Thermoelectric power generation using doped MWCNTs

In this paper, the performance of thermoelectric (TE) devices constructed with the TE elements packed with randomly oriented multiwalled carbon nanotubes (MWCNTs) has been presented. B-doped and N-doped MWCNTs were produced using different doping methods and their thermal and thermoelectric properties have been reported. The carrier type and carrier densities of the doped nanotubes were determined using Mott-Schottky analysis. Doping of the MWCNTs resulted in a simultaneous increase in the Seebeck coefficient and a decrease in the thermal conductivity leading to a significant improvement (up to 1900%) of the figure of merit (ZT) of the TE device. The effects of changing packing density, diameter, and length of the MWCNT-TE elements on the performance of the device were investigated. It was observed that the power generated by the TE device depended directly on the ZT of the device. A TE module was constructed by connecting several TE cells in series with alternating p-type and n-type MWCNT-TE elements and the scale-up of power generation as the number of TE cells was increased was examined. This study is expected to help researchers to evaluate and improve the performance of CNT-based TE devices over conventional devices.     

Synthesis and characterization of thiophene functionalized polystyrene copolymers and their electrochemical properties

Thiophene functionalized polystyrene samples (TFPS) were synthesized by atom transfer radical polymerization (ATRP) of styrene, followed by Suzuki coupling with 3‐thiophene (Th) boronic acid. Conducting graft polymer of TFPS with thiophene was achieved at 1.5 V in tetrabutylammonium tetrafluoroborate/dichloromethane (TBAFB/DM) by electrochemical methods. Spectroelectrochemical analysis of the resulting copolymers [P(TFPS‐co‐Th)] reflected electronic transitions at 449, 721 and 880 nm, revealing π ? π* transition, polaron and bipolaron band formation, respectively. We also successfully established the utilization of dual type complementary colored polymer electrochromic devices using P(TFPS‐co‐Th)/poly(3,4‐ethylenedioxythiophene (PEDOT) in sandwich configuration. The switching ability, stability and optical memory of the electrochromic device were investigated by UV–visible spectrophotometry and cyclic voltammetry. Device switches between brown and blue color with a switching time of 1.3 s were prepared with optical contrast (%ΔT) of 25 %. Copyright © 2005 Society of Chemical Industry     

Demonstrating feasibility of a high temperature polymer electrolyte membrane fuel cell operation with natural gas reformate composition

Experimental data on the performance of a single cell PBI-based HT-PEMFC operated with a fuel composition similar to natural gas reformate and oxygen enriched cathode air are presented. A test studying the effect of CO₂, H₂O and CO in the fuel on fuel cell performance revealed that the presence of CO₂ mainly worsens mass transport, H₂O improves proton conduction and CO influences reaction kinetics as well as causing mass transport limitations. A small increase of the O₂ concentration in the oxidant provided a boost on performance. Electrical efficiency of the fuel cell was improved from 36.6% with H₂/air operation up to 38.2% with synthetic reformate gas/30% O₂ enriched air. Three 1000 h long-term tests at constant load conditions were performed. The first test showed a degradation rate of ?21.4 μV/h and was operated with H₂/30% O₂. The second test was performed with the same kind of MEA but different fuel composition (54% H₂, 15% CO₂ and 31% H₂O) and exhibited a reduction of the degradation rate to ?5.5 μV/h. The main reason for this lifetime improvement is H₂O because its transport from anode to cathode may sweep along PA that soaks catalyst active sites and limits HOR. Moreover, water in rich H₂ reformate streams also relieves formation of CO from CO₂ via RWGS. The third test was performed with a different kind of MEA (extra PTFE content in GDE) but the same fuel composition than the second one. A higher degradation rate of ?22.2 μV/h was observed but it was mainly caused by unprotected shut-downs during operation. Two preliminary long-term tests were also performed with a fuel composition similar to natural gas reformate (54% H₂, 14% CO₂, 1% CO and 31% H₂O). These latest tests revealed that the fuel cell should be operated at higher temperatures to diminish CO catalyst coverage, and that anode purge with dry gases avoids water condensation in gas pipes. In addition, CO poisoning on anode catalyst is time dependent and operation at high current densities enhances CO catalyst coverage.     

