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Light-emitting dendrimer:exciplex host-based solution-processed white organic light-emitting diodes
No full textSolution-processed monochrome and white organic light-emitting diodes (OLEDs) that have a light-emitting layer composed of a 4,4′,4″-tris(carbazol-9-yl)triphenylamine (TCTA) and (5-terphenyl-1,3-phenylene)bis(diphenylphosphine oxide) (POPH) exciplex host and soluble blue, green and/or red phosphorescent dendrimers have been fabricated and characterised. The OLED performance characteristics were found to be scan dependent, with the first scans having large external quantum efficiencies (EQEs) at low luminance, with subsequent scans showing stable performance. The monochrome (blue, green and red) films were found to have high photoluminescence quantum yields, relatively balanced hole and electron mobilities, and the OLEDs had stable EQEs of between 9 and 12% at 100 cd m−2 over multiple scans. The blue, green and red emissive materials were blended with the exciplex host, with their ratio tuned to achieve white emission. The optimal blend ratio provided white OLEDs that had EQEs of 11.7% and 10.6% at 100 cd m−2 and 1000 cd m−2, respectively. The best balance of 1931 Commission Internationale d'Eclairage (CIE) coordinates (0.40,0.40), Colour Rendering Index (70), and Delta uv (0.003) was achieved for an OLED with the light-emitting layer containing the blue, green and red dendrimers in a ratio of 20.0:0.4:0.8 wt%. A feature of the white OLEDs was the stability of the CIE coordinates, with a change of only (0.013,0.005) between a luminance of 100 cd m−2 and 4000 cd m−2
Isolation and self-regulation processes in simulated postfire microsites promote plant species diversity
No full textMechanisms responsible for the high species richness of disturbance-prone floras remain speculative. After fire, speciose shrublands in Australia possess mosaics of microsites that vary widely in seedling density and species richness and provide an ideal context in which to test a) the self-regulation hypothesis that species survive and grow better as they become rarer in the mix, and b) the synergistic hypothesis that species perform relatively better at increasing levels of competition under poorer growing conditions. Both processes should serve to promote species co-occurrence at the local scale. We planted germinants of 10 native shrub species in nutrient-poor sands in 30 cm (high density) and 40 cm (low density) square, buried but open-bottomed, boxes. Each box simulated a field-type microsite, containing one individual (solitary), or 49 individuals with each species contributing three (5% of the total, rare), five (10%, equal), 25 (51%, dominant) or 49 (100%, monoculture) seedlings. Best performance per plant (gauged as % survival × shoot mass per survivor) occurred among all ten species when solitary in the box. When grown in the presence of other plants, mixtures of species performed better on a 1) per plant, and 2) whole microsite, basis than monocultures at both densities, and 3) when rare rather than dominant in the mix, conforming with the self-regulation hypothesis, all independent of species identity. Expected niche differentiation of soil-based resources among species mixes would explain increased fitness per plant with decreasing abundance per species. Overall performance (performance per plant × absolute number of survivors per microsite) was maximized when all species were moderately rare (10% of initial numbers among 10 species) in the mix. Under good (low density) and poor (high density) growing conditions, increasing competition (indexed as total shoot mass) from the dominant species in the mix, led to a gradual fall and merging of shoot mass of the remaining nine species at these two densities, but species richness did not change. This outcome provides only limited support for the synergistic model of species coexistence (species richness should have declined at a decreasing rate) but is consistent with the concept of self-regulation. We conclude that mosaics of microsite types maintain biodiversity of speciose, disturbance-prone ecosystems through both isolating mechanisms (in seed-poor microsites with negligible competition) and compensatory self-regulation mechanisms (in species-rich microsites with intense competition)
How does biochar aging affect NH3 volatilization and GHGs emissions from agricultural soils?
