System Modeling Techniques Research Articles

Interpersonal Access Control in Computer-Mediated Communications: A Systematic Analysis of the Design Space

Certain design projects raise difficult user-interface problems that are not easily amenable to designers' intuition or rapid prototyping due to their novelty, conceptual complexity, and the difficulty of conducting appropriate user studies. Interpersonal access control in computer-mediated communication (CMC) systems is just such a problem. We describe a collection of systematic theory-based analyses of a system prototype that inherited its control mechanism from two preexisting systems. We demonstrate that the collective use of system and user modeling techniques provides insight into this complex design problem and enables us to examine the implications of design decisions for users and implementation. The analyses identify a number of weaknesses in the prototype and are used to propose ways of making substantive refinements to improve its simplicity and appropriateness for two tasks: altering one's accessibility and distinguishing between who can make what kinds of connections. We conclude with a discussion of some critical issues that are relevant for CMC systems, and reflect on the process of applying formal human-computer interaction (HCI) techniques in informal, exploratory design contexts.

Pilot study using SPOT satellite imagery over Apalachicola national forest to determine appropriate spatial scale for area-wide aggregation of surface fluxes

High resolution radiances from SPOT satellite imagery converted to Normalized Difference Vegetation Indices (NDVI) over a 16×16 km2 mixed ground cover study-area in the Apalachicola National Forest in northwest Florida, along with in situ measurements from a Bowen ratio surface flux monitoring system and physical modeling techniques, are used to determine the length manifold beyond which degraded resolution satellite imagery fails to capture flux variability over the scene. The investigation is relevant to an understanding of how bias error is generated in methods designed to produce scale-invariant surface flux estimates from satellite measurements. Error estimates are based on assigning characteristic NDVI values to the four predominant types of ground cover found within the study-area. An open site near the center of the study-area, which satisfies the conditions for surface flux monitoring, is used for obtaining input data for a biosphere-atmosphere exchange model designed to calculate representative fluxes for the different ground covers. Continuous 6-minute meteorological and surface flux measurements were made at the monitoring site for a period of 22 days. These measurements are used in conjunction with surface layer theory to provide surface layer profile estimates of wind speed, temperature, and relative humidity at the tops of the forested sites. The measured and derived meteorological parameters, together with representative biophysical parameters, are used as input to the biosphere-atmosphere exchange model. By representing sensible and latent heat flux distributions due to the variable ground cover with characteristic NDVI values at 20-m resolution, baseline area-wide sensible and latent heat flux quantities are calculated. Error-growth curves as a function of spatial resolution for the fluxes are found by degrading the resolution of the SPOT radiances used to calculate NDVI, and rationing the associated area-wide fluxes to the baseline values. The point at which an error-growth curve becomes invariant represents the edge of a length manifold beyond which the satellite input no longer contains information on surface flux variability, even though NDVI variability continues at all scales up to that of the complete SPOT scene. The error-growth curves are non-linear, with all the error build-up taking place between 20 m and 1.6 km. Decreasing the spatial resolution of the NDVI information down to or below 1.6 km, introduces bias errors in the area-wide surface flux estimates of 10% for sensible heat and 8% for latent heat. The underlying assumptions and modeling produce uncertainty in estimating the manifold limits, however, the principal objective is to show that in using satellite data for scale-invariant surface flux retrieval, there is an optimal spatial resolution factor that can be objectively quantified.

Parallel path aspects of transmission modeling

This paper examines the present methods and power system modeling techniques available to address the effects of parallel load flows resulting from various firm and short-term energy transactions. A survey of significant methodologies is conducted to determine the present status of parallel flow transaction modeling. The strengths and weaknesses of these approaches are identified to suggest areas of further modeling improvements. The motivating force behind this research is to improve transmission system transfer capability assessment accuracy by suggesting a real-time modeling environment that adequately represents the influences of parallel flows while recognizing operational constraints and objectives.

Aggregation operators and fuzzy systems modeling

Abstract A general class of aggregation operators called MICA having the properties of monotonicity, symmetry and an identity element are introduced. We stress the significance of the choice of identity in characterizing the operator. We show that the t -norm and t -conorm are special cases of these operators. Other classees of these operators are introduced, notably an additive class which is very much in the spirit of the kind of aggregation used in neural networks. It is shown how a general description of the fuzzy system modeling technique can be obtained using these operators.

Reference architecture for distributed systems management

Management of computing systems is needed to ensure efficient use of resources and provide reliable and timely service to users. Distributed systems are much more difficult to manage because of their size and complexity, and they require a new approach. A reference architecture for distributed systems management is proposed that integrates system monitoring, information management, and system modeling techniques. Three classes of system management—network services and devices, operating system services and resources, and user applications—are defined within this framework, and a detailed hospital application is presented to clarify the requirements for managing applications. It is argued that the performance management of distributed applications must be considered from all three perspectives. Several management prototypes under study within the COnsortium for Research on Distributed Systems (CORDS) are described to illustrate how such an architecture could be realized.

