Spatio-temporal patterns and driving forces of urban land expansion in china during the economic reform era

Along with its economic reform, China has experienced a rapid urbanization. This study mapped urban land expansion in China using high-resolution Landsat Thematic Mapper and Enhanced Thematic Mapper data of 1989/1990, 1995/1996 and 1999/2000 and analyzed its expansion modes and the driving forces underlying this process during 1990-2000. Our results show that China's urban land increased by 817 thousand hectares, of which 80.8% occurred during 1990-1995 and 19.2% during 1995-2000. It was also found that China's urban expansion had high spatial and temporal differences, such as four expansion modes, concentric, leapfrog, linear and multi-nuclei, and their combinations coexisted and expanded urban land area in the second 5 y was much less than that of the first 5 y. Case studies of the 13 mega cities showed that urban expansion had been largely driven by demographic change, economic growth, and changes in land use policies and regulations.

Epitaxy-Assisted Creation of PCBM Nanocrystals and Its Application in Constructing Optimized Morphology for Bulk-Heterojunction Polymer Solar Cells

PCBM (a C-60 derivative) is so far the most successful electron acceptor for bulk-heterojunction polymer photovoltaic (PV) cells. Here we present a novel method epitaxy-assisted creation of PCBM nanocrystals and their homogeneous distribution in the matrix using freshly cleaved mica sheet as the substrate. The highly matched epitaxy relationship between the unit cell of PCBM crystal and crystallographic (001) surface of mica induces abundant PCBM nuclei, which subsequently develop into nanoscale crystals with homogeneous dispersion in the composite film.

Control for oriented growth of large size KCl crystals by the competition between spontaneous and induced nucleation/growth on a Langmuir-Blodgett film

Langmuir-Blodgett (LB) film of stearic acid was used as template to induce the nucleation and growth of KCl crystals when the KCl solution was cooled from 50 to 25 degrees C. When the LB film template was vertically dipped into the solution, only induced crystals with (1 1 0) orientation were formed. However, if the template was horizontally placed into solutions, both the induced nuclei at the solution/film interface and spontaneous nuclei formed in solution were simultaneously absorbed onto the LB film, and then grew further to form crystals. X-ray diffraction (XRD) patterns and optical microscopy images showed that the orientation and morphology of the crystals were controlled properly by changing the orientation and position of the LB films in the solutions.

A strategy to prepare ultrafine dispersed Fe2O3 nanoparticles

In this article, a novel strategy was applied to prepare dispersed ultrafine alpha-Fe2O3 nanoparticles. The initial Fe(OH)(3) nanoparticles were synthesized by the reaction of NaOH and FeCl3 in alcohol. With the new-formed nanoparticles as nuclei, NaCl crystallized and encapsulated the particles into solid cages. As a result, the nanoparticles were prevented from aggregating and growing. The composite of Fe(OH)(3) and NaCl was calcined and then washed by water to obtain the pure alpha-Fe2O3 nanoparticles.

Phosphine-Free Synthesis of High-Quality CdSe Nanocrystals in Noncoordination Solvents: "Activating Agent" and "Nucleating Agent" Controlled Nucleation and Growth

CdSe nanocrystals (NCs) are prepared in noncoordination solvents (1-octadecene (ODE) and paraffin liquid) with Ion g-chain primary alkylamine as the sole ligand, ODE-Se, and cadmium fatty acid salt as precursors. The obtained NCs meet the four fundamental parameters for high-quality NCs: high crystallinity, narrow size distribution, moderate photoluminescence quantum yield, and broad range size tunableness. Further, by simply regulating the relative molar ratio of alkylamine to cadmium precursor, the regular sized "nuclei" and final obtained NCs can be produced predictably within a certain size range.

Constructing Thin Polythiophene Film Composed of Aligned Lamellae via Controlled Solvent Vapor Treatment

Thin poly(3-butylthiophene) (P3BT) film composed of aligned lamellae attached to the edge of the original film has been achieved via a controlled solvent vapor treatment (C-SVT) method. The polarized optical microscopy operated at both single-polarization and cross-polarization modes has been used to investigate the alignment of the fiber-like lamellae. A numerical simulation method is used to quantitatively calculate angle distributions of the lamellae deviated from the film growth direction. Prepatterned P3BT film edge acts as nuclei which densely initialize subsequent crystal growth by exhausting the materials transported from the partially dissolved film. The growth of new film upon crystallization is actually a self-healing process where the two-dimensional geometric confinement is mainly responsible for this parallel alignment of P3BT crystals. The solvent vapor pressure should be carefully chosen so as to induce crystal growth but avoid liquid instability which will destroy the continuity of the film.

