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Mountain Road, VA, United States

Harnik P.G.,Franklin And Marshall College | Fitzgerald P.C.,Northern Virginia Community College | Payne J.L.,Stanford University | Carlson S.J.,University of California at Davis
Paleobiology | Year: 2014

Determining which biological traits affect taxonomic durations is critical for explaining macroevolutionary patterns. Two approaches are commonly used to investigate the associations between traits and durations and/or extinction and origination rates: analyses of taxonomic occurrence patterns in the fossil record and comparative phylogenetic analyses, predominantly of extant taxa. By capitalizing upon the empirical record of past extinctions, paleontological data avoid some of the limitations of existing methods for inferring extinction and origination rates from molecular phylogenies. However, most paleontological studies of extinction selectivity have ignored phylogenetic relationships because there is a dearth of phylogenetic hypotheses for diverse non-vertebrate higher taxa in the fossil record. This omission inflates the degrees of freedom in statistical analyses and leaves open the possibility that observed associations are indirect, reflecting shared evolutionary history rather than the direct influence of particular traits on durations. Here we investigate global patterns of extinction selectivity in Devonian terebratulide brachiopods and compare the results of taxonomic vs. phylogenetic approaches. Regression models that assume independence among taxa provide support for a positive association between geographic range size and genus duration but do not indicate an association between body size and genus duration. Brownian motion models of trait evolution identify significant similarities in body size, range size, and duration among closely related terebratulide genera. We use phylogenetic regression to account for shared evolutionary history and find support for a significant positive association between range size and duration among terebratulides that is also phylogenetically structured. The estimated range size - duration relationship is moderately weaker in the phylogenetic analysis due to the down-weighting of closely related genera that were both broadly distributed and long lived; however, this change in slope is not statistically significant. These results provide evidence for the phylogenetic conservatism of organismal and emergent traits, yet also the general phylogenetic independence of the relationship between range size and duration. © 2014 The Paleontological Society. All rights reserved. Source

Williams P.E.,Northern Virginia Community College | Williams P.E.,Catholic University of America | Williams P.E.,NASA | Pesnell W.D.,NASA
Solar Physics | Year: 2014

Sixty days of Doppler images from the Solar and Heliospheric Observatory (SOHO) / Michelson Doppler Imager (MDI) investigation during the 1996 and 2008 solar minima have been analyzed to show that certain supergranule characteristics (size, size range, and horizontal velocity) exhibit fluctuations of three to five days. Cross-correlating parameters showed a good, positive correlation between supergranulation size and size range, and a moderate, negative correlation between size range and velocity. The size and velocity do exhibit a moderate, negative correlation, but with a small time lag (less than 12 hours). Supergranule sizes during five days of co-temporal data from MDI and the Solar Dynamics Observatory (SDO) / Helioseismic Magnetic Imager (HMI) exhibit similar fluctuations with a high level of correlation between them. This verifies the solar origin of the fluctuations, which cannot be caused by instrumental artifacts according to these observations. Similar fluctuations are also observed in data simulations that model the evolution of the MDI Doppler pattern over a 60-day period. Correlations between the supergranule size and size range time-series derived from the simulated data are similar to those seen in MDI data. A simple toy-model using cumulative, uncorrelated exponential growth and decay patterns at random emergence times produces a time-series similar to the data simulations. The qualitative similarities between the simulated and the observed time-series suggest that the fluctuations arise from stochastic processes occurring within the solar convection zone. This behavior, propagating to surface manifestations of supergranulation, may assist our understanding of magnetic-field-line advection, evolution, and interaction. © 2013 Springer Science+Business Media Dordrecht. Source

Eckerlin R.P.,Northern Virginia Community College
Comparative Parasitology | Year: 2011

The digestive tracts of 6 silver-haired bats, Lasionycteris noctivagans, from Virginia were examined. Four of the 6 contained the digenetic trematode Urotrematulum attenuatum. Additional collections of this fluke from Ohio and Minnesota are reported. This is the third report of U. attenuatum and the first record of this species from Virginia. © 2011 The Helminthological Society of Washington. Source

