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排序方式: 共有187条查询结果,搜索用时 140 毫秒
1.
Detlev Ringer 《化学,工程师,技术》1991,63(1):30-37
Multi-flow heat exchangers as soldered aluminium plate equipment – State of the art. Soldered aluminium plate heat exchangers are the most frequently used pieces of equipment for heat exchange between clean fluids in cryogenic and low temperature processes. Equipment of this type combines high flexibility in the flow arrangement, high heating surface densities (up to 1400 m2/m3), low pressure drops, and low production costs. This article provides a survey of the present state of the art of their manufacture and thermal dimensioning. In conclusion, new developments are treated. 相似文献
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An overview of the application of the photothermal technique for optical as well as thermophysical characterizations of thin films is given. The peculiarities of this technique are discussed in some detail, and selected important results are pointed out. Emphasis is placed on the influence of both residual absorption and randomly distributed inhomogeneities in thin films on their laser-damage resistance. 相似文献
4.
Annett Schwamborn Hubertina ThillmannMaria Opfermann Detlev Leutner 《Computers in human behavior》2011,27(1):89-93
This study investigated, whether learning from science texts can be enhanced by providing learners with different forms of visualizations (pictures) in addition to text. One-hundred-two 9th and 10th graders read a computer-based text on chemical processes of washing and answered questions on cognitive load (mental effort, perceived difficulty) and comprehension (retention, transfer, drawing). Instruction varied according to a 2 × 2-factorial design with ‘learner-generated pictures’ (yes, no) and ‘provided pictures’ (yes, no) as factors. Results indicate positive main effects of provided pictures on all three comprehension measures and negative main effects on both cognitive load measures. Additional analyses revealed a mediation effect of perceived difficulty on retention and transfer, that is learning with provided pictures decreased cognitive load and enhanced comprehension. Furthermore, results show a positive main effect of learner-generated pictures on drawing and mental effort, but no mediation effect. Taken together, computer-based learning with provided pictures enhances comprehension as it seems to promote active processing while reducing extraneous cognitive processing. Learners, generating pictures, however, seem to have less cognitive resources available for essential and generative processing, resulting in reduced comprehension. These results are in line with cognitive load theory, cognitive theories of multimedia learning, and generative theories of learning. 相似文献
5.
Tim Van Gestel Feng Han Doris Sebold Hans Peter Buchkremer Detlev St?ver 《Microsystem Technologies》2011,17(2):233-242
A solid oxide fuel cell (SOFC) with a thin-film yttria-stabilized zirconia (YSZ) electrolyte was developed and tested. This
novel SOFC shows a similar multilayer set-up as other current anode-supported SOFCs and is composed of a Ni/8YSZ anode, a
gas-tight 8YSZ electrolyte layer, a dense Sr-diffusion barrier layer and a LSCF cathode. To increase the power density and
lower the SOFC operating temperature, the thickness of the electrolyte layer was reduced from around 10 μm in current cells
to 1 μm, using a nanoparticle deposition method. By using the novel 1 μm electrolyte layer, the current density of our SOFC
progressed to 2.7, 2.1 and 1.6 A/cm2 at operation temperatures of 800, 700 and 650°C, respectively, and out-performs all similar cells reported to date in the
literature. An important consideration is also that cost-effective dip-coating and spin-coating methods are applied for the
fabrication of the thin-film electrolyte. Processing of 1 μm layers on the very porous anode substrate material was initially
experienced as very difficult and therefore 8YSZ nanoparticle coatings were developed and optimized on porous 8YSZ model substrates
and transferred afterwards to regular anode substrates. In this paper, the preparation of the novel SOFC is shown and its
morphology is illustrated with high resolution SEM pictures. Further, the performance in a standard SOFC test is demonstrated. 相似文献
6.
