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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Machine learning 41 (2000), S. 175-195 
    ISSN: 0885-6125
    Schlagwort(e): machine learning ; knowledge discovery ; data mining ; relevance ; feature subset selection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The notion of relevance is used in many technical fields. In the areas of machine learning and data mining, for example, relevance is frequently used as a measure in feature subset selection (FSS). In previous studies, the interpretation of relevance has varied and its connection to FSS has been loose. In this paper a rigorous mathematical formalism is proposed for relevance, which is quantitative and normalized. To apply the formalism in FSS, a characterization is proposed for FSS: preservation of learning information and minimization of joint entropy. Based on the characterization, a tight connection between relevance and FSS is established: maximizing the relevance of features to the decision attribute, and the relevance of the decision attribute to the features. This connection is then used to design an algorithm for FSS. The algorithm is linear in the number of instances and quadratic in the number of features. The algorithm is evaluated using 23 public datasets, resulting in an improvement in prediction accuracy on 16 datasets, and a loss in accuracy on only 1 dataset. This provides evidence that both the formalism and its connection to FSS are sound.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Machine learning 41 (2000), S. 123-152 
    ISSN: 0885-6125
    Schlagwort(e): logical theories ; theory revision ; probabilistic theories ; flawed domain theories ; approximate reasoning ; machine learning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Existing methods for exploiting flawed domain theories depend on the use of a sufficiently large set of training examples for diagnosing and repairing flaws in the theory. In this paper, we offer a method of theory reinterpretation that makes only marginal use of training examples. The idea is as follows: Often a small number of flaws in a theory can completely destroy the theory's classification accuracy. Yet it is clear that valuable information is available even from such flawed theories. For example, an instance with severalindependent proofs in a slightly flawed theory is certainly more likely to be correctly classified as positive than an instance with only a single proof. This idea can be generalized to a numerical notion of “degree of provedness” which measures the robustness of proofs or refutations for a given instance. This “degree of provedness” can be easily computed using a “soft” interpretation of the theory. Given a ranking of instances based on the values so obtained, all that is required to classify instances is to determine some cutoff threshold above which instances are classified as positive. Such a threshold can be determined on the basis of a small set of training examples. For theories with a few localized flaws, we improve the method by “rehardening”: interpreting only parts of the theory softly, while interpreting the rest of the theory in the usual manner. Isolating those parts of the theory that should be interpreted softly can be done on the basis of a small number of training examples. Softening, with or without rehardening, can be used by itself as a quick way of handling theories with suspected flaws where few training examples are available. Additionally softening and rehardening can be used in conjunction with other methods as a meta-algorithm for determining which theory revision methods are appropriate for a given theory.
    Materialart: Digitale Medien
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  • 3
    ISSN: 1573-4889
    Schlagwort(e): ion implantation ; oxidation ; thermal ; stainless steel ; ion-beam analysis ; aluminum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract AISI-321 steel samples were implanted with Al ions (implantation-energy:40 keV; dose: 2×1017 ions/cm2). Thermal oxidationof the samples was performed at 450, 550, 600, and 650°C for periodsvarying from 1 to 6 days in air and in a corrosive CO2-containingenvironment. Nuclear Reaction Analysis (NRA) and Rutherford BackscatteringSpectrometry (RBS) were used to investigate the oxidized samples. Asignificant improvement of the oxidation resistance of the implantedmaterial in comparison to the nonimplanted material was observed. Thisespecially applies for samples oxidized at high temperatures. The aluminumdepth distribution determined by NRA [using the resonance at 992 keV of the27Al(p, γ )28Si nuclear reaction] and RBS,indicated no variation of the Al profile in the temperature region450–600°C, whereas at 650°C a slight Al diffusion wasobserved. Scanning electron microscopy (SEM–EDS) was applied to studythe surface morphology and the constitution of the oxide scale formed, aswell as to explain the influence of Al implantation on the oxidation behaviorof AISI-321 austenitic stainless steel.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 53 (2000), S. 467-479 
    ISSN: 1573-4889
    Schlagwort(e): Ni–5Cr–5Al ; oxidation ; magnetron sputtering ; nanocrystalline coating
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A NiO-forming Ni–5Cr–5Al (at.%) alloy has been developed anddeposited as a sputtered nanocrystalline coating. The oxide formation andoxidation behavior of this coating have been studied at 1000°C inair. The oxidation rate markedly decreased with time and the oxidationkinetics obeyed the fourth power law. Complex oxide scales, consisting ofNiO, NiAl2O4 and α-Al2O3,were formed during 200 hr oxidation. The outer oxide layer consisted of NiOand NiAl2O4 and an inner oxide layer ofα-Al2O3. The sputtered Ni–5Cr–5Alnanocrystalline coating showed good oxidation resistance due to theformation of an α-Al2O3 inner layer andexcellent adhesion of the complex oxide scales.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 53 (2000), S. 529-537 
    ISSN: 1573-4889
    Schlagwort(e): ion plating ; steel ; TiAlN coating ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract To improve the high-temperature oxidation resistance of STD61 steels used ashot dies or cutting tools, Ti0.3Al0.2N0.5films were deposited on STD61 steel substrates by arc-ion plating. Thedeposited film consisted of Ti3Al2N2 andTi2N phases. The oxidation characteristics were studied attemperatures ranging from 700 to 900°C in air. The deposited STD61steels displayed excellent oxidation resistance up to 800°C, butexhibited large weight gains and breakaway oxidation at 900°C. Theoxidation products were primarily Fe2O3, TiO, TiO2,and α-Al2O3, the relative amount of each oxidebeing dependent on the oxidation condition. Among various oxides, TiO2and α-Al2O3 were the major oxides at 800°Cfor at least up to 16 hr. However, at a higher temperature or a longeroxidation period, the significant outward diffusion of iron from thesubstrate resulted in the formation of iron oxides, together with otheroxides of Ti and Al.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 155-162 
    ISSN: 1573-4889
    Schlagwort(e): Ni–8Cr–3.5Al ; nanocrystallization ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Magnetron-sputter deposition was used to produce a Ni–8Cr–3.5Al(wt.%) nanocrystalline coating on substrates of the same alloy. Theoxidation behavior of the cast Ni–8Cr–3.5Al alloy and itssputtered coating were investigated at 1000°C in air. Complex,layered-oxide scales composed of Cr2O3 outer layer,mixed spinel NiAl2O4 and NiCr2O4middle layer, and α-Al2O3 inner layer were formedon the Ni–8Cr–3.5Al nanocrystalline coating during 200-hroxidation, whereas Cr2O3, with some NiCr2O4external layer with internal Al2O3, formed on the castalloy. Because of the formation of this α-Al2O3inner layer on the coating, the sputtered Ni–8Cr–3.5Al coatingshowed better oxidation resistance than the cast alloy. The effect ofnanocrystallization on oxide formation is discussed. It was indicated thatthe formation of this α-Al2O3 inner layer was closely related to therapid diffusion of Al through grain boundaries in the nanocrystallinecoating and the relatively high Cr content in Ni–8Cr–3.5Al.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 189-209 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; β-FeAlCr ; coatings ; magnetron sputter-deposition ; ridge-type oxide ; Al2O3 phase transformation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract β-FeAl coatings containing various Cr contents of 6.5–45 wt.%were produced with a closed-field, unbalanced magnetron sputter (CFUMS)deposition technique. Cyclic oxidation tests at 1100°C in air for100 1-hr cycles and isothermal exposures at 1000°C in pure O2 for100 hr were carried out with the coatings and an as-cast FeAlspecimen. All of the coatings showed good scale-spallation resistanceduring cyclic oxidation and the coating with 6.5 wt.% Cr exhibited thelowest oxidation rates in both cyclic and isothermal oxidationexposures. After oxidation, fine-grain ridge-type oxide scales formed onthe coatings, while the oxide scale formed on the cast FeAl showed alarge quantity of θ-Al2O3 blades and large interfacial voids on thebase–alloy surface. The transformation from θ to α-Al2O3was accelerated due to the presence of Cr in the coatings. The fasttransformation considerably reduced oxidation rates, suppressed fastoutward Al diffusion for the growth of a θ-Al2O3 scale, and preventedthe formation of interfacial voids that played a major role in causing thescale spallation.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 549-558 
    ISSN: 1573-4889
    Schlagwort(e): plasma spraying ; chromium steel ; oxidation ; Fe–Cr spinel oxide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract During plasma spraying of metals in air, rapid-oxidation reactions occur, inmost cases. In oxidation products of Cr-rich steels, Fe–Cr spineloxide is often found as a dominant oxide phase. A thermodynamic analysisof a system composed of Fe–13%Cr alloy and water vapor or air showedthat the oxidation product in a wide range of high temperatures isFe3-wCrwO4 (w〉2). This tetragonallydistorted spinel oxide is not stable at room temperature. Water vapor andair were considered as limits of the gaseous-phase composition inatmospheric spraying by a water-stabilized plasma gun, where the compositionof the plasma plume is modified by air entrainment. The equilibriumcalculations enabled determination of the effects of temperature andgas-to-solid ratio on w. To show the existence of chromium-rich,tetragonally distorted spinel oxide experimentally, a typical productresulting from oxidation of 13%Cr–steel particles during their flightin the plasma plume was studied after rapid solidific ation. This was madepossible by trapping and quenching the flying particles in liquid nitrogenat a distance from the plasma-gun nozzle corresponding to thenozzle–substrate distance in conventional plasma spraying. The resultsobtained by X-ray diffraction, Mössbauer spectroscopy, and X-rayfluorescence analysis showed that this oxide, in which w≈2.4, constitutedthe dominant phase in the oxidation product.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials synthesis and processing 8 (2000), S. 359-363 
    ISSN: 1573-4870
    Schlagwort(e): Mechanical activation ; brown coal ; electrophoretic mobility ; oxidation ; humic acids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract This paper presents a study of the influence of mechanochemical activation of coal on the process of formation and degradation of humic acids. The increasing period of mechanical activation of coal causes an increase in hydrophility, electrophoretic mobility, and of electrokinetic potential of surface layers as a result of acidic carboxyl and phenolic OH groups. The effective activation requires a short period of grinding. The increased time of activation causes the secondary processes of grain agglomeration and degradation of humic acids.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 53 (2000), S. 427-449 
    ISSN: 1573-4889
    Schlagwort(e): sulfidation ; carburization ; oxidation ; high-temperature corrosion ; commerical alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A sulfidation/carburization study of seven commercial heat-resistant alloyswas carried out at 900°C in a H2–25 vol.%CH4–14.8N2–4CO–0.6CO2–0.6H2Satmosphere. The equilibrium partial pressures for oxygen (O2) andsulfur (S2) were 1.1×10−22 and 4.1×10−8 atm,respectively, and the carbon activity for this system was unity. The time ofexposure was 500 hr. Relatively thick, mixed sulfide scales were formed onall of the alloys tested. In addition, internal carburization occurred inall of the alloys. Using metal loss (i.e., the reduction in samplethickness) plus internal attack (internal sulfidation plus internalcarburization) as a performance criterion, an alloy with a nominalcomposition of Ni–29 wt.% Co–28Cr–2.75Si performed thebest, showing 0.71 mm of attack. An alloy with a nominal composition ofFe–20 wt.% Ni–25Cr performed the worst, being totally consumedby the test (〉3.18 mm of attack). Alloys containing relatively highamounts of silicon (〉2.5%) showed a dramatic increase in theirsulfidation resistance compared to the other alloys containing lowersilicon contents. The amount of iron present within a given material playeda dominant role in the carburization attack that occurred, with as expected,high-iron alloys showing significant internal carburization because of ahigh solubility and diffusivity of carbon in the matrix. The importance ofthe various alloying elements with respect to sulfidation and carburizationresistance is discussed.
