科研成果

Ecological communities that experience stable climate conditions have been speculated to preserve more specialized interspecific associations and have higher proportions of smaller ranged species (SRS). Thus, areas with disproportionally large numbers of SRS are expected to coincide geographically with a high degree of community-level ecological specialization, but this suggestion remains poorly supported with empirical evidence. Here, we analysed data for hummingbird resource specialization, range size, contemporary climate, and Late Quaternary climate stability for 46 hummingbird–plant mutualistic networks distributed across the Americas, representing 130 hummingbird species (ca 40% of all hummingbird species). We demonstrate a positive relationship between the proportion of SRS of hummingbirds and community-level specialization, i.e. the division of the floral niche among coexisting hummingbird species. This relationship remained strong even when accounting for climate, furthermore, the effect of SRS on specialization was far stronger than the effect of specialization on SRS, suggesting that climate largely influences specialization through species' range-size dynamics. Irrespective of the exact mechanism involved, our results indicate that communities consisting of higher proportions of SRS may be vulnerable to disturbance not only because of their small geographical ranges, but also because of their high degree of specialization.

The governments of Canada and Alberta are implementing a joint plan for oil sands monitoring that includes investigating emissions, transport and downwind chemistry associated with the Canadian oil sands region. As part of that effort, Environment Canada's Global Environmental Multiscale-Modelling Air-quality And CHemistry (GEM-MACH) system was reconfigured for the first time to create nested forecasts of air quality at model grid resolutions down to 2.5 km, with the highest resolution domain including the Canadian provinces of Alberta and Saskatchewan. The forecasts were used to direct an airborne research platform during a summer 2013 monitoring intensive. Subsequent work with the modelling system has included an in-depth comparison of the model predictions to monitoring network observations, and to field intensive airborne and surface supersite observations. A year of model predictions and monitoring network observations were compared, as were model and aircraft flight track values. The relative impact of different model versions (including modified emissions and feedbacks between weather and air pollution) will be discussed. Model-based predictions of indicators of human-health (i.e., Air Quality Health Index) and ecosystem (i.e. deposition of pollutants) impacts for the region will also be described.

We present highly efficient Tb(III)-based organic light-emitting diodes optimized by the subtle choice of bipolar hosts, adjacent layers and double emitting structures. By introducing di(9H-carbazol-9-yl)(phenyl) phosphine oxide (DCPPO) as the host for the first emitting layer, and 9-(4-tert-butylphenyl)-3,6-bis(diphenylphosphine oxide)-carbazole (DPPOC) for the second emitting layer for Tb(PMIP)(3) (PMIP stands for 1-phenyl-3-methyl-4-isobutyryl-pyrazol-5-one), the excitons can be well confined within the double-emitting layer. When 4,4',4 `'-tris(N-carbazolyl) triphenylamine (TCTA) and tris-[3-(3-pyridyl)mesityl] borane (3TPYMB) with high triplet energy levels are used as a hole transporting layer (HTL) and an electron transporting layer (ETL), respectively, the optimized device reaches a maximum efficiency of 52 lm W-1, 57 cd A(-1), i.e. a maximum external quantum efficiency (EQE) of 15%. At a practical brightness of 100 cd m(-2) (4.6 V) the efficiency remains at around 20 lm W-1, 30 cd A(-1).

We present highly efficient Tb(III)-based organic light-emitting diodes optimized by the subtle choice of bipolar hosts, adjacent layers and double emitting structures. By introducing di(9H-carbazol-9-yl)(phenyl) phosphine oxide (DCPPO) as the host for the first emitting layer, and 9-(4-tert-butylphenyl)-3,6-bis(diphenylphosphine oxide)-carbazole (DPPOC) for the second emitting layer for Tb(PMIP)(3) (PMIP stands for 1-phenyl-3-methyl-4-isobutyryl-pyrazol-5-one), the excitons can be well confined within the double-emitting layer. When 4,4',4 `'-tris(N-carbazolyl) triphenylamine (TCTA) and tris-[3-(3-pyridyl)mesityl] borane (3TPYMB) with high triplet energy levels are used as a hole transporting layer (HTL) and an electron transporting layer (ETL), respectively, the optimized device reaches a maximum efficiency of 52 lm W-1, 57 cd A(-1), i.e. a maximum external quantum efficiency (EQE) of 15%. At a practical brightness of 100 cd m(-2) (4.6 V) the efficiency remains at around 20 lm W-1, 30 cd A(-1).

