High Segregation Research Articles

Indium incorporation processes investigated by pulsed and continuous growth of ultrathin InGaN quantum wells

We study the incorporation of indium into AlxGa1−xN/GaN quantum well (QW) structures with high indium concentrations above 25% for QW thicknesses in the range 2nm down to half a c-lattice constant under pulsed and continuous growth conditions. We want to clarify which processes limit the incorporation of indium and lead to a degrading layer structure. The data are discussed in the context of the adlayer proposed by theory (Northrup et al., 2000) [1]. The interplay of the adlayer with the incoming flux, the high desorption rate and segregation of indium can consistently explain the various observed phenomena.

Dry cleaning of fine lignite in a vibrated gas-fluidized bed: Segregation characteristics

The segregation characteristics of fine lignite (−3+1mm) in a vibrated gas-fluidized bed were examined. The pressure drop, ash contents and mass of a certain size fraction in lignite particles as a function of height through the bed, ash separation index, corresponding bed snapshots, and bubble size were investigated by varying superficial gas velocity. The effects of vibration parameters (frequency, amplitude, and vibration intensity) on segregation performance were also determined. Both density segregation and size segregation occurred as a function of superficial gas velocity. With increasing superficial gas velocity, the particle segregation changed to mixing state. An optimum air velocity existed to maximize segregation when fluidization velocities were between the minimum fluidization velocities of flotsam (clean coal) and jetsam (gangue). Bubble-driven flotsam–jetsam mechanism was responsible for the transition from segregation to mixing. The comparative ash segregation index and pressure drop characteristics between the vibro-fluidized bed and fluidized bed also confirmed this mechanism and suggested that application vibration achieved a high segregation performance at a low fluidization velocity because of reduced bubble sizes. The use of dimensionless vibration number (vibration intensity) alone to characterize segregation behavior could lead to misleading conclusions. Frequency and amplitude had strong effects on segregation performance.

High temperature phase transition of mixed (PuO2 + ThO2) investigated by laser melting

A laser heating approach combined with fast pyrometry in a thermal arrest method was used to provide new data for the melting/solidification phase transition in mixed (PuO2+ThO2) at high temperature. At low concentration of ThO2 in PuO2 a minimum in the solidification temperature in the pseudo binary (PuO2+ThO2) was observed. The minimum was found around a composition with 5mol% ThO2. Phase transition temperatures of other compositions are closer to an ideal solution behaviour. To detect changes in the material a complete investigation with electron microscopy, Raman spectroscopy and powder X-ray diffraction was done. Raman vibration modes were found, that are characteristic for materials containing PuO2, and high temperature segregation effects during solidification were described. The results obtained in the present work are compared to other mixed actinide dioxides and compared to the ideal solution case for this system. The presented results show the importance of the high-temperature oxygen chemistry in this actinide oxide phase.

Foreclosures and crime: A city-level analysis in Southern California of a dynamic process

Although a growing body of research has examined and found a positive relationship between neighborhood crime and home foreclosures, some research suggests this relationship may not hold in all cities. This study uses city-level data to assess the relationship between foreclosures and crime by estimating longitudinal models with lags for monthly foreclosure and crime data in 128 cities from 1996 to 2011 in Southern California. We test whether these effects are stronger in cities with a combination of high economic inequality and high economic segregation; and whether they are stronger in cities with high racial/ethnic heterogeneity and high racial segregation. One month, and cumulative three month, six month, and 12-month lags of foreclosures are found to increase city level crime for all crimes except motor vehicle theft. The effect of foreclosures on these crime types is stronger in cities with simultaneously high levels of inequality but low levels of economic segregation. The effect of foreclosures on aggravated assault, robbery, and burglary is stronger in cities with simultaneously high levels of racial heterogeneity and low levels of racial segregation. On the other hand, foreclosures had a stronger effect on larceny and motor vehicle theft when they occurred in a city with simultaneously high levels of racial heterogeneity and high levels of racial segregation. There is evidence that the foreclosure crisis had large scale impacts on cities, leading to higher crime rates in cities hit harder by foreclosures. Nonetheless, the economic and racial characteristics of the city altered this effect.

