Optics of nuclear diffraction with synchrotron radiation using α-57Fe2O3 single crystals

Nuclear Bragg diffraction of synchrotron radiation with -⁵⁷Fe₂O single crystals has achieved a counting rate as high as 20,000 cps at the accumulation ring AR of TRISTAN, KEK. The development of crystal optics using nuclear monochromators is described. Topographic images of -⁵⁷Fe₂0 nuclear diffraction has been observed.     

Optimum tail length of fluorinated double-tail anionic surfactant for water/supercritical CO2 microemulsion formation

The effect of surfactant tail structure on the stability of a water/supercritical CO2 microemulsion (W/scCO2 muE) was examined for various fluorinated double-tail anionic surfactants of different fluorocarbon chain lengths, F(CF2)n (n = 4, 6, 8, and 10), and oxyethylene spacer lengths, (CH2CH2O)(m/2) (m = 2 and 4). The phase behavior of the water/surfactant/CO2 systems was studied over a wide range of CO2 densities from 0.70 to 0.85 g/cm(3) (temperatures from 35 to 75 degrees C and pressures up to 500 bar) and corrected water-to-surfactant molar ratios (W0c). All of the surfactants yielded a W/scCO2 muE phase, that is, a transparent homogeneous phase with a water content larger than that permitted by the solubility of water in pure CO2. With increasing W0c, a phase transition occurred from the muE phase to a macroemulsion or a lamella-like liquid crystal phase. The maximum W0c value was obtained at a tail length of 12-14 A, indicating the presence of an optimum surfactant tail length for W/scCO2 muE formation.     

Single laser pulse induced aggregation of gold nanoparticles

Gold nanoparticles with an average diameter of 11 nm (Au(39000)) were prepared in an SDS aqueous solution. A 80-microm liquid droplet (microdroplet) of the solution was ejected into the atmosphere from a microdroplet nozzle. Structural changes of the gold nanoparticles in the microdroplet, after they were irradiated with a focused single-nanosecond laser pulse at the wavelength of 532 nm, were studied by transmission electron microscopy (TEM) and optical absorption spectroscopy. It was revealed that the gold nanoparticles are fragmented into small particles and then the small fragments aggregate with each other. The aggregation was found to be terminated 100 micros after the laser-pulse excitation.     

Synthesis of Supramolecular A8Bn Miktoarm Star Copolymers by Host-Guest Complexation

We report a new synthetic method to construct supramolecular A₈B_n (n=1, 2, 4) miktoarm star copolymers by host-guest complexation between a resorcinarene-based coordination capsule possessing eight polystyrene chains and 4,4-diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A₈B_n (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size-exclusion chromatography (SEC), and diffusion-ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase-separated in the bulk. The micro-Brownian motion of the A₈B₄ structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.     

The circular cylinder in simple shear at moderate Reynolds numbers: An experimental study

The flow around a neutrally buoyant circular cylinder in simple shear was studied using particle-image velocimetry. Steady experimental results are presented for both torque-free and fixed cylinders at shear-based Reynolds numbers between 8 and 25 at two different flow confinement values. These data, which are to our knowledge the first experimental results for this Reynolds number range, show that the normalized rotation rate decays much more slowly with Reynolds number than previous theoretical predictions for unconfined flow, with the rate of decay decreasing as confinement increases. A new simple model is proposed to explain these effects. Given physical and technological limitations upon steady and unconfined flow experiments and simulations, the effect of confinement on a cylinder in simple shear merits further study. Received: 17 February 2000/Accepted: 22 June 2000     

Steady streaming flows near spheroids oscillated at multiple frequencies

The results of flow visualization and particle image velocimetry (PIV) studies of steady streaming flows near oscillating spheroids (aspect ratios of 0.75, 1, and 1.33) are reported for normalized amplitudes of 0.025–0.15 and Reynolds numbers of 27–89. The oscillations are described by either a single-frequency sine wave or the sum of two such sine waves with different frequencies. For normalized amplitudes of 5% or less, the PIV data suggest that steady streaming flow fields superpose. In other words, the time-independent portion of the velocity field created by forcing the spheroid simultaneously at two different frequencies is found to be the sum of the two steady streaming velocity fields created by forcing the body individually at each of the two frequencies.     

Analysis of twisted nematic liquid crystal Fabry–Perot interferometer (TN-FPI) filter based on the coupled mode theory

The tuning characteristics of a twisted nematic (TN) liquid crystal (LC) Fabry–Perot interferometer (FPI) wavelength filter, which is a basic component of wavelength division multiplexed transmission systems, is analyzed using coupled mode theory. First, a simplified modeling of the refractive index change in the LC layer is presented. Next, various characteristics of the eigen polarization modes of the LC medium and the cavity are derived analytically. Finally, the qualitative interpretation of the behavior of the FPI's resonance spectrum are given.