Chain Propagation Research Articles

Multimodal Fake News Detection Incorporating External Knowledge and User Interaction Feature

With the development of online social media, the number of various news has exploded. While social media provides an information platform for news release and dissemination, it also makes fake news proliferate, which may cause potential social risks. How to detect fake news quickly and accurately is a difficult task. The multimodal fusion fake news detection model is the current research focus and development trend. However, in terms of content, most existing methods lack the mining of background knowledge hidden in the news content and ignore the connection between background knowledge and existing knowledge system. In terms of the propagation chain, the research tends to emphasize only the single chain from the previous communication node, ignoring the intricate communication chain and the mutual influence relationship among users. To address these problems, this paper proposes a multimodal fake news detection model, A-KWGCN, based on knowledge graph and weighted graph convolutional network (GCN). The model fully extracted the features of the content and the interaction between users of the news dissemination. On the one hand, the model mines relevant knowledge concepts from the news content and links them with the knowledge entities in the wiki knowledge graph, and integrates knowledge entities and entity context as auxiliary information. On the other hand, inspired by the “similarity effect” in social psychology, this paper constructs a user interaction network and defines the weighted GCN by calculating the feature similarity among users to analyze the mutual influence of users. Two public datasets, Twitter15 and Twitter16, are selected to evaluate the model, and the accuracy reaches 0.905 and 0.930, respectively. In the comparison experiments, A-KWGCN model has more significant advantages than the other six comparison models in four evaluation indexes. Also, ablation experiments are conducted to verify that knowledge module and weighted GCN module play the significant role in the detection of fake news.

Generalized Fuzzy Subset Method for Time-Varying Multi-State Reliability of Perturbation Failure Coupling Measurement System With Limited Expert Knowledge

In this work, a generalized fuzzy subset (GFS) method is proposed to assess the time-varying multi-state reliability of the perturbation failure coupling measurement (PFCM) system. First, a perturbation-failure coupling mechanism is designed to define the propagation chain of perturbations so as to integrate all the possible perturbations as the inputs of the GFS method. Second, to assess the time-varying multi-state reliability, a GFS reliability model is constructed based on the composite limit state. Furthermore, the concept of the uncertain subset boundary is presented to conduct the reliability assessment via a group of embedded interval type-2 fuzzy sets. To address the deficiency of the GFS reliability model, a data-driven strategy is designed to establish the implicit relation between the limited expert knowledge and the membership function. Finally, the experimental tests are carried out to examine the superiority of the GFS method, and parametric studies are also conducted to study the reliability of the PFCM system.

Collaborative emergency adaptation for ripple effect mitigation in intertwined supply networks

AbstractFor the first time, the ripple effect is examined in the setting of an intertwined supply network. Through simulations, we model the disruption propagation in supply chains having common suppliers. We explore conditions under which a collaborative coordination of re-purposed capacities and shared stocks can help mitigate the ripple effect and improve recovery performance. As a result, we conceptualize the notion of collaborative emergency adaptation contributing to development of “network-of networks” and viability perspective in supply chain resilience management. We illustrate our approach with anyLogistix simulations and deduce some generalized theoretical and managerial insights on how and when a collaborative emergency adaptation can be implemented and help improve supply chain resilience and viability.

KINETIC EQUATIONS FOR RADICAL-CHAIN OXIDATION INVOLVING PROCESS-INHIBITING ALKYL (OR HYDRO)TETRAOXYL FREE RADICAL

The derivation of kinetic equations for the oxidation processes by the free-radical nonbranched-chain mechanism is shown. This derivation is based on the proposed reaction scheme for the initiated addition of free radicals to the multiple bond of the molecular oxygen includes the addition reaction of the peroxyl free radical to the oxygen molecule to form the tetraoxyl free radical. This reaction competes with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which – alkyl(or hydro)tetraoxyl – is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. The rate equations (containing one to three parameters to be determined directly) are deduced using the quasi-steady-state treatment. These kinetic equations were used to describe the γ-induced nonbranched-chain processes of free-radical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing various amounts of oxygen at 296 K. The ratios of rate constants of competing reactions and rate constants of addition reactions to the molecular oxygen are defined. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoinhibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. It is shown that a maximum in these curves arises from the competition between hydrocarbon (or hydrogen) molecules and dioxygen for reacting with the emerging peroxyl 1:1 adduct radical. From the energetic standpoint possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule gas-phase reactions is considered.