Understanding the mechanical behavior of nanocrystalline Al–O thin films with complex microstructures

The mechanical behavior of nanocrystalline (NC) metals has attracted widespread interest, though the majority of efforts have focused on (nominally) pure metals. By comparison, the mechanisms of deformation and strengthening in NC alloys, especially those with high segregation propensity and strong chemical interactions, are less well understood. Here we present a quantitative investigation on the mechanical behavior of such an alloy system. NC Al–O thin films are synthesized by means of confocal co-sputtering, which enables a wide-range and quasi-independent control over impurity content and grain size. Detailed characterization combining transmission electron microscopy with three-dimensional atom probe tomography identify the multiple morphologies of O impurities in a composite-like microstructure, including nanosized α-Al2O3 precipitates, O-rich clusters segregated along grain boundaries, and O solute atoms inside Al grains. Individual contributions of these strengthening features to the mechanical properties of NC Al–O thin films, as measured by instrumented nanoindentation, are then well delineated by a microstructure-informed analytical model. Dislocations emitted from grain boundaries are pinned by the stronger obstacles and cut through the weaker, and we show that the strong chemical interactions of this Al–O system play a dominant role in its pronounced strengthening capability. The influence of O impurities on the plasticity and deformation mechanisms in NC Al films is also discussed based on microtensile testing.

Cohesin without cohesion: a novel role for Pds5 in Saccharomyces cerevisiae.

High fidelity chromosome segregation during mitosis requires that cells identify the products of DNA replication during S-phase and then maintain that identity until anaphase onset. Sister chromatid identity is achieved through cohesin complexes (Smc1, Smc3, and Mcd1 and Irr1/Scc3), but the structure through which cohesins perform this task remains enigmatic. In the absence of unambiguous data, a popular model is that a subset of cohesin subunits form a huge ring-like structure that embraces both sister chromatids. This ‘one-ring two-sister chromatid embrace’ model makes clear predictions – including that premature cohesion loss in mitotic cells must occur through a substantial reduction in cohesin-DNA associations. We used chromatin immunoprecipitation to directly test for cohesin dissociation from well-established cohesin binding sites in mitotic cells inactivated for Pds5 – a key cohesin regulatory protein. The results reveal little if any chromatin dissociation from cohesins, despite a regimen that produces both massive loss of sister chromatid tethering and cell inviability. We further excluded models that cohesion loss in mitotic cells inactivated for Pds5 arises through either cohesin subunit degradation, premature Hos1-dependent Smc3 de-acetylation or Rad61/WAPL-dependent regulation of cohesin dynamics. In combination, our findings support a model that cohesin complexes associate with each sister and that sister chromatid cohesion likely results from cohesin-cohesin interactions. We further assessed the role that Pds5 plays in cohesion establishment during S-phase. The results show that Pds5 inactivation can result in establishment defects despite normal cohesion loading and Smc3 acetylation, revealing a novel establishment role for Pds5 that is independent of these processes. The combination of findings provides important new insights that significantly impact current models of both cohesion establishment reactions and maintenance.

The Oxide Defect of C70250 Alloy

The oxide skin defect during hot rolling process for Cu-Ni-Si alloy strip was investigated. Oxide skin defects were analyzed by means of alloy elements detection and microstructures characterization. The characterization and test results showed that high temperature oxidation and silicon segregation are the main causes of the oxide skin defect. Pilot scale tests indicated that hot processing temperature for C70250 alloy should be lower than 950°C. Reducing atmosphere is recommended during the thermal treatment of Cu-Ni-Si alloys.

