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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    OR spectrum 19 (1997), S. 23-29 
    ISSN: 1436-6304
    Keywords: Job shop scheduling ; dispatching rules ; coordination ; look ahead information ; simulation ; Werkstattsteuerung ; Steuerungsregeln ; Koordination ; Vorausschauende Informationen ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung In diesem Beitrag wird ein neuartiger Ansatz zur Koordination dezentraler Werkstattsteuerungsregeln vorgestellt und mit Hilfe einer Simulationsstudie analysiert. Die Koordination basiert auf vorausschauenden Informationen und enthält einen Auftragsnachfrage-/-angebotsmechanismus. Die Simulations-experimente zeigen, daß durch den Einsatz des Koordinationsmechanismus die Leistung herkömmlicher Steuerungsregeln signifikant verbessert wird.
    Notes: Abstract In this paper a new coordination approach for decentralized job shop scheduling rules is presented and analyzed in a simulation study. The coordination is based on look ahead information and contains a mechanism for demanding and supplying jobs. The simulation experiments show that the performance of conventional scheduling rules is significantly improved using the coordination mechanism.
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  • 2
    Electronic Resource
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    OR spectrum 19 (1997), S. 23-29 
    ISSN: 1436-6304
    Keywords: Key words: Job shop scheduling ; dispatching rules ; coordination ; look ahead information ; simulation ; Schlüsselwörter: Werkstattsteuerung ; Steuerungsregeln ; Koordination ; Vorausschauende Informationen ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung. In diesem Beitrag wird ein neu-artiger Ansatz zur Koordination dezentraler Werkstattsteuerungsregeln vorgestellt und mit Hilfe einer Simulationsstudie analysiert. Die Koordination basiert auf vorausschauenden Informationen und enthält einen Auftragsnachfrage-/-angebotsmechanismus. Die Simulations- experimente zeigen, daß durch den Einsatz des Koordinationsmechanismus die Leistung herkömmlicher Steuerungsregeln signifikant verbessert wird.
    Notes: Abstract. In this paper a new coordination approach for decentralized job shop scheduling rules is presented and analyzed in a simulation study. The coordination is based on look ahead information and contains a mechanism for demanding and supplying jobs. The simulation experiments show that the performance of conventional scheduling rules is significantly improved using the coordination mechanism.
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  • 3
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    Journal of intelligent manufacturing 10 (1999), S. 323-329 
    ISSN: 1572-8145
    Keywords: Computer-aided design ; rapid prototyping ; modeling ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The direct slicing of CAD models created in CADDS V to generate geometric data for rapid prototyping using fused feposition modeling technique (FDM) is presented in this paper. The report file from an explicit model is accessed for obtaining model data. Algorithms have been developed for determining the volumes of model material as well as support materials. New algorithms have been developed for filling the sheet solid. A simulation module has been developed to verify whether the filling is correctly done. Example of a model is manufactured using this approach is also presented in this paper.
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  • 4
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    Journal of intelligent manufacturing 10 (1999), S. 405-421 
    ISSN: 1572-8145
    Keywords: Flexible manufacturing systems control ; intelligent manufacturing ; neural networks ; simulation ; material handling systems ; automated guided vehicles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper presents a framework of intelligent manufacturing scheduling and control with specific applications to operations of rail-guided vehicle systems (RGVS). A RGVS control architecture is discussed with a focus on a simulated experiment in operations of the load/unload area of a real industrial flexible manufacturing system (FMS). In the operation stage of a material handling system (MHS), all shop floor data are subject to change as time goes. These data can be collected using a data acquisition device and stored in a dynamic database. The RGVS simulator used in this experimental study is designed to incorporate some possible situations representing existing material handling scenarios in order to evaluate alternative control policies. At the development stage of the controller, all possible combinations of most commonly encountered scenarios such as RGV failures, production schedule changes, machine breakdowns, and rush orders are to be simulated and corresponding results collected. The data are then structured into training data pairs to properly train an artificial neural network. The neural network, trained by using input/output data sets obtained from a number of simulation runs, will then provide control strategy recommendations. At the application stage, whenever an abnormal scenario occurs, a pre-processor will be activated to pre-screen and prepare an input vector for the trained neural network. If such an abnormal scenario falls outside the existing domain of data sets employed to train the neural network, as judged by the MHS supervisory controller, an off-line training module will be activated to eventually update the neural network. The recommended control strategies will be transmitted to the MHS control for real-time execution. If there is no further abnormal event detected, the dynamic data base (DDB) module simply continues to monitor the MHS activities. The proposed MHS control system combines the features of example based neural network technology and simulation modeling for true intelligent, on-line, pseudo real-time control. Not only will the system assure that feasible material handling control actions be taken, but also it will implement better control decisions through continuous learning from experiences captured as the operation time of the MHS accumulates.
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  • 5
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    Journal of intelligent manufacturing 10 (1999), S. 449-462 
    ISSN: 1572-8145
    Keywords: Control chart ; pattern recognition ; neural network ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Abnormal patterns on manufacturing process control charts can reveal potential quality problems due to assignable causes at an early stage, helping to prevent defects and improve quality performance. In recent years, neural networks have been applied to the pattern recognition task for control charts. The emphasis has been on pattern detection and identification rather than more detailed pattern parameter information, such as shift magnitude, trend slope, etc., which is vital for effective assignable cause analysis. Moreover, the identification of concurrent patterns (where two or more patterns exist together) which are commonly encountered in practical manufacturing processes has not been reported. This paper proposes a neural network-based approach to recognize typical abnormal patterns and in addition to accurately identify key parameters of the specific patterns involved. Both single and concurrent patterns can be characterized using this approach. A sequential pattern analysis (SPA) design was adopted to tackle complexity and prevent interference between pattern categories. The performance of the model has been evaluated using a simulation approach, and numerical and graphical results are presented which demonstrate that the approach performs effectively in control chart pattern recognition and accurately identifies the key parameters of the recognized pattern(s) in both single and concurrent pattern circumstances.
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  • 6
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    Journal of intelligent manufacturing 8 (1997), S. 3-14 
    ISSN: 1572-8145
    Keywords: Production system analysis ; object-oriented approach ; production control ; simulation ; Petri networks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Tool specification for production system control requires the identification of the main characteristics of the production system. The production systems are varied, and the production control tools (such as scheduling algorithms and resource assignment rules) are often dedicated to only one class of these systems. Tool assessment for production system control requires modelling of the production system. We propose a new approach to production systems, to identify the nature and the complexity of the system according to the classification of Conway et al., and to specify a dynamic model that will allow us to simulate production control decisions. This paper presents this object-oriented approach, which identifies the resources and the organization features of the studied system. It then, proposes some predetermined classes of objects, which enable us to classify the system components and to use pre-existing dynamic models. These dynamic models are based on timed and coloured Petri nets. The overall architecture of our methodology follows three steps: top-down analysis of resources and bottom-up recognition of predetermined objects, instantiation and integration of objects, and implementation of objects. An example illustrates its use in the textile industry.
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  • 7
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    Journal of intelligent manufacturing 8 (1997), S. 405-413 
    ISSN: 1572-8145
    Keywords: Manufacturing systems ; decision making systems ; simulation ; discrete and continuous optimization ; discrete ψ-transform method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Algorithms for discrete and continuous optimization are a very important part of decision making systems in manufacturing. Most planning, scheduling and layout problems require these algorithms. In practice, research into efficient algorithms meets two principal obstacles. The first one is linked to the fact that quite often the criteria cannot be expressed in an analytic form, so it is not possible to use existing theoretical resolution methods. The second is due to the fact that most of the problems for which the criteria can be represented in analytic form are NP-hard problems. This situation can be simplified using simulation. But the use of simulation and optimization methods together often gives a local optimum. The proposed method in this paper is based on the use of a discrete modification of ψ-transforms jointly with some heuristics for local optimization. The originality of this approach is in the possibility to avoid a local optimum, while using models of simulation for the computation of values of the criteria. An example of the utilization of the method is given: it concerns the optimization of the launching of the parts in production in systems of the job-shop type. The proposed method is compared with a heuristic known to be very good in the same number of simulations. The results of five tests with different model sizes show the efficiency of the proposed method.
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  • 8
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    Journal of intelligent manufacturing 8 (1997), S. 125-136 
    ISSN: 1572-8145
    Keywords: Artificial intelligence ; simulation ; database management system ; object oriented paradigm ; simulation program generation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Although many studies have illustrated AI-based simulation, the concept of combining databases with AI and simulation is relatively new. Complementing AI and simulation with databases aids in the development of a completely integrated simulation environment that spans the whole simulation life cycle. This study illustrates the design of a simulation program generator, the intelligent simulation code generator (ISCG), which uses a database management system as the user-oriented interface, an object-oriented system to develop the knowledge base and simulation environment, and a target simulation language as the simulation software. The ISCG offers data independence, system independence, simulation-specific transparency, and target language neutrality. Furthermore, the ISCG offers system design flexibility.
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  • 9
    ISSN: 1572-8765
    Keywords: carbonado ; diamond ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of carbonado type synthesized polycrystalline diamonds produced from graphite together with catalytic Ni-Mo alloy doped with TiB2 and BNcub was investigated. It was found that the addition of these boron compounds increases the oxidation resistance of the carbonado type synthesized polycrystalline diamonds. The oxidation mechanism acting on the carbonado type synthesized polycrystalline diamonds and the role of boron compounds in increasing the resistance to the oxygen reaction are discussed.
