430 research outputs found
Identifying drought tolerant short rotation coppice willows
Short rotation coppice (SRC) willows are of interest as they provide a source of renewable carbon for bioenergy and biofuels. One of the major challenges facing future supply of willow biomass is sustaining sufficient yields in drought challenged environments, with research in this area limited to date. The effects of drought responses on Salix germplasm were studied in two pot experiments in a rain out shelter at Rothamsted Research using a split plot design. In both experiments, plants were subjected to two water treatments, drought stressed or well-watered. A temporary water stress was imposed by applying two cycles of drought within a growing season. Experiment 1 aimed to screen 56 diverse Salix genotypes, including subsets of existing genetic mapping populations, to identify potentially informative germplasm
for further study in a more focused second pot experiment. Experiment 2 contained 36 genotypes from two willow full-sibling genetic mapping populations, F and K8. Assessing the potential of mapping population progeny to segregate for
drought traits of interest is an important aim of the study as it offers a potential route to the development of markers for drought tolerance trait selections within the Rothamsted Research willow breeding programme.Phenotypic and final harvest yield measurements were taken on all plants. Primary
results reveal; that pot experiments were effective in producing a useful response to drought stress, that genotypic diversity for drought tolerance exists in Salix, an early drought coinciding with the exponential growth phase has a more negative effect on yield than a drought that occurs later in the growing season, and that top and middle leaf lengths may potentially offer the breeder a high throughput method of assessing the impact of drought on germplas
Exploring Gendered Barriers to Higher Education Leadership for Women in Midlevel Student Affairs Roles
This qualitative case study explored the perceived barriers to leadership for female-identifying student affairs professionals at the midlevel who aspire to, but have not yet attained, a senior student affairs officer role. Women hold 71% of all student affairs positions in higher education compared to men; however, that majority shrinks to 56% for senior-level positions (Pritchard &McChesney, 2018). Thus, a study designed to explore gendered barriers to leadership was warranted. The research questions were designed to explore what barriers, if any, have participants experienced regarding their ability to move into a senior student affairs officer role and to what extent, if at all, participants experience higher education institutions as gendered organizations. A theoretical framework of gender role theory and gendered organizations was used to explore the research questions. The study was conducted in two phases; Phase 1 included a questionnaire in which participants (n = 32) responded to a series of statements about perceived barriers to leadership and gendered workplaces in student affairs. In Phase 2, follow-up interviews were conducted on a random selection of participants (n = 8) from Phase 1.
This study used a theoretical framework that combined the theories of gender role congruity (Eagly & Karau, 2002) and gendered organizations (Acker, 1990), which provided the context for investigating the role structures of the organizations in which participants worked and how social roles impact women’s paths to leadership within student affairs. Findings from the study indicated three themes related to personal barriers, which were impostor syndrome, work-life conflict, and showing emotion is unacceptable. Findings also revealed sociological barriers that included the nature of student affairs work, saying yes to everything, and religion’s influence on gender roles. Implications for practice, as suggested by participants, were a move to more flexible policies about work hours and locations, providing networking and mentoring opportunities, teaching men to be allies to women, and professional development opportunities focused on developing leadership skills
The Crab Nebula's Composition and Precursor Star Mass
We present results of new photoionization calculations for investigating
gaseous regions that represent potentially expected stages of nuclear
processing in the Crab Nebula supernova remnant. In addition to gas resulting
from CNO-processing and oxygen-burning, as previously reported, a large
component of the nebula appears to be carbon-rich. These results suggest that
the precursor star had an initial mass of 9.5 solar masses or more.Comment: manuscript in AASTeX, 6 figures in .eps, submitted to Astronomical
Journa
Possible High-Redshift, Low-Luminosity AGN Activity in the Hubble Deep Field
In the Hubble Deep Field (HDF), twelve candidate sources of high-redshift (z
> 3.5) AGN activity have been identified. The color selection criteria were
established by passing spectra of selected quasars and Seyfert galaxies
(appropriately redshifted and modified for "Lyman forest" absorption), as well
as stars, observed normal and starburst galaxies, and galaxy models for various
redshifts through the filters used for the HDF observations. The actual
identification of AGN candidates also involved convolving a
Laplacian-of-Gaussian filter with the HDF images, thereby removing relatively
flat galactic backgrounds and leaving only the point-like components in the
centers. Along with positions and colors, estimated redshifts and absolute
magnitudes are reported, with the candidates falling toward the faint end of
the AGN luminosity function. One candidate has been previously observed
spectroscopically, with a measured redshift of 4.02. The number of sources
reported here is consistent with a simple extrapolation of the observed quasar
luminosity function to magnitude 30 in B_Johnson. Implications for ionization
of the intergalactic medium and for gravitational lensing are discussed.Comment: 10 pages LaTex plus 2 separate files (Table 1 which is a two-page
landscape LaTex file; and Figure 6 which is a large (0.7 MB) non-encapsulated
postscript file). Accepted for publication in the Astronomical Journa
A Search for Nitrogen Enriched Quasars in the Sloan Digital Sky Survey Early Data Release
A search for nitrogen-rich quasars in the Sloan Digital Sky Survey Early Data
Release (SDSS EDR) catalog has yielded 16 candidates, including five with very
prominent emission, but no cases with nitrogen emission as strong as in
Q0353-383. The quasar Q0353-383 has long been known to have extremely strong
nitrogen intercombination lines at lambda 1486 and lambda 1750 Angstroms,
implying an anomalously high nitrogen abundance of about 15 times solar. It is