Exact and Direct Modeling Technique for Rotor-Bearing Systems with Arbitrary Selected Degrees-of-Freedom

An exact and direct modeling technique is proposed for modeling of rotor-bearing systems with arbitrary selected degrees-of-freedom. This technique is based on the combination of the transfer and dynamic stiffness matrices. The technique differs from the usual combination methods in that the global dynamic stiffness matrix for the system or the subsystem is obtained directly by rearranging the corresponding global transfer matrix. Therefore, the dimension of the global dynamic stiffness matrix is independent of the number of the elements or the substructures. In order to show the simplicity and efficiency of the method, two numerical examples are given.

Exact and Direct Modeling Technique for Rotor-Bearing Systems with Arbitrary Selected Degrees-of-Freedom

An exact and direct modeling technique is proposed for modeling of rotor-bearing systems with arbitrary selected degrees-of-freedom. This technique is based on the combination of the transfer and dynamic stiffness matrices. The technique differs from the usual combination methods in that the global dynamic stiffness matrix for the system or the subsystem is obtained directly by rearranging the corresponding global transfer matrix. Therefore, the dimension of the global dynamic stiffness matrix is independent of the number of the elements or the substructures. In order to show the simplicity and efficiency of the method, two numerical examples are given.

Issues in practical model-based diagnosis

The model-based diagnosis project at the University of Twente has been directed at improving the practical usefulness of model-based diagnosis. In cooperation with industrial partners, the research addressed the modeling problem and the efficiency problem in model-based reasoning. Main results of this research are that (1) re-use of electronically available descriptions of systems for diagnostic purposes is possible, and (2) efficient reasoning can be realized using PDE, hierarchic models, and a simple diagnostic strategy. We have built a prototype diagnostic system which shows the technical feasibility of model-based diagnosis in a computer system. The project was concluded in July 1993 by the development of the ‘Diagnostic Toolbox’. The Diagnostic Toolbox supports the modeling of technical systems for diagnostic purposes, and it contains several model-based reasoning methods.

A mathematical modeling technique for renal counterflow systems

Realistic and comprehensive mathematical models of the renal concentrating mechanism lead to large systems of nonlinear differential equations. Their complexity can be considerably reduced by combining like tubules into common structures. Then the different lengths of the combined tubules have to be modeled by the shunt flow technique. The present paper investigates the validity of this methodology.

不確定性と設計技術

To secure integrity of industrial product, various uncertainties surrounding the design technology must be treated properly. To do this, the uncertainties underlying during the following phases: evaluation of loads, modeling technique of systems of interest, evaluation of material strength, maintenance and inspection and so on, have to be clarified and effective measures to grasp the degree of the uncertainty and to reduce the inherent uncertainty have to be established.The present paper shows the classification of the uncertainties and the fundamental relation with the design technology, and mentions a reliability design method based on probabilistic and statistical techniques, which has been getting popular in many engineering fields, and finally raises some future problems of design methods from the viewpoint of the uncertainties.

RELIABILITY MODELING OF HARDWARE/SOFTWARE SYSTEMS TO SUPPORT ARCHITECTURAL TRADE‐OFFs

ABSTRACTDeveloping complex systems to meet the demands of the current military and commercial marketplaces requires careful architectural design to ensure optimal robustness within the expected use environment. Modeling the reliability of systems that combine hardware and software elements to achieve needed system functionality has been difficult or impossible due to the paucity of techniques for including software and the effects of software failures into system reliability models.This paper reports on and extends the research into system and software modeling techniques which was recently completed by the authors for Hughes Aircraft Company under contract to the U. S. Air Force, Rome Laboratory. An overview of the reliability model development process for combined hardware/software systems which focuses on creating a model which accurately includes the impact of software is provided. A brief discussion of how to use the results of the modeling to assess alternative design approaches is included.

Models for comparison of technical systems by a vector performance criterion

Models of technical systems with possible deviations in their characteristics are constructed. Solvability of the corresponding vector optimization problems is proved. An analog of the scalarization method is developed for this case.

System Modeling Approach for Solute Transport Through Upper Soils

Solute transport through upper soils has been traditionally simulated by following a physically based modeling approach. Unfortunately, the application of physically based models is often limited by difficulties in solving interrelated problems of parameter identification, system boundary definition, and mathematical solution. These problems can be largely alleviated by an alternative modeling approach based on the system theory. In the system approach, dynamic relations between the input of the chemical at the soil surface and its subsequent downward movement are represented by system response functions that do not require knowledge of the intimate structure of relevant transport mechanisms. System modeling techniques were developed and applied in this study to simulate the transport of the pesticide fenamiphos in Hawaiian soils. A comparison of the calculated concentration distributions with field measurements shows that the system model provides satisfactory transport simulation.

