Super-Maxwellian Helium Evaporation from Pure and Salty Water

Helium atoms evaporate from pure water and salty solutions in super-Maxwellian speed distributions, as observed experimentally and modeled theoretically.The experiments are performed by monitoring the velocities of dissolved He atoms that evaporate from microjets of pure water at 252 K and 4–8.5 molal LiCl and LiBr at 232–252 K. The average He atom energies exceed the flux-weighted Maxwell-Boltzmann average of 2RT by 30% for pure water and 70% for 8.5m LiBr. Classical molecular dynamics simulations closely reproduce the observed speed distributions and provide microscopic insight into the forces that eject the He atoms from solution. Comparisons of the density profile and He kinetic energies across the water-vacuum interface indicate that the He atoms are accelerated by He–water collisions within the top 1-2 layers of the liquid. We also find that the average He atom kinetic energy scales with the free energy of solvation of this sparingly soluble gas. This free-energydifference reflects the steeply decreasing potential of mean force on the He atoms in the interfacial region, whose gradient is the repulsive force that tends to expel the atoms. The accompanying sharp decrease in water density suppresses the He–water collisions that would otherwise maintain a Maxwell-Boltzmanndistribution, allowing the He atom to escape at high energies. Helium is especially affected by this reduction in collisions because its weak interactions make energy transfer inefficient

Data_Sheet_1_Collective identity in collective action: evidence from the 2020 summer BLM protests.PDF

Does collective identity drive protest participation? A long line of research argues that collective identity can explain why protesters do not free ride and how specific movement strategies are chosen. Quantitative studies, however, are inconsistent in defining and operationalizing collective identity, making it difficult to understand under what conditions and to what extent collective identity explains participation. In this paper, we clearly differentiate between interest and collective identity to isolate the individual level signals of collective action. We argue that these quantities have been conflated in previous research, causing over estimation of the role of collective identity in protest behavior. Using a novel dataset of Twitter users who participated in Black Lives Matter protests during the summer of 2020, we find that contingent on participating in a protest, individuals have higher levels of interest in BLM on the day of and the days following the protest. This effect diminishes over time. There is little observed effect of participation on subsequent collective identity. In addition, higher levels of interest in the protest increases an individuals chance of participating in a protest, while levels of collective identity do not have a significant effect. These findings suggest that collective identity plays a weaker role in driving collective action than previously suggested. We claim that this overestimation is a byproduct of the misidentification of interest as identity.</p

Ionic conductivity in Bi 2Sn 2O 7 ceramics

Impedance spectroscopy measurements, in the temperature range from room temperature to 600 K, were performed in order to investigate the dielectric and ionic properties of Bi 2Sn 2O 7 ceramics. The results show that the conductivity in this pyrochlore is associated with the hopping of ions. An activation energy of 1.26 eV was observed and the dielectric constant exhibits a strong contribution from ionic conduction. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Ionic conductivity in Bi2Sn2O7 ceramics

Impedance spectroscopy measurements, in the temperature range from room temperature to 600 K, were performed in order to investigate the dielectric and ionic properties of Bi 2Sn 2O 7 ceramics. The results show that the conductivity in this pyrochlore is associated with the hopping of ions. An activation energy of 1.26 eV was observed and the dielectric constant exhibits a strong contribution from ionic conduction. © 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Mixed crystal formation and structural studies in the mullite-type system Bi 2Fe 4O 9Bi 2Mn 4O 10

The limits of metal cation substitution and distribution in the sequence Bi 2Fe 4O 9Bi 2Mn 4O 10 have been investigated by solid state synthesis, X-ray powder diffraction, and Mössbauer spectroscopy. Rietveld refinements conducted for the entire range along the join indicate the structures are orthorhombic with space group Pbam, with partial transition-metal site disorder confirmed and detailed by Mössbauer spectroscopy. Single-phase regions are found near each end-member and a two-phase region is observed at intermediate compositions, extending from about x=1 to 3, according to the general formula of the mixed crystals Bi 2Fe 4-xMn xO 10-δ. An incorporation of Mn at octahedral sites replacing Fe is taken into account for the Bi 2Fe 4O 9-related side of the system. Charge compensation is believed to be effected by addition of O, which gives rise to the formation of FeO 5 pyramids. At the Bi 2Mn 4O 10-related side of the system, substitution of pyramidal Mn 3 by Fe 3 is envisaged. © 2011 Elsevier Inc. All rights reserved