904 research outputs found
Predation on stink bugs (Hemiptera: Pentatomidae) in cotton and soybean agroecosystems
Stink bugs (Hemiptera: Pentatomidae) are significant pests of cotton and soybeans in the southeastern United States with annual control costs exceeding $14 million in these crops. Three of the most prominent stink bug pests are the southern green (Nezara viridula), brown (Euschistus servus) and green (Chinavia hilaris) stink bugs. To determine trophic linkages between generalist arthropod predators and these pests, species-specific 16S molecular markers were designed and used to detect the presence of prey DNA in predator gut-contents. Over 2700 predators were collected over two growing seasons in cotton and soybean in southern Georgia in 2011 and 2012 and screened for stink bug DNA. Trophic linkages were analyzed relative to prey availability, crop type and field location. The frequency of stink bug DNA in predator guts was negligible on E. servus (0.23%) and C. hilaris (0.09%). Overall gut content detection of N. viridula was 3.3% and Geocoris sp. (Hemiptera: Geocoridae), Orius sp. (Hemiptera: Anthocoridae) and Notoxus monodon (Coleoptera: Anthicidae) were the primary predators. This contrasts with previous studies that reported a much more diverse suite of predators consuming stink bugs with much higher frequency of gut-content positives. The discrepancy between studies highlights the need for replicating studies in space and time, especially if the goal is to implement effective and durable conservation biological control in integrated pest management
X-ray Spectral Properties of Low-Mass X-ray Binaries in Nearby Galaxies
We investigated the X-ray spectral properties of a collection of low-mass
X-ray binaries (LMXBs) within a sample of 15 nearby early-type galaxies
observed with Chandra. We find that the spectrum of the sum of the sources in a
given galaxy is remarkably similar from galaxy to galaxy when only sources with
X-ray luminosities less than 10^39 ergs/s (0.3-10 keV) are considered. Fitting
these lower luminosity sources in all galaxies simultaneously yielded a
best-fit power law exponent of Gamma = 1.56 +/- 0.02 (or kT_brem = 7.3 +/- 0.3
keV). This is the tightest constraint to date on the spectral properties of
LMXBs in external galaxies. There is no apparent difference in the spectral
properties of LMXBs that reside inside and outside globular clusters. We
demonstrate how the uniformity of the spectral properties of LMXBs can lead to
more accurate determinations of the temperature and metallicity of the hot gas
in galaxies. Although few in number in any given galaxy, sources with
luminosities of 1-2 x 10^39 ergs/s are present in 10 of the galaxies. The
spectra of these luminous sources are softer than the spectra of the rest of
the sources, and are consistent with the spectra of Galactic black hole X-ray
binary candidates when they are in their very high state. The spectra of these
sources are very different than those of ultraluminous X-ray sources (ULXs)
found within spiral galaxies, suggesting that the two populations of X-ray
luminous objects have different formation mechanisms. The number of sources
with apparent luminosities above 2 x 10^39 ergs/s is equal to the number of
expected background AGN and thus appear to not be associated with the galaxy,
indicating that very luminous sources are absent or very rare in early-type
galaxies. (Abridged)Comment: 11 pages in emulateapj5 style with 4 embedded Postscript figures; to
be accepted by Ap
Leeway for the loyal: a model of employee discretion
This article examines the factors underlying task discretion from an economist's perspective. It argues that the key axis for understanding discretion is the trade-off between the positive effects of discretion on potential output per employee and the negative effects of greater leeway on work effort. In empirical analysis using matched employer-employee data, it is shown that discretion is strongly affected by the level of employee commitment. In addition, discretion is generally greater in high-skilled jobs, although not without exceptions, and lower where employees are under-skilled. Homeworking and flexitime policies raise employee discretion. The impact of teamworking is mixed. In about half of cases team members do not jointly decide about work matters, and the net effect of teams on task discretion in these cases is negative. In other cases, where team members do decide matters jointly, the impact is found to be neutral according to employees' perceptions, or positive according to managers' perceptions. There are also significant and substantial unobserved establishment-level factors which affect task discretion
Exile Vol. XXXI No. 1
Drawing by Chris Bradley 1
How Goes the Wombat, Prithee by Jennie Benford 3
Holy Shit (for Mary) by Stephanie Athey 4-5
..... blues by Britton R. Creelman 6
Photograph (anonymous) 7
Prose by Leigh Walton 9-12
San Jacinto by Petersen S. Thomas 13
Rebuttal by Betsy Oster 15
Running Alone by Ann Townsend McMullen 16
Windows in Florence by Michael Parr 17
Rangers by Caroline Palmer 19
Salamapo by Mary Deborah Clark 20-21
Funeral by J. K. Rand 22
Deeds Give No Title by Douglas Jones 23
Be Careful, There\u27s a Straight Bar Next Door by Karen J. Hall 25
The Rivers of Saigon by Alex Dickson 26
2 Sketches by Alfred Sturla Bodvarsson 27
Upon the Occasion of Reading 236 sonnets at One Sitting by Jeff Masten 28
I just believe in Me by Rob Jackson 29
Close by Stephanie Athey 31
Teller by Katherine Fox Reynolds 32
Woman in Greece by Michael Parr 33
Part of the Job by Joan DeWitt 35-44
Contributor Notes 46
Editorial decision is shared equally among the seven member editorial board. -title page
Polymorphous: Cover Lithograph by Aimee Creelman - title pag
Monitoring and Pay: An Experiment on Employee Performance under Endogenous Supervision
We present an experimental test of a shirking model where monitoring intensity is endogenous and effort a continuous variable. Wage level, monitoring intensity and consequently the desired enforceable effort level are jointly determined by the maximization problem of the firm. As a result, monitoring and pay should be complements. In our experiment, between and within treatment variation is qualitatively in line with the normative predictions of
the model under standard assumptions. Yet, we also find evidence for reciprocal behavior. Our data analysis shows, however, that it does not pay for the employer to solely rely on the reciprocity of employees
Risk factors for delay in symptomatic presentation: a survey of cancer patients
Background: Delay in symptomatic presentation leading to advanced stage at diagnosis may contribute to poor cancer survival. To inform public health approaches to promoting early symptomatic presentation, we aimed to identify risk factors for delay in presentation across several cancers.
