Estimation of HIV seroconversion and effects of age in the San Francisco homosexual population

SUMMARY Using San Francisco city clinic cohort data, we estimate the HIV seroconversion distribution by both non-parametric and parametric methods, and illustrate the effects of age on this distribution. The non-parametric methods include the Turnbull method, the Bacchetti method, the expectation, maximization and smoothing (EMS) method and the penalized spline method. The seroconversion density curves estimated by these nonparametric methods are of bimodal nature with obvious effects of age. As a result of the bimodal nature of the seroconversion curves, the parametric models considered are mixtures of two distributions taken from the generalized log-logistic distribution with three parameters, the Weibull distribution and the log-normal distribution. In terms of the logarithm of the likelihood values, it appears that the non-parametric methods with smoothing as well as without smoothing (i.e. the Turnbull method) provided much better fits than did the parametric models. Among the non-parametric methods, the EMS and the spline estimates are more appealing, because the unsmoothed Turnbull estimates are very unstable and because the Bacchetti estimates have a longer tail. Among the parametric models, the mixture of a generalized log-logistic distribution with three parameters and a Weibull distribution or a log-normal distribution provided better fits than did other mixtures of parametric models.     

基于P2P平台的流媒体服务设计和实现

在分析和比较目前典型P2P流媒体系统之后,提出一种基于自治域的P2PStreaming系统.该系统考虑了网络的松散性,将网络根据对等结点的地理位置来划分成不同的自治域系统,在自治域系统内推选出一些能力比较强的结点称为强结点,由强结点构成系统的中继层,降低自治域内的通讯开销.并在网络拓扑构建过程中借鉴了非结构化P2P的Gnutella组网策略并对其进行改进设计,同时系统设计使用了合理的数据分派算法来提高系统性能.     

A dynamic programming approach of finding an optimal broadcast schedule in minimizing total flow time

We study the problem of (off-line) broadcast scheduling in minimizing total flow time and propose a dynamic programming approach to compute an optimal broadcast schedule. Suppose the broadcast server has k pages and the last page request arrives at time n. The optimal schedule can be computed in O(k³(n+k)^k−1) time for the case that the server has a single broadcast channel. For m channels case, i.e., the server can broadcast m different pages at a time where m < k, the optimal schedule can be computed in O(n^k−m) time when k and m are constants. Note that this broadcast scheduling problem is NP-hard when k is a variable and will take O(n^k−m+1) time when k is fixed and m ≥ 1 with the straightforward implementation of the dynamic programming approach. The preliminary version of this paper appeared in Proceedings of the 11th Annual International Computing and Combinatorics Conference as “Off-line Algorithms for Minimizing the Total Flow Time in Broadcast Scheduling”.     

我国会计准则变更价值相关实证研究

我国的资本市场发展时间短,相应的会计准则也处于不断的更替和完善过程中。通过运用价值相关研究方法中的Feltham-Ohlson模型,检验我国会计准则变更是否达到了准则制定者期望达到的目的。研究发现:1、1996~2001年我国会计信息的价值相关性没有随各项具体会计准则的变更逐年提高,反而逐年降低;2、这种会计准则变更所带来的价值相关性在亏损上市公司和非亏损上市公司具有明显不同,但仍不支持“会计准则变更会提高会计信息含量”的假设;3、与2000年相比,2001年会计数据不但没有更谨慎,反而更“激进”。     

早期拉丁教父的死亡观评析——以德尔图良、安布罗斯和奥古斯丁为例

早年的德尔图良在死亡观上,采取了实用主义的态度,他同情胆怯者,号召人们勇敢面对死亡;晚年的德尔图良成了一名孟他努主义者,因而在死亡问题上采取了偏激的态度,他开始诅咒胆怯者和极力赞扬殉道者。安布罗斯从肉体与灵魂的截然对立出发,认为死亡的本质就是善,因为死亡意味着灵魂离开肉体而获得自由,这种死亡观显然是柏拉图主义影响的结果。作为教会体制代言人的奥古斯丁,则从《圣经》的立场出发重新解读死亡,他认为死亡不是善而是恶,但是这种恶可以被转化为善用;他同情惧死行为,并谴责自杀性的殉道现象,认为这种现象不仅与《圣经》教导相悖逆,而且客观上会鼓动异端邪说,威胁教会统治。     

