沙漠生物结皮土壤发育特征的研究

通过对沙漠生物结皮层相关的土壤特性研究表明,结皮层不仅具有明显的养分富集和细粒物质的聚集作用,而且结皮层腐殖质成份的含量以及其分子结构和复杂程度也在增加。腐殖质光学特性的变化趋势明显反映了不同地区结皮层土壤发育的地带性特征。结皮层持水量明显高于沙层,并对降水再分配有一定影响。     

Frequency shift keyed narrowband interference rejection: optimal exponential weighting factor for the RLS algorithm

Cochannel narrowband interference can limit the performance of direct sequence spread spectrum (DSSS) and high frequency (HF) systems. Narrowband interference (NBI) can be single tone, chirped or frequency shift keyed (FSK) in nature and numerous techniques for its removal have been proposed. Linear adaptive prediction filters based on autoregressive modelling have been suggested owing to their ability to perform in a non-stationary environment. In the FSK narrowband interference case, adaptive filters are susceptible to excess residual errors owing to instantaneous frequency step changes and the finite convergence time required for the filter to adapt to a new interference frequency. The signal degradation owing to this type of interference becomes greater in high SNR regimes and has been found to be a function of the frequency parameters of the FSK interference signal. The paper discusses the convergence and frequency tracking properties of the recursive least squares (RLS) adaptive lattice filter using a posteriori estimation errors in the presence of FSK narrowband interference. An optimal exponential weighting factor that balances convergence time and steady state error is derived for this case of NBI. Results are compared to those of a previously proposed fast converging minimum frequency error (FCMFE) RLS lattice filter.     

Effect of Wall Surface Properties at Different Drying Kinetics on the Deposition Problem in Spray Drying

Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem.     

基于遗传算法的土钉支护结构优化设计研究

通过建立三维有限元模型,对土钉支护的变形和受力性能进行分析,得出土钉力的合理分布。在此基础上,考虑土钉支护的水平位移,采用遗传算法,对土钉支护的结构优化设计进行研究,建立了土钉支护结构的优化设计数学模型,并编制了相应的计算程序。通过算例分析,并与基于极限平衡分析的优化结果相比较,得出合理的土钉支护结构设计的参考结论。     

One-to-Many and Many-to-One Optical Chaos Communications Using Semiconductor Lasers

A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications.     

Sandwich panels with Kagome lattice cores reinforced by carbon fibers

Stretching dominated Kagome lattices reinforced by carbon fibers were designed and manufactured. The sandwich panels were assembled with bonded laminate skins. The mechanical behaviors of the sandwich panels were tested by out-of-plane compression, in-plane compression and three-point bending. Different failure modes of the sandwich structures were revealed. The experimental results showed that the carbon fiber reinforced lattice grids are much stiffer and stronger than foams and honeycombs. It was found that buckling and debonding dominate the mechanical behavior of the sandwich structures, and that more complaint skin sheets might further improve the overall mechanical performance of the sandwich panels.     

Fast-converging minimum frequency error RLS lattice filter for narrowband interference with discrete frequency steps

This paper discusses the fundamental convergence and frequency tracking properties of the recursive-least-squares (RLS) lattice filter in the presence of narrowband interference (NBI) whose frequency varies in discrete steps. It is shown for filters of this type, that the residual forward energy (RFE) after a frequency transition is a function of the input signal-to-noise ratio (SNR), separation of the sequential frequencies and the filter time constant and is exponentially decaying in nature. Reducing the RFE is important in removing unwanted transient artefacts from the desired signal. The convergence behaviour of the RLS algorithm based on a posteriori estimation errors is analysed under a number of conditions by varying the SNR and frequency step size. In order to limit the impact of the RFE while maintaining a minimum frequency tracking error in steady conditions, a fast-converging minimum frequency error (FCMFE) RLS lattice filter is suggested. For comparison, a least-mean-square (LMS) based gradient-adaptive lattice (GAL) filter is also analysed for this class of narrowband interference.     

基于进化规划的自适应IIR滤波

针对基于梯度下降算法的自适应IIR滤波器（AIIRF）具有潜在的不稳定性和性能指标函数容易陷入局部极小而导致性能下降等问题，本文将进化规划用于AI－IRF的优化设计，不仅解决了AIIRF系统稳定性问题，而且有效地实现了滤波器性能指标函数的全局寻优和快速收敛，同时允许大动态范围的输入号。计算机仿真结果验证了基于进化规划算法的AIIRF的性能优于基于梯度算法的AIIRF，尤其对高阶、极点靠近单位圆的自适应IIR滤波器。     

Determination and interpretation of fractal properties of the sandstone pore system

A knowledge of fractal properties of the pore system is extremely useful with regard to the interrelationships between moisture transport and pore structure. The fractal dimension characterises the egree of resolutiondependence of a property. Given a completely interlaced pore system such as that of sandstone, the fractal dimension of the pore volume, or the porosity, quantifies the cross-sectional variability of the pore channels and is thus of great relevance with regard to transport processes. The fractal dimension of the pore surface describes the surface roughness. A newly-developed measuing technique is presented for the simultaneous determination of fractal dimensions of porosity and pore surface and for establishing fraction radii distributions in order to derive relevant parameters for moisture transport.