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Four poly(benzoxazine-co-siloxane) oligomers (PBcSs) were successfully synthesized by improving the synthesis step and controlling the ratio of phenol, bisphenol A, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, m-aminophenyl acetylene, and formaldehyde; the resulting compounds all exhibited good processing properties. Siloxane addition can significantly improve the toughness of the polybenzoxazines. Additionally, compared with the PBcSs containing only phenol structure, the introduction of bisphenol A has a decelerating effect on the polymerization process of the benzoxazine oligomer, which leads to an increase in the exothermic peak temperature. Simultaneously, the PBcS containing bisphenol A also exhibits a higher glass transition temperature and increased thermal stability, but reduced flexural strength. Conversely, compared to the benzoxazine oligomers that do not contain alkynyl groups, the introduction of the terminal alkynyl group can accelerate the polymerization process, decrease the exothermic peak temperature, significantly increase the glass transition temperature, and greatly improve the heat resistance; the 5% thermal decomposition temperature of cured product is increased by up to 101[degrees]C. Furthermore, under conditions that ensure high flexural strength, appropriate alkynyl content can also significantly increase the material's flexural modulus. KEYWORDS heat resistance, oligomers, polybenzoxazine, siloxane, terminal alkynyl groups, 1 | INTRODUCTION Polybenzoxazines have attracted considerable attention as important thermosetting resins owing to their outstanding properties, including flexible molecular design, good dielectric properties, a long shelf life, and no [...]

A novel approach was proposed to enhance the microviscosity sensitivity of molecular rotor probes by integrating flexible rotators and expanded molecular frameworks, addressing the crucial challenge of weakening microviscosity sensitivity in dilute solutions of macromolecules. [ABSTRACT FROM AUTHOR]

Allyl ether naphthol resin (ANPF) was synthesized by introducing 1,5‐dihydroxynaphthalene and 2,7‐dihydroxynaphthalene into phenolic resin and was copolymerized with 4,4′‐bismaleimidodiphenylmethane resin (BDM) to obtain allyl ether naphthol‐modified bismaleimide resins (15‐ANPF‐BDM and 27‐ANPF‐BDM). The resulting thermal stability and glass transition temperature (Tg) were explored by thermogravimetric and dynamic mechanical analyses. The char yield of 15‐ANPF‐BDM at a temperature of 800°C was 46.0%. Additionally, the Tg of 15‐ANPF‐BDM was measured as 311°C, which is an increase of 44°C compared to that of c. The mechanical properties of the ANPF‐BDM/quartz fiber (Qf) composites were also investigated. The results reveal that ANPF‐BDM/Qf composites exhibit similar mechanical strength to APF‐BDM/Qf composites at room temperature. In addition, the mechanical properties of the ANPF‐BDM/ Qf composites demonstrated significant improvement in mechanical properties retained significantly improved at 200°C, with a 68% flexural strength retention and a 96% interlaminar shear retention of 15‐ANPF‐BDM/Qf composites. Thus, ANPF‐BDM/Qf composites exhibit outstanding mechanical properties at 200°C. [ABSTRACT FROM AUTHOR]

In the global ecosystem, the slow decomposition of coniferous forest litter has caused a number of ecological problems, among which is the decay of China's Pinus massoniana litter. It has been pointed out that converting pure P. massoniana plantations into mixed forests with broadleaf species can improve ecosystem services. Therefore, the selection of mixed species is key for the success or failure of the conversion of near-natural forests. In this study, from the perspective of apoplastic decomposition, the leaf litter of P. massoniana was mixed with three common native broadleaf species, namely Choerospondias axillaries, Cinnamomum camphora, and Cyclobalanopsis glauca, using an indoor incubation method to systematically analyse the differences in the decomposition rates of apoplastic material in each mixture, and to provide a theoretical basis for the selection and mixing of tree species for the management of near-natural forests in P. massoniana forests. After 175 days of indoor incubation of the foliar litter under dark conditions at 25 °C, the residual dry matter of the mixed apoplastic litter of P. massoniana and the three broadleaf trees was lower than that of P. massoniana. It indicated that the incorporation of broadleaf apoplastic foliage promoted litter decomposition, with the most pronounced effect in the case of admixture with C. Camphora. Compared with the group of pure P. massoniana alone, the remaining mass and residual rate decreased by 0.56 g and 9.45%, respectively. The regression equation of Olson's negative exponential decay model showed that the P. massoniana + C. Camphora mixture had the fastest decomposition rate (k) of 1.305, an increase of 0.237, a decrease in half-life of 0.11 years, and a decrease in turnover period of 0.49 year, compared to the P. massoniana alone group. Most of the measured values throughout the incubation period were significantly lower than the predicted values, suggesting that there was a non-additive and synergistic effect of litter mixing. [ABSTRACT FROM AUTHOR]

