Omnidirectional broadband absorption enhancement in laterally assembled quadrangle silicon nanowire solar cells

In this paper, effects of geometry and spatial placement of quadrangle silicon nanowires (NWs) on the performance of laterally assembled NW solar cells are investigated. Two different approaches are proposed to reach the broadband absorption enhancement in these types of solar cells. In the first method, a semi-periodic array is used to have a better utilization of the optical antenna effect. The current density can be enhanced as a result of a compromise between the diffraction and optical antenna effects. In the second approach, multiple NWs with different geometries are employed to use the cavity modes of the various NWs. The best current density is achieved for the combination of both of these methods. The different parameters in each structure are selected using the optimization algorithm. Finally, a multilayer structure with the optimized dimensions is proposed to obtain the maximum achievable current density in ultrathin solar cells. The broadband absorption enhancement in the proposed structure is preserved for a wide range of incident angles. Using the multilayer NW arrays, it is possible to improve the absorption enhancement of solar cells without introducing more absorbing material.     

Numerical and experimental study on the flow history effects of axial flow on the Couette–Taylor flow

In this research, experimental and numerical techniques are used to study the flow history effects of axial flow on the Couette–Taylor flow. For the experimental investigation, the flow is visualized using the PIV technique with reflective particles with a density of 1.62 g/cm³. Dispersed in a solution, the particles have a strong refraction index equal to 1.85. In this study, two protocols are adopted to study the effect of an axial flow superimposed on a Couette–Taylor flow, and of the history of the flow. The first one, the direct protocol, consists of imposing an azimuthal flow to the inner cylinder. In this case, when the regime is established, the axial flow is superimposed. The second protocol, the inverse protocol, consists of imposing first the axial flow in the gap of the system, after which an azimuthal flow is conveyed. The Couette–Taylor flow with axial flow is strongly dependent on the flow history (the protocol). Thus, the flow structures and development for different protocols are studied and analyzed here experimentally and numerically. In addition, from the numerical results, mathematical models for the two protocols are presented. For the direct protocol, a new relation between the axial Reynolds number, which stabilizes the Couette–Taylor flow, and the Taylor number is presented; for the inverse protocol, a new mathematical model for the critical Taylor number is developed as a function of the axial Reynolds number and also the first critical Taylor number without axial flow.     

Optimisation of hot mix asphalt performance based on aggregate selection

Researchers over the last four decades have identified and demonstrated the effects of aggregate morphological properties (particularly shape, size distribution, angularity and texture) on the mechanical properties of hot mix asphalt (HMA). Rare studies, however, have clearly established the relationships between the aggregate properties and pavement performance. Therefore, they have not provided methods to optimise aggregate properties at the design stage to improve that performance. This study focuses on understanding the effects of aggregate gradation and type on moisture damage resistance of HMA and on pavement performance as indicated by stiffness and rutting. Results show that basalt aggregate achieves higher moisture susceptibility resistance and stiffness than limestone aggregate. Coarser gradation has the highest permanent deformation, while open gradation 2C provides the lowest moisture damage resistance. Furthermore, dense gradation 4C provides the lowest rutting and the highest stripping resistance. It is indicated that suitable selection of aggregate type and gradation can improve pavement performance and reduce the moisture damage problem of HMA.     

A low voltage vertical comb RF MEMS switch

Design and simulations of a novel RF MEMS switch is reported as a solution to many RF wireless applications. A new comb structure for RF MEMS switch is proposed for low voltage and high frequency operations. Isolation degree and actuation voltage, both improved by the new structure. The mechanical and electromagnetic simulation results show better performance for this new switch compared to parallel plate switch. The simulation is done by the intellisuit and HFSS softwares. The Simulation results show that the actuation voltage is decreased by 13% and the linearity of the switch displacement with respect to the actuation voltage is improved by 22% compared to the parallel plate structure. The HFSS simulation results indicate an insertion loss better than 0.33 dB at 50 GHz and isolation greater than 13.4 dB at 50 GHz.     

