Flexible Cu(In,Ga)Se2 solar cell on stainless steel substrate deposited by multi‐layer precursor method: its photovoltaic performance and deep‐level defects

Cu(In,Ga)Se₂ (CIGS) films on soda‐lime glass and stainless steel (SUS) substrates with several [Ga]/([Ga] + [In]), GGI, and Fe concentrations are fabricated by so‐called “multi‐layer precursor method”. From optical deep‐level transient spectroscopy, deep‐level defect located at 0.8 eV from valence band maximum (E_V) is observed. This defect becomes recombination center when GGI is over 0.4, thereby decreasing cell performances. Fe‐related deep‐level defect is moreover detected in CIGS film on SUS substrate situated at 0.45 eV from E_V. Its density is consistent with Fe concentration in CIGS films. According to SCAPS simulation and experimental results, Fe concentration of above threshold (1.0 × 10¹⁶ atom/cm³) decreases carrier lifetime and carrier density and has more harmful influence on cell performances with GGI of above 0.4. On the other hand, Fe concentration of below threshold (1.0 × 10¹⁶ atom/cm³) has no detrimental impact on cell performances. Namely, conversion efficiency (η) is slightly changed by below 2%. CIGS solar cell on SUS substrate with η of 17.5% is fabricated by decreasing Fe concentration to approximately 5.2 × 10¹⁶ atom/cm³ although higher than the threshold value. Copyright © 2016 John Wiley & Sons, Ltd.     

Properties and Algorithms for Unfolding of Probabilistic Data-Flow Graphs

It is known that any selection statement (e.g. if and switch-case statements) in an application is associated with a probability which could either be predetermined by user input or chosen at runtime. Such a statement can be regarded as a computation node whose computation time is represented by a random variable. This paper focuses on iterative applications (containing loops) reflecting those uncertainties. Such an application can then be transformed to a probabilistic data-flow graph.Two timing models, the time-invariant and time-variant models, are introduced to characterize the nature of these applications. Since there can be many unfolding factors associated with each of the possible graph outcomes, for the time-invariant model, we propose a means of selecting a constant minimum rate-optimal unfolding factor for unfolding the probabilistic graph. We demonstrate that this factor guarantees the best schedule length.We also suggest a good estimate for choosing an unfolding factor for a graph under the time-variant model. Experiments show that using our selection scheme results in an iteration period close to the theoretical iteration bound of the experimental graph. Furthermore, this paper discusses an alternative approach which selects a few optimal schedules (with respect to the graph outcomes) to be stored in the system. The other possibilities will be represented by a modified template graph.     

Color and hardness of durian chips irradiated by controlled low power microwave

Durian cv. Monthong was dried by using controlled low power microwave at atmospheric pressure. Although the hardness of durian chips was higher than that obtained from microwave drying in vacuum, it was comparable to the hardness of conventional products. According to Hunter Lab color parameters, durian surfaces became lighter but their yellowness was decreased after the microwave drying. Compared between 16 and 27 W irradiations, the higher power led to the increase in lightness and yellowness. Cross-sectional micrographs revealing the porous structure confirmed that a lower hardness was obtained in the case of 16 W.     

Parallel simulation of concentration dynamics of nano-particles in High Gradient Magnetic Separation

In this paper, the concentration dynamics of weakly magnetic nano-particles dispersed in a fluid medium during the process of High Gradient Magnetic Separation is studied by using a computational approach. The continuity equations describing the time rate of change of the particle volume concentration in the system are solved numerically by using the finite difference method as initial and boundary value problems. Features of the concentration distribution in the system are depicted both in transient and steady states. Saturation buildup at the steady state and the time required for the occurrence of saturation buildup are given as basic guides for experiments. Parallel algorithms are implemented for simulations of concentration dynamics. The approaches are based on a distributed model, utilizing the message passing interface. Two schemes of parallel computing are developed based on different data-partitioning patterns and benchmark results are compared.     

