164 results for University of Canterbury Library, Hann, C.E.

  • Vertical Wind Tunnel for Prediction of Rocket Flight Dynamics

    Bryson, H.; Sültrop, H.P.; Buchanan, G.; Hann, C.E.; Snowdon, M.; Rao, A.; Slee, A.; Fanning, K.; Wright, D.; McVicar, J.; Clark, B.; Harris, G.; Chen, X.Q. (2016)

    Journal Articles
    University of Canterbury Library

    A customized vertical wind tunnel has been built by the University of Canterbury Rocketry group (UC Rocketry). This wind tunnel has been critical for the success of UC Rocketry as it allows the optimization of avionics and control systems before flight. This paper outlines the construction of the wind tunnel and includes an analysis of flow quality including swirl. A minimal modelling methodology for roll dynamics is developed that can extrapolate wind tunnel behavior at low wind speeds to much higher velocities encountered during flight. The models were shown to capture the roll flight dynamics in two rocket launches with mean roll angle errors varying from 0.26 to 1.5 across the flight data. The identified model parameters showed consistent and predictable variations over both wind tunnel tests and flight, including canard–fin interaction behavior. These results demonstrate that the vertical wind tunnel is an important tool for the modelling and control of sounding rockets.

    View record details
  • A simplified model for mitral valve dynamics

    Moorhead, K.T.; Paeme, S.; Chase, J.G.; Kolh, P.; Pierard, L.; Hann, C.E.; Dauby, P.C.; Desaive, T. (2013)

    Journal Articles
    University of Canterbury Library

    Located between the left atrium and the left ventricle, the mitral valve controls flow between these two cardiac chambers. Mitral valve dysfunction is a major cause of cardiac dysfunction and its dynamics are little known. A simple non-linear rotational spring model is developed and implemented to capture the dynamics of the mitral valve. A measured pressure difference curve was used as the input into the model, which represents an applied torque to the anatomical valve chords. A range of mechanical model hysteresis states were investigated to find a model that best matches reported animal data of chord movement during a heartbeat. The study is limited by the use of one dataset from the literature. However, results clearly highlight some physiological issues, such as the damping and chord stiffness changing within one cardiac cycle. Very good correlation was achieved between modeled and experimental valve angle with 1-10% absolute error in the best case, indicating good promise for future simulation of cardiac valvular dysfunction, such as mitral regurgitation or stenosis. In particular, the model provides a pathway to capturing these dysfunctions in terms of modeled stiffness or elastance that can be directly related to anatomical, structural defects and dysfunction.

    View record details
  • Validation of subject-specific cardiovascular system models from porcine measurements

    Revie, J.A.; Stevenson, D.J.; Chase, J.G.; Hann, C.E.; Lambermont, B.C.; Ghuysen, A.; Kolh, P.; Shaw, G.M.; Heldmann, S.; Desaive, T. (2013)

    Journal Articles
    University of Canterbury Library

    A previously validated mathematical model of the cardiovascular system (CVS) is made subject-specific using an iterative, proportional gain-based identification method. Prior works utilised a complete set of experimentally measured data that is not clinically typical or applicable. In this paper, parameters are identified using proportional gain-based control and a minimal, clinically available set of measurements. The new method makes use of several intermediary steps through identification of smaller compartmental models of CVS to reduce the number of parameters identified simultaneously and increase the convergence stability of the method. This new, clinically relevant, minimal measurement approach is validated using a porcine model of acute pulmonary embolism (APE).

    View record details
  • Model-Based Insulin Sensitivity as a Sepsis Diagnostic in Critical Care

    Blakemore, A.; Wang, S.; Le Compte, A.J.; Wong, X.W.; Shaw, G.M.; Lotz, T.; Hann, C.E.; Chase, J.G. (2008)

