Further comments on ‘A simple criterion for stability of linear discrete systems’

Some additional comments are offered on the stability condition for linear discrete systems in Dabke (1983). It is pointed out that the condition can be naturally extended to cover time-varying systems.     

高温加压气流床内生物质气化特性的实验研究

在15～20 kg/h规模的沉降式加压气化实验装置上,实验研究了高温条件下,不同O/C摩尔比对生物质气化特性的影响,并根据实验气化炉的边界条件,建立了相应的气化模型.模型计算结果与实验结果吻合较好,模型能够很好的预测气化参数对生物质气流床气化特性的影响.研究结果袁明:在气化还原反应区,高温有利于气化反应向吸热方向进行;O/C比在1.0～2.0范围内,随O/C比的增加,CO、H2均呈现先增加后减小的趋势,可燃气体成分(CH4 H2 CO)占总合成气的50%左右;部分燃烧反应区温度在1600 K以上时,碳转化率大于90%,冷煤气效率达到50%左右.     

Properties of hydrogels synthesized by freezing and thawing aqueous polyvinyl alcohol solutions and their applications

The hydrogel synthesized by freezing a polyvinyl alcohol (PVA) aqueous solution and thawing it slowly has high water content, excellent mechanical properties of high tensile strength, elongation and good shape recovery by elasticity. The PVA used had a degree of polymerization of 2500 and a degree of saponification of 99.5 mol%. The solution was obtained by dissolving 7.5 g of PVA in 80 g of water, this was frozen at –50°C for 3 h and then warmed up to room temperature over 10h. This freezing–thawing process was repeated once again and a hydrogel was synthesized. The hydrogel had a water content of about 90 wt%. Its tensile strength was 0.6 MPa and the elongation at break was 130%. The shape of the hydrogel which was deformed by an external force recovered in a short time when it was released from the force. This recovery had good persistence and repeatability. Applying these properties a strain sensor and a gas pressure sensor were tested. Furthermore, a PVA hydrogel rod containing polyacrylic acid was used as a bending actuator. This hydrogel had the ability to deform when direct current was applied.