Synthesis and characterization of a novel proton‐exchange membrane for fuel cells operating at high temperatures and low humidities

The synthesis of a p‐toluidine/formaldehyde (PTF) resin was performed, and the effects of the molar ratio of the individual monomers and the polymerization conditions on the structure of the PTF resin were studied. Fourier transform infrared and ¹³C‐NMR spectra were used to characterize the PTF. Wide‐angle X‐ray diffraction patterns revealed the crystalline structures of various PTFs. Polarized optical microscopy revealed that the molar ratio of the monomers had a strong effect on the crystalline morphologies. A longer polymerization time turned out a polymer with a higher intrinsic viscosity and molecular weight, which led to differences in the proton conductivity. All of the PTFs showed a higher proton conductivity than a commercial Nafion membrane at 90–100°C and 0% relative humidity. The proton conductivity of the PTF series could be improved by sulfonation with sulfuric acid and could be maintained after blending with polyurethane. Pure methanol could be used as a fuel source because of the insolubility and nonwetting properties of PTF in methanol to increase the output current density for a PTF membrane electrode assembly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Design tradeoff analysis of floating-point adders in FPGAs

With gate counts of ten million, field-programmable gate arrays (FPGAs) are becoming suitable for floating-point computations. Addition is the most complex operation in a floating-point unit and can cause major delay while requiring a significant area. Over the years, the VLSI community has developed many floating-point adder algorithms aimed primarily at reducing the overall latency. An efficient design of the floating-point adder offers major area and performance improvements for FPGAs. Given recent advances in FPGA architecture and area density, latency has become the main focus in attempts to improve performance. This paper studies the implementation of standard; leading-one predictor (LOP); and far and close datapath (2-path) floating-point addition algorithms in FPGAs. Each algorithm has complex sub-operations which contribute significantly to the overall latency of the design. Each of the sub-operations is researched for different implementations and is then synthesized onto a Xilinx Virtex-II Pro FPGA device. Standard and LOP algorithms are also pipelined into five stages and compared with the Xilinx IP. According to the results, the standard algorithm is the best implementation with respect to area, but has a large overall latency of 27.059 ns while occupying 541 slices. The LOP algorithm reduces latency by 6.5% at the cost of a 38% increase in area compared to the standard algorithm. The 2-path implementation shows a 19% reduction in latency with an added expense of 88% in area compared to the standard algorithm. The five-stage standard pipeline implementation shows a 6.4% improvement in clock speed compared to the Xilinx IP with a 23% smaller area requirement. The five-stage pipelined LOP implementation shows a 22% improvement in clock speed compared to the Xilinx IP at a cost of 15% more area.     

Spatially resolved near-infrared excited Raman spectroscopy of nanocrystalline diamond films

Scanning Raman spectroscopic measurements were performed on nanocrystalline diamond thin films with 0.5 μm lateral steps and excitation spot limited to 1 μm in diameter using 488 nm and 785 nm excitation wavelengths. The comparison of the spectra measured with different excitation energies showed that in contrast to the well-known five bands in the 488 nm excited Raman spectra of nanocrystalline diamond a number of narrow peaks appears in the spectra when using near-infrared excitation. The intensity and position of the latter vary when moving the excitation spot along the sample. The detailed analysis of the sequences showed that the 785 nm excited Raman spectroscopy allows the detection and identification of the Raman peaks arising from individual diamond crystallites of the nanocrystalline diamond films.     

Production of glass–ceramics from incinerator ash using lab-scale and pilot-scale thermal plasma systems

This research employed two thermal plasma melting systems and vitrification technology to treat incinerator ash. The melted slag was used for the production of glass–ceramics via powder sintering and heat treatment. When using the pilot-scale plasma molten system, the melt was rapidly quenched in water to yield glassy slag. The properties of quenched slag glass–ceramics were superior to that glass–ceramics produced by slowly cooling the slag with air. The glass–ceramics with the best physical/mechanical properties and chemical resistance was produced by heat treatment at 1150 °C for 2 h. Diopside and gehlenite were formed as the major crystalline phases. Glass–ceramics produced from incinerator ash demonstrate great potential for reutilization as non-porous or water permeable materials.     

Effects of Al2O3 on the properties and densification of 8YSZ after pulsed current activated sintering

Dense 8YSZ was subjected to pulsed current activated sintering (PCAS) within 1 min of 8YSZ nanopowder preparation using a co-precipitation method. Sintering was accomplished by combining a pulsed current and mechanical pressure. Highly dense 8YSZ with a relative density of up to 99% was produced under simultaneous application of a pressure of 80 MPa and the pulsed current. The effects of the addition of Al₂O₃ on the sintering behavior, mechanical properties, and ionic conductivities of 8YSZ were investigated.     

