207 research outputs found
NEMA NU4-2008 Performance Evaluation of Albira: A Two-Ring Small-Animal PET System Using Continuous LYSO Crystals
Goals: This paper presents the performance review based on a dual-ring Positron Emission Tomography (PET) scanner being a part
of Bruker Albira: a multi-modal small-animal imaging platform. Each ring of Albira PET contains eight detectors arranged as
octagon, and each detector is built using a single continuous lutetium-yttrium oxyorthosilicate crystal and multi-anode photo
multiplier tube. In two-ring configuration, the scanner covers 94.4 mm in axial- and 80ÂŽ80 mm in trans-axial direction, which is
sufficient to acquire images of small animals (e.g. mice) without the need of moving the animal bed during the scan.
Methods: All measurements and majority of data processing were performed according to the NEMA NU4-2008 standard with one
exception. Due to the scanner geometry, the spatial resolution test was reconstructed using iterative algorithm instead of the
analytical one. The main performance characteristics were compared with those of the other PET sub-systems of tri-modal smallanimal
scanners.
Results: The measured spatial resolution at the centre of the axial field of view in radial, tangential and axial directions was 1.72,
1.70 and 2.45 mm, respectively. The scatter fraction for the mouse-like phantom was 9.8% and for the rat-like phantom, 21.8%. The
maximum absolute sensitivity was 5.30%. Finally, the recovery co-efficients for 5, 4, 3, 2, 1 mm diameter rods in image quality
phantom were: 0.90, 0.77, 0.66, 0.30 and 0.05, respectively.
Conclusion: The Bruker Albira is a versatile small-animal multi-modal device that can be used for variety of studies. Overall the
PET sub-system provides a good spatial resolution coupled with better-than average sensitivity and the ability to produce good
quality animal images when administering low activities
Metal enrichment processes
There are many processes that can transport gas from the galaxies to their
environment and enrich the environment in this way with metals. These metal
enrichment processes have a large influence on the evolution of both the
galaxies and their environment. Various processes can contribute to the gas
transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding
simulations, their efficiencies, and their time scales as far as they are known
to date. It seems that all processes can contribute to the enrichment. There is
not a single process that always dominates the enrichment, because the
efficiencies of the processes vary strongly with galaxy and environmental
properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 17; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays.
It consists of a surface array to measure secondary particles at ground level
and a fluorescence detector to measure the development of air showers in the
atmosphere above the array. The "hybrid" detection mode combines the
information from the two subsystems. We describe the determination of the
hybrid exposure for events observed by the fluorescence telescopes in
coincidence with at least one water-Cherenkov detector of the surface array. A
detailed knowledge of the time dependence of the detection operations is
crucial for an accurate evaluation of the exposure. We discuss the relevance of
monitoring data collected during operations, such as the status of the
fluorescence detector, background light and atmospheric conditions, that are
used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
Effects of watershed land use on nitrogen concentrations and ÎŽ15 Nitrogen in groundwater
Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 77 (2006): 199-215, doi:10.1007/s10533-005-1036-2.Eutrophication is a major agent of change affecting freshwater, estuarine, and marine
systems. It is largely driven by transportation of nitrogen from natural and anthropogenic
sources. Research is needed to quantify this nitrogen delivery and to link the delivery to
specific land-derived sources. In this study we measured nitrogen concentrations and ÎŽ15N
values in seepage water entering three freshwater ponds and six estuaries on Cape Cod,
Massachusetts and assessed how they varied with different types of land use. Nitrate
concentrations and ÎŽ15N values in groundwater reflected land use in developed and pristine
watersheds. In particular, watersheds with larger populations delivered larger nitrate loads with
higher ÎŽ15N values to receiving waters. The enriched ÎŽ15N values confirmed nitrogen loading
model results identifying wastewater contributions from septic tanks as the major N source.
Furthermore, it was apparent that N coastal sources had a relatively larger impact on the N
loads and isotopic signatures than did inland N sources further upstream in the watersheds.
This finding suggests that management priorities could focus on coastal sources as a first
course of action. This would require management constraints on a much smaller population.This work was supported
by funds from the Woods Hole Oceanographic Institution Sea Grant Program, from the
Cooperative Institute for Coastal and Estuarine Environmental Technology, from
Massachusetts Department of Environmental Protection to Applied Science Associates,
Narragansett, RI, as well as from Palmer/McLeod and NOAA National Estuarine Research
Reserve Fellowships to Kevin Kroeger. This work is the result of research sponsored by NOAA
National Sea Grant College Program Office, Department of Commerce, under Grant No.
