Inexpensive metal oxides are the promising catalyst supports for catalytic pyrolysis to produce pyrolysis oil, pyrolysis gas and carbon nanotubes (CNTs). The catalytic co-pyrolysis of tobacco stem (TS) and recycled plastic (PP) is conducted using a Ni/CaO-Al2O3 catalyst with varying CaO/Al2O3 ratios (1:0, 3:1, 1:1, 1:3 and 0:1) in a two-stage fixed bed reactor. Subsequently, TS and PP were decomposed at high temperature to produce pyrolysis oil and H2-rich pyrolysis gas, while CNTs were synthesized using chemical vapor deposition (CVD) on the deposited catalyst (FeMo/MgO). The results demonstrated that Ni-based dual-support catalysts exhibit high total acidity (17-110 mmol/g) and optimal reduction temperature (300-600 degrees C). This is conducive to improve the catalytic cracking reactivity, improve product quality, and achieve CO2 fixation. Ni/Ca-50 enhances C-H cracking, resulting in the production of hydrogen (46 %) and short-chain hydrocarbons, which is beneficial for generating higher-quality CNTs on the deposited catalyst with an ID/IG ratio of 0.52. Meanwhile, Ni/Ca-25 achieved the highest hydrocarbon content (65 %), fostering the generation of carbon source gases necessary for producing high-yield CNTs on FeMo/MgO, evidenced by a TPO weight loss of 40 %. The highly selective Nibased dual-support catalysts hold significant potential for application in catalytic co-pyrolysis, paving the way for the widespread and large-scale deployment of pyrolysis technology.

Hollow transition metal carbides (TMCs) have broad potential applications due to their high melting point, low density, high specific surface area, and good electrical conductivity. However, the conventional preparation of TMCs often involves complex processes and requires high temperature, which limits their practical application. Herein, hollow TMC powders including NbC, VC, ZrC, and TiC were successfully prepared by one-pot molten salt synthesis (MSS) at relatively low temperatures. The formation mechanism and the influence of carbon crystallinity on the synthesis process were investigated. It was found that amorphous carbon precursors act as sacrificial templates in MSS, which can induce the Kirkendall effect to form the hollow structure. When using graphitized carbon microspheres as carbon precursors, the reaction between transition metals and carbon is uneven and relatively sluggish, which prevents the occurrence of the Kirkendall effect, thus hindering the formation of hollow structure. This work provides a facile method to prepare hollow TMCs with the advantages of low synthesis temperature and adjustable morphology.

Morphology regulation and composition design have proved to be effective strategies for the fabrication of desirable microwave absorbers. However, it is still challenging to precisely control the microstructure and components of MAX phases. Herein, an entropy-driven approach, a transition from irregular grains (low entropy) to sheet structure (high entropy), is proposed to modulate the morphology of MAX phases. The theoretical calculation indicates that the morphology evolution can be ascribed to the enlarged energy difference between (11_00) and (0001) facets. The enriched structural defects and optimized morphologies yield significant dipolar polarization, interfacial polarization, multiple reflections, and scattering, which all enhance the electromagnetic wave absorption performance of (V0.25 Ti0.25 Cr0.25 Mo0.25 )2 GaC. Specifically, its minimum reflection loss can reach up to -47.12 dB at 12.13 GHz, and the optimal effective absorption bandwidth is 4.56 GHz (2.03 mm). Meanwhile, (V0.25 Ti0.25 Cr0.25 Mo0.25 )2 GaC shows also pronounced thermal insulation properties affording it good reliability in the harsh working environment. This work offers a novel approach to designing and regulating the morphology of the high entropy MAX phase, and also presents an opportunity to elucidate the relationship between entropy and electromagnetic wave absorption performance.