Spatial variability of epibiotic assemblages on marina pontoons in Singapore

Berthing pontoons, one of the most ubiquitous structures in marinas, are known to provide recruitment substrate for a variety of marine biota but little has been reported on their capacity to support epibiotic organisms in tropical marinas, and even less is known about the factors that shape their distribution in such environments. We surveyed the epibiotic assemblages on the sides of pontoons in three Singapore marinas and examined the environmental conditions that influenced their distribution. A total of 94 taxa were recorded, with each marina hosting 43–65 taxa. Assemblages among marinas were highly distinct, and, key discriminants included components of biotic (alcyonarians, hexacorallians, bivalves, and annelids), as well as abiotic (sediment, bare area and shell fragments) origin. While the assemblage variation among marinas was influenced by local environmental conditions (e.g. water motion and sedimentation rate) and pontoon material, the variation in distribution within each marina was best explained by the distance of the pontoons from the marina’s entrance (epibiotic diversity and taxa richness were lower away from the marina entrance). Knowledge on the distribution of epibiotic assemblages on pontoons is essential to identify the factors that contribute to spatial variation and encourage the design and construction of ecologically-friendly marinas. Our findings suggest that improvements to pontoon design and layout would help to augment marina biodiversity, enhance the ecology of urbanised coasts, and mitigate development impacts.     

Exploiting Technological Indicators for Effective Technology Merger and Acquisition (M&A) Predictions

Mergers and acquisitions (M&A) play increasingly important roles for contemporary business, especially in high‐tech industries that conduct M&As to pursue complementarity from other companies and thereby preserve or extend their competitive advantages. The appropriate selection (prediction) of M&A targets for a given bidder company constitutes a critical first step for an effective technology M&A activity. Yet existing studies only employ financial and managerial indicators when constructing M&A prediction models, and select candidate target companies without considering the profile of the bidder company or its technological compatibility with candidate target companies. Such limitations greatly restrict the applicability of existing studies to supporting technology M&A predictions. To address these limitations, we propose a technology M&A prediction technique that encompasses technological indicators as independent variables and accounts for the technological profiles of both bidder and candidate target companies. Forty‐three technological indicators are derived from patent documents and an ensemble learning method is developed for our proposed technology M&A prediction technique. Our evaluation results, on the basis of the M&A cases between January 1997 and May 2008 that involve companies in Japan and Taiwan, confirm the viability and applicability of the proposed technology M&A prediction technique. In addition, our evaluation also suggests that the incorporation of the technological profiles and compatibility of both bidder and candidate target companies as predictors significantly improves the effectiveness of relevant predictions.     

The determinants and patterns of married women's labor force participation in Korea

The present study investigates the determinants and patterns of married women's labor force participation in Korea. Married women's employment in Korea is largely determined by age, urban residence, household characteristics of the husband's socioeconomic status, family income, fertility, and the lagged effect of work. Older age, rural residence, inferior household economic condition, and recent work experience are the major positive causes of married women's participation in the market work. On the other hand, younger women with preschool children, who currently reside in urban areas, enjoying better household economic conditions (due to higher socioeconomic status of husbands and/or higher family income) are the groups of women with the smallest probability of working in the market. Married women's employment pattern in Korea shows a pattern typical of less-developed and low-income countries in two aspects: married women working and characterized by a low level of education; the difference between urban and rural areas in terms of work participation pattern is remarkable. Although Korea belongs to the advanced group of currently industrializing countries, she lags behind with other developing countries in terms of married women's employment. Moreover, it is difficult to predict in advance that Korea would have similar experiences as those of contemporary advanced countries.