Orientation of Syndiotactic Polystyrene Crystallized in Cylindrical Nanopores

Syndiotactic polystyrene (sPS) nanorods with different diameters have been prepared by using anodic aluminum oxide templates, and the orientation of the sPS crystals in the nanorods has been investigated by FT-IR spectroscopy. It is found that the c axis of the beta' crystals preferentially oriented perpendicular to the axis of the nanorod, and the degree of orientation is lower as the diameter of the nanorod decreases. This unexpected result is attributed to nuclei formed at the surface of the nanopores and their subsequent growth, in addition to the preferential growth compatible with the pore direction by the nuclei formed in the bulk film and in the nanorods.

Crystallization behavior of poly(epsilon-caprolactone) in poly(epsilon-caprolactone) and poly(vinyl methyl ether) mixtures

The morphological development and crystallization behavior of poly(epsilon-caprolactone) (PCL) in miscible mixtures of PCL and poly(vinyl methyl ether) (PVME) were investigated by optical microscopy as a function of the mixture composition and crystallization temperature. The results indicated that the degree of crystallinity of PCL was independent of the mixture composition upon melt crystallization because the glass-transition temperatures of the mixtures were much lower than the crystallization temperature of PCL. The radii of the PCL spherulites increased linearly with time at crystallization temperatures ranging from 42 to 49 degrees C. The isothermal growth rates of PCL spherulites decreased with the amount of the amorphous PVME components in the mixtures. Accounting for the miscibility of PCL/PVME mixtures, the radial growth rates of PCL spherulites were well described by a kinetic equation involving the Flory-Huggins interaction parameter and the free energy for the nuclei formation in such a way that the theoretical calculations were in good agreement with the experimental data. From the analysis of the equilibrium melting point depression, the interaction energy density of the PVME/PCL system was calculated to be -3.95 J/cm(3).

Time-dependent DNA condensation induced by amyloid beta-peptide

The major protein component of the amyloid deposition in Alzheimer's disease is a 39-43 residue peptide, amyloid beta (A beta). A beta is toxic to neurons, although the mechanism of neurodegeneration is uncertain. Evidence exists for non-B DNA conformation in the hippocampus of Alzheimer's disease brains, and A beta was reportedly able to transform DNA conformation in vitro. In this study, we found that DNA conformation was altered in the presence of A beta, and A beta induced DNA condensation in a time-dependent manner. Furthermore, A beta sheets, serving as condensation nuclei, were crucial for DNA condensation, and Cu2+ and Zn2+ ions inhibited A beta sheet-induced DNA condensation. Our results suggest DNA condensation as a mechanism of A beta toxicity.

Relating the molecular structure and crystallization behavior of polypropylene

The crystallization behavior of two polypropylene (PP) resins as used for biaxially oriented polypropylene (BOPP) and general injection mold applications, respectively, has been intensively investigated and compared by means of polarized light optical micrography (POM), differential scanning calorimetry (DSC), conventional transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). It is found that both molecular weight distribution and isotacticity of polypropylene strongly affect its crystallization characteristics, e.g., the number of crystal nuclei at the initial stage, crystallization dynamics, the morphology, size and perfection of crystals in the final product, and so on. The results indicate an appropriate molecular structure is vital in producing high-quality BOPP film.

Fractionated crystallization of dispersed PA6 phase of PP/PP-g-MAH/PA6 blends

Fractionated crystallization behavior of dispersed PA6 phase in PP/PA6 blends compatibilized with PP-g-MAH was investigated by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD) in this work. The lack of usual active heterogeneities in the dispersed droplet was the key factor for the fractionated crystallization of PA6. The crystals formed with less efficient nuclei might contain more defects in the crystal structures than those crystallized with the usual active nuclei. The lower the crystallization temperature, the lesser the perfection of the crystals and the lower crystallinity would be. The fractionated crystallization of PP droplets encapsulated by PA6 domains was also observed. The effect of existing PP-g-MAH-g-PA6 copolymer located at the interface on the fractionated crystallization could not be detected in this work.

