Quantification of tool wear using white light interferometry and three-dimensional computational metrology

Although several wear modes can result from machining, the most common tend to be what are referred to as flank wear and crater wear. Flank wear can be easily measured directly from images of a worn cutting tool, and this is the typical method used to quantify the condition of a tool. On the other hand, crater wear is difficult to quantify, and thus has typically been treated in a qualitative manner. The inability to characterize and compare the two wear modes in a quantitative way is an increasingly important problem as the precision of machining operations improves and cutting moves almost exclusively to the nose radius of cutting tools. This paper introduces a new approach to this problem by proposing a technique to quantify both wear modes for direct comparison. The technique measures the volumetric wear loss in the two regions by comparing three-dimensional wear data obtained by white light interferometry with ideal representations of unworn cutting tools. The resulting wear measurements are compared and related to changes in the cutting process, specifically increases in cutting forces and changes in the topography of machined surfaces.     

Cell synchrony and periodic behaviour in yeast populations

The underlying basis for the behaviour of a population of cells is the cell growth and division cycles of the individual cells. Under certain special circumstances, oscillations in cell cultures can be observed that are a reflection of metabolic oscillations, such as in glycolysis, or cell cycle oscillations from a partially synchronized population. These oscillations can sometimes occur spontaneously, as in the chemostat culture of Saccharomyces cerevisiae at low dilution rates, or can be induced using chemical blockers or entrainment by a periodic nutrient environment. Continuous methods for inducing a synchronized culture include the pulsed chemostat, continuous phasing and self-cycling fermentation. Results obtained by studying both spontaneously oscillating cultures and synchronized cultures have provided insight into the mechanisms responsible for the progress and control of the cell cycle as well as the intimate relationship that exists between the cellular dynamics and the dynamics of the environment.     

Structural Analysis of Highly Relaxed GaSb Grown on GaAs Substrates with Periodic Interfacial Array of 90° Misfit Dislocations

We report structural analysis of completely relaxed GaSb epitaxial layers deposited monolithically on GaAs substrates using interfacial misfit (IMF) array growth mode. Unlike the traditional tetragonal distortion approach, strain due to the lattice mismatch is spontaneously relieved at the heterointerface in this growth. The complete and instantaneous strain relief at the GaSb/GaAs interface is achieved by the formation of a two-dimensional Lomer dislocation network comprising of pure-edge (90°) dislocations along both [110] and [1-10]. In the present analysis, structural properties of GaSb deposited using both IMF and non-IMF growths are compared. Moiré fringe patterns along with X-ray diffraction measure the long-range uniformity and strain relaxation of the IMF samples. The proof for the existence of the IMF array and low threading dislocation density is provided with the help of transmission electron micrographs for the GaSb epitaxial layer. Our results indicate that the IMF-grown GaSb is completely (98.5%) relaxed with very low density of threading dislocations (10⁵ cm⁻²), while GaSb deposited using non-IMF growth is compressively strained and has a higher average density of threading dislocations (>10⁹ cm⁻²).     

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.     

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.     

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.     

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