Fast radix-p discrete cosine transform

A new fast radix-p-algorithm (p 2) for the discrete cosine transform (DCT) and its inverse is presented. It is based on the divide-and-conquer method and on the arithmetic with Chebyshev polynomials. The algorithm can be applied for the efficient calculation of DCT's of arbitrary transform lengths and for the implementation of other discrete Vandermonde transforms withO(N logN) arithmetical operations.     

《自动控制原理》课程中闭环脉冲传递函数算法研究

针对一般方法推导离散系统闭环脉冲传递函数过程繁琐费时的问题,给出一种先连续化求出闭环传递函数再离散化求解的简便方法,并给出使用本方法的单一化条件。对于满足该条件的系统,可直接求用简便方法求取系统的闭环脉冲传递函数,不满足该使用条件的系统,对其中间变量的求取可使用本方法,因而大大简化求解闭环脉冲传递函数的过程,为采样控制系统的分析和设计提供了很大的方便。     

Discrete logarithms inGF(p)

Several related algorithms are presented for computing logarithms in fieldsGF(p),p a prime. Heuristic arguments predict a running time of exp((1+o(1)) ) for the initial precomputation phase that is needed for eachp, and much shorter running times for computing individual logarithms once the precomputation is done. The running time of the precomputation is roughly the same as that of the fastest known algorithms for factoring integers of size aboutp. The algorithms use the well known basic scheme of obtaining linear equations for logarithms of small primes and then solving them to obtain a database to be used for the computation of individual logarithms. The novel ingredients are new ways of obtaining linear equations and new methods of solving these linear equations by adaptations of sparse matrix methods from numerical analysis to the case of finite rings. While some of the new logarithm algorithms are adaptations of known integer factorization algorithms, others are new and can be adapted to yield integer factorization algorithms.     

基于离散单元法的锥形双螺杆输送及混合机理分析

锥形双螺杆挤出机结构模型与其他普通螺杆挤出机相差很大且构成独特,近年来在聚合物加工行业中发挥了很大的作用。设计螺槽深度与螺杆半径比为1∶2、2∶5、1∶3的三种锥形双螺杆挤出机,通过离散单元法模拟了锥形双螺杆挤出机挤出LDPE、HDPE两种颗粒的过程,分析了锥形双螺杆挤出机螺槽内颗粒速度的变化,同时在不同参数下对三种锥形双螺杆挤出机的输送效率进行了比较。利用EDEM软件对LDPE和HDPE颗粒进行离散元分析,得出不同时刻两种颗粒在三种锥形双螺杆挤出机内的混合情况。结果表明,螺槽深度与螺杆半径比为1∶2的锥形双螺杆挤出机的混合效率优于螺槽深度与螺杆半径比为2∶5、1∶3的锥形双螺杆挤出机。     

Prediction of particle motion in a two-dimensional bubbling fluidized bed using discrete hard-sphere model

The solids motion in a gas-solid fluidized bed was investigated using a discrete hard-sphere model. Detailed collision between particles and a nearest list method are presented. The turbulent viscosity of gas phase was predicted by subgrid scale (SGS) model. The interaction between gas and particles phases was governed by Newton's third law. The distributions of concentration, velocity and granular temperature of particles are obtained. The radial distribution function is calculated from the simulated spatio-temporal particle distribution. The normal and shear stresses of particles are predicted from the simulated instantaneous particle velocity. The pressure and viscosity of particles are obtained from both the kinetic theory of granular flow and the calculated stresses of particles. For elastic particles the individual lateral and vertical particle velocity distribution functions are isotropic and Maxwellian. The observed anisotropy becomes more pronounced with increasing degree of inelasticity of the particles.     

考虑水软化-化学风化作用的岩石单轴压缩试验离散元模拟

西南地区以岩石地形为主,较为潮湿。而岩石在工程长期运行中,会受到水和化学风化作用的影响,分别表现出软化、强度降低以及力学性能劣化的特性。因此研究岩石在水、化学风化作用影响下的力学性质极其重要。本文采用离散单元法(DEM)模拟水软化-化学风化因素作用下岩石的单轴压缩试验,得到应力应变曲线以及破坏后微观信息图,从宏微观角度分析岩石受水、化学风化作用下力学性质,破坏模式的变化。模拟结果表明:随着岩石饱和度的增加,岩石的峰值强度、弹性模量不断减小,破坏模式由压剪扭破坏为主逐渐转变为拉剪扭破坏为主;随着化学风化程度增大,岩石峰值强度也随之减小,脆性破坏特征越来越不明显,与室内试验结果相吻合。     

A novel algorithm for layout optimization of injection process with random demands and sequence dependent setup times

Injection molding is an ideal manufacturing process for producing high volumes of products from both thermoplastic and thermo setting materials. Nevertheless, in some cases, this type of manufacturing process decelerates the production rate as a bottleneck. Thus, layout optimization plays a crucial role in this type of problem in terms of increasing the efficiency of the production line. In this regard, a novel computer simulation–stochastic data envelopment analysis (CS-SDEA) algorithm is proposed in this paper to deal with a single row job-shop layout problem in an injection molding process. First, the system is modeled with discrete-event-simulation as a powerful tool for analyzing complex stochastic systems. Then, due to lack of information about some operational parameters, theory of uncertainty is imported to the simulation model. Finally, an output-oriented stochastic DEA model is used for ranking the outputs of simulation model. The proposed CS-SDEA algorithm is capable of modeling and optimizing non-linear, stochastic, and uncertain injection process problems. The solution quality is illustrated by an actual case study in a refrigerator manufacturing company.     

模糊学在点火元件优选中的应用

评价了点火元件的综合性能。文中的点火元件优选工作是模糊概念应用在工程中的尝试。综合评价结果与实际相符合。     

Avalanching flow of cohesive powders

The flow dynamics of cohesive powders is investigated in rotating cylinders with an L : R ratio of 3 : 1 using experiments and DEM simulations. Flow onset and steady-state behavior are compared for free-flowing (cohesionless) dry glass beads, wet glass beads, and “dry” cohesive powders (lactose, microcrystalline cellulose). The avalanching dynamics of powders is substantially different from those observed for free-flowing or wet-cohesive glass beads. Dry cohesive powders exhibit history-dependent flow dynamics, significant dilation, aperiodic avalanche frequencies, and variable avalanche size. These behaviors also provide a route for effective characterization of cohesive forces under dilated conditions characteristic of unconfined flows.     

一种新的基于压缩传感理论解决Pan-Sharpening问题的算法

Pan-Sharpening问题是将高分辨率全色图像和低分辨率多光谱图像融合,重构出高分辨率多光谱图像的过程。压缩传感理论解决了相应目标函数的稀疏解问题(求解含有l0范数的极小化问题)。利用压缩传感理论,提出一种新的解决Pan-Sharpening问题的算法:以离散余弦变换矩阵作为字典进行重构。然后针对重构过程中产生的块效应、色彩偏差和洗涤效应等问题进行相应的处理。QuickBird卫星图像的实验结果表明:与经典算法进行对比,该算法在效果上有一定的优势。