Conductivity enhancement of carbon nanotube and nanofiber-based polymer nanocomposites by melt annealing

The addition of multi-walled carbon nanotubes (MWCNTs) or carbon nanofibers (CNFs) to polymeric melts offers a convenient route to obtain highly conductive plastics. However, when these materials are melt processed, their conductivity can be lost. Here, it is shown that conductivities can be recovered through melt annealing at temperatures above the polymer's glass transition temperature (T_g). We demonstrate these results for both MWCNT and CNF-based composites in polystyrene (PS). The mechanism behind the conductivity increase is elucidated through modeling. It involves a transition from aligned, unconnected particles prior to annealing to an interconnected network after annealing through viscoelastic relaxation of the polymer. Such re-arrangement is directly visualized for the case of the CNF-based composites using confocal microscopy. The annealing-induced increase in particle connectivity is also reflected in dynamic rheological measurements on both MWCNT and CNF composites as an increase in their elastic moduli at low frequencies.     

Kinetics of Ag(I) catalyzed oxidation of amino acids by peroxomonosulphate

Silver(I) catalyzed oxidation of amino acids such as glycine and α-alanine by peroxomonosulphate (PMS) in aqueous perchloric acid medium was found to be first order in [peroxomonosulphate] and fractional order in [amino acid] and [Ag(I)]. The rate equation was derived by assuming equilibrium formation of adduct between amino acids and Ag(I). This adduct was presumed to react with PMS in a slow step to yield (adduct)²⁺, which was self-oxidized in a fast step to give the products. The kinetic results revealed that silver catalyzed reaction occurred approximately 10⁴ times faster than the uncatalyzed reaction and this is attributed to the formation of (adduct)²⁺. The bimolecular rate constant (k) for the slow step and the activation parameters were calculated and the results are discussed.     

Phase Diagram Updates and Evaluations of the Al-Fe-P, B-Fe-U, Bi-Fe-Zn, Cu-Fe-Zn, Fe-Si-Zn and Fe-Ti-V Systems

Updates and evaluations of recent publications on the Al-Fe-P, B-Fe-U, Bi-Fe-Zn, Cu-Fe-Zn, Fe-Si-Zn and Fe-Ti-V systems are presented. Information on their phase diagrams include liquidus projections, isothermal and vertical sections, as well as crystallographic data of the phases present.     

装填有矩形切口螺旋带的管中的湍动传热和压降(英文)

Heat transfer, friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes (STT) and plain twisted tapes (PTT) are investigated experimentally using the water as working fluid. The tapes (STT and PTT) have three twist ratios ( , 4.4 and 6.0) and the Reynolds number ranges from 2000 to 12000. The experimental results reveal that heat transfer rate, friction factor and thermal enhancement factor in the tube equipped with STT are significantly higher than those fitted with PTT. The additional disturbance and secondary flow in the vicinity of the tube wall generated by STT are higher compared to that induced by the PTT is referred as the reason for better performance. Over the range considered, the Nusselt number, friction factor and thermal enhancement factor in a tube with STT are respectively, 1.03 to 1.14, 1.05 to 1.25 and 1.02 to 1.06 times of those in tube with PTT. An empirical correlation is also formulated to match with experimental data of Nusselt number and friction factor for STT and PTT.     

Color stability of frozen whole tilapia exposed to pre‐mortem treatment with carbon monoxide

