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排序方式: 共有1752条查询结果,搜索用时 31 毫秒
51.
Gabriel Rosser Ruth E. Baker Judith P. Armitage Alexander G. Fletcher 《Journal of the Royal Society Interface》2014,11(97)
Most free-swimming bacteria move in approximately straight lines, interspersed with random reorientation phases. A key open question concerns varying mechanisms by which reorientation occurs. We combine mathematical modelling with analysis of a large tracking dataset to study the poorly understood reorientation mechanism in the monoflagellate species Rhodobacter sphaeroides. The flagellum on this species rotates counterclockwise to propel the bacterium, periodically ceasing rotation to enable reorientation. When rotation restarts the cell body usually points in a new direction. It has been assumed that the new direction is simply the result of Brownian rotation. We consider three variants of a self-propelled particle model of bacterial motility. The first considers rotational diffusion only, corresponding to a non-chemotactic mutant strain. Two further models incorporate stochastic reorientations, describing ‘run-and-tumble’ motility. We derive expressions for key summary statistics and simulate each model using a stochastic computational algorithm. We also discuss the effect of cell geometry on rotational diffusion. Working with a previously published tracking dataset, we compare predictions of the models with data on individual stopping events in R. sphaeroides. This provides strong evidence that this species undergoes some form of active reorientation rather than simple reorientation by Brownian rotation. 相似文献
52.
Phase relationships were determined in the Hf-Pt system at temperatures up to 1690 °C using both metallographic and neutron Rietveld refinement techniques. An unusual displacive transformation is observed below 200 °C in the rhombohedral compound Hf3Pt4, similar to that recently discovered in the compound Zr3Pt4. Crystallographic data are presented for the compounds HfPt4, HfPt3, Hf2Pt3, Hf3Pt4, HfPt, and Hf2Pt. A complete phase diagram is presented for the Hf-Pt binary system. 相似文献
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Networks and Spatial Economics - In this paper, we propose a multi-objective spatial analysis framework to evaluate the economic, environmental and health impacts of transport investment strategies... 相似文献
56.
Molecular design of interfacial layers based on conjugated polythiophenes for polymer and hybrid solar cells
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Judith E Houston Sébastien Richeter Sébastien Clément Rachel C Evans 《Polymer International》2017,66(10):1333-1348
In the past two decades, bulk heterojunction organic photovoltaic (OPV) devices have emerged as attractive candidates for solar energy conversion due to their lightweight design and potential for low‐cost, high‐throughput, solution‐phase processability. Interfacial engineering is a proven efficient approach to achieve OPV devices with high power conversion efficiencies. This mini‐review provides an overview of the key structural considerations necessary when undertaking the molecular design of conjugated polyelectrolytes, for application as interfacial layers (ILs). The different roles of ILs are outlined, together with the advantages and disadvantages of competing classes of IL materials. Particular emphasis is placed on the design and synthesis of water‐soluble polythiophene‐based IL materials and the influence of their structural characteristics on their performance as a promising class of IL material. Finally, the challenges and opportunities for polythiophenes as IL materials for OPV devices and other solution‐processed solar cell technologies (e.g. perovskite solar cells) are discussed. © 2017 Society of Chemical Industry 相似文献
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Anat Akiva Johanna Melke Sana Ansari Nalan Liv Robin van der Meijden Merijn van Erp Feihu Zhao Merula Stout Wouter H. Nijhuis Cilia de Heus Claudia Muñiz Ortera Job Fermie Judith Klumperman Keita Ito Nico Sommerdijk Sandra Hofmann 《Advanced functional materials》2021,31(17):2010524
Bone formation (osteogenesis) is a complex process in which cellular differentiation and the generation of a mineralized organic matrix are synchronized to produce a hybrid hierarchical architecture. To study the mechanisms of osteogenesis in health and disease, there is a great need for functional model systems that capture in parallel, both cellular and matrix formation processes. Stem cell-based organoids are promising as functional, self-organizing 3D in vitro models for studying the physiology and pathology of various tissues. However, for human bone, no such functional model system is yet available. This study reports the in vitro differentiation of human bone marrow stromal cells into a functional 3D self-organizing co-culture of osteoblasts and osteocytes, creating an organoid for early stage bone (woven bone) formation. It demonstrates the formation of an organoid where osteocytes are embedded within the collagen matrix that is produced by the osteoblasts and mineralized under biological control. Alike in in vivo osteocytes, the embedded osteocytes show network formation and communication via expression of sclerostin. The current system forms the most complete 3D living in vitro model system to investigate osteogenesis, both in physiological and pathological situations, as well as under the influence of external triggers (mechanical stimulation, drug administration). 相似文献
59.
We present a novel approach to determine the surface roughness on varying scales using atomic force microscopy data. The key factor is to find a suitable background correction for the desired scale. Using the example of the surface of sized and unsized high-tenacity carbon fibers, we present an easy method to find backgrounds for widely varying scales and to evaluate respective topography and surface roughness with the same lateral resolution as the microscope itself. The analysis is done by subtracting a tunable background from the respective height data. By choosing an appropriate background to investigate the surface topography of a carbon fiber on a nm-scale, only small nano-structures with a width of around 20 nm remain after the background subtraction. Evaluating the mean roughness R a of these nano-structures, sized carbon fibers show an overall value of around 0.1 nm while unsized carbon fibers a value of around 0.4 nm. Total background corrected height analysis shows an even distribution of these nano-structures along the fibrils of the unsized fibers, whereas for the sized fibers the nano-structures are not present. The presented method allows analysis and visualization of the distribution of nano-structures on a carbon fiber surface for the first time. This feature is used to visualize the distribution of the sizing and can further be used to investigate the influence of different production parameters on the fiber topography or to evaluate the contribution of mechanical interlocking to the interfacial strength. 相似文献
60.
T. Adinaveen J. Judith Vijaya L. John Kennedy 《Journal of Superconductivity and Novel Magnetism》2014,27(7):1721-1727
Uniform hematite (α-Fe2O3) nanoparticles have been successfully synthesized through a simple one-step low temperature reflux condensing method which requires no surfactants or templates. The crystallite size was calculated by using Debye–Sherrer formula, and it showed the range of 4–27 nm. The lattice parameters of the samples were measured by Rietveld analysis. The morphology of the products was studied by high resolution scanning electron microscopy (HR-SEM), and it was confirmed by high resolution transmission electron microscopy (HR-TEM). The HRTEM images exhibit the well defined lattice fringes of α-Fe2O3 particles that confirm their high crystallinity. The formation of pure α-Fe2O3 was further confirmed by using energy dispersive X-ray (EDX) analysis. The optical properties and the bandgap energy were measured by UV-Visible diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra. The bandgap energy was measured by using Kubelka–Munk method, and the value was found to be 2.26 eV. Magnetic hysteresis (M–H) loops revealed that the as-prepared α-Fe2O3 samples displayed ferromagnetic behavior. These results show that the prepared hematite possess good magnetic properties. 相似文献