Experimental investigation of the difference in B-term dominated band broadening between fully porous and porous-shell particles for liquid chromatography using the Effective Medium Theory

The difference in B-term diffusion between fully porous and porous-shell particles is investigated using the physically sound diffusion equations originating from the Effective Medium Theory (EMT). Experimental data of the B-term diffusion obtained via peak parking measurements on six different commercial particle types have been analyzed (3 porous and 3 non porous). All particles were investigated using the same experimental design and test analytes, over a very broad range of retention factor values. First, the B-term reducing effect of the solid core (inducing an additional obstruction compared to fully porous particles) has been quantified using the Hashin-Shtrikman expression, showing that the presence of a solid core can account for a reduction of about 11% when the core diameter makes up 63% of the total particle diameter (Halo and Poroshell-particles) and a reduction of 16% when the core diameter makes up 73% (Kinetex). Remaining differences can be attributed to differences in the microscopic structure of the meso-porous material (meso-pore diameter, internal porosity or relative void volume). The much lower B-term diffusion of Halo and Kinetex particles compared to the fully porous Acquity particles (some 20-40% difference, of which about 10-15% can be attributed to the presence of the solid core) can hence largely be attributed to the much smaller internal porosity and the smaller pore size of the meso-porous material making up the shell of these particles.     

Modeling gas permeation through membranes by kinetic Monte Carlo: applications to H2, O2, and N2 in hydrated Nafion®

We present a simulation tool in order to predict gas permeation through heterogeneous, microphase separated structures. The method combines dissipative particle dynamics (DPD) with kinetic Monte Carlo (KMC). Morphologies obtained from DPD are mapped onto a high density grid on which gas diffusion takes place. Required input parameters for the KMC calculations are the gas solubility and gas diffusion constant within each of the pure phase components. Our method was tested and validated for permeation of H(2), O(2), and N(2) gasses through hydrated Nafion membranes at various temperatures and water contents. We predict that membranes that contain an equal volume fraction of water, those with the highest ion exchange capacity exhibit the largest N(2) and O(2) permeation rates. For membranes of the same ion exchange capacity the H(2), O(2), and N(2) and permeability increases approximately linearly with Bragg spacing. We also predict that O(2) gas permeation depends much more on bottleneck phenomena within the phase separated morphologies than H(2) gas permeation. Overall, the calculated H(2) and O(2) permeability is found to be slightly lower than experimental values. This is attributed to the robustness of DPD resulting in ～7% larger Bragg spacing as compared with experiment and∕or increased gas solubility within the polymer phase with water uptake.     

Vibrational spectroscopic studies and DFT calculations on tribromoacetate and tribromoacetic acid in aqueous solution

Aqueous solutions of sodium tribromoacetate (NaCBr3CO2) and its corresponding acid (CBr3COOH) have been studied using Raman and infrared spectroscopy. The spectra of the species in solution were assigned according to symmetry Cs. Characteristic bands of CBr3CO2-(aq) and the tribromoacetic acid, CBr3COOH(aq), are discussed. For the hydrated anion, the CO2 group, the symmetric CO2 stretching mode at 1332 cm(-1) and the asymmetric stretching mode at 1651 cm(-1) are characteristic while the CO mode at 1730 cm(-1) is characteristic for the spectra of the acid. The stretching mode, νC-C at 912cm(-1) for CBr3CO2-(aq) is 10 cm(-1) lower in the anion compared with that of the acid. These characteristic modes are compared to those in acetate, CH3CO2-(aq). Coupling of the modes are fairly extensive and therefore DFT calculations have been carried out in order to compare the measured spectra with the calculated ones. The geometrical parameters such as bond length and bond angles of the tribromoacetate, and tribromoacetic acid have been obtained and may be compared with the ones published for other acetates and their conjugated acids. CBr3COOH(aq) is a moderately strong acid and the pKa value derived from quantitative Raman measurements is equal to -0.23 at 23°C. The deuterated acid CBr3COOD in heavy water has been measured as well and the assignments were given.     

First fluorescence spectroscopic investigation of Am(III) complexation with an organic carboxylic ligand, pyromellitic acid

For the first time Am(III) complexation with a small organic ligand could be identified and characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature and trace metal concentration. With pyromellitic acid (1,2,4,5-benzene-tetracarboxylic acid, BTC) as ligand spectroscopic characteristics for the Am-BTC complex system were determined at pH 5.0, an ionic strength of 0.1 M (NaClO4) and room temperature. The fluorescence lifetimes were determined to be 23.2±2.2 ns for Am3+(aq) and 27.2±1.2 ns for the Am-BTC 1:1 complex; the emission maximum for the 5D1-(7)F1 transition is 691 nm for both species. The complex stability constant for the Am-BTC 1:1 complex was calculated to be logβ110=5.42±0.16.     

Approximation by Conic Splines

We show that the complexity of a parabolic or conic spline approximating a sufficiently smooth curve with non-vanishing curvature to within Hausdorff distance ɛ is c ₁ɛ^−1/4 + O(1), if the spline consists of parabolic arcs, and c ₂ɛ^−1/5 + O(1), if it is composed of general conic arcs of varying type. The constants c ₁ and c ₂ are expressed in the Euclidean and affine curvature of the curve. We also show that the Hausdorff distance between a curve and an optimal conic arc tangent at its endpoints is increasing with its arc length, provided the affine curvature along the arc is monotone. This property yields a simple bisection algorithm for the computation of an optimal parabolic or conic spline. The research of SG and GV was partially supported by grant 6413 of the European Commission to the IST-2002 FET-Open project Algorithms for Complex Shapes in the Sixth Framework Program.     

Interior barriers and dimer nucleation on islands

On (1 1 1) islands of platinum as well as iridium self-adsorbed on (1 1 1) planes, it is now established that there are interior barriers impeding the movement of adatoms from the inner region to the steps of the island. We have carried out Monte Carlo simulations of adatoms migrating on such islands to establish the effect of interior barriers on the rate at which adsorbed atoms nucleate to form dimers rather than incorporate into the steps of the island. It is found that interior barriers significantly increase the rate at which dimers are created by collisions of two adatoms, and that the presence of additional step-edge barriers further raises the rate of dimer nucleation.     

Balinski—Tucker simplex tableaus: Dimensions, degeneracy degrees, and interior points of optimal faces

This paper shows the relationship between degeneracy degrees and multiple solutions in linear programming (LP) models. The usual definition of degeneracy is restricted to vertices of a polyhedron. We introduce degeneracy for nonempty subsets of polyhedra and show that for LP-models for which the feasible region contains at least one vertex it holds that the dimension of the optimal face is equal to the degeneracy degree of the optimal face of the corresponding dual model. This result is obtained by means of the so-called Balinski—Tucker (B—T) Simplex Tableaus. Furthermore, we give a strong polynomial algorithm for constructing such a B—T Simplex Tableau when a solution in the relative interior of the optimal face is known. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.     

Isotopic Implicit Surface Meshing

This paper addresses the problem of piecewise linear approximation of implicit surfaces. We first give a criterion ensuring that the zero-set of a smooth function and the one of a piecewise linear approximation of it are isotopic. Then, we deduce from this criterion an implicit surface meshing algorithm certifying that the output mesh is isotopic to the actual implicit surface. This is the first algorithm achieving this goal in a provably correct way.