Controllable preparation of porous ZrB2–SiC ceramics via using KCl space holders

In this work, a novel and facile technique based on using KCl as space holders, along with partial sintering (at 1900 °C for 30 min), was explored to prepare porous ZrB₂–SiC ceramics with controllable pore structure, tunable compressive strength and thermal conductivity. The as-prepared porous ZrB₂–SiC samples possess high porosity of 45–67%, low average pore size of 3–7 μm, high compressive strength of 32–106 MPa, and low room temperature thermal conductivity of 13–34 W m⁻¹ K⁻¹. The porosity, pore structure, compressive strength and thermal conductivity of porous ZrB₂–SiC ceramics can be tuned simply by changing KCl content and its particle size. The effect of porosity and pore structure on the thermal conductivity of as-prepared porous ZrB₂–SiC ceramics was examined and found to be consistent with the classical model for porous materials. The poring mechanism of porous ZrB₂–SiC samples via adding pore-forming agent combined with partial sintering was also preliminary illustrated.     

A novel fabrication procedure for producing high strength hydroxyapatite ceramic scaffolds with high porosity

Hydroxyapatite (HA) scaffolds were fabricated using the space holder method with a pressureless sintering process in a systematically developed manner at different fabrication stages to increase the strength of the scaffold at high porosity. Polyvinyl alcohol (PVA) and Polymethyl methacrylate (PMMA) were used as binders and space holder agents, respectively. The physical properties of the HA scaffolds were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), linear shrinkage test, and porosity measurements. The mechanical properties of the HA scaffolds were analyzed using compressive strength measurements. The results revealed that the HA scaffold met the expected quality requirements with a compressive strength of 2.2 MPa at a porosity of 65.6% with pore sizes distributed in the range of 126–385 μm. The shrinkage of the scaffold diameter occurred by 20.27%, this diameter shrinkage predominantly to the shrinkage of the HA scaffold caused by sintering. Besides, suspect that a higher PMMA concentration causes pore size shrinkage upon sintering. The formation of pore interconnections was evidenced by SEM observations and the ‘translucent light method’ developed in this study. The results of the scaffold phase test using XRD showed that the final scaffold consisted only of the HA phase, as the PVA and PMMA phases burned out during the sintering process.     

User activities and the heterogeneity of urban space:The case of Dahiyat Al Hussein park

Urban researchers have maintained a constant interest in the complexity and continuity of urban space usage. Some have applied actor–network theory (ANT) to investigate the heterogeneity of spaces and present them through the networks of their users’ activities. However, these accounts are predominantly limited in examining the extent to which these spaces may be heterogeneous when exploring such networks. This paper draws on recent ANT scholarship, which employs an ethnographic research conducted in a main park in a housing project at Dahiyat Al Hussein in Amman, Jordan. The findings describe the complex and unpredictable negotiations that occur within spaces by documenting the varieties and interrelations among user activity networks within this common and shared urban space. This research reveals the extent to which spaces, parks in this case, may be heterogeneous by unpacking their usage. The conclusions and insights assert the necessity of paying attention to design detail and creating designs that are responsive to evolving user activities.     

Space charge region effects in bidirectional illuminated P3HT:PCBM bulk heterojunction photodetectors

Organic semiconductors are widely investigated for their application in photovoltaics and photodetectors. We show that the efficiency of these devices is strongly influenced by the position of the space charge region, due to unintentional doping, and wavelength-dependent absorption properties in bulk heterojunctions. Spray-coated P3HT:PCBM bulk heterojunction photodiodes with thicknesses up to 4.2 μm and semitransparent top contact enable the characterization of exciton generation and separation in both irradiation directions. A large difference in external quantum efficiency (EQE) is observed for top and bottom illuminated configurations and is explained by a bias dependent arrangement of the space charge region at the two contact electrodes. Numerical drift–diffusion simulations allow to get insight into first order mechanisms behind the spectral features of EQE data in highly-doped organic photodiodes.     