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  • 10
    ISSN: 1572-9338
    Keywords: integer programming ; discriminant analysis ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract Although there have been several journal articles on the classificatory performance of mathematical programming approaches to the two-group discriminant problem, there has been no simulation study on the classificatory performance of mathematical programming approaches to the multiple-group problem reported in the literature. This study reports the results of a simulation experiment on the classificatory performance of a single-function and a multiple-function mathematical programming model relative to that of the standard parametric procedures for the three-group problem with small training samples. The effect of second-order terms on the classificatory performance of the mathematical programming models for the three-group problem is also investigated. Furthermore, this study theoretically examines the range of parameter values of a multiple-function mathematical programming model for which its number of misclassifications in the training sample cannot exceed that of a single-function model.
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  • 11
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    Annals of operations research 74 (1997), S. 321-332 
    ISSN: 1572-9338
    Keywords: simulation ; modeling ; aerospace ; air route structure ; free flight ; clustering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract Recent work performed for the Federal Aviation Administration to support the development of future concepts of air traffic management has involved simulation modeling of patterns of airspace usage by commercial and business air traffic. The objective of these efforts has been to investigate the impacts of a pattern of airspace usage known as "free flight", whereby pilots and flight dispatchers have much more freedom to choose, say, direct or wind-optimal routing through airspace. One of the figures of merit investigated is a count of "convergence pairs" as a measure of the complexity of various traffic patterns. These are cases when aircraft in the simulation model fly close to each other. Interestingly, geographic plots of convergence pairs accumulated over time bring out certain features or patterns of congested air traffic flows or flight alignments. However, these plots are also thick with "noise" or extraneous convergence pairs, whose presence detracts from the ability to perceive congested air traffic flows. Cluster analysis has been found to be an effective method of filtering these displays so that the congested flow features are discernible. The process developed for this purpose is based on a two-pass clustering approach. The process has worked well for the simulation modeling performed to date. Classification of the locations of convergence pairs into congested flow corridors is visually appealing, and has helped distinguish differences in contrasting scenarios of airspace usage. The paper presents graphical results and describes the clustering algorithms employed.
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  • 12
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    Computational & mathematical organization theory 3 (1997), S. 151-171 
    ISSN: 1572-9346
    Keywords: organizational performance ; planned organizational change ; resistance to change ; system dynamics ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper suggests that an induction of change program leads to atemporary impairment of organizational performance. A System Dynamics Modelportrays the process of planned organizational change. A set of keyvariables that facilitate or impede change is identified, quantified, andintegrated into the model. Three data sets, reproduced by simulation,demonstrate that the model is internally consistent and empiricallyadequate. The paper discusses theoretical and practical implications of the‘initial dip’ phenomenon in processes of planned change.
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  • 13
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    International journal of flexible manufacturing systems 11 (1999), S. 271-289 
    ISSN: 1572-9370
    Keywords: random flexible manufacturing systems ; scheduling ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The increased use of flexible manufacturing systems to efficiently provide customers with diversified products has created a significant set of operational challenges for managers. Many issues concerning procedures and policies for the day-to-day operation of these systems still are unresolved. Previous studies in this area have concentrated on various problems by isolating or simplifying the systems under study. The primary objective of this study is to extend previous research by examining the effects of scheduling rules and routing flexibility on the performance of a constrained, random flexible manufacturing system (FMS). Other experimental factors considered are shop load, shop configuration, and system breakdowns. Within the bounds of this experiment, the results indicate that, in the presence of total routing flexibility, the effects of shop load, system breakdowns, and scheduling rules are significantly dampened. In particular, when total routing flexibility exists, the choice of scheduling rules is not critical. We also show that the behavior of scheduling rules in a more constrained FMS environment (i.e., where system breakdowns occur and material handling capability is limited) is consistent with the findings of previous research conducted under less constrained environments. Finally, results indicate that the shop configuration factor has little or no impact on a system's flow-time performance.
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  • 14
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    Computational & mathematical organization theory 5 (1999), S. 167-192 
    ISSN: 1572-9346
    Keywords: rational choice ; friendship ; Markov processes ; random utility models ; simulation ; empirical test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We propose a class of actor-oriented statistical models for closed social networks in general, and friendship networks in particular. The models are random utility models developed within a rational choice framework. Based on social psychological and sociological theories about friendship, mathematical functions capturing expected utility of individual actors with respect to friendship are constructed. Expected utility also contains a random (unexplained) component. We assume that, given their restrictions and contact opportunities, individuals evaluate their utility functions and behave such that they maximize the expected amount of utility. The behavior under consideration is the expression of like and dislike (choice of friends). Theoretical mechanisms that are modelled are, e.g., the principle of diminishing returns, the tendency towards reciprocated choices, and the preference for friendship relations with similar others. Constraints imposed on individuals are, e.g., the structure of the existing network, and the distribution of personal characteristics over the respondents. The models are illustrated by means of a data-set collected among university freshmen at 7 points in time during 1994 and 1995.
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  • 15
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    International journal of flexible manufacturing systems 11 (1999), S. 19-35 
    ISSN: 1572-9370
    Keywords: integration ; process planning ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Many studies on integration of process planning and production scheduling have been carried out during the last decade. While various integration approaches and algorithms have been proposed, the implementation of these approaches is still a difficult issue. To achieve successful implementation, it is important to examine and evaluate integration approaches or algorithms beforehand. Based on an object-oriented integration testbed, a simulation study that compares different integration algorithms is presented in this paper. Separated planning method and integrated planning methods are examined. Also, situations of both fixed and variable processing times are simulated, and useful results have been observed. The successful simulation with the object-oriented integration testbed eventually will be extended to include other new planning algorithms for examining their effectiveness and implementation feasibility.
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  • 16
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    Annals of operations research 74 (1997), S. 239-257 
    ISSN: 1572-9338
    Keywords: autocorrelation ; L 1 regression ; least absolute deviations ; robust regression ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract Least absolute value (LAV) regression provides a robust alternative to least squares, particularly when the disturbances follow distributions that are nonnormal and subject to outliers. While inference in least squares estimation is well-understood, inferential procedures in the context of LAV estimation have not been studied as extensively, particularly in the presence of non-independent disturbances. In this work, we study three alternative significance test procedures in LAV regression, along with two approaches used to correct for serial correlation. The study is based on large-scale Monte Carlo simulations, and comparisons are made based on both observed significance levels and power.
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  • 17
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    International journal of flexible manufacturing systems 9 (1997), S. 273-298 
    ISSN: 1572-9370
    Keywords: routing flexibility ; dynamic sequencing and dispatching ; simulation ; Taguchi experimental design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The evolving manufacturing environment is characterized by a drive toward increasing flexibility. One possible manifestation of flexibility within an FMS is in the form of routing flexibility. Providing this typically is an expensive proposition, and system designers therefore aim to provide only the required levels commensurate with a given set of operating conditions. This paper presents a framework based on a Taguchi experimental design for studying the nature of the impact of varying levels of routing flexibility on the performance of an FMS. Simulation results indicate that increases in routing flexibility, when made available at the cost of an associated penalty on operation processing time, is not always beneficial. There is an optimal flexibility level, beyond which system performance deteriorates, as judged by the makespan measure of performance. It is suggested that the proposed methodology can be used in practice for not only setting priorities on specific design and control factors but also for highlighting likely factor level combinations that could yield near-optimal shop performance.
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  • 18
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    International journal of flexible manufacturing systems 9 (1997), S. 167-193 
    ISSN: 1572-9370
    Keywords: flexible manufacturing systems ; decentralization ; stochastic equilibrium ; pricing ; benefits ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Flexible manufacturing systems (FMSs) can apply the efficiencies of large-scale production to small batch production. The coordination of FMS activities is a complex task; this paper presents a decentralized pricing mechanism that can be used to estimate the activity–based costs and manage the activities of the FMS efficiently. The pricing mechanism described in this paper does not require systemwide information to compute prices; instead, the pricing mechanism samples and uses the demand information at each CNC machine to compute rental prices at that machine. We derive the theoretical formula for rental prices supporting the optimal performance and propose simulation studies to estimate the rental prices for real-time price changes in a decentralized manner. Results from a preliminary simulation study indicate that stable rental prices can be estimated and significant improvements can be realized by using the pricing mechanism.
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  • 19
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    Journal of computational analysis and applications 1 (1999), S. 349-385 
    ISSN: 1572-9206
    Keywords: Estimation ; geometric compound ; heavy-tail modeling ; Linnik distribution ; Mittag–Leffler law ; mixture ; multivariate Laplace distribution ; random summation ; simulation ; subordination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The paper discusses recent advances in the theory of multivariate geometric stable (GS) distributions. The results presented include characterizations, mixture representations, properties, simulation, and estimation.
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  • 20
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    Annals of operations research 73 (1997), S. 233-252 
    ISSN: 1572-9338
    Keywords: Data Envelopment Analysis ; model specification ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The use of Data Envelopment Analysis for estimating comparative efficiency has become widespread, and there has been considerable academic attention paid to the development of variants of the basic DEA model. However, one of the principal weaknesses of DEA is that - unlike statistically based methods - it yields no diagnostics to help the user determine whether or not the chosen model is appropriate. In particular, the choice of inputs and out-puts depends solely on the judgement of the user. The purpose of this paper is to examine the implications for efficiency scores of using a misspecified model. A simple production process is set up. Simulation models are then used to explore the effects of applying misspecified DEA models to this process. The phenomena investigated are: the omission of significant variables; the inclusion of irrelevant variables; and the adoption of an inappropriate variable returns to scale assumption. The robustness of the results is investigated in relation to sample size; variations in the number of inputs; correlation between inputs; and variations in the importance of inputs. The paper concludes that the dangers of misspecification are most serious when simple models are used and sample sizes are small. In such circumstances, it is concluded that it will usually be to the modeller's advantage to err on the side of including possibly irrelevant variables rather than run the risk of excluding a potentially important variable from the model.
