The carbene and photocatalyst co-catalyzed radical coupling of acyl electrophile and a radical precursor is emerging as attractive method for ketone synthesis. However, previous reports mainly ...limited to prefunctionalized radical precursors and two-component coupling. Herein, an N-heterocyclic carbene and photocatalyst catalyzed decarboxylative radical coupling of carboxylic acids and acyl imidazoles is disclosed, in which the carboxylic acids are directly used as radical precursors. The acyl imidazoles could also be generated in situ by reaction of a carboxylic acid with CDI thus furnishing a formally decarboxylative coupling of two carboxylic acids. In addition, the reaction is successfully extended to three-component coupling by using alkene as a third coupling partner via a radical relay process. The mild conditions, operational simplicity, and use of carboxylic acids as the reacting partners make our method a powerful strategy for construction of complex ketones from readily available starting materials, and late-stage modification of natural products and medicines.
One interest of using biochar as soil amendment is to reduce pesticide adverse effects. In this paper, the sorption and degradation of thiacloprid (THI) in a black soil amended by various biochars ...were systematically investigated, and the mechanisms therein were explored by analyzing the changes in soil physicochemical properties, degrading enzymes and genes and microorganism community. Biochar amendment increased THI sorption in soil, which was associated with an increase in organic carbon and surface area and a decrease in H/C. Amendments of 300-PT (pyrolyzing temperature) biochar promoted the biodegradation of THI by increasing the microbe abundance and improving nitrile hydratase (NHase) activity. In contrast, 500- and 700-PT biochar amendments inhibited biodegradation by reducing THI availability and changing NHase activity and THI-degradative nth gene abundance, and instead promoted chemical degradation mainly through elevated pH, active groups on mineral surface and generation of •OH and other free radicals. Furthermore, THI shifted the soil microbial community, stimulated the NHase activity and elevated nth gene abundance. Biochar amendments also changed soil bacterial community by modulating soil pH, dissolved organic matter and nitrogen and phosphorus levels, which further influenced THI biodegradation. Therefore, the impact of biochars on the fate of a pesticide in soil depends greatly on their type and properties, which should be comprehensively examined when applying biochar to soil.
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•Biochar amendment increased the sorption of thiacloprid (THI) in soil.•Biochars promoted THI chemical degradation by elevated pH, active groups on mineral surface and generation of •OH.•High temperature biochars inhibited THI biodegradation by reducing their availability and decreased NHase activity.•Enhanced NHase activity and nth gene abundance improved THI degradation.•Biochar amendments changed soil bacterial community by altering soil properties and nutrients.
This paper systematically examined the sorption and degradation of THI in soil before and after biochar amendment and elucidated the mechanisms therein.
Axially chiral styrenes bearing a chiral axis between a sterically non-congested acyclic alkene and an aryl ring are difficult to prepare due to low rotational barrier of the axis. Disclosed here is ...an N-heterocyclic carbene (NHC) catalytic asymmetric solution to this problem. Our reaction involves ynals, sulfinic acids, and phenols as the substrates with an NHC as the catalyst. Key steps involve selective 1,4-addition of sulfinic anion to acetylenic acylazolium intermediate and sequential E-selective protonation to set up the chiral axis. Our reaction affords axially chiral styrenes bearing a chiral axis as the product with up to > 99:1 e.r., > 20:1 E/Z selectivity, and excellent yields. The sulfone and carboxylic ester moieties in our styrene products are common moieties in bioactive molecules and asymmetric catalysis.
This study investigates the relationships among souvenir authenticity, perceived value (PV) and behavioral intention (BI) in the context of experiential consumption. Using the customer data from the ...Pearl River Delta region of China, this empirical study adopts a PLS-SEM model to further examine the mediating effect of PV and the moderating effect of experiential consumption on the relationship between souvenir authenticity and BI. In comparison with the non-experiential consumption setting, souvenir authenticity was found to have a greater positive effect on the BI of tourist through PV in the experiential consumption setting. In addition, different dimensions of authenticity and PV are emphasized during souvenir purchases in the experiential consumption. These results deepen the understanding of souvenir authenticity and PV as well as the effects of experiential consumption for postmodern tourists. Managerial implications are provided for practitioners.
•Paper analyses the souvenir purchase behavior of postmodern tourists in the experiential consumption setting.•The effect of souvenir authenticity on BI is enhanced through PV.•Experiential consumption is identified as a moderator in souvenir purchases.•Dimensions of authenticity and PV are emphasized during souvenir purchases in the experiential consumption.•Experiential consumption is recognized as an important step to improving tourists' souvenir purchase intention.
Model-based control methods do not produce satisfactory control results with the batch process control of Czochralski (CZ) silicon monocrystalline with complex nonlinearity, large delay, and ...time-varying dynamics. Therefore, this paper proposes a data-driven model-free adaptive iterative learning control method (MFAILC) to achieve precision control of the batch process. Firstly, to improve the accuracy of the data-driven model, a novel deep learning model for crystal growth process is established by combining a stacked autoencoder (SAE) and a long short-term memory network (LSTM) to extract the working condition information and the dynamic timing features in process data. Traditional model-based control methods are limited by the difficulties in modeling and by the unmodeled dynamics. So, to overcome this problem, the heater controller and the crystal puller controller are designed, based on the iterative dynamic linearization technology, to ensure that the silicon monocrystalline batch manufacturing process always maintains precision control. Also, the discrete-time extended state observer (ESO) is introduced to compensate for the influence of disturbances, to improve the robustness of the control system. Finally, the efficacy of the proposed method is verified by applying it for the predictive modeling and batch control of thermal field temperature and crystal diameter during crystal growth.
