Photocatalytic Activity of Au/TiO2 Photocatalysts for H2 Evolution: Role of the Au Nanoparticles as a Function of the Irradiation Wavelength

An investigation of hydrogen production with a series of Au/TiO₂ photocatalysts reveals that the Au nanoparticles play different roles depending on the wavelength of the light irradiation. Under visible‐light irradiation, the photoactivity is primarily controlled by the intensity of the Au surface plasmon band, whereas under UV irradiation the Au nanoparticles act as co‐catalysts with TiO₂.     

Snaking states on a cylindrical surface in a perpendicular magnetic field

We calculate electronic states on a closed cylindrical surface as a model of a core-shell nanowire. The length of the cylinder can be infinite or finite. We define cardinal points on the circumference of the cylinder and consider a spatially uniform magnetic field perpendicular to the cylinder axis, in the direction South-North. The orbital motion of the electrons depends on the radial component of the field which is nonuniform around the circumference: it is equal to the total field at North and South, but vanishes at the West and East sides. For a strong field, when the magnetic length is comparable to the radius of the cylinder, the electronic states at North and South become localized cyclotron orbits, whereas at East and West the states become long and narrow snaking orbits propagating along the cylinder. The energy of the cyclotron states increases with the magnetic field whereas the energy of the snaking states is stable. Consequently, at high magnetic fields the electron density vanishes at North and South and concentrates at East and West. We include spin-orbit interaction with linear Rashba and Dresselhaus models. For a cylinder of finite length the Dresselhaus interaction produces an axial twist of the charge density relative to the center of the wire, which may be amplified in the presence of the Rashba interaction.     

One-dimensional atomic transport by clusters of self-interstitial atoms in iron and copper

Atomic-scale computer simulation has been used to study the thermally activated atomic transport of self-interstitial atoms (SIAs) in the form of planar clusters in pure Cu and f-Fe. There is strong evidence that such clusters are commonly formed in metals during irradiation with high-energy particles and play an important role in accumulation and spatial distribution of surviving defects. An extensive study of the mobility of SIA clusters containing two to 331 interstitials has been carried out using the molecular dynamics simulation technique for the temperature range from 180 to 1200 K. The results obtained show that clusters larger than three to four SIAs are one-dimensionally mobile in both Cu and Fe. Large clusters of more than 100 SIAs in Cu and 300 SIAs in Fe have significantly reduced mobility. The problem of describing one-dimensional (1D) motion in three-dimensional space is discussed. An attempt is made to describe the mobility of SIA clusters within the approximation of 1D diffusion. For clusters in both metals the effective migration energy of 1D diffusion as estimated via the jump frequency of the cluster centre of mass is found to be independent of the number of SIAs in the clusters, although the cluster jump frequency decreases with increasing cluster size. Mechanisms of 1D mobility of interstitial clusters are discussed.     

Temperature Oscillating mini-calorimeter

A small scale (100 mL) calorimeter is developed. It includes a glass vessel submerged in a thermostatic bath, a compensation electrical heater, and a control system. The typical operation mode consists on introducing the solvents and part of the reactants into the vessel, to stabilise a temperature of the bath (T _j) some degrees below the desired process temperature (T _p) and to adjust the reaction mass temperature (T _r) to T _p using the electrical heater. An oscillating set point is established for Tr, which produces an oscillating response of the applied compensation power (Q _c). Finally, the rest of reactants are dosed to the vessel. A small deviation of T _r and T _p is observed. Even though it can be avoided improving the tuning of the controller, it can be useful for enhancing the calculation of the heat capacity of the reaction mixture (C _P). The signals of T _r, Q _c and T _j are processed on-line using the FFT (Fast Fourier Transform) method as the mathematical tool used to analyse the data obtained, producing accurate values of the heat evolved (Q _c) by the process, the heat transfer coefficient (UA), and the heat capacity of the reaction mixture (C _P). This revised version was published online in July 2006 with corrections to the Cover Date.     

