Improved numerical inversion methods for the recovery of bivariate distributions of polymer properties from 2D probability generating function domains

The 2D probability-generating function technique is a powerful method for modeling bivariate distributions of polymer properties. It is based on the transformation of bivariate population balance equations using 2D probability generating functions (pgf) followed by a recovery of the distributions from the transform domain by numerical inversion. A key step of this method is the inversion of the pgf transforms. Available numerical inversion methods yield excellent results for pgf transforms of distributions with independent dimensions with similar orders of magnitude, for example bivariate molecular weight distributions in copolymerization systems. However, numerical problems are found for 2D distributions in which the independent dimensions have very different ranges of values, such as the molecular weight distribution-branching distribution in branched polymers. In this work, two new 2D pgf inversion methods are developed, which regard the pgf as a complex variable. The superior accuracy of these innovative methods makes them suitable for recovering any type of bivariate distribution. This enhances the capabilities of the 2D pgf modeling technique for simulation and optimization of polymer processes. An application example of the technique in a polymeric system of industrial interest is presented.     

Preparation and characterization of poly(3-octylthiophene)/carbon fiber thermoelectric composite materials

Poly(3-alkylthiophene) (P3AT) with a high Seebeck coefficient has recently been reported. However, P3AT/inorganic conductive composites exhibit relatively poor thermoelectric performance because of their low electrical conductivity. In this work, carbon fiber sheets with a high electrical conductivity were chosen as the inorganic phase, and poly(3-octylthiophene)(P3OT)/carbon fiber composites were prepared by casting P3OT solution onto the carbon fiber sheets. The carbon fiber sheets incorporated into the composites can provide good electrical conductivity, and P3OT can provide a high Seebeck coefficient. The highest power factor of 7.05 μW m⁻¹ K⁻² was obtained for the composite with 50 wt% P3OT. This work suggests a promising method for preparing large-scale thermoelectric composites with excellent properties.     

三维锡膏测厚误差补偿系统的研究

针对三维锡膏测厚系统误差大,易受环境、操作员及操作方法等因素的影响的问题,提出了一种自适应误差补偿方法.使用图像分析法对图像质量进行评价,将评价结果反馈给控制系统,并使用黄金分割法作为搜索策略,实现了系统的自动对焦.提取非焊盘区域的点坐标拟合平面,建立了动态视场(FOV)基准面.实验结果表明,使用文中提出的方法,三维锡...     

开放型周期轨道与超晶格的位错运动行为

在经典力学框架内和Seeger方程基础上,引入正弦平方势,把位错运动方程化为具有外力矩的摆方程。导出了弯结的形成能、弯结宽度、密度以及系统的激活能和弯结对的临界距离等物理量。指出位错在滑移面内的运动可视为弯结沿位错线的迁移与垂直方向的势垒翻越组成。     

Numerical analysis on the thermal performance of a roof-integrated flat-plate solar collector assembly

A numerical experiment has been carried out to study the thermal performance of a large solar collector assembly, which could be integrated as part of the roof structure without undue difficulties. The collector assembly consists of a network of riser tubes and headers as if rows of flat-plate collectors are connected in series to form a large flat-plate collector. Results show that the thermal efficiency of the collector assembly is mainly influenced by the number of riser tubes, collector aspect ratio (H/W), mass flow rate, thermal conductivity and thickness of absorber plate. Differences in the range of 2.5%–8% were detected depending on the specific parameter tested.     

层叠式旋转视频艺术柱的机电系统设计

提出一种立体的、动态的、图像可灵活拼接的层叠式旋转视频艺术柱的机电系统设计方案。内容包括:视频艺术柱的功能和应用;层叠式旋转结构设计;视频板支撑结构设计;视频艺术柱控制系统设计。     

Microstructural evolution and microwave transmission/absorption transition in polymer-derived SiOC ceramics

