干扰对河口湿地生态系统的影响分析

对河口湿地生态系统所受到的自然干扰和人为干扰进行了系统辨识.重点分析了海平面上升、台风暴潮等自然干扰,围垦、大型海岸工程(填海、码头建设等)、环境污染和保护区建设等人为干扰对河口湿地生态系统结构和功能的影响.通过分析认为:人为干扰已成为河口湿地景观演变的主要驱动力,河口湿地生态系统健康发展需要加强对各种干扰的合理调控.     

数据库自然语言查询条件研究

通过对汉语查询句的研究,建立了复合概念、逻辑概念与标准概念的内在联系.通过分析各种查询条件,得出查询条件表达式可以形式化表示为二叉树的结论,在此基础上,构造了查询条件字符块转换为二叉树的一套算法.     

具有长条型内边界外问题的耦合法

本文以具有长条型内边界的二维调和外问题为例，研究一种带有椭圆人工边界的自然边界元与有限元耦合法，给出耦合变分问题的适定性及近似解的误差估计．理论分析及数值结果表明，用该方法求解带长条型内边界的外问题是十分有效的．     

自然数幂和公式系数的递推公式和有关Bernoulli数的计算公式

研究了自然数幂和的表示公式,给出了其系数的一个递推关系式;利用递推关系式,得到幂和的各项系数,并由幂和公式的系数得到了计算Bernoulli数的几个计算公式.     

孔边位移边界条件下的应力分析

根据自然边界元方法给出的圆外弹性问题应力解答,利用Poisson积分公式和自然边界积分方程求出多种形式位移边界条件下的位移场、应变场和应力场,并分析了位移边界条件对应力场的影响。同时与其他计算方法相比较,在边界位移为常数时其结果与文献[2]的解答一致。从本文的算例中不难发现,采用自然边界元方法计算圆外问题时,可以克服一般解析方法只能求解少数特殊位移边值问题的缺点。由于其结果仍为解析解,因此精度也优于数值解答。     

Pattern formation in Rayleigh-Bénard convection: Numerical simulation with a coupled-map-lattice model

The various patterns formed in Rayleigh-Bénard convection under different conditions are numerically simulated with a coupled-map-lattice model. In the case of a lower aspect ratio (L/d=5), the simulations vividly depicted the main features of the transition process from a laminar state to a soft turbulence and then to a hard turbulence. In this case, the cellular structure in a horizontal section is also reproduced. In the case of a larger aspect ratio (L/d=30), the simulations successfully reproduced the spiral-defect chaos and target chaos in the initial stage of the pattern evolution which were recently found in experiments. In this case, for a fluid ofPr=1, it is verified in simulations that both the ideal straight rolls and spiral-defect chaos are stable attractors in the same parameter regime, and that the initial condition is a decisive factor for which one of the two is formed. In the same case, for a fluid ofPr=4, the target patterns are dominant instead of the spirals, the sizes and distributions of the target are also notably dependent on the initial condition.     

大跨度斜拉索输油管桥模型固有振动的实验研究

建立了大跨度斜拉索输油管桥模型实验的相似条件，并以某大跨度管桥为例，采用两种不同的边界条件，对某大跨度斜拉索输油管桥固有振动进行了模型实验，通过实验，测得到了管桥的前几阶自振频率并与有关计算结果进行了比较，比较结果验证了文中的实验方法的可靠性，提出的实验方法可以用于预报类似柔性结构体系的固有振动频率。     

山梨酸钾/柠檬酸对番茄汁保藏的影响

探讨了山梨酸钾、柠檬酸分别与冷藏相结合的方法对番茄汁保藏的影响。试验结果表明:在8周的贮藏过程中,添加0.09%山梨酸钾的番茄汁,其可溶性固性物含量基本稳定,风味色泽变化不大,而添加0.03%和0.06%山梨酸钾的样品可溶性固形物下降15%。添加柠檬酸的样品与对照一样,可溶性固形物下降较大,风味色泽下降更多。所有样品维生素C含量、菌落总数均有较大下降,添加山梨酸钾的样品下降更大,说明山梨酸钾影响维生素C的保存。冷藏番茄汁时,添加0.09%的山梨酸钾更为有效。柠檬酸对番茄汁的保藏作用不大。     

D类音频功率放大器控制方式综述

D类放大器虽然具有很高的效率，但由于功率晶体管的开关工作方式，D类放大器引入的失真通常大于线性放大器，这也是目前D类放大器在音频放大领域并未得到广泛应用的主要原因。D类放大器的控制方式是影响其性能的关键因素之一，研究适合的控制方法以改善D类放大器的保真度，是近年来电力电子技术和音频功放放大领域研究的热点。文中对几种比较新颖的D类音频功放放大器控制方式进行了分析比较。     

Cryptomelane（KxMn8-xO16）： Natural active octahedral molecular sieve（OMS-2）

The Xiangtan manganese deposit (XTM) used to be considered a supergene oxide manganese ore in South China. We reported a new identification of the naturally outcropping cryptomelane by examining the physical, chemical and structural features of the XTM supergene oxide manganese ore. The MnO2 content was over 90%, K2O more than 3%, and water from 2.2%-3.1% which is similar to one in zeolite. The cell parameters of the cryptomelane were given as a0 = 0.9974 nm, b0 = 0.2863 nm, c0 = 0.9693 nm and β= 91.47°. There was a larger pseduotetragonal tunnel in the natural cryptomelane that was formed by [MnO6] octahedral double chains with aperture of 0.462×0.466 nm2, filled with K cations resulting in some Mn3+ substituting for Mn4+ to balance the negative charges of structure. The finding is important not only for prospecting manganese resources in South China, but also in application of octahedral molecular sieve of natural cryptomelane as that developed in the tetragonal molecular sieve of natural zeolite o