Evaluation of hexavalent chromium extraction method EPA method 3060A for soils using XANES spectroscopy

Hexavalent chromium (Cr(VI)) occurrence in soils is generally determined using an extraction step to transfer it to the liquid phase where it is more easily detected and quantified. In this work, the performance of the most common extraction procedure (EPA Method 3060A) using NaOH-Na(2)CO(3) solutions is evaluated using X-ray absorption near edge structure spectroscopy (XANES), which enables the quantification of Cr(VI) directly in the solid state. Results obtained with both methods were compared for three solid samples with different matrices: a soil containing chromite ore processing residue (COPR), a loamy soil, and a paint sludge. Results showed that Cr(VI) contents determined by the two methods differ significantly, and that the EPA Method 3060A procedure underestimated the Cr(VI) content in all studied samples. The underestimation is particularly pronounced for COPR. Low extraction yield for EPA Method 3060A was found to be the main reason. The Cr(VI) present in COPR was found to be more concentrated in magnetic phases. This work provides new XANES analyses of SRM 2701 and its extraction residues for the purpose of benchmarking EPA 3060A performance.     

SiO2–K2O–MgO vitreous films doped with erbium and silver nanoparticles for optical applications

The search of new glass compositions for films produced with high optical transparency throughout the visible spectrum from 0.5 μm to the near infrared region is important for optical integrated applications. In this work, we present the preparation of SiO₂–K₂O–MgO vitreous sol–gel films on SiO₂ substrates co-doped with Er³⁺ and Ag nanoparticles. The silver quantum dots were synthesized in continuous media (ex situ) by chemical reduction and isolation from media by anchoring chemical solution-compatible modifiers (aminosilanes) on their surfaces; then, they were successfully integrated into the glass matrix. We present the study of the preparation process and characterization of sol–gel matrices doped with Ag⁰ nanoparticles and Er³⁺, analyzing the role of synthesis parameters and optical properties, and comparing them with other wave-guide compositions, such as PLZT and SiO₂–B₂O₃.     

Debye screening in single-molecule carbon nanotube field-effect sensors

Point-functionalized carbon nanotube field-effect transistors can serve as highly sensitive detectors for biomolecules. With a probe molecule covalently bound to a defect in the nanotube sidewall, two-level random telegraph noise (RTN) in the conductance of the device is observed as a result of a charged target biomolecule binding and unbinding at the defect site. Charge in proximity to the defect modulates the potential (and transmission) of the conductance-limiting barrier created by the defect. In this Letter, we study how these single-molecule electronic sensors are affected by ionic screening. Both charge in proximity to the defect site and buffer concentration are found to affect RTN amplitude in a manner that follows from simple Debye length considerations. RTN amplitude is also dependent on the potential of the electrolyte gate as applied to the reference electrode; at high enough gate potentials, the target DNA is completely repelled and RTN is suppressed.     

Channel length scaling in graphene field-effect transistors studied with pulsed current-voltage measurements

We investigate current saturation at short channel lengths in graphene field-effect transistors (GFETs). Saturation is necessary to achieve low-output conductance required for device power gain. Dual-channel pulsed current-voltage measurements are performed to eliminate the significant effects of trapped charge in the gate dielectric, a problem common to all oxide-based dielectric films on graphene. With pulsed measurements, graphene transistors with channel lengths as small as 130 nm achieve output conductance as low as 0.3 mS/μm in saturation. The transconductance of the devices is independent of channel length, consistent with a velocity saturation model of high-field transport. Saturation velocities have a density dependence consistent with diffusive transport limited by optical phonon emission.     

Radical and incremental creativity: Antecedents and processes.

This study extends creativity theory and research by differentiating between 2 distinct forms of creative performance: radical and incremental. It also examines the differential effects of certain antecedents on these two forms of creativity. Results demonstrate that intrinsic motivation, problem-driven, and abstract theory-related creative ideas are associated mostly with radical creativity, whereas extrinsic motivation and ideas that are solution-driven and developed on the basis of concrete practices are linked more closely to incremental creativity. Theoretical and managerial implications are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Flow profile of granular avalanches with imposed vertical vibration

We report experimental results on the effect of imposed vertical vibration on the flow of pentagonal grains in a two-dimensional rotation drum. While dimensionless acceleration $\varGamma $ can be tuned either by increasing vibration frequency or amplitude, the former leads to stabilization an increase in the angle of repose while the latter leads to destabilization and a decrease in the critical angle for failure. Increased vibration amplitude leads to continuous avalanching and a more uniform flow profile, with a flowing layer composed of increasingly long-lived, shallower avalanches before a continuous flow regime is reached. The slope and grain-scale roughness of the surface decrease and interface curvature increases as vibration amplitude is increased and collective motion allows relaxation of the surface. While qualitative flow characteristics are similar both with and without vibration, vibration allows the system to evolve continuously in a nearly steady-state profile.     

Costs for integrating wind into the future ERCOT system with related costs for savings in CO2 emissions

Wind power can make an important contribution to the goal of reducing emissions of CO2. The major problem relates to the intrinsic variability of the source and the difficulty of reconciling the supply of electricity with demand particularly at high levels of wind penetration. This challenge is explored for the case of the ERCOT system in Texas. Demand for electricity in Texas is projected to increase by approximately 60% by 2030. Considering hourly load data reported for 2006, assuming that the pattern of demand in 2030 should be similar to 2006, and adopting as a business as usual (BAU) reference an assumption that the anticipated additional electricity should be supplied by a combination of coal and gas with prices, discounted to 2007 dollars of $2 and $6 per MMBTU respectively, we conclude that the bus-bar price for electricity would increase by about 1.1 ￠/kWh at a wind penetration level of 30%, by about 3.4 ￠/kWh at a penetration level of 80%. Corresponding costs for reductions in CO2 range from $20/ton to $60/ton. A number of possibilities are discussed that could contribute to a reduction in these costs including the impact of an expanded future fleet of electrically driven vehicles.     

Synthesis and Structure−Activity Relationships of Imidazopyridine/Pyrimidine- and Furopyridine-Based Anti-infective Agents against Trypanosomiases

Neglected tropical diseases remain among the most critical public health concerns in Africa and South America. The drug treatments for these diseases are limited, which invariably leads to fatal cases. Hence, there is an urgent need for new antitrypanosomal drugs. To address this issue, a large number of diverse heterocyclic compounds were prepared. Straightforward synthetic approaches tolerated pre-functionalized structures, giving rise to a structurally diverse set of analogs. We report on a set of 57 heterocyclic compounds with selective activity potential against kinetoplastid parasites. In general, 29 and 19 compounds of the total set could be defined as active against Trypanosoma cruzi and T. brucei brucei, respectively (antitrypanosomal activities <10 μM). The present work discusses the structure−activity relationships of new fused-ring scaffolds based on imidazopyridine/pyrimidine and furopyridine cores. This library of compounds shows significant potential for anti-trypanosomiases drug discovery.     

ACHEMA 2022: Innovationen und Trends in der Trocknungstechnik

This contribution aims to summarize the highlights of the innovations displayed at ACHEMA 2022 and to report on the observed trends. Aside from new equipment in individual areas of drying, the advances of the exhibiting companies in the areas of digitalization and sustainability were examined in greater detail.