A variety of inert tertiary amides have been successfully transformed into synthetically important chiral propargylamines in high yields with good to excellent enantioselectivities via a relayed ...sequence of Ir catalyzed partial reduction and Cu/GARPHOS catalyzed asymmetric alkynylation with terminal alkynes. The reaction was readily extended to some drug molecules and the transformations of representative products have been demonstrated, thus attesting the practical utilities and the robust nature of the protocol.
An Ir/Cu bimetallic relay catalysis was developed to achieve the challenging asymmetric deoxygenative alkynylation of inert amides under mild conditions, affording a series of synthetically important chiral propargylamines in high yields with good to excellent enantioselectivities.
The use of formic acid (FA) to produce molecular H2 is a promising means of efficient energy storage in a fuel‐cell‐based hydrogen economy. To date, there has been a lack of heterogeneous catalyst ...systems that are sufficiently active, selective, and stable for clean H2 production by FA decomposition at room temperature. For the first time, we report that flexible pyridinic‐N‐doped carbon hybrids as support materials can significantly boost the efficiency of palladium nanoparticle for H2 generation; this is due to prominent surface electronic modulation. Under mild conditions, the optimized engineered Pd/CN0.25 catalyst exhibited high performance in both FA dehydrogenation (achieving almost full conversion, and a turnover frequency of 5530 h−1 at 25 °C) and the reversible process of CO2 hydrogenation into FA. This system can lead to a full carbon‐neutral energy cycle.
Pyridinic‐N‐tuned catalysis: An electron‐rich pyridinic‐N dopant modulates the electronic interactions between the active sites of palladium nanoparticles and the carbon support. Formic acid dehydrogenation at room temperature is significantly boosted by the pyridinic‐N‐doped palladium catalyst, presenting an efficient and reliable route to clean H2 generation and sustainable energy storage.
•A modified EMD–SVM model improved by removing the IMF1 is proposed.•The grid research method is employed to acquire the optimal parameter of SVM.•The EMD–SVM model has a better performance than the ...basic SVM model.•The M-EMDSVM model outperforms the SVM and EMD–SVM models.
It is of great significance for operation, planning and dispatching of hydropower station to predict monthly streamflow accurately. Therefore, the main goal of this study is to investigate the accuracy of a modified EMD–SVM model for monthly streamflow forecasting in the Wei River Basin, which has made an improvement by removing the high frequency (IMF1) based on the conventional EMD–SVM model. The EMD–SVM model is obtained by combining empirical mode decomposition and support vector machine. To acquire the optimal c and g values of SVM, the grid research method was employed. Three quantitative standard statistical performance evaluation measures, root mean squared error (RMSE), mean absolute error (MAE) and mean absolute percentage error (MAPE) were employed to evaluate the performances of the ANN, SVM, EMD–SVM and M-EMDSVM models. The comparison of results reveals that the M-EMDSVM approach has provided a superior alternative to ANN, SVM and EMD–SVM models for forecasting monthly streamflow at Huaxian hydrological station, and its pass rate of prediction reaches up to 82.6% in Huaxian station. To further illustrate the stability and representativeness of the modified EMD–SVM model, the Lintong and Xianyang stations were used to verify the model. The results show that the modified EMD–SVM model has a good stability and great representativeness as well as a high prediction precision.
Abstract
The powerful insecticidal and multi-drug-resistance-reversing activities displayed by the stemofoline group of alkaloids render them promising lead structures for further development as ...commercial agents in agriculture and medicine. However, concise, enantioselective total syntheses of stemofoline alkaloids remain a formidable challenge due to their structural complexity. We disclose herein the enantioselective total syntheses of four stemofoline alkaloids, including (+)-stemofoline, (+)-isostemofoline, (+)-stemoburkilline, and (+)-(11
S
,12
R
)-dihydrostemofoline, in just 19 steps. Our strategy relies on a biogenetic hypothesis, which postulates that stemoburkilline and dihydrostemofolines are biogenetic precursors of stemofoline and isostemofoline. Other highlights of our approach are the use of Horner–Wadsworth–Emmons reaction to connect the two segments of the molecule, an improved protocol allowing gram-scale access to the tetracyclic cage-type core, and a Cu-catalyzed direct and versatile nucleophilic alkylation reaction on an anti-Bredt iminium ion. The synthetic techniques that we developed could also be extended to the preparation of other
Stemona
alkaloids.
Developing untethered millirobots that can adapt to harsh environments with high locomotion efficiency is of interest for emerging applications in various industrial and biomedical settings. Despite ...recent success in exploiting soft materials to impart sophisticated functions which are not available in conventional rigid robotics, it remains challenging to achieve superior performances in both wet and dry conditions. Inspired by the flexible, soft, and elastic leg/foot structures of many living organisms, here we report an untethered soft millirobot decorated with multiple tapered soft feet architecture. Such robot design yields superior adaptivity to various harsh environments with ultrafast locomotion speed (>40 limb length/s), ultra-strong carrying capacity (>100 own weight), and excellent obstacle-crossing ability (stand up 90° and across obstacle >10 body height). Our work represents an important advance in the emerging area of bio-inspired robotics and will find a wide spectrum of applications.
•The propagation time from meteorological to hydrological drought was examined.•The propagation time shows obvious seasonal characteristics.•ENSO and AO are strongly correlated with the propagation ...time on long timescales.•The parameter w values of the Fu’s equation exhibit positive linkages with the propagation time.
