Electrochemical fluorination: state of the art and future tendences

A brief survey of the ECF process for the preparation of perfluorinated organo-compounds is given. The yield of perfluorinated products depends on the experimental conditions and on the nature of the starting material. Some useful rules are reported in order to optimise the ECF process. An improved operational technique allowed to obtain high yield of perfluorodimorpholinepropane (PFDMP) by simultaneous fluorination of dimorpholinepropane and N-methylmorpholine.     

The (InGa)As-(InAl)As resonant tunnelling double barrier structure subjected to a transverse magnetic field

Magneto-tunnelling (B·J) is investigated in a symmetric double barrier resonant tunnelling device based on (InGa)As-(InAl)As. The effects of the Γ conduction band non-parabolicity are observed through the appearance of terms proportional to B³ and B⁴ in the dependence of Vp, the voltage at the current peak position of the I–V characteristics, on the magnetic field. A theoretical analysis considering pertubation theory and a simplified form of the formalism developed by Ekenberg [Phys. Rev. , 7714(1989)] is done which is in qualitative agreement with the experimental results.     

Importance of enolate anions in the high-pressure kinetics of nitroalkanes and nitroaromatics

We review and systematize experimental evidence concerning the extreme high-pressure kinetics of condensed phase nitroalkanes and nitroaromatics. This systematization suggests that enolate aci anions of the nitroalkanes and enolate aci-quinone anions of the nitroaromatics are important in the initial high-pressure kinetics of such systems. Kinetic data from experiments which observed the effect of: (1) small amounts of chemical additives, (2) substitution for protons, (3) difference in chemical isomer, (4) exposure to ultra-violet light, and (5) application of very high pressure can all be rationalized within the framework of our hypothesis. We suggest a static high-pressure ultra-violet absorption spectroscopy experiment on nitromethane that would test the proposed hypothesis.     

Z-scan theoretical analysis for three-, four- and five-photon absorption

In this work, we report a theoretical analysis of three-, four- and five-photon absorption process using the open aperture Z-scan technique. The normalized transmittance equations presented here can be used to fit the experimental data, allowing the determination of material’s multi-photon absorption cross-section. Through simulations, we observed the expected sharpening of the Z-scan curve for higher order nonlinear absorption. The normalized transmittance change as a function of the excitation irradiance displays distinct slopes for process with distinct number of photons, which can be used for determining the origin of the nonlinear processes. Optical limiting curves were also simulated for multi-photon absorption processes, demonstrating that high limiting thresholds occur for higher order processes.     

New tuning rules for fractional PIα controllers

This paper describes a new tuning method for fractional PI^α controllers. The main theoretical contribution of the paper is the analytical solution of a nonlinear function minimization problem, which plays a central role in deriving the tuning formulae. These formulae take advantage of the fractional order α to offer an excellent tradeoff between dynamic performances and stability robustness. Finally, a position control is implemented to compare laboratory experiments with computer simulations. The comparison results show the good performance of the tuning formulae.     

A 3-D dielectrophoretic filter chip

The paper presents a 3-D filter chip employing both mechanical and dielectrophoretic (DEP) filtration, and its corresponding microfabrication techniques. The device structure is similar to a classical capacitor: two planar electrodes, made from a stainless steel mesh, and bonded on both sides of a glass frame filled with round silica beads. The solution with the suspension of particles flows through both the mesh-electrodes and silica beads filter. The top stainless steel mesh (with openings of 60 mum and wires of 30 mum-thickness) provides the first stage of filtration based on mechanical trapping. A second level of filtration is based on DEP by using the nonuniformities of the electric field generated in the capacitor due to the nonuniformities of the dielectric medium. The filter can work also with DC and AC electric fields. The device was tested with yeast cells (Saccharomyces cerevisae) and achieved a maximal trapping efficiency of 75% at an applied AC voltage of 200 V and a flow rate of 0.1 mL/min, from an initial concentration of cells of 5 x 10(5) cells/mL. When the applied frequency was varieted in the range between 20 and 200 kHz, a minimal value of capture efficiency (3%) was notticed at 50 kHz, when yeast cells exhibit negative DEP and the cells are repelled in the space between the beads.     

Elastic Scattering of CH4 by Electron Impact

In this work we present a theoretical study on electrons scattering by CH₄ in the intermediate energy range. More specifically, we report integral and differential cross sections for electron scattering by CH₄ in the (10～300) eV range by the Schwinger multichannel method using plane waves as a trial basis set (SMC-PW). To include exchange effects we have used the Born-Ochkur model. Our aim is to study the numerical stability of the cross sections and our calculated results compared with experimental data and theoretical studies are encouraging.     

Determination of organochlorine pesticide residues in medicinal plants sold in Coimbra, Portugal.

Levels of 14 organochlorine pesticide residues--1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) group (p,p'-DDT, o,p'-DDT, p,p'-DDD, and p,p'-DDE), HCH isomers (alpha-, beta-, and gamma-HCH), hexachlorobenzene (HCB), aldrin, dieldrin, endrin, heptachlor, alpha-endosulfan, and endosulfan sulfate--were evaluated in 127 samples of medicinal plants collected in pharmacies (78 samples) and herb stores (49 samples) in 1996. Samples were divided between 15 national brands and 7 foreign brands. Most samples sold in pharmacies contained residues of gamma-HCH (51.3%). All residues were detected in analyzed samples, with exception of endrin in herb store samples. Detection frequency varied between 51.3% for gamma-HCH and 1.3% for endrin in pharmacy samples, and between 34.7% for HCB and 4.1% for endosulfan sulfate in herb store samples. Maximum residue levels were exceeded in 38 (48.7%) pharmacy samples and in 26 (53.1%) medicinal herb store samples.     

Omeg@Silica: Entrapment and Stabilization of Sustainably Sourced Fish Oil

Fish oil rich in long-chain polyunsaturated fatty acids, vitamin D₃ and carotenoid pigments have been sustainably extracted from anchovy fillet leftovers using biobased limonene. The oil is conveniently stabilized by adsorption on periodic mesoporous silicas. The simplicity of the process, the high load of fish oil, and the biocompatible nature of mesoporous silica support numerous forthcoming applications of this new class of “Omeg@Silica” materials.     

A computational comparison of several formulations for the multi-period incremental service facility location problem

The Multi-period Incremental Service Facility Location Problem, which was recently introduced, is a strategic problem for timing the location of facilities and the assignment of customers to facilities in a multi-period environment. Aiming at finding the strongest formulation for this problem, in this work we study three alternative formulations based on the so-called impulse variables and step variables. To this end, an extensive computational comparison is performed. As a conclusion, the hybrid impulse–step formulation provides better computational results than any of the other two formulations.