Portfolio Assessment in Aerodynamics

A new way of assessing student learning in an aerodynamics course through the use of portfolios is presented. The approach is portable to any engineering course, with a few modifications depending on content. The main idea is to allow students more responsibility for their own learning. Instead of having everyone in the class perform identical activities (homework, experiments, projects, tests, etc.), a cadre of assignments is made available to them. Students choose and perform (within reason) the ones that suit them better in terms of their own strengths and learning styles. The ultimate goal is for each student to demonstrate a minimum level of competence in analytical, computational, experimental, design, communication, and team skills, while pursuing excellence in at least one from the first four categories. The paper describes the various assignments and options the students have for achieving the learning objectives of the course. It also discusses my observations on the effects of this approach to student learning, the impact on faculty time, and the response from the students. The results from the first two offerings of the course with portfolios show promise for improving student motivation and learning.     

A Method for Computing the 2-D Stability Margin Based on a New Stability Test for 2-D Systems

In this paper, a new method to compute the stability margin of 2-D (two-dimensional) discrete systems is considered. The method is based on a recently proposed 2-D stability test by the author. Illustrative examples are also included.     

On the support of voice call continuity across UMTS and wireless LANs

In this paper, we address the architecture and the procedures that can enable voice call handover from UMTS to WLAN and we also study how efficiently the WLAN can support the voice calls transferred from UMTS. Our study is based on a practical simulation model that lets us quantify the maximum number of voice calls that can be handed over from UMTS to WLAN, subject to maintaining the same level of UMTS QoS and respecting some WLAN policies. In addition, several other voice call performance metrics are derived. Our results indicate that an IEEE 802.11e access point can support a limited number of voice calls handed over from UMTS, which depends primarily on the applied WLAN bandwidth sharing policy (i.e., how the bandwidth is shared between WLAN voice and data users) and the QoS requirements. The performance of the WLAN scheduling algorithm is also of paramount importance and in our study we consider the so‐called ARROW scheduler. Although the simulation results are derived for a specific bandwidth sharing policy, they can readily be scaled and provide practical upper bounds for the number of UMTS voice calls that can be seamlessly admitted to a WLAN access point. Copyright © 2007 John Wiley & Sons, Ltd.     

Understanding soluble arsenate removal kinetics by zerovalent iron media

Zerovalent iron filings have been proposed as a filter medium for removing arsenic compounds from potable water supplies. This research investigated the kinetics of arsenate removal from aqueous solutions by zerovalent iron media. Batch experiments were performed to determine the effect of the iron corrosion rate on the rate of As(V) removal. Tafel analyses were used to determine the effect of the As(V) concentration on the rate of iron corrosion in anaerobic solutions. As(V) removal in column reactors packed with iron filings was measured over a 1-year period of continuous operation. Comparison of As(V) removal by freely corroding and cathodically protected iron showed that rates of arsenate removal were dependent on the continuous generation of iron oxide adsorption sites. In addition to adsorption site availability, rates of arsenate removal were also limited by mass transfer associated with As(V) diffusion through iron corrosion products. Steady-state removal rates in the column reactor were up to 10 times faster between the inlet-end and the first sampling port than between the first sampling port and the effluent-end of the column. Faster removal near the influent-end of the column was due to a faster rate of iron oxidation in that region. The presence of 100 microg/L As(V) decreased the iron corrosion rate by up to a factor of 5 compared to a blank electrolyte solution. However, increasing the As(V) concentration from 100 to 20,000 microg/L resulted in no further decrease in the iron corrosion rate. The kinetics of arsenate removal ranged between zeroth- and first-order with respect to the aqueous As(V) concentration. The apparent reaction order was dependent on the availability of adsorption sites and on the aqueous As(V) concentration. X-ray absorption spectroscopy analyses showed the presence of iron metal, magnetite (Fe3O4), an Fe(III) oxide phase, and possibly an Fe(II,III) hydroxide phase in the reacted iron filings. These mixed valent oxide phases are not passivating and permit sustained iron corrosion and continuous generation of new sites for As(V) adsorption.     

Author Index

Authors Index

Author Index     

Fuzzy Logic Decision Mechanism Combined with a Neuro-Controller for Fabric Tension in Robotized Sewing Process

A new approach for flexible automated handling of fabrics in the sewing process is described, which focuses to control the cloth tension applied by a robot. The proposed hierarchical robot control system includes a Fuzzy decision mechanism combined with a Neuro-controller. The expert's actions during the sewing process are investigated and this human behavior is interpreted in order to design the controller. The Fuzzy Logic decision mechanism utilizes only qualitative knowledge concerning the properties of the fabrics, in order to determine the desired tensional force and the location of the robot hand on the fabric. A Neural Network controller regulates the fabric tension to achieve the desired value by determining the robot end effector velocity. The simulation results demonstrate the efficiency of the system as well as the robustness of the controller performance since the effects of the noise are negligible. The system capabilities are more evident when the controller uses its previously acquired experience.     

Synthesis and characterization of poly(methyl methacrylate) star polymers

Star-branched poly(methyl methacrylate)s (PMMA) were synthesized by linking ‘living’ arms (produced by anionic polymerzation) with ethylene glycol dimethacrylate. Stars having arm molecular weights of 10000 and 40000 and between 4.9 and 18.7 branches were produced. The polymers were characterized using light scattering, size exclusion chromatography, and viscometry. It was found that well-defined PMMA stars were obtained only at the higher (40000) arm molecular weight. The stars prepared using the lower molecular weight (c. 10000) arms contained very high molecular weight gel components.