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  • 21
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    Methodology and computing in applied probability 1 (1999), S. 127-190 
    ISSN: 1387-5841
    Keywords: combinatorial optimization ; global optimization ; importance sampling ; markov chain monte carlo ; simulated annealing ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We present a new and fast method, called the cross-entropy method, for finding the optimal solution of combinatorial and continuous nonconvex optimization problems with convex bounded domains. To find the optimal solution we solve a sequence of simple auxiliary smooth optimization problems based on Kullback-Leibler cross-entropy, importance sampling, Markov chain and Boltzmann distribution. We use importance sampling as an important ingredient for adaptive adjustment of the temperature in the Boltzmann distribution and use Kullback-Leibler cross-entropy to find the optimal solution. In fact, we use the mode of a unimodal importance sampling distribution, like the mode of beta distribution, as an estimate of the optimal solution for continuous optimization and Markov chains approach for combinatorial optimization. In the later case we show almost surely convergence of our algorithm to the optimal solution. Supporting numerical results for both continuous and combinatorial optimization problems are given as well. Our empirical studies suggest that the cross-entropy method has polynomial in the size of the problem running time complexity.
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  • 22
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    Journal of intelligent and robotic systems 24 (1999), S. 125-149 
    ISSN: 1573-0409
    Keywords: planning ; control ; multi-fingered robot hand ; optimization ; internal force ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this paper, the problem of controlling multi-fingered robot hands with rolling and sliding contacts is addressed. Several issues are explored. These issues involve the kinematic analysis and modeling, the dynamic analysis and control, and the coordination of a multi-fingered robot hand system. Based on a hand-object system in which the contacts are allowed to both roll and slide, a kinematic model is derived and analyzed. Also, the dynamic model of the hand-object system with relative motion contacts is studied. A control law is proposed to guarantee the asymptotic tracking of the object trajectory together with the desired rolling and/or sliding motions along the surface of the object. A planning approach is then introduced to minimize the contact forces so that the desired motion of the object and the relative motions between the fingers and the object can be achieved. Simulation results which support the theoretical development are presented.
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  • 23
    ISSN: 1432-0630
    Keywords: 42.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Lasing in atomic lines of noble gases and fluorine, prior to excimer radiation, was observed in an electric discharge ArF/XeF excimer laser. Some Ar/Xe lines end at metastable levels, which are very important for the formation of ArF/XeF excimer molecules. Five new lasing lines of atomic fluorine have been obtained. Consideration is given to the use of lasing in atomic and molecular lines, that occurs in one burst, in investigations of the excitation kinetics of excimer states under the conditions of a high-pressure electric discharge.
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  • 24
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    Applied physics 14 (1977), S. 277-282 
    ISSN: 1432-0630
    Keywords: 42.55 ; 52
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The paper deals with the properties andI-V characteristics of discharges in narrow capillaries used, for example, for He−Ne waveguide lasers. It has been observed that discharges in He−Ne waveguide lasers are unstable because of the strongly falling characteristic. A theory is presented which assumes that at low currents wall charges restrict the positive column to a narrow plasma channel and are the main reason for the observed falling characteristic. A numerical evaluation for helium gives results which agree well with experimental data.
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  • 25
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    Applied physics 18 (1979), S. 333-338 
    ISSN: 1432-0630
    Keywords: 87 ; 42.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Energy transfer in DNA-dye-complexes after excitation in the UV down to 220 nm by means of a tunable laser was investigated. DNA of different base composition and polynucleotides were compared. The dyes proflavine, acridine orange and ethidium bromide were used. The energy transfer from DNA-bases to dye molecules was measured in dependence of the excitation wavelength and the base composition of the DNA. Models of the energy transfer from DNA to dye and of the molecular structures of the DNA-dye-complex (intercalation) could be deduced.
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    Applied physics 19 (1979), S. 47-51 
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    Notes: Abstract The possibility of building free-electron lasers and masers with quasi-circular undulators is considered. The two-mirror cavity is replaced by a suitable waveguide. The magnetic field along the orbit has a continuous component superimposed on the alternating one. Besides allowing large freedom for electron guiding and focusing, the structure allows effective negative mass conditions, which may enhance the electron beam modulation when space charge effect are important. Furthermore the radiation frequency can be higher than that in a linear undulator with the same electron energy, and long interaction times are possible in a compact structure.
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  • 27
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    Applied physics 19 (1979), S. 345-351 
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    Notes: Abstract PrP5O14, PrxLa1−xP5O14, and PrxY1−xP5O14 (0≦x≦1) single crystals of laser quality were synthesized and their crystallographic and optical parameters measured. Laser emissions in the visible (λ=637.4 nm) with no mirrors in place (superradiance) and also in various optical resonators have been observed.
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  • 28
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    Applied physics 13 (1977), S. 97-99 
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    Keywords: 42.55 ; 82.50
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    Notes: Abstract First cw laser oscillation with thresholds below 1 mW was observed for various B1Пu → X1 ∑ g + transitions of diatomic molecular sodium excited by different argon laser lines in the range of 454–488 nm. For pump powers of 0.5 W output powers up to 3 mW and single-pass gain up to 0.1 cm−1 were obtained. Some properties of the heat pipe laser system are discussed.
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  • 29
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    Applied physics 13 (1977), S. 383-385 
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    Notes: Abstract An optically pumped FIR laser was operated with a copper mesh Fabr-Perot output coupler. With this device a Gaussian output beam was obtained andthe degree of coupling could be varied continuously, thus allowing optimum coupling. From the measured properties of the wire mesches grains of two FIR laser lines are calculated and the saturation intensities estimated.
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    Applied physics 14 (1977), S. 25-28 
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    Notes: Abstract A new device for magnetically displacing the output mirror of a laser resonator and synchronously tilting an etalon in order to obtain single-mode tuning of a dye laser over a tuning range of at least 10 GHz is described. Comparatively large displacements with good linearity of a coil mounted on a membrane and placed inside the strong magnetic field of a ring magnet are obtained for currents in the order of several hundred milliamperes. Together with etalon flats of appropriate thickness and reflection mounted in the resonator of the laser a versatile instrument for application in intra and extra cavity spectroscopy has been developed.
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  • 31
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    Applied physics 14 (1977), S. 393-398 
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    Notes: Abstract A flowing afterglow method has been used to study a number of reactions of importance in KrF lasers using NF3 as the fluorine donor. Total rate constants are reported for Kr*(3 P 2)+NF3 and Kr++NF3. The thermal energy attachment coefficient has been measured for NF3 and the cross section for the electron excitation process Kr*(3 P 2) +e→Kr*(3 P 1)+e has been estimated. The relevance of these results to discharge pumped KrF lasers is discussed.
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  • 32
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    Applied physics 14 (1977), S. 193-197 
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    Notes: Abstract Planar and cylindrical discharges for argon lasers are compared by plasmatheoretical calculations. The maximum laser output power available in the two arrangements is computed in dependence of various parameters neglecting saturation mechanisms. A transverse discharge arrangement confining the positive column by two parallel walls is described and experimental laser threshold values for the current and pressure are reported.
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  • 33
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    Applied physics 14 (1977), S. 255-268 
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    Keywords: 42.80 ; 42.55 ; 85.60
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    Notes: Abstract GaAs double heterostructure semiconductor injection lasers which now exhibit more than 25000 h cw room temperature lifetime are of great interest for future use as directly modulated transmitters for high bit-rate fiber optical communications. The effects limiting this application are modulation distortions, spectral width and additional spectral broadening in the case of modulation and spontaneous fluctuations of the output power. The dynamic and spectral behavior of injection lasers, the methods of high bit-rate modulation and the improvement of the high bit-rate modulation capability by coupling two lasers are discussed.
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  • 34
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    Applied physics 13 (1977), S. 109-110 
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    Notes: Abstract A simple technique is described that allows the generation of a short pulses (1 ns) from dye lasers pumped by a much longer (7 ns) N2-laser pulse. Dye-laser pulses, either with a narrow bandwidth or a short duration, can thus be obtained with the same N2-laser pump.
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  • 35
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    Applied physics 14 (1977), S. 121-122 
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    Notes: Abstract Frequency-tunable generation by means of F 2 + and F 2 − colour centers in a LiF crystal is reported. Colour centers were created by illuminating LiF crystals with electrons of 3 meV energy at the electron current density of 1 μA/cm2. The pumping source was a ruby laser with a peak power of 20 MW, a pulse duration of 20 ns, and a repetition rate of 1 Hz. The frequency tuning is obtained in the range of 0.88–1.25 μm. Discussed are the ways of pumping of colour centers and the possibility of lasing in the spectral region of 0.85 to 2 μm in the type of colour centers under investigation.
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  • 36
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    Applied physics 18 (1979), S. 257-260 
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    Notes: Abstract We have demonstrated the feasibility of Doppler-free polarization spectroscopy with a train of ultrashort pulses from a synchronously pumped mode-locked dye laser. The sensitivity of the method is compared with saturation spectroscopy with a single-mode laser.
