Weak Attractive Ligand–Polymer and Related Interactions in Catalysis and Reactivity: Impact,Applications, and Modeling

The notion of weak attractive ligand–polymer interactions is introduced, and its potential application, importance, and conceptual links with “cooperative” ligand–substrate interactions are discussed. Synthetic models of weak attractive ligand–polymer interactions are described, in which intramolecular weak C? H???F? C interactions (the existence of which remains contentious) have been detected by NMR spectroscopy and neutron and X‐ray diffraction experiments. These C? H???F? C interactions carry important implications for the design of catalysts for olefin polymerization, because they provide support for the practical feasibility of ortho‐F???H_β ligand–polymer contacts proposed for living Group 4 fluorinated phenoxyimine catalysts. The notion of weak attractive noncovalent interactions between an “active” ligand and the growing polymer chain is a novel concept in polyolefin catalysis.     

Zur Bestimmung des St?rkegehaltes in der Gerste und in anderen Getreidearten

Ohne Zusammenfassung     

Nickel as a chemical modifier for sensitivity enhancement and fast atomization processes in electrothermal atomic absorption spectrometric determination of cadmium in biological and environmental samples.

A systematic study of the efficiency of protons, Ni, Pd and Th as chemical modifiers for the determination of cadmium by electrothermal atomic absorption spectrometry (ETAAS) using fast temperature programs was made for platform atomization. A comparison was made in terms of the salt type, absorbance-time profiles and elimination of the sodium chloride interference. The results were adapted to develop a method for the ETAAS determination of cadmium in biological and environmental samples. The highest sensitivity to determine cadmium in biological and environmental samples was obtained using nickel (together with protons) as a chemical modifier. The accuracy of the method was tested by the determination of cadmium in different certified reference materials. The best detection limit and the characteristic mass of Cd were found to be 0.03 ng mL(-1) and 0.35 pg, respectively.     

Dispersion relations and Omnès representations for $K\to \pi \pi$ decay amplitudes

We derive dispersion relations for decay, using the Lehmann-Symanzik-Zimmermann formalism, which allows the analytic continuation of the amplitudes with respect to the momenta of the external particles. No off-shell extrapolation of the field operators is assumed. We obtain generalized Omnès representations, which incorporate the and S-wave phase shifts in the elastic region of the direct and crossed channels, according to the Watson theorem. The contribution of the inelastic final-state and initial-state interactions is parameterized by the technique of conformal mappings. We compare our results with previous dispersive treatments and indicate how the formalism can be combined with lattice calculations to yield physical predictions. Received: 14 October 2002 / Published online: 14 February 2003     

The reaction NN→NNπ in effective field theory

A consistent counting scheme is presented that allows to study the reactions NN → NNπ within an effective field theory. Within this scheme the chiral expansion is shown to converge contrary to claims in the literature.     

Kinetic evidence of a common mechanism in the oxidations of diethyl sulfide by dichromates and halochromates of heterocyclic bases

The oxidations of diethyl sulfide by potassium dichromate, pyridinium dichromate, quinolinium dichromate, imidazolium dichromate, nicotinium dichromate, isonicotinium dichromate, pyridinium fluorochromate, quinolinium fluorochromate, imidazolium fluorochromate, pyridinium chlorochromate, quinolinium chlorochromate, and pyridinium bromochromate follow identical kinetic orders—first‐order each with respect to the chromium(VI) reagents, sulfide and hydrogen ion, and moderately inhibited by manganese(II) ion. The energy of activation varies linearly with the logarithm of frequency factor and so does the enthalpy of activation with the entropy of activation. Also, the activation free energies do not differ significantly. The dichromates and halochromates of heterocyclic bases oxidize diethyl sulfide via a common mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 1–8, 2003     

Role of the microstructure on the transport properties of Y-doped zirconia and Gd-doped ceria

Transmission electron microscopy characterizations and XPS analyses have allowed us to show the influence of the microstructure and nanochemistry on the transport properties of Y₂O₃-(9 mol%)-stabilized zirconia (YSZ) and Gd₂O₃ (10 mol%)-doped ceria (GDC). The grain boundary electrical conductivity (σ_gb) and oxygen diffusion coefficient (D_o) of conventional YSZ ceramics increase with the grain size, while an opposite behavior was found for GDC samples. This difference was attributed to glassy precipitates present at YSZ grain boundaries. Furthermore, it was shown that kinetic demixing processes take place during cooling, at the end of sintering. This causes important changes in the cationic species distribution at interfaces and plays an important role on the transport properties of these two materials. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.     

Analysis and finite element simulations of a second‐order fluid model in a bounded domain

This article is concerned with the equations governing the steady motion of a viscoelastic incompressible second‐order fluid in a bounded domain. A new proof of existence and uniqueness of strong solutions is given. In addition, using appropriate finite element methods to approximate a coupled equivalent problem, sharp error estimates are obtained using a fixed point argument. The method is applied to the two‐dimensional lid‐driven cavity problem, at low Reynolds number and in a certain range of values of the viscoelastic parameters, to analyze the combined effects of inertia and viscoelasticity on the flow. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007     

Use of traps to study positron annihilation in astrophysically relevant media

We discuss possible experiments which can exploit recently-developed techniques to accumulate, store, and manipulate low-energy positrons to measure the parameters associated with positron annihilation radiation from media of astrophysical interest. Media discussed include collections of dust grains, partially ionized gases, He, H₂, and other molecular gases and gas mixtures, including polycyclic aromatic hydrocarbon (PAH) molecules relevant to the interstellar medium.     

Future contributions toJournal of Crystallographic and Spectroscopic Research

Future contributions toJournal of Crystallographic and Spectroscopic Research