Segregation Dynamics Research Articles

Spouting behavior of binary particle mixtures of different densities: Fluid dynamics and particle segregation

Numerous industrial applications of spouted beds involve a mixture of granular particles, where differences in particle size, density, and shape can cause particle segregation, affecting the quality of flow and decreasing product homogeneity. The aim of this study was to investigate the particle segregation and fluid dynamics of a conical spouted bed operating with a binary mixture of particles of different densities. Using glass beads and polyethylene particles with a diameter of 4mm, we determined the effects of the mass fraction of denser particles and static bed height on the minimum spouting condition and mixture index. The pressure drop and airflow in the minimum spouting condition increased with an increase in bed height or jetsam concentration. Regarding particle segregation, the jetsam particles tended to concentrate near the bottom, at the spout–annulus interface because they have a shorter trajectory than the lighter particles in the fountain region. Jetsam-rich mixtures with high initial static bed heights exhibited more efficient particle mixing, excluding those at the bottom of the bed.

Unravelling the demographic dynamics of ethnic residential segregation.

Selective intraurban migration of ethnic groups is often assumed to be the main microlevel mechanism reproducing ethnic residential segregation. However, other demographic processes, such as natural change and international migration, also matter. This paper contributes to the literature by unravelling the impacts of different demographic processes to changes in ethnic segregation. It uses longitudinal individual‐level register data on the complete population of the Helsinki region in Finland. We calculate observed changes in exposure indices, segregation indices in counterfactual scenarios, and decompositions of population changes. Results indicate that intraregional migration is the main process affecting segregation between Finnish‐origin and non‐Western‐origin populations, but whereas migration of the former increases segregation, migration of the latter decreases it. International migration and natural change among the non‐Western‐origin population are the main processes increasing exposure of the non‐Western‐origin population to other members of the group. No indication is found of a general tendency to “self‐segregate.”

Oracle Estimation of a Change Point in High-Dimensional Quantile Regression

ABSTRACTIn this article, we consider a high-dimensional quantile regression model where the sparsity structure may differ between two sub-populations. We develop ℓ1-penalized estimators of both regression coefficients and the threshold parameter. Our penalized estimators not only select covariates but also discriminate between a model with homogenous sparsity and a model with a change point. As a result, it is not necessary to know or pretest whether the change point is present, or where it occurs. Our estimator of the change point achieves an oracle property in the sense that its asymptotic distribution is the same as if the unknown active sets of regression coefficients were known. Importantly, we establish this oracle property without a perfect covariate selection, thereby avoiding the need for the minimum level condition on the signals of active covariates. Dealing with high-dimensional quantile regression with an unknown change point calls for a new proof technique since the quantile loss function is nonsmooth and furthermore the corresponding objective function is nonconvex with respect to the change point. The technique developed in this article is applicable to a general M-estimation framework with a change point, which may be of independent interest. The proposed methods are then illustrated via Monte Carlo experiments and an application to tipping in the dynamics of racial segregation. Supplementary materials for this article are available online.

From landscapes of utopia to the margins of the green urban life

Today, municipal decision-makers, planners, and investors rely on valuation studies of ecosystem services, public health assessments, and real estate projections to promote a consensual view of urban greening interventions such as new parks, greenways, or greenbelts as a public good with widespread benefits for all residents. However, as new green projects often anchor major investment and high-end development, we ask: Does the green city fulfil its promise for inclusive and far-reaching environmental, health, social, and economic benefits or does it create new environmental inequalities and green mirages? Through case examples of diverse urban greening interventions in cities reflecting different urban development trajectories and baseline environmental conditions and needs (Barcelona, Medellin, and New Orleans), we argue that urban greening interventions increasingly create new dynamics of exclusion, polarization, segregation, and invisibilization. Despite claims about the public good, these interventions take place to the detriment of the most socially and racially marginalized urban groups whose land and landscapes are appropriated through the creation of a ‘green gap’ in property markets. In that sense, green amenities become GreenLULUs (Locally Unwanted Land Uses) and socially vulnerable residents and community groups face a green space paradox, whereby they become excluded from new green amenities they long fought for as part of an environmental justice agenda. Thus, as urban greening consolidates urban sustainability and redevelopment strategies by bringing together private and public investors around a tool for marketing cities with global reach, it also negates a deeper reflection on urban segregation, social hierarchies, racial inequalities, and green privilege.

A piecewise smooth model of evolutionary game for residential mobility and segregation.

