Numerical simulations of the second-order electrokinetic bias observed with the gated injection mode in chips

It is well known that sample introduction via electrokinetic mode leads to a bias in conventional CE, which is proportional to the difference of electrophoretic mobilities between species. In electrophoretic separation chips using the gated injection mode, flow distribution at the crossjunction, which is linked to the electric field strength distribution during the loading step, induces an additional contribution to species discrimination. This second-order bias has a similar effect on quantitation like usual electrokinetic bias: the higher the analyte's apparent mobility, the larger the amount injected into the separation channel. The present paper assesses by numerical simulations the influence of several parameters, namely the injected amount, the electric field distribution, and the analyte-apparent Peclet number on this second-order bias.     

Reliable Functionalization of 5,6-Fused Bicyclic N-Heterocycles Pyrazolopyrimidines and Imidazopyridazines via Zinc and Magnesium Organometallics

DFT-calculations allow prediction of the reactivity of uncommon N-heterocyclic scaffolds of pyrazolo[1,5-a]pyrimidines and imidazo[1,2-b]pyridazines and considerably facilitate their functionalization. The derivatization of these N-heterocycles was realized using Grignard reagents for nucleophilic additions to 5-chloropyrazolo[1,5-a]pyrimidines and TMP₂Zn ⋅ 2 MgCl₂ ⋅ 2 LiCl allowed regioselective zincations. In the case of 6-chloroimidazo[1,2-b]pyridazine, bases such as TMP₂Zn ⋅ MgCl₂ ⋅ 2 LiCl, in the presence or absence of BF₃ ⋅ OEt₂, led to regioselective metalations at positions 3 or 8. Subsequent functionalizations were achieved with TMPMgCl ⋅ LiCl, producing various polysubstituted derivatives (up to penta-substitution). X-ray analysis confirmed the regioselectivity for key functional heterocycles.     

Determination of trace levels of benzodiazepine in urine using capillary electrochromatography-time of flight mass spectrometry

This paper details a method for the separation and determination of ten benzodiazepines in urine using CEC-MS(TOF) and an hexyl acrylate-based porous monolith. The TOF mass spectrometer provides an exact mass of protonated benzodiazepines to three decimal places (1-6 ppm). This high selectivity along with the CEC separation, provides an effective method for the identification of benzodiazepines. Linearity is satisfactory for all compounds in the concentration range of 25-500 ng/mL for lorazepam and 12.5-500 ng/mL for the others. The RSDs are between 1.4-2.3% for retention times and 1.1-9.2% for relative areas. Using the monolithic stationary phase, a preconcentration step is achievable and permits an 75-140-fold improvement in sensitivity. This strategy permits the quantification of these drugs down to 1 ng/mL in urine. This method was used for the analysis of benzodiazepines in spiked urine samples.     

Uniqueness and characterization of capacity constrained Cournot-Nash equilibrium

We add capacity constraints to a multi-market Cournot model in which asymmetric firms have linear demand functions. We show that the problem is equivalent to maximizing a concave objective function over a convex region which ensures the existence of a unique capacity constrained Cournot-Nash equilibrium.     

Electrochromatography in poly(dimethyl)siloxane microchips using organic monolithic stationary phases

This paper shows the in situ synthesis of an hexyl acrylate monolith in PDMS microfluidic devices and its subsequent use as stationary phase for electrochromatography on chip. To overcome the ability of PDMS material to absorb organic monomers, surface modification of the enclosed channels was realized by UV-mediated graft polymerization. This grafting procedure is based on the preliminary adsorption of a photoinitiator onto the PDMS surface and polymerization of charged monomers. Next, hexyl acrylate monoliths were cast in situ using photopolymerization process. The chromatographic behavior of the monolithic column was confirmed by the successful separation of derivatized catecholamines in the PDMS device using a 30 mm effective separation length (100 microm x 100 microm section). Efficiencies reached up to 200,000 plates per meter.     

Temperature dependant polycrystal model application to bainitic steel behavior under tri-axial loading in the ductile–brittle transition

A polycrystal finite element (FE) model describing the temperature evolution of low carbon steel is proposed in order to forecast the local mechanical fields as a function of temperature, for bainitic microstructure submitted to tri-axial loading. The model is designed for finite strains, large lattice rotations and temperatures ranging into the brittle–ductile transition domain. The dislocation densities are the internal variables. At low temperature in Body Centred Cubic (BCC) materials, plasticity is governed by double kink nucleation of screw dislocations, whereas at high temperature, plasticity depends on interactions between mobile dislocations and the forest dislocations. In this paper, the constitutive law and the evolution of the dislocation densities are written as a function of temperature and describe low and high temperature mechanisms. The studied aggregates are built from Electron Back Scattering Diffraction (EBSD) images of real bainitic steel. The aggregate is submitted to a tri-axial loading in order to describe the material at a crack tip. Mechanical parameters are deduced from mechanical tests. The local strain and stress fields, computed for different applied loadings, present local variations which depend on temperature and on tri-axial ratio. The distribution curves of the maximal principal stresses show that heterogeneities respectively increase with temperature and decrease with tri-axial ratio. A direct application of this model provides the evaluation of the rupture probability within the aggregate, which is treated as the elementary volume in the weak link theory. A comparison with the Beremin criterion calibrated on experimental data, shows that the computed fracture probability dispersion induced by the stress heterogeneities is of the same order than the measured dispersion. Temperature and stress tri-axiality ratio effects are also investigated. It is shown that these two parameters have a strong effect on fracture owing to their influence on the heterogeneous plastic strain. These inhomogeneities can initiate cleavage fracture.