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.     

Systematic synthesis of inhibitors of the two first enzymes of the bacterial heptose biosynthetic pathway: towards antivirulence molecules targeting lipopolysaccharide biosynthesis

L-Heptoses (L-glycero-D-manno-heptopyranoses) are constituents of the inner core of lipolysaccharide (LPS), a molecule playing key roles in the mortality of many infectious diseases as well as in the virulence of many human pathogens. The inhibition of the first enzymes of the bacterial heptose biosynthetic pathway is an almost unexplored field to date although it appears to be a very novel way for the development of antivirulence drugs. We report the synthesis of a series of D-glycero-D-manno-heptopyranose 7-phosphate (H7P) analogues and their inhibition properties against the isomerase GmhA and the the kinase HldE, the two first enzymes of the bacterial heptose biosynthetic pathway. The heptose structures have been modified at the 1-, 2-, 6- and 7-positions to probe the importance of the key structural features of H7P that allow a tight binding to the target enzymes; H7P being the product of GmhA and the substrate of HldE, the second objective was to find structures that could simultaneously inhibit both enzymes. We found that GmhA and HldE were extremely sensitive to structural modifications at the 6- and 7- positions of the heptose scaffold. To our surprise, the epimeric analogue of H7P displaying a D-glucopyranose configuration was found to be the best inhibitor of both enzymes but also the only molecule of this series that could inhibit GmhA (IC(50)=34 μM) and HldE (IC(50)=9.4 μM) in the low micromolar range. Noteworthy, this study describes the first inhibitors of GmhA ever reported, and paves the way to the design of a second generation of molecules targeting the bacterial virulence.     

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.     

About the relaxed cocoercivity and the convergence of the proximal point algorithm

The aim of this paper is to study the convergence of two proximal algorithms via the notion of (α, r)-relaxed cocoercivity without Lipschitzian continuity. We will show that this notion is enough to obtain some interesting convergence theorems without any Lipschitz-continuity assumption. The relaxed cocoercivity case is also investigated.     

Morphology and Linear Viscoelasticity of Poly[ethylene‐co‐(1‐octene)]/Layered Silicate Nanocomposites

Poly[ethylene‐co‐(1‐octene)] nanocomposites with different microstructures were prepared with two kinds of organoclay by melt intercalation. X‐ray diffraction and transmission electron microscopy were used to characterize the morphology of the composites. Linear storage moduli of the composites in the melt state were found to increase greatly with increasing the extent of dispersion of silicate layers and showed an obvious sensitivity to the morphologies of the composites.     

Pyridazine,oxazine, pyrrole,and pyrrolo[1,2‐a]quinazoline derivatives from malononitrile dimer

2‐Amino‐1,1,3‐tricyano‐3‐bromopropene was obtained from bromination of 2‐amino‐1,1,3‐tricyanopropene (malononitrile dimer) with N‐bromosuccinimide. This bromo derivative reacts with hydrazine hydrate, phenyl hydrazine, and hydroxylamine hydrochloride to afford pyridazine and oxazine derivatives, respectively. In base‐catalyzed reactions with primary aromatic amines and anthranilic acid derivatives, it produces N‐aryl pyrrol‐3,5‐dicarbonitrile and pyrrolo[1,2‐a]quinazolin‐5‐imine, or pyrrolo[1,2‐a]quinazolin‐5‐one derivatives, respectively. The structures of the newly synthesized heterocycles were established on the basis of elemental analyses and spectral data. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:612–616, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10199