Analysis of photonic crystal waveguide gratings with coupled-mode theory and a finite-element method

Both rod and air-hole types of photonic crystal waveguide gratings are proposed and their coupling coefficients and transmission characteristics are effectively investigated by using a simple coupled-mode theory combined with a finite-element method. The results obtained are compared with the results obtained by using a full numerical simulation method. A new definition for unperturbed waveguides is introduced to obtain accurate coupling coefficients. It is shown that, by using a pi-phase-shifted waveguide structure in the case of an air-hole type of photonic crystal waveguide grating, the coupling coefficient is strongly enhanced. The accuracy of the method is discussed through numerical examples of high-index-contrast waveguide gratings.     

New anatase-type Til-2xNbxAlxO2 solid solution nanoparticles: direct formation, phase stability, and photocatalytic performance

New anatase-type titania solid solutions co-doped with niobium and aluminum (Til-2xNbxAIlxO2 (X = 0 -0.20)) were synthesized as nanoparticles from precursor solutions of TiOSO4, NbCl5, and Al(NO3)3 under mild hydrothermal conditions at 180 degrees C for 5 h using the hydrolysis of urea. The lattice parameters a0 and c0 of anatase slightly and gradually increased, when the content of niobium and aluminum increased from X = 0 to 0.20. The crystallite size of anatase increased from 12 to 28 nm with increasing the value of X from 0 to 0.20. Their photocatalytic activity and adsorptivity were evaluated separately by the measurement of the concentration of methylene blue (MB) remained in the solution in the dark or under UV-light irradiation. The adsorptivity of TiO2 was improved by the formation of anatase-type Til-2xNbxAlxO2 solid solutions. The photocatalytic activity of anatase-type Til-2xNbxAlxO2 solid solutions was superior to that of commercially available anatase-type pure TiO2 (ST-01) and anatase-type pure TiO2 hydrothermally prepared. The new anatase phase of Til-2xNbxAlxO2 (X = 0-0.20) solid solutions existed stably up to 850 0C during heat treatment in air. In comparison with hydrothermal pure TiO2, the starting temperature of anatase-to-rutile phase transformation was delayed by the formation of Ti1-2xNbxAlxO, (X = 0-0.20) solid solutions, although its completing temperature was accelerated.     

Preparation of LaRuO3 films by microwave plasma-enhanced chemical vapor deposition

LaRuO₃ films were prepared by microwave plasma-enhanced chemical vapor deposition, and the effects of La/Ru supply ratio (R_La/Ru) and microwave power (P_M) on phase and microstructure were investigated. Amorphous films of carbonate or hydroxide of La were formed without microwave irradiation. At R_La/Ru < 1.0, RuO₂ films were obtained independent of P_M. At R_La/Ru = 1.6-3.2 and P_M = 0.6-1.2 kW (deposition temperatures of 973-998 K), LaRuO₃ single phase films were prepared. A product mixture of La₂RuO₅ and β-La₃RuO₇ was obtained at R_La/Ru = 4 and P_M = 1.2 kW, while a mixture of RuO₂ and La_4.87Ru₂O₁₂ was formed at R_La/Ru = 4.6 and P_M = 0.6 kW. LaRuO₃ single phase films showed metallic conduction with a high electrical conductivity of 1.6 × 10⁴ S m^− 1 at room temperature.     

In situ STM study of underpotential deposition of bismuth on Au(1 1 0) in perchloric acid solution

The underpotential deposition (UPD) of Bi on Au(1 1 0) was investigated in HClO₄ solution using in situ scanning tunneling microscopy. The UPD of Bi occurred in three steps. A structure, in which Bi atoms formed dimers, was found for the first UPD adlayer. A (1 × 1) image was obtained by STM at the second UPD peak. For the third UPD peak, Bi atoms formed an incommensurate adlayer, and stripes of Bi were observed on terraces. After the third UPD, a structural reconstruction caused by adsorbed Bi was observed.     

