The electrochemical CO2 reduction reaction (CO2RR) using Cu-based catalysts holds great potential for producing valuable multi-carbon products from renewable energy. However, the chemical and ...structural state of Cu catalyst surfaces during the CO2RR remains a matter of debate. Here, we show the structural evolution of the near-surface region of polycrystalline Cu electrodes under in situ conditions through a combination of grazing incidence X-ray absorption spectroscopy (GIXAS) and X-ray diffraction (GIXRD). The in situ GIXAS reveals that the surface oxide layer is fully reduced to metallic Cu before the onset potential for CO2RR, and the catalyst maintains the metallic state across the potentials relevant to the CO2RR. We also find a preferential surface reconstruction of the polycrystalline Cu surface toward (100) facets in the presence of CO2. Quantitative analysis of the reconstruction profiles reveals that the degree of reconstruction increases with increasingly negative applied potentials, and it persists when the applied potential returns to more positive values. These findings show that the surface of Cu electrocatalysts is dynamic during the CO2RR, and emphasize the importance of in situ characterization to understand the surface structure and its role in electrocatalysis.
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Cold clouds in hot media are quickly crushed, shredded, and then accelerated as a result of their interaction with the background gas. The persistence of cold clouds moving at substantial velocities ...in harsh environments is a common yet puzzling feature of many astrophysical systems, from quasar absorption lines probing galactic halos to clouds of dust passing near Sgr A*. Here we run a set of idealized numerical experiments, subjecting a line of cold clouds at a series of mutual separations to a hot background wind. We find that this stream of clouds is able to shield itself from hydrodynamic destruction by accelerating the hot background material, creating a protective layer of co-moving gas. We write down a simple diffusion equation that reproduces the behavior of the simulations, and we discuss the implications for cosmological gas accretion and the putative galactic center dust cloud G2.
Urban areas are currently responsible for ∼70% of the global energy-related carbon dioxide (CO2) emissions, and rapid ongoing global urbanization is increasing the number and size of cities. Thus, ...understanding city-scale CO2 emissions and how they vary between cities with different urban densities is a critical task. While the relationship between CO2 emissions and population density has been explored widely in prior studies, their conclusions were sensitive to inconsistent definitions of urban boundaries and the reliance upon CO2 emission inventories that implicitly assumed population relationships. Here we provide the first independent estimates of direct per capita CO2 emissions (Epc) from spaceborne atmospheric CO2 measurements from the Orbiting Carbon Observatory-2 (OCO-2) for a total 20 cities across multiple continents. The analysis accounts for the influence of meteorology on the satellite observations with an atmospheric model. The resultant upwind source region sampled by the satellite serves as an objective urban extent for aggregating emissions and population densities. Thus, we are able to detect emission 'hotspots' on a per capita basis from a few cities, subject to sampling restrictions from OCO-2. Our results suggest that Epc declines as population densities increase, albeit the decrease in Epc is partially limited by the positive correlation between Epc and per capita gross domestic product. As additional CO2-observing satellites are launched in the coming years, our space-based approach to understanding CO2 emissions from cities has significant potential in tracking and evaluating the future trajectory of urban growth and informing the effects of carbon reduction plans.
The only known study evaluating SARS development in hospital workers was a retrospective study conducted prior to the widespread use of HFNC showing that development of SARS occurred in tracheal ...intubation (35%), HFNC 8%, and 38% (NIPPV) 3; this suggests that both non-invasive (including HFNC) and invasive ventilation approaches carry significant risk. ...since the data regarding transmission are unclear, we suggest, in addition to a negative pressure room, reverse isolation protection efforts with patients on HFNC wearing a mask over the nasal interface or a contained respiratory hood. 1. Comparison of high-flow nasal cannula versus oxygen face mask for environmental bacterial contamination in critically ill pneumonia patients: a randomized controlled crossover trial.
An in-depth review of boundary-layer flow-separation control by a passive method using low-profile vortex generators is presented. The generators are defined as those with a device height between 10% ...and 50% of the boundary-layer thickness. Key results are presented for several research efforts, all of which were performed within the past decade and a half where the majority of these works emphasize experimentation with some recent efforts on numerical simulations. Topics of discussion consist of both basic fluid dynamics and applied aerodynamics research. The fluid dynamics research includes comparative studies on separation control effectiveness as well as device-induced vortex characterization and correlation. The comparative studies cover the controlling of low-speed separated flows in adverse pressure gradient and supersonic shock-induced separation. The aerodynamics research includes several applications for aircraft performance enhancement and covers a wide range of speeds. Significant performance improvements are achieved through increased lift and/or reduced drag for various airfoils—low-Reynolds number, high-lift, and transonic—as well as highly swept wings. Performance enhancements for non-airfoil applications include aircraft interior noise reduction, inlet flow distortion alleviation inside compact ducts, and a more efficient overwing fairing. The low-profile vortex generators are best for being applied to applications where flow-separation locations are relatively fixed and the generators can be placed reasonably close upstream of the separation. Using the approach of minimal near-wall protuberances through substantially reduced device height, these devices can produce streamwise vortices just strong enough to overcome the separation without unnecessarily persisting within the boundary layer once the flow-control objective is achieved. Practical advantages of low-profile vortex generators, such as their inherent simplicity and low device drag, are demonstrated to be critically important for many applications as well.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Developing effective technologies for treatment of spent etchant in printed circuit boards industries is of paramount for sustainable copper reuse and reducing copper discharge. We developed a novel ...closed-loop electrochemical cell for on-site regeneration of spent acidic cupric chloride etchant. It does not have any emissions and recycles all the copper using a three-dimensional graphite felt anode decorated with carbon nanotube (CNT/GF). The CNT/GF anode oxidizes Cu(I) to Cu(II) so that the spent cuprous chloride can be converted to cupric chloride and reused. The decorated CNT layer with abundant oxygen-containing functional groups significantly enhanced the electrocatalytic activity for Cu(II)/Cu(I) redox. The CuCl3 2– is oxidized to CuCl+ at the anode and the CuCl+ is reduced to Cu(0) at the cathode. The closed-loop cycle system converts the catholyte into the anolyte. On average, the energy consumption of Cu(I) oxidation by CNT/GF is decreased by 12%, comparing to that by untreated graphite felt. The oxidation rate of Cu(I) is determined by the current density, and there is no delay for the mass transport of Cu(I). This study highlights the outstanding electrocatalytic performance, the rapid mass-transfer kinetics, and the excellent stability of the CNT/GF electrode, and provides an energy-efficient and zero-emission strategy for the regeneration of etchant waste.
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