New PbSnTe heterojunction laser diode structures with improved performance

Several recent advances in the state-of-the-art of lead tin telluride double heterojunction laser diodes are summarized. Continuous Wave operation to 120 K and pulsed operation to 166 K with single, lowest order transverse mode emission to in excess of four times threshold at 80 K were achieved in buried stripe lasers fabricated by liquid phase epitaxy in the lattice-matched system, lead-tin telluride-lead telluride selenide. At the same time, liquid phase epitaxy was used to produce PbSnTe distributed feedback lasers with much broader continuous single mode tuning ranges than are available from Fabry-Perot lasers. The physics and philosophy behind these advances is as important as the structures and performance of the specific devices embodying the advances, particularly since structures are continually being evolved and the performance continues to be improved

Post-disaster waste management with carbon tax policy consideration

Generally, the activities of post-disaster waste management usually produce high carbon emissions, which can cause damage to the environment. However, the issue of carbon emissions in the post-disaster waste supply chain is neglected. Hence, this paper aims to propose a mixed-integer linear programming model to address the post-disaster waste processing supply chain network design problem with the consideration of a carbon tax policy. The proposed model is developed based on the concept of a mixed strategy of waste separation to reduce carbon emissions. Not only the carbon emission perspective but also the financial perspective for post-disaster waste supply chain management is determined in the objective function. The proposed model was verified and validated by employing a numerical example based on realistic data. Based on the numerical example, the results show that the implementation of a carbon tax policy with the mixed strategy for waste separation can reduce carbon emissions in the post-disaster waste supply chain efficiently. (C) 2021 The Authors. Published by Elsevier Ltd

Surface modification of water purification membranes to improve fouling resistance in oily water filtration

One of the biggest challenges in using water purification membranes is fouling. Surface modification using hydrophilic materials can reduce hydrophobic interactions between membrane surface and hydrophobic foulants, thereby alleviating fouling. In this Ph.D. research, polydopamine (PDA), a highly hydrophilic and universal coating agent, was used to surface-modified reverse osmosis (RO) and ultrafiltration (UF) membranes. PDA modification conditions (e.g., dopamine coating solution concentration, coating time, and pH of coating solution) control PDA deposition and can directly influence the modified membrane properties. Thus, the influence of PDA modification conditions on membrane physical, permeation, selective, and fouling properties were investigated systematically. A fundamental understanding relating the physical and permeation properties and the fouling characteristics of PDA-modified membranes was established. The RO membranes were modified with PDA at various modification conditions. Permeate fluxes during pure water and oil/water emulsion filtrations were studied. The PDA modification increased the permeate fluxes during oil/water emulsion filtration (thus, improved membrane fouling resistance) relative to unmodified membranes regardless of the initial dopamine concentration or deposition time used. However, these changes were only observed for the membranes coated under alkaline conditions, suggesting that the PDA did not deposit well under acidic condition. For UF membranes, molecular weight cutoff (MWCO) and pure water permeance decreased with increasing initial dopamine concentration or deposition time. A permeability and selectivity tradeoff was also observed. Membrane mean pore size and pore size distribution (modeled using log-normal pore size distribution) were investigated via modelling using a hindered solute transport model, Hagen-Poiseuille equation, and a stagnant film model. The PDA modification increased UF membrane surface hydrophilicity regardless of the coating conditions used, but it did not clearly change surface roughness or zeta potential (i.e., surface charge). Membrane fouling propensity was characterized using threshold flux. Compared to unmodified membranes, the threshold flux increased at minimal PDA coatings, but decreased at excessive PDA coatings. These threshold flux changes were likely governed by a tradeoff between surface hydrophilicity increase and pure water permeance decrease. Excessive PDA coatings resulted in decreased pure water permeance and possibly, pore blockage and pore size reduction, leading to higher local permeate flux causing severe fouling and decreased threshold flux.Chemical Engineerin

Approximate frequency analysis of shear wall frame structures

The finite strip method is used to determine the natural frequencies of shear wall frame buildings. The structure can be modelled in two different ways. In the first approach both the shear walls and the frames are idealized simply as an assemblage of finite strips varying thicknesses with given or computed properties, while in the second approach the shear walls are still idealized as a series of finite strips, but the frames are regarded as a number of long columns which are interconnected with each other or with finite strips through the horizontal beams. Numerical results obtained from both models indicate good agreement with finite element solutions. The proposed models can be applied to a wide range of shear wall frame assemblies and are therefore more versatile than most existing models. 14 refs.link_to_subscribed_fulltex

Axisymmetric vibration of multilayer sandwich plates and shells

The study of axisymmetric vibration of multilayer sandwich plates and shells with n stiff layers and n-1 weak cores by the finite element method is presented. A curved multilayer element method is presented and used to investigate the free vibration of circular plates, cylindrical and spherical multilayer shells. Convergent and parametric studies for a wide range of problems indicate excellent agreement with available theoretical results.link_to_subscribed_fulltex

Layout design of outpatient department: simulation study and implementation

Background: Hospital layout is one important factor affecting hospital service quality and, consequently, patient satisfaction. Generally, the layout is designed based on the experience of the hospital specialists without any systematic approaches. Purpose: Due to the increasing number of patients, the case study hospital has built a new multi-floor building to move its Outpatient Department (OPD) to operate there. Therefore, this study aims to apply the Activity Relationship Analysis (ARA) and simulation to design a new OPD layout. Methodology: Data of the previous system were analyzed using the ARA. The results were then used to design three scenarios (A, C, and D) and the other three scenarios (B, E, and F) were proposed by hospital specialists. Then, six layouts were evaluated using simulation tests and the efficiencies of the designs were measured by an average total service time per patient. Results: The simulation results showed that the average total service time of scenario A, D, E, and F were lower than scenario B and C. While the average total service time at the sub-service unit of D was the longest compared to scenario A, E, and F. These results demonstrated that scenario A, E, and F were the most efficient layouts. However, when considered thoroughly by the hospital specialists, scenario A was eventually selected. Conclusion: This study can contribute to scientific literature as it demonstrates the application of the ARA and simulation in the design of the multi-floor layout, an aspect under-researched in existing studies. This study also provides the practical implication suggesting that these techniques should be used together in the layout designs because they can help to determine the correctness and efficiency of the layout design before actual implementation