AlGaAs-GaAs buried heterostructure laser with vertically etched facets and wide-bandgap optical windows by in situ C/sub 2/H/sub 5/Cl gas-phase etching and MOCVD regrowth

Vertical facets and oblique sidewalls are realized in AlGaAs-GaAs graded index separate confinement (GRINSCH) structure along the [01~1] and [01~1~] direction, respectively, with C/sub 2/H/sub 5/Cl gas-phase etching under a SiO/sub 2/ stripe mask. They are immediately embedded with consecutive MOCVD regrowth all around the active layer, to form optical windows and BH-type waveguide at the same time. This in situ process is very effective to reduce the fabrication cost of a semiconductor laser by combining the three processing steps of waveguide definition, facet formation, and facet coating into one consecutive gas manipulation in the same growth furnace.     

Atomically flat diamond (111) surface formation by homoepitaxial lateral growth

A process of homoepitaxial growth of diamond (111) films by microwave plasma-enhanced chemical vapor deposition has been investigated characterizing areas by ex-situ atomic force microscopy. The evolution of surface morphology during a lateral growth of (111) diamond was visualized utilizing a mesa structure as a marker. Lateral growth forms atomically flat surfaces, which show atomically flat terraces over several hundred nm widths and single bilayer steps of (111) diamond.     

Relationship between dipole parameter estimation errors andmeasurement conditions in magnetoencephalography

In this study, a model in a computer simulation uses a single current dipole in a spherical homogeneous medium. Dipole parameters are estimated using a moving dipole procedure. Signal-to-noise ratio (SNR) is defined as the square-root of the ratio of the average signal power to the average noise power over all measurement points. At SNR>20, accurate estimation can be carried out independently of dipole depth and coil size. At SNR<20, dipole depth influences estimation error. When the dipole is located near the center of the sphere, the measurement region should include both extrema of the magnetic field to minimize estimation error. However, when the dipole is not so deep, the position of the measurement region does not influence estimation error. When SNR<4, estimation error increases as coil size increases. Coil size minimizing estimation error is determined by the ratio of environmental magnetic field noise to electrical noise. For a constant size of measurement region, increasing the number of measurement points decreases estimation error to a certain level. This error level depends on SNR     

High concentration of L-arginine suppresses nitric oxide synthase activity and produces reactive oxygen species in NB9 human neuroblastoma cells

Hereditary argininemia manifests as neurological disturbance and mental retardation, features not observed in other amino acidemias. The cytotoxic effect of a high concentration of L-arginine (L-Arg) was investigated using NB9 human neuroblastoma cells (NB9), which express neuronal nitric oxide synthase (nNOS). When the concentration of L-Arg in the medium increased from 50 microM to 2 mM after incubation for 48 hr, the intracellular concentration of L-Arg increased from 68.0 +/- 1 pmol/10(6) cells to 1310.0 +/- 5 pmol/10(6) cells and that of L-citrulline (L-Cit) from undetectable levels to 47.1 +/- 0.2 pmol/10(6) cells (mean +/- SD of three independent analyses). This increase in intracellular L-Arg levels caused a decrease in NOS activity by approximately 71%. Flow cytometric analysis showed that reactive oxygen species (ROS) are produced in NB9 exposed to 2 mM L-Arg. The production of ROS was abolished by a NOS inhibitor, NG-nitro-L arginine-methylester. Production of ROS was also observed when NB9 were treated with L-Cit for 48 hr. To investigate the effect of L-Cit on the activity of NOS, a kinetic study on nNOS was conducted using cellular extracts from NB9. The apparent Km value of nNOS for L-Arg was 8.4 microM, with a Vmax value of 8.2 pmol/min/mg protein. L-Cit competitively inhibited NOS activity, as indicated by an apparent Ki value of 65 nM. These results suggest that L-Cit formed by nNOS in L-Arg-loaded neuronal cells inhibits NOS activity and nNOS in these L-Arg-loaded cells functions as a NADPH oxidase to produce ROS, which may cause neurotoxicity in argininemia.     

Clinical usefulness of 3-D CT endoscopic imaging of cerebral aneurysms

Chronic granulomatous disease (CGD) of childhood is a rare inherited disease in which phagocytic cells fail to produce the normal respiratory burst in response to infectious stimuli, leaving the patient particularly susceptible to infections with bacteria and fungi that produce catalase. Between 1988 and 1993 at the NIH, 58 pulmonary cytology specimens were obtained on 24 CGD patients. The number of specimens per patient ranged from one to 13 with an average 2.4. The 58 specimens included: 33 bronchoalveolar lavages; one bronchial brushing; 20 lung or pleural mass fine-needle aspirates; three pleural fluids, and one sputum. Two lung aspirates with insufficient material, five bronchoalveolar lavages performed post-treatment to confirm clinical resolution of disease, and two bronchoalveolar lavages not submitted for culture were excluded from further analysis. Of the 49 remaining specimens obtained from patients clinically suspected of having a pulmonary infection, cytology demonstrated a pathogenic organism in nine (18%). Microbiologic cultures were positive in 19/49 (39%). Cytology identified fungus in 8/13 (62%) of documented fungal infections, including four cases where microbiology was negative. Bacterial and mixed bacterial/fungal infections were usually not detected by cytology even with appropriate strains. No organisms were identified by cytology in the four cases of nocardia or the three cases of pseudomonas infection. The combination of cytology and microbiology provided the greatest diagnostic sensitivity, yielding a diagnosis in 22/49 cases (45%). Of the 27 cases with negative cytology and microbiology, an infectious agent was identified in eight upon submission of additional material: three cytology specimens and five tissue specimens. In the remaining 19 cases, no organisms were identified, however, the patients were treated presumptively. Characteristic pathologic features of granulomatous inflammation, necrosis, and giant cells were present in fine-needle aspirates, often when on organisms could be identified, but were not seen in other types of respiratory specimens.     

Determination of power reflectivity of quasi-graded distributedBragg reflectors using stopband width

The authors examine the reflectivity of the quasi-graded distributed Bragg reflector using the stopband width. The stopband width of about 1000 Å for a reflectivity of about 99% is able to be measured with an accuracy of ± 1 Å. Thus, the reflectivity is determined with high accuracy from the stopband width. It is found that the quasi-graded distributed Bragg reflector is a high-quality reflector with high reflectivity and low resistance     

Development of InxGa1−xAs-based ohmic contacts for p-type GaAs by radio-frequency sputtering

In_xGa_1−xAs-based ohmic contacts which showed excellent contact properties for n-GaAs were demonstrated to be applicable to p-GaAs ohmic contacts. These contacts, prepared by radio-frequency sputtering, provided low contact resistance (0.2 Ω-mm), excellent thermal stability, smooth surface, and good reproducibility. The contact resistances had a weak dependence on the annealing temperatures, which was desirable in a manufacturing view point. This weak temperature dependence was explained to be due to a unique Schottky barrier height at the metal/p-In_xGa_1−xAs interface which does not depend on the In concentration in the In_xGa_1−xAs layer. The present experiment showed the possibility of simultaneous preparation of ohmic contacts for both n and p-GaAs using the same contact materials.