129 research outputs found
Analysis of Snake Creek Burial Cave Mustela fossils using Linear & Landmark-based Morphometrics: Implications for Weasel Classification & Black-footed Ferret Conservation
Two discreet methods of geometric morphometrics were applied to evaluate the taxonomic utility of each in classifying the craniomandibular region of several Mustela species. Use of both linear measurements and 2-dimensional landmarks proved successful in discriminating between extant M. nigripes (black-footed ferret) and Neovison vison (American mink), in addition to the extant North American weasel species (M. erminea, M. frenata, M. nivalis). Methods were then used to classify Late Pleistocene Mustela spp. fossils collected from Snake Creek Burial Cave (SCBC) of eastern Nevada. Data acquired for unknown predicted group memberships varied markedly among methods and specimens. Nevertheless, results support the presence of M. nigripes and all 3 weasel taxa among the SCBC paleofauna
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Are geometric morphometric analyses replicable? Evaluating landmark measurement error and its impact on extant and fossil Microtus classification.
Geometric morphometric analyses are frequently employed to quantify biological shape and shape variation. Despite the popularity of this technique, quantification of measurement error in geometric morphometric datasets and its impact on statistical results is seldom assessed in the literature. Here, we evaluate error on 2D landmark coordinate configurations of the lower first molar of five North American Microtus (vole) species. We acquired data from the same specimens several times to quantify error from four data acquisition sources: specimen presentation, imaging devices, interobserver variation, and intraobserver variation. We then evaluated the impact of those errors on linear discriminant analysis-based classifications of the five species using recent specimens of known species affinity and fossil specimens of unknown species affinity. Results indicate that data acquisition error can be substantial, sometimes explaining >30% of the total variation among datasets. Comparisons of datasets digitized by different individuals exhibit the greatest discrepancies in landmark precision, and comparison of datasets photographed from different presentation angles yields the greatest discrepancies in species classification results. All error sources impact statistical classification to some extent. For example, no two landmark dataset replicates exhibit the same predicted group memberships of recent or fossil specimens. Our findings emphasize the need to mitigate error as much as possible during geometric morphometric data collection. Though the impact of measurement error on statistical fidelity is likely analysis-specific, we recommend that all geometric morphometric studies standardize specimen imaging equipment, specimen presentations (if analyses are 2D), and landmark digitizers to reduce error and subsequent analytical misinterpretations
Geopier Soil Reinforcement System – Case Histories of High Bearing Capacity Footing Support and Floor Slab Support
The Geopier® Rammed Aggregate Pier system is an innovative ground improvement method developed in the 1980’s that has grown in the United States and more recently in Asia and Europe, for supporting lightly to heavily loaded structures and highway and railroad embankments. The system is unique because it prestresses and prestrains adjacent matrix soils during installation of rammed aggregate piers. It has been successfully used on hundreds of project sites to support building foundations, floor slabs, storage tanks, and roadway embankments founded on both, poor and unsuitable soils as well as fair to good soils. The rammed aggregate pier system controls settlements effectively by reinforcing soils below structures and thus improving bearing capacities and allowable bearing pressures while controlling settlements. Two case histories of specialized applications are presented in this paper: (1) Wind tower projects in Germany, where the Geopier system provides high bearing capacity and overturning moment resistances to support the foundations in soft soils; and (2) Rammed Aggregate Pier soil reinforcement support of foundations and large area floor slab system for a commercial warehouse facility in the Philippines. This paper is of particular significance because it presents case histories of a relatively new soil improvement system tailored to increase foundation bearing capacities for dynamic footing loadings and provide positive settlement control for wide area loads including floor slabs. Design and implementation of the Geopier system are presented. Evaluations of the behavior of Geopier elements based on stiffness modulus test data and an analytical approach to compare modulus test results to the design assumptions are also discussed
Mutations in the E2 glycoprotein and the 3\u27 untranslated region enhance chikungunya virus virulence in mice
Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes debilitating musculoskeletal pain and inflammation and can persist for months to years after acute infection. Although studies of humans and experimentally infected animals suggest that CHIKV infection persists in musculoskeletal tissues, the mechanisms for this remain poorly understood. To evaluate this further, we isolated CHIKV from the serum of persistently infected Rag1 -/- mice at day 28. When inoculated into naive wild-type (WT) mice, this persistently circulating CHIKV strain displayed a capacity for earlier dissemination and greater pathogenicity than the parental virus. Sequence analysis revealed a nonsynonymous mutation in the E2 glycoprotein (E2 K200R) and a deletion within the 3' untranslated region (3'-UTR). The introduction of these changes into the parental virus conferred enhanced virulence in mice, although primary tropism for musculoskeletal tissues was maintained. The E2 K200R mutation was largely responsible for enhanced viral dissemination and pathogenicity, although these effects were augmented by the 3'- UTR deletion. Finally, studies with Irf3/Irf7 -/- and Ifnar1 -/- mice suggest that the E2 K200R mutation enhances viral dissemination from the site of inoculation independently of interferon regulatory factor 3 (IRF3)-, IRF7-, and IFNAR1-mediated responses. As our findings reveal viral determinants of CHIKV dissemination and pathogenicity, their further study should help to elucidate host-virus interactions that determine acute and chronic CHIKV infection
