Rhapsody-G simulations I: the cool cores, hot gas and stellar content of massive galaxy clusters

DOE PAGES

Hahn, Oliver; Martizzi, Davide; Wu, Hao -Yi; ...

2017-01-25

We present the rhapsody-g suite of cosmological hydrodynamic zoom simulations of 10 massive galaxy clusters at the M vir ~10 15 M ⊙ scale. These simulations include cooling and subresolution models for star formation and stellar and supermassive black hole feedback. The sample is selected to capture the whole gamut of assembly histories that produce clusters of similar final mass. We present an overview of the successes and shortcomings of such simulations in reproducing both the stellar properties of galaxies as well as properties of the hot plasma in clusters. In our simulations, a long-lived cool-core/non-cool-core dichotomy arises naturally, andmore » the emergence of non-cool cores is related to low angular momentum major mergers. Nevertheless, the cool-core clusters exhibit a low central entropy compared to observations, which cannot be alleviated by thermal active galactic nuclei feedback. For cluster scaling relations, we find that the simulations match well the M 500–Y 500 scaling of Planck Sunyaev–Zeldovich clusters but deviate somewhat from the observed X-ray luminosity and temperature scaling relations in the sense of being slightly too bright and too cool at fixed mass, respectively. Stars are produced at an efficiency consistent with abundance-matching constraints and central galaxies have star formation rates consistent with recent observations. In conclusion, while our simulations thus match various key properties remarkably well, we conclude that the shortcomings strongly suggest an important role for non-thermal processes (through feedback or otherwise) or thermal conduction in shaping the intracluster medium.« less

rhapsody-g simulations - I. The cool cores, hot gas and stellar content of massive galaxy clusters

NASA Astrophysics Data System (ADS)

Hahn, Oliver; Martizzi, Davide; Wu, Hao-Yi; Evrard, August E.; Teyssier, Romain; Wechsler, Risa H.

2017-09-01

We present the rhapsody-g suite of cosmological hydrodynamic zoom simulations of 10 massive galaxy clusters at the Mvir ˜ 1015 M⊙ scale. These simulations include cooling and subresolution models for star formation and stellar and supermassive black hole feedback. The sample is selected to capture the whole gamut of assembly histories that produce clusters of similar final mass. We present an overview of the successes and shortcomings of such simulations in reproducing both the stellar properties of galaxies as well as properties of the hot plasma in clusters. In our simulations, a long-lived cool-core/non-cool-core dichotomy arises naturally, and the emergence of non-cool cores is related to low angular momentum major mergers. Nevertheless, the cool-core clusters exhibit a low central entropy compared to observations, which cannot be alleviated by thermal active galactic nuclei feedback. For cluster scaling relations, we find that the simulations match well the M500-Y500 scaling of Planck Sunyaev-Zeldovich clusters but deviate somewhat from the observed X-ray luminosity and temperature scaling relations in the sense of being slightly too bright and too cool at fixed mass, respectively. Stars are produced at an efficiency consistent with abundance-matching constraints and central galaxies have star formation rates consistent with recent observations. While our simulations thus match various key properties remarkably well, we conclude that the shortcomings strongly suggest an important role for non-thermal processes (through feedback or otherwise) or thermal conduction in shaping the intracluster medium.

Revealing Thermal Instabilities in the Core of the Phoenix Cluster

NASA Astrophysics Data System (ADS)

McDonald, Michael

2017-08-01

The Phoenix cluster is the most relaxed cluster known, and hosts the strongest cool core of any cluster yet discovered. At the center of this cluster is a massive starburst galaxy, with a SFR of 500-1000 Msun/yr, seemingly satisfying the early cooling flow predictions, despite the presence of strong AGN feedback from the central supermassive black hole. Here we propose deep narrow-band imaging of the central 120 kpc of the cluster, to map the warm (10^4K) ionized gas via the [O II] emission line. In low-z clusters, such as Perseus and Abell 1795, the warm, ionized phase is of critical importance to map out thermal instabilities in the hot gas, and maps of Halpha and [O II] have been used for decades to understand how (and how not) cooling proceeds in the intracluster medium. The data proposed for here, combined with deep ALMA data, a recently-approved Large Chandra Program, and recently-approved multi-frequency JVLA data, will allow us to probe the cooling ICM, the cool, filamentary gas, the cold molecular gas, the star-forming population, and the AGN jets all on scales of <10 kpc. This multi-observatory campaign, focusing on the most extreme cooling cluster, will lead to a more complete understanding of how and why thermal instabilities develop in the hot ICM of cool core clusters.

Deep Chandra study of the truncated cool core of the Ophiuchus cluster

NASA Astrophysics Data System (ADS)

Werner, N.; Zhuravleva, I.; Canning, R. E. A.; Allen, S. W.; King, A. L.; Sanders, J. S.; Simionescu, A.; Taylor, G. B.; Morris, R. G.; Fabian, A. C.

2016-08-01

We present the results of a deep Chandra observation of the Ophiuchus cluster, the second brightest galaxy cluster in the X-ray sky. The cluster hosts a truncated cool core, with a temperature increasing from kT ˜ 1 keV in the core to kT ˜ 9 keV at r ˜ 30 kpc. Beyond r ˜ 30 kpc, the intracluster medium (ICM) appears remarkably isothermal. The core is dynamically disturbed with multiple sloshing-induced cold fronts, with indications for both Rayleigh-Taylor and Kelvin-Helmholtz instabilities. The residual image reveals a likely subcluster south of the core at the projected distance of r ˜ 280 kpc. The cluster also harbours a likely radio phoenix, a source revived by adiabatic compression by gas motions in the ICM. Even though the Ophiuchus cluster is strongly dynamically active, the amplitude of density fluctuations outside of the cooling core is low, indicating velocities smaller than ˜100 km s-1. The density fluctuations might be damped by thermal conduction in the hot and remarkably isothermal ICM, resulting in our underestimate of gas velocities. We find a surprising, sharp surface brightness discontinuity, that is curved away from the core, at r ˜ 120 kpc to the south-east of the cluster centre. We conclude that this feature is most likely due to gas dynamics associated with a merger. The cooling core lacks any observable X-ray cavities and the active galactic nucleus (AGN) only displays weak, point-like radio emission, lacking lobes or jets. The lack of strong AGN activity may be due to the bulk of the cooling taking place offset from the central supermassive black hole.

Searching for the 3.5 keV Line in the Stacked Suzaku Observations of Galaxy Clusters

NASA Technical Reports Server (NTRS)

Bulbul, Esra; Markevitch, Maxim; Foster, Adam; Miller, Eric; Bautz, Mark; Lowenstein, Mike; Randall, Scott W.; Smith, Randall K.

2016-01-01

We perform a detailed study of the stacked Suzaku observations of 47 galaxy clusters, spanning a redshift range of 0.01-0.45, to search for the unidentified 3.5 keV line. This sample provides an independent test for the previously detected line. We detect a 2sigma-significant spectral feature at 3.5 keV in the spectrum of the full sample. When the sample is divided into two subsamples (cool-core and non-cool core clusters), the cool-core subsample shows no statistically significant positive residuals at the line energy. A very weak (approx. 2sigma confidence) spectral feature at 3.5 keV is permitted by the data from the non-cool-core clusters sample. The upper limit on a neutrino decay mixing angle of sin(sup 2)(2theta) = 6.1 x 10(exp -11) from the full Suzaku sample is consistent with the previous detections in the stacked XMM-Newton sample of galaxy clusters (which had a higher statistical sensitivity to faint lines), M31, and Galactic center, at a 90% confidence level. However, the constraint from the present sample, which does not include the Perseus cluster, is in tension with previously reported line flux observed in the core of the Perseus cluster with XMM-Newton and Suzaku.

Mass Distribution in Galaxy Cluster Cores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hogan, M. T.; McNamara, B. R.; Pulido, F.

Many processes within galaxy clusters, such as those believed to govern the onset of thermally unstable cooling and active galactic nucleus feedback, are dependent upon local dynamical timescales. However, accurate mapping of the mass distribution within individual clusters is challenging, particularly toward cluster centers where the total mass budget has substantial radially dependent contributions from the stellar ( M {sub *}), gas ( M {sub gas}), and dark matter ( M {sub DM}) components. In this paper we use a small sample of galaxy clusters with deep Chandra observations and good ancillary tracers of their gravitating mass at both largemore » and small radii to develop a method for determining mass profiles that span a wide radial range and extend down into the central galaxy. We also consider potential observational pitfalls in understanding cooling in hot cluster atmospheres, and find tentative evidence for a relationship between the radial extent of cooling X-ray gas and nebular H α emission in cool-core clusters. At large radii the entropy profiles of our clusters agree with the baseline power law of K ∝ r {sup 1.1} expected from gravity alone. At smaller radii our entropy profiles become shallower but continue with a power law of the form K ∝ r {sup 0.67} down to our resolution limit. Among this small sample of cool-core clusters we therefore find no support for the existence of a central flat “entropy floor.”.« less

Cause and Effect of Feedback: Multiphase Gas in Cluster Cores Heated by AGN Jets

NASA Astrophysics Data System (ADS)

Gaspari, M.; Ruszkowski, M.; Sharma, P.

2012-02-01

Multiwavelength data indicate that the X-ray-emitting plasma in the cores of galaxy clusters is not cooling catastrophically. To a large extent, cooling is offset by heating due to active galactic nuclei (AGNs) via jets. The cool-core clusters, with cooler/denser plasmas, show multiphase gas and signs of some cooling in their cores. These observations suggest that the cool core is locally thermally unstable while maintaining global thermal equilibrium. Using high-resolution, three-dimensional simulations we study the formation of multiphase gas in cluster cores heated by collimated bipolar AGN jets. Our key conclusion is that spatially extended multiphase filaments form only when the instantaneous ratio of the thermal instability and free-fall timescales (t TI/t ff) falls below a critical threshold of ≈10. When this happens, dense cold gas decouples from the hot intracluster medium (ICM) phase and generates inhomogeneous and spatially extended Hα filaments. These cold gas clumps and filaments "rain" down onto the central regions of the core, forming a cold rotating torus and in part feeding the supermassive black hole. Consequently, the self-regulated feedback enhances AGN heating and the core returns to a higher entropy level with t TI/t ff > 10. Eventually, the core reaches quasi-stable global thermal equilibrium, and cold filaments condense out of the hot ICM whenever t TI/t ff <~ 10. This occurs despite the fact that the energy from AGN jets is supplied to the core in a highly anisotropic fashion. The effective spatial redistribution of heat is enabled in part by the turbulent motions in the wake of freely falling cold filaments. Increased AGN activity can locally reverse the cold gas flow, launching cold filamentary gas away from the cluster center. Our criterion for the condensation of spatially extended cold gas is in agreement with observations and previous idealized simulations.

The evolution of the intracluster medium metallicity in Sunyaev Zel'dovich-selected galaxy clusters at 0 < z < 1.5

DOE PAGES

McDonald, M.; Bulbul, E.; Haan, T. de; ...

2016-07-27

Here, we present the results of an X-ray spectral analysis of 153 galaxy clusters observed with the Chandra, XMM-Newton, and Suzaku space telescopes. These clusters, which span 0 < z < 1.5, were drawn from a larger, mass-selected sample of galaxy clusters discovered in the 2500 square degree South Pole Telescope Sunyaev Zel'dovich (SPT-SZ) survey. With a total combined exposure time of 9.1 Ms, these data yield the strongest constraints to date on the evolution of the metal content of the intracluster medium (ICM). We find no evidence for strong evolution in the global (r < R 500) ICM metallicity (dZ/dz = –0.06 ± 0.04 Z ⊙), with a mean value at z = 0.6 ofmore » $$\\langle Z\\rangle =0.23\\pm 0.01$$ Z ⊙ and a scatter of σ Z = 0.08 ± 0.01 Z ⊙. These results imply that the emission-weighted metallicity has not changed by more than 40% since z = 1 (at 95% confidence), consistent with the picture of an early (z > 1) enrichment. We find, in agreement with previous works, a significantly higher mean value for the metallicity in the centers of cool core clusters versus non-cool core clusters. We find weak evidence for evolution in the central metallicity of cool core clusters (dZ/dz = –0.21 ± 0.11 Z ⊙), which is sufficient to account for this enhanced central metallicity over the past ~10 Gyr. We find no evidence for metallicity evolution outside of the core (dZ/dz = –0.03 ± 0.06 Z ⊙), and no significant difference in the core-excised metallicity between cool core and non-cool core clusters. This suggests that strong radio-mode active galactic nucleus feedback does not significantly alter the distribution of metals at $$r\\gt 0.15{R}_{500}$$. Given the limitations of current-generation X-ray telescopes in constraining the ICM metallicity at z > 1, significant improvements on this work will likely require next-generation X-ray missions.« less

SEARCHING FOR COOLING SIGNATURES IN STRONG LENSING GALAXY CLUSTERS: EVIDENCE AGAINST BARYONS SHAPING THE MATTER DISTRIBUTION IN CLUSTER CORES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanchard, Peter K.; Bayliss, Matthew B.; McDonald, Michael

2013-07-20

The process by which the mass density profile of certain galaxy clusters becomes centrally concentrated enough to produce high strong lensing (SL) cross-sections is not well understood. It has been suggested that the baryonic condensation of the intracluster medium (ICM) due to cooling may drag dark matter to the cores and thus steepen the profile. In this work, we search for evidence of ongoing ICM cooling in the first large, well-defined sample of SL selected galaxy clusters in the range 0.1 < z < 0.6. Based on known correlations between the ICM cooling rate and both optical emission line luminositymore » and star formation, we measure, for a sample of 89 SL clusters, the fraction of clusters that have [O II]{lambda}{lambda}3727 emission in their brightest cluster galaxy (BCG). We find that the fraction of line-emitting BCGs is constant as a function of redshift for z > 0.2 and shows no statistically significant deviation from the total cluster population. Specific star formation rates, as traced by the strength of the 4000 A break, D{sub 4000}, are also consistent with the general cluster population. Finally, we use optical imaging of the SL clusters to measure the angular separation, R{sub arc}, between the arc and the center of mass of each lensing cluster in our sample and test for evidence of changing [O II] emission and D{sub 4000} as a function of R{sub arc}, a proxy observable for SL cross-sections. D{sub 4000} is constant with all values of R{sub arc}, and the [O II] emission fractions show no dependence on R{sub arc} for R{sub arc} > 10'' and only very marginal evidence of increased weak [O II] emission for systems with R{sub arc} < 10''. These results argue against the ability of baryonic cooling associated with cool core activity in the cores of galaxy clusters to strongly modify the underlying dark matter potential, leading to an increase in SL cross-sections.« less

Regulation of the X-ray luminosity of clusters of galaxies by cooling and supernova feedback.

PubMed

Voit, G M; Bryan, G L

2001-11-22

Clusters of galaxies are thought to contain about ten times as much dark matter as baryonic matter. The dark component therefore dominates the gravitational potential of a cluster, and the baryons confined by this potential radiate X-rays with a luminosity that depends mainly on the gas density in the cluster's core. Predictions of the X-rays' properties based on models of cluster formation do not, however, agree with the observations. If the models ignore the condensation of cooling gas into stars and feedback from the associated supernovae, they overestimate the X-ray luminosity because the density of the core gas is too high. An early episode of uniformly distributed supernova feedback could rectify this by heating the uncondensed gas and therefore making it harder to compress into the core, but such a process seems to require an implausibly large number of supernovae. Here we show how radiative cooling of intergalactic gas and subsequent supernova heating conspire to eliminate highly compressible low-entropy gas from the intracluster medium. This brings the core entropy and X-ray luminosities of clusters into agreement with the observations, in a way that depends little on the efficiency of supernova heating in the early Universe.

Abell 1142 and the Missing Central Galaxy – A Cluster in Transition?

NASA Astrophysics Data System (ADS)

Jones, Alexander; Su, Yuanyuan; Buote, David; Forman, William; van Weeren, Reinout; Jones, Christine; Gastaldello, Fabio; Kraft, Ralph; Randall, Scott

2018-01-01

Two types of galaxy clusters exist: cool core (CC) clusters which exhibit centrally-peaked metallicity and X-ray emission and non-cool core (NCC) clusters, possessing comparably homogeneous metallicity and X-ray emission distributions. However, the origin of this dichotomy is still unknown. The current prevailing theories state that either there is a primordial entropy limit, above which a CC is unable to form, or that clusters can change type through major mergers and radiative cooling. Abell 1142 is a galaxy cluster that can provide a unique probe of the root of this cluster-type division. It is formed of two merging sub-clusters, each with its own brightest cluster galaxies (BCG). Its enriched X-ray centroid (possible CC remnant) lies between these two BCGs. We present the thermal and chemical distributions of this system using deep (180ks) XMM-Newton observations to shed light on the role of mergers in the evolution of galaxy clusters.

A Global Model for Circumgalactic and Cluster-core Precipitation

NASA Astrophysics Data System (ADS)

Voit, G. Mark; Meece, Greg; Li, Yuan; O'Shea, Brian W.; Bryan, Greg L.; Donahue, Megan

2017-08-01

We provide an analytic framework for interpreting observations of multiphase circumgalactic gas that is heavily informed by recent numerical simulations of thermal instability and precipitation in cool-core galaxy clusters. We start by considering the local conditions required for the formation of multiphase gas via two different modes: (1) uplift of ambient gas by galactic outflows, and (2) condensation in a stratified stationary medium in which thermal balance is explicitly maintained. Analytic exploration of these two modes provides insights into the relationships between the local ratio of the cooling and freefall timescales (I.e., {t}{cool}/{t}{ff}), the large-scale gradient of specific entropy, and the development of precipitation and multiphase media in circumgalactic gas. We then use these analytic findings to interpret recent simulations of circumgalactic gas in which global thermal balance is maintained. We show that long-lasting configurations of gas with 5≲ \\min ({t}{cool}/{t}{ff})≲ 20 and radial entropy profiles similar to observations of cool cores in galaxy clusters are a natural outcome of precipitation-regulated feedback. We conclude with some observational predictions that follow from these models. This work focuses primarily on precipitation and AGN feedback in galaxy-cluster cores, because that is where the observations of multiphase gas around galaxies are most complete. However, many of the physical principles that govern condensation in those environments apply to circumgalactic gas around galaxies of all masses.

Abell 1763: A Giant Gas Sloshing Spiral But No Cool Core

NASA Astrophysics Data System (ADS)

Douglass, Edmund

2017-09-01

We propose a 76 ksec observation of the z=0.23 galaxy cluster Abell 1763. Previous Chandra data reveals the system as host to a large 950 kpc gas sloshing spiral. Atypical of spiral-hosting clusters, an intact cool core is not detected. Its absence suggests the interaction has led to significant disruption since the onset of core sloshing. The primary cluster is accompanied by two X-ray emitting subsystems. Given the orientation of the spiral, both systems are strong candidates for being the perturber responsible for its formation. Abell 1763 provides us with the rare opportunity to examine an infall event (primary + perturber) resulting in sloshing to the point of core disintegration. Detailed analysis will be performed on the disrupted core, the spiral, and the perturber candidates.

Chandra Observations of MS0440.5+0204 & MS0839.9+2938: Cooling Flow Clusters in Formation?

NASA Astrophysics Data System (ADS)

McNamara, Brian

2000-09-01

We propose to observe two redshift z~0.2 clusters, MS0839.9+2938 and MS0440+0204, discovered as bright X-ray sources in the Einstein Medium Sensitivity Survey. The cluster cores are structured in the X-ray and optical bands, and they harbor large cooling flows. Their central cluster galaxies contain luminous nebular emission systems, active star formation, and strong radio sources. Using the Chandra data, we will determine whether the large discrepancies between the X-ray cooling rates and optical star formation rates can be reconciled, and we will test the hypothesis that cooling flows form as cool, dense groups accrete into massive clusters.

REMOVING COOL CORES AND CENTRAL METALLICITY PEAKS IN GALAXY CLUSTERS WITH POWERFUL ACTIVE GALACTIC NUCLEUS OUTBURSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo Fulai; Mathews, William G., E-mail: fulai@ucolick.or

2010-07-10

Recent X-ray observations of galaxy clusters suggest that cluster populations are bimodally distributed according to central gas entropy and are separated into two distinct classes: cool core (CC) and non-cool core (NCC) clusters. While it is widely accepted that active galactic nucleus (AGN) feedback plays a key role in offsetting radiative losses and maintaining many clusters in the CC state, the origin of NCC clusters is much less clear. At the same time, a handful of extremely powerful AGN outbursts have recently been detected in clusters, with a total energy {approx}10{sup 61}-10{sup 62} erg. Using two-dimensional hydrodynamic simulations, we showmore » that if a large fraction of this energy is deposited near the centers of CC clusters, which is likely common due to dense cores, these AGN outbursts can completely remove CCs, transforming them to NCC clusters. Our model also has interesting implications for cluster abundance profiles, which usually show a central peak in CC systems. Our calculations indicate that during the CC to NCC transformation, AGN outbursts efficiently mix metals in cluster central regions and may even remove central abundance peaks if they are not broad enough. For CC clusters with broad central abundance peaks, AGN outbursts decrease peak abundances, but cannot effectively destroy the peaks. Our model may simultaneously explain the contradictory (possibly bimodal) results of abundance profiles in NCC clusters, some of which are nearly flat, while others have strong central peaks similar to those in CC clusters. A statistical analysis of the sizes of central abundance peaks and their redshift evolution may shed interesting insights on the origin of both types of NCC clusters and the evolution history of thermodynamics and AGN activity in clusters.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, M.; Allen, S. W.; Bayliss, M.

We present the results of a Chandra X-ray survey of the 8 most massive galaxy clusters at z>1.2 in the South Pole Telescope 2500 deg^2 survey. We combine this sample with previously-published Chandra observations of 49 massive X-ray-selected clusters at 00.2R500 scaling like E(z)^2. In the centers of clusters (r<0.1R500), we find significant deviations from self similarity (n_e ~ E(z)^{0.1+/-0.5}), consistent with no redshift dependence. When we isolate clusters with over-dense cores (i.e., cool cores), we find that the average over-density profile has not evolved with redshift -- that is, cool cores have not changed in size, density, or totalmore » mass over the past ~9-10 Gyr. We show that the evolving "cuspiness" of clusters in the X-ray, reported by several previous studies, can be understood in the context of a cool core with fixed properties embedded in a self similarly-evolving cluster. We find no measurable evolution in the X-ray morphology of massive clusters, seemingly in tension with the rapidly-rising (with redshift) rate of major mergers predicted by cosmological simulations. We show that these two results can be brought into agreement if we assume that the relaxation time after a merger is proportional to the crossing time, since the latter is proportional to H(z)^(-1).« less

Limits on turbulent propagation of energy in cool-core clusters of galaxies

NASA Astrophysics Data System (ADS)

Bambic, C. J.; Pinto, C.; Fabian, A. C.; Sanders, J.; Reynolds, C. S.

2018-07-01

We place constraints on the propagation velocity of bulk turbulence within the intracluster medium of three clusters and an elliptical galaxy. Using Reflection Grating Spectrometer measurements of turbulent line broadening, we show that for these clusters, the 90 per cent upper limit on turbulent velocities when accounting for instrumental broadening is too low to propagate energy radially to the cooling radius of the clusters within the required cooling time. In this way, we extend previous Hitomi-based analysis on the Perseus cluster to more clusters, with the intention of applying these results to a future, more extensive catalogue. These results constrain models of turbulent heating in active galactic nucleus feedback by requiring a mechanism which can not only provide sufficient energy to offset radiative cooling but also resupply that energy rapidly enough to balance cooling at each cluster radius.

Limits on turbulent propagation of energy in cool-core clusters of galaxies

NASA Astrophysics Data System (ADS)

Bambic, C. J.; Pinto, C.; Fabian, A. C.; Sanders, J.; Reynolds, C. S.

2018-04-01

We place constraints on the propagation velocity of bulk turbulence within the intracluster medium of three clusters and an elliptical galaxy. Using Reflection Grating Spectrometer measurements of turbulent line broadening, we show that for these clusters, the 90% upper limit on turbulent velocities when accounting for instrumental broadening is too low to propagate energy radially to the cooling radius of the clusters within the required cooling time. In this way, we extend previous Hitomi-based analysis on the Perseus cluster to more clusters, with the intention of applying these results to a future, more extensive catalog. These results constrain models of turbulent heating in AGN feedback by requiring a mechanism which can not only provide sufficient energy to offset radiative cooling, but resupply that energy rapidly enough to balance cooling at each cluster radius.

The Onset of Thermally Unstable Cooling from the Hot Atmospheres of Giant Galaxies in Clusters: Constraints on Feedback Models

NASA Astrophysics Data System (ADS)

Hogan, M. T.; McNamara, B. R.; Pulido, F. A.; Nulsen, P. E. J.; Vantyghem, A. N.; Russell, H. R.; Edge, A. C.; Babyk, Iu.; Main, R. A.; McDonald, M.

2017-12-01

We present accurate mass and thermodynamic profiles for 57 galaxy clusters observed with the Chandra X-ray Observatory. We investigate the effects of local gravitational acceleration in central cluster galaxies, and explore the role of the local free-fall time ({t}{ff}) in thermally unstable cooling. We find that the radially averaged cooling time ({t}{cool}) is as effective an indicator of cold gas, traced through its nebular emission, as the ratio {t}{cool}/{t}{ff}. Therefore, {t}{cool} primarily governs the onset of thermally unstable cooling in hot atmospheres. The location of the minimum {t}{cool}/{t}{ff}, a thermodynamic parameter that many simulations suggest is key in driving thermal instability, is unresolved in most systems. Consequently, selection effects bias the value and reduce the observed range in measured {t}{cool}/{t}{ff} minima. The entropy profiles of cool-core clusters are characterized by broken power laws down to our resolution limit, with no indication of isentropic cores. We show, for the first time, that mass isothermality and the K\\propto {r}2/3 entropy profile slope imply a floor in {t}{cool}/{t}{ff} profiles within central galaxies. No significant departures of {t}{cool}/{t}{ff} below 10 are found. This is inconsistent with models that assume thermally unstable cooling ensues from linear perturbations at or near this threshold. We find that the inner cooling times of cluster atmospheres are resilient to active galactic nucleus (AGN)-driven change, suggesting gentle coupling between radio jets and atmospheric gas. Our analysis is consistent with models in which nonlinear perturbations, perhaps seeded by AGN-driven uplift of partially cooled material, lead to cold gas condensation.

The Remarkable Similarity of Massive Galaxy Clusters from z ~ 0 to z ~ 1.9

DOE PAGES

McDonald, M.; Allen, S. W.; Bayliss, M.; ...

2017-06-28

We present the results of a Chandra X-ray survey of the 8 most massive galaxy clusters at z>1.2 in the South Pole Telescope 2500 deg^2 survey. We combine this sample with previously-published Chandra observations of 49 massive X-ray-selected clusters at 00.2R500 scaling like E(z)^2. In the centers of clusters (r<0.1R500), we find significant deviations from self similarity (n_e ~ E(z)^{0.1+/-0.5}), consistent with no redshift dependence. When we isolate clusters with over-dense cores (i.e., cool cores), we find that the average over-density profile has not evolved with redshift -- that is, cool cores have not changed in size, density, or totalmore » mass over the past ~9-10 Gyr. We show that the evolving "cuspiness" of clusters in the X-ray, reported by several previous studies, can be understood in the context of a cool core with fixed properties embedded in a self similarly-evolving cluster. We find no measurable evolution in the X-ray morphology of massive clusters, seemingly in tension with the rapidly-rising (with redshift) rate of major mergers predicted by cosmological simulations. We show that these two results can be brought into agreement if we assume that the relaxation time after a merger is proportional to the crossing time, since the latter is proportional to H(z)^(-1).« less

The Role of Cerenkov Radiation in the Pressure Balance of Cool Core Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Lieu, Richard

2017-03-01

Despite the substantial progress made recently in understanding the role of AGN feedback and associated non-thermal effects, the precise mechanism that prevents the core of some clusters of galaxies from collapsing catastrophically by radiative cooling remains unidentified. In this Letter, we demonstrate that the evolution of a cluster's cooling core, in terms of its density, temperature, and magnetic field strength, inevitably enables the plasma electrons there to quickly become Cerenkov loss dominated, with emission at the radio frequency of ≲350 Hz, and with a rate considerably exceeding free-free continuum and line emission. However, the same does not apply to the plasmas at the cluster's outskirts, which lacks such radiation. Owing to its low frequency, the radiation cannot escape, but because over the relevant scale size of a Cerenkov wavelength the energy of an electron in the gas cannot follow the Boltzmann distribution to the requisite precision to ensure reabsorption always occurs faster than stimulated emission, the emitting gas cools before it reheats. This leaves behind the radiation itself, trapped by the overlying reflective plasma, yet providing enough pressure to maintain quasi-hydrostatic equilibrium. The mass condensation then happens by Rayleigh-Taylor instability, at a rate determined by the outermost radius where Cerenkov radiation can occur. In this way, it is possible to estimate the rate at ≈2 M ⊙ year-1, consistent with observational inference. Thus, the process appears to provide a natural solution to the longstanding problem of “cooling flow” in clusters; at least it offers another line of defense against cooling and collapse should gas heating by AGN feedback be inadequate in some clusters.

The Role of Cerenkov Radiation in the Pressure Balance of Cool Core Clusters of Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lieu, Richard

2017-03-20

Despite the substantial progress made recently in understanding the role of AGN feedback and associated non-thermal effects, the precise mechanism that prevents the core of some clusters of galaxies from collapsing catastrophically by radiative cooling remains unidentified. In this Letter, we demonstrate that the evolution of a cluster's cooling core, in terms of its density, temperature, and magnetic field strength, inevitably enables the plasma electrons there to quickly become Cerenkov loss dominated, with emission at the radio frequency of ≲350 Hz, and with a rate considerably exceeding free–free continuum and line emission. However, the same does not apply to themore » plasmas at the cluster's outskirts, which lacks such radiation. Owing to its low frequency, the radiation cannot escape, but because over the relevant scale size of a Cerenkov wavelength the energy of an electron in the gas cannot follow the Boltzmann distribution to the requisite precision to ensure reabsorption always occurs faster than stimulated emission, the emitting gas cools before it reheats. This leaves behind the radiation itself, trapped by the overlying reflective plasma, yet providing enough pressure to maintain quasi-hydrostatic equilibrium. The mass condensation then happens by Rayleigh–Taylor instability, at a rate determined by the outermost radius where Cerenkov radiation can occur. In this way, it is possible to estimate the rate at ≈2 M {sub ⊙} year{sup −1}, consistent with observational inference. Thus, the process appears to provide a natural solution to the longstanding problem of “cooling flow” in clusters; at least it offers another line of defense against cooling and collapse should gas heating by AGN feedback be inadequate in some clusters.« less

DYNAMICS AND MAGNETIZATION IN GALAXY CLUSTER CORES TRACED BY X-RAY COLD FRONTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keshet, Uri; Markevitch, Maxim; Birnboim, Yuval

2010-08-10

Cold fronts (CFs)-density and temperature plasma discontinuities-are ubiquitous in cool cores of galaxy clusters, where they appear as X-ray brightness edges in the intracluster medium, nearly concentric with the cluster center. We analyze the thermodynamic profiles deprojected across core CFs found in the literature. While the pressure appears continuous across these CFs, we find that all of them require significant centripetal acceleration beneath the front. This is naturally explained by a tangential, nearly sonic bulk flow just below the CF, and a tangential shear flow involving a fair fraction of the plasma beneath the front. Such shear should generate near-equipartitionmore » magnetic fields on scales {approx}<50pc from the front and could magnetize the entire core. Such fields would explain the apparent stability of cool core CFs and the recently reported CF-radio minihalo association.« less

Hierarchical Velocity Structure in the Core of Abell 2597

NASA Technical Reports Server (NTRS)

Still, Martin; Mushotzky, Richard

2004-01-01

We present XMM-Newton RGS and EPIC data of the putative cooling flow cluster Abell 2597. Velocities of the low-ionization emission lines in the spectrum are blue shifted with respect to the high-ionization lines by 1320 (sup +660) (sub -210) kilometers per second, which is consistent with the difference in the two peaks of the galaxy velocity distribution and may be the signature of bulk turbulence, infall, rotation or damped oscillation in the cluster. A hierarchical velocity structure such as this could be the direct result of galaxy mergers in the cluster core, or the injection of power into the cluster gas from a central engine. The uniform X-ray morphology of the cluster, the absence of fine scale temperature structure and the random distribution of the the galaxy positions, independent of velocity, suggests that our line of sight is close to the direction of motion. These results have strong implications for cooling flow models of the cluster Abell 2597. They give impetus to those models which account for the observed temperature structure of some clusters using mergers instead of cooling flows.

Shocks and Cool Cores: An ALMA View of Massive Galaxy Cluster Formation at High Redshifts

NASA Astrophysics Data System (ADS)

Basu, Kaustuv

2017-07-01

These slides present some recent results on the Sunyaev-Zel'dovich (SZ) effect imaging of galaxy cluster substructures. The advantage of SZ imaging at high redshifts or in the low density cluster outskirts is already well-known. Now with ALMA a combination of superior angular resolution and high sensitivity is available. One example is the first ALMA measurement of a merger shock at z=0.9 in the famous El Gordo galaxy cluster. Here comparison between SZ, X-ray and radio data enabled us to put constraints on the shock Mach number and magnetic field strength for a high-z radio relic. Second example is the ALMA SZ imaging of the core region of z=1.4 galaxy cluster XMMU J2235.2-2557. Here ALMA data provide an accurate measurement of the thermal pressure near the cluster center, and from a joint SZ/X-ray analysis we find clear evidence for a reduced core temperature. This result indicate that a cool core establishes itself early enough in the cluster formation history while the gas accumulation is still continuing. The above two ALMA measurements are among several other recent SZ results that shed light on the formation process of massive clusters at high redshifts.

HIGH-REDSHIFT X-RAY COOLING-CORE CLUSTER ASSOCIATED WITH THE LUMINOUS RADIO-LOUD QUASAR 3C 186

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siemiginowska, Aneta; Burke, D. J.; Aldcroft, Thomas L.

2010-10-10

We present the first results from a new, deep (200 ks) Chandra observation of the X-ray luminous galaxy cluster surrounding the powerful (L {approx} 10{sup 47} erg s{sup -1}), high-redshift (z = 1.067), compact-steep-spectrum radio-loud quasar 3C 186. The diffuse X-ray emission from the cluster has a roughly ellipsoidal shape and extends out to radii of at least {approx}60 arcsec ({approx}500 kpc). The centroid of the diffuse X-ray emission is offset by 0.68 {+-} 0.''11 ({approx}5.5 {+-} 0.9 kpc) from the position of the quasar. We measure a cluster mass within the radius at which the mean enclosed density ismore » 2500 times the critical density, r{sub 2500} = 283{sup +18}{sub -13} kpc, of 1.02{sup +0.21}{sub -0.14} x 10{sup 14} M{sub sun}. The gas-mass fraction within this radius is f{sub gas} = 0.129{sup +0.015}{sub -0.016}. This value is consistent with measurements at lower redshifts and implies minimal evolution in the f{sub gas}(z) relation for hot, massive clusters at 0 < z < 1.1. The measured metal abundance of 0.42{sup +0.08}{sub -0.07} Solar is consistent with the abundance observed in other massive, high-redshift clusters. The spatially resolved temperature profile for the cluster shows a drop in temperature, from kT {approx} 8 keV to kT {approx} 3 keV, in its central regions that is characteristic of cooling-core clusters. This is the first spectroscopic identification of a cooling-core cluster at z>1. We measure cooling times for the X-ray emitting gas at radii of 50 kpc and 25 kpc of 1.7 {+-} 0.2 x 10{sup 9} years and 7.5 {+-} 2.6 x 10{sup 8} years, as well as a nominal cooling rate (in the absence of heating) of 400 {+-} 190 M{sub sun} year{sup -1} within the central 100 kpc. In principle, the cooling gas can supply enough fuel to support the growth of the supermassive black hole and to power the luminous quasar. The radiative power of the quasar exceeds by a factor of 10 the kinematic power of the central radio source, suggesting that radiative heating may be important at intermittent intervals in cluster cores.« less

Pressure of the hot gas in simulations of galaxy clusters

NASA Astrophysics Data System (ADS)

Planelles, S.; Fabjan, D.; Borgani, S.; Murante, G.; Rasia, E.; Biffi, V.; Truong, N.; Ragone-Figueroa, C.; Granato, G. L.; Dolag, K.; Pierpaoli, E.; Beck, A. M.; Steinborn, Lisa K.; Gaspari, M.

2017-06-01

We analyse the radial pressure profiles, the intracluster medium (ICM) clumping factor and the Sunyaev-Zel'dovich (SZ) scaling relations of a sample of simulated galaxy clusters and groups identified in a set of hydrodynamical simulations based on an updated version of the treepm-SPH GADGET-3 code. Three different sets of simulations are performed: the first assumes non-radiative physics, the others include, among other processes, active galactic nucleus (AGN) and/or stellar feedback. Our results are analysed as a function of redshift, ICM physics, cluster mass and cluster cool-coreness or dynamical state. In general, the mean pressure profiles obtained for our sample of groups and clusters show a good agreement with X-ray and SZ observations. Simulated cool-core (CC) and non-cool-core (NCC) clusters also show a good match with real data. We obtain in all cases a small (if any) redshift evolution of the pressure profiles of massive clusters, at least back to z = 1. We find that the clumpiness of gas density and pressure increases with the distance from the cluster centre and with the dynamical activity. The inclusion of AGN feedback in our simulations generates values for the gas clumping (√{C}_{ρ }˜ 1.2 at R200) in good agreement with recent observational estimates. The simulated YSZ-M scaling relations are in good accordance with several observed samples, especially for massive clusters. As for the scatter of these relations, we obtain a clear dependence on the cluster dynamical state, whereas this distinction is not so evident when looking at the subsamples of CC and NCC clusters.

AGN Feedback in Clusters of Galaxies

DTIC Science & Technology

2010-01-01

cooling non-radiatively or being heated to higher temperatures. Throughout this paper , we use the term “cooling flow” to indicate clusters with...taurus cluster [51] and M87/ Virgo [24]. Concentric ripple-like features are also seen surrounding the center of Abell 2052, but current analysis shows that...2002) Chandra Imaging of the X-ray Core of the Virgo Cluster . ApJ 579:560-570. 37. Fujita Y et al. (2002) Chandra Observations of the Disruption of the

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, M.; Allen, S. W.; Bayliss, M.

Here, we present the results of a Chandra X-ray survey of the eight most massive galaxy clusters at z > 1.2 in the South Pole Telescope 2500 deg2 survey. We combine this sample with previously published Chandra observations of 49 massive X-ray-selected clusters at 0 < z < 0.1 and 90 Sunyaev–Zel'dovich–selected clusters at 0.25 < z < 1.2 to constrain the evolution of the intracluster medium (ICM) over the past ~10 Gyr. We find that the bulk of the ICM has evolved self-similarly over the full redshift range probed here, with the ICM density atmore » $$r\\gt 0.2{R}_{500}$$ scaling like $$E{(z)}^{2}$$. In the centers of clusters ($$r\\lesssim 0.01{R}_{500}$$), we find significant deviations from self-similarity ($${n}_{e}\\propto E{(z)}^{0.2\\pm 0.5}$$), consistent with no redshift dependence. When we isolate clusters with overdense cores (i.e., cool cores), we find that the average overdensity profile has not evolved with redshift—that is, cool cores have not changed in size, density, or total mass over the past ~9–10 Gyr. We show that the evolving "cuspiness" of clusters in the X-ray, reported by several previous studies, can be understood in the context of a cool core with fixed properties embedded in a self-similarly evolving cluster. We find no measurable evolution in the X-ray morphology of massive clusters, seemingly in tension with the rapidly rising (with redshift) rate of major mergers predicted by cosmological simulations. We show that these two results can be brought into agreement if we assume that the relaxation time after a merger is proportional to the crossing time, since the latter is proportional to $$H{(z)}^{-1}$$.« less

Self-regulated cooling flows in elliptical galaxies and in cluster cores - Is exclusively low mass star formation really necessary?

NASA Technical Reports Server (NTRS)

Silk, J.; Djorgovski, S.; Wyse, R. F. G.; Bruzual A., G.

1986-01-01

A self-consistent treatment of the heating by supernovae associated with star formation in a spherically symmetric cooling flow in a cluster core or elliptical galaxy is presented. An initial stellar mass function similar to that in the solar neighborhood is adopted. Inferred star-formation rates, within the cooling region - typically the inner 100 kpc around dominant galaxies at the centers of cooling flows in XD clusters - are reduced by about a factor of 2, relative to rates inferred when the heat input from star formation is ignored. Truncated initial mass functions (IMFs) are also considered, in which massive star formation is suppressed in accordance with previous treatments, and colors are predicted for star formation in cooling flows associated with central dominant elliptical galaxies and with isolated elliptical galaxies surrounded by gaseous coronae. The low inferred cooling-flow rates around isolated elliptical galaxies are found to be insensitive to the upper mass cutoff in the IMF, provided that the upper mass cutoff exceeds 2 M solar mass. Comparison with observed colors favors a cutoff in the IMF above 1 M solar mass in at least two well-studied cluster cooling flows, but a normal IMF cannot be excluded definitively. Models for NGC 1275 support a young (less than about 3 Gyr) cooling flow. As for the isolated elliptical galaxies, the spread in colors is consistent with a normal IMF. A definitive test of the IMF arising via star formation in cooling flows requires either UV spectral data or supernova searches in the cooling-flow-centered galaxies.

ACCEPT 2: A public library of cluster properties

NASA Astrophysics Data System (ADS)

Donahue, Megan

2012-09-01

The current public ACCEPT database of cluster properties includes radial profiles of Tx, n_elec, entropy, and cooling time. We propose to more than double the current number of clusters in ACCEPT and to expand the current suite of properties to include uniformly measured profiles of gas mass and hydrostatic equilibrium mass along with signatures of dynamical relaxation (centroid shift, power ratios, surface brightness concentration, temperature ratios) and global quantities such as core-excised Tx, Lx, and metallicities. We will explore the relationship between cool cores and dynamical relaxation, the reliability of hydrostatic mass profiles, and the dependence of the gas mass fraction on halo mass, redshift, and the degree of relaxation. ACCEPT2 will enable further community science.

New Detections of Radio Minihalos in Cool Cores of Galaxy Clusters

NASA Technical Reports Server (NTRS)

Giacintucci, Simona; Markevitch, Maxim; Venturi, Tiziana; Clarke, Tracy E.; Cassano, Rossella; Mazzotta, Pasquale

2013-01-01

Cool cores of some galaxy clusters exhibit faint radio minihalos. Their origin is unclear, and their study has been limited by their small number. We undertook a systematic search for minihalos in a large sample of X-ray luminous clusters with high-quality radio data. In this article, we report four new minihalos (A 478, ZwCl 3146,RXJ 1532.9+3021, and A 2204) and five candidates found in the reanalyzed archival Very Large Array observations.The radio luminosities of our minihalos and candidates are in the range of 102325 W Hz1 at 1.4 GHz, which is consistent with these types of radio sources. Their sizes (40160 kpc in radius) are somewhat smaller than those of previously known minihalos. We combine our new detections with previously known minihalos, obtaining a total sample of 21 objects, and briefly compare the cluster radio properties to the average X-ray temperature and the total masses estimated from Planck.We find that nearly all clusters hosting minihalos are hot and massive. Beyond that, there is no clear correlation between the minihalo radio power and cluster temperature or mass (in contrast with the giant radio halos found in cluster mergers, whose radio luminosity correlates with the cluster mass). Chandra X-ray images indicate gas sloshing in the cool cores of most of our clusters, with minihalos contained within the sloshing regions in many of them. This supports the hypothesis that radio-emitting electrons are reaccelerated by sloshing. Advection of relativistic electrons by the sloshing gas may also play a role in the formation of the less extended minihalos.

Turbulent heating in galaxy clusters brightest in X-rays.

PubMed

Zhuravleva, I; Churazov, E; Schekochihin, A A; Allen, S W; Arévalo, P; Fabian, A C; Forman, W R; Sanders, J S; Simionescu, A; Sunyaev, R; Vikhlinin, A; Werner, N

2014-11-06

The hot (10(7) to 10(8) kelvin), X-ray-emitting intracluster medium (ICM) is the dominant baryonic constituent of clusters of galaxies. In the cores of many clusters, radiative energy losses from the ICM occur on timescales much shorter than the age of the system. Unchecked, this cooling would lead to massive accumulations of cold gas and vigorous star formation, in contradiction to observations. Various sources of energy capable of compensating for these cooling losses have been proposed, the most promising being heating by the supermassive black holes in the central galaxies, through inflation of bubbles of relativistic plasma. Regardless of the original source of energy, the question of how this energy is transferred to the ICM remains open. Here we present a plausible solution to this question based on deep X-ray data and a new data analysis method that enable us to evaluate directly the ICM heating rate from the dissipation of turbulence. We find that turbulent heating is sufficient to offset radiative cooling and indeed appears to balance it locally at each radius-it may therefore be the key element in resolving the gas cooling problem in cluster cores and, more universally, in the atmospheres of X-ray-emitting, gas-rich systems on scales from galaxy clusters to groups and elliptical galaxies.

BUOYANCY INSTABILITIES IN A WEAKLY COLLISIONAL INTRACLUSTER MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kunz, Matthew W.; Stone, James M.; Bogdanovic, Tamara

2012-08-01

The intracluster medium (ICM) of galaxy clusters is a weakly collisional plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature gradients of either sign: the magnetothermal instability (MTI) in the outskirts of clusters and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We employ the Athena magnetohydrodynamic code to investigate the nonlinear evolution of these instabilities, self-consistently including the effects of anisotropic viscosity (i.e., Braginskii pressure anisotropy), anisotropic conduction, and radiative cooling. We find that, in all but the innermost regions of cool-coremore » clusters, anisotropic viscosity significantly impairs the ability of the HBI to reorient magnetic-field lines orthogonal to the temperature gradient. Thus, while radio-mode feedback appears necessary in the central few Multiplication-Sign 10 kpc, heat conduction may be capable of offsetting radiative losses throughout most of a cool core over a significant fraction of the Hubble time. Magnetically aligned cold filaments are then able to form by local thermal instability. Viscous dissipation during cold filament formation produces accompanying hot filaments, which can be searched for in deep Chandra observations of cool-core clusters. In the case of MTI, anisotropic viscosity leads to a nonlinear state with a folded magnetic field structure in which field-line curvature and field strength are anti-correlated. These results demonstrate that, if the HBI and MTI are relevant for shaping the properties of the ICM, one must self-consistently include anisotropic viscosity in order to obtain even qualitatively correct results.« less

Star-forming brightest cluster galaxies at 0.25

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, M.; Stalder, B.; Bayliss, M.

2016-01-22

We present a multiwavelength study of the 90 brightest cluster galaxies (BCGs) in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by the South Pole Telescope, utilizing data from various ground- and space-based facilities. We infer the star-formation rate (SFR) for the BCG in each cluster—based on the UV and IR continuum luminosity, as well as the [O ii]λλ3726,3729 emission line luminosity in cases where spectroscopy is available—and find seven systems with SFR > 100 M⊙ yr-1. We find that the BCG SFR exceeds 10 M⊙ yr-1 in 31 of 90 (34%) cases at 0.25 < z < 1.25, compared to ~1%–5% at z ~ 0 from the literature. At z gsim 1, this fraction increases tomore » $${92}_{-31}^{+6}$$%, implying a steady decrease in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific SFR in BCGs is declining more slowly with time than for field or cluster galaxies, which is most likely due to the replenishing fuel from the cooling ICM in relaxed, cool core clusters. At z gsim 0.6, the correlation between the cluster central entropy and BCG star formation—which is well established at z ~ 0—is not present. Instead, we find that the most star-forming BCGs at high-z are found in the cores of dynamically unrelaxed clusters. We use data from the Hubble Space Telescope to investigate the rest-frame near-UV morphology of a subsample of the most star-forming BCGs, and find complex, highly asymmetric UV morphologies on scales as large as ~50–60 kpc. The high fraction of star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times suggests that the dominant mode of fueling star formation in BCGs may have recently transitioned from galaxy–galaxy interactions to ICM cooling.« less

Star-forming brightest cluster galaxies at 0.25 < z < 1.25: A transitioning fuel supply

DOE PAGES

McDonald, M.; Stalder, B.; Bayliss, M.; ...

2016-01-22

In this paper, we present a multiwavelength study of the 90 brightest cluster galaxies (BCGs) in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by the South Pole Telescope, utilizing data from various ground- and space-based facilities. We infer the star-formation rate (SFR) for the BCG in each cluster—based on the UV and IR continuum luminosity, as well as the [O ii]λλ3726,3729 emission line luminosity in cases where spectroscopy is available—and find seven systems with SFR > 100 M ⊙ yr -1. We find that the BCG SFR exceeds 10 M ⊙ yr -1 in 31 of 90 (34%) cases at 0.25 < z < 1.25, compared to ~1%–5% at z ~ 0 from the literature. At z ≳ 1, this fraction increases tomore » $${92}_{-31}^{+6}$$%, implying a steady decrease in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific SFR in BCGs is declining more slowly with time than for field or cluster galaxies, which is most likely due to the replenishing fuel from the cooling ICM in relaxed, cool core clusters. At z ≳ 0.6, the correlation between the cluster central entropy and BCG star formation—which is well established at z ~ 0—is not present. Instead, we find that the most star-forming BCGs at high-z are found in the cores of dynamically unrelaxed clusters. We use data from the Hubble Space Telescope to investigate the rest-frame near-UV morphology of a subsample of the most star-forming BCGs, and find complex, highly asymmetric UV morphologies on scales as large as ~50–60 kpc. Finally, the high fraction of star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times suggests that the dominant mode of fueling star formation in BCGs may have recently transitioned from galaxy–galaxy interactions to ICM cooling.« less

Detection of a pair of prominent X-ray cavities in Abell 3847

NASA Astrophysics Data System (ADS)

Vagshette, Nilkanth D.; Naik, Sachindra; Patil, Madhav. K.; Sonkamble, Satish S.

2017-04-01

We present the results obtained from a detailed analysis of a deep Chandra observation of the bright FRII radio galaxy 3C 444 in Abell 3847 cluster. A pair of huge X-ray cavities are detected along the north and south directions from the centre of 3C 444. X-ray and radio images of the cluster reveal peculiar positioning of the cavities and radio bubbles. The radio lobes and X-ray cavities are apparently not spatially coincident and exhibit offsets by ˜61 and 77 kpc from each other along the north and south directions, respectively. Radial temperature and density profiles reveal the presence of a cool core in the cluster. Imaging and spectral studies showed the removal of substantial amount of matter from the core of the cluster by the radio jets. A detailed analysis of the temperature and density profiles showed the presence of a rarely detected elliptical shock in the cluster. Detection of inflating cavities at an average distance of ˜55 kpc from the centre implies that the central engine feeds a remarkable amount of radio power (˜6.3 × 1044 erg s-1) into the intra-cluster medium over ˜108 yr, the estimated age of cavity. The cooling luminosity of the cluster was estimated to be ˜8.30 × 1043 erg s-1 , which confirms that the AGN power is sufficient to quench the cooling. Ratios of mass accretion rate to Eddington and Bondi rates were estimated to be ˜0.08 and 3.5 × 104, respectively. This indicates that the black hole in the core of the cluster accretes matter through chaotic cold accretion.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, M.; Stalder, B.; Bayliss, M.

In this paper, we present a multiwavelength study of the 90 brightest cluster galaxies (BCGs) in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by the South Pole Telescope, utilizing data from various ground- and space-based facilities. We infer the star-formation rate (SFR) for the BCG in each cluster—based on the UV and IR continuum luminosity, as well as the [O ii]λλ3726,3729 emission line luminosity in cases where spectroscopy is available—and find seven systems with SFR > 100 M ⊙ yr -1. We find that the BCG SFR exceeds 10 M ⊙ yr -1 in 31 of 90 (34%) cases at 0.25 < z < 1.25, compared to ~1%–5% at z ~ 0 from the literature. At z ≳ 1, this fraction increases tomore » $${92}_{-31}^{+6}$$%, implying a steady decrease in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific SFR in BCGs is declining more slowly with time than for field or cluster galaxies, which is most likely due to the replenishing fuel from the cooling ICM in relaxed, cool core clusters. At z ≳ 0.6, the correlation between the cluster central entropy and BCG star formation—which is well established at z ~ 0—is not present. Instead, we find that the most star-forming BCGs at high-z are found in the cores of dynamically unrelaxed clusters. We use data from the Hubble Space Telescope to investigate the rest-frame near-UV morphology of a subsample of the most star-forming BCGs, and find complex, highly asymmetric UV morphologies on scales as large as ~50–60 kpc. Finally, the high fraction of star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times suggests that the dominant mode of fueling star formation in BCGs may have recently transitioned from galaxy–galaxy interactions to ICM cooling.« less

Searching for 300, 000 Degree Gas in the Core of the Phoenix Cluster with HST-COS

NASA Astrophysics Data System (ADS)

McDonald, Michael

2013-10-01

The high central density of the intracluster medium in some galaxy clusters suggests that the hot 10,000,000K gas should cool completely in less than a Hubble time. In these clusters, simple cooling models predict 100-1000 solar masses per year of cooling gas should fuel massive starbursts in the central galaxy. The fact that the typical central cluster galaxy is a massive, "red and dead" elliptical galaxy, with little evidence for a cool ISM, has led to the realization of the "cooling flow problem". It is now thought that mechanical feedback from the central supermassive blackhole, in the form of radio-blown bubbles, is offsetting cooling, leading to an exceptionally precise {residuals of less than 10 percent} balance between cooling and feedback in nearly every galaxy cluster in the local Universe. In the recently-discovered Phoenix cluster, where z=0.596, we observe an 800 solar mass per year starburst within the central galaxy which accounts for about 30 percent of the classical cooling prediction for this system. We speculate that this may represent the first "true" cooling flow, with the factor of 3 difference between cooling and star formation being attributed to star formation efficiency, rather than a problem with cooling. In order to test these predictions, we propose far-UV spectroscopic observations of the OVI 1032A emission line, which probes 10^5.5K gas, in the central galaxy of the Phoenix cluster. If detected at the expected levels, this would provide compelling evidence that the starburst is, indeed, fueled by runaway cooling of the intracluster medium, confirming the presence of the first, bonafide cooling flow.

The Merging Galaxy Cluster A520 - A Broken-Up Cool Core, A Dark Subcluster, and an X-Ray Channel

NASA Technical Reports Server (NTRS)

Wang, Qian H.S.; Markevitch, Maxim; Giacintucci, Simona

2016-01-01

We present results from a deep Chandra X-ray observation of a merging galaxy cluster A520. A high-resolution gas temperature map reveals a long trail of dense, cool clumpsapparently the fragments of a cool core that has been stripped from the infalling subcluster by ram pressure. The clumps should still be connected by the stretched magnetic field lines. The observed temperature variations imply that thermal conductivity is suppressed by a factor greater than 100 across the presumed direction of the magnetic field (as found in other clusters), and is also suppressed along the field lines by a factor of several. Two massive clumps in the periphery of A520, visible in the weak-lensing mass map and the X-ray image, have apparently been completely stripped of gas during the merger, but then re-accreted the surrounding high-entropy gas upon exit from the cluster. The mass clump that hosted the stripped cool core is also re-accreting hotter gas. An X-ray hydrostatic mass estimate for the clump that has the simplest geometry agrees with the lensing mass. Its current gas mass to total mass ratio is very low, 1.5 percent to 3 percent, which makes it a "dark subcluster." We also found a curious low X-ray brightness channel (likely a low-density sheet in projection) going across the cluster along the direction of an apparent secondary merger. The channel may be caused by plasma depletion in a region of an amplified magnetic field (with plasma Beta approximately equal to 10-20). The shock in A520 will be studied in a separate paper.

The white-dwarf cooling sequence of NGC 6791: a unique tool for stellar evolution

NASA Astrophysics Data System (ADS)

García-Berro, E.; Torres, S.; Renedo, I.; Camacho, J.; Althaus, L. G.; Córsico, A. H.; Salaris, M.; Isern, J.

2011-09-01

Context. NGC 6791 is a well-studied, metal-rich open cluster that is so close to us that it can be imaged down to luminosities fainter than that of the termination of its white-dwarf cooling sequence, thus allowing for an in-depth study of its white dwarf population. Aims: White dwarfs carry important information about the history of the cluster. We use observations of the white-dwarf cooling sequence to constrain important properties of the cluster stellar population, such as the existence of a putative population of massive helium-core white dwarfs, and the properties of a large population of unresolved binary white dwarfs. We also investigate the use of white dwarfs to disclose the presence of cluster subpopulations with a different initial chemical composition, and we obtain an upper bound to the fraction of hydrogen-deficient white dwarfs. Methods: We use a Monte Carlo simulator that employs up-to-date evolutionary cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient atmospheres, with carbon-oxygen and helium cores. The cooling sequences for carbon-oxygen cores account for the delays introduced by both 22Ne sedimentation in the liquid phase and by carbon-oxygen phase separation upon crystallization. Results: We do not find evidence for a substantial fraction of helium-core white dwarfs, and hence our results support the suggestion that the origin of the bright peak of the white-dwarf luminosity function can only be attributed to a population of unresolved binary white dwarfs. Moreover, our results indicate that if this hypothesis is at the origin of the bright peak, the number distribution of secondary masses of the population of unresolved binaries has to increase with increasing mass ratio between the secondary and primary components of the progenitor system. We also find that the observed cooling sequence appears to be able to constrain the presence of progenitor subpopulations with different chemical compositions and the fraction of hydrogen-deficient white dwarfs. Conclusions: Our simulations place interesting constraints on important characteristics of the stellar populations of NGC 6791. In particular, we find that the fraction of single helium-core white dwarfs must be smaller than 5%, that a subpopulation of stars with zero metallicity must be ≲12%, while if the adopted metallicity of the subpopulation is solar the upper limit is ~8%. Finally, we also find that the fraction of hydrogen-deficient white dwarfs in this particular cluster is surprinsingly small (≲6%).

Spectroscopy of the Perseus Cluster

NASA Technical Reports Server (NTRS)

Jones, Christine; Mushotzky, Richard F. (Technical Monitor)

2004-01-01

We present preliminary results of a XMM-Newton 50 ks observation of the Perseus Cluster that provides an unprecedented view of the central 0.5 Mpc region. The projected gas temperature declines smoothly by a factor of 2 from a maximum value of approx. 7 keV in the outer regions to just above 3 keV at the cluster center. Over this same range, the heavy-element abundance rises slowly from 0.4 to 0.5 solar as the radius decreases from 14 ft. to 5 ft., and then it rises to a peak of almost 0.7 solar at 1&farcm;25 before declining to 0.4 at the center. Th global east-west asymmetry of the gas temperature and surface brightness distributions, approximately aligned with the chain of bright galaxies, suggests an ongoing merger, although the modest degree of the observed asymmetry certainly excludes a major merger interpretation. The chain of galaxies probably traces the filament along which accretion started some time ago and is continuing at the present time. A cold and dense (low-entropy) cluster core like Perseus is probably well "protected" against the penetration of the gas of infalling groups and poor clusters, whereas in non-cooling core clusters such as Coma and A1367, infalling subclusters can penetrate deeply into the core region. In Perseus, gas associated with infalling groups may be stripped completely at the outskirts of the main cluster and only compression waves (shocks) may reach the central regions. We argue, and show supporting simulations, that the passage of such a wave(s) can qualitatively explain the overall horseshoe shaped appearance of the gas temperature map (the hot horseshoe surrounds the colder, low-entropy core) as well as other features of the Perseus Cluster core. These simulations also show that as compression waves traverse the cluster core, they can induce oscillatory motion of the cluster gas that can generate multiple sharp "edges" on opposite sides of the central galaxy. Gas motions induced by mergers may be a natural way to explain the high frequency of "edges" seen in clusters with cooling cores.

OSO-8 X-ray spectra of clusters of galaxies. 2: Discussion. [hot intracluster gas structures

NASA Technical Reports Server (NTRS)

Smith, B. W.; Mushotzky, R. F.; Serlemitsos, P. J.

1978-01-01

X-ray spectral parameters obtained from 2 to 20 keV OSO-8 data on X-ray clusters and optical cluster properties were examined to obtain information for restricting models for hot intracluster gas structures. Topics discussed include the radius of the X-ray core in relation to the galaxy core radius, the viral mass of hotter clusters, and galaxy density and optical central cluster properties. A population of cool, dim X-ray clusters which have not been observed is predicted. The iron abundance determinations recently quoted for intracluster gas are uncertain by 50 to greater than 100 percent from this nonstatistical cause alone.

Antiferromagnetic exchange coupling measurements on single Co clusters

NASA Astrophysics Data System (ADS)

Wernsdorfer, W.; Leroy, D.; Portemont, C.; Brenac, A.; Morel, R.; Notin, L.; Mailly, D.

2009-03-01

We report on single-cluster measurements of the angular dependence of the low-temperature ferromagnetic core magnetization switching field in exchange-coupled Co/CoO core-shell clusters (4 nm) using a micro-bridge DC superconducting quantum interference device (μ-SQUID). It is observed that the coupling with the antiferromagnetic shell induces modification in the switching field for clusters with intrinsic uniaxial anisotropy depending on the direction of the magnetic field applied during the cooling. Using a modified Stoner-Wohlfarth model, it is shown that the core interacts with two weakly coupled and asymmetrical antiferromagnetic sublattices. Ref.: C. Portemont, R. Morel, W. Wernsdorfer, D. Mailly, A. Brenac, and L. Notin, Phys. Rev. B 78, 144415 (2008)

SUPERMODEL ANALYSIS OF GALAXY CLUSTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fusco-Femiano, R.; Cavaliere, A.; Lapi, A.

2009-11-01

We present the analysis of the X-ray brightness and temperature profiles for six clusters belonging to both the Cool Core (CC) and Non Cool Core (NCC) classes, in terms of the Supermodel (SM) developed by Cavaliere et al. Based on the gravitational wells set by the dark matter (DM) halos, the SM straightforwardly expresses the equilibrium of the intracluster plasma (ICP) modulated by the entropy deposited at the boundary by standing shocks from gravitational accretion, and injected at the center by outgoing blast waves from mergers or from outbursts of active galactic nuclei. The cluster set analyzed here highlights notmore » only how simply the SM represents the main dichotomy CC versus NCC clusters in terms of a few ICP parameters governing the radial entropy run, but also how accurately it fits even complex brightness and temperature profiles. For CC clusters like A2199 and A2597, the SM with a low level of central entropy straightforwardly yields the characteristic peaked profile of the temperature marked by a decline toward the center, without requiring currently strong radiative cooling and high mass deposition rates. NCC clusters like A1656 require instead a central entropy floor of a substantial level, and some like A2256 and even more A644 feature structured temperature profiles that also call for a definite floor extension; in such conditions the SM accurately fits the observations, and suggests that in these clusters the ICP has been just remolded by a merger event, in the way of a remnant cool core. The SM also predicts that DM halos with high concentration should correlate with flatter entropy profiles and steeper brightness in the outskirts; this is indeed the case with A1689, for which from X-rays we find concentration values c approx 10, the hallmark of an early halo formation. Thus, we show the SM to constitute a fast tool not only to provide wide libraries of accurate fits to X-ray temperature and density profiles, but also to retrieve from the ICP archives specific information concerning the physical histories of DM and baryons in the inner and the outer cluster regions.« less

Zooming in on the Starburst at the Core of the Phoenix Cluster

NASA Astrophysics Data System (ADS)

McDonald, Michael

2011-10-01

In a recently published letter to Nature, we report the discovery of the most X-ray luminous galaxy cluster in the known Universe, within which the intracluster medium is cooling at an unprecedented rate. In the core of this cluster, the brightest cluster galaxy is forming stars at an unmatched rate of 740 Msun/yr, which is highly unusual for this class of galaxy which are typically referred to as "red and dead". We suspect that the extreme cooling and star formation rates are intimately linked: the cooling intracluster gas is most likely providing fuel for the starburst. We request 2 orbits of near-UV and optical broadband WFC3-UVIS imaging in order to morphologically classify this starburst as a result of i} cooling, infalling gas {filamentary UV emission}; ii} a recent merger {tidal tails with both UV and optical emission}; or iii} a starburst- or AGN-driven wind {wide opening angle}. These data will also allow us to determine the stellar populations of both the starburst and the underlying, older stellar populations, and will provide a much sharper view of the central AGN, allowing us to more carefully extract the contribution to the extended UV emission from young stars. Our early results have already received substantial attention from the international press, and we expect that a dramatically improved picture of the heart of this cluster would stir up as much, if not more, interest from the public.

Gas Sloshing Regulates and Records the Evolution of the Fornax Cluster

NASA Astrophysics Data System (ADS)

Su, Yuanyuan; Nulsen, Paul E. J.; Kraft, Ralph P.; Roediger, Elke; ZuHone, John A.; Jones, Christine; Forman, William R.; Sheardown, Alex; Irwin, Jimmy A.; Randall, Scott W.

2017-12-01

We present results of a joint Chandra and XMM-Newton analysis of the Fornax Cluster, the nearest galaxy cluster in the southern sky. Signatures of merger-induced gas sloshing can be seen in the X-ray image. We identify four sloshing cold fronts in the intracluster medium, residing at radii of 3 kpc (west), 10 kpc (northeast), 30 kpc (southwest), and 200 kpc (east). Despite spanning over two orders of magnitude in radius, all four cold fronts fall onto the same spiral pattern that wraps around the BCG NGC 1399, likely all initiated by the infall of NGC 1404. The most evident front is to the northeast, 10 kpc from the cluster center, which separates low-entropy high-metallicity gas and high-entropy low-metallicity gas. The metallicity map suggests that gas sloshing, rather than an AGN outburst, is the driving force behind the redistribution of the enriched gas in this cluster. The innermost cold front resides within the radius of the strong cool core. The sloshing timescale within the cooling radius, calculated from the Brunt–Väsälä frequency, is an order of magnitude shorter than the cooling time. It is plausible that gas sloshing is contributing to the heating of the cool core, provided that gas of different entropies can be mixed effectively via Kelvin–Helmholtz instability. The estimated age of the outermost front suggests that this is not the first infall of NGC 1404.

An off-axis galaxy cluster merger: Abell 0141

NASA Astrophysics Data System (ADS)

Caglar, Turgay

2018-04-01

We present structural analysis results of Abell 0141 (z = 0.23) based on X-ray data. The X-ray luminosity map demonstrates that Abell 0141 (A0141) is a bimodal galaxy cluster, which is separated on the sky by ˜0.65 Mpc with an elongation along the north-south direction. The optical galaxy density map also demonstrates this bimodality. We estimate sub-cluster ICM temperatures of 5.17^{+0.20}_{-0.19} keV for A0141N and 5.23^{+0.24}_{-0.23} keV for A0141S. We obtain X-ray morphological parameters w = 0.034 ± 0.004, c = 0.113 ± 0.004, and w = 0.039 ± 0.004, c = 0.104 ± 0.005 for A0141N and A0141S, respectively. The resulting X-ray morphological parameters indicate that both sub-clusters are moderately disturbed non-cool core structures. We find a slight brightness jump in the bridge region, and yet, there is still an absence of strong X-ray emitting gas between sub-clusters. We discover a significantly hotspot (˜10 keV) between sub-clusters, and a Mach number M = 1.69^{+0.40}_{-0.37} is obtained by using the temperature jump condition. However, we did not find direct evidence for shock-heating between sub-clusters. We estimate the sub-clusters' central entropies as K0 > 100 keV cm2, which indicates that the sub-clusters are not cool cores. We find some evidence that the system undergoes an off-axis collision; however, the cores of each sub-clusters have not yet been destroyed. Due to the orientation of X-ray tails of sub-clusters, we suggest that the northern sub-cluster moves through the south-west direction, and the southern cluster moves through the north-east direction. In conclusion, we are witnessing an earlier phase of close core passage between sub-clusters.

The metallicity of the intracluster medium over cosmic time: further evidence for early enrichment

NASA Astrophysics Data System (ADS)

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn; Simionescu, Aurora; Urban, Ondrej; Werner, Norbert; Zhuravleva, Irina

2017-12-01

We use Chandra X-ray data to measure the metallicity of the intracluster medium (ICM) in 245 massive galaxy clusters selected from X-ray and Sunyaev-Zel'dovich (SZ) effect surveys, spanning redshifts 0 < z < 1.2. Metallicities were measured in three different radial ranges, spanning cluster cores through their outskirts. We explore trends in these measurements as a function of cluster redshift, temperature and surface brightness 'peakiness' (a proxy for gas cooling efficiency in cluster centres). The data at large radii (0.5-1 r500) are consistent with a constant metallicity, while at intermediate radii (0.1-0.5 r500) we see a late-time increase in enrichment, consistent with the expected production and mixing of metals in cluster cores. In cluster centres, there are strong trends of metallicity with temperature and peakiness, reflecting enhanced metal production in the lowest entropy gas. Within the cool-core/sharply peaked cluster population, there is a large intrinsic scatter in central metallicity and no overall evolution, indicating significant astrophysical variations in the efficiency of enrichment. The central metallicity in clusters with flat surface brightness profiles is lower, with a smaller intrinsic scatter, but increases towards lower redshifts. Our results are consistent with other recent measurements of ICM metallicity as a function of redshift. They reinforce the picture implied by observations of uniform metal distributions in the outskirts of nearby clusters, in which most of the enrichment of the ICM takes place before cluster formation, with significant later enrichment taking place only in cluster centres, as the stellar populations of the central galaxies evolve.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn

Here, we use Chandra X-ray data to measure the metallicity of the intracluster medium (ICM) in 245 massive galaxy clusters selected from X-ray and Sunyaev–Zel'dovich (SZ) effect surveys, spanning redshifts 0 < z < 1.2. Metallicities were measured in three different radial ranges, spanning cluster cores through their outskirts. We explore trends in these measurements as a function of cluster redshift, temperature and surface brightness ‘peakiness’ (a proxy for gas cooling efficiency in cluster centres). The data at large radii (0.5–1 r500) are consistent with a constant metallicity, while at intermediate radii (0.1–0.5 r500) we see a late-time increase inmore » enrichment, consistent with the expected production and mixing of metals in cluster cores. In cluster centres, there are strong trends of metallicity with temperature and peakiness, reflecting enhanced metal production in the lowest entropy gas. Within the cool-core/sharply peaked cluster population, there is a large intrinsic scatter in central metallicity and no overall evolution, indicating significant astrophysical variations in the efficiency of enrichment. The central metallicity in clusters with flat surface brightness profiles is lower, with a smaller intrinsic scatter, but increases towards lower redshifts. Our results are consistent with other recent measurements of ICM metallicity as a function of redshift. They reinforce the picture implied by observations of uniform metal distributions in the outskirts of nearby clusters, in which most of the enrichment of the ICM takes place before cluster formation, with significant later enrichment taking place only in cluster centres, as the stellar populations of the central galaxies evolve.« less

Acoustic Disturbances in Galaxy Clusters

NASA Astrophysics Data System (ADS)

Zweibel, Ellen G.; Mirnov, Vladimir V.; Ruszkowski, Mateusz; Reynolds, Christopher S.; Yang, H.-Y. Karen; Fabian, Andrew C.

2018-05-01

Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative cooling, one of the most attractive is the dissipation of acoustic waves generated by active galactic nuclei. Fabian et al. showed that if the waves are nearly adiabatic, wave damping due to heat conduction and viscosity must be well below standard Coulomb rates in order to allow the waves to propagate throughout the core. Because of the importance of this result, we have revisited wave dissipation under galaxy cluster conditions in a way that accounts for the self-limiting nature of dissipation by electron thermal conduction, allows the electron and ion temperature perturbations in the waves to evolve separately, and estimates kinetic effects by comparing to a semicollisionless theory. While these effects considerably enlarge the toolkit for analyzing observations of wavelike structures and developing a quantitative theory for wave heating, the drastic reduction of transport coefficients proposed in Fabian et al. remains the most viable path to acoustic wave heating of galaxy cluster cores.

AGN-driven perturbations in the intracluster medium of the cool-core cluster ZwCl 2701

NASA Astrophysics Data System (ADS)

Vagshette, Nilkanth D.; Sonkamble, Satish S.; Naik, Sachindra; Patil, Madhav K.

2016-09-01

We present the results obtained from a total of 123 ks X-ray (Chandra) and 8 h of 1.4 GHz radio (Giant Metrewave Radio Telescope - GMRT) observations of the cool-core cluster ZwCl 2701 (z = 0.214). These observations of ZwCl 2701 showed the presence of an extensive pair of ellipsoidal cavities along the east and west directions within the central region < 20 kpc. Detection of bright rims around the cavities suggested that the radio lobes displaced X-ray-emitting hot gas forming shell-like structures. The total cavity power (mechanical power) that directly heated the surrounding gas and cooling luminosity of the cluster were estimated to be ˜2.27 × 1045 erg s-1 and 3.5 × 1044 erg s-1 , respectively. Comparable values of cavity power and cooling luminosity of ZwCl 2701 suggested that the mechanical power of the active galactic nuclei (AGN) outburst is large enough to balance the radiative cooling in the system. The star formation rate derived from the Hα luminosity was found to be ˜0.60 M⊙ yr-1, which is about three orders of magnitude lower than the cooling rate of ˜196 M⊙ yr-1. Detection of the floor in entropy profile of ZwCl 2701 suggested the presence of an alternative heating mechanism at the centre of the cluster. Lower value of the ratio (˜10-2) between black hole mass accretion rate and Eddington mass accretion rate suggested that launching of jet from the super massive black hole is efficient in ZwCl 2701. However, higher value of ratio (˜103) between black hole mass accretion rate and Bondi accretion rate indicated that the accretion rate required to create cavities is well above the Bondi accretion rate.

Hydrostatic Chandra X-ray analysis of SPT-selected galaxy clusters - I. Evolution of profiles and core properties

NASA Astrophysics Data System (ADS)

Sanders, J. S.; Fabian, A. C.; Russell, H. R.; Walker, S. A.

2018-02-01

We analyse Chandra X-ray Observatory observations of a set of galaxy clusters selected by the South Pole Telescope using a new publicly available forward-modelling projection code, MBPROJ2, assuming hydrostatic equilibrium. By fitting a power law plus constant entropy model we find no evidence for a central entropy floor in the lowest entropy systems. A model of the underlying central entropy distribution shows a narrow peak close to zero entropy which accounts for 60 per cent of the systems, and a second broader peak around 130 keV cm2. We look for evolution over the 0.28-1.2 redshift range of the sample in density, pressure, entropy and cooling time at 0.015R500 and at 10 kpc radius. By modelling the evolution of the central quantities with a simple model, we find no evidence for a non-zero slope with redshift. In addition, a non-parametric sliding median shows no significant change. The fraction of cool-core clusters with central cooling times below 2 Gyr is consistent above and below z = 0.6 (˜30-40 per cent). Both by comparing the median thermodynamic profiles, centrally biased towards cool cores, in two redshift bins, and by modelling the evolution of the unbiased average profile as a function of redshift, we find no significant evolution beyond self-similar scaling in any of our examined quantities. Our average modelled radial density, entropy and cooling-time profiles appear as power laws with breaks around 0.2R500. The dispersion in these quantities rises inwards of this radius to around 0.4 dex, although some of this scatter can be fitted by a bimodal model.

The Gas Distribution in the Outer Regions of Galaxy Clusters

NASA Technical Reports Server (NTRS)

Eckert, D.; Vazza, F.; Ettori, S.; Molendi, S.; Nagai, D.; Lau, E. T.; Roncarelli, M.; Rossetti, M.; Snowden, L.; Gastaldello, F.

2012-01-01

Aims. We present our analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We have exploited the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius, We stacked the density profiles to detect a signal beyond T200 and measured the typical density and scatter in cluster outskirts. We also computed the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compared our average density and scatter profiles with the results of numerical simulations. Results. As opposed to some recent Suzaku results, and confirming previous evidence from ROSAT and Chandra, we observe a steepening of the density profiles beyond approximately r(sub 500). Comparing our density profiles with simulations, we find that non-radiative runs predict density profiles that are too steep, whereas runs including additional physics and/ or treating gas clumping agree better with the observed gas distribution. We report high-confidence detection of a systematic difference between cool-core and non cool-core clusters beyond approximately 0.3r(sub 200), which we explain by a different distribution of the gas in the two classes. Beyond approximately r(sub 500), galaxy clusters deviate significantly from spherical symmetry, with only small differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the ENZO simulations. Conclusions. Comparing our results with numerical simulations, we find that non-radiative simulations fail to reproduce the gas distribution, even well outside cluster cores. Although their general behavior agrees more closely with the observations, simulations including cooling and star formation convert a large amount of gas into stars, which results in a low gas fraction with respect to the observations. Consequently, a detailed treatment of gas cooling, star formation, AGN feedback, and consideration of gas clumping is required to construct realistic models of the outer regions of clusters.

