纤维素氨基甲酸酯溶液制备工艺研究

研究纤维素氨基甲酸酯(CC)溶液的制备工艺及其稳定性。结果表明:在-5~5℃条件下,用聚合度为350~632的纤维素浆粕合成含氮量为2.34%~3.56%的CC能很好地溶解在质量浓度为2.25~3.0 mol/L的氢氧化钠溶液中,形成淡黄色透明溶液。该溶液经过渗透处理,不仅实现了纺丝液中CC与NaOH质量比≥1的要求,且溶液的黏性、稳定性都有所提高,可直接用于纺丝。通过研究发现,尿素、氯化铝及氯化锌在一定范围内对CC有助溶作用。     

A new effective patch radius expression obtained by using a modified tabu search algorithm for the resonant frequency of electrically thick circular microstrip antennae

A new, very simple expression for the effective patch radius is presented for the resonant frequency of electrically thick circular microstrip patch antennae. It is obtained by using a modified tabu search algorithm, and is useful for the computer-aided design (CAD) of microstrip antennae. The theoretical resonant frequency results obtained by using this new effective patch radius expression are in very good agreement with the experimental results available in the literature.     

A combined heuristic approach to dynamic lot sizing problems

A combined heuristic approach for dynamic lot sizing problems has been proposed. The combined heuristic is based on the performance analysis of the Silver-Meal heuristic on different problem sizes and demand patterns. The heuristic performs extremely well on average, and has a worst case performance ratio of two.     

Digital design of variable structure control systems

Reachability conditions are developed for discrete single-input-single-output variable structure control systems described by linear mathematical models in general state-space form to reach a switching function from anywhere in state space. Stability conditions of a sliding mode are investigated. A modified algorithm is proposed to simplify the design procedure. Practical application to a thermal process has been achieved by using the modified algorithm to show the potential for development and practical results are compared with those using the classical PID controller design.     

Linear feedback control with prespecified performance measure

A novel procedure is presented to design a linear constant state feedback controller with a prespecified performance measure. The method is an iterative technique based on the sensitivity of a quadratic cost functional with respect to the feedback gains. At each iteration, a Riccati-type algebraic matrix equation is solved to compute the sensitivity expressions needed to update the feedback gains.     

Application of ferrous sulfate alleviates negative impact of cadmium in rice (<i>Oryza sativa</i> L.)

Soil contamination with toxic heavy metals [such as cadmium (Cd)] is becoming a serious global problem dueto rapid development of social economy. Iron (Fe), being an important element, has been found effective in enhancingplant tolerance against biotic and abiotic stresses. The present study investigated the extent to which different levels ofFerrous sulphate (FeSO₄) modulated the Cd tolerance of rice (Oryza sativa L.), when maintained in artificially Cdspiked regimes. A pot experiment was conducted under controlled conditions for 146 days, by using natural soil,mixed with different levels of CdCl₂ [0 (no Cd), 0.5 and 1 mg/kg] together with the exogenous application of FeSO₄at [0 (no Fe), 1.5 and 3 mg/kg] levels to monitor different growth, gaseous exchange characteristics, oxidative stress,antioxidative responses, minerals accumulation, organic acid exudation patterns of O. sativa. Our results depicted thataddition of Cd to the soil significantly (P < 0.05) decreased plant growth and biomass, gaseous exchange parameters,mineral uptake by the plants, sugars (soluble, reducing, and non-reducing sugar) and altered the ultrastructure ofchloroplasts, plastoglobuli, mitochondria, and many other cellular organelles in Cd-stressed O. sativa compared tothose plants which were grown without the addition of Cd in the soil. However, Cd toxicity boosted the production ofreactive oxygen species (ROS) by increasing the contents of malondialdehyde (MDA), which is the indication ofoxidative stress in O. sativa and was also manifested by hydrogen peroxide (H₂O₂) contents and electrolyte leakage tothe membrane bounded organelles. Although, activities of various antioxidative enzymes like superoxidase dismutase(SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) and non-enzymatic antioxidants likephenolics, flavonoid, ascorbic acid, anthocyanin and proline contents increased up to a Cd level of 0.5 mg/kg in thesoil but were significantly diminished at the highest Cd level of 1 mg/kg in the soil compared to those plants whichwere grown without the addition of Cd in the soil. The negative impacts of Cd injury were reduced by the applicationof FeSO₄ which increased plant growth and biomass, improved photosynthetic apparatus, antioxidant enzymes, minerals uptake together with diminished exudation of organic acids as well as oxidative stress indicators in roots andshoots of O. sativa by decreasing Cd retention in different plant parts. These results shed light on the effectiveness ofFeSO₄ in improving the growth and upregulation of antioxidant enzyme activities of O. sativa in response to Cdstress. However, further studies at field levels are required to explore the mechanisms of FeSO₄-mediated reduction ofthe toxicity of not only Cd, but possibly also other heavy metals in plants.