Novel Direct Nanopatterning Approach to Fabricate Periodically Nanostructured Perovskite for Optoelectronic Applications

While indirectly patterned organic–inorganic hybrid perovskite nanostructures have been extensively studied for use in perovskite optoelectronic devices, it is still challenging to directly pattern perovskite thin films because perovskite is very sensitive to polar solvents and high‐temperature environments. Here, a simple and low‐cost approach is proposed to directly pattern perovskite solid‐state films into periodic nanostructures. The approach is basically perovskite recrystallization through phase transformation with the presence of a periodic mold on an as‐prepared solid‐state perovskite film. Interestingly, this study simultaneously achieves not only periodically patterned perovskite nanostructures but also better crystallized perovskites and improved optical properties, as compared to its thin film counterpart. The improved optical properties can be attributed to the light extraction and increased spontaneous emission rate of perovskite gratings. By fabricating light‐emitting diodes using the periodic perovskite nanostructure as the emission layers, approximately twofold higher radiance and lower threshold than the reference planar devices are achieved. This work opens up a new and simple way to fabricate highly crystalline and large‐area perovskite periodic nanostructures for low‐cost production of high‐performance optoelectronic devices.     

Microencapsulation of reactive amine by interfacially engineered epoxy microcapsules for smart applications

The most common approach for incorporation of extrinsic self-healing functionality relies on introducing healant-loaded micro-containers in the polymeric formulation. In this context, a healing system based on encapsulated epoxy resin and amine hardener appears to be one of the most economically viable solutions, in view of the chemical as well as mechanical compatibility with the matrix. Encapsulation of epoxy resins has been extensively studied while the high reactivity of the amine hardener renders its encapsulation rather difficult and has been attempted with only modest success. The purpose of the present work is to adopt an interfacial polymerization approach for the preparation of epoxy microcapsules encapsulating a reactive amine hardener (triethylene tetramine). The effects of experimental parameters, including reaction temperature, stirring speed and epoxy/amine concentration ratio on the microcapsule formation were investigated. A polymeric surfactant was used to stabilize the suspension to modulate the particle size distribution of the resultant microcapsules. The highest encapsulation efficiencies were obtained when the reaction medium was maintained at 70 °C under stirring (600 rpm) at epoxy/amine ratio of 10/3.2. The microcapsule dimensions and core content could be tailored, following this encapsulation approach of interfacial polymerisation. Under optimal conditions, spherical microcapsules with 100% yield and 12% core content were obtained.     

Hydrochemistry and mercury cycling in a High Arctic watershed

Mass budgets for total mercury, major ions and nutrients were calculated for Amituk Lake, located on Cornwallis Island, Nunavut, Canada. Total mercury in two distinct snowpacks averaged 1.25 and 4.21 ng L(-1); the discharge-weighted concentration of influent streams averaged 0.76 ng L(-1). The recent and pre-industrial Hg(T) fluxes in atmospheric deposition to the catchment were estimated to be 0.57 and 0.23 microg m(-2) but through retention within the catchment and/or re-volatilization from the melting snowpack, these decreased by 69% in the lake inflow. The spring freshet was the prime conduit for transporting Hg(T) into Amituk Lake. Because of limited mixing of surface runoff with the lake water column during snowmelt, 59% of the Hg(T) input was directly discharged through the outflow, 16% entered the lake water column where concentrations increased from 0.23 to 0.33 ng L(-1) from June to August and 25% was deposited to the bottom sediments producing a sediment Hg(T) flux of 3.1 microg m(-2).     

Phosphorous limitation in an arctic river biofilm—A whole ecosystem experiment

A fourth-order arctic river was experimentally enriched with phosphate (7.7 ± 7.0 μ g 1⁻¹) to determine the effect of such a loading (equivalent to a community of 10,000 people) upon the trophically important biofilm. The effect upon a light-grown biofilm (an autotrophic/heterotrophic assemblage) and a dark-grown biofilm (predominantly heterotrophic assemblage) was determined after 28 days of colonization. Seven attributes of the biofilms were monitored, 2 autotrophic indices, chlorophyll , [¹⁴C]HCO₃ incorporation into lipids and 5 heterotrophic indices; [¹⁴C]acetate incorporation into lipids, metabolic heat output, turn-over times of microbially labile glucose and glutamate and mineralization of microbially recalcitrant ring-labelled [¹⁴C]hydroxybenzoic acid. The findings showed that the addition of phosphorus resulted in a substantial stimulation of both autotrophic and heterotrophic processes suggesting that arctic rivers of this type would be liable to cultural eutrophication.     