The paper proposes an evolutionary version of a Schelling-type dynamic system to model the patterns of residential segregation when two groups of people are involved. The payoff functions of agents are the individual preferences for integration which are empirically grounded. Differently from Schelling's model, where the limited levels of tolerance are the driving force of segregation, in the current setup agents benefit from integration. Despite the differences, the evolutionary model shows a dynamics of segregation that is qualitatively similar to the one of the classical Schelling's model: segregation is always a stable equilibrium, while equilibria of integration exist only for peculiar configurations of the payoff functions and their asymptotic stability is highly sensitive to parameter variations. Moreover, a rich variety of integrated dynamic behaviors can be observed. In particular, the dynamics of the evolutionary game is regulated by a one-dimensional piecewise smooth map with two kink points that is rigorously analyzed using techniques recently developed for piecewise smooth dynamical systems. The investigation reveals that when a stable internal equilibrium exists, the bimodal shape of the map leads to several different kinds of bifurcations, smooth, and border collision, in a complicated interplay. Our global analysis can give intuitions to be used by a social planner to maximize integration through social policies that manipulate people's preferences for integration.

Residential segregation and clustering dynamics of migrants in the metropolitan area of Barcelona

Abstract
 During the first decade of the 21st century, the Metropolitan Region of Barcelona underwent an enormous demographic transformation following the arrival of more than 300’000 foreign immigrants. The residential patterns resulting from the settlement of the newcomers drastically changed the composition of the human landscape at all territorial levels, both national and local, confronting policy makers and migration managers with the tremendous challenge of managing the increasing population diversity. Within this context, two linked phenomena are perceived as particularly relevant for social cohesion: (i) the degree of residential segregation between different population groups and (ii) the spatial concentration of the newcomers. To assess the degree and trend of spatial assimilation of different immigrant groups and the process of formation of areas of concentration and their evolution over time, we combine the analysis of residential segregation at the metropolitan level with the application of the local indicator of spatial association (Moran’s I), which allows us to locate areas of residential clustering at the census tract level. Our results show the coexistence of a general trend towards the spatial assimilation of foreign-born populations at the regional level (except for Western Europeans), along with the consolidation, and even extension, of ethnic concentrations at the local level.
 Résumé
 Au cours de la première décennie du 21ème siècle, la région métropolitaine de Barcelone a subi une énorme transformation démographique suite à l’arrivée de plus de 300 000 immigrants étrangers. Les schémas résidentiels résultant de l’ins­tallation des nouveaux arrivants ont considérablement modifié la composition du paysage humain à tous les niveaux territoriaux, nationaux et locaux, confrontant les décideurs et les gestionnaires des migrations à l’énorme défi de gérer la diversité démographique croissante. Dans ce contexte, deux phénomènes liés sont perçus comme particulièrement pertinents pour la cohésion sociale : (i) le degré de ségrégation résidentielle entre différents groupes de population et (ii) la concentration spatiale des nouveaux arrivants. Pour évaluer le degré et les tendances de l’assimi­lation spatiale des différents groupes d’immigrants et le processus de formation des aires de concentration et leur évolution dans le temps, nous combinons l’analy­se de la ségrégation résidentielle au niveau métropolitain avec l’indicateur de Moran d’association spatiale au niveau local, ce qui nous permet de localiser les zones de regroupement résidentiel au niveau des secteurs de recensement. Nos résultats montrent une tendance générale vers l’assimilation spatiale des populations nées à l’étranger au niveau régional (sauf pour les Européens de l’Ouest), simultanément à la consolidation, voire l’extension, des concentrations ethniques au niveau local.

Self-organization in a bimotility mixture of model microswimmers.

We study the cooperation and segregation dynamics in a bimotility mixture of microorganisms which swim at low Reynolds numbers via periodic deformations along the body. We employ a multiparticle collision dynamics method to simulate a two component mixture of artificial swimmers, termed as Taylor lines, which differ from each other only in the propulsion speed. The analysis reveals that a contribution of slower swimmers towards clustering, on average, is much larger as compared to the faster ones. We notice distinctive self-organizing dynamics, depending on the percentage difference in the speed of the two kinds. If this difference is large, the faster ones fragment the clusters of the slower ones in order to reach the boundary and form segregated clusters. Contrarily, when it is small, both kinds mix together at first, the faster ones usually leading the cluster and then gradually the slower ones slide out thereby also leading to segregation.

