Resonant photorefractive effect in InGaAs/GaAs multiple quantum wells

Semi-insulating InGaAs/GaAs multiple quantum wells are fabricated by metal-organic vapor-phase epitaxy and proton implantation. Two-wave mixing gain and four-wave mixing diffraction efficiency are measured at wavelengths of 0.91-0.94microm in the Franz-Keldysh geometry. We observe a large photorefractive effect caused by the excitonic electro-optic effect. The maximum diffraction efficiency reaches ~1.5x10(-4) .     

Breakthrough of natural organic matter from fixed bed adsorbers: investigations based on size-exclusion HPLC

Fixed bed adsorption experiments were performed using four granular activated carbon (GAC) columns designed by packing two size ranges of pulverized and sieved Filtrasorb 400 (d=0.5-0.59 and 1.0-1.19 mm) to two bed depths (L=10 and 20 cm), respectively. Continuous supplying of river water containing a lower content of natural organic matter (NOM) allowed investigation of the breakthrough of aqueous natural organic matrices assessed with lumped quality indices of total dissolved organic carbon (DOC) and ultraviolet absorbance at 260 nm (UV260). The capability of GAC columns in dealing with sudden rise in the load of influent NOM was also displayed by intermittently adding to the influent river water a peaty field groundwater that contained a higher content of NOM. Besides, assisted by the size-exclusion HPLC (SEHPLC), changes in the apparent molecular weight distribution of NOM along the bed depth of GAC columns were evaluated, and an important finding revealing relatively even adsorption for adsorbable NOM constituents within the entire molecular weight range of 1000-5200 g mol⁻¹ as PSS (polystyrene sulfonates) detected for the river and groundwater NOM was obtained. Furthermore, using a previously proposed hypothetical multi-component approach incorporating the ideal adsorbed solution theory and a plug flow homogeneous surface diffusion model, the observed concentration profiles of the river water NOM were predicted.     

Synthesis and Absolute Configuration at C(8) of ‘p‐Menthane‐3,8,9‐triol’ Derived from (–)‐Isopulegol

Two diastereoisomers of the new, potentially insecticidal ‘p‐menthane‐3,8,9‐triol’ (=(2S)‐ and (2R)‐ 2‐[(1R,2R,4R)‐2‐hydroxy‐4‐methylcyclohexyl]propane‐1,2‐diol; (8S)‐ and (8R)‐ 1 ), have been synthesized from (–)‐isopulegol by both conventional dihydroxylation and catalytic Sharpless dihydroxylation (Scheme). The absolute configuration at C(8) of the corresponding orthoformate adduct (8S)‐ 3a was determined by ¹H‐NMR and X‐ray crystallographic analysis (Figure).     

Asymmetric synthesis of anti- and syn-beta-amino alcohols by reductive cross-coupling of transition metal-coordinated planar chiral arylaldehydes with aldimines

Samarium iodide-mediated cross-coupling of N-tosyl ferrocenylideneamine with planar chiral ferrocenecarboxaldehydes or benzaldehyde chromium complexes gave diastereoselectively the corresponding anti-beta-amino alcohol derivatives in good yields, while N-tosyl benzylideneamine produced syn-beta-amino alcohols by coupling with planar chiral arylaldehydes. Dynamic kinetic resolution of a configurationally equilibrated reactive species generated from achiral N-tosyl ferrocenilideneamine and benzylideneamine by reduction with samarium iodide was observed in the cross-coupling with planar chiral arylaldehydes giving both antipodes of beta-amino alcohols depending on the planar chirality. The obtained anti-beta-amino alcohol with the ferrocene ring was utilized as a chiral ligand for catalytic asymmetric reduction of acetophenone.     

Sodium borosilicate glasses prepared by the sol-gel process

A sodium borosilicate gel of composition 80SiO₂·15B₂O₃·5Na₂O (wt%) was prepared from tetraethyl orthosilicate, trimethyl borate, sodium methylate, H₂O, and HCl as the catalyst. Variation of specific surface area and porosity as a function of heating temperature indicated that closed pores were opened at temperatures lower than 400°C and collapsed above 450°C. From TG and DTA curves, about 19% Si and B atoms are evaluated to have −OH bonds. X-ray diffraction patterns indicated crystallization of low-cristobalite out of the gel when it was heated at 700°C for 5 h, showing a difference from a melt-quenched glass of the same composition.     

