Laser diode optical frequency stabilisation technique on ITU-T frequency grid employing modulated sideband light

A novel optical frequency stabilisation technique on the ITU-T frequency grid employing modulated sideband light is proposed. The L-band laser diode second sideband light generated by phase-modulation is locked to a carbon monoxide ¹²C¹⁶O gas absorption line; the original carrier is placed on the ITU-T frequency grid. The square root of Allan variance of 10^-8 has been achieved for a period of 12 h.     

Electronic Structure and Thermoelectric Properties of Si-Based Clathrate Compounds

Thermoelectric properties of Au-substituted Si-based clathrates, Ba₈AuGa₁₃Si₃₂ and Ba₆A₂AuGa _x Si_45−x (A = Sr, Eu, x = 13, 14), were experimentally and theoretically investigated. The polycrystalline samples of the Au-substituted Si-based clathrates were prepared by using the spark plasma sintering technique. The electronic structure of Ba₆A₂AuGa₁₃Si₃₂ was theoretically calculated by ab initio calculations, and the thermoelectric properties of Ba₆A₂AuGa _x Si_45−x were estimated through the calculated electronic structure. The effective mass of Ba₆A₂AuGa _x Si_45−x was experimentally estimated to be greater than that of Ba₈AuGa₁₃Si₃₂. Experimentally observed electronic properties agree with the calculations for Ba₆A₂AuGa _x Si_45−x . The maximum ZT value of Ba₆Sr₂AuGa₁₄Ge₃₁ is about 0.5 at 850 K. The calculated thermoelectric properties agree very well with the experimental results in the range from room temperature to 900 K.     

Models for low-dimensional thermoelectricity

Enhanced thermoelectric performance, expressed in terms of the thermoelectric figure of merit (ZT), has been predicted theoretically for low-dimensional electronic systems under appropriate experimental conditions. Enhanced ZT has been observed experimentally within 2D quantum wells of PbTe, and good agreement between theory and experiment has been obtained. The advantages of low-dimensional systems for thermoelectric applications are described, and prospects for further enhancement of ZT are discussed.     

Superconducting to normal transition of type-II Ta by a rectangular current pulse

The superconducting to normal transition by a rectangular pulse current in type-II Ta has been investigated. The potential drop along the specimen is observed as a function of time. The voltage pattern and the magnitude of the potential drop are obtained as functions of current amplitude, temperature, externally applied magnetic field, the angle between magnetic field and specimen axis, and values. The transition mechanisms are discussed. It is also shown in this experiment that the flux flow or flux creep and flux jump occur. A support to the paramagnetic current flow in the presence of longitudinal magnetic field is given.     

Structural Control of Rashba Spin–Orbit Coupling in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As Quantum Wells

We investigated the correlation between the Rashba spin–orbit coefficient and potential shape of the quantum wells (QW), where values are experimentally deduced from the weak antilocalization analysis. We studied the gate I–V properties of the QW samples and have obtained results consistent with the potential shapes predicted for these QWs.     

Fast agglomerative hierarchical clustering algorithm using Locality-Sensitive Hashing

