Microstructural analysis of sintering behavior of intra-grain pores

A latticebased Monte Carlo simulation approach has been developed for studying the behavior of intragrain pores during the intermediate and final stages of sintering. The changes of the microstructures and the resulting properties of intragrain pores during sintering are easily examined. The sintering behavior such as pore size distribution, average pore size, etc. is in very good agreement with the experimental observations. In addition, the relationships between the number of pores and the average pore volume agree well with theory.     

粘弹性流体在微孔道中流动的受力分析

针对亲油岩石水驱后残余油膜的存在形式及聚合物溶液的粘弹特性,选取粘弹性流体中的上随体Maxwell本构方程并使用计算流体软件Polyflow对模型进行数值分析。对比研究了在不同的松弛时间,不同的孔道宽度下,聚合物溶液作用于残余油膜上的应力T11的变化趋势,并且将水与聚合物溶液的驱替结果进行了比较。结果表明:随着聚合物溶液弹性的增强,对油膜的作用力T11就越强;孔道宽度与油膜高度越接近,对油膜的作用力就越强;聚合物溶液对油膜的作用力较水溶液强。     

酶活性部位柔性的分形分析

引言蛋白质三维结构的研究一直是生物学上一个重要而复杂的问题。通过X晶体衍射和核磁共振技术,人们已经积累了大量的蛋白质结构数据,但进一步解析蛋白质结构与功能间的关系,尚存在一定难度。作为非线性科学分支的分形理论(fractaltheory),以其独特的研究方法揭示了自然界中非线性过程内在的随机性及其所具有的特殊规律性。虽然分形理论在20世纪70年代才首次提出[1],但     

Fractal analysis of surfaces roughened by grit blasting

Surfaces roughened by grit blasting influence the adhesion strength of plasma-sprayed ceramic coatings. The average surface roughness has been used to evaluate the surface topography of such surfaces. It is well known that the adhesion strength of ceramic coatings reaches a maximum value at a certain substrate surface roughness. However, this result cannot be understood based on only surface roughness. The blasted surface has fractal characteristics. There are two types of fractal surfaces, which are characterized by self-similarity and self-affinity. Using fractal analysis to evaluate the surface topography of substrates, the fractal dimension was measured for the roughened surfaces. The maximum fractal dimension was attained at a blasting angle of 75°, where the adhesion strength also reached approximately its maximum value. It is concluded that the fractal dimension is a more appropriate measure than the average surface roughness for evaluation of the adhesion strength of ceramic coatings.     

Fractal analysis of gas adsorption on Syncrude coke

Fractal dimension is an intrinsic, quantitative measure of surface irregularity and provides a convenient parameter for comparing surface physical properties. Several particle size ranges of Syncrude coke were studied by nitrogen and carbon dioxide adsorption. The apparent surface area, A, was observed to increase from 1 to 15 m² g⁻¹ for N₂ and from 65 to 300m² g⁻¹ for CO₂ data with decreased particle size. The fractal dimension, D, was determined from the proportionality: A∝R^D-3, where the surface area is determined by BET or D-P (Dubinin-Polanyi) theories, R is the particle radius and 2D3. The value of D for Syncrude coke was determined to be 2.48 from both N₂ and CO₂ results.     

Fractal analysis of thermooxidative degradation process of polymeric melts

The fractal dimension of a macromolecular coil is used for the characterization of a polymeric melt structure. It is shown that the kinetics of oxygen consumption is defined by both the chemical constitution of a polymer and its structure. The quantitative analysis of the kinetical curves of the oxygen consumption in the thermooxidative degradation process was carried out in the framework of the fractal approach. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2378–2381, 2003     

化学镀非晶镍-磷合金分形分析

在由NiSO4·6H2O、NaH2PO2·H2O、Na3C6H5O7、CH3COONa和KIO3组成的化学镀镍液中,改变配位剂柠檬酸钠的浓度制备了4种不同含磷量的Ni–P合金镀层,用投影覆盖法计算了其表面分形维数,并考察了分形维数与柠檬酸钠浓度及镀层耐硝酸性能的关系。结果表明,镀层的表面分形维数介于2.3298~2.6586之间,与柠檬酸钠浓度具有良好的线性正比关系,而与镀层在硝酸中的腐蚀失重量呈良好的线性负相关。因此,表面分形维数可用于定量表征镀层的耐蚀性。     

