Probing Hadronic Structure with The Decay Δ→Nl+l−\Delta\rightarrow Nl^+l^-

We compute the branching ratio for $\Delta\rightarrow Ne^+e^-$ and $\Delta\rightarrow N\mu^+\mu^-$ in chiral perturbation theory and find that both decays should be observable at CEBAF. With sufficiently low thresholds on the $e^+e^-$ invariant mass a branching ratio of $\sim 10^{-5}$ may be observed for $\Delta\rightarrow Ne^+e^-$. For the $\Delta\rightarrow N\mu^+\mu^-$ decay mode we predict a branching ratio of $3\times 10^{-7}$. The dependence of the M1 and E2 amplitudes on the momentum transfer will provide a useful test of chiral perturbation theory which predicts $\sim 20\%$ variation over the allowed kinematic range.Comment: 6 pages, 3 figures, UCSD/PTH 93-06, QUSTH-93-02, Duke-TH-93-4

Production dynamics of some arctic Chironomus larvae

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110095/1/lno19822740728.pd

Effects of Crude Oil on Aquatic Insects of Tundra Ponds

Aquatic insects are numerous and important in the ecology of tundra thaw ponds, comprising most of the biomass and production. The most common types are the caddisflies Asynarchus and Micrasema, the stonefly Nemoura, the beetle Agabus and especially larvae of the fly family Chironomidae. Studies in vitro showed no detectable mortality of these insects at doses of oil up to 1.5 l/m² Prudhoe Bay crude oil. However, field experiments on two ponds with application rates of about 10 l/m² (Pond E, 1970) and 0.24 l/m² (Pond Omega, 1975) both indicated that selective elimination of Asynarchus and Nemoura had occurred. Chironomidae in Pond Omega displayed much lower rates of adult emergence in 1976 and 1977 than in 1975, immediately before and after oil treatment, with several species in the tribe Tanytarsini most reduced. Pond E did not show low emergence rates, but the proportion of Orthocladiinae was much higher than in reference ponds. Trichotanypus was severely reduced in Pond Omega but unusually abundant in Pond E in 1976 and 1977. Effects of oil seem to be different for different species, and occur at some point during the late larval stages of insects or at metamorphosis, but toxicity experiments did not confirm this. Oil may also interfere with reproduction in insect species which remain mainly on or near the pond surface as adults. Apparent effects in field experiments are not entirely consistent with observations of Canadian researchers. Nevertheless there were several similarities and both followed patterns like those observed in marine benthic communities, such as greater effects on shore fauna, greater effects of low-molecular-weight hydrocarbons, and species-specificity of effects. There is no indication of recovery of Nemoura, Asynarchus or Tanytarsini in Pond E seven years after the spill, but biomass and abundance of the other aquatic insects remains high. We recommend that clean-up measures avoid introducing solvents or dispersants, which might be toxic to insects in the pond

Growing-Season Temperature Change across Four Decades in an Arctic Tundra Pond

We examined temperature dynamics across a 42-year period in a low-centered tundra polygon pond on the Arctic Coastal Plain of northern Alaska to assess potential changes in thermal dynamics for ponds of this type. Using water temperature data from a pond near Barrow (now Utqiaġvik), Alaska, studied intensively during 1971 – 73 and again in 2007 – 12, we built an empirical model coupling historical air temperatures to measured pond temperatures for four summers. We then used the model to predict summer pond temperatures over a 42-year span, including 1974 – 2008, for which direct aquatic temperature records do not exist. Average pond temperatures during the growing season (1 May through 31 October) increased by 0.5˚C decade-1 or 2.2˚C over the 42-year period. Our simulations predicted the average date of spring thaw for the pond as 2 June (± 3 d), which did not change over the 42-year time period. However, average pond temperature during the first 30 days of the growing season increased from 1971 to 2012, suggesting that recently, ponds are warmer in early spring. The average date of pond sediment freeze over the 42 years shifted later by 15 days, from 28 September in 1971 to 13 October in 2012. These changes correspond to a growing season that has increased in length by 14 days, from 118 days in 1971 to 132 days in 2012. Contemporary temperature measurements in other shallow tundra ponds in northern Alaska show a high degree of temporal coherence (r = 0.93 – 0.99), which warrants the general conclusion that tundra ponds on Alaska’s Arctic Coastal Plain have undergone a significant change in thermal dynamics over the past four decades. Our results provide a means to incorporate these pond types into larger-scale simulations of Arctic climate change.Nous avons examiné la dynamique des températures sur une période de 42 ans dans un étang de polygone de toundra concave sur la plaine côtière arctique du nord de l’Alaska dans le but d’évaluer les changements potentiels sur le plan de la dynamique thermique des étangs de ce type. À l’aide des données de la température de l’eau provenant d’un étang situé près de Barrow (maintenant Utqiaġvik), en Alaska, étang ayant fait l’objet d’études intensives de 1971 à 1973 et de 2007 à 2012, nous avons construit un modèle empirique en couplant les températures de l’air historiques aux températures de quatre étés observées à l’étang. Ensuite, nous nous sommes servis de ce modèle pour prévoir les températures estivales de l’étang sur une période de 42 ans, incluant la période allant de 1974 à 2008, pour lesquelles il n’existe pas de données de températures aquatiques directes. Pendant la saison de croissance (du 1er mai au 31 octobre), les températures moyennes de l’étang ont augmenté de 0,5 ˚C par décennie-1 ou de 2,2 ˚C sur la période de 42 ans. Nos simulations ont permis de prévoir une date moyenne pour le dégel du printemps (± 3 j), ce qui n’a pas changé pendant la période de 42 ans. Cependant, la température moyenne de l’étang au cours des 30 premiers jours de la saison de croissance a augmenté entre 1971 et 2012, ce qui laisse entendre que depuis récemment, les étangs sont plus chauds au début du printemps. Sur la période de 42 ans, la date moyenne de gel des sédiments de l’étang a été retardée de 15 jours, passant ainsi du 28 septembre en 1971 au 13 octobre en 2012. Ces changements correspondent à une saison de croissance dont la durée a rallongé de 14 jours, passant de 118 jours en 1971 à 132 jours en 2012. Les mesures de températures contemporaines d’autres étangs de toundra peu profonds du nord de l’Alaska affichent un haut degré de cohérence temporelle (r = 0,93 – 0,99), ce qui permet de tirer la conclusion générale que les étangs de toundra de la plaine côtière arctique de l’Alaska ont connu un important changement sur le plan de la dynamique thermique au cours des quatre dernières décennies. Nos résultats permettent d’incorporer ces types d’étangs à des simulations à plus grande échelle du changement climatique de l’Arctique

Strong and Electromagnetic Decays of the Baryon Decuplet

We discuss the strong and radiative decays of the decuplet of baryon resonances to the baryon octet in chiral perturbation theory. We comment on the implications for the polarisability of the nucleon.Comment: 16 pages + 5 figures (.ps files) appended to file. Uses tables.tex and harvmac.te

A NASA/RAE cooperation in the development of a real-time knowledge-based autopilot

As part of a US/UK cooperative aeronautical research program, a joint activity between the NASA Dryden Flight Research Facility and the Royal Aerospace Establishment on knowledge-based systems was established. This joint activity is concerned with tools and techniques for the implementation and validation of real-time knowledge-based systems. The proposed next stage of this research is described, in which some of the problems of implementing and validating a knowledge-based autopilot for a generic high-performance aircraft are investigated