1,720,978 research outputs found
Monte Carlo analysis of dosimetric issues in space exploration
No full textThe Radiation protection is of paramount importance in the planning of human exploration activities in space. The related risks must be considered with respect to two aspects: devising a proper shielding and providing answers to the requirement of an effective dosimetry evaluation in astronaut’s activities. Both aspects have been considered using the Monte Carlo (MC) code MCNP 6.2 as the reference tool. As case study an application devised for the National Aeronautics and Space Administration (NASA) Artemis program has been chosen. The project aims to establish a sustainable human presence on the Moon, envisioning the realization of an outpost that will serve as a steppingstone for space exploration endeavors. A Class III shelter, in situ resource utilization (ISRU) built habitat for the Moon, has been designed through computational methods and topology optimization techniques, and analyzed in terms of radiation shielding performances and the strictly related structural behavior. The outpost must be able to withstand temperature variations, micrometeorite impacts, and the absence of a substantial atmosphere. Any solution studied to respect the constraints must devise robust and innovative materials and techniques to create habitats that have as goal the shielding from the Galactic Cosmic Rays (GCR) and from the solar flares to provide a safe and habitable environment at the time scales scheduled for the missions. Moreover, the outpost design must incorporate strategies for extracting and utilizing local re- sources. Overcoming such challenges will pave the way for the establishment of a sustainable human presence on the Moon and serve as a crucial leap for future space exploration missions
Shape, Structure and Material Compliance with Radiation Protection Requirements for Extraplanetary Modules
No full textThis research aims to explore a design solution for an innovative extraplanetary module that combines architectural design, structure and radiation protection for sustaining human life on Mars.
The WATER (Water shielded Architectural Tree for Extraplanetary Resiliency) module is designed in order to increment the use of local resources (In Situ Resources Utilization) and robotic fabrication techniques for remote construction before human arrival on Mars.
The key element of the design is the water that can be extracted from the substrate of the Martian regolith. Water plays an essential role in both in supporting life and protecting humans inside the habitat. Because of the reduced gravity and the fine atmosphere, the major load that a structure has to withstand on Mars is the internal pressurization. To balance that load and have a more efficient foundation system, the structure needs to be covered by a thick layer of water that is also extremely important for shielding against the harmful cosmic radiation.
In fact, it is well known that a major threat to extraplanetary exploration is given by high energy cosmic particles and gamma fluxes. This work deals with the radiation protection constraints that should be considered for the WATER module, designed as an optimized possible long term habitat for Mars. The main materials considered for the module are the Martian regolith and, with respect to radiation shielding, the water that will be driven to fill the layer between the external and internal surfaces that will sustain the exposed external structures.
The simulations, carried out with a standard Monte Carlo code like MCNPX and MCNP6, that is able to directly analyze the mesh geometries coming from the WATER module structural Finite Element model, define the optimal conditions in terms of shielding thickness and layer’s material composition.
As output of the analysis, expositions and doses, that the inhabitants of these future architecture should bear, have been obtained.
The final shielding configuration is integrated in the Finite Element model of the project for the structural analysis. The results prove that the water content, subjected to the Martian gravity, helps reducing the tensile stresses inside the structure due to the internal pressurization
Monte Carlo benchmark of the experimental evaluation of the activation processes in an electron linear accelerator for radiotherapy applications
Full text linkSeveral kinds of isotopes are generated during radiotherapy treatments with high-energy electron sources due to the onset of many nuclear reactions. These isotopes are often unstable, can appear both in the device and in the treatment chamber materials and, as a consequence of the decay process, involving also gamma-ray emissions, some additional dose is given to the patient and to the radiotherapy unit staff. These effects have been experimentally monitored with a LaBr detector for gamma spectrometry. Then the measurement setup and data have been benchmarked through Monte Carlo (MC) simulations, with the MCNPX code, aiming to evaluate all kinds of activation, due to both photons and photoneutrons. All the MC activation estimates have been parameterized with respect to the 187W produced in the primary collimator of the accelerator. The simulation results obtained with MCNPX have shown a good agreement with the experimental measurements. The results suggest a possible general approach to perform the activation analysis by coupling the experimental spectrometric measurements with MC calculations to properly identify photopeaks and source components
A digital twin for (64)Cu production with cyclotron and solid target system
Full text linkOne method for finding reliable and cost-effective solutions for designing radioisotope production systems is represented by the “digital twin” philosophy of design. Looking at cyclotron solid targets, uncertainties of the particle beam, material composition and geometry play a crucial role in determining the results. The difference between what has been designed and what can be effectively manufactured, where processes such as electroplating are poorly controllable and generate large non-uniformities in deposition, must also be considered. A digital twin, where the target geometry is 3D scanned from real models, can represent a good compromise for connecting “ideal” and “real” worlds. Looking at the (64)Ni(p,n)(64)Cu reaction, different Unstructured-Mesh MCNP6 models have been built starting from the 3D solid target system designed and put into operation by COMECER. A characterization has been performed considering the designed ideal target and a 3D scan of a real manufactured target measured with a ZEISS contact probe. Libraries and physics models have been also tested due to limited cross-section data. Proton spectra in the target volume, 3D proton-neutron-photon flux maps, average energies, power to be dissipated, shut-down dose-rate, (64)Cu yield compared with various sources of experimental data and beam axial shifting impact, have been estimated. A digital twin of the (64)Ni(p,n)(64)Cu production device has been characterized, considering the real measured target geometry, paving the way for a fully integrated model suitable also for thermal, structural or fluid-dynamic analyses
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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