Determination of petroleum hydrocarbons in contaminated soils using solid-phase microextraction with gas chromatography-mass spectrometry.

Manual solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry is investigated as a possible alternative for the determination of petroleum hydrocarbons in soils. Spiked onto an agricultural soil is a commercial diesel fuel (DF) with the following composition by weight: 12% linear alkanes, 52% saturated hydrocarbons (branched and cyclic), 21% alkylated aromatic hydrocarbons, 6% polycyclic aromatic hydrocarbons, and 9% unidentified compounds. The spiked soil samples are aged three days at room temperature before analysis. The optimal conditions for the SPME of DF from soils are examined and maximum sensitivity is obtained using a 100-microm polydimethylsiloxane fiber at a sampling temperature of 47 degrees C by sonication both in the headspace and directly through a water medium. The reproducibility of the whole technique showed a relative standard deviation of 10%. The parameters that can influence the recovery of DF (such as the time of SPME extraction, the presence of organic solvent and water, and the matrix) are investigated. The linearity is verified in the range of 40 to 1200 mg/L for the direct injection of DF, 0.1 to 1 mg/L for the SPME of DF from water, and 1 to 50 mg/Kg of dry soil for the SPME of DF from soils. The detection limits are respectively 0.5 mg/L, 0.02 mg/L, and 0.1 mg/Kg of dry soil. The method is corroborated by comparing the results with those obtained by the traditional way.     

CFD by first order PDEs

This research originally was aimed at modeling all flows (except free-molecular) by systems of hyperbolic-relaxation equations (moments of the Boltzmann equation), and developing efficient numerical methods for these. Such systems have many potential numerical advantages, mainly because there are no second or higher derivatives to be approximated. This avoids accuracy problems on adaptive unstructured grids, and the source terms, though often stiff, are only local; the compact stencils facilitate code parallelization. A single code could simulate flows up to intermediate Knudsen numbers, and be hybridized with DSMC where needed. In this project, one major problem arose that we have not yet solved: the accurate representation of shock structures. This makes the methodology currently unsuited for, e.g., re-entry flows. We have validated it for subsonic and transonic flows and are concentrating on applications to MEMS-related flows. We discuss the challenges of our approach, present numerical algorithms and results based on the 10-moment model, and report progress in our latest research topic: formulating accurate solid-boundary conditions.     

Sampling from Non-smooth Distributions Through Langevin Diffusion

Methodology and Computing in Applied Probability - In this paper, we propose proximal splitting-type algorithms for sampling from distributions whose densities are not necessarily smooth nor...     

Interaction between excitons in 3D and 2D laser-excited semiconductors

Analytical expressions of the exciton-exciton interaction in 3D and 2D laser-excited semiconductors are approximately derived in rather easy-to-handle forms which enable us to study in detail their dependences on the exciton momenta, the momentum transferred between two excitons and the electron-hole mass ratio.We would like to thank Prof. Nguyen Van Hieu and Prof. Dao Vong Due for their support given to us in the research of highly excited media.     

Combinatorial properties of some classes of matrices over GF(2)

We study several classes of matrices of GF(2) constructed from lists of subsets of finite sets In this paper. We show that all matrices in these classes are representations of connected equicardinal matrix over GF(2). In Matrix terms, these irreducible (defined below) matrices all have the property that every minimal dependent set of column has the same cardinality over GF(2). This fact is shown directly in this paper by elementary matrix considerations. In a subsequent paper, we shall show that these classes of matrices are in fact the classes of canonical forms for all representations of nontrivial binary connected equicardinal matroids.     

Liquid crystalline complexes of 4-alkoxystilbazoles with silver 1,12-dodecylene disulphate

A new series of metal complexes of silver(I) 1,12-dodecylene disulphate with 4-alkoxystilbazole ligands has been synthesized. These difunctional silver stilbazole complexes are mesomorphic, showing a nematic phase at short chain lengths and SmA and SmC phases at longer chain lengths. The single crystal X-ray structure of the hexyloxy homologue shows a polymerized arrangement of sulphate-bridged dimers.     

Worst case uncertainty estimates for routine instrumental analysis

A methodology for the worst case measurement uncertainty estimation for analytical methods which include an instrumental quantification step, adequate for routine determinations, is presented. Although the methodology presented should be based on a careful evaluation of the analytical method, the resulting daily calculations are very simple. The methodology is based on the estimation of the maximum value for the different sources of uncertainty and requires the definition of limiting values for certain analytical parameters. The simplification of the instrumental quantification uncertainty estimation involves the use of the standard deviation obtained from control charts relating to the concentrations estimated from the calibration curves for control standards at the highest calibration level. Three levels of simplification are suggested, as alternatives to the detailed approach, which can be selected according to the proximity of the sample results to decision limits. These approaches were applied to the determination of pesticide residues in apples (CEN, EN 12393), for which the most simplified approach showed a relative expanded uncertainty of 37.2% for a confidence level of approximately 95%.     

Acidity function p(a(H) gamma(Cl)) as a step to pH assessment

The conventional assignment of pH reference buffer standards, pH(S), is achieved by means of a series of procedures that follow from measurement of Harned cell potentials for an electrolyte solution which is the buffer solution of interest. An intermediate step is assessment of the acidity function p( a(H) gamma(Cl))(0), the extrapolated value of a linear representation of the dependence of p( a(H) gamma(Cl)) on m(Cl) for at least three different molalities, m(Cl), of added alkali chloride (0.005; 0.010; 0.015 mol kg(-1) KCl). This experimental value can be compared with a theoretically expected value calculated from the dissociation constants of the buffer species. Whereas these calculations always give negative slopes for diprotic and triprotic acids and zero slope for monoprotic acids, experimental values with negative or positive slopes can be obtained for well fitting straight lines obtained for buffer solutions with ionic strengths from 0.0025 to 0.144 mol kg(-1). Such disagreement between theoretically and experimentally obtained values introduce an extra source of uncertainty in the establishment of pH(S) and on its traceability chain. In this work examples are presented and discussed for which the discrepancy between expected and experimental values leads to different intercept p( a(H) gamma(Cl))(0).     

Microalgae and bioremediation of domestic wastewater

Domestic wastewaters are produced in huge volumes and abundant with carbon, nitrogen and phosphorous, which are a promising source of nutrients for production of microalgae. Microalgae-based bioremediation of domestic wastewater offers various advantages over traditional treatment approaches because the process consumes CO₂, completely removes nitrogen and phosphorous for production of green biomass and oxygen. Moreover, the abundance of biochemical compositions (e.g., lipids, proteins, carbohydrates, bioactive compounds) of microalgae biomass is superior to terrestrial plant biomass in refining to multi-products having variety of commercial values. In this review, the most dominant microalgae used for simultaneous removal of pollutants and production of biomass and metabolites from domestic wastewater are presented. Biorefinery of microalgae biomass produced from domestic wastewater for production of multiple products is also explored. Finally, challenges and perspectives of successful microalgae-based bioremediation of domestic wastewater toward the biorefinery are briefly discussed.