Topography and mechanical properties of single molecules of type I collagen using atomic force microscopy

Although the mechanical behavior of tendon and bone has been studied for decades, there is still relatively little understanding of the molecular basis for their specific properties. Thus, despite consisting structurally of the same type I collagen, bones and tendons have evolved to fulfill quite different functions in living organisms. In an attempt to understand the links between the mechanical properties of these collageneous structures at the macro- and nanoscale, we studied trimeric type I tropocollagen molecules by atomic force microscopy, both topologically and by force spectroscopy. High-resolution imaging demonstrated a mean (± SD) contour length of (287 ± 35) nm and height of (0.21 ± 0.03) nm. Submolecular features, namely the coil-pitch of the molecule, were also observed, appearing as a repeat pattern along the length of the molecule, with a length of ~8 nm that is comparable to the theoretical value. Using force spectroscopy, we established the stretching pattern of the molecule, where both the mechanical response of the molecule and pull-off peak are convoluted in a single feature. By interpreting this response with a wormlike chain model, we extracted the value of the effective contour length of the molecule at (202 ± 5) nm. This value was smaller than that given by direct measurement, suggesting that the entire molecule was not being stretched during the force measurements; this is likely to be related to the absence of covalent binding between probe, sample, and substrate in our experimental procedure

Synthesis and characterization of bulk and thin film antimony-selenium phase change alloys

Phase change alloys have recently gained increasing attention due to their application in developing phase change random memory (PRAM) devices, as Flash memory based devices are rapidly approaching their technological limitations. The most dominant features of PRAM devices are its non-volatile nature, compatible with present day IC\u27s manufacturing process, high density, fast operation, low power consumption etc; Devices built on binary alloys such as Antimony - Selenium (SbSe) exhibit certain superior properties such as fast operation, reduced power consumption, economical etc. compared to that of ternary alloy (GST). In order to understand this behavior in detail, bulk SbxSe 100-x (40 ≤ x ≤ 70) alloys are synthesized and deposited as thin films on silicon (100) plane substrate. Series of experiments such as X-ray diffraction analysis (XRD), Energy dispersive X-ray diffraction (EDAX), Spectroscopic Ellipsometer, Hall test experiments are carried out to characterize both the bulk and thin films. EDAX experiments show the deviation between bulk and thin films compositions is less than 10%. Diffraction patterns of bulk exhibit orthorhombic structure, i.e., Sb2Se3 type where as thin films demonstrate amorphous behavior. Impact of annealing on thin films is studied by heating the films to 170°C under argon (Ar) ambience. Post annealing results of Sb40Se60 thin films show the crystal structure is orthorhombic and crystallization temperature (Tc) increases with increase in Sb content of the compound. Ellipsometry and Hall measurements of annealed films exhibit high refractive index (n), low extinction coefficient (k) and high carrier concentration with associated low carrier mobility. Further the conductivity of annealed Sb40Se60 thin films switches from p to n type

Modeling river bed morphology, roughness, and surface sedimentology using high resolution terrestrial laser scanning

Recent advances in technology have revolutionized the acquisition of topographic data, offering new perspectives on the structure and morphology of the Earth's surface. These developments have had a profound impact on the practice of river science, creating a step change in the dimensionality, resolution, and precision of fluvial terrain models. The emergence of “hyperscale” survey methods, including structure from motion photogrammetry and terrestrial laser scanning (TLS), now presents the opportunity to acquire 3‐D point cloud data that capture grain‐scale detail over reach‐scale extents. Translating these data into geomorphologically relevant products is, however, not straightforward. Unlike traditional survey methods, TLS acquires observations rapidly and automatically, but unselectively. This results in considerable “noise” associated with backscatter from vegetation and other artifacts. Moreover, the large data volumes are difficult to visualize; require very high capacity storage; and are not incorporated readily into GIS and simulation models. In this paper we analyze the geomorphological integrity of multiscale terrain models rendered from a TLS survey of the braided River Feshie, Scotland. These raster terrain models are generated using a new, computationally efficient geospatial toolkit: the topographic point cloud analysis toolkit (ToPCAT). This performs an intelligent decimation of point cloud data into a set of 2.5‐D terrain models that retain information on the high‐frequency subgrid topography, as the moments of the locally detrended elevation distribution. The results quantify the degree of terrain generalization inherent in conventional fluvial DEMs and illustrate how subgrid topographic statistics can be used to map the spatial pattern of particle size, grain roughness, and sedimentary facies at the reach scale.Components of this research were supported by the UK Natural Environment Research Council (grant NE/G005427/1) with additional support from the NERC Geophysical Equipment Facility (Loan 892). Damia Vericat is supported by a Ramon y Cajal fellowship (RYC‐2010‐06264) from the Spanish Ministry of Science

