Synthesis and characterization of a fluorinated polyanhydride

A fluorinated aromatic polyanhydride ( B ) was synthesized from the melt condensation of mixed anhydrides of 4,4′‐(hexafluoroisopropylidene)bis benzoic acid. Although the mixed anhydride from acetic anhydride yielded only a mixture of oligomers (weight‐average molecular weight < 2000), higher weight‐average molecular weight materials in the range of 15,000–18,000 were obtained with trifluoroacetic anhydride. Polymer B was soluble in chloroform and tetrahydrofuran, had a relatively high glass‐transition temperature of 176 °C with no melting point detected to 310 °C, and showed excellent thermal stability (5% weight loss observed at 380 °C by thermogravimetric analysis). The hydrolytic degradation of the fluorinated polyanhydride in a 0.1 M phosphate buffer of pH 7.4 at 37 °C was initially zero‐order, with 35% degradation occurring in 10 days. Loss of film integrity following that led to accelerated degradation, and almost complete dissolution was observed by the 16th day. The stability of the fluorinated polyanhydride in the solid state and in the solvent tetrahydrofuran was also evaluated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3027–3036, 2002     

Rumor spreading in random evolving graphs

We analyze randomized broadcast in dynamic networks modeled as edge‐Markovian evolving graphs. The most realistic range of edge‐Markovian parameters yields sparse and disconnected graphs. We prove that, in this setting, the “push” protocol completes with high probability in optimal logarithmic time. © 2015 Wiley Periodicals, Inc. Random Struct. Alg., 48, 290–312, 2016     

Ni I oscillator strengths

Oscillator strengths of 150 Ni I lines in the spectral range 2800–6200 Å have been obtained by emission and from hook measurements. Relative sets of ?-values were determined by combining emission measurements on a hollow cathode with hook measurements in a high-temperature furnace. No assumption concerning the plasma state is used, and no temperature determination is required. The relative measurements have been placed on an absolute scale by using lifetime data. The uncertainty of the ?-values is 13% on average. Comparisons are made with the results of other authors.     

Circular grating coupler for creating focused azimuthally and radially polarized beams

We show a planar optical circuit design that takes light from an input waveguide and creates a focused azimuthally or radially polarized beam emanating from the surface of the substrate. It is implemented in silicon-on-insulator waveguides and does not require any external components to focus the beam. The focal spot size can be subwavelength and is potentially useful for lithography, imaging, optical data storage, optical trapping, optical excitation of molecules, or coupling to optical fibers.