Rig Hunter | UNASAM - Academia.edu (original) (raw)

Papers by Rig Hunter

Computer Methods in Biomechanics and Biomedical Engineering, 2008

Accurate measurement of knee-joint kinematics is critical for understanding the biomechanical fun... more Accurate measurement of knee-joint kinematics is critical for understanding the biomechanical function of the knee in vivo. Measurements of the relative movements of the bones at the knee are often used in inverse dynamics analyses to estimate the net muscle torques exerted about the joint, and as inputs to finite-element models to accurately assess joint contact. The fine joint translations that contribute to patterns of joint stress are impossible to measure accurately using traditional video-based motion capture techniques. Sub-millimetre changes in joint translation can mean the difference between contact and no contact of the cartilage tissue, leading to incorrect predictions of joint loading. This paper describes the use of low-dose X-ray fluoroscopy, an in vivo dynamic imaging modality that is finding increasing application in human joint motion measurement. Specifically, we describe a framework that integrates traditional motion capture, X-ray fluoroscopy and anatomically-based finite-element modelling for the purpose of assessing joint function during dynamic activity. We illustrate our methodology by applying it to study patellofemoral joint function, wherein the relative movements of the patella are predicted and the corresponding joint-contact stresses are calculated for a step-up task.

Journal of Biomechanics, 2010

Studies of three-dimensional patellar kinematics done with little or no applied load may not accu... more Studies of three-dimensional patellar kinematics done with little or no applied load may not accurately reflect kinematics at physiological load levels, and may provide different results to those acquired with greater applied loads or in physiologic weightbearing. We report the effect of load magnitude on threedimensional patellar kinematics (flexion, spin and tilt; proximal, lateral and anterior translation) using a validated, sequential static, MRI-based method. Ten healthy subjects loaded their study knee to 0% (no load), 15% and 30% bodyweight (BW) using a custom designed loading rig. Differences between loading levels were determined as a function of knee flexion for each kinematic parameter using linear hierarchical random-effects models. Quadratic and random slope terms were included in the models when significant. We found that the patellae flexed less with knee flexion at 30% BW load compared to 0% BW load (po 0.001) and 15% BW (p ¼0.004) load. The patellae showed a slight medial tilt with knee flexion at 30% BW load which was significantly less than the medial tilt seen at 0% BW load (p ¼0.017) and 15% BW load (p ¼ 0.043) with knee flexion. Small but statistically significant differences were also observed for proximal and anterior translation; the patellae were in a more proximal and posterior position at 30% BW load than at 0% BW load (p ¼0.010 and p ¼0.005, respectively) and 15% BW load (p o 0.001 and p¼ 0.029, respectively). Since differences in three-dimensional patellar kinematics were observed between loading levels, magnitudes of prescribed loads must be considered when designing studies and comparing results between studies.

SumTime-Turbine produces textual summaries of archived timeseries data from gas turbines. These s... more SumTime-Turbine produces textual summaries of archived timeseries data from gas turbines. These summaries should help experts understand large data sets that cannot be visually presented in a single graphical display. SumTime-Turbine is based on pattern detection, knowledge-based temporal abstraction (KBTA), and natural language generation (NLG) technology. A prototype version of the system has been implemented and is currently being evaluated.

Wildlife Society Bulletin, 2005

Waterfowl managers in Minnesota and other states are concerned that increased kill rates associat... more Waterfowl managers in Minnesota and other states are concerned that increased kill rates associated with the use of spinning-wing decoys (SWDs) may negatively affect local breeding populations of mallards (Anas platyrhynchos). Accordingly, we conducted 219 experimental hunts to evaluate hunting vulnerability of mallards to SWDs during the 2002 duck season in Minnesota. During each hunt, we tested 2 SWD treatments: 1) SWDs turned OFF (control), and 2) SWDs turned ON (experimental) during alternate 15-minute sampling periods that were separated by 5-minute buffer periods. We found that mallard flocks (>1 duck) were 2.91 times more likely to respond (i.e., approach within 40 m of hunters), and sizes of responding mallard flocks were 1.25 times larger, on average, when SWDs were turned ON than OFF. Mallards killed/hour/hunter/hunt averaged 4.71 times higher (P<0.001) when SWDs were turned ON than OFF. More hatch-year (HY) and after-hatch-year (AHY) mallards were killed when SWDs were turned ON than OFF; however, AHYs were relatively less likely than were HYs to be killed with SWDs turned ON. We found no evidence that SWDs reduced crippling or allowed hunters to harvest relatively more drakes than hens. Using a worst-case scenario model, we predicted that if 47% and 79% of Minnesota hunters had used SWDs in 2000 and 2002, respectively, Minnesota mallard harvests would have increased by a factor of 2. However, increasing use of SWDs by northern hunters may result in a partial redistribution of annual mallard harvests if naive ducks are harvested upon initial exposures to SWDs, and those ducks that survive become habituated to SWDs, as suggested by our results. Our study was confined to a single hunting season in Minnesota and thus did not assess whether vulnerability of mallards to hunters using SWDs varied among years or geographically. A multi-year, flyway-wide study is needed to make stronger and more rigorous inferences regarding potential changes in harvest distribution and annual harvest rates of mallards due to increasing use of SWDs by hunters in North America.

