Several recent theoretical studies develop tools to predict species diversity in large model ecosystems, setting a new benchmark for understanding the mechanism of species coexistence in natural ecosystems.
Single-shot laser-induced damage threshold (LIDT) of free-standing nanometer-thin diamond-like carbon (DLC) foils was measured in vacuum environment for pulse durations from 50 fs to 200 ps. It is found that, due to higher surface defects density, the LIDT of free-standing ultrathin DLC foils is lower than that of bulk DLC by a factor of 3, and the damage fluence is almost a constant of about 0.1 J/cm2 when the pulse duration is longer than 500 fs. Different from DLC films coated on silicon wafer, the damage fluence of free-standing DLC has a weak dependence on their thickness. Based on the measurement, the damage mechanism is illustrated by virtue of the carrier population analysis, and the requirement on the temporal laser contrast when DLC targets are used in relativistic laser-plasma experiment is discussed.
Author(s): Yaomin Zhao, Shiying Xiong, Yue Yang, and Shiyi ChenThere is a continued debate about the generation mechanism of turbulent spots in boundary-layer transition. We use the vortex-surface field to show that the sinuous distortion of vortex surfaces plays an important role in the rapid lateral growth of turbulent spots.[Phys. Rev. Fluids 3, 074701] Published Wed Jul 11, 2018
Solid support-enabled site isolation has previously allowed to use paraldehyde as an acetaldehyde surrogate in aldol reactions. However, only electron-poor aldehydes were tolerated by the system. Herein, we show that the temporary conversion of benzaldehyde into η6-benzaldehyde Cr(CO)3 circumvents this limitation. Asymmetric synthesis of (R)-Phenoperidine, as well as formal syntheses of (R)-Fluoxetine and (R)-Atomoxetine, illustrate the benefits of this strategy.
Black carbon (BC) plays an important role in the Earth's climate system. However, parameterizations of BC size and mixing state have not been well addressed in aerosol-climate models, introducing substantial uncertainties into the estimation of radiative forcing by BC. In this study, we focused on BC emissions from the oil sands (OS) surface mining activities in northern Alberta, based on an aircraft campaign conducted over the Athabasca OS region in 2013. A total of 14 flights were made over the OS source area, in which the aircraft was typically flown in a four-or five-sided polygon pattern along flight tracks encircling an OS facility. Another 3 flights were performed downwind of the OS source area, each of which involved at least three intercepting locations where the well-mixed OS plume was measured along flight tracks perpendicular to the wind direction. Comparable size distributions were observed for refractory black carbon (rBC) over and downwind of the OS facilities, with rBC mass median diameters (MMDs) between similar to 135 and 145 nm that were characteristic of fresh urban emissions. This MMD range corresponded to rBC number median diameters (NMDs) of similar to 60-70 nm, approximately 100% higher than the NMD settings in some aerosol-climate models. The typical in-and out-of-plume segments of a flight, which had different rBC concentrations and photochemical ages, showed consistent rBC size distributions in terms of MMD, NMD and the corresponding distribution widths. Moreover, rBC size distributions remained unchanged at different downwind distances from the source area, suggesting that atmospheric aging would not necessarily change rBC size distribution. However, aging indeed in-fluenced rBC mixing state. Coating thickness for rBC cores in the diameter range of 130-160 nm was nearly doubled (from similar to 20 to 40 nm) within 3 h when the OS plume was transported over a distance of 90 km from the source area.
Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer (CPMA) combined with a differential mobility analyzer (DMA) was deployed to determine the size-resolved effective density of 50 to 350nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55g/cm3, on average. The effective particle density distributions were dominated by a mode peaked at around 1.5g/cm3 for 50 to 350nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6g/cm3 for 150, 240, and 350nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation (NPF) event decreased considerably, indicating the significant contribution of organics to new particle growth.
Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer (CPMA) combined with a differential mobility analyzer (DMA) was deployed to determine the size-resolved effective density of 50 to 350 nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55 g/cm(3), on average. The effective particle density distributions were dominated by a mode peaked at around 1.5 g/cm(3) for 50 to 350 nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6 g/cm(3) for 150, 240, and 350 nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation (NPF) event decreased considerably, indicating the significant contribution of organics to new particle growth. (C) 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
Organic inorganic perovskite solar cells have seen tremendous developments in recent years. As a hole transport material, 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMe-TAD) is widely used in n-i-p perovskite solar cells. However, it may lead to the perovskite film degradation due to the dopant lithium bis-((trifluoromethyl)sulfonyl)amide (Li-TFSI), which has strong hydrophilicity. Cu9S5 is considered as a superior p-type transport material, which also has a favorable energy level matching with the highest occupied molecular orbital of Spiro-OMeTAD. Herein, a solution-processed organic-inorganic-integrated hole transport layer was reported, which is composed of the undoped Spiro-OMeTAD and Cu9S5 layer. Since there is no Li-TFSI doping, it is extremely conductive to the long-term stability of the solar cells. In the meantime, we proposed a method to adjust the lowest unoccupied molecular orbital (LUMO) of SnO2 via nitrogen implantation (N:SnO2). The LUMO of SnO2 can be tuned from -4.33 to -3.91 eV, which matches well with the LUMO of CH3NH3PbI3 (-3.90 eV), and thus helps to reduce hysteresis. The modified hole and electron transport layers were applied in n-i-p perovskite solar cells, which achieve a maximum power conversion efficiency (PCE) of 17.10 and 96% retention of PCE after 1200 h in air atmosphere without any encapsulation.
Marine aerosol particles are an important part of the natural aerosol systems and might have a significant impact on the global climate and biological cycle. It is widely accepted that truly pristine marine conditions are difficult to find over the ocean. However, the influence of continental and anthropogenic emissions on the marine boundary layer (MBL) aerosol is still less understood and non-quantitative, causing uncertainties in the estimation of the climate effect of marine aerosols. This study presents a detailed chemical characterization of the MBL aerosol as well as the source apportionment of the organic aerosol (OA) composition. The data set covers the Atlantic Ocean from 53 degrees N to 53 degrees S, based on four open-ocean cruises in 2011 and 2012. The aerosol particle composition was measured with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), which indicated that sub-micrometer aerosol particles over the Atlantic Ocean are mainly composed of sulfates (50% of the particle mass concentration), organics (21 %) and sea salt (12 %). OA has been apportioned into five factors, including three factors linked to marine sources and two with continental and/or anthropogenic origins. The marine oxy-genated OA (MOOA, 16% of the total OA mass) and marine nitrogen-containing OA (MNOA, 16 %) are identified as marine secondary products with gaseous biogenic precursors dimethyl sulfide (DMS) or amines. Marine hydrocarbon-like OA (MHOA, 19 %) was attributed to the primary emissions from the Atlantic Ocean. The factor for the anthropogenic oxygenated OA (Anth-OOA, 19 %) is related to continental long-range transport. Represented by the combustion oxy-genated OA (Comb-OOA), aged combustion emissions from maritime traffic and wild fires in Africa contributed, on average, a large fraction to the total OA mass (30 %). This study provides the important finding that long-range transport was found to contribute averagely 49% of the submicron OA mass over the Atlantic Ocean. This is almost equal to that from marine sources (51 %). Furthermore, a detailed latitudinal distribution of OA source contributions showed that DMS oxidation contributed markedly to the OA over the South Atlantic during spring, while continental-related longrange transport largely influenced the marine atmosphere near Europe and western and central Africa (15 degrees N to 15 degrees S). In addition, supported by a solid correlation between marine tracer methanesulfonic acid (MSA) and the DMS-oxidation OA (MOOA, R-2>0.85), this study suggests that the DMS-related secondary organic aerosol (SOA) over the Atlantic Ocean could be estimated by MSA and a scaling factor of 1.79, especially in spring.
