623 research outputs found
Problems in Cladistic Classification: Higher-Level Relationships in Land Plants
Recent cladistic analyses of green plants recognize an extensive hierarchical series of relatively well-supported monophyletic groups. Translating this hierarchical pattern of relationships into a usable and informative written classification is important for purposes of scientific communication, research and teaching. However, in the context of the Linnean hierarchy, as manifested in the current International code of Botanical Nomenclature (ICBN), effecting this translation confronts substantial practical difficulties--especially the proliferation of hierarchical levels. These problems are exacerbated by the current emphasis of the ICBN on a hierarchy in which different ranks have different formal rank-based endings. These difficulties could be ameliorated by de-emphasizing the importance of ranks in the ICBN and relaxing the constraints on how they are treated, especially at the higher taxonomic levels. Modifications are needed that permit a more straightforward integration of systematic knowledge and botanical nomenclature, and at the same time foster increased stability in the association between names and the groups of organisms that they designate
Exploring Halo Substructure with Giant Stars: Spectroscopy of Stars in the Galactic Anticenter Stellar Structure
To determine the nature of the recently discovered, ring-like stellar
structure at the Galactic anticenter, we have collected spectra of a set of
presumed constituent M giants selected from the 2MASS point source catalog.
Radial velocities have been obtained for stars spanning ~100 degrees,
exhibiting a trend in velocity with Galactic longitude and an estimated
dispersion of 20 +/- 4 km/sec. A mean metallicity [Fe/H] = -0.4 +/- 0.3
measured for these stars combines with previous evidence from the literature to
suggest a population with a significant metallicity spread. In addition, a
curious alignment of at least four globular clusters of lower mean metallicity
is noted to be spatially and kinematically consistent with this stellar
distribution. We interpret the M giant sample position and velocity variation
with Galactic longitude as suggestive of a satellite galaxy currently
undergoing tidal disruption in a non-circular, prograde orbit about the Milky
Way.Comment: (1) University of Virginia, 4 pages, 3 figures, accepted for
publication in The Astrophysical Journal Letter
Hemisphere-scale differences in conifer evolutionary dynamics
Fundamental differences in the distribution of oceans and landmasses in the Northern and Southern Hemispheres potentially impact patterns of biological diversity in the two areas. The evolutionary history of conifers provides an opportunity to explore these dynamics, because the majority of extant conifer species belong to lineages that have been broadly confined to the Northern or Southern Hemisphere during the Cenozoic. Incorporating genetic information with a critical review of fossil evidence, we developed an age-calibrated phylogeny sampling ∼80% of living conifer species. Most extant conifer species diverged recently during the Neogene within clades that generally were established during the later Mesozoic, but lineages that diversified mainly in the Southern Hemisphere show a significantly older distribution of divergence ages than their counterparts in the Northern Hemisphere. Our tree topology and divergence times also are best fit by diversification models in which Northern Hemisphere conifer lineages have higher rates of species turnover than Southern Hemisphere lineages. The abundance of recent divergences in northern clades may reflect complex patterns of migration and range shifts during climatic cycles over the later Neogene leading to elevated rates of speciation and extinction, whereas the scattered persistence of mild, wetter habitats in the Southern Hemisphere may have favored the survival of older lineages
Association Between Chronic Hepatitis C Virus Infection and Myocardial Infarction Among People Living With HIV in the United States.
Hepatitis C virus (HCV) infection is common among people living with human immunodeficiency virus (PLWH). Extrahepatic manifestations of HCV, including myocardial infarction (MI), are a topic of active research. MI is classified into types, predominantly atheroembolic type 1 MI (T1MI) and supply-demand mismatch type 2 MI (T2MI). We examined the association between HCV and MI among patients in the Centers for AIDS Research (CFAR) Network of Integrated Clinical Systems, a US multicenter clinical cohort of PLWH. MIs were centrally adjudicated and categorized by type using the Third Universal Definition of Myocardial Infarction. We estimated the association between chronic HCV (RNA+) and time to MI while adjusting for demographic characteristics, cardiovascular risk factors, clinical characteristics, and history of injecting drug use. Among 23,407 PLWH aged ≥18 years, there were 336 T1MIs and 330 T2MIs during a median of 4.7 years of follow-up between 1998 and 2016. HCV was associated with a 46% greater risk of T2MI (adjusted hazard ratio (aHR) = 1.46, 95% confidence interval (CI): 1.09, 1.97) but not T1MI (aHR = 0.87, 95% CI: 0.58, 1.29). In an exploratory cause-specific analysis of T2MI, HCV was associated with a 2-fold greater risk of T2MI attributed to sepsis (aHR = 2.01, 95% CI: 1.25, 3.24). Extrahepatic manifestations of HCV in this high-risk population are an important area for continued research
A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: II. Swope Telescope Spectroscopy of M Giant Stars in the Dynamically Cold Sagittarius Tidal Stream
We present moderate resolution (~6 km/s) spectroscopy of 284 M giant
candidates selected from the Two Micron All Sky Survey photometry. Radial
velocities (RVs) are presented for stars mainly in the south, with a number
having positions consistent with association to the trailing tidal tail of the
Sagittarius (Sgr) dwarf galaxy. The latter show a clear RV trend with orbital
longitude, as expected from models of the orbit and destruction of Sgr. A
minimum 8 kpc width of the trailing stream about the Sgr orbital midplane is
implied by verified RV members. The coldness of this stream (dispersion ~10
km/s) provides upper limits on the combined contributions of stream heating by
a lumpy Galactic halo and the intrinsic dispersion of released stars, which is
a function of the Sgr core mass. The Sgr trailing arm is consistent with a
Galactic halo containing one dominant, LMC-like lump, however some lumpier
halos are not ruled out. An upper limit to the total M/L of the Sgr core is 21
in solar units. A second structure that roughly mimics expectations for
wrapped, leading Sgr arm debris crosses the trailing arm in the Southern
Hemisphere; however, this may also be an unrelated tidal feature. Among the <13
kpc M giants toward the South Galactic Pole are some with large RVs that
identify them as halo stars, perhaps part of the Sgr leading arm near the Sun.
