Classical in-plane negative magnetoresistance and quantum positive magnetoresistance in undoped InSb thin films on GaAs (1 0 0) substrates

Magnetoresistance (MR) effects have been investigated in perpendicular and parallel magnetic fields at 300, 80 K and liquid He temperatures for undoped InSb thin films 0.1–2.3 μm thick grown on GaAs(1 0 0) substrates by MBE. At high temperatures, the intrinsic carriers show the parabolic negative MR observable only in magnetic fields parallel to the film. The skipping-orbit effect due to surface boundary scattering in the classical orbits in the plane vertical to the film has been argued to be responsible for the negative MR. At low temperatures (T=80 K), the transport is dominated by the two-dimensional (2D) electrons in the accumulation layers at the InSb/GaAs(1 0 0) hetero interface; MR is positive and shows a logarithmic increase with anisotropy between parallel and perpendicular field orientation, arising from the 2D weak anti-localization (WAL) that reflects the interplay between the spin-Zeeman effect and strong spin–orbit interaction caused by the asymmetric potential at the interface (Rashba term). The zero-field spin splitting energy of Δ₀13 meV, the electron effective mass of m^*0.10m₀ seven times of the band edge mass in bulk InSb and the effective g-factor of |g^*|15 in the accumulation layer have been inferred from fits of MR for the 0.1 μm thick film to the 2D WL theory.     

On equivalence of L p -norms related to Schrödinger type operators on Riemannian manifolds

In this paper, we study Schrödinger type operator on a Riemannian manifold. Under some assumptions on a potential function, we characterize the domain of the square root of the Schrödinger type operator on L ^p space. In the proof, the defective intertwining properties and the Littlewood-Paley inequalities play important roles.     

THE DESIGNS OF HIGH EFFICIENCY LAUNCHER OF QUASI-OPTICAL MODE CONVERTER FOR HIGH POWER GYROTRONS

A high efficiency launcher of quasi-optical (QO) mode converters for high power gyrotrons have been designed and tested. A helical cut launcher radiates the RF power via its straight cut onto the first phase correcting mirror. The launchers have been optimized for the TE_31.8 mode at 170 GHz and TE_22.6 mode at 110 GHz by numerically optimizing a launcher surface. The helical cut of the launcher has been optimized by taking the taper angle into account. Further more, the amplitude of the surface perturbation have been optimized for improved focusing in order to reduce the diffraction losses at the helical cut. Low power measurement shows a good agreement with the design. High efficiency characteristics of the design have also been calculated on the assumption of frequency downshift due to the thermal expansion of the cavity and stepwise frequency tuning by changing the operating mode. Besides, the possibility of high efficiency launcher for higher mode is discussed, and these results give the prospect to high efficiency long pulse gyrotrons.     

Slow cyclotron instability in a high-power backward-wave oscillator

The linear dispersion relation of a backward-wave oscillator (BWO), derived earlier by the authors, is modified to include effects of RF surface current at the beam-vacuum interface. This modified dispersion relation results in an unstable interaction between the slow cyclotron mode (SCM) and the structure mode in addition to the conventional Cherenkov instability caused by the slow space charge mode. Numerical analysis is then carried out using parameters of a BWO experiment at University of Maryland. Fine structure of the SCM instability is elucidated. The analysis indicates that BWO radiation would not be suppressed near cyclotron absorption in an infinitely long system.     

Influence of shell strength on shape transformation of micron-sized,monodisperse, hollow polymer particles

Micron-sized, monodisperse, non-spherical polymer particles with "rugby ball" and "red blood corpuscle"-like shapes were produced by seeded polymerization of the dispersion of (divinylbenzene/vinylbiphenyl/xylene)-swollen polystyrene particles prepared by utilizing the dynamic swelling method which the authors proposed in 1991. Their non-spherical shapes were based on buckling of the shell of the resultant hollow particles. In this article, the reversible shape transformation of the hollow composite polymer particle between spherical and such non-spherical shapes was studied in detail by controlling the shell strength. A part of the shell was buckled by external pressure which was caused by evaporation of xylene from the hollow when the shell had the tensile modulus below the critical value calculated from the pressure-buckling relationship of a spherical shell proposed by Uemura. The plasticization of the shell by a good solvent was one of key factors for the shape transformation.     

Growth Mechanism of Large Monodispersed Silica Particles Prepared from Tetraethoxysilane in the Presence of Sodium Dodecyl Sulfate

Monodispersed silica particles up to ca. 1.2 μm in diameter were prepared by hydrolysis of tetraethoxysilane in the presence of sodium dodecyl sulfate (SDS). The particle size was increased with an increase of SDS added. The geometrical standard deviation of the particles was decreased with an increase of SDS. In the earlier reaction stage, double spherical particles by the coalescence of the particles were frequently observed when large amounts of SDS were added. Particle size was gradually increased after the coalescence occurred and spherical particles were finally obtained. The results of Nielsen’s chronomal analysis suggest that the polynuclear layer growth took place after the coalescence of the particles in the presence of larger amount of SDS.     

Evaluation of Photocatalytic Activity of Transparent Anatase Nanocrystals-Dispersed Silica Films Prepared by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals were precipitated mainly at the surface of the silica-titania gel films with hot water treatment, whereas the addition of poly(ethylene glycol) (PEG) in the films led to the dispersion of anatase nanocrystals in the whole of the films after the treatment. Both films with and without PEG showed high photocatalytic activities for acetaldehyde, NO _x and stearic acid in the gas-solid system, and for methylene blue and potassium iodide in the liquid-solid system. The addition of PEG improved the photocatalytic activities of the resultant films due to the smaller anatase crystallites and the porous film structure. The residual silica under-layer of the superficially anatase-precipitated films is expected to act as a protective one for an organic polymer substrate against the photocatalytic degradation.