Narrow Results

A two-temperature Ising-Schelling model is introduced and studied for describing human segregation. The self-organized Ising model with Glauber kinetics simulated by Müller et al. exhibits a phase transition between segregated and mixed phases mimicking the change of tolerance (local temperature) of individuals. The effect of external noise is considered here as a second temperature added to the decision of individuals who consider a change of accommodation. A numerical evidence is presented for a discontinuous phase transition of the magnetization.

We examine the segregation and mixing dynamics of a dilute bidisperse suspension of particles in a fluid subjected to a temperature gradient. Configurations corresponding to varying uniform bottom wall temperatures, as well as various bottom wall temperature profiles, are examined. Measures of spatial segregation and aggregation are discussed and used to analyze the suspension's dynamics. The results show that the difference in mass lead to transient segregation at short time scales, together with long-term intermixing and aggregation. Comparison of the segregation and aggregation among different configurations reveal that the strength of the temperature gradient is the primary influence on both segregation and aggregation. The particles are driven the fastest into the long – term steady state in the uniform and Gaussian bottom temperature profiles. In addition, the qualitative features of transient segregation do not change if the difference in mass is varied. The results suggest that a fluid undergoing thermal convection can be used to segregate particles, but only at short times, as fluid reaches its steady state. Keeping a fluid indefinitely in a transient state may improve the duration of segregation.

Over the last 25 years a lot of work has been undertaken on constructing continuum models for segregation of particles of different sizes. We focus on one model that is designed to predict segregation and remixing of two differently sized particle species. This model contains two dimensionless parameters: S_r, a measure of the segregation rate, and D_r, a measure of the strength of diffusion. These, in general, depend on both flow and particle properties and one of the weaknesses of the model is that these dependencies are not predicted. They have to be determined by either experiments or simulations.

We present steady-state, periodic, chute-flow simulations using the discrete particle method (DPM) for several bi-disperse systems with different size ratios. The aim is to determine one parameter in the continuum model, i.e. the segregation Péclet number (ratio of the segregation rate to diffusion, S_r/D_r) as a function of the particle size ratio.

Reasonable agreement is found; but, also measurable discrepancies are reported; mainly, in the simulations a thick pure phase of large particles is formed at the top of the flow. Additionally, it was found that the Péclet number increases linearly with the size ratio for low values, but saturates to a value of approximately 7.7.

Ripples or corrugations are common phenomena observed in unpaved roads in less developed countries or regions. They cause several damages in vehicles leading to increased maintenance and product costs. In this paper, we present a computational study about the so-called washboard roads. Also, we study grain segregation on unpaved roads. Our simulations have been performed by the Discrete Element Method (DEM). In our model, the grains are regarded as soft disks. The grains are subjected to a gravitational field and both translational and rotational movements are allowed. The results show that wheels’ of different sizes, weights and moving with different velocities can change corrugations amplitude and wavelength. Our results also show that some wavelength values are related to specific wheels’ speed intervals. Segregation has been studied in roads formed by three distinct grain diameters distribution. We observed that the phenomenon is more evident for higher grain size dispersion.

Segregation of granular particles affects the quality of end products in the pharmaceutical, chemical and food processing industries. Many researchers have worked on controlling the mechanical properties of granular particles to minimize segregation. In this paper, we studied different chute-related factors — inclination angle, friction, fill, channel geometry and base profile — and their effects on segregation. We conducted a small-scale experiment with chute inclined at different angles, and also numerical simulations performed using an open-source discrete element method (DEM) code — LIGGGHTS. We found the optimal condition for minimum segregation of a binary granular mixture. We concluded that segregation is minimized if the stream-wise velocity is low, for example, by keeping the chute at a low inclination $10^{\circ }$ and increasing the wall roughness to 0.14.

Empirical research on occupational segregation has conventionally measured it with Duncan dissimilarity index. This paper adopts an alternative approach — the L index — using the multivariate analysis introduced by Spriggs and Williams, which we extend to explore the impact of economic development on occupational segregation. This enables us to investigate the importance of individuals' attributes in explaining the segregation. Using data from the Labor Force Survey between 1985 and 2005, our results indicate that the L index controlling only for sex is substantial and persistent. However, the full model L index generally implies that occupational segregation has widened after controlling for individuals' attributes. It is found that segregation in the Malaysian labor market is mainly explained by gender, which, on average, accounts for 82% of the segregation. When a measure of macroeconomic conditions and a time variable economic are factored into the model that controls for gender only, the L index remains unchanged.

