Segregation Model Research Articles

Elementary Steps of Catalytic Reactions Occurring on Metallic Alloy Nanoparticles.

Catalytic reactions running in an adsorbed overlayer on metallic alloy nanoparticles are of high interest in the context of applications in the chemical industry. The understanding of the corresponding kinetics is, however, still limited. One of the reasons of this state of the art is the interplay between adsorption and adsorbate-influenced segregation of metal atoms inside alloy nanoparticles. I scrutinize this interplay by using a generic field model of segregation and the mean-field approximation in order to describe adsorption, desorption, and elementary catalytic reactions. Under steady-state conditions, the segregation is demonstrated to be manifested in the change of the dependence of the activation energies of desorption or elementary reactions on coverage, and the sign of this change is positive. The effect of this change on the apparent reaction orders is briefly discussed as well.

The Study of Segregation and its Consequences in the Kabul City

This study investigates urban segregation in Kabul, the capital of Afghanistan, utilizing a multifaceted theoretical framework that integrates various explanatory models of segregation. The research targets the general population of Kabul, with a sample size of 233 individuals selected through a non-probabilistic cluster sampling technique. Data were collected using a comprehensive questionnaire focused on the Afghan context, incorporating insights from relevant studies. The analysis was conducted using SPSS software, employing both descriptive and inferential statistical methods. Demographic characteristics and participant responses in ethnically dominated areas were summarized using frequencies and percentages, while key variables were examined using measures of central tendency, dispersion, and distribution, including mean, standard deviation, variance, skewness, and kurtosis. The segregation tendencies of Kabul residents were analyzed using T-test, ANOVA and Spearman correlation. The results reveal a pronounced level of segregation within Kabul, with significant implications including the reinforcement of ethnocentric attitudes, the preservation of distinct subcultural identities, enhanced feelings of community security, and increased intra-group political and social engagement. The study found that followers of Shia Islam tend to segregate themselves from other religious groups, while the Pashtun ethnic group shows the lowest tendency toward segregation. Additionally, Kabul citizens tend to live among their own religious groups and the lower the level of education of individuals, the greater their tendency to separation.

Why do refugees live near to each other? A utility-based model for spatial segregation of Syrian refugees in Türkiye: 2016–2023 period

PurposeThe main purpose of this research is to understand and explain the clustering and/or segregation patterns of the rapid, massive and unexpected flow of Syrian refugees to Türkiye.Design/methodology/approachThe analytical framework we use consists of three parts. In the first stage, we created a two-group model in which utility is assumed to be a function of consumption and the proportion of the population belonging to the same group living in their neighborhood. We show that equilibrium utility can be reduced to a univariate function that is the population proportion of the group to which one belongs. Then, with the help of a Python-based simulation, we analyze the redistribution dynamics of the groups and clustering patterns. In the final stage, we compute the dissimilarity index to determine the degree of clustering.FindingsAlthough the dilution policy has been implemented, a relatively high spatial segregation of refugees still exists. The dissimilarity index we compute using the latest data shows that almost half of Syrians need to be displaced for a homogeneous geographical distribution.Research limitations/implicationsBy obtaining neighborhood-based housing data, it will be possible to conduct a more detailed analysis at the city level. This will improve policymakers' understanding of refugee policy at both local and national levels.Originality/valueIt is the first study in which a dissimilarity index is computed for Syrian refugees in Türkiye.