Miscibility and crystallization behavior of PBT/epoxy blends

The miscibility and the isothermal crystallization kinetics for PBT/Epoxy blends have been studied by using differential scanning calorimetry, and several kinetic analyses have been used to describe the crystallization process. The Avrami exponents n were obtained for PBT/Epoxy blends. An addition of small amount of epoxy resin (3%) leads to an increase in the number of effective nuclei, thus resulting in an increase in crystallization rate and a stronger trend of instantaneous three-dimensional growth. For isothermal crystallization, crystallization parameter analysis showed that epoxy particles could act as effective nucleating agents, accelerating the crystallization of PBT component in the PBT/Epoxy blends. The Lauritzen-Hoffman equation for DSC isothermal crystallization data revealed that PBT/Epoxy 97/3 had lower nucleation constant K, than 100/0, 93/7, and 90/10 PBT/Epoxy blends. Analysis of the crystallization data of PBT/Epoxy blends showed that crystallization occurs in regime II. The fold surface free energy, sigma(e) = 101.7-58.0 x 10(-3) J/m(2), and work of chain folding, q = 5.79-3.30 kcal/mol, were determined. The equilibrium melting point depressions of PBT/Epoxy blends were observed and the Flory-Huggins interaction parameters were obtained.

Investigation on isothermal and non-isothermal crystallization kinetics of poly (epsilon-caprolactone)

The crystallization kinetics and the development of lamellar structure during the isothermal crystallization of poly (epsilon-caprolactone) (PCL) were investigated by means of differential scanning calorimetry (DSC) and real-time synchrotron small angle X-ray scattering (SR-SAXS) techniques, respectively. The Avrami analysis was performed to obtain the kinetics parameters. The value of Avrami index, n, is about 3, demonstrating a three-dimensional spherulitic growth on heterogeneous nuclei in the process of isothermal crystallization. The activation energy and the surface free energy of chain folding for isothermal crystallization were determined according to the Arrhenius equation and Hoffman-Lauritzen theory, respectively. In the process of nonisothermal crystallization of PCL, the value of Avrami index, n, is about 4, which demonstrates a three-dimensional spherulitic growth on homogeneous nuclei. In addition, lamellar parameters were obtained from the analysis of SR-SAXS data.

Oriented crystallization process of polypropylene fractions

Melting recrystallization processes of melt-sheared films of polypropylene (S28C) fractions have been investigated in situ by polarized optical microscope equipped with CCD camera and hot-stage. Actually, the morphological developments in the melting recrystallization are partially reappearance of oriented crystallization processes during melt-shearing the fractions, which is due to a memory effect of oriented structure of polymer. For low molecular weight fraction, only incomplete spherulites with some orientation along shear direction are observed in the melting recrystallization processes of the sheared films. For middle molecular weight fractions, extended chain fiber crystals(or bands) are formed first at higher temperatures, and the bands can act as self-nuclei (i. e., row nuclei), resulting in epitaxial growth of chain-folded lamellae(or fibril), i. e., the formation of cylindrites, with further decrease of the crystallization temperature. For high molecular weight fraction, however, it is not possible to shear the melt film because of its high melt viscosity. When the low molecular weight fraction in which no fiber crystals or cylindrites are observed, are mixed with small amount(about 1%-2%) of the high molecular weight fraction, quite large number of cylindrites are formed during the melting recrystallization process of its sheared film, which implies that the component of high molecular weight plays an important role in the formation of cylindrites during the shear process of polypropylene.

分级聚丙烯的取向结晶过程

聚丙烯熔体在剪切或应变应力作用下 ,分子链发生取向形成伸直链纤维晶 ,这些先取向形成的纤维晶成为其后结晶的晶核 .这种线形排列的特殊自晶核被称作排核 ( Row nuclei) [1] .排核诱导的结晶温度高于异相核和均相核 .折叠链片晶在排核上附生生长 ,形成具有柱状对称性的超分子结构 ,称为柱状晶 ( Cylindrite) [2 ,3] .聚合物的分子量 ,剪切温度和剪切速度等因素对柱状晶的生成有很大影响 [4 ,5] .本文选用不同级分的聚丙烯样品 ,利用高分子 (特别是取向结晶 )的记忆效应 [6,7] ,研究了剪切后薄膜试样在熔融重结晶过程中柱状晶的形成和发展过程 ,讨论了分子量及其分布 ,特别是高分子量组分对聚丙烯取向结晶过程的影响 ,探索链结构与凝聚态结构间的相互关系 .1　实验部分1 .1　原料　聚丙烯分级样品由中国石油化工集团公司北京化工研究院提供 ,采用升温淋洗分级方法对聚丙烯 S2 8C( Montell,含质量分数为 0 .32 %的共聚乙烯 ,熔融指数 2 .1 )进行分级 .本文选用了1 1 0 ,1 1 8,1 2 5和 1 40℃ 4个级分 ,分别称作 S2 8C1 1 0 ...