    Materialart: Digitale Medien
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  • 11
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; chromia ; alumina ; thin oxide films ; reactive element
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In order to study the effects on oxidation behavior of changing thecomposition of oxide scales without changing the composition of theunderlying alloys, thin films, which contained various amounts of Y2O3,Cr2O3, or Al2O3 have been deposited on Fe–25%Cr andFe–25%Cr–5%Al prior to oxidation. There were major differencesbetween the (Fe–25%Cr)–(Cr2O3–Y2O3) and(Fe–25%Cr–5%Al)–(Al2O3–Y2O3) systems. A film ofCr2O3 on Fe–25%Cr reduced the oxidation rate and Cr2O3–Y2O3films reduced it still further. A film of Al2O3 onFe–25%Cr–5%Al reduced the rate considerably, butAl2O3–Y2O3 films exhibited rates that were greater than those forAl2O3 alone. A film, which consisted entirely of Y2O3, greatly decreasedthe oxidation rate of Fe–25%Cr, but increased that ofFe–25%Cr–5%Al. The changes in oxidation rate produced byY2O3 in the (Fe–25%Cr)–(Cr2O3–Y2O3) system weremuch greater than those produced in the(Fe–25%Cr–5%Al)–(Al2O3–Y2O3) system. As far asoxidation rate is concerned, the optimum amount of Y2O3 in the(Fe–25%Cr)–(Cr2O3–Y2O3) system was found to begreater than or equal to 40% and less than 100%; in theFe–25%Cr–5%Al)–(Al2O3–Y2O3) systemit was approximately 10%. In thermal-cycling tests, the resultsfor the (Fe–25%Cr)–(Cr2O3–Y2O3) system followedthe same pattern as that for the isothermal tests; a film of Y2O3reduced the oxidation rate and a film of Cr2O3–33%Y2O3reduced it still further.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 53 (2000), S. 561-576 
    ISSN: 1573-4889
    Schlagwort(e): Fe–Cr–Al alloy ; oxidation ; molybdenum ; breakaway oxidation ; transformation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Thin foils of Fe–20Cr–5Al alloys are susceptible to breakawayoxidation once the aluminum content of the substrate has fallen below somecritical value. The combined addition of 0.1 wt.% lanthanum and 0, 1, or 2wt% molybdenum has a beneficial effect on the high-temperature oxidation ofsuch foils. Lanthanum has the well-known reactive-element effect on adhesionof the protective alumina scale, thereby increasing the time to onset ofbreakaway oxidation, while, for alloys containing molybdenum, breakawayoxide spreads relatively slowly over the specimen in comparison to alloysthat contain no molybdenum. In particular, molybdenum-containing alloys areable to develop a protective Cr2O3 layer at the breakawayoxide–substrate interface. Conversely, molybdenum-free alloys form aninternal-oxide zone in the substrate adjacent to this interface, rather thana Cr2O3 layer, so breakaway oxide spreads rapidly. A martensitic phase isobserved in the substrate adjacent to the breakaway oxide formed on Fe–20Cr–5Al–La specimens, which means that theα-phase has transferred to the γ -phase at the temperature ofthe oxidation test (1150°C). Conversely, α-phase is retained inthe molybdenum-containing alloy, even after breakaway takes place, sincemolybdenum, which is a strong ferrite former, is enriched in the alloyadjacent to areas of breakaway oxide. The diffusion rate of chromium isslower in the γ than in the α-phase so a continuouschromium-rich oxide layer, which is effective in inhibiting breakawayoxide from spreading, cannot be established at the breakawayoxide–substrate interface for the molybdenum-free alloys.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 63-71 
    ISSN: 1573-4889
    Schlagwort(e): microstructure ; Inconel 625 ; oxidation ; deformation substructure ; deformation twins ; energy-dispersive spectroscopy (EDS) ; internal oxide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The high-temperature, isothermal-oxidation behavior of a superalloy was studied in the as-rolled and deformed conditions. The microstructural changes occurring during the oxidation of samples were examined using optical, scanning electron microscopy (SEM), fine-probe EDS microanalysis, and X-ray diffraction techniques. The topography of the oxide layers formed in the as-rolled and cold-deformed specimens exposed at various temperatures and time intervals is also examined. The kinetics and microstructural results are presented for the comparative study of the structural changes occurring during high-temperature oxidation. It was found that a Cr2O3 external layer was adherent and uniform on the rolled specimens in comparison to the scattered and preferential oxide developed on the deformed specimens. The latter can be attributed to the concurrent dynamic changes occurring in the deformed substructure that subsequently lead to breaking and spallation of the oxide.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 121-138 
    ISSN: 1573-4889
    Schlagwort(e): titanium aluminides ; oxidation ; oxygen-affected zone ; alpha case ; TEM
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The isothermal oxidation behavior of binary Ti–25 at.% Al was studiedat 1073, 1173, and 1273 K in air and oxygen with emphasis on themicrostructure of the subsurface zone underneath the external oxidescale. Thermogravimetric analysis, acoustic-emission (AE) analysis, lightmicroscopy, scanning electron microscopy (SEM), atomic force microscopy(AFM), and cross-sectional transmission electron microscopy (TEM) werecarried out. Three layers could be identified in the subsurface regionconsisting of an internal oxidation zone of α-Al2O3,and α-Ti, a ternary phase with the empirical formulaTi–21Al–15O (at.%), and an oxygen penetration zone consisting ofα2-Ti3Al(O).
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 445-456 
    ISSN: 1573-4889
    Schlagwort(e): quasicrystals ; aluminides ; oxidation ; nodules
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of a quasicrystal with the nominal compositionAl63Cu25Fe12 was studied around 800°Cin environmental and synthetic air by means of thermogravimetric analysis,electron microscopy, and analytical electron spectroscopy. In an earlyoxidation stage, γ-Al2O3 formed with an orientational relationship tothe quasicrystal. At the oxide–metal interface, γ-Al2O3transformed into large hexagonal shaped α-Al2O3grains. The change in surface morphology indicated that at theoxide–gas interface γ-Al2O3 continued togrow as Θ-Al2O3. Locally the metastable aluminalayer was transformed thoroughly into α-Al2O3,which then continued to grow with a nodular morphology. On top of the oxidenodules, several at.% of Cu2+ were detected.
    Materialart: Digitale Medien
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  • 16
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; marginal chromia formers ; water vapor effect ; chromia evaporation ; breakaway corrosion ; flow-rate dependence ; 304L
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The effect of roman PH 2 O and flow rate on the oxidation of 304Lat 873 K in oxygen is reported. High concentrations of water vapor and highflow rates result in breakaway corrosion. The mass gain after 168 hrincreased by four to five times, compared to oxidation in dry O2. Inthe presence of H2O, the corrosion products consisted of arelatively thin (Cr,Fe)2O3 oxide plus large oxide islandsconsisting mainly of Fe2O3. A mechanism explaining theeffect of water vapor on marginal chromia formers is proposed.
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 47-62 
    ISSN: 1573-4889
    Schlagwort(e): oxygen sensor ; oxygen pump ; solid-state electrolyte ; ZrO2 ; oxygen partial pressure ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract An ultralow oxygen partial pressure-controlling system, based on solid-stateelectrochemical principles, has been developed. This system consists of anoxygen sensor and an oxygen pump and is controlled by a PC computer. Theoxygen sensor is used to measure the oxygen partial pressure in an enclosedsystem, while the oxygen pump is used to transport oxygen from the ambientair into the enclosed system or from the enclosed system to the ambientair. The operating conditions of this system have been studied. The resultsshowed that it can be used to establish a stable oxygen partial pressure inthe range of 10−18∼5×105 Pa (1×10−23∼5 atm)in the enclosed system. This system has been used to investigate theselective oxidation of the Cr and the oxide formation on the surface of aNi–Cr alloy under three different low oxygen partial pressures. Theoxide morphology was studied using atomic force microscopy (AFM). The resultsagreed well with those in the literature and also confirm the reliability of this system.
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  • 18
    ISSN: 1573-4889
    Schlagwort(e): TiAl ; oxidation ; phosphorus ; microdiffraction ; doping ; rutile
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Recently it has been found that very small amounts (a few 100 ppm) of Padded to γ -titanium aluminide can significantly alter the oxidationbehavior between 973 and 1273 K. The mechanism responsible for this changeis, however, still not clear. In the present study, phosphorus wasincorporated into the surface of TiAl (containing 50 at.% Al) by ionimplantation and oxidation tests were carried out at 1173 K inair. Improvement of oxidation resistance is only temporary up to 100 hr forphosphorus-implanted TiAl. After 100 hr, the oxidation rate increases andbreakaway oxidation follows. XRD and EPMA showed that the breakawayoxidation is connected with massive nitride formation. Two different modelsare proposed which can explain the effect of phosphorus additions on theoxidation kinetics of TiAl during the protective stage within the first100 hr. The breakaway effect can be explained by penetration of air to themetal–oxide interface zone because of microcrack formation in theoxide scale, which was experimentally proved by acoustic-emission analysis.
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 339-371 
    ISSN: 1573-4889
    Schlagwort(e): Fe–Al alloys ; oxidation ; sulfidation ; nodular growth ; corrosion mechanism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The mechanisms for nodular corrosion-product development were investigatedin various high-temperature gaseous environments. Fe–Al alloys, with5–20 wt.% Al, were exposed in both oxidizing and sulfidizing[p(S2)=10−4 atm, p(O2)=10−25 atm] atmospheres at 700°Cfor times up to 100 hr. The corrosion kinetics were monitored by theuse of a thermogravimetric balance and the morphological developmentthrough light-optical and scanning-electron microscopies,energy-dispersive spectroscopy, electron-probe microanalysis,and quantitative-image analysis. Under both conditions, theelimination of nodule formation was observed by increasing thealuminum content of the alloy, above 5 and 7.5 wt.% Al for oxidizingand sulfidizing environments, respectively, which promoted the growthand maintenance of a continuous surface scale of alumina. For thosealloys that were observed to develop nodular corrosion products, theirmorphological appearance was similar in nature regardless of thecorroding species. The nodules typically consisted of an outeriron-rich product, either sulfide or oxide, that was randomly dispersedacross an alumina scale. Samples from the oxidizing atmosphere displayeda single growth-rate time constant from the kinetics data, suggesting thatthe nodule growth mechanism was by the simultaneous or codevelopment oftwo different (Fe and Al) oxides from the onset of exposure. Measurementof nodule planar diameter and depth of penetration into the alloyindicated that growth occurred through diffusional processes. Kineticsdata from the development of sulfide nodules in the reducingenvironment revealed a different type of mechanism. Multiplegrowth-rate time constants were found due to the localized mechanicalfailure of an initially formed surface scale. At early times in thesulfidizing atmosphere, a low corrosion rate was recorded as acontinuous-alumina scale afforded protection from excessive productdevelopment. However, with the mechanical failure of the scale, sulfurwas able to attack the underlying substrate through a short-circuitdiffusion mechanism that resulted in rapid weight gains from nonprotective,iron sulfide growth. The sulfide morphologies observed were very complex ascontinued growth of the nodule did not solely depend upon the diffusingspecies through the previously formed corrosion products, but also,continued mechanical failure of the oxide scale. It is suggested that thedifference in development mechanisms between the two environments may liein the relative growth rates of the nonprotective, Fe-base corrosionproducts formed.
