Surface characterization of anodized zirconium for biomedical applications

Mechanical properties and corrosion resistance of zirconium make this material suitable for biomedical implants. Its good in vivo performance is mainly due to the presence of a protective oxide layer that minimizes corrosion rate, diminishes the amount of metallic ions released to the biological media and facilitates the osseointegration process.Since the implant surface is the region in contact with living tissues, the characteristics of the surface film are of great interest. Surface modification is a route to enhance both biocompatibility and corrosion resistance of permanent implant materials. Anodizing is presented as an interesting process to modify metal surfaces with good reproducibility and independence of the geometry.In this work the surface of zirconium before and after anodizing in 1 mol/L phosphoric acid solution at a fixed potential between 3 and 30 V, was characterized by means of several surface techniques.It was found that during anodization the surface oxide grows with an inhomogeneous coverage on zirconium surface, modifying the topography. The incorporation of P from the electrolyte to the surface oxide during the anodizing process changes the surface chemistry. After 30 days of immersion in Simulated Body Fluid (SBF) solution, Ca-P rich compounds were present on anodized zirconium.     

Separation dichotomy and wavefronts for a nonlinear convolution equation

This paper is concerned with a scalar nonlinear convolution equation, which appears naturally in the theory of traveling waves for monostable evolution models. First, we prove that, at each end of the real line, every bounded positive solution of the convolution equation should either be separated from zero or be exponentially converging to zero. This dichotomy principle is then used to establish a general theorem guaranteeing the uniform persistence and existence of semi-wavefront solutions to the convolution equation. Finally, we apply our theoretical results to several well-studied classes of evolution equations with asymmetric non-local and non-monotone response. We show that, contrary to the symmetric case, these equations can possess simultaneously stationary, expansion and extinction waves.     

Thermal and structural characterization of SrTi1-xNdxO3

Sr(Ti,Nd)O₃ was synthesized in order to evaluate the influence of the amount of neodymium on the thermal and structural properties of SrTiO₃. The synthesis was carried out using the polymeric precursor method. A small mass gain was observed for the SrTiO₃ and SrTi_0.98Nd_0.02O₃ samples accompanied by an exothermic peak in the DTA curves. Other steps at higher temperatures are assigned to the combustion of the organic material and carbonate. Elimination of defects by previous calcination of the precursors is responsible by the short and long range ordering of the perovskite. Cubic phase was obtained for undoped and doped SrTiO₃.     

On the complexity of deciding whether the distinguishing chromatic number of a graph is at most two

In an article Cheng (2009) [3] published recently in this journal, it was shown that when k≥3, the problem of deciding whether the distinguishing chromatic number of a graph is at most k is NP-hard. We consider the problem when k=2. In regards to the issue of solvability in polynomial time, we show that the problem is at least as hard as graph automorphism, but no harder than graph isomorphism.     

Wind field deduced from marine SAR images

Summary A recently improved model capable of extracting the wind field from SAR imagery without the aid of ?sea truth? is applied to ERS-1 SAR data for the Mediterranean Sea. The model is based on the properties of the relationship between the first two moments of the probabilistic distribution function of SAR signals as well as on spectral analysis of the SAR signal itself.     

Thermal Stability of Sol-Gel Hydrotalcites

Sol-Gel Hydrotalcites were synthesized using magnesium ethoxide and variable aluminum sources: aluminum acetilacetonate, aluminum chloride, aluminum nitrate and aluminum sulfate; in all cases, the gelation was done at pH 10. X-ray diffraction studies show that the crystallinity depends on the aluminum precursor used. The crystallinity was found in the order aluminum acetylcetonate>aluminum chloride>aluminum nitrate>aluminum sulfate. The precursor determines the sintering behavior as well.     

Investigation of proton-proton short-range correlations via the 12C(e,e'pp) reaction

We investigated simultaneously the 12C(e,e'p) and 12C(e,e'pp) reactions at Q2=2 (GeV/c)2, xB=1.2, and in an (e, e'p) missing-momentum range from 300 to 600 MeV/c. At these kinematics, with a missing momentum greater than the Fermi momentum of nucleons in a nucleus and far from the delta excitation, short-range nucleon-nucleon correlations are predicted to dominate the reaction. For (9.5+/-2)% of the 12C(e,e'p) events, a recoiling partner proton was observed back-to-back to the 12C(e,e'p) missing-momentum vector, an experimental signature of correlations.     

A Bioinspired Molybdenum Complex as a Catalyst for the Photo‐ and Electroreduction of Protons

A molybdenum–dithiolene–oxo complex was prepared as a model of some active sites of Mo/W‐dependent enzymes. The ligand, a quinoxaline–pyran‐fused dithiolene, mimics molybdopterin present in these active sites. For the first time, this type of complex was shown to be active as a catalyst for the photoreduction of protons with excellent turnover numbers (500) and good stability in aqueous/organic media and for the electroreduction of protons in acetonitrile with remarkable rate constants (1030 s^?1 at ?1.3 V versus Ag/AgCl). DFT calculations provided insight into the catalytic cycle of the reaction, suggesting that the oxo ligand plays a key role in proton exchange. These results provide a basis to optimize this new class of H₂‐evolving catalysts.