The cross-entropy (CE) method is an adaptive importance sampling procedure that has been successfully applied to a diverse range of complicated simulation problems. However, recent research has shown that in some high-dimensional settings, the likelihood ratio degeneracy problem becomes severe and the importance sampling estimator obtained from the CE algorithm becomes unreliable. We consider a variation of the CE method whose performance does not deteriorate as the dimension of the problem increases. We then illustrate the algorithm via a high-dimensional estimation problem in risk management. 相似文献
Personal ties are generally regarded as important to big business growth in Malaysia, particularly after the New Economic Policy (NEP) in the 1990s. Common types are informal ones established between multi-ethnic big business people and Malay key state and political leaders. Other types of ties, company directorship links and informal ties, are seldom studied especially those between the business people and former state bureaucrats and corporate professionals. Thus, by conceptualising the directorship links and informal personal ties as social networks, the author conducted a sociological analysis of some intra- and inter-ethnic directorship links and ties established by four prominent big businessmen after the NEP in the 1990s. This article reports the main finding on the links and ties becoming a common organisational mechanism of business groups owned and controlled by the businessmen, besides providing access to the state. Therefore, another understanding of inter- and intra-ethnic personal ties in big business growth, especially after the NEP is achieved. 相似文献
Estimation of the time-average variance constant (TAVC) of a stationary process plays a fundamental role in statistical inference for the mean of a stochastic process. Wu (2009) proposed an efficient algorithm to recursively compute the TAVC with \(O(1)\) memory and computational complexity. In this paper, we propose two new recursive TAVC estimators that can compute TAVC estimate with \(O(1)\) computational complexity. One of them is uniformly better than Wu’s estimator in terms of asymptotic mean squared error (MSE) at a cost of slightly higher memory complexity. The other preserves the \(O(1)\) memory complexity and is better then Wu’s estimator in most situations. Moreover, the first estimator is nearly optimal in the sense that its asymptotic MSE is \(2^{10/3}3^{-2} \fallingdotseq 1.12\) times that of the optimal off-line TAVC estimator. 相似文献
High population growth in the tropics is driving urbanisation, removing diverse natural ecosystems. This is causing native species to suffer while introduced synanthropes flourish. City planners are developing urban greenspace networks, in part trying to address this issue. Architects contribute to these greenspace networks by designing elevated and ground level green spaces on large-scale buildings. However, little evidence is available on whether building green spaces support native fauna. This is true for birds in tropical Singapore that support important ecosystem services and have existence value. Therefore, in this study, we conducted bird surveys and statistical analyses to determine, if and how vegetation on three building green space types (ground gardens, roof gardens and green walls) have a positive impact on native or introduced bird species. We found that elevated greenery (roof gardens and green walls) on large-scale buildings supported a higher richness of birds and abundance of urban native birds than control roofs and walls without vegetation. Ground gardens supported similar levels of native species as roof gardens but also a larger proportion of generalist synanthropes. However, we found no tropical forest habitat specialists across any space type. Therefore, we recommend roof gardens and ground gardens as a potential space for urban natives outside of a less competitive ground-level urban environment. Our study also found certain building design elements (height of elevated space, presence of specific plants) supported different species groups. Therefore, we suggest that these ecological requirements for different species groups are considered when designing a building’s green space.
Urban Ecosystems - Anthropogenic noise may mask effective vocal signal transmission by birds, particularly in notes occurring in lower frequencies. Previous studies have shown a correlation of... 相似文献
Recent migration studies have adopted the lens of mobility to examine the stratifying effects of border policies, but few investigate the differential mobility of migrant families and children. This paper aims to contribute to the migration literature by considering the interplay between border policies, family configurations, and differential mobility. We apply the lens of differential mobility to the experiences of Chinese cross-border pupils – young child migrants with Hong Kong permanent residency who reside in Shenzhen, China, and cross the border to attend school. We begin by describing shifts in Hong Kong’s border and immigration policies since 1997, which have created a typology of families differentiated by mixed status, citizenship rights, and mobility. We then turn to four case studies of students with unequal border-crossing experiences to elucidate how border control constrains or promotes family mobility and perpetuates inequalities. 相似文献
This article presents narratives and tropes of transnational tourism from a less considered perspective: rural migrant-origin villagers of Central Java. Drawing from ethnographic fieldwork conducted in Cilacap and Yogyakarta, I analyze how and why some former temporary labor migrants depict their typically harsh experiences in terms of tourism and leisure. Addressing the tendency in current research to approach labor migration and tourism as mutually exclusive or unrelated class categories and experiences, I consider the ways in which former migrants and non-migrant villagers evaluate or identify labor migration in terms of gender, class, religious, and ethno-national subjectivities associated with ‘tourist’ and/or ‘migrant’ categories. Popular and commercial imaginations of leisure travel and tourism importantly shape the subjectivities and positionalities of precarious labor migrants. Foregrounding the relations between tourism and labor migration reveals the multi-scalar ways in which associated discourses and infrastructures of both mutually shape and constitute global socio-economic inequalities. 相似文献
Career counselors must continually enhance their knowledge and skills to assist clients contemplating careers in science, technology, engineering, and mathematics (STEM). Therefore, the authors review STEM disciplines and theory‐driven strategies for assisting diverse individuals to explore, enter, and persist in STEM careers. Appropriate use of career assessments can contribute greatly to this effort. To identify available measures for STEM‐focused domains and constructs, the authors conducted a journal content analysis of stand‐alone STEM‐related career assessments from 1983 to 2016, identifying 39 articles with 153 measures. Notable results included the emergence of social cognitive theory and social cognitive career theory as prevailing frameworks for instrument development, a wide variety of disciplines and journals represented, an underrepresentation of minority samples, and untapped potential for cross‐discipline and researcher–practitioner collaboration. Useful strategies and resources for counselors and recommendations for enhancing career assessments and interventions are addressed. 相似文献