons and the variety and number of substituents. The retention order was purine derivatives with methyl groups, pyrimidine bases and purine derivatives with hydrophilic functional groups, which were retained most strongly on titania. We concluded that the retention of each analyte was caused by the analyte’s hydrophobicity in the case of purine derivatives with methyl groups and pyrimidine bases. In the case of purine and its derivatives with hydrophilic functional groups, it was considered that the retention was dependent on the analyte’s ability to form chelates, and the variety and number of functional groups on C6 and C2.