The Gas Distribution in Galaxy Cluster Outer Regions

NASA Technical Reports Server (NTRS)

Eckert, D.; Vazza, F.; Ettori, S.; Molendi, S.; Nagai, D.; Laue, E. T.; Roncarelli, M.; Rossetti, M.; Snowden, S. L.; Gastaldello, F.

2012-01-01

Aims. We present the analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We exploit the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius. We perform a stacking of the density profiles to detect a signal beyond r200 and measure the typical density and scatter in cluster outskirts. We also compute the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compare our average density and scatter profiles with the results of numerical simulations. Results. As opposed to some recent Suzaku results, and confirming previous evidence from ROSAT and Chandra, we observe a steepening of the density profiles beyond approximately r(sub 500). Comparing our density profiles with simulations, we find that non-radiative runs predict too steep density profiles, whereas runs including additional physics and/or treating gas clumping are in better agreement with the observed gas distribution. We report for the first time the high-confidence detection of a systematic difference between cool-core and non-cool core clusters beyond 0.3r(sub 200), which we explain by a different distribution of the gas in the two classes. Beyond r(sub 500), galaxy clusters deviate significantly from spherical symmetry, with only little differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the simulations. Conclusions. Comparing our results with numerical simulations, we find that non-radiative simulations fail to reproduce the gas distribution, even well outside cluster cores. Although their general behavior is in better agreement with the observations, simulations including cooling and star formation convert a large amount of gas into stars, which results in a low gas fraction with respect to the observations. Consequently, a detailed treatment of gas cooling, star formation, AGN feedback, and taking into account gas clumping is required to construct realistic models of cluster outer regions.

Semiempirical limits on the thermal conductivity of intracluster gas

NASA Technical Reports Server (NTRS)

David, Laurence P.; Hughes, John P.; Tucker, Wallace H.

1992-01-01

A semiempirical method for establishing lower limits on the thermal conductivity of hot gas in clusters of galaxies is described. The method is based on the observation that the X-ray imaging data (e.g., Einstein IPC) for clusters are well described by the hydrostatic-isothermal beta model, even for cooling flow clusters beyond about one core radius. In addition, there are strong indications that noncooling flow clusters (like the Coma Cluster) have a large central region (up to several core radii) of nearly constant gas temperature. This suggests that thermal conduction is an effective means of transporting and redistributing the thermal energy of the gas. This in turn has implications for the extent to which magnetic fields in the cluster are effective in reducing the thermal conductivity of the gas. Time-dependent hydrodynamic simulations for the gas in the Coma Cluster under two separate evolutionary scenarios are presented. One scenario assumes that the cluster potential is static and that the gas has an initial adiabatic distribution. The second scenario uses an evolving cluster potential. These models along with analytic results show that the thermal conductivity of the gas in the Coma Cluster cannot be less than 0.1 of full Spitzer conductivity. These models also show that high gas conductivity assists rather than hinders the development of radiative cooling in the central regions of clusters.

The metallicity of the intracluster medium over cosmic time: further evidence for early enrichment

DOE PAGES

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn; ...

2017-08-26

Here, we use Chandra X-ray data to measure the metallicity of the intracluster medium (ICM) in 245 massive galaxy clusters selected from X-ray and Sunyaev–Zel'dovich (SZ) effect surveys, spanning redshifts 0 < z < 1.2. Metallicities were measured in three different radial ranges, spanning cluster cores through their outskirts. We explore trends in these measurements as a function of cluster redshift, temperature and surface brightness ‘peakiness’ (a proxy for gas cooling efficiency in cluster centres). The data at large radii (0.5–1 r500) are consistent with a constant metallicity, while at intermediate radii (0.1–0.5 r500) we see a late-time increase inmore » enrichment, consistent with the expected production and mixing of metals in cluster cores. In cluster centres, there are strong trends of metallicity with temperature and peakiness, reflecting enhanced metal production in the lowest entropy gas. Within the cool-core/sharply peaked cluster population, there is a large intrinsic scatter in central metallicity and no overall evolution, indicating significant astrophysical variations in the efficiency of enrichment. The central metallicity in clusters with flat surface brightness profiles is lower, with a smaller intrinsic scatter, but increases towards lower redshifts. Our results are consistent with other recent measurements of ICM metallicity as a function of redshift. They reinforce the picture implied by observations of uniform metal distributions in the outskirts of nearby clusters, in which most of the enrichment of the ICM takes place before cluster formation, with significant later enrichment taking place only in cluster centres, as the stellar populations of the central galaxies evolve.« less

INEFFICIENT DRIVING OF BULK TURBULENCE BY ACTIVE GALACTIC NUCLEI IN A HYDRODYNAMIC MODEL OF THE INTRACLUSTER MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, Christopher S.; Balbus, Steven A.; Schekochihin, Alexander A., E-mail: chris@astro.umd.edu

2015-12-10

Central jetted active galactic nuclei (AGNs) appear to heat the core regions of the intracluster medium (ICM) in cooling-core galaxy clusters and groups, thereby preventing a cooling catastrophe. However, the physical mechanism(s) by which the directed flow of kinetic energy is thermalized throughout the ICM core remains unclear. We examine one widely discussed mechanism whereby the AGN induces subsonic turbulence in the ambient medium, the dissipation of which provides the ICM heat source. Through controlled inviscid three-dimensional hydrodynamic simulations, we verify that explosive AGN-like events can launch gravity waves (g-modes) into the ambient ICM, which in turn decays to volume-fillingmore » turbulence. In our model, however, this process is found to be inefficient, with less than 1% of the energy injected by the AGN activity actually ending up in the turbulence of the ambient ICM. This efficiency is an order of magnitude or more too small to explain the observations of AGN-feedback in galaxy clusters and groups with short central cooling times. Atmospheres in which the g-modes are strongly trapped/confined have an even lower efficiency since, in these models, the excitation of turbulence relies on the g-modes’ ability to escape from the center of the cluster into the bulk ICM. Our results suggest that, if AGN-induced turbulence is indeed the mechanism by which the AGN heats the ICM core, its driving may rely on physics beyond that captured in our ideal hydrodynamic model.« less

Subgrid Modeling of AGN-driven Turbulence in Galaxy Clusters

NASA Astrophysics Data System (ADS)

Scannapieco, Evan; Brüggen, Marcus

2008-10-01

Hot, underdense bubbles powered by active galactic nuclei (AGNs) are likely to play a key role in halting catastrophic cooling in the centers of cool-core galaxy clusters. We present three-dimensional simulations that capture the evolution of such bubbles, using an adaptive mesh hydrodynamic code, FLASH3, to which we have added a subgrid model of turbulence and mixing. While pure hydro simulations indicate that AGN bubbles are disrupted into resolution-dependent pockets of underdense gas, proper modeling of subgrid turbulence indicates that this is a poor approximation to a turbulent cascade that continues far beyond the resolution limit. Instead, Rayleigh-Taylor instabilities act to effectively mix the heated region with its surroundings, while at the same time preserving it as a coherent structure, consistent with observations. Thus, bubbles are transformed into hot clouds of mixed material as they move outward in the hydrostatic intracluster medium (ICM), much as large airbursts lead to a distinctive "mushroom cloud" structure as they rise in the hydrostatic atmosphere of Earth. Properly capturing the evolution of such clouds has important implications for many ICM properties. In particular, it significantly changes the impact of AGNs on the distribution of entropy and metals in cool-core clusters such as Perseus.

A non cool-core 4.6-keV cluster around the bright nearby radio galaxy PKS B1416-493

NASA Astrophysics Data System (ADS)

Worrall, D. M.; Birkinshaw, M.

2017-05-01

We present new X-ray (Chandra) and radio (ATCA) observations of the z = 0.09 radio galaxy PKS B1416-493, a member of the southern equivalent of the 3CRR sample. We find the source to be embedded in a previously unrecognized bright kT = 4.6-keV non cool-core cluster. The discovery of new clusters of such high temperature and luminosity within z = 0.1 is rare. The radio source was chosen for observation based on its intermediate FR I/II morphology. We identify a cavity coincident with the northeast lobe, and excess counts associated with the southwest lobe that we interpret as inverse-Compton X-ray emission. The jet power, at 5.3 × 1044 erg s-1, when weighted by radio source density, supports suggestions that radio sources of intermediate morphology and radio power may dominate radio-galaxy heating in the local Universe.

Observational and Numerical Diagnostics of Galaxy Cluster Outer Regions

NASA Technical Reports Server (NTRS)

Eckert, D.; Vazza, F.; Ettori, S.; Molendi, S.; Nagai, D.; Lau, E.; Roncarelli, M.; Rossetti, M.; Snowden, S. L.; Gastaldello, F.

2011-01-01

Aims. We present the analysis of a local (z = 0.04 - 0.2) sample of 31 galaxy clusters with the aim of measuring the density of the X-ray emitting gas in cluster outskirts. We compare our results with numerical simulations to set constraints on the azimuthal symmetry and gas clumping in the outer regions of galaxy clusters. Methods. We exploit the large field-of-view and low instrumental background of ROSAT/PSPC to trace the density of the intracluster gas out to the virial radius. We perform a stacking of the density profiles to detect a signal beyond r(sub 200) and measure the typical density and scatter in cluster outskirts. We also compute the azimuthal scatter of the profiles with respect to the mean value to look for deviations from spherical symmetry. Finally, we compare our average density and scatter profiles with the results of numerical simulations. Results. As opposed to several recent results, we observe a steepening of the density profiles beyond approximately 0.3r(sub 500). Comparing our density profiles with simulations, we find that non-radiative runs predict too steep density profiles, whereas runs including additional physics and/or gas clumping are in better agreement with the observed gas distribution. We note a systematic difference between cool-core and non-cool core clusters beyond approximately 0.3r(sub 200), which we explain by a different distribution of the gas in the two classes. Beyond approximately r(sub 500), galaxy clusters deviate significantly from spherical symmetry, with only little differences between relaxed and disturbed systems. We find good agreement between the observed and predicted scatter profiles, but only when the 1% densest clumps are filtered out in the simulations. Conclusions. The general trend of steepening density around the virial radius indicates that the shallow density profiles found in several recent works were probably obtained along particular directions (e.g., filaments) and are not representative of the typical behavior of clusters. Comparing our results with numerical simulations, we find that non-radiative simulations fail to reproduce the gas distribution, even well outside cluster cores. Therefore, a detailed treatment of gas cooling, star formation, clumping, and AGN feedback is required to construct realistic models of cluster outer regions.

Buoyant AGN Bubbles in the Quasi-isothermal Potential of NGC 1399

NASA Astrophysics Data System (ADS)

Su, Yuanyuan; Nulsen, Paul E. J.; Kraft, Ralph P.; Forman, William R.; Jones, Christine; Irwin, Jimmy A.; Randall, Scott W.; Churazov, Eugene

2017-10-01

The Fornax Cluster is a low-mass cool-core galaxy cluster. We present a deep Chandra study of NGC 1399, the central dominant elliptical galaxy of Fornax. The cluster center harbors two symmetric X-ray cavities coincident with a pair of radio lobes fed by two collimated jets along a north-south axis. A temperature map reveals that the active galactic nucleus (AGN) outburst has created a channel filled with cooler gas out to a radius of 10 kpc. The cavities are surrounded by cool bright rims and filaments that may have been lifted from smaller radii by the buoyant bubbles. X-ray imaging suggests a potential ghost bubble of ≳5 kpc diameter to the northwest. We find that the amount of gas lifted by AGN bubbles is comparable to that which would otherwise cool, demonstrating that AGN-driven outflow is effective in offsetting cooling in low-mass clusters. The cluster cooling timescale is > 30 times longer than the dynamical timescale, which is consistent with the lack of cold molecular gas at the cluster center. The X-ray hydrostatic mass is consistent within 10%, with the total mass derived from the optical data. The observed entropy profile rises linearly, following a steeper slope than that observed at the centers of massive clusters; gas shed by stars in NGC 1399 may be incorporated in the hot phase. However, it is far-fetched for supernova-driven outflow to produce and maintain the thermal distribution in NGC 1399, and it is in tension with the metal content in the hot gas.

X-Ray Spectroscopy of the Cluster of Galaxies Abell 1795 with XMM-Newton

NASA Technical Reports Server (NTRS)

Tamura, T.; Kaastra, J. S.; Peterson, J. R.; Paerels, F.; Mittaz, J. P. D.; Trudolyubov, S. P.; Stewart, G.; Fabian, A. C.; Mushotzky, R. F.; Lumb, D. H.

2000-01-01

The initial results from XMM-Newton observations of the rich cluster of galaxies Abell 1795 are presented. The spatially-resolved X-ray spectra taken by the European Photon Imaging Cameras (EPIC) show a temperature drop at a radius of - 200 kpc from the cluster center, indicating that the ICM is cooling. Both the EPIC and the Reflection Grating Spectrometers (RGS) spectra extracted from the cluster center can be described by an isothermal model with a temperature of approx. 4 keV. The volume emission measure of any cool component (less than 1 keV) is less than a few % of the hot component at the cluster center. A strong O VIII Lyman alpha line was detected with the RGS from the cluster core. The O abundance of the ICM is 0.2-0.5 times the solar value. The O to Fe ratio at the cluster center is 0.5 - 1.5 times the solar ratio.

Cooling Flow Spectra in Ginga Galaxy Clusters

NASA Technical Reports Server (NTRS)

White, Raymond E., III

1997-01-01

The primary focus of this research project has been a joint analysis of Ginga LAC and Einstein SSS X-ray spectra of the hot gas in galaxy clusters with cooling flows is reported. We studied four clusters (A496, A1795, A2142 & A2199) and found their central temperatures to be cooler than in the exterior, which is expected from their having cooling flows. More interestingly, we found central metal abundance enhancements in two of the clusters, A496 and A2142. We have been assessing whether the abundance gradients (or lack thereof) in intracluster gas is correlated with galaxy morphological gradients in the host clusters. In rich, dense galaxy clusters, elliptical and SO galaxies are generally found in the cluster cores, while spiral galaxies are found in the outskirts. If the metals observed in clusters came from proto-ellipticals and proto-S0s blowing winds, then the metal distribution in intracluster gas may still reflect the distribution of their former host galaxies. In a research project which was inspired by the success of the Ginga LAC/Einstein SSS work, we analyzed X-ray spectra from the HEAO-A2 MED and the Einstein SSS to look for temperature gradients in cluster gas. The HEAO-A2 MED was also a non-imaging detector with a large field of view compared to the SSS, so we used the differing fields of view of the two instruments to extract spatial information. We found some evidence of cool gas in the outskirts of clusters, which may indicate that the nominally isothermal mass density distributions in these clusters are steepening in the outer parts of these clusters.

SUPERMODEL ANALYSIS OF A1246 AND J255: ON THE EVOLUTION OF GALAXY CLUSTERS FROM HIGH TO LOW ENTROPY STATES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fusco-Femiano, R.; Lapi, A., E-mail: roberto.fuscofemiano@iaps.inaf.it

2015-02-10

We present an analysis of high-quality X-ray data out to the virial radius for the two galaxy clusters A1246 and GMBCG J255.34805+64.23661 (J255) by means of our entropy-based SuperModel. For A1246 we find that the spherically averaged entropy profile of the intracluster medium (ICM) progressively flattens outward, and that a nonthermal pressure component amounting to ≈20% of the total is required to support hydrostatic equilibrium in the outskirts; there we also estimate a modest value C ≈ 1.6 of the ICM clumping factor. These findings agree with previous analyses on other cool-core, relaxed clusters, and lend further support to themore » picture by Lapi et al. that relates the entropy flattening, the development of the nonthermal pressure component, and the azimuthal variation of ICM properties to weakening boundary shocks. In this scenario clusters are born in a high-entropy state throughout, and are expected to develop on similar timescales a low-entropy state both at the center due to cooling, and in the outskirts due to weakening shocks. However, the analysis of J255 testifies how such a typical evolutionary course can be interrupted or even reversed by merging especially at intermediate redshift, as predicted by Cavaliere et al. In fact, a merger has rejuvenated the ICM of this cluster at z ≈ 0.45 by reestablishing a high-entropy state in the outskirts, while leaving intact or erasing only partially the low-entropy, cool core at the center.« less

Formation of fivefold axes in the FCC-metal nanoclusters

NASA Astrophysics Data System (ADS)

Myasnichenko, Vladimir S.; Starostenkov, Mikhail D.

2012-11-01

Formation of atomistic structures of metallic Cu, Au, Ag clusters and bimetallic Cu-Au clusters was studied with the help of molecular dynamics using the many-body tight-binding interatomic potential. The simulation of the crystallization process of clusters with the number of atoms ranging from 300 to 1092 was carried out. The most stable configurations of atoms in the system, corresponding to the minimum of potential energy, was found during super-fast cooling from 1000 K. Atoms corresponding to fcc, hcp, and Ih phases were identified by the method of common neighbor analysis. Incomplete icosahedral core can be discovered at the intersection of one of the Ih axes with the surface of monometallic cluster. The decahedron-shaped structure of bimetallic Cu-Au cluster with seven completed icosahedral cores was obtained. The principles of the construction of small bimetallic clusters with icosahedral symmetry and increased fractal dimensionality were offered.

Cosmic-Ray Feedback Heating of the Intracluster Medium

NASA Astrophysics Data System (ADS)

Ruszkowski, Mateusz; Yang, H.-Y. Karen; Reynolds, Christopher S.

2017-07-01

Active galactic nuclei (AGNs) play a central role in solving the decades-old cooling-flow problem. Although there is consensus that AGNs provide the energy to prevent catastrophically large star formation, one major problem remains: How is the AGN energy thermalized in the intracluster medium (ICM)? We perform a suite of three-dimensional magnetohydrodynamical adaptive mesh refinement simulations of AGN feedback in a cool core cluster including cosmic rays (CRs). CRs are supplied to the ICM via collimated AGN jets and subsequently disperse in the magnetized ICM via streaming, and interact with the ICM via hadronic, Coulomb, and streaming instability heating. We find that CR transport is an essential model ingredient at least within the context of the physical model considered here. When streaming is included, (I) CRs come into contact with the ambient ICM and efficiently heat it, (II) streaming instability heating dominates over Coulomb and hadronic heating, (III) the AGN is variable and the atmosphere goes through low-/high-velocity dispersion cycles, and, importantly, (IV) CR pressure support in the cool core is very low and does not demonstrably violate observational constraints. However, when streaming is ignored, CR energy is not efficiently spent on the ICM heating and CR pressure builds up to a significant level, creating tension with the observations. Overall, we demonstrate that CR heating is a viable channel for the AGN energy thermalization in clusters and likely also in ellipticals, and that CRs play an important role in determining AGN intermittency and the dynamical state of cool cores.

Linking Dynamical and Stellar Evolution in the Metal-Poor Globular Cluster M92

NASA Astrophysics Data System (ADS)

Kalirai, Jason

2017-08-01

We propose a 5 orbit HST program to acquire UV imaging at the center of the ancient, metal-poor globular cluster NGC 6341 (M92). Our program is designed to achieve two science goals with a single data set, 1.) to directly measure the diffusion of stars through the massive cluster's core, 2.) to pinpoint the phase of post main-sequence evolution at which [Fe/H] = -2.3 stars lose their mass. Our novel technique will achieve these goals by using the full power of WFC3's exquisite UV sensitivity at <0.3 microns combined with its high spatial resolution. We will uncover 1000 newly-formed white dwarfs in the center of M92 and track how their spatial distribution changes as they get older on the cooling sequence. Having just experienced significant mass loss, the youngest remnants with ages <10s of Myr will still be moving slowly like their 0.8 Msun progenitors, whereas the older remnants with t_cool > 100s Myr will be fully relaxed. Using the methodology we developed and successfully applied to 47 Tuc (Heyl et al. 2015a; 2015b), we will watch this dynamical evolution to measure the diffusion coefficient due to gravitational relaxation in the cluster's core and the past timing of stellar mass loss that was responsible for the current cluster mass segregation profile. M92 is the ideal target for this study as it complements our existing study of the relatively metal-rich cluster 47 Tuc; it has an extremely low metallicity of [Fe/H] = -2.3, very low foreground reddening (E(B-V) = 0.02), moderate concentration index, and a theoretically-expected relaxation timescale in its core of 90 Myr, which nicely splits the young and old white dwarfs that can be observed with Hubble.

HOW AGN JETS HEAT THE INTRACLUSTER MEDIUM—INSIGHTS FROM HYDRODYNAMIC SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karen Yang, H.-Y.; Reynolds, Christopher S., E-mail: hsyang@astro.umd.edu

Feedback from active galactic nuclei (AGNs) is believed to prevent catastrophic cooling in galaxy clusters. However, how the feedback energy is transformed into heat, and how the AGN jets heat the intracluster medium (ICM) isotropically, still remain elusive. In this work, we gain insights into the relative importance of different heating mechanisms using three-dimensional hydrodynamic simulations including cold gas accretion and momentum-driven jet feedback, which are the most successful models to date in terms of reproducing the properties of cool cores. We find that there is net heating within two “jet cones” (within ∼30° from the axis of jet precession)more » where the ICM gains entropy by shock heating and mixing with the hot thermal gas within bubbles. Outside the jet cones, the ambient gas is heated by weak shocks, but not enough to overcome radiative cooling, therefore, forming a “reduced” cooling flow. Consequently, the cluster core is in a process of “gentle circulation” over billions of years. Within the jet cones, there is significant adiabatic cooling as the gas is uplifted by buoyantly rising bubbles; outside the cones, energy is supplied by the inflow of already-heated gas from the jet cones as well as adiabatic compression as the gas moves toward the center. In other words, the fluid dynamics self-adjusts such that it compensates and transports the heat provided by the AGN, and hence no fine-tuning of the heating profile of any process is necessary. Throughout the cluster evolution, turbulent energy is only at the percent level compared to gas thermal energy, and thus turbulent heating is not the main source of heating in our simulation.« less

How AGN Jets Heat the Intracluster Medium—Insights from Hydrodynamic Simulations

NASA Astrophysics Data System (ADS)

Yang, H.-Y. Karen; Reynolds, Christopher S.

2016-10-01

Feedback from active galactic nuclei (AGNs) is believed to prevent catastrophic cooling in galaxy clusters. However, how the feedback energy is transformed into heat, and how the AGN jets heat the intracluster medium (ICM) isotropically, still remain elusive. In this work, we gain insights into the relative importance of different heating mechanisms using three-dimensional hydrodynamic simulations including cold gas accretion and momentum-driven jet feedback, which are the most successful models to date in terms of reproducing the properties of cool cores. We find that there is net heating within two “jet cones” (within ∼30° from the axis of jet precession) where the ICM gains entropy by shock heating and mixing with the hot thermal gas within bubbles. Outside the jet cones, the ambient gas is heated by weak shocks, but not enough to overcome radiative cooling, therefore, forming a “reduced” cooling flow. Consequently, the cluster core is in a process of “gentle circulation” over billions of years. Within the jet cones, there is significant adiabatic cooling as the gas is uplifted by buoyantly rising bubbles; outside the cones, energy is supplied by the inflow of already-heated gas from the jet cones as well as adiabatic compression as the gas moves toward the center. In other words, the fluid dynamics self-adjusts such that it compensates and transports the heat provided by the AGN, and hence no fine-tuning of the heating profile of any process is necessary. Throughout the cluster evolution, turbulent energy is only at the percent level compared to gas thermal energy, and thus turbulent heating is not the main source of heating in our simulation.

Revisiting the Cooling Flow Problem in Galaxies, Groups, and Clusters of Galaxies

NASA Astrophysics Data System (ADS)

McDonald, M.; Gaspari, M.; McNamara, B. R.; Tremblay, G. R.

2018-05-01

We present a study of 107 galaxies, groups, and clusters spanning ∼3 orders of magnitude in mass, ∼5 orders of magnitude in central galaxy star formation rate (SFR), ∼4 orders of magnitude in the classical cooling rate ({\\dot{M}}cool}\\equiv {M}gas}(r< {r}cool})/{t}cool}) of the intracluster medium (ICM), and ∼5 orders of magnitude in the central black hole accretion rate. For each system in this sample, we measure the ICM cooling rate, {\\dot{M}}cool}, using archival Chandra X-ray data and acquire the SFR and systematic uncertainty in the SFR by combining over 330 estimates from dozens of literature sources. With these data, we estimate the efficiency with which the ICM cools and forms stars, finding {ε }cool}\\equiv {SFR}/{\\dot{M}}cool}=1.4 % +/- 0.4% for systems with {\\dot{M}}cool}> 30 M ⊙ yr‑1. For these systems, we measure a slope in the SFR–{\\dot{M}}cool} relation greater than unity, suggesting that the systems with the strongest cool cores are also cooling more efficiently. We propose that this may be related to, on average, higher black hole accretion rates in the strongest cool cores, which could influence the total amount (saturating near the Eddington rate) and dominant mode (mechanical versus radiative) of feedback. For systems with {\\dot{M}}cool}< 30 M ⊙ yr‑1, we find that the SFR and {\\dot{M}}cool} are uncorrelated and show that this is consistent with star formation being fueled at a low (but dominant) level by recycled ISM gas in these systems. We find an intrinsic log-normal scatter in SFR at a fixed {\\dot{M}}cool} of 0.52 ± 0.06 dex (1σ rms), suggesting that cooling is tightly self-regulated over very long timescales but can vary dramatically on short timescales. There is weak evidence that this scatter may be related to the feedback mechanism, with the scatter being minimized (∼0.4 dex) for systems for which the mechanical feedback power is within a factor of two of the cooling luminosity.

Galaxy Clusters: A Novel Look at Diffuse Baryons Withstanding Dark Matter Gravity

NASA Astrophysics Data System (ADS)

Cavaliere, A.; Lapi, A.; Fusco-Femiano, R.

2009-06-01

In galaxy clusters, the equilibria of the intracluster plasma (ICP) and of the gravitationally dominant dark matter (DM) are governed by the hydrostatic equation and by the Jeans equation, respectively; in either case gravity is withstood by the corresponding, entropy-modulated pressure. Jeans, with the DM "entropy" set to K vprop r α and α ≈ 1.25-1.3 applying from groups to rich clusters, yields our radial α-profiles these, compared to the empirical Navarro-Frenk-White distribution, are flatter at the center and steeper in the outskirts as required by recent gravitational lensing data. In the ICP, on the other hand, the entropy run k(r) is mainly shaped by shocks, as steadily set by supersonic accretion of gas at the cluster boundary, and intermittently driven from the center by merging events or by active galactic nuclei (AGNs); the resulting equilibrium is described by the exact yet simple formalism constituting our ICP Supermodel. With two parameters, this accurately represents the runs of density n(r) and temperature T(r) as required by up-to-date X-ray data on surface brightness and spectroscopy for both cool core (CC) and non-cool core (NCC) clusters; the former are marked by a middle temperature peak, whose location is predicted from rich clusters to groups. The Supermodel inversely links the inner runs of n(r) and T(r), and highlights their central scaling with entropy nc vprop k -1 c and Tc vprop k 0.35 c , to yield radiative cooling times tc ≈ 0.3(kc /15 keV cm2)1.2 Gyr. We discuss the stability of the central values so focused: against radiative erosion of kc in the cool dense conditions of CC clusters, that triggers recurrent AGN activities resetting it back; or against energy inputs from AGNs and mergers whose effects are saturated by the hot central conditions of NCC clusters. From the Supermodel, we also derive as limiting cases the classic polytropic β-models, and the "mirror" model with T(r) vprop σ2(r) suitable for NCC and CC clusters, respectively; these limiting cases highlight how the ICP temperature T(r) strives to mirror the DM velocity dispersion σ2(r) away from energy and entropy injections. Finally, we discuss how the Supermodel connects information derived from X-ray and gravitational lensing observations.

Radial metal abundance profiles in the intra-cluster medium of cool-core galaxy clusters, groups, and ellipticals

NASA Astrophysics Data System (ADS)

Mernier, F.; de Plaa, J.; Kaastra, J. S.; Zhang, Y.-Y.; Akamatsu, H.; Gu, L.; Kosec, P.; Mao, J.; Pinto, C.; Reiprich, T. H.; Sanders, J. S.; Simionescu, A.; Werner, N.

2017-07-01

The hot intra-cluster medium (ICM) permeating galaxy clusters and groups is not pristine, as it has been continuously enriched by metals synthesised in Type Ia (SNIa) and core-collapse (SNcc) supernovae since the major epoch of star formation (z ≃ 2-3). The cluster/group enrichment history and mechanisms responsible for releasing and mixing the metals can be probed via the radial distribution of SNIa and SNcc products within the ICM. In this paper, we use deep XMM-Newton/EPIC observations from a sample of 44 nearby cool-core galaxy clusters, groups, and ellipticals (CHEERS) to constrain the average radial O, Mg, Si, S, Ar, Ca, Fe, and Ni abundance profiles. The radial distributions of all these elements, averaged over a large sample for the first time, represent the best constrained profiles available currently. Specific attention is devoted to a proper modelling of the EPIC spectral components, and to other systematic uncertainties that may affect our results. We find an overall decrease of the Fe abundance with radius out to 0.9 r500 and 0.6 r500 for clusters and groups, respectively, in good agreement with predictions from the most recent hydrodynamical simulations. The average radial profiles of all the other elements (X) are also centrally peaked and, when rescaled to their average central X/Fe ratios, follow well the Fe profile out to at least 0.5 r500. As predicted by recent simulations, we find that the relative contribution of SNIa (SNcc) to the total ICM enrichment is consistent with being uniform at all radii, both for clusters and groups using two sets of SNIa and SNcc yield models that reproduce the X/Fe abundance pattern in the core well. In addition to implying that the central metal peak is balanced between SNIa and SNcc, our results suggest that the enriching SNIa and SNcc products must share the same origin and that the delay between the bulk of the SNIa and SNcc explosions must be shorter than the timescale necessary to diffuse out the metals. Finally, we report an apparent abundance drop in the very core of 14 systems ( 32% of the sample). Possible origins of these drops are discussed.

Radial Profiles of PKS 0745-191 Galaxy Cluster with XMM-Newton X-Ray Observations

NASA Astrophysics Data System (ADS)

Tumer, A.; Ezer, C.; Ercan, E.

2017-10-01

Since clusters of galaxies are the largest comprehensive samples of the universe, they provide essential information on from the most basic to the most complex physical mechanisms such as nucleosynthesis and supernovae events. Some of these information are provided by the X-ray emission data from Intra Cluster Medium (ICM) which contains hot dilute gas. Recent archieved observation of the X-Ray spectrum of the cool core galaxy cluster PKS 0745-191 provided by XMM-Newton is subjected to data analysis using ESAS package. Followed by spectra analysis utilizing Xspec spectral fitting software, we present the radial profiles of temperature and abundance from the core to 0.5R_500 of brightest distant cluster (z ˜ 0.102) PKS 0745-191. Using the deprojected spectra, the radial distribution of pressure and entropy in the aforementioned region are also presented.

The uniformity and time-invariance of the intra-cluster metal distribution in galaxy clusters from the IllustrisTNG simulations

NASA Astrophysics Data System (ADS)

Vogelsberger, Mark; Marinacci, Federico; Torrey, Paul; Genel, Shy; Springel, Volker; Weinberger, Rainer; Pakmor, Rüdiger; Hernquist, Lars; Naiman, Jill; Pillepich, Annalisa; Nelson, Dylan

2018-02-01

The distribution of metals in the intra-cluster medium (ICM) encodes important information about the enrichment history and formation of galaxy clusters. Here, we explore the metal content of clusters in IllustrisTNG - a new suite of galaxy formation simulations building on the Illustris project. Our cluster sample contains 20 objects in TNG100 - a ˜(100 Mpc)3 volume simulation with 2 × 18203 resolution elements, and 370 objects in TNG300 - a ˜(300 Mpc)3 volume simulation with 2 × 25003 resolution elements. The z = 0 metallicity profiles agree with observations, and the enrichment history is consistent with observational data going beyond z ˜ 1, showing nearly no metallicity evolution. The abundance profiles vary only minimally within the cluster samples, especially in the outskirts with a relative scatter of ˜ 15 per cent. The average metallicity profile flattens towards the centre, where we find a logarithmic slope of -0.1 compared to -0.5 in the outskirts. Cool core clusters have more centrally peaked metallicity profiles (˜0.8 solar) compared to non-cool core systems (˜0.5 solar), similar to observational trends. Si/Fe and O/Fe radial profiles follow positive gradients. The outer abundance profiles do not evolve below z ˜ 2, whereas the inner profiles flatten towards z = 0. More than ˜ 80 per cent of the metals in the ICM have been accreted from the proto-cluster environment, which has been enriched to ˜0.1 solar already at z ˜ 2. We conclude that the intra-cluster metal distribution is uniform among our cluster sample, nearly time-invariant in the outskirts for more than 10 Gyr, and forms through a universal enrichment history.

What We Have Learned About Clusters From a Decade of Arcsecond Resolution X-ray Observations

NASA Technical Reports Server (NTRS)

Markevitch, Maxim

2012-01-01

This talk will briefly review the main findings from Chandra high angular resolution observations of galaxy clusters, emphasizing results on cluster astrophysics. Chandra has discovered shock fronts in merging systems, providing information on the shock Mach number and velocity, and for best-observed shocks, constraining the microphysical properties of the intracluster medium (ICM). Cold fronts, a Chandra discovery, are ubiquitous both in merging clusters and in the cool ccres of relaxed systems. They reveal the structure and strength of the intracluster magnetic fields and constrain the ICM viscosity a combined with radio data, these observations also shed light on the production of ultra-relativistic particles that are known to coexist with thermal plasma. Finally, in nearly all cool cores, Chandra observes cavities in the ICM that are produced by the central AGN. All these phenomena will be extremely interesting for high-resolution SZ studies.

Chandra/HETG Observations of NGC1275

NASA Astrophysics Data System (ADS)

Reynolds, Christopher

2017-09-01

NGC1275 is the active galactic nucleus (AGN) at the heart of the Perseus cluster of galaxies responsible for the mechanical heating of the intracluster medium (ICM) cool core. We propose a deep (500ks) HETG observation of NGC1275, allowing the first high-S/N, high resolution spectrum of this AGN free from contamination by the bright ICM. We will seek the signatures of powerful winds, answering the central question of whether galactic-scale quasar-mode feedback is occuring simultaneously with cluster-scale radio-mode feedback. We also probe circumnuclear gas (i.e. the fuel supply) through the 6.4keV line previously seen by XMM and Hitomi. These issues are crucial unknowns in our models for the evolution of the most massive galaxies and cluster cores.

FUSE Observations of Warm Gas in the Cooling Flow Clusters A1795 and A2597

NASA Technical Reports Server (NTRS)

Oegerle, W. R.; Cowie, L.; Davidsen, A.; Hu, E.; Hutchings, J.; Murphy, E.; Sembach, K.; Woodgate, B.; Fisher, Richard R. (Technical Monitor)

2001-01-01

We present far-ultraviolet spectroscopy of the cores of the massive cooling flow clusters Abell 1795 and 2597 obtained with FUSE. As the intracluster gas cools through 3 x 10(exp 5)K, it should emit strongly in the O VI lambda(lambda)1032,1038 resonance lines. We report the detection of O VI (lambda)1032 emission in A2597, with a line flux of 1.35 +/- 0.35 x 10(exp -15) erg/sq cm s, as well as detection of emission from C III (lambda)977. A marginal detection of C III (lambda)977 emission is also reported for A1795. These observations provide evidence for a direct link between the hot (10(exp 7) K) cooling flow gas and the cool (10(exp 4) K) gas in the optical emission line filaments. Assuming simple cooling flow models, the O VI line flux in A2597 corresponds to a mass deposition rate of approx. 40 solar mass /yr within the central 36 kpc. Emission from O VI (lambda)1032 was not detected in A1795, with an upper limit of 1.5 x 10(exp -15) erg/sq cm s, corresponding to a limit on the mass cooling flow rate of M(28 kpc) less than 28M solar mass/ yr. We have considered several explanations for the lack of detection of O VI emission in A1795 and the weaker than expected flux in A2597, including extinction by dust in the outer cluster, and quenching of thermal conduction by magnetic fields. We conclude that a turbulent mixing model, with some dust extinction, could explain our O VI results while also accounting for the puzzling lack of emission by Fe(sub XVII) in cluster cooling flows.

Spiral Flows in Cool-core Galaxy Clusters

NASA Astrophysics Data System (ADS)

Keshet, Uri

2012-07-01

We argue that bulk spiral flows are ubiquitous in the cool cores (CCs) of clusters and groups of galaxies. Such flows are gauged by spiral features in the thermal and chemical properties of the intracluster medium, by the multiphase properties of CCs, and by X-ray edges known as cold fronts. We analytically show that observations of piecewise-spiral fronts impose strong constraints on the CC, implying the presence of a cold, fast flow, which propagates below a hot, slow inflow, separated by a slowly rotating, trailing, quasi-spiral, tangential discontinuity surface. This leads to the nearly logarithmic spiral pattern, two-phase plasma, ρ ~ r -1 density (or T ~ r 0.4 temperature) radial profile, and ~100 kpc size, characteristic of CCs. By advecting heat and mixing the gas, such flows can eliminate the cooling problem, provided that a feedback mechanism regulates the flow. In particular, we present a quasi-steady-state model for an accretion-quenched, composite flow, in which the fast phase is an outflow, regulated by active galactic nucleus bubbles, reproducing the observed low star formation rates and explaining some features of bubbles such as their Rb vpropr size. The simplest two-component model reproduces several key properties of CCs, so we propose that all such cores harbor a spiral flow. Our results can be tested directly in the next few years, for example by ASTRO-H.

Cosmic-Ray Feedback Heating of the Intracluster Medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruszkowski, Mateusz; Yang, H.-Y. Karen; Reynolds, Christopher S., E-mail: mateuszr@umich.edu, E-mail: hsyang@astro.umd.edu, E-mail: chris@astro.umd.edu

2017-07-20

Active galactic nuclei (AGNs) play a central role in solving the decades-old cooling-flow problem. Although there is consensus that AGNs provide the energy to prevent catastrophically large star formation, one major problem remains: How is the AGN energy thermalized in the intracluster medium (ICM)? We perform a suite of three-dimensional magnetohydrodynamical adaptive mesh refinement simulations of AGN feedback in a cool core cluster including cosmic rays (CRs). CRs are supplied to the ICM via collimated AGN jets and subsequently disperse in the magnetized ICM via streaming, and interact with the ICM via hadronic, Coulomb, and streaming instability heating. We findmore » that CR transport is an essential model ingredient at least within the context of the physical model considered here. When streaming is included, (i) CRs come into contact with the ambient ICM and efficiently heat it, (ii) streaming instability heating dominates over Coulomb and hadronic heating, (iii) the AGN is variable and the atmosphere goes through low-/high-velocity dispersion cycles, and, importantly, (iv) CR pressure support in the cool core is very low and does not demonstrably violate observational constraints. However, when streaming is ignored, CR energy is not efficiently spent on the ICM heating and CR pressure builds up to a significant level, creating tension with the observations. Overall, we demonstrate that CR heating is a viable channel for the AGN energy thermalization in clusters and likely also in ellipticals, and that CRs play an important role in determining AGN intermittency and the dynamical state of cool cores.« less

Breaking Self-Similarity in Poor Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Kempner, J. C.; David, L. P.

2005-12-01

The large scatter in the LX--TX relation among poor clusters in the ˜2--4 keV range indicates that the self-similarity seen among hotter clusters does not apply to their cooler siblings. Many forms of non-gravitational heating have been proposed to break this self-similarity, including cluster mergers, AGN heating, and supernova ``pre-heating.'' We present an analysis of a sample of poor clusters from the Chandra and XMM archives that suggests a cycle of heating and cooling in the cores of these clusters is responsible for the departures from self-similarity. That these differences exist only in the core is strongly suggestive of AGN heating as the dominant mechanism. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number G05-5138A issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-39073, and by NASA contract NAG5-12933.

X-ray emission from clusters of galaxies

NASA Technical Reports Server (NTRS)

Mushotzky, R. F.

1983-01-01

Some X-ray spectral observations of approximately 30 clusters of galaxies from HEAO-1 are summarized. There exists strong correlations between X-ray luminosity, L(x), and temperature kT in the form L(x)alphaT to the 2.3 power. This result combined with the L(x) central galaxy density relation and the virial theorem indicates that the core dadius of the gas should be roughly independent of L(x) or KT and that more luminous clusters have a greater fraction of their virial mass in gas. The poor correlation of KT and optical velocity dispersion seems to indicate that clusters have a variety of equations of state. There is poor agreement between X-ray imaging observations and optical and X-ray spectral measures of the polytropic index. Most clusters show Fe emission lines with a strong indication that they all have roughly 1/2 solar abundance. The evidence for cooling in the cores of several clusters is discussed based on spectral observations with the Einstein solid state spectrometer.

Study on the structural transition of CoNi nanoclusters using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Xia, J. H.; Gao, Xue-Mei

2018-04-01

In this work, the segregation and structural transitions of CoNi clusters, between 1500 and 300 K, have been investigated using molecular dynamics simulations with the embedded atom method potential. The radial distribution function was used to analyze the segregation during the cooling processes. It is found that Co atoms segregate to the inside and Ni atoms preferably to the surface during the cooling processes, the Co147Ni414 cluster becomes a core-shell structure. We discuss the structural transition according to the pair-correction function and pair-analysis technique, and finally the liquid Co147Ni414 crystallizes into the coexistence of hcp and fcc structure at 300 K. At the same time, it is found that the frozen structure of CoNi cluster is strongly related to the Co concentration.

H II REGIONS, EMBEDDED PROTOSTARS, AND STARLESS CORES IN SHARPLESS 2-157

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Chian-Chou; Williams, Jonathan P.; Pandian, Jagadheep D., E-mail: ccchen@ifa.hawaii.edu, E-mail: jpw@ifa.hawaii.edu, E-mail: jagadheep@iist.ac.in

2012-06-20

We present arcsecond resolution 1.4 mm observations of the high-mass star-forming region, Sharpless 2-157, that reveal the cool dust associated with the first stages of star formation. These data are compared with archival images at optical, infrared, and radio wavelengths, and complemented with new arcsecond resolution mid-infrared data. We identify a dusty young H II region, numerous infrared sources within the cluster envelope, and four starless condensations. Three of the cores lie in a line to the south of the cluster peak, but the most massive one is right at the center and associated with a jumble of bright radiomore » and infrared sources. This presents an interesting juxtaposition of high- and low-mass star formation within the same cluster which we compare with similar observations of other high-mass star-forming regions and discuss in the context of cluster formation theory.« less

Physical Origins of Gas Motions in Galaxy Cluster Cores: Interpreting Hitomi Observations of the Perseus Cluster

NASA Astrophysics Data System (ADS)

Lau, Erwin T.; Gaspari, Massimo; Nagai, Daisuke; Coppi, Paolo

2017-11-01

The Hitomi X-ray satellite has provided the first direct measurements of the plasma velocity dispersion in a galaxy cluster. It finds a relatively “quiescent” gas with a line-of-sight velocity dispersion {σ }v,{los}≃ 160 {km} {{{s}}}-1, at 30-60 kpc from the cluster center. This is surprising given the presence of jets and X-ray cavities that indicates on-going activity and feedback from the active galactic nucleus (AGN) at the cluster center. Using a set of mock Hitomi observations generated from a suite of state-of-the-art cosmological cluster simulations, and an isolated but higher resolution simulation of gas physics in the cluster core, including the effects of cooling and AGN feedback, we examine the likelihood of Hitomi detecting a cluster with the observed velocities. As long as the Perseus has not experienced a major merger in the last few gigayears, and AGN feedback is operating in a “‘gentle” mode, we reproduce the level of gas motions observed by Hitomi. The frequent mechanical AGN feedback generates net line-of-sight velocity dispersions ˜ 100{--}200 {km} {{{s}}}-1, bracketing the values measured in the Perseus core. The large-scale velocity shear observed across the core, on the other hand, is generated mainly by cosmic accretion such as mergers. We discuss the implications of these results for AGN feedback physics and cluster cosmology and progress that needs to be made in both simulations and observations, including a Hitomi re-flight and calorimeter-based instruments with higher spatial resolution.

A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes.

PubMed

García-Berro, Enrique; Torres, Santiago; Althaus, Leandro G; Renedo, Isabel; Lorén-Aguilar, Pablo; Córsico, Alejandro H; Rohrmann, René D; Salaris, Maurizio; Isern, Jordi

2010-05-13

NGC 6791 is a well studied open cluster that it is so close to us that can be imaged down to very faint luminosities. The main-sequence turn-off age ( approximately 8 Gyr) and the age derived from the termination of the white dwarf cooling sequence ( approximately 6 Gyr) are very different. One possible explanation is that as white dwarfs cool, one of the ashes of helium burning, (22)Ne, sinks in the deep interior of these stars. At lower temperatures, white dwarfs are expected to crystallize and phase separation of the main constituents of the core of a typical white dwarf ((12)C and (16)O) is expected to occur. This sequence of events is expected to introduce long delays in the cooling times, but has not hitherto been proven. Here we report that, as theoretically anticipated, physical separation processes occur in the cores of white dwarfs, resolving the age discrepancy for NGC 6791.

XMM-Newton X-ray and HST weak gravitational lensing study of the extremely X-ray luminous galaxy cluster Cl J120958.9+495352 (z = 0.902)

NASA Astrophysics Data System (ADS)

Thölken, Sophia; Schrabback, Tim; Reiprich, Thomas H.; Lovisari, Lorenzo; Allen, Steven W.; Hoekstra, Henk; Applegate, Douglas; Buddendiek, Axel; Hicks, Amalia

2018-03-01

Context. Observations of relaxed, massive, and distant clusters can provide important tests of standard cosmological models, for example by using the gas mass fraction. To perform this test, the dynamical state of the cluster and its gas properties have to be investigated. X-ray analyses provide one of the best opportunities to access this information and to determine important properties such as temperature profiles, gas mass, and the total X-ray hydrostatic mass. For the last of these, weak gravitational lensing analyses are complementary independent probes that are essential in order to test whether X-ray masses could be biased. Aims: We study the very luminous, high redshift (z = 0.902) galaxy cluster Cl J120958.9+495352 using XMM-Newton data. We measure global cluster properties and study the temperature profile and the cooling time to investigate the dynamical status with respect to the presence of a cool core. We use Hubble Space Telescope (HST) weak lensing data to estimate its total mass and determine the gas mass fraction. Methods: We perform a spectral analysis using an XMM-Newton observation of 15 ks cleaned exposure time. As the treatment of the background is crucial, we use two different approaches to account for the background emission to verify our results. We account for point spread function effects and deproject our results to estimate the gas mass fraction of the cluster. We measure weak lensing galaxy shapes from mosaic HST imaging and select background galaxies photometrically in combination with imaging data from the William Herschel Telescope. Results: The X-ray luminosity of Cl J120958.9+495352 in the 0.1-2.4 keV band estimated from our XMM-Newton data is LX = (13.4+1.2-1.0) × 1044 erg/s and thus it is one of the most X-ray luminous clusters known at similarly high redshift. We find clear indications for the presence of a cool core from the temperature profile and the central cooling time, which is very rare at such high redshifts. Based on the weak lensing analysis, we estimate a cluster mass of M500/1014 M⊙ = 4.4+2.2-2.0 (stat.) + 0.6 (sys.) and a gas mass fraction of fgas,2500 = 0.11-0.03+0.06 in good agreement with previous findings for high redshift and local clusters.

The State of the Warm and Cold Gas in the Extreme Starburst at the Core of the Phoenix Galaxy Cluster (SPT-CLJ2344-4243)

NASA Astrophysics Data System (ADS)

McDonald, Michael; Swinbank, Mark; Edge, Alastair C.; Wilner, David J.; Veilleux, Sylvain; Benson, Bradford A.; Hogan, Michael T.; Marrone, Daniel P.; McNamara, Brian R.; Wei, Lisa H.; Bayliss, Matthew B.; Bautz, Marshall W.

2014-03-01

We present new optical integral field spectroscopy (Gemini South) and submillimeter spectroscopy (Submillimeter Array) of the central galaxy in the Phoenix cluster (SPT-CLJ2344-4243). This cluster was previously reported to have a massive starburst (~800 M ⊙ yr-1) in the central, brightest cluster galaxy, most likely fueled by the rapidly cooling intracluster medium. These new data reveal a complex emission-line nebula, extending for >30 kpc from the central galaxy, detected at [O II]λλ3726, 3729, [O III]λλ4959, 5007, Hβ, Hγ, Hδ, [Ne III]λ3869, and He II λ4686. The total Hα luminosity, assuming Hα/Hβ = 2.85, is L Hα = 7.6 ± 0.4 ×1043 erg s-1, making this the most luminous emission-line nebula detected in the center of a cool core cluster. Overall, the relative fluxes of the low-ionization lines (e.g., [O II], Hβ) to the UV continuum are consistent with photoionization by young stars. In both the center of the galaxy and in a newly discovered highly ionized plume to the north of the galaxy, the ionization ratios are consistent with both shocks and active galactic nucleus (AGN) photoionization. We speculate that this extended plume may be a galactic wind, driven and partially photoionized by both the starburst and central AGN. Throughout the cluster we measure elevated high-ionization line ratios (e.g., He II/Hβ, [O III]/Hβ), coupled with an overall high-velocity width (FWHM gsim 500 km s-1), suggesting that shocks are likely important throughout the interstellar medium of the central galaxy. These shocks are most likely driven by a combination of stellar winds from massive young stars, core-collapse supernovae, and the central AGN. In addition to the warm, ionized gas, we detect a substantial amount of cold, molecular gas via the CO(3-2) transition, coincident in position with the galaxy center. We infer a molecular gas mass of M_{H_2} = 2.2 ± 0.6 × 1010 M ⊙, which implies that the starburst will consume its fuel in ~30 Myr if it is not replenished. The L IR/M_{H_2} that we measure for this cluster is consistent with the starburst limit of 500 L ⊙/M ⊙, above which radiation pressure is able to disperse the cold reservoir. The combination of the high level of turbulence in the warm phase and the high L IR/M_{H_2} ratio suggests that this violent starburst may be in the process of quenching itself. We propose that phases of rapid star formation may be common in the cores of galaxy clusters, but so short-lived that their signatures are quickly erased and appear only in a subsample of the most strongly cooling clusters.

The Cosmological Impact of Luminous TeV Blazars. III. Implications for Galaxy Clusters and the Formation of Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Pfrommer, Christoph; Chang, Philip; Broderick, Avery E.

2012-06-01

A subset of blazars are powerful TeV emitters, dominating the extragalactic component of the very high energy gamma-ray universe (E >~ 100 GeV). These TeV gamma rays generate ultrarelativistic electron-positron pairs via pair production with the extragalactic background light. While it has generally been assumed that the kinetic energy of these pairs cascades to GeV gamma rays via inverse Compton scattering, we have argued in Broderick et al. (Paper I in this series) that plasma beam instabilities are capable of dissipating the pairs' energy locally on timescales short in comparison to the inverse Compton cooling time, heating the intergalactic medium (IGM) with a rate that is independent of density. This dramatically increases the entropy of the IGM after redshift z ~ 2, with a number of important implications for structure formation: (1) this suggests a scenario for the origin of the cool core (CC)/non-cool core (NCC) bimodality in galaxy clusters and groups. Early-forming galaxy groups are unaffected because they can efficiently radiate the additional entropy, developing a CC. However, late-forming groups do not have sufficient time to cool before the entropy is gravitationally reprocessed through successive mergers—counteracting cooling and potentially raising the core entropy further. This may result in a population of X-ray dim groups/clusters, consistent with X-ray stacking analyses of optically selected samples. Hence, blazar heating works differently than feedback by active galactic nuclei, which we show can balance radiative cooling but is unable to transform CC into NCC clusters on the buoyancy timescale due to the weak coupling between the mechanical energy to the cluster gas. (2) We predict a suppression of the Sunyaev-Zel'dovich (SZ) power spectrum template on angular scales smaller than 5' due to the globally reduced central pressure of groups and clusters forming after z ~ 1. This allows for a larger rms amplitude of the density power spectrum, σ8, and may reconcile SZ-inferred values with those by other cosmological probes even after allowing for a contribution due to patchy reionization. (3) Our redshift-dependent entropy floor increases the characteristic halo mass below which dwarf galaxies cannot form by a factor of approximately 10 (50) at mean density (in voids) over that found in models that include photoionization alone. This prevents the formation of late-forming dwarf galaxies (z <~ 2) with masses ranging from 1010 to 1011 M ⊙ for redshifts z ~ 2 to 0, respectively. This may help resolve the "missing satellite problem" in the Milky Way of the low observed abundances of dwarf satellites compared to cold dark matter simulations and may bring the observed early star formation histories into agreement with galaxy formation models. At the same time, it explains the "void phenomenon" by suppressing the formation of galaxies within existing dwarf halos of masses <3 × 1010 M ⊙ with a maximum circular velocity <60 km s-1 for z <~ 2, hence reconciling the number of dwarfs in low-density regions in simulations and the paucity of those in observations.

Mpc-scale diffuse radio emission in two massive cool-core clusters of galaxies

NASA Astrophysics Data System (ADS)

Sommer, Martin W.; Basu, Kaustuv; Intema, Huib; Pacaud, Florian; Bonafede, Annalisa; Babul, Arif; Bertoldi, Frank

2017-04-01

Radio haloes are diffuse synchrotron sources on scales of ˜1 Mpc that are found in merging clusters of galaxies, and are believed to be powered by electrons re-accelerated by merger-driven turbulence. We present measurements of extended radio emission on similarly large scales in two clusters of galaxies hosting cool cores: Abell 2390 and Abell 2261. The analysis is based on interferometric imaging with the Karl G. Jansky Very Large Array, Very Large Array and Giant Metrewave Radio Telescope. We present detailed radio images of the targets, subtract the compact emission components and measure the spectral indices for the diffuse components. The radio emission in A2390 extends beyond a known sloshing-like brightness discontinuity, and has a very steep in-band spectral slope at 1.5 GHz that is similar to some known ultrasteep spectrum radio haloes. The diffuse signal in A2261 is more extended than in A2390 but has lower luminosity. X-ray morphological indicators, derived from XMM-Newton X-ray data, place these clusters in the category of relaxed or regular systems, although some asymmetric features that can indicate past minor mergers are seen in the X-ray brightness images. If these two Mpc-scale radio sources are categorized as giant radio haloes, they question the common assumption of radio haloes occurring exclusively in clusters undergoing violent merging activity, in addition to commonly used criteria for distinguishing between radio haloes and minihaloes.

NUCLEAR REACTOR CORE DESIGN

DOEpatents

Mahlmeister, J.E.; Peck, W.S.; Haberer, W.V.; Williams, A.C.

1960-03-22

An improved core design for a sodium-cooled, graphitemoderated nuclear reactor is described. The improved reactor core comprises a number of blocks of moderator material, each block being in the shape of a regular prism. A number of channels, extending the length of each block, are disposed around the periphery. When several blocks are placed in contact to form the reactor core, the channels in adjacent blocks correspond with each other to form closed conduits extending the length of the core. Fuel element clusters are disposed in these closed conduits, and liquid coolant is forced through the annulus between the fuel cluster and the inner surface of the conduit. In a preferred embodiment of the invention, the moderator blocks are in the form of hexagonal prisms with longitudinal channels cut into the corners of the hexagon. The main advantage of an "edge-loaded" moderator block is that fewer thermal neutrons are absorbed by the moderator cladding, as compared with a conventional centrally loaded moderator block.

Anisotropic thermal conduction with magnetic fields in galaxy clusters

NASA Astrophysics Data System (ADS)

Arth, Alexander; Dolag, Klaus; Beck, Alexander; Petkova, Margarita; Lesch, Harald

2015-08-01

Magnetic fields play an important role for the propagation and diffusion of charged particles, which are responsible for thermal conduction. In this poster, we present an implementation of thermal conduction including the anisotropic effects of magnetic fields for smoothed particle hydrodynamics (SPH). The anisotropic thermal conduction is mainly proceeding parallel to magnetic fields and suppressed perpendicular to the fields. We derive the SPH formalism for the anisotropic heat transport and solve the corresponding equation with an implicit conjugate gradient scheme. We discuss several issues of unphysical heat transport in the cases of extreme ansiotropies or unmagnetized regions and present possible numerical workarounds. We implement our algorithm into the cosmological simulation code GADGET and study its behaviour in several test cases. In general, we reproduce the analytical solutions of our idealised test problems, and obtain good results in cosmological simulations of galaxy cluster formations. Within galaxy clusters, the anisotropic conduction produces a net heat transport similar to an isotropic Spitzer conduction model with low efficiency. In contrast to isotropic conduction our new formalism allows small-scale structure in the temperature distribution to remain stable, because of their decoupling caused by magnetic field lines. Compared to observations, strong isotropic conduction leads to an oversmoothed temperature distribution within clusters, while the results obtained with anisotropic thermal conduction reproduce the observed temperature fluctuations well. A proper treatment of heat transport is crucial especially in the outskirts of clusters and also in high density regions. It's connection to the local dynamical state of the cluster also might contribute to the observed bimodal distribution of cool core and non cool core clusters. Our new scheme significantly advances the modelling of thermal conduction in numerical simulations and overall gives better results compared to observations.

A CHANDRA-VLA INVESTIGATION OF THE X-RAY CAVITY SYSTEM AND RADIO MINI-HALO IN THE GALAXY CLUSTER RBS 797

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doria, Alberto; Gitti, Myriam; Brighenti, Fabrizio

2012-07-01

We present a study of the cavity system in the galaxy cluster RBS 797 based on Chandra and Very Large Array (VLA) data. RBS 797 (z = 0.35) is one of the most distant galaxy clusters in which two pronounced X-ray cavities have been discovered. The Chandra data confirm the presence of a cool core and indicate a higher metallicity along the cavity directions. This is likely due to the active galactic nucleus outburst, which lifts cool metal-rich gas from the center along the cavities, as seen in other systems. We find indications that the cavities are hotter than themore » surrounding gas. Moreover, the new Chandra images show bright rims contrasting with the deep, X-ray deficient cavities. The likely cause is that the expanding 1.4 GHz radio lobes have displaced the gas, compressing it into a shell that appears as bright cool arms. Finally, we show that the large-scale radio emission detected with our VLA observations may be classified as a radio mini-halo, powered by the cooling flow, as it nicely follows the trend P{sub radio} versus P{sub CF} predicted by the reacceleration model.« less

Powering of Hα Filaments by Cosmic Rays

NASA Astrophysics Data System (ADS)

Ruszkowski, Mateusz; Yang, H.-Y. Karen; Reynolds, Christopher S.

2018-05-01

Cluster cool cores possess networks of line-emitting filaments. These filaments are thought to originate via uplift of cold gas from cluster centers by buoyant active galactic nuclei (AGNs) bubbles, or via local thermal instability in the hot intracluster medium (ICM). Therefore, the filaments are either the signatures of AGN feedback or feeding of supermassive black holes. Despite being characterized by very short cooling times, the filaments are significant Hα emitters, which suggests that some process continuously powers these structures. Many cool cores host diffuse radio mini halos and AGN injecting radio plasma, suggesting that cosmic rays (CRs) and magnetic fields are present in the ICM. We argue that the excitation of Alfvén waves by CR streaming, and the replenishment of CR energy via accretion onto the filaments of high-plasma-β ICM characterized by low CR pressure support, can provide the adequate amount of heating to power and sustain the emission from these filaments. This mechanism does not require the CRs to penetrate the filaments, even if the filaments are magnetically isolated from the ambient ICM, and it may operate irrespectively of whether the filaments are dredged up from the center or form in situ in the ICM. This picture is qualitatively consistent with non-thermal line ratios seen in the cold filaments. Future X-ray observations of the iron line complex with XARM, Lynx, or Athena could help to test this model by providing constraints on the amount of CRs in the hot plasma that is cooling and accreting onto the filaments.

AGN self-regulation in cooling flow clusters

NASA Astrophysics Data System (ADS)

Cattaneo, A.; Teyssier, R.

2007-04-01

We use three-dimensional high-resolution adaptive-mesh-refinement simulations to investigate if mechanical feedback from active galactic nucleus jets can halt a massive cooling flow in a galaxy cluster and give rise to a self-regulated accretion cycle. We start with a 3 × 109 Msolar black hole at the centre of a spherical halo with the mass of the Virgo cluster. Initially, all the baryons are in a hot intracluster medium in hydrostatic equilibrium within the dark matter's gravitational potential. The black hole accretes the surrounding gas at the Bondi rate, and a fraction of the accretion power is returned into the intracluster medium mechanically through the production of jets. The accretion, initially slow (~2 × 10-4 Msolaryr-1), becomes catastrophic, as the gas cools and condenses in the dark matter's potential. Therefore, it cannot prevent the cooling catastrophe at the centre of the cluster. However, after this rapid phase, where the accretion rate reaches a peak of ~0.2Msolaryr-1, the cavities inflated by the jets become highly turbulent. The turbulent mixing of the shock-heated gas with the rest of the intracluster medium puts a quick end to this short-lived rapid-growth phase. After dropping by almost two orders of magnitudes, the black hole accretion rate stabilizes at ~0.006 Msolaryr-1, without significant variations for several billions of years, indicating that a self-regulated steady state has been reached. This accretion rate corresponds to a negligible increase of the black hole mass over the age of the Universe, but is sufficient to create a quasi-equilibrium state in the cluster core.

Supergiants and their shells in young globular clusters

NASA Astrophysics Data System (ADS)

Szécsi, Dorottya; Mackey, Jonathan; Langer, Norbert

2018-04-01

Context. Anomalous surface abundances are observed in a fraction of the low-mass stars of Galactic globular clusters, that may originate from hot-hydrogen-burning products ejected by a previous generation of massive stars. Aims: We aim to present and investigate a scenario in which the second generation of polluted low-mass stars can form in shells around cool supergiant stars within a young globular cluster. Methods: Simulations of low-metallicity massive stars (Mi 150-600 M⊙) show that both core-hydrogen-burning cool supergiants and hot ionizing stellar sources are expected to be present simulaneously in young globular clusters. Under these conditions, photoionization-confined shells form around the supergiants. We have simulated such a shell, investigated its stability and analysed its composition. Results: We find that the shell is gravitationally unstable on a timescale that is shorter than the lifetime of the supergiant, and the Bonnor-Ebert mass of the overdense regions is low enough to allow star formation. Since the low-mass stellar generation formed in this shell is made up of the material lost from the supergiant, its composition necessarily reflects the composition of the supergiant wind. We show that the wind contains hot-hydrogen-burning products, and that the shell-stars therefore have very similar abundance anomalies that are observed in the second generation stars of globular clusters. Considering the mass-budget required for the second generation star-formation, we offer two solutions. Either a top-heavy initial mass function is needed with an index of -1.71 to -2.07. Alternatively, we suggest the shell-stars to have a truncated mass distribution, and solve the mass budget problem by justifiably accounting for only a fraction of the first generation. Conclusions: Star-forming shells around cool supergiants could form the second generation of low-mass stars in Galactic globular clusters. Even without forming a photoionizaton-confined shell, the cool supergiant stars predicted at low-metallicity could contribute to the pollution of the interstellar medium of the cluster from which the second generation was born. Thus, the cool supergiant stars should be regarded as important contributors to the evolution of globular clusters.

Embedded spiral patterns in the massive galaxy cluster Abell 1835

NASA Astrophysics Data System (ADS)

Ueda, S.; Kitayama, T.; Dotani, T.

2017-10-01

We report on the properties of the intracluster medium (ICM) in the central region of the massive galaxy cluster, Abell 1835, obtained with the data from the Chandra X-ray Observatory. We find distinctive spiral patterns in the cool core in the residual image of the X-ray surface brightness after its nominal profile is subtracted. The spiral patterns consist of two arms. One of them appears as positive, and the other appears as negative excesses in the residual image. Their sizes are ˜ 70 kpc and their morphologies are consistent with each other. We find that the spiral patterns extend from the cool core out to the hotter surrounding ICM. We analyze the X-ray spectra extracted from both regions. We obtain that the ICM properties are similar to those expected by gas sloshing. We also find that the ICM in the two regions of spiral patterns is near or is in pressure equilibrium. Abell 1835 may now be experiencing gas sloshing induced by an off-axis minor merger. These results have been already published (Ueda, Kitayama, & Dotani 2017, ApJ, 837, 34).

RADIO AND DEEP CHANDRA OBSERVATIONS OF THE DISTURBED COOL CORE CLUSTER ABELL 133

DOE Office of Scientific and Technical Information (OSTI.GOV)

Randall, S. W.; Nulsen, P. E. J.; Forman, W. R.

2010-10-10

We present results based on new Chandra and multi-frequency radio observations of the disturbed cool core cluster Abell 133. The diffuse gas has a complex bird-like morphology, with a plume of emission extending from two symmetric wing-like features. The plume is capped with a filamentary radio structure that has been previously classified as a radio relic. X-ray spectral fits in the region of the relic indicate the presence of either high-temperature gas or non-thermal emission, although the measured photon index is flatter than would be expected if the non-thermal emission is from inverse Compton scattering of the cosmic microwave backgroundmore » by the radio-emitting particles. We find evidence for a weak elliptical X-ray surface brightness edge surrounding the core, which we show is consistent with a sloshing cold front. The plume is consistent with having formed due to uplift by a buoyantly rising radio bubble, now seen as the radio relic, and has properties consistent with buoyantly lifted plumes seen in other systems (e.g., M87). Alternatively, the plume may be a gas sloshing spiral viewed edge-on. Results from spectral analysis of the wing-like features are inconsistent with the previous suggestion that the wings formed due to the passage of a weak shock through the cool core. We instead conclude that the wings are due to X-ray cavities formed by displacement of X-ray gas by the radio relic. The central cD galaxy contains two small-scale cold gas clumps that are slightly offset from their optical and UV counterparts, suggestive of a galaxy-galaxy merger event. On larger scales, there is evidence for cluster substructure in both optical observations and the X-ray temperature map. We suggest that the Abell 133 cluster has recently undergone a merger event with an interloping subgroup, initialing gas sloshing in the core. The torus of sloshed gas is seen close to edge-on, leading to the somewhat ragged appearance of the elliptical surface brightness edge. We show that the additional buoyant force from a passing subcluster can have a significant effect on the rise trajectories of buoyant bubbles, although this effect alone cannot fully explain the morphology of Abell 133. The radio observations reveal a large-scale double-lobed structure not previously identified in the literature. We conclude that this structure represents a previously unreported background giant radio galaxy at z = 0.293, the northern lobe of which overlies the radio relic in the core of Abell 133. A rough estimate indicates that the contribution of this background lobe to the total radio emission in the region of the relic is modest (<13%).« less

The quiescent intracluster medium in the core of the Perseus cluster.

PubMed

2016-07-07

Clusters of galaxies are the most massive gravitationally bound objects in the Universe and are still forming. They are thus important probes of cosmological parameters and many astrophysical processes. However, knowledge of the dynamics of the pervasive hot gas, the mass of which is much larger than the combined mass of all the stars in the cluster, is lacking. Such knowledge would enable insights into the injection of mechanical energy by the central supermassive black hole and the use of hydrostatic equilibrium for determining cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50-million-kelvin diffuse hot plasma filling its gravitational potential well. The active galactic nucleus of the central galaxy NGC 1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These bubbles probably induce motions in the intracluster medium and heat the inner gas, preventing runaway radiative cooling--a process known as active galactic nucleus feedback. Here we report X-ray observations of the core of the Perseus cluster, which reveal a remarkably quiescent atmosphere in which the gas has a line-of-sight velocity dispersion of 164 ± 10 kilometres per second in the region 30-60 kiloparsecs from the central nucleus. A gradient in the line-of-sight velocity of 150 ± 70 kilometres per second is found across the 60-kiloparsec image of the cluster core. Turbulent pressure support in the gas is four per cent of the thermodynamic pressure, with large-scale shear at most doubling this estimate. We infer that a total cluster mass determined from hydrostatic equilibrium in a central region would require little correction for turbulent pressure.

THE COSMOLOGICAL IMPACT OF LUMINOUS TeV BLAZARS. III. IMPLICATIONS FOR GALAXY CLUSTERS AND THE FORMATION OF DWARF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pfrommer, Christoph; Chang, Philip; Broderick, Avery E., E-mail: christoph.pfrommer@h-its.org, E-mail: aeb@cita.utoronto.ca, E-mail: pchang@cita.utoronto.ca

2012-06-10

A subset of blazars are powerful TeV emitters, dominating the extragalactic component of the very high energy gamma-ray universe (E {approx}> 100 GeV). These TeV gamma rays generate ultrarelativistic electron-positron pairs via pair production with the extragalactic background light. While it has generally been assumed that the kinetic energy of these pairs cascades to GeV gamma rays via inverse Compton scattering, we have argued in Broderick et al. (Paper I in this series) that plasma beam instabilities are capable of dissipating the pairs' energy locally on timescales short in comparison to the inverse Compton cooling time, heating the intergalactic mediummore » (IGM) with a rate that is independent of density. This dramatically increases the entropy of the IGM after redshift z {approx} 2, with a number of important implications for structure formation: (1) this suggests a scenario for the origin of the cool core (CC)/non-cool core (NCC) bimodality in galaxy clusters and groups. Early-forming galaxy groups are unaffected because they can efficiently radiate the additional entropy, developing a CC. However, late-forming groups do not have sufficient time to cool before the entropy is gravitationally reprocessed through successive mergers-counteracting cooling and potentially raising the core entropy further. This may result in a population of X-ray dim groups/clusters, consistent with X-ray stacking analyses of optically selected samples. Hence, blazar heating works differently than feedback by active galactic nuclei, which we show can balance radiative cooling but is unable to transform CC into NCC clusters on the buoyancy timescale due to the weak coupling between the mechanical energy to the cluster gas. (2) We predict a suppression of the Sunyaev-Zel'dovich (SZ) power spectrum template on angular scales smaller than 5' due to the globally reduced central pressure of groups and clusters forming after z {approx} 1. This allows for a larger rms amplitude of the density power spectrum, {sigma}{sub 8}, and may reconcile SZ-inferred values with those by other cosmological probes even after allowing for a contribution due to patchy reionization. (3) Our redshift-dependent entropy floor increases the characteristic halo mass below which dwarf galaxies cannot form by a factor of approximately 10 (50) at mean density (in voids) over that found in models that include photoionization alone. This prevents the formation of late-forming dwarf galaxies (z {approx}< 2) with masses ranging from 10{sup 10} to 10{sup 11} M{sub Sun} for redshifts z {approx} 2 to 0, respectively. This may help resolve the 'missing satellite problem' in the Milky Way of the low observed abundances of dwarf satellites compared to cold dark matter simulations and may bring the observed early star formation histories into agreement with galaxy formation models. At the same time, it explains the 'void phenomenon' by suppressing the formation of galaxies within existing dwarf halos of masses <3 Multiplication-Sign 10{sup 10} M{sub Sun} with a maximum circular velocity <60 km s{sup -1} for z {approx}< 2, hence reconciling the number of dwarfs in low-density regions in simulations and the paucity of those in observations.« less

Multiband observations of Cygnus A: A study of pressure balance in the core of a powerful radio galaxy

NASA Technical Reports Server (NTRS)

Carilli, Chris; Conner, Sam; Dreher, John; Perley, Rick

1990-01-01

Cygnus A is a powerful double radio source associated with a giant elliptical galaxy at the center of a poor cluster of galaxies. The radio source also sits within the core radius of a dense, cooling flow, x ray emitting cluster gas. Optical spectroscopy and narrow band imaging have revealed copious amounts of narrow line emission from the inner 20 kpc of the associated galaxy. Researchers assume H sub o = 75 km sec (-1) Mpc(-1). Discussed here are the pressures in the three components of the Interstellar Medium (ISM) (i.e., the radio, x ray, and line emitting fluids) within a radius of about 15 kpc of the active nucleus of the Cygnus A galaxy.

Thermodynamics of the Coma Cluster Outskirts

NASA Astrophysics Data System (ADS)

Simionescu, A.; Werner, N.; Urban, O.; Allen, S. W.; Fabian, A. C.; Mantz, A.; Matsushita, K.; Nulsen, P. E. J.; Sanders, J. S.; Sasaki, T.; Sato, T.; Takei, Y.; Walker, S. A.

2013-09-01

We present results from a large mosaic of Suzaku observations of the Coma Cluster, the nearest and X-ray brightest hot (~8 keV), dynamically active, non-cool core system, focusing on the thermodynamic properties of the intracluster medium on large scales. For azimuths not aligned with an infalling subcluster toward the southwest, our measured temperature and X-ray brightness profiles exhibit broadly consistent radial trends, with the temperature decreasing from about 8.5 keV at the cluster center to about 2 keV at a radius of 2 Mpc, which is the edge of our detection limit. The southwest merger significantly boosts the surface brightness, allowing us to detect X-ray emission out to ~2.2 Mpc along this direction. Apart from the southwestern infalling subcluster, the surface brightness profiles show multiple edges around radii of 30-40 arcmin. The azimuthally averaged temperature profile, as well as the deprojected density and pressure profiles, all show a sharp drop consistent with an outwardly-propagating shock front located at 40 arcmin, corresponding to the outermost edge of the giant radio halo observed at 352 MHz with the Westerbork Synthesis Radio Telescope. The shock front may be powering this radio emission. A clear entropy excess inside of r 500 reflects the violent merging events linked with these morphological features. Beyond r 500, the entropy profiles of the Coma Cluster along the relatively relaxed directions are consistent with the power-law behavior expected from simple models of gravitational large-scale structure formation. The pressure is also in agreement at these radii with the expected values measured from Sunyaev-Zel'dovich data from the Planck satellite. However, due to the large uncertainties associated with the Coma Cluster measurements, we cannot yet exclude an entropy flattening in this system consistent with that seen in more relaxed cool core clusters.

LoCuSS: connecting the dominance and shape of brightest cluster galaxies with the assembly history of massive clusters

NASA Astrophysics Data System (ADS)

Smith, Graham P.; Khosroshahi, Habib G.; Dariush, A.; Sanderson, A. J. R.; Ponman, T. J.; Stott, J. P.; Haines, C. P.; Egami, E.; Stark, D. P.

2010-11-01

We study the luminosity gap, Δm12, between the first- and second-ranked galaxies in a sample of 59 massive (~1015Msolar) galaxy clusters, using data from the Hale Telescope, the Hubble Space Telescope, Chandra and Spitzer. We find that the Δm12 distribution, p(Δm12), is a declining function of Δm12 to which we fitted a straight line: p(Δm12) ~ -(0.13 +/- 0.02)Δm12. The fraction of clusters with `large' luminosity gaps is p(Δm12 >= 1) = 0.37 +/- 0.08, which represents a 3σ excess over that obtained from Monte Carlo simulations of a Schechter function that matches the mean cluster galaxy luminosity function. We also identify four clusters with `extreme' luminosity gaps, Δm12 >= 2, giving a fraction of . More generally, large luminosity gap clusters are relatively homogeneous, with elliptical/discy brightest cluster galaxies (BCGs), cuspy gas density profiles (i.e. strong cool cores), high concentrations and low substructure fractions. In contrast, small luminosity gap clusters are heterogeneous, spanning the full range of boxy/elliptical/discy BCG morphologies, the full range of cool core strengths and dark matter concentrations, and have large substructure fractions. Taken together, these results imply that the amplitude of the luminosity gap is a function of both the formation epoch and the recent infall history of the cluster. `BCG dominance' is therefore a phase that a cluster may evolve through and is not an evolutionary `cul-de-sac'. We also compare our results with semi-analytic model predictions based on the Millennium Simulation. None of the models is able to reproduce all of the observational results on Δm12, underlining the inability of the current generation of models to match the empirical properties of BCGs. We identify the strength of active galactic nucleus feedback and the efficiency with which cluster galaxies are replenished after they merge with the BCG in each model as possible causes of these discrepancies.

AGN ACTIVITY AND IGM HEATING IN THE FOSSIL CLUSTER RX J1416.4+2315

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miraghaei, H.; Khosroshahi, H. G.; Abbassi, S.

2015-12-15

We study active galactic nucleus (AGN) activity in the fossil galaxy cluster RX J1416.4+2315. Radio observations were carried out using the Giant Metrewave Radio Telescope at two frequencies, 1420 and 610 MHz. A weak radio lobe that extends from the central nucleus is detected in the 610 MHz map. Assuming the radio lobe originated from the central AGN, we show that the energy injection into the intergalactic medium is only sufficient to heat up the central 50 kpc within the cluster core, while the cooling radius is larger (∼130 kpc). In the hardness ratio map, three low energy cavities havemore » been identified. No radio emission is detected for these regions. We evaluated the power required to inflate the cavities and showed that the total energy budget is sufficient to offset the radiative cooling. We showed that the initial conditions would change the results remarkably. Furthermore, the efficiency of the Bondi accretion in powering the AGN has been estimated.« less

Radial distribution of metals in the hot intra-cluster medium as observed by XMM-Newton

NASA Astrophysics Data System (ADS)

Mernier, F.; de Plaa, J.; Kaastra, J.; Zhang, Y.; Akamatsu, H.; Gu, L.; Mao, J.; Pinto, C.; Reiprich, T.; Sanders, J.

