Surface vibrational thermodynamics from ab initio calculations for fcc(1 0 0)

We present vibrational dynamics and thermodynamics for the (1 0 0) surfaces of Cu, Ag, Pd, Pt and Au using a real space approach. The force field for these systems is described by density functional theory. The changes in the vibrational dynamics and thermodynamics from those in bulk are confined mostly to the first-layer. A substantial enhancement of the low-frequency end of the acoustic branch was found and is related to a loosening of the bond at the surface. The thermodynamics of the first-layer also show significant differences (higher heat capacity, lower free energy and higher mean vibrational square amplitudes) from what obtains in bulk. Comparing these results with those calculated using embedded-atom method potentials, we discovered that for Ag(1 0 0) and Cu(1 0 0), the two methods yield very similar results while for Pd(1 0 0), Pt(1 0 0) and Au(1 0 0) there are substantial differences.     

The crossover from collective motion to periphery diffusion for two-dimensional adatom-islands on Cu(111)

The diffusion of two-dimensional adatom-islands (up to 100 atoms) on Cu(111) has been studied, using the self-learning kinetic Monte Carlo method (Trushin et?al 2005 Phys. Rev. B 72 115401). A variety of multiple-?and single-atom processes are revealed in the simulations, and the size dependences of the diffusion coefficients and effective diffusion barriers are calculated for each. From the tabulated frequencies of events found in the simulation, we show a crossover from diffusion due to the collective motion of the island to a regime in which the island diffuses through periphery-dominated mass transport. This crossover occurs for island sizes between 13 and 19 atoms. For islands containing 19-100 atoms the scaling exponent is 1.5, which is in good agreement with previous work. The diffusion of islands containing 2-13 atoms can be explained primarily on the basis of a linear increase of the barrier for the collective motion with the size of the island.     

Cycloaddition reactions in aqueous systems: A two-decade trend endeavor

Cycloaddition reactions are an integral and weighty part of organic chemistry in pedagogy and research as well. The wealthy literature on cycloaddition reactions from their birth up to now, unequivocally witnesses to their leading chemistry. The so-called “conventional solvents” are organic solvents that have indubitably promoted their success. Yet, the toxicity facet of these solvents impedes their use freely and with no fear. Not only is the operating chemist uncomfortable while experimenting, but also the environment is equally threatened. Working out the cycloaddition reactions and other organic ones in aqueous systems would certainly bring some relief to the chemist and to the environment as well. Unusual outcomes in terms of yield, reactivity and selectivity compared to those performed in organic solvents were commonly observed, and have overwhelmed the chemists with surprise indeed. In this review, homo Diels–Alder reactions in aqueous media include those involving the following dienophiles: maleimides, α,β-unsaturated esters, p-benzoquinones, vinyl ketones, phenyl-1-(2-pyridyl)-2-propen-1-one, α,β-unsaturated esters. A special case is the organocatalysis of Diels–Alder cycloaddition of α,β-unsaturated ketones (aldehydes). Of no less importance, some hetero Diels–Alder cycloaddition reactions in water systems are delineated. The impact of additives (salts, organic and inorganic chemicals), micellar catalysis and Lewis/Brønstëd acid catalysis on outcomes of such cycloaddition reactions is discussed. The 1,3-dipolar cycloaddition methodology applied to aqueous media has brought forth a number of heterocyclic compounds, usually with a regio- and stereoselectivity pecularity. These heterocycles include triazoles, tetrazoles, pyrazoles, isoxazoles, isoxazolidines, pyrroles and pyrrolidines. The superiority of copper(I) catalysis in the azide-alkyne cycloaddition (Huisgen cycloaddition) in water is endorsed by a number of examples.     

Simultaneous analysis of polychlorinated biphenyls and organochlorine pesticides in water by headspace solid-phase microextraction with gas chromatography-tandem mass spectrometry

