3,215 research outputs found
Muon Detection of TeV Gamma Rays from Gamma Ray Bursts
Because of the limited size of the satellite-borne instruments, it has not
been possible to observe the flux of gamma ray bursts (GRB) beyond GeV energy.
We here show that it is possible to detect the GRB radiation of TeV energy and
above, by detecting the muon secondaries produced when the gamma rays shower in
the Earth's atmosphere. Observation is made possible by the recent
commissioning of underground detectors (AMANDA, the Lake Baikal detector and
MILAGRO) which combine a low muon threshold of a few hundred GeV or less, with
a large effective area of 10^3 m^2 or more. Observations will not only provide
new insights in the origin and characteristics of GRB, they also provide
quantitative information on the diffuse infrared background.Comment: Revtex, 12 pages, 3 postscript figures, uses epsfig.st
Magnetic Field Tomography
Neutral atoms may be trapped via the interaction of their magnetic dipole
moment with magnetic field gradients. One of the possible schemes is the
cloverleaf trap. It is often desirable to have at hand a fast and precise
technique for measuring the magnetic field distribution. We introduce a novel
diagnostic tool for instantaneous imaging the equipotential lines of a magnetic
field within a region of space (the vacuum recipient) that is not accessible to
massive probes. Our technique is based on spatially resolved observation of the
fluorescence emitted by a hot beam of sodium atoms crossing a thin slice of
resonant laser light within the magnetic field region to be investigated. The
inhomogeneous magnetic field spatially modulates the resonance condition
between the Zeeman-shifted hyperfine sublevels and the laser light and
therefore the amount of scattered photons. We demonstrate this technique by
mapping the field of our cloverleaf trap in three dimensions under various
conditions.Comment: 8 pages, 8 figure
Activity and abundance of methane-oxidizing bacteria in secondary forest and manioc plantations of Amazonian Dark Earth and their adjacent soils
The oxidation of atmospheric CH4 in upland soils is mostly mediated by uncultivated groups of microorganisms that have been identified solely by molecular markers, such as the sequence of the pmoA gene encoding the ?-subunit of the particulate methane monooxygenase enzyme. The objective of this work was to compare the activity and diversity of methanotrophs in Amazonian Dark Earth soil (ADE, Hortic Anthrosol) and their adjacent non-anthropic soil. Secondly, the effect of land use in the form of manioc cultivation was examined by comparing secondary forest and plantation soils. CH4 oxidation potentials were measured and the structure of the methanotroph communities assessed by quantitative PCR (qPCR) and amplicon pyrosequencing of pmoA genes. The oxidation potentials at low CH4 concentrations (10 ppm of volume) were relatively high in all the secondary forest sites of both ADE and adjacent soils. CH4 oxidation by the ADE soil only recently converted to a manioc plantation was also relatively high. In contrast, both the adjacent soils used for manioc cultivation and the ADE soil with a long history of agriculture displayed lower CH4 uptake rates. Amplicon pyrosequencing of pmoA genes indicated that USC?, Methylocystis and the tropical upland soil cluster (TUSC) were the dominant groups depending on the site. By qPCR analysis it was found that USC? pmoA genes, which are believed to belong to atmospheric CH4 oxidizers, were more abundant in ADE than adjacent soil. USC? pmoA genes were abundant in both forested and cultivated ADE soil, but were below the qPCR detection limit in manioc plantations of adjacent soil. The results indicate that ADE soils can harbor high abundances of atmospheric CH4 oxidizers and are potential CH4 sinks, but as in other upland soils this activity can be inhibited by the conversion of forest to agricultural plantations
Activity and abundance of methane-oxidizing bacteria in secondary forest and manioc plantations of Amazonian Dark Earth and adjacent soils.
Activity and abundance of methane-oxidizing bacteria in secondary forest and manioc plantations of Amazonian Dark Earth and their adjacent soils.
The oxidation of atmospheric CH4 in upland soils is mostly mediated by uncultivated groups of microorganisms that have been identified solely by molecular markers, such as the sequence of the pmoA gene encoding the -subunit of the particulate methane monooxygenase enzyme. The objective of this work was to compare the activity and diversity of methanotrophs in Amazonian Dark Earth soil (ADE, Hortic Anthrosol) and their adjacent non-anthropic soil
Análise discriminante do solo em Terra Preta de Índio, Iranduba/AM.
O objetivo deste trabalho foi realizar a análise discriminante do solo da TPI do campo experimental do Caldeirão-Embrapa Amazônia Ocidental no município de Iranduba-AM
Where are the black caimans, Melanosuchus niger (Crocodylia: Alligatoridae), in the Xingu River basin, Brazil?
The black caiman, Melanosuchus niger (Spix, 1825), which can reach a length of 6 meters (Medem, 1981), was considered endangered due to intense hunting for its skin in the 1970s (Rebelo and Magnusson, 1983), but densities in several areas have recovered after the implementation of environmental laws and conservation programs (Da Silveira and Thorbjarnason, 1999), as well as changes in contraband routes.Na publicação: Zilca Campos
Avaliação de métodos rápidos para a quantificação de Staphylococcus aureus em alimentos.
O objetivo do trabalho foi avaliar métodos rápidos para a quantificação de S. aureus em alimentos
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