螺旋天线宽带阻抗匹配技术的研究

介绍了一种用渐变镜像传输线阻抗变换器来实现螺旋天线与50Ω馈线之间的宽带匹配技术.实验结果表明,采用渐变镜像传输线阻抗变换器能在2:1的频带范围内实现 ρ<2.     

Immigration,Ethnicity, and Conflict: The California Chinese, 1849–1882*

Drawing on Bonacich's split market theory, the work of Hechter and Blalock on ethnic conflict, and the literature on social movements, the authors develop a model of factors producing conflict between native and immigrant workers. The model identifies the relative size of the immigrant group, the growth of the immigrant population, the desirability of jobs held by immigrant workers, economic conditions, the development of racist ideology among native workers, and the organization of native workers as factors possibly explaining the frequency of incidents of overt ethnic conflict and efforts to institutionalize discrimination through government action. The model is assessed by examining the situation of Chinese immigrants in California between 1849 and 1882. The data suggest that poor economic conditions, a well-developed racist ideology, and well-organized native workers best explain incidents of ethnic conflict and successful efforts to obtain discriminatory government action.     

A note on information loss in analyzing a mixture model of count data

In this note we consider estimation of a mixture model of count data which is composed of two discrete random variables. Conditional and unconditional estimation procedures are given for estimating the unknown parameter(s) of interest using the likelihood function. Asymptotic relative efficiencies are given to examine the amount of information loss in using the two estimation procedures. Specifically, we study the change in asymptotic relative efficiency, if any, in different parameter settings.     

Linking dichotomous segregation with multi-group segregation: Weighted segregation ratios in selected U.S. metropolitan areas

The U.S. residential landscape is increasingly multi-racial and multi-ethnic, giving rise to the question of how to compare dichotomous segregation among multiple groups living in the same area. To address the problem in the existing dichotomous approach, which offers no common basis for comparing dichotomous segregation among multiple groups, this paper develops a weighted segregation ratio approach based on Theil’s segregation index and its additive decomposability. This approach can be used to bridge information obtained from dichotomous segregation between specific groups (such as black-white and black-Hispanic), and dichotomous segregation between group and non-group (such as white-non-white and black-non-black) in previous studies. We apply both dichotomous and weighted segregation ratio approaches to 1990 and 2000 U.S. census data. Results are interpreted for five selected metropolitan areas as well as for the weighted national average. This new approach yields distinctive findings that portray the complicated process of residential segregation, including the increasing significance of Hispanic segregation and Asian segregation in the decade from 1990 to 2000.     

Out of Sight,Out of Mind? Patterns of Transnational Contact Among Chinese and Indian Immigrants in Toronto1

There has been considerable discussion in recent decades about the integration patterns of new immigrants. Recognizing advancements in technology and the increased economic integration of countries, some researchers have suggested that the emerging integration trend for immigrants is the transnational pattern, whereby immigrants maintain contact with the home countries. To advance the discussion, this study focuses on general transnational contact, a basic form of transnational activity. The study draws from recently collected large‐scale survey data to explore the patterns of transnational contact within two recent immigrant groups, Asian Indians and Chinese, in Toronto. Our findings show that only a small percentage of immigrants maintain intensive and extensive transnational contact. As well, our findings are less consistent with the transnational perspective than with the assimilation perspective on the effects of socioeconomic background on transnational contacts.     

Borrowing Information across Populations in Estimating Positive and Negative Predictive Values

A marker's capacity to predict risk of a disease depends on disease prevalence in the target population and its classification accuracy, i.e. its ability to discriminate diseased subjects from non-diseased subjects. The latter is often considered an intrinsic property of the marker; it is independent of disease prevalence and hence more likely to be similar across populations than risk prediction measures. In this paper, we are interested in evaluating the population-specific performance of a risk prediction marker in terms of positive predictive value (PPV) and negative predictive value (NPV) at given thresholds, when samples are available from the target population as well as from another population. A default strategy is to estimate PPV and NPV using samples from the target population only. However, when the marker's classification accuracy as characterized by a specific point on the receiver operating characteristics (ROC) curve is similar across populations, borrowing information across populations allows increased efficiency in estimating PPV and NPV. We develop estimators that optimally combine information across populations. We apply this methodology to a cross-sectional study where we evaluate PCA3 as a risk prediction marker for prostate cancer among subjects with or without previous negative biopsy.     