Ti2AlC can be used as a microwave absorbent due to its good electrical conductivity. However, Ti2AlC powders synthesized using conventional solid phase reaction show low reflection loss (RL) and narrow effective absorption width (EAB), which greatly limits its application in the field of microwave absorption. Herein, porous lamellar Ti2AlC powders were firstly synthesized in NaCl/KCl molten salt using Ti powders, Al powders, and starch as reaction precursors, and then they were selectively etched with Lewis acid molten salt (CuCl2) to prepare Ti2AlC/Cu/Ti2C hybrids. The results indicated that when the mass fraction of porous lamellar Ti2AlC powder in paraffin was 40 %, the maximum RL and EAB were -44.15 dB and 2.68 GHz, respectively. After Lewis acid molten salt etching, the RL and EAB of Ti2AlC/Cu/Ti2C hybrids increased to -54.88 dB and 4.48 GHz, respectively. The improvement of microwave absorption property could be attributed to the enhancement of polarization and conductivity losses caused by the formation of Ti2C MXene and copper nanoparticles. This study provides a simple way to tune the microstructure and microwave absorption capability of Ti2AlC.

When finite set model predictive control is applied to an O-Z-source inverter (O-ZSI) containing a transformer, there are multiple control variables, it is difficult to adjust the weighting factors, and the currents on both sides of the transformer could change abruptly, making it impossible to calculate and derive reference values to directly predict and control the currents on both sides of the transformer. In this paper, an improved sequential-model predictive control is proposed for O-ZSI with a transformer without adjusting the weighting factors. By equating the transformer as a parallel connection of the excitation inductance with a set of ideal transformers without adjusting the weighting factors, the reference value of the magnetization current of the excitation inductance can be calculated according to the theoretical derivation, which can realize the predictive control of the O-ZSI. Simulation analysis and experimental results show that the proposed control method achieves the sequential-model predictive control of O-ZSI without adjusting the weight factors, with good steady-state and dynamic characteristics.

DNA N6-adenine methylation (N6-methyladenine, 6mA) plays a key regulating role in the cellular processes. Precisely recognizing 6mA sites is of importance to further explore its biological functions. Although there are many developed computational methods for 6mA site prediction over the past decades, there is a large root left to improve. We presented a cross validation-based stacking ensemble model for 6mA site prediction, called 6mA-StackingCV. The 6mA-StackingCV is a type of meta-learning algorithm, which uses output of cross validation as input to the final classifier. The 6mA-StackingCV reached the state of the art performances in the Rosaceae independent test. Extensive tests demonstrated the stability and the flexibility of the 6mA-StackingCV. We implemented the 6mA-StackingCV as a user-friendly web application, which allows one to restrictively choose representations or learning algorithms. This application is freely available at http://www.biolscience.cn/6mA-stackingCV/ . The source code and experimental data is available at https://github.com/Xiaohong-source/6mA-stackingCV .

In this study, a series of V2(Al1-xGax)C microrods are synthesized for the first time in a molten salt system using short carbon fibers as carbon source and sacrificial template. The phase components, structural characteristics, and microwave absorption performance of as-prepared V2(Al1-xGax)C microrods are sys-tematically investigated. The calculated lattice distortion degree results confirm that the phase structure, grain boundary density, and internal stress of V2(Al1-xGax)C microrods can be effectively modulated by controlling the doping amount of gallium element. The synergistic effects of dielectric loss, magnetic loss, multiple reflection and scattering afford the V2(Al1-xGax)C microrods with enhanced microwave absorption intensity and bandwidth. Specifically, V2(Al0.5Ga0.5)C microrod displays a minimum RL value of - 55.62 dB at 12.00 GHz, and the broadest EAB could reach 4.16 GHz with a thickness of 1.75 mm. Compared with the M sites doped MAX phases, A sites doped V2(Al1-xGax)C exhibit more excellent electromagnetic energy at-tenuation capacities.(c) 2022 Elsevier B.V. All rights reserved.