We study a kinetic model for a system of two species of particles interacting via a repulsive long range potential and with a reservoir at fixed temperature. The interaction between the particles is modeled by a Vlasov term and the thermal bath by a Fokker–Planck term. We show that in the diffusive and sharp interface limit the motion of the interfaces at low temperature is described by a Stefan problem or a Mullins–Sekerka motion, depending on the time scale.

We investigate experimentally and via computer simulations the segregation pattern of binary granular mixtures in a vibrated container with bottlenecks. During the vibration the granular motion is more violent at the bottlenecks than at the bellies. Particles with more mobility congregate to the necks, while those with less mobility congregate to the bellies. We use discrete element simulations to reproduce the main characteristics of the experimental observations.

The paper deals with axial segregation in unsteady diffusion dominated directional solidification from melt of a binary alloy in a finite cylindrical ampoule. The study focuses on the influence of the finite length of the ampoule on the concentration profile in a crystal obtained in a microgravity environment. The results are compared to those reported by Kim et al. [J. Crystal Growth183, 490 (1998)] for an infinite crystal. Numerical simulations are performed for two different situations: the initial transient solidification when the melt is uniform in composition, and the multipass solidification when the crystal is grown from the melt, formed by re-melting a crystal with an initial axial composition profile.

Ni-based monocrystal superalloy with fine dendrite, precise orientation and finally elevated service performance is required as turbine blades in advanced aeroengine. In this paper, the melt superheating treatment is carried out for DD3 single crystal superalloy during directional solidification processing. The thermal gradient of solidification interface remains constant for different melt superheating temperatures with the appropriate superheating treatment regulation. It is shown that with the melt superheating temperature increased from 1500°C to 1640°C and then to 1780°C respectively, both the primary and the secondary dendrite arms are obviously refined and the dendrite segregation ratios of Mo, W and Ti are reduced while the deviation angle of (001) crystal orientation can all be controlled within 5°. The dendrite structure refinement and the crystal orientation consistence should be attributed to the melt structure change and heredity which is caused by the superheating treatment.

Self-formation of MgO or Al₂O₃ surface layer on CuMg or CuAl alloys by annealing in H₂ gas was investigated theoretically and experimentally. Theoretical consideration shows that Mg or Al can segregate to the surface of Cu during the annealing, while the enrichment ability is much stronger for Mg. Meanwhile, the MgO or Al₂O₃ surface layer is self-formed by the preferential reaction of Mg or Al with O₂ remnant in H₂ atmosphere. The Al₂O₃ surface layer is expected to play a role in passivating the surface of Cu. However, the MgO layer would suffer failure in passivating the surface due to incorporation of Cu and fissures formed in MgO during the annealing process. Our theoretical predictions are in agreement with experimental observations.

The two-dimensional, soft-sphere molecular dynamics simulations have been performed to study the granular segregation behaviors in a binary granular mixture in tilted compartmentalized container under vertical vibration. It is found that there exist mixed state, left segregated state and right segregated state, which depend on the grain properties such as size ratio and density ratio as well as shaking properties. The particles with large density favor moving to right and the particles with large diameter prefer moving to left, so binary granular mixtures with large density ratio prefer forming right segregation state and the binary mixtures with large diameter favor forming left segregation state. The tilted compartmentalized container can be regarded as a container with a sawtooth base, which leads to stratified flows and thus forming horizontal segregation state under vertical vibration. The tilted bed plays a key role in forming segregation states, whereas the central wall enhances the segregation behaviors.

In this work, the segregation and structural transitions of CoNi clusters, between 1500 and 300 K, have been investigated using molecular dynamics simulations with the embedded atom method potential. The radial distribution function was used to analyze the segregation during the cooling processes. It is found that Co atoms segregate to the inside and Ni atoms preferably to the surface during the cooling processes, the Co${}_{147}$Ni${}_{414}$ cluster becomes a core–shell structure. We discuss the structural transition according to the pair-correction function and pair-analysis technique, and finally the liquid Co${}_{147}$Ni${}_{414}$ crystallizes into the coexistence of hcp and fcc structure at 300 K. At the same time, it is found that the frozen structure of CoNi cluster is strongly related to the Co concentration.

