425 research outputs found
Characterizing the impacts of multi-scale heterogeneity on solute transport in fracture networks
We model flow and transport in three-dimensional fracture networks with
varying degrees of fracture-to-fracture aperture/permeability heterogeneity and
network density to show how changes in these properties can cause the emergence
of anomalous flow and transport behavior. If fracture-to-fracture aperture
heterogeneity is increased in sparse networks, velocity fluctuations can
inhibit high flow rates and solute transport can be delayed, even in cases
where hydraulic aperture is monotonically increased. As the density of the
networks is increased, more connected pathways allow for particles to bypass
these effects. We discover transition behavior where with relatively few
connected pathways in a network from inflow to outflow boundaries, the first
arrival times of particles are not heavily affected by fracture-to-fracture
aperture heterogeneity, but the scaling behavior of the tails is strongly
influenced due to the particles being forced to sample some of the
heterogeneity in the velocity field caused by aperture differences. These
results reinforce the importance of considering multi-scale effects in
fractured systems and can inform flow and transport processes in both natural
and engineered fracture systems, especially the latter where high aperture
fractures are often stimulated and connect to existing fracture networks with
smaller apertures
The First Hour of Extra-galactic Data of the Sloan Digital Sky Survey Spectroscopic Commissioning: The Coma Cluster
On 26 May 1999, one of the Sloan Digital Sky Survey (SDSS) fiber-fed
spectrographs saw astronomical first light. This was followed by the first
spectroscopic commissioning run during the dark period of June 1999. We present
here the first hour of extra-galactic spectroscopy taken during these early
commissioning stages: an observation of the Coma cluster of galaxies. Our data
samples the Southern part of this cluster, out to a radius of 1.5degrees and
thus fully covers the NGC 4839 group. We outline in this paper the main
characteristics of the SDSS spectroscopic systems and provide redshifts and
spectral classifications for 196 Coma galaxies, of which 45 redshifts are new.
For the 151 galaxies in common with the literature, we find excellent agreement
between our redshift determinations and the published values. As part of our
analysis, we have investigated four different spectral classification
algorithms: spectral line strengths, a principal component decomposition, a
wavelet analysis and the fitting of spectral synthesis models to the data. We
find that a significant fraction (25%) of our observed Coma galaxies show signs
of recent star-formation activity and that the velocity dispersion of these
active galaxies (emission-line and post-starburst galaxies) is 30% larger than
the absorption-line galaxies. We also find no active galaxies within the
central (projected) 200 h-1 Kpc of the cluster. The spatial distribution of our
Coma active galaxies is consistent with that found at higher redshift for the
CNOC1 cluster survey. Beyond the core region, the fraction of bright active
galaxies appears to rise slowly out to the virial radius and are randomly
distributed within the cluster with no apparent correlation with the potential
merger of the NGC 4839 group. [ABRIDGED]Comment: Accepted in AJ, 65 pages, 20 figures, 5 table
A statistical review of light curves and the prevalence of contact binaries in the Kuiper Belt
We investigate what can be learned about a population of distant Kuiper Belt Objects (KBOs) by studying the statistical properties of their light curves. Whereas others have successfully inferred the properties of individual, highly variable KBOs, we show that the fraction of KBOs with low amplitudes also provides fundamental information about a population. Each light curve is primarily the result of two factors: shape and orientation. We consider contact binaries and ellipsoidal shapes, with and without flattening. After developing the mathematical framework, we apply it to the existing body of KBO light curve data. Principal conclusions are as follows. (1) When using absolute magnitude H as a proxy for the sizes of KBOs, it is more accurate to use the maximum of the light curve (minimum H) rather than the mean. (2) Previous investigators have noted that smaller KBOs tend to have higher-amplitude light curves, and have interpreted this as evidence that they are systematically more irregular in shape than larger KBOs; we show that a population of flattened bodies with uniform proportions, independent of size, could also explain this result. (3) Our method of analysis indicates that prior assessments of the fraction of contact binaries in the Kuiper Belt may be artificially low. (4) The pole orientations of some KBOs can be inferred from observed changes in their light curves over time scales of decades; however, we show that these KBOs constitute a biased sample, whose pole orientations are not representative of the population overall. (5) Although surface topography, albedo patterns, limb darkening, and other surface properties can affect individual light curves, they do not have a strong influence on the statistics overall. (6) Photometry from the Outer Solar System Origins Survey (OSSOS) survey is incompatible with previous results and its statistical properties defy easy interpretation. We also discuss the promise of this approach for the analysis of future, much larger data sets such as the one anticipated from the upcoming Vera C. Rubin Observatory
A statistical review of light curves and the prevalence of contact binaries in the Kuiper Belt
