Poly(2,7-di-n-pentyldibenzofulvene) showing chiroptical properties in the solid state based purely on a chiral conformation

Poly(2,7-di-n-pentyldibenzofulvene)s with no stereocenters, obtained by anionic polymerization using chiral 9-fluorenyllithium ligand complexes, showed intense circular dichroism in film form due purely to the chiral conformation of the main chain, while no chiroptical properties were detectable in solution.     

Wavefront Curvature Sensing Based on Diffraction Grating and Fractional Fourier Transforms

We propose a new concept for wavefront curvature sensing, which is based on diffraction grating and fractional Fourier transforms systems. An explicit formula is derived expressing the wavefront curvature, and the wavefront shape can also be retrieved rapidly. The experimental setup is presented and numerical simulations show the validity of the proposed method.     

Measurement of frequency noise spectra of frequency-stabilized LD-pumped Nd:YAG laser by using a cavity with separately suspended mirrors

We have developed a frequency stability system for a commercial LD-pumped Nd:YAG laser in a nonplanar ring oscillator geometry (MISER) which is used for our 20-m prototype gravitational wave detector. The frequency of the laser is locked to the rigid cavity resonance frequency, and the relative frequency noise is suppressed down to 3 × 10⁻⁴ Hz/Hz^1/2 the shot-noise limited level at below 1 kHz. We are successful in evaluating the frequency noise level more accurately by means of a separately suspended reirror type cavity (4-m mode-cleaner); the noise level is 2 × 10⁻² Hz/Hz^1/2. As compared to a frequency noise spectrum which is locked to separately suspended mirror type cavities, the frequency noise is lower at a frequency below 400 Hz.     

Design parameters influencing non-uniform current distributions in superconducting multi-stage stranded cables

We have suggested that non-uniform currents occur due to certain design parameters, for example a combination of cabling pitches, in a previous study. In the present study, we evaluate the occurrences of non-uniform current distributions in terms of design parameters, i.e., the combination of cabling pitches, winding methods (solenoidal and pancake winding) and cross-sectional shape of the cable by numerical analyses. Finally, some basic design concepts to solve this problem are proposed.     

A new route to 1,2,4- triazoles and 1,3,4- thiadiazoles from 1-acylbithiourea

The intramolecular cyclization of 1- acylbithiourea 1 gave 1,2,4-triazole 2 and 1,3,4-thiadiazole 3 . The reaction of 1 with p-toluenesulfonyl chloride in the presence of trithylamine afforded 3 . Treatment of 1 with methyl iodide in the absence of any base yielded 2-methylthio-1,3,4-thiadiazole 10 and 2-imino- 1,3,4-thiadiazoline 12 .     

Cold crystallization of polytetrafluoroethylene by γ irradiation

Changes in density and in the corresponding degree of crystallinity with radiation dose are studied experimentally for γ-irradiated polytetrafluoroethylene (PTFE) in the dose range from 1 X 10³ to 1 X 10⁹ R. The relation between the amorphous fraction and the radiation dose is derived from a quantitative analysis of cold crystallization by scission of polymer backbone chains. The characteristic radiation dose, at which one break occurs on the average per initial molecule, is estimated as about 3 X 10⁴ R on the basis of a derived kinetic equation. The theoretical relation is modified by considering microvoids produced in the irradiated samples. The radii of microvoids in the form of spheres are evaluated as about 0.2 nm, and are also related to cage spheres relevant to the chain scission process. Good agreement between the modified theoretical relation and experimental data is attained over the entire range of radiation dose.