To separate the complexities in plasma physics and geometric effects, compact formulas for local geometric properties of a tokamak equilibrium are presented in this paper. They are written in a form ...similar to the Frenet formulas. All of the geometric quantities are expressed in terms of curvature and torsion of the three spatial curves for the moving local frame of reference, i.e., local orthogonal vector basis. In this representation, the local magnetic shear and the normalized parallel current are just the differences between two torsions of the vector basis. All of the geometric properties are coordinate invariants and form a prime set of quantities for describing tokamak plasma equilibrium. This prime set can be evaluated in both flux coordinates with closed flux surfaces and cylindrical coordinates including areas with open field lines, which may allow the extension of some analysis on the open field lines outside the last closed surface. Fundamental differential operators for stability and transport studies can be expressed explicitly in terms of these geometric properties. It can also be used to simplify analytic studies.
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•Metal-catalyzed asymmetric difunctionalization of conjugated dienes in a highly regioselective fashion are realized.•Eight metal catalysts are introduced by the number of ...frequency.•Exquisite choosing diene coupling partners and reaction conditions are crucial for the high efficiency.
1,3-Dienes and derivatives are either feedstock chemicals or easily available materials. Catalytic difunctionalization of 1,3-diene is one of the most powerful methods for carboncarbon bond formation with rapid increase of the molecular complexity and synthetic value in an atom economic way. By choosing proper metals and chiral ligands, a variety of catalytic asymmetric difunctionalization of conjugated dienes in a highly regioselective fashion have been reported. In this digest review, we will summarize recent advances on this topic based on different metals. We will also introduce unique phenomena that include reversal of regio- and diastereoselectivity.
A photoinduced, copper-catalyzed, highly enantioselective dual alkylation/arylation and alkynylation of alkene is reported. A single chiral copper(I) complex serves to enable photoredox catalysis ...and induce enantioselectivity during the reaction. This reaction couples three different components under mild reaction conditions, exhibits a broad substrate scope, and provides facile access to chiral propargylic systems, including those featuring valuable fluorinated substituents.
Abstract
China’s nationwide monitoring network initiated in 2013 has witnessed continuous increases of urban summertime surface ozone to 2019 by about 5% year
−1
, among the fastest ozone trends in ...the recent decade reported in the Tropospheric ozone assessment report. Here we report that surface ozone levels averaged over cities in eastern China cities decrease by 5.5 ppbv in May–August 2020 compared to the 2019 levels, representing an unprecedented ozone reduction since 2013. We combine the high-resolution GEOS-Chem chemical model and the eXtreme Gradient Boosting (XGBoost) machine learning model to quantify the drivers of this reduction. We estimate that changes in anthropogenic emissions alone decrease ozone by 3.2 (2.9–3.6) ppbv (57% of the total 5.5 ppbv reduction) averaged over cities in eastern China and by 2.5 ∼ 3.2 ppbv in the three key city clusters for ozone mitigation. These reductions appear to be driven by decreases in anthropogenic emissions of both nitrogen oxides (NO
x
) and volatile organic compounds, likely reflecting the stringent emission control measures implemented by The Chinese Ministry of Environmental and Ecology in summer 2020, as supported by observed decline in tropospheric formaldehyde (HCHO) and nitrogen dioxides (NO
2
) from satellite and by bottom-up emission estimates. Comparable to the emission-driven ozone reduction, the wetter and cooler weather conditions in 2020 decrease ozone by 2.3 (1.9–2.6) ppbv (43%). Our analyses indicate that the current emission control strategies can be effective for ozone mitigation in China yet tracking future ozone changes is essential for further evaluation. Our study also reveals important potential to combine the mechanism-based, state-of-art atmospheric chemical models with machine learning model to improve the attribution of ozone drivers.
A method for remote radical C-H alkynylation and amination of diverse aliphatic alcohols has been developed. The reaction features a copper nucleophile complex formed
in situ
as a photocatalyst, ...which reduces the silicon-tethered aliphatic iodide to an alkyl radical to initiate 1,
n
-hydrogen atom transfer. Unactivated secondary and tertiary C-H bonds at β, γ, and δ positions can be functionalized in a predictable manner.
Remote C−H alkynylation and amination of aliphatic alcohols.
