Distal metal effects in cobalt porphyrins related to CcO

Cobalt(II) porphyrins were studied to determine the influence of distal site metalation and superstructure upon dioxygen reactivity in active site models of cytochrome c oxidase (CcO). Monometallic, Co(II)(P) complexes when ligated by an axial imidazole react with dioxygen to form reversible Co-superoxide adducts, which were characterized by EPR and resonance Raman (RR). Unexpectedly, certain Co porphyrins with Cu(I) metalated imidazole pickets do not form mu-peroxo Co(III)/Cu(II) products even though the calculated intermetallic distance suggests this is possible. Instead, cobalt-porphyrin-superoxide complexes are obtained with the distal copper remaining as Cu(I). Moreover, distal metals (Cu(I) or Zn(II)) greatly enhance the stability of the dioxygen adduct, such that Co superoxides of bimetallic complexes demonstrate minimal reversibility. The "trapping" of dioxygen by a second metal is attributed to structural and electrostatic changes within the distal pocket upon metalation. EPR evidence suggests that the terminal oxygen in these bimetallic Co-superoxide systems is H-bonded to the NH of an imidazole picket amide linker, which may contribute to enthalpic stabilization of the dioxygen adduct. Stabilization of the dioxygen adduct in these bimetallic systems suggests one possible role for the distal copper in the Fe/Cu bimetallic active site of terminal oxidases, which form a heme-superoxide/copper(I) adduct upon oxygenation.     

Improved acoustic signals discrimination using fractional Fourier transform based phase-space representations

In this communication we propose performing two-dimensional correlation operation between phase-space representations based on the fractional Fourier transform, instead of correlating the signals themselves. A numerical examples clearly indicates superior discrimination performance.     

Nanocrystalline GdBa2HfO5.5 perovskite dielectric material—A single-step synthesis and its characterization

Nanocrystals of GdBa₂HfO_5.5 perovskite ceramic materials, of the family A₂(BB′)O₆, were synthesized using an auto-igniting combustion of a precursor solution containing metal ions, oxidant and a fuel. Phase purity and particulate properties of the as-prepared powder were examined using X-ray diffraction, differential thermal and thermogravimetric analyses, Fourier-transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopic techniques. These nanocrystals were sintered to high density (～98% of the theoretical density) at ～1620 °C for 2 h.The sintering behavior, dielectric constant and dielectric loss factor of the samples showed variations in magnitude with that of the samples prepared by conventional solid-state route.     

Thermal performance of heat pipe with suspended nano-particles

Nanofluids are employed as the working medium for a conventional cylindrical heat pipe. A cylindrical copper heat pipe of 19.5?mm outer diameter and 400?mm length was fabricated and tested with two different working fluids. The working fluids used in this study are DI-water and Nano-particles suspension (mixture of copper nano particle and DI-water). The overall heat transfer coefficient of the heat pipe was calculated based on the lumped thermal resistance network and compared with the heat transfer coefficient of base fluid filled heat pipe. There is a quantitative improvement in the heat transfer coefficient using nano-particles suspension as the working medium. A heat transfer correlation was also developed based on multiple regression least square method and the results were compared with that obtained by the experiment.