The development of multiwire drift chambers for high energy physics

An array comprising eight multiwire drift chambers has been developed and installed in the g-2 muon storage ring at CERN with the main objectives being to measure the circulating beam profile and the momenta of decay electrons. Constructional design features include narrow framework and an extremely thin curved end member, the latter having been converted into a sensitive drift space. Prototype models of the chambers have been used to select the operating parameters and to investigate the general properties and capabilities of such detectors. Argon(90%) and Methane(10%) has been chosen from several gas mixtures tested and has been used extensively throughout this work. Prototype and production. chambers have been operated in the e(^+) accelerator beam at the Daresbury Laboratory using a computerised data acquisition system and spatial resolutions of the order 100 to 150 µ/m have been recorded in magnetic fields up to 7.5 KGauss. This system has also enabled a qualitative study of certain simulated g-2 conditions.A simple model based on classical equations has been used to select an electric field, configuration, which enables good operation in a strong non-uniform magnetic field up to 14.75 KGauss, and to predict the behaviour of drifting electrons in such an environment. The operation of the chambers under experimental conditions has been studied, and initial results from the storage ring are discussed together with proposed future work

Paleoecology of an Interglacial Peat Deposit, Nuyakuk, Southwestern Alaska, U.S.A.

This paper reports the presence of interglacial beetle and pollen assemblages within a Pleistocene peat deposit exposed along the Nuyakuk River of southwestern Alaska. The fossil beetle assemblages contain a number of species not previously identified from eastern Beringian fossil assemblages. The Nuyakuk interglacial deposits are exposed within a 6-m-high terrace along the river, about 4 km beyond the moraine of the penultimate glaciation. Interglacial peat lies within the lowermost meter of the bluff and is overlain by fluvial gravel and loess. Insect fossils were extracted from five peat samples, yielding sixty-seven identified beetle taxa. The insect faunal diversity of the Nuyakuk assemblages is comparable to that found in regional Holocene peat samples. In contrast to assemblages of similar age from interior eastern Beringia, the Nuyakuk fauna contains significant numbers of aquatic, hygrophilous and riparian taxa. Four pollen samples from the Nuyakuk site were analyzed, providing spectra dominated by a few taxa, notably Alnus, Betula, Picea, Gramineae, Cyperaceae, Filicales, and Sphagnum, suggesting a rich alder-birch shrub tundra not much different from the modern regional vegetation. The pollen and insect fossil records also suggest climatic conditions similar to modern.On rapporte la présence d'assemblages de coléoptères et de grains de pollen interglaciaires à l'intérieur d'un dépôt de tourbe du Pleistocene, situé le long de la Nuyakuk River. Ces assemblages de coléoptères fossiles renferment un certain nombre d'espèces qui n'avaient pas été encore identifiées dans les assemblages fossiles de la Béringie orientale. Les dépôts interglaciaires de Nuyakuk, à l'intérieur d'une terrasse de 6 m de hauteur le long de la rivière, située à environ 4 km au-delà la moraine de l'avant-dernière glaciation. La tourbe interglaciaire se trouve dans le dernier mètre de l'escarpement et est recouverte d'un gravier fluviatile et d'un loess. Les insectes fossiles ont été extraits de cinq échantillons de tourbe qui ont livré 67 taxons identifiés de coléoptères. La diversité faunique des insectes des assemblages de Nuyakuk est comparable à celle que l'on trouve dans les assemblages de tourbe de l'Holocène. Contrairement aux autres assemblages de la Béringie orientale de la même époque, la faune de Nuyakuk comprend un grand nombre de taxons aquatiques, hygrophiles et ripariens. Les quatre échantillons polliniques du site de Nuyakuk analysés ont livré des spectres dominés par quelques taxons, dont Alnus, Betula, Picea, Gramineae, Cyperaceae, Filicales et Sphagnum, reflétant ainsi une toundra à bouleau nain et à aulne, semblable à la végétation actuelle de la région. Les données polliniques et sur les insectes fossiles indiquent également des conditions climatiques semblables à celles d'aujourd'hui.Dieser Artikel berichtet ùber interglaziale Kàfer- und Pollen-Vorkommen in einer Torfablagerung aus dem Pleistozàn entlang dem Nuyakuk-FluB im sùdwestlichen Alaska. Dièse Einheiten von Kâfer-Fossilen enthalten eine Anzahl von Arten, die zuvor nicht in Fossil-Einheiten von Ost-Bering identifiziert worden sind. Die interglazialen Ablagerungen von Nuyakuk sind innerhalb einer 6 m hohen Terrasse den FIuB entlang ausgesetzt, etwa 4 km ùber die Moràne der vorletzten Vereisung hinaus. Interglazialer Tort liegt im untersten Meter des Steilhangs und ist von FluBkies und LoB ùberlagert. Aus fùnf Torfproben wurden Insektenfossile entnommen, welche 67 identifizierte Kàfer-Taxa lieferten. Die Vielfalt der Insekten-Fauna der Nuyakuk-Einheiten ist mit der, die man in regionalen Torfproben aus dem Holozàn vorfindet, vergleichbar. Im Gegensatz zu Einheiten àhnlichen Alters vom Innern Ost-Berings enthâlt die Fauna von Nuyakuk eine bedeutende Zahl von Wasser, Feuchtigkeits-liebenden und Ufer-Taxa. Vier Pollen-Proben vom Nuyakuk-Platz wurden analysiert und lieferten durch wenige Taxa dominierte Spektren, vor allem Alnus, Betula, Picea, Gramineae, Cyperaceae, Filicales und Sphagnum, welche auf eine reiche Erlen-Birken-Buschtundra schlieBen lassen, die sich nicht sehr von der modemen regionalen Vegetation unterschied. Die Pollen- und Insektenfossil-Belege lassen auch klimatische Bedingungen vermuten, die den heutigen àhnlich waren

