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A novel approach based on ionic liquid-single-drop microextraction (IL-SDME) online coupling with capillary electrophoresis (CE) was used to determine a toxic alkaloid - colchicine. The IL-SDME procedure was optimized by extractio...
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A novel approach based on ionic liquid-single-drop microextraction (IL-SDME) online coupling with capillary electrophoresis (CE) was used to determine a toxic alkaloid - colchicine. The IL-SDME procedure was optimized by extraction solvent, drop volume controlling, sample volume and pH, extraction time, and ionic strength. Under optimum conditions, enrichment factor was as much as 41-fold with a relative standard deviation of 2.8% (n=3). Linear range of response was observed from 1 to 100 μg/mL, with detection limit of 0.25 μg/mL and correlation coefficient (R~2) of 0.9994. The extraction of colchicine from spiked Lanzhou lily sample was performed and obtaining good result with an average recovery rate of 102.4 and 98.8% at 5 and 50 μg/mL, respectively. Comparing with the previous methods, IL-SDME-CE is really a convenient, economical, and environmentally benign way for determining colchicine.
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A primary goal of the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) was to characterize the short-lived drivers of preindustrial to 2100 climate change in the current generation of climate models. Here w...
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A primary goal of the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) was to characterize the short-lived drivers of preindustrial to 2100 climate change in the current generation of climate models. Here we evaluate historical
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This paper evaluates the current status of global modeling of the organic aerosol (OA) in the troposphere and analyzes the differences between models as well as between models and observations. Thirty-one global chemistry transpor...
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This paper evaluates the current status of global modeling of the organic aerosol (OA) in the troposphere and analyzes the differences between models as well as between models and observations. Thirty-one global chemistry transport models (CTMs) and general circulation models (GCMs) have participated in this intercomparison, in the framework of AeroCom phase II. The simulation of OA varies greatly between models in terms of the magnitude of primary emissions, secondary OA (SOA) formation, the number of OA species used (2 to 62), the complexity of OA parameterizations (gas-particle partitioning, chemical aging, multiphase chemistry, aerosol microphysics), and the OA physical, chemical and optical properties. The diversity of the global OA simulation results has increased since earlier AeroCom experiments, mainly due to the increasing complexity of the SOA parameterization in models, and the implementation of new, highly uncertain, OA sources. Diversity of over one order of magnitude exists in the modeled vertical distribution of OA concentrations that deserves a dedicated future study. Furthermore, although the OA / OC ratio depends on OA sources and atmospheric processing, and is important for model evaluation against OA and OC observations, it is resolved only by a few global models. The median global primary OA (POA) source strength is 56 Tg a?1 (range 34–144 Tg a1) and the median SOA source strength (natural and anthropogenic) is 19 Tg a?1 (range 13–121 Tg a1). Among the models that take into account the semi-volatile SOA nature, the median source is calculated to be 51 Tg a?1 (range 16–121 Tg a1), much larger than the median value of the models that calculate SOA in a more simplistic way (19 Tg a?1; range 13–20 Tg a?1, with one model at 37 Tg a1). The median atmospheric burden of OA is 1.4 Tg (24 models in the range of 0.6–2.0 Tg and 4 between 2.0 and 3.8 Tg), with a median OA lifetime of 5.4 days (range 3.8–9.6 days). In models that reported both OA and sulfate burdens, the median value of the OA/sulfate burden ratio is calculated to be 0.77; 13 models calculate a ratio lower than 1, and 9 models higher than 1. For 26 models that reported OA deposition fluxes, the median wet removal is 70 Tg a?1 (range 28–209 Tg a1), which is on average 85% of the total OA deposition. Fine aerosol organic carbon (OC) and OA observations from continuous monitoring networks and individual field campaigns have been used for model evaluation. At urban locations, the model–observation comparison indicates missing knowledge on anthropogenic OA sources, both strength and seasonality. The combined model–measurements analysis suggests the existence of increased OA levels during summer due to biogenic SOA formation over large areas of the USA that can be of the same order of magnitude as the POA, even at urban locations, and contribute to the measured urban seasonal pattern. Global models are able to simulate the high secondary character of OA observed in the atmosphere as a result of SOA formation and POA aging, although the amount of OA present in the atmosphere remains largely underestimated, with a mean normalized bias (MNB) equal to ?0.62 (?0.51) based on the comparison against OC (OA) urban data of all models at the surface, ?0.15 (+0.51) when compared with remote measurements, and ?0.30 for marine locations with OC data. The mean temporal correlations across all stations are low when compared with OC (OA) measurements: 0.47 (0.52) for urban stations, 0.39 (0.37) for remote stations, and 0.25 for marine stations with OC data. The combination of high (negative) MNB and higher correlation at urban stations when compared with the low MNB and lower correlation at remote sites suggests that knowledge about the processes that govern aerosol processing, transport and removal, on top of their sources, is important at the remote stations. There is no clear change in model skill with increasing model complexity with regard to OC or OA mass concentration. However, the complexity is needed in models in order to distinguish between anthropogenic and natural OA as needed for climate mitigation, and to calculate the impact of OA on climate accurately.
