ALBERT

Notes: Abstract Simulated white noise analysis experiments on a simple integrate-and-fire neuron model with adaptation yields Wiener kernels comparable to those found for a crayfish stretch receptor neuron, for low modulation depths (linear range). At high modulation depths (nonlinear range), this model corresponds well to the neuron only if the “membrane potential” variable is constrained to positive values. An alternative kind of neural model considered is one in which spike initiation processes are ignored, and instead a time-continuous spike frequency variable is used. Such an analytic differential equation model can be represented by a half-wave rectifier with low-pass feedback; simulated white noise analysis of this model shows good correspondence with the stretch receptor, except at the higher frequencies approaching the cell's carrier frequency. The analytic system model is amenable to mathematical analysis using linear and nonlinear systems theory, resulting in equations which relate features of Wiener kernels (peaks, undershoots, time constants, etc.) to previously described features of neurons (threshold, pacemaker sensitivity, adaptation or post-inhibitory rebound).

Notes: Departments

Notes: The development and use of an improved automatic system for the accurate measurement of dissolved organic carbon (D.O.C.) in fresh waters is described. The method, which covers the range 0-25 mgl−1 D.O.C., is based on the oxidation of organic carbon to carbon dioxide by U.V. radiation. The carbon dioxide produced is measured by a non dispersive infra-red gas analyser (I.R.G.A.). The I.R.G.A. is also used in the semi-automatic measurement of particulate organic carbon (P.O.C.) by a combustion method which allows very low concentrations to be measured using samples of 200 ml or less.Results of surveys of two river systems indicate that D.O.C. concentrations of less than 2.0 mg l−1 are typical in unpolluted chalk streams. D.O.C. concentrations of streams draining acid heathland were found to be significantly higher (3-5.5 mg l−1).D.O.C. concentration was found to increase rapidly during a spate, in a river draining areas of mixed underlying geology. The throughput of D.O.C. during the twenty-five to fifty spates which occur annually in the river could amount to 20-30% of the annual flux of D.O.C.P.O.C. concentration in chalk spring waters (0.03–0.04 mg l−1) were found to be higher than expected from preliminary estimates using membrane filtration techniques.The relevance of the measurement of D.O.C. and P.O.C. flux to estimates of the energy budgets of stream ecosystems is discussed and published methods for the automatic measurement of D.O.C. are reviewed.

Notes: Light-trap catches of five tortricid species were recorded at orchard sites in Kent over an 11-year period. The dates on which moths of Hedya nubiferana (Haw.), Cydia pomonella (L.) and Archips podana (Scop.) were caught in light traps were strongly correlated with accumulated temperatures in day-degrees above a base of 8°C. The correlation was less good for catches of Pandemis heparana (Denis & Schiff.) and it was slightly better for those of Cydia pomonella above 10°C than above 8°C. The data were insufficient to calculate temperature sums for catches of Adoxophyes orana (Fisch. v. Rösl.). Moth catches of all five species showed differences between years in the timing of first and second generations. The dates of first catches are compared with dates estimated from the following temperature sums: for H. nubiferana 226 day-degrees above 8°C, for C. pomonella 268 day-degrees above 8°C and 149 day-degrees above 10°C, for Archips podana 326 day-degrees above 8°C and for P. heparana 386 day-degrees above 8°C. In the 11-year period, estimated dates of first catch were within ± 5 days of first actual catch of moths in light traps in nine years for C. pomonella, eight years for H. nubiferana and A. podana, but only five years for P. heparana.

