Image analysis applied to study on frictional-drag reduction by electrolytic microbubbles in a turbulent channel flow

We investigate frictional-drag reduction with electrolytic microbubbles based on image measurement of a turbulent flow in a water channel at Re = 4800 (based on the half channel height). Microbubbles with a diameter ranging 30–200 μm can reduce frictional drag by as much as 30% relative to single-phase flow even at low void fractions (α ≈ 3 × 10⁻⁴); however, drag reduction is only effective within a limited downstream distance from an electrode array. Arrangement of the optical system allows us to measure the bubble-production rate by water electrolysis from images near the wall and to trace the motion of bubbles. We also measure velocity fields using particle-tracking velocimetry based on a shallow depth-of-field approach by segregating tracer particles from microbubbles. Vertically oscillating microbubbles likely represent interaction with vortical structures near the wall, and bubbles approaching the wall appear to induce negative streamwise velocity relative to the surrounding fluid. We relate the wall friction with the double integral of the Reynolds-stress profile and show that its variation due to microbubbles decreases the drag on the wall. Microbubbles tend to coalesce downstream resulting in a fewer bubbles but with greater size; accordingly, the oscillatory motion diminishes, and the frictional drag rather increases.     

Delayed feedback control based on the act-and-wait concept

This paper proposes a delayed feedback control (DFC) based on the act-and-wait concept, which reduces the dynamics of DFC systems to that of discrete-time systems. Based on this concept, a delayed feedback controller is designed for a prototype two-dimensional oscillator using a simple systematic procedure. This control has two advantages: the feedback delay time can be large and it can obtain deadbeat behavior. A numerical example using a double-scroll circuit model demonstrates these theoretical results.     

Second Harmonic Generation in Bis Typed Organic Compounds

In systematic research on a series of new nonlinear organic materials, we found that Bis (4-nitrophenoxy) methane (BNPM) showed a large intensity of second harmonic light, which was 4.4 times as large as that of urea crystal by powder technique and easily crystallized from a solution. The crystal structure of BNPM, obtained by the X-ray diffraction method, was orthorhombic, space group P2₁2₁2 (point group 222), with unit-sell dimension a = 10.205 Å; b = 12.854 Å; c = 4.8822 Å. In addition, we found that the absorption edge of BNPM was 430 nm with a 0.9-mm-thick crystal, and we observed the second harmonic light with BNPM single crystal at the wavelength of 1064 nm and in the range from 906 nm to 990 nm.     

Localization transition of <Emphasis Type="Italic">d</Emphasis>-friendly walkers

 Friendly walkers is a stochastic model obtained from independent one-dimensional simple random walks {S ^k _j } _j≥0 , k=1,2,…,d by introducing ``non-crossing condition': and ``reward for collisions' characterized by parameters . Here, the reward for collisions is described as follows. If, at a given time n, a site in ℤ is occupied by exactly m≥2 walkers, then the site increases the probabilistic weight for the walkers by multiplicative factor exp (β _m )≥1. We study the localization transition of this model in terms of the positivity of the free energy and describe the location and the shape of the critical surface in the (d−1)-dimensional space for the parameters . Received: 13 June 2002 / Revised version: 24 August 2002 Published online: 28 March 2003 Mathematics Subject Classification (2000): 82B41, 82B26, 82D60, 60G50 Key words or phrases: Random walks – Random surfaces – Lattice animals – Phase transitions – Polymers – Random walks     

Determination of methylglyoxal in mouse blood by liquid chromatography with fluorescence detection

A highly sensitive and rapid liquid chromatographic method for the determination of methylglyoxal in mouse blood is described, based on the precolumn conversion of methylglyoxal to a highly fluorescent 3-methyl-6,7-methylenedioxyquinoxaline by reaction with 1,2-diamino- 4,5-methylenedioxybenzene. The method is applied to the determination of methylglyoxal (0.1- 10⁴ pmol) in 5 μ1 of blood.     

Stereochemistry of reduction of the C-24,25 double bond in the conversion of desmosterol into cholesterol

Feeding of the chemically prepared [24-¹³C, 24-²H]desmosterol to cell-free systems derived from rat liver and silkworm gut and to cultured cells of Oryza sativa followed by deuterium-decoupled ¹H, ¹³C shift correlation NMR analysis of the biosynthesized cholesterol revealed the stereospecific incorporation of hydrogen atoms from the re-face of the C-24 position of desmosterol.     

Supported lipid bilayer formation by the giant vesicle fusion induced by vesicle–surface electrostatic attractive interaction

The effect of the electrostatic attractive force between giant unilamellar vesicles (GUVs) and the SiO₂ surface on the formation of a Ca²⁺-free supported lipid bilayer (SLB) was investigated by atomic force microscopy and fluorescence microscopy. When negatively charged GUVs were incubated for 1 h without Ca²⁺, the surface coverage of lipid bilayer was <1% on the SiO₂ surface. In contrast, a high coverage was obtained without addition of Ca²⁺ on the positively charged surface modified by aminopropyldimethylethoxysilane, and the coverage of SLBs decreased with increasing KCl concentrations. The thickness of the water layer under SLB was reduced by modification of APS.     

Selective retention of some polyaromatic hydrocarbons by highly crosslinked polymer networks

Highly crosslinked polymer networks were characterized in terms of structural differences based on the crosslinked network structures with their chromatographic molecular retentivity for some polyaromatic hydrocarbons (PAHs). Because PAHs and some sterically bulky solutes were used in the chromatographic characterization, tiny differences in the crosslinked polymer networks were observed in terms of the chromatographic molecular retentivity. Ethylene dimethacrylate afforded molecular retentivity for anthracene, and this recognition ability changed with the polymerization time. In addition, 1,4‐butanediol dimethacrylate afforded molecular retentivity for pyrene, and this retentivity was larger than that for anthracene. The polymerization methods also affected the resulting polymer networks drastically. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2556–2566, 2005     

Practical conditions and limitations for high-spatial-resolution multisite EPR oximetry

We have previously reported a high-spatial-resolution multisite electron paramagnetic resonance (EPR) oximetry method that is based on consecutive applications of magnetic field gradients with the same direction but different magnitudes. This method that could be called also two-gradient convolution EPR oximetry has no restrictions for the shape of solid paramagnetic materials implanted in tissue and is applicable for any particulate EPR oxygen-sensitive matieral with a Lorentzian line shape. To enhance the utilization of this method, a previously described algorithm was used to develop user-friendly Windows-based software. Practical conditions of application of the method were established using several different model systems. It has been shown that the spectral overlap from the adjacent sites can be neglected if the splitting between the corresponding lines exceeds the largest line width by at least a factor of 1.3. An additional requirement of the method is that the second field gradient should exceed by at least 30% the value of the first gradient. It was confirmed that the error in line width determination at L-band is proportional to the noise-to-signal ratio, and does not exceed 1% a noise-to-signal ratio of 0.1 in a typical in vivo experiment. We demonstrate that the line widths of up to 10 different sites can be determined.