The segregation of Cu atoms in the Cu/Ni multilayers was investigated by means of the full-potential linearized augmented plane-wave method with the generalized-gradient approximation formula. We investigated the segregation of Cu atoms when the Cu/Ni slab is along the (001) and (111) directions, respectively. The results obtained show that at most one-layer Cu atoms can segregate to the Ni surface when Ni films are deposited on the Cu substrate and the segregation of Cu atoms is not sensitive to the orientation of the Cu/Ni slab surface. The result of Cu segregation is to reduce the vacuum effect.

Research on the influence of alloy concentration and distribution on bimetallic cluster plays a key role in exploring new structural material. This paper studies the melting process of icosahedral bimetallic cluster (PdPt)₁₄₇ with different Pt concentrations and different atomic distributions by using molecular dynamics with an embedded atom method. The results indicate that the mixed Pd–Pt cluster shows an irregular phenomenon between 580 and 630 K, i.e. the atomic energy decreases with the increase of temperature. This is because the surface energy of Pd is lower than that of Pt; the decreased energy due to Pd atomic segregation is larger than the increased energy due to heating during the segregation process. In addition, the temperature of Pd atomic segregation is strongly related to Pt concentration. This leads to that Pd atoms prefer to remain on the surface even after the cluster melted.

In this paper, the vertically vibrated binary granular mixtures at atmospheric pressure are studied experimentally. We find a nonstationary segregation state, of which the structure changes with time cyclically. The period of the cyclic segregation is measured and its variation with the vibration conditions is shown. The transition between the segregation states is also discussed, and a phase diagram on the plot of frequency against acceleration amplitude is given. In order to observe the effect of air flow in the segregation process, an alternative container with ventilated bottom is designed. Our experiments show that both regions of the Brazil nut segregation state and the cyclic segregation state shrink obviously by use of the latter container and disappear completely if the whole system is placed in vacuum. These results testify that the air pressure plays a positive role in both the Brazil nut effect and cyclic segregation.

In this paper, the effects of rare earth elements on the bonding strength and stability of TiC/fcc-Fe interface are explored by using the first-principles method based on density functional theory. The results show that the Ti terminal is more stable than the C terminal in the process of forming the interface. The alloying elements tend to segregate at position 2 on the side of fcc-Fe. The segregation of Mo, Nb, Cr and Ce alloying elements increases the interatomic electron cloud enrichment and consumption between the interfaces and enhances the Fe–Ti interactions. The d orbitals of Mo, Nb, Cr and Ce and f orbitals of Ce have strong hybridization with Fe-d orbitals and Ti-d orbitals electrons near the Fermi energy level, indicating an increase in bonding strength and stability of the interfaces. When Fe atoms are replaced by W, Ni and Al atoms, the covalent bond strength between interfacial atoms is reduced, thus weakening the interfacial bonding strength. This provides solid theoretical foundation with regard to further application in austenitic heat-resistant steel fields.

This paper introduces and analyzes some models in the framework of mean field games (MFGs) describing interactions between two populations motivated by the studies on urban settlements and residential choice by Thomas Schelling. For static games, a large population limit is proved. For differential games with noise, the existence of solutions is established for the systems of partial differential equations of MFG theory, in the stationary and in the evolutive case. Numerical methods are proposed with several simulations. In the examples and in the numerical results, particular emphasis is put on the phenomenon of segregation between the populations.

In this paper, we study hyperbolic and parabolic nonlinear partial differential equation models, which describe the evolution of two intersecting pedestrian flows. We assume that individuals avoid collisions by sidestepping, which is encoded in the transition rates of the microscopic 2D model. We formally derive the corresponding mean-field models and prove existence of global weak solutions for the parabolic model. Moreover we discuss stability of stationary states for the corresponding one-dimensional model. Furthermore we illustrate the rich dynamics of both systems with numerical simulations.

Segregation of boron on surface has been studied using the periodical calculations within the local density approximation. The obtained segregation energy (enthalpy) of about -1.9 eV is close to the published data of experimental studies and previous cluster semiempirical calculations. The influence of plane-wave basis set cutoff energy and the slab unit cell depth on the value of segregation energy has been investigated.