Nucleoid Segregation Dynamics and its Variability in Dividing and Filamentous E. Coli

Segregation of the replicating chromosome from a single to two nucleoid bodies is one of the major processes in growing bacterial cells. It is tightly correlated with cell growth and division and this correlation is crucial for cell viability. The mechanism of segregation is still enigmatic: although it is believed that the underlying driving force is purely thermodynamic, it is obvious that the segregation dynamics is tuned by intricate interactions with other cellular processes. These interactions serve for flexibility in a changing environment and may possibly be the source of cell-to-cell phenotypic variability. We exploited the advantage of the chromosomally encoded HU-eGFP to monitor nucleoid segregation in live E. coli cells using time-lapse microscopy. The cells were grown in linear grooves formed in the agarose gel pad, convenient for the image processing of fluorescence intensity profiles along individual cell lineages. Analysis of these profiles produced nucleoid localization trajectories for each cell lineage and was used to obtain the main characteristics of the segregation process, namely, the start of partitioning, rates of separation and final positions, as well as variability of these characteristics throughout the population. Moreover, the same characteristics were determined for non-dividing, filamentous cells growing under the same conditions. Comparison between dividing and filamentous cells is aimed to reveal the involvement of physical boundaries and diffusion barriers in the control of nucleoid segregation dynamics. Our findings shed light on the role of these factors both in the mechanism of segregation and its variability in bacterial cells.

Schelling-type micro-segregation in a Hassidic enclave of Stamford-Hill

This study examines how non-economic inter- and intra-group relationships are reflected in residential pattern, uses a mixed methods approach designed to overcome the principal weaknesses of existing data sources for understanding micro residential dynamics. Micro–macro qualitative and quantitative analysis of the infrastructure of residential dynamics offers a holistic understanding of urban spaces organized according to cultural codes. The case study, the Haredi community, is composed of sects, and residential preferences of the Haredi sect members are highly affected by the need to live amongst ‘friends’ – other members of the same sect. Based on the independent residential records at the resolution of a single family and apartment that cover the period of 20 years the study examine residential dynamics in the Hassidic area of Stamford-Hill, reveal and analyze powerful Schelling-like mechanisms of residential segregation at the apartment, building and the near neighbourhood level. Taken together, these mechanisms are candidates for explaining the dynamics of residential segregation in the area during 1995–2015.

Atomic segregation: Activity at the surface.

In situ transmission electron microscopy resolves atomic structures and dislocation dynamics of surface segregation, providing insights that open a pathway to new advances in interface engineering.

A multi-scaled agent-based model of residential segregation applied to a real metropolitan area

Residential segregation influences many aspects of urban life. It affects people's access to centres of education, healthcare, business and determines the composition of our neighbourhoods, thereby impacting our social network and urban structure. In order to understand the potential impact of policies on residential segregation and complex urban system, a dynamic modelling support tool would be essential. This research article presents a multi-scaled agent-based model capable of simulating the relocation of residents of a representative population of a large urban area in a realistic environment for investigating the dynamics of residential segregation. Using an experiment, we show that this data-driven model can replicate plausible residential distribution and segregation patterns observed in the Auckland region (New Zealand's metropolis). Simulation outcomes are promising, demonstrating the potential of the model for investigating practical policy-relevant questions and acquiring valuable insights into the future state of the urban mosaic landscape and causes behind residential segregation dynamics.

Alternating Dynamics of Segregation and Integration in Human EEG Functional Networks During Working-memory Task

Brain functional networks show high variability in short time windows but mechanisms governing these transient dynamics remain unknown. In this work, we studied the temporal evolution of functional brain networks involved in a working memory (WM) task while recording high-density electroencephalography (EEG) in human normal subjects. We found that functional brain networks showed an initial phase characterized by an increase of the functional segregation index followed by a second phase where the functional segregation faded after the prevailing the functional integration. Notably, wrong trials were associated with different or disrupted sequences of the segregation-integration profiles and measures of network centrality and modularity were able to identify crucial aspects of the oscillatory network dynamics. Additionally, computational investigations further supported the experimental results. The brain functional organization may respond to the information processing demand of a WM task following a 2-step atomic scheme wherein segregation and integration alternately dominate the functional configurations.

Is Aggregate-Dependent Yeast Aging Fortuitous? A Model of Damage Segregation and Aggregate Dynamics

During cytokinesis in Saccharomyces cerevisiae, damaged proteins are distributed unequally between the daughter and mother cells. The retention of these proteins is correlated with yeast aging. Even though evidence suggests that aggregates are retained due to an underlying molecular mechanism, the debate on whether an active mechanism is necessary for this asymmetry remains unsolved. In particular, passive diffusion and a bud-specific dilution remain as possible explanations. Here, a computational and mathematical model is provided to test whether passive mechanisms alone are sufficient to account for the aggregate distribution patterns and the aggregate kinetics observed in living cells. To this author’s knowledge, this is the most comprehensive model available on this subject and the only one combining key potentially essential passive-only mechanisms proposed in existing bibliography—namely, the geometrical effect of the dividing yeast cell on the diffusion of protein aggregates, and the possibility of aggregate binding and aggregate formation at different rates. Results suggest that although passive processes alone can reproduce certain averaged observables from experimental bibliography, they are insufficient to vindicate aggregate activity observed in living budding yeast cells. These results are complemented by showing that under basic forms of active quality control, discrepancies between the outputs of the model and experimental bibliography are reduced.

