578,227 research outputs found
What should an index of school segregation measure?
The article aims to make a methodological contribution to the education segregation literature, providing a critique of previous measures of segregation used in the literature, as well as suggesting an alternative approach to measuring segregation. Specifically, the paper examines Gorard, Fitz and Taylor's finding that social segregation between schools, as measured by free school meals (FSM) entitlement, fell significantly in the years following the 1988 Education Reform Act. Using Annual Schools Census data from 1989 to 2004, the paper challenges the magnitude of their findings, suggesting that the method used by Gorard et al. seriously overstates the size of the fall in segregation. We make the case for a segregation curve approach to measuring segregation, where comparisons of the level of segregation are possible regardless of the percentage FSM eligibility. Using this approach, we develop a new method for describing both the level and the location of school segregation
Segregation by thermal diffusion in granular shear flows
Segregation by thermal diffusion of an intruder immersed in a sheared
granular gas is analyzed from the (inelastic) Boltzmann equation. Segregation
is induced by the presence of a temperature gradient orthogonal to the shear
flow plane and parallel to gravity. We show that, like in analogous systems
without shear, the segregation criterion yields a transition between upwards
segregation and downwards segregation. The form of the phase diagrams is
illustrated in detail showing that they depend sensitively on the value of
gravity relative to the thermal gradient. Two specific situations are
considered: i) absence of gravity, and ii) homogeneous temperature. We find
that both mechanisms (upwards and downwards segregation) are stronger and more
clearly separated when compared with segregation criteria in systems without
shear.Comment: 8 figures. To appear in J. Stat. Mec
Shear-driven size segregation of granular materials: modeling and experiment
Granular materials segregate by size under shear, and the ability to
quantitatively predict the time required to achieve complete segregation is a
key test of our understanding of the segregation process. In this paper, we
apply the Gray-Thornton model of segregation (developed for linear shear
profiles) to a granular flow with an exponential profile, and evaluate its
ability to describe the observed segregation dynamics. Our experiment is
conducted in an annular Couette cell with a moving lower boundary. The granular
material is initially prepared in an unstable configuration with a layer of
small particles above a layer of large particles. Under shear, the sample mixes
and then re-segregates so that the large particles are located in the top half
of the system in the final state. During this segregation process, we measure
the velocity profile and use the resulting exponential fit as input parameters
to the model. To make a direct comparison between the continuum model and the
observed segregation dynamics, we locally map the measured height of the
experimental sample (which indicates the degree of segregation) to the local
packing density. We observe that the model successfully captures the presence
of a fast mixing process and relatively slower re-segregation process, but the
model predicts a finite re-segregation time, while in the experiment
re-segregation occurs only exponentially in time
Female participation increases and gender segregation. ESRI WP564, May 2017
This article examines the impact of a large increase in female participation on occupational segregation. Increases in female participation may decrease occupational segregation if women enter male dominated sectors but may increase segregation if they enter already female dominated sectors. Using Ireland as a test case due to the recent large increase in female participation rates, we firstly carry out a decomposition analysis between 1991 and 2006 and find that the rise in female employment was driven predominantly by increased demand while between one tenth and one fifth of the rise was due to women increasing their share of occupational employment. Formal measures of segregation show that occupational segregation fell over this time period. The formal measures of segregation show that the level of occupational grouping is important with stagnation or smaller falls in segregation using a broad occupational grouping and sharper falls using a more detailed occupational grouping. Our findings support previous U.S. research that found a rise in female participation resulted in a decline in occupational segregation
Quantifying the Energetics and Length Scales of Carbon Segregation to Fe Symmetric Tilt Grain Boundaries Using Atomistic Simulations
Segregation of impurities to grain boundaries plays an important role in both
the stability and macroscopic behavior of polycrystalline materials. The
research objective in this work is to better characterize the energetics and
length scales involved with the process of solute and impurity segregation to
grain boundaries. Molecular dynamics simulations are used to calculate the
segregation energies for carbon within multiple grain boundary sites over a
database of 125 symmetric tilt grain boundaries in Fe. The simulation results
show that the majority of atomic sites near the grain boundary have segregation
energies lower than in the bulk. Moreover, depending on the boundary, the
segregation energies approach the bulk value approximately 5-12 \AA\ away from
the center of the grain boundary, providing an energetic length scale for
carbon segregation. A subsequent data reduction and statistical representation
of this dataset provides critical information such as about the mean
segregation energy and the associated energy distributions for carbon atoms as
a function of distance from the grain boundary, which quantitatively informs
higher scale models with energetics and length scales necessary for capturing
the segregation behavior of impurities in Fe. The significance of this research
is the development of a methodology capable of ascertaining segregation
energies over a wide range of grain boundary character (typical of that
observed in polycrystalline materials), which herein has been applied to carbon
segregation in a specific class of grain boundaries in iron
Mass segregation trends in SDSS galaxy groups
It has been shown that galaxy properties depend strongly on their host
environment. In order to understand the relevant physical processes driving
galaxy evolution it is important to study the observed properties of galaxies
in different environments. Mass segregation in bound galaxy structures is an
important indicator of evolutionary history and dynamical friction timescales.
Using group catalogues derived from the Sloan Digital Sky Survey Data Release 7
(SDSS DR7) we investigate mass segregation trends in galaxy groups at low
redshift. We investigate average galaxy stellar mass as a function of
group-centric radius and find evidence for weak mass segregation in SDSS
groups. The magnitude of the mass segregation depends on both galaxy stellar
mass limits and group halo mass. We show that the inclusion of low mass
galaxies tends to strengthen mass segregation trends, and that the strength of
mass segregation tends to decrease with increasing group halo mass. We find the
same trends if we use the fraction of massive galaxies as a function of
group-centric radius as an alternative probe of mass segregation. The magnitude
of mass segregation that we measure, particularly in high-mass haloes,
indicates that dynamical friction is not acting efficiently.Comment: 6 pages, 2 figures, accepted for publication in MNRAS Letter
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