No full textBiochar has been considered as a potential tool to mitigate soil ammonia (NH3) volatilization and greenhouse gases (GHGs) emissions in recent years. However, the aging effect of biochar on soils remains elusive, which introduces uncertainty on the effectiveness of biochar to mitigate global warming in a long term. Here, a meta-analysis of 22 published works of literature with 217 observations was conducted to systematically explore the aging effect of biochar on soil NH3 and GHGs emissions. The results show that, in comparison with the fresh biochar, the aging makes biochar more effective to decrease soil NH3 volatilization by 7% and less risk to contribute CH4 emissions by 11%. However, the mitigation effect of biochar on soil N2O emissions is decreased by 15% due to aging. Additionally, aging leads to a promotion effect on soil CO2 emissions by 25% than fresh biochar. Our findings suggest that along with aging, particularly the effect of artificial aging, biochar could further benefit the alleviation of soil NH3 volatilization, whereas its potential role to mitigate global warming may decrease. This study provides a systematic assessment of the aging effect of biochar to mitigate soil NH3 and GHGs, which can provide a scientific basis for the sustainable green development of biochar application
Transformation of HCl during pyrolysis of biomass and its model compounds
No full textThe release behavior of chlorine (Cl) during biomass pyrolysis has not been fully understood yet due to the complex transformation of hydrogen chloride (HCl). Here, we systematically investigate the transformation of HCl in vapor phase and its interactions with pyrolyzing biomass/char particles during biomass pyrolysis. Four biomass model compounds (cellulose, xylan, pectin, and alkali lignin) and an acid-washed wood were pyrolyzed in a fixed-bed reactor at 300–600 ℃ to produce Cl-free volatiles that reacted with the HCl injected downstream of the reactor. To explore the vapor–solid interactions of HCl with pyrolyzing biomass/char particles, the acid-washed wood was also pyrolyzed in a HCl atmosphere. The role of potassium (K) in the transformation of HCl was revealed via pyrolyzing a wood loaded with potassium carbonate (K2CO3). For all the experiments, the Cl distributed in char, heavy oil (condensed at 110 ℃), light oil (condensed at 0 ℃), and pyrolytic gases (as CH3Cl) was quantified. The results demonstrate that the vapor-phase reactions of HCl with the volatiles from pectin, lignin, and the acid-washed wood generate considerable amounts of methyl chloride (CH3Cl) but do not contribute to organic Cl in bio-oil. Increasing the temperatures of both pyrolysis and vapor-phase reaction promotes the generation of CH3Cl. The vapor–solid interactions of HCl with pyrolyzing biomass/char particles substantially enhance the formation of CH3Cl during the pyrolysis of the acid-washed wood at 300–500 ℃ because of the possible combination of HCl with the methyl radicals released in the initial stage of lignin pyrolysis. In addition, the vapor–solid interactions cause 120–490 μg/g feedstock of water-soluble Cl and 410–1120 μg/g feedstock of water-insoluble Cl being retained in the chars, which are produced from the capture of HCl by pores and carbon active sites in chars, respectively. The addition of K2CO3 catalyzes the cracking of lignin and thereby enhances the methylation of HCl in both vapor-phase reactions and vapor–solid interactions. It also increases the retention of Cl in the chars due to its capture by K
The impact of steric repulsion on the total free energy of electric double layer capacitors
No full textWe present an analysis of the total free energy of a supercapacitor modelled with a composite diffuse layer (CDL) formed by a steric repulsive potential. The steric potential is modelled with a simple approximation to the Bikerman steric potential, enabling derivation of an analytical expression for the total free energy of the supercapacitor in terms of the size and valency of the electrolyte counterions and electrode potentials. The analytical expression for the total free energy of the supercapacitor matches the exact numerical Bikerman calculation at high potential with relative error close to 1%. This provides an upper bound over the more accurate Carnahan-Starling model. A maximum upper bound for the energy is also provided in the limit where bulk concentrations approach the ion concentration cap. We analyze the relative contribution of the steric interaction to the total free energy. At large voltages, the steric free energy is comparable in magnitude to that of the electrostatic free energy, and introduces ion-size effects in the energy of the supercapacitor. Consequently at high potentials the total free energy exceeds (doubles) the classical energy , indicating that this formula does not correctly describe the available stored energy from the experimentally measured capacitance
It’s all about politics: Migration and resource conflicts in the global south
No full textBoth researchers and policy makers have repeatedly expressed concerns that migration will enhance conflicts regarding renewable resources in destination areas. This concept is fuelled by projections of large future migration flows within the Global South, resulting from armed conflict, global environmental change, and persistent economic inequalities. However, as of yet, there is no conclusive empirical evidence of a nexus between migration, resource competition, and conflict at an aggregate level. Case studies draw contradicting conclusions, and cross-case research on the topic remains scarce. Here, we combine comprehensive qualitative and quantitative data from 20 cases in rural Asia, Latin America and Sub-Saharan Africa. Based on these cases, we investigate why certain areas hosting migrants have resource-related conflicts, while others do not. Using qualitative comparative analysis (QCA), we evaluate and elucidate two combinations of conditions under which resource conflict involving migrants in destination areas occurs: (1) high reliance on natural resources and negative othering of migrants in terms of resource use, and (2) government policies supporting parts of the migrant group coupled with limited resource use possibilities due to conservation efforts or industrial activities. By underlining the crucial role of grievances related to perceived unfair resource access and the strong influence of government actions on local migrant-host dynamics, we challenge deterministic narratives of migration, resource scarcity and conflict
Relation-aware collaborative autoencoder for personalized multiple facet selection
