317 research outputs found
Circumnuclear Structures in Megamaser Host Galaxies
Using HST, we identify circumnuclear (- pc scale) structures in
nine new HO megamaser host galaxies to understand the flow of matter from
kpc-scale galactic structures down to the supermassive black holes (SMBHs) at
galactic centers. We double the sample analyzed in a similar way by Greene et
al. (2013) and consider the properties of the combined sample of 18 sources. We
find that disk-like structure is virtually ubiquitous when we can resolve
pc scales, in support of the notion that non-axisymmetries on these
scales are a necessary condition for SMBH fueling. We perform an analysis of
the orientation of our identified nuclear regions and compare it with the
orientation of megamaser disks and the kpc-scale disks of the hosts. We find
marginal evidence that the disk-like nuclear structures show increasing
misalignment from the kpc-scale host galaxy disk as the scale of the structure
decreases. In turn, we find that the orientation of both the pc scale
nuclear structures and their host galaxy large-scale disks is consistent with
random with respect to the orientation of their respective megamaser disks.Comment: 24 pages, 16 figures, 4 tables; Resubmitted to ApJ after referee's
comment
Preparing Globally and Socially-conscious Engineers: International and Humancentred Design Projects and Activities in the First Year
In recent years, a number of innovative activities involving early design/hands on experiences have been introduced into first and second semester freshman courses at Virginia Tech. The objective is to excite freshmen about the engineering profession and to provide early exposure to topics essential to their preparation as globally and socially conscious engineers. A number of initiatives including a sustainable development design project, study abroad presentations, and a world population activity have been implemented in the first course. In the second course, a design project with a focus on assistive technologies for third world countries has been implemented
Decreasing Post Insulin Hypoglycemia Incidence in End Stage Renal Disease (ESRD) patients
ESRD patients are vulnerable to hypoglycemia due to impaired insulin clearance, glucose metabolism changes, and effects of dialysis. Hypoglycemic events lead to serious and life-threatening complications.
Aims for Improvement:
To decrease the rate of hypoglycemic events amongst ESRD patients receiving insulin for hyperkalemia treatment
Megamaser Disks Reveal a Broad Distribution of Black Hole Mass in Spiral Galaxies
We use new precision measurements of black hole masses from water megamaser
disks to investigate scaling relations between macroscopic galaxy properties
and supermassive black hole (BH) mass. The megamaser-derived BH masses span
10^6-10^8 M_sun, while all the galaxy properties that we examine (including
stellar mass, central mass density, central velocity dispersion) lie within a
narrow range. Thus, no galaxy property correlates tightly with M_BH in ~L*
spiral galaxies. Of them all, stellar velocity dispersion provides the tightest
relation, but at fixed sigma* the mean megamaser M_BH are offset by -0.6+/-0.1
dex relative to early-type galaxies. Spiral galaxies with non-maser dynamical
BH masses do not show this offset. At low mass, we do not yet know the full
distribution of BH mass at fixed galaxy property; the non-maser dynamical
measurements may miss the low-mass end of the BH distribution due to inability
to resolve the spheres of influence and/or megamasers may preferentially occur
in lower-mass BHs.Comment: 6 pages, 4 figures, replaced to fix error: NGC 4594 is not a maser
galax
Using Megamaser Disks to Probe Black Hole Accretion
We examine the alignment between H_2O megamaser disks on sub-pc scales with
circumnuclear disks and bars on <500 pc scales observed with HST/WFC3. The HST
imaging reveals young stars, indicating the presence of gas. The megamaser
disks are not well aligned with the circumnuclear bars or disks as traced by
stars in the HST images. We speculate on the implications of the observed
misalignments for fueling supermassive black holes in gas-rich spiral galaxies.
In contrast, we find a strong preference for the rotation axes of the megamaser
disks to align with radio continuum jets observed on >50 pc scales, in those
galaxies for which radio continuum detections are available. Sub-arcsecond
observations of molecular gas with ALMA will enable a more complete
understanding of the interplay between circumnuclear structures.Comment: Error in Figure 4 corrected, references added. 7 pages, 4 figures, to
be published in the Astrophysical Journa
An amperometric biosensor based on laccase immobilized in polymer matrices for determining phenolic compounds
An amperometric enzyme electrode based on laccase for determining phenolic compounds is proposed. The following three types of polymer materials were used for enzyme immobilization on the surface of a glassy-carbon electrode: positively charged cetyl ethyl poly (ethyleneimine) (CEPEI) and negatively charged commercial Nafion and Eastman AQ 29D polymers. The advantages and disadvantages of each of the above polymers for enzyme immobilization are discussed. The detection limits of the model phenolic compounds hydroquinone and pyrocatechol in a buffer solution on laccase immobilization in a Nation membrane were 3.5 x 10(-8) and 5.0 x 10(-8) M, respectively, at a signal-to-noise ratio of 3. Electrodes with laccase immobilized in Nation and Eastman AQ 29D membranes exhibited the shortest response time. The operating stability and the stability in storage can be significantly improved by the additional incorporation of gelatin in the polymer matrices. Gelatin prevents enzyme inactivation as a result of enzyme modification by the free-radical oxidation products of phenolic compounds
Toward a Topography of Cross-Cultural Theatre Praxis
In this essay we attempt to map out a conceptual framework for analyzing a cluster of related practices subsumed under the broad banner of "cross-cultural theatre". For the purposes of our discussion, cross-cultural theatre encompasses public performance practices characterized by the conjunction of specific cultural resources at the level of narrative content, performance aesthetics, production processes, and/or reception by an interpretive community. The cultural resources at issue may be material or symbolic, taking the form of particular objects or properties, languages, myths, rituals, embodied techniques, training methods, and visual practices - or what James Brandon calls "cultural fragments" (1990:92). Cross-cultural theatre inevitably entails a process of encounter and negotiation between different cultural sensibilities, although the degree to which this is discernible in any performance event will vary considerably depending on the artistic capital brought to a project as well as the location and working processes involved in its development and execution
Associations between hippocampal morphometry and neuropathologic markers of Alzheimer's disease using 7 T MRI
Hippocampal atrophy, amyloid plaques, and neurofibrillary tangles are established pathologic markers of Alzheimer's disease. We analyzed the temporal lobes of 9 Alzheimer's dementia (AD) and 7 cognitively normal (NC) subjects. Brains were scanned post-mortem at 7 Tesla. We extracted hippocampal volumes and radial distances using automated segmentation techniques. Hippocampal slices were stained for amyloid beta (Aβ), tau, and cresyl violet to evaluate neuronal counts. The hippocampal subfields, CA1, CA2, CA3, CA4, and subiculum were manually traced so that the neuronal counts, Aβ, and tau burden could be obtained for each region. We used linear regression to detect associations between hippocampal atrophy in 3D, clinical diagnosis and total as well as subfield pathology burden measures. As expected, we found significant correlations between hippocampal radial distance and mean neuronal count, as well as diagnosis. There were subfield specific associations between hippocampal radial distance and tau in CA2, and cresyl violet neuronal counts in CA1 and subiculum. These results provide further validation for the European Alzheimer's Disease Consortium Alzheimer's Disease Neuroimaging Initiative Center Harmonized Hippocampal Segmentation Protocol (HarP)
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