Rainbow Net analysis of VAXcluster system availability

A system modeling technique, Rainbow Nets, is used to evaluate the availability and mean-time-to-interrupt of the VAXcluster. These results are compared to the exact analytic results showing that reasonable accuracy is achieved through simulation. The complexity of the Rainbow Net implemented for the VAXcluster does not increase as the number of processors increases, but remains constant. This is unlike a Markov model which increases in size exponentially. The constancy is achieved by using tokens with identity attributes (items) that can have additional attributes associated with them (features) which can exist in multiple states. The time to perform the simulation increases, but this is a polynomial increase rather than exponential. With Rainbow Nets, there is no restriction on distributions used for transition firing times. This freedom allows real situations to be modeled more accurately by choosing the distribution which best fits the system performance. This eliminates the need to make the many simplifying assumptions that are typically required to keep analytic calculations from becoming intractable. >

Adaptive on‐line modeling technique for active noise control systems

Active noise control (ANC) systems are required to model direct and acoustic feedback paths as well as the error path on an on‐line basis. In this paper a new adaptive on‐line error‐path modeling technique is presented. An adaptive IIR filter using SHARF algorithm is used to generate the canceling signal. The error path is modeled by a LMS adaptive filter. This new modeling technique uses the canceling signal to train an adaptive model that is placed in parallel with the error path. This process is performed only when certain conditions are satisfied in order to avoid undesired undulations. The modeling process technique differs from two other methods. Ericksson et al. [ U.S. Patent number 4,677,676, 30 June 1987] used an additional auxiliary low level, uncorrelated noise for training processes. Warnaka et al. [U.S. Patent number 4,473,906, 25 September 1984] used the canceling signal for modeling, but the plant being continuously modeled is not really the error path. Comparative performance and real‐time...

The Usage of Computer‐Integrated Manufacturing Technology within Manufacturing Organisations in the North East of England

This article presents the results of a survey of the manufacturing activities of 60 engineering companies located in the North East of England. The survey was carried out in order to identify the extent to which companies in the region are currently using or planning to invest in Computer Integrated Manufacturing technology. Particular emphasis is placed on the usage of computer‐based decision support tools within the production management function. Usage of JIT production management techniques is also considered. Previous investigations have suggested that commercially available decision support tools have some serious limitations which may prevent their widespread use within manufacturing organisations. The survey sought to investigate the nature of these problems and to identify the requirements for more sophisticated decision support tools based on expert system and simulation modelling techniques.

Performance evaluation principles for vector- and multiprocessor systems

Skilful computer system measurement, modelling and performance evaluation techniques are needed for supercomputer architectures. They allow to accurately determine characteristics performance values, to find potential hardware- and software-bottleneck; they also help to efficiently distribute and schedule user tasks. This paper is an extended version of a tutorial contribution at the IEEE CompEuro 87 and surveys fundamental performance issues and their solution for supercomputer architectures.

Modeling and analysis of spacecraft power systems

A comprehensive large-scale power system modeling technique using the multiport coupling method is developed to facilitate design and analysis of present and future spacecraft power systems. The Boeing Computer Service's EASY5 program was used as the host software to meet various modeling and analysis needs for DC, small-signal, and large-signal analyses. Power subsystem or component model development from empirical data and reduced-order model generation using the complex curve-fitting technique are also introduced. A sample spacecraft power system, the simplified Direct Energy Transfer system, is modeled and its performance demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Predicting performance of concurrency control designs

Performance is a high-priority consideration when designing concurrent or distributed systems. The process of designing such a system is complicated by two factors: (1) the current state-of-the-art in concurrent system design is very ad hoc — software design principles for concurrent systems are still in their infancy, and (2) performance evaluation of concurrent systems is quite difficult and it is especially difficult to relate aspects of the design to aspects of the implementation. This paper reports on work with a performance modeling technique for concurrent or distributed systems that allows structured design to be related to the implementation of the concurrency control component of the system. First, a General Process Model (GPM) is used to organize system design information into a six level hierarchy. The abstract performance properties of each level in the hierarchy have been established using concurrency control theory. Next, we describe how to translate the structured system design into efficient concurrency control techniques, using elements of this theory. Finally, a prototype automated design evaluation tool which serves as a central component of the design methodology is described.

Development of a Graduate Course on Modeling and Control of Large-Scale Systems

This paper presents a graduate course in the area of modeling and control of large-scale systems. The objective of the course is to study 1) model simplification techniques in the analysis and simulation of large-scale systems, 2) procedures in assessing systems behavior, and 3) decentralized and hierarchical control design methods. A unique feature of the course is the use of a number of interactive computer programs to assist students in studying in depth and understanding the particularities of large-scale system modeling and control design techniques. The paper describes course contents and the utilization of the interactive computer programs to enhance student comprehension of the concepts involved. Typical homework assignments are discussed to illustrate the utilization of the computer programs. The course is presently offered at West Virginia University.