Effects of Carrier’s sex on the outcome of embryos and pregnancies in 412 couples undergoing preimplantation genetic testing for structural rearrangements

Study designTo ascertain whether the carrier’s sex affects the outcome of embryos and pregnancies in couples undergoing preimplantation genetic testing for structural rearrangements (PGT-SR). MethodsThis retrospective study comprised 412 couples with reciprocal translocations (RecT), Robertsonian translocations (RobT), or inversions (INV) between January 2017 and October 2022. We applied next-generation sequencing (NGS) on 2588 embryos after trophectoderm (TE) biopsy. ResultsGenetically transferable blastocyst rate was higher in the male carrier group (34.0 % vs 31.7 %, P = 0.013) relative to the female carrier group whereas other embryo and pregnancy outcomes remained similar. Further analysis revealed that this result was primarily due to the alteration of segregation patterns in the RobT subgroup, in which the proportion of alternate segregation was higher (84.3 % vs 66.4 %, P < 0.001) in male carriers compared with female carriers. In the RecT subgroup, the genetically transferable blastocyst rate between male and female carriers was similar although the segregation models also changed, such that the frequency of the adjacent-1 segregation pattern was higher in male carriers than in female carriers (42.5 % vs 34.7 %, P = 0.002). In addition, interchromosomal effect (ICE) did not differ between male and female carriers although ICE was lower in male carriers of the RobT subgroup (pure ICE: 35.50 % vs 44.30 %, P = 0.14; total ICE: 35.50 % vs 40.30 %, P = 0.32) and higher in male carriers of the INV subgroup (pure ICE: 42.3 % vs 37.20 %, P = 0.33; total ICE: 40.90 % vs 36.00 %, P = 0.36). ConclusionsThe carrier’s sex was closely associated with the genetically transferable embryo rate in couples undergoing PGT-SR, principally resulted from the change in segregation pattern in the RobT subgroup but not in the RecT and INV subgroups.

Similar patterns of brain activity for holistic representation of working memory: a study in children and adults.

Working memory is the fundamental function of the various cognitive processes and abilities in the overall trajectory of development. Significant advances in multivariate analysis of human functional magnetic resonance imaging data have converged functional segregation models toward integrated representation-based models. However, due to the inherent limitations of the multi-voxel pattern analysis method, we are unable to determine whether the underlying neural representations are spatially similar in the brain. Our study attempts to answer this question by examining the spatial similarity of brain activity during the working memory task in children and adults. Our results reveal similar patterns of activity between the regions involved in working memory. This functional network of similar spatial patterns was observed in both normally developing children and adults. However, the between-region similarity was more pronounced in adults than in children and associated with better performance. We propose an exchange of similar information flows through the brain at an integrated level of working memory processes, underpinning the holistic nature of working memory representation.

Discrete and continuum modelling of rock-ice avalanches: vertical segregation and its feedback on flow mobility

Rock-ice avalanches are rapid, catastrophic mass flows consisting of massive rock and ice particles in alpine regions. Varying material properties of rock and ice particles cause them to spontaneously mix and segregate during the flow. However, the impacts of segregation on the mobility remain poorly understood and are overlooked in current rock-ice avalanche models. Here, we address modeling of segregation and its mobility feedback from both discrete and continuum points of view. Using the discrete element method, we simulate rock-ice avalanches, and the segregation that occur therein, as steady gravity-driven flows of particles different in size, density, and surface friction. Segregation results in sharp particle concentration gradients which, when coupled with the large surface friction difference between rocks and ice, lead to transitions in the flow kinematic profiles. We reveal that rocks and ice contact probabilities are key to modelling the effective friction and volume fraction of the mixture flows. Continuum equations are proposed to model the concentration dependence of the pressure, while segregation-induced flow velocity profiles are modelled using the non-local granular fluidity framework that accounts for microscopic frictional interactions. The findings are expected to promote more sophisticated modeling of rock-ice avalanches necessary for hazard risk reduction and mitigation.

