Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy

The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and soft magnetic shell is studied theoretically. It is assumed that the magnetic shell has a helical anisotropy. The current and field distributions in the composite wire are found by means of a simultaneous solution of Maxwell equations and the Landau–Lifshitz equation. The expressions for the diagonal and off-diagonal impedance are obtained for low and high frequencies. The dependences of the impedance on the anisotropy axis angle and the shell thickness are analyzed. Maximum field sensitivity is shown to correspond to the case of the circular anisotropy in the magnetic shell. It is demonstrated that the optimum shell thickness to obtain maximum impedance ratio is equal to the effective skin depth in the magnetic material.     

Highly reflective AlGaAsSb/InP Bragg reflector at 1.55 μm grown by MOVPE

The metalorganic vapor-phase epitaxy growth of a highly reflective 24-pair AlGaAsSb/InP-distributed Bragg reflector (DBR) is reported for the first time. The influence of the growth parameters such as the V/III input ratio, the growth temperature and the pressure, the total H₂ flow, the gas velocity and the switching sequence of the source gases at the interfaces has been deeply investigated and optimized to achieve stable growth conditions. The DBR achieves a reflectivity as high as 99.5% around 1.55 μm, a uniform stable composition, and an excellent crystal quality over the 2 inch wafer, with a surface free of crosshatch and a defect density below 1/cm². For the optical characterizations, measurements of linear and nonlinear reflectivity, transmission, pump-probe and photoluminescence were done. The interfaces and bulk layers of InP/AlGaAsSb/InP heterostructures were analyzed by transmission electron microscopy. High resolution X-ray diffraction measurements were used to determine the composition shift in the growth plane of the DBR. The measurements show the high quality of the growth and demonstrate that thick AlGaAsSb/InP heterostructures can be grown by metalorganic vapor-phase epitaxy (MOVPE), and in particular DBRs above 1.31 μm.     

Nonlinear transient analysis of moderately thick laminated composite sector plates

This study presents a simple formulation for the nonlinear dynamic analysis of shear-deformable laminated sector plates made up of cylindrically orthotropic layers. The non-axisymmetric formulation in cylindrical coordinates is discretized in space domain using two-dimensional Chebyshev polynomials. Houbolt time marching is used for temporal discretization. Quadratic extrapolation is used for linearization along with fixed-point iteration for obtaining the results. Several combinations of simply supported, clamped and free edge conditions are considered. Convergence study has been carried out and the results are compared with the results of square plates. Effects of boundary conditions, moduli ratio, lamination scheme, sector angle and annularity on the transient deflection response are plotted graphically. Transient responses are compared for step, saw-tooth and sinusoidal loadings.     

Photoluminescence properties of trace amounts of Pr and Tb in yttria-stabilized zirconia

We have investigated the photoluminescence (PL) properties of trace amounts of Pr and Tb in single-crystal samples of yttria-stabilized zironia (YSZ), and found that Pr of the order of 10⁻⁶ mass% and Tb of the order of 10⁻⁵ mass% in YSZ can be detected by the PL spectroscopy. The PL spectra of the YSZ samples for the 280 nm excitation were comprised of several peaks and a broad emission. The peaks were attributed to transitions of Pr³⁺ and Tb³⁺ in the YSZ samples, whereas the broad emission seemed to be attributed to the yttria-associated oxygen vacancies. The peak intensities corresponded to the amounts of Pr and Tb in the YSZ samples, the amounts of which were analyzed by glow discharge mass spectrometry. In the PL excitation spectra, but not in the photoabsorption spectra, small peaks at 376 and 381 nm were observed, and were attributed to the transitions of Tb³⁺ in the YSZ samples. The results of the PL excitation spectra corresponding to the Pr³⁺ line emissions suggest that the charge transfer occurs between the YSZ and Pr ion in it. The trace amounts of these lanthanoids in YSZ would disturb the decay process of the photoinduced electrons to the yttria-associated oxygen vacancies.     