Atomic-scale analysis of liquid-gallium embrittlement of aluminum grain boundaries

Material strengthening and embrittlement are controlled by intrinsic interactions between defects, such as grain boundaries (GBs), and impurity atoms that alter the observed deformation and failure mechanisms in metals. In this work, we explore the role of atomistic-scale energetics on liquid-metal embrittlement of aluminum (Al) due to gallium (Ga). Ab initio and molecular mechanics were employed to probe the formation/binding energies of vacancies and segregation energies of Ga for 〈100〉, 〈110〉 and 〈111〉 symmetric tilt grain boundaries (STGBs) in Al. We found that the GB local arrangements and resulting structural units have a significant influence on the magnitude of the vacancy binding energies. For example, the mean vacancy binding energies for 〈100〉, 〈110〉 and 〈111〉 STGBs in the 1st layer was found to be −0.63, −0.26 and −0.60eV, respectively. However, some GBs exhibited vacancy binding energies closer to bulk values, indicating interfaces with zero sink strength, i.e. these GBs may not provide effective pathways for vacancy diffusion. The results from the present work showed that the GB structure and the associated free volume also play significant roles in Ga segregation and the subsequent embrittlement of Al. The Ga mean segregation energies for 〈100〉, 〈110〉 and 〈111〉 STGBs in the 1st layer were found to be −0.21, −0.09 and −0.21 eV, respectively, suggesting a stronger correlation between the GB structural unit, its free volume and the segregation behavior. Furthermore, as the GB free volume increased, the difference in segregation energies between the 1st layer and the 0th layer increased. Thus, the GB character and free volume provide an important key to understanding the degree of anisotropy in various systems. The overall characteristic Ga absorption length scale was found to be about ∼10, 8 and 12 layers for 〈100〉, 〈110〉 and 〈111〉 STGBs, respectively. In addition, a few GBs of different tilt axes with relatively high segregation energies (between 0 and −0.1eV) at the boundary were also found. This finding provides a new atomistic perspective for the GB engineering of materials with smart GB networks to mitigate or control liquid-metal embrittlement and more general embrittlement phenomena in alloys.

Niche separation by littoral-benthic Chydoridae (Cladocera, Crustacea) in a deep lake - potential drivers of their distribution and role in littoral-pelagic coupling

Niche separation of 22 species of benthic Chydoridae was examined in a depth gradient in the littoral zone of a deep Lake Piaseczno (eastern Poland), by using a trap sampler. Individual species showed high segregation across the littoral zone according to depth, macrophyte biomass, total organic carbon (TOC), conductivity and pH, of which the depth turned out to be the most important. The species Acroperus harpae, Alona affinis, Alonella nana, Leydigia acanthocercoides, Pseudochydorus globosus, Pleuroxus trigonellus and Pleuroxus aduncus were found in the whole littoral zone, but the remaining Chydoridae species displayed clear spatial distribution, e.g. Coronatella rectangula, Acroperus elongatus, Alona guttata, Alonella excisa, Alonella exigua, Rhychotalona falcata, Monospilus dispar and Pleuroxus truncatus settled the shallower parts of the littoral, whereas Eurycercus lamellatus, Camptocercus rectirostris, Pleuroxus laevis, Graptoleberis testudinaria, Alona costata, Pleuroxus uncinatus and Alona intermedia were found mainly in areas located 3-6 m deep. To find out the role of Chydoridae in littoral-pelagic food web coupling, the contribution of chydorids to total number of Cladocera in the guts of fish was estimated showing that they are an important intervening link in nutrient movement from the littoral to the pelagic zone, as their contribution to the total cladoceran number found in guts of fish caught in the pelagic zone was even as high as 98%. This study provides more insight into the nature of constraints associated with littoral-benthic cladocerans’ habitat preferences and their importance in littoral-pelagic coupling.

Interface Migration with Segregation in MoSi<sub>2</sub>-Based Lamellar Alloy Simulated by Phase-Field Method

MoSi2–based alloys are attracting attention as ultra-high temperature structural material for super-high efficiency gas turbine power generation systems. In this study, the effects of Cr-and Zr-addition on interface migration in MoSi2/NbSi2 lamellar silicide were examined by phase field simulations employing the segregation energies evaluated by the first principles calculation in addition to thermodynamic free energy in order to take into account the chemically-driven interfacial segregation. The simulation results indicate that both Cr and Zr can segregate at the lamellar interface to suppress its migration, and the Zr-addition is more effective to lower the interface migration rate than the Cr-addition owing to its higher segregation energy.