Abstract Aim We examined the effects of space, climate, phylogeny and species traits on module composition in a cross-biomes plant–hummingbird network. Location Brazil, except Amazonian region. Methods We compiled 31 local binary plant–hummingbird networks, combining them into one cross-biomes metanetwork. We conducted a modularity analysis and tested the relationship between species’ module membership with traits, geographical location, climatic conditions and range sizes, employing random forest models. We fitted reduced models containing groups of related variables (climatic, spatial, phylogenetic, traits) and combinations of groups to partition the variance explained by these sets into unique and shared components. Results The Brazilian cross-biomes network was composed of 479 plant and 42 hummingbird species, and showed significant modularity. The resulting six modules conformed well to vegetation domains. Only plant traits, not hummingbird traits, differed between modules, notably plants’ growth form, corolla length, flower shape and colour. Some modules included plant species with very restricted distributions, whereas others encompassed more widespread ones. Widespread hummingbirds were the most connected, both within and between modules, whereas widespread plants were the most connected between modules. Among traits, only nectar concentration had a weak effect on among-module connectivity. Main conclusions Climate and spatial filters were the main determinants of module composition for hummingbirds and plants, potentially related to resource seasonality, especially for hummingbirds. Historical dispersal-linked contingency, or environmental variations not accounted for by the explanatory factors here evaluated, could also contribute to the spatial component. Phylogeny and morphological traits had no unique effects on the assignment of species to modules. Widespread species showed higher within- and/or among-module connectivity, indicating their key role connecting biomes, and, in the case of hummingbirds, communities within biomes. Our results indicate that biogeography and climate not only determine the variation of modularity in local plant–animal networks, as previously shown, but also affect the cross-biomes network structure.
Fine particulate matter (PM2.5), largely composed of secondary organic aerosol (SOA), is currently one of the most intractable environmental problems in China. As crucial precursors for SOA, understanding the formation propensity of various volatile organic compound (VOC) species and sources is useful for pollution control. In this work, we estimated the SOA formation potential (SOAP) of anthropogenic VOC emissions based on an improved speciated VOC emission inventory and investigated its distribution in China. According to our estimates, toluene had the largest SOAP, followed by n-dodecane, m-/p-xylene, styrene, n-decane, and n-undecane, while passenger cars, chemical fiber manufacturing, asphalt paving, and building coating were the top five SOAP-contributing sources nationwide. The spatial distribution of SOAP in China shows a distinct pattern of high values in the southeast and low values in the northwest. Beijing–Tianjin–Hebei and surroundings, the Yangtze River Delta, Pearl River Delta, and Sichuan–Chongqing District were found to have the highest SOAP, particularly in urban areas. The major SOAP-contributing species and sources differed among these regions, which was attributed to local industrial and energy structures. Our results suggest that to mitigate PM2.5 pollution in China, more efficient SOAP-based control measures should be implemented instead of current emissions-based policies, and VOC control strategies should be adapted to local conditions.
Chongqing is the largest megacity in southwest China and has a mountainous and humid climate. Online measurements of 96 volatile organic compound (VOC) species were performed at the three sites JYS, CJZ, and NQ, which are located in the northern, central, and southern sections of the Chongqing urban district, respectively. The measurements were performed from August to September 2015, at a time interval of 1 h. The spatiotemporal variation of VOC sources in Chongqing was characterized by combining the positive matrix factorization (PMF) model with the online measurement data. The average total VOC mixing ratios of the CJZ, NQ, and JYS sites were 41.2, 34.1, and 23.0 ppbv, respectively. The mixing ratios of tracers of incomplete combustion, exhibited obvious bimodal profiles at the CJZ and NQ sites, whereas those at the JYS site exhibited little change throughout the day. Isoprene at the three sites followed a similar pattern of average diurnal variations in mixing ratios, with minimums before sunrise and maximums at noon. The dominant sources of acetaldehyde and acetone were secondary anthropogenic sourceand aged air mass transport, respectively, in the city of Chongqing. Seven sources were apportioned to the results of PMF calculation using spatiotemporal VOCs composition data. The Vehicle-related sources were the largest contributor at CJZ and NQ, contributing 44% and 37% of the total VOC mixing ratios, respectively, and exhibited clear diurnal variations. Aged background air, with 68% of total VOC emissions, dominated the VOC emissions at JYS. Solvent utilization was a very important contributor at NQ and coincided with the higher levels of aromatics. O3 formation was generally VOC-limited at NQ and CJZ, and was NOx-limited and transition region alternatively at JYS. Alkenes were important for the O3formation at CJZ, and both alkenes and aromatics were important for the O3 formation at NQ.
