36 research outputs found
Structural Characteristics and Stellar Composition of Low Surface Brightness Disk Galaxies
We present UBVI surface photometry of a sample of low surface brightness
(LSB) disk galaxies. LSB disk galaxies are fairly well described as exponential
disks with no preferred value for either scale length, central surface
brightness, or rotational velocity. Indeed, the distribution of scale lengths
is indistinguishable from that of high surface brightness spirals, indicating
that dynamically similar galaxies (e.g., those with comparable Rv^2) exist over
a large range in surface density.
These LSB galaxies are strikingly blue. The complete lack of correlation
between central surface brightness and color rules out any fading scenario.
Similarly, the oxygen abundances inferred from HII region spectra are
uncorrelated with color so the low metallicities are not the primary cause of
the blue colors. While these are difficult to interpret in the absence of
significant star formation, the most plausible scenario is a stellar population
with a young mean age stemming from late formation and subsequent slow
evolution.
These properties suggest that LSB disks formed from low initial overdensities
with correspondingly late collapse times.Comment: Astronomical Journal, in press 45 pages uuencoded postscript (368K)
including 9 multipart figures also available by anonymous ftp @
ftp.ast.cam.ac.uk /pub/ssm/phot.uu CAP-30-210442962983742937
The mental health care context and patient characteristics: Implications for provider job satisfaction
This research examines job satisfaction among 282 staff providing mental health care to 574 patients with serious mental illness. The mental health staff worked in 18 Department of Veterans Affairs inpatient and outpatient mental health care units at 12 Veterans Affairs Medical Centers located across the contiguous 48 states. The purpose was to identify (1) aspects of the health care context that were associated with provider job satisfaction and (2) administrative and organizational procedures/interventions that might sustain or improve provider job satisfaction. The association of provider job satisfaction with patients' functional status and symptom severity was tested in multilevel statistical models that accounted for provider and unit characteristics. Provider job satisfaction was found to be greater on smaller units and units with higher patient functioning and lower illness severity. Implications of these results are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45774/1/11414_2005_Article_BF02287373.pd
Abundances of Deuterium and Helium-3 in the Protosolar Cloud
The mass spectrometric determinations of the isotopic composition of helium in the solar wind obtained from (1) the Apollo Solar Wind Composition (SWC) experiment, (2) the Ion Composition Instrument (ICI) on the International Sun Earth Explorer 3 (ISEE-3), and (3) the Solar Wind Composition Spectrometer (SWICS) on Ulysses are reviewed and discussed, including new data given by Gloeckler and Geiss (1998). Averages of the 3He/4He ratio in the slow wind and in fast streams are given. Taking account of separation and fractionation processes in the corona and chromosphere, 3He/4He = (3.8 ± 0.5) Ă 10-4 is derived as the best estimate for the present-day Outer Convective Zone (OCZ) of the sun. After corrections of this ratio for secular changes caused by diffusion, mixing and 3He production by incomplete H-burning (Vauclair, 1998), we obtain (D + 3He)/H = (3.6±0.5) Ă 10-5 for the Protosolar Cloud (PSC). Adopting 3He/H = (1.5±0.2) Ă 10-5 for the PSC, as is indicated from the 3He/4He ratio in the âplanetary gas componentâ of meteorites and in Jupiter (Mahaffy et al., 1998), we obtain (D/H)protosolar = (2.1 ± 0.5) Ă 10-5. Galactic evolution studies (Tosi, 1998) show that the measured D and 3He abundances in the Protosolar Cloud and the Local Interstellar Cloud (Linsky, 1998; Gloeckler and Geiss, 1998), lead to (D/H)primordial = (2 - 5) Ă 10-5. This range corresponds to a universal baryon/photon ratio of (6.0 ± 0.8) Ă 10-10, and to Ωb = 0.075 ± 0.015.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43783/1/11214_2004_Article_184083.pd