Silicon‐containing arylacetylene resin (PSA)‐matrix composites hold great potential for aerospace applications due to their excellent heat resistance. In recent years, many PSAs with specific functions have been designed via materials genome approach (MGA), and appropriate resin transfer molding (RTM) curing processes need to be screened to strike a balance between low cost and high quality. In this study, a novel tool based on finite element curing simulation and multiobjective genetic algorithm was developed to optimize the RTM curing process for novel PSA‐matrix composites. The silicon‐containing fluorenylacetylene resin (PSA‐VBF) was selected as the object to systematically characterize its apparent curing kinetics. To address the problem of explosive polymerization of the resin at the injection port during the RTM process, a multiobjective optimization of the curing process using a genetic algorithm was performed to obtain the Pareto front with the maximum temperature gradient at the injection port of the resin, the maximum degree of cure gradient of the composites, and the process time as the objectives. A global sensitivity analysis was also conducted to identify the key parameters. The results demonstrate that the optimized curing process can significantly reduce the temperature gradient and the curing degree gradient with improved curing efficiency. [ABSTRACT FROM AUTHOR]

The pouring of sand casting is accompanied by severe heat conduction, and there is an urgent need to investigate the pyrolysis properties of foundry sand. The main purpose of this study was to investigate the pyrolysis behaviors of resin sand, including precoated sand (PCS), hot box sand (HBS), and warm box sand (WBS), at heating rates of 20 °C/min, 30 °C/min, and 40 °C/min in nitrogen and air atmospheres. The mass loss of the resin sand was monitored continuously with a simultaneous thermal analyzer, and the kinetic parameters of the resin sand were calculated based on the Coats–Redfern method and thermal data. The average mass loss of the resin sand during pyrolysis was 3.03%, which was much smaller than that of the other sands. The volatile release characteristic index of resin sand could not be calculated based on this concept. To solve this issue, the term Tstv/mloss was established, and its value was determined. With increasing heating rates from 20 °C/min to 30 °C/min and from 30 °C/min to 40 °C/min, the mass losses of the resin sand increased by 0.79% and 0.64%, respectively, and the volatile release characteristic indices of the resin sand increased by 3.8 × 10−10 and 1.06 × 10−9, respectively. In addition, the mass losses and volatile release characteristic indices of resin sand in an air atmosphere were greater than those in a nitrogen atmosphere. With increasing heating rate, the activation energy of the resin sand decreased in a nitrogen atmosphere. The findings concerning the thermal decomposition behaviors of resin sand provided a theoretical basis for the pouring step of the sand casting process. [ABSTRACT FROM AUTHOR]

Although various aerogels with electromagnetic wave (EMW) absorbing properties have been extensively explored, the development of aerogels with excellent wave absorption performance, low density, and great heat resistance has still met profound challenges. Herein, polysilazane hybrid phenolic resin aerogels (PRVS aerogels) were prepared using the vinyl addition reaction of polysilazane and cross‐linking reaction between polysilazane and phenolic resin. A SiOCN ceramic aerogel with multistage pore structure was prepared via a simple and quick freeze‐drying method and polymer‐derived ceramic (PDC) methods. The SiOCN ceramic aerogels exhibited low density (0.15–0.27 g/cm3), good heat‐shielding (thermal conductivity in the range of 0.03–0.04 W/(m·K)), and excellent wave absorption performance (i.e., RL was about –31.6 dB@16.48 GHz and EAB was 3.85 GHz when the thickness of the ceramic aerogel was 1.2 mm). Hence, the ceramic aerogel absorbing materials could meet the requirements of "wide absorption bandwidth, strong reflection loss, lightweight and thi thickness". Moreover, the mechanism of low weight, heat insulation, and wave absorption properties of the aerogels were also investigated. We believe this work is of great significance in ceramic aerogels prepared by traditional polymers, which may provide new opportunities for new ceramic aerogels with applications ranging from EMW absorption to aerospace and information technology. [ABSTRACT FROM AUTHOR]

In this study, 1,5‐dihydroxynaphthalene moiety was introduced into a novolac resin structure, and propargyl ether naphthalene phenolic resin (PNPF) was synthesized by the Williamson etherification reaction, which improved the heat resistance of the resin and its processability. The structure of the PNPF resin was characterized using 1H NMR and FTIR analysis, and its processability, heat resistance, thermal expansion, and dielectric properties were evaluated. The results revealed that the addition of 1,5‐dihydroxylhine, increased the reaction activity of the PNPF resin, and decreased its initial curing temperature, with the resin exhibiting excellent processability. The cured resin also showed excellent heat resistance and thermomechanical properties. The 5% weight loss temperature (Td5) and glass transition temperature (Tg) of the resin increased to 437.61 and 362.04°C, respectively, while the coefficient of thermal expansion decreased from 60.17 to 44.52 ppm, with a reduction of 26.01%. Moreover, the dielectric constant and dielectric loss of the cured resin were 3.02 and 0.00239, respectively. [ABSTRACT FROM AUTHOR]