Detlev LeutnerJan L. Plass 《Computers in human behavior》1998,14(4):236
Research on learning styles and their assessment has been the focus of growing interest due to rapid advances in educational multimedia applications. As an alternative to conventional questionnaires, the VV-BOS, a computer-based instrument for direct observation of students' preference for visual or verbal learning material in an authentic learning situation, was developed. A study with 103 second language learners was conducted to assess the reliability and validity of the scale scores provided by this instrument. The visualizer/verbalizer scale scores were highly reliable. They correlated moderately with corresponding VVQ and ELSIE questionnaire scale scores. Students' learning outcome could successfully be predicted using the VV-BOS scale, but not using the questionnaire scales. The results indicate that the direct observation of students' preferential choice behavior is a promising alternative to conventional questionnaires for the assessment of individual differences in multimedia training and instruction. 相似文献
7.
Detlev F. K. Hennings Christoph Metzmacher B. Seriyati Schreinemacher 《Journal of the American Ceramic Society》2001,84(1):179-182
Hydrothermal powders of BaTiO3 and (Ba,Ca)(Ti,Zr)O3 contain large amounts of protons in the oxygen sublattice. The proton defects are compensated by vacancies on metal sites. When the powder is annealed, water is released and the point defects disappear in the temperature range of 100°–600°C. Metal and oxygen vacancies combine to small nanometer-sized intragranular pores. At temperatures of >800°C, the intragranular pores migrate to the grain boundaries and disappear. In multilayer ceramic capacitors that have been prepared from hydrothermal powders, the intragranular pores are preferentially collected at the inner electrodes, which results in "bloating," cracks, and delamination. 相似文献
8.
Robert Mücke Norbert H. Menzler Hans Peter Buchkremer Detlev Stöver 《Journal of the American Ceramic Society》2009,92(S1):S95-S102
High-performance solid oxide fuel cells require a thin and gas-tight electrolyte membrane that must be coated on a porous and relatively rough support. A pretreatment of the delivered submicronmeter electrolyte powder of 8 mol%-yttria-stabilized zirconia (8YSZ) yielded a reduced sintering mismatch between the anode substrate made from NiO/8YSZ and the electrolyte coating. Furthermore, it also enhanced the powder packing inside the green film. Constrained sintering usually leads to inadequate film density and an unfavorable pore deformation and orientation. It was demonstrated that these limitations can be resolved by using a coshrinking substrate in a planar cell design. Relative densities of >97% were achieved, which are higher than those for free-standing layers. Additionally, the camber behavior was investigated in dependence of the temperature program with and without gravity effects, giving an overall suggestion for the cofiring parameters of the electrolyte. 相似文献
9.
Clausnitzer T Limpert J Zöllner K Zellmer H Fuchs HJ Kley EB Tünnermann A Jupé M Ristau D 《Applied optics》2003,42(34):6934-6938
We report on highly efficient transmission gratings in fused silica with a grating period of 800 nm generated by electron-beam lithography. At a wavelength of 1060 nm, 95% diffraction efficiency is achieved under Littrow conditions. The damage threshold, extremely enhanced compared with conventional gold-coated diffraction gratings, makes these gratings the key elements in high average power (>100 W) femtosecond fiber chirped-pulse amplification systems. 相似文献
10.
Singer Philipp; Boison Detlev; M?hler Hanns; Feldon Joram; Yee Benjamin K. 《Canadian Metallurgical Quarterly》2007,121(5):815
Selective deletion of glycine transporter 1 (GlyT1) in forebrain neurons enhances N-methyl-D-aspartate receptor (NMDAR)-dependent neurotransmission and facilitates associative learning. These effects are attributable to increases in extracellular glycine availability in forebrain neurons due to reduced glycine re-uptake. Using a forebrain- and neuron-specific GlyT1-knockout mouse line (CamKIIαCre; GlyT1tm1.2fl/fI), the authors investigated whether this molecular intervention can affect recognition memory. In a spontaneous object recognition memory test, enhanced preference for a novel object was demonstrated in mutant mice relative to littermate control subjects at a retention interval of 2 hr, but not at 2 min. Furthermore, mutants were responsive to a switch in the relative spatial positions of objects, whereas control subjects were not. These potential procognitive effects were demonstrated against a lack of difference in contextual novelty detection: Mutant and control subjects showed equivalent preference for a novel over a familiar context. Results therefore extend the possible range of potential promnesic effects of specific forebrain neuronal GlyT1 deletion from associative learning to recognition memory and further support the possibility that mnemonic functions can be enhanced by reducing GlyT1 function. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献