It is important to investigate the propagation from meteorological to hydrological drought and its potential influence factors, which helps to reveal drought propagation process, thereby being helpful for drought mitigation. In this study, Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSI) were adopted to characterize meteorological and hydrological droughts, respectively. The propagation time from meteorological to hydrological drought was investigated. The cross wavelet analysis was utilized to examine the correlations between hydrological and meteorological droughts in the Wei River Basin (WRB), a typical arid and semi-arid region in China. Moreover, the potential influence factors on the propagation were explored from the perspectives of large-scale atmospheric circulation anomaly and underlying surface characteristics. Results indicated: (1) the propagation time from meteorological to hydrological drought has noticeably seasonal characteristics, that in spring and summer is short, whilst that in autumn and winter is long; (2) hydrological and meteorological droughts are primarily characterized by statistically positive linkages on both long and short time scales; (3) El Niño Southern Oscillation (ENSO) and Arctic Oscillation (AO) are strongly correlated with actual evaporation, thus strongly impacting the propagation time from meteorological to hydrological drought. Additionally, the propagation time has roughly positive associations with the parameter w of the Fu’s equation from the Budyko framework.
Dietary fiber is the undigested carbohydrate that escapes small intestinal digestion and absorption, and then reaches the large intestine for partial or complete fermentation by the colonic ...microbiota. Fermentation of dietary fiber into short-chain fatty acids (i.e., acetic, propionic, and butyric particularly) in the colon has been reported to bring about positive changes in microbiota composition and reduce the risk of colon-related diseases as well as some metabolic syndromes, such as obesity, diabetes, chronic kidney disease, and systemic inflammation.
There is a growing interest in the fate of different dietary fibers in the gastrointestinal tract regarding their rate and extent (location) of fermentation and microbiota changes, particularly from data obtained with static and dynamic in vitro models. These models provide information on the fermentation performance and microbiota modulation by dietary fibers with diverse structures and enable the formulation of functional foods with health benefits.
This review summarizes the fermentation performance of various dietary fibers using in vitro models. Both the physical and chemical structures of dietary fibers are critical factors that determine fermentation rate, short-chain fatty acid profiles and growth of different bacterial groups. Considering the potential relationship between fermentation performance and health, three principles for designing fermentable dietary fiber are proposed: slow fermentation in the colon; high butyrate and/or propionate production; and selective bacterial growth, promoting the beneficial bacteria that improve the intestinal barrier function.
•Advantages and disadvantages of static and dynamic in vitro fecal fermentation models.•Summary of fermentation performance and microbiota modulation of various dietary fibers using in vitro models.•Three principles for designing fermentable dietary fiber are proposed.
Reported herein is the first direct, metal‐catalyzed reductive functionalization of secondary amides to give functionalized amines and heterocycles. The method is shown to have exceptionally broad ...scope with respect to suitable nucleophiles, which cover both hard and soft C nucleophiles as well as a P nucleophile. The reaction exhibits good chemoselectivity and tolerates several sensitive functional groups.
A soft touch: A versatile, direct, metal‐catalyzed reductive functionalization reaction of secondary amides, to give functionalized amines and heterocycles, was developed. A broad substrate scope for both the amide and nucleophile was observed. Viable nucleophiles include reactive and soft C nucleophiles as well as a P nucleophile. The reaction exhibits good chemoselectivity and tolerates several sensitive functional groups (FGs).
•An integrated drought indicator based on variable fuzzy theory was proposed.•This integrated indicator is sensitive to capture drought onset and persistence.•Detected change points were closely ...associated with human activities and ENSO events.
It is of great importance to construct an integrated drought indicator, which is of great importance to drought risk assessment and decision-making. Given the fuzzy nature of drought, the variable fuzzy set theory was applied to develop an Integrated Drought Index (IDI) combining meteorological, hydrological, and agricultural factors across the Yellow River basin in North China. The runoff and soil moisture were derived by driving the calibrated Variable Infiltration Capacity (VIC) model with observed atmospheric forcing. Furthermore, the law of mutual change of quality and quantity was adopted to identify qualitative change points of annual IDI series in the Yellow River basin. The results indicate that: (1) the Integrated Drought Index (IDI) has a better performance compared with Standardized Precipitation Index (SPI) and Standardized streamflow Index (SSFI), and it is more sensitive and effective to capture drought onset and persistence, largely owing to its combination with the information of different drought-related variables; (2) spatially, the middle reaches has a higher drought risk than the rest portions of the Yellow River basin; seasonally, drought risk in spring and winter is larger than other seasons; overall, the IDI of the basin is dominated by an insignificantly downward trend; (3) some qualitative change points of drought were identified in the Yellow River basin, and those are primarily induced by ENSO events and the construction of dams and reservoirs. This study proposed an alternative drought indicator coupled with multivariate drought-related variables by objectively determining their weights based on the entropy weight method, which has a great value in characterizing drought.
Language learning in classrooms has been studied from different perspectives. Among numerous focuses, the present study aims to examine three dimensions—classroom activities, classroom anxiety and ...teacher roles as well as their interactions by investigating 49 students of an English class at university. Quantitative instruments of three 5-likert scales were used to measure the number and the frequency of classroom activities used in the English class, the level of classroom anxiety of students as well as their perceptions of teacher roles. Results showed that the English class was “often” dominated by interactive activities, coupled “sometimes” with language exercises and “occasionally” with real-life tasks. In this activity-dominated English class, learners revealed rather low level of classroom anxiety. In contrast, the overall higher mean of teacher role perceived indicated noticeably facilitating impact of the teacher in class. Correlational analyses disclosed that classroom anxiety was neither significantly correlated with teacher role nor with classroom activity. However, a significant correlation was found between classroom activities and teacher roles. KCI Citation Count: 0
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