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21.
H.-J. Gehrhardt J. Eisenbltter P. Jax H.-J. Maier E. Waschkies 《Nuclear Engineering and Design》1987,102(3)
The investigations were aimed at demonstrating the state of the art of acoustic emission testing (AET) of reactor pressure vessels. The object under investigation was the large reactor pressure vessel of the MPA in Stuttgart, a boiling-water reactor pressure vessel, which was provided with a multitude of flaws in weld seams and in the base material. Six hydrostatic tests approximately up to the working pressure of a boiling-water reactor (71 bar) were carried out. In addition to the global multichannel locating technique, also local monitoring techniques were applied. Global location permitted a large number of different indications to be detected simultaneously. Not all of the known flaws did, however, show the expected number of AE events. On the other hand, it was possible to detect flaws previously unknown to the AE staff in some weld seams; these indications were confirmed by nondestructive testing. It was demonstrated that the locating accuracy of local monitoring using signal analysis was improved by a factor of 20 to 30 compared to global monitoring. 相似文献
22.
John W. Elmer Joe Wong Thorsten Ressler 《Metallurgical and Materials Transactions A》1998,29(11):2761-2773
Spatially resolved X-ray diffraction (SRXRD) is used to map the α → β → α phase transformation in the heat-affected zone (HAZ) of commercially pure titanium gas tungsten arc welds. In situ SRXRD experiments were conducted using a 180-μm-diameter X-ray beam at the Stanford Synchrotron Radiation Laboratory (SSRL)
(Stanford, CA) to probe the phases present in the HAZ of a 1.9 kW weld moving at 1.1 mm/s. Results of sequential linear X-ray
diffraction scans made perpendicular to the weld direction were combined to construct a phase transformation map around the
liquid weld pool. This map identifies six HAZ microstructural regions between the liquid weld pool and the base metal: (1)
α-Ti that is undergoing annealing and recrystallization; (2) completely recrystallized α-Ti; (3) partially transformed α-Ti, where α-Ti and β-Ti coexist; (4) single-phase β-Ti; (5) back-transformed α-Ti; and (6) recrystallized α-Ti plus back-transformed α-Ti. Although the microstructure consisted predominantly of α-Ti, both prior to and after the weld, the crystallographically textured starting material was altered during welding to produce
different α-Ti textures within the resulting HAZ. Based on the travel speed of the weld, the α → β transformation was measured to take 1.83 seconds during heating, while the β → α transformation was measured to take 0.91 seconds during cooling. The α → β transformation was characterized to be dominated by long-range diffusional growth on the leading (heating) side of the weld,
while the β → α transformation was characterized to be predominantly massive on the trailing (cooling) side of the weld, with a massive growth
rate on the order of 100 μm/s. 相似文献
23.
Dr. Christoph Goebel Prof.?Dr. Hans-Arno Jacobsen Victor del Razo Mag.? Christoph Doblander Dipl.-Ing. Jose Rivera Dipl-Inform.?Wirt Jens Ilg Dr. Christoph Flath Prof.?Dr. Hartmut Schmeck Prof.?Dr. Christof Weinhardt Dipl-Inform. Daniel Pathmaperuma Prof.?Dr. Dr.?h.?c. Hans-Jürgen Appelrath Prof.?Dr. Michael Sonnenschein Prof.?Dr. Sebastian Lehnhoff Prof.?Dr. Oliver Kramer Prof.?Dr. Thorsten Staake Prof.?Dr. Elgar Fleisch Prof.?Dr. Dirk Neumann Prof.?Dr. Jens Strüker Dr. Koray Erek Prof.?Dr. Rüdiger Zarnekow Dr. Holger Ziekow Prof.?Dr. J?rg L?ssig 《WIRTSCHAFTSINFORMATIK》2014,56(1):31-39
Due to the increasing importance of producing and consuming energy more sustainably, Energy Informatics (EI) has evolved into a thriving research area within the CS/IS community. The article attempts to characterize this young and highly dynamic field of research by describing current EI research topics and methods and provides an outlook of how the field might evolve in the future. It is shown that two general research questions have received the most attention so far and are likely to dominate the EI research agenda in the coming years: How to leverage information and communication technology (ICT) to (1) improve energy efficiency, and (2) to integrate decentralized renewable energy sources into the power grid. Selected EI streams are reviewed, highlighting how the respective research questions are broken down into specific research projects and how EI researchers have made contributions based on their individual academic background. 相似文献
24.