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 559-574 
    ISSN: 1573-4889
    Schlagwort(e): silver–nickel ; mechanical alloying ; oxidation ; two-phase alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Two nanophase Ni-base alloys containing 50 and 25 at.% Ag prepared by mechanical alloying, denoted Ni–50Ag and Ni–25Ag were oxidized in air at 600 and 700°C for 24 hr. Ni–50Ag underwent internal oxidation of nickel, associated with the formation of a continuous outermost layer of silver metal with scaling rates larger than those for pure nickel. On the contrary, Ni–25Ag formed a continuous NiO layer surmounted by a discontinuous silver layer and internal oxidation was suppressed. The oxidation rate of Ni–25Ag decreased with time much more rapidly than predicted by the parabolic rate law during the initial stage and eventually became parabolic, with rate constants much lower than those for the oxidation of pure nickel. These results are attributed to the two-phase nature and, particularly, to the very small grain size of the two alloys.
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 53 (2000), S. 1-23 
    ISSN: 1573-4889
    Schlagwort(e): Aluminum ; SEM ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Fine powders of aluminum were produced in a pilot-plant, inert-gas atomizerwith a “confined-design” nozzle, which operated vertically upward. Argonand helium at 1.85 MPa and nitrogen at 1.56 MPa were used as the atomizingagent. The morphology of the powder particles was examined by SEM. Powderswere sieved dry and wet. The Sauter mean diameter of the powders varied from20.70 to 10.25 μm depending on the atomizing gas. The distribution ofsizes was bimodal. The mean thickness of oxide on the surface of the powderwas calculated from the total oxygen contents of powder samples (determinedby a Leco analyzer). In addition, ESCA measurements and BET tests werecarried out for surface-oxide thickness and area measurements,respectively. The finest powder produced under helium incorporated thinnersurface-oxide layers than the coarser ones produced under argon andnitrogen. This was due to differences in physical properties (such asdensity, thermal conductivity) and flow properties (such as gasvelocity and relative velocity) of the atomizing gases used, i.e., helium,argon, and nitrogen. The oxide was very irregular in thickness in thecoarse-size range of the Al powders produced under argon and nitrogen. Thiswas presumably because of the high- and low-temperature oxidation ofaluminum droplets during the atomization and subsequent solidification andcooling periods leading to the rough surfaces observed with SEMinvestigation in the present work.
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  • 22
    ISSN: 1573-4889
    Schlagwort(e): γ-TiAl-based intermetallic alloy ; oxidation ; microstructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The influence of microstructure of the two-phase alloyTi–46Al–1Cr–0.2Si on the oxidation behavior in air between600 and 900°C was studied. The oxidation rate, type of scale, and scalespallation resistance were strongly affected by the type of microstructure,i.e., lamellar in as-cast material and duplex after extrusion at1300°C. The oxidation rate was affected by the size and distribution ofthe α2-Ti3Al phase, being faster for the extrudedmaterial with coarse α2-Ti3Al. The type of oxide scaledetermines the spalling resistance. Cast material developed a uniform scalethat spalled off after short exposure times at 800 and 900°C when a criticalthickness was reached. The extruded material presented a heterogeneous scalewith predominant thick regions formed on γ-TiAl-α2-Ti3Algrains and thin scale regions formed on γ-TiAl grains. Thistype of scale could permit an easier relaxation in the matrix of stressesgenerated by both thermal-expansion mismatch between scale and alloy andoxide growth, resulting in a higher spallation resistance.
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 575-589 
    ISSN: 1573-4889
    Schlagwort(e): TiAl ; oxidation ; Si3N4 ; dispersed particles
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation kinetics of TiAl alloys with and without 3 and 5 wt.%additions of Si3N4 particles were studied at 1173 and1273 K in 1 atm of air. The Si3N4 dispersions wereunstable in the matrix phase, so that some of them reacted with titaniumduring sintering to form Ti5Si3 and dissolvednitrogen. The oxide scale formed on TiAl–Si3N4alloys consisted of an outer TiO2, an intermediate(Al2O3+TiO2), and an inner(TiO2+Al2O3) mixed layers. The enhancedalumina-forming tendency, the presence of discrete SiO2 particlesbelow the outer TiO2 layer, and the improved scale adhesion bySi3N4 dispersions were attributable mainly to theincreased oxidation resistance compared to the Si3N4-freeTiAl alloys. Marker experiments showed that, for TiAl–Si3N4 alloys, the primary mode of scale growth was the outward diffusion oftitanium ions for the outer scale and the inward transport of oxygen ionsfor the inner scale.
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Journal of porous materials 7 (2000), S. 373-376 
    ISSN: 1573-4854
    Schlagwort(e): porous silicon ; superlattices ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract Initial stage of porous silicon (PS) formation has been studied in an original way. Multilayer structures constituting of very thin layers of low porosity and thick layers of high porosity have been fabricated and characterised by optical tools and electron microscopy. The non linear behaviour resulting in a change in the dissolution velocity has been quantified by using a stack layer structure. Finally using thermal oxidation it has been shown that, due to the selective oxidation as a function of the porosity, porous silicon can be used to produce a Si/SiO2 like structure.
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Journal of porous materials 7 (2000), S. 335-338 
    ISSN: 1573-4854
    Schlagwort(e): porous silicon ; oxidation ; calorimeter ; desorption ; activation energy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract The oxidation of porous silicon has been studied using differential scanning calorimeter. The oxidation was found to consist of two parts with different activation energies. This indicates the existence of two different reaction mechanism. The results from the hydrogen desorption measurements have been used to study the different oxidation behaviour of the n- and p+-type porous silicon. The results show that the dihydride structure dominates on the surface of the n-type porous silicon, contrary to p+-type porous silicon, where the monohydride is the major structure. Explanations of these features are discussed. Using the activation energy, the surface termination effects are investigated. The best improvement in the activation energy was observed in the sample, whose surface was partially stabilized by ammonium groups.
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Journal of porous materials 7 (2000), S. 339-343 
    ISSN: 1573-4854
    Schlagwort(e): porous silicon ; infrared spectroscopy ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract The Si–Si vibrational states near the surface region of porous silicon has been characterized using Fourier Transform Infrared Spectroscopy (FTIR) due to its enlarged surface area. By means of anodic etch and oxidization experiments, two Si–Si vibration modes of porous silicon have been identified as near the surface regions and in the bulk, respectively. The intensity of absorption peak at 620 cm−1, which originates from the Si–Si bonds vibrations on the surface and near surface regions of porous silicon, is found to vary depending on the length of etch and degree of oxidation of porous silicon, which exists before etching and is recovered again after fully oxidation. The peak of 610 cm−1 doesn't change throughout the oxidation experiment, and to be assigned for Si–Si bond vibrations in the bulk. With an extra irradiation of Nd:Yag laser on the PS sample the Raman and FTIR spectra reveal a red shift. These results can give an interpretation to explain the different phenomenon of Si–Si vibrations of Raman and FTIR spectroscopy.
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  • 27
    Digitale Medien
    Digitale Medien
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    Journal of porous materials 7 (2000), S. 205-208 
    ISSN: 1573-4854
    Schlagwort(e): porous silicon ; oxidation ; liquid crystal
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract In this paper we demonstrate the filling of porous silicon (PS) layers with liquid crystals (LC's) in order to control the reflectance electrically. The preparation of PS and the choice of the right group of LC's will be presented. Especially an oxidation of PS is necessary so that the methods and parameters of oxidation will also be discussed. As a first result the increasing and decreasing of the thickness oscillations in the reflectance as a function of the applied voltage can be observed.
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Journal of porous materials 7 (2000), S. 243-246 
    ISSN: 1573-4854
    Schlagwort(e): porous silicon ; oxidation ; refractive index ; optical waveguide ; optical losses
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract Further results on the optical properties of oxidised porous silicon as a function of porosity and oxidation conditions are presented in this paper. The refractive index varies logarithmically with the oxidation time irrespective of the porosity of the sample and the oxidation temperature. Burried waveguides have been realised from as-prepared and oxidised porous silicon. Optical losses of 18 dB cm−1 at λ = 1.3 μm have been obtained after oxidation at 800°C for 35 min.
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Journal of porous materials 7 (2000), S. 139-142 
    ISSN: 1573-4854
    Schlagwort(e): porous silicon carbide ; oxidation ; effective medium theory ; infrared reflectance (or IR) ; reststrahlen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract We present a study of the infrared reflectance of porous silicon carbide (PSC) formed by the electrochemical dissolution of silicon carbide substrates of both 6H and 4H polytypes. The reflectance from n-PSC, both as-anodized and passivated, is reported for the first time. The passivation of PSC has been accomplished using a short thermal oxidation. Fourier transform infrared (FTIR) reflectance spectroscopy is employed ex situ after different stages of the thermal oxidation process. The characteristics of the reststrahlen band normally observed in bulk SiC are altered by anodization; further changes in the reflectance spectra occur following oxidation for different periods of time. An effective medium theory model that includes air, SiC and SiO2 as component materials is shown to characterize the observed changes in the reflectance spectra after different stages of PSC oxidation.
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Information retrieval 2 (2000), S. 303-336 
    ISSN: 1573-7659
    Schlagwort(e): machine learning ; summarization ; indexing ; keywords ; keyphrase extraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Many academic journals ask their authors to provide a list of about five to fifteen keywords, to appear on the first page of each article. Since these key words are often phrases of two or more words, we prefer to call them keyphrases. There is a wide variety of tasks for which keyphrases are useful, as we discuss in this paper. We approach the problem of automatically extracting keyphrases from text as a supervised learning task. We treat a document as a set of phrases, which the learning algorithm must learn to classify as positive or negative examples of keyphrases. Our first set of experiments applies the C4.5 decision tree induction algorithm to this learning task. We evaluate the performance of nine different configurations of C4.5. The second set of experiments applies the GenEx algorithm to the task. We developed the GenEx algorithm specifically for automatically extracting keyphrases from text. The experimental results support the claim that a custom-designed algorithm (GenEx), incorporating specialized procedural domain knowledge, can generate better keyphrases than a general-purpose algorithm (C4.5). Subjective human evaluation of the keyphrases generated by GenEx suggests that about 80% of the keyphrases are acceptable to human readers. This level of performance should be satisfactory for a wide variety of applications.