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    Notes: Abstract The characteristics of a stable, external-resonator spin-flip Raman laser (SFRL), pumped by a cw carbon monoxide laser of controlled mode quality and spectral content, are determined using a combination of molecular spectroscopy, Raman amplifier and confocal Fabry-Perot interferometer measurements, and heterodyne detection. Single-frequency output of a free-running external-resonator is demonstrated with an inherent linewidth of 〈10 kHz and a short-term frequency jitter of ≃100 kHz. With the resonator length actively controlled to lock an axial mode frequency to the peak of the spontaneous gain, the linewidth of the SFRL output was maintained below 2 MHz. In this mode of operation, small variations in the output tuning rate, corresponding to the magnetic field dependence of the conduction-electrong-factor, were calibrated. Molecular absorption spectra obtained using gas cells both inside and outside the resonator have been used to illustrate the high resolution, wide-range tuning capability and sensitivity of the system. Lambda-doubling of the $$^2 \pi _{3/2} $$ of the Q-branch head of nitric oxide was measured for values ofJ down to 13/2, below which the splitting is less than the Doppler width. The splittings agreed with predictions using parameters obtained by conventional spectra for higherJ-values.
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    Applied physics 19 (1979), S. 241-242 
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    Notes: Abstract Several new laser lines using optically pumped deuterated methanol molecules have been discovered. These not only increase the spectral coverage of pumped methanol isotopes but may assist in the assignment of a molecular structure.
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  • 39
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    Applied physics 19 (1979), S. 399-403 
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    Notes: Abstract The selection of a single longitudinal mode of a dye laser can be achieved with double or triple Michelson reflectors instead of Fabry-Perot etalons inside the laser cavity. These systems can be adapted to commercial multimode dye lasers. They provide a high efficiency and a good geometrical quality of the output beam. With a 7 watt pump power (λ=514.5 nm line of the Ar+ laser), a tunable output power of 1 watt was obtained at the peak of R6G, in the main output beam; the total single-mode power, including the auxiliary output beams, exceeded 1.4 watt. These results correspond to efficiencies of 14% and 20%, respectively (24% and 30% slope efficiencies). We discuss in the text why these efficiencies are comparable to those of ring lasers. In the infrared, with a 4.5 watt pump power (red lines of a Kr+ laser), 250 mW of single-mode output power in the main output beam was obtained at 780 nm with Oxazine 750.
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  • 40
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    Applied physics 19 (1979), S. 427-429 
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    Notes: Abstract Spectral coincidences between CO-laser lines and NO fundamental absorption lines were reinvestigated in order to resolve discrepancies between recently published papers. The absorption of CO laser radiation by NO and NO/Ar mixtures was measured and fitted by calculations using a Voigt profile for the NO line shapes. A new coincidence with a frequency offset of less than the NO Doppler width was found.
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    Notes: Abstract A liquid-nitrogen cooled12C16O laser was operated both Q-switched and cw. A total of 276 lasing transitions were observed in cw using an intracavity grating for line selection. In the Q-switch mode, 230 lines occurred without dispersive element in the cavity.
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  • 42
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    Applied physics 18 (1979), S. 235-241 
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    Notes: Abstract Design and performance characteristics of a tunable ir waveguide Raman laser pumped by a high power dye laser are described. Using SRS up to third Stokes order in compressed H2, the wavelength range from 0.7 to 7 μm has been covered without gaps. Taking advantage of a waveguide structure in the scattering chamber, energy conversion efficiencies better than 1% with power levels in excess of 80 kW for the third Stokes component have been achieved. The experimental results support the theoretical predictions that a 4-wave parametric process is responsible for the production of the third Stokes component.
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    Applied physics 20 (1979), S. 41-50 
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    Keywords: 41 ; 42.55 ; 95
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    Notes: Abstract The interaction of free electrons and free electromagnetic radiation, in the presence of a uniform magnetic field, can result in stimulated emission or absorption. We analyze the dynamics of single electrons by solving the classical, relativistic Lorentz force equations of motion in these combined fields. An electron may gain energy from, or lose energy to, the radiation field, depending crucially on the phase and oscillation frequency of the electron's helical motion within the superposed, circularly polarized light wave. To first order in the radiation field strength, electrons in a monoenergetic, uniformly distributed beam become spatially bunched, but there is no net energy change. To second order, however, the beam may experience a gain or loss of energy, corresponding to attenuation or amplification of radiation. We compare the bunching of this laser process to the bunching processes involved in 1) the Stanford free-electron laser and 2) the cyclotron maser, and find significant differences in each case. Our analytic results provide a clear, simple picture of the interaction process, and can be useful in exploring light amplification in astrophysical magnetic fields, the magnetosphere, or in laboratory devices.
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    Applied physics 20 (1979), S. 61-65 
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    Notes: Abstract We show that a laser can efficiently accelerate charged particles if a magnetic field is introduced to improve the coupling between the particle and the wave. Solving the relativistic equations of motion for an electron in a uniform magnetic field and superposed, circularly polarized electromagnetic wave, we find that in energy-position phase space an electron traces out a curtate cycloid: it alternately gains and loses energy. If, however, the parameters are chosen so that the electron's oscillations in the two fields are resonant, it will continually accelerate or decelerate depending on its initial position within a wavelength of light. A laboratory accelerator operating under these resonant conditions appears attractive: in a magnetic field of 105 Gauss, and the fields of a 5×1012 W, 10 μm wavelength laser, an optimally positioned electron would accelerate to 700 MeV in only 10m.
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    Applied physics 20 (1979), S. 97-99 
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    Notes: Abstract A narrow-band tunable double-wavelength dye laser with a bandwidth of 0.1 cm−1 is described. The output at one of the wavelengths is found to be completely linearly polarized in the plane of incidence.
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  • 46
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    Applied physics 13 (1977), S. 107-108 
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    Notes: Abstract Intense laser oscillation has been observed from ArF molecules at 1933 Å. Excitation of the gas mixture NF3:Ar:He=1:55:630 at total pressures above 2.1 atm was produced by a transverse electric discharge. The range of fine tuning was from 1927 Å to 1936 Å. An output energy of 0.8 mJ was measured from a laser pulse 15 ns in duration.
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  • 47
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    Applied physics 19 (1979), S. 39-41 
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    Notes: Abstract It is shown that when a distributed feedback dye laser is used to generate a train of picosecond pulses, the narrow lines observed in the spectrum are not longitudinal modes, but are due to the intrapulse refractive index changes caused by the heating effect of the pumping pulse.
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  • 48
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    Applied physics 18 (1979), S. 415-419 
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    Notes: Abstract Remarkable intensity fluctuations were observed in the LiNdP4O12 (LNP) laser by placing a moving ground-glass plate across the ouput beam. Resonance-like behaviors were also observed by tuning the moving velocity of the ground-glass plate, with respect to relaxation oscillations. Classical rate equations including the modulation term were given to explain the observed phenomena. Similar intensity fluctuations corresponding to relaxation oscillations were observed when the LNP laser light beam was coupled to an optical fiber.
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    Applied physics 19 (1979), S. 35-37 
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    Notes: Abstract Results of an investigation of 19 organic dyes pumped by a 1.7 MW discharge-pumped XeCl excimer laser are reported. The dye-laser emission covered a wide wavelength range from 340 nm to 710 nm.P-terphenyl shows efficient laser action. The highest energy conversion efficiency exceeds 40% in visible region. In comparison with 250 kW nitrogen laser pumping, higher efficiencies are obtained for most of these dyes in the same dye-laser configuration.
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    Applied physics 19 (1979), S. 185-189 
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    Notes: Abstract We have studied the interaction of stimulated spin-flip Raman scattering and stimulated recombination radiation in n-InSb using a CW CO pump laser. A change in linewidth and output power of second Stokes spin-flip radiation is observed when the tuning curve of the first Stokes stimulated spin-flip radiation and the stimulated recombination radiation cross. The observations are explained using a simple rate equation model.
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    Applied physics 18 (1979), S. 77-80 
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    Notes: Abstract We report, for the first time, on room temperature cw laser action of NdP5O14 and NdAl3(BO3)4 at 1.3 μm wavelength. The emission cross sections of the transition4 F 3/2→4 I 13/2 are 0.24·10−19 cm2 and 1.74·10−19 cm2, respectively. The lowest observed threshold was 45 mW and the slope efficiency was nearly 10%. The minimum threshold is expected to be about 5 mW of absorbed pump light for both materials.
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    Notes: Abstract Laser induced nonlinear absorption profiles in a three-level system have been recorded to study the effect of elastic collisions upon optical coherences. In our particular system, the signal is due to a pure double-quantum term, where we have separated the effect of phase-interrupting collisions from the effect of velocity-changing collisions. Experimental results show that the effect of velocity-changing collisions is very small, and that broadening of the signal is due to phase-interrupting collisions mainly. We are able to determine the increase of the decay rate of the coherent superposition (the “coherence”) of two levels of same parity [Dγ 13/dp=(6.5±1) MHz/Torr] and an upper limit for the mean velocity change (ũ≲5m/s).
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    Applied physics 19 (1979), S. 165-170 
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    Notes: Abstract Computer calculations of ETDL performance indicate that dye laser output can be manipulated by an appropriate choice of a donor (absorber)-acceptor (dye) couple. Studies of relevant laser induced inter- and intramolecular energy transfer processes are presented.
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    Applied physics 19 (1979), S. 221-224 
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    Notes: Abstract Wave front of a light pulse is shown to be unstable as it propagates through a resonant saturable absorber, if its frequency is higher than the resonance frequency of the absorber. When ΔωT 2∼1, a small-scale transverse instability with the dimension of (λl abs)1/2 grows rapidly. Its growth-rate is of the order of the small-signal-absorption length of the medium.
