139 research outputs found
The Leadership Practices of Non-Traditional Students Pursuing a Bachelor\u27s Degree: A Predictive Study
This non-experimental, regression study examined the relationship between leadership practices and academic achievement for a non-traditional student population. The study was conducted at a small, four-year private college in Eastern North Carolina. The sample consisted of N=146 (73 male, 73 female) non-traditional students enrolled in an accelerated bachelor\u27s degree program. Volunteer participants completed the survey which consisted of the Leadership Practice Inventory-Self (LPI) (Kouzes & Posner, 1998) assessment and a demographic questionnaire. Kouzes and Posner\u27s (2007) model of Transformational Leadership Theory is used to explain the leadership practices of non-traditional students. The results of the survey were analyzed using hierarchal multiple regression statistics. The analysis showed the strength of the relationship between the predictor variables (leadership practices) and the criterion variable (GPA) while controlling for demographic and academic data. The results of this study suggest that the leadership practice of Enable Others to Act did have a statistically significant negative relationship on the participants\u27 GPA
Comparison of polymerase chain reaction and bacterial culture for Salmonella detection in the Muscovy duck in Trinidad and Tobago
Objectives: The purpose of this study was to investigate the presence and serovar identity of Salmonella, at the national level, in farmed Muscovy ducks (Cairina moschata) in Trinidad and Tobago, and to compare the relative benefits of bacterial culture to those of polymerase chain reaction (PCR) for use in the routine detection and surveillance of Salmonella in these ducks.
Methods: From March-September 2003, 110 fecal samples were collected from 82 farms across the islands of Trinidad and Tobago. Salmonella was isolated from fresh and frozen samples and the serotype of each was determined through bacterial culture. An in-house, nested PCR that detects all pathogenic Salmonella species was utilized in analyzing the samples.
Results: Five samples were positive for Salmonella by bacterial culture, whereas 44 were positive by the nested PCR. Serovars isolated were Kiambu, Orion, Uganda, and two isolates from Group E1 whose H antigens could not be fully characterized. Of the samples, 87 (79%) gave equivalent PCR results for both enrichment broths-28 were positive for both and 59 were negative for both). However, 16 samples were positive for one broth, but not for the other, with the majority (14 of the 16) resulting positive for Selenite broth. PCR results for seven samples were inconclusive due to ambiguous band size or multiple bands near the expected band size.
Conclusions: In Trinidad and Tobago, the Muscovy duck does not appear to be a significant source of S. typhimurium or S. enteritidis, but it does harbor other Salmonella species. In-house, nested PCR represents a simple, relatively inexpensive and potentially more sensitive method than bacterial culture for the routine surveillance of pathogenic Salmonella in the Muscovy duck
Simultaneous Exoplanet Characterization and deep wide-field imaging with a diffractive pupil telescope
High-precision astrometry can identify exoplanets and measure their orbits
and masses, while coronagraphic imaging enables detailed characterization of
their physical properties and atmospheric compositions through spectroscopy. In
a previous paper, we showed that a diffractive pupil telescope (DPT) in space
can enable sub-microarcsecond accuracy astrometric measurements from wide-field
images by creating faint but sharp diffraction spikes around the bright target
star. The DPT allows simultaneous astrometric measurement and coronagraphic
imaging, and we discuss and quantify in this paper the scientific benefits of
this combination for exoplanet science investigations: identification of
exoplanets with increased sensitivity and robustness, and ability to measure
planetary masses to high accuracy. We show how using both measurements to
identify planets and measure their masses offers greater sensitivity and
provides more reliable measurements than possible with separate missions, and
therefore results in a large gain in mission efficiency. The combined
measurements reliably identify potentially habitable planets in multiple
systems with a few observations, while astrometry or imaging alone would
require many measurements over a long time baseline. In addition, the combined
measurement allows direct determination of stellar masses to percent-level
accuracy, using planets as test particles. We also show that the DPT maintains
the full sensitivity of the telescope for deep wide-field imaging, and is
therefore compatible with simultaneous scientific observations unrelated to
exoplanets. We conclude that astrometry, coronagraphy, and deep wide-field
imaging can be performed simultaneously on a single telescope without
significant negative impact on the performance of any of the three techniques.Comment: 15 pages, 6 figures. This second paper, following the paper
describing the diffractive pupil telescope (DPT) astrometric technique, shows
how simultaneous astrometry and coronagraphy observations, enabled by the DPT
concept, constrain the orbital parameters and mass of exoplanet
How do Most Planets Form? -- Constraints on Disk Instability from Direct Imaging
Core accretion and disk instability have traditionally been regarded as the
two competing possible paths of planet formation. In recent years, evidence
have accumulated in favor of core accretion as the dominant mode, at least for
close-in planets. However, it might be hypothesized that a significant
population of wide planets formed by disk instabilities could exist at large
separations, forming an invisible majority. In previous work, we addressed this
issue through a direct imaging survey of B2--A0-type stars, and concluded that
<30% of such stars form and retain planets and brown dwarfs through disk
instability, leaving core accretion as the likely dominant mechanism. In this
paper, we extend this analysis to FGKM-type stars by applying a similar
analysis to the Gemini Deep Planet Survey (GDPS) sample. The results strengthen
the conclusion that substellar companions formed and retained around their
parent stars by disk instabilities are rare. Specifically, we find that the
frequency of such companions is <8% for FGKM-type stars under our most
conservative assumptions, for an outer disk radius of 300 AU, at 99%
confidence. Furthermore, we find that the frequency is always <10% at 99%
confidence independently of outer disk radius, for any radius from 5 to 500 AU.
