Bulk chemicals produced from renewable resources are receiving considerable attention due to the increase in sustainable practices. In this study, a novel, efficient, and sustainable strategy has ...been proposed to produce versatile petroleum-based monophenols from the natural aromatic polymer, lignin, via the selective cleavage of its specific chemical linkages by a cost-effective catalyst, Ni/MgO. The results demonstrate that 93.4% of lignin is converted, yielding 15.0% monophenols in the presence of 20% Ni/MgO. Importantly, 42.3% of these volatile chemicals are found to be 4-ethyl phenol (the yield is 6.31%), a widely used fine chemical currently obtained from the petrochemical industry. Further comparative investigations on the raw and recovered lignin using heteronuclear single quantum correlation-nuclear magnetic resonance (HSQC-NMR), Fourier transform infrared (FT-IR), quantitative 13C NMR, and the alkaline nitrobenzene oxidation method reveal that the selective breakage of the ester bond between the p-hydroxyphenyl structural unit and the other fragments followed by decarboxylation is responsible for the good performance of the 4-ethyl phenol formation process. Therefore, the results of this work would provide new insights for producing value-added petrochemicals from renewable lignin.
Abstract Thiophene is the organic sulfur with good thermal stability in carbon-based fuel, clarifying the conversion mechanism between thiophene and COS is beneficial for achieving in-situ sulfur ...fixation during CO 2 gasification of carbon-based fuels, but the mechanism has rarely been reported. Therefore, calculations based on density functional theory were performed and 16 reaction paths were proposed in this research, clarifying the decomposition mechanism of thiophene and re-fixation mechanism of COS. The attachment of CO 2 will lead to the destruction of the thiophene ring and the generation of COS, and CO 2 adsorption is the rate-determined step, while the carbon atom that adjacent sulfur atom is the reaction active site. However, the energy barriers of CO 2 addition reactions are lower than those of CO 2 adsorption reactions, and the energy barrier of reactions occurring on the aliphatics are lower than that occurring on the aromatics. The combination of CO 2 and thiophene will thermodynamically lead to the generation of COS and CO. Moreover, gaseous sulfur generated from thiophene decomposition will be converted mutually, while H 2 S will not be converted into COS. Furthermore, COS will be captured by char, forming solid organic sulfur. The re-fixation of COS will occur on aliphatic chains from the decomposition of aromatics.
To be able to predict the DC flashover characteristics of composite insulators, a four-layer BP neural network model is established with composite insulator shed structure parameters as the input. ...Three algorithms (gradient descent with momentum, RMSProp gradient descent, and Adam gradient descent) are applied, and the DC pollution flashover experimental data of composite insulators are used as training data. The results show that all three algorithms have good prediction capabilities. Among them, the Adam gradient descent model has the best prediction result, which can make the average prediction with an error of less than 4% and a maximum error of less than 8%, so these results can provide a reference for the design of composite insulators in DC voltage and product performance verifications.
The worldwide increase in the number of patients with dementia is becoming a growing problem, while Alzheimer's disease (AD), a primary neurodegenerative disorder, accounts for more than 70% of all ...dementia cases. Research on the prevention or reduction of AD occurrence through food ingredients has been widely conducted. In particular, histidine-containing dipeptides, also known as imidazole dipeptides derived from meat, have received much attention. Imidazole dipeptides are abundant in meats such as poultry, fish, and pork. As evidenced by data from recent human intervention trials conducted worldwide, daily supplementation of carnosine and anserine, which are both imidazole dipeptides, can improve memory loss in the elderly and reduce the risk of developing AD. This article also summarizes the latest researches on the biochemical properties of imidazole dipeptides and their effects on animal models associated with age-related cognitive decline. In this review, we focus on the results of human intervention studies using supplements of poultry-derived imidazole dipeptides, including anserine and carnosine, affecting the preservation of cognitive function in the elderly, and discuss how imidazole dipeptides act in the brain to prevent age-related cognitive decline and the onset of dementia.
