2,964 research outputs found
Free vibrations of delaminated beams
Free vibration of laminated composite beams is studied. The effect of interply delaminations on natural frequencies and mode shapes is evaluated both analytically and experimentally. A generalized vibrational principle is used to formulate the equation of motion and associated boundary conditions for the free vibration of a composite beam with a delamination of arbitrary size and location. The effect of coupling between longitudinal vibration and bending vibration is considered. This coupling effect is shown to significantly affect the calculated natural frequencies and mode shapes of the delaminated beam
Recurrent shell infall events in a B0.5e star: HD 58978 1979-1988
Infall from the circumstellar envelope onto the bright B0.5 IVe star, HD 58978 was studied. The IUE data indicate that the star was surrounded by a low and moderately ionized circumstellar shell at least 12 times between 1979 and 1988. During 6 of these episodes, the signatures of cool circumstellar material were redshifted with respect to the photosphere by 20 to 80 km/sec. The data indicate that the transition from infall to minimal shell absorption can occur in under 10 days, and are consistent either with infall phases lasting up to 6 months, or with infall episodes shorter than 10 to 15 days. The long term behavior of the shell episodes is compared with variability in the stellar wind
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Were Presolar Grains Destroyed by the Nebular Process Responsible for the Volatile Element Fractionation?
We present SiC abundances from a number of CM and CR chondrites using NanoSIMS raster ion imaging of acid residues. We find higher SiC abundances for CRs than previously estimated based on noble gases
The HR 4796A Debris System: Discovery of Extensive Exo-Ring Dust Material
The optically and IR bright, and starlight-scattering, HR 4796A ring-like
debris disk is one of the most (and best) studied exoplanetary debris systems.
The presence of a yet-undetected planet has been inferred (or suggested) from
the narrow width and inner/outer truncation radii of its r = 1.05" (77 au)
debris ring. We present new, highly sensitive, Hubble Space Telescope (HST)
visible-light images of the HR 4796A circumstellar debris system and its
environment over a very wide range of stellocentric angles from 0.32" (23 au)
to ~ 15" (1100 au). These very high contrast images were obtained with the
Space Telescope Imaging Spectrograph (STIS) using 6-roll PSF-template
subtracted coronagraphy suppressing the primary light of HR 4796A and using
three image plane occulters and simultaneously subtracting the background light
from its close angular proximity M2.5V companion. The resulting images
unambiguously reveal the debris ring embedded within a much larger,
morphologically complex, and bi-axially asymmetric exoring scattering
structure. These images at visible wavelengths are sensitive to, and map, the
spatial distribution, brightness, and radial surface density of micron size
particles over 5 dex in surface brightness. These particles in the exo-ring
environment may be unbound from the system and interacting with the local ISM.
Herein we present a new morphological and photometric view of the larger than
prior seen HR 4796A exoplanetary debris system with sensitivity to small
particles at stellocentric distances an order of magnitude greater than has
previously been observed.Comment: 28 pages, 17 figures, accepted for publication in the Astronomical
Journal 21 December 201
Tree-based Coarsening and Partitioning of Complex Networks
Many applications produce massive complex networks whose analysis would
benefit from parallel processing. Parallel algorithms, in turn, often require a
suitable network partition. For solving optimization tasks such as graph
partitioning on large networks, multilevel methods are preferred in practice.
Yet, complex networks pose challenges to established multilevel algorithms, in
particular to their coarsening phase.
One way to specify a (recursive) coarsening of a graph is to rate its edges
and then contract the edges as prioritized by the rating. In this paper we (i)
define weights for the edges of a network that express the edges' importance
for connectivity, (ii) compute a minimum weight spanning tree with
respect to these weights, and (iii) rate the network edges based on the
conductance values of 's fundamental cuts. To this end, we also (iv)
develop the first optimal linear-time algorithm to compute the conductance
values of \emph{all} fundamental cuts of a given spanning tree. We integrate
the new edge rating into a leading multilevel graph partitioner and equip the
latter with a new greedy postprocessing for optimizing the maximum
communication volume (MCV). Experiments on bipartitioning frequently used
benchmark networks show that the postprocessing already reduces MCV by 11.3%.
Our new edge rating further reduces MCV by 10.3% compared to the previously
best rating with the postprocessing in place for both ratings. In total, with a
modest increase in running time, our new approach reduces the MCV of complex
network partitions by 20.4%
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Adding Phylogenies to QGIS and Lifemapper for Evolutionary Studies of Species Diversity
Phylogenetic data from the “Tree of Life” have explicit spatial and temporal components when paired with species distribution and ecological data for testing contributions to biological community assembly at different geographic scales of species interaction. Important questions in biology about the degree of niche suitability and whether the history of a community’s assembly for an area can affect whether the species in a community are more or less phylogenetically related can be answered using several different spatially-filtered measures of phylogenetic diversity. Phylogenetic analyses which support the description of ecological processes are usually achieved in a handful of software libraries that are narrowly focused on a single set of tasks. Very few applications scale to large datasets and most do not have an explicit spatial component without relying on external visualization packages. This prompted us to explore bringing phylogenetic data into an open-source GIS environment. The Lifemapper Macroecology/Range & Diversity QGIS plug-in is a custom plug-in which we use to calculate and map biodiversity indices that describe range-diversity relationships derived from large multi-species datasets. We describe extensions to that plug-in which expand the Lifemapper set of ecological tools to link phylogenies to spatially derived ’diversity field’ statistics that describe the phylogenetic composition of natural communities
High-Contrast NIR Polarization Imaging of MWC480
One of the key predictions of modeling from the IR excess of Herbig Ae stars
is that for protoplanetary disks, where significant grain growth and settling
has occurred, the dust disk has flattened to the point that it can be partially
or largely shadowed by the innermost material at or near the dust sublimation
radius. When the self-shadowing has already started, the outer disk is expected
to be detected in scattered light only in the exceptional cases that the scale
height of the dust disk at the sublimation radius is smaller than usual.
High-contrast imaging combined with the IR spectral energy distribution allow
us to measure the degree of flattening of the disk, as well as to determine the
properties of the outer disk. We present polarimetric differential imaging in
band obtained with Subaru/HiCIAO of one such system, MWC 480. The HiCIAO
data were obtained at a historic minimum of the NIR excess. The disk is
detected in scattered light from 0\farcs2-1\farcs0 (27.4-137AU). Together with
the marginal detection of the disk from 1998 February 24 by HST/NICMOS, our
data constrain the opening half angle for the disk to lie between
1.3. When compared with similar measures in CO for
the gas disk from the literature, the dust disk subtends only 30% of the
gas disk scale height (H/R0.03). Such a dust disk is a factor of 5-7
flatter than transitional disks, which have structural signatures that giant
planets have formed.Comment: 21 pages, 6 figures, 1 table, ApJ accepted 2012-05-0
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Water-Resources Investigations Report 83-4010
From purpose and scope: The purpose of this investigation was to estimate the water-yielding potential and water-quality characteristics of a stratified-drift deposits in five areas of Connecticut
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