Time-Dependence of the Mass Accretion Rate in Cluster Cooling Flows

We analyze two time-dependent cluster cooling flow models in spherical symmetry. The first assumes that the intracluster gas resides in a static external potential, and includes the effects of optically thin radiative cooling and mass deposition. This corresponds to previous steady-state cooling flow models calculated by White & Sarazin (1987). Detailed agreement is found between steady-state models and time-dependent models at fixed times in the simulations. The mass accretion rate is found either to increase or remain nearly constant once flows reach a steady state. The time rate of change of the accretion rate is strongly sensitive to the value of the mass deposition parameter q, but only mildly sensitive to the ratio beta of gravitational binding energy to gas temperature. We show that previous scaling arguments presented by Bertschinger (1988) and White (1988) are valid only for mature cooling flows with weak mass deposition (q ~< 1). The second set of models includes the effects of a secularly deepening cluster potential and secondary infall of gas from the Hubble flow. We find that such heating effects do not prevent the flows from reaching a steady state within an initial central cooling time.Comment: 22 pages (AASTeX) with 16 EPS figures; accepted for publication in The Astrophysical Journa

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

X-ray Properties of the Abell 644 Cluster of Galaxies

We use new ASCA observations and archival ROSAT Position Sensitive Proportional Counter (PSPC) data to determine the X-ray spectral properties of the intracluster gas in Abell 644. From the overall spectrum, we determine the average gas temperature to be 8.64 (+0.67,-0.56) keV, and an abundance of 0.32 (+/-0.04) $Z_{\odot}$. The global ASCA and ROSAT spectra imply a cooling rate of 214 (+100,-91) $M_{\odot}$ yr$^{-1}$. The PSPC X-ray surface brightness profile and the ASCA data suggest a somewhat higher cooling rate. We determine the gravitational mass and gas mass as a function of radius. The total gravitating mass within 1.2 Mpc is $6.2\times10^{14}$ $M_{\odot}$, of which 20% is in the form of hot gas. There is a region of elevated temperature 1.5-5 arcmin to the west of the cluster center. The south-southwest region of the cluster also shows excess emission in the ROSAT PSPC X-ray image, aligned with the major axis of the optical cD galaxy in the center of the cluster. We argue that the cluster is undergoing or has recently undergone a minor merger. The combination of a fairly strong cooling flow and evidence for a merger make this cluster an interesting case to test the disruption of cooling flow in mergers.Comment: 26 pages LaTeX including 9 eps figures + 4 pages LaTeX tables (landscape); accepted to ApJ, uses aaspp

Unobtrusive measurement of psychological constructs in organizational research

Measurement in organizational psychology is dominated by the use of approaches that require the cooperation of a respondent—namely, questionnaires and interviews. The goal of this article is to increase and improve the use of unobtrusivemeasures as a supplementalmeans toassess psychological constructs in organizational research. Specifically, we first illustrate themerit and necessity of utilizing unobtrusive measures. Next, we review the literature employing unobtrusive measures to assess psychological constructs and then discuss threats to validity associated with these approaches. Finally, we offer recommendations to enhance the effectiveness of unobtrusive measures in future research

Perinatal Group B Streptococcal Disease Prevention, Minnesota

In 2002, revised guidelines for preventing perinatal group B streptococcal disease were published. In 2002, all Minnesota providers surveyed reported using a prevention policy. Most screen vaginal and rectal specimens at 34–37 weeks of gestation. The use of screening-based methods has increased dramatically since 1998

Northern Bobwhite Habitat Use in a Forest-Dominated System (Poster Abstract)

Changes in land use that reduce habitat availability and quality for northern bobwhites (Colinus virginianus) are thought to be the major cause of bobwhite population decline in the Southeast. Increased conversion of open habitats to densely stocked pine plantations has contributed to habitat loss. We examined bobwhite habitat use in the Upper Coastal Plain of Georgia, a landscape dominated by forests and agriculture. The purposes of this study were to monitor habitat selection by bobwhites in this forest and agriculture system and to determine what role pine plantations, including those established as a conservation practice of the Conservation Reserve Program, have within bobwhite’s selection of habitat types. To date little research has been conducted to determine bobwhite habitat selection within this forest and agriculture dominated system. Many bobwhite research studies have been undertaken on intensively managed lands in the southeastern United States. Many landowners and land managers may not have the resources necessary to manage their lands exclusively for bobwhites. This study was conducted on lands where landowners had multiple objectives in mind, such as agriculture, timber, and wildlife. We determined home range sizes and habitat selection of 55 radiomarked bobwhites during 1997–2000. Selection of habitats by radiomarked bobwhites supported our hypotheses that they would prefer early-successional habitats within the forest-dominated study area. Selected habitats included fallow fields and open-canopy planted pines whereas agricultural areas and closed-canopy planted pines were avoided. Thinning to create open-canopy planted pine stands will benefit bobwhites by providing additional early successional habitat. Bobwhites selected open canopy planted pine and fallow field habitats in preference to closed-canopy planted pine and agricultural areas. Our results suggest that managing fallow fields and open canopy planted pine habitat for bobwhites will provide preferred habitat within this landscape and is feasible for the average landowner