DEM study of the size-induced segregation dynamics of a ternary-size granular mixture in the rolling-regime rotating drum

Segregation induced by size, shape, or density difference of the granular material is inevitable in both natural and industrial processes; unfortunately, the underlying mechanism is still not fully understood. In view of the ubiquitous continuous particle size distributions, this study builds on the considerable knowledge gained so far from binary-size mixtures and extends it to a ternary-size mixture to understand the impact of the presence of a third particle size in the three-dimensional rotating drum operating in the rolling flow regime. The discrete element method is employed. The evolution of segregation, the active-passive interface, and the dynamical response of the particle-scale characteristics of the different particle types in the two regions are investigated. The results reveal that the medium particles are spatially sandwiched in between the large and small particles in both the radial and axial directions and therefore exhibit behaviors intermediate to the other two particle types. Compared to the binary-size mixture, the presence of the medium particles leads to (i) higher purity of small particles in the innermost of the radial core, causing a decrease of the translational velocity of small particles; (ii) decrease and increase of the collision forces exerted on, respectively, the large and small particles in both regions; and (iii) increase in the relative ratio of the active-passive exchange rates of small to large particles. The results obtained in the current study therefore provide valuable insights regarding the size-segregation dynamics of granular mixtures with constituents of different sizes.

Racial residential segregation in multiple neighborhood markets: a dynamic sorting study

Various degrees of residential segregation by income and race generally exist in U.S. cities. This study extends Sethi and Somanathan’s theoretical model (J Polit Econ 112:1296–1321, 2004) by presenting an agent-based sorting, repeated-game model to quantify the patterns of segregation from a broader perspective. Based on the belief that residential racial segregation is a probabilistic problem without assured results, a numerical model—calibrated to U.S. household income data—is proposed to examine residential segregation by income and racial preferences. Similar to the SimSeg model developed by Fosset (J Math Sociol 30:185–274, 2006a; J Math Sociol 35:114–145, 2011), the numerical model we construct is based on a simple format which also explores segregation dynamics. The simulation results exhibit various degrees of segregation probability in a hypothetical three-neighborhood scenario. It also reveals that although income plays an important role, racial consciousness—the measurement of an agent’s attitude toward the racial composition of the neighborhood—is the dominant factor in determining residential segregation.

The Strata-1 experiment on small body regolith segregation

The Strata-1 experiment studies the mixing and segregation dynamics of regolith on small bodies by exposing a suite of regolith simulants to the microgravity environment aboard the International Space Station (ISS) for one year. This will improve our understanding of regolith dynamics and properties on small asteroids, and may assist in interpreting analyses of samples from missions to small bodies such as OSIRIS-REx, Hayabusa-1 and -2, and future missions to small bodies. The Strata-1 experiment consists of four evacuated tubes partially filled with regolith simulants. The simulants are chosen to represent models of regolith covering a range of complexity and tailored to inform and improve computational studies. The four tubes are regularly imaged while moving in response to the ambient vibrational environment using dedicated cameras. The imagery is then downlinked to the Strata-1 science team about every two months. Analyses performed on the imagery includes evaluating the extent of the segregation of Strata-1 samples and comparing the observations to computational models. After Strata-1's return to Earth, x-ray tomography and optical microscopy will be used to study the post-flight simulant distribution. Strata-1 is also a pathfinder for the new “1E” ISS payload class, which is intended to simplify and accelerate emplacement of experiments on board ISS.

Numerical study on the axial segregation dynamics of a binary-size granular mixture in a three-dimensional rotating drum

Granular materials are ubiquitous in our daily life and inherent in multitudinous industrial processes. Differences in the granular properties such as size and density inevitably induce segregation. By means of the discrete element method, a binary-size mixture in a three-dimensional rotating drum is numerically simulated to explore the segregation dynamics of the granular material along the axial direction. Snapshots of the distribution of the two particle types in the rotating drum are presented with respect to time to illustrate the spatial evolution of the size-induced segregation structure. The space-time plots of various axial characteristics indicate that (i) radial segregation does not affect the axial distribution of total mass and mass fraction, but axial segregation leads to the formation of axial bands; (ii) greater non-dimensionalized collision forces for both the large and small particles develop where the large particles dominate; and (iii) axial segregation gives rise to the variation of the gyration radii of both particle types along the drum length. In addition, axial flow of both particle types in both directions indicates the dynamic axial exchanges, and the effect of the end walls on the axial flow direction is limited to less than 25% of the drum length from the end walls.

