Abstract Planar alignment of disc-like nanomaterials is required to transfer their superior anisotropic properties from microscopic individual structures to macroscopic collective assemblies. However, such alignment by electrical or magnetic field is challenging due to their additional degrees of orientational freedom compared to that of rod-like nanostructures. Here, the realization of planar alignment of suspended graphene sheets using a rotating magnetic field produced by a pair of small NdFeB magnets and subsequent demonstration of high optical anisotropy and potential novel device applications is reported. Compared to partially aligned sheets with a static magnetic field, planar aligned graphene suspensions exhibit a near-perfect order parameter, much higher birefringence and anisotropic absorption/transmission. A unique feature of discotic nanomaterial assemblies is that the observed order parameter and optical property can vary from isotropic to partial and complete alignment depending on the experimental configuration. By immobilizing and patterning aligned graphene in a UV-curable polymer resin, we further demonstrated an all-graphene permanent display, which exhibits wide-angle, high dark-bright contrast in either transmission or reflection mode without any polarizing optics. The ability to control and pattern graphene orientation in all three dimensions opens up new exploration and broad device applications of graphene.
Soil carbon sequestration plays an important role in mitigating anthropogenic increases in atmospheric CO2 concentrations. Recent studies have shown that biodiversity increases soil organic carbon (SOC) storage in experimental grasslands. However, the effects of species diversity on SOC storage in natural ecosystems have rarely been studied, and the potential mechanisms are yet to be understood. The results presented here show that favorable climate conditions, particularly high precipitation, tend to increase both species richness and belowground biomass, which had a consistent positive effect on SOC storage in forests, shrublands, and grasslands. Nitrogen deposition and soil pH generally have a direct negative effect on SOC storage. Ecosystem management that maintains high levels of plant diversity can enhance SOC storage and other ecosystem services that depend on plant diversity.Despite evidence from experimental grasslands that plant diversity increases biomass production and soil organic carbon (SOC) storage, it remains unclear whether this is true in natural ecosystems, especially under climatic variations and human disturbances. Based on field observations from 6,098 forest, shrubland, and grassland sites across China and predictions from an integrative model combining multiple theories, we systematically examined the direct effects of climate, soils, and human impacts on SOC storage versus the indirect effects mediated by species richness (SR), aboveground net primary productivity (ANPP), and belowground biomass (BB). We found that favorable climates (high temperature and precipitation) had a consistent negative effect on SOC storage in forests and shrublands, but not in grasslands. Climate favorability, particularly high precipitation, was associated with both higher SR and higher BB, which had consistent positive effects on SOC storage, thus offsetting the direct negative effect of favorable climate on SOC. The indirect effects of climate on SOC storage depended on the relationships of SR with ANPP and BB, which were consistently positive in all biome types. In addition, human disturbance and soil pH had both direct and indirect effects on SOC storage, with the indirect effects mediated by changes in SR, ANPP, and BB. High soil pH had a consistently negative effect on SOC storage. Our findings have important implications for improving global carbon cycling models and ecosystem management: Maintaining high levels of diversity can enhance soil carbon sequestration and help sustain the benefits of plant diversity and productivity.
Raman scattering provides key information of the biological environment through light-molecule interaction; yet, it is generally very weak to detect. Surface-enhanced Raman scattering (SERS) can boost the Raman signal by several orders-of-magnitude, and thus is highly attractive for biochemical sensing. However, conventional super-resolution imaging of SERS is challenging as the Raman signal is generated from the virtual state which cannot be easily modulated as fluorescence. Here, we demonstrate super-resolution microscopy with a surface-enhanced Raman scattering (SERS) signal, with a resolution of approximately 50 nm. By modulating the polarization angle of the excitation laser, the SERS nanorods display a dramatic anisotropy effect, allowing nanoscale orientation determination of multiple dipoles with dense concentration. Furthermore, a well-established defocused analysis was performed to reconfirm the orientation accuracy of super-resolved SERS nanorods. Sub-diffraction resolution was achieved in the imaging of SERS nanorod labeled vesicles in fixed macrophages. Finally, we demonstrate dynamic SERS nanorod tracking in living macrophages, which provides not only the particle trajectory with high spatial resolution but also the rotational changes at the nanometer scale. This pioneering study paves a new way for subcellular super-resolution imaging with the SERS effect, shedding light on wider biological applications.
Combining rigid twisted spirobifluorene with two strongly electron-withdrawing terpyridine moieties to form a ``(A)(n)-D-(A)(n)'' structure is an effective way to achieve electron transport materials (ETMs) with high triplet energy, suitable frontier orbital levels, excellent thermal stability and electrochemical stability for long-lived and highly efficient organic light-emitting diodes (OLEDs), 2,2'-di([2,2':6',2 `'-terpyridin]-4'-yl)-9,9'-spirobi[fluorene] (22-TPSF) and 2,7-di([2,2':6',2 `'-terpyridin]-4'-yl)-9,9'-spirobifluorene (27-TPSF), both of which are better than the conventional ETM 1,3,5-tris(N-phenylbenzimidazol-2-yl-benzene (TPBi). In addition, the crystal packing mode in their single crystals undergoes a significant transformation from the sandwich arrangement of 22-TPSF into the brick wall arrangement of 27-TPSF, causing a big difference in electron transport mobility, which changes from 0.012 to 0.104 cm(2) V-1 s(-1) as calculated through density functional theory. This variation leads to a phenomenon where the 22-TPSF based devices display a lower maximum external quantum efficiency of 22.9% and a shorter half-life (T-50) of 173925 hours at an initial luminance of 100 cd m(-2) than the 27-TPSF based devices. These findings highlight the great potential of the ETM structured as ``(A)(n)-D-(A)(n)'' using the terpyridine and spirobifluorene moieties; moreover, the positional isomerism effect allows remarkable tuning of the electron transport mobility and makes an obvious influence on OLED performance and lifetime.
