Segregation Dynamics Research Articles

The studies of ParA and ParB dynamics reveal asymmetry of chromosome segregation in mycobacteria.

Active segregation of bacterial chromosomes usually involves the action of ParB proteins, which bind in proximity of chromosomal origin (oriC) regions forming nucleoprotein complexes - segrosomes. Newly duplicated segrosomes are moved either uni- or bidirectionally by the action of ATPases - ParA proteins. In Mycobacterium smegmatis the oriC region is located in an off-centred position and newly replicated segrosomes are segregated towards cell poles. The elimination of M. smegmatis ParA and/or ParB leads to chromosome segregation defects. Here, we took advantage of microfluidic time-lapse fluorescent microscopy to address the question of ParA and ParB dynamics in M. smegmatis and M. tuberculosis cells. Our results reveal that ParB complexes are segregated in an asymmetrical manner. The rapid movement of segrosomes is dependent on ParA that is transiently associated with the new pole. Remarkably in M. tuberculosis, the movement of the ParB complex is much slower than in M. smegmatis, but segregation as in M. smegmatis lasts approximately 10% of the cell cycle, which suggests a correlation between segregation dynamics and the growth rate. On the basis of our results, we propose a model for the asymmetric action of segregation machinery that reflects unequal division and growth of mycobacterial cells.

Is There a Jump in the Transition?

This article develops a statistical test for the presence of a jump in an otherwise smooth transition process. In this testing, the null model is a threshold regression and the alternative model is a smooth transition model. We propose a quasi-Gaussian likelihood ratio statistic and provide its asymptotic distribution, which is defined as the maximum of a two parameter Gaussian process with a nonzero bias term. Asymptotic critical values can be tabulated and depend on the transition function employed. A simulation method to compute empirical critical values is also developed. Finite-sample performance of the test is assessed via Monte Carlo simulations. The test is applied to investigate the dynamics of racial segregation within cities across the United States.

Crisis, Urban Segregation and Social Innovation in Catalonia

This paper questions the contribution of social innovation to the capacity of disadvantaged communities to resist the effects of the 2008 financial crisis and its social repercussions. It does so on the basis of a study on the dynamics of urban segregation and social innovation in the context of the crisis in Catalonia (Spain). The study adopts a multi-method approach that combines statistical analysis of urban segregation dynamics in the 2001-2012 period; the mapping of social innovation practices across the region; and a cross-case comparison of six case studies. The paper highlights the structural and metropolitan character of urban segregation in the region, which has been significantly aggravated both by the crisis and the residential transformation that occurred during the years of the housing bubble. It also shows that social innovation practices are distributed very unevenly in spatial terms, being concentrated in middle-income areas with a tradition of social mobilisation. In summary, the paper states the limits of social innovation as a driver for socio-spatial cohesion in cities and stresses the need for stronger (redistributive) public policies.

Photocurrent imaging of phase segregation in a ternary polymer blend induced via a non-solvent route

Control of phase separation length scales of polymers in a solution-processed film of binary (two-component) polymer blends is the most important step to realize significant photocharge generation and transport efficiencies leading to efficient solar cells. The dynamics of phase segregation becomes more complex in ternary (three-component) polymer blends. In the three-component blend, one component serves as sensitizer, and other two act as donor and acceptor polymer. The sensitizer absorbs photons and the energy is quickly transferred to the host donor. Subsequently, efficient charge transfer occurs at the host donor/acceptor interface. Depending on the relative amount of phase segregation between sensitizer/donor, sensitizer/acceptor and donor/acceptor, the different photophysical mechanisms (viz. energy transfer and charge transfer) are either boosted or suppressed. The correct kind of morphology should allow efficient energy transfer at the sensitizer/donor interface followed by efficient charge transfer at the donor/acceptor interface. We attempt to address these requirements by modulating the nanomorphology of a ternary blend via tailoring the non-solvent concentration in the ternary polymer blend solution. Here, we study the effect of non-solvent mixing and resultant film morphology is characterized by wide-field local photocurrent imaging and photoluminescence imaging in a confocal microscope set-up.