Numerical simulations of ultrathin CdTe solar cells with a ZnxCd1−xS window layer and a Cu2O hole transport layer

CdTe solar cells are investigated using a solar cell capacitance simulator software. First, a conventional fluorine-doped tin oxide (FTO)/i-SnO₂/CdS/CdTe structure is simulated using input experimental data to verify the simulation process. To make the cell more economical, the thickness of the CdTe layer is decreased, resulting in a degradation of the device performance. To decrease the minority-carrier recombination loss of the designed structure, a p-type Cu₂O layer is exploited at the back contact as a hole transport electron blocking layer (HT–EBL). To address the performance degradation, a ZnS/CdS bilayer is used as the window layer. The interdiffusion of Cd into the ZnS due to annealing treatment and the formation of Zn_xCd_1?xS compound are also studied. Cell parameters include the thickness, doping concentration, and carrier lifetime are then optimized to enhance the power conversion efficiency (PCE). The proposed FTO/i-SnO₂/Zn_0.5Cd_0.5S/CdTe/Cu₂O configuration shows the best PCE of 17.5%, short-circuit current density (J_sc) of 27.8 mA/cm², open-circuit voltage (V_oc) of 0.87 V, and fill factor of 72.34% under AM1.5G illumination.

     

Scatter search algorithm for supplier selection and order lot sizing under multiple price discount environment

Supplier selection is one the most important elements of supply chain management. This function involves evaluation of many factors such as, cost of parts/materials, size of order, quality, and delivery performance. Therefore, this problem is categorized as multi-criteria decision making problems. Different approaches have been applied in order to assess and select the suppliers when suppliers offer discount on the unit price. In practical conditions, buyers may face a situation where different types of discount may be offered by candidate suppliers. None of the previous studies have considered different discount schemes simultaneously. In this article a mathematical model is introduced which consider different types of discount (all-unit cost, incremental discount, and total business volume discount) through multi-objective formulation for single item purchasing problem. In addition, constraints such as suppliers’ capacity and demand are taken into consideration in the model. Due to the complexity of the problem a proposed scatter search algorithm (SSA) is presented to solve this problem. Finally several sample problems have been solved by the proposed SSA and the exact (branch and bound) method. The results illustrate slight relative errors to compare with reasonable saving in computational times.     

A web-based expert system for the planning and completion of multilateral wells

This study introduces the development of a web-based fuzzy expert system (MULTSYS) for aiding in the preliminary planning and completion of multilateral wells. The reasoning process is based on a systematic planning approach for screening and selecting multilateral well candidates, lateral-section completion types, and junction complexity levels. A modular approach was employed. It consists of a number of knowledge modules which are integrated to provide various conclusions at different levels. The system has been fully implemented to run on the web and provides an excellent example of how a number of heterogeneous tools and applications can be integrated on the web. Rule-based knowledge sources and the inference mechanisms were implemented using ReSolver. The system clearly demonstrated the integration of the various tools in a seamless user-friendly environment. The structure of the developed system is presented together with case studies to demonstrate its main functionality.     

Pinch technology: an efficient tool for chemical-plant energy and capital-cost saving

Through its 20 year history, pinch analysis has proved to be a simple concept in a field known for complex mathematical methods. Reports of industrial applications claim design improvements in energy saving, as well as reduced capital investment costs, due to optimising the number of heat exchangers required for the same heat duty, after pinch technology was introduced. Some of the recent pinch developments are: pressure drop optimisation, distillation column profiles, low temperature process design, batch process integration, water and waste water minimisation and emissions targeting. This paper attempts to describe this technology, considering both new designs or modifications applied to chemical process plants.     

Macroeconomic impacts of oil price volatility: mitigation and resilience

Dependency on oil-derived fuels in various sectors, most notably in mobility, has left the global economy vulnerable to several macroeconomic economic side effects. Numerous studies have addressed the effect of price volatility on specific economic parameters. However, the current literature lacks a comprehensive review of the interactions between global macroeconomic performance and oil price volatility (OPV). Price volatility is intrinsic in commodity markets, but has been advancing at a faster rate in the crude oil market in comparison to other commodities over the past decade, reflecting the status of oil as the most globalised commodity. In this paper, the analytical literature review and analysis of the behavioral responses of macroeconomic agents to OPV shows that such volatility has several damaging and destabilizing macroeconomic impacts that will present a fundamental barrier to future sustainable economic growth if left unchecked. To ensure macroeconomic isolation from OPV, a combination of supply and demand-side policies have been recommended that can help to mitigate and build resilience to the economic uncertainty advanced by OPV.