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Segregation Effects (segregation + effects)

Distribution by Scientific Domains

Polymers and Materials Science	40%

Selected Abstracts

Racial discrimination in the Brazilian labour market: wage, employment and segregation effects

JOURNAL OF INTERNATIONAL DEVELOPMENT, Issue 8 2004
Jean-Louis Arcand
The social science literature has done much to document pervasive racial discrimination in Brazil and there is little doubt that a very dark colour is a handicap to social advancement. Nevertheless, very few empirical economic studies have attempted to quantify the impact of ethnic discrimination in Brazil. Using data culled from the Pesquisa National por Amostra de Domicílios (PNAD), this paper fills this void by analysing ethnic wage and employment gaps, as well as occupational segregation in Brazil, using the Oaxaca decomposition methodology. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Core,shell structure and segregation effects in composite droplet polymer blends

AICHE JOURNAL, Issue 4 2003
Joël Reignier
Core,shell morphology formation within the dispersed phase was studied for composite droplet polymer-blend systems comprising a high-density polyethylene matrix, polystyrene shell and different molecular weights of poly(methyl methacrylate) core material. The blends were prepared in the melt using an internal mixer, and the morphology was analyzed by electron microscopy. Changing the viscoelastic properties of the core in the dispersed phase dramatically affects PS-PMMA segregation within the dispersed composite droplet itself. A high-molecular-weight-PMMA core contains a large quantity of occluded PS inclusions, while the low-molecular-weight PMMA results in a perfectly segregated PS shell and PMMA core. These phenomena were attributed to the viscosity of the PMMA. Using the latter system, a direct microscopic study of the shell formation process demonstrates unambiguously that under conditions of perfect segregation, the onset of complete shell formation corresponds to a shell thickness that is close to two times the radius of gyration of polystyrene. Thus, the thinnest possible shell in such a system possesses a molecular-scale thickness. The system with the high-molecular-weight-PMMA core demonstrates an onset of complete shell formation that is displaced to higher concentrations due to the poor segregation effect. By counterbalancing the effects of viscosity ratio and interfacial effects on the composite droplet size, it is possible to generate perfectly segregated core,shell dispersed-phase morphologies of almost identical size with a controlled shell thickness ranging from 40 to 300 nm. [source]

Combinatorial Ink-Jet Printer for Ceramics: Calibration

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003
Mohammad Masoud Mohebi
This article describes an ink-jet printer for the construction of combinatorial libraries and functionally graded ceramics. It can mix and print all possible compositions for high-throughput screening. The number of components is set by the number of mixing valves that deliver ceramic ink from pressurized reservoirs into a circulation chamber. Compositional control is by either complete or incremental change. Organic liquids and ceramic inks are used in a systematic three-stage calibration. The calibration protocol accounts for the effects of ink viscosity, reservoir pressure, valve-opening time, and temperature, but reveals unexpected segregation effects that occur in the ink after deposition. [source]

Verallgemeinerungsfähige Merkmale und Besonderheiten des Sprühkompaktierens

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 1 2003
K. Bauckhage
Sprayforming; Modelling Microstructure; Geometry Abstract Dadurch, daß beim Sprühkompaktieren die schnelle Erstarrung und Abkühlung des Materials das Ausmaß von Entmischungen eindämmen, können Makroseigerungen unterbunden und Anreicherungen an den Korngrenzen deutlich verringert werden. Ferner wird das Risiko der Lunker- und Warmrißbildung durch den Impuls des Massetransportes während des Kompaktiervorganges stark reduziert. Dies bedeutet, daß solche Materialien, die bspw. beim Gießen zu starker Seigerung neigen und besonders anfällig für die Lunkerbildung und/oder Warmrißbildung sind sowie bei Umformverfahren zur Zeilenbildung von Carbiden, Nitriden oder Sulfiden neigen, mit Hilfe des Sprühkompaktierens im Freiformverfahren mit großen Abmaßen chemisch homogen und fehlerfrei herstellbar werden. Ein besonderes Merkmal sprühkompaktierter Deposits ist ihr feines Gefüge und ihre vergleichsweise hohe Duktilität. Die Besonderheiten des neuartigen Urformverfahrens werden anhand von Beispielen erläutert. Characteristic Features and Specific Qualifications of the Sprayforming Process to be Generalized The solidification and cooling process of spray formed materials predominates the extent of any segregation and separation process, which is conducive to avoid macro-segregation and to diminish concentration of alloying components at the grain boundaries. The risk of coarse porosity or of hot cracking is reduced significantly by the momentum of the mass flow during spray deposition. This means that those materials which e.g. during the casting process tend to establish strong segregation effects and cavities and/or hot cracks as well as those which tend to create filaments of carbides, nitrides or sulphides during rolling can be generated by the spray forming process in large dimensions with chemical homogeneity and without any of those defects. A characteristic feature of spray formed materials is the fine equiaxed grain structure and the high ductility. Specific features of this new free forming process will be discussed. [source]

InGaAs/GaAs quantum wells and quantum dots on GaAs(11n) substrates studied by photoreflectance spectroscopy

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2007
J. S. Rojas-Ramirez
Abstract Pseudomorphic InGaAs/GaAs quantum wells (QWs) and self-assembled InAs quantum dots (QDs) were grown by molecular beam epitaxy (MBE) on GaAs(11n)A substrates. Photoreflectance spectroscopy was employed to investigate the transitions in the heterostructures. The transitions in QWs have two contributions, a blue shift due to the compressive strain, and a red shift due to the quantum confined Stark effect produced by the piezoelectric field. A traditional theoretical interpretation of the QWs transitions employing a simple well model with sharp interfaces shows discrepancies with the experimental results. In order to satisfactorily explain the transitions we proposed to include segregation effects of Indium at the wells interfaces. The matrix transfer method was implemented to numerically solve the Schrödinger equation taking into account In segregation effects by including an asymmetric potential well with a profile depending on the details of the In incorporation. With segregation effects included, the calculated transitions fit very well the PR spectra. On the other hand, the transitions in self-assembled QDs were obtained by fitting the PR spectra employing a first derivative line-shape function. For n = 2, 4, 5, two functions were required to fit the spectra. For n = 3 only one function was required, in agreement with the more uniform QDs size distribution observed by atomic force microscopy on GaAs(113)A. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]