Using elastic energy considerations to explain rafting in Ni-based superalloys with a high gamma volume fraction

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the Degree of Master of ScienceA simple three-dimensional model of a high y' volume fraction Ni-based alloy is developed. The model is based on the idea that a unit volume in the superalloy can be represented by a cuboidal precipitate with thin 'slabs' of matrix material 'stuck' onto its faces in such a way that coherency is maintained. Rafting is investigated by considering the changes in total energy whon the cuboidal precipitates start to flatten into plate shapes or lengthen into rod shapes. It is assumed that inelastic effects are negligible. Internal and external stresses and strains are determined. Expressions for the derivative of the total energy with respect to a shape parameter are then calculated in the absence of applied stress and in the presence of applied stress. Predictions of rafting behaviour are made for six alloys. Excellent agreement is found with experimental evidence but it is suggested that the agreement is fortuitous.AC 201

Ram pressure statistics for bent tail radio galaxies

In this paper we use the MareNostrum Universe Simulation, a large scale, hydrodynamic, non-radiative simulation in combination with a simple abundance matching approach to determine the ram pressure statistics for bent radio sources (BRSs). The abundance matching approach allows us to determine the locations of all galaxies with stellar masses $> 10^{11} MSol$ in the simulation volume. Assuming ram pressure exceeding a critical value causes bent morphology, we compute the ratio of all galaxies exceeding the ram pressure limit (RPEX galaxies) relative to all galaxies in our sample. According to our model 50% of the RPEX galaxies at $z = 0$ are found in clusters with masses larger than $10^{14.5}MSol$ the other half resides in lower mass clusters. Therefore, the appearance of bent tail morphology alone does not put tight constraints on the host cluster mass. In low mass clusters, $M < 10^{14}MSol$, RPEX galaxies are confined to the central 500 kpc whereas in clusters of $> 10^{15}Msol$ they can be found at distances up to 1.5Mpc. Only clusters with masses $> 10^{15}MSol$ are likely to host more than one BRS. Both criteria may prove useful in the search for distant, high mass clusters.Comment: 10 pages, 10 figures, Submitted to the Monthly Notices of the Royal Astronomical Societ

Theory and Statistics of Weak Lensing from Large-Scale Mass Inhomogeneities

Weak lensing by large-scale mass inhomogeneities in the Universe induces correlations in the observed ellipticities of distant sources. We first review the harmonic analysis and statistics required of these correlations and discuss calculations for the predicted signal. We consider the ellipticity correlation function, the mean-square ellipticity, the ellipticity power spectrum, and a global maximum-likelihood analysis to isolate a weak-lensing signal from the data. Estimates for the sensitivity of a survey of a given area, surface density, and mean intrinsic source ellipticity are presented. We then apply our results to the FIRST radio-source survey. We predict an rms ellipticity of roughly 0.011 in $1^\circ \times 1^\circ$ pixels and 0.018 in $20' \times 20'$ pixels if the power spectrum is normalized to $\sigma_8 \Omega^{0.53} = 0.6$, as indicated by the cluster abundance. The signal is significantly larger in some models if the power spectrum is normalized instead to the COBE anisotropy. The uncertainty in the predictions from imprecise knowledge of the FIRST redshift distribution is about 25% in the rms ellipticity. We show that FIRST should be able to make a statistically significant detection of a weak-lensing signal for cluster-abundance-normalized power spectra.Comment: 10 pages, 4 figure

Probing the bias of radio sources at high redshift

The relationship between the clustering of dark matter and that of luminous matter is often described using the bias parameter. Here, we provide a new method to probe the bias of intermediate-to-high-redshift radio continuum sources for which no redshift information is available. We matched radio sources from the Faint Images of the Radio Sky at Twenty centimetres survey data to their optical counterparts in the Sloan Digital Sky Survey to obtain photometric redshifts for the matched radio sources.We then use the publicly available semi-empirical simulation of extragalactic radio continuum sources (S3) to infer the redshift distribution for all FIRST sources and estimate the redshift distribution of unmatched sources by subtracting the matched distribution from the distribution of all sources. We infer that the majority of unmatched sources are at higher redshifts than the optically matched sources and demonstrate how the angular scales of the angular two-point correlation function can be used to probe different redshift ranges. We compare the angular clustering of radio sources with that expected for dark matter and estimate the bias of different samples.Web of Scienc

