A probability model of system downtime with implications for optimal warranty design

Traditional approaches toward modeling the availability of a system often do not formally take into account uncertainty over the parameter values of the model. Such models are then frequently criticized because the observed reliability of a system does not match that predicted by the model. This paper extends a recently published segregated failures model so that, rather than providing a single figure for the availability of a system, uncertainty over model parameter values is incorporated and a predictive probability distribution is given. This predictive distribution is generated in a practical way by displaying the uncertainties and dependencies of the parameters of the model through a Bayesian network (BN). Permitting uncertainty in the reliability model then allows the user to determine whether the predicted reliability was incorrect due to inherent variability in the system under study, or due to the use of an inappropriate model. Furthermore, it is demonstrated how the predictive distribution can be used when reliability predictions are employed within a formal decision‐theoretic framework. Use of the model is illustrated with the example of a high‐availability computer system with multiple recovery procedures. An BN is produced to display the relations between parameters of the model in this case and to generate a predictive probability distribution of the system's availability. This predictive distribution is then used to make two decisions under uncertainty concerning the offered warranty policies on the system: a qualitative decision and an optimization over a continuous decision space. Copyright © 2009 John Wiley & Sons, Ltd.     

Validation of Models Predicting Nucleation Rates from Induction Times and Metastable Zone Widths

Three approaches for estimation of nucleation rates from induction time and metastable zone width (MSZW) were validated based on directly measured nucleation rates for paracetamol in ethanol. To quantitatively predict nucleation kinetics using Kubota's methods it is necessary to know the minimum detectable number concentration of nuclei. This was found by determination of light transmission of a series of diluted suspensions of newly nucleated crystals where the size had already been assessed by optical reflection measurement (ORM). The measured nucleation rates strongly depended on both temperature and supersaturation. The Nyvlt method predicted nucleation rates in this system reasonably well; however, it gave slightly low estimates for all temperatures. The methods of Kubota provided nucleation rates that were low by an order of magnitude.     

Effects of recombination parameters in pn indium phosphide solar cells

This work, using a numerical code PC-1D, describes the effects of surface and bulk recombination on the performance of p⁺n indium phosphide solar cells. It is shown that surface recombination velocity and minority carrier diffusion lengths play a dominant role in controlling the efficiency of p⁺n cells. In order to have an acceptable series resistance, a p⁺n cell must have an emitter that is thicker than a n⁺p cell emitter. Consequently the performance of a p⁺n cell is more sensitive to the front surface recombination velocity. Improved surface and bulk recombination parameters can lead to cell efficiencies in excess of 24% AMO at 25°C.     

Anterior colporrhaphy reinforced with Marlex mesh for the treatment of cystoceles

The present study was carried out in order to examine the efficiency of selenium/vitamin E on the health status in the first eight weeks of life in Se-deficient neonate calves. The experiments were done with 54 calves from two farms. Animals with low selenium level p.n. (< 40 micrograms/l) were randomly classified alternatively to be treated (gr. I) or to serve as control (gr. II). The calves of group I were treated with 0.2 mg selenium and 60 mg vitamin E per kg body weight subcutaneously on the first and third day p.n.; they got another treatment with half of the dosage in the fourth week of life. Group II received a placebo (0.9% sterile NaCl-solution). Clinical and haematological examination brought following results: Group I showed a lower infection rate and the duration of infection (especially in the case of pneumonia) was shorter than in the controls. During two days, after initial selenium substitution, the GSH-Px-activity was clearly higher in the animals of group I. The amount of antibiotics and special diets per calf was lower in group I. In conclusion it can be said, that the application of selenium and vitamin E seemed to improve the status of health in the Se-deficient calves, although the results could not be assured statistically.     

Distributed feedback lasers in chiral media

The combined effects of chirality and gain (or loss) on wave propagation and coupling in periodic structures is investigated here. The focus is on distributed feedback (DFB) lasers in a transversely unbounded periodic slab with spatially modulated electromagnetic parameters. The analysis uses a coupled-mode approach employing a canonical physical model of chiral materials to predict the effects of modulated chirality admittance on DFB lasers. Results for DFB laser behavior in chiral media are compared and contrasted to that in achiral media. It is found that, under certain circumstances, the electric and magnetic field coupling, which is characteristic of chiral materials, results in a lower threshold gain for DFB lasers in media with a given index of refraction and characteristic impedance. It is also found that chiral index-coupled or gain-coupled DFB lasers exhibit the same spectral mode properties as achiral DFB lasers     

Comprehensive benefit of flood resources utilization through dynamic successive fuzzy evaluation model: A case study

Taking the flood resources utilization in Baicheng, Jilin during 2002–2007 as the research background, and based on the entropy weight and multi-level & multi-objective fuzzy optimization theory, this research established a multi-level & semi-constructive index system and dynamic successive evaluation model for comprehensive benefit evaluation of regional flood resources utilization. With the year 2002 as the base year, the analyzing results showed that there existed a close positive correlation between flo...     

METHODOLOGY CHOICE,COMPLEXITY TEXTURE,SELF-REFLECTION

Substantial efforts have been dedicated toward the development of systems methodologies for “problem solving,” with various research groups concentrating on particular approaches. Recently, however, there have been moves toward reconciling these varying approaches within one overall framework, thus cutting out “isolationism” and inevitable ensuing sniping. This paper provides an overview of three attempts to promote such openness and conciliation (in terms of theory, methodology, and ideology), draws them together, and then demonstrates the practical importance of a critical approach through a series of contrasting applications and by reflecting on ideas from the three approaches.     

EDFA-based DWDM lightwave transmission systems with end-to-end power and SNR equalization

An approximate analysis is presented which can be used to predict the performance of power and signal-to-noise ratio (SNR) equalization schemes when applied to dense wavelength-division multiplexing (DWDM) lightwave systems employing erbium-doped fiber amplifier (EDFA) cascades. Expressions are provided which relate the maximum number of amplifiers, EDFA gain imbalance, bit rate (R/sub b/), transmitter power, receiver dynamic range and number of channels. The relative advantages of these two equalization strategies are quantified by comparing the maximum number of amplifiers allowed by each scheme. It is shown that, while SNR equalization represents, on balance, the more desirable equalization strategy for future EDFA-based DWDM lightwave transmission systems, under certain conditions power equalization may be a better choice. When employing an APD receiver, for instance, power equalization can support 1.9 times more amplifiers than SNR equalization. However, when employing the more conventional preamplified PIN/FET receiver, SNR equalization can support 1.7 times more amplifiers than power equalization.