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101.
WE Jacott 《Canadian Metallurgical Quarterly》1997,102(6):15-6, 21
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Systems used in complex, multi-agency environments have a number of inherent problems and challenges that in many cases, lead
to systems failure. The area of system failure has been the subject of extensive research in the past. It has been well documented
in a number of places that information systems are difficult to build and are prone to failure. This paper examines system
failure from a social perspective in the context of building systems in complex environments. Through a case study modelling
approach, a framework has been developed to assist in building information systems in such complex multi-agency environments.
The paper introduces this framework through a study of a number of challenges confronting the builder of information systems
in complex, social, multi-agency environments. We examine the role of task accountability and problems identifying authority
as key reasons why systems are rejected by users. We introduce a task accountability model to help understand this problem.
We conclude by identifying work still to be carried out within the study. 相似文献
105.
The author discusses the influence of depth on the transmission of narrow slots and presents curves of calculated and measured transmission that exhibit depth resonances. The measurements are made by illuminating the front face of an aluminum box that is 50 cm on each side. At these resonances, the transmission is shown to be much higher than predicted by zero-depth models 相似文献
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Accounting for uncertainty in control-relevant statistics 总被引:1,自引:1,他引:0
To make appropriate decisions based on common indices used in control, both the point estimates and their uncertainties must be known. Many control-relevant statistics, such as model predictions, gain margins and other frequency domain quantities, are functions of parameters of process models. Confidence regions for these quantities are most often calculated under the assumption that these quantities have an asymptotic limiting normal distribution. These confidence regions may be erroneous, and very misleading, as the asymptotic results ignore the influence of parameter nonlinearities. In addition, proximity of the model parameters to stability/invertibility boundaries also distorts the confidence regions from those predicted from asymptotic theory. Generalized profiling is a flexible numerical method for constructing confidence intervals and confidence regions for model parameters, and functions of model parameters. Applications in nonlinear regression [D. Bates, D. Watts, Nonlinear Regression Analysis and Its Applications, John Wiley & Sons, New York, 1988] indicate that it provides a much more accurate representation of uncertainty in those instances when the asymptotic uncertainty results are inaccurate or misleading. Generalized profiling is based on the likelihood approach to quantifying uncertainty. The numerical construction of these likelihood uncertainty regions requires solution to a series of constrained optimization problems. Computationally efficient diagnostic tests, motivated by profiling, are developed. These can be effectively employed as screening tools to indicate when the asymptotic results are most likely to be inadequate. 相似文献
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RH Cleveland M Schluchter BP Wood WE Berdon MI Boechat KA Easley M Meziane RB Mellins KI Norton E Singleton L Trautwein 《Canadian Metallurgical Quarterly》1997,27(11):880-887
Dorsal fusion with the internal fixator has become the standard treatment of instabilities and deformities of the thoracolumbar spine. With our new device, the modular spine fixator (MSF), which has been specially designed for short-distance instrumentations, we have increasingly been treating unstable injuries of the thoracolumbar spine by one-level stabilization. Prerequisite is an accurate evaluation of the indication, including CT and MRI to assess the involvement of the intervertebral disc and the ligamental structures. The operative technique differs in some details from the procedure in more-multi-level instrumentations, especially concerning the application of the pedicle screws. The instrumentation is always combined with posterior allogenic bone grafting. Since the beginning of 1993 we also perform anterior autogenic transpedicular bone grafting. Between January 1991 and July 1995, 57 one-level stabilizations with the MSF were performed. Of the 57 patients operated on 39, 27 men and 12 women, with an average age of 41 years, have had a clinical and radiographic follow-up examination so far, on average, 27 months after the accident. Seventeen patients were completely free of pain and 17 patients (were only) sensitive to weather changes or had minor pain during great physical stress. Five patients had pain even during slight physical stress or at rest. The preoperatively measured Cobb angle was 15.1 degrees on average, after the operation 5.2 degrees, and at the time of the follow-up examination amounted to 8.1 degrees. The patients' range of motion was normal. Only five minor complications have been seen. No implant fatigue failure has been noted in this series. We derive from these results that, for correct indications, one-level stabilization can be performed successfully and should be firmly established in the operative treatment of unstable fractures of the thoracolumbar spine. 相似文献