    Journal Articles
    University of Canterbury Library

    Background: Timely diagnosis and treatment of sepsis in critical care require significant clinical effort, experience, and resources. Insulin sensitivity is known to decrease with worsening condition and could thus be used to aid diagnosis. Some glycemic control protocols are able to identify insulin sensitivity in real time. Methods: Receiver operating characteristic curves and cutoff insulin sensitivity values for diagnosing sepsis were calculated for model-based insulin sensitivity (SI) and a simpler metric (SSI) that was estimated from glycemic control data of 30 patients with sepsis and can be calculated in real time without use of a computer. Results were compared to the insulin sensitivity profiles of a general intensive care unit population of 113 patients without sepsis and 30 patients with sepsis, comprising a total of 26,453 patient hours. Patients with sepsis were identified as having sepsis based on a sepsis score (ss) of 3 or higher (ss = 0–4 for increasing severity). Patients with type I or type II diabetes were excluded. Ethics approval for this study was granted by the South Island Regional Ethics Committee. Results: Receiver operating characteristic cutoff values of SI = 8 × 10-5 liter mU-1 min-1 and SSI = 2.8 × 10-4 liter mU-1 min-1 were determined for ss = 3. The model-based SI fell below this value in 15% of all patient hours. The SI test had a negative predictive value of 99.8%. The test sensitivity was 78% and specificity was 82%. However, the positive predictor value was 2.8%. Slightly lower sensitivity (68.8%) and specificity (81.7%), but equally good negative prediction (99.7%), were obtained for the estimated SSI. Conclusions: Insulin sensitivity provides a negative predictive diagnostic for sepsis. High insulin sensitivity rules out sepsis for the majority of patient hours and may be determined noninvasively in real time from glycemic control protocol data. Low insulin sensitivity is not an effective diagnostic, as it can equally mark the presence of sepsis or other conditions.

    View record details
  • Development of a Clinical Type 1 Diabetes Metabolic System Model and in Silico Simulation Tool

    Wong, X.W.; Chase, J.G.; Hann, C.E.; Lotz, T.; Lin, J.; Le Compte, A.J.; Shaw, G.M. (2008)

    Journal Articles
    University of Canterbury Library

    Invited journal symposium paper

    View record details
  • In Silico Simulation of Long-Term Type 1 Diabetes Glycemic Control Treatment Outcomes

    Wong, X.W.; Chase, J.G.; Hann, C.E.; Lotz, T.; Lin, J.; Le Compte, A.J.; Shaw, G.M. (2008)

    Journal Articles
    University of Canterbury Library

    Invited journal symposium paper

    View record details
  • A Subcutaneous Insulin Pharmacokinetic Model for Computer Simulation in a Diabetes Decision Support Role: Validation and Simulation

    Chase, J.G.; Hann, C.E.; Shaw, G.M.; Lotz, T.F.; Lin, J.; Le Compte, A.J.; Wong, J. (2008)

    Journal Articles
    University of Canterbury Library

    Companion paper #2

    View record details
  • A Benchmark Data Set for Model-Based Glycemic Control in Critical Care

    LeCompte, A.J.; Shaw, G.M.; Blakemore, A.; Wong, J.; Lin, J.; Hann, C.E.; Chase, J.G. (2008)

    Journal Articles
    University of Canterbury Library

    Comes with free download data set file ( http://www.journalofdst.org/Journal/pdf/July2008/VOL-2-4-ORG4-CHASE-DATA-SUPPLEMENT-DS1.XLS ) and was made free immediately by the journal as a result

    View record details
  • Impact of system identification methods in metabolic modeling and control

    Wong, J.; Shaw, G.M.; Hann, C.E.; Lotz, T.; Lin, J.; Chase, J.G. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    Metabolic modelling can significantly improve control of hyperglycaemia. Clinical control demands physiological accuracy in identifying patient specific parameters. However, typically used non-linear and non-convex identification methods and models can deliver sub-optimal results, affecting control prediction. This research compares a typical non-linear method and a novel linear, convex method for an accepted metabolic control model using retrospective clinical control data. Results show increased errors in fitting for the non-linear fitting method. A significant (140-660X) increase in computational efficiency is also reported. The methods and results presented can be readily applied and generalised to a wider set of pharmacokinetic and pharmacodynamic systems that use similar linear and non-linear models.

    View record details
  • Identification of time-varying cardiac disease state using a minimal cardiac model with reflex actions

    Hann, C.E.; Andreassen, S.; Smith, B.W.; Shaw, G.M.; Chase, J.G.; Jensen, P.L. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    A minimal cardiac model that accurately captures the essential cardio- vascular system dynamics has been developed. Standard parameter identification methods for this model are highly non-linear and non-convex, hindering clinical application, given the limited measurements available in an intensive care unit. This paper presents an integral based identification method that transforms the problem into a linear, convex problem. Five common disease states including four fundamental types of shock, are identified to within 10% without false identification. Clinically, it enables medical staff to rapidly obtain a patient specific model to assist in diagnosis and therapy selection.

