Influence of polyimide precursor synthesis route and ortho-position functional group on thermally rearranged (TR) polymer properties: Conversion and free volume

Thermal rearrangement of polyimides with ortho-position groups to polybenzoxazoles and related structures has been of recent interest for producing gas separation membranes. This study explores the influence of synthesis route and ortho-position functional group on the thermal rearrangement process and the fractional free volume of thermally rearranged (TR) polymers produced from polyimides derived from 3,3′-dihydroxy-4,4′-diamino-biphenyl and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (HAB–6FDA). Acetate, propanoate, and pivalate ortho-position functional groups were considered. Thermogravimetric analysis (TGA) was used to study thermal rearrangement at temperatures between 350 and 450 °C, and evolved gases from TGA were analyzed via mass spectrometry to characterize the byproducts of thermal rearrangement and thermal degradation. CO₂ was the major byproduct of thermal rearrangement for all samples, and its evolution began well before the onset of thermal degradation. When non-hydroxyl ortho-position groups were present in the polymers, several byproducts other than CO₂ were also observed due to the loss of these ortho-position groups before thermal rearrangement. Free volume generally increased with increasing extent of thermal rearrangement, but precise values of free volume could not be accurately determined for polymers with propanoate and pivalate ortho-position functional groups due to uncertainties in the chemical structure of partially converted materials. For polymers with acetate and hydroxyl ortho-position groups, free volume could be determined within the uncertainty of density measurements. Thermal rearrangement behavior and free volume results for acetate containing polymers synthesized via different routes were very similar. Based on these results, the chemical structure of the ortho-position functional group has a larger impact on TR polymer properties than the polyimide precursor synthesis route.     

Scale and scope of environmental planning transformations: The Israeli case

This paper explores the scale and scope of transformations in the environmental planning field, and the factors that may advance or impede their widespread adoption. A conceptual model is offered which examines scope (defined as type, breadth and structure of the transformation), and the scale of its impact (categorized as stakeholder, organizational, institutional or societal) and applies it to the analysis of several cases in Israel where environmental transformations, affecting the way in which planning is conducted, have been adopted. Conclusions include identification of conditions for facilitating and advancing transformations, including knowledge of innovative alternatives, initiative, willingness to adopt new practices, and identification of policy windows that emerge during conflict, reform, or crisis. The fostering of relations between environmental non-government organizations and planning systems and leadership roles are also significant in catalyzing environmental transformation.     

Decoupling the Direct and Indirect Biological Effects of ZnO Nanoparticles Using a Communicative Dual Cell‐Type Tissue Construct

While matter at the nanoscale can be manipulated, the knowledge of the interactions between these nanoproducts and the biological systems remained relatively laggard. Current nanobiology study is rooted on in vitro study using conventional 2D cell culture model. A typical study employs monolayer cell culture that simplifies the real context of which to measure any nanomaterial effect; unfortunately, this simplification also demonstrated the limitations of 2D cell culture in predicting the actual biological response of some tissues. In fact, some of the characteristics of tissue such as spatial arrangement of cells and cell–cell interaction, which are simplified in 2D cell culture model, play important roles in how cells respond to a stimulus. To more accurately recapitulate the features and microenvironment of tissue for nanotoxicity assessments, an improved organotypic‐like in vitro multicell culture system to mimic the kidney endoepithelial bilayer is introduced. Results showed that important nano‐related parameters such as the diffusion, direct and indirect toxic effects of ZnO nanoparticles can be studied by combining this endoepithelial bilayer tissue model and traditional monolayer culture setting.     

Characterization of the phosphatic mineral of the barnacle Ibla cumingi at atomic level by solid-state nuclear magnetic resonance: comparison with other phosphatic biominerals

Ibliform barnacles are among the few invertebrate animals harnessing calcium phosphate to construct hard tissue. The ³¹P solid-state NMR (SSNMR) signal from the shell plates of Ibla cumingi (Iblidae) is broader than that of bone, and shifted by ca 1 ppm to low frequency. ¹H–³¹P heteronuclear correlation (HETCOR) experiments show a continuum of different phosphorus/phosphate atomic environments, close to hydrogen populations with resonance frequencies between ca 10 and 20 ppm. Associated ¹H and ³¹P chemical shifts argue the coexistence of weakly (high ³¹P frequency, low ¹H frequency) to more strongly (lower ³¹P frequency, higher ¹H frequency) hydrogen-bonded hydrogen phosphate-like molecular/ionic species. There is no resolved signal from discrete OH⁻ ions. ¹³C SSNMR shows chitin, protein and other organic biomolecules but, unlike bone, there are no significant atomic scale organic matrix–mineral contacts. The poorly ordered hydrogen phosphate-like iblid mineral is strikingly different, structurally and compositionally, from both vertebrate bone mineral and the more crystalline fluoroapatite of the linguliform brachiopods. It probably represents a previously poorly characterized calcium phosphate biomineral, the evolution of which may have reflected either the chemical conditions of ancestral seas or the mechanical advantages of phosphatic biomineralization over a calcium carbonate equivalent.     