The morphology of MAX phase powders significantly influences their microwave absorption properties. However, the traditional synthesis via solid-state reactions produces irregular powders, and the preparation of MAX phase powders with specific morphology remains a challenge. Herein, (V0.8Ti0.1Cr0.1)(2)AlC MAX phase microrods were fabricated for the first time in NaCl/KCl molten salts using vanadium, titanium, chromium, aluminum, and short carbon fibers as precursors. It was found that despite acting as a carbon source, carbon fibers also acted as sacrificial templates. By adjusting the molar ratio of metal powders and short carbon fibers, a series of carbon fiber@(V0.8Ti0.1Cr0.1)(2)AlC microrods with core-sheath structure were also obtained. Carbon fiber@(V0.8Ti0.1Cr0.1)(2)AlC microrods with a molar ratio of 8:2 showed the optimum microwave absorption performance. The reflection loss (RL) value reached up to -63.26 dB at 2.40 mm, and the effective absorption bandwidth (EAB) was about 5.28 GHz with a thickness of 2.02 mm. Based on the electromagnetic parameter analysis and theoretical simulation, the enhanced microwave absorption performance was attributed to the synergistic effect of different factors like dielectric loss, magnetic loss, multiple reflection, and scattering. This work offers a facile route to modulate the morphology of MAX phase powders and may accelerate its application as microwave absorbers. (C) 2021 Published by Elsevier Ltd on behalf of Chinese Society for Metals.

Enhancers are short DNA segments that play a key role in biological processes, such as accelerating transcription of target genes. Since the enhancer resides anywhere in a genome sequence, it is difficult to precisely identify enhancers. We presented a bi-directional long-short term memory (Bi-LSTM) and attention-based deep learning method (Enhancer-LSTMAtt) for enhancer recognition. Enhancer-LSTMAtt is an end-to-end deep learning model that consists mainly of deep residual neural network, Bi-LSTM, and feed-forward attention. We extensively compared the Enhancer-LSTMAtt with 19 state-of-the-art methods by 5-fold cross validation, 10-fold cross validation and independent test. Enhancer-LSTMAtt achieved competitive performances, especially in the independent test. We realized Enhancer-LSTMAtt into a user-friendly web application. Enhancer-LSTMAtt is applicable not only to recognizing enhancers, but also to distinguishing strong enhancer from weak enhancers. Enhancer-LSTMAtt is believed to become a promising tool for identifying enhancers.

The microstructure and morphology of Ti3AlC2 powders not only affect the preparation of Ti3C2 MXene but also have a great influence on their potential applications, such as microwave absorbers, alloy additives, or catalytic supports. However, the synthesis of Ti3AlC2 powders with desired microstructure and morphology remains a challenge. Herein, hollow Ti3AlC2 microrods were prepared for the first time in NaCl/KCl molten salts by using titanium, aluminum, and short carbon fibers as starting materials. It was found that the short carbon fibers not only performed as carbon source but also acted as sacrificial template. Furthermore, it was revealed that TiC and Ti2AlC were initially formed on the surface of carbon fibers. The subsequent reactions between the outer Ti, Al and the inner carbon were dominated by the Kirkendall effect which gave rise to the formation of a hollow structure. Based on this mechanism, hollow Ti3AlC2 microspheres and a series of hollow TiC, Ti2AlC, and V2AlC powders were also successfully fabricated. This work provides a facile route to synthesize hollow MAX phases and may give enlightenment on preparing other hollow carbide powders via the Kirkendall effect in the molten salts.

Coherent vortex structures in subgrid scale (SGS) motions are important for preferential concentration and collision of particles with small and intermediate Stokes number (Xiong et al., 2019). In this study, a new large eddy simulation (LES) strategy that combines wavelet filtered large eddy simulation with a differential filter SGS model is proposed. First, a wavelet filtered direct numerical simulation (WFDNS) enables good preservation of SGS structures due to the high compressibility and local fidelity of the wavelet filter. Second, a differential filter (DF) model, containing only a parameter related to the nominal filter width, is used to dynamically reconstruct unresolved eddies. The SGS model presented here is verified using direct numerical simulation (DNS) data for particle-laden homogenous isotropic turbulence. Compared to the classical spectral-filtered DNS (FDNS) model, the new SGS model enables to achieve better agreement with DNS results related to the dispersed-phase statistics, such as particle acceleration, particle-seen fluid kinetic energy, particle-seen Lagrangian integral time etc. Furthermore, obtained results also exhibit the advantages of a proposed model over the stochastic Langevin model in the prediction of particle dynamics, especially collision-related statistics such as radial distribution function, radial relative velocities, and particle collision rates. Moreover, the model also demonstrates good performance in application to particle-pair related statistics at different Reynolds numbers and different filter depths. This is attributed to the ability of this model to multispectrally enhance coherent vortex structures in SGS, which is promising to apply for recovering SGS effects in the LES of turbulent particle-laden flows.

