1,720,984 research outputs found
Computational methods and studies in nanomagnetics
No full textComputational study of magnetic materials has been crucial for the development of new technologies in areas such as data storage. One challenge with current computational methods is that the dipolar field calculation dominates the computation time. In this work we show how the fast multipole method can be applied to this problem, and other long range force and potential calculations, through symbolic generation of operator functions in a generic fashion. We study the equilibrium states found in triangular and square samples of the helimagnetic material FeGe, in which skyrmions have been observed, by varying the size and applied field. We show that the equilibrium states of such systems is modified in comparison to previously studied disk systems of this material, with larger sample sizes required for skyrmions to form the ground state. We show the final states obtained from relaxation of a uniform magnetisation in order to provide data for experimental comparison. We then study the energy barriers between ferromagnetic and skyrmion states in Cobalt monolayers when triangular, square and Bezier edge defects are introduced, and show how this varies by size and by whether the dipolar field is included in the calculation. Finally, we study the equilibrium behaviour of Bloch points in FeGe disks and nanotracks made up of two layers in which the Dzyaloshinskii-Moriya interaction has opposing chirality. We then study the dynamic behaviour under an in-plane magnetic field, showing that the Bloch point reaches a velocity linearly proportional to the applied field
Dataset for "Fmmgen: Automatic Code Generation of Operators for Cartesian Fast Multipole and Barnes-Hut Methods"
No full textThis repository provides the dataset, build and run scripts for the paper "Fmmgen: Automatic Code Generation of Cartesian Fast Multipole and Barnes-Hut Operators", by Ryan Alexander Pepper and Hans Fangohr. </span
fmmgen: Automatic Code Generation of Operators for Cartesian Fast Multipole and Barnes-Hut Methods
No full textThe Barnes-Hut and Fast Multipole Methods are widely utilised methods applied in order to reduce the computational cost of evaluating long range forces in -body simulations. Despite this, applying existing libraries to simple problems with higher order source points, such as dipoles, is not straightforward or efficient because individual libraries are optimised towards specific problems, normally solving for the potential and field of a set of Coulombic particles. In this paper we detail the implementation and testing of a software package, fmmgen, in which the source code for Barnes-Hut and Fast Multipole operator functions for calculating calculate the potential, field or both from arbitrary ordered sources is easily generated through symbolic algebra
Dataset for "Field-driven Bloch Point Motion in Chiral Systems"
No full textThis dataset provides micromagnetic simulation data collected from a series of computational experiments on the effects of applied magnetic fields on chiral two-layered systems, in which each layer has opposing chirality. Simulations were performed with the open-source software Finmag (10.5281/zenodo.1216011), and OOMMF (https://math.nist.gov/oommf/).
The dataset is split into several directories, and the data is either stored in VTK files (which can be opened by a variety of free tools such as Paraview and MayaVi), and CSV files. In all CSV files, units are given where the data has dimensionality. </span
Dataset for "Edge Defects and Energy Barriers in Skyrmion Monolayers"
No full textDataset for "Edge Defects and Energy Barriers in Skyrmion Monolayers" This dataset provides data from a series of atomistic simulations from experiments on the effects of varying the size of defects on a monolayer of Cobalt, where defects of three shapes (square, triangle and bezier) are varied in size, and the effect of the demagnetising interaction viewed. The simulations were performed with the open-source software Fidimag (10.5334/jors.223, 10.5281/zenodo.2650286). The dataset is split into several directories, and the data is either stored in VTK files (which can be opened by a variety of free tools, for e.g. Paraview and MayaVi, TecPlot), and CSV files and NDT files, which can be opened in standard numerical data libraries and software (e.g. Pandas, NumPy, Excel, LibreOffice Calc) or opened in a text editor for viewing directly. energy-barrier-data This folder contains space delimited NDT files which give the energy information history across a set of simulations. This contains 6 folders: squ-nd, tri-nd, bez-nd and squ-wd, tri-wd, bez-wd which correspond to data for the square, triangle and bezier defects, calculated without and with the demagnetising interaction respectively. For the triangle datasets, the files are labelled with the width of the defect. For the square datasets, the files are labelled with the width and height of the defect. For the bezier datasets, the files are labelled with the width, and the height of the control point for a bezier curve. Each row in the data file gives the energy of a set of images in the Nudged Elastic Band Method at a given iteration; thus, the final row is the converged energy data. energy-term-data-triangles This folder contains more detailed energy information calculated for the converged triangle images. These CSV files are labelled with the width of the defect, and 'nd' for no demagnetising interaction, and 'wd' if the demagnetistaion is present (e.g. 