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Notes: [Auszug] If we consider the interfacial curvature at a long plane vertical boundary in an infinite liquid, one of the principal radii of curvature is infinite and the problem is essentially two-dimensional. Thus, for equilibrium at the interface we have : where T is the interfacial tension, B the principal ...

Notes: [Auszug] High-power lasers that fit into a university-scale laboratory can now reach focused intensities of more than 1019 W cm-2 at high repetition rates. Such lasers are capable of producing beams of energetic electrons, protons and γ-rays. ...

Notes: Weed competition can decrease crop yield and profit. Herbicides are applied to reduce weed populations, minimize crop loss and maximize profit. Traditional practice is to apply herbicides at a uniform rate over an entire field. Complete knowledge of the weed distribution and appropriate instrumentation on the spraying equipment would allow the farm manager to apply the ‘correct’ locally varying herbicide application rate. The locally variable rate would be greater in areas of high weed density and less where there are few weeds. A locally varying treatment would have both economic and environmental advantages. A major challenge facing farm managers is the unavoidable uncertainty in the spatial distribution of weeds in any particular field. This uncertainty in weed distribution influences the optimal locally varying herbicide rate. A mathematical model is presented to calculate the optimal herbicide application rate using geostatistical models of uncertainty in weed density combined with principles from decision making. Weed data from a 34-ha field near Saskatoon, Saskatchewan, Canada, illustrate the application of these tools. Weed control was achieved with a significant reduction in total herbicide use.

Notes: The influence of herbicides on weed community dynamics is an issue of agroecological concern. A field study was initiated in 1986 with zero-, minimum-, and conventional-tillage systems. In 1989 and 1990, the fourth and fifth years of study, weed community diversity and relative composition were assessed prior to and following the application of post-emergence non-residual herbicides. Weed communities were assessed at the level of tillage system to balance the effect of different crop sequences and crop-herbicide combinations within each comparison. In general, herbicides did not reduce community diversity when compared by Shannon's H’and dominance-diversity curves. An increase in species richness and evenness, as assessed by Shannon's E and Margalef's DMG occurred in some cases. Differences in relative community composition among tillage systems were apparent before the application of herbicides, but disappeared following herbicide application. The use of herbicides in this study reduced weed densities, maintained weed diversity, and inhibited community changes that were due to changing tillage systems.

Notes: Diploid (2n = 18) and tetraploid (2n=36) cyto-types of Matricaria perforata Mérat have sepa rate geographic distributions in Canada. Since seeds are the only means of reproduction, a knowledge of the relationship between tempera ture and germination is important for an under standing of the potential spread of these two invasive cytotypes in Canada. Germination re sponse patterns of six diploid and four tetraploid populations were compared at constant and al ternating temperatures ranging from 0 to 45°C. Tests were performed on achenes collected from plants grown in a common garden for one gen eration at the location of one of the tetraploid sources. The general pattern of germination was similar for both cytotypes. The upper and lower limits for germination were 40°C and 5°C, respectively. Optimum germination occurred at alternating temperatures of 30/10°C. No primary dormancy was found. Although the general response pattern was similar and little variation existed among populations, germination did dif fer at suboptimal constant temperatures; tetraploid populations germinated 28 to 39% more than the diploids within the suboptimal range. These genetic differences may reflect adaptation to prolonged cold winters since the tetraploid populations were collected from more northern latitudes than the diploid populations. Effet de la température sur la germination de populations diploïdes et tétraploïdes de Matri-caria perforate Méret Les cytotypes diploïdes (2n = 18) et tétraploïdes (2n=36) de Matricaria perforata Mérat ont des distributions géographiques séparées. Comme les graines sont I'unique moyen de reproduction, la connaissance des relations entre température et germination est importante pour comprendre le potentiel d'expansion de ces deux cytotypes au Canada. La germination de six populations diploïdes el de qualre tétraploïdes a été com-parée a températures constantes et alternées comprises entre 0 et 45°C. Des essais ont été réalisés sur des akénes prélevés sur des plantes cultivées dans une même pépinière pendant une génération, sur le site d'une des sources de tétraploïdes. Les exigences de germination étaient similaires pour les deux cytotypes. Les limites supérieure et inférieure de germination étaient 40 et 5°C. L'optimum de germination était observé pour une alternance 30/10°C. Aucune dormance primaire n'a été trouvée. Bien que les exigences de germination étaient simi-laires et que peu de variations existaient à l'intérieur des populations, la germination dif-férait à des températures sub-optimales constan-tes. Les populations tétraploïdes germaient mieux (28 à 39%) que les diploïdes aux températures sub-optimales. Ces différences génétiques pourraient réfléter une adaptation aux hivers froids prolongés puisque les populations tétraploïdes étalent récoltées a des lattitudes plus septentrionales que les diploïdes. Wirkung der Temperatur auf die Keimung diploider itnd tetraploider Populationen von Matricaria perforata MératDiploide (2n=18) und tetraploide (2n=36) Populationen von Matricaria perforata Mérat haben in Kanada getrennte Verbreitungsge-biete. Da sich diese Art nur über Samen fortpflanzt, ist es wichtig, die Beziehung zwi-schen Temperatur und Keimung für dies beiden Cytotypen zu kennen, um die mögliche Ausbrei-tung abschätzen zu können. Das Keimungsver-halten bei konstanter und wechselnder Temperatur zwischen 45 und 5°C wurde bei 6 diploiden und 4 tetraploiden Populationen un-tersucht, wozu die Achänen von Pflanzen genommen wurden, die für eine Vegetationspe-riode in einem Garten am Standort einer der tetraploiden Herkunft angezogen worden waren. Beide Cytotypen verhielten sich ähnlich. Die Temperaturmaxima waren 40 und 5°C, das Optimum lag bei der wechselnden Temperatur von 30/10°C. Primäre Dormanz wurde nicht be-obachtet. Obwohl das Keimungsverhalten grundsätzlich ähnlich war und sich die Populationen wenig unterschieden, gab es bei der suboptimalen konstanten Temperatur Unter-schiede, indem dort Samen der tetraploiden Populationen 28 bis 39 % besser als die diploider keimten. In diesem Verhalten könnte sich eine Anpassung an längere kalte Winter wider-spiegeln, denn die tetraploiden Populationen stammten aus nördlicheren Gebieten als die diploiden.