•The oxidized V2CTx is synthesized via H2O2 assisted hydrothermal oxidation.•Both O-terminated groups and VO2 (A) increased significantly after oxidation.•The oxidized V2CTx displayed good electrochemical performances.

Large-scale pilot studies of oxy-fuel combustion have demonstrated that it is a promising CO2 capture technology. In this study, steady-state and dynamic models of oxy-fuel combustion were developed using the Yingcheng 35 MWth oxy-fuel combustion pilot facility as a prototype. Using specific features of Aspen software, a customized drum and furnace radiation model was developed to make it easier to represent the real features of the 35 MWth facility. The mode switching process between air combustion and oxy-fuel combustion is focused on, in particular, using both a "step by step" and a "simultaneous" switching scheme. It is found that maintaining the gas flow in oxygen and recirculation flue at different slopes for different switching stages can be an effective switching strategy. "Simultaneous" switching produces a better and smoother dynamic response during the switching process and is more exergy-efficient. Together, these results can help to improve the operation of facilities and control system design.

本文以某0.5MW富氧燃烧煤粉炉为研究对象,采用改进的气体、颗粒辐射特性模型以及富氧燃烧骨架机理,对煤粉空气燃烧以及不同烟气循环倍率下的富氧燃烧进行了数值模拟,对炉内气流分布、温度分布以及壁面热流进行了详细地分析.研究结果表明,不同燃烧条件下,预测的壁面辐射热流与试验测量值具有很好的一致性;烟气循环倍率对炉内温度以及传热具有很好的调节作用,在本文中,当循环倍率为67％时,富氧燃烧的炉内峰值温度与空气燃烧基本一致,但传热能力增强;当循环倍率为71％时,富氧燃烧的传热量与空气燃烧一致.

The configurations of burner streams under oxy-fuel combustion are highly affected by its increased initial oxygen level. In this study, an air combustion and oxy-fuel combustion compatible configuration strategy for burner streams is proposed for a 200 MWe tangentially fired boiler, by aid of numerical simulation. Firstly, to achieve a momentum of primary and secondary streams that is similar to that of air combustion, the tertiary stream is switched-off in oxy-fuel combustion. In addition, the opposing tangential primary stream technology is suggested to reduce the gas temperature deviation in the upper furnace, which affects the quality of the steam and the safe operation of the boiler. For the present study, the appropriate opposing tangential angle is 5 degrees-7 degrees relative to the original primary stream design, and the ratio of opposing tangential momentum flow moment should be controlled at the low limit of 0.8 to decrease gas temperature deviation. To achieve a supported flame by the secondary stream, the momentum of the bottom secondary stream in oxy-fuel combustion should not be less than that in air combustion. The study illustrates for the first time that, the key design features of tangentially fired burners under oxy-fuel combustion. Although there are significant changes in the oxidant volume, oxidant composition, and chemical under oxy-fuel combustion conditions, the design criteria of oxy-fuel tangentially fired boiler, in terms momentum of the primary stream, momentum of the bottom secondary stream, and momentum ratio and flow moment ratio of the secondary stream to primary stream, are consistent with those under air combustion.

Nano-SiO2 was grafted onto the carbon fabric surface under microwave-hydrothermal condition to improve the tribological properties of carbon fabric/resin friction materials with different treatment temperature. The carbon fibers and prepared samples were characterized by the Fourier transform infrared spectrophotometer, contact angle instrument, energy dispersive spectroscopy, universal material testing machine and field emission scanning electron microscopy. The tribological behaviors of the carbon fabric/resin friction materials were evaluated by a friction tester. The results indicated that nano-SiO2 particles were successfully grafted onto carbon fabric surface under microwave-hydrothermal condition, especially at 200℃ (contact angle was almost close to 0°), which obviously improved the hydrophilicity of carbon fabric surface. The wear rate of carbon fabric/resin friction materials with microwave-hydrothermal temperature of 200℃ reduced by 81.4%, ranging from 4.3 × 10−5 mm3J−1 to 0.8 × 10−5 mm3J−1. It could effectively enhance the bonding strength of carbon fabric and resin, which improved the friction-reduction and anti-wear abilities of the friction materials.