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  • 31
    Digitale Medien
    Digitale Medien
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    Journal of intelligent information systems 14 (2000), S. 199-216 
    ISSN: 1573-7675
    Schlagwort(e): machine learning ; data mining ; learning from noisy data ; natural induction ; AQ learning ; decision rules ; separate and conquer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In concept learning and data mining tasks, the learner is typically faced with a choice of many possible hypotheses or patterns characterizing the input data. If one can assume that training data contain no noise, then the primary conditions a hypothesis must satisfy are consistency and completeness with regard to the data. In real-world applications, however, data are often noisy, and the insistence on the full completeness and consistency of the hypothesis is no longer valid. In such situations, the problem is to determine a hypothesis that represents the best trade-off between completeness and consistency. This paper presents an approach to this problem in which a learner seeks rules optimizing a rule quality criterion that combines the rule coverage (a measure of completeness) and training accuracy (a measure of inconsistency). These factors are combined into a single rule quality measure through a lexicographical evaluation functional (LEF). The method has been implemented in the AQ18 learning system for natural induction and pattern discovery, and compared with several other methods. Experiments have shown that the proposed method can be easily tailored to different problems and can simulate different rule learners by modifying the parameter of the rule quality criterion.
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  • 32
    Digitale Medien
    Digitale Medien
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    Journal of intelligent information systems 15 (2000), S. 207-220 
    ISSN: 1573-7675
    Schlagwort(e): knowledge discovery ; machine learning ; rough sets ; inconsistency
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Consistency and completeness are defined in the context of rough set theory and shown to be related to the lower approximation and upper approximation, respectively. A member of a composed set (union of elementary sets) that is consistent with respect to a concept, surely belongs to the concept. An element that is not a member of a composed set that is complete with respect to a concept, surely does not belong to the concept. A consistent rule and a complete rule are useful in addition to any other rules learnt to describe a concept. When an element satisfies the consistent rule, it surely belongs to the concept, and when it does not satisfy the complete rule, it surely does not belong to the concept. In other cases, the other learnt rules are used. The results in the finite universe are extended to the infinite universe, thus introducing a rough set model for the learning from examples paradigm. The results in this paper have application in knowledge discovery or learning from database environments that are inconsistent, but at the same time demand accurate and definite knowledge. This study of consistency and completeness in rough sets also lays the foundation for related work at the intersection of rough set theory and inductive logic programming.
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Applied intelligence 13 (2000), S. 7-17 
    ISSN: 1573-7497
    Schlagwort(e): bioindicators ; machine learning ; regression trees ; rivers ; water quality
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We address the problem of inferring chemical parameters of river water quality from biological ones. This task is important for enabling selective chemical monitoring of river water quality. We apply machine learning, in particular regression tree induction, to biological and chemical data on the water quality of Slovenian rivers. Regression trees are constructed that predict values of chemical parameters from data on the presence of bioindicator taxa at the species and family levels.
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Applied intelligence 13 (2000), S. 19-40 
    ISSN: 1573-7497
    Schlagwort(e): Bayesian networks ; machine learning ; waste water treatment plants
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Bayesian Networks have been proposed as an alternative to rule-based systems in domains with uncertainty. Applications in monitoring and control can benefit from this form of knowledge representation. Following the work of Chong and Walley, we explore the possibilities of Bayesian Networks in the Waste Water Treatment Plants (WWTP) monitoring and control domain. We show the advantages of modelling knowledge in such a domain by means of Bayesian networks, put forth new methods for knowledge acquisition, describe their applications to a real waste water treatment plant and comment on the results. We also show how a Bayesian Network learning environment was used in the process and which characteristics of data in the domain suggested new ways of representing knowledge in network form but with uncertainty representations formalisms other than probability. The results of applying a possibilistic extension of current learning methods are also shown and compared.
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Autonomous robots 8 (2000), S. 345-383 
    ISSN: 1573-7527
    Schlagwort(e): multiagent systems ; machine learning ; survey ; robotics ; intelligent agents ; robotic soccer ; pursuit domain ; homogeneous agents ; heterogeneous agents ; communicating agents
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract Distributed Artificial Intelligence (DAI) has existed as a subfield of AI for less than two decades. DAI is concerned with systems that consist of multiple independent entities that interact in a domain. Traditionally, DAI has been divided into two sub-disciplines: Distributed Problem Solving (DPS) focuses on the information management aspects of systems with several components working together towards a common goal; Multiagent Systems (MAS) deals with behavior management in collections of several independent entities, or agents. This survey of MAS is intended to serve as an introduction to the field and as an organizational framework. A series of general multiagent scenarios are presented. For each scenario, the issues that arise are described along with a sampling of the techniques that exist to deal with them. The presented techniques are not exhaustive, but they highlight how multiagent systems can be and have been used to build complex systems. When options exist, the techniques presented are biased towards machine learning approaches. Additional opportunities for applying machine learning to MAS are highlighted and robotic soccer is presented as an appropriate test bed for MAS. This survey does not focus exclusively on robotic systems. However, we believe that much of the prior research in non-robotic MAS is relevant to robotic MAS, and we explicitly discuss several robotic MAS, including all of those presented in this issue.
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  • 36
    Digitale Medien
    Digitale Medien
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    Information retrieval 3 (2000), S. 87-103 
    ISSN: 1573-7659
    Schlagwort(e): neural networks ; news agent ; recurrent plausibility network ; text classification ; machine learning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The research project AgNeT develops Agents for Neural Text routing in the internet. Unrestricted potentially faulty text messages arrive at a certain delivery point (e.g. email address or world wide web address). These text messages are scanned and then distributed to one of several expert agents according to a certain task criterium. Possible specific scenarios within this framework include the learning of the routing of publication titles or news titles. In this paper we describe extensive experiments for semantic text routing based on classified library titles and newswire titles. This task is challenging since incoming messages may contain constructions which have not been anticipated. Therefore, the contributions of this research are in learning and generalizing neural architectures for the robust interpretation of potentially noisy unrestricted messages. Neural networks were developed and examined for this topic since they support robustness and learning in noisy unrestricted real-world texts. We describe and compare different sets of experiments. The first set of experiments tests a recurrent neural network for the task of library title classification. Then we describe a larger more difficult newswire classification task from information retrieval. The comparison of the examined models demonstrates that techniques from information retrieval integrated into recurrent plausibility networks performed well even under noise and for different corpora.
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  • 37
    Digitale Medien
    Digitale Medien
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    International journal of computer vision 38 (2000), S. 15-33 
    ISSN: 1573-1405
    Schlagwort(e): computer vision ; machine learning ; pattern recognition ; people detection ; face detection ; ear detection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper presents a general, trainable system for object detection in unconstrained, cluttered scenes. The system derives much of its power from a representation that describes an object class in terms of an overcomplete dictionary of local, oriented, multiscale intensity differences between adjacent regions, efficiently computable as a Haar wavelet transform. This example-based learning approach implicitly derives a model of an object class by training a support vector machine classifier using a large set of positive and negative examples. We present results on face, people, and car detection tasks using the same architecture. In addition, we quantify how the representation affects detection performance by considering several alternate representations including pixels and principal components. We also describe a real-time application of our person detection system as part of a driver assistance system.
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  • 38
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    Digitale Medien
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    Powder metallurgy and metal ceramics 39 (2000), S. 560-562 
    ISSN: 1573-9066
    Schlagwort(e): niobium ; coating ; silicon ; corrosion ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Coatings based on TiSi2 have been used to protect niobium alloys from corrosion at temperatures up to 1300°C. Kinetic oxidation curves are given for these coatings on niobium. The phase compositions of the coatings have been determined and also of the layers formed during oxidation. EPMA has been applied to the element distributions in the coating, from which it is concluded that the silicon is mobile. The high resistance to oxygen of coatings based on TiSi2 is due to the formation of films of TiO2 and SiO2 on them.
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  • 39
    Digitale Medien
    Digitale Medien
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    Statistics and computing 10 (2000), S. 73-83 
    ISSN: 1573-1375
    Schlagwort(e): clustering ; mixture modelling ; minimum message length ; MML ; Snob ; induction ; coding ; information theory ; statistical inference ; machine learning ; classification ; intrinsic classification ; unsupervised learning ; numerical taxonomy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract Minimum Message Length (MML) is an invariant Bayesian point estimation technique which is also statistically consistent and efficient. We provide a brief overview of MML inductive inference (Wallace C.S. and Boulton D.M. 1968. Computer Journal, 11: 185–194; Wallace C.S. and Freeman P.R. 1987. J. Royal Statistical Society (Series B), 49: 240–252; Wallace C.S. and Dowe D.L. (1999). Computer Journal), and how it has both an information-theoretic and a Bayesian interpretation. We then outline how MML is used for statistical parameter estimation, and how the MML mixture modelling program, Snob (Wallace C.S. and Boulton D.M. 1968. Computer Journal, 11: 185–194; Wallace C.S. 1986. In: Proceedings of the Nineteenth Australian Computer Science Conference (ACSC-9), Vol. 8, Monash University, Australia, pp. 357–366; Wallace C.S. and Dowe D.L. 1994b. In: Zhang C. et al. (Eds.), Proc. 7th Australian Joint Conf. on Artif. Intelligence. World Scientific, Singapore, pp. 37–44. See http://www.csse.monash.edu.au/-dld/Snob.html) uses the message lengths from various parameter estimates to enable it to combine parameter estimation with selection of the number of components and estimation of the relative abundances of the components. The message length is (to within a constant) the logarithm of the posterior probability (not a posterior density) of the theory. So, the MML theory can also be regarded as the theory with the highest posterior probability. Snob currently assumes that variables are uncorrelated within each component, and permits multi-variate data from Gaussian, discrete multi-category (or multi-state or multinomial), Poisson and von Mises circular distributions, as well as missing data. Additionally, Snob can do fully-parameterised mixture modelling, estimating the latent class assignments in addition to estimating the number of components, the relative abundances of the parameters and the component parameters. We also report on extensions of Snob for data which has sequential or spatial correlations between observations, or correlations between attributes.
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  • 40
    ISSN: 1573-4854
    Schlagwort(e): oxidized porous silicon ; anodization ; oxidation ; dielectric isolation ; optical waveguide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract A brief review of 20-years research of formation, processing and utilizing of oxidized porous silicon (OPS) is presented. Electrolytes to form porous silicon (PS) layers, special features of PS chemical cleaning and thermal oxidation are discussed. OPS application for dielectric isolation of components of bipolar ICs and for the formation of silicon-on-insulator structures has been demonstrated. Although these OPS-based techniques have found limited current commercial use, experience gained is applicable to the fabrication of optoelectronic devices. Specifically, integrated optical waveguides based on OPS have been developed.