Rosetta-Alice Observations of Exospheric Hydrogen and Oxygen on Mars
The European Space Agency's Rosetta spacecraft, en route to a 2014 encounter
with comet 67P/Churyumov-Gerasimenko, made a gravity assist swing-by of Mars on
25 February 2007, closest approach being at 01:54UT. The Alice instrument on
board Rosetta, a lightweight far-ultraviolet imaging spectrograph optimized for
in situ cometary spectroscopy in the 750-2000 A spectral band, was used to
study the daytime Mars upper atmosphere including emissions from exospheric
hydrogen and oxygen. Offset pointing, obtained five hours before closest
approach, enabled us to detect and map the HI Lyman-alpha and Lyman-beta
emissions from exospheric hydrogen out beyond 30,000 km from the planet's
center. These data are fit with a Chamberlain exospheric model from which we
derive the hydrogen density at the 200 km exobase and the H escape flux. The
results are comparable to those found from the the Ultraviolet Spectrometer
experiment on the Mariner 6 and 7 fly-bys of Mars in 1969. Atomic oxygen
emission at 1304 A is detected at altitudes of 400 to 1000 km above the limb
during limb scans shortly after closest approach. However, the derived oxygen
scale height is not consistent with recent models of oxygen escape based on the
production of suprathermal oxygen atoms by the dissociative recombination of
O2+.Comment: 17 pages, 8 figures, accepted for publication in Icaru
Reverberation Mapping of the Kepler-Field AGN KA1858+4850
KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among
the brightest active galaxies monitored by the Kepler mission. We have carried
out a reverberation mapping campaign designed to measure the broad-line region
size and estimate the mass of the black hole in this galaxy. We obtained 74
epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m
telescope from February to November of 2012, and obtained complementary V-band
images from five other ground-based telescopes. We measured the H-beta light
curve lag with respect to the V-band continuum light curve using both
cross-correlation techniques (CCF) and continuum light curve variability
modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53
(+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta
root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s.
Combining these two results and assuming a virial scale factor of f = 5.13, we
obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the
mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also
obtained consistent but slightly shorter emission-line lags with respect to the
Kepler light curve. Thanks to the Kepler mission, the light curve of
KA1858+4850 has among the highest cadences and signal-to-noise ratios ever
measured for an active galactic nucleus; thus, our black hole mass measurement
will serve as a reference point for relations between black hole mass and
continuum variability characteristics in active galactic nuclei
The Automated Palomar 60-Inch Telescope
We have converted the Palomar 60-inch telescope (P60) from a classical night
assistant-operated telescope to a fully robotic facility. The automated system,
which has been operational since September 2004, is designed for moderately
fast (t <~ 3 minutes) and sustained (R <~ 23 mag) observations of gamma-ray
burst afterglows and other transient events. Routine queue-scheduled
observations can be interrupted in response to electronic notification of
transient events. An automated pipeline reduces data in real-time, which is
then stored on a searchable web-based archive for ease of distribution. We
describe here the design requirements, hardware and software upgrades, and
lessons learned from roboticization. We present an overview of the current
system performance as well as plans for future upgrades.Comment: Accepted in PASP; 26 pages, 7 figures; high resolution version at
http://www.srl.caltech.edu/~cenko/public/papers/p60.p
GRB 090426: The Environment of a Rest-Frame 0.35-second Gamma-Ray Burst at Redshift z=2.609
We present the discovery of an absorption-line redshift of z = 2.609 for GRB
090426, establishing the first firm lower limit to a redshift for a gamma-ray
burst with an observed duration of <2 s. With a rest-frame burst duration of
T_90z = 0.35 s and a detailed examination of the peak energy of the event, we
suggest that this is likely (at >90% confidence) a member of the short/hard
phenomenological class of GRBs. From analysis of the optical-afterglow spectrum
we find that the burst originated along a very low HI column density sightline,
with N_HI < 3.2 x 10^19 cm^-2. Our GRB 090426 afterglow spectrum also appears
to have weaker low-ionisation absorption (Si II, C II) than ~95% of previous
afterglow spectra. Finally, we also report the discovery of a blue, very
luminous, star-forming putative host galaxy (~2 L*) at a small angular offset
from the location of the optical afterglow. We consider the implications of
this unique GRB in the context of burst duration classification and our
understanding of GRB progenitor scenarios.Comment: Submitted to MNRA
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