Stoichiometric formation of methyl methacrylate oligomer by triethylaluminum in the presence of azobisisobutyronitrile

The yield of methyl methacrylate (MMA) polymerization as a function of triethylaluminum (TEA) concentration for a constant azobisisobutyronitrile (AIBN) concentration at 50°C has been measured. The polymerization yield does not differ markedly from that with AIBN alone as long as the initial TEA concentration is held smaller than four times the initial AIBN concentration. A sudden decrease in yield and molecular weight is observed at TEA/AIBN concentration ratios between 4 and 5. A plot of M?_w^?1 vs. TEA gives a rate-transfer constant of 89 1./mole-sec. If the reaction mixture is vacuum-evaporated with a previous addition of water, instead of precipitating the polymer, the formation of a considerable amount of MMA oligomer is detected for TEA/AIBN concentration ratios larger than 4. On the average, each TEA molecule in excess of four times the initial amount of AIBN yields one oligomer molecule. The data are consistent with a radical polymerization mechanism for the high molecular weight polymer and with a nonradical one for the oligomer formation.     

Complexity of Gaussian-radial-basis networks approximating smooth functions

Complexity of Gaussian-radial-basis-function networks, with varying widths, is investigated. Upper bounds on rates of decrease of approximation errors with increasing number of hidden units are derived. Bounds are in terms of norms measuring smoothness (Bessel and Sobolev norms) multiplied by explicitly given functions a(r,d)$a(r,d)$ of the number of variables d$d$ and degree of smoothness r$r$. Estimates are proven using suitable integral representations in the form of networks with continua of hidden units computing scaled Gaussians and translated Bessel potentials. Consequences on tractability of approximation by Gaussian-radial-basis function networks are discussed.     

Combining standard addition method and second-order advantage for direct determination of salicylate in undiluted human plasma by spectrofluorimetry

Second-order advantage turns possible a determination in the presence of unknown interferences. This work presented an application of the second-order advantage provided by parallel factor analysis (PARAFAC). The aim was the direct determination of salicylic acid (SA), the main product of aspirin degradation, in undiluted human plasma by spectrofluorimetry. The strategy of this analysis combined the use of PARAFAC, for extraction of the pure analyte signal, with the standard addition method, for a determination in the presence of a strong matrix effect caused by the quenching effect of the proteins present in the plasma. For each sample, four standard additions were performed, in triplicates. A specific PARAFAC model was built for each triplicate of each sample, from three-way arrays formed by 436 emission wavelengths, 7 excitation wavelengths and 5 measurements (sample plus 4 additions). In all the cases, the models were built with three factors and explained more than 99.90% of the total variance. The obtained loadings were related to SA and two background interferences. The scores related to SA were used for a linear regression in the standard addition method. Good results were obtained for determinations in the SA concentration range from 3.0 to 24.0 μg ml⁻¹, providing errors of prediction between 0.7 and 6.3%.     

A novel method to prepare inorganic water-soluble nanocrystals

Calcium sulphate dihydrate nanocrystals of 25-100 nm width have been synthesized in 100% purity and yield by means of a method--the cryo-vacuum process--consisting of rapid freezing of quasi-saturated solutions and subsequent vacuum assisted sublimation of water. Transmission electron microscopy reveals both curled nano-lamellae and smaller, irregular particles; electron diffraction patterns demonstrated that the particles are crystalline. This is a very powerful method for the 'clean' synthesis of moderately and completely water-soluble inorganic materials.     

Enhanced electro-catalytic degradation of chloroorganic compounds in the presence of ultrasound

The application of finely divided (black) Pd and Pd-Fe powder in the sono-electro-catalytic reduction of chlorophenoxy herbicides (2,4-D) and chlorophenols (2,4-DCP) in aqueous solutions allows for effective destruction of toxic chlorinated aromatic compounds. At 20 degrees C complete conversion of these compounds is observed within 10 min. On bimetallic Pd/Fe catalyst, intermediates due to the oxidation reaction are detected in addition to the products of dechlorination. The bimetallic catalyst appears to be energetically and economically superior to the Pd. In both cases, the reaction times were considerably shortened in comparison with traditional electro-catalytic processes.     

General models of Einstein gravity with a non-Newtonian weak-field limit

We investigate Einstein theories of gravity, coupled to a scalar field j{\varphi} and point-like matter, which are characterized by a scalar field-dependent matter coupling function e^H(j){e^{H(\varphi)}} . We show that under mild constraints on the form of the potential for the scalar field, there are a broad class of Einstein-like gravity models—characterized by the asymptotic behavior of H—which allow for a non-Newtonian weak-field limit with the gravitational potential behaving for large distances as ln r. The Newtonian term GM/r appears only as sub-leading. We point out that this behavior is also shared by gravity models described by f (R) Lagrangians. The relevance of our results for the building of infrared modified theories of gravity and for modified Newtonian dynamics is also discussed.     

Atmospheric aqueous-phase photoreactivity: correlation between the hydroxyl radical photoformation and pesticide degradation rate in atmospherically relevant waters

In the present study, we investigated the correlation between the hydroxyl radical formation rate (R_˙OH) and the degradation of a pesticide (mesotrione) in synthetic cloud water solutions and in two real atmospheric cloud waters collected at the top of puy de Dôme station (France). Using terephthalic acid as the hydroxyl radical chemical probe, we established the linear correlation between the photogenerated hydroxyl radical under polychromatic wavelengths and the pesticide degradation rate: (m s^?1) = (1.61 ± 0.15) × 10^?1(m s^?1). Moreover, the formation rate of hydroxyl radical in two natural cloud waters was estimated considering H₂O₂ and NO₃^? and the difference between the predicted values and those experimentally obtained could be attributed to the presence of other photochemical sources: iron‐complexes and total organic matter. The organic constituents could play a dual role of sources and scavengers of photoformed hydroxyl radicals in the aqueous phase.     

Analysis of stress and strain in tension cylindrical sample

One of the basic engineering problem occurring during the numerical analysis is to define the function of yield stress of material in the real conditions of a technological process. These properties are necessary to calculate the deformation and the state of stress and strain in the surface layer of an object. An inappropriate selection of the mechanical properties of the material is the reason of the occurrence of errors in numerical calculations of a continuous object, considered as a boundary and initial problem. Scientific investigations are being conducted with the aim to develop a database concerning yield stresses for different metals, depends on complex conditions of thermo-dynamical loads, e.g. temperature, the equivalent of the strain and the strain rate. The article presents a method of the determination of this dependence while using an experimental and numerical analysis. During the model investigations on the INSTRON testing machine, the force of elongation of the sample is measured and then calculations are made of the displacement of nodes of finite elements, plotted on outside surface of sample. The process is considered as a multi nonlinear problem. For this reason, an incremental method of motion and deformation of solid in an updated Lagrange formulation is used. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Iodosobenzene Diacetate and Diphenyl Diselenide: An Electrophilic Selenenylating Agent of Double Bonds

Phenylseleno-acetoxylation, hydroxylation, etherification and lactonization products are obtained in good yields from the reaction of alkenes with diphenyl diselenide and iodosobenzene diacetate, in acetonitrile.