Integrating human factors into discrete event simulation: a proactive approach to simultaneously design for system performance and employees’ well being

The aim of this research is to: (1) Develop an approach to integrating both human fatigue-recovery patterns and human learning into Discrete Event Simulation models of a production system to predict productivity and quality; (2) Validate the predicted fatigue against operators’ perceived fatigue; and (3) Demonstrate how this Human Factors-enabled simulation approach can be applied in a case study comparing two manufacturing line designs in the context of electronics assembly. The new approach can predict the accumulation of operator fatigue, fatigue-related quality effects and productivity changes based on system design configurations. In the demonstration comparison, fatigue dosage was 7–33% lower in the proposed system where HF was taken into consideration at the engineering design (ED) stage. In the existing system, the fatigue dose measure correlated with quality deficits with 26% of the variance accounted for – a large portion given the multi-causal nature of production deficits. ED models that do not include human aspects may provide unreliable results in terms of productivity and quality estimates. This research shows that it is possible to design production systems that are more productive while being less hazardous for the system operator.     

Prediction of carbon dioxide separation from gas mixtures in petroleum industries using the Levenberg–Marquardt algorithm

In this study, two mathematical models for hydrate formation process to separate carbon dioxide by a combination of two different kinds of organic and surfactant promoters are presented. Promoters such as sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, and dodecyl trimethyl ammonium chloride as surfactant promoters; also, tetrahydrofuran, cyclopentane, 1,3-dioxolane, and 2-methyl tetrahydrofuran as organic promoters have been used in recent years. The results showed that a combination of 3000 ppm of surfactant promoters and 4 wt% organic promoters had the highest separation rate of carbon dioxide and; consequently, the investigated models were based on this optimum condition. As a matter of fact, by using these simulations the hydrate formation behavior was predicted with high accuracy; moreover, conducting consuming experiments is not essential anymore. To sum up, in the present research both Vandermonde matrix model and Levenberg-Marquardt algorithm were applied to predict the hydrate formation behavior; in addition, their results were precisely considered and validated with experimental data.     

Physical and mechanical properties of a poly-3-hydroxybutyrate-coated nanocrystalline hydroxyapatite scaffold for bone tissue engineering

A major challenge for tissue engineers is the design of scaffolds with appropriate physical and mechanical properties. The present research discusses the formation of ceramic scaffolding in tissue engineering. Hydroxyapatite (HAp) powder was made from bovine bone by thermal treatment at 900?°C; 40, 50 and 60%wt porous HAp was then produced using the polyurethane sponge replication method. Scaffolds were coated with poly-3-hydroxybutyrate (P3HB) for 30?s and 1?min in order to increase the scaffold??s mechanical properties. XRD, SEM and FT-IR were used to study phase structure, morphology and agent groups, respectively. In XRD and FT-IR data, established hydrogen bands between polymer and ceramic matrix confirm that the scaffold is formed as a composite. The scaffold obtained with 50%wt HAp and a 30?s coating was 90% porous, with an average diameter of 100?C400???m, and demonstrated a compressive strength and modulus of 1.46 and 21.27?MPa, respectively. Based on these results, this scaffold is optimised for the aforementioned properties and can be utilised in bone tissue engineering.     

Optimisation of a combined Stirling cycle–organic Rankine cycle using a genetic algorithm

In a Stirling cycle a huge amount of energy is wasted due to the losses. This wasted energy may be utilised as a heat source for the boiler of an organic Rankine cycle (ORC). Combination of these two cycles leads to an increased cycle efficiency compared to a single Stirling cycle and the analysis and optimisation of the integrated system is carried out. Optimisation is performed using the genetic algorithm and considering three decision variables: the temperature of the cold tank of the Stirling cycle, the pressure ratio and the temperature of the ORC condenser. In optimisation, the efficiency is considered as the objective function and the highest value is achieved by adjusting the decision variables. Using this method, the efficiency of the overall combined cycle was improved in which the highest efficiency was obtained to be 41.5%.     

First-principles DFT study of SO2 and SO3 adsorption on 2PANI: a model for polyaniline response

Interaction of SO_x (x?=?2,3) molecules on active sites of dianiline (as a model for polyaniline, denoted here as 2PANI) was studied using density functional theory at the BLYP-D/6-31+G(d) level of theory. Natural population analysis was used to find out the charge distribution as well as the net transferred charge of SO_x upon adsorption on 2PANI and the result has been compared with Mulliken charge analysis to evaluate the sensing ability of 2PANI. The computed density of states point to the remarkable orbital hybridization between SO_x and 2PANI during the adsorption process. As a consequence, the results of UV–VIS confirm the sensing ability of 2PANI toward SO₂ and SO₃. Based on our results, it can be found that at proper configuration the SO₂ and SO₃ molecules can be adsorbed on 2PANI with adsorption energies (E_ads) of ?18.2 and ?62.9?kJ/mol (BSSE), respectively.     

Effect of transition metal doping on the sintering and electrochemical properties of GDC buffer layer in SOFCs

A dense Ce_0.9Gd_0.1O_2−d (GDC) interlayer is an essential component of the SOFCs to inhibit interfacial elemental diffusion between zirconia-based electrolytes (eg YSZ) and cathodes. However, the characteristic high sintering temperature of GDC (>1400°C) makes it challenging to fabricate an effective highly dense interlayer owing to the formation of more resistive (Zr,Ce)O₂ interfacial solid solutions with YSZ at those temperatures. To fabricate a useful GDC interlayer, we studied the influence of transition metal (TM) (Co, Cu, Fe, Mn, & Zn) doping on the sintering and electrochemical properties of GDC. Dilatometry data showed dramatic drops in the necking and final sintering temperatures for the TM-doped GDCs, improving the densification of the GDC in the order of Fe > Co > Mn > Cu > Zn. However, the electrochemical impedance data showed that among various transition metal dopants, Mn doping resulted in the best electrochemical properties. Anode supported SOFCs with Mn-doped, nano, and commercial-micron GDC interlayers were compared with regard to their performance and stability levels. Although all of the SOFCs showed stable performance, the SOFC with the Mn-doped GDC interlayer showed the highest power density of 1.14 W cm⁻² at 750°C. Hence, Mn-doped GDC is suggested for application as an effective diffusion barrier layer in SOFCs.     

Taguchi Optimization of Solvent-Antisolvent Crystallization to Prepare Ammonium Perchlorate Particles

The sphericity and size of ammonium perchlorate (AP) particles significantly influence the properties of composite propellants. As the AP particles become more spherical, the accumulation coefficient increases, the viscosity during casting decreases, and the particle loading and burning rate increase. Hence, the production of micronized AP particles with an average size between 1 and 20 μm is important to increase the loading percentage of AP in the composite propellant. Here, the Taguchi experimental design was used to optimize the solvent-antisolvent crystallization (SAC) process for the preparation of micronized AP particles with higher sphericity. SAC parameters such as the type of antisolvent, the solvent-to-antisolvent ratio, the antisolvent temperature, the stirring speed, and the retention time were investigated at four levels. The type of antisolvent and the solvent-to-antisolvent ratio were found to mainly contribute to improving the sphericity and size of the AP particles, respectively.