Temporal dynamics of racial segregation in the United States: An analysis of household residential mobility

ABSTRACTThis is the first study of temporal segregation dynamics based on the full analysis of household residential mobility, including non-moves and intra- and inter-neighborhood moves in the United States over the last four decades (1971–2009). Analysis results demonstrate the decreases in both white flight and white avoidance over time. Whites stayed shorter in black-white neighborhoods than in predominantly white neighborhoods until 1990, but this has been no longer significant during the past two decades. The tendency that whites are less likely to move to racially homogeneous neighborhoods than moving within or across racially mixed neighborhoods was significant only after 1990. These two results explain the aggregate-level segregation trend that black-white neighborhoods have experienced the most significant drop in the probability of transitioning into racially homogeneous neighborhoods and that the share of racially mixed neighborhoods has significantly increased over time. Analysis results further suggest that increasing racial diversity and the reduction in racial segregation in metropolitan areas have likely contributed to changes in whites’ residential mobility.

Multilocus Imaging of the E. coli Chromosome by Fluorescent In Situ Hybridization.

Fluorescence in situ hybridization (FISH) is a widely used technique to detect and localize specific DNA or RNA sequences in cells. Although supplanted in many ways by fluorescently labeled DNA binding proteins, FISH remains the only cytological method to examine many genetic loci at once (up to six), and can be performed in any cell type and genotype. These advantages have proved invaluable in studying the spatial relationships between chromosome regions and the dynamics of chromosome segregation in bacteria. A detailed protocol for DNA FISH in E. coli is described.

Dynamics of granular segregation in quasi two-dimensional system

Segregation during flow of granular materials is important from an industrial point of view. Considerable work has been done on granular segregation in heap flows by continuous pouring. We studied the flow and segregation of granular mixtures during heap formation in a quasi two-dimensional rectangular bin by intermittent pouring. The heap formed by repeatedly pouring a fixed mass of the mixture. Each feeding results in the formation of a layer of the mixture on the surface of the heap. The system is a simplified model for the feeding of raw materials to a blast furnace, which is widely used for the manufacture of iron and steel. Experiments were carried out to study the dynamics of granular materials during heap formation. The number density, area fraction and average velocity of small and big particles are plotted across the flowing depth with time. Results shows that larger particles are always on top flowing over small particles. During flow small particles easily percolate through the gaps between the large particles. A thin layer of small particles is also observed at the free surface. Here the system never reached a steady state as we are pouring the mixture intermittently and system is closed. The velocity increases initially and then decreases towards the end. The number density (i.e. area fraction) profile changes for small and big particles during flow. Image analysis is done to detect the position of each particle on the side wall. Each experiment is repeated six times to get average data.

Generadores y transversalidad del discurso sobre inmigración en el ámbito metropolitano de Sevilla

Problems related to immigrant integration reveal the importance of developing a holistic analysis of the underlying dynamics of residential mobility, segregation and integration. In this sense, aspects such as discourse analysis can represent an important contribution to both the analysis of causes and consequences of residential segregation, as to a proper design of inclusive immigration public policy. Through a qualitative analysis, this study focuses on the development of a social discourse, along with its expansion and effects on immigration in Seville´s Metropolitan Area. The results show that, despite the important role of the media in the diffusion of this speech, other factors such as the vision of residents and former residents, or occasional travel, should be taken into account to understand how immigration imaginary and the role it plays in the integration and residential segregation, is built.

Simulation of size segregation in granular flow with material point method

Segregation is common in granular flows consisting of mixtures of particles differing in size or density. In gravity-driven flows, both gradients in total pressure (induced by gravity) and gradients in velocity fluctuation fields (often associated with shear rate gradients) work together to govern the evolution of segregation. Since the local shear rate and velocity fluctuations are dependent on the local concentration of the components, understanding the co-evolution of segregation and flow is critical for understanding and predicting flows where there can be a variety of particle sizes and densities, such as in nature and industry. Kinetic theory has proven to be a robust framework for predicting this simultaneous evolution but has a limit in its applicability to dense systems where collisions are highly correlated. In this paper, we introduce a model that captures the coevolution of these evolving dynamics for high density gravity driven granular mixtures. For the segregation dynamics we use a recently developed mixture theory (Fan & Hill 2011, New J. Phys; Hill & Tan 2014, J. Fluid Mech.) which captures the combined effects of gravity and fluctuation fields on segregation evolution in high density granular flows. For the mixture flow dynamics, we use a recently proposed viscous-elastic-plastic constitutive model, which can describe the multi-state behaviors of granular materials, i.e. the granular solid, granular liquid and granular gas mechanical states (Fei et al. 2016, Powder Technol.). The platform we use for implementing this model is a modified Material Point Method (MPM), and we use discrete element method simulations of gravity-driven flow in an inclined channel to demonstrate that this new MPM model can predict the final segregation distribution as well as flow velocity profile well. We then discuss ongoing work where we are using this platform to test the effectiveness of particular segregation models under different boundary conditions.

