Aboriginal Children and Their Caregivers Living with Low Income: Outcomes from a Two-Generation Preschool Program

The development of preschool children of Aboriginal heritage is jeopardized by the inter-generational transmission of risk that has created, and continues to create, social disadvantage. Early intervention programs are intended to mitigate the impact of social disadvantage. Yet, evidence of the effectiveness of these programs for children of Aboriginal heritage is limited. The purpose of this study was to examine the effects of a two-generation, multi-cultural preschool program on 45 children of Aboriginal heritage and their caregivers. We used a single-group, pretest (program intake)/posttest (program exit) design with follow-up when the children were 7 years old. We used an observational measure of child receptive language (Peabody Picture Vocabulary Test–III) and caregiver-reported measures of child development (Nipissing District Developmental Screen), risk for child maltreatment (Adult-Adolescent Parenting Inventory; AAPI), parenting stress (Parenting Stress Index; PSI), self-esteem (Rosenberg Self-Esteem scale; RSE), and life skills (Community Life Skills scale; CLS). Using paired t-tests we found statistically significant increases in child receptive language scores between intake and exit, and repeated-measures ANOVA showed that these improvements were maintained up to age 7 years. For caregivers, Pearson’s correlations demonstrated that risk for child maltreatment, parenting stress, self-esteem, and life skills were stable over time. Results of this study suggest that children of Aboriginal heritage can benefit from participation in a two-generation, multi-cultural preschool program. Their caregivers may have received greater benefit if issues of intergenerational transmission of the negative influences of residential schools were addressed as part of programming

Observation of the Gamma-Ray Binary HESS J0632+057 with the HESS, MAGIC, and VERITAS Telescopes

The results of gamma-ray observations of the binary system HESS J0632 + 057 collected during 450 hr over 15 yr, between 2004 and 2019, are presented. Data taken with the atmospheric Cherenkov telescopes H.E.S.S., MAGIC, and VERITAS at energies above 350 GeV were used together with observations at X-ray energies obtained with Swift-XRT, Chandra, XMM-Newton, NuSTAR, and Suzaku. Some of these observations were accompanied by measurements of the H alpha emission line. A significant detection of the modulation of the very high-energy gamma-ray fluxes with a period of 316.7 +/- 4.4 days is reported, consistent with the period of 317.3 +/- 0.7 days obtained with a refined analysis of X-ray data. The analysis of data from four orbital cycles with dense observational coverage reveals short-timescale variability, with flux-decay timescales of less than 20 days at very high energies. Flux variations observed over a timescale of several years indicate orbit-to-orbit variability. The analysis confirms the previously reported correlation of X-ray and gamma-ray emission from the system at very high significance, but cannot find any correlation of optical H alpha parameters with fluxes at X-ray or gamma-ray energies in simultaneous observations. The key finding is that the emission of HESS J0632 + 057 in the X-ray and gamma-ray energy bands is highly variable on different timescales. The ratio of gamma-ray to X-ray flux shows the equality or even dominance of the gamma-ray energy range. This wealth of new data is interpreted taking into account the insufficient knowledge of the ephemeris of the system, and discussed in the context of results reported on other gamma-ray binary systems

Determining local geometrical features of grain boundaries from microscopy

Grain boundaries are solid-solid interfaces whose dynamics is driven by their local curvature. As they are fluctuating interfaces and have a width comparable to the lattice spacing of the surrounding grains, the determination of their local geometrical characteristics is difficult. Here we present a method to determine the local normal direction, tangent plane and curvature of grain boundaries from microscopy images using point sampled surface analysis techniques. We apply our algorithm to study the boundary of a shrinking grain in a two-dimensional colloidal polycrystalline material. Our method is easily generalized to three dimensions, which makes it applicable to the wide range of interfaces encountered in soft matter

Determining local geometrical features of grain boundaries from microscopy

Grain boundaries are solid-solid interfaces whose dynamics is driven by their local curvature. As they are fluctuating interfaces and have a width comparable to the lattice spacing of the surrounding grains, the determination of their local geometrical characteristics is difficult. Here we present a method to determine the local normal direction, tangent plane and curvature of grain boundaries from microscopy images using point sampled surface analysis techniques. We apply our algorithm to study the boundary of a shrinking grain in a two-dimensional colloidal polycrystalline material. Our method is easily generalized to three dimensions, which makes it applicable to the wide range of interfaces encountered in soft matter