Migraine and plant antioxidant: Review article

Even though the pathophysiology of migraine has been the subject of many works, the precise molecular mechanism regarding the disturbances that underlie migraine remains unknown. Additionally, it is thought that oxidative stress contributes significantly to migraine development. For many years, the idea that migraine sufferers experience oxidative stress was addressed. The so-called nutraceutics, which include antioxidants, have received a lot of attention in the last few years among the substances which may be utilized to cure migraines. Antioxidants that are supplied with the food prevent the oxidative stress through suppressing the propagation, initiation, and actual oxidative chain reaction. The agents now being utilized to prevent migraines do in fact have certain antioxidative activity. Antioxidants that have been addressed in this research are growing more regularly utilized through the migraine sufferers not just because of low or even lack of side effects, yet as well due to their efficiency (shortening of an episode duration or reduced frequency of migraine episodes).

The Uncertainty of SNO Cross-Calibration for Satellite Infrared Channels

The on-orbit radiometric calibration is a fundamental task in quantitative remote sensing applications. A widely used calibration method is the cross-calibration based on Simultaneous Nadir Observation (SNO), which involves using high-precision reference instruments to calibrate lower-precision onboard instruments. However, despite efforts to match the observation time, spatial location, field geometry, and instrument spectra, errors can still be introduced during the matching processes and linear regression analysis. This paper focuses on the error generated by sample matching and the error fitting method generated by the sample fitting method. An error propagation analysis is performed to develop a generic model for assessing the uncertainty of the SNO cross-calibration method itself in meteorological satellite infrared channels. The model is validated using the payload parameters of the Hyperspectral Infrared Atmospheric Sounder (HIRAS) and the Medium Resolution Spectral Imager (MERSI) instruments aboard the FengYun-3D (FY-3D). Simulation experiments are performed considering typical bright temperatures, different background fields, and varying matching threshold conditions. The results demonstrate the effectiveness of the proposed model in capturing the error propagation chain in the SNO cross-calibration process. The model provides valuable insight into error analysis in the SNO cross-calibration method and can assist in determining the optimal sample matching threshold for achieving radiometric calibration accuracy.

Suppression effects of energy-absorbing materials on natural gas explosion in utility tunnels

The energy-absorbing material of metal foam have enormous potential in mitigating the consequences of natural gas explosion disaster in urban utility tunnels. When double-layer metal foam with different pore structures of first larger pores and then smaller pores (LP-SP model), the suppression efficiency of explosion overpressure can reach more than 60% and is 2–3 times that of first smaller pores and then larger pores (SP-LP model), and the error between that and that of the same thickness all with smaller pore structure is only 0.86%. Similarly, the metal foams with the LP-SP model can block the explosion flame propagation chain entirely, while reversing the combination order weakens the suppression effect on the explosion flame. Two suppression mechanisms of double-layer metal foam, including the Sudden Shrinkage Effect (SSE) of the LP-SP model and the Amplification Effect (AE) of the SP-LP model. The metal foam barrier device based on SSE is designed for utility tunnels, which can take effect within 0.1 s under electromagnetic force and gravity. This study can provide scientific theoretical support for designing gas explosion suppression measures in utility tunnels.

Nickel-Catalyzed Alkene Difunctionalization as a Method for Polymerization.

