The wings of butterflies are relatively heavier than those of other insects, and the inertial force and torque due to the wing mass are likely to have a significant effect on agility and manoeuvrability in the flapping flight of butterflies. In the present study, the effect of wing mass on the free flight of butterflies is investigated by numerical simulations based on an immersed boundary–lattice Boltzmann method. We use a butterfly-like model consisting of two square wings with mass connected by a rod-shaped body. We simulate the free flights of the model by changing the ratio of the wing mass to the total mass of the model and also changing the mass distributions of the wings. As a result, we find that the aerodynamic vertical and horizontal forces decrease as the wing-mass ratio increases, since for a large wing-mass ratio the body has large vertical and horizontal oscillations in each stroke and consequently the speeds of the wing tip and the leading edge relatively decrease. In addition, we find that the wing-mass ratio has a dominant effect on the rotational motion of the model, and a large wing-mass ratio reduces aerodynamic force and intensifies the time variation of the pitching angle. From the results of our free flight simulations, we clarify the critical wing-mass ratio between upward flight and downward flight and find that the critical wing-mass ratio is a function of the non-dimensional total mass and almost independent of the wing length. Then, we evaluate the effect of the wing-mass distribution on the critical wing-mass ratio. Finally, we discuss the limitations of the model.

The current trends in stimulated Brillouin scattering and optical phase conjugation are overviewed. This report is formed by the selected papers presented in the “Fifth International Workshop on stimulated Brillouin scattering and phase conjugation 2010” in Japan. The nonlinear properties of phase conjugation based on stimulated Brillouin scattering and photo-refraction can compensate phase distortions in the high power laser systems, and they will also open up potentially novel laser technologies, e.g., phase stabilization, beam combination, pulse compression, ultrafast pulse shaping, and arbitrary waveform generation.

The high-density and low temperature microwave plasma utilizing a spokewise antenna was successfully applied to fast deposition of highly crystallized and photconductive microcrystalline silicon (μ-Si:H) films at low temperatures. The deposition rate and film crytstallinity significantly depend on the axial distribution of the plasma parameters. Best crystallinity was obtained at the axial distance Z from the quartz glass plate, where the spread of the ion beam energy impinging to the growing surface was minimum. By optimizing the axial distance Z and total pressure, highly crystallized μ-Si:H films could be fabricated with a high deposition rate of ∼47Å/s in the SiH4 and Ar mixture plasma with no use of the H2 dilution. An intentional control of the ion beam energy is also attempted using a mesh grid electrode to suppress the ion bombardment to the growing surface.

The improvement of thickness distribution and crystallinity in ZnO thin films prepared by radio frequency (rf) planer magnetron sputtering has been studied. Optimum thickness distribution of less than ± 2.2% in a 3-inch wafer is obtained by changing the substrate angle to the ZnO target and is in accordance with cosine law. The c-axis orientation perpendicular to the silicon substrate is confirmed by x-ray diffraction. The stress of ZnO thin films is larger than 0.3GPa and its distribution is independent of the substrate angle that is set at a slant to the optimum angle for thickness distribution. These results indicate that thickness distribution of ZnO thin films heavily depends on the substrate angle, while the stress and its distribution are independent of the setting angle of the substrate. Stress distribution is attributed to the distribution of argon ions and sputtered molecules impinging a wafer.

The spectral and the time dependent piezoelectric photoacoustic (PPA) measurements under the continuous light illumination were carried out at 85 K to investigate nonradiative recombination processes involving EL2 defect levels in carbon doped semi-insulating (SI) GaAs. The decrease of the PPA signal due to the photoquenching effect of EL2 was observed for a short period of illumination of 1.12 eV. It was found that the photoquenching becomes drastic with increasing the carbon concentration. After fully photoquenching, the PPA signal increased again through a local minimum by the continuous light illumination and finally exceeded the initial value before illumination until the saturation level was reached. The deep donor level EL6 and its metastable state are proposed. EL6 level donates electrons to compensate a part of carbon acceptors after photoquenching. The nonradiative recombination through this level generates the PPA signal. The usefulness of the PPA technique for studying the nonradiative transition through deep levels in semiconductor is suggested.

This paper examines the conduction band offset, ∆Ec, and interface charge density, σ, of disordered InGaP and GaAs heterointerfaces by controlling the AsH 3 cover time and flow rate at the growth interval from GaAs to InGaP. Short AsH, cover time (0.05 min) creates high ΔEc of 0.2 eV and low σ of 6.3×l0 10cm −2. Extending the AsH 3 cover time by 50 times cuts ΔEc to almost 0 eV and increases σ by one order. Interface morphology for long-AsH3 -cover-time samples observed by atomic force microscopy shows a terrace structure on GaAs surface, which means the surface is As rich. These results suggest that an As-poor GaAs surface is essential to achieving high-quality InGaP/GaAs heterointerfaces.