Grain boundary segregation for the Fe-P system: Insights from atomistic modeling and Bayesian inference

In this work we re-assess experimental data for grain boundary (GB) segregation of P in bcc Fe with thermodynamic and statistical methods. The data are based on Auger-Electron-Spectroscopy (AES) measurements which have provided P GB concentrations for various bulk contents and temperatures for ferrite. While in the previous investigations of this system a single-site McLean equation was used to extract segregation enthalpy and entropy, we employ multi-site segregation models as suggested by atomistic simulations. We use a recently introduced methodology based on inter-atomic potentials to calculate the segregation energy spectrum, as well as vibrational entropy and solute-solute interactions of P in polycrystalline Fe, thereby obtaining a three-dimensional distribution of energy, entropy and interactions. Using this trivariate distribution we predict P GB concentrations and compare them to the experimental measurements. Furthermore, we calibrate the parameters of physical models of increasing complexity to the experimental data with an inverse modeling approach based on Bayesian inference. While it is not possible to seamlessly link the results from AES to atomistic modeling, our investigation provides significant new insights for thermodynamic modeling of GB segregation. The vibrational entropy deduced from experiment differs from physics based atomistic simulations even when taking the spectral nature of energy, entropy and interactions into account. However, the correlations of the quantities are in good agreement when considering the trivariate model. Our investigation highlights the need for new and more accurate experimental datasets of GB segregation.

Coupling Photogeneration with Thermodynamic Modeling of Light-Induced Alloy Segregation Enables the Identification of Stabilizing Dopants

Coupling Photogeneration with Thermodynamic Modeling of Light-Induced Alloy Segregation Enables the Identification of Stabilizing Dopants

Geographies of socio-economic inequality

Abstract Over many decades, academics, policymakers, and governments have been concerned with both the presence of inequalities and the impacts these can have on people when concentrated spatially in urban areas. This concern is especially related to the influence of spatial inequalities on individual outcomes in terms of health, education, work and income, and general well-being amongst other outcomes. In this commentary, we provide an overview of the literature on spatial inequalities and on contextual and neighbourhood effects. We address some of the main challenges in modelling contextual effects and provide evidence that no single study can definitively provide the answer to the question whether—and how much—spatial context effects are relevant for understanding individual outcomes. It is only when taken together that the rich body of research on spatial context effects shows convincingly that spatial context effects are relevant. The commentary ends with the presentation of the vicious circle of the segregation model and suggest some ways in which this vicious circle of spatial inequality and segregation can be broken.

Resonance-induced particle mixing and segregation phenomena in a forced oscillation fluidized bed

The mixing and segregation of binary particles in a fluidized bed are typically characterized by inherent unpredictability. However, this phenomenon can be effectively regulated by applying vibrating airflow and the resonance effect generated therein. This study found that the application of the resonance effect leads to an increase in the voidage of fluidized beds, which is conducive to changing the state of particle dispersion. In addition, the variation in particle characteristics and proportions has a significant impact on the behavior of particles. If there is a substantial difference between particle characteristics and proportions, even with the application of pulsation frequency, it will not change the type of floating particles. Furthermore, phase diagrams and particle segregation models were successfully established for the pulsed fluidized bed, allowing for accurate prediction of binary particle segregation and mixing phenomena. This research provides a comprehensive theoretical foundation for regulating particle mixing and segregation.

Models of data processing and logical access segregation considering the heterogeneity of entities in information systems

The subject of the research is the process of logical access segregation to data in information systems. The aim of the article is to improve the accuracy and reliability of modeling processes for data processing and logical access segregation considering the heterogeneity of entities in information systems. The tasks to be solved include: conducting a comparative analysis of modern data access distribution models, integrating simpler role-based models, synthesizing hierarchical role-based models, developing enforced typing models based on trust relationships, and presenting the main provisions of the security policy integration process. The methods used are: systems analysis, component design, logical and simulation modeling in the form of role-based access segregation models. The results obtained include: development of data processing models and logical access segregation in information systems that take into account the heterogeneity of entities and the multi-level structure of information systems. The models differ from known ones by considering the heterogeneity of entities and the multi-level structure of information systems. This has increased scalability by up to 35% due to a modular approach to defining security policies. Additionally, the developed model demonstrates 25% higher implementation practicality as it easily integrates with existing access control systems and adapts to various platforms and environments. The proposed models are effective for large information systems and distributed environments due to their modularity and ability to adapt to different operational conditions. This ensures reliable access control in systems with numerous subjects and objects. The implementation of multi-level RBAC models has improved the accuracy and reliability of results.

