Catalyst surface at a fractal of cost—a quest for optimal catalyst loading

Intuition tells us that any decrease in the catalytically active surface area should result in an equivalent decrease in the reaction yield and efficiency. Our findings counter this by showing that the active surface and hence the catalyst loading can be reduced drastically in the diffusion-limited heterogeneous reaction systems, while the conversion rate remains essentially unchanged by using fractals for spatial distribution of the catalyst load. The results of this study provide an unusual circumstance for optimal design of chemically active surfaces and can be used to drastically reduce cost of heterogeneous chemical and biological reactors, sensors, and electrodes of fuel cells. The proposed approach can be exploited to its fullest extent in chemical microsystems by utilizing the latest advances in our abilities to manipulate matter on the micro/nano scale.     

Influence of initial chain conformation on the formation of mesoglobule phase in a dilute heteropolymer solution

We have observed, for the first time, that when the initial chain conformation changed from coil to globule, the association of linear poly(N-vinylcaprolactam-co-sodium acrylate) chains could gradually change from a reaction limited to diffusion limited process, reflected in a change of the fractal dimension of the resultant aggregates from ∼2.5 to ∼1.6. Such an influence of the initial chain conformation has been overlooked in past studies of the formation of the mesoglobule phase in a dilute heteropolymer solution.     

The foaming mechanism and properties of SiO2–Al2O3–CaO-based foamed ceramics with varied foaming agents

To select suitable high-temperature foaming agents, SiO₂–Al₂O₃–CaO-based foam ceramics (SACFC) were successfully prepared with different foaming agents based on phosphorus tailings and coal gangue. The effects of high-temperature foaming agents (CaCO₃, carbon black, MnO₂ and Fe₂O₃) on the microstructure and compressive strength of the SACFC were investigated, and the corresponding foaming mechanism was revealed. The results indicated that CaCO₃ could increase the porosity of SACFC due to high-temperature decomposition. However, the precipitation of needle-like anorthite reduced the mechanical properties. Because the high-temperature oxidation temperature of carbon black was lower than the molten phase formation temperature, bubbles floated up and gathered on the surface of SACFC, leading to a decrease in strength. The continuous release of O₂ from MnO₂ during the sintering process promoted the growth and aggregation of large pores, which was detrimental to the strength. The CO₂ generated by the redox of Fe₂O₃ by CO/C was the main factor for the foaming of SACFC. During the high-temperature foaming, the synergy effect of Fe²⁺ and Fe³⁺ promoted the formation of a uniformly distributed pore structure. When 2 wt.% Fe₂O₃ was added, SACFC obtained the optimal comprehensive performance with bulk density and compressive strength of 0.78 g/cm³ and 3.50 MPa.     

Application of Fractal Theory for Prediction of Shrinkage of Dried Kiwifruit Using Artificial Neural Network and Genetic Algorithm

In current research, fractal theory has been applied for estimation of shrinkage of osmotically dehydrated and air-dried kiwifruit using a combination of neural network and genetic algorithm. Kiwifruits were dehydrated at different conditions and digital images of final dried products were taken. Kiwifruit-background interface lines were detected using a threshold combined with an edge detection approach and their corresponding fractal dimensions were calculated based on a box counting method. A neural network was constructed using fractal dimension and moisture content as inputs to predict shrinkage of dried kiwifruit and a genetic algorithm was applied for optimization of the neural network's parameters. The results indicated good accuracy of optimal model (correlation coefficient of 0.95) and high potential application of fractal theory and described intelligent model for shrinkage estimation of dried kiwifruit.     

Structure of Crack in Thermally Dried Sludge Cake

We examined in this work the drying characteristics of wastewater sludge, considering the weight loss using an electronic balance and the morphology change of drying cake by an X-ray micro-computerized tomography scanner (micro-CT). The drying rates for sludge cake was 50-60% of the pure water test. The corresponding micro-CT images were scanned to explore the change in cake volume and development of internal crack over drying. The Otsu's method was applied to bilevel the scanned images, based on which the three-dimensional model for crack's internal structure was reconstructed. The cake porosity and the geometric factors of cracks, such as the compactness, the boundary fractal dimension, and the Sierpinski carpet fractal dimension, were evaluated. The shrinkage of cake volume and the development of internal crack occurred simultaneously. The skin layer formed by the former mechanism retards further drying. On the other hand, the internal cracks were shown to exhibit zigzagging with a noncircular cross section and fractal-like boundary, which should be able to enhance local drying. A possible role of change in crack structure on the rate of drying was discussed.     

二氧化锰电极在碱性电液中的分形行为

利用阻抗法研究了二氧化锰电极在碱液中放电时的分形行为。计算了几种MnO_2电极在不同放电深度下的分维(D_f),并使其与MnO_2的某些性质(参数)相关。分维显示出MnO_2电极不规则的几何性质,并取决于放电态下的组成。     

“两改”对省电力公司财务状况的影响

本文从由于农网改造和农电体制改革引起省电力公司财务费用、折旧和管理费用增加,以及资产负债率、线损率上升等方面,分析了严重影响省电力公司财务状况的原因,提出了解决影响省电力公司财务状况问题的对策.要改善我省电力公司财务状况,首先要争取国家的优惠政策,其次要完善县公司的法人治理结构和提高企业的管理水平等.     

传统机械加工表面形貌评定的缺陷及发展方向

本文通过对传统机械加工表面形貌评定体系的分析，指出其不能完整地、从本质上反映表面的特征。并提出轮廓长度率、表面真面积率、表面分形维数D、比例系数K四个评定参数，通过分析可以看出这组参数比传统方法所具有的优越性和代替传统方法的可能性。     

Bubble size fractal dimension,gas holdup,and mass transfer in a bubble column with dual internals

As the scale of residual oil treatment increases and cleaner production improves in China, slurry bubble column reactors face many challenges and opportunities for residual oil hydrogenation technology. The internals development is critical to adapt the long-term stable operation. In this paper, the volumetric mass transfer coefficient, gas holdup and bubble size in a gas–liquid up-flow column are studied with two kinds of internals. The gas holdup and volumetric mass transfer coefficient increase by 120% and 42% when the fractal dimension of bubbles increases from 0.56 to 2.56, respectively. The enhanced mass transfer processing may improve the coke suppression ability in the slurry reactor for residual oil treatment. The results can be useful for the exploration of reacting conditions, scale-up strategies, and oil adaptability. This work is valuable for the design of reactor systems and technological processes.