Superheated emulsions as high-energy neutron dosemeters

Superheated emulsions being inexpensive, easy to fabricate, and having tissue equivalent composition make them as one of the popular neutron dosemeters. One more advantage is that they can be made insensitive to gamma rays by the choice of the sensitive liquid. It is observed that the response of commercially available bubble detector to neutron decreases above 20 MeV while its response is roughly flat in the 0.1-15 MeV region. This restricts its application as a dosemeter to high-energy neutrons. The response of bubble detector from Bubble Technology Industries, has been observed by using Pb-breeder for high-energy neutrons from different facilities in Japan. It is observed that 2-3 cm Pb-breeder is effective in increasing the response of the detector to the nominal value. Theoretical calculation using MCNPX code indicates an increase in neutrons in the energy range of 0.1-10 MeV with Pb-breeder. The present work indicates the possibility of using the bubble detector as a dosemeter to high-energy neutron using a Pb-breeder of proper thickness.     

Ferroelectricity near room temperature in co-crystals of nonpolar organic molecules

The research on ferroelectric materials-mostly inorganic compounds or organic polymers-is increasingly motivated by both basic scientific concerns and the potential for practical applications in electronics and optics. Ferroelectricity in organic solids would be important for the development of all-organic electronic and photonic devices. The conventional approach to making organic ferroelectrics is based on the use of polar molecules. Here we report that through supramolecular assembly of nonpolar conjugated molecules, a remarkable ferroelectric response can be obtained in co-crystals of low-molecular-weight organic compounds. Co-crystals of phenazine and chloranilic acid reveal large spontaneous polarization and sizable room-temperature dielectric constants exceeding 100. The present findings provide an approach to making potentially useful organic ferroelectric materials.     

Integrated AlGaAs two-beam LD-PD array fabricated by reactive ion beam etching

Monolitically integrated AlGaAs two-beam laser diode (LD)- photodiode (PD) arrays are described. LDs and PDs have etched facets fabricated by reactive ion beam etching (RIBE). LDs in the array exhibit threshold currents as low as 18 mA and external quantum efficiencies of more than 30% per facet. A PD can detect more than 20% of a light beam emitted from an LD facing it. Crosstalk between the two LD-PD columns (separated by 50 ?m), on the other hand, is suppressed to less than ?20 dB by an AlGaAs optical barrier (5 ?m thick) fabricated between them.     

Application of the limulus amebocyte lysate test to measurement of endotoxin in therapeutic human plasma protein fraction. Comparison with the rabbit pyrogen test]

We applied the limulus amebocyte lysate (LAL) test to the detection of bacterial endotoxins in therapeutic human plasma protein fraction (PPF) and compared the LAL-test with the rabbit pyrogen test. Two endotoxin-specific LAL-reagents were used for the colorimetric method and turbidimetric kinetic method. The amounts of added endotoxin to the PPF were correctly estimated by either method. The results of four independent assays for the 53 samples of PPF corresponded well with each other (correlation coefficient: 0.851-0.959, regression coefficient: 0.898-1.151). The amounts of endotoxin in the PPF estimated by the LAL-test significantly correlated with the rise of body temperature in rabbits (correlation coefficient: 0.547-0.642, and 0.911-0.934 for the endotoxin added samples). These results suggest that the LAL-test could be used as an alternative method for the rabbit pyrogen test to PPF.     

Liquid-crystal luminaire consisting of an optical shutter and a metal halide lamp

We made a liquid-crystal (LC) luminaire for the first time to our knowledge by combining a metal halide lamp and an optical shutter composed of a compound of a very high nematic-isotropic point (172 degrees C) LC and a polymer (CLCP). The shutter can modulate high-power light independently of the state of polarization because the CLCP film becomes transparent or opalescent when either sufficiently high or no voltage is applied to it. To solve the problem, which is peculiar to CLCP films, that the color temperature of light modulated by the film changes with the film's transmittance, a pulse-width modulation method that varies the time ratio of the on and off states of the shutter was developed. The performance characteristics of the luminaire were as follows: illuminance range, 192 to 10,400 lx at a distance of 5 m from the luminaire; rise and decay times, 1.4 and 1.5 ms; color temperature, 4060-5600 K; operation room temperature, ~150 degrees C; stable operation time, more than 2000 h. Experimental results show the feasibility of applications of this luminaire in various fields, including television, movie, and stage lighting.     