Surface and morphological characterization of polysiloxane-block-polyimides

Two series of polysiloxane-block-polyimides were synthesized by the method of solution imidization of the polyamic acids prepared from the dianhydride/diamine combinations of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA)/2,2-bis[4-(4-aminophenoxy) phenyl] propane (BAPP) (Series A) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA)/bis[4-(3-aminophenoxy) phenyl] sulfone (BAPSM) (Series B) with three kinds of w-diamino-poly(dimethylsiloxane) with different number-average molecular weight added as a part of diamine. These polysiloxane-block-polyimides, having various compositions and chain lengths of the polysiloxane segments, were subjected to solution casting to prepare their films, and their surface and interface properties were analyzed by contact angle, XPS, AFM, and SEM. It was found that the surface tension and surface topography were greatly influenced by the composition and molecular weight of the polysiloxane segments because of their surface enrichment, which was affected by the environment and substrate with which the copolyimides had contacted. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2239–2251, 1997     

Structure analysis of a soluble polysiloxane-block-polyimide and kinetic analysis of the solution imidization of the relevant polyamic acid

A series of polysiloxane-block-polyimides were synthesized by solution imidization of the polyamic acids derived from the combination of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and diamino(polysiloxane) (PSX (M_w = 750)) in N-methyl-2-pyrrolidone (NMP). Their structures were analyzed by ¹H-, ¹³C-, and ²⁹Si-NMR spectra as well as by IR spectroscopy. The solid-state NMR spectrum was also measured to determine the spin–lattice relaxation time of the copolyimides. The observed relaxation times of both aromatic and polysiloxane segments were similar in the copolyimides having 10–30 wt % of PSX, while those in the copolyimide with 50 wt % of PSX was significantly different. This may be attributed to the morphology change due to the increase in PSX composition in the polymer backbone. The reduced viscosity of the copolyimides could be controlled by changing the monomer ratio in the feed or by adding an end-capping reagent such as phthalic anhydride into the polymerization system. The kinetic study of the solution imidization revealed that the imidization reaction obeyed second-order kinetics. The activation energy calculated for this imidization was 99.2 kJ/mol, being similar to that for the imidization of the DSDA-based aromatic polyimides. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2237–2245, 1998     

Grafting of Polymer Brushes from Xanthate-Functionalized Silica Particles

Monodisperse silica particles (SiPs) were surface-modified with a newly designed silane coupling agent comprising a triethoxysilane and an alkyl halide, namely, 6-(triethoxysilyl)hexyl 2-bromopropionate, which was further treated with potassium O-ethyl dithiocarbonate (PEX) to immobilize xanthate molecules on the particle surfaces. Surface-initiated macromolecular design via interchange of xanthates (MADIX) polymerization of vinyl acetate (VAc) was conducted with the xanthate-functionalized SiPs. The polymerization was well controlled and produced SiPs coated with poly(vinyl acetate) (PVAc) with a well-defined target molar mass and a graft density of about 0.2 chains nm⁻². Dynamic light scattering and TEM measurements revealed that the hybrid particles were highly dispersible in good solvents without any aggregation. The PVAc brushes were hydrolyzed with hydrochloric acid to produce poly(vinyl alcohol) brushes on the SiP surfaces. In addition, the number of xanthate molecules introduced on the SiP surfaces could be successfully controlled by adjusting the concentration of PEX. Thus, the SiPs have two functionalities: xanthates able to act as a MADIX chain-transfer agent and alkyl bromide initiation sites for atom transfer radical polymerization (ATRP). By using these unique bifunctional particles, mixed polymer brushes were constructed on the SiPs by MADIX of VAc followed by ATRP of styrene or methyl methacrylate.     

Purification through Zeno-like measurements

A series of frequent measurements on a quantum system (Zeno-like measurements) is shown to result in the "purification" of another quantum system in interaction with the former. Even though the measurements are performed on the former system, their effect drives the latter into a pure state, irrespectively of its initial (mixed) state, provided certain conditions are satisfied.     

Highly stable gold(III) complex with a hydantoin ligand in alkaline media

A novel gold(III) complex with a monodentate 5,5-dimethylhydantoin ligand, [Au(dmh)4]-, is square planar in geometry, inert and highly stable in alkaline solutions because of soft acid-base interactions, and electrochemically reduced near -0.3 V vs Ag/AgCl to give a gold(0) film with a high current efficiency.