The enhancement of photoluminescence of n-type porous silicon by Hall-effect assistance during electrochemical anodization

In this study, n-type porous silicon (n-PS) films with high-aspect-ratio Si-tips are formed with the assistance of Hall-effect during the electrochemical anodization. Lorentz force sweeps down the majority carriers (electrons) in n-type Si to enhance the anodization etching. Surface layers are inverted from n-type to p-type, so sufficient holes can continuously appear on the surface to participate in chemical reaction during the etching process. Illumination is not necessary in this process, so the problem of illumination-depth limitation is solved. The etching current, morphology, and photoluminescence of the n-PS prepared in this way are investigated. Strong visible photoluminescence emissions at room temperature are demonstrated on n-PS.     

Experimental results on the influence of concentrated liquid aerosols on the onset voltage of corona discharge

Positive and negative current–voltage characteristics of a needle-grid electrostatic precipitator were measured for different electrode geometries and aerosols. Besides the well-known effect of corona quenching, additional findings show an interaction of fluid aerosols with the active electrode. A shift of the current–voltage characteristics was observed towards lower as well as higher voltages, as a function of the electrode geometry and the conductivity of the fluid aerosol.     

Parametric X-rays along the velocity direction of an emitting particle under conditions of the Cherenkov effect

Peculiarities in the parametric X-rays along the velocity direction of a relativistic electron emitting in a regime where the Cherenkov effect is important are considered. It is shown that the emission yield can be increased substantially due to the modification of the anomalous photoabsorption.     

Electrically forced microthreading of highly viscous dielectric liquids

The behaviour of three high viscosity (4875, 12 125 and 58 560 mPa s), dielectric liquids was investigated at flow rates of 10⁻¹⁰, 10⁻¹² and 10⁻¹⁴ m³ s⁻¹ and the applied voltage range 6–15 kV. In these experiments, due to the low electrical conductivity of the liquids (10⁻¹³ S m⁻¹) and therefore the ensuing high electrical relaxation time, classical electrohydrodynamic atomization conditions are not satisfied. Only dripping and unstable jetting were observed at 4875 mPa s. A transition from no jetting to stable microthreading was observed for the 12 125 and 58 560 mPa s samples. The relics accompanying the transition were found to change from discrete droplets to a continuous filament. Stable microthreading, which generates uniform filaments, was obtained for the 12 125 mPa s sample at flow rates 10⁻¹⁰ and 10⁻¹² m³ s⁻¹ and in the case of the 58 560 mPa s sample at all the flow rates investigated. The high viscosity assisted stable microthreading with the filament diameter decreasing with increasing applied voltage and more dramatically decreasing with reducing flow rate.     

Magnetic pole pinning at rectangular defects on MnAs/GaAs(0 0 1)

Strong magnetic poles at characteristic rectangular defects have been observed using a magnetic force microscope on a MnAs(  1 0 0) thin film with the thickness of 30 nm. The MnAs thin film was epitaxially grown on a GaAs(0 0 1) substrate. The magnetic poles were in one-arranging direction, being independent of the magnetization direction of the film. The poles were pinned at the edges of the rectangular defects until just below the Curie temperature, and formed a stable magnetic-field loop on the MnAs surface. The stability of the magnetic pole pinning shows the distinctive feature of the magnetic domain structure on the surface with a strong anisotropy, which was built in the heterostructure of MnAs and GaAs.     

The 7th Asian Symposium on Visualization

The 7th Asian Symposium on Visualization (7ASV) was successfully held in Singapore from 3^rd to 7^th November 2003. This event was originally scheduled from 26^th to 30^th May 2003, but had to be postponed because of the outbreak of SARS (Severe Acute Respiratory Syndrome) in some parts of the world. A total number of 122 participants attended the Symposium of which, 107 were foreign participants from 16 countries (excluding Singapore) worldwide. There were 104 papers covering broad range of topics presented at the Symposium which were delivered in 2×7 long sessions, and 9 keynote papers.