GaInP/AlGaInP index waveguide-type visible laser diodes with dry-etched mesa stripes

GaInP/AlGaInP index waveguide-type visible-light laser diodes with dry-etched mesa stripes have been fabricated by Cl/sub 2/ reactive ion beam etching for the first time. The AlGaInP cladding layer, which is normally very difficult to dry etch due to problems with Al oxidation and the low volatility of In and its reaction products, was etched smoothly with high depth accuracy. The etched mesa stripes were buried by metal organic vapour-phase epitaxy without crystal discontinuity at the regrown surface. The threshold current under room-temperature pulsed operation is 35 mA (L=300 mu m), which is almost the same value as that for wet-etched lasers.<>     

ARROW-B type polarization splitter with asymmetric Y-branchfabricated by a self-alignment process

We have proposed and demonstrated a polarization splitter based on an ARROW-B type waveguide. This device has an asymmetric Y-branch configuration, connecting a waveguide with a large modal birefringence to a low-birefringent waveguide which is channeled by a stripe lateral confinement structure. The device can achieve a high extinction ratio without precise mask alignment, since these two waveguides are connected by a self-alignment process. In addition, a low insertion loss is achieved because of adiabatic Y-branching. We designed this device at the wavelength of 1.55 μm and fabricated it using RF sputtering. As a result, high extinction ratios of -19.4 dB for TE mode and -19.0 dB for TM mode were achieved     

Phytotoxicity and fate of 1,1,2-trichloroethylene: a laboratory study

1,1,2-Trichloroethylene (TCE), a chlorinated organic contaminant, poses serious environmental concerns. A study was conducted to evaluate the phytotoxicity of TCE to a crop species and its fate in vermiculite. Growth bioassays were carried out using carrot (Daucus carota L.) as the test species. Three different concentrations, 0.25, 0.50, and 1 ppm were used to evaluate phytotoxicity of TCE. When added to petri plates with cotton pads, TCE did not have any effect on carrot seedling growth. However, when added to vermiculite, it significantly suppressed growth. Shoot growth was inhibited only at the 1 ppm concentration. Recovery experiments were carried out to study the fate of TCE in vermiculite. A significant decline in the percent recovery was observed with time. Interestingly, TCE additional peaks (unknown organic molecules) were detected with declining concentrations. The available chloride ion concentration in vermiculite containing 1 ppm of TCE for 24 hr was significantly higher compared to control.     

Fabrication of subwavelength structure for improvement in light-extraction efficiency of light-emitting devices using a self-assembled pattern of block copolymer

A new fabrication method to improve the optical extraction efficiency of light-emitting devices is presented. The morphology of a self-assembled block copolymer was transferred to the surface of a compound semiconductor to achieve a subwavelength columnar structure. The optical extraction efficiency of the substrates with subwavelength columnar structures of 350 nm pillar height, 130 nm diameter, and 180 nm pitch, improved 2.2 times compared to unprocessed substrates. This method does not require expensive exposure lithography tools and is therefore suitable for conventional semiconductor processes.     

Small-angle X-ray scattering from heparin in solution

Summary X-ray small-angle scattering fron heparin in solution was measured, and compared with theoretical curves based on various nolecular models. Good agreement was obtained for the model consisting of -D-glcosamine in the ⁴C₁ conformation and -L-iduronate in the ¹C₄ conformation. It was suggested that the helical conformation is maintained even in solution, at least in part. The helix pitch was estimated to be 0.75–0.85 nm.     

Experimental analysis of lightning overvoltages induced on low-voltage distribution lines

Problems have often been caused in low-voltage distribution lines such as single-phase 100/200 V and three-phase 200-V systems. For instance, the burning of low-voltage devices and the unnecessary operation of ground fault interrupters have occurred, which are caused possibly by lightning overvoltages. Experimental analysis was performed on the generation modes of lightning overvoltages on low-voltage distribution lines. A scale model line, one-fourth the size of an actual power distribution line of Tokyo Electric Power Company (TEPCO), was installed for experimental analysis on the lightning protection of an overhead ground wire, an overhead common grounding wire (system neutral conductor), surge arresters and pole transformers against the overvoltages induced on low-voltage distribution lines due to a nearby lightning stroke. A balloon was flown at a location 30 km away from the scale model line in a normal direction to it. A 200-m long wire is suspended from the balloon to simulate a lightning path. Pulse current is applied to the simulated path using a pulse generator and the voltages induced on the line conductors are measured. This paper analyzes those overvoltages by means of the experimental and the theoretical methods.     

Cultural variations in optimistic and pessimistic bias: Do Easterners really expect the worst and Westerners really expect the best when predicting future life events?

