Abstract
High-speed railway aerodynamics is the key basic science for solving the bottleneck problem of high-speed railway development. This paper systematically summarizes the aerodynamic research ...relating to China’s high-speed railway network. Seven key research advances are comprehensively discussed, including train aerodynamic drag-reduction technology, train aerodynamic noise-reduction technology, train ventilation technology, train crossing aerodynamics, train/tunnel aerodynamics, train/climate environment aerodynamics, and train/human body aerodynamics. Seven types of railway aerodynamic test platform built by Central South University are introduced. Five major systems for a high-speed railway network—the aerodynamics theoretical system, the aerodynamic shape (train, tunnel, and so on) design system, the aerodynamics evaluation system, the 3D protection system for operational safety of the high-speed railway network, and the high-speed railway aerodynamic test/computation/analysis platform system—are also introduced. Finally, eight future development directions for the field of railway aerodynamics are proposed. For over 30 years, railway aerodynamics has been an important supporting element in the development of China’s high-speed railway network, which has also promoted the development of high-speed railway aerodynamics throughout the world.
The oil–water separation has attracted heightened attention because of the ever‐increasing amounts of oily water produced from the daily activities of humans and industrial processes. Membrane ...technology as an advanced water purification approach has offered an indispensable option due to its cost‐effective, energy‐efficient, and easy‐to‐operate characteristics. However, traditional membrane materials suffer from severe fouling, which counteracts the superiority of applying membranes in oil–water separation applications. Thanks to the emerging bioinspired interface research, a series of special wettability not only endows membrane surfaces with outstanding antifouling properties but also breaks though the long‐standing tradeoff effect between membrane permeability and selectivity. In this review, the recent advances of membranes used for oil–water separation with special wettability and perspectives on the on‐going research are presented. The authors first discuss the wetting phenomenon on membrane surface, and then highlight the gradually evolved specially wettable system and its coupling with membrane materials. Next, relatively comprehensive preparation methods and applications of oil–water filtration membranes utilizing special wettability are summarized. Finally, the authors conclude the current achievements and challenges in specially wettable membranes for oil–water separation and outlook the future in this field.
Bioinspired special wettability has opened new possibilities to improve membranes and their performances in separation processes. This review offers a state‐of‐the‐art assessment of the latest research work on selective membrane materials under the concept of special wettability for highly efficient oil–water separation. Wetting phenomenon, special wettability in membranes, and comprehensive membrane preparation methods are presented.
Polymeric materials used in spacecraft require to be protected with an atomic oxygen (AO)‐resistant layer because AO can degrade these polymers when spacecraft serves in low earth orbit (LEO) ...environment. However, mechanical damage on AO‐resistant coatings can expose the underlying polymers to AO erosion, shortening their service life. In this study, the fabrication of durable AO‐resistant coatings that are capable of autonomously healing mechanical damage under LEO environment is presented. The self‐healing AO‐resistant coatings are comprised of 2‐ureido‐41H‐pyrimidinone (UPy)‐functionalized polyhedral oligomeric silsesquioxane (POSS) (denoted as UPy‐POSS) that forms hydrogen‐bonded three‐dimensional supramolecular polymers. The UPy‐POSS supramolecular polymers can be conveniently deposited on polyimides by a hot pressing process. The UPy‐POSS polymeric coatings are mechanically robust, thermally stable, and transparent and have a strong adhesion toward polyimides to endure repeated bending/unbending treatments and thermal cycling. The UPy‐POSS polymeric coatings exhibit excellent AO attack resistance because of the formation of epidermal SiO2 layer after AO exposure. Due to the reversibility of the quadruple hydrogen bonds between UPy motifs, the UPy‐POSS polymeric coatings can rapidly heal mechanical damage such as cracks at 80 °C or under LEO environment to restore their original AO‐resistant function.
Self‐healing atomic oxygen (AO)‐resistant coatings are fabricated by depositing 2‐ureido‐41H‐pyrimidinone (UPy)‐functionalized polyhedral oligomeric silsesquioxane (POSS) on polyimides. The coatings composed of hydrogen‐bonded UPy‐POSS supramolecular polymers are mechanically robust, thermally stable, and transparent and exhibit excellent AO resistance. The AO‐resistant coatings can autonomously heal mechanical damage under a low‐earth‐orbit environment to restore their AO‐resistant function.
