4,058 research outputs found
Reduced Genetic Variation in Populations of Black Cherry (Prunus serotina subsp. serotina, Rosaceae) at Its Western Range Limit in Kansas
Citation: Beck, J. B., Ferguson, C. J., Mayfield, M. H., & Shaw, J. (2015). Reduced Genetic Variation in Populations of Black Cherry (Prunus serotina subsp. serotina, Rosaceae) at Its Western Range Limit in Kansas. Northeastern Naturalist, 21(3), 472-478. doi:10.1656/045.021.0313We compared genetic variation at five nuclear simple sequence repeat loci between three populations of Black Cherry (Prunus serotina subsp. serotina) at the edge of its western range in Kansas to four populations from within the range interior. Although within-population expected heterozygosity did not differ between edge and core populations, allelic richness was significantly lower in the edge populations. This finding is consistent with a loss of rare alleles due to genetic drift in demographically unstable edge populations
The Assembly of Diversity in the Morphologies and Stellar Populations of High-Redshift Galaxies
We have studied the evolution in the morphologies, sizes, stellar-masses,
colors, and internal color dispersion (ICD) of galaxies at z=1 and 2.3, using a
near-IR, flux-limited catalog for the HDF-N. At z=1 most luminous galaxies have
morphologies of early-to-mid Hubble-types, and many show transformations
between their rest-frame UV-optical morphologies. Galaxies at z=2.3 have
compact and irregular morphologies with no clearly evident Hubble-sequence
candidates. The mean galaxy size grows from z=2.3 to 1 by 40%, and the density
of galaxies larger than 3 kpc increases by 7 times. At z=1, the size-luminosity
distribution is broadly consistent with that of local galaxies, with passive
evolution. However, galaxies at z=2.3 are smaller than the large present-day
galaxies, and must continue to grow in size and stellar mass. We have measured
the galaxies' UV-optical ICD, which quantifies differences in morphology and
the relative amount of on-going star-formation. The mean and scatter in
galaxies' total colors and ICD increase from z=2.3 to 1. At z=1 many galaxies
with large ICD are spirals, with a few irregular systems. Few z=2.3 galaxies
have high ICD, and those that do are actively merging. We interpret this as
evidence for the presence of older and more diverse stellar populations at z=1
that are not generally present at z>2. We conclude that the star-formation
histories of galaxies at z>2 are dominated by discrete, recurrent bursts, which
quickly homogenize the galaxies' stellar content, and are possibly associated
with mergers. The increase in the stellar-population diversification by z<1.4
implies that merger-induced starbursts occur less frequently than at higher
redshifts, and more quiescent star-forming modes dominate. This transition
coincides with the emergence of Hubble-sequence galaxies. [Abridged]Comment: Accepted for publication in the Astrophysical Journal. 20 pages, in
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Origins of Neural Progenitor Cell-Derived Axons Projecting Caudally after Spinal Cord Injury.
Neural progenitor cells (NPCs) transplanted into sites of spinal cord injury (SCI) extend large numbers of axons into the caudal host spinal cord. We determined the precise locations of neurons in the graft that extend axons into the caudal host spinal cord using AAV9-Cre-initiated retrograde tracing into floxed-TdTomato-expressing NPC grafts. 7,640 ± 630 grafted neurons extended axons to a single caudal host spinal cord site located 2 mm beyond the lesion, 5 weeks post injury. While caudally projecting axons arose from neurons located in all regions of the graft, the majority of caudally projecting graft neurons (53%) were located within the caudal one-third of the graft. Numerous host corticospinal axons formed monosynaptic projections onto caudally projecting graft neurons; however, we find that the majority of host axonal neuronal projections formed by neural progenitor cell interneuronal "relays" across sites of SCI are likely polysynaptic in nature
The Stellar Populations and Evolution of Lyman Break Galaxies
Using deep near-IR and optical observations of the HDF-N from the HST NICMOS
and WFPC2 and from the ground, we examine the spectral energy distributions
(SEDs) of Lyman break galaxies (LBGs) at 2.0 < z < 3.5. The UV-to-optical
rest-frame SEDs of the galaxies are much bluer than those of present-day spiral
and elliptical galaxies, and are generally similar to those of local starburst
galaxies with modest amounts of reddening. We use stellar population synthesis
models to study the properties of the stars that dominate the light from LBGs.
