Production of defects in ZBLAN, ZBLAN:Tm and ZBLAN:Cr glasses by ultra-short pulses laser interaction

In this work we have studied pure and thulium- and chromium-doped ZBLAN glasses irradiated by ultra-short laser pulses. A Ti:sapphire CPA system was used, producing a 500 Hz train of pulses, centered at 830 nm, with 375 μJ of energy and 50 fs of duration (FWHM). The beam was focused by a 20 mm lens, producing a converging beam with a waist of 12 μm. The absorption spectra before and after laser irradiation were obtained showing production of color centers in pure, thulium-doped and chromium-doped ZBLAN glasses. A damage threshold of 9.56 T W/cm² was determined for ZBLAN.     

The Norwegian and the Englishman

I sketch the lives and work of the Norwegian physicist Kristian Birkeland (1867–1917) and the English mathematician Sydney Chapman (1888–1970), focusing particularly on Chapman’s controversy with Birkeland over the origin and development of auroras, a controversy that Chapman conducted with Birkeland for more than fifty years after Birkeland’s death. Sidney Borowitz is Professor Emeritus of Physics at New York University.     

Luminescent nano-composites generated from a spray

The spray-pyrolysis (SP) synthesis technique has been employed to obtain SiO₂:Eu³⁺ and γ-AlOOH:Eu³⁺. It was possible to obtain sub-micrometric spherical particles of SiO₂ with luminescent Eu³⁺ ions bonded to the silica surface or embedded in amorphous silica beads, by controlling the synthesis and annealing process. Boehmite γ-AlOOH doped with Eu³⁺ nanoparticles were synthesized by SP at moderate temperature (200 °C) with Eu³⁺ ions bonded to the surface hydroxyls of the boehmite nanocrystals. Luminescent nano-composites were obtained by controlled reaction of γ-AlOOH:Eu³⁺ nanocrystals with ASN (asparagine). In these nano-composites, the Eu³⁺ are held at the surface of the boehmite nanocrystals and partially shielded from interactions with additional luminescence quenchers (hydroxyl groups, water molecules).     

Free radical ring-opening polymerization and its use to make biodegradable polymers and functionally terminated oligomers

Since a carbon-oxygen double bond is considerably more stable than a carbon-carbon double bond, it has been possible to use this driving force to promote free radical ring-opening polymerization of unsaturated heterocyclic compounds. This process, for the first time, has permitted the introduction of functional groups, such as esters, amides and carbonates, into the backbone of addition polymers. Hydrolysis of the copolymers with common monomers produced oligomers capped with hydroxyl, amino or carboxylic acid groups. The presence of an ester group in a copolymer, such as in a copolymer of ethylene, render the copolymer biodegradable.     

Short-chain polyphosphates: Extraction effects on migration and size estimation of Saccharomyces cerevisiae extracts with polyacrylamide gel electrophoresis

Polyacrylamide gel electrophoresis is commonly used to characterize the chain length of polyphosphates (polyP), more generally called condensed phosphates. After separation, nonradioactive, optical polyP staining is limited to chain lengths greater than 15 ${\mathrm{PO}}_3^{-}$monomers with toluidine blue or 4′,6-diamidino-2-phenylindole. PolyP chain lengths longer than 62${\mathrm{PO}}_3^{-}$monomers were correlated to the shortest DNA ladders. In this study, synthetic linear polyPs (Sigma-Aldrich “Type 45”, estimated mean length of 45 ${\mathrm{PO}}_3^{-}$ monomers), trimetaphosphate (trimetaP: 3 ${\mathrm{PO}}_3^{-}$ ring), tripolyphosphate (tripolyP), pyrophosphate (PP_i), and inorganic orthophosphate (o-P_i) were visualized after separation by an in situ hydrolytic degradation process to o-P_i that was subsequently stained with methyl green. Statistically insignificant migration reduction of synthetic short-chain polyP after perchloric acid or phenol–chloroform extraction was confirmed with the Friedman test. ³¹P diffusion–ordered NMR spectroscopy confirmed that extraction also reduced PP_i diffusivity by <10%. Linear regression between the R_f peak migration value and the logarithm of synthetic polyP molecular weights enabled estimation of extracted polyP chain lengths from 2 to 45 ${\mathrm{PO}}_3^{-}$monomers. Linear polyP extracts from Saccharomyces cerevisiae grown in aerobic conditions were generally shorter than extracts cultured in anaerobic conditions. Extractions from both aerobic and anaerobic S. cerevisiae included tripolyP and o-P_i, but no PP_i.