Parallel trends observed in the dynamics and kinetics of the family of reactions O(3P)+XY→OX+Y (X,Y, halogen atoms) using the quasi-classical trajectory method

Summary We calculate several features in the dynamical behaviour of the reactions O(³P)+XY→OX+Y (XY=Br₂, BrCl) using the quasi-classical trajectory method. The results are compared to analogous results for the reactions O(³P)+Cl₂, I₂. The similarities observed in this homologous series of reactions indicate that the dynamics are influenced to a significant degree by the long-range repulsive forces between the reactants.     

A multicriteria accreditation system for information technology skills and qualifications

Employees must acquire new competences and qualifications throughout their lives, in order to be able to deal with the multiple changes in the labour market. The specific knowledge and competences, acquired either formally or non-formally, must be recognized so that they can be transferred and utilized. The existing titles of studies and accreditation mechanisms do not generally cover this need. This paper aims to propose an integrated approach for the evaluation of information technology knowledge and skills, regardless of where and how they have been acquired, so as to apply a continuous education and training policy. The proposed multicriteria methodology for the evaluation of qualifications and skills concerns candidates wishing to be accredited in an information technology specialization or profession. The methodology refers to the evaluation of the professional experience, studies and vocational training of the candidates for accreditation. It contains the analysis and modelling of the qualitative criteria as well as the implementation of multicriteria aggregation–disaggregation techniques attributing value to each criterion. Then, the candidates are classified in categories of professionals using the Electre Tri method, accepting as input data the multicriteria assessments on each criterion. The proposed evaluation approach has been adapted to the Greek educational system and is applied to a specific example of candidate.     

Modern Modelling Methods in Drying

Several modern modelling techniques are presented as tools for drying science and technology, namely pore networks, discrete element method and population balances. After first presenting results from their own research, the authors indicate what future contributions to a better understanding of the drying process at different levels—single porous particles, agitated and fluidised beds—may be expected.     

Micelle mediated extraction of magnesium from water samples with trizma-chloranilate and determination by flame atomic absorption spectrometry

This article describes an analytical method for the determination of magnesium taking advantage of the cloud point phenomenon employing a suitable chelating agent (chloranilate) for Mg analysis. The method encompasses pre-concentration of the metal chelate followed by flame atomic absorption spectrometry (FAAS) analysis. The chelating agent chosen for this task is a newly synthesised salt of chloranilic acid, trizma-chloranilate, which reacts with Mg but at the same time has a very low affinity for other metallic cations like silicon, aluminium and sodium, which interfere with the determination of Mg in FAAS. The condensed surfactant phase with the metal chelate(s) is introduced into the flame of an atomic absorption spectrometer after its treatment with an acidified methanolic solution. In this way, complex and time-consuming steps for sample treatment are avoided while increased sensitivity is achieved by the presence of both methanol and surfactant in the aspirated sample. The analytical curve was rectilinear in the range of 5-220 mugl(-1) and the limit of detection was as low as 0.75 mugl(-1) with a standard deviation of 5.2%. The method was applied for the determination of Mg in natural and mineral waters with satisfactory results and recoveries in the range of 97-102%.     

Determination of diethylhexyladipate and acetyltributylcitrate in aqueous extracts after cloud point extraction coupled with microwave assisted back extraction and gas chromatographic separation

The determination of commercial plasticizers (di-(2-ethylhexyl)adipate (DEHA) and acetyl tributyl citrate (ATBC)) in aqueous solutions is described. The newly proposed technique of applying microwaves to cloud point extracts in order to enable combination with gas chromatographic analysis has been used for this purpose. Both plasticizers were entrapped in the micelles of the non-ionic surfactant Triton X-114 and removed from the bulk phase by centrifugation. Micellization was enhanced by increasing the ionic strength of the solution with concentrated NaCl. Extraction recoveries of the proposed method were over 95% for water and 3% (w/v) aqueous acetic acid and over 85% for 10% (v/v) aqueous ethanol, respectively. The calibration curves obtained, following the proposed methodology have a linear range between 50 and 2000 microg/L for each analyte while the detection limits were as low as 15 and 19 microg/L for DEHA and ATBC, respectively, with an RSD below 5% even for low concentrations. As an analytical demonstration the proposed methodology was applied for the determination of the migration levels of the selected plasticizers from a PVC food packaging film into aqueous simulants.     

In situ SAXS investigation of dibromomethane adsorption in ordered mesoporous silica

A SAXS/WAXS apparatus with the aid of a specially designed sample cell capable for performing both SAXS and WAXS experiments was used for adsorption studies in nanoporous materials. The applicability of the instrument for structural investigations and its ability for adsorption experiments because of the advanced sample environment were demonstrated by carrying out in situ SAXS measurements during gas physisorption. SAXS profiles of ordered mesoporous silica were measured at selected equilibrium points alongside a dibromomethane (CH₂Br₂) adsorption isotherm at 293 K. SBA-15 was the adsorbent of choice because it consists of a regular 2D hexagonal array of cylindrical mesopores that gives rise to Bragg reflections in the small-angle regime. CH₂Br₂ was selected as a contrast-matching fluid because it has almost the same electron density as silica. We obtained high-quality data comparable to those resulting from experiments performed in synchrotron light sources which produce intense beams of x-rays and support advanced instrumentation for high-resolution diffraction and SAXS studies. The Bragg peaks of the pore lattice are clearly visible for the evacuated sample and at the early stages of the adsorption process. The intensity decrease and the elimination of the Bragg peaks for the saturated sample suggest that an almost perfect contrast matching was achieved. A model has been used for monitoring the fluid condensation and evaporation regime in SBA-15 by taking into account both the Bragg scattering and the diffuse scattering for spatially random pore filling. The results show the absence of spatial correlations between filled pores suggesting random pore filling.     

A modified protocol for isolation and purity evaluation of a staphylococcal acidic polysaccharide by chromatography and capillary electrophoresis

The extracellular slime of Staphylococcus epidermidis contains, amongst various macromolecules, an acidic polysaccharide (PS) of a molecular mass of 20 kDa with significant antigenic and biological properties. The isolation procedure used so far includes multiple fractionations in anion‐exchange chromatographic columns before its final purification by gel filtration chromatography. This protocol is laborious, time‐consuming and includes the risk of unnecessary loss of PS quantities. Because of the significance of this PS, a modified protocol resulting in an easier and quicker isolation procedure was developed. Furthermore, identification, purity, charge density and molecular integity of the isolated polysaccharide were evaluated by a reverse‐polarity capillary electrophoresis method. Copyright © 2010 John Wiley & Sons, Ltd.     

RMSD and Symmetry

A common approach for comparing the structures of biomolecules or solid bodies is to translate and rotate one structure with respect to the other to minimize the pointwise root-mean-square deviation (RMSD). We present a new, robust numerical algorithm that computes the RMSD between two molecules or all the mutual RMSDs of a list of molecules and, if desired, the corresponding rotation matrix in a minimal number of operations as compared to previous algorithms. The RMSD gradient can also be computed. We address the problem of symmetry, both in alignment (possible alternative alignments due to indistinguishable atoms) as well as geometry. In the latter case, it is possible to have degenerate superposition. A necessary condition is optimal superimposability to one's mirror image. Double (respectively, triple) degeneracy results in a one- (respectively, two)-parameter family of rotations leaving the superposition invariant. The software, frmsd , is freely available at http://www.ams.stonybrook.edu/~coutsias/codes/frmsd.tgz . © 2019 Wiley Periodicals, Inc.