1,387 research outputs found
Background Simulations of the Wide Field Imager of the ATHENA X-Ray Observatory
The ATHENA X-ray Observatory-IXO is a planned multinational orbiting X-ray
observatory with a focal length of 11.5m. ATHENA aims to perform pointed
observations in an energy range from 0.1 keV to 15 keV with high sensitivity.
For high spatial and timing resolution imaging and spectroscopic observations
the 640x640 pixel^2 large DePFET-technology based Wide field Imager (WFI) focal
plane detector, providing a field of view of 18 arcsec will be the main
detector. Based on the actual mechanics, thermal and shielding design we
present estimates for the WFI cosmic ray induced background obtained by the use
of Monte-Carlo simulations and possible background reduction measures.Comment: IEEE NSS MIC Conference 2011, Valencia, Spai
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Spatial and temporal variablity of nonmethane hydrocarbon mixing ratios and their relation to photochemical lifetime
The relationship between temporal and spatial variability of C2-C8 nonmethane hydrocarbon mixing ratios and their HO lifetimes (τ) is presented for samples collected during the 1993 North Atlantic Regional Experiment (NARE) and from other urban and remote sites. The C2-C4 alkanes, acetylene and benzene typically define a trend of the form slnx=Aτ-b where slnx is the standard deviation of the ln of the mixing ratio. The relationship extended over a wider range of hydrocarbons in winter. The exponent b ranged in value from 0.2±0.023 for winter urban data where C2-C8 hydrocarbons defined a strongly correlated trend, to 0.56±0.15 for C2-C4 hydrocarbons at a coastal site in Nova Scotia during NARE. The trends are significantly different from that given by the Junge relationship [Junge, 1974]. Data from the Azores do not display such a trend and were likely influenced by local emissions. Variance trends are a useful analytical tool for examining the validity of hydrocarbon measurements
Pulmonary Toxoplasmosis, a Rare but Severe Manifestation of a Common Opportunistic Infection in Late HIV Presenters: Report of Two Cases
Abstract : Pulmonary toxoplasmosis is rare, particularly in the era of highly active antiretroviral therapy (HAART). Here, we describe two severe cases in patients not known to be HIV-infected. In both patients, early diagnosis and therapy led to a favourable outcome. Pulmonary toxoplasmosis should be considered in the differential diagnosis in potentially HIV-infected patients with respiratory symptom
Validation of Geant4-based Radioactive Decay Simulation
Radioactive decays are of concern in a wide variety of applications using
Monte-Carlo simulations. In order to properly estimate the quality of such
simulations, knowledge of the accuracy of the decay simulation is required. We
present a validation of the original Geant4 Radioactive Decay Module, which
uses a per-decay sampling approach, and of an extended package for Geant4-based
simulation of radioactive decays, which, in addition to being able to use a
refactored per-decay sampling, is capable of using a statistical sampling
approach. The validation is based on measurements of calibration isotope
sources using a high purity Germanium (HPGe) detector; no calibration of the
simulation is performed. For the considered validation experiment equivalent
simulation accuracy can be achieved with per-decay and statistical sampling
Radioactive Decays in Geant4
The simulation of radioactive decays is a common task in Monte-Carlo systems
such as Geant4. Usually, a system either uses an approach focusing on the
simulations of every individual decay or an approach which simulates a large
number of decays with a focus on correct overall statistics. The radioactive
decay package presented in this work permits, for the first time, the use of
both methods within the same simulation framework - Geant4. The accuracy of the
statistical approach in our new package, RDM-extended, and that of the existing
Geant4 per-decay implementation (original RDM), which has also been refactored,
are verified against the ENSDF database. The new verified package is beneficial
for a wide range of experimental scenarios, as it enables researchers to choose
the most appropriate approach for their Geant4-based application
Refactoring, reengineering and evolution: paths to Geant4 uncertainty quantification and performance improvement
Ongoing investigations for the improvement of Geant4 accuracy and
computational performance resulting by refactoring and reengineering parts of
the code are discussed. Issues in refactoring that are specific to the domain
of physics simulation are identified and their impact is elucidated.
Preliminary quantitative results are reported.Comment: To be published in the Proc. CHEP (Computing in High Energy Physics)
201
Quantifying the unknown: issues in simulation validation and their experimental impact
The assessment of the reliability of Monte Carlo simulations is discussed,
with emphasis on uncertainty quantification and the related impact on
experimental results. Methods and techniques to account for epistemic
uncertainties, i.e. for intrinsic knowledge gaps in physics modeling, are
discussed with the support of applications to concrete experimental scenarios.
Ongoing projects regarding the investigation of epistemic uncertainties in the
Geant4 simulation toolkit are reported.Comment: To be published in the Proceedings of the 13th ICATPP Conference on
Astroparticle, Particle, Space Physics and Detectors for Physics
Applications, Villa Olmo, Como, 3-7 October 201
Laser-microdissection unravels cell-type specific transcription in > arbuscular mycorrhizal roots, including CAAT-box TF gene expression correlating with fungal contact and spread
Arbuscular mycorrhizae (AM) are the most widespread symbioses on Earth, promoting nutrient supply of most terrestrial plant species. To unravel gene expression in defined stages of Medicago truncatula root colonization by AM fungi, we here combined genome-wide transcriptome profiling based on whole mycorrhizal roots with real-time RT-PCR experiments that relied on characteristic cell-types obtained via laser-microdissection. Our genome-wide approach delivered a core set of 512 genes significantly activated by the two mycorrhizal fungi Glomus intraradices and Glomus mossae. Focussing on 62 of these genes being related to membrane transport, signaling, and transcriptional regulation, we distinguished whether they are activated in arbuscule-containing or the neighbouring cortical cells harbouring fungal hyphae. In addition, cortical cells from non-mycorrhizal roots served as a reference for gene expression under non-colonized conditions. Our analysis identified 25 novel arbuscule-specific genes and 37 genes expressed both in the arbuscule-containing and the adjacent cortical cells colonized by fungal hyphae. Amongst the AM-induced genes specifying transcriptional regulators were two members encoding CAAT-box binding transcription factors (CBF), designated MtCbf1 and MtCbf2. Promoter analyses demonstrated that both genes were already activated by the first physical contact between the symbionts. Subsequently, and corresponding to our cell-type expression patterns, they were progressively up-regulated in those cortical areas colonized by fungal hyphae, including the arbuscule-containing cells. The encoded CBFs thus represent excellent candidates for regulators that mediate a sequential reprogramming of root tissues during the establishment of an AM symbiosi
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