Unequal Mobilities Research Articles

Asymmetric rectified electric fields: nonlinearities and equivalent circuits.

Recent experiments [S. H. Hashemi et al., Phys. Rev. Lett., 2018, 121, 185504] have shown that a long-ranged steady electric field emerges when applying an oscillating voltage over an electrolyte with unequal mobilities of cations and anions confined between two planar blocking electrodes. To explain this effect we analyse full numerical calculations based on the Poisson-Nernst-Planck equations by means of analytically constructed equivalent electric circuits. Surprisingly, the resulting equivalent circuit has two capacitive elements, rather than one, which introduces a new timescale for electrolyte dynamics. We find a good qualitative agreement between the numerical results and our simple analytic model, which shows that the long-range steady electric field emerges from the different charging rates of cations and anions in the electric double layers.

The social justice issues of smoke im/mobilities

ABSTRACT In 2014, the Hazelwood mine fire burned for 45 days. Local communities were impacted by smoke and ash, and there were reports of raised carbon monoxide levels. Local news and social media reported residents experiencing numerous physical symptoms of smoke inhalation, including bleeding noses, coughing, wheezing and chest tightness. Paper masks to filter particulate matter were made available to residents to wear outside. The dust and ash constantly seeped into homes and offices, which required cleaning daily and sometimes multiple times during the day. Smoke was free to move across physical and bodily boundaries while those most vulnerable were hampered by lack of movement: pregnant women, the elderly and children were advised to leave the area. However, this suggestion to ‘simply’ move ignored the context of a community disproportionately impacted through years of economic decline and societal change. This paper explores the unequal mobilities of smoke and people that arose as a result of this event and draws on concepts of mobility justice (Sheller 2018) and emergency mobilities (Adey 2016) to reflect on the political dimensions of uneven mobility in times of crisis.

Towards inclusive transport: The responsiveness of intercity bus services to the needs of people with disabilities in Tamale, Ghana

AbstractPeople with disabilities (PWDs) have an equal right to independent mobility and dignified involvement in society, which is intrinsically related to their access to inclusive public transit systems. Yet, very often PWDs face injustices of unequal mobilities emanating from a combination of access barriers. Based on qualitative interviews and Focus Group Discussions with PWDs and station managers, this exploratory study assessed the responsiveness of public intercity bus services to the needs of PWDs with vision, hearing and walking/climbing difficulties. The findings show that, despite the Persons with Disabilities Act's passage in 2006, intercity public bus transportation services in Tamale, Ghana, do not meet the needs of PWDs. Intercity bus stations and vehicles are not disability‐friendly, leading to people with disabilities facing severe discrimination and having a more difficult time using intercity bus services. This is due to a combination of environmental barriers, legislative/policy inadequacies, negative public attitudes and low compliance of transport operators to transport provisions in the Disability Act. PWDs express deep‐seated feelings of marginalisation and resentment about the uneven access to transport services and the violation of their rights to autonomy in movement. It is concluded that the journey experiences of PWDs have a significant adverse influence on their travel decisions and full participation in society. Hence, suggestions for further research and policy recommendations to promote inclusive transport systems have been proffered.

Unique times, unequal mobilities: Daily mobility during the de‐escalation of the COVID‐19 pandemic

AbstractScholars have highlighted drastic reductions in daily mobility during the early stages of the COVID‐19 pandemic lockdown. But what happened when restrictions were relaxed though risk remained ubiquitous? How did patterns of mobility change and how were they structured by socioeconomic resources and social roles? We address these questions using a cross‐sectional representative sample (n = 2942) of the population of Andalusia, Spain, after a month and a half of severe lockdown in 2020. We find that older people were the least mobile group and that people living with children and in extended households were less likely to move to take care of others, unlike before the pandemic. Men were more likely to carry out daily mobilities for which women had been traditionally responsible, such as care mobilities. Women were also more likely to be immobile and less likely to commute. Finally, manual and nonqualified workers were more likely to commute, but they were just as likely as any other group to carry out other types of mobility. These results highlight the social character of mobility in a unique context. We emphasize the need to disaggregate daily mobility based on different purposes as well analysing how these are practised by different sociodemographic groups if we want to provide rigorous descriptions of a core component of individuals’ daily life.