Immigration and Neighborhood Change: Methodological Possibilities for Future Research

The recent settlement of immigrant populations into a wider range of geographies and communities across the United States raises new questions about the dynamics of residential segregation and complicates assumptions about how neighborhoods change—or don't—and why. While multiple theories attempt to explain the relationship between race/ethnicity, immigration, and neighborhood change, sociological examinations have been limited by the lack of systematic and frequently collected data. That is, the residential churn of neighborhoods, particularly in the market for rental housing where racial/ethnic minorities and immigrants predominate, often outpaces analysts’ ability to gather cross–neighborhood and cross–city data. In this essay we describe how online sources can help answer questions about race/ethnicity, immigration, and neighborhoods by providing large amounts of readily updatable data. An array of platforms designed to provide homeseekers with information about their housing options can also be used by sociologists for making claims about neighborhood change across multiple geographies. We review recent research that uses online data and describe an ongoing study by the authors that examines trends in the settlement patterns of immigrants and the rental housing market across the 50 largest MSAs in the United States. Online data sources can more accurately capture immigration and neighborhood processes, yielding better theories about the impact of immigration on neighborhood change.

Segregation dynamics of a binary-size mixture in a three-dimensional rotating drum

The knowledge of the granular segregation phenomenon induced by size or density differences in the ubiquitous polydisperse systems is important, hence numerous studies have focused on this for the simple yet practical rotating drum. However, in view of the distinctly different characteristics of the two regions (namely, active and passive) for a drum operated in the rolling regime, an understanding of the segregation dynamics in each region is warranted, but remains a gap to date. Accordingly, this study aimed at numerically studying the segregation dynamics of the solid phase in a three-dimensional rotating drum consisting of a binary-size mixture via the Discrete Element Method (DEM). The results demonstrate that the total kinetic energy, the angle of repose, the time-averaged streamwise (i.e., parallel to the bed surface) velocity and the position of the active-passive interface are global parameters, which are not influenced by size-segregation and thereby provides a critical basis for comparing different systems of various polydispersities. Also, the quick onset of the rapid radial segregation leads to sharp initial changes of the variables associated with the two particle types, after which the slow axial segregation leads to a gradual change of these variables over time. Furthermore, size-segregation leads to the redistribution of the particle number of the two particle types in the active and passive regions. Relative to the monodisperse system, the collision forces exerted on the small and large particles are slightly higher and lower, respectively. The results here provide important insights on the dynamics associated with the inevitable segregation phenomenon, which contributes to better operation and predictive capability of the rotating drum.

Propuestas para el desarrollo de la interculturalidad en la educación en el tiempo libre de base comunitaria en Cataluña

INTRODUCTION. The educational programmes carried out during leisure time and with a community approach played an important role in the development of social cohe¬sion in Catalonia. In this paper the value of this contribution is recognized, but at the same time, the existence of educational concentration and segregation dynamics is identified as a problem for interculturality. For this reason, some proposals presented here can help these organizations to manage interculturally their projects, for example, reflecting the sociocultur¬al diversity of the community within they are developed. METHOD. The framework of this paper is a research project oriented to contribute to the strengthening of intercultural vision in this context. The goals were: identify organizational and educational conditions which fa¬cilitate or not the development of interculturality; and, make proposals for their sustainability or improvement. Some qualitative technics were used to collect data: documentary analysis, semi-structured interviews and discussion groups. And Atlas-Ti program, as well as, discourse critical analysis procedure were used to analyse the data. RESULTS. The results pointed out that, even though there are advantageous and disadvantageous conditions to interculturality, those that restrict the sociocultural diversity of participants influence more. And it was con¬firmed that educational teams have not developed, or very little, their community dimension. DISCUSSION. On the basis of the results obtained and the literature reviewed is suggested, on one hand, the impulse of some organizational actions oriented to participation, diversity attention and training actions. On the other, it is noted the appropriateness of designing and launching actions, together with the educational community, to manage the existence of over-representation of some sociocultural profiles among participants, and finally, it is pro¬posed the constitution of diversity attention’ community teams to manage interculturality among educational community and oriented to overcome the concentration and segregation educational dynamics.