Fault-Tolerance

Furthermore, as a check of defect tolerance, large, multiple-switch NanoCells were tested for defect tolerance through the SPICE interface. With all switches in the on position, the cell showed NAND logic with on-to-off output current thresholds of approximately 20 1. Switches were then chosen at random and set to the off position and the cell was evaluated periodically (data not shown). The average NanoCell tested had 1826 switches, and 60% of these switches could be turned to the off non-conducting state before the cell lost NAND functionality with the minimum output on-to-off ratio set-point of 10 1. This indicates a high tolerance for numerous faults in the NanoCell architecture. 

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Preskill J 1999 Battling decoherence the fault-tolerant quantum computer P/rys. Today June... 

The hardware and software used to implement LIMS systems must be vahdated. Computers and networks need to be examined for potential impact of component failure on LIMS data. Security concerns regarding control of access to LIMS information must be addressed. Software, operating systems, and database management systems used in the implementation of LIMS systems must be vahdated to protect against data cormption and loss. Mechanisms for fault-tolerant operation and LIMS data backup and restoration should be documented and tested. One approach to vahdation of LIMS hardware and software is to choose vendors whose products are precertified however, the ultimate responsibihty for vahdation remains with the user. Vahdating the LIMS system s operation involves a substantial amount of work, and an adequate vahdation infrastmcture is a prerequisite for the constmction of a dependable and flexible LIMS system. 

Pearson, A.R., Sutton, R., Burns, R.S. and Robinson, P. (2000) A Kalman Filter Approach to Fault Tolerance Control in Autonomous Underwater Vehicles. In Proc. 14th International Conference on Systems Engineering, Coventry, 12-14 September, 2, pp. 458 63. 

Recently, a new approach called artificial neural networks (ANNs) is assisting engineers and scientists in their assessment of fuzzy information, Polymer scientists often face a situation where the rules governing the particular system are unknown or difficult to use. It also frequently becomes an arduous task to develop functional forms/empirical equations to describe a phenomena. Most of these complexities can be overcome with an ANN approach because of its ability to build an internal model based solely on the exposure in a training environment. Fault tolerance of ANNs has been found to be very advantageous in physical property predictions of polymers. This chapter presents a few such cases where the authors have successfully implemented an ANN-based approach for purpose of empirical modeling. These are not exhaustive by any means. 

A., et al. (2002) Uppaal Implementation Secrets. Proceedings of 7th International Symposium on Formal Techniques in Real-Time and Fault Tolerant Systems, Springer, Berlin, pp. 3-22. 

Design and implement a reliable and fault-tolerant basic process control system to ensure the design limitations of the primary containment system are not exceeded. 

Reliability and availability Does the running system reliably continue to perform correctly over extended periods of time What proportion of time is the system up and running In the presence of failure, does it degrade gracefully rather than shut down completely Reliability is measured as the mean time to system failure availability is the proportion of time the system is functioning. Both qualities are typically dealt with by making the architecture fault-tolerant using duplicated hardware and software resources. 

A process or a facility satisfies the single fault tolerance principle when it has been designed or equipped in such a way that a single fault does not lead to the occurrence of the undesired event. This applies also to safety-related systems. 

Fault-tolerance capability and even self-repair ability of the molecular circuit... 

With less than perfect (i.e., real) systems, in the absence of (successful) fault tolerance, failures may occur and will presumably need to be tolerated somehow by the encompassing (possibly socio-technical) system. However, this notion of failure tolerance is just fault tolerance at the next system level. 

However, for structuring to have some direct relevance to questions of operational dependability, and in particular fault tolerance, it must be what might be described as strong—strong structuring actually controls interactions within and between systems, and limits error propagation in both time and space, i.e., constitutes real not just perceived or imagined boundaries. 

The Idealized Fault-Tolerant Component diagram (see Figure 3) is a simple, indeed simplistic, structuring technique that shows one approach to distinguishing between various sorts of system interactions, in particular identifying and classifying those that relate to system activity aimed at error recovery. 

Powell et al. 2001] D. Powell, A. Adelsbach, C. Cachin, S. Creese, M. Dacier, Y. Deswarte, T. McCutcheon, N. Neves, B. Pfitzmann, B. Randell, R. Stroud, P. Verfssimo and M. Waidner. MAFTIA (Malicious-and Accidental-Fault Tolerance for Internet Apphcations), in Supplement of the 2001 Int. Conf. on Dependable Systems and Networks, pp. D32-D35, Goteborg, Sweden, IEEE Computer Society Press, 2001. 

Randell 1975] B. Randell, System Structure for Software Fault Tolerance, IEEE Trans, on Software Engineering, vol. SE-1, no. 2, pp.220-232, 1975. 

Xu et al. 1995] J. Xu, B. Randell, A. Romanovsky, RJ. Stroud and Z. Wu. Fault Tolerance in Concurrent Object-Oriented Software through Coordinated Error Recovery, in Proceedings 25th Int. Symp. Fault-Tolerant Computing (FTCS-25), Los Angeles, IEEE Computer Society Press, 1995. 

Once a fault has been detected, in some applications a controller reconfiguration for the self-correction of the fault is required (fault accommodation). A fault-tolerant control system possesses this capability, and its adoption is of the utmost... 

Fault-tolerant Flight Control and Guidance Systems Guillaume Ducard... 

Fault-tolerant Control Systems Hassan Noura, Didier Theilliol, Jean-Christophe Ponsart and Abbas Chamseddine... 

Readers from the fields of process, chemical and control engineering may find these monographs from the Advances in Industrial Control series of complementary interest Fault-tolerant Control Systems by Hassan Noura, Didier Theilliol, Jean-Christophe Ponsart and Abbas Chamseddine (ISBN 978-1-84882-652-6, 2009) Predictive Functional Control by Jacques Richalet and Donal O Donovan (ISBN 978-1-84882-492-8, 2009) and Process Control by Jie Bao and Peter L. Lee (ISBN 978-1-84628-892-0, 2007). 

El-Farra, N.H., Gani, A., and Christofides, P. D. (2005). Fault-tolerant control of process systems using communication networks. AIChE J., 51, 1665-1682. 

Progress has been made on the control structure problem. Despite its flaws, optimal control is now used in industry, though in a somewhat modified form and couched in terms of model predictive control. This new framework is much more intuitive. With this framework, fault tolerance can be... 

Despite the optimistic overtones, robust control is not a solved problem. Some difficult theoretical questions remain in the synthesis area. The available software is, at best, experimental the controller is complex and its structure is not obvious. It generally uses all the measurements and all the manipulated variables in a centralized fashion. On-line tuning is difficult except when the IMC structure is employed [8], Fault tolerance, that is, continued satisfactory or at least stable performance in the event of an actuator or sensor failure, cannot be guaranteed. 

The optimal robust controller designed with one of the new synthesis techniques is generally not of a form that can be readily implemented. The main benefit of the new synthesis procedure is that it allows the designer to establish performance bounds that can be reached under ideal conditions. In practice, a decentralized (multiloop) control structure is preferred for ease of start-up, bumpless automatic to manual transfer, and fault tolerance in the event of actuator or sensor failures. Indeed, a practical design does not start with controller synthesis but with the selection of the variables that are to be manipulated and measured. It is well known that this choice can have more profound effects on the achievable control performance than the design of the controller itself. This was demonstrated in a distillation example [17, 18] in which a switch from reflux to distillate flow as the manipulated variable removes all robustness problems and makes the controller design trivial. 

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