We investigate what can be learned about a population of distant Kuiper Belt Objects (KBOs) by studying the statistical properties of their light curves. Whereas others have successfully inferred the properties of individual, highly variable KBOs, we show that the fraction of KBOs with low amplitudes also provides fundamental information about a population. Each light curve is primarily the result of two factors: shape and orientation. We consider contact binaries and ellipsoidal shapes, with and without flattening. After developing the mathematical framework, we apply it to the existing body of KBO light curve data. Principal conclusions are as follows. (1) When using absolute magnitude H as a proxy for the sizes of KBOs, it is more accurate to use the maximum of the light curve (minimum H) rather than the mean. (2) Previous investigators have noted that smaller KBOs tend to have higher-amplitude light curves, and have interpreted this as evidence that they are systematically more irregular in shape than larger KBOs; we show that a population of flattened bodies with uniform proportions, independent of size, could also explain this result. (3) Our method of analysis indicates that prior assessments of the fraction of contact binaries in the Kuiper Belt may be artificially low. (4) The pole orientations of some KBOs can be inferred from observed changes in their light curves over time scales of decades; however, we show that these KBOs constitute a biased sample, whose pole orientations are not representative of the population overall. (5) Although surface topography, albedo patterns, limb darkening, and other surface properties can affect individual light curves, they do not have a strong influence on the statistics overall. (6) Photometry from the Outer Solar System Origins Survey (OSSOS) survey is incompatible with previous results and its statistical properties defy easy interpretation. We also discuss the promise of this approach for the analysis of future, much larger data sets such as the one anticipated from the upcoming Vera C. Rubin Observatory
An Expert Consensus Statement on the Management of Large Chondral and Osteochondral Defects in the Patellofemoral Joint
© The Author(s) 2020. Background: Cartilage lesions of the patellofemoral joint constitute a frequent abnormality. Patellofemoral conditions are challenging to treat because of complex biomechanics and morphology. Purpose: To develop a consensus statement on the functional anatomy, indications, donor graft considerations, surgical treatment, and rehabilitation for the management of large chondral and osteochondral defects in the patellofemoral joint using a modified Delphi technique. Study Design: Consensus statement. Methods: A working group of 4 persons generated a list of statements related to the functional anatomy, indications, donor graft considerations, surgical treatment, and rehabilitation for the management of large chondral and osteochondral defects in the patellofemoral joint to form the basis of an initial survey for rating by a group of experts. The Metrics of Osteochondral Allografts (MOCA) expert group (composed of 28 high-volume cartilage experts) was surveyed on 3 occasions to establish a consensus on the statements. In addition to assessing agreement for each included statement, experts were invited to propose additional statements for inclusion or to suggest modifications of existing statements with each round. Predefined criteria were used to refine statement lists after each survey round. Statements reaching a consensus in round 3 were included within the final consensus document. Results: A total of 28 experts (100% response rate) completed 3 rounds of surveys. After 3 rounds, 36 statements achieved a consensus, with over 75% agreement and less than 20% disagreement. A consensus was reached in 100.00% of the statements relating to functional anatomy of the patellofemoral joint, 88.24% relating to surgical indications, 100.00% relating to surgical technical aspects, and 100.00% relating to rehabilitation, with an overall consensus of 95.5%. Conclusion: This study established a strong expert consensus document relating to the functional anatomy, surgical indications, donor graft considerations for osteochondral allografts, surgical technical aspects, and rehabilitation concepts for the management of large chondral and osteochondral defects in the patellofemoral joint. Further research is required to clinically validate the established consensus statements and better understand the precise indications for surgery as well as which techniques and graft processing/preparation methods should be used based on patient- and lesion-specific factors
The Fifth Data Release of the Sloan Digital Sky Survey
This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky
Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and
represents the completion of the SDSS-I project (whose successor, SDSS-II will
continue through mid-2008). It includes five-band photometric data for 217
million objects selected over 8000 square degrees, and 1,048,960 spectra of
galaxies, quasars, and stars selected from 5713 square degrees of that imaging
data. These numbers represent a roughly 20% increment over those of the Fourth
Data Release; all the data from previous data releases are included in the
present release. In addition to "standard" SDSS observations, DR5 includes
repeat scans of the southern equatorial stripe, imaging scans across M31 and
the core of the Perseus cluster of galaxies, and the first spectroscopic data
from SEGUE, a survey to explore the kinematics and chemical evolution of the
Galaxy. The catalog database incorporates several new features, including
photometric redshifts of galaxies, tables of matched objects in overlap regions
of the imaging survey, and tools that allow precise computations of survey
geometry for statistical investigations.Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS
Sixth Data Release (DR6) is now public, available from http://www.sdss.or
Factors Associated with Refusal of Rapid HIV Testing in an Emergency Department
HIV screening studies in the emergency department (ED) have demonstrated rates of HIV test refusal ranging from 40–67%. This study aimed to determine the factors associated with refusal to undergo routine rapid HIV testing in an academic ED in Boston. HIV counselors offered routine testing to 1,959 patients; almost one-third of patients (29%) refused. Data from a self-administered survey were used to determine independent correlates of HIV testing refusal. In multivariate analysis, women and patients with annual household incomes of $50,000 or more were more likely to refuse testing, as were those who reported not engaging in HIV risk behaviors, those previously HIV tested and those who did not perceive a need for testing. Enrollment during morning hours was also associated with an increased risk of refusal. Increased educational efforts to convey the rationale and benefits of universal screening may improve testing uptake among these groups
The Seventh Data Release of the Sloan Digital Sky Survey
This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor
correction
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