Photocatalytic degradation of organic pollutants in water and in air. An analytical approach

This paper reports on the development of three specific methods allowing to better understand the mechanism of the photocatalytic degradation of organic pollutants both in air and in gas phases. The first method uses a home made IR cell to study the TiO₂ surface during the photocatalytic degradation. The second method uses an ATD/GC/MS system to study the gas phase at a ppbv level during the degradation while the third one uses an HPLC/NMR system to discriminate between different positional isomers.     

Markov models for evaluating risk-informed in-service inspection strategies for nuclear power plant piping systems

As part of an EPRI sponsored research project to develop technology for risk informed in-service inspection evaluations, new methods and databases were developed to predict piping system reliability. The methods include a Markov modeling technique for predicting the influence of alternative inspection strategies on piping system reliability, and Bayes' uncertainty analysis methods for quantifying uncertainties in piping system reliability parameters. This article describes these methods and associated databases needed for their quantification with particular emphasis on the application of the Markov piping reliability model. Insights are developed regarding reliability metrics that should be used in Probabilistic Risk Assessments for estimating time dependent frequencies of loss of coolant accidents and internal flooding events. The methodology for developing estimates of all the input parameters of the piping reliability models is described including the quantitative treatment of uncertainties in risk informed applications. Examples are presented to demonstrate the practical aspects of applying the Markov model and developing the inputs needed for its quantification.     

Database development and uncertainty treatment for estimating pipe failure rates and rupture frequencies

Estimates of failure rates for nuclear power plant piping systems are important inputs to Probabilistic Risk Assessments (PRA) and risk informed applications of PRA. Such estimates are needed for initiating event frequencies for Loss of Coolant Accidents and internal flooding events and for risk informed evaluations of piping system in-service inspection programs. A critical issue in the estimation of these parameters is the treatment of uncertainties, which can exceed an order of magnitude deviation from failure rate point estimates. Sources of uncertainty include failure data reporting issues, scarcity of data, poorly characterized component populations, and uncertainties about the physical characteristics of the failure mechanisms and root causes. A methodology for quantifying these uncertainties using a Bayes' uncertainty analysis method was developed for the EPRI risk informed in-service inspection program and significantly enhanced in subsequent applications. In parallel with these efforts, progress has been made in the development of pipe failure databases that contain the quantity and quality of information needed to support piping system reliability evaluations. Examples are used in this paper to identify technical issues with previous published estimates of pipe failure rates and the numerical impacts of these issues on the pipe failure rates and rupture frequencies are quantified.     

Inductive Teaching and Learning Methods: Definitions,Comparisons, and Research Bases

Traditional engineering instruction is deductive, beginning with theories and progressing to the applications of those theories. Alternative teaching approaches are more inductive. Topics are introduced by presenting specific observations, case studies or problems, and theories are taught or the students are helped to discover them only after the need to know them has been established. This study reviews several of the most commonly used inductive teaching methods, including inquiry learning, problem‐based learning, project‐based learning, case‐based teaching, discovery learning, and just‐in‐time teaching. The paper defines each method, highlights commonalities and specific differences, and reviews research on the effectiveness of the methods. While the strength of the evidence varies from one method to another, inductive methods are consistently found to be at least equal to, and in general more effective than, traditional deductive methods for achieving a broad range of learning outcomes.     

A nonlinear mixed-effects model for degradation data obtained from in-service inspections

Monitoring of degradation and predicting its progression using periodic inspection data are important to ensure safety and reliability of engineering systems. Traditional regression models are inadequate in modeling the periodic inspection data, as it ignores units specific random effects and potential correlation among repeated measurements. This paper presents an advanced nonlinear mixed-effects (NLME) model, generally adopted in bio-statistical literature, for modeling and predicting degradation in nuclear piping system. The proposed model offers considerable improvement by reducing the variance associated with degradation of a specific unit, which leads to more realistic estimates of risk.     