Diffusiophoresis of hydrophobic spherical particles in a solution of general electrolyte

The present article deals with the diffusiophoresis of hydrophobic rigid colloids bearing arbitrary ζ-potential. We derived the generic expression for the diffusiophoretic velocity of such a colloid exposed in an externally applied concentration gradient of the general electrolyte solution. The derived expression takes into account the relaxation effect and is applicable for all values of surface ζ-potential and hydrodynamic slip length at large κa (κa≥ca.50), where κ−1 is the thickness of the electric double layer and a is the particle radius. We further derived several closed-form expressions for particle velocity derived under various electrostatic and hydrodynamic conditions when the particle is exposed in an applied concentration gradient of binary symmetric (e.g., z:z), asymmetric (1:2, 2:1, 3:1, 1:3), and a mixed electrolyte (mixture of 1:1 and 2:1 electrolytes). The results for diffusiophoretic velocity are further illustrated graphically to indicate the mutual interaction of chemiphoresis, induced electrophoresis due to unequal mobilities of cations and anions of the electrolyte, and the mechanism by which the sufficiently charged particle migrates opposite to the direction of the applied concentration gradient. The impact of hydrophobicity is further discussed.

Transportation Justice in Vermont Communities of High Environmental Risk

Transportation justice studies have largely focused on metropolitan areas, and the transportation disparities in rural areas and their most disadvantaged population are not well understood. Our study explored transportation injustices in high environmental risk communities in Vermont. We found that low-income communities and people of color disproportionately face inequitable access to transportation services: they are more likely to be concerned about lack of transportation, more likely to not own or lease a personal vehicle and rely more heavily on public transportation. Our study also found that those without a personal vehicle and those largely dependent on public transportation have less access to healthy food, are likely to go hungry, have greater reports of asthma, and have less access to primary care physicians and jobs. The transportation policies in the state are also procedurally unjust. These disadvantages, combined with higher exposures to environmental risks, also pose implications for public health and well-being. A combined transition toward sustainable mobility and transportation justice should prioritize greater equity in the distribution of transportation investment in infrastructure and services; recognition of historical patterns that inform current uneven and unequal mobilities; procedural and democratic engagement of the marginalized in transportation design, planning and policy-making; a capabilities approach to plan transportation systems that improve opportunities, wellness, and quality of life for the most disadvantaged population. Consideration should also be given to designing a sustainable transportation transition that prioritizes attention for all modes of transport accessibility and mobility, including non-motorized and public transit modes, in planning and policies so that streets are not dominated by a single mode of transportation, such as cars.

Of Rags and Riches in the Caribbean: Creolizing Migration Studies

In this article, we re-connect highly unequal mobilities in the Caribbean that have so far escaped the purview of migration research and challenge dominant understandings of migrant integration: By replacing the methodological Occidentalism shaping the field through a creolized decolonial lens, we show how the precarious position of Haitians in the Greater Caribbean and particularly in French Guiana testifies to how colonial histories shape unequal mobilities until the present. We juxtapose these patterns between the first independent Black Republic and territories still under colonial occupation with short-cuts to global mobility available to investors in commodified citizenships in the Caribbean.

Essential workers' pandemic mobilities and the changing meanings of the commute.

This commentary reflects on the pandemic commute and its significance for, on one hand, engaging with the problematic category of essential work, and on the other, future geographical research on transport and mobilities. Drawing on essential workers' contributions to the ‘Not working from home’ public engagement project, I outline some experiences of commuting during the COVID‐19 pandemic. I illustrate the role of pandemic commuting in defining, and wrestling with, what the category of essential work might mean. I then discuss the ways in which attending to pandemic commutes may extend and reshape existing research on unequal mobilities. Some of the future research directions made more urgent by a focus on pandemic commutes include critical engagements with: first, intersectional inequalities in the journey to work; second, the category of ‘essential journeys’ as used in transport policy and practice; third, the positionality of academic researchers who work on the topic of commuting; and finally, the treatment of commuting time as an integral part of working time.

