Isotropic compression behavior of granular assembly with non-spherical particles by X-ray micro-computed tomography and discrete element modeling

The particle morphological properties, such as sphericity, concavity and convexity, of a granular assembly significantly affect its macroscopic and microscopic compressive behaviors under isotropic loading condition. However, limited studies on investigating the microscopic behavior of the granular assembly with real particle shapes under isotropic compression were reported. In this study, X-ray computed tomography(μCT) and discrete element modeling(DEM) were utilized to investigate isotropic compression behavior of the granular assembly with regard to the particle morphological properties,such as particle sphericity, concavity and interparticle frictions. The μCT was first used to extract the particle morphological parameters and then the DEM was utilized to numerically investigate the influences of the particle morphological properties on the isotropic compression behavior. The image reconstruction from μCT images indicated that the presented particle quantification algorithm was robust, and the presented microscopic analysis via the DEM simulation demonstrated that the particle surface concavity significantly affected the isotropic compression behavior. The observations of the particle connectivity and local void ratio distribution also provided insights into the granular assembly under isotropic compression. Results found that the particle concavity and interparticle friction influenced the most of the isotropic compression behavior of the granular assemblies.     

Distributed lifetime optimization in wireless sensor networks using alternating direction method of multipliers

Due to the limited energy of sensor nodes in wireless sensor networks, extending the network lifetime is a major challenge that can be formulated as an optimization problem. In this paper, we propose a distributed iterative algorithm based on alternating direction method of multipliers with the aim of maximizing sensor network lifetime. The features of this algorithm are the use of local information, low overhead of message passing, low computational complexity, fast convergence, and, consequently, reduced energy consumption. In this study, we present the convergence results and the number of iterations required to achieve the stopping criterion. Furthermore, the impact of problem size (number of sensor nodes) on the solution and constraints violation is studied, and, finally, the proposed algorithm is compared with one of the well‐known subgradient‐based algorithms.     

Solubility of Fructose in Water–Ethanol and Water–Methanol Mixtures by Using H‐Bonding Models

The solubility of fructose in water–ethanol and water–methanol mixtures and the saturated density of each solution at 20, 30, and 40 °C over a range of water mass percentage have been measured. Also, a new modification of the Wilson model has been proposed to describe solubility data satisfactorily. The H‐UNIQUAC and H‐NRTL models were applied and a comparison between these 3 models was carried out. These 3 models were used to estimate the experimental data which was reported in this study. The comparison of the results showed that the H‐Wilson model has the lowest AAD% between these 3 models in correlating the solubility data and the saturated density.     

Effect of fiber hybridization on energy absorption and synergy in concrete

In the present study, steel and polypropylene (PP) fibers have been utilized with the intent of obtaining hybrid fiber-reinforced concrete (HFRC) with desirable mechanical properties. An attempt has been made to scrutinize the properties of HFRC with the main concentration being on energy absorption characteristics of concrete and the efficacy of fiber hybridization in producing synergy. Accordingly, a total of 180 specimens, representing 20 different mixtures have been cast and evaluated through compressive, split tensile, and flexural tests. The relevant flexural toughness of the specimens was calculated using ASTM C1018, ASTM C1609, JSCE, and PCS methods, and the effectiveness of these methods was evaluated based on the experimental results. It was observed that steel fibers are more effective in the improvement of flexural toughness in the presence of PP fibers. Furthermore, synergy associated with the combination of fibers at different stages of deflection of the beam specimens was observed and analyzed.     

Amine and thiol functionalization of SBA-15 nanoparticles for highly efficient adsorption of sulforaphane

