1,818 research outputs found
The snail-killing flies of Alaska (Diptera: Sciomyzidae)
Information is given on the geographic distribution, habitat preferences, larval foods, and immature stages for 57 species of 9 genera of Sciomyzidae known to occur in Alaska. An illustrated key to adults is included. Alaska as a habitat for sciomyzid flies is discussed, and information on feeding habits of the larvae is summarized
Economic Injury Level for Bermudagrass Stem Maggot (Diptera: Muscidae) in Bermudagrass Forage Production in Texas
The bermudagrass stem maggot, Atherigona reversura Villeneuve, was first reported damaging bermudagrass Cynodon dactylon (L.) Pers grown for forage in 2010 in the southeastern US. Damage results from individual larvae feeding internally on the vascular tissue just above the terminal node of the grass stem. Damage slows plant growth and reduces forage accumulation. To address the need for economic guidelines to manage this new pest, the relationship between the percent of stems damaged by bermudagrass stem maggot and forage yield was measured in commercial bermudagrass hay fields in northcentral Texas during 2016 and 2017. The slope of the linear regression, representing the yield loss per percent stem damage, was used to calculate economic injury levels for a range of hay market values and control costs. The impact of stem damage on protein content, energy and digestibility of bermudagrass hay was also investigated. In this study, percent ADF was positively correlated with bermudagrass stem damage, suggesting that stem damage was associated with increased fiber and reduced digestible energy. TDN was significantly and negatively correlated with increasing bermudagrass stem maggot damage. These results suggest a trend of declining crude protein and energy and an increase in fiber content associated with increasing bermudagrass stem maggot damage. This apparent loss of forage quality is consistent with the observed leaf death and cessation of new growth resulting from bermudagrass stem maggot feeding. However, the R2 value for the relationship between each of these forage quality attributes and stem damage was very low, ranging from 0.03-0.07, and therefor the impact of stem maggot feeding on forage quality remains unclear and additional studies are needed
XMM-Newton observations of HD189733 during planetary transits
We report on two XMM-Newton observations of the planetary host star HD189733.
The system has a close in planet and it can potentially affect the coronal
structure via interactions with the magnetosphere. We have obtained X-ray
spectra and light curves from EPIC and RGS on board XMM-Newton which we have
analyzed and interpreted. We reduced X-ray data from primary transit and
secondary eclipse occurred in April 17th 2007 and May 18th 2009, respectively.
In the April 2007 observation only variability due to weak flares is
recognized. In 2009 HD189733 exhibited a X-ray flux always larger than in the
2007 observation. The average flux in 2009 was higher than in 2007 observation
by a factor of 45%. During the 2009 secondary eclipse we observed a softening
of the X-ray spectrum significant at level of ~3 sigma. Further, we observed
the most intense flare recorded at either epochs. This flare occurred 3 ks
after the end of the eclipse.The flare decay shows several minor ignitions
perhaps linked to the main event and hinting for secondary loops that emit
triggered by the main loop. Magneto-Hydro-Dynamical (MHD) simulations show that
the magnetic interaction between planet and star enhances the density and the
magnetic field in a region comprised between the planet and the star because of
their relative orbital/rotation motion. X-ray observations and model
predictions are globally found in agreement, despite the quite simple MHD model
and the lack of precise estimate of parameters including the alignment and the
intensity of stellar and planetary magnetic fields. Future observations should
confirm or disprove this hypothesis, by determining whether flares are
systematically recurring in the light curve at the same planetary phase.Comment: Accepted for publication on The Astrophysical Journa
Infrared Eclipses of the Strongly Irradiated Planet WASP-33b, and Oscillations of its Host Star
We observe two secondary eclipses of the strongly irradiated transiting
planet WASP-33b in the Ks band, and one secondary eclipse each at 3.6- and 4.5
microns using Warm Spitzer. This planet orbits an A5V delta-Scuti star that is
known to exhibit low amplitude non-radial p-mode oscillations at about
0.1-percent semi-amplitude. We detect stellar oscillations in all of our
infrared eclipse data, and also in one night of observations at J-band out of
eclipse. The oscillation amplitude, in all infrared bands except Ks, is about
the same as in the optical. However, the stellar oscillations in Ks band have
about twice the amplitude as seen in the optical, possibly because the
Brackett-gamma line falls in this bandpass. We use our best-fit values for the
eclipse depth, as well as the 0.9 micron eclipse observed by Smith et al., to
explore possible states of the exoplanetary atmosphere, based on the method of
Madhusudhan and Seager. On this basis we find two possible states for the
atmospheric structure of WASP-33b. One possibility is a non-inverted
temperature structure in spite of the strong irradiance, but this model
requires an enhanced carbon abundance (C/O>1). The alternative model has solar
composition, but an inverted temperature structure. Spectroscopy of the planet
at secondary eclipse, using a spectral resolution that can resolve the water
vapor band structure, should be able to break the degeneracy between these very
different possible states of the exoplanetary atmosphere. However, both of
those model atmospheres absorb nearly all of the stellar irradiance with
minimal longitudinal re-distribution of energy, strengthening the hypothesis of
Cowan et al. that the most strongly irradiated planets circulate energy poorly.