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  • 41
    Digitale Medien
    Digitale Medien
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    Journal of porous materials 7 (2000), S. 63-66 
    ISSN: 1573-4854
    Schlagwort(e): porous silicon ; oxidation ; IR spectroscopy ; vibrational analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract Oxidation behavior of porous silicon under various environments of dry and wet air, and solution with and without appropriate oxidant at mild temperatures has been investigated. The progress of oxidation was followed by infrared spectroscopy. The presence of water vapor greatly accelerates the oxidation rate in comparison with the rate in dry air. The oxidized states are clarified with the help of oxidation experiments of partially hydrogen-desorbed porous silicon, which does not contain SiH2 and SiH3 as the hydride species. An oxidation mechanism is proposed to explain that oxidation is accelerated in the presence of water vapor and at the partially hydrogen-desorbed porous silicon. Further, oxidation behavior of porous silicon in solution containing appropriate oxidant is also investigated. The rate is very rapid and the oxidation does not produce the back-bond oxidized state of OySiHx in contrast to the oxidation in air.
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  • 42
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    User modeling and user adapted interaction 10 (2000), S. 147-180 
    ISSN: 1573-1391
    Schlagwort(e): user modeling ; machine learning ; information retrieval ; intelligent agents ; recommender systems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We present a framework for adaptive news access, based on machine learning techniques specifically designed for this task. First, we focus on the system's general functionality and system architecture. We then describe the interface and design of two deployed news agents that are part of the described architecture. While the first agent provides personalized news through a web-based interface, the second system is geared towards wireless information devices such as PDAs (personal digital assistants) and cell phones. Based on implicit and explicit user feedback, our agents use a machine learning algorithm to induce individual user models. Motivated by general shortcomings of other user modeling systems for Information Retrieval applications, as well as the specific requirements of news classification, we propose the induction of hybrid user models that consist of separate models for short-term and long-term interests. Furthermore, we illustrate how the described algorithm can be used to address an important issue that has thus far received little attention in the Information Retrieval community: a user's information need changes as a direct result of interaction with information. We empirically evaluate the system's performance based on data collected from regular system users. The goal of the evaluation is not only to understand the performance contributions of the algorithm's individual components, but also to assess the overall utility of the proposed user modeling techniques from a user perspective. Our results provide empirical evidence for the utility of the hybrid user model, and suggest that effective personalization can be achieved without requiring any extra effort from the user.
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  • 43
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    International journal of computer vision 38 (2000), S. 45-57 
    ISSN: 1573-1405
    Schlagwort(e): computer vision ; machine learning ; facial modelling ; facial animation ; morphing ; optical flow ; speech synthesis ; lip synchronization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We present MikeTalk, a text-to-audiovisual speech synthesizer which converts input text into an audiovisual speech stream. MikeTalk is built using visemes, which are a small set of images spanning a large range of mouth shapes. The visemes are acquired from a recorded visual corpus of a human subject which is specifically designed to elicit one instantiation of each viseme. Using optical flow methods, correspondence from every viseme to every other viseme is computed automatically. By morphing along this correspondence, a smooth transition between viseme images may be generated. A complete visual utterance is constructed by concatenating viseme transitions. Finally, phoneme and timing information extracted from a text-to-speech synthesizer is exploited to determine which viseme transitions to use, and the rate at which the morphing process should occur. In this manner, we are able to synchronize the visual speech stream with the audio speech stream, and hence give the impression of a photorealistic talking face.
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  • 44
    Digitale Medien
    Digitale Medien
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    Data mining and knowledge discovery 4 (2000), S. 251-280 
    ISSN: 1573-756X
    Schlagwort(e): data mining ; knowledge discovery ; machine learning ; genetic algorithms ; financial prediction ; rule learning ; investment decision making ; systematic trading
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Prediction in financial domains is notoriously difficult for a number of reasons. First, theories tend to be weak or non-existent, which makes problem formulation open ended by forcing us to consider a large number of independent variables and thereby increasing the dimensionality of the search space. Second, the weak relationships among variables tend to be nonlinear, and may hold only in limited areas of the search space. Third, in financial practice, where analysts conduct extensive manual analysis of historically well performing indicators, a key is to find the hidden interactions among variables that perform well in combination. Unfortunately, these are exactly the patterns that the greedy search biases incorporated by many standard rule learning algorithms will miss. In this paper, we describe and evaluate several variations of a new genetic learning algorithm (GLOWER) on a variety of data sets. The design of GLOWER has been motivated by financial prediction problems, but incorporates successful ideas from tree induction and rule learning. We examine the performance of several GLOWER variants on two UCI data sets as well as on a standard financial prediction problem (S&P500 stock returns), using the results to identify one of the better variants for further comparisons. We introduce a new (to KDD) financial prediction problem (predicting positive and negative earnings surprises), and experiment with GLOWER, contrasting it with tree- and rule-induction approaches. Our results are encouraging, showing that GLOWER has the ability to uncover effective patterns for difficult problems that have weak structure and significant nonlinearities.
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  • 45
    Digitale Medien
    Digitale Medien
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    Minds and machines 9 (1999), S. 543-564 
    ISSN: 1572-8641
    Schlagwort(e): Bayesianism ; complexity ; decision theory ; fast and frugal heuristics ; machine learning ; philosophy of science ; predictive accuracy ; simplicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Philosophie
    Notizen: Abstract The theory of fast and frugal heuristics, developed in a new book called Simple Heuristics that make Us Smart (Gigerenzer, Todd, and the ABC Research Group, in press), includes two requirements for rational decision making. One is that decision rules are bounded in their rationality –- that rules are frugal in what they take into account, and therefore fast in their operation. The second is that the rules are ecologically adapted to the environment, which means that they `fit to reality.' The main purpose of this article is to apply these ideas to learning rules–-methods for constructing, selecting, or evaluating competing hypotheses in science, and to the methodology of machine learning, of which connectionist learning is a special case. The bad news is that ecological validity is particularly difficult to implement and difficult to understand. The good news is that it builds an important bridge from normative psychology and machine learning to recent work in the philosophy of science, which considers predictive accuracy to be a primary goal of science.
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  • 46
    Digitale Medien
    Digitale Medien
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    Journal of intelligent and robotic systems 26 (1999), S. 123-135 
    ISSN: 1573-0409
    Schlagwort(e): named-entity recognition ; information extraction ; machine learning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract Named-entity recognition (NER) involves the identification and classification of named entities in text. This is an important subtask in most language engineering applications, in particular information extraction, where different types of named entity are associated with specific roles in events. In this paper, we present a prototype NER system for Greek texts that we developed based on a NER system for English. Both systems are evaluated on corpora of the same domain and of similar size. The time-consuming process for the construction and update of domain-specific resources in both systems led us to examine a machine learning method for the automatic construction of such resources for a particular application in a specific language.
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  • 47
    Digitale Medien
    Digitale Medien
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    Journal of intelligent and robotic systems 26 (1999), S. 325-352 
    ISSN: 1573-0409
    Schlagwort(e): machine learning ; water distribution network ; knowledge acquisition ; forecasting ; exception handling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract The human-assisted application of machine learning techniques in the domain of water distribution networks is presented, corresponding to a research work done in the context of the European Esprit project WATERNET. One part of this project is a learning system that intends to capture knowledge from historic information collected during the operation of water distribution networks. The captured knowledge is expected to contribute to the improvement of the operation of the network. Presented ideas correspond to the first development phase of the learning system, focusing specially on the adopted methodology. The interactions between different classes of human experts and the learning system are also discussed. Finally some experimental results are presented.
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  • 48
    Digitale Medien
    Digitale Medien
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    Journal of intelligent and robotic systems 24 (1999), S. 99-124 
    ISSN: 1573-0409
    Schlagwort(e): behaviour decomposition ; behaviour learning ; intelligent navigation ; decision tress ; ITI ; machine learning ; robotics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract This paper presents a new approach to the intelligent navigation of a mobile robot. The hybrid control architecture described combines properties of purely reactive and behaviour-based systems, providing the ability both to learn automatically behaviours from inception, and to capture these in a distributed hierarchy of decision tree networks. The robot is first trained in the simplest world which has no obstacles, and is then trained in successively more complex worlds, using the knowledge acquired in the previous worlds. Each world representing the perceptual space is thus directly mapped on a unique rule layer which represents in turn the robot action space encoded in a distinct decision tree. A major advantage of the current implementation, compared with the previous work, is that the generated rules are easily understood by human users. The paper demonstrates that the proposed behavioural decomposition approach provides efficient management of complex knowledge, and that the learning mechanism is able to cope with noise and uncertainty in sensory data.
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  • 49
    Digitale Medien
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    Plasma chemistry and plasma processing 19 (1999), S. 131-151 
    ISSN: 1572-8986
    Schlagwort(e): Styrene ; oxidation ; silent discharge ; plasma ; dielectric barrier
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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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  • 50
    Digitale Medien
    Digitale Medien
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    Plasma chemistry and plasma processing 19 (1999), S. 383-394 
    ISSN: 1572-8986
    Schlagwort(e): Nonthermal plasma ; benzene ; Al2O3 ; BaTiO3 ; oxidation ; absorption ; atmospheric pressure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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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  • 51
    Digitale Medien
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    Plasma chemistry and plasma processing 19 (1999), S. 421-443 
    ISSN: 1572-8986
    Schlagwort(e): Streamer corona ; NO x removal ; nonthermal plasma ; oxidation ; reduction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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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  • 52
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    Physics and chemistry of minerals 26 (1999), S. 506-512 
    ISSN: 1432-2021
    Schlagwort(e): Key words Anapaite ; Mössbauer spectroscopy ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Abstract Mössbauer spectra (MS) of anapaite (Ca2 Fe2+(PO4)2 · 4H2O) and of a sample after being immersed in a 4% H2O2 solution at room temperature (RT) over 12 days (hereafter an4ox) were collected at temperatures in the range 4.2 to 420 K and 11 to 300 K respectively. All MS consist of symmetrical doublets, hence magnetic ordering was not observed. The temperature dependencies of the Fe2+ centre shifts of anapaite and an4ox were analysed with the Debye model for the lattice vibrations. The characteristic Mössbauer temperatures were found as 370 K ± 25 K and 340 K ± 25 K, and the intrinsic isomer shifts as 1.427 ± 0.005 mm/s and 1.418 ± 0.005 mm/s respectively. From the external-field (60 kOe) MS recorded at 4.2 and 189 K for the non-treated sample, the principal component V zz of the electric field gradient (EFG) is determined to be positive and the asymmetry parameter η ≈ 0.2 and 0.4 respectively. The temperature variations of the quadrupole splittings, ΔE Q(T), cannot be interpreted on the basis of the thermal population of the 5 D electronic levels resulting from the tetragonal compression of the O6 co-ordination. The low-temperature linear behaviour of ΔE Q(T) is attributed to a strong orbit-lattice coupling. A field of 60 kOe applied to anapaite at 4.2 K produces magnetic hyperfine splitting with effective hyperfine fields of −136, −254 and −171 kOe along the principal axes Ox, Oy and Oz of the EFG tensor respectively. Additional oxidation treatments in solutions with various H2O2 concentrations up to 20% and subsequent Mössbauer experiments at room temperature, have revealed that the anapaite structure is not sensitive to oxidation since eventually only a small amount of Fe2+ (∼6.5%) is converted into Fe3+.