Subgrid scale (SGS) structures in large eddy simulations (LES) of turbulent particle-laden flows significantly influence particle dynamics, especially those of small inertial particles. In this study, homogenous isotropic turbulence with Taylor's Reynolds number of 102.3 is generated by a direct numerical simulation (DNS) and a wavelet-based coherent vortex extraction method is implemented to extract the coherent SGS structures and then investigate their effects on particle dynamics, including single-particle and particle-pair statistics. Compared to the classical spectral-filtered DNS (FDNS), which cuts off only the high wavenumber components regardless of the turbulence structures in the SGS motions, the wavelet filtered DNS (WFDNS) can retain more coherent vortex structures in the SGS flow field with the help of the high compression rate characteristics of wavelet transformation. Comparing the results of WFDNS and FDNS at the identical effective grid number, it can be found that the single-particle statistics are mainly controlled by the macro energy-containing structures, and the SGS coherent vortex structures play important roles in the particle-pair dynamics, including the radial distribution function, radial relative velocity, and collision kernel. Therefore, in view of the characteristic of wavelet filtering that preserves the SGS coherent structure, the wavelet-based structural filter should be particularly suitable for LES modeling of particle-laden flow. (C) 2018 Elsevier Ltd. All rights reserved.

The behavior of particle cloud in a high Reynolds number (13500) turbulent opposed-jet flow with a moderate nozzle separation (12 times the nozzle diameter) is investigated by a two-phase large eddy simulation. Euler/Lagrangian approaches are applied to simulate gas and particle phases, respectively. Two-way coupling is considered, and a deterministic hard-sphere collision model is used to deal with the interparticle collision. Three particle Stokes numbers (8, 37, and 180) and three particle volume fractions (2 x 10(-5), 1.5 x 10(-4), and 4.8 x 10(-3)) are tested. Particle inertia and interparticle collisions are found to exert a significant effect on particle distribution and velocity characteristics, a strong interaction is observed between particle cloud and gas impingement plane. Particle inertia strengthens the penetration of particles in the opposite stream, thus widening the particle aggregation region and decreasing the peak value of particle concentration. The mixing of rightward and leftward-moving particles in the particle penetration distance noticeably decreases the particle axial mean velocity and increases the particle axial fluctuation velocity. Furthermore, interparticle collisions suppress the reciprocating penetration of particles in the opposed jets and force the particles to accumulate near the impingement plane. Meanwhile, interparticle collisions increase the particle radial mean and radial fluctuation velocities by energy transfer from the axial direction to the radial direction. The unstable gas impingement plane can drive the swing of particle aggregation region, especially for the small inertia particles and massive interparticle collisions. By contrast, the particle cloud can enhance the stability of gas impingement plane, which significantly reduces the gas velocity fluctuation in the impinging region. (C) 2017 Elsevier B.V. All rights reserved.

This paper reports the oxy-fuel combustion characteristics in a pilot-scale furnace with a bituminous coal. After discussing the design principles of oxy-fuel burners in detail, a swirling low-NOx burner system is specially designed to achieve the compatible combustion of air-fuel combustion and oxy-fuel combustion. The initial O-2 concentrations vary between 22 and 30% by volume in the oxy-fuel combustion. A reliable transition process is performed between different combustion modes. Measurements of flame images, burnout rate, heat transfer, and pollution emission are carried out. The results show that compatible and stable combustion with low NOx emissions is achieved in different combustion modes. A high time-averaged CO2 concentration of 81.5% by volume is achieved in the dry flue gas. In this test facility, compared to air-fuel combustion, the averaged burnout rate of pulverized coal slightly increases (similar to 97%) despite the decrease in flame temperature. There is an optimal initial O-2 concentration between 26 and 30% by volume, which can achieve a similar heat transfer process with air-fuel combustion. By using a low-NOx oxy-fuel burner system and flue gas recycle, NOx emissions decrease to a level that is 30-50% of that in air-fuel combustion. The oxy-fuel combustion with a low-NOx oxy-fuel burner system is confirmed for efficiently and cleanly burning pulverized coal.