We consider a one-dimensional superprocess with a supercritical local branching mechanism $\psi$ , where particles move as a Brownian motion with drift $-\rho$ and are killed when they reach the origin. It is known that the process survives with positive probability if and only if $\rho , where $\alpha=-\psi'(0)$. When $\rho , Kyprianou et al. [18] proved that $\lim_{t\to \infty}R_t/t =\sqrt{2\alpha}-\rho$ almost surely on the survival set, where $R_t$ is the rightmost position of the support at time t. Motivated by this work, we investigate its large deviation, in other words, the convergence rate of $\mathbb{P}_{\delta_x} (R_t >\gamma t+\theta)$ as $t \to \infty$ , where $\gamma >\sqrt{2 \alpha} -\rho$ , $\theta \ge 0$. As a by-product, a related Yaglom-type conditional limit theorem is obtained. Analogous results for branching Brownian motion can be found in Harris et al. [13]. [ABSTRACT FROM AUTHOR]

Herein, the catalytic effects of aromatic amines with different structures on the room temperature curing of bisphenol E cyanate (BECy) have been studied using differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. Our results revealed that the mixed amine comprised of aniline and N,N-dimethyl-p-phenylenediamine (AN/NNDPA) bearing primary amino groups in its structure was a highly effective catalyst for the room temperature curing of cyanate esters. When the cyanate ester and mixed amine were combined at a molar ratio of 100:5 and cured at room temperature for 5 days, the curing degree of BECy resin reached 79.7%. The room temperature curing mechanism of the BECy-AN/NNDPA system was investigated using pyrolysis gas chromatography-mass spectrometry (PY GC-MS). Our results showed that the formation reactions of the intermediate structure and cyclotrimerization reactions occurred during the room-temperature curing process. The activation energies of BECy and different aromatic amine systems at different heating rates were determined using non-isothermal DSC. The results further demonstrated the catalytic effect of AN/NNDPA on the cyanate ester curing reaction. BECy-AN/NNDPA cured at room temperature has suitable heat resistance and a 5% weight loss temperature (Td5) of 361°C. [ABSTRACT FROM AUTHOR]

Developing skin-like biomimetic materials with electromechanical and sensing sensitive properties, so-called E-skin, demonstrate the potential to serve as novel sensors for surface strain measurement. Thus, a versatile bionic E-skin that can perceive strain signals was fabricated based on an electronic/ionic-conductive polymer, named as the CNC@PPy/CS-Cit3−/PVA gel. Notably, the citrate ion (Cit3−) formed tridentate coordination with N-glucosamine units of chitosan (CS) to form an interpenetrating CS-Cit3− polymer network. More importantly, the coordinated Cit3− could enhance the mechanical properties of the gels and serve as movable "bridges" among the cellulose nanocrystals@polypyrrole (CNC@PPy) nanoparticles. The as-developed conductive gels exhibited consecutive conductive networks with high conductivity (up to 0.97 ± 0.05 S m−1). The sensitivity of this electronic/ionic-conductive skin could be divided into two separate regions at different strain ranges (the GF was 5.27 for strain under 0–2.8% and the GF was 1.24 for strain under 2.8–650%). Owing to the rapid response time (∼160 ms) and recovery time (∼100 ms), remarkable fatigue resistance, and biocompatibility, the E-skin-based sensor can precisely distinguish physiological signals and joint motions of the body. It was envisioned that the bionic E-skin would achieve broad applications as sensors in medical monitoring and implantable bioelectronics. [ABSTRACT FROM AUTHOR]

A deep understanding of the relationship between the knowledge acquired and the graduation requirements is essential for students to precisely meet the graduation requirements and to become human resources with specific knowledge, skills and professionalism. In this paper, we define the ontology layer of the knowledge graph by deeply analyzing the relationship between graduation requirement, course and knowledge. Based on the implementation of the concept of Outcome Based Education, we use Knowledge extraction, fusion, reasoning techniques to construct a hierarchical knowledge graph with the main line of "knowledge-course-graduation requirements. In the process of knowledge extraction, in order to alleviate the huge labor overhead brought by traditional extraction methods, this paper adopts a transfer learning method to extract triadic knowledge using the multi-task framework EERJE, Finally, knowledge reasoning was also performed with the help of LLM to further expand the knowledge scope. The comprehensiveness, correctness and relatedness of the data were evaluated through the experiment, and the F1 value of the ternary group extraction was 87.76%, the accuracy rate of entity classification was 85.42%, the data coverage was more comprehensive, and the results showed that the data quality was better, and the knowledge graph constructed in this way can fully optimize the organization and management of teaching resources, help students intuitively and comprehensively grasp the correlation and difference between graduation requirements and various knowledge points, and let the Students can carry out personalized independent learning through the navigation mode of knowledge graph, strengthen their weak links, and complete the relevant graduation requirements, which effectively improves the degree of students' graduation requirements achievement. This new paradigm of knowledge graph enabled teaching is of reference significance for engineering education majors to improve the degree of graduation requirements achievement. [ABSTRACT FROM AUTHOR]