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排序方式: 共有911条查询结果,搜索用时 15 毫秒
91.
Ulrike Cress Katrin Wodzicki Martina Bientzle Andreas Lingnau 《International Journal of Computer-Supported Collaborative Learning》2011,6(2):307-321
Computer-supported collaborative learning has an unexploited potential of becoming an effective learning method for pupils
with intellectual disabilities. This paper aims at showing how some specific requirements of this target group may be met
by structuring a learning situation with the help of floor control, which restricts the opportunities of a learning dyad to act simultaneously within the learning environment. It was expected
that floor control could improve communication between pupils with intellectual disabilities by explicitly structuring and restricting activities
in the learning environment and making it necessary for the pupils to communicate. To examine if floor control really supports the collaboration process in the hypothesized way, two different versions of a CSCL environment were implemented
and compared. The results revealed improved task-related communication and a higher quality of interaction outcomes. 相似文献
92.
Christian Glaßer Katrin Herr Christian Reitwießner Stephen Travers Matthias Waldherr 《Theory of Computing Systems》2010,46(1):80-103
We investigate the complexity of equivalence problems for {∪,∩,−,+,×}-circuits computing sets of natural numbers. These problems were first introduced by Stockmeyer and Meyer (1973). We
continue this line of research and give a systematic characterization of the complexity of equivalence problems over sets
of natural numbers. Our work shows that equivalence problems capture a wide range of complexity classes like NL, C
=
L, P,Π2P, PSPACE, NEXP, and beyond. McKenzie and Wagner (2003) studied related membership problems for circuits over sets of natural numbers. Our results also have consequences for these membership problems: We provide an
improved upper bound for the case of {∪,∩,−,+,×}-circuits. 相似文献
93.
To increase the fractional energy savings achieved with solar thermal combisystems the store volume may be increased. Installation of large stores in single-family houses is, however, often limited by space constraints. In this article the influence of the store dimensions, as well as internal and external auxiliary volume configurations, are investigated for large solar water stores by annual dynamic TRNSYS simulations. The results show that store sizes up to 4 m3 may be used in solar heating systems with 30 m2 collector area. It is further shown that well-insulated stores are rather insensitive to the geometry. Stores deviating from the conventional dimensions still yield high fractional energy savings. Furthermore, the simulations show that the performance of an internal auxiliary volume configuration in most cases exceeds that of a solution with an external auxiliary unit. The practical limitations of very thin auxiliary volumes must, however, be further investigated. 相似文献
94.
Neurological complications arising from schistosomiasis are uncommon, and reports of Manson's schistosomiasis presenting as an intracerebral mass lesion are particularly rare. The authors describe the case of a 26-year-old man with a 3-month history of headaches and visual abnormalities. He had immigrated to Canada from Brazil 4 years previously. The patient's general physical and neurological examinations were unremarkable. Magnetic resonance (MR) imaging revealed an enhancing lesion with surrounding edema and mild mass effect in the right occipital lobe. A stereotactic brain biopsy demonstrated intraparenchymal granulomas surrounding Schistosoma masoni eggs. The patient's symptoms resolved following treatment with praziquantel and steroid medications; follow-up MR imaging yielded normal findings. This case demonstrates that neuroschistosomiasis should be considered when an individual presenting with an intracerebral mass has lived in a region in which this disease is endemic. 相似文献
95.
96.
Concepts for Groundwater Purification Contamination of water‐bearing strata is, in contrast to the contamination of surface waters, for most people not noticeable. However this does not lead, at least in Germany, to reduced awareness about the problem, as drinking water and groundwater are closely connected in the public’s mind. The cleanup of contaminated groundwater is generally aimed at a negligibly low or tolerable remaining risk for the subjects of the protection. The goals of the cleanup should always be considered in the light of the appropriateness of the time and effort involved and the environmental balance of cleanup measures. Otherwise there is the danger that technical environmental protection however well meant is directed against the environment, because the associated use of resources is greater than that for the protection or regeneration at which it is targeted. Different cleanup concepts are represented in the order of decreasing intensity of the technical measures. 相似文献
97.