still the only one of its kind known. A preliminary search through the EDR
using the observed property of the weak C IV emission seen in Q0353-383
resulted in a sample of 23 objects with unusual emission or absorption-line
properties, including one very luminous redshift 2.5 star-forming galaxy. We
present descriptions, preliminary emission-line measurements, and spectra for
all the objects discussed here.Comment: 20 pages, 5 figures, submitted to AJ; final refereed versio
Multiple sclerosis or neuromyelitis optica? Re-evaluating an 18th-century illness using 21st-century software
In this paper we report the application of an extensive database of symptoms, signs, laboratory findings and illnesses, to the diagnosis of an historical figure. The medical diagnosis of Augustus d'Este (1794–1848) – widely held to be the first documented case of multiple sclerosis – is reviewed, using the detailed symptom diary, which he kept over many years, as clinical data. Some of the reported features prompted the competing claim that d'Este suffered from acute porphyria, which in turn was used in support of the hypothesis that his grandfather, King George III, also suffered from the disease. We find that multiple sclerosis is statistically the most likely diagnosis, with neuromyelitis optica a strong alternative possibility. The database did not support a diagnosis of any of the acute porphyrias
Methylation of histone H4 lysine 20 by PR-Set7 ensures the integrity of late replicating sequence domains in Drosophila
The methylation state of lysine 20 on histone H4 (H4K20) has been linked to chromatin compaction, transcription, DNA repair and DNA replication. Monomethylation of H4K20 (H4K20me1) is mediated by the cell cycle-regulated histone methyltransferase PR-Set7. PR-Set7 depletion in mammalian cells results in defective S phase progression and the accumulation of DNA damage, which has been partially attributed to defects in origin selection and activation. However, these studies were limited to only a handful of mammalian origins, and it remains unclear how PR-Set7 and H4K20 methylation impact the replication program on a genomic scale. We employed genetic, cytological, and genomic approaches to better understand the role of PR-Set7 and H4K20 methylation in regulating DNA replication and genome stability in Drosophila cells. We find that deregulation of H4K20 methylation had no impact on origin activation throughout the genome. Instead, depletion of PR-Set7 and loss of H4K20me1 results in the accumulation of DNA damage and an ATR-dependent cell cycle arrest. Coincident with the ATR-dependent cell cycle arrest, we find increased DNA damage that is specifically limited to late replicating regions of the Drosophila genome, suggesting that PR-Set7-mediated monomethylation of H4K20 is critical for maintaining the genomic integrity of late replicating domains
Trapped Ion Imaging with a High Numerical Aperture Spherical Mirror
Efficient collection and analysis of trapped ion qubit fluorescence is
essential for robust qubit state detection in trapped ion quantum computing
schemes. We discuss simple techniques of improving photon collection efficiency
using high numerical aperture (N.A.) reflective optics. To test these
techniques we placed a spherical mirror with an effective N.A. of about 0.9
inside a vacuum chamber in the vicinity of a linear Paul trap. We demonstrate
stable and reliable trapping of single barium ions, in excellent agreement with
our simulations of the electric field in this setup. While a large N.A.
spherical mirror introduces significant spherical aberration, the ion image
quality can be greatly improved by a specially designed aspheric corrector lens
located outside the vacuum system. Our simulations show that the spherical
mirror/corrector design is an easy and cost-effective way to achieve high
photon collection rates when compared to a more sophisticated parabolic mirror
setup.Comment: 5 figure
Emission-Line Galaxy Surveys as Probes of the Spatial Distribution of Dwarf Galaxies. I. The University of Michigan Survey
Objective-prism surveys which select galaxies on the basis of line-emission
are extremely effective at detecting low-luminosity galaxies and constitute
some of the deepest available samples of dwarfs. In this study, we confirm that
emission-line galaxies (ELGs) in the University of Michigan (UM)
objective-prism survey (MacAlpine et al. 1977-1981) are reliable tracers of
large-scale structure, and utilize the depth of the samples to examine the
spatial distribution of low-luminosity (M -18.0) dwarfs relative to
higher luminosity giant galaxies (M -18.0) in the Updated Zwicky
Catalogue (Falco et al. 1999). New spectroscopic data are presented for 26 UM
survey objects. We analyze the relative clustering properties of the overall
starbursting ELG and normal galaxy populations, using nearest neighbor and
correlation function statistics. This allows us to determine whether the
activity in ELGs is primarily caused by gravitational interactions. We conclude
that galaxy-galaxy encounters are not the sole cause of activity in ELGs since
ELGs tend to be more isolated and are more often found in the voids when
compared to their normal galaxy counterparts. Furthermore, statistical analyses
performed on low-luminosity dwarf ELGs show that the dwarfs are less clustered
when compared to their non-active giant neighbors. The UM dwarf samples have
greater percentages of nearest neighbor separations at large values and lower
correlation function amplitudes relative to the UZC giant galaxy samples. These
results are consistent with the expectations of galaxy biasing.Comment: 17 pages, 4 tables, 10 figures. Accepted for publication in the Ap
Carbon stars at high Galactic latitude
Photometry and kinematics are presented for a sample of objective prism selected carbon stars towards the north and south Galactic poles. Distances are determined by fitting the infrared colors to a giant branch. If these stars are like the carbon stars seen in dwarf spheroidal galaxies, the median distance of the sample is 28 kpc. If they are more like the carbon stars found recently in the Galactic bulge, they may be only half as distant. The surface density of carbon stars as a function of distance is remarkably consistent with an R^(1/4) density profile for the Galactic halo. This density profile can be traced to ≈ 15 scale radii and fills a volume similar to that occupied by globular clusters. The data yield an effective
radius of either 7.0 or 3.5 kpc depending on choice of distance scale. The velocity dispersion of the sample is 96 + 12 km/s. A kinematic model in which vertical velocity dispersion is independent of height above the Galactic plane seems in best accord with the data
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