Концептуалізація моделей адаптації сучасних мігрантів з України в Ізраїлі

The article is devoted to the conceptualization of the sociological construct of adaptation of migrants based on the theory of ethnic stratification and the concept of a two-level dimension of adaptation: the dimension of value orientations and social inclusion, within the framework of an empirical study on the adaptation strategies of modern migrants from Ukraine to Israel. Depending on the level of social inclusion and value orientations of migrants regarding the ethnic affiliation of migrants, which is characteristic of migrants from Ukraine in Israel, five possible adaptation models of migrants were identified: assimilation, value integration, inclusive integration, multiculturalism and segregation, each of which is inherent certain categories of migrants from Ukraine in Israel. The model of assimilation is widespread among religious Jewish migrants. Models of multiculturalism and value integration are widespread among secular Jewish migrants. Models of segregation and inclusive integration are inherent in the category of non-Jewish migrants.

A dynamic model of wealth segregation

AbstractWe propose a dynamic model where the real estate market generates wealth segregation within a town. The model develops on the Schelling’s checkerboard dynamics with one main difference: Agents are fully characterized by their wealth, which changes with the progress of the model dynamics. The driver of the segregation is a positive neighborhood externality such that households’ utility is increasing in the average wealth of the neighbors. The identification of a potential function enables prediction of the long-run limiting behavior of the dynamics: Wealth segregation is an endemic result, unless a perturbation at the individual level is introduced. Public policies that mimic the perturbation can reduce wealth segregation.

Continuum modelling of size segregation and flow in dense, bidisperse granular media: accounting for segregation driven by both pressure gradients and shear-strain-rate gradients

Dense mixtures of particles of varying size tend to segregate based on size during flow. Granular size segregation impacts many industrial and geophysical processes, but the development of coupled, continuum models capable of predicting the evolution of segregation dynamics and flow fields in dense granular media across different geometries remains a challenge. One reason is because size segregation stems from two driving forces: pressure gradients and shear-strain-rate gradients. Another reason is the challenge of integrating segregation models with rheological constitutive equations for dense granular flow. In this paper we develop a continuum model that accounts for pressure-gradient-driven and shear-strain-rate-gradient-driven segregation, coupled to rheological modelling of a dense granular medium across the quasi-static and dense inertial flow regimes. To calibrate and test the continuum model, we perform discrete element method (DEM) simulations of dense flow of bidisperse granular systems in two flow geometries in which both segregation driving forces are present: inclined plane flow and planar shear flow with gravity. Steady-state DEM data from inclined plane flow is used to determine the dimensionless material parameters in the pressure-gradient-driven segregation model for both spheres and disks. Then, predictions of the continuum model are tested against DEM data across different cases of inclined plane flow and planar shear flow with gravity, while varying parameters such as the size of the flow geometry, the flow speed and the initial conditions. We find that it is crucial to account for both driving forces to capture segregation dynamics across both flow geometries with a single set of parameters.

An agent-based model of school tracking, accountability, and segregation

ABSTRACT Extant research on the effect of education system characteristics on school socio-economic segregation does not consider education as a complex system. This paper’s contribution lies in using agent-based modelling to simulate the effect of the interaction between families’ strategies for school selection and two education system characteristics: tracking – a system where students of different academic abilities are separated in different schools – and school accountability – the public availability of information on school quality. The model shows that school tracking and accountability tend to at the same time attenuate and increase school socio-economic segregation, but overall both policies tend to exacerbate segregation by eliciting competition for the best schools. The policy implications are: (i) tracking has a stronger exacerbating effect on segregation than accountability, (ii) the two polices interact to create compounding effects and (iii) by reducing residential segregation between families the segregating effect on schools of the two policies diminishes dramatically.