    View record details
  • Efficient computation of the infimum in H∞ control for seismic structures

    Wu, W-H.; Hann, C.E.; Chase, J.G. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    An important consideration in the design of H∞ controllers is the optimal norm of the H∞ control problem. This value determines the lowest value of the H∞ norm that can be obtained with the problem and system defined. Hence, it represents a design limit, but one that is computationally intractable and difficult to obtain. A new method for determining the optimal H∞ norm of a state feedback system is presented. It is based on the application of discriminant to check a stability condition on the Hamiltonian matrix that is associated with the infimum value. In addition, a generalized eigenvalue problem is deduced from the discriminant stability condition to avoid any required iteration. The overall approach provides a highly accurate approximation of the optimal value with minimum computation compared to other approaches in the literature.

    View record details
  • Clinical validation of a model-based glycaemic control design approach and comparison to other clinical protocols

    Chase, J.G.; Shaw, G.M.; Hann, C.E.; LeCompte, A.; Lonergan, T.; Willacy, M.B.; Wong, X-W.; Lin, J.; Lotz, T. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    Invited paper in special session

    View record details
  • Insulin + nutrition control for tight critical care glycaemic regulation

    Chase, J.G.; Wong, J.; Lin, J.; LeCompte, A.; Lotz, T.; Lonergan, T.; Willacy, M.B.; Hann, C.E.; Shaw, G.M. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    A new insulin and nutrition control method for tight glycaemic control in critical care is presented from concept to clinical trials to clinical practice change. The primary results show that the method can provide very tight glycaemic control in critical care for a very critically ill cohort. More specifically, the final clinical practice change protocol provided 2100 hours of control with average blood glucose of 5.8 +/- 0.9 mmol/L for an initial 10 patient pilot study. It also used less insulin, while providing the same or greater nutritional input, as compared to retrospective hospital control for a relatively very critically ill cohort with high insulin resistance.

    View record details
  • Clinical cardiovascular identification with limited data and fast forward simulation

    Hann, C.E.; Chase, J.G.; Shaw, G.M.; Andreassen, S.; Smith, B.W. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    A minimal cardiac model has been developed that captures the major dynamics of the cardio-vascular system (CVS). This model is extended to simulate time varying disease state including reflex actions and an integral based identification method is presented that enables linear and convex parameter identification. Two common time varying disease states are identified to within 10% without false identification. Also the valve law in this model is reformulated in terms of Heaviside functions, and a unique closed form analytical solution is obtained for the ventricular interaction equation. This enables rapid forward simulations of the model. Clinically, the method ensures medical staff can rapidly obtain a patient specific model and can simulate a large number of therapy combinations to find the best treatment

    View record details
  • Highly correlated model-based testing of insulin sensitivity – initial results for a proposed low-intensity test

    Lotz, T.; Chase, J.G.; McAuley, K.A.; Shaw, G.M.; Wong, X-W.; Lin, J.; LeCompte, A.; Hann, C.E.; Mann, J.I. (2006)

    Conference Contributions - Other
    University of Canterbury Library

    View record details
  • Real-time integral based structural health monitoring

    Singh-Levett, I.; Chase, J.G.; Hann, C.E.; Deam, B.L. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    An algorithm has been developed to provide real-time structural health monitoring during earthquake events. For a given input ground acceleration the algorithm matches the Bouc-Wen hysteresis model to structural response data using piecewise least squares fitting. The methodology identifies pre-yield and post-yield stiff-ness, elastic and plastic components of displacement and final residual displacement. This approach is particularly useful for rapid assessment of structural safety by owners or civil defense authorities. The algorithm is tested with simulated response data using the El Centro and Kobe earthquake records. Using simulated data for a two degree of freedom shear building model, the algorithm captures stiffness to within 2% of the real value and permanent deflection to within 5% when significant non-linear response occurs. This is achieved with acceleration data sampled at 1KHz and displacement data sampled at 10Hz

    View record details
  • Determining the seismic transfer function infimum for a structural design

    Hann, C.E.; Chase, J.G.; Wu, W-H. (2006)