Alkene dicarbofunctionalization is a rapidly emerging tool for complex molecule synthesis that installs two carbon fragments regioselectively across an alkene. This method has the potential to engineer stereodefined polymers, yet the application of difunctionalization reactions to polymer synthesis remains unexplored. Herein, we describe the first example of a Ni-catalyzed difunctionalization of alkenes with arylboronic esters and aryl bromides innate to the alkene. The polymerization reaction proceeds regioselectively with the addition of the aryl bromide to the terminal alkenyl carbon and arylboronic ester to the internal benzylic carbon. The resultant poly[arylene-α-(aryl)ethylene]s comprise aryl groups installed at regular intervals along the polymer backbone through chain propagation in two directions. Polymers with molecular weights generally ranging from 30 to 175 kDa were obtained after successful fractionation from oligomeric species. Thermal analysis of the poly[arylene α-(aryl)ethylene]s revealed stability up to ∼399 °C, with a Tg of 90 °C, both of which are similar in value to poly(styrene)s and poly(phenylene methylene)s.

A DFT Study of the Copolymerization of Methyl Vinyl Sulfone and Ethylene Catalyzed by Phosphine–Sulfonate and α-Diimine Palladium Complexes

Density functional theory (DFT) calculations were comparatively carried out to reveal the origins of different catalytic performances from phosphine–benzene sulfonate (A, [{P^O}PdMe(L)] (P^O = Κ2-P,O-Ar2PC6H4SO3 with Ar = 2-MeOC6H4)) and α-diimine (B, [{N^N}PdMe(Cl)] (N^N = (ArN=C(Me)-C(Me)=NAr) with Ar = 2,6-iPr2C6H3)) palladium complexes toward the copolymerization of ethylene and methyl vinyl sulfone (MVS). Having achieved agreement between theory and experiment, it was found that the favorable 2,1-selective insertion of MVS into phosphine–sulfonate palladium complex A was due to there being less structural deformations in the catalyst and monomer. Both the MVS and ethylene insertions were calculated, and the former was found to be more favorable for chain initiation and chain propagation. In the case of α-diimine palladium system B, the resulting product of the first MVS insertion was quite stable, and the stronger O-backbiting interaction hampered the insertion of the incoming ethylene molecule. These computational results are expected to provide some hints for the design of transition metal copolymerization catalysts.

Controllable Synthesis of Heterofunctionalized Polyethers via Intramolecular Phosphonium Bisborane Lewis Pair-Catalyzed Immortal Ring-Opening Polymerization

A metal-free phosphonium bisborane Lewis pair (PBB-Br) was demonstrated to realize the immortal ring-opening polymerization (iROP) of propylene oxide (PO) under mild conditions with alcohols as chain-transfer agents (CTAs). Narrow dispersed poly(propylene oxides) (PPOs) with controllable molecular weights predicted from the [PO]0/([PBB-Br]0 + [CTAs]0) molar ratio were obtained in quantitative conversion. These findings indicated the iROP feature of PBB-Br-catalyzed PO polymerization. The rapid, reversible, and quantitative chain transfer assured the iROP characteristic for an intramolecular Lewis pair catalyst PBB-Br, so various well-defined heterofunctionalized PPOs were easily produced. All the α,ω-difunctionalized PPOs were carefully characterized. Density functional theory (DFT) calculations reveal that the chain transfer to the CTA process is almost barrierless (0.8 kcal mol–1) and thermodynamically favorable as compared to chain propagation. Moreover, PPO-based block copolyethers were easily obtained in one-pot using epoxide mixtures. This research demonstrated that the delicately designed intramolecular synergistic Lewis pair offered a powerful and controllable method to prepare various heterofunctionalized PPO samples with high values.

