Advances in wireless technology and supporting infrastructure provide unprecedented opportunity for ubiquitous real-time healthcare and fitness monitoring without constraining the activities of the ...user. Wirelessly connected miniaturized sensors and actuators placed in, on, and around the body form a body area network for continuous, automated, and unobtrusive monitoring of physiological signs to support medical, lifestyle and entertainment applications. BAN technology is in the early stage of development, and several research challenges have to be overcome for it to be widely accepted. In this article we study the core set of application, functional, and technical requirements of the BAN. We also discuss fundamental research challenges such as scalability (in terms of data rate, power consumption, and duty cycle), antenna design, interference mitigation, coexistence, QoS, reliability, security, privacy, and energy efficiency. Several candidate technologies poised to address the emerging BAN market are evaluated, and their merits and demerits are highlighted. A brief overview of standardization activities relevant to BANs is also presented.
The breakage behaviour of a pre-crushed carbonate sand sheared within a miniature triaxial loading apparatus is investigated using high-spatial resolution X-ray micro-tomography. Full-field 3D CT ...images of the sand sample are acquired at different loading stages of the test. This enables the quantitative investigation of the temporal and spatial evolution of soil microstructures throughout the test, including particle size, particle shape and local strains. A particle tracking approach capable of identifying fragments of crushed particles is presented, which allows the identification of different particle crushing modes (i.e., chipping, major splitting and fragmentation) occurring during the shear. Particle breakage is found to exhibit clear localization around the shear band as it develops. Meanwhile, the failure modes of particles crushed during shear are found to be related to their particle-scale characteristics, which include particle size and particle shape. Specifically, particles with a smaller size are more likely to fail in the major splitting mode, while particles with highly irregular shapes tend to fail in the fragmentation mode. The image data and experimental findings presented in this study will be useful to develop and validate advanced approaches for discrete element modelling of crushable soils with realistic particle shape.
•Particle tracking capable of identifying fragments of crushed particles.•Particle shape evolution of carbonate sands during shear.•Correlation between particle breakage and strain localization.•Effects of particle size, shape and internal voids on particle crushing modes.
Inspired by the layered aragonite platelet/nanofibrillar chitin/protein ternary structure and integration of extraordinary strength and toughness of natural nacre, artificial nacre based on clay ...platelet/nanofibrillar cellulose/poly(vinyl alcohol) is constructed through an evaporation-induced self-assembly technique. The synergistic toughening effect from clay platelets and nanofibrillar cellulose is successfully demonstrated. The artificial nacre achieves an excellent balance of strength and toughness and a fatigue-resistant property, superior to natural nacre and other conventional layered clay/polymer binary composites.
Nacre (mother-of-pearl), made of inorganic and organic constituents (95 vol% aragonite calcium carbonate (CaCO
3
) platelets and 5 vol% elastic biopolymers), possesses a unique combination of ...remarkable strength and toughness, which is compatible for conventional high performance materials. The excellent mechanical properties are related to its hierarchical structure and precisely designed organicinorganic interface. The rational design of aragonite platelet strength, aspect ratio of aragonite platelets, and interface strength ensures that the strength of nacre is maximized under platelet pull-out failure mode. At the same time, the synergy of strain hardening mechanisms acting over multiple scales results in platelets sliding on one another, and thus maximizes the energy dissipation of viscoplastic biopolymers. The excellent integrated mechanical properties with hierarchical structure have inspired chemists and materials scientists to develop biomimetic strategies for artificial nacre materials. This
critical review
presents a broad overview of the state-of-the-art work on the preparation of layered organicinorganic nanocomposites inspired by nacre, in particular, the advantages and disadvantages of various biomimetic strategies. Discussion is focused on the effect of the layered structure, interface, and component loading on strength and toughness of nacre-mimic layered nanocomposites (148 references).
This critical review presents a broad overview of the state-of-the-art work on the preparation of layered organicinorganic nanocomposites inspired by nacre, in particular, the advantages and disadvantages of various biomimetic strategies.
The lighting industry has been going through fundamental digital revolution: with light sources going for LED, drivers going digital, and control going networked. This revolution creates the flush of ...energy-efficient and modern-designed home lights, and also frees up the way of using lights together with the proliferation of smart devices, sensors, and internet of things. The control of lights becomes fast and rich-flavored, going beyond on/off, dimming, to color (or color temperature) change and scene setting, with intelligence to react to human mood and activity, and adapt to environments. To fully explore the benefits of the new generation lights, the last hop (x10 meters) connectivity is key. ZigBee Light Link (ZLL) 1 gives the lighting industry a global communication standard for interoperable and very easy-to-use consumer lighting and control products. It allows consumers to gain wireless control over all their LED fixtures, light bulbs, timers, remotes and switches. Products using this standard will let consumers change lighting remotely to reflect ambiance, task or season, all while managing energy use and making their homes greener.