    Conference Contributions - Published
    University of Canterbury Library

    The overall seismic structural design problem, for a given structure, may be considered in terms of its transfer function from the ground motion input to the response output. In this regard, it is the transfer function infimum, or the greatest lower bound, over all possible ground motions that is of interest, as it defines the maximum structural response to any ground motion. More importantly, this infimum value can change over time as damage occurs, and tracking it in real-time would provide significant health monitoring information. However, determining this value, especially for large or complex models, is computationally intense and numerically very ill-conditioned. This research presents a highly efficient, stable and computationally rapid method for determining the seismic transfer function infimum for any structural model undergoing a ground motion. This method is based on the Routh-Hurwitz criterion and provides a simple semi-analytical approach, enabling real-time computation for a given model

    View record details
  • Integral-based identification of patient specific parameters for a minimal cardiac model

    Hann, C.E.; Chase, J.G.; Shaw, G.M. (2006)

    Journal Articles
    University of Canterbury Library

    A minimal cardiac model has been developed which accurately captures the essential dynamics of the cardiovascular system (CVS). However, identifying patient specific parameters with the limited measurements often available, hinders the clinical application of the model for diagnosis and therapy selection. This paper presents an integral based parameter identification method for fast, accurate identification of patient specific parameters using limited measured data. The integral method turns a previously non-linear and non-convex optimization problem into a linear and convex identification problem. The model includes ventricular interaction and physiological valve dynamics. A healthy human state and two disease states, Valvular Stenosis and Pulmonary Embolism, are used to test the method. Parameters for the healthy and disease states are accurately identified using only discretized flows into and out of the two cardiac chambers, the minimum and maximum volumes of the left and right ventricles, and the pressure waveforms through the aorta and pulmonary artery. These input values can be readily obtained non-invasively using echo-cardiography and ultra-sound, or invasively via catheters that are often used in Intensive Care. The method enables rapid identification of model parameters to match a particular patient condition in clinical real time (3-5 minutes) to within a mean value of 4 – 8% in the presence of 5 – 15% uniformly distributed measurement noise. The specific changes made to simulate each disease state are correctly identified in each case to within 5% without false identification of any other patient specific parameters. Clinically, the resulting patient specific model can then be used to assist medical staff in understanding, diagnosis and treatment selection.

    View record details
  • Fast normalized cross correlation for motion tracking using basis functions

    Hii, A.; Hann, C.E.; Chase, J.G.; Van Houten, E.E.W. (2006)

    Journal Articles
    University of Canterbury Library

    Digital Image-based Elasto-tomography (DIET) is an emerging method for noninvasive breast cancer screening. Effective clinical application of the DIET system requires highly accurate motion tracking of the surface of an actuated breast with minimal computation. Normalized cross correlation (NCC) is the most robust correlation measure for determining similarity between points in two or more images providing an accurate foundation for motion tracking. However, even using fast fourier transform (FFT) methods, it is too computationally intense for rapidly managing several large images. A significantly faster method of calculating the NCC is presented that uses rectangular approximations in place of randomly placed landmark points or the natural marks on the breast. These approximations serve as an optimal set of basis functions that are automatically detected, dramatically reducing computational requirements. To prove the concept, the method is shown to be 37-150 times faster than the FFT-based NCC with the same accuracy for simulated data, a visco-elastic breast phantom experiment and human skin. Clinically, this approach enables thousands of randomly placed points to be rapidly and accurately tracked providing high resolution for the DIET system

    View record details
  • Model predictive glycaemic regulation in critical illness using insulin and nutrition input: a pilot study

    Wong, X-W.; Chase, J.G.; Shaw, G.M.; Hann, C.E.; Lotz, T.; Lin, J.; Singh-Levett, I.; Hollingsworth, L.J.; Wong, O.S.W.; Andreassen, S. (2006)

    Journal Articles
    University of Canterbury Library

    This paper develops and presents a pilot study of a long-term controller for safe regulation of glycaemia under elevated insulin resistance and glucose intolerance in critically ill patients by modulating enteral nutrition inputs in addition to conventional basal-bolus intravenous insulin therapy. Clinical proof-of-concept pilot trials of the algorithm are performed which show the algorithm adaptability to time-varying intraas well as inter-patient variability in condition while requiring relatively infrequent glucose measurement. This research is a step towards randomized, comparative cohort studies of clinical outcomes using the developed protocol. Previous blood glucose control research includes controlled experiments in insulin infusion by Hovorka et al. [26], Chee et al. [27], and Chase et al. [18, 28]. Adaptive bolus-based control using insulin-alone by Chase et al. [18], is the basis of this work. The primary difference in this research is the improvement in control under elevated insulin resistance by modulation of nutritional support in addition to insulin input

    View record details