黄土丘陵区土壤团聚体分形特征及其对植被恢复的响应

采用计算分形维数的方法,对黄土丘陵区典型草原带土壤团聚体的分形特征及其对植被恢复的响应进行研究。结果表明:1)在植被恢复初期,土壤>10 mm粒级的团聚体含量在0~20和20~40 cm层次均较高,含量为331.4~525.6 g/kg。随植被恢复年限增加,10~7、7~5、5~3、3~2、2~1 mm粒级的团聚体绝对含量下降差异不明显。1~0.5、0.5~0.25和<0.25 mm小粒级土壤团聚体含量,在植被恢复初期(7 a)较高。2)随着植被恢复年限增加,土壤>5 mm粒级的水稳性团聚体含量相对下降很快,恢复7 a之后,大粒级土壤团聚体表现为上层含量比下层含量低的趋势。相对于干筛结果而言,土壤水稳性团聚体的粒径分布更为均匀、稳定,恢复7 a之后的土壤>0.25mm团聚体含量占到40%~50%,而>5 mm的土壤团聚体则占10%~23%。植被恢复过程中,土壤团聚体由大的团块向小颗粒的土壤团聚体转换,粒径分布更为均匀,土壤结构逐渐改善。3)不同恢复年限土壤团聚体分形维数变化范围为表层2.75~2.86,表下层2.77~2.89,变化范围小,20~40 cm土层的分形维数大于0~20 cm,恢复植被可使土壤分形...

农田土壤特性的空间变异性及分形特征

对 2 4 m× 2 4 m面积内的 49个观测点进行了土壤含水量和坚实度的空间变异性研究。根据测定结果 ,用经典统计方法计算了均值、标准差、变异系数等统计特征值 ,认为该法不能定量的描述土壤特性的空间变异性。于是 ,用分形理论计算了含水量与坚实度的分形维数。结果表明 ,在一定范围内 ,土壤具有分形特征 ,分形维数可表示土壤特性在空间的不均一程度

黄土高原分形沟网研究

推测认为黄土高源沟网具有分形性。根据Hoton定律推导沟网分维计算式 ,确定沟网分形结构 ,分形理论求算得小流域沟网的分维D =1.9接近于平面空间时的D =2理论值。统计分析发现流域边界周长、长轴、短轴、长短轴比、汇合角等地貌指标随流域面积的变化。从而证明黄土高源流域的自相似性

Spatial-temporal characteristics of siping urban expansion based on remote sensing and GIS

Based on the RS and GIS methods, Siping city is selected as a study case with four remote sensing images in 25 years. Indices of urban morphology such as fractal dimension and compactness are employed to research the characteristics of urban expansion. Through digital processing and interpreting of the images, the process and characteristics of urban expansion are analysed using urban area change, fractal dimension and compactness. The results showed that there are three terms in this period. It expended fastest in the period of 1979~1991, and in the period of 1992~2001, the emphases on urban redevelopment made it expended slower. And this is in agreement with the Siping Statistical Yearbook. This indicates that the united of metrics of urban morphology and statistical data can be used to satisfactorily describe the process and characteristics of urban expansion. © 2008 IEEE.

Spontaneous formation of two-dimensional gold networks at the air-water interface and their application in surface-enhanced Raman scattering (SERS)

Two-dimensional (2-D) gold networks were spontaneously formed at the air-water interface after HAuCl4 reacted with fructose at 90 degrees C in a sealed vessel, in a reaction in which fructose acted as both a reducing and a protecting agent. Through fine-tuning of the molar ratio of HAuCl4 to fructose, the thus-formed 2-D gold networks can be changed from a coalesced pattern to an interconnected pattern. In the coalesced pattern, some well-defined single-crystalline gold plates at the micrometer-scale could be seen, while in the interconnected pattern, many sub-micrometer particles and some irregular gold plates instead of well-defined gold plates appeared. It is also found that the 2-D gold networks in the form of an interconnected pattern can be used as substrates for surface-enhanced Raman scattering (SERS) because of the strong localized electromagnetic field produced by the gaps between the neighboring particles in the 2-D gold networks.

Superhydrophobic PTFE surfaces by extension

A rather simple but yet effective way to achieve a superhydrophobic film by extending a Teflon film is proposed. The water contact angle can be increased from 118 to 165degrees by extending to ca. 190%. The fibrous crystals and the increasing distance between the fibrous crystals are believed responsible for the high water-contact angle. It indicates that the density of the aligned microstructures is very important for the superhydrophobicity.

Surfactantless synthesis of multiple shapes of gold nanostructures and their shape-dependent SERS spectroscopy

A useful method for the synthesis of various gold nanostructures is presented. The results demonstrated that flowerlike nanoparticle arrays, nanowire networks, nanosheets, and nanoflowers were obtained on the solid substrate under different experimental conditions. In addition, surface-enhanced Raman scattering (SERS) spectra of 4-aminothiophenol (4-ATP) on the as-prepared gold nanostructures of various shapes were measured, and their shape-dependent properties were evaluated. The intensity of the SERS signal was the smallest for the gold nanosheets, and the flowerlike nanoparticle arrays gave the strongest SERS signals.

