4,509 research outputs found
Hot Disks And Delayed Bar Formation
We present observational evidence for the inhibition of bar formation in
dispersion-dominated (dynamically hot) galaxies by studying the relationship
between galactic structure and host galaxy kinematics in a sample of 257
galaxies between 0.1 z 0.84 from the All-Wavelength Extended Groth
Strip International Survey (AEGIS) and the Deep Extragalactic Evolutionary
Probe 2 (DEEP2) survey. We find that bars are preferentially found in galaxies
that are massive and dynamically cold (rotation-dominated) and on the stellar
Tully-Fisher relationship, as is the case for barred spirals in the local
Universe. The data provide at least one explanation for the steep (3)
decline in the overall bar fraction from z=0 to z=0.84 in L and brighter
disks seen in previous studies. The decline in the bar fraction at high
redshift is almost exclusively in the lower mass (10 log M(\Msun)
11), later-type and bluer galaxies. A proposed explanation for this
"downsizing" of the bar formation / stellar structure formation is that the
lower mass galaxies may not form bars because they could be dynamically hotter
than more massive systems from the increased turbulence of accreting gas,
elevated star formation, and/or increased interaction/merger rate at higher
redshifts. The evidence presented here provides observational support for this
hypothesis. However, the data also show that not every disk galaxy that is
massive and cold has a stellar bar, suggesting that mass and dynamic coldness
of a disk are necessary but not sufficient conditions for bar formation -- a
secondary process, perhaps the interaction history between the dark matter halo
and the baryonic matter, may play an important role in bar formation.Comment: In press, ApJ, 13 pages, 5 figures (3 color
Gas Absorption Column Refurbishment
The purpose of this project was to refurbish the gas absorption column in the Moody Engineering Building for use as a supplement to some engineering classes. The group broke the project up into five subsections and each subsection was addressed based on different requirements. After completing the refurbishment, each subsystem was tested separately before the system was tested as a whole. After completing the final system test, the results were analyzed and grades given based on completion of goals for each subsystem. The final project was viewed as a success because the majority of work was completed and the system is operational such that it can be used in classes next year
Evidence for an ecological cost of enhanced herbicide metabolism in Lolium rigidum
1. In some cases, evaluation of resource competitive interactions between herbicide resistant vs. susceptible weed ecotypes provides evidence for the expression of fitness costs associated with evolved herbicide-resistant gene traits. Such fitness costs impact in the ecology and evolutionary trajectory of resistant populations.
2. Neighbourhood experiments were performed to quantify competitive effects and responses between herbicide-susceptible (S) and resistant (R) Lolium rigidum individuals in which resistance is due to enhanced herbicide metabolism mediated by cytochrome P450.
3. In two-way competitive interactions between the S and R phenotypes, individuals of the S phenotype were the stronger effect competitors on both a per capita and per unit-size basis. The S phenotype also exhibited a stronger competitive response to wheat plants than did the R phenotype, displaying significantly greater (30%) above-ground biomass at the vegetative stage. When subjected to competition from wheat, R individuals produced significantly fewer reproductive tillers and allocated fewer resources to reproductive traits than individuals of the S phenotype.
4. The role of potential mechanisms underlying this resistance cost driven by traits such as plant size and tolerance to low resource availability, as well as the evolutionary implications of the results are discussed.
5. Synthesis. Evolved herbicide resistance due to enhanced-herbicide metabolism mediated by cytochrome-P450 in L. rigidum has been shown to be accompanied with an impaired ability to compete for resources. These results are consistent with the resource-based theory that predicts a negative trade-off between growth and plant defence
Systematic Blueshift of Line Profiles in the Type IIn Supernova 2010jl: Evidence for Post-Shock Dust Formation?
Type IIn SNe show spectral evidence for strong interaction between their
blast wave and dense circumstellar material (CSM) around the progenitor star.
