Network topology and the theory of rubber elasticity

The earliest investigations on rubber elasticity, commencing in the 19th century, were necessarily limited to phenomenological interpretations. The realisation that polymers consist of very long molecular chains. commencing c. 1930, gave impetus to the molecular theory of rubber elasticity (1932-). according to which the high deformability of an elastomer, and the elastic force generated by deformation, stem from the configurations accessible to long molecular chains. Theories of rubber elasticity put forward from 1934-1946 relied on the assumption that the junctions of the rubber network undergo displacements that are affine in macroscopic strain. The theory of James and Guth (1947) dispensed with this premise, and demonstrated instead that the mean positions of the junctions of a ‘phantom’ network consisting of Gaussian chains devoid of material properties are affine in the strain. The vital significance of the distinction between the actual distribution of chain vectors in a network and their distribution if the junctions would be fixed at their mean positions went unnoticed for nearly 30 years. Experimental investigations, commencing with the incisive work of Gee in 1946. revealed large departures from the relationship of stress to strain predicted by the theories cited. This discrepancy prompted extensive studies, theoretical and experimental, during succeeding years. Inquiry into the fundamentals of polymer networks, formed for example by interlinking very long polymer molecules, exposed the need to take account of network imperfections, typically consisting of chains attached at only one end to a network junction. Various means were advocated to make corrections for these imperfections. The cycle rank ζ of the network has been shown (1976) to be the fundamental measure of its connectivity, regardless of the junction functionality and pattern of imperfections. Often overlooked is the copious interpenetration of the chains comprising typical elastomeric networks. Theories that attempt to represent such networks on a lattice are incompatible with this universal feature. Moreover, the dense interpenetration of chains may limit the ability of junctions in real networks to accommodate the fluctuations envisaged in the theory of phantom networks. It was suggested in 1975 that departures from the form predicted for the elastic equation of state are due to constraints on the fluctuations of junctions whose effect diminishes with deformation and with dilation. Formulation of a self-consistent theory based on this suggestion required recognition of the non-affine connection between the chain vector distribution function and the macroscopic strain in a real network, which may partake of characteristics of a phantom network in some degree. Implementation of the idea was achieved through postulation of domains of constraint affecting the equilibrium distribution of fluctuations of network junctions from their mean positions. This led in due course to a theory that accounts for the relationship of stress to strain virtually throughout the ranges of strain accessible to measurement. The theory establishes connections between structure and elastic properties. This is achieved with utmost frugality in arbitrary parameters.     

The effect of pitch and collimation on radiation dose in spiral CT

1 Introduction Spiral computed tomography (CT) was intro- duced in clinical practice in 1980s. Its distinctive characteristic is continuous data acquisition and con- tinuous tube rotation with high speed while simulta- neously translating the patient through the gantry.[1] Owing to these functions the spiral CT possesses the ability to scan an entire organ volume within a single breathhold. Thus, the anatomical section is contiguous and therefore the reliable demonstration of small le- sions…     

Accuracy of the zero crossings of the second directional derivative as an edge detector

In this paper the accuracy of the second directional derivative edge detector is analyzed, based on a number of idealized edge models. The results are compared with those for the Laplacian edge detector. Errors are shown to be small under a number of conditions. These conditions are less severe for the second directional derivative than for the Laplacian edge detector. Spurious or phantom edges can be removed by checking the sign of the third directional derivative, though this is not enough to remove all large errors. Indeed, it is also shown that large errors will be obtained if no threshold is set on the magnitude of a third order derivative.This work was supported by the Belgian National Fund for Scientific Research (NFWO).     

成熟度、施肥量、留叶数与烟叶组织结构和比叶重的关系

对不同成熟度、施肥量、留叶数处理的烟叶组织结构、比叶重进行研究,结果表明:烟叶的厚度、栅栏组织和海绵组织厚度以完熟叶>初熟叶>过熟叶,并随施肥量增加而变厚。成熟度提高,上二棚叶比叶重下降;施肥量与腰叶比叶重负相关,与上二棚叶比叶重正相关。留叶数增多.上二棚叶厚度交薄,腰叶和上二棚叶比叶重均降低。     

激光生物热作用的一维瞬态温度分布规律研究

采用数学物理方程的定解求法解一维热传导偏微分方程 ;讨论结果的物理意义 ,与相关实验作对比分析。结果表明 ,激光热源在一维生物组织空间引起的温升一般随时间呈指数形式增大 ;随激光照射处的距离呈指数形式减少。     

Total carotenoid differences in scallop tissues of Chlamys nobilis (Bivalve: Pectinidae) with regard to gender and shell colour

The aim of this study was to investigate whether total carotenoid content (TCC) in noble scallop Chlamys nobilis is related to body tissue, shell colour, and gender. TCC was determined by a UV–vis recording spectrophotometer in tissue of gonad, adductor, mantle, and gill separately sampled from male and female individuals with orange and brown shell colours from the same cultured population. TCC was significantly different among body tissues, depending on shell colour and gender, ranging from 0.73 to 59.85 μg g⁻¹. In general, TCC was greater in the order of gonad > mantle > adductor > gill. In the same gender, orange shell colour individuals contained significantly higher TCC than brown ones in all four tissues (P < 0.05). In the same shell colour, female contained significantly higher TCC than male in gonad and adductor tissues (P < 0.05).     

Residue depletion of sulfachlorpyrazine in edible tissues of broiler chickens

The residue depletion profile of sulfachlorpyrazine was studied in healthy broilers after oral administration of Sulfatyf®, given at a dose of 50?mg sulfachlorpyrazine (SCP) per kg body weight once daily for 3 consecutive days. Twenty-five medicated broilers were slaughtered on the 5th, 10th, 14th and 16th day of post-medication, and muscle, fat with skin, liver and kidney tissues were sampled and analysed using an high-performance liquid chromatography (HPLC) method with satisfactory recovery (74.5%?±?2.9%) and specificity. The estimated values of LOD and LOQ were 18.40 and 55.70?ng?ml^?1, respectively. On the 5th and 10th day of post-medication, the concentrations of SCP residue in all samples examined were higher than the corresponding MRLs established by the European Union and the highest SCP concentrations were measured in muscle. A maximum withdrawal time of 14 days was calculated to ensure consumer safety.     

盐水方肠的品质优化

通过单因素和正交试验,确定大豆分离蛋白、大豆组织蛋白和卡拉胶在盐水方肠中的最适添加比例分别为22%、15%和0.99%。