Synthesis and properties of organosoluble polyimides derived from 2,2′‐dibromo‐ and 2,2′,6,6′‐tetrabromo‐4,4′‐oxydianilines

Two new aromatic diamines, 2,2′‐dibromo‐4,4′‐oxydianiline (DB‐ODA 4 ) and 2,2′,6,6′‐tetrabromo‐4,4′‐oxydianiline (TB‐ODA 5 ), have been synthesized by oxidation, bromination, and reduction of 4,4′‐oxydianiline (4,4′‐ODA). Novel polyimides 6a–f and 7a–f were prepared by reacting DB‐ODA ( 4 ) and TB‐ODA ( 5 ) with several dianhydrides by one‐step method, respectively. The inherent viscosities of these polyimides ranged from 0.31 to 0.99 dL/g (0.5 g/dL, in NMP at 30°C). These polyimides showed enhanced solubilities compared to those derived from 4,4′‐oxydianiline and corresponding dianhydrides. Especially, polyimides 7a , derived from rigid PMDA and TB‐ODA ( 5 ) can also be soluble in THF, DMF, DMAc, DMSO, and NMP. These polyimides also exhibited good thermal stability. Their glass transition temperatures measured by thermal mechanical analysis (TMA) ranged from 251 to 328°C. When the same dianhydrides were used, polyimides 7 containing four bromide substituents had higher glass transition temperatures than polyimides 6 containing two bromide substituents. The effects of incorporating more polarizable bromides on the refractive indices of polyimides were also investigated. The average refractive indices (n_av) measured at 633 nm were from 1.6088 to 1.7072, and the in‐plane/out‐of‐plane birefringences (Δn) were from 0.0098 to 0.0445. It was found that the refractive indices are slightly higher when polyimides contain more bromides. However, this effect is not very obvious. It might be due to loose chain packing resulted from bromide substituents at the 2,2′ and 2,2′,6,6′ positions of the oxydiphenylene moieties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Graphite-based indirect laser sintered fuel cell bipolar plates containing carbon fiber additions

Critical considerations for laser sintered (LS) graphite bipolar plates are the strength of the parts in the green, brown and finished states as well as the final part electrical conductivity. The effect of 0-26 volume percent chopped carbon fiber (CF) on strength and electrical conductivity of LS graphite bipolar plates was evaluated. Fiber additions improved the green and brown strength significantly. Finished part flexural strength increased from 35 MPa to almost 50 MPa with CF additions. The electrical conductivity of finished parts was lowered by CF additions.     

Resource brokering using a multi‐site resource allocation strategy for computational grids

Grid computing employs heterogeneous resources which may be installed on different platforms, hardware/software, computer architectures, and perhaps using different computer languages to solve large‐scale computational problems. As many more Grids are being developed worldwide, the number of multi‐institutional collaborations is growing rapidly. However, to realize Grid computing's full potential, it is expected that Grid participants must be able to share one another's resources. This paper presents a resource broker that employs the multi‐site resource allocation (MSRA) strategy and the dynamic domain‐based network information model that we propose to allocate Grid resources to submitted jobs, where the Grid resources may be dispersed at different sites, and owned and governed by different organizations or institutes. The jobs and resources may also belong to different clusters/sites. Resource statuses collected by the Ganglia, and network bandwidths gathered by the Network Weather Service, are both considered in the proposed scheduling approach. A dynamic domain‐based model for network information measurement is also proposed to choose the most appropriate resources that meet the jobs' execution requirements. Experimental results show that MSRA outperformed the other tested strategies. Copyright © 2010 John Wiley & Sons, Ltd.     

Optimal design of parallel channel patterns in a micro methanol steam reformer

This study describes the performance of micro methanol steam reformers with channel widths optimized using the simplified conjugate gradient method (SCGM), which uses a minimum objective function of the H₂ mass fraction standard deviation in channels. A three-dimensional numerical model and optimal simplified conjugate gradient algorithm were built to predict and search for the effects of channel widths and flow rate on the performance of chemical reactions. Furthermore, this simulation model was compared to; and corresponded well with existing experimental data. Distributions of velocity, temperature, and gas concentrations (CH₃OH, CO, H₂, and CO₂) were predicted, and the methanol conversion ratio was also evaluated. The mole fraction of CO contained in the reformed gas, which is essential to preventing poisoning of the catalyst layers of fuel cells, is also investigated. In the optimization search process, the governing equations use the continuity, momentum, heat transfer, and species equations to evaluate the performance of the steam reformer. The results show that channel width optimization can not only increase the methanol conversion ratio and hydrogen production rate but also decrease the concentration of carbon monoxide. The velocity and mixture gas density distributions in channels are discussed and plotted at various locations for an inlet liquid flow rate of 0.3 cc min⁻¹. Full development is not obtained in the downstream channel flow, the velocity in channel is increased from 1.28 m s⁻¹ to 2.36 m s⁻¹ at location Y = 1 mm–32 mm, respectively. This can be attributed to a continuous increase in the lightweight H₂ species as a result of chemical reactions in the channels.     

