一种基于过零点的时延测量方法

信号传输时间（时延）的测量,是雷达、声纳系统的关键技术之一。本文研究了一种基于过零点的时延测量方法,在建立过零点搜索模型的基础上推导得出时延测量的测量结果表达式;定量分析了高斯白噪声条件下过零点时延测量的测量精度,得到测量误差的理论表达式。仿真与实验表明,过零点时延测量精度与信号频率、过零点数目、信噪比密切相关,当信噪比较高时,其测量精度与经典FFT法相当,而优势在于过零点时延测量的算法简单、计算量小,适用于对实时性要求较高的测量场合。     

螺杆挤压机混合能力的分析

分析螺槽中熔体的流动状态 ,运用加权平均总应变来评价螺杆挤压机的混合能力 ,进而提出提高混合能力的途径。对于单螺纹螺杆 ,稍长的计量段 ,稍浅的计量段螺槽及较高的螺杆转速 ,有利于混合作用 ;开发新型螺杆 ,如犁钉分流混合螺杆 ;研制高效混合型螺杆挤压机 ,如球窝型高效混合型螺杆挤压机     

LAG WINDOW ESTIMATION OF THE DEGREE OF DIFFERENCING IN FRACTIONALLY INTEGRATED TIME SERIES MODELS

Abstract. In this paper we consider the estimation of the degree of differencing d in the fractionally integrated autoregressive moving-average time series model ARFIMA ( p, d, q ). Using lag window spectral density estimators we develop a regression type estimator of d which is easy to calculate and does not require prior knowledge of p and q. Some large sample properties of the estimator are studied and the performance of the estimator for small samples is investigated using the simulation method for a range of commonly used lag windows. Some practical recommendations on the choice of lag windows and the choice of the window parameters are provided.     

短纤维直径对橡胶复合材料性能的影响

制备了 3种具有不同直径、相同长径比及其分布的涤纶短纤维增强氯丁橡胶基复合材料。对屈服强度及伸长率、断裂强度及伸长率以及撕裂强度等力学性能的研究发现 :在相同长径比及其分布情况下 ,与传统混合法则不同的是屈服强度和伸长率不相等 ,也不是只取决于短纤维的直径 ,而是受直径和长度的共同作用 ;在相同的纤维体积分数时 ,复合材料的断裂强度基本相同 ,而断裂形变和撕裂强度随纤维直径的减小而增大     

Product and process parameters determination for quality and cost

The purpose of this study is to conduct a concurrent product and process parameters determination for further cost reduction and quality enhancement. The process design-related parameters, such as process mean, process tolerance and product design-related parameters, such as product tolerance, are considered simultaneously in the proposed approach. To reflect the response from these three key controllable characteristics: process mean, process tolerance and product tolerance, the key measurement score, which is the sum of the mean cost, tolerance cost, quality loss and failure cost, is used to evaluate the present model. Two examples are provided for demonstrating the application of single and multiple quality characteristics.     

两步法合成大粒径丁苯胶乳

研究了聚甲基丙烯酸甲酯（MMA）对丁苯（BS）胶乳的附聚作用以增大丁苯胶乳粒径；探讨了无机盐、体系pH值及体系中MMA胶乳与BS胶乳的固含量比（R值）对附聚后丁苯胶乳的粒径及稳定性的影响。结果表明：适当添加无机盐可以稳定胶乳体系，最佳用量（质量分数）为0．1％～0．2％；适当增大体系pH值，可增大胶乳粒径；在附聚过程中，当R值在两个附聚峰附近时，可增大丁苯胶乳的粒径。     

沙棘柔性坝拦沙效应的试验研究

在野外试验基地进行了沙棘柔性坝拦沙效应试验。基于试验数据,分析了不同含沙水流条件下沙棘柔性坝对沿程含沙量及出入口悬沙粒径分布的影响,并探讨了沙棘柔性坝的阻力特性。结果表明,沙棘柔性坝对不同含沙水流的拦沙效果显著不同,对原型沙B的拦截效果最好,其次为原型沙A,最后为模型沙。对250~1 000μm粒径范围内的原型沙拦截效果最佳,且原型沙含沙量与中值粒径之间呈现正相关关系,对100~1 000μm粒径范围内的模型沙的拦截效果较好。各不同含沙水流条件下的沿程含沙量主要受沙棘柔性坝阻力的影响。本研究有助于深入理解沙棘柔性坝的拦沙效应,并对沙棘植物柔性坝这一生态工程在砒砂岩区沟道的推广应用提供理论依据。     

THIRD-ORDER ASYMPTOTIC PROPERTIES OF ESTIMATORS IN GAUSSIAN ARMA PROCESSES WITH UNKNOWN MEAN

Abstract. This paper deals with the third-order asymptotic theory for Gaussian autoregressive moving-average (ARMA) processes with unknown mean μ. We are interested in the estimation of ρ = ( α₁…, α_p, β₁…, β_q ), where α ₁…, α_ρ and β ₁…, β_q are the coefficients of the autoregressive part and the moving-average part, respectively. First, we investigate the third-order asymptotic optimality of the bias adjusted maximum likelihood estimator (MLE) of ρ in the presence of the nuisance parameters μ and ² (innovation variance). Next, for a Gaussian AR(1μ μ, ²), we propose a mean corrected estimator α_c1c2 of the autoregressive coefficient. We make a comparison between the bias adjusted estimator α_c1c2* and the bias adjusted MLE, in terms of their probabilities of concentration around the true value, or equivalently, in terms of their mean squared errors. Finally some numerical studies are provided in order to verify the third-order asymptotic theory.     

分子筛催化剂波面移动床传热特性研究

采用粉粒体传热的两区模型和微元体能量平衡理论 ,研究和分析了不同颗粒粒径的分子筛催化剂对波面移动床换热器各传热系数的影响。实验结果表明 :分子筛催化剂颗粒粒径的大小对壁面传热系数和总传热系数影响大 ,而对中央区的传热系数无影响。     

经编二元网在双加压法硝酸装置的应用

通过对双加压法硝酸装置铂网使用情况和铂网脱边事故的统计，分析了氧化炉采用平编三元网存在的问题；论述了经编二元网的特性和优点；计算了铂网的生产强度和接触时间，确定了铂网丝径；总结了硝酸装置使用经编二元网的运行效果和经济效益，结果表明，吨酸氨耗降低了2．48kg，铂耗降低了10mg，经编二元网优于平编三元网。