S. M. Donovan J. D. Mackenzie C. R. Abernathy S. J. Pearton P. C. Chow J. Van Hove 《Journal of Electronic Materials》1997,26(11):1292-1296
The effects of growth temperature and nitrogen plasma biasing on the electrical and structural properties of InN grown using
electron cyclotron resonance metalorganic molecular beam epitaxy (ECR MOMBE) have been investigated. These results are compared
to those found from InN grown using a higher energy radio frequency (rf) plasma source (rf MOMBE). By varying the bias of
the nitrogen plasma or the growth temperature, it is possible to achieve smooth surface morphologies. However, biasing can
also be used to increase the mobility by a factor of two while the growth temperature has only a small effect. By contrast,
use of an rf plasma improves mobility by nearly a factor of ten. None of the growth conditions investigated were found to
significantly alter the electron concentration, which was measured to be 1−5 × 1020 cm−3. 相似文献
98.
A polytitanocarbosilane has been prepared from polycarbosilane and titanium n-butoxide.29Si MAS-NMR was used to characterize the various steps of the conversion process of the polymer into the final ceramic. The reaction of titanium butoxide with polycarbosilane introduces oxygen into the polymer that seems to play an important role in the pyrolysis process. In the first stage up to 1000 ° C, the study reveals the cleavage of Si-C bonds and the formation of SiC4-xOx units. In the second stage, above 1000 ° C, the number of Si-O bonds decreases, probably due to a carbothermal reduction process. At 1500 ° C, the product can be described as a mixture of crystalline SiC and TiC with no excess carbon. 相似文献
99.
Katrin Borcea-Pfitzmann Marit Hansen Katja Liesebach Andreas Pfitzmann Sandra Steinbrecher 《Datenschutz und Datensicherheit - DuD》2007,31(9):671-675
Interacting in the Internet, users should be empowered to use only those subsets of their personal attributes, called partial
identities, which are appropriate for the actual situation and context. Refraining from acting under few and easily linkable
partial identities is a prerequisite for trustworthy privacy. Traditionally user-controlled identity management systems primarily
support individuals interacting with organisations, but mainly ignore special needs which arise if individuals interact with
each other. To support online communities those systems have to change.
From TU Dresden: Prof. Dr. Andreas Pfitzmann, head of the privacy and security group, and the research assistants Dipl.-Inform. Katrin Borcea-Pfitzmann,
Dipl. Medien-inf. Katja Liesebach and Dipl.-Inform. Sandra Steinbrecher.
From ULD, Kiel: Dipl.-Inform. Marit Hansen, head of PET division.
Research Focus: Privacy in Identity Management and Application Design
This work was funded in part by the PRIME project which receives research funding from the European Union’s Sixth Framework
Programme and the Swiss Federal Office for Education and Science. 相似文献
100.
Limit and shakedown analysis of nozzle/cylinder intersections under internal pressure and in-plane moment loading 总被引:7,自引:0,他引:7
C. Nadarajah D. Mackenzie J.T. Boyle 《International Journal of Pressure Vessels and Piping》1996,68(3):261-272
A simple technique called the elastic compensation method developed previously by Mackenzie & Boyle is used in combination with full three-dimensional finite-element analysis to obtain limit and shakedown interaction diagrams for nozzle/cylinder intersections subject to combined internal pressure and in-plane nozzle moment loading. The results are compared with solutions from the literature and also with detailed elasto-plastic thin shell finite-element analysis. It is found that the simple elastic compensation procedure can provide good estimates of plastic failure mechanisms for complex three-dimensional structures. A detailed discussion of various issues which arose relates to finite-element modelling and the measures taken to improve the results are also documented. 相似文献