Effect of alumina-formers addition on the isothermal oxidation of TI-AL based intermetallics

The main objective of this study is to investigate the effect of adding the alumina former elements on the isothermal oxidation behavior of Ti-Al based intermetallics. High temperature oxidation test was carried out on Ti-Al based intermetallics namely the Ti-48Al-0.5Ag, Ti-48Al-2Cr-1.5Ag and Ti-48Al-2Cr- 1.5Ag-0.5W oxidized isothermally at 900°C. The kinetic rates of oxidation for the intermetallics were near to parabolic and the addition of Chromium (Cr) increased the kinetic rate of oxidation. Examination on the surfaces of oxide scales by using the Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM) and the X-ray Diffraction (XRD), revealed that the phases formed on the scale surfaces were dependent on the composition of the base alloy and the kinetic rates of oxidation. Analysis of the scale cross section found that the adherence of the scale to the base alloy improved by the addition of the alumina former elements. Based on the Energy Dispersive X-ray (EDX) spot and line scan analysis performed on the cross sectional of the scale, all the intermetallics showed an Al-depleted zone and the formation of aluminum oxide in the scale even at the early stage of the scale development. This indicated that the outward diffusion of aluminum to form Al2O3 is promoted by the addition of alumina former elements. Microhardness-indentation results revealed that the hardness values were different across the cross section of the scale. The hardness was the highest in the scale due to the presence of high TiO2 content

Quasiparticle bandgap engineering of graphene and graphone on hexagonal boron nitride substrate

Graphene holds great promise for post-silicon electronics, however, it faces two main challenges: opening up a bandgap and finding a suitable substrate material. In principle, graphene on hexagonal boron nitride (hBN) substrate provides potential system to overcome these challenges. Recent theoretical and experimental studies have provided conflicting results: while theoretical studies suggested a possibility of a finite bandgap of graphene on hBN, recent experimental studies find no bandgap. Using the first-principles density functional method and the many-body perturbation theory, we have studied graphene on hBN substrate. A Bernal stacked graphene on hBN has a bandgap on the order of 0.1 eV, which disappears when graphene is misaligned with respect to hBN. The latter is the likely scenario in realistic devices. In contrast, if graphene supported on hBN is hydrogenated, the resulting system (graphone) exhibits bandgaps larger than 2.5 eV. While the bandgap opening in graphene/hBN is due to symmetry breaking and is vulnerable to slight perturbation such as misalignment, the graphone bandgap is due to chemical functionalization and is robust in the presence of misalignment. The bandgap of graphone reduces by about 1 eV when it is supported on hBN due to the polarization effects at the graphone/hBN interface. The band offsets at graphone/hBN interface indicate that hBN can be used not only as a substrate but also as a dielectric in the field effect devices employing graphone as a channel material. Our study could open up new way of bandgap engineering in graphene based nanostructures.Comment: 8 pages, 4 figures; Nano Letters, Publication Date (Web): Oct. 25 2011, http://pubs.acs.org/doi/abs/10.1021/nl202725

Integrating Al with NiO nano honeycomb to realize an energetic material on silicon substrate

Nano energetic materials offer improved performance in energy release, ignition, and mechanical properties compared to their bulk or micro counterparts. In this study, the authors propose an approach to synthesize an Al/NiO based nano energetic material which is fully compatible with a microsystem. A two-dimensional NiO nano honeycomb is first realized by thermal oxidation of a Ni thin film deposited onto a silicon substrate by thermal evaporation. Then the NiO nano honeycomb is integrated with an Al that is deposited by thermal evaporation to realize an Al/NiO based nano energetic material. This approach has several advantages over previous investigations, such as lower ignition temperature, enhanced interfacial contact area, reduced impurities and Al oxidation, tailored dimensions, and easier integration into a microsystem to realize functional devices. The synthesized Al/NiO based nano energetic material is characterized by scanning electron microscopy, X-ray diffraction, differential thermal analysis, and differential scanning calorimetry

An evaluation of mark and recapture techniques for estimating tigerfish biomass in Lake Kariba

The effectiveness of 2 mark and recapture techniques was evaluated using tiger fish, Hydrocynus vittatus. The 2 techniques used were: tagging with a plastic tag and fluorescent spray marking. While the tagging method resulted as the logical method to use within the constraints of the tiger fish study, it cannot be considered completely reliable for the estimation of population size in Lake Kariba