Influence of surface texturization on the light trapping andspectral response of silicon solar cells

A quantitative model that explains the spectral response, internal quantum efficiency, total short-circuit current, open-circuit voltage, and efficiency of high-efficiency solar cells with textured front surface and Lambertian back-surface reflectors is presented. A comparison of the textured cell characteristics is made with those of planar cells, and the separate roles of the front surface reflection coefficient and internal quantum efficiency in enhancing the short-circuit current have been investigated. It is shown that, in the case of large diffusion lengths, almost all the contribution to the increase of spectral response on texturization is due to the reduced reflection coefficient whereas, for small diffusion lengths, there is a significant increase in internal quantum efficiency on texturization, especially in the region of higher wavelengths. However, there is a small decrease in open-circuit voltage for large diffusion lengths, whereas no significant change is observed for small diffusion lengths on texturization. Nevertheless, there is a net gain in power conversion efficiency which is larger for smaller diffusion lengths     

Electrical and chemical diagnostics of transformers insulation. B.Accelerated aged insulation samples

This paper describes the analysis of accelerated aged insulation samples to investigate the degradation processes observed in the insulation from aged power transformers. Short-term accelerated ageing experiments were performed on paper-wrapped insulated conductors and on pressboard samples. The condition of aged insulation samples was investigated by two relatively new diagnostic techniques: (a) measurements of interfacial polarization spectra by a DC method; and (b) measurements of molecular weight and its distribution by gel permeation chromatography (GPC). Several other electrical properties of the paper/pressboard samples were also studied. Possible correlations have been investigated among the different measured properties. The GPC results have been used to predict how power transformer insulation molecular weights change with temperature and time     

Mechanical behavior and microstructure characterization of sinter-forged SiC particle reinforced aluminum matrix composites

A novel, low-cost sinter-forging approach to processing particle reinforced metal matrix composites for high-performance applications was examined. The microstructure of the sinter-forged composites exhibited relatively uniform distribution of SiC particles, which appeared to be somewhat aligned perpendicular to the forging direction. The degree of alignment and interparticle bond strength was not as high as that observed for the extruded composite. The sinter-forged composite exhibited higher Young’s modulus and ultimate tensile strength than the extruded material, but lower strain-to-failure. The higher modulus and strength were attributed to the absence of any significant processing-induced particle fracture, while the lower strain-to-failure was caused by poorer matrix interparticle bonding compared to the extruded material. Fatigue behavior of sinter-forged composites was similar to that of the extruded material. Fe-rich inclusions were extremely detrimental to fatigue life. Cleaner processing, which eliminated the inclusions, enhanced the fatigue life of the sinter-forged composites to levels similar to that of the extruded material.     

Solid state reactions of cordierite precursor oxides and effect of CaO doping on the thermal expansion behaviour of cordierite honeycomb structures

The extruded cordierite honeycomb structure from a stoichiometric formulation of talc, kaolinite, and alumina was subjected to TGA-DSC, dilatometric and XRD investigations. The experimental observations were made to identify the phase transformation sequence in order to understand the solid state reactions involved in the cordierite formation. A maximum cordierite content of 90% was achieved for the samples sintered at 1693 K with a soaking time of 4 h, corresponding to a lowest coefficient of thermal expansion (CTE) of 0.74 × 10^–6/K (along the direction of extrusion) was observed. Attempts were made to establish correlations with cordierite content, processing temperature and CTE of the samples. A few mechanisms are proposed to explain our observations. Attempts are also made to rationalize the low CTE observed along the direction of extrusion on the basis of orientation of anisotropic cordierite crystals as revealed by the transverse I-ratio calculated from the XRD patterns. Effect of CaO doping on CTE of cordierite has been studied in the present work. It was observed that though there is an increase in bulk thermal expansion of cordierite honeycombs on CaO doping due to the absence of micro-cracks as reveled by thermal cycling hysteresis, axial anisotropy was found to be reduced significantly.     

Network Model for Rural Roadway Tolling with Pavement Deterioration and Repair

The objective of roadway tolling in rural areas is often tied to revenue generation for roadway maintenance. Thus, rural pricing models should directly incorporate a pavement deterioration and maintenance model. However, the interactions between these models are not simple, because tolls cause traffic diversion, which in turn affects deterioration rates and forecasted revenue. This article describes a rural pricing model which calculates diversion endogenously with a network assignment model. This model captures deterioration rates and pavement condition in the toll‐setter's objective function, maximizing long‐run net present value of the highway infrastructure. A novel deterioration model is used which is particularly suitable for computational efficiency. The resulting model is discontinuous and nondifferentiable, and involves solving a combinatorial knapsack problem as a subproblem. Thus, a simulated annealing‐based algorithm is presented to solve it, in the framework of a new solution method built upon partitioning the feasible region. A demonstration is made using a network representing the state of Wyoming (28 zones, 60 nodes, and 188 links). Sensitivity analyses reveal that although the locations for optimal tolling are relatively stable as demand changes, the revenue collected can vary substantially. Relatively simple models are used throughout for computational reasons, and future research should investigate strategies for incorporating more advanced pavement and network models.     