Mechanistic Insight into Anion‐Binding Catalytic Living Cationic Polymerization

AbstractExploiting non‐covalent interactions to catalyze challenging ionic polymerizations is an ambitious goal but is in its infancy. We recently demonstrated non‐covalent anion‐binding catalysis as an effective methodology to enable living cationic polymerization (LCP) of vinyl ethers in an environmentally benign manner. Here, we further elucidate the structure‐reactivity relationships of the elaborately designed seleno‐cyclodiphosph(V)azanes catalysts and the roles of anion‐binding interactions by a combined theoretical DFT study and experimental study. The investigation suggests that the distinct cis‐cyclodiphosph(V)azane framework combined with “selenium effect” and electron‐withdrawing 3,5‐(CF3)2‐Phenyl substitution pattern in catalyst enables a critical contribution to accessing excellent stability, anion affinity and solubility under polymerization conditions. Thus, the catalyst could leverage anion‐binding interactions to precisely control reversible and transient dormant‐active species equilibrium, allowing it to dynamically bind, recognize and pre‐organize propagating ionic species and monomer, thereby facilitating efficient chain propagation and minimizing irreversible chain transfer events under mild conditions. The more in‐depth understanding of the mechanism for anion‐binding catalytic LCP reported herein should help to guide future catalyst design and to extend this concept to broader polymerization systems where ionic species serve as crucial intermediates.

Mechanistic Insight into Anion-Binding Catalytic Living Cationic Polymerization.

Exploiting non-covalent interactions to catalyze challenging ionic polymerizations is an ambitious goal but is in its infancy. We recently demonstrated non-covalent anion-binding catalysis as an effective methodology to enable living cationic polymerization (LCP) of vinyl ethers in an environmentally benign manner. Here, we further elucidate the structure-reactivity relationships of the elaborately designed seleno-cyclodiphosph(V)azanes catalysts and the roles of anion-binding interactions by a combined theoretical DFT study and experimental study. The investigation suggests that the distinct cis-cyclodiphosph(V)azane framework combined with "selenium effect" and electron-withdrawing 3,5-(CF3 )2 -Phenyl substitution pattern in catalyst enables a critical contribution to accessing excellent stability, anion affinity and solubility under polymerization conditions. Thus, the catalyst could leverage anion-binding interactions to precisely control reversible and transient dormant-active species equilibrium, allowing it to dynamically bind, recognize and pre-organize propagating ionic species and monomer, thereby facilitating efficient chain propagation and minimizing irreversible chain transfer events under mild conditions. The more in-depth understanding of the mechanism for anion-binding catalytic LCP reported herein should help to guide future catalyst design and to extend this concept to broader polymerization systems where ionic species serve as crucial intermediates.

New Insights on the Kinetics of Persulfate‐Initiated Itaconic Acid Free‐Radical Polymerization

AbstractA mathematical model is proposed that couples the decomposition kinetics of persulfate (S2O82−) and the free radical polymerization kinetics of itaconic acid (IA); the results are compared with experimental data reported in the literature. It is found that the former is highly affected by the acidification of the aqueous medium which is caused by the equilibrium dissociation of IA but mainly by HSO4− produced by side reactions of the S2O82− decomposition. This qualitatively explains the dependence of d[S2O82−]/dt with [IA] and the initial concentration of persulfate ([S2O82−]0), reported in the literature. According to the model results, temperature overshoots are very likely to occur in the experiments so there is doubt whether the reaction order >1 with respect to [IA] that is sometimes reported in the literature for the rate of polymerization (Rp) is an artifact related to an imprecise temperature (T) control or is due to a more complex mechanism. Due to the higher activation energy of the persulfate decomposition compared to the propagation reaction, small variations of T can lead to significant variations of d[S2O82−]/dt but to an almost imperceptible effect on Rp. Recommendations for future experimental work and refinement of the kinetic model are provided.

Studies on polyoxymethylene dimethyl ethers production from dimethoxymethane and 1,3,5-trioxane over [formula omitted

Polyoxymethylene dimethyl ethers (OMEs) with physical properties similar to those of diesel has received significant attention as green additives for soot emission suppression. Herein, series of SO42-/ZrO2–TiO2 catalysts were developed for OMEs production from dimethoxymethane (DMM) and 1,3,5-trioxane through sequential formaldehyde monomer insertion into CO bond of DMM. Not Lewis but Brønsted acid sites were identified to be active for the decomposition of 1,3,5-trioxane into formaldehyde unit, however, both of them are effective for the chain propagation of DMM via formaldehyde unit insertion into CO bond. Kinetic studies indicated each chain growth step exhibited the same parameters and activation barrier on corresponding Brønsted and Lewis acid sites due to the same reaction mechanism and very similar chemical structure of OMEs. Also, the catalytic stability investigation suggested the deactivation behavior was derived from the carbon deposition, and the decay factor could be exponentially correlated with the amount of coke accumulation.

