Synthesis of amorphous niobium-nickel alloys by vapor quenching

Thin film samples (10–15 μm thick) of niobium-nickel alloys in the composition range Nb-5 to 95 at. % Ni were vapor quenched bu r.f. sputtering onto fused quartz substrates held at a temperature of 180°C. It was found that fully glassy alloys were synthesized in the composition range Nb-30 to 85 at. % Ni, which is 2.5 times larger than that reported for splat-quenched alloys. Crystallization temperatures exhibited a maximum near the deepest eutectic in this alloys system and are comparable with those of splat-quenched materials. Nearest neighbor distances are in agreement with results for splat-quenched materials while “effective particle sizes” are consistently smaller. These results are discussed relative to the mechanism by which glassy alloys are synthesized during vapor quenching and the structure of the glassy state.     

A Dedicated On-Board Dual-Energy Computer Tomograph

A dedicated on-board dual energy computer tomograph able to generate both tomographic and digital radiographic images of unconsolidated sediments cores with a diameter up to 12 cm and a height up to 1 m was built and tested on-board of the R/V Mare Nigrum. This instrument, designed to be used on-board of any oceanographic research vessel with minimum adaptations, can work very well on stationary laboratory too, provided that there is adequate protection against hard X-rays. The tomograph has a single 160 kV X-ray tube and two set of 240 in-line X-ray detectors separated by a copper attenuator (dual-energy arrangement) allowing one to obtain tomographic as well as digital radiographic images depicting the distribution of both density and effective atomic number of the objects. In tomographic and radiographic mode, the spatial resolution of reconstructed images of the linear attenuation coefficient is about 0.5 mm while in dual-energy mode, when reconstructed images depict the distribution of densities and effective atomic numbers that requires an additional smoothing filtering, the spatial resolution is about 1 mm.     

Development and Experimental Testing of an Optical Micro-Spectroscopic Technique Incorporating True Line-Scan Excitation

Multiphoton micro-spectroscopy, employing diffraction optics and electron-multiplying CCD (EMCCD) cameras, is a suitable method for determining protein complex stoichiometry, quaternary structure, and spatial distribution in living cells using Förster resonance energy transfer (FRET) imaging. The method provides highly resolved spectra of molecules or molecular complexes at each image pixel, and it does so on a timescale shorter than that of molecular diffusion, which scrambles the spectral information. Acquisition of an entire spectrally resolved image, however, is slower than that of broad-bandwidth microscopes because it takes longer times to collect the same number of photons at each emission wavelength as in a broad bandwidth. Here, we demonstrate an optical micro-spectroscopic scheme that employs a laser beam shaped into a line to excite in parallel multiple sample voxels. The method presents dramatically increased sensitivity and/or acquisition speed and, at the same time, has excellent spatial and spectral resolution, similar to point-scan configurations. When applied to FRET imaging using an oligomeric FRET construct expressed in living cells and consisting of a FRET acceptor linked to three donors, the technique based on line-shaped excitation provides higher accuracy compared to the point-scan approach, and it reduces artifacts caused by photobleaching and other undesired photophysical effects.     

Formation of CoFe2O4/PVA-SiO2 nanocomposites: Effect of diol chain length on the structure and magnetic properties

The paper presents the influence of diol (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol) on the formation of magnetic crystalline cobalt ferrite embedded in polyvinyl alcohol-silica hybrid matrix at 200?°C. Formation of crystalline oxides (CoFe₂O₄, Co₃O₄ and Co₂SiO₄) was studied by X-ray diffraction and Fourier transformed infrared spectroscopy. The effect of annealing temperature and diol chain length on the cobalt ferrite nanocrystallites size was investigated. Using transmission electron microscopy, the size and shape of particles obtained at 200?°C were recorded and compared to those obtained by annealing at 500, 800 and 1100?°C. The saturation magnetization (M_s) and coercive field were calculated from the magnetic hysteresis loops of nanocomposites. The M_s was influenced by the particle size and crystallinity only for nanocomposites annealed at 800 and 1100?°C, when the magnetic domains started to form and to be larger than the critical particle size. The diols used in the synthesis influence both the oxidic phase formation and its properties.