Wandering: An Essay on Histories, Genders, Mobilities, and Forms

Wandering: An Essay on Histories, Genders, Mobilities, and Forms

On the Voronoi Implicit Interface Method

We present careful numerical convergence studies, using parameterized curves to reach very high resolutions in two dimensions, of a level set method for multiphase curvature motion known as the Voronoi implicit interface method. Our tests demonstrate that in the unequal, additive surface tension case, the Voronoi implicit interface method does not converge to the desired limit. We then present a variant that maintains the spirit of the original algorithm and appears to fix the nonconvergence. As a bonus, the new variant extends the Voronoi implicit interface method to unequal mobilities.

Oscillating Electric Fields in Liquids Create a Long-Range Steady Field.

We demonstrate that application of an oscillatory electric field to a liquid yields a long-range steady field, provided the ions present have unequal mobilities. The main physics is illustrated by a two-ion harmonic oscillator, yielding an asymmetric rectified field whose time average scales as the square of the applied field strength. Computations of the fully nonlinear electrokinetic model corroborate the two-ion model and further demonstrate that steady fields extend over large distances between two electrodes. Experimental measurements of the levitation height of micron-scale colloids versus applied frequency accord with the numerical predictions. The heretofore unsuspected existence of a long-range steady field helps explain several long-standing questions regarding the behavior of particles and electrically induced fluid flows in response to oscillatory potentials.

Migration and Development after 2015

In this paper, I will interrogate the new ‘Sustainable Development Goals’ (SDGs), with a view to understanding the place of migration therein. This analysis is undertaken for the purpose of anticipating (or forecasting) the unintended consequences of the inclusion of migration within this new development agenda. The key argument advanced in this paper is that the SDGs represent a normative framing of migration that sustains a problematic understanding of migration, and reproduces a vision of development that has long been implicated in the production of unequal and deleterious migrant mobilities. I show that while the SDGs redress the previous silence on migration in the Millennium Development Goals, they continue to normalize a problematic understanding of the role of migration in the global organisation of development. This will, in all likelihood, do little to transform the structural and political impediments to sustainable and equitable migrations, and thus deny the promises of development to many people on the move.

The Kirkendall effect in the phase field crystal model

The Kirkendall effect stems from unequal mobilities of atomic species, which give rise to a net flux of vacancies during interdiffusion in substitutional alloys. In this work, we study a simple binary phase field crystal model to include unequal atomic mobilities and demonstrate that the model captures many phenomena associated with the Kirkendall effect, including the center of mass motion, vacancy supersaturation that can lead to pore formation, and enhanced vacancy concentration near grain boundaries.

High‐resolution computer simulation of electrophoretic mobilization in isoelectric focusing

Cationic and anionic electrophoretic mobilization for focusing of hemoglobins (Hb's) in the presence of 100 carrier ampholytes covering a pI range of 6.00-7.98 was studied by computer simulation at a constant current density of 300 A/m(2). Electropherograms that would be produced by whole column imaging and by single detectors placed at different locations along the focusing column are presented. Upon mobilization, peak heights of the Hb zones decrease, but the zones retain a relatively sharp constant profile and are migrating at a constant velocity. A further peak decrease occurs during readjustment at the locations of the original buffer/column interfaces, indicating that detection sensitivity is the lowest at these locations. An anionic carrier ampholyte mobility smaller than that of its cationic species produces a cathodic drift which is smaller than the transport rate used for electrophoretic mobilization. Compared to the case with equal mobilities of carrier ampholyte species, a small increase (decrease) is predicted for the cationic (anionic) mobilization rate within the focusing column. Simulation data suggest that electrophoretic mobilization after focusing and focusing with concurrent electrophoretic mobilization are comparable isotachophoretic processes that occur when there is an uninterrupted flux of an ion through the focusing column. Cathodic drift caused by unequal mobilities of the species of carrier ampholytes, electrophoretic mobilization, and decomposition occurring at the pH gradient edges are related electrophoretic processes.

