Diffusion couple preparation using cast coating technique

A novel diffusion couple preparation technique suitable for the measurement of diffusivities in molten metals and semiconductors via the long capillary method has been developed. The so-called cast coating technique involves casting of a molten alloy, which contains the impurity element to be diffused, on top of the pure solvent rods. Planar, oxide and defect free interfaces were produced at the alloy/solvent junction of the diffusion couple following basic solidification principles and a controlled atmosphere. It was noted that the thermal properties of both the molten alloy and the mould were critical in determining the location and planarity of the diffusion couple interface. The Sn/Sn-1 wt% Au and Pb/Pb-1 wt% Au diffusion couples in conjunction with moulds machined from graphite, porous graphite and a machinable ceramic were chosen as a case study.     

A mathematical modeling approach to resource allocation for railroad-highway crossing safety upgrades

State Departments of Transportation (S-DOT's) periodically allocate budget for safety upgrades at railroad-highway crossings. Efficient resource allocation is crucial for reducing accidents at railroad-highway crossings and increasing railroad as well as highway transportation safety. While a specific method is not restricted to S-DOT's, sorting type of procedures are recommended by the Federal Railroad Administration (FRA), United States Department of Transportation for the resource allocation problem. In this study, a generic mathematical model is proposed for the resource allocation problem for railroad-highway crossing safety upgrades. The proposed approach is compared to sorting based methods for safety upgrades of public at-grade railroad-highway crossings in Tennessee. The comparison shows that the proposed mathematical modeling approach is more efficient than sorting methods in reducing accidents and severity.     

Joint decisions on inventory replenishment and emission reduction investment under different emission regulations

Carbon emission regulation policies have emerged as mechanisms to control firms’ carbon emissions. To meet regulatory requirements, firms can make changes in their production planning decisions or invest in green technologies. In this study, we analyse a retailer’s joint decisions on inventory replenishment and carbon emission reduction investment under three carbon emission regulation policies. Particularly, we extend the economic order quantity model to consider carbon emissions reduction investment availability under carbon cap, tax and cap-and-trade policies. We analytically show that carbon emission reduction investment opportunities, additional to reducing emissions as per regulations, further reduce carbon emissions while reducing costs. We also provide an analytical comparison between various investment opportunities and compare different carbon emission regulation policies in terms of costs and emissions. We document the results of a numerical study to further illustrate the effects of investment availability and regulation parameters.     

FAPbI3‐Based Perovskite Solar Cells Employing Hexyl‐Based Ionic Liquid with an Efficiency Over 20% and Excellent Long‐Term Stability

Formamidinium lead triiodide (FAPbI₃)‐based perovskite materials are of interest for photovoltaics in view of their close‐to‐ideal bandgap, allowing absorption of photons over a broad solar spectrum. However, FAPbI₃‐based materials suffer from a notorious phase transition from the photoactive black phase (α‐FAPbI₃) to nonperovskite yellow phase (δ‐FAPbI₃) under ambient conditions. This transition dramatically reduces light absorbtion, thus, degrading the photovoltaic performance and stability of ensuring solar cells. In this study, 1‐hexyl‐3‐methylimidazolium iodide (HMII) ionic liquid (IL) is employed as an additive for the first time in FAPbI₃ perovskite to overcome the above‐mentioned issues. HMII incorporation facilitates the grain coarsening of FAPbI₃ crystal owing to its high‐polarity and high‐boiling point, which yields liquid domains between neighboring grains to reduce the activation energy of the grain‐boundary migration. As a result, the FAPbI₃ active layer exhibits micron‐sized grains with substantially suppressed parasitic traps with an Urbach energy reduced by 2 meV. Hence, the resulting perovskite solar cell achieves an efficiency of 20.6% with notable increase in open circuit voltage (V_OC) of 80 mV compared with HMII‐free cells (17.1%). More importantly, the HMII‐doped FAPbI₃‐based cells show a striking enhancement in shelf‐stability under high humidity and thermal stress, retaining >80% of their initial efficiencies at 60 ± 10% relative humidity and ≈95% at 65 °C.     

On some difference sequence spaces of fuzzy numbers

In this paper, using the difference operator of order m and a lacunary sequence \(\theta = (k_{r})\), we introduce and examine some classes of sequences of fuzzy numbers. Furthermore, we study some of their properties like completeness, solidity, symmetricity and convergence free. We also give some inclusion relations related to these classes.     

Synthesis of monodisperse CdS nanorods catalyzed by Au nanoparticles

Semiconductor nanocrystals (dots, rods, wires, etc.) exhibit a wide range of electrical and optical properties that differ from those of the corresponding bulk materials. These properties depend on both nanocrystal size and shape. Compared with nanodots, nanorods have an additional degree of freedom, the length or aspect ratio, and reduced symmetry, which leads to anisotropic properties. In this paper, we report the Au nanoparticlecatalyzed colloidal synthesis of monodisperse CdS nanorods. Based on systematic high resolution transmission electron microscopy studies, we propose a growth mechanism for these nanorods. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Reflection and transmission coefficients of multiple chiral layers

During the last decades, there has been an increasing interest in the research and use of chiral materials due to the possibility of manufacturing them at the optical, millimeter wave and microwave frequencies. Important attention has been focused on the properties of chiral media because the developments in constructing artificial chiral materials provide additional freedom for design processes via the chirality parameter[1―6]. In fact, reflec- tance of a chiral plate absorber studied by Lia…     

Near‐Unity Emitting Copper‐Doped Colloidal Semiconductor Quantum Wells for Luminescent Solar Concentrators

Doping of bulk semiconductors has revealed widespread success in optoelectronic applications. In the past few decades, substantial effort has been engaged for doping at the nanoscale. Recently, doped colloidal quantum dots (CQDs) have been demonstrated to be promising materials for luminescent solar concentrators (LSCs) as they can be engineered for providing highly tunable and Stokes‐shifted emission in the solar spectrum. However, existing doped CQDs that are aimed for full solar spectrum LSCs suffer from moderately low quantum efficiency, intrinsically small absorption cross‐section, and gradually increasing absorption profiles coinciding with the emission spectrum, which together fundamentally limit their effective usage. Here, the authors show the first account of copper doping into atomically flat colloidal quantum wells (CQWs). In addition to Stokes‐shifted and tunable dopant‐induced photoluminescence emission, the copper doping into CQWs enables near‐unity quantum efficiencies (up to ≈97%), accompanied by substantially high absorption cross‐section and inherently step‐like absorption profile, compared to those of the doped CQDs. Based on these exceptional properties, the authors have demonstrated by both experimental analysis and numerical modeling that these newly synthesized doped CQWs are excellent candidates for LSCs. These findings may open new directions for deployment of doped CQWs in LSCs for advanced solar light harvesting technologies.