Scalar mixing and strain dynamics methodologies for PIV/LIF measurements of vortex ring flows

Fluid mixing operations are central to possibly all chemical, petrochemical, and pharmaceutical industries either being related to biphasic blending in polymerisation processes, cell suspension for biopharmaceuticals production, and fractionation of complex oil mixtures. This work aims at providing a fundamental understanding of the mixing and stretching dynamics occurring in a reactor in the presence of a vortical structure, and the vortex ring was selected as a flow paradigm of vortices commonly encountered in stirred and shaken reactors in laminar flow conditions. High resolution laser induced fluorescence and particle imaging velocimetry measurements were carried out to fully resolve the flow dissipative scales and provide a complete data set to fully assess macro- and micro-mixing characteristics. The analysis builds upon the Lamb-Oseen vortex work of Meunier and Villermaux [“How vortices mix,” J. Fluid Mech. 476, 213–222 (2003)] and the engulfment model of Baldyga and Bourne [“Simplification of micromixing calculations. I. Derivation and application of new model,” Chem. Eng. J. 42, 83–92 (1989); “Simplification of micromixing calculations. II. New applications,” ibid. 42, 93–101 (1989)] which are valid for diffusion-free conditions, and a comparison is made between three methodologies to assess mixing characteristics. The first method is commonly used in macro-mixing studies and is based on a control area analysis by estimating the variation in time of the concentration standard deviation, while the other two are formulated to provide an insight into local segregation dynamics, by either using an iso-concentration approach or an iso-concentration gradient approach to take into account diffusion.

Learning How to Squat: Cooperation and Conflict between Refugees and Natives in Rome

This article investigates the relationship between refugees’ integration and residential segregation by analysing Eritreans’ participation in local squatting practices in Rome. While it has often been assumed that residential concentration is linked to lack of participation in wider society, this case study points to counterintuitive implications of integration and segregation dynamics. After revisiting the relevant debate with specific focus on socialization and agency, I illustrate that, on the one hand, these housing practices are instances of cooperation between refugees and natives—specifically, within the frame of the local housing rights movement. On the other hand, I highlight how Eritrean involvement in squatting practice has also led to spontaneous segregation and ongoing mistrust towards local society. Considering refugees’ own agency, even under deprived circumstances, is of crucial importance to understanding both how different aspects of housing segregation and local integration are produced and, the conditions under which cooperation between refugees and local squatters is established and, in some instances, interrupted.

Controlling segregation speed of entangled polymers by the shapes: A simple model for eukaryotic chromosome segregation.

We report molecular dynamics simulations of the segregation of two overlapping polymers motivated by chromosome segregation in biological cells. We investigate the relationship between polymer shapes and segregation dynamics and show that elongation and compaction make entangled polymers segregate rapidly. This result suggests that eukaryotic chromosomes take such a characteristic rod-shaped structure, which is induced by condensins, to achieve rapid segregation.

Breaking Resilient Patterns of Inequality in Santiago de Chile: Challenges to Navigate towards a More Sustainable City

Resilience can have desirable and undesirable consequences. Thus, resilience should not be viewed as a normative desirable goal, but as a descriptor of complex systems dynamics. From this perspective, we apply resilience thinking concepts to assess the dynamics of inequality, spatial segregation, and sustainability in Chile’s capital city of Santiago. Chile’s economy boosted since democracy was restored in 1990, but continuity of neoliberal reforms and transformations of Pinochet’s dictatorship (1973–1990) seem to have locked Chilean cities in resilient, albeit unsustainable, patterns of uneven development. Socio-economic data from Santiago shows highly resilient patterns of urban inequality and segregation from 1992 to 2009 despite democratic efforts, political agendas and discourses packed with calls for reducing poverty and inequality. We present a conceptual model based on the notion of stability landscapes to explore potential trade-offs between resilience and sustainable development. We mapped Santiago’s spatio-temporal inequality trends and explored if these patterns support an inequality-resilience stability landscape. Analysis of temporal and spatial distribution of development assets across four human development dimensions (i.e., income, education, health, democracy) revealed potential socio-political and spatial feedbacks supporting the resilience of inequality and segregation in Santiago. We argue that urban sustainability may require breaking this resilience, a process where bottom-up stressors such as social movements could play a key role.