Mathematical analyses of casino rebate systems for VIP gambling

In Macao, the VIP gaming revenue accounts for over two thirds of the total gaming revenue. Since the VIP gaming market is highly competitive, several incentives such as rebates are used to attract the VIP players. There are two commonly used rebate systems in the VIP gaming market: rebate on buy-in and rebate on actual loss. The analysis of rebate on buy-in is relatively easy. However, the analysis of rebate on actual loss is more complicated, which involves the Unit Normal Linear Loss Integral. Using empirical data, MacDonald derived a simple approximation formula for computing the rebate rate on actual loss. In this paper, we use mathematical analysis to derive more accurate approximation formulas for computing the rebate rate on actual loss. Some practical examples are given to compare the accuracies of these formulas. We also discuss how these two rebate systems affect the fluctuations of the results.     

Impact of Community on Personal Well-Being in Urban China

ABSTRACT

As the work-unit system fell after economic reform in China, neighborhoods replaced work units as the primary provider of vital social services for the urban population and became a new social space for enhancing the quality of people's well-being. This study examined the neighborhood characteristics that influenced personal well-being of residents. Drawn by multistage sampling and administered by face-to-face interviews, the survey included a sample of 976 participants from 31 neighborhoods in urban Shanghai. Results indicate that neighboring behaviors enhanced subjective well-being of the young and middle-aged residents but had no impact on older people. Sense of community, on the other hand, was found to contribute to well-being of all age groups and was particularly strong among older people in more deprived neighborhoods. Findings inform development of community practice strategies for vitalizing community efficacy and fostering individual well-being in urban China. Recommendations for future research are made using the results of this study.     

Neighborhood change within the Canadian ethnic mosaic, 1986–1991

This paper examines the neighborhoodpatterns in three major Canadian metropolitan areasbetween 1986 and 1991. Data are obtained from 1986 and1991 profile census files and two Special Tabulationsof 1986 and 1991 Canadian census. The data indicatethat the first pathway of neighborhood change is thediversification that takes place among charter-onlyneighborhoods with the introduction of a sizableEuropean presence, followed by Asians and then blacks. The second pathway featuring racial uniformityprimarily takes place in multi-ethnic neighborhoodscontaining one or more visible minority groups. Multivariate analysis suggests that the increase inracial and ethnic diversity in neighborhoods isrelated to the efforts of visible minorities,especially Asians, seeking out neighborhoods withEuropeans.     

An Unfinished Reflexive Journey: Social Work Students' Reflection on their Placement Experiences

The fieldwork placement is recognized as one of the major componentsof social work education and a major determinant of its quality.A key aspect of the learning process in the fieldwork placementis the exposition of practice encounters to the students’critical reflection. Given the importance of the process of‘reflection’ or ‘reflective learning’,a qualitative study based on the reflective logs of social workstudents was conducted to explore the meaning of social workfield education and the learning experiences of social workstudents during their placement. The study findings revealedthat disturbing events experienced by students in their fieldworkwere a catalyst to their reflective process. Meanwhile, theirundue concern with knowledge and skills application within acircumscribed knowledge frame suggests the dominant influenceof scientism and competence-based practice in social work, inwhich learning outcomes and instrumental and technical reasoningare highly emphasized. Discovery of ‘self’ was alsothe major premise in the students’ reflection logs, inwhich a majority of them took their prevailing self-identityas a constant state to be verified in interaction with othersin the fieldwork placement. Reflexivity is manifested in askingfundamental questions about assumptions generated by formaland practice theories; it addresses the multiple interrelationsbetween power and knowledge, and acknowledges the inclusionof self in the process of knowledge creation in social workpractice. Its realization in social work education requiresthe social work educators’ reflexive examination of thedynamics that influence the construction of curriculum, whichin turn construct our prospective social workers.