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排序方式: 共有820条查询结果,搜索用时 15 毫秒
11.
In earlier work, we have observed discrepancies relating to the early hydration of calcium aluminate cement (CAC) when comparing data from heat flow calorimetry of CAC paste with results from mortar strength tests using the crushing method. Here, we investigated on this phenomenon and found that the sand which is used as a filler exerts a major influence on CAC hydration resulting in acceleration. Furthermore, in particular fine filler materials such as, for example, microsilica, fine limestone powder, and especially α- and γ-Al2O3 also produced a strong hydration accelerating effect which is dependent on their specific surface area. The mechanism underlying the acceleration is that under alkaline conditions their negative surface charge attracts calcium ions as was confirmed via inductively coupled plasma atomic emission measurements. Such a layer generates favourable conditions for the nucleation of CAC hydration products (C-A-H phases). The resulting crystalline hydrates which form on the surface of the filler particles submerged in CAC cement pore solution were visualized via SEM imaging. This way, specifically selected fillers can significantly accelerate CAC hydration and save precious lithium salts which are commonly used to boost the early strength of CAC. 相似文献
12.
Sacrificial etching is one of the most important process steps in micro-electro-mechanical systems technology, since it enables
the generation of free-standing structures. These structures are often the main part of micro-mechanical devices, intended
to sense or induce a mechanical movement. The etching process transforms an initial multi-segmented geometry and depends on
material properties and several process conditions. One of the crucial issues for etching is the etching selectivity on different
materials. The major task for the simulation is to give an answer, how sacrificial layer surfaces regress in time under the
influence of process parameters and to which magnitude surrounding material segments are affected by the etching process.
For this purpose we have developed a fully three-dimensional topography simulation tool, Etcher-Topo3D, which is capable to
deal with realistic process conditions. The main concept is demonstrated in this work. During simulation the topography of
the initial multi-segment geometry is changed which is handled by a level-set algorithm. After a simulation is finished, the
level-set representation has usually to be converted back to a mesh representation to enable further analysis. To illustrate
the main features of our simulation tool several examples of MEMS structures with a sacrificial layer are presented. 相似文献
13.
Caroline Schulten Hans M. Tensi Johann Högerl 《JOM Journal of the Minerals, Metals and Materials Society》1996,48(5):57-59
Chinese TLV-bronze mirrors dating to the Han dynasty (206 B.C.-220 A.D.) were popular objects of everyday life as well as highly esteemed works of art. The decorated back of the mirror characterizes the culture of this period as well as the excellent early Chinese casting techniques. 相似文献
14.
Redaktion: Johann Bizer 《Datenschutz und Datensicherheit - DuD》2011,35(6):422-429
DuD Recht
DuD Recht 相似文献15.
Dimitra?Giannakopoulou David?H.?Bushnell Johann?SchumannEmail author Heinz?Erzberger Karen?Heere 《Annals of Mathematics and Artificial Intelligence》2011,63(1):5-30
In order to address the rapidly increasing load of air traffic operations, innovative algorithms and software systems must
be developed for the next generation air traffic control. Extensive verification of such novel algorithms is key for their
adoption by industry. Separation assurance algorithms aim at predicting if two aircraft will get closer to each other than
a minimum safe distance; if loss of separation is predicted, they also propose a change of course for the aircraft to resolve
this potential conflict. In this paper, we report on our work towards developing an advanced testing framework for separation
assurance. Our framework supports automated test case generation and testing, and defines test oracles that capture algorithm
requirements. We discuss three different approaches to test-case generation, their application to a separation assurance prototype,
and their respective strengths and weaknesses. We also present an approach for statistical analysis of the large numbers of
test results obtained from our framework. 相似文献
16.
Julia Mueller Katja Hutter Johann Fueller Kurt Matzler 《Information Systems Journal》2011,21(6):479-501
Virtual worlds, as electronic environments where individuals can interact in a realistic manner in form of avatars, are increasingly used by gamers, consumers and employees. Therefore, they provide opportunities for reinventing business processes. Especially, effective knowledge management (KM) requires the use of appropriate information and communication technology (ICT) as well as social interaction. Emerging virtual worlds enable new ways to support knowledge and knowing processes because these virtual environments consider social aspects that are necessary for knowledge creating and knowledge sharing processes. Thus, collaboration in virtual worlds resembles real‐life activities. In this paper, we shed light on the use of Second Life (SL) as a KM platform in a real‐life setting. To explore the potential and current usage of virtual worlds for knowledge and knowing activities, we conducted a qualitative study at IBM. We interviewed IBM employees belonging to a special workgroup called ‘Web 2.0/virtual worlds’ in order to gain experience in generating and exchanging knowledge by virtually collaborating and interacting. Our results show that virtual worlds – if they are able to overcome problems like platform stability, user interface or security issues – bear the potential to serve as a KM platform. They facilitate global and simultaneous interaction, create a common context for collaboration, combine different tools for communication and enhance knowledge and knowing processes. 相似文献
17.
