1,830 research outputs found
Tenfold your photons -- a physically-sound approach to filtering-based variance reduction of Monte-Carlo-simulated dose distributions
X-ray dose constantly gains interest in the interventional suite. With dose
being generally difficult to monitor reliably, fast computational methods are
desirable. A major drawback of the gold standard based on Monte Carlo (MC)
methods is its computational complexity. Besides common variance reduction
techniques, filter approaches are often applied to achieve conclusive results
within a fraction of time. Inspired by these methods, we propose a novel
approach. We down-sample the target volume based on the fraction of mass,
simulate the imaging situation, and then revert the down-sampling. To this end,
the dose is weighted by the mass energy absorption, up-sampled, and distributed
using a guided filter. Eventually, the weighting is inverted resulting in
accurate high resolution dose distributions. The approach has the potential to
considerably speed-up MC simulations since less photons and boundary checks are
necessary. First experiments substantiate these assumptions. We achieve a
median accuracy of 96.7 % to 97.4 % of the dose estimation with the proposed
method and a down-sampling factor of 8 and 4, respectively. While maintaining a
high accuracy, the proposed method provides for a tenfold speed-up. The overall
findings suggest the conclusion that the proposed method has the potential to
allow for further efficiency.Comment: 6 pages, 3 figures, Bildverarbeitung f\"ur die Medizin 202
Precision measurements of the top quark mass in the dileptonic top quark pair decay channel at ATLAS
Die Masse des Top Quarks ist ein fundamentaler Parameter des Standardmodells und ihre präzise Bestimmung ist von großer Bedeutung für die Teilchenphysik. In dieser Dissertation werden Messungen der Top Quark Masse im dileptonischen Zerfallskanal von Top Quark Paaren präsentiert und experimentelle und theoretische Aspekte der Präzisionsmessung untersucht.
Neben technischen Maßnahmen zur Gewährleistung optimaler Nachweiskapazität für zukünftige Datennahme werden Messungen der Top Quark Masse mit den Daten der Jahre 2011 und 2012 des ATLAS Detektors durchgeführt, basierend auf Proton-Proton Kollisionen mit einer Schwerpunktsenergie von √s = 7 und 8 TeV. Verschiedene Techniken zur Reduzierung der statistischen und wichtigsten systematischen Unsicherheiten werden angewandt, was zur bisher genauesten Einzelmessung der Top Quark Masse im dileptonischen Top Quark Paar Zerfallskanal weltweit führt.
Durch eine Kombination mit ATLAS Messungen unter Berücksichtigung der Korrelationen wird die Präzision weiter erhöht. Die in einer Blindstudie ermittelte Masse des Top Quarks ist mtop = 172.40 ± 0.31 (stat) ± 0.62 (syst) GeV/c2 = 172.40 ± 0.70 GeV/c2, wobei die Unsicherheit von der begrenzten Auflösung der Jetenergiemessungen dominiert wird.
Außerdem werden mit einer Entfaltungsmethode die Daten von Detektoreffekten bereinigt und die ersten Schritte zu einer Messung der Top Quark Masse auf dem Niveau stabiler Teilchen durchgeführt. Anschließend werden die Auswirkungen von vollen QCD Rechnungen in zweiter Ordnung Störungstheorie auf Top Quark Massenmessungen untersucht
Capturing Practices of Knowledge Work for Information Systems Design
Despite abundant tools and systems claiming support for knowledge work, many have failed to be accepted by users. Designing information systems (ISs) for knowledge work is a challenging task, but results on how knowledge work is actually performed is scarce and so are instruments that help to translate results into artefacts useful for IS design. This paper takes the perspective of work practices and proposes an approach to collaboratively study and analyze practices of knowledge work. The approach uses stereotypes of users, called personas, in order to inform IS design activities. The persona concept is enriched with respect to behaviour concerning practices of knowledge work. Furthermore, a procedure for selecting primary personas out of a set of personas is suggested based on cluster analysis. The approach is illustrated with the case of a collaborative ethnographically-informed study of seven organizations in four European countries. The proposed approach is the more suitable, the more innovative, big and diverse the project, the planned product, the developers and the target group are. User-centered design activities benefit from personas by reduced effort for involving end-users and a continuous focus on characteristics of critical users and their way of performing practices of knowledge work
Double Your Views - Exploiting Symmetry in Transmission Imaging
For a plane symmetric object we can find two views - mirrored at the plane of
symmetry - that will yield the exact same image of that object. In consequence,
having one image of a plane symmetric object and a calibrated camera, we can
automatically have a second, virtual image of that object if the 3-D location
of the symmetry plane is known. In this work, we show for the first time that
the above concept naturally extends to transmission imaging and present an
algorithm to estimate the 3-D symmetry plane from a set of projection domain
images based on Grangeat's theorem. We then exploit symmetry to generate a
virtual trajectory by mirroring views at the plane of symmetry. If the plane is
not perpendicular to the acquired trajectory plane, the virtual and real
trajectory will be oblique. The resulting X-shaped trajectory will be
data-complete, allowing for the compensation of in-plane motion using epipolar
consistency. We evaluate the proposed method on a synthetic symmetric phantom
and, in a proof-of-concept study, apply it to a real scan of an anthropomorphic
human head phantom.Comment: Accepted for MICCAI 2018 (8 Pages
Metal-Enhanced Fluorescence of Chlorophylls in Single Light-Harvesting Complexes
Ensemble and single-molecule spectroscopy demonstrates that both emission and absorption of peridinin−chlorophyll−protein photosynthetic antennae can be largely enhanced through plasmonic interactions. We find up to 18-fold increase of the chlorophyll fluorescence for complexes placed near a silver metal layer. This enhancement, which leaves no measurable effects on the protein structure, is observed when exciting either chlorophyll or carotenoid and is attributed predominantly to an increase of the excitation rate in the antenna. The enhancement mechanism comes from plasmon-induced amplification of electromagnetic fields inside the complex. This result is an important step toward applying plasmonic nanostructures for controlling the optical response of complex biomolecules and improving the design and functioning of artificial light-harvesting systems
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