The authors compared levels of optimistic and pessimistic bias in the prediction of positive and negative life events between European Americans and Japanese. Study 1 showed that European Americans compared with Japanese were more likely to predict positive events to occur to self than to others. The opposite pattern emerged in the prediction of negative events. Study 2 replicated these cultural differences. Furthermore, positive associations emerged between predictions and occurrence of life events 2 months later for both European Americans and Japanese. Across both studies, results of within-groups analyses indicated that both groups expected negative events to be more likely to occur to others than to self (optimistic bias). In addition, Japanese expected positive events to be more likely to occur to others than to self (pessimistic bias). However, European Americans failed to show the expected optimistic bias for positive events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

STM probe-assisted site-control of self-organized InAs quantum dots on GaAs surfaces

A site-control technique for individual InAs quantum dots (QDs) has been developed by using scanning tunneling microscope (STM) probe-assisted nanolithography and self-organizing molecular-beam epitaxy. We find that nano-scale deposits can be created on a GaAs surface by applying voltage and current pulses between the surface and a tungsten tip of the STM, and that they act as “nano-masks” on which GaAs does not grow directly. Accordingly, subsequent thin GaAs growth produces GaAs nano-holes above the deposits. When InAs is supplied on this surface, QDs are self-organized at the hole sites, while hardly any undesirable Stranski-Krastanov QDs are formed in the flat surface region. Using this technique with nanometer precision, a QD pair with 45-nm pitch is successfully fabricated. An erratum to this article is available at .     

Migration of surrogate contaminants in paper and paperboard into water through polyethylene coating layer

The migration of five surrogate contaminants, anthracene, benzophenone, dimethyl phthalate, methyl stearate and pentachlorophenol, from paper and paperboard into water through a polyethylene (PE) coating layer was investigated. Virgin paper and paperboard coated with PE films of 0.012 and 0.030mm thickness were spiked evenly with standard 1-ml solutions containing 5mg of each surrogate. The spiked papers were placed in contact with the PE coating layer at 10 and 24 °C for 21 days. The resulting surrogate migration through the PE layer into 100ml water was measured by an analytical method developed here that used gas chromatography equipped with a flame ionization detector. Non-polar surrogates of anthracene and methyl stearate did not show any significant migration. In the case of the thin layer coating of 0.012mm, polar water-soluble contaminants of benzophenone, dimethyl phthalate and pentachlorophenol showed an equilibrated or maximized migration after 1 day, even at a refrigerated temperature of 10 °C. A thick PE coating of 0.030mm thickness delayed the progress of contaminant migration, which was also slower at lower temperature. Our results indicate that polyethylene coatings should not be seen as a complete barrier against possible contaminants in paper packaging materials under chilled or ambient conditions. Several variables such as coating thickness, temperature and suspected contaminants need to be considered to control the possible contamination risk from recycled or printed paper.     

Paralytic shellfish poison (PSP) profiles and toxification of short-necked clams fed with the toxic dinoflagellate Alexandrium tamarense

As a part of our studies on paralytic shellfish poison (PSP) accumulation kinetics in bivalves, short-necked clam Tapes japonia was experimentally contaminated with PSP by being fed with the toxic dinoflagellate Alexandrium tamarense for 2, 4, 6, 8 and 10 days, and the processes of PSP accumulation and bioconversion were investigated: the toxicity level was determined by mouse bioassay and toxin components were identified by high-performance liquid chromatography (HPLC). The strain of A. tamarense used in this study possessed a specific toxicity of 186.7 +/- 81 (mean +/- S.D., n = 5) x 10(-6) MU/cell. Total toxin concentration of this strain was 140.4 +/- 61 (mean S.D., n = 5) fmol/cell. The toxicity level of short-necked clams increased almost in parallel with the abundance of A. tamarense, reaching 1.8, 3.2, 3.8, 3.5 and 4.6 MU/g meat for 2, 4, 6, 8 and 10 days of feeding, respectively. The accumulation rates of PSP toxins, which are the ratio of the total amount of toxins accumulated in the bivalves to the estimated intake in each feeding experiment, were 7.5, 8.1, 5.7, 4.2 and 4.4% for 2, 4, 6, 8 and 10 days, respectively. At the end of each exposure period, many undigested algal cells were found in pseudofeces under microscopic observation. There was a remarkable difference in the relative proportions of the predominant toxin components between A. tamarense and short-necked clams. The most notable difference was the change in the relative amounts of C2 (carbamoyl-N-sulfo-11beta-hydroxysaxitoxin sulfate), GTX1 and GTX 4 during the first two days. In the toxic bivalves, the amount of C2, which is dominant in A. tamarense, decreased to below half a percent after being ingested. Subsequently, the amount of GTX1 in the shellfish meat reached 50.1 mol%, while that of GTX4 decreased to about half of that in A. tamarense. As for the configuration of 11-hydroxysulfate, PSP components in A. tamarense exist almost exclusively as beta-epimers (GTX3, GTX4, C2 and C4), accounting for 72.8 mol% of the total. This contrasts with the case of the short-necked clams, where the beta-epimers represented 25.8, 33.8, 30.8, 36.8 and 28.5 mol% of the total after 2, 4, 6, 8 and 10 days, respectively. PSP components seemed to be converted rapidly at an early stage of the feeding of A. tamarense.