射频六端口OFDM解调器研究

该文提出了一种新的基于射频六端口网络的多频带OFDM解调器。推导了该解调器的数学模型,仿真了用于WLAN802.11a通信系统时,射频六端口网络的本振电平、输入信号电平对解调器性能的影响。研究了射频六端口网络中正交电桥和同相电桥分别存在相位幅度不平衡时和同时存在相位幅度不平衡时解调器误差矢量幅度的特性。讨论了解调器的动态范围、接收性能等指标。结果表明结合当前的MMIC集成水平,使用射频六端口网络可以实现多频带、多制式、多载波的OFDM解调器。     

ON BOOTSTRAP HYPOTHESIS TESTING

We describe methods for constructing bootstrap hypothesis tests, illustrating our approach using analysis of variance. The importance of pivotalness is discussed. Pivotal statistics usually result in improved accuracy of level. We note that hypothesis tests and confidence intervals call for different methods of resampling, so as to ensure that accurate critical point estimates are obtained in the former case even when data fail to comply with the null hypothesis. Our main points are illustrated by a simulation study and application to three real data sets.     

一种准最佳数字传输系统的性能分析与实现

提出一种在数字传输系统中易于实现的发、收滤波器特性的准最佳分配方案:将信道升余弦滚降特性和宽码输入补偿网络特性都以平方根形式均分于发、收两端。分析和计算了这种系统的等效信噪比损失;用计算机优化方法设计了形成滤波器;最后计算了此系统残存符号间干扰所引起的损失。     

一种适用于无线ATM通信的差错控制方案

研究了无线ＡＴＭ通信的差错控制方案，提出了应根据多媒体业务类型、速率等参数，以及移动环境等，自适应地选择合适的差错控制技术和参数的思想。文中提出的差错控制方案主要包括ＦＥＣ（可变深度的交织、卷织码、ＢＣＨ码）和限时／非限时ＳＡＲＱ等技术，计算机仿真结果表明了所提方案的有效性。     

The selection of zero-non-zero patterned cointegrating vectors in error-correction modelling

An effective and efficient search algorithm has been developed to select from an 1(1) system zero-non-zero patterned cointegrating and loading vectors in a subset VECM, B^q(l)y(t-1) + B^q-1 (L)Ay(t) = ε( t ) , where the long term impact matrix Bq(l) contains zero entries. The algorithm can be applied to higher order integrated systems. The Finnish money-output model presented by Johansen and Juselius (1990) and the United States balanced growth model presented by King, Plosser, Stock and Watson (1991) are used to demonstrate the usefulness of this algorithm in examining the cointegrating relationships in vector time series.     

Do Drivers of Small Cars Take Less Risk in Everyday Driving?

Previously reported observed data on risky everyday driving are brought together and reanalyzed in order to focus on the relation between risky driving and the size of the car being driven, as indicated by car mass. The measures of risky driving include separation between vehicles in heavy freeway traffic and speed on a two lane road. Observed seat belt use provides a third measure of driver risk. Confounding effects arising from the observed association between car mass and driver age are taken into account by segmenting the data into three driver age groups. Driver risk taking is found to increase with increasing car mass for each of these three aspects of everyday driving. The implications of these results with respect to driver fatality rates are discussed in terms of a simple model relating observed risky driving to the likelihood of involvement in a severe crash.     

定位误差的简明计算研究

主要阐述了定位误差的基本概念和分析计算方法，并举例说明其运用.     

Women's Scientific Employment and Family Formation: A Longitudinal Perspective

We focus here on the retention of highly qualified women scientists in science‐based employment in England and Wales. Using linked Census records from the Longitudinal Study 1971–1991 we show that women's education and employment rates in science, engineering and technology increased somewhat, although some fields show persistently low representation. We then compare retention in employing women with health‐related degrees with that of women with degrees in science, engineering and technology, showing that the latter group has markedly lower retention rates. Those who stay on in science‐based employment have children later than other types of graduate and their rates of non‐motherhood are higher. Four‐fifths of women in health‐related occupations were mothers, compared to only two‐fifths in science, engineering and technology. Our findings have implications for policymakers who wish to make best use of the knowledge base: attention should be paid to retention, as well as the more usual focus on qualifications and recruitment. The findings also suggest the potential for institutionally based theories to explain why highly qualified women have such low retention rates in science‐based employment.     

从尘埃里开出花来——论张爱玲小说中的“居室经验”

以文本细读为研究方法,分析了张爱玲小说中具有古旧风韵的“居室经验”,指出其“居室经验”具体体现为败落的家庭生活场景、旧势家族的“礼仪道德”以及冰冷的人情感受,所以,“居室经验”是张爱玲小说中最有意味的部分,也是其民间姿态的一种坚守方式。     

A new class of measurement-error models,with applications to dietary data

Measurement-error modelling occurs when one cannot observe a covariate, but instead has possibly replicated surrogate versions of this covariate measured with error. The vast majority of the literature in measurement-error modelling assumes (typically with good reason) that given the value of the true but unobserved (latent) covariate, the replicated surrogates are unbiased for latent covariate and conditionally independent. In the area of nutritional epidemiology, there is some evidence from biomarker studies that this simple conditional independence model may break down due to two causes: (a) systematic biases depending on a person's body mass index, and (b) an additional random component of bias, so that the error structure is the same as a one-way random-effects model. We investigate this problem in the context of (1) estimating distribution of usual nutrient intake, (2) estimating the correlation between a nutrient instrument and usual nutrient intake, and (3) estimating the true relative risk from an estimated relative risk using the error-prone covariate. While systematic bias due to body mass index appears to have little effect, the additional random effect in the variance structure is shown to have a potentially important effect on overall results, both on corrections for relative risk estimates and in estimating the distribution of usual nutrient intake. However, the effect of dietary measurement error on both factors is shown via examples to depend strongly on the data set being used. Indeed, one of our data sets suggests that dietary measurement error may be masking a strong risk of fat on breast cancer, while for a second data set this masking is not so clear. Until further understanding of dietary measurement is available, measurement-error corrections must be done on a study-specific basis, sensitivity analyses should be conducted, and even then results of nutritional epidemiology studies relating diet to disease risk should be interpreted cautiously.