Pd‐Colloids‐Catalyzed/Ag2O‐Oxidized General and Selective Esterification of Benzylic Alcohols

Palladium colloids obtained from the degradation of Hermann–Beller palladacycle proved to be an efficient catalytic system in combination with silver oxide as a selective oxidant for the oxidative esterification of differently substituted benzyl alcohols in MeOH as solvent. Excellent reactivity exhibited by the catalytic system also allowed the alcoholic coupling partner to be changed from MeOH to a wide range of alcohols having diverse functionalities. The mildness of the developed protocol also made it possible to employ propargyl alcohol as the coupling partner without any observation of any interference of the terminal alkyne. Selective oxidative coupling of a primary alcoholic functional group over secondary in the case of glycols and glycerols was also made possible using the developed catalyst system. To test the relevancy of Pd/Ag combined catalysis mixed Pd/Ag colloids were synthesized, characterized by TEM, XRD and XPS and applied to oxidative‐esterification successfully.     

Photoinduced formation and aggregation of silver nanoparticles at the surface of carboxymethylcellulose films

Formation and aggregation of photolytic silver nanoparticles at the surface of silver salt of carboxymethylcellulose films (CMCAg films) have been investigated. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize silver nanoparticles at the film surface. When the CMCAg films were irradiated with UV light in wet air at room temperature for 30–60 min, silver nanoparticles of ca. 10 nm size were formed at the irradiated surface. According to the FE-SEM observation, the growth of the particle diameter and aggregation of nanoparticles took place after prolonged irradiation, and finally, the irradiated side of the film surface was densely covered with the silver nanoparticles of ca. 35 nm size. Chemical composition analysis by the XPS measurements has confirmed the increase in the atomic concentration of silver with irradiation time. It is suggested that silver atoms and clusters can move in the film and precipitate at the irradiated surface.     

The Structure of Disjoint Iteration Groups on the Circle

The aim of the paper is to investigate the structure of disjoint iteration groups on the unit circle that is, families of homeomorphisms such that and each F ^veither is the identity mapping or has no fixed point ((V, +) is an arbitrary 2-divisible nontrivial (i.e., card V> 1) abelian group).     

Alumina nanotubes: preparation and textural,structural and morphological characterization

Alumina nanotube was synthesized by hydrolysis of aluminum isopropoxide followed by gelation and drying under hypercritical condition. The influence of temperature on the structural, textural, and morphological properties of the material was studied by powder X-ray diffraction, infrared spectroscopy, nitrogen adsorption, thermal analysis, scanning and transmission electronic microscopy. The as-prepared alumina (300°C) was formed by boehmite crystallites. Its structure collapsed after heating (500–1200 °C) yielding γ, δ and θ alumina nanophases. The aerogel surface area changed from 254 to 99 m² g⁻¹ in this heating range. The formation of alumina nanotubes was verified by transmission microscopy analysis at the heating range.     

Controlling the orientation of ZnO nanorod arrays using TiO<Subscript>2</Subscript> thin film templates dip-coated by sol–gel

The oriented ZnO nanorod arrays have been synthesized on a silicon wafer that coated with TiO₂ films by aqueous chemical method. The morphologies, phase structure and the photoluminescence (PL) properties of the as-obtained product were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and PL spectrum. The nanorods were about 100 nm in diameter and more than 1 μm in length, which possessed wurtzite structure with a c axis growth direction. The room-temperature PL measurement of the nanorod arrays showed strong ultraviolet emission. The effect of the crystal structure and the thickness of TiO₂ films on the morphologies of ZnO nanostructures were investigated. It was found that the rutile TiO₂ films were appropriate to the oriented growth of ZnO nanorod arrays in comparison with anatase TiO₂ films. Moreover, flakelike ZnO nanostructures were obtained with increasing the thickness of anatase TiO₂ films.     

Solving linear systems using wavelet compression combined with Kronecker product approximation

Discrete wavelet transform approximation is an established means of approximating dense linear systems arising from discretization of differential and integral equations defined on a one-dimensional domain. For higher dimensional problems, approximation with a sum of Kronecker products has been shown to be effective in reducing storage and computational costs. We have combined these two approaches to enable solution of very large dense linear systems by an iterative technique using a Kronecker product approximation represented in a wavelet basis. Further approximation of the system using only a single Kronecker product provides an effective preconditioner for the system. Here we present our methods and illustrate them with some numerical examples. This technique has the potential for application in a range of areas including computational fluid dynamics, elasticity, lubrication theory and electrostatics. AMS subject classification 65F10, 65T60, 65F30 Judith M. Ford: This author was supported by EPSRC Postdoctoral Research Fellowship ref: GR/R95982/01. Current address: Royal Liverpool Children's NHS Trust, Liverpool, L12 2AP. Eugene E. Tyrtyshnikov: This author was supported by the Russian Fund of Basic Research (grant 02-01-00590) and Science Support Foundation.     