Reducing Data Hazards on Multi-pipelined DSP Architecture with Loop Scheduling

Computation intensive DSP applications usually require parallel/pipelined processors in order to meet specific timing requirements. Data hazards are a major obstacle against the high performance of pipelined systems. This paper presents a novel efficient loop scheduling algorithm that reduces data hazards for such DSP applications. This algorithm has been embedded in a tool, called SHARP, which schedules a pipelined data flow graph to multiple pipelined units while hiding the underlying data hazards and minimizing the execution time. This paper reports significant improvement for some well-known benchmarks showing the efficiency of the scheduling algorithm and the flexibility of the simulation tool.     

Analysis of steel production in Thailand: Environmental impacts and solutions

Steels were the upstream of various products. The environmental performance of steel can affect those of the downstream products. In this work, environmental impacts of individual steels, i.e. slab, hot-rolled, cold-rolled, hot-dipped galvanized, and electro-galvanized steels, were studied, via life cycle assessment. The impact assessment methods of IPCC 2007 GWP 100a and Eco-indicator 99 (H) were used to cover the impact categories of Global warming potential, Fossil fuels, Ecotoxicity, Minerals, Carcinogens, and Respiratory inorganics. In all categories, the slab showed the lowest impacts and the hot-dipped galvanized steel showed the highest impacts. The main causes of the impacts were attributed to these inputs; steel, energy, and zinc. The emissions from steel production plants showed relatively low impacts. Small amount of zinc input can cause huge environmental impacts. The impacts of Fossil fuels, Minerals, and Ecotoxicity, of 1-kg zinc were 2.9, 116.9, and 39.6 times of those caused by 1-kg cold-rolled steel, respectively. The reduction of zinc consumption and the improvement of zinc production process, in terms of reduction of heavy metal emissions, could largely improve environmental performance of the galvanized steels.     

A Fourth-Order Compact Finite Difference Scheme for Higher-Order PDE-Based Image Registration

Image registration is an ill-posed problem that has been studied widely in recent years. The so-called curvature-based image registration method is one of the most effective and well-known approaches, as it produces smooth solutions and allows an automatic rigid alignment. An important outstanding issue is the accurate and efficient numerical solution of the Euler-Lagrange system of two coupled nonlinear biharmonic equations, addressed in this article. We propose a fourth-order compact (FOC) finite difference scheme using a splitting operator on a 9-point stencil, and discuss how the resulting nonlinear discrete system can be solved efficiently by a nonlinear multi-grid (NMG) method. Thus after measuring the h-ellipticity of the nonlinear discrete operator involved by a local Fourier analysis (LFA), we show that our FOC finite difference method is amenable to multi-grid (MG) methods and an appropriate point-wise smoothing procedure. A high potential point-wise smoother using an outer-inner iteration method is shown to be effective by the LFA and numerical experiments. Real medical images are used to compare the accuracy and efficiency of our approach and the standard second-order central (SSOC) finite difference scheme in the same NMG framework. As expected for a higher-order finite difference scheme, the images generated by our FOC finite difference scheme prove significantly more accurate than those computed using the SSOC finite difference scheme. Our numerical results are consistent with the LFA analysis, and also demonstrate that the NMG method converges within a few steps.     

Simulation design and evaluation of hybrid PV/T assisted desiccant integrated HA-IR drying system (HPIRD)

The aim of this research is to make a simulation design for a hybrid PV/T assisted desiccant integrated HA-IR drying system (HPIRD) which has two components: a photovoltaic air collector (PVAC), and a desiccant silica gel bed (DB). The PVAC and DB have been improved by fins and different bed shapes for improved performance of the drying system. The designed simulation system used TRNSYS and CFX programs with new PVAC and DB components. The two new models were used to develop a new drying system and compared it with a common system. The drying test chose the optimal simulated case and compared it with the experimental results.The simulation results indicated that the PVAC_AF and v-shape DB were suitable, and they also indicated consistent results when compared to the experiment. Thus, the HPIRD used the optimal case to develop a system. The performance evaluation studies indicated that the HPIRD drying test at 60 °C and velocity of 0.6 m/s reduced the drying time by 44% with less energy consumption (63%) compared to hot air drying. HPIRD drying also gave better results over hot air-infrared drying. Finally, drying time, drying rate and energy consumption were reduced considerably with the hybrid drying system.