Ignition of thermally sensitive explosives between a contact surface and a shock

The dynamics of ignition between a contact surface and a shock wave is investigated using a one-step reaction model with Arrhenius kinetics. Both large activation energy asymptotics and high-resolution finite activation energy numerical simulations are employed. Emphasis is on comparing and contrasting the solutions with those of the ignition process between a piston and a shock, considered previously. The large activation energy asymptotic solutions are found to be qualitatively different from the piston driven shock case, in that thermal runaway first occurs ahead of the contact surface, and both forward and backward moving reaction waves emerge. These waves take the form of quasi-steady weak detonations that may later transition into strong detonation waves. For the finite activation energies considered in the numerical simulations, the results are qualitatively different to the asymptotic predictions in that no backward weak detonation wave forms, and there is only a weak dependence of the evolutionary events on the acoustic impedance of the contact surface. The above conclusions are relevant to gas phase equation of state models. However, when a large polytropic index more representative of condensed phase explosives is used, the large activation energy asymptotic and finite activation energy numerical results are found to be in quantitative agreement

Ancient and Modern Agriculture.

17 p

Late Quaternary Environments, Denali National Park and Preserve, Alaska

Late Quaternary pollen, plant macrofossils, and insect fossils were studied from sites along three rivers in the foothills north of the Alaska Range in Denali National Park and Preserve. The aim was to carry out a reconnaissance of late Quaternary organic sediments in the region, emphasizing the mid-Wisconsin, or Boutellier interstadial interval. Samples of probable early-to mid-Boutellier age (ca. 60 000 to 40 000 B.P.) from Unit 2 at the Toklat High Bluffs site indicate open boreal woodland with dense alder shrub vegetation. Organic Unit 1 at the Foraker River Slump site indicates open taiga with shrubs of probable Boutellier age. Fossil evidence from the youngest horizon in this unit indicates graminoid tundra environments, marking the transition from interstadial to late Wisconsin glacial environments. Early Holocene samples from the Foraker exposures suggest birch shrub tundra; coniferous forest apparently became established only after 6500 B.P. Local variations in forest composition at the Foraker and Sushana sites were probably the result of disturbances, such as fire.Les grains de pollen et les pièces macrofossiles de plantes et d'insectes, caractérisant le quaternaire tardif, ont été étudiés dans des sites localisés le long de trois rivières coulant à proximité du versant nord de l'Alaska Range, dans le parc national et la réserve Denali. Cette étude porte essentiellement sur les sédiments organiques de la région, plus particulièrement ceux caractérisant l'intervalle interstadiaire Boutellier (milieu de la période du Wisconsin). Les échantillons récoltés dans l'unité numéro deux du site Toklat High Bluffs et datant probablement du début ou du milieu de l'intervalle Boutellier (60 000 à 40 000 BP) témoignent de la présence d'une forêt boréale ouverte avec couvert arbustif dense composé essentiellement d'aulnes. Les macrorestes et le pollen de l'unité organique numéro un du site Foraker River Slump témoignent, pour leur part, de la présence d'une taïga ouverte parsemée d'arbustes. Selon toute vraisemblance, cette taïga daterait de l'intervalle Boutellier. Les macrorestes et le pollen contenus dans l'horizon le plus jeune de cette unité indiquent que le paysage était constitué d'une toundra herbacée, marquant ainsi une transition entre la végétation caractérisant l'interstade Boutellier et celle de la fin de la période wisconsinienne. Les échantillons datant du début de la période holocène du site Foraker suggèrent la présence d'une toundra arbustive composée surtout de bouleaux. La forêt coniférienne ne se serait établie qu'après 6500 BP. Les différences observées au niveau de la composition forestière des sites Foraker et Sushana résultent probablement de l'impact de perturbations, tel le feu

