139 research outputs found
Howison et al 2017 Bioturbation Biocompaction
No full textTITLE: Biotically driven vegetation mosaics in grazing ecosystems: the battle between bioturbation and biocompaction
AUTHORS: Ruth A. Howison, Han Olff, Johan van de Koppel, and Christian Smit
Corresponding author: Ruth A. Howison ([email protected])
BifurcationModel.zip
Bifurcation model resulting in figures 2 and 3, designed and written by Johan van de Koppel and Ruth Howison, using R. R Core Team (2015). R: A language and environment for statistical computing. R
Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/.
Phase planes depicting the bifurcation analysis of simple plant-herbivore models, showing the more classical A) Herbivore-plant quality feedback, and B) Water-infiltration feedback.
Phase planes depicting the bifurcation analysis of plant-herbivore models with bioturbation, showing that the interplay between bioturbation and biocompaction strongly expands the conditions under which heterogeneity can persist in grazing ecosystems, with A) only bioturbation feedback and B) the consequence of combining bioturbation and biocompaction feedbacks."
GIS_Rainfall_Texture_Analysis.zip
Analysis by Ruth Howison and Han Olff, using ESRI ArcMap 10.3 for Desktop Global prediction of the regions where patchiness generated by bioturbation and biocompaction is possible, eliminating for unsuitable conditions, specifically certain soil characteristics and rainfall. Incompatible soils include; permafrost, sand (> 70% sand fraction and 20% organic material dry mass), and rainfall 1200 mm/yr and representing limits to forage quantity and quality required to maintain large herbivores.
Data sources used:
harmonized world soil database (HWSD) version 1.21, 2) Rainfall parameters were delineated using the global precipitation surface available from BioClim.org (Hijmans et al. 2005
Twice Forty Years Of Learning: An Educational Biography of Robert Reid Howison (1820-1906)
No full textThe two primary purposes of this study were to develop an educational biography on the life of Robert Reid Howison, a nineteenth-century Virginia lawyer, minister, historian, and author, and to examine Howison's efforts as an educator.
Chapter One presents an approach to the study, guiding questions, and the research methodology of educational biography. Chapter Two examines Howison's learning experiences during his childhood and youth, from his birth in 1820 to 1841. These learning experiences were primarily connected with institutions of education, such as family, school, church, work, as well as his self-initiated learning and membership in a learning society. Chapter Two analyzes Howison's learning experiences during his prime adult years, 1841-1870, and discusses how, as an adult, family became less of an institution influencing his learning and became more of an opportunity to educate others. His self-initiated learning, coupled with institutions of education in the community, became more prominent during these years. His first book, A History of Virginia From Its Discovery and Settlement, revealed Howison both as a learner and educator as he conducted the necessary research for the book with the intent to teach the history of Virginia to the young men of the day. He also contributed other scholarship efforts such as writing a complete history of the Civil War. Chapter Four details Howison's later years, from 1870 to his death in 1906. During this time he authored two additional major works, God and Creation and A Students' History of the United States. Many of Howison's shorter works written during these years, such as newspaper and periodical articles, reveal his philosophy of education. Howison was also a lecturer on American History at Fredericksburg College, an event combining his work as an educator with his lifelong interest in reading and writing history. Chapter Five presents conclusions and recommendations to the study, particularly concerning the research methodology of educational biography as applied to the life of Robert Howison. His detailed description of his lifelong learning experiences, as described in his unpublished autobiography Twice Forty Years of American Life, were useful in establishing the significant learning experiences throughout his life as well as documenting the outcomes or results of his learning.Ph. D
Integrating Administrative Data for Policy Insights
No full textPublished as: Hastings JS, Howison M, Lawless T, Ucles J, White P. Unlocking Data to Improve Public Policy. Communications of the ACM 62(10): 48-53. https://doi.org/10.1145/333515
Unlocking Data to Improve Public Policy
No full textPublished as: Hastings JS, Howison M, Lawless T, Ucles J, White P. Unlocking Data to Improve Public Policy. Communications of the ACM 62(10): 48-53. https://doi.org/10.1145/333515
Comparing GPU Implementations of Bilateral and Anisotropic Diffusion Filters for 3D Biomedical Datasets
No full textWe compare the performance of hand-tuned CUDA implementations of bilateral and anisotropic diffusion filters for denoising 3D MRI datasets. Our tests sweep comparable parameters for the two filters and measure total runtime, memory bandwidth, computational throughput, and mean squared errors relative to a noiseless reference dataset
Physics driven behavioural clustering of free-falling paper shapes
