High-Mobility and High-Optical Quality Atomically Thin WS 2

The rise of atomically thin materials has the potential to enable a paradigm shift in modern technologies by introducing multi-functional materials in the semiconductor industry. To date the growth of high quality atomically thin semiconductors (e.g. WS2) is one of the most pressing challenges to unleash the potential of these materials and the growth of mono- or bi-layers with high crystal quality is yet to see its full realization. Here, we show that the novel use of molecular precursors in the controlled synthesis of mono- and bi-layer WS2 leads to superior material quality compared to the widely used direct sulfidization of WO3-based precursors. Record high room temperature charge carrier mobility up to 52 cm2/Vs and ultra-sharp photoluminescence linewidth of just 36 meV over submillimeter areas demonstrate that the quality of this material supersedes also that of naturally occurring materials. By exploiting surface diffusion kinetics of W and S species adsorbed onto a substrate, a deterministic layer thickness control has also been achieved promoting the design of scalable synthesis routes

English and Black Walnut Phenolic Antioxidant Activity in Vitro and Following Human Nut Consumption

ABSTRACT Background: Walnut consumption may reduce the risk of cardiovascular disease by providing antioxidant protection to low density lipoproteins (LDL). Aim: This study compared the phenolic profile and antioxidant activity of English versus black walnuts. Methods: Nuts were extracted in methanol or acetone prior to analysis with HPLC/LC-MS-MS for phenolic identification and quantitation. The ability to prevent oxidation of LDL was examined in vitro using walnut extracts and ex vivo after walnut consumption for 28 days. Results: Flavonoids identified/quantified with HPLC/LC-MS-MS included the phenolic acids 5-caffeoylquinic acid, 3-caffeoylquinic acid (black walnut only), 4-caffeoylquinic acid, and the flavonol glycosides querceti

Pre-Conceptual Design of a Fluoride-Salt-Cooled Small Modular Advanced High Temperature Reactor (SmAHTR)

This document presents the results of a study conducted at Oak Ridge National Laboratory during 2010 to explore the feasibility of small modular fluoride salt-cooled high temperature reactors (FHRs). A preliminary reactor system concept, SmATHR (for Small modular Advanced High Temperature Reactor) is described, along with an integrated high-temperature thermal energy storage or salt vault system. The SmAHTR is a 125 MWt, integral primary, liquid salt cooled, coated particle-graphite fueled, low-pressure system operating at 700 C. The system employs passive decay heat removal and two-out-of-three , 50% capacity, subsystem redundancy for critical functions. The reactor vessel is sufficiently small to be transportable on standard commercial tractor-trailer transport vehicles. Initial transient analyses indicated the transition from normal reactor operations to passive decay heat removal is accomplished in a manner that preserves robust safety margins at all times during the transient. Numerous trade studies and trade-space considerations are discussed, along with the resultant initial system concept. The current concept is not optimized. Work remains to more completely define the overall system with particular emphasis on refining the final fuel/core configuration, salt vault configuration, and integrated system dynamics and safety behavior

Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements

The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twentyone laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp- 1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1

Pre-Conceptual Design of a Fluoride-Salt-Cooled Small Modular Advanced High Temperature Reactor (SmAHTR)

This document presents the results of a study conducted at Oak Ridge National Laboratory during 2010 to explore the feasibility of small modular fluoride salt-cooled high temperature reactors (FHRs). A preliminary reactor system concept, SmATHR (for Small modular Advanced High Temperature Reactor) is described, along with an integrated high-temperature thermal energy storage or salt vault system. The SmAHTR is a 125 MWt, integral primary, liquid salt cooled, coated particle-graphite fueled, low-pressure system operating at 700 C. The system employs passive decay heat removal and two-out-of-three , 50% capacity, subsystem redundancy for critical functions. The reactor vessel is sufficiently small to be transportable on standard commercial tractor-trailer transport vehicles. Initial transient analyses indicated the transition from normal reactor operations to passive decay heat removal is accomplished in a manner that preserves robust safety margins at all times during the transient. Numerous trade studies and trade-space considerations are discussed, along with the resultant initial system concept. The current concept is not optimized. Work remains to more completely define the overall system with particular emphasis on refining the final fuel/core configuration, salt vault configuration, and integrated system dynamics and safety behavior

Carbon nanotube architectures with metallic nanoparticles towards energy applications

