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971.
Stephen S. Nonnenmann Mohammad A. Islam Brian R. Beatty Eric M. Gallo Terrence McGuckin Jonathan E. Spanier 《Advanced functional materials》2012,22(23):4957-4961
The synthesis of cylindrical silicon‐core and ferroelectric oxide perovskite‐shell nanowires and their response characteristics as individual three‐terminal nanoscale electronic devices is reported. The co‐axial nanowire geometry facilitates large ferroelectric field‐effect modulation (>104) of nanowire conductivity following sequential application and removal of an applied dc field. Source‐drain current–voltage traces collected during sweeps of ferroelectric gate potential and switching of the component of shell outward and inward polarization provide direct evidence of ferroelectric coupling on nanowire channel conductance. Despite a very small (1:20) ferroelectric‐to‐semiconductor channel thickness ratio, an unexpectedly strong electrostatic coupling of ferroelectric polarization to channel conductance is observed because of the co‐axial gate geometry and curvature‐induced strain enhancement of ferroelectric polarization. 相似文献
972.
Scott N. Schiffres Kyu Hun Kim Lin Hu Alan J. H. McGaughey Mohammad F. Islam Jonathan A. Malen 《Advanced functional materials》2012,22(24):5251-5258
The thermal conductivity of gas‐permeated single‐walled carbon nanotube (SWCNT) aerogel (8 kg m?3 density, 0.0061 volume fraction) is measured experimentally and modeled using mesoscale and atomistic simulations. Despite the high thermal conductivity of isolated SWCNTs, the thermal conductivity of the evacuated aerogel is 0.025 ± 0.010 W m?1 K?1 at a temperature of 300 K. This very low value is a result of the high porosity and the low interface thermal conductance at the tube–tube junctions (estimated as 12 pW K?1). Thermal conductivity measurements and analysis of the gas‐permeated aerogel (H2, He, Ne, N2, and Ar) show that gas molecules transport energy over length scales hundreds of times larger than the diameters of the pores in the aerogel. It is hypothesized that inefficient energy exchange between gas molecules and SWCNTs gives the permeating molecules a memory of their prior collisions. Low gas‐SWCNT accommodation coefficients predicted by molecular dynamics simulations support this hypothesis. Amplified energy transport length scales resulting from low gas accommodation are a general feature of CNT‐based nanoporous materials. 相似文献
973.
“Fuel-Cell Urbanism” proposes a new water-energy infrastructural urban plan for Tokyo, leveraging its legacy of visionary infrastructure against the contemporary problematic importation of water and energy from its hinterlands. This project interrogates the reciprocal relationship between H20 and energy within the hydrogen fuel cell, proposing a distributed model of shared clean water and energy generation within the public realm of the city. We propose this new infrastructural landscape, implemented at the scale of the urban design block and repeated throughout the metropolis, in contrast to the twentieth-century hydro-based energy generation practices of city-wide regional energy sourcing and individual zero-energy domestic models. Rather, this new block-scale infrastructure fosters a sense of district-scale collective accountability, wherein energy and water are shared resources for those who work and live together within the space of the everyday. 相似文献
974.
An analytical formulation was developed to estimate the load‐sharing and planetary loads of a three‐point suspension wind turbine drivetrain considering the effects of non‐torque loads, gravity and bearing clearance. A three‐dimensional dynamic drivetrain model that includes mesh stiffness variation, tooth modifications and gearbox housing flexibility was also established to investigate gear tooth load distribution and non‐linear tooth and bearing contact of the planetary gears. These models were validated with experimental data from the National Renewable Energy Laboratory's Gearbox Reliability Collaborative. Non‐torque loads and gravity induce fundamental excitations in the rotating carrier frame, which can increase gearbox loads and disturb load sharing. Clearance in the carrier bearings reduces the bearing stiffness significantly. This increases the amount of pitching moment transmitted from the rotor to the gear meshes and disturbs the planetary load share, thereby resulting in edge loading. Edge loading increases the likelihood of tooth pitting and planet‐bearing fatigue, leading to reduced gearbox life. Additionally, at low‐input torque, the planet‐bearing loads are often less than the minimum recommended load and thus susceptible to skidding. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
975.
Pourrezaei P Drzewicz P Wang Y Gamal El-Din M Perez-Estrada LA Martin JW Anderson J Wiseman S Liber K Giesy JP 《Environmental science & technology》2011,45(19):8452-8459
Coagulation/flocculation (CF) by use of alum and cationic polymer polyDADMAC, was performed as a pretreatment for remediation of oil sands process-affected water (OSPW). Various factors were investigated and the process was optimized to improve efficiency of removal of organic carbon and turbidity. Destabilization of the particles occurred through charge neutralization by adsorption of hydroxide precipitates. Scanning electron microscope images revealed that the resultant flocs were compact. The CF process significantly reduced concentrations of naphthenic acids (NAs) and oxidized NAs by 37 and 86%, respectively, demonstrating the applicability of CF pretreatment to remove a persistent and toxic organic fraction from OSPW. Concentrations of vanadium and barium were decreased by 67-78% and 42-63%, respectively. Analysis of surface functional groups on flocs also confirmed the removal of the NAs compounds. Flocculation with cationic polymer compared to alum, caused toxicity toward the benthic invertebrate, Chironoums dilutus, thus application of the polymer should be limited. 相似文献
976.