The single linkage method is a fundamental agglomerative hierarchical clustering algorithm. This algorithm regards each point as a single cluster initially. In the agglomeration step, it connects a pair of clusters such that the distance between the nearest members is the shortest. This step is repeated until only one cluster remains. The single linkage method can efficiently detect clusters in arbitrary shapes. However, a drawback of this method is a large time complexity of O(n ²), where n represents the number of data points. This time complexity makes this method infeasible for large data. This paper proposes a fast approximation algorithm for the single linkage method. Our algorithm reduces the time complexity to O(nB) by rapidly finding the near clusters to be connected by Locality-Sensitive Hashing, a fast algorithm for the approximate nearest neighbor search. Here, B represents the maximum number of points going into a single hash entry and it practically diminishes to a small constant as compared to n for sufficiently large hash tables. Experimentally, we show that (1) the proposed algorithm obtains clustering results similar to those obtained by the single linkage method and (2) it runs faster for large data than the single linkage method. Hisashi Koga received the M.S. and Ph.D. degree in information science in 1995 and 2002, respectively, from the University of Tokyo. From 1995 to 2003, he worked as a researcher at Fujitsu Laboratories Ltd. Since 2003, he has been a faculty member at the University of Electro-Communications, Tokyo (Japan). Currently, he is an associate professor at the Graduate School of Information Systems, University of Electro-Communications. His research interest includes various kinds of algorithms such as clustering algorithms, on-line algorithms, and algorithms in network communications. Tetsuo Ishibashi received the M.E. degree in information systems design from the Graduate School of Information Systems at the University of Electro-Communications in 2004. Presently, he is a system engineer at Fujitsu Broad Solution & Consulting Inc. Toshinori Watanabe received the B.E. degree in aeronautical engineering in 1971 and the D.E. degree in 1985, both from the University of Tokyo. In 1971, he worked at Hitachi as a researcher in the field of information systems design. His experience includes demand forecasting, inventory and production management, VLSI design automation, knowledge-based nonlinear optimizer, and a case-based evolutionary learning system nicknamed TAMPOPO. He also engaged in FGCS (Fifth Generation Computer System) project of Japan and developed a new hierarchical message-passing parallel cooperative VLSI layout problem solver that ran on PIM (Parallel Inference Machine) in 1991. Since 1992, he has been a professor at the Graduate School of Information Systems, University of Electro-Communications, Tokyo, Japan. His areas of interest include media analysis, learning intelligence, and the semantics of information systems. He is a member of the IEEE.     

Compensation of Interchannel Crosstalk Induced by Optical Fiber Nonlinearity in Carrier Phase-Locked WDM System

A scheme that compensates the waveform distortion induced by nonlinear interchannel crosstalk such as four-wave mixing (FWM) and cross-phase modulation as well as self-phase modulation in phase-locked wavelength-division-multiplexing transmission systems is proposed. Reduction of FWM-induced waveform distortion by controlling the phase relationship between neighbouring channels and its cancellation by precompensation is successfully demonstrated     

Order-disorder transition and its effect on microwave quality factor Q in Ba(Zn1/3Nb2/3)O3 system

Influences of composition deviation from stoichiometry and heat treatment on crystal phases and Q factor in Ba(Zn_1/3Nb_2/3)O₃(BZN) were studied. The structural order and the crystal phases strongly depended on the slight composition deviation from stoichiometric BZN. The maximum Q factor was obtained at the vicinity of the stoichiometric BZN. In the other regions, non-stoichiometric disordered BZN or ordered BZN with secondary phase were formed, and their Q factors were found to be low. For the stoichiometric BZN, the order-disorder phase transition occurred between 1300 and 1400^°C. The crystal-structural ordering of the stoichiometric BZN was improved by post-annealing at below its transition temperature, conserving the density and the grain size. However, no significant Q factor improvement was found. The Q factor of the stoichiometric BZN strongly depends on the density and grain size not on the crystal-structural order. These results suggest that the ceramic microstructure such as the pore and grain boundary, the secondary phase and lattice defect caused by non-stoichiometry affect the variation of the Q factor in BZN system than the crystal-structural ordering.     

Flashover voltage of alumina ceramic contaminated by metal vapor in vacuum interrupters

We investigated the influence of metal vapor contamination of ceramic surfaces on flashover voltage (FOV) in vacuum. First, disk shape alumina (Al/sub 2/O/sub 3/) ceramics with surface resistivity (/spl rho/) of 10/sup 2/-10/sup 15/ /spl Omega/ were produced using deposition phenomena of metal vapor emitted from CuCr contacts. The impulse FOV for the ceramics decreased, as /spl rho/ reduced; FOV, the conditioning effect on FOV, and the scattering of FOV decreased when /spl rho/ was below 10/sup 12/ /spl Omega/. Therefore, the criterion value /spl rho/, which maintains excellent flashover performances of ceramic surface, is 10/sup 12/ /spl Omega/. Second, experimental vacuum interrupters (VIs) were produced to measure breakdown voltage before and after forty short-circuit current switchings with 20-40 kA/sub rms/ and were disassembled to measure the /spl rho/ of their inner ceramic surface. In a VI, which has inside diameters at both ends of the main shield much larger than the contact diameter, /spl rho/ was reduced to 10/sup 4/ /spl Omega/, further decreasing breakdown voltage between terminals.