5,553 research outputs found
INITIAL CHARACTERIZATION OF MAJOR HISTOCOMPATIBILITY COMPLEX (MHC) CLASS IIB EXON 2 IN AN ENDANGERED RATTLESNAKE, THE EASTERN MASSASAUGA (SISTRURUS CATENATUS)
Genes of the major histocompatibility complex (MHC) play an important role in the vertebrate immune system and exhibit remarkably high levels of polymorphism, maintained by strong balancing selection. While the conservation implications of MHC variation have been explored in a variety of vertebrates, non-avian reptiles (most notably snakes) have received less attention. To address this gap and take the first steps toward more extensive population-level analyses, we cloned and sequenced MHC IIB exon 2 in an endangered rattlesnake, the Eastern Massasauga (Sistrurus catenatus). Based on three individuals, we found evidence of at least four putatively functional loci. These sequences exhibited relatively high levels of variation and significantly higher rates of nonsynonymous to synonymous substitutions, especially within the antigen-binding sites, indicating strong positive selection. Phylogenetic analysis revealed a pattern of trans-species polymorphism, also suggesting positive selection. These results contribute to our understanding of MHC variation in non-avian reptiles and form a basis for more studies of MHC variation in snakes of conservation concern
Microevolution in Island Water Snakes
Examples presented demonstrate that
evolutionary outcomes depend not
only on those processes that operate
within populations(e,g.,selection) but
also on interactions (via gene flow)
among populations. Factors affecting
rates of gene flow are likely to
produce evolutionary change even
when within-population processes remain
constant. These examples also
illustrate that the combined effects of
selection and gene flow are not restricted
to organisms found on islands
like those in western Lake Erie but
may be important in any organism
whose distribution spans a range of
habitat types. As human activities produce
changes in habitat characteristics
and distribution (e.g., by fragmenting
formerly continuous habitats), changes
in selection regimes and rates of gene
flow may produce microevolutionary
changes in other organisms that mirror
those seen in island water snakes
Calcutta Botanic Garden and the colonial re-ordering of the Indian environment
This article examines three hand-painted colour maps that accompanied the annual report of the Calcutta Botanic Garden for 1846 to illustrate how the Garden’s layout, uses and functions had changed over the previous 30 years. The evolution of the Calcutta Botanic Garden in the first half of the nineteenth-century reflects a wider shift in attitudes regarding the relationship between science, empire and the natural world. On a more human level the maps result from, and illustrate, the development of a vicious personal feud between the two eminent colonial botanists charged with superintending the garden in the 1840s
Self-gravitating fragmentation of eccentric accretion disks
We consider the effects of eccentricity on the fragmentation of
gravitationally unstable accretion disks, using numerical hydrodynamics. We
find that eccentricity does not affect the overall stability of the disk
against fragmentation, but significantly alters the manner in which such
fragments accrete gas. Variable tidal forces around an eccentric orbit slow the
accretion process, and suppress the formation of weakly-bound clumps. The
"stellar" mass function resulting from the fragmentation of an eccentric disk
is found to have a significantly higher characteristic mass than that from a
corresponding circular disk. We discuss our results in terms of the disk(s) of
massive stars at ~0.1pc from the Galactic Center, and find that the
fragmentation of an eccentric accretion disk, due to gravitational instability,
is a viable mechanism for the formation of these systems.Comment: 9 pages, 7 figures. Accepted for publication in Ap
Design approaches and materials processes for ultrahigh efficiency lattice mismatched multi-junction solar cells
In this study, we report synthesis of large area
(>2cm^2), crack-free GaAs and GaInP double
heterostructures grown in a multi-junction solar cell-like
structure by MOCVD. Initial solar cell data are also
reported for GaInP top cells. These samples were grown
on Ge/Si templates fabricated using wafer bonding and ion
implantation induced layer transfer techniques. The double
heterostructures exhibit radiative emission with uniform
intensity and wavelength in regions not containing
interfacial bubble defects. The minority carrier lifetime of
~1ns was estimated from photoluminescence decay
measurements in both double heterostructures.
We also report on the structural characteristics of
heterostructures, determined via atomic force microscopy
and transmission electron microscopy, and correlate these
characteristics to the spatial variation of the minority
carrier lifetime
Intelligent assistance in scientific data preparation
Scientific data preparation is the process of extracting usable scientific data from raw instrument data. This task involves noise detection (and subsequent noise classification and flagging or removal), extracting data from compressed forms, and construction of derivative or aggregate data (e.g. spectral densities or running averages). A software system called PIPE provides intelligent assistance to users developing scientific data preparation plans using a programming language called Master Plumber. PIPE provides this assistance capability by using a process description to create a dependency model of the scientific data preparation plan. This dependency model can then be used to verify syntactic and semantic constraints on processing steps to perform limited plan validation. PIPE also provides capabilities for using this model to assist in debugging faulty data preparation plans. In this case, the process model is used to focus the developer's attention upon those processing steps and data elements that were used in computing the faulty output values. Finally, the dependency model of a plan can be used to perform plan optimization and run time estimation. These capabilities allow scientists to spend less time developing data preparation procedures and more time on scientific analysis tasks
Neutral Mass Spectrometer (NMS) for the Lunar Atmosphere and Dust Environment Explorer (LADEE) Mission
The Lunar Atmosphere and Dust Environment Explorer (LADEE) mission currently scheduled for launch in early 2013 aboard a Minotaur V will orbit the moon at a nominal periselene of 50 km to characterized the lunar atmosphere and dust environment. The science instrument payload includes a neutral mass spectrometer as well as an ultraviolet spectrometer and a dust detector. Although to date only He, Ar-40, K, Na and Rn-222 have been firmly identified in the lunar exosphere and arise from the solar wind (He), the lunar regolith (K and Na) and the lunar interior (Ar-40, Rn-222), upper limits have been set for a large number of other species, LADEE Neutral Mass Spectrometer (NMS) observations will determine the abundance of several species and substantially lower the present upper limits for many others. Additionally, LADEE NMS will observe the spatial distribution and temporal variability of species which condense at nighttime and show peak concentrations at the dawn terminator (e,g, Ar-40), possible episodic release from the lunar interior, and the results of sputtering or desorption processes from the regolith. In this presentation, we describe the LADEE NMS hardware and the anticipated science results
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