Gradient-index contact lens

A gradient-index (GRIN) contact lens (CL) is proposed to decrease spherical aberration and to increase the diopter. A plastic radial GRIN rod was successfully obtained by using the vapor-phase diffusion copolymerization technique. The resulting index distribution of the GRIN rod was almost parabolic against the distance from the center axis, and the Δn value was -0.030. The GRIN CL was prepared by grinding and polishing the rod. It is theoretically and experimentally concluded that using the radial GRIN material can significantly improve the optical properties of CL's.     

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     

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.     

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.     

H2O self-diffusion restricted by clay platelets with immobilized bound H2O layers: PGSE NMR study of water-rich saponite gels

The role of bound or less-mobile H₂O layers near negatively charged clay platelets in water-rich saponite gels as obstacles to the diffusion of unbound H₂O molecules in the pore-space was examined. Self-diffusion coefficients of H₂O molecules, D, in gels of synthetic Na-rich saponite were measured by pulsed-gradient spin-echo proton nuclear magnetic resonance (PGSE proton NMR) to evaluate these obstruction effects. The clay weight fraction, w, of the gel samples ranged from 0.0 to 27.9 wt.% and the sample temperature was 20.0 to 60.6 °C. The NMR results showed that D normalized by D₀ was independent of sample temperature and decreased with increasing w: ln(D/D₀)=1.33[exp(−0.0290w)−1] where D₀ was D in bulk water. This diffusion behavior was interpreted through random-walk computer simulations of a gel-structure model originally developed for montmorillonite, hectorite and stevensite. In the model, unbound H₂O diffuses in the porous gel structure by avoiding randomly distributed obstacles representing clay platelets sandwiched between completely immobilized bound H₂O layers. A quantitative dependence of the platelet volume fraction and the bound H₂O layers thickness on D/D₀ was obtained by the simulations. The ratio, χ=(volume of clay platelets and immobilized H₂O layers)/(volume of clay platelets), was introduced as a measure of the thickness of the immobilized H₂O layers. χ was estimated to be 5.7 for water-rich saponite gels (w≤7.99 wt.%) by fitting the results of the random-walk simulation to the PGSE NMR diffusion data. This value corresponds to an immobilized bound H₂O layer thickness of 2.4 nm assuming that each clay particle in the gels consists of a single 1-nm-thick platelet. The thickness of immobilized H₂O layers in water-rich gels of six smectite species was identified on this basis to decrease in the following order: montmorillonite (χ=18, 13)>saponite (χ=5.7)>hectorite (χ=4.2, 4.0)>stevensite (χ=3.6). This order correlates well with the order of the cation exchange capacity (CEC), suggesting that the thickness of the bound H₂O layers increases with increasing layer charge. The present study confirmed that the gel-structure model developed previously for montmorillonite, hectorite and stevensite was also applicable to saponite.     

Cutting performance of an indexable insert drill for difficult-to-cut materials under supplied oil mist

In this study, the cutting performance of an indexable insert drill with an asymmetric geometry for cutting difficult-to-cut materials was investigated. A solid twist drill with a symmetric geometry was used to compare the cutting characteristics. The cutting characteristics were evaluated using the thrust force, inner-surface roughness of the drilled hole, wear behavior, and tool temperature. Workpieces made of stainless steel, titanium alloy, and nickel-based alloy were selected as difficult-to-cut materials, and carbon steel was also selected. The tool temperature was higher in the order of carbon steel, stainless steel, titanium alloy, and nickel-based alloy for every drill under minimum quantity lubrication cutting. The influence of the workpiece material on the thrust force was different from that of the tool temperature for the indexable insert drill, whereas that of the solid twist drill was similar to the tool temperature tendency. When cutting the titanium alloy and nickel-based alloy, the tool temperature and thrust force of the indexable insert drill were lower than those of the solid-type twist drill. The inner-surface roughness of a hole drilled with the indexable insert drill had almost the same quality as that of a hole drilled with the solid-type twist drill when cutting the difficult-to-cut materials. The wear behavior of the indexable insert drill was remarkably different from that of the solid-type twist drill, and the flaking of the coating and the abrasion wear at the rake face were notable in the indexable insert drill.