The depuration of gas-phase polychlorinated biphenyls (PCBs) from a slow-growing evergreen shrub, Skimmia japonica Thunb., was studied to investigate the reversibility of uptake and the compartmentalization of PCB congeners within leaves with respect to air-plant exchange processes. Depuration of PCBs was monitored over periods of hours, days, and weeks. Equilibrium had not been attained between air and leaves during the uptake phase after many weeks. Depuration followed two-phase clearance kinetics, with phase 1 occurring over the order of hours and phase 2 continuing slowly over weeks. In phase 1, a substantial part (ca. 40%) of the PCB burden that the plants had accumulated over weeks was lost in 2-3 h. This observation is further evidence for the close dynamic coupling of air and vegetation compartments. In the second phase, very slow depuration over 28 d only removed a further approximately 25% of the accumulated PCB burden. Depuration rates in phase 2 varied between compounds and were not influenced by growth dilution. Depuration rates for both phases were not correlated with KOA, indicating that plant-air mass transfer coefficients were proportional to plant-air partition coefficients and, therefore, probably dominated by the plant-side resistance to diffusion. Photolysis and metabolism are unlikely to have influenced the rates of congener disappearance. Pathways into the leaf and possible storage locations within the plant are discussed with respect to the observed differences between uptake and clearance rates. Uptake and depuration are not mirror image processes, with a fraction of accumulated PCBs effectively stored in the leaves. This has important implications for terrestrial food chain transfer and global cycling with leaf concentrations remaining elevated long after a contamination event. 相似文献
977.
The upper Hudson River (NY) was subjected to massive PCB contamination over a period of three decades. A large inventory of PCBs remains in contaminated sediments of the river, most notably in the Thompson Island Pool. During the summer, flow crossing the Thompson Island Pool exhibits a large and consistent PCB load gain. This load gain is not associated with scouring flows and is not accompanied by an increase in suspended solids. A variety of hypotheses have been proposed to explain this load gain, including flux of contaminated porewater and dissolution of unverified reservoirs of pure PCBs. A wealth of congener-specific PCB data is available for the site throughout the 1990s. Interpretation of the Thompson Island Pool load gain is facilitated by examination of the PCB congener signature of the gain and comparison to the signature of potential sources. This examination suggests that neither the flux of porewater nor the dissolution of unaltered Aroclors are the predominant source of the load gain. Instead, the congener signature is consistent with a mixed source consisting of porewater flux and non-scour flux of contaminated sediments. The non-scour sediment flux, which reaches a maximum in the beginning of the summer growing season, is likely driven by a variety of biological and anthropogenic processes, including bioturbation by benthic organisms, bioturbation by demersal fish, scour by propwash, mechanical scour by boats and floating debris in nearshore areas, and uprooting of macrophytes. 相似文献
978.
Illicit trade in tobacco products presents a threat to public health because it undermines the use of tax and price policies, which are among the most effective mechanisms for reducing tobacco consumption. Parties to the WHO Framework Convention on Tobacco Control (FCTC) are in the final stages of negotiating a protocol aimed at strengthening international cooperation in the fight against illicit tobacco trade. While an effective multilateral response to illicit tobacco trade would make a significant contribution to global tobacco control, achieving this through the FCTC forum is challenging. First, while illicit tobacco trade is a health problem, the expertise, experience and capacity needed to combat illicit trade are not traditionally found in health agencies. The development of links with other agencies, both domestic and international, is critical to ensure both an effective response and an efficient use of limited governmental and non-governmental resources. Second, in many parts of the world, the tobacco industry cooperates closely with governments in the combating of illicit trade. This cooperation poses risks for tobacco control, particularly if relationships and norms of cooperation spill over into other areas of FCTC implementation. An examination of the industry's positioning suggests that it sees an opportunity to portray itself as 'legitimate' and 'responsible', a friend of governments, and a way to integrate itself into FCTC processes. This paper makes suggestions for moving forward in this challenging area towards ensuring that the approach taken actually reduces illicit tobacco trade, strengthens tobacco tax policies and does not operate to undermine the FCTC. 相似文献
979.
Loker S Bastin C Miglior F Sewalem A Schaeffer LR Jamrozik J Osborne V 《Journal of dairy science》2011,94(7):3693-3699
The objective of this research was to estimate the genetic parameters of body condition score (BCS) in the first 3 lactations in Canadian Holstein dairy cattle using a multiple-lactation random regression animal model. Field staff from Valacta milk recording agency (Sainte-Anne-de-Bellevue, QC, Canada) collected BCS from Québec herds several times throughout each lactation. Approximately 32,000, 20,000, and 11,000 first-, second-, and third-parity BCS were analyzed, respectively, from a total of 75 herds. Body condition score was a moderately heritable trait over the lactation for parity 1, 2, and 3, with average daily heritabilities of 0.22, 0.26, and 0.30, respectively. Daily heritability ranged between 0.14 and 0.26, 0.19 and 0.28, and 0.24 and 0.33 for parity 1, 2, and 3, respectively. Genetic variance of BCS increased with days in milk within lactations. The low genetic variance in early lactation suggests that the evolution of the ability to mobilize tissue reserves in early lactation provided cattle with a major advantage, and is, therefore, somewhat conserved. The increasing genetic variance suggests that more genetic differences were related to how well cows recovered from the negative energy balance state. More specifically, increasing genetic variation as lactation progressed could be a reflection of genetic differences in the ability of cows to efficiently control the rate of mobilization of tissue reserves, which would not be crucial in early lactation. The shape of BCS curves was similar across parities. From first to third parity, differences included the progressively deeper nadir and faster rate of recovery of condition. Daily genetic correlations between parities were calculated from 5 to 305 DIM, and were summed and divided by 301 to obtain average daily genetic correlations. The average daily genetic correlations were 0.84 between parity 1 and 2, 0.83 between parity 1 and 3, and 0.86 between parity 2 and 3. Although not 1, these genetic correlations are still strong, so much of the variation observed in BCS was controlled by the same genes for each of the first 3 lactations. If a genetic evaluation for BCS is developed, regular collection of first-lactation BCS records should be sufficient for genetic evaluation. 相似文献
980.