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排序方式: 共有750条查询结果,搜索用时 15 毫秒
681.
In this paper analytical evidence on crystal structure and hydration behaviour of C3A solid solutions with MgO, SiO2, Fe2O3, Na2O and K2O is given. Samples were prepared using an innovative sol-gel process as precursor, examined by X-ray powder diffraction, infra-red spectroscopy and the crystal structure was refined by the Rietveld method. A significant shift of lattice parameters was found for C3A solid solutions with SiO2, Fe2O3 or Na2O but only minor changes were detected for K2O. The hydration of C3A solid solutions in the absence of CaSO4 was accelerated for samples doped with SiO2 or K2O and it was retarded in the case of MgO, Fe2O3 or Na2O. The hydration in the presence of CaSO4 was accelerated when C3A was doped with K2O or Na2O, whereas Fe2O3 strongly retarded the hydration. The doping with SiO2 nearly had no influence on the hydration, the effect of MgO was not straight forward. 相似文献
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685.
Dietmar Gerteisen 《Journal of Applied Electrochemistry》2007,37(12):1447-1454
This work presents a new concept for realising a reference electrode configuration in a PEM fuel cell by means of laser ablation.
The laser beam is used to evaporate a small part of the electrode of a catalyst-coated membrane (CCM) to isolate the reference
electrode from the active catalyst layer. This method enables the simultaneous ablation of the electrodes on both sides of
the CCM because the membrane is transparent for the laser beam. Therefore, a smooth electrode edge without electrode misalignment
can be realised. A test fuel cell was constructed which together with the ablated CCM enables the separation of the total
cell losses during operation into the cathode, anode and membrane overpotentials in PEFC as well as in DMFC mode. The methanol
tolerance of a selenium-modified ruthenium-based catalyst (RuSe
x
) was investigated under real fuel cell conditions by measuring polarisation curves, electrochemical impedance spectroscopy
(EIS) and current interrupt measurements (CI). 相似文献
686.
Markus Dietmar Schofer Ulrich Boudriot Sarah Bockelmann Andreas Walz Joachim Heinz Wendorff Andreas Greiner Jürgen Rudolf Josef Paletta Susanne Fuchs-Winkelmann 《Journal of materials science. Materials in medicine》2009,20(7):1535-1540
The aim of this study was to functionalize synthetic poly-(l-lactic) (PLLA) nanofibers by direct incorporation of cRGD, in order to promote adhesion, growth and osteogenic differentiation
of human mesenchymal stem cells (hMSC) in vitro. The cRGD was incorporated into PLLA nanofibers either by emulsion [PLLA-cRGD
(d)] or suspension [PLLA-cRGD (s)]. Matrices were seeded with hMSC and cultivated over a period of 28 days under growth conditions
and analyzed during the course. Although the mode of incorporation resulted in different distributions of the RGD peptide,
it had no impact on the fiber characteristics when compared to corresponding unblended PLLA control fibers. However, hMSC
showed better adherence on PLLA-cRGD (d). Nevertheless, this advantage was not reflected during the course of cultivation.
Furthermore, the PLLA-cRGD (s) fibers mediated the osteogenic potential of collagen (determined as the expression and deposition
of collagen and osteocalcin) to some extent. Further studies are needed in order to optimize the RGD distribution and concentration. 相似文献
687.
Yefang Zhou Dietmar W Hutmacher Sae‐Lim Varawan Tit Meng Lim 《Polymer International》2007,56(3):333-342
The filling of bone defects in load‐bearing areas requires scaffolds possessing physical properties that are in the range of those of the host bone. In this report, composite scaffolds comprising medical‐grade polycaprolactone and tricalcium phosphate (mPCL‐TCP) (80:20), which have been designed for load‐bearing applications, are characterized and compared with mPCL scaffolds, using in vitro studies. The composite scaffolds exhibited improved hydrophilicity, compressive modulus and strength. Human alveolar osteoblasts (AOs) grown on the composite achieved higher seeding efficiencies and more uniform distribution when compared with mPCL preparations alone. AOs demonstrated better proliferation, denser multilayered cell‐sheets and showed earlier expression of bone matrix‐related proteins on the composite than on mPCL during 28 days in vitro culture. The calcium content in the media decreased in both scaffold/cell constructs. Alkaline phosphatase activity increased significantly in mPCL matrices after osteogenic induction but no distinct change was observed in the composite. Osteocalcin expression was down‐regulated by induction in the composite but was up‐regulated in mPCL at both RNA and protein level. Immuno‐reactive signals for osteopontin and collagen type I, in combination with mineral nodules were found to be stronger in mPCL‐TCP scaffolds. We conclude that the composite scaffolds were more hydrophilic and had improved mechanical properties over mPCL scaffolds. Moreover, the primary AOs achieved better cell proliferation, and showed earlier and different matrix protein expression patterns on the composite scaffolds than on the mPCL scaffolds. Copyright © 2006 Society of Chemical Industry 相似文献
688.
689.
Dietmar Vollbrecht 《化学,工程师,技术》1998,70(6):696-704
Solid State Fermentation-Bioreactors – Part 1: Stationary Types . After World War II, solid state fermentations (SSF) in automated facilities developed rapidly in East Asia countries, especially Japan, to achieve a present annual market volume of about $ eight billion. In contrast, SSF, after having been introduced in Western countries at the onset of this century, became almost completely neglected. The comparative ease of running SSF bioreactors and in particular their low processing costs and considerably higher yields in comparison with submerged fermentation (STF) suggest that this technology might have great economic importance in producing food and pharmaceutically valuable substances such as antibiotics, anti-carcinogenic substances, antioxidants, flavors, fragrances, health foods, hypocholesterinemic agents, pigments, starter cultures, protein-enriched feed, thrombolytic enzymes, vasoactive agents, vitamins etc. 相似文献
690.
For the EPR an improved defence-in-depth concept is applied. In an evolutionary way, accident control is developed from existing French and German PWR designs, thereby achieving a high safety level quantified by probabilistic safety assessment. Independent of that, severe accidents are considered in the design. By a robust containment and severe accident mitigation measures, the need for offsite emergency response actions (population evacuation or relocation) is restricted to the immediate plant vicinity. This paper gives an overview of the features introduced for, and the analyses correlated to, the dedicated primary depressurization, melt–coolant interaction, melt stabilization, hydrogen control, and containment heat removal. 相似文献