Light-duty gasoline vehicles have drawn public attention in China due to their significant primary emissions of particulate matter and volatile organic compounds (VOCs). However, little information on secondary aerosol formation from exhaust for Chinese vehicles and fuel conditions is available. In this study, chamber experiments were conducted to quantify the potential of secondary aerosol formation from the exhaust of a port fuel injection gasoline engine. The engine and fuel used are common in the Chinese market, and the fuel satisfies the China V gasoline fuel standard. Substantial secondary aerosol formation was observed during a 4-5 hr simulation, which was estimated to represent more than 10 days of equivalent atmospheric photo-oxidation in Beijing. As a consequence, the extreme case secondary organic aerosol (SOA) production was 426 +/- 85 mg/kg-fuel, with high levels of precursors and OH exposure. The low hygroscopicity of the aerosols formed inside the chamber suggests that SOA was the dominant chemical composition. Fourteen percent of SOA measured in the chamber experiments could be explained through the oxidation of speciated single-ring aromatics. Unspeciated precursors, such as intermediate-volatility organic compounds and semi-volatile organic compounds, might be significant for SOA formation from gasoline VOCs. We concluded that reductions of emissions of aerosol precursor gases from vehicles are essential to mediate pollution in China. (C) 2017 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
In this paper, measurements of air pollutants made at a ground site near Fort McKay in the Athabasca oil sands region as part of a multi-platform campaign in the summer of 2013 are presented. The observations included measurements of selected volatile organic compounds (VOCs) by a gas chromatograph-ion trap mass spectrometer (GC-ITMS). This instrument observed a large, analytically unresolved hydrocarbon peak (with a retention index between 1100 and 1700) associated with intermediate-volatility organic compounds (IVOCs). However, the activities or processes that contribute to the release of these IVOCs in the oil sands region remain unclear. Principal component analysis (PCA) with varimax rotation was applied to elucidate major source types impacting the sampling site in the summer of 2013. The analysis included 28 variables, including concentrations of total odd nitrogen (NOy), carbon dioxide (CO2), methane (CH4), ammonia (NH3), carbon monoxide (CO), sulfur dioxide (SO2), total reduced-sulfur compounds (TRSs), speciated monoterpenes (including alpha- and beta-pinene and limonene), particle volume calculated from measured size distributions of particles less than 10 and 1 mu m in diameter (PM10-1 and PM1), particle-surface-bound polycyclic aromatic hydrocarbons (pPAHs), and aerosol mass spectrometer composition measurements, including refractory black carbon (rBC) and organic aerosol components. The PCA was complemented by bivariate polar plots showing the joint wind speed and direction dependence of air pollutant concentrations to illustrate the spatial distribution of sources in the area. Using the 95% cumulative percentage of variance criterion, 10 components were identified and categorized by source type. These included emissions by wet tailing ponds, vegetation, open pit mining operations, upgrader facilities, and surface dust. Three components correlated with IVOCs, with the largest associated with surface mining and likely caused by the unearthing and processing of raw bitumen.
Determination of the limiting nutrient of phytoplankton is critical to the lake eutrophication management. The average value of total nitrogen/total phosphorus (TN/TP) ratio is widely used to determine the limiting nutrient; while it suffers from the risk of the incorrect description of data and neglecting dynamics of the nutrient limitation. A probabilistic method was thereby proposed in this study to explore dynamics of nutrient limitation, including (a) indicator definition as the probability of TN/TP ratio failing in Redfield ratio line (PFR), indicating the possibility of TN limitation, to improve a probabilistic measure for the nutrient limitation; (b) Bayesian ANOVA analysis for posterior distributions of different treatments; and (c) dynamics determination as PFRs to show dynamics of nutrient limitation. Lake Xingyun in Southwestern China was taken as a case to explore the interannual and seasonal dynamics of the nutrient limitation. According to modeling results, we deducted that (a) for the interannual dynamics, the limiting nutrient shifted from TP to TN; and (b) for the seasonal dynamics, TN and TP were co-limiting. Deductions were further confirmed by the observed data. With the proposed probabilistic method, the co-limitation of TN and TP was identified for the seasonal dynamics; while using the average ratio solely denied the possibility of co-limitation. The current study also revealed that, due to neglecting the interannual and seasonal dynamics of nutrient limitation, the average ratio might mislead the eutrophication management strategy by recommending reducing TN and TP concentration together. The proposed probabilistic method demonstrated that TN was the limiting nutrient during the growing season of the phytoplankton in recent years and actions should focus on the TN concentration reduction. (C) 2017 Elsevier B.V. All rights reserved.
