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  • 1
    ISSN: 0375-9474
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Weed research 36 (1996), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Bud-sprouting dynamics, sprouting base temperature and reserve mobilization of rhizomes and stolons of Cynodon dactylon (L.) Pers. were characterized in a laboratory experiment under dark conditions. In addition, the dynamics of sprout emergence were determined during 2 years under field conditions. In the laboratory experiment, buds from the vegetative structures did not sprout at temperatures below 7^C. The rate of sprouting increased with temperature within the range 11–33^C, and a base temperature of 7.71^C was determined for bud sprouting of rhizome and stolons of the weed. An exponential model is proposed relating the percentage of sprout emergence in the field to accumulated thermal units, calculated as the sum of the daily mean air temperature above the base temperature of bud sprouting. This model satisfactorily predicted the dynamics of C. dactylon sprout emergence in sunflower (Helianthus annuus L.) crop fields. The efficiency of carbohydrate reserve use during sprout growth was highly dependent on temperature and type of vegetative structure The efficiency was maximum at 20^C and was higher for rhizomes than for stolons. The main factors influencing bud sprouting and early weed establishment are discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Infrared Physics 31 (1991), S. 167-171 
    ISSN: 0020-0891
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 9 (1990), S. 101-112 
    ISSN: 1573-4862
    Keywords: Boundary integral equations ; scattering ; elastic ; acoustic ; ultrasonic immersion scanning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The boundary integral equation method is applied to a class of time-harmonic acoustic scattering problems where the bounded elastic scatterer is submerged in a fluid. An exact mathematical model is presented for a finite scatterer with a closed surface, where the surface integral equations are exclusively used to represent the fluid-solid or acoustic-elastic interaction of the scattering process. The numerical procedure involves application of point collocation with quadratic isoparametric approximations that reduce the integral equations to a discrete set of complex linear algebraic equations. Examples emphasize the potential of the method to solve three-dimensional problems of practical interest. Limitations of the formulations and the extension to the case of a semi-infinite plane and curved fluid-solid interface are discussed in the latter part of the paper.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-4889
    Keywords: internal oxidation ; carburization ; computer simulation ; finite-difference technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A computer-based method is used to simulate the process of penetration of a foreign element (e.g., oxygen) into an alloy connected with internal precipitation of a compound of this element with a solute in the alloy. The method employed is based on the solution of the differential equations corresponding to this high-temperature corrosion phenomenon with the help of the finite-difference technique. To demonstrate the possibilities of the calculation method, various cases were treated which differ especially regarding the thermodynamic stability of the internal precipitates. The calculated concentration profiles and penetration depths obtained are reported and discussed. In the case of internal precipitates of high stability, the results are compared with the approaches derived in the literature for internal oxidation and are used to determine the parameter ranges in which the analytical equations apply. The results obtained for the case of a less-stable compound is used to illustrate the influence of the solubility product on the concentration profiles.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Oxidation of metals 43 (1995), S. 527-542 
    ISSN: 1573-4889
    Keywords: Co−Nb alloys ; high temperature ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of two Co−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H2−CO2 mixtures providing an oxygen pressure of 10−24 atm at 600°C and 10−20 atm at 700 and 800°C, below the dissociation pressure of cobalt oxide. At 600 and 700°C both alloys showed only a region of internal oxidation composed, of a mixture of alpha cobalt and of niobium oxides (NbO2 and Nb2O5) and at 700°C also the double oxide CoNb2O6, which formed from the Nb-rich Co3Nb phase. No Nb-depleted layer formed in the alloy at the interface with the region of internal oxidation at these temperatures. Upon oxidation at 800°C a transition between internal and external oxidation of niobium was observed, especially for Co−30Nb. This corrosion mode is associated with the development of a single-phase, Nb-depleted region at the surface of the alloy. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in cobalt and to the relation between the microstructures of the alloys and of the scales.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oxidation of metals 43 (1995), S. 561-579 
    ISSN: 1573-4889
    Keywords: Fe−Nb alloys ; high temperature ; corrosion ; low oxygen pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of two Fe−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800°C under low oxygen pressures, similar to those prevailing in environments of the coal-gasification type. The reaction produced only an internal oxidation of niobium to form two niobium oxides (NbO2 and Nb2O5) and in some cases a double Fe−Nb oxide. The kinetics of this reaction were very slow at 600°C but rather fast at 700 and 800°C. A peculiar feature of the internal oxidation of these alloys is that the distribution of the internal oxides follows closely that of the Nb-rich phase in the original two-phase alloys. This behavior, as well as the lack of formation of external scales of niobium oxides, is mainly a result of the limited solubility of niobium in iron and of the consequent presence of two metal phases in the alloys.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Oxidation of metals 44 (1995), S. 399-415 
    ISSN: 1573-4889
    Keywords: Ni−Nb alloys ; high temperature ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of two Ni−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H2−CO2 mixtures providing an oxygen pressure of 10−24 atm at 600° C and 10−20 atm O2 at 700 and 800° C, these pressures being less than the dissociation pressure of nickel oxide. The scales formed on both alloys at 600 and 700° C show only a region of internal oxidation composed of a mixture of alpha nickel and niobium oxides (Nb2O5 or/and NbO2), which formed from both the metal phases present, i.e., Ni8Nb and Ni3Nb. Only small, or even no, Nb depletion was observed in the alloys close to the interface with the zone of internal oxidation at these temperatures. On the contrary, samples of both alloys corroded at 800° C produced a continuous external scale of niobium oxides without internal oxidation. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in nickel.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Oxidation of metals 50 (1998), S. 71-88 
    ISSN: 1573-4889
    Keywords: OXIDATION ; Ti3Al-Nb ; COATINGS ; SPUTTERED NiCrAlY ; ION-PLATED TIN
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A single sputtered NiCrAlY coating and a complexcoating of inner ion-plated TiN and outer sputteredNiCrAlY were prepared on the intermetallic compoundTi3Al-Nb. Their oxidation behavior wasexamined at 850, 900, and 950°C in air by thermalgravimetry combined with XRD, SEM, and EDAX. The resultsshowed that Ti3Al-Nb followed approximatelyparabolic oxi dation, forming an outer thinAl2O3-rich scale and an inner TiO2-rich layer doped withNb at the three temperatures. The TiO2-richlayer doped with Nb dominated the oxidation reaction.The single NiCrAlY coating did not follow parabolicoxidation exactly at 850 and 950°C, but oxidizedapproximately in a parabolic manner, because theinstantaneous parabolic constants changed slightly withtime. Besides the Al2O3 scale,TiO2 formed from the coating surface at the coating-substrate interface. Thedeterioration of the coating accelerated with increasingtemperature. The NiCrAlY-TiN coating showed two-stageparabolic oxidation at 850 and 900°C, and anapproximate parabolic oxidation at 950°C. The TiN layerwas effective as a barrier to inhibit coating-alloyinterdiffusion.
    Type of Medium: Electronic Resource
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