Extended Method of Fast Allocation of USC’s for Millimeter-Wave DWDM-ROF Transmission Over ZDSF

Four-wave mixing (FWM) may happen efficiently and introduce crosstalk at the signal channels in dense-wavelength-division- multiplexing (DWDM) systems employing zero-dispersion-shifted fiber (ZDSF). This paper presents extended method of fast allocation of unequally spaced channels (USCs) to minimize FWM crosstalk in millimeter-wave (MMW) DWDM radio-over-fiber (ROF) systems. When all of the MMW sub-carriers are at same frequency, by spacing the channels unequally using the extended method, all FWM products except the ones bound to be generated at the signal frequencies, can be excluded from the signal channels. While when the MMW sub-carriers are allowed to be different in frequencies, all of the FWM products can be excluded from the signal channels by spacing the channels unequally. Transmission of 622 Mbit/s BPSK data over 40 kilometers ZDSF, with and without wavelength interleaving, are simulated, for both schemes with equally and unequally spaced channels. Results comparison shows that the link performances can be clearly improved, when the channels are unequally spaced using the extended method.     

NMR velocimetry studies of the steady-shear rheology of a concentrated hard-sphere colloidal system

NMR velocimetry has been used to observe the steady-shear rheological behaviour of a concentrated suspension of hard-sphere like 370 nm diameter PMMA core-shell latex particles at the volume fraction Φ = 0.46, the liquid core of the spheres rendering possible NMR observation of the particles themselves. Rheological measurements in a cone-and-plate geometry indicate that when aged (i.e. left at rest for two weeks), the material exhibits yield stress behaviour at very low shear rates. For shear rates greater than 1 s ^{- 1} a transition to liquid-like behaviour was observed, leading to a rejuvenated fluid state which exhibits shear-thinning behaviour over a wide range of shear rates. A similar yield stress behaviour was reflected in NMR velocimetry measurements in a Couette geometry, where the solid-to liquid transition could be clearly observed. Under steady-state flow, the fluid state inside the radius at which yield stress was observed, exhibited shear-thinning behaviour with a power law exponent n slowly approaching unity with increasing shear rate. This behaviour has some similarities with a model of Derec et al. in which aging and rejuvenation effects compete. Substantial wall slip was observed both at the inner and at the outer wall, an effect which disappeared as the shear rate was increased. No radial particle migration from the high-shear region at the inner wall was observed.     

Perchlorate Reduction by Nanoscale Iron Particles

We report herein the near complete reduction of perchlorate (ClO ) to chloride by nanoscale iron particles. The nanoparticles also reduce chlorate (ClO ), chlorite (ClO ) and hypochlorite (ClO ) to chloride. No reaction was observed with microscale iron powder under identical conditions. The temperature sensitivity of the perchlorate-nanoparticle reaction is evidenced by progressively increasing rate constant values of 0.013, 0.10, 0.64 and 1.52 mg perchlorate per g nanoparticles per hour (mg-g^-1-hr^-1), respectively, at temperatures of 25, 40, 60 and 75°C. The activation energy of perchlorate-iron reaction was calculated to be 79.02 ± 7.75 kJ/mole. Despite favorable thermodynamics, the relatively large activation energy for this reaction suggests that perchlorate reduction is limited by the slow kinetics. The nanoscale iron particles may represent a potential treatment method for perchlorate-contaminated water.     

Experimental investigation into the pool boiling heat transfer of aqueous based γ-alumina nanofluids

This paper is concerned about pool boiling heat transfer using nanofluids, a subject of several investigations over the past few years. The work is motivated by the controversial results reported in the literature and the potential impact of nanofluids on heat transfer intensification. Systematic experiments are carried out to formulate stable aqueous based nanofluids containing γ-alumina nanoparticles (primary particle size 10–50 nm), and to investigate their heat transfer behaviour under nucleate pool boiling conditions. The results show that alumina nanofluids can significantly enhance boiling heat transfer. The enhancement increases with increasing particle concentration and reaches ∼ ∼40% at a particle loading of 1.25% by weight. Discussion of the results suggests that the reported controversies in the thermal performance of nanofluids under the nucleate pool boiling conditions be associated with the properties and behaviour of the nanofluids and boiling surface, as well as their interactions.This revised version was published online in August 2005 with a corrected issue number.