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In this paper, we prove the global existence and exponential stability of solutions in H _+ ~i (i=1, 2, 4) for one-dimensional compressible and radiative magnetohydrodynamics (MHD) equations in a bounded domain Ω:. =(0, 1).
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Many global aerosol and climate models, including the widely used Community Atmosphere Model version 5 (CAM5), have large biases in predicting aerosols in remote regions such as upper troposphere and high latitudes. In this study, we conduct CAM5
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Covering: up to September 2020 Hundreds of nucleoside-based natural products have been isolated from various microorganisms, several of which have been utilized in agriculture as pesticides and herbicides, in medicine as therapeut...
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Covering: up to September 2020 Hundreds of nucleoside-based natural products have been isolated from various microorganisms, several of which have been utilized in agriculture as pesticides and herbicides, in medicine as therapeutics for cancer and infectious disease, and as molecular probes to study biological processes. Natural products consisting of structural modifications of each of the canonical nucleosides have been discovered, ranging from simple modifications such as single-step alkylations or acylations to highly elaborate modifications that dramatically alter the nucleoside scaffold and require multiple enzyme-catalyzed reactions. A vast amount of genomic information has been uncovered the past two decades, which has subsequently allowed the first opportunity to interrogate the chemically intriguing enzymatic transformations for the latter type of modifications. This review highlights (i) the discovery and potential applications of structurally complex pyrimidine nucleoside antibiotics for which genetic information is known, (ii) the established reactions that convert the canonical pyrimidine into a new nucleoside scaffold, and (iii) the important tailoring reactions that impart further structural complexity to these molecules.
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A nonlinear viscoelastic constitutive model for early age concrete is presented in this paper. In this model, time-dependent properties, such as the elastic modulus, and thermal and autogenous shrinkage defounations, are computed ...
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A nonlinear viscoelastic constitutive model for early age concrete is presented in this paper. In this model, time-dependent properties, such as the elastic modulus, and thermal and autogenous shrinkage defounations, are computed by a stochastic multi-scale method, in which three different scales are specified according to the requirement of separation of scales, and different scales are linked by means of the asymptotic expansion theory with the help of specific representative volume elements (RYE). Thus, a cross-scale research from the cement paste to the macro structure of concrete is realized, and performance-based optimization of cement-based materials becomes possible. The developed constitutive model is implemented in commercial finite element software. Then, by means of a comparative study involving a numerical simulation and a full-scale experiment of a segment of the Hong Kong-Zhuhai-Macao immersed tunnel to obtain the temperature field and the strain field, the proposed constitutive model is validated. Thus a completely cross-scale constitutive model from the cement paste to the macro structure of concrete is realized, avoiding a variety of non-standardized and highly specialized test methods for concrete. After that, the stress field of the structure is analyzed. It is a prerequisite for structural analysis aimed at the investigation of cracking. Finally, taking different kinds of cement and aggregate as example, combinatorial optimization of material is conducted. And it is concluded that the type of cement and aggregate has an important influence on the early-age performance of investigated immersed tunnel. P.O.42.5 cement and limestone appears to be a good choice for control of cracking in engineering practice.
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In this paper, we study the existence of positive solutions and sign-changing solutions for the following boundary value problem in the half-space. {Δu=0, in R_+~(N+1), ?u/?n +λg(x)u = f(u), on ? R_+~(N+1), Where λ is a positiv...
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In this paper, we study the existence of positive solutions and sign-changing solutions for the following boundary value problem in the half-space. {Δu=0, in R_+~(N+1), ?u/?n +λg(x)u = f(u), on ? R_+~(N+1), Where λ is a positive parameter and the nonlinear term f is superlinear at zero and asymptotically linear at infinity.
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We report on the population of 47 compact binary mergers detected with a false-alarm rate of <1 yr(-1) in the second LIGO-Virgo Gravitational-Wave Transient Catalog. We observe several characteristics of the merging binary black hole (BBH) population not discernible until now. First, the primary mass spectrum contains structure beyond a power law with a sharp high-mass cutoff; it is more consistent with a broken power law with a break at 39.7(-9.1)(+20.3) M-circle dot or a power law with a Gaussian feature peaking at 33.1(-5.6)(+4.0) M-circle dot (90% credible interval). While the primary mass distribution must extend to similar to 65 M-circle dot or beyond, only 2.9(-1.7)(+3.5)% of systems have primary masses greater than 45 M-circle dot. Second, we find that a fraction of BBH systems have component spins misaligned with the orbital angular momentum, giving rise to precession of the orbital plane. Moreover, 12%-44% of BBH systems have spins tilted by more than 90 degrees, giving rise to a negative effective inspiral spin parameter, chi(eff). Under the assumption that such systems can only be formed by dynamical interactions, we infer that between 25% and 93% of BBHs with nonvanishing vertical bar chi(eff)vertical bar > 0.01 are dynamically assembled. Third, we estimate merger rates, finding R-BBH = 23.9(-8.6)(+14.3) Gpc(-3) yr(-1) for BBHS and R-BNS = 3...
