Photoelastic Effects in Phosphate Glasses

The stress-optical coefficients of RO-Pz05 glasses (R = Mg, Ca, Sr, Ba, and Zn) were measured, and the photoelasticity mechanisms were analyzed based on the equation expressing the relation among the photoelastic constants, the elastic moduli, and the refractive index of glasses. No simple relation was found between the stress-optical coefficient and the elastic modulus, indicating that the factor (p – q), where p and q are the Neumann strain-optical coefficients, is important. The change of (p – q) with glass composition is governed mainly by changes in the effect of the atoms, rather than the lattice. The atomic effect increases with decreasing radius of the divalent cation, except for Zn²⁺. The ZnO-containing glasses exhibit extraordinarily large atomic effects. The photo-elasticity mechanism is discussed in relation to the nature of the chemical bonds.     

Modelling of an automated guided vehicle system (AG VS) in a just-in-time (JIT) environment

Like other production systems, just-in-time (JIT) systems need to address the issue of material transport between workstations such as those served by automated guided vehicles (AGVs). Unlike other production systems, however, the JIT philosophy imposes strict requirements on inventory levels and supply-demand protocols which render conventional AGV delivery strategies ineffective and counter-productive. This paper describes the modelling of an AGV system (AGVS) in a JIT environment in a way that is consistent with JIT principles. The influence of a ‘JIT perspective’ is emphasized throughout the model by introducing threshold values for both input and output queues, performance measures that emphasize lower inventories in addition to transport efficiency, and a new dispatching rule that implements better inventory and transport control. The dispatching rule is shown to perform better in a JIT environment than previously developed AGV dispatching rules in both transport and logistic criteria.     

Compositional Trends in Photoelastic Constants of Borate Glasses

The stress-optical coefficients of binary and ternary borate glasses were measured and the factor ( p·q ), where p and q are the Neumann strain-optical coefficients, was determined. As a modifier oxide was added to B₂O₃ glass, the stress-optical coefficient decreased monotonically. It was found that the stress-optical coefficient is determined mainly by the elastic modulus, but the factor ( p·q ) becomes significant when the content and polarizability of the modifier cation are high. It was also found that the factor ( p·q ) decreases when the content and polarizability of the modifier cation increase. The ( p·q ) was divided into the lattice effect and the atomic effect, and their compositional dependences were discussed.     

Risk‐based water resources planning in practice: a blueprint for the water industry in England

Resilient water supplies in England need to be secured in the face of challenges of population growth, climate change and environmental sustainability. We propose a blueprint for water resources planning that uses system simulation modelling to estimate the frequency, duration and severity of water shortages at present and in the context of future plans and scenarios. We use multiobjective optimisation tools to explore trade‐offs between these risk metrics and cost of alternative plans, and we use sensitivity analysis to identify plans that robustly achieve targets for tolerable risk, alongside other performance objectives. The results of a case study in the Thames basin demonstrate that the proposed methodology is feasible given commonly available data sets and models. The proposed method provides evidence with which to develop water resource management plans that demonstrably balance the risks of water shortages, costs to water users and environmental constraints in an uncertain future.     

Estimating economic value of agricultural water under changing conditions and the effects of spatial aggregation

Given the high proportion of water used for agriculture in certain regions, the economic value of agricultural water can be an important tool for water management and policy development. This value is quantified using economic demand curves for irrigation water. Such demand functions show the incremental contribution of water to agricultural production. Water demand curves are estimated using econometric or optimisation techniques. Calibrated agricultural optimisation models allow the derivation of demand curves using smaller datasets than econometric models. This paper introduces these subject areas then explores the effect of spatial aggregation (upscaling) on the valuation of water for irrigated agriculture. A case study from the Rio Grande-Rio Bravo Basin in North Mexico investigates differences in valuation at farm and regional aggregated levels under four scenarios: technological change, warm-dry climate change, changes in agricultural commodity prices, and water costs for agriculture. The scenarios consider changes due to external shocks or new policies. Positive mathematical programming (PMP), a calibrated optimisation method, is the deductive valuation method used. An exponential cost function is compared to the quadratic cost functions typically used in PMP. Results indicate that the economic value of water at the farm level and the regionally aggregated level are similar, but that the variability and distributional effects of each scenario are affected by aggregation. Moderately aggregated agricultural production models are effective at capturing average-farm adaptation to policy changes and external shocks. Farm-level models best reveal the distribution of scenario impacts.     

一种从XML数据中发现关系信息的方法

提出了一种发现蕴藏在不同XML文档嵌套结构中的关系信息及其出现模式的新方法.可根据用户兴趣,发现描述不同实体之间联系的关系信息,抽取关系实例及其在文档中的出现模式.具体解决方案是:首先识别和收集包含用户感兴趣的实体的XML文档片段:然后根据文档片段标签的语义和文档片段的结构计算文档片段的相似度,并采用自适应阈值方法按相似度聚类文档片段.使得包含同一种关系的文档片段聚集在同一个片段簇:最后从XML文档片段簇中抽取关系实例及其出现模式.实验结果表明,对于包含有意义标签的各种XML文档,该方法能够准确地识别和抽取出描述指定实体之间联系的各种关系信息.     

Photoelastic Effects in Silicate Glasses

The photoelasticity of R_nO_mSiO₂(R_nO_m=Li₂O, Na₂O, K₂O, and ZnO), Li₂O-Al₂O₃-SiO₂, Na₂O-Al₂O₃-SiO₂, and Na₂O-ZnO-SiO₂ glasses was analyzed on the basis of the following equation relating the stress-optical coefficient and the strain-optical coefficient:
where C is the stress-optical coefficient, n is the refractive index, G is the shear modulus, pI2and pI1are the Pockels strain-optical coefticients, and p and q are the Neumann strain-optical coefficients. No simple relation was found between the stress-optical coefficient and the shear modulus, and the factor (p−q) was found to be an essential factor deter- mining the stress-optical coefficient of silicate glasses. It was found that (p−q) decreases markedly with increasing content of modifier oxide, and that the change of (p − q) with composition is governed by the change of the atomic effect, while the lattice effect does not change as much. It is argued that the bridging oxygen with covalent bonds increases the atomic effect and the nonbridging oxygen with ionic bonds reduces the atomic effect.