BACKGROUND: Color of muscle foods plays a major role in consumer perception of meat quality. Carbon monoxide (CO) has been successfully used for improving color of packaged meat and fish products. In this study, we wanted to investigate pre‐mortem treatment of live tilapia using 100% CO for its ability to improve the color of frozen whole tilapia. We compared untreated and CO‐treated whole, gutted tilapia, frozen for 2 and 4 months at ? 20 °C. Frozen tilapia samples were thawed overnight at 4 °C, filleted and analyzed for their color, heme peak wavelength and CO concentration. RESULTS: Euthanasia using CO significantly increased redness (a* value) and lightness (L* value) of tilapia white and red muscle. Frozen storage significantly (P < 0.05) decreased redness of both CO‐treated and untreated tilapia. However, even after 4 months of frozen storage, a*‐value of CO‐treated tilapia was similar to fresh untreated tilapia fillets. Heme peak wavelengths of CO‐euthanized tilapia were higher than in untreated tilapia and there was no significant (P > 0.05) decrease in heme peak wavelengths of CO‐treated tilapia white and red muscle during frozen storage. The CO content of frozen euthanized tilapia fillets was significantly (P > 0.05) higher than in untreated fillets. In general, red muscle tissue of euthanized tilapia had a higher concentration of CO than white muscle. CONCLUSION: Color stability of tilapia fillets was significantly improved by pre‐mortem CO treatment. The color of CO‐treated fillets was retained during frozen storage compared to untreated fillets. Hence, pre‐mortem CO treatment could be used as a new method for improving color of tilapia. Copyright © 2008 Society of Chemical Industry     

Beyond waterfalls and dams: Riverscape genetics of two endemic mountain loaches in the Western Ghats biodiversity hotspot

Riverscape genetics of fish, though extensively studied in temperate regions, have received limited interest in tropical rivers, especially in montane systems which not only harbour several endemic and threatened species, but are also subjected to extensive habitat modifications. We determine the population genetic structure of two endemic balitorid loaches (Bhavania australis and Travancoria elongata) in response to natural (25 m high waterfall) and artificial (23 m high and 290 m long hydropower dam) barriers in a small mountain riverscape in the Western Ghats Hotspot. Population genetics analysis using mitochondrial cytochrome b gene sequence showed low nucleotide diversity, haplotype diversity and genetic differentiation among populations, for both species, suggesting that barriers did not influence genetic structuring. Though migration analysis also revealed that barriers did not affect movement of the two species through the riverscape, patterns in mutation-scaled immigration rates and population sizes differed between the two species supporting our observation that they rarely co-exist in the same habitat, likely as an effect of competitive exclusion. Mismatch distribution and Bayesian skyline plot suggested recent expansion in the populations of B. australis and corresponding population decline in T. elongata in the last 100 years, which probably explains the widespread and abundant distribution of B. australis as opposed to the narrow endemism and rarity of T. elongata. Our results provide novel insights into the ecology of balitorid loaches and their response to riverine barriers in a tropical mountain landscape.     

Development and Integration of Sub-hourly Rainfall–Runoff Modeling Capability Within a Watershed Model

Increasing urbanization changes runoff patterns to be flashy and instantaneous with decreased base flow. A model with the ability to simulate sub-daily rainfall–runoff processes and continuous simulation capability is required to realistically capture the long-term flow and water quality trends in watersheds that are experiencing urbanization. Soil and Water Assessment Tool (SWAT) has been widely used in hydrologic and nonpoint sources modeling. However, its subdaily modeling capability is limited to hourly flow simulation. This paper presents the development and testing of a sub-hourly rainfall–runoff model in SWAT. SWAT algorithms for infiltration, surface runoff, flow routing, impoundments, and lagging of surface runoff have been modified to allow flow simulations with a sub-hourly time interval as small as one minute. Evapotranspiration, soil water contents, base flow, and lateral flow are estimated on a daily basis and distributed equally for each time step. The sub-hourly routines were tested on a 1.9 km² watershed (70% undeveloped) near Lost Creek in Austin Texas USA. Sensitivity analysis shows that channel flow parameters are more sensitive in sub-hourly simulations (Δt = 15 min) while base flow parameters are more important in daily simulations (Δt = 1 day). A case study shows that the sub-hourly SWAT model reasonably reproduces stream flow hydrograph under multiple storm events. Calibrated stream flow for 1 year period with 15 min simulation (R ² = 0.93) shows better performance compared to daily simulation for the same period (R ² = 0.72). A statistical analysis shows that the improvement in the model performance with sub-hourly time interval is mostly due to the improvement in predicting high flows. The sub-hourly version of SWAT is a promising tool for hydrology and non-point source pollution assessment studies, although more development on water quality modeling is still needed.