Express-diagnostics of the properties of ЫРЫ materials using chrono-topographic analysis of thermal vision data

Subject of research: the article is devoted to the development of a methodology for express diagnostics of material properties based on the measurement of macrokinetic parameters of the SHS process.
 Purpose of research: plotting the dependence of the microhardness of SHS products on the propagation velocity of the SHS wave and its temperature.
 Methods and objects of research: the research objects were the SHS process in the Ni-Al system and the reaction products; To measure the propagation velocity of a high-temperature synthesis wave, an original method of chrono-topographic analysis of thermal imaging data was used; temperature control was carried out by an original method of spectral-brightness pyrometry. The study of the microhardness of experimental samples was carried out using an FM-800 microhardness tester.
 Main results of research: in the course of experimental studies, it was shown that the error in determining the propagation velocity of the SHS wave by the method of chrono-topographic analysis of thermal imaging data is 0.1 %, and the error in temperature measurement by the method of spectral-brightness pyrometry is estimated at 0.5 %. It is concluded that the main factor influencing the total error in the SHS wave propagation velocity in the experiment is the inaccuracy of setting the charge parameters for a set of samples. The absolute value of the total error was 3.2 %. A diagnostic trajectory has been constructed that makes it possible, based on the SHS propagation rate and reaction temperature, to evaluate the microhardness of the product and draw a conclusion about the quality of charge preparation for the production of a material with desired properties.

Estimation of the chain propagation rate constants of propylene polymerization and ethylene‐1‐hexene copolymerization catalyzed with MgCl2‐supported Ziegler–Natta catalysts

AbstractIn olefin polymerization with MgCl2‐supported Ziegler–Natta (Z–N) catalysts, the apparent propagation rate constant (kp)a calculated by Rp = (kp)a [C*] CMe (CMe is equilibrium monomer concentration in the reaction system) declines with reaction time for gradually developed monomer diffusion limitation in the polymer/catalyst particles. In this work, a simplified multi‐grain particle model was proposed to build correlation between (kp)a and other kinetic parameters that can be determined experimentally. Rate profiles of propylene polymerization and ethylene‐1‐hexene copolymerization by three MgCl2‐supported Z–N catalysts were determined, and the (kp)a data was calculated using [C*] determined by quench‐labelling the propagation chains with acyl chloride. Decline of (kp)a in each polymerization process was precisely fitted by the linear correlation between lg(kp)a and [(ρcatmp)/(ρpmcat) + 1]1/3 developed on the particle model. Real propagation rate constant (kp) was estimated by extrapolating the fitting line to the starting point of polymerization, where no concentration gradient exists. According to the particle model, the slope of the lg(kp)a versus [(ρcatmp)/(ρpmcat) + 1]1/3 line (lgd) represents the degree of monomer diffusion limitation. Variations of parameter d found in the studied reaction systems can be reasonably explained based on the knowledge of olefin diffusion in the polymer phase.

Direct synthesis of extra-heavy olefins from carbon monoxide and water

Extra-heavy olefins (C12+=), feedstocks to synthesize a wide range of value-added products, are conventionally generated from fossil resources via energy-intensive wax cracking or multi-step processes. Fischer-Tropsch synthesis with sustainably obtained syngas as feed-in provides a potential way to produce C12+=, though there is a trade-off between enhancing C-C coupling and suppressing further hydrogenation of olefins. Herein, we achieve selective production of C12+=via the overall conversion of CO and water, denoted as Kölbel-Engelhardt synthesis (KES), in polyethylene glycol (PEG) over a mixture of Pt/Mo2N and Ru particles. KES provides a continuously high CO/H2 ratio, thermodynamically favoring chain propagation and olefin formation. PEG serves as a selective extraction agent to hinder hydrogenation of olefins. Under an optimal condition, the yield ratio of CO2 to hydrocarbons reaches the theoretical minimum, and the C12+= yield reaches its maximum of 1.79 mmol with a selectivity (among hydrocarbons) of as high as 40.4%.

