Inversion of three-stage stress-strain relation for stainless steel in tension and compression

Presented in this paper is a new stress-strain relation for stainless steel alloys that provides the stress as an explicit function of the strain. The relation is an approximate inversion of a recently proposed three-stage stress-strain relation based on a modified Ramberg-Osgood equation. The three-stage relation is a much more accurate formulation than the previous two-stage formulations and is applicable to both tensile as well as compressive stresses. The new relation is derived by making a rational function assumption on the fractional deviation of the actual stress-strain curve from an idealized linear elastic behaviour. The new expression is valid over the full range of the stress well beyond the elastic region. The validity of the inverted expression is tested over a wide range of material parameters. These tests demonstrate that, the new expression results in stress-strain curves which are both qualitatively and quantitatively in excellent agreement with the fully iterated numerical solution of the full-range stress-strain relation with a maximum error below 4%.     

Comprehensive classification of collaboration approaches in E-learning

There are a number of approaches to learning such as traditional approaches (teacher-centered) and collaborative approaches (learner-centered). Nowadays, the concepts of collaboration and social interactions are the major trends in education. Therefore, many researchers embrace these concepts to offer the educational field enhanced learning environments which are supported by communication and collaboration techniques. The adaptation causes the existence of varied approaches which are addressing the collaborative learning techniques. As a result, there is a need for a mechanism to study those approaches and highlight their eminence. The aim of this paper is to give a comprehensive overview about the state-of-art in collaborative learning, especially by integrating social media tools. To do so, the study adopts a classification framework based on four different views (subject, purpose, method, and tool). The framework has been used to compare ten collaborative e-learning approaches. The finding indicates the potential of all approaches in developing an online learning environment for remote collaborative learning despite the lack of fulfilling all the requirements highlighted in the four views.     

Effects of heavy metals and polyelectrolytes in humic substance coagulation under saline conditions

Charge neutralisation plays a major role in heavy metal and humic substance removal in water treatment. Humic substances have no readily identifiable structure and they consist of anionic macromolecules of low to moderate molecular weight. Humic substances are easily coagulated using cationic metals and polyelectrolytes. Different concentrations of humic substances have been coagulated with different concentrations of heavy metals and/or polyelectrolytes. The charge neutralisation was determined using U.V. spectrophotometer. Humic substance removal increased with increasing salinity level until reaching a point where HS destabilization is considered complete and salinity no longer play a role in HS removal. Humic substance removal increased with increasing heavy metals concentration and precipitation was experienced at high concentrations of heavy metals (15–20 mg/L) and low concentration of humic substances (10 mg/L). In addition, HS removal also increased with increasing polyelectrolyte concentration. Diallydimethylammonium chloride (PDADMAC) polyelectrolyte was more effective in humic substance coagulation compared to copolymer of dimethyl aminoethyl acrylate (CoAA). The addition of heavy metals in polyelectrolyte coagulation increased humic substance removal due to the combined charge neutralization of the metals and polyelectrolytes.     

Experimental and theoretical investigation of thermal conductivity of some water-based nanofluids

Modified transient plane source method has been applied for thermal conductivity measurements of three water-based nanofluids containing Al₂O₃, TiO₂, and graphene nanoparticles. Experiments were conducted at different temperatures and concentrations. The effects of sort of nanoparticles, concentration, and diameter of nanoparticles as well as temperature were studied by comparing the experimental results with the predictions of ten preceding models. The overall performances of these models were compared in terms of percent error. Percent errors were observed in the current study ranging from vicinity of zero up to nearly 110% that belonged to Bruggeman model in predicting the thermal conductivity ratio of graphene/water nanofluids. All ten models performed acceptably in calculating thermal conductivity ratio of Al₂O₃ nanofluids with the maximum percent error of 2.16%. Four correlations are proposed based on the experimental results of this work three of which are special to each nanofluid and the fourth one is overall. These models succeeded to predict the thermal conductivity ratio of the studied nanofluids with considerably lower percent errors which was maximum 5.19% observed in predicting the thermal conductivity ratio of graphene/water nanofluid.     