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    Applied physics 19 (1979), S. 257-264 
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    Notes: Abstract Employing injection-locking techniques an oscillator configuration was found comprising in a simple way all the features required for fusion directed high-power CO2 laser systems. The oscillator provides emission in single axial modes on rotational transitions which can be freely selected by feeding fluencies of a few mW/cm2 at the particular transition into the oscillator cavity. In the same way simultaneous emission on selectable lines can be achieved. By the same principle the oscillator can be forced to emit in any orientation of polarization. The set up is relatively simple, the alignment rather uncritical, and the operation reliable. Gaussian-shaped nanosecond pulses with low forepulse power are produced with the help of a pulse cutter and saturable multiline absorber. The set up is described and its features are demonstrated by measurements.
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    Applied physics 13 (1977), S. 1-3 
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    Notes: Abstract Disappearance of NF3 and appearance of NF2 and N2F2 in an excimer laser is followed quantitatively with a mass spectrometer. A model for the kinetics is presented.
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    Applied physics 13 (1977), S. 55-58 
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    Notes: Abstract NdxLa1−xP5O14 (0.25≦x≦1) single crystals, placed within a confocal optical resonator, were pumped with ruby laser fundamental and second-harmonic nanosecond pulses. In both cases laser oscillations at 1.05 μm exceeding in duration many times the pumping pulse were obtained.
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    Applied physics 14 (1977), S. 343-350 
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    Notes: Abstract By means of nonlinear absorption spectroscopy data necessary for the interpretation of molecular spectra can be obtained in such spectral regions, where conventional spectroscopic methods yield only a quasi-continuous absorption curve. Using a Zeeman-tuned He−Ne laser at the wavelength of 3.39μm we have measured significant differences in the intensity and temperature behaviour for several ethane absorption lines, the analysis of which made possible a preliminary qualitative assignment of these lines.
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    Applied physics 14 (1977), S. 377-380 
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    Notes: Abstract Due to spatial hole burning, standing-wave dye lasers require a large amount of selectivity inside the cavity for single-mode operation. The output power of these lasers is limited by losses caused by the frequency selecting elements. In a travelling-wave laser, on the other hand, spatial hole burning does not exist, thereby eliminating the need for high selectivity. A travelling-wave cw dye laser was realized by unidirectional operation of a ring laser, yielding single mode output powers of 1.2 W at 595 nm and of 55 mW in the UV-region with intracavity frequency doubling.
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    Notes: Abstract The room temperature cw oscillation at 1.05 and 1.32 μm of lithium neodymium tetraphosphate [LiNd(PO3)4, LNP] lasers in an external resonator and, for the first time, also in a Fabry-Perot resonator with directly applied mirrors is reported. The growth and fluorescence properties of the LNP crystals are briefly described. Laser parameters such as threshold pump power, output power, differential efficiency, optical gain, emission cross section and laser modes are both measured and calculated. Laser experiments show the threshold pump power to be lower for 1.05 μm than for 1.32 μm emission because of the smaller emission cross section; the pump power density is lower for the external resonator than for the Fabry-Perot resonator because of its higher mode losses.
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    Applied physics 14 (1977), S. 199-203 
    ISSN: 1432-0630
    Keywords: 42.55 ; 82.50
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Loss of gain in a dye medium as a result of decomposition by pump photons is considered in terms of disappearance of dye molecules and the appearance of a new, single chemical product having absorption in the fluorescence band. The cases of small signal gain and saturated gain are applied to a single pass through a transversely excited amplifier. Loss of output, defined as “quantum yield of laser deterioration”,Q L , is related to the true quantum yield of molecular destruction of the dye,Q M , and other known parameters. For the experimentally common, saturated gain condition, the smallestQ L can be isQ M , which requires a photochemically bleachable dye with high gain, preferably at high concentration, in a long cavity, operating at high injection and pumping fluxes. Reversing these conditions, the highest valueQ L can be, compared withQ M , is unrestricted.
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  • 62
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    Applied physics 19 (1979), S. 243-245 
    ISSN: 1432-0630
    Keywords: 42.55
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Stable step-tunable simultaneous double-wavelength emission from any branch combination of the 9.6 and 10.6 μm bands of a cw CO2 laser is reported in which the relative strengths of the two signals may be controlled.
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  • 63
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    Applied physics 18 (1979), S. 177-181 
    ISSN: 1432-0630
    Keywords: 42.55 ; 42.65 ; 33
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We have studied experimentally stimulated Raman scattering and 4-wave-interaction processes occuring in hydrogen gas, which is excited by a Nd:YAG-pumped dye laser. The tuning ranges of the various Stokes and anti-Stokes lines, which are generated with high efficiency, cover the spectrum from 185 to 880 nm without a gap.
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  • 64
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    Applied physics 20 (1979), S. 129-134 
    ISSN: 1432-0630
    Keywords: 42.55 ; 33 ; 82.50
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Collisional coupling between theB, C, andD states of KrF is measured in a discharge pumped KrF laser. Detection of the time resolved populations in the three states via measurement of the side fluorescence in theB→X, C→A, andD→X bands is used to record the collisional relaxation from theC andD state to theB state during laser emission. The experimentally determined limits for the collisional coupling times are τB-C≦1 ns and τB-D,τC-D〈20 ns at total pressures of 2 bar. Investigation of theB→X fluorescence band shows that the vibrational manifold of theB state is not thermalized during laser emission. TheV-V,T coupling time is estimated to be τV-V,T=4±2 ns. The influence of collisional coupling on energy extraction in the KrF laser is discussed.
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  • 65
    ISSN: 1432-0630
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract An analytical treatment of the ultrashort-pulse generation in a solid-state laser is given taking into account gain saturation. The probability for the breakdown of the picosecond-pulse evolution caused by the amplification depletion is calculated. The influence of the active medium saturation on the satellite-pulse probability is investigated. Both probabilities characterize the mode-locking behaviour of the laser system and are calculated for various laser parameters to find an optimum laser regime.
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  • 66
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    Applied physics 19 (1979), S. 127-130 
    ISSN: 1432-0630
    Keywords: 42.55 ; 42.65
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    Notes: Abstract The possibility of using stimulated emission from the recombination of electron-positron pairs for obtaining coherent γ-rays is considered. The critical number of pairs needed for the process is calculated.
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  • 67
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    Applied physics 19 (1979), S. 359-361 
    ISSN: 1432-0630
    Keywords: 42.55
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    Notes: Abstract This paper describes a 1 m-long CW HCN discharge laser with a hollow dielectric rectangular discharge tube of 5×20 cm2 cross-section. For optimum working conditions, the characteristics of the amplifying medium have been made constant over the cross-section, by using an additional magnetic field. Then, the unsaturated gain for the 337 μm line is 6.8% m−1. It is shown to be dependent on the smaller dimension of the cross-section rather than on the other dimension. By using the tube as a waveguide, laser output power of 1 Watt might be obtained with a discharge length of 4 m, instead of the 12m-long discharge required to get the same output power from a cylindrical waveguide laser.
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  • 68
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    Applied physics 20 (1979), S. 257-259 
    ISSN: 1432-0630
    Keywords: 87 ; 42.55
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    Notes: Abstract Selective electronic excitation of single kinds of DNA bases were performed with dye lasers. Different DNA-dye-complexes were used and the selective excitation could be proved by the varying strength of the interaction between the bases and the dye molecules.
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  • 69
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    Applied physics 20 (1979), S. 261-264 
    ISSN: 1432-0630
    Keywords: 42.65 ; 42.55
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The method of Stimulated Mandelshtam-Brillouin Scattering (SMBS) is utilized in a powerful laser to obtain better transverse beam quality by phase conjugation. The principle is explained, and the conclusions are substantiated by experimental results.
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  • 70
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    Acta mechanica solida Sinica 10 (1997), S. 283-298 
    ISSN: 0894-9166
    Keywords: fracture mechanics ; finite element ; simulation ; curved beam ; pipeline ; arrest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Mechanical arrestors are frequently used in gas transmission pipelines to prevent the possibility of long running cracks. These arrestors have the effect of reducing the pipe from opening as the crack passes. This decreases the available crack driving force and, as a result, crack arrest may take place. This essentially is a second line of defence against catastrophic failure in the event crack initiation cannot always be prevented. A novel analyzing method presented in this paper has been developed to investigate the suitability of these crack arrestors. This is based on a fluid/structure/fracture interaction package, PFRAC. A dynamic finite element approach has been developed for a three dimension curved beam with initial plane curvature, which has been implemented in PFRAC to simulate the behaviour of the arrestor. The contact conditions between the pipe wall and the arrestor, along with the various computational procedures, are described. Several numerical results for a cracked pipe with arrestors are presented and compared with those for pipes without arrestors.
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    Journal of nanoparticle research 1 (1999), S. 267-276 
    ISSN: 1572-896X
    Keywords: nanoparticles ; microemulsions ; reaction engineering ; formation model ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract Engineering aspects of the preparation of palladium nanoparticles in non-ionic w/o-microemulsions are examined. In order to achieve reproducible synthesis conditions a semi-batch reactor with a standardized design is used. Influences of the stirring rate and of different ways of concentration control on the product properties are observed. For reproducible synthesis it is important to establish appropriate and defined preparation conditions. Monodisperse palladium particles of around 5 nm size are obtained by adding the microemulsion containing the palladium salt at a constant feed rate to the precharged microemulsion containing the reducing agent. A quantitative kinetic model is proposed to describe particle formation in microemulsions. Unknown parameters of the model have been estimated by independent examinations or can be achieved by fitting to the experimental data.