NA86RG0075, Woods Hole Oceanographic Institution Sea Grant Project No. R/M-40
Extent and Causes of Chesapeake Bay Warming
Coastal environments such as the Chesapeake Bay have long been impacted by eutrophication stressors resulting from human activities, and these impacts are now being compounded by global warming trends. However, there are few studies documenting long-term estuarine temperature change and the relative contributions of rivers, the atmosphere, and the ocean. In this study, Chesapeake Bay warming, since 1985, is quantified using a combination of cruise observations and model outputs, and the relative contributions to that warming are estimated via numerical sensitivity experiments with a watershedâestuarine modeling system. Throughout the Bayâs main stem, similar warming rates are found at the surface and bottom between the late 1980s and late 2010s (0.02 +/- 0.02C/year, mean +/- 1 standard error), with elevated summer rates (0.04 +/- 0.01C/year) and lower rates of winter warming (0.01 +/- 0.01C/year). Most (~85%) of this estuarine warming is driven by atmospheric effects. The secondary influence of ocean warming increases with proximity to the Bay mouth, where it accounts for more than half of summer warming in bottom waters. Sea level rise has slightly reduced summer warming, and the influence of riverine warming has been limited to the heads of tidal tributaries. Future rates of warming in Chesapeake Bay will depend not only on global atmospheric trends, but also on regional circulation patterns in mid-Atlantic waters, which are currently warming faster than the atmosphere.
Supporting model data available at: https://doi.org/10.25773/c774-a36
Espalhamento e secagem de filme de amido-glicerol-fibra preparado por "tape-casting"
O objetivo deste trabalho foi avaliar processos de espalhamento e secagem de filme de amido-glicerol-fibras de celulose, preparado por "tape-casting". O espalhamento da suspensĂŁo foi avaliado a 50, 150 e 250 cm min-1, seguido de secagem em estufa com circulação forçada de ar, a 40 ou 70ÂșC; avaliou-se tambĂ©m o espalhamento da suspensĂŁo a 150 cm min-1, seguido da secagem do filme sobre suporte de "tape-casting" a 22ÂșC e 60% de umidade relativa, com velocidades do ar de 4, 6 e 8 m s-1 no tĂșnel de secagem. Ensaios reolĂłgicos mostraram que o espalhamento das suspensĂ”es a temperaturas inferiores a 50ÂșC apresentou mĂłdulo de elasticidade superior ao mĂłdulo viscoso, em todo o espectro de frequĂȘncias de oscilação. As microscopias mostraram filmes secos a 40 e 70ÂșC sem defeitos de formação, e cujas propriedades mecĂąnicas nĂŁo diferiam. A velocidade de espalhamento e a do ar nĂŁo modificam o tempo de secagem nem as propriedades dos filmes. O tempo de secagem pode ser reduzido para aproximadamente duas horas, o que Ă© importante para a produção dos filmes em larga escala
Sediment routing and basin evolution in Proterozoic to Mesozoic east Gondwana: A case study from southern Australia
Sedimentary rocks along the southern margin of Australia host an important record of the break-up history of east Gondwana, as well as fragments of a deeper geological history, which collectively help inform the geological evolution of a vast and largely underexplored region. New drilling through Cenozoic cover has allowed examination of the Cretaceous rift-related Madura Shelf sequence (Bight Basin), and identification of two new stratigraphic units beneath the shelf; the possibly Proterozoic Shanes Dam Conglomerate and the interpreted Palaeozoic southern Officer Basin unit, the Decoration Sandstone. Recognition of these new units indicates an earlier basinal history than previously known. Lithostratigraphy of the new drillcore has been integrated with that published from onshore and offshore cores to present isopach maps of sedimentary cover on the Madura Shelf. New palynological data demonstrate progression from more localised freshwater-brackish fluvio-lacustrine clastics in the early Cretaceous (Foraminisporis wonthaggiensis â Valanginian to Barremian) to widespread topography-blanketing, fully marine, glauconitic mudrocks in the mid Cretaceous (Endoceratium ludbrookiae â Albian). Geochronology and Hf-isotope geochemistry show detrital zircon populations from the Madura Shelf are comparable to those from the southern Officer Basin, as well as Cenozoic shoreline and palaeovalley sediments in the region. The detrital zircon population from the Shanes Dam Conglomerate is defined by a unimodal ~1400 Ma peak, which correlates with directly underlying crystalline basement of the Madura Province. Peak ages of ~1150 Ma and ~1650 Ma dominate the age spectra of all other samples, indicating a stable sediment reservoir through much of the Phanerozoic, with sediments largely sourced from the Albany-Fraser Orogen and Musgrave Province (directly and via multiple recycling events). The Madura Shelf detrital zircon population differs from published data for the Upper CretaceousCeduna Delta to the east, indicating significant differences in sediment provenance and routing between the Ceduna Sub-basin and central Bight Basin
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