High-definition PIV analysis on vortex shedding in the cylinder wake

A high-definition analysis based on flow topology is made on the vortex motions under natural and lock-on conditions in the near-wake region of a circular cylinder, where two-dimensional flow fields in the wake-transition regime are measured by a time-resolved PIV system. The Reynolds stress distributions are examined in view of the mean separation streamline and the trajectory ofthe vortex center. It is shown that, by the lock-on, the Reynolds stresses become stronger and their dispositions match well with the shortened wake bubble, indicating perfect synchronization of shedding to the oscillatory forcing flow in the near field, which causes increased lift and drag forces.     

Effects of annealing temperature and method on structural and optical properties of TiO2 films prepared by RF magnetron sputtering at room temperature

TiO₂ thin film was deposited on non-heated Si(1 0 0) substrate by RF magnetron sputtering. The as-deposited films were annealed by a conventional thermal annealing (CTA) and rapid thermal annealing (RTA) at 700 and 800 °C, and the effects of annealing temperature and method on optical properties of studied films were investigated by measuring the optical band gaps and FT-IR spectra. And we also compared the XRD patterns of the studied samples. The as-deposited film showed a mixed structure of anatase and brookite. Only rutile structures were found in samples annealed above 800 °C by CTA, while there are no special peaks except the weak brookite B(2 3 2) peak for the sample annealed at (or above) 800 °C by RTA. FT-IR spectra show the broad peaks due to Ti-O vibration mode in the range of 590-620 cm⁻¹ for the as-deposited film as well as samples annealed by both annealing methods at 700 °C. The studied samples all had the peaks from Si-O vibration mode, which seemed to be due to the reaction between TiO₂ and Si substrate, and the intensities of these peaks increased with increasing of annealing temperature. The optical band gap of the as-deposited film was 3.29 eV but it varied from 3.39 to 3.43 eV as the annealing temperature increased from 700 to 800 °C in the samples annealed by CTA. However, it varied from 3.38 to 3.32 eV as the annealing temperature increased from 700 to 800 °C by RTA.     

Highly enantioselective phase-transfer catalytic alkylation in the preparation of non-natural alpha-amino acids via solid phase synthesis using aldimine linker

A new Merrifield-resin-derived glycinimine tert-butyl ester (9) was prepared and applied to the enantioselective synthesis of non-natural alpha-amino acids. High enantioselectivities (86 to >99% ee) were accomplished by employing the aldimine linker under phase-transfer alkylation conditions, using 50% aqueous CsOH in toluene/chloroform (7:3) at 0 degrees C in the presence of N-(9-anthracenylmethyl)-O(9)-allylcinchonidium bromide (10 mol %).     

Effect of metal ions on the stability of metallothionein in the degradation by cellular fractions in vitro

Metallothioneins (MT), small molecular weight metal binding proteins are known to play an important protective role against heavy metal toxicity, either as antioxidants or pre-oxidants. However, the mode of metabolic fate of MTs in various metal complexes is not clearly understood. This study was carried out to better understand the mode of selective turnover rate of various form of MT in complexes with different metals. The degradation of in vitro translated mouse 35S-cysteine-MT was examined in lysosomal or cytosolic fractions from mouse liver by gel electrophoresis and autoradiography. Overnight incubations of MT showed extensive proteolysis in the lysosomal fraction but not in cytosolic fractions. However, Cu2+-MT was found to be stable under the same experimental condition. In contrast, Zn did not interfere with MT degradation. These results suggest that lysosomes are chiefly responsible for MT removal and appears to be selective on the metals involved in the MT complex. In vitro, translated, radiolabeled MT provides a suitable substrate for investigating the characteristics of MT degradation.     

Disposable amperometric glucose sensor electrode with enzyme-immobilized nitrocellulose strip

Electrochemical properties of screen-printed carbon paste electrodes (CPEs) with a glucose oxidase-immobilized and hexamineruthenium (III) chloride ([Ru(NH₃)₆]³⁺) containing nitrocellulose (NC) strip were examined. The NC strip (2×8 mm) placed on the CPEs printed on polyester (PE) film is tightly sealed using another PE film on the top with open edges on both sides. Samples containing macromolecules and particles (e.g. proteins and blood cells) are applied at one edge of the NC strip and reach the detection area, chromatographically separating small molecules (e.g. glucose, ascorbate, acetaminophen, and uric acid) of analytical interests. Since sample volumes and the amount of catalytic reagents (mediator and glucose oxidase) are precisely predefined by the dimension and pore size (8 μm) of the NC strip, the sensor-to-sensor reproducibility and accuracy of analysis are greatly improved. The use of [Ru(NH₃)₆]³⁺ mediator, which exhibits characteristic substantially lowers the applied potential (0.0 V vs Ag/AgCl) for glucose determination and eliminates the interference from other oxidizable species, providing improved analytical results.     

Determination of antiferromagnetic exchange coupling in the tetrahedral thiolate-bridged diferrous complex [Fe2(SEt)6]2-

Protein-bound iron-sulfur clusters and their synthetic analogues are characterized by tetrahedral metal sites, multiple oxidation levels, and exchange coupling. The recent attainment of several all-ferrous protein clusters and the presence of sulfide- and thiolate-bridged sites in the all-ferrous state of the nitrogenase P-cluster provides an imperative for determination of exchange coupling between tetrahedral Fe(II) sites with sulfur bridges. The cluster in the previously reported compound (Et(4)N)(2)[Fe(2)(SEt)(6)] is centrosymmetric with distorted tetrahedral coordination and a planar Fe(2)(mu-SEt)(2) bridge unit. The compound is diamagnetic at 4.2 K, indicating antiferromagnetic coupling. The lower limit J > 80 cm(-)(1) (H = JS(1).S(2)) is obtained by M?ssbauer spectroscopy. Analysis of magnetic susceptibility data affords J = 165 +/- 15 cm(-)(1). It is noteworthy that the J value of the diferrous pair obtained here is comparable to the J values reported for the mixed-valence state of plant-type Fe(2)S(2) ferredoxins. The near temperature independence of the quadrupole splitting (DeltaE(Q) = 3.25 mm/s at 4.2 K and 3.20 mm/s at 180 K) indicates that no excited orbital states are appreciably populated at temperatures less than 300 K. The paramagnetism arises solely from thermal population of the S = 1 state of the spin ladder. This work provides the only measure of antiferromagnetic coupling by Fe(II) pairs in a tetrahedral sulfur environment.