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    Plasma chemistry and plasma processing 19 (1999), S. 131-151 
    ISSN: 1572-8986
    Keywords: Styrene ; oxidation ; silent discharge ; plasma ; dielectric barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A silent discharge plasma reactor has been developed to study the oxidation of styrene vapor in argon/oxygen mixtures. A number of analytical techniques were employed to determine the destruction efficiency and to characterize the intermediate products. The destruction efficiency was measured as a function of initial styrene concentration, temperature, and energy density of the plasma. The formation of solid products was observed in most experiments. At low temperature (100°C), the solid deposit was polymeric in nature, while at high temperature (300°C) the solid appeared to be amorphous carbon. A combination of high temperature and high energy density resulted in high destruction efficiency and minimal production of solid films. The destruction efficiency vs. energy density is shown to be more complex than a simple model predicting exponential behavior. Several reasons for the discrepancy are suggested. The “e-folding” energy density for the destruction of styrene is compared to literature values for other organic compounds, measured using similar types of plasma reactors.
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    Plasma chemistry and plasma processing 19 (1999), S. 383-394 
    ISSN: 1572-8986
    Keywords: Nonthermal plasma ; benzene ; Al2O3 ; BaTiO3 ; oxidation ; absorption ; atmospheric pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The combination of plasma discharge and adsorption was examined for oxidation of dilute benzene in air in a plasma reactor packed with a mixture of BaTiO 3 pellets and porous Al 2 O 3 pellets (i.e., an alumina hybrid reactor). The oxidative decomposition of benzene was enhanced by the benzene concentrating on the Al 2 O 3 pellets. Furthermore, there was a higher selectivity to CO 2 in the products from the hybrid than from a plasma reactor packed with BaTiO 3 pellets alone. The presence of the Al 2 O 3 pellets suppressed the formation of N 2 O.
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    Plasma chemistry and plasma processing 19 (1999), S. 421-443 
    ISSN: 1572-8986
    Keywords: Streamer corona ; NO x removal ; nonthermal plasma ; oxidation ; reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract In this paper, the NO-to-NO 2 conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO x removal experiments in N 2 +NO x and N 2 +O 2 +NO x gaseous mixtures, it is supposed that the reverse reaction NO 2 +O→NO+O 2 may not only limit NO 2 production in N 2 +NO x mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NO→N 2 +O, induce negligible NO removal provided the O 2 concentration is larger than 3.6%. With adding H 2 O into the reactor, the produced NO 2 per unit removed NO can be significantly reduced due to NO 2 oxidation. NH 3 injection could also significantly decrease the produced NO 2 via NH and NH 2 - related reduction reactions. Almost 100% of NO 2 can be removed in gaseous mixtures of N 2 +O 2 +H 2 O+NO 2 with negligible NO production.
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    Plasma chemistry and plasma processing 19 (1999), S. 487-504 
    ISSN: 1572-8986
    Keywords: Hydrogen plasma ; arcjets ; simulation ; LBI method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The governing equations describing a flowing stream of a hydrogen plasma encountered in applications, such as diamond deposition, and in devices, such as arcjet thrusters, are solved numerically using the linearized implicit (LBI) Method of Briley and McDonald. The results of simulations under the assumption that the plasma can be described by a single temperature are compared with detailed experimental measurements of flow characteristics and species concentrations in a 1 kW arcjet. These comparisons show that by formulating the problem in terms of known experimental operating conditions, such as mass flow rate, power, and current levels, it is possible to predict many of the characteristics of the flowing plasma. As expected, predictions from this one-temperature model show that some deviations from the experimental results occur near the exit plane of the channel, where unequal electron and heavy particle temperatures are encountered because of lower pressures.
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    Journal of nondestructive evaluation 18 (1999), S. 117-126 
    ISSN: 1573-4862
    Keywords: Nondestructive evaluation ; layered cylindrical structures ; cylindrical waves ; simulation ; inverse problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract For the characterization of the unknown material properties of a layered cylindrical structure, axially symmetric wave signals transmitted and reflected by the structure have been used. Since only a single wave mode propagates in the structure, the measurement and analysis of the transmitted and reflected signals can be simplified significantly. The evaluation of the material properties of the layers can be achieved with great accuracy. In this paper, we first derive the transmission and reflection coefficients for the layered cylindrical structure sonified axisymmetrically by an incident cylindrical wave. We then relate the spectra of the transmitted and reflected wave signals to the transmission and reflection coefficients as ratio functions. The time-domain signals transmitted and reflected by the structure can then be reconstructed from a routine application of the Fourier integrals. A three-layered aluminum/epoxy/aluminum tube is used to illustrate the application of the expressions for both the forward and inverse problems. The results show that the technique developed in this study can be used very effectively for the characterization of layered cylindrical structures.
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    Oxidation of metals 11 (1977), S. 57-62 
    ISSN: 1573-4889
    Keywords: oxidation ; scale growth
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Equations are presented to modify the classical theoretical expressions for the parabolic rate constant for the case in which the scale has a large composition range and a large variation in molar volume. The modifications appear as simple averages, together with a factor f.Evaluation of f for some hypothetical cases shows that it is near unity unless the composition gradient has an extreme deviation from linearity.
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    Oxidation of metals 11 (1977), S. 193-198 
    ISSN: 1573-4889
    Keywords: oxidation ; scaling ; wustite ; magnetite ; iron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The theory of the growth of two oxide layers by Yurek et al. has been applied to the oxidation of iron at 1100° C. The theoretical parabolic rate constants for the simultaneous growth of the two oxide layers were calculated from radioactive tracer diffusion coefficients for wustite and magnetite. Good agreement was found between the theoretical and experimental values of the ratio of scale thicknesses.
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    Oxidation of metals 9 (1975), S. 45-67 
    ISSN: 1573-4889
    Keywords: oxidation ; hot corrosion ; nickel alloys ; composites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation and hot corrosion behavior of a tungsten-fiber, reinforced Ni~ 20Cr alloy has been examined under the following exposure conditions: (a) pure oxygen at 1 atm pressure; (b) sulfidation in H2–10 %H2S; (c) presulfidation in H2–10 %H2S followed by oxidation in oxygen; and (d) oxidation in 1 atm oxygen after precoating with approximately 1 mg/cm2 of Na2SO4. Rapid oxidation of the tungsten fibers causes considerable distortion of the matrix and catastrophic degradation of the matrix follows. Inter diffusion between the matrix and the fibers is also important. During sulfidation, only the matrix forms sulfides, the fibers remaining unaffected. Consequently, presulfidation, although having a dramatic effect on the oxidation of the matrix does not have a damaging effect on the fibres. Equally, the presence of sodium sulfate is not critical, although severe oxidation of the exposed tungsten fibers is still observed.
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    Oxidation of metals 9 (1975), S. 275-305 
    ISSN: 1573-4889
    Keywords: oxidation ; Ni-Cr alloys ; rare-earth oxide dispersion ; dispersion-strengthened alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of Ni-20%Cr alloys containing approximately 3 vol.% Y2O3, ThO2, and A12O3 as dispersed particles has been examined in the temperature range 900 to 1200° C in slowly flowing oxygen at 100 Torr. The results show that the oxidation behavior of the Y2O3-, ThO2-, Al2O3-, and Ce02-containing alloys is very similar and that some anomalies in the behavior of the ThO2-containing alloy might be explained by the slower rate of chromium diffusion in this coarse-grained alloy. Two Al2O3-containing alloys were studied. One with a relatively coarse dispersoid size behaved in a manner analogous to a dispersion-free Ni-30% Cr alloy at 1100°C. The other alloy contained a dispersion of fine Al2O3 particles and behaved exactly like the Y2O3-containing alloy at 1000 and 1100°C, but at 1200° C oxidized at a faster rate. It has been shown that the adherent scales on dispersion-containing alloys have a stabilized fine grain size, whereas the nonadherent scales on dispersion-free alloys undergo grain growth.
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    Oxidation of metals 47 (1997), S. 381-410 
    ISSN: 1573-4889
    Keywords: Ni-Base superalloys ; Astroloy ; Waspaloy ; Udimet 720 ; oxidation ; chromia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Several commercially available Ni-base superalloys were exposed isothermally in air at temperatures between 750° and 1000°C and also under cyclic conditions at 1000°C. The kinetics of oxidation were determined and the scales were analyzed by electron microscopy and X-ray diffraction. Thin adherent chromia-rich scales formed on the alloys at 750°C after 1000 hr. Although Waspaloy showed the lowest weight gain in this test, it also showed the deepest internal corrosion due to oxidation of the grain-boundary carbides. At temperatures up to 1000°C the external scales were also chromia-rich but there was greater internal corrosion. Titanium in the alloys oxidized, diffusing through the chromia scale to form faceted rutile (TiO2) grains at the surface as well as forming TiO2 and TiN internally. The amount of rutile at the oxide surface increased with temperature and alloy Ti concentration. Alumina formed as discrete internal oxides below the chromia scale, although Astroloy when oxidized isothermally at 1000°C developed a semicontinuous internal layer of alumina due to its higher Al content. Under cyclic conditions Astroloy formed a thicker, less-protective scale of transition oxides probably due to its lower Cr content.
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  • 82
    ISSN: 1573-4889
    Keywords: oxidation ; Incoloy 909 ; superalloy ; scale ; high temperature ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si superalloy (Incoloy 909 type alloy), was investigated at temperatures between 1000 K and 1400 K in Ar-(1, 10%)H20 atmosphere using metallographic, electron probe microanalysis, and X-ray diffraction techniques. The oxide scales consist of an external scale and an internal scale which has an intergranular scale (above 1200 K) and an intergranular scale. The oxide phases in each scale are identified asα-Fe2,O3 (below 1200 K) or FeO (above 1300 K) and CoO · Fe2O3 and FeO · Nb2O5, respectively. The morphologies, the oxide phases and the oxidation rates do not depend on the partial pressure of H2O in the range between one and ten percent in Ar gas. The rate constants for the intergranular-scale formation in this alloy are about one-tenth as large as those in Fe-36%Ni alloy reported previously. At all the temperatures the scales grow according to a parabolic rate law and the apparent activation energies for the processes are estimated.
