610 research outputs found
Photoconductance of a submicron oxidized line in surface conductive single crystalline diamond
We report on sub-bandgap optoelectronic phenomena of hydrogen-terminated
diamond patterned with a submicron oxidized line. The line acts as an energy
barrier for the two-dimensional hole gas located below the hydrogenated diamond
surface. A photoconductive gain of the hole conductivity across the barrier is
measured for sub-bandgap illumination. The findings are consistent with
photogenerated electrons being trapped in defect levels within the barrier. We
discuss the spatial and energetic characteristics of the optoelectronic
phenomena, as well as possible photocurrent effects
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
Research in Geant4 electromagnetic physics design, and its effects on computational performance and quality assurance
The Geant4 toolkit offers a rich variety of electromagnetic physics models;
so far the evaluation of this Geant4 domain has been mostly focused on its
physics functionality, while the features of its design and their impact on
simulation accuracy, computational performance and facilities for verification
and validation have not been the object of comparable attention yet, despite
the critical role they play in many experimental applications. A new project is
in progress to study the application of new design concepts and software
techniques in Geant4 electromagnetic physics, and to evaluate how they can
improve on the current simulation capabilities. The application of a
policy-based class design is investigated as a means to achieve the objective
of granular decomposition of processes; this design technique offers various
advantages in terms of flexibility of configuration and computational
performance. The current Geant4 physics models have been re-implemented
according to the new design as a pilot project. The main features of the new
design and first results of performance improvement and testing simplification
are presented; they are relevant to many Geant4 applications, where
computational speed and the containment of resources invested in simulation
production and quality assurance play a critical role.Comment: 4 pages, 4 figures and images, to appear in proceedings of the
Nuclear Science Symposium and Medical Imaging Conference 2009, Orland
Ordinal patterns in epileptic brains: Analysis of intracranial EEG and simultaneous EEG-fMRI
Epileptic seizures are associated with high behavioral stereotypy of the patients. In the EEG of epilepsy patients characteristic signal patterns can be found during and between seizures. Here we use ordinal patterns to analyze EEGs of epilepsy patients and quantify the degree of signal determinism. Besides relative signal redundancy and the fraction of forbidden patterns we introduce the fraction of under-represented patterns as a new measure. Using the logistic map, parameter scans are performed to explore the sensitivity of the measures to signal determinism. Thereafter, application is made to two types of EEGs recorded in two epilepsy patients. Intracranial EEG shows pronounced determinism peaks during seizures. Finally, we demonstrate that ordinal patterns may be useful for improving analysis of non-invasive simultaneous EEG-fMR
Geant4-related R&D for new particle transport methods
A R&D project has been launched in 2009 to address fundamental methods in
radiation transport simulation and revisit Geant4 kernel design to cope with
new experimental requirements. The project focuses on simulation at different
scales in the same experimental environment: this set of problems requires new
methods across the current boundaries of condensed-random-walk and discrete
transport schemes. An exploration is also foreseen about exploiting and
extending already existing Geant4 features to apply Monte Carlo and
deterministic transport methods in the same simulation environment. An overview
of this new R&D associated with Geant4 is presented, together with the first
developments in progress.Comment: 4 pages, to appear in proceedings of the Nuclear Science Symposium
and Medical Imaging Conference 2009, Orland
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
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