Under the assumption that the star-formation rate is continuous or decreasing
with time, the best-fitting models provide a lower bound on the LBG mass
estimates. LBGs with ``L*'' UV luminosities are estimated to have minimum
stellar masses ~ 10^10 solar masses, or roughly 1/10th that of a present-day L*
galaxy. By considering the effects of a second component of maximally-old
stars, we set an upper bound on the stellar masses that is ~ 3-8 times the
minimum estimate. We find only loose constraints on the individual galaxy ages,
extinction, metallicities, initial mass functions, and prior star-formation
histories. We find no galaxies whose SEDs are consistent with young (< 10^8
yr), dust-free objects, which suggests that LBGs are not dominated by ``first
generation'' stars, and that such objects are rare at these redshifts. We also
find that the typical ages for the observed star-formation events are
significantly younger than the time interval covered by this redshift range (~
1.5 Gyr). From this, and from the relative absence of candidates for quiescent,
non-star-forming galaxies at these redshifts in the NICMOS data, we suggest
that star formation in LBGs may be recurrent, with short duty cycles and a
timescale between star-formation events of < 1 Gyr. [Abridged]Comment: LaTeX, 37 pages, 21 figures. Accepted for publication in the
Astrophysical Journa
Barrier Formation in the Human Fetus is Patterned
We recently demonstrated patterned stratum corneum maturation and skin barrier formation during fetal development in rodents and rabbit. The presence of skin patterning in these mammals led us to predict patterned barrier formation during human infant development. Here we extend our mammalian study and demonstrate patterned stratum corneum development and skin barrier formation in the pre-term human infant. Surprisingly, we show initiation of human barrier regionally as early as 20–24 wk gestational age (22–26 wk menstrual age), bringing barrier formation close to the time of periderm disaggregation. We use the mouse model to show that patterns of periderm disaggregation mirrors barrier formation. Periderm disaggregation follows and recapitulates barrier pattern, suggesting a relationship between the processes. This work reveals regional patterning in skin maturation and barrier formation in the human infant and demonstrates that initiation of human skin barrier formation in utero coincides with the current lower limit of viability of the pre-term infant
The Internal Ultraviolet-to-Optical Color Dispersion: Quantifying the Morphological K-Correction
We present a quantitative measure of the internal color dispersion within
galaxies, which quantifies differences in morphology as a function of
wavelength. We apply this statistic to a local galaxy sample with archival
images at 1500 and 2500 Angstroms from the Ultraviolet Imaging Telescope, and
ground-based B-band observations to investigate how the color dispersion
relates to global galaxy properties. The intenal color dispersion generally
correlates with transformations in galaxy morphology as a function of
wavelength, i.e., it quantifies the morphological K-correction. Mid-type spiral
galaxies exhibit the highest dispersion in their internal colors, which stems
from differences in the bulge, disk, and spiral-arm components. Irregulars and
late-type spirals show moderate internal color dispersion, which implies that
young stars generally dominate the colors. Ellipticals, lenticulars, and
early-type spirals generally have low or negligible internal color dispersion,
which indicates that the stars contributing to the UV-to-optical emission have
a very homogeneous distribution. We discuss the application of the internal
color dispersion to high-redshift galaxies in deep, Hubble Space Telescope
images. By simulating local galaxies at cosmological distances, many of the
galaxies have luminosities that are sufficiently bright at rest--frame optical
wavelengths to be detected within the limits of the currently deepest
near-infrared surveys even with no evolution. Under assumptions that the
luminosity and color evolution of the local galaxies conform with the measured
values of high-redshift objects, we show that galaxies' intrinsic internal
color dispersion remains measurable out to z ~ 3.Comment: Accepted for publication in the Astrophysical Journal. 41 pages, 13
figures (3 color). Full resolution version (~8 Mb) available at
http://mips.as.arizona.edu/~papovich/papovich_astroph.p
Radiation-Induced Leiomyosarcoma: Does Antimetabolite Chemotherapy Contribute? A Report of Three Cases
Purpose: Radiation therapy in low and high doses is known to be associated with the occurrence of late secondary sarcomas.
The addition of chemotherapy has not been clearly demonstrated as a contributing factor. We describe three patients with
radiation-associated leiomyosarcoma who had also received antimetabolite chemotherapy
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Innovating Pedagogy 2015: Open University Innovation Report 4
This series of reports explores new forms of teaching, learning and assessment for an interactive world, to guide teachers and policy makers in productive innovation. This fourth report proposes ten innovations that are already in currency but have not yet had a profound influence on education. To produce it, a group of academics at the Institute of Educational Technology in The Open University collaborated with researchers from the Center for Technology in Learning at SRI International. We proposed a long list of new educational terms, theories, and practices. We then pared these down to ten that have the potential to provoke major shifts in educational practice, particularly in post-school education. Lastly, we drew on published and unpublished writings to compile the ten sketches of new pedagogies that might transform education. These are summarised below in an approximate order of immediacy and timescale to widespread implementation
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