Ion size effects at ionic exclusion from dielectric interfaces and slit nanopores

A previously developed field-theoretic model [R.D. Coalson et al., J. Chem. Phys. 102, 4584 (1995)] that treats core collisions and Coulomb interactions on the same footing is investigated in order to understand ion size effects on the partition of neutral and charged particles at planar interfaces and the ionic selectivity of slit nanopores. We introduce a variational scheme that can go beyond the mean-field (MF) regime and couple in a consistent way pore modified core interactions, steric effects, electrostatic solvation and image-charge forces, and surface charge induced electrostatic potential. We show that in the dilute limit, the MF and the variational theories agree well with MC simulation results, in contrast to a recent RPA method. The partition of charged Yukawa particles at a neutral dielectric interface (e.g air-water or protein-water interface) is investigated. It is shown that as a result of the competition between core collisions that push the ions towards the surface, and repulsive solvation and image forces that exclude them from the interface, a concentration peak of finite size ions sets in close to the dielectric interface. We also characterize the role played by the ion size on the ionic selectivity of neutral slit nanopores. We show that the complex interplay between electrostatic forces, excluded volume effects induced by core collisions and steric effects leads to an unexpected reversal in the ionic selectivity of the pore with varying pore size: while large pores exhibits a higher conductivity for large ions, narrow pores exclude large ions more efficiently than small ones

Diffuse-Charge Dynamics in Electrochemical Systems

The response of a model micro-electrochemical system to a time-dependent applied voltage is analyzed. The article begins with a fresh historical review including electrochemistry, colloidal science, and microfluidics. The model problem consists of a symmetric binary electrolyte between parallel-plate, blocking electrodes which suddenly apply a voltage. Compact Stern layers on the electrodes are also taken into account. The Nernst-Planck-Poisson equations are first linearized and solved by Laplace transforms for small voltages, and numerical solutions are obtained for large voltages. The ``weakly nonlinear'' limit of thin double layers is then analyzed by matched asymptotic expansions in the small parameter $\epsilon = \lambda_D/L$, where $\lambda_D$ is the screening length and $L$ the electrode separation. At leading order, the system initially behaves like an RC circuit with a response time of $\lambda_D L / D$ (not $\lambda_D^2/D$), where $D$ is the ionic diffusivity, but nonlinearity violates this common picture and introduce multiple time scales. The charging process slows down, and neutral-salt adsorption by the diffuse part of the double layer couples to bulk diffusion at the time scale, $L^2/D$. In the ``strongly nonlinear'' regime (controlled by a dimensionless parameter resembling the Dukhin number), this effect produces bulk concentration gradients, and, at very large voltages, transient space charge. The article concludes with an overview of more general situations involving surface conduction, multi-component electrolytes, and Faradaic processes.Comment: 10 figs, 26 pages (double-column), 141 reference

Solvation free energy profile of the SCN- ion across the water-1,2-dichloroethane liquid/liquid interface. A computer simulation study

The solvation free energy profile of a single SCN- ion is calculated across the water-1,2-dichloroethane liquid/liquid interface at 298 K by the constraint force method. The obtained results show that the free energy cost of transferring the ion from the aqueous to the organic phase is about 70 kJ/mol, The free energy profile shows a small but clear well at the aqueous side of the interface, in the subsurface region of the water phase, indicating the ability of the SCN- ion to be adsorbed in the close vicinity of the interface. Upon entrance of the SCN- ion to the organic phase a coextraction of the water molecules of its first hydration shell occurs. Accordingly, when it is located at the boundary of the two phases the SCN- ion prefers orientations in which its bulky S atom is located at the aqueous side, and the small N atom, together with its first hydration shell, at the organic side of the interface

Observations of the Interaction and Transport of Fine Mode Aerosols With Cloud and/or Fog in Northeast Asia From Aerosol Robotic Network and Satellite Remote Sensing

