A single‐atom Pt1/CeO2 catalyst formed by atom trapping (AT, 800 °C in air) shows excellent thermal stability but is inactive for CO oxidation at low temperatures owing to over‐stabilization of Pt2+ ...in a highly symmetric square‐planar Pt1O4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity; however, the NPs are easily oxidized, leading to drastic activity loss. Herein we show that tailoring the local environment of isolated Pt2+ by thermal‐shock (TS) synthesis leads to a highly active and thermally stable Pt1/CeO2 catalyst. Ultrafast shockwaves (>1200 °C) in an inert atmosphere induced surface reconstruction of CeO2 to generate Pt single atoms in an asymmetric Pt1O4 configuration. Owing to this unique coordination, Pt1δ+ in a partially reduced state dynamically evolves during CO oxidation, resulting in exceptional low‐temperature performance. CO oxidation reactivity on the Pt1/CeO2_TS catalyst was retained under oxidizing conditions.
A highly active and robust single‐atom Pt1/CeO2 catalyst was developed for CO oxidation by tailoring the local environment of isolated Pt2+ through thermal‐shock synthesis (see picture). Ultrafast shockwaves in an inert atmosphere generated Pt single atoms in an asymmetric Pt1O4 configuration, resulting in greatly enhanced low‐temperature activity that was retained under oxidizing conditions.
A vida de uma canção é surpreendente. No seu devir, reúne múltiplos ingredientes que lhe podem garantir condições para o sucesso e longevidade, para o fulgor seguido de saturação e de rápido ...declínio, para a invisibilidade inglória ou para o ressurgimento tardio. A canção passa por compositores, letristas, arranjadores, cantores, músicos e maestros, produtores, técnicos, locutores e apresentadores, até que chega finalmente a uma audiência, através da qual se dissemina de forma imprevisível. D...
Although word-of-mouth (WOM) activity has been studied as an outcome variable of other constructs such as satisfaction, less attention has been given to the antecedents and moderators of WOM when ...considering WOM as a central construct. Hence, we propose a model of WOM antecedents and moderators using a meta-analytic review. The results show that all antecedents have significant effects on WOM activity, with customer commitment showing the strongest effect. The following hypotheses are also supported: (1) WOM valence is a significant moderator, (2) cross-sectional studies show a stronger influence of satisfaction and loyalty on WOM activity than longitudinal studies, and (3) studies of WOM behavior show a weaker link between loyalty and WOM activity than studies of WOM intentions. In addition, we show that satisfaction has a stronger relationship with positive WOM than loyalty, whereas (dis)loyalty has a stronger relationship with negative WOM than does (dis)satisfaction. We discuss this finding based on the different natures of positive and negative WOM.
Constructed wetlands (CWs) performance enhancement can be done with intensification strategies. A recent strategy still in study is the coupling with Microbial Electrochemical Technologies (MET). An ...alternative system using electro-conductive biofilters instead of electrodes and circuits used in MET, resulted in the development of a Microbial Electrochemical-based CW (METland). This system relies on electroactive bacteria (EAB) metabolism to transfer electrons to an electro-conductive material, thus boosting substrate consumption, and diminishing electron availability for biomass build-up and methane generation. In previous studies this biofilters have shown an improvement in biodegradation rates in comparison with subsurface flow CW. However, this set-up is still in development, hence there are uncertainties regarding the dynamics involve in the removal of pollutants. Considering that, this work aimed at establishing the capacity and removal kinetics of organic matter and nutrients in an Electroactive Biofilm-Based CW (EABB-CW). Two electro-conductive materials were tested (PK-A and PK-LSN) in planted and non-planted mesocosms and compared with sand. The systems were operated in a continuous upflow mode for 32 weeks and fed with real wastewater. The electro-conductive systems reached removal efficiencies up to 88% for BOD5, 90% for COD, 46% for NH4-N, and 86% for PO4-P. Organic matter removal in electro-conductive systems was possible even at loading rates 10-fold higher than recommended for horizontal flow CWs. First-order area-based removal constants (k), calculated for organic matter and nutrients are higher than values typically reported for saturated CW and in certain cases comparable with vertical flow CW. The organic removal was correlated with electron current densities measures, as indicator of the presence of EAB. The tested EABB-CW profiles as a promising CW type for the removal of organic matter and PO4-P with margin for modifications to improve nitrogen removal. Future studies with pilot/real scale systems are proposed to validate the findings of this study.
