Improving assessment of urban racial segregation by partitioning a region into racial enclaves

Frequently, a single-value metric is needed to rank urban regions with respect to the level of multiracial segregation or to compare a segregation level of a single urban region at two different times. Assessment of segregation depends not only on a metric used but also on a choice of region’s partitioning. The standard practice is to partition the region into single-scale subregions. In the United States, census tracts are the subregions of choice. Census aggregation units including tracts are delineated without direct regard to racial homogeneity and are in fact heterogeneous. Consequently, using tracts as subdivisions leads to the underestimation of the segregation level of the entire region. Here we propose to partition a region into racial enclaves - units having boundaries that align with transitions between different racial compositions. By reflecting true demographic structure, such units minimize their internal racial inhomogeneity resulting in improved assessment of segregation. Enclaves are defined as aggregates of adjacent census blocks (smallest and the most racially homogeneous census units) of similar composition. In a typical US urban region effective population size of enclaves is an order of magnitude larger than the size of a census tract and yet the segregation calculated based on enclaves is larger than segregation based on census tracts. The proposed methodology is described and applied to a set of 61 largest cities in the U.S. in their metropolitan statistical areas (MSAs) as well as their urban areas (UAs) boundaries using 1990 and 2010 block-level data. The method is compared to the standard methodology using correlations between cities’ segregation rankings.

Improving assessment of urban racial segregation by partitioning a region into racial enclaves

Frequently, a single-value metric is needed to rank urban regions with respect to the level of multiracial segregation or to compare a segregation level of a single urban region at two different times. Assessment of segregation depends not only on a metric used but also on a choice of region’s partitioning. The standard practice is to partition the region into single-scale subregions. In the United States, census tracts are the subregions of choice. Census aggregation units including tracts are delineated without a direct regard to racial homogeneity and are in fact heterogeneous. Consequently, using tracts as subdivisions leads to the underestimation of the segregation level of the entire region. Here we propose to partition a region into racial enclaves—units having boundaries that align with transitions between different racial compositions. By reflecting true demographic structure, such units minimize their internal racial inhomogeneity resulting in improved assessment of segregation. Enclaves are defined as aggregates of adjacent census blocks (smallest and the most racially homogeneous census units) of similar composition. In a typical US urban region, effective population size of enclaves is an order of magnitude larger than the size of a census tract and yet the segregation calculated based on enclaves is larger than segregation based on census tracts. The proposed methodology is described and applied to a set of 61 largest cities in the US in their metropolitan statistical areas as well as their urban areas boundaries using 1990 and 2010 block-level data. The method is compared to the standard methodology using correlations between cities’ segregation rankings.

An Approach to Micro Segregation Level and Presence of Quench Cracks in Medium Carbon Low Alloy Steels

Samples from forged and heat-treated steel products with known quench crack histories have been mapped in order to study a possible relation between banding segregation and quench cracking. The steels were medium carbon low alloy steels, ingot and continuous cast, as well as vacuum arc remelt D6AC. EDS X-ray mapping was applied to characterize the banding segregation pattern from casting i.e. gradient of chemical composition that creates direction dependent properties. Trends for segregation ratios followed the expectations: the segregation ratios were higher for the quench sensitive steels.34CrNiMo6, ingot- and continuous cast, was then supplied for testing. Segregation level was pre-checked for decision for heat treatment and testing of as quenched tensile properties. There is an indication of 90 % reduction of the difference between Rm and Rp0.2, the work hardening, for the steel with lowest quality.

Effect of Mushy Zone Permeability on the Formation of Centerline Segregation in Slab Casting

A complex mathematical model characterizing the centerline segregation level in the mid region of continuously cast slabs was developed. The basic heat transfer and solidification model connected to the semi-empirical liquid feeding model (LMI - Liquid Motion Intensity model) gives the possibility to estimate the centerline segregation parameters of slab cast under industrial circumstances. Solid shell deformation changes the volume of the space available for the liquid inside the slab and hereby also changes the conditions of liquid supply.

Microstructure and Properties of As-Cast Cu-20Ni-5Sn Alloy

Cu-20Ni-5Sn alloy has not only high content of Ni melted point 1453°C, but also low melting point elements of Sn melted at 231.9°C, therefore, the grain structure of alloy as-cast is in perfect dendrite that lends to form segregation and inverse segregation of Sn, so that the hot rolling (cogging) processing is restricted. The influence of casting methods, cooling rate and heat treatment on the microstructures and properties of as-cast Cu-20Ni-5Sn alloy were investigated. The results show that, compared to the ingot casted in iron mold and graphite mold, the microstructure of Cu-20Ni-5Sn ingot prepared by horizontal continuous casting is the finest and the Sn segregation level is in lowest. The microstructure of the ingot casted in graphite mold is in the most perfected dendritic and with the highest segregation of Sn, the microstructure of ingot in iron molding is in the middle. The ingots must be homogenized before cold-processing. Homogenization treatment can eliminate Sn segregation and dissolve the non-equilibrium phase of ingots.

Grain-Boundary Segregation of Phosphorus and Inter-Granular Fracture Behavior under Low Tensile Stresses

The present work is an effort to provide experimental results focusing on segregation behavior of phosphorus at grain boundary and the intergranular fracture behavio under low tensile stresses. AES (Auger electron spectroscopy) experiments and dynamic analyses on the non-equilibrium grain-boundary segregation (NGS) of phosphorus and the SEM photos of intergranular fracture in Auger specimens in 12Cr1MoV steel were carried out in this paper. The variation of phosphorus segregation level in grain boundary under different low tensile stresses and at different temperature were obtained. Results show that NGS of phosphorus occurred in the experimental steel while subjected to low tensile stresses. Maximum values of phosphorus segregation level were obtained at the critical times. SEM photos of intergranular fracture in Auger specimens of the test steel show that the intergranular fracture rate increased with increasing concentration of phosphorus. The intergranular fracture behavior is accordant with the segregation behavior of phosphorus at grain boundary.

Research on Inner Cooling Apparatus Sets in the Mold of 700mm×700mm Bloom

Based on the problems emerged from market, 700mm×700mm super-large billet has been advanced. This paper calculated the casting speed and the depth of liquid core according to empirical formula for 700mm×700mm super-large billet, based on calculate and feasibility analysis acquired the appropriate casting speed is 0.2 m/min. A new mold has been advance based on mold thermoanalysis that is complex mold. Theoretically analyzed the function of setting inner cooling and deflected SEN, indicate that complex mold can improve heat transfer efficiency and equiaxed crystal ratio, reducing center segregation; level rotary flow can uniform molten steel ingredient and growth of shell, reduce the impact depth, achieve the effect of E-EMS; calculation show that reduce the depth of liquid core by applying complex mold, finally, reduce infrastructure fee of caster.