Analysis of Sun photometer measured and satellite retrieved aerosol optical depth (AOD) datahas shown that major aerosol pollution events with very highfine mode AOD (>1.0 in midvisible) in theChina/Korea/Japan region are often observed to be associated with significant cloud cover. This makesremote sensing of these events difficult even for high temporal resolution Sun photometer measurements.Possible physical mechanisms for these events that have high AOD include a combination of aerosolhumidification, cloud processing, and meteorological covariation with atmospheric stability andconvergence. The new development of Aerosol Robotic Network Version 3 Level 2 AOD with improved cloudscreening algorithms now allow for unprecedented ability to monitor these extremefine mode pollutionevents. Further, the spectral deconvolution algorithm (SDA) applied to Level 1 data (L1; no cloud screening)provides an even more comprehensive assessment offine mode AOD than L2 in current and previous dataversions. Studying the 2012 winter-summer period, comparisons of Aerosol Robotic Network L1 SDA dailyaveragefine mode AOD data showed that Moderate Resolution Imaging Spectroradiometer satellite remotesensing of AOD often did not retrieve and/or identify some of the highestfine mode AOD events in thisregion. Also, compared to models that include data assimilation of satellite retrieved AOD, the L1 SDAfinemode AOD was significantly higher in magnitude, particularly for the highest AOD events that were oftenassociated with significant cloudiness

Satellite quantification of methane emissions from South American countries: a high-resolution inversion of TROPOMI and GOSAT observations

We use 2021 TROPOMI and GOSAT satellite observations of atmospheric methane in an analytical inversion to quantify national methane emissions from South America at up to 25 km × 25 km resolution. From the inversion, we derive optimal posterior estimates of methane emissions, adjusting a combination of national anthropogenic emission inventories reported by individual countries to the United Nations Framework Convention on Climate Change (UNFCCC), the UNFCCC-based Global Fuel Exploitation Inventory (GFEIv2), and the Emissions Database for Global Atmospheric Research (EDGARv7) as prior estimates. We also evaluate two alternative wetland emission inventories (WetCHARTs and LPJ-wsl) as prior estimates. Our best posterior estimates for wetland emissions are consistent with previous inventories for the Amazon but lower for the Pantanal and higher for the Paraná. Our best posterior estimate of South American anthropogenic emissions is 48 (41–56) Tg a−1, where numbers in parentheses are the range from our inversion ensemble. This is 55 % higher than our prior estimate and is dominated by livestock (65 % of anthropogenic total). We find that TROPOMI and GOSAT observations can effectively optimize and separate national emissions by sector for 10 of the 13 countries and territories in the region, 7 of which account for 93 % of continental anthropogenic emissions: Brazil (19 (16–23) Tg a−1), Argentina (9.2 (7.9–11) Tg a−1), Venezuela (7.0 (5.5–9.9) Tg a−1), Colombia (5.0 (4.4–6.7) Tg a−1), Peru (2.4 (1.6–3.9) Tg a−1), Bolivia (0.96 (0.66–1.2) Tg a−1), and Paraguay (0.93 (0.88–1.0) Tg a−1). Our estimates align with the prior estimates for Brazil, Bolivia, and Paraguay but are significantly higher for other countries. Emissions in all countries are dominated by livestock (mainly enteric fermentation) except for oil–gas in Venezuela and landfills in Peru. Methane intensities from the oil–gas industry are high in Venezuela (33 %), Colombia (6.5 %), and Argentina (5.9 %). The livestock sector shows the largest difference between our top-down estimate and the UNFCCC prior estimates, and even countries using complex bottom-up methods report UNFCCC emissions significantly lower than our posterior estimate. These discrepancies could stem from underestimations in IPCC-recommended bottom-up calculations or uncertainties in the inversion from aggregation error and the prior spatial distribution of emissions.</p

Development of a virtual environment for teaching and learning biomedical techniques and equipment for the study of human pathogens.