High‐resolution computer simulation of the dynamics of isoelectric focusing: In quest of more realistic input parameters for carrier ampholytes

The impact of the systematic variation of either DeltapK(a) or mobility of 140 biprotic carrier ampholytes on the conductivity profile of a pH 3-10 gradient was studied by dynamic computer simulation. A configuration with the greatest DeltapK(a) in the pH 6-7 range and uniform mobilities produced a conductivity profile consistent with that which is experimentally observed. A similar result was observed when the neutral (pI = 7) ampholyte is assigned the lowest mobility and mobilities of the other carriers are systematically increased as their pI's recede from 7. When equal DeltapK(a) values and mobilities are assigned to all ampholytes a conductivity plateau in the pH 5-9 region is produced which does not reflect what is seen experimentally. The variation in DeltapK(a) values is considered to most accurately reflect the electrochemical parameters of commercially available mixtures of carrier ampholytes. Simulations with unequal mobilities of the cationic and anionic species of the carrier ampholytes show either cathodic (greater mobility of the cationic species) or anodic (greater mobility of the anionic species) drifts of the pH gradient. The simulated cationic drifts compare well to those observed experimentally in a capillary in which the focusing of three dyes was followed by whole column optical imaging. The cathodic drift flattens the acidic portion of the gradient and steepens the basic part. This phenomenon is an additional argument against the notion that focused zones of carrier ampholytes have no electrophoretic flux.

Real-time small-angle x-ray scattering study of the early stage of phase separation in the SiO2-BaO-K2O system.

Time-resolved small-angle x-ray scattering was used to study the early stage of phase separation in a silicate system. Scattering patterns were acquired in real time as a sample was quenched in situ from a temperature ${\mathit{T}}_{1}$ in the single-phase region directly to a temperature ${\mathit{T}}_{2}$ in the two-phase region and held isothermally. This was made possible by using a high-intensity synchrotron x-ray source, a fast position-sensitive detector, a sample heater capable of rapid quenches, and a sample composition chosen to give good scattering contrast and relatively slow kinetics. The composition studied, 90 mol% ${\mathrm{SiO}}_{2}$, 5 mol% BaO, and 5 mol% ${\mathrm{K}}_{2}$O, undergoes subliquidus phase separation at temperatures below 1021 K to form alkali-oxide-rich and alkali-oxide-poor amorphous phases. The temperatures used were ${\mathit{T}}_{1}$=1074 K and ${\mathit{T}}_{2}$=1014, 995, 970, and 950 K. While the resultant data agree qualitatively with the linearized thermodynamics of the Cahn-Hilliard-Cook (CHC) theory of spinodal decomposition (i.e., the structure factor changes exponentially with time at each wave number), they do not agree with the simple diffusive kinetics used in the CHC theory. The data are in very good agreement with a modified theory incorporating diffusion-induced-flow (DIF) kinetics, in which one considers both the generation of stress arising from unequal mobilities of the diffusing species and the relaxation of this stress through deformation. Values of the material parameters as a function of temperature obtained from fits of the DIF theory to the data are in reasonable agreement with independent measurements and estimates based on a regular-solution model. For amorphous systems in particular, these results provide direct evidence that viscous flow is the rate-limiting step for the interdiffusion of network-forming and network-modifying species over the short length scales involved in the early stage of phase separation.

Aluminum Bromide‐1‐Methyl‐3‐Ethylimidazolium Bromide Ionic Liquids: II . Transport Numbers

The external transport numbers relative to a porous glass separator and the internal transport numbers relative to bromine were determined for the bromide room temperature ionic liquid at 60°C over the range of mole fractions, . The average external transport number of the 1‐methyl‐3‐ethylimidazolium cation was found to be , while the average internal transport number of this ion was found to be over this concentration range. However, the internal transport number of the cation was greater than this value for compositions in which and less than 1.01 in the range . These results suggest that the extant anions in each composition range may exhibit unequal mobilities.

Calculations of bipolar charging of aerosols

The acquisition of electric charge by the particles of an aerosol is a subject which heretofore has received only incomplete treatment, much of it based upon intuitive considerations. In this paper we present a rigorous treatment of the subject based upon the difference equations for charging of monodisperse and polydisperse aerosols in the presence of ions of both signs but unequal mobilities. The stochastic equations are written and the conditions of their solution are described for positive and negative small ions of mobilities 1.4 cm 2/V-sec and 1.9 cm 2/V-sec, respectively. Numerical calculations are presented of the time-dependent charge distributions and small ion number densities. Their relation to small-ion production, aerosol particle number concentration, and polydispersity is discussed. These results are compared where possible with calculated and experimental results of other workers. These calculations demonstrate for the first time that for bipolar charging a significant difference arises in polarity between the larger and smaller particle components of a polydisperse aerosol owing to unequal charging rates.

