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

Lagrangian coherent structures in n-dimensional systems

Numerical simulations and experimental observations reveal that unsteady fluid systems can be divided into regions of qualitatively different dynamics. The key to understanding transport and stirring is to identify the dynamic boundaries between these almost-invariant regions. Recently, ridges in finite-time Lyapunov exponent fields have been used to define such hyperbolic, almost material, Lagrangian coherent structures in two-dimensional systems. The objective of this paper is to develop and apply a similar theory in higher dimensional spaces. While the separatrix nature of these structures is their most important property, a necessary condition is their almost material nature. This property is addressed in this paper. These results are applied to a model of Rayleigh-Bénard convection based on a three-dimensional extension of the model of Solomon and Gollub

Frictional dynamics of viscoelastic solids driven on a rough surface

We study the effect of viscoelastic dynamics on the frictional properties of a (mean field) spring-block system pulled on a rough surface by an external drive. When the drive moves at constant velocity V, two dynamical regimes are observed: at fast driving, above a critical threshold Vc, the system slides at the drive velocity and displays a friction force with velocity weakening. Below Vc the steady sliding becomes unstable and a stick-slip regime sets in. In the slide-hold-slide driving protocol, a peak of the friction force appears after the hold time and its amplitude increases with the hold duration. These observations are consistent with the frictional force encoded phenomenologically in the rate-and-state equations. Our model gives a microscopical basis for such macroscopic description.Comment: 10 figures, 7 pages, +4 pages of appendi

Particle streak velocity field measurements in a two-dimensional mixing layer

Using digital image processing of particle streak photography, the streamwise and perpendicular components of the velocity field were investigated, in the mid‐span plane of a two‐dimensional mixing layer, with a 6:1 velocity ratio. The Reynolds number of the flow, based on the local vorticity thickness and the velocity difference across the layer, ranged from 1360 to 2520, in the plane of observation. The significant result of this experiment was that the region of vorticity bearing fluid is confined to a small fraction of the flow. A second finding, consistent with the small regions of concentrated vorticity, was the observation of instantaneous streamwise velocity reversal, in the laboratory frame, in small regions of the flow

Cosmic Neutron Star Merger Rate and Gravitational Waves constrained by the R Process Nucleosynthesis

The cosmic evolution of the neutron star merger (NSM) rate can be deduced from the observed cosmic star formation rate. This allows to estimate the rate expected in the horizon of the gravitational wave detectors advanced Virgo and ad LIGO and to compare those rates with independent predictions. In this context, the rapid neutron capture process, or r process, can be used as a constraint assuming NSM is the main astrophysical site for this nucleosynthetic process. We compute the early cosmic evolution of a typical r process element, Europium. Eu yields from NSM are taken from recent nucleosynthesis calculations. The same approach allows to compute the cosmic rate of Core Collapse SuperNovae (CCSN) and the associated evolution of Eu. We find that the bulk of Eu observations at high iron abundance can be rather well fitted by either CCSN or NSM scenarios. However, at lower metallicity, the early Eu cosmic evolution favors NSM as the main astrophysical site for the r process. A comparison between our calculations and spectroscopic observations at very low metallicities allows to constrain the coalescence timescale in the NSM scenario to about 0.1 to 0.2 Gyr. These values are in agreement with the coalescence timescales of some observed binary pulsars. Finally, the cosmic evolution of Eu is used to put constraints on the NSM rate, the merger rate in the horizon of the gravitational wave detectors advanced Virgo/ad LIGO, as well as the expected rate of electromagnetic counterparts to mergers (kilonovae) in large near-infrared surveys.Comment: accepted in MNRAS, 19 page

A model of commodity money, with applications to Gresham's Law and the debasement puzzle

We develop a model of commodity money and use it to analyze the following two questions motivated by issues in monetary history: What are the conditions under which Gresham's Law holds? And, what are the mechanics of a debasement (lowering the metallic content of coins)? The model contains light and heavy coins, imperfect information, and prices determined via bilateral bargaining. There are equilibria with neither, both, or only one type of coin in circulation. When both circulate, coins may trade by weight or by tale. We discuss the extent to which Gresham's Law holds in the various cases. Following a debasement, the quantity of reminting depends on the incentives oÃered by the sovereign. Equilibria exist with positive seigniorage and a mixture of old and new coins in circulation.Money ; Money theory ; Gresham's law

A model of commodity money, with applications to Gresham's law and the debasement puzzle

We develop a model of commodity money and use it to analyze the following two questions motivated by issues in monetary history: What are the conditions under which Gresham's Law holds? And, what are the mechanics of a debasement (lowering the metallic content of coins)? The model contains light and heavy coins, imperfect information, and prices determined via bilateral bargaining. There are equilibria with neither, both, or only one type of coin in circulation. When both circulate, coins may trade by weight or by tale. We discuss the extent to which Gresham's Law holds in the various cases. Following a debasement, the quantity of reminting depends on the incentives offered by the sovereign. Equilibria exist with positive seigniorage and a mixture of old and new coins in circulation.Coinage ; Gresham's law

Design of a simulation environment for laboratory management by robot organizations

This paper describes the basic concepts needed for a simulation environment capable of supporting the design of robot organizations for managing chemical, or similar, laboratories on the planned U.S. Space Station. The environment should facilitate a thorough study of the problems to be encountered in assigning the responsibility of managing a non-life-critical, but mission valuable, process to an organized group of robots. In the first phase of the work, we seek to employ the simulation environment to develop robot cognitive systems and strategies for effective multi-robot management of chemical experiments. Later phases will explore human-robot interaction and development of robot autonomy