Compaction and Segregation of DNA in Escherichia coli.

Theoretical and experimental approaches have been applied to study the polymer physics underlying the compaction of DNA in the bacterial nucleoid. Knowledge of the compaction mechanism is necessary to obtain a mechanistic understanding of the segregation process of replicating chromosome arms (replichores) during the cell cycle. The first part of this review discusses light microscope observations demonstrating that the nucleoid has a lower refractive index and thus, a lower density than the cytoplasm. A polymer physics explanation for this phenomenon was given by a theory discussed at length in this review. By assuming a phase separation between the nucleoid and the cytoplasm and by imposing equal osmotic pressure and chemical potential between the two phases, a minimal energy situation is obtained, in which soluble proteins are depleted from the nucleoid, thus explaining its lower density. This theory is compared to recent views on DNA compaction that are based on the exclusion of polyribosomes from the nucleoid or on the transcriptional activity of the cell. These new views prompt the question of whether they can still explain the lower refractive index or density of the nucleoid. In the second part of this review, we discuss the question of how DNA segregation occurs in Escherichia coli in the absence of the so-called active ParABS system, which is present in the majority of bacteria. How is the entanglement of nascent chromosome arms generated at the origin in the parental DNA network of the E. coli nucleoid prevented? Microscopic observations of the position of fluorescently-labeled genetic loci have indicated that the four nascent chromosome arms synthesized in the initial replication bubble segregate to opposite halves of the sister nucleoids. This implies that extensive intermingling of daughter strands does not occur. Based on the hypothesis that leading and lagging replichores synthesized in the replication bubble fold into microdomains that do not intermingle, a passive four-excluding-arms model for segregation is proposed. This model suggests that the key for segregation already exists in the structure of the replication bubble at the very start of DNA replication; it explains the different patterns of chromosome arms as well as the segregation distances between replicated loci, as experimentally observed.

The Dark Side of the pollen: BSA-seq identified genomic regions linked to male sterility in globe artichoke

Globe artichoke (Cynara cardunculus var. scolymus; 2n = 2x = 34) is a food crop consumed for its immature flower heads. Traditionally, globe artichoke varietal types are vegetatively propagated. However, seed propagation makes it possible to treat the crop as annual, increasing field uniformity and reducing farmers costs, as well as pathogens diffusion. Despite globe artichoke’s significant agricultural value and the critical role of heterosis in the development of superior varieties, the production of hybrids remains challenging without a reliable system for large-scale industrial seed production. Male sterility (MS) presents a promising avenue for overcoming these challenges by simplifying the hybridization process and enabling cost-effective seed production. However, within the Cynara genus, genic male sterility has been linked to three recessive loci in globe artichoke, with no definitive genetic mechanism elucidated to date. A 250 offsprings F2 population, derived from a cross between a MS globe artichoke and a male fertile (MF) cultivated cardoon (C. cardunculus var. altilis) and fitting a monogenic segregation model (3:1), was analyzed through BSA-seq, aiming at the identification of genomic regions/genes affecting male sterility. Four QTL regions were identified on chromosomes 4, 12, and 14. By analyzing the sequence around the highest pick on chromosome 14, a cytochrome P450 (CYP703A2) was identified, carrying a deleterious substitution (R/Q) fixed in the male sterile parent. A single dCAPS marker was developed around this SNP, allowing the discrimination between MS and MF genotypes within the population, suitable for applications in plant breeding programs. A 3D model of the protein was generated by homology modeling, revealing that the mutated amino acid is part of a highly conserved motif crucial for protein folding.