Funke SA Otte N Eggert T Bocola M Jaeger KE Thiel W 《Protein engineering, design & selection : PEDS》2005,18(11):509-514
Chiral compounds can be produced efficiently by using biocatalysts. However, wild-type enzymes often do not meet the requirements of a production process, making optimization by rational design or directed evolution necessary. Here, we studied the lipase-catalyzed hydrolysis of the model substrate 1-(2-naphthyl)ethyl acetate both theoretically and experimentally. We found that a computational equivalent of alanine scanning mutagenesis based on QM/MM methodology can be applied to identify amino acid positions important for the activity of the enzyme. The theoretical results are consistent with concomitant experimental work using complete saturation mutagenesis and high-throughput screening of the target biocatalyst, a lipase from Bacillus subtilis. Both QM/MM-based calculations and molecular biology experiments identify histidine 76 as a residue that strongly affects the catalytic activity. The experiments demonstrate its important influence on enantioselectivity. 相似文献
25.
A commercial lithium aluminosilicate glass-ceramic material is investigated by high-resolution transmission electron microscopy after different heat treatments. Evidence is presented that epitaxy of β-quartz crystals on ZrTiO4 -type crystallites is the critical step initiating silicate crystallization. 相似文献
26.
Gerhard Maier Vendula Knopfova Brigitte Voit Pham Huu Ly Bui Tien Dung Do Bich Thanh 《大分子材料与工程》2004,289(10):927-932
Summary: Segmented block copolymers, consisting of non‐polar soft segments from hydroxyl‐terminated liquid natural rubber (HTNR) and polar hard segments from α,ω‐diisocyanato telechelics obtained by “criss‐cross”‐cycloaddition, have been synthesized. The block copolymer formation took place under relatively mild reaction conditions at 80 °C in dichloroethane in the presence of dibutyltin dilaurate as a catalyst. The resulting block copolymers were characterized by spectroscopic techniques (1H NMR, FTIR, UV‐vis spectroscopy) as well as GPC for molar mass determination. The block copolymers were compression molded in a hot stage press, and the resulting samples were characterized by DSC and stress‐strain measurement. The solubility and phase morphology of the materials have also been studied.
27.
Ressler Thorsten Wienold Julia Jentoft Rolf E. Neisius Thomas Günter Marco M. 《Topics in Catalysis》2002,18(1-2):45-52
The potentials of X-ray absorption spectroscopy (XAS) (quantitative phase composition and average valence together with a short-range order structure analysis) combined with a time-resolution in the second range make time-resolved (TR-) XAS a powerful tool for investigating the reactivity of solids in catalysis and solid-state chemistry. General aspects of TR-XAS investigations are discussed (i.e., instrumentation, data analysis). In addition, some experiments illustrate how the kinetics of solid-state reactions in heterogeneous catalysis can be elucidated from TR-XAS studies. 相似文献
28.
Three examples are revisited in which the reaction rate could be reliably correlated with point defect chemistry highlighting
the role of point defects as acid–base active centers. In the case of dehydrohalogenation of tertiary butyl chloride, AgCl
becomes increasingly active as heterogeneous catalyst, if AgCl is homogeneously or heterogeneously doped. By such a procedure
the silver vacancy concentration is adequately increased. The oxygen incorporation into SrTiO3 offers an example in which the surface mechanism in terms of adsorbed species, oxygen vacancies and electronic centers has
been elucidated. Appropriate surface coatings give rise to significant catalytic effects. Increasing iron (acceptor) doping
not only changes the point defect chemistry but also the nature of the rate determining step. Lastly, the electrocatalytic
function of Sr-doped LaMnO3 is considered as regards oxygen reduction reaction and O2− incorporation into Y-doped ZrO2 in the context of solid oxide fuel cells. Again the defect chemistry is of prime importance for the reaction rate. 相似文献
29.
Joachim Maier 《Journal of the American Ceramic Society》1993,76(5):1228-1232
The tracer diffusion coefficient is analyzed for the case in which internal ionization equilibria have to be considered, using the concept of conservative ensembles. The relationships of the tracer diffusion coefficient with other phenome-nological parameters, viz., the chemical diffusion coefficient and the diffusion coefficient derived from the ionic conductivity, as well as with the defect diffusivities are given. The importance of mobile partially ionized or neutral defects is highlighted. In this respect the formulation of the tracer diffusion as an ambipolar diffusion of the different isotopes is helpful. 相似文献
30.
As the number of messages and social relationships embedded in social networking sites (SNS) increases, the amount of social information demanding a reaction from individuals increases as well. We observe that, as a consequence, SNS users feel they are giving too much social support to other SNS users. Drawing on social support theory (SST), we call this negative association with SNS usage ‘social overload’ and develop a latent variable to measure it. We then identify the theoretical antecedents and consequences of social overload and evaluate the social overload model empirically using interviews with 12 and a survey of 571 Facebook users. The results show that extent of usage, number of friends, subjective social support norms, and type of relationship (online-only vs offline friends) are factors that directly contribute to social overload while age has only an indirect effect. The psychological and behavioral consequences of social overload include feelings of SNS exhaustion by users, low levels of user satisfaction, and a high intention to reduce or even stop using SNS. The resulting theoretical implications for SST and SNS acceptance research are discussed and practical implications for organizations, SNS providers, and SNS users are drawn. 相似文献