6,138 research outputs found

    A statnet Tutorial

    Get PDF
    The statnet suite of R packages contains a wide range of functionality for the statistical analysis of social networks, including the implementation of exponential-family random graph (ERG) models. In this paper we illustrate some of the functionality of statnet through a tutorial analysis of a friendship network of 1,461 adolescents.

    ergm: A Package to Fit, Simulate and Diagnose Exponential-Family Models for Networks

    Get PDF
    We describe some of the capabilities of the ergm package and the statistical theory underlying it. This package contains tools for accomplishing three important, and inter-related, tasks involving exponential-family random graph models (ERGMs): estimation, simulation, and goodness of fit. More precisely, ergm has the capability of approximating a maximum likelihood estimator for an ERGM given a network data set; simulating new network data sets from a fitted ERGM using Markov chain Monte Carlo; and assessing how well a fitted ERGM does at capturing characteristics of a particular network data set.

    Actions of certain arithmetic groups on Gromov hyperbolic spaces

    Full text link
    We study the variety of actions of a fixed (Chevalley) group on arbitrary geodesic, Gromov hyperbolic spaces. In high rank we obtain a complete classification. In rank one, we obtain some partial results and give a conjectural picture.Comment: v1: 23 pages, 4 figures. v2: 24 pages, 4 figures. Fixed a bad typo in Claim 3.3 and made some other small changes. v3: A few small clarifications. To appear in AG

    statnet: Software Tools for the Representation, Visualization, Analysis and Simulation of Network Data

    Get PDF
    statnet is a suite of software packages for statistical network analysis. The packages implement recent advances in network modeling based on exponential-family random graph models (ERGM). The components of the package provide a comprehensive framework for ERGM-based network modeling, including tools for model estimation, model evaluation, model-based network simulation, and network visualization. This broad functionality is powered by a central Markov chain Monte Carlo (MCMC) algorithm. The coding is optimized for speed and robustness.

    First-Year Students' Beliefs About Smartness and Their Beliefs About the Relationship Between Smartness and Socioeconomic Status

    Get PDF
    In undergraduate engineering programs, we know that students who express beliefs about smartness that are normative (such as prioritizing cognitive ability) are more favored for success, and we know that students hailing from lower-socioeconomic backgrounds are less likely to succeed than their peers with higher-socioeconomic backgrounds. However, there is currently a relative lack of research pertaining to the intersection between socioeconomic status and beliefs about smartness. To contribute to this gap, this study addresses the following research question: What do first-year engineering students believe about smartness, and what do they believe about the relationship between smartness and socioeconomic status? I collected qualitative data through one-on-one interviews with fourteen first-year engineering students about their beliefs about smartness and the relationship between smartness and socioeconomic status (SES). Through an iterative, qualitative coding process, I analyzed interviews and developed themes based on their responses. I found that students expressed three major beliefs about smartness: that it was defined by achievement, that it was defined by effort, and that it was a local construct. Students expressed the belief that smartness was effort much more commonly when discussing peers they perceived as not smart. This indicates that students believe that smartness is a mixture of achievement and effort, and that the two have varying importance depending on whether students are discussing smartness or a lack of smartness. I also found that most students believed smartness and SES to be linked in some way, but some students believed the two concepts to not be linked at all. All students, however, acknowledged similar advantages of students with high SES. Further investigation is recommended to more thoroughly investigate students' beliefs about the relationship between smartness and SES.College of EngineeringNo embargoAcademic Major: Materials Science and Engineerin

    An Intervention to Promote Growth Mindset and STEM Self-Efficacy of High School Students: Exploring the Complexity of Beliefs

    Get PDF
    The marginalization of women in engineering is a persistent problem. The overall goal of our collaborative project was to promote interest and participation in science, technology, engineering, and mathematics (STEM), particularly for high school girls. We took an action research approach with a local high school science teacher to develop, implement, and research the impact of a classroom-based intervention designed to encourage growth mindset and STEM self-efficacy beliefs using mixed methods. We analyzed pre- and postsurvey data collected using a control-treatment design to determine the impact of the intervention on high school boys’ and girls’ self-efficacy and mindset beliefs. We also conducted semi-structured, one-on-one interviews with purposefully selected participants from the treatment group to further explore students’ mindset and STEM self-efficacy beliefs qualitatively. We found that the intervention did result in a statistically significant change towards more growth-oriented beliefs for the high school girls who received the intervention as compared to the control group. We found that the intervention did not result in any statistically significant change in the girls’ self-efficacy beliefs, the boys’ mindset beliefs, or the boys’ self-efficacy beliefs. The qualitative analysis revealed that after receiving the intervention, students held contradictory beliefs about the role of effort and the role of innate ability in STEM achievement. Further, we found that context and gender mattered in how students justified their self-efficacy: boys and girls both expressed the belief that effort would lead to their ability to succeed in science classes, but the girls were less likely than the boys to express the belief that effort would lead to their ability to succeed in the context of a science career. By connecting our findings to broader cultural narratives, we suggest that for the continued success of intervention efforts aimed at promoting a growth mindset and STEM self-efficacy, particularly for girls, such efforts should include opportunities for students to reflect upon and unpack the broader cultural narratives about effort, innate ability, and the gendered stereotypes about STEM ability that inform their beliefs. Finally, from the perspective of a high school science teacher, we also advocate for more representation of women among science teachers and classroom speakers and the importance of explicitly connecting class content and success in classrooms to real-world contexts

    The Effect of Negative-Energy Shells on the Schwarzschild Black Hole

    Get PDF
    We construct Penrose diagrams for Schwarzschild spacetimes joined by massless shells of matter, in the process correcting minor flaws in the similar diagrams drawn by Dray and 't Hooft, and confirming their result that such shells generate a horizon shift. We then consider shells with negative energy density, showing that the horizon shift in this case allows for travel between the heretofore causally separated exterior regions of the Schwarzschild geometry. These drawing techniques are then used to investigate the properties of successive shells, joining multiple Schwarzschild regions. Again, the presence of negative-energy shells leads to a causal connection between the exterior regions, even in (some) cases with two successive shells of equal but opposite total energy.Comment: 12 pages, 10 figure

    Traversable Wormholes in Geometries of Charged Shells

    Get PDF
    We construct a static axisymmetric wormhole from the gravitational field of two charged shells which are kept in equilibrium by their electromagnetic repulsion. For large separations the exterior tends to the Majumdar-Papapetrou spacetime of two charged particles. The interior of the wormhole is a Reissner-Nordstr\"om black hole matching to the two shells. The wormhole is traversable and connects to the same asymptotics without violation of energy conditions. However, every point in the Majumdar-Papapetrou region lies on a closed timelike curve.Comment: 9 pages, LaTeX, 1 figur
    • …
    corecore