Stress Rupture of PMC's in End-Loaded Bending

This paper introduces a method to study the time dependent behavior of polymer matrix composites. An end-loaded bending method and fixture are developed to emphasize the contribution of changes in matrix properties to the behavior of fiber dominated composites loaded in the fiber direction. This method has distinct advantages over other methods such as tensile stress rupture and three- and four-point bending rupture methods. This paper discusses the design and fabrication of an end-loaded bending fixture. A brief analysis is presented which relates strain level to end-to-end distance, eliminating the need for strain gauges. Time-dependent rupture in bending of polymer matrix composites is reported.     

核电厂管道振动原因分析及对策

管道是核电厂主要的组成部份。核电厂管道的振动往往引起管道的振动疲劳,长期积累致使管道开裂,严重时核电厂被迫停堆检修,甚至造成灾难性事故。为了减少此类事件的发生,本文总结了诱发核电厂管道振动的主要原因,有旋转设备的振动、水锤、流体脉动、气蚀、气液两相流、风载荷、地震载荷和人为误差等几种,并列举了相关事件案例,提出了常见的整改方案。本文旨在为核电厂管道的设计、建造、维护与整改等工作提供必要的参考依据。     

Artificial intelligence techniques for prediction of the capacity of RC beams strengthened in shear with external FRP reinforcement

The prediction of the shear capacity of reinforced concrete beams retrofitted in shear by means of externally bonded FRP is very complex as demonstrate the studies carried out up to date. As alternative to the conventional methods two approaches based on artificial intelligence are proposed for the first time. Firstly, the use of neural networks as a means of predicting shear capacity without the need of using complex models and, secondly, the use of genetic algorithms as a means of determining suitably how the shear mechanism works. Predictions obtained with both approaches are compared to experimental values.     

Principal trends in modern ecology and its mathematical tools: An analysis of publications

The paper deals with a scientometric analysis of publications from the journals “Ecology” and “Ecologia” (Russia) based on the frequencies of individual and cojoint encountering of ecological and mathematical keywords in these publications. Two main research approaches are revealed: population ecology and system ecology. The first one is used primarily in studies of plant communities, while the other in terrestrial animals and birds. Water communities are the subject of both approaches. The most spread mathematical methods are the methods of mathematical statistics which can be clustered into four groups: standard ones, multivariate methods, in particular multiple regression and multivariate analysis of variance, nonparametric or allowing deviations from normality, and methods of analysis of categorical data. Differential equations and stochastic process are used much lesser. The intensities of using mathematical methods are notably different in two journals. This paper (originally published in Russian in The Journal of General Biology) was inspired, like many others, by Professor V. V. Nalimov, and he contributed much in fruitful discussion and advices.     

Micromodel-based simulations for laminated composites

We develop a calculation strategy for the simulation of a complete microscopic model. This strategy enables one to account for damage mechanisms in laminated composites. The model mixes discrete and continuous approaches by introducing potential rupture surfaces and a damageable continuous medium. This approach requires suitable calculation tools unavailable in industrial analysis codes. The strategy presented is multiscale in space and is based on a decomposition of the domain into substructures and interfaces. This strategy enables one to simulate complex problems with multiple cracks. In practice, to use such a model, the strategy must be improved in order to handle very large numbers of substructures and interfaces and to estimate the rupture criteria for the surfaces introduced into the model. We provide simple examples which demonstrate the capabilities of the microscopic model.     

Formalisation of a new prognosis model for supporting proactive maintenance implementation on industrial system

The importance of the maintenance function has increased because of its role in keeping and improving system availability and safety, as well as product quality. To support this role, the maintenance concept has undergone several major developments that have led to proactive considerations mainly based on a prognosis process, which normally allows selection of the best maintenance action to be carried out. This paper proposes the deployment and experimentation of a prognosis process within an e-maintenance architecture. The deployment follows a methodology based on the combination of both a probabilistic approach for modelling the degradation mechanism and of an event one for dynamical degradation monitoring. The feasibility and benefits of this new prognosis process is investigated with an experiment using a manufacturing TELMA (TELe-MAintenance) platform supporting the unwinding of metal bobbins.     

