Polycaprolactone/polystyrene bioblends characterized by thermogravimetry, modulated differential scanning calorimetry and infrared photoacoustic spectroscopy

Polymer blends comprising at least one biodegradable polymer with other polymers are referred to as bioblends. Successful development of bioblends requires the biodegradable polymers to be compatible with other polymer components. Compatibility is normally assessed through the evaluation of the degree of intermolecular interactions between individual components. In this work, the degree of interaction in binary bioblends comprising biodegradable polycaprolactone (PCL) and polystyrene (PS) was investigated using thermogravimetric analysis (TGA), modulated differential scanning calorimetry (MDSC) and Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). The TGA studies indicated that incorporation of PCL in PS results in thermal destabilization of PCL/PS bioblends. The MDSC studies showed that some parameters, such as the enthalpies of melting and crystallization, favored partial miscibility of PS in PCL, while others, such as change in the glass transition temperature, favored immiscibility. The FTIR-PAS spectra suggested the presence of intermolecular n-π interactions between PCL and PS and supported the results of TGA and MDSC analyses of PCL/PS bioblends.     

Numerical solution of the oxygen diffusion problem in cylindrically shaped sections of tissue

A mathematical model is presented which describes the diffusion of oxygen in absorbing tissue, and numerical solution of its partial differential equation is obtained by the finite difference equations. The diffusion with absorption model is associated with the process of a moving boundary which marks the furthest penetration of oxygen in the absorbing cylindrically shaped sections of tissue and also allows for an initial distribution of oxygen through the absorbing tissue. Copyright © 2007 John Wiley & Sons, Ltd.     

Electrochemical Behavior of Dental Ni‐Cr Wirolloy Coated with Eco‐friendly Films in Artificial Saliva

The electrochemical corrosion behavior of the non‐precious Ni‐Cr Wirolloy, being used in dentistry, was investigated before and after applying of two types of eco‐friendly coatings, polyvinyl silsesquioxane (PVS) and nano‐hydroxyapatite (nHAP) separately in artificial saliva solution at 37 °C for 14 d of immersion. The study aimed to investigate the effectiveness of the introduced coating films in enhancing the corrosion resistance of the alloy, and in decreasing the leaching of the toxic Ni ions from the alloy into the environment. The electrochemical corrosion investigation methods used are; open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The evaluated results revealed that the electrochemically coated alloy with PVS. prepared at cathodic potential showed higher corrosion resistance and more stable film compared to that prepared by conventional dip‐coating method. At the same time, the nHAP electrochemically coated film provided the best anti‐corrosion properties over all examined time intervals. The obtained results were confirmed via surface analysis, which assured the formation of the prepared coatings on the alloy surface. Chemical analysis of the corrosion product/solutions showed that the effect of electrochemically deposited nHAP and PVS. polymer films in suppression of Ni ions leaching is similar and slightly higher than that of the chemically coated PVS. one; however, all of them are efficient in decreasing the leaching of the risky Ni ions into the solution.     

On the Superlinear Convergence Order of the Logarithmic Barrier Algorithm

Since the pioneering work of Karmarkar, much interest was directed to penalty algorithms, in particular to the log barrier algorithm. We analyze in this paper the asymptotic convergence rate of a barrier algorithm when applied to non-linear programs. More specifically, we consider a variant of the SUMT method, in which so called extrapolation predictor steps allowing reducing the penalty parameter r_k +1}k are followed by some Newton correction steps. While obviously related to predictor-corrector interior point methods, the spirit differs since our point of view is biased toward nonlinear barrier algorithms; we contrast in details both points of view. In our context, we identify an asymptotically optimal strategy for reducing the penalty parameter r and show that if r_k+1=r _k with < 8/5, then asymptotically only 2 Newton corrections are required, and this strategy achieves the best overall average superlinear convergence order (1.1696). Therefore, our main result is to characterize the best possible convergence order for SUMT type methods.     

Estimateur a posteriori en norme L∞ pour les équations elliptiquesL∞-a posteriori error estimator for elliptic equations

In this Note, we show that modification of Bank–Wieser estimator introduce an L^∞-a posteriori error estimator for conforming and nonconforming methods. We prove, without saturation assumption nor comparison with residual estimators, the equivalence with the L^∞ error. To cite this article: A. Agouzal, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 411–415.     

Effect of multiple localized geometric imperfections on stability of thin axisymmetric cylindrical shells under axial compression

Stability of imperfect elastic cylindrical shells which are subjected to uniform axial compression is analyzed by using the finite element method. Multiple interacting localized axisymmetric initial geometric imperfections, having either triangular or wavelet shapes, were considered. The effect of a single localized geometric imperfection was analyzed in order to assess the most adverse configuration in terms of shell aspect ratios. Then two or three geometric imperfections of a given shape and which were uniformly distributed along the shell length were introduced to quantify their global effect on the shell buckling strength. It was shown that with two or three interacting geometric imperfections further reduction of the buckling load is obtained. In the ranges of parameters that were investigated, the imperfection wavelength was found to be the major factor influencing shell stability; it is followed by the imperfection amplitude, then by the interval distance separating the localized imperfections. In a wide range of parameters this last factor was recognized to have almost no effect on buckling stresses.     

Hierarchically porous nanostructures through phosphonate-metal alkoxide condensation and growth using functionalized dendrimeric building blocks

Controlled titanium alkoxide mineralization in the presence of phosphonated, dendrimeric nano-building blocks provides a new family of hierarchically porous dendrimer-bridged titanium dioxide materials.     

Synthesis of New (4‐Acetonylidene‐2,6,8,9‐tetramethyl‐7H‐imidazo[1,5,4‐e,f][1,5]benzodiazepine) Derivatives

Imidazobenzodiazepine derivatives were obtained by cyclization of the condensation products 7‐amino‐2,5,6‐trimethylbenzimidazole with acetylacetone and ethyl acetoacetate. By careful examination of spectroscopic data and the open‐chain intermediate isolation, we have identified the formed compound structure.