Time-limited and band-limited environment: Signals and systems

Of concern is an environment made up of signals and systems tightly confined both in time and frequency. Such an environment is often encountered in transmission line circuits, radar, sonar, and optical circuits, and when the principal signals are well-defined sharp pulses. It will be seen that once this environment is achieved, the signals and systems possess some attractive properties. A conventional system may preserve the symmetry of a propagating signal or change its symmetry from even to odd or from odd to even. Another system may be used to predict the arrival of an incoming pulse with a high degree of accuracy. Electrical networks may also be associated with these properties. Approximation problems, existence theorems, and realization schemes will be addressed and developed.     

Impulse stress wave propagation in elongated bodies: Apparent deviations from circuit realizability principles

Of concern is the undistorted propagation of pulse stress waves in long thin bodies. The primary signals are arbitrarily sharp pulses projected along thex-axis. It will be seen that these pulses travel close to the speed of sound in unbounded media. Secondary pulses follow representing interactive disturbances traveling along they-axis. But the process brings out certain anomalies in circuit realizability requirements. These issues, transmission parameters, and coupling between the various signals are studied in detail. The results are supported by experiments.Work supported by TecSonics Inc., Twinsburg Ohio.     

Perceived costs and benefits as determinants of user behaviour: an experiment with matchmaking

A cost-benefit approach is employed to model the discretionary use of a computerized information system. The model is constructed by integrating a systemic view of human-computer interaction with a contingency model for selecting decision strategies. It is then used to analyse the effect of presentation format on search behaviour.

An experiment on matchmaking was performed using two formats: sequential and parallel. Subjects were asked to find the best spouse for a candidate using an information retrieval system that displayed information about the individuals according to the subject's specific requests. The subject's search behaviour and perception of complexity were recorded. A first analysis of the protocols revealed different behaviours, as predicted by the cost-benefit mechanism. A second analysis incorporated a measure of individual differences in perception to gain a better understanding of the effects of display format on perceived complexity and, thereby, on behaviour. The findings support the use or the cost-benefit model. The design implications of the model are also discussed.     

A method of analysis of the relaxation data for evaluation of the chemical diffusion coefficient in the case of partial rate control by surface reaction

A general method of regression analysis of the experimental data concerning relaxation experiments on binary compounds for the evaluation of the chemical diffusion coefficient is presented for cases in which the surface reaction exerts a partial control of the overall equilibration kinetics, assuming that the surface reaction follows a linear type of rate law. A rigorous method of analysis of data for the case of exclusive rate control by solid-state diffusion is also developed as a special solution. Application of the method to theoretically calculated curves indicates the correctness of the procedure developed. Limitations connected with the possible occurrence of forms different from the linear for the surface rate law are finally considered.     

Bridging the requirements–implementation modeling gap with object–process methodology

A model-based system development cycle involves two semantically distinct aspects: the requirements specification and the implementation model. Due to the conceptual and semantic differences between these two major system lifecycle stages, the transition from requirements to implementation is inherently a noncoherent process. Consequently, the system requirements are not faithfully transformed into the working system. This paper introduces an effective solution via an Integrated Modeling Paradigm (IMP) that combines the requirements and implementation domain models into a unified system model that continuously represents the system as it evolves. The IMP was implemented in an Object–Process Methodology (OPM) development environment. This implementation reinforces OPM with the capability to bridge the significant conceptual gap that lies right at the heart of the development process. A user survey has shown that this OPM-based solution is easy to use and can indeed help bridge the information gap, yielding a better match between the required and implemented systems than the currently accepted practice.     

The model multiplicity problem: experimenting with real-timespecification methods

The object-process methodology (OPM) specifies both graphically and textually the system's static-structural and behavioral-procedural aspects through a single unifying model. This model singularity is contrasted with the multimodel approach applied by existing object oriented system analysis methods. These methods usually employ at least three distinct models for specifying various system aspects: mainly structure, function, and behavior. Object modeling technique (OMT), the main ancestor of the unified modeling language (UML), extended with timed statecharts, represents a family of such multimodal object oriented methods. Two major open questions related to model multiplicity vs. model singularity have been: 1) whether or not a single model, rather than a combination of several models, enables the synthesis of a better system specification; and 2) which of the two alternative approaches yields a specification that is easier to comprehend. The authors address these questions through a double-blind controlled experiment. To obtain conclusive results, real time systems, which exhibit a more complex dynamic behavior than nonreal time systems were selected as the focus of the experiment. We establish empirically that a single model methodology, OPM, is more effective than a multimodel one, OMT, in terms of synthesis. We pinpoint specific issues in which significant diiferences between the two methodologies were found. The specification comprehension results show that there were significant differences between the two methods in specific issues     

MOSAICA: A web-2.0 based system for the preservation and presentation of cultural heritage

The question of how to present cultural heritage resources in a way that attracts potential users is becoming important in our ever-changing world. This paper describes MOSAICA system – a web 2.0-based toolbox, dedicated for the preservation and presentation of cultural heritage. This paper also describes an evaluation study that examined MOSAICA system’s usability and social impact. Online questionnaires and semi-structured interviews were administered among users from Israel, France, and Poland. Findings indicated positive views related to MOSAICA’s usage in terms of knowledge gain, ease of use, and attractiveness. Findings also indicated that learning about the stories, customs, and traditions of diverse cultures, via hypertext narratives, may enhance positive dispositions toward open-mindedness, in general, and non-judgmental views, in specific. MOSAICA system provides a generic framework for users, of any culture and religion, to actively engage in preserving their heritage via activities such as investigation, exploration, and storytelling.     