Microstructural and compositional analysis of strontium-doped lead zirconate titanate thin films on gold-coated silicon substrates

This article discusses the results of transmission electron microscopy (TEM)-based characterization of strontium-doped lead zirconate titanate (PSZT) thin films. The thin films were deposited by radio frequency magnetron sputtering at 300°C on gold-coated silicon substrates, which used a 15 nm titanium adhesion layer between the 150 nm thick gold film and (100) silicon. The TEM analysis was carried out using a combination of high-resolution imaging, energy filtered imaging, energy dispersive X-ray (EDX) analysis, and hollow cone illumination. At the interface between the PSZT films and gold, an amorphous silicon-rich layer (about 4 nm thick) was observed, with the film composition remaining uniform otherwise. The films were found to be polycrystalline with a columnar structure perpendicular to the substrate. Interdiffusion between the bottom metal layers and silicon was observed and was confirmed using secondary ion mass spectrometry. This occurs due to the temperature of deposition (300°C) being close to the eutectic point of gold and silicon (363°C). The diffused regions in silicon were composed primarily of gold (analyzed by EDX) and were bounded by (111) silicon planes, highlighted by the triangular diffused regions observed in the two-dimensional TEM image

Techniques for the realization of ultra- reliable spaceborne computer Final report

Bibliography and new techniques for use of error correction and redundancy to improve reliability of spaceborne computer

Biodegradation of phenoxyacetic acid in soil by Pseudomonas putida PP0301(pR0103), a constitutive degrader of 2, 4–dichlorophenoxyacetate

The efficacy of using genetically engineered microbes (GEMs) to degrade recalcitrant environmental toxicants was demonstrated by the application of Pseudomonas putida PP0301(pR0103) to an Oregon agricultural soil amended with 500 u.g/g of a model xenobiotic, phenoxyacetic acid (PAA). P. putida PP0301(pR0103) is a constitutive degrader of 2, 4–dichlorophenoxyacetate (2, 4–D) and is also active on the non–inducing substrate, PAA. PAA is the parental compound of 2, 4–dichlorophenoxyacetic acid (2, 4–D) and whilst the indigenous soil microbiota degraded 500 ng/g 2, 4–D to less than 10 J–g/g, PAA degradation was insignificant during a 40–day period. No significant degradation of PAA occurred in soil inoculated with the parental strain P. putida PP0301 or the inducible 2, 4–D degrader P. putida PP0301(pR0101). Moreover, co–amendment of soil with 2, 4–D and PAA induced the microbiota to degrade 2, 4–D; PAA was not degraded. P. putida PP0301–(pR0103) mineralized 500–Μg/g PAA to trace levels within 13 days and relieved phytotoxicity of PAA to Raphanus sativus (radish) seeds with 100% germination in the presence of the GEM and 7% germination in its absence. In unamended soil, survival of the plasmid–free parental strain P. putida PP0301 was similar to the survival of the GEM strain P. putida PP0301(pR0103). However, in PAA amended soil, survival of the parent strain was over 10 000–fold lower (< 3 colony forming units per gram of soil) than survival of the GEM strain after 39 days.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75471/1/j.1365-294X.1992.tb00160.x.pd