Electric-field control of electron–hole wave functions in a wide quantum well

The electric field dependence of the electron/hole wave function and the radiation energy of an exciton in a Be-δ-doped 80 nm quantum well (QW) is studied experimentally and compared it with variational calculation. The photoluminescence (PL) spectra show Stark shifts depending on the gate electric field and PL intensity of the exciton of the first excited state has a dip in the electric-field dependence which reflects the node of the electron wave function.     

Measurement of Stress Intensity Factors of a Mixed-Mode Interface Crack by a Speckle Photography

The image-processing system based on a two-dimensional Fourier transform is presented for the analysis of Young’s fringes pattern created from a double-exposure speckle photograph. The fringe spacing and orientation are determined using only one Young’s fringes pattern without any other diffraction halo patterns. The stress-intensity factors of a mixed-mode interface crack were measured by speckle photography. A compact normal and shear specimen with an interface crack was employed. This specimen enables us to carry out the experiment under various kinds of mixed-mode loading. A steel and an epoxy resin were used as dissimilar materials. The displacement along the crack lines at the free surface was measured by speckle photography. The K₁ and K₁₁ values were determined by a least squares method using displacement data along the crack lines. Three-dimensional finite element analysis was carried out on the same specimen. An accuracy of stress intensity factors obtained by the speckle photography was discussed by comparison of results obtained by the finite element analysis.Presented at 1996 International Workshop on Interferometry (IWI ‘96), August 27–29, Saitama, Japan.     

Microphase separation and ion‐conduction mechanisms in polypropylene oxide/lithium perchlorate (LiClO4) complexes

Broadband dielectric spectroscopy was used to examine ion‐conduction mechanisms in polypropylene oxide (PPO) with a molecular weight of 4000 complexed with LiClO₄. Two distinct conduction mechanisms were proposed with respect to high and low salt concentration regions. In a concentrated regime (Li/O >10%), the segmental motion of PPO molecules is significantly slowed down by enhanced cation coordination that results in a marked decrease in molar conductivity. We found a linear relationship between the ionic diffusion coefficient and the relaxation frequency of slowed segmental motion over broad temperature and salt‐concentration ranges. The use of a random walk scheme revealed that ions hop around at the same rate as slowed segmental motion for a monomer length. In a dilute regime (Li/O <0.1%), ions are temporarily localized in a limited domain. The direct current conductivity is achieved by structural renewal that releases ions from such localization and provides a diffusional character. At intermediate salt concentrations, microphase separation into ion‐depleted and ion‐rich regions was evidenced by the coexistence of fast and slow segmental processes. The molar conductivity revealed a maximum at Li/O = 3%. Its decrease at higher salt concentrations was attributed to the slowing down of segmental motion, and that at lower salt concentrations was attributed to localization of ionic motion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 613–622, 2002; DOI 10.1002/polb.10123     

Molecular motion and 1H NMR relaxation of aqueous poly(N-isopropylacrylamide) solution under high pressure

In order to obtain useful information about the molecular motion and structure of poly(N-isopropylacrylamide) (PNiPAM) in aqueous solution, proton spin-lattice relaxation times, proton spin-spin relaxation times, and volume changes were measured at pressures from 1 to 400 kg/cm² as a function of temperature. We found that the molecular motion and the structure of water and PNiPAM in PNiPAM/water solution transitionally change at gelation temperature (31°C). The effect of pressure on such transitional changes is studied. It is suggested that application of pressure to the system prevents the gelation.     

Synthesis of heterocyclic bioregulators and semiochemicals

Chemistry and biology of oxygen heterocycles as insect pheromones are reviewed referring to exo-brevicomin, disparlure, japonilure and olean. Synthesis of koninginin A, a microbial metabolite, is discussed. Two azetidine alkaloids, penaresidin A and penazetidine A, were synthesized.     

Synthesis and properties of new chiral dopants containing a δ-lactone ring for practical ferroelectric liquid crystal mixtures

A series of new optically active δ-lactones were synthesized as chiral dopants for ferroelectric liquid crystals (FLCs). The response time of an FLC mixture containing 4 mol% (S)-2,2-dimethyl-5-[2-fluoro-4-(5-n-octylpyrimidin-2-yl)-phenoxy[methyl-δ-valerolactone was 25 μs at 25°C. (0-90 per cent change in light transmission, 10 V μm^-1). The synthesis and properties of these materials as practical chiral dopants are reported.