Additive manufacturing of architected catalytic ceramic substrates based on triply periodic minimal surfaces

The exhibited geometry of catalytic substrates can have a significant influence on the chemical activity and efficiency. Controlling their geometry can be challenging using the traditional techniques. In this work, we propose new and novel catalytic substrates with architected and controllable topologies based on the minimal surfaces framework. A novel design approach and an additive manufacturing (AM) technique were proposed to manufacture the catalytic substrates using ceramic materials. After 3D printing, their mechanical and flow properties were investigated experimentally. An elastic-plastic-damage coupled model was employed to investigate the underlying deformation mechanism of the investigated substrates. Results showed that the CLP substrate exhibited the highest mechanical properties as well as the least pressure drop among the tested substrates. Also, numerical simulations showed that the strut-based substrates exhibit stress localization which leads to faster failure, while stress is distributed more homogeneously in the sheet-based substrates. While the model showed to have a good agreement in the experimental and simulation stress-strain responses, the damage mechanism was not fully captured by the numerical simulations. This was attributed mainly to the process-induced defects in the form of microcracks and microvoids that can alter the nature of deformation and damage.     

An efficient routing protocol for cognitive radio networks of energy-limited devices

Telecommunication Systems - In the era of Internet-of-things (IoT), the future 5G networks are supposed to provide ubiquitous connectivity, high speed, as well as low latency and energy efficiency...     

Preparation and characterization study on maleic acid cross-linked poly(vinyl alcohol)/chitin/nanocellulose composites

In the quest on improving composite formulations for environmental sustainability, maleic acid (MA) cross-linked poly(vinyl alcohol) (PVA)-α-chitin composites reinforced by oil palm empty fruit bunch fibers (OPEFB)-derived nanocellulose crystals (NCC) had been successfully prepared. Based on the Fourier transform infrared (FTIR) spectroscopic analysis, it was proven that molecular interactions of the cross-linker to the polymeric networks was through conjugated ester linkage. Differential scanning calorimetry (DSC) showed that the influence of MA was minimal toward crystallization in the PVA/chitin/NCC composite. Maximum tensile strength, elongation at break and Young's modulus of the respective PVA/chitin/NCC composites were achieved at different content of MA, dependent on the PVA/chitin mass ratio. Among all compositions, a maximum Young's modulus was achieved at 30 wt% MA loading in PVA/chitin-30/NCC, amounting to 2,413.81 ± 167.36 MPa. Moreover, the mechanical properties and selected physicochemical properties (swelling, gel content, and contact angle) of the PVA/chitin/NCC composites could be tailored by varying the chitin content (10–30 wt%) and MA content (10–50 wt% based on total mass of composite). In brief, this chemically cross-linked PVA-based biocomposites formulated with sustainable resources exhibited tunable physicochemical and mechanical properties.     

Selective Recovery of Uranium from El-Sebaiya Phosphate Rocks Using Urea

Radiochemistry - Urea CO(NH2)2 is an effective selective lixiviant for uranium from phosphate raw material. Experiments were performed to determine the factors of uranium dissolution from...     

An Investigation of Low Velocity Impact Properties of Rotationally Molded Skin–Foam–Skin Sandwich Structure

In this study, the low velocity impact properties of rotationally molded skin–foam–skin sandwich structures were investigated experimentally since there is a need for a greater understanding of the impact behavior of these composites in service to extend the range of their applications. Polyethylene rotationally molded sandwich structures were manufactured at various skin and core layer thickness combinations and tested using an instrumented low velocity drop weight impact testing machine at 20–100 J impact energy levels, at room temperature. This allowed the identification of the impact response, failure mode, and the effects of the skin and core layer thickness on impact resistance. Force–deflection curves, maximum force, contact time, maximum deflection versus impact energy curves were analyzed. Samples were seen to fail due to the indentation dart piercing the upper and lower skins, with crushing and consolidation seen in the core foamed layer. Delamination at the core/skin interface was not observed. It was found that fracture initiates from the lower skin and then continues to grow to the upper skin via the foamed core layer. The impact resistance was noted to increase with increasing skin and core layer thickness; though an increase in skin layer thickness had a greater contribution than an increase in the core layer thickness. POLYM. ENG. SCI., 60: 387–397, 2019. © 2019 Society of Plastics Engineers     

Feasibility of Ni/Ti and Ni/GF cathodes in microbial electrolysis cells for hydrogen production from fermentation effluent: A step toward real application

The low cost, low over-potential loss, good catalytic properties for hydrogen evolution reaction (HER), high corrosion stability, commercially available, and could be applied in pH-neutral solution and ambient temperature are important properties for the cathode materials when it is applied in microbial electrolysis cell (MEC) technology. This study has two-pronged objectives: the first is to investigate the feasibility of titanium (Ti) and graphite felt (GF) coated with nickel (Ni), and the second is to generate hydrogen from the fermentation effluent (FE). The electrodeposition (ED) method was used to deposit Ni catalyst onto Ti (Ni/Ti) and GF (Ni/GF) surfaces. The scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy were used to characterize the cathode morphology and element composition. The catalytic properties of Ni/Ti and Ni/GF could be evaluated using the linear sweep voltammetry tests. The maximum volumetric H₂ production rates of MEC using Ni/Ti and Ni/GF cathodes were obtained at 0.39 ± 0.01 and 0.33 ± 0.03 m³ H₂ m⁻³ d⁻¹ respectively. The Ni/Ti and Ni/GF cathodes could be used as alternative cathodes while producing hydrogen from FE.     

Biomimetic Approach for the Production of 3D Woven Spherical Composite Applied in Apparel Protection and Performance

Applied Composite Materials - Current sports bras are typically manufactured via a cut and sew process resulting in a high volume of post-production material waste. Seams derived from this cut and...     

A hidden Markov model to detect regime changes in cryptoasset markets

The objective of this work is to understand the dynamics of cryptocurrency prices. Specifically, how prices switch between different regimes, going from “bull” to “stable” and “bear” times. For this purpose, we propose a hidden Markov model that aims at explaining the evolution of Bitcoin prices through different, unobserved states. The implementation of the proposed model includes a likelihood ratio test that allows to compare models with different states and with different covariance structures. Our empirical findings show that the time movements of Bitcoin prices across different exchange markets are well-described by the proposed model. In particular, a parsimonious model with a diagonal covariance matrix leads to better predictions, compared with a model with a full covariance matrix.