Co2(CO)8-mediated endo mode cyclization of epoxy-alcohol: synthesis of 2-ethynyl-3-hydroxy-2-methyltetrahydropyran and 2-ethynyl-3-hydroxy-3-methyltetrahydropyran derivatives

Successive treatment of 4,5-epoxy-5-methyl-7-trimethylsilyl-6-heptyne-1-ol with Co2(CO)8 at 0 degrees C and a catalytic amount of BF3 x OEt2 at -78 degrees C gave the tetrahydropyran derivatives with the cobalt-complexed moiety. Similarly 4,5-epoxy-4-methyl-7-trimethylsilyl-6-heptyne-1-ol underwent ring closure under the above conditions to provide the corresponding tetrahydropyran derivatives. The preferential endo mode cyclization over the exo one was observed in these experiments.     

Numerical analysis of turbulent flow separation in a rectangular duct with a sharp 180‐degree turn by algebraic Reynolds stress model

Turbulent flow in a rectangular duct with a sharp 180‐degree turn is difficult to predict numerically because the flow behavior is influenced by several types of forces, including centrifugal force, pressure‐driven force, and shear stress generated by anisotropic turbulence. In particular, this type of flow is characterized by a large‐scale separated flow, and it is difficult to predict the reattachment point of a separated flow. Numerical analysis has been performed for a turbulent flow in a rectangular duct with a sharp 180‐degree turn using the algebraic Reynolds stress model. A boundary‐fitted coordinate system is introduced as a method for coordinate transformation to set the boundary conditions next to complicated shapes. The calculated results are compared with the experimental data, as measured by a laser‐Doppler anemometer, in order to examine the validity of the proposed numerical method and turbulent model. In addition, the possibility of improving the wall function method in the separated flow region is examined by replacing the log‐law velocity profile for a smooth wall with that for a rough wall. The analysis results indicated that the proposed algebraic Reynolds stress model can be used to reasonably predict the turbulent flow in a rectangular duct with a sharp 180‐degree turn. In particular, the calculated reattachment point of a separated flow, which is difficult to predict in a turbulent flow, agrees well with the experimental results. In addition, the calculation results suggest that the wall function method using the log‐law velocity profile for a rough wall over a separated flow region has some potential for improving the prediction accuracy. Copyright © 2007 John Wiley & Sons, Ltd.     

Production of core/shell polystyrene/poly(3,5-xylidine) composite particles by chemical oxidative seeded dispersion polymerization

Micron-sized monodispersed polystyrene (PS)/poly(3,5-xylidine) (PXy) composite particles were produced by chemical oxidative seeded dispersion polymerization of 3,5-xylidine at 20 °C with 1.6-μm-sized monodispersed PS seed particles in HCl aqueous solution, the pH of which was always kept at 2.5 with a pH stat. The composite particles produced consisted of a PS core and a PXy shell. Received: 16 December 1998 Accepted in revised form: 25 March 1999     

A travelling-wave beam deflector cleave-coupled to a diode laser

A new technique for scanning a diode laser beam is introduced where the beam is deflected in a current-injection-type travelling-wave beam deflector integrated with a diode laser. The deflector, which is formed outside the laser cavity, is cleave-coupled to the cavity. An anti-reflection coating on the deflector output facet suppresses the light returning to the laser. As a result, very smooth deflection of the radiation peak with low background intensity is realized in this device, while retaining high efficiency and low threshold current.     

Aragonite twinning in gastropod nacre

Aragonite twinning in gastropod nacre has been investigated using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) with the focused ion beam (FIB) sample preparation technique. At the growth front of nacre, Haliotis discus hannai and Omphalius rusticus form a “stack-of-coins” structures, which consist of pseudo-hexagonal and elliptical aragonite tablets, respectively. SEM, EBSD, and TEM analyses revealed that these tablets are monolithic single crystal and almost free of the {1 1 0} twins that are common in aragonite of biotic or abiotic origin. The longest diagonal of the hexagon and the longer axis of the ellipse are parallel to the a-axis of aragonite. The crystal orientation of each tablet in a stack, measured by TEM-Kikuchi pattern analysis, is almost the same but there is occasionally {1 1 0} twin-like relationship between adjacent tablets along the stacking. On the other hand, the fibrous aragonite layer formed prior to the nacreous structure is composed of polycrystalline aragonite with high density of {1 1 0} twins. TEM observation suggests that the interlamellar organic sheet prevents the inheritance of the twins, by selecting only single domain of the twins, through the mineral bridge.     

