Synthesis of oscillating adaptive feedback systems

A synthesis theory is developed which allows system design to proceed from practical specifications on system command and/or disturbance response to a design which is very nearly optimal in terms of feedback sensor noise effects. The approach taken is to replace the nonlinear element by a mean square error minimizing approximation (dual-input describing function), and then use linear frequency domain synthesis techniques subject to additional constraints imposed by the limit cycle and the approximator. Synthesis techniques are also developed for a similar system using an externally excited oscillating signal with the above approach. The results remove the design of the systems considered from the realm of simulation and experimentation, permitting true synthesis and the optimization that accompanies it

Computer-aided design of second and third-order systems with parameter variations and time response constraints

Computerized design of second and third order systems with parameter variations and time response constraint

Microbial evaluation of the viscous heater for commercial applications in faecal sludge treatment

Risk of infection from human pathogens by contact with untreated faecal sludge (FS) poses a threat to worker health. The aim of this study was to assess the commercial potential of a 1000 L h-1 viscous heater (VH) to minimise this risk as a component of a black soldier fly larvae (BSFL) production pipeline. Changes in source material properties during sludge processing, temperature stability and microbial treatment efficacy were evaluated. Inactivation of heterotrophic bacteria in FS treated in the VH was measured at 60 ℃ and 80 ℃. Approximately 1‑ to 3-log inactivation was observed, independent of residence time. Maintaining temperature stability proved difficult with variable sludge viscosity and manual control of flow rate and engine power. Adding operational controls based on effluent temperature would compensate for variable sludge properties. Preparing FS for treatment in the VH proved challenging due to the small particle size required and the large quantity of detritus present

Sintering effects on chemical and physical properties of bioactive ceramics

The objective of this study was to characterize the chemical and physical properties of bioactive ceramics prepared from an aqueous paste containing hydroxyapatite (HA) and beta tri-calcium phosphate (β-TCP). Prior to formulating the paste, HA and β-TCP were calcined at 800 °C and 975 °C (11 h), milled, and blended into 15%/85% HA/β-TCP volume-mixed paste. Fabricated cylindrical rods were subsequently sintered to 900 °C, 1100 °C or 1250 °C. The sintered specimens were characterized by helium pycnometry, X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), and inductively coupled plasma (ICP) spectroscopy for evaluation of porosity, crystalline phase, functional-groups, and Ca:P ratio, respectively. Mechanical properties were assessed via 3-point bending and diametral compression. Qualitative microstructural evaluation using scanning electron microscopy (SEM) showed larger pores and a broader pore size distribution (PSD) for materials sintered at 900 °C and 1100 °C, whereas the 1250 °C samples showed more uniform PSD. Porosity quantification showed significantly higher porosity for materials sintered to 900 °C and 1250 °C (p< 0.05). XRD indicated substantial deviations from the 15%/85% HA/β-TCP formulation following sintering where lower amounts of HA were observed when sintering temperature was increased. Mechanical testing demonstrated significant differences between calcination temperatures and different sintering regimes (p < 0.05). Variation in chemical composition and mechanical properties of bioactive ceramics were direct consequences of calcination and sintering.Peer reviewedChemical Engineerin

Increasing Learning in Introductory Geoscience Courses Using Lecture Tutorials

Students often leave introductory geoscience courses without learning the scientific perspective, and we developed Lecture Tutorials to help alleviate this problem. Lecture Tutorials are 10-20 minute interactive worksheets that students complete in small groups in class after a short introductory lecture. They are specifically designed to combat alternative conceptions and increase learning on difficult topics. Our study shows that Lecture Tutorials increase student learning in the classroom more than just lecture alone. On related multiple choice questions asked before and after the Lecture Tutorial (but after a short lecture on the topic), student scores increased 19%. When a subset of these questions was given before and after an extended lecture instead of a Lecture Tutorial, student scores did not increase by a statistically significant amount. On the multiple choice assessment questions given on exams relating to the information covered in the Lecture Tutorials, students who completed the Lecture Tutorials scored significantly higher than students who heard just lecture. In addition, students feel that they are an important and useful part of their learning experience. Lecture Tutorials are being disseminated and are available for instructor use

Increasing learning in introductory geoscience courses using lecture tutorials

Students often leave introductory geoscience courses without learning the scientific perspective, and we developed Lecture Tutorials to help alleviate this problem. Lecture Tutorials are 10-20 minute interactive worksheets that students complete in small groups in class after a short introductory lecture. They are specifically designed to combat alternative conceptions and increase learning on difficult topics. Our study shows that Lecture Tutorials increase student learning in the classroom more than just lecture alone. On related multiple choice questions asked before and after the Lecture Tutorial (but after a short lecture on the topic), student scores increased 19%. When a subset of these questions was given before and after an extended lecture instead of a Lecture Tutorial, student scores did not increase by a statistically significant amount. On the multiple choice assessment questions given on exams relating to the information covered in the Lecture Tutorials, students who completed the Lecture Tutorials scored significantly higher than students who heard just lecture. In addition, students feel that they are an important and useful part of their learning experience. Lecture Tutorials are being disseminated and are available for instructor use