A practicable strategy to rationally obtain the reversible mechanochromic luminescent (MCL) material with high‐contrast ratio (green versus red) has been established. By introducing a volatile third ...party (small‐sized solvent molecules) into the lattice of charge transfer (CT) cocrystal of mixed‐stacking 1:1 coronene (Cor.) and napthalenetetracarboxylic diimide (NDI), a noteworthy reconfigurable molecular assembly is ingeniously achieved owing to the loosely packing arrangement as well as weakened intermolecular interactions. Accordingly, the CT excited state, strongly corresponding to the molecular stacking modes, can be intentionally tailored through external stimulus (heating, grinding, or solvent), accompanying distinct changes in photophysical properties. Subsequently, a high‐contrast reversible MCL with highly sensitive and good reproducibility is realized and the underlying mechanism is thoroughly revealed.
A simple and practicable strategy is established to obtain high‐contrast reversible mechanoresponsive PL switching by introducing a volatile third party into the lattice of mixed‐stacking CT cocrystal. This has the purpose of constructing the loosely packing mode to realize a facile control of molecular assemblies and CT excitons in the solid state.
Carbonate soils, known as bioclastic deposits, have been classified as ‘problematic soils’ in many offshore and ocean engineering applications. Carbonate soils have many complicated mechanical ...properties, e.g., low shear strength and high compressibility, mainly determined by their unique microstructures that include weak carbonate minerals, complex particle morphology, and abundant intra-particle pores. However, current knowledge of these microstructures, especially regarding intra-particle pore structure, does not yet match our understanding of the complicated behaviors of the soils. In this context, this paper presents a detailed quantitative study of the particle morphology and intra-particle pore structure of carbonate sand particles based on the results of X-ray micro-computed tomography (μCT) scanning and image processing techniques. By investigating particle shape, this paper first introduces a triangular classification method for carbonate particles in terms of their aspect ratios. The continuous pore size distribution, fractal dimension, and Euler characteristic are then defined to characterize the cumulative volume fraction, complexity, and connectivity of the precisely reconstructed intra-particle pore structure, respectively. The classification results indicate that the proposed classification method is a significant step toward the establishment of a novel classification framework for carbonate soils in engineering applications. The quantitative results characterizing the topological properties of the intra-particle pore structure and their statistical analysis provide deep insight into the hydro-physical permeability and biogeologic origins of carbonate soils.
•X-ray micro-computed tomography scanning and image processing of marine deposited carbonate soils.•Reconstruction and characterization of particle morphology and intraparticle pore structure of carbonate soils.•Intrinsic correlation between particle microstructure and geological origin of carbonate soils.
The inter-particle contact evolution of two sheared granular materials, i.e., a spherical glass bead (GB) specimen and an angular Leighton Buzzard Sand (LBS) specimen, is investigated ...non-destructively using X-ray micro-tomography. A miniature triaxial apparatus is developed for the testing with in-situ scanning. Full-field X-ray CT images of the two specimens are obtained at different shearing stages. A series of image processing and analysis techniques in combination with a particle-tracking approach is developed to detect the inter-particle contacts and to determine the contact gain, the contact loss, and the contact movement during each shear increment. It is found that the average coordination number (CN) experiences a strong change in the pre-peak shearing stage, and tends to reach a steady value after the peak. As the shear progresses, the average CN of the particles with different sizes follows the same trend as the overall average CN. Additionally, as the shear progresses, the branch vectors of the specimens, which, prior to shearing, are nearly isotropically distributed for the rounded GB and concentrated along the horizontal direction for the angular LBS, are found to show a directional preference towards the loading direction. The contact gain and the contact loss, which contribute to this directional preference, and the contact movement, which leads to the attenuation of the directional preference, are shown to be the two competing factors determining the evolution of the fabric anisotropy of granular materials. The higher degree of fabric anisotropy in the shear bands is shown to be mainly attributed to the higher percentages of contact gain and contact loss when compared to that of the entire samples.
The particle micromorphology created by geological processes is an essential characteristic in determining the mechanical properties of natural sands. Based on micro X-ray computed tomography (μCT) ...data, we introduce a mathematical procedure using spherical harmonics to characterize and reconstruct the particle micromorphology in three dimensions. The basic geometric properties of natural sand particles, volume and surface area, and two empirical engineering indices, sphericity and angularity, are the main focus of the investigation using spherical harmonic analysis. By validating the spherical harmonic analysis against the tomography data, it is shown to be a robust technique for reproducing particle micromorphology in terms of the shape irregularity and surface texture. The precision of the method depends on the resolution of the μCT and the maximum harmonic degree used. Finally, by using principal component analysis for spherical harmonic descriptors of the scanned particles, two different kinds of sand assemblies consisting of statistically reconstructed particles with random shapes but major morphological features are successfully generated. This approach will be useful for the efficient discrete element modeling of real sands in the future.
•Three dimensional characterization and reconstruction of sand particles using micro X-ray tomography and spherical harmonics•Calculating geometrical properties of sand particles by the mathematical method•Generation of random-shaped particle assembly by principal component analysis
PDF