2017-10-01

The hot intra-cluster medium (ICM), which accounts for ˜80% of the baryonic content in galaxy clusters, is rich in heavy elements. Since these metals have been produced by stars and supernovae before enriching the ICM, measuring metal abundance distributions in galaxy clusters and groups provides essential clues to determine the main astrophysical source(s) and epoch(s) of the ICM enrichment. In this work, we present radial abundance profiles averaged over 44 nearby cool-core galaxy clusters, groups, and massive ellipticals (the CHEERS sample) measured with XMM-Newton EPIC. While most of the Fe of the Universe is thought to be synthesised by Type Ia supernovae (SNIa), lighter elements, such as O, Mg, Si or S, are mostly produced by core-collapse supernovae (SNcc). The derived average radial profiles of the O, Mg, Si, S, Ar, Ca, Fe, and Ni abundances out to ˜ 0.5 r_{500} allows us to accurately compare the distributions of SNIa and SNcc products in clusters and groups. By comparing our results with recent chemo-dynamical simulations, we discuss the interpretation of the profiles in the context of early and late ICM enrichments.

Simulation studies of glassy nanoclusters

NASA Astrophysics Data System (ADS)

Bowles, Richard

2015-03-01

Glassy materials are amorphous solids usually formed by rapidly cooling a liquid below its equilibrium freezing temperature, trapping the particles in a liquid-like structure at the glass transition temperature. While appearing throughout nature and industry, these systems continue to challenge the way we think about the dynamics and thermodynamics of condensed matter and a fundamental understanding of the glass state remains elusive. This talk describes molecular simulation studies of glassy behaviour in binary Lennard-Jones nanoclusters. We show that the relaxation dynamics of the clusters is nonuniform and the core of the cluster goes through a glass transition at higher temperatures than at the surface. As the nanoclusters are cooled, they also exhibit a fragile-strong crossover in their dynamics and we explore how this phenomena is linked to the potential energy landscape of the clusters. Finally, we compare the properties of nanoclusters formed through vapour condensation, directly to the glassy state, with those of glassy clusters formed through traditional supercooling. The condensation clusters are shown to form ultra-stable glassy states analogous to the ultra-stable glasses formed by thin film vapour deposition onto a cold substrate. In all, our work suggests that nanoscale clusters exhibit some unique glassy features, while also offering potential insights into the fundamental nature of the glass transition.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, Michael; Bautz, Marshall W.; Benson, Bradford

We present Hubble Space Telescope Wide Field Camera 3 observations of the core of the Phoenix cluster (SPT-CLJ2344-4243) in five broadband filters spanning rest-frame 1000-5500 A. These observations reveal complex, filamentary blue emission, extending for >40 kpc from the brightest cluster galaxy. We observe an underlying, diffuse population of old stars, following an r {sup 1/4} distribution, confirming that this system is somewhat relaxed. The spectral energy distribution in the inner part of the galaxy, as well as along the extended filaments, is a smooth continuum and is consistent with that of a star-forming galaxy, suggesting that the extended, filamentarymore » emission is not due to the central active galactic nucleus, either from a large-scale ionized outflow or scattered polarized UV emission, but rather a massive population of young stars. We estimate an extinction-corrected star formation rate of 798 {+-} 42 M{sub Sun} yr{sup -1}, consistent with our earlier work based on low spatial resolution ultraviolet, optical, and infrared imaging. The lack of tidal features and multiple bulges, combine with the need for an exceptionally massive (>10{sup 11} M{sub Sun }) cold gas reservoir, suggest that this star formation is not the result of a merger of gas-rich galaxies. Instead, we propose that the high X-ray cooling rate of {approx}2700 M{sub Sun} yr{sup -1} is the origin of the cold gas reservoir. The combination of such a high cooling rate and the relatively weak radio source in the cluster core suggests that feedback has been unable to halt cooling in this system, leading to this tremendous burst of star formation.« less

State of the metal core in nanosecond exploding wires and related phenomena

NASA Astrophysics Data System (ADS)

Sarkisov, G. S.; Sasorov, P. V.; Struve, K. W.; McDaniel, D. H.

2004-08-01

Experiments show that an expanding metal wire core that results from a nanosecond electrical explosion in vacuum consists primarily of three different states: solid, microdrop, and gas-plasma. The state of the wire core depends both on the amount of energy deposited before the voltage breakdown and on the heating conditions. For small amounts of deposited energy (on the order of solid-stage enthalpy), the wire core remains in a solid state or is partially disintegrated. For a high level of deposited energy (more than vaporization energy) the wire core is in a gas-plasma state. For an intermediate level of deposited energy (more than melting but less than vaporization), the wire disintegrates into hot liquid microdrops or clusters of submicron size. For a wire core in the cluster state, interferometry demonstrates weak (or even absent) phaseshift. Light emission shows a "firework effect"—the long late-time radiation related to the emission by the expanding cylinder of hot microparticles. For the wire core in a gas-plasma state, interferometry demonstrates a large phaseshift and a fast reduction in light emission due to adiabatic cooling of the expanding wire core. The simulation of this firework effect agrees well with experimental data, assuming submicron size and a temperature approaching boiling for the expanded microparticles cylinder.

ROLE OF MAGNETIC FIELD STRENGTH AND NUMERICAL RESOLUTION IN SIMULATIONS OF THE HEAT-FLUX-DRIVEN BUOYANCY INSTABILITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avara, Mark J.; Reynolds, Christopher S.; Bogdanovic, Tamara, E-mail: mavara@astro.umd.edu, E-mail: chris@astro.umd.edu, E-mail: tamarab@gatech.edu

2013-08-20

The role played by magnetic fields in the intracluster medium (ICM) of galaxy clusters is complex. The weakly collisional nature of the ICM leads to thermal conduction that is channeled along field lines. This anisotropic heat conduction profoundly changes the instabilities of the ICM atmosphere, with convective stabilities being driven by temperature gradients of either sign. Here, we employ the Athena magnetohydrodynamic code to investigate the local non-linear behavior of the heat-flux-driven buoyancy instability (HBI) relevant in the cores of cooling-core clusters where the temperature increases with radius. We study a grid of two-dimensional simulations that span a large rangemore » of initial magnetic field strengths and numerical resolutions. For very weak initial fields, we recover the previously known result that the HBI wraps the field in the horizontal direction, thereby shutting off the heat flux. However, we find that simulations that begin with intermediate initial field strengths have a qualitatively different behavior, forming HBI-stable filaments that resist field-line wrapping and enable sustained vertical conductive heat flux at a level of 10%-25% of the Spitzer value. While astrophysical conclusions regarding the role of conduction in cooling cores require detailed global models, our local study proves that systems dominated by the HBI do not necessarily quench the conductive heat flux.« less

THE ENTIRE VIRIAL RADIUS OF THE FOSSIL CLUSTER RX J1159+5531. I. GAS PROPERTIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, Yuanyuan; Buote, David; Gastaldello, Fabio

2015-06-01

Previous analysis of the fossil-group/cluster RX J1159+5531 with X-ray observations from a central Chandra pointing and an offset-north Suzaku pointing indicate a radial intracluster medium (ICM) entropy profile at the virial radius (R{sub vir}) consistent with predictions from gravity-only cosmological simulations, in contrast to other cool-core clusters. To examine the generality of these results, we present three new Suzaku observations that, in conjunction with the north pointing, provide complete azimuthal coverage out to R{sub vir}. With two new Chandra ACIS-I observations overlapping the north Suzaku pointing, we have resolved ≳50% of the cosmic X-ray background there. We present radial profilesmore » of the ICM density, temperature, entropy, and pressure obtained for each of the four directions. We measure only modest azimuthal scatter in the ICM properties at R{sub 200} between the Suzaku pointings: 7.6% in temperature and 8.6% in density, while the systematic errors can be significant. The temperature scatter, in particular, is lower than that studied at R{sub 200} for a small number of other clusters observed with Suzaku. These azimuthal measurements verify that RX J1159+5531 is a regular, highly relaxed system. The well-behaved entropy profiles we have measured for RX J1159+5531 disfavor the weakening of the accretion shock as an explanation of the entropy flattening found in other cool-core clusters but is consistent with other explanations such as gas clumping, electron-ion non-equilibrium, non-thermal pressure support, and cosmic-ray acceleration. Finally, we mention that the large-scale galaxy density distribution of RX J1159+5531 seems to have little impact on its gas properties near R{sub vir}.« less

Low-temperature transonic cooling flows in galaxy clusters

NASA Technical Reports Server (NTRS)

Sulkanen, Martin E.; Burns, Jack O.; Norman, Michael L.

1989-01-01

Calculations are presented which demonstrate that cooling flow models with large sonic radii may be consistent with observed cluster gas properties. It is found that plausible cluster parameters and cooling flow mass accretion rates can produce sonic radii of 10-20 kpc for sonic point temperatures of 1-3 x 10 to the 6th K. The numerical calculations match these cooling flows to hydrostatic atmosphere solutions for the cluster gas beyond the cooling flow region. The cooling flows produce no appreciable 'holes' in the surface brightness toward the cluster center, and the model can be made to match the observed X-ray surface brightness of three clusters in which cooling flows had been believed to be absent. It is suggested that clusters with low velocity dispersion may be the natural location for such 'cool' cooling flows, and fits of these models to the X-ray surface brightness profiles for three clusters are presented.

X-RAY DIAGNOSTICS OF THERMAL CONDITIONS OF THE HOT PLASMAS IN THE CENTAURUS CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, I.; Makishima, K.; Kitaguchi, T.

2009-08-10

X-ray data of the Centaurus cluster, obtained with XMM-Newton for 45 ks, were analyzed. Deprojected EPIC spectra from concentric thin-shell regions were reproduced equally well by a single-phase plasma emission model, or by a two-phase model developed by ASCA, both incorporating cool (1.7-2.0 keV) and hot ({approx} 4 keV) plasma temperatures. However, EPIC spectra with higher statistics, accumulated over three-dimensional thick-shell regions, were reproduced better by the two-phase model than by the singe-phase one. Therefore, hot and cool plasma phases are inferred to co-exist in the cluster core region within {approx} 70 kpc. The iron and silicon abundances of themore » plasma were reconfirmed to increase significantly toward the center, while that of oxygen was consistent with being radially constant. The implied nonsolar abundance ratios explain away the previously reported excess X-ray absorption from the central region. Although an additional cool ({approx} 0.7 keV) emission was detected within {approx} 20 kpc of the center, the RGS data gave tight upper limits on any emission with temperatures below {approx} 0.5 keV. These results are compiled into a magnetosphere model, which interprets the cool phase as confined within closed magnetic loops anchored to the cD galaxy. When combined with the so-called Rosner-Tucker-Vaiana mechanism which applies to solar coronae, this model can potentially explain basic properties of the cool phase, including its temperature and thermal stability.« less

Simulations of the galaxy cluster CIZA J2242.8+5301 - I. Thermal model and shock properties

NASA Astrophysics Data System (ADS)

Donnert, J. M. F.; Beck, A. M.; Dolag, K.; Röttgering, H. J. A.

2017-11-01

The giant radio relic in CIZA J2242.8+5301 provides clear evidence of an Mpc-sized shock in a massive merging galaxy cluster. Here, we present idealized SPH hydrodynamical and collisionless dark matter simulations, aiming to find a model that is consistent with that large range of observations of this galaxy cluster. We first show that in the northern shock, the observed radio spectral index profile and integrated radio spectrum are consistent with the observed upstream X-ray temperature. Using simulations, we first find that only a cool-core versus non-cool-core merger can lead to the observed elongated X-ray morphology. We then carry out simulations for two merging clusters assuming a range of NFW and β-model density profiles and hydrostatic equilibrium. We find a fiducial model that mimics the overall morphology of the shock structures, has a total mass of 1.6 × 1015 M⊙ and a mass ratio of 1.76. For this model, the derived Mach number for the northern shock is 4.5. This is almost a factor 2 higher compared to the observational determination of the Mach number using X-ray observations or measurements of the radio injection spectral index. We could not find numerical models that both fit the X-ray properties and yielded such low Mach numbers. We discuss various ways of understanding this difference and argue that deep X-ray observations of CIZA J2242.8+5301 will be able to test our model and reconcile the differences.

Witnessing the Formation of a Brightest Cluster Galaxy in a Nearby X-ray Cluster

NASA Astrophysics Data System (ADS)

Rasmussen, Jesper; Mulchaey, John S.; Bai, Lei; Ponman, Trevor J.; Raychaudhury, Somak; Dariush, Ali

2010-07-01

The central dominant galaxies in galaxy clusters constitute the most massive and luminous galaxies in the universe. Despite this, the formation of these brightest cluster galaxies (BCGs) and the impact of this on the surrounding cluster environment remain poorly understood. Here we present multiwavelength observations of the nearby poor X-ray cluster MZ 10451, in which both processes can be studied in unprecedented detail. Chandra observations of the intracluster medium (ICM) in the cluster core, which harbors two optically bright early-type galaxies in the process of merging, show that the system has retained a cool core and a central metal excess. This suggests that any merger-induced ICM heating and mixing remain modest at this stage. Tidally stripped stars seen around either galaxy likely represent an emerging intracluster light component, and the central ICM abundance enhancement may have a prominent contribution from in situ enrichment provided by these stars. The smaller of the merging galaxies shows evidence for having retained a hot gas halo, along with tentative evidence for some obscured star formation, suggesting that not all BCG major mergers at low redshift are completely dissipationless. Both galaxies are slightly offset from the peak of the ICM emission, with all three lying on an axis that roughly coincides with the large-scale elongation of the ICM. Our data are consistent with a picture in which central BCGs are built up by mergers close to the cluster core, by galaxies infalling on radial orbits aligned with the cosmological filaments feeding the cluster. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, Michael; Bautz, Marshall W.; Swinbank, Mark

We present new optical integral field spectroscopy (Gemini South) and submillimeter spectroscopy (Submillimeter Array) of the central galaxy in the Phoenix cluster (SPT-CLJ2344-4243). This cluster was previously reported to have a massive starburst (∼800 M {sub ☉} yr{sup –1}) in the central, brightest cluster galaxy, most likely fueled by the rapidly cooling intracluster medium. These new data reveal a complex emission-line nebula, extending for >30 kpc from the central galaxy, detected at [O II]λλ3726, 3729, [O III]λλ4959, 5007, Hβ, Hγ, Hδ, [Ne III]λ3869, and He II λ4686. The total Hα luminosity, assuming Hα/Hβ = 2.85, is L {sub Hα} =more » 7.6 ± 0.4 ×10{sup 43} erg s{sup –1}, making this the most luminous emission-line nebula detected in the center of a cool core cluster. Overall, the relative fluxes of the low-ionization lines (e.g., [O II], Hβ) to the UV continuum are consistent with photoionization by young stars. In both the center of the galaxy and in a newly discovered highly ionized plume to the north of the galaxy, the ionization ratios are consistent with both shocks and active galactic nucleus (AGN) photoionization. We speculate that this extended plume may be a galactic wind, driven and partially photoionized by both the starburst and central AGN. Throughout the cluster we measure elevated high-ionization line ratios (e.g., He II/Hβ, [O III]/Hβ), coupled with an overall high-velocity width (FWHM ≳ 500 km s{sup –1}), suggesting that shocks are likely important throughout the interstellar medium of the central galaxy. These shocks are most likely driven by a combination of stellar winds from massive young stars, core-collapse supernovae, and the central AGN. In addition to the warm, ionized gas, we detect a substantial amount of cold, molecular gas via the CO(3-2) transition, coincident in position with the galaxy center. We infer a molecular gas mass of M{sub H{sub 2}} = 2.2 ± 0.6 × 10{sup 10} M {sub ☉}, which implies that the starburst will consume its fuel in ∼30 Myr if it is not replenished. The L {sub IR}/M{sub H{sub 2}} that we measure for this cluster is consistent with the starburst limit of 500 L {sub ☉}/M {sub ☉}, above which radiation pressure is able to disperse the cold reservoir. The combination of the high level of turbulence in the warm phase and the high L {sub IR}/M{sub H{sub 2}} ratio suggests that this violent starburst may be in the process of quenching itself. We propose that phases of rapid star formation may be common in the cores of galaxy clusters, but so short-lived that their signatures are quickly erased and appear only in a subsample of the most strongly cooling clusters.« less

The Origin of Molecular Clouds in Central Galaxies

NASA Astrophysics Data System (ADS)

Pulido, F. A.; McNamara, B. R.; Edge, A. C.; Hogan, M. T.; Vantyghem, A. N.; Russell, H. R.; Nulsen, P. E. J.; Babyk, I.; Salomé, P.

2018-02-01

We present an analysis of 55 central galaxies in clusters and groups with molecular gas masses and star formation rates lying between {10}8 {and} {10}11 {M}ȯ and 0.5 and 270 {M}ȯ {{yr}}-1, respectively. Molecular gas mass is correlated with star formation rate, Hα line luminosity, and central atmospheric gas density. Molecular gas is detected only when the central cooling time or entropy index of the hot atmosphere falls below ∼1 Gyr or ∼35 keV cm2, respectively, at a (resolved) radius of 10 kpc. These correlations indicate that the molecular gas condensed from hot atmospheres surrounding the central galaxies. We explore the origins of thermally unstable cooling by evaluating whether molecular gas becomes prevalent when the minimum of the cooling to free-fall time ratio ({t}{cool}/{t}{ff}) falls below ∼10. We find that (1) molecular gas-rich systems instead lie between 10< \\min ({t}{cool}/{t}{ff})< 25, where {t}{cool}/{t}{ff}=25 corresponds approximately to cooling time and entropy thresholds of 1 Gyr and 35 {keV} {{cm}}2, respectively; (2) \\min ({t}{cool}/{t}{ff}) is uncorrelated with molecular gas mass and jet power; and (3) the narrow range 10< \\min ({t}{cool}/{t}{ff})< 25 can be explained by an observational selection effect, although a real physical effect cannot be excluded. These results and the absence of isentropic cores in cluster atmospheres are in tension with models that assume thermal instability ensues from linear density perturbations in hot atmospheres when {t}{cool}/{t}{ff}≲ 10. Some of the molecular gas may instead have condensed from atmospheric gas lifted outward by buoyantly rising X-ray bubbles or by dynamically induced uplift (e.g., mergers, sloshing).

A Unique Sample of Extreme-BCG Clusters at 0.2 < z < 0.5

NASA Astrophysics Data System (ADS)

Garmire, Gordon

2017-09-01

The recently-discovered Phoenix cluster harbors the most extreme BCG in the known universe. Despite the cluster's high mass and X-ray luminosity, it was consistently identified by surveys as an isolated AGN, due to the bright central point source and the compact cool core. Armed with hindsight, we have undertaken an all-sky survey based on archival X-ray, OIR, and radio data to identify other similarly-extreme systems that were likewise missed. A pilot study demonstrated that this strategy works, leading to the discovery of a new, massive cluster at z 0.2 which was missed by previous X-ray surveys due to the presence of a bright central QSO. We propose here to observe 6 new clusters from our complete northern-sky survey, which harbor some of the most extreme central galaxies known.

Asymmetric ejecta of cool supergiants and hypergiants in the massive cluster Westerlund 1

NASA Astrophysics Data System (ADS)

Andrews, H.; Fenech, D.; Prinja, R. K.; Clark, J. S.; Hindson, L.

2018-06-01

We report new 5.5 GHz radio observations of the massive star cluster Westerlund 1, taken by the Australia Telescope Compact Array, detecting nine of the ten yellow hypergiants (YHGs) and red supergiants (RSGs) within the cluster. Eight of nine sources are spatially resolved. The nebulae associated with the YHGs Wd1-4a, -12a, and -265 demonstrate a cometary morphology - the first time this phenomenon has been observed for such stars. This structure is also echoed in the ejecta of the RSGs Wd1-20 and -26; in each case the cometary tails are directed away from the cluster core. The nebular emission around the RSG Wd1-237 is less collimated than these systems but once again appears more prominent in the hemisphere facing the cluster. Considered as a whole, the nebular morphologies provide compelling evidence for sculpting via a physical agent associated with Westerlund 1, such as a cluster wind.

INFRARED OBSERVATIONAL MANIFESTATIONS OF YOUNG DUSTY SUPER STAR CLUSTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez-González, Sergio; Tenorio-Tagle, Guillermo; Silich, Sergiy, E-mail: sergiomtz@inaoep.mx

The growing evidence pointing at core-collapse supernovae as large dust producers makes young massive stellar clusters ideal laboratories to study the evolution of dust immersed in a hot plasma. Here we address the stochastic injection of dust by supernovae, and follow its evolution due to thermal sputtering within the hot and dense plasma generated by young stellar clusters. Under these considerations, dust grains are heated by means of random collisions with gas particles which result in the appearance of  infrared spectral signatures. We present time-dependent infrared spectral energy distributions that are to be expected from young stellar clusters. Our results aremore » based on hydrodynamic calculations that account for the stochastic injection of dust by supernovae. These also consider gas and dust radiative cooling, stochastic dust temperature fluctuations, the exit of dust grains out of the cluster volume due to the cluster wind, and a time-dependent grain size distribution.« less

Cosmological Simulations of Galaxy Clusters

NASA Astrophysics Data System (ADS)

Borgani, Stefano; Kravtsov, Andrey

2011-02-01

We review recent progress in the description of the formation and evolution of galaxy clusters in a cosmological context by using state-of-art numerical simulations. We focus our presentation on the comparison between simulated and observed X-ray properties, while we will also discuss numerical predictions on properties of the galaxy population in clusters, as observed in the optical band. Many of the salient observed properties of clusters, such as scaling relations between X-ray observables and total mass, radial profiles of entropy and density of the intracluster gas, and radial distribution of galaxies are reproduced quite well. In particular, the outer regions of cluster at radii beyond about 10 per cent of the virial radius are quite regular and exhibit scaling with mass remarkably close to that expected in the simplest case in which only the action of gravity determines the evolution of the intra-cluster gas. However, simulations generally fail at reproducing the observed "cool core" structure of clusters: simulated clusters generally exhibit a significant excess of gas cooling in their central regions, which causes both an overestimate of the star formation in the cluster centers and incorrect temperature and entropy profiles. The total baryon fraction in clusters is below the mean universal value, by an amount which depends on the cluster-centric distance and the physics included in the simulations, with interesting tensions between observed stellar and gas fractions in clusters and predictions of simulations. Besides their important implications for the cosmological application of clusters, these puzzles also point towards the important role played by additional physical processes, beyond those already included in the simulations. We review the role played by these processes, along with the difficulty for their implementation, and discuss the outlook for the future progress in numerical modeling of clusters.

The Complete Local-Volume Groups Sample (CLoGS): Early results from X-ray and radio observations

NASA Astrophysics Data System (ADS)

Vrtilek, Jan M.; O'Sullivan, Ewan; David, Laurence P.; Giacintucci, Simona; Kolokythas, Konstantinos

2017-08-01

Although the group environment is the dominant locus of galaxy evolution (in contrast to rich clusters, which contain only a few percent of galaxies), there has been a lack of reliable, representative group samples in the local Universe. In particular, X-ray selected samples are strongly biased in favor of the X-ray bright, centrally-concentrated cool-core systems. In response, we have designed the Complete Local-Volume Groups Sample (CLoGS), an optically-selected statistically-complete sample of 53 groups within 80 Mpc which is intended to overcome the limitations of X-ray selected samples and serve as a representative survey of groups in the local Universe. We have supplemented X-ray data from Chandra and XMM (70% complete to date, using both archival and new observations, with a 26-group high richness subsample 100% complete) with GMRT radio continuum observations (at 235 and 610 MHz, complete for the entire sample). CLoGS includes groups with a wide variety of properties in terms of galaxy population, hot gas content, and AGN power. We here describe early results from the survey, including the range of AGN activity observed in the dominant galaxies, the relative fraction of cool-core and non-cool-core groups in our sample, and the degree of disturbance observed in the IGM.

THERMODYNAMICS OF THE COMA CLUSTER OUTSKIRTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simionescu, A.; Werner, N.; Urban, O.

2013-09-20

We present results from a large mosaic of Suzaku observations of the Coma Cluster, the nearest and X-ray brightest hot ({approx}8 keV), dynamically active, non-cool core system, focusing on the thermodynamic properties of the intracluster medium on large scales. For azimuths not aligned with an infalling subcluster toward the southwest, our measured temperature and X-ray brightness profiles exhibit broadly consistent radial trends, with the temperature decreasing from about 8.5 keV at the cluster center to about 2 keV at a radius of 2 Mpc, which is the edge of our detection limit. The southwest merger significantly boosts the surface brightness,more » allowing us to detect X-ray emission out to {approx}2.2 Mpc along this direction. Apart from the southwestern infalling subcluster, the surface brightness profiles show multiple edges around radii of 30-40 arcmin. The azimuthally averaged temperature profile, as well as the deprojected density and pressure profiles, all show a sharp drop consistent with an outwardly-propagating shock front located at 40 arcmin, corresponding to the outermost edge of the giant radio halo observed at 352 MHz with the Westerbork Synthesis Radio Telescope. The shock front may be powering this radio emission. A clear entropy excess inside of r{sub 500} reflects the violent merging events linked with these morphological features. Beyond r{sub 500}, the entropy profiles of the Coma Cluster along the relatively relaxed directions are consistent with the power-law behavior expected from simple models of gravitational large-scale structure formation. The pressure is also in agreement at these radii with the expected values measured from Sunyaev-Zel'dovich data from the Planck satellite. However, due to the large uncertainties associated with the Coma Cluster measurements, we cannot yet exclude an entropy flattening in this system consistent with that seen in more relaxed cool core clusters.« less

Tracing Gas Motions in the Centaurus Cluster

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, James; Fabian, A.C.; Sanders, J.S.

2006-03-01

We apply the stochastic model of iron transport developed by Rebusco et al. (2005) to the Centaurus cluster. Using this model, we find that an effective diffusion coefficient D in the range 2 x 10{sup 28} - 4 x 10{sup 28} cm{sup 2}s{sup -1} can approximately reproduce the observed abundance distribution. Reproducing the flat central profile and sharp drop around 30-70 kpc, however, requires a diffusion coefficient that drops rapidly with radius so that D > 4 x 10{sup 28} cm{sup 2}s{sup -1} only inside about 25 kpc. Assuming that all transport is due to fully-developed turbulence, which is alsomore » responsible for offsetting cooling in the cluster core, we calculate the length and velocity scales of energy injection. These length scales are found to be up to a factor of {approx} 10 larger than expected if the turbulence is due to the inflation and rising of a bubble. We also calculate the turbulent thermal conductivity and find it is unlikely to be significant in preventing cooling.« less

Cooling and clusters: when is heating needed?

PubMed

Bryan, Greg; Voit, Mark

2005-03-15

There are (at least) two unsolved problems concerning the current state of the ther- mal gas in clusters of galaxies. The first is to identify the source of the heating which onsets cooling in the centres of clusters with short cooling times (the 'cooling-flow' problem). The second to understand the mechanism which boosts the entropy in cluster and group gas. Since both of these problems involve an unknown source of heating it is tempting to identify them with the same process, particularly since active galactic nuclei heating is observed to be operating at some level in a sample of well-observed 'cooling-flow' clusters. Here we show, using numerical simulations of cluster formation, that much of the gas ending up in clusters cools at high redshift and so the heating is also needed at high redshift, well before the cluster forms. This indicates that the same process operating to solve the cooling-flow problem may not also resolve the cluster-entropy problem.

The end of the White Dwarf Cooling Sequence of NGC 6752

NASA Astrophysics Data System (ADS)

Bedin, Luigi

2017-08-01

We propose to study the last HST-accessible white dwarf (WD) cooling sequence (CS) for a nearby globular cluster (GC), the chemically complex, extreme blue horizontal branch cluster NGC 6752. Over 97% of stars end their lives as WDs, and the WD CS provides constraints not only on the age, but also potentially the star formation history of a GC. The CS of WDs also lies in the least-explored region of the color-magnitude diagram of old stellar populations. Recent deep imaging with HST has successfully reached the end of the WD CS in only three classical old GCs, M4, NGC 6397 and 47 Tuc, and reveals an unexpectedly complex, and double-peaked, WD CS in the metal rich old open cluster NGC 6791. One more investigation is in progress on the massive globular Omega Centauri, where over 14 sub-populations are known to exist.While almost every cluster is known to host multiple populations, every single cluster is unique. NGC 6752 is a bridge between the relatively simple globular clusters, and Omega Cen, the most complex globular cluster known. NGC 6752 has an extended blue horizontal branch, a collapsed core and 3 chemically distinct populations. It is our last chance to add diversity to our very limited sample of WD CS, so far containing only 3 globular clusters, one old open cluster, and the complex Omega Cen system. We need to undertake this investigation while HST is still operational, as there is no foreseeable opportunity in the post-HST era to have one extra WD CS in the homogeneus optical photometric system of HST.

Gas Dynamics in the Fornax Cluster: Viscosity, turbulence, and sloshing

NASA Astrophysics Data System (ADS)

Kraft, Ralph; Su, Yuanyuan; Sheardown, Alexander; Roediger, Elke; Nulsen, Paul; Forman, William; Jones, Christine; Churazov, Eugene

2018-01-01

We present results from deep Chandra and XMM-Newton observations of the ICM in the Fornax cluster, and combine these data with specifically-tailored hydrodynamic simulations for an unprecedented view of the gas dynamics in this nearby cluster. We report the detection of four sloshing fronts (Su+2017). Based on our simulations, all four of these fronts can plausibly be attributed to the infall of the early-type galaxy NGC 1404 into the cluster potential. We argue that the presence of these sloshing cold fronts, the lack of its own extended gas halo, and the approximately transonic infall velocity indicate that this must be at least the second core passage for NGC 1404. Additionally, there is virtually no stripped tail of cool gas behind NGC 1404, conclusively demonstrating that the stripped gas is efficiently mixed with the cluster ICM. This mixing most likely occurs via small-scale Kelvin-Helmholtz instabilities formed in the high Reynolds number flow.

Multifrequency VLA observations of PKS 0745 - 191 - The archetypal 'cooling flow' radio source?

NASA Technical Reports Server (NTRS)

Baum, S. A.; O'Dea, C. P.

1991-01-01

Ninety-, 20-, 6- and 2-cm VLA observations of the high-radio-luminosity cooling-flow radio source PKS 0745 - 191 are presented. The radio source was found to have a core with a very steep spectrum (alpha is approximately -1.5) and diffuse emission with an even steeper spectrum (alpha is approximately -1.5 to -2.3) without clear indications of the jets, hotspots, or double lobes found in the other radio sources of comparable luminosity. It is inferred that the energy to power the radio source comes from the central engine, but the source's structure may be heavily influenced by the past history of the galaxy and the inflowing intracluster medium. It is shown that, while the radio source is energetically unimportant for the cluster as a whole, it is important on the scale of the cooling flow. The mere existence of cosmic rays and magnetic fields within a substantial fraction of the volume inside the cooling radius has important consequences for cooling-flow models.

FRONTIER FIELDS CLUSTERS: CHANDRA AND JVLA VIEW OF THE PRE-MERGING CLUSTER MACS J0416.1-2403

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogrean, G. A.; Weeren, R. J. van; Jones, C.

2015-10-20

Merging galaxy clusters leave long-lasting signatures on the baryonic and non-baryonic cluster constituents, including shock fronts, cold fronts, X-ray substructure, radio halos, and offsets between the dark matter (DM) and the gas components. Using observations from Chandra, the Jansky Very Large Array, the Giant Metrewave Radio Telescope, and the Hubble Space Telescope, we present a multiwavelength analysis of the merging Frontier Fields cluster MACS J0416.1-2403 (z = 0.396), which consists of NE and SW subclusters whose cores are separated on the sky by ∼250 kpc. We find that the NE subcluster has a compact core and hosts an X-ray cavity,more » yet it is not a cool core. Approximately 450 kpc south–southwest of the SW subcluster, we detect a density discontinuity that corresponds to a compression factor of ∼1.5. The discontinuity was most likely caused by the interaction of the SW subcluster with a less massive structure detected in the lensing maps SW of the subcluster's center. For both the NE and the SW subclusters, the DM and the gas components are well-aligned, suggesting that MACS J0416.1-2403 is a pre-merging system. The cluster also hosts a radio halo, which is unusual for a pre-merging system. The halo has a 1.4 GHz power of (1.3 ± 0.3) × 10{sup 24} W Hz{sup −1}, which is somewhat lower than expected based on the X-ray luminosity of the cluster if the spectrum of the halo is not ultra-steep. We suggest that we are either witnessing the birth of a radio halo, or have discovered a rare ultra-steep spectrum halo.« less

Split radiator design for heat rejection optimization for a waste heat recovery system

DOEpatents

Ernst, Timothy C.; Nelson, Christopher R.

2016-10-18

A cooling system provides improved heat recovery by providing a split core radiator for both engine cooling and condenser cooling for a Rankine cycle (RC). The cooling system includes a radiator having a first cooling core portion and a second cooling core portion. An engine cooling loop is fluidly connected the second cooling core portion. A condenser of an RC has a cooling loop fluidly connected to the first cooling core portion. A valve is provided between the engine cooling loop and the condenser cooling loop adjustably control the flow of coolant in the condenser cooling loop into the engine cooling loop. The cooling system includes a controller communicatively coupled to the valve and adapted to determine a load requirement for the internal combustion engine and adjust the valve in accordance with the engine load requirement.

Active Galactic Nucleus Feedback with the Square Kilometre Array and Implications for Cluster Physics and Cosmology

NASA Astrophysics Data System (ADS)

Iqbal, Asif; Kale, Ruta; Majumdar, Subhabrata; Nath, Biman B.; Pandge, Mahadev; Sharma, Prateek; Malik, Manzoor A.; Raychaudhury, Somak

2017-12-01

Active Galactic Nuclei (AGN) feedback is regarded as an important non-gravitational process in galaxy clusters, providing useful constraints on large-scale structure formation. It modifies the structure and energetics of the intra-cluster medium (ICM) and hence its understanding is crucially needed in order to use clusters as high precision cosmological probes. In this context, particularly keeping in mind the upcoming high quality radio data expected from radio surveys like Square Kilometre Array (SKA) with its higher sensitivity, high spatial and spectral resolutions, we review our current understanding of AGN feedback, its cosmological implications and the impact that SKA can have in revolutionizing our understanding of AGN feedback in large-scale structures. Recent developments regarding the AGN outbursts and its possible contribution to excess entropy in the hot atmospheres of groups and clusters, its correlation with the feedback energy in ICM, quenching of cooling flows and the possible connection between cool core clusters and radio mini-halos, are discussed. We describe current major issues regarding modeling of AGN feedback and its impact on the surrounding medium. With regard to the future of AGN feedback studies, we examine the possible breakthroughs that can be expected from SKA observations. In the context of cluster cosmology, for example, we point out the importance of SKA observations for cluster mass calibration by noting that most of z>1 clusters discovered by eROSITA X-ray mission can be expected to be followed up through a 1000 hour SKA1-mid programme. Moreover, approximately 1000 radio mini halos and ˜ 2500 radio halos at z<0.6 can be potentially detected by SKA1 and SKA2 and used as tracers of galaxy clusters and determination of cluster selection function.

X-Ray spectroscopy of cooling flows

NASA Technical Reports Server (NTRS)

Prestwich, Andrea

1996-01-01

Cooling flows in clusters of galaxies occur when the cooling time of the gas is shorter than the age of the cluster; material cools and falls to the center of the cluster potential. Evidence for short X-ray cooling times comes from imaging studies of clusters and X-ray spectroscopy of a few bright clusters. Because the mass accretion rate can be high (a few 100 solar mass units/year) the mass of material accumulated over the lifetime of a cluster can be as high as 10(exp 12) solar mass units. However, there is little evidence for this material at other wavelengths, and the final fate of the accretion material is unknown. X-ray spectra obtained with the Einstein SSS show evidence for absorption; if confirmed this result would imply that the accretion material is in the form of cool dense clouds. However ice on the SSS make these data difficult to interpret. We obtained ASCA spectra of the cooling flow cluster Abell 85. Our primary goals were to search for multi-temperature components that may be indicative of cool gas; search for temperature gradients across the cluster; and look for excess absorption in the cooling region.

YOUNG STELLAR CLUSTERS WITH A SCHUSTER MASS DISTRIBUTION. I. STATIONARY WINDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palous, Jan; Wuensch, Richard; Hueyotl-Zahuantitla, Filiberto

2013-08-01

Hydrodynamic models for spherically symmetric winds driven by young stellar clusters with a generalized Schuster stellar density profile are explored. For this we use both semi-analytic models and one-dimensional numerical simulations. We determine the properties of quasi-adiabatic and radiative stationary winds and define the radius at which the flow turns from subsonic to supersonic for all stellar density distributions. Strongly radiative winds significantly diminish their terminal speed and thus their mechanical luminosity is strongly reduced. This also reduces their potential negative feedback into their host galaxy interstellar medium. The critical luminosity above which radiative cooling becomes dominant within the clusters,more » leading to thermal instabilities which make the winds non-stationary, is determined, and its dependence on the star cluster density profile, core radius, and half-mass radius is discussed.« less

Increasing Black Hole Feedback-induced Quenching with Anisotropic Thermal Conduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kannan, Rahul; Vogelsberger, Mark; Pfrommer, Christoph

Feedback from central supermassive black holes is often invoked to explain the low star formation rates (SFRs) in the massive galaxies at the centers of galaxy clusters. However, the detailed physics of the coupling of the injected feedback energy with the intracluster medium (ICM) is still unclear. Using high-resolution magnetohydrodynamic cosmological simulations of galaxy cluster formation, we investigate the role of anisotropic thermal conduction in shaping the thermodynamic structure of clusters, and in particular, in modifying the impact of black hole feedback. Stratified anisotropically conducting plasmas are formally always unstable, and thus more prone to mixing, an expectation borne outmore » by our results. The increased mixing efficiently isotropizes the injected feedback energy, which in turn significantly improves the coupling between the feedback energy and the ICM. This facilitates an earlier disruption of the cool-core, reduces the SFR by more than an order of magnitude, and results in earlier quenching despite an overall lower amount of feedback energy injected into the cluster core. With conduction, the metallicity gradients and dispersions are lowered, aligning them better with observational constraints. These results highlight the important role of thermal conduction in establishing and maintaining the quiescence of massive galaxies.« less

Shivering heat production and body fat protect the core from cooling during body immersion, but not during head submersion: a structural equation model.

PubMed

Pretorius, Thea; Lix, Lisa; Giesbrecht, Gordon

2011-03-01

Previous studies showed that core cooling rates are similar when only the head or only the body is cooled. Structural equation modeling was used on data from two cold water studies involving body-only, or whole body (including head) cooling. Exposure of both the body and head increased core cooling, while only body cooling elicited shivering. Body fat attenuates shivering and core cooling. It is postulated that this protection occurs mainly during body cooling where fat acts as insulation against cold. This explains why head cooling increases surface heat loss with only 11% while increasing core cooling by 39%. Copyright © 2011 Elsevier Ltd. All rights reserved.

New Observational Evidence of Flash Mixing on the White Dwarf Cooling Curve

NASA Technical Reports Server (NTRS)

Brown, T. M.; Lanz, T.; Sweigart, A. V.; Cracraft, Misty; Hubeny, Ivan; Landsman, W. B.

2011-01-01

Blue hook stars are a class of subluminous extreme horizontal branch stars that were discovered in UV images of the massive globular clusters w Cen and NGC 2808. These stars occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. Using new theoretical evolutionary and atmospheric models, we have shown that the blue hook stars are very likely the progeny of stars that undergo extensive internal mixing during a late helium-core flash on the white dwarf cooling curve. This "flash mixing" produces hotter-than-normal EHB stars with atmospheres significantly enhanced in helium and carbon. The larger bolometric correction, combined with the decrease in hydrogen opacity, makes these stars appear sub luminous in the optical and UV. Flash mixing is more likely to occur in stars born with a high helium abundance, due to their lower mass at the main sequence turnoff. For this reason, the phenomenon is more common in those massive globular clusters that show evidence for secondary populations enhanced in helium. However, a high helium abundance does not, by itself, explain the presence of blue hook stars in massive globular clusters. Here, we present new observational evidence for flash mixing, using recent HST observations. These include UV color-magnitude diagrams of six massive globular clusters and far-UV spectroscopy of hot subdwarfs in one of these clusters (NGC 2808).

A cluster in a crowded environment: XMM-Newton and Chandra observations of A3558

NASA Astrophysics Data System (ADS)

Rossetti, M.; Ghizzardi, S.; Molendi, S.; Finoguenov, A.

2007-03-01

Combining XMM-Newton and Chandra data, we have performed a detailed study of Abell 3558. Our analysis shows that its dynamical history is more complicated than previously thought. We have found some traits typical of cool core clusters (surface brightness peaked at the center, peaked metal abundance profile) and others that are more common in merging clusters, like deviations from spherical symmetry in the thermodynamic quantities of the ICM. This last result has been achieved with a new technique for deriving temperature maps from images. We have also detected a cold front and, with the combined use of XMM-Newton and Chandra, we have characterized its properties, such as the speed and the metal abundance profile across the edge. This cold front is probably due to the sloshing of the core, induced by the perturbation of the gravitational potential associated with a past merger. The hydrodynamic processes related to this perturbation have presumably produced a tail of lower entropy, higher pressure and metal rich ICM, which extends behind the cold front for~500 kpc. The unique characteristics of A3558 are probably due to the very peculiar environment in which it is located: the core of the Shapley supercluster. Appendices A and B are only available in electronic form at http://www.aanda.org

Presence of glassy state and large exchange bias in nanocrystalline BiFeO3

NASA Astrophysics Data System (ADS)

Srivastav, Simant Kumar; Johari, Anima; Patel, S. K. S.; Gajbhiye, N. S.

2017-11-01

We investigated the static and dynamic aspects of the magnetic properties for single phase nanocrystalline BiFeO3 with average crystallite size of 35 nm. The frequency dependence of the peak is observed in the real part of ac susceptibility χ‧ac vs T measurement and described well by the Vogel-Fulcher law as well as the power law. These analyses indicated the existence of cluster glass state with significant interaction among the spin clusters and results in cluster-glass like cooperative freezing at low temperature. The influence of temperature and magnetic field cooling on the exchange bias effect is investigated. A training effect is also observed. We have reported a significantly high ZFC & FC exchange bias of 200 Oe & 450 Oe at 300 K and 900 Oe & 2100 Oe at 5 K. The obtained results are interpreted in the framework of core-shell model, where the core of the BFO nanoparticles shows antiferromagnetic behavior and surrounded by CG-like ferromagnetic (FM) shell associated to uncompensated surface spins.

Cool neutral hydrogen in the direction of an anonymous OB association

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bania, T.M.

1983-08-01

H I self-absorption is seen in the direction l = 55./sup 0/6 probably physically associated with an anonymous OB association which has the Cepheid GY Sagittae as a member. The cool H I is in two clouds at least 15 pc in diameter located 3.25 kpc from the Sun. If their temperature is approx. =50 K, the cloud masses are approx. =10/sup 3/ M/sub sun/. The neutral atomic hydrogen clouds are probably warm envelopes surrounding cold molecular cloud cores because CO observations in this region show two molecular clouds nearly coincident with the absorbing H i gas. Since the OBmore » association is only approx. =10/sup 7/ years old, these clouds are likely to be part of the original cloud complex from which the stellar cluster formed. The H i clouds are part of the larger Arecibo survey of self-absorption which suggests that many of the Arecibo clouds are associated with heretofore unidentified star clusters. Even if this is generally not the case, the Arecibo objects have accurate kinematic distances and thus provide a new sample of cool H I clouds whose thermodynamic properties can be studied.« less

Testing Precipitation-Driven Feedback Models in Nearby Ellipticals

NASA Astrophysics Data System (ADS)

Donahue, Megan

2016-09-01

We propose to analyze the inner cooling-time and entropy profiles of 12 elliptical galaxies with strong radio AGN. X-ray studies of galaxy-cluster cores and massive ellipticals indicate that feedback from an AGN replaces energy radiated by these objects. The AGN at 10 pc seems tuned to the thermodynamic state of gas on 10 kpc scales, but how that occurs is a resilient mystery. The precipitation model posits if the AGN does not provide enough heat, then thermal instabilities rain cold clouds on it, increasing accretion from Bondi to 100 times that rate when t_cool drops below 10 t_ff. We will test precipitation-driven feedback models by measuring t_cool and gravitational potential within the central kpc and to see how radio power is related to t_c/t_ff at small radii in these galaxies.

Self-similarity of temperature profiles in distant galaxy clusters: the quest for a universal law

NASA Astrophysics Data System (ADS)

Baldi, A.; Ettori, S.; Molendi, S.; Gastaldello, F.

2012-09-01

Context. We present the XMM-Newton temperature profiles of 12 bright (LX > 4 × 1044 erg s-1) clusters of galaxies at 0.4 < z < 0.9, having an average temperature in the range 5 ≲ kT ≲ 11 keV. Aims: The main goal of this paper is to study for the first time the temperature profiles of a sample of high-redshift clusters, to investigate their properties, and to define a universal law to describe the temperature radial profiles in galaxy clusters as a function of both cosmic time and their state of relaxation. Methods: We performed a spatially resolved spectral analysis, using Cash statistics, to measure the temperature in the intracluster medium at different radii. Results: We extracted temperature profiles for the clusters in our sample, finding that all profiles are declining toward larger radii. The normalized temperature profiles (normalized by the mean temperature T500) are found to be generally self-similar. The sample was subdivided into five cool-core (CC) and seven non cool-core (NCC) clusters by introducing a pseudo-entropy ratio σ = (TIN/TOUT) × (EMIN/EMOUT)-1/3 and defining the objects with σ < 0.6 as CC clusters and those with σ ≥ 0.6 as NCC clusters. The profiles of CC and NCC clusters differ mainly in the central regions, with the latter exhibiting a slightly flatter central profile. A significant dependence of the temperature profiles on the pseudo-entropy ratio σ is detected by fitting a function of r and σ, showing an indication that the outer part of the profiles becomes steeper for higher values of σ (i.e. transitioning toward the NCC clusters). No significant evidence of redshift evolution could be found within the redshift range sampled by our clusters (0.4 < z < 0.9). A comparison of our high-z sample with intermediate clusters at 0.1 < z < 0.3 showed how the CC and NCC cluster temperature profiles have experienced some sort of evolution. This can happen because higher z clusters are at a less advanced stage of their formation and did not have enough time to create a relaxed structure, which is characterized by a central temperature dip in CC clusters and by flatter profiles in NCC clusters. Conclusions: This is the first time that a systematic study of the temperature profiles of galaxy clusters at z > 0.4 has been attempted. We were able to define the closest possible relation to a universal law for the temperature profiles of galaxy clusters at 0.1 < z < 0.9, showing a dependence on both the relaxation state of the clusters and the redshift. Appendix A is only available in electronic form at http://www.aanda.org

Chandra observations of dying radio sources in galaxy clusters

NASA Astrophysics Data System (ADS)

Murgia, M.; Markevitch, M.; Govoni, F.; Parma, P.; Fanti, R.; de Ruiter, H. R.; Mack, K.-H.

2012-12-01

Context. The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, considering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. Aims: We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. Methods: We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. Results: The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters. Conclusions: We calculated the non-thermal pressure of the radio lobes assuming that the radio sources are in the minimum energy condition. For all dying sources we found that this is on average about one to two orders of magnitude lower than that of the external gas, as found for many other radio sources at the center of galaxy groups and clusters. We found marginal evidence for the presence of X-ray surface brightness depressions coincident with the fossil radio lobes of the dying sources in A2276 and ZwCl 1829.3+691. We estimated the outburst age and energy output for these two dying sources. The energy power from the AGN outburst is significantly higher than the X-ray luminosity in both clusters. Indeed, it is sufficient that a small fraction of this power is dissipated in the intra-cluster medium to reheat the cool cores. Appendix is available in electronic form at http://www.aanda.org

Chandra Observations of Dying Radio Sources in Galaxy Clusters

NASA Technical Reports Server (NTRS)

Murgia, M.; Markevitch, M.; Govoni, F.; Parma, P.; Fanti, R.; de Ruiter, H. R.; Mack, K.-H.

2012-01-01

Context. The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, considering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. Aims. We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. Methods. We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. Results. The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters. Conclusions. We calculated the non-thermal pressure of the radio lobes assuming that the radio sources are in the minimum energy condition. For all dying sources we found that this is on average about one to two orders of magnitude lower than that of the external gas, as found for many other radio sources at the center of galaxy groups and clusters. We found marginal evidence for the presence of X-ray surface brightness depressions coincident with the fossil radio lobes of the dying sources in A2276 and ZwCl 1829.3+691. We estimated the outburst age and energy output for these two dying sources. The energy power from the AGN outburst is significantly higher than the X-ray luminosity in both clusters. Indeed, it is sufficient that a small fraction of this power is dissipated in the intra-cluster medium to reheat the cool cores.

The mystery of the "Kite" radio source in Abell 2626: Insights from new Chandra observations

NASA Astrophysics Data System (ADS)

Ignesti, A.; Gitti, M.; Brunetti, G.; O'Sullivan, E.; Sarazin, C.; Wong, K.

2018-03-01

Context. We present the results of a new Chandra study of the galaxy cluster Abell 2626. The radio emission of the cluster shows a complex system of four symmetric arcs without known correlations with the thermal X-ray emission. The mirror symmetry of the radio arcs toward the center and the presence of two optical cores in the central galaxy suggested that they may be created by pairs of precessing radio jets powered by dual active galactic nuclei (AGNs) inside the core dominant galaxy. However, previous observations failed to observe the second jetted AGN and the spectral trend due to radiative age along the radio arcs, thus challenging this interpretation. Aim. The new Chandra observation had several scientific objectives, including the search for the second AGN that would support the jet precession model. We focus here on the detailed study of the local properties of the thermal and non-thermal emission in the proximity of the radio arcs, in order to obtain further insights into their origin. Methods: We performed a standard data reduction of the Chandra dataset deriving the radial profiles of temperature, density, pressure and cooling time of the intra-cluster medium. We further analyzed the two-dimensional (2D) distribution of the gas temperature, discovering that the south-western junction of the radio arcs surrounds the cool core of the cluster. Results: We studied the X-ray surface brightness and spectral profiles across the junction, finding a cold front spatially coincident with the radio arcs. This may suggest a connection between the sloshing of the thermal gas and the nature of the radio filaments, raising new scenarios for their origin. A tantalizing possibility is that the radio arcs trace the projection of a complex surface connecting the sites where electrons are most efficiently reaccelerated by the turbulence that is generated by the gas sloshing. In this case, diffuse emission embedded by the arcs and with extremely steep spectrum should be most visible at very low radio frequencies.

What Do the Hitomi Observations Tell Us About the Turbulent Velocities in the Perseus Cluster?

NASA Astrophysics Data System (ADS)

ZuHone, John A.; Miller, Eric D.; Bulbul, Esra; Zhuravleva, Irina

2017-08-01

Recently, the Hitomi X-ray Observatory provided the first-ever direct measurements of Doppler line shifting and broadening from the hot plasma in clusters of galaxies via its observations of the Perseus Cluster. It has been reported that these observations demonstrate that the ICM in Perseus is "quiescent". It is indisputable that the velocities inferred from the measured line shifts and broadening are low, but what do these observations imply about the structure of the velocity field on scales smaller than the Hitomi PSF? We use hydrodynamic simulations of gas motions in a cool-core cluster in combination with synthetic Hitomi observations in order to compare the observed line-of-sight velocities to the 3D velocity structure of the ICM, and assess the impact of Hitomi's spatial resolution and the effects of varying the underlying ICM physics.

An Optical and X-Ray Study of Abell 576, a Galaxy Cluster with a Cold Core

NASA Astrophysics Data System (ADS)

Mohr, Joseph J.; Geller, Margaret J.; Fabricant, Daniel G.; Wegner, Gary; Thorstensen, John; Richstone, Douglas O.

1996-10-01

We analyze the galaxy population and dynamics of the galaxy cluster A576; the observational constraints include 281 redshifts (230 new), R- band CCD galaxy photometry over a 2 h^-1^ Mpc x 2 h^-1^ Mpc region centered on the cluster, an Einstein IPC X-ray image, and an Einstein MPC X-ray spectrum. We focus on an 86% complete magnitude-limited sample (R_23.5_ < 17) of 169 cluster galaxies. The cluster galaxies with emission lines in their spectra have a larger velocity dispersion and are significantly less clustered on this 2 h^-1^ Mpc scale than galaxies without emission lines. We show that excluding the emission-line galaxies from the cluster sample decreases the velocity dispersion by 18% and the virial mass estimate by a factor of 2. The central cluster region contains a nonemission galaxy population and an intracluster medium which is significantly cooler (σ_core_ = 387_-105_^+250^ km s^-1^ and T_x_ = 1.6_-0.3_^+0.4^ keV at 90% confidence) than the global populations (σ = 977_-96_^+124^ km s^- 1^ for the nonemission population and T_X_ > 4 keV at 90% confidence). Because (1) the low-dispersion galaxy population is no more luminous than the global population and (2) the evidence for a cooling flow is weak, we suggest that the core of A576 may contain the remnants of a lower mass subcluster. We examine the cluster mass, baryon fraction, and luminosity function. The cluster virial mass varies significantly depending on the galaxy sample used. Consistency between the hydrostatic and virial estimators can be achieved if (1) the gas temperature at r~1 h^-1^ Mpc is T_X_ ~ 8 keV (the best-fit value) and (2) several velocity outliers are excluded from the virial calculation. Although the best-fit Schechter function parameters and the ratio of galaxy to gas mass in A576 are typical of other clusters, the baryon fraction is relatively low. Using the consistent cluster binding mass, we show that the gas mass fraction is ~3 h^-3/2^% and the baryon fraction is ~4%.

The return of the merging galaxy subclusters of El Gordo?

DOE PAGES

Ng, Karen Y.; Dawson, William A.; Wittman, D.; ...

2015-08-25

Merging galaxy clusters with radio relics provide rare insights to the merger dynamics as the relics are created by the violent merger process. We demonstrate one of the first uses of the properties of the radio relic to reduce the uncertainties of the dynamical variables and determine the three-dimensional (3D) configuration of a cluster merger, ACT-CL J0102-4915, nicknamed El Gordo. From the double radio relic observation and the X-ray observation of a comet-like gas morphology induced by motion of the cool core, it is widely believed that El Gordo is observed shortly after the first core passage of the subclusters. Here, we employ a Monte Carlo simulation to investigate the 3D configuration and dynamics of El Gordo. Using the polarization fraction of the radio relic, we constrain the estimate of the angle between the plane of the sky and the merger axis to be α=21°±more » $$9\\atop{11}$$. We find the relative 3D merger speed of El Gordo to be 2400 ± $$400\\atop{200}$$ km s -1 at pericentre. The two possible estimates of the time since pericentre (TSP) are 0.46 ± $$0.09\\atop{0.16}$$ and 0.91± $$0.22\\atop{0.39}$$ Gyr for the outgoing and returning scenario, respectively. We put our estimates of the TSP into context by showing that if the time-averaged shock velocity is approximately equal to or smaller than the pericentre velocity of the corresponding subcluster in the centre-of-mass frame, the two subclusters are more likely to be moving towards, rather than away, from each other, post apocentre. Finally, we compare and contrast the merger scenario of El Gordo with that of the Bullet Cluster, and show that this late-stage merging scenario explains why the south-east (SE) dark matter lensing peak of El Gordo is closer to the merger centre than the SE cool core.« less

The return of the merging galaxy subclusters of El Gordo?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ng, Karen Y.; Dawson, William A.; Wittman, D.

Merging galaxy clusters with radio relics provide rare insights to the merger dynamics as the relics are created by the violent merger process. We demonstrate one of the first uses of the properties of the radio relic to reduce the uncertainties of the dynamical variables and determine the three-dimensional (3D) configuration of a cluster merger, ACT-CL J0102-4915, nicknamed El Gordo. From the double radio relic observation and the X-ray observation of a comet-like gas morphology induced by motion of the cool core, it is widely believed that El Gordo is observed shortly after the first core passage of the subclusters. Here, we employ a Monte Carlo simulation to investigate the 3D configuration and dynamics of El Gordo. Using the polarization fraction of the radio relic, we constrain the estimate of the angle between the plane of the sky and the merger axis to be α=21°±more » $$9\\atop{11}$$. We find the relative 3D merger speed of El Gordo to be 2400 ± $$400\\atop{200}$$ km s -1 at pericentre. The two possible estimates of the time since pericentre (TSP) are 0.46 ± $$0.09\\atop{0.16}$$ and 0.91± $$0.22\\atop{0.39}$$ Gyr for the outgoing and returning scenario, respectively. We put our estimates of the TSP into context by showing that if the time-averaged shock velocity is approximately equal to or smaller than the pericentre velocity of the corresponding subcluster in the centre-of-mass frame, the two subclusters are more likely to be moving towards, rather than away, from each other, post apocentre. Finally, we compare and contrast the merger scenario of El Gordo with that of the Bullet Cluster, and show that this late-stage merging scenario explains why the south-east (SE) dark matter lensing peak of El Gordo is closer to the merger centre than the SE cool core.« less

Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low-Mass White Dwarfs

NASA Astrophysics Data System (ADS)

Kalirai, Jasonjot S.; Bergeron, P.; Hansen, Brad M. S.; Kelson, Daniel D.; Reitzel, David B.; Rich, R. Michael; Richer, Harvey B.

2007-12-01

We present the first detailed study of the properties (temperatures, gravities, and masses) of the NGC 6791 white dwarf population. This unique stellar system is both one of the oldest (8 Gyr) and most metal-rich ([Fe/H]~+0.4) open clusters in our Galaxy and has a color-magnitude diagram (CMD) that exhibits both a red giant clump and a much hotter extreme horizontal branch. Fitting the Balmer lines of the white dwarfs in the cluster using Keck/LRIS spectra suggests that most of these stars are undermassive, =0.43+/-0.06 Msolar, and therefore could not have formed from canonical stellar evolution involving the helium flash at the tip of the red giant branch. We show that at least 40% of NGC 6791's evolved stars must have lost enough mass on the red giant branch to avoid the flash and therefore did not convert helium into carbon-oxygen in their core. Such increased mass loss in the evolution of the progenitors of these stars is consistent with the presence of the extreme horizontal branch in the CMD. This unique stellar evolutionary channel also naturally explains the recent finding of a very young age (2.4 Gyr) for NGC 6791 from white dwarf cooling theory; helium-core white dwarfs in this cluster will cool ~3 times slower than carbon-oxygen-core stars, and therefore the corrected white dwarf cooling age is in fact >~7 Gyr, consistent with the well-measured main-sequence turnoff age. These results provide direct empirical evidence that mass loss is much more efficient in high-metallicity environments and therefore may be critical in interpreting the ultraviolet upturn in elliptical galaxies. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

78 FR 63516 - Initial Test Program of Emergency Core Cooling Systems for New Boiling-Water Reactors

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-24

... NUCLEAR REGULATORY COMMISSION [NRC-2012-0134] Initial Test Program of Emergency Core Cooling....79.1, ``Initial Test Program of Emergency Core Cooling Systems for New Boiling-Water Reactors.'' This... emergency core cooling systems (ECCSs) for boiling- water reactors (BWRs) whose licenses are issued after...

Probing the non-thermal emission in Abell 2146 and the Perseus cluster with the JVLA

NASA Astrophysics Data System (ADS)

Gendron-Marsolais, Marie-Lou; Hlavacek-Larrondo, Julie; van Weeren, Reinout; Clarke, Tracy; Intema, Huib; Russell, Helen; Edge, Alastair; Fabian, Andy; Olamaie, Malak; Rumsey, Clare; King, Lindsay; McNamara, Brian; Fecteau-Beaucage, David; Hogan, Michael; Mezcua, Mar; Taylor, Gregory; Blundell, Katherine; Sanders, Jeremy

2018-01-01

Jets created from accretion onto supermassive black holes release relativistic particles on large distances. These strongly affect the intracluster medium when located in the center of a brightest cluster galaxy. The hierarchical merging of subclusters and groups, from which cluster originate, also generates perturbations into the intracluster medium through shocks and turbulence, constituting a potential source of reacceleration for these particles. I will present deep multi-configuration low radio frequency observations from the Karl G. Jansky Very Large Array of two unique clusters, probing the non-thermal emission from the old particle population of the AGN outflows.Recently awarded of 550 hours of Chandra observations, Abell 2146 is one of the rare clusters undergoing a spectacular merger in the plane of the sky. Our recent deep multi-configuration JVLA 1.4 GHz observations have revealed the presence of a structure extending to 850 kpc in size, consisting of one component associated with the upstream shock and classified as a radio relic, and one associated with the subcluster core, consistent with a radio halo bounded by the bow shock. Theses structures have some of the lowest radio powers detected thus far in any cluster. The flux measurements of the halo, its morphology and measurements of the dynamical state of the cluster suggest that the halo was recently created (~ 0.3 Gyr after core passage). This makes A2146 extremely interesting to study, allowing us to probe the complete evolutionary stages of halos.I will also present results on 230-470 MHz JVLA observations of the Perseus cluster. Our observations of this nearby relaxed cool core cluster have revealed a multitude of new structures associated with the mini-halo, extending to hundreds of kpc in size. Its irregular morphology seems to be have been influenced both by the AGN activity and by the sloshing motion of the cluster’ gas. In addition, it has a filamentary structure similar to that seen in radio relics found in merging clusters.These results both illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies.

Has Earth's Plate Tectonics Led to Rapid Core Cooling?

NASA Astrophysics Data System (ADS)

de Montserrat Navarro, A.; Morgan, J. P.; Vannucchi, P.; Connolly, J. A.

2016-12-01

Earth's mantle and core are convecting planetary heat engines. The mantle convects to lose heat from secular cooling, internal radioactivity, and core heatflow across its base. Its convection generates plate tectonics, volcanism, and the loss of 35 TW of mantle heat through Earth's surface. The core convects to lose heat from secular cooling, small amounts of internal radioactivity, and the freezing-induced growth of a compositionally denser inner core. Until recently, the geodynamo was thought to be powered by 4 TW of heatloss across the core-mantle boundary. More recent determinations of the outer core's thermal conductivity (Pozzo et al., 2012; Gomi et al., 2013) would imply that >15 TW of power should conduct down its adiabat. Secular core cooling has been previously thought to be too slow for this, based on estimates for the Clapeyron Slope for high-pressure freezing of an idealized pure-iron core (cf. Nimmo, 2007). The 500-1000 kg m-3 seismically-inferred jump in density between the liquid outer core and solid inner core allows a direct estimate of the Clapeyron Slope for the outer core's actual composition which contains 0.08±0.02 lighter elements (S,Si,O,Al, H,…) mixed into a Fe-Ni alloy. A PREM-like 600 kg m-3 density jump yields a Clapeyron Slope for which there has been 774K of core cooling during the freezing and growth of the inner core, cooling that has been releasing an average of 21 TW of power during the past 3 Ga. If so, core cooling could easily have powered Earth's long-lived geodynamo. Another implication is that the present-day mantle is strongly `bottom-heated', and diapiric mantle plumes should dominate deep mantle upwelling. This mode of core and mantle convection is consistent with slow, 37.5K/Ga secular cooling of Earth's mantle linked to more rapid secular cooling of the core (cf. Morgan, Rüpke, and White, 2016). Efficient plate subduction, hence plate tectonics, is a key ingredient for such rapid secular core cooling.We also show how a more complete thermodynamic version of Birch's accretional energy calculation predicts that accretion with FeNi-sinking-linked differentiation between an Earth-like mantle and core would naturally generate a core that, post-accretion, was both hotter than overlying mantle and 1000K hotter than today.

ISM stripping from cluster galaxies and inhomogeneities in cooling flows

NASA Technical Reports Server (NTRS)

Soker, Noam; Bregman, Joel N.; Sarazin, Craig L.

1990-01-01

Analyses of the x ray surface brightness profiles of cluster cooling flows suggest that the mass flow rate decreases towards the center of the cluster. It is often suggested that this decrease results from thermal instabilities, in which denser blobs of gas cool rapidly and drop below x ray emitting temperatures. If the seeds for the thermal instabilities are entropy perturbations, these perturbations must enter the flow already in the nonlinear regime. Otherwise, the blobs would take too long to cool. Here, researchers suggest that such nonlinear perturbations might start as blobs of interstellar gas which are stripped out of cluster galaxies. Assuming that most of the gas produced by stellar mass loss in cluster galaxies is stripped from the galaxies, the total rate of such stripping is roughly M sub Interstellar Matter (ISM) approx. 100 solar mass yr(-1). It is interesting that the typical rates of cooling in cluster cooling flows are M sub cool approx. 100 solar mass yr(-1). Thus, it is possible that a substantial portion of the cooling gas originates as blobs of interstellar gas stripped from galaxies. The magnetic fields within and outside of the low entropy perturbations can help to maintain their identities, both by suppressing thermal conduction and through the dynamical effects of magnetic tension. One significant question concerning this scenario is: Why are cooling flows seen only in a fraction of clusters, although one would expect gas stripping to be very common. It may be that the density perturbations only survive and cool efficiently in clusters with a very high intracluster gas density and with the focusing effect of a central dominant galaxy. Inhomogeneities in the intracluster medium caused by the stripping of interstellar gas from galaxies can have a number of other effects on clusters. For example, these density fluctuations may disrupt the propagation of radio jets through the intracluster gas, and this may be one mechanism for producing Wide-Angle-Tail radio galaxies.

The evolution of cooling flows. I - Self-similar cluster flows. [of gas in intergalactic medium

NASA Technical Reports Server (NTRS)

Chevalier, Roger A.

1987-01-01

The evolution of a cooling flow from an initial state of hydrostatic equilibrium in a cluster of galaxies is investigated. After gas mass and energy are injected into the cluster at an early phase, the gas approaches hydrostatic equilibrium over most of the cluster and cooling becomes important in the dense central regions. As time passes, cooling strongly affects an increasing amount of gas. The effects of mass removal from the flow, the inclusion of magnetic or cosmic-ray pressure, and heat conduction are considered individually.

77 FR 36014 - Initial Test Program of Emergency Core Cooling Systems for Boiling-Water Reactors

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-15

... NUCLEAR REGULATORY COMMISSION [NRC-2012-0134] Initial Test Program of Emergency Core Cooling... for public comment draft regulatory guide (DG), DG-1277, ``Initial Test Program of Emergency Core... acceptable to implement with regard to initial testing features of emergency core cooling systems (ECCSs) for...

Cooperativity in self-limiting equilibrium self-associating systems

NASA Astrophysics Data System (ADS)

Freed, Karl F.

2012-11-01

A wide variety of highly cooperative self-assembly processes in biological and synthetic systems involve the assembly of a large number (m) of units into clusters, with m narrowly peaked about a large size m0 ≫ 1 and with a second peak centered about the m = 1 unassembled monomers. While very specific models have been proposed for the assembly of, for example, viral capsids and core-shell micelles of ß-casein, no available theory describes a thermodynamically general mechanism for this double peaked, highly cooperative equilibrium assembly process. This study provides a general mechanism for these cooperative processes by developing a minimal Flory-Huggins type theory. Beginning from the simplest non-cooperative, free association model in which the equilibrium constant for addition of a monomer to a cluster is independent of cluster size, the new model merely allows more favorable growth for clusters of intermediate sizes. The theory is illustrated by computing the phase diagram for cases of self-assembly on cooling or heating and for the mass distribution of the two phases.

Galaxy Clusters and Their Central Supermassive Black Holes: Case of M87

NASA Astrophysics Data System (ADS)

Churazov, Eugene; Sazonov, Sergey; Sunyaev, Rashid; Forman, William; Jones, Christine; Böhringer, Hans

Observations suggest that AGN activity regulates the thermal state of the gas by injecting energy into the intra-cluster medium in the cores of relaxed clusters, where radiative cooling time is often as short as few 108 years. Bubbles of relativistic plasma are inflated by a supermassive black hole and rise buoyantly through the gaseous atmosphere, leading to a number of spectacular phenomena like expanding shocks, X-ray dim and radio bright cavities, X-ray dim and radio dim "ghost" cavities (aged version of "normal" cavities), filaments in the wakes of the rising bubbles formed by the entrained low entropy gas, etc. Simple estimates of the energetics involved (based on the estimates of the energy content of bubbles/cavities and their life-time) suggest that amount of mechanical energy supplied by AGNs is sufficient to offset gas cooling losses in objects vastly different in size and luminosity. This hints on some form of self-regulation controlling the AGN power as the gas cools or gets heated. One can build a toy model where accretion rate (and therefore the amount of energy provided by the AGN) is sensitive to the gas properties, in particular to its entropy, thus closing the feedback loop. How the mechanical energy, provided by the AGN, is dissipated depends on the ICM microphysics (e.g. magnetic fields, viscosity, conduction etc). However it is easy to imagine the situation when close to 100% of mechanical energy is eventually dissipated in the cluster core, regardless of the particular physical process involved. Comparison of the gravitational potential profiles of the elliptical galaxies derived from X-ray and optical data suggests that the combined contribution of cosmic rays, magnetic fields and micro-turbulence to the gas pressure is of order 10-30%. This in turn suggests that the dissipation time scale of the energy deposited by the AGN is a similar 10-30% fraction of the gas cooling time. The same process of AGN-ICM interaction, operating in nearby clusters, could be important at z = 2 - 3 when present day massive ellipticals were forming. The importance of this process depends critically on the physics of accretion. An analogy with the Galactic stellar mass black holes suggests that a black hole can switch from the radiation dominated mode to the mechanically dominated mode when the accretion rate drops below the fraction 10-2 - 10-1 of the Eddington value. Given that the coupling constant of these two forms of energy output with the ICM can differ by a factor of 104 - 105 this change in the accretion mode may explain the switch of a SMBH (and its parent galaxy) from the QSO-type behavior and an intense star formation to the radiatively inefficient AGN and essentially passive evolution of the parent galaxy.

The most massive black holes on the Fundamental Plane of black hole accretion

NASA Astrophysics Data System (ADS)

Mezcua, M.; Hlavacek-Larrondo, J.; Lucey, J. R.; Hogan, M. T.; Edge, A. C.; McNamara, B. R.

2018-02-01

We perform a detailed study of the location of brightest cluster galaxies (BCGs) on the Fundamental Plane of black hole (BH) accretion, which is an empirical correlation between a BH X-ray and radio luminosity and mass supported by theoretical models of accretion. The sample comprises 72 BCGs out to z ˜ 0.3 and with reliable nuclear X-ray and radio luminosities. These are found to correlate as L_X ∝ L_R^{0.75 ± 0.08}, favouring an advection-dominated accretion flow as the origin of the X-ray emission. BCGs are found to be on average offset from the Fundamental Plane such that their BH masses seem to be underestimated by the MBH-MK relation a factor ˜10. The offset is not explained by jet synchrotron cooling and is independent of emission process or amount of cluster gas cooling. Those core-dominated BCGs are found to be more significantly offset than those with weak core radio emission. For BCGs to on average follow the Fundamental Plane, a large fraction ( ˜ 40 per cent) should have BH masses >1010 M⊙ and thus host ultramassive BHs. The local BH-galaxy scaling relations would not hold for these extreme objects. The possible explanations for their formation, either via a two-phase process (the BH formed first, the galaxy grows later) or as descendants of high-z seed BHs, challenge the current paradigm of a synchronized galaxy-BH growth.

Effect of core cooling on the radius of sub-Neptune planets

NASA Astrophysics Data System (ADS)

Vazan, A.; Ormel, C. W.; Dominik, C.

2018-02-01

Sub-Neptune planets are very common in our Galaxy and show a large diversity in their mass-radius relation. In sub-Neptunes most of the planet mass is in the rocky part (hereafter, core), which is surrounded by a modest hydrogen-helium envelope. As a result, the total initial heat content of such a planet is dominated by that of the core. Nonetheless, most studies contend that the core cooling only has a minor effect on the radius evolution of the gaseous envelope because the cooling of the core is in sync with the envelope; that is most of the initial heat is released early on timescales of 10-100 Myr. In this Letter we examined the importance of the core cooling rate for the thermal evolution of the envelope. Thus, we relaxed the early core cooling assumption and present a model in which the core is characterized by two parameters: the initial temperature and the cooling time. We find that core cooling can significantly enhance the radius of the planet when it operates on a timescale similar to the observed age, i.e. Gyr. Consequently, the interpretation of the mass-radius observations of sub-Neptunes depends on the assumed core thermal properties and the uncertainty therein. The degeneracy of composition and core thermal properties can be reduced by obtaining better estimates of the planet ages (in addition to their radii and masses) as envisioned by future observations.

Weighing the giants- V. Galaxy cluster scaling relations

NASA Astrophysics Data System (ADS)

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn; von der Linden, Anja; Applegate, Douglas E.; Kelly, Patrick L.; Burke, David L.; Donovan, David; Ebeling, Harald

2016-12-01

We present constraints on the scaling relations of galaxy cluster X-ray luminosity, temperature and gas mass (and derived quantities) with mass and redshift, employing masses from robust weak gravitational lensing measurements. These are the first such results obtained from an analysis that simultaneously accounts for selection effects and the underlying mass function, and directly incorporates lensing data to constrain total masses. Our constraints on the scaling relations and their intrinsic scatters are in good agreement with previous studies, and reinforce a picture in which departures from self-similar scaling laws are primarily limited to cluster cores. However, the data are beginning to reveal new features that have implications for cluster astrophysics and provide new tests for hydrodynamical simulations. We find a positive correlation in the intrinsic scatters of luminosity and temperature at fixed mass, which is related to the dynamical state of the clusters. While the evolution of the nominal scaling relations over the redshift range 0.0 < z < 0.5 is consistent with self-similarity, we find tentative evidence that the luminosity and temperature scatters, respectively, decrease and increase with redshift. Physically, this likely related to the development of cool cores and the rate of major mergers. We also examine the scaling relations of redMaPPer richness and Compton Y from Planck. While the richness-mass relation is in excellent agreement with recent work, the measured Y-mass relation departs strongly from that assumed in the Planck cluster cosmology analysis. The latter result is consistent with earlier comparisons of lensing and Planck scaling relation-derived masses.

Erratum: Weighing the giants – V. Galaxy cluster scaling relations

DOE PAGES

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn; ...

2017-02-21

We present constraints on the scaling relations of galaxy cluster X-ray luminosity, temperature and gas mass (and derived quantities) with mass and redshift, employing masses from robust weak gravitational lensing measurements. These are the first such results obtained from an analysis that simultaneously accounts for selection effects and the underlying mass function, and directly incorporates lensing data to constrain total masses. Our constraints on the scaling relations and their intrinsic scatters are in good agreement with previous studies, and reinforce a picture in which departures from self-similar scaling laws are primarily limited to cluster cores. However, the data are beginningmore » to reveal new features that have implications for cluster astrophysics and provide new tests for hydrodynamical simulations. We find a positive correlation in the intrinsic scatters of luminosity and temperature at fixed mass, which is related to the dynamical state of the clusters. While the evolution of the nominal scaling relations over the redshift range 0.0 < z < 0.5 is consistent with self similarity, we find tentative evidence that the luminosity and temperature scatters respectively decrease and increase with redshift. Physically, this likely related to the development of cool cores and the rate of major mergers. We also examine the scaling relations of redMaPPer richness and Compton Y from Planck. While the richness{mass relation is in excellent agreement with recent work, the measured Y {mass relation departs strongly from that assumed in the Planck cluster cosmology analysis. Furthermore, the latter result is consistent with earlier comparisons of lensing and Planck scaling-relation-derived masses.« less

Weighing the giants– V. Galaxy cluster scaling relations

DOE PAGES

Mantz, Adam B.; Allen, Steven W.; Morris, R. Glenn; ...

2016-09-07

Here, we present constraints on the scaling relations of galaxy cluster X-ray luminosity, temperature and gas mass (and derived quantities) with mass and redshift, employing masses from robust weak gravitational lensing measurements. These are the first such results obtained from an analysis that simultaneously accounts for selection effects and the underlying mass function, and directly incorporates lensing data to constrain total masses. Our constraints on the scaling relations and their intrinsic scatters are in good agreement with previous studies, and reinforce a picture in which departures from self-similar scaling laws are primarily limited to cluster cores. However, the data aremore » beginning to reveal new features that have implications for cluster astrophysics and provide new tests for hydrodynamical simulations. We find a positive correlation in the intrinsic scatters of luminosity and temperature at fixed mass, which is related to the dynamical state of the clusters. While the evolution of the nominal scaling relations over the redshift range 0.0 < z < 0.5 is consistent with self-similarity, we find tentative evidence that the luminosity and temperature scatters, respectively, decrease and increase with redshift. Physically, this likely related to the development of cool cores and the rate of major mergers. We also examine the scaling relations of redMaPPer richness and Compton Y from Planck. While the richness–mass relation is in excellent agreement with recent work, the measured Y–mass relation departs strongly from that assumed in the Planck cluster cosmology analysis. Furthermore, the latter result is consistent with earlier comparisons of lensing and Planck scaling relation-derived masses.« less

Passive containment cooling system

DOEpatents

Conway, Lawrence E.; Stewart, William A.