Notes: Secondary seed dormancy has been linked to seedbank persistence of volunteer oilseed rape (Brassica napus) in western Canada. It has been suggested that there is a genetic component to secondary seed dormancy expression in oilseed rape, but little is known of its importance in relation to non-genetic factors. In a series of experiments we investigated the relative importance of genotype, seed size, time of windrowing and pre- and post-harvest environment on the expression of secondary seed dormancy. We found that genotype contributed between 44 and 82% to the total variation in secondary seed dormancy. A broad range in secondary seed dormancy expression was observed among 16 genotypes examined. Nevertheless, three-quarters of the genotypes investigated exhibited relatively high potential for the expression of secondary seed dormancy (back-transformed mean 71% dormant seeds). Seed size contributed 21% to the total variation, while the influence of seed maturity (harvest regime) on secondary seed dormancy expression was negligible. Despite diverging environmental conditions during the four growing seasons spanning these experiments, the influence of pre-harvest environment on seed dormancy expression was relatively small and ranged from 0.1% to 4.5%. Secondary seed dormancy potential decreased over time during seed storage. This decrease was greatest when seeds were stored at ambient temperatures and least when seeds were stored at −70°C.

Notes: Design and performance of a 100-cell seed germinator capable of simultaneously generating 100 different diurnal temperature cycles with extremes lying between 0 and 45°C is discussed. Each individual cell is equipped with a separate electronic temperature controller employing a thermistor for temperature sensing. The set temperature for each cell is determined by a precision reference resistor in the controller circuit. Six different reference resistors corresponding to six different temperatures are provided for each cell. The reference resistors are mounted on plug-in modules with one module for each cell. Heating or cooling of the individual cells is provided by thermoelectric heat pumps. Temperature cycling, which approximates a sine function, is achieved by switching the six reference resistors, one at a time, into the controller circuits at appropriate times during a 24h period. Each cell is designed to accept a standard 100 mm Petri dish to contain the seeds. The cells have glass covers to allow entry of light essential for germination of some species.The benefit of using this type of germinator to assess the germination response of Alyssum alyssoides L., Artemisia absinthium L., Euphorbia esula L. and Setaria viridis (L.) Beauv., is discussed. Three dimensional germination response surfaces are given for the four species.

Notes: Synchrotron-excited resonant-photoemission measurements at rare-earth 4d → 4f and transition-metal 3p → 3d thresholds have been carried out using a variety of complex cuprates and nickelates on stations 6.1 (grazing-incidence monochromator) and 6.2 (toroidal-grating monochromator) at the SRS CLRC Daresbury Laboratory. The systems studied are Nd2Ni1 − xCuxO4, La2 − xSrxNi1− yFeyO4 + δ and Bi2Sr2Ca1 − xYxCu2O8 + δ. A combination of EDC and constant-initial-state data is used to examine the 4f and 3d contributions to the valence-band density of states and their binding-energy positions relative to the Fermi energy. This allows the study of the valence states of the transition-metal ions and their modulation on doping. For La2 − xSrxNi1 − yFeyO4 + δ, this approach is used to infer a valence state of ≥ 3.0 for Fe. In the case of Bi2Sr2Ca1 − xYxCu2O8 + δ, the effect of Cu valence modulation on the 3p resonance is observed as x is varied. This is discussed in the light of controversy surrounding shifts in core-level photoemission with doping for this system.

Notes: [Auszug] In this communication the changes in creep behaviour brought about by pre-stressing a filled rubber (a conventional N-cyclohexyl benzthiazyl sulphenamide accelerated sulphur vulcanizate containing forty parts by weight of lamp carbon black per hundred parts of rubber) are briefly described. The ...