Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models

Both community ecology and conservation biology seek further understanding of factors governing the advance of an invasive species. We model biological invasion as an individual-based, stochastic process on a two-dimensional landscape. An ecologically superior invader and a resident species compete for space preemptively. Our general model includes the basic contact process and a variant of the Eden model as special cases. We employ the concept of a "roughened" front to quantify effects of discreteness and stochasticity on invasion; we emphasize the probability distribution of the front-runner's relative position. That is, we analyze the location of the most advanced invader as the extreme deviation about the front's mean position. We find that a class of models with different assumptions about neighborhood interactions exhibit universal characteristics. That is, key features of the invasion dynamics span a class of models, independently of locally detailed demographic rules. Our results integrate theories of invasive spatial growth and generate novel hypotheses linking habitat or landscape size (length of the invading front) to invasion velocity, and to the relative position of the most advanced invader.Comment: The original publication is available at www.springerlink.com/content/8528v8563r7u2742

Image Guided Orthopaedic Surgery Design and Analysis

Within the next few years it is envisaged that a number of computer assisted surgery products will become available. For many surgical procedures, outcome of surgery will rely on the accuracy and repeatability with which a computer assisted surgical tool performs its task. This paper presents a Computer Assisted Orthopaedic System (CAOS) which takes an image guided approach to planning and implementing a trajectory, to assist an orthopaedic surgeon. Accurate delivery of this trajectory is achieved via an intelligent guide. This paper details the design issues and identifies the registration and calibration techniques used by the CAOS intelligent guide. The paper also enumerates, and where possible quantifies, the factors that influence the accuracy performance of the system. Accuracy trees are used to show the root source of inaccuracies and how they propagate and combine in a system. Keywords: Orthopaedic surgery; passive manipulators; image intensifier; registration; calibration; co..

A Computer Assisted Orthopaedic System for Distal Locking of Intramedullary Nails

The CAOS system aims to assist the orthopaedic surgeon in performing intramedullary nail locking, through the introduction of suitable technology into the operating theatre environment. The system comprises three components, the Smart Image Intensifier, Trajectory Tactician and Intelligent Drill Guide. The Trajectory Tactician is tailored to the requirements of intramedullary nail locking. The method requires the capture of two distortion free x-ray images that are processed, extracting both the projections of the nail edge boundaries and the projections of the distal locking holes. Mathematical modelling determines the position and orientation of the nail, which can be confirmed by semi-automatic positioning of the Smart Image Intensifier to achieve a perfect circle projection of the selected distal locking hole. The trajectory is then implemented using the Intelligent Drill Guide. 1. Introduction The CAOS (Computer Assisted Orthopaedic Systems) group, a joint venture between the Un..

Sensitive and Feasible Specimen Collection and Testing Strategies for Diagnosing Tuberculosis in Young Children

Importance: Criterion-standard specimens for tuberculosis diagnosis in young children, gastric aspirate (GA) and induced sputum, are invasive and rarely collected in resource-limited settings. A far less invasive approach to tuberculosis diagnostic testing in children younger than 5 years as sensitive as current reference standards is important to identify. Objective: To characterize the sensitivity of preferably minimally invasive specimen and assay combinations relative to maximum observed yield from all specimens and assays combined. Design, Setting, and Participants: In this prospective cross-sectional diagnostic study, the reference standard was a panel of up to 2 samples of each of 6 specimen types tested for Mycobacterium tuberculosis complex by Xpert MTB/RIF assay and mycobacteria growth indicator tube culture. Multiple different combinations of specimens and tests were evaluated as index tests. A consecutive series of children was recruited from inpatient and outpatient settings in Kisumu County, Kenya, between October 2013 and August 2015. Participants were children younger than 5 years who had symptoms of tuberculosis (unexplained cough, fever, malnutrition) and parenchymal abnormality on chest radiography or who had cervical lymphadenopathy. Children with 1 or more evaluable specimen for 4 or more primary study specimen types were included in the analysis. Data were analyzed from February 2015 to October 2020. Main Outcomes and Measures: Cumulative and incremental diagnostic yield of combinations of specimen types and tests relative to the maximum observed yield. Results: Of the 300 enrolled children, the median (interquartile range) age was 2.0 (1.0-3.6) years, and 151 (50.3%) were female. A total of 294 met criteria for analysis. Of 31 participants with confirmed tuberculosis (maximum observed yield), 24 (sensitivity, 77%; interdecile range, 68%-87%) had positive results on up to 2 GA samples and 20 (sensitivity, 64%; interdecile range, 53%-76%) had positive test results on up to 2 induced sputum samples. The yields of 2 nasopharyngeal aspirate (NPA) samples (23 of 31 [sensitivity, 74%; interdecile range, 64%-84%]), of 1 NPA sample and 1 stool sample (22 of 31 [sensitivity, 71%; interdecile range, 60%-81%]), or of 1 NPA sample and 1 urine sample (21.5 of 31 [sensitivity, 69%; interdecile range, 58%-80%]) were similar to reference-standard specimens. Combining up to 2 each of GA and NPA samples had an average yield of 90% (28 of 31). Conclusions and Relevance: NPA, in duplicate or in combination with stool or urine specimens, was readily obtainable and had diagnostic yield comparable with reference-standard specimens. This combination could improve tuberculosis diagnosis among children in resource-limited settings. Combining GA and NPA had greater yield than that of the current reference standards and may be useful in certain clinical and research settings.. © 2021 American Medical Association. All rights reserved.12 month embargo; published: 22 February 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]