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•EABB-CWs show organic matter removal rates comparable with conventional wetlands•High organic matter removal even at inlet loading rates 10× higher than HFCW•COD removal rates could be related to electron flux in electro-conductive systems•Removal rate constants (K) of EABB-CWs are higher than reported for HF and VFCWs•Electro-conductive materials with iron traces ease PO4-P removal
Constructed wetlands are an effective biofilter-based technology for treating wastewater in a sustainable way; however, their main disadvantage is a large area footprint. To cope with this limitation ...a new generation of constructed wetlands, the METlands®, have been recently reported. METlands® replace gravel with a granular electrically conductive material to enhance the oxidative metabolisms of electroactive bacteria by facilitating the flux of electron through the material and, consequently, increase bioremediation rates. In this work we evaluated the performance of a new electron sink (e-sink) device with the purpose of controlling and enhancing the electrochemical consumption of electrons from microbial metabolism without energy consumption. The e-sink device was integrated inside the biofilter bed and was tested using different electron acceptors with high redox potentials, like oxygen and hypochlorite. Interestingly, the presence of the e-sink allowed novel redox gradients to form inside the METland® and, consequently, a new electron flow was demonstrated by measuring both the electric potential and current density profiles of the bed. Three independent biofilters were constructed and operated under flooded conditions. Ec-coke and electroconductive biochar (ec-biochar) were used as electrically conductive bed materials, while gravel was used as an inert control. Furthermore, e-sink integration inside the electrically conductive bed outperformed METlands® for removing pollutants, already much more efficient than standard gravel biofilters. COD removal was increased from 90% in METland® to 95% in the e-sink METland® as compared to 75% for the control, while total nitrogen removal was enhanced from 64% in METland® to 71% in e-sink METland® as compared to 55% for the control. Our results indicate that increasing the electrochemical availability of electron acceptors by using the e-sink will be a suitable method for controlling the electron flow inside the filter bed and can be integrated in full scale METlands® for achieving high removal rates.
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•Electric potential is a useful measurement for understanding the behaviour of the electron flux in the METland® bed.•The new e-sink device allows for the control of the flux of electrons inside the METland® generating new redox gradients.•The e-sink allows supplying unlimited electron acceptors without interfering with the wastewater composition.•The use of e-sink in METland® increases the COD removal efficiency reaching values of 98% in urban wastewater.
Nevado del Ruiz volcano (NRV), Columbia, is one of the most dangerous volcanoes in the world and caused the death of 25,000 people in 1985. Using a new algorithm for repeated tomography, we have ...found a prominent seismic anomaly with high values of the Vp/Vs ratio at depths of 2-5 km below the surface, which is associated with a shallow magma reservoir. The amplitude and shape of this anomaly changed during the current phase of unrest which began in 2010. We interpret these changes as due to the ascent of gas bubbles through magma and to degassing of the reservoir. In 2011-2014, most of this gas escaped through permeable roof rocks, feeding surface fumarole activity and leading to a gradual decrease of the Vp/Vs ratio in the reservoir. This trend was reversed in 2015-2016 due to replenishment of the reservoir by a new batch of volatile-rich magma likely to sustain further volcanic activity. It is argued that the recurring "breathing" of the shallow reservoir is the main cause of current eruptions at NRV.
We analyze orbital solutions for 48 massive multiple-star systems in the Cygnus OB2 association, 23 of which are newly presented here, to find that the observed distribution of orbital periods is ...approximately uniform in log P for P < 45 days, but it is not scale-free. We identify six stars, all supergiants, that exhibit aperiodic velocity variations of ~30 km ssup -1 attributed to atmospheric fluctuations.
Conductive polymer composites are manufactured by randomly dispersing conductive particles along an insulating polymer matrix. Several authors have attempted to model the piezoresistive response of ...conductive polymer composites. However, all the proposed models rely upon experimental measurements of the electrical resistance at rest state. Similarly, the models available in literature assume a voltage-independent resistance and a stress-independent area for tunneling conduction. With the aim of developing and validating a more comprehensive model, a test bench capable of exerting controlled forces has been developed. Commercially available sensors-which are manufactured from conductive polymer composites-have been tested at different voltages and stresses, and a model has been derived on the basis of equations for the quantum tunneling conduction through thin insulating film layers. The resistance contribution from the contact resistance has been included in the model together with the resistance contribution from the conductive particles. The proposed model embraces a voltage-dependent behavior for the composite resistance, and a stress-dependent behavior for the tunneling conduction area. The proposed model is capable of predicting sensor current based upon information from the sourcing voltage and the applied stress. This study uses a physical (non-phenomenological) approach for all the phenomena discussed here.
During the 1990s the Kagera region of Tanzania experienced a forced migration shock. A series of geographical barriers led to a higher concentration of forced migrants in some parts of the region ...relative to others, resulting in a natural experiment. Using panel data (pre and post forced migration shock), we find that greater exposure to the refugee shock resulted in Tanzanians having a lower likelihood of working outside the household as employees. However, employees more affected by the shock had a higher probability of being in professional occupations and being part of a pensions program.
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