Beyond abstract elementary classes: On the model theory of geometric lattices

Based on Crapo's theory of one point extensions of combinatorial geometries, we find various classes of geometric lattices that behave very well from the point of view of stability theory. One of them, $({\mathbf{K}}^3,?)$, is ω-stable, it has a monster model and an independence calculus that satisfies all the usual properties of non-forking. On the other hand, these classes are rather unusual, e.g. in $({\mathbf{K}}^3,?)$ the Smoothness Axiom fails, and so $({\mathbf{K}}^3,?)$ is not an AEC.     

Icosahedral Au(72): a predicted chiral and spherically aromatic golden fullerene

Quantum chemical calculations demonstrate the spherical aromaticity and high thermodynamic stability of Au(72), a predicted I-symmetric golden fullerene.     

Comparative study of photodegradation of wood by a UV laser and a xenon light source

A detailed study of photodegradation of wood surfaces by xenon light source and a UV laser has been carried out. Silver birch, rubberwood, Scots pine and chir pine wood veneers were irradiated with a xenon light source or a 244 nm argon ion laser. The changes in chemical structure of wood surfaces were monitored by UV resonance Raman (UVRR), photoacoustic Fourier transform infrared (FTIR-PAS) and UV-vis reflectance spectroscopies. The depth profile of xenon lamp irradiated wood surfaces was carried out by measuring FTIR-PAS spectra at different moving mirror velocities. The UVRR and FTIR-PAS spectra of irradiated wood surfaces showed degradation of aromatic structure in lignin combined with strong formation of carbonyl structures. The FTIR-PAS spectra measured from xenon irradiated wood surfaces indicate that hardwood lignin degrades at a faster rate than softwood lignin. The UVRR spectra of xenon irradiated wood show a significant decrease in the intensities of aromatic structures at 1602 cm⁻¹. This is accompanied by a significant band broadening and notable shift towards longer wavenumbers, which has been attributed to the formation of o- and p-quinone structures as degradation products. The formation of quinone structures was also supported by the generation of a broad absorption band between 350 and 600 nm in UV-vis reflectance spectra of irradiated wood surfaces. There was a significant broadening in the region of 1500-1000 cm⁻¹ in UVRR spectra due to the formation of unsaturated structures as a result of lignin degradation. The UVRR spectra of laser irradiated wood showed similar behaviour i.e., overall broadening and a rapid reduction in the intensity of lignin aromatic structure. The rate of degradation by laser was very high. However, the extent of band broadening was higher in xenon irradiated wood indicating the generation of several different types of structures as compared to laser irradiation, which produces only particular type of structures. UVRR spectra of laser irradiated Whatman paper showed significant photodegradation of cellulose by UV laser. The UV degradation rate of lignin was much higher than cellulose.     

Residual lignin inhibits thermal degradation of cellulosic fiber sheets

The market for cellulosic fiber based food packaging applications is growing together with the importance of improving the thermal durability of these fibers. To shed light on this, we investigated the role of residual lignin in pulp on the thermal stability of refined pulp sheets. The unbleached, oxygen delignified, and fully bleached pulp sheets were studied after four separate refining degrees. Comparison by Gurley air resistance, Bendtsen porosity, and the oxygen transmission rate tests showed that lignin containing sheets had better air and oxygen barrier properties than fully bleached sheets. Sheet density and light scattering coefficient measurements further confirmed that the lignin containing pulps underwent more intense fibrillation upon refining that changed the barrier properties of the sheets. Thermal treatments (at 225 °C, 20 and 60 min, in water vapor atmospheres of 1 and 75 v/v %) were applied to determine the thermal durability of the sheets. The results revealed that the residual lignin in pulps improved the thermal stability of the pulp sheets in the hot humid conditions. This effect was systematically studied by tensile strength, brightness, and light absorption coefficient measurements. The intrinsic viscosity results support the findings and suggest that lignin is able to hinder the thermal degradation of pulp polysaccharides. In spite of the fact that lignin is known to enhance the thermal yellowing of paper, no significant discoloration of the pulp sheets containing residual lignin was observed in the hot humid conditions (75 v/v %). Our results support the idea of lignin strengthening the thermal durability of paper.     

Novel use of mesoporous aluminas as supports for Cp2ZrCl2 and Cp*ZrMe3: Ethylene polymerization and formation of polyethylene nanofibers

Mesoporous aluminas with average pore sizes of 4.3–7.8 nm were prepared by anodization of an aluminum film (AAO), and by a sol–gel templating method (TPL). In addition to a commercial alumina and sulfated TPL, the aluminas were used as supports for cyclopentadienyl zirconocene dichloride (Cp₂ZrCl₂) and trimethyl(η5‐pentamethylcyclopentadienyl)zirconium (Cp*ZrMe₃) and tested in the polymerization of ethylene. The metallocenes supported on the alumina prepared with the templating method and its sulfated modification exhibited polymerization activities of 440 and 350 kg_PE/(mol_Zr × h × bar), respectively, comparable to that obtained with silica‐supported metallocenes (390 kg_PE/(mol_Zr × h × bar)). The acid site distribution of the aluminas was studied with FTIR and temperature programmed desorption (TPD) of pyridine, and also the amount of medium and strong acid sites was determined gravimetrically from the adsorption of pyridine. Relative to the surface area, AAO with the highest amount of acid sites (2.10 μmol_py/m) adsorbed Cp₂ZrCl₂ and Cp*ZrMe₃ the most. Study of the polymers' morphology with a scanning electron microscope revealed polyethylene nanofibers in all the polymer samples, also in those obtained from the reference polymerizations with homogeneous Cp₂ZrCl₂ and Cp*ZrMe₃. This finding suggests that a catalyst support with a tubular pore structure is not a prerequisite for the formation of polymer nanofibers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4002–4012, 2007     

Isospin Breaking in the Reaction at Threshold

 The model for charge symmetry breaking in the reaction applied earlier around the Δ region is used to calculate the integrated forward-backward asymmetry of the cross section close to threshold. The mixing of the π and η mesons appears as strongly dominant at these energies. This contrasts elastic np scattering experiments, where the np mass difference in OPE dominates, or closer to the Δ region. Received August 31, 1998; accepted in final form January 13, 1999     

On all-optical laser cleaning and inspection of contaminated concave metal surfaces

A technique for all-optical laser cleaning and surface quality monitoring of concave metal surfaces is suggested. Contaminated pharmaceutical punches from a tablet compression machine were cleaned using high-energy laser pulses. Image information obtained from a diffractive-optical-element-based sensor was used in inspection of the surface quality change of the concave punches due to laser cleaning. Alternative method for mechanical cleaning of punches is introduced, which is based on simultaneous laser cleaning and surface quality inspection of the punches.     

Free-form lens design for wide-angle imaging with an equidistance projection scheme

An algorithm of free-form lens design is presented that can realize wide-angle imaging in conjunction with conventional imaging devices. The wide-angle image obtained through the free-form lens and the camera is not affected by distortions. The formula for the free-form lens surfaces is derived. The surface profile of the free-form lens can be generated through solving a differential equation expressing the camera-viewing angle as a function of the angle of incidence on the free-form lens surface. The surfaces preserve a linear relationship between the angle of incidence of light onto the surface and the angle of refraction into the imaging device.