Segregasi Gender dalam Organisasi Spasial Pesantren-Pesantren Besar di Pulau Jawa

The presence of female santris in big pesantren in Java, which started around 1930, demanded the organization of spatial patterns related to intergender relations in the form of a segregation of activity zones between male and female santris. This study assesses the dynamics of gender segregation in the spatial organization of 18 big pesantren located on Java Island since their establishment until now. The data were collected through field observation, interviews and study of historical documents. The results show that gender segregation in the spatial organization of the pesantren is manifested through the concepts of gender specific zones, territoriality, and boundary. Levels of tolerance and flexibility towards gender segregation are observed within the formal activity zone (madrasah or school), but not in non-formal (boarding houses) and informal (playgrounds, sports, recreation and social activities) zones. Big pesantren in West Java show the highest degree of tolerance towards gender segregation in formal activity zones, followed by big pesantren in Central Java, and lastly by those in East Java. The Kyai as a charismatic leader, policy creator, and decision maker for the interests and benefits of the pesantren, has a significant influence on the level of tolerance of the pesantren as an institution towards gender segregation between male and female santris in the formal activity zone (madrasah or school).

Evolutionary dynamics of cytoplasmic segregation and fusion: Mitochondrial mixing facilitated the evolution of sex at the origin of eukaryotes

Sexual reproduction is a trait shared by all complex life, but the complete account of its origin is missing. Virtually all theoretical work on the evolution of sex has been centered around the benefits of reciprocal recombination among nuclear genes, paying little attention to the evolutionary dynamics of multi-copy mitochondrial genomes. Here I develop a mathematical model to study the evolution of nuclear alleles inducing cell fusion in an ancestral population of clonal proto-eukaryotes. Segregational drift maintains high mitochondrial variance between clonally reproducing hosts, but the effect of segregation is opposed by cytoplasmic mixing which tends to reduce variation between cells in favor of higher heterogeneity within the cell. Despite the reduced long-term population fitness, alleles responsible for sexual cell fusion can spread to fixation. The evolution of sex requires negative epistatic interactions between mitochondrial mutations under strong purifying selection, low mutation load and weak mitochondrial-nuclear associations. I argue that similar conditions could have been maintained during the late stages of eukaryogenesis, facilitating the evolution of sexual cell fusion and meiotic recombination without compromising the stability of the emerging complex cell.

A Divided Capital: Residential Segregation In Ankara

Turkey has undergone large-scale structural changes in social, political, and economic spheres in 2000s. In changing political climate of 2000s, not only social and political geographies, but also residential patterns of cities have been subject to abrupt changes. The development of construction sector reached a speed never seen before in country’s urbanisation history. Growing numbers of transformation and renewal projects took place mainly in older and historical central areas and former gecekondu sites of many greater cities. The relationship of new “upper” and “lower” classes both with rest of society and city has also radically changed. But, despite dynamism of this new era, our knowledge about extent of this transformation process is still relatively poor. Our knowledge on bases, scale and possible impacts of this transformation is still limited and partial. On these grounds, this article attempts to understand of this transformation process in year of 2000 through socio-economic residential segregation in capital city of Turkey, Ankara, where this transformation process is heavily felt. It is claimed that as one of most debated issues in Turkish public agenda, examining segregation in analytical ways can provide useful insights and valuable clues as to understanding socio-economic structure of cities. The findings of study show that Ankara is a highly divided city in socio-economic lines and urban dynamics of recent years are highly correlated with characteristic divisions of city. The study, in this sense, not only provides an extended look into segregation dynamics of city, but also sheds light on the roots of this active and dynamic period of 2000s, and thereby reveals last picture of city before great transformation . Key words: Socio-economic segregation, residential segregation, status groups, transformation, Ankara.