Enhanced Natural Gas and Condensate Recovery by Carbon Dioxide and Methane Flooding

Abstract

The authors quantitatively investigates the recovery efficiency, pattern behavior, and relative permeability of (a) condensate following supercritical carbon dioxide (CO₂) injection, methane (CH₄) injection, and the injection of their mixtures; and (b) natural gas of various compositions following pure supercritical CO₂ injection. A high-pressure high-temperature experimental laboratory was established to simulate reservoir conditions and to perform relative permeability measurements on sandstone cores. This work is part of an integrated enhanced natural gas and condensate recovery project conducted for a local reservoir in Western Australia. This data will help the operators develop operational and design strategies for their present and future EOR projects.     

Green route synthesis of nanoporous copper oxide for efficient supercapacitor and capacitive deionization performances

We demonstrate a simple template-free green method to prepare copper oxide (CuO) nanoporous material using copper acetate as a single precursor with Piper nigrum (Indian black pepper) dried fruit extract as a reducing medium under microwave irradiation. The surface properties and morphology of the obtained CuO material were assessed using powder X-ray diffractometer, X-ray photoelectron spectrometer, field-emission scanning electron microscope with elemental mapping analysis, focused ion beam high-resolution transmission electron microscope, and N₂ adsorption-isotherm techniques. The characterization results reveal that the prepared CuO is a single monoclinic crystalline phase, and nanoporous in morphology with a specific surface area of 81.23 m² g⁻¹ and containing pore sizes between 3–8 nm. Nanoporous CuO showed excellent electrochemical energy storage performance with the specific capacitance of 238 Fg⁻¹ at 5 mVs⁻¹ when compared with commercially available CuO (75 Fg⁻¹). Also, nanoporous CuO showed efficient desalting performance in the capacitive deionization system. This eco-friendly synthesis derived nanoporous CuO can be applied as high-performance supercapacitor material for high-energy storage devices and desalination processes.     

Sizing and modelling of photovoltaic water pumping system

With the decline in price of the photovoltaics (PVs) their use as a power source for water pumping is the most attractive solution instead of using diesel generators or electric motors driven by a grid system. In this paper, a method to design a PV pumping system is presented and discussed, which is then used to calculate the required size of the PV for an existing farm. Furthermore, the amount of carbon dioxide emissions saved by the use of PV water pumping system instead of using diesel-fuelled generators or electrical motor connected to the grid network is calculated. In addition, an experimental set-up is developed for the PV water pumping system using both DC and AC motors with batteries. The experimental tests are used to validate the developed MATLAB model. This research work demonstrates that using the PV water pumping system is not only improving the living conditions in rural areas but it is also protecting the environment and can be a cost-effective application in remote locations.     

Sub-Picosecond Carrier Dynamics Explored using Automated High-Throughput Studies of Doping Inhomogeneity within a Bayesian Framework

Bottom–up production of semiconductor nanomaterials is often accompanied by inhomogeneity resulting in a spread in electronic properties which may be influenced by the nanoparticle geometry, crystal quality, stoichiometry, or doping. Using photoluminescence spectroscopy of a population of more than 11 000 individual zinc-doped gallium arsenide nanowires, inhomogeneity is revealed in, and correlation between doping and nanowire diameter by use of a Bayesian statistical approach. Recombination of hot-carriers is shown to be responsible for the photoluminescence lineshape; by exploiting lifetime variation across the population, hot-carrier dynamics is revealed at the sub-picosecond timescale showing interband electronic dynamics. High-throughput spectroscopy together with a Bayesian approach are shown to provide unique insight in an inhomogeneous nanomaterial population, and can reveal electronic dynamics otherwise requiring complex pump-probe experiments in highly non-equilibrium conditions.