Impact of Labile Ligands on Catalyst Initiation and Chain Propagation in Ni-Catalyzed Ethylene/Acrylate Copolymerization

Polar polyolefin synthesis by coordination polymerization is of high interest, but the catalysts’ low activity limits industrial implementation. Herein, we demonstrate how the nature of the labile ligand, L, impacts the performance of neutral nickel catalysts supported by bidentate phosphine-phenoxide and phosphine-enolate ligands in ethylene/acrylate copolymerization. By tuning L, the copolymerization activity reaches ∼24000 kg/(mol h). In situ studies indicate that a weaker L leads to faster chain propagation and more efficient catalyst initiation. Overall, this work highlights the potential of a strategy to improve catalyst activity in polar polyolefin synthesis complementary to design optimization for the bidentate ligand.

Selectively Regulating Asymmetric Photopolymerization Via Competition Between Circularly Polarized UV and Visible Light

AbstractCircularly polarized light (CPL) has attracted considerable interest since it can impart chiral bias into photochemical reactions and open up a novel opportunity for synthesizing chiral polymer materials. Despite numerous reports describing the chiral induction effect with single CPL, the synergistic or competitive effect between two types of CPL—i.e., circularly polarized ultraviolet light (CPUV) for triggering asymmetric polymerization while circularly polarized visible light (CPVL) only for accelerating helical chain propagation—is rarely reported. Here, this work demonstrates that the selective regulation on the asymmetric photopolymerization can be realized by the arbitrarily coupled irradiation with CPUV and CPVL, either constructively or destructively. In the former case, further chirality amplification can be achieved. Remarkably, for the latter case, the opposite handed CPVL can bias the polymer helicity during the chain propagation process and thereby overrule the helical preference inducted by CPUV. This work highlights the importance of chiral induction effect in helical chain propagation process and is highly valuable for deeper understanding of helical preference in CPL‐triggered asymmetric photopolymerization.

Study on mechanical properties and damage mechanism of recycled concrete containing silica fume in freeze–thaw environment

In order to study the uniaxial compressive mechanical properties and damage evolution of recycled aggregate concrete (RAC) containing silica fume (SF) under freeze–thaw cycles, the RAC with SF replaced partial cement was prepared. The replacement rates were 0% and 9%. The RAC were subjected to 0, 50, 75, 100, 125 freeze–thaw cycles and uniaxial compression tests. The microstructure, micro-crack propagation process and reaction products were observed by acoustic emission (AE) and scanning electron microscope (SEM). The statistical damage theory was used to explore the mesoscopic damage evolution mechanism of RAC. The results showed that the peak stress and modulus of elasticity of the specimen tended to decrease, the peak strain and mass loss rate gradually increased with the increase of the number of freeze–thaw cycles(N). The compressive strength of RAC with S = 0% decreases from −41.52MPa to −11.23MPa when N increases from 0 to 125. The addition of SF produced additional volcanic ash reactions, resulting in an increase in ettringite (AFt), which reduces the porosity of RAC and is able to increase the compressive strength at different N significantly. Compressive strength increases by 21.84% and 12.06% at N = 0 and 125, respectively. Considering the existence of two mesoscopic damage modes of fracture and yield, the deformation failure mechanism of RAC was analyzed from the perspective of effective stress. The all five characteristic parameters characterizing the mesoscopic damage show significant regular change with increase of the number of cycles. The relationship between the macroscopic mechanical properties of RAC and the mesoscopic damage mechanism was established by analyzing the evolution law for the characteristic parameters.