1991-01-01

A containment cooling system utilizes a naturally induced air flow and a gravity flow of water over the containment shell which encloses a reactor core to cool reactor core decay heat in two stages. When core decay heat is greatest, the water and air flow combine to provide adequate evaporative cooling as heat from within the containment is transferred to the water flowing over the same. The water is heated by heat transfer and then evaporated and removed by the air flow. After an initial period of about three to four days when core decay heat is greatest, air flow alone is sufficient to cool the containment.

STAR FORMATION ACTIVITY IN CLASH BRIGHTEST CLUSTER GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fogarty, Kevin; Postman, Marc; Connor, Thomas

2015-11-10

The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5σ) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and Hα+[N ii] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR ≳ 100 M{sub ⊙} yr{sup −1}. These measurements are supplemented with [O ii], [O iii], and Hβ fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing starmore » formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9+3021, and create 2D maps of stellar properties on scales down to ∼350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ∼0.5–1.0 Gyr timescales, although some filaments are consistent with much younger (≲100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions.« less

The dance of heating and cooling in galaxy clusters: three-dimensional simulations of self-regulated active galactic nuclei outflows

NASA Astrophysics Data System (ADS)

Gaspari, M.; Melioli, C.; Brighenti, F.; D'Ercole, A.

2011-02-01

It is now widely accepted that heating processes play a fundamental role in galaxy clusters, struggling in an intricate but fascinating ‘dance' with its antagonist, radiative cooling. Last-generation observations, especially X-ray, are giving us tiny hints about the notes of this endless ballet. Cavities, shocks, turbulence and wide absorption lines indicate that the central active nucleus is injecting a huge amount of energy in the intracluster medium. However, which is the real dominant engine of self-regulated heating? One of the models we propose is massive subrelativistic outflows, probably generated by a wind disc or just the result of the entrainment on kpc scale by the fast radio jet. Using a modified version of the adaptive mesh refinement code FLASH 3.2, we have explored several feedback mechanisms that self-regulate the mechanical power. Two are the best schemes that answer our primary question, that is, quenching cooling flow and at the same time preserving a cool core appearance for a long-term evolution (7 Gyr): one is more explosive (with efficiencies ˜ 5 × 10-3-10-2), triggered by central cooled gas, and the other is gentler, ignited by hot gas Bondi accretion (with ɛ= 0.1). These three-dimensional simulations show that the total energy injected is not the key aspect, but the results strongly depend on how energy is given to the intracluster medium. We follow the dynamics of the best models (temperature, density, surface brightness maps and profiles) and produce many observable predictions: buoyant bubbles, ripples, turbulence, iron abundance maps and hydrostatic equilibrium deviation. We present an in-depth discussion of the merits and flaws of all our models, with a critical eye towards observational concordance.

Core-melt source reduction system

DOEpatents

Forsberg, C.W.; Beahm, E.C.; Parker, G.W.

1995-04-25

A core-melt source reduction system for ending the progression of a molten core during a core-melt accident and resulting in a stable solid cool matrix. The system includes alternating layers of a core debris absorbing material and a barrier material. The core debris absorbing material serves to react with and absorb the molten core such that containment overpressurization and/or failure does not occur. The barrier material slows the progression of the molten core debris through the system such that the molten core has sufficient time to react with the core absorbing material. The system includes a provision for cooling the glass/molten core mass after the reaction such that a stable solid cool matrix results. 4 figs.

Core-melt source reduction system

DOEpatents

Forsberg, Charles W.; Beahm, Edward C.; Parker, George W.

1995-01-01

A core-melt source reduction system for ending the progression of a molten core during a core-melt accident and resulting in a stable solid cool matrix. The system includes alternating layers of a core debris absorbing material and a barrier material. The core debris absorbing material serves to react with and absorb the molten core such that containment overpressurization and/or failure does not occur. The barrier material slows the progression of the molten core debris through the system such that the molten core has sufficient time to react with the core absorbing material. The system includes a provision for cooling the glass/molten core mass after the reaction such that a stable solid cool matrix results.

Magnetic suspension using high temperature superconducting cores

NASA Technical Reports Server (NTRS)

Scurlock, R. G.

1992-01-01

The development of YBCO high temperature superconductors, in wire and tape forms, is rapidly approaching the point where the bulk transport current density j vs magnetic field H characteristics with liquid nitrogen cooling will enable its use in model cores. On the other hand, BSCCO high temperature superconductor in wire form has poor j-H characteristics at 77 K today, although with liquid helium or hydrogen cooling, it appears to be superior to NbTi superconductor. Since liquid nitrogen cooling is approx. 100 times cheaper than liquid helium cooling, the use of YBCO is very attractive for use in magnetic suspension. The design is discussed of a model core to accommodate lift and drag loads up to 6000 and 3000 N respectively. A comparison is made between the design performance of a liquid helium cooled NbTi (or BSCCO) superconducting core and a liquid nitrogen cooled YBCO superconducting core.

10 CFR Appendix A to Part 50 - General Design Criteria for Nuclear Power Plants

Code of Federal Regulations, 2012 CFR

2012-01-01

... Heat Removal 34 Emergency Core Cooling 35 Inspection of Emergency Core Cooling System 36 Testing of Emergency Core Cooling System 37 Containment Heat Removal 38 Inspection of Containment Heat Removal System 39 Testing of Containment Heat Removal System 40 Containment Atmosphere Cleanup 41 Inspection of...

10 CFR Appendix A to Part 50 - General Design Criteria for Nuclear Power Plants

Code of Federal Regulations, 2011 CFR

2011-01-01

... Heat Removal 34 Emergency Core Cooling 35 Inspection of Emergency Core Cooling System 36 Testing of Emergency Core Cooling System 37 Containment Heat Removal 38 Inspection of Containment Heat Removal System 39 Testing of Containment Heat Removal System 40 Containment Atmosphere Cleanup 41 Inspection of...

Cool Star Beginnings: YSOs in the Perseus Molecular Cloud

NASA Astrophysics Data System (ADS)

Young, Kaisa E.; Young, Chadwick H.

2015-01-01

Nearby molecular clouds, where there is considerable evidence of ongoing star formation, provide the best opportunity to observe stars in the earliest stages of their formation. The Perseus molecular cloud contains two young clusters, IC 348 and NGC 1333 and several small dense cores of the type that produce only a few stars. Perseus is often cited as an intermediate case between quiescent low-mass and turbulent high-mass clouds, making it perhaps an ideal environment for studying ``typical low-mass star formation. We present an infrared study of the Perseus molecular cloud with data from the Spitzer Space Telescope as part of the ``From Molecular Cores to Planet Forming Disks (c2d) Legacy project tep{eva03}. By comparing Spitzer's near- and mid-infrared maps, we identify and classify the young stellar objects (YSOs) in the cloud using updated extinction corrected photometry. Virtually all of the YSOs in Perseus are forming in the clusters and other smaller associations at the east and west ends of the cloud with very little evidence of star formation in the midsection even in areas of high extinction.

A ROSAT HRI observation of the cooling flow cluster MS0839.9+2938.

NASA Astrophysics Data System (ADS)

Nesci, R.; Perola, G. C.; Wolter, A.

1995-07-01

A ROSAT HRI observation of the cluster MS0839.9+2938 at z=0.194 is presented. It confirms the earlier suggestion, based on the detection of extended Hα emission, that the inner regions of this cluster are dominated by a cooling flow. Within the cooling radius a marginally significant evidence is found of structures in the surface brightness, which are similar to those more significantly found in two less distant cooling flow clusters (A2029 and 2A0335+096). We note that, although its barycentre falls on top of the central giant elliptical galaxy, the azimuthally averaged brightness distribution does not peak at that position and actually stays flat out to about 40kpc (10") from the galaxy centre. From comparison with the two clusters mentioned above, this situation seems peculiar, and it is suggested that it could arise from photoelectric absorption by cold gas within the cooling flow, with an equivalent column density in the order of 5x10^21^/cm^2^ within ~10" from the centre, a factor 2-3 higher than the column spectroscopically detected in the comparison clusters.

A Supervised Statistical Learning Approach for Accurate Legionella pneumophila Source Attribution during Outbreaks

PubMed Central

Buultjens, Andrew H.; Chua, Kyra Y. L.; Baines, Sarah L.; Kwong, Jason; Gao, Wei; Cutcher, Zoe; Adcock, Stuart; Ballard, Susan; Schultz, Mark B.; Tomita, Takehiro; Subasinghe, Nela; Carter, Glen P.; Pidot, Sacha J.; Franklin, Lucinda; Seemann, Torsten; Gonçalves Da Silva, Anders

2017-01-01

ABSTRACT Public health agencies are increasingly relying on genomics during Legionnaires' disease investigations. However, the causative bacterium (Legionella pneumophila) has an unusual population structure, with extreme temporal and spatial genome sequence conservation. Furthermore, Legionnaires' disease outbreaks can be caused by multiple L. pneumophila genotypes in a single source. These factors can confound cluster identification using standard phylogenomic methods. Here, we show that a statistical learning approach based on L. pneumophila core genome single nucleotide polymorphism (SNP) comparisons eliminates ambiguity for defining outbreak clusters and accurately predicts exposure sources for clinical cases. We illustrate the performance of our method by genome comparisons of 234 L. pneumophila isolates obtained from patients and cooling towers in Melbourne, Australia, between 1994 and 2014. This collection included one of the largest reported Legionnaires' disease outbreaks, which involved 125 cases at an aquarium. Using only sequence data from L. pneumophila cooling tower isolates and including all core genome variation, we built a multivariate model using discriminant analysis of principal components (DAPC) to find cooling tower-specific genomic signatures and then used it to predict the origin of clinical isolates. Model assignments were 93% congruent with epidemiological data, including the aquarium Legionnaires' disease outbreak and three other unrelated outbreak investigations. We applied the same approach to a recently described investigation of Legionnaires' disease within a UK hospital and observed a model predictive ability of 86%. We have developed a promising means to breach L. pneumophila genetic diversity extremes and provide objective source attribution data for outbreak investigations. IMPORTANCE Microbial outbreak investigations are moving to a paradigm where whole-genome sequencing and phylogenetic trees are used to support epidemiological investigations. It is critical that outbreak source predictions are accurate, particularly for pathogens, like Legionella pneumophila, which can spread widely and rapidly via cooling system aerosols, causing Legionnaires' disease. Here, by studying hundreds of Legionella pneumophila genomes collected over 21 years around a major Australian city, we uncovered limitations with the phylogenetic approach that could lead to a misidentification of outbreak sources. We implement instead a statistical learning technique that eliminates the ambiguity of inferring disease transmission from phylogenies. Our approach takes geolocation information and core genome variation from environmental L. pneumophila isolates to build statistical models that predict with high confidence the environmental source of clinical L. pneumophila during disease outbreaks. We show the versatility of the technique by applying it to unrelated Legionnaires' disease outbreaks in Australia and the UK. PMID:28821546

A cooling flow in a high-redshift, X-ray-selected cluster of galaxies

NASA Astrophysics Data System (ADS)

Nesci, Roberto; Gioia, Isabella M.; Maccacaro, Tommaso; Morris, Simon L.; Perola, Giuseppe C.; Schild, Rudolph E.; Wolter, Anna

1989-09-01

The X-ray cluster of galaxies IE 0839.9 + 2938 was serendipitously discovered with the Einstein Observatory. CCD imaging at R and V wavelengths show that the color of the dominant elliptical galaxy of this cluster is significantly bluer than the colors of the next brightest cluster galaxies. Strong emission lines, typical of cD galaxies with cooling flows, are present in the spectrum of the dominant galaxy, from which a redshift of 0.193 is derived. The emitting line region is spatially resolved with an extension of about 13 kpc. All the collected data suggest that this cluster is one of the most distant cooling flow clusters known to date.

A cooling flow in a high-redshift, X-ray-selected cluster of galaxies

NASA Technical Reports Server (NTRS)

Nesci, Roberto; Perola, Giuseppe C.; Gioia, Isabella M.; Maccacaro, Tommaso; Morris, Simon L.

1989-01-01

The X-ray cluster of galaxies IE 0839.9 + 2938 was serendipitously discovered with the Einstein Observatory. CCD imaging at R and V wavelengths show that the color of the dominant elliptical galaxy of this cluster is significantly bluer than the colors of the next brightest cluster galaxies. Strong emission lines, typical of cD galaxies with cooling flows, are present in the spectrum of the dominant galaxy, from which a redshift of 0.193 is derived. The emitting line region is spatially resolved with an extension of about 13 kpc. All the collected data suggest that this cluster is one of the most distant cooling flow clusters known to date.

Deep Chandra , HST-COS, and megacam observations of the Phoenix cluster: Extreme star formation and AGN feedback on hundred kiloparsec scales

DOE PAGES

McDonald, Michael; McNamara, Brian R.; Perimeter Institute for Theoretical Physics, Waterloo; ...

2015-09-28

In this study, we present new ultraviolet, optical, and X-ray data on the Phoenix galaxy cluster (SPT-CLJ2344-4243). Deep optical imaging reveals previously undetected filaments of star formation, extending to radii of ~50–100 kpc in multiple directions. Combined UV-optical spectroscopy of the central galaxy reveals a massive (2 × 10 9 M ⊙), young (~4.5 Myr) population of stars, consistent with a time-averaged star formation rate of 610 ± 50 M ⊙ yr –1. We report a strong detection of O vi λλ1032,1038, which appears to originate primarily in shock-heated gas, but may contain a substantial contribution (>1000 M ⊙ yrmore » –1) from the cooling intracluster medium (ICM). We confirm the presence of deep X-ray cavities in the inner ~10 kpc, which are among the most extreme examples of radio-mode feedback detected to date, implying jet powers of 2 – 7 × 10 45 erg s –1. We provide evidence that the active galactic nucleus inflating these cavities may have only recently transitioned from "quasar-mode" to "radio-mode," and may currently be insufficient to completely offset cooling. A model-subtracted residual X-ray image reveals evidence for prior episodes of strong radio-mode feedback at radii of ~100 kpc, with extended "ghost" cavities indicating a prior epoch of feedback roughly 100 Myr ago. This residual image also exhibits significant asymmetry in the inner ~200 kpc (0.15R 500), reminiscent of infalling cool clouds, either due to minor mergers or fragmentation of the cooling ICM. Taken together, these data reveal a rapidly evolving cool core which is rich with structure (both spatially and in temperature), is subject to a variety of highly energetic processes, and yet is cooling rapidly and forming stars along thin, narrow filaments.« less

HIFLUGCS: X-ray luminosity-dynamical mass relation and its implications for mass calibrations with the SPIDERS and 4MOST surveys

NASA Astrophysics Data System (ADS)

Zhang, Yu-Ying; Reiprich, Thomas H.; Schneider, Peter; Clerc, Nicolas; Merloni, Andrea; Schwope, Axel; Borm, Katharina; Andernach, Heinz; Caretta, César A.; Wu, Xiang-Ping

2017-03-01

We present the relation of X-ray luminosity versus dynamical mass for 63 nearby clusters of galaxies in a flux-limited sample, the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS, consisting of 64 clusters). The luminosity measurements are obtained based on 1.3 Ms of clean XMM-Newton data and ROSAT pointed observations. The masses are estimated using optical spectroscopic redshifts of 13647 cluster galaxies in total. We classify clusters into disturbed and undisturbed based on a combination of the X-ray luminosity concentration and the offset between the brightest cluster galaxy and X-ray flux-weighted center. Given sufficient numbers (I.e., ≥45) of member galaxies when the dynamical masses are computed, the luminosity versus mass relations agree between the disturbed and undisturbed clusters. The cool-core clusters still dominate the scatter in the luminosity versus mass relation even when a core-corrected X-ray luminosity is used, which indicates that the scatter of this scaling relation mainly reflects the structure formation history of the clusters. As shown by the clusters with only few spectroscopically confirmed members, the dynamical masses can be underestimated and thus lead to a biased scaling relation. To investigate the potential of spectroscopic surveys to follow up high-redshift galaxy clusters or groups observed in X-ray surveys for the identifications and mass calibrations, we carried out Monte Carlo resampling of the cluster galaxy redshifts and calibrated the uncertainties of the redshift and dynamical mass estimates when only reduced numbers of galaxy redshifts per cluster are available. The resampling considers the SPIDERS and 4MOST configurations, designed for the follow-up of the eROSITA clusters, and was carried out for each cluster in the sample at the actual cluster redshift as well as at the assigned input cluster redshifts of 0.2, 0.4, 0.6, and 0.8. To follow up very distant clusters or groups, we also carried out the mass calibration based on the resampling with only ten redshifts per cluster, and redshift calibration based on the resampling with only five and ten redshifts per cluster, respectively. Our results demonstrate the power of combining upcoming X-ray and optical spectroscopic surveys for mass calibration of clusters. The scatter in the dynamical mass estimates for the clusters with at least ten members is within 50%.

AGN Feedback and Cooling Flows: Problems with Simple Hydrodynamic Models

NASA Astrophysics Data System (ADS)

Vernaleo, John C.; Reynolds, Christopher S.

2006-07-01

In recent years it has become increasingly clear that active galactic nuclei, and radio galaxies in particular, have an impact on large-scale structure and galaxy formation. In principle, radio galaxies are energetic enough to halt the cooling of the virialized intracluster medium (ICM) in the inner regions of galaxy clusters, solving the cooling flow problem and explaining the high-mass truncation of the galaxy luminosity function. We explore this process through a series of high-resolution, three-dimensional hydrodynamic simulations of jetted active galaxies that act in response to cooling-mediated accretion of an ICM atmosphere. We find that our models are incapable of producing a long-term balance of heating and cooling; catastrophic cooling can be delayed by the jet action but inevitably takes hold. At the heart of the failure of these models is the formation of a low-density channel through which the jet can freely flow, carrying its energy out of the cooling core. It is possible that this failure is due to an oversimplified treatment of the fast jet (which may underestimate the ``dentist drill'' effect). However, it seems likely that additional complexity (large-angle jet precession or ICM turbulence) or additional physics (magnetohydrodynamic effects and plasma transport processes) is required to produce a spatial distribution of jet heating that can prevent catastrophic cooling. This work also underscores the importance of including jet dynamics in any feedback model, as opposed to the isotropically inflated bubble approach taken in some previous works.

CHANDRA Observations OF The Shock Heated Gas Around 3c 288 And 3c 449

NASA Astrophysics Data System (ADS)

Lal, Dharam V.; Kraft, R. P.; Evans, D. A.; Hardcastle, M. J.; Nulsen, P. E. J.; Croston, J. H.; Forman, W. R.; Jones, C.; Lee, J. C.

2010-03-01

The inflation of radio bubbles in the hot gas atmospheres of clusters of galaxies plays an important role in the overall energy budget of the ICM. Regular gentle (i.e. subsonic) nuclear outbursts may be able to provide sufficient energy to the gas in the cool cores of clusters to offset radiative losses and regulate large cooling flows; and one method to supplement the total energy input into the gas is for the lobes to initially drive strong shocks into the gas. We present results from Chandra/ACIS-S observations of the hot gas atmospheres of two powerful, nearby radio galaxies in poor clusters: 3C 288 and 3C 449. We measure the total energy of the current outburst to be a few times 10^{59} ergs for 3C 288 (T = 2.8 keV, L_X = 1.4 × 10^{44} ergs) and ˜10^{58} ergs for 3C 449 (T = 1.5 keV, L_X = 2.0 × 10^{42} ergs). We find multiple surface brightness discontinuities in the gas, which are probably shocks and are indicative of supersonic heating by the inflation of the radio lobe. We do not find X-ray cavity in 3C 288, whereas cavities are associated with both the radio lobes in 3C 449.

The Hot Phase of a Cold Black Hole Fountain: Unifying Chandra with ALMA

NASA Astrophysics Data System (ADS)

Tremblay, Grant

2016-09-01

A stunning new ALMA observation of the Cool Core Cluster Abell 2597 has revealed that a supermassive black hole can act much like a mechanical pump in a water fountain, inflating a billion solar mass radially expanding molecular bubble that is pushed far out into the galaxy outskirts, only to fall back inward again to feed the AGN. Previous 120 ksec Chandra observations show that this fountain exists amid exquisitely complex X-ray structures, including what may be the first direct observational evidence in support of buoyant X-ray cavity heating models invoked to inhibit cooling flows at late epochs. Mapping the hot phase of the fountain, however, remains impossible absent more X-ray counts. We propose a deep Legacy-class observation to illustrate the combined power of Chandra and ALMA.

Stripped interstellar gas in cluster cooling flows

NASA Technical Reports Server (NTRS)

Soker, Noam; Bregman, Joel N.; Sarazin, Craig L.

1991-01-01

It is suggested that nonlinear perturbations which lead to thermal instabilities in cooling flows might start as blobs of interstellar gas which are stipped out of cluster galaxies. Assuming that most of the gas produced by stellar mass loss in cluster galaxies is stripped from the galaxies, the total rate of such stripping is roughly 100 solar masses/yr, which is similar to the rates of cooling in cluster cooling flows. It is possible that a substantial portion of the cooling gas originates as blobs of interstellar gas stripped from galaxies. The magnetic fields within and outside of the low-entropy perturbations may help to maintain their identities by suppressing both thermal conduction and Kelvin-Helmholtz instabilities. These density fluctuations may disrupt the propagation of radio jets through the intracluster gas, which may be one mechanism for producing wideangle-tail radio galaxies.

The Inhomogeneous Centers of Cooling Flows in Galaxy Clusters

NASA Astrophysics Data System (ADS)

Sharma, Mangala

2004-04-01

The intracluster medium (ICM) in the centers of galaxy clusters is cool, dense and may be imhomogeneous. We present Chandra X-ray Observatory imaging spectroscopic data on two galaxy clusters, Abell 1991 and MS 0839.8+2938, that have cooling flows in their central few hundred kpc. Their cD galaxies show current star formation, and host compact radio sources. The hot ICM at both their centers has nonhomogeneities on kiloparsec scales. These finer structures are likely to be signatures of the formation of clusters through infall of smaller, cooler subclusters.

A Gemini view of the galaxy cluster RXC J1504-0248: insights on the nature of the central gaseous filaments

NASA Astrophysics Data System (ADS)

Soja, A. C.; Sodré, L.; Monteiro-Oliveira, R.; Cypriano, E. S.; Lima Neto, G. B.

2018-07-01

We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a structure with a strong cool core in a near redshift (z = 0.216). We performed a combined analysis using photometric and spectroscopic data obtained at Gemini South Telescope. We estimated the cluster mass through gravitational lensing, obtaining M200 = 5.3 ± 0.4 × 1014 h_{70}^{-1} M⊙ within R200 = 1.56 ± 0.04 h^{-1}_{70} Mpc, in agreement with a virial mass estimate. This cluster presents a prominent filamentary structure associated with its brightest cluster galaxy, located mainly along its major axis and aligned with the X-ray emission. A combined study of three emission line diagnostic diagrams has shown that the filament emission falls in the so-called transition region of these diagrams. Consequently, several ionizing sources should be playing a meaningful role. We have argued that old stars, often invoked to explain low-ionization nuclear emission-line region emission, should not be the major source of ionization. We have noticed that most of the filamentary emission has line ratios consistent with the shock excitation limits obtained from shock models. We also found that line fluxes are related to gas velocities (here estimated from line widths) by power laws with slopes in the range expected from shock models. These models also show, however, that only ˜10 per cent of H α luminosity can be explained by shocks. We conclude that shocks probably associated with the cooling of the intracluster gas in a filamentary structure may indeed be contributing to the filament nebular emission, but cannot be the major source of ionizing photons.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ueda, Shutaro; Hayashida, Kiyoshi; Anabuki, Naohisa

We report the Suzaku/XIS and HXD and Chandra/ACIS-I results on the X-ray spectra of the Phoenix cluster at the redshift z = 0.596. The spectrum of the intracluster medium (ICM) is well reproduced with the emissions from low-temperature (∼3.0 keV and ∼0.76 solar) and high-temperature (∼11 keV and ∼0.33 solar) plasmas; the former is localized at the cluster core, while the latter distributes over the cluster. In addition to these ICM emissions, a strongly absorbed power-law component is found, which is due to an active galactic nucleus (AGN) in the cluster center. The absorption column density and unobscured luminosity ofmore » the AGN are ∼3.2 × 10{sup 23} cm{sup –2} and ∼4.7 × 10{sup 45} erg s{sup –1} (2-10 keV), respectively. Furthermore, a neutral iron (Fe I) K-shell line is discovered for the first time with the equivalent width (EW) of ∼150 eV at the rest frame. The column density and the EW of the Fe I line are exceptionally large for such a high-luminosity AGN, and hence the AGN is classified as a type 2 quasi-stellar object (QSO). We speculate that a significant fraction of the ICM cooled gas would be consumed to maintain the torus and to activate the type 2 QSO. The Phoenix cluster has a massive starburst in the central galaxy, indicating that suppression in the cooling flow is less effective. This may be because the onset of the latest AGN feedback has occurred recently and has not yet been effective. Alternatively, the AGN feedback is predominantly in radiative mode, not in kinetic mode, and the torus may work as a shield to reduce its effect.« less

Analysis of Mass Profiles and Cooling Flows of Bright, Early-Type Galaxies AO2, AO3 and Surface Brightness Profiles and Energetics of Intracluster Gas in Cool Galaxy Clusters AO3

NASA Technical Reports Server (NTRS)

White, Raymond E., III

1998-01-01

This final report uses ROSAT observations to analyze two different studies. These studies are: Analysis of Mass Profiles and Cooling Flows of Bright, Early-Type Galaxies; and Surface Brightness Profiles and Energetics of Intracluster Gas in Cool Galaxy Clusters.

Chandra Observation of the WAT Radio Source/ICM Interaction in Abell 623

NASA Astrophysics Data System (ADS)

Anand, Gagandeep; Blanton, Elizabeth L.; Randall, Scott W.; Paterno-Mahler, Rachel; Douglass, Edmund

2017-01-01

Galaxy clusters are important objects for studying the physics of the intracluster medium (ICM), galaxy formation and evolution, and cosmological parameters. Clusters containing wide-angle tail (WAT) radio sources are particularly valuable for studies of the interaction between these sources and the surrounding ICM. These sources are thought to form when the ram pressure from the ICM caused by the relative motion between the host radio galaxy and the cluster bends the radio lobes into a distinct wide-angle morphology. We present our results from the analysis of a Chandra observation of the nearby WAT hosting galaxy cluster Abell 623. A clear decrement in X-ray emission is coincident with the southern radio lobe, consistent with being a cavity carved out by the radio source. We present profiles of surface brightness, temperature, density, and pressure and find evidence for a possible shock. Based on the X-ray pressure in the vicinity of the radio lobes and assumptions about the content of the lobes, we estimate the relative ICM velocity required to bend the lobes into the observed angle. We also present spectral model fits to the overall diffuse cluster emission and see no strong signature for a cool core. The sum of the evidence indicates that Abell 623 may be undergoing a large scale cluster-cluster merger.

A cooling flow in a high-redshift, X-ray-selected cluster of galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nesci, R.; Perola, G.C.; Gioia, I.M.

The X-ray cluster of galaxies IE 0839.9 + 2938 was serendipitously discovered with the Einstein Observatory. CCD imaging at R and V wavelengths show that the color of the dominant elliptical galaxy of this cluster is significantly bluer than the colors of the next brightest cluster galaxies. Strong emission lines, typical of cD galaxies with cooling flows, are present in the spectrum of the dominant galaxy, from which a redshift of 0.193 is derived. The emitting line region is spatially resolved with an extension of about 13 kpc. All the collected data suggest that this cluster is one of themore » most distant cooling flow clusters known to date. 28 refs.« less

LITHIUM DEPLETION IS A STRONG TEST OF CORE-ENVELOPE RECOUPLING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Somers, Garrett; Pinsonneault, Marc H., E-mail: somers@astronomy.ohio-state.edu

2016-09-20

Rotational mixing is a prime candidate for explaining the gradual depletion of lithium from the photospheres of cool stars during the main sequence. However, previous mixing calculations have relied primarily on treatments of angular momentum transport in stellar interiors incompatible with solar and stellar data in the sense that they overestimate the internal differential rotation. Instead, recent studies suggest that stars are strongly differentially rotating at young ages but approach a solid body rotation during their lifetimes. We modify our rotating stellar evolution code to include an additional source of angular momentum transport, a necessary ingredient for explaining the openmore » cluster rotation pattern, and examine the consequences for mixing. We confirm that core-envelope recoupling with a ∼20 Myr timescale is required to explain the evolution of the mean rotation pattern along the main sequence, and demonstrate that it also provides a more accurate description of the Li depletion pattern seen in open clusters. Recoupling produces a characteristic pattern of efficient mixing at early ages and little mixing at late ages, thus predicting a flattening of Li depletion at a few Gyr, in agreement with the observed late-time evolution. Using Li abundances we argue that the timescale for core-envelope recoupling during the main sequence decreases sharply with increasing mass. We discuss the implications of this finding for stellar physics, including the viability of gravity waves and magnetic fields as agents of angular momentum transport. We also raise the possibility of intrinsic differences in initial conditions in star clusters using M67 as an example.« less

Effects of Cooling During Exercise on Thermoregulatory Responses of Men With Paraplegia.

PubMed

Bongers, Coen C W G; Eijsvogels, Thijs M H; van Nes, Ilse J W; Hopman, Maria T E; Thijssen, Dick H J

2016-05-01

People with spinal cord injury (SCI) have an altered afferent input to the thermoregulatory center, resulting in a reduced efferent response (vasomotor control and sweating capacity) below the level of the lesion. Consequently, core body temperature rises more rapidly during exercise in individuals with SCI compared with people who are able-bodied. Cooling strategies may reduce the thermophysiological strain in SCI. The aim of this study was to examine the effects of a cooling vest on the core body temperature response of people with a thoracic SCI during submaximal exercise. Ten men (mean age=44 years, SD=11) with a thoracic lesion (T4-T5 or below) participated in this randomized crossover study. Participants performed two 45-minute exercise bouts at 50% maximal workload (ambient temperature 25°C), with participants randomized to a group wearing a cooling vest or a group wearing no vest (separate days). Core body temperature and skin temperature were continuously measured, and thermal sensation was assessed every 3 minutes. Exercise resulted in an increased core body temperature, skin temperature, and thermal sensation, whereas cooling did not affect core body temperature. The cooling vest effectively decreased skin temperature, increased the core-to-trunk skin temperature gradient, and tended to lower thermal sensation compared with the control condition. The lack of differences in core body temperature among conditions may be a result of the relative moderate ambient temperature in which the exercise was performed. Despite effectively lowering skin temperature and increasing the core-to-trunk skin temperature gradient, there was no impact of the cooling vest on the exercise-induced increase in core body temperature in men with low thoracic SCI. © 2016 American Physical Therapy Association.

Special Session 2: Cosmic Evolution of Groups and Clusters

NASA Astrophysics Data System (ADS)

Vrtilek, J. M.; David, L. P.

2015-03-01

During the past decade observations across the electromagnetic spectrum have led to broad progress in the understanding of galaxy clusters and their far more abundant smaller siblings, groups. From the X-rays, where Chandra and XMM have illuminated old phenomena such as cooling cores and discovered new ones such as shocks, cold fronts, bubbles and cavities, through rich collections of optical data (including vast and growing arrays of redshifts), to the imaging of AGN outbursts of various ages through radio observations, our access to cluster and group measurements has leaped forward, while parallel advances in theory and modeling have kept pace. This Special Session offered a survey of progress to this point, an assessment of outstanding problems, and a multiwavelength overview of the uses of the next generation of observatories. Holding the symposium in conjuction with the XXVIIIth General Assembly provided the significant advantage of involving not only a specialist audience, but also interacting with a broad cross-section of the world astronomical community.

Beyond Hydrodynamic Modeling of AGN Heating in Galaxy Clusters

NASA Astrophysics Data System (ADS)

Yang, Hsiang-Yi Karen

Clusters of galaxies hold a unique position in hierarchical structure formation - they are both powerful cosmological probes and excellent astrophysical laboratories. Accurate modeling of the cluster properties is crucial for reducing systematic uncertainties in cluster cosmology. However, theoretical modeling of the intracluster medium (ICM) has long suffered from the "cooling-flow problem" - clusters with short central times or cool cores (CCs) are predicted to host massive inflows of gas that are not observed. Feedback from active galactic nuclei (AGN) is by far the most promising heating mechanism to counteract radiative cooling. Recent hydrodynamic simulations have made remarkable progress reproducing properties of the CCs. However, there remain two major questions that cannot be probed using purely hydrodynamic models: (1) what are the roles of cosmic rays (CRs)? (2) how is the existing picture altered when the ICM is modeled as weakly collisional plasma? We propose to move beyond limitations of pure hydrodynamics and progress toward a complete understanding of how AGN jet-inflated bubbles interact with their surroundings and provide heat to the ICM. Our objectives include: (1) understand how CR-dominated bubbles heat the ICM; (2) understand bubble evolution and sound-wave dissipation in the ICM with different assumptions of plasma properties, e.g., collisionality of the ICM, with or without anisotropic transport processes; (3) Develop a subgrid model of AGN heating that can be adopted in cosmological simulations based on state-of-the-art isolated simulations. We will use a combination of analytical calculations and idealized simulations to advance our understanding of each individual physical process. We will then perform the first three-dimensional (3D) magnetohydrodynamic (MHD) simulations of self-regulated AGN feedback with relevant CR and anisotropic transport processes in order to quantify the amount and distribution of heating from the AGN. Our proposed work will elucidate the poorly understood CR and anisotropic transport processes in the weakly collisional ICM and shed light on the long-standing mystery of AGN heating in CC clusters. Our investigation, which incorporates plasma effects into fluid models and provides physical foundation for cosmological simulations, will serve as an important bridge between physics on both micro and macro scales. This study will enable robust modeling of the radio-mode feedback of AGN in cosmological simulations of cluster and galaxy formation. It will also directly impact observational studies of clusters including NASA missions such as Chandra, XMM-Newton, Astro-H/Hitomi, Fermi, HST, and Planck.

Earth's Fiercely Cooling Core - 24 TW

NASA Astrophysics Data System (ADS)

Morgan, Jason P.; Vannucchi, Paola

2014-05-01

Earth's mantle and core are convecting planetary heat engines. The mantle convects to lose heat from slow cooling, internal radioactivity, and core heatflow across its base. Its convection generates plate tectonics, volcanism, and the loss of ~35 TW of mantle heat through Earth's surface. The core convects to lose heat from slow cooling, small amounts of internal radioactivity, and the freezing-induced growth of a compositionally denser inner core. Core convection produces the geodynamo generating Earth's geomagnetic field. The geodynamo was thought to be powered by ~4 TW of heatloss across the core-mantle boundary, a rate sustainable (cf. Gubbins et al., 2003; Nimmo, 2007) by freezing a compositionally denser inner core over the ~3 Ga that Earth is known to have had a strong geomagnetic field (cf. Tarduno, 2007). However, recent determinations of the outer core's thermal conductivity(Pozzo et al., 2012; Gomi et al., 2013) indicate that >15 TW of power should conduct down its adiabat. Conducted power is unavailable to drive thermal convection, implying that the geodynamo needs a long-lived >17 TW power source. Core cooling was thought too weak for this, based on estimates for the Clapeyron Slope for high-pressure freezing of an idealized pure-iron core. Here we show that the ~500-1000 kg/m3 seismically-inferred jump in density between the liquid outer core and solid inner core allows us to directly infer the core-freezing Clapeyron Slope for the outer core's actual composition which contains ~8±2% lighter elements (S,Si,O,Al, H,…) mixed into a Fe-Ni alloy. A PREM-like 600 kg/m3 - based Clapeyron Slope implies there has been ~774K of core cooling during the freezing and growth of the inner core, releasing ~24 TW of power during the past ~3 Ga. If so, core cooling can easily power Earth's long-lived geodynamo. Another major implication of ~24 TW heatflow across the core-mantle boundary is that the present-day mantle is strongly 'bottom-heated', and diapiric mantle plumes should dominate deep mantle upwelling.

Modeling and Comparison of Options for the Disposal of Excess Weapons Plutonium in Russia

DTIC Science & Technology

2002-04-01

fuel LWR cooling time LWR Pu load rate LWR net destruction frac ~ LWR reactors op life mox core frac Excess Separated Pu HTGR Cycle Pu in Waste LWR MOX...reflecting the cycle used in this type of reactor. For the HTGR , the entire core consists of plutonium fuel , therefore a core fraction is not specified...cooling time Time spent fuel unloaded from HTGR reactor must cool before permanently stored 3 years Mox core fraction Fraction of

Boiling water neutronic reactor incorporating a process inherent safety design

DOEpatents

Forsberg, C.W.

1985-02-19

A boiling-water reactor core is positioned within a prestressed concrete reactor vessel of a size which will hold a supply of coolant water sufficient to submerge and cool the reactor core by boiling for a period of at least one week after shutdown. Separate volumes of hot, clean (nonborated) water for cooling during normal operation and cool highly borated water for emergency cooling and reactor shutdown are separated by an insulated wall during normal reactor operation with contact between the two water volumes being maintained at interfaces near the top and bottom ends of the reactor vessel. Means are provided for balancing the pressure of the two water volumes at the lower interface zone during normal operation to prevent entry of the cool borated water into the reactor core region, for detecting the onset of excessive power to coolant flow conditions in the reactor core and for detecting low water levels of reactor coolant. Cool borated water is permitted to flow into the reactor core when low reactor coolant levels or excessive power to coolant flow conditions are encountered.

Boiling water neutronic reactor incorporating a process inherent safety design

DOEpatents

Forsberg, Charles W.

1987-01-01

A boiling-water reactor core is positioned within a prestressed concrete reactor vessel of a size which will hold a supply of coolant water sufficient to submerge and cool the reactor core by boiling for a period of at least one week after shutdown. Separate volumes of hot, clean (non-borated) water for cooling during normal operation and cool highly borated water for emergency cooling and reactor shutdown are separated by an insulated wall during normal reactor operation with contact between the two water volumes being maintained at interfaces near the top and bottom ends of the reactor vessel. Means are provided for balancing the pressure of the two volumes at the lower interface zone during normal operation to prevent entry of the cool borated water into the reactor core region, for detecting the onset of excessive power to coolant flow conditions in the reactor core and for detecting low water levels of reactor coolant. Cool borated water is permitted to flow into the reactor core when low reactor coolant levels or excessive power to coolant flow conditions are encountered.

THE X-RAY SPECTRUM OF THE COOLING-FLOW QUASAR H1821+643: A MASSIVE BLACK HOLE FEEDING OFF THE INTRACLUSTER MEDIUM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, Christopher S.; Lohfink, Anne M.; Babul, Arif

2014-09-10

We present a deep Suzaku observation of H1821+643, an extremely rare example of a powerful quasar hosted by the central massive galaxy of a rich cooling-core cluster of galaxies. Informed by previous Chandra studies of the cluster, we achieve a spectral separation of emission from the active galactic nucleus (AGN) and the intracluster medium (ICM). With a high degree of confidence, we identify the signatures of X-ray reflection/reprocessing by cold and slowly moving material in the AGN's immediate environment. The iron abundance of this matter is found to be significantly sub-solar (Z ≈ 0.4 Z {sub ☉}), an unusual findingmore » for powerful AGN but in line with the idea that this quasar is feeding from the ICM via a Compton-induced cooling flow. We also find a subtle soft excess that can be described phenomenologically (with an additional blackbody component) or as ionized X-ray reflection from the inner regions of a high inclination (i ≈ 57°) accretion disk around a spinning (a > 0.4) black hole. We describe how the ionization state of the accretion disk can be used to constrain the Eddington fraction of the source. Applying these arguments to our spectrum implies an Eddington fraction of 0.25-0.5, with an associated black hole mass of 3--6×10{sup 9} M{sub ⊙}.« less

Black Hole Accretion and Feedback Driven by Thermal Instability

NASA Astrophysics Data System (ADS)

Gaspari, M.; Ruszkowski, M.; Oh, S. P.; Churazov, E.; Brighenti, F.; Ettori, S.; Sharma, P.; Temi, P.

2013-03-01

Multiwavelength data indicate that the cores of several galaxy clusters are moderately cooling, though not catastrophically, showing signs of filamentary extended multiphase gas. Through 3D AMR hydrodynamic simulations, we study the impact of thermal instability in the evolution of the intracluster medium. Common moderate turbulence of just over 100 km/s leads to the growth of nonlinear thermal instability within the central few tens kpc. In the presence of a global counterbalancing heating, the condensation of extended filamentary cold gas is violent, occurring when the cooling time falls below 10 times the free-fall time. The frequent stochastic collisions, fragmentations and shearing motions between the cold clouds, filaments and the central torus, efficiently reduce angular momentum. Tracking the accreting gas with a dynamical range of 10 million, we find that the accretion rate is boosted up to 100 times with respect to the Bondi rate. In a commonly turbulent and quasi-stable atmosphere, the mode of black accretion is cold and chaotic, substantially different from the classic idealized scenario. Only in the transonic regime, turbulent dissipation starts to inhibit thermal instability. On sub-parsec scales the cold phase is channeled via a funnel, triggering the black hole feedback likely linked to mechanical jets/outflows. As shown by long-term self-regulated simulations, the interplay of chaotic cold accretion and AGN feedback is crucial in order to avoid the cooling catastrophe and to reproduce the key thermodynamical features of observed clusters.

Apparatus and method for controlling the temperature of the core of a super-conducting transformer

DOEpatents

Golner, Thomas; Pleva, Edward; Mehta, Shirish

2006-10-10

An apparatus for controlling the temperature of a core of a transformer is provided that includes a core, a shield surrounding the core, a cast formed between the core and the shield, and tubing positioned on the shield. The cast directs heat from the core to the shield and cooling fluid is directed through the tubing to cool the shield.

Cooling system for a nuclear reactor

DOEpatents

Amtmann, Hans H.

1982-01-01

A cooling system for a gas-cooled nuclear reactor is disclosed which includes at least one primary cooling loop adapted to pass coolant gas from the reactor core and an associated steam generator through a duct system having a main circulator therein, and at least one auxiliary cooling loop having communication with the reactor core and adapted to selectively pass coolant gas through an auxiliary heat exchanger and circulator. The main and auxiliary circulators are installed in a common vertical cavity in the reactor vessel, and a common return duct communicates with the reactor core and intersects the common cavity at a junction at which is located a flow diverter valve operative to effect coolant flow through either the primary or auxiliary cooling loops.

Cooling of Accretion-Heated Neutron Stars

NASA Astrophysics Data System (ADS)

Wijnands, Rudy; Degenaar, Nathalie; Page, Dany

2017-09-01

We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.

THE BLUE HOOK POPULATIONS OF MASSIVE GLOBULAR CLUSTERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Thomas M.; Smith, Ed; Sweigart, Allen V.

2010-08-01

We present new Hubble Space Telescope ultraviolet color-magnitude diagrams of five massive Galactic globular clusters: NGC 2419, NGC 6273, NGC 6715, NGC 6388, and NGC 6441. These observations were obtained to investigate the 'blue hook' (BH) phenomenon previously observed in UV images of the globular clusters {omega} Cen and NGC 2808. Blue hook stars are a class of hot (approximately 35,000 K) subluminous horizontal branch stars that occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. By coupling new stellar evolution models to appropriate non-LTE synthetic spectra, we investigate various theoretical explanations for thesemore » stars. Specifically, we compare our photometry to canonical models at standard cluster abundances, canonical models with enhanced helium (consistent with cluster self-enrichment at early times), and flash-mixed models formed via a late helium-core flash on the white dwarf cooling curve. We find that flash-mixed models are required to explain the faint luminosity of the BH stars, although neither the canonical models nor the flash-mixed models can explain the range of color observed in such stars, especially those in the most metal-rich clusters. Aside from the variation in the color range, no clear trends emerge in the morphology of the BH population with respect to metallicity.« less

Gravitational Conundrum? Dynamical Mass Segregation versus Disruption of Binary Stars in Dense Stellar Systems

NASA Astrophysics Data System (ADS)

de Grijs, Richard; Li, Chengyuan; Zheng, Yong; Deng, Licai; Hu, Yi; Kouwenhoven, M. B. N.; Wicker, James E.

2013-03-01

Upon their formation, dynamically cool (collapsing) star clusters will, within only a few million years, achieve stellar mass segregation for stars down to a few solar masses, simply because of gravitational two-body encounters. Since binary systems are, on average, more massive than single stars, one would expect them to also rapidly mass segregate dynamically. Contrary to these expectations and based on high-resolution Hubble Space Telescope observations, we show that the compact, 15-30 Myr old Large Magellanic Cloud cluster NGC 1818 exhibits tantalizing hints at the >~ 2σ level of significance (>3σ if we assume a power-law secondary-to-primary mass-ratio distribution) of an increasing fraction of F-star binary systems (with combined masses of 1.3-1.6 M ⊙) with increasing distance from the cluster center, specifically between the inner 10''-20'' (approximately equivalent to the cluster's core and half-mass radii) and the outer 60''-80''. If confirmed, then this will offer support for the theoretically predicted but thus far unobserved dynamical disruption processes of the significant population of "soft" binary systems—with relatively low binding energies compared to the kinetic energy of their stellar members—in star clusters, which we have access to here by virtue of the cluster's unique combination of youth and high stellar density.

A spin-down clock for cool stars from observations of a 2.5-billion-year-old cluster.

PubMed

Meibom, Søren; Barnes, Sydney A; Platais, Imants; Gilliland, Ronald L; Latham, David W; Mathieu, Robert D

2015-01-29

The ages of the most common stars--low-mass (cool) stars like the Sun, and smaller--are difficult to derive because traditional dating methods use stellar properties that either change little as the stars age or are hard to measure. The rotation rates of all cool stars decrease substantially with time as the stars steadily lose their angular momenta. If properly calibrated, rotation therefore can act as a reliable determinant of their ages based on the method of gyrochronology. To calibrate gyrochronology, the relationship between rotation period and age must be determined for cool stars of different masses, which is best accomplished with rotation period measurements for stars in clusters with well-known ages. Hitherto, such measurements have been possible only in clusters with ages of less than about one billion years, and gyrochronology ages for older stars have been inferred from model predictions. Here we report rotation period measurements for 30 cool stars in the 2.5-billion-year-old cluster NGC 6819. The periods reveal a well-defined relationship between rotation period and stellar mass at the cluster age, suggesting that ages with a precision of order 10 per cent can be derived for large numbers of cool Galactic field stars.

The JCMT Gould Belt Survey: Dense Core Clusters in Orion B

NASA Astrophysics Data System (ADS)

Kirk, H.; Johnstone, D.; Di Francesco, J.; Lane, J.; Buckle, J.; Berry, D. S.; Broekhoven-Fiene, H.; Currie, M. J.; Fich, M.; Hatchell, J.; Jenness, T.; Mottram, J. C.; Nutter, D.; Pattle, K.; Pineda, J. E.; Quinn, C.; Salji, C.; Tisi, S.; Hogerheijde, M. R.; Ward-Thompson, D.; The JCMT Gould Belt Survey Team

2016-04-01

The James Clerk Maxwell Telescope Gould Belt Legacy Survey obtained SCUBA-2 observations of dense cores within three sub-regions of Orion B: LDN 1622, NGC 2023/2024, and NGC 2068/2071, all of which contain clusters of cores. We present an analysis of the clustering properties of these cores, including the two-point correlation function and Cartwright’s Q parameter. We identify individual clusters of dense cores across all three regions using a minimal spanning tree technique, and find that in each cluster, the most massive cores tend to be centrally located. We also apply the independent M-Σ technique and find a strong correlation between core mass and the local surface density of cores. These two lines of evidence jointly suggest that some amount of mass segregation in clusters has happened already at the dense core stage.

XMM-Newton Observations of the Cluster of Galaxies Sersic 159-03

NASA Technical Reports Server (NTRS)

Kaastra, J. S.; Ferrigno, C.; Tamura, T.; Paerels, F. B. S.; Peterson, J. R.; Mittaz, J. P. D.

2000-01-01

The cluster of galaxies Sersic 159-03 was observed with the XMM-Newton X-ray observatory as part of the Guaranteed Time program. X-ray spectra taken with the EPIC and RGS instruments show no evidence for the strong cooling flow derived from previous X-ray observations. There is a significant lack of cool gas below 1.5 keV as compared to standard isobaric cooling flow models. While the oxygen is distributed more or less uniformly over the cluster, iron shows a strong concentration in the center of the cluster, slightly offset from the brightness center but within the central cD galaxy. This points to enhanced type Ia supernova activity in the center of the cluster. There is also an elongated iron-rich structure ex- tending to the east of the cluster, showing the inhomogeneity of the iron distribution. Finally, the temperature drops rapidly beyond 4' from the cluster center.

Star Formation Activity in CLASH Brightest Cluster Galaxies

NASA Astrophysics Data System (ADS)

Fogarty, Kevin; Postman, Marc; Connor, Thomas; Donahue, Megan; Moustakas, John

2015-11-01

The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5σ) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and Hα+[N ii] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR ≳ 100 M⊙ yr-1. These measurements are supplemented with [O ii], [O iii], and Hβ fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing star formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9+3021, and create 2D maps of stellar properties on scales down to ˜350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ˜0.5-1.0 Gyr timescales, although some filaments are consistent with much younger (≲100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

Origin of central abundances in the hot intra-cluster medium. I. Individual and average abundance ratios from XMM-Newton EPIC

NASA Astrophysics Data System (ADS)

Mernier, F.; de Plaa, J.; Pinto, C.; Kaastra, J. S.; Kosec, P.; Zhang, Y.-Y.; Mao, J.; Werner, N.

2016-08-01

The hot intra-cluster medium (ICM) is rich in metals, which are synthesised by supernovae (SNe) explosions and accumulate over time into the deep gravitational potential well of clusters of galaxies. Since most of the elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse (SNcc) supernovae, measuring their abundances gives us direct information on the nucleosynthesis products of billions of SNe since the epoch of the star formation peak (z ~ 2-3). In this study, we use the EPIC and RGS instruments on board XMM-Newton to measure the abundances of nine elements (O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni) from a sample of 44 nearby cool-core galaxy clusters, groups, and elliptical galaxies. We find that the Fe abundance shows a large scatter (~20-40%) over the sample, within 0.2r500 and especially 0.05r500. Unlike the absolute Fe abundance, the abundance ratios (X/Fe) are uniform over the considered temperature range (~0.6-8 keV) and with a limited scatter. In addition to an unprecedented treatment of systematic uncertainties, we provide the most accurate abundance ratios measured so far in the ICM, including Cr/Fe and Mn/Fe which we firmly detected (>4σ with MOS and pn independently). We find that Cr/Fe, Mn/Fe, and Ni/Fe differ significantly from the proto-solar values. However, the large uncertainties in the proto-solar abundances prevent us from making a robust comparison between the local and the intra-cluster chemical enrichments. We also note that, interestingly, and despite the large net exposure time (~4.5 Ms) of our dataset, no line emission feature is seen around ~3.5 keV.

Active galactic nucleus feedback in clusters of galaxies

PubMed Central

Blanton, Elizabeth L.; Clarke, T. E.; Sarazin, Craig L.; Randall, Scott W.; McNamara, Brian R.

2010-01-01

Observations made during the last ten years with the Chandra X-ray Observatory have shed much light on the cooling gas in the centers of clusters of galaxies and the role of active galactic nucleus (AGN) heating. Cooling of the hot intracluster medium in cluster centers can feed the supermassive black holes found in the nuclei of the dominant cluster galaxies leading to AGN outbursts which can reheat the gas, suppressing cooling and large amounts of star formation. AGN heating can come in the form of shocks, buoyantly rising bubbles that have been inflated by radio lobes, and the dissipation of sound waves. PMID:20351250

Abundance gradients in cooling flow clusters: Ginga Large Area Counters and Einstein Solid State Spectrometer spectra of A496, A1795, A2142, and A2199

NASA Technical Reports Server (NTRS)

White, Raymond E., III; Day, C. S. R.; Hatsukade, Isamu; Hughes, John P.

1994-01-01

We analyze the Ginga Large Area Counters (LAC) and Einstein Solid State Spectrometer (SSS) spectra of four cooling flow clusters, A496, A1795, A2142, and A2199, each of which shows firm evidence of a relatively cool component. The inclusion of such cool spectral components in joint fits of SSS and LAC data leads to somewhat higher global temperatures than are derived from the high-energy LAC data alone. We find little evidence of cool emission outside the SSS field of view. Metal abundances appear to be centrally enhanced in all four clusters, with varying degrees of model dependence and statistical significance: the evidence is statistically strongest for A496 and A2142, somewhat weaker for A2199 and weakest for A1795. We also explore the model dependence in the amount of cold, X-ray-absorbing matter discovered in these clusters by White et al.

Evaluation of 2 Heat-Mitigation Methods in Army Trainees.

PubMed

Sefton, JoEllen M; McAdam, J S; Pascoe, David D; Lohse, K R; Banda, Robert L; Henault, Corbin B; Cherrington, Andrew R; Adams, N E

2016-11-01

 Heat injury is a significant threat to military trainees. Different methods of heat mitigation are in use across military units. Mist fans are 1 of several methods used in the hot and humid climate of Fort Benning, Georgia.  To determine if (1) the mist fan or the cooling towel effectively lowered participant core temperature in the humid environment found at Fort Benning and (2) the mist fan or the cooling towel presented additional physiologic or safety benefits or detriments when used in this environment.  Randomized controlled clinical trial.  Laboratory environmental chamber.  Thirty-five physically active men aged 19 to 35 years.  (1) Mist fan, (2) commercial cooling towel, (3) passive-cooling (no intervention) control. All treatments lasted 20 minutes. Participants ran on a treadmill at 60% V̇o 2 max.  Rectal core temperature, heart rate, thermal comfort, perceived temperature, perceived wetness, and blood pressure.  Average core temperature increased during 20 minutes of cooling (F 1,28 = 64.76, P < .001, η p 2 = 0.70), regardless of group (F 1,28 = 3.41, P = .08, η p 2 = 0.11) or condition (F 1,28 < 1.0). Core temperature, heart rate, and blood pressure did not differ among the 3 conditions. Perceived temperature during 20 minutes of cooling decreased (F 1,30 = 141.19, P < .001, η p 2 = 0.83) regardless of group or condition. Perceived temperature was lower with the mist-fan treatment than with the control treatment (F 1,15 = 7.38, P = .02, η p 2 = 0.32). The mist-fan group perceived themselves to be cooler even at elevated core temperatures.  The mist fan and cooling towel were both ineffective at lowering core temperature. Core temperature continued to increase after exercise in all groups. The mist fan produced feelings of coolness while the core temperature remained elevated, possibly increasing the risk of heat illness.

Evaluation of 2 Heat-Mitigation Methods in Army Trainees

PubMed Central

Sefton, JoEllen M.; McAdam, J. S.; Pascoe, David D.; Lohse, K. R.; Banda, Robert L.; Henault, Corbin B.; Cherrington, Andrew R.; Adams, N. E.

2016-01-01

Context: Heat injury is a significant threat to military trainees. Different methods of heat mitigation are in use across military units. Mist fans are 1 of several methods used in the hot and humid climate of Fort Benning, Georgia. Objectives: To determine if (1) the mist fan or the cooling towel effectively lowered participant core temperature in the humid environment found at Fort Benning and (2) the mist fan or the cooling towel presented additional physiologic or safety benefits or detriments when used in this environment. Design: Randomized controlled clinical trial. Setting: Laboratory environmental chamber. Patients or Other Participants: Thirty-five physically active men aged 19 to 35 years. Intervention(s): (1) Mist fan, (2) commercial cooling towel, (3) passive-cooling (no intervention) control. All treatments lasted 20 minutes. Participants ran on a treadmill at 60% V̇o2max. Main Outcome Measure(s): Rectal core temperature, heart rate, thermal comfort, perceived temperature, perceived wetness, and blood pressure. Results: Average core temperature increased during 20 minutes of cooling (F1,28 = 64.76, P < .001, ηp2 = 0.70), regardless of group (F1,28 = 3.41, P = .08, ηp2 = 0.11) or condition (F1,28 < 1.0). Core temperature, heart rate, and blood pressure did not differ among the 3 conditions. Perceived temperature during 20 minutes of cooling decreased (F1,30 = 141.19, P < .001, ηp2 = 0.83) regardless of group or condition. Perceived temperature was lower with the mist-fan treatment than with the control treatment (F1,15 = 7.38, P = .02, ηp2 = 0.32). The mist-fan group perceived themselves to be cooler even at elevated core temperatures. Conclusions: The mist fan and cooling towel were both ineffective at lowering core temperature. Core temperature continued to increase after exercise in all groups. The mist fan produced feelings of coolness while the core temperature remained elevated, possibly increasing the risk of heat illness. PMID:27710091

The X-ray ribs within the cocoon shock of Cygnus A

NASA Astrophysics Data System (ADS)

Duffy, R. T.; Worrall, D. M.; Birkinshaw, M.; Nulsen, P. E. J.; Wise, M. W.; de Vries, M. N.; Snios, B.; Mathews, W. G.; Perley, R. A.; Hardcastle, M. J.; Rafferty, D. A.; McNamara, B. R.; Edge, A. C.; McKean, J. P.; Carilli, C. L.; Croston, J. H.; Godfrey, L. E. H.; Laing, R. A.

2018-06-01

We use new and archival Chandra observations of Cygnus A, totalling ˜1.9 Ms, to investigate the distribution and temperature structure of gas lying within the projected extent of the cocoon shock and exhibiting a rib-like structure. We confirm that the X-rays are dominated by thermal emission with an average temperature of around 4 keV, and have discovered an asymmetry in the temperature gradient, with the southwestern part of the gas cooler than the rest by up to 2 keV. Pressure estimates suggest that the gas is a coherent structure of single origin located inside the cocoon, with a mass of roughly 2 × 1010 M⊙. We conclude that the gas is debris resulting from disintegration of the cool core of the Cygnus A cluster after the passage of the jet during the early stages of the current epoch of activity. The 4 keV gas now lies on the central inside surface of the hotter cocoon rim. The temperature gradient could result from an offset between the centre of the cluster core and the Cygnus A host galaxy at the switch-on of current radio activity.

Late-time Cooling of Neutron Star Transients and the Physics of the Inner Crust

NASA Astrophysics Data System (ADS)

Deibel, Alex; Cumming, Andrew; Brown, Edward F.; Reddy, Sanjay

2017-04-01

An accretion outburst onto a neutron star transient heats the neutron star’s crust out of thermal equilibrium with the core. After the outburst, the crust thermally relaxes toward equilibrium with the neutron star core, and the surface thermal emission powers the quiescent X-ray light curve. Crust cooling models predict that thermal equilibrium of the crust will be established ≈ 1000 {days} into quiescence. Recent observations of the cooling neutron star transient MXB 1659-29, however, suggest that the crust did not reach thermal equilibrium with the core on the predicted timescale and continued to cool after ≈ 2500 {days} into quiescence. Because the quiescent light curve reveals successively deeper layers of the crust, the observed late-time cooling of MXB 1659-29 depends on the thermal transport in the inner crust. In particular, the observed late-time cooling is consistent with a low thermal conductivity layer near the depth predicted for nuclear pasta that maintains a temperature gradient between the neutron star’s inner crust and core for thousands of days into quiescence. As a result, the temperature near the crust-core boundary remains above the critical temperature for neutron superfluidity, and a layer of normal neutrons forms in the inner crust. We find that the late-time cooling of MXB 1659-29 is consistent with heat release from a normal neutron layer near the crust-core boundary with a long thermal time. We also investigate the effect of inner crust physics on the predicted cooling curves of the accreting transient KS 1731-260 and the magnetar SGR 1627-41.

The Physics of Cooling Flow Clusters with Central Radio Sources

NASA Technical Reports Server (NTRS)

Sarazin, Craig L.

2005-01-01

Central galaxies in rich clusters are the sites of cluster cooling flows, with large masses of gas cooling through part of the X-ray band. Many of these galaxies host powerful radio sources. These sources can displace and compress the X-ray gas leading to enhanced cooling and star formation. We observed the bright cooling flow Abell 2626 with a strangely distorted central radio source. We wished to understand the interaction of radio and X-ray thermal plasma, and to determine the dynamical nature of this cluster. One aim was to constrain the source of additional pressure in radio "holes" in the X-ray emission needed to support overlying shells of X-ray gas. We also aimed to study the problem of the lack of kT < 1-2 keV gas in cooling flows by searching for abundance inhomogeneities, heating from the radio source, and excess absorption. We also have a Chandra observation of this cluster. There were problems with the pipeline processing of this data due to a telemetry dropout. We are publishing the Chandra and XMM data together. Delays with the Chandra data have slowed up the publication. At the center of the cluster, there is a complex interaction of the odd, Z-shaped radio source, and the X-ray plasma. However, there are no clear radio bubbles. Also, the cluster SO galaxy IC 5337, which is projected 1.5 arcmin west of the cluster center, has unusual tail-like structures in both the radio and X-ray. It appears to be falling into the cluster center. There is a hot, probably shocked region of gas to the southwest, which is apparently due to the merger of a subcluster in this part of the system. There is also a merging subcluster to the northeast. The axes of these two mergers agrees with a supercluster filament structure.

Flash Mixing on the White-Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808

NASA Technical Reports Server (NTRS)

Brown, Thomas M.; Sweigart, Allen V.; Lanz, Thierry; Landsman, Wayne B.; Hubeny, Ivan; Fisher, Richard R. (Technical Monitor)

2001-01-01

We present an ultraviolet color-magnitude diagram (CMD) spanning the hot horizontal branch (HB), blue straggler, and white dwarf populations of the globular cluster NGC 2808. These data, obtained with the Space Telescope Imaging Spectrograph (STIS), demonstrate that NGC 2808 harbors a significant population of hot subluminous HB stars, an anomaly only previously reported for the globular cluster omega Cen. Our theoretical modeling indicates that the location of these subluminous stars in the CMD, as well as the high temperature gap along the HB of NGC 2808, can be explained if these stars underwent a late helium-core flash while descending the white dwarf cooling curve. We show that the convective zone produced by such a late helium flash will penetrate into the hydrogen envelope, thereby mixing hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the "born again" scenario for producing hydrogen-deficient stars following a late helium-shell flash. The flash mixing of the envelope greatly enhances the envelope helium and carbon abundances that, in turn, leads to a discontinuous increase in the HB effective temperatures. We argue that the hot HB gap is associated with this theoretically predicted dichotomy in the HB properties. Moreover, the changes in the emergent spectral energy distribution caused by these abundance changes are primarily responsible for explaining the hot subluminous HB stars. Although further evidence is needed to confirm that a late helium-core flash can account for the subluminous HB stars and the hot HB gap, we demonstrate that an understanding of these stars requires the use of appropriate theoretical models for their evolution, atmospheres, and spectra.

Average Heating Rate of Hot Atmospheres in Distant Galaxy Clusters by Radio AGN: Evidence for Continuous AGN Heating

NASA Astrophysics Data System (ADS)

Ma, Cheng-Jiun; McNamara, B.; Nulsen, P.; Schaffer, R.

2011-09-01

X-ray observations of nearby clusters and galaxies have shown that energetic feedback from AGN is heating hot atmospheres and is probably the principal agent that is offsetting cooling flows. Here we examine AGN heating in distant X-ray clusters by cross correlating clusters selected from the 400 Square Degree X-ray Cluster survey with radio sources in the NRAO VLA Sky Survey. The jet power for each radio source was determined using scaling relations between radio power and cavity power determined for nearby clusters, groups, and galaxies with atmospheres containing X-ray cavities. Roughly 30% of the clusters show radio emission above a flux threshold of 3 mJy within the central 250 kpc that is presumably associated with the brightest cluster galaxy. We find no significant correlation between radio power, hence jet power, and the X-ray luminosities of clusters in redshift range 0.1 -- 0.6. The detection frequency of radio AGN is inconsistent with the presence of strong cooling flows in 400SD, but cannot rule out the presence of weak cooling flows. The average jet power of central radio AGN is approximately 2 10^{44} erg/s. The jet power corresponds to an average heating of approximately 0.2 keV/particle for gas within R_500. Assuming the current AGN heating rate remained constant out to redshifts of about 2, these figures would rise by a factor of two. Our results show that the integrated energy injected from radio AGN outbursts in clusters is statistically significant compared to the excess entropy in hot atmospheres that is required for the breaking of self-similarity in cluster scaling relations. It is not clear that central AGN in 400SD clusters are maintained by a self-regulated feedback loop at the base of a cooling flow. However, they may play a significant role in preventing the development of strong cooling flows at early epochs.

THE COOLING REQUIREMENTS AND PROCESS SYSTEMS OF THE SOUTH AFRICAN RESEARCH REACTOR, SAFARI 1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Colley, J.R.

1962-12-01

The SAFARI 1 research reactor is cooled and moderated by light water. There are three process systems, a primary water system which cools the reactor core and surroundings, a pool water system, and a secondary water system which removes the heat from the primary and pool systems. The cooling requirements for the reactor core and experimental facilities are outlined, and the cooling and purification functions of the three process systems are described. (auth)

A Gemini view of the galaxy cluster RXC J1504-0248: insights on the nature of the central gaseous filaments

NASA Astrophysics Data System (ADS)

Soja, A. C.; Sodré, L., Jr.; Monteiro-Oliveira, R.; Cypriano, E. S.; Lima Neto, G. B.

2018-03-01

We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a structure with a strong cool core in a near redshift (z = 0.216). We performed a combined analysis using photometric and spectroscopic data obtained at Gemini South Telescope. We estimated the cluster mass through gravitational lensing, obtaining M200 = 5.3 ± 0.4 × 1014h_{70}^{-1} M⊙ within R200 = 1.56 ± 0.04 h^{-1}_{70} Mpc, in agreement with a virial mass estimate. This cluster presents a prominent filamentary structure associated to its BCG, located mainly along its major axis and aligned with the X-ray emission. A combined study of three emission line diagnostic diagrams has shown that the filament emission falls in the so-called transition region of these diagrams. Consequently, several ionizing sources should be playing an meaningful role. We have argued that old stars, often invoked to explain LINER emission, should not be the major source of ionization. We have noticed that most of the filamentary emission has line ratios consistent with the shock excitation limits obtained from shock models. We also found that line fluxes are related to gas velocities (here estimated from line widths) by power-laws with slopes in the range expected from shock models. These models also show, however, that only ˜10% of Hα luminosity can be explained by shocks. We conclude that shocks probably associated to the cooling of the intracluster gas in a filamentary structure may indeed be contributing to the filament nebular emission, but can not be the major source of ionizing photons.

Cluster fescue (Festuca paradoxa Desv.): A multipurpose native cool-season grass

Treesearch

Nadia E. Navarrete-Tindall; J.W. Van Sambeek; R.A. Pierce

2005-01-01

Native cool-season grasses (NCSG) are adapted to a wide range of habitats and environmental conditions, and cluster fescue (Festuca paradoxa Desv.) is no exception. Cluster fescue can be found in unplowed upland prairies, prairie draws, savannas, forest openings, and glades (Aiken et al. 1996). Although its range includes 23 states in the continental...

Reconstruction of a digital core containing clay minerals based on a clustering algorithm.

PubMed

He, Yanlong; Pu, Chunsheng; Jing, Cheng; Gu, Xiaoyu; Chen, Qingdong; Liu, Hongzhi; Khan, Nasir; Dong, Qiaoling

2017-10-01

It is difficult to obtain a core sample and information for digital core reconstruction of mature sandstone reservoirs around the world, especially for an unconsolidated sandstone reservoir. Meanwhile, reconstruction and division of clay minerals play a vital role in the reconstruction of the digital cores, although the two-dimensional data-based reconstruction methods are specifically applicable as the microstructure reservoir simulation methods for the sandstone reservoir. However, reconstruction of clay minerals is still challenging from a research viewpoint for the better reconstruction of various clay minerals in the digital cores. In the present work, the content of clay minerals was considered on the basis of two-dimensional information about the reservoir. After application of the hybrid method, and compared with the model reconstructed by the process-based method, the digital core containing clay clusters without the labels of the clusters' number, size, and texture were the output. The statistics and geometry of the reconstruction model were similar to the reference model. In addition, the Hoshen-Kopelman algorithm was used to label various connected unclassified clay clusters in the initial model and then the number and size of clay clusters were recorded. At the same time, the K-means clustering algorithm was applied to divide the labeled, large connecting clusters into smaller clusters on the basis of difference in the clusters' characteristics. According to the clay minerals' characteristics, such as types, textures, and distributions, the digital core containing clay minerals was reconstructed by means of the clustering algorithm and the clay clusters' structure judgment. The distributions and textures of the clay minerals of the digital core were reasonable. The clustering algorithm improved the digital core reconstruction and provided an alternative method for the simulation of different clay minerals in the digital cores.

Joint scaling properties of Sunyaev-Zel'dovich and optical richness observables in an optically-selected galaxy cluster sample

NASA Astrophysics Data System (ADS)

Greer, Christopher Holland

Galaxy cluster abundance measurements are an important tool used to study the universe as a whole. The advent of multiple large-area galaxy cluster surveys across multiple ensures that cluster measurements will play a key role in understanding the dark energy currently thought to be accelerating the universe. The main systematic limitation at the moment is the understanding of the observable-mass relation. Recent theoretical work has shown that combining samples of clusters from surveys at different wavelengths can mitigate this systematic limitation. Precise measurements of the scatter in the observable-mass relation can lead to further improvements. We present Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations of the Sunyaev-Zel'dovich (SZ) signal for 28 galaxy clusters selected from the Sloan Digital Sky Survey (SDSS) maxBCG catalog. This cluster sample represents a complete, volume-limited sample of the richest galaxy clusters in the SDSS between redshifts 0.2 ≥ z ≥ 0.3, as measured by the RedMaPPer algorithm being developed for the Dark Energy Survey (DES; Rykoff et al. 2012). We develop a formalism that uses the cluster abundance in tandem with the galaxy richness measurements from SDSS and the SZ signal measurements from CARMA to calibrate the SZ and optical observable-mass relations. We find that the scatter in richness at fixed mass is σlog λ| M = 0.24+0.09-0.07 using SZ signal calculated by integrating a cluster pressure profile to a radius of 1 Mpc at the redshift of the cluster. We also calculate the SZ signal at R500 and find that the choice of scaling relation used to determined R500 has a non-trivial effect on the constraints of the observable-mass relationship. Finally, we investigate the source of disagreement between the positions of the SZ signal and SDSS Brightest Cluster Galaxies (BCGs). Improvements to the richness calculator that account for blue BCGs in the cores of cool-core X-ray clusters, as well as multiple BCGs in merger situations will help reduce σ log λ|M further. This work is the first independent calibration of the RedMaPPer algorithm that is being designed for the Dark Energy Survey.

Gas-cooled nuclear reactor

DOEpatents

Peinado, Charles O.; Koutz, Stanley L.

1985-01-01

A gas-cooled nuclear reactor includes a central core located in the lower portion of a prestressed concrete reactor vessel. Primary coolant gas flows upward through the core and into four overlying heat-exchangers wherein stream is generated. During normal operation, the return flow of coolant is between the core and the vessel sidewall to a pair of motor-driven circulators located at about the bottom of the concrete pressure vessel. The circulators repressurize the gas coolant and return it back to the core through passageways in the underlying core structure. If during emergency conditions the primary circulators are no longer functioning, the decay heat is effectively removed from the core by means of natural convection circulation. The hot gas rising through the core exits the top of the shroud of the heat-exchangers and flows radially outward to the sidewall of the concrete pressure vessel. A metal liner covers the entire inside concrete surfaces of the concrete pressure vessel, and cooling tubes are welded to the exterior or concrete side of the metal liner. The gas coolant is in direct contact with the interior surface of the metal liner and transfers its heat through the metal liner to the liquid coolant flowing through the cooling tubes. The cooler gas is more dense and creates a downward convection flow in the region between the core and the sidewall until it reaches the bottom of the concrete pressure vessel when it flows radially inward and up into the core for another pass. Water is forced to flow through the cooling tubes to absorb heat from the core at a sufficient rate to remove enough of the decay heat created in the core to prevent overheating of the core or the vessel.

Faint blue counts from formation of dwarf galaxies at z approximately equals 1

NASA Technical Reports Server (NTRS)

Babul, Arif; Rees, Martin J.

1993-01-01

The nature of faint blue objects (FBO's) has been a source of much speculation since their detection in deep CCD images of the sky. Their high surface density argues against them being progenitors of present-day bright galaxies and since they are only weakly clustered on small scales, they cannot be entities that merged together to form present-day galaxies. Babul & Rees (1992) have suggested that the observed faint blue counts may be due to dwarf elliptical galaxies undergoing their initial starburst at z is approximately equal to 1. In generic hierarchical clustering scenarios, however, dwarf galaxy halos (M is approximately 10(exp 9) solar mass) are expected to form at an earlier epoch; for example, typical 10(exp 9) solar mass halos will virialize at z is approximately equal to 2.3 if the power-spectrum for the density fluctuations is that of the standard b = 2 cold dark matter (CDM) model. Under 'ordinary conditions' the gas would rapidly cool, collect in the cores, and undergo star-formation. Conditions at high redshifts are far from 'ordinary'. The intense UV background will prevent the gas in the dwarf halos from cooling, the halos being released from their suspended state only when the UV flux has diminished sufficiently.

Shivering heat production and core cooling during head-in and head-out immersion in 17 degrees C water.

PubMed

Pretorius, Thea; Cahill, Farrell; Kocay, Sheila; Giesbrecht, Gordon G

2008-05-01

Many cold-water scenarios cause the head to be partially or fully immersed (e.g., ship wreck survival, scuba diving, cold-water adventure swim racing, cold-water drowning, etc.). However, the specific effects of head cold exposure are minimally understood. This study isolated the effect of whole-head submersion in cold water on surface heat loss and body core cooling when the protective shivering mechanism was intact. Eight healthy men were studied in 17 degrees C water under four conditions: the body was either insulated or exposed, with the head either out of the water or completely submersed under the water within each insulated/exposed subcondition. Submersion of the head (7% of the body surface area) in the body-exposed condition increased total heat loss by 11% (P < 0.05). After 45 min, head-submersion increased core cooling by 343% in the body-insulated subcondition (head-out: 0.13 +/- 0.2 degree C, head-in: 0.47 +/- 0.3 degree C; P < 0.05) and by 56% in the body-exposed subcondition (head-out: 0.40 +/- 0.3 degree C and head-in: 0.73 +/- 0.6 degree C; P < 0.05). In both body-exposed and body-insulated subconditions, head submersion increased the rate of core cooling disproportionally more than the relative increase in total heat loss. This exaggerated core-cooling effect is consistent with a head cooling induced reduction of the thermal core, which could be stimulated by cooling of thermosensitive and/or trigeminal receptors in the scalp, neck, and face. These cooling effects of head submersion are not prevented by shivering heat production.

Numerical models of jet disruption in cluster cooling flows

NASA Technical Reports Server (NTRS)

Loken, Chris; Burns, Jack O.; Roettiger, Kurt; Norman, Mike

1993-01-01

We present a coherent picture for the formation of the observed diverse radio morphological structures in dominant cluster galaxies based on the jet Mach number. Realistic, supersonic, steady-state cooling flow atmospheres are evolved numerically and then used as the ambient medium through which jets of various properties are propagated. Low Mach number jets effectively stagnate due to the ram pressure of the cooling flow atmosphere while medium Mach number jets become unstable and disrupt in the cooling flow to form amorphous structures. High Mach number jets manage to avoid disruption and are able to propagate through the cooling flow.

The AGN-driven shock in NGC 4472

NASA Astrophysics Data System (ADS)

Gendron-Marsolais, Marie-Lou; Kraft, Ralph P.; Bogdan, Akos; Forman, William R.; Hlavacek-Larrondo, Julie; Jones, Christine; Nulsen, Paul; Randall, Scott W.; Roediger, Elke

2016-04-01

Chandra observations of most cool core clusters of galaxies have revealed large cavities where the inflation of the jet-driven radio bubbles displace the cluster gas. In a few cases, outburst shocks, likely driven by cavity inflation, are detected in the ambient gas. AGN-driven shocks may be key to balancing the radiative losses as shocks will increase the entropy of, and thereby heat, the diffuse gas. We will present initial results on deep Chandra observations of the nearby (D=17 Mpc) early-type massive elliptical galaxy NGC 4472, the most optically luminous galaxy in the local Universe, lying on the outskirts of the Virgo cluster. The X-ray observations show clear cavities in the X-ray emission at the position of the radio lobes, and rings of enhanced X-ray emission just beyond the lobes. We will present results from our analysis to determine whether the lobes are inflating supersonically or are rising buoyantly. We will compare the energy and power of this AGN outburst with previous powerful radio outbursts in clusters and groups to determine whether this outburst lies on the same scaling relations or whether it represents a new category of outburst.