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  • 53
    ISSN: 1572-8978
    Schlagwort(e): Plasma polymers ; oxidation ; XPS ; photoelectron binding energy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract The incorporation of oxygen into nitrogen-containing plasma deposited polymers was studied by X-ray Photoelectron Spectroscopy (XPS). As the oxygen content of the plasma polymer increased, the binding energy of the N 1s photoelectrons increased. Conversely, the binding energy of the O 1s photoelectrons was inversely proportional to the nitrogen content of the plasma polymer. The data from a large number of samples all obeyed the same “universal” correlations of photoelectron binding energy versus chemical composition. The data were described by the same curve regardless of whether the oxygen was incorporated rapidly into the thin film during plasma deposition or whether the oxygen was added slowly during spontaneous oxidation of the film in air. This implies that the same thermodynamic principles of radical reactions governed the addition of oxygen to the plasma polymer. The shift in the O 1s and N 1s photoelectron binding energies as a function of chemical composition was used to monitor the proximity of nitrogen and oxygen. By contrasting the experimental data with a simple binomial model which described the random addition of oxygen to a lattice containing carbon and nitrogen, we were able to show that oxygen was preferentially added near nitrogen-containing groups in plasma polymers.
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  • 54
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    Applied intelligence 10 (1999), S. 225-246 
    ISSN: 1573-7497
    Schlagwort(e): information extraction ; automatic pattern acquisition ; machine learning ; EuroWordNet
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The most extended way of acquiring information for knowledge based systems is to do it manually. However, the high cost of this approach and the availability of alternative Knowledge Sources has lead to an increasing use of automatic acquisition approaches. In this paper we present M-TURBIO, a Text-Based Intelligent System (TBIS) that extracts information contained in restricted-domain documents. The system acquires part of its knowledge about the structure of the documents and the way the information is presented (i.e., syntactic-semantic rules) from a training set of these. Then, a database is created by means of applying these syntactic-semantic rules to extract the information contained in the whole document.
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  • 55
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    Digitale Medien
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    Applied intelligence 11 (1999), S. 15-30 
    ISSN: 1573-7497
    Schlagwort(e): neural networks ; structured objects ; machine learning ; classification ; similarity ; nearest neighbor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Labeled graphs are an appropriate and popular representation of structured objects in many domains. If the labels describe the properties of real world objects and their relations, finding the best match between two graphs turns out to be the weakly defined, NP-complete task of establishing a mapping between them that maps similar parts onto each other preserving as much as possible of their overall structural correspondence. In this paper, former approaches of structural matching and constraint relaxation by spreading activation in neural networks and the method of solving optimization tasks using Hopfield-style nets are combined. The approximate matching task is reformulated as the minimization of a quadratic energy function. The design of the approach enables the user to change the parameters and the dynamics of the net so that knowledge about matching preferences is included easily and transparently. In the last section, some examples demonstrate the successful application of this approach in classification and learning in the domain of organic chemistry.
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  • 56
    Digitale Medien
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    Applied intelligence 11 (1999), S. 259-275 
    ISSN: 1573-7497
    Schlagwort(e): missing data ; industrial databases ; multiple imputation ; machine learning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract A limiting factor for the application of IDA methods in many domains is the incompleteness of data repositories. Many records have fields that are not filled in, especially, when data entry is manual. In addition, a significant fraction of the entries can be erroneous and there may be no alternative but to discard these records. But every cell in a database is not an independent datum. Statistical relationships will constrain and, often determine, missing values. Data imputation, the filling in of missing values for partially missing data, can thus be an invaluable first step in many IDA projects. New imputation methods that can handle the large-scale problems and large-scale sparsity of industrial databases are needed. To illustrate the incomplete database problem, we analyze one database with instrumentation maintenance and test records for an industrial process. Despite regulatory requirements for process data collection, this database is less than 50% complete. Next, we discuss possible solutions to the missing data problem. Several approaches to imputation are noted and classified into two categories: data-driven and model-based. We then describe two machine-learning-based approaches that we have worked with. These build upon well-known algorithms: AutoClass and C4.5. Several experiments are designed, all using the maintenance database as a common test-bed but with various data splits and algorithmic variations. Results are generally positive with up to 80% accuracies of imputation. We conclude the paper by outlining some considerations in selecting imputation methods, and by discussing applications of data imputation for intelligent data analysis.
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  • 57
    Digitale Medien
    Digitale Medien
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    Information retrieval 1 (1999), S. 193-216 
    ISSN: 1573-7659
    Schlagwort(e): information retrieval ; text mining ; topic spotting ; text categorization ; knowledge management ; problem decomposition ; machine learning ; neural networks ; probabilistic models ; hierarchical models ; performance evaluation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract With the recent dramatic increase in electronic access to documents, text categorization—the task of assigning topics to a given document—has moved to the center of the information sciences and knowledge management. This article uses the structure that is present in the semantic space of topics in order to improve performance in text categorization: according to their meaning, topics can be grouped together into “meta-topics”, e.g., gold, silver, and copper are all metals. The proposed architecture matches the hierarchical structure of the topic space, as opposed to a flat model that ignores the structure. It accommodates both single and multiple topic assignments for each document. Its probabilistic interpretation allows its predictions to be combined in a principled way with information from other sources. The first level of the architecture predicts the probabilities of the meta-topic groups. This allows the individual models for each topic on the second level to focus on finer discriminations within the group. Evaluating the performance of a two-level implementation on the Reuters-22173 testbed of newswire articles shows the most significant improvement for rare classes.
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  • 58
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    Applied intelligence 11 (1999), S. 59-77 
    ISSN: 1573-7497
    Schlagwort(e): theory refinement ; machine learning ; artificial neural networks ; logic programming ; computational biology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper presents the Connectionist Inductive Learning and Logic Programming System (C-IL2P). C-IL2P is a new massively parallel computational model based on a feedforward Artificial Neural Network that integrates inductive learning from examples and background knowledge, with deductive learning from Logic Programming. Starting with the background knowledge represented by a propositional logic program, a translation algorithm is applied generating a neural network that can be trained with examples. The results obtained with this refined network can be explained by extracting a revised logic program from it. Moreover, the neural network computes the stable model of the logic program inserted in it as background knowledge, or learned with the examples, thus functioning as a parallel system for Logic Programming. We have successfully applied C-IL2P to two real-world problems of computational biology, specifically DNA sequence analyses. Comparisons with the results obtained by some of the main neural, symbolic, and hybrid inductive learning systems, using the same domain knowledge, show the effectiveness of C-IL2P.
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  • 59
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    Applied intelligence 11 (1999), S. 135-148 
    ISSN: 1573-7497
    Schlagwort(e): knowledge discovery ; machine learning ; texture ; feature selection ; image processing ; clusturing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Knowledge discovery from image data is a multi-step iterative process. This paper describes the procedure we have used to develop a knowledge discovery system that classifies regions of the ocean floor based on textural features extracted from acoustic imagery. The image is subdivided into rectangular cells called texture elements (texels); a gray-level co-occurence matrix (GLCM) is computed for each texel in four directions. Secondary texture features are then computed from the GLCM resulting in a feature vector representation of each texel instance. Alternatively, a region-growing approach is used to identify irregularly shaped regions of varying size which have a homogenous texture and for which the texture features are computed. The Bayesian classifier Autoclass is used to cluster the instances. Feature extraction is one of the major tasks in knowledge discovery from images. The initial goal of this research was to identify regions of the image characterized by sand waves. Experiments were designed to use expert judgements to select the most effective set of features, to identify the best texel size, and to determine the number of meaningful classes in the data. The region-growing approach has proven to be more successful than the texel-based approach. This method provides a fast and accurate method for identifying provinces in the ocean floor of interest to geologists.
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  • 60
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    Journal of intelligent information systems 13 (1999), S. 195-234 
    ISSN: 1573-7675
    Schlagwort(e): data mining ; knowledge discovery ; machine learning ; knowledge representation ; attribute-oriented generalization ; domain generalization graphs
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Attribute-oriented generalization summarizes the information in a relational database by repeatedly replacing specific attribute values with more general concepts according to user-defined concept hierarchies. We introduce domain generalization graphs for controlling the generalization of a set of attributes and show how they are constructed. We then present serial and parallel versions of the Multi-Attribute Generalization algorithm for traversing the generalization state space described by joining the domain generalization graphs for multiple attributes. Based upon a generate-and-test approach, the algorithm generates all possible summaries consistent with the domain generalization graphs. Our experimental results show that significant speedups are possible by partitioning path combinations from the DGGs across multiple processors. We also rank the interestingness of the resulting summaries using measures based upon variance and relative entropy. Our experimental results also show that these measures provide an effective basis for analyzing summary data generated from relational databases. Variance appears more useful because it tends to rank the less complex summaries (i.e., those with few attributes and/or tuples) as more interesting.
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  • 61
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    Neural processing letters 10 (1999), S. 201-210 
    ISSN: 1573-773X
    Schlagwort(e): neural networks ; learning ; minimal distance methods ; similarity-based methods ; machine learning ; interpretation of neural functions ; classification
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Multilayer Perceptrons (MLPs) use scalar products to compute weighted activation of neurons providing decision borders using combinations of soft hyperplanes. The weighted fun-in activation function may be replaced by a distance function between the inputs and the weights, offering a natural generalization of the standard MLP model. Non-Euclidean distance functions may also be introduced by normalization of the input vectors into an extended feature space. Both approaches influence the shapes of decision borders dramatically. An illustrative example showing these changes is provided.
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  • 62
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    Journal of intelligent manufacturing 9 (1998), S. 161-166 
    ISSN: 1572-8145
    Schlagwort(e): Autonomous agents ; behaviours ; self-organization ; machine learning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract During the last few years, in an attempt to provide an efficient alternative to classical methods to designing robot control structures, the behaviour-based approach has emerged. Its success has largely been a result of the bottom-up development of a number of fast, tightly coupled control processes. This new approach, however, has some important limitations because of its lack of goal directedness and flexibility. This paper describes a self-improving control system that would deal with some of these problems. The system is based on two levels of arbitration, a local level which enables the robot to survive in a particular real-world situation, and a global level which ensures that the robot reactions be consistent with the required goal. Emphasis is put on the local arbitration level: it is shown how the local priorities can be computed and learnt and some simulation results are presented.