No full textMany complex physical systems exhibit a rich variety of discrete behavioural modes. Often, the system complexity limits the applicability of standard modelling tools. Hence, understanding the underlying physics of different behaviours and distinguishing between them is challenging. Although traditional machine learning techniques could predict and classify behaviour well, typically they do not provide any meaningful insight into the underlying physics of the system. In this paper we present a novel method for extracting physically meaningful clusters of discrete behaviour from limited experimental observations. This method obtains a set of physically plausible functions that both facilitate behavioural clustering and aid in system understanding. We demonstrate the approach on the V-shaped falling paper system, a new falling paper type system that exhibits four distinct behavioural modes depending on a few morphological parameters. Using just 49 experimental observations, the method discovered a set of candidate functions that distinguish behaviours with an error of 2.04%, while also aiding insight into the physical phenomena driving each behaviour. © 2019 Howison et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.CREATE-LABTH was supported by EPSRC RG92738 (https://epsrc.ukri.org/) and Mathworks Ltd RG90950 378 (https://uk.mathworks.com/?requestedDomain=). JH was supported by EP/N029003/1 (https://gow.epsrc.ukri.org/NGBOViewGrant.aspx?GrantRef=EP/N029003/1). The funders ha
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CAD Tools for Creating Space-filing 3D Escher Tiles
No full textWe discuss the design and implementation of CAD tools for creating decorative solids that tile 3-space in a regular, isohedral manner. Starting with the simplest case of extruded 2D tilings, we describe geometric algorithms used for maintaining boundary representations of 3D tiles, including a Java implementation of an interactive constrained Delaunay triangulation library and a mesh-cutting algorithm used in layering extruded tiles to create more intricate designs. Finally, we demonstrate a CAD tool for creating 3D tilings that are derived from cubic lattices. The design process for these 3D tiles is more constrained, and hence more difficult, than in the 2D case, and it raises additional user interface issues
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GPU-accelerated denoising of 3D magnetic resonance images
No full textThe raw computational power of GPU accelerators enables fast denoising of 3D MR images using bilateral filtering, anisotropic diffusion, and non-local means. In practice, applying these filtering operations requires setting multiple parameters. This study was designed to provide better guidance to practitioners for choosing the most appropriate parameters by answering two questions: what parameters yield the best denoising results in practice? And what tuning is necessary to achieve optimal performance on a modern GPU? To answer the first question, we use two different metrics, mean squared error (MSE) and mean structural similarity (MSSIM), to compare denoising quality against a reference image. Surprisingly, the best improvement in structural similarity with the bilateral filter is achieved with a small stencil size that lies within the range of real-time execution on an NVIDIA Tesla M2050 GPU. Moreover, inappropriate choices for parameters, especially
scalingparameters, can yield very poor denoising performance. To answer the second question, we perform an autotuning study to empirically determine optimal memory tiling on the GPU. The variation in these results suggests that such tuning is an essential step in achieving real-time performance. These results have important implications for the real-time application of denoising to MR images in clinical settings that require fast turn-around times
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H5hut: A High-Performance I/O Library for Particle-based Simulations
No full textParticle-based simulations running on large high-performance computing systems over many time steps can generate an enormous amount of particle- and field-based data for post-processing and analysis. Achieving high-performance I/O for this data, effectively managing it on disk, and interfacing it with analysis and visualization tools can be challenging, especially for domain scientists who do not have I/O and data management expertise. We present the H5hut library, an implementation of several data models for particle-based simulations that encapsulates the complexity of HDF5 and is simple to use, yet does not compromise performance
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Hybrid Parallelism for Volume Rendering on Large, Multi-core Systems
No full textThis work studies the performance and scalability characteristics of "hybrid" parallel programming and execution as applied to raycasting volume rendering -- a staple visualization algorithm -- on a large, multi-core platform. Historically, the Message Passing Interface (MPI) has become the de-facto standard for parallel programming and execution on modern parallel systems. As the computing industry trends towards multi-core processors, with four- and six-core chips common today and 128-core chips coming soon, we wish to better understand how algorithmic and parallel programming choices impact performance and scalability on large, distributed-memory multi-core systems. Our findings indicate that the hybrid-parallel implementation, at levels of concurrency ranging from 1,728 to 216,000, performs better, uses a smaller absolute memory footprint, and consumes less communication bandwidth than the traditional, MPI-only implementation
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