We also simulate migration at a wide range of rates, and find that the
conclusions hold even if the companions move substantially after formation.
Hence, core accretion remains the likely dominant formation mechanism for the
total planet population, for every type of star from M-type through B-type.Comment: 10 pages, 4 figures, accepted for publication in Ap
Analysis of Neptune's 2017 Bright Equatorial Storm
We report the discovery of a large (8500 km diameter) infrared-bright
storm at Neptune's equator in June 2017. We tracked the storm over a period of
7 months with high-cadence infrared snapshot imaging, carried out on 14 nights
at the 10 meter Keck II telescope and 17 nights at the Shane 120 inch reflector
at Lick Observatory. The cloud feature was larger and more persistent than any
equatorial clouds seen before on Neptune, remaining intermittently active from
at least 10 June to 31 December 2017. Our Keck and Lick observations were
augmented by very high-cadence images from the amateur community, which
permitted the determination of accurate drift rates for the cloud feature. Its
zonal drift speed was variable from 10 June to at least 25 July, but remained a
constant m s from 30 September until at least 15
November. The pressure of the cloud top was determined from radiative transfer
calculations to be 0.3-0.6 bar; this value remained constant over the course of
the observations. Multiple cloud break-up events, in which a bright cloud band
wrapped around Neptune's equator, were observed over the course of our
observations. No "dark spot" vortices were seen near the equator in HST imaging
on 6 and 7 October. The size and pressure of the storm are consistent with
moist convection or a planetary-scale wave as the energy source of convective
upwelling, but more modeling is required to determine the driver of this
equatorial disturbance as well as the triggers for and dynamics of the observed
cloud break-up events.Comment: 42 pages, 14 figures, 6 tables; Accepted to Icaru
Bringing "The Moth" to Light: A Planet-Sculpting Scenario for the HD 61005 Debris Disk
The HD 61005 debris disk ("The Moth") stands out from the growing collection
of spatially resolved circumstellar disks by virtue of its unusual swept-back
morphology, brightness asymmetries, and dust ring offset. Despite several
suggestions for the physical mechanisms creating these features, no definitive
answer has been found. In this work, we demonstrate the plausibility of a
scenario in which the disk material is shaped dynamically by an eccentric,
inclined planet. We present new Keck NIRC2 scattered-light angular differential
imaging of the disk at 1.2-2.3 microns that further constrains its outer
morphology (projected separations of 27-135 AU). We also present complementary
Gemini Planet Imager 1.6 micron total intensity and polarized light detections
that probe down to projected separations less than 10 AU. To test our
planet-sculpting hypothesis, we employed secular perturbation theory to
construct parent body and dust distributions that informed scattered-light
models. We found that this method produced models with morphological and
photometric features similar to those seen in the data, supporting the premise
of a planet-perturbed disk. Briefly, our results indicate a disk parent body
population with a semimajor axis of 40-52 AU and an interior planet with an
eccentricity of at least 0.2. Many permutations of planet mass and semimajor
axis are allowed, ranging from an Earth mass at 35 AU to a Jupiter mass at 5
AU.Comment: Accepted to AJ; added Figure 5 and minor text edit
The Peculiar Debris Disk of HD 111520 as Resolved by the Gemini Planet Imager
Using the Gemini Planet Imager (GPI), we have resolved the circumstellar
debris disk around HD 111520 at a projected range of ~30-100 AU in both total
and polarized -band intensity. The disk is seen edge-on at a position angle
of ~165 along the spine of emission. A slight inclination or
asymmetric warping are covariant and alters the interpretation of the observed
disk emission. We employ 3 point spread function (PSF) subtraction methods to
reduce the stellar glare and instrumental artifacts to confirm that there is a
roughly 2:1 brightness asymmetry between the NW and SE extension. This specific
feature makes HD 111520 the most extreme examples of asymmetric debris disks
observed in scattered light among similar highly inclined systems, such as HD
15115 and HD 106906. We further identify a tentative localized brightness
enhancement and scale height enhancement associated with the disk at ~40 AU
away from the star on the SE extension. We also find that the fractional
polarization rises from 10 to 40% from 0.5" to 0.8" from the star. The
combination of large brightness asymmetry and symmetric polarization fraction
leads us to believe that an azimuthal dust density variation is causing the
observed asymmetry.Comment: 9 pages, 8 Figures, 1 table, Accepted to Ap
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