Our measurement of the central phase of the eclipse yields e*cos(omega)=0.0003
+/-0.00013, which we regard as being consistent with a circular orbit.Comment: 23 pages, 9 figures, 3 tables, accepted for the Astrophysical Journa
Forward and Inverse Modeling of the Emission and Transmission Spectrum of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds
The Neptune-mass GJ 436b is one of the most-studied transiting exoplanets
with repeated measurements of both its thermal emission and transmission
spectra. We build on previous studies to answer outstanding questions about
this planet, including its potentially high metallicity and tidal heating of
its interior. We present new observations of GJ 436b's thermal emission at 3.6
and 4.5 micron, which reduce uncertainties in estimates of GJ 436b's flux at
those wavelengths and demonstrate consistency between Spitzer observations
spanning more than 7 years. We analyze the Spitzer thermal emission photometry
and Hubble WFC3 transmission spectrum in tandem. We use a powerful dual-pronged
modeling approach, comparing these data to both self-consistent and retrieval
models. We vary the metallicity, intrinsic luminosity from tidal heating,
disequilibrium chemistry, and heat redistribution. We also study the effect of
clouds and photochemical hazes on the spectra, but do not find strong evidence
for either. The self-consistent and retrieval modeling combine to suggest that
GJ 436b has a high atmospheric metallicity, with best fits at or above several
hundred times solar metallicity, tidal heating warming its interior with
best-fit intrinsic effective effective temperatures around 300--350 K, and
disequilibrium chemistry. High metal-enrichments (>600x solar) can only occur
from the accretion of rocky, rather than icy, material. Assuming Tint~300--350
K, we find that Q'~2x10^5--10^6, larger than Neptune's Q', and implying a long
tidal circularization timescale for the planet's orbit. We suggest that
Neptune-mass planets may be a more diverse class than previously imagined, with
metal-enhancements potentially spanning several orders of magnitude, to perhaps
over 1000x solar metallicity. High fidelity observations with instruments like
JWST will be critical for characterizing this diversity.Comment: 15 pages, 18 figures. Revised for publication in Ap
Rewriting Disciplines: STEM Students’ Longitudinal Approaches to Writing in (and across) the Disciplines
Drawing on three cases from a larger (N=169) longitudinal study of student writing development, this article shows how STEM students “rewrote” disciplines to suit their writerly purposes as they moved through their undergraduate years. Students made it clear that the institutional dimensions of disciplines, visible in administrative units or departments that control resources and records, remained visible in their mental landscapes, but they had a much more flexible view of the epistemological dimensions of disciplines. Rather than entering a field as novices aiming to emulate the writing of its experts, they drew on the intellectual resources of multiple disciplines in order to carry out their own projects. The goals and choices of these students suggest that the term new disciplinarity has implications for the ways WID is conceptualized. As theorized by Markovitch and Shinn (2011, 2012), new disciplinarity posits elasticity as a central feature of disciplines, calls the spaces between disciplines borderlands, and affirms the dynamic nature of projects and borderlands with the term temporality. As such, new disciplinarity offers terms and a theoretical framework that conceptualize the intellectual negotiations of students
Schubert complexes and degeneracy loci
Given a generic map between flagged vector bundles on a Cohen-Macaulay
variety, we construct maximal Cohen-Macaulay modules with linear resolutions
supported on the Schubert-type degeneracy loci. The linear resolution is
provided by the Schubert complex, which is the main tool introduced and studied
in this paper. These complexes extend the Schubert functors of Kra\'skiewicz
and Pragacz, and were motivated by the fact that Schur complexes resolve
maximal Cohen-Macaulay modules supported on determinantal varieties. The
resulting formula in K-theory provides a "linear approximation" of the
structure sheaf of the degeneracy locus, which can be used to recover a formula
due to Fulton.Comment: 23 pages, uses tabmac.sty; v2: corrected typos and added reference
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