Kinetics of a thermooxidative degradation of polyethylene: Fractal analysis

It is shown that kinetics of polyethylene thermooxidative degradation is influenced by both spatial and temporary (energetic) disorder of structure. Thus, the theorem of subordination is carried out (i.e., the multiplicative behavior of exponents describing these kinds of disorder is observed). As heat aging is usually carried out at rather high temperatures, this circumstance leads in an increase of contribution of temporary (energetic) disorder. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2348–2351, 2004     

Reexamination of capillary phenomena in cylindrical pores and application to pore size analysis

The way to account for curvature dependence of the surface tension in capillary phenomena is reexamined for the case of cylindrical pores (Section 2). The relationship between γ, the interface area s and the adsorbed quantity N is discussed and it is suggested that the change d(γs) should be considered in the free enthalpy calculation instead of γds. In opposition to a recent paper this refinement introduces only small changes in adsorption layer thickness and in equilibrium evaporation pressures.Attention is focused on the length assumption which is always in treatments of the cylindrical pore model (Section 3). Only in a few instances have long cylindrical pores been identified [14, 15]. In ordinary porous material, when the cylindrical model can be regarded as fitting, most pores will at best be short segments. Quantitative corrections for this departure from ideality cannot be introduced, for the average length in a pore class is not known. However, it is interesting to evaluate the magnitude of the errors involved. The Broekhoff—de Boer treatment of the meniscus curvature and shape provides the basis for such an evaluation (Section 4). The low results often obtained from the adsorption isotherm can, at least partially, be explained by the assimilation of short pores to long ones.     

Fractal analysis of polymer molecular weight distribution: Dynamic scaling

The correctness of the molecular weight distribution (MWD) of a poly(dimethyl diallyl ammonium chloride) type was shown in the frame‐work of the dynamic distribution function of the irreversible aggregation cluster–cluster model. The buildup of a generalized distribution curve confirms the possibility to describe the polymerization processes within the framework of the mentioned model and allows one to predict the kinetics of MWD changes as the function of the initial monomer concentration c₀ and reaction time t. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2382–2384, 2003     

Fractal analysis of morphology of PE/PA blends: Composition

Composition effect on the phase morphology in polyethylene (PE) with polyamide (PA) blends was investigated by pattern analysis of scanning electron micrographs. The average diameter denoted as d_g is defined to discuss the morphology of the blends and further, different fractal dimensions, D_M and D_N, were introduced to characterize the phase morphology. Scale function S_N(r) and S_M(r) are defined to study the selfsimilarity of the phase morphology. The plots of S_N(r)/S_N(r)m (the maximum of S_N(r)) versus r/rm (the maximum of r) and S_M(r)/S_M(r)m (the maximum of S_M(r)) versus r/rm showed the selfsimilar formation of the phase pattern. Furthermore, we calculated the fractal dimension D of different PE/PA blends. The results showed that the fractal dimension was an effective parameter to describe the spacial distribution of dispersed particles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fractal analysis of invasion depth of extraneous fluids in porous media

Applications of the fractal theory to analyze transport properties of porous media in science and engineering have received steady attention in the past two decades. However, the theory was rarely used to analyze invasion by extraneous fluids into a permeable bed where there is initially no such fluid present. Spills and leaks of non-aqueous phase liquids (NAPLs) and formation damage in drilling and completion wells are two typical examples. In this work, a fractal capillary model is proposed to analyze the depth of extraneous fluid invasion, where the tortuosity of capillaries and capillary pressure effect are taken into account. The quantitative relationship between average flow velocity and average beeline velocity are discussed based on the fractal geometry theory. Based on the proposed model, the depth of extraneous fluid invasion can be determined when the operation conditions, extraneous fluid properties and formation structure parameters are available, and the model predictions are in good agreement with the available data.     

