1,720,960 research outputs found
Spatially Continuous Depletion Algorithm for Monte Carlo Simulations
Full text linkTo correctly predict reactor behavior during cycle operations, the evolution of nuclide number densities throughout the core must be accurately modeled. The time-varying spatial distribution of nuclide number densities is typically resolved by discretizing the Monte Carlo geometry into smaller cells over which number densities are assumed to be spatially invariant.
The nuclide number densities in these smaller cells are integrated through time using reaction rate tallies on the same discretized geometry. However, detailed distributions of nuclide number densities in a full three dimensional simulation can require a prohibitive amount of tallies, and the spatial
discretization of the base geometry makes coupling to external multiphysics tools difficult. In this paper a method for solving for spatially continuous number density distributions during depletion calculations
will be described. The spatially continuous number densities can be used in the transport method proposed by Brown and Martin which allows for transporting neutrons through a material with continuously varying properties such as temperature and nuclide number densities. Coupled with the ability of Functional Expansion Tallies (FETs) [2] to represent tallied quantities as continuous functions, it is possible to both solve for and make use of spatially continuous nuclide number densities. The need for this capability was alluded to by Brown et. al., but no solution has yet been proposed. With a continuous depletion method, recent work which utilized
FETs and continuous material tracking to incorporate multiphysics
feedback in Monte Carlo simulations can be extended to simulations that include depletion analysis.United States. Department of Energy (Nuclear Energy University Programs Graduate Fellowship
Windowed multipole sensitivity to target accuracy of the optimization procedure
Full text linkThis paper compares the accuracy of the windowed multipole direct Doppler broadening method to that of the ENDF-B/VII.1 libraries that come with MCNP6. Various windowed multipole libraries were generated with different maximum allowed relative errors. Then, the libraries were compared to the MCNP6 data via resonance integral and through single assembly Monte Carlo analysis. Since the windowed multipole uses resonance parameters, resonance integrals are only affected by the number of resonances included in the library and not by the order of the background fitting function. The relative performance of each library with varying maximum allowed error was evaluated. It was found that setting a maximum target relative error of 0.1% in the library provided highly accurate data that closely matches the MCNP6 data for all temperatures of interest, while still having suitable computational performance. Additionally, a library with a maximum relative error of 1% also provided reasonable accuracy on eigenvalue and reaction rates with a noticeable improvement on performance, but with a few statistically significant differences with the MCNP6 data.United States. Department of Energy (Consortium for Advanced Simulation of Light Water Reactors (CASL), contract No. DE-AC05-00OR22725)United States. Department of Energy (Center for Exascale Simulation of Advanced Reactors (CESAR), contract No. DE-AC02-06CH11357))United States. Department of Energy (Nuclear Energy University Programs Graduate Fellowship, contract No. DE-NE-0000102
Using Fractional Cascading to Accelerate Cross Section Lookups in Monte Carlo Neutron Transport Calculations
Full text linkWe describe and test a technique for carrying out energy grid searches in continuous-energy Monte Carlo (MC) neutron transport calculations that represents an optimal compromise between grid search performance and memory footprint. The method, based on the fractional cascading technique and referred to as the cascade grid, is tested within the OpenMC Monte Carlo code, and performance results comparing the method with existing approaches are presented for the Hoogenboom-Martin reactor benchmark. The cascade grid achieves significant speedups in calculation rate with negligible initialization overhead while not increasing the memory footprint by more than 2x.
Windowed multipole for cross section Doppler broadening
No full textThis paper presents an in-depth analysis on the accuracy and performance of the windowed multipole Doppler broadening method. The basic theory behind cross section data is described, along with the basic multipole formalism followed by the approximations leading to windowed multipole method and the algorithm used to efficiently evaluate Doppler broadened cross sections. The method is tested by simulating the BEAVRS benchmark with a windowed multipole library composed of 70 nuclides. Accuracy of the method is demonstrated on a single assembly case where total neutron production rates and U238 capture rates compare within 0.1% to ACE format files at the same temperature. With regards to performance, clock cycle counts and cache misses were measured for single temperature ACE table lookup and for windowed multipole. The windowed multipole method was found to require 39.6% more clock cycles to evaluate, translating to a 7.9% performance loss overall. However, the algorithm has significantly better last-level cache performance, with 3 fewer misses per evaluation, or a 65% reduction in last-level misses. This is due to the small memory footprint of the windowed multipole method and better memory access pattern of the algorithm. Keywords: Monte Carlo; Multipole; Doppler broadenin
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
Development and analysis of high order neutron transport-depletion coupling algorithms
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 141-145).The coupling of depletion and neutron transport together creates a particularly challenging mathematical problem. Due to the stiffness of the ODE, special algorithms needed to be developed to minimize the number of transport simulations required. In addition, for stochastic transport, both the time step and the number of particles per time step need to be considered. In recent years, many new coupling algorithms have been developed. However, relatively little analysis of the numeric and stochastic convergence of these techniques has been performed. In this document, several new algorithms are introduced. Some are improvements of current techniques, some are taken from similar problems in other fields, and some are derived from scratch for this specific problem. These were then tested on several test problems to investigate their convergence. With regard to numerical error, the CF4 algorithm (a commutator-free Lie integrator) outperformed all tested algorithms. In number of transport simulations to achieve a 0.1% gadolinium relative error, CF4 requires half the simulations. With regard to stochastic error, it was found that once a time step is sufficiently reduced, errors are mostly a function of the number of particles used during the simulation. The remaining variability is due to how stochastic noise propagates through each numerical integrator. Using this information, a technique is developed to minimize the cost of running a depletion simulation.by Colin Josey.Ph. D
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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