No full textCollaborative-based personalization has been one of the most successful techniques used in building personalization for recommender systems and facet selection. The technique predicts users’ interests based on the preferences of similar people or items. The prediction is usually made on one single group of users or items/facets. However, multiple facet selection creates a different challenge where the prediction needs to be based on the similarity among different groups of users and facets. In conventional collaborative approach, user–facet representation is created from the concatenation of user preferences on each facet. This creates a spared representation which affects the accuracy of the personalized model. It is essential to develop a more suitable representation that effectively represents the collaborative preferences given across multiple facets and a predictive model to estimate the possible preferences across those groups. Multiple facets appear to be correlated to each other and this can be useful for associating the existing preferences. None of the previous works has addressed the issue due to the association of facet relationships. Hence, this paper aims to examine the effectiveness of a new approach that utilizes multiple-facet relationships to associate the collaborative interests across different facets. This study proposes a new collaborative-based personalization model for multiple facet selection, called Relation-aware Collaborative Autoencoder (RCAE) Model. A new embedding methodology was introduced for incorporating multiple facet relationships into user–facet interaction. Evaluations based on four real-world datasets demonstrated that the proposed model utilizing facet relationships has achieved significant improvement over the conventional collaborative approach
Uninterrupted path planning system for Multi-USV sampling mission in a cluttered ocean environment
No full textThis paper presents an uninterrupted collision-free path planning system that facilitates the operational performance of multiple unmanned surface vehicles (USVs) in an ocean sampling mission. The proposed uninterrupted path planning system is developed based on the integration of a novel B-Spline data frame and particle swarm optimization (PSO)-based solver engine. The new B-spline data framing structure provides smart sampling of the candidate spots without needing full stop for completing the sampling tasks. This enables the USVs to encircle the area smoothly while simultaneously correcting the heading angle toward the next spot and preventing sharp changes in the vehicle's heading. Then, the optimization engine generates optimal, smooth, and constraint-aware path curves for multiple USVs to conduct the sampling mission from start point to the rendezvous point. The path generated incorporates controllability over the vehicles' velocity profile to prevent experiencing zero velocity and frequent stop/start switching of the controller. To achieve faster convergence of the optimization routine, a suitable search space decomposition scheme is proposed. Extensive simulation studies emulating a realistic ocean sampling mission are conducted to examine the feasibility and effectiveness of the proposed path planning system. This encapsulates modelling a realistic maritime environment of Indonesian Archipelago in Banda Sea including ocean waves, obstacles, and no-fly zones and introducing several performance indices to benchmark the path planning system performance. This process is accompanied by a comparative study of the proposed path planning system with a well-known state-of-the art piecewise, rapidly exploring random tree (RRT), and differential evolution-based path planning algorithms. The results of the simulation confirm the suitability and robustness of the proposed path planning system for the uninterrupted ocean sampling missions
Beneficial effect of iron oxide/hydroxide minerals on sulfuric acid baking and leaching of monazite
No full textThe sulfuric acid bake/leach process is an established industrial process for the extraction of rare earths from hard-rock monazite ores/concentrates. The chemical reactions in the monazite acid bake can be strongly influenced by the gangue mineralogy of the ore/concentrate. In this work, the beneficial effect of three iron oxide/hydroxide minerals, namely hematite, goethite and magnetite, added to high grade monazite concentrate in the acid bake (temperature range of 200–800°) and leach process was investigated to understand the role of iron gangue. Baked solids and leach residues were characterised by elemental analyses, XRD, SEM-EDS and FT-IR. It was found that the addition of iron minerals to the monazite acid bake had a significant impact on bake chemistry, acting to significantly increase the leaching of both the rare earth elements and thorium, compared to monazite alone, mainly for temperatures above 300 °C. The increased dissolution of rare earth elements and thorium was attributed to the formation of an amorphous and insoluble iron sulfate-polyphosphate type phase in preference to insoluble rare earth and thorium containing polyphosphates identified during acid baking of monazite alone. After baking at 650 °C, the iron sulfate-polyphosphate type phase was altered to a more soluble form, leading to an increase in dissolution of iron, phosphorus and thorium. Acid baking at 800 °C led to the formation of FePO4, Fe2O3, CePO4 (monazite) and in some cases CeO2, causing a decrease in leaching of rare earths and thorium, and either an increase or a decrease in leaching of iron and phosphorus depending on the formation of FePO4 versus Fe2O3
Hydrochar amendments stimulate soil nitrous oxide emission by increasing production of hydroxyl radicals and shifting nitrogen functional genes in the short term: A culture experiment
No full textThe application of waste biomass-derived hydrochar to soil may cause extremely intensive nitrous oxide (N2O) fluxes that can challenge our current mechanistic understanding of the global nitrogen cycle in the biosphere. In this study, two waste biomasses were used to prepare cyanobacterial biomas-derived hydrochar (CHC) and wheat straw-derived hydrochar (SHC) for short-term incubation experiments to identify their effects and mechanisms of waste biomass-derived hydrochar on soil N2O efflux, with time-series samples collected for N2O efflux and soil analysis. The results showed that CHC and SHC caused short-term bursts of N2O effluxes without nitrogen inputs. Moreover, the enrichment of exogenous organics and nutrients at the hydrochar-soil interface was identified as the key factor for enhancing N2O fluxes, which stimulated microbial nitrification (i.e., increased gene copy number of ammonia oxidizing bacteria) and denitrification (i.e., increased gene copy number of nitrate and N2O reducing bacteria) processes. The concentrations of Fe (II) and hydroxyl radicals (HO•) were 6.49 and 5.63 times higher, respectively, in the hydrochar layer of CHC than SHC amendment. Furthermore, structural equation models demonstrated that HO•, as well as soil microbiomes, played an important role in driving N2O fluxes. Together, our findings provide a deeper insight into the assessment and prognosis of the short-term environmental risk arising from agricultural waste management in integrated agriculture. Further studies under practical field application conditions are warranted to verify the findings