Uniform Contribution of Supernova Explosions to the Chemical Enrichment of Abell 3112 out to R{sub 200}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ezer, Cemile; Ercan, E. Nihal; Bulbul, Esra

2017-02-10

The spatial distribution of the metals residing in the intra-cluster medium (ICM) of galaxy clusters records all the information on a cluster’s nucleosynthesis and chemical enrichment history. We present measurements from a total of 1.2 Ms Suzaku XIS and 72 ks Chandra observations of the cool-core galaxy cluster Abell 3112 out to its virial radius (∼1470 kpc). We find that the ratio of the observed supernova type Ia explosions to the total supernova explosions has a uniform distribution at a level of 12%–16% out to the cluster’s virial radius. The observed fraction of type Ia supernova explosions is in agreementmore » with the corresponding fraction found in our Galaxy and the chemical enrichment of our Galaxy. The non-varying supernova enrichment suggests that the ICM in cluster outskirts was enriched by metals at an early stage before the cluster itself was formed during a period of intense star formation activity. Additionally, we find that the 2D delayed detonation model CDDT produce significantly worse fits to the X-ray spectra compared to simple 1D W7 models. This is due to the relative overestimate of Si, and the underestimate of Mg in these models with respect to the measured abundances.« less

Isolated core vs. superficial cooling effects on virtual maze navigation.

PubMed

Payne, Jennifer; Cheung, Stephen S

2007-07-01

Cold impairs cognitive performance and is a common occurrence in many survival situations. Altered behavior patterns due to impaired navigation abilities in cold environments are potential problems in lost-person situations. We investigated the separate effects of low core temperature and superficial cooling on a spatially demanding virtual navigation task. There were 12 healthy men who were passively cooled via 15 degrees C water immersion to a core temperature of 36.0 degrees C, then transferred to a warm (40 degrees C) water bath to eliminate superficial shivering while completing a series of 20 virtual computer mazes. In a control condition, subjects rested in a thermoneutral (approximately 35 degrees C) bath for a time-matched period before being transferred to a warm bath for testing. Superficial cooling and distraction were achieved by whole-body immersion in 35 degree water for a time-matched period, followed by lower leg immersion in 10 degree C water for the duration of the navigational tests. Mean completion time and mean error scores for the mazes were not significantly different (p > 0.05) across the core cooling (16.59 +/- 11.54 s, 0.91 +/- 1.86 errors), control (15.40 +/- 8.85 s, 0.82 +/- 1.76 errors), and superficial cooling (15.19 +/- 7.80 s, 0.77 +/- 1.40 errors) conditions. Separately reducing core temperature or increasing cold sensation in the lower extremities did not influence performance on virtual computer mazes, suggesting that navigation is more resistive to cooling than other, simpler cognitive tasks. Further research is warranted to explore navigational ability at progressively lower core and skin temperatures, and in different populations.

ROSAT HRI images of Abell 85 and Abell 496: Evidence for inhomogeneities in cooling flows

NASA Technical Reports Server (NTRS)

Prestwich, Andrea H.; Guimond, Stephen J.; Luginbuhl, Christian B.; Joy, Marshall

1995-01-01

We present ROSAT high-resolution images of two clusters of galaxies with cooling flows, Abell 496 and Abell 85. In these clusters, X-ray emission on small scales above the general cluster emission is significant at the 3 sigma level. There is no evidence for optical counterparts. If real, the enhancements may be associated with clumps of gas at a lower temperature and higher density than the ambient medium, or hotter, denser gas perhaps compressed by magnetic fields. These observations can be used to test models of how thermal instabilities form and evolve in cooling flows.

ROSAT HRI images of Abell 85 and Abell 496: Evidence for inhomogeneities in cooling flows

NASA Technical Reports Server (NTRS)

Prestwich, Andrea H.; Guimond, Stephen J.; Luginbuhl, Christian; Joy, Marshall

1994-01-01

We present ROSAT HRI images of two clusters of galaxies with cooling flows, Abell 496 and Abell 85. In these clusters, x-ray emission on small scales above the general cluster emission is significant at the 3 sigma level. There is no evidence for optical counterparts. The enhancements may be associated with lumps of gas at a lower temperature and higher density than the ambient medium, or hotter, denser gas perhaps compressed by magnetic fields. These observations can be used to test models of how thermal instabilities form and evolve in cooling flows.

Kinematic fingerprint of core-collapsed globular clusters

NASA Astrophysics Data System (ADS)

Bianchini, P.; Webb, J. J.; Sills, A.; Vesperini, E.

2018-03-01

Dynamical evolution drives globular clusters towards core collapse, which strongly shapes their internal properties. Diagnostics of core collapse have so far been based on photometry only, namely on the study of the concentration of the density profiles. Here, we present a new method to robustly identify core-collapsed clusters based on the study of their stellar kinematics. We introduce the kinematic concentration parameter, ck, the ratio between the global and local degree of energy equipartition reached by a cluster, and show through extensive direct N-body simulations that clusters approaching core collapse and in the post-core collapse phase are strictly characterized by ck > 1. The kinematic concentration provides a suitable diagnostic to identify core-collapsed clusters, independent from any other previous methods based on photometry. We also explore the effects of incomplete radial and stellar mass coverage on the calculation of ck and find that our method can be applied to state-of-art kinematic data sets.

Parameters of oscillation generation regions in open star cluster models

NASA Astrophysics Data System (ADS)

Danilov, V. M.; Putkov, S. I.

2017-07-01

We determine the masses and radii of central regions of open star cluster (OCL) models with small or zero entropy production and estimate the masses of oscillation generation regions in clustermodels based on the data of the phase-space coordinates of stars. The radii of such regions are close to the core radii of the OCL models. We develop a new method for estimating the total OCL masses based on the cluster core mass, the cluster and cluster core radii, and radial distribution of stars. This method yields estimates of dynamical masses of Pleiades, Praesepe, and M67, which agree well with the estimates of the total masses of the corresponding clusters based on proper motions and spectroscopic data for cluster stars.We construct the spectra and dispersion curves of the oscillations of the field of azimuthal velocities v φ in OCL models. Weak, low-amplitude unstable oscillations of v φ develop in cluster models near the cluster core boundary, and weak damped oscillations of v φ often develop at frequencies close to the frequencies of more powerful oscillations, which may reduce the non-stationarity degree in OCL models. We determine the number and parameters of such oscillations near the cores boundaries of cluster models. Such oscillations points to the possible role that gradient instability near the core of cluster models plays in the decrease of the mass of the oscillation generation regions and production of entropy in the cores of OCL models with massive extended cores.

Regulation of star formation in giant galaxies by precipitation, feedback and conduction.

PubMed

Voit, G M; Donahue, M; Bryan, G L; McDonald, M

2015-03-12

The Universe's largest galaxies reside at the centres of galaxy clusters and are embedded in hot gas that, if left undisturbed, would cool quickly and create many more new stars than are actually observed. Cooling can be regulated by feedback from accretion of cooling gas onto the central black hole, but requires an accretion rate finely tuned to the thermodynamic state of the hot gas. Theoretical models in which cold clouds precipitate out of the hot gas via thermal instability and accrete onto the black hole exhibit the necessary tuning. Recent observational evidence shows that the abundance of cold gas in the centres of clusters increases rapidly near the predicted threshold for instability. Here we report observations showing that this precipitation threshold extends over a large range in cluster radius, cluster mass and cosmic time. We incorporate the precipitation threshold into a framework of theoretical models for the thermodynamic state of hot gas in galaxy clusters. According to that framework, precipitation regulates star formation in some giant galaxies, while thermal conduction prevents star formation in others if it can compensate for radiative cooling and shut off precipitation.

Work volume and strength training responses to resistive exercise improve with periodic heat extraction from the palm.

PubMed

Grahn, Dennis A; Cao, Vinh H; Nguyen, Christopher M; Liu, Mengyuan T; Heller, H Craig

2012-09-01

Body core cooling via the palm of a hand increases work volume during resistive exercise. We asked: (a) "Is there a correlation between elevated core temperatures and fatigue onset during resistive exercise?" and (b) "Does palm cooling between sets of resistive exercise affect strength and work volume training responses?" Core temperature was manipulated by 30-45 minutes of fixed load and duration treadmill exercise in the heat with or without palm cooling. Work volume was then assessed by 4 sets of fixed load bench press exercises. Core temperatures were reduced and work volumes increased after palm cooling (Control: Tes = 39.0 ± 0.1° C, 36 ± 7 reps vs. Cooling: Tes = 38.4 ± 0.2° C, 42 ± 7 reps, mean ± SD, n = 8, p < 0.001). In separate experiments, the impact of palm cooling on work volume and strength training responses were assessed. The participants completed biweekly bench press or pull-up exercises for multiple successive weeks. Palm cooling was applied for 3 minutes between sets of exercise. Over 3 weeks of bench press training, palm cooling increased work volume by 40% (vs. 13% with no treatment; n = 8, p < 0.05). Over 6 weeks of pull-up training, palm cooling increased work volume by 144% in pull-up experienced subjects (vs. 5% over 2 weeks with no treatment; n = 7, p < 0.001) and by 80% in pull-up naïve subjects (vs. 20% with no treatment; n = 11, p < 0.01). Strength (1 repetition maximum) increased 22% over 10 weeks of pyramid bench press training (4 weeks with no treatment followed by 6 weeks with palm cooling; n = 10, p < 0.001). These results verify previous observations about the effects of palm cooling on work volume, demonstrate a link between core temperature and fatigue onset during resistive exercise, and suggest a novel means for improving strength and work volume training responses.

REVIEWS OF TOPICAL PROBLEMS: Cooling of neutron stars and superfluidity in their cores

NASA Astrophysics Data System (ADS)

Yakovlev, Dmitrii G.; Levenfish, Kseniya P.; Shibanov, Yurii A.

1999-08-01

We study the heat capacity and neutrino emission reactions (direct and modified Urca processes, nucleon-nucleon bremsstrahlung, Cooper pairing of nucleons) in the supranuclear density matter of neutron star cores with superfluid neutrons and protons. Various superfluidity types are analysed (singlet-state pairing and two types of triplet-state pairing, without and with gap nodes at the nucleon Fermi surface). The results are used for cooling simulations of isolated neutron stars. Both the standard cooling and the cooling enhanced by the direct Urca process are strongly affected by nucleon superfluidity. Comparison of the cooling theory of isolated neutron stars with observations of their thermal radiation may give stringent constraints on the critical temperatures of the neutron and proton superfluidities in the neutron star cores.

Density-based cluster algorithms for the identification of core sets

NASA Astrophysics Data System (ADS)

Lemke, Oliver; Keller, Bettina G.

2016-10-01

The core-set approach is a discretization method for Markov state models of complex molecular dynamics. Core sets are disjoint metastable regions in the conformational space, which need to be known prior to the construction of the core-set model. We propose to use density-based cluster algorithms to identify the cores. We compare three different density-based cluster algorithms: the CNN, the DBSCAN, and the Jarvis-Patrick algorithm. While the core-set models based on the CNN and DBSCAN clustering are well-converged, constructing core-set models based on the Jarvis-Patrick clustering cannot be recommended. In a well-converged core-set model, the number of core sets is up to an order of magnitude smaller than the number of states in a conventional Markov state model with comparable approximation error. Moreover, using the density-based clustering one can extend the core-set method to systems which are not strongly metastable. This is important for the practical application of the core-set method because most biologically interesting systems are only marginally metastable. The key point is to perform a hierarchical density-based clustering while monitoring the structure of the metric matrix which appears in the core-set method. We test this approach on a molecular-dynamics simulation of a highly flexible 14-residue peptide. The resulting core-set models have a high spatial resolution and can distinguish between conformationally similar yet chemically different structures, such as register-shifted hairpin structures.

CHEMICAL DIAGNOSTICS OF THE MASSIVE STAR CLUSTER-FORMING CLOUD G33.92+0.11. I. {sup 13}CS, CH{sub 3}OH, CH{sub 3}N, OCS, H{sub 2}S, SO{sub 2}, and SiO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minh, Young Chol; Liu, Hauyu Baobab; Galvań-Madrid, Roberto

2016-06-20

Large chemical diversity was found in the gas clumps associated with the massive star cluster-forming G33.92+0.11 region with sub-arcsecond angular resolution (0.″6–0.″8) observations with ALMA. The most prominent gas clumps are associated with the dust emission peaks A1, A2, and A5. The close correlation between CH{sub 3}OH and OCS in the emission distributions strongly suggests that these species share a common origin of hot core grain mantle evaporation. The latest generation of star clusters are forming in the A5 clump, as indicated by multiple SiO outflows and its rich hot core chemistry. We also found a narrow SiO emission associatedmore » with the outflows, which may trace a cooled component of the outflows. Part of the chemical complexity may have resulted from the accreting gas from the ambient clouds, especially in the northern part of A1 and the southern part of A2. The chemical diversity found in this region is believed to mainly result from the different chemical evolutionary timescales of massive star formation. In particular, the abundance ratio between CH{sub 3}OH and CH{sub 3}CN may be a good chemical clock for the early phase of star formation.« less

RF cavity using liquid dielectric for tuning and cooling

DOEpatents

Popovic, Milorad [Warrenville, IL; Johnson, Rolland P [Newport News, VA

2012-04-17

A system for accelerating particles includes an RF cavity that contains a ferrite core and a liquid dielectric. Characteristics of the ferrite core and the liquid dielectric, among other factors, determine the resonant frequency of the RF cavity. The liquid dielectric is circulated to cool the ferrite core during the operation of the system.

Study on core radius minimization for long life Pb-Bi cooled CANDLE burnup scheme based fast reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afifah, Maryam, E-mail: maryam.afifah210692@gmail.com; Su’ud, Zaki; Miura, Ryosuke

2015-09-30

Fast Breeder Reactor had been interested to be developed over the world because it inexhaustible source energy, one of those is CANDLE reactor which is have strategy in burn-up scheme, need not control roads for control burn-up, have a constant core characteristics during energy production and don’t need fuel shuffling. The calculation was made by basic reactor analysis which use Sodium coolant geometry core parameter as a reference core to study on minimum core reactor radius of CANDLE for long life Pb-Bi cooled, also want to perform pure coolant effect comparison between LBE and sodium in a same geometry design.more » The result show that the minimum core radius of Lead Bismuth cooled CANDLE is 100 cm and 500 MWth thermal output. Lead-Bismuth coolant for CANDLE reactor enable to reduce much reactor size and have a better void coefficient than Sodium cooled as the most coolant for FBR, then we will have a good point in safety analysis.« less

X-ray-emitting filaments in the cooling flow cluster A2029

NASA Technical Reports Server (NTRS)

Sarazin, Craig L.; O'Connell, Robert W.; Mcnamara, Brian R.

1992-01-01

High-resolution X-ray observations of the cluster A2029 are presented which confirm the presence of a cooling flow, despite the lack of optical line emission or evidence for recent star formation. The cooling rate and radius are about 370 solar mass/yr and 230 kpc, respectively. Emission from the inner cooling flow is dominated by a number of X-ray-emitting filaments. This may be the first case where such inhomogeneities are clearly resolved. The filaments are theorized to be supported in part by magnetic fields and may be connected with the filaments of very strong Faraday rotation seen in several nearly cooling flows.

Temperature Profiles of Different Cooling Methods in Porcine Pancreas Procurement

PubMed Central

Weegman, Brad P.; Suszynski, Thomas M.; Scott, William E.; Ferrer, Joana; Avgoustiniatos, Efstathios S.; Anazawa, Takayuki; O’Brien, Timothy D.; Rizzari, Michael D.; Karatzas, Theodore; Jie, Tun; Sutherland, David ER.; Hering, Bernhard J.; Papas, Klearchos K.

2014-01-01

Background Porcine islet xenotransplantation is a promising alternative to human islet allotransplantation. Porcine pancreas cooling needs to be optimized to reduce the warm ischemia time (WIT) following donation after cardiac death, which is associated with poorer islet isolation outcomes. Methods This study examines the effect of 4 different cooling Methods on core porcine pancreas temperature (n=24) and histopathology (n=16). All Methods involved surface cooling with crushed ice and chilled irrigation. Method A, which is the standard for porcine pancreas procurement, used only surface cooling. Method B involved an intravascular flush with cold solution through the pancreas arterial system. Method C involved an intraductal infusion with cold solution through the major pancreatic duct, and Method D combined all 3 cooling Methods. Results Surface cooling alone (Method A) gradually decreased core pancreas temperature to < 10 °C after 30 minutes. Using an intravascular flush (Method B) improved cooling during the entire duration of procurement, but incorporating an intraductal infusion (Method C) rapidly reduced core temperature 15–20 °C within the first 2 minutes of cooling. Combining all methods (Method D) was the most effective at rapidly reducing temperature and providing sustained cooling throughout the duration of procurement, although the recorded WIT was not different between Methods (p=0.36). Histological scores were different between the cooling Methods (p=0.02) and the worst with Method A. There were differences in histological scores between Methods A and C (p=0.02) and Methods A and D (p=0.02), but not between Methods C and D (p=0.95), which may highlight the importance of early cooling using an intraductal infusion. Conclusions In conclusion, surface cooling alone cannot rapidly cool large (porcine or human) pancreata. Additional cooling with an intravascular flush and intraductal infusion results in improved core porcine pancreas temperature profiles during procurement and histopathology scores. These data may also have implications on human pancreas procurement since use of an intraductal infusion is not common practice. PMID:25040217

Constraints on the interaction between dark matter and Baryons from cooling flow clusters.

PubMed

Qin, B; Wu, X P

2001-08-06

Other nongravitational heating processes are needed to resolve the disagreement between the absence of cool gas components in the centers of galaxy clusters revealed recently by Chandra and XMM observations and the expectations of conventional radiative cooling models. We propose that the interaction between dark matter and baryonic matter may act as an alternative for the reheating of intracluster medium (ICM) in the inner regions of clusters, in which kinetic energy of dark matter is transported to ICM to balance radiative cooling. Using the Chandra and XMM data, we set a useful constraint on the dark-matter-baryon cross section: sigma(xp)/m(x) approximately 1x10(-25) cm(2) GeV-1, where m(x) is the mass of dark matter particles.

Suspended-Bed Reactor preliminary design, /sup 233/U--/sup 232/Th cycle. Final report (revised)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karam, R.A.; Alapour, A.; Lee, C.C.

1977-11-01

The preliminary design Suspended-Bed Reactor is described. Coated particles about 2 mm in diameter are used as the fuel. The coatings consist of three layers: (1) low density pyrolytic graphite, 70 ..mu.. thick, (2) silicon carbide pressure vessel, 30 ..mu.. thick, and (3) ZrC layer, 50 ..mu.. thick, to protect the pressure vessel from moisture and oxygen. The fuel kernel can be either uranium-thorium dicarbide or metal. The coated particles are suspended by helium gas (coolant) in a cluster of pressurized tubes. The upward flow of helium fluidizes the coated particles. As the flow rate increases, the bed of particlesmore » is lifted upward to the core section. The particles are restrained at the upper end of the core by a suitable screen. The overall particle density in the core is just enough for criticality condition. Should the helium flow cease, the bed in the core section will collapse, and the particles will flow downward into the section where the increased physical spacings among the tubes brings about a safe shutdown. By immersing this section of the tubes in a large graphite block to serve as a heat sink, dissipation of decay heat becomes manageable. This eliminates the need for emergency core cooling systems.« less

A novel complex networks clustering algorithm based on the core influence of nodes.

PubMed

Tong, Chao; Niu, Jianwei; Dai, Bin; Xie, Zhongyu

2014-01-01

In complex networks, cluster structure, identified by the heterogeneity of nodes, has become a common and important topological property. Network clustering methods are thus significant for the study of complex networks. Currently, many typical clustering algorithms have some weakness like inaccuracy and slow convergence. In this paper, we propose a clustering algorithm by calculating the core influence of nodes. The clustering process is a simulation of the process of cluster formation in sociology. The algorithm detects the nodes with core influence through their betweenness centrality, and builds the cluster's core structure by discriminant functions. Next, the algorithm gets the final cluster structure after clustering the rest of the nodes in the network by optimizing method. Experiments on different datasets show that the clustering accuracy of this algorithm is superior to the classical clustering algorithm (Fast-Newman algorithm). It clusters faster and plays a positive role in revealing the real cluster structure of complex networks precisely.

Inert-Gas Condensed Co-W Nanoclusters: Formation, Structure and Magnetic Properties

NASA Astrophysics Data System (ADS)

Golkar-Fard, Farhad Reza

Rare-earth permanent magnets are used extensively in numerous technical applications, e.g. wind turbines, audio speakers, and hybrid/electric vehicles. The demand and production of rare-earth permanent magnets in the world has in the past decades increased significantly. However, the decrease in export of rare-earth elements from China in recent time has led to a renewed interest in developing rare-earth free permanent magnets. Elements such as Fe and Co have potential, due to their high magnetization, to be used as hosts in rare-earth free permanent magnets but a major challenge is to increase their magnetocrystalline anisotropy constant, K1, which largely drives the coercivity. Theoretical calculations indicate that dissolving the 5d transition metal W in Fe or Co increases the magnetocrystalline anisotropy. The challenge, though, is in creating a solid solution in hcp Co or bcc Fe, which under equilibrium conditions have negligible solubility. In this dissertation, the formation, structure, and magnetic properties of sub-10 nm Co-W clusters with W content ranging from 4 to 24 atomic percent were studied. Co-W alloy clusters with extended solubility of W in hcp Co were produced by inert gas condensation. The different processing conditions such as the cooling scheme and sputtering power were found to control the structural state of the as-deposited Co-W clusters. For clusters formed in the water-cooled formation chamber, the mean size and the fraction crystalline clusters increased with increasing power, while the fraction of crystalline clusters formed in the liquid nitrogen-cooled formation chamber was not as affected by the sputtering power. For the low W content clusters, the structural characterization revealed clusters predominantly single crystalline hcp Co(W) structure, a significant extension of W solubility when compared to the equilibrium solubility, but fcc Co(W) and Co3W structures were observed in very small and large clusters, respectively. At high W content, clusters with hcp Co(W), fcc Co(W) or Co3W structures were observed. The magnetic measurements at 10 K and 300 K revealed that the coercivity, saturation magnetization and magnetocrystalline anisotropy of the clusters formed in the water-cooled formation chamber were higher than for clusters formed in the liquid nitrogen-cooled formation chamber. The coercivity and magnetocrystalline anisotropy of the clusters increased as long as W was dissolved into the hcp Co structure. With increasing fraction of Co3W and fcc Co(W) clusters, as observed in the high-W content sample, the magnetic properties deteriorated significantly. The highest coercivity and magnetocrystalline anisotropy of 893 Oe and 3.9 x 106 ergs/cm3, respectively, was obtained at 10 K for the 5 at.% W clusters sputtered at 150 W in the water-cooled formation chamber.

Non-thermal emission in the core of Perseus: results from a long XMM-Newton observation

NASA Astrophysics Data System (ADS)

Molendi, S.; Gastaldello, F.

2009-01-01

We employ a long XMM-Newton observation of the core of the Perseus cluster to validate claims of a non-thermal component discovered with Chandra. From a meticulous analysis of our dataset, which includes a detailed treatment of systematic errors, we find the 2-10 keV surface brightness of the non-thermal component to be less than about 5 × 10-16 erg~cm-2 s-1 arcsec-2. The most likely explanation for the discrepancy between the XMM-Newton and Chandra estimates is a problem in the effective area calibration of the latter. Our EPIC-based magnetic field lower limits do not disagree with Faraday rotation measure estimates on a few cool cores and with a minimum energy estimate on Perseus. In the not too distant future Simbol-X may allow detection of non-thermal components with intensities more than 10 times lower than those that can be measured with EPIC; nonetheless even the exquisite sensitivity within reach for Simbol-X might be insufficient to detect the IC emission from Perseus.

Gas turbine bucket wall thickness control

DOEpatents

Stathopoulos, Dimitrios; Xu, Liming; Lewis, Doyle C.

2002-01-01

A core for use in casting a turbine bucket including serpentine cooling passages is divided into two pieces including a leading edge core section and a trailing edge core section. Wall thicknesses at the leading edge and the trailing edge of the turbine bucket can be controlled independent of each other by separately positioning the leading edge core section and the trailing edge core section in the casting die. The controlled leading and trailing edge thicknesses can thus be optimized for efficient cooling, resulting in more efficient turbine operation.

AGN Feedback And Evolution of Radio Sources: Discovery of An X-Ray Cluster Associated With Z=1 Quasar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siemiginowska, Aneta; /Harvard-Smithsonian Ctr. Astrophys.; Cheung, C.C.

2006-01-11

We report the first significant detection of an X-ray cluster associated with a powerful (L{sub bol} {approx} 10{sup 47} erg sec{sup -1}) radio-loud quasar at high redshift (z=1.06). Diffuse X-ray emission is detected out to {approx} 120 kpc from the CSS quasar 3C 186. A strong Fe-line emission at the z{sub rest} = 1.06 confirms its thermal nature. We find that the CSS radio source is highly overpressured with respect to the thermal cluster medium by 2-3 orders of magnitude. This provides direct observational evidence that the radio source is not thermally confined as posited in the ''frustrated'' scenario formore » CSS sources. Instead, the radio source may be young and at an early stage of its evolution. This source provides the first detection of the AGN in outburst in the center of a cooling flow cluster. Powerful radio sources are thought to be triggered by the cooling flows. The evidence for the AGN activity and intermittent outbursts comes from the X-ray morphology of low redshift clusters, which usually do not harbour quasars. 3C186 is a young active radio source which can supply the energy into the cluster and potentially prevent its cooling. We discuss energetics related to the quasar activity and the cluster cooling flow, and possible feedback between the evolving radio source and the cluster.« less

The history of chemical enrichment in the intracluster medium from cosmological simulations

NASA Astrophysics Data System (ADS)

Biffi, V.; Planelles, S.; Borgani, S.; Fabjan, D.; Rasia, E.; Murante, G.; Tornatore, L.; Dolag, K.; Granato, G. L.; Gaspari, M.; Beck, A. M.

2017-06-01

The distribution of metals in the intracluster medium (ICM) of galaxy clusters provides valuable information on their formation and evolution, on the connection with the cosmic star formation and on the effects of different gas processes. By analysing a sample of simulated galaxy clusters, we study the chemical enrichment of the ICM, its evolution, and its relation with the physical processes included in the simulation and with the thermal properties of the core. These simulations, consisting of re-simulations of 29 Lagrangian regions performed with an upgraded version of the smoothed particle hydrodynamics (SPH) gadget-3 code, have been run including two different sets of baryonic physics: one accounts for radiative cooling, star formation, metal enrichment and supernova (SN) feedback, and the other one further includes the effects of feedback from active galactic nuclei (AGN). In agreement with observations, we find an anti-correlation between entropy and metallicity in cluster cores, and similar radial distributions of heavy-element abundances and abundance ratios out to large cluster-centric distances (˜R180). In the outskirts, namely outside of ˜0.2 R180, we find a remarkably homogeneous metallicity distribution, with almost flat profiles of the elements produced by either SNIa or SNII. We investigated the origin of this phenomenon and discovered that it is due to the widespread displacement of metal-rich gas by early (z > 2-3) AGN powerful bursts, acting on small high-redshift haloes. Our results also indicate that the intrinsic metallicity of the hot gas for this sample is on average consistent with no evolution between z = 2 and z = 0, across the entire radial range.

The Perseus Cluster: Bridging the Extremes of Stellar Systems

NASA Astrophysics Data System (ADS)

Harris, William

2017-08-01

The Perseus cluster (Abell 426) at d=75 Mpc is as massive and diverse as Virgo and Coma and displays a rich laboratory for studying galaxy evolution. Its massive X-ray halo gas component and its high proportion of large early-type galaxies point to a long history of dynamical interaction amongst the cluster members. The central supergiant, NGC 1275, is perhaps the most active galaxy in the local universe, with a spectacular network of H-alpha filaments, cooling flows, feedback, and prominent star formation in plain view. We propose to use the Globular Cluster (GC) populations in the Perseus region with two-band imaging to pursue three connected goals: the stellar Intracluster Medium (ICM); its Ultra-Diffuse Galaxies (UDGs); and the GC populations in the Perseus core galaxies. Our analysis of a few HST/ACS Archival images covering the Perseus core strongly indicates that a substantial Intragalactic GC component is present. Our newly discovered sample of UDGs in Perseus covers the entire parameter space of these intriguing galaxies and will be thoroughly sampled in our study: are they 'failed' underluminous galaxies with high masses, or are they a mixed bag? For all our goals, the GC populations will act as powerful tracers of the dominant old stellar populations - their metallicity distributions and total populations in the ICM, the UDGs, and the three largest E galaxies in Perseus. As a bonus, we expect to find 200 new Ultra-Compact Dwarfs (UCDs) and half a dozen rare compact ellipticals (cEs). The scientific payoffs will include a broader understanding of the nature and history of all these types of galaxies and their stripped stellar material.

Ionized Gas Motions and the Structure of Feedback near a Forming Globular Cluster in NGC 5253

NASA Astrophysics Data System (ADS)

Cohen, Daniel P.; Turner, Jean L.; Consiglio, S. Michelle; Martin, Emily C.; Beck, Sara C.

2018-06-01

We observed Brackett α 4.05 μm emission toward the supernebula in NGC 5253 with NIRSPEC on Keck II in adaptive optics mode, NIRSPAO, to probe feedback from its exciting embedded super star cluster (SSC). NIRSPEC's Slit-viewing Camera was simultaneously used to image the K-band continuum at ∼0.″1 resolution. We register the IR continuum with HST imaging, and find that the visible clusters are offset from the K-band peak, which coincides with the Brα peak of the supernebula and its associated molecular cloud. The spectra of the supernebula exhibit Brα emission with a strong, narrow core. The linewidths are 65–76 km s‑1, FWHM, comparable to those around individual ultra-compact H II regions within our Galaxy. A weak, broad (FWHM ≃ 150–175 km s‑1) component is detected on the base of the line, which could trace a population of sources with high-velocity winds. The core velocity of Brα emission shifts by +13 km s‑1 from NE to SW across the supernebula, possibly indicating a bipolar outflow from an embedded object or a link to a foreground redshifted gas filament. The results can be explained if the supernebula comprises thousands of ionized wind regions around individual massive stars, stalled in their expansion due to critical radiative cooling and unable to merge to drive a coherent cluster wind. Based on the absence of an outflow with large mass loss, we conclude that feedback is currently ineffective at dispersing gas, and the SSC retains enriched material out of which it may continue to form stars.

Hubble Catches Stellar Exodus in Action

NASA Image and Video Library

2015-05-14

Using NASA’s Hubble Space Telescope, astronomers have captured for the first time snapshots of fledging white dwarf stars beginning their slow-paced, 40-million-year migration from the crowded center of an ancient star cluster to the less populated suburbs. White dwarfs are the burned-out relics of stars that rapidly lose mass, cool down and shut off their nuclear furnaces. As these glowing carcasses age and shed weight, their orbits begin to expand outward from the star cluster’s packed downtown. This migration is caused by a gravitational tussle among stars inside the cluster. Globular star clusters sort out stars according to their mass, governed by a gravitational billiard ball game where lower mass stars rob momentum from more massive stars. The result is that heavier stars slow down and sink to the cluster's core, while lighter stars pick up speed and move across the cluster to the edge. This process is known as "mass segregation." Until these Hubble observations, astronomers had never definitively seen the dynamical conveyor belt in action. Astronomers used Hubble to watch the white-dwarf exodus in the globular star cluster 47 Tucanae, a dense swarm of hundreds of thousands of stars in our Milky Way galaxy. The cluster resides 16,700 light-years away in the southern constellation Tucana. Credits: NASA, ESA, and H. Richer and J. Heyl (University of British Columbia, Vancouver, Canada); acknowledgement: J. Mack (STScI) and G. Piotto (University of Padova, Italy)

Apparatus for controlling nuclear core debris

DOEpatents

Jones, Robert D.

1978-01-01

Nuclear reactor apparatus for containing, cooling, and dispersing reactor debris assumed to flow from the core area in the unlikely event of an accident causing core meltdown. The apparatus includes a plurality of horizontally disposed vertically spaced plates, having depressions to contain debris in controlled amounts, and a plurality of holes therein which provide natural circulation cooling and a path for debris to continue flowing downward to the plate beneath. The uppermost plates may also include generally vertical sections which form annular-like flow areas which assist the natural circulation cooling.

Cooling interventions for athletes: An overview of effectiveness, physiological mechanisms, and practical considerations

PubMed Central

Bongers, Coen C. W. G.; Hopman, Maria T. E.; Eijsvogels, Thijs M. H.

2017-01-01

ABSTRACT Exercise-induced increases in core body temperature could negative impact performance and may lead to development of heat-related illnesses. The use of cooling techniques prior (pre-cooling), during (per-cooling) or directly after (post-cooling) exercise may limit the increase in core body temperature and therefore improve exercise performance. The aim of the present review is to provide a comprehensive overview of current scientific knowledge in the field of pre-cooling, per-cooling and post-cooling. Based on existing studies, we will discuss 1) the effectiveness of cooling interventions, 2) the underlying physiological mechanisms and 3) practical considerations regarding the use of different cooling techniques. Furthermore, we tried to identify the optimal cooling technique and compared whether cooling-induced performance benefits are different between cool, moderate and hot ambient conditions. This article provides researchers, physicians, athletes and coaches with important information regarding the implementation of cooling techniques to maintain exercise performance and to successfully compete in thermally stressful conditions. PMID:28349095

Metal concentration and X-ray cool spectral component in the central region of the Centaurus cluster of galaxies

NASA Technical Reports Server (NTRS)

Fukazawa, Yasushi; Ohashi, Takaya; Fabian, Andrew C.; Canizares, Claude R.; Ikebe, Yasushi; Makishima, Kazuo; Mushotzky, Richard F.; Yamashita, Koujun

1994-01-01

Spatially resolved energy spectra in the energy range 0.5-10 keV have been measured for the Centaurus cluster of galaxies with Advanced Satellite for Cosmology and Astrophysics (ASCA). Within 10 min (200 kpc) from the cluster center, the helium-like iron K emission line exhibits a dramatic increase toward the center rising from an equivalent width approximately 500 eV to approximately 1500 eV corresponding to an abundance change from 0.3 to 1.0 solar. The presence of strong iron L lines indicates an additional cool component (kT approximately 1 keV) within 10 min from the center. The cool component requires absorption in excess of the galactic value and this excess absorption increases towards the central region of the cluster. In the surrounding region with radius greater than 10 min, the spectra are well described by a single temperature thermal model with kT approximately 4 keV and spatially uniform abundances at about 0.3-0.4 times solar. The detection of metal-rich hot and cool gas in the cluster center implies a complex nature of the central cluster gas which is likely to be related to the presence of the central cD galaxy NGC 4696.

Assessment of Effectiveness of Cool Coat in Reducing Heat Strain among Workers in Steel Industry.

PubMed

Parameswarappa, S B; Narayana, J

2017-01-01

A research study was conducted to assess the effectiveness of cool coat in reducing heat strain among workers exposed to heat in a steel plant located in south India. The study consists of assessing heat strain of workers exposed to heat in a steel plant by measuring physiological reactions of workers such as pulse rate and core body temperature with and without cool coat. The coal coat taken for this study was procured from M/s Yamuna Industries, Noida. Out of 140 employees exposed to heat hazard, 101 employees were examined in this study. Study was done in important production units in steel plant having heat hazard. Workers were interviewed and examined and information regarding thermal comfort was collected. First, the heat strain was assessed when the workers were not using cool coats. The air temperature was measured at all hot zone workplaces and found in the range of 34 0 C to 39.4 0 C (Mean: 36.54 0 C & S.D: 1.54). Physiological response such as core body temperature, pulse rate and blood pressure of workers exposed to heat hazard were measured before & after work to know the heat strain sustained by workers when they were working. Maximum core body temperature after work was found to be 39.3 0 C (Mean; 38.52 & S.D; 0.7). Maximum pulse rate of workers after work was found to be 120 beats/minute (Mean; 94.96 beats/minute, S.D: 13.11). The study indicate core body temperature of workers was found more than the permissible exposure limit prescribed by ACGIH, indicating the heat strain sustained by workers is significant, whereas the pulse rate and blood pressure was found normal & not exceeded the limits. Second, with cool coat, the heat strain was assessed among 10 workers selected from the 101 employees. Core body temperature was measured before and soon after work, The core body temperature recorded soon after work was in the range of 35.5 - 37.20C (Mean 36.36, SD= 0.52), indicating a drop in the core body temperature. In this study, a core body temperature rise in the range of 1 0 -1.4 0 C was noticed when the employees were not wearing cool coats. Whereas, with the usage of cool coat a rise in core body temperature was not found and in many coat wearing workers a drop in core body temperature (0.2 to 0.9 0 C) was noticed. Employees revealed that the cool coats was comfortable to use and provided the thermal comforts. The study concluded that the cool coat taken for this study was found effective in reducing the heat strain.

Assessment of Effectiveness of Cool Coat in Reducing Heat Strain among Workers in Steel Industry

PubMed Central

Parameswarappa, S. B.; Narayana, J.

2017-01-01

A research study was conducted to assess the effectiveness of cool coat in reducing heat strain among workers exposed to heat in a steel plant located in south India. The study consists of assessing heat strain of workers exposed to heat in a steel plant by measuring physiological reactions of workers such as pulse rate and core body temperature with and without cool coat. The coal coat taken for this study was procured from M/s Yamuna Industries, Noida. Out of 140 employees exposed to heat hazard, 101 employees were examined in this study. Study was done in important production units in steel plant having heat hazard. Workers were interviewed and examined and information regarding thermal comfort was collected. First, the heat strain was assessed when the workers were not using cool coats. The air temperature was measured at all hot zone workplaces and found in the range of 34 0 C to 39.4 0 C (Mean: 36.54 0 C & S.D: 1.54). Physiological response such as core body temperature, pulse rate and blood pressure of workers exposed to heat hazard were measured before & after work to know the heat strain sustained by workers when they were working. Maximum core body temperature after work was found to be 39.3 0 C (Mean; 38.52 & S.D; 0.7). Maximum pulse rate of workers after work was found to be 120 beats/minute (Mean; 94.96 beats/minute, S.D: 13.11). The study indicate core body temperature of workers was found more than the permissible exposure limit prescribed by ACGIH, indicating the heat strain sustained by workers is significant, whereas the pulse rate and blood pressure was found normal & not exceeded the limits. Second, with cool coat, the heat strain was assessed among 10 workers selected from the 101 employees. Core body temperature was measured before and soon after work, The core body temperature recorded soon after work was in the range of 35.5 - 37.20C (Mean 36.36, SD= 0.52), indicating a drop in the core body temperature. In this study, a core body temperature rise in the range of 1 0 -1.4 0 C was noticed when the employees were not wearing cool coats. Whereas, with the usage of cool coat a rise in core body temperature was not found and in many coat wearing workers a drop in core body temperature (0.2 to 0.9 0 C) was noticed. Employees revealed that the cool coats was comfortable to use and provided the thermal comforts. The study concluded that the cool coat taken for this study was found effective in reducing the heat strain. PMID:29391745

Heating and Cooling Rates With an Esophageal Heat Exchange System.

PubMed

Kalasbail, Prathima; Makarova, Natalya; Garrett, Frank; Sessler, Daniel I

2018-04-01

The Esophageal Cooling Device circulates warm or cool water through an esophageal heat exchanger, but warming and cooling efficacy in patients remains unknown. We therefore determined heat exchange rates during warming and cooling. Nineteen patients completed the trial. All had general endotracheal anesthesia for nonthoracic surgery. Intraoperative heat transfer was measured during cooling (exchanger fluid at 7°C) and warming (fluid at 42°C). Each was evaluated for 30 minutes, with the initial condition determined randomly, starting at least 40 minutes after induction of anesthesia. Heat transfer rate was estimated from fluid flow through the esophageal heat exchanger and inflow and outflow temperatures. Core temperature was estimated from a zero-heat-flux thermometer positioned on the forehead. Mean heat transfer rate during warming was 18 (95% confidence interval, 16-20) W, which increased core temperature at a rate of 0.5°C/h ± 0.6°C/h (mean ± standard deviation). During cooling, mean heat transfer rate was -53 (-59 to -48) W, which decreased core temperature at a rate of 0.9°C/h ± 0.9°C/h. Esophageal warming transferred 18 W which is considerably less than the 80 W reported with lower or upper body forced-air covers. However, esophageal warming can be used to supplement surface warming or provide warming in cases not amenable to surface warming. Esophageal cooling transferred more than twice as much heat as warming, consequent to the much larger difference between core and circulating fluid temperature with cooling (29°C) than warming (6°C). Esophageal cooling extracts less heat than endovascular catheters but can be used to supplement catheter-based cooling or possibly replace them in appropriate patients.

Using White Dwarf Companions of Blue Stragglers to Constrain Mass Transfer Physics

NASA Astrophysics Data System (ADS)

Gosnell, Natalie M.; Leiner, Emily; Geller, Aaron M.; Knigge, Christian; Mathieu, Robert D.; Sills, Alison; Leigh, Nathan

2018-06-01

Complete membership studies of old open clusters reveal that 25% of the evolved stars follow pathways in stellar evolution that are impacted by binary evolution. Recent studies show that the majority of blue straggler stars, traditionally defined to be stars brighter and bluer than the corresponding main sequence turnoff, are formed through mass transfer from a giant star onto a main sequence companion, resulting in a white dwarf in a binary system with a blue straggler. We will present constraints on the histories and mass transfer efficiencies for two blue straggler-white dwarf binaries in open cluster NGC 188. The constraints are a result of measuring white dwarf cooling temperatures and surface gravities with HST COS far-ultraviolet spectroscopy. This information sets both the timeline for mass transfer and the stellar masses in the pre-mass transfer binary, allowing us to constrain aspects of the mass transfer physics. One system is formed through Case C mass transfer, leaving a CO-core white dwarf, and provides an interesting test case for mass transfer from an asymptotic giant branch star in an eccentric system. The other system formed through Case B mass transfer, leaving a He-core white dwarf, and challenges our current understanding of the expected regimes for stable mass transfer from red giant branch stars.

Star Formation Rates in Cooling Flow Clusters: A UV Pilot Study with Archival XMM-Newton Optical Monitor Data

NASA Technical Reports Server (NTRS)

Hicks, A. K.; Mushotzky, R.

2006-01-01

We have analyzed XMM-Newton Optical Monitor (OM) UV (180-400 nm) data for a sample of 33 galaxies. 30 are cluster member galaxies, and nine of these are central cluster galaxies (CCGs) in cooling flow clusters having mass deposition rates which span a range of 8 - 525 Solar Mass/yr. By comparing the ratio of UV to 2MASS J band fluxes, we find a significant UV excess in many, but not all, cooling flow CCGs, a finding consistent with the outcome of previous studies based on optical imaging data (McNamara & O'Connell 1989; Cardiel, Gorgas, & Aragon-Salamanca 1998; Crawford et al. 1999). This UV excess is a direct indication of the presence of young massive stars, and therefore recent star formation, in these galaxies. Using the Starburst99 spectral energy distribution (SED) model of continuous star formation over a 900 Myr period, we derive star formation rates of 0.2 - 219 solar Mass/yr for the cooling flow sample. For 2/3 of this sample it is possible to equate Chandra/XMM cooling flow mass deposition rates with UV inferred star formation rates, for a combination of starburst lifetime and IMF slope. This is a pilot study of the well populated XMM UV cluster archive and a more extensive follow up study is currently underway.

Revealing the sub-nanometere three-dimensional microscture of a metallic meteorite

NASA Astrophysics Data System (ADS)

Einsle, J. F.; Harrison, R.; Blukis, R.; Eggeman, A.; Saghi, Z.; Martineau, B.; Bagot, P.; Collins, S. M.; Midgley, P. A.

2017-12-01

Coming from from the core of differentiated planetesimals, iron-nickel meteorites provide some of the only direct material artefacts from planetary cores. Iron - nickel meteorites contain a record of their thermal and magnetic history, written in the intergrowth of iron-rich and nickel-rich phases that formed during slow cooling over millions of years. Of intense interest for understanding the thermal and magnetic history is the `'cloudy zone''. This nanoscale intergrowth that has recently been used to provide a record of magnetic activity on the parent body of stony-iron meteorites. The cloudy zone consists of islands of tetrataenite surrounded by a matrix phase, Here we use a multi-scale and multidimensional comparative study using high-resolution electron diffraction, scanning transmission electron tomography with chemical mapping, atom probe tomography and micromagnetic simulations to reveal the three-dimensional architecture of the cloudy zone with sub-nanometre spatial resolution. Machine learning data deconvolution strategies enable the three microanalytical techniques to converge on a consistent microstructural description for the cloudy zone. Isolated islands of tetrataenite are found, embedded in a continuous matrix of an FCC-supercell of Fe27Ni5 structure, never before identified in nature. The tetrataenite islands are arranged in clusters of three crystallographic variants, which control how magnetic information is encoded into the nanostructure during slow cooling. The new compositional, crystallographic and micromagnetic data have profound implications for how the cloudy zone acquires magnetic remanence, and requires a revision of the low-temperature metastable phase diagram of the Fe-Ni system. This can lead to a refinement of core dynamics in small planetoids.

Distant Galaxy Clusters Hosting Extreme Central Galaxies

NASA Astrophysics Data System (ADS)

McDonald, Michael

2014-09-01

The recently-discovered Phoenix cluster harbors the most star-forming central cluster galaxy of any cluster in the known Universe, by nearly a factor of 10. This extreme system appears to be fulfilling early cooling flow predictions, although the lack of similar systems makes any interpretation difficult. In an attempt to find other "Phoenix-like" clusters, we have cross-correlated archival all-sky surveys (in which Phoenix was detected) and isolated 4 similarly-extreme systems which are also coincident in position and redshift with an overdensity of red galaxies. We propose here to obtain Chandra observations of these extreme, Phoenix-like systems, in order to confirm them as relaxed, rapidly-cooling galaxy clusters.

The Morphologies and Alignments of Gas, Mass, and the Central Galaxies of CLASH Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Donahue, Megan; Ettori, Stefano; Rasia, Elena; Sayers, Jack; Zitrin, Adi; Meneghetti, Massimo; Voit, G. Mark; Golwala, Sunil; Czakon, Nicole; Yepes, Gustavo; Baldi, Alessandro; Koekemoer, Anton; Postman, Marc

2016-03-01

Morphology is often used to infer the state of relaxation of galaxy clusters. The regularity, symmetry, and degree to which a cluster is centrally concentrated inform quantitative measures of cluster morphology. The Cluster Lensing and Supernova survey with Hubble Space Telescope (CLASH) used weak and strong lensing to measure the distribution of matter within a sample of 25 clusters, 20 of which were deemed to be “relaxed” based on their X-ray morphology and alignment of the X-ray emission with the Brightest Cluster Galaxy. Toward a quantitative characterization of this important sample of clusters, we present uniformly estimated X-ray morphological statistics for all 25 CLASH clusters. We compare X-ray morphologies of CLASH clusters with those identically measured for a large sample of simulated clusters from the MUSIC-2 simulations, selected by mass. We confirm a threshold in X-ray surface brightness concentration of C ≳ 0.4 for cool-core clusters, where C is the ratio of X-ray emission inside 100 h70-1 kpc compared to inside 500 {h}70-1 kpc. We report and compare morphologies of these clusters inferred from Sunyaev-Zeldovich Effect (SZE) maps of the hot gas and in from projected mass maps based on strong and weak lensing. We find a strong agreement in alignments of the orientation of major axes for the lensing, X-ray, and SZE maps of nearly all of the CLASH clusters at radii of 500 kpc (approximately 1/2 R500 for these clusters). We also find a striking alignment of clusters shapes at the 500 kpc scale, as measured with X-ray, SZE, and lensing, with that of the near-infrared stellar light at 10 kpc scales for the 20 “relaxed” clusters. This strong alignment indicates a powerful coupling between the cluster- and galaxy-scale galaxy formation processes.

IBS FOR ION DISTRIBUTION UNDER ELECTRON COOLING.

DOE Office of Scientific and Technical Information (OSTI.GOV)

FEDOTOV,A.V.; BEN-ZVI,I.; EIDELMAN, YU.

Standard models of the intra-beam scattering (IBS) are based on the growth of the rms beam parameters for a Gaussian distribution. As a result of electron cooling, the core of beam distribution is cooled much faster than the tails, producing a denser core. In this paper, we compare various approaches to IBS treatment for such distribution. Its impact on the luminosity is also discussed.

Competitive repetition suppression (CoRe) clustering: a biologically inspired learning model with application to robust clustering.

PubMed

Bacciu, Davide; Starita, Antonina

2008-11-01

Determining a compact neural coding for a set of input stimuli is an issue that encompasses several biological memory mechanisms as well as various artificial neural network models. In particular, establishing the optimal network structure is still an open problem when dealing with unsupervised learning models. In this paper, we introduce a novel learning algorithm, named competitive repetition-suppression (CoRe) learning, inspired by a cortical memory mechanism called repetition suppression (RS). We show how such a mechanism is used, at various levels of the cerebral cortex, to generate compact neural representations of the visual stimuli. From the general CoRe learning model, we derive a clustering algorithm, named CoRe clustering, that can automatically estimate the unknown cluster number from the data without using a priori information concerning the input distribution. We illustrate how CoRe clustering, besides its biological plausibility, posses strong theoretical properties in terms of robustness to noise and outliers, and we provide an error function describing CoRe learning dynamics. Such a description is used to analyze CoRe relationships with the state-of-the art clustering models and to highlight CoRe similitude with rival penalized competitive learning (RPCL), showing how CoRe extends such a model by strengthening the rival penalization estimation by means of loss functions from robust statistics.

A study of cooling flows in poor clusters of galaxies

NASA Technical Reports Server (NTRS)

Kriss, Gerard A.; Dillingham, Stephen

1995-01-01

We observed three poor clusters with central dominant galaxies (AWM 4, MKW 4, and MKW 3's) using the Position Sensitive Proportional Counter on the ROSAT X-ray satellite. The images reveal smooth, symmetrical X-ray emission filling the cluster with a sharp peak on each central galaxy. The cluster surface brightness profiles can be decomposed using superposed King models for the central galaxy and the intracluster medium. The King model parameters for the cluster portions are consistent with previous observations of these clusters. The newly measured King model parameters for the central galaxies are typical of the X-ray surface brightness distributions of isolated elliptical galaxies. Spatially resolved temperature measurements in annular rings throughout the clusters show a nearly isothermal profile. Temperatures are consistent with previously measured values, but are much better determined. There is no significant drop in temperature noted in the innermost bins where cooling flows are likely to be present, nor is any excess absorption by cold gas required. All cold gas columns are consistent with galactic foreground absorption. We derive mass profiles for the clusters assuming both isothermal temperature profiles and cooling flow models with constant mass flow rates. Our results are consistent with previous Einstein IPC observations by Kriss, Cioffi, & Canizares, but extend the mass profiles out to 1 Mpc in these poor clusters.

Cooling rate dependence of structural order in Al90Sm10 metallic glass

NASA Astrophysics Data System (ADS)

Sun, Yang; Zhang, Yue; Zhang, Feng; Ye, Zhuo; Ding, Zejun; Wang, Cai-Zhuang; Ho, Kai-Ming

2016-07-01

The atomic structure of Al90Sm10 metallic glass is studied using molecular dynamics simulations. By performing a long sub-Tg annealing, we developed a glass model closer to the experiments than the models prepared by continuous cooling. Using the cluster alignment method, we found that "3661" cluster is the dominating short-range order in the glass samples. The connection and arrangement of "3661" clusters, which define the medium-range order in the system, are enhanced significantly in the sub-Tg annealed sample as compared with the fast cooled glass samples. Unlike some strong binary glass formers such as Cu64.5Zr35.5, the clusters representing the short-range order do not form an interconnected interpenetrating network in Al90Sm10, which has only marginal glass formability.

Blue stragglers in the core of the globular cluster 47 Tucanae

NASA Technical Reports Server (NTRS)

Paresce, F.; Meylan, G.; Shara, M.; Baxter, D.; Greenfield, P.

1991-01-01

High-resolution observations of the core of the globular cluster 47 Tucanae with the Faint Object Camera on the Hubble Space Telescope reveal a high density of 'blue straggler' stars, occupying the upper end of the main sequence from which all stars in the cluster should have long since evolved. Their presence in the dense core supports the hypothesis that they formed by stellar collision and coalescence, and, as the heaviest objects in the cluster, have drifted to the core.

Statistical methods for astronomical data with upper limits. II - Correlation and regression

NASA Technical Reports Server (NTRS)

Isobe, T.; Feigelson, E. D.; Nelson, P. I.

1986-01-01

Statistical methods for calculating correlations and regressions in bivariate censored data where the dependent variable can have upper or lower limits are presented. Cox's regression and the generalization of Kendall's rank correlation coefficient provide significant levels of correlations, and the EM algorithm, under the assumption of normally distributed errors, and its nonparametric analog using the Kaplan-Meier estimator, give estimates for the slope of a regression line. Monte Carlo simulations demonstrate that survival analysis is reliable in determining correlations between luminosities at different bands. Survival analysis is applied to CO emission in infrared galaxies, X-ray emission in radio galaxies, H-alpha emission in cooling cluster cores, and radio emission in Seyfert galaxies.

77 FR 64148 - Advisory Committee on Reactor Safeguards (ACRS) Meeting of the ACRS Subcommittee on Regulatory...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-10-18

... Regulatory Guides (RG) RG 1.79, ````Preoperational Testing of Emergency Core Cooling Systems for Pressurized Water Reactors,'' Revision 2 and RG 1.79.1, ``Initial Test Program of Emergency Core Cooling Systems for...

Methamphetamine injecting is associated with phylogenetic clustering of hepatitis C virus infection among street-involved youth in Vancouver, Canada*

PubMed Central

Cunningham, Evan; Jacka, Brendan; DeBeck, Kora; Applegate, Tanya A; Harrigan, P. Richard; Krajden, Mel; Marshall, Brandon DL; Montaner, Julio; Lima, Viviane Dias; Olmstead, Andrea; Milloy, M-J; Wood, Evan; Grebely, Jason

2015-01-01

Background Among prospective cohorts of people who inject drugs (PWID), phylogenetic clustering of HCV infection has been observed. However, the majority of studies have included older PWID, representing distant transmission events. The aim of this study was to investigate phylogenetic clustering of HCV infection among a cohort of street-involved youth. Methods Data were derived from a prospective cohort of street-involved youth aged 14–26 recruited between 2005 and 2012 in Vancouver, Canada (At Risk Youth Study, ARYS). HCV RNA testing and sequencing (Core-E2) were performed on HCV positive participants. Phylogenetic trees were inferred using maximum likelihood methods and clusters were identified using ClusterPicker (Core-E2 without HVR1, 90% bootstrap threshold, 0.05 genetic distance threshold). Results Among 945 individuals enrolled in ARYS, 16% (n=149, 100% recent injectors) were HCV antibody positive at baseline interview (n=86) or seroconverted during follow-up (n=63). Among HCV antibody positive participants with available samples (n=131), 75% (n=98) had detectable HCV RNA and 66% (n=65, mean age 23, 58% with recent methamphetamine injection, 31% female, 3% HIV+) had available Core-E2 sequences. Of those with Core-E2 sequence, 14% (n=9) were in a cluster (one cluster of three) or pair (two pairs), with all reporting recent methamphetamine injection. Recent methamphetamine injection was associated with membership in a cluster or pair (P=0.009). Conclusion In this study of street-involved youth with HCV infection and recent injecting, 14% demonstrated phylogenetic clustering. Phylogenetic clustering was associated with recent methamphetamine injection, suggesting that methamphetamine drug injection may play an important role in networks of HCV transmission. PMID:25977204

AGN jet-driven stochastic cold accretion in cluster cores

NASA Astrophysics Data System (ADS)

Prasad, Deovrat; Sharma, Prateek; Babul, Arif

2017-10-01

Several arguments suggest that stochastic condensation of cold gas and its accretion on to the central supermassive black hole (SMBH) is essential for active galactic nuclei (AGNs) feedback to work in the most massive galaxies that lie at the centres of galaxy clusters. Our 3-D hydrodynamic AGN jet-ICM (intracluster medium) simulations, looking at the detailed angular momentum distribution of cold gas and its time variability for the first time, show that the angular momentum of the cold gas crossing ≲1 kpc is essentially isotropic. With almost equal mass in clockwise and counterclockwise orientations, we expect a cancellation of the angular momentum on roughly the dynamical time. This means that a compact accretion flow with a short viscous time ought to form, through which enough accretion power can be channeled into jet mechanical energy sufficiently quickly to prevent a cooling flow. The inherent stochasticity, expected in feedback cycles driven by cold gas condensation, gives rise to a large variation in the cold gas mass at the centres of galaxy clusters, for similar cluster and SMBH masses, in agreement with the observations. Such correlations are expected to be much tighter for the smoother hot/Bondi accretion. The weak correlation between cavity power and Bondi power obtained from our simulations also matches observations.

Geminga: A cooling superfluid neutron star

NASA Technical Reports Server (NTRS)

Page, Dany

1994-01-01

We compare the recent temperature estimate for Geminga with neutron star cooling models. Because of its age (approximately 3.4 x 10(exp 5) yr), Geminga is in the photon cooling era. We show that its surface temperature (approximately 5.2 x 10(exp 5) K) can be understood by both types of neutrino cooling scenarios, i.e., slow neutrino cooling by the modified Urca process or fast neutrino cooling by the direct Urca process or by some exotic matter, and thus does not allow us to discriminate between these two competing schemes. However, for both types of scenarios, agreement with the observed temperature can only be obtained if baryon pairing is present in most, if not all, of the core of the star. Within the slow neutrino cooling scenario, early neutrino cooling is not sufficient to explain the observed low temperature, and extensive pairing in the core is necessary to reduce the specific heat and increase the cooling rate in the present photon cooling era. Within all the fast neutrino cooling scenarios, pairing is necessary throughout the whole core to control the enormous early neutrino emission which, without pairing suppression, would result in a surface temperature at the present time much lower than observed. We also comment on the recent temperature estimates for PSR 0656+14 and PSR 1055-52, which pertain to the same photon cooling era. If one assumes that all neutron stars undergo fast neutrino cooling, then these two objects also provide evidence for extensive baryon pairing in their core; but observational uncertainties also permit a more conservative interpretation, with slow neutrino emission and no pairing at all. We argue though that observational evidence for the slow neutrino cooling model (the 'standard' model) is in fact very dim and that the interpretation of the surface temperature of all neutron stars could be done with a reasonable theoretical a priori within the fast neutrino cooling scenarios only. In this case, Geminga, PSR 0656+14, and PSR 1055-52 all show evidence of baryon pairing down to their very centers.

Temperature profiles of different cooling methods in porcine pancreas procurement.

PubMed

Weegman, Bradley P; Suszynski, Thomas M; Scott, William E; Ferrer Fábrega, Joana; Avgoustiniatos, Efstathios S; Anazawa, Takayuki; O'Brien, Timothy D; Rizzari, Michael D; Karatzas, Theodore; Jie, Tun; Sutherland, David E R; Hering, Bernhard J; Papas, Klearchos K

2014-01-01

Porcine islet xenotransplantation is a promising alternative to human islet allotransplantation. Porcine pancreas cooling needs to be optimized to reduce the warm ischemia time (WIT) following donation after cardiac death, which is associated with poorer islet isolation outcomes. This study examines the effect of four different cooling Methods on core porcine pancreas temperature (n = 24) and histopathology (n = 16). All Methods involved surface cooling with crushed ice and chilled irrigation. Method A, which is the standard for porcine pancreas procurement, used only surface cooling. Method B involved an intravascular flush with cold solution through the pancreas arterial system. Method C involved an intraductal infusion with cold solution through the major pancreatic duct, and Method D combined all three cooling Methods. Surface cooling alone (Method A) gradually decreased core pancreas temperature to <10 °C after 30 min. Using an intravascular flush (Method B) improved cooling during the entire duration of procurement, but incorporating an intraductal infusion (Method C) rapidly reduced core temperature 15-20 °C within the first 2 min of cooling. Combining all methods (Method D) was the most effective at rapidly reducing temperature and providing sustained cooling throughout the duration of procurement, although the recorded WIT was not different between Methods (P = 0.36). Histological scores were different between the cooling Methods (P = 0.02) and the worst with Method A. There were differences in histological scores between Methods A and C (P = 0.02) and Methods A and D (P = 0.02), but not between Methods C and D (P = 0.95), which may highlight the importance of early cooling using an intraductal infusion. In conclusion, surface cooling alone cannot rapidly cool large (porcine or human) pancreata. Additional cooling with an intravascular flush and intraductal infusion results in improved core porcine pancreas temperature profiles during procurement and histopathology scores. These data may also have implications on human pancreas procurement as use of an intraductal infusion is not common practice. © 2014 John Wiley & Sons A/S Published by John Wiley & Sons Ltd.

Temperature Map of the Perseus Cluster of Galaxies Observed with ASCA

NASA Technical Reports Server (NTRS)

Furusho, T.; Yamasaki, N. Y.; Ohashi, T.; Shibata, R.; Ezawa, H.; White, Nicholas E. (Technical Monitor)

2000-01-01

We present two-dimensional temperature map of the Perseus cluster based on multi-pointing observations with the Advanced Spacecraft for Cosmology Astrophysics (ASCA) Gas Imaging Spectrometer (GIS), covering a region with a diameter of approximately 2 deg. By correcting for the effect of the X-ray telescope response, the temperatures were estimated from hardness ratios and the complete temperature structure of the cluster with a spatial resolution of about 100 kpc was obtained for the first time. There is an extended cool region with a diameter of approximately 20 arcmin and kT approx. 5 keV at about 20 arcmin east from the cluster center. This region also shows higher surface brightness and is surrounded by a large ring-like hot region with kT approx. > 7 keV, and likely to be a remnant of a merger with a poor cluster. Another extended cool region is extending outward from the IC 310 subcluster. These features and the presence of several other hot and cool blobs suggest that this rich cluster has been formed as a result of a repetition of many subcluster mergers.

Effects of a New Cooling Technology on Physical Performance in US Air Force Military Personnel.

PubMed

O'Hara, Reginald; Vojta, Christopher; Henry, Amy; Caldwell, Lydia; Wade, Molly; Swanton, Stacie; Linderman, Jon K; Ordway, Jason

2016-01-01

Heat-related illness is a critical factor for military personnel operating in hyperthermic environments. Heat illness can alter cognitive and physical performance during sustained operations missions. Therefore, the primary purpose of this investigation was to determine the effects of a novel cooling shirt on core body temperature in highly trained US Air Force personnel. Twelve trained (at least 80th percentile for aerobic fitness according to the American College of Sports Medicine, at least 90% on the US Air Force fitness test), male Air Force participants (mean values: age, 25 ± 2.8 years; height, 178 ± 7.9cm; body weight 78 ± 9.6kg; maximal oxygen uptake, 57 ± 1.9mL/kg/ min; and body fat, 10% ± 0.03%) completed this study. Subjects performed a 70-minute weighted treadmill walking test and 10-minute, 22.7kg sandbag shuttle test under two conditions: (1) "loaded" (shirt with cooling inserts) and (2) "unloaded" (shirt with no cooling inserts). Core body temperature, exercise heart rate, capillary blood lactate, and ratings of perceived exertion were recorded. Core body temperature was lower (ρ = .001) during the 70-minute treadmill walking test in the loaded condition. Peak core temperature during the 70-minute walking test was also significantly lower (ρ = .038) in the loaded condition. This lightweight (471g), passive cooling technology offers multiple hours of sustained cooling and reduced core and peak body temperature during a 70-minute, 22.7kg weighted-vest walking test. 2016.

Core Collapse: The Race Between Stellar Evolution and Binary Heating

NASA Astrophysics Data System (ADS)

Converse, Joseph M.; Chandar, R.

2012-01-01

The dynamical formation of binary stars can dramatically affect the evolution of their host star clusters. In relatively small clusters (M < 6000 Msun) the most massive stars rapidly form binaries, heating the cluster and preventing any significant contraction of the core. The situation in much larger globular clusters (M 105 Msun) is quite different, with many showing collapsed cores, implying that binary formation did not affect them as severely as lower mass clusters. More massive clusters, however, should take longer to form their binaries, allowing stellar evolution more time to prevent the heating by causing the larger stars to die off. Here, we simulate the evolution of clusters between those of open and globular clusters in order to find at what size a star cluster is able to experience true core collapse. Our simulations make use of a new GPU-based computing cluster recently purchased at the University of Toledo. We also present some benchmarks of this new computational resource.

The effects of passive heating and head-cooling on perception of exercise in the heat.

PubMed

Simmons, Shona E; Mündel, Toby; Jones, David A

2008-09-01

The capacity to perform exercise is reduced in a hot environment when compared to cooler conditions. A limiting factor appears to be a higher core body temperature (T (core)) and it has been suggested that an elevated T (core) reduces the drive to exercise, this being reflected in higher ratings of perceived exertion (RPE). The purpose of the present study was to determine whether passive heating to increase T (core) would have a detrimental effect on RPE and thermal comfort during subsequent exercise in the heat and whether head-cooling during passive heating would attenuate these unpleasant sensations of an elevated T (core) during subsequent exercise in the heat. Nine physically-active, non-heat-acclimated volunteers [6 males, 3 females; age: 21 +/- 1 year, VO(2max) 50 +/- 9 ml kg(-1).min(-1), peak power output: 286 +/- 43 W (mean +/- SD)] performed two 12-minute constant-load cycling tests at 70% VO(2max) in a warm-dry environment (34 +/- 1 degrees C, relative humidity <30%) separated by a period of passive heating in a sauna (68 +/- 3 degrees C) to increase T (core). In one trial, subjects had their head and face cooled continually in the sauna (HC), the other trial was a control (CON). Passive heating increased T (core) by 1.22 +/- 0.03 degrees C in the CON and by 0.75 +/- 0.07 degrees C in the HC trial (P < 0.01). Passive heating increased weighted mean skin temperature (T (msk)) in both the CON and HC trials (P < 0.01), however, head-cooling lowered T (msk) during passive heating (P < 0.05). Exercise time following passive heating was reduced in both the CON and HC trials (P < 0.05). Passive heating increased RPE (P < 0.01), however, RPE was lower following passive heating with head-cooling (P < 0.05). There was a significant correlation between T (core) and RPE (r = 0.82, P < 0.001). In conclusion, our results suggest increased RPE during exercise in the heat is primarily due to the increase in T (core). Furthermore, head-cooling attenuates the rise in T (core) and the effect on RPE is proportional to the rise on T (core).

Cooling rate dependence of simulated Cu{sub 64.5}Zr{sub 35.5} metallic glass structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryltsev, R. E.; Ural Federal University, 19 Mira Str., 620002 Ekaterinburg; L.D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, 2 Kosygina Str., 119334 Moscow

Using molecular dynamics simulations with embedded atom model potential, we study structural evolution of Cu{sub 64.5}Zr{sub 35.5} alloy during the cooling in a wide range of cooling rates γ ∈ (1.5 ⋅ 10{sup 9}, 10{sup 13}) K/s. Investigating short- and medium-range orders, we show that the structure of Cu{sub 64.5}Zr{sub 35.5} metallic glass essentially depends on cooling rate. In particular, a decrease of the cooling rate leads to an increase of abundances of both the icosahedral-like clusters and Frank-Kasper Z16 polyhedra. The amounts of these clusters in the glassy state drastically increase at the γ{sub min} = 1.5 ⋅ 10{supmore » 9} K/s. Analysing the structure of the glass at γ{sub min}, we observe the formation of nano-sized crystalline grain of Cu{sub 2}Zr intermetallic compound with the structure of Cu{sub 2}Mg Laves phase. The structure of this compound is isomorphous with that for Cu{sub 5}Zr intermetallic compound. Both crystal lattices consist of two types of clusters: Cu-centered 13-atom icosahedral-like cluster and Zr-centered 17-atom Frank-Kasper polyhedron Z16. That suggests the same structural motifs for the metallic glass and intermetallic compounds of Cu–Zr system and explains the drastic increase of the abundances of these clusters observed at γ{sub min}.« less

Wide-Field CCD Photometry around Nine Open Clusters

NASA Astrophysics Data System (ADS)

Sharma, Saurabh; Pandey, A. K.; Ogura, K.; Mito, H.; Tarusawa, K.; Sagar, R.

2006-10-01

In this paper we study the evolution of the core and corona of nine open clusters using the projected radial density profiles derived from homogeneous CCD photometric data obtained with the 105 cm Kiso Schmidt telescope. The age and galactocentric distance of the target clusters vary from 16 to 2000 Myr and 9 to 10.8 kpc, respectively. Barring Be 62, which is a young open cluster, other clusters show a uniform reddening across the cluster region. The reddening in Be 62 varies from E(B-V)min=0.70 mag to E(B-V)max=1.00 mag. The coronae of six of the clusters in the present sample are found to be elongated; however, on the basis of the present sample it is not possible to establish any correlation between the age and shape of the core. The elongated core in the case of the young cluster Be 62 may reflect the initial conditions in the parental molecular cloud. The other results of the present study are as follows: (1) Core radius rc and corona size rcn/cluster radius rcl are linearly correlated. (2) The rc, rcn, and rcl are linearly correlated with the number of stars in that region. (3) In the age range 10-1000 Myr, the core and corona shrink with age. (4) We find that in the galactocentric distance range 9-10 kpc, the core and corona/cluster extent of the clusters increase with the galactocentric distance.

THE JCMT GOULD BELT SURVEY: DENSE CORE CLUSTERS IN ORION A

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lane, J.; Kirk, H.; Johnstone, D.

The Orion A molecular cloud is one of the most well-studied nearby star-forming regions, and includes regions of both highly clustered and more dispersed star formation across its full extent. Here, we analyze dense, star-forming cores identified in the 850 and 450 μ m SCUBA-2 maps from the JCMT Gould Belt Legacy Survey. We identify dense cores in a uniform manner across the Orion A cloud and analyze their clustering properties. Using two independent lines of analysis, we find evidence that clusters of dense cores tend to be mass segregated, suggesting that stellar clusters may have some amount of primordial mass segregationmore » already imprinted in them at an early stage. We also demonstrate that the dense core clusters have a tendency to be elongated, perhaps indicating a formation mechanism linked to the filamentary structure within molecular clouds.« less

OBSERVING CASCADES OF SOLAR BULLETS AT HIGH RESOLUTION. II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scullion, E.; Engvold, O.; Lin, Y.

High resolution observations from the Swedish 1-m Solar Telescope revealed bright, discrete, blob-like structures (which we refer to as solar bullets) in the Hα 656.28 nm line core that appear to propagate laterally across the solar atmosphere as clusters in active regions (ARs). These small-scale structures appear to be field aligned and many bullets become triggered simultaneously and traverse collectively as a cluster. Here, we conduct a follow-up study on these rapidly evolving structures with coincident observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly. With the co-aligned data sets, we reveal (a) an evolving multithermal structure in the bullet clustermore » ranging from chromospheric to at least transition region temperatures, (b) evidence for cascade-like behavior and corresponding bidirectional motions in bullets within the cluster, which indicate that there is a common source of the initial instability leading to bullet formation, and (c) a direct relationship between co-incident bullet velocities observed in Hα and He ii 30.4 nm and an inverse relationship with respect to bullet intensity in these channels. We find evidence supporting that bullets are typically composed of a cooler, higher density core detectable in Hα with a less dense, hotter, and fainter co-moving outer sheath. Bullets unequivocally demonstrate the finely structured nature of the AR corona. We have no clear evidence for bullets being associated with locally heated (or cooled), fast flowing plasma. Fast MHD pulses (such as solitons) could best describe the dynamic properties of bullets whereas the presence of a multithermal structure is new.« less

Shocking features in the merging galaxy cluster RXJ0334.2-0111

NASA Astrophysics Data System (ADS)

Dasadia, Sarthak; Sun, Ming; Morandi, Andrea; Sarazin, Craig; Clarke, Tracy; Nulsen, Paul; Massaro, Francesco; Roediger, Elke; Harris, Dan; Forman, Bill

2016-05-01

We present a 66 ks Chandra X-ray observation of the galaxy cluster RXJ0334.2-0111. This deep observation revealed a unique bow shock system associated with a wide angle tail (WAT) radio galaxy and several intriguing substructures. The temperature across the bow shock jumps by a factor of ˜1.5 (from 4.1 to 6.2 keV), and is consistent with the Mach number M = 1.6_{-0.3}^{+0.5}. A second inner surface brightness edge is a cold front that marks the border between infalling subcluster cool core and the intracluster medium of the main cluster. The temperature across the cold front increases from 1.3_{-0.8}^{+0.3} to 6.2_{-0.6}^{+0.6} keV. We find an overpressurized region ˜250 kpc east of the cold front that is named `the eastern extension (EE)'. The EE may be a part of the third subcluster in the ongoing merger. We also find a tail shaped feature that originates near the bow shock and may extend up to a distance of ˜1 Mpc. This feature is also likely overpressurized. The luminous FR-I radio galaxy, 3C89, appears to be the cD galaxy of the infalling subcluster. We estimated 3C89's jet power from jet bending and the possible interaction between the X-ray gas and the radio lobes. A comparison between the shock stand-off distance and the Mach number for all known shock front/cold front combinations suggests that the core is continuously shrinking in size by stripping.

Cooling rate dependence of structural order in Al 90Sm 10 metallic glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Yang; Zhang, Yue; Zhang, Feng

2016-07-07

Here, the atomic structure of Al 90Sm 10 metallic glass is studied using molecular dynamics simulations. By performing a long sub-T g annealing, we developed a glass model closer to the experiments than the models prepared by continuous cooling. Using the cluster alignment method, we found that “3661” cluster is the dominating short-range order in the glass samples. The connection and arrangement of “3661” clusters, which define the medium-range order in the system, are enhanced significantly in the sub-T g annealed sample as compared with the fast cooled glass samples. Unlike some strong binary glass formers such as Cu 64.5Zrmore » 35.5, the clusters representing the short-range order do not form an interconnected interpenetrating network in Al 90Sm 10, which has only marginal glass formability.« less

Cooling rate dependence of structural order in Al{sub 90}Sm{sub 10} metallic glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Yang; Ames Laboratory, US Department of Energy, Ames, Iowa 50011; Zhang, Yue

2016-07-07

The atomic structure of Al{sub 90}Sm{sub 10} metallic glass is studied using molecular dynamics simulations. By performing a long sub-T{sub g} annealing, we developed a glass model closer to the experiments than the models prepared by continuous cooling. Using the cluster alignment method, we found that “3661” cluster is the dominating short-range order in the glass samples. The connection and arrangement of “3661” clusters, which define the medium-range order in the system, are enhanced significantly in the sub-T{sub g} annealed sample as compared with the fast cooled glass samples. Unlike some strong binary glass formers such as Cu{sub 64.5}Zr{sub 35.5},more » the clusters representing the short-range order do not form an interconnected interpenetrating network in Al{sub 90}Sm{sub 10,} which has only marginal glass formability.« less

Core assembly storage structure

DOEpatents

Jones, Jr., Charles E.; Brunings, Jay E.

1988-01-01

A structure for the storage of core assemblies from a liquid metal-cooled nuclear reactor. The structure comprises an enclosed housing having a substantially flat horizontal top plate, a bottom plate and substantially vertical wall members extending therebetween. A plurality of thimble members extend downwardly through the top plate. Each thimble member is closed at its bottom end and has an open end adjacent said top plate. Each thimble member has a length and diameter greater than that of the core assembly to be stored therein. The housing is provided with an inlet duct for the admission of cooling air and an exhaust duct for the discharge of air therefrom, such that when hot core assemblies are placed in the thimbles, the heat generated will by convection cause air to flow from the inlet duct around the thimbles and out the exhaust duct maintaining the core assemblies at a safe temperature without the necessity of auxiliary powered cooling equipment.

Liquid metal cooled nuclear reactors with passive cooling system

DOEpatents

Hunsbedt, Anstein; Fanning, Alan W.

1991-01-01

A liquid metal cooled nuclear reactor having a passive cooling system for removing residual heat resulting from fuel decay during reactor shutdown. The passive cooling system comprises a plurality of cooling medium flow circuits which cooperate to remove and carry heat away from the fuel core upon loss of the normal cooling flow circuit to areas external thereto.

The Bar Mode Instability in Deleptonizing Fizzlers

NASA Astrophysics Data System (ADS)

Imamura, James N.; Durisen, R. H.