Models of ventricular mechanics have been developed over the last 20 years to include finite defo... more Models of ventricular mechanics have been developed over the last 20 years to include finite deformation theory, anisotropic and inhomogeneous material properties and an accurate representation of ventricular geometry using finite element methods. The sequence of electrical activation in the myocardium is also modeled using ionic current based cellular models and reaction-diffusion equations at the tissue level solved with multi-grid techniques on a fine resolution mesh defined in the material coordinates of the deforming finite element mechanics mesh. This talk will describe the development of a finite element model of the geometry and fibrous-sheet structure of the pig myocardium applied to the solution of the equations governing cardiac electro-mechanics. The finite element model of the left and right ventricular myocardium, using geometric measurements from potassium arrested pig hearts, is defined in rectangular Cartesian coordinates with tri-cubic Hermite basis functions1. Measurements of fibre and sheet orientations2,3 are obtained with a purpose-built instrument that combines a 3D confocal microscope with a precision mill4. Passive material properties are measured on tissue segments using purpose-built biaxial and shear testing rigs and are fitted with the "pole-zero" constitutive law parameters5. Active myofilament properties are measured using isolated trabeculae and fitted with the HMT model6. Stress and strain distributions throughout the cardiac cycle are determined by solving the governing equations from finite deformation elasticity theory, using the above anatomical model and constitutive parameters, and with ventricular pressure boundary conditions7.

Animal Behaviour, 2008

Sound waves typically radiate from a vocalizing animal with unequal amplitude in different direct... more Sound waves typically radiate from a vocalizing animal with unequal amplitude in different directions; this may profoundly affect communication, favouring adaptations that use or compensate for this directionality. Previous studies suggest that variation in directionality among vocalization types is related to function, with vocalizations such as alerts being relatively omnidirectional, thus maximizing the number of surrounding receivers, and vocalizations such as courtship calls being relatively directional, thus reducing eavesdropping by beaming sounds at the targeted receiver. Here we examine variation within a vocalization type, bird songs, to test hypotheses about how variation in song directionality relates to singing behaviour and the social context of singing. We measured the directionality and amplitude of red-winged blackbird songs in the field using calibrated microphones encircling the bird. We found variation in directionality among song types, possibly allowing males to select songs from their repertoires with directionality to suit the social context. We found support for the hypothesis that the amplitude and directionality of songs are related, with more-directional songs delivered at higher amplitudes. In addition, we found support for the hypothesis that directionality is negatively related to the degree of male rotation on the perch between vocalizations, suggesting that males may combine omnidirectional songs and rotation to broadcast their songs, and may face the receiver and produce directional songs during direct interactions. We also observed variation in directionality among note types within songs. These results suggest that directionality plays an important role in shaping song structure and singing behaviour in red-winged blackbirds.

From a historical perspective we can distinguish an initial period in the DNA microarray technolo... more From a historical perspective we can distinguish an initial period in the DNA microarray technology in which almost all publications were related to reproducibility and sensitivity issues. Thus, many classical microarray papers dating from the late nineties were simple proof-of-prineiple experiments (Eisen et al., 1998); (Perou et al., 1999)

In the time domain complex non-linear systems can be difficult and cumbersome to manipulate and u... more In the time domain complex non-linear systems can be difficult and cumbersome to manipulate and understand; transforming them into the frequency domain using the signals Instantaneous Frequency (IF) allowing simplifications, that make analysis of these circuits more ...

