On air entrainment in coatings

A series of experiments that clarify how air bubbles become entrained into coatings are described. The contact line dynamics at the air-liquid interface surrounding a fiber is characterized for a typical coating die operating under atmospheric and pressurized conditions. Glycerin and other viscous liquids are used to reveal that a critical fiber speed exists at which air entrainment begins. The observations confirm that the critical capillary number Ca(c) depends on the physical properties of the coating material, in the form of the Morton number. When the liquid supply is pressurized, the experiments show that adjusting the pressure can stabilize the displaced free surface interface at a prescribed location. Controlling the meniscus location in this way eliminates air entrainment. The threshold occurs when the applied pressure balances the shear exerted on the coating by the moving fiber. Using this approach it is possible to eliminate air entrainment and attain stable wetting at very large values of the capillary number, e.g., Ca congruent with 50.     

A novel regiodivergent resolution reaction mediated by a homochiral lithium amide base

The reaction of a racemic perhydroisoquinolene derivative 9 with the homochiral lithium amide basse 3 in the presence of Me₃SiCl in an regiodivergent fashion to give the two non-racemic regioisomeric enol silanes 10 and 11. Conversion of 10 into enone 15, an intermediate useful in the synthesis of the alkaloid (+)-yohimbine, was also possible.     

Stereoselective synthesis of beta-(chloro)vinylsilanes using a regio- and (E)-stereoselective bis-stannylation of unsymmetrically substituted butadiynes: application to the synthesis of a masked triyne

[reaction: see text] A highly regio- and stereoselective bis-stannylation of unsymmetrically substituted butadiyne 3 provides bis-stannane 4. Selective lithiation of the internal tin residue effects a 1,4-retro-Brook rearrangement to afford vinylsilane 5. This was elaborated into the novel diethynylethene 1, which also functions as a masked triyne.     

Synthesis of (2-aminoethyl)ferrocenes from the reaction of lithium amides with vinylferrocene

Lithium amides react with vinylferrocene in the presence of TMEDA to provide the corresponding (2-aminoethyl)ferrocenes in good to excellent yields. A range of secondary amines can be employed in this amidolithiation reaction, with cyclic derivatives affording particularly good yields of the 2-aminoethyl-substituted ferrocene product. This operationally simple procedure provides one of the most straightforward routes to this class of mono-substituted ferrocene.     

Asymmetric synthesis of the erythrinan alkaloid system using a chiral lithium amide base desymmetrisation as the key step

A new asymmetric approach to the erythrinan alkaloid system is described, which involves chiral base desymmetrisation of a ring fused imide and a 6-exo-trig radical cyclisation as the key steps.     

新开花粉蛋白的盐酸胍去折叠过程

本文利用荧光光谱和园二色光谱了新开花粉蛋白的盐酸胍去折叠过程。结果显示：新开花粉蛋白的盐酸胍去折叠是一个只包含天然蛋白和变性终态的二态过程,与已经报道的天花粉蛋白的盐酸胍去折叠的过程不同。     

Rapid access to polycyclic indolines related to the stephacidin alkaloids using a radical cascade

A new and very rapid access to indoline intermediates useful for the synthesis of alkaloids related to the stephacidins has been established using a radical cascade process initiated from a sulphur-substituted diketopiperazine.     

Review of nanofluids for heat transfer applications

Research on nanofluids has progressed rapidly since its enhanced thermal conductivity was first repotted about a decade ago,though much controversy and inconsistency have been reported,and insufficient understanding of the formulation and mechanism of nanofluids further limits their applications.This work presents a critical review of research on heat transfer applications of nanofluids with the aim of identifying the limiting factors so as to push forward their further development.     

Full-field laser metrology for fluid velocity measurement

This paper reviews the development of full-field laser metrology from its inception as a dynamic extension of scattered light speckle photography, a voherent optical technique originally developed to make full-field measurements of quasi-static displacements in transparent solids, to its present applications in fluid dynamic studies. The full-field laser velocimetry technique, including both double exposure and multiple exposure recording methods, is discussed in detail, and comparison is made of their advantages and disadvantages in applications to steady and unsteady flows. Both the coherent light speckle and the particle image modes of operation are defined and evaluated. Computer aided ‘point-wise’ (Young's fringe) and ‘global’ (Fourier filtering) methods of optically analyzing the specklegrams are also discussed. Finally, experiments in which full-field laser velocimetry has been applied to a study of convective flow in a liquid are described, thus illustrating the potential of this new, non-onvasive optical technique.