2009-01-01

Core collapse in massive rotating nonmagnetic stars may hangup before neutron star densities are reached when rotationally supported or partially rotation supported, hot, lepton-rich objects known as fizzlers form. For typical massive core masses, fizzlers may form if the core has angular momentum J > 1049 g cm2 s-1. Newly formed fizzlers are stable to secular and dynamic nonaxisymmetric instabilities because of the high electron fraction per baryon, Ye > 0.3, and high entropy per baryon, Sn = 1-2 k of fizzler material, and the long-term evolution of a fizzler to neutron star density is driven by deleptonization and cooling of the lepton-rich fizzler material. Both processes lead to pressure loss which causes the fizzler to contract and spin-up. All deleptonizing fizzlers eventually become subject to gravito-rotation-driven nonaxisymmetric instabilities before they reach neutron star density. We study the development of barlike instabilities in deleptonizing fizzlers. We find that vigorous growth in barlike modes occurs only after the bar mode dynamic instability threshold is passed. Because barlike modes break axial symmetry, a burst of gravitational wave (GW) radiation is produced as barlike modes develop. For typical fizzler properties, the GW radiation will have frequency 300-600 Hz with strains of 10-23-10-23, for fizzlers at distances of 15 Mpc ( Virgo cluster of galaxies). Fizzlers in the Virgo cluster would be easily detectable by the gravitational wave obervatory LIGO if the barlike mode persisted for several hundred cycles. We find that barlike modes in fizzlers persist for at least 15-30 cycles in our simulations, depending on the deleptonization rate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, Michael; McNamara, Brian R.; Perimeter Institute for Theoretical Physics, Waterloo

In this study, we present new ultraviolet, optical, and X-ray data on the Phoenix galaxy cluster (SPT-CLJ2344-4243). Deep optical imaging reveals previously undetected filaments of star formation, extending to radii of ~50–100 kpc in multiple directions. Combined UV-optical spectroscopy of the central galaxy reveals a massive (2 × 10 9 M ⊙), young (~4.5 Myr) population of stars, consistent with a time-averaged star formation rate of 610 ± 50 M ⊙ yr –1. We report a strong detection of O vi λλ1032,1038, which appears to originate primarily in shock-heated gas, but may contain a substantial contribution (>1000 M ⊙ yrmore » –1) from the cooling intracluster medium (ICM). We confirm the presence of deep X-ray cavities in the inner ~10 kpc, which are among the most extreme examples of radio-mode feedback detected to date, implying jet powers of 2 – 7 × 10 45 erg s –1. We provide evidence that the active galactic nucleus inflating these cavities may have only recently transitioned from "quasar-mode" to "radio-mode," and may currently be insufficient to completely offset cooling. A model-subtracted residual X-ray image reveals evidence for prior episodes of strong radio-mode feedback at radii of ~100 kpc, with extended "ghost" cavities indicating a prior epoch of feedback roughly 100 Myr ago. This residual image also exhibits significant asymmetry in the inner ~200 kpc (0.15R 500), reminiscent of infalling cool clouds, either due to minor mergers or fragmentation of the cooling ICM. Taken together, these data reveal a rapidly evolving cool core which is rich with structure (both spatially and in temperature), is subject to a variety of highly energetic processes, and yet is cooling rapidly and forming stars along thin, narrow filaments.« less

James Webb Space Telescope Core 2 Test - Cryogenic Thermal Balance Test of the Observatorys Core Area Thermal Control Hardware

NASA Technical Reports Server (NTRS)

Cleveland, Paul; Parrish, Keith; Thomson, Shaun; Marsh, James; Comber, Brian

2016-01-01

The James Webb Space Telescope (JWST), successor to the Hubble Space Telescope, will be the largest astronomical telescope ever sent into space. To observe the very first light of the early universe, JWST requires a large deployed 6.5-meter primary mirror cryogenically cooled to less than 50 Kelvin. Three scientific instruments are further cooled via a large radiator system to less than 40 Kelvin. A fourth scientific instrument is cooled to less than 7 Kelvin using a combination pulse-tube Joule-Thomson mechanical cooler. Passive cryogenic cooling enables the large scale of the telescope which must be highly folded for launch on an Ariane 5 launch vehicle and deployed once on orbit during its journey to the second Earth-Sun Lagrange point. Passive cooling of the observatory is enabled by the deployment of a large tennis court sized five layer Sunshield combined with the use of a network of high efficiency radiators. A high purity aluminum heat strap system connects the three instrument's detector systems to the radiator systems to dissipate less than a single watt of parasitic and instrument dissipated heat. JWST's large scale features, while enabling passive cooling, also prevent the typical flight configuration fully-deployed thermal balance test that is the keystone of most space missions' thermal verification plans. This paper describes the JWST Core 2 Test, which is a cryogenic thermal balance test of a full size, high fidelity engineering model of the Observatory's 'Core' area thermal control hardware. The 'Core' area is the key mechanical and cryogenic interface area between all Observatory elements. The 'Core' area thermal control hardware allows for temperature transition of 300K to approximately 50 K by attenuating heat from the room temperature IEC (instrument electronics) and the Spacecraft Bus. Since the flight hardware is not available for test, the Core 2 test uses high fidelity and flight-like reproductions.

Heat capacity of the neutron star inner crust within an extended nuclear statistical equilibrium model

NASA Astrophysics Data System (ADS)

Burrello, S.; Gulminelli, F.; Aymard, F.; Colonna, M.; Raduta, Ad. R.

2015-11-01

Background: Superfluidity in the crust is a key ingredient for the cooling properties of proto-neutron stars. Present theoretical calculations employ the quasiparticle mean-field Hartree-Fock-Bogoliubov theory with temperature-dependent occupation numbers for the quasiparticle states. Purpose: Finite temperature stellar matter is characterized by a whole distribution of different nuclear species. We want to assess the importance of this distribution on the calculation of heat capacity in the inner crust. Method: Following a recent work, the Wigner-Seitz cell is mapped into a model with cluster degrees of freedom. The finite temperature distribution is then given by a statistical collection of Wigner-Seitz cells. We additionally introduce pairing correlations in the local density BCS approximation both in the homogeneous unbound neutron component, and in the interface region between clusters and neutrons. Results: The heat capacity is calculated in the different baryonic density conditions corresponding to the inner crust, and in a temperature range varying from 100 KeV to 2 MeV. We show that accounting for the cluster distribution has a small effect at intermediate densities, but it considerably affects the heat capacity both close to the outer crust and close to the core. We additionally show that it is very important to consider the temperature evolution of the proton fraction for a quantitatively reliable estimation of the heat capacity. Conclusions: We present the first modelization of stellar matter containing at the same time a statistical distribution of clusters at finite temperature, and pairing correlations in the unbound neutron component. The effect of the nuclear distribution on the superfluid properties can be easily added in future calculations of the neutron star cooling curves. A strong influence of resonance population on the heat capacity at high temperature is observed, which deserves to be further studied within more microscopic calculations.

Color gradients in cooling flow cluster central galaxies and the ionization of cluster emission line systems

NASA Technical Reports Server (NTRS)

Romanishin, W.

1988-01-01

Preliminary results are given for a program to measure color gradients in the central galaxies in clusters with a variety of cooling flow rates. The objectives are to search for extended blue continuum regions indicative of star formation, to study the spatial distribution of star formation, and to make a quantitative measure of the amount of light from young stars, which can lead to a measure of the star formation rate (for an assumed initial mass function). Four clusters with large masses and large cluster H-alpha emission fluxes are found to have an excess of blue light concentrated to the centers of the cluster central galaxy. Assumption of a disk IMF leads to the conclusion that the starlight might play a major role in ionizing the emission line gas in these clusters.

Emergency core cooling system

DOEpatents

Schenewerk, William E.; Glasgow, Lyle E.

1983-01-01

A liquid metal cooled fast breeder reactor provided with an emergency core cooling system includes a reactor vessel which contains a reactor core comprising an array of fuel assemblies and a plurality of blanket assemblies. The reactor core is immersed in a pool of liquid metal coolant. The reactor also includes a primary coolant system comprising a pump and conduits for circulating liquid metal coolant to the reactor core and through the fuel and blanket assemblies of the core. A converging-diverging venturi nozzle with an intermediate throat section is provided in between the assemblies and the pump. The intermediate throat section of the nozzle is provided with at least one opening which is in fluid communication with the pool of liquid sodium. In normal operation, coolant flows from the pump through the nozzle to the assemblies with very little fluid flowing through the opening in the throat. However, when the pump is not running, residual heat in the core causes fluid from the pool to flow through the opening in the throat of the nozzle and outwardly through the nozzle to the assemblies, thus providing a means of removing decay heat.

Application of reliability-centered maintenance to boiling water reactor emergency core cooling systems fault-tree analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Y.A.; Feltus, M.A.

1995-07-01

Reliability-centered maintenance (RCM) methods are applied to boiling water reactor plant-specific emergency core cooling system probabilistic risk assessment (PRA) fault trees. The RCM is a technique that is system function-based, for improving a preventive maintenance (PM) program, which is applied on a component basis. Many PM programs are based on time-directed maintenance tasks, while RCM methods focus on component condition-directed maintenance tasks. Stroke time test data for motor-operated valves (MOVs) are used to address three aspects concerning RCM: (a) to determine if MOV stroke time testing was useful as a condition-directed PM task; (b) to determine and compare the plant-specificmore » MOV failure data from a broad RCM philosophy time period compared with a PM period and, also, compared with generic industry MOV failure data; and (c) to determine the effects and impact of the plant-specific MOV failure data on core damage frequency (CDF) and system unavailabilities for these emergency systems. The MOV stroke time test data from four emergency core cooling systems [i.e., high-pressure coolant injection (HPCI), reactor core isolation cooling (RCIC), low-pressure core spray (LPCS), and residual heat removal/low-pressure coolant injection (RHR/LPCI)] were gathered from Philadelphia Electric Company`s Peach Bottom Atomic Power Station Units 2 and 3 between 1980 and 1992. The analyses showed that MOV stroke time testing was not a predictor for eminent failure and should be considered as a go/no-go test. The failure data from the broad RCM philosophy showed an improvement compared with the PM-period failure rates in the emergency core cooling system MOVs. Also, the plant-specific MOV failure rates for both maintenance philosophies were shown to be lower than the generic industry estimates.« less

Decay Heat Removal from a GFR Core by Natural Convection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Wesley C.; Hejzlar, Pavel; Driscoll, Michael J.

2004-07-01

One of the primary challenges for Gas-cooled Fast Reactors (GFR) is decay heat removal after a loss of coolant accident (LOCA). Due to the fact that thermal gas cooled reactors currently under design rely on passive mechanisms to dissipate decay heat, there is a strong motivation to accomplish GFR core cooling through natural phenomena. This work investigates the potential of post-LOCA decay heat removal from a GFR core to a heat sink using an external convection loop. A model was developed in the form of the LOCA-COLA (Loss of Coolant Accident - Convection Loop Analysis) computer code as a meansmore » for 1D steady state convective heat transfer loop analysis. The results show that decay heat removal by means of gas cooled natural circulation is feasible under elevated post-LOCA containment pressure conditions. (authors)« less

Magnetization measurements and XMCD studies on ion irradiated iron oxide and core-shell iron/iron-oxide nanomaterials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Maninder; Qiang, You; Jiang, Weilin

2014-12-02

Magnetite (Fe3O4) and core-shell iron/iron-oxide (Fe/Fe3O4) nanomaterials prepared by a cluster deposition system were irradiated with 5.5 MeV Si2+ ions and the structures determined by x-ray diffraction as consisting of 100% magnetite and 36/64 wt% Fe/FeO, respectively. However, x-ray magnetic circular dichroism (XMCD) indicates similar surfaces in the two samples, slightly oxidized and so having more Fe3+ than the expected magnetite structure, with XMCD intensity much lower for the irradiated core-shell samples indicating weaker magnetism. X-ray absorption spectroscopy (XAS) data lack the signature for FeO, but the irradiated core-shell system consists of Fe-cores with ~13 nm of separating oxide crystallite,more » so it is likely that FeO exists deeper than the probe depth of the XAS (~5 nm). Exchange bias (Hex) for both samples becomes increasingly negative as temperature is lowered, but the irradiated Fe3O4 sample shows greater sensitivity of cooling field on Hex. Loop asymmetries and Hex sensitivities of the irradiated Fe3O4 sample are due to interfaces and interactions between grains which were not present in samples before irradiation as well as surface oxidation. Asymmetries in the hysteresis curves of the irradiated core/shell sample are related to the reversal mechanism of the antiferromagnetic FeO and possibly some near surface oxidation.« less

Development work for a borax internal core-catcher for a gas-cooled fast reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donne, M.D.; Dorner, S.; Schumacher, G.

1978-07-01

Preliminary thermal calculations show that a corecatcher, which is able to cope with the complete meltdown of the core and blankets of a 1000-MW(electric) gas-cooled fast reactor, appears to be feasible. This core-catcher is based on borax (Na/sub 2/B/sub 4/O/sub 7/) dissolving the oxide fuel and the fission products occurring in oxide form. The borax is contained in steel boxes forming a 2.2-m-thick slab on the base of the reactor cavity inside the prestressed concrete reactor vessel (PCRV), just underneath the reactor core. After a complete meltdown accident, the fission products, in oxide form, are dispersed in the pool formedmore » by the liquid borax. The metallic fission products are contained in the steel lying below the borax pool and in contact with the water-cooled PCRV liner. The volumetric power density of the molten core is conveniently reduced as it is dissolved in the borax, and the resulting heat fluxes at the borders of the pool can be safely carried away through the PCRV liner and its water cooling system.« less

Correlation buildup during recrystallization in three-dimensional dusty plasma clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schella, André; Mulsow, Matthias; Melzer, André

2014-05-15

The recrystallization process of finite three-dimensional dust clouds after laser heating is studied experimentally. The time-dependent Coulomb coupling parameter is presented, showing that the recrystallization starts with an exponential cooling phase where cooling is slower than damping by the neutral gas friction. At later times, the coupling parameter oscillates into equilibrium. It is found that a large fraction of cluster states after recrystallization experiments is in metastable states. The temporal evolution of the correlation buildup shows that correlation occurs on even slower time scale than cooling.

Paleomagnetic evidence for dynamo activity driven by inward crystallisation of a metallic asteroid

NASA Astrophysics Data System (ADS)

Bryson, James F. J.; Weiss, Benjamin P.; Harrison, Richard J.; Herrero-Albillos, Julia; Kronast, Florian

2017-08-01

The direction in which a planetary core solidifies has fundamental implications for the feasibility and nature of dynamo generation. Although Earth's core is outwardly solidifying, the cores of certain smaller planetary bodies have been proposed to inwardly solidify due to their lower central pressures. However, there have been no unambiguous observations of inwardly solidified cores or the relationship between this solidification regime and planetary magnetic activity. To address this gap, we present the results of complimentary paleomagnetic techniques applied to the matrix metal and silicate inclusions within the IVA iron meteorites. This family of meteorites has been suggested to originate from a planetary core that had its overlaying silicate mantle removed by collisions during the early solar system. This process is thought to have produced a molten ball of metal that cooled rapidly and has been proposed to have inwardly solidified. Recent thermal evolution models of such a body predict that it should have generated an intense, multipolar and time-varying dynamo field. This field could have been recorded as a remanent magnetisation in the outer, cool layers of a solid crust on the IVA parent core. We find that the different components in the IVA iron meteorites display a range of paleomagnetic fidelities, depending crucially on the cooling rate of the meteorite. In particular, silicate inclusions in the quickly cooled São João Nepomuceno meteorite are poor paleomagnetic recorders. On the other hand, the matrix metal and some silicate subsamples from the relatively slowly cooled Steinbach meteorite are far better paleomagnetic recorders and provide evidence of an intense (≳100 μT) and directionally varying (exhibiting significant changes on a timescale ≲200 kyr) magnetic field. This is the first demonstration that some iron meteorites record ancient planetary magnetic fields. Furthermore, the observed field intensity, temporal variability and dynamo lifetime are consistent with thermal evolution models of the IVA parent core. Because the acquisition of remanent magnetisation by some IVA iron meteorites require that they cooled below their Curie temperature during the period of dynamo activity, the magnetisation carried by Steinbach also provides strong evidence favouring the inward solidification of its parent core.

Demonstration of passively cooled high-power Yb fiber amplifier

NASA Astrophysics Data System (ADS)

Bradford, Joshua; Cook, Justin; Antonio-Lopez, Jose Enrique; Shah, Larry; Amezcua Correa, Rodrigo; Richardson, Martin

2018-02-01

This work investigates the feasibility of passive cooling in high-power Yb amplifiers. Experimentally, an all-glass airclad step-index (ACSI) amplifier is diode-pumped with 400W and provides 200W power levels. With only natural convection to extract heat, core temperatures are estimated near 130°C with no degradation of performance relative to cooled architectures. Further, advanced analysis techniques allow for core temperature determination using thermal interferometry without the need for complicated stabilization or calibration.

Effect of Vortex Circulation on Injectant from a Single Film-Cooling Hole and a Row of Film-Cooling Holes in a Turbulent Boundary Layer. Part 1. Injection Beneath the Vortex Downwash

DTIC Science & Technology

1989-06-01

coefficients vortex circulation, symbols used in vorticity plots representing circulation values derived from different vortex core models injection...derived from different vortex core models dimensionless core size parameter: t wice the a verage core radius divided by t h e i n jection hole...Wall Heating, xjd=109.2, m=0.5, Single Injection Hole Vortex w, Temp. Difference Range (.5- 2.5) degree s 91. Local Temperature Distribution

Using Firn Air for Facility Cooling at the WAIS Divide Site

DTIC Science & Technology

2014-09-17

reduce logistics costs at remote field camps where it is critical to maintain proper temperatures to preserve sensitive deep ice cores. We assessed the...feasibility of using firn air for cooling at the West Antarc- tic Ice Sheet (WAIS) Divide ice core drilling site as a means to adequately and...efficiently refrigerate ice cores during storage and processing. We used estimates of mean annual temperature, temperature variations, and firn

Diffuse light and building history of the galaxy cluster Abell 2667

NASA Astrophysics Data System (ADS)

Covone, G.; Adami, C.; Durret, F.; Kneib, J.-P.; Lima Neto, G. B.; Slezak, E.

2006-12-01

Aims.We searched for diffuse intracluster light in the galaxy cluster Abell 2667 (z=0.233) from HST images in three broad band-filters. Methods: .We applied an iterative multi-scale wavelet analysis and reconstruction technique to these images, which allows to subtract stars and galaxies from the original images. Results: .We detect a zone of diffuse emission southwest of the cluster center (DS1) and a second faint object (ComDif) within DS1. Another diffuse source (DS2) may be detected at lower confidence level northeast of the center. These sources of diffuse light contribute to 10-15% of the total visible light in the cluster. Whether they are independent entities or part of the very elliptical external envelope of the central galaxy remains unclear. Deep VLT VIMOS integral field spectroscopy reveals a faint continuum at the positions of DS1 and ComDif but do not allow a redshift to be computed, so we conclude if these sources are part of the central galaxy or not. A hierarchical substructure detection method reveals the presence of several galaxy pairs and groups defining a similar direction to the one drawn by the DS1 - central galaxy - DS2 axis. The analysis of archive XMM-Newton and Chandra observations shows X-ray emission elongated in the same direction. The X-ray temperature map shows the presence of a cool core, a broad cool zone stretching from north to south, and hotter regions towards the northeast, southwest, and northwest. This might suggest shock fronts along these directions produced by infalling material, even if uncertainties remain quite large on the temperature determination far from the center. Conclusions: .These various data are consistent with a picture in which diffuse sources are concentrations of tidal debris and harassed matter expelled from infalling galaxies by tidal stripping and undergoing an accretion process onto the central cluster galaxy; as such, they are expected to be found along the main infall directions. Note, however, that the limited signal to noise of the various data and the apparent lack of large numbers of well-defined independent tidal tails, besides the one named ComDif, preclude definitive conclusions on this scenario.

Searching for cluster magnetic fields in the cooling flows of 0745-191, A2029, and A4059

NASA Technical Reports Server (NTRS)

Taylor, Gregory B.; Barton, Elizabeth J.; Ge, Jingping

1994-01-01

We have performed sensitive polarimetric radio observations with the Very Large Array (VLA) of three galaxies: PKS 0745-191, PKS 1508+059, and PKS 2354-350, embedded in x-ray cooling flow clusters. High sensitivity, multifrequency maps of all three, along with spectral index and Faraday rotation measure (RM) maps of PKS 1508+059 and PKS 2354-350 are presented. For PKS 1508+059 and PKS 2354-350 models of the electron density of the intracluster medium (ICM) have been used to set lower limits of 0.1 and 2.7 microG, respectively, on the magnetic field in the ICM based on the observed RMs. In an x-ray selected sample of cooling flow clusters with an associated radio source, 57% (8/14) are found to have absolute RMs in excess of 800 radians/sq m. This sample includes the three sources of this study and all the other high RM sources found to date at zeta less than 0.4. These facts are consistent with the high RM phenomenon being produced by magnetic fields associated with the relatively dense, hot x-ray gas in cooling flow clusters.

Hundred Thousand Degree Gas in the Virgo Cluster of Galaxies

NASA Astrophysics Data System (ADS)

Sparks, W. B.; Pringle, J. E.; Carswell, R. F.; Donahue, M.; Martin, R.; Voit, M.; Cracraft, M.; Manset, N.; Hough, J. H.

2012-05-01

The physical relationship between low-excitation gas filaments at ~104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~107 K in the centers of many galaxy clusters is not understood. It is unclear whether the ~104 K filaments have cooled and condensed from the ambient hot (~107 K) medium or have some other origin such as the infall of cold gas in a merger, or the disturbance of an internal cool reservoir of gas by nuclear activity. Observations of gas at intermediate temperatures (~105-106 K) can potentially reveal whether the central massive galaxies are gaining cool gas through condensation or losing it through conductive evaporation and hence identify plausible scenarios for transport processes in galaxy cluster gas. Here we present spectroscopic detection of ~105 K gas spatially associated with the Hα filaments in a central cluster galaxy, M87, in the Virgo Cluster. The measured emission-line fluxes from triply ionized carbon (C IV 1549 Å) and singly ionized helium (He II 1640 Å) are consistent with a model in which thermal conduction determines the interaction between hot and cold phases.

Evaluation of advanced cooling therapy's esophageal cooling device for core temperature control.

PubMed

Naiman, Melissa; Shanley, Patrick; Garrett, Frank; Kulstad, Erik

2016-05-01

Managing core temperature is critical to patient outcomes in a wide range of clinical scenarios. Previous devices designed to perform temperature management required a trade-off between invasiveness and temperature modulation efficiency. The Esophageal Cooling Device, made by Advanced Cooling Therapy (Chicago, IL), was developed to optimize warming and cooling efficiency through an easy and low risk procedure that leverages heat transfer through convection and conduction. Clinical data from cardiac arrest, fever, and critical burn patients indicate that the Esophageal Cooling Device performs very well both in terms of temperature modulation (cooling rates of approximately 1.3°C/hour, warming of up to 0.5°C/hour) and maintaining temperature stability (variation around goal temperature ± 0.3°C). Physicians have reported that device performance is comparable to the performance of intravascular temperature management techniques and superior to the performance of surface devices, while avoiding the downsides associated with both.

Brain stem sites mediating specific and non-specific temperature effects on thermoregulation in the pekin duck.

PubMed Central

Martin, R; Simon, E; Simon-Oppermann, C

1981-01-01

1. Thermodes were chronically implanted into various levels of the brain stem of sixteen Pekin ducks. The effects of local thermal stimulation on metabolic heat production, core temperature, peripheral skin temperature and respiratory frequency were investigated. 2. Four areas of thermode positions were determined according to the responses observed and were histologically identified at the end of the investigation. 3. Thermal stimulation of the lower mid-brain/upper pontine brain stem (Pos. III) elicited an increase in metabolic heat production, cutaneous vasoconstriction and rises in core temperature in response to cooling at thermoneutral and cold ambient conditions and, further, inhibition of panting by cooling and activation of panting by heating at warm ambient conditions. The metabolic response to cooling this brain stem section amounted to -0.1 W/kg. degrees C as compared with -7 W/kg. degrees C in response to total body cooling. 4. Cooling of the anterior and middle hypothalamus (Pos. II) caused vasodilatation in the skin and did not elicit shivering. The resulting drop in core temperature at a given degree of cooling was greater than the rise in core temperature in response to equivalent cooling of the lower mid-brain/upper pontine brain stem. 5. Cooling of the preoptic forebrain (Pos. I) and of the myelencephalon (Pos. IV) did not elicit thermoregulatory reactions. 6. It is concluded that the duck's brain stem contains thermoreceptive structures in the lower mid-brain/upper pontine section. However, the brain stem as a whole appears to contribute little to cold defence during general hypothermia because of the inhibitory effects originating in the anterior and middle hypothalamus. Cold defence in the duck, which is comparable in strength to that in mammals, has to rely on extracerebral thermosensory structures. PMID:7310688

Cooling Flows

NASA Astrophysics Data System (ADS)

Fabian, A.; Murdin, P.

2000-11-01

A subsonic cooling flow occurs when the hot gaseous atmosphere of a galaxy, group or cluster of galaxies cools slowly. Such atmospheres occur as a result of gas having fallen into the DARK MATTER well of the object and heated by gravitational energy release. A dominant cooling process is the emission of radiation by the gas. As cooling proceeds the gas sinks further in the potential well, giving ...

Long-term changes in the heat-mortality relationship according to heterogeneous regional climate: a time-series study in South Korea.

PubMed

Heo, Seulkee; Lee, Eunil; Kwon, Bo Yeon; Lee, Suji; Jo, Kyung Hee; Kim, Jinsun

2016-08-03

Several studies identified a heterogeneous impact of heat on mortality in hot and cool regions during a fixed period, whereas less evidence is available for changes in risk over time due to climate change in these regions. We compared changes in risk during periods without (1996-2000) and with (2008-2012) heatwave warning forecasts in regions of South Korea with different climates. Study areas were categorised into 3 clusters based on the spatial clustering of cooling degree days in the period 1993-2012: hottest cluster (cluster H), moderate cluster (cluster M) and cool cluster (cluster C). The risk was estimated according to increases in the daily all-cause, cardiovascular and respiratory mortality per 1°C change in daily temperature above the threshold, using a generalised additive model. The risk of all types of mortality increased in cluster H in 2008-2012, compared with 1996-2000, whereas the risks in all-combined regions and cooler clusters decreased. Temporal increases in mortality risk were larger for some vulnerable subgroups, including younger adults (<75 years), those with a lower education and blue-collar workers, in cluster H as well as all-combined regions. Different patterns of risk change among clusters might be attributable to large increases in heatwave frequency or duration during study periods and the degree of urbanisation in cluster H. People living in hotter regions or with a lower socioeconomic status are at higher risk following an increasing trend of heat-related mortality risks. Continuous efforts are needed to understand factors which affect changes in heat-related mortality risks. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

Shocks and Bubbles in a Deep Chandra Observation of the Cooling Flow Cluster Abell 2052

DTIC Science & Technology

2009-01-01

the bubble rims related to radio source outbursts have been found in a few clusters including M87/ Virgo (Forman et al. 2005), Hydra A (Nulsen et al...Printed in the U.S.A. SHOCKS AND BUBBLES IN A DEEP CHANDRA OBSERVATION OF THE COOLING FLOW CLUSTER ABELL 2052 E. L. Blanton1, S. W. Randall2, E. M...Douglass1, C. L. Sarazin3, T. E. Clarke4,5, and B. R. McNamara2,6,7 1 Institute for Astrophysical Research , Boston University, 725 Commonwealth Avenue

ACUTE CARDIOVASCULAR EFFECTS OF FIREFIGHTING AND ACTIVE COOLING DURING REHABILITATION

PubMed Central

Burgess, Jefferey L.; Duncan, Michael D.; Hu, Chengcheng; Littau, Sally R.; Caseman, Delayne; Kurzius-Spencer, Margaret; Davis-Gorman, Grace; McDonagh, Paul F.

2012-01-01

Objectives To determine the cardiovascular and hemostatic effects of fire suppression and post-exposure active cooling. Methods Forty-four firefighters were evaluated prior to and after a 12 minute live-fire drill. Next, 50 firefighters undergoing the same drill were randomized to post-fire forearm immersion in 10°C water or standard rehabilitation. Results In the first study, heart rate and core body temperature increased and serum C-reactive protein decreased but there were no significant changes in fibrinogen, sE-selectin or sL-selectin. The second study demonstrated an increase in blood coagulability, leukocyte count, factors VIII and X, cortisol and glucose, and a decrease in plasminogen and sP-selectin. Active cooling reduced mean core temperature, heart rate and leukocyte count. Conclusions Live-fire exposure increased core temperature, heart rate, coagulability and leukocyte count; all except coagulability were reduced by active cooling. PMID:23090161

78 FR 64027 - Preoperational Testing of Emergency Core Cooling Systems for Pressurized-Water Reactors

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-25

...The U.S. Nuclear Regulatory Commission (NRC) is issuing a revision to regulatory guide (RG), 1.79, ``Preoperational Testing of Emergency Core Cooling Systems for Pressurized-Water Reactors.'' This RG is being revised to incorporate guidance for preoperational testing of new pressurized water reactor (PWR) designs.

Monte Carlo Analysis of the Battery-Type High Temperature Gas Cooled Reactor

NASA Astrophysics Data System (ADS)

Grodzki, Marcin; Darnowski, Piotr; Niewiński, Grzegorz

2017-12-01

The paper presents a neutronic analysis of the battery-type 20 MWth high-temperature gas cooled reactor. The developed reactor model is based on the publicly available data being an `early design' variant of the U-battery. The investigated core is a battery type small modular reactor, graphite moderated, uranium fueled, prismatic, helium cooled high-temperature gas cooled reactor with graphite reflector. The two core alternative designs were investigated. The first has a central reflector and 30×4 prismatic fuel blocks and the second has no central reflector and 37×4 blocks. The SERPENT Monte Carlo reactor physics computer code, with ENDF and JEFF nuclear data libraries, was applied. Several nuclear design static criticality calculations were performed and compared with available reference results. The analysis covered the single assembly models and full core simulations for two geometry models: homogenous and heterogenous (explicit). A sensitivity analysis of the reflector graphite density was performed. An acceptable agreement between calculations and reference design was obtained. All calculations were performed for the fresh core state.

Microchip transponder thermometry for monitoring core body temperature of antelope during capture.

PubMed

Rey, Benjamin; Fuller, Andrea; Hetem, Robyn S; Lease, Hilary M; Mitchell, Duncan; Meyer, Leith C R

2016-01-01

Hyperthermia is described as the major cause of morbidity and mortality associated with capture, immobilization and restraint of wild animals. Therefore, accurately determining the core body temperature of wild animals during capture is crucial for monitoring hyperthermia and the efficacy of cooling procedures. We investigated if microchip thermometry can accurately reflect core body temperature changes during capture and cooling interventions in the springbok (Antidorcas marsupialis), a medium-sized antelope. Subcutaneous temperature measured with a temperature-sensitive microchip was a weak predictor of core body temperature measured by temperature-sensitive data loggers in the abdominal cavity (R(2)=0.32, bias >2 °C). Temperature-sensitive microchips in the gluteus muscle, however, provided an accurate estimate of core body temperature (R(2)=0.76, bias=0.012 °C). Microchips inserted into muscle therefore provide a convenient and accurate method to measure body temperature continuously in captured antelope, allowing detection of hyperthermia and the efficacy of cooling procedures. Copyright © 2015 Elsevier Ltd. All rights reserved.

Does the diurnal increase in central temperature interact with pre-cooling or passive warm-up of the leg?

PubMed

Racinais, Sébastien; Blonc, Stephen; Oksa, Juha; Hue, Olivier

2009-01-01

Seven male subjects volunteered to participate in an investigation of whether the diurnal increase in core temperature influences the effects of pre-cooling or passive warm-up on muscular power. Morning (07:00-09:00h) and afternoon (17:00-19:00h) evaluation of maximal power output during a cycling sprint was performed on different days in a control condition (room at 21.8 degrees C, 69% rh), after 30min of pre-cooling in a cold bath (16 degrees C), or after 30min of passive warm-up in a hot bath (38 degrees C). Despite an equivalent increase from morning to afternoon in core temperature in all conditions (+0.4 degrees C, P<0.05), power output displayed a diurnal increase in control condition only. A local cooling or heating of the leg in a neutral environment blunted the diurnal variation in muscular power. Because pre-cooling decreases muscle power, force and velocity irrespective of time-of-day, athletes should strictly avoid any cooling before a sprint exercise. In summary, diurnal variation in muscle power output seems to be more influenced by muscle rather than core temperature.

Core–shell interaction and its impact on the optical absorption of pure and doped core-shell CdSe/ZnSe nanoclusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xinqin; Cui, Yingqi; Zeng, Qun

The structural, electronic, and optical properties of core-shell nanoclusters, (CdSe){sub x}@(CdSe){sub y} and their Zn-substituted complexes of x = 2–4 and y = 16–28, were studied with density functional theory calculations. The substitution was applied in the cores, the shells, and/or the whole clusters. All these clusters are characterized by their core-shell structures in which the core-shell interaction was found different from those in core or in shell, as reflected by their bondlengths, volumes, and binding energies. Moreover, the core and shell combine together to compose a new cluster with electronic and optical properties different from those of separated individuals,more » as reflected by their HOMO-LUMO gaps and optical absorptions. With the substitution of Cd by Zn, the structural, electronic, and optical properties of clusters change regularly. The binding energy increases with Zn content, attributed to the strong Zn–Se bonding. For the same core/shell, the structure with a CdSe shell/core has a narrower gap than that with a ZnSe shell/core. The optical absorption spectra also change accordingly with Zn substitution. The peaks blueshift with increasing Zn concentration, accompanying with shape variations in case large number of Cd atoms are substituted. Our calculations reveal the core-shell interaction and its influence on the electronic and optical properties of the core-shell clusters, suggesting a composition–structure–property relationship for the design of core-shell CdSe and ZnSe nanoclusters.« less

Exploring cosmic origins with CORE: Cluster science

NASA Astrophysics Data System (ADS)

Melin, J.-B.; Bonaldi, A.; Remazeilles, M.; Hagstotz, S.; Diego, J. M.; Hernández-Monteagudo, C.; Génova-Santos, R. T.; Luzzi, G.; Martins, C. J. A. P.; Grandis, S.; Mohr, J. J.; Bartlett, J. G.; Delabrouille, J.; Ferraro, S.; Tramonte, D.; Rubiño-Martín, J. A.; Macìas-Pérez, J. F.; Achúcarro, A.; Ade, P.; Allison, R.; Ashdown, M.; Ballardini, M.; Banday, A. J.; Banerji, R.; Bartolo, N.; Basak, S.; Basu, K.; Battye, R. A.; Baumann, D.; Bersanelli, M.; Bonato, M.; Borrill, J.; Bouchet, F.; Boulanger, F.; Brinckmann, T.; Bucher, M.; Burigana, C.; Buzzelli, A.; Cai, Z.-Y.; Calvo, M.; Carvalho, C. S.; Castellano, M. G.; Challinor, A.; Chluba, J.; Clesse, S.; Colafrancesco, S.; Colantoni, I.; Coppolecchia, A.; Crook, M.; D'Alessandro, G.; de Bernardis, P.; de Gasperis, G.; De Petris, M.; De Zotti, G.; Di Valentino, E.; Errard, J.; Feeney, S. M.; Fernández-Cobos, R.; Finelli, F.; Forastieri, F.; Galli, S.; Gerbino, M.; González-Nuevo, J.; Greenslade, J.; Hanany, S.; Handley, W.; Hervias-Caimapo, C.; Hills, M.; Hivon, E.; Kiiveri, K.; Kisner, T.; Kitching, T.; Kunz, M.; Kurki-Suonio, H.; Lamagna, L.; Lasenby, A.; Lattanzi, M.; Le Brun, A. M. C.; Lesgourgues, J.; Lewis, A.; Liguori, M.; Lindholm, V.; Lopez-Caniego, M.; Maffei, B.; Martinez-Gonzalez, E.; Masi, S.; Mazzotta, P.; McCarthy, D.; Melchiorri, A.; Molinari, D.; Monfardini, A.; Natoli, P.; Negrello, M.; Notari, A.; Paiella, A.; Paoletti, D.; Patanchon, G.; Piat, M.; Pisano, G.; Polastri, L.; Polenta, G.; Pollo, A.; Poulin, V.; Quartin, M.; Roman, M.; Salvati, L.; Tartari, A.; Tomasi, M.; Trappe, N.; Triqueneaux, S.; Trombetti, T.; Tucker, C.; Väliviita, J.; van de Weygaert, R.; Van Tent, B.; Vennin, V.; Vielva, P.; Vittorio, N.; Weller, J.; Young, K.; Zannoni, M.

2018-04-01

We examine the cosmological constraints that can be achieved with a galaxy cluster survey with the future CORE space mission. Using realistic simulations of the millimeter sky, produced with the latest version of the Planck Sky Model, we characterize the CORE cluster catalogues as a function of the main mission performance parameters. We pay particular attention to telescope size, key to improved angular resolution, and discuss the comparison and the complementarity of CORE with ambitious future ground-based CMB experiments that could be deployed in the next decade. A possible CORE mission concept with a 150 cm diameter primary mirror can detect of the order of 50,000 clusters through the thermal Sunyaev-Zeldovich effect (SZE). The total yield increases (decreases) by 25% when increasing (decreasing) the mirror diameter by 30 cm. The 150 cm telescope configuration will detect the most massive clusters (>1014 Msolar) at redshift z>1.5 over the whole sky, although the exact number above this redshift is tied to the uncertain evolution of the cluster SZE flux-mass relation; assuming self-similar evolution, CORE will detect 0~ 50 clusters at redshift z>1.5. This changes to 800 (200) when increasing (decreasing) the mirror size by 30 cm. CORE will be able to measure individual cluster halo masses through lensing of the cosmic microwave background anisotropies with a 1-σ sensitivity of 4×1014 Msolar, for a 120 cm aperture telescope, and 1014 Msolar for a 180 cm one. From the ground, we estimate that, for example, a survey with about 150,000 detectors at the focus of 350 cm telescopes observing 65% of the sky would be shallower than CORE and detect about 11,000 clusters, while a survey with the same number of detectors observing 25% of sky with a 10 m telescope is expected to be deeper and to detect about 70,000 clusters. When combined with the latter, CORE would reach a limiting mass of M500 ~ 2‑3 × 1013 Msolar and detect 220,000 clusters (5 sigma detection limit). Cosmological constraints from CORE cluster counts alone are competitive with other scheduled large scale structure surveys in the 2020's for measuring the dark energy equation-of-state parameters w0 and wa (σw0=0.28, σwa=0.31). In combination with primary CMB constraints, CORE cluster counts can further reduce these error bars on w0 and wa to 0.05 and 0.13 respectively, and constrain the sum of the neutrino masses, Σ mν, to 39 meV (1 sigma). The wide frequency coverage of CORE, 60–600 GHz, will enable measurement of the relativistic thermal SZE by stacking clusters. Contamination by dust emission from the clusters, however, makes constraining the temperature of the intracluster medium difficult. The kinetic SZE pairwise momentum will be extracted with 0S/N=7 in the foreground-cleaned CMB map. Measurements of TCMB(z) using CORE clusters will establish competitive constraints on the evolution of the CMB temperature: (1+z)1‑β, with an uncertainty of σβ lesssim 2.7× 10‑3 at low redshift (z lesssim 1). The wide frequency coverage also enables clean extraction of a map of the diffuse SZE signal over the sky, substantially reducing contamination by foregrounds compared to the Planck SZE map extraction. Our analysis of the one-dimensional distribution of Compton-y values in the simulated map finds an order of magnitude improvement in constraints on σ8 over the Planck result, demonstrating the potential of this cosmological probe with CORE.

A highly efficient multi-core algorithm for clustering extremely large datasets

PubMed Central

2010-01-01

Background In recent years, the demand for computational power in computational biology has increased due to rapidly growing data sets from microarray and other high-throughput technologies. This demand is likely to increase. Standard algorithms for analyzing data, such as cluster algorithms, need to be parallelized for fast processing. Unfortunately, most approaches for parallelizing algorithms largely rely on network communication protocols connecting and requiring multiple computers. One answer to this problem is to utilize the intrinsic capabilities in current multi-core hardware to distribute the tasks among the different cores of one computer. Results We introduce a multi-core parallelization of the k-means and k-modes cluster algorithms based on the design principles of transactional memory for clustering gene expression microarray type data and categorial SNP data. Our new shared memory parallel algorithms show to be highly efficient. We demonstrate their computational power and show their utility in cluster stability and sensitivity analysis employing repeated runs with slightly changed parameters. Computation speed of our Java based algorithm was increased by a factor of 10 for large data sets while preserving computational accuracy compared to single-core implementations and a recently published network based parallelization. Conclusions Most desktop computers and even notebooks provide at least dual-core processors. Our multi-core algorithms show that using modern algorithmic concepts, parallelization makes it possible to perform even such laborious tasks as cluster sensitivity and cluster number estimation on the laboratory computer. PMID:20370922

Hot and turbulent gas in clusters

DOE PAGES

Schmidt, W.; Engels, J. F.; Niemeyer, J. C.; ...

2016-03-20

The gas in galaxy clusters is heated by shock compression through accretion (outer shocks) and mergers (inner shocks). These processes also produce turbulence. To analyse the relation between the thermal and turbulent energies of the gas under the influence of non-adiabatic processes, we performed numerical simulations of cosmic structure formation in a box of 152 Mpc comoving size with radiative cooling, UV background, and a subgrid scale model for numerically unresolved turbulence. By smoothing the gas velocities with an adaptive Kalman filter, we are able to estimate bulk flows towards cluster cores. This enables us to infer the velocity dispersionmore » associated with the turbulent fluctuation relative to the bulk flow. For haloes with masses above 10 13 M ⊙, we find that the turbulent velocity dispersions averaged over the warm-hot intergalactic medium (WHIM) and the intracluster medium (ICM) are approximately given by powers of the mean gas temperatures with exponents around 0.5, corresponding to a roughly linear relation between turbulent and thermal energies and transonic Mach numbers. However, turbulence is only weakly correlated with the halo mass. Since the power-law relation is stiffer for the WHIM, the turbulent Mach number tends to increase with the mean temperature of the WHIM. This can be attributed to enhanced turbulence production relative to dissipation in particularly hot and turbulent clusters.« less

Pd-Ag chronometry of IVA iron meteorites and the crystallization and cooling of a protoplanetary core

DOE PAGES

Matthes, M.; Fischer-Godde, M.; Kruijer, T. S.; ...

2017-09-07

To constrain the timescales and processes involved in the crystallization and cooling of protoplanetary cores, we examined the Pd-Ag isotope systematics of the IVA iron meteorites Muonionalusta and Gibeon. A Pd-Ag isochron for Muonionalusta provides an initial 107Pd/ 108Pd = (2.57 ± 0.07) × 10 -5. The three metal samples analyzed from Gibeon plot below the Muonionalusta isochron, but these samples also show significant effects of cosmic ray-induced neutron capture reactions, as is evident from 196Pt excesses in the Gibeon samples. After correction for neutron capture effects on Ag isotopes, the Gibeon samples plot on the Muonionalusta isochron, indicating thatmore » these two IVA irons have indistinguishable initial 107Pd/ 108Pd. Collectively, the Pd-Ag data indicate cooling of the IVA core below Pd-Ag closure between 2.9 ± 0.4 Ma and 8.9 ± 0.6 Ma after CAI formation, where this age range reflects uncertainties in the initial 107Pd/ 108Pd ratios of the solar system, which in turn result from uncertainties in the Pb-Pb age of Muonionalusta. The Ag isotopic data indicate that the IVA core initially evolved with a modestly elevated Pd/Ag, but the low Ag concentrations measured for some metal samples indicate derivation from a source with much lower Ag contents and, hence, higher Pd/Ag. These contrasting observations can be reconciled if the IVA irons crystallized from an initially more Ag-rich core, followed by extraction of Fe-S melts during compaction of the nearly solidified core. Owing to its strong tendency to partition into Fe-S melts, Ag was removed from the IVA core during compaction, leading to the very low Ag concentration observed in metal samples of IVA irons. Alternatively, Ag was lost by evaporation from a still molten metallic body just prior to the onset of crystallization. The Pd-Ag isotopic data indicate that Muonionalusta cooled at >500 K/Ma through the Pd-Ag closure temperature of ~900 K, consistent with the rapid cooling inferred from metallographic cooling rates for IVA irons. Finally, combined, these observations are consistent with cooling of IVA irons in a metallic body with little or no silicate mantle.« less

Pd-Ag chronometry of IVA iron meteorites and the crystallization and cooling of a protoplanetary core

NASA Astrophysics Data System (ADS)

Matthes, M.; Fischer-Gödde, M.; Kruijer, T. S.; Kleine, T.

2018-01-01

To constrain the timescales and processes involved in the crystallization and cooling of protoplanetary cores, we examined the Pd-Ag isotope systematics of the IVA iron meteorites Muonionalusta and Gibeon. A Pd-Ag isochron for Muonionalusta provides an initial 107Pd/108Pd = (2.57 ± 0.07) × 10-5. The three metal samples analyzed from Gibeon plot below the Muonionalusta isochron, but these samples also show significant effects of cosmic ray-induced neutron capture reactions, as is evident from 196Pt excesses in the Gibeon samples. After correction for neutron capture effects on Ag isotopes, the Gibeon samples plot on the Muonionalusta isochron, indicating that these two IVA irons have indistinguishable initial 107Pd/108Pd. Collectively, the Pd-Ag data indicate cooling of the IVA core below Pd-Ag closure between 2.9 ± 0.4 Ma and 8.9 ± 0.6 Ma after CAI formation, where this age range reflects uncertainties in the initial 107Pd/108Pd ratios of the solar system, which in turn result from uncertainties in the Pb-Pb age of Muonionalusta. The Ag isotopic data indicate that the IVA core initially evolved with a modestly elevated Pd/Ag, but the low Ag concentrations measured for some metal samples indicate derivation from a source with much lower Ag contents and, hence, higher Pd/Ag. These contrasting observations can be reconciled if the IVA irons crystallized from an initially more Ag-rich core, followed by extraction of Fe-S melts during compaction of the nearly solidified core. Owing to its strong tendency to partition into Fe-S melts, Ag was removed from the IVA core during compaction, leading to the very low Ag concentration observed in metal samples of IVA irons. Alternatively, Ag was lost by evaporation from a still molten metallic body just prior to the onset of crystallization. The Pd-Ag isotopic data indicate that Muonionalusta cooled at >500 K/Ma through the Pd-Ag closure temperature of ∼900 K, consistent with the rapid cooling inferred from metallographic cooling rates for IVA irons. Combined, these observations are consistent with cooling of IVA irons in a metallic body with little or no silicate mantle.

Pd-Ag chronometry of IVA iron meteorites and the crystallization and cooling of a protoplanetary core

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matthes, M.; Fischer-Godde, M.; Kruijer, T. S.

To constrain the timescales and processes involved in the crystallization and cooling of protoplanetary cores, we examined the Pd-Ag isotope systematics of the IVA iron meteorites Muonionalusta and Gibeon. A Pd-Ag isochron for Muonionalusta provides an initial 107Pd/ 108Pd = (2.57 ± 0.07) × 10 -5. The three metal samples analyzed from Gibeon plot below the Muonionalusta isochron, but these samples also show significant effects of cosmic ray-induced neutron capture reactions, as is evident from 196Pt excesses in the Gibeon samples. After correction for neutron capture effects on Ag isotopes, the Gibeon samples plot on the Muonionalusta isochron, indicating thatmore » these two IVA irons have indistinguishable initial 107Pd/ 108Pd. Collectively, the Pd-Ag data indicate cooling of the IVA core below Pd-Ag closure between 2.9 ± 0.4 Ma and 8.9 ± 0.6 Ma after CAI formation, where this age range reflects uncertainties in the initial 107Pd/ 108Pd ratios of the solar system, which in turn result from uncertainties in the Pb-Pb age of Muonionalusta. The Ag isotopic data indicate that the IVA core initially evolved with a modestly elevated Pd/Ag, but the low Ag concentrations measured for some metal samples indicate derivation from a source with much lower Ag contents and, hence, higher Pd/Ag. These contrasting observations can be reconciled if the IVA irons crystallized from an initially more Ag-rich core, followed by extraction of Fe-S melts during compaction of the nearly solidified core. Owing to its strong tendency to partition into Fe-S melts, Ag was removed from the IVA core during compaction, leading to the very low Ag concentration observed in metal samples of IVA irons. Alternatively, Ag was lost by evaporation from a still molten metallic body just prior to the onset of crystallization. The Pd-Ag isotopic data indicate that Muonionalusta cooled at >500 K/Ma through the Pd-Ag closure temperature of ~900 K, consistent with the rapid cooling inferred from metallographic cooling rates for IVA irons. Finally, combined, these observations are consistent with cooling of IVA irons in a metallic body with little or no silicate mantle.« less

REACTOR UNLOADING

DOEpatents

Leverett, M.C.

1958-02-18

This patent is related to gas cooled reactors wherein the fuel elements are disposed in vertical channels extending through the reactor core, the cooling gas passing through the channels from the bottom to the top of the core. The invention is a means for unloading the fuel elements from the core and comprises dump values in the form of flat cars mounted on wheels at the bottom of the core structure which support vertical stacks of fuel elements. When the flat cars are moved, either manually or automatically, for normal unloading purposes, or due to a rapid rise in the reproduction ratio within the core, the fuel elements are permtted to fall by gravity out of the core structure thereby reducing the reproduction ratio or stopping the reaction as desired.

Apparatus for controlling molten core debris

DOEpatents

Golden, Martin P. [Trafford, PA; Tilbrook, Roger W. [Monroeville, PA; Heylmun, Neal F. [Pittsburgh, PA

1977-07-19

Apparatus for containing, cooling, diluting, dispersing and maintaining subcritical the molten core debris assumed to melt through the bottom of a nuclear reactor pressure vessel in the unlikely event of a core meltdown. The apparatus is basically a sacrificial bed system which includes an inverted conical funnel, a core debris receptacle including a spherical dome, a spherically layered bed of primarily magnesia bricks, a cooling system of zig-zag piping in graphite blocks about and below the bed and a cylindrical liner surrounding the graphite blocks including a steel shell surrounded by firebrick. Tantalum absorber rods are used in the receptacle and bed.

Warming and Cooling: The Medieval Climate Anomaly in Africa and Arabia

NASA Astrophysics Data System (ADS)

Lüning, Sebastian; Gałka, Mariusz; Vahrenholt, Fritz

2017-11-01

The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000-1200 Common Era. Here we present a palaeotemperature synthesis for the MCA in Africa and Arabia, based on 44 published localities. The data sets have been thoroughly correlated and the MCA trends palaeoclimatologically mapped. The vast majority of available Afro-Arabian onshore sites suggest a warm MCA, with the exception of the southern Levant where the MCA appears to have been cold. MCA cooling has also been documented in many segments of the circum-Africa-Arabian upwelling systems, as a result of changes in the wind systems which were leading to an intensification of cold water upwelling. Offshore cores from outside upwelling systems mostly show warm MCA conditions. The most likely key drivers of the observed medieval climate change are solar forcing and ocean cycles. Conspicuous cold spikes during the earliest and latest MCA may help to discriminate between solar (Oort Minimum) and ocean cycle (Atlantic Multidecadal Oscillation, AMO) influence. Compared to its large share of nearly one quarter of the world's landmass, data from Africa and Arabia are significantly underrepresented in global temperature reconstructions of the past 2,000 years. Onshore data are still absent for most regions in Africa and Arabia, except for regional data clusters in Morocco, South Africa, the East African Rift, and the Levant coast. In order to reconstruct land palaeotemperatures more robustly over Africa and Arabia, a systematic research program is needed.

Thermal instability in gravitationally stratified plasmas: implications for multiphase structure in clusters and galaxy haloes

NASA Astrophysics Data System (ADS)

McCourt, Michael; Sharma, Prateek; Quataert, Eliot; Parrish, Ian J.

2012-02-01

We study the interplay among cooling, heating, conduction and magnetic fields in gravitationally stratified plasmas using simplified, plane-parallel numerical simulations. Since the physical heating mechanism remains uncertain in massive haloes such as groups or clusters, we adopt a simple, phenomenological prescription which enforces global thermal equilibrium and prevents a cooling flow. The plasma remains susceptible to local thermal instability, however, and cooling drives an inward flow of material. For physically plausible heating mechanisms in clusters, the thermal stability of the plasma is independent of its convective stability. We find that the ratio of the cooling time-scale to the dynamical time-scale tcool/tff controls the non-linear evolution and saturation of the thermal instability: when tcool/tff≲ 1, the plasma develops extended multiphase structure, whereas when tcool/tff≳ 1 it does not. (In a companion paper, we show that the criterion for thermal instability in a more realistic, spherical potential is somewhat less stringent, tcool/tff≲ 10.) When thermal conduction is anisotropic with respect to the magnetic field, the criterion for multiphase gas is essentially independent of the thermal conductivity of the plasma. Our criterion for local thermal instability to produce multiphase structure is an extension of the cold versus hot accretion modes in galaxy formation that applies at all radii in hot haloes, not just to the virial shock. We show that this criterion is consistent with data on multiphase gas in galaxy groups and clusters; in addition, when tcool/tff≳ 1, the net cooling rate to low temperatures and the mass flux to small radii are suppressed enough relative to models without heating to be qualitatively consistent with star formation rates and X-ray line emission in groups and clusters.

Thermal effects of dorsal head immersion in cold water on nonshivering humans.

PubMed

Giesbrecht, Gordon G; Lockhart, Tamara L; Bristow, Gerald K; Steinman, Allan M

2005-11-01

Personal floatation devices maintain either a semirecumbent flotation posture with the head and upper chest out of the water or a horizontal flotation posture with the dorsal head and whole body immersed. The contribution of dorsal head and upper chest immersion to core cooling in cold water was isolated when the confounding effect of shivering heat production was inhibited with meperidine (Demerol, 2.5 mg/kg). Six male volunteers were immersed four times for up to 60 min, or until esophageal temperature = 34 degrees C. An insulated hoodless dry suit or two different personal floatation devices were used to create four conditions: 1) body insulated, head out; 2) body insulated, dorsal head immersed; 3) body exposed, head (and upper chest) out; and 4) body exposed, dorsal head (and upper chest) immersed. When the body was insulated, dorsal head immersion did not affect core cooling rate (1.1 degrees C/h) compared with head-out conditions (0.7 degrees C/h). When the body was exposed, however, the rate of core cooling increased by 40% from 3.6 degrees C/h with the head out to 5.0 degrees C/h with the dorsal head and upper chest immersed (P < 0.01). Heat loss from the dorsal head and upper chest was approximately proportional to the extra surface area that was immersed (approximately 10%). The exaggerated core cooling during dorsal head immersion (40% increase) may result from the extra heat loss affecting a smaller thermal core due to intense thermal stimulation of the body and head and resultant peripheral vasoconstriction. Dorsal head and upper chest immersion in cold water increases the rate of core cooling and decreases potential survival time.

Exchange biased Co3O4 nanowires: A new insight into its magnetic core-shell nature

NASA Astrophysics Data System (ADS)

Thomas, S.; Jose, A.; Thanveer, T.; Anantharaman, M. R.

2017-06-01

We investigated interfacial exchange coupling effect in nano casted Co3O4 nanowires. Magnetometry measurements indicated that the magnetic response of the wires has two contributions. First one from the core of the wire which has characteristics of a 2D-DAFF(two-dimensional diluted antiferromagnet in a field). The second one is from uncompensated surface spins which get magnetically ordered towards the field direction once field cooled below 25 K. Below 25 K, the net magnetization of the core of the wire gets exchange coupled with the uncompensated surface spins giving rise to exchange bias effect. The unique 2D-DAFF/spin-glass core/shell heterostructure showed a pronounced training effect in the first field cycling itself. The magnitude of exchange bias field showed a maximum at intermediate cooling fields and for the higher cooling field, exchange bias got reduced.

Decrement in manual arm performance during whole body cooling.

PubMed

Giesbrecht, G G; Bristow, G K

1992-12-01

Six subjects performed three manual arm tasks: 1) prior to immersion in 8 degrees C water; 2) soon after immersion to the neck, but prior to any decrease in core temperature; and 3) every 15 min until core temperatures decreased 2-4.5 degrees C. The tasks were speed of flexion and extension of the fingers, handgrip strength and manual dexterity. There was no immediate effect of cold immersion; however, all scores decreased significantly after core temperature decreased 0.5 degrees C. Further decrease in core temperature was associated with a progressive impairment of performance, although at a slower rate than during the first 0.5 degrees C decrease. Flexion and extension of the fingers was affected relatively more than handgrip strength or manual dexterity. Decrement in performance is a result of peripheral cooling on sensorimotor function with a probable additional effect of central cooling on cerebral function.

Bow Shock in Merging Cluster A520: The Edge of the Radio Halo and the Electron–Proton Equilibration Timescale

NASA Astrophysics Data System (ADS)

Wang, Qian H. S.; Giacintucci, Simona; Markevitch, Maxim

2018-04-01

We studied the prominent bow shock in the merging galaxy cluster A520 using a deep Chandra X-ray observation and archival VLA radio data. This shock is a useful diagnostic tool, owing to its clear geometry and relatively high Mach number. At the “nose” of the shock, we measure a Mach number of M={2.4}-0.2+0.4. The shock becomes oblique away from the merger axis, with the Mach number falling to ≃1.6 around 30° from the nose. The electron temperature immediately behind the shock nose is consistent with that from the Rankine–Hugoniot adiabat, and is higher (at a 95% confidence) than expected for adiabatic compression of electrons followed by Coulomb electron–proton equilibration, indicating the presence of equilibration mechanisms faster than Coulomb collisions. This is similar to an earlier finding for the Bullet cluster. We also combined four archival VLA data sets to obtain a better image of the cluster’s giant radio halo at 1.4 GHz. An abrupt edge of the radio halo traces the shock front, and no emission is detected in the pre-shock region. If the radio edge were due only to adiabatic compression of relativistic electrons in pre-shock plasma, we would expect a pre-shock radio emission detectable in this radio data set; however, an interferometric artifact dominates the uncertainty, so we cannot rule this model out. Other interesting features of the radio halo include a peak at the remnant of the cool core, suggesting that the core used to have a radio minihalo, and a peak marking a possible region of high turbulence.

Primordial black holes in globular clusters

NASA Technical Reports Server (NTRS)

Sigurdsson, Steinn; Hernquist, Lars

1993-01-01

It has recently been recognized that significant numbers of medium-mass back holes (of order 10 solar masses) should form in globular clusters during the early stages of their evolution. Here we explore the dynamical and observational consequences of the presence of such a primordial black-hole population in a globular cluster. The holes initially segregate to the cluster cores, where they form binary and multiple black-hole systems. The subsequent dynamical evolution of the black-hole population ejects most of the holes on a relatively short timescale: a typical cluster will retain between zero and four black holes in its core, and possibly a few black holes in its halo. The presence of binary, triple, and quadruple black-hole systems in cluster cores will disrupt main-sequence and giant stellar binaries; this may account for the observed anomalies in the distribution of binaries in globular clusters. Furthermore, tidal interactions between a multiple black-hole system and a red giant star can remove much of the red giant's stellar envelope, which may explain the puzzling absence of larger red giants in the cores of some very dense clusters.

Emergency cooling analysis for the loss of coolant malfunction

NASA Technical Reports Server (NTRS)

Peoples, J. A.

1972-01-01

This report examines the dynamic response of a conceptual space power fast-spectrum lithium cooled reactor to the loss of coolant malfunction and several emergency cooling concepts. The results show that, following the loss of primary coolant, the peak temperatures of the center most 73 fuel elements can range from 2556 K to the region of the fuel melting point of 3122 K within 3600 seconds after the start of the accident. Two types of emergency aftercooling concepts were examined: (1) full core open loop cooling and (2) partial core closed loop cooling. The full core open loop concept is a one pass method of supplying lithium to the 247 fuel pins. This method can maintain fuel temperature below the 1611 K transient damage limit but requires a sizable 22,680-kilogram auxiliary lithium supply. The second concept utilizes a redundant internal closed loop to supply lithium to only the central area of each hexagonal fuel array. By using this method and supplying lithium to only the triflute region, fuel temperatures can be held well below the transient damage limit.

Fuel Breeding and Core Behavior Analyses on In Core Fuel Management of Water Cooled Thorium Reactors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Permana, Sidik; Department of Physics, Bandung Institute of Technology, Gedung Fisika, Jl. Ganesha 10, Bandung 40132; Sekimoto, Hiroshi

2010-12-23

Thorium fuel cycle with recycled U-233 has been widely recognized having some contributions to improve the water-cooled breeder reactor program which has been shown by a feasible area of breeding and negative void reactivity which confirms that fissile of 233U contributes to better fuel breeding and effective for obtaining negative void reactivity coefficient as the main fissile material. The present study has the objective to estimate the effect of whole core configuration as well as burnup effects to the reactor core profile by adopting two dimensional model of fuel core management. About more than 40 months of cycle period hasmore » been employed for one cycle fuel irradiation of three batches fuel system for large water cooled thorium reactors. All position of fuel arrangement contributes to the total core conversion ratio which gives conversion ratio less than unity of at the BOC and it contributes to higher than unity (1.01) at the EOC after some irradiation process. Inner part and central part give the important part of breeding contribution with increasing burnup process, while criticality is reduced with increasing the irradiation time. Feasibility of breeding capability of water-cooled thorium reactors for whole core fuel arrangement has confirmed from the obtained conversion ratio which shows higher than unity. Whole core analysis on evaluating reactivity change which is caused by the change of voided condition has been employed for conservative assumption that 100% coolant and moderator are voided. It obtained always a negative void reactivity coefficient during reactor operation which shows relatively more negative void coefficient at BOC (fresh fuel composition), and it becomes less negative void coefficient with increasing the operation time. Negative value of void reactivity coefficient shows the reactor has good safety properties in relation to the reactivity profile which is the main parameter in term of criticality safety analysis. Therefore, this evaluation has confirmed that breeding condition and negative coefficient can be obtained simultaneously for water-cooled thorium reactor obtains based on the whole core fuel arrangement.« less

Cooling System to Treat Exercise-Induced Hyperthermia

DTIC Science & Technology

2016-06-01

temperatures . Additionally, individual variations in sweat rates, ventilation rates, fitness levels, and oxygen consumption were not...gastrointestinal MHR maximum heart rate NASA National Aeronautics and Space Administration Tc core temperature UCHS uncompensated heat stress VO2peak peak oxygen consumption ...the effectiveness of a cooling pump based patient thermal management system supplied by Aspen Systems on lowering core body temperature

Anisotropic magnetic field observed at 300 K in citrate-coated iron oxide nanoparticles: effect of counterions

NASA Astrophysics Data System (ADS)

Misra, Sushil K.; Li, Lin; Mukherjee, Sudip; Ghosh, Goutam

2015-12-01

Iron oxide nanoparticles (IONPs) have been synthesized by chemical co-precipitation method and coated with three citrates, namely, tri-lithium citrate (TLC), tri-sodium citrate (TSC), or tri-potassium citrate (TKC). In these `core-shell' structures, the `core' is a cluster of average 3 IONPs which is enveloped by a `shell' of citrate molecules and counterions, and thus called `core-shell' nano-clusters (CS-NCs), of average size 20 to 22 nm. The counterions in the three CS-NCs differ in ionic radii (r_{{ion}}), in the order of Li+ < Na+ < K+. Our aim was to investigate the effect of counterions on magnetic interactions between CS-NCs in different powder samples at 300 K, using vibrating sample magnetometer and electron magnetic resonance (EMR) techniques. The hysteresis loops showed negligible coercivity field ( H c) in all samples. The saturation magnetization ( M S) was the highest for TLC-coated CS-NCs. The blocking temperature ( T B), obtained from zero-field-cooled measurements, was >300 K for TLC-coated CS-NCs and <300 K for TSC- and TKC-coated CS-NCs. The EMR linewidth (∆ B PP), measured at 300 K, was also the broadest for TLC-coated CS-NCs. At low temperatures, Δ B PP was found to increase more significantly for TSC- and TKC-coated CS-NCs than for TLC-coated CS-NCs. These results indicate a significant anisotropic field effect; arising due to thermal motion of counterions at 300 K, on the magnetic interactions in TLC-coated CS-NCs. To our knowledge, this is the first report on the effect of counterions on magnetic interactions between CS-NCs.

Simulation of cracking cores when molding piston components

NASA Astrophysics Data System (ADS)

Petrenko, Alena; Soukup, Josef

2014-08-01

The article deals with pistons casting made from aluminum alloy. Pistons are casting at steel mold with steel core. The casting is provided by gravity casting machine. The each machine is equipped by two metal molds, which are preheated above temperature 160 °C before use. The steel core is also preheated by flame. The metal molds and cores are heated up within the casting process. The temperature of the metal mold raise up to 200 °C and temperature of core is higher. The surface of the core is treated by nitration. The mold and core are cooled down by water during casting process. The core is overheated and its top part is finally cracked despite its intensive water-cooling. The life time cycle of the core is decreased to approximately 5 to 15 thousands casting, which is only 15 % of life time cycle of core for production of other pistons. The article presents the temperature analysis of the core.

Spatiotemporal modeling of node temperatures in supercomputers

DOE PAGES

Storlie, Curtis Byron; Reich, Brian James; Rust, William Newton; ...

2016-06-10

Los Alamos National Laboratory (LANL) is home to many large supercomputing clusters. These clusters require an enormous amount of power (~500-2000 kW each), and most of this energy is converted into heat. Thus, cooling the components of the supercomputer becomes a critical and expensive endeavor. Recently a project was initiated to investigate the effect that changes to the cooling system in a machine room had on three large machines that were housed there. Coupled with this goal was the aim to develop a general good-practice for characterizing the effect of cooling changes and monitoring machine node temperatures in this andmore » other machine rooms. This paper focuses on the statistical approach used to quantify the effect that several cooling changes to the room had on the temperatures of the individual nodes of the computers. The largest cluster in the room has 1,600 nodes that run a variety of jobs during general use. Since extremes temperatures are important, a Normal distribution plus generalized Pareto distribution for the upper tail is used to model the marginal distribution, along with a Gaussian process copula to account for spatio-temporal dependence. A Gaussian Markov random field (GMRF) model is used to model the spatial effects on the node temperatures as the cooling changes take place. This model is then used to assess the condition of the node temperatures after each change to the room. The analysis approach was used to uncover the cause of a problematic episode of overheating nodes on one of the supercomputing clusters. Lastly, this same approach can easily be applied to monitor and investigate cooling systems at other data centers, as well.« less

Structural transition in sputter-deposited amorphous germanium films by aging at ambient temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okugawa, M.; Nakamura, R., E-mail: nakamura@mtr.osakafu-u.ac.jp; Numakura, H.

The structure of amorphous Ge (a-Ge) films prepared by sputter-deposition and the effects of aging at ambient temperature and pressure were studied by pair-distribution-function (PDF) analysis from electron scattering and molecular dynamics simulations. The PDFs of the as-deposited and aged samples for 3–13 months showed that the major peaks for Ge-Ge bonds decrease in intensity and broaden with aging for up to 7 months. In the PDFs of a-Ge of molecular dynamics simulation obtained by quenching liquid at different rates, the major peak intensities of a slowly cooled model are higher than those of a rapidly cooled model. Analyses onmore » short- and medium-range configurations show that the slowly cooled model includes a certain amount of medium-range ordered (MRO) clusters, while the rapidly cooled model includes liquid-like configurations rather than MRO clusters. The similarity between experimental and computational PDFs implies that as-deposited films are similar in structure to the slowly cooled model, whereas the fully aged films are similar to the rapidly cooled model. It is assumed that as they undergo room-temperature aging, the MRO clusters disintegrate and transform into liquid-like regions in the same matrix. This transition in local configurations is discussed in terms of instability and the non-equilibrium of nanoclusters produced by a vapor-deposition process.« less

Astronomers Discover Spectacular Structure in Distant Galaxy

NASA Astrophysics Data System (ADS)

1999-01-01

Researchers using the National Science Foundation's Very Large Array (VLA) radio telescope have imaged a "spectacular and complex structure" in a galaxy 50 million light-years away. Their work both resolves a decades-old observational mystery and revises current theories about the origin of X-ray emission coming from gas surrounding the galaxy. The new VLA image is of the galaxy M87, which harbors at its core a supermassive black hole spewing out jets of subatomic particles at nearly the speed of light and also is the central galaxy of the Virgo Cluster of galaxies. The VLA image is the first to show detail of a larger structure that originally was detected by radio astronomers more than a half-century ago. Analysis of the new image indicates that astronomers will have to revise their ideas about the physics of what causes X-ray emission in the cores of many galaxy clusters. Frazer Owen of the National Radio Astronomy Observatory (NRAO) in Socorro, NM; Jean Eilek of the New Mexico Institute of Mining and Technology (NM Tech) in Socorro, NM; and Namir Kassim of the Naval Research Laboratory in Washington, DC, announced their discovery at the American Astronomical Society's meeting today in Austin, TX. The new observations show two large, bubble-like lobes, more than 200,000 light-years across, that emit radio waves. These lobes, which are intricately detailed, apparently are powered by gravitational energy released from the black hole at the galaxy's center. "We think that material is flowing outward from the galaxy's core into these large, bright, radio-emitting 'bubbles,'" Owen said. The newly-discovered "bubbles" sit inside a region of the galaxy known to be emitting X-rays. Theorists have speculated that this X-ray emission arises when gas that originally was part of the Virgo Cluster of galaxies, cools and falls inwards onto M87 itself, at the center of the cluster. Such "cooling flows" are commonly thought to be responsible for strong X-ray emission in many galaxy clusters. "The new structures that we found in M87 show that the story is much more complicated," Eilek said. "What we know about radio jets suggests that the energy being pumped into this region from the galaxy's central black hole exceeds the energy being lost in the X-ray emission. This system is more like a heating flow than a cooling flow. We're going to have to revise our ideas about the physics of what's going on in regions like this." M87, discovered by the French astronomer Charles Messier in 1781, is the strongest radio-emitting object in the constellation Virgo. Its jet was described by Lick Observatory astronomer Heber Curtis in 1918 as "a curious straight ray ... apparently connected with the nucleus by a thin line of matter." In 1954, Walter Baade reported that the jet's light is strongly polarized. M87's X-ray emission was discovered in 1966. M87 is the largest of the thousands of galaxies in the Virgo Cluster. The Local Group of galaxies, of which our own Milky Way is one, is part of the Virgo Cluster's outskirts. The galaxy's radio emissions first were observed by Australian astronomers in 1947, but the radio telescopes of that time were unable to discern much detail. They could, however, show that there is a structure more than 100,000 light-years across. Subsequent radio images, particularly those made using the sharp radio "vision" of the VLA, were primarily aimed at studying the inner 10,000 light-years or so, and showed great detail in the galaxy's jet. Astronomers even have followed the motions of concentrations of material within the jet over time. These observations, however, did not show much about the larger structure that was seen by earlier radio astronomers, leaving its details largely a mystery. Radio Images of M87 at Vastly Different Size Scales The mystery was solved by using the VLA to observe at longer radio wavelengths, thus revealing larger-scale structures. The processing speeds of modern computers and recently-developed imaging techniques also were necessary to show the exquisite details seen in the newest VLA image of M87. The result was spectacular. "Not only did we see beautiful details that we hadn't seen before, but we also got a new and more complicated idea of the physics of this region," Owen said. "The theories about cooling flows offered an explanation for the X-ray emission in galaxy clusters, but critics contended that other evidence we should see for this infalling matter, such as new stars forming in the denser parts of the flows, was absent," Owen said. "Now, in this case, we see that the inward flow can be counterbalanced by the energy coming outward from the galaxy's core, so the material may not become dense enough to trigger star formation." The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. This is a VLA image of the galaxy M87, showing details of the large-scale, radio-emitting "bubbles" believed to be powered by the black hole at the galaxy's center. The galaxy's center (and the black hole) lie deep within the bright, reddish region in this image. The structure in this image is approximately 200,000 light-years across. This image was made at a radio wavelength of 90 centimeters. CREDIT: F.N. Owen, J.A. Eliek and N.E. Kassim, National Radio Astronomy Observatory, Associated Universities, Inc.

Formation of Core-Shell Ethane-Silver Clusters in He Droplets.

PubMed

Loginov, Evgeny; Gomez, Luis F; Sartakov, Boris G; Vilesov, Andrey F

2017-08-17

Ethane core-silver shell clusters consisting of several thousand particles have been assembled in helium droplets upon capture of ethane molecules followed by Ag atoms. The composite clusters were studied via infrared laser spectroscopy in the range of the C-H stretching vibrations of ethane. The spectra reveal a splitting of the vibrational bands, which is ascribed to interaction with Ag. A rigorous analysis of band intensities for a varying number of trapped ethane molecules and Ag atoms indicates that the composite clusters consist of a core of ethane that is covered by relatively small Ag clusters. This metastable structure is stabilized due to fast dissipation in superfluid helium droplets of the cohesion energy of the clusters.

Shaken Snow Globes: Kinematic Tracers of the Multiphase Condensation Cascade in Massive Galaxies, Groups, and Clusters

NASA Astrophysics Data System (ADS)

Gaspari, M.; McDonald, M.; Hamer, S. L.; Brighenti, F.; Temi, P.; Gendron-Marsolais, M.; Hlavacek-Larrondo, J.; Edge, A. C.; Werner, N.; Tozzi, P.; Sun, M.; Stone, J. M.; Tremblay, G. R.; Hogan, M. T.; Eckert, D.; Ettori, S.; Yu, H.; Biffi, V.; Planelles, S.

2018-02-01

We propose a novel method to constrain turbulence and bulk motions in massive galaxies, galaxy groups, and clusters, exploring both simulations and observations. As emerged in the recent picture of top-down multiphase condensation, hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (∼107 K) are perturbed by subsonic turbulence, warm (∼104 K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (<100 K) raining in the core via chaotic cold accretion (CCA). We show that all phases are tightly linked in terms of the ensemble (wide-aperture) velocity dispersion along the line of sight. The correlation arises in complementary long-term AGN feedback simulations and high-resolution CCA runs, and is corroborated by the combined Hitomi and new Integral Field Unit measurements in the Perseus cluster. The ensemble multiphase gas distributions (from the UV to the radio band) are characterized by substantial spectral line broadening (σ v,los ≈ 100–200 {km} {{{s}}}-1) with a mild line shift. On the other hand, pencil-beam detections (as H I absorption against the AGN backlight) sample the small-scale clouds displaying smaller broadening and significant line shifts of up to several 100 {km} {{{s}}}-1 (for those falling toward the AGN), with increased scatter due to the turbulence intermittency. We present new ensemble σ v,los of the warm Hα+[N II] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). Finally, we show that the physically motivated criterion C ≡ t cool/t eddy ≈ 1 best traces the condensation extent region and the presence of multiphase gas in observed clusters and groups. The ensemble method can be applied to many available spectroscopic data sets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.

Low-Frequency VLA Observations of Abell 754: Evidence for a Cluster Radio Halo and Possible Radio Relics

DTIC Science & Technology

2001-10-01

core passage of the dark matter subcluster, was not violent enough to produce a shock wave in the dense main cluster core. The core was only...such as Chandra. At later merger stages, turbulent gas motion, which is stirred by violently relaxing dark matter cores, should have erased many of

Unexpected electronic perturbation effects of simple PEG environments on the optical properties of small cadmium chalcogenide clusters

NASA Astrophysics Data System (ADS)

Fukunaga, Naoto; Konishi, Katsuaki

2015-12-01

Poly(ethylene glycol) (PEG) has been widely used for the surface protection of inorganic nanoobjects because of its virtually `inert' nature, but little attention has been paid to its inherent electronic impacts on inorganic cores. Herein, we definitively show, through studies on optical properties of a series of PEG-modified Cd10Se4(SR)10 clusters, that the surrounding PEG environments can electronically affect the properties of the inorganic core. For the clusters with PEG units directly attached to an inorganic core (R = (CH2CH2O)nOCH3, 1-PEGn, n = 3, ~7, ~17, ~46), the absorption bands, associated with the low-energy transitions, continuously blue-shifted with the increasing PEG chain length. The chain length dependencies were also observed in the photoluminescence properties, particularly in the excitation spectral profiles. By combining the spectral features of several PEG17-modified clusters (2-Cm-PEG17 and 3) whose PEG and core units are separated by various alkyl chain-based spacers, it was demonstrated that sufficiently long PEG units, including PEG17 and PEG46, cause electronic perturbations in the cluster properties when they are arranged near the inorganic core. These unique effects of the long-PEG environments could be correlated with their large dipole moments, suggesting that the polarity of the proximal chemical environment is critical when affecting the electronic properties of the inorganic cluster core.Poly(ethylene glycol) (PEG) has been widely used for the surface protection of inorganic nanoobjects because of its virtually `inert' nature, but little attention has been paid to its inherent electronic impacts on inorganic cores. Herein, we definitively show, through studies on optical properties of a series of PEG-modified Cd10Se4(SR)10 clusters, that the surrounding PEG environments can electronically affect the properties of the inorganic core. For the clusters with PEG units directly attached to an inorganic core (R = (CH2CH2O)nOCH3, 1-PEGn, n = 3, ~7, ~17, ~46), the absorption bands, associated with the low-energy transitions, continuously blue-shifted with the increasing PEG chain length. The chain length dependencies were also observed in the photoluminescence properties, particularly in the excitation spectral profiles. By combining the spectral features of several PEG17-modified clusters (2-Cm-PEG17 and 3) whose PEG and core units are separated by various alkyl chain-based spacers, it was demonstrated that sufficiently long PEG units, including PEG17 and PEG46, cause electronic perturbations in the cluster properties when they are arranged near the inorganic core. These unique effects of the long-PEG environments could be correlated with their large dipole moments, suggesting that the polarity of the proximal chemical environment is critical when affecting the electronic properties of the inorganic cluster core. Electronic supplementary information (ESI) available: Details of synthetic procedures and characterisation data of the PEGylated thiols and clusters and additional absorption, photoluminescence emission and excitation spectral data. See DOI: 10.1039/c5nr06307h

Search for cold gas in clusters with and without cooling flows

NASA Technical Reports Server (NTRS)

Grabelsky, D. A.; Ulmer, M. P.