An international innovative teaching group from different EU Universities (De Montfort University, Leicester, UK; University of San Pablo CEU, Madrid, Spain; University of Miguel Hernandez, Elche, Spain) and biomedical scientists registered by the Health and Care Professions Council (HCPC, UK) are developing a complete e-learning package in medical parasitology for undergraduate and postgraduate students that study Health Sciences. This package, named DMU e-Parasitology, is accessible through the DMU website (http://parasitology.dmu.ac.uk) and will present different modules including a virtual laboratory module for the study of traditional and novel biomedical laboratory techniques and equipment for detecting, identifying and studying human pathogens, specifically parasites. These techniques could also be potentially used to study other pathogens such as bacteria or viruses. The virtual biomedical laboratory is under development, but is available in the DMU website here: http://parasitology.dmu.ac.uk/learn/laboratory.htm. To develop this new module of the DMU e-Parasitology, we are using Storyline 360 software and the scaffolding and methods used to build the theoretical module (Peña-Fernández et al., 2017) [1]. To facilitate the navigation, study and comprehension of the final user, we have divided the virtual laboratory into a series of sub-sections that include different units; the sub-sections so far are: microscopes (with units such as the electron microscope); molecular biology (e.g. polymerase chain reaction and gel electrophoresis); biological safety cabinets and cell/parasite culture; biochemical and immunological techniques (e.g. magnetic immunoseparation); histology (e.g. microtome) and staining techniques (e.g. Kinyoun staining). The virtual laboratory units are highly interactive and present short videos of academics and/or technicians working in real conditions with the different laboratory equipment such as a thermocycler, a microtome, or a biological safety cabinet, as well as performing a specific technique such as a staining to determine pathogens. Therefore, the user of this virtual environment will receive a complete and “real” experience of the work in a biomedical laboratory. The DMU e-Parasitology package, and specifically its virtual laboratory environment, could help technicians and students across the world to learn how to work in a biomedical laboratory as well as to perform techniques to identify and diagnose human pathogens such as microsporidia or Plasmodium spp. Thus, the virtual resource is supported by a virtual library that includes a real collection of clinical slides that will provide the user with the functionality of a light and/or an immunofluorescence microscope. In conclusion, the virtual laboratory may serve as a high quality and reliable on-line environment for the learning of techniques and equipment. These resources can be used to improve the learning of undergraduate and postgraduate students of human health sciences as well as to develop CPD training. Moreover, the virtual laboratory module may impact in the teaching of laboratory techniques and skills in developing countries due to their limited resources. This communication will explore the design and development of the virtual laboratory environment that will be publicly accessible by the end of 2018

Leveraging hope & experience: Towards an integrated model of transformative learning, community and leadership for sustainability action and change

How can we engage in futures-oriented ‘hope work’ in the face of extraordinary global challenges, and from within the confines of a commodified higher education system? This chapter traces the experience of a group of staff and students at Manchester Metropolitan University Business School, who came together to explore this question through an experimental, emergent, and creative process of co-operative inquiry. This shared safe space enabled relations of trust, openness and enjoyment to emerge, which were conducive to learning, community-building, and shared leadership. Thus our shared experience enabled us to shed new and critical light on transformative learning, transformative community and transformative leadership. However, in place of three separate concepts, our findings lead us to a composite, integrated and mutually reinforcing model centred on a set of connecting 2 principles. These in turn are rooted in our subjective experiences of our practical cares and concerns, both individual and shared. Emerging from within an experiential ontology, then, this integrated model offers a reflexive alternative to the top-down approach to sustainability teaching and strategy that currently prevails in many higher education institutions. We share here our experience and the theoretical model it catalysed – along with suggestions for practical actions. In so doing, we hope that we might inspire others to experiment (in their own way) with more organic, less hierarchical, and potentially more enduring approaches to the pedagogy and practice of sustainability