AFM-based mechanical characterization of single nanofibres

Nanofibres are found in a broad variety of hierarchical biological systems as fundamental structural units, and nanofibrillar components are playing an increasing role in the development of advanced functional materials. Accurate determination of the mechanical properties of single nanofibres is thus of great interest, yet measurement of these properties is challenging due to the intricate specimen handling and the exceptional force and deformation resolution that is required. The atomic force microscope (AFM) has emerged as an effective, reliable tool in the investigation of nanofibrillar mechanics, with the three most popular approaches—AFM-based tensile testing, three-point deformation testing, and nanoindentation—proving preferable to conventional tensile testing in many (but not all) cases. Here, we review the capabilities and limitations of each of these methods and give a comprehensive overview of the recent advances in this field

A TEMPORAL AND SPATIAL ANALYSIS OF EROSION PROCESSES IN CALANCHI BADLANDS. A CASE STUDY FROM THE UPPER ORCIA VALLEY WITH STATE-OF-THE-ART METHODOLOGIES

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Image-based surface reconstruction in geomorphometry – merits, limits and developments

Photogrammetry and geosciences have been closely linked since the late 19th century due to the acquisition of high-quality 3-D data sets of the environment, but it has so far been restricted to a limited range of remote sensing specialists because of the considerable cost of metric systems for the acquisition and treatment of airborne imagery. Today, a wide range of commercial and open-source software tools enable the generation of 3-D and 4-D models of complex geomorphological features by geoscientists and other non-experts users. In addition, very recent rapid developments in unmanned aerial vehicle (UAV) technology allow for the flexible generation of high-quality aerial surveying and ortho-photography at a relatively low cost. The increasing computing capabilities during the last decade, together with the development of high-performance digital sensors and the important software innovations developed by computer-based vision and visual perception research fields, have extended the rigorous processing of stereoscopic image data to a 3-D point cloud generation from a series of non-calibrated images. Structure-from-motion (SfM) workflows are based upon algorithms for efficient and automatic orientation of large image sets without further data acquisition information, examples including robust feature detectors like the scale-invariant feature transform for 2-D imagery. Nevertheless, the importance of carrying out well-established fieldwork strategies, using proper camera settings, ground control points and ground truth for understanding the different sources of errors, still needs to be adapted in the common scientific practice. This review intends not only to summarise the current state of the art on using SfM workflows in geomorphometry but also to give an overview of terms and fields of application. Furthermore, this article aims to quantify already achieved accuracies and used scales, using different strategies in order to evaluate possible stagnations of current developments and to identify key future challenges. It is our belief that some lessons learned from former articles, scientific reports and book chapters concerning the identification of common errors or "bad practices" and some other valuable information may help in guiding the future use of SfM photogrammetry in geosciences

An automatic time lapse camera setup for multi-vision 3D-reconstruction of morphological changes

In the cause of a five year monitoring campaign on an Alpine slope in the Lainbach catchment, Southern Germany, high erosion rates were documented by terrestrial laser scanners (TLS) and unmanned airborne vehicles (UAV). As a result of different denudation processes erosion rates differ between summer and winter periods. The latter became evident after comparing both TLS-measured time spans. However, process differentiation and their contribution to the overall denudation remained challenging due to the discontinuous data collection every few weeks. In order to record these erosion processes an array of four automatically triggered cameras was installed capturing frames in ten minutes time steps as long as there is daylight. This work in progress aims to produce long term time series of morphodynamic changes in an active catchment by applying multi-vision structure from motion algorithms from a set of four cameras. Geomorphic processes caused by special weather phenomena can thus be interpreted in combination with climatic data acquired right next to the slope. Preliminary model calculations from the chosen perspectives produced adequate results with point counts of around 5.5 Mio for the 120m2 slope. The point density proved to be dependent on the weather conditions, thus foggy and dull images will be excluded. A validation of the approach will be achieved by comparison of the time lapse point clouds with the TLS scans and UAV surveys as the monitoring will continue

Simulation of rainfall effects on sediment transport on steep slopes in an Alpine catchment

The Alps represent a young high mountain range with strong geomorphological activity. As the major source area in Central Europe they deliver large quantities of sediments to the lowlands. However, knowledge on process differentiation is still insufficient to separate summer and winter periods of denudation. To increase understanding of sediment mobilizing procedures, artificial rainfall experiments are carried out to generate data for the physical based soil erosion model EROSION 3D. Additionally, state-of-the-art close-range remote sensing methods were applied for validation. The first rainfall simulations show promising and plausible results for the summer period and approve the experimental setup. Nevertheless, further research is required for covering all year seasonal dynamics