1990-01-01

The dominant galaxy in each of approx. 40 clusters was studied using co-added Infrared Astronomy Satellite (IRAS) survey data, and 11 of these galaxies were observed for CO (J=1 to 0) emission with the 12 m telescope at Kitt Peak. Half of the galaxies in the sample are in clusters reported to have cooling flows while the other half are not. Six of the galaxies appear to have been detected by IRAS at fairly low flux levels, in addition to one previously known strong detection; all seven have reported cooling flows. No detectable CO emission (to 2 to 3 mK) was found in any of the 11 galaxies observed. Assuming accretion rates of approx. 100 Solar Mass yr(-1), the star formation rates and efficiencies in these galaxies must be quite high in order to render the CO undetectable. At the same time, the infrared luminosities of these galaxies is unremarkable, suggesting that the correlation between star formation efficiency and infrared luminosity found for spirals may not hold for cooling flows.

XMM-Newton observation of the Coma Galaxy cluster. The temperature structure in the central region

NASA Astrophysics Data System (ADS)

Arnaud, M.; Aghanim, N.; Gastaud, R.; Neumann, D. M.; Lumb, D.; Briel, U.; Altieri, B.; Ghizzardi, S.; Mittaz, J.; Sasseen, T. P.; Vestrand, W. T.

2001-01-01

We present a temperature map and a temperature profile of the central part (r < 20' or 1/4 virial radius) of the Coma cluster. We combined 5 overlapping pointings made with XMM/EPIC/MOS and extracted spectra in boxes of 3.5'x3.5'. The temperature distribution around the two central galaxies is remarkably homogeneous (r<10'), contrary to previous ASCA results, suggesting that the core is actually in a relaxed state. At larger distance from the cluster center we do see evidence for recent matter accretion. We confirm the cool area in the direction of NGC 4921, probably due to gas stripped from an infalling group. We find indications of a hot front in the South West, in the direction of NGC 4839, probably due to an adiabatic compression. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). EPIC was developed by the EPIC Consortium led by the Principal Investigator, Dr. M. J. L. Turner. The consortium comprises the following Institutes: University of Leicester, University of Birmingham, (UK); CEA/Saclay, IAS Orsay, CESR Toulouse, (France); IAAP Tuebingen, MPE Garching, (Germany); IFC Milan, ITESRE Bologna, IAUP Palermo, Italy. EPIC is funded by: PPARC, CEA, CNES, DLR and ASI.

Spectroscopic Analyses of the "Blue Hook" Stars in Omega Centauri: A Test of the Late Hot Flasher Scenario

NASA Technical Reports Server (NTRS)

Moehler, S.; Sweigart, Allan V.; Landsman, W. B.; Dreizler, S.; Rabin, Douglas M. (Technical Monitor)

2002-01-01

(Omega) Cen contains the largest population of very hot horizontal branch (HB) stars known in a globular cluster. Recent UV observations (Whitney et al. 1998; D'Cruz et al. 2000) show a significant population of hot stars below the zero-age horizontal branch ("blue hook" stars), which cannot be explained by canonical stellar evolution. Stars which suffer unusually large mass loss on the red giant branch and thus experience the helium core flash while descending the white dwarf cooling curve could populate this region. Theory predicts that these "late hot flashers" should show higher temperatures than the hottest canonical HB stars and should have helium- and carbon-rich atmospheres. We obtained and analysed medium resolution spectra of a sample of blue hook stars to derive their atmospheric parameters. The blue hook stars are indeed both hotter (T(sub eff)>35,000 K) and more helium-rich than classical extreme HB stars. In addition we find indications for a large enhancement of the carbon abundance relative to the cluster abundance.

Cost-effectiveness of gammaCore (non-invasive vagus nerve stimulation) for acute treatment of episodic cluster headache.

PubMed

Mwamburi, Mkaya; Liebler, Eric J; Tenaglia, Andrew T

2017-11-01

Cluster headache is a debilitating disease characterized by excruciatingly painful attacks that affects 0.15% to 0.4% of the US population. Episodic cluster headache manifests as circadian and circannual seasonal bouts of attacks, each lasting 15 to 180 minutes, with periods of remission. In chronic cluster headache, the attacks occur throughout the year with no periods of remission. While existing treatments are effective for some patients, many patients continue to suffer. There are only 2 FDA-approved medications for episodic cluster headache in the United States, while others, such as high-flow oxygen, are used off-label. Episodic cluster headache is associated with comorbidities and affects work, productivity, and daily functioning. The economic burden of episodic cluster headache is considerable, costing more than twice that of nonheadache patients. gammaCore adjunct to standard of care (SoC) was found to have superior efficacy in treatment of acute episodic cluster headaches compared with sham-gammaCore used with SoC in ACT1 and ACT2 trials. However, the economic impact has not been characterized for this indication. We conducted a cost-effectiveness analysis of gammaCore adjunct to SoC compared with SoC alone for the treatment of acute pain associated with episodic cluster headache attacks. The model structure was based on treatment of acute attacks with 3 outcomes: failures, nonresponders, and responders. The time horizon of the model is 1 year using a payer perspective with uncertainty incorporated. Parameter inputs were derived from primary data from the randomized controlled trials for gammaCore. The mean annual costs associated with the gammaCore-plus-SoC arm was $9510, and mean costs for the SoC-alone arm was $10,040. The mean quality-adjusted life years for gammaCore-plus-SoC arm were 0.83, and for the SoC-alone arm, they were 0.74. The gammaCore-plus-SoC arm was dominant over SoC alone. All 1-way and multiway sensitivity analyses were cost-effective using a threshold of $20,000. gammaCore dominance, representing savings, was driven by superior efficacy, improvement in quality of life (QoL), and reduction in costs associated with successful and consistent abortion of episodic attacks. These findings serve as additional economic evidence to support coverage for gammaCore. Additional real-world data are needed to characterize the long-term impact of gammaCore on comorbidities, utilization, QoL, daily functioning, productivity, and social engagement of these patients, and for other indications.

COOLED NEUTRONIC REACTOR

DOEpatents

Binner, C.R.; Wilkie, C.B.

1958-03-18

This patent relates to a design for a reactor of the type in which a fluid coolant is flowed through the active portion of the reactor. This design provides for the cooling of the shielding material as well as the reactor core by the same fluid coolant. The core structure is a solid moderator having coolant channels in which are disposed the fuel elements in rod or slug form. The coolant fluid enters the chamber in the shield, in which the core is located, passes over the inner surface of said chamber, enters the core structure at the center, passes through the coolant channels over the fuel elements and out through exhaust ducts.

Apparatus for controlling molten core debris. [LMFBR

DOEpatents

Golden, M.P.; Tilbrook, R.W.; Heylmun, N.F.

1977-07-19

Disclosed is an apparatus for containing, cooling, diluting, dispersing and maintaining subcritical the molten core debris assumed to melt through the bottom of a nuclear reactor pressure vessel in the unlikely event of a core meltdown. The apparatus is basically a sacrificial bed system which includes an inverted conical funnel, a core debris receptacle including a spherical dome, a spherically layered bed of primarily magnesia bricks, a cooling system of zig-zag piping in graphite blocks about and below the bed and a cylindrical liner surrounding the graphite blocks including a steel shell surrounded by firebrick. Tantalum absorber rods are used in the receptacle and bed. 9 claims, 22 figures.

Time-dependent heat transfer in the spherical Earth: Implications on the power and thermal evolution of the core

NASA Astrophysics Data System (ADS)

Hofmeister, A. M.; Criss, R. E.

2015-12-01

We quantitatively investigate the time-dependence of heat conduction for a post-core, spherical Earth that is not convecting, due to compositional layering, based on hundreds of measurements of thermal diffusivity (D) for insulators and metals. Consistency of our solutions for widely ranging input parameters indicates how additional heat transfer mechanisms (mantle magmatism and convection) affect thermal evolution of the core. We consider 1) interior starting temperatures (T) of 273-5000 K, which represent variations in primordial heat, 2) different distributions and decay of long-lived radioactive isotopes, 3) additional heat sources in the core (primordial or latent heat), and 4) variable depth-T dependence of D. Our new analytical solution for cooling of a constant D sphere validates our numerical results. The bottom line is that the thermally insulating nature of minerals, combined with constraints of spherical geometry, limits steep thermal gradients to the upper mantle, consistent with the short length scale (x ~700 km) of cooling over t = 4.5 Ga indicated by dimensional analysis [x2 ~ 4Dt], and with plate tectonics. Consequently, interior temperatures vary little so the core has remained hot and is possibly warming. Findings include: 1) Constant vs. variable D affects thermal profiles only in detail, with D for the metallic core being inconsequential. 2) The hottest zone in Earth may lie in the uppermost lower mantle; 3) Most radiogenic heat is released in Earth's outermost 1000 km thereby driving an active outer shell; 4) Earth's core is essentially isothermal and is thus best described by the liquid-solid phase boundary; 5) Deeply sequestered radioactivity or other heat will melt the core rather than by run the dynamo (note that the heat needed to have melted the outer core is 10% of radiogenic heat generated over Earth's history); 6) Inefficient cooling of an Earth-sized mass means that heat essentially remains where it is generated, until it is removed by magmatism; 7) Importantly, the observed plate velocities are consistent with a Nusselt number of 1, i.e. the present day cooling is essentially conductive. Conductive cooling plus magmatism largely governs Earth's thermal structure and dynamics, below a unicellular upper mantle. Core dynamics and magnetism are likely driven by rotational effects.

77 FR 19740 - Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant Accident

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-02

... NUCLEAR REGULATORY COMMISSION [NRC-2010-0249] Water Sources for Long-Term Recirculation Cooling... Regulatory Guide (RG) 1.82, ``Water Sources for Long-Term Recirculation Cooling Following a Loss-of-Coolant... regarding the sumps and suppression pools that provide water sources for emergency core cooling, containment...

Application of formal optimization techniques in thermal/structural design of a heat-pipe-cooled panel for a hypersonic vehicle

NASA Technical Reports Server (NTRS)

Camarda, Charles J.; Riley, Michael F.

1987-01-01

Nonlinear mathematical programming methods are used to design a radiantly cooled and heat-pipe-cooled panel for a Mach 6.7 transport. The cooled portion of the panel is a hybrid heat-pipe/actively cooled design which uses heat pipes to transport the absorbed heat to the ends of the panel where it is removed by active cooling. The panels are optimized for minimum mass and to satisfy a set of heat-pipe, structural, geometric, and minimum-gage constraints. Two panel concepts are investigated: cylindrical heat pipes embedded in a honeycomb core and an integrated design which uses a web-core heat-pipe sandwich concept. The latter was lighter and resulted in a design which was less than 10 percent heavier than an all actively cooled concept. The heat-pipe concept, however, is redundant and can sustain a single-point failure, whereas the actively cooled concept cannot. An additional study was performed to determine the optimum number of coolant manifolds per panel for a minimum-mass design.

Convection Destroys the Core/Mantle Structure in Hybrid C/O/Ne White Dwarfs

NASA Astrophysics Data System (ADS)

Brooks, Jared; Schwab, Josiah; Bildsten, Lars; Quataert, Eliot; Paxton, Bill

2017-01-01

A hybrid C/O/Ne white dwarf (WD)—an unburned C/O core surrounded by an O/Ne/Na mantle—can be formed if the carbon flame is quenched in a super-AGB star or white dwarf merger remnant. We show that this segregated hybrid structure becomes unstable to rapid mixing within 2000 years of the onset of WD cooling. Carbon burning includes a weak reaction that removes electrons, resulting in a lower electron-to-baryon ratio ({Y}{{e}}) in the regions processed by carbon burning compared to the unburned C/O core, making the O/Ne mantle denser than the C/O core as the WD cools. This is unstable to efficient mixing. We use the results of {\\mathtt{MESA}} models with different size C/O cores to quantify the rate at which the cores mix with the mantle as they cool. In all cases, we find that the WDs undergo significant core/mantle mixing on timescales shorter than the time available to grow the WD to the Chandrasekhar mass (MCh) by accretion. As a result, hybrid WDs that reach MCh due to later accretion will have lower central carbon fractions than assumed thus far. We briefly discuss the implications of these results for the possibility of SNe Ia from hybrid WDs.

Improvements in Ionized Cluster-Beam Deposition

NASA Technical Reports Server (NTRS)

Fitzgerald, D. J.; Compton, L. E.; Pawlik, E. V.

1986-01-01

Lower temperatures result in higher purity and fewer equipment problems. In cluster-beam deposition, clusters of atoms formed by adiabatic expansion nozzle and with proper nozzle design, expanding vapor cools sufficiently to become supersaturated and form clusters of material deposited. Clusters are ionized and accelerated in electric field and then impacted on substrate where films form. Improved cluster-beam technique useful for deposition of refractory metals.

Heat conduction in cooling flows. [in clusters of galaxies

NASA Technical Reports Server (NTRS)

Bregman, Joel N.; David, L. P.

1988-01-01

It has been suggested that electron conduction may significantly reduce the accretion rate (and star foramtion rate) for cooling flows in clusters of galaxies. A numerical hydrodynamics code was used to investigate the time behavior of cooling flows with conduction. The usual conduction coefficient is modified by an efficiency factor, mu, to realize the effects of tangled magnetic field lines. Two classes of models are considered, one where mu is independent of position and time, and one where inflow stretches the field lines and changes mu. In both cases, there is only a narrow range of initial conditions for mu in which the cluster accretion rate is reduced while a significant temperature gradient occurs. In the first case, no steady solution exists in which both conditions are met. In the second case, steady state solutions occur in which both conditions are met, but only for a narrow range of initial values where mu = 0.001.

Effect of Impacts on the Cooling Rates of Differentiated Planetesimals

NASA Astrophysics Data System (ADS)

Lyons, R. J.; Bowling, T. J.; Ciesla, F. J.; Davison, T. M.; Collins, G. S.

2018-05-01

I have modeled planetismal impacts in the early solar system, following their formation, differentiation, and cooling. I found that small collisions can expose the core, resulting in more than an order of magnitude increase in the cooling rates.

Simulating the impact of dust cooling on the statistical properties of the intra-cluster medium

NASA Astrophysics Data System (ADS)

Pointecouteau, Etienne; da Silva, Antonio; Catalano, Andrea; Montier, Ludovic; Lanoux, Joseph; Roncarelli, Mauro; Giard, Martin

2009-08-01

From the first stages of star and galaxy formation, non-gravitational processes such as ram pressure stripping, SNs, galactic winds, AGNs, galaxy-galaxy mergers, etc. lead to the enrichment of the IGM in stars, metals as well as dust, via the ejection of galactic material into the IGM. We know now that these processes shape, side by side with gravitation, the formation and the evolution of structures. We present here hydrodynamic simulations of structure formation implementing the effect of the cooling by dust on large scale structure formation. We focus on the scale of galaxy clusters and study the statistical properties of clusters. Here, we present our results on the TX-M and the LX-M scaling relations which exhibit changes on both the slope and normalization when adding cooling by dust to the standard radiative cooling model. For example, the normalization of the TX-M relation changes only by a maximum of 2% at M=1014M⊙ whereas the normalization of the LX-TX changes by as much as 10% at TX=1keV for models that including dust cooling. Our study shows that the dust is an added non-gravitational process that contributes shaping the thermodynamical state of the hot ICM gas.

Electronic and geometric structures of Au30 clusters: a network of 2e-superatom Au cores protected by tridentate protecting motifs with u3-S

NASA Astrophysics Data System (ADS)

Tian, Zhimei; Cheng, Longjiu

2015-12-01

Density functional theory calculations have been performed to study the experimentally synthesized Au30S(SR)18 and two related Au30(SR)18 and Au30S2(SR)18 clusters. The patterns of thiolate ligands on the gold cores for the three thiolate-protected Au30 nanoclusters are on the basis of the ``divide and protect'' concept. A novel extended protecting motif with u3-S, S(Au2(SR)2)2AuSR, is discovered, which is termed the tridentate protecting motif. The Au cores of Au30S(SR)18, Au30(SR)18 and Au30S2(SR)18 clusters are Au17, Au20 and Au14, respectively. The superatom-network (SAN) model and the superatom complex (SAC) model are used to explain the chemical bonding patterns, which are verified by chemical bonding analysis based on the adaptive natural density partitioning (AdNDP) method and aromatic analysis on the basis of the nucleus-independent chemical shift (NICS) method. The Au17 core of the Au30S(SR)18 cluster can be viewed as a SAN of one Au6 superatom and four Au4 superatoms. The shape of the Au6 core is identical to that revealed in the recently synthesized Au18(SR)14 cluster. The Au20 core of the Au30(SR)18 cluster can be viewed as a SAN of two Au6 superatoms and four Au4 superatoms. The Au14 core of Au30S2(SR)18 can be regarded as a SAN of two pairs of two vertex-sharing Au4 superatoms. Meanwhile, the Au14 core is an 8e-superatom with 1S21P6 configuration. Our work may aid understanding and give new insights into the chemical synthesis of thiolate-protected Au clusters.Density functional theory calculations have been performed to study the experimentally synthesized Au30S(SR)18 and two related Au30(SR)18 and Au30S2(SR)18 clusters. The patterns of thiolate ligands on the gold cores for the three thiolate-protected Au30 nanoclusters are on the basis of the ``divide and protect'' concept. A novel extended protecting motif with u3-S, S(Au2(SR)2)2AuSR, is discovered, which is termed the tridentate protecting motif. The Au cores of Au30S(SR)18, Au30(SR)18 and Au30S2(SR)18 clusters are Au17, Au20 and Au14, respectively. The superatom-network (SAN) model and the superatom complex (SAC) model are used to explain the chemical bonding patterns, which are verified by chemical bonding analysis based on the adaptive natural density partitioning (AdNDP) method and aromatic analysis on the basis of the nucleus-independent chemical shift (NICS) method. The Au17 core of the Au30S(SR)18 cluster can be viewed as a SAN of one Au6 superatom and four Au4 superatoms. The shape of the Au6 core is identical to that revealed in the recently synthesized Au18(SR)14 cluster. The Au20 core of the Au30(SR)18 cluster can be viewed as a SAN of two Au6 superatoms and four Au4 superatoms. The Au14 core of Au30S2(SR)18 can be regarded as a SAN of two pairs of two vertex-sharing Au4 superatoms. Meanwhile, the Au14 core is an 8e-superatom with 1S21P6 configuration. Our work may aid understanding and give new insights into the chemical synthesis of thiolate-protected Au clusters. Electronic supplementary information (ESI) available: The AdNDP localized natural bonding orbitals of the valence shells of the Au30S(SH)18 cluster. IR spectra, absorption spectra and coordinates of Au30S(SCH3)18, Au30(SCH3)18 and Au30S2(SCH3)18 clusters. See DOI: 10.1039/c5nr05020k

Gfr Core Neutronics Studies at CEA

NASA Astrophysics Data System (ADS)

Bosq, J. C.; Brun-Magaud, V.; Rimpault, G.; Tommasi, J.; Conti, A.; Garnier, J. C.

2006-04-01

The Gas cooled Fast Reactor (GFR) is a high priority in the CEA R&D program on Future Nuclear Energy Systems. After preliminary neutronics and thermo-aerolic studies, a first He-cooled 2400MWth core design based on a series of carbide CERCER plates arranged in an hexagonal wrapper were selected. Although GFR subassembly and core design studies are still at an early stage of development, it is nonetheless possible to identify a number of nuclear data needs that could have some impact on the actual design: new materials, decay heat contributors….

A US coordination Facility for the Spectrum-X-Gamma Observatory

NASA Technical Reports Server (NTRS)

Forman, W.; West, Donald (Technical Monitor)

2001-01-01

We have completed our efforts in support of the Spectrum X Gamma mission under a NASA grant. These activities have included direct support to the mission, developing unifying tools applicable to SXG and other X-ray astronomy missions, and X-ray astronomy research to maintain our understanding of the importance and relevance of SXG to the field. SXG provides: 1) Simultaneous Multiwavelength Capability; 2) Large Field of View High Resolution Imaging Spectroscopy; 3) Sensitive Polarimetry with SXRP (Stellar X-Ray Polarimeter). These capabilities will ensure the fulfillment of the following objectives: understanding the accretion dynamics and the importance of reprocessing, upscattering, and disk viscosity around black holes; studying cluster mergers; spatially resolving cluster cooling flows to detect cooling gas; detecting cool gas in cluster outskirts in absorption; mapping gas in filaments around clusters; finding the 'missing' baryons in the Universe; determining the activity history of the black hole in the Galactic Center of our own central black hole; determining pulsar beam geometry; searching for the Lense-Thirring effect in black hole sources; constraining emission mechanisms and accretion geometry in AGN.

Off-Center Collisions between Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Ricker, P. M.

1998-03-01

We present numerical simulations of off-center collisions between galaxy clusters made using a new hydrodynamical code based on the piecewise-parabolic method (PPM) and an isolated multigrid potential solver. The current simulations follow only the intracluster gas. We have performed three high-resolution (256 × 1282) simulations of collisions between equal-mass clusters using a nonuniform grid with different values of the impact parameter (0, 5, and 10 times the cluster core radius). Using these simulations, we have studied the variation in equilibration time, luminosity enhancement during the collision, and structure of the merger remnant with varying impact parameter. We find that in off-center collisions the cluster cores (the inner regions where the pressure exceeds the ram pressure) behave quite differently from the clusters' outer regions. A strong, roughly ellipsoidal shock front, similar to that noted in previous simulations of head-on collisions, enables the cores to become bound to each other by dissipating their kinetic energy as heat in the surrounding gas. These cores survive well into the collision, dissipating their orbital angular momentum via spiral bow shocks. After the ellipsoidal shock has passed well outside the interaction region, the material left in its wake falls back onto the merger remnant formed through the inspiral of the cluster cores, creating a roughly spherical accretion shock. For less than one-half of a sound crossing time after the cores first interact, the total X-ray luminosity increases by a large factor; the magnitude of this increase depends sensitively on the size of the impact parameter. Observational evidence of the ongoing collision, in the form of bimodality and distortion in projected X-ray surface brightness and temperature maps, is present for one to two sound crossing times after the collision but only for special viewing angles. The remnant actually requires at least five crossing times to reach virial equilibrium. Since the sound crossing time can be as large as 1-2 Gyr, the equilibration time can thus be a substantial fraction of the age of the universe. The final merger remnant is very similar for impact parameters of 0 and 5 core radii. It possesses a roughly isothermal core with central density and temperature twice the initial values for the colliding clusters. Outside the core, the temperature drops as r-1, and the density roughly as r-3.8. The core radius shows a small increase due to shock heating during the merger. For an impact parameter of 10 core radii, the core of the remnant possesses a more flattened density profile with a steeper drop-off outside the core. In both off-center cases, the merger remnant rotates, but only for the 10 core-radius case does this appear to have an effect on the structure of the remnant.

Revisiting Scaling Relations for Giant Radio Halos in Galaxy Clusters

NASA Technical Reports Server (NTRS)

Cassano, R.; Ettori, S.; Brunetti, G.; Giacintucci, S.; Pratt, G. W.; Venturi, T.; Kale, R.; Dolag, K.; Markevitch, Maxim L.

2013-01-01

Many galaxy clusters host megaparsec-scale radio halos, generated by ultrarelativistic electrons in the magnetized intracluster medium. Correlations between the synchrotron power of radio halos and the thermal properties of the hosting clusters were established in the last decade, including the connection between the presence of a halo and cluster mergers. The X-ray luminosity and redshift-limited Extended GMRT Radio Halo Survey provides a rich and unique dataset for statistical studies of the halos. We uniformly analyze the radio and X-ray data for the GMRT cluster sample, and use the new Planck Sunyaev-Zel'dovich (SZ) catalog to revisit the correlations between the power of radio halos and the thermal properties of galaxy clusters. We find that the radio power at 1.4 GHz scales with the cluster X-ray (0.1-2.4 keV) luminosity computed within R(sub 500) as P(sub 1.4) approx. L(2.1+/-0.2) - 500). Our bigger and more homogenous sample confirms that the X-ray luminous (L(sub 500) > 5 × 10(exp 44) erg/s)) clusters branch into two populations-radio halos lie on the correlation, while clusters without radio halos have their radio upper limits well below that correlation. This bimodality remains if we excise cool cores from the X-ray luminosities. We also find that P(sub 1.4) scales with the cluster integrated SZ signal within R(sub 500), measured by Planck, as P(sub 1.4) approx. Y(2.05+/-0.28) - 500), in line with previous findings. However, contrary to previous studies that were limited by incompleteness and small sample size, we find that "SZ-luminous" Y(sub 500) > 6×10(exp -5) Mpc(exp 2) clusters show a bimodal behavior for the presence of radio halos, similar to that in the radio-X-ray diagram. Bimodality of both correlations can be traced to clusters dynamics, with radio halos found exclusively in merging clusters. These results confirm the key role of mergers for the origin of giant radio halos, suggesting that they trigger the relativistic particle acceleration.

Crossover from disordered to core-shell structures of nano-oxide Y{sub 2}O{sub 3} dispersed particles in Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Higgins, M. P.; Wang, L. M.; Gao, F., E-mail: gaofeium@umich.edu

Molecular dynamic simulations of Y{sub 2}O{sub 3} in bcc Fe and transmission electron microscopy (TEM) observations were used to understand the structure of Y{sub 2}O{sub 3} nano-clusters in an oxide dispersion strengthened steel matrix. The study showed that Y{sub 2}O{sub 3} nano-clusters below 2 nm were completely disordered. Y{sub 2}O{sub 3} nano-clusters above 2 nm, however, form a core-shell structure, with a shell thickness of 0.5–0.7 nm that is independent of nano-cluster size. Y{sub 2}O{sub 3} nano-clusters were surrounded by off-lattice Fe atoms, further increasing the stability of these nano-clusters. TEM was used to corroborate our simulation results and showed a crossover frommore » a disordered nano-cluster to a core-shell structure.« less

Cluster glass induced exchange biaslike effect in the perovskite cobaltites

NASA Astrophysics Data System (ADS)

Luo, Wanju; Wang, Fangwei

2007-04-01

Exchange biaslike phenomenon is observed in the Ba doped perovskite polycrystalline LaCoO3. The magnetic hysteresis loop shifts in both horizontal and vertical directions at 5K when the samples are cooled down to 5K in a magnetic field. The nature of this magnetic anisotropy is ascribed to the freezing properties of the local anisotropy in the cluster glass system. The magnetic shifts in horizontal and vertical directions can be derived directly under the principle that the spins of a cluster are frozen in random orientations and aligned to the field direction upon zero field and field cooling, respectively.

Chandra "Hears" A Black Hole For The First Time

NASA Astrophysics Data System (ADS)

2003-09-01

NASA's Chandra X-ray Observatory detected sound waves, for the first time, from a super-massive black hole. The "note" is the deepest ever detected from an object in the universe. The tremendous amounts of energy carried by these sound waves may solve a longstanding problem in astrophysics. The black hole resides in the Perseus cluster, located 250 million light years from Earth. In 2002, astronomers obtained a deep Chandra observation that shows ripples in the gas filling the cluster. These ripples are evidence for sound waves that have traveled hundreds of thousands of light years away from the cluster's central black hole. perseus animation Illustration of Ripples in Perseus "We have observed the prodigious amounts of light and heat created by black holes, now we have detected the sound," said Andrew Fabian of the Institute of Astronomy (IoA) in Cambridge, England, and leader of the study. In musical terms, the pitch of the sound generated by the black hole translates into the note of B flat. But, a human would have no chance of hearing this cosmic performance, because the note is 57 octaves lower than middle-C (by comparison a typical piano contains only about seven octaves). At a frequency over a million, billion times deeper than the limits of human hearing, this is the deepest note ever detected from an object in the universe. "The Perseus sound waves are much more than just an interesting form of black hole acoustics," said Steve Allen, also of the IoA and a co-investigator in the research. "These sound waves may be the key in figuring out how galaxy clusters, the largest structures in the universe, grow," Allen said. For years astronomers have tried to understand why there is so much hot gas in galaxy clusters and so little cool gas. Hot gas glowing with X-rays should cool, and the dense central gas should cool the fastest. The pressure in this cool central gas should then fall, causing gas further out to sink in towards the galaxy, forming trillions of stars along the way. Scant evidence has been found for such a flow of cool gas or star formation. This forced astronomers to invent several different ways to explain why the gas contained in clusters remained hot, and, until now, none of them was satisfactory. perseus animation Animation of Sound Waves Generated in Perseus Cluster of Ripples in Perseus Heating caused by a central black hole has long been considered a good way to prevent cluster gas from cooling. Although jets have been observed at radio wavelengths, their effect on cluster gas was unclear since this gas is only detectable in X-rays, and early X-ray observations did not have Chandra's ability to find detailed structure. Previous Chandra observations of the Perseus cluster showed two vast, bubble-shaped cavities in the cluster gas extending away from the central black hole. Jets of material pushing back the cluster gas have formed these X-ray cavities, which are bright sources of radio waves. They have long been suspected of heating the surrounding gas, but the mechanism was unknown. The sound waves, seen spreading out from the cavities in the recent Chandra observation, could provide this heating mechanism. A tremendous amount of energy is needed to generate the cavities, as much as the combined energy from 100 million supernovae. Much of this energy is carried by the sound waves and should dissipate in the cluster gas, keeping the gas warm and possibly preventing a cooling flow. If so, the B-flat pitch of the sound wave, 57 octaves below middle-C, would have remained roughly constant for about 2.5 billion years. Perseus is the brightest cluster of galaxies in X-rays, and therefore was a perfect Chandra target for finding sound waves rippling through the hot cluster gas. Other clusters show X-ray cavities, and future Chandra observations may yet detect sound waves in these objects.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, Michael; Bautz, Marshall W.; Miller, Eric D.

We present new ultraviolet, optical, and X-ray data on the Phoenix galaxy cluster (SPT-CLJ2344-4243). Deep optical imaging reveals previously undetected filaments of star formation, extending to radii of ∼50–100 kpc in multiple directions. Combined UV-optical spectroscopy of the central galaxy reveals a massive (2 × 10{sup 9} M{sub ⊙}), young (∼4.5 Myr) population of stars, consistent with a time-averaged star formation rate of 610 ± 50 M{sub ⊙} yr{sup −1}. We report a strong detection of O vi λλ1032,1038, which appears to originate primarily in shock-heated gas, but may contain a substantial contribution (>1000 M{sub ⊙} yr{sup −1}) from themore » cooling intracluster medium (ICM). We confirm the presence of deep X-ray cavities in the inner ∼10 kpc, which are among the most extreme examples of radio-mode feedback detected to date, implying jet powers of 2–7 × 10{sup 45} erg s{sup −1}. We provide evidence that the active galactic nucleus inflating these cavities may have only recently transitioned from “quasar-mode” to “radio-mode,” and may currently be insufficient to completely offset cooling. A model-subtracted residual X-ray image reveals evidence for prior episodes of strong radio-mode feedback at radii of ∼100 kpc, with extended “ghost” cavities indicating a prior epoch of feedback roughly 100 Myr ago. This residual image also exhibits significant asymmetry in the inner ∼200 kpc (0.15R{sub 500}), reminiscent of infalling cool clouds, either due to minor mergers or fragmentation of the cooling ICM. Taken together, these data reveal a rapidly evolving cool core which is rich with structure (both spatially and in temperature), is subject to a variety of highly energetic processes, and yet is cooling rapidly and forming stars along thin, narrow filaments.« less

Merger driven star-formation activity in Cl J1449+0856 at z=1.99 as seen by ALMA and JVLA

NASA Astrophysics Data System (ADS)

Coogan, R. T.; Daddi, E.; Sargent, M. T.; Strazzullo, V.; Valentino, F.; Gobat, R.; Magdis, G.; Bethermin, M.; Pannella, M.; Onodera, M.; Liu, D.; Cimatti, A.; Dannerbauer, H.; Carollo, M.; Renzini, A.; Tremou, E.

2018-06-01

We use ALMA and JVLA observations of the galaxy cluster Cl J1449+0856 at z=1.99, in order to study how dust-obscured star-formation, ISM content and AGN activity are linked to environment and galaxy interactions during the crucial phase of high-z cluster assembly. We present detections of multiple transitions of 12CO, as well as dust continuum emission detections from 11 galaxies in the core of Cl J1449+0856. We measure the gas excitation properties, star-formation rates, gas consumption timescales and gas-to-stellar mass ratios for the galaxies. We find evidence for a large fraction of galaxies with highly-excited molecular gas, contributing >50% to the total SFR in the cluster core. We compare these results with expectations for field galaxies, and conclude that environmental influences have strongly enhanced the fraction of excited galaxies in this cluster. We find a dearth of molecular gas in the galaxies' gas reservoirs, implying a high star-formation efficiency (SFE) in the cluster core, and find short gas depletion timescales τdep<0.1-0.4 Gyrs for all galaxies. Interestingly, we do not see evidence for increased specific star-formation rates (sSFRs) in the cluster galaxies, despite their high SFEs and gas excitations. We find evidence for a large number of mergers in the cluster core, contributing a large fraction of the core's total star-formation compared with expectations in the field. We conclude that the environmental impact on the galaxy excitations is linked to the high rate of galaxy mergers, interactions and active galactic nuclei in the cluster core.

Observed Evolution of the Upper-level Thermal Structure in Tropical Cyclones

NASA Astrophysics Data System (ADS)

Rivoire, L.; Birner, T.; Knaff, J. A.

2016-12-01

Tropical cyclones (TCs) are associated with tropopause-level cooling above the well-known tropospheric warm core. While the investigation of tropopause-level structures started as early as 1951, there is no clear consensus on the mechanisms involved. In addition, the large-scale average vertical and radial structure of the tropopause-level cooling is yet to be examined. Tropopause-level cooling destabilizes the upper atmosphere to convection, which potentially allows existing convection to reach higher altitudes. This is of particular importance during the early stages of tropical cyclogenesis. Other important characteristics of the tropopause-level cooling include its amplitude, its position relative to that of the warm core, its radial extent, and its evolution during the lifetime of TCs. These potentially influence TC structure, surface pressure gradients and maximum winds, intensity evolution, and outflow entropy. We use the 322 hurricane-strength TCs from the best-track archive in 2007-2014, along with high vertical resolution temperature measurements from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC). These measurements are composited about the Lifetime Maximum Intensity (LMI) to examine the evolution of the fine-scale upper-level thermal structure inside TCs. We find that the tropopause-cooling has an amplitude similar to that of the warm core. Relative to the far-field structure (the area average between 1300-1500 km radii), tropopause-level cooling is found to occur several days before the warm core is established. Cold anomalies extend up to 1000 km away from the storm center, and may take part in a large-scale poleward transport of cold, dry air in the UTLS. Lastly, cold air masses move away from the storm center (and warm core) after LMI, and their remains lie around the 400-700 km radius -essentially inward of the radius of maximum tangential anticyclonic winds in the outflow layer. We discuss these results in the light of the previously cited TC characteristics, and highlight the importance of an improved description of the upper-level thermal structure in TCs. We also discuss the likely mechanisms involved in TC-induced tropopause-level cooling.

Thermal stability of Pt nanoclusters interacting to carbon sublattice

NASA Astrophysics Data System (ADS)

Baidyshev, V. S.; Gafner, Yu. Ya.; Gafner, S. L.; Redel, L. V.

2017-12-01

The catalytic activity of Pt clusters is dependent not only on the nanoparticle size and its composition, but also on its internal structure. To determine the real structure of the nanoparticles used in catalysis, the boundaries of the thermal structure stability of Pt clusters to 8.0 nm in diameter interacting with carbon substrates of two types: a fixed α-graphite plane and a mobile substrate with the diamond structure. The effect of a substrate on the processes melting of Pt nanoclusters is estimated. The role of the cooling rate in the formation of the internal structure of Pt clusters during crystallization is studied. The regularities obtained in the case of "free" Pt clusters and Pt clusters on a substrate are compared. It is concluded that platinum nanoparticles with diameter D ≤ 4.0 nm disposed on a carbon substrate conserve the initial fcc structure during cooling.

Cooling vests with phase change materials: the effects of melting temperature on heat strain alleviation in an extremely hot environment.

PubMed

Gao, Chuansi; Kuklane, Kalev; Holmér, Ingvar

2011-06-01

A previous study by the authors using a heated thermal manikin showed that the cooling rates of phase change material (PCM) are dependent on temperature gradient, mass, and covering area. The objective of this study was to investigate if the cooling effects of the temperature gradient observed on a thermal manikin could be validated on human subjects in extreme heat. The subjects wore cooling vests with PCMs at two melting temperatures (24 and 28°C) and fire-fighting clothing and equipment, thus forming three test groups (vest24, vest28 and control group without the vest). They walked on a treadmill at a speed of 5 km/h in a climatic chamber (air temperature = 55°C, relative humidity = 30%, vapour pressure = 4,725 Pa, and air velocity = 0.4 m/s). The results showed that the PCM vest with a lower melting temperature (24°C) has a stronger cooling effect on the torso and mean skin temperatures than that with a higher melting temperature (28°C). Both PCM vests mitigate peak core temperature increase during the resting recovery period. The two PCM vests tested, however, had no significant effect on the alleviation of core temperature increase during exercise in the heat. To study the possibility of effective cooling of core temperature, cooling garments with PCMs at even lower melting temperatures (e.g. 15°C) and a larger covering area should be investigated.

X-ray and optical emission-line filaments in the cooling flow cluster 2A 0335 + 096

NASA Technical Reports Server (NTRS)

Sarazin, Craig L.; O'Connell, Robert W.; Mcnamara, Brian R.

1992-01-01

We present a new high-resolution X-ray image of the 2A 0335 + 096 cluster of galaxies obtained with the High Resolution Imager (HRI) aboard the ROSAT satellite. The presence of dense gas having a very short cooling time in the central regions confirms its earlier identification as a cooling flow. The X-ray emission from the central regions of the cooling flow shows a great deal of filamentary structure. Using the crude spectral resolution of the HRI, we show that these filaments are the result of excess emission, rather than foreground X-ray absorption. Although there are uncertainties in the pointing, many of the X-ray features in the cooling flow region correspond to features in H-alpha optical line emission. This suggests that the optical emission line gas has resulted directly from the cooling of X-ray-emitting gas. The filament material cannot be in hydrostatic equilibrium, and it is likely that other forces such as rotation, turbulence, and magnetic fields influence the dynamical state of the gas.

The Initial Physical Conditions of Kepler-36 b and c

NASA Astrophysics Data System (ADS)

Owen, James E.; Morton, Timothy. D.

2016-03-01

The Kepler-36 planetary system consists of two exoplanets at similar separations (0.115 and 0.128 au), which have dramatically different densities. The inner planet has a density consistent with an Earth-like composition, while the outer planet is extremely low density, such that it must contain a voluminous H/He envelope. Such a density difference would pose a problem for any formation mechanism if their current densities were representative of their composition at formation. However, both planets are at close enough separations to have undergone significant evaporation in the past. We constrain the core mass, core composition, initial envelope mass, and initial cooling time of each planet using evaporation models conditioned on their present-day masses and radii, as inferred from Kepler photometry and transit timing analysis. The inner planet is consistent with being an evaporatively stripped core, while the outer planet has retained some of its initial envelope due to its higher core mass. Therefore, both planets could have had a similar formation pathway, with the inner planet having an initial envelope-mass fraction of ≲10% and core mass of ˜4.4 M⊕, while the outer had an initial envelope-mass fraction of the order of 15%-30% and core mass ˜7.3 M⊕. Finally, our results indicate that the outer planet had a long (≳30 Myr) initial cooling time, much longer than would naively be predicted from simple timescale arguments. The long initial cooling time could be evidence for a dramatic early cooling episode such as the recently proposed “boil-off” process.

Potential Application of a Thermoelectric Generator in Passive Cooling System of Nuclear Power Plants

NASA Astrophysics Data System (ADS)

Wang, Dongqing; Liu, Yu; Jiang, Jin; Pang, Wei; Lau, Woon Ming; Mei, Jun

2017-05-01

In the design of nuclear power plants, various natural circulation passive cooling systems are considered to remove residual heat from the reactor core in the event of a power loss and maintain the plant's safety. These passive systems rely on gravity differences of fluids, resulting from density differentials, rather than using an external power-driven system. Unfortunately, a major drawback of such systems is their weak driving force, which can negatively impact safety. In such systems, there is a temperature difference between the heat source and the heat sink, which potentially offers a natural platform for thermoelectric generator (TEG) applications. While a previous study designed and analyzed a TEG-based passive core cooling system, this paper considers TEG applications in other passive cooling systems of nuclear power plants, after which the concept of a TEG-based passive cooling system is proposed. In such a system, electricity is produced using the system's temperature differences through the TEG, and this electricity is used to further enhance the cooling process.

Turbofan Engine Core Compartment Vent Aerodynamic Configuration Development Methodology

NASA Technical Reports Server (NTRS)

Hebert, Leonard J.

2006-01-01

This paper presents an overview of the design methodology used in the development of the aerodynamic configuration of the nacelle core compartment vent for a typical Boeing commercial airplane together with design challenges for future design efforts. Core compartment vents exhaust engine subsystem flows from the space contained between the engine case and the nacelle of an airplane propulsion system. These subsystem flows typically consist of precooler, oil cooler, turbine case cooling, compartment cooling and nacelle leakage air. The design of core compartment vents is challenging due to stringent design requirements, mass flow sensitivity of the system to small changes in vent exit pressure ratio, and the need to maximize overall exhaust system performance at cruise conditions.

Water immersion for post incident cooling of firefighters; a review of practical fire ground cooling modalities.

PubMed

Brearley, Matt; Walker, Anthony

2015-01-01

Rapidly cooling firefighters post emergency response is likely to increase the operational effectiveness of fire services during prolonged incidents. A variety of techniques have therefore been examined to return firefighters core body temperature to safe levels prior to fire scene re-entry or redeployment. The recommendation of forearm immersion (HFI) in cold water by the National Fire and Protection Association preceded implementation of this active cooling modality by a number of fire services in North America, South East Asia and Australia. The vascularity of the hands and forearms may expedite body heat removal, however, immersion of the torso, pelvis and/or lower body, otherwise known as multi-segment immersion (MSI), exposes a greater proportion of the body surface to water than HFI, potentially increasing the rates of cooling conferred. Therefore, this review sought to establish the efficacy of HFI and MSI to rapidly reduce firefighters core body temperature to safe working levels during rest periods. A total of 38 studies with 55 treatments (43 MSI, 12 HFI) were reviewed. The core body temperature cooling rates conferred by MSI were generally classified as ideal (n = 23) with a range of ~0.01 to 0.35 °C min(-1). In contrast, all HFI treatments resulted in unacceptably slow core body temperature cooling rates (~0.01 to 0.05 °C min(-1)). Based upon the extensive field of research supporting immersion of large body surface areas and comparable logistics of establishing HFI or MSI, it is recommended that fire and rescue management reassess their approach to fireground rehabilitation of responders. Specifically, we question the use of HFI to rapidly lower firefighter core body temperature during rest periods. By utilising MSI to restore firefighter Tc to safe working levels, fire and rescue services would adopt an evidence based approach to maintaining operational capability during arduous, sustained responses. While the optimal MSI protocol will be determined by the specifics of an individual response, maximising the body surface area immersed in circulated water of up to 26 °C for 15 min is likely to return firefighter Tc to safe working levels during rest periods. Utilising cooler water temperatures will expedite Tc cooling and minimise immersion duration.

Fully stripped? The dynamics of dark and luminous matter in the massive cluster collision MACSJ0553.4-3342

NASA Astrophysics Data System (ADS)

Ebeling, H.; Qi, J.; Richard, J.

2017-11-01

We present the results of a multiwavelength investigation of the very X-ray luminous galaxy cluster MACSJ0553.4-3342 (z = 0.4270; hereafter MACSJ0553). Combining high-resolution data obtained with the Hubble Space Telescope and the Chandra X-ray Observatory with ground-based galaxy spectroscopy, our analysis establishes the system unambiguously as a binary, post-collision merger of massive clusters. Key characteristics include perfect alignment of luminous and dark matter for one component, a separation of almost 650 kpc (in projection) between the dark-matter peak of the other subcluster and the second X-ray peak, extremely hot gas (kT > 15 keV) at either end of the merger axis, a potential cold front in the east, an unusually low gas mass fraction of approximately 0.075 for the western component, a velocity dispersion of 1490_{-130}^{+104} km s-1, and no indication of significant substructure along the line of sight. We propose that the MACSJ0553 merger proceeds not in the plane of the sky, but at a large inclination angle, is observed very close to turnaround, and that the eastern X-ray peak is the cool core of the slightly less massive western component that was fully stripped and captured by the eastern subcluster during the collision. If correct, this hypothesis would make MACSJ0553 a superb target for a competitive study of ram-pressure stripping and the collisional behaviour of luminous and dark matter during cluster formation.

CONCEPTUAL DESIGN OF A LUNAR REGOLITH CLUSTERED-REACTOR SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

John Darrell Bess

2009-06-01

It is proposed that a fast-fission, heatpipe-cooled, lunar-surface power reactor system be divided into subcritical units that could be launched safely without the incorporation of additional spectral shift absorbers or other complex means of control. The reactor subunits are to be emplaced directly into the lunar regolith utilizing the regolith not just for shielding but as the reflector material to increase the neutron economy of the system. While a single subunit cannot achieve criticality by itself, coordinated placement of additional subunits will provide a critical reactor system for lunar surface power generation. A lunar regolith clustered-reactor system promotes reliability, safety,more » and ease of manufacture and testing at the cost of a slight increase in launch mass per rated power level and an overall reduction in neutron economy when compared to a single-reactor system. Additional subunits may be launched with future missions to increase the cluster size and power according to desired lunar base power demand and lifetime. The results address the potential uncertainties associated with the lunar regolith material and emplacement of the subunit systems. Physical distance between subunits within the clustered emplacement exhibits the most significant feedback regarding changes in overall system reactivity. Narrow, deep holes will be the most effective in reducing axial neutron leakage from the core. The variation in iron concentration in the lunar regolith can directly influence the overall system reactivity although its effects are less than the more dominant factors of subunit emplacement.« less

Internally Cooled Monolithic Silicon Nitride Aerospace Components

NASA Technical Reports Server (NTRS)

Best, Jonathan E.; Cawley, James D.; Bhatt, Ramakrishna T.; Fox, Dennis S.; Lang, Jerry (Technical Monitor)

2000-01-01

A set of rapid prototyping (RP) processes have been combined with gelcasting to make ceramic aerospace components that contain internal cooling geometry. A mold and core combination is made using a MM6Pro (Sanders Prototyping, Inc.) and SLA-250/40 (3Dsystems, Inc.). The MM6Pro produces cores from ProtoBuild (trademarked) wax that are dissolved in room temperature ethanol following gelcasting. The SLA-250/40 yields epoxy/acrylate reusable molds. Parts produced by this method include two types of specimens containing a high density of thin long cooling channels, thin-walled cylinders and plates, as well as a model hollow airfoil shape that can be used for burner rig evaluation of coatings. Both uncoated and mullite-coated hollow airfoils has been tested in a Mach 0.3 burner rig with cooling air demonstrating internal cooling and confirming the effectiveness of mullite coatings.

GAS COOLED NUCLEAR REACTORS

DOEpatents

Long, E.; Rodwell, W.

1958-06-10

A gas-cooled nuclear reactor consisting of a graphite reacting core and reflector structure supported in a containing vessel is described. A gas sealing means is included for sealing between the walls of the graphite structure and containing vessel to prevent the gas coolant by-passing the reacting core. The reacting core is a multi-sided right prismatic structure having a pair of parallel slots around its periphery. The containing vessel is cylindrical and has a rib on its internal surface which supports two continuous ring shaped flexible web members with their radially innermost ends in sealing engagement within the radially outermost portion of the slots. The core structure is supported on ball bearings. This design permits thermal expansion of the core stracture and vessel while maintainirg a peripheral seal between the tvo elements.

Did Oligocene crustal thickening precede basin development in northern Thailand? A geochronological reassessment of Doi Inthanon and Doi Suthep

NASA Astrophysics Data System (ADS)

Gardiner, Nicholas J.; Roberts, Nick M. W.; Morley, Christopher K.; Searle, Michael P.; Whitehouse, Martin J.

2016-01-01

The Doi Inthanon and Doi Suthep metamorphic core complexes in northern Thailand are comprised of amphibolite-grade migmatitic gneisses mantled by lower-grade mylonites and metasedimentary sequences, thought to represent Cordilleran-style core complexes exhumed through the mobilization of a low-angle detachment fault. Previous studies have interpreted two metamorphic events (Late Triassic and Late Cretaceous), followed by ductile extension between the late Eocene and late Oligocene, a model which infers movement on the detachment at ca. 40 Ma, and which culminates in a rapid unroofing of the complexes in the early Miocene. The Chiang Mai Basin, the largest such Cenozoic Basin in the region, lies immediately to the east. Its development is related to the extension observed at Doi Inthanon and Doi Suthep, however it is not definitively dated, and models for its development have difficulty reconciling Miocene cooling ages with Eocene detachment movement. Here we present new in-situ LA-ICP-MS and SIMS U-Pb age data of zircon and monazite grains from gneiss and leucogranite samples taken from Doi Inthanon and Doi Suthep. Our new zircon data exhibit an older age range of 221-210 Ma, with younger ages of ca. 72 Ma, and 32-26 Ma. Our monazite data imply an older age cluster at 83-67 Ma, and a younger age cluster of 34-24 Ma. While our data support the view of Indosinian basement being reworked in the Cretaceous, they also indicate a late Eocene-Oligocene tectonothermal event, resulting in prograde metamorphism and anatexis. We suggest that this later event is related to localized transpressional thickening associated with sinistral movement on the Mae Ping Fault, coupled with thickening at the restraining bend of the Mae Yuan Fault to the immediate west of Doi Inthanon. Further, this upper Oligocene age limit from our zircon and monazite data would imply a younger Miocene constraint on movement of the detachment, which, when combined with the previously recorded Miocene cooling ages, has implications for a model for the onset of extension and subsequent development of the Chiang Mai Basin in the early mid-Miocene.

MOLECULAR GAS ALONG A BRIGHT H α FILAMENT IN 2A 0335+096 REVEALED BY ALMA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vantyghem, A. N.; McNamara, B. R.; Hogan, M. T.

2016-12-01

We present ALMA CO(1–0) and CO(3–2) observations of the brightest cluster galaxy (BCG) in the 2A 0335+096 galaxy cluster ( z  = 0.0346). The total molecular gas mass of 1.13 ± 0.15 × 10{sup 9} M {sub ⊙} is divided into two components: a nuclear region and a 7 kpc long dusty filament. The central molecular gas component accounts for 3.2 ± 0.4 × 10{sup 8} M {sub ⊙} of the total supply of cold gas. Instead of forming a rotationally supported ring or disk, it is composed of two distinct, blueshifted clumps south of the nucleus and a series of low-significance redshifted clumps extending toward a nearby companionmore » galaxy. The velocity of the redshifted clouds increases with radius to a value consistent with the companion galaxy, suggesting that an interaction between these galaxies <20 Myr ago disrupted a pre-existing molecular gas reservoir within the BCG. Most of the molecular gas, 7.8 ± 0.9 × 10{sup 8} M {sub ⊙}, is located in the filament. The CO emission is co-spatial with a 10{sup 4} K emission-line nebula and soft X-rays from 0.5 keV gas, indicating that the molecular gas has cooled out of the intracluster medium over a period of 25–100 Myr. The filament trails an X-ray cavity, suggesting that the gas has cooled from low-entropy gas that has been lifted out of the cluster core and become thermally unstable. We are unable to distinguish between inflow and outflow along the filament with the present data. Cloud velocities along the filament are consistent with gravitational free-fall near the plane of the sky, although their increasing blueshifts with radius are consistent with outflow.« less

Unusual behavior in magnesium-copper cluster matter produced by helium droplet mediated deposition.

PubMed

Emery, S B; Xin, Y; Ridge, C J; Buszek, R J; Boatz, J A; Boyle, J M; Little, B K; Lindsay, C M

2015-02-28

We demonstrate the ability to produce core-shell nanoclusters of materials that typically undergo intermetallic reactions using helium droplet mediated deposition. Composite structures of magnesium and copper were produced by sequential condensation of metal vapors inside the 0.4 K helium droplet baths and then gently deposited onto a substrate for analysis. Upon deposition, the individual clusters, with diameters ∼5 nm, form a cluster material which was subsequently characterized using scanning and transmission electron microscopies. Results of this analysis reveal the following about the deposited cluster material: it is in the un-alloyed chemical state, it maintains a stable core-shell 5 nm structure at sub-monolayer quantities, and it aggregates into unreacted structures of ∼75 nm during further deposition. Surprisingly, high angle annular dark field scanning transmission electron microscopy images revealed that the copper appears to displace the magnesium at the core of the composite cluster despite magnesium being the initially condensed species within the droplet. This phenomenon was studied further using preliminary density functional theory which revealed that copper atoms, when added sequentially to magnesium clusters, penetrate into the magnesium cores.

Thermionic nuclear reactor with internal heat distribution and multiple duct cooling

DOEpatents

Fisher, C.R.; Perry, L.W. Jr.

1975-11-01

A Thermionic Nuclear Reactor is described having multiple ribbon-like coolant ducts passing through the core, intertwined among the thermionic fuel elements to provide independent cooling paths. Heat pipes are disposed in the core between and adjacent to the thermionic fuel elements and the ribbon ducting, for the purpose of more uniformly distributing the heat of fission among the thermionic fuel elements and the ducts.

Core-halo age gradients and star formation in the Orion Nebula and NGS 2024 young stellar clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.

2014-06-01

We analyze age distributions of two nearby rich stellar clusters, the NGC 2024 (Flame Nebula) and Orion Nebula cluster (ONC) in the Orion molecular cloud complex. Our analysis is based on samples from the MYStIX survey and a new estimator of pre-main sequence (PMS) stellar ages, Age{sub JX} , derived from X-ray and near-infrared photometric data. To overcome the problem of uncertain individual ages and large spreads of age distributions for entire clusters, we compute median ages and their confidence intervals of stellar samples within annular subregions of the clusters. We find core-halo age gradients in both the NGC 2024more » cluster and ONC: PMS stars in cluster cores appear younger and thus were formed later than PMS stars in cluster peripheries. These findings are further supported by the spatial gradients in the disk fraction and K-band excess frequency. Our age analysis is based on Age{sub JX} estimates for PMS stars and is independent of any consideration of OB stars. The result has important implications for the formation of young stellar clusters. One basic implication is that clusters form slowly and the apparent age spreads in young stellar clusters, which are often controversial, are (at least in part) real. The result further implies that simple models where clusters form inside-out are incorrect and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.« less

Blue straggler formation at core collapse

NASA Astrophysics Data System (ADS)

Banerjee, Sambaran

Among the most striking feature of blue straggler stars (BSS) in globular clusters is the presence of multiple sequences of BSSs in the colour-magnitude diagrams (CMDs) of several globular clusters. It is often envisaged that such a multiple BSS sequence would arise due a recent core collapse of the host cluster, triggering a number of stellar collisions and binary mass transfers simultaneously over a brief episode of time. Here we examine this scenario using direct N-body computations of moderately-massive star clusters (of order 104 {M⊙). As a preliminary attempt, these models are initiated with ≈8-10 Gyr old stellar population and King profiles of high concentrations, being ``tuned'' to undergo core collapse quickly. BSSs are indeed found to form in a ``burst'' at the onset of the core collapse and several of such BS-bursts occur during the post-core-collapse phase. In those models that include a few percent primordial binaries, both collisional and binary BSSs form after the onset of the (near) core-collapse. However, there is as such no clear discrimination between the two types of BSSs in the corresponding computed CMDs. We note that this may be due to the less number of BSSs formed in these less massive models than that in actual globular clusters.

Melting and solidification behavior of Cu/Al and Ti/Al bimetallic core/shell nanoparticles during additive manufacturing by molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Rahmani, Farzin; Jeon, Jungmin; Jiang, Shan; Nouranian, Sasan

2018-05-01

Molecular dynamics (MD) simulations were performed to investigate the role of core volume fraction and number of fusing nanoparticles (NPs) on the melting and solidification of Cu/Al and Ti/Al bimetallic core/shell NPs during a superfast heating and slow cooling process, roughly mimicking the conditions of selective laser melting (SLM). One recent trend in the SLM process is the rapid prototyping of nanoscopically heterogeneous alloys, wherein the precious core metal maintains its particulate nature in the final manufactured part. With this potential application in focus, the current work reveals the fundamental role of the interface in the two-stage melting of the core/shell alloy NPs. For a two-NP system, the melting zone gets broader as the core volume fraction increases. This effect is more pronounced for the Ti/Al system than the Cu/Al system because of a larger difference between the melting temperatures of the shell and core metals in the former than the latter. In a larger six-NP system (more nanoscopically heterogeneous), the melting and solidification temperatures of the shell Al roughly coincide, irrespective of the heating or cooling rate, implying that in the SLM process, the part manufacturing time can be reduced due to solidification taking place at higher temperatures. The nanostructure evolution during the cooling of six-NP systems is further investigated. [Figure not available: see fulltext.

Related Core Academic Knowledge and Skills. Georgia Core Standards for Occupational Clusters.

ERIC Educational Resources Information Center

Georgia Univ., Athens. Dept. of Occupational Studies.

This document lists the industry-identified core academic knowledge and skills that should be possessed by all Georgia students who are enrolled in occupational cluster programs and are preparing to enter the work force or continue their occupational specialization at the postsecondary level. First, 63 related communications competencies are…

Mapping the filaments in NGC 1275

NASA Astrophysics Data System (ADS)

Cobos, Aracely Susan; Rich, Jeffrey; Great Observatories All-sky LIRG Survey (GOALS)

2018-01-01

The giant elliptical brightest cluster galaxies (BCGs) at the centers of many massive clusters are often surrounded by drawn-out forms of gaseous material. It is believed that this gaseous material is gas condensing from the intracluster medium (ICM) in a “cooling flow,” and it can directly impact the growth of the BCG. The galaxy NGC 1275 is one of the closest giant elliptical BCGs and lies at the center of the Perseus cluster. NGC 1275 has large filaments that are thought to be associated with a cooling flow, but they may also be affected by its AGN. To investigate the relationship between the AGN and the cooling flow we have mapped the filaments around NGC 1275 with the Cosmic Web Imager, an image-slicing integral field spectrograph at Palomar Observatories. We employ standard emission-line ratio diagnostics to determine the source of ionizing radiation. We use our analysis to investigate whether the formation of the extended filaments is a result of gas from the ICM collapsing onto the galaxy as it cools or if it is possible that the filaments are a result of the cluster’s interaction with the outflow driven by the AGN.

The effect of starting or stopping skin cooling on the thermoregulatory responses during leg exercise in humans.

PubMed

Demachi, K; Yoshida, T; Kume, M; Tsuneoka, H

2012-07-01

To assess the effects of starting or stopping leg cooling on the thermoregulatory responses during exercise, 60 min of cycling exercise at 30% of maximal oxygen uptake was performed under 4 conditions using tube trouser perfused with water at 10 °C; no leg cooling (NC), starting of leg cooling after 30 min of exercise (delayed cooling, DC), continuous leg cooling (CC), and stopping of continuous leg cooling after 30 min of exercise (SC) at an environmental temperature of 28.5 °C. During exercise under the DC conditions, an instantaneous increase in the esophageal temperature (Tes), a suppression of the cutaneous vascular conductance at the forearm (%CVC), and a decrease in the mean skin temperature (Tsk) were observed after leg cooling. The total sweat loss (Δm sw,tot) was lower under the DC than the NC condition. In the SC study, however, the Tes remained constant, while the %CVC increased gradually after leg cooling was stopped, and the Δm sw,tot was greater than that under the CC condition. These results suggest that during exercise, rapid skin cooling of the leg may cause an increase in core temperature, while also enhancing thermal stress. However, stopping skin cooling did not significantly affect the core temperature long-term, because the skin blood flow and sweat rate subsequently increased. © Georg Thieme Verlag KG Stuttgart · New York.

Powering Earth's dynamo with magnesium precipitation from the core.

PubMed

O'Rourke, Joseph G; Stevenson, David J

2016-01-21

Earth's global magnetic field arises from vigorous convection within the liquid outer core. Palaeomagnetic evidence reveals that the geodynamo has operated for at least 3.4 billion years, which places constraints on Earth's formation and evolution. Available power sources in standard models include compositional convection (driven by the solidifying inner core's expulsion of light elements), thermal convection (from slow cooling), and perhaps heat from the decay of radioactive isotopes. However, recent first-principles calculations and diamond-anvil cell experiments indicate that the thermal conductivity of iron is two or three times larger than typically assumed in these models. This presents a problem: a large increase in the conductive heat flux along the adiabat (due to the higher conductivity of iron) implies that the inner core is young (less than one billion years old), but thermal convection and radiogenic heating alone may not have been able to sustain the geodynamo during earlier epochs. Here we show that the precipitation of magnesium-bearing minerals from the core could have served as an alternative power source. Equilibration at high temperatures in the aftermath of giant impacts allows a small amount of magnesium (one or two weight per cent) to partition into the core while still producing the observed abundances of siderophile elements in the mantle and avoiding an excess of silicon and oxygen in the core. The transport of magnesium as oxide or silicate from the cooling core to underneath the mantle is an order of magnitude more efficient per unit mass as a source of buoyancy than inner-core growth. We therefore conclude that Earth's dynamo would survive throughout geologic time (from at least 3.4 billion years ago to the present) even if core radiogenic heating were minimal and core cooling were slow.

Magnetism and Mössbauer study of formation of multi-core γ -Fe2O3 nanoparticles

NASA Astrophysics Data System (ADS)

Kamali, Saeed; Bringas, Eugenio; Hah, Hien-Yoong; Bates, Brian; Johnson, Jacqueline A.; Johnson, Charles E.; Stroeve, Pieter

2018-04-01

A systematic investigation of magnetic nanoparticles and the formation of a core-shell structure, consisting of multiple maghemite (γ -Fe2O3) nanoparticles as the core and silica as the shell, has been performed using various techniques. High-resolution transmission electron microscopy clearly shows isolated maghemite nanoparticles with an average diameter of 13 nm and the formation of a core-shell structure. Low temperature Mössbauer spectroscopy reveals the presence of pure maghemite nanoparticles with all vacancies at the B-sites. Isothermal magnetization and zero-field-cooled and field-cooled measurements are used for investigating the magnetic properties of the nanoparticles. The magnetization results are in good accordance with the contents of the magnetic core and the non-magnetic shell. The multiple-core γ -Fe2O3 nanoparticles show similar behavior to isolated particles of the same size.

The Relationship Between Brightest Cluster Galaxy Star Formation and the Intracluster Medium in CLASH

NASA Astrophysics Data System (ADS)

Fogarty, Kevin; Postman, Marc; Larson, Rebecca; Donahue, Megan; Moustakas, John

2017-09-01

We study the nature of feedback mechanisms in the 11 CLASH brightest cluster galaxies (BCGs) that exhibit extended ultraviolet and nebular line emission features. We estimate star formation rates (SFRs), dust masses, and starburst durations using a Bayesian photometry-fitting technique that accounts for both stellar and dust emission from the UV through far-IR. By comparing these quantities to intracluster medium (ICM) cooling times and freefall times derived from X-ray observations and lensing estimates of the cluster mass distribution, we discover a tight relationship between the BCG SFR and the ICM cooling time to freefall time ratio, {t}{cool}/{t}{ff}, with an upper limit on the intrinsic scatter of 0.15 dex. Furthermore, starburst durations may correlate with ICM cooling times at a radius of 0.025 {R}500, and the two quantities converge upon reaching the gigayear regime. Our results provide a direct observational link between the thermodynamical state of the ICM and the intensity and duration of BCG star formation activity, and appear consistent with a scenario where active galactic nuclei induce condensation of thermally unstable ICM overdensities that fuel long-duration (>1 Gyr) BCG starbursts. This scenario can explain (a) how gas with a low cooling time is depleted without causing a cooling flow and (b) the scaling relationship between SFR and {t}{cool}/{t}{ff}. We also find that the scaling relation between SFR and dust mass in BCGs with SFRs < 100 {M}⊙ yr-1 is similar to that in star-forming field galaxies; BCGs with large (> 100 {M}⊙ yr-1) SFRs have dust masses comparable to extreme starbursts.

NGC 2548: clumpy spatial and kinematic structure in an intermediate-age Galactic cluster

NASA Astrophysics Data System (ADS)

Vicente, Belén; Sánchez, Néstor; Alfaro, Emilio J.

2016-09-01

NGC 2548 is a ˜400-500 Myr old open cluster with evidence of spatial substructures likely caused by its interaction with the Galactic disc. In this work we use precise astrometric data from the Carte du Ciel - San Fernando (CdC-SF) catalogue to study the clumpy structure in this cluster. We confirm the fragmented structure of NGC 2548 but, additionally, the relatively high precision of our kinematic data lead us to the first detection of substructures in the proper motion space of a stellar cluster. There are three spatially separated cores each of which has its own counterpart in the proper motion distribution. The two main cores lie nearly parallel to the Galactic plane whereas the third one is significantly fainter than the others and it moves towards the Galactic plane separating from the rest of the cluster. We derive core positions and proper motions, as well as the stars belonging to each core.

Charge-doping and chemical composition-driven magnetocrystalline anisotropy in CoPt core-shell alloy clusters

NASA Astrophysics Data System (ADS)

Ruiz-Díaz, P.; Muñoz-Navia, M.; Dorantes-Dávila, J.

2018-03-01

Charge-doping together with 3 d-4 d alloying emerges as promising mechanisms for tailoring the magnetic properties of low-dimensional systems. Here, throughout ab initio calculations, we present a systematic overview regarding the impact of both electron(hole) charge-doping and chemical composition on the magnetocrystalline anisotropy (MA) of CoPt core-shell alloy clusters. By taking medium-sized Co n Pt m ( N = n + m = 85) octahedral-like alloy nanoparticles for some illustrative core-sizes as examples, we found enhanced MA energies and large induced spin(orbital) moments in Pt-rich clusters. Moreover, depending on the Pt-core-size, both in-plane and off-plane directions of magnetization are observed. In general, the MA of these binary compounds further stabilizes upon charge-doping. In addition, in the clusters with small MA, the doping promotes magnetization switching. Insights into the microscopical origins of the MA behavior are associated to changes in the electronic structure of the clusters. [Figure not available: see fulltext.

Cooling hyperthermic firefighters by immersing forearms and hands in 10 degrees C and 20 degrees C water.

PubMed

Giesbrecht, Gordon G; Jamieson, Christopher; Cahill, Farrell

2007-06-01

Firefighters experience significant heat stress while working with heavy gear in a hot, humid environment. This study compared the cooling effectiveness of immersing the forearms and hands in 10 and 20 degrees C water. Six men (33 +/- 10 yr; 180 +/- 4 cm; 78 +/- 9 kg; 19 +/- 5% body fat) wore firefighter 'turn-out gear' (heavy clothing and breathing apparatus weighing 27 kg) in a protocol including three 20-min exercise bouts (step test, 78 W, 40 degrees C air, 40% RH) each followed by a 20-min rest/cooling (21 degrees C air); i.e., 60 min of exercise, 60 min of cooling. Turn-out gear was removed during rest/cooling periods and subjects either rested (Control), immersed their hands in 10 or 20 degrees C water (H-10, H-20), or immersed their hands and forearms in 10 or 20 degrees C water (HF-10, HF-20). In 20 degrees C water, hand immersion did not reduce core temperature compared with Control; however, including forearm immersion decreased core temperature below Control values after both the second and final exercise periods (p < 0.001). In 10 degrees C water, adding forearm with hand immersion produced a lower core temperature (0.8 degrees C above baseline) than all other conditions (1.1 to 1.4 degrees C above baseline) after the final exercise period (p < 0.001). Sweat loss during Control (1458 g) was greater than all active cooling protocols (1146 g) (p < 0.001), which were not different from each other. Hand and forearm immersion in cool water is simple, reduces heat strain, and may increase work performance in a hot, humid environment. With 20 degrees C water, forearms should be immersed with the hands to be effective. At lower water temperatures, forearm and/or hand immersion will be effective, although forearm immersion will decrease core temperature further.

Nonpharmacologic Approach to Minimizing Shivering During Surface Cooling: A Proof of Principle Study1

PubMed Central

Shah, Nirav G.; Cowan, Mark J.; Pickering, Edward; Sareh, Houtan; Afshar, Majid; Fox, Dawn; Marron, Jennifer; Davis, Jennifer; Herold, Keith; Shanholtz, Carl B.; Hasday, Jeffrey D.

2012-01-01

Purpose This study had two objectives: (1) to quantify the metabolic response to physical cooling in febrile patients with Systemic Inflammatory Response Syndrome (SIRS); and (2) to provide proof for the hypothesis that the efficiency of external cooling and the subsequent shivering response are influenced by site and temperature of surface cooling pads. Methods To quantify shivering thermogenesis during surface cooling for fever, we monitored oxygen consumption (VO2) in six febrile patients with SIRS during conventional cooling with cooling blankets and ice packs. To begin to determine how location and temperature of surface cooling influences shivering, we compared 5 cooling protocols for inducing mild hypothermia in six healthy volunteers. Results In the SIRS patients, core temperature decreased 0.67°C per hour, all patients shivered, VO2 increased 57.6% and blood pressure increased 15% during cooling. In healthy subjects, cooling with the 10°C vest was most comfortable and removed heat most efficiently without shivering or VO2 increase. Cooling with combined vest and thigh pads stimulated the most shivering and highest VO2, and increased core temperature. Reducing vest temperature from 10°C to 5°C failed to increase heat removal secondary to cutaneous vasoconstriction. Capsaicin, an agonist for TRPV1 warm-sensing channels, partially reversed this effect in 5 subjects. Conclusions Our results identify the hazards of surface cooling in febrile critically ill patients and support the concept that optimization of cooling pad temperature and position may improve cooling efficiency and reduce shivering. PMID:22762936

Nonpharmacologic approach to minimizing shivering during surface cooling: a proof of principle study.

PubMed

Shah, Nirav G; Cowan, Mark J; Pickering, Edward; Sareh, Houtan; Afshar, Majid; Fox, Dawn; Marron, Jennifer; Davis, Jennifer; Herold, Keith; Shanholtz, Carl B; Hasday, Jeffrey D

2012-12-01

This study had 2 objectives: (1) to quantify the metabolic response to physical cooling in febrile patients with systemic inflammatory response syndrome (SIRS) and (2) to provide proof for the hypothesis that the efficiency of external cooling and the subsequent shivering response are influenced by site and temperature of surface cooling pads. To quantify shivering thermogenesis during surface cooling for fever, we monitored oxygen consumption (VO(2)) in 6 febrile patients with SIRS during conventional cooling with cooling blankets and ice packs. To begin to determine how location and temperature of surface cooling influence shivering, we compared 5 cooling protocols for inducing mild hypothermia in 6 healthy volunteers. In the patients with SIRS, core temperature decreased 0.67 °C per hour, all patients shivered, VO(2) increased 57.6%, and blood pressure increased 15% during cooling. In healthy subjects, cooling with the 10 °C vest was most comfortable and removed heat most efficiently without shivering or VO(2) increase. Cooling with combined vest and thigh pads stimulated the most shivering and highest VO(2) and increased core temperature. Reducing vest temperature from 10 °C to 5 °C failed to increase heat removal secondary to cutaneous vasoconstriction. Capsaicin, an agonist for the transient receptor potential cation channel subfamily V member 1 (TRPV1) warm-sensing channels, partially reversed this effect in 5 subjects. Our results identify the hazards of surface cooling in febrile critically ill patients and support the concept that optimization of cooling pad temperature and position may improve cooling efficiency and reduce shivering. Copyright © 2012 Elsevier Inc. All rights reserved.

Inner Core Rotation from Geomagnetic Westward Drift and a Stationary Spherical Vortex in Earth's Core

NASA Technical Reports Server (NTRS)

Voorhies, Coerte V.

1998-01-01

The idea that geomagnetic westward drift indicates convective leveling of the planetary momentum gradient within Earth's core is pursued in search of a differentially rotating mean state, upon which various oscillations and secular effects might be superimposed. The desired state conforms to roughly spherical boundary conditions, minimizes dissipative interference with convective cooling in the bulk of the core, yet may aid core cooling by depositing heat in the uppermost core and lower mantle. The variational calculus of stationary dissipation applied to a spherical vortex within the core yields an interesting differential rotation profile, akin to spherical Couette flow bounded by thin Hartmann layers. Four boundary conditions are required. To concentrate shear induced dissipation near the core-mantle boundary, these are taken to be: (i) no-slip at the core-mantle interface; (ii) geomagnetically estimated bulk westward flow at the base of the core-mantle boundary layer; (iii) no-slip at the inner-outer core interface; and, to describe magnetic locking of the inner core to the deep outer core; (iv) hydrodynamically stress-free at the inner-outer core boundary. By boldly assuming the axial core angular momentum anomaly to be zero, the super-rotation of the inner core relative to the mantle is calculated to be at most 1.5 deg./yr.

Inner Core Rotation from Geomagnetic Westward Drift and a Stationary Spherical Vortex in Earth's Core

NASA Technical Reports Server (NTRS)

Voorhies, C. V.

1999-01-01

The idea that geomagnetic westward drift indicates convective leveling of the planetary momentum gradient within Earth's core is pursued in search of a differentially rotating mean state, upon which various oscillations and secular effects might be superimposed. The desired state conforms to roughly spherical boundary conditions, minimizes dissipative interference with convective cooling in the bulk of the core, yet may aide core cooling by depositing heat in the uppermost core and lower mantle. The variational calculus of stationary dissipation applied to a spherical vortex within the core yields an interesting differential rotation profile akin to spherical Couette flow bounded by thin Hartmann layers. Four boundary conditions are required. To concentrate shear induced dissipation near the core-mantle boundary, these are taken to be: (i) no-slip at the core-mantle interface; (ii) geomagnetically estimated bulk westward flow at the base of the core-mantle boundary layer; (iii) no-slip at the inner-outer core interface; and, to describe magnetic locking of the inner core to the deep outer core, (iv) hydrodynamically stress-free at the inner-outer core boundary. By boldly assuming the axial core angular momentum anomaly to be zero, the super-rotation of the inner core is calculated to be at most 1.5 degrees per year.

PEERING INTO THE CORE OF A GLOBULAR CLUSTER

NASA Technical Reports Server (NTRS)

2002-01-01

Astronomers have used NASA's Hubble Space Telescope to peer into the center of a dense swarm of stars called Omega Centauri. Located some 17,000 light-years from Earth, Omega Centauri is a massive globular star cluster, containing several million stars swirling in locked orbits around a common center of gravity. The stars are packed so densely in the cluster's core that it is difficult for ground-based telescopes to make out individual stars. Hubble's high resolution is able to pick up where ground-based telescopes leave off, capturing distinct points of light from stars at the very center of the cluster. Omega Centauri is so large in our sky that only a small part of it fits within the field of view of the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope. Yet even this tiny patch contains some 50,000 stars, all packed into a region only about 13 light-years wide. For comparison, a similarly sized region centered on the Sun would contain about a half dozen stars. The vast majority of stars in this Hubble image are faint, yellow-white dwarf stars similar to our Sun. The handful of bright yellow-orange stars are red giants that have begun to exhaust their nuclear fuel and have expanded to diameters about a hundred times that of the Sun. A number of faint blue stars are also visible in the image. These are in a brief phase of evolution between the dwarf stage and the red-giant stage, during which the surface temperature is high. The stars in Omega Centauri are all very old, about 12 billion years. Stars with a mass as high as that of our Sun have already completed their evolution and have faded away as white dwarfs, too faint to be seen even in the Hubble image. The stars in the core of Omega Centauri are so densely packed that occasionally one of them will actually collide with another one. Even in the dense center of Omega Centauri, stellar collisions will be infrequent. But the cluster is so old that many thousands of collisions have occurred. What happens when stars collide? These Hubble images were taken to help answer that question. When stars collide head-on, they probably just merge together and make one bigger star. But if the collision is a near miss, they may go into orbit around each other, forming a close binary star system. Searching for a needle in a haystack, scientists have found two binary star systems in these Hubble images that may have had such an origin. Both of them are close pairs in which once component is a white dwarf that pulls gas off of its companion. When the gas falls onto the surface of the white dwarf, it is heated to the point that it emits ultraviolet light. These unusual emissions enabled scientists to pinpoint these two faint stars among the myriad of other faint stars in the cluster. Omega Centauri is the most luminous and massive globular star cluster in the Milky Way. It is one of the few globular clusters that can be seen with the unaided eye. Named by Johann Bayer in 1603 as the 24th brightest object in the constellation Centaurus, it resembles a small cloud in the southern sky and might easily be mistaken for a comet. This Hubble WFPC2 image was taken on June 11, 1997 in ultraviolet, red, and H-alpha filters. The science team, led by Dr. Adrienne Cool of San Francisco State University includes Jennifer Carson, a former SFSU student who is now at UCLA, Charles Bailyn at Yale and Jonathan Grindlay at Harvard. These data are currently being used by Jeff Carlin and Daryl Haggard, two SFSU students, to look for optical counterparts of X-ray sources recently discovered with the Chandra Observatory. This image was produced by the Hubble Heritage Team (STScI/AURA). Credits: NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: A. Cool (SFSU)

Observations of different core water cluster ions Y-(H2O)n (Y = O2, HOx, NOx, COx) and magic number in atmospheric pressure negative corona discharge mass spectrometry.

