A Performance Comparison of Continuous and Discontinuous Finite Element Shallow Water Models

We present a comparative study of two finite element shallow water equation (SWE) models: a generalized wave continuity equation based continuous Galerkin (CG) model—an approach used by several existing SWE models—and a recently developed discontinuous Galerkin (DG) model. While DG methods are known to possess a number of favorable properties, such as local mass conservation, one commonly cited disadvantage is the larger number of degrees of freedom associated with the methods, which naturally translates into a greater computational cost compared to CG methods. However, in a series of numerical tests, we demonstrate that the DG SWE model is generally more efficient than the CG model (i) in terms of achieving a specified error level for a given computational cost and (ii) on large-scale parallel machines because of the inherently local structure of the method. Both models are verified on a series of analytic test cases and validated on a field-scale application.     

Integrator backstepping techniques for the tracking control ofpermanent magnet brush DC motors

An integrator backstepping technique is introduced for the design of high-performance motor controllers. The approach is applied to the design of embedded computed torque and output feedback controllers for permanent magnet brush DC (BDC) motors. The proposed controllers are simulated and experimentally verified on a user-developed digital signal processor (DSP) based data acquisition and control (DAC) system. Although the BDC motor is well researched, the results motivate extensions of the proposed techniques to the development of similar controllers for more complex electromechanical systems, such as separately excited DC, permanent magnet stepper, brushless DC, switched reluctance, and AC induction servo motors     

A Fast DC Current Breaker

A fast dc current breaker circuit is presented and analyzed. Relevant design and control parameters are also derived. Furthermore, logic control implementation and power circuit component protection are discussed. It is shown that a simple control strategy is best suited for static loads at predefined load current levels. Also theoretical results are compared with experimental results.     

Pacemaker interference by magnetic fields at power line frequencies

Human exposure to external 50/60-Hz electric and magnetic fields induces electric fields within the body. These induced fields can cause interference with implanted pacemakers. In the case of exposure to magnetic fields, the pacemaker leads are subject to induced electromotive forces, with current return paths being provided by the conducting body tissues. Modern computing resources used in conjunction with millimeter-scale human body conductivity models make numerical modeling a viable technique for examining any such interference. In this paper, an existing well-verified scalar-potential finite-difference frequency-domain code is modified to handle thin conducting wires embedded in the body. The effects of each wire can be included numerically by a simple modification to the existing code. Results are computed for two pacemaker lead insertion paths, terminating at either atrial or ventricular electrodes in the heart. Computations are performed for three orthogonal 60-Hz magnetic field orientations. Comparison with simplified estimates from Faraday's law applied directly to extracorporeal loops representing unipolar leads underscores problems associated with this simplified approach. Numerically estimated electromagnetic interference (EMI) levels under the worst case scenarios are about 40 microT for atrial electrodes, and 140 microT for ventricular electrodes. These methods could also be applied to studying EMI with other implanted devices such as cardiac defibrillators.     

A comparison of three developmental stage scoring systems

In social psychological research the stage metaphor has fallen into disfavor due to concerns about bias, reliability, and validity. To address some of these issues, I employ a multidimensional partial credit analysis comparing moral judgment interviews scored with the Standard Issue Scoring System (SISS) (Colby and Kohlberg, 1987b), evaluative reasoning interviews scored with the Good Life Scoring System (GLSS) (Armon, 1984b), and Good Education interviews scored with the Hierarchical Complexity Scoring System (HCSS) (Commons, Danaher, Miller, and Dawson, 2000). A total of 209 participants between the ages of 5 and 86 were interviewed. The multidimensional model reveals that even though the scoring systems rely upon different criteria and the data were collected using different methods and scored by different teams of raters, the SISS, GLSS, and HCSS all appear to measure the same latent variable. The HCSS exhibits more internal consistency than the SISS and GLSS, and solves some methodological problems introduced by the content dependency of the SISS and GLSS. These results and their implications are elaborated.     

Fluorescent lamp cold starting improvement

Three approaches to improving the efficacy and startup time of commercially available cold cathode fluorescent lamps under cold ambient conditions are evaluated in this paper: heating the tube on one side; heating the tube on two sides; and heating the circumference of the outer tube. The internal power density generated by ion bombardment of the cathode and collisions in the plasma are indirectly obtained by matching simulated axial wall temperatures with those obtained by experiment at room temperature. The estimated power density is used to evaluate the temporal evolution of the axial surface wall temperature under different ambient conditions immediately after a cold start. All simulation results have been obtained using PHOENICS, a computational fluid flow program. Experiments have shown a good correlation between the time taken for the light output to reach an acceptable value and the time taken for the inner tube cold spot to reach a temperature of 0/spl deg/C. These results have been used to estimate heating time for different heater geometries and heater powers. The study shows that the conduction of heat to the outer glass envelope is the limiting process that controls the startup time. Modest improvement in startup time can be achieved by increasing heating power or by moving the heater to the side of the lamp. However, only a heater which entirely surrounds the lamp is capable of substantially decreasing the startup time.     

Fault identification for robot manipulators

Several factors must be considered for robotic task execution in the presence of a fault, including: detection, identification, and accommodation for the fault. In this paper, a nonlinear observer is used to identify a class of actuator faults once the fault has been detected by some other method. Advantages of the proposed fault-identification method are that it is based on the nonlinear dynamic model of a robot manipulator (and hence, can be extended to a number of general Euler Lagrange systems), it does not require acceleration measurements, and it is independent from the controller. A Lyapunov-based analysis is provided to prove that the developed fault observer converges to the actual fault. Experimental results are provided to illustrate the performance of the identification method.     

A Discontinuous Galerkin Method for Three-Dimensional Shallow Water Equations

We describe the application of a local discontinuous Galerkin method to the numerical solution of the three-dimensional shallow water equations. The shallow water equations are used to model surface water flows where the hydrostatic pressure assumption is valid. The authors recently developed a DG\linebreak method for the depth-integrated shallow water equations. The method described here is an extension of these ideas to non-depth-integrated models. The method and its implementation are discussed, followed by numerical examples on several test problems.This revised version was published online in July 2005 with corrected volume and issue numbers.     

Homography-based visual servo tracking control of a wheeled mobile robot

A visual servo tracking controller is developed in this paper for a monocular camera system mounted on an underactuated wheeled mobile robot (WMR) subject to nonholonomic motion constraints (i.e., the camera-in-hand problem). A prerecorded image sequence (e.g., a video) of three target points is used to define a desired trajectory for the WMR. By comparing the target points from a stationary reference image with the corresponding target points in the live image and the prerecorded sequence of images, projective geometric relationships are exploited to construct Euclidean homographies. The information obtained by decomposing the Euclidean homography is used to develop a kinematic controller. A Lyapunov-based analysis is used to develop an adaptive update law to actively compensate for the lack of depth information required for the translation error system. Experimental results are provided to demonstrate the control design.     

A thresholding method for blood-aggregate images

Among the wide ranging forms of medical diagnostic modalities, blood analysis is one of the most common, and is likely to become more important as various blood related diseases become more pervasive. Histogram-based methods are among the most popular for thresholding a biomedical image of blood aggregates in a plastic tube. However, these methods often do not provide good results over the entire area of interest, because the statistical assumptions of the methods are violated: i.e., the results are not independent of the blood aggregate location in the tube. Here, the authors apply some useful modifications to three popular histogram methods in order to meet the statistical criteria for independent samples, and thus improve the methods' accuracy. These modifications include a top-hat (mathematical) transformation to compensate for background variations