The AMANDA Neutrino Telescope

With an effective telescope area of order $10^4$ m$^2$ for TeV neutrinos, a threshold near $\sim$50 GeV and a pointing accuracy of 2.5 degrees per muon track, the AMANDA detector represents the first of a new generation of high energy neutrino telescopes, reaching a scale envisaged over 25 years ago. We describe early results on the calibration of natural deep ice as a particle detector as well as on AMANDA's performance as a neutrino telescope.Comment: 12 pages, Latex2.09, uses espcrc2.sty and epsf.sty, 13 postscript files included. Talk presented at the 18th International Conference on Neutrino Physics and Astrophysics (Neutrino 98), Takayama, Japan, June 199

Search for Supernova Neutrino-Bursts with the AMANDA Detector

The core collapse of a massive star in the Milky Way will produce a neutrino burst, intense enough to be detected by existing underground detectors. The AMANDA neutrino telescope located deep in the South Pole ice can detect MeV neutrinos by a collective rate increase in all photo-multipliers on top of dark noise. The main source of light comes from positrons produced in the CC-reaction of anti-electron neutrinos on free protons \antinue + p \to e^+ + n. This paper describes the first supernova search performed on the full sets of data taken during 1997 and 1998 (215 days of live time) with 302 of the detector's optical modules. No candidate events resulted from this search. The performance of the detector is calculated, yielding a 70% coverage of the Galaxy with one background fake per year with 90% efficiency for the detector configuration under study. An upper limit at the 90% c.l. on the rate of stellar collapses in the Milky Way is derived, yielding 4.3 events per year. A trigger algorithm is presented and its performance estimated. Possible improvements of the detector hardware are reviewed.Comment: 20 pages, 14 figures. Submitted to Astroparticle Physic

The Cosmic Positron Fraction: Implications of a New Measurement

The first balloon flight of the HEAT instrument in 1994 yielded results on the cosmic ray positron fraction with good statistical and systematic accuracy over the range 4.5-50 GeV. These results do not confirm the distinct increase in the positron fraction above 10 GeV that was reported in several other experiments. This seems to rule out a number of models that were proposed to explain the apparent positron excess. In the context of the leaky box model, we conclude from our data that at most 2-3% of the total electron flux (e + + e \Gamma ) arriving near Earth could consist of positrons from primary sources. 1 Introduction Electrons and positrons are distinguished from the nuclear cosmic rays by their low mass and the absence of hadronic interactions. Therefore, at high energies their propagation through the galaxy becomes dominated by radiative energy losses. Different mechanisms may also contribute to the sources of these particles, but are difficult to identify on the basis o..

Influência da cobertura morta no comportamento dos herbicidas imazaquin e clomazone The influence of straw mulch on the behaviour of the residual herbicides imazaquin and clomazone

Experimentos de campo e bioensaios em casa-de-vegetação foram realizados para se estudar a influência da cobertura morta de trigo (Triticum aestivum L.) no comportamento dos herbicidas imazaquin {ácido 2-[4,5 dihidro-4-metil-4-(1-metiletil)-5-oxo-1H-imidazol-2-ilo]-3-quinolinacarboxílico} e clomazone {2-[(2-clorofenil)metil]-4,4-dimetil-3-isoxazolidinona}, aplicados em pré-emergência na cultura da soja [Glycine max (L.) Merril], no sistema de plantio direto. O clomazone mostrou evidências de ter sido interceptado pela cobertura morta. A presença da cobertura morta não influiu na retenção do imazaquin, sendo este lixiviado da palha para o solo com as chuvas que ocorreram após a aplicação.<br>Field experiments and glass house bioassays were conducted to determine the influence of winter wheat (Triticum aestivum L.) straw mulch on the behaviour of the herbicides imazaquin {2-[4,5-dihydro-4-methyl-4-(1-ethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} and clomazone {2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3- isoxazolidinone}, wich had been applied to pre-emergence soybean (Glycine max)in a no-till system. There was evidence that clomazone had been intecepted by the straw whilst imazaquin was leached into the soil by rain