TiO2@carbon core-shell nanostructure supports for platinum and their use for methanol electrooxidation

Nanostructures consisting of TiO₂ particles as a core and carbon as a shell (TiO₂@C) were prepared by heat treatment of TiO₂ nanoparticles at 700 or 900 °C in a methane atmosphere. X-ray diffraction and transmission electron microscopy showed that a carbon shell layer was formed whose thickness increased with increasing reaction temperature. These structures were used as supports for platinum nanoparticles and the hybrid particles exhibit improved catalytic activity and stability toward methanol electrooxidation compared to Pt on a carbon black (Vulcan XC-72R). It is likely that enhanced catalytic properties of the Pt on TiO₂@C could be due to the stability of the core-shell support in comparison with carbon black support.     

Minimally processed ready-to-eat baby-leaf vegetables: Production,processing, storage,microbial safety,and nutritional potential

The market for minimally processed ready-to-eat (RTE) baby-leaf vegetables (BLVs) has been rapidly growing and offering to consumers convenient and appealing products, rich in health beneficial bioactive compounds. These vegetables are harvested at a very early stage of maturation and prepared with minimal processing methods such as cutting, washing, rinsing, and packaging with the modified atmosphere of O₂, CO₂, and relative humidity (RH). Maintenance of microbial safety, color, texture, aroma, and nutrients are the major problems associated with commercial production and marketing of BLVs. This review discusses the theoretical aspects and recent developments in the maintenance of nutritional quality and microbial safety during production, processing, sanitization, packaging, and storage of BLVs. The varietal improvements in BLVs for wider adaptability and disease resistance are also discussed. Additionally, future research challenges in these contexts are identified.     

Piezoelectric Microvibration Mitigates Estrogen Loss-Induced Osteoporosis and Promotes Piezo1, MicroRNA-29a,and Wnt3a Signaling in Osteoblasts

Biophysical stimulation alters bone-forming cell activity, bone formation and remodeling. The effect of piezoelectric microvibration stimulation (PMVS) intervention on osteoporosis development remains uncertain. We investigated whether 60 Hz, 120 Hz, and 180 Hz PMVS (0.05 g, 20 min/stimulation, 3 stimulations/week for 4 consecutive weeks) intervention affected bone integrity in ovariectomized (OVX) mice or osteoblastic activity. PMVS (120 Hz)-treated OVX mice developed fewer osteoporosis conditions, including bone mineral density loss and trabecular microstructure deterioration together with decreased serum resorption marker CTX-1 levels, as compared to control OVX animals. The biomechanical strength of skeletal tissue was improved upon 120 Hz PMVS intervention. This intervention compromised OVX-induced sparse trabecular bone morphology, osteoblast loss, osteoclast overburden, and osteoclast-promoting cytokine RANKL immunostaining and reversed osteoclast inhibitor OPG immunoreactivity. Osteoblasts in OVX mice upon PMVS intervention showed strong Wnt3a immunoreaction and weak Wnt inhibitor Dkk1 immunostaining. In vitro, PMVS reversed OVX-induced loss in von Kossa-stained mineralized nodule formation, Runx2, and osteocalcin expression in primary bone-marrow stromal cells. PMVS also promoted mechanoreceptor Piezo1 expression together with increased microRNA-29a and Wnt3a expression, whereas Dkk1 rather than SOST expression was repressed in MC3T3-E1 osteoblasts. Taken together, PMVS intervention promoted Piezo1, miR-29a, and Wnt signaling to upregulate osteogenic activity and repressed osteoclastic bone resorption, delaying estrogen deficiency-induced loss in bone mass and microstructure. This study highlights a new biophysical remedy for osteoporosis.     

Chemical Stresses Induced by Boundary Layer Diffusion in a Cylindrical Sandwich Composite

The chemical stresses developed in a cylindrical sandwich composite during radial boundary layer diffusion have been investigated. The system consists of a thin layer A of circular cross section sandwiched between two semi-infinite outer layers B, with the diffusivity of diffusant in A (D_A) being much greater than that in B (D_B). Two boundary conditions, the constant surface concentration and the instantaneous surface concentration, were considered. The concentration distributions were obtained by the Bessel-Laplace transform method. The stress functions were solved analytically based on the linear elasticity. Numerical computations were performed to illustrate the effects of the diffusivity ratio (D_A/D_B) and of the thickness of the central layer A on stress distributions. The results show that the induced stress in layer A increases as the diffusivity ratio, or its thickness, increases, in consistency with the general findings for composites of rectangular geometry.