Methods: We surveyed 2371 patients with 15 cancers about nature and duration of symptoms using a postal questionnaire. We calculated relative risks for delay in presentation (time from symptom onset to first presentation >3 months) by cancer, symptoms leading to diagnosis and reasons for putting off going to the doctor, controlling for age, sex and deprivation group.
Results: Among 1999 cancer patients reporting symptoms, 21% delayed presentation for >3 months. Delay was associated with greater socioeconomic deprivation but not age or sex. Patients with prostate (44%) and rectal cancer (37%) were most likely to delay and patients with breast cancer least likely to delay (8%). Urinary difficulties, change of bowel habit, systemic symptoms (fatigue, weight loss and loss of appetite) and skin symptoms were all common and associated with delay. Overall, patients with bleeding symptoms were no more likely to delay presentation than patients who did not have bleeding symptoms. However, within the group of patients with bleeding symptoms, there were significant differences in risk of delay by source of bleeding: 35% of patients with rectal bleeding delayed presentation, but only 9% of patients with urinary bleeding. A lump was a common symptom but not associated with delay in presentation. Twenty-eight percent had not recognised their symptoms as serious and this was associated with a doubling in risk of delay. Embarrassment, worry about what the doctor might find, being too busy to go to the doctor and worry about wasting the doctor’s time were also strong risk factors for delay, but were much less commonly reported (<6%).
Interpretation: Approaches to promote early presentation should aim to increase awareness of the significance of cancer symptoms and should be designed to work for people of the lowest socioeconomic status. In particular, awareness that rectal bleeding is a possible symptom of cancer should be raised
Increasing Dominance - the Role of Advertising, Pricing and Product Design
Despite the empirical relevance of advertising strategies in concentrated markets, the economics literature is largely silent on the effect of persuasive advertising
strategies on pricing, market structure and increasing (or decreasing) dominance. In a simple model of persuasive advertising and pricing with differentiated goods,
we analyze the interdependencies between ex-ante asymmetries in consumer appeal, advertising and prices. Products with larger initial appeal to consumers will
be advertised more heavily but priced at a higher level - that is, advertising and price discounts are strategic substitutes for products with asymmetric initial appeal.
We find that the escalating effect of advertising dominates the moderating effect of pricing so that post-competition market shares are more asymmetric than pre-competition differences in consumer appeal. We further find that collusive advertising (but competitive pricing) generates the same market outcomes, and that network effects lead to even more extreme market outcomes, both directly and via
the effect on advertising
The dark haloes of early-type galaxies in low-density environments: XMM-Newton and Chandra observations of NGC 57, NGC 7796 and IC 1531
We present analysis of Chandra and XMM-Newton observations of three
early-type galaxies, NGC 57, NGC 7796 and IC 1531. All three are found in very
low density environments, and appear to have no neighbours of comparable size.
NGC 57 has a halo of kT~0.9 keV, solar metallicity gas, while NGC 7796 and IC
1531 both have ~0.55 keV, 0.5-0.6 Zsol haloes. IC 1531 has a relatively compact
halo, and we consider it likely that gas has been removed from the system by
the effects of AGN heating. For NGC 57 and NGC 7796 we estimate mass, entropy
and cooling time profiles and find that NGC 57 has a fairly massive dark halo
with a mass-to-light ratio of 44.7 (4.0,-8.5) Msol/Lsol (1 sigma uncertainties)
at 4.75 Re. This is very similar to the mass-to-light ratio found for NGC 4555
and confirms that isolated ellipticals can possess sizable dark matter haloes.
We find a significantly lower mass-to-light ratio for NGC 7796, 10.6
(+2.5,-2.3) Msol/Lsol at 5 Re, and discuss the possibility that NGC 7796 hosts
a galactic wind, causing us to underestimate its mass.Comment: 14 pages, 9 figures, accepted for publication in MNRA
Testing for Complementarity: Glyphosate Tolerant Soybeans and Conservation Tillage
Many decisions in agriculture are made over combinations of inputs and/or practices that may form a technology system linked through complementarity. The presence of complementarity among producer decisions can have far-reaching implications for market outcomes and for the effectiveness of policies intended to influence them. Identifying complementarity relations, however, is made difficult by the presence of unobserved heterogeneity. Drawing on recent methodological advances, in this paper we develop a test for complementarity between glyphosate tolerant soybeans and conservation tillage that overcomes certain limitations of previous studies. Specifically, we develop a structural discrete choice framework of joint soybean-tillage adoption that explicitly models both complementarity and the correlation induced by unobserved heterogeneity. The model is estimated with a large unbalanced panel of farm-level choices spanning the 1998–2011 period. We find that glyphosate tolerant soybeans and conservation tillage are complementary practices. In addition, our estimation shows that farm operation scale promotes the adoption of both conservation tillage and glyphosate tolerant seed, and that all of higher fuel prices, more droughty conditions, and soil erodibility increase use of conservation tillage. We apply our results to simulate annual adoption rates for both conservation tillage and no-tillage in a scenario without glyphosate tolerant soybeans available as a choice. We find that the adoption of conservation tillage and no-tillage have been about 10% and 20% higher, respectively, due to the advent of glyphosate tolerant soybeans
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