Plasma etching of polypropylene films and fibres

The introduction of a 1000 Å scale corrugated structure, aligned perpendicular to the filament axis, into oriented semi-crystalline polymers on plasma etching is shown to result from restructuring of the partially etched surface and not, as has previously been proposed, to correspond to morphological detail in the unetched material. The detail exposed on plasma etching polypropylene is shown to vary extensively with the etching conditions used. The exposed surface is compared with those resulting from peeling and chromic acid etching. Plasma etching is, however, shown to be useful in exposing coarse morphological detail such as spherulites, and in providing a convenient route for rapidly stripping the polymeric sample. The restructured partially etched surface may then be removed easily by, for example, a brief chromic acid treatment, exposing the sample interior to microscopic examination.Issued as NRCC no. 16534     

现代高压直流输电技术及直流阀技术

在最近20年内高压直流晶闸管阀和高压直流输电技术的发展,使得用高压直流输电更经济、更可靠。越来越多的输电线路使用高压直流进行电力传输。现代的高压直流晶闸管阀以组件式结构、大功率和水冷晶闸管、智能晶闸管控制单元、全面的计算机阀控制和严格的试验为特征。容性换流技术、数字式光纤互感器、有源直流滤波器和连续可调交流滤波器的使用,有效地提高了高压直流输电的质量,产生了更健全的高压直流输电系统。作为新一代高压直流换流器的电压控制型换流器,使得小容量电力传输经济可行。     

The influence of specimen refractive index,detector signal integration,and non-uniform scan speed on the imaging properties in confocal microscopy

Refraction of light in a specimen volume may cause aberrations that influence the imaging properties in confocal microscopy. In this paper the influence on three-dimensional resolution and geometry is experimentally investigated for a uniform specimen volume. It is found that the depth resolution is more severely affected than the lateral resolution. This is unfortunate, because even under ideal conditions the depth resolution is lower than the lateral resolution. Lateral image geometry is little affected by the specimen refractive index, whereas the depth scale can be considerably elongated or compressed. The influence of a finite detector integration time is also considered. This can give a noticeable, but not particularly severe effect on the image resolution in the line-scan direction. Because the integration time can be accurately controlled, a shorter integration time can be used when maximum resolution is essential, albeit at the price of a higher noise level. In scanning fluorescence microscopy a non-uniform scan speed may give large variations in bleaching over the specimen surface. Experiments illustrate how serious such non-uniform bleaching effects can be when a specimen area is repeatedly scanned, for example when recording optical serial sections.     

Degradation of phytate by Pichia kudriavzevii TY13 and Hanseniaspora guilliermondii TY14 in Tanzanian togwa

The fermented cereal-based gruel togwa is used as weaning food for children in Tanzania. Togwa is rich in minerals but these are often not available for uptake in the human intestine due to natural inhibitors, such as phytate (IP(6)). The yeasts Pichia kudriavzevii TY13, Hanseniaspora guilliermondii TY14 and TY20, isolated from Tanzanian togwa, and selected for high phytase activity in complex yeast medium YPD, were now studied regarding their ability to degrade IP(6) in maize-based model togwa. A modified constitutively high-phytase producing Saccharomyces cerevisiae BY80 and commercial Aspergillus ficuum phytase were included for comparison. In addition, a strain of Lactobacillus plantarum was included in the model-togwa set-up. All yeasts in the study grew and reached final cell density 1.5-2 log units higher than the start value. S. cerevisiae BY80 degraded 85% of the IP(6) in 48 h; the same degradation level as with A. ficuum phytase (89%). Of the togwa-isolated yeasts, P. kudriavzevii TY13 and H. guilliermondii TY14 showed strong phytate degradation in the model-togwa; 95% or more of the initial IP(6) was degraded after 48 h. This corresponds to a remaining level of 0.4 and 0.3μmol IP(6)/g dw. Co-inoculation with L. plantarum did not increase IP(6) degradation. Moreover, fermentation with P. kudriavzevii TY13 yielded a successive increase in inorganic phosphate (P(i)), from 0.7 to 5.4 mM, suggesting a phytase production in TY13 which is fairly insensitive to P(i) repression. The study shows that phytate in a model togwa is available for yeast phytase enzymes, and addresses the importance of strain selection for effectively degrading the phytate. Certain yeasts originating from togwa seem to have developed a natural high phytase production, and P. kudriavzevii TY13 and H. guilliermondii TY14 seem particularly well adapted to phytate degradation in togwa, and is our choice for further studies and strain improvement.     

Industrial Dynamics: A Review of the Literature 1990–2009

This paper reviews the literature in the field of industrial dynamics (ID) as it has emerged since I first introduced the term in 1985. Nearly 8,000 articles in 12 major journals have been reviewed and classified under five broad themes that constitute the basic questions in ID: (1) the causes of industrial development and economic growth, including the dynamics and evolution of industries and the role of entrepreneurship; (2) the nature of economic activity in the firm and the dynamics of supply, particularly the role of knowledge; (3) how the boundaries and interdependence of firms change over time and contribute to economic transformation; (4) technological change and its institutional framework, especially systems of innovation; (5) the role of public policy in facilitating adjustment of the economy to changing circumstances at both micro- and macro-levels. Under each theme, the main findings and their implications for theory and policy are summarized. The paper concludes with a summary of the contribution of industrial dynamics to a better understanding of industrial transformation and economic growth and reflections on challenges for future research.     

Dynamic-mechancial response of graphita/epoxy composite laminates and neat resin

The dynamic mechanical properties of carbon-fiber-reinforced, epoxy-matric-composite laminates subjected to loading perpendicular to the plane of lamination and of neat epoxy resin are reported. The dynamic mechanical measurements were performed in the frequency range from 0.1 to 40 Hz and at temperatures between 20° and 200°C at deformation levels within the linear viscoelastic region by the use of a Dynastat apparatus. It is found that thein-phase and out-of phase stiffnesses superpose to form master curves covering a frequency range of 12 decades. By a suitable scaling procedure of the master curves, it is found that thein-phase stiffiness has tbe same shape and the out-of-phase stiffness has the same dispersion for all laminates irrespective of the stacking sequence and are nearly identical to those for neat epoxy resin, An empirical function for the relaxation modulus is developed that, when converted to dynamic modulus, gives a good overall agreement for both components of the dynamic stiffness as a function of frequency. Absorbed moisture is found to cause a reduction in thhe elevated temperature mechanical properties of a laminate due to a reduction in the glass-transition temperature of the resin. It is also found thatthemositure absorption is a reversible process, in the sense that the initially dry properties of the laminate are recovered afterredrying the wet sample.     

Electrostatic Adsorption of a Colloidal Sintering Agent on Silicon Nitride Particles

Pressureless sintering of silicon nitride requires addition of sintering agents. The main part of this study was done in order to homogenize the distribution of sintering agents, in this case Y₂O₃, in a silicon nitride matrix. Colloidal 10-nm Y₂O₃ Particles were electrostatically adsorbed on Si₃N₄ particle surfaces. The adsorption was studied by X-ray fluorescence analysis and electrophoretic measurements. Addition of Y₂O₃ sol to a Si₃N₄ suspension decreased the viscosity of the suspension. The slip casting properties of Si₃N₄ suspensions with added Y₂O₃ sol were examined, and the homogeneity of Y₂O₃ in the green compacts was compared with conventionally prepared samples. An improved microstructural homogeneity was obtained when Y₂O₃ sol particles were adsorbed on the Si₃N₄ particle surfaces.