Abstract
Non-Hermitian skin effect(NHSE) describes a unique non-Hermitian phenomenon that all eigen-modes are localized near the boundary, and has profound impact on a wide range of bulk properties. ...In particular, topological systems with NHSE have stimulated extensive research interests recently, given the fresh theoretical and experimental challenges therein. Here we propose a readily implementable scheme for achieving NHSE with band topology in ultracold gases. Specifically, the scheme realizes the one-dimensional optical Raman lattice with two types of spin-orbit coupling (SOC) and an additional laser-induced dissipation. By tuning the dissipation and the SOC strengths, NHSE and band topology can be individually controlled such that they can coexist in a considerable parameter regime. To identify the topological phase in the presence of NHSE, we have restored the bulk-boundary correspondence by invoking the non-Bloch band theory, and discussed the dynamic signals for detection. Our work serves as a guideline for engineering topological lattices with NHSE in the highly tunable environment of cold atoms, paving the way for future studies of exotic non-Hermitian physics in a genuine quantum many-body setting.
With the development of information technology, computer networks have become a part of people’s lives and work. However, computer viruses and malicious network attacks make network security face ...huge challenges, and more accurate detection of attacks has become the focus of attention to current computer fields. This paper proposes an intrusion detection model, which is mainly based on the XGBoost (Extreme Gradient Boosting), and uses the WOA (Whale Optimization Algorithm) to find the best parameters for it. The collected network data are first preprocessed by the PCA (Principal Component Analysis) dimensionality reduction method, and then, the preprocessed data are imported into the WOA-XGBoost algorithm so that the overall model has better intrusion detection capabilities for data after training. The experimental results are applied to the well-known KDD CUP 99 data in the computer network field, and compared with the accuracy of the results obtained by parameter adjustment in the traditional way, it shows that the intrusion detection model under this method has better accuracy.
Regeneratively cooled scramjets are successfully used as propulsion devices in hypersonic vehicles. During operation, scramjets experience acceleration. This special process causes a dynamic flow ...process, and heat transfer in the cooling channel commonly occurs, which may cause hazards and control difficulties for scramjets. A dynamic numerical model with a modified heat transfer coefficient calculation method was established to study the transient flow and heat transfer processes in a cooling channel. The dynamic characteristics of the flow and heat transfer under different conditions were calculated and are discussed, including the changes in the inlet fuel mass flow, heat flux, and pressure working conditions. The results indicate that the stable time of the cooling channel outlet fuel temperature is related to the rate of change in the inlet mass flow and heat flux. The stable time of the outlet fuel temperature under decreasing heat flux working conditions was approximately 12.5 s. These results summarize the dynamic flow and heat transfer characteristics, which are significant for designing cooling channels in scramjets.
We study an atom-cavity hybrid system where fermionic atoms in a one-dimensional lattice are subject to a cavity-induced dynamic gauge potential. The gauge coupling leads to highly degenerate steady ...states in which the fermions accumulate to one edge of the lattice under an open boundary condition. Such a phenomenon originates from the many-body Liouvillian superoperator of the system, which, being intrinsically non-Hermitian, is unstable against boundary perturbations and manifests the non-Hermitian skin effect. Contrary to the single-body case, the steady state of a multiatom system is approached much slower under the open boundary condition, as the long-time damping of the cavity mode exhibits distinct rates at different times. This stagewise slowdown is attributed to the competition between light-assisted hopping and the dynamic gauge coupling, which significantly reduces the steady-state degeneracy under the open boundary condition, as distinct hosts of quasisteady states dominate the dynamics at different timescales.
Clean coal technology is the important thrust to the achievement of “carbon neutralization”; clearing the transformation mechanism of thiophene, the dominant organic sulfur species in coal, is ...conducive to promoting the development of sulfur removal technology. DFT calculations were performed, and 28 reaction paths were proposed in this research, clarifying the decomposition mechanism of thiophene and the fixation mechanism of H2S. Thiophene is pyrolyzed mainly through the hydrogen-transfer reaction, which occurs at above 2000 K rather than 800 K. The hydrogen transfer between the C–C bond rather than the C–S bond causes the ring opening. Hydrogen promotes the decomposition of thiophene, which happens at 800 K, with a molar ratio of hydrogen to thiophene of 5. Therefore, thiophene is decomposed at 800 K mainly through the hydrogenation reaction that occurs at para carbons and the C–S bond, the H2S elimination reaction, and the generation of ethane. Furthermore, H2S can be converted into thiophene through the addition reaction with unsaturated hydrocarbon, or the dehydration reaction with hydroxyl or carboxyl groups. The combination between H2S and the aliphatic compound occurs at 800 K, which is mainly influenced by the species of the functional group rather than the composition and morphology of the carbon chain. Meanwhile, the conversion of aromatic compounds tends to the generation of aryl mercaptan rather than thiophene at around 800 K.
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