Inventaire des mauvaises herbes dans les pépinières ornementales du Québec

Un inventaire des mauvaises herbes réalisé au cours de l'été 1986 a permis de visiter 53% des superficies en production ornementale au Québec. Les infestations de mauvaises herbes étaient maintenues à de faibles niveaux dans les pépinières visitées grâce aux sarclages manuels et aux hersages mécaniques fréquents. L'inventaire a révélé que les mauvaises herbes vivaces étaient les plus difficiles à réprimer dans les pépinières. Les mauvaises herbes vivaces les plus fréquemment rencontrées étaient la vesce jargeau (Vicia cracca), le chiendent (Agropyron repens), la prèle des champs (Equisetum arvense) et le souchet comestible (Cyperus esculentus). Les mauvaises herbes identifiées dans les pépinières étaient, pour la plupart, des espèces communes à d'autres cultures. Toutefois, la rorippe d'Islande (Rorippa islandica), la rorippe sylvestre (Rorippa sylvestris) et la cardamine de Pennsylvanie (Cardamine pensylvanica), mauvaises herbes moins connues, ont démontré un fort potentiel d'envahissement dans les pépinières ornementales.A weed survey of fields in ornamental production was conducted in Quebec in 1986 during which 53 % of the production sites were visited. Because of the intensity of hand-weeding and mechanical cultivation used in the fields, no major weed infestations were observed. Weeds most difficult to control were mainly perennial species such as tufted vetch (Vicia cracca), quackgrass (Agropyron repens), field horsetail (Equisetum arvense), and yellow nutsedge (Cyperus esculentus). Most of the weeds identified were species common to other crops. However, marsh yellow cress (Rorippa islandica), yellow field cress (Rorippa sylvestris), and bitter cress (Cardaminepensylvanica) were lesser known weed species that showed a great potential of increase in ornamental nursery production

Facteurs impliqués dans la levée des mauvaises herbes au champ

La levée des mauvaises herbes au champ est le résultat du bris de la dormance des graines, de leur germination et de la croissance du germe jusqu'à la surface du sol. Une revue de ces conditions et des facteurs qui les influencent fait l'objet de cette étude. Des levées importantes à certaines périodes de Tannée démontrent que les graines enfouies dans le sol sont, au cours de ces périodes, dans un état physiologique favorable à leur germination. Cependant, les semences ne sont pas toujours aptes à germer et passent par des états d'inhibition: dormance ou quiescence. Plusieurs facteurs environnementaux et souvent une combinaison de ceux-ci peuvent déclencher la germination. Les trois principaux facteurs qui ont été identifiés comme ayant des répercussions majeures sur la germination des graines sont la température, l'humidité et la lumière. Comme la levée est issue de la germination, il est souvent difficile de dissocier les facteurs qui régissent chacune d'elles. En effet, dès que la graine a germé, le processus de levée débute. La levée est aussi affectée par les conditions environnant la croissance du germe, et ce, jusqu'à ce qu'il atteigne la surface du sol. En climat tempéré, au printemps, la levée est principalement modulée par la température, l'eau et l'état physique du sol. Le sol constitue une barrière physique que le germe doit franchir pour atteindre la surface du sol. La croûte qui se forme parfois à la surface du sol peut être aussi une entrave à la levée. L'état de dormance des graines et les conditions climatiques requises pour la germination et la levée diffèrent d'une espèce à l'autre, compliquant ainsi les généralisations qui pourraient être faites du patron d'émergence des mauvaises herbes dans un champ.Weed emergence in the field results from breaking of seed dormancy, seed germination and growth of the seedling to the soil surface. This work reviews the factors that affect these mechanisms. Flushes of weed emergence during certain time periods demonstrate that buried seeds are in a physiological state favorable to germination. However, seeds are not always able to germinate as they may be dormant or quiescent. Several environmental factors or their combination can initiate germination. The three main factors that have been identified as being the most important for seed germination are temperature, moisture, and light. Since emergence is closely tied to germination, it is often difficult to separate the factors affecting each process. Weed emergence is initiated as soon as the seed germinates. Emergence is also influenced by factors affecting seedling growth until it reaches the soil surface. In temperate regions, in the spring, weed emergence is mainly affected by temperature, water and soil physical state. In order to reach the soil surface, the weed seedling must pass through a soil layer which constitutes a physical barrier. Soil crust can also be an obstacle to weed emergence. Seed dormancy and the environmental conditions required for germination and growth vary from species to species and complicate any generalisations that could be made concerning the pattern of emergence of weeds in a given field