Bushaw-Newton K.L.,Northern Virginia Community College | Ewers E.C.,Uniformed Services University of the Health Sciences | Velinsky D.J.,Academy of Natural Sciences of Philadelphia | Ashley J.T.F.,Academy of Natural Sciences of Philadelphia | And 2 more authors.
Environmental Science and Pollution Research | Year: 2012

Background aim and scope: Though the tidal Anacostia River, a highly polluted riverine system, has been well characterized with regard to contaminants, its overall resident bacterial populations have remained largely unknown. Improving the health of this system will rely upon enhanced understanding of the diversity and functions of these communities. Bacterial DNA was extracted from archived (AR, year 2000) and fresh sediments (RE, year 2006) collected from various locations within the Anacostia River. Using a combination of metabolic and molecular techniques, community snapshots of sediment bacterial diversity and activity were produced. Results: Employing Biolog EcoPlates, metabolic analysis of RE sediments from July revealed similar utilization of amines, amino acids, carbohydrates, carboxylic acids, and polymers at all sites. Normalized optical density measurements demonstrated that for most compounds, utilizations were similar though when differences did occur, the downstream site was enhanced compared to one or both of the upstream sites. Using denaturing gradient gel electrophoresis, bacterial diversity fingerprints of operational taxonomic units (OTUs) were obtained. Dendograms of the banding patterns revealed qualitative relationships as well as differences between replicate samples from similar sites. Replicates from the AR sites shared several common OTUs, while RE sites were more varied. Species richness and Shannon diversity indices generally increased with increasingly downstream locations, and were significant for the AR sediments (analysis of variance, P<0.0001). Carbon and nitrogen content and concentration of fine grain sediment (<63 μm) were positively correlated with OTU richness (r2 = 0.37, P = 0.0008; r2 = 0.45, P<0.0001; r2 = 0.48, P = 0.001, respectively). Conclusions: This study demonstrated that the bacterial communities from all regions sampled were not only metabolically active with the capacity to utilize several different compounds as energy sources but also were genetically diverse. This study is the first to focus on the overall bacterial community, providing insight into this vital component of stream ecosystems. Understanding the bacterial components of aquatic systems such as the Anacostia River will increase our knowledge of the overall structure and function of the ecological communities in polluted systems, subsequently enhancing our ability to improve the health of this important tidal river. © 2011 Springer-Verlag. Source

Jiang D.,University of Western Ontario | Bentley C.,University of Maryland University College | Bentley C.,Northern Virginia Community College
Journal of Geophysical Research: Solid Earth | Year: 2012

Deformation fabrics in Earth's crust and mantle are commonly used to constrain the tectonic history, deformation mechanisms, and rheological properties of the lithosphere. Their formation involves heterogeneous and multiscale deformation processes that current single-scale models cannot capture. Here we present a micromechanics-based MultiOrder Power Law Approach (MOPLA) for the simulation of multiscale fabrics in crustal scale high-strain zones. We consider the progressive deformation in a crustal high-strain zone on three different scales. On the macroscopic scale, representing the average assemblage of rock units at a point, we regard the rock mass as a continuum made of many first-order elements. The progressive deformation of first-order elements in the macroscopic flow field simulates tectonic transposition. On the scale of an individual first-order element, we regard it as an Eshelby inhomogeneity embedded in a poly element continuum. We apply Eshelby's inhomogeneity formalism for power law materials to relate the flow field inside a first-order element to the macroscopic flow field. On the scale pertinent to structures observed on the outcrop or smaller scale, the partitioned flow fields inside individual first-order elements are used to examine the fabric development. We implement MOPLA in MathCad, apply the approach to a natural example of the Cascade Lake shear zone, and discuss the implications of multiscale deformation. Our model predicts lineation patterns observed in natural high-strain zones that have remained unexplained by single-scale models. © 2012. American Geophysical Union. All Rights Reserved. Source

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