Modelling natural capital: The case of landscape restoration on the South Downs, England

Habitat suitability modelling has shown itself to be an important decision support tool for those concerned with the problem of where to target habitat and landscape restoration efforts. However, present approaches generally focus upon the biophysical characteristics of habitats and sites, and tend to ignore the social values associated with landscapes and habitat features. As a result current approaches only partially resolve the problems we face when dealing with a multifunctional landscape. In this paper, we examine how these limitations of current approaches may be overcome.The paper shows that present approaches to suitability modelling can be broadened by linking them to ideas about natural capital and landscape function. The approach is illustrated by means of a case study from the South Downs of England. It is suggested that by using the approach to model the spatial aspects of the natural capital associated with a given landscape, we may provide the user community with a framework that more fully addresses management issues that arise in the context of a sustainable, multifunctional landscape. In the case of the South Downs we show that restoration strategies that seek to take account of the multiple functions of downland differ from those which focus exclusively on enhancing or restoring the biodiversity of these areas.     

Elastic and inelastic analysis for weld failure prediction of two adjacent steel buildings

Two adjacent buildings near the epicenter of the January 17th Northridge earthquake, one with weld fractures and one without weld fractures, are considered in this research. Both buildings are six stories in height, and their primary lateral force resisting system comprises special moment resisting frames above grade. The buildings considered are referred to herein as the East Building and the West Building. Two basic types of computer studies were performed. One was an elastic 3-D analysis using SAP90, and the other an inelastic 2-D analysis using DRAIN-2DX. Three different models were, created for the elastic analysis. Two for the East Building, designated the ‘benchmark model’, and the ‘probable model’, and one for the West Building, designated the ‘West Building model’. Two different models were created for the inelastic analysis only for the East Building, also called the benchmark model and the probable model. The East Building was unoccupied at the time of the earthquake, hence two models were created for this building. The benchmark model is representative of the design state of the building, while the probable model is representative of the state of the building at the time of the earthquake. The West Building, which was fully occupied at the time of the earthquake, was modeled similarly to the benchmark. Elastic and inelastic studies were performed on these models to determine if a correlation exists between analysis and observed behavior. The findings from the analysis showed no damage to the West Building with possible damage to the East Building. This result is corroborated by the damage survey.     

Numerical calculation of separated flow past a circular cylinder using panel technique

In the present investigation, a potential flow model based on panel technique, has been developed for calculation of bubble type separated flow past smooth and rough circular cylinder. Free vortex lines are assumed to emanate from the points of separation that converge downstream of the body. The converged wake shape is iteratively obtained by integrating the velocity vectors at the collocation points on the wake panels. Effect of vorticity dispersion in the wake, which plays the dominant role in the flow separation phenomena, is incorporated in the flow model. It has been observed that separated flow past circular cylinder for different Reynolds number and surface roughness can be calculated with reasonable accuracy with appropriate values of vorticity dispersion factor (λ).     

Acoustic emissions during fracture toughness tests of steels exhibiting varying ductility

This investigation is primarily aimed at examining steels with varying ductility using characteristics of acoustic emission (AE). Four steels (AISI 1060, AISI 1080, SA333 grade 6 and AISI 304LN) were selected and their structure property relations were characterized using standard metallographic examinations, hardness and tensile properties. Fracture toughness of these steels was determined as per the guidelines of ASTM standard E1820 with simultaneous recording of AE signals. The results of these investigations have been used to demonstrate that: (a) nature of the variation of AE cumulative counts with time is different for linear and non-linear load–displacement plots, (b) synergistic analysis of the rate of change of cumulative energy, cumulative counts and intensity of AE signals provide the point of crack initiation in a material, and (c) fracture toughness of a material estimated using AE parameters is lower compared to that obtained by ASTM standard procedure.     

Development of a theoretical process map for laser cladding using two-dimensional conduction heat transfer model

In blown powder laser cladding process, the powder travels across the laser path, gets heated up by absorbing laser energy, and finally melts on the substrate under the intense laser beam; as the substrate moves away this melt pool solidifies to form a continuous built-up layer. In the present study a two-dimensional conduction heat transfer equation has been solved using finite volume method to develop a theoretical process map for laser cladding. The developed process map indicates a range of scanning speed and powder feed rate for the feasibility of the process; the lower limit is dictated by the maximum melt pool temperature, and the higher limit by poor bonding due to lack of melting of the substrate (i.e. low dilution). Parametric regions for thick and thin cladding with low dilution can be decided from the process map. It is found that the process range expands with the increase in total absorbed power as well as power directly absorbed by the powder. Correlations for maximum melt pool temperature and dilution are presented. A process map for identifying the form and scale of the microstructure in the solidified layer is also presented.