Morphologies in solvent-annealed thin films of symmetric diblock copolymer

We have systematically studied the thin film morphologies of symmetric poly(styrene)-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer after annealing to solvents with varying selectivity. Upon neutral solvent vapor annealing, terraced morphology is observed without any lateral structures on the surfaces. When using PS-selective solvent annealing, the film exhibits macroscopically flat with a disordered micellar structure. While PMMA-selective solvent annealing leads to the dewetting of the film with fractal-like holes, with highly ordered nanoscale depressions in the region of undewetted films. In addition, when decreasing the swelling degree of the film in the case of PMMA-selective solvent annealing, hills and valleys are observed with the coexistence of highly ordered nanoscale spheres and stripes on the surface, in contrast to the case of higher swelling degree. The differences are explained qualitatively on the basis of polymer-solvent interaction parameters of the different components.

Carboxyl-cored dendrimer and toluene-assisted fabrication of uniform platinum nanodendrites at a water/oil interface and their potential application as a catalyst

Uniform platinum nanodendrites have been prepared at a water/oil interface by a facile catalyst-free method at room temperature. This is carried out by introducing NaBH4 into the platinum precursor solution in the presence of the second generation of carboxyl-cored dendrimer ([G-2]-CO2H dendrimer) and toluene to act as a protective agent and a linker, respectively. The average fractal dimension of 1.61 of the obtained platinum nanodendrites is calculated by analysing the transmission electron micrographs using the programs Fractal Dimension Version 1.1 and Fractal Dimension Calculator. Control experiments show that the fabrication of platinum nanodendrites can be operated with a wide parameter window, which undoubtedly raises the degree of control of the synthesis process. The potential application of such a nanostructure as a catalyst is investigated, and the results reveal that they show highly efficient catalytic properties for the typical redox reaction between hexacyanoferrate (III) and thiosulfate ions at 301 K.

Macroporous fluoropolymeric films templated by silica colloidal assembly: A possible route to super-hydrophobic surfaces

A super-hydrophobic surface was obtained on a three-dimensional (313) polyvinylidene fluoride (PVDF) macroporous film. The porous films were fabricated through self-assembled silica colloidal templates. The apparent water contact angle of the surface can be tuned from 106 degrees to 153 degrees through altering the sintering temperature and the diameter of the colloidal templates. A composite structure of micro-cavities and nanoholes on the PVDF surface was responsible for the super-hydrophobicity. The wettability of the porous surfaces was described by the use of the Cassie-Baxter model and Wenzel's equation.

Growth of cationic lipid toward bilayer, lipid membrane by solution spreading: scanning probe microscopy study

The growth of cationic lipid dioctadecyldimethylammonium bromide (DODAB) toward bilayer lipid membrane (BLM) by solution spreading on cleaved mica surface was studied by atomic force microscopy (AFM). Bilayer of DODAB was formed by exposing mica to a solution of DODAB in chloroform and subsequently immersing into potassium chloride solution for film developing. AFM studies showed that at the initial stage of the growth, the adsorbed molecules exhibited the small fractal-like aggregates. These aggregates grew up and expanded laterally into larger patches with time and experienced from monolayer to bilayer, finally a close-packed bilayer film (5.4 +/- 0.2 nm) was approached. AFM results of the film growth process indicated a growth mechanism of nucleation, growth and coalescence of dense submonolayer, it revealed the direct information about the film morphology and confirmed that solution spreading was an effective technique to prepare a cationic bilayer in a short time.

Branched crystal morphology of linear polyethylene crystallized in a two-dimensional diffusion-controlled growth field

The branched crystal morphology of linear polyethylene formed at various temperatures from thin films has been studied by atomic-force microscopy (AFM), transmission electron microscopy (TEM), electron diffraction (ED) pattern and polymer decoration technique. Two types of branched patterns, i.e. dendrite and seaweed patterns, have been visualized. The fractal dimension d(f) = 1.65 of both dendrite and some of seaweed patterns was obtained by using the box-counting method, although most of the seaweed patterns are compact. Selected-area ED patterns indicate that the fold stems tilt about 34.5degrees around the b-axis and polymer decoration patterns show that the chain folding direction and regularity in two (200). regions are quite different from each other. Because of chain tilting, branched crystals show three striking features: 1) the lamella-like branches show two (200) regions with different thickness; 2) the crystals usually bend towards the thin region; 3) the thick region grows faster by developing branches, thus branches usually occur outside the thick region. The branched patterns show a characteristic width w, which gives a linear relationship with the crystallization temperature on a semilogarithmic plot.

SURFACE FRACTALS IN BLOCK-COPOLYMERS

A surface fractal model was presented to describe the interface in block copolymers. It gives a simple power-law relationship between the scattering intensity I(q) and the wave vector q in a relatively wide range as qxi >> 1, I(q) is-proportional-to q(D-6

高分子混合体系相分离过程相结构的自相似与分形

本工作用激光光散射和光学显微镜手段研究了聚甲基丙烯酸甲醋(PMMA)和聚醋酸乙烯酯[PVAc]共混体系相分离过程。结果表明系统的相态结构呈现较强的自相似,结构函数在大波矢处具有q~(-6)的渐近行为,相结构具有分形特征,其分形维数[Fractal Dimension]D约为1,64,初步认为结构函数的标度[Scaling]行为是由于相结构的分形特征所致。

小波变换理论应用进展

本文介绍了小波变换理论 ,讨论了基本小波函数的选取准则和小波变换算法 ,分析了小波变换与人工智能等其它方法的结合方式和特点 .通过介绍小波变换在信号瞬态分析、图像边沿检测、图像去噪、模式识别、数据压缩、分形信号分析等方面的应用实例 ,讨论了小波变换在处理非平稳信号和复杂图像时的优势 .最后 ,对小波变换理论的发展及其应用前景作了描述 .