Static headspace and purge-and-trap gas chromatography for epichlorohydrin determination in drinking water

Epichlorohydrin (ECH) can enter drinking-water supplies due to leaching from epoxy resins in contact with water and/or through the use of flocculating water treatment agents. Potential human exposure from drinking waters poses a particular concern on account of toxicological studies showing severe acute and long-term toxic effects of ECH. Recently a parametric value of 0.1 μg/L for ECH in drinking water has been established by European Union.A few methods for ECH determination in water are available. However, they usually adopt cumbersome procedures for sample preparation and provide sensitivity not matching the EU criteria for water monitoring purposes.In this study we investigated the analytical performance of gas extraction techniques, such as static headspace (HS) and purge and trap (P&T), coupled to gas chromatography (GC) with an electron capture detector (GC-ECD) for the determination of ECH in drinking water. The influence of different parameters affecting the analytical response was studied in details in order to enhance the method sensitivity, thus fulfilling the regulatory requirements.The P&T GC-ECD method was proved capable of determining ECH in water for human consumption at a detection limit of 0.01 μg/L fully complying the regulatory levels. On the contrary, the HS GC-ECD method is far less sensitive (LOD≅40 μg/L) than the previous cited method. The P&T GC-ECD method is simple, rapid, automated, safe for operators and does not require large sample volumes. Therefore, it is useful for routine laboratory activities both for control and research actions.     

Thermodynamics of adiabatically loaded cold bosons in the Mott insulating phase of one-dimensional optical lattices

In this work we give a consistent picture of the thermodynamic properties of bosons in the Mott insulating phase when loaded adiabatically into one-dimensional optical lattices. We find a crucial dependence of the temperature in the optical lattice on the doping level of the Mott insulator. In the undoped case, the temperature is of the order of the large onsite Hubbard interaction. In contrast, at a finite doping level the temperature jumps almost immediately to the order of the small hopping parameter. These two situations are investigated on the one hand by considering limiting cases like the atomic limit and the case of free fermions. On the other hand, they are examined using a quasi-particle conserving continuous unitary transformation extended by an approximate thermodynamics for hardcore particles.     

Optimal control of nonlinear evolution equations with nonmonotone nonlinearities

In this paper, we prove the existence of optimal admissible pairs for a large class of strongly nonlinear evolution equations, involving nonmonotone nonlinearities. An example of a nonlinear parabolic optimal control system is also worked out in detail.The author wishes to thank Professor T. S. Angell for useful comments and suggestions.This research was supported by NSF Grant No. DMS-88-02688.     

A method for calculating static transmission errors of plastic spur gears using FEM evaluation

There are many ways to calculate the static transmission errors of steel gears, but none is developed for plastic gears. Since the Young's modulus of the plastic material is lower than that of steel by two orders, the effects of large tooth deflection on the static transmission errors of plastic gears become significant. A multi-tooth contact analysis using finite element method for calculating the static transmission errors of plastic spur gears is established to compare with the existing method for steel spur gears. According to the comparison results, a modification of the existing method is proposed for plastic spur gears and verified by the same finite element contact analysis.     

Magnetic properties of the low dimensional spin system (VO)PO:ESR and susceptibility

Experimental results on magnetic resonance (ESR) and magnetic susceptibility are given for single crystalline (VO)₂P₂O₇. The crystal growth procedure is briefly discussed. The susceptibility is interpreted numerically using a model with alternating spin chains. We determine J =51 K and . Furthermore we find a spin gap of meV from our ESR measurements. Using elastic constants no indication of a phase transition forcing the dimerization is seen below 300 K. Received: 22 December 1997 / Accepted: 17 March 1998     

Dielectric constants,molar polarizations,and refractive indices for 2-butoxyethanol + hexane and +heptane at 30° and 40°C

Static dielectric constants and refractive indices of 2-butoxyethanol-n-hexane and-n-heptane mixtures were measured at 30 and 40°C and the various dielectric excess functionsviz. dielectric constants, molar polarizations, and orientation polarizations were evaluated. The excess dielectric constants and molar polarizations were found to be unsymmetrical and negative over the entire range of mole fraction. The trend in the variation of excess orientation polarization has shown three characteristic regions. The excess functions were smoothed through a variable degree polynomial. The results show the dominance of dipole-dipole interactions in the butoxyethanol deficient regions and weak specific interactions with unlike alkane molecules at higher butoxyethanol mole fractions.