Influence of buried structure on polarization sensitivity instrained bulk semiconductor optical amplifiers

In order to achieve an accurate design of polarization-insensitive semiconductor optical amplifiers based on tensile strained bulk InGaAsP, the reduction of strain in the active layer of the buried heterostructure and its influence on polarization sensitivity are analyzed numerically for the first time. The gain calculation, including the strain distribution in the active layer, is examined based on the k · p method for the different active layers. It is found that the strain introduced during the epitaxial growth is strongly reduced after regrowth of the burying layer. In an active layer having the aspect ratio of 1 : 4, the strain reduction causes more than a 0.5-dB deviation in the polarization sensitivity of the gain. From a comparison with the experimental results, it is shown that including the effect of the burying layer in the calculation gives an accurate determination of the amount of strain for the polarization independence     

Stabilizing effect of the cyclodextrins additive to spray-dried particles of curcumin/polyvinylpyrrolidone on the supersaturated state of curcumin

Although curcumin is considered to have various therapeutic effects, its use as a functional food or supplement is restricted owing to its low water solubility and bioavailability. To increase the solubility of curcumin in water, the use of polyvinylpyrrolidone (PVP) and vinylpyrrolidone-vinyl acetate copolymers with a pyrrolidone skeleton was noted to be promising. In particular, the bi-component formulations of curcumin/PVP prepared through spray drying exhibited an amorphous state in powder X-ray diffraction observations and temporally increased the apparent solubility of curcumin to over 5000 times that of untreated curcumin; nevertheless, after 24 h, the solubility decreased owing to the unstable supersaturated state of curcumin. The addition of α-cyclodextrin (α-CyD) in the bi-component curcumin/PVP formulation helped maintain the supersaturated state of curcumin, whereas the addition of β- and γ-CyD led to the collapse of the supersaturated state. The addition of α-CyD can likely help inhibit the nucleation and crystal growth of curcumin, through the interaction among the solubilized units of curcumin/PVP and α-CyD.     

Determination of residual avoparcin in chicken muscle by HPLC with ultraviolet and amperometric detection

An analytical method was developed for determination of residual avoparcin in chicken muscle by measuring alpha- and beta-avoparcin, major components of the pharmaceutical preparation avoparcin, using HPLC with UV and amperometric detectors. The analytical HPLC was run on a Cosmosil 5C18-AR column (4.6 mm x 25 cm) with a gradient formed from A: 2.5% acetic acid, 0.01 mol/L sodium heptane sulfonic acid-acetonitrile (88.5:11.5) (pH 4.0) and B: 2.5% acetic acid-acetonitrile (10:90), using UV and amperometric detection (AMD) with glassy-carbon electrode (+900 mV). Avoparcin was extracted from chicken muscle by homogenization with methanol-0.2 mol/L sulfuric acid (6:4) followed by centrifugation after pH adjustment to 4 with 1 mol/L sodium hydroxide. The supernatant was evaporated to dryness, and the residue was dissolved in water. The aqueous layer was adjusted to pH 4 by adding 1 mol/L sodium hydroxide. Then it was purified on a Sep-Pak tC18 plus ENV cartridge. The cartridge was washed with water, and retained substances were eluted with 50% methanol. The eluate was evaporated to dryness under reduced pressure. The residue was dissolved in water and determined by HPLC. Recoveries of avoparcin spiked in chicken muscle were 73.1-88.1% at levels of 2-10 micrograms/g. The detection limits were 0.5 microgram/g (UV) and 0.2 microgram/g (AMD).     

Aging behavior and surge endurance of 870-900 nm AlGaAs lasers with nonabsorbing mirrors

The reliability of 870-900 nm AlGaAs TJS lasers has been investigated. An emission wavelength longer than 870 nm is realized by utilizing the band tailing effect due to heavy Zn-diffusion in the active region. A nonabsorbing mirror structure is employed to eliminate both gradual degradation and catastrophic damage of the facets. Stable continuous operation for over 10 000 hours has been confirmed at ambient temperatures higher than 50°C and output powers more than 5 mW/ facet. MTTF longer than 10⁵hours is expected for screened devices. Surge endurance has been improved to be nearly one order of magnitude higher than that for a conventional structure.     

Resonator filters using shear horizontal-type leaky surface acoustic wave consisting of heavy-metal electrode and quartz substrate

The authors have succeeded in exciting a new type of leaky surface acoustic wave (LSAW) having only a shear horizontal (SH) component that has a large electromechanical coupling factor, a large reflection coefficient, and excellent temperature stability, by combining interdigital transducers (IDTs) and reflectors made of heavy-metal films such as gold (Au), tantalum (Ta), and tungsten (W) on the ST-cut 90/spl deg/ X propagation (direction perpendicular to the X-axis) quartz substrate. This LSAW does not have a propagation decay. The square of the electromechanical coupling factor is 2.1-2.7 times larger than, the reflection coefficient is 30 times larger than, and the temperature characteristic is the same as those of a Rayleigh wave on an ST-cut X propagation quartz substrate. The authors applied this SH LSAW to resonators and resonator filters. As a result, we succeeded in developing the low loss and very small-sized resonators and resonator filters (1/5-1/4 of conventional device sizes) with IDTs with a small number of finger pairs and very small reflectors, for the first time.     

An asymmetric Y-branching circuit using total reflectionfor semiconductor integrated optical circuits

A new structure for a compact optical branching circuit is proposed. An asymmetric Y-branching circuit using total reflection is fabricated on an AlGaAs/GaAs wafer. Good branching operation is observed in a single-mode branching circuit with a branching angle of 45°. The exact origins of loss in the branching circuit are also clarified     

Dislocation reduction in gaas grown on Si by MOMBE using multiple indium atomic plane structures

This paper investigates the effectiveness of multiple indium atomic planes in reducing the dislocation density in GaAs epitaxial layers grown by metalorganic molecular beam epitaxy on GaAs-coated Si substrates prepared by metalorganic chemical vapor deposition.In situ reflection high-energy electron diffraction patterns show that, during the growth of multiple indium atomic-plane structures, two-dimensional growth takes place. Cross-sectional transmission electron microscope observation shows that InAs sublayers are commensurate; hence the critical thickness of the InAs layer in this structure is more than one-monolayer. Cathodoluminescence examination indicates that the defect density decreases as the number (<60) of indium atomic planes increases. This new structure is more effective in dislocation reduction than conventional In_0.1Ga_0.9As/GaAs strained-layer superlattices.     

Extra-axial ependymoma--case report

A 13-year-old boy presented with a very unusual ependymoma extending extra-axially. Computed tomography demonstrated a tumor with a cyst and calcification adjacent to the dura and extending over the right occipital and parietal lobes. The cyst wall and solid tumor were enhanced postcontrast. Magnetic resonance imaging revealed that the solid tumor was isointense on T1-weighted images and a mixed iso- and high-intensity on T2-weighted images. The solid tumor and tissue surrounding the cyst were enhanced markedly by gadolinium-diethylenetriaminepentaacetic acid. Sagittal and coronal images demonstrated a multilocular tumor shadow. Cerebral angiography demonstrated a tumor fed by a posterior branch of the right middle meningeal artery but no feeders from the internal carotid and vertebral arteries. The tumor was removed en bloc. The histological diagnosis was clear cell-type ependymoma.