An application of non-asbestos papers to the dental field: mechanical properties and structural change

New non-asbestos papers composed of glass fibres and ceramic fibres were examined for dental application. The fibre liners showed a larger deformation ability than conventional asbestos paper, and had a smaller water uptake than the conventional liner. In addition, the setting expansion in new non-asbestos papers was increased at 60 min after investing, similarly to the setting expansion behaviour in a conventional liner. After casting a silver alloy using the new fibre liners, a microstructure mainly of primary solid formed, with a smaller amount of complex phases. The microstructures formed were similar to those in the conventional asbestos liner.     

Developing technology in the vicinity of science: An examination of the relationship between science intensity (of patents) and technological productivity within the field of biotechnology

In this paper we investigate — at a country level — the relationship between the science intensity of patents and technological productivity, taking into account differences in terms of scientific productivity. The number of non patent references in patents is considered as an approximation of the science intensity of technology whereas a country’s technological and scientific performance is measured in terms of productivity (i.e., number of patents and publications per capita). We use USPTO patent-data pertaining to biotechnology for 20 countries covering the time period 1992–1999. Our findings reveal mutual positive relationships between scientific and technological productivity for the respective countries involved. At the same time technological productivity is associated positively with the science intensity of patients. These results are confirmed when introducing time effects. These observations corroborate the construct validity of science intensity as a distinctive indicator and suggest its usefulness for assessing science and technology dynamics.     

画法几何--工程通用的语言,国际友谊的桥梁--广东工业大学与波兰格但斯克工业大学图学合作介绍

广东工业大学工程与计算机图学教研室与波兰格但斯克工业大学可视化技术系,从1998年起建立了双边在工程图学画法的几何教育技术现代化方面的合作关系。这项合作的内容包括图学教育软件开发与运用,多媒体技术,虚拟现实技术、互联网上的远程教育软件的开发与运用及有关教育方面的问题,同时也迁伸到机械CAD和其它教育管理方面的交流,通过交流,了解了波兰在图学教育方面与我校的区别。     

印刷与包装人才培养的改革与创新 ——坚持校企合作与开展国际交流

武汉大学印刷与包装系通过在企业建立实习基地、与企业共建校内专业实验室以及企业在学校设立各种奖助学金等方式实现以学生为中心的多元化的校企合作,通过举办＂珞珈印刷论坛＂、拓展境外学习以及开展对外联合办学等方式实现形式多样的国际交流,以期适应全球化人才培养模式的需要,造就有一定实践能力及国际视野的创新型优秀人才。     

Study of the non-covalent interactions in Langmuir-Blodgett films: An interplay between π−π and dipole-dipole interactions

This work describes Langmuir-Blodgett (L-B) monolayer and multilayer assemblies constructed from a series of NLO-active azo-benzene derivatives possessing terminal moieties of variable dipole moment. The terminal groups are electron acceptors (acetyl, nitro, and cyano) and are connected to a common amphiphilic azo-benzene segment. Our experimental and theoretical results show that the interplay between two dominant non-covalent interactions within the assemblies, namely dipolar and π−π stacking interactions, dictate the packing density, structural order, as well as the electronic properties of the final films. L-B films of the acetyl derivative, which has the weakest total dipole across the azo-benzene chromophore, exhibits the highest packing density and the largest blue shift in the UV-visible absorption spectrum. This is rationalized by relatively strong π−π interactions between the azo-benzene chromophores overwhelming weak intermolecular dipole-dipole interactions. More importantly, the small internal dipole in the acetyl functional groups encourages packing in a configuration that lowers the overall energy and increases the packing density. In the case of the cyano and nitro derivatives, both L-B films show decrease in packing density and a weaker electronic coupling due to unfavorable overall dipole interaction that offsets the π−π interaction. We show that such unfavorable interactions lead to the formation of a staggered and loosely packed configuration. Our work demonstrates that a subtle difference in molecular structure can have a dramatic impact on aggregation, and consequently on the electronic and optical properties of nano-assemblies. This work demonstrates a way of controlling the formation of nanoscale structures at the molecular level through the control of noncovalent interactions.     

An approach to the formation and growth of new phases with application to polymer crystallization: effect of finite size,metastability, and Ostwald's rule of stages

This article aims to link the mainstream subject of chain-folded polymer crystallization with the rather speciality field of extended-chain crystallization, the latter typified by the crystallization of polyethylene (PE) under pressure. Issues of wider generality are also raised for crystal growth, and beyond for phase transformations. The underlying new experimental material comprises the prominent role of metastable phases, specifically the mobile hexagonal phase in polyethylene which can arise in preference to the orthorhombic phase in the phase regime where the latter is the stable regime, and the recognition of thickening growth as a primary growth process, as opposed to the traditionally considered secondary process of thickening. The scheme relies on considerations of crystal size as a thermodynamic variable, namely on melting-point depression, which is, in general, different for different polymorphs. It is shown that under specifiable conditions phase stabilities can invert with size; that is a phase which is metastable for infinite size can become the stable phase when the crystal is sufficiently small. As applied to crystal growth, it follows that a crystal can appear and grow in a phase that is different from that in its state of ultimate stability, maintaining this in a metastable form when it may or may not transform into the ultimate stable state in the course of growth according to circumstances. For polymers this intermediate initial state is one with high-chain mobility capable of thickening growth which in turn ceases (or slows down) upon transformation, when and if such occurs, thus locking in a finite lamellar thickness. The complete situation can be represented by a P, T, 1/l (l crystal thickness) phase-stability diagram which, coupled with kinetic considerations, embodies all recognized modes of crystallization including chain-folded and extended-chain type ones. The task that remains is to assess which applies under given conditions of P and T. A numerical assessment of the most widely explored case of crystallization of PE under atmospheric pressure indicates that there is a strong likelihood (critically dependent on the choice of input parameters) that crystallization may proceed via a metastable, mobile, hexagonal phase, which is transiently stable at the smallest size where the crystal first appears, with potentially profound consequences for the current picture of such crystallization. Crystallization of PE from solution, however, would, by such computations, proceed directly into the final stage of stability, upholding the validity of the existing treatments of chain-folded crystallization. The above treatment, in its wider applicability, provides a previously unsuspected thermodynamic foundation of Ostwald's rule of stages by stating that phase transformation will always start with the phase (polymorph) which is stable down to the smallest size, irrespective of whether this is stable or metastable when fully grown. In the case where the phase transformation is nucleation controlled, a ready connection between the kinetic and thermodynamic considerations presents itself, including previously invoked kinetic explanations of the stage rule. To justify the statement that the crystal size can control the transformation between two polymorphs, a recent result on 1 -4-poly-trans-butadiene is invoked. Furthermore, phase-stability conditions for wedge-shaped geometries are considered, as raised by current experimental material on PE. It is found that inversion of phase stabilities (as compared to the conditions pertaining for parallel-sided systems) can arise, with consequences for our scheme of polymer crystallization and with wider implications for phase transformations in tapering spaces in general. In addition, in two of the Appendices two themes of overall generality (arising from present considerations for polymers) are developed analytically; namely, the competition of nucleation-controlled phase growth of polymorphs as a function of input parameters, and the effect of phase size on the triple point in phase diagrams. The latter case leads, inter alia to the recognition of previously unsuspected singularities, with consequences which are yet to be assessed.