Notes: The effectiveness of 122 herbicides in inhibiting growth of buds from single-node sections of couch (Agropyron repens (L.) Beauv.) rhizomes was evaluated under glasshouse conditions. Treatments were made by planting twenty-five couch rhizome segments in washed silica sand and watering them with nutrient solution containing from 10−2 to 10−8 M concentrations of the herbicides. Final evaluations were made 21 days after planting. At 10−5 M or lower concentrations, nineteen herbicides inhibited couch bud growth to less than 5 % of that in the untreated cultures. This concentration is approximately 0–28 kg/ha calculated on a 15-cm plough-slice basis. Herbicide groups showing the greatest inhibition of quackgrass rhizomes were the anilides and amides, carba-mates, and toluidines. Overall, pronamide (3,5-dichloro-N-(1,1-dimethylpropynyl)-benzamide) demonstrated the greatest activity. Many of the herbicides shown to be effective in this study do not generally control quackgrass under field conditions. Their lower activity in the field may be due to excessive decomposition, soil-herbicide interactions, or lack of rhizome exposure to the herbicides. Some herbicides which provide couch control under field conditions were not effective in this study. The reduced effectiveness of these chemicals under the conditions tested probably occurred because the herbicides were active only when applied post-emergence, because the primary action mechanisms were on processes other than bud development, or because the observation period was too short to detect complete results.Influence des herbicides sur le developpement des bourgeons du chiendentL'activité inhibitrice de la croissance des bourgeons de fragments de rhizomes de chiendent (Agropyron repens (L.) Beauv.) comportant un seul noeud, a étéévaluée en serre pour 122 herbicides. Les traitements ont été effectués en plantant 25 fragments de rhizome de chiendent dans un sable de silice Iavé et en leur apportant une solution nutritive contenant les herbicides k des concentrations allant de 10−2à 10−8 M. Les évaluations finales ont été faites 21 jours aprés la plantation. A la concentration a 10−5 M ou a des concentrations plus faibles, dix-neuf herbicides inhibérent la croissance des bourgeons de chiendent jusqu'a moins de 5 % de celle des cultures non traitées. Cette concentration correspond approximativement k un traitement à 0,28 kg/ha calculé sur la base d'un labour à 15 cm. Les groupes d'her-bicides manifestant la plus forte inhibition des rhizomes de chiendent furent les anilides, les amides, les carbamates et les toluidines. Le plus actif fut la pronamide (3,5-dichloro-N-(1,1-dimothylpropynil)-benzamide). Beaucoup des herbicides qui se montrerent efficaces dans cette étude ne l'etaient pas contre le chiendent au champ. Leur activité plus faible au champ peut été due k une decomposition excessive, k des interactions sol-herbicide, ou au défaut de contact entre les rhizomes et les herbicides. Quelques herbicides qui s'avfirent efficaces au champ contre le chiendent ne l'ont pas été dans cet essai. La réduction d'efficacité des produits dans les conditions de essaisest probablement manifest Se en raison du fait que les herbicides furent actifs seulement en traitements de post-levée, parce que les mocanismes d'action primaire s'exerecérent sur des processus autres que le développement des bourgeons, ou parce que la période d'observation fut trop courte pour detecter des résultats complets.Einfluss von Herbiziden auf die Knospenenlwicklung bei der QueckeEs wurde die Wirkung von 122 Herbiziden auf die Hemmung des Knospenwachstums von Rhizomabschnitten der Quecke (Agropyron repens (L.) Beauv.) mit jeweils einem Nodium, unter Gewachshausbedingungen untersucht. Die Behand-lungen wurden folgendermassendurchgefuhrt: 25 Abschnitte von Queckenrhizomen wurden in gewaschenen Quarzsand gepfianzt und mit Nahrlosung gegossen, die Herbizid in 10−2 bis 10−8 M Konzentration enthielt. Die endgultige Aus-wertungerfolgte 21 Tage nach dem Pflanzen. Bei 10−5 M oder niedrigeren Konzentrationen hemmten 19 Herbizide das Wachstum der Queckenknospen um weniger als 5% im Vergleich zu Unbehandelt. Diese Konzentration entspricht etwa einer Aufwandmenge von 028 kg/ha bezogen auf 15 cm Pfiugtiefe. Die grossteHemmwirkung gegenuber den Queckenrhizomen zeigten die Herbizide aus der Gruppe der Anilide, Amide, Carbamate und Toluidine. Insgesamt wies Pronamid (3,5-Dichlor-N-(1,1-dimethylpropinyl)-benzamid) die grosste Aktivitat auf. Viele der Herbizide, die unter den Versuchs-bedingungen wirksam waren, bekSaAmpfen die Quecke im Freiland gewöhnlich nicht. Die geringere Wirksamkeit dieser Herbizide im Freiland kann auf ubermessigen Abbau, auf Boden-Herbizide-Wechselbeziehungen oder auf fehlenden Kontakt des Rhizoms mit dem Herbizid zuruckzufuhren sein. Andererseits waren einige Herbizide, die eine Be-kampfung der Quecke unter Freilandbedingungen gewähr-leisten, in diesem Versuch nicht wirksam. Die verringerte Wirksamkeit diser Verbindungen unter den hier herrschenden Bedingungen, kann darauf zuruckgefuhrt werden, dass die Herbizide nur wirksam sind, wenn sie im Nachauflauf eingesetzt werden weil die primaren Wirkungsmechanismen an andere Prozesse als die Knospenentwicklung gebunden sind, Oder weil der Beobachtungszeitraum zu kurz war, um zu einer endgultigen Aussage zu gelangen.

Notes: [Auszug] The crude pitch, for example, asphalt, is first refined by distillation and pitch fibres melt-spun onto spools. The fibres are then subjected to controlled oxidation and carbonization (to 1,000 C) similarly to methods previously used3. The resulting carbon fibres (representing a weight yield in ...