On additives, morphological evolution and dielectric breakdown in low density polyethylene

A series of low density polyethylene systems has been studied with respect to structural evolution and short-term dielectric breakdown behaviour. All materials were based upon a single polymer, that is commonly used in high voltage applications, but with different additives. In all three of these systems, multiple melting transitions were observed, as a result of molecular fractionation effects during crystallization. In the virgin polymer, a space-filling banded spherulitic morphology was found to develop at low temperatures (102 °C and below) whereas, at higher temperatures, only a few isolated axialites were observed. Inclusion of the antioxidant resulted in greatly increased nucleation densities, such that, at low temperatures, no evidence of spherulitic organisation remained. At higher temperatures, sheaf-like lamellar aggregates developed, which were much smaller and much more numerous than in the case of the virgin polymer. Further addition of dicumyl peroxide (DCP) resulted in the rapid formation of a crosslinked network at 200 °C. Some crosslinking also occurred at 150 °C, but over a much longer timescale. Where extensive crosslinking occurred prior to crystallization, the resulting gel inhibited structural development, such that only a few small, isolated sheaves were able to form at 102 °C. In view of the principal application area of this material, the breakdown strength of each of the above systems was then measured and the whole data set was analysed statistically. When structural factors were considered alongside the statistics, no clear trends emerged to indicate that either the compositional or morphological variations were reflected in the short-term electrical failure processes.     

Two-dimensional Anhydrous Cadmium(II) Phthalate

The in situ hydrolysis of phthalyl-γ-glutaminyl-histidine with Cd(ClO₄)₂·6H₂O in the presence of water and methanol affords a novel two-dimensional cadmium coordination polymer, a new phase, anhydrous cadmium(II) phthalate, ( 1 ). The structure was determined by single crystal X-ray diffraction. Crystal data: P2₁/c, a = 13.8168(14), b = 7.0351(7), c = 8.2054(8) Å, β = 105.540(2)°, V = 768.43(13) ų, Z = 4, R₁ = 0.0380, wR₂ = 0.1111.     

High photosensitivity in cis-polyphenylacetylene films irradiated with 60Co γ-ray

This paper reports that ⁶⁰Co γ-ray irradiation can convert cis-polyphenylacetylene (cis-PPA) films prepared with rare-earth coordination catalysts to highly photosensitive materials. The dependence of the photosensitivity on irradiation dose, preparation methods, and microstructure of the PPA films has been investigated by means of a potential discharge technique. The photosensitivity was enhanced with increasing irradiation dose. The critical dose to produce a light response was 5 × 10³ Gy. The maximum surface potential discharge rate was 618 V/s, and the dark decay was approximately 2 V/s for cis-PPA films irradiated with ⁶⁰Co γ-ray (dose: 2 × 10⁵ Gy). The cis-transoidal-PPA and an electrophotographic photoreceptor device incorporating cis-PPA showed a higher irradiation effect. The structure and properties of ⁶⁰Co γ-ray irradiated rare-earth PPA films are similar to the unirradiated films.     

Structure and superconductivity in FexCu1−xBa2YCu2O7+y superconductors synthesized by high pressure

Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Mössbauer effect have been made on Fe_xCu_1−xBa₂YCu₂O_7+y superconductors (0.00≤x≤0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Mössbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuO_x chains have fivefold-oxygen coordination. These are important reasons for the enhancement of T_c in the HP-samples.     

On fixed point and almost fixed point problems of lower semicontinuous type multivalued mappings

In the present paper, some new almost fixed point theorems and fixed point theorems for lower semicontinuous type multivalued mappings are obtained in metrizable H-spaces.     

左消半群M与幂单半群B的Schǔzenberger积

本文讨论了每个元都有幂等元作为右单位元的左消半群与幂单半群N的Schuzenberger积M◇N的ρ类，证明了这种半群M与N的Schuzenberger积M◇N的ρ类是右E一半适合半群和弱E-headged半群．     

Nanotechnology in the Chemical Industry – Opportunities and Challenges

The traditional chemical industry has become a largely mature industry with many commodity products based on established technologies. Therefore, new product and market opportunities will more likely come from speciality chemicals, and from new functionalities obtained from new processing technologies as well as new microstructure control methodologies. It is a well-known fact that in addition to its molecular structure, the microstructure of a material is key to determining its properties. Controlling structures at the micro- and nano-levels is therefore essential to new discoveries. For this article, we define nanotechnology as the controlled manipulation of nanomaterials with at least one dimension less than 100nm. Nanotechnology is emerging as one of the principal areas of investigation that is integrating chemistry and materials science, and in some cases integrating these with biology to create new and yet undiscovered properties that can be exploited to gain new market opportunities. In this article market opportunities for nanotechnology will be presented from an industrial perspective covering electronic, biomedical, performance materials, and consumer products. Manufacturing technology challenges will be identified, including operations ranging from particle formation, coating, dispersion, to characterization, modeling, and simulation. Finally, a nanotechnology innovation roadmap is proposed wherein the interplay between the development of nanoscale building blocks, product design, process design, and value chain integration is identified. A suggestion is made for an R&D model combining market pull and technology push as a way to quickly exploit the advantages in nanotechnology and translate these into customer benefits.     

Synthesis,structure, spectroscopic and magnetic properties of a novel two-dimensional copper(II) complex Na2[Cu(pba)] · 6H2O [pba = 1,3-propylenebis(oxamato)]

The copper(II) complex Na₂[Cu(pba)] · 6H₂O has been synthesized and its structure determined. It consists of a novel two-dimensional network of [Cu(pba)]^2– anions connected to each other through the sodium ion as a bridge. Spectroscopic and magnetic properties have been measured and a spin distribution calculation has been carried out with the GAUSSIAN-94. Theoretical calculations indicate the rather larger spin density on nitrogen atoms should be responsible for the satellite lines appearing beside the main hyperfine coupling signs of copper(II). The antiferromagnetic interaction may be due to the intermolecular interaction and/or different copper(II) ions through the Na⁺ bridge in the same layer.     

A New Cycloartane from Sphaerophysa salsula

A novel cycloartane,named sphaerophysone A,9,19-cycloart-7β,24β,25-triol-1-en-3-one,was isolated from the ethanol extract of Sphaerophysa salsula DC.The structure was elucidated on the basis of spectral evidences and confirmed by X-ray analysis,the stereochemistry of the compound was also defined by X-ray analysis.     

用GSP进行"波动"教学案例

学生的学习需求是指学生要达到的目标水平与他现在实际水平之间的差距．本课的教学目标是：了解波的形成条件及过程、波的种类、振动和波的关系；理解波的传播规律和波的图象．学生的实际是只学过振动和振动的图象，会使用《几何画板》软件．此差距很明显．这就要求教师根据建构主义学习理论，通过创设情景、搭脚手架来降低知识的梯度，真正把教学目标转化为学生自己的学习需求．