The positions and RVs of Southern Hemisphere M giants are compared with those
of southern globular clusters potentially stripped from the Sgr system and
support for association of Pal 2 and Pal 12 with Sgr debris is found. Our
discussion includes description of a masked-filtered cross-correlation
methodology that achieves better than 1/20 of a resolution element RVs in
moderate resolution spectra.Comment: 41 pages, 6 figures, Astronomical Journal, in press (submitted Nov.
24, 2003; tentatively scheduled for July 2004 issue
The Fan Observatory Bench Optical Spectrograph (FOBOS)
The Fan Observatory Bench Optical Spectrograph (FOBOS) is intended for
single-object optical spectroscopy at moderate resolution (R~1500-3000) using a
fiber-fed, bench-mounted design to maintain stability. Whenever possible, the
instrument uses off-the-shelf components to maintain a modest cost. FOBOS
supports Galactic astronomy projects that require consistently well-measured
(~5 km/sec) radial velocities for large numbers of broadly distributed and
relatively bright (V<14) stars. The spectrograph provides wavelength coverage
throughout the optical spectrum, although the instrument design was optimized
for use in the range 470-670 nm. Test data indicate that the instrument is
stable and capable of measuring radial velocities with precision better than 3
km/sec at a resolution of R~1500 with minimal calibration overhead.Comment: Accepted for publication in the May 2005 issue of the PAS
The Ursinus Weekly, November 12, 1970
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Signal transduction in light-oxygen-voltage receptors lacking the adduct- forming cysteine residue
Light–oxygen–voltage (LOV) receptors sense blue light through the
photochemical generation of a covalent adduct between a flavin-nucleotide
chromophore and a strictly conserved cysteine residue. Here we show that,
after cysteine removal, the circadian-clock LOV-protein Vivid still undergoes
light-induced dimerization and signalling because of flavin photoreduction to
the neutral semiquinone (NSQ). Similarly, photoreduction of the engineered LOV
histidine kinase YF1 to the NSQ modulates activity and downstream effects on
gene expression. Signal transduction in both proteins hence hinges on flavin
protonation, which is common to both the cysteinyl adduct and the NSQ. This
general mechanism is also conserved by natural cysteine-less, LOV-like
regulators that respond to chemical or photoreduction of their flavin
cofactors. As LOV proteins can react to light even when devoid of the adduct-
forming cysteine, modern LOV photoreceptors may have arisen from ancestral
redox-active flavoproteins. The ability to tune LOV reactivity through
photoreduction may have important implications for LOV mechanism and
optogenetic applications
Three-dimensional visualization of fossil flowers, fruits, seeds, and other plant remains using synchrotron radiation X-ray tomographic microscopy (SRXTM): new insights into Cretaceous plant diversity
The application of synchrotron radiation X-ray tomographic microscopy (SRXTM) to the study of mesofossils of Cretaceous age has created new possibilities for the three-dimensional visualization and analysis of the external and internal structure of critical plant fossil material. SRXTM provides cellular and subcellular resolution of comparable or higher quality to that obtained from permineralized material using thin sections or the peel technique. SRXTM also has the advantage of being non-destructive and results in the rapid acquisition of large quantities of data in digital form. SRXTM thus refocuses the effort of the investigator from physical preparation to the digital post-processing of X-ray tomographic data, which allows great flexibility in the reconstruction, visualization, and analysis of the internal and external structure of fossil material in multiple planes and in two or three dimensions. A review of recent applications in paleobotany demonstrates that SRXTM will dramatically expand the level of information available for diverse fossil plants. Future refinement of SRXTM approaches that further increases resolution and eases digital post-processing, will transform the study of mesofossils and create new possibilities for advancing paleobotanical knowledge. We illustrate these points using a variety of Cretaceous mesofossils, highlighting in particular those cases where SRXTM has been essential for resolving critical structural details that have enhanced systematic understanding and improved phylogenetic interpretation
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