As research in Computer-Supported Collaborative Learning (CSCL) expands its understanding of joint knowledge building, new perspectives on how social reality is constructed become necessary. Our research concentrates on the longitudinal or diachronic trajectories of Virtual Math Teams (VMT) at The Math Forum, an online community supporting mathematical inquiry. We investigate how these virtual teams constitute themselves while engaged in building collaborative knowledge. We describe as well, through the lens of positioning theory, the interactional activities that allow participants to situate themselves, others, and their collective knowledge resources over time. Our analysis suggests that positioning work is central to constructing a sustained problem space and illustrates how the configurations of positions and resources that co-participants put forward through interaction might change across a team’s trajectory. These changes constitute and are sensitive to the participants’ evolving reasoning routines and other forms of joint participation uniquely related knowledge building. In addition, we show that the VMT activity system affords participants a level of disciplinary engagement which is partly illustrated by active engagement in positioning work. Finally, we suggest that an interactional approach to roles and participation provides a fruitful framework for researchers, designers, and practitioners interested in understanding and creating engaging CSCL interactions. 相似文献
18.
Jonathan Ollar Charles Mortished Royston Jones Johann Sienz Vassili Toropov 《Structural and Multidisciplinary Optimization》2017,55(6):2029-2044
In this work a two step approach to efficiently carrying out hyper parameter optimisation, required for building kriging and gradient enhanced kriging metamodels, is presented. The suggested approach makes use of an initial line search along the hyper-diagonal of the design space in order to find a suitable starting point for a subsequent gradient based optimisation algorithm. During the optimisation an upper bound constraint is imposed on the condition number of the correlation matrix in order to keep it from being ill conditioned. Partial derivatives of both the condensed log likelihood function and the condition number are obtained using the adjoint method, the latter has been derived in this work. The approach is tested on a number of analytical examples and comparisons are made to other optimisation approaches. Finally the approach is used to construct metamodels for a finite element model of an aircraft wing box comprising of 126 thickness design variables and is then compared with a sub-set of the other optimisation approaches. 相似文献
19.
Johann Márquez-Barja Carlos T. Calafate Juan-Carlos Cano Pietro Manzoni 《Computer Communications》2011,34(8):985-997
Wireless technologies, under the “Anywhere, Anytime” paradigm, offer users the promise of being always attached to the network. Mobile devices enabled with multiple wireless technologies make possible to maintain seamless connectivity in highly dynamic scenarios such as vehicular networks (VNs), switching from one wireless network to another by using vertical handover techniques (VHO). In this paper we present an overview of VHO techniques, along with the main algorithms, protocols and tools proposed in the literature. In addition we suggest the most appropriate VHO techniques to efficiently communicate in VN environments considering the particular characteristics of this type of networks. 相似文献
20.
Huth J Buchholz M Kraus JM Mølhave K Gradinaru C v Wichert G Gress TM Neumann H Kestler HA 《Computer methods and programs in biomedicine》2011,104(2):227-234
The direct observation of cells over time using time-lapse microscopy can provide deep insights into many important biological processes. Reliable analyses of motility, proliferation, invasive potential or mortality of cells are essential to many studies involving live cell imaging and can aid in biomarker discovery and diagnostic decisions. Given the vast amount of image- and time-series data produced by modern microscopes, automated analysis is a key feature to capitalize the potential of time-lapse imaging devices. To provide fast and reproducible analyses of multiple aspects of cell behaviour, we developed TimeLapseAnalyzer. Apart from general purpose image enhancements and segmentation procedures, this extensible, self-contained, modular cross-platform package provides dedicated modalities for fast and reliable analysis of multi-target cell tracking, scratch wound healing analysis, cell counting and tube formation analysis in high throughput screening of live-cell experiments. TimeLapseAnalyzer is freely available (MATLAB, Open Source) at http://www.informatik.uni-ulm.de/ni/mitarbeiter/HKestler/tla. 相似文献