Changes in the ethnic composition of neighbourhoods: Analysis of household's response and asymmetric preference structures

AbstractTheoretical models of ethnic residential segregation indicate asymmetries in preferences as the key driver of ethnic segregation dynamics. This study uses a pivoted choice experiment to empirically analyse the asymmetric preference structures for ethnic composition of neighbourhoods. We assume that the utilities of various alternative residential locations are dependent on the experienced levels of co‐ethnics or ethnic minorities in the current neighbourhood of residence, where the increases in current ethnic concentrations could be evaluated differently than decreases. Results from a discrete choice model estimated on data from Swiss city of Lugano confirm the existence of asymmetries, showing that individuals tend to be averse to decreases in the share of their co‐nationals, while being indifferent to any increases.

PRÁTICAS DE SEGREGAÇÃO E RESISTÊNCIA NAS ORGANIZAÇÕES: UMA ANÁLISE DISCURSIVA SOBRE OS "ROLEZINHOS" NA CIDADE DE BELO HORIZONTE (MG)

RESUMO Objetivo: O objetivo do artigo é compreender como os discursos da mídia eletrônica apresentam reflexos e refrações das práticas de resistência dos jovens nos espaços organizacionais dos shopping centers. Essas práticas são denominadas atualmente "rolezinhos". Originalidade/lacuna/relevância/implicações: Considerando os espaços urbanos produzidos socialmente e as cidades como palcos práticos e discursivos de dinâmicas simbólicas segregatórias, analisamos os processos de ocupação dos shopping centers - intitulados pela mídia eletrônica de "rolezinhos" - na cidade de Belo Horizonte, em Minas Gerais, por jovens da periferia. Principais aspectos metodológicos: Adotamos a análise de discurso francesa como base metodológica da pesquisa. Ocorpus de análise é constituído por discursos presentes em 15 portais eletrônicos de notícias sobre a cidade de Belo Horizonte, em Minas Gerais, que produziram, durante o ano de 2013, 18 reportagens sobre a ocupação coletiva de shopping centers por jovens da periferia. Síntese dos principais resultados: As práticas de resistência ampliam as fronteiras dos espaços organizacionais, na medida em que deslocam pontos de controle das ações dos sujeitos e questionam a construção do shopping center como espaço organizacional de segregação avesso a grupos sociais desfavorecidos, enfatizando o potencial de resistência e de ressignificação de grupos marginalizados nessas organizações. Principais considerações/conclusões: Entendemos os "rolezinhos" como questionamento dos limites do espaço organizacional que produziram deslocamentos das fronteiras das organizações. Eles são efeitos de alterações de relações de forças socioeconômicas que estavam na rua e, quando expandidas para espaços organizacionais, provocaram tensões que continuam latentes, pois a rua continua sua dinâmica e novamente questionará essas fronteiras.

Mapping of multi-elements during melting and solidification using synchrotron X-rays and pixel-based spectroscopy.

A new synchrotron-based technique for elemental imaging that combines radiography and fluorescence spectroscopy has been developed and applied to study the spatial distribution of Ag, Zr and Mo in an Al alloy during heating and melting to 700, and then re-soldification. For the first time, multi-element distributions have been mapped independently and simultaneously, showing the dissolution of Ag- and Zr-rich particles during melting and the inter-dendritic segregation of Ag during re-solidification. The new technique is shown to have wide potential for metallurgical and materials science applications where the dynamics of elemental re-distribution and segregation in complex alloys is of importance.

Microeconomic model of residential location incorporating life cycle and social expectations

This paper is focused on the dynamics of residential location decisions based on the microeconomic theory of urban land use, in which we assume that each property is assigned to the agent with the highest bid. The agents' behavior includes expectations of their future based on the life cycle or social influence processes, which are anticipated or solved using a hypothesis of imitation of the behavior of other households currently living in those situations. Relocation decisions are then modeled, incorporating expected utilities by means of transition probabilities among households. An imitation multi-objective bid function is postulated for each alternative location depending on the expected income per unit of time, the current household value of amenities and the expected value obtained by the imitated agent in this location. A multinomial logit model is assumed to calculate the location equilibrium, where willingness to pay is determined by dwelling characteristics and spatial socioeconomic segregation (location externalities). Numerical examples and simulations are presented using linear bid functions to explain the proposed modeling approach and the impact of imitation on the dynamics of residential segregation.