The Interaction of Radio Sources and X-ray-Emitting Gas in Cooling Flows

Recent observations of the interactions between radio sources and the X-ray-emitting gas in cooling flows in the cores of clusters of galaxies are reviewed. The radio sources inflate bubbles in the X-ray gas, which then rise buoyantly outward in the clusters transporting energy to the intracluster medium (ICM). The bright rims of gas around the radio bubbles are cool, rather than hot, and do not show signs of being strongly shocked. Energy deposited into the ICM over the lifetime of a cluster through several outbursts of a radio source helps to account for at least some of the gas that is missing in cooling flows at low temperatures.Comment: Invited Review, "The Riddle of Cooling Flows in Galaxies and Clusters of Galaxies," Charlottesville, VA, USA. May 31 - June 4, 2003, see http://www.astro.virginia.edu/coolflow/ Editors: Reiprich, T. H., Kempner, J. C., and Soker, N.; 8 page

SPEAKING VOLUMES: PROFESSIONAL GROWTH IN BOOK STUDIES

The purpose of this qualitative dissertation is to provide a description of the professional book study experience and gain insight into its use to support teacher professional development. Research on the use of professional book studies has been conducted in colleges, and by university researchers in public school settings. There is also a large field of research on leisure book clubs, providing insight into their popularity. Little research exists, however, on professional book studies from the point of view of the educators who were the participants. This qualitative case study examined the perceptions of 12 educators who voluntarily participated in multiple professional book studies over a period of four years in order to answer the following research questions: 1) What are the participants’ perceptions of the book study experience as a professional development activity? 2) According to the participants’ perceptions, how does participation in professional book studies lead to long-term learning? Data included reflective summaries and blogs completed in conjunction with each book club and open-ended interviews conducted after all book club participation was completed. As a result of the data analysis, two major themes were developed: Process and Product. The Process Theme data provided insight into what occurred in the book studies. The case study members believed that the book study groups helped them to comprehend the text at a deeper level, allowed them to practice strategies in a knowledge community, and provided them with a source of collaboration and camaraderie leading to development of long-term relationships. In the Product Theme, participants provided insight into how they changed their instructional practice, academic thinking, and personal beliefs. This case study demonstrates the positive changes that can occur when elements of effective professional development are incorporated into book studies. The data analysis indicated the development of a knowledge community where participants felt supported and challenged to try out new strategies in their workplaces. Finally, it is suggested that some participants appeared to experience transformative learning

Counts-in-Cylinders in the Sloan Digital Sky Survey with Comparisons to N-body Simulations

Environmental statistics provide a necessary means of comparing the properties of galaxies in different environments and a vital test of models of galaxy formation within the prevailing, hierarchical cosmological model. We explore counts-in-cylinders, a common statistic defined as the number of companions of a particular galaxy found within a given projected radius and redshift interval. Galaxy distributions with the same two-point correlation functions do not necessarily have the same companion count distributions. We use this statistic to examine the environments of galaxies in the Sloan Digital Sky Survey, Data Release 4. We also make preliminary comparisons to four models for the spatial distributions of galaxies, based on N-body simulations, and data from SDSS DR4 to study the utility of the counts-in-cylinders statistic. There is a very large scatter between the number of companions a galaxy has and the mass of its parent dark matter halo and the halo occupation, limiting the utility of this statistic for certain kinds of environmental studies. We also show that prevalent, empirical models of galaxy clustering that match observed two- and three-point clustering statistics well fail to reproduce some aspects of the observed distribution of counts-in-cylinders on 1, 3 and 6-Mpc/h scales. All models that we explore underpredict the fraction of galaxies with few or no companions in 3 and 6-Mpc/h cylinders. Roughly 7% of galaxies in the real universe are significantly more isolated within a 6 Mpc/h cylinder than the galaxies in any of the models we use. Simple, phenomenological models that map galaxies to dark matter halos fail to reproduce high-order clustering statistics in low-density environments.Comment: 17 pages, 10 figures. Accepted, Ap

Chandra Observation of the Radio Source / X-ray Gas Interaction in the Cooling Flow Cluster Abell 2052

