Static and Dynamic Error Correction of a Computer-Aided Mechanical Navigation Linkage for Arthroscopic Hip Surgery

While beneficially decreasing the necessary incision size, arthroscopic hip surgery increases the surgical complexity due to loss of joint visibility. To ease such difficulty, a computer-aided mechanical navigation system was developed to present the location of the surgical tool relative to the patient¿s hip joint. A preliminary study reduced the position error of the tracking linkage with limited static testing trials. In this study, a correction method, including a rotational correction factor and a length correction function, was developed through more in-depth static testing. The developed correction method was then applied to additional static and dynamic testing trials to evaluate its effectiveness. For static testing, the position error decreased from an average of 0.384 inches to 0.153 inches, with an error reduction of 60.5%. Three parameters utilized to quantify error reduction of dynamic testing did not show consistent results. The vertex coordinates achieved 29.4% of error reduction, yet with large variation in the upper vertex. The triangular area error was reduced by 5.37%, however inconsistent among all five dynamic trials. Error of vertex angles increased, indicating a shape torsion using the developed correction method. While the established correction method effectively and consistently reduced position error in static testing, it did not present consistent results in dynamic trials. More dynamic paramters should be explored to quantify error reduction of dynamic testing, and more in-depth dynamic testing methodology should be conducted to further improve the accuracy of the computer-aided nagivation system.

Anisotropy in plastic deformation of extruded magnesium alloy sheet during tensile straining at high temperature

Experimental measurements are used to characterize the anisotropy of flow stress in extruded magnesium alloy AZ31 sheet during uniaxial tension tests at temperatures between 350°C and 450°C, and strain rates ranging from 10-5 to 10-2 s-1. The sheet exhibits lower flow stress and higher tensile ductility when loaded with the tensile axis perpendicular to the extrusion direction compared to when it is loaded parallel to the extrusion direction. This anisotropy is found to be grain size, strain rate, and temperature dependent, but is only weakly dependent on texture. A microstructure based model (D. E. Cipoletti, A. F. Bower, P. E. Krajewski, Scr. Mater., 64 (2011) 931–934) is used to explain the origin of the anisotropic behavior. In contrast to room temperature behavior, where anisotropy is principally a consequence of the low resistance to slip on the basal slip system, elevated temperature anisotropy is found to be caused by the grain structure of extruded sheet. The grains are elongated parallel to the extrusion direction, leading to a lower effective grain size perpendicular to the extrusion direction. As a result, grain boundary sliding occurs more readily if the material is loaded perpendicular to the extrusion direction.

Influence of Engineering Instructors' Teaching and Learning Beliefs on Pedagogies in Engineering Science Courses

This study explored how academics' beliefs about teaching and learning influenced their teaching in engineering science courses typically taught in the second or third year of 4-year engineering undergraduate degrees. Data were collected via a national survey of 166 U. S. statics instructors and interviews at two different institutions with 17 instructors of engineering science courses such as thermodynamics, circuits and statics. The study identified a number of common beliefs about how to best support student learning of these topics; each is discussed in relation to the literature about student development and learning. Specific recommendations are given for educational developers to encourage use of research-based instructional strategies in these courses.

Estimates of Use of Research-Based Instructional Strategies in Core Electrical or Computer Engineering Courses

Many research-based instruction strategies (RBISs) have been developed; their superior efficacy with respect to student learning has been demonstrated in many studies. Collecting and interpreting evidence about: 1) the extent to which electrical and computer engineering (ECE) faculty members are using RBISs in core, required engineering science courses, and 2) concerns that they express about using them, are important aspects of understanding how engineering education is evolving. The authors surveyed ECE faculty members, asking about their awareness and use of selected RBISs. The survey also asked what concerns ECE faculty members had about using RBISs. Respondent data showed that awareness of RBISs was very high, but estimates of use of RBISs, based on survey data, varied from 10% to 70%, depending on characteristics of the strategy. The most significant concern was the amount of class time that using an RBIS might take; efforts to increase use of RBISs must address this.