Headspace solid-phase microextraction combined with gas chromatography-ion trap tandem mass spectrometry (HS-SPME-GC-ITMS-MS) method has been developed and studied for the simultaneous determination of 15 organochlorine pesticides (OCPs) and 20 polychlorinated biphenyls (PCBs) in aqueous samples. To perform the HS-SPME polydimethylsiloxane (PDMS) (7, 30 and 100 microm film thickness) and polydimethylsiloxane-divinylbenzene (PDMS-DVB) fibers were initially compared on the basis of their absorption capacities for the selected compounds, and PDMS 100 microm film thickness was selected to accomplish the rests of essays. The influence of various parameters on OCPs and PCBs extraction efficiency by HS-SPME was thoroughly studied using GC-electron capture detector (ECD). Parameters such as collision induced dissociation (CID) resonant excitation amplitude and RF storage level were optimized to increase specificity and sensibility for ITMS-MS analysis. The performance of proposed HS-SPME-GC-ITMS-MS methodology with respect to linearity, reproducibility and limit of detection (LOD) was evaluated by water spiked with target compounds. The linear range of most compounds was found to be between 0.01 and 1 ng mL(-1) and the limits of detection were between 0.4 and 26 pg mL(-1). The reproducibility of the method (n = 6), expressed as relative standard deviation (RSD), was between 5 and 21%. Finally, developed procedure was applied to determine selected OCPs and PCBs in river water samples in concentration below 0.1 ng mL(-1) can be easily carried out with ultra-selectivity and precision.     

Structural and textural features of TiO<Subscript>2</Subscript>/SAPO-34 nanocomposite prepared by the sol–gel method

This paper focuses on the synthesis of nanocomposite materials, TiO₂/SAPO-34, using the sol–gel method, which involves preparing a mixture between as-synthesized or calcined SAPO-34 zeolite and TiO₂ gel under hydrothermal crystallization and then calcining it at 400 °C for the formation of the TiO₂ anatase phase. The structural and textural features of the obtained materials were determined by various physico-chemical techniques such as thermogravimetric analysis, X-ray diffraction, scanning electronic microscopy, nitrogen sorption at 77 K, energy dispersive X-ray analysis and ultraviolet–visible spectrometry. The DRX results showed that calcination at 400 °C of the mixture between the calcined SAPO-34 and TiO₂ gel led to the collapse of the original framework of zeolite, but formed the anatase TiO₂ in a nano-spherical morphology; however, the use of as-synthesized SAPO-34 supports provides a mixture phase between SAPO-34 and TiO₂ anatase after calcination. The photocatalytic properties of the SAPO-34/TiO₂ and TiO₂-type materials were tested for the removal of methylene blue (MB) dye. The MB degradation proved to increase as a function of contact time, catalyst mass and the initial concentration of MB.     

Photosensitive polymers with cinnamate units in the side position of chains: Synthesis, monomer reactivity ratios and photoreactivity

Ethyl α-cyano-4-(methacryloxy)cinnamate was synthesized to prepare new photosensitive polymers. Homopolymerization and copolymerizations were carried out in solution in chloroform at 65 °C using AIBN as an initiator. Methyl methacrylate was chosen as comonomer for the studies of copolymerzation. The structures formed were characterized by IR and ¹H NMR spectroscopies. The values of reactivity ratios of the comonomers calculated according to the Finneman-Ross method indicated that the reactivity of the synthesized photosensitive monomer is lower than that of MMA. Thin films of the obtained polymers were prepared to study their ability to crosslink under UV irradiation. The photodimerization of the cinnamate moieties was characterized.     

General Energy Decay for a Viscoelastic Equation of Kirchhoff Type with Acoustic Boundary Conditions

This paper is concerned with a viscoelastic equation of Kirchhoff type with acoustic boundary conditions in a bounded domain of \(\mathbb {R}^{n}.\) We show that, under suitable conditions on the initial data, the solution exists globally in time. Then, we prove the general energy decay of global solutions by applying a lemma of Martinez, which allows us to get our decay result for a class of relaxation functions wider than that usually considered.     

Ck-regularity for the $$\bar \partial $$ -equation with a support condition

Let D be a C ^d q-convex intersection, d ≥ 2, 0 ≤ q ≤ n ? 1, in a complex manifold X of complex dimension n, n ≥ 2, and let E be a holomorphic vector bundle of rank N over X. In this paper, C ^k -estimates, k = 2, 3,...,∞, for solutions to the \(\bar \partial \)-equation with small loss of smoothness are obtained for E-valued (0, s)-forms on D when n ? q ≤ s ≤ n. In addition, we solve the \(\bar \partial \)-equation with a support condition in C ^k -spaces. More precisely, we prove that for a \(\bar \partial \)-closed form f in C _0,q ^k (X D,E), 1 ≤ q ≤ n ? 2, n ≥ 3, with compact support and for ε with 0 < ε < 1 there exists a form u in C _0,q?1 ^k?ε (X D,E) with compact support such that \(\bar \partial u = f\) in \(X\backslash \bar D\). Applications are given for a separation theorem of Andreotti-Vesentini type in C ^k -setting and for the solvability of the \(\bar \partial \)-equation for currents.