ALBERT

Notes: With the increasingly widespread employment of charge-coupled devices as detectors, there is much interest in methods of processing the data which they produce. Taking the reflection grating spectrometer instrument on the European Space Agency's recently launched X-ray MultiMirror Mission spacecraft as an example, some novel techniques for removing unwanted data are explored. Entirely independent of compression techniques which may be employed elsewhere in the same system, deletion of unwanted data as close as possible to the source can be desirable to save subsequent processor time, or communications bandwidth—both quantities that are typically in short supply in the spacecraft case. This article sets out the general case for choosing to remove unwanted pixel data close to the source, considers the implications of this on the overall quantity of data, and then examines some methods for reducing the data volume. © 2000 American Institute of Physics.

Notes: The persistence and movement of residues of alachlor, alrazine and metribuzin were measured in a mini-lysimeter system in the field. This comprised a number of soil columns (11 cm diametert; 30 cm long), and permitted the vertical distribution of residues to be determined at. intervals alter application and the collection and analysis of leaehale water. Laboratory experiments were also performed to determine the degradation rates of the three herbicides and their strengths of adsorption by the test soil. The results showed an order of degradation rate of metribuzin〉 alachlor〉atrazine and an order of adsorption of alacblor〉atrazine〉melribuzin. Movement of residues in the soil columns and concentrations in the leachate were inversely related to the strength of adsorption. Parameters derived from the laboratory data were used in conjunction with weather data for the period of the field experiment in three mathematical models of pesticide leaching: VARLEACH, LEACHP and PRZM2. In most instances, the models gave acceptable predictions of the distribution of residues in soil. This was particularly so for the less mobile compound alachlor. With the most mobile compound, metribuzin, residues were not well predicted at the later sampling dates. All three models gave accurate predictions of the volumes of drainage water, but none of them predicted the concentrations of herbicide in the leachate, presumably because they do not take account of preferential flow pathways of water and solute in the soil.

Notes: In field experiments to investigate the effect of repeated application of eight herbicides on their persistence in the soil, the rates of loss of metribuzin, metolachlor and isoproturon were shown to be unaffected by up to three previous doses of the same herbicide. With linuron, there was a small but significant enhancement of biodegradation by two or more previous applications. The persistence of monolinuron, propyzamide and metamitron was shorter in plots that had been treated once, twice or three times previously than in plots treated for the first time, but the effects were often small. In the case of napropamide, rates of loss were considerably increased by a single previous dose.In laboratory experiments with soil from the field plots, there was again no evidence of enhanced biodegradation of metribuzin, metolachlor or isoproturon. However, the rate of linuron degradation was enhanced by a single application. This effect was most marked after 12 weeks, but had disappeared by 57 weeks after initial treatment of the soil in the field. Considerable enhancement of monolinuron, propyzamide and metamitron degradation rates was also observed. The effects were again most pronounced after 12 weeks; however, with these compounds, they were still apparent more than 1 year later. Enhancement of napropamide biodegradation was most stable when assessed in laboratory incubations; the effects from a single pretreatment were still apparent more than 12 months later. Etudes complementaires de la degradation accélerée de certains herbicides appliques au sol Dans des essais de plein champ conduits pour etudier 1'influence d'applications répetées de 8 herbicides sur leur persistance dans le sol, les taux de perte de métribuzine, métolachlor et isoproturon n'ont pas été affectés jusqu'à 3 applications précédentes du même herbicide. Avec le linuron, il y a eu une faible mais significative augmentation de la dégradation aprés 2 ou 3 applications. La persistance du monolinuron, de la propyzamide et de la métamitrone éiait plus courte dans les parcelles déjà traitées une, deux ou trois fois que dans celles traitées pour la premiére fois, mais les effets étaient souvent faibles. Avec la napropromide, les taux ont été considérablement accrus aprés une seule application.Dans des essais de laboratoire avec du sol venant des parcelles de plein champ, il n'y a pas eu de nouveau d'accélération de la biodégradation pour la métribuzine, le métolachlor ou 1'isoproturon. Cependant, la dégradation du linuron a été renforcée par une seule application. Cet effet a été plus fort qu'aprés 12 semaines, mais a disparu 57 semaines aprés le traitement du sol au champ. Un accroissement important de la dégradation du monolinuron, de la propyzamide et de la métamitrone a étéégalement observéLes effets étaient de nouveau maxima aprés 12 semaines; cependant avec ces produits, ils étaient encore apparent une année plus tard. L'accé1ération de la biodégradation de la napropromide était la plus stable dans les observations de laboratoire; les effets d'une seule application étaient encore apparents plus de 12 mois plus tard. Weitere Untersuchungen zum beschleunigten Abbau von Bodenherbiziden In Feldversuchen zur Persistenz von 8 Herbiziden bei wiederholter Ausbringung ging bei Metribuzin, Metolachlor und Isoproturon nach 3-maliger Ausbringung desselben Herbizids die Verlustrate nicht zurück. Bei Linuron war der mikrobielle Abbau nach 2 oder mehr Vorbehandlungen nur leicht, aber signifikant erhöht. Die Persistenz von Monolinuron, Propyzamid und Metamitron war bei l-, 2- oder 3-maliger Vorbehandlung geringer als bei erstmaliger Behandlung, doch waren die Wirkungen oft klein. Bei Napropamid erhöhte sich die Verlustrate bereits nach einer Vorbehandlung beträchtlich. Auch in Laborversuchen mit Böden aus den Freilandparzellen konnte bei Metribuzin, Metolachlor und Isoproturon kein verstärkter mikrobieller Abbau nachgewiesen werden. Bei Linuron dagegen erhöhte sich die Abbaurate schon nach einmaliger Applikation. Diese Wirkung war nach 12 Wochen am deutlichsten ausgeprägt, verschwand jedoch nach 57 Wochen nach dem Behandlungstermin. Eine erheblich größere Abbaurate wurde auch bei Monolinuron, Propyzamid und Metamitron beobachtet, am deutlichsten nach 12 Wochen, aber auch noch nach mehr als l Jahr. Bei Napropamid war die Verstärkung der Biodegradation im Labor am bestRaUndigsten; die Wirkungen einmaliger Vorbehandlungen bestanden noch nach mehr als 1 Jahr.