It is reported that the self‐forming CrTaO4 oxide scale can protect refractory high‐entropy alloys from oxidation, superior to Cr2O3. In this paper, the phase stability, mechanical, and thermal ...properties of three polymorphous phases of CrTaO4 are systematically investigated from first‐principles density functional theory calculations. The mechanical properties predicted using the strain–energy methods indicated that all three phases are mechanically stable. The temperature dependence of elastic constants and polycrystalline moduli of three phases demonstrated the thermal softening as temperature increase. The Helmholtz‐free energies as a function of volume and temperature are derived from phonon dispersions within the quasi‐harmonic approximation at six strained volumes. The calculated apparent bulk coefficients of thermal expansion of these three phases are evaluated, the highest value approximately 13.4× 10−6 K−1 within a temperature range of 500–2000 K for the rutile I41md phase. The lattice thermal conductivity calculated by the Debye–Callaway model suggested that the rutile type I41md phase has the lowest value of approximately 2.1 W/m/K at 1800 K. The other two phases, C2/m and P2/c, exhibit higher values due to relatively lower Grüneisen parameters and larger phonon velocities. The melting point of CrTaO4 is predicted to be between 1975 and 2449 K using ab initio molecular dynamics simulations. This work provides a comprehensive theoretical understanding of the thermodynamic, mechanical, and thermal properties for the new material CrTaO4 and serves as an example of a viable computational design strategy for improved oxidation resistance of refractory alloys at high temperatures.
Spatiotemporal organization of distinct biological processes in cytomimetic compartments is a crucial step towards engineering functional artificial cells. Mimicking controlled bi‐directional ...molecular communication inside artificial cells remains a considerable challenge. Here we present photoswitchable molecular transport between programmable membraneless organelle‐like DNA coacervates in a synthetic microcompartment. We use droplet microfluidics to fabricate membraneless non‐fusing DNA coacervates by liquid‐liquid phase separation in a water‐in‐oil droplet, and employ the interior DNA coacervates as artificial organelles to imitate intracellular communication via photo‐regulated uni‐ and bi‐directional transfer of biomolecules. Our results highlight a promising new route to assembly of multicompartment artificial cells with functional networks.
Photoswitchable bi‐directional trafficking of biomolecules between programmable DNA‐based artificial membraneless organelles in a cell‐like microcompartment has been achieved to imitate intracellular communication towards construction of advanced functional artificial cells.
The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research ...activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourth, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.
Melting is a high temperature process that requires extensive sampling of configuration space, thus making melting temperature prediction computationally very expensive and challenging. Over the past ...few years, I have built two methods to address this challenge, one via direct density functional theory (DFT) molecular dynamics (MD) simulations and the other via deep learning graph neural networks. The DFT approach is based on statistical analysis of small-size solid–liquid coexistence MD simulations. It eliminates the risk of metastable superheated solid in the fast-heating method, while also significantly reducing the computer cost relative to the traditional large-scale coexistence method. Being both accurate and efficient (at the speed of several days per material), it is considered as one of the best methods for direct DFT melting temperature calculation. The deep learning method is based on graph neural networks that effectively handles permutation invariance in chemical formula, which drastically improves efficiency and reduces cost. At the speed of milliseconds per material, the model is extremely fast, while being moderately accurate, especially within the composition space expanded by the dataset. I have implemented both methods into automated computer code packages, making them publicly available and free to download. The DFT and deep learning methods are highly complementary to each other, and hence they can be potentially well integrated into a framework for melting temperature prediction. I demonstrated examples of applying the methods to materials design and discovery of high-melting-point materials.
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Ginseng, one of the most widely used traditional herbal medicines and dietary supplements, has historically been recognized as a tonic herb and adaptogen that can enhance the body's tolerance to ...various adversities. Ginsenosides are a diverse group of steroidal saponins that comprise the major secondary metabolites of ginseng and are responsible for its multiple pharmacological effects. Emerging evidence suggests that hormetic phytochemicals produced by environmentally stressed plants can activate the moderate cellular stress response mechanisms at a subtoxic level in humans, which may enhance tolerance against severe dysfunction or disease. In this review, we initially describe the role of ginsenosides in the chemical defense of plants from the genus Panax suffering from biotic and abiotic stress. Next, we summarize the diverse evolutionarily conserved cellular stress response pathways regulated by ginsenosides and the subsequent stress tolerance against various dysfunctions or diseases. Finally, the structure–activity relationship involved in the effect of ginsenosides is also analyzed. The evidence presented in this review implicates that ginseng as “the King of all herbs” could be regarded as a well‐characterized example of the critical role of cellular stress response mechanisms in understanding the health benefits provided by herbal medicines from an evolutionary and ecological perspective.
► A new hybrid ARIMA-ANN model is proposed to forecast wind speed. ► A new hybrid ARIMA-Kalman model is proposed to predict wind speed. ► A detailed comparison of multi-step forecasting performance ...is provided. ► The two new hybrid models can obtain high-precision multi-step results. ► The two presented models are suitable for non-stationary wind speed.
Wind speed prediction is important to protect the security of wind power integration. The performance of hybrid methods is always better than that of single ones in wind speed prediction. Based on Time Series, Artificial Neural Networks (ANN) and Kalman Filter (KF), in the study two hybrid methods are proposed and their performance is compared. In hybrid ARIMA-ANN model, the ARIMA model is utilized to decide the structure of an ANN model. In hybrid ARIMA-Kalman model, the ARIMA model is employed to initialize the Kalman Measurement and the state equations for a Kalman model. Two cases show both of them have good performance, which can be applied to the non-stationary wind speed prediction in wind power systems.
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