Organoboron compounds are highly valuable in synthetic chemistry. In particular, α-borylcarbonyl compounds have shown versatile synthetic applications, owing to fruitful chemistries of both the boryl ...and carbonyl moieties. However, the synthesis of these molecules still remains tedious and time-consuming. Here we report a straightforward and practical route to synthesize α-borylcarbonyl molecules based on a regioselective radical α-borylation of α,β-unsaturated carbonyl compounds. The reaction features unusual α-regioselectivity and high functional-group compatibility. Further synthetic applications of new α-borylated products were also demonstrated. DFT and kinetic studies implicated that the α-regioselectivity of β-aryl-α,β-unsaturated carbonyl compounds was determined by the thermodynamically more favorable radical α-addition step, whereas the formation of α-addition products from β-alkyl-α,β-unsaturated carbonyl compounds was driven by an energetically favored hydrogen atom transfer step. Given that α,β-unsaturated carbonyl compounds can be easily obtained in abundance and variety, this method enjoys great advantages in diverse and economical synthesis of valuable α-borylcarbonyl molecules.
Urban greenery, especially trees, has been proven to be one of the effective measures for urban heat island mitigation. However, no consistent findings have been found for the relationship between ...greenery abundance and cooling magnitude; while some previous studies discovered a linear relationship, others opined it could a non-linear one. In addition, there are rare studies exploring whether or not the strength of the relationship is dependent on urban density. Therefore, in this study, we aim to discuss cooling efficiency by measuring the relationship between greenery coverage ratio and the cooling effects of greenery. Parametric studies were conducted in a validated ENVI-met model, with different combinations of urban densities (Low, Mid, and High) and tree coverage ratios (2–30% at 2% interval, and 56% for full area coverage other than building). Then the pattern of the cooling efficiency was explored under three urban densities scenarios and two selected temporal periods on a typical summer daytime. For a subtropical climate background, results showed a non-linear (logarithmic) pattern for tree coverage ratio (TCR) and cooling effects, irrespective of the urban density, temporal periods, and heat indicators. When TCR reached 20–30%, the optimal cooling efficiency of trees were achieved, irrespective of building densities and temporal periods. The optimal threshold for greenery coverage in this study can provide science-based suggestions to urban planners and designers for better microclimate and thermal comfort environments at the neighborhood scale.
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•Relationship between tree coverage and its cooling efficiency was established.•The cooling efficiency of tree coverage under different urban densities were studied.•Non-linear pattern between tree coverage ratios and cooling effects was revealed.•The optimal cooling efficiency could be achieved by 20–30% tree coverage ratio.•The implication of cooling efficiency pattern for urban planning was discussed.
Helium mass spectrometry leak detection technology requires that the leak detection medium of spacecraft test object is helium, but the general working medium of spacecraft electric propulsion system ...is xenon. The existing helium mass spectrometry leak detection technology can not realize the in-situ leak detection of all kinds of working media. The in situ mass spectrometry leak detection technology of spacecraft working medium based on mass spectrometry has been widely concerned for its advantages of direct leak detection of working medium and obtaining real leak rate, but the sampling and leak detection of mass spectrometry under atmospheric environment is one of its difficulties. In this paper, a leak detection model and test system of spacecraft working medium in situ mass spectrometry are established, and theoretical and experimental studies are carried out. The research results show that, The leak detection sensitivity of in situ working mass spectrometry is better than 1.0 × 10−8 Pa m3/s by shunt current limiting sampling method in atmospheric environment. The appropriate shunt pumping speed and shunt chamber pressure have important influence on in situ leak detection of working medium. When the pressure of capillary shunt chamber is higher than 550Pa, the test system has better stability and repeatability. Not only the background noise of the leak detection by mass spectrometry is reduced, the detection accuracy is improved, and the response time of the system is shortened.
•This paper established a model based on flow limiting shunt sampling mass spectrometry.•This paper analyzed the correlation effect of the parameters of flow limiting shunt sampling.•The appropriate shunt pumping speed and shunt chamber pressure have important influence on in situ leak detection.•It is necessary to analyze and design the leak testing system from the theoretical and experimental aspects.
Sepsis-associated encephalopathy (SAE) is commonly complicated by septic conditions, and is responsible for increased mortality and poor outcomes in septic patients. Uncontrolled neuroinflammation ...and ischemic injury are major contributors to brain dysfunction, which arises from intractable immune malfunction and the collapse of neuroendocrine immune networks, such as the cholinergic anti-inflammatory pathway, hypothalamic-pituitary-adrenal axis, and sympathetic nervous system. Dysfunction in these neuromodulatory mechanisms compromised by SAE jeopardizes systemic immune responses, including those of neutrophils, macrophages/monocytes, dendritic cells, and T lymphocytes, which ultimately results in a vicious cycle between brain injury and a progressively aberrant immune response. Deep insight into the crosstalk between SAE and peripheral immunity is of great importance in extending the knowledge of the pathogenesis and development of sepsis-induced immunosuppression, as well as in exploring its effective remedies.
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