Ultrafast Internal Conversion in a Model Anthocyanin–Polyphenol Complex: Implications for the Biological Role of Anthocyanins in Vegetative Tissues of Plants

The red flavylium cations of anthocyanins form ground‐state charge‐transfer complexes with several naturally occurring electron‐donor copigments, such as hydroxylated flavones and hydroxycinnamic or benzoic acids. Excitation of the 7‐methoxy‐4‐methyl‐flavylium–protocatechuic acid complex results in ultrafast (240 fs) internal conversion to the ground state of the complex by way of a low‐lying charge‐transfer state. Thus, both uncomplexed anthocyanins, whose excited state decays by fast (5–20 ps) excited‐state proton transfer, and anthocyanin–copigment complexes have highly efficient mechanisms of deactivation that are consistent with the proposed protective role of anthocyanins against excess solar radiation in the vegetative tissues of plants.     

A nonlocal nonlinear diffusion equation with blowing up boundary conditions

We deal with boundary value problems (prescribing Dirichlet or Neumann boundary conditions) for a nonlocal nonlinear diffusion operator which is analogous to the porous medium equation. First, we prove existence, uniqueness and the validity of a comparison principle for these problems. Next, we impose boundary data that blow up in finite time and study the behavior of the solutions.     

Structural changes of Ag+–Na+ ion exchanged soda-lime glasses investigated by scanning electron microscopy and infrared reflectivity

The combination of infrared spectroscopy and scanning electron microscopy allowed the monitoring of the structural changes of a soda-lime glass submitted to increasing durations of Ag⁺–Na⁺ ion exchange in a molten salt bath at 350 °C. Both techniques show an insertion of silver ions in the glass structure that is about 10% higher than the departure of sodium ions. The electro neutrality of the compounds is preserved with local alterations which lead to a higher degree of depolymerization of the silicate network. During the exchange process only sodium leaves the matrix and its content does not go beyond a threshold of about 50% of the initial content.     

Structural,magnetic and transport properties of ion beam deposited Co thin films

Magnetic nanostructures display new and interesting physical phenomena and are currently used in a large variety of applications. We studied the structural, magnetic and transport properties of Co thin films deposited by ion beam sputtering. We probed the influence of the buffer layer material (Al, Cu, Ru or Ta) and thickness (10–100 Å) on the structural properties of Co thin films. Using X-ray diffraction we observed that textured fcc Co films can be grown on amorphous Ta as thin as 20 Å but for the other buffer layers no texture is observed. We also studied by magneto-optical Kerr effect (MOKE) the magnetic properties of the Co thin films as a function of Co thickness (100–1000 Å). Finally, the electrical resistivity and anisotropic magnetoresistance (AMR) of our Co thin films (on a Ta buffer) was obtained as a function of Co thickness.     

Central Paths in Semidefinite Programming, Generalized Proximal-Point Method and Cauchy Trajectories in Riemannian Manifolds

The relationships among the central path in the context of semidefinite programming, generalized proximal-point method and Cauchy trajectory in a Riemannian manifolds is studied in this paper. First, it is proved that the central path associated to a general function is well defined. The convergence and characterization of its limit point is established for functions satisfying a certain continuity property. Also, the generalized proximal-point method is considered and it is proved that the correspondingly generated sequence is contained in the central path. As a consequence, both converge to the same point. Finally, it is proved that the central path coincides with the Cauchy trajectory in a Riemannian manifold. This work was supported in part by CNPq Grant 302618/2005-8, by PRONEX(CNPq), CAPES-PICDT and FUNAPE/UFG.     

Topological invariants in forced piecewise-linear FitzHugh–Nagumo-like systems

Mathematical models for periodically-forced excitable systems arise in many biological and physiological contexts. Chaotic dynamics of a forced piecewise-linear Fitzhugh–Nagumo-like system under large-amplitude forcing was identified by Othmer and Xie in their work [J. Math. Biol. 39 (1999) 139]. Using kneading theory we study the topological entropy of some chaotic return maps associated with a singular system. Finally we introduce a new topological invariant to distinguish isentropic dynamics and we exhibit numerical results about maps with the same topological entropy, that suggest the existence of a relation between the parameters A and θ, when T is fixed.     

The choroid plexus response to a repeated peripheral inflammatory stimulus

Background  

Chronic systemic inflammation triggers alterations in the central nervous system that may relate to the underlying inflammatory component reported in neurodegenerative disorders such as multiple sclerosis and Alzheimer's disease. However, it is far from being understood whether and how peripheral inflammation contributes to induce brain inflammatory response in such illnesses. As part of the barriers that separate the blood from the brain, the choroid plexus conveys inflammatory immune signals into the brain, largely through alterations in the composition of the cerebrospinal fluid.     

Highly efficient and chemoselective reduction of sulfoxides using the system silane/oxo-rhenium complexes

This work reports a novel method for the reduction of sulfoxides with silanes catalyzed by high valent oxo-rhenium(V) and (VII) complexes. The catalytic system PhSiH₃/ReIO₂(PPh₃)₂ (1 mol %) proved to be highly efficient for the reduction of a wide range of sulfoxides in excellent yields under mild conditions. This novel methodology is also highly chemoselective, tolerating several functional groups such as –CHO, –CO₂R, –Cl, –NO₂, and double or triple bonds.