Precipitation and Dissolution Potentials of Electrolytes in D 2 O , Acetone, and Formamide

Precipitation, dissolution, diffusion, and phase potentials of , , and have been measured in , acetone, and formamide in nitrogen atmosphere. The techniques adopted were similar to those used previously by Rastogi and Shukla for , , , and in . The true dissolution and precipitation potentials were found to be negative for and in and (smaller numerically in the latter) and for in . However, the dissolution potential of and in acetone and formamide and of in acetone is positive and of higher magnitude. The temperature, concentration, and time dependence of the dissolution potentials have been investigated. The decay of the precipitation potential and of the apparent diffusion potential with time has been studied. The experimental results show that the precipitation potential increases with undercooling. The transport number of K+ and Br− in formamide has also been measured. The results support the hypothesis that the precipitation and dissolution potentials arise on account of the unequal mobilities of the ions moving to and away from the crystal face.

A Streamline Model for Secondary Recovery

Abstract A mathematical model particularly suitable for secondary recovery predictions is described. The model is based upon the flow lines generated by the superposition of line sources and sink solutions and is easily adaptable to arbitrary well patterns and fluid displacement mechanisms. Nonunity mobility ratios and reservoir stratification may be modeled. The model may be used with relatively small digital computing equipment. Previous models of this type have used the generated flow lines to outline "flow bundles", thus requiring a prior knowledge of the geometric shape of each of these bundles so that the flow through each could be computed. The modeling method described does not require any such prior knowledge of these flow lines since the volumetric flow in a stream bundle is computed as each chosen streamline is generated. This feature makes the model particularly adaptable to arbitrary well patterns. patterns. Examples are given to show the application of this model to both single and multiphase flow. Introduction Streamline models of secondary recovery projects result from the use of line source and sink solutions to the diffusivity equation to represent injection and production wells. Muskat described these solutions and their application to simplified problems. He used semi-analytic techniques to problems. He used semi-analytic techniques to obtain breakthrough sweep efficiencies for regular, dispersed injection patterns at a mobility ratio of 1. Collins described a finite-difference approximation for determining streamlines for unit mobility ratios in arbitrary well patterns. Both Muskat and Collins described image-well techniques for mathematically bounding the area being studied. Collins' finite-difference method is particularly adaptable to the use of a high-speed computer for obtaining streamlines and travel times along streamlines. Higgins and Leightons have described a technique for approximating the waterflood recovery of oil using streamlines generated by single-fluid how models (such as the method described by Collins). Their technique uses these streamlines to divide the total flow area into "stream channels", which flow in parallel between injection and production wells. Each stream channel is divided into a number of recovery rectilinear flow cells, in series, which closely approximate the shape of the stream channel. Through the use of shape factors determined for each flow cell, a Buckley and Leverett type of frontal displacement in each stream channel is computed. Combining the results from all stream channels gives the waterflood production history by this method. Once the stream channels, the flow cells, and the shape factors have been determined, a single computer program is used to obtain the production history. production history. Hauber has also described a method using stream channels formed by single-fluid streamlines. In this method, the cross-sectional area of each stream channel, as a function of length along a center streamline, is determined mathematically from the stream function, and an integration technique is used to determine the flow through each stream channel. Hauber applied this method to piston-like displacement in a five-spot injection piston-like displacement in a five-spot injection pattern. pattern. The stream-channel concept has been used and elaborated upon in subsequent publications dealing with the displacement of oil by fluids of unequal mobilities. This use of stream channels requires a prior knowledge of the single-fluid streamlines for the well spacing to be studied, so that flow cells and their shape factors, or the area functions of the channels, may be determined. The purpose of this paper is to describe a method which produces equivalent results but requires no prior knowledge of the streamlines or stream channels to be used. It is not necessary to know the eventual destinations of the "stream channels" in order to obtain production histories for arbitrary well patterns and either of the types of displacement patterns and either of the types of displacement mechanism mentioned above. SPEJ P. 7