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  • 63
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    Journal of intelligent manufacturing 9 (1998), S. 323-329 
    ISSN: 1572-8145
    Schlagwort(e): Intelligent manufacturing ; machine learning ; neuro–fuzzy systems ; genetic algorithms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Intelligence is strongly connected with learning adapting abilities, therefore such capabilities are considered as indispensable features of intelligent manufacturing systems (IMSs). A number of approaches have been described to apply different machine learning (ML) techniques for manufacturing problems, starting with rule induction in symbolic domains and pattern recognition techniques in numerical, subsymbolic domains. In recent years, artificial neural network (ANN) based learning is the dominant ML technique in manufacturing. However, mainly because of the ‘black box’ nature of ANNs, these solutions have limited industrial acceptance. In the paper, the integration of neural and fuzzy techniques is treated and former solutions are analysed. A genetic algorithm (GA) based approach is introduced to overcome problems that are experienced during manufacturing applications with other algorithms.
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  • 64
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    Journal of intelligent manufacturing 9 (1998), S. 331-338 
    ISSN: 1572-8145
    Schlagwort(e): Simulation ; modelling ; machine learning ; evolutionary algorithms ; artificial neural network
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The use of simulation technology as a tool for planning and control is of increasing significance in most fields of production. The main part of the expenditure concerning simulation analyses is the modelling of the considered production. Despite the use of modern building-block-oriented modelling technology, this modelling can often not be done by the user, but only by external experts. Against this backdrop, an adaptive simulation system is being developed by the Institute for Industrial Manufacturing and Management (IFF) at the University of Stuttgart. It independently adapts to real production processes, i.e. it learns about the interdependencies of production processes, and, in this way, supports the user in constructing and maintaining the model. In terms of information technology, the research in the field of artificial intelligence, especially in the subdomain of machine learning, is the basis for the realization of such adaptive systems.
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  • 65
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    Journal of chemical crystallography 28 (1998), S. 119-123 
    ISSN: 1572-8854
    Schlagwort(e): Azetidine ; azetine ; ring opening ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract 1-Acetyl-3-bromo-3-phenylazetidine (1), C11H12BrNO, has been synthesized and characterized by spectroscopic methods and single crystal X-ray analysis. It crystallizes in the space group P2 1/c with a = 8.633(1), b = 7.461(1), c = 17.204(1) Å, β = 98.403(7)°, V = 1096.2(2) Å3, Z = 4, D calc = 1.540 g cm−3. The azetidine ring is nearly planar since the four atoms are within ±0.039(5) Å of the mean square plane calculated for the heterocycle. The attempt to obtain a highly strained 2-azetine derivative from the above compound gave, surprisingly, 1-phenyl-2-(N-acetyl-N-formyl)-aminoethanone (2), C11H11NO3. This compound has been also characterized by spectroscopic methods and single crystal X-ray analysis. It crystallizes in the space group P212121, with a = 5.4719(3), b = 8.3205(6), c = 23.298(3) Å, V = 1060.7(2) Å3, Z = 4, D calc = 1.286 g cm−3. The aminoethanone residue is in a near planar conformation where the torsion angles are 7(2)° for N–C–C–=O and −173(2)° for N–C–C–C(Ph).
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  • 66
    Digitale Medien
    Digitale Medien
    Springer
    Constraints 3 (1998), S. 239-253 
    ISSN: 1572-9354
    Schlagwort(e): machine learning ; game playing ; spatial cognition ; extensible architectures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper describes an architecture that begins with enough general knowledge to play any board game as a novice, and then shifts its decision-making emphasis to learned, game-specific, spatially-oriented heuristics. From its playing experience, it acquires game-specific knowledge about both patterns and spatial concepts. The latter are proceduralized as learned, spatially-oriented heuristics. These heuristics represent a new level of feature aggregation that effectively focuses the program's attention. While training against an external expert, the program integrates these heuristics robustly. After training it exhibits both a new emphasis on spatially-oriented play and the ability to respond to novel situations in a spatially-oriented manner. This significantly improves performance against a variety of opponents. In addition, we address the issue of context on pattern learning. The procedures described here move toward learning spatially-oriented heuristics for autonomous programs in other spatial domains.
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  • 67
    Digitale Medien
    Digitale Medien
    Springer
    Minds and machines 8 (1998), S. 317-351 
    ISSN: 1572-8641
    Schlagwort(e): artificial intelligence ; frame problem ; causal induction ; machine learning ; logicism ; Bayesian learning ; MML
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Philosophie
    Notizen: Abstract I analyze the frame problem and its relation to other epistemological problems for artificial intelligence, such as the problem of induction, the qualification problem and the "general" AI problem. I dispute the claim that extensions to logic (default logic and circumscriptive logic) will ever offer a viable way out of the problem. In the discussion it will become clear that the original frame problem is really a fairy tale: as originally presented, and as tools for its solution are circumscribed by Pat Hayes, the problem is entertaining, but incapable of resolution. The solution to the frame problem becomes available, and even apparent, when we remove artificial restrictions on its treatment and understand the interrelation between the frame problem and the many other problems for artificial epistemology. I present the solution to the frame problem: an adequate theory and method for the machine induction of causal structure. Whereas this solution is clearly satisfactory in principle, and in practice real progress has been made in recent years in its application, its ultimate implementation is in prospect only for future generations of AI researchers.
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  • 68
    Digitale Medien
    Digitale Medien
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    Machine learning 31 (1998), S. 115-139 
    ISSN: 0885-6125
    Schlagwort(e): neural network controllers ; machine learning ; innateness ; biologically inspired robotics ; quantification in robotics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract The aim was to investigate a method of developing mobile robot controllers based on ideas about how plastic neural systems adapt to their environment by extracting regularities from the amalgamated behavior of inflexible (non-plastic) innate s ubsystems interacting with the world.Incremental bootstrapping of neural network controllers was examined. The objective was twofold. First, to develop and evaluate the use of prewired or innate robot controllers to bootstrap backpropagation learning for Multi-Layer Perceptron (MLP) controllers. Second, to develop and evaluate a new MLP controller trained on the back of another bootstrapped controller. The experimental hypothesis was that MLPs would improve on the performance of controllers used to train them. The performances of the innate and bootstrapped MLP controllers were compared in eight experiments on the tasks of avoiding obstacles and finding goals. Four quantitative measures were employed: the number of sensorimotor loops required to complete a task; the distance traveled; the mean distance from walls and obstacles; the smoothness of travel. The overall pattern of results from statistical analyses of these quantities su pported the hypothesis; the MLP controllers completed the tasks faster, smoother, and steered further from obstacles and walls than their innate teachers. In particular, a single MLP controller incrementally bootstrapped by a MLP subsumption controller was superior to the others.
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  • 69
    Digitale Medien
    Digitale Medien
    Springer
    Machine learning 30 (1998), S. 165-194 
    ISSN: 0885-6125
    Schlagwort(e): machine learning ; pattern recognition ; learning from examples ; large image databases ; data mining ; automatic cataloging ; detection of natural objects ; Magellan SAR ; JARtool ; volcanoes ; Venus ; principal components analysis ; trainable
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Dramatic improvements in sensor and image acquisition technology have created a demand for automated tools that can aid in the analysis of large image databases. We describe the development of JARtool, a trainable software system that learns to recognize volcanoes in a large data set of Venusian imagery. A machine learning approach is used because it is much easier for geologists to identify examples of volcanoes in the imagery than it is to specify domain knowledge as a set of pixel-level constraints. This approach can also provide portability to other domains without the need for explicit reprogramming; the user simply supplies the system with a new set of training examples. We show how the development of such a system requires a completely different set of skills than are required for applying machine learning to “toy world” domains. This paper discusses important aspects of the application process not commonly encountered in the “toy world,” including obtaining labeled training data, the difficulties of working with pixel data, and the automatic extraction of higher-level features.
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  • 70
    ISSN: 1572-8986
    Schlagwort(e): RF SiCl4 discharge ; mass spectrometry ; kinetics ; decomposition ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Time-resolved mass spectrometry was used for analysis of the plasma reactions in radio frequency (RF) SiCl 4 and SiCl 4 −O 2 discharges as functions of starting partial pressure and electrical power. Molecular concentrations of the reactants and products from SiCl 4 alone and with O 2 were obtained from the mass spectra and used for plotting the kinetic curves. The SiCl 4 and O 2 consumption rates were calculated from the kinetic curves and compared with results of theoretical simulation of the reaction. Direct electron impact decomposition was found to be the main pathway for pure SiCl 4 conversion. On the contrary, the consumption of SiCl 4 in the SiCl 4 +O 2 mixtures was largely chemical. The experimental macrokinetics are in agreement with a model in which oxidation is caused by the atomic oxygen.
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  • 71
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials synthesis and processing 6 (1998), S. 191-195 
    ISSN: 1573-4870
    Schlagwort(e): Transmission electron microscopy observation ; interfacial microstructure ; oxidation ; ZrC ; cubic ZrO2 ; amorphous carbon film
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Microstructure at the interface of ZrC and ZrO2 formed by oxidation of a single crystal of ZrC with 100 faces at 600°C at an oxygen pressure of 2 kPa was observed by high-resolution transmission electron microscopy and scanning electron microscopy. The ZrO2 scale was shown to consist of two subscales, zones 1 and 2. The interfacial area in zone 1 was composed of regular lattice fringes corresponding to the 111, 200, and 220 lattices of cubic ZrO2 (c-ZrO2) crystallites 2 to 10 nm in size and an amorphous phase. The growth of crystallites occurred in zone 2, which visualized the interface of zones 1 and 2. Black thin films reminiscent of zone 1 were successfully separated, which were composed of amorphous carbon in which c-ZrO2 particles 2 to 20 nm in size were included.
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  • 72
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials synthesis and processing 6 (1998), S. 335-338 
    ISSN: 1573-4870
    Schlagwort(e): PbZrO3 ; oxidation ; nonstoichiometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract This paper reports the results of work function (WF) changes of undoped PbZrO3 during subsequent isothermal oxidation and reduction experiments at 500°C in the p(O2) range between 10 and 2.1 × 104 Pa. The results, obtained during three consecutive runs, indicate that heating at 500°C leads to continuous changes of surface properties resulting in a complex WF vs. time characteristic. The WF changes during the first oxidation are determined by a p(O2)-induced structural transition. The second oxidation results in two competitive processes, such as rapid increase of oxygen non-stoichiometry followed by a structural transition. Finally, the third oxidation is determined by changes of oxygen nonstoichiometry.
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  • 73
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials synthesis and processing 6 (1998), S. 373-377 
    ISSN: 1573-4870
    Schlagwort(e): Zirconia ; oxidation ; preparation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract This paper reports surface electrical properties of zirconia studied using work function measurements in the temperature range 297–1173 K during oxidation. It was found that surface preparation procedures, such as grinding and polishing, result in a change of its reactivity with oxygen. The effects produced by the preparation can be removed during thermal treatment at 1473 K.