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We report on the population of 47 compact binary mergers detected with a false-alarm rate of <1 yr(-1) in the second LIGO-Virgo Gravitational-Wave Transient Catalog. We observe several characteristics of the merging binary black hole (BBH) population not discernible until now. First, the primary mass spectrum contains structure beyond a power law with a sharp high-mass cutoff; it is more consistent with a broken power law with a break at 39.7(-9.1)(+20.3) M-circle dot or a power law with a Gaussian feature peaking at 33.1(-5.6)(+4.0) M-circle dot (90% credible interval). While the primary mass distribution must extend to similar to 65 M-circle dot or beyond, only 2.9(-1.7)(+3.5)% of systems have primary masses greater than 45 M-circle dot. Second, we find that a fraction of BBH systems have component spins misaligned with the orbital angular momentum, giving rise to precession of the orbital plane. Moreover, 12%-44% of BBH systems have spins tilted by more than 90 degrees, giving rise to a negative effective inspiral spin parameter, chi(eff). Under the assumption that such systems can only be formed by dynamical interactions, we infer that between 25% and 93% of BBHs with nonvanishing vertical bar chi(eff)vertical bar > 0.01 are dynamically assembled. Third, we estimate merger rates, finding R-BBH = 23.9(-8.6)(+14.3) Gpc(-3) yr(-1) for BBHS and R-BNS = 320(-240)(+490) Gpc(-3) yr(-1) for binary neutron stars. We find that the BBH rate likely increases with redshift (85% credibility) but not faster than the star formation rate (86% credibility). Additionally, we examine recent exceptional events in the context of our population models, finding that the asymmetric masses of GW190412 and the high component masses of GW190521 are consistent with our models, but the low secondary mass of GW190814 makes it an outlier.
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This study implemented first, second and glaciation aerosol indirect effects (AIE) on resolved clouds in the two-way coupled Weather Research and Forecasting Community Multiscale Air Quality (WRF–CMAQ) modeling system by includin...
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This study implemented first, second and glaciation aerosol indirect effects (AIE) on resolved clouds in the two-way coupled Weather Research and Forecasting Community Multiscale Air Quality (WRF–CMAQ) modeling system by including parameterizations for both cloud drop and ice number concentrations on the basis of CMAQ-predicted aerosol distributions and WRF meteorological conditions. The performance of the newly developed WRF–CMAQ model, with alternate Community Atmospheric Model (CAM) and Rapid Radiative Transfer Model for GCMs (RRTMG) radiation schemes, was evaluated with observations from the Clouds and the See http://ceres.larc.nasa.gov/. Earth's Radiant Energy System (CERES) satellite and surface monitoring networks (AQS, IMPROVE, CASTNET, STN, and PRISM) over the continental US (CONUS) (12 km resolution) and eastern Texas (4 km resolution) during August and September of 2006. The results at the Air Quality System (AQS) surface sites show that in August, the normalized mean bias (NMB) values for PM2.5 over the eastern US (EUS) and the western US (WUS) are 5.3% (?0.1%) and 0.4% (?5.2%) for WRF–CMAQ/CAM (WRF–CMAQ/RRTMG), respectively. The evaluation of PM2.5 chemical composition reveals that in August, WRF–CMAQ/CAM (WRF–CMAQ/RRTMG) consistently underestimated the observed SO42- by ?23.0% (?27.7%), ?12.5% (?18.9%) and ?7.9% (?14.8%) over the EUS at the Clean Air Status Trends Network (CASTNET), Interagency Monitoring of Protected Visual Environments (IMPROVE) and Speciated Trends Network (STN) sites, respectively. Both configurations (WRF–CMAQ/CAM, WRF–CMAQ/RRTMG) overestimated the observed mean organic carbon (OC), elemental carbon (EC) and and total carbon (TC) concentrations over the EUS in August at the IMPROVE sites. Both configurations generally underestimated the cloud field (shortwave cloud forcing, SWCF) over the CONUS in August due to the fact that the AIE on the subgrid convective clouds was not considered when the model simulations were run at the 12 km resolution. This is in agreement with the fact that both configurations captured SWCF and longwave cloud forcing (LWCF) very well for the 4 km simulation over eastern Texas, when all clouds were resolved by the finer resolution domain. The simulations of WRF–CMAQ/CAM and WRF–CMAQ/RRTMG show dramatic improvements for SWCF, LWCF, cloud optical depth (COD), cloud fractions and precipitation over the ocean relative to those of WRF default cases in August. The model performance in September is similar to that in August, except for a greater overestimation of PM2.5 due to the overestimations of SO42-, NH4+, NO3-, and TC over the EUS, less underestimation of clouds (SWCF) over the land areas due to the lower SWCF values, and fewer convective clouds in September. This work shows that inclusion of indirect aerosol effect treatments in WRF–CMAQ represents a significant advancement and milestone in air quality modeling and the development of integrated emissions control strategies for air quality management and climate change mitigation.
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