The role of design-principles in designing courses that promote collaborative learning in higher-education

Design-patterns and design-principles represent two approaches, which elicit design knowledge from successful learning environments and formulate it as design guidelines. The two approaches are fairly similar in their strategies, but differ in their research origins. This study stems from the design-principles approach, and explores how learning is affected by curriculum-materials designed according to two main design-principles: (a) engage learners in peer instruction, and (b) reuse student artifacts as resource for further learning. These principles were employed in three higher-education courses and examined with 385 students. Data analysis was conducted in two trajectories: In the “bird’s eye view” trajectory we used a “feature” unit of analysis to illustrate how learning was supported by features designed according to the two design-principles in each of the courses. In the “design-based research” trajectory we focused on one feature, a web-based Jigsaw activity, in a philosophy of education course, and demonstrated how it was refined via three design iterations. Students were required to specialize in one of three philosophical perspectives, share knowledge with peers who specialized in other perspectives, and reuse the shared knowledge in new contexts. Outcomes indicated that the design in the first iteration did not sufficiently support student ability to apply the shared knowledge. Two additional design-principles were employed in the next iterations: (c) provide knowledge representation and organization tools, and (d) employ multiple social-activity structures. The importance of combining several design-principles for designing curricular materials is discussed in terms of Alexander’s design-pattern language and his notion of referencing between design-patterns.     

OPM vs. UML--Experimenting with Comprehension and Construction of Web Application Models

Object-Process Methodology (OPM), which is a holistic approach to modeling and evolving systems, views objects and processes as two equally important entities that describe the system's structure and behavior in a single model. Unified Modeling Language (UML), which is the standard object-oriented modeling language for software systems, separates the system model into various aspects, each of which is represented in a different view (diagram type).The exponential growth of the Web and the progress of Internet-based architectures have set the stage for the proliferation of a variety of Web applications, which are classified as hybrids between hypermedia and information systems. Such applications require a modeling approach that is capable of clearly specifying aspects of their architecture, communication, and distributive nature. Since UML and OPM are two candidates for this task, this study has been designed to establish the level of comprehension and the quality of the constructed Web application models using each one of these two approaches.In the experiment we carried out, third year undergraduate information systems engineering students were asked to respond to comprehension and construction questions about two representative Web application models. The comprehension questions related to the system's structure, dynamics, and distribution aspects. The results suggest that OPM is better than UML in modeling the dynamics aspect of the Web applications. In specifying structure and distribution aspects, there were no significant differences. The results further suggest that the quality of the OPM models students built in the construction part was superior to that of the corresponding UML models.     

Geosynthetic Reinforced Multitiered Walls

Current design of mechanically stabilized earth (MSE) walls shows that the tensile stress in the reinforcement increases rapidly with height. To take advantage of both the aesthetics and the economics of MSE walls while considering high heights, multitiered walls are often used. In such walls, an offset between adjacent tiers is used. If the offset is large enough, the tensile stress in the reinforcement in lower tiers is reduced. However, a rational design methodology for multitiered MSE walls that accurately predicts wall performance is lacking. AASHTO 98 design guidelines are limited to two-tiered walls with zero batter. In fact, this design is purely empirical using “calibrated” lateral earth pressures adopted from limited guidelines developed for metallic strip walls. Empirical data available for multitiered walls is limited and it seems to be nonexistent for geosynthetic walls. In fact, generation of an extensive database for tiered walls is a major challenge since there are practically limitless configurations for such systems. As an alternative, this study presents the results of parametric studies conducted in parallel using two independent types of analyses: One is based on limiting equilibrium (LE) and one on continuum mechanics. The premise of this work is that if the two uncoupled analyses produce similar results, an acceptable level of confidence in the results can be afforded. This confidence stems from the fact that LE is currently being used for design of reinforced and unreinforced slopes (i.e., having a slope angle less than 70°); the agreement with continuum mechanics facilitates its extrapolation to use in MSE walls. Parametric studies were carried out to assess the required tensile strength as a function of reinforcement length and stiffness, offset distance, the fill and foundation strength, water, surcharge, and number of tiers. It is concluded that LE analyses may be extended to the analysis of multitiered walls.