We report sublimation of crystalline GeTe nanowires at elevated temperatures in vacuum imaged by in situ transmission electron microscopy. The GeTe nanowires exhibit significant melting point suppression in the presence of Au contamination. A nanosized effusion cell is formed by coating the GeTe core with a SiO(2) shell, where the core can be evaporated or sublimated from the open end of the shell at high temperatures. By measuring the speed of the moving interface between the condensed and vapor phases, we determined the vaporization coefficient of these nanowires to be greater than or equal to approximately 10(-3) over a wide range of temperatures. At the final stage of the nanowire vaporization, the material loss occurs at a higher rate, which is evidence of a higher vaporization coefficient for nanosized GeTe. This in situ technique offers a quantitative method of investigating phase transition dynamics and kinetics of nanomaterials, an important topic for designing nanoscale devices to be operated at high temperatures such as phase change memory.
Abstract Focus misses are common in image capture, such as when the camera or the subject moves rapidly in sports and macro photography. One option to sharpen focus‐missed photographs is through single image deconvolution, but high‐frequency data cannot be fully recovered; therefore, artifacts such as ringing and amplified noise become apparent. We propose a new method that uses assisting, similar but different, sharp image(s) provided by the user (such as multiple images of the same subject in different positions captured using a burst of photographs). Our first contribution is to theoretically analyze the errors in three sources of data—a slightly sharpened original input image that we call the target , single image deconvolution with an aggressive inverse filter, and warped assisting image(s) registered using optical flow. We show that these three sources have different error characteristics, depending on image location and frequency band (for example, aggressive deconvolution is more accurate in high‐frequency regions like edges). Next, we describe a practical method to compute these errors, given we have no ground truth and cannot easily work in the Fourier domain. Finally, we select the best source of data for a given pixel and scale in the Laplacian pyramid. We accurately transfer high‐frequency data to the input, while minimizing artifacts. We demonstrate sharpened results on out‐of‐focus images in macro, sports, portrait and wildlife photography.
Two major mechanisms that could potentially be responsible for toughening in mineralized tissues, such as bone and dentin, have been identified—microcracking and crack bridging. While evidence has been reported for both mechanisms, there has been no consensus thus far on which mechanism plays the dominant role in toughening these materials. In the present study, we seek to present definitive experimental evidence supporting crack bridging, rather than microcracking, as the most significant mechanism of toughening in cortical bone and dentin. In vitro fracture toughness experiments were conducted to measure the variation of the fracture resistance with crack extension [resistance–curve (R-curve) behavior] for both materials with special attention paid to changes in the sample compliance. Because these two toughening mechanisms induce opposite effects on the sample compliance, such experiments allow for the definitive determination of the dominant toughening mechanism, which in the present study was found to be crack bridging for microstructurally large crack sizes. The results of this work are of relevance from the perspective of developing a micromechanistic framework for understanding fracture behavior of mineralized tissue and in predicting failure in vivo.
Cellulose microfibrils play essential roles in the organization of plant cell walls, thereby allowing a growth habit based on turgor. The fibrils are made by 30 nm diameter plasma membrane complexes composed of approximately 36 subunits representing at least three types of related CESA proteins. The complexes assemble in the Golgi, where they are inactive, and move to the plasma membrane, where they become activated. The complexes move through the plasma membrane during cellulose synthesis in directions that coincide with the orientation of microtubules. Recent, simultaneous, live-cell imaging of cellulose synthase and microtubules indicates that the microtubules exert a direct influence on the orientation of cellulose deposition. Genetic studies in Arabidopsis have identified a number of genes that contribute to the overall process of cellulose synthesis, but the role of these proteins is not yet known.
La validite de la relation Bibliotheque/Recherche est delimitee par certaines grandes lignes de caractere obligatoire: une philosophie de l'information, l'actualite comme base unique, une organisation prospective et des structures compatibles, une capacite a cooperer, une approche de specialiste de haut niveau. (INTD)