Are positive emotions just as “positive” across cultures?

Whereas positive emotions and feeling unequivocally good may be at the heart of well-being among Westerners, positive emotions often carry negative associations within many Asian cultures. Based on a review of East-West cultural differences in dialectical emotions, or co-occurring positive and negative feelings, we predicted culture to influence the association between positive emotions and depression, but not the association between negative emotions and depression. As predicted, in a survey of over 600 European-, immigrant Asian-, and Asian American college students, positive emotions were associated with depression symptoms among European Americans and Asian Americans, but not immigrant Asians. Negative emotions were associated with depression symptoms among all three groups. We also found initial evidence that acculturation (i.e., nativity) may influence the role of positive emotions in depression: Asian Americans fell “in between” the two other groups. These findings suggest the importance of studying the role of culture in positive emotions and in positive psychology. The use of interventions based on promoting positive emotions in clinical psychology among Asian clients is briefly discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Nanoporous materials from stable and metastable structures of 1,2-PB-b-PDMS block copolymers

Experimental procedures used at the preparation and characterization stages of nanoporous materials (NPM) from 1,2-polybutadiene-b-polydimethylsiloxane (1,2-PB-b-PDMS) block copolymers are presented. The NPM were obtained from self-assembled block copolymers after firstly cross-linking 1,2-PB (the matrix component) and secondly degrading PDMS (the expendable component). Depending on the temperature of the cross-linking reaction different morphologies can be ‘frozen’ from the same block copolymer. Starting with a block copolymer precursor of lamellar morphology at room temperature, the gyroid structure or a metastable structure showing hexagonal symmetry (probably HPL) were permanently captured by cross-linking the precursor at 140 °C or at 85 °C, respectively. PDMS was degraded by reaction with tetrabutylamonium fluoride; considerations on the mechanism of cleaving reaction are presented. The characterization of the materials at different stages of preparation includes gravimetry, infrared spectroscopy, small angle x-ray scattering, electron microscopy and isothermal nitrogen adsorption experiments.     

Water Absorption of Poly(lactic acid) Nanocomposites: Effects of Nanofillers and Maleated Rubbers

Injection-molded poly(lactic acid)/organo-montmorillonite (PLA/OMMT) and poly(lactic acid)/ nano-precipitated calcium carbonate (PLA/NPCC) were exposed to a water absorption test at 30°C for 70 days. The analysis was focused on the water diffusion kinetics and impact strength changes induced by the hydrolysis. The diffusion exponent (n) values of all the PLA samples are less than 0.5, indicating the Fickian diffusion model (case I) is obeyed. Adding nanofillers and maleated rubbers (SEBS-g-MAH or EPR-g-MAH) increased equilibrium moisture content but decreased diffusion coefficient values of PLA. The recoverability and retention-ability of the maleated rubbers toughened PLA/OMMT and PLA/NPCC after water absorption are excellent.     

Superplastic elongation characteristic of fine grained magnesium alloy ZK60

This paper employs simple rolling process plus annealing to refine the grain size of magnesium alloy ZK60. This goal is effectively achieved, obtaining grains as fine as ∼3.7 μm. Such a specimen shows an elongation of 642%, and its ultimate fracture surface exhibits intergranular separation and significant grain growth. Additionally, the effects of the specimen’s geometry and tensile test axis with respect to the rolling direction on superplastic elongation is studied, which has not been done before.     

Hydroxygenkwanin Increases the Sensitivity of Liver Cancer Cells to Chemotherapy by Inhibiting DNA Damage Response in Mouse Xenograft Models

Molecules involved in DNA damage response (DDR) are often overexpressed in cancer cells, resulting in poor responses to chemotherapy and radiotherapy. Although treatment efficacy can be improved with the concomitant use of DNA repair inhibitors, the accompanying side effects can compromise the quality of life of patients. Therefore, in this study, we identified a natural compound that could inhibit DDR, using the single-strand annealing yeast-cell analysis system, and explored its mechanisms of action and potential as a chemotherapy adjuvant in hepatocellular carcinoma (HCC) cell lines using comet assay, flow cytometry, Western blotting, immunofluorescence staining, and functional analyses. We developed a mouse model to verify the in vitro findings. We found that hydroxygenkwanin (HGK) inhibited the expression of RAD51 and progression of homologous recombination, thereby suppressing the ability of the HCC cell lines to repair DNA damage and enhancing their sensitivity to doxorubicin. HGK inhibited the phosphorylation of DNA damage checkpoint proteins, leading to apoptosis in the HCC cell lines. In the mouse xenograft model, HGK enhanced the sensitivity of liver cancer cells to doxorubicin without any physiological toxicity. Thus, HGK can inhibit DDR in liver cancer cells and mouse models, making it suitable for use as a chemotherapy adjuvant.