Multilayer Hierarchical Model for Mobility Management in IPv6: A Mathematical Exploration

The mobility solution provided by Mobile IPv6 (MIPv6) imposes too much signaling load to the network and enforces large handoff latency to end user. Hierarchical MIPv6 (HMIPv6) on the other hand, is designed by organizing MIPv6 in layered architecture and performs better than MIPv6 in terms of handoff latency and signaling load. Observation shows that, there is still possibility to shrink the handoff latency and the signaling load by further extending HMIPv6 into multiple layers. To explore this possibility of enhanced performance through layered architecture, this paper aimed at mathematical exploration of an N-layered MIPv6 network architecture in order to figure out the optimal levels of hierarchy for mobility management. A widespread analysis is carried out on various parameters such as location update frequency and cost, handoff latency and packet delivery cost. Influence of queuing delay on handoff latency is examined by modeling M/M/1/K queue in the architecture and user mobility is modeled using Markov chain. Analytical investigation reveals that three levels of hierarchy in MIPv6 architecture provide an optimal solution for mobility management.     

Effect of phenolic resin infiltration content on the structural and electrochemical properties of hierarchical porous carbons

Hierarchical porous (micro-, meso- and macro-porous) carbons (HPCs) are synthesized by a facile replica template method with phenolic resin (PR) as a carbon source and hollow mesoporous silica as a hard template. The morphology of the HPCs can be easily controlled by altering the mass ratio of PR to SiO₂ spheres. Structural characterizations reveal that a well-defined HPC with a large surface area of 1141 m² g^?1 is formed when PR/SiO₂ is 1:1. With further increasing PR infiltration content, macropores of carbons disappear while solid structures appear. A possible formation mechanism for the morphological transformation of HPCs is proposed. The effect of phenolic resin infiltration content on the electrochemical properties of HPCs-based materials as supercapacitor electrodes is further evaluated. The HPCs-1(PR/SiO₂ = 1) electrode exhibits the highest specific capacitance of 256 F g^?1 due to its faster diffusion of electrolyte ions and lower charge transfer resistance. The relationship between the morphology and the electrochemical behavior of HPCs is also elucidated.     

25th Anniversary Article: Interfacing Nanoparticles and Biology: New Strategies for Biomedicine

The exterior surface of nanoparticles (NPs) dictates the behavior of these systems with the outside world. Understanding the interactions of the NP surface functionality with biosystems enables the design and fabrication of effective platforms for therapeutics, diagnostics, and imaging agents. In this review, we highlight the role of chemistry in the engineering of nanomaterials, focusing on the fundamental role played by surface chemistry in controlling the interaction of NPs with proteins and cells.     

1‐Aza‐15‐Crown‐5 Functionalized Graphene Oxide for 2D Graphene‐Based Li+‐ion Conductor

Attachment of Li⁺ ion on graphene surface to realize Li⁺‐ion conductor is a real challenge because of the weak interaction between the ions and the functional groups of graphene oxide; although, a large number of theoretical results are already available in the literature. To overcome this problem, graphene oxide is functionalized by 1‐aza‐15‐crown‐5, the cage‐like structure containing four oxygens that can bind Li⁺ ion through electrostatic interaction. Li⁺ migration on graphene surface has been investigated using ac relaxation mechanism. Perfect Debye‐type relaxation behavior with β (relaxation exponent) value ≈1 resulting from single ion is observed. The activation energy of Li⁺ migration arising due to cation‐π interaction is found to be 0.37 eV, which agrees well with recently reported theoretical value. It is believed that this study will help to design isolated ion conductors for Li⁺‐ion battery.     

Three-dimensional finite element analysis of multi-stage hot forming of railway wheels

Three-dimensional finite element analyses has been carried out using DEFORM 3D software on multi-stage hot forming of railway wheels involving the processes of upsetting, forging, and punching of wheels. Thermal analysis related to heating the blank in furnace and all intermediate heat transfer stages between deforming operations have been conducted. Rigid viscoplastic finite element method has been utilized for coupled thermo-mechanical analysis of the processes. Modeling of punching the wheel bore has been carried out using Cockcroft and Latham fracture criterion. Evolution of thermo-mechanical parameters at selected points within the workpiece has been studied in detail. The method of simulating the effects of various process parameters has been explained using relevant mathematical relations. This study shows that design, optimization, and analysis of process perturbations for multi-stage railway wheel manufacturing process can be done efficiently in three-dimensional finite element simulations instead of conventional time and cost intensive trials. It might be necessary to use the results of finite element analysis in shop-floor to enhance productivity and reduce wheel rejection.