PubMed

Sekimoto, Kanako; Takayama, Mitsuo

2011-01-01

Reliable mass spectrometry data from large water clusters Y(-)(H(2)O)(n) with various negative core ions Y(-) such as O(2)(-), HO(-), HO(2)(-), NO(2)(-), NO(3)(-), NO(3)(-)(HNO(3))(2), CO(3)(-) and HCO(4)(-) have been obtained using atmospheric pressure negative corona discharge mass spectrometry. All the core Y(-) ions observed were ionic species that play a central role in tropospheric ion chemistry. These mass spectra exhibited discontinuities in ion peak intensity at certain size clusters Y(-)(H(2)O)(m) indicating specific thermochemical stability. Thus, Y(-)(H(2)O)(m) may correspond to the magic number or first hydrated shell in the cluster series Y(-)(H(2)O)(n). The high intensity discontinuity at HO(-)(H(2)O)(3) observed was the first mass spectrometric evidence for the specific stability of HO(-)(H(2)O)(3) as the first hydrated shell which Eigen postulated in 1964. The negative ion water clusters Y(-)(H(2)O)(n) observed in the mass spectra are most likely to be formed via core ion formation in the ambient discharge area (760 torr) and the growth of water clusters by adiabatic expansion in the vacuum region of the mass spectrometers (≈1 torr). The detailed mechanism of the formation of the different core water cluster ions Y(-)(H(2)O)(n) is described. Copyright © 2010 John Wiley & Sons, Ltd.

Prototype CoolCup cryolipolysis applicator with over 40% reduced treatment time demonstrates equivalent safety and efficacy with greater patient preference.

PubMed

Kilmer, Suzanne L

2017-01-01

Cryolipolysis is a safe, effective non-surgical procedure to reduce fat. For most cryolipolysis treatments, tissue is pulled between parallel cooling plates with a treatment duration of 60 minutes. A novel contoured cup, medium-sized applicator was developed to increase tissue contact with reduced skin tension and reduced treatment time. This prototype contoured cup was investigated with a standard cryolipolysis applicator to evaluate safety, efficacy, and patient preference. A prototype CoolCup medium-sized vacuum applicator (CoolSculpting System, ZELTIQ Aesthetics) was used to treat n = 19 subjects in the flanks. Randomly assigned, one flank received standard treatment with the CoolCore applicator (-10°C for 60 minutes). The contralateral flank received treatment from the CoolCup (-11°C for 35 minutes). The clinical study primary efficacy endpoint was 70% correct identification of baseline photographs by independent physician review. Incidence of adverse device effects was monitored. Fat layer reduction was measured by ultrasound and subject surveys were administered 12 weeks post-treatment. Equivalent efficacy was demonstrated between the CoolCore standard treatment and the prototype CoolCup. Independent review from three blinded physicians found 81% correct identification of baseline photographs for the standard treatment and 79% for the CoolCup. Ultrasound measurements indicated mean fat layer reduction of 4.38 mm for the standard treatment and 4.40 mm for the CoolCup; no statistically significant difference was found when comparing treatment efficacy of the two applicators (P = 0.96). Patient questionnaires revealed 85% preferred CoolCup because of shorter treatment duration and greater comfort. Procedural assessments revealed 45% lower pain scores for CoolCup. Immediate post-treatment clinical assessments revealed 82% less bruising. Typical side effects, such as numbness and erythema, were similar. There were no adverse events. This clinical study of a prototype medium-sized vacuum applicator with a cooled contoured surface indicates that the CoolCup produces equivalent safety and efficacy to the standard CoolCore cryolipolysis applicator. With a 42% reduction in treatment time, the procedure was found to be more comfortable because of lower vacuum skin tension and shorter treatment duration. Lasers Surg. Med. 49:63-68, 2017. © 2016 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc. © 2016 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Galaxy And Mass Assembly (GAMA): the effect of galaxy group environment on active galactic nuclei

NASA Astrophysics Data System (ADS)

Gordon, Yjan A.; Pimbblet, Kevin A.; Owers, Matt S.; Bland-Hawthorn, Joss; Brough, Sarah; Brown, Michael J. I.; Cluver, Michelle E.; Croom, Scott M.; Holwerda, Benne W.; Loveday, Jonathan; Mahajan, Smriti; Wang, Lingyu

2018-04-01

In galaxy clusters, efficiently accreting active galactic nuclei (AGNs) are preferentially located in the infall regions of the cluster projected phase-space, and are rarely found in the cluster core. This has been attributed to both an increase in triggering opportunities for infalling galaxies, and a reduction of those mechanisms in the hot, virialized, cluster core. Exploiting the depth and completeness (98 per cent at r < 19.8 mag) of the Galaxy And Mass Assembly survey (GAMA), we probe down the group halo mass function to assess whether AGNs are found in the same regions in groups as they are in clusters. We select 451 optical AGNs from 7498 galaxies with log10(M*/M⊙) > 9.9 in 695 groups with 11.53 ≤ log10(M200/M⊙) ≤ 14.56 at z < 0.15. By analysing the projected phase-space positions of these galaxies, we demonstrate that when split both radially, and into physically derived infalling and core populations, AGN position within group projected phase-space is dependent on halo mass. For groups with log10(M200/M⊙) > 13.5, AGNs are preferentially found in the infalling galaxy population with 3.6σ confidence. At lower halo masses, we observe no difference in AGN fraction between core and infalling galaxies. These observations support a model where a reduced number of low-speed interactions, ram pressure stripping and intra-group/cluster medium temperature, the dominance of which increase with halo mass, work to inhibit AGN in the cores of groups and clusters with log10(M200/M⊙) > 13.5, but do not significantly affect nuclear activity in cores of less massive structures.

Crustal Cooling in the Neutron Star Low-Mass X-Ray Binary KS 1731-260

NASA Astrophysics Data System (ADS)

Merritt, Rachael L.

Neutron stars in binary systems can undergo periods of accretion (outburst), where in- falling material heats the crust of the star out of thermal equilibrium with the core. When accretion stops (quiescence), we can directly observe the thermal relaxation of the crust. Crustal cooling of accretion-heated neutron stars provides insight into the stellar interior of neutron stars. The neutron star X-ray transient, KS 1731-260, was in outburst for 12.5 years before returning to quiescence in 2001. Here, we present a 150 ks Chandra observation of KS 1731-260 taken in August 2015, about 14.5 years into quiescence. We find that the neutron star surface temperature is consistent with the previous observation, suggesting the crust has reached thermal equilibrium with the core. Using a theoretical thermal evolution code, we fit the observed cooling curves and constrain the core temperature, composition, and the required level of extra shallow heating.

MERCHANT MARINE SHIP REACTOR

DOEpatents

Mumm, J.F.; North, D.C. Jr.; Rock, H.R.; Geston, D.K.

1961-05-01

A nuclear reactor is described for use in a merchant marine ship. The reactor is of pressurized light water cooled and moderated design in which three passes of the water through the core in successive regions of low, intermediate, and high heat generation and downflow in a fuel region are made. The foregoing design makes a compact reactor construction with extended core life. The core has an egg-crate lattice containing the fuel elements confined between a lower flow baffle and upper grid plate, with the latter serving also as part of a turn- around manifold from which the entire coolant is distributed into the outer fuel elements for the second pass through the core. The inner fuel elements are cooled in the third pass.

Merchant Marine Ship Reactor

DOEpatents

Sankovich, M. F.; Mumm, J. F.; North, Jr, D. C.; Rock, H. R.; Gestson, D. K.

1961-05-01

A nuclear reactor for use in a merchant marine ship is described. The reactor is of pressurized, light water cooled and moderated design in which three passes of the water through the core in successive regions of low, intermediate, and high heat generation and downflow in a fuel region are made. The design makes a compact reactor construction with extended core life. The core has an egg-crate lattice containing the fuel elements that are confined between a lower flow baffle and upper grid plate, with the latter serving also as part of a turn- around manifold from which the entire coolant is distributed into the outer fuel elements for the second pass through the core. The inner fuel elements are cooled in the third pass. (AEC)

Reactor core isolation cooling system

DOEpatents

Cooke, F.E.

1992-12-08

A reactor core isolation cooling system includes a reactor pressure vessel containing a reactor core, a drywell vessel, a containment vessel, and an isolation pool containing an isolation condenser. A turbine is operatively joined to the pressure vessel outlet steamline and powers a pump operatively joined to the pressure vessel feedwater line. In operation, steam from the pressure vessel powers the turbine which in turn powers the pump to pump makeup water from a pool to the feedwater line into the pressure vessel for maintaining water level over the reactor core. Steam discharged from the turbine is channeled to the isolation condenser and is condensed therein. The resulting heat is discharged into the isolation pool and vented to the atmosphere outside the containment vessel for removing heat therefrom. 1 figure.

Reactor core isolation cooling system

DOEpatents

Cooke, Franklin E.

1992-01-01

A reactor core isolation cooling system includes a reactor pressure vessel containing a reactor core, a drywell vessel, a containment vessel, and an isolation pool containing an isolation condenser. A turbine is operatively joined to the pressure vessel outlet steamline and powers a pump operatively joined to the pressure vessel feedwater line. In operation, steam from the pressure vessel powers the turbine which in turn powers the pump to pump makeup water from a pool to the feedwater line into the pressure vessel for maintaining water level over the reactor core. Steam discharged from the turbine is channeled to the isolation condenser and is condensed therein. The resulting heat is discharged into the isolation pool and vented to the atmosphere outside the containment vessel for removing heat therefrom.

Near-Edge X-ray Absorption Fine Structure within Multilevel Coupled Cluster Theory.

PubMed

Myhre, Rolf H; Coriani, Sonia; Koch, Henrik

2016-06-14

Core excited states are challenging to calculate, mainly because they are embedded in a manifold of high-energy valence-excited states. However, their locality makes their determination ideal for local correlation methods. In this paper, we demonstrate the performance of multilevel coupled cluster theory in computing core spectra both within the core-valence separated and the asymmetric Lanczos implementations of coupled cluster linear response theory. We also propose a visualization tool to analyze the excitations using the difference between the ground-state and excited-state electron densities.

SEEDisCs: How Clusters Form and Galaxies Transform in the Cosmic Web

NASA Astrophysics Data System (ADS)

Jablonka, P.

2017-08-01

This presentation introduces a new survey, the Spatial Extended EDisCS Survey (SEEDisCS), which aims at understanding how clusters assemble and the level at which galaxies are preprocessed before falling on the cluster cores. I focus on the changes in galaxy properties in the cluster large scale environments, and how we can get constraints on the timescale of star formation quenching. I also discuss new ALMA CO observations, which trace the fate of the galaxy cold gas content along the infalling paths towards the cluster cores.

Multi-phase model development to assess RCIC system capabilities under severe accident conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirkland, Karen Vierow; Ross, Kyle; Beeny, Bradley

The Reactor Core Isolation Cooling (RCIC) System is a safety-related system that provides makeup water for core cooling of some Boiling Water Reactors (BWRs) with a Mark I containment. The RCIC System consists of a steam-driven Terry turbine that powers a centrifugal, multi-stage pump for providing water to the reactor pressure vessel. The Fukushima Dai-ichi accidents demonstrated that the RCIC System can play an important role under accident conditions in removing core decay heat. The unexpectedly sustained, good performance of the RCIC System in the Fukushima reactor demonstrates, firstly, that its capabilities are not well understood, and secondly, that themore » system has high potential for extended core cooling in accident scenarios. Better understanding and analysis tools would allow for more options to cope with a severe accident situation and to reduce the consequences. The objectives of this project were to develop physics-based models of the RCIC System, incorporate them into a multi-phase code and validate the models. This Final Technical Report details the progress throughout the project duration and the accomplishments.« less

OPTICAL COLORS OF INTRACLUSTER LIGHT IN THE VIRGO CLUSTER CORE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rudick, Craig S.; Mihos, J. Christopher; Harding, Paul

2010-09-01

We continue our deep optical imaging survey of the Virgo cluster using the CWRU Burrell Schmidt telescope by presenting B-band surface photometry of the core of the Virgo cluster in order to study the cluster's intracluster light (ICL). We find ICL features down to {mu}{sub B} {approx}29 mag arcsec{sup -2}, confirming the results of Mihos et al., who saw a vast web of low surface brightness streams, arcs, plumes, and diffuse light in the Virgo cluster core using V-band imaging. By combining these two data sets, we are able to measure the optical colors of many of the cluster's lowmore » surface brightness features. While much of our imaging area is contaminated by galactic cirrus, the cluster core near the cD galaxy, M87, is unobscured. We trace the color profile of M87 out to over 2000'', and find a blueing trend with radius, continuing out to the largest radii. Moreover, we have measured the colors of several ICL features which extend beyond M87's outermost reaches and find that they have similar colors to the M87's halo itself, B - V {approx}0.8. The common colors of these features suggest that the extended outer envelopes of cD galaxies, such as M87, may be formed from similar streams, created by tidal interactions within the cluster, that have since dissolved into a smooth background in the cluster potential.« less

Unusual behavior in magnesium-copper cluster matter produced by helium droplet mediated deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emery, S. B., E-mail: samuel.emery@navy.mil; Little, B. K.; Air Force Research Laboratory, Munitions Directorate, 2306 Perimeter Rd., Eglin AFB, Florida 32542

2015-02-28

We demonstrate the ability to produce core-shell nanoclusters of materials that typically undergo intermetallic reactions using helium droplet mediated deposition. Composite structures of magnesium and copper were produced by sequential condensation of metal vapors inside the 0.4 K helium droplet baths and then gently deposited onto a substrate for analysis. Upon deposition, the individual clusters, with diameters ∼5 nm, form a cluster material which was subsequently characterized using scanning and transmission electron microscopies. Results of this analysis reveal the following about the deposited cluster material: it is in the un-alloyed chemical state, it maintains a stable core-shell 5 nm structuremore » at sub-monolayer quantities, and it aggregates into unreacted structures of ∼75 nm during further deposition. Surprisingly, high angle annular dark field scanning transmission electron microscopy images revealed that the copper appears to displace the magnesium at the core of the composite cluster despite magnesium being the initially condensed species within the droplet. This phenomenon was studied further using preliminary density functional theory which revealed that copper atoms, when added sequentially to magnesium clusters, penetrate into the magnesium cores.« less

The Chandra Strong Lens Sample: Revealing Baryonic Physics In Strong Lensing Selected Clusters

NASA Astrophysics Data System (ADS)

Bayliss, Matthew

2017-08-01

We propose for Chandra imaging of the hot intra-cluster gas in a unique new sample of 29 galaxy clusters selected purely on their strong gravitational lensing signatures. This will be the first program targeting a purely strong lensing selected cluster sample, enabling new comparisons between the ICM properties and scaling relations of strong lensing and mass/ICM selected cluster samples. Chandra imaging, combined with high precision strong lens models, ensures powerful constraints on the distribution and state of matter in the cluster cores. This represents a novel angle from which we can address the role played by baryonic physics |*| the infamous |*|gastrophysics|*| in shaping the cores of massive clusters, and opens up an exciting new galaxy cluster discovery space with Chandra.

The Chandra Strong Lens Sample: Revealing Baryonic Physics In Strong Lensing Selected Clusters

NASA Astrophysics Data System (ADS)

Bayliss, Matthew

2017-09-01

We propose for Chandra imaging of the hot intra-cluster gas in a unique new sample of 29 galaxy clusters selected purely on their strong gravitational lensing signatures. This will be the first program targeting a purely strong lensing selected cluster sample, enabling new comparisons between the ICM properties and scaling relations of strong lensing and mass/ICM selected cluster samples. Chandra imaging, combined with high precision strong lens models, ensures powerful constraints on the distribution and state of matter in the cluster cores. This represents a novel angle from which we can address the role played by baryonic physics -- the infamous ``gastrophysics''-- in shaping the cores of massive clusters, and opens up an exciting new galaxy cluster discovery space with Chandra.

Core cooling under accident conditions at the high-flux beam reactor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tichler, P.; Cheng, L.; Fauske, H.

The High-Flux Beam Reactor (HFBR) at Brookhaven National Laboratory (BNL) is cooled and moderated by heavy water and contains {sup 235}U in the form of narrow-channel, parallel-plate-type fuel elements. During normal operation, the flow direction is downward through the core. This flow direction is maintained at a reduced flow rate during routine shutdown and on loss of commercial power by means of redundant pumps and power supplies. However, in certain accident scenarios, e.g. loss-of-coolant accidents (LOCAs), all forced-flow cooling is lost. Although there was experimental evidence during the reactor design period (1958-1963) that the heat removal capacity in the fullymore » developed natural circulation cooling mode was relatively high, it was not possible to make a confident prediction of the heat removal capacity during the transition from downflow to natural circulation. Accordingly, a test program was initiated using an electrically heated section to simulate the fuel channel and a cooling loop to simulate the balance of the primary cooling system.« less

The Core Values that Support Health, Safety, and Well-being at Work

PubMed Central

Zwetsloot, Gerard I.J.M.; Scheppingen, Arjella R. van; Bos, Evelien H.; Dijkman, Anja; Starren, Annick

2013-01-01

Background Health, safety, and well-being (HSW) at work represent important values in themselves. It seems, however, that other values can contribute to HSW. This is to some extent reflected in the scientific literature in the attention paid to values like trust or justice. However, an overview of what values are important for HSW was not available. Our central research question was: what organizational values are supportive of health, safety, and well-being at work? Methods The literature was explored via the snowball approach to identify values and value-laden factors that support HSW. Twenty-nine factors were identified as relevant, including synonyms. In the next step, these were clustered around seven core values. Finally, these core values were structured into three main clusters. Results The first value cluster is characterized by a positive attitude toward people and their “being”; it comprises the core values of interconnectedness, participation, and trust. The second value cluster is relevant for the organizational and individual “doing”, for actions planned or undertaken, and comprises justice and responsibility. The third value cluster is relevant for “becoming” and is characterized by the alignment of personal and organizational development; it comprises the values of growth and resilience. Conclusion The three clusters of core values identified can be regarded as “basic value assumptions” that underlie both organizational culture and prevention culture. The core values identified form a natural and perhaps necessary aspect of a prevention culture, complementary to the focus on rational and informed behavior when dealing with HSW risks. PMID:24422174

Globular cluster formation - The fossil record

NASA Technical Reports Server (NTRS)

Murray, Stephen D.; Lin, Douglas N. C.

1992-01-01

Properties of globular clusters which have remained unchanged since their formation are used to infer the internal pressures, cooling times, and dynamical times of the protocluster clouds immediately prior to the onset of star formation. For all globular clusters examined, it is found that the cooling times are much less than the dynamical times, implying that the protoclusters must have been maintained in thermal equilibrium by external heat sources, with fluxes consistent with those found in previous work, and giving the observed rho-T relation. Self-gravitating clouds cannot be stably heated, so that the Jeans mass forms an upper limit to the cluster masses. The observed dependence of protocluster pressure upon galactocentric position implies that the protocluster clouds were in hydrostatic equilibrium after their formation. The pressure dependence is well fitted by that expected for a quasi-statically evolving background hot gas, shock heated to its virial temperature. The observations and inferences are combined with previous theoretical work to construct a picture of globular cluster formation.

Photometric Calibrations of Gemini Images of NGC 6253

NASA Astrophysics Data System (ADS)

Pearce, Sean; Jeffery, Elizabeth

2017-01-01

We present preliminary results of our analysis of the metal-rich open cluster NGC 6253 using imaging data from GMOS on the Gemini-South Observatory. These data are part of a larger project to observe the effects of high metallicity on white dwarf cooling processes, especially the white dwarf cooling age, which have important implications on the processes of stellar evolution. To standardize the Gemini photometry, we have also secured imaging data of both the cluster and standard star fields using the 0.6-m SARA Observatory at CTIO. By analyzing and comparing the standard star fields of both the SARA data and the published Gemini zero-points of the standard star fields, we will calibrate the data obtained for the cluster. These calibrations are an important part of the project to obtain a standardized deep color-magnitude diagram to analyze the cluster. We present the process of verifying our standardization process. With a standardized CMD, we also present an analysis of the cluster's main sequence turn off age.

White Dwarfs in Star Clusters: The Initial-Final Mass Relation for Stars from 0.85 to 8 M$_\\odot$

NASA Astrophysics Data System (ADS)

Cummings, Jeffrey; Kalirai, Jason; Tremblay, P.-E.; Ramírez-Ruiz, Enrico

2018-01-01

The spectroscopic study of white dwarfs provides both their mass, cooling age, and intrinsic photometric properties. For white dwarfs in the field of well-studied star clusters, this intrinsic photometry can be used to determine if they are members of that star cluster. Comparison of a member white dwarf's cooling age to its total cluster's age provides the evolutionary timescale of its progenitor star, and hence the mass. This is the initial-final mass relation (IFMR) for stars, which gives critical information on how a progenitor star evolves and loses mass throughout its lifetime, and how this changes with progenitor mass. Our work, for the first time, presents a uniform analysis of 85 white dwarf cluster members spanning from progenitor masses of 0.85 to 8 M$_\\odot$. Comparison of our work to theoretical IFMRs shows remarkable consistency in their shape but differences remain. We will discuss possible explanations for these differences, including the effects of stellar rotation.

Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

NASA Astrophysics Data System (ADS)

Foley, Bradford J.; Driscoll, Peter E.

2016-05-01

Earth's climate, mantle, and core interact over geologic time scales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore, plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution.

Stellar Mass and 3.4 μm M/L Ratio Evolution of Brightest Cluster Galaxies in COSMOS since z ∼ 1.0

NASA Astrophysics Data System (ADS)

Cooke, Kevin C.; Fogarty, Kevin; Kartaltepe, Jeyhan S.; Moustakas, John; O’Dea, Christopher P.; Postman, Marc

2018-04-01

We investigate the evolution of star formation rates (SFRs), stellar masses, and M/L 3.4 μm ratios of brightest cluster galaxies (BCGs) in the COSMOS survey since z ∼ 1 to determine the contribution of star formation to the growth-rate of BCG stellar mass over time. Through the spectral energy density (SED) fitting of the GALEX, CFHT, Subaru, Vista, Spitzer, and Herschel photometric data available in the COSMOS2015 catalog, we estimate the stellar mass and SFR of each BCG. We use a modified version of the iSEDfit package to fit the SEDs of our sample with both stellar and dust emission models, as well as constrain the impact of star formation history assumptions on our results. We find that in our sample of COSMOS BCGs, star formation evolves similarly to that in BCGs in samples of more massive galaxy clusters. However, compared to the latter, the magnitude of star formation in our sample is lower by ∼1 dex. Additionally, we find an evolution of BCG baryonic mass-to-light ratio (M/L 3.4 μm) with redshift which is consistent with a passively aging stellar population. We use this to build upon Wen et al.'s low-redshift νL 3.4 μm–M Stellar relation, quantifying a correlation between νL 3.4 μm and M Stellar to z ∼ 1. By comparing our results to BCGs in Sunyaev–Zel’dovich and X-ray-selected samples of galaxy clusters, we find evidence that the normalization of star formation evolution in a cluster sample is driven by the mass range of the sample and may be biased upwards by cool cores.

Understanding the Current Dynamical States of Globular Clusters

NASA Astrophysics Data System (ADS)

Pooley, David

2008-09-01

We appear to be on the verge of a major paradigm shift in our understanding of the current dynamical states of Galactic globular clusters. Fregeau (2008) brought together two recent theoretical breakthroughs as well as an observational breakthrough made possible by Chandra -- that a globular cluster's X-ray source population scales with its dynamical encounter frequency -- to persuasively argue that we have misunderstood the dynamical states of Galactic globular clusters. The observational evidence hinges on Chandra results from clusters which are classified as "core collapsed," of which there are only a handful of observations. I propose a nearly complete census with Chandra of the rest of the "core collapsed" globular clusters.

Development concept for a small, split-core, heat-pipe-cooled nuclear reactor

NASA Technical Reports Server (NTRS)

Lantz, E.; Breitwieser, R.; Niederauer, G. F.

1974-01-01

There have been two main deterrents to the development of semiportable nuclear reactors. One is the high development costs; the other is the inability to satisfy with assurance the questions of operational safety. This report shows how a split-core, heat-pipe cooled reactor could conceptually eliminate these deterrents, and examines and summarizes recent work on split-core, heat-pipe reactors. A concept for a small reactor that could be developed at a comparatively low cost is presented. The concept would extend the technology of subcritical radioisotope thermoelectric generators using 238 PuO2 to the evolution of critical space power reactors using 239 PuO2.

State-of-the-art multi-wavelength observations of nearby brightest group/cluster galaxies

NASA Astrophysics Data System (ADS)

Gendron-Marsolais, Marie-Lou; Hlavacek-Larrondo, Julie

2018-01-01

Nearby galaxy groups and clusters are crucial to our understanding of the impact of nuclear outbursts on the intracluster medium as their proximity allows us to study in detail the processes of feedback from active galactic nuclei in these systems. In this talk, I will present state-of-the-art multi-wavelength observations signatures of this mechanism.I will first show results on multi-configuration 230-470 MHz observations of the Perseus cluster from the Karl G. Jansky Very Large Array, probing the non-thermal emission from the old particle population of the AGN outflows. These observations reveal a multitude of new structures associated with the “mini-halo” and illustrate the high-quality images that can be obtained with the new JVLA at low radio-frequencies.Second, I will present new observations with the optical imaging Fourier transform spectrometer SITELLE (CFHT) of NGC 1275, the Perseus cluster's brightest galaxy. With its wide field of view, it is the only integral field unit spectroscopy instrument able to cover the large emission-line filamentary nebula in NGC 1275. I will present the first detailed velocity map of this nebula in its entirety and tackle the question of its origin (residual cooling flow or dragged gas).Finally, I will present deep Chandra observations of the nearby early-type massive elliptical galaxy NGC 4472, the most optically luminous galaxy in the local Universe, lying on the outskirts of the Virgo cluster. Enhanced X-ray rims around the radio lobes are detected and interpreted as gas uplifted from the core by the buoyant rise of the radio bubbles. We estimate the energy required to lift the gas to constitute a significant fraction of the total outburst energy.I will thus show how these high-fidelity observations of nearby brightest group/cluster galaxies are improving our understanding of the AGN feedback mechanism taking place in galaxy groups and clusters.

Hubble Catches Stellar Exodus in Action

NASA Image and Video Library

2015-05-14

Using NASA’s Hubble Space Telescope, astronomers have captured for the first time snapshots of fledging white dwarf stars beginning their slow-paced, 40-million-year migration from the crowded center of an ancient star cluster to the less populated suburbs. White dwarfs are the burned-out relics of stars that rapidly lose mass, cool down and shut off their nuclear furnaces. As these glowing carcasses age and shed weight, their orbits begin to expand outward from the star cluster’s packed downtown. This migration is caused by a gravitational tussle among stars inside the cluster. Globular star clusters sort out stars according to their mass, governed by a gravitational billiard ball game where lower mass stars rob momentum from more massive stars. The result is that heavier stars slow down and sink to the cluster's core, while lighter stars pick up speed and move across the cluster to the edge. This process is known as "mass segregation." Until these Hubble observations, astronomers had never definitively seen the dynamical conveyor belt in action. Astronomers used Hubble to watch the white-dwarf exodus in the globular star cluster 47 Tucanae, a dense swarm of hundreds of thousands of stars in our Milky Way galaxy. The cluster resides 16,700 light-years away in the southern constellation Tucana. Read more: www.nasa.gov/feature/goddard/hubble-catches-stellar-exodu... Credits: NASA, ESA, and H. Richer and J. Heyl (University of British Columbia, Vancouver, Canada); acknowledgement: J. Mack (STScI) and G. Piotto (University of Padova, Italy) NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

A Multi-wavelength Mass Analysis of RCS2 J232727.6-020437, A ˜3 × 1015 M⊙ Galaxy Cluster at z = 0.7

NASA Astrophysics Data System (ADS)

Sharon, K.; Gladders, M. D.; Marrone, D. P.; Hoekstra, H.; Rasia, E.; Bourdin, H.; Gifford, D.; Hicks, A. K.; Greer, C.; Mroczkowski, T.; Barrientos, L. F.; Bayliss, M.; Carlstrom, J. E.; Gilbank, D. G.; Gralla, M.; Hlavacek-Larrondo, J.; Leitch, E.; Mazzotta, P.; Miller, C.; Muchovej, S. J. C.; Schrabback, T.; Yee, H. K. C.; RCS-Team

2015-11-01

We present an initial study of the mass and evolutionary state of a massive and distant cluster, RCS2 J232727.6-020437. This cluster, at z = 0.6986, is the richest cluster discovered in the RCS2 project. The mass measurements presented in this paper are derived from all possible mass proxies: X-ray measurements, weak-lensing shear, strong lensing, Sunyaev-Zel’dovich effect decrement, the velocity distribution of cluster member galaxies, and galaxy richness. While each of these observables probe the mass of the cluster at a different radius, they all indicate that RCS2 J232727.6-020437 is among the most massive clusters at this redshift, with an estimated mass of {M}200˜ 3× {10}15{h}70-1 {M}⊙ . In this paper, we demonstrate that the various observables are all reasonably consistent with each other to within their uncertainties. RCS2 J232727.6-020437 appears to be well relaxed—with circular and concentric X-ray isophotes, with a cool core, and no indication of significant substructure in extensive galaxy velocity data. Based on observations obtained with : MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l’Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii; the NASA/ESA Hubble Space Telescope (HST), obtained from the data archive at the Space Telescope Institute. STScI is operated by the association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-2655; the 6.5 m Magellan telescopes located at Las Campanas Observatory, Chile;

DIFFERENT DYNAMICAL AGES FOR THE TWO YOUNG AND COEVAL LMC STAR CLUSTERS, NGC 1805 AND NGC 1818, IMPRINTED ON THEIR BINARY POPULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geller, Aaron M.; Grijs, Richard de; Li, Chengyuan

2015-05-20

The two Large Magellanic Cloud star clusters, NGC 1805 and NGC 1818, are approximately the same chronological age (∼30 Myr), but show different radial trends in binary frequency. The F-type stars (1.3–2.2 M{sub ⊙}) in NGC 1818 have a binary frequency that decreases toward the core, while the binary frequency for stars of similar mass in NGC 1805 is flat with radius, or perhaps bimodal (with a peak in the core). We show here, through detailed N-body modeling, that both clusters could have formed with the same primordial binary frequency and with binary orbital elements and masses drawn from themore » same distributions (defined from observations of open clusters and the field of our Galaxy). The observed radial trends in binary frequency for both clusters are best matched with models that have initial substructure. Furthermore, both clusters may be evolving along a very similar dynamical sequence, with the key difference that NGC 1805 is dynamically older than NGC 1818. The F-type binaries in NGC 1818 still show evidence of an initial period of rapid dynamical disruptions (which occur preferentially in the core), while NGC 1805 has already begun to recover a higher core binary frequency, owing to mass segregation (which will eventually produce a distribution in binary frequency that rises only toward the core, as is observed in old Milky Way star clusters). This recovery rate increases for higher-mass binaries, and therefore even at one age in one cluster, we predict a similar dynamical sequence in the radial distribution of the binary frequency as a function of binary primary mass.« less

High-Efficiency, Low-Weight Power Transformer

NASA Technical Reports Server (NTRS)

Welsh, J. P.

1986-01-01

Technology for design and fabrication of radically new type of conductioncooled high-power (25 kVA) lightweight transformer having outstanding thermal and electrical characteristics. Fulfills longstanding need for conduction-cooled transformers and magnetics with low internal thermal resistances. Development techniques limited to conductive heat transfer, since other techniques such as liquid cooling, forced liquid cooling, and evaporative cooling of transformers impractical in zero-gravity space environment. Transformer uniquely designed: mechanical structure also serves as thermal paths for conduction cooling of magnetic core and windings.

Compaction-Driven Evolution of Pluto's Rocky Core: Implications for Water-Rock Interactions

NASA Astrophysics Data System (ADS)

Gabasova, L. R.; Tobie, G.; Choblet, G.

2018-05-01

We model the compaction of Pluto's rocky core after accretion and explore the potential for hydrothermal circulation within the porous layer, as well as examine its effect on core cooling and the persistence of a liquid internal ocean.

Surface brightness profiles and structural parameters for 53 rich stellar clusters in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Mackey, A. D.; Gilmore, G. F.

2003-01-01

We have compiled a pseudo-snapshot data set of two-colour observations from the Hubble Space Telescope archive for a sample of 53 rich LMC clusters with ages of 106-1010 yr. We present surface brightness profiles for the entire sample, and derive structural parameters for each cluster, including core radii, and luminosity and mass estimates. Because we expect the results presented here to form the basis for several further projects, we describe in detail the data reduction and surface brightness profile construction processes, and compare our results with those of previous ground-based studies. The surface brightness profiles show a large amount of detail, including irregularities in the profiles of young clusters (such as bumps, dips and sharp shoulders), and evidence for both double clusters and post-core-collapse (PCC) clusters. In particular, we find power-law profiles in the inner regions of several candidate PCC clusters, with slopes of approximately -0.7, but showing considerable variation. We estimate that 20 +/- 7 per cent of the old cluster population of the Large Magellanic Cloud (LMC) has entered PCC evolution, a similar fraction to that for the Galactic globular cluster system. In addition, we examine the profile of R136 in detail and show that it is probably not a PCC cluster. We also observe a trend in core radius with age that has been discovered and discussed in several previous publications by different authors. Our diagram has better resolution, however, and appears to show a bifurcation at several hundred Myr. We argue that this observed relationship reflects true physical evolution in LMC clusters, with some experiencing small-scale core expansion owing to mass loss, and others large-scale expansion owing to some unidentified characteristic or physical process.

Deep CCD Photometry of the Rich Galaxy Cluster Abel 1656 Characteristics of the Dwarf Elliptical Galaxy Population in the Cluster Core

NASA Astrophysics Data System (ADS)

Secker, Jeffrey Alan

1995-01-01

We have developed a statistically rigorous and automated method to implement the detection, photometry and classification of faint objects on digital images. We use these methods to analyze deep R- and B-band CCD images of the central ~ 700 arcmin ^2 of the Coma cluster core, and an associated control field. We have detected and measured total R magnitudes and (B-R) colors for a sample of 3741 objects on the galaxy cluster fields, and 1164 objects on a remote control field, complete to a limiting magnitude of R = 22.5 mag. The typical uncertainties are +/- 0.06 and +/-0.12 mag in total magnitude and color respectively. The dwarf elliptical (dE) galaxies are confined to a well-defined sequence in the color range given by 0.7<= (B-R)<= 1.9 mag: within this interval there are 2535 dE candidates on our fields in the cluster core, and 694 objects on the control field. With an image scale of 0.53 arcsec/pixel and seeing near 1.2 arcsec, a large fraction of the dE galaxy candidates are resolved. We find a significant metallicity gradient in the radial distribution of the dwarf elliptical galaxies, which goes as Z~ R^{-0.32 } outwards from the cluster center at NGC 4874. As well, there is a strong color-luminosity correlation, in the sense that more luminous dE galaxies are redder in the mean. These effects give rise to a radial variation in the cluster luminosity function. The spatial distribution of the faint dE galaxies is well fit by a standard King model with a central surface density of Sigma _0 = 1.44 dEs arcmin^{ -2}, a core radius R_{ rm c} = 18.7 arcmin (~eq 0.44 Mpc), and a tidal radius of 1.44 deg ( ~eq 2.05 Mpc). This core is significantly larger than R_{rm c} = 12.3 arcmin (~eq 0.29 Mpc) found for the bright cluster galaxies. The composite luminosity function for Coma galaxies is modeled as the sum of a log -normal distribution for the giant galaxies and a Schechter function for the dwarf elliptical galaxies, with a faint -end slope of alpha = -1.41, consistent with known faint-end slopes for the Virgo and Fornax clusters. The early-type dwarf-to-giant ratio for the Coma cluster core is consistent with that of the Virgo cluster, and thus with the rich Coma cluster being formed as the merger of multiple less-rich galaxy clusters.

A General Precipitation-limited L X–T–R Relation among Early-type Galaxies

NASA Astrophysics Data System (ADS)

Voit, G. Mark; Ma, C. P.; Greene, J.; Goulding, A.; Pandya, V.; Donahue, M.; Sun, M.

2018-01-01

The relation between X-ray luminosity (L X) and ambient gas temperature (T) among massive galactic systems is an important cornerstone of both observational cosmology and galaxy-evolution modeling. In the most massive galaxy clusters, the relation is determined primarily by cosmological structure formation. In less massive systems, it primarily reflects the feedback response to radiative cooling of circumgalactic gas. Here we present a simple but powerful model for the L X–T relation as a function of physical aperture R within which those measurements are made. The model is based on the precipitation framework for AGN feedback and assumes that the circumgalactic medium is precipitation-regulated at small radii and limited by cosmological structure formation at large radii. We compare this model with many different data sets and show that it successfully reproduces the slope and upper envelope of the L X–T–R relation over the temperature range from ∼0.2 keV through ≳ 10 {keV}. Our findings strongly suggest that the feedback mechanisms responsible for regulating star formation in individual massive galaxies have much in common with the precipitation-triggered feedback that appears to regulate galaxy-cluster cores.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bogdán, Ákos; Van Weeren, Reinout J.; Kraft, Ralph P.

Although the energetic feedback from active galactic nuclei (AGNs) is believed to have a profound effect on the evolution of galaxies and clusters of galaxies, details of AGN heating remain elusive. Here, we study NGC 193—a nearby lenticular galaxy—based on X-ray (Chandra) and radio (Very Large Array and Giant Meter-wave Radio Telescope) observations. These data reveal the complex AGN outburst history of the galaxy: we detect a pair of inner X-ray cavities, an outer X-ray cavity, a shock front, and radio lobes extending beyond the inner cavities. We suggest that the inner cavities were produced ∼78 Myr ago by a weakermore » AGN outburst, while the outer cavity, the radio lobes, and the shock front are due to a younger (13-26 Myr) and 4-8 times more powerful outburst. Combining this with the observed morphology of NGC 193, we conclude that NGC 193 likely represents the first example of a second, more powerful, AGN outburst overrunning an older, weaker outburst. These results help us to understand how the outburst energy is dissipated uniformly in the core of galaxies, and therefore may play a crucial role in resolving how AGN outbursts suppress the formation of large cooling flows at cluster centers.« less

Where do the 3.5 keV photons come from? A morphological study of the Galactic Center and of Perseus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlson, Eric; Jeltema, Tesla; Profumo, Stefano, E-mail: erccarls@ucsc.edu, E-mail: tesla@ucsc.edu, E-mail: profumo@ucsc.edu

We test the origin of the 3.5 keV line photons by analyzing the morphology of the emission at that energy from the Galactic Center and from the Perseus cluster of galaxies. We employ a variety of different templates to model the continuum emission and analyze the resulting radial and azimuthal distribution of the residual emission. We then perform a pixel-by-pixel binned likelihood analysis including line emission templates and dark matter templates and assess the correlation of the 3.5 keV emission with these templates. We conclude that the radial and azimuthal distribution of the residual emission is incompatible with a darkmore » matter origin for both the Galactic center and Perseus; the Galactic center 3.5 keV line photons trace the morphology of lines at comparable energy, while the Perseus 3.5 keV photons are highly correlated with the cluster's cool core, and exhibit a morphology incompatible with dark matter decay. The template analysis additionally allows us to set the most stringent constraints to date on lines in the 3.5 keV range from dark matter decay.« less

Measurements of resonant scattering in the Perseus cluster core with Hitomi SXS

NASA Astrophysics Data System (ADS)

Sato, K.; Zhuravleva, I.

2017-10-01

Hitomi (ASTRO-H) SXS allows us to investigate fine structures of emission lines in extended X-ray sources for the first time. Thanks to its high energy resolution of 5 eV at 6 keV in orbit, Hitomi SXS finds a quiescent atmosphere in the Intra cluster medium of the Perseus cluster core where the gas has a line-of-sight velocity dispersion below 200 km/sec from the line width in the spectral analysis (Hitomi collaboration, Nature, 2016). The resonant scattering is also important to measure the gas velocity as a complementary probe of the direct measurement from the line width. Particularly in the cluster core, resonant scattering should be taken into account when inferring physical properties from line intensities because the optical depth of the He-alpha resonant line is expected to be larger than 1. The observed line flux ratio of Fe XXV He-α resonant to forbidden lines is found to be lower in the cluster core when compared to the outer region, consistent with resonant scattering of the resonant line and also in support of the low turbulent velocity.

AIR COOLED NEUTRONIC REACTOR

DOEpatents

Fermi, E.; Szilard, L.

1958-05-27

A nuclear reactor of the air-cooled, graphite moderated type is described. The active core consists of a cubicle mass of graphite, approximately 25 feet in each dimension, having horizontal channels of square cross section extending between two of the opposite faces, a plurality of cylindrical uranium slugs disposed in end to end abutting relationship within said channels providing a space in the channels through which air may be circulated, and a cadmium control rod extending within a channel provided in the moderator. Suitable shielding is provlded around the core, as are also provided a fuel element loading and discharge means, and a means to circulate air through the coolant channels through the fuel charels to cool the reactor.

Performance potential of gas-core and fusion rockets - A mission applications survey.

NASA Technical Reports Server (NTRS)

Fishbach, L. H.; Willis, E. A., Jr.

1971-01-01

This paper reports an evaluation of the performance potential of five nuclear rocket engines for four mission classes. These engines are: the regeneratively cooled gas-core nuclear rocket; the light bulb gas-core nuclear rocket; the space-radiator cooled gas-core nuclear rocket; the fusion rocket; and an advanced solid-core nuclear rocket which is included for comparison. The missions considered are: earth-to-orbit launch; near-earth space missions; close interplanetary missions; and distant interplanetary missions. For each of these missions, the capabilities of each rocket engine type are compared in terms of payload ratio for the earth launch mission or by the initial vehicle mass in earth orbit for space missions (a measure of initial cost). Other factors which might determine the engine choice are discussed. It is shown that a 60 day manned round trip to Mars is conceivable.-

Annular core liquid-salt cooled reactor with multiple fuel and blanket zones

DOEpatents

Peterson, Per F.

2013-05-14

A liquid fluoride salt cooled, high temperature reactor having a reactor vessel with a pebble-bed reactor core. The reactor core comprises a pebble injection inlet located at a bottom end of the reactor core and a pebble defueling outlet located at a top end of the reactor core, an inner reflector, outer reflector, and an annular pebble-bed region disposed in between the inner reflector and outer reflector. The annular pebble-bed region comprises an annular channel configured for receiving pebble fuel at the pebble injection inlet, the pebble fuel comprising a combination of seed and blanket pebbles having a density lower than the coolant such that the pebbles have positive buoyancy and migrate upward in said annular pebble-bed region toward the defueling outlet. The annular pebble-bed region comprises alternating radial layers of seed pebbles and blanket pebbles.

Gas expulsion vs gas retention in young stellar clusters II: effects of cooling and mass segregation

NASA Astrophysics Data System (ADS)

Silich, Sergiy; Tenorio-Tagle, Guillermo

2018-05-01

Gas expulsion or gas retention is a central issue in most of the models for multiple stellar populations and light element anti-correlations in globular clusters. The success of the residual matter expulsion or its retention within young stellar clusters has also a fundamental importance in order to understand how star formation proceeds in present-day and ancient star-forming galaxies and if proto-globular clusters with multiple stellar populations are formed in the present epoch. It is usually suggested that either the residual gas is rapidly ejected from star-forming clouds by stellar winds and supernova explosions, or that the enrichment of the residual gas and the formation of the second stellar generation occur so rapidly, that the negative stellar feedback is not significant. Here we continue our study of the early development of star clusters in the extreme environments and discuss the restrictions that strong radiative cooling and stellar mass segregation provide on the gas expulsion from dense star-forming clouds. A large range of physical initial conditions in star-forming clouds which include the star-forming cloud mass, compactness, gas metallicity, star formation efficiency and effects of massive stars segregation are discussed. It is shown that in sufficiently massive and compact clusters hot shocked winds around individual massive stars may cool before merging with their neighbors. This dramatically reduces the negative stellar feedback, prevents the development of the global star cluster wind and expulsion of the residual and the processed matter into the ambient interstellar medium. The critical lines which separate the gas expulsion and the gas retention regimes are obtained.

High-dose amrinone is required to accelerate rewarming from deliberate mild intraoperative hypothermia for neurosurgical procedures.

PubMed

Inoue, Satoki; Kawaguchi, Masahiko; Sakamoto, Takanori; Kitaguchi, Katsuyasu; Furuya, Hitoshi; Sakaki, Toshisuke

2002-07-01

Since the time available to provide the cooling and rewarming is limited during deliberate mild hypothermia, the technique to accelerate the cooling and rewarming rate of core temperature has been studied. Amrinone has been reported to accelerate the cooling rate but not the rewarming rate of core temperature during deliberate mild hypothermia. The failure of amrinone effect on the rewarming rate might be due to an insufficient dose of amrinone during hypothermic conditions. The authors therefore tested whether higher doses of amrinone can accelerate the rewarming rate of core temperature during deliberate mild hypothermia for neurosurgery. After institutional approval and informed consent, 30 patients were randomly assigned to one of three groups. Patients in the control group (n = 10) did not receive amrinone; patients in the AMR 15 group (n = 10) received 15 microg x kg(-1) x min(-1) amrinone with a 1.0-mg/kg loading dose of amrinone at the beginning of cooling; and patients in the ReAMR group (n = 10) received 5 microg x kg(-1) x min(-1) amrinone with 1.0-mg/kg loading and reloading doses of amrinone at the beginning of cooling and rewarming, respectively. Administration of amrinone was started just after the induction of cooling and continued until the end of anesthesia. Anesthesia was maintained with nitrous oxide in oxygen, propofol, and fentanyl. After induction of anesthesia, patients were cooled, and tympanic membrane temperature was maintained at 34.5 degrees C. After completion of the main surgical procedures, patients were actively rewarmed and extubated in the operating room. The cooling and rewarming rates of core temperature were both significantly faster in both amrinone groups than in the control group. During the cooling and rewarming periods, forearm minus fingertip temperature gradient was significantly smaller in both amrinone groups than in the control group. During the rewarming period, heart rate and mean arterial pressure in the AMR 15 group were significantly faster and lower, respectively, than in the control group. Systemic vascular resistance in the AMR 15 group was smaller than in the control group throughout the study; on the other hand, only the value after the start of rewarming in the ReAMR group was smaller than in the control group. Amrinone at an infusion rate of 15 or 5 microg x kg(-1) x min(-1) with a reloading at the beginning of rewarming accelerated the rewarming rate of core temperature during deliberate mild hypothermia. This suggests that high-dose amrinone is required to accelerate rewarming from deliberate mild intraoperative hypothermia for neurosurgical procedures.

Free cooling phase-diagram of hard-spheres with short- and long-range interactions

NASA Astrophysics Data System (ADS)

Gonzalez, S.; Thornton, A. R.; Luding, S.

2014-10-01

We study the stability, the clustering and the phase-diagram of free cooling granular gases. The systems consist of mono-disperse particles with additional non-contact (long-range) interactions, and are simulated here by the event-driven molecular dynamics algorithm with discrete (short-range shoulders or wells) potentials (in both 2D and 3D). Astonishingly good agreement is found with a mean field theory, where only the energy dissipation term is modified to account for both repulsive or attractive non-contact interactions. Attractive potentials enhance cooling and structure formation (clustering), whereas repulsive potentials reduce it, as intuition suggests. The system evolution is controlled by a single parameter: the non-contact potential strength scaled by the fluctuation kinetic energy (granular temperature). When this is small, as expected, the classical homogeneous cooling state is found. However, if the effective dissipation is strong enough, structure formation proceeds, before (in the repulsive case) non-contact forces get strong enough to undo the clustering (due to the ongoing dissipation of granular temperature). For both repulsive and attractive potentials, in the homogeneous regime, the cooling shows a universal behaviour when the (inverse) control parameter is used as evolution variable instead of time. The transition to a non-homogeneous regime, as predicted by stability analysis, is affected by both dissipation and potential strength. This can be cast into a phase diagram where the system changes with time, which leaves open many challenges for future research.

Chandra Observations of Hydra A

NASA Technical Reports Server (NTRS)

McNamara, Brian; Lavoie, Anthony R. (Technical Monitor)

2000-01-01

We present Chandra X-ray Observations of the Hydra A cluster of galaxies, and we report the discovery of structure in the central 80 kpc of the cluster's X-ray-emitting gas. The most remarkable structures are depressions in the X-ray surface brightness, approx. 25 - 35 kpc diameter, that are coincident with Hydra A's radio lobes. The depressions are nearly devoid of X-ray-emitting gas, and there is no evidence for shock-heated gas surrounding the radio lobes. We suggest the gas within the surface brightness depressions was displaced as the radio lobes expanded subsonically, leaving cavities in the hot atmosphere. The gas temperature declines from 4 keV at 70 kpc to 3 keV in the inner 20 kpc of the brightest cluster galaxy (BCG), and the cooling time of the gas is approx. 600 Myr in the inner 10 kpc. These properties are consistent with the presence of a approx. 34 solar mass/yr cooling flow within a 70 kpc radius. Bright X-ray emission is present in the BCG surrounding a recently-accreted disk of nebular emission and young stars. The star formation rate is commensurate with the cooling rate of the hot gas within the volume of the disk, although the sink for the material that may be cooling at larger radii remains elusive.

Experimental and numerical CHT-investigations of cooling structures formed by lost cores in cast housings for optimal heat transfer

NASA Astrophysics Data System (ADS)

Kohlstädt, S.; Vynnycky, M.; Gebauer-Teichmann, A.

2018-05-01

This paper investigates the cooling performance of six different lost core designs for automotive cast houses with regard to their cooling efficiency. For this purpose, the conjugate heat transfer (CHT) solver, chtMultiregion, of the freely available CFD-toolbox OpenFOAM in its implementation of version 2.3.1 is used. The turbulence contribution to the Navier-Stokes equations is accounted for by using the RANS Menter SST k - ω model. The results are validated for one of the geometries by comparing with experimental data. Of the six investigated cooling structures, the one that forces the fluid flow to change its direction the most produces the lowest temperatures on the surface of the cast housing. This good cooling performance comes at the price of the highest pressure loss in the cooling fluid and hence increased pump power. It is also found that the relationship between performance and pressure drop is by no means generally linear. Slight changes in the design can lead to a structure which cools almost as well, but at much decreased pressure loss. Regarding the absolute values, the simulations showed that the designed cooling structures are suitable for handling the cooling requirements in the particular applications and that the maximum temperature stays below the critical limits of the electronic components.

a Dosimetry Assessment for the Core Restraint of AN Advanced Gas Cooled Reactor

NASA Astrophysics Data System (ADS)

Thornton, D. A.; Allen, D. A.; Tyrrell, R. J.; Meese, T. C.; Huggon, A. P.; Whiley, G. S.; Mossop, J. R.

2009-08-01

This paper describes calculations of neutron damage rates within the core restraint structures of Advanced Gas Cooled Reactors (AGRs). Using advanced features of the Monte Carlo radiation transport code MCBEND, and neutron source data from core follow calculations performed with the reactor physics code PANTHER, a detailed model of the reactor cores of two of British Energy's AGR power plants has been developed for this purpose. Because there are no relevant neutron fluence measurements directly supporting this assessment, results of benchmark comparisons and successful validation of MCBEND for Magnox reactors have been used to estimate systematic and random uncertainties on the predictions. In particular, it has been necessary to address the known under-prediction of lower energy fast neutron responses associated with the penetration of large thicknesses of graphite.

CHAP-2 heat-transfer analysis of the Fort St. Vrain reactor core

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kotas, J.F.; Stroh, K.R.

1983-01-01

The Los Alamos National Laboratory is developing the Composite High-Temperature Gas-Cooled Reactor Analysis Program (CHAP) to provide advanced best-estimate predictions of postulated accidents in gas-cooled reactor plants. The CHAP-2 reactor-core model uses the finite-element method to initialize a two-dimensional temperature map of the Fort St. Vrain (FSV) core and its top and bottom reflectors. The code generates a finite-element mesh, initializes noding and boundary conditions, and solves the nonlinear Laplace heat equation using temperature-dependent thermal conductivities, variable coolant-channel-convection heat-transfer coefficients, and specified internal fuel and moderator heat-generation rates. This paper discusses this method and analyzes an FSV reactor-core accident thatmore » simulates a control-rod withdrawal at full power.« less

Forced convective head cooling device reduces human cross-sectional brain temperature measured by magnetic resonance: a non-randomized healthy volunteer pilot study.

PubMed

Harris, B A; Andrews, P J D; Marshall, I; Robinson, T M; Murray, G D

2008-03-01

This pilot study in five healthy adult humans forms the pre-clinical assessment of the effect of a forced convective head cooling device on intracranial temperature, measured non-invasively by magnetic resonance spectroscopy (MRS). After a 10 min baseline with no cooling, subjects received 30 min of head cooling followed by 30 min of head and neck cooling via a hood and neck collar delivering 14.5 degrees C air at 42.5 litre s(-1). Over baseline and at the end of both cooling periods, MRS was performed, using chemical shift imaging, to measure brain temperature simultaneously across a single slice of brain at the level of the basal ganglia. Oesophageal temperature was measured continuously using a fluoroptic thermometer. MRS brain temperature was calculated for baseline and the last 10 min of each cooling period. The net brain temperature reduction with head cooling was 0.45 degrees C (SD 0.23 degrees C, P=0.01, 95% CI 0.17-0.74 degrees C) and with head and neck cooling was 0.37 degrees C (SD 0.30 degrees C, P=0.049, 95% CI 0.00-0.74 degrees C). The equivalent net reductions in oesophageal temperature were 0.16 degrees C (SD 0.04 degrees C) and 0.36 degrees C (SD 0.12 degrees C). Baseline-corrected brain temperature gradients from outer through intermediate to core voxels were not significant for either head cooling (P=0.43) or head and neck cooling (P=0.07), indicating that there was not a significant reduction in cooling with progressive depth into the brain. Convective head cooling reduced MRS brain temperature and core brain was cooled.

Quantifying opening-mode fracture spatial organization in horizontal wellbore image logs, core and outcrop: Application to Upper Cretaceous Frontier Formation tight gas sandstones, USA

NASA Astrophysics Data System (ADS)

Li, J. Z.; Laubach, S. E.; Gale, J. F. W.; Marrett, R. A.

2018-03-01

The Upper Cretaceous Frontier Formation is a naturally fractured gas-producing sandstone in Wyoming. Regionally, random and statistically more clustered than random patterns exist in the same upper to lower shoreface depositional facies. East-west- and north-south-striking regional fractures sampled using image logs and cores from three horizontal wells exhibit clustered patterns, whereas data collected from east-west-striking fractures in outcrop have patterns that are indistinguishable from random. Image log data analyzed with the correlation count method shows clusters ∼35 m wide and spaced ∼50 to 90 m apart as well as clusters up to 12 m wide with periodic inter-cluster spacings. A hierarchy of cluster sizes exists; organization within clusters is likely fractal. These rocks have markedly different structural and burial histories, so regional differences in degree of clustering are unsurprising. Clustered patterns correspond to fractures having core quartz deposition contemporaneous with fracture opening, circumstances that some models suggest might affect spacing patterns by interfering with fracture growth. Our results show that quantifying and identifying patterns as statistically more or less clustered than random delineates differences in fracture patterns that are not otherwise apparent but that may influence gas and water production, and therefore may be economically important.

A scaling and experimental approach for investigating in-vessel cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henry, R.E.

1997-02-01

The TMI-2 accident experienced the relocation of a large quantity of core material to the lower plenum. The TMI-2 vessel investigation project concluded that approximately 20 metric tonnes of once molten fuel material drained into the RPV lower head. As a result, the lower head wall experienced a thermal transient that has been characterized as reaching temperatures as high as 1100{degrees}C, then a cooling transient with a rate of 10 to 100{degrees}C/min. Two mechanisms have been proposed as possible explanations for this cooling behavior. One is the ingression of water through core material as a result of interconnected cracks inmore » the frozen debris and/or water ingression around the crust which is formed on internal structures (core supports and in-core instrumentation) in the lower head. The second focuses on the lack of adhesion of oxidic core debris to the RPV wall when the debris contacts the wall. Furthermore, the potential for strain of the RPV lower head when the wall is overheated could provide for a significant cooling path for water to ingress between the RPV and the frozen core material next to the wall. To examine these proposed mechanisms, a set of scaled experiments have been developed to examine the potential for cooling. These are performed in a scaled system in which the high temperature molten material is iron termite and the RPV wall is carbon steel. A termite mass of 40 kg is used and the simulated reactor vessels have water in the lower head at pressures up to 2.2 MPa. Furthermore, two different thicknesses of the vessel wall are examined with the thicker vessel having virtually no potential for material creep during the experiment and the thinner wall having the potential for substantial creep. Moreover, the experiment includes the option of having molten iron as the first material to drain into the RPV lower head or molten aluminum oxide being the only material that drains into the test configuration.« less

The effect of a 48 h fast on the thermoregulatory responses to graded cooling in man.

PubMed

Macdonald, I A; Bennett, T; Sainsbury, R

1984-10-01

The thermoregulatory responses to graded cooling were measured in 11 healthy male subjects after a 12 h fast and after a 48 h fast. The cooling stimulus was produced by changing the temperature of the skin of the trunk and legs with a water-perfused suit. Five levels of skin temperature from 35.5 to 24 degrees C were applied on each occasion. After a 12 h fast, core temperature was maintained during cooling. This maintenance of core temperature was associated with an increase in metabolic rate and a reduction in blood flow to the hand and to the forearm. After 48 h of fasting, the subjects could not maintain core temperature during cooling, and a decrease of 0.36 +/- 0.05 degrees C occurred as the suit temperature was reduced from 35.9 to 24 degrees C. Metabolic rate was slightly higher after the 48 h fast than after the 12 h fast, but similar increases in metabolic rate were observed during cooling. Vasoconstriction in the hand was initially less after a 48 h fast than after a 12 h fast, but at the lowest suit temperature, hand blood flow was similar, and low, on both occasions. After 48 h of fasting, forearm blood flow was elevated at all suit temperatures, being approximately twice the level recorded after the 12 h fast. Venous plasma noradrenaline levels did not change during cooling after the 12 h fast, whilst after 48 h of fasting a significant increase in noradrenaline level was observed at the lowest suit temperature. The results of this study provide further evidence that fasting induces an impairment of autonomic reflex mechanisms, but it is not clear whether this is due to a suppression of sympathetic nervous activity.

The Origin of IRS 16: Dynamically Driven In-Spiral of a Dense Star Cluster to the Galactic Center?

NASA Astrophysics Data System (ADS)

Portegies Zwart, Simon F.; McMillan, Stephen L. W.; Gerhard, Ortwin

2003-08-01

We use direct N-body simulations to study the in-spiral and internal evolution of dense star clusters near the Galactic center. These clusters sink toward the center owing to dynamical friction with the stellar background and may go into core collapse before being disrupted by the Galactic tidal field. If a cluster reaches core collapse before disruption, its dense core, which has become rich in massive stars, survives to reach close to the Galactic center. When it eventually dissolves, the cluster deposits a disproportionate number of massive stars in the innermost parsec of the Galactic nucleus. Comparing the spatial distribution and kinematics of the massive stars with observations of IRS 16, a group of young He I stars near the Galactic center, we argue that this association may have formed in this way.

Luminosity and cooling of highly magnetized white dwarfs: suppression of luminosity by strong magnetic fields

NASA Astrophysics Data System (ADS)

Bhattacharya, Mukul; Mukhopadhyay, Banibrata; Mukerjee, Subroto

2018-06-01

We investigate the luminosity and cooling of highly magnetized white dwarfs with electron-degenerate cores and non-degenerate surface layers where cooling occurs by diffusion of photons. We find the temperature and density profiles in the surface layers or envelope of white dwarfs by solving the magnetostatic equilibrium and photon diffusion equations in a Newtonian framework. We also obtain the properties of white dwarfs at the core-envelope interface, when the core is assumed to be practically isothermal. With the increase in magnetic field, the interface temperature increases whereas the interface radius decreases. For a given age of the white dwarf and for fixed interface radius or interface temperature, we find that the luminosity decreases significantly from about 10-6 to 10-9 L⊙ as the magnetic field strength increases from about 109 to 1012 G at the interface and hence the envelope. This is remarkable because it argues that magnetized white dwarfs are fainter and can be practically hidden in an observed Hertzsprung-Russell diagram. We also find the cooling rates corresponding to these luminosities. Interestingly, the decrease in temperature with time, for the fields under consideration, is not found to be appreciable.

MAPPING THE GAS TURBULENCE IN THE COMA CLUSTER: PREDICTIONS FOR ASTRO-H

DOE Office of Scientific and Technical Information (OSTI.GOV)

ZuHone, J. A.; Markevitch, M.; Zhuravleva, I.

2016-02-01

Astro-H will be able for the first time to map gas velocities and detect turbulence in galaxy clusters. One of the best targets for turbulence studies is the Coma cluster, due to its proximity, absence of a cool core, and lack of a central active galactic nucleus. To determine what constraints Astro-H will be able to place on the Coma velocity field, we construct simulated maps of the projected gas velocity and compute the second-order structure function, an analog of the velocity power spectrum. We vary the injection scale, dissipation scale, slope, and normalization of the turbulent power spectrum, andmore » apply measurement errors and finite sampling to the velocity field. We find that even with sparse coverage of the cluster, Astro-H will be able to measure the Mach number and the injection scale of the turbulent power spectrum—the quantities determining the energy flux down the turbulent cascade and the diffusion rate for everything that is advected by the gas (metals, cosmic rays, etc.). Astro-H will not be sensitive to the dissipation scale or the slope of the power spectrum in its inertial range, unless they are outside physically motivated intervals. We give the expected confidence intervals for the injection scale and the normalization of the power spectrum for a number of possible pointing configurations, combining the structure function and velocity dispersion data. Importantly, we also determine that measurement errors on the line shift will bias the velocity structure function upward, and show how to correct this bias.« less

Mapping the Gas Turbulence in the Coma Cluster: Predictions for Astro-H

NASA Technical Reports Server (NTRS)

ZuHone, J. A.; Markevitch, M.; Zhuravleva, I.

2016-01-01

Astro-H will be able for the first time to map gas velocities and detect turbulence in galaxy clusters. One of the best targets for turbulence studies is the Coma cluster, due to its proximity, absence of a cool core, and lack of a central active galactic nucleus. To determine what constraints Astro-H will be able to place on the Coma velocity field, we construct simulated maps of the projected gas velocity and compute the second-order structure function, an analog of the velocity power spectrum. We vary the injection scale, dissipation scale, slope, and normalization of the turbulent power spectrum, and apply measurement errors and finite sampling to the velocity field. We find that even with sparse coverage of the cluster, Astro-H will be able to measure the Mach number and the injection scale of the turbulent power spectrum-the quantities determining the energy flux down the turbulent cascade and the diffusion rate for everything that is advected by the gas (metals, cosmic rays, etc.). Astro-H will not be sensitive to the dissipation scale or the slope of the power spectrum in its inertial range, unless they are outside physically motivated intervals. We give the expected confidence intervals for the injection scale and the normalization of the power spectrum for a number of possible pointing configurations, combining the structure function and velocity dispersion data. Importantly, we also determine that measurement errors on the line shift will bias the velocity structure function upward, and show how to correct this bias.

System Study: Reactor Core Isolation Cooling 1998-2014

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schroeder, John Alton

2015-12-01

This report presents an unreliability evaluation of the reactor core isolation cooling (RCIC) system at 31 U.S. commercial boiling water reactors. Demand, run hours, and failure data from fiscal year 1998 through 2014 for selected components were obtained from the Institute of Nuclear Power Operations (INPO) Consolidated Events Database (ICES). The unreliability results are trended for the most recent 10 year period, while yearly estimates for system unreliability are provided for the entire active period. No statistically significant trends were identified in the RCIC results.

Discovery of a Galaxy Cluster with a Violently Starbursting Core at z = 2.506

NASA Astrophysics Data System (ADS)

Wang, Tao; Elbaz, David; Daddi, Emanuele; Finoguenov, Alexis; Liu, Daizhong; Schreiber, Corentin; Martín, Sergio; Strazzullo, Veronica; Valentino, Francesco; van der Burg, Remco; Zanella, Anita; Ciesla, Laure; Gobat, Raphael; Le Brun, Amandine; Pannella, Maurilio; Sargent, Mark; Shu, Xinwen; Tan, Qinghua; Cappelluti, Nico; Li, Yanxia

2016-09-01

We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z spec = 2.506, which contains 11 massive (M * ≳ 1011 M ⊙) galaxies in the central 80 kpc region (11.6σ overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from Hα. The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M 200c = 1013.9±0.2 M ⊙, making it the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches ˜3400 M ⊙ yr-1 with a gas depletion time of ˜200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (˜25%, compared to 3%-5% in the field). The presence of both a collapsed, cluster-sized halo and a predominant population of massive SFGs suggests that this structure could represent an important transition phase between protoclusters and mature clusters. It provides evidence that the main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster, providing new insights into massive cluster formation at early epochs. The large integrated stellar mass at such high redshift challenges our understanding of massive cluster formation.

DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2.506

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Tao; Elbaz, David; Daddi, Emanuele

2016-09-01

We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z {sub spec} = 2.506, which contains 11 massive (M {sub *} ≳ 10{sup 11} M {sub ⊙}) galaxies in the central 80 kpc region (11.6 σ overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from H α . The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M {sub 200} {sub c} = 10{sup 13.9±0.2} M {sub ⊙}, making it the most distant X-ray-detectedmore » cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches ∼3400 M {sub ⊙} yr{sup −1} with a gas depletion time of ∼200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (∼25%, compared to 3%–5% in the field). The presence of both a collapsed, cluster-sized halo and a predominant population of massive SFGs suggests that this structure could represent an important transition phase between protoclusters and mature clusters. It provides evidence that the main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster, providing new insights into massive cluster formation at early epochs. The large integrated stellar mass at such high redshift challenges our understanding of massive cluster formation.« less

Keep the brain cool--endovascular cooling in patients with severe traumatic brain injury: a case series study.

PubMed

Fischer, Marlene; Lackner, Peter; Beer, Ronny; Helbok, Raimund; Klien, Stephanie; Ulmer, Hanno; Pfausler, Bettina; Schmutzhard, Erich; Broessner, Gregor

2011-04-01

As brain temperature is reported to be extensively higher than core body temperature in traumatic brain injury (TBI) patients, posttraumatic hyperthermia is of particular relevance in the injured brain. To study the influence of prophylactic normothermia on brain temperature and the temperature gradient between brain and core body in patients with severe TBI using an intravascular cooling system and to assess the relationship between brain temperature and intracranial pressure (ICP) under endovascular temperature control. Prospective case series study conducted in the neurologic intensive care unit of a tertiary care university hospital. Seven patients with severe TBI with a Glasgow Coma Scale score of 8 or less were consecutively enrolled. Prophylactic normothermia, defined as a target temperature of 36.5°C, was maintained using an intravascular cooling system. Simultaneous measurements of brain and urinary bladder temperature and ICP were taken over a 72-hour period. The mean bladder temperature in normothermic patients was 36.3 ± 0.4°C, and the mean brain temperature was determined as 36.4 ± 0.5°C. The mean temperature difference between brain and bladder was 0.1°C. We found a significant direct correlation between brain and bladder temperature (r = 0.95). In 52.4% of all measurements, brain temperature was higher than core body temperature. The mean ICP was 18 ± 8 mm Hg. Intravascular temperature management stabilizes both brain and body core temperature; prophylactic normothermia reduces the otherwise extreme increase of intracerebral temperature in patients with severe TBI. The intravascular cooling management proved to be an efficacious and feasible method to control brain temperature and to avoid hyperthermia in the injured brain. We could not find a statistically significant correlation between brain temperature and ICP.

Thermal effects of whole head submersion in cold water on nonshivering humans.

PubMed

Pretorius, Thea; Bristow, Gerald K; Steinman, Alan M; Giesbrecht, Gordon G

2006-08-01

This study isolated the effect of whole head submersion in cold water, on surface heat loss and body core cooling, when the confounding effect of shivering heat production was pharmacologically eliminated. Eight healthy male subjects were studied in 17 degrees C water under four conditions: the body was either insulated or uninsulated, with the head either above the water or completely submersed in each body-insulation subcondition. Shivering was abolished with buspirone (30 mg) and meperidine (2.5 mg/kg), and subjects breathed compressed air throughout all trials. Over the first 30 min of immersion, exposure of the head increased core cooling both in the body-insulated conditions (head out: 0.47 +/- 0.2 degrees C, head in: 0.77 +/- 0.2 degrees C; P < 0.05) and the body-exposed conditions (head out: 0.84 +/- 0.2 degrees C and head in: 1.17 +/- 0.5 degrees C; P < 0.02). Submersion of the head (7% of the body surface area) in the body-exposed conditions increased total heat loss by only 10%. In both body-exposed and body-insulated conditions, head submersion increased core cooling rate much more (average of 42%) than it increased total heat loss. This may be explained by a redistribution of blood flow in response to stimulation of thermosensitive and/or trigeminal receptors in the scalp, neck and face, where a given amount of heat loss would have a greater cooling effect on a smaller perfused body mass. In 17 degrees C water, the head does not contribute relatively more than the rest of the body to surface heat loss; however, a cold-induced reduction of perfused body mass may allow this small increase in heat loss to cause a relatively larger cooling of the body core.

THE RED SEQUENCE AT BIRTH IN THE GALAXY CLUSTER Cl J1449+0856 AT z = 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strazzullo, V.; Pannella, M.; Daddi, E.

We use Hubble Space Telescope /WFC3 imaging to study the red population in the IR-selected, X-ray detected, low-mass cluster Cl J1449+0856 at z = 2, one of the few bona fide established clusters discovered at this redshift, and likely a typical progenitor of an average massive cluster today. This study explores the presence and significance of an early red sequence in the core of this structure, investigating the nature of red-sequence galaxies, highlighting environmental effects on cluster galaxy populations at high redshift, and at the same time underlining similarities and differences with other distant dense environments. Our results suggest thatmore » the red population in the core of Cl J1449+0856 is made of a mixture of quiescent and dusty star-forming galaxies, with a seedling of the future red sequence already growing in the very central cluster region, and already characterizing the inner cluster core with respect to lower-density environments. On the other hand, the color–magnitude diagram of this cluster is definitely different from that of lower-redshift z ≲ 1 clusters, as well as of some rare particularly evolved massive clusters at similar redshift, and it is suggestive of a transition phase between active star formation and passive evolution occurring in the protocluster and established lower-redshift cluster regimes.« less

Comparison of active cooling devices to passive cooling for rehabilitation of firefighters performing exercise in thermal protective clothing: A report from the Fireground Rehab Evaluation (FIRE) trial

PubMed Central

Hostler, David; Reis, Steven E; Bednez, James C; Kerin, Sarah; Suyama, Joe

2010-01-01

Background Thermal protective clothing (TPC) worn by firefighters provides considerable protection from the external environment during structural fire suppression. However, TPC is associated with physiological derangements that may have adverse cardiovascular consequences. These derangements should be treated during on-scene rehabilitation periods. Objective The present study examined heart rate and core temperature responses during the application of four active cooling devices, currently being marketed to the fire service for on-scene rehab, and compared them to passive cooling in a moderate temperature (approximately 24°C) and to an infusion of cold (4°C) saline. Methods Subjects exercised in TPC in a heated room. Following an initial exercise period (BOUT 1) the subjects exited the room, removed TPC, and for 20 minutes cooled passively at room temperature, received an infusion of cold normal saline, or were cooled by one of four devices (fan, forearm immersion in water, hand cooling, water perfused cooling vest). After cooling, subjects donned TPC and entered the heated room for another 50-minute exercise period (BOUT 2). Results Subjects were not able to fully recover core temperature during a 20-minute rehab period when provided rehydration and the opportunity to completely remove TPC. Exercise duration was shorter during BOUT 2 when compared to BOUT 1 but did not differ by cooling intervention. The overall magnitude and rate of cooling and heart rate recovery did not differ by intervention. Conclusions No clear advantage was identified when active cooling devices and cold intravenous saline were compared to passive cooling in a moderate temperature after treadmill exercise in TPC. PMID:20397868

Does Core Area Theory Apply to STIs in Rural Environments?

PubMed Central

Gesink, Dionne C; Sullivan, Ashleigh B; Norwood, Todd; Serre, Marc L; Miller, William C

2012-01-01

Background Our objective was to determine the extent to which geographical core areas for gonorrhea and syphilis are located in rural areas, as compared to urban areas. Methods Incident gonorrhea (January 1, 2005 to December 31, 2010) and syphilis (January 1, 1999 to December 31, 2010) rates were estimated and mapped by census tract and quarter. Rurality was measured using percent rural and rural-urban commuting area (RUCA; rural, small town, micropolitan, or urban). SaTScan was used to identify spatiotemporal clusters of significantly elevated rates of infection. Clusters lasting five years or longer were considered core areas; clusters of shorter duration were considered outbreaks. Clusters were overlaid on maps of rurality and qualitatively assessed for correlation. Results Twenty gonorrhea core areas were identified; 65% in urban centers, 25% in micropolitan areas, and the remaining 10% were geographically large capturing combinations of urban, micropolitan, small town and rural environments. Ten syphilis core areas were identified with 80% in urban centers and 20% capturing two or more RUCAs. All ten of the syphilis core areas (100%) overlapped with gonorrhea core areas. Conclusions Gonorrhea and syphilis rates were high for rural parts of North Carolina; however, no core areas were identified exclusively for small towns or rural areas. The main pathway of rural STI transmission may be through the interconnectedness of urban, micropolitan, small town and rural areas. Directly addressing STIs in urban and micropolitan communities may also indirectly help address STI rates in rural and small town communities. PMID:23254115

Hubble Space Telescope survey of the Perseus cluster - III. The effect of local environment on dwarf galaxies

NASA Astrophysics Data System (ADS)

Penny, Samantha J.; Conselice, Christopher J.; de Rijcke, Sven; Held, Enrico V.; Gallagher, John S.; O'Connell, Robert W.

2011-01-01

We present the results of a Hubble Space Telescope (HST) study of dwarf galaxies in the outer regions of the nearby rich Perseus cluster, down to MV=-12, and compare these with the dwarf population in the cluster core from our previous HST imaging. In this paper, we examine how properties such as the colour-magnitude relation, structure and morphology are affected by environment for the lowest mass galaxies. Dwarf galaxies are excellent tracers of the effects of environment due to their low masses, allowing us to derive their environmentally based evolution, which is more subtle in more massive galaxies. We identify 11 dwarf elliptical (dE) and dwarf spheroidal (dSph) galaxies in the outer regions of Perseus, all of which are previously unstudied. We measure the (V-I)0 colours of our newly discovered dEs, and find that these dwarfs lie on the same red sequence as those in the cluster core. The morphologies of these dwarfs are examined by quantifying their light distributions using concentration, asymmetry and clumpiness (CAS) parameters, and we find that dEs in the cluster outskirts are on average more disturbed than those in the core, with = 0.13 ± 0.09 and = 0.18 ± 0.08, compared to = 0.02 ± 0.04, = 0.01 ± 0.07 for those in the core. Based on these results, we infer that these objects are `transition dwarfs', likely in the process of transforming from late-type to early-type galaxies as they infall into the cluster, with their colours transforming before their structures. When we compare the number counts for both the core and outer regions of the cluster, we find that below MV=-12, the counts in the outer regions of the cluster exceed those in the core. This is evidence that in the very dense region of the cluster, dwarfs are unable to survive unless they are sufficiently massive to prevent their disruption by the cluster potential and interactions with other galaxies. Based on observations made with the NASA/ESA HST, obtained (from the Data Archive) at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-10201 and GO-10789