Zinc oxide (ZnO) thin films have been grown by radio frequency sputtering on glass, Al, Au and R cut sapphire substrates. Microstructures of the ZnO / substrate interface have been observed by transmission electron microscope. The purpose of this study is to elucidate the crystal growth mechanism of ZnO thin films using various substrates that have different crystallinity and crystal structures. An amorphous layer with a thickness of about 5 nm is observed at the ZnO/glass interface, and c axis orientation perpendicular to the substrate is observed on this amorphous layer. Mianstructurts at the ZnO/buffer metal interface, on the other hand, are significantly different from those of ZnO/glass interface. A thick amorphous layer of about 15 nm is observed at the ZnO/Al interface, presumably consisting of Al2O3 interface layer material. ZnO thin film grown on Au buffer layers is distinctly different from both ZnO on glass and Al. No amorphous layer is formed at the ZnO/Au interface, and c axis orientation begins directly from the Au surface. Epitaxially grown ZnO thin film is confirmed on a R-cut sapphire substrate. These results dearly demonstrate that ZnO thin films prepared by radio frequency sputtering are strongly influenced by the substrate surface crystallinity at the topmost layer of the substrate.

High quality wide gap hydrogenated amorphous silicon has been prepared using the chemical annealing technique. It was possible to prepare materials with band gaps ranging 1.8 to 2.1 eV by varying the preparation parameters. Low defect densities less than (3–8) x 1015 cm-3 could be maintained over the entire band gap range. Improved stability for light soaking was also observed in the wide gap materials.

The piezoelectric photoacoustic (PPA) measurements before and after the secondary light illumination for 3 minutes were carried out at 85 K to investigate the electron and hole photoionization processes of EL2 in carbon concentration controlled semi-insulating (SI) GaAs. The result showed a broad peak around 1.0 eV and a hump up to the band gap energy. These were due to hole and electron photoionization processes of EL2, respectively, and these processes were clearly observed from a nonradiative recombination point of view for the first time. In addition, we found that the hole photoionization process of EL2 is not influenced by the secondary light illumination at low temperature. Although the electron photoionization underwent photoquenching effect upon an illumination of 1.12 eV, the hole photoionization process did not change even after a long period of illumination. The positively charged EL2 donor state may not transform to the metastable state.

Electroluminescent diodes utilizing poly(3-alkylthiophene) (PAT) containing fluorescent dyes have been fabricated and their unique enhancement of emission efficiency has been studied for PAT diodes doped with different fluorescent dye materials. Remarkable enhancement of electroluminescent efficiency has been observed, and the mechanism of emission enhancement in PAT diode by doping of fluorescent dye has been discussed in PAT with different aLkyl-side-chain length.

High quality a-Si:H thin films with varied optical gaps in the range from 1.55 to 2.1 eV were fabricated by various methods, i.e., the standard RF glow discharge of silane, “Chemical Annealing” and ECR-H-plasma from SiCl2H2 under in situ monitoring with an ellipsome try. Despite marked differences in the local structure, all these films showed low defect density as low as (3–5) × 1015 cm3. In addition, the stability for light soaking was improved markedly for the films made by promoting intensively structural relaxation with atomic hydrogen.

The photoluminescence (PL) and optically detected magnetic resonance (ODMR) spectra of poly(3-hexylthiophene) in solutions of CCl4, toluene, and CH2Cl2, and films cast from these solutions, are described and discussed. In solution, the PL yield is 7%, and increases with increasing temperature. In oxygen-free, protected films cast from these solutions, the room-temperature yield is ∼0.7%, the spectra is red shifted by ∼0.5eV, and strong peaks at 1.52, 1.69, and 1.86eV appear. In films and CH2Cl2 solutions, the ODMR is resolvable into narrow and broad components, and its intensity ΔL/L is ∼5 × l0−5 at room temperature. A strong photoinduced oxidation process quenches the PL upon exposure to O2 but not water, at a rate possibly limited by O2 diffusion.

The oscillator strengths of two ultraviolet molecular lines expected to be seen in diffuse interstellar clouds have been measured. For the 1290.257 A° line of HC1, f=0.16±0.06. For the 1114.225 A° line of H2O, f=(5.0±2.0)x10−3. These results have been used in conjunction with observational data to compare measured and predicted column densities of these molecules in the ζ Óphiuchi cloud.