4,743 research outputs found
The Color-Magnitude Relation in Coma: Clues to the Age and Metallicity of Cluster Populations
We have observed three fields of the Coma cluster of galaxies with a narrow
band (modified Stromgren) filter system. Observed galaxies include 31 in the
vicinity of NGC 4889, 48 near NGC 4874, and 60 near NGC 4839 complete to
M_5500=-18 in all three subclusters. Spectrophotometric classification finds
all three subclusters of Coma to be dominated by red, E type (ellipticals/S0's)
galaxies with a mean blue fraction, f_B, of 0.10. The blue fraction increases
to fainter luminosities, possible remnants of dwarf starburst population or the
effects of dynamical friction removing bright, blue galaxies from the cluster
population by mergers. We find the color-magnitude (CM) relation to be well
defined and linear over the range of M_5500=-13 to -22. After calibration to
multi-metallicity models, bright ellipticals are found to have luminosity
weighted mean [Fe/H] values between -0.5 and +0.5, whereas low luminosity
ellipticals have [Fe/H] values ranging from -2 to solar. The lack of CM
relation in our continuum color suggests that a systematic age effect cancels
the metallicity effects in this bandpass. This is confirmed with our age index
which finds a weak correlation between luminosity and mean stellar age in
ellipticals such that the stellar populations of bright ellipticals are 2 to 3
Gyrs younger than low luminosity ellipticals.Comment: 26 pages AAS LaTeX, 6 figures, accepted for publication in A
The Three-Dimensional Structure of Cassiopeia A
We used the Spitzer Space Telescope's Infrared Spectrograph to map nearly the
entire extent of Cassiopeia A between 5-40 micron. Using infrared and Chandra
X-ray Doppler velocity measurements, along with the locations of optical ejecta
beyond the forward shock, we constructed a 3-D model of the remnant. The
structure of Cas A can be characterized into a spherical component, a tilted
thick disk, and multiple ejecta jets/pistons and optical fast-moving knots all
populating the thick disk plane. The Bright Ring in Cas A identifies the
intersection between the thick plane/pistons and a roughly spherical reverse
shock. The ejecta pistons indicate a radial velocity gradient in the explosion.
Some ejecta pistons are bipolar with oppositely-directed flows about the
expansion center while some ejecta pistons show no such symmetry. Some ejecta
pistons appear to maintain the integrity of the nuclear burning layers while
others appear to have punched through the outer layers. The ejecta pistons
indicate a radial velocity gradient in the explosion. In 3-D, the Fe jet in the
southeast occupies a "hole" in the Si-group emission and does not represent
"overturning", as previously thought. Although interaction with the
circumstellar medium affects the detailed appearance of the remnant and may
affect the visibility of the southeast Fe jet, the bulk of the symmetries and
asymmetries in Cas A are intrinsic to the explosion.Comment: Accepted to ApJ. 54 pages, 21 figures. For high resolution figures
and associated mpeg movie and 3D PDF files, see
http://homepages.spa.umn.edu/~tdelaney/pape
Recommended from our members
LES Software for the Design of Low Emission Combustion Systems for Vision 21 Plants, Quarterly Report
Three SIMVAL LES calculations were completed this quarter: {phi} (equivalence ratio) of (1) 0.55, (2) 0.625, and (3) 0.7. The predictions were first analyzed, and then compared to existing experimental data of pressure dynamics, NO{sub x}, and CO emissions. It appears that the combustor flowfield changes for the {phi} of 0.55 case (compared to the other two cases), and this flowfield change results in a slight reduction in the pressure dynamics compared to the {phi} of 0.625 case. The predicted pressure rms values were 1.0 psi or less for the three cases. Good agreement was seen between predicted and measured NO{sub x} emissions for the cases with {phi} = 0.55 and {phi} = 0.625. The CO predictions were higher than the measurements, but possible reasons were identified. A new SIMVAL dataset recorded June, 2004, is being processed and will be transmitted to CFDRC in the near future. The previous two datasets had known deficiencies. This new dataset will be compared to the LES predictions in the next quarter
Particle export from the upper ocean over the continental shelf of the west Antarctic Peninsula: A long-term record, 1992–2007
Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 2118-2131, doi:10.1016/j.dsr2.2008.04.028.Includes supplemental materialsWe report on results of a long-term (1993-2007) time series sediment trap moored at 170 m to
the west of the Antarctic Peninsula in the mid-continental shelf region (350 m depth; 64º30’ S,
66º00’ W). This is a region characterized by late spring-summer diatom blooms, moderately high
seasonal primary productivity (50-150 mmol C m-2 d-1 in December-February) and high
phytoplankton and krill biomass in the seasonal sea ice zone. The mass flux ranged from near 0