This study presents a novel material for highly efficient adsorption of sulforaphane based on SBA-15. The SBA-15 nanoparticles were synthesized using natural silica by hydrothermal method and functionalized with thiol and amine groups by the post-synthesis grafting procedure. All adsorbents were characterized by various techniques including BET, LAXRD, FT-IR, FE-SEM, and CHNS. The batch adsorption experiments revealed that the adsorption efficiency of SBA-15 for sulforaphane can be mainly influenced by the introduction of functional groups and the best adsorption performance was observed for amine-functionalized SBA-15 (SBA-15-NH₂) compared to pure SBA-15 and thiol-functionalized SBA-15 (SBA-15-SH) with the highest adsorption efficiency of about 97%. Preliminary adsorption studies of sulforaphane onto SBA-15-NH₂ were performed in aqueous solutions with different pH values and various organic solvents. Also, the effects of adsorbent dosage, contact time, and initial sulforaphane concentration on sulforaphane adsorption using SBA-15-NH₂ were studied. Langmuir and Redlich-Peterson isotherm models were the best-fitting models for the experimental data, followed by Temkin, Freundlich, and Dubinin-Radushkevich models. The adsorption process could be well described by the pseudo-first-order kinetic model based on kinetic parameters, correlation coefficient, and error functions. Meanwhile, the intra-particle diffusion model showed a multi-linear plot with three steps demonstrating slow diffusion into mesopores as a rate-limiting step.     

Sufficient conditions for the convergence of a class of nonlinear distributed consensus algorithms

This paper is concerned with the convergence of a class of continuous-time nonlinear consensus algorithms for single integrator agents. In the consensus algorithms studied here, the control input of each agent is assumed to be a state-dependent combination of the relative positions of its neighbors in the information flow graph. Using a novel approach based on the smallest order of the nonzero derivative, it is shown that under some mild conditions the convex hull of the agents has a contracting property. A set-valued LaSalle-like approach is subsequently employed to show the convergence of the agents to a common point. The results are shown to be more general than the ones reported in the literature in some cases. An illustrative example demonstrates how the proposed convergence conditions can be verified.     

Damage evaluation and deformation behavior of mine tailing-based Geopolymer under uniaxial cyclic compression

Geopolymerized mine tailings (MTs), as an alternative to reuse the mine wastes, can be used for construction materials (e.g., geopolymer concrete and bricks) depending on their mechanical properties. Their strength values, which can range from a couple of MPa to tens of MPa, are significant evidence for their application in the construction industry. In practice, geopolymers activated with different NaOH molarities can significantly affect the mechanical properties of MTs. The mechanical behavior of geopolymers under monotonic loading also has been widely investigated. However, the potential hazard of the exposure of geopolymer concrete/bricks to cyclic loading has received limited attention. This paper presents a study we conducted on geopolymers made by activation of MTs under cyclic loading to understand their crack and damage behaviors, including the influence of factors such as NaOH molarity and loading patterns. The influence of NaOH molarity on the elastic and plastic strains of the geopolymer specimen at different cycles was explored. A series of unconfined compression tests of cubic specimens with different NaOH molarities as well as microscopic investigations and observations via XRD, FTIR, and SEM were carried out in this study. The Young's modulus of the geopolymer was found to increase followed by a decrease with the cycles for all the selected NaOH molarities. The geopolymers activated with lowest NaOH molarity were first to start damage and activated with the highest NaOH molarity were the last to damage. The damage variable was shown to increase rapidly at the initial cycles and then gradually approached the maximum value.     

Melt-spun liquid core fibers: physical and morphological characteristics

Application of different polymers and fillers in multi-component fibers has recently emerged as an effective approach in textile industries. Recent investigations have extensively demonstrated that hollow fibers can be melt-spun and subsequently filled with liquids; however, introduction of a liquid into a fiber core and filling it up with that liquid, specifically at extended lengths, remains challenging. In this study, based on the results previously obtained for the simulation and extrusion of polymer melt and liquid co-flowing, continuous production of the liquid core bi-component filaments via melt spinning through specially designed spinneret is discussed. In fact, core/shell bi-component filaments 50 μm in diameter consisting of polypropylene sheath and complex ester core were produced undergoing 1500 m/min continuous melt spinning with drawing ratio of 5. Physical properties of the developed fibers were investigated which were in acceptable condition with those of the reference solid and hollow fibers. Successful presence of a liquid in an eccentric channel 15 μm in diameter was demonstrated by microscopic observation. Furthermore, the ester oil was retained inside the fiber due to its low contact angle against polypropylene, thereby resolving the need for sealing the fiber’s outlet. Also, TGA and FTIR analysis confirmed the presence of liquid inside the bi-component fibers. DSC tests showed a similar crystallinity for liquid core and hollow fibers, which was about 37 %, while solid fiber had 5 % more crystallinity. Due to the vast available liquids and polymers with various properties, developed liquid core fibers will provide a suitable platform for a large number of applications in future.