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  • 74
    Digitale Medien
    Digitale Medien
    Springer
    Journal of materials synthesis and processing 6 (1998), S. 407-410 
    ISSN: 1573-4870
    Schlagwort(e): CaB6 ; oxidation ; weight gain ; calcium borate ; oxidation resistance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of CaB6 powders at high temperatures was investigated. The sample oxidized at 873 to 973 K for 25 hours exhibited weight gain with increasing oxidation temperature; the oxidation proceeded in accordance with the parabolic law during the initial oxidation stage. On the other hand, the weight gain of the sample oxidized at and above 1073 K for 4 h was approximately 80%; however even if the oxidation time was prolonged, an additional weight change did not occur. Based on the results of the X-ray diffraction analysis, calcium borate (CaB4O7) was present on the surface of the sample oxidized at 1073 K. The sample showed a good oxidation resistance at 1273 to 1373 K, because the surface film of calcium borate (CaB2O4) formed by oxidation acted as an oxidation resistant layer.
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Applied intelligence 9 (1998), S. 231-243 
    ISSN: 1573-7497
    Schlagwort(e): fuzzy logic ; machine learning ; fault diagnosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper describes a fuzzy diagnostic model that contains a fast fuzzy rule generation algorithm and a priority rule based inference engine. The fuzzy diagnostic model has been implemented in a fuzzy diagnostic system for the End-of-Line test at automobile assembly plants and the implemented system has been tested extensively and its performance is presented.
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  • 76
    Digitale Medien
    Digitale Medien
    Springer
    Applied intelligence 9 (1998), S. 217-230 
    ISSN: 1573-7497
    Schlagwort(e): pattern recognition ; machine learning ; feature selection ; dimensionality reduction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract Feature selection is a problem of finding relevant features. When the number of features of a dataset is large and its number of patterns is huge, an effective method of feature selection can help in dimensionality reduction. An incremental probabilistic algorithm is designed and implemented as an alternative to the exhaustive and heuristic approaches. Theoretical analysis is given to support the idea of the probabilistic algorithm in finding an optimal or near-optimal subset of features. Experimental results suggest that (1) the probabilistic algorithm is effective in obtaining optimal/suboptimal feature subsets; (2) its incremental version expedites feature selection further when the number of patterns is large and can scale up without sacrificing the quality of selected features.
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  • 77
    Digitale Medien
    Digitale Medien
    Springer
    Applied intelligence 8 (1998), S. 33-41 
    ISSN: 1573-7497
    Schlagwort(e): genetic programming ; genetic algorithms ; computational genetics ; machine learning ; adaptive systems ; mobile robot ; robotics ; robot ; wall-following
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract This paper demonstrates the use of genetic programming (GP) for the development of mobile robot wall-following behaviors. Algorithms are developed for a simulated mobile robot that uses an array of range finders for navigation. Navigation algorithms are tested in a variety of differently shaped environments to encourage the development of robust solutions, and reduce the possibility of solutions based on memorization of a fixed set of movements. A brief introduction to GP is presented. A typical wall-following robot evolutionary cycle is analyzed, and results are presented. GP is shown to be capable of producing robust wall-following navigation algorithms that perform well in each of the test environments used.
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  • 78
    Digitale Medien
    Digitale Medien
    Springer
    Autonomous robots 5 (1998), S. 317-334 
    ISSN: 1573-7527
    Schlagwort(e): neural network controllers ; machine learning ; innateness ; biologically inspired robotics ; quantification in robotics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract The aim was to investigate a method of developing mobile robot controllers based on ideas about how plastic neural systems adapt to their environment by extracting regularities from the amalgamated behavior of inflexible (nonplastic) innate subsystems interacting with the world. Incremental bootstrapping of neural network controllers was examined. The objective was twofold. First, to develop and evaluate the use of prewired or innate robot controllers to bootstrap backpropagation learning for Multilayer Perceptron (MLP) controllers. Second, to develop and evaluate a new MLP controller trained on the back of another bootstrapped controller. The experimental hypothesis was that MLPs would improve on the performance of controllers used to train them. The performances of the innate and bootstrapped MLP controllers were compared in eight experiments on the tasks of avoiding obstacles and finding goals. Four quantitative measures were employed: the number of sensorimotor loops required to complete a task; the distance traveled; the mean distance from walls and obstacles; the smoothness of travel. The overall pattern of results from statistical analyses of these quantities supported the hypothesis; the MLP controllers completed the tasks faster, smoother, and steered further from obstacles and walls than their innate teachers. In particular, a single MLP controller incrementally bootstrapped by a MLP subsumption controller was superior to the others.
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  • 79
    ISSN: 1572-8765
    Schlagwort(e): carbonado ; diamond ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 80
    Digitale Medien
    Digitale Medien
    Springer
    Machine learning 26 (1997), S. 147-176 
    ISSN: 0885-6125
    Schlagwort(e): machine learning ; inductive logic programming ; regression ; real-valued variables ; first-order logic ; applications of machine learning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We present a new approach, called First Order Regression (FOR), to handling numerical information in Inductive Logic Programming (ILP). FOR is a combination of ILP and numerical regression. First-order logic descriptions are induced to carve out those subspaces that are amenable to numerical regression among real-valued variables. The program FORS is an implementation of this idea, where numerical regression is focused on a distinguished continuous argument of the target predicate. We show that this can be viewed as a generalisation of the usual ILP problem. Applications of FORS on several real-world data sets are described: the prediction of mutagenicity of chemicals, the modelling of liquid dynamics in a surge tank, predicting the roughness in steel grinding, finite element mesh design, and operator's skill reconstruction in electric discharge machining. A comparison of FORS' performance with previous results in these domains indicates that FORS is an effective tool for ILP applications that involve numerical data.
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  • 81
    ISSN: 1572-8412
    Schlagwort(e): archaeological typology ; ceramics ; knowledge acquisition ; machine learning ; Sudan
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Medien- und Kommunikationswissenschaften, Kommunikationsdesign
    Notizen: Abstract The authors here show that machine learning techniques can be used for designing an archaeological typology, at an early stage when the classes are not yet well defined. The program (LEGAL, LEarning with GAlois Lattice) is a machine learning system which uses a set of examples and counter-examples in order to discriminate between classes. Results show a good compatibility between the classes such as the yare defined by the system and the archaeological hypotheses.
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  • 82
    Digitale Medien
    Digitale Medien
    Springer
    Journal of intelligent and robotic systems 20 (1997), S. 251-273 
    ISSN: 1573-0409
    Schlagwort(e): robot control ; adaptive behavior ; robust intelligent control ; multi-robot systems ; machine learning ; neural networks ; genetic algorithms ; cognitive architecture.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Maschinenbau
    Notizen: Abstract The objective of this paper is to present a cognitive architecture thatutilizes three different methodologies for adaptive, robust control ofrobots behaving intelligently in a team. The robots interact within a worldof objects, and obstacles, performing tasks robustly, while improving theirperformance through learning. The adaptive control of the robots has beenachieved by a novel control system. The Tropism-based cognitive architecturefor the individual behavior of robots in a colony is demonstrated throughexperimental investigation of the robot colony. This architecture is basedon representation of the likes and dislikes of the robots. It is shown thatthe novel architecture is not only robust, but also provides the robots withintelligent adaptive behavior. This objective is achieved by utilization ofthree different techniques of neural networks, machine learning, and geneticalgorithms. Each of these methodologies are applied to the tropismarchitecture, resulting in improvements in the task performance of the robotteam, demonstrating the adaptability and robustness of the proposed controlsystem.
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  • 83
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 381-410 
    ISSN: 1573-4889
    Schlagwort(e): Ni-Base superalloys ; Astroloy ; Waspaloy ; Udimet 720 ; oxidation ; chromia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 84
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Incoloy 909 ; superalloy ; scale ; high temperature ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 85
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 47 (1997), S. 445-464 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Fe-Cr-Al alloy ; water vapor ; ESCA ; RHEED
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 86
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 47 (1997), S. 507-524 
    ISSN: 1573-4889
    Schlagwort(e): alloys ; high temperature ; oxidation ; transient state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 87
    ISSN: 1573-4889
    Schlagwort(e): high temperatures ; oxidation ; transient state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 88
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 48 (1997), S. 1-39 
    ISSN: 1573-4889
    Schlagwort(e): Ni-base ODS superalloys ; oxidation ; initial stages of oxidation ; alumina ; chromia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 89
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 48 (1997), S. 129-141 
    ISSN: 1573-4889
    Schlagwort(e): decarburization ; nickel ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 90
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; kinetics ; iron ; iron-nitride
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 91
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 201-214 
    ISSN: 1573-4889
    Schlagwort(e): titanium-aluminum alloys ; niobium ; intermetallics ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 92
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 215-224 
    ISSN: 1573-4889
    Schlagwort(e): nanocrystallization ; oxidation ; mechanism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 289-302 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; titanium ; rutile ; scale ; high temperature ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 329-345 
    ISSN: 1573-4889
    Schlagwort(e): zirconium ; X-ray diffraction ; oxidation ; phase analysis ; texture
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 357-380 
    ISSN: 1573-4889
    Schlagwort(e): chromium ; copper ; binary alloys ; two-phase alloys ; oxidation ; high temperatures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 96
    ISSN: 1573-4889
    Schlagwort(e): iron ; oxidation ; CeO2 coating ; in situ ; growth stress ; residual stress ; texture ; X ray diffraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 97
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 527-551 
    ISSN: 1573-4889
    Schlagwort(e): chloridation ; oxidation ; Fe-Cr alloys ; Ni-Cr alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 553-596 
    ISSN: 1573-4889
    Schlagwort(e): chloridation ; oxidation ; HCl ; high-temperature alloys ; high-temperature corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 99
    ISSN: 1573-4889
    Schlagwort(e): binary alloys ; oxidation ; transient state ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The initial transient stage in the oxidation of binary alloys forming scales exclusively composed of the most stable oxide is examined by means of a simplified approach which avoids the numerical integration of the diffusion equation for the transport of the metal components in the alloy. At variance with previous solutions to this problem obtained by means of numerical methods, this treatment takes into account also the effect of the gas-scale reaction at the outer surface of the oxide. The concentration of the most-reactive component at the alloy surface changes gradually with time from the initial bulk value towards the corresponding steady-state value without involving any minimum, while the overall rate of the reaction presents a gradual transition from an initial nearly linear towards final parabolic behavior.
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 247-258 
    ISSN: 1573-4889
    Schlagwort(e): Ni3Al-base alloy ; sputtering ; nanocrystalline coating ; oxidation ; scale adhesion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Isothermal and cyclic oxidation resistance at 1000°C in air were investigated for a cast Cr-containing Ni3Al-base alloy and its sputtered nanocrystalline coating. The results indicated that both the cast Ni3Al alloy and its sputtered coating exhibit excellent isothermal oxidation resistance as a result of the formation of Al2O3 scales. However, the cast alloy possesses very poor cyclic oxidation resistance because of the spallation of the initially formed Al2O3 scale during cooling and subsequent formation of NiO. On the contrary, the sputtered Ni3(AlCr) nanocrystalline coating exhibits very good cyclic oxidation resistance due to the significant improvement of the adhesion of Al2O3.
    Materialart: Digitale Medien
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