Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.     

Novel monolithic columns with templated porosity

The analysis of several organophosphorus and carbamate pesticide residues in the bodies of honeybees using gas chromatography (GC) and gel permeation chromatography (GPC) clean-up is described. Freeze-dried or lyophilized insect samples were blended with diatomaceous earth (Extrelut) then underwent elution with methylene chloride. This extraction method has shown good recovery on various spike standard levels. Samples are cleaned up by GPC with a Bio Beads SX 3 column and a cyclohexane-ethylacetate (1:1) eluant. Organophosphorus and carbamate compounds are quantified using capillary gas chromatography. Good linearity ranges were observed for all compounds. The extraction process was rapid and results were good, despite the complexity of the matrix on which it was applied. It allowed a reduction both in cost and the consumption of solvents, thereby safeguarding the health of the analyst and the environment. Environmental monitoring using bees was confirmed to be a valid procedure.     

A finite element formulation for global linear stability analysis of a nominally two‐dimensional base flow

A stabilized finite element method, to carry out the linear stability analysis of a two‐dimensional base flow to three‐dimensional perturbations that are periodic along span, is presented. The resulting equations for the time evolution of the disturbance requires a solution to the generalized eigenvalue problem. The analysis is global in nature and is also applicable to non‐parallel flows. Equal‐order‐interpolation functions for velocity and pressure are utilized. Stabilization terms are added to the Galerkin formulation to admit the use of equal‐order‐interpolation functions and to eliminate node‐to‐node oscillations that might arise in advection‐dominated flows. The proposed formulation is tested on two flow problems. First, the mode transitions in the circular Couette flow are investigated. Two scenarios are considered. In the first one, the outer cylinder is at rest, while the inner one spins. Two linearly unstable modes are identified. The primary mode is real and represents the axisymmetric Taylor vortices. The second mode is complex and consists of spiral vortices. For the counter‐rotating cylinders, the primary transition is via the appearance of spiral vortices. Excellent agreement with results from earlier studies is observed. The formulation is also utilized to investigate the parallel and oblique modes of vortex shedding past a cylinder for the Re = 100 flow. It is found that the flow is associated with a large number of unstable oblique shedding modes. The parallel mode of vortex shedding is a special case of this family of modes and is associated with the largest growth rate. Copyright © 2014 John Wiley & Sons, Ltd.     

Oscillator models for multiphoton optical bistability and phase conjugacy

Nonlinear oscillator models are constructed to treat the bistability in situations involving elementary excitations in solids. Such models are shown to be useful not only in describing single photon but also multiphoton bistability. The resulting bistability both with and without cavity is considered. The two-photon excitonic bistability in CuCl is in detail. The effect of local field corrections can also be incorporated, in a simple manner, in such models.     

A simple procedure for the preparation of fritless columns by entrapping conventional high performance liquid chromatography sorbents

A rapid and direct method for immobilizing conventional high performance liquid chromatography (HPLC) packing material inside fritless capillaries has been developed. Due to the simple composition of the entrapment matrix (tetraethoxysilane, alkyltriethoxysilane, ethanol and water), straightforward manufacturing procedure and modest equipment requirement, the method can readily be transferred to any laboratory and easily automated. The entrapment procedure has minimal influence on the structure and chromatographic properties of the original reverse-phase sorbent. Various immobilization solutions have been tested, and a comparison between columns entrapped with different immobilization mixtures and conventional packed capillaries is presented. High efficiency separations were obtained using tert-butyl-triethoxysilane entrapped columns in both capillary electrochromatography (reduced plate heights of 1.1-1.4 were measured) and microliquid chromatography (reduced plate heights of 2.2-2.6 were observed) formats. Elimination of frits, stabilization of the packed bed and on-the-fly customization of column length render mechanically robust columns that are remarkably stable over time, from which manufacturing imperfections can be removed easily.     

Silicate entrapped columns--new columns designed for capillary electrochromatography

Designed especially for capillary electrochromatography (CEC), silicate-entrapped columns are made by trapping particles of chromatographic packing material in a network of silica. Once entrapped, the capillary no longer requires frits. This renders a more homogeneous and stable packed bed. Accidental breakage of the fragile frits is not an issue with these robust columns. Columns packed with reverse-phase material subjected to silicate entrapment demonstrated faster separations of retained analytes and increased efficiencies compared with nonentrapped columns. The method was also used to prepare chiral CEC columns by entrapping a molecular imprinted polymeric (MIP) packing having minimal surface charge density, thus being unable alone to support sufficient electroosmotic flow for CEC.