Lexomic Tools and Methods for Textual Analysis: Providing Deep Access to Digitized Texts

This project hybridizes traditional humanistic approaches to textual scholarship, such as source study and the analysis of style, with advanced computational and statistical comparative methods, allowing scholars "deep access" to digitized texts and textual corpora. Our multi-disciplinary collaboration enables us to discover patterns in (and between) texts previously invisible to traditional methods. Going forward, we will build on the success of our previous Digital Humanities Start-up Grant by further developing tools and documentation (in an open, on-line community) for applying advanced statistical methodologies to textual and literary problems. At the same time we will demonstrate the value of the approach by applying the tools and methods to texts from a variety of languages and time periods, including Old English, medieval Latin, and Modern English works from the twentieth-century Harlem Renaissance

Off-Diagonal Elements of the DeWitt Expansion from the Quantum Mechanical Path Integral

The DeWitt expansion of the matrix element M_{xy} = \left\langle x \right| \exp -[\case{1}{2} (p-A)^2 + V]t \left| y \right\rangle, $(p=-i\partial)$ in powers of $t$ can be made in a number of ways. For $x=y$ (the case of interest when doing one-loop calculations) numerous approaches have been employed to determine this expansion to very high order; when $x \neq y$ (relevant for doing calculations beyond one-loop) there appear to be but two examples of performing the DeWitt expansion. In this paper we compute the off-diagonal elements of the DeWitt expansion coefficients using the Fock-Schwinger gauge. Our technique is based on representing $M_{xy}$ by a quantum mechanical path integral. We also generalize our method to the case of curved space, allowing us to determine the DeWitt expansion of \tilde M_{xy} = \langle x| \exp \case{1}{2} [\case{1}{\sqrt {g}} (\partial_\mu - i A_\mu)g^{\mu\nu}{\sqrt{g}}(\partial_\nu - i A_\nu) ] t| y \rangle by use of normal coordinates. By comparison with results for the DeWitt expansion of this matrix element obtained by the iterative solution of the diffusion equation, the relative merit of different approaches to the representation of $\tilde M_{xy}$ as a quantum mechanical path integral can be assessed. Furthermore, the exact dependence of $\tilde M_{xy}$ on some geometric scalars can be determined. In two appendices, we discuss boundary effects in the one-dimensional quantum mechanical path integral, and the curved space generalization of the Fock-Schwinger gauge.Comment: 16pp, REVTeX. One additional appendix concerning end-point effects for finite proper-time intervals; inclusion of these effects seem to make our results consistent with those from explicit heat-kernel method

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics

Zinc Single Crystal Deformation Experiments using a "6 Degrees of Freedom" Apparatus

A new experimental technique to study crystallographic slip system activity in metallic single crystals deformed under a condition of uniaxial stress is applied to study the behavior of Zn single crystals. The experimental apparatus allows essentially unconstrained shape change of inherently anisotropic materials under a condition of uniaxial stress by allowing 3 translational and 3 rotational degrees of freedom during compression; hence we have named the experiment 6 degrees of freedom (6DOF). The experiments also utilize a 3-D digital image correlation system to measure full-field displacement fields, which are used to calculate strain and make direct observations of slip system activity. We show that the experimental results associated with a pristine zinc single crystal are precisely consistent with the theoretical predicted shape change (sample distortion) assuming that the most favored slip system on the basal plane is the only one that is active. Another experiment was performed on a processed and annealed Zn single crystal to investigate slip that is inconsistent with the critical resolved shear stress (CRSS) theory. These experiments on zinc illustrate the ability of the 6DOF experiment, together with image correlation (IC) data, to measure slip system activity with a high degree of fidelity

The <i>Ectocarpus</i> genome and the independent evolution of multicellularity in brown algae

Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related1. These seaweeds are the dominant species in rocky coastal ecosystems and they exhibit many interesting adaptations to these, often harsh, environments. Brown algae are also one of only a small number of eukaryotic lineages that have evolved complex multicellularity (Fig. 1).We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae, closely related to the kelps (Fig. 1). Genome features such as the presence of an extended set of light-harvesting and pigment biosynthesis genes and new metabolic processes such as halide metabolism help explain the ability of this organism to cope with the highly variable tidal environment. The evolution of multicellularity in this lineage is correlated with the presence of a rich array of signal transduction genes. Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic2 approaches to explore these and other aspects of brown algal biology further