Construction of an 800-kb contig in the near-centromeric region of the rice blast resistance gene Pi-ta2 using a highly representative rice BAC library

We constructed a rice Bacterial Artificial Chromosome (BAC) library from green leaf protoplasts of the cultivar Shimokita harboring the rice blast resistance gene Pi-ta. The average insert size of 155 kb and the library size of seven genome equivalents make it one of the most comprehensive BAC libraries available, and larger than many plant YAC libraries. The library clones were plated on seven high density membranes of microplate size, enabling efficient colony identification in colony hybridization experiments. Seven percent of clones carried chloroplast DNA. By probing with markers close to the blast resistance genes Pi-ta2(closely linked to Pi-ta) and Pi-b, respectively located in the centromeric region of chromosome 12 and near the telomeric end of chromosome 2, on average 2.2 +/- 1.3 and 8.0 +/- 2.6 BAC clones/marker were isolated. Differences in chromosomal structures may contribute to this wide variation in yield. A contig of about 800 kb, consisting of 19 clones, was constructed in the Pi-ta2 region. This region had a high frequency of repetitive sequences. To circumvent this difficulty, we devised a "two-step walking" method. The contig spanned a 300 kb region between markers located at 0 cM and 0.3 cM from Pi-ta. The ratio of physical to genetic distances (> 1,000 kb/cM) was more than three times larger than the average of rice (300 kb/cM). The low recombination rate and high frequency of repetitive sequences may also be related to the near centromeric character of this region. Fluorescent in situ hybridization (FISH) with a BAC clone from the Pi-b region yielded very clear signals on the long arm of chromosome 2, while a clone from the Pi-ta2 region showed various cross-hybridizing signals near the centromeric regions of all chromosomes.     

Speech Structure and Its Application to Robust Speech Processing

Speech communication consists of three steps: production, transmission, and hearing. Every step inevitably involves acoustic distortions due to gender differences, age, microphone- and room-related factors, and so on. In spite of these variations, listeners can extract linguistic information from speech as easily as if the communications had not been affected by variations at all. One may hypothesize that listeners modify their internal acoustic models whenever extralinguistic factors change. Another possibility is that the linguistic information in speech can be represented separately from the extralinguistic factors. In this study, being inspired by studies of humans and animals, a novel solution to the problem of intrinsic variations is proposed. Speech structures invariant to these variations are derived as transform-invariant features and their linguistic validity is discussed. Their high robustness is demonstrated by applying the speech structures to automatic speech recognition and pronunciation proficiency estimation. This paper also describes the immaturity of the current implementation and application of speech structures.     

In situ mask designed for selective growth of InAs quantum dots in narrow regions developed for molecular beam epitaxy system

We have developed an in situ mask that enables the selective formation of molecular beam epitaxially grown layers in narrow regions. This mask can be fitted to a sample holder and removed in an ultrahigh-vacuum environment; thus, device structures can be fabricated without exposing the sample surfaces to air. Moreover, this mask enables the observation of reflection high-energy electron diffraction during growth with the mask positioned on the sample holder and provides for the formation of marker layers for ensuring alignment in the processes following the selective growth. To explore the effectiveness of the proposed in situ mask, we used it to grow quantum dot (QD) structures in narrow regions and verified the perfect selectivity of the QD growth. The grown QDs exhibited high optical quality with a photoluminescence peak at approximately 1.30 mum and a linewidth of 30 meV at room temperature. The proposed technique can be applied for the integration of microstructures into optoelectronic functional devices.     

A compact electron gun using field emitter array

A compact electron gun using field emitter array has been developed. With a simple triode configuration consisting of FEA, mid-electrode and anode electrode, the electron gun produces a parallel beam with a diameter of 0.5 mm. This electron gun is applicable for compact radiation sources such as Cherenkov free-electron lasers.