Macro-Distribution of Alloy Elements along the Thickness of the Twin Roll Cast Billet

The macro-distribution of alloy elements in a billet affects its following processing property, and even the mechanical property of the finishing products. In this study AA1235 aluminum alloy was twin-roll cast into a billet with a thickness of 7.0mm. The billet was dissolved layer by layer. ICP-AES was used to analysis the element distribution through thickness. It has been found that Fe and Si were concentrated at both the bottom surface and the top surface of the billet. A higher concentration of Fe was observed at the bottom surface than that at the top surface owing to the density segregation. The center of the billet had lowest concentration of these two elements. Fe had a higher segregation in the twin roll cast billet than Si.

CFD Modelling of Nanoparticles Dispersion in a Dust Explosion Apparatus

A computational fluid dynamics simulation (CFD) has been developed in order to describe the dispersion of a confined gas-solid flow in a typical test designed for the determination of dusts cloud flammability (modified Hartmann apparatus). For this purpose, an analysis of the biphasic flow development inside such an explosion tube has been performed. The equipment considered in this study consists of a vertical tube in which a flammable dust is dispersed by the injection of air at high pressure to be ignited after a time period in which the mixture can be considered as homogeneous (commonly 60 ms). This analysis has been focused on the assessment of flow conditions pertaining to the agglomeration and fragmentation of the disperse phase. Previous studies performed by Bouillard et al (2010) established significant variations in the combustion process for solid materials notably with a submicronic size distribution. For this reason, the present study has been intended to determine the zones where turbulence causes variations on the particles size distribution (agglomeration/fragmentation dynamics) and therefore on their mechanism of combustion. In this order, a CFD simulation has been developed by using an Euler- Lagrange approach. Based on previous studies (Bouillard et al., 2010) and on industrial considerations, aluminium powders were chosen for this case study. Different Reynolds Averaged Navier-Stokes (RANS) turbulence models were compared to analyze flow variables associated to computational cost and description of the dispersion phenomena. A transonic flow condition is reached at zones near the injection. The model was adjusted by inclusion of specific characteristics that described the mutual interactions between the two phases and other effects such as Brownian motion for non-turbulent regions. After adjusting the biphasic CFD simulation to the design specifications of the apparatus, this analysis has led to the identification of a unsteady behaviour with high segregation levels during the first 30 ms of dispersion. This fact is associated to the high number of collisions among the aggregates and the variations in their size distribution during a typical characterization test. Nevertheless, it has been evidenced that the homogeneity assumption in the mixture can be accepted because the minimum explosive concentration (0.03-0.14 kg/m3) is accomplished at ignition time in the regions where the electrodes are located. This fact has confirmed the importance of turbulence on solids segregation which causes fluctuations on determined parameters according to ignition delay. Due to the strong influence of fragmentation phenomenon on sub-micronic particles, this study was mainly focused on nanoparticles suspensions. From an industrial point of view, this choice is relevant as it will allow the quantification of nanopowders dispersion risk, both for toxicological and explosion considerations.

Metropolitan-level ethnic residential segregation, racial identity, and body mass index among U.S. Hispanic adults: a multilevel cross-sectional study

BackgroundThe few studies that have examined whether metropolitan-level ethnic residential segregation is associated with obesity among Hispanics are mixed. The segmented assimilation theory, which suggests patterns of integration for immigrant groups varies by social factors, may provide an explanation for these mixed findings. In this study we examined whether one social factor, racial identity, modified the association between ethnic residential segregation and body mass index (BMI) among Hispanics.MethodsWe used data on 22,901 male and 37,335 non-pregnant female Hispanic adult participants of the 2003–2008 U.S. Behavioral Risk Factor Surveillance System living in 227 metropolitan or micropolitan areas (MMSAs). Participants self-identified as White, Black, and ‘some other race’. BMI was calculated using self-reported height and weight; the Hispanic isolation index was used to measure Hispanic residential segregation. Using multi-level linear regression models, we examined the association of Hispanic residential segregation with BMI, and we investigated whether this relationship varied by race.ResultsAmong men, Hispanic segregation was unassociated with BMI after adjusting for age, race, MMSA-level poverty, and MMSA-level population size; there was no variation in this relationship by race. Among women, significant associations between Hispanic segregation and BMI in models adjusted for demographics and MMSA-level confounders became attenuated with further adjustment for education and language of exam. However, there was statistically significant variation by race (Pinteraction = 0.03 and 0.09 for Hispanic Blacks and Hispanics who identified as some other race, respectively, vs. Hispanic Whites). Specifically, higher segregation was associated with higher mean BMI among Hispanic Whites, but it was associated with lower mean BMI among Hispanic Blacks. Segregation was unassociated with BMI among Hispanic women identifying as some other race.ConclusionsThis heterogeneity highlights the persistent influence of race on structural processes that can have downstream consequences on health. As Hispanics grow as a proportion of the U.S. population, especially across urban centers, understanding the health consequences of residence in segregated areas, and whether or not these impacts vary across different groups, will be important for the design of more comprehensive solutions to prevent adverse health outcomes.