环境设计专业学习空间设计探析--以教室改造的参与式设计为例

学习空间的设计必须基于教育理念、学习模式、技术设施与精神氛围等因素展开,以更开放、灵活及多样化的有趣形态来吸引使用者。对于已掌握基本设计方法并具有一定设计思维的环境设计专业学生而言,设计与自身学习行为关联的学习空间,能体现"参与式设计"的特殊意义:即一方面以有着直观体验感受的熟悉空间作为训练案例来有效地整合设计能力;另一方面则通过用户与设计者身份的叠加,从使用者体验一维到对空间发展的专业预设考虑一维共同实现学习空间设计理念的更新。     

融入局部几何特征的流形谱聚类图像分割

为了改善谱聚类图像分割的精准性和时效性,文中提出融入局部几何特征的流形谱聚类图像分割算法.首先,考虑图像数据的流形结构,在数据点的K近邻域内执行局部PCA,得到数据间本征维数的关系.然后,引入流形学习中的局部线性重构技术,通过混合线性分析器得到数据间局部切空间的相似性,结合二者构造含有局部几何特征的相似性矩阵.再利用Nystr m技术逼近待分割图像的特征向量,对构造的k个主特征向量执行谱聚类.最后,在Berkeley数据集上的对比实验验证文中算法的准确性和时效性优势.     

Current-ramp assisted sintering of 3YSZ: Electrochemical and microstructural comparison to flash and thermal sintering

Flash sintering features an unoptimized and uncontrolled rise in current density and sample conductivity. By using a controlled current-ramp technique with a predetermined ramp function, microstructure and electrochemical properties can be improved. This current-ramp method is investigated through use of test functions that follow square-root, linear, and parabolic time dependence with comparison to conventional flash sintering and thermal sintering. Steeper ramp functions during the sintering result in higher activation energy, suggesting a change in the vacancy concentration for both the bulk and grain boundary regions. Estimation of the grain boundary domain width suggests a grain size dependence of the unique space charge contribution to conduction independent of sintering method. Contrary to conventional wisdom, flash sintering can actually result in enhanced grain growth compared to controlled current-ramps and conventional sintering, implying that uncontrolled rise in current to a set cutoff may not be the optimal method for densification.     

The Localization of “Imported” Urban Form in Northeast China: The Case Study on Circular–Radial Space in Dalian City

After the “imported” urban forms, which originated from foreign cultures, were transplanted into Chinese cities, they generate brand-new urbanscape but suffer from a lack of cultural roots and a disconnection with the mainstream of contemporary urban planning. Thus, their current value and potential in urban renewal are questioned. The study takes the circular–radial space from the Baroque cities as an example to clarify the motivation of its import from the west to northeast China. It further clarifies their adaptive changes in form and function in the local urban context, through a case study on Dalian City. The study finds that different geometric patterns of existing circular–radial space were influenced by European, American, and Japanese urban planning theories to varying degrees, but with equal emphasis on symbolism and functionality. Their implementation in Dalian has a continuity in time and space. But due to the changes in topography, traffic, and planning concepts, their forms and functions tend to be independent, their connection weakens, and their importance recedes after the street network. The circular–radial space in Dalian led to distinctive urbanscape. But during their inheritance and transformation, the rationality of new forms and functions, as well as the necessity of continuing the initial ones need to be dialectically considered, so as to avoid dogmatic revival and antique reproduction. Finally, the study reconsiders the concept of “localization” of “imported” urban form, and constructs a general research pattern to provide a new perspective for understanding the transformation of similar types of urban forms.     

Preparation and Characterization of High-Strength Geopolymer Based on BH-1 Lunar Soil Simulant with Low Alkali Content

The construction of a lunar base and habitation on the Moon has always been on researchers’ minds. Building materials used in in situ lunar resources are of great significance for saving expensive space freight. In this study, a new type of lunar soil simulant named Beihang (BH)-1 was developed. The chemical mineral composition and microstructure of BH-1 closely resemble those of real lunar soil, as verified by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and reflectance spectra. This research also synthesized a geopolymer based on BH-1 cured at simulated lunar atmospheric conditions. We also investigated the effect of supplementing aluminum (Al) sources on the enhancement of geopolymer strength based on BH-1. The rheological behavior of alkali-activated BH-1 pastes was determined for workability. XRF, XRD, Fourier transform infrared spectroscopy, SEM coupled with energy dispersive spectroscopy, and ²⁷Al magic angle spinning-nuclear magnetic resonance were used to characterize resulting geopolymers. Rheological test findings showed that the rheology of BH-1 pastes fits the Herschel–Bulkley model, and they behaved like a shear-thinning fluid. The results showed that the 28-day compressive strength of the BH-1 geopolymer was improved by up to 100.8%. Meanwhile, the weight of additives required to produce per unit strength decreased, significantly reducing the mass of materials transported from the Earth for the construction of lunar infrastructure and saving space transportation costs. Microscopic analyses showed that the mechanism to improve the mechanical properties of the BH-1 geopolymer by adding an additional Al source enhances the replacement of silicon atoms by Al atoms in the silicon–oxygen group and generates a more complete and dense amorphous gel structure.