Risk indicators as a tool for risk control

This paper presents a general methodology for the establishment of risk indicators that can be used as a tool for risk control during operation of offshore petroleum installations. The risk indicators established are based on the platform specific quantitative risk analysis (QRA). The general methodology is evaluated against comparable approaches both in offshore and nuclear industry. There are two distinct features of this methodology. The first is that it is truly risk-based with the intention of covering the total risk picture. The second is that the identification of the risk factors contributing most to the total risk is based on realistic changes of each factor assessed by the platform personnel, not a theoretically assumed change. The set of risk indicators for one specific installation is presented along with test results.     

A failure mechanism consistency test method for accelerated degradation test

Accelerated degradation test (ADT) is generally used to accelerate degradation processes in products to estimate their lifespan and to assess their reliability in a short period of time. How to perform the failure mechanism consistency test is crucial in the application of the ADT method. Existing failure mechanism consistency test methods assume that degradation rates among individual products are the same. However, these methods do not take degradation dispersions caused by manufacturing technologies into consideration. To address this issue, a failure mechanism consistency test method for ADT based on the activation energy invariant method and the likelihood ratio test is proposed. First, a degradation modeling method for ADT is introduced. Then, the logarithmic maximum likelihood function values of the degradation models are estimated based on the two-step maximum likelihood estimation (MLE) method. Finally, the decision rule is proposed based on the likelihood ratio test. The method mentioned above is, then, used on the real degradation data of carbon-film resistors and bullet O-rings, and its effectiveness is verified. Furthermore, based on the failure mechanism change point in RTV5370 siloxane rubbers, the simulated degradation data are degenerated to compare the proposed method with the method not considering individual differences in different ADT programs and degradation dispersions.     

Application of fracture mechanics to nuclear piping systems

With the introduction of Nuclear Energy into the power industry, rigid requirements for the design of piping have been set up to prevent accidents that may cause dangers to the health and safety of the public. Of particular concern is the rupture of a pipe. In this paper, nuclear piping systems are examined from a fracture mechanics viewpoint considering present day ASME code standards. Included are calculations of the critical crack length for a typical piping system. A brief discussion of the pipe whip phenomenon is also given.     

Pipe failure probability—the Thomas paper revisited

Almost twenty years ago, in Volume 2 of Reliability Engineering (the predecessor of Reliability Engineering and System Safety), a paper by H. M. Thomas of Rolls Royce & Associates Ltd. presented a generalized approach to the estimation of piping and vessel failure probability. The ‘Thomas-approach’ used insights from actual failure statistics to calculate the probability of leakage and conditional probability of rupture given leakage. It was intended for practitioners without access to data on the service experience with piping and piping system components.This article revisits the Thomas paper by drawing on insights from development of a new database on piping failures in commercial nuclear power plants worldwide (SKI-PIPE). Partially sponsored by the Swedish Nuclear Power Inspectorate (SKI), the R&D leading up to this note was performed during 1994–1999. Motivated by data requirements of reliability analysis and probabilistic safety assessment (PSA), the new database supports statistical analysis of piping failure data. Against the background of this database development program, the article reviews the applicability of the ‘Thomas approach’ in applied risk and reliability analysis. It addresses the question whether a new and expanded database on the service experience with piping systems would alter the original piping reliability correlation as suggested by H. M. Thomas.     

Design factors,reliability, and durability prediction of wet layup carbon/epoxy used in external strengthening

Although fiber reinforced polymer composites are increasingly used through the wet layup process for the rehabilitation of deteriorating and understrength concrete structures, there is very little validated information regarding performance over extended time periods. This has resulted in the use of excessively conservative factors in design in some cases, and unconservative estimates, or complete disregard of degradation effects on some characteristics, in others. In this paper two commonly used predictive approaches are used to provide estimates of long-term deterioration for a range of material characteristics which are compared to experimental data obtained over a 3 years period of exposure. It is shown that although predicted durability of tensile characteristics is extremely good for thin sections used conventionally, the rates of deterioration increase significantly with increase in the number of reinforcing layers used. In addition there is deterioration of other characteristics, especially related to interlaminar and intralaminar properties, that need to be considered. It is noted that both methods are unable to accurately account for effects of initial post-cure seen in ambient cured carbon/epoxy systems, although the conventional Arrhenius predictions provide good correlation with experiments once this mechanism has ceased. A methodology that is capable of accounting for temperature variation during exposure is also outlined. The predictions are compared with safety factors prescribed by ACI-440 and TR-55 and some inherent disadvantages of such approaches is highlighted. The basis for the estimation of safety factors based on a reliability approach using Weibull parameters is presented and typical results are shown, emphasizing some weaknesses in current design methodologies in the area of FRP rehabilitation of concrete.     