A data-driven agent-based model of primary school segregation in Amsterdam

ABSTRACT Theoretical agent-based models of residential and school choice have shown that substantial segregation can emerge as an (unintended) consequence of interactions between individual households and feedback mechanisms, despite households being relatively tolerant. However, for school choice, existing models have mostly been highly stylized, leaving open whether they are relevant for understanding school segregation in concrete empirical settings. To bridge this gap, this study develops an empirically calibrated agent-based model focusing on primary school choice in Amsterdam. Consistent with existing models, results show that substantial school segregation emerges when schools are chosen based on a trade-off between composition and distance, and also when households are relatively tolerant. Additionally, findings of (hypothetical) policy simulations suggest that it is important to understand which preferences for school composition and distance households have and how these interact. We find that the effects of policies aiming to reduce school segregation through geographical restricting mechanisms are highly dependent on those interacting preferences. Also, we assessed the contribution of residential segregation to school segregation. Our findings may have implications for methodologies aiming to estimate school choice preferences, such as discrete choice models, as these methodologies do not explicitly control for implications of these interactions and feedback mechanisms, which might lead to incorrect inference.

The behaviour of plastic particles during pyrolysis in bubbling fluidized bed reactors: Incipient agglomeration and axial segregation

Plastic-fluidized bed interaction has been investigated by non-invasive X-ray imaging techniques in the temperature range of 500–650 °C and under pyrolysis conditions. Experiments were conducted by feeding a single polypropylene particle using either overbed or underbed feeding methods. The fluidized bed was operated from minimum fluidization conditions to bubbling regime, up to 2Umf. Interestingly, experimental observations show that the understanding of the mixing/segregation behaviour of polypropylene in a hot fluidized bed does not appear to be as straightforward as in the case of more conventional feedstocks, such as biomass. Further analysis and an alternative point of view to investigate the complex behaviour observed for plastic feedstock have been provided. The interaction between the fluidized bed and a single polypropylene particle was modelled by means of an axial segregation model, and a physics-assisted stochastic approach. In the second case, it was possible to simulate the formation of the sand-plastic agglomerate (incipient agglomeration stage) and the evolution of its density over time. The models were then validated by means of axial segregation data obtained via X-ray imaging techniques and by measuring the physical properties of real sand-polypropylene agglomerates produced within the bed operating at high temperatures. Results obtained in this study show that the unpredictable sinking-floating behaviour of the plastic particles is not related to the change in density associated to the formation of the sand-polypropylene agglomerates over time.

Liquid flow field and residence time distribution in a baffleless oscillatory flow coil reactor

Baffleless coils can operate as continuous oscillatory flow reactors to produce pharmaceutical products where process intensification is intended. A method to evaluate mixing performance and its impact on reaction conversion is residence time distribution (RTD) analysis. Liquid macromixing in a long baffleless coil reactor (L = 24 m, dt = 4.57 mm) at ranges of oscillation amplitude (11.75–58.75 mm), frequency (0–3.68 Hz), and net flow rate (30–120 g⋅min−1) was investigated based on measured RTDs fitted to the skewed normal distribution model. The impact of operating conditions on the RTD was supported by analyzing the liquid flow field derived from CFD simulations. The RTD variance under different oscillation conditions suggests a near plug flow pattern, although deviations from ideality such as skewness and long tailing were always observed. The model parameters, along with the RTD variance, were correlated to the operating conditions lumped in an oscillatory Dean number that used the flow amplitude as characteristic length (Deox). Values of Deox varied between 150 and 11000, and the RTD variance at the different net flow rates was minimized for 300 < Deox < 600, as also evidenced from the minimum cross-sectional variance of the simulated time-averaged axial velocity profile. Normalizing the data allowed comparison to similar coil studies with different geometrical dimensions and operating conditions, leading to generalized correlations for the RTD model parameters. Finally, chemical conversion was assessed for first- and second-order single phase reactions at different Damköhler numbers using the segregation and maximum mixedness micromixing models combined with the fitted RTDs. The performance of the coil remained consistent with a plug flow reactor despite its departures from ideal flow.