During the past several years, methylammonium lead halide perovskites have been widely investigated as light absorbers for thin-film photovoltaic cells. Among the various device architectures, the inverted planar heterojunction perovskite solar cells have attracted special attention for their relatively simple fabrication and high efficiencies. Although promising efficiencies have been obtained in the inverted planar geometry based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) sulfonic acid (PEDOT:PSS) as the hole transport material (HTM), the hydrophilicity of the PEDOT:PSS is a critical factor for long-term stability. In this paper, a CuOx hole transport layer from a facile solution-processed method was introduced into the inverted planar heterojunction perovskite solar cells. After the optimization of the devices, a champion PCE of 17.1% was obtained with an open circuit voltage (V-oc) of 0.99 V, a short-circuit current (J(sc)) of 23.2 mA cm(-2) and a fill factor (FF) of 74.4%. Furthermore, the unencapsulated device cooperating with the CuOx film exhibited superior performance in the stability test, compared to the device involving the PEDOT:PSS layer, indicating that CuOx could be a promising HTM for replacing PEDOT:PSS in inverted planar heterojunction perovskite solar cells.

High-resolution historical emission inventories of crop residue burning in fields in China were developed for the period 1990–2013. More accurate time-varying statistical data and locally observed emission factors were utilized to estimate crop residue open burning emissions at provincial level. Then pollutants emissions were allocated to a high spatial resolution of 10 km × 10 km and a high temporal resolution of 1 day based on the Moderate Resolution Imaging Spectroradiometer (MODIS) Fire Product (MOD/MYD14A1). Results show that China’s CO emissions have increased by 5.67 times at an annual average rate of 24% from 1.06 Tg in 1990 to 7.06 Tg in 2013; the emissions of CO2, CH4, NMVOCs, N2O, NOx, NH3, SO2, PM2.5, OC, and BC have increased by 595%, 500%, 608%, 584%, 600%, 600%, 543%, 571%, 775%, and 500%, respectively, over the past 24 years. Spatially, the regions with high emissions had been notable expanding over the years, especially in the central eastern districts, the Northeastern of China, and the Sichuan Basin. Strong temporal pattern were observed with the highest emissions in June, followed by March to May and October. This work provides a better understanding of the spatiotemporal representation of agricultural fire emissions in China and can benefit both air quality modeling and management with improved accuracy.

Recent decades witnessed the increase in production and uses of HCFC-22 (chlorodifluoromethane, CHClF2) and its alternative, HFC-410A (a blend of difluoromethane and pentafluoroethane), in China in response to the booming of room air conditioners (RACs) for both domestic use and exports. HCFC-22 is an ozone-depleting substance under the Montreal Protocol, while both HCFC-22 and HFC-410A are greenhouse gases (GHGs). This study provides a most comprehensive consumption and emission inventory of refrigerants emissions (HCFC-22 and HFC-410A) from RAC sector during 1995-2014, for the first time. Our estimates show that HCFC-22 emissions increased from 0.7 Gg/yr in 1995 to 48.2 Gg/yr in 2014. The accumulative emissions contributed to global total HCFCs emissions by 4.4% (3.3%-6.1%) CFC-11-equivalent (CFC-11-eq) and 5.4% (4.1%-7.5%) CO2-equivalent (CO2-eq) during 1995-2012. If left uncontrolled, accumulative emissions of HFC-410A will be12.4 (7.1-20.2) CO2-eq Pg during 2015-2050, which can offset the global climate benefits achieved by the Montreal Protocol. The HFC-410A emissions from China's RAC sector are estimated to be of importance to both global HFCs emissions and China's GHG emissions. Further, we probed the emission mitigation performances of the current 2014 North American Proposal scenario and a modified more ambitious scenario. The emissions of two mitigation scenarios are only 28% and 22% of the emissions without mitigation actions, respectively. This study is the first effort to map the transition of eliminated substance HCFC-22 and its alternative HFC-410A in RAC sector. Therefore, alternative chemicals should be scrutinized with cautions before they are promoted and applied. 

The formation of (Fe, Cr)(OH)3 nanoparticles determines the fate of aqueous Cr in many aquatic environments. Using small-angle X-ray scattering, precipitation rates of (Fe, Cr)(OH)3 nanoparticles in solution and on quartz were quantified from 0.1 mM Fe(III) solutions containing 0–0.25 mM Cr(III) at pH = 3.7 ± 0.2. Concentration ratio of aqueous Cr(III)/Fe(III) controlled the chemical composition (x) of (Fex, Cr1–x)(OH)3 precipitates, solutions’ supersaturation with respect to precipitates, and the surface charge of quartz. Therefore, the aqueous Cr(III)/Fe(III) ratio affected homogeneous (in solution) and heterogeneous (on quartz) precipitation rates of (Fex, Cr1–x)(OH)3 through different mechanisms. The sequestration mechanisms of Cr(III) in precipitates were also investigated. In solutions with high aqueous Cr(III)/Fe(III) ratios, surface enrichment of Cr(III) on the precipitates occurred, resulting in slower particle growth in solutions. From solutions with 0–0.1 mM Cr(III), the particles on quartz grew from 2 to 4 nm within 1 h. Interestingly, from solution with 0.25 mM Cr(III), particles of two distinct sizes (2 and 6 nm) formed on quartz, and their sizes remained unchanged throughout the reaction. Our study provided new insights on homogeneous and heterogeneous precipitation of (Fex, Cr1–x)(OH)3 nanoparticles, which can help determine the fate of Cr in aquatic environments.