荧光衍生化试剂2-(4-羧基苯基)-4,5-萘并咪唑的合成及在HPLC测定醇类中的应用

 合成了一种用于醇类分析的高灵敏度的荧光衍生化试 剂2-(4-羧基苯基)-4,5-萘并咪唑(CNI),将其在二氯甲烷中于80 ℃条件下与醇缩合成酯 ,并采用RP-HPLC法进行分离检测,色谱柱为Zorbax Bp C8柱(250　mm×4.6　mm i.d.) ,流动 相为V(乙腈)∶V(甲醇)=90∶10的溶液,荧光检测波长λex 345 nm, λem 485　nm。同时,测定了人血清中的胆固醇,其最低检出质量浓度为1.0 μg /L。     

Finding of remarkable synergistic effect on the aroxyl-radical-scavenging rates under the coexistence of α-tocopherol and catechins

Measurements of aroxyl radical (ArO^•)-scavenging rate constants () of antioxidants (AOHs) (α-tocopherol (α-TocH) and three catechins (CatHs) (ie, epicatechin (EC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG)) were performed in ethanol solution, using stopped-flow spectrophotometry. values were measured not only for each AOH, but also for the mixtures of two AOHs (α-TocH and CatH). A notable synergistic effect that the value of α-TocH increases 1.29, 1.84, and 1.65 times under the coexistence of constant concentrations of EC, EGC, and EGCG, respectively, was observed for the solutions including α-TocH and CatH. Similarly, values of CatHs (EC, EGC, and EGCG) increased 1.72, 2.25, and 2.34 times under the coexistence of constant concentrations of α-TocH, respectively. UV-Vis absorption of α-tocopheroxyl radical (α-Toc^•) (λ_max = 428 nm), which had been produced by reaction of α-TocH with ArO^•, decreased remarkably under the coexistence of α-TocH and CatHs due to the fast α-TocH-regeneration reaction by CatHs. The result suggests that the prooxidant reaction due to α-Toc^• is suppressed by the coexistence of CatHs. By analyzing the formation and decay curves of α-Toc^•, it has been ascertained that one molecule of EGCG having three OH groups at B-ring may rapidly regenerate three molecules of α-Toc^• to α-TocH.     

AC transport current loss of assembled conductor of HTS tapes

We study experimentally and theoretically the AC transport current loss characteristics of a tape in multiple tapes assembled in single layer and subject to external field produced by transport currents of adjacent tapes. We measured the AC transport current losses of a Bi2223 silver-sheathed tape in a single layer arrangement of three tapes using our newly developed potential leads arrangement to avoid spurious loss components caused by the magnetization in the adjacent tapes. In the paper, the influence of the external AC field produced by adjacent tapes on the loss characteristics is studied based on the experimental results and theoretical analysis.     

Theβ + decay of the new isotope86Mo and the first observation of86m Nb

Theβ ⁺ decay of⁸⁶Mo has been firstly investigated by means ofβγ spectroscopy. The⁸⁶Mo nuclei were produced by fusion-evaporation reactions of⁵⁴ Fe (³⁵Cl, 1 p2n) and⁵⁸Ni (³²S,2p 2n) at beam energies of 103 and 120 MeV, respectively. Threeγ rays of 47.3, 49.8 and 187.0 keV were unambiguously identified to follow theβ ⁺ decay of⁸⁶Mo by results ofXγ andβγ coincidence and cross-bombardment. A half life and a maximumβ ⁺-ray energy of⁸⁶Mo were determined to be 19.6±1.1 s and 3.9±0.4 MeV, respectively. A decay scheme of⁸⁶Mo is proposed in this article. Furthermore, a decay of⁸⁶Nb has been studied using the same combinations of projectiles and targets, and a newβ-decaying isomer^86m Nb was observed with a half life of 56.3±8.3 s.