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排序方式: 共有215条查询结果,搜索用时 12 毫秒
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Hanglong Wu Heiner Friedrich Joseph P. Patterson Nico A. J. M. Sommerdijk Niels de Jonge 《Advanced materials (Deerfield Beach, Fla.)》2020,32(25):2001582
Innovations in liquid-phase electron microscopy (LP-EM) have made it possible to perform experiments at the optimized conditions needed to examine soft matter. The main obstacle is conducting experiments in such a way that electron beam radiation can be used to obtain answers for scientific questions without changing the structure and (bio)chemical processes in the sample due to the influence of the radiation. By overcoming these experimental difficulties at least partially, LP-EM has evolved into a new microscopy method with nanometer spatial resolution and sub-second temporal resolution for analysis of soft matter in materials science and biology. Both experimental design and applications of LP-EM for soft matter materials science and biological research are reviewed, and a perspective of possible future directions is given. 相似文献
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Daniel Weymann Reinhard Well Carolin von der Heide Jürgen Böttcher Heiner Flessa Wilhelmus H. M. Duijnisveld 《Nutrient Cycling in Agroecosystems》2009,85(3):299-312
Production and accumulation of the major greenhouse gas nitrous oxide (N2O) in surface groundwater might contribute to N2O emissions to the atmosphere. We report on a 15N tracer study conducted in the Fuhrberger Feld aquifer in northern Germany. A K15NO3 tracer solution (60 atom%) was applied to the surface groundwater on an 8 m2 measuring plot using 45 injection points in order to stimulate production of 15N2O by denitrification and to detect its contribution to emissions at the soil surface. Samples from the surface groundwater, from the unsaturated zone and at the soil surface were collected in regular intervals over a 72-days period. Total N2O fluxes at the soil surface were low and in a range between ?7.6 and 29.1 μg N2O-N m?2 h?1. 15N enrichment of N2O decreased considerably upwards in the profile. In the surface groundwater, we found a 15N enrichment of N2O between 13 and 42 atom%. In contrast, 15N enrichment of N2O in flux chambers at the soil surface was very low, but a detectable 15N enrichment was found at all sampling events. Fluxes of groundwater-derived 15N-N2O were very low and ranged between 0.0002 and 0.0018 kg N2O-N ha?1 year?1, indicating that indirect N2O emissions from the surface groundwater of the Fuhrberger Feld aquifer occurring via upward diffusion are hardly significant. Due to these observations we concluded that N2O dynamics at the soil–atmosphere interface is predominantly governed by topsoil parameters. However, highest 15N enrichments of N2O throughout the profile were obtained in the course of a rapid drawdown of the groundwater table. We assume that such fluctuations may enhance diffusive N2O fluxes from the surface groundwater to the atmosphere for a short time. 相似文献
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The birth of 'Dolly', the first mammal cloned from an adult donor cell, has sparked a flurry of research activities to improve cloning technology and to understand the underlying mechanism of epigenetic reprogramming of the transferred somatic cell nucleus. Especially in ruminants, somatic cell nuclear transfer (SCNT) is frequently associated with pathological changes in the foetal and placental phenotype and has significant consequences for development both before and after birth. The most critical factor is epigenetic reprogramming of the transferred somatic cell nucleus from its differentiated status into the totipotent state of the early embryo. This involves an erasure of the gene expression program of the respective donor cell and the establishment of the well-orchestrated sequence of expression of an estimated number of 10 000-12 000 genes regulating embryonic and foetal development. The following article reviews the present knowledge on the epigenetic reprogramming of the transferred somatic cell nucleus, with emphasis on DNA methylation, imprinting, X-chromosome inactivation and telomere length restoration in bovine development. Additionally, we briefly discuss other approaches towards epigenetic nuclear reprogramming, including the fusion of somatic and embryonic stem cells and the overexpression of genes crucial in the formation and maintenance of the pluripotent status. Improvements in our understanding of this dramatic epigenetic reprogramming event will be instrumental in realising the great potential of SCNT for basic biological research and for various agricultural and biomedical applications. 相似文献
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The role of collagen in bone apatite formation in the presence of hydroxyapatite nucleation inhibitors 总被引:1,自引:0,他引:1
Nudelman F Pieterse K George A Bomans PH Friedrich H Brylka LJ Hilbers PA de With G Sommerdijk NA 《Nature materials》2010,9(12):1004-1009
Bone is a composite material in which collagen fibrils form a scaffold for a highly organized arrangement of uniaxially oriented apatite crystals. In the periodic 67 nm cross-striated pattern of the collagen fibril, the less dense 40-nm-long gap zone has been implicated as the place where apatite crystals nucleate from an amorphous phase, and subsequently grow. This process is believed to be directed by highly acidic non-collagenous proteins; however, the role of the collagen matrix during bone apatite mineralization remains unknown. Here, combining nanometre-scale resolution cryogenic transmission electron microscopy and cryogenic electron tomography with molecular modelling, we show that collagen functions in synergy with inhibitors of hydroxyapatite nucleation to actively control mineralization. The positive net charge close to the C-terminal end of the collagen molecules promotes the infiltration of the fibrils with amorphous calcium phosphate (ACP). Furthermore, the clusters of charged amino acids, both in gap and overlap regions, form nucleation sites controlling the conversion of ACP into a parallel array of oriented apatite crystals. We developed a model describing the mechanisms through which the structure, supramolecular assembly and charge distribution of collagen can control mineralization in the presence of inhibitors of hydroxyapatite nucleation. 相似文献
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Membranes in medical process engineering . Synthetic membranes not only represent the essential components of an artificial kidney or an artificial lung but are also used as wound dressing and in systems for controlled release of drugs in certain long-term therapeutic measures or as part of an artificial pancreas. By far the greatest present economic significance of membranes is their use in the so-called artificial kidney. Considerable cost saving would result if patients could undertake ?home dialysis”?. This requires the development of new, simpler artificial kidneys and thus higher-performance membranes. The latest trend in ?artificial kidneys”?, the so-called method of ?hemodiafiltration”? warants special mention. The separation process is no longer effected only by diffusion but also by convection, i.e. the driving force is the pressure difference between the two sides of the membrane. This paper addresses problems encountered in the development and use of membranes in medicine, recent applications such as the controlled release of active components, or plasma separation, and demonstrates the potential of membranes in medicine. 相似文献
108.
Heiner Müller-Merbach Jochen Zowe G. Feichtinger G. Fandel F. Rücksteiner T. Gal 《OR Spectrum》1985,7(3):190-194
Ohne Zusammenfassung 相似文献
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Mechatronische Lösungen für trockenlaufende Vakuumpumpen. Mechatronic solutions for dry vacuum pumps
Heiner Ksters 《真空研究与实践》2005,17(5):274-279
Mechatronik is a combination from Mechanics and electronic and can be defined as a special view and method of engineering. The main difference compared with the traditional way of mechanical and electronic design is the other way of specification and engineering. Interfaces and specification are focused on different blocks and modules on a functional way, independent how it is realized. The results are not only new innovative solutions with better usage of the modern control possibilities. Also for the interfacing, installation and support this way of engineering give many advantages and possibilities for cost reduction. This paper shows on dry vacuum pumps and systems in the chemical and pharmaceutical industry the actual solutions which are available to use these advantages. 相似文献