Evaluation of the Green function for 3-D wave-body interactions in a channel

This study deals with a 3-D boundary-value problem that arises when free-surface waves interact with a stationary body or body system in a channel or wave tank of rectangular cross-section. A consistent asymptotic analysis and an efficient numerical solution is presented of the Green function that satisfies the linear free- surface condition and the non-penetration condition on the channel bottom and the sidewalls. The formulation is based on the open-sea Green function and the complete series of images is evaluated accurately based on the asymptotic analysis. It is demonstrated that the Green function has a square-root singular behavior due to the sidewalls when the wave frequency approaches one of the resonant frequencies. The numerical results for the Green function presented in this paper are believed to have an absolute accuracy of 10^–5.     

Element substitution algorithm for general two-terminal network reliability analyses

The computation of the reliability of two-terminal networks is a classical reliability problem. For these types of problems, one is interested, from a general perspective, in obtaining the probability that two specific nodes can communicate. This paper presents a holistic algorithm for the analysis of general networks that follow a two-terminal rationale. The algorithm is based on a set replacement approach and an element inheritance strategy that effectively obtains the minimal cut sets associated with a given network. The vast majority of methods available for obtaining two-terminal reliability are generally based on assumptions about the performance of the network. Some methods assume network components can be in one of two states: (i) either completely failed; or (ii) perfectly functioning, others usually assume that nodes are perfectly reliable and thus, these methods have to be complemented or transformed to account for node failure, and the remaining methods assume minimal cut sets can be readily computed in order to analyze more complex network and component behavior. The algorithm presented in this paper significantly differs from previous approaches available in the literature in the sense that it is based on a predecessor matrix and an element substitution technique that allows for the exact computation of minimal cut sets and the immediate inclusion of node failure without any changes to the pseudo-code. Several case networks are used to validate and illustrate the algorithms.     

A probabilistic physics-of-failure model for prognostic health management of structures subject to pitting and corrosion-fatigue

A combined probabilistic physics-of-failure-based model for pitting and corrosion-fatigue degradation mechanisms is proposed to estimate the reliability of structures and to perform prognosis and health management. A mechanistic superposition model for corrosion-fatigue mechanism was used as a benchmark model to propose the simple model. The proposed model describes the degradation of the structures as a function of physical and critical environmental stresses, such as amplitude and frequency of mechanical loads (for example caused by the internal piping pressure) and the concentration of corrosive chemical agents. The parameters of the proposed model are represented by the probability density functions and estimated through a Bayesian approach based on the data taken from the experiments performed as part of this research. For demonstrating applications, the proposed model provides prognostic information about the reliability of aging of structures and is helpful in developing inspection and replacement strategies.     

Low- and high-temperature vitrification as a new approach to biostabilization of reproductive and progenitor cells

Cells held in a liquid milieu undergo processes that cause progressive loss of viability. To prevent such degradation, cells need to be placed in conditions that essentially stop all chemical reactions for the duration of the time of storage. Because intracellular ice formation is lethal to most eukaryotic cells, stable storage of viable cells can be achieved only if intracellular vitrification without ice formation has occurred. This has been done by several methods, including equilibrium (slow) freezing, lyophilization (freeze-drying), and ice-free vitrification at subzero temperatures at moderate-to high cooling rates in the presence of cryoprotectants (‘conventional’ vitrification). In this paper, we discuss the mechanisms of vitrification, and specific aspects, advantages, and pitfalls of the different approaches. Particular emphasis is put on novel methods of cell preservation, such as cryoprotectant-free vitrification of sperm and high temperature vitrification by air/vacuum drying of progenitor and other nucleated cells.