'w_0.5_nd.csv' is the file for a width 0.5nm triangular defect with no demagnetising interaction). These files have columns corresponding to the different magnetic energies (Exchange, Anisotropy, DMI, Demagnetising) in Joules for each image in the NEBM calculation, along with the total energy of each state. vtks This folder contains VTK files of some of the states used to create figures. There are six folders * no-defect and no-defect-wd which correspond to the set of images from simulations of the nanostructure with no defect present * squ-5.0_5.0 and squ-wd-5.0_5.0 which are for the sample with a 5.0nm by 5.0nm defect * tri-7.0 and tri-wd-7.0 which are for the sample with a triangular defect of width 7.0nm.</span
GC-05 - Towards reproducible micromagnetic workflows using Ubermag
No full textMicromagnetics complements theoretical and experimental methods to support research in magnetism. The Object-Oriented MicroMagnetic Framework (OOMMF) 1 is a micromagnetic simulation tool solving non-linear time-dependent partial differential equations using the finite-difference method. It is probably the most widely used simulation tool in the micromagnetics community. It was written in C++, wrapped with Tcl, and driven through configuration files that follow the Tcl syntax. The typical computational workflow the user must follow to simulate a particular problem is to write a configuration file. After that, the user runs OOMMF by providing the configuration file to the OOMMF executable. When the OOMMF run is complete, results are saved in OOMMF-specific file formats. Finally, the user analyzes the result files.One of the specific goals of a computational micromagnetic study is parameter-space exploration. More precisely, the user repeats the simulation for different values of input parameters by changing them in the configuration file. It is often difficult to automate this, and it is challenging for the user to keep a log of all steps performed in the entire micromagnetic study. Besides, postprocessing and analysis of results is performed outside OOMMF, using techniques and scripts that are mostly developed by the user, or carried out manually. Consequently, it is hard to track, record, and convey the exact simulation procedure. Without this information, resulting publications are generally not reproducible.To address this situation, we developed a Python interface to the OOMMF executable to expose OOMMF to a general-purpose programming language supported by Jupyter. This allows us to conduct micromagnetic simulations from within the Jupyter notebook 2 to capitalize on the benefits of this environment. We developed a set of Python libraries we refer to as Ubermag, which expose the computational capabilities of OOMMF so that it can be controlled from Python. These Python libraries provide a domain-specific language to define a micromagnetic problem. A micromagnetic model, defined using the domain-specific language, is not aware of the particular simulation tool that will perform the actual micromagnetic simulation, and it is only used to describe the model. When a simulation is required, the model is translated into the OOMMF configuration file, the OOMMF executable is called, and the output files are read. By exposing the micromagnetic simulation capabilities to Python and driving the research from Jupyter Notebook, we have available all the benefits of the Jupyter research environment and all tools from Python's scientific stack are readily available.Ubermag and the Jupyter environment simplify the efforts to make micromagnetics publications reproducible. For each figure in the publication, one notebook can be provided. Using Binder 3, the community can inspect and re-run all the calculations in the cloud and make the publication reproducible
User interfaces for computational science: a domain specific language for OOMMF embedded in Python
No full textComputer simulations are used widely across the engineering and science disciplines, including in the research and development of magnetic devices using computational micromagnetics. In this work, we identify and review different approaches to configuring simulation runs: (i) the re-compilation of source code, (ii) the use of configuration files, (iii) the graphical user interface, and (iv) embedding the simulation specification in an existing programming language to express the computational problem. We identify the advantages and disadvantages of different approaches and discuss their implications on effectiveness and reproducibility of computational studies and results. Following on from this, we design and describe a domain specific language for micromagnetics that is embedded in the Python language, and allows users to define the micromagnetic simulations they want to carry out in a flexible way. We have implemented this micromagnetic simulation description language together with a computational backend that executes the simulation task using the Object Oriented MicroMagnetic Framework (OOMMF). We illustrate the use of this Python interface for OOMMF by solving the micromagnetic standard problem 4. All the code is publicly available and is open source
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
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