Preparation and photoconduction of rapidly quenched films in the Bi2O3-TiO2 system

The rapidly quenched films in the Bi₂O₃-TiO₂ system (0 to 60% TiO₂) were prepared using a twin-roller type apparatus. The films precipitated Bi₂O₃ solid solutions of different types in the composition ranges, with TiO₂ contents of 0 to 5, 7.5 to 10 and 12.5 to 40%, respectively. The first solid solution had a tetragonal structure of -form. The second, though also crystallized in the tetragonal structure, adopted a disordered modification of the -form. The third solid solution was -form (defect fluorite structure). The formation of amorphous phase commenced in the composition with 30% TiO₂, and the films became completely amorphous beyond 50% TiO₂. The quenched films showed a certain instability to decompose or transform into the different phase assemblage by annealing at higher temperatures (about 400 to 500° C, except 260° C for the pure Bi₂O₃ film). The quenched films were also characterized by a high photoconductivity. The photoconduction mechanism was suggested to be associated with a structural imperfection of Bi₂O₃ accompanied by a certain amount of pentavalent bismuth ion.     

Reduction of second- and third-order harmonic distortion bynonlinear absorption in gain-coupled distributed-feedback laser diodes

We have calculated the characteristics of second- and third-order harmonic distortion in gain-coupled distributed feedback (DFB) lasers using a set of three rate equations. In these calculations, the relaxation oscillation, nonlinear gain compression, and nonlinear loss compression are taken into account. We have found that modulation distortion due to nonlinear gain compression is reduced significantly in the gain-coupled DFB laser of absorptive-grating type. This improvement occurs because gain compression is compensated by loss compression within the grating     

Improvement in thermal stability of B-C-N thin films fabricated by magnetron sputtering using graphite and BN co-target

Thermal stability of amorphous boron-carbon-nitride (B-C-N) films fabricated by magnetron sputtering using a graphite and BN co-target was studied by X-ray photoelectron spectroscopy, infrared absorption spectroscopy, Raman spectroscopy and scanning electron microscopy. The boron-rich B-C-N films showed the higher thermal stability. These results suggest that an incorporation of B atoms into the amorphous CN networks improves the thermal stability. This improvement can be explained in terms of the creation of boron-nitrogen bonds and/or boron-carbon bonds.     

Laterally coupled strained MQW ridge waveguide distributed-feedbacklaser diode fabricated by wet-dry hybrid etching process

The fabrication and the characteristics of the laterally coupled GaInAsP-InP quantum-well ridge waveguide distributed-feedback (DFB) lasers are presented. The electron beam (EB) lithography and the wet and dry hybrid etching technique have been used to fabricate the deep grating structures for the DFB lasers on and beside the sidewalls of the narrow ridge waveguide. The threshold current was 18.5 mA at 20°C, and the sidemode suppression ratios (SMSRs) were ensured to be more than 40 dB for as-cleaved devices with various cavity lengths. The continuous-wave output powers of over 15 mW/facet have been observed, while transverse and longitudinal modes have remained in single mode at this output level     

Demonstration of an Optical Isolator with a Semiconductor Guiding Layer that was Obtained by Use of a Nonreciprocal Phase Shift

We present the experimental study of an optical isolator with a semiconductor guiding layer that was obtained by use of a nonreciprocal phase shift. The isolator is equipped with an optical interferometer composed of tapered couplers, nonreciprocal phase shifters, and a reciprocal phase shifter. The nonreciprocal phase shifter was constructed by wafer direct bonding between the semiconductor guiding layer and the magneto-optic cladding layer. The isolator, designed for the 1.55-mum wavelength, was fabricated to investigate the characteristics of each component. By applying an external magnetic field to the nonreciprocal phase shifter, we achieved an isolation ratio of approximately 4.9 dB in the interferometric isolator.     

Strong promoting activity of phenylethyl isothiocyanate and benzyl isothiocyanate on urinary bladder carcinogenesis in F344 male rats

Post-initiation effects of phenylethyl isothiocyanate (PEITC) and benzyl isothiocyanate (BITC) on hepatocarcinogenesis and urinary bladder carcinogenesis were examined in rats pretreated with diethylnitrosamine (DEN) and N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN). Groups of 21 rats received a single intraperitoneal injection of 200 mg/kg body weight of DEN. Starting 2 days thereafter, they were administered 0.05% BBN in the drinking water for 4 weeks. Three days after completion of the carcinogen treatment, they were placed on a diet containing PEITC or BITC at a dose of 0.1%, or a basal diet alone for 32 weeks and then killed for autopsy. Further groups of 6 rats each were similarly treated with PEITC, BITC or basal diet alone for 32 weeks without prior DEN and BBN exposure. In the liver, although the incidences of liver tumors were not significantly affected, the multiplicity of foci larger than 0.5 cm in diameter was slightly increased by PEITC. In the urinary bladder, the incidences of papillary or nodular (PN) hyperplasias and carcinomas were significantly elevated by PEITC or BITC after DEN and BBN initiation. In the groups without initiation, PN hyperplasia was found in all rats of both PEITC and BITC groups, along with papillomas and carcinomas in some animals. Tumors and PN hyperplasias in the groups treated with PEITC and BITC are characterized by downward growth. Our results thus showed PEITC and BITC to be strong promoters of urinary bladder carcinogenesis with some complete carcinogenic potential.     

Rice grain quality: A comparison of imported varieties,local varieties with new varieties adopted in Benin

This study was carried out in the grain quality laboratory of the Africa Rice Center in Benin to determine the physicochemical and cooking characteristics of some rice varieties consumed in Benin where is widely cultivated and consumed as a staple. The physicochemical properties of fifteen rice varieties, five imported, five previously cultivated in Benin and five upland varieties, newly developed by the Africa Rice Center were compared. Protein content ranged from 6.4 to 7.7% among the imported and previously cultivated varieties and from 10.6 to 10.8% among the newly developed varieties by the Africa Rice Center. The gel consistencies of the previously cultivated ranged from 6.0 to 71.3 mm with the exception of ADNY 11 which had a gel consistency of 100 mm while the imported and newly developed varieties had gel consistencies ranging from 95 to 100 mm. The cooking times differed among varieties. Two previously cultivated varieties – ADNY 11 and TOX LONG – had cooking times of less than 20 min while a newly developed variety, NERICA 1 had the longest cooking time of 26 min. It is suggested that greater attention be subsequently paid to grain quality characteristics in African rice breeding programs in order to meet consumer preferences on the continent.     

Selective oxidation for enhancement of magneto-optic effect inoptical isolator with semiconductor guiding layer

Selective oxidation of an AlInAs layer grown on an InP substrate is studied with a view to enhancing the magneto-optic effect in an optical isolator with a semiconductor guiding layer. The isolator operates with a nonreciprocal phase shift in a magneto-optic waveguide. The waveguide with an AlInAs oxide cladding layer miniaturises the nonreciprocal phase shifter to several hundreds of microns