16,573 research outputs found
Po-production in lead: A benchmark between Geant4, FLUKA and MCNPX
On the last SATIF a comparison between the measured activities of the
polonium isotopes Po-208, Po-209 and Po-210 and the simulated results using
MCNPX2.7.0 was presented. The lead samples were cut from the SINQ spallation
target at the Paul Scherrer Institut (PSI) and irradiated in 2000/2001 by 575
MeV protons. The Po-isotopes were separated using radiochemical methods by the
group of D. Schumann at PSI and measured. Choosing the default model in MCNPX,
Bertini-Dresner, the prediction underestimated the measured activities by up to
several orders of magnitude. Therefore the Li\`ege intranuclear-cascade model
(INCL4.6) coupled to the de-excitation model ABLA07 were implemented into
MCNPX2.7.0 and very good agreement was found to the measurement. The reason for
the disagreement was traced back to a suppression of alpha reactions on the
lead isotopes leading to Po and neglecting the triton capture on Pb-208, which
leads to Pb-210 and decays into Po-210 with a much longer life time (22.3
years) than the decay of Po-210 itself (138 days). The prediction of the
Po-isotope activities turns out to be a sensitive test for models and codes as
it requires the accurate treatment of reaction channels not only with neutrons,
protons and pions but also with alphas and tritons, which are not considered in
intra-nuclear cascade models of the first generation. Therefore it was decided
to perform a benchmark by comparing the results obtained with MCNPX2.7.0 using
INCL4.6/ABLA07 to the predictions of FLUKA and Geant4. Since the model of the
SINQ spallation source requires an elaborate geometry a toy model was setup.
The toy model has a simplified geometry preserving the main features of the
original geometry. The results for the activities of the three Po-isotopes and
Pb-210 as well as the energy spectra for alphas and tritons obtained with the
three particle transport Monte Carlo codes are presented.Comment: 15 pages, 11 figures, Presented paper at the 13th Meeting of the
task-force on Shielding aspects of Accelerators, Targets and Irradiation
Facilities (SATIF-13), HZDR, October 10-12, 2016, Dresden, German
Hyperspectral Unmixing Overview: Geometrical, Statistical, and Sparse Regression-Based Approaches
Imaging spectrometers measure electromagnetic energy scattered in their
instantaneous field view in hundreds or thousands of spectral channels with
higher spectral resolution than multispectral cameras. Imaging spectrometers
are therefore often referred to as hyperspectral cameras (HSCs). Higher
spectral resolution enables material identification via spectroscopic analysis,
which facilitates countless applications that require identifying materials in
scenarios unsuitable for classical spectroscopic analysis. Due to low spatial
resolution of HSCs, microscopic material mixing, and multiple scattering,
spectra measured by HSCs are mixtures of spectra of materials in a scene. Thus,
accurate estimation requires unmixing. Pixels are assumed to be mixtures of a
few materials, called endmembers. Unmixing involves estimating all or some of:
the number of endmembers, their spectral signatures, and their abundances at
each pixel. Unmixing is a challenging, ill-posed inverse problem because of
model inaccuracies, observation noise, environmental conditions, endmember
variability, and data set size. Researchers have devised and investigated many
models searching for robust, stable, tractable, and accurate unmixing
algorithms. This paper presents an overview of unmixing methods from the time
of Keshava and Mustard's unmixing tutorial [1] to the present. Mixing models
are first discussed. Signal-subspace, geometrical, statistical, sparsity-based,
and spatial-contextual unmixing algorithms are described. Mathematical problems
and potential solutions are described. Algorithm characteristics are
illustrated experimentally.Comment: This work has been accepted for publication in IEEE Journal of
Selected Topics in Applied Earth Observations and Remote Sensin
Nonlinear unmixing of hyperspectral images: Models and algorithms
When considering the problem of unmixing hyperspectral images, most of the literature in the geoscience and image processing areas relies on the widely used linear mixing model (LMM). However, the LMM may be not valid, and other nonlinear models need to be considered, for instance, when there are multiscattering effects or intimate interactions. Consequently, over the last few years, several significant contributions have been proposed to overcome the limitations inherent in the LMM. In this article, we present an overview of recent advances in nonlinear unmixing modeling
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
Multipurpose S-shaped solvable profiles of the refractive index: application to modeling of antireflection layers and quasi-crystals
A class of four-parameter solvable profiles of the electromagnetic admittance
has recently been discovered by applying the newly developed Property & Field
Darboux Transformation method (PROFIDT). These profiles are highly flexible. In
addition, the related electromagnetic-field solutions are exact, in closed-form
and involve only elementary functions. In this paper, we focus on those who are
S-shaped and we provide all the tools needed for easy implementation. These
analytical bricks can be used for high-level modeling of lightwave propagation
in photonic devices presenting a piecewise-sigmoidal refractive-index profile
such as, for example, antireflection layers, rugate filters, chirped filters
and photonic crystals. For small amplitude of the index modulation, these
elementary profiles are very close to a cosine profile. They can therefore be
considered as valuable surrogates for computing the scattering properties of
components like Bragg filters and reflectors as well. In this paper we present
an application for antireflection layers and another for 1D quasicrystals (QC).
The proposed S-shaped profiles can be easily manipulated for exploring the
optical properties of smooth QC, a class of photonic devices that adds to the
classical binary-level QC.Comment: 14 pages, 18 fi
SiSeRHMap v1.0: A simulator for mapped seismic response using a hybrid model
SiSeRHMap is a computerized methodology capable of drawing up prediction maps of
seismic response. It was realized on the basis of a hybrid model which combines different
approaches and models in a new and non-conventional way. These approaches
5 and models are organized in a code-architecture composed of five interdependent
modules. A GIS (Geographic Information System) Cubic Model (GCM), which is a layered
computational structure based on the concept of lithodynamic units and zones,
aims at reproducing a parameterized layered subsoil model. A metamodeling process
confers a hybrid nature to the methodology. In this process, the one-dimensional linear
10 equivalent analysis produces acceleration response spectra of shear wave velocitythickness
profiles, defined as trainers, which are randomly selected in each zone. Subsequently,
a numerical adaptive simulation model (Spectra) is optimized on the above
trainer acceleration response spectra by means of a dedicated Evolutionary Algorithm
(EA) and the Levenberg–Marquardt Algorithm (LMA) as the final optimizer. In the fi15
nal step, the GCM Maps Executor module produces a serial map-set of a stratigraphic
seismic response at different periods, grid-solving the calibrated Spectra model. In addition,
the spectra topographic amplification is also computed by means of a numerical
prediction model. This latter is built to match the results of the numerical simulations
related to isolate reliefs using GIS topographic attributes. In this way, different sets
20 of seismic response maps are developed, on which, also maps of seismic design response
spectra are defined by means of an enveloping technique
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