Nonlinear Modeling and Control of a Unicycle

A unicycle system is composed of a unicycle and a rider. This system is inherently unstable, but together with a skilled rider can be autonomously controlled and stabilized. A dynamical investigation, a control design and a numerical solution of a nonlinear unicycle autonomous model are presented. The use of a nonlinear model for the control design is shown in this paper to be of great importance. A three-rigid-body physical model was selected for the dynamical study of the system. In a linearized model important physical characteristics of the unicycle system disappear (e.g. interactions between the longitudinal and lateral systems are being neglected), and therefore it is not recommended to be used for the control design. A nonlinear control law, which replaces the rider in stabilizing the model, was derived in the present work, using a nonlinear unicycle model. A simulation study shows good performance of this controller. Time spectral element methods are developed and used for integrating the nonlinear equations of motion. The approach employs the time discontinuous Galerkin method which leads to A-stable high order accurate time integration schemes.     

A self-adaptive fe system based on recursive spatial decomposition and multigrid analysis

This paper introduces an automatic self-adaptive finite element system for 3-D stress analysis of homogeneous elastic solids described in a Solid Modelling System (SMS). This system reduces the role of the analyst into two basic tasks: defining the problem (i.e. geometry, material properties and boundary conditions) and specifying the desired accuracy in the analysis. The approach followed in this work is based on Recursive Spatial Decomposition (RSD) of solids defined in a SMS. The system includes procedures for meshing, analysis, error estimation, and adaptive remeshing and reanalysis. The various procedures share the same hierarchical data structure built on the RSD.     

Designing winning robots by careful design of their development process

We present a comprehensive robot development process and its evaluation. We designed this process in the context of a robotics course in high schools. The motivation for designing this new process was improving the robustness and reliability of robots developed by students and preparing students for becoming better designers. The newly designed process proved to be highly successful in designing top quality robots. In the process design, we explored and adapted existing design tools and methods to the specific designers, the nature of the product, the environment, the product needs, and the design context goals. At the end of this thorough design, we selected a synergetic integration of six tools and methods to compose the new comprehensive development process for this product context: conceptual design, fault-tolerant design, atomic requirements, fuzzy logic for control, creative thinking, and microprogramming-based design. The design skills of the students that learned the design process and the performance of robots they designed and participated in an international robotics contest were examined. The high school teams that studied the proposed process won the first places in an international contest. The robots developed by the students had better performance than robots built by engineers and faculty teams. Professional experts rated the robots’ designs as excellent. The students that studied the process demonstrated high level of diverse design skills including creativity and design management capabilities. Additionally, they improved their science subject grades and their attitude toward engineering. Both the results obtained by the study and the authors’ experience in teaching robotics demonstrate that the proposed robot development process could be taught successfully in high school and that it leads to superior robotic products. Our experience also indicates that this process could serve industry design by improving the robustness of robots operating in uncertain environments and supporting fast change management practices.     

The role of an academic institute in setting national environmental policy: The case of Israel

Two major players are active in determining the development of environmental policies: the government and “the public.” These diverse players have intrinsic limitations and are often driven by different agenda, different aims, and different means. Therefore, inconsistent actions and lack of a clear agenda and action plan characterize the environmental policy. There is an essential role for a third player, namely, a team that is as professional and as objective as possible. The Samuel Neaman Institute (SNI) has taken it upon itself to serve as this third party, and has been providing the scientific background needed to develop and propose a rational and environmental set of priorities for Israel since 1998.     

A Photovoltaic C60-Si Heterojunction

A heterojunction was prepared by depositing a thin film of C₆₀ on a p-Si substrate. Photovoltaic properties were observed using a UV-filtered solar simulator and natural sun light. Surface Photovoltage Spectroscopy was employed to distinguish between the nature of photoconversion in the C₆₀ and Si layers.     

Film thickness in horizontal annular flow

Film thickness in horizontal annular flow in small diameter pipes (8-12 mm) was measured as a function of circumferential position. In addition a simple analytical model for the prediction of the film thickness at the top and bottom of the pipe is proposed.     

Electronic characterization of heterojunctions by surface potential monitoring

An original approach for studying the formation of semiconductor heterojunctions and their electronic properties is discussed and illustrated. Monitoring the changes in the surface potential during the heterojunction formation lends itself to direct measurement of the band discontinuities, Debye length, and the width of the space-charge region at heterojunction interfaces. The contribution of an interface dipole is considered. The technique is demonstrated by a technologically significant experimental example.