to over 1 g m-2 d-1 and was near 0 to >30% organic carbon (mean 8%). Sedimentation from the
upper ocean as estimated by the trap collections at 170 m exhibited strong seasonality with high
fluxes (1-10 mmol C m-2 d-1) in November-March following ice retreat and very low fluxes
(<0.001 mmol C m-2 d-1) during the Austral winter and under sea ice cover. An average of 85%
of the annual export of 212 mmol C m-2 occurred during the seasonal peak flux episodes. Over
the trap record, the annual peak flux episode has tended to occur later in the Austral summer,
advancing by about 40 days since 1993. The time-integrated sedimentation during the peak flux
episode was <1 – 50% of the SeaWiFS-estimated primary production (mean 4%) at the trap site
over the period 1998-2006. The elemental composition of material captured in the traps had an
average C:N:P of 212:28:1, greater than the canonical Redfield values. High C:P ratios (400-
600) corresponded with the annual flux peak, indicating preferential loss of P from the sinking
particles in the summer, ice-free period. The composition of the exported material more closely
approximated the Redfield composition during the low-flux, winter period.This research was supported by NSF Grants OPP 9011927, 9632763 and 0217282 for the
Palmer Long Term Ecological Research project
Comment: Cultural eutrophication of natural lakes in the United States is real and widespread
This is the published version
Preparation of carbon dioxide adsorbents from the chemical activation of urea–formaldehyde and melamine–formaldehyde resins
10 pages, 4 figures, 3 tables.-- Available online Aug 14, 2006.Adsorption is considered to be one of the more promising technologies for the capture of CO2 from flue gases. In general, nitrogen enrichment is reported to be effective in enhancing the specific adsorbent–adsorbate interaction for CO2. Nitrogen enriched carbons were produced from urea–formaldehyde and melamine–formaldehyde resins polymerised in the presence of K2CO3 as a chemical activation agent, with activation undertaken over a range of temperatures. CO2 adsorption capacity was determined to be dependent upon both textural properties and more importantly nitrogen functionality. Adsorbents capable of capturing above 8 wt.% CO2 at 25°C were produced from the chemical activation of urea–formaldehyde resin at 500°C. Chemical activation seems to produce more effective adsorbents than CO2 activation.The authors are grateful for support for this work provided by the Research Fund for Coal and Steel (RFC-CR-03008) and for CP a grant from Plan I + D + I Gobierno del Principado de Asturias.Peer reviewe
A novel targeted/untargeted GC-Orbitrap metabolomics methodology applied to Candida albicans and Staphylococcus aureus biofilms
Introduction:
Combined infections from Candida albicans and Staphylococcus aureus are a leading cause of death in the developed world. Evidence suggests that Candida enhances the virulence of Staphylococcus—hyphae penetrate through tissue barriers, while S. aureus tightly associates with the hyphae to obtain entry to the host organism. Indeed, in a biofilm state, C. albicans enhances the antimicrobial resistance characteristics of S. aureus. The association of these microorganisms is also associated with significantly increased morbidity and mortality. Due to this tight association we hypothesised that metabolic effects were also in evidence.
Objectives:
To explore the interaction, we used a novel GC-Orbitrap-based mass spectrometer, the Q Exactive GC, which combines the high peak capacity and chromatographic resolution of gas chromatography with the sub-ppm mass accuracy of an Orbitrap system. This allows the capability to leverage the widely available electron ionisation libraries for untargeted applications, along with expanding accurate mass libraries and targeted matches based around authentic standards.
Methods:
Optimised C. albicans and S. aureus mono- and co-cultured biofilms were analysed using the new instrument in addition to the fresh and spent bacterial growth media.
Results:
The targeted analysis experiment was based around 36 sugars and sugar phosphates, 22 amino acids and five organic acids. Untargeted analysis resulted in the detection of 465 features from fresh and spent medium and 405 from biofilm samples. Three significantly changing compounds that matched to high scoring library fragment patterns were chosen for validation.
Conclusion:
Evaluation of the results demonstrates that the Q Exactive GC is suitable for metabolomics analysis using a targeted/untargeted methodology. Many of the results were as expected: e.g. rapid consumption of glucose and fructose from the medium regardless of the cell type. Modulation of sugar-phosphate levels also suggest that the pentose phosphate pathway could be enhanced in the cells from co-cultured biofilms. Untargeted metabolomics results suggested significant production of cell-wall biosynthesis components and the consumption of non-proteinaceous amino-acids
- …