Within this thesis we demonstrate the formation of 3-dimensional, potentially freestanding, entangled carbon nanotube architectures through the use of previously untested organo-metallic catalysts, Iron (III) Tosylate, Cobalt (II) Tosylate, and Nickel (II) Tosylate. The effect of catalyst concentration, hydrocarbon decomposition temperature and growth time were examined in terms of the produced architectures morphologies. As capacitive devices these as produced carbon nanotube architectures demonstrated impressive maximum capacitances of up to 182.9 F/g with a power density of 15 kW/kg and an energy density of 4.06 Wh/kg. In addition we develop and optimise the decoration of metallic nanoparticles including, platinum, palladium, gold, ruthenium and various bi-metallic particles onto both individual carbon nanotubes and pre-formed carbon nanotube architectures in under 60s through the use of microwave chemistry. In addition to being exceptionally rapid this reduction technique was shown to be extremely versatile, with a range of different metallic architectures being synthesised, ranging from individual particles, to clustered particle morphologies. The role of pH, microwave intensity and salt concentration were examined. The most efficient configuration of platinum nanoparticles onto the entangled carbon nanotube architecture produced a maximum capacitive response of 640 F/g at a maximum energy density of 5.25 Wh/kg and a maximum power density of 77 kW/kg. Examination of this electrode as a cathode in a hydrogen fuel cell yielded extremely promising results with a maximum current density of 3000 mA/cm2 and a power density of 940 mW/cm2 corresponding to an efficiency of 0.81 mgPt/kW, approaching the United States Department of Energy target of 0.3 mgPt/kW. This work provides a pathway to the development of 3-dimensionally structured carbon/metal nanoparticle composite materials for a broad range of applications, specifically focused on electrochemical devices

The fates of weed seeds

A method for studying the fates of unprotected seeds buried in soil was developed. Using this method, studies were conducted from 1992 to 1995 at Lincoln, Nebraska, to quantify the fates of buried seeds of four weed species, Helianthus annuus, Hibiscus trionum, Rumex crispus and Sorghum bicolor. Another experiment was conducted in 1994 at Mead, Nebraska, to quantify pre-dispersal and post-dispersal predation of H. annuus seeds. Fewer than 5% of buried seeds gave rise to emerged seedlings in any year for any species. Three different dormancy patterns were exhibited by the four species. Large differences were seen in the survival patterns of buried seeds of the different species. Survival of H. annuus declined by about 20% in the first year. Virtually all such death occurred during the spring-to-autumn period. Five to 20% of H. trionum seeds died over the first winter but thereafter survival was constant. Between 55% and 80% of R. crispus died during their first year buried, mostly during the spring-to-autumn period. Eighty to 90% of S. bicolor seeds died during their first winter. The extent of decline in seed survival during the first year after burial differed for seeds buried in different years for all species except H. annuus. For seeds buried simultaneously, both the extent and temporal pattern of decline differed between the first and second years in the ground. Pre-dispersal predation of H. annuus seeds was less than 5% whereas post-dispersal predation averaged 48%. Position in the field had no clear effect upon predation. Small mammals were probably the principal predators. These studies provide estimates of the probabilities of transition through several lifecycle stages for these weeds. The estimates could be used in population dynamics models, but there are potentially serious problems with such models. I discuss the problem of temporal variation in transition probabilities for long-term population dynamics prediction and several aspects of elasticity analysis that make the results of such modelling of much less value than is commonly believed

Fe/Co-based Bimetallic MOF-derived Co3Fe7@NCNTFs Bifunctional Electrocatalyst for High-Efficiency Overall Water Splitting

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electrocatalytic water splitting to produce hydrogen and oxygen is regarded as one of the most promising methods to generate clean and sustainable energy for replacing fossil fuels. However, the design and development of an efficient bifunctional catalyst for simultaneous generation of hydrogen and oxygen remains extremely challenging yet is critical for the practical implementation of water electrolysis. Here, we report a facile method to fabricate novel N-doped carbon nanotube frameworks (NCNTFs) by the pyrolysis of a bimetallic metal organic framework (MIL-88-Fe/Co). The resultant electrocatalyst, Co3Fe7@NCNTFs, exhibits excellent oxygen evolution reaction (OER) activity, achieving 10 mA/cm2 at a low overpotential of just 264 mV in 1 M KOH solution, and 197 mV for the hydrogen evolution reaction. The high electrocatalytic activity arises from the synergistic effect between the chemistry of the Co3Fe7 and the NCNTs coupled to the novel framework structure. The remarkable electrocatalytic performance of our bifunctional electrocatalyst provides a promising pathway to high-performance overall water splitting and electrochemical energy devices

Carbon nanotube architectures as catalyst supports for proton exchange membrane fuel cells

Catalyst support materials exhibit great influence on the performance and durability of proton exchange membrane (PEM) fuel cells. This minireview article summarises recent developments into carbon nanotube-based support materials for PEM fuel cells, including the membrane electrode assembly (MEA). The advantages of using CNTs to promote catalyst performance and stability, a perspective on research directions and strategies to improve fuel cell performance and durability are discussed. It is hoped that this mini-review will act as a conduit for future developments in catalyst supports and MEA design for PEM fuel cells