Influence of silicon and addition elements on the mechanical behavior of ferritic ductile cast iron

An experimental study of mechanical properties and microstructural analysis was carried out on different compositions of ferritic spheroidal graphite cast iron. The influence of silicon on the ductility and strength of the material was noticed. The observation of microstructure and failure modes allowed us to explain the important role of chemical composition on the initiation and propagation of cracks. The high silicon segregation between the graphite nodules and the joints of eutectic cells decreases the mechanical material resistance. A metallurgical development was indispensable and necessary to ensure characteristics conformed to the industrial requirements.

Priority setting by sites and by species using rarity, richness and phylogenetic diversity: the case of neotropical glassfrogs (Anura: Centrolenidae)

The identification of priority areas and species for conservation is an urgent endeavor in view of environmental changes threatening biological diversity. New macroecological tools that take advantage of the rapid accumulation of distribution and phylogenetic data have been developed recently to tackle that challenge. Here we use the novel concept of the diversity and dispersion fields, complemented with phylogenetic information, to identify priorities for the conservation of neotropical glass frogs (Centrolenidae), both from the perspective of sites and of species. Through the novel approach used here, the priority level of species and sites could be determined by combinations of different traits based both on diversity (species richness and phylogenetic diversity) and distribution (geographic rarity and phylogenetic endemism). Patterns of diversity and distribution for Centrolenidae, such as extreme level of restrictedness, high levels of rarity and high segregation among species, were readily revealed by the use of range-diversity plots. Results were in some cases consistent with studies based on traditional analyses, but the inclusion of phylogenetic information added a historical-evolutionary perspective that further enhanced the analyses. We identified priority species (such as Rulyrana susatamai and Nymphargus griffithsi) and sites (such as the Guiana Shield) that harbor the evolutionary history of the group but that had been overlooked in prior studies. We suggest that for priority setting and gap analysis, phylogenetic information should not be treated as a full substitute for traditional measures of diversity but as a complementary tool.

Tertiary dendritic instability in late stage solidification of Ni-based superalloys

Derivatives of the commercial alloy CMSX-4 were directionally solidified and characterized with respect to their final dendrite microstructure. The results indicate that Ni-based superalloys with high segregation levels show significant instability in secondary dendrite arms and an increased tendency for tertiary arm formation, respectively. Phase-field simulations were used to explore the impact of chemical composition on morphological instability and tertiary arm formation during the directional solidification of Ni-based superalloys. It is found that an increase in specific alloying elements in the overall alloy composition leads to pronounced segregation at the end of solidification. This causes strong growth restriction of the secondary arms and triggers tertiary arm formation. The proposed mechanism explains experimental microstructures found in modifications of the base alloy CMSX-4.

Abstract T P131: Residential Ethnic Segregation and Stroke Risk in Mexican Americans in the BASIC Project