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    Oxidation of metals 47 (1997), S. 445-464 
    ISSN: 1573-4889
    Keywords: oxidation ; Fe-Cr-Al alloy ; water vapor ; ESCA ; RHEED
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Fe-21.5 wt. %Cr-5.6 wt. %Al oxidation, at 1000°C, in dry or wet oxygen shows that steam has an influence on the oxide-scale growth mechanism. Steam modifies the kinetics of early-stage oxidation. In dry oxygen, an initial fast linear regime is observed during one hour. Under wet conditions, weight-gain curves follow the same parabolic regime over the entire oxidation test. The scale structure strongly depends on the presence of steam in the gaseous environment. With dry oxygen, the scale is composed mainly ofα-Al2O3 after the initial formation ofγ-Al2O3 identified by ESCA and RHEED. The kinetics transient stage corresponds to the necessary time for the internal part of the initialγ-Al2O3 scale to transform into a continuousα-Al2O3 diffusion barrier. Under wet oxygen conditions, transient oxides are identified as (Mg, Fe) (Cr, Al)2O4, MgAl2O4 (orthorhombic), Al2O3 (hexagonal), these oxides transform into MgAl2O4 (cubic), Cr3O4, Fe2O3,α-Al2O3, with time. When water vapor does not change drastically oxidation kinetics, the induced presence of iron and chromium in the oxide scale could be responsible for weakening the protectiveness of alumina scales.
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    Oxidation of metals 47 (1997), S. 507-524 
    ISSN: 1573-4889
    Keywords: alloys ; high temperature ; oxidation ; transient state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The initial transient high-temperature oxidation stage for binary alloys forming the most-stable oxide has been examined by means of a numerical procedure based on the finite-difference method. At variance with previous models, the present treatment takes into account the effect of the rate of the reaction at the scale/gas interface over the corrosion kinetics. The calculations concerning the transient stage are developed either using the general parabolic rate law to represent the overall scaling kinetics or using the rate law of the reaction at the scale/gas interface as a boundary condition without imposing any particular rate law to the overall process. A correct analysis of the oxidation behavior of binary alloys during the transient stage must take into account the kinetics effect of the rate of the surface reaction. The concentration of the most-reactive element at the alloy/scale interface changes regularly with time, decreasing gradually from the initial bulk value to its final steady-state value. The present results are in good agreement with those obtained by means of an approximate analytical model developed previously.
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  • 85
    ISSN: 1573-4889
    Keywords: high temperatures ; oxidation ; transient state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The transient state in the oxidation of solid solutions of a most-noble componentA in a most-reactive componentB (beta phase) for binaryA-B alloys presenting a limited reciprocal solubility of the two metals has been examined assuming that theirB content is sufficient for the exclusive growth of externalBO scales. Above a criticalB content of the alloy theBO scales may grow directly on the surface of the beta phase, while below this limit they can only form over a layer ofB-depleted solid solution ofB inA (alpha phase), which appears after a critical time. An approximate analytical expression for the profile of concentration ofB in the alloy has been adopted to calculate the flux ofB in the metal. Moreover, the effect of the reaction between the gas and the external oxide surface has been taken into account using a procedure developed by Wagner for the oxidation of pure metals. The corrosion kinetics as well as all the parameters involved, such as the concentration ofB at the alloy-scale interface, have been calculated as functions of the corrosion time. The results show that, as time proceeds, the instantaneous parabolic rate constant increases and the concentration ofB at the alloy-scale interface decreases, both tending gradually to their corresponding steady-state values. It is also predicted that if the rate of transformation of the beta phase in the alpha phase after the alloy reaches the composition of equilibrium at the interface with the oxide is lower than the corresponding rate of displacement of the alloy surface due to scale growth, the corrosion of beta phase alloys may eventually lead to the formation of two phase mixtures of alpha phase andBO which are expected to grow at much larger rates than in the presence of a uniform continuous alpha layer.
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    Oxidation of metals 48 (1997), S. 1-39 
    ISSN: 1573-4889
    Keywords: Ni-base ODS superalloys ; oxidation ; initial stages of oxidation ; alumina ; chromia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Mechanically-alloyed Ni-base ODS superalloys currently receive attention for application in future gas turbines because they exhibit outstanding mechanical properties at high temperatures. They also protect themselves against oxidation by forming chromia and/or alumina scales. However, little attention has been given so far to the initial stages of oxidation of Ni-base ODS superalloys, containing Cr as well as Al in considerable amounts. In the current work, oxidation at 1150°C was studied for different holding times up to 200 hr for the commercial materials MA6000 and PM3030 which contain. Al in increasing amounts. MA 754, a chromia former, was investigated as a reference. It was shown that for the potential alumina formers MA6000 and PM3030 the continuity and therefore protectiveness of the secondary Al2O3 at later stages is indeed determined by the initial stages of oxidation.
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    Oxidation of metals 48 (1997), S. 129-141 
    ISSN: 1573-4889
    Keywords: decarburization ; nickel ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A commercial-grade nickel containing small amounts of carbon, manganese, and silicon was exposed to air for periods up to 288 hr at 1050°C to study the effect of oxidation on the formation of oxides of these impurity elements. Exposure of nickel to air led to decarburization. The maximum amount of decarburization occurred during the initial period of air exposure and the loss in carbon was more in the metal with a smaller section size. Decarburization in the metal produced voids in the oxide scale due to the formation of CO2 gas. It has been shown further that CO and/or CO2 gas bubbles, which form in high purity nickel on grain boundaries during exposure to air at elevated temperatures, cannot exist in commercial-grade nickel where manganese is present as an impurity. Instead, oxides of manganese form in the grain boundaries as well as in the matrix. This is because manganese oxide is more stable than CO or CO2 gas.
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  • 88
    ISSN: 1573-4889
    Keywords: oxidation ; kinetics ; iron ; iron-nitride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of α-Fe and ɛ-Fe2N1−z at 573 K and 673 K in O2 at 1 atm was investigated by thermogravimetrical analysis, X-ray diffraction, light-optical microscopy, scanning electron microscopy and electron probe X-ray microanalysis. Upon oxidation at 573 K and 673 K, on α-Fe initially α-Fe2O3 develops, whereas on ɛ-Fe2N1−z initially Fe3O4 develops. In an early stage of oxidation the oxidation rate of ɛ-Fe2N1−z appears to be much larger than of α-Fe. This can be attributed largely to an effective surface area available for oxygen uptake, which is much larger for ɛ-Fe2N1−z than for α-Fe due to the porous structure of ɛ-Fe2N1−z as prepared by gaseous nitriding of iron. The development of a magnetite layer in-between the hematite layer and the α-Fe substrate, at a later stage of oxidation, enhances layer-growth kinetics. After 100 min oxidation at 673 K the (parabolic) oxidation rates for α-Fe and ɛ-Fe2N1−z become about equal, indicating that on both substrates the oxide growth is controlled by the same rate limiting step which is attributed to short-circuit diffusion of iron cations. Oxidizing ɛ-Fe2N1−z increases the nitrogen concentration in the remaining ɛ-iron nitride, because the outward flux of iron cations, necessary for oxide growth, leads to an accumulation of nitrogen atoms left behind.
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  • 89
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    Oxidation of metals 48 (1997), S. 201-214 
    ISSN: 1573-4889
    Keywords: titanium-aluminum alloys ; niobium ; intermetallics ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In a recent study, CO2 has been reported to enhance the oxidation rate of binary titanium-aluminum alloys. The detrimental effect of CO2 was not, however, observed in a ternary alloy containing niobium. In this paper, possible explanations for these observations are examined. First, results from the literature regarding the effects of niobium in improving the resistance of titanium-aluminum alloys are briefly reviewed. Second, a thermodynamic analysis which offers a possible explanation for the beneficial effect of niobium in eliminating the CO2-enhanced oxidation of titanium-aluminum alloys is presented.
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  • 90
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    Oxidation of metals 48 (1997), S. 215-224 
    ISSN: 1573-4889
    Keywords: nanocrystallization ; oxidation ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Many mechanisms for the effect of reactive elements on the selective oxidation and scale adhesion of alloys have been proposed. However, nanocrystallization (or microcrystallization) has recently been found to have almost the same effect as that of reactive elements. This note reviews the effect of nanocrystallization on the selective oxidation and adhesion of Al2O3 scale with particular reference to the author's own results.
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  • 91
    ISSN: 1573-4889
    Keywords: oxidation ; titanium ; rutile ; scale ; high temperature ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of pure titanium has been investigated in the temperature range of 1000 K to 1300 K in CO2 or Ar-10%CO2. Optical microscopy, electron probe microanalyses, and X-ray measurements on the oxide scales formed during oxidation indicate that their structures are nearly independent of temperature and the corrosion atmosphere. The scales consisted of two layers, an external one and an internal one, having a rutile (TiO2) structure. The parabolic rate law was confirmed for growth of the external scale and the permeation depth of oxygen in titanium with apparent activation energies of 266 and 226 kJ/mol, respectively. The rate-determining diffusion species in the oxidation processes are discussed.