Inter‐laboratory comparison of elemental analysis and gas chromatography/combustion/isotope ratio mass spectrometry. II. δ15N measurements of selected compounds for the development of an isotopic Grob test

An inter‐laboratory exercise was carried out by a consortium of five European laboratories to establish a set of compounds, suitable for calibrating gas chromatography/combustion/isotope ratio mass spectrometry (GC‐C‐IRMS) devices, to be used as isotopic reference materials for hydrogen, carbon, nitrogen and oxygen stable isotope measurements. The set of compounds was chosen with the aim of developing a mixture of reference materials to be used in analytical protocols to check for food and beverage authentication. The exercise was organized in several steps to achieve the certification level: the first step consisted of the a priori selection of chemical compounds on the basis of the scientific literature and successive GC tests to set the analytical conditions for each single compound and the mixture. After elimination of the compounds that turned out to be unsuitable in a multi‐compound mixture, some additional oxygen‐ and nitrogen‐containing substances were added to complete the range of calibration isotopes. The results of δ¹³C determinations for the entire set of reference compounds have previously been published, while the δD and δ¹⁸O determinations were unsuccessful and after statistical analysis of the data the results did not reach the level required for certification. In the present paper we present the results of an inter‐laboratory exercise to identify and test the set of nitrogen‐containing compounds present in the mixture developed for use as reference materials for the validation of GC‐C‐IRMS analyses in individual laboratories. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of preheating and hematite content of clay brick pavers on the characteristics of lines marked with a Nd:YAG laser

This paper reports the clay brick pavers marking by vitrification with a continuous wave Nd:YAG laser (1064 nm). The influence of a preheating and the chemical composition of the bricks on the morphological, visual and dimensional characteristics was studied. The lines marked at room temperature resulted in a discontinuous green glassy phase due to the presence of defects. A remarkable reduction of the defect amount, resulting in smooth, gleaming and darker lines, was obtained when preheating the bricks at 350 °C. The green tone, width, depth and cross-section area of the lines depend on the bricks’ chemical composition and thermal condition, as well as, on the laser energy density. Thus, decorative patterns of good visual quality can be marked by laser vitrification on clay brick pavers preheated at 350 °C.     

A New Chance-Constrained Maximum Capture Location Problem

The paper presents a new model based on the basic Maximum Capture model, MAXCAP. The new Chance-Constrained Maximum Capture model introduces a stochastic threshold constraint, which recognises the fact that a facility can be open only if a minimum level of demand is captured. A metaheuristic based on Max-Min Ant System and Tabu Search procedure is presented to solve the model. This is the first time that the Max-Min Ant system is adapted to solve a location problem. Computational experience and an application to 55-node network are also presented.     

Dimeric liquid‐crystalline epoxyimine monomers: Influence of dipolar moments on mesomorphic behavior and the formation of liquid‐crystalline thermosets

We examine some of the structural aspects that influence the mesomorphic behavior of liquid‐crystalline dimeric epoxy resins with imine groups in the mesogens. We synthesized two new series of monomers and compared them with previously synthesized monomers. Compared with previously studied series, the imine group in the new monomers is oriented differently with respect to the ether and ester groups linked to the end of the mesogenic unit. Our results confirmed the importance of polarization of the mesogenic groups and the presence of an ester group in the inner position in the formation of smectic mesophases. By curing with primary and tertiary amines, we demonstrate that these two requirements are necessary if liquid‐crystalline thermosets are to be obtained with different degrees of order. These studies were carried out with differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1465–1477, 2003     

Liquid‐crystalline thermosets from liquid‐crystalline epoxy resins containing bisazomethinebiphenylene mesogens in the central core: Copolymerization with a nonmesomorphic epoxy resin

A new series of liquid‐crystalline epoxy resins was synthesized, and their mesomorphic behavior was investigated with differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray scattering. These glycidylic compounds had central aromatic imine mesogens derived from benzidine and aliphatic spacers of up to 10 methylene units that linked the mesogens to the glycidylic groups. Crosslinking these monomers with primary aromatic diamines led to nematic networks, some of which contained crystal inclusions. However, through curing with tertiary amines as catalytic agents or through copolymerization with different proportions of the nonmesomorphic epoxy monomer and primary amines as crosslinking agents, smectic C organized thermosets were prepared when the spacers had at least four methylene carbons. When they had fewer than four, the networks were nematic. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3631–3643, 2004     

Cationic copolymerization of diglycidyl ether of bisphenol A with phthalide or 3,3′‐diphtalide catalyzed by lanthanide triflates

Mixtures of the diglycidylether of bisphenol A (DGEBA) and phthalide (PT) or 3,3′‐diphthalide (DPT) were cured using ytterbium or lanthanum triflate as catalyst. The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and quantify the evolution of the epoxide and lactone groups. The T_g of the crosslinked materials increased when the proportion of lactone in the curing mixture decreased. The kinetics was studied with DSC experiments and isoconversional procedures. The differences in the reactivity of the systems were related to the Lewis acidity of the lanthanide salt used as initiator. The increase in the proportion of lactone leads to an increase in the reaction rate. The shrinkage was determined from the densities before and after curing and its evolution was studied by thermomechanical analysis. The materials obtained were characterized by thermogravimetry and dynamic mechanical thermal analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1711–1721, 2006