Anomalous grain growth in a polycrystalline monolayer of colloidal hard spheres

Understanding grain growth is key for controlling the microstructure and the mechanical properties of most polycrystalline materials, including metals, alloys and ceramics. However, the precise mechanisms and kinetics of grain growth remain poorly understood both at the theoretical level and experimentally as direct observation is cumbersome in atomic systems. Here, we study the grain growth process in a polycrystalline monolayer of colloidal hard spheres. We find that the bond-orientational correlation function satisfiees the dynamic scaling hypothesis and has the general scaling form predicted for systems containing random domain walls. However, the associated correlation length grows slower than ~ t^1/2 that corresponds to normal curvature-driven grain growth. To understand the origin of this anomalous grain growth, we directly monitor the evolution of the grain boundary network by measuring the so-called grain boundary character distribution. We show that there is a strong annihilation of large angle grain boundaries while small angle grain boundaries become relatively more present. Using scaling arguments, we derive the time dependence of the correlation length and show its good agreement with the data. We conclude that the origin of anomalous grain growth is the curvature-driven coarsening of the large angle grain boundaries at a rate which depends on their relative length in the total grain boundary network

Anomalous grain growth in a polycrystalline monolayer of colloidal hard spheres

Understanding grain growth is key for controlling the microstructure and the mechanical properties of most polycrystalline materials, including metals, alloys and ceramics. However, the precise mechanisms and kinetics of grain growth remain poorly understood both at the theoretical level and experimentally as direct observation is cumbersome in atomic systems. Here, we study the grain growth process in a polycrystalline monolayer of colloidal hard spheres. We find that the bond-orientational correlation function satisfiees the dynamic scaling hypothesis and has the general scaling form predicted for systems containing random domain walls. However, the associated correlation length grows slower than ~ t^1/2 that corresponds to normal curvature-driven grain growth. To understand the origin of this anomalous grain growth, we directly monitor the evolution of the grain boundary network by measuring the so-called grain boundary character distribution. We show that there is a strong annihilation of large angle grain boundaries while small angle grain boundaries become relatively more present. Using scaling arguments, we derive the time dependence of the correlation length and show its good agreement with the data. We conclude that the origin of anomalous grain growth is the curvature-driven coarsening of the large angle grain boundaries at a rate which depends on their relative length in the total grain boundary network

Equilibrium grain boundary segregation and clustering of impurities in colloidal polycrystalline monolayers

We investigate the segregation of impurities to grain boundaries in colloidal polycrystalline monolayers using video-microscopy. A model colloidal alloy is prepared by embedding large spherical impurities in a polycrystalline monolayer of small host colloidal hard spheres, which stops grain growth at a finite grain size. The size ratio between the impurities and the host particles determines whether they behave as interstitial or substitutional impurities in the bulk crystal, akin to those in real alloys. We find that the partitioning of impurities between the grains and the grain boundaries is in very good agreement with the Langmuir-McLean adsorption model for equilibrium grain boundary segregation. This enables the direct measurement of the free energy of adsorption for the two types of impurities. Near saturation, we characterise the spatial distribution of the adsorbed impurities and find that it strongly depends on their interstitial or substitutional nature. This is because the relative importance of clustering and mixing due to non-additivity is determined by geometrical constraints imposed by the crystalline host lattice

Shrinkage mechanisms of grain boundary loops in two-dimensional colloidal crystals

We discuss the various mechanisms involved in the spontaneous shrinkage of circular grain boundaries in two-dimensional colloidal crystals. We provide experimental evidence that these grain boundary loops shrink owing to three intermittent mechanisms proposed for atomic materials, namely purely curvature-driven migration, coupled grain boundary migration, and grain boundary sliding. Throughout shrinkage, the product of the radius and misorientation of the grain boundary loop remains higher than a fundamental limit resulting from the specific dislocation structure of grain boundary loops, except for the very last stage where the loop character is lost. Despite its complexity, this process can be effectively described by a single kinetic coefficient, allowing for a simplified description of grain boundary loop kinetics

Equilibrium grain boundary segregation and clustering of impurities in colloidal polycrystalline monolayers

We investigate the segregation of impurities to grain boundaries in colloidal polycrystalline monolayers using video-microscopy. A model colloidal alloy is prepared by embedding large spherical impurities in a polycrystalline monolayer of small host colloidal hard spheres, which stops grain growth at a finite grain size. The size ratio between the impurities and the host particles determines whether they behave as interstitial or substitutional impurities in the bulk crystal, akin to those in real alloys. We find that the partitioning of impurities between the grains and the grain boundaries is in very good agreement with the Langmuir-McLean adsorption model for equilibrium grain boundary segregation. This enables the direct measurement of the free energy of adsorption for the two types of impurities. Near saturation, we characterise the spatial distribution of the adsorbed impurities and find that it strongly depends on their interstitial or substitutional nature. This is because the relative importance of clustering and mixing due to non-additivity is determined by geometrical constraints imposed by the crystalline host lattice