We present a Chandra observation of Abell 2052, a cooling flow cluster with a central cD that hosts the complex radio source 3C 317. The data reveal ``holes'' in the X-ray emission that are coincident with the radio lobes. The holes are surrounded by bright ``shells'' of X-ray emission. The data are consistent with the radio source displacing and compressing, and at the same time being confined by, the X-ray gas. The compression of the X-ray shells appears to have been relatively gentle and, at most, slightly transonic. The pressure in the X-ray gas (the shells and surrounding cooler gas) is approximately an order of magnitude higher than the minimum pressure derived for the radio source, suggesting that an additional source of pressure is needed to support the radio plasma. The compression of the X-ray shells has speeded up the cooling of the shells, and optical emission line filaments are found coincident with the brightest regions of the shells.Comment: accepted for publication in ApJ Letters; for high-resolution color figures, see http://www.astro.virginia.edu/~elb6n/abell2052.htm

Galaxy Cluster Environments of Radio Sources

Using the Sloan Digital Sky Survey (SDSS) and the FIRST (Faint Images of the Radio Sky at Twenty Centimeters) catalogs, we examined the optical environments around double-lobed radio sources. Previous studies have shown that multi-component radio sources exhibiting some degree of bending between components are likely to be found in galaxy clusters. Often this radio emission is associated with a cD-type galaxy at the center of a cluster. We cross-correlated the SDSS and FIRST catalogs and measured the richness of the cluster environments surrounding both bent and straight multi-component radio sources. This led to the discovery and classification of a large number of galaxy clusters out to a redshift of z ~ 0.5. We divided our sample into smaller subgroups based on their optical and radio properties. We find that FR I radio sources are more likely to be found in galaxy clusters than FR II sources. Further, we find that bent radio sources are more often found in galaxy clusters than non-bent radio sources. We also examined the environments around single-component radio sources and find that single-component radio sources are less likely to be associated with galaxy clusters than extended, multi-component radio sources. Bent, visually-selected sources are found in clusters or rich groups ~78% of the time. Those without optical hosts in SDSS are likely associated with clusters at even higher redshifts, most with redshifts of z > 0.7.Comment: 47 pages, 24 figures. Accepted by A

Real-Time Support: Using eCoaching to Increase Preservice Teachers’ Confidence to Teach

The role of teacher education preparation programs is to equip preservice teachers (PSTs) with the knowledge and skills to support the development of all students. To do this, university faculty must establish and monitor PST’s progress toward quality standards for teaching. eCoaching is a professional learning tool that provides real-time feedback to PSTs during instruction. In this article, the authors present eCoaching as a professional learning strategy. An overview of eCoaching logistics, perceived impact of eCoaching on PSTs, a description of eCoaching in action, and an explanation of how it meshes with current support practices are provided

The Influence Of Students\u27 Cognitive Style On A Standardized Reading Test Administered In Three Different Formats

The purpose of this study was to examine the means of scores on three forms of a standardized reading comprehension test taken by community college students in developmental reading classes. The three forms of the test were administered as a timed multiple-choice test, a constructed response test, and an un-timed multiple-choice test. Scores on the Group Embedded Figures Test (GEFT) were used to classify the students who participated in the study as having field dependent (LOW GEFT), mid-field dependent/independent (MID GEFT), or fieldindependent (HIGH GEFT) tendencies. The paired samples test was used to analyze the scores among the students classified as LOW GEFT, MID GEFT, and HIGH GEFT for mean differences in scores on the three test formats. The data revealed that for LOW GEFT students, the format of the test impacted their scores, with the mean of the scores of the un-timed multiple-choice test being significantly higher than the timed multiple-choice test and the constructed response format. The data also showed that for the MID GEFT students the mean of the scores for the un-timed multiple-choice test was significantly higher than the means for the timed multiple-choice test scores and the constructed response test scores. However, no significant mean difference was found between the timed multiple-choice test scores and the constructed response test scores. For the HIGH GEFT students, significant mean difference existed only between the un-timed multiple-choice and the timed multiple choice scores. The means of reading comprehension test scores on the three formats between the LOW GEFT, MID GEFT, and HIGH GEFT students indicated significant mean difference between the timed multiple choice test scores but not between the means of the scores for the constructed response and the un-timed multiple-choice test scores. Demographically, when the means of the reading test scores were analyzed with ethnicity as the controlling variable, the Hispanic students had a significantly higher mean on the scores for the constructed response test format. No other significant mean differences were found between the scores of the African American, Caucasian, Hispanic, or Native American students. When the means of the reading test scores were analyzed with gender as the controlling variable, no significant mean difference was found between the reading comprehension scores of the men and women. This study indicated that cognitive style had more impact on students’ performance on a standardized test of reading comprehension than did ethnicity or gender. The un-timed multiple-choice format also had an equalizing effect on the means of the scores for these students