Journal of Artificial Intelligence Research, 2003

Natural language generation (nlg) systems are computer software systems that produce texts in Eng... more Natural language generation (nlg) systems are computer software systems that produce texts in English and other human languages, often from non-linguistic input data. nlg systems, like most ai systems, need substantial amounts of knowledge. However, our experience in two nlg projects suggests that it is difficult to acquire correct knowledge for nlg systems; indeed, every knowledge acquisition (ka) technique we tried had significant problems. In general terms, these problems were due to the complexity, novelty, and poorly understood nature of the tasks our systems attempted, and were worsened by the fact that people write so differently. This meant in particular that corpus-based ka approaches suffered because it was impossible to assemble a sizable corpus of high-quality consistent manually written texts in our domains; and structured expert-oriented ka techniques suffered because experts disagreed and because we could not get enough information about special and unusual cases to build robust systems. We believe that such problems are likely to affect many other nlg systems as well. In the long term, we hope that new ka techniques may emerge to help nlg system builders. In the shorter term, we believe that understanding how individual ka techniques can fail, and using a mixture of different ka techniques with different strengths and weaknesses, can help developers acquire nlg knowledge that is mostly correct.

Ocean Dynamics, 2006

Overtides and compound tides are generated by nonlinear mechanisms operative primarily in shallow... more Overtides and compound tides are generated by nonlinear mechanisms operative primarily in shallow waters. Their presence complicates tidal analysis owing to the multitude of new constituents and their possible frequency overlap with astronomical tides. The science of nonlinear tides was greatly advanced by the pioneering researches of Christian Le Provost who employed analytical theory, physical modeling, and numerical modeling in many extensive studies, especially of the tides of the English Channel. Le Provost’s complementary work with satellite altimetry motivates our attempts to merge these two interests. After a brief review, we describe initial steps toward the assimilation of altimetry into models of nonlinear tides via generalized inverse methods. A series of barotropic inverse solutions is computed for the M $_4$ tide over the northwest European Shelf. Future applications of altimetry to regions with fewer in situ measurements will require improved understanding of error covariance models because these control the tradeoffs between fitting hydrodynamics and data, a delicate issue in coastal regions. While M $_4$ can now be robustly determined along the Topex/Poseidon satellite ground tracks, many other compound tides face serious aliasing problems.

Journal of Neurology Neurosurgery and Psychiatry, 2007

To explore the driving problems associated with Parkinson&amp;amp;amp;amp;amp;amp;amp;amp... more To explore the driving problems associated with Parkinson&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease (PD) and to ascertain whether any clinical features or tests predict driver safety. The driving ability of 154 individuals with PD referred to a driving assessment centre was determined by a combination of clinical tests, reaction times on a test rig and an in-car driving test. The majority of cases (104, 66%) were able to continue driving although 46 individuals required an automatic transmission and 10 others needed car modifications. Ability to drive was predicted by the severity of physical disease, age, presence of other associated medical conditions, particularly dementia, duration of disease, brake reaction, time on a test rig and score on a driving test (all p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001). The level of drug treatment and the length of driving history were not correlated. Discriminant analysis revealed that the most important features in distinguishing safety to drive were severe physical disease (Hoehn and Yahr stage 3), reaction time, moderate disease associated with another medical condition and high score on car testing. Most individuals with PD are safe to drive, although many benefit from car modifications or from using an automatic transmission. A combination of clinical tests and in-car driving assessment will establish safety to drive, and a number of clinical correlates can be shown to predict the likely outcome and may assist in the decision process. This is the largest series of consecutive patients seen at a driving assessment centre reported to date, and the first to devise a scoring system for on-road driving assessment.

Journal of Geophysical Research, 2008

1] The shelf sea seasonal thermocline is a critical interface within the marine environment, sepa... more 1] The shelf sea seasonal thermocline is a critical interface within the marine environment, separating the euphotic zone from nutrient-rich deep water. Fluxes across the thermocline therefore represent a key biogeochemical pathway. In this paper we quantify the rate of mixing across the seasonal thermocline for a location in the Celtic Sea and investigate the processes responsible for driving thermocline fluxes. Profiles of the rate of dissipation of turbulent kinetic energy (e) show enhanced dissipation within the thermocline region ($6 Â 10 À5 W m À3 ). The diffusivity implied by these measurements is $0.5 cm 2 s À1 , similar to previous shelf sea studies, and is sufficient to explain the observed warming of the deep water, suggesting that vertical mixing is the dominant control on water column structure. Two potential sources of mixing energy are identified, the internal tide and near-inertial waves. The mechanism of energy transfer from the candidate mixing mechanisms to turbulence is not clear. Thermocline dissipation rates were found to have no Richardson number dependence, but scaled positively with N 2 and S 2 , in agreement with a previous turbulence parameterization. Application of this model to our data does a good job of capturing the mean characteristics of the observed heating flux across the thermocline, although none of the short-term fluctuations in mixing were reproduced.