Effects of using combined essential oils on quality parameters of bio‐yogurt

Present study aims to develop a new type of probiotic yogurt with ginger and chamomile essential oils (EOs) at therapeutic levels (0.2 and 0.4%) by evaluating its some physical, chemical, microbiological and sensory characteristics. Probiotic types of yogurt samples and those with 0.4% ginger EO gave the largest counts of viable probiotic bacteria in the rates of 8.32 cfu/g and 8.01 cfu/g, respectively. It gave larger syneresis rate (8.64 mL/25 g) on the first day than the rest of the samples while C1 (only probiotic strain with direct vat set starter culture) sample represented the lowest rate (5.9 mL/25 g) on day 21. Among the samples with various contents, C2 (inoculated probiotic strain with 0.2% essential oil ginger) and C3 (inoculated probiotic strain with 0.4% essential oil ginger) were found to be organoleptically the most acceptable with close scores to that of control.

Practical applications

Antibacterial and antioxidant activities of essential oils have received considerable attention in food preservation. During bio‐yogurt storage, the edible film incorporating ginger and chamomile essential oils showed reducing effect on the microbial growth and extended the shelf‐life of samples.     

UTILIZATION OF PRETREATED MOLASSES FOR SERINE ALKALINE PROTEASE PRODUCTION WITH RECOMBINANT BACILLUS SPECIES

Recombinant Bacillus amyloliquefaciens, Bacillus cereus, Bacillus subtilis , and Bacillus licheniformis were used for the production of serine alkaline protease (SAP) utilizing chemically and/or physically pretreated molasses. The highest enzyme activity was obtained with r- Bacillus subtilis , with the complex medium involving physically treated molasses having 20 kg m -3 initial sucrose concentration in small-scale, agitation- and heating rate-controlled bioreactors at t=63 h. Effects of oxygen transfer were investigated in 3.5 dm 3 laboratory bioreactors under two different agitation rates with r- B. subtilis . Increase in the oxygen transfer rate increased the observed activity and caused the cultivation time of maximum activity shift to the earlier stages of the fermentation. At Q/V=0.5 vvm and N=750 min -1 , SAP activity reached 2250U cm -3 at t=36 h.     

Life study of a PBI-PEM fuel cell by current distribution measurement

PBI-based polymer electrolyte membrane (PEM) fuel cells have short durability comparing with Nafion ones. It is known that the presence of phosphoric acid accelerates catalyst sintering, and the polymer is susceptible to getting degraded via oxidative degradation. However, the influence of the current distribution on the degradation process has not been investigated. In this work, current distribution was measured continuously during a steady state life test that was performed in a 50-cm² PBI-PEM fuel cell. The membrane-electrode assembly was prepared using techniques that are supposed to ensure satisfactory reproducibility at global level. Two different stages, i.e., activation and degradation, were identified. They show disparities in both global and local performance. It was found that the current distribution map is very heterogeneous, with variations around ±50 % with respect to the average value during the whole lifetime of the cell. The non-uniformity of the current profile increases during the degradation, but it cannot be concluded that the current density distribution contributes to the short lifetime.     

Communication Requirements and Interconnect Optimization for High-End Scientific Applications

The path toward realizing next-generation petascale and exascale computing is increasingly dependent on building supercomputers with unprecedented numbers of processors. To prevent the interconnect from dominating the overall cost of these ultrascale systems, there is a critical need for scalable interconnects that capture the communication requirements of ultrascale applications. It is, therefore, essential to understand high-end application communication characteristics across a broad spectrum of computational methods, and utilize that insight to tailor interconnect designs to the specific requirements of the underlying codes. This work makes several unique contributions toward attaining that goal. First, we conduct one of the broadest studies to date of high-end application communication requirements, whose computational methods include: finite difference, lattice Boltzmann, particle-in-cell, sparse linear algebra, particle-mesh ewald, and FFT-based solvers. Using derived communication characteristics, we next present the fit-tree approach for designing network infrastructure that is tailored to application requirements. The fit-tree minimizes the component count of an interconnect without impacting application performance compared to a fully connected network. Finally, we propose a methodology for reconfigurable networks to implement fit-tree solutions. Our Hybrid Flexibly Assignable Switch Topology (HFAST) infrastructure, uses both passive (circuit) and active (packet) commodity switch components to dynamically reconfigure interconnects to suit the topological requirements of scientific applications. Overall, our exploration points to several promising directions for practically addressing the interconnect requirements of future ultrascale systems.     

Statistical investigation of wave power potential in the North Aegean Sea

Clean Technologies and Environmental Policy - Wave energy is recognized as a significant renewable energy source with a high energy density and very low environmental impact. Today, in parallel...