Photodegradation of butyl acrylate in the troposphere by OH radicals: kinetics and fate of 1,2‐hydroxyalcoxy radicals

The rate constant of the reaction of OH radicals with butyl acrylate was studied for the first time using an atmospheric simulation chamber at 298 K and ～750 Torr of air or nitrogen. The decay of the organics was followed using a gas chromatograph with a flame ionization detector (GC‐FID), and the rate constant was determined using a relative rate method with different references. The obtained average value of (1.80 ± 0.26) × 10^?11 cm³ molecule^?1 s^?1 is in agreement with previous determinations of the rate constants of OH radicals with acrylates and methacrylates in the literature. Additionally, product identification under atmospheric conditions was performed for the first time by the GC‐MS technique. Butyl glyoxalate was observed as the degradation product in accordance with the addition of OH to the less substituted carbon atom of the double bond, followed by decomposition of the 1,2‐hydroxyalkoxy radicals formed. Room temperature rate coefficient was used to estimate the atmospheric lifetime of the ester studied. Reactivity trends are discussed in terms of the substituent effects and the length of the hydrogenated chain of the ester. The atmospheric persistence of BUAC was calculated taking into account the experimental rate constant obtained. Copyright © 2008 John Wiley & Sons, Ltd.     

Cryopreservation of embryogenic cultures from mature Quercus suber trees using vitrification

Recent progress in somatic embryogenesis from selected mature trees of Quercus suber, has led to a demand for maintenance of a large number of selected embryogenic lines. To facilitate the management of this material a protocol for the long-term storage of this germplasm should be defined. This study reports on the use of a simple vitrification procedure for the successful cryopreservation of three cork oak embryogenic lines. High embryo recovery levels (88-93 percent) were obtained by first preculturing 2-4 mg clumps of two or three globular embryos on semisolid medium containing 0.3 M sucrose for three days, followed by incubation in PVS2 vitrification solution at 0 degree C for 60 min before direct immersion in liquid nitrogen. The mean number of embryos produced per explant was significantly greater for cryostored embryos than for untreated stock cultures, but the productivity of the latter was recovered in subsequent subcultures of the material produced by cryostored embryos. The germination and plant regeneration rates achieved by cultures derived from cryostored embryos, around 60 percent, were similar to those of non-cryopreserved stock cultures.     

Half-quadratic cost functions for phase unwrapping

We present a generic regularized formulation, based on robust half-quadratic regularization, for unwrapping noisy and discontinuous wrapped phase maps. Two cases are presented: the convex case and the nonconvex case. The unwrapped phase with the convex formulation is unique and robust to noise; however, the convex function solution deteriorates as a result of real discontinuities in phase maps. Therefore we also present a nonconvex formulation that, with a parameter continuation strategy, shows superior performance.     

Unstable Particles, Gauge Invariance and the Δ++ Resonance Parameters

The elastic and radiative ⁺ p scattering are studied in the framework of an effective Lagrangian model for the ⁺⁺ resonance and its interactions. The finite width effects of this spin-3/2 resonance are introduced in the scattering amplitudes through a complex mass scheme to respect electromagnetic gauge invariance. The resonant pole ( ⁺⁺) and background contributions ( ⁰, , , and neutron states) are separated according to the principles of the analytic S-matrix theory. The mass and width parameters of the ⁺⁺ obtained from a fit to experimental data on the total cross section are in agreement with the results of a model-independent analysis based on the analytic S-matrix approach. The magnetic dipole moment determined from the radiative ⁺ p scattering is nuclear magnetons.     

Synthesis of carbon nanotubes by CVD: Effect of acetylene pressure on nanotubes characteristics

The effect of acetylene partial pressure on the structural and morphological properties of multi-walled carbon nanotubes (MWCNTs) synthesized by CVD on iron nanoparticles dispersed in a SiO₂ matrix as catalyst was investigated. The general growing conditions were: 110 cm³/min flow rate, 690 °C synthesis temperature, 180 Torr over pressure and two gas compositions: 2.5% and 10% C₂H₂/N₂. The catalyst and nanotubes were characterized by HR-TEM, SEM and DRX. TGA and DTA were also carried out to study degradation stages of synthesized CNTs. MWCNTs synthesized with low acetylene concentration are more regular and with a lower amount of amorphous carbon than those synthesized with a high concentration. During the synthesis of CNTs, amorphous carbon nanoparticles nucleate on the external wall of the nanotubes. At high acetylene concentration carbon nanoparticles grow, covering all CNTs’ surface, forming a compact coating. The combination of CNTs with this coating of amorphous carbon nanoparticles lead to a material with high decomposition temperature.     

Voltammetric analysis of Pb(II) in natural waters using a carbon paste electrode modified with 5-mercapto-1-methyltetrazol grafted on hexagonal mesoporous silica

A hexagonal mesoporous silica (HMS) functionalized with a 5-mercapto-1-methyltetrazole derivative was employed to prepare a chemically modified carbon paste electrode for Pb(II) detection in aqueous solution by square wave adsorptive stripping voltammetry. The optimal operating conditions were 5 min preconcentration time at pH 6.5, and 120 s electrolysis time in 0.2 mol L^?1 HCl. Under these conditions, the voltammetric signal increased linearly with the preconcentration time in the range 1 to 10 min and with the Pb(II) concentration in the range 1 to 100?µg L^?1. The electrode was reproducible and sensitive. Simultaneous determination of Pb, Cd and Cu was also carried out with the electrode. The accuracy of the method was validated by analysing Pb(II) in tap water and groundwater samples.