What Contribution Did Economic Evidence Make to the Adoption of Universal Newborn Hearing Screening Policies in the United States?

Universal newborn hearing screening (UNHS), when accompanied by timely access to intervention services, can improve language outcomes for children born deaf or hard of hearing (D/HH) and result in economic benefits to society. Early Hearing Detection and Intervention (EHDI) programs promote UNHS and using information systems support access to follow-up diagnostic and early intervention services so that infants can be screened no later than 1 month of age, with those who do not pass their screen receiving diagnostic evaluation no later than 3 months of age, and those with diagnosed hearing loss receiving intervention services no later than 6 months of age. In this paper, we first document the rapid roll-out of UNHS/EHDI policies and programs at the national and state/territorial levels in the United States between 1997 and 2005. We then review cost analyses and economic arguments that were made in advancing those policies in the United States. Finally, we examine evidence on language and educational outcomes that pertain to the economic benefits of UNHS/EHDI. In conclusion, although formal cost-effectiveness analyses do not appear to have played a decisive role, informal economic assessments of costs and benefits appear to have contributed to the adoption of UNHS policies in the United States

Chandra Observations of the Disruption of the Cool Core in Abell 133

We present the analysis of a Chandra observation of the galaxy cluster Abell 133, which has a cooling flow core, a central radio source, and a diffuse, filamentary radio source which has been classified as a radio relic. The X-ray image shows that the core has a complex structure. The most prominent feature is a "tongue" of emission which extends from the central cD galaxy to the northwest and partly overlaps the radio relic. One possibility is that this tongue is produced by Kelvin-Helmholtz (KH) instabilities through the interaction between the cold gas around the cD galaxy and hot intracluster medium. We estimate the critical velocity and time scale for the KH instability to be effective for the cold core around the cD galaxy. We find that the KH instability can disrupt the cold core if the relative velocity is >~400 km s^-1. We compare the results with those of clusters in which sharp, undisrupted cold fronts have been observed; in these clusters, the low temperature gas in their central regions has a more regular distribution. In contrast to Abell 133, these cluster cores have longer timescales for the disruption of the core by the KH instability when they are normalized to the timescale of the cD galaxy motion. Thus, the other cores are less vulnerable to KH instability. Another possible origin of the tongue is that it is gas which has been uplifted by a buoyant bubble of nonthermal plasma that we identify with the observed radio relic. From the position of the bubble and the radio estimate of the age of the relic source, we estimate avelocity of ~700 km s^-1 for the bubble. The structure of the bubble and this velocity are consistent with numerical models for such buoyant bubbles. (abridged)Comment: 38 pages, 15 figures, accepted for publication in Ap

Constraints on UV Absorption in the Intracluster Medium of Abell 1030

We present results from an extensive HST spectroscopic search for UV absorption lines in the spectrum of the quasar B2~1028+313, which is associated with the central dominant galaxy in the cluster Abell~1030 ($z=0.178$). This is one of the brightest known UV continuum sources located in a cluster, and therefore provides an ideal opportunity to obtain stringent constraints on the column densities of any cool absorbing gas that may be associated with the intracluster medium (ICM). Our HST spectra were obtained with the FOS and GHRS, and provide continuous coverage at rest-frame wavelengths from $\sim 975$ to 4060~\AA, thereby allowing the investigation of many different elements and ionization levels. We utilize a new technique that involves simultaneous fitting of large numbers of different transitions for each species, thereby yielding more robust constraints on column densities than can be obtained from a single transition. This method yields upper limits of $\lesssim 10^{11} - 10^{13}$ cm$^{-2}$ on the column densities of a wide range of molecular, atomic and ionized species that may be associated with the ICM. We also discuss a possible \Lya and C IV absorption system associated with the quasar. We discuss the implications of the upper limits on cool intracluster gas in the context of the physical properties of the ICM and its relationship to the quasar.Comment: Astrophysical Journal, in press, 19 pages, includes 5 PostScript figures. Latex format, uses aas2pp4.sty and epsfig.sty file