Shape Influence in Buckling of GFRP Pultruded Columns

A theoretical and experimental study on the buckling of pultruded columns under an axial load is reported. The tests were carried out on wide-flange (H-shape) and narrow-flange (I-shape) pultruded structural profiles reinforced with glass fibers (GFRP). The aim of the research was to provide more detailed information on the effective buckling behavior, the interaction between local and global buckling, and the type of failure, considering different slenderness ratios, from 9 to 195. Also, a comparison between the results of a finite-element analysis and experimental data is shown.     

{W^{1,1}_0} -solutions for elliptic problems having gradient quadratic lower order terms

In this paper we deal with solutions of problems of the type $$\left\{\begin{array}{ll}-{\rm div} \Big(\frac{a(x)Du}{(1+|u|)^2} \Big)+u = \frac{b(x)|Du|^2}{(1+|u|)^3} +f \quad &{\rm in} \, \Omega,\\ u=0 &{\rm on} \partial \, \Omega, \end{array} \right.$$ where ${0 < \alpha \leq a(x) \leq \beta, |b(x)| \leq \gamma, \gamma > 0, f \in L^2 (\Omega)}$ and Ω is a bounded subset of ${\mathbb{R}^N}$ with N ≥ 3. We prove the existence of at least one solution for such a problem in the space ${W_{0}^{1, 1}(\Omega) \cap L^{2}(\Omega)}$ if the size of the lower order term satisfies a smallness condition when compared with the principal part of the operator. This kind of problems naturally appears when one looks for positive minima of a functional whose model is: $$J (v) = \frac{\alpha}{2} \int_{\Omega}\frac{|D v|^2}{(1 + |v|)^{2}} + \frac{12}{\int_{\Omega}|v|^2} - \int_{\Omega}f\,v , \quad f \in L^2(\Omega),$$ where in this case a(x) ≡ b(x) = α > 0.     

Relaxation properties of porphyrin, diprotonated porphyrin, and isoelectronic tetraoxaporphyrin dication in the S2 state

The fluorescence spectra of unsubstituted porphyrin (H2P), diprotonated porphyrin (H4P2+), and isoelectronic tetraoxaporphyrin dication (TOxP2+) have been measured in solution at room temperature. The S2-->S0 fluorescence has been observed, much more intense for TOxP2+ than for H4P2+ and H2P. In the TOxP2+ case, the S2-->S0 fluorescence spectrum is remarkably sharp and shows an excellent mirror symmetry with respect to S0-->S2 absorption. On the contrary, the spectra of H4P2+ and H2P are shifted and more extended with respect to the absorption counterparts. The differences have been attributed primarily to the change of the equilibrium geometry upon excitation, larger in H2P and H4P2+ than in TOxP2+ and in the case of H4P2+ to the nonplanar conformation of the macrocycle. Also the S1-->S0 spectra of H2P, H4P2+, and TOxP2+ have been measured and more qualitatively discussed. The S1 and S2 fluorescence decays have been observed for H4P2+ and TOxP2+ exciting with ultrashort pulses. The S2 lifetime of TOxP2+ is of the order of the temporal resolution of our experimental apparatus, whereas that of H4P2+ is shorter. The S2-->S0 quantum yield of TOxP2+ has been estimated to be 0.035, approximately 3 orders of magnitude higher than that of H4P2+. It is proposed on the basis of ab initio model calculations that excited states of the H4P2+(CF3COO-)2 complex with charge-transfer character are responsible of the increased extension of the S2-->S0 spectrum with respect to that of H2P.     

Biomonitoring of the atmospheric pollution using lichens in the metropolitan area of São Paulo city,Brazil

The atmospheric pollution of São Paulo city is a serious problem due to the expansion of industrial area, increasing number of vehicles and population density. This work presents results obtained in the analysis of lichens collected in different sites of São Paulo city and in non-polluted areas of Atlantic Forest. Concentrations of twenty elements were determined in Canoparmelia texana species and comparisons were made between the results obtained in lichens from different sites. High concentrations of the elements As, Ba, Cd, Co, Cr, Fe, La, Mn, Sb and Zn were found for samples collected in sites located near industries and petrochemical plant. Br and Sb concentrations were also high in lichens from sites affected by vehicular emissions.     

On the equivalence of the weighted least squares and the generalised least squares estimators,with applications to kernel smoothing

This paper establishes the conditions under which the generalised least squares estimator of the regression parameters is equivalent to the weighted least squares estimator. The equivalence conditions have interesting applications in local polynomial regression and kernel smoothing. Specifically, they enable to derive the optimal kernel associated with a particular covariance structure of the measurement error, where optimality has to be intended in the Gauss-Markov sense. For local polynomial regression it is shown that there is a class of covariance structures, associated with non-invertible moving average processes of given orders which yield the Epanechnikov and the Henderson kernels as the optimal kernels.     

A Product Formula Approach to a Nonhomogeneous Boundary Optimal Control Problem Governed by Nonlinear Phase-field Transition System

In this paper we prove the convergence of an iterative scheme of fractional steps type for a non-homogeneous Cauchy-Neumann boundary optimal control problem governed by non-linear phase-field system, when the boundary control is dependent both on time and spatial variables. Moreover, necessary optimality conditions are established for the approximating process. The advantage of such approach leads to a numerical algorithm in order to approximate the original optimal control problem.