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  • 92
    ISSN: 1573-4889
    Keywords: zirconium ; X-ray diffraction ; oxidation ; phase analysis ; texture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of zirconium at high temperature (T〉 400°C) leads to reaction products of two allotropic oxide (ZrO2 monoclinic and ZrO2 tetragonal). The distribution and proportion of these two phases were studied as a function of time and space by X-ray diffraction techniques. Quantitative analyses are possible after some corrections, and we demonstrate the presence of a phase gradient in the oxide scale. The interest of this nondestructive method is then discussed.
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  • 93
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    Oxidation of metals 48 (1997), S. 357-380 
    ISSN: 1573-4889
    Keywords: chromium ; copper ; binary alloys ; two-phase alloys ; oxidation ; high temperatures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation in air of three two phase Cu-Cr alloys with nominal Cr contents of 25, 50, and 75 wt. % was studied at 700–900°C. The alloys corroded nearly parabolically, except at 900°C, when the corrosion rates decreased with time more rapidly than predicted by the parabolic rate law. The corrosion rate decreased for higher Cr contents in the alloy under constant temperature and generally increased with temperature for the same alloy composition. The scales were complex and consisted in most cases of an outermost copper oxide layer free from chromium and an inner layer composed of a matrix of copper oxide or of the double oxide Cu2Cr2O4, often containing particles of chromium metal surrounded by chromia and then by the double oxide. Metallic copper was also frequently mixed with chromia. Cr-rich regions tended to form continuous chromia layers at the base of the scale, especially at the highest temperature. No chromium depletion was observed in the alloy.
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  • 94
    ISSN: 1573-4889
    Keywords: iron ; oxidation ; CeO2 coating ; in situ ; growth stress ; residual stress ; texture ; X ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In situ XRD stress determinations have been performed during oxidation of pure iron (p(O2=2 × 10−3 Pa,T=800°C)). The compressive stress, initially present in the substrate due to surface preparation, is completely released at 400°C. Under the test conditions, the in situ compressive-stress level determined in the FeO scale during oxidation is not strongly dependent upon the presence of a ceria coating. On blank and coated specimens, the compressive stress varies from −400 ± 80 MPa to −150 ± 100 MPa during 30 hr oxidation. The decrease is quicker at the beginning of the test performed on blank specimens. Epitaxial relationships between the wüstite scale and iron (under low-pressure starting conditions) caused thein situ compressive stress in the oxide scale to be two times greater compared to the usual test conditions. This indicates that epitaxial relationships can be a source of stress in an oxide scale that ceria coatings may lower compressive stresses.
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  • 95
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    Oxidation of metals 48 (1997), S. 527-551 
    ISSN: 1573-4889
    Keywords: chloridation ; oxidation ; Fe-Cr alloys ; Ni-Cr alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The chloridation-oxidation behavior of Fe-Cr (0–25 wt. %Cr) and Ni-Cr (0–20 wt.%Cr) alloys was studied at 800°C in three different H2-HCl-H2O(ν) environments. In a low-HCI and low-H2O(ν) environment, where Cr2O3 is thermodynamically stable, the corrosion resistance of the Fe-Cr alloys increased with increasing Cr content in the alloys. In a high-HCl and high-H2O(ν) environment, where FeCr2O4 is stable and CrCl2 is metastable, the corrosion resistance of the Fe-Cr alloys depended similarly on the Cr content. Low-Cr-Fe-Cr alloys exhibited large weight losses, while Fe-Cr alloys with higher than 19 wt. %Cr showed good corrosion resistance. In an environment of high-HCl in the absence of H2O(ν), the evaporative corrosion rate was fast and limited by gas phase diffusion, and independent of the Cr content in the Fe-Cr alloys. Ni and Ni-Cr alloys generally showed good corrosion resistance in the environments of high H2O(ν) because of the low NiCl2 vapor pressure and formation of a protective Cr2O3 scale. However, in the environment of high HCl in the absence of H2O(ν), selective formation and evaporation of CrCl2 occur, which results in Cr depletion and networks of voids for even a high-Cr Ni-Cr alloy.
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  • 96
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    Oxidation of metals 48 (1997), S. 553-596 
    ISSN: 1573-4889
    Keywords: chloridation ; oxidation ; HCl ; high-temperature alloys ; high-temperature corrosion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Chloridation-oxidation studies of nine commercial high-temperature alloys were carried out at 800°C in three different H2-HCl-H2O(ν) environments: (A) both low HCl and H2O(ν) partial pressures, where either Cr2O3 or FeCr2O4 is stable, (B) both high HCl and H2O(ν) partial pressures, where FeCrO4 is stable and CrCl2 is metastable, and (C) high HCl partial pressure in the absence of H2O(ν), where either CrCl2 or Cr2O3 is stable. Although alloy 600 has the lowest Cr content of these nine alloys, it showed excellent corrosion resistance in all three environments because of its high Ni content. Alloy 304, with the lowest Ni content of the nine alloys, exhibited poor corrosion resistance in the environment C, fair resistance in the environment B and good resistance in the environment A. Alloy 800 showed very good resistance in Environment A, and fair corrosion resistance in Environment B; however, it suffered linear weight-loss kinetics when exposed to Environment C The alloys 617, 214, HR-160, X, 230 and 86 have good corrosion resistance in Environments A and B because of their relatively high contents of oxide-scale-forming elements Cr and/or Al. In Environment C, chlorine dramatically decreased the adhesion of the scale on the surface, and aluminum in alloys 617 and 214 hardly showed its usual beneficial effect in combating corrosion, nor does silicon in alloy HR-160. Different corrosion mechanisms are proposed for the alloys in the different environments.
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  • 97
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    Oxidation of metals 9 (1975), S. 415-425 
    ISSN: 1573-4889
    Keywords: vanadium carbide ; vanadium oxycarbide ; oxidation ; parabolic rate law ; cubic rate law ; chemisorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of an oxycarbide of vanadium, VO0.6C0.7, and of a vanadium carbide, VC0.98, was studied athermally up to temperatures of 800° C and isothermally between 400 and 580° C at oxygen pressures ranging from 10−2 to 1 atm. The oxycarbide followed the parabolic rate law below 450° C with V2O5 forming as the only reaction product. The activation energy was 49 kcal/mole. VC0.98 did not form an oxide in this temperature range, but rather dissolved oxygen, the activation energy being 26.6 kcal/mole. No oxygen pressure dependence on the kinetics was found for either sample in this temperature range. Both samples followed the cubic rate law during oxidation in the range of 500–580° C during which V2O5 formed. There was a P1/3 dependence and the activation energy was the same for both materials, 51 kcal/mole. The cubic rate law and the positive pressure dependency (rather than an anticipated negative dependency) were attributed to an electric field associated with oxygen ions chemisorbed on a thin layer of V2O5.
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  • 98
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    Oxidation of metals 9 (1975), S. 459-472 
    ISSN: 1573-4889
    Keywords: Cr ; oxidation ; kinetics ; Cr2O3 grain size ; short-circuit diffusion ; surface ; preparation ; Fe-Cr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Cr was oxidized in 1 aim O2 at 980, 1090, and 1200°C. ElectropolishedCr and some orientations of etched Cr oxidize rapidly and develop compressive stress in the growing Cr2O3; other orientations oxidize slowly, apparently free of stress. SEM examination of fracture sections shows that the thick oxide is polycrystalline whereas the thin oxide on etched Cr is monocrystalline. It is deduced that the monocrystalline oxide grows by lattice diffusion of cations outward, and the polycrystalline layer by the two-way transport of cation diffusion outward and anion diffusion inward along oxide grain boundaries. The consequent formation of oxide within the body of the polycrystalline layer generates compressive stress and leads to wrinkling by plastic deformation. The activation energy for oxidation of Cr by cation lattice transport is 58 kcal/mole. Polycrystalline Cr2O3 forms on Fe-26Cr alloy, whether electropolished or etched; oxidation is accordingly rapid and accompanied by compressive stress.
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  • 99
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    Oxidation of metals 11 (1977), S. 23-56 
    ISSN: 1573-4889
    Keywords: oxidation ; carburization ; carbonaceous gases ; superalloys ; stainless steels ; film formation ; structure of oxide scales ; preoxidation ; metal dusting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Formation and deterioration of oxide films on several contemporary high-temperature alloys was studied in various carbonaceous gas atmospheres. Scanning electron microscopy and metallographic examination were applied to films on Fe-Cr-Ni and Ni-Cr-Al type alloy compositions exposed in CH 4/H2 and CO/CO2 atmospheres at temperatures up to 900° C and pressures up to 900 psi (6.2 × 106 N/m2). The effects of various preoxidation treatments were evaluated. Reduction of certain oxide phases is observed to promote catalytic gas decomposition. Al2O3 components in the films are observed to be stable under the reducing conditions experienced. Carbon uptake by various alloys is found to be quite sensitive to surface finish, with an observed increase in penetration with surface roughness.
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  • 100
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    Oxidation of metals 11 (1977), S. 225-239 
    ISSN: 1573-4889
    Keywords: tantalum ; oxidation ; high temperature ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of tantalum in oxygen-nitrogen and oxygen-inert gas mixtures at925°C has been studied. The oxygen pressure was close to 0.5 atm in all experiments, and partial pressures of the second component of from 0 to 180 Torr were employed. Spherical specimens were used to provide quantitatively significant kinetic data. A model has been proposed which suggests that the oxygen pressure at the reaction interface close to the metal surface is lower than the external pressure because of the finite permeability of the porous outer oxide layer, and that the inert gas effectively reduces the permeability. The model gives good quantitative agreement with the experimental results.
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