SN2010jl was the brightest core-collapse SN in 2010, and it was a Type IIn
explosion with strong CSM interaction. Andrews et al. recently reported
evidence for an IR excess in SN2010jl, indicating either new dust formation or
the heating of CSM dust in an IR echo. Here we report multi-epoch spectra of
SN2010jl that reveal the tell-tale signature of new dust formation:
emission-line profiles becoming systematically more blueshifted as the red side
of the line is blocked by increasing extinction. The effect is seen clearly in
the intermediate-width (400--4000 km/s) component of H beginning
roughly 30d after explosion. Moreover, we present near-IR spectra demonstrating
that the asymmetry in the hydrogen-line profiles is wavelength dependent,
appearing more pronounced at shorter wavelengths. This evidence suggests that
new dust grains had formed quickly in the post-shock shell of SN 2010jl arising
from CSM interaction. Since the observed dust temperature has been attributed
to an IR echo and not to new dust, either (1) IR excess emission at m is not a particularly sensitive tracer of new dust formation in SNe, or
(2) some assumptions about expected dust temperatures might require further
study. Lastly, we discuss one possible mechanism other than dust that might
lead to increasingly blueshifted line profiles in SNeIIn, although the
wavelength dependence of the asymmetry argues against this hypothesis in the
case of SN2010jl.Comment: 6 pages, 4 figures, submitted to A
The Metallicities of Low Stellar Mass Galaxies and the Scatter in the Mass-Metallicity Relation
In this investigation we quantify the metallicities of low mass galaxies by
constructing the most comprehensive census to date. We use galaxies from the
SDSS and DEEP2 survey and estimate metallicities from their optical emission
lines. We also use two smaller samples from the literature which have
metallicities determined by the direct method using the temperature sensitive
[OIII]4363 line. We examine the scatter in the local mass-metallicity (MZ)
relation determined from ~20,000 star-forming galaxies in the SDSS and show
that it is larger at lower stellar masses, consistent with the theoretical
scatter in the MZ relation determined from hydrodynamical simulations. We
determine a lower limit for the scatter in metallicities of galaxies down to
stellar masses of ~10^7 M_solar that is only slightly smaller than the expected
scatter inferred from the SDSS MZ relation and significantly larger than what
is previously established in the literature. The average metallicity of
star-forming galaxies increases with stellar mass. By examining the scatter in
the SDSS MZ relation, we show that this is mostly due to the lowest metallicity
galaxies. The population of low mass, metal-rich galaxies have properties which
are consistent with previously identified galaxies that may be transitional
objects between gas-rich dwarf irregulars and gas-poor dwarf spheroidals and
ellipticals.Comment: Accepted to ApJ. 17 pages, 17 figure
A framework for improving early detection of breast cancer in sub-Saharan Africa: A qualitative study of help-seeking behaviors among Malawian women
Many women in Africa are diagnosed with advanced breast cancer. We explored Malawian breast cancer patients’ perspectives about their diagnosis and ability to access care to identify help-seeking behaviors and to describe factors influencing delay
An Empirical Taxonomy of Hospital Governing Board Roles
To develop a taxonomy of governing board roles in U.S. hospitals. Data Sources . 2005 AHA Hospital Governance Survey, 2004 AHA Annual Survey of Hospitals, and Area Resource File. Study Design . A governing board taxonomy was developed using cluster analysis. Results were validated and reviewed by industry experts. Differences in hospital and environmental characteristics across clusters were examined. Data Extraction Methods . One-thousand three-hundred thirty-four hospitals with complete information on the study variables were included in the analysis. Principal Findings . Five distinct clusters of hospital governing boards were identified. Statistical tests showed that the five clusters had high internal reliability and high internal validity. Statistically significant differences in hospital and environmental conditions were found among clusters. Conclusions . The developed taxonomy provides policy makers, health care executives, and researchers a useful way to describe and understand hospital governing board roles. The taxonomy may also facilitate valid and systematic assessment of governance performance. Further, the taxonomy could be used as a framework for governing boards themselves to identify areas for improvement and direction for change.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75623/1/j.1475-6773.2008.00835.x.pd
Criteria for the diagnosis of corticobasal degeneration
Current criteria for the clinical diagnosis of pathologically confirmed corticobasal degeneration (CBD) no longer reflect the expanding understanding of this disease and its clinicopathologic correlations. An international consortium of behavioral neurology, neuropsychology, and movement disorders specialists developed new criteria based on consensus and a systematic literature review. Clinical diagnoses (early or late) were identified for 267 nonoverlapping pathologically confirmed CBD cases from published reports and brain banks. Combined with consensus, 4 CBD phenotypes emerged: corticobasal syndrome (CBS), frontal behavioral-spatial syndrome (FBS), nonfluent/agrammatic variant of primary progressive aphasia (naPPA), and progressive supranuclear palsy syndrome (PSPS). Clinical features of CBD cases were extracted from descriptions of 209 brain bank and published patients, providing a comprehensive description of CBD and correcting common misconceptions. Clinical CBD phenotypes and features were combined to create 2 sets of criteria: more specific clinical research criteria for probable CBD and broader criteria for possible CBD that are more inclusive but have a higher chance to detect other tau-based pathologies. Probable CBD criteria require insidious onset and gradual progression for at least 1 year, age at onset ≥50 years, no similar family history or known tau mutations, and a clinical phenotype of probable CBS or either FBS or naPPA with at least 1 CBS feature. The possible CBD category uses similar criteria but has no restrictions on age or family history, allows tau mutations, permits less rigorous phenotype fulfillment, and includes a PSPS phenotype. Future validation and refinement of the proposed criteria are needed
Rule violation errors are associated with right lateral prefrontal cortex atrophy in neurodegenerative disease
Good cognitive performance requires adherence to rules specific to the task at hand. Patients with neurological disease often make rule violation errors, but the anatomical basis for rule violation during cognitive testing remains debated. The current study examined the neuroanatomical correlates of rule violation (RV) errors made on tests of executive functioning in 166 subjects diagnosed with neurodegenerative disease or as neurologically healthy. Specifically, RV errors were voxel-wisely correlated with gray matter volume derived from high-definition MR images using voxel-based morphometry implemented in SPM2. Latent variable analysis showed that rule violation errors tapped a unitary construct separate from repetition errors. This analysis was used to generate factor scores to represent what is common among rule violation errors across tests. The extracted rule violation factor scores correlated with tissue loss in the lateral middle and inferior frontal gyri and the caudate nucleus bilaterally. When a more stringent control for global cognitive functioning was applied using Mini Mental State Exam scores, only the correlations with the right lateral prefrontal cortex remained significant. These data underscore the importance of right lateral prefrontal cortex in behavioral monitoring and highlight the potential of rule violation error assessment for identifying patients with damage to this region
- …