Clustering of HI galaxies in the HI parkes all sky survey and arecibo legacy fast alfa survey

We investigate the clustering of H I-selected galaxies in the Arecibo Legacy Fast ALFA Survey (ALFALFA) and compare results with those obtained for the H I Parkes All Sky Survey (HIPASS). Measurements of the angular correlation function and the inferred 3D clustering are compared with results from direct spatial-correlation measurements. We are able to measure clustering on smaller angular scales and for galaxies with lower H I masses than was previously possible. We calculate the expected clustering of dark matter using the redshift distributions of the HIPASS and ALFALFA, and show that the ALFALFA sample is somewhat more antibiased with respect to dark matter than the HIPASS sample

What Made Me the Teacher I Am Today? A Reflection by Selected Leonore Annenberg-Woodrow Wilson Teaching Fellows

The report offers a series of short essays from 18 teachers, each reflecting on what inspired and guided them into the teaching profession. Some of the highlights include:"I've come to realize that my learning process in the classroom actually feels a whole lot like the science I practiced at the bench: engineering experimental procedures, collecting and analyzing data, and formulating questions about next steps. It turns out that my scientific worldview can really improve learning outcomes for my students," said Kristin Milks, a biology and earth science teacher in Bloomington, IN, who enrolled in a teacher preparation program shortly after completing her Ph.D. in biochemistry."What transforms someone from being a good teacher to being a great teacher is the passion to make connections with students, to constantly evaluate and adjust their practice to do what is in the students' best interest," said Catherine Ann Haney, a Virginia Spanish teacher who has recently been teaching in Santiago, Chile."Enrolling in a teacher education program, instead of starting my career as a teacher first and then obtaining my master's degree after, meant I had a cohort of other soon-to-be teachers to learn with as we persevered through a very rigorous and demanding year," said Jeremy Cress, a math teacher in Philadelphia."I realized that being a good math teacher does not mean explaining clearly, making kids like me, or making math fun. Rather, it means giving students the opportunity to solve problems by themselves from start to finish, to struggle and persevere, and to learn from each other's particular strengths," said Brittany Leknes, a math teacher from Sunnyvale, CA."Together my students and I co-create their identities, their sense of themselves, and their understanding of their place in society. Because I believe wholly in my students' own power, I teach to disrupt school cultures that suggest that students need to be anything less than their whole selves," said Kayla Vinson, who taught social students in the Harlem Children's Zone.Created in 2007, the Leonore Annenberg-Woodrow Wilson Teaching Fellowship was designed to serve as the equivalent of a national "Rhodes Scholarship" for teaching. Working with Stanford University, the University of Pennsylvania, the University of Virginia, and the University of Washington, the Woodrow Wilson Foundation provided $30,000 stipends for exceptionally able candidates to complete a yearlong master's degree program. In exchange, the teacher candidates agreed to teach for three years in high-need secondary schools across the country. The Leonore Annenberg Teaching Fellowship was funded through grants from the Annenberg Foundation and Carnegie Corporation of New York. It served as the basis for the Woodrow Wilson Foundation's successful Teaching Fellowship program, which now operates in five states (Georgia, Indiana, Michigan, New Jersey, and Ohio), operating in partnership with 28 universities. Woodrow Wilson Teaching Fellows complete a rigorous yearlong master's degree program, coupled with a robust yearlong clinical experience. Once they earn their degrees, Woodrow Wilson Teaching Fellows teach in high-need STEM classrooms, while receiving three years of coaching and mentoring

Role for DNA Methylation in the Regulation of miR-200c and miR-141 Expression in Normal and Cancer Cells