Superconductivity in polycrystalline diamond thin films

Superconductivity was discovered in heavily boron-doped diamond thin films deposited by the microwave plasma assisted chemical vapor deposition (MPCVD) method. Advantages of the MPCVD deposited diamond are the controllability of boron concentration in a wide range, and a high boron concentration, especially in (111) oriented films, compared to that of the high-pressure high-temperature method. The superconducting transition temperatures are determined to be 8.7 K for T_c onset and 5.0 K for zero resistance by transport measurements. And the upper critical field is estimated to be around 7 T.     

Study on the bulk junction type organic solar cells with double zinc oxide layer

The optical and photovoltaic properties of a photovoltaic cell with a structure of indium–tin oxide (ITO)/double ZnO/poly(3-hexylthiophene) (PAT6):PCBM/Ag have been investigated. The double layer ZnO was a composite of a sputtered ZnO layer and oriented zinc oxide nanopillars layer which was fabricated by a new method at low temperature (343 K). It is concluded that the double layer ZnO plays an important role in collecting photogenerated electrons and acts as a conducting path to the electrode. Insertion of the double layer ZnO in the photovoltaic cells produced enhanced performance with the power conversion efficiency of 1.42% under AM1.5 illumination.     

Strain measurement by a diffraction grating method

A simplified system was proposed for measuring a normal strain from the location of a laser beam spot diffracted by a diffraction grating attached to the surface of a specimen. An He-Ne laser beam illuminated the grating and the ± 1-order diffracted beam spots were measured with a single PCD (plasma-coupled device) optical sensor connected with a personal computer. The diffracted intensity distribution was approximated by a Gaussian function and the x-coordinate of its principal axis was used as the location of the spot. The strain of a cantilever beam specimen measured bythis method agreed well with the theoretical value and that measured with a strain gage.     

Circadian clocks optimally adapt to sunlight for reliable synchronization

Circadian oscillation provides selection advantages through synchronization to the daylight cycle. However, a reliable clock must be designed through two conflicting properties: entrainability to synchronize internal time with periodic stimuli such as sunlight, and regularity to oscillate with a precise period. These two aspects do not easily coexist, because better entrainability favours higher sensitivity which may sacrifice regularity. To investigate conditions for satisfying the two properties, we analytically calculated the optimal phase–response curve with a variational method. Our results indicate an existence of a dead zone, i.e. a time period during which input stimuli neither advance nor delay the clock. A dead zone appears only when input stimuli obey the time course of actual solar radiation, but a simple sine curve cannot yield a dead zone. Our calculation demonstrates that every circadian clock with a dead zone is optimally adapted to the daylight cycle.     

Study of partially-switched states of ferroelectrics in relation to the spatial inhomogeneity of their domain structure

In this paper we reexamine the possibility of using ferroelectric materials for adaptive learning artificial intelligence applications, by exploiting their capability to be set in electrically-controlled multivalue polarization states. Our experiments on a Pb(Zr,Ti)O₃ ceramic sample consisted in conveniently selecting the input pulse electric field and temperature of the sample during field application, in order to create partially-switched states. Employing strong/weak electric field pulses allows to control the analog polarization levels by a linear or logarithmic addition of pulses. The partially-switched states are mapped with enhanced resolution when domains with dissimilar evolution stages are present. Applying electric fields while heating the sample allows to reduce the switching time and shifts down the switching threshold. Thus, in addition to artificial intelligence applications, these results provide hints for energy-saving devices that exploit the intrinsic high mobility of small fluctuating domains.     

Design method for a new control system for an autonomous underwater vehicle using linear matrix inequalities

The independent administrative corporation Japan Agency for Marine–Earth Science and Technology (JAMSTEC) has developed a small light autonomous underwater vehicle (AUV) named marine robot experimental 1 (MR-X1).¹ The motion control of MR-X1 is considered in this article. Since the dynamics of MR-X1 mainly depends on its own speed, the motion control is a nonlinear control system. We propose a new controller design method for this system using linear matrix inequalities (LMIs). This algorithm gives a solution as a linear matrix inequality, and can be adapted to solve many LMIs simultaneously. LMIs can be obtained by substituting several speeds into the dynamics of the MR-X1. The proposed controller, which can be derived from the solution of the LMIs, was adapted to MR-X1 and showed good performance in experiments. This work was presented in part at the 11th International Symposium on Artificial Life and Robotics, Oita, Japan, January 23–25, 2006