The diffusion of liquids in pores

An equation for the diffusion of solute molecules in pores filled with liquids has been developed. It has been found to represent the diffusion of a variety of materials, from simple molecules to fractions of petroleum asphaltenes.     

Fractal analysis of polypropylene composite filled with nano‐calcium carbonate

Polypropylene (PP) and nano‐calcium carbonate (CaCO₃) composites were prepared by melt mixing in a corotating twin‐screw extruder. Transmission electron microscopy study and particle size analysis revealed the dispersion and the size distribution of CaCO₃ in PP. With the increase of loading of filler, CaCO₃ nanoparticles densely aggregated together and the dispersion of filler became bad. The fractal dimensions of the composites were determined using fractal concept. The fractal dimensions of D and D_k described the irregularities of the shape of an object and the distributions of particle populations, respectively. The D and D_k values were influenced by the content of filler, i.e., the D values increased, and the D_k values decreased with the increase of loading of filler. When the loading of filler was low, the values of D and D_k of PP composites differ slightly than the counterparts of PP/PP‐g‐MA (50 wt %) blend. For 20 wt %, they were almost identical. This fact showed that the fractal dimension was correlated with the dispersion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface roughness during storage of chocolate: Fractal analysis and possible mechanisms

Laser scanning microscopy and fractal analysis were used to determine roughness in the surface of chocolate samples stored under cycling temperature conditions (16 to 26°C) for 24 d. The four samples varied in the source of fat: 100% cocoa butter (CB), lauric and nonlauric fat replacers, and CB with 2% of nonlauric fat replacer. The response variable was the area-scale fractal complexity (Asfc), equivalent to a fractal dimension. Asfc increased with time to an asymptotic value (AV) in much the same way as whiteness index, both being accepted proxies of surface bloom. Images produced from topographical data revealed clearly the increase in roughness. Chocolate samples prepared with CB replacers exhibited an induction period and a slower rate of change in surface roughness than chocolate containing only CB. A linear relationship between a normalized roughness and the square root of time was followed by CB chocolate samples for the period before reaching AV. This result suggests that either diffusion or capillary flow may be the mechanism involved in fat migration to the surface.     

Fractal Benzenoids

The possibility of fractal benzenoids built upon a (deterministically) regular self-similar structure are proposed. Of various possibilities considered a simpler class of “trigonal” structures is identified. Possible directed synthetic schemes are described. Further, Kekulé structure counts are made as well as conjugated-circuits estimates of resonance energies. Results, for the general trigonal class as well as for particular cases are given.     

Fractal Nanotechnology

Self-similar patterns are frequently observed in Nature. Their reproduction is possible on a length scale 10²–10⁵ nm with lithographic methods, but seems impossible on the nanometer length scale. It is shown that this goal may be achieved via a multiplicative variant of the multi-spacer patterning technology, in this way permitting the controlled preparation of fractal surfaces.     

Calculation of the impedance of noncylindrical pores Part II: Experimental verification on pores drilled into stainless steel

The method of one-dimensional modelling of the pore impedance is validated on pores drilled in AISI 316 stainless steel. Impedance measurements were carried out in 0.511 sulphuric acid solution. Experimentally, it is found that, for cylindrical pores with a radius/pore length-ratio smaller than 0.5, the one-dimensionality condition is satisfied. Furthermore, impedance measurements on noncylindrical, scaled-up pores provide evidence that a geometric constant A_g has to be introduced, as in Part I. In accordance with this theory it is found that for pores with narrowing cross section A_g is less than 1/3, while for pores with a broadening cross section A_g is greater than 1/3. Moreover, it is shown that the matrix method, presented in Part I, provides a way of calculating the impedance of a non-cylindrical pore by using a highly reduced number of discs, N, compared to the recursion method of Keiser et al. This is an advantage in fitting procedures.     

多级孔分子筛材料的研究进展

综述了近年来多级孔分子筛的研究进展,主要分为直接合成法和后处理法。直接合成法包括硬模板法和软模板法,后处理法包括脱铝法、脱硅法以及脱铝脱硅联用法。总结了各种处理方法的优点以及存在的问题,旨在为多级孔分子筛的制备提供更多的理论依据,并对其发展前景进行了展望。