Formaldehyde (HCHO) in the ambient air not only causes cancer but is also an ideal
indicator of volatile organic compounds (VOCs), which are major precursors of
ozone (O3) and secondary organic ...aerosol (SOA) near the surface. It
is meaningful to differentiate between the direct emission and the secondary
formation of HCHO for HCHO pollution control and sensitivity studies of
O3 production. However, understanding of the sources of HCHO is
still poor in China, due to the scarcity of field measurements (both
spatially and temporally). In this study, tropospheric HCHO vertical column
densities (VCDs) in the Yangtze River Delta (YRD), East China, where HCHO
pollution is serious, were retrieved from the Ozone Mapping and Profiler
Suite (OMPS) onboard the Suomi National Polar-orbiting Partnership
(Suomi-NPP) satellite from 2014 to 2017; these retrievals showed good
agreement with the tropospheric HCHO columns measured using ground-based
high-resolution Fourier transform infrared spectrometry (FTS) with a
correlation coefficient (R) of 0.78. Based on these results, the cancer
risk was estimated both nationwide and in the YRD region. It was calculated
that at least 7840 people in the YRD region would develop cancer in their
lives due to outdoor HCHO exposure, which comprised 23.4 % of total
national cancer risk. Furthermore, the contributions of primary and secondary
sources were apportioned, in addition to primary and secondary tracers from
surface observations. Overall, the HCHO from secondary formation contributed
most to ambient HCHO and can be regarded as the indicator of VOC reactivity
in Hangzhou and in urban areas of Nanjing and Shanghai from 2015 to 2017, due
to the strong correlation between total HCHO and secondary HCHO. At
industrial sites in Nanjing, primary emissions more strongly influenced
ambient HCHO concentrations in 2015 and showed an obvious decreasing trend.
Seasonally, HCHO from secondary formation reached a maximum in summer and a
minimum in winter. In the spring, summer, and autumn, secondary formation had
a significant effect on the variation of ambient HCHO in urban regions of
Nanjing, Hangzhou, and Shanghai, whereas in the winter the contribution from
secondary formation became less significant. A more thorough understanding of
the variation of the primary and secondary contributions of ambient HCHO is
needed to develop a better knowledge regarding the role of HCHO in
atmospheric chemistry and to formulate effective control measures to decrease
HCHO pollution and the associated cancer risk.
Remote sensing of atmospheric hydrogen fluoride (HF) is challenging because it has weak absorption signatures in the atmosphere and is surrounded by strong absorption lines from interfering gases. In ...this study, we first present a multi-year time series of HF total columns over Hefei, China by using high-resolution ground-based Fourier transform infrared (FTIR) spectrometry. Both near-infrared (NIR) and mid-infrared (MIR) solar spectra suites, which are recorded following the requirements of Total Carbon Column Observing Network (TCCON) and Network for the Detection of Atmospheric Composition Change (NDACC), respectively, are used to retrieve total column of HF (THF) and column-averaged dry-air mole fractions of HF (XHF). The NIR and MIR observations are generally in good agreement with a correlation coefficient (R) of 0.87, but the NIR observations are found to be (6.90 ± 1.07 (1σ)) pptv, which is lower than the MIR observations. By correcting this bias, the combination of NIR and MIR observations discloses that the XHF over Hefei showed a maximum monthly mean value of (64.05 ± 3.93) pptv in March and a minimum monthly mean value of (45.15 ± 2.93) pptv in September. The observed XHF time series from 2015 to 2020 showed a negative trend of (−0.38 ± 0.22) % per year. The variability of XHF is inversely correlated with the tropopause height, indicating that the variability of tropopause height is a key factor that drives the seasonal cycle of HF in the stratosphere. This study can enhance the understanding of ground-based high-resolution remote sensing techniques for atmospheric HF and its evolution in the stratosphere and contribute to forming new reliable remote sensing data for research on climate change.
A deep neural network is developed and trained on magnetic measurements (input) and EFIT poloidal magnetic flux (output) on the EAST tokamak. In optimizing the network architecture, we use automatic ...optimization to search for the best hyperparameters, which helps in better model generalization. We compare the inner magnetic surfaces and last-closed-flux surfaces with those from EFIT. We also calculated the normalized internal inductance, which is completely determined by the poloidal magnetic flux and can further reflect the accuracy of the prediction. The time evolution of the internal inductance in full discharge is compared with that provided by EFIT. All of the comparisons show good agreement, demonstrating the accuracy of the machine learning model, which has high spatial resolution compared with the off-line EFIT while still meeting the time constraint of real-time control.
This study analyzed the characteristics of air pollution and specific pollution periods within the Harbin-Changchun (HC) metropolitan area during 2014–2020. Regarding annual, seasonal, and monthly ...variations of the six pollutants, the change trend in 11 cities of HC showed strong consistency in spatial distribution. The western cities (Songyuan, Daqing, and Siping) were vulnerable to dust storms from Inner Mongolia. The concentrations of all air pollutants, except O3-8h, showed downward fluctuation trends from 2014 to 2018 and remained stable from 2018 to 2020 in terms of annual variations. The inter-annual trend of significant reductions in SO2 and SO2/PM2.5 during the heating period indicated that strict emission reduction measures posed by the government were highly successful. The ratio of PM2.5/SO2 was used to identify open biomass burning (OBB), which showed a double peak (October–November (Oct–Nov), March–April (Mar–Apr)). The burning prohibition shifted the OBB from Oct–Nov to Mar–Apr.
•Long-term records of air pollution were presented for Harbin-Changchun (HC) region.•PM2.5 tended to decrease whereas O3 concentrations were largely unchanged.•SO2 exhibited an apparent decreasing trend for the HC region.•Open burning activities remained evident despite strict bans on agricultural fires.•The western cities in HC were strongly impacted by dust during spring.
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