1,432 research outputs found
Implications of the WTO Agreement on Sanitary and Phytosanitary Measures
International Relations/Trade,
Biological Control of Alfalfa Blotch Leafminer (Diptera: Agromyzidae) in Ontario: Status and Ecology of Parasitoids (Hymenoptera: Braconidae, Eulophidae) 20 Years After Introduction
Two European parasitoid species were released in Ontario during the late 1970\u27s to control the alfalfa blotch leafminer, Agromyza frontella (Rondani) (Diptera: Agromyzidae). One of these, Dacnusa dryas (Nixon) (Hymenoptera: Braconidae), rapidly became established and the other, Chrysocharis liriomyzae (= C. punctifacies) (Delucchi) (Hymenoptera: Eulophidae) was never recovered in Ontario. In 1999, we found both D. dryas and C. liriomyzae parasitizing first-generation A. frontella in Ontario in 1999. The combined parasitism rate for both species as revealed by larval dissections was 97.5% by the end of the first A. frontella generation. Of the adult parasitoids reared, 86% were D. dryas and 14% were C. liriomyzae. Most parasitized larvae contained a single unencapsulated (i.e., healthy) larva, along with one or more encapsulated eggs. No larvae were encapsulated, but the overall egg encapsulation rate was 47%. By the end of the first A. frontella generation, 86% of parasitized hosts contained at least one unencapsulated parasitoid and could therefore produce an adult parasitoid, and 12% of parasitized hosts escaped parasitism by containing only encapsulated parasitoids. The sex ratio of D. dryas was even at emergence, but strongly female-biased in sweep samples from the field. Egg loads of D. dryas females were all greater than zero and as high in the field as our highest laboratory estimates, suggesting that egg availability does not limit fitness under the conditions that we observed in the field
Zonal flow scaling in rapidly-rotating compressible convection
The surface winds of Jupiter and Saturn are primarily zonal. Each planet
exhibits strong prograde equatorial flow flanked by multiple alternating zonal
winds at higher latitudes. The depth to which these flows penetrate has long
been debated and is still an unsolved problem. Previous rotating convection
models that obtained multiple high latitude zonal jets comparable to those on
the giant planets assumed an incompressible (Boussinesq) fluid, which is
unrealistic for gas giant planets. Later models of compressible rotating
convection obtained only few high latitude jets which were not amenable to
scaling analysis.
Here we present 3-D numerical simulations of compressible convection in
rapidly-rotating spherical shells. To explore the formation and scaling of
high-latitude zonal jets, we consider models with a strong radial density
variation and a range of Ekman numbers, while maintaining a zonal flow Rossby
number characteristic of Saturn.
All of our simulations show a strong prograde equatorial jet outside the
tangent cylinder. At low Ekman numbers several alternating jets form in each
hemisphere inside the tangent cylinder. To analyse jet scaling of our numerical
models and of Jupiter and Saturn, we extend Rhines scaling based on a
topographic -parameter, which was previously applied to an
incompressible fluid in a spherical shell, to compressible fluids. The
jet-widths predicted by this modified Rhines length are found to be in
relatively good agreement with our numerical model results and with cloud
tracking observations of Jupiter and Saturn.Comment: 17 pages, 12 figures, 3 tables, accepted for publication in PEP
Effects of a radially varying electrical conductivity on 3D numerical dynamos
The transition from liquid metal to silicate rock in the cores of the
terrestrial planets is likely to be accompanied by a gradient in the
composition of the outer core liquid. The electrical conductivity of a volatile
enriched liquid alloy can be substantially lower than a light-element-depleted
fluid found close to the inner core boundary. In this paper, we investigate the
effect of radially variable electrical conductivity on planetary dynamo action
using an electrical conductivity that decreases exponentially as a function of
radius. We find that numerical solutions with continuous, radially outward
decreasing electrical conductivity profiles result in strongly modified flow
and magnetic field dynamics, compared to solutions with homogeneous electrical
conductivity. The force balances at the top of the simulated fluid determine
the overall character of the flow. The relationship between Coriolis and
Lorentz forces near the outer boundary controls the flow and magnetic field
intensity and morphology of the system. Our results imply that a low