Thermodynamic and Acoustic Properties of Mixtures of Dibromomethane + Heptane

Densities and speeds of ultrasound in binary mixtures of dibromomethane with heptane have been measured within the temperature range from 288.15 K to 318.15 K. From the experimental data, the thermodynamic excess volume, molar isobaric expansion, molar isentropic compression, and ultrasonic speed were calculated. The excess volume and excess isentropic compression have opposite signs, whereas the excess isobaric expansion is an S-shaped function of the mole fraction. An explanation was suggested to account for the excesses in terms of intermolecular interactions. It involved energetic and steric factors. Moreover, it was shown that the positive excess sound speed results almost entirely from the negative excess compression.     

An inquiry of the opinions of the French and Belgian populations as regards risk

IRSN (France) and SCK-CEN (Belgium), two institutes of research and expertise in radiation protection and nuclear safety, simultaneously organised a very similar public opinion survey in their respective countries in November 2002. The study explores subjects such as: major people's concerns, perception of environmental risks, perception of risks in general, the role of experts in decision making, opinions on nuclear matters and aspects of nuclear emergency preparedness. In each country, more than 1000 citizens representing the general public have been consulted in face-to-face interviews. The field work has been performed by professional companies (BVA in France and Research International in Belgium). The paper shows that industrial and technological risks are not perceived as one of the major public concerns, although many other risks, of different nature are considered to be high. The actions of the authorities to provide protection against the consequences of many risks or disasters are not considered to be sufficient, and many respondents claim not to believe the information they receive. There exists a large difference between the opinion of French and Belgian public, and within the different language groups in Belgium, with regard to who should be in charge of the control of the hazardous industries. Many of the "actors" within the nuclear industry are not known by the respondents. The perception of the technical competence or the truth being told shows large variations between the main actors (such as members of the nuclear industry, the government or the media). Majorities within the population believe that a disaster as serious as the Chernobyl one can happen in their country and that in case of a nuclear accident, the authorities would not be capable to protect the population adequately.     

Effective moduli of multi-scale composites

The effective moduli of a multi-scale composite are evaluated by a bottom-up (hierarchical) modeling approach. We focus on a two-scale structure in which the small scale includes a platelet array inside a matrix, and the large scale contains fibers inside a composite matrix. We demonstrate that the principal moduli of the multi-scale composite can be fine-tuned by the platelet arrangement and orientation. As a case study, we consider the phenomenon of fiber micro-buckling within the multi-scale composite. It is found that the compressive micro-buckling strength can be considerably increased for specific platelet orientations. The multi-scale design approach presented here can be used to generate novel families of composite materials with tunable mechanical properties.     

AlGaN/GaN high electron mobility transistors with implanted ohmic contacts

Selective area silicon implantation for source/drain regions was integrated into the fabrication of molecular beam epitaxy-grown AlGaN/GaN HEMTs. Dopant activation was achieved by rapid thermal annealing at 1100 °C in flowing N₂ ambient for 120 s with an AlN encapsulation. Linear transmission line measurements showed that the resistance of the overlay Ti/Al/Ni/Au ohmic contacts was reduced by 61% compared to the control sample. After the Schottky Ni/Au gate formation, the typical DC characteristics displayed a higher current drive, smaller knee voltage and better gate control properties for HEMTs with implanted source and drain regions.     

Phase-shifting interferometry by a covariance-based method

A novel generalized approach to phase-shifting interferometry in which phase distribution in an interferogram is evaluated in the presence of nonsinusoidal waveforms and piezoactuator device miscalibration is proposed. The approach is based on the underlying rotational invariance of signal subspaces spanned by two temporally displaced data sets. The advantage of the proposed method lies in its ability to identify arbitrary phase-step values pixelwise from an interference signal buried in noise. The robustness of the proposed method is investigated by addition of white Gaussian noise during the simulations.     

Laboratory abnormalities in thrombotic thrombocytopenic purpura. Canadian Apheresis Group

Thrombotic thrombocytopenic purpura is an uncommon disorder that requires prompt recognition and intervention to prevent death. To date, information regarding the classic laboratory abnormalities in the disease has been derived from small numbers of patients whose laboratory tests have been done at many different sites. We report the laboratory findings in 135 patients who presented with thrombotic thrombocytopenic purpura to 17 Canadian centres. 50 men and 85 women had a mean platelet count of 25.3+/-19.4x10(9)/l. The initial platelet count correlated with mortality; 32% of patients with a platelet count of 20x10(9)/l or less died compared with 18% of patients with a platelet count >20x10(9)/l (P=0.058). The platelet-associated IgG was elevated in 88% at presentation whereas the indirect platelet suspension immunofluorescence test was positive in only 18%, 93% of the sera showed reactivity against platelets following protein blotting. All sera tested also showed reactivity against endothelial cells. Immune complexes were seen in all patients, whereas the platelet aggregating factor was detected in 59%. Although the von Willebrand factor was elevated in the majority of patients at entry, the multimer pattern was variable and showed no predictive pattern. Renal dysfunction was common (18%).