Closed-form solutions of performability

Methods which yield closed form performability solutions for continuous valued variables are developed. The models are similar to those employed in performance modeling (i.e., Markovian queueing models) but are extended so as to account for variations in structure due to faults. In particular, the modeling of a degradable buffer/multiprocessor system is considered whose performance Y is the (normalized) average throughput rate realized during a bounded interval of time. To avoid known difficulties associated with exact transient solutions, an approximate decomposition of the model is employed permitting certain submodels to be solved in equilibrium. These solutions are then incorporated in a model with fewer transient states and by solving the latter, a closed form solution of the system's performability is obtained. In conclusion, some applications of this solution are discussed and illustrated, including an example of design optimization

Performability modeling with continuous accomplishment sets

A general modeling framework that permits the definition, formulation, and evaluation of performability is described. It is shown that performability relates directly to system effectiveness, and is a proper generalization of both performance and reliability. A hierarchical modeling scheme is used to formulate the capability function used to evaluate performability. The case in which performance variables take values in a continuous accomplishment set is treated explicitly

Computation-based reliability analysis

The structural and functional complexity of man-made systems is reported, showing the reliability analysis task becoming much more complex. Quantative methods are discussed for analyzing system quality. The reliability equations that are developed for systems employing modular redundancy and sparing are discussed to illustrate the need for computation-based reliability analysis

Theory of reliable systems

An attempt was made to refine the current notion of system reliability by identifying and investigating attributes of a system which are important to reliability considerations. Techniques which facilitate analysis of system reliability are included. Special attention was given to fault tolerance, diagnosability, and reconfigurability characteristics of systems

Models and techniques for evaluating the effectiveness of aircraft computing systems

System models that provide a basis for the formulation and evaluation of the performability of commercial aircraft computer system are developed. Quantitative measures of the system effectiveness are formulated. Analytic and simulation techniques for evaluation of the effectiveness and performability of a proposed or existing aircraft computer were studied

On-line diagnosis of unrestricted faults

A formal model for the study of on-line diagnosis is introduced and used to investigate the diagnosis of unrestricted faults. A fault of a system S is considered to be a transformation of S into another system S' at some time tau. The resulting faulty system is taken to be the system which looks like S up to time tau, and like S' thereafter. Notions of fault tolerance error are defined in terms of the resulting system being able to mimic some desired behavior as specified by a system similar to S. A notion of on-line diagnosis is formulated which involves an external detector and a maximum time delay within which every error caused by a fault in a prescribed set must be detected. It is shown that if a system is on-line diagnosable for the unrestricted set of faults then the detector is at least as complex, in terms of state set size, as the specification. The use of inverse systems for the diagnosis of unrestricted faults is considered. A partial characterization of those inverses which can be used for unrestricted fault diagnosis is obtained

Contextual Permission: A Solution to the Free Choice Paradox

In this paper, we give a solution to the Free Choice Paradox. This is done in two stages. First, we have a close look at the logical interpretation of the natural language statements that lead to the paradox. This leads to making the important distinction of permitting an action in isolation or permitting it in combination with some or any other action, i.e. in a certain context. This distinction is made formal by the introduction of a new operator on actions, which forces them to be performed in isolation. With this distinction made clear it is possible to give a "new", stronger definition for the permission operator, which solves the Free Choice Paradox and which does not lead to any new inconsistencies or paradoxes

Modification and improvements to cooled blades Patent

Modification and improvement of turbine blades for maximum cooling efficienc

Phased models for evaluating the performability of computing systems

A phase-by-phase modelling technique is introduced to evaluate a fault tolerant system's ability to execute different sets of computational tasks during different phases of the control process. Intraphase processes are allowed to differ from phase to phase. The probabilities of interphase state transitions are specified by interphase transition matrices. Based on constraints imposed on the intraphase and interphase transition probabilities, various iterative solution methods are developed for calculating system performability

Lattice constraints on the thermal photon rate

We estimate the photon production rate from an SU(3) plasma at temperatures of about 1.1Tc and 1.3Tc. Lattice results for the vector current correlator at spatial momenta k ~ (2-6)T are extrapolated to the continuum limit and analyzed with the help of a polynomial interpolation for the corresponding spectral function, which vanishes at zero frequency and matches to high-precision perturbative results at large invariant masses. For small invariant masses the interpolation is compared with the NLO weak-coupling result, hydrodynamics, and a holographic model. At vanishing invariant mass we extract the photon rate which for k \gsim 3T is found to be close to the NLO weak-coupling prediction. For k \lsim 2T uncertainties remain large but the photon rate is likely to fall below the NLO prediction, in accordance with the onset of a strongly interacting behaviour characteristic of the hydrodynamic regime.Comment: 20 pages. v2: clarifications adde