A−2 production in π−p interactions at 3.9 GeV/c

The reaction π^?p → A^?₂p at 3.9 GeV/c incident momentum is studied using data corresponding to the ?^°π^?, ηπ^? and K^δ_sK^? decay modes of the A^?₂. Unnatural parity exchange is found to be important at this energy. The natural parity exchange component of the differential cross section exhibits structure at t′ ≈ GeV².     

Disorder-to-order transition of 1,4-dimethylnaphthalene: Formation of molecular complex with water and p-xylene on Al2O3 (0001)

Amorphous 1,4-dimethylnaphthalene, DMN, that can be prepared by vacuum deposition on Al2O3 exhibits relatively intense excimer fluorescence. Upon heating the surface, the adlayer undergoes a disorder-to-order transition, signaled by a decrease in excimer and an increase in monomer fluorescence. In a bilayer experiment, water, which has a lower desorption temperature than DMN, is vacuum deposited first, followed by DMN. When the surface is heated, water percolates through the DMN and forms a molecular H2O-DMN surface complex that desorbs simultaneously. The stoichiometric ratio of this complex was determined to be (DMN)(1.4+/-0.3).H2O. When the bilayer was formed with p-xylene, a complex of DMN-p-xylene was observed that had the stoichiometry of (DMN)(7.9+/-1).p-xylene.     

Gas and liquid permeation properties of modified interfacial composite reverse osmosis membranes

Gas permeation tests using nitrogen, oxygen, hydrogen, helium and carbon dioxide were performed to assess how membrane modification procedures affect the separating layer morphology of thin-film composite reverse osmosis membranes. Gas selectivity data provided evidence for the presence of nanoscale separating layer defects in dry samples of six commercial membrane types. These defects were eliminated when the membrane surface was coated with a polyether–polyamide block copolymer (PEBAX 1657), as indicated by a 25-fold decrease in gas permeance and at least a 2-fold increase in most selectivity values. Treatment with n-butanol followed by drying reduced water flux and gas flux by 30% and 75%, respectively, suggesting that using n-butanol as a solvent for applying coatings negatively affects membrane performance. The results of this study demonstrate that gas permeation measurements can be used to detect morphological features that impact gas and water membrane flux.     

Classification of Convex Ancient Solutions to Curve Shortening Flow on the Sphere

We prove that the only closed, embedded ancient solutions to the curve shortening flow on \(\mathbb {S}^2\) are equators or shrinking circles, starting at an equator at time \(t=-\infty \) and collapsing to the north pole at time \(t=0\). To obtain the result, we first prove a Harnack inequality for the curve shortening flow on the sphere. Then an application of the Gauss–Bonnet, easily allows us to obtain curvature bounds for ancient solutions leading to backwards smooth convergence to an equator. To complete the proof, we use an Aleksandrov reflection argument to show that maximal symmetry is preserved under the flow.     

Self-trapped excitons in silicon dioxide: mechanism and properties

Irradiating silica produces self-trapped excitons (STEs) that spontaneously create atomic-scale distortions on which they localize themselves. Despite enduring interest in STEs and subsequent defects in this key technological material, the trapping mechanism and geometry remain a mystery. Our ab initio study of STEs in alpha-quartz using a many-electron Green's function approach answers both questions. The STE comprises a broken O-Si bond with the hole localized on the defected oxygen and the electron on the defected silicon atom in a planar sp2 conformation. The results further explain quantitatively the measured STE spectra.