Herein, we present the structural evolution of polymer-derived SiOC ceramics with the pyrolysis temperature and the corresponding change in their microwave dielectric properties. The structure of the SiOC ceramics pyrolyzed at a temperature lower than 1200 °C is amorphous, and the corresponding microwave complex permittivity is pretty low; thus, the ceramics exhibit wave transmission properties. The Structural arrangement of free carbon in the SiOC ceramics mainly happens in the temperature range of 1200 °C-1300 °C due to the separation from the Si–O–C network and graphitization, while the structural arrangement of the Si-based matrix mainly occurs in the range of 1300 °C-1400 °C owing to the separation of SiC₄ from the Si–O–C network to form nanocrystalline SiC. In pyrolysis temperature range of 1200 °C-1400 °C, the microwave permittivity of SiOC shows negligible change. At a pyrolysis temperature exceeding 1400 °C, the carbothermal reaction of free carbon and the Si–O backbone becomes significant, leading to the formation of crystalline SiC. The as-formed SiC and residual defective carbon improve the polarization loss of SiOC ceramics. In this case, the SiOC ceramics show significantly increased complex permittivity, exhibiting electromagnetic absorption characteristics. These characteristics promote the application of polymer-derived SiOC ceramics to high-temperature electromagnetic absorption materials.     

Study on electrochemical performance of porous integrated PANI-Fe in supercapacitors

The iron-coordinated polyaniline (PANI-Fe) integrated nanomaterials was prepared by chemical oxidative and in-situ electrochemical polymerization, which was applied to supercapacitor electrodes. The N–Fe coordination bond is formed between FeCl₃ and the N of quinone diimine to enhance the interaction of the polyaniline molecular chain. The PANI-Fe electrode material forms a crosslinked porous fiber framework through two-step oxidation, which greatly improves the energy storage capacity of PANI-Fe. PANI-Fe achieves higher capacitance of 642 F g⁻¹ at 1 A g⁻¹ than PANI of 310 F g⁻¹, and maintains high capacitance retention of 82.4 % when the current density increases from 1 to 10 A g⁻¹. According to first-principles calculations, the Fermi energy (N(E)) of PANI-Fe drop down to 0.265 eV from 0.901 eV of PANI, which proves that its conductivity is improved. The change of the electrostatic potential of PANI-Fe indicates that the formation of the N–Fe coordination bond can improve the carrier transport behavior. PANI-Fe has a smaller HOMO-LUMO energy gap than PANI, indicating that the formation of N–Fe coordination bonds can increase the electrical activity of PANI.     

Advances in micro-mechanical modeling using a bonded-particle model and periodic homogenization within discrete element framework applied to heterogeneous ceramics

The Discrete Element Method (DEM) can account for microcracks initiations and propagations within the microstructure and their impact on the macroscopic properties of ceramics. Combing the DEM with the Periodic Homogenization (PH) allows working with a limited number of elements, thus facilitating the multiscale transition of the elastic properties of ceramics: from the microscale (inclusion/pores scale) to the macroscopic elastic behavior of such continuum media. However, the PH approach for a continuum media is currently less developed in DEM than the FEM. Hence, this study aims to consolidate a DEM framework, using a bonded-particle model and PH to improve the prediction of the elastic properties (Cij tensor) of ceramics. Here, a face-centered cubic unit cell is combining? with periodic boundary conditions to build a 3D representative volume element in DEM to model the macroscopic elastic properties of model materials and is validated by experimental data, analytical and FEM approaches.     

The CMAS corrosion behavior of high-entropy (Y0.2Dy0.2Er0.2Tm0.2Yb0.2)4Hf3O12 hafnate material prepared by ultrafast high-temperature sintering (UHS)

High-temperature molten calcium-magnesium-alumina-silicate (CMAS) corrosion has become a fatal factor for the failure of aero-engine thermal barrier coatings. In this study, a promising entropy-stabilized (Y_0.2Dy_0.2Er_0.2Tm_0.2Yb_0.2)₄Hf₃O₁₂ (5YH) hafnate was prepared by the emerging ultrafast high-temperature sintering (UHS), and its corrosion and wetting behavior of molten CMAS were investigated. For the corrosion mechanism, the precipitation of the high-entropy apatite phase promotes the formation of the HfO₂ phase, and it can improve the density and stability of the slow-growing reaction layer, hindering the further penetration of molten CMAS. At 1300 ℃, a reaction layer with a three-layered morphology is generated, resulting from the decreased viscosity of the molten CMAS. Moreover, computational analysis shows that molten CMAS on the 5YH surface has a larger contact angle (17°) than traditional YSZ (13°), and the spreading area is about 90 % of traditional YSZ, which benefits for its good CMAS corrosion resistance.