conductivity layer near the top of Mercury's liquid outer core is consistent
with its weak magnetic field.Comment: 30 pages, 11 figures, 2 tables. To be published in Physics of Earth
and Planetary Interiors (PEPI)
THE POLITICAL ECONOMY OF THE URUGUAY ROUND NEGOTIATIONS: A VIEW FROM GENEVA
International Relations/Trade,
Explaining Jupiter's magnetic field and equatorial jet dynamics
Spacecraft data reveal a very Earth-like Jovian magnetic field. This is
surprising since numerical simulations have shown that the vastly different
interiors of terrestrial and gas planets can strongly affect the internal
dynamo process. Here we present the first numerical dynamo that manages to
match the structure and strength of the observed magnetic field by embracing
the newest models for Jupiter's interior. Simulated dynamo action primarily
occurs in the deep high electrical conductivity region while zonal flows are
dynamically constrained to a strong equatorial jet in the outer envelope of low
conductivity. Our model reproduces the structure and strength of the observed
global magnetic field and predicts that secondary dynamo action associated to
the equatorial jet produces banded magnetic features likely observable by the
Juno mission. Secular variation in our model scales to about 2000 nT per year
and should also be observable during the one year nominal mission duration.Comment: 7 pages, 4 figures, accepted for publication in Geophysical Research
Letter
Characteristic scales of earthquake rupture from numerical models
International audienceNumerical models of earthquake rupture are used to investigate characteristic length scales and size distributions of repeated earthquakes on vertical, planar fault segments. The models are based on exact solutions of static three-dimensional (3-D) elasticity. Dynamical rupture is approximated by allowing the static stress field to expand from slip motions at a single velocity. To show how the vertical fault width affects earthquake size distributions for a broad range of fault behaviors, two different fault strength models are used; a smooth model and a heterogeneous asperity model. The smooth model is a simplified version of the Dieterich-Ruina rate and state dependent friction law. The heterogeneous asperity model uses a slip-dependent random powerlaw strength distribution. It is shown that the characteristic scale of fault segmentation is proportional to the vertical width of a seismogenic fault. This conclusion holds for both the smooth and the heterogeneous models. For the smooth models characteristic quake distributions result, with populations of large events that are obviously distinct from smaller events. The distributions of large events have well-defined mean lengths and moments. The heterogeneous models result in Gutenberg-Richter (GR) powerlaw distributions of event sizes up to a characteristic quake size. Quakes larger than the characteristic size fall off the GR distribution such that the powerlaw would greatly overestimate the probability of occurrence of the larger events
Delinquency, Depression, Religiosity, and Social Support in the Prediction of Substance Use: Findings from ADD Health
Delinquency, depression, religiosity, and social support have been demonstrated to relate to substance use in adolescence. We examined relations between these factors and substance use (cigarette use, marijuana use, frequency of intoxication using alcohol, and lifetime substance use) using the National Study of Adolescent to Adult Health (ADD Health), a large-scale nationally representative epidemiological study (N = 6504). Our results suggested that: 1) in simple correlations, delinquency and depression appeared to be related to higher levels of all forms of substance use, whereas religiosity and social support appeared to be inversely related with all forms of substance use, 2) in multiple and logistic regression analysis, delinquency remained a predictor of all forms of substance use, 3) depression predicted cigarette use and marijuana use but did not predict frequency of intoxication or lifetime substance use, 4) religiosity predicted lower levels of all forms of substance use, and 5) social support predicted less frequency of substance use but did not predict lifetime use. Results suggest that delinquency and depression may be risk factors for youth substance use, and that religiosity and social support may be associated with decreased risk for substance use. In addition, our analyses suggest that some of these relations may be confounded by other factors or combinations of factors
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