Raman studies in SmCFI* phases

The study of the Raman intensity of the 'breathing' mode of the benzene rings as a function of the temperature in smectic phases revealed strong anomalies of the intensities I_ZZ and I_YY in SmC_FI2* and SmC_FI1* phases, as well as an important shift of the principal optical direction with respect to other smectic phases. The analysis of these results provided evidence for significant structural changes at the SmC*-SmC_FI* and SmC_FI*-SmC_A* phase transitions, because the molecules can no longer be treated as cylindrical rods. No anomalies in the tilt angle were found. Experimental results suggest a relationship between the deviation of the optical axis and the particular structure of the SmC_FI* phases. The deviation of I_ZZ maxima as a function of the rotation angle Ψ and the behaviour evident under an electric field in SmC_FI* and SmC_A* phases clearly excludes the coexistence of SmC_A* and SmC* local domains in SmC_FI* phases.     

Unilateral Fin Line Directional Coupler

Photonic band gap (PBG) crystals have been used as a perfectly reflecting substrate for many millimeter wave applications. In this work the fin line directional coupler with substrate PBG was analyzed using the TTL - Transverse Transmission Line - method. Compared to other full wave methods the TTL is an efficient tool to determine the coupler characteristics, making possible a significant algebraic simplification of the equations involved in the process. In order to analyze this structure the effective dielectric constant, the attenuation constant and the coupling were determined. The results obtained for this application and the conclusions are presented. This work was partially financed by CNPQ.     

<Emphasis Type="Italic">N</Emphasis>-Arylamine derivatives of 3-hydroxy-4-pyridinones: solution studies and bioevaluation in view of Al-detoxification roles

A study of a series of bifunctional 3-hydroxy-4-pyridinone derivatives, containing side-chains with various alkyl-aryl-amine-amides as extra-functional groups, was conducted to assess the relevance of those groups to the Al-chelating affinity, the lipo–hydrophilic balance of the compounds, and ⁶⁷Ga biodistribution in mice, in view of their potential use as Al-decorporating agents; the results were compared with those for the drug Deferriprone. Their acid–base properties and Al-chelating affinity in aqueous solution were studied by potentiometric techniques. These ligands form very stable tris-chelated Al complexes and the non-chelating extra-groups are only responsible for small differences in the complex stability (pAl1.2). At physiological pH the major ligand/complex species have different charges, because of the different extent of protonation of the ligands. The introduction of the different groups induces a well-balanced stepwise-like lipo–hydrophilic character (–0.2<log D_oct./water<+1.1). The effect of each ligand on the biodistribution of ⁶⁷Ga in overloaded mice is rapid blood clearance for all of them, but with different biodistribution patterns, namely excretion pathways and brain uptake/clearance, thus suggesting potential different clinical use.     

Time evolution of the eddy viscosity in two-dimensional navier-stokes flow

The time evolution of the eddy viscosity associated with an unforced two-dimensional incompressible Navier-Stokes flow is analyzed by direct numerical simulation. The initial condition is such that the eddy viscosity is isotropic and negative. It is shown by concrete examples that the Navier-Stokes dynamics stabilizes negative eddy viscosity effects. In other words, this dynamics moves monotonically the initial negative eddy viscosity to positive values before relaxation due to viscous term occurs.     

Stability of perturbed nonlinear parabolic equations with Sturmian property

We study stability of an equilibrium f∗ of autonomous dynamical systems under asymptotically small perturbations of the equation. We show that such stability takes place if the domain of attraction of the equilibrium f∗ contains a one-parametric ordered family . In the stability analysis we need a special S-relation (a kind of “restricted partial ordering”) to be preserved relative to the family . This S-relation is inherited from the Sturmian zero set properties for linear parabolic equations. As main applications, we prove stability of the self-similar blow-up behaviour for the porous medium equation, the p-Laplacian equation and the dual porous medium equation in with nonlinear lower-order perturbations. For such one-dimensional parabolic equations the S-relation is Sturm's Theorem on the nonincrease of the number of intersections between the solutions and particular solutions with initial data in . This Sturmian property plays a key role and is true for the unperturbed PME, but is not true for perturbed equations.     

Solvent effect on the free‐radical copolymerization of 2‐hydroxyethyl methacrylate with t‐butyl acrylate

The free‐radical copolymerization of 2‐hydroxyethyl methacrylate with t‐butyl acrylate was carried out at 50 °C in bulk and in 3 mol · L^?1 1,4‐dioxane and N,N′‐dimethylformamide solutions. Differences between the apparent reactivity ratios determined in this work indicated a noticeable solvent effect. This is explained with a qualitative bootstrap effect. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2043–2048, 2001     

Spectral Properties of Interval Exchange Maps

 In [7], Nogueira and Rudolph proved that for irreducible permutations not of rotation class almost every (a.e.) interval exchange transformation (i.e.t.) is topological weak mixing. It is conjectured that the claim holds if topological weak mixing is replaced by weak mixing. Here we study the behaviour of eigenfunctions of i.e.t. Our analysis gives alternative proofs of results due to Katok and Stepin [4] and Veech [10]: for certain permutations a.e. i.e.t. is weak mixing and for irreducible permutations a.e. i.e.t. is totally ergodic. (Received 1 February 2001)     

Modelling free surfaces in oscillating pipe flows

An oscillating pipe flow with a free surface is investigated numerically and experimentally. The pipe diameter is 12mm. Due to this small diameter capillary forces play an important role. Therefore special attention has to be paid to the flow field near the free surface. The numerical model is based on the fundamental flow equations. The free surface is resolved according to the volume-of-fluid method. The model equations are solved on a moving grid. In the experiment, pictures of the flow field are taken near the free surface. The effects occuring near the interface will be presented here. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Review and perspectives on energy dispersive high resolution PIXE and RYIED

Until 2008, high-resolution particle-induced x-ray emission (HR-PIXE) work used mostly wavelength dispersive spectrometers and aimed at fundamental problems and application demonstrations. The method was hardly used for applications in general, mostly due to the small energy window and solid angle of most equipment. In the last 14 years, a few facts pushed HR-PIXE out and beyond this framework. Here, we focus on the developments following the observation of x-ray relative yield ion energy dependence (RYIED) effects on transitions to the same sub-shell, in PIXE experiments, in 2004, and the installation, in 2008, of the first energy dispersive HR-PIXE (EDS HR-PIXE) system. Both facts are among those that were concurrent to the emergence of new problems and perspectives in PIXE and in fundamental atomic physics in the recent past. This review covers these 14 years of results on these issues and the answers they recently led to. Evidence for new problems and perspectives, including the potential access to chemical bonding and/or solid state information, based on EDS HR-PIXE work, are discussed. Furthermore, the grounds for the possibility of developments leading to a new field of atomic solid state physics are presented.