Monte Carlo Calculations of Atmospheric Electrons Compared with Data from HEAT

The GEANT/FLUKA detector simulation and particle interaction package was used to develop a Monte Carlo program to estimate atmospheric secondary flux produced by primary cosmic rays, as a function of depth in the atmosphere. Of special interest is the calculation of secondary electrons and positrons near the top of the atmosphere. The HEAT instrument measured primary and secondary electrons ranging in energy from 500 MeV to 50 GeV during a high altitude balloon flight during May, 1994 from Ft. Sumner, New Mexico. It is assumed that electrons with rigidities below geomagnetic cutoff consist of both secondary and reentrant albedo electrons. The MC calculations are compared to the flux of secondary electrons as measured by the HEAT instrument. 1 Introduction Despite better measurements of primary cosmic ray spectra and interaction cross sections during the last 30 years, calculations of atmospheric secondaries still differ by as much as a factor of two. In order to correct for atmospheri..

Influência da cobertura morta no comportamento do herbicida atrazine Influence of the mulch on the behavior of atrazine

A cobertura morta, oriunda da dessecação ou rolagem de plantas utilizadas para esta finalidade, faz parte do sistema de semeadura direta. Ao mesmo tempo que essa cobertura promove redução na densidade populacional das espécies invasoras, intercepta os herbicidas quando aplicados sobre sua superfície. Alguns autores têm sugerido aumentar as doses dos herbicidas, o que tem gerado polêmica sobre o assunto. Com o objetivo de estudar o comportamento do herbicida atrazine sobre cobertura morta, realizaram-se experimento de campo, bioensaios e análises cromatográficas de resíduos com esse herbicida, nas doses 0,0; 1,25; 2,50; 3,75 e 5,00 kg/ha do ingrediente ativo, aplicando-o em solo descoberto e sobre cobertura morta de palha de aveia preta, com 4,5 e 9,0 t/ha. Amostras de solo de 0 a 10 cm de profundidade foram coletadas após a aplicação, antes e depois de uma irrigação de 20 mm para uso em bioensaios e análises cromatográficas de resíduo. A irrigação foi realizada 24 horas após a aplicação do herbicida. Os resultados mostraram que, nas amostras de solo coletadas antes da irrigação, 85% de cada dose foi interceptada nos dois tratamentos com cobertura morta. A irrigação de 20 mm foi suficiente para lixiviar praticamente todo o herbicida da palha para o solo, não havendo diferença significativa com os teores encontrados em solo descoberto. A cobertura morta reduziu a população de Brachiaria plantaginea, única espécie presente no experimento, para 20 e 5 plantas/m2, respectivamente, nas coberturas com 4,5 e 9,0 t/ha de matéria seca, enquanto que em solo descoberto, a população da espécie foi de 700 plantas/m2. Os controles obtidos com as doses de 1,25 kg/ha, nas duas quantidades de palha estudadas, foram superiores ao controle obtido com a dose de 5,00 kg/ha em solo descoberto, indicando que a cobertura morta, por sí só, exerce bom controle de B. plantaginea. A ocorrência de chuva após a aplicação de atrazine na palha, melhora sua eficiência de controle.<br>The plant residues are the main part of the no-till system. These covers reduce density of weed population, but intercept herbicides when applied on its surface. Some people suggest to increase the rate to compensate herbicide losses. Field experiment, bioassays and chromatographic analysis were made using atrazine at the rates zero, 1,25; 2,5; 3,75 and 5,0 kg/ha a.i. on 4.500 and 9.000 kg/ha of oat residues and soil without mulch. Soil samples were collected immediately after atrazine application. Twenty-four hours after atrazine application the field was irrigated with 20 mm and more samples were collected for bioassays and chromatographic analysis. The results showed that before irrigation, the oat residues intercepted close to 85% of any rate applied over 4500 and 9000 kg/ha respectively. Irrigation was enough to leach nearly all atrazine to soil surface. Nomulched soil and without herbicide presented close to 700 plants/m2 of Brachiaria plantaginea. Soil not treated with atrazine but covered with 4500 or 9000 kg/ha of oat residues, presented 20 and 5 plants/m2 of B. plantaginea, respectively. Control obtained with 1250 g/ha of atrazine in both covers was better than 5000 g/ha of atrazine on nonmulched soil