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Search Results: 1 - 10 of 224164 matches for " Chuck R. Bower "
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Cosmic-Ray Positrons: Are There Primary Sources?
Stephane Coutu,Steven W. Barwick,James J. Beatty,Amit Bhattacharyya,Chuck R. Bower,Christopher J. Chaput,Georgia A. de Nolfo,Michael A. DuVernois,Allan Labrador,Shawn P. McKee,Dietrich Muller,James A. Musser,Scott L. Nutter,Eric Schneider,Simon P. Swordy,Gregory Tarle,Andrew D. Tomasch,Eric Torbet
Physics , 1999, DOI: 10.1016/S0927-6505(99)00011-0
Abstract: Cosmic rays at the Earth include a secondary component originating in collisions of primary particles with the diffuse interstellar gas. The secondary cosmic rays are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.
The Monster's Fiery Breath and its Impact on Galaxy Formation
R. G. Bower
Physics , 2009, DOI: 10.1063/1.3293034
Abstract: My aim in this talk is to make clear that there are two sides to galaxy formation: the properties of the galaxies themselves, and the properties of the material that is left over from the galaxy formation process. To date, galaxy formation studies have focused on correctly predicting the properties of galaxies, and I will review the tremendous level of success in this area. However, these models usually ignore the ``flip side'' of galaxy formation: the intergalactic medium and the intra-group/intra-cluster medium (ICM). Yet, Chandra and XMM have given us a good view of the ICM and their results present an equally important challenge for theoretical models. I will show that this challenge is far from easy to meet, but describe the Bower et al 2008 model of galaxy formation which successfully combines both sides of the observational constraints.
The Ks-band Luminosity and Stellar Mass Functions of Galaxies in z~1 Clusters
Tadayuki Kodama,R. G. Bower
Physics , 2003, DOI: 10.1046/j.1365-2966.2003.07093.x
Abstract: We present the near-infrared (Ks-band) luminosity function of galaxies in two z~1 cluster candidates, 3C336 and Q1335+28. A third cluster, 3C289, was observed but found to be contaminated by a foreground system. Our wide field imaging data reach to Ks=20.5 (5sigma), corresponding to ~M*+2.7 with respect to the passive evolution. The near-infrared luminosity traces the stellar mass of a galaxy due to its small sensitivity to the recent star formation history. Thus the luminosity function can be transformed to the stellar mass function of galaxies using the $J-K$ colours with only a small correction (factor<2) for the effects of on-going star formation. The derived stellar mass function spans a wide range in mass from ~3 x 10^{11}Msun down to ~6 x 10^{9}Msun (set by the magnitude limit). The form of the mass function is very similar to lower redshift counterparts such as that from 2MASS/LCRS clusters (Balogh et al. 2001) and the z=0.31 clusters (Barger et al. 1998). This indicates little evolution of galaxy masses from z=1 to the present-day. Combined with colour data that suggest star formation is completed early (z>>1) in the cluster core, it seems that the galaxy formation processes (both star formation and mass assembly) are strongly accerelated in dense environments and has been largely completed by z=1. We investigate whether the epoch of mass assembly of massive cluster galaxies is earlier than that predicted by the hierarchical galaxy formation models. These models predict the increase of characteristic mass by more than factor ~3 between z=1 and the present day. This seems incompatible with our data.
Reconstructing the History of Star Formation in Rich Cluster Cores
T. Kodama,R. G. Bower
Physics , 2000, DOI: 10.1046/j.1365-8711.2001.03981.x
Abstract: We address the current crucial issues on the formation and evolution of cluster galaxies: ie., connection between the Butcher-Oemler effect, assembly of cluster galaxies, truncation of star formation, and the origin of S0 galaxies. We construct the field corrected colour-magnitude (CM) diagrams for 7 CNOC clusters (0.23M*+1). Truncation of star formation is, however, found to be relatively milder (with a time scale of 1 Gyr) than suggested by the viorent processes such as ram-pressure stripping and/or mergers/harassment. The BO effect is after all found to be a combination of three effects, namely, increasing field star formation activity, increasing galaxy infall rate, and the truncatin of star formation after the accretion. Our approach naturally leads to the history of galaxy assembly and `global' star foramtion for `cluster' galaxies.
Two new bird records for the Tsitsikamma National Parks
D. F Bower,R. J. M Crawford
Koedoe : African Protected Area Conservation and Science , 1983, DOI: 10.4102/koedoe.v26i1.598
Abstract: Skead C.J. & R. Liversidge (1967, Koedoe 10:43-62) list 204 birds that could occur in the Tsitsikamma National Parks. However, close reading of their manuscript suggests that there have been no definite records for at least ten of these species and that their inclusion was based on the possibility, often historical, of occurrence.
Galaxy Evolution: Internally or Externally Driven?
M. L. Balogh,R. G. Bower
Physics , 2002,
Abstract: The globally-averaged star formation rate in the Universe has been steadily declining since at least z~1. This may be due either to very local processes operating within the average galaxy, or to external, environmental effects. Specifically, the build-up of structure may be responsible for terminating star formation in some galaxies and thus decreasing the global average. We summarize our previous and ongoing work to distinguish between these possibilities, by determining the average star formation rate as a function of redshift and environment, out to z=0.5.
Kinematics of the Nuclear Ionized Gas in the Radio Galaxy M84 (NGC 4374)
G. A. Bower,R. F. Green
Physics , 1997, DOI: 10.1086/311109
Abstract: We present optical long-slit spectroscopy of the nucleus of the nearby radio galaxy M84 (NGC 4374 = 3C 272.1) obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). Our spectra reveal that the nuclear gas disk seen in WFPC2 imaging by Bower et al. (1997, ApJ, 483, L33) is rotating rapidly. The velocity curve has an S-shape with a peak amplitude of 400 km/s at 0.1" = 8 pc from the nucleus. To model the observed gas kinematics, we construct a thin Keplerian disk model that fits the data well if the rotation axis of the gas disk is aligned with the radio jet axis. These models indicate that the gas dynamics are driven by a nuclear compact mass of 1.5 x 10^9 Msun with an uncertainty range of (0.9 - 2.6) x 10^9 Msun and that the inclination of the disk with respect to the plane of the sky is 75 - 85 degrees. Of this nuclear mass, only <= 2 x 10^7 Msun can possibly be attributed to luminous mass. Thus, we conclude that a dark compact mass (most likely a supermassive black hole) resides in the nucleus of M84.
Infrared video of a warm water surface in the presence and absence of surfactant monolayers
S. M. Bower,J. R. Saylor
Physics , 2009,
Abstract: Infrared (IR) videos are presented which show a warm water surface undergoing convective processes. These fluid dynamics videos show the water surface with: 1) no surfactant monolayer material present, 2) a liquid-phase monolayer of oleyl alcohol, and 3) a solid-phase monolayer of cetyl alcohol.
Rese a de "Historia del siglo XX, Barcelona" de Eric Hobsbawn
Chuck Churchill
Política y cultura , 1996,
Abstract:
Metastability of a granular surface in a spinning bucket
Chuck Yeung
Physics , 1998, DOI: 10.1103/PhysRevE.57.4528
Abstract: The surface shape of a spinning bucket of granular material is studied using a continuum model of surface flow developed by Bouchaud et al. and Mehta et al. An experimentally observed central subcritical region is reproduced by the model. The subcritical region occurs when a metastable surface becomes unstable via a nonlinear instability mechanism. The nonlinear instability mechanism destabilizes the surface in large systems while a linear instability mechanism is relevant for smaller systems. The range of angles in which the granular surface is metastable vanishes with increasing system size.
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