The microRNA-200 family participates in the maintenance of an epithelial phenotype and loss of its expression can result in epithelial to mesenchymal transition (EMT). Furthermore, the loss of expression of miR-200 family members is linked to an aggressive cancer phenotype. Regulation of the miR-200 family expression in normal and cancer cells is not fully understood.Epigenetic mechanisms participate in the control of miR-200c and miR-141 expression in both normal and cancer cells. A CpG island near the predicted mir-200c/mir-141 transcription start site shows a striking correlation between miR-200c and miR-141 expression and DNA methylation in both normal and cancer cells, as determined by MassARRAY technology. The CpG island is unmethylated in human miR-200/miR-141 expressing epithelial cells and in miR-200c/miR-141 positive tumor cells. The CpG island is heavily methylated in human miR-200c/miR-141 negative fibroblasts and miR-200c/miR-141 negative tumor cells. Mouse cells show a similar inverse correlation between DNA methylation and miR-200c expression. Enrichment of permissive histone modifications, H3 acetylation and H3K4 trimethylation, is seen in normal miR-200c/miR-141-positive epithelial cells, as determined by chromatin immunoprecipitation coupled to real-time PCR. In contrast, repressive H3K9 dimethylation marks are present in normal miR-200c/miR-141-negative fibroblasts and miR-200c/miR-141 negative cancer cells and the permissive histone modifications are absent. The epigenetic modifier drug, 5-aza-2′-deoxycytidine, reactivates miR-200c/miR-141 expression showing that epigenetic mechanisms play a functional role in their transcriptional control.We report that DNA methylation plays a role in the normal cell type-specific expression of miR-200c and miR-141 and this role appears evolutionarily conserved, since similar results were obtained in mouse. Aberrant DNA methylation of the miR-200c/141 CpG island is closely linked to their inappropriate silencing in cancer cells. Since the miR-200c cluster plays a significant role in EMT, our results suggest an important role for DNA methylation in the control of phenotypic conversions in normal cells

Longitudinal assessment of cognitive and psychosocial functioning after Hurricanes Katrina and Rita: Exploring disaster impact on middle-aged, older, and oldest-old adults

The authors examined the effects of Hurricanes Katrina and Rita on cognitive and psychosocial functioning in a lifespan sample of adults 6-14 months after the storms. Participants were recruited from the Louisiana Healthy Aging Study. Most were assessed during the immediate impact period and retested for this study. Analyses of pre- and post-disaster cognitive data confirmed that storm-related decrements in working memory for middle-aged and older adults observed in the immediate impact period had returned to pre-hurricane levels in the post-disaster recovery period. Middle-aged adults reported more storm-related stressors and greater levels of stress than the two older groups at both waves of testing. These results are consistent with a burden perspective on post-disaster psychological reactions. © 2012 Wiley Periodicals, Inc

Radio Continuum Surveys with Square Kilometre Array Pathfinders

In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia), e-MERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MeerKAT (South Africa), and the Murchison Widefield Array. Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. A radio continuum survey is being planned on each of them with the primary science objective of understanding the formation and evolution of galaxies over cosmic time, and the cosmological parameters and large-scale structures which drive it. In pursuit of this objective, the different teams are developing a variety of new techniques, and refining existing ones. To achieve these exciting scientific goals, many technical challenges must be addressed by the survey instruments. Given the limited resources of the global radio-astronomical community, it is essential that we pool our skills and knowledge. We do not have sufficient resources to enjoy the luxury of re-inventing wheels. We face significant challenges in calibration, imaging, source extraction and measurement, classification and cross-identification, redshift determination, stacking, and data-intensive research. As these instruments extend the observational parameters, we will face further unexpected challenges in calibration, imaging, and interpretation. If we are to realise the full scientific potential of these expensive instruments, it is essential that we devote enough resources and careful study to understanding the instrumental effects and how they will affect the data. We have established an SKA Radio Continuum Survey working group, whose prime role is to maximise science from these instruments by ensuring we share resources and expertise across the projects. Here we describe these projects, their science goals, and the technical challenges which are being addressed to maximise the science return