Background: Neighborhoods with high racial-ethnic segregation may have weak community cohesion, low neighborhood trust, and high levels of stress which may impact stroke risk factors such as hypertension. We tested the hypothesis that greater residential ethnic segregation is associated with higher stroke risk in a bi-ethnic community. Methods: Strokes were identified from the BASIC Project in Nueces County, Texas from 2000-2010. Residential ethnic segregation (range: 0-1) was derived for each census tract (used to define neighborhoods) in the county based on 2000 census data. The measure reflects the probability that a Mexican American (MA) shares their neighborhood with another MA and was categorized into: 1) predominantly non-Hispanic white (NHW, <0.3), 2) ethnically mixed (0.3-0.7), or 3) predominately MA (>0.7). Poisson models were used to examine the association between residential ethnic segregation and stroke risk unadjusted and adjusted for age, sex, ethnicity and neighborhood income. Effect modification by ethnicity was examined in the fully adjusted model, and models were run stratified by ethnicity. Results: A total of 2,857 strokes were included. Median residential ethnic segregation was 0.52 (IQR: 0.38-0.77). In the unadjusted model, predominately MA census tracts had greater stroke risk than predominantly NHW census tracts [ethnically mixed: RR=1.23 (95% CI: 1.12-1.35); predominately MA: RR=1.67 (95% CI: 1.51-1.83)]. After adjustment, residential ethnic segregation was not associated with stroke risk [ethnically mixed: RR=1.00 (95% CI: 0.71-1.42); predominately MA: RR=1.11(95% CI: 0.76-1.61)]. Effect modification by ethnicity was not significant (p=0.37), but in the stratified model limited to MAs, predominately MA census tracts had a trend toward higher stroke risk compared to MAs living in predominately NHW census tracts [RR=1.41 (95% CI: 0.94-2.12)] after adjustment for demographics and neighborhood income. Conclusions: Stroke risk for MAs was greater in neighborhoods with high ethnic segregation than in predominantly NHW neighborhoods suggesting that features of highly segregated neighborhoods may contribute to elevated stroke risk in MAs.

Understanding intra-regional variation in gender inequality in East Asia: Decomposition of cross-national differences in the gender earnings gap

This study examines cross-national differences in gender earnings gaps in Japan, Korea, and Taiwan. It applies an extended model of the gender gap decomposition method, and tests four hypotheses, each of which focuses on a different possible source of the cross-national difference in gender gap. The decomposition results support the hypothesis emphasizing the cross-national difference in the distribution of males and females and the hypothesis emphasizing the difference in pay discrimination; the results do not support the hypothesis that the differences occur because of cross-national differences in females’ human capital. The main reasons for the larger gender earnings gaps in Japan and Korea than in Taiwan are higher segregation by gender and higher degrees of within-job pay discrimination in Japan and Korea. Despite similarities in welfare policies toward women, the difference in employment practices creates a substantial intra-regional variation in gender pay inequality in East Asia.

Occupational Segregation by Race and Ethnicity in the United States: Differences Across States

Gradín C., Del Río C. and Alonso-Villar O. Occupational segregation by race and ethnicity in the United States: differences across states, Regional Studies. Using the 2005–07 American Community Survey, this paper analyses the extent of geographical disparities in occupational segregation by race/ethnicity across US states. The results show that there is a great geographical variation in segregation. A large part is driven by spatial disparities in workers' characteristics, mainly due to differences in the distribution of ethnic/racial minorities and their immigration/linguistic profiles. Taking these characteristics into account reduces this variation and reshapes the segregation map, with the highest segregation moving from states in the Southwest to those in the East Central region, where minorities face more segregating labour markets.

Cohesinopathies of a Feather Flock Together

Roberts Syndrome (RBS) and Cornelia de Lange Syndrome (CdLS) are severe developmental maladies that present with nearly an identical suite of multi-spectrum birth defects. Not surprisingly, RBS and CdLS arise from mutations within a single pathway—here involving cohesion. Sister chromatid tethering reactions that comprise cohesion are required for high fidelity chromosome segregation, but cohesin tethers also regulate gene transcription, promote DNA repair, and impact DNA replication. Currently, RBS is thought to arise from elevated levels of apoptosis, mitotic failure, and limited progenitor cell proliferation, while CdLS is thought to arise, instead, from transcription dysregulation. Here, we review new information that implicates RBS gene mutations in altered transcription profiles. We propose that cohesin-dependent transcription dysregulation may extend to other developmental maladies; the diagnoses of which are complicated through multi-functional proteins that manifest a sliding scale of diverse and severe phenotypes. We further review evidence that cohesinopathies are more common than currently posited.