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.     

Small peptides as ligands for catalytic asymmetric alkylations of olefins. Rational design of catalysts or of searches that lead to them?

Amino acid-based chiral ligands have been developed for use in Cu-catalyzed enantioselective allylic alkylations and conjugate additions that allow access to optically enriched compounds that are otherwise difficult to prepare. These chiral ligands are easily modified and have been identified through mechanism-based library screening. The data presented point to the significance of the availability of a collection of catalysts, since subtle variations in substrate or nucleophile structure often call for a different optimal chiral ligand. Can a catalyst be truly "rationally designed" or do we design our search pathway that eventually leads us to such a catalyst? What is meant by a "general catalyst"? Do we need a class of effective catalysts instead? These and related questions are addressed in the context of the above studies.     

Surface relaxation of rutile TiO2 (110)-(1×1) from ion shadowing/blocking measurements

Determination, by ion scattering, of the height of the oxygen atom rows above the five-fold-coordinated titanium atoms on the (1×1) surface of TiO₂(110) confirms that the five-fold-coordinated Ti atoms lie slightly lower than the six-fold-coordinated Ti atoms. The height difference is in good agreement with X-ray diffraction measurements.     

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.     

Nilpotent Lie and Leibniz Algebras

We extend results on finite dimensional nilpotent Lie algebras to Leibniz algebras and counterexamples to others are found. One generator algebras are used in these examples and are investigated further.     

Extension of the resonant scattering technique to liquid crystals without resonant element

We report X-ray resonant scattering experiments performed on the prototype liquid-crystalline compound MHPOBC doped with a chemical probe containing a resonant atom (selenium). We determined directly for the first time the microscopic 3- and 4-layer structure of the ferrielectric subphases ( SmC_FI1^* and SmC_FI2^*) present in MHPOBC. Despite the low fraction of the selenium probe, the resonant signal is strong enough to allow an unambiguous determination of the basic structure of the ferrielectric subphases. These experiments demonstrate that the resonant scattering technique can be extended to liquid crystalline materials without resonant element and may stimulate new studies. A non-resonant Bragg reflection was also found in the SmC_FI1^* phase in pure MHPOBC, consistent with the 3-layer distorted model, but never detected before.     

p-carboxylation of linear high molecular-mass polystyrene

A simple method is reported for the post-polymerization partial p-carboxylation of linear polystyrene without degradation or crosslinking of the polymer. The method is based on Friedel–Crafts acetylation of the polystyrene under mild conditions, followed by oxidation of the acetyl groups by means of a phase-transfer-catalyzed haloform reaction. The method is well suited for the synthesis of high molecular mass, monodisperse ionomers with p-carboxylate groups situated randomly along the polystyrene chain. © 1993 John Wiley & Sons, Inc.     

Determination of percentage of RoundUp Ready soya in soya flour using real-time polymerase chain reaction: interlaboratory study

An interlaboratory study was conducted to evaluate a method for determination of the percentage of RoundUp Ready (RR) soya in soya flour using Taqman technology. The method included DNA extraction from the test portion with cetyltrimethylammonium bromide buffer followed by chloroform extraction and Wizard resin cleanup steps. The DNA was then assayed with primer and probe sets specific for lectin as the endogenous control and the RR insert as the target. The percentage of RR soya in the soya fraction of the sample was calculated by using a matrix-matched standard curve. Ten samples of split-level blind duplicates were sent to 22 laboratories in 12 countries worldwide. Test portions contained 0, 0.5, 0.7,1.6, 2, and 3.9% (w/w) RR soya prepared gravimetrically from commercially available RR standard reference materials. Based on the results for test materials, the relative standard deviation for repeatability (RSDr) for the method ranged from 9.3 to 19.3% and, for reproducibility (RSDR), ranged from 20.3 to 33.7%.     

Pyroelectric properties of an antiferroelectric liquid crystal

The effects of temperature and applied voltage on the pyroelectric properties of an antiferroelectric liquid crystal are given. It has been found that the pyroelectric signal depends strongly on the bias voltage across the sample. The pyroelectric signal behaviour is interpreted with the aid of spontaneous polarization data and good agreement is found between the results from the pyroelectric and polarization techniques. The spontaneous polarization of the sample exhibits the temperature- and field-induced `Devil's staircase' behaviour, as predicted by the Ising model.